^0fc0a Fishery Bulletin SrATES O* + SEp* 1982 \ Vol. 80, No. 1 January 1982 MANOOCH, CHARLES S., Ill, and CHARLES A. BARANS. Distribution, abundance, and age and growth of the tomtate, Haemulon aurolineatum, along the southeastern United States coast 1 MURAWSKI, STEVEN A.. JOHN W. ROPES, and FREDRIC M. SERCHUK. Growth of the ocean quahog, Arctica islandica, in the Middle Atlantic Bight. . . 21 TUCKER, JOHN W., JR. Larval development of Citharichthys cornutus, C. gym- norhinus, C. spilopterus, and Etropus crossotus (Bothidae), with notes on larval occurrence 35 WIEBE, P. H., S. H. BOYD, B. M. DAVIS, and J. L. COX. Avoidance of towed nets by the euphausiid Nematoscetis megalops 75 LAROCHE, JOANNE LYCZKOWSKI, SALLY L. RICHARDSON, and AN- DREW A. ROSENBERG. Age and growth of a pleuronectid, Parophrys vetulus, during the pelagic larval period in Oregon coastal waters 93 HJORT, R. C, and C. B. SCHRECK. Phenotypic differences among stocks of hatchery and wild coho salmon, Oncorhynchus kisutch, in Oregon, Washington, and California 105 BAGLIN, RAYMOND E., JR. Reproductive biology of western Atlantic bluefin tuna 121 IRVINE, A. B., R. S. WELLS, and M. D. SCOTT. An evaluation of techniques for tagging small odontocete cetaceans 135 Notes CONOVER, DAVID 0., and STEVEN A. MURAWSKI. Offshore winter migra- tion of the Atlantic silverside, Menidia menidia 145 ROSENBERG, ANDREW A., and JOANNE LYCZKOWSKI LAROCHE. Growth during metamorphosis of English sole, Parophrys vetulus 150 PRATT, HAROLD L., JR., JOHN G. CASEY, and ROBERT B. CONKLIN. Ob- servations on large white sharks, Carcharodon earcharias, off Long Island, New York 153 GIBSON, D. M. A note on the estimation of trimethylamine in fish muscle 157 CRASS, DENNIS W., and ROBERT H. GRAY. Snout dimorphism in white stur- geon, Acipenser transmontawus, from the Columbia River at Hanford, Washing- ton 158 V. Seattle, Washington U.S. DEPARTMENT OF COMMERCE Malcolm Baldrige, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION John V. Byrne, Administrator NATIONAL MARINE FISHERIES SERVICE William G. Gordon, Assistant Administrator Fishery Bulletin The Fishery Bulletin carries original research reports and technical notes on investigations in fishery science, engineering, ant economics. The Bulletin of the United States Fish Commission was begun in 1881; it became the Bulletin of the Bureau of Fisheries ir, 1904 and the Fishery Bulletin of the Fish and Wildlife Service in 1941. Separates were issued as documents through volume 46; the last document was No. 1 103. Beginning with volume 47 in 1931 and continuing through volume 62 in 1963, each separate appeared as a numbered bulletin. A new system began in 1963 with volume 63 in which papers are bound together in a single issue of the bulle- tin instead of being issued individually. Beginning with volume 70, number 1, January 1972, the Fishery Bulletin became a periodi- cal, issued quarterly. In this form, it is available by subscription from the Superintendentof Documents, U.S. Government Printing Office, Washington, DC 20402. It is also available free in limited numbers to libraries, research institutions. State and Federal agencies, and in exchange for other scientific publications. EDITOR Dr. Carl J. Sindermann Scientific Editor, Fishery Bulletin Northeast Fisheries Center Sandy Hook Laboratory National Marine Fisheries Service, NOAA Highlands, NJ 07732 Editorial Committee Dr. Bruce B. Collette Dr. Donald C. Malins National Marine Fisheries Service National Marine Fisheries Service Dr. Edward D. Houde Dr. Jerome J. Pella Chesapeake Biological Laboratory National Marine Fisheries Service Dr. Merton C. Ingham Dr. Jay C. Quast National Marine Fisheries Service National Marine Fisheries Service Dr. Reuben Lasker Dr. Sally L. Richardson National Marine Fisheries Service Gulf Coast Research Laboratory The Fishery Bulletin (USPS 090-870) is published quarterly by Scientific Publications Office, National Marine Fisheries Service, NOAA, 7600 Sand Point Way NE. BIN C15700, Seattle, WA 98115. Second class postage paid to Finance Department. USPS, Washington, DC 20260. Although the contents have not been copyrighted and may be reprinted entirely, reference to source is appreciated. The Secretary of Commerce has determined that the publication of this periodical is necessary in the transaction of the public business required by law of this Department Use of funds for printing of this periodical has been approved by the Director of the Office of Management and Budget through 31 March 1982. Fishery Bulletin CONTENTS Vol. 80, No. 1 January 1982 MANOOCH, CHARLES S., Ill, and CHARLES A. BARANS. Distribution, abundance, and age and growth of the tomtate, Haemulon aurolineatum, along the southeastern United States coast 1 MURAWSKI, STEVEN A., JOHN W. ROPES, and FREDRIC M. SERCHUK. Growth of the ocean quahog, Arctica islandica, in the Middle Atlantic Bight. . . 21 TUCKER, JOHN W., JR. Larval development of Citharichthys cornutus, C. gym- norhinus, C. spilopterus, and Etropus crossotus (Bothidae), with notes on larval occurrence 35 WIEBE, P. H., S. H. BOYD, B. M. DAVIS, and J. L. COX. Avoidance of towed nets by the euphausiid Nematoscelis megalops 75 LAROCHE, JOANNE LYCZKOWSKI, SALLY L. RICHARDSON, and AN- DREW A. ROSENBERG. Age and growth of a pleuronectid, Parophrys vehdus, during the pelagic larval period in Oregon coastal waters 93 HJORT, R. C, and C. B. SCHRECK. Phenotypic differences among stocks of hatchery and wild coho salmon, Oncorhynchus kisutch, in Oregon, Washington, and California 105 BAGLIN, RAYMOND E., JR. Reproductive biology of western Atlantic bluefin tuna 121 IRVINE, A. B., R. S. WELLS, and M. D. SCOTT. An evaluation of techniques for tagging small odontocete cetaceans 135 Notes CONOVER, DAVID 0., and STEVEN A. MURAWSKI. Offshore winter migra- tion of the Atlantic silverside, Menidia menidia 145 ROSENBERG, ANDREW A., and JOANNE LYCZKOWSKI LAROCHE. Growth during metamorphosis of English sole, Parophrys vetulus 150 PRATT, HAROLD L., JR., JOHN G. CASEY, and ROBERT B. CONKLIN. Ob- servations on large white sharks, Carcharodon carcharias, off Long Island, New York 153 GIBSON, D. M. A note on the estimation of trimethylamine in fish muscle .... 157 CRASS, DENNIS W., and ROBERT H. GRAY. Snout dimorphism in white stur- geon, Acipenser transmontanus, from the Columbia River at Hanford, Washing- ton 158 Seattle, Washington 1982 For sale by the Superintendent of Documents. U.S. Government Printing Office, Washington. DC 20402— Subscription price per year: $15.00 domestic and $18.50 foreign. Cost per single issue: $4.50 domestic and $5.05 foreign. The National Marine Fisheries Service (NMFS) does not approve, recommend or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to NMFS, or to this publication fur- nished by NMFS, in any advertising or sales promotion which would indicate or imply that NMFS approves, recommends or endorses any proprietary prod- uct or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or pur- chased because of this NMFS publication. DISTRIBUTION, ABUNDANCE, AND AGE AND GROWTH OF THE TOMTATE, HAEMULON AUROLINEATUM, ALONG THE SOUTHEASTERN UNITED STATES COAST1 Charles S. Manooch III2 and Charles A. Barans3 ABSTRACT Tomtates, Haemulon aurolineatum, were widely distributed over sponge-coral habitats throughout the South Atlantic Bight region in depths of 9 to 55 m, although they were occasionally caught in large numbers over sandy bottom habitats. Fish were most common in offshore areas during winter and were not taken in waters of <10°C south of Cape Fear, N.C. Juveniles (<148 mm TL) were caught in the same geographical areas as adults, but were collected in warmer waters than adults during fall and winter. Spawning occurred during the spring. Individuals collected by hook and line and trawl were aged by scales and otoliths. Back-calculated mean total lengths were from 103.0 mm at age I, to 280.5 at age IX. The von Bertalanffy growth equation is I, =310(1 -exp - 0.22017 (t + 1.28)), where t is age in years, and /, is total length at age. The oldest fish sampled was age IX, 289 mm TL. Annual total mortality based on catch curves from 1,496 fish landed by the recreational fishery from 1972 to 1978 was 59% (instantaneous total annual mortality = 0.89). We found that the tomtate grows faster, does not live as long, and has a higher natural mortality rate than most other reef fishes previously studied in the South Atlantic Bight. The tomtate, Haemulon aurolineatum, is a small grunt (Haemulidae), which occurs from Cape Cod, Mass., to Brazil, including the Caribbean, Gulf of Mexico, and Central American coast. The species, previously referred to as Bathystoma rimator, B. aurolineatum, and Haemulon rima- tor (Courtenay 1961), is known vernacularly as xira in Brazil; cuji in Venezuela; rancho, juez, and chankay in Mexico; and mulita, mula, mari- quita, and maruca in Puerto Rico. The tomtate is taken primarily by hook and line off the southeastern United States and by traps, hook and line, and trawl in the more south- ern areas of its range. Unfortunately, commer- cial landings of tomtates in the United States are reported in the collective term "grunts," which includes many different species of the family and therefore precludes species identifications that are needed for fishery management. A Soviet- Cuban cooperative fisheries research program on the Campeche Banks revealed the tomtate as 'Contribution No. 192, Southeast Fisheries Center Beau- fort Laboratory, National Marine Fisheries Service, NOAA; No. 189, MARMAP Program; No. 127, South Carolina Marine Resources Center, Marine Resources Institute. 2Southeast Fisheries Center Beaufort Laboratory, National Marine Fisheries Service, NOAA, Beaufort, NC 28516. 3South Carolina Wildlife and Marine Resources Depart- ment, Marine Resources Research Institute, Charleston, SC 29412. the main demersal species caught by trawl from 1962 to 1972 (Sokolova 1969; Sauskan and Olae- chea 1974). Also, exploratory trawling off South Carolina found large quantities of tomtates (Wenner et al. 1979a). Recreational headboat4 fishermen fishing from North Carolina to Cape Canaveral, Fla., caught an average of 23.2 t (metric tons) of tom- tates in 1976 and 1977 (Dixon5). This species was the most commonly caught haemuline, although second in weight landed to the white grunt, Haemulon plumieri. In this paper we describe the relative abun- dance, spatial and temporal distributions, spawning, age, growth, and mortality for tom- tates along the southeastern United States. METHODS Distribution and Relative Abundance Eight groundfish survey cruises spanning all four seasons (Table 1 ) were conducted on the con- 4A boat for hire where anglers are charged on a per person basis. 6R. L. Dixon, Southeast Fisheries Center Beaufort Labora- tory, NMFS, NOAA, Beaufort, NC 28516, pers. commun. Jan- uary 1978. Manuscript accepted September 1981. FISHERY BULLETIN: VOL. 80, NO. 1, 1982. FISHERY BULLETIN: VOL. 80, NO. 1 Table 1.— Groundfish cruises of the RV Dolphin. No. ot No. of tows No. of Cruise Dates trawls with tomtates tomtates DP-7305 23 Oct. -16 Nov. 1973 86 18 2,075 DP-7402 1 Apr. - 9 May 1974 112 19 442 DP-7403 13 Aug. -19 Sept 1974 87 14 581 DP-7501 16 Jan. -10 Apr. 1975 92 10 1,212 DP-7503 30 Aug. -19 Sept 1975 87 20 1,298 DP-7601 12 Jan. - 7 Feb. 1976 86 15 4,005 DP-7603 28 Aug. -21 Sept 1976 89 15 1,749 DP-7701 17 Jan. - 9 Mar. 1977 93 11 3,260 tinental shelf and upper continental slope be- tween Cape Fear, N.C., and Cape Canaveral, Fla., except in spring 1974 when sampling ex- tended to Cape Hatteras. A preassigned number of stations was selected randomly (Grosslein 1969) with a set number in each of six depth zones (9-18 m; 19-27 m; 28-55 m; 56-110 m; 111- 183 m; 184-366 m). Bottom water temperatures were measured at each station with mechanical or expendable bathythermographs. Thirty-minute trawls were made continuously (day and night) from the RV Dolphin, at 6.5 km/h with a towing wire scope of 2.5-3.0:1. The trawl was a 3/4-scale version of a "Yankee No. 36" with a 16.5 m footrope, 11.9 m headrope, and 1.3 cm stretch mesh cod end liner (Wilk and Silverman 1976). Fork lengths (later converted to total lengths) of all fish collected by trawl were recorded to the nearest centimeter. Frozen fish samples were taken to the laboratory for further investiga- tions. An index of relative abundance (Musick and McEachran 1972) was calculated for each depth zone by the following expression: Index of Relative Abundance 2 1n(x+l) nh where nh = number of trawls in the Mh depth zone, and x = number of individuals for each tow in a given depth zone. Because previous investi- gators have shown that trawl catches are usually distributed as a negative binomial (Elliott 1971; Taylor 1953), a In (x + 1) transformation was made on the relative abundance data to permit statistical tests to determine if the differences among habitats within depth zones were signifi- cant. Estimates of biomass standing stock were cal- culated with both transformed, In (x + 1), and untransformed data for comparison of the result- ing values. The stratified mean catch/tow (Coch- ran 1977) was calculated by the expression: *- = N k iNhVh] where yst = stratified mean catch(kg)/tow, N = total area, Nh = area of Mh depth zone (from plani- meter chart measurements), yh = mean catch/tow in the Mh depth zone, and k = number of zones in the set. The area of live-bottom habitat in each depth zone («44.5%) was estimated from the frequency of occurrence of sponge and coral in catches dur- ing 5 yr of bottom trawling with the stratified random sampling design. The areas of sandy- bottom habitats were obtained by subtraction. The estimated population variance of the mean catch(kg)/tow was also calculated by Clark and Brown (1977): S2 = N mi [Nhy2]- NyJ + ! Sf \(Nh- *=i r + (Nh-N)(Nh-nh) N nh ] where S = estimated population variance, and Sh2 = variance of the Mh zone. The mean catch/tow (yh) of the transformed In (x + 1) data was estimated for each depth zone following the methodology of Bliss (1967): E(yh) = exp (yh + S2/2) where E(yh) = the estimated (retransformed) mean catch(kg)/tow in the Mh depth zone, yh and S2, both expressed in logarithmic units, are the zone mean and its variance. The same methodol- ogy was applied to obtain the stratified mean catch/tow from transformed data for the whole study area. Biomass estimates were expanded by the area swept method (Rohr and Gutherz 1977), using S&ot = X (Ph) (A„) h -1 where SStot = total standing stock, MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE P = average population expressed as kilograms per km2 in the /?th depth zone, and Ah = total area of the Mh depth zone. The sweep of the "3/4 Yankee trawl" was 8.748 m (Azarovitz6), and 3.241 km was the distance cov- ered during a standard trawl. It should be noted that all estimates were minimum estimates be- cause the sampling efficiency of our gear with regard to tomtates was unknown. Standing stock values calculated for sandy-bottom areas incor- porated such a large number of zero catches that the transformation did not normalize the data, so the resulting values should be considered sus- pect. Age and Growth Scales, otoliths, fish lengths, and fish weights were collected from 1,496 tomtates from the rec- reational headboat fishery operating from North Carolina to Cape Canaveral from 1972 through 1978 and from approximately 100 juvenile fish collected by research trawling off South Caro- lina. Total fish length was recorded in milli- meters and weight in grams. Scales were removed from beneath the tip of the posteriorly extended pectoral fin, soaked in a one-tenth aqueous solution of phenol, cleaned and mounted dry between two glass slides, and viewed at 40X magnification on a scale projector. Measurements were made and recorded from the scale focus to each annulus and to the scale edge in the anterior field for marginal increment analyses and back-calculating fish length at the time of annulus formation. Otoliths (sagittae) were removed by making a transverse cut in the cranium with a hacksaw midway between the posterior edge of the orbit and the preopercle. The skull was pried open and the otoliths were removed with forceps, washed in water, and stored dry in labeled vials. Rings were counted by placing the otoliths in a black- ened-bottom watch glass and then viewing the structures through a binocular dissecting micro- scope with the aid of reflected light. Some of the otoliths from large (older) fish were sectioned with a Buchler, Isomet, 1 1-1 1807 low-speed saw to facilitate aging. Measurements were not re- corded from otoliths since these structures were used only as a method of validating age deter- mined by reading scales. Lengths by age for fish from all years com- bined were back-calculated from a scale radius- fish length regression. The regression equation was based on the relationship of magnified (40X) scale length to total fish length. Since a majority of the scale measurements were clustered around a relatively narrow size range, we based our regression on a subsample of scale radius and body length measurements. After grouping the measurements into 25 mm body length intervals, we selected approximately 12 from each interval to ensure that the regression provided good representation. The prediction equation took the form TL = a SR1'; where TL = total length, SR = scale radius, a = intercept, and b = slope. We substituted the means of the distances from the focus to each annulus for SR in the above equa- tion, calculated the mean fish length for the time of each annulus formation, and then calculated mean growth increment for each age group. Calculation of a theoretical growth curve is useful in modeling of growth in natural popula- tions of fish. Growth parameters such as theo- retical maximum attainable size (LJ, growth coefficient (K), and theoretical time of the begin- ning of growth (to), may be used in constructing population models. The most popular theoretical growth curve, the von Bertalanffy (lt = L^{\ — exp — K(t — to))) was fitted to back-calculated length at age data (Ricker 1975; Everhart et al. 1975). This particular equation also allows us to make comparisons with results obtained by other researchers. The growth parameter, Lx, was first derived by fitting a Walford (1946) line: Z,+1 = Lx (1 - k) + kl, to back-calculated data where h = total length at age t, and k = slope of the Walford line. The slope (A-) is equal to e*, thus our first estimate of K = In k. Preliminary values of Lx were ob- tained by solving the equation Lx = ^-intercept/ (1 — k), and by regressing annual growth incre- ment (X) against fish length at the beginning of the incremental period ( Y) (Jones 1976). By plot- ting loge (L^ - lt) against t and by using trial val- ues of L„ ranging from lower than the prelimi- 6T. Azarovitz. Northeast Fisheries Center Woods Hole Lab- oratory. National Marine Fisheries Service, NOAA, Woods Hole, Mass., pers. commun. January 1978. 7Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. FISHERY BULLETIN: VOL. 80, NO. 1 nary values to much greater, we determined the best Lx that resulted in the straightest line. The growth coefficient (K) was the slope of this line and was used to solve for t0: to = y - intercept of natural log line - logP L3 K We checked the U value to see if it was biased toward younger or older fish by using the equa- tion to = t(l/K) In (1 - h/LJ for separate ages I- IX (Jones 1976). Mortality Estimates We calculated annual total mortality estimates by analyzing catch curves (Beverton and Holt 1957) based on fully recruited age fish and older. If the log, of the age frequency in the catch is plotted on age, the slope of the linear descending right limb of the curve is equal to the mean in- stantaneous total mortality (Z). To calculate mortality rates, we first needed to assign ages to the 1,100 or so unaged fish. We grouped fish of known age by 25 mm length intervals, calculated the percentage of fish of each observed age in each group, and used these percentages to esti- mate the number of fish of each age for the un- aged group (Ricker 1975). Length- Weight and Fork Length- Total Length Relationships To calculate length-weight and length conver- sion relationships fish lengths were subsampled to provide a fairly equal distribution throughout the size range of fish examined during this study. The length-weight relationship was expressed exponentially, whereas the fork length-total length equation was expressed as a simple linear regression. Spawning Gonads were examined macroscopically by season to determine the approximate time of spawning. Observations on the development of testes were used collaboratively with measure- ments recorded from ovaries. Ovaries were weighed to calculate a seasonal gonad index, or the percentage of gonad weight to fish weight. RESULTS Distribution and Relative Abundance Tomtates were collected throughout the South Atlantic Bight (Figs. 1-4). Although most of the continental shelf is sandy "open-shelf habitat" (Struhsaker 1969), the greatest catches of tom- tates were directly associated with the irregu- larly distributed sponge-coral ("live bottom") habitats (as defined by Wenner et al. 1979a). In- dices of relative abundance over live-bottom areas were significantly larger (P<0.01) than abundance indices from sandy-bottom catches in all seasons and years, except during the cold winter of 1977 (Table 2). Although tomtates occurred in 30-70% of the collections from the sponge-coral habitat, 79.6% of the total number caught during seven cruises, excluding the cold winter of 1977, were at sponge-coral stations (Table 3). During all seasons, catches of tomtates over sand were infrequent, but occasionally large (Wenner et al. 1979a, b, c, d). Occurrence of tomtates in both sandy-bottom and live-bottom habitats increased the difficulty in biomass esti- mations. Information from catches over the sponge-coral habitat with the 30-min tows was expanded to preliminary estimates of biomass (Tables 4, 5), although the catch represented a mixed habitat collection of unknown propor- tions. Standing crop estimates of tomtates from the region between Cape Fear and Cape Canav- eral ranged from 1,730 t (minimum catch, sum- mer 1974) to 12,878 t (maximum catch, winter 1976). Although biomass estimates were calcu- lated separately for each depth zone and stand- ing crop estimates were calculated separately for catches from live-bottom and sandy-bottom habitats (Table 6), all estimates represent mini- mal values because fish availability and vulner- ability to the trawl were not considered. Tomtates, both juvenile (<137 mm TL) and adult, were more abundant in catches in the northern part of the South Atlantic Bight than in catches in the south. During all seasons sampled, between 1973 and 1977, the catch north of lat. 32°32'N, an arbitrary shelf division, was be- tween 59 and 89% of the total catch. The one ex- ception occurred during the cold winter of 1977, when 98% of the total catch (3,192 fish) was made south of lat. 32°30'N at a single station. MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE FIGURE 1. — Spatial distribution and catch per tow of tomtates between Cape Fear and Cape Canaveral, 1 April- 9 May 1974. FISHERY BULLETIN: VOL. 80, NO. 1 80^ 79* V \ 78* ^> 77* 76* 75* ■J? &* V Cape I Feor ll 3 25 .•'10 TOTAL NUMBER OF FISH SUMMER 1974 * None O I to 6 (3 6 to 51 3 51 to 101 9 101 to 501 • 501 to 10,000 34* 33" 75' 32* 31* 30* 76 29 28 27 77' 28* 81° 80* 27* 79* 78° FIGURE 2.— Spatial distribution and catch per tow of tomtates between Cape Fear and Cape Canaveral, 13 August- 19 September 1974. MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE 75* TOTAL NUMBER OF FISH FALL 1973 x None O I to 6 3 6 to 51 3 51 to 101 * 101 to 501 • 501 to 10,000 \ 34* 33' 73 32 \ 31* w 76* 29* 28* 27* 77* 78° FIGURE 3.— Spatial distribution and catch per tow of tomtates between Cape Fear and Cape Canaveral, 23 October-16 November 1973. FISHERY BULLETIN: VOL. 80, NO. 1 79* 78* 77* 76* 75' V TOTAL NUMBER OF FISH WINTER 1976 x None O I to 6 (5 6 to 51 3 51 to 101 • 101 to 501 • 501 to 10,000 34" 33* 75* 32* 31* 30* '76* 29* 28* 27 77' 28* 81* 80" 27* 79° 78° FIGURE 4.— Spatial distribution and catch per tow of tomtates between Cape Fear and Cape Canaveral, 12 January-7 February 1976. 8 MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE Table 2.— f-test and chi-square results of com- parisons between numbers of tomtates in catches over live-bottom and sandy-bottom habitats. Table 4.— Mean catch/tow (f/J values for trawl-caught tom- tates on untransformed and transformed [In (kg + 1)] data by depth and habitat zone for summer 1974. Bliss' (1967) estima- tion of the mean was applied to the transformed values. f-test of X2 test y„ biomass yv biomass Area of No. I In (x + 1) «i Ix Depth (kg/tow) (kg/tow) zone of Seasons n df of — n df (m) Habitat untransformed transformed (km2) tows Fall 1973 375" 65 14.79" 9-18 live 5.272 12.981 2.622 2 Spring 1974 4.70" 85 15.69" sand 0.324 0.163 15,461 14 Summer 1974 4 15" 66 24.73" 19-27 live 6.804 6804 2.730 1 Winter 1975 2.83" 68 93.36" sand 0.218 0101 16,100 18 Summer 1975 8 18" 66 69.46" 28-55 live 3991 5.196 3,794 5 Winter 1976 877" 67 350.41" sand 0.000 0.000 22,367 14 Summer 1976 11.04" 67 193.32" 56-110 live 1 285 1 120 692 6 Winter 1977 1.59n.s. 70 40.42" sand 0 000 0.000 4,083 8 *" = significant at 0.01 level; n.s. = nonsignificant at 0.05 level. Table 3.— Catches of tomtates associated with collec- tions within the "live bottom"-sponge/coral habitats. Live bottom stations Tomtate catch % with Total % from Cruise date N tomtates number live bottom Fall 1973 10 39 2,075 296 Spring 1974 11 42 442 55.7 Summer 1974 14 50 581 76.2 Winter 19751 9 30 1,212 78.4 Summer 1975 18 70 1,298 98.2 Winter 1976 11 53 4,005 976 Summer 1976 8 53 1,749 91.7 Winter 19772 11 55 3,260 1.5 Average 50 79.6 'Sampling season prolonged into spring. 2Unusually cold winter, data omitted from average. Table 5.— Mean catch/tow (l2cm FALL 1973 14 0 l~l 10 8 L0-. r- < I.O—i _l UJ 05- >I3 cm _7_ 4 2| ».i"i.n i • • i • i £ WINTER 1976 f I <'2cm O- Depth(m)9-I8 19-27 28-55 56-110 111-183 184^366 I I i i i i X UJ 0.5- Q Z 1.0-1 I.O-i 0.5- >l3cm SPRING 1974 2 -Z. 2T 20 4 JL ± 28 18 0.5- 1.0- 21 rn r~ 1 ° ° l5cm Depth(m)9-I8 19-27 28-55 56 - lio' III- 183 ' 184-366 I ■ ■ I I I "D Figure 5.— Index of relative abundance for tomtates by depth zone during four seasons O'uveniles above the axis, adults be- low: fraction numerator = number of trawls with tomtates- denominator = total number of trawls in depth zone). higher temperature intervals (Fig. 6). Young tomtates (20-63 mm) have previously been col- lected during December in the Florida Keys at a water temperature of 16.2°C (Springer and Woodburn 1960). During summer (1975) juve- niles were collected only in the coolest thermal zone (24.0°-27.9°C), while during spring (1974) both juveniles and adults were collected in the same thermal interval (16.0°-23.9°C). ^°omt^tet may avoid water temperatures of <10 L. b ish were never caught at <10 3°C dur- ing any season, even at five sponge-coral stations in areas where large numbers were caught at >10°C during the previous winter (Fig. 7). 10 SUMMER 1975 FALL 1973 24-27°C 28-3IOC I6-I9°C r- 5 10 15 20 25 5 WINTER 1976 < soon I2-I5°C X O 100 < U X CO o 20-23°C 24-27°C -r — i 1 1 r 5 10 15 20 25 £ SPRING 1974 I6-I9-C 20-23°C ~l ' i ' I' i 5 10 15 20 25 FISH LENGTH(cm) Figure 6. -Length-frequency distributions (TL) of tomtates by bottom water temperature interval (4°C). Age and Growth Validity of Rings as Annuli Both scales and otoliths were used to age tom- tates. Approximately 75% (397 of 529) of the scale samples and 85% (177 of 208) of the otoliths were legible. Since tomtates have been aged by read- ing scales (Sokolova 1969), we did not try spe- cifically to validate the methods presented here. Several findings, however, pursuant to the goals of this paper, indicate that rings on tomtate scales and otoliths are true annuli. Close exami- nation of otoliths from young-of-year tomtates, collected by trawl, clearly show the formation of one ring per year, and that the first ring (annu- lus) forms between the fall and spring collection periods. The mean length of fish progressively in- creased as the number of scale or otolith rings increased and otoliths and scales agreed closely (Table 7). For instance, if aged by scales, age-I fish averaged 135.4 mm TL; age-II, 181.9; age- Ill, 203.3; age-IV, 220.0; age-V, 234.5; age- VI 255.7; and age- VII, 265.8. If aged by otoliths,' age-I fish averaged 134.3 mm TL; age-II, 164.7; MANOOCH and BARANS. DISTRIBUTION AND ABUNDANCE OF TOMTATE 76* 75° TOTAL NUMBER OF FISH WINTER 1977 « None O I to 6 <3 6 to 51 3 51 to 101 9 101 to 501 • 501 to 10,000 ^ 34* 33* 75 32 3IC 30° 76* 29* 28° 27 V 27° 79° 78° Figure 7.— Spatial distribution and catch per tow of tomtates between Cape Fear and Cape Canaveral during the cold winter of 1977. 11 FISHERY BULLETIN: VOL. 80, NO. 1 TABLE 7.— Comparison of mean empirical length-age data obtained by reading tomtate scales and otoliths. Scales Otoliths Mean Mean Difference Age TL Range in TL Range in in means group N 22 (mm) 84.7 length (mm) SD N (mm) length (mm) SD (mm) 0 50-142 28 1 54 89.8 50-142 29.9 5.1 1 9 1354 109-171 25.6 23 134.3 80-157 21.5 1.1 2 45 181.9 153-206 13.3 43 164.7 150-185 9.7 17.2 3 81 2030 180-221 9.6 16 197.1 161-212 14.7 5.9 4 134 220.0 195-238 10.5 19 213.0 193-227 11.1 7.0 5 66 234.5 208-257 11.3 12 232.2 226-242 4.1 2.3 6 28 255.7 245-268 6.3 9 253.1 240-262 6.5 2.6 7 5 265.8 260-272 5.5 1 267.0 — — 1.2 8 4 277.0 270-280 5.0 9 3 2867 282-289 4.0 Total 397 age-Ill, 197.1; age-IV, 213.0; age-V, 232.2; age- VI, 253.1; and age- VII, 267.0 mm. The relative length frequencies of the mea- sured distance from the focus of the scale to each ring progressively increased with the number of rings. Significant features of the plotted curves were the occurrence of one mode for each ring, the consistent location of a specific mode on the X-axis for fish of different ages, the increased overlap for each additional ring, and the pro- gressive decrease in the distance between modes for each successive year, indicating less linear growth each year as the fish ages. Growth There was relatively little difference in the mean annual increments of fish aged by scales and those of fish aged by otoliths (Table 7). An- nual growth increments for fish aged by scales for ages I-V were: HI, 46.5 mm; II-III, 21.1 mm; III-IV, 17.0 mm; and IV-V, 14.5 mm. After age V, growth appears to be more irregular, prob- ably a result of the relatively small sample sizes for ages VI, VII, VIII, and IX (Table 7). Lengths by age for fish from all years were back-calculated from a scale radius-fish length regression. The prediction equation was TL = 1.7489 SR09512; r = 0.93 and AT = 103, where TL = total length, and SR = scale radius. By substituting the means of the distances from the focus to each annulus for SR in the above equation, we were able to calculate the mean fish length at the time of each annulus formation, and the mean annual growth increment for each age (Table 8). The von Bertalanffy equation was used to de- scribe theoretical growth. The growth param- eters Lx and K were first calculated by fitting a Walford (1946) line to back-calculated data. The equation was Itn = 90.833 + 0.6747*,, r = 0.982. Our first estimate of K was L 0.6747 or 0.3935. This value was used to obtain Lx by solving the equation Lx = ^-intercept / (1 — k). The initial value for Lx of 289, and the subsequent value of 285.7 obtained by regressing annual growth in- crement {X) against fish length at the beginning of the incremental period (Y) (Jones 1976), Table 8.— Calculated total lengths (millimeters) of 346 tomtates aged by scales. Ob« ierved ige N Mean cal culated total length at end of year ; 1 2 3 4 5 6 7 8 9 1 9 1037 II 45 108 1 173.0 III 75 102 5 171.1 199.1 IV 123 102.6 1684 198.8 214.1 V 56 101 0 1678 2007 2167 226.7 VI 26 102.2 165.5 198.8 221.1 235 7 245 1 VII 5 99.6 165.3 200.9 224.4 240.8 251 3 2588 VIII 4 105 3 171.7 195.5 215.1 2286 2420 252.1 2608 IX Total 3 346 1025 170.6 200.9 222 1 237.7 253.0 264 5 273.5 280.5 Wei ghted mean 103.0 169.3 1993 2160 230.4 2462 2580 2662 280.5 Increment 103.0 66.3 30.0 16.7 14.4 15.8 11.8 8.2 14.3 No. calculations 346 337 292 217 94 38 12 7 3 12 MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE seemed low. Therefore, we plotted logf (L^ — /,) against t by using trial values of Lx ranging from 285 to 310 mm. The straightest line resulted from Lx of 310 mm. The slope of the line, —0.22017, was selected as the growth coefficient {K) and was used to obtain U (—1.28). Our best estimate of the equation describing the theoreti- cal growth of tomtates is It = 310 (1 - exp - 0.22017(* + 1.28)). annual mortality estimate for 1972 through 1978 was 59% (Z = 0.887). By year, instantaneous mor- tality rates were 1974, 0.669; 1975, 1.035; 1976, 1.017; 1977, 1.041; and 1978, 0.972. Too few fish were sampled from the fishery in 1972 and 1973 to construct catch curves. The instantaneous mortality rate(s) for tomtates was higher than those previously obtained for white grunt, Z = 0.65 (Manooch 1976), or for red porgy, Z= 0.58 (Manooch and Huntsman 1977). Observed, back-calculated, and theoretical lengths at age are presented in Table 9. Table 9.— Total lengths of tomtates at age (ob- served, back-calculated, and theoretical). Age Length at age (mm) Observed Back-calculated Theoretical 1 135 4 103.0 1224 2 181.9 169.3 159.4 3 203.0 199.3 189.2 4 220.0 216.0 213.1 5 234.5 230.4 232.2 6 255.7 246.2 247.6 7 265.8 258.0 259.9 8 2770 266.2 269.8 9 286.7 280.5 277.8 Length- Weight and Fork Length- Total Length Relationships Fish ranging from 52 to 280 mm TL were used to calculate a length-weight relationship. The equation W = 0.0000086L30905, r = 0.996 and N = 70, where W = weight in grams and L = total length in millimeters, describes this relation- ship. The equation TL = -1.8196 + 1.1540 FL, r = 0.99 and TV = 100 was derived to convert lengths. Mortality Estimates By age IV, tomtates are fully recruited to the hook and line fishery, the only important method of harvesting this species off the southeastern United States. Instantaneous mortality (Z) esti- mates were obtained by analyzing catch curves of fish aged IV and older (Fig. 8). The mean total 7.0 6.0 > O 5.0 z Ul P. 4.0 a 3.0 o o 2.0 1.0 N= 1.496 Z=-0.887 r= -0.985 m E m 2n 2m ix AGE Figure 8. — Catch curve for tomtates caught by hooked line off the southeastern United States, 1974-77. Spawning Indirect evidence indicates that tomtates of the South Atlantic Bight spawn primarily in April and May. Running ripe males and partly spent females were caught in April 1979 (28-42 m; 16.4°-19.4°C), while a major decrease in mean ovarian weight and maximum ovary weight of mature females occurred after the spring (April 1974) sampling period (Table 10). Throughout the year, many (>38%) of the females sampled each season were in the maturing and ripe condi- tion. The presence of juveniles (33-90 mm TL; mode 80 mm) in bottom trawl collections during summer, and the progressive increase in modal fish lengths in length-frequency distributions Table 10.— Gonad condition of adult tomtates (>15 cm TL) from the South Atlantic Bight. Mean Maximum Runn nq ovarian wt. Gonad ovarian wt. Season Sex N ripe % (9) index' (g) Summer 1974 F 31 5 0.6 0.6 1.7 Fall 1973 F 48 2 0.5 0.5 1.4 Winter 1976 F 36 9 1.3 1.1 8.6 Spring 19792 M 13 77 — — — F 34 0 4.2 3.4 17.0 'Gonad index = (ovary wt./fish wt.) X 100. 2Females 77% with hydrated eggs. 13 FISHERY BULLETIN: VOL. 80, NO. 1 through a seasonal cycle (Fig. 9), indicated that these juveniles were spawned in spring. 200-, SUMMER 1975 X o < LU X en UJ CD 800- 700- 600- 500- 400- 300- 200- 100- 200- 100- N=4005 — r WINTER 1976 "1 I T "1 — I — r X 1 1 1 — T" SPRING 1974 N = 442 i — i — i — i — i i — i — i — i — i — i — i — r 2 4 6 8 10 12 14 16 18 20 22 24 26 FISH LENGTH (cm) Figure 9.— Length-frequency distributions (FL) from the total catch of tomtates between Cape Fear and Cape Canaveral during each of four seasons. DISCUSSION Distribution and Abundance Tomtates are considered abundant in several habitats in and to the south of the South Atlantic Bight, and indicate daily movements between habitats. Within the Bight, tomtates were com- mon over both live-bottom and shelf-edge habi- tats during earlier (1959-64) exploratory fishing (Struhsaker 1969). Farther south, tomtates were found over broad sandy areas off southern Flor- ida (Craig 1976), near coral stacks in the Tor- tugas Islands (Longley and Hildebrand 1941), and in grass beds and other open areas in the Bahamas (Bohlke and Chaplin 1968). Tomtates were common from nearshore to the offshore reefs in Florida and were abundant on the shrimp grounds of the Dry Tortugas and the Gulf of Mexico (Courtenay 1961). In the Virgin Islands, changes in distribution with respect to habitat type were associated with feeding be- havior. Tomtates feed as individuals or in small schools at night over open sand (Collette and Tal- bot 1972), and they spend the day on the reef segregated into size groups; juveniles school over the highest part of the reef, while adults hover low between the coral colonies (Smith and Tyler 1972). Juvenile tomtates may occur in several habi- tats, either inshore or offshore, which include "live bottom" and rocky outcrops similar to those occupied by adults. Small tomtates (*«33 mm) were abundant over artificial reefs (Parker et al. 1979) and natural ridges in spring through fall off the Carolinas and have been found in the mouths and stomachs of black sea bass in the same areas (Parker8). Young tomtates also fre- quent grass beds (Randall 1968), subtidal mud flats (Reid 1954), and nearshore areas around wharfs (Jordan and Evermann 1896). The pres- ence of young fish among spines of sea urchins (Johnson 1978) suggests that microhabitats may be important to the survival of some early life stages. Juveniles of French grunts, H. flavolin- eatum, and white grunts, H. plumieri, form large multispecies schools closely associated with par- ticular coral formations (microhabitats) during the day and follow precise routes (>100 m) to and from feeding areas (sea grass beds) at night (Ogden and Ehrlich 1977). Biomass and standing stock calculations for tomtate from groundfish trawling were consid- ered preliminary, minimal estimates. More satisfactory estimates should incorporate infor- mation on 1) abundance/biomass sampling con- ducted completely within a known area of a given habitat type, 2) the correct proportional allocation of a day/night catch factor for each habitat sampled, 3) the vulnerability of tomtate to the sampling gear, and 4) estimates of biomass from untrawlable, rocky outcrop, habitats. Un- fortunately, none of the above information is available at present, so our estimates were based upon continuous day/night sampling imposed on the very random nature of sponge-coral habitat distribution. Discrete, short duration trawling completely within the boundaries of the patchy sponge-coral habitats could be directed by pre- trawl bottom mapping with underwater TV 8R. 0. Parker, Southeast Fisheries Center Beaufort Labora- tory, National Marine Fisheries Service, NOAA, Beaufort, NC 28516, pers. commun. January 1978. 14 MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE (Powles and Barans 1980). This method would allow more accurate quantification of relative abundance differences between habitats and be- tween day and night sampling. Then, a biomass factor could be developed to proportion fish availability to the trawl during daytime collec- tions in sponge-coral habitats and during night in sand bottom habitats. Also, the vulnerability of tomtate, or any groundfish in the South Atlan- tic Bight, to trawl gear is unknown. Several experiments with a headrope mounted TV sys- tem would do much to fill this data gap. Biomass estimates from rocky habitats may have to be extrapolated from nearshore diver counts or off- shore TV counts, but many problems remain in the interpretation of these data. In general, a composite estimate of tomtate biomass or stand- ing stock in the South Atlantic Bight should include difficult to obtain fish behavior informa- tion. Tomtate are relatively shallow water (<50 m) groundfish with a more pronounced tendency for annual depth migrations in populations south of the South Atlantic Bight. Tomtates in the Cam- peche Bank area were most abundant in waters <30 m during all seasons (Sauskan and Olaechea 1974), while tomtates occurred only at depths of <10 m in the Bahamas (Bohlke and Chaplin 1968). Although tomtates remain inshore during winter in Florida (Courtenay 1961), they are not caught by inshore shrimp trawlers off South Carolina (Keiser 1976) and appear to avoid shal- low waters (<20 m) north of Florida during win- ter. There is the possibility that during ex- tremely cold winters, slight migrations (shifts in distribution) southward occur. In contrast to the results of this study, tomtates of the Campeche Bank move onshore during win- ter and fall and offshore in spring and summer and are recruited to the fishery in shallow waters, a great distance from the deeper area where spawning takes place (Sauskan and Olae- chea 1974). The difference in location of spawn- ing and recruitment and lack of large adult fish over reefs in Florida (Stone et al. 1979) and in commercial trawl catches (Sokolova 1969) sug- gests separation of juvenile and adult popula- tions, especially south of Florida. Age and Growth The fact that scales may be used to accurately determine the age of a warmwater marine fish species is not particularly surprising. Scales have been used to age other reef fishes that occur with tomtates in the South Atlantic Bight. Ma- nooch (1976) found annuli on scales from white grunt collected off the Carolinas; Manooch and Huntsman (1977) aged red porgy, Pagrus pag- rus, using both scales and otoliths; and Grimes (1978) determined the age of vermilion snapper, Rhomboplites aurorubens, by reading scales. The theoretical parameters derived in this study are compared with those for tomtates from the Campeche Banks, and with cooccurring spe- cies in the South Atlantic Bight in Table 11. The Campeche Banks fish did not live as long — 5 or 7 yr compared with 9 in the South Atlantic Bight — and had a slightly smaller maximum size (Lx), 295 mm compared with 310 mm. Con- sequently, the growth coefficient, although very similar, is slightly higher— 0.235 compared with 0.200. With the exception of black sea bass, Cen- tra pristis striata, sympatric species previously studied in the South Atlantic Bight were longer lived and slower growing (Table 11). Table 11.— Growth parameters for six species of demersal fish. Scientific L^ Longevity Common name name Area Author M K (TL. mm) (yr) Tomtate Haemulon aurolineatum N.C., S.C, Ga , east coast Florida Campeche Banks This paper Calculated from 0.22017 310 9 Sokolova (1969) 0235 295 5 Sauskan and Olaechea 7 (1974) White grunt H. plumieri N.C., S.C. Manooch (1976) 0.4 & 0.6 0.108 640 13 Red porgy Pagrus pagrus N.C., S.C. Manooch and Huntsman (1977) 0.2 0096 763 15 Vermilion Rhomboplites N.C., S.C. Grimes (1976) 0.25 0 198 627 10 snapper aurorubens Gag Mycteroperca microlepis N.C, S.C. Ga., east coast Florida Manooch and Haimovici (1978) 0.20 0.121 1,290 13 Black sea Centropristis N.C, S.C. Mercer1 0.30 0.220 352 8 bass striata 'Linda Mercer, Virginia Institute of Marine Sciences, Gloucester Point, Va 15 FISHERY BULLETIN: VOL. 80, NO. 1 Spawning Growth rates of juvenile tomtates (>130 mm TL/first year) in the South Atlantic Bight and rates estimated from larvae of similar species support the spawning season indicated by analy- sis of gonads. If growth of very early stages of tomtates approximates the 14 mm SL/30 d for white grunts (Saksena and Richards 1975) and French grunts (Brothers and McFarland In press), tomtates of 30-90 mm TL caught in early September may have been spawned between early April and June. Identification of peak spawning period of tomtate by associated larval abundance was impossible due to difficulties in identifying larval haemulids. Populations of tomtates farther south appear to have a prolonged spawning season. Munro et al. (1973) reported collections of ripe females be- tween January and August in Jamaica, while Cervigon (1966) suggested that tomtates spawn throughout the year in Brazil. Tomtates from Campeche Bank spawn primarily during July- September at depths of >50 m and again during winter at shallower depths (Sauskan and Olae- chea 1974). Management We believe management of the tomtate fishery should be considered for three reasons. First, the species is easily captured by a variety of fishing techniques: hook and line, trap, and unlike most other reef fishes, by trawl. Second, fishing effort applied to this, and other associated, species will probably increase. And third, the tomtate is a member of a rather delicate faunal community and is a major source of food for higher trophic level, piscivorous fishes. Unwise harvest of one species could have both physical and energetic impacts on the community as a whole. While regional catches of tomtates may at times be quite large, for instance by recreational anglers on headboats fishing inshore waters, the species ranks low in terms of poundage landed in the South Atlantic Bight by both recreational and commercial fishermen. Because tomtates are small and not competitive in value with other reef fishes in the commercial market, commer- cial hook and line fishermen usually discard the species or use it as bait for larger predatory fishes, such as groupers and snappers (Wen- ner9). Given the geographical range of H. aurolin- eatum, its abundance as indicated by exploratory trawling, and relatively low harvest by fisher- men, one could label it as an "underutilized spe- cies" in the South Atlantic Bight. However, assigning tomtates this status requires a thor- ough understanding of currently operating fish- eries plus a knowledge about the role of the species in the ecosystem. We do not recommend such a designation at this time. Although the distribution of tomtate is contin- uous from the southeastern coast of the United States to the Campeche Banks, the stock fished in each area should be considered separate for assessment and fishery management. Our study and the studies of Sokolova (1969) and Sauskan and Olaechea (1974) show that tomtates are a relatively short-lived, fast-growing reef fish with a high annual mortality rate when com- pared with other reef fishes of the region. Fish with these biological traits usually are not as readily overfished as those that grow more slowly, those that live longer, and those with a lower annual mortality rate. However, many fast-growing, high-mortality species such as mackerels (Scomberomorus), some tunas (Thun- nus), and menhaden (Brevoortia), which are im- portant to large fisheries, have demonstrated some signs of being overfished. By comparing our study with those on the Campeche Bank, we can look at one stock caught at present primarily by hook and line and the other by a more intensive gear, the trawl. The major difference between the South Atlantic Bight tomtates and those from Campeche Bank is that the Atlantic stock is older and larger. There are several explanations other than bio- logical changes in ecology or genetics for the dif- ferences between these stocks. In our study, the tomtates were caught by recreational fishermen using hook and line while those from Campeche Bank were trawled. Hook and line fishing may be more selective of larger fish and some of the smaller fish may be discarded by the fishermen resulting in larger fish of each age being sam- pled. A more likely explanation is that the large, old Atlantic fish have a generally low exploita- tion rate. The Soviet-Cuban trawlers have fished Campeche Bank since 1964 with catches of grunts averaging over 20,000 tons a year and ex- *C. A. Wenner, South Carolina Wildlife and Marine Re- sources Department, Marine Resources Research Institute, Charleston, SC 29412, pers. commun. January 1978. 16 MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE ceeding 60,000 in 1971 and 1975 for the region according to FAO Yearbooks. If, as we suspect, most of these catches were tomtate, the Cam- peche stock has been much more exploited than the Atlantic for the past 10 yr. Regional harvest of tomtates by hook and line will probably remain low. Recreational anglers will continue to catch small numbers, and com- mercial handliners will continue to regard H. aurolineatum as "trash fish" or bait. Any in- crease in the harvest will probably involve an expansion of a trawl fishery off South Carolina, Georgia, and northeast Florida. Prior to development of any U.S. groundfish trawl fishery for tomtate, the possibility of habi- tat destruction by trawl gear should be investi- gated. Some bottom trawl harvest techniques may have detrimental effects on the substrate community in which tomtate are most abundant. Destruction or removal of the sponge/coral in- vertebrates and crab species, or damage to Ocu- lina coral beds, may indirectly reduce future yields of tomtate and other fish species. Also, during several seasons trawls may catch juveniles of a species important to both commer- cial and sport fisheries prior to their recruitment to harvest by hook and line. Bottom trawling for tomtate in "live bottom" areas would catch large numbers of small, commercially unimportant fish species and invertebrates which would in- crease costs of sorting unless the entire catch was processed as a mixed species product. In our study the greatest relative abundance (catch/tow) of adults was during winter at which time commercial harvesting could take advan- tage of any concentrations of fish resulting from a shift to a more offshore distribution of the popu- lation. Reduction of fishing effort during late winter and early spring would allow the un- fished stock to spawn and juveniles to be re- cruited to the fishery at a larger size, possibly regulated by net mesh size. Even in this case, a drastic reduction in population size could ad- versely affect the recreational headboat fishery. ACKNOWLEDGMENTS We thank the Captain and crew of the RV Dol- phin for cooperation and patient efforts through- out the field work; Victor Burrell, Jr., Director of the South Carolina Marine Resources Research Institute for support and encouragement; Julian Mikell for preliminary summary, especially gonad/maturity data; Karen Swanson and Herb Gordy for graphic arts; Dean Ahrenholz, Gene Huntsman, and John Merriner for reviewing the manuscript; and Beverly Ashby and Beverly Harvey for typing. Parts of this research were sponsored by the National Marine Fisheries Service (MARMAP Program Office) under contract No. 6-35147. LITERATURE CITED Beverton, R. J. H., and S. J. Holt. 1957. On the dynamics of exploited fish populations. Fish. Invest. M inist. Agric. Fish. Food (G.B.) Ser. II, 19, 533 p. Bliss, C. I. 1967. Statistics in biology. 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Biology and population abundance of the tomtate (Haemulon aurolineatum) (Cuvier and Valenciennes, 1830, Pomadasyidae, Perciformes) on Campeche Bank. [In Russ.] In A. S. Bogdanov (editor), Soviet-Cuban fishery research, Vol. 4, p. 135-510. Institute de Inves- tigacion Cientifica de la Economia Pesquera Marina y de la Oceanografia de toda la Union (VNIRO), Centro de Investigaciones Pesqueras (CIP), Mosc. Smith, C. L., and J. C. Tyler. 1972. Space resource sharing in a coral reef fish commu- nity. In B. B. Collette and S. A. Earle (editors), Results of the Tektite program: Ecology of coral reef fishes, p. 125-170. Natl. Hist. Mus. Los Ang. Cty., Sci. Bull. 14. Sokolova, L. V. 1969. Distribution and biological characteristics of the main commercial fish of Campeche Bank. In A. S. Bog- danov (editor), Soviet-Cuban fishery research, p. 208- 224. Isr. Program Sci. Transl., Jerusalem. Springer, V. G., and K. D. Woodburn. 1960. An ecological study of the fishes of the Tampa Bay area. Fla. Board Conserv. Mar. Lab. Prof. Pap. Ser. 1, 104 p. Stone, R. B., H. L. Pratt, R. O. Parker, Jr., and G. E. Davis. 1979. A comparison of fish populations on an artificial and natural reef in the Florida Keys. Mar. Fish. Rev. 41(9):1-11. Struhsaker, P. 1969. Demersal fish resources: Composition, distribu- tion, and commercial potential of the continental shelf stocks off southeastern United States. Fish. Ind. Res. 4:261-300. Taylor, C. C. 1953. Nature of variability in trawl catches. U.S. Fish Wildl. Serv., Fish. Bull. 54:145-166. Walford, L. A. 1946. A new graphic method for describing the growth of animals. Biol. Bull. (Woods Hole) 90:141-147. Wenner, C. A., C. A. Barans, B. W. Stender, and F. H. Berry. 1979a. Results of MARMAP otter trawl investigations in the South Atlantic Bight. I. Fall 1973. S.C. Mar. Re- sour. Cent. Tech. Rep. 33, 79 p. 1979b. Resultsof MARMAPotter trawl investigations in the South Atlantic Bight. II. Spring, 1974. S.C. Mar. Resour. Cent. Tech. Rep. 40, 78 p. MANOOCH and BARANS: DISTRIBUTION AND ABUNDANCE OF TOMTATE 1979c. Results of MARMAP otter trawl investigations in Wilk, S. J., AND M. J. Silverman. the South Atlantic Bight. III. Summer, 1974. S.C. 1976. Fish and hydrographic collections made by there- Mar. Resour. Cent. Tech. Rep. 41, 62 p. search vessels Dolphin and Delaware //during 1968-72 1979d. Resultsof MARMAPottertrawl investigations in from New York to Florida. U.S. Dep. Commer., the South Atlantic Bight. IV. Winter-early Spring, NOAA Tech. Rep. NMFS SSRF-697, 159 p. 1975. S.C. Mar. Resour. Cent. Tech. Rep. 44, 59 p. 19 GROWTH OF THE OCEAN QUAHOG, ARCTICA ISLANDICA, IN THE MIDDLE ATLANTIC BIGHT Steven A. Murawski, John W. Ropes, and Fredric M. Serchuk1 ABSTRACT In situ growth rate of the ocean quahog, Arctica islandica, was investigated at a site 53 m deep off Long Island, New York, during 1970-80. Specimens notched during summer 1978 and recaptured 1 and 2 calendar years later yielded information on shell growth and the periodicity of supposed annual marks. Growth of specimens recaptured after 1 year at liberty (n = 67, 59-104 mm shell length) was described by SL,.\ =2.0811 +0.9802 SL,, where SL is shell length in millimeters at age t. Average shell length of marked specimens recaptured during summer 1980 increased 1.17 mm (w = 200), approximately twice that of ocean quahogs recaptured in 1979 (0.56 mm). Band for- mation on the external surface of small ocean quahogs (less than about 60 mm) was apparently an annual event since small specimens recaptured in 1979 formed one such mark during the interval between release and recapture. Small specimens sampled during summer exhibited relatively wide marginal growth from the last external mark to the shell edge, while winter samples had formed new annuli at the shell margin, thus, external bands were formed during early autumn- early winter. Internal banding in shell cross sections of small ocean quahogs correlated in number and position with external features. An equation representing back-calculated growth, based on external banding patterns of small unmarked specimens (19-60 mm) captured during summer 1978, was: SL = 75.68-81.31 (0.9056)', where tis age in years. Length-frequency samples were avail- able for the vicinity of the marking study from routine dredge surveys of clam resources during 1970-80. Growth rates inferred from progressions of length-frequency modes in 1970 and 1980 sam- ples were similar to those computed from mark-recapture and age-length equations. Ocean quahogs are apparently among the slowest growing and longest lived of the continental shelf pelecypods; annual increases in shell length were 6.3% at age 10, 0.5% at age 50, and 0.2% at an estimated age of 100 years. Research on the population dynamics of the ocean quahog, Arctica islandica, has become in- creasingly important in recent years. An inten- sive fishery for the species developed off New Jersey and the Delmarva Peninsula during the mid-1970's. The resulting increases in U.S. land- ings were dramatic: from 588 1 of shucked meats in 1975 to a record 15,748 1 by 1979. Estimates of the growth rate and longevity of ocean quahogs inhabiting the Middle Atlantic Bight are neces- sary to assess potential impacts of various har- vesting strategies on the resources (Murawski and Serchuk2; Mid-Atlantic Fishery Manage- ment Council3). ■Northeast Fisheries Center Woods Hole Laboratory, Na- tional Marine Fisheries Service, NOAA, Woods Hole, MA 02543. 2Murawski,S. A., and F. M. Serchuk. 1979. Distribution, size composition, and relative abundance of ocean quahog, Arctica islandica, populations off the Middle Atlantic Coast of the United States. ICES/CM. 1979/K:26, Shellfish Comm., 22 p. 3Mid-Atlantic Fishery Management Council. 1979. Amendment No. 2 for the surf clam and ocean quahog fishery Several early studies alluded to the age and growth rate of Arctica islandica, yet citations were largely anecdotal and generally did not re- flect critical evaluations of the rate of growth or the validity of aging criteria. Turner (1949) reported an observation by G. Thorson that "European investigators who have studied the chemical composition of the shell found reason to believe that it took six years or more for mahog- any (ocean) quahaugs (quahogs) to reach average size." Loosanoff (1953) stated that ocean quahogs he examined for reproductive studies "were adults, several years old, and averaged 3% to 4 inches (89-102 mm) in length." Jaeckel (1952) noted Cyprina (=Arctica islandica) could per- haps attain ages up to 20 "Sie kann hohes Alter (Vielleicht bis zu 20 Jahven) erreichen." Skula- dottir4 did not elaborate on aging methodologies Manuscript accepted August 1981. FISHERY BULLETIN: VOL. 80. NO. 1. 1982. management plan and final supplemental environmental im- pact statement. Mid-Atlantic Fishery Management Council, Dover, Del., 114 p. 4Skuladottir, U. 1967. Kraffadyr og skeldyr (Crustacean and mollusks). Radstefna Isl. Verkfraedinga. 52:13-23. 21 FISHERY BULLETIN: VOL. 80. NO. 1 but claimed "the oldest clams were up to 18 years and about 9 cm long. The bulk was in the 10-14 year group and 7-8.7 cm long." The external color of large ocean quahogs (greater than about 60 mm shell length) is usu- ally solid black; however, the periostracum of small individuals is variable in color, grading from pale yellow to deep brown (Loven 1929; Hiltz5). Concentric dark bands appearing in the shell surface of small specimens have thus been interpreted as annuli by several authors. Although Loven did not present age-size rela- tionships explicitly, he did note the presence of external "annual rings" ("Jahresringe") and pre- sented photographs of a size range of small ocean quahogs, illustrating the relationship between numbers of rings and shell lengths. Chandler6 measured the maximum diameters of concentric rings and derived growth relationships based on eight specimens (96 total measurements, to milli- meters). The largest number of such rings ap- pearing on an individual ocean quahog was 21; the corresponding shell length was 58.5 mm. Caddy et al.7 presented growth curves, based on external markings, for small ocean quahogs from the Northumberland Strait and Passama- quoddy Bay. Average length at age was consis- tently greater for the more southern area. Unpublished manuscripts by Chene8and Mea- gher and Medcof9 document efforts to more pre- cisely establish ocean quahog growth rates. Mark and recapture experiments were con- ducted in Brandy Cove, New Brunswick. Notched specimens (n = 14), averaging 57.4 mm (shell length) when recaptured, grew an average of 0.6 mm (shell height) between September 1970 (Proceedings of the conference of Islandic Professional Engi- neers. Fish. Res. Board Can., Biol. Stn., St. Andrews, N.B., Trans. Bur., No. 1206.) 5Hiltz, L. M. 1977. The ocean clam (Arctica islandica). A literature review. Fish. Mar. Serv. Tech. Branch, Halifax N.S., Tech. Rep. 720, 177 p. 6Chandler, R. A. 1965. Ocean quahaug resources of Southeastern Northumberland Strait. Fish. Res. Board. Can., Manuscr. Rep. (Biol.) 828, 9 p. 7Caddy, J. F., R. A. Chandler, and D. G. Wildler. 1974. Biology and commercial potential of several underexploited molluscs and Crustacea on the Atlantic coast of Canada. Pre- sented at Federal-Provincial committee meeting on Utiliza- tion of Atlantic Resources, Montreal, Feb. 5-7 1974. Prepared at Fisheries Research Board of Canada, St. Andrews Biologi- cal Station, N.B. "Chene, P. L. 1970. Growth, PSP accumulation and other features of ocean clams (Arctica islandica). Fish. Res. Board Can., St. Andrews Biol. Stn., Orig. Manuscr. Rep. 1104, 34 p. sMeagher, J. J., and J. C. Medcof. 1972. Shell rings and growth rate of ocean clams (Arctica islandica). Fish. Res. Board Can., St. Andrews Biol. Stn., Orig. Manuscr. Rep. 1105, 26 p. and September 1971. Sequential observations of eight small ocean quahogs (mean length 20.16 mm) was undertaken to assess growth rates and seasonal changes in the color patterns of the peri- ostracum. These individuals were held in cages and grew an average 17% in length from 4 June to 31 August 1971. Periostracum formed during the interval was brown, contrasting with yellow material formed before the study was begun. However, this banding pattern may not have been indicative of a normally occurring annual event since "the caged clams were sensitive to experimental treatments and produced distur- bance rings each time they were air-exposed for observation" (Meagher and Medcof footnote 9). Several recent studies have examined banding patterns present in shell cross sections and have attempted to validate the hypothesis of band for- mation as an annual event. Jones (1980) noted that marginal increments of shell deposition be- yond the last band followed a seasonal progres- sion; bands were formed once per year between September and February. The most rapid pro- duction of shell was from late spring to early summer; annulus formation overlapped the spawning period in mature individuals. Thomp- son et al. (1980) presented size-frequency data of small specimens from the Baltic Sea and inter- preted external and cross-sectional banding in these specimens as supporting evidence for an- nual periodicity of band formation in larger (older) specimens from the Middle Atlantic Bight. Thompson et al. further stated that pre- liminary results from radiochemical analysis of shells corroborated age analysis based on shell banding patterns. We initiated a project during summer 1978 to assess in situ growth rates of ocean quahogs at a deepwater site off Long Island, N.Y. Objectives of the study were to obtain growth increment data directly from mark-recapture, further eval- uate the potential of banding patterns (both ex- ternal and in shell cross section) as indicators of age, and correlate growth measurements with a 10-yr time-series of length frequencies collected in the vicinity of the marking site. Length- weight relationships have been established for the Middle Atlantic, based on a synoptic winter survey (Murawski and Serchuk 1979); however, no data have been published on seasonal varia- tions. An additional objective of the project was to compare winter and summer length-weight relations at the marking site. 22 MURAWSKI ET AI..: GROWTH OF OCEAN QUAHOG. ARCT1CA ISLANDICA FIELD STUDIES Intermittent surveys of offshore clam re- sources of the Middle Atlantic Bight have been conducted since 1965 by the National Marine Fisheries Service, and its predecessor the Bu- reau of Commercial Fisheries (Merrill and Ropes 1969; Murawski and Serchuk footnote 2; Serchuk et al.10). Cruises were designed to yield information on temporal and areal aspects of dis- tribution, size composition, and relative abun- dance of both surf clam, Spisula solidissima, and ocean quahog. Stations were sampled in a grid array prior to 1978; surveys from 1978 to 1980 employed a stratified-random scheme. Commer- cial-type hydraulic clam dredges were modified to retain small individuals and used as survey gear; dredge specifications and vessels varied somewhat among cruises (Serchuk et al. footnote 10; Table 1). We selected an area for intensive field study of ocean quahog growth, based on an evaluation of pre-1978 survey data and knowledge of commer- cial fleet activities. Specific criteria were: 1) suf- ficient clam densities for rapid capture of indi- viduals used in the marking experiment, 2) abundant numbers of clams over a wide size range, 3) clam densities similar to sites fre- quented by fishing vessels, and 4) lack of pre- vious exploitation and low probability of near- future use. These specifications were met at a site 48 km south-southeast of Shinnecock Inlet, Long Island, at lat. 40°25.1'N, long. 72°23.7'W. '"Serchuk, F. M.. S. A. Murawski, E. M. Henderson, and B.E.Brown. 1979. The population dynamics basis for man- agement of offshore surf clam populations in the Middle Atlan- tic. Proceedings of the Northeast Clam Industries - Manage- ment for the Future, Coop. Ext. Serv. Univ. Mass. -MIT Sea Grant, p. 83-101. Water depth was 53 m, and substrata consisted of coarse sand and shell, primarily ocean quahog and sea scallop, Placopecten magellanicus. Live invertebrates present in survey samples in- cluded Lunatia heros, Echinarachnius parma, Venericardia borealis, Aphrodite aculeata, and Astarte spp., in addition to ocean quahog and sea scallop. Water depth at the study site precluded ex- tended periods of bottom time using normal scuba methods, thus we elected to sample ocean quahogs with commercial and research dredging vessels. The probability of recapturing marked ocean quahogs at the site was considered to be relatively low because of water depth, width of sampling gear, difficulties in positioning the ves- sel at a precise location, and the accuracy of the loran-C navigation system. Hence it was decided to mark and redistribute large numbers. Incremental increases in clam shell growth corresponding to known time durations can be measured if a point of reference is initially estab- lished at the margin of the growing shell. Growth is determined directly from recaptured speci- mens and shell length at marking can either be measured or back-calculated. Thus we needed only to indelibly etch the shell edge of live qua- hogs and return them to the sea bed, obviating the laborious and time-consuming process of measuring and number-coding individuals prior to release. Notching techniques have been used success- fully to study growth rate and to validate the periodicity of band formation in a number of bi- valve species including soft shell clam, Mya arenaria (Mead and Barnes 1904); hard shell clam, Mercenaria mercenaria (Belding 1912); American oyster, Crassostrea virginica (Loosa- noff and Nomejko 1949); sea scallop (Stevenson Table 1. — Characteristics of survey gear and length-frequency statistics of ocean quahogs collected near lat. 40°25' N, long. 72°24' W, in the Middle Atlantic Bight, 1970-80. Dates Hydraulic dredge blade width (cm) Spacing between1 bars or rings (mm) Shell ler igth (mm) Vessel X SD Range n RV Delaware II 13 August 1970 122 30 2741 20.1 25-105 107 RV Delaware II 24 April 1976 122 30 74.1 16.6 40-115 271 RV Delaware II 27 February 1977 122 30 73.4 14.5 45-104 234 RV Delaware II 1 January-2 February 1978 122 30 74.5 14.3 34-113 211 FV Diane Maria3 26 July-5 August 1978 254 13 74.5 15.4 31-112 1.262 RV Delaware II 9 January 1979 152 25 71.4 145 33-116 1,317 RV Delaware II* 14-21 August 1979 152 25-51 76.5 15.2 38-111 811 RV Delaware II 8 February 1980 152 51 74.2 13.8 38-117 5.546 RV Delaware II* 9 September 1980 152 51 74.8 13.4 40-108 1.899 'Dimension in the portion of the dredge where catch is accumulated 2Samples measured to the nearest 0 5 cm. initiation of marking study 4Recapture of marked individuals. 23 FISHERY BULLETIN: VOL. 80, NO. 1 and Dickie 1954; Merrill et al. 1966); and surf clam (Ropes and Merrill 1970; Jones etal. 1978). Accordingly, we marked ocean quahogs by cut- ting shallow grooves from the ventral margin up the shell surface using thin carborundum discs mounted on an electric grinder (Ropes and Mer- rill 1970). Two parallel grooves 2 mm apart were cut into each shell to distinguish our marks from shells scratched by natural processes or during dredging (Fig. 1). Marking operations were conducted from 26 July to 5 August 1978 (Table 1). A total of 41,816 ocean quahogs was notched by the previously de- scribed technique. Batches of 3,000-5,000 clams were dredged from within 9 km of the planting site, marked, and redistributed. The method of marking and planting clams was rapid; about 1,600 clams were marked per hour. A grid sys- tem based on loran-C coordinates, was used to indicate the location of each batch. Length-fre- quency samples were obtained during the mark- ing phase (Table 1), and 134 small ocean quahogs (19-60 mm) were retained for maturity studies and analyses of exterior and cross-sectional banding. An intensive effort to recapture marked indi- viduals was undertaken, 1 calendar year after planting, during 14-21 August 1979 (Table 1). Forty-three hydraulic dredge tows, each of about 5-min duration, were completed at the site. A Northstar 600011 loran-C set and an Epsco loran- C plotter were used in the systematic search of a 20,000 m2 area. A total of 14,043 ocean quahogs was examined; 74 (0.5%) had been marked. Re- captured specimens were photographed, mea- sured, and frozen intact at sea. A random sample of 126 unmarked ocean quahogs was frozen for length-weight comparison with marked indi- viduals. Marked individuals were again recaptured, approximately 2 yr after planting, on 9 Septem- ber 1980 (Table 1). Two dredge tows yielded 1,899 ocean quahogs; 249 individuals (13.1%) had been marked. Length-frequency measurements were ob- tained from the site during routine assessment surveys in January 1979 and February 1980. Sampling within 10 km of the site was historic- ally serendipitous; catch data were available from four surveys between 1970 and February 1978 (Table 1). Lengths of ocean quahogs taken near the site exhibited a consistent bimodal fre- quency distribution throughout the time-series. Growth rate information from the mark-recap- ture and shell banding experiments was thus compared with that generated from modal pro- gression in sequential length frequencies. A random sample of 278 ocean quahogs taken from the site during February 1980 was frozen whole for length-weight comparison with the August 1979 sample. Small ocean quahogs (<60 mm) were also frozen intact for analysis of the timing of periodic band formation in the shells. LABORATORY STUDIES M ark- Recapture Recaptured specimens were thawed but kept moist during all phases of analysis to prevent shell cracking and disintegration of the perio- stracum. A total of 67 of the 74 specimens recap- tured in 1979 and 200 of 249 specimens recap- tured in 1980 were suitable for growth analysis; the remaining samples were either shell frag- ments or from quahogs obviously dead when re- covered. Shells were measured to the nearest 0.01 mm, using calipers or dissecting microscope equipped with an ocular micrometer. Perio- stracum obscured the shell edge of most speci- mens and was subsequently removed from the vicinity of the mark prior to measurement. Shell lengths were obtained by pressing the perio- stracum against the valves with calipers. Growth increments of recaptured ocean qua- hogs were determined as the linear increase in shell dimension along an imaginary line passing through the umbo and equidistant between grooves that formed the mark (Fig. 1). The linear distance between the umbo and shell edge at the mark was designed as h'\ shell length at marking was computed for each quahog by: Oi-/f — o/v(*l [ {h'm - h',) ] (1) "Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. where SL, = shell length (longest linear dimen- sion) at marking, SLm = shell length at recapture, h\= linear measurement between umbo and edge of the shell equi- distance between grooves, at marking, h'tn = linear measurement between umbo and edge of the shell 24 MURAWSKI ET AL.: GROWTH OF OCEAN QUAHOG, ARCTICA ISLANDICA Figure 1.— Ocean quahog shells used for growth analyses taken near lat. 40° 25'N. long. 72°24'W, in the Middle At- lantic Bight, (a) Specimen 65 mm. shell length, marked during July-August 1978 and recaptured during August 1979. Arrow indicates external growth band formed during the interval be- tween marking and recapture, (b) Ar- row indicates shell growth of a 68 mm specimen from July-August 1978 to Au- gust 1979 with periostracum removed, (c) Arrows indicate positions of most re- cently formed external growth bands on small individuals from August 1979 (right, 43 mm) and February 1980 (left, 45 mm) samples. 25 FISHERY BULLETIN: VOL. 80, NO. 1 equidistant between grooves, at recapture. Marginal growth in shell length was thus equiv- alent to the bracketed term. Implicit in Equation (1) is the assumption that ratios between the linear parameters SL and h! did not change between marking and recapture (isometric growth). The assumption is supported by comparisons of various standard shell dimen- sions (i.e., shell length, height, and width, Chan- dler footnote 6; Northeast Fisheries Center Woods Hole Laboratory unpubl. data), particu- larly considering the relatively small percent changes in shell size between marking and re- capture (Table 2). 1 40 - • • _T • + • ..♦ LP s 1 05 -2. • < •* ^^2 • N = 67 2 Ld UJ or o 0 70 • • • • .. • • Y = 2.0811 -0.0198x r = - 0 774 1 I (- o or o 0 35 • • • • • • • • • • I 60 70 80 90 100 SHELL LENGTH ( MM ) L Table 2.— Growth of ocean quahogs marked during August 1978, and recaptured during August 1979 (n = 67), and Septem- ber 1980 (n = 200), at lat. 40°25' N, long. 72°24' W, in the Middle Atlantic Bight. Parameter Year Mean (mm) SD (mm) Range (mm) Shell length at 1979 77.31 14.67 59.12-104 40 recovery 1980 7901 13.91 57.69-103.66 Calculated growth 1979 0.56 0.38 0.08-1.38 increment in shell 1980 1.17 1.04 0.07-4.32 length Calculated shell 1979 7676 14.97 58.15-104.09 length at marking 1980 77.84 14.75 55.46-103.43 Three methods were used to fit growth equa- tions to mark-recapture data. For ocean quahogs recovered 1 calendar year after marking, length at recapture was related to length at marking using Ford-Walford and linear annual increment plots described by Gulland (1969; Fig. 2). Ad- ditionally, a nonlinear exponential equation was fit to increment data and results compared with those assuming the von Bertalanffy model. The von Bertalanffy parameters L^ and K were also estimated using the BGC4 computer program ( Abramson 1971 ). The program was designed for determining growth parameters when lengths of unaged individuals are known at two points in time, based on the algorithm of Fabens (1965). Equations derived from mark-recapture data can be used to describe relative growth from an arbitrary point in time (i.e., SLM, SLt,2, ... SL,.„), but without at least one independently derived age-length observation, absolute growth curves cannot be established. Accordingly, anal- yses of external banding patterns of small ocean quahogs were critical in "fixing" growth curves from mark-recapture. Figure 2.— Relation between calculated increment of growth in shell length (millimeters) and initial length for ocean qua- hogs marked during July- August 1978 and recaptured during August 1979 near lat. 40°25'N, long. 72°24'W, in the Middle Atlantic Bight. Shell Banding Small ocean quahogs retained from the July- August 1978 cruise were analyzed for external and internal shell banding patterns. Sequential growth of individual ocean quahogs was followed by measuring the maximum dimension (shell length) of exterior bands appearing on the perio- stracum, using calipers (Fig. 1). Maximum shell length beyond the last band was also recorded. The opposite valve was sectioned from the umbo to the ventral margin and polished (Saloman and Taylor 1969; Jones et al. 1978). An acetate im- pression of the polished surface was made and mounted between glass slides. Images were en- larged with a microprojector to reveal internal banding patterns. Internal lines present in shell cross sections correlated in number and position with external bands when the latter were distinct. The perio- stracum on some shells was eroded near the umbo, obscuring external bands. In these cases "annuli" nearest the umbo were located on the peels, but measurements of shell size could not be made (Table 3). External marks present near the shell margins on some larger specimens also could not be discerned; internal banding was again used to estimate age. Shell length statistics were computed for each age/annulus subclass, weighted lengths at annuli for all ages and 26 MURAWSKI ET AL.: GROWTH OF OCEAN QUAHOG, ARCTICA ISLANDICA Table 3.— Back-calculated growth (shell length, in millimeters) of small ocean quahogs. Samples taken from lat. 40°25' N, long. 72°24' W, 26-29 July 1978, in the Middle Atlantic Bight. Number of annuli Length at capture Length at annulus 1 2 3 4 5 6 7 8 9 10 11 12 13 2 x SD n 18.00 0.00 1 700 000 1 12.30 000 1 3 x SD n 23.36 3.42 9 4.59 0.78 9 1059 266 9 1801 3.14 9 4 x SD n 2973 200 14 4.39 0.73 14 1004 2.13 14 1699 238 14 2438 1 96 14 5 x SD n 34.58 3.19 26 4.43 0.07 26 8.80 1.50 26 14.45 2.29 26 21.72 3.08 26 29.72 3.41 26 6 x SD n 3849 2.73 27 4.07 059 '25 7.77 1.57 27 13.40 249 27 19.13 258 27 26.09 2.73 27 33.88 2.92 27 7 x SD n 41 66 200 29 4.16 1.10 '27 7.66 1.34 29 12.10 1.72 29 17.42 1.57 29 2387 1.87 29 3081 1 98 29 37.61 2.05 29 8 x SD n 46.24 1.78 10 392 0.98 10 7.59 1.44 10 1229 2.39 10 16.92 2.77 10 23 64 2.38 10 29 95 2.52 10 36.63 2.22 10 42.76 1.99 10 9 x SD n 47.60 000 1 3.10 0.00 1 7.50 000 1 11.00 0.00 1 15 90 000 1 21.30 0.00 1 27.40 000 1 33.50 000 1 39.20 0.00 1 44 90 0.00 1 10 x SD n 4823 0.59 3 3.67 0.29 3 6.47 0.50 3 11.77 1.19 3 15.97 2.48 3 20.80 2.31 3 25.57 235 3 31.17 1.89 3 36.90 2.07 3 40 40 0.36 3 45.30 0.30 3 11 X SD n 54 35 205 2 3.90 0.00 '1 5.70 0.42 2 935 0.78 2 13.80 0.28 2 20.30 368 2 27.60 4.81 2 34.20 283 2 40 20 1.41 2 4445 1.06 2 48.50 0.71 2 51.95 1.20 2 12 x SD n 53.87 395 3 3.73 0.35 3 7.23 1.38 3 10.07 2.30 3 12.97 3.28 3 19.13 4.15 3 27.00 9.37 3 31.60 8.56 3 3567 7.90 3 3950 842 3 43.50 8.23 3 44.75 1.91 22 49.55 2.90 2 13 x SD n 53 90 000 1 1 5.20 000 1 9.70 0.00 1 12.80 0.00 1 17.50 0.00 1 22.20 000 1 2800 0.00 1 34.70 0.00 1 38 30 000 1 4370 0.00 1 46 40 0.00 1 50 00 0.00 1 52.00 0.00 1 142 x SD n 51.15 5.16 2 3.85 0.50 2 7.30 2.26 2 10.65 2.19 2 15.30 0.42 2 22 40 0.57 2 29.10 1.56 2 33.75 1.34 2 38.75 0.07 2 43.40 1.98 2 48.10 0.00 1 162 x SD n 57.93 290 4 4.00 0.00 '2 695 1.11 4 12.05 2.24 4 1850 249 4 24.80 3.95 4 31.53 3.75 4 37.25 2.91 4 4260 260 4 46.57 1.59 3 50.30 1.84 2 55.30 0.00 1 182 x SD n 57.10 0.99 2 360 0.00 '1 7.55 2.05 2 10.95 3.89 2 1640 5.80 2 2460 5.37 2 29.85 4.46 2 40.10 0.00 1 43 40 000 1 46 80 000 1 49.00 0.00 1 ALLx SD n Min Max 38.94 8.65 134 18.7 60.4 4.21 0.85 125 2.5 70 8.27 1.95 134 5.1 15.8 13.59 3.03 133 7.8 22.5 19.17 369 124 9.3 267 25.44 3.95 110 14.5 364 31.13 3.75 83 18.6 38.1 36.28 3.47 56 24.5 41.9 40.40 4.01 27 29.3 462 42.82 4.41 16 32.4 488 46.52 4.32 13 36.0 52.3 4918 4.58 6 43.4 55.3 4970 2.07 3 47.5 51.6 52.00 0.00 1 52.0 520 'External mark eroded but mark present in shell cross section "Number of annuli exceeds the number of lengths at annulus because marks could be distinguished in shell cross sections that were too closely spaced to discern on shell surfaces. lengths at capture were also determined (Table 3). Specimens recaptured in 1979 ranged in shell length from 59 to 104 mm, most had a deep brown or black periostracum. Several specimens did, however, exhibit the characteristic external banding pattern (Fig. 1), and were useful in vali- dating the presumed annual periodicity of marks. Marginal shell growth beyond the last exter- nal mark was strikingly different among small ocean quahogs from August 1979 and February 1980 samples. Mean lengths at capture for indi- vidual age classes from summer 1978 (particu- larly ages 1-9) were substantially greater than lengths at the last annulus, and were nearly equivalent to mean lengths at the last annulus for the next age class (Table 3). Ocean quahogs from winter 1980 invariably had formed or were forming an annulus at the shell margin (Fig. 1). A similar pattern was noted in shell cross sections. 27 FISHERY BULLETIN: VOL. 80. NO. 1 Modified exponential and logistic growth equations were fitted to mean back-calculated lengths at age, from the July 1978 samples (Table 3), using the asymptotic regression and nonlinear least squares computer programs BMD06R and~ BMD07R, respectively (Dixon 1977; Fig.. 3). Few aged shells were as large as those recap- tured (Tables 2, 3). Growth functions generated from aging data were thus extrapolated to the size range of recaptured specimens and results compared with annual growth increments pre- dicted from mark-recapture (Figs. 2, 3). An age- size point necessary to initiate the mark-recap- ture growth function was computed from growth equations fitted to age-length data generated in shell banding experiments; the mark-recapture equation was then iterated to encompass most shell lengths present at the marking site (Figs. 4,5). SL„,= 20811 +09802 SL 60 50 40 £ 30 ui X C/5 20 10 SL = 7568-81.31 (0.9056) AGE o OBSERVED ■• PREDICTED 6 8 10 12 AGE (YEARS) 14 16 18 Figure 3.— Observed and predicted shell lengths at age for small ocean quahogs sampled during July 1978 near lat. 40°25' N. long. 72°24'W. in the Middle Atlantic Bight. Length-Weight Shell length-drained meat weight relation- ships were computed for samples taken during August 1979 and February 1980. Laboratory 28 SHELL LENGTH MEAT WEIGHT 10 20 30 40 50 60 AGE I YEARS) 0 80 90 100 Figure 4.— Predicted shell lengths (millimeters) and drained meat weights (grams) at age for ocean quahogs at lat. 40°25' N, long. 72°24'W, in the Middle Atlantic Bight. Growth in length is described by an equation derived from studies of external banding patterns of small individuals (left of dot), and the Ford-Walford equation from mark-recapture data (right of dot). Weights at age are derived by applying the overall length- weight equation presented in Table 5 to calculated mean lengths at age. and statistical methods are given in Murawski and Serchuk (1979). Equations for recaptured and unmarked specimens from August 1979 were compared by covariance analysis to assess effects of marking (Table 4). Presumably, if physiological processes of the animal were sig- nificantly disrupted by the marking procedures, the adjusted mean of the length-weight equation might be statistically lower than that of controls. Seasonal variability in length-weight was in- vestigated by comparing summer and winter equations (Table 5). RESULTS AND DISCUSSION New shell growth of recaptured individuals was clearly discernible in small specimens (<70 mm) not only at the mark, but all along the Table 4.— Ocean quahog shell length-meat weight regression equations, and analysis of covariance for marked and un- marked individuals sampled at lat. 40°25' N, long. 72°24' W, in the Middle Atlantic Bight, during August 1979. Linear regression parameters Sample Intercept (a) Slope (6) r n Marked Unmarked -9.8373 2.9530 -9.0170 2.7637 0.975 55 0 953 126 Test of adjusted mean Test of slope Sample Adjusted mean dl F df F Marked Unmarked 0 fi709 2 8714 1'178 °001 nS 1,177 2.13 n.s. n.s. = P>0.05. MURAWSKI ET AL.: GROWTH OF OCEAN QUAHOG, ARCTICA ISLANDICA Table 5.— Ocean quahog shell length-meat weight regression equations, and analysis of covariance for August 1979 and Feb- ruary 1980 samples taken near lat. 40°25' N, long. 72°24' W, in the Middle Atlantic Bight. Linear regression parameters Sample Intercept (a) Slope (b) r n August 1979 February 1980 All data -9.2901 2.8274 -8.6865 2.7086 -9.0627 2.7871 0.961 181 0.976 278 0.967 459 Test of adjusted mean Test of slope Sample Adjusted mean df F df F February 1980 August 1979 l™l 1,456 58.86" 1,455 3.22 n.s. 20 40 60 80 100 120 SHELL LENGTH ( MM ) "P<0.01; n.s. = P>0.05. ventral margin when the periostracum was re- moved (Fig. 1). A growth interruption was pro- duced at the previous shell edge of small speci- mens; new material was formed slightly below the earlier shell margin and was shinglelike in appearance (Fig. 1). Growth in larger ocean quahogs was less distinct and thus more diffi- cult to measure. Where clear growth interrup- tions were not present, a faint yellowish band contrasting with white shell material was inter- preted as a marking-induced check and growth was measured from that point. Shell growth was assessed midway between grooves that formed the mark since, in the case of larger specimens, the depth of the grooves was actually greater than the amount of new shell deposited (Figs. 1, 2). A total of 11,658 ocean quahogs was measured directly from dredge catches at the marking site during 1970-80 (Table 1; Figs. 5, 6). Although minimum spacing of bars or rings in the rear portion of dredges varied somewhat (Table 1), size selectivity was apparently not significantly altered. Repeated tows were made at the mark- ing site during August 1979 with 25 X 25 mm and later 51 X 51 mm wire mesh in the after por- tion of the dredge. Size distributions of ocean quahogs were nearly identical before and after the alteration. A possible explanation for the lack of differential selectivity is that shell, sand, and live invertebrates may have clogged the dredge at the beginning of tows, negating fur- ther filtering ability. Two discrete length-frequency modes were ex- hibited in all sets of samples (Figs. 5, 6). Few small ocean quahogs (<50 mm) were encoun- FlGURE 5. — Length-frequency distributions (1 mm intervals) of ocean quahogs sampled near lat. 40°25'N, long. 72°24'W, in the Middle Atlantic Bight, April 1976-February 1980. 29 FISHERY BULLETIN: VOL. 80. NO. 1 60 80 SHELL LENGTH (MM) Figure 6.— Length-frequency distributions (5 mm intervals) of ocean quahogs sampled near lat. 40°25'N, long. 72°24'W, in the Middle Atlantic Bight, August 1970 and February 1980. tered from 1976 to 1980 (Fig. 5) and, considering uniformity of modes over time, recruitment was probably equally poor during 1971-76. Thus, cor- responding modes in the 1970 and 1980 samples were probably composed of the same year classes (Fig. 6). Average size of the small mode in- creased about 13 mm during the 9%-yr interval between August 1970 and February 1980, while the large group shifted about 3 mm (Figs. 5, 6; Table 1). Size progression of modes was minimal during 1976-80; intersample variation may be primarily related to differential sample sizes (Table 1). The effects of a sevenfold increase in sampling intensity can be seen by comparing August 1979 and February 1980 frequencies. Modes are smoothed in the latter sample, yet re- spective peaks are at precisely the same 1 mm in- tervals in both (65 and 90 mm). Average shell sizes ranged from 71 to 77 mm; however, trends in shell length among samples were not apparent (Table 1). The average lengths of recaptured ocean qua- hogs (Table 2) were slightly greater than con- current length-frequency samples (Table 1), although length extremes of the marked indi- viduals were not as great. Recaptured ocean qua- hogs also exhibited the bimodal length-frequency distribution (Fig. 2), indicating recaptured specimens represented a relatively unbiased sample of marked individuals and the ocean quahog population in the immediate vicinity of the study area. Calculated increments of shell growth from ocean quahogs recaptured in 1979 ranged from 0.08 to 1.38 mm, and averaged 0.56 mm (Table 2). Those recaptured in 1980 30 grew an average of 1.17 mm (range 0.07-4.32 mm). Thus, incremental growth approximately doubled between summer 1979 and summer 1980, implying growth rates were similar dur- ing the 2 yr of the experiment and that marking procedures probably did not significantly dis- rupt growth patterns. Growth increments of ocean quahogs at liberty 1 yr generally declined with increasing shell length, although there was substantial variation about a linear fit (Fig. 2). The linear equation for predicting annual incre- ment of growth from initial length is given in Figure 2; the Ford-Walford equation is: SLm = 2.0811 + 0.9802 SLt, where SL is shell length (in millimeters) at age t. An exponential equation fitted to data in Figure 2(7= 14.1216 (exp (— 0.0459X))) explained about 8% more of the re- sidual variance about the predicted line than did the linear equation. However, growth rates im- plied from length-frequency analyses were sub- stantially greater than those from the exponen- tial fit, and were similar to rates computed from the linear (von Bertalanffy) model. Thus, the latter model was considered more valid. Esti- mates of the asymptotic length (LJ and growth coefficient (K) from two fitting methods are: BGCU Annual increment L^ (mm) K 107.06 0.0195 104.95 0.0200 Values of L^ from the two methods are >99.5% (BGC4) and 98.5% (annual increment) of the cumulative 1980 length-frequency distribution at the study site. Estimates of K are relatively low and characteristic of slow-growing, long- lived species (Beverton and Holt 1959). Analyses of shell banding features present in small specimens indicate both external and in- ternal marks are produced once during the bio- logical year in these sizes. Several of the small recaptured ocean quahogs exhibited concentric external rings, and these specimens formed one such band during the interval between marking and recapture (Fig. la). Studies of small un- marked individuals retained from summer and winter sampling demonstrate that external and internal marks generally correspond in number and position. Internal marks were particularly useful in age determination when external marks were eroded near the umbo or closely spaced at the shell margin. Small ocean quahogs captured during the summer exhibited wide MURAWSKI KT AL.: GROWTH OF OCEAN QUAHOG. ARCTICA ISLANDICA marginal increments of shell growth from the last external and internal marks to the shell edge, whereas winter samples had recently formed annuli (Fig. lc; Table 3). Thus, mark for- mation probably occurs during the last half of the calendar year. These observations are consis- tent with data presented by Jones (1980). In a study of the seasonality of incremental shell growth, he noted that internal growth bands in shell cross sections were formed from September to February. The formation of growth bands apparently overlaps the spawning period (Jones 1980); however, both events may be related to other physiological or environmental stimuli since specimens that were reproductively imma- ture formed bands concurrently with mature ocean quahogs. Back-calculated mean lengths at age varied considerably depending on the subset of data analyzed in Table 3. Mean lengths at age for all year classes (bottom rows in Table 3) were gener- ally smaller than mean lengths at the last com- plete annulus (rightmost diagonal vector), and growth of recent age groups (2-8) appeared more rapid than for older ocean quahogs (Lee's phe- nomenon; see Ricker 1969). However, conclu- sions regarding the growth of older age groups (9-18) are tenuous due to the relatively small numbers of these ages sampled (87% of the sam- ples were <8-yr-old). Age analyses were limited to ocean quahogs that exhibited suitable contrast on the shell sur- face to discern external concentric rings. Thus, the oldest aged ocean quahogs (particularly ages 14-18) may represent the smallest, slowest grow- ing individuals of their year classes; faster grow- ing individuals may have reached sizes asso- ciated with color changes of the periostracum. Nevertheless, back-calculated mean lengths at age for 14- to 18-yr-old ocean quahogs did not tend to be progressively smaller than means for ages 9-13, perhaps indicating that size selectivity of older individuals was not a significant bias (Table 3). The objectives of fitting statistical models to age-length data were to describe growth during the juvenile and early adult phases of life, and more importantly, to predict ages associated with the lengths of the smallest recaptured speci- mens (59-65 mm) thereby linking the age-length data and mark-recapture results into a contin- uous growth function. Recognizing the disparate nature of data subsets in Table 3, a series of ex- ponential and logistic growth equations were fitted to: 1) weighted mean back-calculated lengths at age for all quahogs, 2) weighted mean lengths at age for ages 2-8, and 3) mean lengths at the last completed annuli (rightmost diagonal vector) for ages 2-10 and 2-13. For our purposes, the applicability of a particular model fit was judged not only by the total amount of variance between length and age explained by the equa- tion, but by predicted annual growth increments in the 59-65 mm range. An appropriate model would fit as much of the age-sample data as pos- sible and yield calculated annual growth incre- ments consistent with those observed from re- captured specimens. Exponential equations utilizing weighted mean back-calculated lengths for ages 2-8, and lengths at the last complete annulus for ages 2-13 yielded unacceptable fits by our criteria. The former equation was calculated with informa- tion from the linear portion of the growth curve, predicted lengths beyond age 8 were unrealistic- ally high. The latter equation incorporated one negative growth increment (between ages 11 and 12) and thus the calculated asymptote was only 62.8 mm; predicted annual growth near the asymptote was considerably less than observed increments for that size (Fig. 2). The logistic growth equation fitted to weighted mean lengths at age for all ocean quahogs (SL = 52.09/1 + exp(2.4722 - 0.4702(0)) was superior to the respective exponential fit considering the residual sums of squares criterion. The reverse was true for the logistic equation describing mean lengths at the last annulus for ages 2-10 (SL = 43.12/1 + exp(2.9361 - 0.8069 (*))). How- ever, asymptotic lengths were, for both logistic equations, well below the range of shell lengths considered in the mark-recapture experiments. Thus, extrapolation of logistic age-length re- lationships, necessary for initializing the Ford- Walford equation, was not feasible. On the contrary, the two exponential equations yielded reasonable asymptotic lengths and adequately described ocean quahog growth relative to that inferred from modal progressions in 1970 and 1980 length-frequency distributions (Fig. 6) and observed growth increments (Fig. 2). Exponential growth equations computed from weighted mean lengths at age for all ocean qua- hogs and mean lengths at the last annulus for ages 2-10 were: SL = 75.68-81.31 (0.9056)' and SL = 72.70-75.22 (0.8935)', respectively. Mean lengths at age predicted from the two equations generally reflect differences among data sets 31 FISHERY BULLETIN: VOL. 80, NO. 1 over the range of shell sizes used to fit the func- tions: however, estimated lengths at age con- verge near the sizes of the smallest recaptured specimens. Estimated lengths at age 20 were 64.49 and 64.29 mm, respectively. Correspond- ing growth increments from age 20-21 were 1.06 and 0.84 mm, well within the range of ob- served growth for those sizes (Fig. 2). If calcu- lated lengths at age 20 are assumed to be the starting points for the Ford-Walford equation (SL,n = 2.0811 + 0.9802 SLt), the two acceptable exponential equations yield virtually identical growth curves when the Ford-Walford relation- ship is iterated. Additional growth analyses were conducted using the regression equation fitted to weighted mean back-calculated lengths for all ages because the maximum amount of in- formation was used and the equation's behavior in the vicinity of marking data was consistent with empirical observations. However, further research on the growth patterns of small ocean quahogs is indicated in order to resolve differ- ences between various data subsets in Table 3 and thus to define a more appropriate growth model for these sizes. A composite growth curve incorporating the aged samples and mark-recapture data is given in Figure 4. The Ford-Walford equation was iterated to age 100 and a predicted shell length of 96.91 mm. Although ocean quahogs reach a size of at least 117 mm in the vicinity of the marking site (Table 1), ages substantially in excess of 100 are not necessarily implied because of the statis- tical variability in the marking data used to fit the predictor (Fig. 2). Annual growth in shell length is rapid during the first 20 yr of life, but declines significantly thereafter. Average yearly shell growth is 6.3% at age 10, 0.5% at age 50, and 0.2% at age 100. Estimates of the von Bertalanffy parameter to (age at zero length) were computed as -27.29 yr and -27.62 yr for the BGC4 and annual incre- ment equations respectively, with SL20 = 64.49 mm (Gulland 1969, equation 3.5). Although pre- dicted lengths at ages >20 are similar to those in Figure 4, a relatively poor fit to younger ages re- sults from both von Bertalanffy equations. The validity of using the age-length functions given in Figure 4 to describe ocean quahog growth at the marking site can be assessed by comparing predicted growth to that from modal progressions in length-frequency samples. Fre- quency distributions from 1976 to 1980 exhibit inter-sample variability in the position of major modes but no progressive shifts are discernible (Fig. 5). However, expected growth during the 5- yr period (Fig. 4) was smaller than could prob- ably be identified, given the precision of length- frequency sampling (Table 1; Fig. 5). Length modes can be used to compute growth at the site between August 1970 and February 1980 (Fig. 6). Average growth of the smaller mode (52 mm in 1970) was about 13 mm, and the larger mode (87 mm in 1970) added about 3 mm shell length during the 9Y2-yr interval (Figs. 5, 6). Ocean qua- hogs 52 mm in length are about 12-yr-old and average 21-yr-old at 65 mm; the estimated age of 87 mm individuals is 60 yr and 90 mm quahogs average 70-yr-old (Figs. 3, 4). Thus, predicted growth during the period 1970-80 is strikingly similar to that inferred from length mode pro- gressions, implying that age analyses and mark- recapture data adequately describe historical ocean quahog growth at the site. The age-length relationships presented herein have been computed for shell sizes in excess of 95 mm and ages up to 100 yr. However, computed relationships for large sizes (>65 mm) are based on average growth rates from mark-recapture results and not from aging of individual speci- mens. It is likely, based on these analyses, that ocean quahogs do reach 100 yr in age; however, direct age determination of large individuals is contingent upon development and validation of suitable methodologies. Internal banding pat- terns present in shell cross sections were useful in aging small specimens since formation of the bands apparently occurs once annually. Seasonal shell formation patterns (Jones 1980) and age analyses of large individuals based on internal banding (Thompson et al. 1980; Jones 1980) are generally consistent with our data. Analysis of shell cross sections of large recaptured speci- mens may be useful in determining the periodi- city of internal banding and the validity of the aging technique for large ocean quahogs; study of this material continues. The regressions of shell length vs. drained meat weight for marked and unmarked ocean quahogs taken during August 1979 were not sig- nificantly different in slope or adjusted mean (Table 4). If in fact soft-tissue robustness is a valid index of relative condition, then marked in- dividuals apparently suffered no lasting effects from the stress of dredging and handling. This observation is supported by the conclusions that incremental shell growth of marked specimens was similar to that computed from progressive 32 MURAWSKI ET AL.: GROWTH OF OCEAN QUAHOG, ARCTICA ISLANUICA length frequencies of the population as a whole, and growth rates of marked individuals were nearly equal between 1978-79 and 1979-80. Length-weight equations from February 1980 and August 1979 were parallel (Table 5); winter samples were apparently heavier in drained meat weight at a given shell length than summer samples. However, the magnitude of predicted differences in weight at length was small (4-11% for 65-115 mm ocean quahogs). Differences may be related to weight changes associated with sexual development, or merely a statistical artifact. Samples from winter and summer were combined to predict average weight for a given length during the year (Table 5). The resulting length-weight equation was applied to computed lengths at age to derive an age-weight relationship (Fig. 4). Initial weight gains are proportionally greater than concomitant length increases, but growth rates are nearly identical at the oldest predicted ages. Average annual increases in drained meat weight are 18.1% at age 10, 1.6% at age 50, and 0.2% at age 100 (Fig. 4). Growth rates determined from the examina- tion of concentric external banding patterns in- dicate small ocean quahogs may grow faster off Long Island than in the Northumberland Strait and in Passamaquoddy Bay (Caddy et al. foot- note 7). However, data are insufficient to con- clude that a latitudinal cline in ocean quahog growth exists. Factors influencing growth rates in a particular area are speculative; however, density dependence must be considered. Muraw- ski and Serchuk (footnote 2) noted relative popu- lation stability and poor recruitment for ocean quahogs in the Middle Atlantic during 1965-77. Stable population size, poor recruitment, and slow growth are characteristic of populations under density dependent regulation. Investiga- tion of ocean quahog growth rates at various den- sities may help to elucidate their interrelation- ship and indicate the population consequences of cropping high density areas. ACKNOWLEDGMENTS In particular we thank ships' personnel and scientific parties aboard the various research vessels during field sampling phases of the proj- ect. Significant technical contributions were made by Lt. Comdr. Ron Smolowitz, NOAA Corps, and Dea Freid of the Northeast Fisheries Center. 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Barnes. 1904. Observations on the soft-shell clams. Thirty- fourth Annu. Rep. Comm. Inland Fish., R.I., p. 26-28. Merrill, A. S., J. A. Posgay, and F. E. Nichy. 1966. Annual marks on shell and ligament of sea scallop, Placopecten magellanicus. U.S. Fish Wildl. Serv., Fish. Bull. 65:299-311. Merrill, A. S., and J. W. Ropes. 1969. The general distribution of the surf clam and ocean quahog. Proc. Natl. Shellfish. Assoc. 59:40-45. Murawski, S. A., and F. M. Serchuk. 1979. Shell length— meat weight relationships of ocean 33 FISHERY BULLETIN: VOL. 80, NO. 1 quahogs, Arctica islandica, from the Middle Atlantic Shelf. Proc. Natl. Shellfish. Assoc. 69:40-46. RlCKER, W. E. 1969. Effects of size-selective mortality and sampling bias on estimates of growth, mortality, production, and yield. J. Fish Res. Board Can. 26:479-541. Ropes, J. W., and A. S. Merrill. 1970. Marking surf clams. Proc. Natl. Shellfish. Assoc. 60:99-106. Saloman, C. H., and J. L. Taylor. 1969. Age and growth of large southern quahogs from a Florida Estuary. Proc. Natl. Shellfish. Assoc. 59:46- 51. Stevenson, J. A., and L. M. Dickie. 1954. Annual growth rings and rate of growth of giant scallop, Placopecten magellanicus (Gmelin) in the Digby area of the Bay of Fundy. J. Fish. Res. Board Can. 11:660-671. Thompson, I., D. S. Jones, and D. Dreibelbis. 1980. Annual internal growth banding and life history of the ocean quahog, Arctica islandica (Mollusca: Bival- via). Mar. Biol. (Berl.) 57:25-34. Turner, H. J., Jr. 1949. The mahogany quahaug resources of Massachu- setts. In Report on investigations of improving the shellfish resources of Massachusetts, p. 12-16. Com- monw. Mass., Dep. Conserv., Div. Mar. Fish. 34 LARVAL DEVELOPMENT OF CITHARICHTHYS CORNUTUS, C. GYMNORHINUS, C SPILOPTERUS, AND ETROPUS CROSSOTUS (BOTHIDAE), WITH NOTES ON LARVAL OCCURRENCE1 2 John W. Tucker, Jr.3 ABSTRACT Developmental series of 4 of the 12 species of Citharickthys and Etropus known from the western North Atlantic and Gulf of Mexico are illustrated and described. The series consist of C. cornutus (preflexion to nearly transformed, 2.2-17.4 mm body length. BL), C. gymnorhinus (preflexion to late transformation, 4.4-12.9 mm BL), C. spilopterus (preflexion to juvenile, 3.7-25.4 mm BL), and E. crossotus (preflexion to nearly transformed, 4.6-10.8 mm BL). Data from this study and that for 2 species previously described permit identification of larvae of 6 of the 12 species. For the species investigated, caudal fin formula (4-5-4-4) is the most reliable indi- cator for the group of genera Citharichthys, Cyclopsetta, Etropus, and Syacium. Number of elongate dorsal rays, degree of cephalic spination, and pigmentation are most useful for determining genus for known forms. Number of elongate dorsal rays, number of caudal vertebrae, pigmentation, mor- phology, and number of gill rakers are most useful for identification of Citharichthys and Etropus larvae that have been described. Citharichthys cornutus larvae have no pectoral melanophore, little notochordal pigmentation, heavy lateral pigmentation, 3 elongate dorsal rays, and develop 6 left pelvic rays and 25-26 caudal vertebrae. Flexion is complete at 9-10 mm SL and transformation at about 18 mm SL. Larvae have been collected during all seasons. Caudal fin development in C. cornutus is typical of the four species described here. Citharichthys gymnorhinus larvae have no pectoral melanophore, little notochordal pigmentation, light lateral pigmentation except for a caudal band, 3 elongate dorsal rays, and de- velop only 5 left pelvic rays and 23-24 caudal vertebrae. Flexion is complete at 7-8 mm SL and trans- formation probably at about 18 mm SL. Larvae have been collected during all seasons. Citharichthys spilopterus larvae have no pectoral melanophore, little notochordal pigmentation, light lateral pig- mentation, a blunt snout, a deep body, 2 elongate dorsal rays, and develop 6 left pelvic rays and 23-24 (rarely 25) caudal vertebrae. Flexion is complete at 7-8 mm SL and transformation at 9-11 mm SL. Larvae have been collected from September through April. Etropus crossotus larvae have a melano- phore at the base of the pectoral fin, heavy notochordal pigmentation, heavy lateral pigmentation, 2 elongate dorsal rays, and develop 6 left pelvic rays and 25-26 (very rarely 24) caudal vertebrae. Flexion is complete at 9-10 mm SL and transformation at 10-12 mm SL. Larvae have been collected in May and August and probably occur from March to August. Twelve species of the flatfish genera Citharich- thys and Etropus (subfamily Paralichthyinae, family Bothidae) are recognized from the west- ern North Atlantic (Table 1). Because of their small size at maturity, these fishes are presently used only by the petfood and fish meal industries (Topp and Hoff 1972). However, the abundance of larvae (Richardson and Joseph 1973; Smith et "Contribution No. 1037, Virginia Institute of Marine Sci- ence, Gloucester Point, VA 23062. 2Derived from a thesis submitted to North Carolina State University in partial fulfillment of the requirements for the Master of Science degree. 3School of Marine Science of the College of William and Mary. Virginia Institute of Marine Science, Gloucester Point, VA 23062. Manuscript accepted October 1981. FISHERY BULLETIN: VOL. 80. NO. 1. 1982. al. 1975; Dowd 1978) and adults (Dawson 1969; Topp and Hoff 1972; Christmas and Waller 1973) indicates that some species may represent sig- nificant components of estuarine and marine food webs. Larvae in the Citharichthys-Etropus complex are difficult to distinguish and are often ignored or classified as "unidentified bothids" in species composition analyses (e.g., Fahay 1975). Of the 12 western North Atlantic species, only C. arcti- frcms and E. microstomas have been described in detail (Richardson and Joseph 1973). Citharich- thys cornutus, C. gymnorhinus, C. macrops, and E. rimosus have been briefly described by Dowd (1978). Larvae of the remaining species have not been reported previously. Hsiao (1940) mis- 35 FISHERY BULLETIN: VOL. 80, NO. 1 takenly described Bothus sp. larvae as E. cros- sotus. In this paper I present descriptions of larvae of C. cornutus, C. gymnorhinus, C. spilopterus, and E. crossotus and summarize data useful for iden- tifying Citharichthys and Etropus larvae. MATERIALS AND METHODS Abbreviations The following institutional abbreviations are used: CP&L = Carolina Power and Light Com- pany, Raleigh, N.C.; GCRL = Gulf Coast Re- search Laboratory, Ocean Springs, Miss.; GMBL = Grice Marine Biological Laboratory, College of Charleston, S.C.; LSU = Louisiana State Univer- sity, Baton Rouge; NCSU = North Carolina State University, Raleigh; NMFS = National Marine Fisheries Service, NOAA (four laboratories — Beaufort, Galveston, Panama City, and La Jolla); OSU = Oregon State University, Corvallis; RSMAS = Rosenstiel School of Marine and Atmospheric Science, University of Miami, Fla.; SCMRRI = South Carolina Marine Resources Research Institute, Charleston; Texas A&M = Texas A&M University, College Station; UNC = University of North Carolina, Institute of Ma- rine Sciences, Morehead City; USNM = U.S. National Museum of Natural History, Smith- sonian Institution, Washington, D.C.; VIMS = Virginia Institute of Marine Science, Gloucester Point. Specimens Larval and juvenile specimens used in this study were obtained from several sources. Forty- seven C cornutus specimens from SCMRRI (MARMAP ichthyoplankton survey) collections in the South Atlantic Bight and five specimens from RSMAS collections from the Gulf of Mexico off western Florida were used for morpho- metries, counts, and general development. Seven additional RSMAS specimens were used for counts. Other specimens from NMFS (Beaufort) collections in Onslow Bay, off North Carolina, were used for comparison. Twenty-eight C gym- norhinus specimens from SCMRRI collections and 12 from RSMAS collections were used for morphometries, counts, and general develop- ment. Other specimens from NMFS (Beaufort) collections were used for comparison. Fifty-five C. spilopterus specimens from NCSU and per- 36 sonal collections in the Cape Fear River estuary, one from a CP&L collection in the ocean just off Cape Fear, and three from Texas A&M collec- tions in the Gulf of Mexico off Texas were used for morphometries, counts, and general develop- ment. Other specimens from Texas A&M, NMFS (Beaufort, Galveston, and Panama City), and RSMAS collections were used for compari- son and additional count data. Thirty E. cros- sotus specimens from LSU collections from the Gulf of Mexico off Louisiana and one from a NCSU collection were used for morphometries, counts, and general development. Other speci- mens from Texas A&M collections were used for comparison. Comparative larval material of other species was also examined. Citharichthys sp. A (prob- ably C. abbotti) specimens came from Texas A&M; Citharichthys arctifrons specimens from NMFS (Beaufort), SCMRRI, and VIMS; a Cith- arichthys sp. B (probably C. dinoceros) specimen from RSMAS; and Citharichthys (macrops'!) specimens from GCRL, RSMAS, and VIMS. Larvae of the eastern Pacific species Citharich- thys sordidus, C stigmaeus, and C xanthostigma came from NMFS (La Jolla). Other specimens of Pacific Citharichthys spp. came from OSU; Etropus microstomus specimens from NMFS (Beaufort) and VIMS; Etropus sp. A (probably E. rimosus) specimens from CP&L, NMFS (Panama City), and RSMAS; Cyclopsetta fim- briata specimens from NMFS (Beaufort), RSMAS, SCMRRI, and Texas A&M; and Syaci- um papillosum specimens from RSMAS and Texas A&M. Juvenile and adult specimens were examined to determine permanent characters. Specimens of C. arctifrons, C. macrops, C. spilopterus, E. crossotus, E. intermedius (cf. E. crossotus), E. microstomus, and E. rimosus came from USNM; Citharichthys cornutus and C. gymnorhinus specimens from GMBL; Citharichthys macrops specimens from UNC and a personal collection; and Citharichthys spilopterus and E. crossotus specimens from NCSU. Description of caudal skeleton development was based on study of the entire developmental series of C. cornutus and comparison with the series of the three other species described. Calcified components of the caudal skeletons of nearly all the specimens could be seen following light staining with Alizarin Red S in 1% aqueous potassium hydroxide solution. Twenty cleared and stained (Taylor 1967) specimens were exam- TUCKER: LARVAL DEVELOPMENT OF CITHAR1CHTHYS AND ETROPUS ined: C. arctifrons, (2) 40, 117 mm SL; C. comu- tus, (1) 51.5 mm SL; C. spilopterus, (2)41.6, -100 mm SL; C. macrops, (2) 45.7, ~100 mm SL; E. crossotus, (1) 49.4 mm SL; E. microstomus, (12) ~30-100 mm SL. Radiographs of juveniles and adults also were studied: C. arctifrons, (1) 100 mm SL; C. comutus, (16) 30-67 mm SL; C. gym- norhinus, (3) 23-37 mm SL; C. macrops, (75) 47- 113 mm SL; C. spilopterus, (65) 23-109 mm SL; E. crossotus, (62) 29-92 mm SL; E. intermedius (cf. E. crossotus), (2) 80, 92 mm SL; E. micro- stomus, (1)66 mm Sh;E. rimosus, (1)104 mmSL. Counts All larvae were lightly stained with Alizarin Red S in 1% aqueous potassium hydroxide solu- tion for making counts and observing the sequence of ossification. Most specimens were fairly transparent and internal structures were visible without clearing. The following counts were taken from larvae and juveniles with a stereomicroscope: precaudal neural spines, caudal neural spines, hemal spines, precaudal centra, caudal centra (including urostyle), caudal fin rays supported by each hypural ele- ment, dorsal fin rays, anal fin rays, left and right pelvic fin rays, left and right preopercular spines, left and right frontal-sphenotic spines, and left and right upper (premaxillary) and lower (dentary) larval teeth. Morphometries Measurements of various body parts of repre- sentative specimens were made on the left side with an ocular micrometer in a stereomicro- scope. The only exceptions were standard and total lengths of the six longest C. spilopterus (19.4-25.4 mm SL), which were made with di- viders and a millimeter scale. Measurements are defined as follows: Body length (BL) = snout tip to notochord tip for preflexion and flexion larvae (notochord length, NL); snout tip to posterior margin of hypurals for postflexion larvae and juveniles (SL). Upper jaw length = snout tip to posterior mar- gin of maxillary. Lower jaw length = anterior tip of dentary to posterior margin of articular just above the angular. Snout length = horizontal distance from snout tip to anterior margin of left pigmented eye. Eye diameter = horizontal diameter of left pig- mented eye. Head length (HL) = horizontal distance from snout tip to anterior margin of cleithrum at the body midline. Snout to anus length = horizontal distance from snout tip through midline of body to vertical line through anus. Total length = snout tip to posterior margin of finfold prior to caudal fin ray development, then to posterior tip of longest caudal ray. Head depth = greatest vertical depth of head; in preflexion larvae, this is near or just behind the posterior half of the eye, but with develop- ment the greatest depth is progressively more posterior. Body depth at pelvic fin = vertical distance from dorsal to ventral body margin at base of second pelvic ray. Body depth at loop of gut = vertical distance from dorsal to ventral body margin at the deepest par t of the gut ( C. comutus and C. gym- norhinus only). Body depth at anus = vertical distance from dor- sal to ventral body margin at anus. Body depth at third hemal spine = vertical dis- tance from dorsal to ventral body margin at third hemal spine. Caudal peduncle depth = prior to dorsal and anal fin formation, the vertical distance from dorsal to ventral body margin at the shallowest part of the caudal peduncle; after dorsal and anal fin formation, at the posterior edge of dor- sal and anal fins. Developmental Terminology Body length is a useful basis for linking char- acters of unidentified specimens with those in larval descriptions. However, body length may not be the most appropriate basis for comparing larvae of different species, especially bothids, which undergo notochord flexion and transfor- mation at different sizes, usually within a nar- row range for a single species but over a wide range for the family or even within a genus (e.g., Citharichthys). In this paper, both body length and stage of development are indicated for devel- opmental events. Stage of development is de- fined by degree of notochord flexion or degree of transformation. Terminology is similar to that of 37 FISHERY BULLETIN: VOL. 80, NO. 1 Moser et al. (1977) and Sumida et al. (1979), with slight modification because of the peculiarities of bothid development. Preflexion stage = notochord is straight. Early caudal formation = a substage of preflex- ion in which the notochord is still straight, but the caudal fin has begun to form. Flexion stage = notochord is turning upward. There are three substages: Early flexion = notochord is slightly flexed; midflexion = noto- chord is S-shaped and flexed about 30°-60°; late flexion = notochord is turned up and is no longer S-shaped but is not yet in final position. Postflexion stage = notochord is in final position, but transformation is not complete. Transforming larvae = those in which dorsal mi- gration of the right eye can be detected with low magnification. The period of transforma- tion is divided into thirds, depending on the position of the right eye. Juveniles = those specimens in which the right eye has reached its final position on the left side of the head and in which all fin rays have formed. Reported size ranges at transforma- tion are based on available specimens and might not encompass the full possible size ranges. Environmental stimuli inducing transformation may be encountered at differ- ent sizes. Terminology of components of the caudal skel- eton follows Amaoka (1969), except as noted. The caudal fin formula was described by Gutherz (1971) as the number of caudal rays supported by each caudal element, dorsal to ventral. Gutherz (1971) described certain cranial spines of Cyclopsetta fimbriata larvae as origi- nating from the sphenotic bones. Futch and Hoff (1971) described similar spines of Syacium papillosum larvae as originating from the fron- tal bones. In the Citharichthys and Etropus larvae I have examined, similar spines are at the suture between frontal and sphenotic bones. The origin of these could not be determined with cer- tainty, and therefore they are called "frontal- sphenotic" spines. For the larvae described here, the first elon- gate dorsal ray is actually the second ray of that fin. Larval Identification Four developmental series were assembled, primarily on the basis of similar meristics, shape, and pigmentation. Transforming larvae and juveniles were identified first by the pres- ence of known adult characters. Additional lar- val characters observed in those specimens were then used to aid in identification of the smaller specimens. Because all transformed specimens were sinis- tral and the right eye of all transforming speci- mens was migrating, it was decided that the four larval series belonged to one or more of the flat- fish families Bothidae, Scophthalmidae, or Cy- noglossidae. Morphological characters exhibited in the larval series and shared by larvae of these three families are lateral compression, deep head, deep abdomen, and looped gut, and in early larvae a raised and rounded dorsal profile of the head and slender caudal region. Only one scoph- thalmid species, Scophthalmus aquosus, is known from the western North Atlantic (Gutherz 1967; Hensley 1977). The distinctive rhomboid shape, long-based pelvic fins, and dense pigmentation of S. aquosus larvae were lacking in my series of larvae. The small eyes, small head, and confluent dorsal, caudal, and anal fins of cynoglossids were also lacking. In addition, cynoglossids from this region have fewer caudal (usually 9-14) and pelvic (usually 4 left, 0 right) rays than the specimens in my se- ries. Therefore, Scophthalmidae and Cynoglossi- dae were eliminated from consideration. Gutherz (1971) summarized known characters most useful for identifying bothid larvae. Futch (1977) summarized subfamilial larval charac- ters and tentatively recognized two subfamilies, Paralichthyinae and Bothinae. The following discussion is limited to western North Atlantic species. Four paralichthyine genera.— Citharich- thys, Cyclopsetta, Etropus, and Syacium — have a similar combination of transitory (larval) and permanent characters that distinguish them from other bothid genera. These include: 1) adult caudal fin ray formula of 4-5-4-4; 2) placement of the left pelvic fin on the ventral midline and the right above the ventral midline, both origi- nating behind the cleithra (Gutherz 1971); 3) the same basic larval shape; 4) similar larval pig- mentation—on the gas bladder, in dorsal and anal lines, and in the caudal region; 5) larval pre- opercular spines (at least in Citharichthys cor- nutus, C gymnorhinus, C. spilopterus, Cyclop- setta fimbriata, C. chittendeni, Etropus crossotus, E. microstomus, and Syacium papillosum); 6) larval frontal-sphenotic spines (at least Cith- 38 TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND KTROPUS arichthys arctifrons, C. cornutus, C. gymno- rhinus, C. spiloptems, Cyclopsetta fimbriata, C. ch ittendeni, E. crossotus, E. microstomus, and S. papillosum). Caudal formula, pelvic fin place- ment, shape, and pigmentation of larvae in the four series corresponded to this group. Cyclopsetta spp. have 26-28 caudal vertebrae (Gutherz 1967). Larvae of C. fimbriata, C. chit- tendeni, and S. papillosum have 5-10 elongate dorsal rays and well-developed preopercular and frontal-sphenotic spines (Gutherz 1971; Futch and Hoff 1971; Evseenko 1979). Futch and Hoff (1971) listed Syacium generic larval characters. Other Cyclopsetta and Syacium larvae are prob- ably similar. Larvae in the four developmental series had lower caudal vertebral count ranges than Cyclopsetta spp., only 2-3 elongate dorsal rays, and relatively small preopercular and fron- tal-sphenotic spines. Therefore, these two genera were ruled out, leaving Citharichthys and Etropus. Identification to species is described in the individual species accounts. For aid in determining species of Citharich- thys and Etropus, frequency distributions of cau- dal vertebral, anal ray, and dorsal ray counts were tabulated from the literature, and from radiographs of juveniles and adults from the Atlantic off the southeastern United States (Append. Tables 1-3). Ranges of gill raker counts were tabulated from the literature (Append. Table 4). Number of caudal vertebrae (Append. Table 1) was the count most useful for distin- guishing larvae. Vertebral counts can be made before ossification during early or midflexion, and overlap is not excessive. However, care is necessary to avoid inaccurate counts because of fused centra. Caudal neural spines and hemal spines, both of which number one less than cau- dal vertebrae, will stain with alizarin and some- times can be counted before caudal vertebrae, during early or midflexion. The number of gill rakers on the lower limb of the first arch (Ap- pend. Table 4) can be counted in most specimens during transformation and can be very useful for identification of older larvae. The number of anal rays (Append. Table 2) is next in usefulness, followed by the number of dorsal rays (Append. Table 3); however, the overlaps for these counts are great. Efficiency can be gained by plotting individual anal versus dorsal counts on a graph, so that the counts can be used simultaneously. The adult complements of anal and dorsal rays are present by the end of transformation. After the largest specimens in each series were identified, the identities of successively smaller larvae were verified. The most useful characters for untransformed specimens were lateral, pec- toral, and notochordal pigment; number of elon- gate dorsal rays; number of caudal vertebrae; number and size of left pelvic rays; and head shape. DESCRIPTION OF DEVELOPMENTAL STAGES Citharichthys cornutus (Figs. 1-5) Identification Larvae approaching transformation had com- plete complements of countable characters. Those specimens were identified by comparing the following larval counts with known adult counts. Number of specimens is given in paren- theses. Caudal fin formula = 4-5-4-4 (27) Caudal vertebrae = 25(11)-26(16) Gill rakers (lower limb, first left) = 12 (1) Left pelvic rays = 6 (17) Anal rays = 60-66(11) Dorsal rays = 78-84 (11) Of the potential species listed in Table 1, only C. cornutus has counts that agree with these. In addition, larvae were captured over the outer shelf, slightly farther offshore than C. gymnorhi- nus (Fig. 1). This is consistent with bathymetric distribution of adults. Distinguishing Characters Citharichthys cornutus larvae have no pectoral melanophore, and notochordal pigment is re- stricted to the caudal region. Three elongate dorsal rays are present from preflexion (about 4 mm) through transformation. Caudal vertebrae (25-26) can be counted by early flexion (6 mm). Lateral pigment is relatively heavy. Flexion is complete at 9-10 mm SL. The larval mouth and eye are large. Morphology is similar to that of C. gymnorhinus. However, the left pelvic fin of C. cornutus has a full complement of six rays, and in larvae the first ray is not reduced in size. The left pelvic fin of C. gymnorhinus has only five rays, and in larvae the first ray is much reduced com- pared with that of C. cornutus. Length of C. 39 FISHERY BULLETIN: VOL. 80, NO. 1 Table 1.— Distribution of adults of Cithariehthys and Etropus species known from the western North Atlantic and status of knowledge of their larvae.1 Species Geographic range of adults Depth range of adults (m) Larval descriptions C. arctifrons E. microstomas C. cornutus C. gymnorhinus C. spilopterus E. crossotus C. macrops E. rimosus C. abbotti C. amblybregmatus C. arenaceus C. dinoceros C. uhleri2 E. intermedws3 Georges Bank to Yucatan 22-682 Richardson and Joseph 1973 New York to South Carolina 5-91 Richardson and Joseph 1973 Georgia to Brazil 27-366 This paper Florida to Guyana 37-201 This paper New Jersey to Brazil (rare north of Virginia) 1-73 This paper Chesapeake Bay to French Guiana 1-86 This paper Southern Atlantic and Gulf coasts of the United States 1-91 Brief description in Dowd 1978 North Carolina to Mississippi River 5-190 Brief description in Dowd 1978 Veracruz to Campeche, Mexico 0-2 Unknown Western Caribbean off Nicaragua 139-197 Unknown West Indies to Brazil Shallow Unknown Florida to Nicaragua 183-1829 Unknown Haiti Unknown Trinidad to Rio de Janeiro 27 Unknown ons compiled from Goode and Bean 1896; Gutherz 1967, Dawson 1969; Gutherzand Blackman 1970; Toppand Hoff 1977; Wenner et al. 1979; and original data for C. spilopterus. E. crossotus, and C macrops (i.e., 1 m depths). nar.eus Dawson 1969 'Distribut 1972; Leslie . 2cf C. arenaceus, Dawson 1969 3cf. E. crossotus, Gutherz 1967 Figure 1.— Occurrence of Citharichtkys cornutus and C. gym- norhinus larvae off the southeastern United States. Numbers are the sums of bongo and neuston tows made per 1° quadran- gle during four RV Dolphin fall, winter, and spring cruises in 1973 and 1974. Symbols indicate positive tows. cornutus at transformation is about 18 mm. Lar- vae may appear in collections year-round. Pigmentation Pigmentation of C. cornutus larvae is rela- tively heavy. Gas bladder, gut, and lateral tail 40 pigment are the most striking. By 2.2 mm NL and throughout larval development, the dorsal one-third of the left side of the gas bladder is fairly heavily pigmented. This pigment may be diffuse or in the form of stellate or punctate melanophores. With growth, the number of mel- anophores increases. The maximum number in a preflexion specimen was five (4.8 mm). The right side of the gas bladder is usually unpigment- ed. During preflexion (2.2 mm, see Fig. 4A), two or three melanophores are present on both the dorsal and the ventral body margins about half- way between the anus and the notochord tip. Another one or two melanophores are present between these two clusters near the lateral mid- line. Later in development, pigment in this area forms a band. One or two small melanophores may be present on the ventral finfold just poste- rior to the hindgut. Three or four melanophores are on the caudal finfold near the ventral body margin just anterior to the notochord tip. Two melanophores are on the ventral surface of the gut loop; additional melanophores appear there during development. A small melanophore ap- pears along the posterodorsal surface of the mid- gut at about 3 mm. Melanophores begin appear- ing on the ventral body margin anterior to the cleithrum at about 3 mm. At about 4.7 mm, one or two melanophores appear along the posterior margin of the articular. Flexion larvae (see Fig. 4B) usually have four or five melanophores on the dorsal one-third of the left side of the gas bladder. Midlateral caudal pigmentation consists of up to six dashlike mel- anophores. Additional, dashlike clusters of pig- ment appear along the dorsal and ventral body TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND ETROPUS margins between the anus and the caudal fin base. During midflexion (6 mm, see Fig. 4B), inter- nal pigment appears along the dorsal notch be- tween the midbrain and hindbrain, and one or two round melanophores appear below the notch. Visible internal notochordal pigment is re- stricted to the vicinity of the external caudal band. The dorsal surfaces of one to three forming centra are darkened by about 6 mm. Several melanophores are present along the ventral body margin from just above the tip of the urohyal to just behind the cleithrum. Internal pigment appears between the hindgut and anal fin origin by midflexion. By late flexion (8 mm, see Fig. 4C), both sides of the gas bladder are obscured by body muscula- ture, and pigment appears diffuse. Notochordal pigment appears as fine dashes along the dorsal surfaces of three to six centra of caudal vertebrae 15-21. As many as 30 or more melanophores may be present along the ventral surface of the gut loop. Pigment along the posterodorsal surface of the midgut extends to the gas bladder and ap- pears as a black lining over the gut. One or more melanophores appear on or just behind the posterodorsal margin of the preopercle. Melano- phores have developed along the elongate second left pelvic ray and begin to develop along the elongate dorsal rays at 8-9 mm. Some larvae have small melanophores near the distal tips of rays at the middle of both dorsal and anal fins. By 8 mm, a group of melanophores has appeared along the middle of the caudal fin. The posterior margin of the articular is covered with a stellate melanophore. By postflexion (9 mm), myoseptal pigment is present in the caudal band as well as adjacent to dorsal and ventral lines. Internal pigment along the brain surface looks diffuse. Pigment appears on the dorsal fin membrane adjacent to the first dorsal ray at about 11 mm. Body musculature tends to obscure dorsal notochordal pigment in larvae longer than 12 mm. Additional midlateral dashlike melanophores appear near the caudal fin base at 13-14 mm (see Fig. 5A). By about 14 mm, all five dorsal and four ventral pigment lines have formed, and myoseptal pigment is well developed. A small amount of pigment is present along the anteroventral edge of the maxillary by about 14 mm. Late transforming larvae have about three small internal melano- phores near the pectoral fin base and just for- ward of the cleithrum beneath the angle of the last gill arch (barely visible through the opercle); these probably develop by about 14 mm. Ventral pigment from the urohyal to the cleithrum per- sists until late transformation. By late transfor- mation (see Fig. 5B), midlateral dashlike melan- ophores are present anterior to the caudal band. Morphology (Figs. 4, 5; Tables 2, 3) General morphological features include later- al compression, a deep head, a deep abdomen, and a looped gut. In early larvae the dorsal pro- file of the head is raised and rounded and the caudal region is slender. The eye is nearly spheri- cal during early development but becomes ellip- soidal in transforming larvae. A ventral choroid fissure is visible from 3-4 mm NL until about the end of the postflexion stage. The nasal capsule is visible by about 3 mm NL. The gas bladder is prominent just above the foregut until the end of postflexion. It bulges slightly on the left side of the body and is not as obvious on the right. A loop forms in the gut by 2 mm NL. The liver occupies a large portion of the anteroventral region of the abdomen. Adult morphometries given in the fol- lowing discussion were derived from Topp and Hoff (1972). The mouth is relatively large in larvae and adults. Larval upper jaw length/BL increases slightly from 10.3% (preflexion) to 11.0% (flexion) and then decreases to 9.8% (postflexion). Adult upper jaw length/BL is 12.8%, range 11.8-13.7%. Larval upper law length/HL decreases from 37% to 34%. Adult upper jaw length/HL is 45%. Lar- val lower jaw length/BL increases slightly from 13.3% (preflexion) to 13.9% (flexion) and then de- creases slightly to 13.0% (postflexion). Larval lower jaw length/HL decreases slightly from 48% to 46% and is only slightly greater than that of C. gymnorhinus. Larval snout length is moderate. Larval snout length/BL increases slightly from 6.2% (preflex- ion) to 7.1% (flexion) and then decreases slightly to 6.3% (postflexion). Adult snout length/BL is 5.5%, range 4.8-6.2%. Larval snout length/HL is constant at about 22-23%. Adult snout length/HL is 19.5%. The larval eye is large, and the relative size of the adult eye is greater than that of any other western North Atlantic Citharichthys or Etropus species except C. amblybregmatus. Larval eye diameter/BL is constant at 9.8% during preflex- ion and flexion and then decreases to 8.5% (post- flexion). Adult orbit length/BL is 10.0%, range 41 FISHERY BULLETIN: VOL. 80, NO. 1 Table 2.— Measurements (mm) of larvae of Citharichthys cornutus. Pref = preflexion, ECF = early caudal formation, Early = early flexion, Mid = midflexion, Late = late flexion, Post = postflexion. S = symmetrical, 1 = 0 to one-third of the way to the dorsal ridge, 2 = one-third to two-thirds of the way to the dorsal ridge, 3 = two- thirds to all the way to the dorsal ridge, R = on the dorsal ridge. sz O) c a >- •D O m c o .2. m Q. a Ol c a> S CO CD 5 o _l D) C 2> W o c w £ E ra TJ . LU O) c a> n ca CD I CO C ca 0£ .- CT1 =3 C O CD C — w -C a> c JD "cO o 1- sz Q. . O "O o o — m CO c CD Q. CD T> >^ "D O CO CD c a. CO £ E O. CD CD J= ■D n O " CO a o c z> ■o CD Q. it O CD Ol ca c o X CD LL. c o o o. CD >. CD -C Ol rr 22 0.33 0.12 0.27 062 1.1 '0.76 '0.61 '0.61 '0.53 '026 Pref S 32 0.35 0.41 0.21 0.31 1.0 1.7 1.2 '1.1 '10 '0.79 '036 Pref S 37 0.40 0.47 0.25 0.37 1.1 1.9 3.8 1.2 '1.2 '12 '0.88 '0.47 Pref s 4.0 0.56 028 0.44 1.1 1.9 14 '1.4 '15 '1.2 '064 Pref s 4.1 0.59 027 0.43 1.2 2.1 4.2 '1.3 '0.57 Pref s 4.5 0.47 0.57 0.27 043 1.2 18 4.6 1.4 '14 '11 '065 Pref s 45 0.44 0.61 0.23 040 1.1 1.9 4.6 1.5 '1.4 '1.5 '1.2 '0.63 Pref s 4.6 050 0.71 0.29 047 1.3 2.2 4.7 1.8 1 7 1.5 0.83 ECF s 48 0.51 0.66 026 0.48 1.3 2.2 5.0 1.6 '1.6 '1.6 '1.4 '082 ECF s 49 0.28 0.47 1.3 2.1 5.0 '1.6 '18 '1.5 '083 ECF s 5.0 0.58 0.73 0.37 0.53 1.5 2.2 1.7 1.9 ECF s 5.7 0.48 0.63 0.32 0.50 1.5 2.3 5.8 1.9 1.9 1 9 1 1 ECF s 5.7 0.53 0.65 0.35 0.52 1.5 2.5 20 1.9 2.0 1.0 ECF s 58 0.65 0.81 0.33 0.63 1.7 2.7 2.2 2.5 2.6 25 16 0 57 Mid s 6.0 063 0.78 0.40 0.53 1.7 2.4 2.1 2.2 2.4 2.2 1.4 Early s 6.1 0.69 0.86 0.37 0.63 1.8 3.1 2.4 2.7 3.0 2.6 1.8 061 Mid s 63 0 66 0.84 1 8 2.6 7.4 2.4 2.5 1 7 0.59 Mid s 6.3 0.75 0.96 0.46 0.65 3.0 2.5 28 3.1 2.7 1 8 0.64 Mid s 64 070 0.92 0.41 063 1.8 2.9 7.5 2.5 2.8 3.0 2.7 1.8 0.64 Mid 1 64 0.70 089 0.44 0.63 1.8 3.0 7.2 24 2.6 28 2.5 1.6 054 Mid s 64 0.77 0.90 0.55 0.63 3.0 2.5 2.8 3.1 27 1.9 0.65 Late 1 69 0.87 1.1 0.53 0.73 2.3 3.2 8.6 28 3.2 3.6 3.3 2.3 088 Late 1 7.2 0.76 0.96 0.46 0.74 2.2 3.2 2.8 3.0 3.4 3.1 2.1 084 Late s 7.2 0.77 1.0 0.47 0.75 2.2 3.2 8.7 2.7 3.0 35 3.3 2.2 080 Late s 7.6 090 1.2 0.60 077 2.5 3.6 3.2 37 4.2 4.0 3.0 1.0 Late s 7.6 0.77 099 0.51 0.73 2.2 3.6 9.2 3.0 3.2 3.0 2.3 082 Late s 7.6 0.83 1.0 050 077 2.3 3.3 28 32 3.6 3.3 2.3 088 Late 2 7.6 084 1.1 0.50 23 37 9.3 3.0 3.6 4.0 3.5 2.6 090 Late s 7.7 090 1.1 0.65 0.73 2.4 34 3.2 3.5 3.7 3.5 2.6 0.94 Late s 7 9 0.81 1.0 0.54 0.74 2.4 3.9 9.5 3.5 3.8 3.6 2.5 090 Late 1 82 091 1.2 0 64 0.81 2.6 3.6 3.7 4.1 4.0 3.0 1.1 Late 1 8.2 0.87 1.1 0.62 0.76 2.5 3.6 3.1 3.4 3.5 3.3 2.5 0.87 Late 1 83 097 1.3 0.71 0.81 2.7 4 1 3.5 4.0 4 8 4.3 3.0 1.1 Late 1 8.3 096 1 2 051 085 26 105 40 46 4.1 30 1.1 Late s 84 090 1.1 0.61 0.80 2.7 4.2 10.2 3.4 38 4.4 3.9 2.8 0.94 Late 1 86 0 90 1.1 066 0.81 2.7 4.1 10.7 3.2 3.7 4.4 4.1 3.0 1 0 Late 2 88 095 1.2 0.61 080 2.6 3.7 3.2 3.8 3.9 3.9 29 10 Late 2 8.9 0.90 1 1 062 080 2.6 3.9 3.4 3.8 4.1 38 2.9 1 0 Late 2 10.4 1.1 1.4 074 093 32 4.6 12.9 4.0 4.6 5.3 5.1 40 1 4 Post 3 10.6 1.1 1.5 0 77 1.0 3.2 4.8 13.2 4,1 48 5.8 5.6 4.1 1.5 Post 3 10.6 1.2 1.5 0.73 0.94 3.2 4.6 3.9 4.6 5.3 5.1 4.1 14 Post 1 109 1.2 1.5 0.79 099 3 2 4.3 4.0 4.7 5.7 5.3 4.1 1.4 Post 3 11 5 1.2 1.6 0.74 1.1 3.4 4.9 14.1 4.0 4.6 5 5 5.3 4.1 1.4 Post 3 12.0 1 1 1.6 089 0 99 3.5 4.6 14.7 43 4.9 5.1 52 4.3 1.4 Post 3 12.1 1.3 16 0.73 1.1 3.6 50 46 5 1 6.1 6.0 4.9 1 6 Post 2 12.8 1.1 1.6 0.64 1 1 3.5 5.0 44 4.9 5.8 5.5 4.6 16 Post 3 129 1 2 1.6 073 1.0 3.5 5.1 4.8 5.2 6 1 59 4.8 1.6 Post 3 130 1.2 16 0 72 1.0 3.5 4.8 15.9 45 54 5.9 59 5.3 16 Post 3 138 1 2 1.7 0.70 1.2 3.7 5.2 5.4 5.9 6.7 6.5 5.5 18 Post 3 15.4 1 4 1.8 095 1.2 40 5.6 185 5 1 6 1 69 68 6 1 1.9 Post 3 174 1.6 2.2 1.2 1.2 48 5.6 21.2 5.7 6.6 7.5 7.6 7.2 2.2 Post 3 17.4 1.7 2.1 1.0 15 4.8 5.6 6.3 6.5 7.7 6.8 2.0 Post R 'Measurement does not include dorsal or anal pterygiophores 9.2-11.1%. Larval eye diameter/HL decreases from 36% to 30% and is similar to that of C. gym- norhinus. Adult orbit length/HL is 35.5%. The head is relatively large in larvae and mod- erate in adults. Larval head length/BL increases from 28% (preflexion) to 30% (flexion) and then decreases to 28% (postflexion). Postflexion head length/BL is similar to those of C. arctifrons and C. ffymnorhinus. Adult head length/BL is 28%, range 27-30%. Larval head depth/BL increases from 34% (preflexion) to 39% (flexion) and then decreases slightly to 36% (postflexion). Larval snout to anus length is relatively great until postflexion. Snout to anus length/BL is 46% during preflexion and flexion and then decreases greatly to 39% (postflexion). The body is relatively deep in larvae and mod- erate in adults. Larval body depth at pelvic fin/ 42 TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND ETROPUS Table 3.— Body proportions of larvae and juveniles of three species of Citharichthys and one species of Etropus. Except for body length, values are in percentage of body length (BL) or of head length (HL) and are given as: mean ± stan- dard deviation (range). (Values derived from Tables 2, 5, 6, 7.) Measurement C. cornutus C. gymnorhinus C. spilopterus E . crossotus Body length (mm) Preflexion 4.6 (3.2-5.7) 46 (4.4-5.0) 3.7 4.6 Flexion 7.4 (5.8-8.9) 6.7 (5.3-7.7) 64 (5.7-6.8) 6.8 (4.9-9.5) Postflexion 12.9 (10.4-17.4) 104 (7.9-12.9) 9.4 (8.3-10.6) 10.2 (9.3-10.8) Early juvenile 10.0 (8 7-11.6) Midjuvenile 20.5 (14.3-25.4) Upper jaw length/BL Preflexion 10 3±1 0(8.4-1 1.6) 9.5+0.7(8.3-10.3) 99 7.0 Flexion 11.0±0.6(10. 1-12.5) 9.3+0.4(8.3-10.0) 7.2+0.8(6.3-7.9) 7.2+0.7(5.9-8.4) Postflexion 9.8+0.8(8.6-10.8) 9.3+0.7(8.1-11.3) 6.7+0.6(5.6-7.9) 7.1+0.5(6.4-7.8) Early juvenile 7.3+0.4(6.1-8.1) Midjuvenile 9.0+0 4(8 4-9.7) Lower jaw length/BL Preflexion 13.3±1. 3(1 1.0-15.3) 11 .5+1 0(10.2-12.9) 12.1 9.6 Flexion 13.9+0.9(12.4-15.5) 12.7+0.6(11.6-13.6) 9.9+0.7(9.1-10.4) 9.6+1.0(8.5-12.3) Postflexion 13.0+0.8(11.9-14.4) 12.7+0.6(11.6-14.2) 9.1+0.5(8 2-10 2) 9.8+0.5(9.2-10.6) Early juvenile 10.3+0.5(8.9-11.5) Midjuvenile 13.1+0.4(12.5-13 8) Snout length/BL Preflexion 6.2+0.7(5.1-7.4) 5 .2+1. 1(3.7-6.7) 7.5 5.2 Flexion 7 1+0.8(5.7-8.6) 5 8+0.6(4.9-7.0) 7.6+0.8(6.8-8.1) 6.4+0.7(5.1-7.5) Postflexion 6.3±0.8(5.0-7.4) 6.1+0.6(4.8-7.6) 6.4+0.6(5.6-7.4) 6.8+0.9(5.4-7.6) Early juvenile 5.8+0.6(4.4-7.2) Midjuvenile 5 0+0.5(4.3-5.5) Eye diameter/BL Preflexion 9 8+0.7(8.8-11 0) 8 8+0.5(8.1-9.5) 9.7 7.4 Flexion 9.8+0.5(8.8-10 8) 8.9+0.8(6.9-10.0) 7.9+0.2(7.6-8.1) 6 9+0.4(6.1-7.7) Postflexion 8.5+0.6(7.2-9.4) 8 8+0 5(7.9-9.8) 6.5+0.6(5.5-7.6) 6 3±0.3(6 1-6.9) Early juvenile 6.8+0.5(5.9-7.7) Midjuvenile 7.0+0.6(6.5-8.2) Head length/BL Preflexion 27.6±2.2(23.8-31.2) 24.8+1.0(23.8-26.6) 28.0 23.4 Flexion 30.4±1 .5(28.0-33.1) 27.9+1.9(25.0-31.1) 26.4+0.8(25.5-27.0) 26 4+1.3(24.2-28 7) Postflexion 28.4+1.6(25.9-30.5) 28.6+1.7(26 8-33.8) 23.9+1.0(22.4-25.7) 26.4+1.5(24 4-28 8) Early juvenile 25.4+0.8(23.9-27.1) Midjuvenile 25.0+0.7(24.2-26.2) Snout to anus length/BL Preflexion 45.8+4.7(39.4-54.1) 43.0±1. 2(42.0-45.1) 40.0 39.1 Flexion 45.9+2.9(40.1-51 2) 44.2+2.0(40.2-46.6) 39 0+1.4(37.5-40.2) 44.2+2.0(39 8-48.0) Postflexion 39.3±4.1 (32.1-45.8) 39.7+2.9(34.6-46 2) 31.8+1.2(29.7-33.5) 38 8+3.2(33.5-42.2) Early juvenile 31.0+1.3(28.8-34.0) Midjuvenile 31 .6±1. 2(29.8-34.3) Total length/BL Preflexion 102.3±0.7(101 .6-103.5) 102.0±0. 6(101. 5-102. 9) 102.2 101.5 Flexion 121.0+39(112.3-126.5) 1160 + 126(102.0-126.2) 128.0 115 0+8.8(100.7-127.4} Postflexion 123 0±1 .4(120 6-124.9) 121 3+1.0(119.8-122.5) 123.1+1.2(121.4-125.0) 122.3+1.3(119.7-123.4) Early juvenile 123.9+2.0(119.4-129.4) Midjuvenile 125.4+1.6(123.4-128.0) Head depth/BL Preflexion 34.5+2.3(31.4-38.8) 29 0±1. 8(26.7-31 .4) 36.6 28.6 Flexion 38.7+2.0(34.3-42 5) 33.3+2.3(28 3-36 2) 39.4+2 0(38.1-41.7) 33.8+1.6(30.7-36 4) Postflexion 36.2+1.9(32.9-38 8) 33.3±1. 6(31 .0-36.3) 32 8+1.1(31.0-34 9) 33.1+1.6(31.5-35 8) Early juvenile 32.0+1.1(29 8-34.9) Midjuvenile 31 .0±1. 0(29 6-33 0) Depth at pelvic fin/BL Preflexion 33.6±2.0(31 .2-37.6) 29.8+2.6(27.0-33.5) 40.3 26.2 Flexion 43.6+2.9(37.1-49.1) 37.5+3.1(31.9-42.7) 46.7+0.9(45 9-47.7) 39.0+4.0(32.7-49.7) Postflexion 41.3+2.4(37.4-45.8) 39.0+1.7(36.4-43.9) 39 0+1.1(36 9-40 8) 40.2+2.4(36.2-43.6) Early juvenile 37.2±1. 2(34.7-40.3) Midjuvenile 35.0+0.9(33.3-36.4) Depth at loop of gut/BL Preflexion 33.7+1.9(31.0-37.0) 29.2+2.9(25.5-33.9) Flexion 48.4+4.4(39 6-57.4) 39.1+4.3(32.7-45.0) Postflexion 48 0+3.6(42 6-54.7) 43.9+2.2(41.5-50.2) Depth at anus/BL Preflexion 28.4+3.6(23 8-33.7) 24.9+2.5(22.4-29.2) 38.7 21 4 Flexion 44.5+4.0(36.1-52 4) 36.9+4.4(30.3-44.2) 50 6+1 2(49 2-51.4) 37.8+5.6(29.3-45.7) Postflexion 46.6+2.8(43.0-52.9) 42.2+1 7(39.7-47.0) 42 9+1.6(39 9-44.9) 43.1+3.5(36.3-46.2) Early juvenile 39.5+1.4(35.9-43.3) Midjuvenile 38.7+0.7(37.2-39.7) Depth at third hemal spine/BL Preflexion 15.6±2.5(1 1.2-19 .5) 14.2+2.3(11.9-18.2) 22.6 116 Flexion 31.4+3.9(22 8-39 8) 26 6+4.3(19.7-33 2) 40 8+2.9(38.7-44.0) 28.2+7.3(18.2-39 1) Postflexion 38.6±1 .9(35.6-41 .8) 34.8+2.8(28.6-42.0) 38.0+1.4(35.3-39.8) 37.7+1.5(36.2-40 2) Early juvenile 37.0+1.4(34.6-40 0) Midjuvenile 40.2±1. 0(39.0-42 3) 43 FISHERY BULLETIN: VOL. 80, NO. 1 Table 3.— Continual. Measurement C. cornutus C. gymnorhinus C. spilopterus E. crossotus Caudal peduncle depth/BL Flexion Postflexion Early juvenile Midjuvenile Upper jaw length/HL Preflexion Flexion Postflexion Early juvenile Midjuvenile Lower jaw length/HL Preflexion Flexion Postflexion Early juvenile Midjuvenile Snout length/HL Preflexion Flexion Postflexion Early juvenile Midjuvenile Eye diameter/HL Preflexion Flexion Postflexion Early juvenile Midjuvenile 11.4+1.4(8.4-13.8) 12.7±0.6(11.6-13 8) 37.4+2.7(32.6-40.7) 36.0+1.8(33.2-39 1) 34.4+1.6(31 6-36.6) 48.0+4.9(41.0-56.5) 45.5±2.9(39.5-51.4) 45.9+1.1(43.6-47.7) 22.4+1 5(20 2-25.2) 23.0+2.0(19.3-27.2) 22.3+2.3(18.4-25 5) 35.6±2 .1(31.0-39.6) 32.2+2.1(29.6-37.5) 29 9+1.5(26 3-31.7) 11.6+1.6(9.3-14.4) 13.2±0. 7(12.2-14. 7) 38.3+2.0(34.9-40.9) 33.3+2.1(29.2-37.6) 32.6+1.9(29.4-37.5) 46.5+3 2(42.7-51.2) 45.6±2. 2(42. 5-49.6) 44.5+1.8(40 2-46.8) 20 8+4.1(15 4-26.8) 20.9+1.6(19.0-24.6) 21.3±1. 9(17.6-24 0) 35 4+2.2(32 3-38.2) 31.9±2.7(27.8-39.1) 30.6+1 6(27.4-33.9) 14.4±1.6(13.1-16 2) 13.5±0.5(12.7-14.3) 13.6+0.6(12.2-14.6) 11.4±0.6(10.0-12.3) 35.6 27.2+2.4(24.7-29.4) 28.1+2.2(24.0-33.8) 28.7+1.5(25.4-31.3) 36.2+1.4(33.9-38 4) 43.3 37.5±1. 4(35.9-38 6) 38.2+1.7(35.9-41.5) 40 5±2 1(36.9-44.1) 52.6+1.5(50 9-55 9) 269 28 8+3 3(25 0-31.2) 27.0±2.5(23.2-31.4) 23.0±2.3(18.3-27.1) 19.9+1.7(17.5-22 5) 34.6 29 9+0.5(29.4-30.3) 27.1+2.0(23.4-31.1) 26.8±2.0(23. 1-30.0) 27.8±1 6(26.4-31.2) 9.6+3 0(4 7-13.4) 12.6+0.6(11.8-13.4) 299 27.2+2.4(21.6-30 5) 26 9±1. 1(24. 7-27 6) 41.1 36.3±3.2(30 8-46 8) 37.2+1 .5(35.4-39 0) 224 24.3+1.9(21.0-28 0) 25 9±2.7(22.3-29 1) 31.8 26.0+1.8(22.0-30.6) 23 6+0.4(23.3-24 3) BL increases from 34% (preflexion) to 44% (flex- ion) and then decreases slightly to 41% (post- flexion). Larval body depth at loop of gut/BL increases from 34% (preflexion) to 48% (flexion and postflexion). Larval body depth at anus/BL increases greatly from 28% to 47%. Larval body depth at third hemal spine/BL increases greatly from 16% to 39%. Adult body depth/BL is 46%, range 43-50%. Larval caudal peduncle depth/BL increases from 11.4% (flexion) to 12.7% (postflex- ion). Adult caudal peduncle depth/BL is 10.5%, range 9.7-11.4%. Fin and Axial Skeleton Formation Development of the caudal skeleton of C. cor- nutus from larva to juvenile (Fig. 2A-E) is typi- cal of the four species described in this paper. The major difference among them is the rate of development. Flexion is complete at about 7-8 mm in C. gymnorhinus and C. spilopterus and at about 9-10 mm in C. cornutus and E. crosso- tus. During preflexion, before caudal formation (2.2-4.5 mm NL), the notochord is straight and there is no evidence of hypural formation. Dur- ing early caudal formation (4.6-5.7 mm NL, Fig. 2A) the notochord is straight and the outline of incipient hypurals 2+3 and 4+5 are visible, but neither hypurals nor incipient caudal rays are calcified. During early flexion (6.0 mm NL, Fig. 2B) the notochord begins to turn upward. Hypurals 2+3 and 4+5 (sometimes hypural 1) and caudal rays begin to stain with alizarin, and the last neural and hemal spines stain with alizarin. Caudal rays form in about equal numbers dorsally and ventrally during flexion, beginning at the posteroventral corner of hypural 4+5 and the posterodorsal corner of hypural 2+3. The 6.0 mm specimen (Fig. 2B) was the smallest in which calcification of caudal rays had begun. During midflexion (6.1-6.4 mm NL, Fig. 2C) the noto- chord is S-shaped and hypurals 1 and 6 and the epural begin to stain with alizarin. During late flexion (6.4-8.9 mm NL, Fig. 2D) the notochord tip points upward and is nearly flexed but is still in contact with hypural 6 and the epural; all hypurals stain with alizarin and the last neural spine touches hypural 6. All rays are formed by about 7.5 mm NL. When flexion is complete (10.4-17.4 mm SL, Fig. 2E) the urostyle is separate from hypural 6 and the epural, and all caudal rays stain with alizarin. Fusion of the epural with hypural 6, and fusion of hypural 4+5 with the urostyle occur at about the time of transformation. The terminol- ogy of Amaoka (1969) is followed here; however, actual fusion of hypurals 2 with 3 and 4 with 5 was not observed. The adult caudal skeleton of C. cornutus (Fig. 3A) is composed of a urostyle, or terminal half 44 TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND ETROPUS A B D Figure 2.— Development of the caudal skeleton of Citharichthys cornutus: A. Preflexion (early caudal formation), 5.7 mm NL; B. Early flexion, 6.0 mm NL; C. Midflexion,6.4mmNL; D. Late flexion, 8.2 mm NL;E. Postflexion, 13.7 mm SL. NS = neural spine, HS = hemal spine, H Yl = hypural 1, HY2+3 = hypurals 2 and 3, 4+5 = hypurals 4 and 5, H Y6 = hypural 6, EP =epural, PV = penulti- mate centrum, UR = urostyle. Scale = 1 mm. centrum (according to Hensley 1977, in the bothid Engyophrys senta this bone consists of the first and second ural centra and the first preural centrum); a penultimate, or second preural, cen- trum (see Hensley 1977); an enlarged hemal spine from the second preural centrum support- ing hypural 1; autogenous, proximally free, hypural 1 which supports three unbranched and one branched ray (equivalent to "parhypural" of some authors— e.g., Futch 1977; Hensley 1977— 45 FISHERY BULLETIN: VOL. 80, NO. 1 see Sumida et al. 1979); autogenous, fused hy- purals 2 and 3, articulating ventrally with the urostyle and supporting four branched rays; fused hypurals 4 and 5, fused with the tip of the urostyle and supporting five branched rays; an autogenous, proximally free element consisting of hypural 6 fused anteriorly with the single epural, one branched and three unbranched rays supported by hypural 6; no evidence of a uro- neural; an enlarged neural spine from the second preural centrum supporting the epural. The cau- dal skeletons of the four species described here are similar to Amaoka's (1969) type 4, except for the lack of a uroneural. Dendritic splitting of hypurals 2+3 and 4+5 occurs in Etropus crossotus by about 40 mm SL (Fig. 3B). The hypurals of adult specimens of Citharichthys spp. examined were sometimes grooved but never split as in E. crossotus. Hypur- als 2+3 and 4+5 of E. microstomas and E. rimosus were similar to those of Citharichthys spp. except for an apparent tendency to split slightly at the distal margins. In C. comutus larvae all precaudal neural spines stain with alizarin by about 4.8 mm NL. Some caudal neural spines and hemal spines stain with alizarin at 4.8 mm NL and all do by 6.1 mm NL. The urostyle stains with alizarin at 6.3 mm NL. All precaudal and caudal centra stain with alizarin by 7.2 mm NL. The smallest speci- FlGURE 3.— Caudal skeletons of two bothids: A. Citharichthys comutus, 51.5 mm SL; B. Etropus crossotus, 49.4 mm SL. Abbreviations as in Fijrure 2. Scale - 1 mm. 46 TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND ETROPUS men in which caudal centra could be counted was 5.8 mm NL (midflexion). The second, third, and fourth dorsal rays are elongate and widely separated at the bases from preflexion (about 4 mm NL) through transfor- mation (17.4 mm SL). During early caudal formation (5.0 mm NL), rays near the middle of the dorsal fin begin to calcify. Calcification pro- ceeds anteriorly and posteriorly. Adult counts are present from late flexion (6.4 mm NL) on- ward. The first ray and the most posterior rays are calcified just prior to transformation (17.4 mm SL). During early caudal formation (5.0 mm NL), anal rays near the middle of the fin begin to cal- cify. Calcification proceeds anteriorly and pos- teriorly. Adult counts are present from late flexion (about 8 mm NL) onward. The most pos- terior rays are calcified just prior to transforma- tion (17.4 mm SL). Development of the left pelvic fin precedes that of the right fin. The left pelvic fin bud ap- pears during preflexion (3.7 mm NL). Rays develop between preflexion (4.0 mm NL) and late flexion (about 8.9 mm NL). The most ante- rior two rays are the first to appear; the second is elongate and the first slightly elongate. The right pelvic fin bud appears during early caudal for- mation (4.9 mm NL). Rays develop between mid- flexion (6.0 mm NL) and late or postflexion (9-10 mm BL). Each complete fin has six rays. Rayless, fanlike, larval pectoral fins were present on the smallest available specimen (pre- flexion, 2.2 mm NL). Calcification of rays in the left fin occurs between about 13 mm and 17.4 mm SL. Calcification of rays in the right fin had not begun in the largest specimen (17.4 mm SL). Cephalic Spination Preopercular spines (Table 4) were present in the smallest preflexion specimen (2.2 mm NL, Fig. 4A). With development (Fig. 4B, C), addi- tional spines appear until maximum numbers of about 33 on the left (range 26-52) and 39 on the right (range 23-50) are reached during late flex- ion (6.4-8.9 mm NL). Thereafter, spines are lost until none or only a few remain at transforma- tion (17.4 mm SL, Fig. 5B). Frontal-sphenotic spines were evident in the second smallest preflexion specimen (3.2 mm NL) and throughout the larval series, though less conspicuous near transformation (13-17 mm SL). The lowermost spine on the left side is usually just above the center of the eye and on the right side slightly anterior to the center of the eye. (During transformation those on the right side are at the anterior margin of the skull.) The spines are arranged in a slightly posteriorly con- cave arch following the curve of the skull. There are usually six (up to eight) spines per side, in- cluding three stronger spines arising from a small bulge of the skull. Larval Teeth (Table 5) No teeth are present at 2.2 mm NL (Fig. 4A). At 3.2-4.1 mm NL, larvae usually have two upper and two lower teeth on each side. A 5.3 mm NL preflexion specimen had three upper and four lower teeth on each side. The same numbers were present in the largest early caudal formation specimen (5.7 mm NL). During flexion, numbers of teeth increase from about four upper and five lower (about 6 mm NL) to about eight upper and seven lower (8.9 mm NL) on each side. Postflex- ion larvae (10.4-13.8 mm SL) have about nine upper and nine lower teeth on each side. The nearly transformed specimen (17.4 mm SL, Fig. 5B) had fewer upper teeth on the left side (about 11) than on the right side (19) but the same num- ber (about 15) in both lower jaws. Transformation Migration of the right eye may begin as early as midflexion (6.4 mm NL) or as late as postflex- ion (10.6 mm SL). The right eye moves from the right side of the head through a space between the dorsal fin and supraorbital bars (Fig. 5A) as in Cyclopsetta fimbriata (Gutherz 1971). The right eye reaches its final position on the left side of the head by about 18 mm SL. No early juvenile specimen was available, but eye migration in one of the 17.4 mm specimens was nearly complete (Fig. 5B). Occurrence Larvae were collected in the Atlantic during February, March, April, May, October, and No- vember (Powles4). There was no apparent size progression by month, indicating an extended spawning season. Water depth was 46-640 m. 4H. W. Powles, Assistant Marine Scientist, South Carolina Marine Resources Research Institute, P.O. Box 12559, Charles- ton, SC 29412, pers. commun. July 1976. 47 FISHERY BULLETIN: VOL. 80, NO. 1 a c 2 oJ ' be El .2 a 3"° WW f. OS >> Q. I. 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Transforming larva, 14.2 mm; B. Nearly transformed larva, 17.4 mm; C. Adult, 37.2 mm. Scale = 1 mm. Surface temperature and salinity were 20.4°- 27.3°C and 35.5-36.8"/... Almost no larvae were caught east of the average Gulf Stream axis (Fig. 1). The reported northern limit for adults is Flor- ida (with one exception— an adult male taken off Cape Hatteras (Stewart5)). Larval occurrences shown in Figure 1 are evidence of the effective- 5D. J. Stewart, Graduate Student, Laboratory of Limnology, University of Wisconsin, Madison, WI 53706, pers. commun. June 1978. ness of Gulf Stream transport. The eastward shift of positive tows just north of lat. 32°N cor- responds to the location of a semipermanent meander of the Gulf Stream induced by the Charleston Rise (at about lat. 32°N, long. 79°W (Pietrafesa et al. 1978)). In the eastern Gulf of Mexico, larvae smaller than 4 mm NL were common in January, Febru- ary, May, June, July, August, and November, indicating year-round spawning in that area (Dowd 1978). 50 TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND ETROPUS Citharichthys gymnorhinus (Figs. 1, 6, 7) Identification Larvae approaching transformation had com- plete complements of countable characters. Those specimens were identified by comparing the following larval counts with known adult counts. Number of specimens is given in paren- theses. Caudal fin formula = 4-5-4-4 (15) Caudal vertebrae = 23(3)-24(18) Gill rakers (lower limb, first left) = ~12 (1) Left pelvic rays = 5 (12) Anal rays = 55-59 (11) Dorsal rays = 70-75 (11) Of the potential species listed in Table 1, only C. gymnorhinus has counts that agree with these (it is unique in having only five left pelvic rays). In addition, larvae were captured over the outer shelf, but not as far offshore as C. cornutus (Fig. 1). This is consistent with bathymetric distribu- tion of adults. Distinguishing Characters Citharichthys gymnorhinus larvae have no pectoral melanophore, and notochordal pigment is restricted to the caudal region. Three elongate dorsal rays are present from preflexion (4.6 mm) through postflexion (probably through transfor- mation). Caudal vertebrae (23-24) can be counted by early flexion (6 mm). Lateral pigment is rela- tively sparse except for the caudal band. Flexion is complete at 7-8 mm SL. Morphology is similar to that of C. cornutus. However, the left pelvic fin of C. gymnorhinus has a full complement of only five rays, and in larvae the first ray is much re- duced in size compared with that of C. cornutus. Length of C. gymnorhinus at transformation is probably about 18 mm. Larvae may appear in collections year-round. Pigmentation Pigmentation of C. gymnorhinus larvae is moderate. Gas bladder and caudal band pigment are the most striking. By 4.6 mm and throughout larval develop- ment, the dorsal one-third of the left side of the gas bladder is fairly heavily pigmented, usually with distinct melanophores. With growth, the number of melanophores increases. There are usually more of them than in C. cornutus larvae. The maximum number in a preflexion specimen was about 15 (4.6 mm, Fig. 6A). The right side of the gas bladder is either unpigmented or has only one or two melanophores. By 4.6 mm (Fig. 6A) a caudal band of melano- phores is present on the dorsal and ventral fin- folds and sides and margins of the body about halfway from the anus to the notochord tip. This band is more distinct and regular than in other 51 FISHERY BULLETIN: VOL. 80, NO. 1 Figure 6.-Larval stages of Citharichthys gymnorhin- ws: A. Preflexion, 4.6 mm; B. Late flexion, 6.7 mm. Scale = 1 mm. 52 TUCKER: LARVAL DEVELOPMENT OF C1THARICHTHYS AND ETROPUS Figure 7.— Larval stages of Citharichthys gymnorhinus: A. Transforming, 9.6 mm; B. Transforming, 12.6 mm. Scale = 1 mm. 53 FISHERY BULLETIN: VOL. 80, NO. 1 known larvae of western North Atlantic Cithar- ichthys and Etropus species. In preflexion lar- vae, before pelvic rays form, one or two melano- phores are present on the ventral body margin at the future site of the pelvic fin. By 4.6 mm and throughout development (at least to 13 mm), a few external melanophores are present along the posterior surface of the gut loop. A small melano- phore is found over the posterodorsal surface of the midgut of preflexion larvae. Flexion larvae (Fig. 6B) usually have 15-20 melanophores on the dorsal one-third of the left side of the gas bladder. The caudal band is mostly confined to the body and contains myo- septal pigment. Visible internal notochordal pigment is restricted to the vicinity of the exter- nal caudal band. The dorsal surfaces of one or two forming centra are darkened at about 5 mm. By about 6 mm and throughout development (at least to 13 mm), there may be a few melano- phores along the ventral surface of the gut loop. By late flexion, notochordal pigment appears as fine dashes along four to six centra of caudal ver- tebrae 13-19. By late flexion, pigment along the posterodorsal surface of the midgut extends to the gas bladder and appears as a black lining over the gut. By postflexion (about 8 mm, Fig. 7A), both sides of the gas bladder usually are obscured by body musculature, and pigment in this area ap- pears diffuse. Small melanophores appear on the left pelvic fin membrane along both sides of the elongate second ray. Body musculature tends to obscure notochordal pigment in larvae longer than 12 mm. Morphology (Figs. 6, 7; Tables 3, 6) General morphological features are similar to those of C. comutus, with the qualification that the smallest C. gymnorhinus specimen examined was 4.6 mm NL. Adult morphometries given in the following discussion were derived from Gutherz and Blackman (1970) and Topp and Hoff (1972). The mouth is relatively large in larvae and adults. Larval upper jaw length/BL is fairly con- stant at 9.3-9.5%. Adult upper jaw length/BL is 11.2%, range 9.9-13.0%. Larval upper jaw length/ HL decreases greatly from 38% (preflexion) to 33% (flexion and postflexion). Adult upper jaw length/HL is 41%, range 39-45%. Larval lower jaw length/BL increases from 11.5% to 12.7%. Adult lower jaw length/BL is 13.2%, range 11.6- 14.8%. Larval lower jaw length/HL decreases slightly from 46% to 44% and is only slightly less than that of C. comutus. Adult lower jaw length/ HL is 48%, range 43-53%. The larval snout is pointed but relatively short. Larval snout length/BL increases slightly from 5.2% to 6.1%. Adult snout length/BL is 5.4%, range 4.6-6.6%. Larval snout length/HL is con- stant at 21%. Adult snout length/HL is 20%, range about 18-20%. The eye is relatively large in larvae and adults (only slightly smaller than that of C. comutus). Larval eye diameter/BL is constant at about 8.8%. Adult orbit length/BL is 9.6%, range 8.0- 11.4% (Topp and Hoff 1972); eye diameter/BL is 10.1%, range 9.1-11.0% (Gutherz and Blackman 1970). Larval eye diameter/HL decreases from 35% to 31% and is similar to that of C. comutus. Adult orbit length/HL is 35% (Topp and Hoff 1972); eye diameter/HL is 36.5%, range 33-38% (Gutherz and Blackman 1970). The head is fairly long but shallow in larvae and of moderate length in adults. Larval head length/BL increases greatly from 25% to 29%. Postflexion head length/BL is similar to those of C. arctifrons and C. comutus. Adult head length/ BL is 27%, range 25-29%. Larval head depth/BL increases from 29% to 33% and is similar to that of E. crossotus. Larval snout to anus length is fairly great until postflexion. Snout to anus length/BL increases slightly from 43% (preflexion) to 44% (flexion) and then decreases to 40% (postflexion). This length is similar to that of E. crossotus during flexion and postflexion. With the exception of a relatively deep caudal peduncle, the body is of moderate depth in larvae and adults. Larval body depth at pelvic fin/BL increases from 30% to 39%. Larval body depth at loop of gut/BL increases from 29% to 44%. Larval body depth at anus/BL increases greatly from 25% to 42% and during flexion and postflexion is similar to that of E. crossotus. Larval body depth at third hemal spine/BL increases greatly from 14% to 35%. Adult body depth/BL is 47%, range 39-50%. Larval caudal peduncle depth/BL in- creases from 11.6% (flexion) to 13.2% (postflex- ion). Adult caudal peduncle depth/BL is 11.5%, range 10.5-12.6%. Fin and Axial Skeleton Formation Caudal skeleton development is similar to that of C. comutus. Size ranges of available speci- 54 TUCKER: LARVAL DEVELOPMENT OF CITHAKICHTHYS AND ETROPUS Table 6.— Measurements (mm) of larvae of Citharickthys gymnorhinus. Pref = preflexion, ECF = early caudal formation, Early = early flexion, Mid = midflexion, Late = late flexion, Post = postflexion. S = sym- metrical, 1 = 0 to one-third of the way to the dorsal ridge, 2 = one-third to two-thirds of the way to the dorsal ridge, 3 = two-thirds to all the way to the dorsal ridge. sz Dl c a> >- "D O CD sz Ol c a S ro CD a. a. Z> sz Ol c 0) 5 . LU SZ Ol c 0) ■D CO CD I c/) C CO 0£ — Ol zs c O CD c — CO SZ o> c a> ~m o sz a 01 ■o ■o CO CD I ro ft CO « — So, a.— CD o 13 a. >- o "O o o — CO to C CD ro sz Q. CD ■o >. ■o o CO CD c Q. (/I £ E Q. CD CD-C ■o-o >i n sz o *" CO V c •o CD Q. _ SZ Sa Zl > u cS H CO •a c E be s- o ■a «4-H O e be !- o £ 3 O E l* , 1 eci 0) ii >> u a> cfl +j be X s-, £ o £ c EC o CO -»-> crt hn CU E c (!) C > 3 1-3 o d -C en cS > I* cS ^^ £ E OJ OS «*-c o X) CS 0) ffi §■ a. J1 u as D O 60 TUCKER: LARVAL DEVELOPMENT OF C1THARICHTHYS AND ETROPUS Table 7.— Measurements (mm) of larvae and juveniles of Citharichthys sptiopterus. ECF = early caudal formation, Late = late flexion, Post = postflexion. S = symmetrical, 1 = 0 to one- third of the way to the dorsal ridge, 2 = one-third to two-thirds of the way to the dorsal ridge, 3 = two-thirds to all the way to the dorsal ridge, R = on the dorsal ridge, T = transformed. O) c V >> T3 O CD O) c 0) 3 .5. o. a D Ol c a> 5 re a> 3 o _i O) c o c CO a; ai E 5 T3 ai >. LU O) c Q) ■a re I C re 0£ — o> => c O I re £ c is ft CO C re re Q. 0) TD >. ■D O m CD c a. en «re £ E a. a; a>-<= ■°-o >*— ■D r. o ~ m o c D CD a It re-° O a> O) re c o X c o '55 o a a> >. CD .c n 3.7 0.37 0.45 028 0.36 1.0 1.5 3.8 1.4 '1.5 '1.4 '084 ECF s 5.7 0.42 0.58 0.46 0.46 1.5 22 2.4 2.7 2.9 2.2 074 Late s 6.7 042 0.61 0.53 0.51 1.7 25 8.5 2.5 3.1 3.3 2.6 093 Late s 68 0.54 0.71 046 0.54 1.8 2.7 2.6 3.2 3.5 3.0 1.1 Late 1 8.3 066 080 0.55 0.53 20 2.7 10.4 2.8 3.4 3.7 32 1.2 Post 3 8.7 0.66 0 88 0.53 0.54 2.3 2.8 11.3 3.0 3.5 3.8 3.4 1.3 Post T 8.9 0.54 0.83 0.50 0.52 2.0 3.0 11.1 3.0 3.6 4.0 3.5 1.2 Post 1 8.9 0.61 0.82 0.61 0.56 2.1 29 11.0 3.0 3.6 4.0 3.4 12 Post 2 89 065 0.85 0.50 0.63 2.2 2.9 11.1 3.1 3.5 3.8 3.4 1.3 Post R 90 0.73 1.0 0.58 0.58 2.4 2.9 11.7 3.1 3.5 3.6 3.4 1.2 Post T 9.0 0.62 0.81 0.60 0.58 22 2.8 110 3.0 3.6 4.0 3.6 1.2 Post s 9.1 0.58 0.80 0.56 0.60 2.1 2.9 11.3 3.0 3.4 36 3.3 1.2 Post 3 91 0.70 0.90 0.65 060 2.4 3.1 112 29 3.3 3.4 3.1 1.2 Post T 9.1 0.67 0.93 056 0.60 23 3.0 11.2 29 3.3 3.5 3.3 1.3 Post T 9.2 0.70 093 058 0.70 2.4 2.8 11.4 32 3.7 3.9 3.6 1.3 Post R 9.2 0.64 0.97 046 0.64 2.3 2.7 11.4 2.9 3.6 3.8 3.4 1.3 Post T 92 0.67 0.87 0.60 062 2.4 2.8 114 3.0 3.6 3.8 3.5 1.3 Post T 9.2 0.68 089 0.62 060 2.3 2.8 11.2 2.9 34 39 3.2 1.3 Post R 93 0.57 080 056 060 22 2.9 11.4 30 3.6 3.9 34 1.2 Post 1 93 0.67 090 065 063 24 2.9 11.7 3.0 34 3.8 3.7 1.3 Post T 9.4 068 093 0.53 068 2.4 2.7 11.7 3.0 3.5 3.7 3.4 1.3 Post T 9.4 069 1.0 056 068 23 3.0 11.6 3.1 35 3.7 38 1.4 Post T 9.4 0.67 094 059 0.67 24 29 11.7 29 3.4 3.7 3.3 1.3 Post T 95 071 1.0 060 0.68 2.4 3.1 118 3.0 3.6 3.8 3.4 1.3 Post T 96 066 0.91 0.71 0.53 2.3 3.1 12.0 3.3 3.8 4.1 38 1.4 Post R 9.7 069 0.93 0.64 0.68 2.5 2.9 11.8 3.2 3.6 3.9 3.6 1.3 Post R 9.7 0.61 0.80 0.70 0.56 2.2 3.3 11.9 3.2 3.9 4.3 3.7 1.2 Post S 9.8 0.65 089 0.58 0.74 2.4 3.2 11.9 3.1 3.8 4.1 36 1.2 Post 1 9.8 0.67 0.87 0.70 064 2.4 3.2 119 3.1 3.8 44 38 1.2 Post 1 10.0 0.72 1.0 054 0.72 2.5 3.0 12.2 3.2 3.6 3.8 3.6 1.3 Post T 10.0 0.76 1.0 0.67 0.73 2.6 3.2 12.5 3.2 3.8 3 9 37 1.4 Post T 10.0 1.1 0.73 2.5 3.0 12.2 3.2 3.7 4.0 3.6 1.3 Post T 102 068 0.90 0.70 0.67 2.4 3.2 12.4 3.2 39 4.2 3.8 1.3 Post 3 102 0.71 1.0 056 064 2.6 3 1 125 3.1 3.5 3.7 3.6 1.4 Post T 10.2 0.78 1.1 0.58 0.75 2.5 32 12.7 3.4 39 4.2 39 1.4 Post T 10.2 0.73 1.1 0.53 0.76 26 3.2 125 33 38 4.0 3.8 1.4 Post T 10.2 1.0 060 0.70 2.4 3.2 12.2 33 3.9 4.1 39 1.4 Post T 10.3 0.83 1.1 0.64 064 2.6 32 12.7 3.4 3.8 4.1 3.8 1.4 Post T 10.3 0.79 1.1 060 0.74 2.7 33 13.0 3.4 3.9 4.2 3.9 1.4 Post T 10.5 0.76 1.1 0.60 0.71 2.6 3.4 13.0 3.4 3.8 4.2 4.0 1.4 Post T 10.5 0.59 0.92 060 066 2.4 3.2 12.9 3.5 3.9 4.4 4.2 1.4 Post R 10.6 0.73 1.1 0.63 068 2.7 32 13.1 3.4 4.0 4.2 4,0 1.4 Post T 10.6 0.65 1.1 050 0.67 2.6 3.2 13.1 3.5 4.0 4.3 4.1 1.4 Post T 10.6 060 090 064 0 60 2.5 3.2 13.0 3.4 4.1 4.5 4.1 1.4 Post 1 10.7 0.74 0.95 0.47 0.77 2.6 3.2 13.0 3.2 3.8 4.1 3.9 1.4 Post T 10.8 0.82 1.1 0.65 0.72 2.7 3.3 13.3 3.2 39 4.2 3.8 1.4 Post T 10.9 0.76 1.1 0.55 066 2.7 3.1 13.4 3.4 4.0 4.3 4.0 1.4 Post T 10.9 0.75 1.1 0.62 0.67 2.8 3.2 13.3 3.3 4.0 4.3 4.0 1.4 Post T 11.0 0.81 1.1 0.61 0.65 27 3.2 3.4 3.8 4.0 39 1.3 Post T 11.6 0.84 1.3 0.61 089 3.1 3.8 143 3.7 4.2 4.5 4.4 1.5 Post T 143 1.3 1.9 0.77 1.2 3.8 4.9 18.3 4.6 5.2 5.6 5.6 1.6 Post T 16.6 1.6 2.3 0.91 1.3 4.4 5.3 21 0 5.5 5.9 6.6 7.0 1.7 Post T 167 1.5 2.2 0.75 1.1 4.0 5.0 5.2 60 64 6.6 1.9 Post T 19.4 1.7 2.5 084 1.3 48 6.0 24.1 5.8 6.7 7.5 7.8 2.2 Post T 220 2.1 3.0 1.2 14 54 6.8 27.9 69 7.6 8.6 90 2 7 Post T 23.1 1.9 29 1 1 1.6 5.6 7.1 285 7.0 7.7 8.6 90 2.7 Post T 23.3 2.1 3.1 1.2 1.6 5.8 72 289 7.2 84 92 94 2.8 Post T 24.0 2.2 3.1 1.1 1.6 60 7.8 30.0 7.4 8.3 92 97 2 6 Post T 254 2.3 3.2 1.3 1.6 6.2 8 1 31.9 7.5 89 9.7 3.0 Post T 'Measurement does not include dorsal or anal pteryglophores. Fin and Axial Skeleton Formation Caudal skeleton development apparently is similar to that of C. cornutus. Size ranges of available larval specimens in each stage are as follows: Early caudal formation, 3.7 mm NL; late flexion, 5.7-6.8 mm NL; postflexion, 9.0-10.6 mm SL. All caudal rays are calcified by 5.7 mm. All precaudal neural spines, the first 13 caudal neural spines, the first 13 hemal spines, and no 61 FISHERY BULLETIN: VOL. 80. NO. 1 precaudal or caudal centra stain with alizarin at 3.7 mm NL. All neural spines and hemal spines, some precaudal centra, and the urostyle stain with alizarin at 5.7 mm NL. All precaudal and caudal centra stain with alizarin at 6.7 mm NL. The smallest specimen in which caudal centra could be counted was 5.7 mm NL (late flexion). The second and third dorsal rays are moder- ately elongate and moderately separated at the bases from preflexion (3.7 mm NL) through transformation (about 10 mm SL). No other dor- sal rays were formed at 3.7 mm, but adult counts were present from 5.7 mm NL onward. All dor- sal rays had calcified by postflexion (8.3 mm SL). No anal rays were formed at 3.7 mm, but adult counts were present from 5.7 mm onward. All anal rays had calcified by 8.3 mm. The second left pelvic ray is formed by 3.7 mm; in larger specimens it is elongate. By 5.7 mm, four left and four right pelvic rays are calcified. All six rays in each fin are calcified by 6.8 mm NL. Rayless, fanlike, larval pectoral fins were present in the smallest specimen (3.7 mm). Calci- fication of rays in the left fin begins during post- flexion (9-10 mm SL), and is complete by the end of transformation (9-11 mm SL). Cephalic Spination Preopercular spines (Table 4) were present from early caudal formation (3.7 mm NL, Fig. 8A) through transformation (10.2 mm SL). Maximum numbers may be reached during or before late flexion (31 left, about 36 right); how- ever, counts from early and midflexion larvae are lacking and those from older ones are highly variable. No preopercular spines are evident in juveniles. The 3.7 mm NL specimen had one frontal- sphenotic spine on each side. Several postflexion (8-10 mm SL) specimens had one or two rela- tively inconspicuous frontal-sphenotic spines on each side. These spines may be more numerous in larvae smaller than 5.7 mm NL. None are evi- dent in juveniles. Larval Teeth (Table 5) The early caudal formation (3.7 mm NL, Fig. 8A) specimen had two upper and three lower teeth on each side. During late flexion and post- flexion (5.7-10.6 mm BL), larvae usually have four upper and five lower teeth on each side. Transforming larvae and early juveniles (9.1- 10.7 mm SL) usually have about five upper left (probably about five upper right) and five or six lower left (probably five to eight lower right) teeth. Transformation Migration of the right eye may begin as early as late flexion (6.8 mm NL) or as late as postflex- ion (10.6 mm SL). The right eye moves from the right side of the head around the dorsal fin origin (Fig. 9 A) as in Citharichthys arctifrons and Etropus microstovnus (Richardson and Joseph 1973). The right eye reaches its final position on the left side of the head at about 9-11 mm SL. Occurrence Larvae were collected from September through December in the Gulf of Mexico off Texas (Daher6) and from October through April in the Cape Fear River estuary, North Carolina (pers. obs.). Temperature and salinity ranges at capture locations in the Cape Fear River were 4.1°-26.6°C and 0.0-31.77... Etropus crossotus (Figs. 10, 11) Identification Larvae approaching transformation had com- plete complements of countable characters. Those specimens were identified by comparing the following larval counts with known adult counts. Number of specimens is given in paren- theses. Caudal fin formula = 4-5-4-4 (15) Caudal vertebrae = 24(1), 25(19), 26(3) Gill rakers (lower limb, first left) = ~7 (1) Left pelvic rays = 6 (11) Anal rays = 60-66 (13) Dorsal rays = 76-84 (13) Of the potential species listed in Table 1, only E. crossotus has counts that agree with these. In addition, most specimens were captured west of the Mississippi River in the Gulf of Mexico, an 6M. A. Daher, Graduate Student, Department of Wildlife Science, Texas A&M University, College Station, TX 77843. pers. commun. June 1978. 62 TUCKER: LARVAL DEVELOPMENT OF C ITH A RICHTHYS AND ETROPUS area from which other Etropus spp. have not been reported. Distinguishing Characters Etropus crossotus larvae have a dashlike melanophore at the base of each pectoral fin. In- ternal pigment along the dorsal surface of the notochord is extensive. Two elongate dorsal rays are present from preflexion (4.6 mm) through transformation. Caudal vertebrae (25-26, very rarely 24) can be counted by midflexion (5.4 mm). Lateral pigment is relatively heavy. Flex- ion is complete at 9-10 mm SL. The larval mouth and eye are small. The left pelvic fin has a full complement of six rays. Length at transforma- tion is 10-12 mm. Larvae usually appear in col- lections from March through August. Pigmentation Pigmentation of E. crossotus larvae is rela- tively heavy. Pigment on the gas bladder and on the ventral and dorsal surfaces of the body is the most striking. Most useful for identification is in- ternal pigment along the dorsal surface of the notochord and a melanophore at the base of the pectoral fin. By about 4.6 mm (Fig. 10A) and throughout larval development, the dorsal one-third of the Figure 10.— Larval stages of Etropus crossotus: A. Preflexion (early caudal formation), 4.6 mm; B. Midflexion, 6.0 mm. Scale = 1 mm. 63 left side of the gas bladder is fairly heavily pig- mented, usually with three or four distinct mel- anophores. The right side of the gas bladder is similarly pigmented until late flexion. Internal notochordal pigment consists of a series of fine dashes along the dorsal surface and is more ex- tensive then in known Citharichthys larvae. Pre- f lex ion and early flexion larvae have up to about 12 pigment dashes between the gas bladder and caudal centrum 15. From about caudal centra 15 to 18 (range 14-20) there is a distinct series of heavy dashes which usually form a nearly solid line throughout development. An internal mel- anophore that appears to be associated with the notochord is located below the hindbrain near the otic capsule, where the notochord joins the brain. Dashlike clusters of pigment develop along the dorsal and ventral body margins be- tween the pectoral fin and the caudal fin base. These clusters have not completely formed in the preflexion specimen, but three dorsal clusters and ventral pigment are present. During pre- flexion, a melanophore may be present on the ventral edge of the caudal finfold, opposite the midpoint of incipient hypural bones. Throughout larval development, a continuous or broken line of pigment (the length of three to five centra) is on the lateral midline about two- thirds of the way from the anus to the notochord tip. One or two melanophores are on each side of the symphysis of the lower jaw. The posterior margin of the articular is covered with a stellate melanophore. A stellate melanophore is present at the junction of left and right branchiostegal membranes, just forward of the isthmus. About one to three internal melanophores are present near the pectoral fin base and just forward of the cleithrum beneath the angle of the last gill arch (visible through the opercle). Usually, a melano- phore is on the anterodorsal edge of the urohyal. The ventral body margin between the isthmus and pelvic fin is fairly heavily pigmented with a few distinct melanophores or a continuous band of pigment. Several melanophores are present along the ventral and lateral surfaces of the abdomen and sometimes along the hindgut near the anus. The lower edge of both pectoral fin bases is lined with a dashlike melanophore. The second left pelvic ray has melanophores along its distal end. A series of small melanophores is pres- ent along the distal tips of anal pterygiophores. During early flexion (4.9 mm), one, or rarely two, diffuse internal melanophores appear above the hindbrain. 64 FISHERY BULLETIN: VOL. 80, NO. 1 During midflexion (5-6 mm, Fig. 10B), mela- nophores appear along the distal ends of the elon- gate dorsal rays. A group of melanophores may be present at the distal ends of the middle anal rays. Melanophores begin appearing at the bases and along the sides of middle caudal rays. During flexion, internal notochordal pigment increases. Midflexion and late flexion larvae have up to about 5 pigment dashes between the cleithrum and gas bladder and up to about 18 dashes between the gas bladder and caudal cen- trum 15. From midflexion through postflexion, a small amount of pigment usually is on the antero- ventral edge of the maxillary. By late flexion (6 mm), the gas bladder has be- come oriented toward the left side, and greater development of musculature obscures the gas bladder from the right side. By about 8.5 mm, musculature begins to obscure notochordal pig- ment, except for the heavy dashes in the caudal band area. There is no evidence of a melanophore on the opercle; however, one or two small melano- phores occasionally appear on the interopercle during late flexion. By about 8.5 mm, concentra- tions of pigment have formed around the first through third left pelvic rays. Pigment at the dis- tal margin of the right pelvic fin appears at about the same time. During postflexion (10.5 mm, Fig. 11A), a small melanophore appears on the upper lip. Groups of melanophores are present along the margins of dorsal and anal fins of some speci- mens. In the nearly transformed specimen (10.3 mm, Fig. 11B), heavy posterior notochordal pigment is still obvious. Additional internal melano- phores have appeared posterior to the hindbrain. Myoseptal pigment is well developed, mostly adjacent to dorsal and anal pigment clusters. As in Citharichthys larvae, this forms a caudal band. A midlateral cluster of melanophores is present near the caudal fin. Melanophores have formed along the anterior surface of the head from the snout to the dorsal fin. External and in- ternal melanophores are present along the hind- gut. Melanophores have formed along the proxi- mal ends of groups of some dorsal and anal rays. Morphology (Figs. 10, 11; Tables 3, 8) General morphological features are similar to those of Citharichthys cornutus, with the qualifi- cation that the smallest E. crossotus specimen examined was 4.6 mm NL. Adult morphomet- TUCKER: LARVAL DEVELOPMENT OF C1THAR1CHTHYS AND ETROPUS Figure 11.— Larval stages of Etropus crossotus: A. Transforming, 10.5 mm; B. Nearly transformed, 10.3 mm. Scale = 1 mm. rics given in the following discussion are from Gutherz (1967). The larval mouth is relatively small. During flexion and postflexion relative mouth size is similar to that of C. spilopterus. The adult mouth is the smallest of known western North Atlantic Etropus and Citharichthys species. Larval upper jaw length/BL is fairly constant at 7.0-7.2%. Lar- val upper jaw length/HL decreases from 30% to 27% (preflexion to postflexion). Adult upper jaw length/HL is 21-27%. Larval lower jaw length/ BL is fairly constant at 9.6-9.8%. Larval lower 65 FISHERY BULLETIN: VOL. 80, NO. 1 Table 8.— Measurements (mm) of larvae and a juvenile of Etropuscrossotus. Pref = preflexion, ECF = early caudal formation, Early = early flexion, Mid = midflexion, Late = late flexion, Post = postflexion. S= symmetrical, 1 =0 to one-third of the way to the dorsal ridge, 2 = one-third to two-thirds of the way to the dorsal ridge, 3 = two-thirds to all the way to the dorsal ridge, T = nearly transformed. c 0) c O) c CD to c a to CD c CD IS E CO O) c 3 ■D to C CO o.c c Q. CO ■D to CO c CO CO .c a CO x> CO c a. CO £ E Q. <» co-c CO o c ■o CO a _ .c 5°- CO a> CO "to c o c o CO o a to >. CO o Q. Q. 3 o o c CD CO CO O CO c — CO o CO CO B& o ■a .c o -* d <» CO"0 CO ai CD 3 _i oo LU I CO r- I co CO CO O u. rr 4.6 0.32 044 0.24 0.34 1.1 1.8 4.6 1.3 '1.2 1098 1053 ECF S 4.9 0.35 0.43 0.27 0.37 1.2 2.1 1.6 1.6 1.4 089 0.23 Early S 5.4 0.38 0.50 0.32 0.39 1.4 24 5.6 1.7 1.9 1.7 099 0.27 Early S 54 0.43 066 0.32 041 1.4 2.4 6.0 1.9 2.1 1.9 1.3 0.48 Mid S 5.5 0.40 0.53 0.40 0.36 1.4 2.5 5.8 1.9 2.0 1.8 1.3 0.43 Mid S 5.5 0.37 0.52 0.35 040 1.5 2.6 6.0 1.9 2.0 1.8 1.2 0.43 Mid S 5.6 043 0.57 0.33 0.40 1.4 2.4 5.9 1.8 2.1 1.9 1.3 0.37 Mid s 5.7 0.40 0.51 0.33 0.37 1.4 2.4 5.7 1.7 1.9 1.7 1.1 0.31 Mid s 5.7 0.35 0.49 0.29 0.35 1.4 2.4 6.0 1.8 1.9 1.8 1.2 0.35 Mid s 5.8 0.34 0.49 0.35 0.38 1.4 1.8 1.9 1.2 0.34 Mid s 6.0 0.43 0.56 0.40 0.42 1.6 2.7 65 2.0 2.2 2.1 1.4 0.43 Mid s 6.0 0.37 0.51 0.32 041 1.5 2.8 6.6 2.0 3.0 18 1.3 0.52 Mid s 6.0 0.50 0.62 0.42 0.43 1.6 2.8 68 2.1 2.4 2.2 1.6 0.53 Mid s 6.1 0.51 0.72 0.37 0.47 1.7 2.6 2.1 2.3 2.3 1.6 068 Late S 62 0.41 0.57 0.38 0.41 1.6 3.0 7.2 2.2 2.5 2.4 1.8 0.63 Late s 6.9 0.50 0.67 0.47 0.46 1.9 3.2 8.2 2.3 2.8 2.6 2.0 0.73 Late S 7.4 0.54 0.74 0.53 0.49 20 3.3 8.8 2.5 3.1 3.0 2.5 0.83 Late 82 049 0.70 0.56 0.50 2.3 38 10.1 2.8 3.5 3.7 3.0 1.1 Late 8.3 0.53 0.71 0.53 0.54 2.2 3.6 10.1 2.8 3.3 3.5 2.8 1.0 Late s 8.3 063 0.78 0.53 0.54 22 3.6 10.1 2.9 3.5 3.8 3.2 1.1 Late 8.5 0.69 084 0.63 0.58 2.4 3.6 10.8 3.0 3.6 3.7 3.1 1.1 Late 9.1 0.70 092 0.57 0.61 24 3.6 11.4 3.0 3.7 39 3.4 1.2 Late 93 0.73 0.96 0.70 0.67 2.7 3.9 3.4 4.0 4.1 3.5 1.2 Late 9.3 0.64 0.84 0.63 0.65 26 4.0 11.9 3.4 38 4.1 3.6 1.2 Late 9.3 0.60 0.86 0.67 0.57 2.4 3.9 11.2 3.0 3.8 4.0 3.4 1.1 Post 9.5 0.71 090 0.70 0.63 2.6 4.0 11.9 3.3 4.0 4.3 3.7 1.3 Late 9.6 0.72 096 0.73 0.61 26 4.1 11.9 3.4 4.2 4.4 39 1.3 Post 10.3 0.80 1.1 0.75 071 3.0 3.4 127 33 3.7 3.7 3.7 1.2 Post 10.5 0.75 0.99 0.63 0.66 2.7 4.0 12.9 3.5 4.3 4.8 4,0 1.3 Post 2 10.5 0.76 1.1 080 0.64 28 4.1 12.9 3.5 4.2 4.6 4.0 1.3 Post 3 10.8 0.71 1.0 0.59 2.6 4.1 13.2 3.4 4.3 4.7 4,1 1.4 Post 1 'Measurement does not inc ude do rsal or anal pt srvaioD lores. jaw length/HL decreases greatly from 41%to 36- 37%. The larval snout is moderate but exhibits a relatively fast growth rate. Snout length/BL in- creases from 5.2% to 6.8%. Snout length/HL increases from 22% to 26%. The eye is relatively small in larvae and mod- erate in adults. Larval eye diameter/BL de- creases from 7.4% to 6.3%. Larval eye diameter/ HL decreases greatly from 32% to 24%. Adult eye diameter/HL is about 22-28%. The larval head is of moderate length but rela- tively shallow depth. In adults, the head is the shortest of known western North Atlantic Etro- pus and Citharichthys species. Larval head length/BL increases from 23% to 26%. Adult head length/BL is 20-25%. Larval head depth/BL increases from 29% to 33-34% and is similar to that of C. gymnorhinns. Larval snout to anus length is moderate. Snout 66 to anus length/BL increases from 39% (pref lex- ion) to 44% (flexion) and then decreases to 39% (postflexion). This length is similar to that of C. gymnorhinus during flexion and postflexion. Early larvae are relatively shallow, but ab- dominal and tail depths increase quickly, and as adults, this species and E. rimosus are the deep- est bodied of known western North Atlantic Etropus and Citharichthys species. During post- flexion, the dorsal and ventral profiles of E. cros- sotus are relatively convex. Larval body depth at pelvic fin/BL increases greatly from 26% to 40%. Larval body depth at anus/BL increases greatly from 21% to 43% and is similar to that of C. gym- norhinus during flexion and postflexion. Larval body depth at third hemal spine/BL increases greatly from 12% to 38%. Adult body depth/BL is 50-58%. Larval caudal peduncle depth/BL in- creases from 9.6% (flexion) to 12.6% postflex- ion). TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND ETROPUS Fin and Axial Skeleton Formation Caudal skeleton development is similar to that of C. cornutus. Size ranges of available speci- mens in each stage are as follows: Early caudal formation, 4.6 mm NL; early flexion, 4.9-5.4 mm NL; midflexion, 5.4-6.0 mm NL; late flexion, 6. 1- 9.5 mm NL; postflexion, 9.3-10.8 mm SL. Caudal rays become calcified between early flexion (4.9 mm NL) and late flexion (about 6.5 mm NL). All precaudal neural spines stain with alizarin at 4.6 mm NL. Some caudal neural spines and hemal spines stain with alizarin at 4.6 mm NL, and all do by 5.6 mm NL. All precaudal and cau- dal centra stain with alizarin at about 6.0 mm NL. The urostyle stains with alizarin at 6.2 mm NL. The smallest specimen in which caudal centra could be counted was 5.4 mm NL (midflexion). The second and third dorsal rays are elongate and moderately separated at the bases from pre- flexion (4.6 mm NL) through transformation (about 11 mm SL). During early flexion (4.9 mm NL), rays near the middle of the fin begin to cal- cify. Calcification proceeds anteriorly and pos- teriorly. Adult counts are present from late flex- ion (about 8.0 mm NL) onward. The first ray and most posterior rays are calcified prior to trans- formation (by about 9.6 mm SL). During early flexion (4.9 mm NL), anal rays near the middle of the fin begin to calcify. Calci- fication proceeds anteriorly and posteriorly. Adult counts are present from late flexion (about 8.0 mm NL) onward. The most posterior rays are calcified during late flexion (about 9.3 mm NL). Development of the left pelvic fin precedes that of the right. The left pelvic fin bud appears dur- ing preflexion (before 4.6 mm NL). Rays develop between early caudal formation (4.6 mm NL) and late flexion (8.5 mm NL). The second ray is the first to appear; it is elongate. The first ray appears soon after the second; it may be slightly elongate. The right pelvic fin bud appears dur- ing midflexion (5.5 mm NL). Rays develop between midflexion (5.8 mm NL) and late flexion (8.5 mm NL). Each complete fin has six rays. Rayless, fanlike, larval pectoral fins are present on the smallest available specimen (4.6 mm NL). Calcification of rays in the left fin oc- curs during late transformation (10-11 mm SL). Fig. 10A). With development (Fig. 10B), addi- tional spines appear until maximum numbers of about 24 on the left (range 18-29) and 22 on the right (range 16-27) are reached during midflex- ion (5.4-6.0 mm NL). Thereafter, spines are lost until none or only a few remain at transforma- tion (Fig. 11B). Most specimens had three or four relatively inconspicuous frontal-sphenotic spines on each side, including one or two that were noticeably stronger. Larval Teeth (Table 5) The early caudal formation specimen (4.6 mm NL, Fig. 10A) had three upper and five lower teeth on each side. Early flexion larvae (4.9-5.4 mm NL) have three upper and five or six lower teeth on each side. During midflexion (5.4-6.0 mm NL), there are three to five upper and five to seven lower teeth on each side. During late flex- ion (6.1-9.5 mm NL), larvae usually have four upper and seven lower teeth on each side. During postflexion (9.3-10.8 mm SL), there are usually four or five upper and seven lower teeth on each side. The nearly transformed specimen ( 10.3 mm SL, Fig. 11B) had seven upper and more than nine lower teeth on each side. Transformation Migration of the right eye may begin as early as late flexion (7.4 mm NL) or as late as postflex- ion (10.8 mm SL). The right eye moves from the right side of the head around the dorsal fin origin (Fig. 11 A) as in C. arctifrons and E. microstomas (Richardson and Joseph 1973). The right eye reaches its final position on the left side of the head at about 10-12 mm SL. Occurrence Larvae were collected in the Cape Fear River Estuary during May (pers. obs.) and in the Gulf of Mexico off Louisiana west of the Mississippi River Delta during July and August (Walker7). Moe and Martin (1965) suggested a spawning season from March to at least June for the east- ern Gulf of Mexico off Florida (based on ripe Cephalic Spination Preopercular spines (Table 4) were present in the smallest preflexion specimen (4.6 mm NL, 7H. J. Walker, Research Technician, North Carolina State University, Cape Fear Estuarine Laboratory, P.O. Box 486, Southport, NC 28461, pers. commun. July 1977. 67 FISHERY BULLETIN: VOL. 80, NO. 1 females). Capture of a ripe female from the same area in June was reported by Topp and Hoff (1972). Christmas and Waller (1973) suggested that spawning may be nearly continuous throughout the year. However, that observation was partly based on the occurrence of one juve- nile specimen during January and another dur- ing February that could have been spawned in the late summer or early fall. Therefore, the sea- son may extend beyond August, but the evidence is not yet complete. Comparisons Larval Characters Morphology seems to be influenced by the en- vironment and duration of larval existence. Cith- arichthys cornutus and C. gymnorhinus are found in deeper water and may have longer pel- agic larval stages than C. spilopterus or E. cros- sotus. In some respects, the latter two species are similar to each other and dissimilar to the first two. Citharichthys spilopterus and E. crossotus have only two elongate dorsal rays, as opposed to three in the other two species. They have smaller, less conspicuous frontal-sphenotic spines, and fewer larval teeth. (However, the jaws of C. spil- opterus later grow at a relatively fast rate and acquire correspondingly more adult teeth.) Dur- ing transformation, the origin of the dorsal fin is slightly farther forward relative to the right eye in C. cornutus and C. gymnorhinus than in the other two species. (However, after transforma- tion the dorsal origin is more anterior relative to the right eye in all three Citharichthys species than in E. crossotus.) Citharichthys spilopterus and E. crossotus larvae have smaller eyes and mouths than the other two. They also complete transformation at a smaller size. Known similarities among Citharichthys lar- vae that are not shared with Etropus larvae include the absence of a pectoral melanophore (except possibly in C. macrops), less extensive internal notochordal pigmentation, and, later, more gill rakers. Except for a shallower body and smaller eyes, C. arctifrons larvae are mor- phologically similar to those of C. cornutus and C. gymnorhinus. Etropus microstomus larvae are similar to those of E. crossotus. Larval Occurrence Differences among distributions of larvae (Append. Table 5) can be helpful in identifying them to species. Months of occurrence of larvae reported here are those in which larvae have been collected throughout the ranges of the re- spective species (except that data for C. macrops are from the southern part of its range, and data for C. arctifrons and C. arenaceus are from the northern parts of their ranges). Because most sampling was not continuous throughout the year, presence in other months is not precluded; however, enough is known to delineate approxi- mate spawning seasons for most of the species. Larval occurrence of C. cornutus, C. gymno- rhinus, C. spilopterus, and E. crossotus was dis- cussed in the earlier species' accounts. Throughout their ranges, E. microstomus spawns from March through August and E. rimosus spawns from September to April (Leslie 1977). Leslie suggested that spawning of the two species may be temporally distinct. This con- flicts with spawning of E. microstomus reported from May to December (Richardson and Joseph 1973), and my information is not sufficient to re- solve this conflict. However, Scherer and Bourne (1980) collected E. microstomus eggs in Septem- ber and larvae in October in Block Island Sound, which is north of the reported adult range (Table 1). In the eastern Gulf of Mexico, larvae of E. rimosus smaller than 4 mm NL were common in November, January, February, and May (Dowd 1978). Small juveniles (>13 mm SL) of C. abbotti were caught in the Gulf of Mexico from Veracruz to Campeche, Mexico, in June and September (Dawson 1969), indicating a spawning season approximately from May through August, or longer. Citharichthys macrops larvae smaller than 4 mm NL were caught in the eastern gulf in May and November (Dowd 1978). Topp and Hoff (1972) reported juveniles from the same part of the gulf during the fall and winter. The season probably extends from May through November, and possibly longer. Richardson and Joseph (1973) reported a spawning season approximately from May to December for C. arctifrons in the Chesapeake Bight, with peak spawning from July through October. Dawson ( 1969) reported a 27 mm SL specimen of C. arenaceus caught in the British West Indies in November. This may indicate summer spawn- ing, probably during August or September at least. 68 TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS; AND ETROPUS Citharichthys amblybregmatus and C. dinocer- os are deep water forms. Because of the constancy of their environment, they may have extended spawning seasons, but little is known of their habits. Considering the geographic and bathymetric distributions of adults (Table 1) and probable spawning periods (Append. Table 5), it is un- likely that large numbers of larvae of different species of western North Atlantic Citharichthys and Etropus cooccur in the ichthyoplankton at any given time. Among the six deepwater spe- cies, C. amblybregmatus and C. dinoceros larvae probably occur relatively far from shore. Appar- ently, there is little difference between larval occurrence of C. gymnorhinus and C. cornutus, but spawning centers or peak periods could be distinct. Topp and Hoff (1972) suggested that adults of the two species were bathymetrically separated, C gymnorhinus being found in shal- lower water. Etropus rimosus adults occur in shallow water and do not spawn during the sum- mer. Citharichthys arctifrons has a more north- ern distribution than the preceding three species and its spawning peak is in the summer, prob- ably earlier than that of E. rimosus. Among the three coastal species, the geographic range of C. arenaceus is distinct from those of the other two, and C. macrops and E. microstomas cooccur only off the Carolinas. In this area of overlap, C. macrops probably spawns in the fall and E. microstomus in the spring. Among the three estuarine and coastal species, C. abbotti spawns in the warmer months and may be restricted to very shallow water. Citharichthys spilopterus spawns in the colder months, beginning in late summer in the Gulf of Mexico and in mid to late fall off the Carolinas. Etropus crossotus may spawn from March through the summer, or later, in the gulf, but probably does not begin off the Carolinas until after most spawning activity of C. spilopterus is finished. SUMMARY The caudal fin formula (4-5-4-4) is the most re- liable character for linking larval specimens to the group of paralichthyine genera Citharich- thys, Cyclopsetta, Etropus, and Syacium. The most useful characters for identification to genus are number of elongate dorsal rays, de- gree of cephalic spination, and pigmentation. Known western North Atlantic Syacium and Cyclopsetta larvae have 5-10 elongate dorsal rays and well-developed preopercular and frontal- sphenotic spines. Known western North Atlantic Citharichthys larvae have two or three elongate dorsal rays, small (or no) preopercular spines, small frontal-sphenotic spines, no pectoral mel- anophore (except possibly C macrops), little notochordal pigmentation, usually large eyes and mouths, and (except for C. arctifrons) high gill raker counts. Known western North Atlantic Etropus larvae have no or two elongate dorsal rays, small preopercular and frontal-sphenotic spines, a melanophore at the base of the pectoral fin, extensive notochordal pigmentation, small eyes, and low gill raker counts. Table 9 summarizes the most useful charac- ters for distinguishing larvae of the six species of western North Atlantic Citharichthys and Etro- pus that have been described in detail. The best characters for determining species are number of elongate dorsal rays, number of caudal verte- brae, pectoral and notochordal pigmentation, number of left pelvic rays (C. gymnorhinus), head shape and snout to anus length (C. spilop- terus), number of gill rakers, and length at trans- formation. Citharichthys arctifrons larvae have three elongate dorsal rays, no preopercular spines, many caudal vertebrae, a small eye, large mouth, and few gill rakers. Citharichthys cor- nutus larvae have three elongate dorsal rays, a strong first left pelvic ray, heavy pigmentation, a large eye and mouth, and relatively many gill rakers. Citharichthys gymnorhinus larvae have three elongate dorsal rays, few caudal vertebrae, five left pelvic rays (with the first weak), a dis- tinct caudal pigment band, large eye and mouth, and relatively many gill rakers. Citharichthys spilopterus larvae have two elongate dorsal rays, few caudal vertebrae, little pigmentation, a small eye and mouth, very blunt anterior profile, short snout to anus length, and relatively many gill rakers. Etropus crossotus larvae have two elongate dorsal rays, heavy pigmentation, a small eye and mouth, and many (for the genus) gill rakers. Etropus microstomus larvae have no elongate dorsal rays, a small eye, and few gill rakers. ACKNOWLEDGMENTS I wish to thank the following individuals and institutions for their contributions to this study: for loans and gifts of specimens — E. H. Ahlstrom (NMFS, La Jolla); Charles Bennett, William 69 Table 9.— The most useful FISHERY BULLETIN: VOL. 80, NO. 1 characters, in order of ontogenetic appearance, for distinguishing larvae of four species of Cith- ariehthys and two species of Etropus. Character C. arctHrons* C. cornutus C. gymnorhinus C spilopterus E. crossotus E. microstomas* Pectoral melanophore (before transformation) Absent Absent Absent Absent Present Present Notochordal pigment (before transformation) Caudal only Caudal only Caudal only Caudal only From brain to caudal area From brain to caudal area Elongate dorsal rays (before transformation) 3 3 3 2 2 0 Caudal vertebrae 26-28 25-26 23-24 223-24(25) 2(24)25-26 224-25(26) Lateral pigment (before transformation) Moderate Heavy Moderate Light Heavy Moderate Length at flexion (mm) 9 9-10 7-8 7-8 9-10 7 Left pelvic rays (full complement) 6 6 5 6 6 6 Left preopercular spines (during preflexion- 0 14-31-22 17-22-31 31-31-16 17-20-11 Several flexion-postflexion) Eye diameter/BL in % (during preflexion- 7 10-10- 8 9- 9- 9 10- 8- 7 7- 7- 6 7 flexion-postflexion) Upper jaw length/BL in % (during preflexion- 10 10-11-10 10- 9- 9 10- 7- 7 7- 7- 7 9 flexion-postflexion) Lower jaw length/BL in % (during preflexion- 13-14-13 12-13-13 12-10- 9 10-10-10 flexion-postflexion) Snout to anus length/BL in % (during preflexion- 42 46-46-39 43-44-40 40-39-32 39-44-39 40 flexion-postflexion) Gill rakers on the lower limb of the first arch 6- 8 10-15 9-14 9-15 6- 9 4- 7 (at transformation) Length at transformation (mm) 13-15 -18 -18 9-11 10-12 10-12 Snout spine (at about transformation) May be present Present (in males?) Present (in males9) Absent Absent Absent Symphyseal spine (after transformation) Absent Present (in males?) Present (in males?) Absent Absent Absent 'Data for C. arctifrons and E. mtcrostomus are mostly from Richardson and Joseph (1973). 'Uncommon counts given in parentheses. Birkhead, Ronald Hodson, Wilson Laney, Ed- ward Pendleton, and others (NCSU); Norman Chamberlain (GMBL); Alan Collins (NMFS, Panama City); Mary Ann Daher and John McEachran (Texas A&M); Lise Dowd and Ed- ward Houde (RSMAS); Kathy Kearns (CP&L); Walter Nelson (NMFS, Beaufort); John Olney (VIMS); Howard Powles and Bruce Stender (SCMRRI); Sally Richardson (GCRL); Frank Schwartz (UNC); Victor Springer (USNM); and Frank Truesdale and H. J. Walker (LSU). Tech- nical assistance was provided by Robin Cuth- bertson, Jay Geaghan, Ronald Hodson, Marsha Shepard, and William Watson (NCSU); Frank McKinney (USNM); and the Beaufort NMFS Laboratory. Data and advice were provided by E. H. Ahlstrom, Lise Dowd, Elmer Gutherz (NMFS, Pascagoula), Drew Leslie (Florida State University), Sally Richardson, and How- ard Powles. Nancy Brown Tucker (VIMS) assisted in preparation of the manuscript. John Miller (NCSU), Allyn Powell (NMFS, Beaufort), E. H. Ahlstrom, Jeff Govoni (VIMS), John Olney (VIMS), William Nicholson (NMFS, Beaufort), John Reintjes (NMFS, Beaufort), William Hass- ler (NCSU), B. J. Copeland (NCSU), Leonard Pietrafesa (NCSU), and two anonymous review- ers offered many helpful suggestions for im- proving the manuscript. Carolina Power and Light Company provided financial support. LITERATURE CITED Amaoka, K. 1969. Studies on the sinistral flounders found in the waters around Japan— Taxonomy, anatomy and phylog- eny. J. Shimoneseki Univ. Fish. 18:65-340. Christmas, J. Y., and R. S. Waller. 1973. Estuarine vertebrates, Mississippi. In J. Y. Christmas (editor), Cooperative Gulf of Mexico estua- rine inventory and study, Mississippi, p. 320-403. Gulf Coast Res. Lab., Ocean Springs, Miss. Dawson, C. E. 1969. Citharichthys abbotti, a new flatfish (Bothidae) from the southwestern Gulf of Mexico. Proc. Biol. Soc. Wash. 82:355-372. 70 TUCKER: LARVAL DEVELOPMENT OF CITHARICHTHYS AND ETROPUS DOWD, C. E. 1978. Abundance and distribution of Bothidae (Pisces, Pleuronectiformes) larvae in the eastern Gulf of Mexico, 1971-72 and 1973. M.S. Thesis, Univ. Miami, Miami, 106 p. EVSEENKO, S. A. 1979. Larvae of the flounder Cydopsetta Gill, 1888 (Bothidae, Pisces) from the northwestern Atlantic. Biol. Morya 1979(2):67-75. Fahay, M. P. 1975. An annotated list of larval and juvenile fishes cap- tured with surface-towed meter net in the South Atlan- tic Bight during four RV Dolphin cruises between May 1967 and February 1968. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-685, 39 p. Futch, C. R. 1977. Larvae of Trichopsetta ventralis (Pisces: Bothidae), with comments on intergeneric relationships within the Bothidae. Bull. Mar. Sci. 27:740-757. Futch, C. R., and F. H. Hoff, Jr. 1971. Larval development of Syacium papillosum (Bothi- dae) with notes on adult morphology. Fla. Dep. Nat. Resour. Mar. Res. Lab., Leafl. Ser., Vol. IV, Pt. 1, No. 20, 22 p. Goode, G. B., and T. H. Bean. 1896. Oceanic ichthyology. U.S. Natl. Mus., Spec. Bull., 553 p. GUTHERZ, E. J. 1967. Field guide to the flatfishes of the family Bothidae in the western North Atlantic. U.S. Fish Wildl. Serv., Circ. 263, 47 p. 1970. Characteristics of some larval bothid flatfish, and development and distribution of larval spotfin flounder, Cydopsetta fimbriata (Bothidae). U.S. Fish Wildl. Serv., Fish. Bull. 68:261-283. GUTHERZ, E. J., AND R. R. BLACKMAN. 1970. Two new species of the flatfish genus Citha richthys (Bothidae) from the western North Atlantic. Copeia 1970:340-348. Hensley, D. A. 1977. Larval development of Engyophrys senta (Bothi- dae), with comments on intermuscular bones in flat- fishes. Bull. Mar. Sci. 27:681-703. Hsiao, S. C. T. 1940. A new record of two flounders, Etropus crossotus Goode and Bean and Ancylopsetta dilecta (Goode and Bean), with notes on postlarval characters. Copeia 1940:195-198. Leslie, A. J., Jr. 1977. The systematics of Etropus microstomus (Gill) and E. rimosus Goode and Bean (Pisces: Bothidae), with eco- logical notes. M.S. Thesis, Florida State Univ., Talla- hassee, 81 p. Moe, M.A., Jr., and G. T. Martin. 1965. Fishes taken in monthly trawl samples offshore of Pinellas County, Florida, with new additions to the fish fauna of the Tampa Bay area. Tulane Stud. Zool. 12: 129-151. Moser, H. G., E. H. Ahlstrom, and E. M. Sandknop. 1977. Guide to the identification of scorpionfish larvae (family Scorpaenidae) in the eastern Pacific with com- parative notes on species of Sebastes and Helicolenus from other oceans. U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circ. 402, 71 p. Pietrafesa, L. J., J. O. Blanton, and L. P. Atkinson. 1978. Evidence for deflection of the Gulf Stream at the Charleston Rise. Gulfstream 4(9):3-7. Richardson, S. L., and E. B. Joseph. 1973. Larvae and young of western North Atlantic bothid flatfishes Etropus microstomus and Citharich- thys arctifrons in the Chesapeake Bight. Fish. Bull., U.S. 71:735-767. SCHERER, M. D., AND D. W. BOURNE. 1980. Eggs and early larvae of smallmouth flounder, Etropus microstomus. Fish. Bull., U.S. 77:708-712. Smith, W. G., J. D. Sibunka, and A. Wells. 1975. Seasonal distributions of larval flatfishes (Pleuro- nectiformes) on the continental shelf between Cape Cod, Massachusetts, and Cape Lookout, North Carolina, 1965-66. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-691, 68 p. Sumida, B. Y., E. H. Ahlstrom, and H. G. Moser. 1979. Early development of seven flatfishes of the east- ern North Pacific with heavily pigmented larvae (Pi- sces, Pleuronectiformes). Fish. Bull., U.S. 77:105-145. Taylor, W. R. 1967. An enzyme method of clearing and staining small vertebrates. Proc. U.S. Natl. Mus. 122(3596), 17 p. Topp, R. W., and F. H. Hoff, Jr. 1972. Flatfishes (Pleuronectiformes). Mem. Hourglass Cruises, 4 (Pt. 2), 135 p. Wenner, C. A., C. A. Barans, B. W. Stender, and F. H. Berry. 1979. Results of MARMAP otter trawl investigations in the South Atlantic Bight. I. Fall 1973. S.C. Mar. Re- sour. Cent., Tech. Rep. 33, 79 p. 71 FISHERY BULLETIN: VOL. 80. NO. 1 Appendix Table 1.— Frequency distributions of caudal vertebral counts for western North Atlantic species of Citharichthys and Etropus. i Species 21 22 23 24 25 26 27 28 29 W X C. abbotli 19 96 9 124 21 92 C. arenaceus 3 38 8 49 22 10 C. gymnorhmus 9 27 36 23 75 C. spilopterus 23 109 8 140 23 89 E. rimosus 3 50 53 5 m 24.54 E. microstomus 51 61 2 114 24 57 C. macrops 27 46 73 24.63 E. crossotus 1 69 15 85 25.16 C. cornutus 15 29 44 25 66 C. amblybregmatus 5 16 21 25.76 C. arctifrons 5 34 3 42 26.95 C. dinoceros (2) (2) 'Compiled from Gutherz 1967; Dawson 1969; Gutherz and Blackman 1970; Leslie 1977; S L. Richardson, Research Assistant Professor, School of Oceanography, Oregon State Univer- sity, Corvallis, OR 97331, pers. commun December 1976 (unpubl. data for E microstomus and C. arctifrons), and original data for larvae, juveniles, and adults of C gymnorhinus, C spilopterus, C macrops, E, crossotus, and C. cornutus. 2Extremes of counts. Appendix Table 2.-Frequency distributions of anal fin ray counts for western North Atlantic species of Citharichthys and Etropus.1 Species 48 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 ~68 69 70~ C. arenaceus (2) 1 11 8 14 9 3 E. microstomus (2) 1 12 8 14 22 32 31 23 15 6 5 (2) C. gymnorhinus 2 4339 13 6 10 32 C. abbotti 1 5 13 37 35 22 14 4 1 E. rimosus 1 5 5 17 25 42 57 57 38 41 16 6 1 C. spilopterus (2) 15 24 30 41 26 11 4 (2) C. macrops 116 2 5 17 16 13 E. crossotus 1 1 , 6 10 12 C. arctifrons (2j 117 6 C. cornutus (2) 3 2 7 4 C. amblybregmatus 1 3 2 3 1 q C. dinoceros 12 10 12 13 13 3 (2) 10 23 16 8 6 6 3 11 76 N * 46 53.fr. 160 57.fl 55 56.(| 132 55.! 311 59: 151 58f 73 61 t 60 63. 83 65.3 27 63.CI 22 67.CI n (2> 'Compiled from Gutherz 1967; Dawson 1969; Gutherz and Blackman 1970; Topp and Hoff 1972' Leslie 1977 9 l Rirharrt^n nOM„^ « . . r> < Oceanography, Oregon State University, Corvallis. OR 97331, pers commun December 1976 (unpubl date for C arcWmn^d^Zt^lf^ Pro essor' Sch°°' 0 C gymnorhinus. C spilopterus. C. macrops, E. crossotus. and C. cornutus lunpuDi aata tor c. arctifrons), and original data for juveniles and adults of Extremes of counts, not included in totals. Appendix Table 3,-Freguency distributions of dorsal fin ray counts for western North Atlantic species of Citharichthys and Etropus.* sPecies 67 68 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 90 95 E. microstomus n 2 1 2 7 8 22 21 26 24 23 12 6 4 1 1 (2) C. arenaceus (2) 1 2 11 10 9 7 3 2 C. gymnorhinus 7 8 12 9 8 5 3 1 E. rimosus 2 8 16 18 43 57 52 48 40 17 4 4 1 C. abbotti 1 5 13 23 30 23 23 11 2 1 C. spilopterus 1 4 4 14 35 32 24 26 11 5 1 C. cornutus 1 1 1 3 5 8 6 5 1 1 1 C. macrops 1 1 1 1 3 9 10 12 12 11 C. arctifrons 1 1 3 8 8 14 14 17 7 2 E crossotus 0.05). Clearest evidence for differential day/night net avoidance by N. megalops is found in the catch data obtained by the 1 m2 MOCNESS (Fig. 3). Without exception, for each of the eight day/ night pairs of tows taken on Knorr 65 and Knorr 71, the day estimate of numbers per square t uu o — o 80 0 80 oo 60 0 — o X °x * 40 h- x x *x x° )f X XX o • _ • • • 20 • ADOLESCENT ° FEMALE x MALE 1 ' i 10 20 NEMATOSCELIS MEGALOPS TOTAL BODY LENGTH (mm) 40 Figure 2.— Relationship between total body length, carapace length, and wet weight of Nematoscelis megalops. 79 APRIL 1977 KNORR 65 FISHERY BULLETIN: VOL. 80. NO. 1 OCTOBER/NOVEMBER 1977 KNORR 71 RING BOB STATION 1 MOC 1-62 MOC1-63 MOC 10-21 MOC 10-28 (00 10 1 10 100 100 10 1 10 100 5} 200 f- 400 >■ 600 P- 600 is 1000 0 jg 200 iS r- 400 j- 600 n. ki 800 1000 7m'=6 2 */m2=35 1 */m2»2.1 RING AL STATION 2 MOC 1-72 MOC 1-71 MOC 10-35 10 1 10 100 10 1 1 ' Ol ;/m' = 7 7 7m' = 0 8 .07 7m2 =26 4 *m'=<01 SLOPE WATER 0 £ 200 is ^ 400 J 600 ft. ^ 800 1000 STATION 3 MOC 1-73 MOC 10-36 10 1 10 1 I 1_ O * °0 o o o o 7m2=0 9 738 O O »/_* /m'=0 6 STATION 4 MOC 1-76 MOC 1-75 MOC 10-38 100 10 0 100 200 400 600 800 1000 1 10 100 7m' = 14 8 046 7m2 =22 7 1 DAY | NIGHT A NOT SAMPLED * 10° C ISOTHERM DEPTH 7m2 = 28 4 RING EMERSON STATION 6 MOC 199 MOC 198 MOC 10-59 MOC 10-58 100 10 1 10 100 100 10 I 10 100 0 0 0 0 0 0 0 0 0 ■ ■ * r~~: ■ 1 * - ■ 0 7m2 = 1? 7 7m2 = 73 7m2=5 6 RING FRANKLIN 7m2 = 14 9 0 200 400 600 800 1000 STATION 7 M0CH02 MOC 1-103 MOC 10-61 MOC 10-62 10 1 10 100 100 10 1 10 too 7m2=06 7m' =17 3 7m* » 46 2 7m2 -- 31 5 0 200 400 600 800 WOO STATION 8 MOC 1-109 MOC 1-110 MOC 10-65 MOC 10-66 100 10 1 10 100 7m' =6 3 7m2 =8 5 */m2 = 27 3 SLOPE WATER '/m' = 22 9 0 200 400 600 800 1000 STATION 9 MOC 1-117 MOC 1-116 MOC 10-67 MOC 10-68 7m' = 4 1 7m' = 135 4 */m2 = 31 1 7m2 = 914 -1 MOC 1-96 MOC 1-97 STATION 5 MOC 10-57 1 10 100 7m'=73 2 7m' = 4 31 8 7m2 =235 2 0 200 400 600 800 1000 0 200 400 600 800 1000 Figure 3.— Vertical distribution of Nematoscelis megalops in the Slope Water and in variously aged cold core rings based on collec- tions made with the 1 m2 and 10 m2 MOCNESSes on two cruises taken 6 mo apart. Night samples are blacked; day samples are crosshatched. 80 WIEBE ET AL.: AVOIDANCE OF TOWED NETS BY NEMATOSCEUS MEGALOPS meter for the water column is less than the cor- responding night catch. In every case, sampling extended below the maximum depth of occur- rence of the population and there is no evidence that any individuals of the population migrated vertically out of the depth zone sampled during the day. Therefore, it is highly significant that all of the day values were less than the respective night ones (P<0.005). This result gains impor- tance if we also consider 10 other day/night pairs of 1 m2 MOCNESS tows in which N. megalops was collected on previous cruises (Chain 125, Knorr 53, Knorr 62). For nine of these pairs, moderately to dramatically higher catches in the night tow were obtained (Table 2). The single ex- ception to this pattern was a pair of Slope Water tows taken near the continental shelf in the wake region of a warm core ring (tows 41, 42). But these two tows were displaced in space by several miles, and the night tow was taken nearer the warm core ring where a lower catch might have been expected. Of the 18 day/night pairs of 1 m2 MOCNESS tows, 17 yield higher density estimates at night. Patchiness in the distribution of N. megalops contributed to variability to these estimates but as an unbiased variance component, it does not affect our expectation that one-half of the day and one-half of the night tows in day/night pairs should be the larger. Thus it is unlikely that patchiness of this species is responsible for the significantly higher night catches that we have observed (P<0.001). We know of no other expla- nation than avoidance to explain this result. There are only five pairs of 10 m2 MOCNESS observations of the vertical distribution of N. megalops. For two of these, the integrated day catch is larger than the corresponding night catch and, therefore, night catches are not sig- nificantly larger than day catches (P>0.05). This result either means that there is no day/night dif- ferential avoidance of the 10 m2 net or that in the face of other sources of error such as patchiness, we have too few day/night pairs of observations to observe the avoidance effect. If avoidance were affecting only the smaller net then at least we would expect that the 1 m2 net day catches per unit volume would be consistently smaller than the corresponding 10 m2 net day catches. We might also expect that night catches with the 1 m2 net would be smaller than the 10 m2 net. Neither comparison yields a significant result (P>0.05; day MOCNESS 1 tows greater than day MOCNESS 10 tows in four out of seven com- parisons; night MOCNESS 1 tows greater than night MOCNESS 10 tows in three out of seven comparisons). Thus within the limits of error, by day or by night both net systems provide com- parable estimates of the number of N. megalops living in the water column at a given station. It is possible that the lack of differences in the catching rates between the two nets is due to the different mesh sizes. Small individuals might have been caught more efficiently by the 1 m2 net while larger individuals could have avoided this net better and conversely for the 10 m2 net except that small individuals would have been lost due to escapement through the mesh. The size-fre- quency data in Figures 4 and 5 do not support this possibility. While there is considerable vari- ability between net tow pairs, in terms of abso- lute abundance, neither net system systemati- cally catches large or small individual N. mega- lops in the size range counted better than the other. A similar observation can be made if com- parisons are made on the relative abundances in a given size class (Fig. 6). There is one other potentially significant trend in the data that is important to note. The magni- tude of the day/night avoidance does not appear to be uniform with depth. For the 1 m2 MOC- NESS, largest differences between paired night and day catches where both are positive occur when the center of distribution of N. megalops is above 300-400 m and minimum differences occur at or below these depths (Table 2). Linear regression of the ratio of night to day catch (N/D) versus depth of the center of the distribution at night (50% of occurrence with depth) is signifi- cant at P = 0.1. There is a similar pattern in the 10 m2 MOCNESS tows, although as mentioned above, the day/night differences in catching rates are considerably smaller. In summary, there is clear evidence for differ- ential day/night avoidance of the 1 m2 MOC- NESS. Furthermore, there are no significant differences in the size range of adolescent or adult N. megalops caught by the 1 m2 or 10 m2 MOCNESS systems nor in either system's esti- mates of its abundance in the water column at a given station when day or night pairs are com- pared. Although differences between pairs of day/night catches for the 10 m2 MOCNESS are statistically not significant, the entire data set when considered as a whole strongly suggests that N. megalops is also avoiding the 10 m2 net, albeit to a lesser extent. 81 FISHERY BULLETIN: VOL. 80. NO. 1 ""1 RING BOB STATION I MOC 10-27 D MOC 1-63 N n-K>9 P2 MOC 10 28 N APRIL 1977 KNORR 65 RING AL STATION 2 MOC 1-72 D MOC 10-35 0 SLOPE WATER STATION 3 MOC I 73 a MOC K> 36 D STATION 4 MOC I 75 N "■98 IP n.485 MOC 10-38 N OCTOBER /NOVEMBER KNORR 71 O CO coo RING EMERSON STATION 6 MOC I 99 0 MOC 1-98 N n.27 n-58 MOC K) 59 0 STATION 7 MOC t 102 0 r-|i MOC 10 61 D 'ii.ii i i i ■ 0 50 100 150 MOC K) 58 N ■ ■ . i i i i i i i i ■ i RING FRANKLIN MOC I 103 N J MOC K) 62 N MOC 1-117 0 L J ...... LU MOC 10 65 D STATION 9 MOC K> 67 0 ' MOC H09 0 WET WEIGHT (mg) SLOPE WATER MOC 1116 N MOC 10 68 N MOC 10 66 N I ' ' I ' ' I 0 50 100 150 STATION 5 MOC I 97 N 0 50 K>0 D = DAY N ■ NIGHT FIGURE 4. — Comparison of the composite size-frequency distribution (expressed as No./l,000 m3 for a given wet weight interval)of Nematoscelis megalops caught by the MOC NESS 1 (shaded) and the MOC NESS 10 (crosshatched) for tows taken on the same day or night, n = the number of individuals used to construct the histogram. Application of Barkley Avoidance Theory Catch Since it is likely that N. megalops avoids both net systems, it must detect the approach of either net at some distance in front of the net, resulting in a response which permits a certain percentage of the population to avoid capture. Determina- tion of the avoidance percentage and reaction distance requires an indirect approach, since no other means are available. The theoretical framework on the process of net avoidance devel- oped by Barkley (1964, 1972) provides a means for estimating these parameters according to a quantitative theoretical model. Barkley (1972) formulated the problem in the following way: (volume sampled) X (no. of organisms unit volume ) X (probability of capture) — (losses) (1) "Losses" refers to individuals which are enclosed by the net but escape through the net meshes. For the size range of individuals which consti- tute our "catch," the "losses" term is essentially zero. Since the volume of water sampled has been rather carefully measured, the "probability of capture" (Pc) is of greatest concern. Pc is related to the mean reaction distance (.r<>), the radius of the net mouth (R), the net's speed (U), and the organism's mean escape speed (u,) by the equa- 82 WIEBE ET AL.: AVOIDANCE OF TOWEL) NETS BY NKMATOSCKL1S MEGALOPS RING BOB 6 \ S 01 - MOC I 62 0 MOC 1-63 N APRIL 1977 KNORR 65 RING AL SLOPE WATER STATION 2 STATION 3 MOC 1 72 0 MOC 1-73 D MOC 1-27 D I I I M I I I I I M I I MOC 10 28 N ' MOC 10 35 D RING EMERSON STATION 6 MOC I 99 0 OCTOBER/NOVEMBER KNORR 71 STATION 9 MOC 1-117 D MOC 10-59 0 m <| I I I i IJ1 I MOC 1-102 0 MOC 10-58 N i i i i i i i i MOC 1-103 N RING FRANKLIN MOC 1-109 0 TT - MOC 10-61 0 0 50 100 150 MOC 10-62 N 0 50 WO 150 MOC 10 65 0 WET WEIGHT (mg) MOC 10 36 0 ''''' i i i i I i i j SLOPE WATER MOC 1 116 N TV MOC l-IIO N MOC 10-66 N ' ' ' ' ' ' ' i i i i i i . i i i i 0 50 100 150 STATION 4 MOC 1 75 N IMF MOC 10 38 N j j i i i i STATION 5 MOC 1-97 N MOC 10-57 N i I i L I M I I I I I I 0 50 100 150 0- DAY N' NIGHT Figure 5.— Comparison of the difference between paired MOCNESS 1 and MOCNESS 10 catches in No./l,000 m3 for a given wet weight interval. For shaded columns above the line, the MOCNESS 1 catch is greater than the MOCNESS 10 catch and vice versa for crosshatched columns below the line. tion derived by Barkley (1972, equation 6) wherein: 10 m2 MOCNESS catch volume sampled Pc = 1 Jo u,. R(lf ue2)Vi (2) This expression assumes that as the net moves forward through the water, an individual senses the oncoming net and at a distance Xo in front of the net begins a swimming response in a direc- tion away from the net which is optimal for avoidance. Thus, this equation provides an esti- mate of the minimum probability of capture. As a first step in applying these equations to our data, we may recall that for both the paired night tows and the paired day tows differences between the two net systems were not signifi- cant, i.e., 1 m2 MOCNESS catch volume sampled If we assume that the number of organisms per unit volume was a constant during the time each pair of tows was taken, then: 10 m2 MOCNESS P, = 1 m2 MOCNESS Pr and 1 - XloUe 2\'/ i50(ioo' -u;) X\Uf 2\ 4 3 4 3 .01 Figure 7.— Examples of relative es- cape speed of Nematoscelis megalops individuals versus the catch per 1,000 m3. Superimposed on this plot are the theoretically derived curves of Xr>/R as a function Pc and uj U adjusted to give a "best" fit of the observed points. 85 FISHERY BULLETIN: VOL. 80, NO. 1 if individual escape speeds remained constant. However, further analysis reveals that the dif- ference in Xo for a given day/night catch differ- ential could be a function of the relationship between the observed night catch and the true water column abundance. This is clearly evident if we express the ratio of the day catch per vol- It could be argued that the day/night catch dif- ferential is due to differences in escape speed of the individuals rather than a change in their re- action distance. To explore this we have also solved Equation (3) for the ratio of day escape speed, ud, to night escape speed, uN, after assum- ing xD = xN. + m r- -. •-■ & 2 * x_ 2 Ir _ 2 2 ~x~ R L J _ (5) ume sampled {DC) and night catch per volume sampled {NC) in terms of real abundance (^4) and percent capture as expressed in Equation (2): DC NC If we assume that the daytime escape speed, Ud, is equal to the nighttime speed, w,v, and solve for the ratio of the daytime reaction distance, xd, to the nighttime reaction distance, Xn, we have: Xd/Xs 1 - We have evaluated this equation assuming a true abundance of 100 individuals per volume, night- time catches of 99, 90, 10, 1, and 0.1 individuals per volume, and daytime catches of 50, 10 and 1% of the nighttime catch. The ratios of xD/xNi plotted as a function of the ratio of NC/A Fig. 8a), shows that only very small differences in re- action distance between day and night are re- quired to explain large day/night catch differen- tials when the night catch is 10% or less of the true water column abundance. The fact that we see no significant difference in day/night reac- tion distances suggests our nighttime catches also could be affected strongly by avoidance, and that even at night we have significantly under- estimated the numbers of N. megalops in the water column. Note that the ratio of day/night escape speeds is a function of xs and R as well as DC, NC, and A. The escape speed and radius of net were not in (3) Equation (4) for the ratio of day/night reaction distances. We have evaluated this ratio using the same values noted above. With these results (Fig. 8b), we reach a conclusion similar to that for re- (4) action distance, namely, if reaction distance re- mains constant between day and night, then small differences in escape speed can explain the day/night catch differential when the night catch is 10% or less of the true abundance. There is, however, an entirely different expla- nation which may account for this outcome in application of Barkley avoidance theory to our data. In fitting these data to Barkley's plots of percent capture versus the ratio of x0/R, two assumptions were required: 1 ) that all changes in size frequency are due to avoidance and 2) that swimming speed is a function of body size. The second assumption can be examined if one has day/night pairs of tows taken at the same station location with the same size of net. With swim- ming speed a function of size, Barkley's model 86 WIKBE ET AL.: AVOIDANCE OF TOWEL) NETS BY NEMATOSCELIS MEGALOPS IOOO.Of 100.0 ^ ^ 10.0 1.0 DC = Day Catch NC= Night Catch Xn = Day Reaction Distance Xn = Night Reaction Distance A - True Abundance — o — o 2DC = NC — I0DONC — 100 DC - NC ~ UD=Day Escape Speed Un= Night Escape Speed 100.0 t ^ 10.0 °-° 2 DC = NC — 10DC=NC x— 100DC = NC NC/A Figure 8.— Relationships between the ratio of night catch to true abundance (NC/A) and a) the ratio of day and night reac- tion distances (x,,/xs), and b) the ratio of day and night escape speeds ( u„/uv). predicts that the ratio of the number of individ- uals caught per size class at night (NC) to those caught during the day (DC) will increase with in- creasing individual size (the inverse of Equation 3). This relationship is illustrated in Table 4 where uN and Ho are assumed to be equal and 10 body lengths/s, Xd — 175 cm, xn = 150 cm, R = 50 cm, and U = 100 cm/s. This ratio increases dramatic- ally with individual size until at the largest size, the model predicts all individuals avoid capture. No such pattern emerges if we compute the ratio NC/DC for each size class in our paired day/ Table 3.—Nematoscelvi megalops reaction distances (xo) for the 1 m2 and 10 m* MOCNESS nets derived from the plots like those in Figure 7. Station Cruise Tow Day/Night Xo/fl Xo 1 Knorr 65 M-1-62 D 3.4 1.7 M-10-27 33 5 0 M-1-63 N 34 17 M-10-28 34 5 0 3 Knorr 65 M-1-73 D 34 1.7 M- 10-36 (') (') 4 Knorr 65 M-1-75 N (') (') M- 10-38 34 5 0 5 Knorr 71 M-1-97 N 4.5 2.3 M-10-57 44 66 6 Knorr 71 M-1-99 D 4.5 23 M-10-59 4 4 6.5 M-1-98 N 4 5 23 M-10-58 4 4 6.6 7 Knorr 71 M-1-102 D 4.4 22 M-10-61 (') (') M-1-103 N 44 22 M-10-62 44 66 8 Knorr 71 M-1-109 D 35 1.8 M-10-65 44 66 M-1-110 N 43 22 M-10-66 4 3 64 9 Knorr 71 M-1-117 D 3.5 18 M-10-67 4.4 66 M-1-116 N 4.4 22 M-10-68 4.3 65 'Not sufficient points to derive an estimate, Station 2 omitted for this reason. Table 4.— The ratio of night catch to day catch as a function of individual swimming speed (it*) as predicted by Barkley's avoidance model (inverse of Equation 3). we is assumed to be a function of body size as described in the text. Body wet weight Ue Night Day (mg) (cm/s) catch' catch Ratio 20 1508 0294 0217 1 35 30 1632 0253 0 177 1.43 40 17 56 0 216 0.141 1.53 50 18 80 0.181 0.108 1 66 60 20 04 0.149 0080 1 84 70 21.28 0.120 0056 2 12 80 2252 0 093 0036 2.57 90 2376 0.070 0020 342 100 25.00 0.050 0.009 547 110 2624 0033 0002 14.57 120 27 48 0022 0 000 — 'Catch units are proportion of individuals present per unit volume night MOCNESS 1 or MOCNESS 10 tows (Table 5). Thus, the assumption of increasing swimming speed with increasing size does not appear to be valid, i.e., for the size range of indi- viduals used in this study, avoidance swimming speeds are essentially the same. One implication of this finding is that the size-frequency distribu- tions evident in the field data may not be seri- ously biased by the avoidance although the esti- mates of average density clearly are. 87 FISHERY BULLETIN: VOL. 80, NO. 1 Table 5.— Ratios of night to day catches (number per square meter) of Nematoscelis megalops as a func- tion of size for stations where both the MOCNESS 1 and the MOCNESS 10 were taken. <» indicates only the night tow caught individuals in the given size class; 0 indicates the opposite patterns. Body wet weight (mg) MOCNESS 1- -tow no.: MOCNESS 10— tow no .: 117/116 62/63 99/98 102/103 109/110 27/28 59/58 61/62 65/66 67/68 10 OC — — — — — OO 4.4 0 0 20 OC _ 12 333 0.3 — 24 1 1 <0 1 40 30 66.6 1.3 17 OO 26 59 26 04 08 2 2 40 45.5 4.0 OC 37 26 48 36 08 48 29 50 79 56 0 oc 1 9 36 7 7 02 56 59 60 46 1.1 — oc 08 32 — 05 28 59 70 2.1 7.7 — OO 07 26 — 09 OC 1.8 80 0.6 7 7 — — 0.7 29 — 2.5 1.0 OC 90 24 OO — OO — 35 — 125 1.7 63 100 OO OC — — OO 1.0 — — OO — 110 120 130 — OO — — 0 7.1 0 — — — — - - — — - 0 — - - - DISCUSSION From this application of the Barkley avoid- ance theory, it appears that estimates of N. mega- lops water column abundance could be substan- tially underestimated by both nets, even at night. Minimum probabilities of capture derived from best fits to model expectations are 0.1 or less for night catches and 0.01 or less for day catches. However, the fact that we cannot demonstrate a dependence of the ratio of night to day catches on the size of individuals caught strongly suggests the size dependent swimming speed assumption required to apply the model is not valid for this species, a result which is apparently supported by Kils's (1979) data for Euphausia superba escape swimming (tail swimming). Being unable to make this assumption means that the field population size-frequency distribution which was observed is probably not materially affected by avoidance. Undeniably some fraction of the N. megalops population is avoiding the net systems, and the problem is serious enough to merit an effort to reduce this bias, i.e., to prevent the avoidance from taking place. The usual strategies suggested to reduce net avoidance, increasing net speed or net size, have serious shortcomings in this case. Our evidence strongly implies that N. megalops' response to increased net size is to increase its reaction dis- tance so that the catch rate remains relatively constant. Barkley (1972) reached the same con- clusion in a comparison of 1 m diameter net and 3 m IKMT (Isaacs-Kidd midwater trawl) catching rates of the northern anchovy, Engraulis mor- dax. It is possible that by going to still larger nets (i.e., >10 m2 mouth areas), a reduction in the bias could be effected. However, larger nets would be impractical, if not impossible, to handle on most oceanographic vessels. As Barkley (1964) has demonstrated, in- creased net speed is not a feasible strategy for avoidance reduction since increasing the towing speed of a net requires a compensatory reduction in net size. The practical limits to increasing the tow speed are reached at 2 to 3 kn, because of un- avoidably extreme wire angles and inordinate amounts of wire required to fish even at moder- ate depths (to 1,000 m). High speed tows gener- ally result in damaged specimens, reducing their value in studies requiring taxonomic identifica- tion or in physiological and biochemical mea- surements. Finally, as speed of net is increased, the effects of escapement through the meshes is enhanced. Another means of reducing avoidance, that of camouflaging the net to reduce an animal's abil- ity to detect its presence and thereby reducing the avoidance reaction distance, has been dis- cussed briefly by Clutter and Anraku (1968). There is evidence that it may be an effective strategy for species such as N. rae.ga/o/xs'(LeBras- seur and McAllister, unpublished data cited by Clutter and Anraku 1968). To use this approach, one must first know what kind of a signal the ani- mal is using to detect the oncoming net. Camou- flaging the net can be accomplished by reducing the signal until it becomes part of the back- ground (omnidirectional noise). Alternatively, the noise level could be increased until the signal is no longer detectable. Signals emanating from a net and towing cable include deformation of flow, near field (displacement dominant) or far field (pressure dominant) sound, and light (bioluminescence) (Clutter and Anraku 1968). The importance of 88 WIEBE ET AL.: AVOIDANCE OF TOWED NETS BY NEMATOSCELIS MEGALOPS these different signals obviously depends upon the net structure and towing cable configuration and upon the ability of N. megalops to sense the various signals. Although there is no direct ex- perimental information about N. megalops' sen- sory capabilities or about the signals being gen- erated by MOCNESS, it seems clear that the primary avoidance stimulus involves day to night variations in light. Nemaioscelis megalops must use vision to detect the net and can better avoid the net during the day than at night be- cause during the day the net is better illumi- nated. A fundamental link between the amount of light present and the magnitude of the avoid- ance is provided by our observation that as indi- viduals live deeper in the water column under substantially reduced daytime light levels, day/ night differences in catch rates decline. But if we accept the results gained by the application of Barkley's model which indicate substantial avoidance takes place at night in the absence of bright sunlight, then other factors must also be important. We propose that bio- luminescence is the principal signal and that vision remains the principal means of detection. Three linesof evidence support the importance of bioluminescence as an avoidance cue. First, in an experiment conducted in the early 1960's, Boden (1969) equipped an IKMT with light meters so that he could monitor the amount of light produced above, below, in front of, and in- side the trawl as it was towed at night. Biolumi- nescent light above the trawl was less than below the trawl but both were considerably lower than that ahead of or in the net. Light within the net was so bright that it recorded off scale and indi- vidual flashes were often too numerous to be re- corded as such. Light ahead of the net was also exceedingly bright. Boden (1969) speculated that the light ahead of the net was caused by or- ganisms flashing either in response to the light within the net or to pressure or sound waves propagating forward from the net. Second, Neshyba's (1967) experiments with a submarine photometer and strobe light showed that meso- pelagic and epipelagic organisms could be stimulated to produce significant amounts of bio- luminescence (10 4 juW/cm2) for a sustained pe- riod by proper strobe light flashing. In the ab- sence of artificial flashing, he observed a much lower level of irregular flashing (108-107 /zW/ cm2) similar to that reported by Kampa and Boden (1956), Clarke and Backus (1964), and Boden et al. (1965). Third, it is known that the eyes of euphausiids and decapod shrimps living at midwater depths during the day (i.e., 200-600 m)are sensitive to light levels (10 7 to possibly 10 9 yuW/cm2, Clarke 1970) significantly lower than that produced as a result of bioluminescence. These lines of evidence suggest that the light generated by organisms when they come in di- rect contact with the nets or encounter turbu- lence caused by the net is used by individuals ahead of the net to detect its presence and begin an avoidance response. It seems likely that the light ahead of the net observed by Boden (1969) was caused by the same kind of response mech- anism described by Neshyba(1967), i.e., flashing in response to flashing. The tactic of reducing the visual contrast be- tween a net and the surrounding water was demonstrated by LeBrasseur and McAllister (unpublished data cited by Clutter and Anraku 1968) to reduce the avoidance error for euphau- siids both day and night. However, if biolumi- nescence in and ahead of the net is an important cue as we suspect it to be, then a more active means of camouflaging the net is required. It is known from recent evidence (Warner et al. 1979) that decapod Crustacea living at the same depth as N. megalops are easily "blinded" by even moderate amounts of light. This suggests the possibility of equipping the mouth of a net with a "blinding" light system to be used to periodically illuminate a region ahead of the net with enough light to temporarily blind individuals in the net. With the light out, individuals so affected by the light pulse would be unable to see and, therefore, to respond to the much lower light generated by zooplankton being captured by the net. We pos- tulate that individuals outside the zone of tem- porary blindness may respond by electing a startle response, but, because the volume illumi- nated would be so large, their movement would be random with respect to the volume to be fil- tered by the net. Clearly, considerably more re- search is required before this strategy could be considered feasible. There are two precautionary notes that must be made. First, in spite of avoidance error, verti- cal distribution patterns obtained in sampling this species with MOCNESS at different times under different hydrographic regimes are repli- cable (Fig. 3). That is, although avoidance error is strongly affecting the numerical estimates, the shape of the vertical distributions seem much less affected. Thus, in spite of the avoidance, we believe we are obtaining valuable ecological in- 89 FISHERY BULLETIN: VOL. 80, NO. 1 formation about this species. Second, for most species of euphausiids and many copepods, chae- tognaths, and pteropods in our collections, we have no evidence that differential day/night avoidance is taking place. Therefore, for many ecological studies of oceanic zooplankton, nets still seem the most effective tool to use to quanti- tatively collect them. ACKNOWLEDGMENTS We gratefully acknowledge the assistance given us by R. Backus and J. Craddock in work- ing up the MOCNESS 10 samples. L. Haury, A. Morton, J. Wormuth, A. Hart, and C. Polloni pro- vided valuable assistance in making the MOC- NESS 1 collections at sea, and G. Flierl provided helpful suggestions for interpreting the data. We thank C. Miller and L. Haury for critically read- ing the manuscript and we thank the officers and crew of the RV Knorr and RV Chain for their skillful operation of the vessels. This study was supported by the Office of Naval Research con- tracts N00014-66-CO241 NRO38-004, N00014- 74-C0252 NR083-004, and N00014-79-C-0071 NRO83-004 and the National Science Founda- tion grants DES74-02793 AOl and OCE77- 09132. LITERATURE CITED Barkley, R. A. 1964. The theoretical effectiveness of towed-net sam- plers as related to sampler size and to swimming speed of organisms. J. Cons. 29:146-157. 1972. Selectivity of towed-net samplers. Fish. Bull., U.S. 70:799-820. Boden, B. P. 1969. Observations of bioluminescence on SOND 1965 cruise of R.R.S. 'Discovery'. J. Mar. Biol. Assoc. U.K. 49:669-682. Boden, B. P., E. M. Kampa, and J. M. Snodgrass. 1965. Measurements of spontaneous bioluminescence in the sea. Nature (Lond.) 208:1078-1080. Boyd, S. H., P. H. Wiebe, and J. L. Cox. 1978. Limits of Nematoscelis megalops in the Northwest Atlantic in relation to Gulf Stream cold core rings. II. Physiological and biochemical effects of expatriation. J. Mar. Res. 36:143-159. Brinton, E. 1967. Vertical migration and avoidance capability of eu- phasiids in the California Current. Limnol. Oceanogr. 12:451-483. Clarke, G. L. 1970. Light conditions in the sea in relation to the diurnal vertical migrations of animals. InG. B. Farquhar(edi- tor), Proceedings of an international symposium on bio- logical sound scattering in the ocean, p. 41-48. U.S. Gov. Print. Off., Wash., D.C. Clarke, G. L., and R. H. Backus. 1964. Interrelations between the vertical migration of deep scattering layers, bioluminescence, and changes in daylight in the sea. Bull. Inst. Oceanogr. Monaco 64(1318), 36 p. Clutter, R. I., and M. Anraku. 1968. Avoidance of samplers. In Zooplankton sam- pling, p. 57-76. UNESCO Monogr. Oceanogr. Metho- dol. 2. Fleminger, A., and R. I. Clutter. 1965. Avoidance of towed nets by zooplankton. Limnol. Oceanogr. 10:96-104. Haury, L. R., J. A. McGowan, and P. H. Wiebe. 1978. Patterns and processes in the time-space scales of plankton distributions. In J. H. Steele (editor), Spatial pattern in plankton communities, p. 277-327. Plenum Press, N.Y. Isaacs, J. D. 1965. Larval sardine and anchovy interrelationships. Calif. Coop. Oceanic Fish. Invest. Rep. 10:102-140. Kampa, E. M., and B. P. Boden. 1956. Light generation in a sonic-scattering layer. Deep-Sea Res. 4:73-92. KlLS, U. 1979. Swimming speed and escape capacity of Antarctic krill, Euphausia superba. Meeresforschung 27:264- 266. Lai, D. Y., and P. L. Richardson. 1977. Distribution and movement of Gulf Stream rings. J. Phys. Oceanogr. 7:670-683. Laval, Ph. 1974. Un modele mathematique de l'evitement d'un filet a plancton, son application pratique, et sa verifi- cation indirecte en recourant au parasitisme de l'amphi- pode hyperide Vibilia armata Bovallius. J. Exp. Mar. Biol. Ecol. 14:57-87. Mackas, D. L., and C. M. Boyd. 1979. Spectral analysis of zooplankton spatial hetero- geneity. Science (Wash., D.C.) 204:62-64. Mauchline, J. 1967. Volume and weight characteristics of species of Euphausiacea. Crustaceana 13:241-248. McEwen, G. F., M. W. Johnson, and Th. R. Folsom. 1954. A statistical analysis of the performance of the Fol- som plankton sample splitter, based upon test observa- tions. Arch. Meteorol. Geophys. Bioklimatol., Ser. A Meteorol. Geophys. 7:502-527. McGowan, J. A., and V. J. Fraundorf. 1966. The relationship between size of net used and esti- mates of zooplankton diversity. Limnol. Oceanogr. 11: 456-469. Murphy, G. I., and R. I. Clutter. 1972. Sampling anchovy larvae with a plankton purse seine. Fish. Bull., U.S. 70:789-798. Neshyba, S. 1967. Pulsed light stimulation of marine biolumines- cence in situ. Limnol. Oceanogr. 12:222-235. Ortner, P. B., P. H. Wiebe, L. Haury, and S. Boyd. 1978. Variability in zooplankton biomass distribution in the northern Sargasso Sea: The contribution of Gulf Stream cold core rings. Fish. Bull., U.S. 76:323-334. Richardson, P. L. 1980. Gulf Stream ring trajectories. J. Phys. Oceanogr. 10:90-104. 90 WIEBE ET AL.: AVOIDANCE OE TOWED NETS BY NEMATOSCEUS MEGALOPS RlCKER, W. E. 1973. Linear regressions in fishery research. J. Fish. Res. Board Can. 30:409-434. Semenov, V. N. 1969. Observations of krill behaviour in an aquarium. Tr. VNIRO 66:235-239. Smith, P. E., R. C. Counts, and R. I. Clutter. 1968. Changes in filtering efficiency of plankton nets due to clogging under tow. J. Cons. 32:232-248. Vannucci, M. 1968. Loss of organisms through the meshes. In Zoo- plankton sampling, p. 77-86. UNESCO Monogr. Oceanogr. Methodol. 2. Warner. J. A., M. I. Latz, and J. F. Case. 1979. Cryptic bioluminescence in a midwater shrimp. Science (Wash., D.C.) 203:1109-1110. Wiebe, P. H. 1971. A computer model study of zooplankton patchiness and its effects on sampling error. Limnol. Oceanogr. 16:29-38. Wiebe, P. H., and S. Boyd. 1978. Limits of Nematoscelis megalops in the Northwest- ern Atlantic in relation to Gulf Stream cold core rings. Part I. Horizontal and vertical distributions. J. Mar. Res. 36:119-142. Wiebe, P. H., K. H. Burt, S. H. Boyd, and A. W. Morton. 1976. A multiple opening/closing net and environmental sensing system for sampling zooplankton. J. Mar. Res. 34:313-326. Wiebe, P. H., and W. R. Holland. 1968. Plankton patchiness: Effects on repeated net tows. Limnol. Oceanogr. 13:315-321. Wiebe, P. H., G. D. Grice, and E. Hoagland. 1973. Acid-iron waste as a factor affecting the distribu- tion and abundance of zooplankton in the New York Bight. II. Spatial variations in the field and implications for monitoring studies. Estaurine Coastal Mar. Sci. 1: 51-64. 91 AGE AND GROWTH OF A PLEURONECTID, PAROPHRYS VETULUS, DURING THE PELAGIC LARVAL PERIOD IN OREGON COASTAL WATERS Joanne Lyczkowski Laroche, Sally L. Richardson,1 and Andrew A. Rosenberg- ABSTRACT The age of 331 field-collected English sole, Parophrys vetulus, larvae, 3.1-20.0 mm SL, was deter- mined using daily otolith growth increments. Age in days from hatching was estimated by adding 5, the number of days prior to first increment formation in the laboratory, to the number of increments counted on sagittae. Number of otolith growth increments among larvae of known age in the labo- ratory ranged widely. Yet daily periodicity of increment formation in P. vetulus was inferred from the observations that even under poor growing conditions some larvae added one increment each day since first formation and that, unlike the remaining laboratory-reared larvae in which no pattern was evident, increment addition among larvae in the sea appeared to follow a stable and uniform pattern. Gompertz and von Bertalanffy growth models fitted the resultant size-at-age data equally well; therefore, only the Gompertz model is presented. Larval growth rate decreased from 0.3 mm per day at 8-9 days of age to <0.1 mm per day between 73 and 74 days. The oldest specimen was 74 days old. but most of the larval and transforming specimens collected in plankton samples were <70 days old . Previous estimates of age at length of larval P. vetulus, based on length-frequency modal progres- sion analysis, overestimated the age of larvae >5.5 mm SL by 2-3 times and, correspondingly, the duration of pelagic life was overestimated, 18-20 weeks compared to 8-10 weeks based on otolith- estimated age. Saccular otoliths grow by addition of layers of material differing in the relative amount of the protein, otolin, and calcium carbonate in the aragonite form (Degens et al. 1969; Pannella 1971). This results in growth units or increments composed of an inner light band and an outer dark band. Once the cycle of formation has been established for a species, otolith growth incre- ments can be used to estimate a fish's age and as a record of its past growth. Daily periodicity of increment formation has been confirmed in numerous species by the number of first-order growth increments within annuli in fish over 1 yr of age (Pannella 1971, 1974), by inspection of otoliths from reared fish of known age (Brothers et al. 1976; Taubert and Coble 1977), or from fish maintained in the laboratory for a known period of time (Struhsaker and Uchiyama 1976). Bands of daily increments are often grouped into fort- nightly and monthly growth patterns (Pannella 'Gulf Coast Research Laboratory, East Beach Drive, Ocean Springs, MS 39564. department of Oceanography, Dalhousie University, Halifax, N.S., Canada. Manuscript accepted August 1981. FISHERY BULLETIN: VOL. 80, NO. 1. 1982. 1974; Rosenberg 1980). Subdaily increments, which appear faint and indistinct, when com- pared to daily increments, have been found in some species (Taubert and Coble 1977; Brothers and McFarland in press). The daily increment method of aging larval and juvenile fishes can be used in fishery re- search to document the timing and duration of spawning, development, and major life history stages and events. The singlemost important application is the accurate determination of growth rates during early life in the sea. This technique has been applied to relatively few species, however, and much remains to be learned about how growth may change during development and under varying environmental conditions. Once specific growth rates are avail- able, age-dependent larval mortality rates can be estimated and used to improve estimates of spawning stock biomass and also, perhaps, pro- vide insight into recruitment success. This paper documents the existence of daily growth increments in laboratory-reared and field-caught larvae of an eastern North Pacific pleuronectid, the English sole, Parophrys vetulus. It provides the first accurate estimates of 93 FISHERY BULLETIN: VOL. 80. NO. 1 age at length for larvae of this species and describes the growth of larvae collected in Oregon coastal waters during the 1977-78 spawning season. It is the first detailed study of larval growth of a pleuronectid throughout the pelagic period, and further, provides a basis for the documentation of growth during trans- formation to the adult form (Rosenberg and Laroche 1982) and of juveniles in nursery grounds off the Oregon coast (Rosenberg 1980). METHODS Spawning and Rearing Procedures Ripe adult P. vetulus were collected during fall and winter 1978 with a 12 m otter trawl off the Oregon coast in the vicinity of Hecata Head, approximately lat. 44°10'N, long. 124°18'W, 68-77 m water depth. Eggs were artificially fer- tilized on shipboard (Bagenal and Braum 1971) and transported back to the laboratory in sea- water-filled plastic bags. In the laboratory, eggs were incubated and larvae reared at 12°-13°C and under a 14-h light, 10-h dark photoperiod in filtered seawater taken from the area where the adults were captured. Eggs held in 4 1 glass jars hatched in 3-3% d. The newly hatched larvae were transferred by pipette to new 4 1 glass jars or 8 and 9 1 plastic tubs in which a bloom of the green flagellate Tetraselmis sp. was maintained throughout the rearing period. Approximately every 2 d, one- fourth to one-third of the water in rearing con- tainers was replaced. On day 4 after hatching, Gymnodinium splendens, a naked dinoflagellate, and Brachionus plicatilis, a rotifer, were intro- duced into the rearing containers. After 1-2 wk, G. splendens was no longer added because larvae did not appear to eat this organism. Prey con- centrations were not measured but B. plicatilis, the primary food item, was maintained at high levels, i.e., rotifers were readily visible through- out rearing containers. Artemia salina nauplii and the harpacticoid copepod, Tisbe sp., pro- vided secondary food sources. One to ten larvae were preserved in ~80% ethanol each day after hatching for the first 35 d; subsequently, older larvae were preserved at irregular intervals. Larvae were reared from two separate spawnings, in early and late fall 1978, but since rearing conditions were identi- cal, age and growth data from the two were com- bined. Field and Laboratory Procedures Parophrys vetulus larvae were collected in the field with 70 cm, 0.505 mm mesh bongo nets in bottom to surface stepped, oblique tows. Samples were taken approximately monthly from November 1977 to June 1978 in Yaquina Bay, Oreg., and 2-7 km offshore (lat. ~44°37'N; long. 124°05'W). Samples were drained and pre- served in ~80% ethanol; within 12-18 h the samples were drained again and fresh preserva- tive was added. With each plankton sample sur- face temperature, surface and bottom salinity were recorded and a bathythermograph cast was made. In the laboratory all fish larvae were removed from plankton samples and stored in ~80% ethanol. Otoliths were removed from P. vetulus larvae within 6 mo of initial preservation be- cause longer storage resulted in erosion or com- plete dissolution of the otoliths. Prior to otolith removal P. vetulus larvae were placed in freshwater for ~l-2 min (somewhat longer for specimens >15 mm) to remove or di- lute ethanol in the tissue. A larva was then placed in a drop of water on either a glass slide or large rectangular cover slip under a dissecting micro- scope fitted with polarizing filter and analyzer. Standard length (SL) was measured with an ocular micrometer to the nearest 0.1 mm and both sagittae were dissected out with fine probes at 25 X or 50 X magnification. The larva was re- moved from the slide or slip and the otoliths were left to dry concave side up. Sagittae were then permanently mounted under a cover slip with Pro-Texx,3 a clear mounting medium. Rectan- gular cover slip mounts, which were thought to improve the optical properties of the preparation, were taped for support to a thin piece of brass for viewing under the microscope. Otolith growth increments, consisting of an inner light band and a narrower, sharply delineated, continuous outer dark band adjacent to it, were counted using a compound micro- scope with bright field illumination at 800 X or 1,250 X magnification. Faint bands inside the otolith nucleus in reared larvae and "subdaily" or weak rings between well-defined growth incre- ments in some older (>30 d old) field-caught fish were not counted. Counts were made on only one sagitta of the pair and were repeated until a :iReference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 94 I^KIK'HK KT AL.: AGE AND GROWTH OF PAROPHRYS VETULUS final, "best" count was reached. Successive counts and verification counts which were made by the original reader at a later time usually did not vary by more than ±2. Age estimates could not be obtained for 10% of the field-caught larvae because increments were faint and indistinct or the otoliths were misshapen. Maximum otolith and nucleus diameters were measured to the nearest micron. Photomicrographs were taken at 500 X or 1,000 X magnification under a light microscope. Shrinkage of larvae preserved in 80% ethanol was compared with shrinkage after preservation in 10% seawater-diluted Formalin, the fixative most commonly used to preserve plankton samples. Thirty 7-day-old reared larvae were measured alive and immediately preserved in either 80% ethanol (15) or 10% Formalin ( 15). The live, mean standard lengths of the two groups of larvae were 4.34 and 4.42 mm. After 4 mo in preservative the mean standard length of the ethanol-preserved group was 4.20 mm and of the Formalin-preserved group, 4.196 mm. Mean percent shrinkage or 100(original SL — pre- served SL/original SL) was 3.2% in the ethanol- preserved group and 5.1% in the Formalin- preserved group. The difference in amount of shrinkage between the two groups was highly significant (ANOVA, P<0.01). Care must be taken, therefore, when comparing estimates of size at age based on measurements of larvae pre- served in different fixatives. From this limited investigation it became apparent that Formalin- preserved P. vetulus larvae appear to be some- what smaller at age than ethanol-preserved fish. Statistical Procedures Gompertz and von Bertalanffy growth models were fitted to larval P. vetulus data because the form of the length-age plot was nonlinear with a distinct upper asymptote. A detailed discussion of the Gompertz function, which is the primary model used in this paper, and methods for ob- taining initial parameter estimates are pre- sented by Zweifel and Lasker (1976). The gen- eralized equation of this model is: L, = Loexp[x(l-e-Q')j, where L, = length at age f; Lo = length at t = 0 (i.e., where the curve intercepts the y-axis); and K= — > or the specific growth rate at t = 0 divided by the rate of exponential decay. Un- transformed data were used in this model be- cause the standard deviation of larval lengths at age remained relatively constant and did not in- crease with age, indicating variance homogene- ity within the data set. The Gallucci and Quinn (1979) version of the von Bertalanffy equation was employed, utilizing the new parameter, w = kLx, where k is the growth constant, and Lx, the asymptotic maximum size, which for P. vetulus larvae is the maximum size attained in the plankton prior to transformation into benthic juveniles. The general form of this equation is: Lt = f (l - exp [- kit - *>)] I . where t0 is the time when Lo = 0 (i.e., where the curve intercepts the x-axis). The SPSS NONLINEAR4 program employ- ing Marquardt's algorithm was used to fit both models. A measure of goodness of fit was pro- vided by the residual sums of squares (RSS), the standard error of the regression (or standard deviation of the residuals), and approximate 95% confidence limits for each parameter assuming linearity. Linear confidence theory can be ap- plied here because the assumption of linearity at the final (least squares) parameter values is a reasonable one (Conway et al. 1970; Kimura 1980). A comparison of the RSS at the final pa- rameter values to the linear estimate RSS pro- vides a measure of the linearity of the sum of squares (SS) function (SPSS NONLINEAR pro- gram). Absolute growth rate or k-U expressed in millimeters per day and specific growth rate or In La — In L\ k-U X 100 expressed as percent per day of length were calculated (Ricker 1979). RESULTS Increment Formation Parophrys vetulus larvae survived and grew in the laboratory for over 35 d after hatching, with some individuals eventually transforming into juveniles. However, growth after yolk-sac ab- sorption, between days 4 and 5, was retarded and 4SPSS NONLINEAR. Statistical Package for the Social Sciences, Vogelback Computing Center, Northwestern Uni- versity, Evanston, IL 60201. 95 FISHERY BULLETIN: VOL. 80. NO. 1 not comparable to growth in the field. Despite this, growth increments were visible on the otoliths of over 300 reared larvae. Increments, though extremely narrow and crowded, were even visible on the otoliths of larvae as old as 54 d. In the laboratory, the highest incidence of larvae with one growth increment occurred on days 5 and 6 (Table 1; Fig. la, b). This coincided with the time that larvae first began to swim actively near the surface of rearing containers and search for food. By day 5 larvae had also acquired darkly pigmented, iridescent eyes and functional mouths, and had utilized all or almost all their yolk. Age at first increment formation in the field was ascertained by comparing mean otolith diameter (jum) of field-caught larvae with a single increment, to mean otolith diameter of laboratory-reared larvae of known age (Table 1 ). The otolith diameter, 23.8 nm, of field-caught larvae with only one growth increment (SL = 3.7 mm) fell between the mean values for lab- oratory-reared larvae at 5 d, 23.1 (SL = 4.2 mm), and at 6 d, 24.2 (SL = 3.9 mm). Age of all field-caught larvae with one otolith growth increment was, therefore, taken to be 6 d. Age at first increment formation varied among in- dividuals in the laboratory and may, likewise, vary in the field; however, for the purpose of developing a generalized growth model, a single, best estimate of this event was made. The appar- ent smaller size of field-caught larvae with one increment most likely resulted from shrinkage during capture prior to preservation (Theilacker 1980). Larvae sampled in the laboratory were pipetted alive directly into preservative, thus re- ducing the amount of handling-induced shrink- age. Although laboratory results were somewhat ambiguous, daily periodicity of otolith growth increment formation in P. vetulus was inferred from the following observations: 1) despite less than optimum rearing conditions some 14-, 17-, and 20-d-old larvae had added one increment each day since first formation on day 4 (Table 2); 2) no other periodical pattern in increment formation (i.e., other than daily) was observed among laboratory-reared larvae; 3) increment addition among larvae in the sea appeared to follow a stable and uniform pattern. The wide range in number of otolith increments among reared larvae of known age may have been caused by poor growing conditions which re- sulted in stunted body and otolith growth (Table 2). Reared larvae of northern anchovy also failed a Figure 1.— Photomicrographs of Parophrys vetulus otoliths (X 1,000). a. Sagitta (22 ^m in diameter) prior to first in- crement formation from a 4-d-old, laboratory-reared larva; b. Sagitta (24 /iiti in diameter) with two complete increments (highlighted with black lines) from a6-d-old, laboratory-reared larva; c. Sagitta (22 ^m in diameter) with two complete incre- ments (highlighted with black lines) from a 7-d-old, field- caught larva. 96 .AROC'HK ETAL.: AGE AND GROWTH OF PAROPHRYS VETULUS Table 1. — Comparison of mean otolith diameters (OD) of laboratory-reared and field-collected Pnrophrys vetulus larvae. Age of reared larvae represents days from hatching. Age Mean OD No No. growth increments Mean OD No No growth (days) (pm) larvae 0 1 2 3 4 (//no larvae Increments 0 146 10 10 1 16.6 12 12 2 188 10 9 1 3 205 11 10 1 4 21.6 14 13 1 21 3 7 0 5 23.1 24 10 10 4 23.8 4 1 6 24.2 19 4 4 8 2 1 246 10 2 to consistently form growth increments when maintained on low rations (Methot and Kramer 1979). In P. vetulus, delayed inception of incre- ment formation, up to 8 d after hatching, may also have accounted for some of the apparent irregularity in increment formation in the lab- oratory (Table 2). Another factor contributing to ambiguity of laboratory results was the diffi- culty in counting otolith increments in older larvae. Increments in most laboratory-reared fish after 16-25 d were exceedingly faint and, in some fish, no increments could be discerned (Fig. 2a, b). Growth increments were, in gen- eral, clearer and more distinct on the otoliths of field-caught P. vetulus larvae than on otoliths of laboratory-reared fish (Figs, lc, 2c). The steady increase in number of increments with increas- ing otolith diameter and length of pretransfor- mation larvae in the field is evidence that the irregularity in increment formation observed in the laboratory did not occur under natural feed- ing conditions (Figs. 3, 4). Age and Growth Age of field-caught P. vetulus larvae in days from hatching was estimated by adding 5, the number of days prior to appearance of the first otolith growth increment, to the number of in- crements counted on sagittae. Counts of growth increments were obtained from 338 larval and transforming, pelagic specimens ranging from 2.4 to 20.0 mm SL (Fig. 4). But age could be esti- mated for only 331 larvae because increment formation had not yet begun in seven small speci- mens, 2.4-3.7 mm SL (Fig. 5). The oldest P. vetulus taken in plankton samples during 1977- 78 was 74 d (2.4 mo) old and 17.8 mm SL. The next oldest larvae ranged from 65 to 70 d old and were 19-20 mm SL. The length of pelagic life of P. vetulus can be estimated directly from these data to be 2-2.5 mo. Few P. vetulus larvae >20 mm SL, the size at which larvae transform to benthic juveniles (Ahlstrom and Moser 1975; Rosenberg and Laroche footnote 3), were taken in extensive plankton collections off Oregon during the spring months in 1972-75 (Laroche and Richardson 1979). The largest larva taken in those collections was 22 mm SL. Behavior of reared P. vetulus larvae further supports a pelagic phase of 2+ mo. At approxi- mately 60 d of age, larval P. vetulus maintained in the laboratory first exhibited the tendency to rest on their sides on the bottom and to swim with their bodies at an angle to the vertical (J. L. Laroche unpubl. data). Table 2.— Summary of growth in body length (SL) and otolith diameter (OD), and counts of growth increments on otoliths of laboratory-reared Parophrys vetulus larvae. N= number of larvae from which growth increment counts were taken; (N) - number of larvae used in mean otolith diameter calculation. No growth Age (days) Mean SL Range SL (mm) Mean OD Range OD increments N (mm) (fjm) (fjm) Mea 1 Range 4 14 4.1 3.7-4.4 21.6 20-25 0 0-2 5 24 4.2 3.8-4.5 23.1 20-25 1 0-2 6 19(17) 39 3.1-4.2 24.2 23-27 2 0-4 9 9 4.0 3.7-4.1 24.7 23-26 3 2-4 10 13 4.2 37-46 25.7 25-27 4 3-6 14 13 49 5.8-4.2 287 27-33 8 5-10 17 13 54 45-63 296 28-33 10 5-13 20 7(6) 5.7 5 .1-6.4 31.8 30-36 10 5-16 21 6 59 5.4-6.6 31.2 30-34 13 10-16 26 18(17) 7.0 5.6-8.6 334 30-37 14 10-20 97 FISHERY BULLETIN: VOL. 80. NO. 1 * y a Figure 2.— Photomicrographs of Parophrys vetulus otoliths ( X 1,000). a. Sagitta (30 ^m in diameter) with 16 complete incre- ments from a 21-d-old, laboratory-reared larva; b. Sagitta (32 jum in diameter) with no discernible increments from a 22-d-old. laboratory-reared larva; c. Sagitta (102 ^m in diameter) with 42 complete increments from a 47-d-old, field-caught larva. 98 LA ROCHE ET AL.: ACE AND OROWTH OF PAROPHRYS VETULUS O 00 •00 O PJ OJ IO oo o co o • • • • .V*. •«« . 4 ID k- O 5 0) •a e j= bo 3 OS o bo C £ «- o If) to CM C C V) a! t O a > t= a <1 00 £ CO CO o O 111 t. o ^ 0) V 0> £ ~; ^ jt TT k 43 ^ -*j --j V^i +j k. o O 3 ca in in l O t_ O) 42 E 3 Z 1 CO w as (M S1N3W3UDNI HIMOdO JO ON 99 FISHERY BULLETIN: VOL. 80, NO. 1 70 50 I I a; 1 5 25 _..f> •a. i.. Mi. . 7"7'\ j i i i_ _i i i — i- 5 10 15 STANDARD LENGTH (mm) 20 FIGURE 4.— Number of otolith growth increments related to standard length of 338 larval and transforming, field-caught Parophrys vetulus. Our description of early growth of P. vetulus in Oregon coastal waters at temperatures ranging from 9° to 11°C is based on the ages and lengths of 331 specimens, 3.1-20.0 mm SL, with otolith growth increments. Gompertz and von Berta- lanffy models yielded good and nearly identical fits to the data and similar estimates of growth rate; therefore, the results of only one model (Gompertz) are presented (Table 3; Fig. 5). RSS and linear estimate RSS of the Gom- pertz growth parameters were very similar; thus, the assumption of linearity in computing 95% confidence limits is reasonable, and the computed limits indicate relatively narrow con- fidence regions around the parameters (Table 3). Previous estimates of age at length of larval P. vetulus were derived from the progression of modes in length-frequency distributions of larvae from a time series of (10% Formalin pre- served) plankton samples (Laroche and Richard- son 1979). A comparison of those results with age at length estimated by the Gompertz equation (Zwiefel and Lasker 1976) indicates that the length-frequency method overestimated the age of larvae >5.5 mm SL by 2-3 times (Table 4). Estimates of specific and absolute rates of growth were calculated from length at age for various ages as predicted by the Gompertz model (Table 5). Specific growth rate steadily de- creased between 8 and 74 d. Absolute growth rate was fairly uniform between 8 and 31 d, slowed somewhat between 31 and 41 d, but was more drastically reduced between 73 and 74 d, at which time larvae undergo transformation, a Table 3.— Gompertz equation and estimated parameters describing the growth of 331 Parophrys vetulus larvae in Oregon waters during the 1977-78 spawning season. RSS = residual sum of squares; SE = standard error of the regres- sion; S2 = variance; CL = confidence limits. Equation L, = 2.073 exp[2.354 (1- Parameters S2 _e -0.045,,] RSS Linear est. RSS RSS SE 520 83 1256 Approximate 95% CL Lo = 2.073 K =2.354 a =0 045 0023 0003 0.00001 564892 535.762 533854 564 892 536.093 533.635 L, = 1.779, Li = 2.367 /_, =2.245, U =2.462 L, = 0.040, L2 = 0.050 Table 4.— Age of Parophrys vetulus larvae; (A) estimated from modal progression in length-frequency distributions of larvae caught during 1971 in biweekly and weekly Formalin-preserved plankton samples (Laroche and Richardson 1979), (B) estimated by the Gompertz equation based on otolith increment counts from ethanol-preserved larvae caught in 1977-78. Estimated age (weeks) SL (mm) 5.5 7.5 95 11.5 13.5 15.5 17.5 w f • -z. : * • < " • v i • en 50 1 1 i : 1 i i 1 1 \ 2 354(l-e""0045h Lt= 2073 e35U ' i i i 1 i i i i 25 50 ESTIMATED AGE (days) 75 Figure 5.— Gompertz curve and equation fitted to length at age of 331 larval and transforming, field-caught Parophrys vetulus with at least one otolith growth increment. period characterized by reduced growth in length (Rosenberg and Laroche 1982). The plot of otolith diameter on standard length of pelagic larval and transforming P. vetulus re- vealed an allometric relationship (Fig. 6). A dis- tinctive feature of this plot was the apparent con- tinued, even accelerated growth of sagittae as P. vetulus larvae reached the size of transforma- tion, 18-20 mm SL, when rate of growth in body length slows down. Physical evidence of acceler- ated growth in otolith diameter relative to body length can be seen by the increased width of the outermost increments on otoliths of larvae older than 30 d (e.g., outer 9-10 increments on sagitta in Fig. 2c). The otolith diameter to standard length relationship, once a mathematical formu- lation has been computed, can be used to back- calculate individual growth histories of larvae and juveniles (Rosenberg 1980; Methot in press), as has been done for adult fishes (Tesch 1968; Ricker 1969). DISCUSSION As in numerous other temperate and some tropical species of fishes, growth increments on the otoliths of P. vetulus larvae appear to be formed daily after yolk-sac absorption when larvae become capable of exogenous feeding. Counts of these increments provide more pre- cise and accurate estimates of larval age and growth rates throughout the larval period than have previously been available. This informa- tion, when combined with abundance data, allows computation of age-dependent mortality rates resulting in more accurate estimates of larval mortality in the sea. Empirically, both the Gompertz and von Bertalanffy growth models fit the larval P. vetulus data well. Both yielded similar values for length at age and growth rates from which age- dependent mortality estimates can be made. There has been much disagreement, on theoreti- cal grounds, as to the appropriateness of either model for describing growth in fishes, although they are mathematically quite similar (e.g., Zweifel and Lasker 1976; Ricker 1979). Despite numerous attempts to attribute biological signif- icance to mathematical models of growth, the best criterion available for choosing a particular model is still goodness of fit to the data (Ricker 1979). In that respect, both models were appro- priate to this data set. A practical measure of the appropriateness of mathematical models is the relative accuracy and stability of pertinent parameter estimates (Gallucci and Quinn 1979). In the Gompertz 101 FISHERY BULLETIN: VOL. 80, NO. 1 230 208 - ■ 228 . '213 210 193 I 150- 125 i 100- 75 50- 3. ~ ■ • • • • • - ■ • . • • '•2 •• • • .* V. •• 2 2* •—€ mm* • • «• 2* « .. «, • am • - - - -•- mm me • ••• • • • 25 nf •• • • *k *: - * : Figure 6.— Otolith diameter related to standard length of 338 larval and transforming, field-caught Parophrys vetulus. J L J I I L _1_ 10 15 STANDARD LENGTH (mm) 20 102 LARIH'HE ETAL.: A(!K AND CROWTH OF PAROPHRYS VETULUS model, the parameter L0 or the y-intercept has been used as an estimator of length at hatching (Zweifel and Lasker 1976). However, the value of this parameter, 2.07 mm SL, for the P. vetulus data set was low compared to mean hatching lengths of reared larvae: 2.60 (N = 11) and 2.91 (N = 10) mm SL at 12°-13°C (Laroche unpubl. data); and 2.85 (N = 25) mm TL at 10°-1 1 °C (Orsi 1968). Net-caught larvae on which the growth model is based would appear smaller at age be- cause of increased shrinkage during capture (Theilacker 1980). This may account for some of the difference in predicted and observed hatch- ing lengths. Another probable cause of this dis- crepancy is the lack of data points in the <6 d of age region of the plot, i.e., before growth incre- ment formation begins. The value of Lo is based on extrapolation beyond the actual data and may be, therefore, of questionable use as a measure of the appropriateness of this model. Comparison with larval growth in the field at similar temperatures of another pleuronectid, Pseudopleuronectes americanus, provided evi- dence that growth rates predicted by the Gompertz model for Parophrys vetulus are realistic. Larval Pseudopleuronectes americanus between the ages of 28 and 42 d, growing in large enclosures in Narragansett Bay at 10°- 15°C, had a specific growth rate of 1.9% per day of standard length (Laurence et al. 1979). The predicted specific growth rate of Parophrys vetulus of the same age, growing at9°-ll°C, was 2.2%. Larval Pseudopleuronectes americanus be- tween 28 and 42 d of age grew from 6.6 to 8.6 mm SL, while Parophrys vetulus larvae grew from 11.2 to 15.3 mm SL. Although these two species differ in size at age, both transform at approxi- mately the same age, 8-10 wk, and appear to grow at similar rates between 4 and 6 wk of age. Since length at hatching, ~2-3 mm SL, is similar for both species, higher rates of growth prior to and after 4-6 wk probably accounts for the greater size at age of P. vetulus and greater size at transformation, >18 mm SL in P. vetulus versus <10 mm for Pseudopleuronectes ameri- canus. A comparison of otolith-estimated and length- frequency derived age-at-length data indicated that the latter method overestimated age of Parophrys vetulus larvae >5.5 mm SL by 2-3 times. This resulted in a gross overestimate of duration of the pelagic life of this species, 18-22 wk (Laroche and Richardson 1979) compared to 8-10 wk based on the age data presented here. It is unlikely that these large differences are solely the result of different preservatives. Such a large discrepancy between the two methods demon- strates the serious inaccuracies that could result from attempts to estimate age and growth rates from length-frequency data. Such data predict- ably yield low estimates of growth, especially for species with protracted spawning, because of continual recruitment of small larvae to the pop- ulation. Problems of net avoidance by larger specimens further bias length-frequency dis- tributions. The otolith aging method developed in this study could be used further to investigate growth and survival among different cohorts of P. vetulus larvae. Spawning in this species is highly variable in both frequency and timing (Laroche and Richardson 1979). Peak spawning can be bimodal in some years with a 2-4 mo separation between peaks (Kruse and Tyler5). Larvae pro- duced in those two peaks could develop and grow under very different temperature regimes and feeding conditions, which could result in two distinct groups of larvae differing in rates of growth, mortality, and relative contribution to that year class. ACKNOWLEDGMENTS The following individuals are gratefully ac- knowledged for their significant contributions to this study. Rindy Ostermann and Betsy B. Washington assisted in all phases of collection of ripe adult specimens, larval rearing, otolith removal, and data compilation. Rae Deane Leatham and Percy L. Donaghay instructed the first author in culture techniques and generously provided the equipment and space in their laboratory for parts of this work. Eric Lynn, National Marine Fisheries Service, NOA A, La Jolla, Calif., sent us cultures of larval food organisms. Gary Hettman, Oregon Department of Fish and Wildlife, kept us informed throughout the fall and winter of the likely locations of English sole spawning con- centrations. Waldo W. Wakefield and Marky Bud Willis assisted at sea in collecting spawning fish. Chip Hogue, Paul Montagua, Gene Ruff, and Andrew Carey provided laboratory space 5Kruse, G. H., and A. V. Tyler. 1980. Influence of physical facotrs on the English sole (Parophrys vetulus) spawning season. Unpubl. manuscr., 25 p. Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331. 103 FISHERY BULLETIN: VOL. 80, NO. 1 and their microscope for otolith observations. Otolith photomicrographs were taken with the help and guidance of Michael D. Richardson, Naval Ocean Research and Development Activi- ties, Bay St. Louis, Miss. This work is a result of research sponsored by the Oregon State University Sea Grant College Program (04-8-M01-144), supported by NOAA Office of Sea Grant, Department of Commerce. LITERATURE CITED Ahlstrom, E. H., and H. G. Moser. 1975. Distributional atlas of fish larvae in the California Current region: flatfishes, 1955 through 1960. Calif. Coop. Oceanic Fish. Invest. Atlas 23, 207 p. Bagenal, T. B.. and E. Braum. 1971. Eggs and early life history. In W. E. Ricker (editor), Methods for assessment of fish production in fresh waters, 2d ed., p. 166-198. IBP (Int. Biol. Programme) Handb. 3. Brothers, E. B., and W. N. McFarland. In press. Correlations between otolith microstructure, growth, and life history transitions in newly recruited French grunts [Haemulon flavolineatum (Desmarest), Haemulidae]. Rapp. P.-V. Reun. Cons. Int. Explor. Mer. 178. Brothers, E. B., C. P. Mathews, and R. Lasker. 1976. Daily growth increments in otoliths from larval and adult fishes. Fish. Bull., U.S. 74:1-8. Conway, G. R., N. R. Glass, and J. C. Wilcox. 1970. Fitting nonlinear models to biological data by Marquardt's algorithm. Ecology 51:503-507. Degens, E. T., W. G. Deuser, and R. L. Haedrich. 1969. Molecular structure and composition of fish otoliths. Mar. Biol. (Berl.) 2:105-113. Gallucci, V. F., and T. J. Quinn, II. 1979. Reparameterizing, fitting, and testing a simple growth model. Trans. Am. Fish. Soc. 108:14-25. Kimura, D. K. 1980. Likelihood methods for the von Bertalanffy growth curve. Fish. Bull., U.S. 77:765-776. Laroche, J. L., and S. L. Richardson. 1979. Winter-spring abundance of larval English sole, Parophrys vetulus, between the Columbia River and Cape Blanco, Oregon during 1972-1975, with notes on occurrences of three other pleuronectids. Estuarine Coastal Mar. Sci. 8:455-476. Laurence, G. C, T. A. Halavik, B. R. Burns, and A. S. Smigielski. 1979. An environmental chamber for monitoring "in situ" growth and survival of larval fishes. Trans. Am. Fish. Soc. 108:197-203. Methot, R. D., Jr. In press. Spatial covariation of daily growth rates of larval nothern anchovy, Engraulis mordax, and northern lanternfish, Stenobrachius leucopsarus. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178. Methot, R. D., Jr., and D. Kramer. 1979. Growth of northern anchovy, Engraulis mordax, larvae in the sea. Fish. Bull., U.S. 77:413-423. Orsi, J. J. 1968. The embryology of the English sole, Parophrys vetulus. Calif. Fish Game 54:133-155. Pannella, G. 1971. Fish otoliths: daily growth layers and periodical patterns. Science (Wash., D.C.) 173:1124-1127. 1974. Otolith growth patterns: an aid in age determina- nation in temperate and tropical fishes. In T. B. Bagenal (editor). The proceedings of an international symposium on the ageing of fish, p. 28-39. Unwin Brothers, Surrey, Engl. Ricker, W. E. 1969. Effects of size-selective mortality and sampling bias on estimates of growth, mortality, production, and yield. J. Fish. Res. Board Can. 26:479-541. 1979. Growth rates and models. In W. S. Hoar, D. J. Randall, and J. R. Brett (editors), Fish physiology, Vol. VIII, p. 677-742. Acad. Press, N.Y. Rosenberg, A. A. 1980. Growth of juvenile English sole, Parophrys vetulus, in estuarine and open coastal nursery grounds. M.S. Thesis, Oregon State Univ., Corvallis, 51 p. Rosenberg, A. A., and J. L. Laroche. 1982. Growth during metamorphosis of English sole, Parophrys vetulus. Fish. Bull., U.S. 80(1):150-153. Struhsaker, P., and J. H. Uchiyama. 1976. Age and growth of the nehu, Stolephorus purpureus (Pisces: Engraulidae), from the Hawaiian Islands as indicated by daily growth increments of sagittae. Fish. Bull., U.S. 74:9-17. Taubert, B. D., and D. W. Coble. 1977. Daily rings in otoliths of three species of Lepotnis and Tilapia mossambica. J. Fish. Res. Board Can. 34: 332-340. TESCH, F. W. 1968. Age and growth. In W. E. Ricker (editor), Methods for assessment of fish production in fresh waters, 2d ed., p. 93-123. IBP (Int. Biol. Programme) Handb. 3. Theilacker, G. H. 1980. Changes in body measurements of larval northern anchovy, Engraulis mordax, and other fishes due to handling and preservation. Fish. Bull., U.S. 78:685- 692. ZWEIFEL, J. R., AND R. LASKER. 1976. Prehatch and posthatch growth of fishes — a general model. Fish. Bull., U.S. 74:609-621. 104 PHENOTYPIC DIFFERENCES AMONG STOCKS OF HATCHERY AND WILD COHO SALMON, ONCORHYNCHUS KISUTCH, IN OREGON, WASHINGTON, AND CALIFORNIA1 R. C. Hjort and C. B. Schreck ABSTRACT Similarities in phenotypic characters (isozyme gene frequencies, life history, and morphology) among 35 stocks of coho salmon, Oncorhynchus kisutch, from Oregon, Washington, and California were compared by using agglomerative and divisive cluster analyses. Coho salmon stocks from similar environments were phenotypically similar. Five groups of stocks were identified by the agglomerative cluster analysis: 1) wild stocks from the northern Oregon coast, 2) wild stocks from the southern Oregon coast, 3) stocks from hatcheries that used wild coho salmon for an egg and sperm source, 4) stocks from large stream systems, and 5) hatchery stocks from the northern Oregon coast. Three trends were indicated by the clustering patterns: 1) stocks that were geographically close tended to be phenotypically similar, 2) stocks from large stream systems were more similar to each other than to stocks from smaller stream systems, independent of geographic proximity, and 3) hatchery stocks were more similar to each other than to wild stocks, and wild stocks were more similar to each other than to hatchery stocks. These trends may be useful to fishery managers for selecting donor stocks from hatcheries for transplanting to stream systems or transferring to other hatcheries. Individual phenotypic characters were correlated with characters of the stream sys- tems. Results of two agglomerative cluster analyses, one of certai n characters of the stocks and one of certain characters of the stream systems, demonstrated a lack of correspondence between stream types and stock phenotypes. Genetic diversity among stocks of anadromous salmonids (Simon and Larkin 1970) is a biologi- cal characteristic that is more frequently dis- cussed than used in fishery management. The tendency to return to native streams reduces gene flow among salmon populations and en- ables the individual stocks to adapt to the native stream systems. The mixing of stocks highly adapted to their native stream systems with other stocks, or transplanting them to other stream systems, may reduce the rate of return or survival rate of the donor stock (Ritter 19753; Bams 1976). If the survival rate of a salmon stock is related to its degree of adaptation to its stream system, fishery managers may be able to in- crease survival of hatchery fish by planting them in recipient streams having native stocks geneti- 'Oregon State University Agricultural Experiment Station Technical Paper Number 5477. Oregon Cooperative Fishery Research Unit, Oregon State University, Corvallis, OR 97331. Cooperators are Oregon State University, Oregon Department of Fish and Wildlife, and U.S. Fish and Wildlife Service. 'Ritter, J. A. 1975. Lower ocean survival ratio for hatch- ery reared Atlantic salmon (Salmo salar) stocks released in rivers other than their native streams. Int. Counc. Explor. Sea, Anadromous and Catadromous Fish Comm., C. M. 1975/ M 26, 10 p. cally similar to the planted fish. Higher survival should be especially important during the first several generations, while the transplanted stock is adapting to the recipient environment. An additional advantage of using genetically similar stocks might be a reduction in the intro- gression of divergent hatchery genotypes into wild stocks (Reisenbichler and Mclntyre 1977). Genetic descriptions of salmon stocks could benefit salmon management by assisting fishery managers in selecting hatchery stocks and in protecting wild stocks. Obviously, determination of genetic similarity among stocks is not now pos- sible for the entire genome; however, similarity can be estimated by comparing genetically re- lated characters. Two biochemical characters that vary among stocks of coho salmon, Oncor- hynehus kisutch, are transferrin (Utter et al. 1970) and phosphoglucose isomerase (PGI) (May 1975), the electrophoretic expressions both of which were established by breeding studies to be genetically determined. Life history and mor- phological characters also vary among salmonid stocks. Time of spawning (Roley 1973) and fre- quency of occurrence of jacks in the population (Feldmann 1974) both have a genetic basis in Manuscript accepted August 1981. FISHERY BULLETIN: VOL. 80. NO. 1. 1982. 105 FISHERY BULLETIN: VOL. 80. NO. 1 coho salmon but probably have an environmen- tal component as well. A genetic basis, as shown in rainbow trout, Salmo gairdneri, has also been established for numbers of vertebrae (Winter et al. 1980a), scales in the lateral series (Winter et al. 1980a), scale rows (Neave 1944), gill rakers (Smith 1969), branchiostegals (MacGregor and MacCrimmon 1977), and anal fin rays (Mac- Gregor and MacCrimmon 1977). Ricker (1970) hypothesized that the meristic characters of salmonids probably have both genetic and en- vironmental components. The difficulty of deter- mining the importance of these phenotypic characters to the fitness of the stock does not pre- clude the possibility that they could, through selection or pleiotrophic effects, have a bearing on fitness as suggested by Barlow (1961). The objective of this study was to characterize stocks of coho salmon by using enzyme gene fre- quencies, life history characters, and morpho- logical characters. Secondarily, we hoped this in- formation would help provide a basis for select- ing donor stocks in Oregon hatchery programs. The stocks were selected so that comparisons could be made among geographical areas and stream types and between hatchery and wild stocks. We calculated a measure of a phenotypic similarity and used cluster analysis to display the relationships among stocks. Because cluster analyses are arbitrary (Blackith and Reyment 1971), we used two clustering strategies. Factors affecting genetic similarity were hypothesized by determining environmental characteristics common to the similar stocks. Although our analysis is primarily systematic, we correlated the phenotypic characters with variables characteristic of the stream systems. Although correlations do not prove a functional significance, they are included here because in- ferences and hypotheses can be developed from the correlations for future studies. METHODS Sampling We evaluated 10 characters for 15 hatchery stocks (based on samples of 75-100 juvenile coho salmon of the 1976 brood from 14 hatcheries in Washington, Oregon, and California and 9 hatcheries from Oregon for the 1977 brood year) and 12 wild stocks (based on samples of 30-100 juvenile coho salmon of the 1976 and 1977 broods, collected by electrofishing from 12 Oregon stream systems). (See Figure 1 for locations of hatcheries and stream systems.) Because some of the hatcheries have used nonnative egg sources, and stream systems have been stocked with juvenile and adult coho salmon, few pure native stocks remain. We did not use hatchery stocks or • HATCHERY • WILD 1 N TEN MADR CALIFORNIA Figure 1.— Map indicating sample site locations of wild and hatchery coho salmon stocks. Location codes are as follows with the hatcheries in parentheses: ALSE. Alsea River (Fall Creek Hatchery); BEAV, Beaver Creek; BIGC, BigCreek(BigCreek Hatchery); COLM. Columbia River (Cascade Hatchery in 1976 and Bonneville Hatchery in 1977); COQL, Coquille River; COWL, Cowlitz River (hatchery stock reared at Cascade Hatchery in 1976 and Big Creek Hatchery in 1977); KLAM, Klamath River (Irongate Hatchery); MADR, Mad River (Mad River Hatchery); NEHA, Nehalem River; NEST, Nestucca River; NONE, North Nehalem River (North Nehalem River Hatchery); QUIL, Quilcene River (Quilcene River Hatchery); QUIN, Quinault River Hatchery); ROGU, Rogue River (Cole Rivers Hatchery); SALM, Salmon River Hatchery); SAND, Sandy River (Sandy River Hatchery); SILZ, Siletz River; TENM, Tenmile Lakes; TRAS, Trask River (Trask River Hatchery); TRIN, Trinity River (Trinity River Hatchery); UMPQ, Umpqua River (hatchery stock collected from Smith River and reared at Cole Rivers Hatchery). 106 IIJORT and SCHRECK: PHRNOTYI'IC DIFFFRFNC'KS AMONC COHO SALMON fish from tributaries of streams that had re- ceived a large supplement of a normative hatch- ery stock in the previous 6yr. This was to ensure that characterization of the genotype would re- flect environmental considerations rather than introgression of foreign stocks. Morphological Characters For each sample, 15 carcasses were frozen for later counts. Scales in the lateral series were counted in the second row above the lateral line, starting with the anteriormost scale and ter- minating at the hypural plate. Scales above the lateral line were counted from the anterior in- sertion of the dorsal fin to the lateral line. Anal ray counts did not include the short rudimentary anterior rays, and branched rays were counted as one. The total number of gill rakers on the first gill arch was recorded. Alizarin red was used to highlight rudimentary gill rakers. The total number of branchiostegal rays from both sides was counted. Vertebral counts, made on X-ray plates, included the last three upturned centra. Accuracy of morphological counts was checked by recounting two fish from each sample. If errors were found, additional fish from that sample were recounted to correct for any error. Electrophoresis Blood and white muscle samples were col- lected from the fish that were not used for morphological counts. The caudal peduncle was severed and the blood collected in heparin- ized microhematocrit tubes that were then cen- trifuged and stored at — 10°C. White muscle samples (1 cm3) were removed from the anterior dorsal portion of the frozen carcasses, homo- genized with 2 or 3 drops of water, and then cen- trifuged to clear the supernatant. Only the blood serum and supernatant were used for elec- trophoresis. The methodology for electrophoresis of trans- ferrin and phosphoglucose isomerase followed the basic principles of May (1975) with some modifications by Solazzi.4 The gel and elctrode buffers were described by Ridgway et al. (1970). Four genotypes of transferrin (AA, AC, CC, and BC) in the serum samples were interpreted ac- 4Solazzi, M. F. 1977. Methods manual for the electro- phoretic analysis of steelhead trout (Salmo gairdneri). Oreg. Dep. Fish Wildl., Res. Sect., Inf. Rep. Ser. Fish. 77-7, 35 p. cording to Utter et al. (1970). Transferrin was recorded as the frequency of the "A" allele, since the "B" allele was relatively rare. The variant allele for the second locus of phosphoglucose isomerase, first observed in white muscle tissue by May (1975), was recorded as the frequency of this variant allele. Life History The life history characters we used were time of peak spawning and proportion of females in the adult population. We estimated the peak spawning times on the basis of interviews with district fishery biologists and hatchery man- agers. Whenever possible, we verified the esti- mates with spawning ground survey records and hatchery records. We stratified the peak spawn- ing times into five segments of 2 wk each. The proportions of adult females (3 yr olds) were estimated from hatchery records and spawning ground surveys. This character is an indirect measure of the proportion of jacks (males that mature at 2 yr of age) in the popula- tion. Populations with high proportions of jacks in a given year should have relatively higher pro- portions of females returning the next year. A direct measure of the proportion of jacks cannot be used because body size differences between jacks and 3-yr-old adults affect the catch in gill net fisheries, retention in hatchery holding ponds, recovery of carcasses on spawning ground surveys, and catch rate in sport fisheries. Environmental Data Stream characteristics include distance up- stream to spawning grounds, basin area, area and length of the estuary on the stream system, latitude, gradient, spring runoff, the presence or absence of the myxosporidan parasite, Cerata- myxa shasta, and the presence or absence of the following nine species of fish: carp, Cyprinus carpio; Oregon chub, Hybopsis crameri; north- ern squawfish, Ptycholcheilus oregonensis; speckled dace, Rhinichthys osculus; redside shiner, Richardsonius balteatus; largescale sucker, Catostomus macrocheilus; brown bull- head, Ictalurus nebulosus; largemouth bass, Micropterus salmoides; and striped bass, Morone saxatilis. To separate the populations that have short and potentially long swimming distances to the spawning grounds, we measured spawn- ing distances from the mouth of the stream sys- 107 FISHERY BULLETIN: VOL. 80. NO. 1 tem to the upper limit of coho salmon spawning, as estimated from Anadromous Fish Distribu- tion Maps5 and interviews with district fishery biologists. Inasmuch as, intuitively, latitude should be correlated with the temperature and flow regimes of the stream systems, we deter- mined the latitude at the mouth of each stream system. Gradients were calculated from tide- water to the upper limit of coho spawning as a basis for estimating the difficulty of the spawn- ing migration. Because estuary size and length is an estimate of exposure to vibriosis (Harrel et al. 1976) and potential richness of feeding grounds (Myers 1979), we measured the estuary lengths, stream elevations, and distances on United States Geographical Survey Quadrangle Maps. Inasmuch as high flows could have an effect on both the early life history and the smolting proc- esses of juvenile coho salmon, we determined the presence of a spring runoff from snowmelt by interviewing district biologists. We obtained in- formation on the distributions of other fish species in Oregon stream systems from C. E. Bond,6 and on the distribution of Ceratamyxa shasta from J. E. Sanders.7 We obtained temperature data from hatchery records to help interpret the morphological data for the hatchery stocks. The average tempera- ture for the first month of incubation was used, because previous studies have indicated that this time is a period during ontogeny when morpho- logical features may be most sensitive to the effects of temperature (Taning 1952). Statistics We calculated averages for the morpho- logical characters, enzyme gene frequencies, and the proportion of females for each stock, and used multivariate analysis of variance and Rao's (1970) test for additional information to deter- mine whether morphological characters differed significantly among stocks. In Rao's test, the statistical significance of each morphological character is determined, given that the other morphological characters are already in the model. Because environmental data on spawn- 5Anadromous Fish Distribution Maps. Oregon State Water Resources Board, Salem, Oreg. ^arl E. Bond, Professor of Fisheries, Oregon State Univer- sity, Corvallis. OR 97331, pers. commun. April 1979. 7James E. Sanders, Assistant Fish Pathologist, Oregon Dep. Fish Wildl., Corvallis, OR 97331, pers. commun. February 1979. ing distance, estuary length, estuary size, basin area, and gradient were skewed, we transformed them to natural logarithms to stabilize the vari- ance and improve normality. We standardized the stock characters (z = 0, S2 = 1) for the cluster analyses, using the standard normal standardization. This standardization expresses the stock character as standard deviations from the character means, thus giving equal weight to each character. We calculated correlation coeffients (Snedecor and Cochran 1967) between the stock characters and the environmental data for all stocks, and between the morphological characters and tem- perature data for hatchery stocks only. The levels of significance for the correlation coefficients were also calculated as described by Snedecor and Cochran (1967). We used two cluster analysis programs to dis- play similarities among stocks. One, a nonhier- archical divisive cluster analysis, minimized the total sum of squares between observations and the cluster means (Mclntire 1973). In the other, a hierarchical agglomerative cluster analysis, Euclidean distance was used as the dissimilar- ity measure, and the clustering strategy was group average (see Sneath and Sokal [1973] or Clifford and Stephenson [1975] for terminology). Standardized data were used in both programs. We used canonical variate analysis to investi- gate the relation among the clusters from the agglomerative cluster analysis (Clifford and Stephenson 1975). Canonical variate analysis produces canonical variables that project groups of multivariate data onto axes separating the groups as much as possible. We plotted the ca- nonical variables against each other in two- dimensional space to determine the relationships among clusters and the discreteness of the clusters. RESULTS AND DISCUSSION Morphological Characters Significant differences (a = 0.01) for each morphological character (Tables 1-3) as indi- cated by multivariate analysis of variance and Rao's test of additional information existed among the 35 samples which consisted of wild and hatchery stocks from two brood years. When morphological characters for each stock between brood years were compared for each of the hatch- eries that were sampled in both years of the study 108 HJORTand SCHRECK: PHENOTYPIC DIFFERENCES AMONG COHO SALMON TABLE 1.— Means, standard errors (in parentheses), and ranges for the morphological characters of the 1976 brood year hatchery samples of juvenile coho salmon and the hatchery water incubation temperatures for the first month of incubation. Sample sizes were 15. The data are listed in north to south order of the sampling locations. Stock and (in parentheses) incubation water tempera- tures (°C) Scales in lateral series Scales above lateral line Anal rays Gill rakers Branchi- ostegals Vertebrae Washington Quilcene River Hatchery (7.3) 126 93 (97) 116-132 28.13 (38) 25-30 14.07 (15) 13-15 2233 (.19) 21-23 27 87 (26) 26-30 64 40 (13) 64-65 Quinault River Hatchery (7 3) 13267 (48) 130-136 2993 (.33) 28-32 1353 (16) 13-15 22 53 (.24) 21-24 2667 (.21) 25-28 6550 (.13) 65-66 Oregon: Cascade Hatchery (6.9) (Columbia River) 13307 (.56) 128-135 28 20 (40) 26-32 1400 (.20) 12-15 22.20 (.35) 20-25 27.27 (37) 25-29 6680 (.22) 66-68 Big Creek Hatchery (6.4) (Columbia River) 132 67 (.57) 128-136 2880 (.28) 28-31 14.31 (.13) 13-15 2287 (17) 22-24 2607 (30) 24-28 65 80 (15) 65-67 Cowlitz Hatchery stock. Cascade Hatchery (6.9) 133 60 (.63) 131-137 27 87 (.24) 26-29 1380 (.14) 13-15 22.20 (.26) 21-24 28 13 (.24) 27-30 6447 (22) 65-68 Sandy River Hatchery (7.0) (Columbia River) 133.13 (72) 128-137 2827 (.42) 24-30 14.33 (13) 14-15 22.07 (.34) 20-25 28 20 (26) 26-30 6607 (21) 65-67 North Nehalem River Hatchery (7.8) 131 93 (64) 128-138 28 33 (30) 26-36 1400 (14) 13-15 2267 (.27) 21-24 2673 (32) 24-28 65 80 (.17) 65-67 Trask River Hatchery (9 8) 132 13 (48) 128-135 2880 (47) 26-32 13.93 (12) 13-15 22 13 (31) 20-24 26 40 (.32) 24-29 6607 (.18) 65-67 Salmon River Hatchery (6.2) 129 40 (54) 125-132 27 00 (.59) 23-33 13 60 (.19) 13-15 22 13 (.24) 21-24 2540 (.24) 24-27 64 93 (30) 62-66 Fall Creek Hatchery (5 7) (Alsea River) 132 00 (.50) 129-135 2867 (.29) 27-31 1400 (.17) 13-15 23 20 (.20) 22-25 27.13 (34) 25-29 65 80 ( 17) 65-67 Umpqua Hatchery stock (Smith River), Cole Rivers Hatchery (3 5) 131 20 (51) 127-134 26 00 (.34) 24-28 13.47 (.19) 13-15 22 13 (.22) 21-23 25 13 (24) 24-26 65 33 (.23) 64-67 California: Irongate Hatchery (5.3) (Klamath River) 13273 (78) 129-138 2907 (18) 28-30 1380 (.14) 13-15 2233 (25) 21-24 27 00 (28) 25-28 6607 (30) 64-68 Trinity River Hatchery (7.3) (Klamath River) 130 87 (.75) 126-137 2827 (.64) 24-33 1360 (.13) 13-14 22 00 (.31) 19-23 26.00 (59) 20-28 66 00 (.14) 65-67 Mad River Hatchery (8.5) 129.20 (.88) 121-134 25.27 (.37) 22-27 13.40 (19) 12-15 2093 (.33) 19-23 23.47 (.51) 20-27 65.60 (.31) 63-68 (Table 4), the agreement between brood years was not particularly high, especially for scale rows and branchiostegal ray counts. Although meristic counts and water temper- atures during the incubation period of the eggs are usually correlated (Barlow 1961), we found that lateral series scale counts provided the only meristic character significantly (a = 0.05) cor- related with the temperature of the hatchery water during incubation. Under the extant en- vironmental conditions, incubation tempera- tures may have little effect in determining the morphological characters of our stocks. Among all possible statistically significant correlations between morphological characters and the stream characteristics in Table 5, only vertebral number and estuary length, and verte- bral number and spawning distance, had corre- lation coefficients >r = 0.50 (Table 6). All other correlations each accounted for <25% of the variation observed. Possibly we overlooked some important environmental gradients, or possibly the selective forces occur during peri- odic environmental extremes or pulses that were not accounted for in our environmental data. Each of the counts significantly correlated with at least two of the characters of the stream sys- tems, suggesting that, if these characters are the 109 FISHERY BULLETIN: VOL. 80, NO. 1 Table 2.— Means, standard errors (in parentheses), and ranges for morphological characters of the 1977 brood year hatchery samples of juvenile coho salmon and the hatchery water incubation temperatures for the first month of incubation. Sample sizes were 15. The data are listed in north to south order of the sampling location. Stock and (In parentheses) Incubation water tempera- tures (°C) Scales in lateral series Scales above lateral line Anal rays Gill rakers Branchi- ostegals Vertebrae Bonneville Hatchery (5.4) (Columbia River) 133 33 (.61) 129-138 2673 (.27) 25-29 1393 (.12) 13-15 22 53 (29) 21-25 27 00 (-32) 25-29 65 80 ( 15) 65-67 Big Creek Hatchery (7.2) 133 60 (46) 130-136 27.20 (.33) 26-30 13.53 (.13) 13-14 23 13 (.22) 22-25 25 60 (24) 23-27 6607 (.21) 65-67 Cowlitz Hatchery stock (7 2) (Big Creek Hatchery) 132 20 (.40) 129-135 26 60 (.41) 25-30 13.60 ( 13) 13-14 21.80 (.22) 20-23 2600 (.34) 24-28 65 67 (.16) 65-67 North Nehalem Hatchery (7.7) 130.93 (.42) 128-134 27.73 (25) 26-29 13.73 (.15) 13-15 23.07 (.27) 21-24 26.13 (.29) 24-28 6527 (.18) 64-66 Trask River Hatchery (9 9) 130.33 (.42) 128-133 25.53 (.32) 23-27 13.67 (.13) 13-14 2273 (.23) 21-24 25 60 (.32) 24-28 65.40 (24) 63-66 Salmon River Hatchery (7 8) 130.53 (.59) 127-135 26 80 (28) 25-29 1367 (.16) 13-14 2240 (.16) 22-24 2627 (.25) 25-29 65 53 (.19) 64-66 Fall Creek Hatchery (7.4) (Alsea River) 131.53 (-68) 127-136 2620 (.33) 24-28 1380 (.17) 13-15 22 53 (.27) 21-24 2607 (.23) 25-28 66.13 (19) 65-67 Umpqua Hatchery stock (8.6) (Smith River) Cole Rivers Hatchery 129 07 (.37) 126-131 26 40 (-32) 24-29 1340 (.13) 13-14 21.47 (.17) 21-23 2587 (.24) 24-28 65 40 (.13) 65-66 Cole Rivers Hatchery (8 6) (Rogue River) 130 33 (.66) 125-134 26 20 (.33) 24-28 13 80 ( 17) 13-15 22.20 (.30) 20-24 26 20 (.24) 25-28 65 20 (26) 64-67 result of selection, several interacting selective forces were involved. Life History Characters Earlier peak spawning times (Table 7) were strongly associated with the northern stream systems and with stream systems having large estuaries (Table 6). However, the correlation of peak spawning time with size of estuary may be biased by the large number of samples from Columbia River hatcheries: spawning times of stocks from the Columbia River are earlier than those of coastal stocks, and the Columbia River has a large estuary. Selection for earlier spawn- ing times through hatchery practices may be the cause for the differences in spawning times be- tween hatchery and wild stocks in the North Nehalem, Trask, and Alsea Rivers. Selection for earlier spawning times has been observed in a steelhead trout hatchery program (Millenbach 1973). At hatcheries using wild stocks as sources for eggs and sperm, peak spawning times were similar to those of naturally spawning fish in the respective stream system. The proportion of females (Table 7) ap- peared to be higher in the southern stream sys- tems, suggesting that jacks were more common there. The effective sex ratio, including jacks, at the time of spawning should be close to 1:1 (Fisher 1930). If only 3-yr-old males and females are counted, the proportion of females should be X).50, the margin above 0.50 depending on how many jacks returned in the previous year. How- ever, the proportion of males was higher than that of females in stocks from the Quilcene, Quinault, Sandy, North Nehalem, Nehalem, Trask, Salmon, Alsea, Umpqua, and Rogue Rivers. Nikolskii (1969) reviewed several pos- sible causes for sex ratios departing from 1:1; however, the reason for the high proportion of males in these stocks is not known. Isozyme Gene Frequencies Transferrin gene frequencies (Figs. 2, 3), cor- related significantly with six of the stream characters (Table 6). The best model from step- wise multiple regression explained only 68% of the variation in gene frequencies. Analysis of the relationships of the "A" allele frequencies with basin area (Fig. 4) and latitude (Fig. 5) explained the variation more simply than did the stepwise regression model. These correlations showed 110 HJORTand SCHRECK: PHENOTYPIC DIFFERENCES AMONG COIK) SALMON Table 8.— Means, standard errors (in parentheses), and ranges of morphological char- acters for 1977 brood year samples of wild juvenile eoho salmon. Sample size was 12 for all stream systems except Tenmile Lakes and Coquille River (15 each). The data are listed in north to south order of the sampling locations. Stream system North Nehalem River Nehalem River Trask River Nestucca River Salmon River Siletz River Beaver Creek Alsea River Umpqua River Tenmile Lakes Coquille River Rogue River Scales in lateral series Scale rows above lateral core Anal fin rays Gill rakers Branchi- ostegals Verte- brae 13225 27.75 13 58 23 25 26 75 65 50 (.88) (33) ( 15) (37) (.25) (.26) 126-137 26-30 13-14 22-25 26-28 63-66 132.50 2667 1375 2300 27 33 6575 (.77) (35) (.13) (25) (.22) (25) 127-136 25-29 13-14 22-24 26-28 64-67 131 17 26 50 1400 2292 2658 65 83 (.47) (.31) ( 12) (31) (26) ( 11) 128-133 24-28 13-15 21-24 25-28 65-66 132 17 26-83 14.00 2292 27.25 65.58 (68) (.40) (12) (34) (.28) (.19) 128-136 25-29 13-15 21-25 26-29 65-67 131.83 26 92 1367 23 08 2667 65 00 (61) (31) (.14) (.29) (19) (.17) 128-135 24-28 13-14 22-25 26-28 64-66 130.33 27 08 1358 23 00 27.50 65.25 (61) (.29) (.15) (21) (.23) (28) 128-135 26-29 13-14 22-24 26-29 63-67 132.27 27 33 13 27 2327 27 18 65 33 (.49) (38) (.20) (36) (.30) ( 14) 130-135 25-29 12 14 21-25 26-29 65-66 131 25 27 17 1367 23 17 26 83 6525 (37) (30) (.19) (34) (.30) (-18) 129-134 26-29 12-14 21-25 26-28 64-66 131 75 2683 13 25 22 92 27 00 65.83 (.70) (40) (13) (19) (28) (.27) 128-136 25-30 13-14 22-24 26-29 65-68 131.73 26 20 13.47 22.53 2660 65.73 (.58) (28) ( 13) ( 19) (31) (.25) 128-136 25-29 13-14 21-24 25-28 64-67 131 67 26 27 13.27 2240 26.47 65.93 (.43) (-43) (18) ( 19) (.27) (21) 129-134 24-30 13-14 21-24 24-28 65-67 132.75 2658 1400 2250 2692 6542 (59) (26) ( 17) (31) (40) (15) 131-137 25-28 13-15 21-25 24-29 65-66 Table 4.— Hatchery stocks of coho salmon in which dif- ferences in morphological characters occurred between the 1976 and 1977 brood years as determined by a two-sample test. Scales Lateral above Branchi- series lateral Anal Gill ostegal Verte- Hatchery scales line rays rakers rays brae Cascade-Bonneville Cowlitz stock Big Creek Trask River Salmon River Alsea River Umpqua River *P<0.05; "P<0 01 that the stocks from large stream systems and the southernmost stream systems had high fre- quencies of the "A" allele, whereas the fre- quencies in the smaller stream systems and northern stream systems were highly variable. Combining these two relationships helps explain the pattern of transferrin gene frequencies. Fre- quencies of the "A" allele were high in stocks from large stream systems regardless of lati- tude, and in southern stocks regardless of stream size. Stocks from smaller stream systems on the northern Oregon coast and in Washington had higher frequencies of the "C" allele. The factors affecting the patterns of trans- ferrin gene frequencies in coho salmon stocks are not known. However, Utter et al. (1980) sug- gested that the frequencies may be influenced by bacteriostatic properties associated with the dif- ferent transferrin alleles. Genotypes of trans- ferrin had differential mortality when exposed to bacterial kidney disease in studies by Suzumoto et al. (1977) and Winter et al. (1980b), and to vibriosis, cold-water disease, and furun- culosis in a study by Pratschner (1978). Trans- ferrin genotype was also related both to differ- ences in juvenile growth rates and to propensity to return as jacks (Mclntyre and Johnson 1977). Ill FISHERY BULLETIN: VOL. 80, NO. 1 100L 80 UJ _l y 60 _i < 40 UJ S 20 or UJ Q. "-66|}62 H o-|976 — 1977 57 69 66 63 ,. 68 68 51 65 68 I I I 1 _75 63 62 ii •65 63 Figure 2. — Transferrin gene fre- quencies of hatchery coho salmon. Samples are arranged from north to south. Vertical lines represent 95% confidence intervals; numbers above the line show sample sizes. Location codes are as in Figure 1. * ~ w> WASH COLUMBIA OREGON CALIF Table 5.— Environmental data for the stream systems sampled in this study. Spawning Estuary Estuary Gradi- Runoff Basin distance Lati- area length ent in area Stream system (km) tude (ha) (km) (m/km) spring (km2) Washington Quilcene River 13 47.75 '512 32 192 yes 2179 Quinault River 92 47 33 '64 32 2.8 yes 21,123 Oregon Columbia River Cascade- Bonneville Hatcheries 235 4625 '37,513 2365 0 yes 351,769 Cowlitz Hatchery stock 193 4625 '37,513 1094 08 yes 26.418 Big Creek Hatchery 60 46.25 '37.513 43 4 142 no 288 Sandy River Hatchery 270 4625 '37,513 1947 7.1 yes 21.299 North Nehalem River 45 4625 "1,128 11.3 86 no '233 Nehalem River 195 4568 "1,128 24.1 24 no 22.192 Trask River 72 4552 "3,480 209 9.5 no 5455 Nestucca River 76 45 16 "400 12.9 7.7 no 2657 Salmon River 29 4505 "82 64 130 no 6194 Siletz River 122 44 93 "475 37.0 34 no 2797 Beaver Creek 21 44.52 '3 3.2 4 3 no '31 Alsea River 93 44.43 "858 193 32 no 61,227 Umpqua River 372 43.68 "2,285 45.0 1.9 yes 61 1,801 Smith River7 122 4368 "2,285 24 1 2.5 no 2898 Tenmile Lakes 24 43.57 '1 1.6 3.2 no 5254 Coquille River 138 43.11 "308 660 34 no 62,738 Rogue River 249 42.44 "251 64 1.9 yes 613,199 California Klamath River 293 41.58 '200 3.2 2 2 yes 831.314 Trinity River 235 41 58 '200 3.2 24 yes 87.383 Mad River 72 40 95 '200 64 6.5 no 81.255 'Provided by district biologists. 2Pacific Northwest River Basins Commission 1966. 1967. 1968, 1969, 1972 River Mile Indices Hydrol Hydraul Comm. Personal estimate of area utilized by coho in the Columbia drainage "Gaumer. T . D Demory, and L Osis 1973 Estuary resources use study Fish Comm Oreg , Div Manage Res 5Water Resources Board of Oregon 1969 Oregon long range requirements for water Salem, Oreg . 397 p Svilsey and Ham Incorp 1974 Estuarme resources of the Oregon coast A natural resource inventory report to the Oregon Coastal Conservation and Development Commission, Portland. Oreg . 233 p 'Source of Umpqua Hatchery stock "United States Geological Survey 1977 Water resources data for California water year 1977 Water Data Rep CA 77-2. Therefore, diseases, life history characteristics, and other factors may play a role in maintaining the patterns of transferrin gene frequencies. Transferrin gene frequencies were in good agreement between the two year classes of Ore- gon coast wild stocks, despite the small size of some of the samples (Fig. 3). The heterogeneity between year classes was greater for the Oregon 112 H.IORT and SCHRKCK: PHKNOTYPIC DIFFKRKNCKS AMONC (OHO SALMON FIGURE 3.— Transferrin gene frequencies of wild coho salmon stocks for 1976 and 1977 brood years. Stocks are arranged from north to south. Bars represent 95% con- fidence intervals and the sample sizes are above the bars. Location codes are as in Figure 1. 23 54 50 28 UJ Ld < UJ c_> or UJ 0- uu- o-l976 . -1977 IP 50 T < < 80- 17 60- 40- 52 to 73 58 32 i 63 > i i >4 58 109 J642| i 49 f 1 20- o i 87 T 86 I J ■*■ ii i -1- n- K60 1 69 i 1 1 1 1— i i »" m s Table 6.— Statistically significant correlation coefficients between the characteristics of the coho salmon stocks and the environmental characteristics of their respective stream systems, r = 0.28 at a = 0.05 and 0.37 at a = 0.01. Characteristics Stock Environmental Correlation Scales in lateral series Spawning distance 0418 Estuary size 0.341 Estuary length 0430 Gradient -0 368 Scale rows Latitude 0360 Spring runoff 0-315 Anal rays Estuary size 0.414 Latitude 0382 Gill rakers Latitude 0346 Basin area -0353 Spring runoff -0319 Branchiostegals Latitude 0431 Spring runoff 0 381 Vertebrae Estuary size 0350 Basin area 0.445 Gradient -0.432 Spawning distance 0 549 Estuary length 0533 Proportion of females Latitude -0426 Time of peak spawning Estuary size -0613 Spring runoff -0.345 Estuary length -0391 Latitude -0702 Phosphoglucose isomerase Spring runoff -0410 Transferrin Estuary length 0326 Latitude -0381 Spawning distance 0.590 Basin area 0588 Spring runoff 0528 Gradient -0 596 coast hatchery stocks (Fig. 2). The gene fre- quencies of hatchery stocks may have been altered by earlier importing of stocks with dif- ferent gene frequencies, or by disease epizootics. If fish with certain transferrin genotypes have different resistances to diseases, and if epizootics are more severe because of the higher densities of ttOr ar>- 60-- < ;< 40- • g *H" 10 BASIN AREA (Ln SO. Ml.) Figure 4.— Transferrin gene frequencies for wild and hatchery coho salmon stocks arranged by basin area, in ln square miles. fish in hatcheries, then the transferrin gene fre- quency of a given year class could be altered without affecting the other two year classes. The phosphoglucose isomerase variant (Table 7) was present only in samples from Oregon stocks — particularly those from the northern Oregon coast. May ( 1975) reported this variant in Washington stocks. Similarity of Stocks The groups of stocks of coho salmon found to be most similar by the agglomerative cluster analysis (Fig. 6) were composed of northern 113 FISHERY BULLETIN: VOL. 80. NO. 1 o £ ■*-» ■*-> c <— at o t- L. :« V > ~ CD 13 In o c t. +j CD - - o o — o o 3 c bl c o ■ *N jr ~ _ -4-» ~ en J=. 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CO CO CO CD > 5 o a? at- ro Pro tioi fem o o1 it CD to r C CD S .E O- CO 1- °- CO CO CO CD >- ' ^-'co 0o« a. r <0 Pro tioi fem E CD CO >~ CO E CO CD (/) I I I p o O O O O Tf • en lo en O O 1 r*-. ~- > > > o o o Z Z Z > O z a > u O (D Z O o Q u u o 03 - r^ 01 CD 05 ai co i- CD CD h- O) O) Ol ooooo odduuuudddud (DCVJCUQJCUaJCVCDQJQJCDCD QQQQQQQQQQQQ CDCOCDNCDCOCOCOnCO «^ a>c7iO)Looia>oiO)Tj- Oc^r* 0)0)t7)O)0)CJ)(J)0)0)tT) cocncococD^Tconromm-^ o ooooooooooo CO re 1 1 flag ■^ 3 3 en _ raO O £ O 5 O u 1 8 ? ^ « ^^ - 2 cd o ra rr CD CD > ra tr -c ^ CD CO "O N i- 1 OC > CD CD CD re CD rf lO ■CD 5 2 5rr - EH > S Se <" 5 s e £ zzhZwcomohO CT en O o B2 > I ro DC CD I CO .c ro >. CO c c (- o c ) CD i- ; e & ; ^ o O 114 H.IORT ami SCHKKCK: I'HKNOTYI'IC DIFFERENCES AMONG ('OHO SALMON WOr 80 20 43* 45* LATITUDE 'N 4T Figure 5.— Transferrin gene frequencies for wild and hatch- ery coho salmon stocks arranged by latitudes. STOCK Figure 6. — Dendrogram of the agglomerative cluster analysis for all stocks of wild and hatchery coho salmon of two brood years, 1976 and 1977. Euclidean distance was the dis- similarity measure and group average was the clustering strategy. Location codes are as in Figure 1. The other codes are as follows: H6, hatchery stock of the 1976 brood year; H7, hatchery stock of the 1977 brood year; and W7, wild stock from the 1977 brood year. Oregon coast wild stocks (cluster 1), southern Oregon coast wild stocks (cluster 2), stocks from hatcheries that used wild stocks for the egg source (cluster 3), stocks from large river sys- tems (cluster 4), hatchery stocks and two wild stocks from the northern Oregon coast (cluster 5), and three individual hatchery stocks from California and Washington (clusters 6-8). Canonical variate analysis on the five larger clusters produced three canonical variables that were significant (a = 0.05). When these three variables were plotted against each other, only clusters 1 and 5 (consisting of wild stocks and hatchery stocks, both from the northern Oregon coast) were not completely separate in three- dimensional space. The other three clusters were discrete, suggesting that intercluster differ- ences were stronger than between clusters 1 and 5. Statistical testing for differences between the clusters would not be valid because the necessary assumption of randomness of data is violated. The results of the canonical variate analy- sis must be interpreted with caution because the variation within each cluster was reduced by our using the averages of the morphological char- acters. This reduction of variation facilitates dis- crimination between clusters by canonical vari- ate analysis, so that quantitative comparisons of cluster discreteness cannot be made. Individual phenotypes undoubtedly overlap between stocks or between clusters; however, the multivariate analysis of variance did indicate that significant differences existed among the stocks for each of the morphological characters. We characterized the stocks by the average phenotypes in order to estimate the phenotypes typical for each stream system, and on that basis the results of the canon- ical variate analysis suggested that there were discrete differences between all clusters except 1 and 5. The results of the agglomerative and divisive cluster analyses were similar. At the 13-cluster level of the divisive analysis (Table 8), all but two clusters were identical with clusters from the agglomerative cluster analysis dendrogram. The results of these analyses should be inter- preted cautiously, because they are based on only 10 characteristics— a small number compared with the total number of genetically related characteristics possible. If other characteristics had been used, the results might have differed. Thus, we did not emphasize the exact order or the levels of dissimilarity at which any two clusters joined together; rather, we observed only general trends in the clustering patterns. Three general trends are apparent in the clustering patterns of the agglomerative cluster analysis dendrogram. First, the stocks from the larger stream systems (Columbia, Rogue, and Klamath Rivers) were more similar to each other than to the stocks from smaller streams. The only exceptions to this trend were wild stock from the Umpqua River and the Umpqua and Rogue hatchery stocks. The Umpqua wild stock was 115 FISHERY BULLETIN: VOL. 80, NO. 1 Table 8.— Coho salmon stocks at the 13 cluster level of the divisive cluster analysis. "Wild" denotes wild stocks. Cluster no Divisive cluster analysis stock Brood year 1 Cascade Hatchery 1976 Cowlitz Hatchery 1976 Sandy Hatchery 1976 2 Salmon River Hatchery 1976, 1977 Rogue River Hatchery 1977 Umpqua River Hatchery 1976, 1977 3 North Nehalem wild 1977 Nestucca River wild 1977 Salmon River wild 1977 Siletz River wild 1977 Beaver Creek wild 1977 Alsea River wild 1977 4 Quilcene Hatchery 1976 5 Nehalem River wild 1977 Trask River wild 1977 6 Mad River Hatchery 1976 7 North Nehalem Hatchery 1976, 1977 Trask Hatchery 1976 Alsea Hatchery 1976 8 Umpqua River wild 1977 Tenmile Lake wild 1977 Coquille River wild 1977 9 Trask Hatchery 1977 Alsea Hatchery 1977 10 Quinault Hatchery 1977 11 Bonneville Hatchery 1977 Cowlitz Hatchery 1977 Rogue wild stock 1977 12 Irongate Hatchery 1976 Trinity Hatchery 1976 13 Big Creek Hatchery 1976, 1977 associated with the other southern Oregon coast wild stocks, and the Rogue and Umpqua hatch- ery stocks were in the cluster with other hatch- eries that used wild stocks as egg sources. The second trend observed in the dendrogram was geographical clustering. Three stocks from Washington and California were dissimilar to the Oregon stocks, and the Oregon wild stocks clustered into two groups, northern and southern coastal stocks. The third trend in the dendrogram was for hatchery and wild stocks to cluster independent- ly. One of the clusters was composed entirely of wild stocks from the northern Oregon coast, and another included all but one of the northern Ore- gon coast hatchery stocks, in addition to two wild stocks from the northern Oregon coast. The hatchery stock excluded from this cluster (no. 5) was from the Salmon River, a stock developed from eggs of wild coho salmon; both brood years of this stock were in the cluster of hatcheries that used wild stocks as an egg source. The rest of the northern Oregon coast hatcheries used return- ing hatchery-reared adults for egg sources. The two wild stocks in this cluster were from the Trask and Nehalem Rivers. They are also simi- lar to the other wild stocks; however, because of the mechanics of the group-average clustering strategy, they both clustered first with the hatch- ery stocks. The average Euclidean distance be- tween the Nehalem wild stock and the other wild stocks was less than that between the Nehalem wild stock and the hatchery stocks of cluster 5. The close relationships of the stocks in clusters 1 and 5 were also apparent in the results of the canonical variate analysis, which showed these two clusters to be continuous. The three trends in the clustering pattern indi- cated that coho salmon stocks from similar en- vironments had similar phenotypes. These trends provide some guidance for the transfer of coho salmon stocks. Geographical clustering in- dicates that the phenotypic or perhaps genetic similarity between stocks probably decreases as the distance between stocks increases. Mc- Intyre8 showed a strong negative correlation for the distance between stream systems and the genetic similarity of the steelhead trout stocks in those stream systems. If a similar relation be- tween phenotype and distance exists among coho salmon stocks, survival rate would be expected to vary inversely with the distance that the stock is transferred from its native stream. The crucial question from the management standpoint, assuming the relationships we found are real, is how far stocks can be transferred before de- creasing survival rate and the increasing genetic impact on the native stocks reduce the practical- ity of such transfers. Although geographical distance can be an im- portant factor in selecting a donor stock, other considerations must also be taken into account. The difference between stocks from large and small stream systems illustrates a problem in basing stock transfers primarily on geograph- ical distance. Stocks from large stream systems were more similar to stocks in distant large systems than to stocks in small stream systems that were geographically close. Other environ- mental variables may also differ, affecting the phenotypes of geographically close stocks. Characteristics such as time of peak spawning or transferrin genotype may be closely related to flow and temperature regimes or to disease organisms present in the stream systems. These characteristics and others not included in this "Mclntyre. J. D. 1976. The report of interbreedingof arti- ficially propagated and native stocks of steelhead trout. Oreg. Dep. Fish Wildl., Res. Sect, Steelhead Annu. Rep., 22 p. 116 HJORT and SCHRECK: PHKNOTYIMC DIFFERENCES AMONG COHO SALMON study all should play a role in choosing stocks for transfer to other stream systems. The third trend mentioned (that of hatchery and wild stocks diverging toward different phenotypes) presents a problem to managers who must choose the best stock for transfer to other stream systems. The separate clustering of hatchery and wild stocks suggests that hatch- ery stocks have become dissimilar to wild stocks — even those that inhabit the same drain- age. Studies with steelhead trout indicated that hatchery fish survived better in hatchery ponds, whereas wild fish had higher survival in streams (Reisenbichler and Mclntyre 1977). The dis- similarity between hatchery and wild stocks may play a role in reducing the survival of hatchery-reared coho salmon when they are re- leased into a stream system. CONCLUSIONS Individual characters of the stocks examined by us showed a variety of responses to stream characters. Time of peak spawning was strongly correlated with latitude, whereas other charac- ters were significantly correlated with several environmental gradients, suggesting that interactions determining stock phenotypes are complex. The variability of the stock character may also change along environmental gradients, as demonstrated by the transferrin genotype (Figs. 4, 5). The results of the cluster analysis indicate that stocks that are geographically close are similar, that stocks from large stream systems are simi- lar to each other, that stocks from coastal stream systems are similar to each other, and that hatch- Similarity of Stream Systems and Wild Stocks Because coho salmon appear to have similar phenotypes in similar environments, one could possibly relate phenotypes of stocks with de- scriptions of their stream basins (Tables 5, 9). However, comparisons of an agglomerative cluster analysis of wild stocks (Fig. 7) with a cluster analysis of stream characters (Fig. 8) in- dicated that they were less similar than we had anticipated — although we expected some differ- ences because the stream characters were not necessarily related to taxonomic characters used in this study. Table 9.— Fish species and myxosporidan parasite. Cerata- myxa skasta, present in the Oregon stream systems. X = present. Stream systems CO o °>.c CD 0 CD 3 a W II u> — cr 3 5 o CO o a CO "> T3 a it* in CD m Q-ra T3 CO CD 33 on c/> CD 3 O Em oro TO X co co 2-c CO Nehalem River Trask River Nestucca River Salmon River Siletz River Beaver Creek Alsea River Smith River Umpqua River Tenmile Lake Coquille River Rogue River X X X X X X •I in 4.0 3.5 3.0. 2.5 z.o 1.5 1.0. .5 >- l- a. in HI 5.0. 4.5 4.0. 3.51 3.0 2.51 Z.O 1.5 1.0 .5 STOCK STREAM SYSTEM Figure 7.— Dendrogram of the agglomerative cluster analy- sis for wild coho salmon stocks with a Euclidean distance dissimilarity measure and group average clustering strategy. Location codes are as in Figure 1. Figure 8.— Dendrogram of the agglomerative cluster analy- sis for stream systems with a Euclidean distance measure and group average clustering strategy. Location codes are as in Figure 1. 117 FISHERY BULLETIN: VOL. 80. NO. 1 ery and wild stocks are dissimilar. In general, coho salmon stocks from similar environments appear to have similar phenotypes; however, groupings obtained from cluster analyses of coho salmon stocks and corresponding stream systems were dissimilar. This dissimilarity may be a result of our using only a small number of characters for analysis. As additional characters are considered, additional trends may become evident. The characters in this study, in concert with other characters, should be used in future evaluations of genetic similarities between stocks for an eventual characterization of stocks that will ensure effective transplantation. In addition to providing information which may be useful for selecting donor stocks for hatchery programs, the results of this study also suggest a potential weakness in hatchery supple- mentation. Selection through hatchery environ- ment and hatchery practices may be changing the overall phenotype of hatchery stocks, as well as the between-year variability of individual genotypes (as we found for transferrin). If these changes result in reduced performance of the donor stocks in other stream systems, practices designed to increase hatchery production must be weighed against the actual benefits to wild production. We believe that this study demonstrates a re- lationship between phenotypic characters and certain habitat types. The differences in pheno- type that are attributable to hatchery or wild origin, geographic proximity, and small or large stream systems may provide a first basis for judging the advisability of stock transfers. ACKNOWLEDGMENTS We express our appreciation to Carl Bond for his suggestions concerning the morphological characters, to Norbert Hartmann for his advice concerning the analysis of the data, to Fred Utter for taking the time to share his knowledge of electrophoresis, and to Al McGie for providing data on the proportion of females on spawning ground surveys. Funds for this project were pro- vided by the Oregon Department of Fish and Wildlife. LITERATURE CITED Bams, R. A. 1976. Survival and propensity for homing as affected by presence or absence of locally adapted paternal genes in two transplanted populations of pink salmon (Oncorhyn- chusgorbuscha). J. Fish. Res. Board Can. 33:2716-2725. Barlow, G. W. 1961. Causes and significance of morphological variation in fishes. Syst. Zool. 10:105-117. Blackith, R. E., and R. A. Reyment. 1971. Multivariate morphometries. Acad. Press, Lond., 412 p. Clifford, H. T., and W. Stephenson. 1975. An introduction to numerical classification. Acad. Press, N.Y.. 229 p. Feldmann, C. L. 1974. The effect of accelerated growth and early release on the timing, size and number of returns of coho salmon (Oncorhynchus kisutch). M.S. Thesis, Univ. Washing- ton, Seattle, 46 p. Fisher, R. A. 1930. The genetical theory of natural selection. Oxf. Univ. Press. (Clarendon), Lond., 272 p. Harrell, L. W., A. J. Novotny, M. H. Schiewe, and H. 0. Hodgins. 1976. Isolation and description of two vibrios pathogenic to Pacific salmon in Puget Sound, Washington. Fish. Bull, U.S. 74:447-449. MacGregor, R. B., and H. R. MacCrimmon. 1977. Evidence of genetic and environmental influences on meristic variation in the rainbow trout, Salmogaird- neri Richardson. Environ. Biol. Fishes 2:25-33. May, B. 1975. Electrophoretic variation in the genus Oncorhyn- chus: The methodology, genetic basis, and practical applications to fisheries research and management. M.S. Thesis, Univ. Washington, Seattle, 95 p. McIntire, C. D. 1973. Diatom associations in Yaquina Estuary, Oregon: a multivariate analysis. J. Phycol. 9:254-259. McIntyre, J. D., and A. K. Johnson. 1977. Relative yield of two transferrin phenotypes of coho salmon. Prog. Fish-Cult. 39:175-177. MlLLENBACH, C. 1973. Genetic selection of steelhead trout for manage- ment purposes. In M. W. Smith and W. M. Carter (edi- tors), International Atlantic salmon symposium, p. 253- 257. Int. Atl. Salmon Found., N.Y. Myers, K. W. 1979. Comparative analysis of stomach contents of cul- tured and wild juvenile salmonids in Yaquina Bay, Ore- gon. In S. J. Lipovsky and C. A. Simenstad (editors), Fish food habits and studies, Proceedings of the Second Pacific Northwest Technical Workshop, p. 155-162. Wash. Sea Grant Publ., Univ. Washington. Seattle. Neave, F. 1944. Racial characteristics and migratory habits in Salmo gairdneri. J. Fish. Res. Board Can. 6:245- 251. Nikolskii, G. V. 1969. Theory of fish population dynamics as the biologi- cal background for rational exploitation and manage- ment of fishery resources. Oliver and Boyd, Edinb., 323 p. Pratschner, G. A. 1978. The relative resistance of six transferrin pheno- types of coho salmon (Oncorhynchus kisutch) to cytopha- gosis, furunculosis, and vibriosis. M.S. Thesis, Univ. Washington, Seattle, 71 p. 118 HJORTaml SCHKKCK: I'HF.NOTVI'H' DIFFERENCES AMONO COHO SALMON Rao, C. R. 1970. Advanced statistical methods in biometric re- search. Hafner Publ. Co., Darien. Conn., 390 p. REISENBICHLER, R. R., AND J. D. MclNTYRE. 1977. Genetic differences in growth and survival of juve- nile hatchery and wild steelhead trout, Salmo gairdneri. J. Fish. Res. Board Can. 34:123-128. RlCKER, W. E. 1970. Hereditary and environmental factors affecting certain salmonid populations. In R. C. Simon and P. A. Larkin (editors), The stock concept of Pacific salmon, p. 19-160. H. R. MacMillan Lectures in Fisheries, Univ. British Columbia, Vancouver. Ridgway, G. J., S. W. Sherburne, and R. D. Lewis. 1970. Polymorphism in the esterases of Atlantic herring. Trans. Am. Fish. Soc. 99:147-151. ROLEY, D. D. 1973. An evaluation of the selective breeding of steelhead trout (Salmi) gairdneri gairdneri) and coho salmon (Oncorhynchus kisutch) at Eagle Creek National Fish Hatchery, Oregon. M.S. Thesis. Univ. Washington, Seattle. 198 p. Simon, R. C. and P. A. Larkin (editors). 1970. The stock concept of Pacific salmon. H. R. Mac- Millan Lectures in Fisheries, Univ. British Columbia. Vancouver. 231 p. Smith, S. B. 1969. Reproductive isolation in summer and winter races of steelhead trout. In T. G. Northcote (editor), Symposium on salmon and trout in streams, p. 21-38. H. R. MacMillan Lectures in Fisheries, Univ. British Columbia, Vancouver. Sneath, P. H. A., and R. R. SOKOL. 1973. Numerical taxonomy, the principles and practice of numerical classification. W. H. Freeman, San Franc, 573 p. Snedecor, G. W„ and W. G. Cochran. 1967. Statistical methods. 6th ed. Iowa State Univ. Press, Ames, 593 p. SlJZUMOTO, B. K., C. B. SCHRECK, AND J. D. MclNTYRE. 1977. Relative resistance of three transferrin genotypes of coho salmon (Oncorhynchus kisutch) and their hema- tological responses to bacterial kidney disease. J. Fish. Res. Board Can. 34:1-8. Taning, A. V. 1952. Experimental study of meristic characters in fishes. Biol. Rev. (Camb.) 27:169-193. Utter, F. M., W. E. Ames, and H. O. Hodgins. 1970. Transferrin polymorphism in coho salmon {Onco- rhynchus kisutch). J. Fish. Res. Board Can. 27:2371- 2373. Utter, F. M., D. Campton, S. Grant, G. Milner, J. Seeb, and L. Wishard. 1980. Population structures of indigenous salmonid spe- cies of the Pacific Northwest. In W.J. McNeil and D. C. Himsworth (editors), Salmonid ecosystems of the North Pacific, p. 285-304. Oreg. State Univ. Press, Corval- lis. Winter, G. W., C. B. Schreck, and J. D. McIntyre. 1980a. Meristic comparison of four stocks of steelhead trout (Salmo gairdneri). Copeia 1980:160-162. 1980b. Resistance of different stocks and transferrin genotypes of coho salmon, Oncorhynchus kisutch. and steelhead trout, Salmo gairdneri. to bacterial kidney disease and vibriosis. Fish. Bull., U. S. 77:795-802. 119 REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA1 Raymond E. Baglin, Jr.2 ABSTRACT Ovaries of bluefin tuna, Thunnus thynnus, were collected from the Gulf of Mexico, Florida Straits, Middle Atlantic Bight of the western North Atlantic, and off the northeast coast of the United States. There was relatively little development towards maturity in age 1 through age 7 fish from the Middle Atlantic Bight as evidenced by low gonosomatic index values and histological examination of ovaries. Well-developed ovaries were present in giant bluefin tuna from the Gulf of Mexico and Florida Straits, with heaviest spawning occurring in May. For bluefin tuna measuring 205-269 cm fork length and 156-324 kg round weight, the average number of eggs measuring 0.33 mm in diameter and larger was estimated at 60.3 million, and the average number of eggs measuring 0.47 mm in diameter and larger was estimated at 34.2 million. Atlantic bluefin tuna, Thunnus thynnus, are seasonally distributed over most of the North Atlantic. They are found from Newfoundland to Brazil and from Norway to the Canary Islands (Gibbs and Collette 1967). In the western Atlantic, a sport fishery for bluefin tuna exists off the east coast of the United States from Maine through North Carolina and along the western Bahamas and the eastern coast of Canada. Also, a substantial commercial bluefin tuna fishery exists in the western Atlantic. There is purse seining along the east coast of the United States from Massachusetts to North Carolina and a handline and harpoon fishery off Massachusetts and Maine. A sub- stantial Japanese longline fishery is present off the east coast of the United States and in the Gulf of Mexico. In the eastern Atlantic, a sport fishery for bluefin tuna exists around the Canary Islands and a substantial commercial fishery occurs off Europe and North Africa. Purse seining is conducted off the Atlantic coast of Norway and Morocco, the Mediterranean coast of France, the Adriatic coast of Italy and Yugoslavia, in the Tyrrhenian Sea off Italy, and occasionally in the North Sea off Denmark. An important hook-and- line bait fishery occurs in the Bay of Biscay off France and Spain, off Morocco, the Azores, the 'Contribution Number 81-34 M, Southeast Fisheries Center Miami Laboratory, National Marine Fisheries Service, NOAA, Miami, FL 33149. 2National Marine Fisheries Service, NOAA, c/o Alaska Department of Fish and Game, P.O. Box 686, Kodiak, AK 99615. Canary Islands, the Mediterranean coast of Spain, and occasionally off Turkey. Trap fisheries were present off southern Portugal, southern Spain, and the Straits of Gibraltar, as well as along the Mediterranean coast of Morocco, Tunisia, and Sicily. There is a significant Japanese longline bluefin tuna fishery in the Mediterranean Sea, Bay of Biscay, and off western Europe. There has been a substantial reduction in the Atlantic-wide catch of bluefin tuna from 38,500 1 in 1964 to 12,500 t in 1973 with no large reductions in effort (Miyake et al3.) A number of studies have been made, and are continuing, to understand the reason for this decline (Parks 1977; Shingu and Hisada 1980; Parrack 1980). Of the various aspects of the dynamics of fish populations, the measure of reproductive potential is of primary importance since it is a basic determinant of productivity. It is used to separate subpopulations, to estimate mortality, and, with ichthyoplankton data, to estimate stock size. Two major bluefin tuna spawning areas are located in the Atlantic approximately 4,000 mi apart: In the Gulf of Mexico (Richards 1976; Montolio and Juarez 1977; Rivas 1978) and the Florida Straits (Rivas 1954; Baglin 1976) during April, May, and June; and in the Mediterranean Sea during May, June, and July (Frade and Manacas 1933; Rodriguez-Roda 1964). Al- 3Miyake, M. P., A. De Boisset, and S. Manning (compilers). 1974. Int. Comm. Conserv. Atl. Tunas, Stat. Bull. 5. Unnumbered pages. Manuscript accepted May 1981. FISHERY BULLETIN: VOL. 80, NO. 1, 1982. 121 FISHERY BULLETIN: VOL. 80, NO. 1 though these two spawning grounds have been well documented, a question remains whether bluef in tuna spawn elsewhere and at other times. Mather4 believes that some bluefin tuna prob- ably spawn in late spring near the northern edge of the Gulf Stream off the eastern United States. Berrien et al. (1978) have reported collecting bluefin tuna larvae from this area during April and June 1966. These larvae, however, could have drifted to this area from spawning grounds farther south. In this paper, I describe bluefin tuna ovaries from the Middle Atlantic Bight (the U.S. coastal area between Cape Cod and Cape Hatteras) and examine the possibility that this may be another significant spawning area for bluefin tuna. Also, I make some comparisons of female gonadal development between the known spawning areas. My literature review on bluefin tuna shows there is a need for additional information on the bluefin tuna's reproductive potential. A wide range in fecundity estimates was found. Frade (1950) reported that an eastern Atlantic 160 kg bluefin tuna produced 18.7 million eggs. Williamson (1962) stated that the ovaries of a 272.4 kg western Atlantic bluefin tuna con- tained about 1.0 million eggs. Rodriguez-Roda (1967) estimated that off southern Spain a 54 kg fish could produce 5.5 million eggs and a 235 kg bluefin tuna could produce over 30.0 million eggs. Baglin (1976) estimated that a 188.4 kg western Atlantic bluefin tuna could produce 16.7 million eggs and that a 271.5 kg bluefin tuna could produce 31.4 million eggs. Baglin and Rivas (1977) indicated that a 324 kg western Atlantic tuna could produce 57.6 million eggs. I deter- mined the fecundity of bluefin tuna taken from the United States sport fishery in the Florida Straits and Gulf of Mexico and from the Japanese longline fishery in the Gulf of Mexico and compared my findings with previous estimates. I have also examined monthly sex ratios for western Atlantic bluefin tuna. MATERIALS AND METHODS Bluefin tuna from the Gulf of Mexico, Florida Straits, Middle Atlantic Bight, and off the northeast coast of the United States were sampled from anglers' catches. Bluefin tuna samples from purse seine catches came from the Middle Atlantic Bight and the northeast coast of the United States. Bluefin tuna were also sampled from the Japanese longline fishery in the Gulf of Mexico and from the New England handgear fishery. Throughout this paper the classification system of Rivas (1979) was used. Thus, small bluefin tuna are 50-129 cm fork length (FL) and 3-44 kg round weight, medium bluefin tuna are 130-180 cm FL and 45-130 kg round weight, and giant bluefin tuna are >180 cm FL and >130 kg round weight. Sex data were obtained from 283 small and medium bluefin tuna captured by commercial and sport fishermen off the Middle Atlantic Bight (1974-77). Also, sex data were obtained from 3,429 giant bluefin tuna captured by sport and commercial fishermen in the Gulf of Mexico and along the northeast coast of the United States from North Carolina to Maine, and from fish taken by sport fishermen in the Bahamas (1975-78). Straight fork length (cm) was measured with calipers and round weight was recorded in pounds and later converted to kilograms. In some instances where either weight or length was unknown, a functional regression (Baglin 1980) was used for estimating the missing measurement. Small and medium fish were assigned an age based on a length-weight-age conversion table presented by Coan (1976). No ages were assigned to giant fish because of the difficulty experienced in aging them accurately. Ovaries were examined from 81 small and medium bluefin tuna caught from 1974 through 1977 and from 403 giant bluefin tuna collected during 1965 through 1968 and 1974 through 1978. Ovaries were stored in 10% Formalin5 and later blotted dry and weighed in grams. The gonosomatic index (GSI) (ovary weight as a percentage of total body weight) was used as a gross indicator of maturity. Only fork length was taken from Japanese longline samples from the Gulf of Mexico for which the GSI was calculated using an estimated body weight from the length- weight relationship of Baglin (1980). A detailed examination of ovaries from 292 "Mather. F. J., III. 1973. The bluefin tuna situation. Proc. 16th Annu. Int. Game Fish. Res. Conf., p. 93-120. 5Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 122 BAGLIN. JR.: REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA fish was conducted using histological tech- niques. Ovaries were sectioned at 8 yu and stained either with haematoxylin and eosin or trichrome stain. The oocytes were grouped into stages according to the classification system of Kraft and Peters (1963) and Smith (1965). From each prepared slide, a measurement was taken of the largest egg diameter. The egg diameters were measured with an ocular micrometer at 30 X magnification, and the orientation of egg diameters was assumed to be random. Stage of maturity was thus based on the histological examinations. A test was made for heterogeneity of egg size within the ovary. Thin cross sections were taken from the anterior, middle, and posterior parts of one ovary of a mature fish and each section was subdivided into three subsamples, representing the center, midregion, and periphery of the ovary (Otsu and Uchida 1959). Egg diameters from each area were then measured and compared statistically. Fecundity, defined as the potential number of mature eggs (yolked ova) that could be spawned during one reproductive season, was estimated by using a dry weight method. This consisted of taking samples from the anterior, middle, and posterior parts of each ovary. The eggs from each of these sections and from the remainder of the ovaries were then separated from the ovarian tissue by straining them over a wire screen under running water. The egg samples from each section, in an aqueous solution, were stirred and a subsample from each was pipetted into a beaker. These eggs were stirred and approxi- mately 1-2 g wet weight were taken to be used for the fecundity estimate. The yolked eggs, which were counted and fecundity estimated, were divided into two size categories. Eggs 0.46 mm and larger that were counted were well developed and fully yolked. A second size category for which eggs were counted included smaller eggs (0.32 mm in diameter) that were not in quite as advanced stage of development, but that could possibly undergo further development and be spawned during one reproductive season. The subsample was then weighed to the nearest 0. 1 mg, and the weight of the remaining eggs was recorded in grams. Fecundity estimates, rounded to the nearest 0.1 million eggs, were calculated from the relationship C - (AD/B) + A, where A is the number of mature ova in the subsample, B is the weight of the ova in the subsample, C is the number of mature ova, and D is the weight of ova from both ovaries minus the weight of the subsample. RESULTS AND DISCUSSION Sex Composition From 1974 through 1977, sex was determined for 283 small and medium bluefin tuna from the Middle Atlantic Bight during June, July, and August (Table 1). No significant difference from an expected 1:1 sex ratio was found. Sampling for the remaining months was inadequate. From 1975 through 1978, sex was determined for 3,429 giant bluefin tuna from the Gulf of Mexico, March through June; Bahamas, April through June; and from the northeast coast of the United States, July through October (Table 1). The deviation from an expected 1 : 1 sex ratio was significant for April, May, July, and August. Females were more prevalent than males in spawning aggregations during April and May. Males were more prevalent in feeding schools during July and August. No significant dif- ference from an expected 1:1 sex ratio was found for March, June, September, and October. Sampling during the remaining months was in- adequate. These findings suggest that some giant bluefin tuna segregate into distinct areal groups according to the predominating sex and that sex ratios may change with season. Table 1.— Monthly sex ratios for small and medium (1974-77) and giant (1975-78) western Atlantic bluefin tuna. Sex ratio Size category Month Number males/females Small and medium June 204 1.02 July 35 0.84 August 44 1.10 Giant March 66 1.00 April 292 '0.75 May 356 '0.63 June 106 093 July 800 '1 46 August 1,049 '1.74 September 694 093 October 66 1.13 'Significant departure from null hypothesis at 0.05 level (chi-square). Gonosomatic Index, Gross Morphology, and Size of Ova The external appearance alone of tuna ovaries is inadequate for gross classification of maturity stage (Bunag 1956). The GSI (also called gonad index, maturity index, gonadosomic or gonadal- 123 FISHERY BULLETIN: VOL. 80, NO. 1 somatic index), along with egg diameter measurements, has been a successfully used criterion for selecting specimens for fecundity studies and for determining the spawning peri- ods for various species of fish (Vladykov 1956; Peterson 1961; Erdman, 1968; Mathur and Ramsey 1974; Baglin 1979). On the basis of the GSI and the gross morphology and size of ova from the preserved ovaries, western Atlantic female bluefin tuna may be assigned to one of the following developmental stages: I. Immature — Ovaries are thin, hollow tubes; nearly spherical, transparent oocytes range from 0.03 to 0.13 mm in diameter (these eggs were stained with acetocar- mine to facilitate measuring). These oocytes were also present during all other developmental stages, and there was no sign of previous spawning. GSI ranges from 0.1 to 0.3. II. Maturing — Ovaries are flaccid, opaque ova up to about 0.63 mm in diameter. GSI ranges from 0.4 to 1.9. III. Mature — Ovaries are firm and full of eggs, with many yellow-orange ova up to 0.85 mm in diameter. GSI ranges from 2.0 to 5.3. IV. Ripe — None of the fish studied were found to be in this developmental stage. However, a few transparent ripe eggs were found in an individual classified as Stage III. The largest of these eggs was 1.16 mm in diameter with an oil droplet 0.30 mm in diameter. This egg corresponds to Stage V of Rodriguez-Roda (1967). A fish would be classified as being ripe only when a substantial number of eggs of this size are present. V. Spent— Ovaries are flaccid; completely spent fish had a few degenerating eggs up to 0.63 mm in diameter. Fish in this stage taken in the summer and early fall months had ovaries with a large amount of fatty tissue. GSI >0.2 but <2.0. Size and reproductive data by estimated age and month are presented in Table 2 for 81 small and medium female bluefin tuna from the Middle Atlantic Bight of the western Atlantic and for 15 small and medium eastern Atlantic female bluefin tuna collected by Rodriguez- Roda (1967) and by Cort et al. (1976). Relatively Table 2.— Length, weight, and gonadal data for 81 small and medium female western Atlantic bluefin tuna collected during 1974- 77 and for 15 small and medium female eastern Atlantic bluefin collected during 1963 by Rodriguez-Roda (1967) and during 1976 by Cortet al, (1976). Month Fork length (cm) X SE Range Round weic Iht (kg) Ovary we ight (g) Gonosomatic X SE index (%) Range Age X SE Range X SE Range Number Western Atlantic 3 June 100 0.59 97-102 19.6 0.57 16.3-23.2 25 39 5-52 0 1 0.02 0.03-0 28 12 July 96 95-100 18.7 16.8-21 8 16 10-23 0.1 0.06-0.14 6 August 101 98-105 20.7 18.8-22.2 18 8-51 01 0.03-0.23 6 4 June 108 107-109 25.4 24.5-26.3 15 10-20 01 0.04-0 08 2 July 121 118-122 34.2 26 8-38.1 76 68-80 02 0.21-0 26 3 August 115 106-124 29.5 19 1-409 49 17-94 0.2 009-0.26 4 5 June 133 1.42 126-138 44 1 1.18 36.3-499 97 95 44-148 02 0 11-0 33 12 July 133 126-140 47.2 43.6-508 190 149-231 0.4 029-0 53 2 August 129 126-131 41.0 37.9-454 69 40-119 02 0 11-0 26 4 6 June August 150 150 1 44 142-157 59.1 58.1 2.34 45.4-75.4 204 126 18.5 102-222 04 02 0.03 0 17-0.51 12 1 7 June 163 090 157-169 80.2 2.53 65.4-91.7 434 97.9 175-1,605 0.5 0 10 0 17-1 75 14 July 160 158-165 60.3 53.1-68.1 142 62-211 02 0.13-0.31 3 Eastern Atlantic 4 July 111 '26.2 150 0.6 1 5 May June July August 130 125 126 134 54.0 '37.0 '37.8 48 0 740 500 450 460 1.4 14 1.2 1.0 1 1 1 1 6 June July August 149 148 152 '61.7 '61.0 63.5 900 860 470 1.5 1.4 07 1 3 2 7 June 171 110.0 1,920 1.9 1 8 May August 180 185 113.0 106.0 2,500 660 2.2 0 6 1 2 'Round weight estimated using functional regression of Baglin (1980) 124 BAGLIN, JR.: REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA little development towards maturity was evident in the age 1 through age 7 western Atlantic fish with the exception of one age 7 fish collected in June with a GSI of 1.75. The eastern Atlantic small and medium fish, on the average, have a larger mean GSI than the western Atlantic small and medium fish. The largest GSI (2.2) calcu- lated from the eastern Atlantic small- and medium-sized bluefin tuna was found for a fish captured during May at an estimated age of 8 yr. Body and ovary size, by month, for 403 western and 75 eastern Atlantic female giant bluefin tuna are presented in Table 3, with the calculated monthly GSI presented in Figures 1 and 2. The average body and ovary size of the female giant fish from the western Atlantic was larger than that of the eastern Atlantic fish for each month. Well-developed ovaries were present in western Atlantic giant bluefin tuna during April and May. These fish were collected from the Gulf of Mexico longline and sport fishery and from the Florida Straits sport fishery. Ovarian development was minimal during October, as indicated by a low mean GSI, 3.6 3.2 Table 3.— Length, weight, and gonadal data for 403 female giant western Atlantic bluefin tuna collected during 1965-68, 1974-78, and for 75 female giant eastern Atlantic bluefin tuna collected during 1963 by Rodriguez -Rod a (1967). Fork len gth (cm) Round wei X SE ght (kg) Range O vary we ght (g) Num- ber Month X SE Range X SE Range Western Atlantic March 237 3.5 199-256 245 102 143-307 2.849 448 331-6.810 25 April 242 27 190-264 262 8.1 1 1 7-335 8,380 564 409-13,166 41 May 240 1.4 205-269 244 48 156-324 7,708 475 900-14.960 73 June 246 1.7 213-270 262 58 159-351 5.023 341 950-13.600 68 July 254 10 218-272 295 33 205-375 1.927 89 600-7,000 96 August 257 13 224-282 320 44 213-424 2.857 158 600-6.250 79 Sept 256 31 235-269 330 7.5 297-374 2,770 533 750-6.500 11 Oct 242 38 212-257 308 16.8 Easterr 186-370 Atlantic 1,137 71 700-1,400 10 May 211 1.8 200-225 190 4.2 155-219 2.758 318 1.540-6,820 17 June 213 26 204-230 189 5.9 167-235 3,148 403 1,780-6,280 12 July 214 2.3 189-244 169 58 130-263 1,493 117 700-3.580 30 August 207 22 197-232 149 56 125-226 1,112 85 840-1.980 16 MAR. APR. MAY JUNE JULY AUC. SEPT. OCT. N = 2S N = «l N = 73 N = 6S N = 96 N=79 N=ll N=10 3.2-| 3.0 2.8 2.6 2.4 2.2- 2.0 1.8 1.6 1.4 1.2 1.0 .8 .6 .4' .2- O MAY N = 17 1UNE N=12 JULY N=30 AUG. Nil. Figure 1. — Seasonal variation in gonosomatic index of 403 female giant western Atlantic bluefin tuna collected from 1965 through 1968 and 1974 through 1978. The number, mean (horizontal line), range (vertical line), 1 SD on each side of the mean (open box), and 2 SE on each side of the mean (shaded box) are shown. Figure 2.— Seasonal variation in gonosomatic index of 75 fe- male giant eastern Atlantic bluefin tuna collected during 1963 by Rodriguez-Roda (1967). The number, mean (horizontal line), range (vertical line), 1 SD on each side of the mean (open box), and 2 SE on each of the mean (shaded box) are shown. 125 FISHERY BULLETIN: VOL. 80, NO. 1 and reached a peak during April and May as indicated by the highest GSI. Sampling was inadequate for November through February. Well-developed ovaries were present mainly during May and June in eastern Atlantic giant bluefin tuna from the traps at Barbate (Rodriguez-Roda 1967). In May, the mean GSI for the western Atlantic was greater than that for the eastern Atlantic. No great difference was found between the mean GSI for the western and eastern Atlantic giant bluefin tuna for June, July, and August for which data were available for comparison. The plots of the GSI indicate that giant bluefin tuna spawning occurs earlier in the western Atlantic (the drop in GSI occurring in June) than in the eastern Atlantic (the drop in GSI occurring in July). Heterogeneity of Egg Diameters A significant difference in egg diameters was found for the center, midregion, and periphery of the anterior section of an ovary from a mature fish (F=6.1;df = 2, 631; P<0.005). No significant difference in egg diameters was found for the center, midregion, and periphery of the middle or posterior sections of the ovary. A significant difference in egg diameters was also found among the anterior, middle, and posterior sec- tions (F= 11.6; df = 2, 1,843; P<0.001). Because some heterogeneity occurred, estimates of fecundity were based on eggs from each section of both ovaries. Heterogeneity of egg size within an ovary has also been shown for albacore, Thunnus alalunga, (Otsu and Uchida 1959); swordfish, Xiphias gladius, (Uchiyama and Shomura 1974); and white marlin, Tetrapturus albidus, (Baglin 1979). Histology of the Ovaries Microscopic examinations were made of ovarian tissues from 119 small and medium bluefin tuna and 173 giant bluefin tuna. Diameters measured from these prepared slides were considerably smaller than those measured from whole eggs fixed in 10% Formalin (see footnote 5). The oocytes were grouped into the following stages of oogenesis using the system of Kraft and Peters (1963), Smith (1965), and Moe (1969). Stage 1 — Thin layer of cytoplasm surrounding a 126 relatively large nucleus with a single nucle- olus; oocytes are <0.03 mm in diameter. Stage 2 — Dark cytoplasm and many peripheral nucleoli are in the nucleus oocytes are 0.03 mm through 0.13 mm in diameter (resting stage). Stage 3— Yolk vesicles appear in cytoplasm; the membrane called the zona radiata, also referred to as zona pellucida (Hoar 1969) and vitelline membrane (Bodola 1966), appears at the end of this stage; oocytes are 0.17 mm through 0.30 mm in diameter (early vitello- genic stage). Stage 4 — Thick zona radiata, yolk vesicles, and yolk globules are present; oocytes are 0.33 mm through 0.63 mm in diameter (late vitellogenic stage). Stage 5— This final stage was seldom observed during histological analysis. It evidently takes place during a short period of time immediate- ly before ovulation. Eggs in this stage have a lightly staining granular yolk mass with few yolk vesicles and yolk globules, a thin zona radiata, and an irregular shape caused by sectioning. Histological examination of female bluefin ovary sections from the Middle Atlantic Bight revealed the following: Age 1 — Very little sexual differentiation was present in age 1 bluefin tuna (N= 17) collected during May, June, July, and August. Some oogonia were observed within the lamellae. Age 2 — The first appearance of oocyte develop- ment occurred in age 2 bluefin tuna collected during July (N - 4). Both stage 1 and stage 2 oocytes were present, although stage 2 oocytes were most numerous. Age 3— Many stage 2 oocytes and a few stage 1 oocytes were found in age 3 bluefin tuna collected during January and June (N - 13). Only stage 2 oocytes were found in age 3 bluefin tuna collected during July and August (N= 10). Age 4 — Stage 2 oocytes were present in all age 4 females collected during June (Af = 36) (Fig. 3). Also in 11% of these fish, some vitellogenic stage 3 oocytes undergoing absorption were present. Only stage 2 oocytes were present in age 4 bluefin tuna collected during July and August (N = 10). Age 5— Mostly stage 2 oocytes were present in age 5 fish collected during June (N = 16), BAGLIN, JR.: REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA Figure 3.— Ovarian tissue from an age 4 bluefin tuna (119 cm, 33.6 kg) collected off the Middle Atlantic Bight during June 1977. Stage 2 oocytes are present, as indicated by arrow. although a few stage 1 oocytes were also observed. Also, in 44% of these fish some stage 3 oocytes were present, many undergoing absorption. One individual also had some stage 4 oocytes present. These oocytes were in the process of degeneration. Mostly stage 2 oocytes were present in age 5 fish collected during July (N= 2). Both of these fish also had some stage 3 oocytes present, which were undergoing absorption. Stage 2 oocytes were present in all fish collected during August (N = 4). Only one of these fish had stage 3 oocytes present. These stage 3 oocytes were also undergoing absorp- tion. Age 6 — The majority of oocytes observed in age 6 bluefin tuna collected during June (N = 12) were in stage 2 of development and only a few stage 1 oocytes were observed. Many of these fish (83%) had some stage 3 oocytes present, most undergoing the process of degeneration (Fig. 4). One individual had some stage 4 oocytes present, which were also degenerat- ing. Only stage 2 oocytes were found in an age 6 bluefin tuna collected during August. Age 7 — Mostly stage 2 oocytes were found in age 7 fish collected during June (N - 15). Also, some stage 1 oocytes were present in most of these fish and 47% had stage 3 oocytes present, many of which were undergoing absorption. Only stage 2 oocytes were found in an age 7 fish collected during July and another age 7 fish taken during October. Some gonadal development, therefore, occurs in these medium female bluefin tuna. However, the simulation of gonadal maturation by young fish that probably do not spawn has been re- ported for king mackerel, Scomberomorus cavalle, (Beaumariage 1973) and Atlantic sail- fish, Istiophorus platypterus, (Jolley 1977). These authors based their determination on the size of the stage 4 oocytes, on their compactness within the lamellae, and on the appearance of many de- generating oocytes. My observations of medium bluefin tuna seem to correspond with the findings of the above authors, although the most 127 FISHERY BULLETIN: VOL. 80, NO. 1 I mm _ ^*A< Figure 4.— Ovarian tissue from an age 6 bluefin tuna (153 cm, 59.5 kg) collected off the Middle Atlantic Bight during June 1976. Resting stage 2 oocytes are present (upper arrow), as are stage 3 oocytes undergoing the process of degeneration (lower arrow). developed oocytes in the majority of fish that I examined were in stage 3 of development, and the average were in stage 2 based on the mean size of the oocytes measured (Fig. 5). I believe, therefore, that the Middle Atlantic Bight is not a significant spawning area during the summer and probably not at any other time of the year, but samples are not available for other seasons. Also, recently there has been speculation by Rivas (1978) that some of these medium bluefin tuna may migrate during May and June across the Atlantic to the Mediter- ranean Sea to spawn. According to Sella (1929) eastern Atlantic bluefin tuna begin to reproduce in their third year, when they attain a weight of about 15 kg. Rodrlguez-Roda (1967) found that 50% of eastern Atlantic bluefin tuna females are mature at 97.5 cm or 3 yr of age. However, the smallest bluefin tuna that he estimated fecun- dity for was 130.5 cm and 54 kg, which corre- sponds to an age 5 fish according to Coan (1976). Frade and Manacas (1933) found very little development in age 3 females from the eastern Atlantic. Cort et al. (1976) found developing oocytes in eastern Atlantic bluefin tuna measur- ing 148 and 152 cm from the Gulf of Gascony. These fish would be age 6 according to Coan (1976). The only published record I have found of age of maturity of western Atlantic bluefin tuna is that of Westman and Neville (1942). Observing the gross morphology of ovaries, they indicated that western Atlantic bluefin tuna 5 yr of age appeared to be mature, although the gonads gave no indication of the presence of eggs. I have also examined the unpublished cruise report of the MV Delaware, June 1957. Using the conversion table of Coan (1976), all age 3 female bluefin tuna were judged immature, and most age 4 (2 out of 3) were judged immature. No description of the ovaries on an age 5 fish was given, and 67% of age 6 females (N = 6) had well-developed eggs. My analysis of western Atlantic bluefin tuna ovaries indicates that age 6 would probably be 128 BAGLIN, JR.: REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA .55- .50- .45 ^ .40' z "~ .35 QE }HJ .30 U | ... Q .20 (9 (9 W .15 Z !3 io .05 8 l_ _l_ MARCH APRIL MAY JUNE JULY AUG. SEPT. OCT. N=25 N = 65 N = 27 N = 17 N=10 N = 10 N = 16 N = 3 JUNE N = 91 JULY N = 12 AUG. N-16 Figure 5.— Mean egg diameter of largest ovarian egg as determined from histological sections from monthly samples (N) of A) female giant bluef in tuna from the Gulf of Mexico and the Florida Straits (March through June 1955, 65-67. 76-78) and from off New England (July through October 1974-75, 77), and B) female bluefin tuna ages 3-7 from off the Middle Atlantic Bight (June through August 1974-77). the earliest age at which a majority of females could possibly reach maturity. However, a majority of vitellogenic oocytes in these age 6 fish were being absorbed and most likely would not have been spawned during the years when these fish were taken. As previously noted, I observed no vitellogenic oocytes in age 3 fish, but if Sella (1929) and Rodriguez-Roda (1967) are correct, eastern Atlantic bluefin tuna may reach maturity at an earlier age than their western Atlantic counterparts. Vitellogenic oocytes were not found in the two giant bluefin tuna (205 and 207 cm) taken during the March 1966 MV Delaware Cruise 66-2 (lat. 37°24'N, long. 67°32'W). Vitellogenic oocytes were found in one of three giant fish ( 190-213 cm) taken during April 1965 on the MV Delaware Cruise 65-3 (lat. 35°54'N, long. 72°51'W). Evidently this area of the western North Atlantic was not an important spawning area for bluefin tuna during March-April. Vitellogenic oocytes (stages 3 or 4) were present in all giant bluefin tuna taken from the Gulf of Mexico and Florida Straits during 1955, 1967, 1976, 1977, and 1978 during March {N = 24), April (N = 61), and May (N= 54) (Figs. 6, 7). In one of two fish taken in June 1967 and 1977, stage 3 and stage 4 oocytes were present; in the other fish all the vitellogenic oocytes had been spawned or absorbed. On the average, the larg- est oocytes in all of the fish for July (N - 10), August (N - 10), September (N= 16), and October (N = 12) from off New England during 1974, 1975, and 1977 were in stage 2 (Fig. 8). Vitellogenic oocytes were generally absent from these fish. I found degeneration and absorption of ad- vanced unovulated eggs more common as the season progressed. This agrees with the findings of Frade and Manacas (1933) for eastern Atlantic bluefin tuna. Distinctive atretic bodies, formed from the remnants of oocytes that were not shed, were present in the female giant bluefin tuna collected during March through October. Topp and Hoff (1971) also reported atretic body formation in the ovaries of a single giant female collected from the west Florida coast during May. As previously described by Smith (1965), these atretic bodies form a characteristic brownish mass, the corpus atreticum, and are made up of amorphous brownish granules, phagocytes, and clear yellow pigment globules (Fig. 9). I found that empty follicles left behind after the ripe oocytes are released degenerate rapidly. This was also observed for eastern Atlantic bluefin tuna by 129 FISHERY BULLETIN: VOL. 80, NO. 1 130 BAGLIN. JR.: REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEEIN TUNA Figure 6.— Ovarian tissue from a giant bluefin tuna (250 cm) collected off the Gulf of Mexico during March 1978. Early stage 4 oocytes (upper arrow), stage 2 oocytes (middle arrow), and stage 3 oocytes (lower arrow) are present. Figure 7.— Ovarian tissue from a giant bluefin tuna (205 cm) collected off the Gulf of Mexico during May 1978. Late stage 4 oocytes (upper arrow), stage 2 oocytes (middle arrow), and stage 3 oocytes (lower arrow) are present. Frade and Manacas (1933), who speculated that the rapid degeneration of the follicles could be caused by pressure exerted by neighboring oocytes. My findings also confirm that western Atlantic bluefin tuna released eggs intermit- tently during April, May, and June, the majority during May. Fecundity Estimates Fecundity estimates were obtained for 28 western Atlantic bluefin tuna, which were collected from the Gulf of Mexico and Florida Straits during April, May, and June of 1967, 1968, 1974, 1975, 1976, and 1978 (Table 4). The reliability of the dry gravimetric method was tested by estimating the fecundity of an individual fish by counting and weighing eggs from four subsamples. Based on these four estimates, the average number of eggs >0.46 mm in diameter was 41.6 million with a range from 40.0 to 43.0 million and a standard error of the mean (SE) of 0.76. The average number of eggs >0.32 mm in diameter was 76.0 million with a range from 72.5 to 82.5 million and SE = 2.2. I am presenting two estimates of potential fecundity, and the estimate based on eggs >0.32 mm in diameter essentially coincides with the size of 0.33 mm used by Rodriguez-Roda (1967) for eastern Atlantic bluefin tuna. This would be the potential number of eggs that could be spawned, assuming there was no degeneration or absorption of advanced unovulated eggs. My histological examinations of bluefin ovaries, Figure 8.— Ovarian tissue from a giant bluefin tuna (256 cm, 268 kg) collected off the northeast coast of the United States during August 1975. Stage 2 oocytes are present, as indicated by arrow. 131 FISHERY BULLETIN: VOL. 80. NO. 1 FIGURE 9.— Ovarian tissue from a giant bluefin tuna (264 cm, 297 kg) collected off the northeast coast of the United States during July 1975. Brown bodies are present, as indicated by arrows. however, revealed the presence of atretic bodies. It was impossible to quantify the number of eggs constituting these atretic bodies, although I assume that absorption would occur principally with the smaller vitellogenic ova. Therefore, I have also estimated the number of eggs >0.46 mm in the most advanced size mode that could potentially be spawned during one spawning season. For bluefin tuna 205-269 cm FL and 156- 324 kg round weight, the average number of eggs 0.33 mm in diameter and larger was estimated as 60.3 million (SE = 4.04) and the average number of eggs 0.47 mm in diameter and larger was estimated as 34.2 million (SE = 2.15). No apparent relationship was found for fecundity as a function of length or estimated weight for the size range of bluefin tuna I studied. MacGregor (1968) said that the relationships of length and weight to egg production are masked in many species of fish, because egg production occurs over a relatively short range in size, and because variation in number of eggs produced at each length is great. Bailey (1964) found no obvious relationship between fecundity and fish size for American smelt, Osmerus mordax. Schenck and Whiteside (1977) and Loesch and Lund (1977) found a great amount of variability in fecundity for a given fish size for the fountain darter, Etheostoma fonticola, and blueback herring, Alosa aestivalis. Since histological examinations of ovaries and estimated GSI showed that the bluefin tuna are multiple spawners, it is possible that some of the fish selected for fecundity estimates had previously shed eggs. Also the rate of absorption of vitellogenic ova could have varied for the fish selected for fecundity estimates. I found, however, that the dry weight of eggs could be used for estimating fecundity. The following relationships were found: F= 5.2895 + 0.0167 W (F? = 0.64), where F is the number of ova >0.46 mm in diameter and W is the dry weight of all eggs separated from the ovarian connective tissue. 132 BAGLIN. JR.: REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA Table 4.— Length, weight, and gonadal data for 28 female western Atlantic bluef in tuna from the Gulf of Mexico and the Florida Straits collected during April, May, and June 1967, 1968, 1974, 1975, 1976, and 1978. The mean and standard error of the mean are given at the bottom of the columns. Body length (cm) Estimated body weight (kg) Dry weight of eggs (9) Gono- somatic index (%) Estimated no. of eggs >0.46 mm >0.32 mm diameter diameter (millions) (millions) 205 156 1.260 5.3 13.6 32.7 222 '188 696 2 1 167 22.7 229 217 1.202 3 1 24.2 46.4 229 217 2.177 5.0 555 960 229 217 1.481 28 339 64.4 231 224 1,330 4.4 268 41 1 236 '197 1.329 32 284 40.3 236 '189 1.404 3.2 296 44.7 238 246 1,788 4.1 390 639 238 246 1,703 4.2 40.1 64.5 238 246 1.796 3.8 34.4 61.7 241 254 1.483 3.4 29.8 62.4 241 254 2.436 48 480 849 241 '247 1,560 3.9 330 44.0 244 263 1.750 36 25.2 56.7 244 263 1.452 3.4 232 42.1 244 263 2,121 5.0 493 93.3 252 289 2.770 4 7 396 946 254 298 1,942 29 41.6 76.0 — 307 1,681 2.5 32.0 59.2 256 307 1.950 2 6 422 79.5 257 '232 1.200 29 243 338 257 309 750 1.9 162 26.2 259 316 2.750 4 2 326 769 259 316 2.500 44 488 806 261 '272 1,488 2.6 31.4 42.3 262 '324 2,593 4.5 57.6 81.6 269 '284 1.950 4.6 40.6 74.8 X243 255 1,734 3.7 342 60.3 SE 2.78 8.37 10279 0.18 2 15 4.04 'Actual weight determined F = -0.9057 + 0.0353 WO? = 0.81), where F is the number of ova >0.32 mm in diameter and W is the dry weight of all eggs separated from the ovarian connective tissue. A reduction in fecundity in older fish has been reported by Bodola (1966) for gizzard shad, Dorosoma cepedianum, and by Loesch and Lund (1977) for blueback herring. No such decline in number of eggs was found for western Atlantic bluefin tuna. My fecundity estimates for western Atlantic bluefin tuna are considerably greater than the estimate given by Williamson (1962). He, however, did not describe how he arrived at his estimate for a western Atlantic bluefin tuna. My estimates more closely agree with estimates presented by Frade (1950) and Rodriguez-Roda (1967) for eastern Atlantic bluefin tuna. Although my estimates were based generally on larger fish, it appears that western Atlantic bluefin tuna are considerably more fecund than eastern Atlantic bluefin tuna. ACKNOWLEDGMENTS I thank L. R. Rivas and W. J. Richards of the Southeast Fisheries Center Miami Laboratory, National Marine Fisheries Service, NOAA and C. L. Smith of the American Museum of Natural History for their many helpful comments on the manuscript. I also thank the two anonymous reviewers who read the manuscript and offered helpful suggestions. LITERATURE CITED Baglin, R. E., Jr. 1976. A preliminary study of the gonadal development and fecundity of the western Atlantic bluefin tuna. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 5 (SCRS-1975):279-289. 1979. Sex composition, length-weight relationship, and reproduction of the white marlin, Tetrapturus albidus, in the western North Atlantic Ocean. Fish. Bull., U.S. 76:919-926. 1980. Length-weight relationships of western Atlantic bluefin tuna, Thunnus thynnus. Fish. Bull., U.S. 77:995-1,000. Baglin, R. E., Jr., and L. R. Rivas. 1977. Population fecundity of western and eastern North Atlantic bluefin tuna, Thunnus thynnus. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 6 (SCRS- 1976):361-365. Bailey, M. M. 1964. Age, growth, maturity, and sex composition of the American smelt, Osmerus mordax (Mitchill), of Western Lake Superior. Trans. Am. Fish. Soc. 93:382-395. Beaumariage, D. S. 1973. Age, growth, and reproduction of king mackerel, Scomberomorus cavalla, in Florida. Fla. Mar. Res. Publ. 1, 45 p. Berrien, P. L., M. P. Fahay, A. W. Kendall, Jr., and W. G. Smith. 1978. Ichthyoplankton from the RV DOLPHIN survey of Continental Shelf waters between Martha's Vineyard, Massachusetts and Cape Lookout, North Carolina 1965- 66. Sandy Hook Lab. Northeast Fish. Cent., Natl. Mar. Fish. Serv. Tech. Ser. Rep. 15, 152 p. Bodola, A. 1966. Life history of the gizzard shad, Dorosoma cepedianum (Lesueur), in Western Lake Erie. U.S. Fish Wildl. Serv., Fish. Bull. 65:391-425. Bunag, D. M. 1956. Spawning habits of some Philippine tuna based on diameter measurements of the ovarian ova. Philippine J. Fish. 4:145-175. Coan, A. 1976. Length, weight, and age conversion tables for Atlantic tunas. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 5 (SCRS-1975):64-66. Cort, J. L., C. A. Fernandez Pato, and E. De Cardenas. 1976. Observations sur la maturation sexuelle du thon rouge, Thunnus thynnus (L.), du golfe de Gascogne. Cons. Int. Explor. Mer, 6 p. Erdman, D. S. 1968. Spawning cycle, sex ratio, and weights of blue 133 FISHERY BULLETIN: VOL. 80, NO. 1 marlin off Puerto Rico and the Virgin Islands. Trans. Am. Fish. Soc. 97:131-137. Frade, F. 1950. Estudos de pescarias do ultramar Portugues os atuns. Minist. Colon. Junta Invest. Colon., Lisbon, 30 P- Frade, F., and S. Manacas. 1933. Sur l'etat de maturite des gonades chez le thon rouge genetique (note Preliminaire). C. R. Assoc. Anat., 15 p. Gibbs, R. H., Jr., and B. B. Collette. 1967. Comparative anatomy and systematics of the tunas, genus Thunnus. U.S. Fish Wildl. Serv., Fish. Bull. 66:65-130. Hoar, W. S. 1969. Reproduction. In W. S. Hoar and D. J. Randall (editors), Fish physiology, Vol. Ill, p. 1-72. Acad. Press, N.Y. Jolley, J. W. , Jr. 1977. The biology and fishery of Atlantic sailfish, Istiophorus platypterus, from southeast Florida. Fla. Mar. Res. Publ. 28, 31 p. Kraft, A. N., and H. M. Peters. 1963. Vergleichende Studien uber die Oogenese in der Guttung Tilapia (Cichlidae, Teleostei). Z. Zellforsch. Mikrost. Anat. 61:434-485. Loesch, J. G., and W. A. Lund, Jr. 1977. A contribution to the life history of the blueback herring, Alosa aestivalis. Trans. Am. Fish. Soc. 106:583-589. MacGregor, J. S. 1968. Fecundity of the northern anchovy, Engraulis mordax Girard. Calif. Dep. Fish Game 54:281-288. Mathur, D., and J. S. Ramsey. 1974. Reproductive biology of the rough shiner, Notopis baileyi, in Halawakee Creek, Alabama. Trans. Am. Fish. Soc. 103:88-93. Moe, M. A., Jr. 1969. Biology of the red grouper, Epinepheius morio (Valenciennes), from the eastern Gulf of Mexico. Fla. Dep. Nat. Resour. Mar. Res. Lab., Prof. Pap. Ser. 10, 91 P- Montolio, M., and M. Juarez. 1977. El desove de Thunnus tkynnus thynnus en el Golfo de Mexico - Estimado preliminar de la magnitud de la poblacion en desove a partir de la abundancia de larvas. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 6 (SCRS-1976):337-344. Otsu, T., and R. N. Uchida. 1959. Sexual maturity and spawning of albacore in the Pacific Ocean. U.S. Fish Wildl. Serv., Fish. Bull. 59:287-305. Parks, W. W. 1977. Cohort and equilibrium yield-per-recruit analyses for the Atlantic bluefin tuna fisheries system accounting two system configurations and two natural mortality models. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 6 (SCRS-1976):385-4. Parrack, M. L. 1980. Trends on the abundance and age structure of Atlantic bluefin tuna. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 9 (SCRS-1979):563-580. Peterson, C. L. 1961. Fecundity of the anchoveta (Cetengraulis mysti- cetus) in the Gulf of Panama. Inter-Am. Trop. Tuna Comm. Bull. 6:55-68. Richards, W. J. 1976. Spawning of bluefin tuna. (Thunnus thynnus) inthe Atlantic Ocean and adjacent seas. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 5 (SCRS-1975):267- 278. Rivas, L. R. 1954. A preliminary report on the spawning of the western north Atlantic bluefin tuna (Thunnus thynnus) in the Straits of Florida. Bull. Mar. Sci. Gulf Caribb. 4:302-322. 1978. Preliminary models of annual life history cycles of the North Atlantic bluefin tuna. In G. D. Sharp and A. E. Dizon (editors), The physiological ecology of tunas, p. 369-393. Acad. Press, San Franc. 1979. Proposed terminology for size groups of the North Atlantic bluefin tuna (Thunnus thynnus). Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 8 (SCRS- 1978):441-446. RODRiGUEZ-RODA, J. 1964. Biologia del Atiin, Thunnus thynnus (L.), de la costa sudatlantica de Espana. Invest. Pesq. 25:33- 146. 1967. Fecundidad del atiin, Thunnus thynnus (L), de la costa sudatlantica de Espana. Invest. Pesq. 31:33- 52. Schenck, J. R.. and B. G. Whiteside. 1977. Reproduction, fecundity, sexual dimorphism and sex ratio of Etheostoma fonticola (Osteichthyes:Per- cidae). Am. Midi. Nat. 98:365-375. Sella, M. 1929. Migrations and habitat of the tuna (Thunnus thynnus L.), studied by the method of the hooks, with observations on growth, on the operation of the fisheries, etc. Translated by W. G. Van Campen, U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 76, 20 p. Shingu, C, and K. Hisada. 1980. Analysis on the Atlantic bluefin tuna stock. Int. Comm. Conserv. Atl. Tunas, Collect. Vol. Sci. Pap. 9 (SCRS-1979):595-600. Smith, C. L. 1965. The patterns of sexuality and the classification of serranid fishes. Am. Mus. Novit. 2207, 20 p. Topp, R. W., and F. H. Hoff. 1971. An adult bluefin tuna, Thunnus thynnus, from a Florida west coast urban waterway. Fish. Bull., U.S. 69:251-252. UCHIYAMA, J. H., AND R. S. SHOMLIRA. 1974. Maturation and fecundity of swordfish, Xiphias gladius, from Hawaiian waters. In R. S. Shomura and F. Williams (editors). Proceedings of the International Billfish Symposium, Kailua-Kona, Hawaii, 9-12 August 1972. Part 2. Review and contributed papers, p. 142- 148. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-675. Vladykov, V. D. 1956. Fecundity of wild speckled trout Salvelinus fontinalis in Quebec lakes. J. Fish. Res. Board Can. 13:799-841. Westman, J. R.. and W. C. Neville. 1942. The tuna fishery of Long Island, New York. N.Y. Board Superv., Nassau Cty., 30 p. Williamson, G. R. 1962. The bluefin tuna in Newfoundland waters. New- foundland Tourist Dev. Off., Saint John's, Newfound- land, Can., 23 p. 134 AN EVALUATION OF TECHNIQUES FOR TAGGING SMALL ODONTOCETE CETACEANS A. B. Irvine,1 R. S. Wells, and M. D. Scott' ABSTRACT Ninety tags — various combinations of radio tags, spaghetti tags, Roto tags, freeze brands, and tags bolted to the dorsal fin — were placed on 47 Atlantic bottlenose dolphins, Tursiops truncatus, captured near Sarasota, Florida, between January 1975 and July 197(i. In 18 months of field obser- vation, 910 tagged dolphins were sighted; 781 were identifiable, and 129 were not. Twelve naturally marked dolphins were also observed. Radio tagged animals were tracked for as long as 22 days. Repeated observations of tagged animals permitted evaluation of effect on animals and relative merits of the various tags. Freeze brands were most readable from a distance(<30 m ). and most long lived (4.8 years). Other tags were too short lived (bolt tags) or too small to be identified from a dis- tance) Roto tags and spaghetti tags), and all caused tissue destruction. Radio tags caused unexpected dorsal fin damage and were frequently lost prematurely. Taken together, the results suggest that freeze brands are least harmful, and that static tags should be tested on each species to be studied prior to attachment in the field. Cetaceans are difficult to study in the field. Most individuals move almost constantly, rise to the surface only briefly to breathe, and are difficult to differentiate from conspecifics. To facilitate individual recognition, researchers have devel- oped several tagging techniques and tested them on small odontocete cetaceans. Nishiwaki et al. (1966) placed streamer tags on captive rough- toothed dolphins, Steno bredanensis, and concluded that none were effective. On the other hand Perrin et al. (1979) recovered spaghetti tags, another type of streamer, from free-ranging dolphins, Stenella spp., in the eastern tropical Pacific up to 1,478 d after attachment. Roto tags were placed on the spotted dolphin, S. attenuata, and one marked individual was repeatedly identified from a semisubmersible over a period of 3^2 yr (Norris and Pryor 1970). Evans et al. (1972) successfully used radio transmitters, large plastic "button" tags, spaghetti tags, and freeze brands on a total of five species in the Pacific Ocean and Gulf of Mexico. Leatherwood and Evans (1979) have recently reviewed devel- opments and uses of radio tags on cetaceans. Irvine and Wells (1972) reported that an 'Gainesville Field Station, Denver Wildlife Research Center, 412 NE. 16th Ave., Gainesville, FL 32601. department of Zoology, University of Florida, Gainesville. Fla.; present address: Center for Coastal Marine Studies. Uni- versity of California, Santa Cruz, Santa Cruz, CA 95064. department of Zoology, University of Florida, Gainesville, Fla.; present address: Inter-American Tropical Tuna Commis- sion, Scripps Institute of Oceanography, La Jolla, CA 92037. improved button tag was sighted 3 mo after attachment to a bottlenose dolphin, Turxiops truncatus, near Sarasota, Fla. Despite all these improvements in tagging technology, however, little information has been available about long- term effectiveness or affect on the wearers of any type of tag. The tagging program of Irvine and Wells (1972) was reinitiated in the same area in January 1975, after a 4-yr lapse. Using radio transmitters, visual tags, and natural marks we studied the movements and activities of bottle- nose dolphins. Between 29 January 1975 and 25 July 1976, 47 dolphins were captured, tagged, and released a total of 90 times. A summary of the tagging program and an evaluation of the tagging methods used are included below. Detailed analysis of the tagging program results is presented by Irvine et al. (1979,4 1981). METHODS The study was conducted along 40 km of coast south from Tampa Bay, Fla. The study area included shallow channels and bays bounded by a chain of barrier islands (NOS Chart No. Irvine, A. B., M.D. Scott. R. S. Wells. J. H. Kaufmann, and W. E. Evans. 1979. A study of the movements and activities of the Atlantic bottlenose dolphin, Tursiops truncatus, includ- ing an evaluation of tagging techniques. Available National Technical Information Service, 5285 Port Roval Road, Spring- field, VA 22151 as PB-298042, 54 p. Manuscript accepted July 1981. FISHERY BULLETIN: VOL. 80. No. 1, 1982. 135 FISHERY BULLETIN: VOL. 80, NO. 1 11425). Dolphins were captured by encircling one to nine animals with a 455 m X 4.5 m net dropped from a fast moving boat in shallow water. An inner circle enclosure method (Asper 1975) was used to minimize escapes. The inner circle was partitioned so that individual dolphins could be isolated and entangled without collapsing the entire net on remaining animals. Tangled dolphins were removed from the net and placed for tagging in a stretcher, usually held in the water alongside a boat. All animals were sexed, measured, and photographed before tagging. Previously tagged dolphins were examined and retagged as necessary before being released. The study area was surveyed as thoroughly as possible at least biweekly in a 7.3 m Wellcraft Fisherman5 boat equipped with a 3 m tuna tower. All dolphin sightings were recorded during 228 surveys; photographs were taken to facilitate identification of tags and distinctive dorsal fins. Radio Tags An improvement (Model PT 219) of the radio tag developed for small pelagic cetaceans by Ocean Applied Research Corporation (Martin et al. 1971) had not been tested on T. truneatus. In our first efforts, the transmitter was attached with plastic straps to a foam-lined fiber glass saddle and secured to the dorsal fin with a stainless steel bolt through the fin. Because saddles provided by the manufacturer were too small for most T. truneatus, the transmitters were attached to fiber glass saddles molded by the authors (Fig. 1 A, C). The saddles were lined with open cell foam to protect the animal from abrasion and to allow water circulation for thermoregulation. Transmitter saddles were attached using techniques developed by other investigators (see review by Leatherwood and Evans 1979). The first seven saddles were attached with single bolts through the dorsal fin. The last three saddles were attached with bolts fore and aft to provide greater stability against water flow (Fig. 1C). Spring-loaded bolts with dissolving nuts were designed to release the saddle and transmitter from the dolphin sometime after the 1-2 mo life of the lithium batteries. Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA, or the U.S. Fish and Wildlife Service. Ten radio tags (designated RT-1 through RT- 10) were attached to dolphins between 29 January 1975 and 9 June 1976. The RT-1 transmitter consisted of a single 35 cm long X 3.7 cm diameter tube with a 63 cm high spring steel antenna on the forward end. Transmissions from RT-1 gradually failed within 2 h, ap- parently due to saltwater leakage into the battery case. Cause of failure could not be confirmed because the transmitter was missing from the saddle when it was sighted 2 d after attachment. Transmitters on subsequent radio tags were attached to the saddle with bolted aluminum plates (Fig. 1A, C) instead of plastic straps. The transmitter antenna on RT-2 was ob- served to be broken off at the base 5 d after attachment. Consequently, transmitter pack- ages on RT-3 through RT-10 were modified to two tubes, 19.2 cm long X 3.8 cm diameter, connected by copper tubing at the forward end. A flexible 42.5 cm high whip antenna extended vertically from the rear of the starboard tube. The tubes, with transmitter assembly in one and batteries in the other, were bolted to either side of the saddle, and the connecting tubing was solidly encased in fiber glass (Fig. 1C). Visual Tags The button tags described by Evans et al. (1972) had proven not to be durable on T. truneatus (Irvine and Wells 1972). Therefore, we elected to try rectangular fiber glass "visual tags" (Fig. 2). These tags were 10 cm X 7.5 cm and made of 0.4 cm thick yellow laminated fiber glass with 5.1 cm high black tape numerals epoxied to the surface. Each tag was held in place by Teflon bolts with stainless steel washers and cotter pins. The bolts were placed near the anterior edge of the tag to produce a streaming effect as the dolphin moved through the water. The bolt hole was bored through the fin and cauterized with a heated rod, and sheathed with Plexiglas tubing in the same manner as for radio tags. Double bolt tags, also yellow rectangles with black numerals, were cut from 0.2 cm thick fiber glass and varied in size from 9.0 cm X 12.9 cm to 10 cm X 15 cm, depending on the size of the dorsal fin to be tagged. The bolts were located near the anterior and posterior edges of the tag. Numerals were 7.7 cm high. Because cotter pins had sheared some of the Teflon bolts on single 136 IRVINE ET AL: AN EVALUATION OF TAGGING CETACEANS FIGURE 1.— A. Single tube transmitter with spring antenna forward (on dolphin RT-2). B. Dorsal fin 8 mo after transmitter in A was attached. C. Twin tube transmitter assembly with whip antenna aft. Dissolving nuts are top center and below the forward portion of the tube. D. Dorsal fin from C 22 d after the transmitter's installation. Note discolored, apparently necrotic, area around forward hole and apparent migration path of top bolt. bolt tags, double bolt tags were attached with 0.64 cm stainless steel bolts and nuts. Freeze Brands When first captured, all dolphins were freeze branded with 5 cm high numerals on both sides of the dorsal fin and on the body below the fin (Figs. ID, 2C, D). Recaptured animals were rebranded as necessary to improve visibility of existing brands. Application times of 15 s with irons cooled in a mixture of Dry Ice and alcohol were used to brand the dolphins captured before August 1975. Thereafter, liquid nitrogen was used as the coolant. The application time remained 15 s. When possible, the skin was rubbed with an alcohol swab to lower the skin temperature by evaporative cooling prior to branding. Before April 1976, the branding irons were applied to the skin with a gentle rocking motion to assure even contact. After that time the irons were held firmly against the skin without motion, and brand visibility was greatly improved. In some cases, however, parts of the brand did not show because of uneven contact (Figs. ID, 2C, D). Roto Tags Numbered Roto tags (NASCO Inc., Ft. Atkinson, Wis., Jumbo size) were attached to the trailing edge of the dorsal fin of all dolphins handled after January 1976. Red tags were attached to females and yellow tags to males. The 137 FISHERY BULLETIN: VOL. 80. NO. 1 Figure 2.— A. Single bolt visual tag held by Teflon bolt and cotter pin. Note tag bolt scar from 1970-71 study. B. Double bolt tag, Roto tag (at top rear of fin), and spaghetti tag (lower right). C. Double bolt tag on free-swimming dolphin. Note freeze brand with incomplete left digit on body below fin. D. Algae-covered tag 2 mo after initial installation. Note indented area of skin where water flow against tag on opposite side of fin caused pressure on near side. Note also discolored tissue around forward bolt hole. TABLE 1.— Comparison of tagging techniques. No. tags installed Tag longevity' No. sight- ings/tag mean total No. identifi- cations/tag mean total % identifiable sightings- other observers No. tags of known fate Tags of known fate lost, broken, or removed Tags of known fate obscured by fouling % total no. Tags fate bee tissu % of known removed ;ause of e damage Tag no % total no. total no Visual tags 16 <5 min to 4 88 78 200 32 6 14 86 12 14 2 14 2 (single bolt) Visual tags 19 >2 mo <2 wk to 10.00 190 984 187 16 16 63 10 31 5 25 4 (double bolt) Roto tags 53 >2 mo <1 d to >5.5 mo 6.45 342 0.53 28 0 48 40 19 10 5 4 2 Spaghetti tags 17 <1 mo to >13 mo 2.53 43 0 0 12 50 6 0 25 3 Freeze brands 247 >4.8 yr 6.57 309 589 277 2 39 — — — — — — Natural marks3 12 >6yr 7.25 87 7.25 87 1 12 — — — — — - 'Length of time tag was attached and identifiable. 2Many were redone or "touched up " 'Recognizable dorsal fins. numbers on the tags were too small to be read from the observation boat, but the color codes 138 were useful for recognition of sex, and the positions of a tag often indicated identity. IRVINE ET AL: AN EVALUATION OF TAGGING CETACEANS Spaghetti Tags Spaghetti tags (Floy Tag and Manufacturing, Inc., Seattle, Wash., Model FH 69A) were tested on some dolphins captured from April through June 1976. The attachment technique was similar to that described by Evans et al. (1972), except that the tags were applied to animals in a stretcher. Natural Marks Some dolphins had disfigured or uniquely shaped dorsal fins. A photo catalog of these recognizable untagged animals was compiled as a reference for field identification. RESULTS Nine hundred ten tagged dolphins were sighted; 781 were identifiable, and 129 others were not. When field identification was uncer- tain, photographs of combinations and locations of tags or tag remnants were often examined to verify individual identities. A compilation of tagging and sighting results is presented in Table 1. Radio Tags Ten dolphins were radio tagged and tracked for up to 22 d (Table 2). Eight of these were later recaptured and examined. In five instances, the saddle was lost, apparently because the bolt ripped through the fin (for example, see Figure IB). Fin damage was apparent 3 to 6 wk after tagging by which time saddles no longer fit snugly over the leading edge of the fin. When loosened, the saddles titled backwards creating an obvious drag; this shifting caused the bolts to migrate dorsoposteriorly. When RT-8 was re- captured after wearing a transmitter for 22 d, the two bolt holes had not healed nor appeared infected. The forward bolt had migrated dor- soposteriorly about 1.5 cm (Fig. ID), and the saddle was fouled with algal growth and mono- filament line. When RT-9 was recaptured after 46 d, the saddle and rear bolt were missing, but the front bolt was still present but bent, with part of the dissolving nut attached. The partially healed wounds appeared discolored and necrotic, but showed no obvious signs of infection. Only RT-6 showed no fin damage from the radio tag, but the tag (with malfunctioning transmitter) was removed <8 h after attachment. Two dolphins, RT-9 and RT-10, developed aberrant swimming behavior after 10 and 17 d, respectively. Both animals were observed to respire without bringing the dorsal fin to the surface in a typical cetacean rolling motion, although each could move rapidly under water. Evaluation of the problem was impossible because RT-9 evaded recapture attempts during this period, and RT-10 was not sighted during capture operations. One animal, RT-7, died 17 d after tagging, apparently of causes unrelated to the radio tag. Necropsy results implicated pulmonary damage from parasitism as a cause of death. It could not be determined if the capture-tagging process contributed to the cause of death. Tissue autolysis precluded histopathological examina- tion, and no parasites were found. Table 2.— Radio tagging results. Tag Dolphin Dolphin Date Duration of Probable reason for no. Tag description sex length (cm) attached transmission cessation of transmission RT-1 Single cylinder; forward spring antenna Male 251 29 Jan. 1975 2h Water leak (?) RT-2 Single cylinder; forward spring antenna Male 210 28 Apr 1975 5d Broken antenna RT-3 Twin cylinder; aft spring antenna Male 249 15 Jun. 1975 20 h' Seawater switch failure (?) RT-4 Twin cylinder; aft flexible antenna Female 252 1 Aug. 1975 6d2 Unknown RT-5 Twin cylinder; aft flexible antenna Female 257 2 Oct 1975 7d3 Seawater switch failure (?) RT-6 Twin cylinder; aft flexible antenna Male 226 15 Dec 1975 7h Seawater switch malfunction; transmitter removed RT-7 Twin cylinder; aft flexible antenna Male 239 14 Feb 1976 17d Functioning transmitter removed from dead dolphin after 21 d RT-8 Twin cylinder; aft flexible antenna Male 221 15 Apr. 1976 22 d Functioning transmitter removed because of fin damage RT-9 Twin cylinder; aft flexible antenna Female 256 8 May 1976 lOd Unknown. Dolphin did not bring fin above the surface RT-10 Twin cylinder; aft flexible antenna Female 250 9 June 1976 17d Unknown. Dolphin did not bring fin above the surface 'inconsistent signals during the last 6 h direction finder malfunction after 6 d inconsistent signals during the last 3 d 139 FISHERY BULLETIN: VOL. 80. NO. 1 Visual Tags Sixteen single bolt tags were attached between January and December 1975. One was lost within seconds, and three others were lost within 24 h. Two tags had twisted after 2 mo, damaging the fin and requiring removal of the tag. Another tag was believed to have ripped through the fin of a third animal. Two recaptured dolphins had bolt migration scars, and the tags were lost. Of 32 single bolt tags identified in the field, only 3 were sighted more than 2 wk after tagging. From December 1975 through May 1976, 19 dolphins were tagged with double bolt tags. Tags were identified on free-ranging dolphins 187 times through July of 1976, and one tag was sighted 2 mo after attachment. Broken tags were observed eight times, and nine sightings were unidentified due to algae and barnacle fouling (Fig. 2D). Several tags were observed to have only the upper anterior edges broken, implying that breakage was from physical contact. During recaptures, four intact tags were re- moved because barnacles on the inner surface of the tag caused skin abrasions. Six broken tags were removed. Bolt migration was not as common as with single bolt tags, probably because of the stability offered by the rear bolt. Although none of the bolt wounds appeared fully healed, none appeared infected when the animals were recaptured and examined. Visual tags were often discernible up to 200 m away. The numerals were rarely readable at distances >50 m, but even broken tags, tag bolts, and tag scars were useful for identification of some dolphins. Freeze Brands Freeze brands were recognizable on marked animals at distances of <30 m, although photographic analysis was often necessary to confirm identification. Some brands were difficult to identify because they were incom- plete or because of the relatively poor color con- trast of the brand against the skin (Figs. ID, 2C). One of the dolphins captured by Irvine and Wells (1972) in March 1971 and freeze branded (on both sides of the dorsal fin) was captured again in December 1975. The animal had a readable freeze brand on only one side of the fin. On another dolphin branded in the same manner in March 1971 and additionally recognizable because of a deformed lower jaw, the brand was readable in May 1971 (Evans et al. 1972), butthe brand was no longer visible upon recapture in February 1976. Roto Tags From February 1976 through July 1976, 53 Roto tags were placed on 38 dolphins, including 3 animals released with 2 tags. Roto tags were known to be lost from 17 animals and were replaced on 10 of them. A healed indented notch on the trailing edge of the fin was the only evidence of tag loss. Two Roto tags were replaced due to barnacle fouling on the inner surfaces. Brown algae and/or barnacles obscured the tag numbers on most recaptured dolphins, but the tags were still readable on close examination. Roto tag color could be observed from up to 70 m in calm seas. When examined photographi- cally, position of the tag on the fin or placement in relation to other tags or marks helped verify identity. No dolphins were identified exclusively with Roto tags. Spaghetti Tags Seventeen spaghetti tags were attached to 13 dolphins, including 4 dolphins initially released with two tags. None of the animals reacted noticeably to the attachment process. Six tags were missing from four animals re- captured 10 wk after tagging. Three tags were removed from three other dolphins because the entry wounds appeared to be festering. Animals that had lost their tags bore healed but discolored scars that were similar in size to the festering entry wounds described above. No scratches or other evidence that the dolphins may have attempted to remove the tags by rubbing were noted. The wounds, up to 1.9 cm in diameter, apparently were created by movement of the base of the tag streamer on the skin. One spaghetti tag was observed in May 1977, 345 d after attachment. Several orange colored spaghetti tags became faded within 4 wk, an observation not reported by other investiga- tors. Natural Marks Twelve untagged dolphins with recognizable natural marks were identified a total of 87 times. Photographs of an individual taken first in 1970- 71, then during this study in 1976, and by Wells 140 IRVINE ET AL: AN EVALUATION OF TAGGING CETACEANS et al.6 in 1980 suggest that natural marks are relatively permanent. DISCUSSION The most obvious shortcoming of tags attached to the dorsal fin was the short longevity. Water drag, tissue rejection, and attempts by dolphins to shed tags may have contributed to tag loss and fin damage. We had hoped that tissue would grow tightly around the bolt sheaths and insulate the wound from bolt-induced tissue irritation; however, healing apparently never occurred while bolts were in place. Since tag wounds did not heal, different attachment methods or new designs are needed. Transmitter packages on two killer whales, Orcinus orca, were held for 6 mo by pins implanted diagonally to the plane of the leading edge of the fin (Erickson7), and may offer an alternative method of attachment. The relatively larger fin of a killer whale (vs. a dolphin) may, however, have increased chances of success. Carbon bolts attach human prosthetic devices,8 and are another attachment method yet to be tested on marine mammals. Radio tags have proved useful to study the ecology of small odontocetes (Evans 1971, 1974; Evans et al. 1972; Gaskin et al. 1975; Wursig 1976), but the configuration used in this study is not recommended for use on T. trwneatus. The fin damage, premature transmitter loss, and unusual swimming behavior which we ob- served, may influence study results. These factors have not been previously documented. Radio tags caused no obvious behavioral effects during captive tests on Delphinus delphis (Martin et al. 1971). In field studies, however, the radio tagged animals have been infrequently sighted and never recaptured, so possible long- term effects of the tags on the animals are unknown. 6Wells, R. S.. M.D. Scott, A. B. Irvine, and P. T. Page. 1981. Observations during 1980 of bottlenose dolphins, Tursiops truncatus, marked during 1970-1976, on the west coast of Florida. Report to National Marine Fisheries Service, Con- tract No. N A80-GA-A-195, 21 p. Available Center for Coastal Marine Studies. University of California, Santa Cruz, CA 95064. 7Erickson, A. W. 1977. Population studies of killer whales {Orcinus orca) in the Pacific Northwest: a radio-marking and tracking study of killer whales. Available National Techni- cal Information Service, 5285 Port Royal Road, Springfield, VA 22151 as PB-285615, 34 p. "Anonymous. 1977. The application of high purity carbon technology for Rehabilitation Engineering Center at Rancho Los Amigos Hospital. John F. Kennedy Space Center (NASA) Report SED-77-100, 146 p. Kennedy Space Center. Cape Kennedy, FL 32899. Freeze branding proved the most durable marking method. The variability of marks on the animals captured 5 yr after branding indicates that tissue response to the branding process is inconsistent. Freeze brands have remained readable after several years in captivity, but optimal coolants, application times, and pres- sures have yet to be determined (Cornell et al.9). Our resighting, after almost 5 yr, is the longest yet reported. Twenty-one of 26 of the dolphins originally tagged in this study were observed during 1980 and had freeze brands that were either completely readable in photographs or were legible enough to confirm identifications indicated by other characteristics (Wells et al. footnote 6). Maximum longevity of freeze brands is still unknown, however. The comparatively high incidence of spaghetti tag loss reported here is noteworthy because this tagging method has been previously used with no reports of rejection or abscess (Sergeant and Brodie 1969; Evans et al. 1972; Perrin et al. 1979). Recent tests on captive dolphins have shown, however, that tag loss may be related to tissue rejection, attachment impact, or to the angle of dart entry (Jennings10). Recognition of natural marks provided useful supplementary information in our study, and has been used to study bottlenose dolphins in Texas (Gruber 1981; Shane and Schmidly11) and Argentina (Wursig and Wursig 1977). Close approach to the animals is usually required for field recognition, however, and we felt that photoidentification was necessary to verify most of our sightings. This tagging study has demonstrated that repeated sightings of tagged dolphins are possible and can provide substantial amounts of information about the behavioral ecology of small cetaceans (Wells et al. 1980; Irvine et al. 1981). Selection of the tags to be used should, however, involve consideration of tagging and resighting effort, tag visibility and durability, and potential harm to the tagged animal. Visual Cornell, L. H., E. D. Asper. K. Osborn, and M. J. White. 1979. Investigations on cryogenic marking procedures for marine mammals. Available National Technical Informa- tion Service, 5285 Port Royal Road. Springfield, VA 22151 as PB-291570, 24 p. 10J. G. Jennings, Fishery Biologist, Southwest Fisheries Center, National Marine Fisheries Service. NOAA, P.O. Box 271, La Jolla, CA 92038, pers. commun. October 1978. "Shane, S. H., and D. J. Schmidly. 1978. Population biology of Atlantic bottlenose dolphin. Tursiops truncatus, in Aransas Pass, Texas. Available National Technical Informa- tion Service, 5285 Port Royal Road, Springfield, VA 22151 as PB-283393, 130 p. 141 FISHERY BULLETIN: VOL. 80. NO. 1 tags are most detectable, but are not durable and may damage the dorsal fin tissues. Freeze brands are durable, but not highly visible. Roto tags are of limited use for field identification except in unusual close range situations (e.g., Norris and Pryor 1970), although a combination color and location of the tag can identify an individual. For free-ranging dolphins, spaghetti tags are the only current tagging option, but identification of these tags usually requires collection of the animal. If animals are to be captured initially, combinations of tag types and use of natural marks can provide effective field identification. Although radio tagging and tag or mark identifications are valuable tools for ecological studies of cetaceans, more development and testing of tags and attachment techniques are needed. Investigators should realize that tagging methods which are successful on one species may not work well on another species. Prior to field studies, tags should be tested on the species to be studied. We also recommend intensive follow-up sighting surveys to maxi- mize data return and to determine the effect of tags and marks on free-ranging animals. ACKNOWLEDGMENTS This project was supported by Marine Mammal commission Contract MM4AC004 to J. H. Kaufmann, W. E. Evans, D. K. Caldwell, and A. B. Irvine; and Contract MM5AC0018 to Kaufmann, Irvine, and Evans. We are indebted to Clyde Jones and Howard Campbell of the Denver Wildlife Research Center and to Robert Hofman of the Marine Mammal Commission for support and encouragement. We also thank Mike Bogan, Larry Hobbs, Steve Leatherwood, and Galen Rathbun for their constructive comments on versions of the manuscript. Field work and data analysis were greatly assisted by volunteers from New College (University of South Florida) and the University of Florida, to whom we are indebted. We thank G. Marlow and M. Haslette and staff from the St. Petersburg Aquatarium for dolphin collections through October 1975, and Snake Eubanks and Joe Mora for their fine work thereafter. We also thank John Morrill (New College, Environmental Studies Program) for providing office space, Mary Moore and Carol Blanton for furnishing dock space, Fred Worl for supplying us with liquid nitrogen, and especially Fran and Jack Wells for providing floor space and much patience to the dolphin trackers, who regularly invaded their home. Estella Duell and Joan Randell typed the manuscript. LITERATURE CITED Asper, E. D. 1975. Techniques of live capture of smaller cetacea. J. Fish. Res. Board Can. 32:1191-1196. Evans, W. E. 1971. Orientation behavior of delphinids: radio tele- metric studies. Ann. N.Y. Acad. Sci. 188:142-160. 1974. Radio- telemetric studies of two species of small odontocete cetaceans. In W. E. Schevill (editor). The whale problem: A status report, p. 385-394. Harv. Univ. Press, Camb., Mass. Evans, W. E., J. D. Hall, A. B. Irvine, and J. S. Leatherwood. 1972. Methods for tagging small cetaceans. Fish. Bull., U.S. 70:61-65. Gaskin, D. E., G. J. D. Smith, and A. P. Watson. 1975. Preliminary study of movements of harbor por- poises (Phocoena phocoena) in the Bay of Fundy using radiotelemetry. Can. J. Zool. 53:1466-1471. Gruber, J. A. 1981. Ecology of the Atlantic bottlenose dolphin (Tursiops truncal us) in the Pass Cavallo area of Matagorda Bay, Texas. M.S. Thesis, Texas A&M Univ., College Station, 182 p. Irvine, A. B., M. D. Scott, R. S. Wells, and J. H. Kaufmann. 1981. Movements and activities of the Atlantic bottle- nose dolphin. Tursiops truncatus, near Sarasota, Florida. Fish. Bull. U.S. 79(4):67 1-688. Irvine, A. B., and R. S. Wells. 1972. Results of attempts to tag Atlantic bottlenosed dolphins (Tursiops truncatus). Cetology 13:1-5. Leatherwood, S., and W. E. Evans. 1979. Some recent uses and potentials of radio-telemetry in field studies of cetaceans. In H. E. Winn and B. L Olla (editors), Behavior of marine animals, Vol. 3, p. 1-31. Plenum Press, N.Y. Martin, H., W. E. Evans, and C. A. Bowers. 1971. Methods for radio tracking marine mammals in the open sea. IEEE 1971 Conf. Eng. Ocean Environ., p. 44-49. Nishiwaki, M., M. Nakajima, and T. Tobayama. 1966. Preliminary experiments for dolphin marking. Sci. Res. Whales Inst. Tokyo 20:101-107. Norris, K. S., and K. W. Pryor. 1970. A tagging method for small cetaceans. J. Mammal. 51:609-610. Perrin, W. F., W. E. Evans, and D. B. Holts. 1979. Movements of pelagic dolphins (Stenella spp.) in the eastern tropical Pacific as indicated by results of tagging, with summary of tagging operations, 1969-76. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF- 737, 14 p. Sergeant, D. E., and P. F. Brodie. 1969. Tagging white whales in the Canadian arctic. J. Fish. Res. Board Can. 26:2201-2205. Wells, R. S., A. B. Irvine, and M. D. Scott. 1980. The social ecology of inshore odontocetes. In L. M. Herman (editor), Cetacean behavior, p. 263-317. Wiley Interscience, N.Y. 142 IRVINE ET AL: AN EVALUATION OF TAGGING CETACEANS WURSIG, B. WiJRSIG, B.. AND M. Wi'lRSK;. 197fi. Radio tracking of dusky porpoises (Lagen- 1977. The photographic determination of group size, orhynchus obscurus) in the South Atlantic: preliminary composition, and stability of coastal porpoises ( Tu /slops analysis. ACMRR Scientific Consultation on Marine truncatus). Science (Wash., D.C.) 198:755-756. Mammals. Bergen, Norway, 21 p. 143 NOTES OFFSHORE WINTER MIGRATION OF THE ATLANTIC SILVERSIDE, MENIDIA MENIDIA ' The Atlantic silverside, Menidia menidia, is an abundant fish in coastal waters of the western Atlantic ranging from Florida to Nova Scotia. During spring, summer, and fall, the habitat of M. menidia includes intertidal creeks, marshes, and the shore zone of estuaries and embayments (Hildebrand and Schroeder 1928; Bigelow and Schroeder 1953). In such areas, ichthyofaunal surveys often cite M. menidia as the most numer- ous species encountered (Mulkana 1966; Rich- ards and Castagna 1970; Chestmore et al. 1973; Briggs 1975; Anderson etal. 1977; Hillmanetal. 1977). The entire life cycle of M. menidia is com- pleted in 1 yr. Reproduction occurs in the spring, juveniles grow rapidly during the summer and reach full adult size by late fall. However, con- siderable uncertainty exists concerning winter ecology and habitat. In populations from Chesa- peake Bay northward, Atlantic silversides are rare or absent from the shallow waters of the shore zone in midwinter ( Warfel and Merriman 1944; Bayliff 1950; Hoff and Ibara 1977; Conover and Ross in press). Hildebrand and Schroeder (1928) and Richards and Castagna (1970) re- ported that M. menidia were captured in mid- winter with bottom trawls in deepwater areas of Chesapeake Bay and deep estuarine channels in eastern Virginia. Catches of M. menidia have also been occasionally reported up to 15 km off- shore (Clark et al. 1969; Fahay 1975). However, Needier (1940) noted that Atlantic silversides could be taken through the ice in Malpeque Bay, P.E.I, (although he presented no data concerning relative seasonal abundance), and investigations in South Carolina found an abundance of M. menidia in intertidal marsh creeks during win- ter (Cain and Dean 1976; Shenker and Dean 1979). Because the Atlantic silverside is an important forage fish (Merriman 1941; Bayliff 1950; Bige- low and Schroeder 1953) and reaches a high level of biomass in the shore zone of marshes and estu- aries (7.8 g/m2 wet weight) (Conover and Ross in 'Contribution No. 73 of the Massachusetts Cooperative Fish- ery Research Unit. press), the winter movement patterns of this an- nual species could represent a significant path- way of energy flow from and/or within estuarine systems. This paper demonstrates that Atlantic silversides migrate offshore in winter, and we discuss aspects of their winter ecology and distri- bution by examining catch records of the bottom trawl survey program of the Northeast Fisheries Center (NEFC) of the National Marine Fisheries Service (NMFS). Methods A modern series of standardized bottom trawl surveys was begun in 1963 by the Bureau of Com- mercial Fisheries (BCF) Woods Hole Laboratory (Grosslein 1969). Initially, fall surveys encom- passed the general range of offshore groundfish stocks of primary interest (i.e., gadoids) and thus was confined to the area between Hudson Can- yon and Nova Scotia and depths from 27 to 366 m. Later, as the goals and emphasis of the survey program expanded to include a wider variety of species, both fall and spring surveys were con- ducted and the sampling area was extended southward to Cape Hatteras (1967). The offshore survey region was stratified into geographic zones based on depth contours and area (Gross- lein 1969). A stratified random sampling design was employed to locate trawl stations within depth strata and the number of stations was allo- cated in proportion to stratum area. A standard No. 36 Yankee bottom trawl with a 1.25 cm stretched mesh cod end liner was towed at each station for 30 min at an average of 3.5 kn; how- ever, spring offshore surveys since 1973 have used the larger No. 41 Yankee trawl. Stations were sampled continuously 24 h/d during cruises. Synoptic bottom trawl surveys in the near- shore environment were begun in 1972 by the NMFS Sandy Hook Laboratory. Early surveys in the inshore region (defined as depth strata of 5-27 m) assessed the technical and geographic feasibility of using offshore sampling gear in waters as shallow as 5 m. Since autumn 1972, inshore surveys have been conducted each fall and spring with summer cruises added in 1977 and a winter cruise in 1978. Of 18 inshore cruises through 1978, most (17) included the region from FISHERY BULLETIN: VOL. 80. NO. 1. 1982 145 Cape Cod to Cape Hatteras, 4 included the Gulf of Maine, and 7 included the region from Cape Hat- teras to Cape Fear. During 1972-75, all inshore surveys used either a % modified Yankee trawl or the No. 36 Yankee trawl. Since 1976, a No. 41 Yankee trawl has been used. Towing procedures were the same as described for offshore surveys. The seasonal and geographic variation in the ex- tent of inshore surveys reflects their evolution as a monitoring tool. Capture data employed in this study included date, location, time, depth, surface and bottom temperatures, and number collected. Catch loca- tions from all surveys were plotted to the nearest 10' of latitude and longitude on depth contour maps by season. Surface and bottom tempera- tures and depth frequencies were plotted for each occasion that M. menidia were captured. Results Standard bottom trawl tows at 2,057 stations from inshore surveys collected 979 M. menidia at 107 sites (5.2% occurrence), while offshore tows at 10,209 stations captured 464 M. menidia at 72 sites (0.7% occurrence). Because sampling effort by season was not uniform with respect to in- shore and offshore surveys or geographic zones, analysis of catch per effort data (catch fre- quency) was compiled by month for inshore and offshore surveys in three geographic regions (i.e., Gulf of Maine-Georges Bank, Cape Cod- Cape Hatteras, Cape Hatteras-Cape Fear). In the inshore surveys, effort was primarily concen- trated in the Cape Cod-Cape Hatteras region, where the percent frequency of capture of M. menidia was negligible in summer, increased in November (4.9%), peaked in January (34.3%), and declined through the spring (Table 1). Num- ber of stations sampled in the inshore surveys of the Gulf of Maine-Georges Bank and Cape Hat- teras-Cape Fear regions was inadequate for monthly or regional comparisons. In offshore surveys, the monthly pattern of occurrence of M. menidia was similar to that of inshore surveys; catch frequency was zero in summer and autumn, peaked in January (3.8%) in the Gulf of Maine-Georges Bank and in February (11.2%) in the Cape Cod-Cape Hatteras regions, and de- clined thereafter (Table 2). These data support the hypothesis of an offshore winter migration. The geographic distribution of catches by sea- son (Fig. 1) indicates that most collections are confined to a zone within roughly 50 km of the shoreline and within the 40 m depth contour. One collection occurred 170 km from the mainland. Although most catches appear to occur between Cape Cod and Cape Hatteras and especially in the New York Bight, sampling effort among in- shore surveys was much greater in this region as previously noted (Table 1). Although only four collections of M. menidia were observed south of Cape Hatteras (two off Cape Fear, S.C., and two off Cape Romain, S.C.; not appearing in Figure 1), no offshore or inshore surveys were conducted south of Cape Hatteras in winter when catches might be expected. Surface temperatures recorded at 141 of the inshore and offshore stations where Atlantic silversides were captured ranged from l°to22°C, but 86% of these were within a range of 2°-6°C (x = 4.9°C; Fig. 2A). Bottom temperatures re- corded at 135 collecting sites revealed a similar Table 1.— Percent frequency of occurrence of Men idia men id- ia at stations sampled in the inshore survey region (depth strata of 5-27 m) of the NMFS bottom trawl survey program over the continental shelf of eastern North America. Catch sta- tistics are from cruises conducted from 1972 to 1979 and are pooled by month and area of capture. The number in paren- theses is the total number of stations sampled. Gulf of M aine and Cape Cod- Cape Hatteras- Month Georges Bank Cape Hatteras Cape Fear Jan. — (0) 34.3 (70) 0.0 (2) Feb. — (0) — (0) — (0) Mar — (0) 21.4 (206) 0.0 (18) Apr 0.0 (7) 9.6 (240) 00 (25) May — (0) 0.7 (141) — (0) June — (0) 00 (33) — (0) July 0.0 (3) 0.0 (41) 00 (47) Aug 0.0 (80) 0.5 (216) 00 (31) Sept — (0) 0.0 (150) 0.0 (82) Oct. — (0) 0.2 (398) 00 (40) Nov. 0.0 (10) 4.9 (183) 9 1 (22) Dec. — (0) 0.0 (6) 33.3 (6) Table 2.— Percent frequency of occurrence of Men idia men id- ia at stations sampled in the offshore survey region (depth strata 27-366 m) of the NMFS bottom trawl survey program over the continental shelf of eastern North America. Catch sta- tistics are from cruises conducted from 1963 to 1979 and are pooled by month and area of capture. The number in paren- theses is the total number of stations sampled. Month Gulf of Maine and Georges Bank Cape Cod- Cape Hatteras Cape Hatteras- Cape Fear Jan. 38 (159) — (0) — (0) Feb. 04 (221) 11.2 (98) — (0) Mar 00 (386) 43 (925) 0.0 (18) Apr. 02 (1.270) 1.5 (518) — (0) May 0.0 (456) 0.0 (2) — (0) June — (0) — (0) — (0) July 0.0 (310) 0.0 (114) 0.0 (41) Aug. 00 (522) 0.0 (336) — (0) Sept — (0) 0.0 (344) 00 (9) Oct. 0.0 (1,265) 0.0 (1.219) — (0) Nov 0.0 (1.628) 00 (154) — (0) Dec 00 (155) 0.0 (55) — (0) 146 LONG ISLAND CHESAPEAKE BAY GEORGES BANK O 9 . FALL * WINTER • SPRING O 50 IOO Km \CAPE V1ATTERAS Figure 1. — Location of Atlantic silverside catches by season during inshore and offshore bottom trawl surveys of the National Marine Fisheries Service, Cape Hatteras to Nova Scotia, 1963-79 (fall = Sept.-Nov.; winter = Dec.-Feb.; spring = Mar.-May). Seven catch locations do not appear: Two off the northern coast of Maine, one off the outer coast of southern Nova Scotia, two off Cape Fear, S.C., and two off Cape Romain, S.C. pattern: the majority (86%) of all Atlantic silver- side collections occurred within a range of 2°-6° C (x = 5.1°C; Fig. 2B). These data indicate that M. menidia occur over the continental shelf pri- marily under winter temperature conditions after fall overturn when temperatures are iso- thermal. The distribution of Atlantic silversides with respect to depth was examined by comparing catch frequency to depth of capture in 5 m inter- vals. The majority of catches occurred in waters <50 m deep (86%), and 42% of all catches were in depths of 10-20 m (Fig. 3). Maximum depth of capture was 126 m. Some aspects of the winter ecology of Atlantic silversides while at sea can be revealed by exam- ining their vertical distribution in the water column. Vertical distribution was inferred from diel variations in capture times partitioned in- to six 4-h intervals. Chi-square analysis com- paring catch frequency in each time interval to all others combined showed that catch frequen- cies during night intervals (2000-0359 h) were significantly less than expected (P<0.01; Table 3), while catch frequencies during midday inter- vals (0800-1559 h) were significantly greater than expected (P<0.01). Apparently, M. menidia occurred nearer the bottom during daylight hours and hence were more susceptible to bot- tom trawl tows conducted during the day. These observations indicate that while at sea, Atlan- tic silversides are vertical migrators like other planktivores such as Atlantic herring, Ciupea harengus, (Blaxter 1975) and American shad, Alosa sapidissima, (Neves and Depres 1979). 147 o c 40 r 30 20 10 < - -- 1 2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 SURFACE TEMPERATURE °C ° 40 r = 30 a. < 20 >- U 5 lO o .. I-... 10 20 30 40 50 60 70 80 90 100 120 DEPTH ( m ) 140 Figure 3.— Water depths at which Atlantic silversides were captured during inshore and offshore bottom trawl surveys of the National Marine Fisheries Service over the eastern North American continental shelf, 1963-79. >■ U o 50 r 40 30 20 10 B _u_u_ 1 2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 BOTTOM TEMPERATURE °C Figure 2.— Water temperatures at stations where Atlantic silversides were captured during inshore and offshore bottom trawl surveys conducted by the National Marine Fisheries Service during 1963-79 over the eastern North American con- tinental shelf. A. Surface temperatures (n = 141). B. Bottom temperatures (w = 135). Discussion The results of this study demonstrate that populations of M. menidia north of Cape Hat- teras undergo an offshore winter migration from inland to inner continental shelf waters. Atlantic silverside winter habitat probably also includes Table 3.— Chi-square analysis of diel variations in catch fre- quencies of Atlantic silversides in combined inshore (5-27 m) and offshore (27-366 m) trawl surveys conducted by NMFS, 1963-79, over the continental shelf of eastern North America. Time of capture (est.) Tows Menidia capt jring (no.) Observed Expected 2 X 0000-0359 11 298 14.3"* 0400-0759 28 298 0.1 0800-1159 46 298 10.5*" 1200-1559 43 298 7.0" 1600-1959 35 298 1.1 2000-2359 16 298 7.7" Totals 179 179 " P<0 01 "*P<0 005 deep inland waters not sampled by NMFS sur- veys, as Hildebrand and Schroeder (1928) and Richards and Castagna (1970) have noted. Since the lower lethal temperature for M. menidia in short-term experiments was 1°-2°C (Hoff and Westman 1966; Conover unpubl. data), the off- shore migration may be promoted by potentially stressful or lethal low water temperatures in shallow inland waters during midwinter. Con- over and Ross (in press) and Warfel and Merri- man (1944) found that Atlantic silversides leave the New England shore zone in November as water temperatures drop to about 6°-8°C. The timing of Atlantic silverside disappearance from shallow inland waters corresponds closely with their appearance in deeper offshore waters. If the offshore migration of Atlantic silver- sides is primarily motivated by low temperature stress, than offshore movements in warmer waters, such as south of Cape Hatteras, would not be expected. Even though our data cannot 148 address this question directly, evidence from ich- thyofaunal surveys in South Carolina indicate that M. menidia abundance remains high in intertidal creeks (Cain and Dean 1976; Shenker and Dean 1979) and in the surf zone of barrier beaches (Anderson et al. 1977) throughout win- ter. The relative abundance of Atlantic silversides over the continental shelf is difficult to judge from this study, since bottom trawling is a rela- tively ineffective method for catching small pelagic fish such as M. men idia (see Conover and Ross in press). In addition, the low overall catch frequency for M. menidia reported herein is pri- marily due to the relatively small number of sta- tions sampled in midwinter when maximum catches might be expected. Neves and Depres (1979) used similar NMFS offshore survey data on a larger pelagic species, the American shad, and reported catches at 527 of the 10,435 stations sampled (5.05%). Considering the methods used, the percent occurrences of M. menidia in the in- shore and offshore surveys of the mid-Atlantic during midwinter (34 and 11%, respectively) may indicate considerable abundance. In a previous study, Conover and Ross (in press) showed that Atlantic silversides reach a high level of biomass during late fall in marsh areas and also suffer a high rate of winter mor- tality (90-99%). Their hypothesis that winter movement and mortality patterns of M. menidia represent a one-way export of biomass from the shore zone of bays, marshes, and estuaries to off- shore communities is strengthened by this study. The causes of high winter mortality experienced by Atlantic silversides at northern latitudes are unknown but conceivably could include preda- tion and perhaps physiological stress imposed by the migration itself and prolonged exposure to cold temperatures. Atlantic silversides could be an important forage fish over the inner continen- tal shelf, but it will require an analysis of the food habits of offshore fishes in midwinter to address this question. Acknowledgments The authors wish to thank the staff of the Re- source Surveys Investigation Section and other members of the staff at NMFS, Woods Hole, who have participated in the cruises, and B. E. Brown and M. R. Ross for reviewing the manuscript. The senior author also received support from the Graduate School of the University of Massa- chusetts and the Massachusetts Cooperative Fishery Research Unit, which is jointly spon- sored by the Massachusetts Division of Marine Fisheries, the Massachusetts Division of Fish and Wildlife, the University of Massachusetts, and the U.S. Fish and Wildlife Service. Literature Cited Anderson, W. D., Jr., J. K. Dias, R. K. Dias, D. M. Cupka, and N. A. Chamberlain. 1977. The macrofauna of the surf zone off Folly Beach, South Carolina. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-704, 23 p. Bayliff, W. H., Jr. 1950. The life history of the silverside Menidia menidia (Linnaeus). Chesapeake Biol. Lab. Publ. 90, 27 p. Sol- omons Island, Md. BlGELOW, H. B., AND W. C. SCHROEDER. 1953. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv., Fish. Bull. 53, 577 p. Blaxter, J. H. S. 1975. The role of light in the vertical migration of fish— a review. In G. C. Evans. R. Bainbridge, and O. Rack- ham (editors), Light as an ecological factor: II, p. 189- 210. Blackwell Sci. Publ., Oxf. Briggs, P. T. 1975. Shore-zone fishes of the vicinity of Fire Island In- let, Great South Bay, New York. N. Y. Fish Game J. 22: 1-12. Cain, R. L., and J. M. Dean. 1976. Annual occurrence, abundance and diversity of fish in a South Carolina intertidal creek. Mar. Biol. (Berl.) 36:369-379. Chesmore, A. P., D. J. Brown, and R. D. Anderson. 1973. A study of the marine resources of Essex Bay. Mass. Div. Mar. Fish. Monogr. Ser. 13, 38 p. Clark, J., W. G. Smith, A. W. Kendall, Jr., and M. P. Fahay. 1969. Studies of estuarine dependence of Atlantic coastal fishes. U.S. Bur. Sport Fish. Wildl. Tech. Pap. 28, 132 P- Conover, D. O., and M. R. Ross. In press. Patterns in seasonal abundance, growth and biomass of the Atlantic silverside, Menidia menidia, in a New England estuary. Estuaries. Fahay, M. P. 1975. An annotated list of larval and juvenile fishes cap- tured with surface-towed meter net in the South Atlan- tic Bight during four RV Dolphin cruises between May 1967 and February 1968. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-685, 39 p. Grosslein, M. D. 1969. Groundfish survey program of BCF Woods Hole. Commer. Fish. Rev. 31(8-9):22-30. Hildebrand, S. F., and W. C. Schroeder. 1928. Fishes of Chesapeake Bay. Bull. U.S. Bur. Fish. 43(1), 366 p. Hillman, R. E., N. W. Davis, and J. Wennemer. 1977. Abundance, diversity, and stability in shore-zone fish communities in an area of Long Island Sound affected by the thermal discharge of a nuclear power station. Estuarine Coastal Mar. Sci. 5:355-381. 149 Hoff, J. G., AND R. M. Ibara. 1977. Factors affecting the seasonal abundance, com- position and diversity of fishes in a southeastern New England estuary. Estuarine Coastal Mar. Sci. 5:665- 678. Hoff, J. G., and J. R. Westman. 1966. The temperature tolerances of three species of ma- rine fishes. J. Mar. Res. 24:131-140. Merriman, D. 1941. Studies on the striped bass (Roccus saxatilis) of the Atlantic coast. U.S. Fish Wildl. Serv., Fish. Bull. 50 (35), 77 p. MULKANA, M. S. 1966. The growth and feeding habits of juvenile fishes in two Rhode Island estuaries. Gulf Res. Rep. 2:97-168. Needler, A. W. H. 1940. A preliminary list of the fishes of Malpeque Bay. Proc. Nova Scotia Inst. Sci. 20:33-41. Neves, R. J., and L. Depres. 1979. The oceanic migration of American shad, Alosa sapidissima, along the Atlantic coast. Fish. Bull., U.S. 77:199-212. Richards, C. E., and M. Castagna. 1970. Marine fishes of Virginia's eastern shore (inlet and marsh, seaside waters). Chesapeake Sci. 11:235-248. Shenker, J. M., and J. M. Dean. 1979. The utilization of an intertidal salt marsh creek by larval and juvenile fishes: Abundance, diversity and temporal variation. Estuaries 3:154-163. Warfel, H. E., and D. Merriman. 1944. Studies on the marine resources of southern New England. I. An analysis of the fish population of the shore zone. Bull. Bingham Oceanogr. Collect., Yale Univ. 9(2):1-91. David O. Conover Massachusetts Cooperative Fishery Research Unit Department of Forestry and Wildlife Management University of Massachusetts, Amherst, MA 01003 Present address: Marine Sciences Research Center State University of New York at Stony Brook Stony Brook, NY 11 79 J, Steven A. Murawski Northeast Fisheries Center Woods Hole Laboratory National Marine Fisheries Service, NOAA Woods Hole, MA 025b3 GROWTH DURING METAMORPHOSIS OF ENGLISH SOLE, PAROPHRYS VETULUS Among fishes, the period of transformation from the larval to adult form is marked not only by changes in morphology, behavior and in some species, habitat (Jakobczyk 1965; Sale 1969; Hoar 1976; Marliave 1977), but in growth rate as well. Ontogenetic changes in growth have not been well documented principally because a method for determining age of larvae and juve- niles has not, until recently, been available. The discovery of daily growth rings on otoliths has made possible the precise determination of age, in days, of larval and juvenile fishes (Brothers et al. 1976). Changes in growth rates during differ- ent life history stages which could be correlated with behavioral and habitat changes were ob- served in the French grunt, Haemulonflavoline- atum (Brothers and MacFarland in press). Struhsaker and Uchiyama (1976) observed an inflection point in the age-length plot of larval and juvenile nehu, Stolephorus purpureus, indi- cating a change in growth rate. This inflection point corresponded with the size when body depth began to increase in proportion to the length of the fish, but not with changes in diet or habitat that occur over the course of develop- ment. Age estimates based on counts of otolith growth increments have now allowed us to de- termine growth during metamorphosis of the pleuronectid Parophrys vetulus Girard. Methods The results of this study are based on the stan- dard length (SL) in millimeters and age in days of 127 pelagic larvae and transforming individ- uals of P. vetulus ranging 10-20 mm SL, and 106 benthic 0-age individuals from 18 to 35 mm SL. Pelagic specimens were collected off Newport, Oreg. (approximately lat. 44°37'N, long. 124°06' W), from November 1977 through June 1978 with a 70 cm bongo net with 0.505 mm Nitex1 mesh (see Laroche et al. 1982 for sampling de- tails). Benthic P. vetulus were collected off Moolach Beach, Oreg., 10 km north of Newport, during September 1978 through September 1979 with a 1.5 m wide beam trawl (7 mm stretch mesh). The removal and mounting of saccular otoliths from larvae followed the methods outlined in Methot and Kramer (1979) except that otoliths were mounted on rectangular glass cover slips to improve the optical properties of the prepara- tion. Otolith growth increments were counted at 800 or 1250 X under bright-field illumination. A complete description of the counting technique and validation of the daily periodicity of the rings can be found in Laroche et al. (1982). ■Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 150 FISHERY BULLETIN: VOL. 80. NO. 1, 1982 Otoliths from the benthic individuals were re- moved, mounted on glass microscope slides and ground to a sagittal thin section through the nu- cleus using 600 grit carborundum paper. Incre- ment counts on these ground sections were made at 250-400 X using either bright-field or polar- ized illumination. The age of each fish was defined as the number of daily otolith growth increments plus five, the age at first increment formation for this species (Laroche et al. 1982). In order to characterize changes in body form during metamorphosis, body depth, snout to anus length, lower jaw length, and the distance of migration of the left eye, of 65 larvae and 0-age benthic specimens were measured to the nearest 0.1 mm. Results and Discussion A plot of the length-at-age of P. vetulus larvae and juveniles taken in both pelagic and benthic collections exhibits a prominent plateau between 60 and 120 d of age and between 18 and 22 mm SL (Fig. 1). This plateau shows that there is a period of reduced growth in body length when these fish are undergoing metamorphosis. Plots of body depth and snout to anus length versus standard length both have a well-defined inflec- tion point between 18 and 22 mm SL (Figs. 2, 3). Other morphometric measurement plots (lower jaw length and distance of migration of the left eye) (not shown) also contain an inflection between 18 and 22 mm SL, but less clearly. Changes in body morphology during the growth plateau are illustrated by examining a develop- mental series just prior to metamorphosis (Fig. 4A) and comparing individuals of similar sizes within the plateau (Fig. 4B). Changes in body depth are most pronounced, but eye migration and changes in head morphology are also evi- dent. The definition of two distinct growth stanzas separated by a plateau conforms to several of the criteria outlined by Ricker (1979). However, as he points out, the timing of the inflection points on the size-at-age plot depends on whether length or weight is measured. We have not measured weight in this study. Due to the shape of the length-at-age plot we might expect the length-weight relationship for this species to be complex in form over the inter- val considered here. The age of 18-20 mm SL P. vetulus, taken in 1 ! 1 1 i i 1 1 1 1 O »o O E 30 o O O O £ OOO o o »do o QDOD 0% - O (DO O O o> O O CO O i. O 20 mm ESL, dial calipers were used. The reason for using ENL and ESL rather than standard length (SL) was that in most specimens the sword (bill) was damaged and standard length measurement would have been inaccurate. A series of 220 Xiphias gladius from 3.7 mm ENL to 668 mm ESL captured with plankton nets, or by night light and dip netting, or taken from dolphin fish, Coryphaena hippurus, stomachs were cleared and stained for cartilage and bone by a combined method after Taylor (1967) and Dingerkus and Uhler (1977). Mea- surements of the specimens were taken after clearing and staining, because almost all Xiphias were twisted before clearing but were easily straightened after the clearing. Although we had many smaller sized Xiphias larvae, we could have used more juveniles for our study (Fig. 1). Most of our specimens were col- lected in the Gulf of Mexico but a few were caught in the Caribbean Sea and Atlantic Ocean (Fig. 2). All specimens were examined in 100% glycerin and under 100X to 150X magnification with a high-quality binocular dissecting microscope. Cartilage was viewed with the help of alcian blue stain, but cartilaginous structures that some- times stained weakly or not at all were viewed by manipulating light intensity and the angle of the substage mirror. Onset of ossification was deter- mined by light (pink) alizarin uptake, usually around the margin of a structure. Illustrations were drawn with the help of a camera lucida. The osteological terms used in this study follow those used by Gosline (1961a, b), Nybelin (1963), Gibbs and Collette (1967), Monod (1968), and Potthoff (1975, 1980). Counts of pterygiophores and fin rays include very small vestigial structures. PECTORAL FIN The pectoral fin rays in Xiphias were the first of all fin rays to begin development. The first rays were present at 4.8-5.6 mm ENL (Tables 1, 2). Development of the rays started on the dorsal border of the larval fin blade and proceeded in a Figure 1.— Length-frequency distribution of cleared and stained Xiphias gladim used for this study. 131 188 225 668 4 5 5.5 6.5 7.5 8.5 9.5 10 5 115 12 5 13 5 14 5 15 5 16 5 17 5 18 5 19 5 20 5 25 5 35 5 45 5 65 5 LENGTH.mmENLor ESL 162 POTTHOFF and KELLEY: OSTKOLOCICAL DKVKLOPMKNT IN SWORDFISH Figure 2.— Capture localities (black dots) of larval and juve- nile Xiphias glad i us used in this study. A locality may repre- sent more than one capture. rays were still developing, 2 specimens differed by two rays (1.3%) between sides, 63 differed by one ray (40.9%), and 80 Xiphias (57.8%) had the same count on both pectoral fins. Of 20 specimens 19.6-668 mm ESL, which had adult counts, 10 differed by one ray between sides and 10 had the same count on both sides. The position of the pectoral fin in Xiph ias is on the side of larvae but changes during growth to ventrad in adults near the spot where the pelvic fin is located in most Perciformes. Xiphias lacks a pelvic fin and no vestiges of it were found during development (Gregory and Conrad 1937; Leim and Scott 1966; Ovchinnikov 1970; Yasuda et al. 1978). PECTORAL FIN SUPPORTS Table 1. — Summary of fin development sequence in cleared and stained larvae of Xiph tan gladius. PRC = principal caudal rays, SCR = secondary caudal rays. Length ENL or ESL (mm) Fin First appearance of rays All specimens have rays Full complement of rays Number of rays in fully developed fin Caudal PCR SCR Dorsal fin Anal fin Pectoral fin 5.4 5.4 7.8 5.5 5.3 4.8 6.1 6.1 11.6 6.1 6.1 5.6 26.7 8.8-11.0 26.7 8 1-13.9 78-10.6 14.2-196 34-38 17 8-10 dorsal 8-11 ventral 44-49 16-19 16-19 ventral direction. Adult counts of 16-19 rays were first obtained at 13.3 mm ESL and all specimens >19.5 mm ESL had the adult count (N = 20, X= 17.6, SD = 0.89) (Table 2). Pectoral fin ray counts differed for individual specimens between sides. Of 154 specimens 4.6 mm ENL-19.5 mm ESL, in which the pectoral The pectoral rays were directly and indirectly supported by the bones of the pectoral girdle and its suspensorium. In fully developed juveniles the girdle consisted on each side of a scapula and a distal scapular radial (which supported the dorsalmost ray directly and which orginated from scapular cartilage), four large radials (which supported the remainder of the rays directly), a coracoid, and a cleithrum (Figs. 3-5). The scapula was connected to the coracoid by cartilage (Figs. 4, 5). The pectoral suspensorium consisted of a posttemporal, a supracleithrum, and a single postcleithrum. The posttemporal and supracleithrum were connected from the rear of the skull to the lateral side of the posterior process of the cleithrum. The single post- cleithrum extended over the abdominal area and articulated on the medial side of the posterior process of the cleithrum (Figs. 3-5). The pectoral Table 2.— Development of left pectoral fin rays for Xiphias gladius (3.7 mm ENL-225, 668 mm ESL). X = mean, SD = standard deviation. Length, mm ENL or ESL Number of rays 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 SD 3.6-4.5 4.6-5.5 5.6-6.5 6.6-7.5 7 6-8.5 8.6-9.5 9.6-10.5 10.6-11.5 11.6-12 5 12.6-13.5 13.6-14.5 14.6-15.5 15.6-16.5 16.6-17 .5 17.6-18.5 18.6-195 196-668 7 20 2 2 6 2 2 1 — — 1 1 10 1.6 64 89 10.7 11.3 12.6 13.1 14.1 14.5 14.8 14.8 16.4 165 16.3 17.6 2.03 2 19 1.12 1.37 1.08 1.33 1.20 0.60 1.80 089 1.57 045 1.20 208 089 163 FISHERY BULLETIN: VOL. 80, NO. 2 Fnfld Figure 3.— Left lateral external view of the pectoral girdle and suspensorium from Xiphias gladius, showing the ontogeny. Starting from left the specimens' lengths in millimeters are: top, 5.1 ENL; 7.6 ESL; bottom, 21.4 ESL. A, anterior process of the coraco-scapular carti- lage; Bl, larval pectoral fin blade; CI, cleithrum; Cor, coracoid; Fnfld, larval finfold; P, posterior process of the coraco-scapular cartilage; PCI, posterior process of cleithrum; PstCl, post- cleithrum; Pt, posttemporal; R, radial orignat- ing from larval fin blade; ScF, scapular fora- men; SCI, supracleithrum; ScR, cartilaginous distal radial originating from scapular carti- lage. Cartilage, white; ossifying, stippled. PstCl Figure 4.— Left lateral external view of the pectoral girdle and suspensorium from Xiphias gladius, showing the ontogeny. The specimens' lengths in millimeters ESL are: left, 33.0; right, 64.6. Sc, scapula; for other abbreviations, see Figure 3. Cartilage, white; ossifying, stippled. 164 POTTHOFF and KELLEY: OSTEOLOGKAL DEVELOPMENT IN SWORDFISH Table 3.— Development of the pectoral girdle and sus- pensorium for 190 Xiphias gladius (3.7 mm ENL-64.6 mm ESL). length ranges (mm, ENL, or ESL) are from "first ob- servance" to "first observance in all specimens." PstCl Figure 5.— Left lateral external view of the pectoral girdle and suspensorium from a 187 mm ESL Xiphias gladius. For abbreviations, see Figures 3 and 4. Cartilage, white; ossify- ing, stippled. girdle is only briefly mentioned in Gregory and Conrad (1937) and no detailed description is given. Our smallest 3.7 mm ENL specimen already had rudiments of a pectoral girdle, consisting of a rod-shaped bony cleithrum, an inverted Y- shaped coraco-scapular cartilage without scapular foramen, and a larval fin blade (similar to the 5.1 mm ENL specimen in Fig. 3) (Table 3). The cleithrum later developed a shelflike dorsal posterior process (Figs. 3-5). The coraco- scapular cartilage at first had long dorsal and long posterior processes and a short anterior process. It developed a foramen on the dorsal process, and the anterior process grew relatively larger and ossified into part of the coracoid, while the posterior process atrophied. Ossifica- tion of the scapula started around the scapular foramen and spread over the dorsal process forming the scapula (Figs. 3, 4; Table 3). The larval fin consisted of two parts: a flat cartilagin- ous semicircular blade surrounded on the cir- Appearance in Part cartilage Ossification Posttemporal — 5.3 Supracleithrum — 53 Postcleithrum — 53 Cleithrum — <3.7 Posterior process of c eithrum — 6.2-6.9 Coraco-scapular cartll age <3.7 — Scapular foramen 4.6-5.1 — Scapula — 6.6-8.1 Coracoid — 5.4-6.5 Scapular radial 55-9.3 10.6-15.0 Radial No. 1 52-5.6 8.8 Radial No 2 5.2-5.9 90-10.0 Radial No 3 5.4-9.1 9 1-12.0 Radial No. 4 6.8-9.1 133-147 cumference by a finfold containing larval actinopterygia (Fig. 3). The semicircular carti- laginous pectoral fin blade developed into the four large radials by first forming elongate holes in the blade. These holes then gradually enlarged to the border of the semicircular cartilage blade, forming separate cartilaginous radials, which later ossified (Figs. 3-5; Table 3). The pectoral suspensorium, consisting of the posttemporal, supracleithrum, and postclei- thrum, was of dermal origin (did not form from cartilage) and was first seen ossifying at 5.3 mm ENL (Table 3). The posttemporal was at first a flat rectangular bone with spines. The spines were lost and a dorsal and ventral process developed, giving the posttemporal the charac- teristic inverted C shape (Figs. 3-5; Table 3). The supracleithrum was short at first and had spines. It also lost its spines and developed a long pos- terior process which articulated laterally with the posterior process of the cleithrum (Figs. 3-5; Table 3). Lengthening of the supracleithrum accommodates the migration of the pectoral fin from a lateral position in the larvae to a more ventral position in the adults (Ovchinnikov 1970). The postcleithrum was an elongate rod- shaped bone without spines from the start and articulated medially with the posterior process of the cleithrum (Figs. 3-5; Table 3). DORSAL FIN Dorsal fin rays first appeared almost at the same sizes as the anal and caudal rays (Tables 1, 4). The dorsal fin rays developed in the dorsal finfold first at the middle of the body above the 10th-14th myomere in specimens 5.5-6.1 mm ENL. With growth, addition of dorsal fin rays 165 Table 4.— Summary of dorsal fin ray development for 208 Xiphias gladius (3.7 mm ENL-225, 668 mm ESL). Length. Range, number Mean, number mm ENL of dorsal dorsal fin or ESL N fin rays rays SD 3.6-45 7 0 0 — 4.6-5.5 47 0-32 1.3 617 5.6-6.5 31 0-38 23.0 1392 6.6-75 14 27-42 35.7 4.49 7.6-8.5 21 36-45 41.0 2.75 8.6-9.5 13 40-44 42.2 1.44 9.6-10 5 11 40-45 422 1.66 10.6-11.5 8 42-47 438 1 70 11.6-12.5 9 40-48 449 2.40 12.6-135 4 42-46 43.8 1 80 13.6-145 5 43-48 44.8 201 14.6-668.0 38 44-49 464 1.23 Figure 6.— Schematic representation of dorsal and anal fin and pterygiophore development in Xiphias gladius in relation to the vertebral column and head. Pterygio- phores are represented white when cartilagi- nous and black when ossifying. Scales represent interneural and interhaemal space numbers and points on scales align with tips of neural and haemal spines. FISHERY BULLETIN: VOL. 80. NO. 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 1 1 — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i-~i u^mssssm"^ 5-0 mm ENL ft ummmms 5.3mm ENL /////////////// f/L wmvm w\\\v 5.6 mm ESL ^m^^WWW^MWM¥ j 1 2 3 4 S 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 ^///////////////////////WM/// ^mw////////////////////////// //////? was in an anterior and posterior direction. The posterior part of the dorsal fin was complete at a smaller size before the anterior part. Adult dorsal fin counts of 44-49 rays (14.6-668 mm ESL, N = 38, X = 46.4, SD = 1.23) were first ob- served at 8.1 mm ESL, and all specimens longer than 13.8 mm ESL had the adult count (Fig. 6; Table 4). Our counts are in agreement with Arata (1954). Some of Arata's specimens, how- ever, did not have adult counts. The sequence of dorsal fin ray development is similar in Xiphias to that of Curyphaena reported by Potthoff (1980). DORSAL FIN PTERYGIOPHORES In juvenile and adult specimens of Xiphias 14.1-668 mm ESL, the pterygiophores consisted of a jointed proximal and distal radial support- ing a fin ray. The distal radial was located between the bifurcate base of the fin ray. Each proximal and distal radial and fin ray were forming a series, hence a serial association. Each fin ray also closely approximated the following posterior pterygiophore in a secondary associa- tion. Distal radials were present for all fin rays in 14 out of 37 juvenile specimens. Of the remaining 23 specimens 19 had one anteriormost ray and 4 had two anteriormost rays without distal radials (Table 5). Exceptions to the serial and secondary fin ray associations were found at the beginning and end of the fins. The anteriormost pterygio- phore supported from one to three rays, most often two (Fig. 7). This pterygiophore consisted of one piece of cartilage, or of a Y-shaped piece, or of two fused pieces (Figs. 7, 8). In 1 of 38 speci- Table 5.— Percent and number of anterior dorsal and anal fin rays without distal radials for 37 Xiphiasgladius( 14.7-668 mm ESL). Percent and number under 0 are specimens in which all fin ravs had distal radials. Number of anter lor dorsal and anal fin rays Item 0 1 2 Percent without dorsal distal radial(N) Percent without anal distal radial(W) 37,8(14) 86.5(32) 51 4(19) 13.5(5) 108(4) 1000(37) 166 POTTHOFF and KELLEY: OSTEOLOGICAL DEVELOPMENT IN SWORDFISH Art, most Number, dorsal in rays associated dorsal pterrgiophore shape with in tenormos t pterfgiophore 1 2 3 c? 4 23 2 f 6 (7 2 (ntfrior moit Nm er, anal fin rajs associated ■III ptptuiophoif shape with anteriormost pterygiophore 1 2 3 \ 1 21 K 10 4 . 0 1 Figure 7.— Threee possible shapes of anteriormost dorsal and anal pterygiophores for 37 Xiphias gladius 14.7-668 mm ESL and the number of fin rays associated with each pterygiophore shape. 025mm mens, no rays were associated with the anterior most pterygiophore. The posteriormost dorsal fin ray was double and was serially associated with the posteriormost pterygiophore (Figs. 9, 10). The double ray lacked a secondary associa- tion, but a stay was present under the double ray (Figs. 9, 10). Middle radials were absent in Xiphias. Total dorsal pterygiophore count was either equal to or one to two less than the dorsal fin ray count, depending on the number of rays associated with the anteriormost pterygiophore. In larvae, juveniles, and small adults of Xiphias the dorsal proximal radials inserted in the interneural spaces. In 39 juveniles and small adults with fully formed fins, the first inter- neural space (bounded by head and first neural spine) lacked inserting pterygiophores or pre- dorsal bones. The second interneural space (bounded by first and second neural spines) had four to seven {X- 5.2), the third space had three tofive (X - 4.2), the fourth space had two to three (X = 2.9), the fifth space had two to three (X= 2.4), and the remainder of the interneural spaces had one to three pterygiophores, but usually two Figure 8.— Left lateral view of the two anteriormost dorsal fin pterygiophores with their associated rays in the second interneural space for various sizes of Xiphias gladius. Starting from left the specimens' lengths in millimeters ESL are: top row, 15.9, 20.4; middle row, 26.7, 33.6; bottom row, 52.4, 225. D, distal radial; NPr. neural prezygapophysis; Ns, neural spine; P, proximal radial; R, fin ray. Carti- lage, white; ossifying, stippled. (Fig. 11). Usually the posteriormost dorsal pterygiophore inserted in the 22d interneural space and occasionally in the 21st (Fig. 11; Tables 6, 7). In Xiphias, dorsal fin pterygiophores first appeared in cartilage before the fin rays at 4.8 mm ENL, but not until 6.0 mm ENL did all specimens have cartilaginous pterygiophores. Two Xiphias, 5.1 and 5.6 mm ENL, lacked dorsal pterygiophores but had some cartilagi- nous anal pterygiophores. Dorsal pterygiophores were first seen at the center of the body between the 11th and 18th interneural spaces (Fig. 6; 167 FISHERY BULLETIN: VOL. 80, NO. 2 D Figure 10.— Posterior-most dorsal pterygiophore and its stay from a 668 mm ESL Xiphias gladius. Top, left lateral view of proximal and distal radial, double ray and stay; bottom, dorsal view of stay, enlarged. For abbreviations, see Figures 8 and 9. Cartilage, white; bone, stippled. 2.0 mm Figure 9.— Left lateral view of the posterior- most dorsal pterygiophore from Xiphias gla- dius, showing the ontogeny. Starting from the top and going to the bottom the specimens' lengths in millimeters ESL are: 15.9, 20.4, 26.7, 33.6, 52.4, 225, length unknown for last on bot- tom, weight 61 lb. St, stay; for other abbrevia- tions, see Figure 8. Cartilage, white; ossifying, stippled. Table 6.— Adult and juvenile position of posterior- most dorsal and anal fin pterygiophores in their interneural and interhaemal spaces for 116 Xiphias gladius (7.1-668 mm ESL). Interneural space numbers DORSAL FIN i 18 CO 1 1 CO IO CO ro I co i co i ro i i ro i co i to 1 ro ro 1 ro ro 1 ro 1 ro ro 1 CO 1 CO O 1 CO F 29 36 23 36 37 39 33 38 31 29 35 34 33 32 32 29 26 33 30 30 E 6 i I \ 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 0 5 i 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 C 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 20 21 22 B 5 1 2 3 4 5 6 7 8 £ 10 11 12 13 1415 16 1 71 819J2021 22232425 16|17 1 8 19 20 21 B 10 2 2 2 1 C 11 2 2 2 1 D 28 34 29 37 26 E 03 1 1 CO — i 1 CO 1 ro O 1 ro F ANALFIft Interhaemal space numbers Item 21 20 21 21 22 21 22 22 Number of specimens 29 7 79 1 Percent of specimens 25.0 6.0 68 1 0 9 Table 7). Addition of cartilaginous pterygio- phores was in both anterior and posterior direc- tions. The posteriormost interneural space number 21 or 22 was filled first (Fig. 6; Table 7). Addition of pterygiophores was then in an anterior direction until the anterior interneural Figure 11. — Schematic presentation of common arrangement of pterygiophores and fin rays in relation to neural and haemal spines and vertebrae in 39 Xiphias gladius (14.7-668 mm ESL). Method of presentation modified after Matsui (1967). A, skull and vertebrae numbers; B, interneural and interhaemal space numbers; C, number of pterygiophores with highest frequency of occurrence found in the respective ("B") interneural or interhaemal space; D, number of fin rays associated with pterygiophores for indicated interneural or interhaemal space; E, highest frequency of occurrence in 39 Xiphias for the number of pterygiophores indicated in "C"; F, range of number of pterygiophores found in the respective ("B") interneural and interhaemal spaces. space number 2 was occupied (Fig. 6; Table 7). Fin rays followed pterygiophore appearance at the center of the body. Addition of rays followed addition of pterygiophores, with some cartila- ginous pterygiophores present anterior and posterior to the developing rays (Fig. 6). Ossification of dorsal pterygiophores first started at 6. 1 mm E N L in the same area and pro- ceeded in the same direction as the cartilage development. Every specimen >8.0 mm ESL had some ossifying pterygiophores, and between 18.2 and 26.7 mm ESL all pterygiophores were ossi- fying. The last pterygiophore to ossify was the anteriormost in the second interneural space. 168 I'OTTHOFF and KELLEY: OSTEOLOGICAL DEVELOPMENT IN SWORUFISH Table 7.— Development of dorsal and anal fin pterygiophores in the interneural and interhaemal spaces for 205 Xiphias gladius. X - mean. With pterygiophores With ossifying pterygiophores Length, Anteriormost space no. (X) Posterlormost space no. (X) Anteriormost space no. (X) Posteriormost space no (X) or ESL Interneural Interhaemal Interneural Interhaemal Interneural Interhaemal Interneural Interhaemal 3.6-4.5 (') (') (') (') (2) (2) (2) <2> 4 6-55 '3-11(5 0) '16-18(17 .1) '17-22(20.0) '19-21(20 1) <2) (2) (2) (2) 56-65 '2-6 (3.2) 16-18(165) '20-22(21 4) 20-22(20.6) 27-9 (8 0) 216-17(16.8) 216-18(17.0) 217-19(180) 6 6-7 5 2-4 (2.8) 16-17(16.4) 21-22(21 6) 20-21(20 5) 24-14(92) 216-17(16.5) 214-19(173) 217-20(189) 7 6-8 5 2-3 (2.1) 16-17(16.5) 21-22(21 9) 20-21(20 9) 23-1 1(5.4) 216-18(16.4) 213-22(19 1) 217-21(190) 8.6-9 5 2-3 (2.1) 16-17(16.2) 21-22(21 8) 20-21(21 1) 3-12(4.7) 16-17(16.2) 14-22(194) 16-21(192) 9.6-105 2-3 (2.1) 16-17(163) 21-22(21 7) 20-21(20 6) 2-5 (3.5) 16-17(16.3) 19-22(20.5) 19-21(198) 10.6-11 5 2 16-17(164) 21-22(21 9) 20-21(20.9) 2-5 (3.8) 16-17(162) 18-22(207) 19-21(20 2) 11.6-12.5 2 16-17(16.4) 21-22(21 7) 20-21(20 6) 2-4 (2.8) 16-17(16.4) 18-22(208) 19-21(20 4) 126-135 2 16-17(16.8) 21-22(21 5) 20-21(20 8) 2-3 (2.5) 16-17(16.8) 21-22(21 3) 19-21(20.0) 13.6-145 2 16-17(16.4) 21-22(21.4) 20-21(20 6) 2-3 (2.2) 16-17(16.4) 20-22(21.0) 20-21(20.4) 14.6-155 2 16-17(166) 21-22(21.8) 20-21(20 8) 2 16-17(16.8) 21-22(21 8) 20-21(20 8) 15.6-165 2 16-17(162) 21-22(21.4) 20-21(20 4) 2-3 (2.4) 16 21-22(21 4) 20-21(20 4) 166-668 2 16-17(16.4) 21-22(21.5) 20-22(207) 2 16-17(164) 21-22(21.5) 19-21(20.6) 'No pterygiophores developed in all or some specimens; these were not used for calculation of means 2No pterygiophores ossified in all or some specimens; these were not used for calculation of means Pterygiophores under the middle of the dorsal fin completed development first. Proximal and distal radials first appeared as one piece of carti- lage. Then the distal radial cartilage separated from the proximal radial. Ossification of the proximal radial cartilage started at the middle and spread outwards proximally and distally toward the ends. The ends remained carti- laginous in adults, and small sagittal keels developed ventrad during ossification (Fig. 12). Extensive lateral keels were observed on the pterygiophores in^he largest 668 mm ESL speci- men. The posteriormost pterygiophores ossified later, but in the same sequence as those in the middle area. The last pterygiophores supported a double ray in series and a stay was present (Figs. 9, 10). The posteriormost pterygiophore and the stay ossified from the same piece of carti- lage (Figs. 9, 10). The anteriormost pterygiophores were the last to ossify. The first anteriormost pterygiophore developed a large anterior sagittal keel (Fig. 8). Distal radials developed from a piece of carti- lage that separated during development from the distal portion of the cartilaginous pterygio- phores and was situated between the bifurcate bases of the serial fin rays (Figs. 8, 12, 13). Ossi- fication of all distal radials occurred after cartilage separation. At first the left and right sides of the distal radial cartilage ossified to form two pieces of bone. Ossification continued until the two bones were joined (Figs. 14, 15). All dorsal fin rays associated with the distal radials had bifurcated bases (Figs. 14, 15). 1.0mm Figure 12.— Left lateral view of a dorsal pterygio- phore from the 11th interneural space of Xiphias gladius, showing the ontogeny. Starting from the top and going to the bottom the specimens' lengths in millimeters ESL are: 15.9, 20.4, 26.7, 33.6, 52.4, 225. For abbreviations, see Figure 8. Cartilage, white; ossifying, stippled. ANAL FIN Anal fin rays first appeared at about the same sizes as the dorsal and caudal rays (Tables 1, 8). The anal rays developed in the anal finfold first at the middle of the fin below myomeres 18-20 in specimens 5.3-6.1 mm ENL. Anal rays were 169 FISHERY BULLETIN: VOL. 80, NO. 2 0.5mm Figure 13.— Anteriormost three vertebrae and pterygiophores with fin rays from a 35.9 mm ESL Xiphias gladius. C, centrum; D, distal radial; F, neural foramen; HPo, haemal post- zygapophysis; NPo, neural postzygapophysis; NPr, neural prezygapophysis; Ns, neural spine; P, proximal radial; Pa, parapophysis; R, ray. 0.5mm 0.1mm 0-5 mm 1 mm Figure 14.— Anterior view of the 12th dorsal ray and its distal radial from Xiph ias gladias, showing the ontogeny. Starting from left the specimens' lengths in millimeters ESL are: top, 64.6, 187; bottom, 225, 668. D, distal radial; R, fin ray. Car- tilage, white; ossifying, stippled. 0.25 mm Figure 15. — Anterior view of two fin rays and their distal radials from juvenile Xiphias gladius. The specimens' lengths in millimeters ESL are: left, 225, first anteriormost dorsal ray; right, 668, next to last posteriormost dorsal ray. D, distal radial; R, fin ray. Cartilage, white; bone, stippled. added in an anterior and posterior direction (Fig. 6). Adult anaUounts of 16-19 rays (10.6-668 mm ESL, TV = 66, X = 17.1, SD = 0.81) were first observed at 7.8 mm ESL and all specimens longer than 10.6 mm ESL had the adult counts (Fig. 6; Table 8). Our counts generally agree with those of Arata (1954), except we had two speci- mens with 19 anal rays; Arata had none. Table 8.— Development of anal fin rays for 213 Xiphias gladius (3.7 mm ENL-225, 668 mm ESL). X = mean, SD = standard deviation. Length, mm ENL Number of anal f n rays or ESL 0 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 X SD 3.6-4.5 7 — — 4.6-5.5 43 2 — — — — 1 — 1 0.6 2.06 5.6-65 6 — — 2 — 1 3 — 8 2 4 2 4 1 95 5 17 6.6-75 1 — 5 1 4 2 1 14.2 1.50 7.6-85 1 8 5 5 2 160 0.92 8.6-95 2 8 3 16.1 0.72 9.6-10.5 1 6 3 1 1 16.6 1.04 10 6-668 13 37 15 1 17.1 0.81 170 POTTHOFF and KELLEY: OSTEOEOUK'AL DEVELOPMENT IN SWOKDFISH ANAL FIN PTERYGIOPHORES The description of the dorsal fin pterygio- phores in the previous section may be applied to anal fin pterygiophores because of the similari- ties between the two. Anal pterygiophores were inserted in the interhaemal spaces. These spaces were numbered the same as the opposing inter- neural spaces. Anteriormost (first) interhaemal space number 16 or 17 was bound anteriorly by the stomach, intestine, and anus and posteriorly by the first haemal spine. The first haemal spine was positioned on the 16th or 17th centrum. If it occurred on the 16th centrum, it was of variable length and often did not reach the pterygio- phores. If the first haemal spine was on the 17th centrum, it always reached past the pterygio- phores. The count for the 16th and 17th interhaemal space was summed because we were not always able to determine a division between the two spaces (Fig. 11). Total number of anal pterygiophores in 31 of 37 specimens with full counts was one less than the anal fin ray count. In 2 of 37 specimens, it was the same and in 4 of 37 it was two less. The ante- riormost anal pterygiophore supported from one to three rays, most often two (Fig. 7). This pterygiophore consisted of one piece of carti- lage, normal in shape (Fig. 16), or of a vestige (Fig. 7). The vestigial piece may fuse to the next posterior pterygiophore to form an inverted Y shape (Fig. 16), or the inverted Y shape may originate from one piece of cartilage (Figs. 7, 16). An anterior sagittal keel developed on the ante- riormost anal pterygiophore (Fig. 16), but this keel was not as large as on the first dorsal pterygiophore (Fig. 8). The posteriormost anal pterygiophore had the same structure as its dorsal counterpart and in- serted most often into the 20th or 21st inter- haemal space, which was usually one space ante- rior to the posteriormost dorsal insertion (Fig. 11; Table 6). In juveniles and small adults of Xiphias with fully formed fins the anteriormost interhaemal spaces 16 and 17 had 8-11 (X = 9.9, N = 40) pterygiophores. The remaining three or four interhaemal spaces had one to two or one to three pterygiophores each (Fig. 11). The pos- teriormost 21st interhaemal space had none or one to two pterygiophores. Only 1 specimen out of 116 had a pterygiophore in the 22d inter- haemal space (Table 6). Development and structure of the anal fin Figure 16.— Left lateral view of two or three anteriormost anal fin pterygiophores from Xiphias gladius, showing the ontogeny. Starting from left the specimens' lengths in milli- meters ESL are: top row, 15.9, 20.4; bottom row, 33.0, 64.6, 225. D, distal radial; P, proximal radial; R, fin ray. Cartilage, white; ossifying, stippled. pterygiophores was the same as in the dorsal supports. Cartilaginous anal pterygiophores first appeared before anal fin rays and most of the time concurrently with dorsal pterygiophores below myomeres 18-20 (which approximately corresponds to interhaemal spaces 18-20) (Fig. 6; Table 7). Addition of cartilaginous pterygio- phores was in an anterior and posterior direction. The posteriormost interhaemal spaces 20 or 21 were filled first. Last to develop was the anterior- most anal pterygiophore (Fig. 6). Fin rays fol- lowed pterygiophore appearance as in the dorsal fin (Fig. 6). Ossification of anal fin pterygiophores first started between 6.0 and 8.0 mm ENL or ESL in the same area of first appearance in cartilage and proceeded in the same directions as cartilage development (Fig. 6; Table 7). All anal pterygio- phores were ossifying between 12.0 and 25.1 mm ESL. Development and ossification of individual anal pterygiophores is similar to the dorsal pterygiophores (Fig. 16). The posteriormost anal pterygiophore develops a stay and supports a double ray serially as does its dorsal counterpart. Distal radials developed in the anal fin as in the dorsal fin (Fig. 14). Almost all rays had a distal radial between their bifurcate base. Only 5 out of 171 FISHERY BULLETIN: VOL. 80, NO. 2 37 specimens did not have a distal radial for the anteriormost ray (Table 5). CAUDAL FIN Caudal fin rays first appeared at about the same sizes as the dorsal and anal rays (Table 1). The caudal fin rays developed in the caudal fin- fold ventrad in preflexion larvae first on hypurals 2 and 3 and were added in an anterior and pos- terior direction. After complete notochord flexion between 6.3 and 8.0 mm ESL, the secondary caudal rays developed dorsad and ventrad in an anterior direction. Caudal rays were first seen in a 5.4 mm ENL specimen and all larvae longer than 6.1 mm ENL had some caudal rays developing (Table 9). The full complement of 9+8 principal rays developed between 8.8 and 11.0 mm ESL. All Xiphias longer than 26.6 mm ESL had the adult_count of (8-10)+9+8+(9- ll)=34-38 (N = 15, X = 35.9, SD = 1.55) rays (Tables 9, 10). The upper and lower caudal lobe had equal numbers of rays or they differed by one ray (Table 10). A procurrent spur (Johnson 1975) was not oberved in Xiphias. CAUDAL FIN SUPPORTS The caudal fin rays were supported by some of the bones of the hypural complex and only two posteriormost centra (PU2 and urostyle) were in- volved in the support (Fig. 17). The bones which supported the fin rays directly or indirectly in larvae and juveniles of Xiphias were two centra (PU2 and urostyle), one specialized neural arch, three epurals, one paired uroneural, five auto- genous hypural bones, one autogenous par- hypural, and one autogenous haemal spine. One of 164 specimens examined had the unusual count of 16+11=27 vertebrae and had two autogenous haemal spines on preural centra 2 and 3. We were able to see all these supporting bones during development (Figs. 18-23; Table 11), but in the adults some parts were ontogeneti- cally fused. Between 3.7 and 6.2 mm ENL, Xiphias had a straight notochord in the caudal area. Notochord flexion was between 6.3 and 8.0 mm ENL. Before notochord flexion hypurals 1-4, the parhypural (Ph), and the haemal spine and arch (Hs) of the future preural centrum 2 were developing ventrad in cartilage (Fig. 18; Table 11). Dorsad the neural arch (Ns) of the future preural cen- trum 3, the specialized neural arch ("Na") of the Table 9.— Caudal fin ray development for 200 Xiphias gla- dius (3.7 mm ENL-225, 668 mm ESL). SCR, secondary caudal rays. PCR, principal caudal rays. X= mean, SE = standard error of the mean. Specimens are undergoing notochord flexion between dashed lines at 6.3-8.0 mm ENL. Length, Upper Lower Total fin ray count mm ENL or ESL SCR PCR PCR SCR Range X SE N 3.6-4.5 0 0 0 0 0 — — 7 4.6-5.5 0 0-3 0-3 0 0-6 0.2 1.36 46 56-65 0 0-6 0-8 0 0-14 49 3.83 30 66-7.5 0 2-7 2-8 0 4-15 9.9 2 99 14 76-8.5 0 4-8 4-8 0-1 8-17 13.7 262 19 86-9.5 0-1 5-9 6-8 0-2 11-19 15.5 277 12 9.6-10.5 0 7-9 8 0-2 16-20 17.6 1.33 11 10.6-11.5 0-1 7-9 8 0-2 16-20 18.1 1.50 9 11.6-12.5 0-2 9 8 2 19-21 19.6 085 8 126-13.5 0-3 9 8 1-3 18-23 21 3 2.20 4 13.6-155 0-3 9 8 2-3 19-23 21.5 1.41 8 15.6-17.5 3-5 9 8 3-5 23-27 243 1.71 6 17.6-265 4-7 9 8 4-8 25-32 26.0 1.99 11 266-668 8-10 9 8 9-11 34-38 35.9 1.55 15 Table 10.— Adult caudal fin ray counts for 15 Xiphias gladius (26.7- 225, 668 mm ESL). USCR = upper secondary caudal rays, PCR = prin- cipal caudal rays, LSCR = lower secondary caudal rays. Total fin ray count USCR + PCR + LSCR N 34 8 + 17 + 9 4 35 9 + 17 + 9 2 36 9 + 17 + 10 3 37 10 + 17 + 10 3 38 10 + 17 + 11 3 future preural centrum 2, and the three epurals (Ep) were developing from cartilage (Fig. 19). Appearance of the cartilaginous parts was from anterior to posterior. After notochord flexion a cartilaginous hypural 5 (Hy) and a bony uroneu- ral (Un) developed between 9.8 and 12.5 mm ESL (Figs. 20-21; Table 11). The parhypural and hypurals 1-5 developed from separate pieces of cartilage. This is shown for the parhypural and hypurals 1-2 in Figure 18. Joining of the proximal portions of the par- hypural and hypurals 1-2 by cartilage starts with the parhypural and hypural 1 between 5.4 and 5.6 mm ENL and extends to hypural 2 at 5.7 mm ENL. All specimens have the parhypural and hypurals 1-2 joined proximally with carti- lage at 6.9 mm ENL or ESL as shown in Figures 19 and 20. Hypurals 3-5 are never joined by carti- lage during development (Figs. 19-21). The car- tilaginous proximal joint is lost during develop- ment when the hypurals are fully ossified between 27 and 34 mm ESL (Fig. 22). Ossification of the cartilage bone in the caudal complex of Xiphias started with the preural 172 POTTHOFF anil KELLEY: OSTEOLOGICAL DEVELOPMENT IN SWORDFISH Figure 17.— Left lateral view of the adult caudal complex from Xiphias gladius of un- known length, 48 lb, showing fin ray articula- tion in relation to the caudal parts. Ep, epural; Hs, autogenous haemal spine; PCR, principal caudal rays; Ph, parhypural; Pu, preural centrum; SCR, secondary caudal rays; Un, uroneural; Ur, urostyle. Caudal complex bones, white; caudal rays, stippled. 10mm PCR Figure 18.— Left lateral view of the caudal complex of a 5.1 mm ENL Xiphias gladius. Ha, haemal arch; Hy, hypural; Nc, notochord; Na, neural arch; Ph, parhypural. Cartilage, stip- pled. i 1 0.25 mm Figure 19.— Left lateral view of the caudal complex of a 8.8 mm ESL Xiphias gladius. Hs, haemal spine; "Na", specialized neural arch; Ns, neural spine; for other abbrevia- tions, see Figures 17 and 18. Cartilage, white; bone, stippled. PCR SCR Figure 20.— Left lateral view of the caudal complex of a 12.6 mm ESL Xiphias gladius. HPr, haemal prezygapophysis; NPr, neural prezygapophysis; for other abbrevia- tions, see Figures 17-19. Cartilage, white; ossifying, stippled. Table 1 1.— Length ranges at which parts of the caudal complex appear in cartilage and ossify in 173 Xiphias gladius (5.4 mm ENL-225 mm ESL). Pu = preural centrum. Brackets denote fusion of separate structures during development. Length range Length range (mm. ENL or ESL) (mm. ENL or ESL) of first appearance of first evidence First evidence of in cartilage of ossification fusion (mm. ESL) Pu2 centrum — 6.2- 90 Specialized neural arch 5.4-6.5 7 1-12.3 Epural anterior 5.7-6.8 10.3-13.7 middle 54-6.8 10.3-13.7 posterior 5.4-7.1 162-176 Uroneural — 98-12.3 Hypural 5 9.8-12.5 16.0-17.7 Hypural 4 5.7-7.9 94-13.7 Hypural 3 53-6 1 7 1-10 7 Urostyle — 6.2-9.1 Hypural 2 5 1-56 7.1-9.7 Hypural 1 5.0-5.5 7.1-9.2 Parhypural 5.0-5.5 7.1-9.2 Pu2 haemal spine 5.1-6.1 7.1-10.9 17.2-267 131 -? 17.2-226 173 Figure 21.— The caudal complex of a 21.4 mm ESL Xiphias gladius. A, left lateral view of the complex; B, left lateral view of normal uroneural, enlarged. HPo, haemal post- zygapophysis; NPo, neural postzygapophysis; for other abbre- viations, see Figures 17-20. Cartilage, white; ossifying, stippled. FISHERY BULLETIN: VOL. 80. NO. 2 SCR PCR 0.25 mm PCR Figure 22.— The caudal complex of a 52.4 mm ESL Xiphias gladius. A, left lateral view of the complex; B, left lat- eral view of the anomalous uroneural, enlarged. A, anomalous secondary haemal spine; F, neural foramen; for other abbreviations, see Figures 19-21. Cartilage, white; ossifying, stippled. 0.25 mm Un Hy5 Figure 23.— The bones of the caudal complex from an adult Xiphias gladius length un- known, 61 lb. A, left lateral view of the caudal bones; B, left lateral view of the normal uro- neural, enlarged. For abbreviations, see Figures 19-21. Cartilage, white; bone, stippled. NPr NPo 10mm 2mm 174 POTTHOKK ami KELLEY: OSTEOLOGICAL DEVELOI'MKNT IN SWORDFISH centrum 2 and the urostyle at 6.2 mm ENL-9.1 mm ESL. Ossification then proceeded from the haemal spine of the preural centrum 2 dorsad to the hypurals. Last to ossify between 16.0 and 17.7 mm ESL was hypural 5 (Table 11). The special- ized neural arch of preural centrum 2 began ossification at 7.1-12.3 mm ESL followed by the three epurals. The posteriormostepural was last to ossify between 16.2 and 17.6 mm ESL (Table 11). The paired uroneural was not a cartilage bone and it was first present between 9.8 and 12.3 mm ESL before epural ossification (Table 11). In a few specimens the uroneural had an anomalous shape as if it had fused from two parts (Fig. 22). During development of the hypural complex, a parhypurapophysis and a hypurapophysis (Lundberg and Baskin 1969; Nursall 1963) were observed on the parhypural and hypural 1. From a dorsal view the parhypural and hypural 1 are bifurcated as shown in Figure 24. This bifurca- tion can be observed in the adults on the autogenous parhypural but is absent on hypural 1, which then is fused to the hypural plate. A tunnellike foramen develops between the tips and rear of the parhypural prezygapophyses for the haemal canal on the proximal surface of the parhypural. This tunnel was not yet developed in a 44.1 mm ESL specimen (Fig. 24) but was fully formed in our 668 mm ESL specimen. In adults of Xiphias, hypurals 1-4 fuse with each other and the urostyle, forming a single hypural plate with a notch posteriorly at the center. Grooves present on the plate formed be- cause of articulating rays (Gregory and Conrad 1937) (Fig. 23). The epurals, the uroneural, hypural 5, the parhypural, and the haemal spine of preural centrum 2 remained autogenous in the adults. Fusion between hypurals 4 and 3 and 1 and 2 started distad from the articular cartilage in an anterior direction at 17.2-26.7 mm ESL (Figs. 21, 22; Table 11). Fusion of the two hypural plates, however, was in a posterior direction starting proximally. We could not determine the size at which the dorsal and ventral hypural plates fused with each other and with the urostyle because of insufficient samples (Fig. 1; Table 11). The parhypural and hypurals 1-5 supported the principal caudal rays. Only on one occasion did the haemal spine of preural centrum 2 support a principal caudal ray, but this is not shown in Table 12. The distribution of principal rays on the hypural bones can only be seen in Haemal Canal 0.5 mm FIGURE 24.— The parhypural and hypural 1 from a 44.1 mm ESL Xiphias gladius. A, dorsal view, enlarged; B, left lateral view. Hyp, hypurapophysis; Phyp, parhypurapophysis. Carti- lage, white; bone, stippled. larvae and small juveniles (Figs. 19-22; Table 12). Table 12.— Distribution of principal caudal rays on the hypurals in 66 Xiphias gladius (8.8- 64.6 mm ESL). Number of principal caudal rays Part 1 2 3 4 5 6 Parhypural 2 61 3 Hypural 1 1 18 47 Hypural 2 49 17 Hypural 3 15 48 3 Hypural 4 1 18 43 4 Hypural 5 38 28 VERTEBRAL COLUMN Of 164 Xiphias 5.3 mm ENL-668 mm ESL, 1 (0.6%) had 15+10=25 vertebrae, 95 (57.9%) had 15+11=26, 65 (39.7%) had 16+10=26, and 3 (1.8%) had 16+11=27 (Nakamura et al. 1968; Ovchin- nikov 1970). All centra except the first anteriormost, the urostyle, and preural centrum 2 had neural pre- and postzygapophyses, and neural arches and spines (Figs. 25-27). The first anteriormost centrum lacked a neural prezygapophysis(Figs. 13, 27), preural centrum 2 had a neural prezyg- apophysis, a specialized (open) neural arch, and a neural postzygapophysis (Figs. 22, 23). The urostyle had only a neural prezygapophysis (Figs. 21-23). All precaudal vertebrae except the anteriormost had parapophyses (Figs. 13, 25, 175 FISHERY BULLETIN: VOL. 80, NO. 2 1mm Figure 25.— Left lateral view of the second anteriormost vertebra from Xiphias gladius, showing the ontogeny. Start- ing from left the specimens' lengths in millimeters are: top, 5.1 ENL, 7.8 ESL.12.6 ESL; center, 21.4 ESL, 52.4 ESL; bottom, 225 ESL. F, neural foramen; Nc, notochord; NPo, neural postzygapophysis; NPr, neural prezygapophysis; Ns, neural spine; Pa, parapophysis. Cartilage, white (except in 5.1 mm ENL specimen in top row left where entire stippling signifies cartilage); ossifying, stippled. 26). Haemal postzygapophyses were present on precaudal vertebrae numbers 3 to 15, sometimes on 2 to 15 (Figs. 13, 26). All caudal vertebrae had nonautogenous haemal spines, except preural centrum 2 and the urostyle. Preural centrum 2 had an autogenous haemal spine. The urostyle had an autogenous parhypural with a tunnellike foramen for the haemal canal. The parhypural is homologous to the autogenous haemal spine of preural centrum 2 (Figs. 20-24). The 16th centrum sometimes lacked a haemal spine, sometimes had a vestigial haemal spine, or it had a normal haemal spine. Haemal pre- and postzygapophyses were present on all caudal centra except on preural centrum 2 and the urostyle. Neural foramina were present on most precaudal and caudal centra on larger specimens (Figs. 13, 22, 23, 25-28). Five out of eight Xiphias with all ribs devel- oped had six paired ventral ribs, which loosely articulated with the parapophyses on centra 1-4, 14, and 15 (Figs. 25-27). Two specimens had seven pairs of ribs on centra 1-5, 14, and 15 and on centra 1-4 and 13-15. One Xiphias had nine pairs on centra 1-6 and 14-16. The neural arches fuse distally during ossifica- tion to form neural spines. The fusion and spine formation is over a size range and proceeds from posterior in an anterior direction (Fig. 27; Table 13). Our largest four specimens of Xiphias, 131- 668 mm ESL, had three to six anterior neural arches and spines split. These arches and spines remain split in adults (Bruce B. Collette3). Development of the centra starts with the appearance of distally opened cartilaginous neural arches. One arch was seen behind the head on top of the notochord in our smallest 3.7 mm ENL specimen (Fig. 29). As length in Xiphias increased, more arches were added in a posterior direction (Fig. 29; Table 14). All specimens >6.5 mm ENL had the complete count of 25 neural arches. Two cartilaginous split haemal arches were first observed at 5.0 mm ENL when 16 neural arches were present. The two haemal arches were opposite the 16th and future 17th neural arch. Additional haemal arches and spines were added in a posterior direction (Fig. 29; Table 15). 3Bruce B. Collette, Systematic Zoologist, National Marine Fisheries Service, NOAA, Systematics Laboratory, Washing- ton, DC 20560, pers. commun. July 1981. Table 13.— Number of split neural arches and spines counted from anterior to posterior for various size ranges in 159 Xiphias gladius 5.5 mm ENL-668 mm ESL. N = number of specimens, X= mean. Length, mm ENL or ESL Centrum number with split neural arches and spines 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 N X 5.5-6.9 15 2 5 3 3 5 113 1 1 2 5 38 17.1 7.0-133 5 5 12 18 18 10 3 2 1 — 2 — — — — 1 77 107 13 6-64.6 2 6 8 17 6 — 1 40 86 131-668 1 — 2 1 4 48 176 POTTHOFF and KELLEY: OSTEOLOGICAL DEVELOPMENT IN SWORDFISH 0.25 mm 1mm Figure 26.— Left lateral view of the 15th vertebra from Xiphias gladius, showing the ontogeny. Starting from top left the specimens in millimeters ENL or ESL are as in Figure 25. FBr, foraminal bridge; HPo, haemal postzygapophysis; for other abbreviations, see Fig- ure 25. Cartilage, white (except in 5.1 mm ENL specimen in top row left, where entire stippling signifies cartilage); ossifying, stippled. 0-25mm Figure 27.— First and second anteriormost ver- tebrae from a 12.8 mm ESL Xiphias gladius. Top, left lateral view; bot- tom, dorsal view. For abbreviations, see Fig- gures 25 and 26. All specimens >6.0 mm ENL had the complete count of eight or nine haemal arches and spines. Ossification of the vertebral column started at 4.4 mm ENL anteriorly at the bases of the neural arches. All specimens longer than 5.0 mm ENL had some anterior vertebral column ossification. The ossification was in a posterior direction as length increased until all centra including the urostyle were ossifying in some specimens between 6.1 mm ENL and 8.1 mm ESL(Fig.29). In specimens >8.1 mm ESL all entra had some ossification. The development of the neural and haemal pre- and postzygapophyses is shown in Figures 20-23 and 25-28. Neural prezygapophyses devel- oped on all centra except the anteriormost cen- trum (Figs. 13, 27) and neural postzygapophyses developed on all centra except the urostyle (Figs. 21-23, 25-28). Haemal prezygapophyses devel- oped on all haemal spines and shifted dorsad and anteriorly onto the centrum during ontogeny (Figs. 20-23, 28); the haemal prezygapophyses on preural centrum 2 and on the parhypural re- mained on the autogenous haemal spine and the autogenous parhypural (Figs. 21-23). A neural foramen developed on each centrum except on the urostyle by first developing a neural postzygapophysis (Figs. 25-28). Then an anteriorly directed process developed on the anterodorsal side of the postzygapophysis, which joined the neural spine forming a neural foraminal bridge (Figs. 27, 28). The neural prezygapophysis of the second anterior centrum developed an entirely different shape than all other prezygapophyses and could be taken for a neural spine on small juvenile or 177 FISHERY BULLETIN: VOL. 80, NO. 2 Figure 28.— Left lateral view of the 17th vertebra from Xiphias gladius, showing the ontogeny. Starting from top left the speci- mens in millimeters ENL or ESL are as in Figure 25. Hs, haemal spine; HPr, haemal prezygapophysis; for other abbreviations, see Figures 25 and 26. Cartilage, white (except in 5.1 mm ENL specimen in top row left, where entire stippling signifies cartilage); ossifying, stippled. Table 14. — Development of the neural spines on the anterior to posterior numbered centra for 97 Xiphias gladius 3.7-7.0 mm ENL or ESL. N = number of specimens, X = mean. Length, mm ENL or ESL Centra with neural spines 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 N X 3.6-4.0 1 1 — 4.1-4.5 3 1 — 1 — — — 1 6 28 4.6-5.0 1 2 8 5 2 — 1 — — 1 — — — — 1 21 5.3 5.1-5.5 1 1 1 1 1 — - 2 — — 1 1 — — — — — 1 — 6 5 5 26 18.7 5.6-6.0 1 2 — 3 6 5 17 23.5 6.1-6.5 3 3 11 17 24.5 6.6-7.0 9 9 25.0 178 POTTHOFF anrl KELLEY: OSTEOLOGICAI, DEVELOPMENT IN SWORDFISH 2 4 6 8 10 12 14 16 18 20 22 24 26 I I I I I I I I I I I I I I I I I I I I I I I 1 3.7mm JUL^- 4.4mm 53 mm 6-2 mm 7.2 mm Figure 29.— Schematic presentation of the vertebral column development in Xiphias gladius. Ticks on scale denote centra number and are aligned with the middle of the centrum. Indicated millimeter mea- surements are ENL or ESL. Carti- lage, white; ossifying, stippled. Table 15. — Development of the haemal spines on the anterior to posterior numbered centra for 53 Xiphias gladius 5.0-6.5 mm ENL. N - number of specimens, A' = mean. Length, mm ENL or ESL Centra with hae mal spines 17 18 19 20 21 22 23 24 25 N X 5.0 1 1 17.0 5.1-5.5 1 1 — 1 1 4 3 8 19 23.4 5.6-60 1 — 2 1 2 1 9 16 23.6 6.1-6.5 17 17 25.0 larger specimens (Figs. 8, 13, 25, 27). This prezygapophysis is considerably longer than the neural spine except in large juveniles and adults (Fig. 25). Ribs developed from a short piece of proximal cartilage. The cartilage later ossified and bone cells were added distally directly in the length- ening process of the rib during development. One pair of ribs was first seen on the anteriormost centrum at 8.0 mm ESL in some specimens. All Xiphias >12.2 mm ESL had at least one pair of ribs developing. Development was in a posterior direction on the first four centra and in an anterior direction on centra 15 and 14. When centra 1-3 had developing ribs, usually a pair also was present on centrum 15. Ribs developed over a wide size range. The smallest specimen with a full set of ribs on centra 1-4, 14, and 15 measured 25.1 mm ESL and all specimens larger than 55.1 mm ESL had the full rib complement. Xiphias usually developed ribs on centra 1-4, 14, and 15, but a few specimens also had ribs on centra 5, 6, 13, and 16. BRANCHIOSTEGAL RAYS Branchiostegal rays were first seen in a 4.2 mm ENL specimen and all Xiphias >4.2 mm ENL had some rays. The 4.2 mm ENL Xiphias had four rays on each side but a 4.5 mm ENL specimen had only two (Table 16). Branchioste- gals were added from posterior to anterior di- rection, specimens with developing branchios- tegals had either the same count on both sides or differed by one ray between sides. Adult counts of seven or eight rays were first observed at 5.0 mm ENL and all Xiphias >6.6 mm ENL had 179 FISHERY BULLETIN: VOL. 80, NO. 2 Table 16.— Development of the branchiostegal rays on the left and right sides for 211 Xiphias gladius (3.7 mm ENL-225, 668 mm ESL). A^number of specimens, X=mean, SD = standard deviation. Length, Number branchiostegal rays, left N Number branchiostegal rays , right or ESL 0 12 3 4 5 6 7 8 X SD 0 12 3 4 5 6 7 8 X SD 3.6-4.5 1 4.6-55 5.6-6.5 6.6-668 — 1 - 3 7 1 8 1 11 19 2 24 71 3.6 2.12 5.9 1.34 6 7 1 0.57 56 7.4 0.45 7 45 32 127 1 — 1 1 2 8 1 6 1 13 3 16 21 78 2 8 49 3.4 2.12 6 0 1.34 7.1 057 7.4 0.45 180 POTTHOFF and KELLEY: OSTEOLOGICAL DEVELOPMENT IN SWORDFISH adult counts (Table 16). Of 127 Xiphias (6.6 mm ENL-668 mm ESL), 59 (46.4%) had seven bran- chiostegals on both sides, 37 (29.2%) had eight on both sides, and 31 (24.4%) had seven rays on one side and eight on the other. SQUAMATION Larvae of Xiphias developed four rows of scales on each side with smaller "scatter" scales between the rows (Fig. 30). First to appear be- tween 5.3 and 6.1 mm ENL were some ventral "row" scales on the stomach. These scales were added during growth anterior to the pectoral symphysis and posteriorly to the ventral hypurals. Dorsal row scales were first seen be- tween 5.7 and 6.9 mm ENL, approximately be- tween the 3d and 15th centrum. The addition of dorsal row scales during growth was in an ante- rior direction to the top of the head and in a pos- terior direction to the dorsal hypurals. The two lateral scale rows were first seen in some specimens between 6.5 mm ENL and 8.6 mm ESL, extending from the posterior border of the pectoral fin to about the 16th centrum. Scales were added anteriorly only to the dorsal lateral row to about the operculum and posteriorly to the urostyle. Scatter scales, between the dorsal, ventral, and lateral scale rows first developed between 6.2 and 7.1 mm ENL on the stomach just posterior to the pectoral fin and dorsad to the ventral scale row (Fig. 30). Scatter scales, which were smaller than row scales, spread from the stomach dorsad during growth until the left and right sides in an area from the 4th centrum to the 18th centrum were covered (Fig. 30). Further addition of scatter scales was then in an anterior and posterior direction covering the whole body, the sword, and the caudal fin rays at 61.5 mm ESL, but not the pectoral, dorsal, and anal fins. In our 187 mm ESL specimen the dorsal, anal, and pectoral fin rays were covered with scatter scales. In the literature, Arata (1954); Leim and Scott (1966); Nakamura et al. (1968), and Palko et al. (1981) stated that adult Xiph ias lack scales. Figure 30.— Larval and juvenile Xiphias gladius, depicting the ontogeny of squamation. The size of scales was exaggerated in proportion to the body. Starting from the top and going to the bottom the specimens' lengths in millimeters are: 5.3 ENL, 6.2 ENL, 7.6 ESL, 11.5 ESL, 35.4 ESL, 188 ESL. Our largest 668 mm ESL specimen had scales (Fig. 31), seen through the dissecting microscope on a cleared and stained piece of skin. In this specimen the row scales could no longer be dis- tinguished from the scatter scales. Development of individual scales is similar for the row and scatter scales, except scatter scales start out smaller than row scales but increase in size to equal the row scales during development. Each scale starts as an oval-shaped structure with one posteriorly recurved spine. During development more posteriorly recurved spines are acquired in a row at the center of the scales and the scale margins become progressively crenated (Fig. 32). Finally, in specimens >200 mm ESL the marginal scale crenations become fewer and the recurved spines develop into blunt stubs (Fig. 32). Individual row scales have approximately the same number of spines in a developing specimen, but this does not apply for the scatter scales. Our largest 668 mm ESL Xiphias had developed variable scales which had from one to seven blunt stubby spines; row scales were not distin- guishable from scatter scales in this specimen (Figs. 31, 32). Arata's (1954) work on scale devel- opment agrees with our findings. 0.25mm Figure 31.— Enlarged view of the skin from a 668 mm ESL Xiphias gladius, showing scales with two to six posteriorly re- curved spines. White spaces between scales are skin. Anterior is to the left. 181 FISHERY BULLETIN: VOL. 80, NO. 2 Figure 32.— Scales from Xiphias gladius, showing ontogeny. Starting from left the specimens' lengths in millimeters are: top, 5.4 ENL, 6.2 ENL, 25.1 ESL; bottom, 61.5 ESL, 225 ESL, 668 ESL. Each size in top and bottom rows has an external view (top) and a lateral view (bottom). 0.01mm 1.0mm 0.10 mm 1.0 mm 1.0 mm DISCUSSION Xiphias gladius is a highly modified perci- form fish which, in our opinion, should not be placed as the monotypic family Xiphiidae in the suborder Scrombroidei, as was done by Green- wood et al. (1966). We agree with Gosline (1968) and Fierstine (1974), who placed the monotypic family Xiphiidae under the separate suborder Xiphiioidei. However, Gregory and Conrad (1937) compared Xiphias bones with those of Istiophorus and concluded that xiphiids and istiophorids are separate but parallel families of common scombroid stock. G. David Johnson, who examined the branchial arches of Xiph ias, istio- phorids, and scombrids (unpubl. data), has evi- dence that Xiph ias belongs with the scombroids. We will discuss the modifications and variations that we noted in Xiph ias and compare these with other fish families. The pectoral fin position in Xiphias larvae is lateral, but during growth to adults the fin moves ventrad to an almost pelvic position. Xiphias probably lost its pelvic fin during phylogeny. Remnants of a basipterygium were not found by us or other workers during develop- ment of the larvae (Yasuda et al. 1978). Pectoral fin ray counts of the left and right sides were equal or differed by one ray in juvenile Xiphias. Similar results were obtained for Archosargus (Houde and Potthoff 1976), Coryphaena (Potthoff 1980), and Scombrolabrax (Potthoff et al. 1980). In tunas, larger differences in pectoral fin ray counts between sides were found (Potthoff 1974). With the publication of Dingerkus and Uhler's (1977) cartilage staining technique, Fritzsche and Johnson (1980) reported the development of pectoral radials from a sheet of cartilage in Morone. Swinnerton (1905) reported the same for Salmo salar by using the "reconstruction in wax from serial sections" technique; he called the cartilaginous blade "fin-plate." We saw the same happening in Xiph ias and labeled the sheet of cartilage "blade" (Bl) in Figure 3. It is likely that pectoral radials develop from a cartilagi- nous blade in all Perciformes, and perhaps all lower fishes. Starks (1930) reported a cartilagi- nous blade (radial plate) in adult Dallia pecto- ral is and Roberts (1981) in the salmoniform Sun- dasalangidae; we believe this to be an example of a neotenic structure. The pectoral girdle in Xiphias is reduced as compared with a basic perciform pectoral girdle such as that found in Coryphaena (Potthoff 1980) and in at least some scombrids, e.g., Sardini (Collette and Chao 1975), Acanthoeybium (Conrad 1938), and Thu>nius(de Sylva 1955). In Xiphias, the supratemporal and intertemporal bones are absent and there is only one post- cleithrum. Adult Xiphias have two dorsal and two anal 182 1'OTTIIOFF an.] KKI.I.KV: OSTKOLOOICAI, I)K VKI.OI'M KNT IN SWOKDFISH fins (Leim and Scott 1966; Ovchinnikov 1970), but larvae and juveniles have one continuous dorsal and anal fin (Nakamuraetal. 1951; Yabe et al. 1959). During development the fin rays in the center of the fins stop growing and the rays become subcutaneous. The subcutaneous rays and their pterygiophores are present in the adults and were dissected in our largest 668 mm SL specimen. In three scombrid genera, Scomber, RastreUiger, and Auxis, we find a first dorsal and second dorsal fin separation similar to that in adult Xiphias, except that in these scombrids the two fins are separate initially even though the first and second dorsal fin pterygio- phores are continuous (Kramer 1960; Potthoff pers. obs. on Auxis). There is only one anal fin in these three scombrid genera, whereas adult Xiphias have two anal fins. All dorsal rays in Xiphias are bifurcated at their bases (Figs. 14, 15) as in Coryphaena (Potthoff 1980). This probably is not the case in most perciforms where the spinous rays of the first dorsal fin have a closed base with a foramen and the distal radials are situated outside the bases of the first dorsal fin spinous rays (Kramer 1960; Potthoff 1974, 1975; Potthoff et al. 1980). The anteriormost dorsal pterygiophores in Xiphias insert in the second interneural space (Figs. 11, 13), asinthegempylidsandtrichiurids (Potthoff et al. 1980), but not as in the serranids, sparids, apogonids, scombrolabracids, and scrombrids where the anteriormost pterygio- phores insert in the third interneural space (Matsui 1967; Fraser 1972; Potthoff 1974, 1975; Houde and Potthoff 1976; Fritzsche and Johnson 1980; Potthoff et al. 1980), and not as in the coryphaenids in which they insert in the first space (Potthoff 1980). No predorsal bones were present in Xiphias. All scombrids and most scombroids also lack predorsal bones, however some gempylids, e.g., Ruvettus (Potthoff et al. 1980), have one predorsal. Most other perci- formes have predorsals in the first and second interneural spaces. The first dorsal pterygiophore in Xiphias is variable in development (Figs. 7, 8) and originates either from one or two pieces of cartilage. In scombrids (Potthoff 1974, 1975), a two-part development of the first dorsal pterygio- phore was not evidenced, but in Morone it was (Fritzsche and Johnson 1980). The last (posteriormost) pterygiophore of Xiphias has a serially associated double ray and a stay (Figs. 9, 10). In Xiphias, as probably in all Perciformes, the stay develops from the prox- imal radial cartilage. The stay is not posteriorly bifurcated as in most scombrids (Potthoff pers. obs.), nor does it ossify into two parts as in most gempylids and some trichiurids (Potthoff et al. 1980). Xiphias lacks middle radials as does Cory- phaena (Potthoff 1980), whereas many Per- ciformes probably have middle radials at least for some of the posteriormost dorsal and anal pterygiophores (Kramer 1960; Berry 1969; Potthoff 1974, 1975; Houde and Potthoff 1976; Potthoff et al. 1980; Fritzsche and Johnson 1980). In Xiphias the caudal rays are supported by only two centra (urostyle and preural centrum 2) (Figs. 17, 21, 22). This is unusual, because in most perciforms three centra support the caudal rays (Berry 1969; Houde and Potthoff 1976; Potthoff 1980; Potthoff et al. 1980; Fritzsche and Johnson 1980), and in most scombrids four or five centra support the caudal rays (Collette and Chao 1975; Potthoff 1975; Collette and Russo 1978), except in Scomber and RastreUiger where three centra support caudal rays (Potthoff pers. obs.). Xiphias lacks a second uroneural in the caudal complex which is present in the basic perciform caudal such as in Archosargus (Houde and Potthoff 1976), Elagatis (Berry 1969), Scom- brolabrax (Potthoff et al. 1980), Morone (Fritzsche and Johnson 1980), and Coryphaena (Potthoff 1980), but is absent in the scombrids (Potthoff 1975). The single uroneural of Xiphias does not fuse to the urostyle in adults as in Thunnini and Sardini (Collette and Chao 1975; Potthoff 1975; Collette and Russo 1978), but in several specimens anomalous shapes of the uroneural were observed (Fig. 22). We believe that Xiph ias has lost preural cen- trum 3, because a centrum having an autogenous haemal spine and a neural spine with articular cartilage is lacking (Figs. 20-23). However, 1 specimen out of 164 examined with the unusual vertebral count of 16+11=27 (typical counts 15+ 11 or 16+10=26) had two autogenous haemal spines on preural centra 2 and 3. To our knowl- edge, a perciform caudal with only one autogen- ous haemal spine as in Xiphias has not been reported previously. We cannot totally rely on Monod (1968) or any other osteological descrip- tive work dealing only with adult fish because Potthoff (1975) showed that some autogenous hypural parts fuse during development and can- not be recognized in adults. There is considerable fusion of caudal complex 183 FISHERY BULLETIN: VOL. 80, NO. 2 bones in Xiphias. Hypurals 1-4 and the urostyle fuse to one posteriorly notched hypural plate during development (Fig. 23); the three epurals, the uroneural pair, hypural 5, and the par- hypural remain autogenous, whereas in Thun- nini and Sardini only one epural remains autogenous and the paired uroneural fuses to the urostyle (Collette and Chao 1975; Potthoff 1975; Collette and Russo 1978). In Xiphias, hypurals 1- 4 develop initially from distinctly separate pieces of cartilage and fusion of the hypurals into the notched hypural plate occurs. In Scombridae a similar yet different development takes place, because in Thunnini hypurals 1 and 2 originate from one distinctly larger piece of cartilage, whereas in Scomber (Pneumatophorus), hypurals 1 and 2 originate from separate pieces of cartilage as in Xiphias (Kramer 1960). The caudal rays in adult scombrids, except Scombrini, cover the whole hypural plate (Collette and Chao 1975; Collette and Russo 1978), whereas in Xiphias a smaller area is covered by the rays (Figs. 17, 22, 23). When the rays are disarticulated from the hypural plate in adult Xiphias, long vertical depressions caused by the rays can be observed on the hypural plate (Fig. 23). Xiphias has a greater number of precaudal than caudal vertebrae (Fig. 6) (Leim and Scott 1966; Ovchinnikov 1970). The same tencency was observed in the gempylids (Matsubara and Iwai 1958; Potthoff et al. 1980) and the opposite tendency in the scombrids (Conrad 1938; de Sylva 1955; Mago Leccia 1958; Kramer 1960; Gibbs and Collette 1967; Matsui 1967; Potthoff and Richards 1970; Collette and Chao 1975). Generally, the tendency in the perciform fishes is to have a higher caudal vertebral count; the most typical count being 10+14=24 vertebrae (John- son 1981). The neural and haemal arches in Xiphias first develop distally opened (split) (Fig. 27). Dur- ing development the neural and haemal arches fuse forming spines. Fusion of the neural and haemal spines proceeds from posterior in an ante- rior direction (Table 13). In other perciforms studied by Potthoff, split arches were sometimes observed on small larvae on the anteriormost first and second centra only, but these two arches fused to spines during development. Adult Xiphias retain three to six anteriormost split neural arches (Bruce B. Collette footnote 3). Rib development and position is unique in Xiphias. Commonly, perciforms have pairs of dorsal (epipleural) ribs on the precaudal verte- brae starting on the first centrum and pleural ribs starting on the third centrum (Houde and Potthoff 1976; Potthoff et al. 1980). These ribs develop from anterior in a posterior direction. Xiphias, however, has lost many of its ribs. Generally, there are only one pair of ribs on each of the first four centra, which develop from anterior in a posterior direction and one pair on the last two precaudal vertebrae which develop from posterior in an anterior direction. We do not know if the ribs in Xiphias were originally epipleural, pleural, or a combination of epi- pleural and pleural. We were able to determine, however, the cartilage origin of ribs in Xiphias. Tibbo et al. (1961) stated that ribs in adult Xiphias are short and poorly developed, but no details on rib position were given. An account of rib development in lower and higher fishes is given by Emelianov (1935). He found that some bony fish develop ribs from cartilage, in others rib development from cartilage is bypassed and ribs develop directly from bone cells, and still in others, parts of the ribs develop from cartilage and other parts of the same rib develop directly from bone. In Xiphias the proximal portions of each rib originate from cartilage, the distal portions develop directly as bone. The branchiostegal ray count in Xiphias may vary by one ray from specimen to specimen or it may vary between left and right sides in a speci- men. Usually, branchiostegal ray counts are conservative and characterize fish families and sometimes genera (Kishinouye 1923; McAllister 1968; Fraser 1972; Ahlstrom etal. 1976; Kendall 1979; Matsuura 1979), however variability has been reported in some groups such as Carangidae (McAllister 1968). We cannot make firm conclusions about the phylogenetic status of Xiphias. From our study we conclude that Xiph ias is a perciform fish that differs from other perciforms to warrant the separate suborder Xiphiioidei. We were unable to determine relationship with the scombroids (gempylids, scombrids). A comparison with istiophorids remains to be done, and we believe we furnished sufficient material to facilitate such a comparison. ACKNOWLEDGMENTS We thank Bruce B. Collette, Edward D. Houde, G. David Johnson, Izumi Nakamura, 184 P0TTH0FF and KELLFY: OSTEOLOGICAL DEVELOPMENT IN SWORDFISH William J. Richards, and Joseph L. Russo for their critical comments on the manuscript. We thank Joaquin Javech for the fine illustrations. Our thanks also go to the persons who supplied us with specimens: Steven Berkeley, Edward D. Houde, G. David Johnson, Mark M. Leiby, William J. Richards, and Donald P. de Sylva. We thank Steven Loher for taking osteological ob- servations and Kelly Clark for clearing and staining. We thank Phyllis Fisher for typing the manuscript. LITERATURE CITED Ahlstrom, E. H., J. L. Butler, and B. Y. Sumida. 1976. Pelagic stromateoid fishes (Pisces, Perciformes) of the eastern Pacific: kinds, distributions, and early life histories and observations on five of these from the northwest Atlantic. Bull. Mar. Sci. 26:285-402. Arata, G. F., Jr. 1954. A contribution to the life history of the swordfish, Xiphias gladius Linnaeus, from the South Atlantic coast of the United States and the Gulf of Mexico. Bull. Mar. Sci. Gulf Caribb. 4:183-243. Berry, F. H. 1969. Elagatis bipinnulata (Pisces: Carangidae): Mor- phology of the fins and other characters. Copeia 1969: 454-463. COLLETTE, B. B., AND L. N. CHAO. 1975. Systematics and morphology of the bonitos {Sa rda) and their relatives (Scombridae, Sardini). Fish. Bull., U.S. 73:516-625. COLLETTE, B. B., AND J. L. RUSSO. 1978. An introduction to the Spanish mackerels, genus Scorn beromorus. In Proceedings of the Mackerel Col- loquium, p. 3-16. Gulf States Mar. Fish. Comm., Brownsville, Tex. Conrad, G. M. 1938. The osteology and relationships of the wahoo (Acanthocybium solandri), a scombroid fish. Am. Mus. Novit. 1000, 32 p. de Sylva, D. P. 1955. The osteology and phylogenetic relationships of the blackfin tuna, Thunnus atlanticus (Lesson). Bull. Mar. Sci. Gulf Caribb. 5:1-41. DlNGERKUS, G., AND L. D. UHLER. 1977. Enzyme clearing of alcian blue stained whole small vertebrates for demonstraton of cartilage. Stain Technol. 52:229-232. Ehrenbaum, E. 1905. Fam. Xiphiidae, Xiphias gladius L. In E. Ehrenbaum, Nordisches Plankton, Zoologischer Teil, Vol. 1, p. 35. Von Lipsius & Tischer, Kiel and Leipzig. New ed.— A. Asher & Co., Amsterdam, 1964. Emelianov, S. W. 1935. Die Morphologie der Fischrippen. Zool. Jahrb., Abt. Anat. Ontog. Tiere 60:133-262. Fierstine, H. L. 1974. The paleontology of billfish— the state of the art. In R. S. Shomuraand F.Williams (editors). Proceedings of the International Billfish Symposium, Kailua-Kona, Hawaii, 9-12 August 1972. Part 2. Review and con- tributed papers, p. 34-44. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-675. Fraser, T. H. 1972. Comparative osteology of the shallow water cardi- nal fishes (Perciformes: Apogonidae) with reference to the systematics and evolution of the family. Rhodes Univ., J. L. B. Smith Inst. Ichthyol. Spec. Publ. 34, 105 p. Fritzsche, R. A., and G. D. Johnson. 1980. Early osteological development of white perch and striped bass with emphasis on identification of their larvae. Trans. Am. Fish. Soc. 109:387-406. Gibbs. R. H., Jr., and B. B. Collette. 1967. Comparative anatomy and systematics of the tunas, genus Thunnus. U.S. Fish Wildl. Serv., Fish. Bull. 66:65-130. Gosline, W. A. 1961a. The perciform caudal skeleton. Copeia 1961: 265-270. 1961b. Some osteological features of modern lower teleostean fishes. Smithson. Misc. Collect. 142(3), 42 p. 1968. The suborders of perciform fishes. Proc. U.S. Natl. Mus. 124(3647), 78 p. Greenwood, P. H., D. E. Rosen, S. H. Weitzman, and G. S. Myers. 1966. Phyletic studies of teleostean fishes, with a provi- sional classification of living forms. Bull. Am. Mus. Nat. Hist. 131:341-355. Gregory, W. K., and G. M. Conrad. 1937. The comparative osteology of the swordfish (Xiphias) and the sailfish (Istiophorus). Am. Mus. Novit. 952, 25 p. Houde, E. D., and T. Potthoff. 1976. Egg and larval development of the sea bream Archosargus rhomboidalis (Linnaeus): Pisces, Sparidae. Bull. Mar. Sci. 26:506-529. Johnson, G. D. 1975. The procurrent spur: an undescribed perciform caudal character and its phylogenetic implications. Occas. Pap. Calif. Acad. Sci. 121, 23 p. 1981. The limits and relationships of the Lutjanidae and associated families. Bull. Scripps Inst. Oceanogr., Univ. Calif. Vol. 24, 114 p. Jones, S. 1958. Notes on eggs, larvae, and juveniles of fishes from Indian waters. I. Xiphias gladius Linnaeus. Indian J. Fish. 5:357-361. 1962. Notes on eggs, larvae and juveniles of fishes from Indian waters. XIV. Further notes on Xiphias gladius Linnaeus. Indian J. Fish. 9(Sect. A):525-529. Kendall, A. W., Jr. 1979. Morphological comparisons of North American sea bass larvae (Pisces: Serranidae). U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circ. 428, 50 p. Kishinouye, K. 1923. 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U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-675. Matsubara, K., and T. Iwai. 1958. Anatomy and relationships of the Japanese fishes of the family Gempylidae. Mem. Coll. Agric. Kyoto Univ., Fish. Ser. Spec. No., p. 23-54. Matsui, T. 1967. Review of the mackerel genera Scomber and Rastrelliger with description of a new species of Rastrelliger. Copeia 1967:71-83. Matsuura, K. 1979. Phylogeny of the superfamily Balistoidea (Pisces: Tetraodontiformes). Mem. Fac. Fish., Hokkaido Univ. 26:49-169. McAllister, D. E. 1968. The evolution of branchiostegals and associated opercular, gular, and hyoid bones and the classification of teleostome fishes, living and fossil. Natl. Mus. Can., Bull. 221, 239 p. Monod, T. 1968. Le complexe urophore des poissons teleosteens. Mem. Inst. Fond. Afr. Noire 81, 705 p. Nakamura, I., T. Iwai, and K. Matsubara. 1968. A review of the sailfish, spearfish, marlin, and swordfish of the world. [InJpn.] Kyoto Univ., Misaki Mar. Biol. Inst, Spec. Rep. 4, 95 p. (Engl, transl. by National Marine Fisheries Service.) Nakamura, H., T. Kamimura, Y. Yabuta, A. Suda, S. Ueyanagi, S. Kikawa, M. Honma, M. Yukinawa, and S. MORIKAWA. 1951. Notes of the life-history of the sword-fish, Xiphias gladius Linnaeus. Jpn. J. Ichthyol. 1:264-271. Nursall, J. R. 1963. The hypurapophysis, an important element of the caudal skeleton. Copeia 1963:458-459. Nybelin, 0. 1963. Zur Morphologie und Terminologie des Schwanz- skelettes der Actinopterygier. Ark. Zool., Ser. 2, 15:485-516. OVCHINNIKOV, V. V. 1970. Swordfishes and billfishes in the Atlantic Ocean; ecology and functional morphology, fin Russ.] Atl. Sci. Res. Inst. Fish. Oceanogr. (Engl, transl. by Isr. Program Sci. Transl., 77 p.; available U.S. Dep. Commer., Natl. Tech. Inf. Serv., Springfield, Va., as TT71-50011.) Palko, B. J., G. L. Beardsley, and W. J. Richards. 1981. Synopsis of the biology of the swordfish, Xiphias gladius Linnaeus. U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circ. 441, 21 p. Potthoff, T. 1974. Osteological development and variation in young tunas, genus Thunnus (Pisces, Scombridae), from the Atlantic Ocean. Fish. Bull., U.S. 72:563-588. 1975. Development and structure of the caudal complex, the vertebral column, and the pterygiophores in the blackfin tuna (Thunnus atlanticus, Pisces, Scombridae). Bull. Mar. Sci. 25:205-231. 1980. Development and structure of fins and fin supports in dolphin fishes Coryphaena hi ppurus and Coryphaena eguiselis (Coryphaenidae). Fish. Bull., U.S. 78:277- 312. Potthoff, T., and W. J. Richards. 1970. Juvenile bluefin tuna, Thunnus th ynnus (Linnaeus), and other scombrids taken by terns in the Dry Tortugas, Florida. Bull. Mar. Sci. 20:389-413. Potthoff, T., W. J. Richards, and S. Ueyanagi. 1980. Development of Scombrolabrax heterolepis (Pisces, Scombrolabracidae) and comments on familial relation- ships. Bull. Mar. Sci. 30:329-357. Regan, C. T. 1924. A young swordfish (Xiph ias gladius), with a note on Clupeolabrus. Ann. Mag. Nat. Hist., Ser. 9, 13:224-225. Richards, W. J. 1974. Evaluation of identification methods for young billfishes. In R. S. Shomura and F. Williams (editors), Proceedings of the International Billfish Symposium, Kailua-Kona, Hawaii, 9-12 August 1972, Part 2. Review and contributed papers, p. 62-72. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-675. Roberts, T. R. 1981. Sundasalangidae, a new family of minute freshwater salmoniform fishes from Southeast Asia. Proc. Calif. Acad. Sci., Ser. 4, 42:295-302. Sanzo, L. 1910. Uovo e larva di pesce-soada (Xiphias gladius L.). Riv. Mens. Pesca Idrobiol. 12:206-209. 1922. Uovae larve di Xiph ias gladiush. Mem. R. Com. Talassogr. Ital., ano 79, 17 p. Starks, E. C. 1930. The primary shoulder girdle of the bony fishes. Stanford Univ. Publ., Biol. Sci. 6:147-240. Swinnerton, H. H. 1905. A contribution to the morphology and development of the pectoral skeleton of teleosteans. Q. J. Microsc. Sci., New Ser., 49:363-382. TAning, A. V. 1955. On the breeding areas of the swordfish (Xiphias). Deep-Sea Res., Pap. Mar. Biol. Oceanogr., suppl. to vol. 3:438-450. Taylor, W. R. 1967. An enzyme method of clearing and staining small vertebrates. Proc. U.S. Natl. Mus. 122(3596), 17 p. Tibbo, S. N., L. R. Day, and W. F. Doucet. 1961. The swordfish (Xiphias gladius L.), its life-history and economic importance in the northwest Atlantic. Fish. Res. Board Can., Bull. 130. 47 p. Yabe, H. 1951 . Larva of the swordfish, Xiph ias gladius. [In Jpn., Engl, summ.] Jpn. J. Ichthyol. 1:260-263. Yabe, H., S. Ueyanagi, S. Kikawa, and H. Watanabe. 1959. Study on the life-history of the sword-fish, Xiphias gladius Linnaeus. [In Jpn., Engl, summ.] Rep. Nankai Reg. Fish. Res. Lab. 10:107-150. (Transl. by Musam Fujiya available.) Yasuda, F., H. Kohno, A. Yatsu, H. Ida, P. Arena, F. Li Greci, and Y. Taki. 1978. Embryonic and early larval stages of the sword- fish, Xiphias gladius, from the Mediterranean. J. Tokyo Univ. Fish. 65:91-97. 186 AGE AND GROWTH OF LARVAL ATLANTIC HERRING, CLUPEA HARENGUS L., IN THE GULF OF MAINE-GEORGES BANK REGION BASED ON OTOLITH GROWTH INCREMENTS R. Gregory Lough, Michael Pennington, George R. Bolz, and Andrew A. Rosenberg1 ABSTRACT An estimate of the age and growth of herring larvae over their first 6 months of life is made by examining presumed daily growth increments in their otoliths. A Gompertz growth curve fitted to 311 autumn-spawned specimens collected in the Gulf of Maine-Georges Bank region describes the mean length at age (based on a range of 7-160 otolith increments (from an initial hatching size of 5. 7 mm SL to a mean length of 30.9 mm at 175 days. A larva with 7 growth increments isestimated to be on average 25 days old with a mean length of 12.7 mm. Larvae reared in the laboratory at 10°C began initial increment deposition on average 4.5 days from hatching at the time of yolk-sac absorption, and the second increment was deposited an average of 12 days from hatching. The rearing experi- ments were terminated before an increment-day relation could be established, but the third incre- ment was estimated to be formed on average 22 days from hatching. Support for the assumption that increment deposition becomes daily at least after the third increment is made by two independent methods. Based on the fitted Gompertz curve, average growth rates for herring larvae increased from 0.25 mm/day at hatch to 0.30 mm/day at 20 days and declined to <0.15 mm/day after 75 days of age during the winter period. This agrees closely with estimated field rates. Atlantic herring, Clupea harengus L., spawn de- mersal eggs during late summer-autumn on the shoaler «40 m bottom depth) regions of Georges Bank and around the perimeter of the Gulf of Maine ( Bigelow and Schroeder 1953; Boyer et al. 1973; Lough and Bolz 19792). Hatching occurs after 8-9 d at 10°C (Cooper et al.3), and shortly thereafter the larvae are dispersed throughout the water column by the vigorous tidal stirring characteristic of this region (Bumpus 1976). By following length-frequency means or modes be- tween successive surveys, average larval growth rates have been estimated on field populations of larvae in the Gulf of Maine-Georges Bank region by Tibbo et al. (1958), Tibbo and Legare (1960), Das (1968, 1972), Graham et al. (1972), Sameoto (1972), Boyar et al. (1973), Lough et al. (1979),4 'Northeast Fisheries Center Woods Hole Laboratory, Na- tional Marine Fisheries Service, NOAA, Woods Hole, MA 02543. -'Lough, R. G., and G. R. Bolz. 1979. A description of the sampling methods, and larval herring (Clupea harengus L.) data for surveys conducted from 1968-1978 in the Georges Bank and Gulf of Maine areas. Northeast Fisheries Center, Natl. Mar. Fish. Serv., NOAA, Woods Hole Lab. Ref. 79-06, 230 p. Cooper, R. A., J. R. Uzmann, R. A. Clifford, and K. J. Pecci. 1975. Direct observations of herring ( Clupea harengus haren- gus L.) egg beds on Jeffreys Ledge, Gulf of Maine in 1974. ICNAF Res. Doc. 75/93, 6 p. 4Lough, R. G., G. R. Bolz, M. D. Grosslein, and D. C. Potter. 1979. Abundance and survival of sea herring (Clu pea haren- and others. Larval herring grow at an overall average rate of about 5 mm/mo (0.2 mm/d) from hatch (6 mm SL) to metamorphosis in the spring. Metamorphosis is a gradual transition to adult characteristics generally achieved by the time the fish are 50-55 mm, but some studies report metamorphosis occurring at much smaller lengths of 30-35 mm (Blaxter and Staines 1971; Boyar et al. 1973; Ehrlich et al. 1976; Doyle 1977). Knowledge of larval herring growth is an im- portant component in the estimation of age- specific mortality rates, which can be used to study variations in larval survival in relation to size of succeeding year classes. However, field estimates of larval growth only provide average rates of growth so that their use in comparative studies is limited by the sometimes polymodal length frequencies and subjective nature of con- necting corresponding length modes. With the development of accurate growth models, popula- tions can be compared by region and season with various environmental factors which may be affecting growth and hence survival of larvae. Techniques are now available for the accurate aging of larval and juvenile fishes based on Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80, NO. 2. 1982. gus L.) larvae in relation to environmental factors, spawning stock size, and recruitment for the Georges Bank area, 1968- 1977 seasons. ICNAF Res. Doc. 79/VI/112, 47 p. 187 FISHERY BULLETIN: VOL. 80, NO. 2 growth increments or lamellae in their otoliths, thus providing a detailed chronological record of events in the growth history of an individual fish (Pannella 1971, 1974; Scott 1973; Brothers et al. 1976; Struhsaker and Uchiyama 1976; Ralston 1976; Taubert and Coble 1977; Barkman 1978; Methot and Kramer 1979; Radtke 19805; Radtke and Waiwood 1980; Steffensen 1980; Wilson and Larkin 1980; Uchiyama and Struhsaker 1981; Barkman et al. 1981; Brothers 1981; Brothers and McFarland 1981; Methot 1981). Evidence for the presence of apparent daily otolith growth increments in larval herring collected along western Gulf of Maine in October 1976 was given in a preliminary report by Rosenberg and Lough.6 Further work by Lough et al.7 led to the development of a growth model extending through the autumn-winter period. Townsend and Graham (1981) recently used otolith aging techniques to examine the age structure of larval herring entering the Sheepscot River, Maine, estuary during autumn-winter 1978-79. The objective of this study is to summarize our findings on the age and growth of larval herring otoliths during the first 6 mo of life, from hatch- ing to a length of ca. 31 mm, based on larvae reared in the laboratory and collected in the Gulf of Maine-Georges Bank region. Also, aGompertz growth curve is fitted to the length-at-age data based on "daily" growth increment in their oto- liths to describe the shape of the average larval herring growth curve in this region from Octo- ber through March 1976-77. The present study was initiated by the International Commission for the Northwest Atlantic Fisheries (ICNAF) (Lough et al. 1981) and the U.S. participation was conducted concurrently as part of the MAR- MAP (Marine Resources Monitoring, Assess- ment, and Prediction) program of the Northeast Fisheries Center, which measures long-term changes in the variability of fish stock abun- dance off the northeast coast of the United States (Sherman 1980). METHODS Larval herring for otolith studies were col- lected at selected stations within a standard grid of sampling stations covering the western Gulf of Maine, Georges Bank, and Nantucket Shoals areas on five ICNAF larval herring surveys con- ducted from October 1976 through March 1977 (Table 1, Fig. 1). Larvae normally were collected at stations where high densities were encoun- tered. Standard ICNAF double-oblique contin- uous hauls (61 cm bongo net, 0.505 and 0.333 mm mesh nets) were made at each station to a maxi- mum depth of 100 m, or to within 5 m of the bot- tom in shoaler areas, while the vessel was under- way at 3.5 kn. A standard haul ranges in duration from 5 to 25 min; each bongo net filtering be- tween 100 and 1,000 m3 of water depending on the duration (maximum depth) of the haul. Fur- ther details of the sampling gear and protocols can be found in Lough and Bolz (footnote 2). Immediately after the nets were brought aboard the vessel, larvae were sorted from the untreated 0.505 mm mesh plankton sample and frozen in dishes. Extra hauls occasionally were made to collect sufficient numbers of larvae. Tempera- 1 1 I I fi t/6 J55 ) t //? \L~ rA-!!~s\y * ' —" /&'/ )^^X(P ,5*' / VI — 44° * a' efts If l/f I * V 'J * f'* \}\ 1 L %f *--» r < rJ •' "44 \ \ > ^S # 38 s V / ;J. 105 ~> / / *122 ( — 7 '• )( GULF OF MAINE "-< '^— - / s"\ZS'P I CST'< 102 , — ^ i t \ ~r~\ ( \ *v — 42° V "^^2 • no ! jSfcn L-/~' — 7 ~~N 72 ) '** \ * /' 35 GEORGES f f — NANTUCKET BANK i SHOALS / •20 • ,„ '*' a 33 100 M^ _- • 19 /' / ^--. --- " / ~— -~ s ~40' 1 70° I 68" 1 66- I 5Radtke, R. L. 1980. The formation and growth of otoliths from redfish (Sebastes spp.) larvae from the Flemish Cap (Di- vision 3M). NAFO SCR Doc. 80/1 X/ 153, 6 p. 6Rosenberg, A. S., and R. G. Lough. 1977. A preliminary report on the age and growth of larval herring (Clupea haren- giis) from daily growth increments in otoliths. ICES CM. 1977/L:22. 15 p. Figure 1.— Station locations in the Gulf of Maine-Georges Bank region where larval herring were collected for otolith aging over the 1976 spawning season. 7Lough, R. G., M. R. Pennington, G. R. Bolz, and A. S. Rosen- berg. 1980. A growth model for larval sea herring (Clupea harenyus L.) in the Georges Bank-Gulf of Maine area based on otolith growth increments. ICES CM. 1980/H:65, 22 p. 188 LOlHill KT AI..: ACK AND GROWTH OK LARVAL ATLANTIC HERRING 5 o 3 ca _c o> 3 .2" o o ~ 5 CD TO c aa P CO be CD c be O s_ - * ° i ■s ° c O * a- o c- -a cd 8 >> t« "^ C efl CD a> E *. .S a) o *j cu c &•- en £ be j S be l- 3 t. O cd j- J= -C ca > t- ca i—* Z s c 3 O 3 ca ca .o c o ca (72 W J CO < o c » ra - E CD O CD CO ~ ~ T3 Ol E <= C F m cd cz O - S Z™ 2 EO o c5° C\J E^ g^E o m CD i m 55 „.2>S Is' PI Q O 2 O to s Eg o p O CO CO to ^ oS — . o — • a> a) co *— — o —CD co o CO O CO CM i- CO N CD tJ; cDtbcsjco cnj r^ ^ cm ■. M I - I V H -* ^ V* I — -» » ■■ -*• t-i-C\JCM I- CM ^t CM CNJ tJ O CO *~ CN CNJ r- r- co cm r^. CM ^ CM CO i- •^ CO CD CO O CM O *- i- c\i cm - in ^ co t- o w o oir^p'- cm r^ -(J- N r- CO CO r- CJ) CO CO CO o i- i- t-CMi-^-CM CM CM CM CM CO lO O) O) S CO CO CO CO t- O) p O h-- CM CO CO C\i o cp ^r in tt CO CO s s cb cd o m p O O CO CO ZQQZ Z ZZZZZ ZZQO Q o m m o o cm to o o in t-cooco o Ot-i-co m ocsjcoom ocmcmco co CO^incO CD O ID O »- O) SOCOCD CM O'-'-O O OOt-i-O O *- *~ *- cm 1^ CD OOOU O CDCDCUCDCD 0) D ■3 n c OO o C CJ 0) CD CD ■ a) O zo? O Z S w CNJ CJ in r^ o n r\j n o \r> O O u-> o CNJ in m Cl PI in t CJ co T— CM CO O i— co o o o 0 O 0 0 0 o CD CO i^ r- s CD CO n CD co < 1 c ) O C5 CD UD UD UD UJ CO UJ UJ r-. CD CJJ IV h- f- r^ CD COCO^t1^- i- »-»-C\ICO'- oococo a ■c o 5 5 CO ■D c CO Q) to 3 «~ 2 en 5 > CO co CD CO 0) ^2 C « CD CD CO g- a E E2 H CD .*: o 3 ™ E >■ ZO ture data at each station were obtained from ex- pendable bathythermograph traces or surface bucket readings. Larvae were reared from fertilized eggs in the laboratory in order to determine the age at which increment deposition first begins in larval her- ring otoliths. A batch of herring eggs, stripped from several ripe and running adults collected along the western Gulf of Maine near Jeffreys Ledge, was fertilized on 17 October 1978 and reared at the NMFS Narragansett Laboratory at 10°C by G. Laurence for use in various feeding experiments. Larvae were maintained in special rearing aquaria described by Beyer and Laur- ence (1981) with a photoperiod of 12 h light and 12 h dark and fed wild plankton at high den- sities (>3 plankters/ml). Approximately 15 lar- vae were removed from the rearing aquaria daily from hatching on 28 October through 15 November and preserved in 75% ethyl alcohol. Prior to removing the otoliths, larvae were staged according to Doyle (1977) and measured for standard length (snout to caudal peduncle) and head length (snout to sagitta in normal posi- tion) to the nearest 0.1 mm. The largest otoliths (sagittae) were removed from both sides of the head when possible and mounted in Canada bal- sam or Permount.8 The otoliths were whole mounted and little difficulty was found in read- ing them intact so that further preparation was unnecessary. The 2-sagittae and 2-astericae ob- tained per individual from the laboratory-reared larvae were virtually impossible to distinguish at this early stage; however, the number of growth increments was identical for both sets of otoliths from the same individual. The otoliths were viewed by transmitted light and growth increments were counted using a Zeiss compound microscope-video system with a magnification range of 630X for the largest oto- liths and 1000X or 2000X for the smallest. Differ- ential interference microscopy was particularly helpful in distinguishing increments of the smallest otoliths. The resolving power of our microscope is in the range of 0.2-0.5 /nm. A mini- mum of three counts was made on all otoliths or counts were repeated until a mean value was reached with a maximum acceptable range of 5% variability. Routine otolith measurements made to the nearest micron as illustrated in Figure 2 included the following: 1) anterior-posterior di- 8Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 189 FISHERY BULLETIN: VOL. 80, NO. 2 %. - ;. f< ' BHAi D Figure 2.— Sagittae of herring larvae, Clupea harengus. Bar on photographs represents 10 fim; pr - primordium, a = anterior, p = posterior, nc = nuclear check. A. Otolith from laboratory-reared larva, 8.4 mm SL, showing 2 growth increments (1000X). Additional increments are optical artifacts. B. Otolith with 23 increments showing band of thin, poorly defined 4-5 increments around nucleus; 18.6 mm SL; Annandale 76-01, Stn. 38. C. Otolith with 51 increments (630X). Note the first 3-4 thin, poorly defined increments immediately surrounding nuclear check; 19.9 mm SL; Researcher 76-01, Stn. 105. D. Otolith with 54 incre- ments (630X), posterior view. Note pattern of increment thickness from initial thin, poorly defined 7-9 increments encircling a heavy nuclear check increasing to maximum thickness at 10th-35th increments and then decreasing thickness towards the edge; 21.6 mm SL; Researcher 76-01, Stn. 35. ameter (otolith length); 2) lateral diameter: a line perpendicular to anterior-posterior axis; 3) nu- cleus diameter: whole otolith at hatching without increments or to inner edge of first increment; 4) anterior radius: nucleus center (primordium) to anterior edge; and 5) posterior radius: nucleus center (primordium) to posterior edge. Selected otoliths were photographed, enlargements made, and increment thicknesses were mea- sured across a posterior radius from the nucleus using a Zeiss MOP Digital Image Analyzer Sys- tem. All field-collected larvae used in this study for otolith aging were frozen, whereas the labora- tory-reared larvae were preserved in 75% ethyl alcohol, and larvae referred to in other corrobo- rative field studies were preserved in Formalin. Theilacker (1980) reported that the amount of shrinkage of northern anchovy larvae, Engraulis mordax, varies with fish size and duration of time larvae are retained within the net. Larvae smaller than 11 mm SL net-treated for 20 min could shrink as much as 19% of their live length prior to preservation. We estimate that nearly all herring larvae collected on ICNAF surveys have been dead at least 20 min prior to preservation. An additional 3% shrinkage due to 5% Formalin preservation was recommended by Theilacker 190 LOUGH ET AL.: ACE AND GROWTH OF LARVAL ATLANTIC HERRING for all body parts after net-treatment, whereas preservation in ethyl alcohol (80%) did not cause any additional shrinkage in standard length. Townsend and Graham (1981) indicated that frozen herring larvae (27-45 mm TL) may shrink 3-4% more than Formalin-preserved larvae. From our experience we find that length mea- surements of frozen larvae can be more variable than those of Formalin-preserved larvae; how- ever, a thorough study has not been made. No correction factor was applied to our field-col- lected frozen larvae because of the uncertainty of time prior to preservation and the effect of freezing on shrinkage. We do not feel that the Gompertz population growth curve fit to the un- corrected field-collected larvae would be signifi- cantly altered with respect to shape compared with corrected data. When a direct comparison is made in this paper between laboratory-reared and field-estimated larval lengths, a shrinkage correction factor applied to the lab data will be specified based on Theilacker's ( 1980) work which probably is adequate for all clupeidlike larvae. RESULTS Otoliths from 311 herring larvae caught in plankton hauls were processed in this study cov- ering their first 6 mo of life from October through March 1977 (Table 1, Fig. 1). Approxi- mately 58% of the larvae were collected along the western Gulf of Maine, 23% from Nantucket Shoals, and 19% from Georges Bank. ICNAF surveys have never been conducted during the month of January so that there is a gap in time in our collection of larval otolith data from mid- December 1976 to mid-February 1977. The field- collected larvae ranged in length from 11 to 35 mm with most of the western Gulf of Maine lar- vae falling into the 11-31 mm size range; the Georges Bank larvae, 19-25 mm; and the Nan- tucket Shoals larvae, 26-35 mm. The number of otolith increments counted from the field-col- lected larvae ranged from 7 to 160. Since we were not able to collect any recently hatched lar- vae <11 mm length for otoliths on these surveys, laboratory-reared larvae had to suffice for the smallest size. Laboratory-Reared Larvae Hatching of the laboratory-reared larvae occurred over a 5-d period with 50% hatch esti- mated on 28 October 1978 for a mean incubation of 11 d. Yolk-sac resorption was estimated to be 50% complete 4-5 d after hatching, and 99% com- plete 6 d after hatching. The larvae began actively feeding at yolk-sac resorption and ap- peared to be healthy without any abnormalities throughout the more than 3 wk of rearing. Mor- tality over the first 13 d from hatching averaged 12%/d which is considered low. The age of larvae from hatching midpoint with 0-3 increments is given in Table 2 and Figure 3. The first incre- ment appeared on larval otoliths that ranged in age from 0 to 9 d from hatch with a middate of 4.5 d which indicates that the first increment is de- posited near the end of yolk-sac resorption. Lar- vae staged according to Doyle (1977) showed a progression of the three substages la-lc over the first 3 d from hatch so that after the third day only remnants of yolk sac remained. The second growth increment occurred in lar- vae 6-18+ d old with a middate of 12 d from hatch or 7.5 d from the middate of the first increment formation. The third increment was observed for the first time on a larva 16 d from hatch, but un- fortunately sampling was terminated before the Table 2.— Distribution of otolith growth increments, age in days from hatching midpoint, and mean stan- dard length of herring larvae reared in the laboratory at 10°C. Age (d) Mean standard length (mm)1 No Increments Midpoint Range larvae 0 3 0-6 8.0 8 1 4.5 0-9 8.1 25 2 12 6-18 + 9 1 21 3 (22 est.) 16- 9.5 3 'Measurements made on larvae preserved in 75% ethyl alcohol Unpreserved mean length of 55 larvae at hatch was 7.66 mm, standard deviation of 0 58 (Beyer and Laurence 1981). UJ a o 0 2 DAYS FROM HATCH Figure 3. — Otolith increment deposition for herring larvae sampled from 50% hatch through 18 d of rearing in the labora- tory at 10°C. Encircled points represent yolk-sac larvae. Num- bers above points denote numbers of larvae >1. 191 FISHERY BULLETIN: VOL. 80. NO. 2 complete age distribution of 3-increment larvae could be determined. If the range of ages of 3- increment larvae is similar to the 2-increment larvae, then the estimated age of 3-increment larvae would range from 16 to 28 d with a mid- date of 22 d from hatch. Otolith Growth The growth and morphology of young herring otoliths has been described previously by Hempel (1959) for specimens ranging in length (total) from 25 to 130 mm collected in the German Bight, by Watson (1964) for Maine herring of 85- 285 mm TL, and by Messieh (1975) for Bay of Fundy herring of 32-118 mm TL. Here we de- scribe the growth and morphology of herring otoliths (sagitta) in relation to head length for Gulf of Maine-Georges Bank larvae ranging in size from 5.7 mm (hatching) to 35 mm SL (prior to metamorphosis). The shape of the larval herring otolith at hatching is essentially spherical having a slight convex distal side and a flat proximal side with three or four furrows radiating from a distinc- tive central core called a primordium (see Fig. 2). A slight protuberance is apparent on the anterior edge of the otolith from larvae starting at about 20 mm SL which develops into the adult rostrum. With further elongation along the anterior-posterior axis, the otoliths become gen- erally pear-shaped at metamorphosis (45 mm TL) and attain the typical shape of adult herring otoliths by 75 mm (Messieh 1975). The mean diameter of the nucleus, defined here as the size of the otolith at hatching prior to increment deposition, is 22.5 ^m (1.1 /xm SD) based on the laboratory-reared larvae. The otolith increases exponentially in length (anterior-posterior axis) to a mean size of 456 /um at 35 mm SL based on the composite field data. Successive dark and light layers are deposited around the nucleus as the otolith grows. A single growth increment comprised of a dark plus light band is generally presumed to represent 1 d. The otolith nucleus of the field-caught larvae is readily discernible as its margin is usually darkened to form a nuclear check (see Fig. 2). In some otoliths an additional increment was seen inside of the check. Messieh and Moore9 also have observed 1 or 2, and some- times up to 5, faint increments inside the nuclear check of otoliths from herring larvae collected in the Gulf of St. Lawrence. However, no nuclear check was evident in otoliths of the laboratory- reared larvae and no increments were observed within the defined nucleus. Nuclear diameters of the field-caught larvae all fell within the 95% confidence limit of the mean nuclear diameter determined from the laboratory-reared larvae. Immediately surrounding the nucleus of the field-caught larvae, the first 3-9 growth incre- ments appear to be less well defined than suc- ceeding increments, i.e., lower optical density and thinner in width. Distinctive, darker than normal growth layers were noted across an oto- lith transect but they did not suggest any pattern or complex periodicity as observed by Pannella (1971), nor was there any evidence of subdaily rings as observed for some species by Taubert and Coble (1977), Brothers (1981), and Brothers and McFarland (1981). Scanning electron microscopy techniques will be necessary to re- solve the presence or absence of faint incre- ments. The thickness of successive growth increments was measured on otoliths from three field- caught larvae along a posterior radius starting from the nucleus edge (Fig. 4). Measurements were made only through the penultimate incre- ment in each case as the marginal increment was still in the process of formation and could not always be read clearly. Increment thickness ranged from about 0.6 to 2.4 ^m along the radii. All three otoliths show the same general pattern of increment thickness up to about 23 increments where the first 7-10 increments are relatively thin (0.8-1.5 jum) and increase to near maximum thickness (2.3 yum) by about 75 increments. The thickness of the first 3 increments from the lab- oratory-reared larvae was consistently 0.8-1.0 /xm, which compares closely with the initial in- crement thickness of the field-caught larvae. Otolith B tends to suggest a prolonged period of relatively thick increments before thinner ones start to be formed, whereas otolith C appears to form thin increments immediately after maxi- mum increment thickness at around 15 incre- ments. The form of the otolith growth curves can be seen more readily in Figure 5 where otolith radii are plotted against the number of incre- ments for the three larvae. These curves suggest that otolith growth is initially slow, increases 9S. N. Messieh and D. S. Moore, Marine Fish Division, Fish- eries and Oceans, Bedford Institute of Oceanography, Dart- mouth, N.S., Canada, B2Y 4A2, pers. commun. August-Sep- tember 1981. 192 LOUCH KT AL.: A(JK AND GROWTH OK LARVAL ATLANTIC HKRRING FIGURE 4. — Change in increment thickness for three field-collected her- ring larvae. Measurements were made along a posterior radius from nucleus edge through the penultimate incre- ment. A. Total of 23 increments (see Fig. 2B); 18.6 mm SL larva; Annan- dale 76-01, Stn. 38. B. Total of 54 increments (see Fig. 2D); 21.6 mm SL larvae; Researcher 76-01, Stn. 35. C. Total of 150 increments, only initial 80 measured; 31.0 mm SL larva; Anton Dohm 77-01, Stn. 33. 2.5 o o CO CO LLl 0.5 \ 10 hi v v A -~ . n,1 / A ' V I I 'fUl 20 30 40 50 INCREMENT 60 70 80 110.0 100.0 900 800 o 70 0 cc / ,-'• 10 30 40 50 INCREMENT 70 80 Figure 5.— Otolith radii vs. number of increments for the same three larvae in Figure 4. rapidly, and then levels off at some point. This same general pattern of otolith microstructure was observed by Brothers and McFarland (1981) for French grunts. Various allometric relations were examined between otolith size and growth of the field- caught larvae, and a few are presented here to show the homogeneity of the measurements from the three spawning populations sampled: west- ern Gulf of Maine, Georges Bank, and Nantucket Shoals. A plot of the otolith anterior vs. posterior radii in Figure 6 shows a linear relationship. The posterior radius becomes increasingly longer than the anterior radius with increment deposi- tion. Otolith length plotted against head length 200 -5: cc 100 o Y = 5.33 + 0.77 X r = 0.94 W. GULF OF MAINE • GEORGES BANK O NANTUCKET SHOALS O 50 100 150 200 POSTERIOR RADIUS ( MICRONS ) 250 Figure 6.— Otolith anterior-posterior relation for herring lar- vae collected from the three areas: western Gulf of Maine, Georges Bank, and Nantucket Shoals, with composite regres- sion line and correlation coefficient (r). 193 FISHERY BULLETIN: VOL. 80, NO. 2 in Figure 7 also can be expressed by a simple lin- ear relationship. The long axis of the otolith shows a positive allometry with respect to head length for recently hatched larvae to a size of about 35 mm SL. Hempel (1959) reported nearly isometric growth between head and otolith length after metamorphosis for German Bight herring. 500 450 - 400 - o °y O y° Ul 350 O o ojj 1 0 as0 ? 300 - Y = -79.1 + 86.09 X orf>u sQ I 250 r = 0.90 o o UJ 200 <%$ $PB *%& oVo J ■,<*•" 1 - O 150 O $0* • W. GULF OF MAINE GEORGES BANK • O 100 50 - NANTUCKET SHOALS 0 0 1 2 3 4 5 6 HEAD LENGTH ( MM ) Figure 7. — Otolith length (anterior + posterior radii)-head length relation for herring larvae collected from the three areas: western Gulf of Maine, Georges Bank, and Nantucket Shoals, with composite regression line and correlation coeffi- cient (r). function of age where r, the number of incre- ments, represents age plus some unknown con- stant (see Pennington 1979 for details of the model fit). The fitted equation was found to be L = 12.70 exp[0.89(l - exp[-0.03(r - 7)])] for r>7, (1) where 12.70 = Li, the mean length of a 7-incre- ment larvae. Equation (1) may be rewritten as L = 30.90 exp[-1.07 exp(-0.03 r)], r>l, (2) where 30.90 = Lx, the asymptotic limit of mean growth during the October-March period. As- suming: 1) for at least r>7, increments are de- posited daily and 2) a curve in the form of Equa- tion (2) approximates growth from hatch, then denoting age by x, x = r + c, r>7, from 1), where c is an unknown constant, or r = x — c, x>c + 7. Thus Larval Growth A composite plot of larval length versus num- ber of otolith increments is presented in Figure 8. A Gompertz growth curve was fitted to the field data to produce a description of the mean growth of larval herring based on the 311 speci- mens with otolith growth increments ranging from 7 to 160. The Gompertz-type curve (Laird 1969) has been used to describe growth of a wide variety of organisms that often grow exponen- tially at a rate which is decaying exponentially. Previous use of the Gompertz model to more accurately describe the growth of young fish has been made by Kramer and Zweifel (1970), Saka- gawa and Kimura (1976), Zweifel and Lasker (1976), and Methot and Kramer (1979). Using the field data as a starting point, it was assumed that increments were deposited daily at least after the 7th increment so that the equation L = L7 exp[fc(l - exp[-«(r - 7)])], r>7, was taken to represent mean larval length as a 194 L = 30.90 exp(-1.07 exp[-0.03(x - c)]), x>c + 7, (3) ' ■■■.•"' - v—-""-"" :T^~- • - :£■■}. ■' ""C 30.90e" . „ -0.03. 1.70e ' - ■■<*■■?■:■ ■ & -. - 1 i 1 fio 7 70 90 OTOLITH INCREMENTS 80 100 120 ESTIMATED AGE ( DAYS I Figure 8.— Composite standard length-otolith increment plot for field-collected herring larvae in the Gulf of Maine-Georges Bank region, October 1976-March 1977. A Gompertz curve is fitted to larval length at estimated age, x, over their first 6 mo of life from a mean hatch length of 5.7 mm to an asymptotic limit of mean growth of 30.9 mm. A larva with 7 otolith incre- ments is estimated to be on average 24.8 d old. See text for de- tails. LOUGH ET AL: AGE AND GROWTH OF LARVAL ATLANTIC HERRING which, if assumption 2) is reasonable, Equation (3) holds for ,r>0. Letting L0 denote mean length at hatch (x = 0), then solving Equation (3) for c yields, Ln(3.431 - Ln U) - 0.065 0.026 Table 3 gives an estimate of the age of larvae with 7 increments (24.8 d) derived from the mean length of recently hatched larvae collected on the Jeffreys Ledge spawning beds (Cooper et al. foot- note 3). When the mean hatching size (L0) = 5.7 mm, c — 17.8 d, and from Equation (3), length as a function of age is given by L = 30.90 exp[-1.70 exp(-0.03 x)\ x>0. (4) From Equation (4) the mean length at age along with 95% confidence limits, and growth rate (millimeters/day) are estimated from the time of hatch through 175 d in Table 4. Also, the fitted growth curve is shown in Figure 8 with the estimated larval age referenced to the lower scale. The growth curve is based on data with more than 6 increments and a mean length of 5.7 mm at hatch. Obviously, if the functional form changes between age 0 and the age correspond- ing to 7 increments, then the predicted age of fish with 7 or more increments is biased. This growth curve is based on larvae that sur- vived to the age when caught. Therefore, the back-casted curve represents the mean length of larvae for a given age which survive and hence, may be higher than the mean length of the total population. The mean lengths at age of laboratory-reared larvae having 1 and 2 increments from Table 2 fall reasonably close to the extrapolated curve near the origin. The mean length of the labora- tory-reared larvae at hatch was reported by Beyer and Laurence (1981) to be 7.66 mm (SD = 0.58 mm). After correcting for a 20-min net- treatment and Formalin preservation shrinkage factor to compare with the field data, their re- ported mean hatching size is estimated to be 6.4 mm, which is not significantly different from the Jeffreys Ledge diver-collected, Formalin-pre- served yolk-sac larvae of 5.7 mm mean SL. An estimate of \/var(.r |r), the standard devia- tion of age for a fixed number of increments, was made from the field data by Pennington (1979), and its value of 2.9 d compares closely with the Table 'i.— Age of larval herring with 7 otolith growth incre- ments estimated from an initial mean hatching size of 5.7 mm (0.54 mm SD) and 95% confidence intervals of the mean. Stan- dard lengths of 100 newly hatched yolk-sac larvae (Formalin' preserved) were measured from egg bed samples collected by divers2 on the Jeffreys Ledge study site (38 m depth), 8 October 1974. Hatch 95% confidence Estimated age of larva 95% confidence length (L0) . lntervals with 7 increments mlervals (mm) lower upper (d) lower upper 5.7 5.6 5.8 248 244 25.2 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 2Northeast Fisheries Center's Manned Undersea Research and Tech- nology (MURT) Dive Team. Table 4.— Mean standard length at age, 95% confidence limits, and growth rate (mm/d) of larval herring from hatch through 175 d estimated from the Gompertz growth model fit. Mean 95% confide nee limits Growth rate Age(d) length (mm) lower upper (mm/d) 0 5.7 5.4 6.0 025 1 59 56 6.2 0.26 2 62 5.9 6.5 0.26 3 64 6.2 6.7 0.26 4 67 6.4 7.0 0.27 5 70 6.7 7.3 0.27 6 7.2 69 7.5 0.27 7 7.5 7.2 7.8 0.28 8 78 75 8.1 028 9 8 1 7.8 8.4 0.28 10 84 8 1 8.7 029 20 113 11.0 11.6 030 30 142 14.0 14.5 0.29 40 170 16.8 17.2 0.27 50 19.5 193 197 0.23 75 243 24.0 24.6 0.15 100 27.3 268 277 0 09 125 29.0 28.4 29.5 0.05 150 299 29.3 30.5 0.03 175 30.4 298 31.0 0.01 rough estimate of 3.1 d obtained from the labora- tory data (Lough et al. footnote 7). The first larva with 3 increments observed during the laboratory-rearing occurred on day 16 after estimated hatch. The mean age of fish with 3 increments cannot be estimated directly because sampling stopped after 18 d. But assum- ing a range of ages of 12 d (4 standard devia- tions), the mean age of a 3-increment larva would be approximately 22 d. Assuming daily incre- ment deposition for the population after the third increment, a 7-increment larva would have an average age of 26 d, which compares well with the field estimate of 25 d. Messieh and Moore (footnote 9), working with autumn-spawned herring larvae in the Gulf of St. Lawrence, recently estimated the age of larvae at the time of the nuclear check completion to be 15-17 d from hatching on average. 195 FISHERY BULLETIN: VOL. 80, NO. 2 Growth Curve Compared with Other Field Studies Direct observations of herring egg beds by div- ers were made on Jeffreys Ledge, Gulf of Maine, in 1974 by Cooper et al. (footnote 3). Spawning occurred between 29 September and 3 October 1974 at about 35-50 m depth when the bottom water temperature was 9.6°C. Larval hatching began on this site on 6 October and was com- pleted by 11 October, a 5-d period. Careful visual examination of the egg bed by the divers sug- gested that major hatching began on 7-8 Octo- ber. Newly hatched larvae collected on the egg bed have already been reported in Table 3 to have a mean Formalin-preserved length of 5.7 mm (0.5 mm SD). A special 24-h vertical series of plankton hauls was made slightly downstream of the egg bed 11-12 October (Delaware 7/74-12). The mean Formalin-preserved length of all lar- vae collected by day and night hauls was 6.7 mm (0.6 mm SD) (Lough and Cohen10). Approxi- mately 4 d transpired between the middates of maximum hatching and their collection by the 24-h vertical study yielding an average growth rate of 0.25 mm/d. According to the fitted Gom- pertz growth curve (Table 4), 4-d-old larvae are estimated to have reached a mean length of 6.7 mm at a mean growth rate of 0.26 mm/d (range: 0.25-0.27 mm/d) which are essentially the same as the field estimates. Graham and Chenoweth (1973) made direct observations of larval herring over egg beds on northeastern Georges Bank during autumn 1973. Submersible observations indicated that hatching occurred between 25 September and 5 October, a 10-d period. Larvae hatched in sea- water from eggs brought on shipboard 27 Sep- tember varied in length from 5 to 7 mm with over 90% at 6 mm. On 1 October, larvae collected within the vicinity of the egg beds varied from 5 to 9 mm in length but the mean was 7.1 mm about 4 d from hatching (27 September-1 October). Growth rate of these recently hatched larvae over the 4 d was estimated to be 0.28 mm/d, which is slightly higher but still comparable with the fitted growth curve. Growth of larval herring based on the Gom- I0Lough, R. G., and R. E. Cohen. 1982. Vertical distribu- tion of recently-hatched herring larvae and associated zoo- plankton on Jeffreys Ledge and Georges Bank, October 1974. Lab. Ref. 82-10. Northeast Fisheries Center Woods Hole Laboratory, National Marine Fisheries Service, NOAA, Woods Hole, MA 02543. pertz curve was 0.25 mm/d at hatch, increased to 0.30 mm/d at 20 d, and declined thereafter to <0.15 mm/d after 75 d. The average growth rate over 150 d from hatch was 0.20 mm/d which is similar to average seasonal estimates found in most other studies of herring larvae. By follow- ing length-frequency modes for Georges Bank- Nantucket Shoals herring larvae collected on the 1971-78 ICNAF surveys, Lough etal. (footnote 4) found an average rate of 0.195 mm/d as the best compromise to describe average growth over the 7-30 mm size classes (163 d). Boyar et al. (1973) estimated larval herring growth in the Georges Bank-Gulf of Maine region, September-June, to average 0.17 mm/d with a range of 0.14-0.25 mm/d. The form of the growth curve appears to be universal for herring larvae with a cessation in growth most noticeable during mid-larval life before increasing rapidly again at the time of metamorphosis. When Sette (1943) replotted the Clyde Sea, spring-spawned larval herring data of Marshall et al. (1937), he concluded that two logarithmic curves provided a better description of growth with a decrease in slope at a length of 19.5 mm. Graham et al. (1972) also showed a de- crease in growth after about 20 mm for autumn- spawned herring larvae along the coastal west- ern Gulf of Maine. Townsend and Graham (1981) followed two groups of larvae that entered the Sheepscot River estuary of Maine that grew about 0.2-0.3 mm/d from October to early Janu- ary and from late February to early March, but experienced similar cessation of growth from late January to early February. Das (1968, 1972) followed length modes of Bay of Fundy-Gulf of Maine area herring larvae from hatching in Sep- tember and estimated growth rates to be 0.29 mm/d in the autumn, gradually declining to <0.14 mm/d during late autumn and winter months, and then increasing geometrically to >0.36 mm/d in the spring and early summer. Messieh and Moore (footnote 9) also reported a rapid increase in growth at metamorphosis for herring larvae collected in the Gulf of St. Law- rence. DISCUSSION The available data indicate that the age and growth of herring larvae in the Gulf of Maine- Georges Bank region can be accurately esti- mated from otolith microstructure, although we have no direct evidence of the increment-day relation. A Gompertz growth curve fitted to the 196 LOUGH KT AL.: AGE AND GROWTH OF LARVAL ATLANTIC HERRING field-caught larvae, which describes the length at age from an initial mean hatching size of 5.7 mm to an upper asymptotic mean length of 30.9 mm, agrees well with average growth rate esti- mates from other studies. Our field data begin with a 7-increment larva of 12.6 mm SL, which also is nearly identical to the mean length at increment age estimated by the growth curve. From the growth model a 7-increment larva is estimated to be on average 25 d from hatch (5.7 mm) having grown at an average rate of 0.28 mm/d. This implies that increment deposition does not occur daily over these 25 d or that varia- tion in the timing of first increment deposition is high. If one assumes daily increment deposition from yolk-sac resorption (4.5 d), a 7-increment larva would be 11.5 d old, inferring the larva has grown at an average rate of 0.60 mm/d, which is rather high based on field and laboratory esti- mates. Herring larvae <15 mm have estimated growth rates typically in the range of 0.25-0.30 mm/d with an upper limit of about 0.35 mm/d. The apparent delay in increment formation observed in the laboratory-reared herring larvae after the first increment at yolk-sac resorption may be due to rearing conditions, although we have no reason to suspect they were less than optimal. Other studies have shown that the for- mation of daily growth increments can be af- fected by variations in food ration, temperature, light-dark cycle, age of fish, and stressful condi- tions in general (see references in first section of paper). Increment formation appears to be spe- cies-specific and, for clupeoid species like En- graulis mordax (Brothers et al. 1976) and Clupea harengus (this study) with relatively small eggs and short incubation period, the initial incre- ments begin at the time of yolk-sac resorption (Radtke and Waiwood 1980). A dark band or check observed around the nucleus of most of the larval otoliths collected in the field, but not ap- parent in the laboratory-reared larvae, may cor- respond to the time of yolk-sac resorption as Radtke and Waiwood (1980) found for larval cod otoliths. The nuclear check may be the result of i several thin increments grouped together. Uchi- yama and Struhsaker (1981), working with Pacific tunas, found that countable growth in- crements were formed only when the fishes were fed to satiation throughout the day. The nuclear check and the succeeding 10 or so thin incre- ments observed for the field-caught herring lar- vae may be related to the inability of a first- feeding larva to meet its maximum daily ration during the transition from its yolk supply to exogenous feeding. Initial feeding efficiency is low for herring larvae, <5% success at yolk-sac resorption, but increases to about 40% 2 wk after hatching and 70% after 5 wk (Blaxter and Staines 1971). Karris (1959) observed a rapid leveling off of growth after hatch in four species of fish and Zweifel and Lasker (1976), after fitting a two- stage Laird-Gompertz growth curve to a number of larval fish species, one from hatching to yolk- sac resorption and another to more rapid growth at the onset of feeding, suggested that this phe- nomenon was almost universal in larval growth. It is conceivable that during this period of re- duced growth, increment deposition also may be delayed or diminished until the larva learns to capture sufficient numbers of prey and begins growing rapidly again. Although larval herring appear to be very re- sistant to the range of temperatures normally encountered (Blaxter 1960), the effect of tem- perature on increment formation is not known. Water temperatures observed in herring spawn- ing areas in the Gulf of Maine-Georges Bank region are typically as high as 12°-14°C in early autumn and decline to near 0°C in winter (Table 1), approaching their lower lethal limit (Graham and Davis 1971; Chenoweth 1970). Yolk-sac utili- zation in herring larvae is directly related to water temperature (Blaxter 1956; Blaxter and Hempel 1963, 1966; Blaxter and Ehrlich 1974) and variations in water temperature at hatch can reduce or extend the time to first feedi ng and consequently, otolith increment formation. Yolk- sac resorption is completed at 4-5 d at 10°C and 6 d at 8°C. Feeding of larvae is believed to com- mence at or prior to the end of yolk-sac resorption when the maximum body weight (excluding yolk sac) is reached after about 3 d at 8°C and 2 d at 12°C. Larvae reared at 10°C would initiate feed- ing 2-3 d after hatch. There is some evidence to indicate that early larval herring growth is better at higher temperatures (Blaxter 1962), although food availability is considered the more important factor in controlling growth processes and survival of larval fish in general (May 1974). Increment formation of the green sunfish, Le- pomis cyanellus, could be stopped when growth was slowed sufficiently by simulated winter con- ditions (Taubert and Coble 1977). The slowing of growth during the winter period observed for larval herring in the Gulf of Maine-Georges Bank region also may affect their increment for- mation but further research will be required to 197 FISHERY BULLETIN: VOL. 80, NO. 2 determine the effect of environmental variables on the relationship between otolith and larval growth. ACKNOWLEDGMENTS We thank P. Hamer and R. Cohen for their help with the laboratory and data processing. G. Laurence, NMFS Narragansett Laboratory, R.I., graciously provided the laboratory-reared larvae and unpublished experimental data used in this study. This report is M ARM AP Contribu- tion MED/NEFC 81-6. LITERATURE CITED Barkman, R. C. 1978. The use of otolith growth rings to age young Atlan- tic silversides, Menidia menidia. Trans. Am. Fish. Soc. 107:790-792. Barkman, R. C, D. A. Bengston, and A. D. Beck. 1981. 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Scotl. 1, 18 p. Blaxter, J. H. S., and K. F. Ehrlich. 1974. Changes in behavior during starvation of herring and plaice larvae. In J. H. S. Blaxter (editor), The early life of fish, p. 575-588. Springer- Verlag. Berl. Blaxter, J. H. S., and G. Hempel. 1963. The influence of egg size on herring larvae (Clupea harengus L.). J. Cons. Cons. Int. Explor. Mer 28:211- 240. 1966. Utilization of yolk by herring larvae. J. Mar. Biol. Assoc. U.K. 46:219-234. Blaxter, J. H. S., and M. E. Staines. 1971. Food searching potential in marine fish larvae. In D. J. Crisp (editor), Fourth European Marine Biology Symposium, p. 467-485. Cambridge Univ. Press, Cam- bridge. Boyar, H. C, R. R. Marak, F. E. Perkins, and R. A. Clifford. 1973. Seasonal distribution and growth of larval herring (Clupea harengus L.) in the Georges Bank-Gulf of Maine area from 1962 to 1970. J. Cons. Cons. Int. Explor. Mer 35:36-51. Brothers. E. B. 1981. 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Fish. Res. Bull. 10:141-149. Graham, J. J.. S. B. Chenoweth, and C. W. Davis. 1972. Abundance, distribution, movements, and lengths of larval herring along the western coast of the Gulf of Maine. Fish. Bull., U.S. 70:307-321. Graham, J. J., and C. W. Davis. 1971. Estimates of mortality and year-class strength of larval herring in western Maine, 1964-67. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 160:147-152. Hempel, G. 1959. Zum Wachstum der Otolithen bei Jungheringen. Helgol. Wiss. Meeresunters. 6:241-259. Kramer, D., and J. R. Zweifel. 1970. Growth of anchovy larvae (Engraulis mordax Gir- ard) in the laboratory as influenced by temperature. Calif. Coop. Oceanic Fish. Invest. Rep. 14:84-87. 198 LOUGH KT AL.: AGE AND GROWTH OF LARVAL ATLANTIC HERRING Laird, A. K. 1969. The dynamics of growth. Res./Dev. 20(8):28-31. Lough, R. G., (!. R. Bolz. M. D. Grosslein, and D. C. Potter. 1981. Abundance and survival of sea herring (Clupea harengus L.) larvae in relation to environmental factors, spawning stock size, and recruitment for the Georges Bank area. 1968-77. In R. Lasker and K. Sherman (editors). The early life history of fish: recent studies. Kapp. P.-V. Reun. Cons. Int. Explor. Mer 178:220-222. Marshall, S. M., A. G. Nicholls, and A. P. Orr. 1937. On the growth and feeding of the larval and post- larval stages of the Clyde herring. J. Mar. Biol. Assoc. U.K. 22:245-268. May, R. C. 1974. Larval mortality in marine fishes and the critical period concept. In J. H. S. Blaxter (editor), The early life history of fish, p. 3-19. Springer- Verlag, Berl. Messieh. S. N. 1975. Growth of the otoliths of young herring in the Bay of Fundy. Trans. Am. Fish. Soc. 104:770-772. Methot, R. D. 1981. Spatial covariation of daily growth rates of lar- val northern anchovy, Engraulis mordax, and northern lampfish, Stenobrach ius leucopsarus. In R. Lasker and K. Sherman (editors), The early life history of fish: recent studies. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:424-431. Methot, R. D., Jr., and D. Kramer. 1979. Growth of northern anchovy, Engraulis mordax, larvae in the sea. Fish. Bull, U.S. 77:413-423. Pannella, G. 1971. Fish otoliths: daily growth layers and periodical patterns. Science (Wash., D.C.) 173:1124-1127. 1974. Otolith growth patterns: an aid in age determina- tion in temperate and tropical fishes. In T. B. Bagenal (editor), Proceedings of an international symposium on the ageing of fish, p. 28-39. Unwin Brothers, Surrey, Engl. Pennington. M. R. 1979. Fitting a growth curve to field data. In J. K. Ord, G. P. Patil, and C. Taillie (editors), Statistical distribu- tions in ecological work, p. 419-428. Int. Coop. Publ. House, Fairland, Md. Radtke, R. L., and K. G. Waiwood. 1980. Otolith formation and body shrinkage due to fixa- tion in larval cod (Gadus morhua). Can. Tech. Rep. Fish. Aquat. Sci. 929, 10 p. Ralston, S. 1976. Age determination of a tropical reef butterflyfish utilizing daily growth rings of otoliths. Fish. Bull., U.S. 74:990-994. Sakawaga, G. T., and M. Kimura. 1976. Growth of laboratory-reared northern anchovy, Engraulis mordax, from southern California. Fish. Bull., U.S. 74:271-279. Sameoto, D. D. 1972. Distribution of herring (Clupea harengus) larvae along the southern coast of Nova Scotia with observa- tions on their growth and condition factor. J. Fish. Res. Board Can. 29:507-515. Scott, J. S. 1973. Otolith structure and growth in northern sand lance, Ammodi/tes duhius, from the Scotian Shelf. Int. Comm. Northwest Atl. Fish. Res. Bull. 10:107-115. Sette, O. E. 1943. Biology of the Atlantic mackerel (Scomber scont- brus) of North America. Part I: Early life history, in- cluding growth, drift, and mortality of the egg and larval population. U.S. Fish Wildl. Serv., Fish. Bull. 50:149- 237. Sherman, K. 1980. MARMAP, a fisheries ecosystem study in the Northwest Atlantic: Fluctuations in ichthyoplankton- zooplankton components and their potential for impact on the system. In F. P. Diemer, F. J. Vernberg, and D. Z. Mirkes (editors), Advanced concepts in ocean mea- surements for marine biology, p. 9-37. Belle W. Baruch Institute for Marine Biology and Coastal Research. Univ. S.C. Press, Columbia. Steffensen, E. 1980. Daily growth increments observed in otoliths from juvenile East Baltic cod. Dana 1:29-37. Struhsaker, P., and J. H. Uchiyama. 1976. Age and growth of the nehu, Stolephorus purpur- eas (Pisces: Engraulidae), from the Hawaiian Islands as indicated by daily growth increments of sagittae. Fish. Bull., U.S. 74:9-17. Taubert, B. D., and D. W. Coble. 1977. Daily rings in otoliths of three species of Lepomis and Tilapia mossambica. J. Fish. Res. Board Can. 34:332-340. Theilacker, G. H. 1980. Changes in body measurements of larval northern anchovy. Engraulis mordax, and other fishes due to handling and preservation. Fish. Bull., U.S. 78:685- 692. Tibbo, S. N., and J. E. Henri Legare. 1960. Further study of larval herring (Clupea harengus L.) in the Bay of Fundy and Gulf of Maine. J. Fish. Res. Board Can. 17:933-942. Tibbo, S. N., J. E. Henri Legare, L W. Scattergood, and R. F. Temple. 1958. On the occurrence and distribution of larval her- ring (Clupea harengus L.) in the Bay of Fundy and the Gulf of Maine. J. Fish. Res. Board Can. 15:1451-1469. Townsend, D. W., and J. J. Graham. 1981. Growth and age structure of larval Atlantic her- ring, Clupea harengus harengus, in the Sheepscot River estuary, Maine, as determined by daily growth incre- ments in otoliths. Fish. Bull., U.S. 79:123-130. Uchiyama, J. H., and P. Struhsaker. 1981. Age and growth of skipjack tuna, Katsmconus pel- amis, and yellowfin tuna, Thunnus albacares, as indi- cated by daily growth increments of sagittae. Fish. Bull., U.S. 79:151-162. Watson, J. E. 1964. Determining the age of young herring from their otoliths. Trans. Am. Fish. Soc. 93:11-20. Wilson, K. H., and P. A. Larkin. 1980. Daily growth rings in the otoliths of juvenile sock- eye salmon (Qncorhynchus nerka). Can. J. Fish. Aquat. Sci. 37:1495-1498. Zweifel. J. R., and R. Lasker. 1976. Prehatch and posthatch growth of fishes— a gen- eral model. Fish. Bull.. U.S. 74:609-621. 199 INCREMENT FORMATION IN THE OTOLITHS OF EMBRYOS, LARVAE, AND JUVENILES OF THE MUMMICHOG, FUNDULUS HETEROCHTUS1 R. L. Radtke2 and J. M. Dean3 ABSTRACT The formation of otoliths and the effect of light cycles on increment formation were studied in embryos, larvae, and juvenile mummichogs, Fundulus heteroditus. We found that increments in the sagitta of mummichogs were a reliable indicator of the daily age of the fish. Calcification of the sagitta was initiated in the core, after matrix formation, at stage 24 of embryological development. The sagitta was the first calcified tissue to develop and there were two or three increments formed before hatching. Daily increment formation in the sagitta was initiated by light and controlled by a 24-hour photoperiod. When embryos were subjected to a 24-hour dark or <24-hour (6L:6D) photo- period, daily increment formation was disrupted. Laboratory experiments at24°C and 30°C con- firmed that there was one increment formed each day, which was independent of growth rate and which validated the age of fish in field collections. Wild populations reproduce in the intertidal zone, a physically stressed environment and, judging by the age, which was estimated from incremental data, reproduction is synchronized with tidal cycles. Interpretation of increments in the hard tissues of fish has long been utilized as a method to esti- mate age composition of adult populations. Most of the interpretive emphasis has been placed on otoliths and scales. However, the process of age determination isnotasimpleone(Bagenal 1974). Otoliths are especially useful for determining the age of fishes, such as larval forms, which lack scales or have very small ones. The otoliths of teleosts consist of deposits of cal- cium carbonate in the form of aragonite (Irie 1955; Degens et al. 1969). The morphology of these structures is so specific it can be used as a taxonomic character (Messieh 1972; Hecht 1978). Three structures (the sagitta, lapillus, and the asteriscus) are found in the membranous labyrinth of inner ear on each side of the brain cavity (Lowenstein 1971; Popper and Coombs 1980). The sagitta is often the largest and is most often used for age determinations and, unless otherwise stated, was the otolith used in the present study. ■This is contribution 390 of the Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, SC 29208. 2Belle W. Baruch Institute for Marine Biology and Coastal Research and the Department of Biology, University of South Carolina, Columbia, SC; present address: The Pacific Game- fish Foundation, P.O. Box 25115, Honolulu, HI 96825. 3Belle W. Baruch Institute for Marine Biology and Coastal Research and the Department of Biology, University of South Carolina, Columbia, SC 96825. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80, NO. 2, 1982. Pannella(1971, 1974) postulated that daily in- crements are found in otoliths of adult fishes, and Brothers et al. (1976) showed that such incre- ments can indeed be found in otoliths of young fishes and be used for age estimation. Struhsaker and Uchiyama (1976) postulated that back calcu- lation of daily increment data from otoliths could be used to age the nehu, a tropical marine fish, and Ralston (1976) obtained similar results with a tropical butterfly fish. Taubert and Coble (1977) did direct age observations of otoliths in juvenile freshwater fish and Barkman (1978) was equally successful with the young of a tem- perate estuarine species Menidia menidia. A more accurate daily journal is available in the otoliths of most young fishes than can be found in their scales, since scales are often absent in the early stages of development (Bagenal 1974), and scale metabolism is dynamic (Yamada and Watabe 1979). The discovery of daily increments in otoliths increases the resolution and precision of age de- termination and promises to provide fishery biologists with new levels of information. The deposition of the increments in a rhythmic fash- ion could be a mark of a daily event, and possibly a measure of growth, but the full extent of the influence of external and internal factors on the formation of otolith increments has not been de- termined. There is need of knowledge about the age com- 201 FISHERY BULLETIN: VOL. 80. NO. 2 position of larval fish populations, since this in- formation can provide estimates of growth, mor- tality, and rates of survival (Gulland 1977). The highest mortality of fishes is during the growth period from larvae to juveniles (Hjort 1914; Tanaka 1972) and consequently, the survival and growth of larval fishes has a pronounced effect upon recruitment (Larkin 1978). It should be possible, by using otoliths for estimation of the age, to determine the growth rates and the age structure of larval fish populations. Daily increments have been correlated with natural temperature cycles, light and food for freshwater species by Brothers (1978, 19804). Taubert and Coble (1977) postulated that daily increments in otoliths of freshwater sunfish re- sulted from a 24-h diurnal light cycle that en- trained an internal clock. To utilize daily depositional increments of the otoliths in the analysis of fish population dynam- ics, it is important to understand the physiologi- cal mechanisms involved in the formation and growth of increments and otoliths. Age estima- tion requires knowledge of 1) age when incre- ment formation begins; 2) factors which control the deposition of daily increments in the otoliths; and 3) length of time daily increments are formed without growth interruption. Informa- tion in these areas will make it possible to better understand age and growth in wild populations of fish. An important area for research in the field of age and growth is the experimental study of the factors which influence the deposition of incre- ments in otoliths. Brothers et al. (1976) showed that daily increments began to form at different ages in different species. Some species hatch with increments already formed, while others apparently do not form increments until later. Thus, it is necessary to study the formation of in- crements in each species and correlate incre- ment formation with external factors before accurate age determinations can be made. The mummichog, Fundulus heteroclitus, is an abundant estuarine fish and an important com- ponent of the estuarine ecosystem (Cain and Dean 1976; Valiela et al. 1977; Kneib and Stiven 1978; Merideth and Lotrich 1979). The biology of Fundulus is well-known and its embryology is well-defined (Armstrong and Child 1965). The objectives of this study were to 1) delineate 4E. B. Brothers, Section of Ecology and Systematics, Cornell University, Ithaca, NY 14850, pers. commun. October 1980. the structure and formation of otoliths in the embryological and early larval stages of the mummichog, 2) determine the effect of photo- period on incrementdeposition in embryonic and postlarval mummichog otoliths, 3) measure the effects of temperature on body growth and the deposition of increments in otoliths, and 4) test whether growth and age data can be obtained in wild populations of mummichogs by counting the increments in otoliths. METHODS Adult F. heteroclitus used as spawning stock were collected from North Inlet Estuary (lat. 32°20'N, long. 79°10'W) and North Edisto Estu- ary (lat. 32°26'N, long. 80°12'W), near George- town, S.C. Fertilized eggs were collected as pre- viously described by Middaugh and Dean (1977). Only embryos which developed according to the criteria of Armstrong and Child (1965) were uti- lized in the embryological studies, and only lar- vae which hatched within 6 h of hatch induction were used in the growth studies. The embryo is the stage from fertilization to hatching; from hatching to yolk-sac absorption is the larval stage and the mummichog was considered a juvenile after yolk-sac absorption (Hubbs 1943). The terms used to describe growth increments in otoliths are confused, as the increments in lar- vae are variously referred to as lamellae, rings, or layers. The term increment in this study re- fers to a unit formed by an unbroken incremental zone and a discontinuous zone after core forma- tion (Fig. 1), Wild and Foreman (1979). Newly hatched larvae were kept at 24°C and 30°C±1°C (Radtke and Dean 1979) and were fed brine shrimp, Artemia nauplii, ad libitum and maintained in L12:D12 with a daily change of water (30%„) to determine the effect of the rate of growth on otolith size and increment number. A daily sample of 10 larvae was collected for laboratory experiments from each group for the first 10 d, and every 5 d thereafter for 30 d. Stan- dard lengths (SL) were measured on each larva and its otoliths were removed. Photomicro- graphs were made of each otolith for increment counts. Juvenile mummichogs were collected from We Creek in North Edisto Estuary on 9 June 1977 (28°C, 297..). Each fish was weighed, measured for standard length (SL), and its otoliths extract- ed for increment counts from photographs. Sta- tistical analyses of the data were done with 202 RADTKE and DEAN: INCREMENT FORMATION OF OTOLITHS OF MUMMR'HOO Figure 1.— SEM of the sagitta from a 12-d-old Fundulus heteroclitus. I is the unbroken incremental zone, D is the discontinuous zone, and I + D = 1 increment. Bar = 1 p. 203 FISHERY BULLETIN: VOL. 80. NO. 2 standard tests and models as described in Sokal and Rohlf (1969). Removal, Preparation, and Inspection of Otoliths Otoliths were removed from embryos, larvae, and juveniles with fine insect needles mounted on wood rods. The larvae are transparent and the otoliths are birefringent under polarized light, so it is possible to view the sagitta during the dissection. The sagittae were washed with dis- tilled water, dried, and mounted on glass slides with Euparol5 mounting medium, and viewed with a compound light microscope. Photomicrographs were made of each otolith for counts of increments and measurement of otolith diameters. (Thelof the outside edge of the sagitta was considered as a portion of the last in- crement.) To make increment counts, the back of each photograph was marked and the photo- graphs were shuffled. The counting process was performed three times, which gave three un- biased readings for each otolith. If two of the counts were identical, that value was accepted as the increment count for a particular otolith. In cases where all counts differed, the middle count was chosen unless all counts varied more than two increments from each other, in which case that otolith was disqualified and not used in the final tabulation. Sagitta were measured at the widest diameter on the photographs using a cali- per calibrated on a photographed micrometer. Sagittae viewed with light microscopy showed fine lines in the I that were concentric with the D; these fine lines have been referred to as "sub- units." In the otoliths of young mummichogs the so-called subunits could not be observed in decal- cified sections with light microscopy or SEM (Fig. 1). The D and I compose an increment and are readily differentiated with light microscopy in Fundulus sagittae (Fig. 2). Whole sagittae used for SEM studies were attached to viewing stubs in 5-min epoxy resin. The sagittae were ground to the core in the trans- verse plane on graded grinding stones, polished with diamond-polishing compound, and cleaned with 95% ethanol. The polished surface was de- calcified with 7% EDTA (pH 7.4)(disodium ethy- lenediaminetertacetate) for 1 to 5 min. The speci- mens were coated with gold ( 150A) and observed with a SEM. 5Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. Embryological Formation of Otoliths Fertilized eggs were kept in light 12 h and in the dark 12 h (L12:D12) at24°C in hatching jars with recirculating seawater (30 ..). A sample of 10 eggs was collected each day until hatching and viewed under polarized light (120X) to de- termine when calcification was initiated. The embryos were classified according to Armstrong and Child (1965) with the number of embryos with calcified sagitta noted in each stage. Calcified sagittae were removed from the em- bryos and mounted for examination with light microscopy to determine the time of increment formation. Ten- and 14-d embryological sagittae were viewed using SEM to confirm the light microscope observations. Effect of Light on Increment Formation in Embryos and Larvae To determine the influence of light on incre- ment formation, developing embryos and larvae were subject to the following conditions: EMBRYOS: Group ED24— Embryo-dark-24 h, fertilized in the dark, kept in constant darkness until sam- pled 3 d after hatching. Group EL24— Embryo-light-24 h, fertilized in the light, kept in constant light until sampled 3 d after hatching. Group ED24+L— Embryo-dark-24+L, fertilized in the dark, kept in constant darkness except for 1 min of light exposure 10 d after fertiliza- tion. Sampled 3 d after hatching. Group EL12:D12— Embryo-light-12 h:dark-12 h, fertilized, placed in L12:D12 and sampled daily. All groups were maintained at 24°C and the water (30 '/..) was changed daily. The water was changed in the ED24 group and ED24+L group by pouring the eggs onto a 505 jjl mesh net mounted on the end of 10 cm plastic tubing. The eggs were then washed off the netting with a wash bottle and the entire exercise was per- formed in total darkness. Hatching in the ED24 group and ED24+L group was determined by touch, because embryos are hard and easily dis- tinguished when they have hatched. A daily 204 RADTKE and DEAN: INCREMENT FORMATION OF OTOLITHS OF MUMMK'HOO Figure 2.— Light micrograph of a Fundulus heteroclitus sagitta on the day of hatching. C is the core and II and 12 are increments formed after core formations but prior to hatching. Bar = 0.05 mm. sample of three eggs was taken after day 14 to determine the events in otolith development. Sagitta were removed from 10 larvae of each group according to the above schedule and photo- micrographed. LARVAE: Developing embryos were maintained at 24°C in L12:D12 in hatching jars with running sea- water (30'/..). Upon hatching, the larvae were di- 205 FISHERY BULLETIN: VOL. 80, NO. 2 vided and subjected to the following conditions: Group LaD24— Larvae-dark-24 h, constant darkness. Group LaL24— Larvae-light-24 h, constant light. Group LaL6:D6— Larvae-light-6 h:dark-6 h. Group LaL12:D12— Larvae-light-12 h:dark- 12 h. All groups were fed newly hatched brine shrimp ad libitum and kept at 24°C with daily changes of water at 30V... Samples of 10 larvae from each group were taken at days 0,6,9, and 16 except the L12:D12 group, which was sampled daily. Sagitta were removed from each sample and photomicrographed. Scanning electron mi- crographs were made of samples for comparison with the light micrographs. RESULTS Formation of Otoliths in Embryos The sagittae were the first tissues to calcify and were discernible on days 3 and 4 at embry- onic developmental stages 24-28 (Armstrong and Child 1965). An amorphous mass was discernible in the labyrinth region of the larva before calcifi- cation was initiated. This mass, the core organic matrix, had a gellike consistency and could be dissected. Calcification was initiated in the core of the sagitta of 30% of the embryos on day 3 and 100% of the cores showed calcification by day 4 (Fig. 3). Increment formation began on day 12, and 20% had one increment. On day 13, 80% had one increment and 20% had two increments. On day 14, the day of hatch, 20% had one increment, 70% had two increments (Fig. 2), and 10% had three increments. Calcification began with formation of crystals which extended to the edge of the core matrix. Histochemical analyses have shown that calcifi- cation begins in the core at the same time that the core becomes birefringent (J. Yamada6). Multi- ple spherules (Fig. 4a, b) are common in the calci- fied core but their origin and sequence of devel- opment is unknown. The newly formed sagittae had a mean diameter of 0.024±0.004 mm. Calci- fication continued and additional crystals ex- tended beyond the original boundary in an in- terlocking fashion until the diameter reached 0.048+0.008 mm at day 9 and developmental stage 36. At this time only the core region could be observed, with no increments (Fig. 3). Two days later (on day 11 postfertilization), incre- ment formation was initiated around the core, and the mean sagitta diameter had reached 0.074±0.008 mm. When viewed with trans- mitted light, the concentric increments consisted of alternate narrow, dark discontinuous zones (D) and wider, lighter, incremental zones (I) (Fig. 3). The D intersected the I at right angles and were concentric with the core and outer sur- face of the otolith. Upon hatching at day 14, post- fertilization, two or three increments were readily discernible as daily increments started forming 2-3 d before hatching. Otoliths examined with the SEM confirmed the increment counts determined under trans- mitted light and showed the orientation of the crystals (Fig. 1). Effect of Light on Increment Formation in Embryos and Larvae The light cycle to which an embryo or larva was exposed had an effect on increment forma- tion and hatching time. Embryos in the L12:D12 cycle had two or three increments prior to hatch- ing and one increment per day after hatching (Table 1, Fig. 3). Embryos kept in L12:D12 hatched at 14 d while those exposed to other light cycles had longer incubation times and a differ- ence in increment formation during incubation and after hatching was apparent in the other groups (Table 2). Embryos incubated inconstant dark (ED24)had a delayed hatch, suppressed in- crement formation (Fig. 5), and a smaller otolith Table 1. — Sagitta were from Fundulusheteroclitus embryos and larvaeincubatedonaL12:D12eycleat 24°C (N = 10/d). 6Faculty of Fisheries, Hokkaido University, Hakodate. Hokkaido, Japan, pers. commun. Age (days Otolith diameter after hatching) Increment count (mm) 0 2.75±0.5 0.128*0011 1 400 ±0.0 0 150+0015 2 450+0.5 0.158 ±0.015 3 5.50±0.5 0 180+0 140 4 620 + 1.1 0 187+0011 5 7.20±1.0 0203+0003 6 8.50 + 1.1 0.220 ±0.1 11 7 950+06 0 240+0.110 8 1060+0.8 0255+0.042 9 12.00±1.0 0.268+0 058 10 1260+0.9 0.280+0.018 15 17 50±1.2 0350+0.120 206 RADTKE and DKAN: INCREMENT FORMATION OF OTOLITHS OF MUMMICHOG m .02 mm Figure 3.— Light micrograph of the core of the sagitta of Fundulus heteroclitus taken on day 10 of embryo formation. No increments have yet formed. Bar = 0.02 mm. diameter (Table 2A, Fig. 5). The embryos incu- bated in constant light (EL24) hatched at 15 d postfertilization and showed 6.0+0.67 incre- ments when sampled 3 d after hatching (Table 2B). Constant light conditions did not signifi- cantly alter increment formation; the constant light group (EL24) showed the same number of increments as in the EL12:D12 group at 3 d of age. Thus, the effect of light on embryonic incre- ment formation and otolith diameters was the same for the EL24 and EL12:D12 groups. A 1-min light stimulus on day 10 of ED24+L 207 FISHERY BULLETIN: VOL. 80, NO. 2 ** W FIGURE 4.— a) SEM of the core of the sagitta of Fundulus heteroclitus showing the core (C) and the multiple primordia (P) sur- rounds the spherules. Bar = 1 n. b) SEM showing a spherule (S) in the multiple primordia (P) of the core (C) or the sagitta. B = 0.5 M. 208 RADTKK and DKAN: INCRKMKNT FORMATION OF OTOLITHS OF MUMMICHOO resulted in increment formation (Table 2C) in embryos otherwise maintained in constantdark- ness. Increment counts for ED24+L were less TABLE 2.— Effect of photoperiod and light stimuli on incre- ment formation in sagittal otoliths of Fundulus heteroclitus embryos. A) B) C) A B C Embryos were incubated in total darkness and sagitta were removed 3 d after hatching. (ED24) Embryos were incubated in constant light and sagitta were removed 3 d after hatching. (EL24) Embryos were incubated in constant darkness with 1 mm of light at day 10 of development. Sagitta were removed 3 d after hatching. N = 10 in all groups. (ED24+L) Sagitta diameter (mm) (X+SD) Increment numbers (X±SD) 0.071 ±0.008 0.177+0.013 0.14610012 0.610.77 6.0±0.67 4.7±0.48 than those of the EL24 group and the EL12:D12 group at 3 d after hatching, but were very close to the increment counts found at day 2 of the EL12: D12 group. The effect of light on larvae which were main- tained under EL12:D12 during embryonic de- velopment and then transferred to constant darkness after hatching was notasevidentasthe effect of light was in the embryos maintained in constant darkness. Larvae raised in constant darkness (LaD24) showed a rapid addition of in- crements between day 0 and day 6 after hatch- ing, but few increments formed after day 6 (Table 3). When the LaD24 data were compared with the data from the larvae hatched and raised % ,^•4" Figure 5.— Light micrograph of the sagitta from a newly hatched larvae incubated for the total embryonic period in total darkness. Core formation is present but no increments have formed. Bar = 0.02 mm. 209 FISHERY BULLETIN: VOL. 80, NO. 2 Otolith diameter Increment count (mm) 275+05 0.128+0.011 13.89±1.69 0.181+0.010 1522+083 0.190+0.010 15.60±2.01 0.204+0.015 Table 3.— Otoliths are from Fundulus heteroclitus larvae. Embryos were incubated on a L12:D12 cycle and the larvae transferred to constant darkness at 24 °C immediately after hatching. Age 0 6 9 16 in EL12:D12 (Table 1), sagitta of LaD24 had re- duced increment numbers after day 6 and sagitta diameters in experimental fish were smaller than those found in the control (LaL12:D12). Some groups that had increment formation (LaD24 and LaL6:D6) during the first 6 d had in- crements formed after day 6 that were unclear and it was difficult to differentiate the D and I in the outer areas. However, the LaL12:D12 group showed distinct increments beyond day 6. The ED24 group larvae were sluggish upon hatching as were the ED24+L group. The larvae appeared to be normal in every other fashion except that the yolk sacs were notably smaller than the 12L:12D group. Effect of Temperature and Body Growth on Otolith Formation in Larvae An increase in temperature caused an increase in the growth rate in the larvae (Fig. 6a). The 30°C group grew significantly faster than the 24°C group (P<0.05). The 30°C larvae, also formed otoliths (Fig. 6b) which were significantly larger (P<0.05) in di- ameters than those in fish held at24°C. However, the difference in growth rates had no effect on the increment counts from either group (Fig. 6c). Both showed daily increment formation in their otoliths but the faster growing otoliths had wider daily increments, which accounted for the in- creased diameter measurements. When the oto- lith diameter data were pooled and compared with length data, the relationship was highly correlated (r = 0.95; Fig. 7). Estimation of Age of Wild Fish It is difficult to gain any insight into the age structure of the wild population from the length- frequency histograms, e.g., larvae collected 9 June 1977 had a standard length-frequency x t- o -z. UJ 35r 30 25 20 15 10 5 30°C Y=6.I7 + .83X '' r=.99 ,'/ 24°C Y = 6.26 +.66X r=.99 J L J I 0.7- 0.6 /-\ ^ ^ 0.5 v^ rr LlI 0.4 h- LJ 2 0.3 < Q 0.2 0.1 0 35 30 w 25 i- lu 20 UJ IK en 15 o ^ 10 5 0. B 30°C Y = .I25 +.0I9X ,' r=.98 / 24°C Y = .131 + .0I5X r = .98 J i 30UC Y=2.82 + IX hr = .99 24°C Y=2.58 +IX r=.99 -L -L J 10 15 20 25 30 AGE (DAYS) Figure 6.— A regression plot of A) standard length (SL), B)the diameter of the sagitta, and C) the numbers of increments of the sagitta of Fundvlus heteroclitus reared at 24°C and 30°C plotted against age of the fish. 210 RADTKK and DKAN: INCREMENT FORMATION OF OTOLITHS OF MUMMICHOO 15 20 LENGTH ( MM I Figure 7.— A regression plot of the diameters of all of the 24° and 30° Fundulus heteroclitus sagitta plotted against the stan- dard length of the fish. mode of 23 mm (Fig. 8a). However, otolith incre- ment-frequency histograms of the sample en- abled us to differentiate cohorts (Fig. 8b). A statistical analysis of the data from the field population showed that the relationship between the length of the fish and otolith diameter was linear (y = 0.01 + 0.027a, r = 0.90). The relation- ship of increment number and otolith diameter was curvilinear (y = 0.7601- 0.02 17.r + 0.000rx2, r = 0.92). Thus, the diameter of the otolith in- creased as the fish grew; the width of the incre- ment was wider in younger, smaller fish than in older, larger fish; and the number of increments increased as the length of the fish increased. When the time of hatching was estimated, using increment counts (Fig. 9a), groups were found that correlated with the occurrence of new and full moons. We observed that the increments tended to be more distinct in larvae collected from the field than in laboratory-reared larvae. When ages were adjusted for the two or three prehatching increments, the relationship was even more obvious (Fig. 9b). Incremental data indicated that the fish collected hatched at the new and full moon spring tides. DISCUSSION Embryological Formation of Otoliths Otoliths (sagittae) are the first calcified tissues to form in developing F. heteroclitus embryos, and although they are prominent and easily observed features that have been presented in numerous developmental studies, their forma- tion is not discussed. Long and Ballard (1976) clearly showed otoliths that formed at stage 20 in LENGTH { MM jll^ INCREMENTS Figure 8.— a) A length-frequency histogram of all fish col- lected in the sample, b) A histogram showing the frequency of the increment number of the sagitta of same fish as in 8a. • s o • o a *i .U* IS iIj 30l 1 a .si JUNE DATE (1977) JUNE DATE (19771 Figure 9.— Fundulus heteroclitus larvae collected on 9 June 1977. a) Estimated hatching dates are determined from num- bers of increments in the sagitta; b) estimated hatching times are adjusted for the two increments formed prior to hatching. Also represented are diurnal high tides (upper lines) and low tides (lower lines) and lunar phase (open circles = full moon, closed circles = new moon). embryos of the white sucker, and Armstrong and Child (1965) showed otoliths in mummichog em- bryos at stage 23 with calcification at stage 24, 211 FISHERY BULLETIN: VOL. 80. NO. 2 which agreed with this study, but their ontogeny is not well known. The importance and function- al nature of the early otolith calcification has not yet been determined. Two or three increments were easily visible in the mummichog otolith at the time of hatching. Accurate age determination of field samples could be affected until the number of increments formed at the time of hatching is considered. Brothers et al. (1976) studied increment forma- tion in several fish species and found that the California grunion, Leuresthes tenuis, had two increments at hatching. Some species, such as the northern anchovy, Engraulis mordax, had no increment formation until the time of yolk-sac absorption, 6 d after hatching (Methot and Kramer 1979). Taubert and Coble (1977) found that three species of Lepomis began increment formation at swim up. Scott (1973) studied the otolith structure in larvae of the northern sand lance, Ammodytes dubius, and suggested that otoliths first formed in the postlarvae at a mean total length of 2.4 cm. However, his interpreta- tion was a result of back calculations, not direct observations of otol iths from known age or larval stages of the fish. We have found that multiple spherules in the core of the sagitta, followed by numerous incre- ments, are formed prior to hatching in the Asiatic salmon or masou, Oncorhynchus masou; chum salmon, 0. keta; pink salmon, 0. gorbuscha; Arctic char, Salvelinus alpinus; brook trout, S. fontinalis; rainbow trout, Salmo gairdneri; and the sculpin, Cottus nozawa. The juveniles of the live bearing guppy, Lebistes reticulatus, and mosquitofish, Gambusia affinis, form a large number of increments prior to being spawned (Radtke and Dean unpubl. data). Mummichogs, California grunion, and the Atlantic silverside, Menidia menidia, have tidally correlated incu- bation periods of about 10 to 14 d and the salmo- nids incubation period can exceed 50 d. In con- trast, the northern anchovy and spot, Leiostomus xardhurus, have short incubation periods of <2 d. This indicates that embryos which have longer incubation periods and large yolk sacs may form several increments before hatching, while em- bryos that have short incubation periods might not start increment formation until hatching or after yolk-sac absorption (Brothers et al. 1976; Methot and Kramer 1979). Much work remains to be done on a range of species before we can attempt to interpret the functional significance of increment formation in embryos. The Effect of Light on Increment Formation in Embryos and Larvae The increments observed in otoliths in this and other studies (Pannella 1971; Brothers et al. 1976; Struhsaker and Uchiyama 1976; Taubert and Coble 1977; Barkman 1978; Methot and Kramer 1979) appear to be indicators of daily biological events. Rhythmic physiological activi- ties, such as the occurrence of rhythmic mineral deposition in coral (Wells 1963), crayfish gastro- liths (Scudamore 1947), and marine bivalves (Clark 1968; Pannella and MacClintock 1968), are controlled to a large extent by environmental changes synchronized to the diurnal astronomi- cal cycle. The only examination of the effect of endogen- ous daily biological rhythms on fish otoliths was by Taubert and Coble (1977), who studied the effect of environmental factors on daily incre- ment formation of Tilapia mossambica larvae hatched in constant light. Their different experi- mental groups all showed increment formation but it was not always daily. They found normal increment formation in all experimental groups with a 24-h periodicity and any other cycle other than 24-h period disrupted increment formation. Since daily cycles are known to occur in blood chemistry of fish (Garcia and Meier 1973), those daily chemical changes could be reflected in the daily increments of the otoliths. Mugiya (1966) found monthly changes in total and diffusible calcium in the endolymph of the semicircular canals of the rainbow trout and the flatfish, Kareius bicolaratus, and he related his finding to the formation of the opaque and translucent zones found in adult otoliths. Daily changes in the calcium metabolism of the fish also occur (Mugiya et al. 1980) which are reflected in the formation of the I and D. Daily increments were formed in F. heterocli- tus larvae kept in a L12:D12 cycle, but were absent when the developing embryos were kept in constant darkness (Fig. 5). Light had a defi- nite effect on increment formation, as embryos kept in constant light showed increment forma- tion and otolith diameters that were comparable with the L12:D12 group. An insight into this dis- crepancy was gained in the analysis of the group which initiated increment formation after a light stimulus on day 10 after fertilization. The possibility that light is a synchronizing stimulus at the cellular level was demonstrated by Pitten- 212 RADTKK and DEAN: INCRKMKNT FORMATION OF OTOLITHS OF MUMMIOIKx; drigh and Bruce (1957), who showed that a light stimulus synchronized emergence in fruit flies. More study is necessary to determine the timing of light needed for increment formation as well as the quantity and quality of light necessary. Whether the control of increment formation is an endogenous or exogenous rhythm (Harker 1957) is beyond the scope of these experiments. But the experiment on increment initiation in the dark group with 1 min of light exposure on day 10 in- dicated that light can act as a synchronizing stimulus, similar to that observed by Pittendrigh and Bruce (1957). Mugiya et al. (1980) found that D formation was initiated when light inter- rupted a photo period of 12L:12D or longer light period, but they did not determine the minimum dark period necessary for formation of the Dor the free running period for the D and I. When F. heteroclitus larvae were hatched in L12:D12 and then placed in light regimes other than a 24-h photoperiod, the increment forma- tion became aphasic in each group and incre- ment formation occurred at a slower rate. The "biological clock" of this group seemed to be out of phase under photoperiods other than those with a 24-h periodicity. A great deal of very exciting work is necessary to resolve these funda- mental questions on increment control. Effects of Temperature and Body Growth on Otolith Formation in Larvae Under the various experimental conditions employed in this study, daily otolith increments formed regardless of body growth or otolith growth rate (Fig. 6a, b, c), so it was possible to determine age and daily growth rates of individ- ual larvae which lived under different environ- mental conditions. Although F. heteroclitus lar- vae grew faster at 30°C than at24°C, the number of increments was still directly related to chrono- logical age. This documents the reliability of oto- lith increments for the age estimation of mum- michog larvae. It has been demonstrated that daily increments exist in several other species of fish (Pannella 1971, 1974; Brothers et al. 1976; Struhsaker and Uchiyama 1976; Ralston 1976; Taubert and Coble 1977) and the relationship be- tween increment counts and fish and otolith size was shown for the Atlantic silversides(Barkman 1978). In this study, otolith diameter increased with increased body length and increments formed on a daily basis with wider increments found in younger fish than older fish. This is con- sistent with the fact that younger fish are grow- ing faster, and although the relationship is non- linear, it is predictable and these results are consistent with those of Methot and Kramer (1979). Estimation of Age of Wild Fish Daily increments observed in field samples were easier to interpret than increments found in laboratory-reared larvae. We were not able to make age estimations of field collections of mum- michogs from length-frequency histograms, but it was possible to determine the age and growth rate of individual larvae from increment counts. Ralston (1976) and Struhsaker and Uchiyama (1976) determined growth rates of the millet- seed butterfly fish, Chaetodon miliaris, and the nehu, Stolephorus purpureus, respectively, and found that the growth, as represented in incre- mental units in the otolith, was nearly linear. Similar results were obtained by Barkman (1978) for Atlantic silversides and Methot and Kramer (1979). Our results are consistent with theirs: that increment formation is independent of growth rate but is age dependent; thus growth rates can be estimated for individual larval fish. Analysis of the age structure of samples of wild larval mummichogs showed that larvae hatched on or near the time of full and new moons. This is corroborated by observations on the reproduc- tive biology of F. heteroclitus by Taylor et al. (1977, 1979) and DiMichele and Taylor (1978), New Zealand white bait, Galaxias maculatus, by McDowell (1968), and Atlantic silversides by Middaugh (1981). Eggs of the California grun- ion, an intertidal spawner, have been found to hatch during spring tides (Clark 1925) and have otolith increments at hatching (Brothers et al. 1976). An analysis of age structure of wild populations of mummichog larvae, as deter- mined from their otoliths showed that South Carolina mummichogs spawn from March to mid-August and have a lunar spawning perio- dicity during that season. Analysis of otolith in- crements enabled us to differentiate individual fish in the wild population of the same size but of different ages. Photoperiod is a critical factor in increment formation, but other factors such as diurnal migratory behavior, rhythmic feeding, tempera- ture, respiration, and tidal rhythms might also 213 FISHERY BULLETIN: VOL. 80. NO. 2 play significant roles. Even though the control and/or mechanism of daily increment formation in larval fish is not fully understood, the incre- ments are a powerful tool for analysis of individ- ual growth and age determination of very young fish. ACKNOWLEDGMENTS We wish to thank R. Feller and D. Middaugh for their constructive criticism and D. Dunkel- berger for his assistance with the SEM work. This manuscript was based on a dissertation sub- mitted as partial fulfillment of the Ph.D. degree, University of South Carolina. LITERATURE CITED Armstrong, P. B., and J. S. Child. 1965. Stages in the normal development of Fundulus heteroclitus. Biol. Bull. (Woods Hole) 128:143-168. Bagenal, T. B. (editor). 1974. The proceedings of an international symposium on the ageing of fish. Unwin Brothers, Surrey, Engl., 234 p. Barkman, R. C. 1978. The use of otolith growth rings to age young Atlan- tic silversides, Menidia menidia. Trans. Am. Fish. Soc. 107:790-792. Brothers, E. B. 1978. Exogenous factors and the formation of daily and subdaily growth increments in fish otoliths. (Abstr.) Am. Zool. 18:631. Brothers, E. B., C. P. Mathews, and R. Lasker. 1976. Daily growth increments in otoliths from larval and adult fishes. Fish. Bull., U.S. 74:1-8. Cain, R. L.. and J. M. Dean. 1976. Annual occurrence, abundance and diversity of fish in a South Carolina intertidal creek. Mar. Biol. (Berl.) 36:369-379. Clark, F. N. 1925. The life history of Leuresthes tenuis, an atherine fish with tide controlled spawning habits. Calif. Dep. Fish Game, Fish Bull. 10, 51 p. Clark, G. R., II. 1968. Mollusk shell: Daily growth lines. Science (Wash., D.C.) 161:800-802. Degens, E. T., W. G. Deuser, and R. L. Haedrich. 1969. Molecular structure and composition of fish oto- liths. Mar. Biol. (Berl.) 2:105-113. DlMlCHELE, L., AND M. H. TAYLOR. 1978. Environmental influences on the hatching of Fun- dulus heteroclitus. (Abstr.) Physiologist 21(4):29. Garcia, L. E., and A. H. Meier. 1973. Daily rhythms in concentration of plasma Cortisol in male and female gulf killifish, Fundulus grandis. Biol. Bull. (Woods Hole) 144:471-479. Gulland, J. A. (editor). 1977. Fish population dynamics. Wiley, Lond.. 372 p. Hecht, T. 1978. A descriptive systematic study of the otoliths of the neopterygean marine fishes of South Africa. Part I. In- troduction. Trans. R. Soc. S. Afr. 43:191-197. Hjort, J. 1914. Fluctuations in the great fisheries of northern Eur- ope viewed in the light of biological research. Rapp. P.- P.-V. Reun. Cons. Int. Explor. Mer 20:5-38. Hubbs, C. L. 1943. Terminology of early stages of fishes. Copeia 1943:260. Irie, T. 1955. The crystal texture of the otolith of a marine tele- ost, Pseudosciaena. J. Fac. Fish. Anim. Hus. Hiro- shima Univ. 1:1-13. Knieb, R. T., and A. E. Stiven. 1978. Growth, reproduction and feeding of Fundulus heteroclitus on a North Carolina salt marsh. J. Exp. Mar. Biol. Ecol. 31:121-140. Larkin, P. A. 1978. Fisheries management — an essay for ecologists. Annu. Rev. Ecol. Syst. 9:57-73. Long, W. L., and W. W. Ballard. 1976. Normal embryonic stages of the white sucker, Catostomus commersoni. Copeia 1976:342-351. Lowenstein, O. 1971. The labyrinth. In W. S. Hoar and D. J. Randall (editors). Fish physiology. Vol. 5, p. 207-240. Acad. Press, N.Y. McDowell, R. M. 1968. Galaxias maculatvs (Jenyns), the New Zealand whitebait. N.Z. Mar. Dep. Fish Res. Div. Bull, New Ser. 2, p. 1-84. Merideth, W. H., and V. A. Lotrich. 1979. Production dynamics of a tidal creek population of Fundulus heteroclitus (Linnaeus). Estuarine Coastal Mar. Sci. 8:99-118. Messieh, S. N. 1972. Use of otoliths in identifying herring stocks in the southern Gulf of St. Lawrence and adjacent waters. J. Fish. Res. Board Can. 29:1113-1118. Methot, R. D., Jr., and D. Kramer. 1979. Growth of northern anchovy, Engraulis mordajc, larvae in the sea. Fish. Bull.. U.S. 77:413-423. Middaugh, D. P. 1981. Reproductive ecology and spawning periodicity of the Atlantic silverside, Menidia menidia. Copeia 1981:766-775. Middaugh, D. P., and J. M. Dean. 1977. Comparative sensitivity of eggs, larvae, and adults of the estuarine teleosts, Fundulus heteroclitus and Me- nidia menidia to cadmium. Bull. Environ. Contam. Toxicol. 17:645-652. Mugiya, Y. 1966. Calcification of fish and shell-fish— VI. Seasonal change in calcium and magnesium concentration of the otolith fluid in some fish, with special reference to the zone formation of their otolith. Bull. Jpn. Soc. Sci. Fish. 32:549-557. Mugiya, Y., N. Watabe, J. Yamada, J. M. Dean, D. G. Dun- kelberger, and M. Shimizu. 1981. Diurnal rhythm in otolith formation in the gold- fish, Carassius auratus. Comp. Biochem. Physiol. 68A:659-662. Pannella, G. 1971. Fish otoliths: Daily growth layers and periodical patterns. Science (Wash., D.C.) 173:1124-1127. 1974. Otolith growth patterns: an aid in age determina- tion in temperate and tropical fishes. In T. B. Bagenal 214 RADTKE and DEAN: INCREMENT FORMATION OF OTOLITHS OK MUMMK'lloo (editor). The proceedings of an international symposium on the ageing of fish, p. 28-39. Unvvin Brothers. Sur- rey, Engl. Pannella. G., and C. MacClintock. 1968. Biological and environmental rhythms reflected in molluscan shell growth. Paleontol. Soc. Mem. 2:64- 80. PlTTENDRIGH, C. S., AND V. G. BRUCE. 1957. An oscillator model for biological clocks, In D. Rudnich (editor), Rhythmic and synthetic processes in growth, p. 75-109. Princeton Univ. Press, Princeton. Popper. A. N.. and S. Coombs. 1980. Auditor mechanisms in teleost fishes. Am. Sci. 68:429-440. Radtke, R. L., and J. M. Dean. 1979. Feeding, conversion efficiencies and growth of lar- val mummiehogs, Fundulus heteroclitus. Mar. Biol. (Berl.) 55:231-237. Ralston, S. 1976. Age determination of a tropical reef butterflyfish utilizing daily growth rings of otoliths. Fish. Bull., U.S. 74:990-994. Scott, J. S. 1973. Otolith structure and growth in northern sand lance, Ammodytes ditbius. from the Scotian shelf. Int. Comm. Northwest Atl. Fish. Res. Bull. 10:107-116. Scudamore. H. H. 1947. The influence of the sinus glands upon molting and associated changes in the crayfish. Physiol. Zool. 20:187-208. Sokal, R., and F. Rohlf. 1969. Biometry: The principles and practice of statistics in biological research. Freeman, San Franc, 776 p. Strihsaker, P., and J. H. Uchiyama. 1976. Age and growth of the nehu, Stole/thorns purpur- etts(Pisces: Engraulidae), from the Hawaiian Islands as indicated by daily growth increments of sagittae. Fish. Bull., U.S. 74:9-17. Tanaka, M. 1972. Studies on the structure and function of the diges- tive system in teleost larvae— V. Epithelial changes in the posterior-gut and protein ingestion. [In Jpn., Engl, summ.] Jpn. J. Ichthyol. 19:172-180. Taubert, B. D., and D. W. Coble. 1977. Daily rings in otoliths of three species of Lepomis and Tilapia mossambica. J. Fish. Res. Board Can. 34:332-340. Taylor, M. H., L. DiMichele, and G. J. Leach. 1977. Egg stranding in the life cycle of the mummichog. Fundulus !nt, rod it us. Copeia 1977:397-399. Taylor, M. H., G. J. Leach, L. DiMichele, W. M. Levitan, and W. F. Jacob. 1979. Lunar spawning cycle in the mummichog, Fun dulus heteroclitus (Pisces: Cyprinodontidae). Copeia 1979:291-297. Valiela, I., J. E. Wright, J. M. Teal, and S. B. Volkmann. 1977. Growth, production and energy transformations in the salt-marsh killifish Fundulus heteroclitus. Mar. Biol. (Berl.) 40:135-144. Wells. J. W. 1963. Coral growth and geochronometry. Nature (Lond.) 197:948-950. Wild, A., and T. J. Foreman. 1980. The relationship between otolith increments and time for yellowfin and skipjack tuna marked with tetra- cycline. [In Engl, and Span.] Inter-Am. Trop. Tuna Comm. Bull. 17:509-560. Yamada. J., and N. Watabe. 1979. Studies on fish scale formation and resorption. I. Fine structure and calcification of the scales in Fundulus heteroclitus (Athereniformes: Cyprinodontidae). J. Morphol. 159:49-66. 215 THE LARVAL DEVELOPMENT OF SERGESTES SIMILIS HANSEN (CRUSTACEA, DECAPODA, SERGESTIDAE) REARED IN THE LABORATORY Margaret Knight1 and Makoto Omori2 ABSTRACT The larval development of Sergestes similis Hansen reared in the laboratory includes the following stages: nauplius I-IV, protozoea I-III, and zoea I-II. These forms together with the first two postlarval stages are described and illustrated. Sergestes sim His and S. arcticus, closely related species which comprise the arcticus species group, are very similar in larval as well as adult morphology especially in the ornate armature of protozoeal carapace apparently specific to the group. In contrast, the two species of the atlanticus group, S. atlanticus and S. comutus, differ distinctly from each other in carapace armature of the protozeal stages. The difference between these two species groups in variation within each group indicates that larval morphology may be of value in the study of interspecific relationships within Sergestes. Sergestes similis and Sergia lucens, species of closely related genera, differ in number of naupliar stages, in armature of body in protozoeal and zoeal phases, and in development of some appendages. The pelagic shrimp Sergestes similis is abundant in the North Pacific Drift ranging from Japan to North America between 40° and 50°N, and is a prominent constituent of the plankton in the cooler waters of the California Current. Within the genus Sergestes (Omori 1974), S. similis is located in the arcticus species group, as defined by Yaldwyn (1957), which includes only the two species 5. arcticus Kroyer and S. similis Hansen. Sergestes arcticus is widely distributed, occurring in the North Atlantic, the Mediter- ranean, and all sectors of the Southern Ocean, while S. similis is restricted to the subarctic and transitional zones of the North Pacific; available data indicates that the species are geographi- cally isolated from one another (Judkins 1972). The life history and distribution of S. similis and its importance in oceanic ecosystems of the Pacific have been discussed by Pearcy and Forss (1969), Omori et al. (1972), and Omori and Gluck (1979). The purpose of this paper is to describe and illustrate the larval development of S. similis and to compare the larvae with those of the closely related species S. arcticus described by Wasserloos (1908), Hansen (1922), and Gurney •Scripps Institution of Oceanography, University of Cali- fornia, La Jolla, CA 92093. 2Research Laboratory of fisheries resources. Tokyo University of Fisheries, Konan, Minato-ku, Tokyo 108, Japan. Manuscript accedpted October 1981. FISHERY BULLETIN: VOL. 80, NO. 2, 1982. and Lebour (1940). The larvae of S. similis are also compared with the early stages of S. atlanticus and S. comutus (Gurney and Lebour 1940), which comprise the atlanticus group, to note the difference in variation within species groups in protozoeal morphology, and with the larvae of Sergia lucens (Omori 1969) to note the differences between species of closely related genera. The description of Sergestes similis is based on both individuals reared in the laboratory by Omori (1979) during his study of the growth, feeding, and mortality of larval and postlarval stages of the species off southern California, and on specimens from preserved plankton samples. Gurney and Lebour (1940), in the major work on larvae of the genus, remarked that "perhaps the most interesting feature of the development of Sergestes is the striking difference which exists between the larvae of the different species, while the adults are often separable with diffi- culty," and suggested that knowledge of the larvae, when complete, may give a better indica- tion of the relationships of species than adult morphology. METHODS Omori (1979) described the procedures used for rearing the larvae of S. similis in the lab- oratory. Larvae from the population of the 217 FISHERY BULLETIN: VOL. 80, NO. 2 species off the coast of southern California were obtained for study from preserved plankton samples taken on Scripps Institution of Ocean- ography Expedition X and CalCOFI Cruises 6904 and 6905 during April and May of 1964 and 1965. At least five individuals of each developmental stage were dissected in glycerine for study of appendages. Some specimens of each stage were prepared for study and dissection by digesting away all soft tissue in heated aqueous KOH and then staining with Chlorazol Black E. Drawings were prepared with the drawing attachment of a Wild M203 microscope. Measurements of reared and planktonic larvae of S. similis were compared by Omori (1979, table 6); the mean body lengths (with standard deviation in parentheses) of larval stages obtained at 14°C are repeated here by stage for convenience. The larvae were mea- sured along the midline from anterior margin of forehead to posterior margin of telson. The postnaupliar developmental phases have been named protozoea, zoea, and postlarva following Omori (1979), and the terminology of Gurney and Lebour (1940) has been followed in describing the armature of carapace. In the protozoeal phase the outgrowths of the carapace are referred to as processes with secondary spines and spinules, while in the zoeal and postlarval stages the outgrowths are called spines with secondary spinules. Segmentation of two of the appendages proved difficult to determine. The basal segmentation of the exopod of the second antenna in protozoeal stages I-III was not clear. In S. similis it appeared that there were incomplete sutures within segments 1 and 3, giving 12 outer margin and 10 inner margin sutures; we have numbered the segments along the inner margin. The articu- lation of coxa, basis, and endopod of the second maxilla in protozoeal and zoeal phases also proved confusing. We have followed Gurney (1942) in referring to the medial lobes as bifid endites of coxa and basis, and have assumed from the morphology of the postlarval appendage that the endopod consists of 5 segments, although the articulation of segment 1 and basis was not clear. In the description of larval stages, only changes in structure and armature of body and appendages are discussed; if an appendage is not 3Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. mentioned, it may be assumed that there has been no change from the preceding stage except increase in size. In order to compare the basic pattern of development between Sergestes similis and Sergia lucens, we reexamined a number of larvae and postlarvae of S. lucens from the rearing experiment in July 1965. RESULTS The larval development of Sergestes similis includes the following stages: nauplius I-IV, protozoea I-III, and zoea I-II. The first two postlarval stages are also described. Nauplius I (Fig. la, e) Body length: 0.34 mm (0.01). Body ovoid with two posterior spines which curve posterodorsally and are slightly swollen basally. Antennule (Fig. 2a) unsegmented with 4 smooth setae, 2 terminal and 2 subterminal, and small terminal spine. Antenna (Fig. 3a) unsegmented; exopod with 5 setae; endopod with 3 setae, 2 terminal and 1 sub- terminal; all setae smooth. Mandible (Fig. 4a) biramous and unseg- mented, each ramus with 3 smooth setae. Nauplius II (Fig. lb) Body length: 0.38 mm (0.01). Body slightly longer and narrower posteriorly than in stage I, with 2 pairs of spines on posterior margin, outer pair very short, tiny rudiments of third inner pair sometimes visible. Antennule (Fig. 2b) with 1 subterminal medio- ventral seta and 3 terminal processes including 2 setae with setules and 1 small aesthetasc. Antenna (Fig. 3b) unsegmented; exopod with 6 setae and sometimes with small distal spine, distolateral seta smooth and others plumose; endopod with 2 plumose setae and 1 small spine terminally. Mandible (Fig. 4b) with 3 plumose setae on each ramus. Nauplius III (Fig. lc, f) Body length: 0.42 mm (0.02). Body with posterior portion tapering, pos- terior margin slightly indented medially with 4 218 KNIGHT and OMORI: LARVAL DEVELOPMENT OF SERGESTES SIMILIS Figure 1. — Sergestes similis. Nauplius I-IV, a-d, dorsal view; nauplius I, III-IV, e-g. lateral view without appendages. pairs of spines, outer pair tiny, relatively long third pair armed with spinules and articulated basally. Antennule (Fig. 2c) sometimes with a second seta on inner margin, incipient segmentation, and few rows of tiny spinules. Antenna (Fig. 3c) with incipient segmentation of protopod and exopod sometimes visible; exopod with 7 setae and small distal spine, distal 2 setae with small setules, other setae plumose; endopod with 3 terminal setae and 1 seta on inner margin. 219 FISHERY BULLETIN: VOL. 80, NO. 2 1 J Figure 2.— Sergestes similis. Antennules: a-d, nauplius I-IV; e-g, protozoea I-III; h-i, zoea I-II; j, postlarva I; setules omitted on i and j. 220 KNICHT and OMORI: LARVAL DKVKLOl'MKNT OK Sh'RCh'STKS SIMILIS f h Figure S.—Sergestes similis. Antenna: a-d, nauplius I-IV; e, protozoea I;f-g,zoeaI-II; h, postlarval.tipof scale; setules omitted on g. 221 FISHERY BULLETIN: VOL. 80, NO. 2 FIGURE 4.— Sergestes similis. Mandibles: a-c, nauplius MI, IV; d-f, protozoea I-III; g-h, zoea MI; i, postlarva I. Labrum: j, protozoea I; k, zoea I. 222 KNICHT and OMORL LARVAL DKVKLOI'MKNT OF SERGESTES SIMILIS Mandible unchanged. Anlagen of maxillules, maxillae, and first and second maxillipeds visible. Nauplius IV (Fig. Id, g) Body length: 0.49 mm (0.03). Body with abdomen forming, posterior margin with distinct medial indentation and 4 pairs spines, third pair still relatively long, rudi- ments of fifth inner pair sometimes visible, spinules present on spines 2-4, and sometimes on 1; third pair articulated, other spines fused with telson. Antennule (Fig. 2d) with 2 inner setae, terminal setation unchanged; proximal two- thirds with indistinct segmentation most clearly visible along inner margin; about 17 rows of tiny spinules encircle antennule associated, in segmented section, with distal margin of seg- ment. Antenna (Fig. 3d) with protopod of 2 indistinct segments; exopod with approximately 8 seg- ments (basal segmentation unclear, specimens cleared and stained have indication of 10 seg- ments on outer margin and about 8 on inner margin), with 8 or 9 setae and sometimes a small distal spine, distal 3 setae with small setules, others plumose; endopod at least 2-segmented, small distinct distal segment with 4 terminal setae, proximal segment with 2 setae on outer margin and sometimes with incomplete basal segmentation; both rami encircled with rows of tiny spinules. Mandible (Fig. 4c) with basal portion swelling with development of gnathal lobe, tissue with- drawing from rami. Rudiments of maxillules, maxillae, and 2 pairs of maxillipeds present posterior to mandibles. Protozoea I (Fig. 5a, b) Body length: 0.82 mm (0.02). Carapace with following processes: 1 pair anterolateral, each branching to 3 large spines and occasionally 1-3 small spines (5 of 20 reared larvae with small spines on one or both processes, 20 larvae from the plankton with 3 large spines only); 1 pair lateral with 1-3 large basal spinules; 1 posterodorsal with few large basal spinules, usually 2; all processes with small spinules to tip. Anterior margin of forehead with pair of small papillae. Prominent, round dorsal organ present in protozoeal phase. Thorax with evidence of segmentation, abdomen unsegmented. Telson forked, each fork with 2 small smooth ventral spines and 4 long curving processes armed with spinules. Antennule (Fig. 2e) of 3 segments, proximal segment subdivided into 5 small segments; proximal and middle segments with 1 and 2 setae, distal segment with 8 processes including 5 setae, 3 terminal and 2 proximal, and 3 aesthetascs. Gurney (1942) noted that distal seg- ment with aesthetascs is homologous with outer flagellum of later stages and that peduncle is therefore of 2 segments. Antenna (Fig. 3e) with exopod of 10 segments, terminal segment with 3 setae, segments 2-9 with 1 distal seta on inner margin, segments 3 and 5 with 1 distal seta on outer margin as well; endopod 2-segmented, distal segment with 5 terminal setae, long proximal segment with 5 setae on inner margin— 3 distal and 2 proximal on slight protuberance; basis with 2 setae on inner margin; structure unchanged in proto- zoeal phase. Mandibles (Fig. 4d) without palp, gnathal lobe of each mandible with 1 strong serrated spine on cutting edge between incisor teeth and molar area. Labrum (Fig. 4j) with long anteroventral spine in protozoeal phase. Maxillule (Fig. 6a) with exopod a small round lobe bearing 4 plumose setae; endopod 3- segmented with 3-2-5 setae progressing distally; basal and coxal endites with 4 and 5 setae, re- spectively. Maxilla (Fig. 7a) with segmentation indistinct; exopod small and oblong with 5 long plumose setae; endopod 5-segmented with setation of 4-2- 2-2-3, segment 1 rarely with 3 setae; basal and coxal endites bifid, the 4 median lobes with 8-4-4- 4 setae. First maxilliped (Fig. 8a) with exopod of 1 seg- ment bearing 7 long plumose marginal setae; endopod 4-segmented with 3-2-2-5 setae; basis with 12 setae in groups of 3 along medial margin; coxa with 5 setae; inner margins with fine setules as well. Second maxilliped (Fig. 9a) with exopod of 1 segment bearing 6 marginal plumose setae; endopod 4-segmented with 2-1-2-5 setae; basis with 5 and coxa with 2 setae. Third maxilliped a small bud. Protozoea II (Fig. 10a, b) Body length: 1.21 mm (0.10). 223 FISHERY BULLETIN: VOL. 80. NO. 2 Figure 5. — Sergestes similis. Protozoea I: a, dorsal view; b, lateral view. Carapace with rostrum but without pair of anterolateral processes; all processes with relatively large spines which branch distally into several small spinules, the processes themselves do not branch distally but bear small spinules to tip; rostral process with 3 pairs of spines, each lateral process usually with 7, rarely 6 or 8, spines, and posterior process with 2-4, usually 3 or 4, pairs of spines. Eyes stalked and moveable with papilla on anterior margin of stalk. Thorax 224 KNICHT and OMORI: LARVAL DKVKLOl'MKNT OF SERGh'STKS SIMIUS Figure 6.— Sergestes similis. Maxillule: a, protozoea I; b, protozoea II, coxal and basal endites; c, protozoea III, basal endite; d, zoea I; e, postlarva I. with segments delineated; abdomen and telson as in preceding stage. Antennule (Fig. 2f) with 4 subdivisions of proximal segment and distal segment with 9 processes, including 5 setae and 4 aesthetascs. Mandibles (Fig. 4e) with median armature asymmetrical, right mandible with 2 and left mandible with 5 strong spines, the spine nearest molar area is strongest on each mandible, 2 long spines on right mandible separated by short tooth. Maxillule (Fig. 6b) with 6 setae on basal endite and 6 or 7, usually 7, setae on coxal endite. Maxilla (Fig. 7b) with setation of 8-4-5-5 on medial lobes. First maxilliped with 7 or 8, usually 8, setae on coxa. Second maxilliped with endopod setation of 2- 2-2-5; basis with 5 or 6, rarely 6, setae. Third maxilliped a small rudiment, some- times slightly bifid at tip. Anlagen of thoracic legs 1-5 may be visible. Trotozoea III (Fig. 11a, b) Body length: 1.90 mm (0.18). Carapace with 1 pair supraorbital processes which curve dorsolateral^ in addition to arma- ture of preceding stage; all processes but rostrum armed with strong spines which branch 225 FISHERY BULLETIN: VOL. 80. NO. 2 Figure T.—Sergestes similis. Maxilla: a, protozoea I; b, protozoea II, basal endite; c, zoea I; d, postlarva I. distally into spinules, all processes terminate in single spine and bear spinules to tip; supra- orbital processes each with 9-14, usually 10-12, spines; each lateral process with 5-8, usually 7, spines; and posterodorsal process with 7-13, 226 usually 10-12, spines. Eyestalks longer than in stage II. Abdomen with 5 segments articulated, segment 6 still fused with telson; segments 1-5 with 1 pair lateral spines, segment 6 with bira- mous, unsegmented, nonsetose uropods and 1 KNKJHT and OMORI: LARVAL DEVELOPMENT OF SEHCKSTKS SIMILIS d c Figure 8. — Sergestes simiiis. First maxilliped: a-b, protozoea I, III; c, zoea I; d, postlarva I; setules omitted on b and c. pair small ventolateral spines proximal to uropods; smooth ventral spines of telson rela- tively larger than in stage I. Antennule (Fig. 2g) with proximal of 3 seg- ments without subdivisions and segment 2 with 5 setae, otherwise setation unchanged. Mandibles (Fig. 4f) usually with 3 and 6 spines on right and left cutting edges, 1 of 10 larvae 227 FISHERY BULLETIN: VOL. 80, NO. 2 Figure 9.—Sergestes similis. Second maxilliped: a-b, protozoea I, III; c, zoea I; d, postlarva I; setules omitted on b. 228 KNICHT and OMORI: LARVAL DEVELOPMENT OF SERGESTES SIMILIS Figure 10.— Sergestes similis. Protozoea II: a, dorsal view; b, lateral view. 229 FISHERY BULLETIN: VOL. 80, NO. 2 Figure ll.—Sergestes sim ilia. Protozoea III: a, dorsal view; b, lateral view; c, third maxilliped and thoracic legs of late stage larva. 230 KNICHT and OMORI: LARVAL DF.VF.LOI'MKNT OF SKRCESTES SIMMS with armature of stage II, long spine nearest incisor teeth on right mandible separated from other long spines by several small teeth. Maxillule (Fig. 6c) with 7 setae on both basal and coxal endites; as in earlier stages distal stout seta on basal endite with long basal spinules, other stout setae with short spinules. Maxilla with setation of 9-5-6-5 on medial lobes, rarely with 8 setae on proximal lobe of coxal endite. First maxilliped (Fig. 8b) with 9 setae on exopod. Second maxilliped (Fig. 9b) with endopod setation of 3-2-2-5 and exopod with 8 setae; coxa with 1 or 2 setae. Third maxilliped and thoracic legs 1-5 (Figs, lie, 12a, d) biramous, unsegmented, and nonsetose with exopod slightly longer than endopod. Zoea I (Figs. 13, 14a) Body length: 3.25 mm (0.13). Carapace altered with change in phase, now with 10 spines including rostrum, 1 pair supra- orbital, 1 pair hepatic, 2 pairs lateral, and 1 posterodorsal, all spines armed only with spinules except rostrum which bears a strong basal dorsal spine with spinules; dorsal organ present in zoeal phase but smaller than in pre- ceding stages. Eyes with long slender stalk bearing single ventral papilla in both stages of phase. Abdomen of 6 segments with following arma- ture: segments 1-5 with 1 pair lateral spines which decrease in length posteriorly, segments 1-6 with 1 posterodorsal spine longest on segments 3-5, segment 6 with 1 pair small ventrolateral spines and segment 1 with 1 pair triangular dorsolateral processes; posterodorsal and lateral spines armed with spinules, lateral spines of segments 1 and 2 with relatively long spinules proximally on posterior margin, seg- ments with dorsal and lateral setae as figured. Telson (Fig. 15e) slender with 1 pair lateral spines on rounded margin and produced distally into 2 long slender spines which bear 4 spinules near one-third their length and tiny spinules distally. Antennule (Fig. 2h) with peduncle unseg- mented and with following armature: basal lateral spine; 13-16, usually 15, long plumose setae along inner, outer, and distal ventral margins; smaller setae distributed near basal spine and along dorsal surface of peduncle in clusters of 2-2-3-1-3. Flagella unsegmented; outer flagellum with 3 small spines and 1 seta distally, and dorsal tier of 6 aesthetascs near two- thirds the length of flagellum; inner ramus very small with 2 terminal spines. Antenna (Fig. 3f) with scale (exopod) slender bearing 1 small subterminal ventral seta, 1 subterminal seta on outer margin, and 10 or 11, usually 11, setae on distal and inner margins, all setae with setules, terminal setae relatively stout and graded in size from short lateral to long medial seta; flagellum (endopod) with about 8 segments, proximal segment about the length of scale, distal segment with 4 terminal spines, 1 seta projecting laterally from each side, and 1 seta directed anteriorly; a strong spine with basal spinule appears on inner margin of flagellum before midpoint of segment 1 and dis- tally on segment 6. Mandibles (Fig. 4g) with 4 and 7 relatively long spines on right and left blades between incisor teeth and molar surfaces, bud of palp present. Labrum (Fig. 4k) with anteroventral spine present but shorter than in preceding phase. Maxillule (Fig. 6d) with 11 setae on basal endite. Maxilla (Fig. 7c) with exopod modified bear- ing 1 long plumose seta on proximal lobe and 4 small processes approximately in position of plumose setae of preceding stage; endopod un- changed; medial lobes with setation of 9-5-6-6. First maxilliped (Fig. 8c) with form as in protozoeal phase; exopod with 13 marginal setae; endopod with setation of 4-3-2-5; basis with 13 and coxa with 8 setae. Second maxilliped (Fig. 9c) somewhat modi- fied, long flexible exopod with 7 or 8, rarely 8, setae and resembling exopod of thoracic leg rather than form of preceding phase; endopod 4- segmented with 3-0-2-5 setae; basis with 9 and coxa with 2-4 setae. Third maxilliped (Fig. 12b) functional and pediform; exopod with 19-23, usually 21, setae; endopod 4-segmented, usually with setation of 3- 4-4-5, rarely with 5 setae on segment 2; basis with 4 setae, coxa nonsetose. Legs 1-5 functional; legs 1-3 (Fig. 12e) similar, shorter than third maxilliped; exopods with 20- 22, frequently 21, setae; endopods 4-segmented with 3-4-4-4 setae and bases with 3 or 4 setae. Legs 4 and 5 (Fig. 16c, d) smaller than first three pairs; exopods with 17-19 setae; endopods 231 FISHERY BULLETIN: VOL. 80, NO. 2 O.I mm I 1 Figure 12.— Sergestes similis. Third maxilliped: a, protozoea III; b, zoea I; c, postlarva I. Leg 1: d, protozoea III; e, zoea I; f, postlarva I. 232 KNIOHT and OMORI: LARVAL DKVKLOl'M KNT OF SKRdh'STKS SIM I LIS Figure 13.— Sergestes similis. Zoea I, dorsal view. 233 FISHERY BULLETIN: VOL. 80, NO. 2 Figure 14.— Sergestes similis. Abdomen, lateral view: a, zoea I; b, zoea II. 3-segmented with 3-3-4 setae on leg 4, rarely 4 setae on segment 2, and 2-3-4 setae on leg 5; bases with 1 seta, coxae nonsetose. Pleopods (Fig. 15a) present on abdominal seg- ments 1-5 and variable in size within stage; exopods nonsetose decreasing in length from pleopod 1 to 5; pleopod 5 with nonsetose endopod about two-thirds length of exopod, pleopod 4 with small bud of endopod, pleopods 2 and 3 sometimes with some swelling in position of endopod. Uropods with rami articulated; protopod with lateral spine and posterior projection (Fig. 14a); exopod and endopod long, slender, and fringed with plumose setae except proximal to smooth spine on lateral margin of exopod. Zoea II (Figs. 14b, 17) Body length: 4.42 mm (0.20). Carapace, abdomen, and telson (Fig. 15f) with armature as in preceding stage; spines shorter relative to size of larva and lateral spines of abdominal segments 1 and 2 without long pos- terior spinules. Antennule (Fig. 2i) with peduncle bearing 16- 19, usually 17 or 18, marginal plumose setae and small setae in clusters of 3-4-3-1-3; outer flagellum with 1 distal seta and usually unseg- mented, sometimes constricted at two points distal to tier of 6 aesthetascs, rarely with weak sutures; inner ramus without spines. Antenna (Fig. 3g) with scale armed with long subterminal spine on outer margin bearing spinules, a small subterminal ventral seta, and 14 or 15 marginal plumose setae, terminal setae no longer stout; flagellum long, with 19-25 seg- ments in three reared larvae, terminal segment with 2 spines and 3 setae, 1 seta projects laterally from each side. Mandibles (Fig. 4h) with armature un- changed; palp larger than in zoea I, unseg- mented and nonsetose. Labrum with short remnant of anteroventral spine. 234 KNIGHT and OMOKI: LARVAL PKVKLOI'MKNT OF SKKUKSTKS SI.MIIJS e f 9 Figure 15.— Sergestes similis. Pleopods: a-b, zoea I-II; c-d, postlarva I-II. Telson: e-f, zoea I-II; g-h, postlarva I-II. Maxillule with 12 or 13, usually 12, setae on basal endite and 8 or 9 setae on coxal endite. Maxilla unchanged except that exopod relatively larger with small processes now tiny. First maxilliped with 13 or 14, usually 13, setae on exopod. Second maxilliped with endopod setation of 4- 2-3-5, rarely 5 and 4 setae on segments 1 and 3; exopod with 7 setae; basis with 9 or 10 and coxa with 3 or 4 setae. Third maxilliped with 4 or 5, rarely 4, setae on distal segment of endopod and 3 setae on basis. Legs 1-3 with endopod slightly longer than exopod, legs 2 and 3 with distal margin of 235 FISHERY BULLETIN: VOL. 80. NO. 2 endopod segment 3 swelling in formation of chela (Fig. 16a); exopods with 20-24, usually 22, setae; endopods usually with setation of 3-4-5-4, rarely 5 and 4 setae on segments 2 and 3; bases with 3 or 4 setae. Leg 4 exopod with 18- 21 setae, endopod usually with setation of 3-3-4, rarely with 2 and 4 setae on segments 1 and 2. Leg 5 exopod with 16-19 setae, endopod usually with setation of 2-3-4, rarely with 3 setae on segment 1. Pleopods (Fig. 15b) nonsetose but longer than in preceding stage, exopods again decreasing in length from anterior to posterior pairs; pleopods 2-5 with endopod which increases in size posteriorly with variation in size within stage with age. 0. 1 mm I 1 c-d,f Figure 16.— Sergestes similis. Leg 2: a, zoea II; b, postlarva I. Leg 4: c, zoea I. Leg 5: d, zoea I. Legs 4 and 5: e-f, postlarva HI. 236 KNIGHT and OMORI: LARVAL DEVELOPMENT OF Sk'RHhSTh'S SIMIUS Figure n.—Sergestes similis. Zoea II, dorsal view. 237 FISHERY BULLETIN: VOL. 80. NO. 2 Postlarva I (Fig. 18a) Body length: 5.07 mm (0.26). Carapace with armature reduced, 2 pairs of lateral spines of preceding phase missing or only tiny remnants; rostrum, supraorbital, and hepatic spines, and posterodorsal spine shorter relative to length of carapace. Abdomen with lateral spines of segments 1-5 and posterodorsal spines of segments 1 and 2 small and without spinules. Telson (Fig. 15g) with posterior fork spines much shorter in relation to body of telson than in zoeal phase, with spinules reduced and with pair of plumose setae on inner margin near base of fork; relative length of terminal setae and fork spines vary within stage. Antennule (Fig. 2j) with peduncle 3-seg- mented and fringed with marginal plumose setae, basal segment with statocyst and lateral spine; rows of small setae now situated on distal margins of segments; outer flagellum with 10 segments, proximal segments 1-3 with 1-2-6 medioventral aesthetascs, 6 aesthetascs of seg- ment 3 set proximally on small protuberance; inner flagellum with 2 segments. Antenna (Fig. 3h) with subterminal lateral spine of scale smaller than in zoea II, scale with 20-22 marginal setae; flagellum very long, about 2.6 times body length in one reared larva. Mandibles (Fig. 4i) with cutting edges smooth between simplified incisor and molar processes, left mandible with notch opposing incisor tooth of right mandible; palp with 5-7 setae and some- times indistinctly 2-segmented. Labrum without spine. Maxillule (Fig. 6e) with endopod reduced to small nonsetose rudiment and with tiny vestige of exopod, basal and coxal endites with increased numbers of setae. Maxilla (Fig. 7d) with endopod reduced to small nonsetose rudiment; scaphognathite (exopod) large with 17 or 18 marginal setae, 1 posterior seta relatively long; coxal and basal endites bifid, medial lobes with 2-2-4-4 to 6 setae. First maxilliped (Fig. 8d) with small non- setose exopod and endopod, coxa with medial setae and small epipodite, basis with broad flat medial lobe armed with setae along inner margin. Second and third maxillipeds and legs 1-3 with small nonsetose remnant of exopod. Second maxilliped (Fig. 9d) with endopod long, 5-segmented, recurved at articulation of merus and carpus, and armed with strong setae, articulation of ischium and basis indistinct if visible; coxa with bud of epipodite. Third maxilliped (Fig. 12c) with endopod long, 5-segmented, and with strong marginal setae. Leg 1 (Fig. 12f) with clusters of strong barbed setae at articulation of propodus and carpus, legs 2 (Fig. 16b) and 3 with small setose chela, leg 2 with small spine on lateral margin of ischium. Leg 3 slightly longer than first maxilliped. Legs 4 and 5 (Fig. 16e) reduced to irregular, nonsetose bifid rudiments. Pleopods (Fig. 15c) with setose exopods; endopod of pleopod 5 setose, rarely endopod 4 with 1 or 2 terminal setae, as before endopods increase and exopods decrease in length from anterior to posterior pairs; protopod with 1 distal seta on inner margin of pleopods 1-3; endopods vary in size within stage. Postlarva II (Fig. 18b) Body length: 5.80 mm (0.20). Carapace and abdomen with armature reduced in size, small posterodorsal spine of carapace may be missing and dorsal spines of abdomen segments 1 and 2 very small. Telson (Fig. 15h) with posterolateral spines reduced in length and usually with 3 pairs plumose lateral setae in addition to terminal pair. Antennule with outer flagellum, in exuvia of one reared larva, with about 17 segments and in- creased number of aesthetascs on proximal seg- ments; inner flagellum with 2 or 3 segments. Antenna with subterminal lateral spine of scale smooth or with few spinules and reduced in length, scale with 24-28 marginal setae. Mandibles with palp 2-segmented bearing 11- 14, usually 11 or 12, setae. Maxillule with endopod more distinctly shaped; vestige of exopod not present. Maxilla with 25-27 setae on scaphognathite; endopod larger than in preceding stage with outer basal seta and sometimes inner seta; medial lobes with setation of 2-3-5 to 8-8 or 9. First maxilliped with endopod, exopod, and epipodite larger than in postlarva I, rarely endopod slightly longer than exopod with some indication of segmentation. Second and third maxillipeds and legs 1-3 without vestige of exopod; legs 1 and 2 with small ischial spine; legs 4 and 5 (Fig. 16f) more distinctly formed, nonsetose, and with leg 4 longer than leg 5. Pleopods 3-5 (Fig. 15d) with setose endopods, 238 KNIGHT and OMORI: LARVAL DKVKLOPMKNT OK SlCUdKSTKS SIMIUS Figure 18.— Sergestes similis. a, postlarva I; b, postlarva II. 239 FISHERY BULLETIN: VOL. 80, NO. 2 rarely endopod of pleopod 2 with 1 or 2 small setae; protopods of pleopods 1-3 with 2 setae; those of pleopods 4 and 5 with or without 1 seta on protopod. DISCUSSION Yaldwyn (1957) defined two subgenera, Sergestes s.s. and Sergia, within what he termed the rather unwieldy genus Segestes s.l. Recently, the subgenera were raised to full genera by Omori (1974). The species of Sergestes have specialized luminescent modifications of the gastrohepatic gland called organs of Pesta and are without cuticular pigmentation and dermal photophores, while species of Sergia are without organs of Pesta and, with some exceptions, have uniform cuticular pigmentation and often dermal photophores. The two genera are themselves divided into species groups, six in Sergestes and three in Sergia, which appear to be easily distinguished and are considered to be natural phyletic units (Judkins 1978). The arcticus group includes only two species, Sergestes arcticus and S. similis, and is characterized by the morphology of third maxilliped, fifth pereiopod, antennular pedun- cle, and petasma (Yaldwyn 1957). Sergestes similis differs from S. arcticus in having a more slender and fragile body and antennular peduncle, in a longer and more upwardly directed rostrum, in proportions of posterior arthrobranchs above the third and fourth pereiopods, and in some proportions and armature of petasma and thelycum (Milne 1968). The close relationship of S. similis and S. arcticus which has been inferred from adult morphology may also be seen in their larval morphology, especially in the shape of eye, in the ornate armature of protozoeal carapace, and in the armature of carapace, abdomen, and telson in the zoeal phase. Gurney and Lebour (1940) described larvae now known to be representative of all of the species groups within Sergestes s.l. and noted that the protozoea II and III of S. arcticus were very distinct in form of eye and peculiarly branched spines. They described some features of protozoea II and III, zoea I and II, and postlarva I of S. arcticus and gave figures of the second protozoea and zoea, with telson of postlarva I. They stated that the "brushlike endings" of the long spines on rostral, lateral, and posterior processes of protozoea II and on supraorbital, lateral, and posterior processes of protozoea III were most characteristic of the species. The protozoea II and III of S. similis, identified in this study, have the same distinctive armature of carapace spines. The larval stages of S. arcticus discussed by Gurney and Lebour (1940) resemble the compar- able stages of S. similis in the details they described and figured. Gurney and Lebour, however, do not deal with the structure of mouth- parts and thoracic appendages; rather, they note that these appendages seem to be uniform throughout the genus and refer the reader to the earlier descriptions of S. arcticus by Wasserloos (1908) and Hansen (1922). Gurney, in a later work (1942), does figure the appendages of protozoea III of S. cornutus, an atlanticus group species, and they appear very similar to those of the same stage of S. similis. The protozoeal stages of S. arcticus described by Wasserloos (1908), on the other hand, differ from those of S. similis in setation and/or segmentation of antennule, antenna, and mouthparts, but appendages are not figured; the armature of carapace differs in protozoea II and III on lateral and supraorbital processes, re- spectively. The species appear similar in described and figured features of the zoeal phase. Hansen (1922) offered a brief summary of Wasserloos' description of the protozoeal phase and added both generic and specific comments, with figures, on the zoea and postlarva of S. arcticus from his own observations. He noted that the mouthparts of the protozoea are like those of the zoeal stages which he described in some detail but which do not always agree with details of the protozoeal phase described by Wasserloos. Hansen also noted that the rostrum in protozoea III is little modified from stage II, yet conspicuous secondary spines are lost in this molt. In the zoeal phase, S. similis larvae differ from those of S. arcticus, as described by Hansen, in segmentation of maxillule and first maxil- liped. Unfortunately, because the descriptions of S. arcticus by Wasserloos (1908) and Hansen (1922) were found to be inconsistent with each other and with that of Gurney and Lebour (1940), and they could not be interpreted with confidence, a detailed comparison with S. similis was not possible. A reexamination of the larval stages of S. arcticus is needed to detect specific differences that may exist between the apparently very similar arcticus group species. 240 KNIGHT and OMORI: LARVAL DEVELOPMENT OF Sh'RCKSTh'S SIMIL1S Gurney and Lebour (1940) believed the elaborate protozoeal phase of Sergestes s.l. to be of particular importance, as it might "point to a satisfactory subgeneric grouping of the adults." They separated the second and third protozoeae of thirteen species of Sergestes s.l., representative of all of the nine species groups later defined by Yaldwyn (1957), into three types: dohrni, ortmanni, and hispida. The carapace has the same number of processes in all three types but the armature of the processes differs as follows: dohrn i type with numerous long lateral spines on supraorbital, lateral, and posterior processes; ortmanni type with long spines on supraorbital processes but with long spines only at the bases of lateral and posterior processes on carapace; h ispida type without long spines on supraorbital, lateral, or posterior processes, although there may be basal spines on lateral and posterior processes. Gurney and Lebour observed that the ortmanni armature seems to be derived from the dohrni type in that it retains long lateral spines on supraorbital processes. These larval types do correspond with three divisions of species within Sergestes s.l. Of the species described by Gurney and Lebour (1940), the hispida type larvae all belong to the genus Sergia, while the dohrni and ortmanni types belong to Sergestes; S. corniculum is of the ortmanni type, but all other species of Sergestes identified are of the dohrni type. The zoeal stages could not be separated into groups which corresponded to the protozoeal types. Gurney and Lebour (1940) noted that the dohrni type carapace was found in a number of species which were not supposed to be particu- larly closely related and which could not be grouped further by structure of the protozoeal phase. The identification of S. similis larvae has proved this untrue with respect to the arcticus group species, but apparently it does apply to species of the atlanticus group, the only other species group within Sergestes, or Sergia, all of whose protozoeal stages are identified. Gurney and Lebour described the larvae of Sergestes atlanticus and S. cornutus, the two species which comprise the atlanticus group, and observed that larval morphology did not corroborate the close relationship implied by the morphology of adult petasma. The carapace armature in protozoea II and III of the arcticus and atlanticus groups is compared in Table 1 to show the range of variation within each group; the species groups themselves are not considered to be closely re- lated within the genus (Judkins 1972). Sergestes arcticus and S. similis may have the same armature in both protozoeal stages, while S. atlanticus and S. cornutus differ in each stage; all of the lateral spines of the atlanticus group have smooth tips rather than the brushlike endings characteristic of the arcticus group. The difference in larval morphology within the atlanticus group is in accordance with the signi- ficant difference described by Foxton (1972) between S. atlanticus and S. cornutus in morphology of the organs of Pesta. This dis- crepancy was one of two exceptions noted by Foxton to a generalization that species of Sergestes that are the most similar in other adult diagnostic characters usually have identical or closely similar organs of Pesta; he does not note any difference between the arcticus group Table 1.— Comparison of the number of long lateral spines which arm carapace processes in protozoea II and III of two species groups of Sergestes; the lateral spines have smooth tips in the atlanticus group and branching tips ("brushlike endings") in the arcticus group (descriptions of the atlanticus group and S. arcticus are taken from Gurney and Lebour (1940). Carapace articus group atlanticus g roup processes S. similis S arcticus S. atlanticus S cornutus Protozoea II Rostrum 6 in 3 pairs as similis 7 rather irregularly arranged 8 in 4 pairs + 2 ventral Lateral, each 6-8, usually 7 '7 9 8 Posterior 4-8, with 3 large pairs 6 in 3 pairs 6, process swollen basally 4 in 2 pairs Protozoea III: Rostrum with spinules only as similis 3 ventral 7 ventral Supraorbital, each 9-14. usually 10- 9. orientation as ca 15; processes curve 12-19; processes direct- 12; processes in similis inward to meet and ed anterolateral^ curve postero- overlap lateral^ Lateral, each 5-8, usually 7 7 17-20 12-14 Posterior 7-13. usually 10- 12 in 5-6 pairs 10 in 5 pairs 16 arranged in circle on large basal swelling 8 in 4 pairs 'Gurney and Lebour (1940) report eight long spines on the lateral carapace process, but their figure shows seven with brushlike endings and the simple spmulose tip of process, the common armature in S. similis 241 species in morphology of this feature. The cor- respondence between variation in morphology of protozoeal stages and organs of Pesta within the two species groups indicates that, with identifi- cation of additional species, larval morphology may prove useful in the study of interspecific re- lationships within Sergestes, as predicted by Gurney and Lebour (1940). The larvae of S. similis were also compared with those of hispida type Sergia lucens (Omori 1969), one of the seven species comprising the challengeri group. They were found to differ in body armature, as expected from difference in protozeal type, in form of telson, and in develop- ment of some appendages, as shown in Table 2. They also differ in number of naupliar stages. Four distinct stages were observed in the naupliar phase of Sergestes similis, while in Sergia lucens nauplius I and II were found and the latter developed gradually to molt into protozoea I. When this finding is coupled with the observations by Nakazawa (1916, 1932), they suggest that there are zero to two molts during the naupliar phase of S. lucens. An assessment of the significance of these observations requires additional knowledge of larval development within the two closely related genera and their species groups. FISHERY BULLETIN: VOL. 80, NO. 2 ACKNOWLEDGMENTS This work was supported by the Marine Life Research Program, the Scripps Institution of Oceanography's component of the California Cooperative Oceanic Fisheries Investigations. We are very grateful to Kuni Hulsemann and her colleagues for a translation of Wasserloos (1908), to A. Fleminger for the method and materials to treat larvae with KOH and Chlorazol Black E, and to E. Brinton for criticism of the manuscript. LITERATURE CITED FOXTON. P. 1972. Further evidence of the taxonomic importance of the organs of Pesta in the genus Sergestes (Natantia, Penaeidea). Crustaceana 22:181-189. Gurney, R. 1942. Larvae of decapod Crustacea. RaySoc. Publ. 129, 306 p. Ray Soc, Lond. Gurney, R., and M. V. Lebour. 1940. Larvae of decapod Crustacea. Part VI; The genus Sergestes. Discovery Rep. 20:1-68. Hansen, H. J. 1922. Crustaces decapodes (Sergestides) provenant des campagnes des yachts "Hirondelle" et "Princess Alice" (1885-1915). Resultats des Campagnes Scien- tifiques Accomplis sur son Yacht, par Albert I" 64:1- 232. Table 2.— Some differences between larvae of Sergestes similis and Sergia lucens. Feature Sergestes similis Sergia lucens Carapace armature: Protozoea I Protozoea II Protozoea III Zoea l-ll Postlarva I Abdomen armature; Zoea l-ll Telson: Zoea l-ll Postlarva I Antennule: Zoea l-ll Antenna: Zoea I Mandible: First maxilliped: Zoea l-ll anterolateral process branches to 3 spines posterodorsal process a single spine with basal spinules all processes with long spines which branch to spin- ules distally rostrum with small spinules, armature ot other pro- cesses as in II with 2 pairs lateral spines lateral spines remnants only, other spines present lateral spines decrease in length posteriorly, spines 1 and 2 with relatively long spinules in I fork with 2 outer and 2 inner spinules, invagination does not reach lateral spines fork relatively wide with tiny spinules outer flagellum unsegmented in rarely 2- or 3-seg- mented in II and shorter than peduncle endopod 8-segmented and longer than rostrum palp appears in zoea I exopod with 13 or 14 setae anterolateral process branches to 4 spines posterodorsal process branches to 3 spines all processes with small spinules only as in II with 3 pairs lateral spines rostrum and small posterodorsal spine present; supra- orbital spine and basal spine of rostrum sometimes present, lateral and hepatic spines missing lateral spines increase in length posteriorly, without long spinules in I fork with 1 outer and 5/6 inner spinules in I, with 2 outer spinules in II, invagination about as deep as lateral spines fork narrow, with 2 large inner setae outer flagellum 2-segmented in I, ca. 8-segmented in II, and longer than peduncle endopod 2-segmented and shorter than rostrum palp appears in zoea II, rarely in zoea I exopod with 12 setae 242 KNIGHT and OMORI: LARVAL DEVKLOl'MKNT OF SKRdKSTh'S SIMILIS JUDKINS, D. C. 1972. A revision of the decapod crustacean genus Sergestes (Natantia, Penaeidea) sensu lain, with emphasis on the systematics and geographical distribu- tion of Neosergestes, new genus. Ph.D. Thesis, Univ. California, San Diego, 274 p. 1978. Pelagic shrimps of the Sergestes edwardsii species group (Crustacea: Decapoda: Sergestidae). Smithson. Contrib. Zool. 256, 34 p. Milne, D. S. 1968. Sergestes similis Hansen and S. consobrinus n. sp. (Decapoda) from the northeastern Pacific. Crusta- ceana 14:21-34. Nakazawa, K. 1916. [On the development of Sakura-ebi.] [In Jpn.] Zool. Mag. Tokyo 28:485-494. 1932. [On the metamorphosis of Sakura-ebi.] [In Jpn.] Zool. Mag. Tokyo 44:21-23. Omorl M. 1969. The biology of a sergestid shrimp Sergestes lueens Hansen. Bull. Ocean Res. Inst. Univ. Tokyo 4, 83 p. 1974. The biology of pelagic shrimps in the ocean. Adv. Mar. Biol. 12:233-324. 1979. Growth, feeding, and mortality of larval and early postlarval stages of the oceanic shrimp Sergestes sim His Hansen. Limnol. Oceanogr. 24:273-288. Omorl M., and D. Gluck. 1979. Life history and vertical migration of the pelagic shrimp Sergestes similis off the southern California coast. Fish. Bull., U.S. 77:183-198. Omorl M., A., Kawamura, and Y. Aizawa. 1972. Sergestes similis Hansen, its distribution and im- portance as food of fin and sei whales in the North Pacific Ocean. In A. Y. Takenouti (chief editor), Biological oceanography of the northern Pacific Ocean, p. 373-391. Idemitsu Shoten, Tokyo. Pearcy, W. G., and C. A. Forss. 1969. The oceanic shrimp Sergestes similis off the Oregon coast. Limnol. Oceanogr. 14:755-765. Wasserloos, E. 1908. Zur Kenntnis der Metamorphose von Sergestes arc- ticus Kr. Zool. Anz. 33:303-331. Yaldwyn, J. C. 1957. Deep-water Crustacea of the genus Sergestes (Decapoda, Natantia) from Cook Strait, New Zealand. Zool. Publ. Victoria Univ., Wellington 22, 27 p. 243 GROWTH OF JUVENILE ENGLISH SOLE, PAROPHRYS VETULUS, IN ESTUARINE AND OPEN COASTAL NURSERY GROUNDS Andrew A. Rosenberg1 ABSTRACT The growth of English sole juveniles, during 1978-79, from estuarine and open coastal nursery grounds on the Oregon coast is described in detail. Counts of fortnightly growth rings on otoliths were used to determine size-at-age. Mean growth rates were similar for the two areas, but variabil- ity in size-at-age was much greater among fish captured in the estuary. Back calculation of individual growth, using radial measurements on the otoliths, showed that growth proceeds linearly during the first year of life. Differences in average growth among indi- vidual fish account for the high variability in size-at-age among fish found in the estuary. Fish from the estuary grew slightly faster, on average, in 1979 compared with 1978. The settlement date of English sole larvae to the benthic habitat, determined from age data, occurred over the winter and spring in the open coastal nursery area. In the estuary, settlement was concentrated in the early winter. The life cycle of many marine fishes contains a stage in which the juveniles of the species are concentrated in a specific area or nursery ground where the adults are uncommon. On both the east and west coasts of North America, es- tuarine areas are extensively used as nursery grounds for a large number of species (Gunter 1961; Pearcy 1962; McHugh 1967; Haedrich in press). Many east coast fishes are considered to be dependent on estuarines during early life. On the west coast, estuarine dependence has not been clearly demonstrated (McHugh 1967; Pearcy and Myers 1974). The high productivity of estuarine areas, pro- viding improved growth conditions for juvenile fish, the apparent lack of large predators, and re- duction of competition among age groups of a species are frequently invoked explanations for estuarine dependence (Haedrich in press; Kuipers 1977). Unfortunately, it is difficult to test these hypotheses for most species of fish, be- cause it is uncommon to find a species which uses both estuarine and nonestuarine nursery envi- ronments in a small geographic area. The commercially important pleuronectid Parophrys vetulus Girard, found off the Oregon coast, uses both estuarine and nonestuarine habi- tats as nursery areas during the first year of life (Laroche and Holton 1979). This study examines the growth of the English sole, Parophrys vetulus, •School of Oceanography, Oregon State University, Cor- vallis, Oreg.; present address: Department of Biology, Dal- housie University, Halifax, Nova Scotia, B3H 4J1 Canada. juveniles from two nursery grounds: the Ya- quina Bay estuary (Pearcy and Myers 1974) and the open coastal area off Moolach Beach, Oreg. (Laroche and Holton 1979). Size-at-age data, obtained from daily and fort- nightly growth ring counts on otoliths, are used to detail growth during the first year. Daily growth rings on otoliths have been documented in many species of fish (Pannella 1971; Brothers et al. 1976; Struhsaker and Uchiyama 1976; Tau- bert and Coble 1977). Pannella (1974) reported fortnightly banding patterns in several species as well. Laroche et al. (1982) have provided lab- oratory evidence for the daily periodicity of growth rings on P. vetulus otoliths. METHODS Sampling was conducted from September 1978 through September 1979 at Moolach Beach and Yaquina Bay. The sampling stations are shown in Figure 1. A tow was made at each station with a 1.5 m wide beam trawl lined with 7 mm stretch mesh. Tows were for 5 min in Yaquina Bay and for 10 min at Moolach Beach. The beam trawl was equipped with a 1.0 m circumference odom- eter wheel to measure distance travelled on the bottom. Measurements of bottom temperature and salinity were made at each station. All fish captured were preserved in a strongly buffered 10% solution of Formalin2 in seawater. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80, NO. 2, 1982. 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 245 FISHERY BULLETIN: VOL. 80, NO. 2 In the laboratory, all fish were identified and measured for standard length (SL). Both saccu- lar otoliths were removed from each English sole. In cases where large numbers of P. vetulus were captured, individuals were selected to cover the size range of the sample. The otoliths were mounted on microscope slides in the syn- thetic mounting medium Protexx. One otolith from each fish was ground on 600 grit carborundum paper to a thin section along a sagittal plane through the nucleus. The sections were examined under 250X magnification, using either bright-field or polarized illumination. Counts of fortnightly rings were made on each otolith. No fortnightly rings could be detected in the central area of the otoliths, which apparently represents the time the larvae are in the plank- ton. Therefore, daily rings were counted from the nucleus out to the first fortnightly ring. The actual age of each fish was calculated by sum- FlGURE 1.— The study area. Sam- pling stations are indicated by the letters A through G. ming the number of daily rings in the nuclear area, the number of fortnightly rings times 14, and the mean age of first ring formation, which was taken to be 5 d for this species (Larocheetal. 1982). The count of rings on each otolith was repeated until the same count was obtained three times. As a further check on the accuracy of the counts, a set of 42 otoliths was recounted several months later and a mean error computed. Counts of the number of daily rings between fortnightly rings on 40 otoliths and the number of fortnightly rings between consecutive annual rings on 15 otoliths from older specimens were made as tests of fortnightly periodicity. Individual growth curves of 25 fish were back calculated by making radial measurements to every other fortnightly ring along the same axis from the nucleus to the anterior edge of the oto- lith. From these measurements and the linear relationship between otolith radius and standard length of the fish,3 lengths-at-age for the various points in the life of an individual were calculated. RESULTS Counts of daily rings between fortnightly rings yielded a mean of 13.95 with a standard devia- tion of 0.68. The mean number of fortnightly rings between consecutive annual rings was 26 with a standard deviation of 1.13. The mean dif- ference between repeated counts of fortnightly rings made a substantial period of time apart was 1.45 rings. Figure 2 shows the daily and fort- 3A regression of standard length on anterior otolith radius was performed on 60 data points. The resulting equation was: F = 0.86x + 4.5, where Y is standard length in mm and jc is the distance from the nucleus to the anterior edge of the otolith in arbitrary units, r2 for this regression is 0.98. 246 ROSENBERG: GROWTH OF JUVENILE ENGLISH SOLE ■98 mm Figure 2.— An otolith from a 110 mm SL Parophrys vetulus captured in Yaquina Bay. Arrows indicate clear fortnightly rings. There are 21 fortnightly rings on this otolith. The actual age was calculated to be 363 d (see text). nightly patterns of a P. vetulus otolith. The first fortnightly ring is formed consistently when the fish is 60 to 75 d old, i.e., the beginning of the metamorphic period (Rosenberg and Laroche 1982). Basic growth data for the two nursery areas were obtained from size-at-age information. The data for 218 fish captured at Moolach Beach (Fig. 3) show that there are two linear portions of the data, with different slopes, separated by an 247 FISHERY BULLETIN: VOL. 80, NO. 2 Figure 3.— Size-at-age data for Pa- rophrys vetulus captured in the Moo- lach Beach nursery area. 20 40 60 80 100 120 140 160 160 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 Age (days) inflection point. There is no evidence of an upper asymptote in the data, so the use of growth models such as the Gompertz or von Bertalanffy equations is inappropriate. A least squares mul- tiple regression on these data was performed using the following model: Y = Bo + BiX + B2Ai + B3A2 + E (1) where Y is the standard length in millimeters, X is the age in days, A\ is a dummy variable whose value is zero to the left of the inflection point and one to the right of the inflection point, and A2 is equal to X times A\, i.e., the interaction term. The B terms are the regression coefficients and E indicates the error terms. The point of inflec- tion which produced the smallest residual sum of squares was found to be 140 d for the Moolach Beach data. The fitted equation is: Y = 16.87 + 0.051X - 32.92A + 0.2SA2. An analysis of variance for the regression (Table 1A) shows that a good fit was obtained with this model, and the data set has a relatively low esti- mated variance. The slopes of the regression be- low and above 140 d were computed as 0.051 and 0.279, respectively. These slopes are estimates of the mean growth rate per day for juvenile P. vetulus utilizing the Moolach Beach nursery area. The lower portion of the data, below 140 d of age, shows a plateau in growth attributed to the metamorphic period (Rosenberg and Laroche 1982). Regression of the size-at-age data for Yaquina Bay juveniles (Fig. 4: 186 data points) yields the fitted equation: Y = 13.01 + 0.083X - 33.45,4, + 0.201^2. 248 The analysis of variance for this model (Table IB) once again shows that a good fit was obtained, but the estimated variance is much higher than for the Moolach Beach data. The inflection point with the smallest residual sum of squares was also 140 d of age for the Yaquina Bay data. The slopes below and above the inflection are 0.083 and 0.284, respectively. The first step in comparing the regression lines of growth for English sole from the two nursery grounds was to test for statistical equal- ity of variances. This was done by examination of the ratio of the mean square errors of the fitted regressions, 19.88 for the Moolach Beach data and 95.01 for the Yaquina Bay data. The ratio is distributed as F(184:216) and the variances are significantly different at the P = 0.001 level. Since the variances are unequal, statistical tests for equality of slopes or intercepts are not strictly valid (Scheffe 1959). However, the slopes are similar, 0.279 and 0.284. Back-calculated growth for individuals from both areas are in good agreement with growth Table 1.— Analysis of variance for the least squares multiple regression analysis of size-at-age data. A Moolach Beach regression Y = 16 87 + 0.01 5X - 32.92 A, + 023 A2 Multiple R = 0.975 R2 = 0.950 Source DF Sum of squares Mean square Regressior 3 80815.2 269384 Residual 214 42537 19.9 F value = 13550 B Yaquina Bay regression: Y = 1301 + 0083X - 33.45 A, + 0.201 A2 Multiple R = 0 943 R2 = 0.890 Source DF Sum of squares Mean square Regressior 3 1395756 46525.2 Residual 182 17308.1 95.1 F value = 489 3 ROSENBERG: GROWTH OF JUVENILE ENGLISH SOLE Figure 4.— Size-at-age data for Pa- rophrys vetulus captured in the Ya- quina Bay nursery area. I50T 140 130 120- 110- 100 90 80 70 60 50 40 30 20 10 0 YAQUINA BAY tzi- ' ' . %; 20 40 60 80 100 120 140 160 180 200 220 240 260 280 3O0 320 340 360 380 400 420 440 460 480 500 Age ( days ) estimates from the size-at-age data (Figs. 5, 6). The plots are, in general, linear. Slight changes in slope do occur in all the lines. This may indi- cate small variations in individual growth through the juvenile period, changes in the lin- ear nature of the relationship between otolith growth and overall fish growth, or measurement error. By inspection, these variations do not occur at coincident times among individuals. For the Moolach Beach data (Fig. 5), the average slope of the eight lines ranged from 0.20 to 0.28. Average growth was not significantly different in the 2 yr (nonparametric rank sum test). Individual growth back calculated from the otoliths of 16 fish captured in Yaquina Bay range in average slope from 0.19 to 0.32 (Fig. 6). The growth rates of fish collected in 1978 versus 1979 were significantly different (P — 0.05, nonpara- metric rank sum test). The range in average slope for the 1978 group is 0.19 to 0.25 and for the 1979 group, 0.21 to 0.32. Since the sample size was small, this test is inconclusive, but examina- tion of the size-at-age data by year (Fig. 7) tends to support the results of the back calculations. The influx of fish to the Moolach Beach nur- sery ground, determined by back calculating the date of recruitment to the sampling gear for each fish, was distributed over the winter and spring (Fig. 8). During the summer, recruitment de- clined and was zero by July 1978 and by Septem- ber 1979. For juveniles captured in the estuary, recruit- ment appeared to be concentrated over a few winter months (Fig. 9). A sharp peak is evident o ■D O to 120 110- 100 90 80 70 a> 60 50- 40" 30" 20 10 0 MOOLACH BEACH JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 1978 JAN FEB MAR APR MAY JUN JUL AUG 1979 SEP Figure 5.— Back-calculated growth of eight individual Parophrys vetulus from Moolach Beach during 1978-79. 249 FISHERY BULLETIN: VOL. 80, NO. 2 o (75 JAN FEB MAR ' APR MAY JUN JUL AUG SEP 1978 I 1979 Figure 6.— Back-calculated growth of 16 individual Parophrys vetulus from Yaquina Bay during 1978-79. 120 YAQUINA BAY & 1978 • 1979 41 a ■ " * .'A m • V' ••• • .. »:- . • ••• • • • 160 240 320 Age (days ) Figure 7.— Size-at-age data plotted by year of capture of Pa- rophrys vetulus. in November, December, and January. As in the Moolach Beach data, recruitment goes to zero in the summer, but reappears in the fall among Yaquina Bay fish. DISCUSSION Several previous studies have attempted to estimate growth rates for English sole juveniles (Table 2). For the purposes of comparison with the data reported here, the total length measure- ments used in other studies were converted to MOOLACH BEACH _c OC T NOV DEC 1977 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ' JAN FEB MAR APR MA, JUN JUL AUG SEP 1978 '. 1979 Monlh ot Recruitment Figure 8.— Distribution of Parophrys vetulus recruitment to the sampled population at Moolach Beach during 1978-79. Full recruitment to the sampling gear was estimated to occur at 120 d of age. standard length using the relationship given by Laroche and Holton (1979). The recalculated daily growth estimates from all of these other studies are similar, but are substantially higher than my estimated daily growth rates. Smith and Nitsos (1969) and Van Cleve and El-Sayed (1969) determined growth during the first year of life by back calculating the size of the fish when the first detectable annulus on the inter- opercular bone was formed. This occurs during the fish's first slow growth season, which may be at various ages due to the protracted spawning period of this species. Growth back calculations of individual fish (Figs. 5, 6) do not show a clear slow growth period during the first year. 250 ROSENBERG: GROWTH OF JUVENILE ENGLISH SOLE YAQUINA BAY rfUm OCT NOV OEC ; JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC'JAN FEB MAR APR MAT JUN JUL AUG SEP 1977 ! 1978 '• 1979 Month of Recruitment Figure 9.— Distribution of Parophrys vetulus recruitment to the sampled population in the Yaquina Bay estuary during 1978-79. Full recruitment to the sampling gear was estimated to occur at 120 d of age. The other two studies (Westrheim 1955; Ken- dall 1966) utilize the technique of following modal progressions through time in length- frequency distributions. These estimates are strongly influenced by the efficiency of the sam- pling gear. If the smaller fish are sampled less efficiently than the larger, growth will be over- estimated. Emigration of small individuals, immigration of larger fish, and differential mor- tality of small fish would all produce overesti- mates of growth using this method. Also, length- frequency modal progression may give variable results dependent on the method of choosing the modes. Variability in the size-at-age data was much higher for fish sampled in the estuary compared with those sampled in the open coastal area, but the mean growth rates for fish from the two areas were similar. Physical factors may affect growth variability. Yaquina Bay has highly variable temperature and salinity. Frey4 found differ- ences of up to 57.. salinity and 2°C between high and low tides in the lower bay. Bottom tempera- ture in the estuary ranges between 5° and 15°C through the year, and salinity from virtually 0 to 347... At Moolach Beach in contrast, a more con- stant environment may be expected. The open coastal region does not have a large source of freshwater to influence salinity and tempera- ture. Huyer (1977) and Huyer and Smith (1978) reported that bottom water salinity off the Ore- gon coast fluctuates about 17.. from winter to summer. Temperature varies from 6.5°C in sum- mer, due to seasonal upwelling, to about 10°C in winter. There are two ways in which growth variabil- ity can be reduced. Either outlying individuals have their growth rates altered towards the mean or they are removed from the population. Particularly good or bad growth conditions in an area would affect the growth of all individuals, and alter the mean. Emigration and mortality are the two possible removal processes. The size- at-age plot for Moolach Beach (Fig. 3) and other data (Laroche and Holton 1979) indicate that most P. vetulus juveniles move out of the near- shore area at between 70 and 80 mm SL. Emi- gration from the estuary appears to be at a larger size, approximately 100 mm SL (Westrheim 1955; Olson and Pratt 1973). Predation in the estuary is probably low com- pared with the open coast. Few large fishes are regularly found in the bay, although birds may be significant predators. Kuipers (1977), in a study of an estuarine nursery for plaice in the Wadden Sea, reported predation mortality to be low in contrast to a coastal nursery area studied by Steele and Edwards (1970). Finally, intraspecific competition may affect growth. The estimated densities of juvenile Eng- lish sole in the estuary are a consistent order of magnitude greater than at Moolach Beach (Kry- gier and Pearcy5). Competition may potentially 4B. Frey, School of Oceanography, Oregon State University, Corvallis, OR 97331, pers. commun. March 1980. 5E. E. Krygier and W. G. Pearcy, School of Oceanography, Oregon State University, Corvallis, OR 97331, pers. commun. March 1980. Table 2.— Summary of growth estimates from previous studies: the data has been recal- culated so that direct comparisons can be made (see text). Location Size at 1 yr of age (mm SL) Yaquina Bay, Oreg Monterey Bay. Calif Puget Sound, Wash Puget Sound. Wash Daily growth rate (mm/d) 117 0.40 108-126 0.36-0 43 128 0 44 — winter 0 48 summer 0.73 Source Westrheim 1956 Smith and Nttsos 1969 Van Cleve and El-Sayed 1969 Kendall 1966 251 FISHERY BULLETIN: VOL. 80, NO. 2 emphasize differences among individuals and increase observed variability. The most plausible mechanism for explaining low growth variability at Moolach Beach com- bines limitation and removal processes. If the population is food limited in the open ocean and selective predation on smaller, slower growing individuals is occurring, the observed variability in size-at-age will be small. Using the otolith aging technique this hypothesis is testable. It re- quires a comparison of the size-at-age distribu- tion of fish found in the stomachs of predators with the distribution shown in Figure 3. A hypothesis arising from this study is that survival, not growth, is enhanced in the estua- rine nursery ground compared with the open coast. Testing of this hypothesis will be an impor- tant step in understanding the role that estuaries play in the life history of many fishes. ACKNOWLEDGMENTS I would like to thank W. G. Pearcy, C. B. Miller, and A. V. Tyler for their guidance and assist- ance; B. Frey, E. Krygier, and C. Creech for pro- viding accessory data; and J. L. Laroche and W. Wakefield for their invaluable assistance throughout the course of this study. Funding was provided by Oregon State Uni- versity Sea Grant Project No. A/OPF-1. LITERATURE CITED Brothers, E. B., C. P. Mathews, and R. Lasker. 1976. Daily growth increments in otoliths from larval and adult fishes. Fish. Bull., U.S. 74:1-8. Gunter, G. 1961. Some relations of estuarine organisms to salinity. Limnol. Oceanogr. 6:182-190. Haedrich, R. L. In press. Estuarine fishes. In B. H. Ketehum (editor), Ecosystems of the world: Vol. 22. Estuaries and enclosed seas. Elsevier Press, Amsterdam. Huyer, A. 1977. Seasonal variation in temperature, salinity and density over the continental shelf off Oregon. Limnol. Oceanogr. 22:442-453. Huyer, A., and R. L. Smith. 1978. Physical characteristics of Pacific northwestern coastal waters. In R. W. Krauss (editor), The marine plant biomass of the Pacific Northwest coast, p. 37-55. Oregon State Univ. Press, Corvallis. Kendall, A. W., Jr. 1966. Sampling juvenile fishes on some sandy beaches of Puget Sound, Washington. M.S. Thesis, Univ. Wash- ington, Seattle, 77 p. Kuipers, B. R. 1977. On the ecology of juvenile plaice on a tidal flat in the Wadden Sea. Neth. J. Sea Res. 11:56-91. Laroche, J. L., S. L. Richardson, and A. A. Rosenberg. 1982. Age and growth of a pleuronectid, Parophrys vetu- lus, during the pelagic larval period in Oregon coastal waters. Fish. Bull., U.S. 80:93-104. Laroche, W. A., and R. L. Holton. 1979. Occurrence of 0-age English sole, Parophrys vetu- lus, along the Oregon coast: an open coast nursery area? Northwest Sci. 53:94-96. McHugh, J. L. 1967. Estuarine nekton. In G. H. Lauff (editor). Estu- aries, p. 581-620. Am. Assoc. Adv. Sci. Publ. 83. Misitano, D. A. 1976. Size and stage of development of larval English sole, Parophrys vetulus, at time of entry into Humboldt Bay. Calif. Fish Game 62:93-98. Olson, R. E., and I. Pratt. 1973. Parasites as indicators of English sole (Parophrys vetulus) nursery grounds. Trans. Am. Fish. Soc. 102: 405-411. Pannella, G. 1971. Fish otoliths: daily growth layers and periodical patterns. Science (Wash., D.C.) 173:1124-1127. 1974. Otolith growth patterns: an aid in age determina- tion in temperate and tropical fishes. In T. B. Bagenal (editor), The proceedings of an international symposium on the ageing of fish, p. 28-39. Unwin Brothers, Sur- rey, Engl. Pearcy, W. G. 1962. Ecology of an estuarine population of winter floun- der, Pseudopleuronectes americanus(Wa.\ba.um). Bull. Bingham Oceanogr. Collect., Yale Univ. 18:1-78. Pearcy, W. G., and S. S. Myers. 1974. Larval fishes of Yaquina Bay, Oregon: A nursery ground for marine fishes? Fish. Bull., U.S. 72:201-213. Rosenberg, A. A., and J. L. Laroche. 1982. Growth during metamorphosis of English sole, Parophrys vetulus. Fish. Bull., U.S. 80:152-155. Scheffe, H. 1959. The analysis of variance. Wiley, N.Y., 477 p. Smith, J. G., and R. J. Nitsos. 1969. Age and growth studies of English sole, Parophrys vetulus, in Monterey Bay, California. Pac. Mar. Fish. Comm. Bull. 7:73-79. Steele, J. H., and R. R. C. Edwards. 1970. The ecology of 0-group plaice and common dabs in Loch Ewe. IV. Dynamics of the plaice and dab popula- tions. J. Exp. Mar. Biol. Ecol. 4:174-187. Struhsaker, P., and J. H. Uchiyama. 1976. Age and growth of the nehu, Stolephorus purpur- eus (Pisces: Engraulidae), from the Hawaiian Islands as indicated by daily growth increments of sagittae. Fish. Bull., U.S. 74:9-17. Taubert, B. D., and D. W. Coble. 1977. Daily rings in otoliths of three species of Lepomis and Tilapia mossambica. J. Fish. Res. Board Can. 34:332-340. Van Cleve, R., and S. Z. El-Sayed. 1969. Age, growth, and productivity of an English sole (Parophrys vetulus) population in Puget Sound, Wash- ington. Pac. Mar. Fish. Comm. Bull. 7:51-71. Westrheim, S. J. 1955. Size composition, growth and seasonal abundance of juvenile English sole (Parophrys vetulus) in Yaquina Bay. Fish. Comm. Oreg. Res. Briefs 6:4-9. 252 POPULATION FLUCTUATIONS OF CALIFORNIA SEA LIONS AND THE PACIFIC WHITING FISHERY OFF CENTRAL CALIFORNIA1 David G. Ainley, Harriet R. Huber,2 and Kevin M. Bailey3 ABSTRACT Seasonal fluctuations in the number, age ratios, and diet of California sea lions, Zalopkus califor- nianus, were studied at the Farallon Islands, central California, from 1971 to 1980. During these years, average monthly numbers increased geometrically, except for April and May. Before 1977, the annual peak in population occurred during April and May, almost no animals were present late June to early July, and a slight peak occurred during fall; adult males predominated. Beginning in 1977, fall numbers equaled or exceeded those in spring, large numbers remained throughout summer, and subadults predominated. We hypothesize that seasonal fluctuations in sea lion num- bers were related to the availability of their principal prey, Pacific whiting, Merluccius productus, and that the changes that began in 1977 were related to termination of the whiting fishery off central California beginning that year. The California sea lion, Zalophus californianus, ranges along the North American west coast from the Gulf of California to British Columbia. Bartholomew (1967) hypothesized that most adult males migrate to the north from breeding sites in Baja California and southern California beginning in midsummer and remain there until the early spring when they return south, and that females and young animals remain in the vicin- ity of breeding areas or move somewhat south- ward during the nonbreeding season. This has become the accepted explanation to account for the seasonal movements in the population (e.g., Mate 1975). Preliminary analysis of census and diet information collected at the Farallon Islands during 1971-80 led to a related hypoth- esis that the movements of male sea lions toward the north could be a response to the seasonal oc- currence and availability of an important prey species, the Pacific whiting, Merluccius produc- tus (Huber et al.4). This information was later quoted by Fiscus (1979). Additional analysis, presented here, provides more insight into the ecological relationship between the two species. The Pacific whiting is an abundant midwater fish of the continental slope and shelf off Cali- 'Contribution No. 232 of the Point Reyes Bird Observatory. 2Point Reyes Bird Observatory, Stinson Beach, CA 94970. 3College of Fisheries, University of Washington, Seattle, WA 98195 l o o o o CO CO ro uj o o o o en ai o o CO CD o o 10 o TIME OF CENSUSES Figure 1.— The number of California sea lions hauled out during hourly periods at Shubrick Point, Southeast Farallon Island; the mean and ± standard deviation are shown based on 12 all-day watches during April and May 1974. FISHERY BULLETIN: VOL. 80, NO. 2 RESULTS AND DISCUSSION California Sea Lion Biology Aside from the one pup born at Southeast Farallon, every year since 1974 except 1978 (plus its mother and at least one bull) (Pierotti et al. 1977; Huber et al. [footnote 4]; Point Reyes Bird Observatory unpubl. data), the California sea lion population was comprised of nonbreeding males. Major breeding sites are located in the southern California islands (Bartholomew 1967; LeBoeuf and Bonnell 1980). From 1971 to 1976 a large peak in numbers was reached each year at the Farallones in late April or early May, when animals migrating south toward southern breed- ing sites hauled out for short periods (Fig. 2). A majority of animals departed (temporarily?) each evening to feed (Hobson 1966); about an hour after dawn they began to return and by early afternoon maximum numbers were hauled out. Numbers present each day rapidly declined in late May, and by late June only a few Zalophus hauled out. Population size increased again in late July, reached a peak in August or Septem- ber that was much smaller than in spring, and than declined to a level maintained through the <" 500- z o 1977-80 EC LU [TJ 3 Z 500- Figure 2.— The mean ( ± standard deviation) number of Cali- fornia sea lions hauled out at Southeast Farallon Island each month during two periods: 1971/73-76 and 1977-80; below each curve are the number of censuses each month and above are the proportion of adults present. 254 AINLEY ET AL.: POPULATION FLUCTUATIONS OF SEA LIONS winter. Average monthly population size in- creased slightly from one year to another (Fig. 3). The proportion of adults present each month ranged between 73 and 95%. Since 1977, population fluctuations of the Cali- fornia sea lions have been markedly different in several ways. First, except for April and May, average monthly population size began to in- crease rapidly from one year to the next (Fig. 3). This was especially evident for the summer and fall and thus, secondly, by 1978 the timing of the annual maximum population had shifted and fall counts were exceeding those of the spring peak (Fig. 2). In fact, for each month except April and May, average monthly numbers in- creased geometrically from 1971-73 to 1980 (least squares; r ranged 0.7745 to 0.9537, P<0.01). Finally, the percentage of adults during 1977-80 was reduced to a range between 15 and 35%. These differed significantly from percentages of adults in the period 1971/73-76 (P<0.01; per- centage test, Sokal and Rohlf 1969:608). Young animals were thus migrating north rather than remaining in southern California and Baja Cali- fornia waters as Bartholomew (1967) had noted in earlier years. Seasonal population fluctuations and age ratios at the Farallones from 1971 to 1976 were largely similar to those at coastal sites, as mea- sured at Ano Nuevo Island (80 km away, Orr and Poulter 1965; Lance and Peterson 1968), and 1971/73 74 Figure 3. — The average number of California sea lions hauled out annually at Southeast Farallon Island. Dots above each year are monthly averages; the curve is described by the geo- metric equation: y = a\x, where a = 9.5 X 10"8 and A = e02979; r = 0.6557, P<0.01. sites farther north (Mate 1975). Exceptional at the Farallones was the fact that there was almost no fall peak, whereas at coastal sites it greatly exceeded the peak in spring. When the fall peak increased in 1977 the Farallon pattern became similar to coastal sites. However, it is possible that the age composition, for which few compar- ative data are available, and the size of the spring peak were changing then at the Farallons. At coastal sites there is a small spring peak and a large fall peak, but at the Farallones the two peaks became equal in magnitude. The diet of California sea lions at the Faral- lones, as revealed by regurgitated items, has been comprised of at least 20 species of prey (Table 1) (some otoliths could actually have come from the stomachs of sea lion prey). Outstanding were the predominance of Pacific whiting, par- ticularly from April to August, and the diversifi- cation in diet from September to March. The whiting eaten averaged 25 to 36 cm in length and were 2 to 3 yr of age (Bailey and Ainley in press). Except for the short period during summer when they were away at breeding sites, Califor- nia sea lions were most abundant when whiting predominated in their diet. At coastal sites of central California, the market squid, Loligo opalescens, along with whiting and northern anchovies, Engraulis mordax, are dominant prey of this pinniped (Morejohn et al. 1978). California Sea Lions and the Pacific Whiting Fishery From 1967 to 1972 most Pacific whiting were caught off the coasts of British Columbia, Wash- ington, and Oregon (Fig. 4). After 1972, catches increased off the California coast, and especially high catches of around 100,000 t occurred from 1974 to 1976. This southward shift of fishing is believed to be due to a depletion of large adults in the Pacific Northwest. Fishing off central Cali- fornia targeted juvenile whiting.5 After the FCMA restriction on fishing south of lat. 39°N, the total whiting catch dropped significantly (Fig. 4). Whiting prevalence in the diet of Farallon sea lions was directly correlated to the average monthly number of trawlers fishing for whiting in the Farallon area (Table 2; r = 0.747, t = 3.55, 5Anonymous. 1976. Summary of National Marine Fish- eries Service views on the status of the Pacific hake resource. Unpubl. rep., 4 p. Northwest and Alaska Fisheries Center. NMFS. NOAA, 2725 Montlake Blvd. E., Seattle. WA 98115. 255 FISHERY BULLETIN: VOL. 80, NO. 2 Table 1.— Percent composition of California sea lion diet as determined by otoliths and beaks regurgitated at haul out sites, Southeast Farallon Island, 1974-78. Months: J F M A M J J A S O N D Cephalopods Octopus rubescens 1 2 Berryteuthis (?) sp. 1 Gonatus sp. 1 Loligo opalescens 3 Fishes Merluccius productus 54 36 28 87 94 98 96 84 38 43 28 30 Sebastes spp 45 27 61 11 5 <1 14 30 16 69 30 Porichthys notatus 1 6 1 1 <1 <1 1 31 1 Engraulis mordax 20 <1 1 Glyptocephalus zachirus 1 <1 10 1 1 40 Chilara taylori 8 <1 9 Parophrys vetulus 2 <1 3 Genyonemus lineatus <1 <1 2 2 Citharichthys sordidus 1 2 3 Microgadus proximus 1 2 <1 <1 Atherinopsis californiensis <1 <1 Leptocottus armatus <1 2 Zalembius rosaceus <1 2 Microstomas pacificus <1 Trachurus symmetricus 4 <1 <1 Clupea pallasi <1 Lyopsetta exilis <1 Total prey (no.) 11 147 55 550 1,077 291 45 535 267 102 140 10 IOO z cr o < < I- o o IOO" o o I967 69 71 Figure 4.— The total catch of whiting in the Pacific coast fish- ery and the proportion of that catch taken off California, 1967- 79. df = 10, P<0.01, Spearman rank correlation). Considering the whole coast of California, trawl- ers concentrated near the Farallones, at least from 1974 to 1976, when fishery surveillance rec- ords were available to us. If we assume that the number of trawlers and the prevalence of whit- ing in sea lion diets, in conjunction with sea lion population size, reflect whiting availability, we conclude that both sea lions and humans were attracted to continental slope waters at the same time in order to catch whiting. The only differ- ence was that the sea lions departed at the peak of Table 2.— Number of stern trawlers fishing for Pacific whit- ing over the California continental slope between lat. 39° and 37°N from January through December 1974-77; data summar- ized from NMFS monthly surveillance reports. Year M M O N 1974 0 0 13 43 55 60 57 55 11 0 0 0 1975 3 8 60 64 90 64 2 ? 0 0 0 0 1976 0 0 10 35 55 50 38 13 0 0 0 0 1977 0 0 0 0 0 0 0 0 0 0 0 0 x 1974/76 1 2 28 47 67 58 32 34 3 0 0 0 harvest in order to return to traditional breeding sites. Associated with the unavailability of whiting, both fishing activity and the preponderance of whiting in the sea lion diet dropped off from Sep- tember to March. During the winter months adult whiting migrate off the continental shelf to spawn in deeper waters of the continental slope (Bailey 1980), and juveniles probably show the same behavior. In addition, during the spawning months they do not diurnally migrate but remain deep (Nelson and Larkins 1970). They are thus unavailable to both the fishery and the sea lions. We offer the following hypothesis to explain the patterns observed in the sea lions' behavior. First, they are attracted to continental slope waters of central California by whiting which, due to their own migrations, become available there during spring and summer. The trawler fishery, also attracted by greater fish availabil- ity, was perhaps depleting whiting stocks sea- sonally to such an extent during the early to mid- 1970's that by late summer when sea lions were 256 AINLEY FT AL.: POPULATION FLUCTUATIONS OF SEA LIONS returning north from breeding sites, offshore waters near the Farallones were no longer as attractive to the pinnipeds as during the spring. The sea lions thus remained along the coast to feed on other prey. Then in 1977, when trawlers no longer fished for whiting off central Califor- nia, the sea lions responded in three ways, all possibly due to increased food supply during summer and fall: 1) Young animals moved farther north or farther off the coast than previ- ously, 2) more adults remained during summer instead of migrating south, and 3) adults return- ing from southern breeding sites moved offshore in larger numbers than they had in previous falls. The size of the sea lion population peak during spring was not affected by termination of the fishery, because fishing was only just getting under way each year at that time. Adding coincidental support to the hypothesis that the 1966/76 whiting fishery off central Cali- fornia was indirectly depressing the numbers of California sea lions in the vicinity are data from other localities. Populations of California sea lions at breeding sites on southern California islands have been increasing geometrically for the past several decades (Bartholomew 1967; LeBoeuf and Bonnell 1980; LeBoeuf6). At the crease in numbers at the Farallon Islands is likely a reflection of this. Successive counts at coastal Ano Nuevo Island during the early 1960's also reflected this increase, but beginning some- time between 1963 and 1967 numbers began a decline there that lasted through 1975; since then, however, they have begun to increase again (LeBoeuf and Bonnell 1980; LeBoeuf). At the Monterey breakwater, about 80 km farther south, D. J. Miller7 has noted that numbers of subadult California sea lions since about 1978 have been much higher than in previous years. Changes in the occurrence of another pinni- ped, the northern fur seal, Callorhinus ursinus, at the Farallones, provide additional support to the hypothesis. Also an important whiting pred- ator (Fiscus 1979), this species breeds at San Miguel Island in southern California and in the Bering Sea, and during the nonbreeding season frequents waters of the California continental slope. From 1970 to 1976 we observed individual fur seals at the farallones on only 3 single days, 6B. J. LeBoeuf, Division of Natural Sciences. University of California at Santa Cruz, Santa Cruz, CA 95064, pers. com- mun. June 1981. 7D. J. Miller, California Department of Fish and Game. Mon- terey, CA 93940. pers. commun. June 1981. each 2 yr apart. Since then, however, their occur- rence has changed dramatically: the species has occurred annually during the summer and fall, and at least 10 different individuals(determined by tags or peculiar scars) have hauled out, some repeatedly, for periods of variable length. Two that hauled out were tagged at San Miguel; another has hauled out for 5 yr in succession. The fur seal breeding population on San Miguel Island has been increasing geometrically from the early 1960's to the present(LeBoeuf and Bon- nell 1980) and the increasing occurrence of this species on the Farallones is likely a reflection of this trend. The dramatic jump in numbers at the Farallones beginning after 1976, however, is out of line with the continuous increase in breeding numbers. Cessation of the whiting fishery off central California in 1976 may account for the change at the Farallones, just as this may be re- sponsible for the change in population dynamics of California sea lions in central California. ACKNOWLEDGMENTS Field work at the Farallon Islands was funded by the Point Reyes Bird Observatory, U.S. Fish and Wildlife Service, Marine Mammal Commis- sion, and National Marine Fisheries Service (Marine Mammal Laboratory and Southwest Fisheries Center). Logistic support was provided by the U.S. Coast Guard and the Oceanic Society, San Francisco Bay Chapter. The Farallones com- prise a national wildlife refuge, and we thank the personnel of the San Francisco Bay National Wildlife Refuge for their help. Marine mammal food items were collected under NMFS permit No. 146; fish otoliths were identified by J. E. Fitch and cephalopod beaks were identified by D. G. Ainley; G. Galbraith, Division of Enforce- ment and Surveillance, NMFS, provided data on the occurrence of whiting trawlers. C. S. Strong, T. J. Lewis, R. J. Boekelheide, R. P. Henderson, R. R. Le Valley, S. H. Morrell, J. W. Higbee, B. Bainbridge, K. Darling, and W. Clow assisted with counts. O'B. Young helped to prepare the manuscript. Valuable comments were offered by R. L. DeLong, D. P. DeMaster, C. H. Fiscus, B.J. LeBoeuf, and P. F. Major. LITERATURE CITED Bailey, K. M. 1980. Recent changes in the distribution of hake larvae: causes and consequences. Calif. Coop. Oceanic Fish. Invest. Rep. 21:167-171. 257 FISHERY BULLETIN: VOL. 80, NO. 2 Bailey, K. M., and D. G. Ainley. In press. The dynamics of California sea lion predation on Pacific whiting. Fish. Res. Bartholomew, G. A. 1967. Seal and sea lion populations of the California Islands. In R. N. Philbrick (editor), Proceedings of the symposium on the Biology of the California Islands, p. 229-244. Santa Barbara Botanic Garden, Santa Barbara. Dark, T. A. 1975. Age and growth of Pacific hake, Merluccius pro- duces. Fish. Bull., U.S. 73:336-355. Dark, T. A., M. 0. Nelson, J. J. Traynor, and E. P. Nunna- LEE. 1980. The distribution, abundance and biological char- acteristics of Pacific whiting, Merluccius productus, in the California-British Columbia region during July- September 1977. Mar. Fish. Rev. 42(3-4):17-33. Fiscus, C. H. 1979. Interactions of marine mammals and Pacific hake. Mar. Fish. Rev. 41(10):l-9. Hobson, E. F. 1966. Visual orientation and feeding in seals and sea lions. Nature (Lond.) 210:326-327. Lance, C. C, and R. S. Peterson. 1968. Seasonal fluctuations in populations of California sea lions. Ano Nuevo Rep. 2:30-36. (Univ. Calif., Santa Cruz.) LeBoeuf, B. J., and M. L. Bonnell. 1980. Pinnipeds of the California Islands: abundance and distribution. In D. M. Power (editor), The California Islands: Proceedings of a Multidisciplinary Symposium, p. 475-493. Santa Barbara Museum of Natural His- tory. Mate, B. R. 1975. Annual migrations of the sea lions Eumetopias jubatus and Zalophus californianus along the Oregon coast. Rapp. -P.-V. Reun. Cons. Int. Explor. Mer 169: 455-461. Morejohn, G. V., J. T. Harvey, and L. T. Krasnow. 1978. The importance of Loligo opalescens in the food web of marine vertebrates in Monterey Bay, California. In C. W. Recksiek and H. W. Frey (editors), Biological, oceanographic, and acoustic aspects of the market squid, Loligo opalescens Berry, p. 67-98. Calif. Dep. Fish Game, Fish. Bull. 169. Nelson, M. O., and H. A. Larkins. 1970. Distribution and biology of Pacific hake: A synop- sis. In Pacific hake, p. 23-33. U.S. Fish Wildl. Serv. Circ. 332. Orr, R. T., and T. C. Poulter. 1965. The pinniped population of Ano Nuevo Island, California. Proc. Calif. Acad. Sci., Ser. 4, 32:377- 404. Pierotti, R. J., D. G. Ainley, T. J. Lewis, and M. C. Coulter. 1977. Birth of a California sea lion on Southeast Farallon Island. Calif. Fish Game 63:64-66. SOKAL, R. R., AND F. J. ROHLF. 1969. Biometry. W. H. Freeman, San Franc, 776 p. 258 FEEDING BEHAVIOR OF THE HUMPBACK WHALE, MEGAPTERA NOVAEANGLIAE, IN THE WESTERN NORTH ATLANTIC James H. W. Hain,1 Gary R. Carter,1 Scott D. Kraus,2 Charles A. Mayo,3 and Howard E. Winn1 ABSTRACT Observations on the feeding behavior of the humpback whale, Megaptera novaeangliae, were made from aerial and surface platforms from 1977 to 1980 in the continental shelf waters of the north- eastern United States. The resulting catalog of behaviors includes two principal categories: Swim- ming/lunging behaviors and bubbling behaviors. A behavior from a given category may be used independently or in association with others, and by individual or groups of humpbacks. The first category includes surface lunging, circular swimming/thrashing, and the "inside loop" behavior. In the second category, a wide variety of feeding-associated bubbling behaviors are described, some for the first time. The structures formed by underwater exhalations are of two major types: 1) bubble cloud— a single, relatively large (4-7 m diameter), dome-shaped cloud formed of small, uniformly sized bubbles; and 2) bubble column— a smaller (1-1.5 m diameter) structure composed of larger, randomly sized bubbles, used in series or multiples. Both basic structures are employed in a variety of ways. Many of these behaviors are believed to be utilized to maintain naturally occurring concentrations of prey, which have been identified as the American sand lance, Ammodytes americanus, and occasionally as herring, Clupea harengus. This paper reports on the feeding behavior of the humpback whale, Megaptera novaeangliae, in the continental shelf waters of the northeastern United States. We describe several feeding be- haviors reported for the first time, as well as a number of behaviors known from other areas but not previously reported for these waters. Our col- lective observations provide the beginning of a more complete catalog than has previously been available. Early observations of humpback feeding be- havior were made by Ingebrigtsen (1929) from the Norwegian Sea near Bear Island: "It [the humpback] employed two methods of capturing 'krill' when the latter was on the sur- face of the water. One was to lie on its side on the surface and swim round in a circle at great speed, while it lashed the sea into a foam with flukes and tail and so formed a ring of foam. The frightened 'krill' gathered together in the circle. This done the humpback dived under the foam-ring and a moment later came up in the center to fill its open mouth with 'krill' and ■Graduate School of Oceanography, University of Rhode Island, Kingston, RI 02881. 2Present address: New England Aquarium, Central Wharf Boston, MA 02110. 3Provincetown Center for Coastal Studies, P.O. Box 826, Provincetown, MA 02657. ^n . « water, after which it lay on its side, closed its mouth, and the catch was completed. "The other method was to go a short distance below the surface of the water, swimming in a ring while at the same time it blew off. The air rose to the surface like a thick wall of air bub- bles and these formed the 'net'. The 'krill' saw this well of air bubbles, were frightened into the centre, and then the manoeuvre of the first method was repeated." Some 45 yr later, "bubblenetting" was reported from Alaskan humpbacks by Jurasz and Jurasz (1978), and later described in detail (Jurasz and Jurasz 1979). With the exception of the work of Watkins and Schevill (1979), accounts of feeding behavior of this species in the waters of the west- ern North Atlantic are few and largely anecdot- al. MATERIALS AND METHODS Observations were made from dedicated air- craft (a Cessna 337 Skymaster and a Beechcraft AT-114), from dedicated surface vessels (the 27.5 m Dolphin III and the 21.3 m Tioga), from plat- forms-of-opportunity, and from shore stations. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80, NO. 2, 1982. "Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 259 FISHERY BULLETIN: VOL. 80, NO. 2 All data were collected by experienced observ- ers. Photographs taken in both 35 mm and 70 mm format documented most observations, and were supplemented by written and occasionally tape-recorded field notes. From the aircraft, ob- servers estimated the critical dimensions of feed- ing-associated structures with respect to refer- ences such as the whale's body or flipper length. From shipboard, more precise measurements were obtained through reference to known dimensions on the vessel, or to a 25 cm diameter fiberboard disk which had been deployed in the immediate vicinity of the whale. RESULTS Feeding behaviors were observed on more than 150 occasions in the period April 1977 to May 1980. Observations were made in the area of West Quoddy Head, Mt. Desert Rock, Stellwagen Bank, the waters east and southeast of Cape Cod, and southeast of Block Island (Fig. 1). Feeding, or apparent feeding, was reported for individ- uals and for groups of up to 20 whales. Behaviors Circular Swimming/Thrashing On 2 December 1978, a single humpback whale was observed and photographed swim- ming in a broad (23 m) circle, roiling the surface as it swam. Tail slashing (a rapid sideways sweeping of the flukes) may have accompanied this behavior. Dense flocks of birds were present over the whale, and dolphins were present by the head and body. The presence of both of these feeding-associated elements, as well as the re- semblance to observations by Ingebrigtsen (1929), suggested that feeding was taking place. This initial observation was substantiated in May 1980 when a number of shipboard observa- tions confirmed the behavior as feeding asso- ciated. An initial thrust of the flukes was fol- lowed by the whale's swimming in a broad circle, roiling the surface with flippers and flukes. This was followed in many, but not all, cases by a feed- ing rush through the circle. This behavior was repeated many times by a single animal over a period of several hours. The circular swimming/thrashing behavior, observed on two occasions, each time involving a single whale, is considered relatively uncom- mon. FIGURE 1.— Study area where observations of feeding behav- iors were made. Place names on chart are those referred to in text. Lunge Feeding Lunge feeding is defined as an upward rush at the water surface with the longitudinal axis of the body intersecting the plane of the surface at an angle of 30°-90°. As the whale breaks the surface, the mouth is agape, and quite often a greatly distended throat region is seen. Up to one-third of the body length clears the surface before the whale falls or settles back into the water. Observations and photographs of prey at the surface, in the mouths of the whales, and picked up by closely associated birds leave no doubt that this is a capture mode of feeding be- havior. This common behavior has been recorded in 21% of our feeding observations, from single animals as well as from groups. When several animals fed together, the lunges often were simultaneous and in close proximity (3 m). In several cases, two or more animals came in con- tact, bumping each other as they lunged. Bouts of lunge feeding may contain on the order of 20 lunges (3 animals in one case) in 25 min. The speed at which the lunge takes place is highly variable. At times, the whale bursts through the surface in a vigorous upward rush. At other times, the rise to the surface and the subsequent extension of the rostrum and dis- 260 HAIN ET AL.: FEEDING BEHAVIOR OF HUMPBACK WHALE tended lower jaw above the surface are quite gradual. In several instances, humpbacks were observed feeding in this manner (the slow, grad- ual rise) in formation. Five or six whales ar- ranged side by side and slightly staggered of one another acted in unison. This behavior has been similarly described from Alaskan waters and termed "echeloned" lunge feeding (Jurasz and Jurasz 1979). Inside Loop Behavior On 23 May 1980, a single humpback was ob- served feeding for over 1 h. The whale repeatedly displayed a behavior we have termed an "inside loop." As the whale begins a shallow dive, it sharply strikes the water's surface with its flukes. This action creates an area of turbulence in the water estimated to have an average diame- ter of 9 m. This area of foam and bubbles is seen clearly as the whale swims away at a shallow dive angle with the pectoral fins held horizon- tally. The whale, swimming rapidly, then rolls 180°, so that the white ventral surface of the flukes can be seen just below the surface. An in- side loop (a sharp U-turn in the vertical plane) follows immediately, so that the whale is now swimming toward the area of turbulence. Fi- nally, the whale is seen rising vertically in a slow lunge, with mouth widely agape, through the center of the turbulence created by the fluke slap. The horizontal distance covered by this "out-and-back" motion was on the order of l%-2 body lengths of the whale. The behavioral se- quence is illustrated diagrammatically in Figure 2. Several variations on the basic behavior were observed. The humpback did not feed through the area of turbulence in every instance. Occa- sionally, the whale would surface to the side of the disturbance, not always feeding. On other occasions, a second whale would enter the gen- eral area and subsequently be seen lunge feeding through the disturbance created by the flukes of the first whale, either alone or in unison with the original whale. The inside loop behavior, observed on a single occasion, involving a single whale later joined by a second, is at present considered relatively un- common. Bubbling Behaviors Underwater exhalations or bubbling behav- iors were seen in association with feeding, or apparent feeding, in 52% of our feeding observa- tions. These exhalations appear to be of two ma- jor types, forming what we have termed "bubble columns" and "bubble clouds." In general, bubble columns and bubble clouds have been observed with about equal frequency. BUBBLE COLUMNS.-Bubble columns are formed by the underwater exhalations of a whale swimming from 3 to 5 m (estimated) below the surface. As the bubble bursts are released, they rise vertically to the surface in the form of a somewhat ragged column. The columns are 1-2 m in diameter and are composed of random-sized bubbles estimated to be generally >2 cm. Series of from 4 to 15 bubble columns are used to form rows, semicircles, and complete circles or bubble nets (Figs. 3, 4). JV> B Figure 2.— "Inside loop" type of feeding behavior. A. Upon making a shallow dive, humpback whale strikes the surface sharply with flukes. B. Fluke slap creates an area of turbu- lence (foam/bubbles) as whale swims away in a shallow dive, flippers held horizontally. C. Whale executes a 180° roll and now does a sharp inside loop, or U-turn in the vertical plane. D. Whale lunge feeds through the area of disturbance created by original fluke slap. 261 FISHERY BULLETIN: VOL. 80, NO. 2 B )^ Figure 3.— The seven types of bubbling behaviors associated with feeding in humpbacks. A through D are structures using bubble columns, which are 1- 1'/2 m in diameter and composed of nonuniform-sized bubbles (estimated at >2 cm). E through G are bubble cloud structures, 4-7 m in diameter, and composed of uniform-sized bubbles (estimated at<2cm). A. Bubble row. B. Bubble row with "crook," whale feeding location shown. C.V or semicircle shaped bubble curtain. Whale feeds in and through open side of the semicircle. D. Complete cir- cular formation, or bubble net. E. Single bubble cloud. In this example, one of several variations, whale lunge feeds through center. F. Triangular formation of multiple bubble clouds. G. Linear formation of multiple bubble clouds. In the simplest configuration, bubble rows, the whale creates a line of columns (generally 4-6). When this has been completed, the whale turns sharply and feeds, open-mouthed, either at or below the surface, at an acute angle to the screen formed by the row of bubble columns. In some cases, the whale continues to release bubble bursts during its turn, so that the line of bubble 262 columns has a "crook" in the end where the whale feeds. The behavior associated with a semicircle of bubble columns is similar, in that once a semi- circle (or "V") has been constructed, the whale appears and feeds toward the concave portion of the screen. Complete circles of bubble columns, termed bubble nets (Jurasz and Jurasz 1979), have been HAIN ET AL.: FEEDING BEHAVIOR OF HUMPBACK WHALE I A • \ i/ i B c r ' ***"***. N. 0 V D y - . -■■% -^ > \ ^ - • V > * E F Figure 4.— Aerial views of bubble net construction by a humpback whale. A through E are 5 frames from a 29-frame sequence; F is from a sequence immediately following. Underwater exhalations are used to form a bubble net approximately 15 m in diameter, composed of some 15 individual bubble columns. Arrows in B indicate undersides of left pectoral fin and flukes. In A through C, whale is rotated on its longitudinal axis so that the blowhole and dorsal surface are toward the center of the circle. In D, whale turns sharply about on the right pectoral fin and prepares to pass through the center of the net. A stream of turbulence is seen trailing from the dorsal fin area, which is being sharply thrust to the whale's left. In E, the whale is seen in feeding posture, mouth agape, under- water in the center of the net. In F, the whale surfaces and blows weakly before exiting the area of the net. Photographs by S. Kraus. 263 FISHERY BULLETIN: VOL. 80, NO. 2 seen on a relatively few occasions, approximately 8% of our observations. Our clearest observations have been from aircraft, particularly on 23 April 1979 when several sequences of bubble net for- mation were photographed (Fig. 4). The whale, maintaining its longitudinal body axis on a nearly horizontal plane, swims some 3-5 m (esti- mated) below the surface in a circular pattern. The dorsal surface (and blowhole) of the whale is rotated toward the center of the circle so that the flippers are oriented nearly in the vertical plane. As the whale swims in this manner, approxi- mately 15 bubble bursts are released, which rise to the surface as columns and appear to form an effective corral. As the circle or net nears com- pletion, the whale appears to pivot on the axis of the flippers. The flukes are thrust to the outside, and a stream of underwater turbulence is seen trailing from the region of the dorsal fin. The whale then banks to the inside and turns sharply into and through the center of the net — all below the surface of the water. The aerial photographs show apparent feeding, i.e., the mouth is agape and the lower jaw region is greatly distended. Only after this stage does the whale rise to the surface, pause, and blow one or more times be- fore exiting the area of the bubble net. Measure- ments show the circle to be approximately equal in diameter to the whale's length— about 13-15 m. While bubble nets constructed in both the clockwise and counterclockwise directions have been observed, the clockwise direction appears to be more common. There are several variations to the behavior described above. Shipboard observations in May 1980 showed that bubble nets are not restricted to 360° circles, but instead may include from V/4- 2 complete revolutions as the whale swims in a spiral of decreasing radius. Often, smaller bursts of smaller bubbles made up the greater portion of the outer ring, with the bursts and bubbles both increasing in size within the inner ring. Additionally, a line of bubbles 10-30 m in length would often directly precede the forma- tion of the circular portion of the bubble net. This gave the overall structure the shape of a "6" or a "9." Finally, surface lunge feeding (gradual rise type), rather than underwater feeding, was re- ported from this series of shipboard observa- tions. BUBBLE CLOUDS.-Bubble clouds form the second major category of bubbling behaviors associated with feeding. There are several marked differences to the bubble columns de- scribed above. In this case, a single underwater exhalation forms a single, relatively large (4-7 m diameter), dome-shaped "cloud" made up of small (estimated to be <2 cm), uniformly sized individual bubbles (Fig. 5). In a few observations where we were able to see the early stages of bub- ble cloud formation, the cloud appeared quite narrow initially, about 2-3 m in diameter, but ex- panded as it rose toward the surface. In many observations, schools of American sand lance, Ammodytes americanus, were visible over wide areas in patches at the surface in the general area of feeding activity, but prior to the onset of any bubbling behavior in their immediate vicin- ity. In all observations, the whale dove out of sight to produce the bubble cloud which rose gradually toward the surface. The prey, appear- ing as a disturbance at the surface, would at times leap vigorously into the air when the bub- ble cloud surfaced into the school. The subsequent appearance of the whale rela- tive to the bubble cloud displayed a good deal of variation. Observations to date suggest five pos- sible variations, as illustrated in Figure 6. When lunge feeding through the cloud's center was seen (Fig. 6A), the speed of the lunge was slower than lunge feeding observed in the absence of clouds. In the second type of behavioral sequence (Fig. 6B, the slow, horizontal appearance of the whale in the surfaced cloud), over 70 bubble cloud observations recorded from shipboard in 1978-79 suggest a repetitive, rigidly patterned activity composed of the following: 1) The whale sounds, usually with flukes in the air. 2) A cloud of bubbles appears beneath the sea surface up to 21/4-3% min after sounding. 3) The whale, not obviously swimming, rises slowly to the surface. Its back first appears in the center of the spent cloud of bubbles 5-9 s after the first bubbles in the cloud reach the surface. 4) Three to ten blows and slow, shallow diving precede the sounding dive which begins the next sequence. In this common activity, the actual feeding prob- ably takes place in the cloud and below the sur- face, with the whale's appearance marking the conclusion of the episode. Although no feeding is visible at the surface, the presence of a number of important elements (prey abundant in bubble clouds, similarity of structure to those in known 264 HAIN ET AL.: FEEDING BEHAVIOR OF HUMPBACK WHALE feeding events, repeated occurrence in known feeding areas, and the presence of feeding birds) is strongly suggestive of a feeding-associated be- havior. Bubble clouds were also observed being used in series or multiples. These clouds possess the characteristics described above but are used in groups, generally three, by one or more hump- backs. Two varieties have been seen (Fig. 3F, G): 1) individuals or groups of humpbacks blow clouds in either triangular or random patterns, and feed in the midst of the clouds or within a particular cloud— observed on a number of occa- sions and considered relatively common; and 2) an individual whale was seen to blow three lin- early connected clouds, and then swim on the surface very slowly through the formation- observed on a single occasion and considered un- common. A final variation, which may or may not be directly associated with feeding, is poorly under- stood. At times, a lunge-feeding whale will ex- hale underwater, lunge feed to the surface, and be followed shortly by one to three bubble clouds appearing at the surface, closely adjacent to the whale but arriving at the surface after the whale instead of before, as described above. Behavioral Strategies Figure 5.— Aerial views of bubble cloud formation and asso- ciated feeding. A. Dome-shaped bubble cloud, formed by underwater exhalation, seen rising toward surface. B. Bub- ble cloud after intercepting plane of surface— upper portion of structure is flattened. C. Lunge-feeding whale appears through center of bubble cloud. Photographs by A. Frothing- ham. It has been our experience that a given hump- back whale will generally repeat a fairly rigid feeding pattern over a period of time. However, several individual humpbacks or groups of humpbacks feeding in the same area may or may not display the same feeding strategy. Several examples illustrate this observation. In two instances on Stellwagen Bank in 1978, all humpback whales (five and seven individuals) within a 20 km2 area displayed bubble cloud feeding (slow rise type) for an entire 1-h period of observation. Every whale in sight appeared to be using the same strategy. During two of the three observation periods on one day in 1979, bubble clouds were formed by one individual in the vicinity of extensive schools of American sand lance, while three other whales were lunge feeding (no bubbling asso- ciated) several hundred meters away. On a third occasion, a single humpback on the northern side of a school of American sand lance was observed forming bubble clouds (with ap- parent subsurface feeding), while three other animals, working the same school of American 265 FISHERY BULLETIN: VOL. 80, NO. 2 B Figure 6.— The five feeding variations associated with bubble clouds. A. Whale lunge feeds vertically through the center of the cloud, as in Figure 5. B. Whale apparently feeds under- water and upon completion rises slowly through the center of the spent bubble cloud; the whale's body is on a horizontal plane and the mouth is not agape. C. Whale lunge feeds to one side of cloud. D. Whale surfaces alongside cloud, emits a weak blow, dives, and reappears lunge feed- ing through the center of the cloud. E. Whale swims vertically up alongside the rising cloud, and then passes horizontally, mouth agape, between the still-rising cloud and the water's surface. sand lance, were generating bubbles in rows, as well as randomly, and lunge feeding. Prey Species Shipboard observations, primarily on Stell- wagen Bank, provide direct visual and photo- graphic evidence that concentrated schools of American sand lance are a frequent prey species in the area. American sand lance was identified in 50% of feeding events from the Dolphin III on Stellwagen Bank in 1978 and in 75% of observa- tions in 1979. Photographs show American sand lance in the corners of the whale's mouth, being picked up by closely associated birds, and in con- centrated surface schools in which the whale is feeding. At least one other species is a target for hump- back feeding. It appeared that humpbacks in the West Quoddy Head area took herring, Clupea harengus, close inshore and in coves, using the bubble cloud and lunge feeding techniques on a number of occasions.5 DISCUSSION Humpback whales in the North Atlantic feed on a wide variety of prey species, with krill and schooling fishes the most important (Tomilin 1967). In Canadian waters, humpbacks feed heavily on capelin, with krill second in impor- 5S. K. Katona and P. V. Turnbull, College of the Atlantic, Bar Harbor, ME 04609, pers. commun. October 1980. 266 HAIN KT AL.: FKKDINC BEHAVIOR OF HUMPBACK WHAI.K tance, although the data also suggest haddock, mackerel, whitefish, and sand lance (Mitchell 1973; Sergeant 19756). The American sand lance has been suggested as a prey species in the Cape Cod area by Overholtz and Nicolas (1979). Our direct evidence confirms their observations and demonstrates the importance of this prey species in these waters. The sand lance is similar in size, summer habitat, and schooling behavior to the more northern capelin, Mallotus villosus (Over- holtz and Nicolas 1979), and therefore may oc- cupy a similar role in the diet of humpbacks in more temperate latitudes. Interestingly, Meyer et al. (1979) reported a significant increase in the relative abundance of sand lance since 1975 on Stellwagen Bank, a trend which was typical of the northwestern Atlantic from Cape Hatterasto the Gulf of Maine. Indirect evidence suggests herring as a prey species in the northern Gulf of Maine. Watkins and Schevill (1979) also tentatively identified herring, along with pollock, Pollachius virens, from Cape Cod waters. These observations will require confirmation as additional knowledge on prey species in New England waters is gained. With regard to the capture mode of feeding be- havior, our observations on lunge feeding closely corroborate those of Watkins and Schevill (1979) and Jurasz and Jurasz (1979). The observations on underwater feeding by humpbacks were almost always in association with bubble struc- tures, although Watkins and Schevill (1979) described several instances of underwater feed- ing in the absence of such structures. "Apparent circling behavior" during feeding was reported by Watkins and Schevill (1979). Our description of what we term circular swim- ming/thrashing behavior expands somewhat on their observations. We speculate that the use of anatomical structures and swimming motion in the manner described bears some generic resem- blance to the "flick feeding" reported from Alas- kan waters by Jurasz and Jurasz (1979). This would seem to be particularly true for the inside loop behavior we have described. These behav- iors may be placed together into a major subdivi- sion of feeding behaviors, the various bubbling behaviors being the other major subdivision. The effect of the whale's feeding behavior on the prey species, and the advantage conferred to the whale, remains a subject for conjecture, since few data are available. The bubbling behaviors are perhaps the most intriguing. Based on ex- periments with artificial bubble curtains, it is known that under certain circumstances, cur- tains of bubbles form an effective barrier to schooling fish (Brett and Alderdice 1958; Smith 1961; Bates and VanDerwalker 1964). Whatever the precise mechanism, it seems reasonable to conclude that humpback whale bubble nets can, and do, effectively corral schools of prey. Whether bubble nets concentrate the prey7 or merely enclose and maintain naturally occurring concentrations of prey (as hypothesized here) can only be resolved by further study. The humpback appears well suited to these be- haviors; Edel and Winn (1978) have described in some detail the locomotion, maneuverability, and flipper movement required to execute the behaviors described here. It has been suggested (Howell 1970; Brodie 1977) that flashes from the long, white flippers are used to concentrate or herd the prey. This may play a role in the circling behavior, the bubble-netting, and perhaps other types of feeding. In the case of bubble-netting, in addition to their hydrodynamic function, the ver- tical orientation of the two extended flippers may act in unison with the bubble screen to help form the "curtain" which herds and/or entraps the prey. While bubbling behavior appears to be com- monly associated with feeding (52% of our feed- ing observations), some caution is in order. Underwater bubbling, even in the presence of feeding activity, may not always be directly re- lated to feeding (see also Watkins and Schevill 1979). Underwater exhalations from humpbacks in nonfeeding situations have also been observed. On occasion, underwater exhalation by hump- backs when approached by ships has been re- corded. From field observations and study of photographs, the possibility that some swim- ming and bubbling behavior may be "play" be- havior, particularly when displayed in the pres- ence of closely associated dolphins, is recognized. In the Pacific, Hubbs (1965) described under- water exhalations with no clearly apparent func- tion, and Forestell and Herman8 described the 6Sergeant, D. E. 1975. An additional food supply for humpback (Megaptera noraeangiiae) and minke whales (Ba- laenoptera acutorostrata). Int. Counc. Explor. Sea, Mar. Mamm. Comm., CM. 1975/No. 13:1-7. 7Earle, S. A. 1979. Quantitative sampling of krill (Eu- phausia pacifica) related to feeding strategies of humpback whales (Megaptera novaeangtiae) in Glacier Bay, Alaska. Paper presented at The Third Biennial Conference of the Biol- ogy of Marine Mammals, 7-11 Oct. 1979, Seattle, Wash. "Forestell, P. H., and L. M. Herman. 1979. Behavior of 267 FISHERY BULLETIN: VOL. 80. NO. 2 apparent use of bubble screens as camouflage by an escort whale in order to protect a calf or mother-calf pair. It is likely that some functions of bubbling still remain to be discovered. At times, bubbling may be purely adventitious. The humpback possesses a diverse repertoire of feeding behaviors. Whether environmental factors influence the choice of feeding method is presently unknown. Perhaps, as suggested by others (Jurasz and Jurasz 1979; Watkins and Schevill 1979), various prey species or densities elicit different feeding strategies and behaviors. For less mobile prey or high prey densities, rela- tively simple devices may be sufficient. For more mobile and evasive species, or for more efficient feeding in lower densities, more sophisticated methods may be advantageous. ACKNOWLEDGMENTS This study was supported by the Bureau of Land Management, U.S. Department of the In- terior, under contract number AA551-CT8-48 to the Cetacean and Turtle Assessment Program, University of Rhode Island. For their skill and assistance, we thank Captain A. Avellar and the crew of the Dolphin HI; Captain W. Simmons and the crew of the Tioga; and survey pilots T. Flynn, J. McMicken, and J. Rutledge. We grate- fully acknowledge the critical review of the manuscript by R. Edel, S. Katona, J. Roanowicz, and W. Watkins. LITERATURE CITED Bates, D. W., and J. G. VanDerwalker. 1964. Exploratory experiments on the deflection of juve- nile salmon by means of water and air jets. Fish-Pas- sage Res. Prog. Rev. Prog., U.S. Bur. Commer. Fish., Seattle 3:1-14. escort accompanying mother-calf pairs of humpback whales. Paper presented at The Third Biennial Conference of Marine Mammals, 7-11 Oct. 1979, Seattle, Wash. Brett, J. R., and D. F. Alderdice. 1958. Research on guiding young salmon at two British Columbia field stations. Fish. Res. Board Can., Bull. 117, 75 p. Brodie, P. F. 1977. Form, function and energetics of Cetacea: A dis- cussion. In R. J. Harrison (editor), Functional anatomy of marine mammals, Vol. 3, p. 45-58. Acad. Press, N.Y. Edel, R. K., and H. E. Winn. 1978. Observations on underwater locomotion and flip- per movement of the humpback whale Megaptera novae- angliae. Mar. Biol. (Berl.) 48:279-287. Howell, A. B. 1970. Aquatic mammals; their adaptation to life in the water. Dover Publ., N.Y. Hubbs, C. L. 1965. Data on speed and underwater exhalation of a humpback whale accompanying ships. Hvalr. Skr. 48: 42-44. INGEBRIGTSEN, A. 1929. Whales caught in the North Atlantic and other seas. Int. Counc. Explor. Sea, Rapp. P.-V. Reun. 56:1-26. Jurasz, C, and V. Jurasz. 1978. Humpback whales in southeastern Alaska. Alaska Geogr. 5(4):116-127. • 1979. Feeding modes of the humpback whale, Megaptera novaeangliae, in Southeast Alaska. Sci. Rep. Whales Res. Inst., No. 31:69-83. Meyer, T. L., R. A. Cooper, and R. W. Langton. 1979. Relative abundance, behavior, and food habits of the American sand lance, Ammodytes americanus, from the Gulf of Maine. Fish. Bull., U.S. 77:243-253. Mitchell, E. D. 1973. Draft report on humpback whales taken under spe- cial scientific permit by eastern Canadian land stations, 1969-1971. Int. Comm. Whaling, 23d Rep. Comm., Lond., p. 138-154. OVERHOLTZ, W. J., AND J. R. NICOLAS. 1979. Apparent feeding by the fin whale, Balaenoptera physalus, and humpback whale, Megaptera novaeangli- ae, on the American sand lance, Ammodytes americanus, in the Northwest Atlantic. Fish. Bull., U.S. 77:285- 287. Smith, K. A. 1961. Air-curtain fishing for Maine sardines. Commer. Fish. Rev. 23(3):1-14. Tomilin, A. D. 1967. Mammals of the USSR and adjacent countries. Cetacea 9:1-717. Isr. Prog. Sci. Transl. Jerusalem. Watkins, W. A., and W. E. Schevill. 1979. Aerial observation of feeding behavior in four ba- leen whales: Eubalaena glacialis, Balaenoptera bore- alis, Megaptera novaeangliae. and Balaenoptera physa- lus. J. Mammal. 60:155-163. 268 THE INTERRELATION OF WATER QUALITY, GILL PARASITES, AND GILL PATHOLOGY OF SOME FISHES FROM SOUTH BISCAYNE BAY, FLORIDA Renate H. Skinner1 ABSTRACT This study investigated monogenetic trematode infestation of the gills and gill pathology of yellow- fin mojarra, Gerres cinereus (Gerreidae); gray snapper, Lutjanus griseus (Lutjanidae); and timucu (needlefish), Strongylura timucu (Belonidae) in relation to water quality in south Biscayne Bay, Florida. Two habitats of the three species in the bay, one in the southeast and the other in the south- west, differed in water quality whereas physical and environmental parameters were similar. The water in southwest Biscayne Bay contained.high amounts of ammonia, trace metals, and pesticides which were not present in the southeast bay. The gills of hosts from the habitat with inferior water quality were heavily infested with the Monogenea (Platyhelminthes) Neodiplectanwm wenningeri (on G. cinereus), Ancyrocephalus sp. (on L. griseus), and Ancyrocephalus parvus (on S. timucu) and suffered from excessive mucus secretion, epithelial hyperplasia, fusion of gill lamellae, clubbing and fusion of filaments, and aneurisms. Only light infestations and little or no abnormal tissue changes were noted in fish from the area of good water quality. The findings led to the conclusion that the pollutants in the water acted as an irritant, stressing the fisji, and producing physical and physiological changes which reduced resistance to infestation by Monogenea. Manmade pollution of coastal waters of south- east Florida has reached a critical level in the most populated areas, causing substantial envi- ronmental degradation (Carter 1974) and the loss of valuable fishing grounds, and making some areas unsuitable for recreation. In recent years, the pollution of Biscayne Bay, Fla. (Fig. 1) has become a major issue. The shore of north Bis- cayne Bay is bordered by Miami and Miami Beach, and lined by bulkheads. It receives a large amount of runoff water from the metropol- itan areas (Waite 1976). Although the south- western part of the bay still retains much of its natural shoreline and mangrove forests, it is broken by drainage canals intended to lower the water level in neighboring agricultural and ur- ban areas. These canals therefore carry agricul- tural, industrial, and urban wastes into that part of the bay (Waite 1976). The southeastern shore- line of Biscayne Bay is formed by a chain of islands which is part of Biscayne National Park with no major direct sources of water pollution. The purpose of this study was to investigate if differences existed in the ectoparasite fauna and possible gill pathology in the same three species of fish living in southwest Biscayne Bay in the '3834 El Prado Boulevard, Miami, FL 33133. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80. NO. 2. 1982. entrances of three drainage canals on one hand and the relatively clean waters of the southeast bay in the National Park on the other. The effect of water quality on the incidence and intensity of infestation by ectoparasites was investigated along with the frequency and kind of abnormal tissue changes of the gills. Included were those ectoparasites that came close to 100% incidence on their hosts and had a direct life cycle. Three species of Monogenea of the suborder Monopis- thocotylea fell into this category. Monogenea (Platyhelminthes) of the gills are common in fish. Since parasites affect the health of fish, they can be the cause of or a contributing factor to host mortality and epizootics (Iversen et al. 1971). Disease and mass mortality in aquacul- ture, often occurring under crowded conditions, are known to have been caused by the genera Gyrodactylus, Dactylogyrus, and Tetraonchus (Wobeser et al. 1976). Since exchange of gases in the gills takes place through a single thin epithe- lial layer separating the blood from the external environment (Anderson and Mitchum 1974), parasites may cause extensive damage to host gill tissue. Although many adverse circumstances weak- en fish and make them more susceptible to dis- eases, presently available literature is mainly concerned with bacterial diseases (Pippy and 269 FISHERY BULLETIN: VOL. 80, NO. 2 Black Creek Canal Moody Canal Mowry Canal ATLANTIC OCEAN N + 10 km FIGURE 1.— Collection stations in south Biscayne Bay, Fla. Hare 1969; Bullock et al. 1971; Burrows 1972; Snieszko 1974). Information concerning parasit- ic diseases in relation to water quality has been obtained in artificial situations such as aquacul- ture facilities rather than the natural environ- ment. According to Hoffman (1976) eutrophica- tion and pollution probably affect helminth parasites as well as the hosts, but no precise studies have been made. Deleterious effects on various marine biota due to manmade pollution have been investigated, among them disease of fishes and Crustacea (O'Connor 1976; Overstreet and Howse 1977; Sindermann 1979). Overstreet and Howse (1977) suggested that poor environ- mental conditions may favor parasitic infesta- tion by stressing the host, causing disease and lowering resistance. In pioneering literature on fish diseases, gill damage other than parasitic was described as due to exposure (Osburn 1911), industrial pollu- tants (Plehn 1924), and fertilizers (Schaperclaus 1954). More recent literature implicates phenols (Reichenbach-Klinke 1965), ammonia (Reichen- bach-Klinke 1966; Smith and Piper 1975), pesti- cides (Lowe 1964; Walsh and Ribelin 1975), and environmental stress, defined as a change from the normal which reduces the chances for survi- val (Snieszko 1974). Damage to the gills in re- sponse to various toxins in the water was reported by Herbert and Shurben (1964), who suggested 270 SKINNER: INTERRELATION OF WATER QUALITY. GILL PARASITES, AND GILL PATHOLOGY that "sublethal effects of each poison can sum within the individual fish and kill it." Minimal risk, hazard and lethal levels, and median lethal concentrations (LC50, the concentration that kills 50% of the test organisms in 96 h) of certain pollu- tants in the marine environment are published by the National Academy of Sciences Environ- mental Studies Board (1972). Although both the National Academy of Sciences and conservation organizations have emphasized the need for eco- logical information on long-term effects of pesti- cides on wildlife at sublethal doses, most field studies are done after the animals have been found dead. Mitrovic (1972) asked for studies of subtle damage resulting from long-term expo- sure at subacute levels. Local studies are needed, since environmental conditions vary with loca- tion, and temperature, salinity, and pH play a part in the toxicity of poisons (Trussel 1972). Subtle indications of damage, according to John- son (1968), may be a change in behavior caused by lowered efficiency of the organism. He sug- gested that the illustration of physiological and ecological effects of sublethal quantities of envi- ronmental pollutants will lead to a more realistic view in establishing tolerance levels for all toxic pollutants. This requires year-round monitoring to take into consideration seasonal variation, variation in drainage as a result of precipitation, runoff, and irrigation, as well as fluctuating physical or chemical factors. MATERIALS AND METHODS The study period extended from May 1975 to August 1976. The three host species were yellow- fin mojarra, Gerres cinereus (Walbaum), a bot- tom feeder; gray snapper, Lutjanus griseus (Lin- naeus), a predator; and timucu (needlefish), Strongylura timucu (Walbaum), a surface feeder, since they were available on both sides of south Biscayne Bay and remained in one locality for extended periods (Cervigon 1966; Randall 1968; Cressey and Collette 1971; Starck 1971). Collection stations for the fish were the mouths of Black Creek, Moody, and Mowry Canals; the Arsenicker Keys; Elliott Key; and a canal in Sands Key (Fig. 1). South Florida Water Man- agement District maintains salinity control structures a short distance inland from the south- western shoreline of Biscayne Bay at Black Creek, Moody, and Mowry Canals. Directly up- stream from the gates the water is brackish. The flood gates open automatically according to the difference in the water level on both sides when the water exceeds a certain height on the upland side. For many months during the study period the gates of the salinity structures remained closed because of the low freshwater table inland and the danger of saltwater intrusion into inland wells. Fish were collected downstream from the salinity control structures near the entrances of Moody and Mowry Canals into the bay, at the confluence of Black Creek and Goulds Canals where they enter the bay, in mangrove creeks and close to shore at Arsenicker and Elliott Keys, and in a manmade canal and lagoon in the inte- rior of Sands Key. Collections were made between April 1975 and August 1976 during three to five trips per week, depending upon weather conditions. The total number of fish collected was 356, of which 186 were from the southwest locations and 170 from southeast Biscayne Bay (Table 1). Only one spe- cies was collected on a given day from one area to prevent exchange of parasites from one host spe- cies to the other. The yellowfin mojarra were caught by gill net, 75 mm mesh size (stretch), and occasionally on hook and line; the gray snapper on hook and line; and the timucu (needlefish) on hook and line, and by beach seine. Collection trips to the stations were alternated regularly, depending on weather conditions and need. Be- cause of the gear used, size ranges of fish were the same in both localities. Sex ratios were simi- lar, with an average of 52% males and 48% fe- males. Fish were collected at depths between 0.5 m and 2.5 m. Water samples for the salinity read- ings were obtained from depths of 0.3 m, 1.0 m, and 3.0 m. An average of 2.5 salinity measure- ments per month were made at each station and each depth. To avoid contamination a closed, weighted plastic bottle was lowered to the desired depth where it opened and filled with water. Additional salinity data for the years 1975 and 1976 from Black Creek, Mowry, and Moody Canals downstream from salinity structures were made available by the U.S. Geological Sur- vey (USGS) and South Florida Water Manage- Table 1.— Numbers of fish hosts collected in the southeast and southwest locations in Biscayne Bay, Fla., between May 1975 and August 1976. S E Biscayne Bay S W Biscayne Bay Gerres cinereus Lut/anus griseus Strongylura timucu Total 69 57 44 170 52 80 54 186 271 FISHERY BULLETIN: VOL. 80, NO. 2 ment District (SFWMD) (unpubl. data). Tem- perature and dissolved oxygen measurements were taken at 0.3 m and 1.0 m depths. The aver- age of two or three readings represent one mea- surement. The average number of measurements was two to three per month at each station. Data of hydrogen ion concentration expressed as pH were obtained from the Dade County Depart- ment of Environmental Resources Management (DERM) and USGS (unpubl. data). DERM and USGS obtained routine monthly water quality data for Black Creek, Mowry, and Moody Canals downstream from salinity struc- tures and made them available for this study. The DERM laboratory also made water quality analyses of eight southeast Biscayne Bay water samples collected at intervals of 2 mo. The sam- ples, taken from slick-free water (see Discussion section), were kept in plastic bottles which con- tained a few milliliters of hydrosulfuric acid for preservation, and were refrigerated until arrival in the laboratory. Chemical analyses were made for total ammonia nitrogen, nitrite, nitrate, phos- phate, and total organic carbon. DERM and USGS furnished data on heavy metals in Black Creek and Mowry Canals and pesticides in Black Creek Canal. Fish were kept alive in an aerated plastic con- tainer until arrival and dissection at the labora- tory. Body surface, fins, gills, gill covers, and mouth were searched for parasites; the gill arches and single parasites fixed and preserved; and the parasites identified and counted. When parasites were too numerous for total counts, estimations of numbers per gill arch were made from counts per gill filament. Formalin,2 AFA (alcohol-formol-acetic acid) fixative, and Bouin's solution were used to fix whole gill arches and trematodes. They were preserved in 70%ethanol. For the purpose of identification whole mounts were made of Trematoda using Harris hema- toxylin and Permount. Whenever possible, origi- nal descriptions of parasites were used for identi- fication together with Yamaguti's (1963, 1971) keys for identification of trematode genera. His- tological sections of 12 entire gill arches from 12 fish were examined. Arches were decalcified prior to embedding and cut at 8 /xm. Sections were mounted, stained with hematoxylin and eosin (H&E) and Periodic Acid Schiff (PAS). Histological techniques were after the method described by Humason (1972). Statistical evalua- tion of all station salinity data consisted of calcu- lations of standard deviation (Snedecor and Cochran 1967). RESULTS Water Quality Variations in salinity occur in Biscayne Bay from year to year because of climatic conditions. The salinity readings of all stations were similar during the dry season of 1976, mainly January to June (Table 2). Maximum salinities in both the bay and canal entrances were 40-417.. at this time. More freshwater discharge into the canals and Biscayne Bay during the rainy season in the fall accounted for a slight drop in salinity and some fluctuation mainly in the canals at that time. The lowest salinity reading from surface water samples from the entrance of Moody Canal in September indicated that freshwater dis- charge was more noticeable in this narrow canal than in the others. Some salinity measurements were taken immediately after freshwater dis- charge (see Table 2, footnotes). A typical reading showed that the fresh water flowed as a shallow surface layer about 30 cm deep out of the canals. During freshwater discharge, salinity at the sur- face varied from 57.. to 157..; at a depth of 30 cm it rose by 15-207.., and at a depth of 1 m it was close to the reading before the discharge, indicating that there was little vertical mixing. The statistical analysis of monthly averages of salinity data of all stations of 1.0 m depth showed that two-thirds of the values fell within one stan- dard deviation of 1.85 on each side of the mean of 36.87... Temperatures reflected seasonal changes at all stations and were similar, with most values between 20° and 30°C (Table 2). Differences may reflect the time of day when readings were taken. Dissolved oxygen concentration fluctuated mainly at canal entrances. Values ranged from 4 ppm to above 8 ppm (Table 2). Values below 6.8 ppm did not occur in southeast Biscayne Bay. Phosphates, ammonia, nitrites, and nitrates present at the collection sites from May 1975 to August 1976 are listed in Table 3. The southeast Biscayne Bay water quality data were similar to those of de Sylva3 and Bader and Roessler4. In general, southeast bay values were low in all 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 3de Sylva, D. P. 1970. Ecology and distribution of post- larval fishes in southern Biscayne Bay, Florida. Univ. Miami 272 SKINNKR: INTERRELATION OF WATFR QUALITY. GILL PARASITES, AND OILL I'ATIIOLOOY — M ■*-> co >> co CQ o> c & o en s en o> •S j= 3 O CO XI C aS & 03 4) C oa en jj CO £ © 3 i — i o en x C -j = 01 o. +J T3 a c eS _rt fc ■/ t- ■5 -*j c c Hi u co c o o >> — p O P a ■— ' — c c 0> US bi >. >> X •~ o Z ~ 0 CD j> § "3 en .ii Cfl 0> 0> -z s~ tu — ' !_ 3 -*-> S3 •~ OJ a o 0) be ot) t- 0) > DC] _>, c o CM w J oa < I Q. „ E CL d d) > O < D d> > < o c o 5 a. E 01 1- X re 5 6 z eji > < _ • c '— 5 >~ E 03 CO X re 5 6 z ~~- C .2 CD CO « o n o _i I Q. E o. Q. > O < D O) > < O c o 5 a. E tg X re 5 o Z D) > < C *-" 5 >. E re CO X re 5 o Z -~. c o a, re re O T3 o - ' SSSNNCONSCOCONS cgrroiOiDCDOJOJO C0COCOCOC\IC\jC\JC\JCNiCvJC\JC\l oO'-oooin'-'-coifitoo) COCOCOCOC\IC\JCNC\JC\JC\JC\)C\J COCOCOCOCOCSJC\JC>iO0C\JC\JC\J COCOCO'^C^CNJ'^-^tCOCO'— C\J mmif)^"coa>coooa)o>ooLn CNicvjcompCNjpcqo c\j cq cnj ^t -«t '^t -^ (b s cb cd tb ui tj tj o i a)--oos(OOwm(D(Oo C\J I WCOCOCOC\IC\JC\JC\JC\iC\jC\JCO .*-C\JTtCMCM | i- CO CNJ C\J »- CNJ S^>i?fCi"iPcDcococccofS o 13 o o 5 CO CO CO CO CO CO CD r>-OtQ.>CJri}t:'-2> §33ll2<2- m m£ir>£'£cni0£><0<0jc\jcsjc\icNjc>jcocococo CVJCOCOCOCOt-t-COCNJOJCOCOCOCOCVJ TrcocMcocoiooiLnoicoqw't inu^i^r^c\ji-CM^(Ococ\jcocp ^^^^^to^iricb^ririifico a>o^O'-'-cj>r^cNiojcoiO(ors- C>JC>JCOCOCOCVlCNiC\JC>JCMC>JC>JCVJ oiaioO'-oscNi-coinmin CNC\JC0C0C0C\ICNIC\JC\JC\JCS1CNJC\J a>CT>o*-*-r-c\jcvj(omr--co C\JC\JCOCOCOCNJC\JC\ICNJ rjia^ > 6 3 3 3 ec um<0)OZQ CO § re o.re ? u. S < S 5 -^ TtLf)uoco^rcDtcocor^cocococJ> cw cococococococococococococo 6 y TfNO)COCO(OCOCOCOCOOO>0 ™ COCOCOCOCOCOCOCOCOCO^CO'J m n'-CNTtCM^f'-COCMCO'-COCVJOvJ CD eg cjo^^ro^^^-o^^^oioio^o^oi m^c>,cJ)Q.--'>cjcfjii;'-S' ?5^ 5 o 5 E 5 o o 5 c OJ Q. o 5 c o to c OJ QJ CO C a eg o re a CO *" o LO a 01 CO c 3 CO Cr re cr CD c "O cn co ID) ci) c OJ c c "D re > a -a re c eg OJ > a >> >. CO c c c re in ai re LO en LO to in co m 0) eg r^ r^ a O) o> E (^ QJ > >^ 3 U 3 _j u> d> —3 ~3 3 < G r^ O o CO ir> rg n « 273 FISHERY BULLETIN: VOL. 80. NO. 2 Table 3.— Monthly nutrient1 values (mg/1) in southeast and southwest Biseayne Bay, Fla., locations (at depth 0.3-1.0 m) (Dade County Department of Environmental Resources Management unpubl. data). Location/ Location/ date PC TOC TAN N02 N03 date PO4 TOC TAN N02 NO3 SE. Biseayne Bay at Elliot Key S.W Biseayne Bay at Mowry Canal July 1975 0.00 7.0 0.00 0.00 0.00 May 1975 0.02 — 0.48 0.01 0.00 Sept. 1975 0.00 1 0 0.00 0.00 001 June 1975 0.00 6.0 0.44 0.01 0.20 Dec. 1975 0.02 9.0 0 00 0.00 0.07 July 1975 000 1.0 030 002 0.12 Feb. 19762 0.05 120 0.00 0.003 0002 Sept. 1975 0.00 1.0 0.10 0.01 0.02 Apr. 1976 0.00 0.00 0.00 0.002 Oct. 1975 0.01 3.0 0.05 0.02 0.68 June 1976 0.017 0.00 0 002 0025 Dec. 1975 0.01 1.0 0.04 001 0.50 July 19763 0.338 0.224 0.012 000 0 265 Jan. 1976 0.11 3.0 0.04 0.03 0.59 Aug. 19763 0.380 0336 0.012 000 0.168 Feb. 19762 0.40 30 0.05 0.01 0.48 Mar. 1976 0.07 — — — — S.W. Biseayne Bay at Black Creek Canal Apr. 1976 0.01 2.0 0.03 0.01 0.17 May 1975 0.32 7.0 0.10 0.01 0.01 May 1976 0.05 3.0 0.04 002 0.70 June 1975 0.64 7.0 0.48 0.02 0.30 Aug. 19763 0.01 6.0 0.03 0.01 0.32 July 1975 0.12 4.0 0.72 0.21 0.48 Aug. 1975 0.48 — — — S.W Biseayne Bay at Moody Canal Sept 1975 0.40 60 0.59 0.10 056 May 1975 000 — 0.06 0.00 0.00 Oct. 1975 0.25 4.0 0.45 0.06 0.43 June 1975 002 10 0.04 0.00 0.01 Nov. 1975 0.09 — — — July 1975 0.00 — — — — Dec. 1975 0.25 40 0.44 0.24 1.5 Sept. 1975 0.01 — — — — Jan. 1976 0.00 40 1.0 030 2.1 Oct. 1975 0.02 1.0 0.06 0.02 0.32 Feb. 19762 0.50 60 0.51 0 11 1.8 Dec. 1975 0.01 3.0 0.04 0.02 0.48 Mar. 1976 0.18 — — — Jan. 1976 0.00 3.0 0.04 003 0.50 Apr. 1976 — 6.0 0.03 0.16 1.2 Mar. 1976 0.14 3.0 003 0.01 0.30 May 1976 1.0 0.32 0.03 0.36 Aug. 19763 0.04 11.0 0.31 0.01 008 'TOC = Total organic carbon, TAN and in suspension. 2Arsenicker Keys. 3Sands Key. Total ammonia nitrogen. The term "total" refers to the amount present both in solution nutrients. Nutrient concentrations were consid- erably higher in the southwest, especially am- monia values. The water sample taken in April 1976 near Arsenicker Keys contained high total organic carbon compared with the other samples because of the proximity of an extensive man- grove coastline and the presence of mangrove detritus in the water. The two July 1976 water samples from Sands Key were taken in a canal and small lagoon inside the Key surrounded by mangroves and connected to the bay. At low tide, about two-thirds of the bottom muds of the lagoon Sch. Mar. Atmos. Sci., Prog. Rep. Fed. Water Qual. Admin., 198 p. 4Bader, R. G., and M. A. Roessler. 1971. An ecological study of south Biseayne Bay and Card Sound, Florida. Rosen- stiel Sch. Mar. Atmos. Sci., Univ. Miami. were exposed, the canal was rich in fish, and wading birds fed in the flats at low tide. The somewhat higher content of ammonia, nitrates, and phosphates was due to decaying vegetation, the exposed mud flats, animal concentrations, and little flushing. Trace metals were present in water samples from the southwest locations only (Table 4). None were detected with standard methods in water samples from the southeast bay. Those pesticides either present or not de- tected in the water in Black Creek during the time of this study are shown in Table 5. None were detected with standard methods in the southeast bay. As in all the other southeast bay samples, no pesticides or heavy metals were de- tected in Sands Key samples. The junction of Black Creek and Goulds Canals and the south- Table 4.— Potentially harmful trace metals (m g/1, total ) in southwest Biseayne Bay locations of Black Creek and Mowry Canals, Fla., from May 1975 to May 1976 (USGS unpubl. data). Black Creek Canal Mowry Canal Hazard Minimal risk May Oct Jan Apr. May Oct Jan. Apr marine marine 1975 1975 1976 1976 1975 1975 1976 1976 biota1 biota' Source As 2 2 — 2 — 1 1 1 50 10 Paints; pesti- cides; industry Pb 4 7 19 20 ~ 7 9 38 50 10 Gasoline fuel; industry Mn 4 20 0 0 — 0 0 0 100 20 Industry, paints Hg 02 02 02 0.5 0.1 02 06 0.1 Pesticides; paint plastics and paper industry Zn 2 2 20 0 — — — — 100 20 Plating industry 'Natl Acad Sci., Natl. Acad Eng . Environ Stud Board (1972) 274 SKINNER: INTERRELATION OF WATER QUALITY, GILL PARASITES. AND GILL PATHOLOGY Table 5.— Pesticides (/ug/1) in southwest Biscayne Bay location of Black Creek Canal, Fla., from July 1975 to August 1976 (USGS unpubl. data).1 Date Diazinon2 2,4-D3 Silvex4 Parathion5 July 1975 Dec 1975 Aug. 1976 0.02 0.06 0.00 0.00 0.00 0.27 002 0.00 0 10 0.02 0.00 'Pesticides not found present in Black Creek Canal water samples were: Aldrin. Chlordane. DDD, DDE. DDT. Dieldrin. Endrin, Ethion, Heptachlor, Heptachlorepoxide. Lindane. Malathion, Methyl-parathion, Methy Itrithi- on, PCB, Toxaphene. Trithion. and 2,4,5-T. 20,0-Diethyl 0-(2-isopropyl-6-methyl-4-pynmidinyl) phosphorothioate 32,4-Dichlorophenoxy (acetic acid). 42-(2.4.5-Trichlorophenoxy) propionic acid. 50,0-Diethyl-0-p-nitrophenyl phosphorothioate west bay was found to be the highest in nutrients and trace metals. Direct sources of pollution may have been waste discharge from boats, marinas, agriculture, suburban developments, and the nearby county dump. Slightly lesser amounts were found at the Moody and Mowry stations which were located some distance from inhabited areas. Pesticide data were not available from the Moody and Mowry stations, although chemical pest and weed control conducted at the time along the banks and in the vicinity of the canals would have been a direct source of pesticides in the water. Parasites The parasite fauna in both the southeast and southwest Biscayne Bay habitats was similar in kind for all three hosts, consisting mainly of pre- viously reported ectoparasites of marine fishes of the same and related species or those sharing similar habitats. The three monogenetic gill parasites — Neodiplectanum wenningeri, Ancyro- cephalus sp., and A. parvus— showed close to 100% incidence and were therefore suitable for this study. Incidence of infestation was as fol- lows: N. wenningeri on G. cinereus, 97% in south- east Biscayne Bay, 100% in southwest Biscayne Bay locations; Ancyrocephalus sp. on L. griseus, 100% in southeast Biscayne Bay, 100% in south- west Biscayne Bay; A. parvus on S. timucu, 100% in southeast Biscayne Bay, 100% in southwest Biscayne Bay. The difference in intensity of infestation of hosts by these parasites was striking, with few parasites on host gills from the southeast loca- tions and extremely large counts on hosts from the southwest locations (Table 6). Pathological Changes in Host Gills Neodiplectanum wenningeri created compara- tively little histological disturbance of the gills when infestation was light. Damage was often mechanical and gill lamellae were deflected. In severe cases of infestation, however, the lamellae were covered with N. wenningeri, and an in- crease in mucus production was noticed along with clubbing of filaments where parasites were attached. Similarly, when numerous, Ancyro- cephalus sp. and A. parvus caused pathological changes at the site of attachment. Localized host reaction to the parasites' hooks included epithe- lial hyperplasia and heavy mucus production (Fig. 2), and the respiratory epithelium was lost in some instances. Often the side of the filament opposite the worm attachment was also affected Table 6.— Averages of some nutrients, trace metals, and pesticides in water samples, and Monogenea and gill pathology of the three host species in southeast Biscayne Bay and southwest Biscayne Bay at Black Creek Canal from May 1975 to August 1976. Southeast E iiscayne Bay Sol ithwest Biscayne Bay at Black Creek Canal No. of No of Component Min. Avg. Max. samples Mm. Avg. Max. samples Total ammonia nitrogen mg/l 000 0.00 0012 6 003 045 1.0 11 Arsenic fjg/\ 0 00 000 0.00 6 2.0 20 2.0 3 Lead jug/1 0.00 0.00 000 6 4.0 12.5 20.0 4 Manganese /jg/l 000 0.00 0.00 6 4.0 60 20.0 4 Mercury fjg/\ 0.00 0.00 0.00 6 0.2 0.28 0.5 4 Diazinon fjg/\ 0.00 000 0.00 6 0.02 0026 006 3 2,4-D fjg/\ 0.00 0.00 0.00 6 000 0.09 0.27 3 Silvex /jg/l 0.00 0.00 0.00 6 000 0.04 0.10 3 Parathion /L/g/l 0.00 0.00 0.00 6 0.00 0.01 0.02 2 Neodiplectanum wenningeri no./gill arch 0.00 0625 5 69 25 725 >100 52 Ancyrocephalus sp no./gill arch 0.1 1.4 8 57 69 124.75 >500 80 Ancyrocephalus parvus no./gill arch 0.3 2.25 4.5 44 61 8925 >200 54 Pathological changes' None None Slight 170 Moderate Severe Severe 186 Slight = mucus production above normal: moderate of lamellae, loss of structure. ■ heavy mucus production and epithelial hyperplasia; severe = fusion 275 FISHERY BULLETIN: VOL. 80. NO. 2 Figure 2.— Photomicrograph of Ancyrocephalus sp. on the gills of Lutjanus griseus, 22.0 cm SL, from southwest Biscayne Bay, Fla. (PAS, 75X) showing hyperplasia, loss of respiratory epithelium, excessive mucus, lamellar fusion, and aneurisms, a) para- site; b) mucus. in a similar manner (Fig. 3). In addition to injury caused by the hooks of the parasite, the lamellae were deflected and adhered to each other, thus reducing the gill surface effective for gas ex- change. In severe cases when a number of worms were attached to the tips of filaments, clubbing of filaments was almost always present, as was obliteration of normal filament structure. The affected filaments appeared white in fresh prep- arations and the gills were congested with mu- cus. Histological changes of the gills not associated with parasites were found in hosts from south- west Biscayne Bay stations. Few southeast Bis- cayne Bay fish showed above-normal production of mucus in the gills. Increased mucus produc- tion was evident in all fish from the southwest locations, and pathological changes ranged from moderate to severe (Table 6). Abnormal color changes were frequent in southwest Biscayne Bay fish and were usually associated with over- production of mucus which congested the gills. Histological sections of gills from these fish showed that whole filaments were lined with mucus and that it filled the spaces between the filaments. Additionally, mucus-producing cells were concentrated, sometimes in several layers, at the tips of gill filaments which had lost their normal structure. Fusion of gill lamellae along entire filaments, epithelial hyperplasia, club- bing of lamellae or obliteration of lamellar struc- ture, aneurisms, and clubbing of filaments occurred frequently, along with proliferation of cells at the bases of lamellae. DISCUSSION According to Grundmann et al. (1976), hel- minth populations in a natural environment are well regulated to a point of host comfort. Although the results from the southeastern habi- tat in this study agreed with this statement, those from the southwest bay locations did not. Disease caused by parasites often requires exogenous as well as endogenous factors (Sindermann 1979). Exogenous factors, as defined by Cameron 276 SKINNER: INTERRELATION OF WATER QUALITY, GILL PARASITES. AND GILL PATHOLOGY (If (UE "■*)&*#> V a A. i3? .* ^r£ b : , x} * Figure 3.— Photomicrograph of two Aneyrocephalus partus on the gills of S. timncu, 24.3 cm SL, from southwest Biscayne Bay, Fla. (PAS, 300X). Lamellae are deflected and obstructed, a) and b) parasites. (1958), are alterations in the ecology of the para- sites or hosts by some abnormal or unnatural event, most often manmade. The most outstanding difference between the southeast Biscayne Bay and southwest locations was the difference in chemical water quality. According to Klontz (1972), fish are so intimately associated with their aqueous environment that physical or chemical changes in this environ- ment are often rapidly reflected as measurable physiological changes in the fish. In general, re- actions of fish gills to an irritant include inflam- mation, hyperplasia, lamellar fusion, excessive mucus production, clubbing of filaments or la- mellae, and formation of aneurisms. Aneurisms may be a specific tissue reaction due to injury or toxic substances, especially am- monia or herbicides in the water or food (Eller 1975). Ammonia frequently has been reported to cause extensive gill damage. Although much of the data on the degree of toxicity of ammonia is not satisfactory (National Academy of Sciences Environmental Studies Board 1972), it has been shown that the more toxic component of ammonia solutions is the unionized ammonia (NH3). An in- crease in pH from the normal level increases the toxicity, because along with temperature it con- trols the degree of dissociation (Trussel 1972). A decrease in dissolved oxygen concentration in- creases the toxicity of unionized ammonia (Na- tional Academy of Sciences Environmental Studies Board 1972). Even low concentrations may cause pathological changes in marine and freshwater organisms (Doudoroff and Katz 1950; Flis 1968; Larmoyeux and Piper 1973). In addition to exhibiting gill damage, after expo- sure to NH3 freshwater fish were susceptible to ectoparasites, according to Reichenbach-Klinke (1966). Prolonged exposure to nonlethal dosage of ammonia in salmon led to hyperplasia of gill epithelium and epizootic bacterial gill disease in a study by Burrows (1964). Pollutants such as metals and pesticides show similar effects on fish gills (Gardner 1975). The LC50 and sublethal effects of pesticides are pres- ently under scrutiny. According to Anderson (1971), for pollutants not to influence the physiol- ogy and behavior of fish, "safe" concentrations 277 FISHERY BULLETIN: VOL. 80, NO. 2 should be 0.01-0.05 of the lethal concentrations. Since a small rise in temperature or salinity can shift the LC50 by one order of magnitude (Eisler 1972), most pesticides may be more harmful than previously assumed. A synergistic effect of sev- eral sublethal concentrations of pollutants is pos- sible. They may exist in such low concentrations that conventional analysis or collection methods will not detect them, especially herbicidal con- taminants. However, Seba and Corcoran (1969) found that surface slicks formed by a film of or- ganic matter concentrated pesticides in south- west Biscayne Bay to detectable levels, up to 137 times as much as slicks in the Florida Current. Although the reaction of gill tissue to toxic chemicals appears to be nonspecific in regard to the particular chemicals present, and it is there- fore difficult to indict any one particular com- ponent or group of components in nature, the overall result of gill damage is impairment of function. Regardless of cause, pathological changes reduce the useful respiratory surface and make gas exchange difficult, which stresses the fish and eventually weakens it. Disease has been known to change behavior in fish (National Academy of Sciences 1973) and in- fluence their chance for survival. Impaired func- tion of an organ and reduced efficiency require expenditure of energy which cannot be used for other life processes such as feeding, reproduc- tion, and predator avoidance. In case of gill dam- age, metabolic activity must be reduced to a minimum in order to reduce oxygen demand (Wedemeyer et al. 1976), and the fish become weakened and stressed. Selye's (1950) definition of stress was used in reference to fish by Wede- meyer (1970): "the sum of all the physiological responses by which an animal tries to maintain or reestablish a normal metabolism in the face of a physical or chemical force." Unfortunately, some of the metabolic changes may also contrib- ute to increased susceptibility to disease (Wede- meyer et al. 1976). When fish are weakened by environmental fac- tors, chemicals, or poor nutrition, their resist- ance to infestation and infection by Monogenea, Trichodina, and bacteria is reduced (Schaper- claus 1954; Wedemeyer et al. 1976). These facts are well known to the aquaculture and aquarium industries. Most research on immune reactions is done in human and veterinary medicine, but parallels can be drawn since fishes' immune sys- tems, although less advanced, resemble those of other vertebrates (Sindermann 1970). Mucus antibody may be active against some external in- festations (Anderson 1974); thus, a parasite must be able to avoid the immune reaction of the host (Williams 1970). Stress-provoked physiological changes may cause a disturbance of the host's im- mune system, and damaged or irritated gills can then become heavily infested with parasites. Snieszko (1974) shared the belief of other scien- tists that the aggravating effect of stress from various types of pollution caused a high inci- dence of infectious disease in fishes, and men- tioned that this belief, unfortunately, was not yet adequately documented. Sindermann (1979) summarized some of the recent supporting evi- dence that toxins have a deleterious effect on the immune response of fishes. This study of Bis- cayne Bay fishes suggests that, in the presence of sublethal quantities of pollutants in a natural marine environment, fish suffered from gill damage which produced stress, physiological and physical compensation, leading to weaken- ing, reduced immunity, and heavy parasitic in- festation. ACKNOWLEDGMENTS I thank Edwin S. Iversen, Eugene F. Corcoran, and Donald P. de Sylva of the Rosenstiel School of Marine and Atmospheric Science, University of Miami; and George T. Hensley and Lanny R. Udey of the School of Medicine, University of Miami, for their advice and assistance during this study. Special thanks go to James T. Tilmant, Bis- cayne National Monument; James F. Redford, Jr., Dade County Commissioner; Henry J. Schmitz and Edward Gancher, Dade County De- partment of Environmental Resources Manage- ment; Robert L. Taylor, South Florida Water Management District; and Keith Dekle, Florida Power and Light Company, for help with field work and obtaining water quality data. I am grateful to Fay Mucha, Rosenstiel School of Marine and Atmospheric Science, University of Miami; and Elaine Kraus, Medical School, University of Miami, for assistance with histo- logical work and photomicrography. Funds were provided by the Rosenstiel Fund, University of Miami, RSMAS. The Richard G. Bader Memorial Student Fund supplied a gill net and photographic material. This is a contri- bution from the Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149. 278 SKINNER: INTERRELATION OF WATER QUALITY. GILL PARASITES. AND GILL PATHOLOGY LITERATURE CITED Anderson, B. G., and D. L. Mitchum. 1974. Atlas of trout histology. Wyo. Game Fish Dep., Cheyenne, 110 p. Anderson, D. P. 1974. Diseases of fishes. Book 4; Fish immunology. T.F.H. 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Man's impact on the chemistry of Biscayne Bay. In A. Thorhaug and A. Volker (editors), Biscayne Bay: Past/Present/Future, p. 279-285. Univ. Miami Sea Grant Spec. Rep. 5. Walsh, A. H., and W. E. Ribelin. 1975. The pathology of pesticide poisoning. In W. E. Ribelin and G. Migaki (editors), The pathology of fishes, p. 515-541. Univ. Wis. Press, Madison. Wedemeyer, G. 1970. The role of stress in the disease resistance of fishes. In S. F. Snieszko (editor), A symposium on diseases of fishes and shellfishes, p. 30-35. Am. Fish. Soc, Spec. Publ. 5. Wedemeyer, G. A., F. P. Meyer, and L. Smith. 1976. Diseases of fishes. Book 5: Environmental stress and fish diseases. T.F.H. Publ., Neptune City, N.J., 192 p. Williams, H. 1970. Host-specificity of fish parasites. J. Parasitol. 56(2):482-483. Wobeser, G., L. F. Kratt, R. F. J. Smith, andG. Acompanado. 1976. Proliferative branchiitis due to Tetraonchus rau- chi (Trematoda: Monogenea) in captive arctic grayling (Thymallus arcticus). J. Fish. Res. Board Can. 33: 1817-1821. Yamaguti, S. 1963. Systema helminthum. Vol. IV. Monogenea and Aspidocotylea. Intersci. Publ., N.Y., 699 p. 1971. Synopsis of digenetic trematodes of vertebrates, Vol. I, 1074 p. Keigaku Publ. Co., Tokyo. 280 THE EFFECT OF PROTEASE INHIBITORS ON PROTEOLYSIS IN PARASITIZED PACIFIC WHITING, MERLUCCIUS PRODUCTUS, MUSCLE Ruth Miller and John Spinelli1 ABSTRACT Since the enactment of the Fishery Conservation and Management Act of 1976, the U.S. fishing industry has intensified its interest in Pacific whiting, Merluccius products, as an additional food resource. In some fishing areas, Pacific whiting is infected with a protozoan parasite, Myxosporidia kudoa, which produces a proteolytic enzyme that degrades the textural quality of muscle as it is processed or cooked. Several enzyme inhibitors were evaluated for their potential to inactivate the enzyme, thereby preserving the texture of the fish during processing. It was found that protease inhibitors such as those found in egg white, potato, and soy and lima beans were ineffective as inhibitors. Compounds that react with sulfhydryl groups, on the other hand, were found to be active inhibitors. These compounds include hydrogen peroxide (free and alkaline), potassium bromate, iodoacetate, and N- ethylmaleimide. The most promising results were obtained with potassium bromate or combinations of dibasic phosphate peroxide and potassium bromate. These reagents mixed into ground parasitized pacific whiting muscle inhibited proteolysis sufficiently during frozen storage and later cooking to maintain texture comparable with nonparasitized fish. The Fishery Conservation and Management Act of 1976 has intensified the interest of the fishing industry in Pacific whiting, Merluccius produc- tus, as an additional food resource. Although Pacific whiting has been extensively fished by the Russian and Polish fishing fleets, it has attracted only slight commercial interest in the United States, primarily because its texture and color are somewhat less desirable than that of other gadoid species such as cod and haddock. In 1970, Dassow et al. observed that the textural change in cooked Pacific whiting was due to the presence of a protozoan parasite, Myxosporidia kudoa. This parasite produces a proteolytic enzyme capable of breaking the chemical bonds of the muscle fibers which are responsible for the characteristic texture of fresh fish. The activity of the enzyme increases as the temperature increases. Thus, during conventional processes such as baking, broiling, or pan frying, the gradual increase in heat enhances proteolysis until the product reaches the temperature of inactivation of the enzyme. One method of handling the problem of the parasitic enzyme is rapid cooking (deep-fat frying of sticks and por- tions) where the temperature of inactivation is achieved before proteolysis destroys the texture 'Utilization Research Division Northwest and Alaska Fisheries Center, National Marine Fisheries Service, NOAA, 2725 Montlake Boulevard East, Seattle, WA 98112. of the fish (Patashnik et al.2). Another possibility would be to inactivate the enzyme with an inhibitor. In the work presented here, several enzymic inhibitors were evaluated to determine their effectiveness in inhibiting proteolysis in Pacific whiting muscle. The concentration of enzyme inhibitor sufficient to prevent organoleptic textural alteration was also determined. METHODS Pacific whiting were caught off the coast of Astoria, Oreg., by commercial trawlers, filleted and frozen within 24 h, and stored at — 20°C. The presence of the parasite was determined directly by visual evidence of black and white spores, by microscopic identification of the spores, or, indirectly, by baking a segment of muscle in a covered container for 20 min at 162°C. Soft or mushy muscle indicated the presence of the parasitic enzyme. To ascertain the effects of enzyme inhibitors under uniform conditions, tests for proteolytic activity were carried out on diluted blends of fish Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80. NO. 2. 1982. 2Patashnik, M.. H.S. Groninger. H. Barnett, G. Kudo, and B. Koury. 1981. Pacific coast whiting (Merlucciuit productus). I. Abnormal muscle texture caused by myxosporidian-induced proteolvsis. In prep., 34 p. Northwest and Alaska Fisheries Center* Natl. Mar. Fish. Serv., NOAA, 2725 Montlake Blvd. E., Seattle. WA 98112. 281 FISHERY BULLETIN: VOL. 80, NO. 2 muscle and on ground (minced) muscle. Condi- tions for testing were kept close to those under which we knew the parasitic enzyme functioned. The pH was maintained at that of the fish (6.8), the substrate was the fish muscle, and the tem- perature was moderate (45°C). Blended Fish Blended fish muscle was prepared by blending two parts 0.1 M NaCl with one part ground fish in a Lourdes Blender3 in a quantity large enough to serve for several tests. The pH (6.8) of the solutions of the various potential inhibitors was maintained by the addition of dilute NaOH or HC1. In a 50 ml polycarbonate tube, 2 ml of the blended fish was mixed with 1 ml 0.1 M NaCl, as a control, or with 1 ml of the potential inhibitor. The tubes, covered with parafilm, were incu- bated for 90 min at 45°C. Duplicate samples of the control and test material were kept at 0°C in order to know the soluble protein level before in- cubation. This figure was subtracted from the quantity of soluble protein that was the result of increased proteolysis in the incubated sample. The reaction was stopped by the addition of 3 ml of 10% trichloroacetic acid. After 30 min at room temperature, the tubes were centrifuged at 9,750 g for 10 min. Protein determinations by the Lowry method (Lowry et al. 1951) were done on 1 ml of the supernatant. The effectiveness of the inhibitor was gauged by comparison of the proteolysis of the control (0.1 M NaCl) with that of the potential inhibitor. Since over a period of time the amount of proteolysis was bound to vary, a control was run with each experiment. In order to calculate the amount of inhibition, an arbi- trary figure of 100% was assigned to the control and the effectiveness of the inhibitor was expres- sed as percent inhibition by the following formula: g protein/ml of test X 100 = % proteolysis g protein/ml of control 100 — % proteolysis = % inhibition. Ground Fish Ground fish was prepared by putting partially frozen fillets through a 4mm die. Ten parts of ground fish were thoroughly mixed with 1 part 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. of 0.1 M NaCl or the inhibitor solution. Three grams of this material was incubated in a 50 ml covered polycarbonate tube for 30 min at 45°C. The reaction was stopped by the addition of 3 ml of 10% trichloroacetic acid. The remaining treatment was the same as with the blended fish. Preparation of Ground Fish Blocks for Storage A quantity (about 200 g) of the ground para- sitized Pacific whiting was mixed with 0.1 M NaCl (approximately the ionic strength of muscle) as a control or an inhibitor in the ratio of 10 parts fish to 1 part solution. Before the blocks were placed in storage, aliquots were taken to test for inhibition and inhibitor residues. The blocks (3" X 1" X 8") were stored at -20°C for 1 mo. At the end of the month, aliquots were retested for inhibition and inhibitor residues. Effect of Proteolytic Inhibition on Texture The blocks of parasitized whiting made for the storage study and a similar block made from nonparasitized Pacific whiting were used to test the effectiveness of maintaining texture by inhibiting proteolysis. Duplicate portions (3" X 1" X Y2") were cut from each block and baked in a covered dish (31/2" X 2" X l1//'). The baked por- tions were randomly mixed before presenting them to an experienced panel for texture and organoleptic evaluation. In order to express the results in numerical values, numbers were assigned to the texture categories: firm (1); soft (2); mushy (3). Aliquots were taken at the same time to test for percent inhibition. Oxidative Effect on Amino Acids Amino acid analyses, using the Beckman 118 CL Amino Acid Analyzer (Spackman et al. 1958), were done on acid hydrolysates of non- parasitized fish, parasitized fish with no treatment, and parasitized fish which had been treated with either 0.5% disodium phosphate peroxide plus 0.025% potassium bromate or 0.5% dipotassium phosphate peroxide plus 0.025% potassium bromate. Enzyme Inhibitors All chemicals were of reagent grade. Trypsin 282 MILLER and SPINELLI: EFFECT OF PROTEASE INHIBITORS ON PROTEOLYSIS inhibitors were purchased from Sigma Com- pany. Dibasic phosphate peroxides were pre- pared in our laboratory according to the method of Nakatani and Katagiri (1970). The potato extract was prepared in our laboratory accord- ing to the method of Melville and Ryan (1972). Test for the Presence of Peroxides or Bromates The following method of measuring peroxides and bromates was adapted from two methods, that of Price and Lee (1970) and that of the Asso- ciation of Official Analytical Chemists handbook (1975): 4 ml H20 1 ml of oxidant standard or 1 g fish 1 ml saturated KI 1 ml 0.001 M ammonium molybdate in 1 N H2SO4. Shake for 1 min, titrate to a light yellow with 0.1 N sodium thiosulfate, and add a few drops of 1% starch; continue titrating to the end point. Both hydrogen peroxide and potassium bromate liberate iodine by oxidation; therefore, this method can be used to indicate the presence of either one. Quantification was determined by comparison with a known standard expressed in milliequivalents. RESULTS AND DISCUSSION Tests with Blended Fish Blended fish was used to test a variety of potential inhibitors which are listed with concentrations and results in Table 1. The enzyme inhibitors tested included trypsin inhib- itors from four sources: soybeans, lima beans, turkey egg white, and chicken egg white. We also tested crude potato extract which has been shown to contain several protease inhibitors (Melville and Ryan 1972; Ryan et al. 1974; Bryant et al. 1976; Hass et al. 1976). None of the tested enzyme inhibitors caused significant in- hibition in concentrations that would be suitable for use in food systems. From the remaining potential inhibitors which included metal chelators, oxidizers, and sulfhydryl binding compounds, we found hydro- gen peroxide, potassium bromate, dibasic phos- phate peroxides, iodoacetate, and N-ethylmaleim- TABLE 1.— Protease inhibitors. Inhibitor Concentration Active site Effect' EDTA 0.3X10'' M 0.3X10 3 M 0.3X10 '5 M Chelates, Metals ± + + Sodium pyrophosphate 5 5 5 XXX CO CO CO 000 Mg, Mn, Zn, other metals ± ± Sodium oxalate 0.3X10 ■' M 0.3X10 '3 M Ca. Mg ± Cysteine 0.3X10 ' M 0.3X10 3 M 0.3X10 5 M Fe, Cu, other metals + ± ± o-Phenanthroline 0.3X10"2 M 0.3X10"4 M Fe. Co, Zn, other metals ± Sodium fluoride 0.3X1 0"1 M 0.3X1 0'3 M Mg, Ca. other metals ± Iodoacetate 0.3X10"' M 0.3X10'2 M 2.0X10 2 M Sulfhydryls, imid- azoles, thio ethers - N-ethylmaleimide 0.3X1 0'2 M 1.5X10 2 M 0.75X10 2 M Sulfhydryls - Hydrogen peroxide 1.0% 0.1% 0.5% Oxidizes - Disodium phosphate peroxide 0.3% 0.5% Oxidizes _ Dipotassium phosphate peroxide 0.3% 0.5% Oxidizes — Potassium bromate 0.05% 0.025% 0.001% Oxidizes - Soybean 1 mg/ml Trypsin ± Lima bean 5 mg/ml Trypsin ± Chicken egg white 5 mg/ml Trypsin ± Turkey egg white 5 mg/ml Trypsin ± Potato extract 2.5 mg/ml 5.0 mg/ml 10.0 mg/ml Chymotrypsin ± Carboxypeptidase ± Serine endopeptidase ± Metallocarboxy pep- tidase ± 'increased proteolysis change ±. +, decreased proteolysis — , no signficant ide to warrant further investigation. The reaction with iodoacetate and N-ethylmaleimide indicated that we were dealing with a thiol enzyme. Tests with Ground Fish Both hydrogen peroxide (H2O2) and potas- sium bromate (KBrOa) are currently being used in the U.S. food industry to impart desired func- tional and organoleptic properties to the foods to which they are added. For example, KBr03 is used in breadmaking to improve the physical properties of the dough (Tsen 1968). H2O2 has been used as a preservative in dairy products (Cuq et al. 1973) and as a bleaching agent in some fish products (Sims et al. 1975; James and McCrudden 1976). The dibasic phosphate perox- ides have been used as a stablilizer for H2O2 in various food products such as soy products, meat, fish, and cereals (Pintauro 1974). 283 FISHERY BULLETIN: VOL. 80. NO. 2 After testing for inhibition effects in the (model) blended system, tests were conducted on ground (minced) parasitized Pacific whiting to test those which demonstrated inhibitory potential and could be used in food systems. Hydrogen Peroxide In the ground parasitized Pacific whiting, hydrogen peroxide was significantly less effec- tive in inactivating the proteolytic enzyme than it had been with the blended fish. This was explained by the fact that catalase is known to be present in muscle to destroy hydrogen peroxide formed in aerobic muscle fiber (Deisseroth and Dounce 1970). There was a difference between the blended and ground muscle both in protein concentration and distribution of the catalase. In order to demonstrate the difference more specif- ically, we compared the protein concentration and the catalase activity in the two systems. Pro- teins were determined by the macro-Kjeldahl, percent protein N method. Catalase activity was determined by measuring the disappearance of peroxide residues after 0.3% H2O2 (0.146 meq) was mixed with 1 g of blended or ground fish. The results in Table 2 show 40% less protein, which includes catalase, in blended fish than in ground fish. When 0.3% H1O2 was added to the blended fish, hydrogen peroxide was more slowly de- graded and thereby had longer contact time with the enzyme of the parasite. The location of the catalase was shown by washing out all intercel- lular catalase from ground muscle, then ^in- stituting the catalase activity by crushing or manipulating the washed muscle fibers. A con- centration of 3% H202 was needed to counteract all catalase activity, but a concentration of this magnitude also destroyed the tissue structure. It was obvious that hydrogen peroxide alone would be impractical to use as a protease inhibitor. Potassium Bromate Because of the difference in protein concentra- tion in ground fish, it was necessary to increase the concentration of potassium bromate from Table 2.— Comparison of protein concentration and peroxide residues in blended or ground parasitized Pacific whiting. 0.01% to 0.05% in order to achieve a 63-66% in- hibition of proteolytic activity. This was shown to be sufficient to maintain the texture of para- sitized Pacific whiting. Tsen (1968) suggested that there was a syn- ergistic effect between potassium bromate, a slow oxidizer, and faster oxidizers such as iodates, acetone peroxide, or azodecarbonamide; therefore, potassium bromate was tested with hydrogen peroxide in varying concentrations. The results were not synergistic but 0.025% KBr03 with 0.5% H2O2 was as effective as 0.05% KBr03 (Table 3). Table 3.— Effect of hydrogen peroxide and potassium bromate on proteolysis in ground parasitized Pacific whiting. Oxidant % inhibiton Control— no treatment 0 0.5% H202 43 0.05% KBr03 63 0.025% KBrOs 47 0.01% KBr03 35 0.05% KBr03 in 0.5% H202 66 0.025% KBr03 in 0.5% H202 64 Treatment Percent protein N % peroxide residues remaining of fish 0 time 5 mm Blended fish Ground fish 988 16.51 100 (0.146 meq) 28 (0.041 meq) 76 (0.1 10 meq) 9 (0.010 meq) Dibasic Phosphate Peroxides The adduct of hydrogen peroxide with dibasic phosphates has been found to facilitate the use of hydrogen peroxide by stabilizing it in food sys- tems (Pintauro 1974). It seemed possible that these compounds might protect hydrogen perox- ide from catalase long enough for it to be effective in inhibiting proteolysis. We tested 0.3% and 0.5% of both disodium phosphate peroxide (Na2HPCv H2O2) and dipotassium phosphate peroxide (K2HPO4H2O2) with ground parasitized Pacif- ic whiting. When these compounds were compared in terms of milliequivalents of perox- ides with equivalent concentrations of hydrogen peroxide alone, disodium phosphate peroxide had 23% milliequivalents of peroxide and dipo- tassium phosphate peroxides 15%. The dipotas- sium phosphate peroxide seemed less stable than disodium phosphate peroxide judging from its effervescence. Both dibasic phosphate peroxides were tested alone and with potassium bromate (Table 4). As found earlier in combination with hydrogen peroxide, 0.025% KBr03 enhanced the proteolytic inhibition of both concentrations of dibasic phosphate peroxides which meant effec- tive inhibition could be achieved with lower con- centrations of each of the oxidants. The results of testing these inhibitors estab- lished concentrations and combinations which 284 MILLER and SPINKLLI: EFFECT OF PROTEASE INHIBITORS ON PROTEOLYSIS Table 4.— Effect of dibasic phosphate peroxide on proteolysis in ground parasitized Pacific whiting- Oxidant % inhibition Control— no treatment 0 0.3% Na2HP04-H202 35 0 3% K2HP04H202 9 0.3% Na2HP04H202 + 0.025% KBr03 64 0 3% K2HPO„-H202 + 0.025% KBr03 62 0 5% Na2HP04H202 45 0.5% K2HP04-H202 24 0 5% Na2HP04H202 + 0 025% KBrOa 73 0 5% K2HP04-H202 + 0.025% KBr03 67 were effective in inactivating the parasitic enzyme in parasitized Pacific whiting. We then determined whether 1) the inactivation would be maintained during a freeze-thaw cycle after 1 mo of storage at — 20°C, 2) inactivation was suf- ficient to maintain a desirable texture, and 3) the treatment with oxidizing agents would adverse- ly affect the amino acids, thereby decreasing the nutritional quality of the protein. Effect of Frozen Storage The prolonged effect of frozen storage on in- hibition was determined on samples of ground parasitized Pacific whiting treated with various inhibitors. Aliquots of these samples were tested at the time of preparation for percent inhibition and the presence of oxidant residues. All samples were stored at — 20°C for 1 mo at which time these tests were repeated, and as the results show in Table 5 there was no decrease in the inhibition of proteolysis. The ground fish treated with 0.5% H2O2 had no detectable residues even imme- diately after treatment, but maintained the in- activity of the enzyme. The residual bromate was dependent on concentration. The samples con- taining 0.025% and 0.05% KBr03 still had slight amounts of bromate. Bushuk and Hlynka (1960) reported that 80 ppm of bromate in bread dough disappeared completely after baking for 20 min. We baked portions of ground fish, treated with 0.05% KBr03, for 20 min at 162°C. There were no detectable residues indicating there would not be significant residues in normally cooked fish. Effect of Inhibition on Texture Results of the organoleptic evaluation for tex- ture are shown in Table 6. These results demon- strate that there is a correlation between the per- centage of inhibition and the maintenance of firm texture. Samples which had the highest inhibition were judged to have texture compar- able with nonparasitized fish. Oxidative Effect on Amino Acids Some amino acids are susceptible to oxidation, particularly methionine which is readily oxidized to methionine sulfoxide and, under severe conditions, to methionine sulfone. We were using relatively mild conditions compared with other investigators, but we lacked informa- tion on the effect of potassium bromate or the combination of potassium bromate and hydrogen peroxide. We therefore compared the amino acid profiles of acid hydrolysates of nonparasitized Pacific whiting, parasitized with no treatment, and two samples of parasitized ground fish, one of which was treated with 0.5% Na2HP04H202 + 0.025% KBr03, the other with 0.5% K2HP04- H2O2 + 0.025% KBr03. We compared the profiles for differences that might suggest significant de- struction of any of the amino acids. Acid hydrol- ysis converts methionine sulfoxide to methionine so a difference would only show if methionine were converted to methionine sulfone. No signif- icant differences were found in any of the amino acids (Table 7). Table 5.— Storage study of oxidants in ground parasitized Pacific whiting. % Oxidant inhibition resi due Oxidant Otime 1 mo 0 time 1 mo Control— no treatment 0 0 0 0 0 5% Na2HP04H202 + 0.025% KBrOa 73 81 +2 + 0.5% K2HPO«-H202 + 0.025% KBr03 67 75 + + 0.5% Na2HP04H202 + 0.01% KBr03 62 59 + N.D.3 0.5% K2HPO„-H20 + 0.01% KBr03 37 46 + N.D. 0.5% H202 49 52 N.D. N.D. 0 05% KBr03 66 66 + + 0.5% H202 + 0.025% KBr03 63 69 + + 0.5% Na2HP04H202 + 0.5% H202 34 47 + N.D. 'Storage at -20°C 2+ = presence of residue oxidant. 3N.D. = not detectable. Table 6.— Texture evaluation of treated parasitized Pacific whiting. Sample and treatment Texture evaluation Nonparasitized Pacific whiting Parasitized Pacific whiting— no treatment Parasitized Pacific whiting treated with 0.5% H202 Parasitized Pacific whiting treated with 0 05% KBr03 Parasitized Pacific whiting treated with 0 5% Na2HP04-H202 + 0 025% KBr03 Parasitized Pacific whiting treated with 0.5% K2HP04H202 + 0.025% KBr03 Parasitized Pacific whiting treated with 0 5% K2HP04-H202 % inhibition '1.1 2.6 2.6 13 1.1 69 14 63 18 64 2.8 28 'Categories: 1 = firm, 2 = soft. 3 = mushy 285 FISHERY BULLETIN: VOL. 80, NO. 2 Treatment of Fillets Since a large portion of any food fish such as Pacific whiting is sold in the form of fillets, it would be preferable to treat the fillets as well as the minced fish. Recently Spinelli4 reported on the use of adding aqueous additives into fillets by high pressure injection. The work showed that it is possible to disperse precisely given amounts of aqueous additives into fillets taken from several species of fish. SUMMARY The proteolytic activity in minced parasitized Pacific whiting can be effectively inhibited by the addition of hydrogen peroxide, potassium bromate, dibasic phosphate peroxides, iodo- acetate, and N-ethylmaleimide. In human food systems, the only acceptable compounds of those mentioned to achieve this inhibition are hydro- gen peroxide, potassium bromate, or the dibasic phosphate peroxides. The most effective inhib- itors at low concentrations were 0.05% KBr03 and either 0.5% Na2HP04H202 + 0.025% KBr03 or 0.5% K2HP04H202 + 0.025% KBr03. These inhibitors retained their inhibitory effect during 1 mo of storage at — 20°C. The inhibition was suf- ficient to maintain a firm texture when portions of the treated ground parasitized Pacific whiting were cooked. Catalase in whiting muscle rapidly degraded added hydrogen peroxide, but did not destroy potassium bromate; however, potassium bromate was reduced to undetectable levels when the material was cooked. LITERATURE CITED Association of Official Analytical Chemists. 1975. Official methods of analysis, 12th ed. Assoc. Off. Anal. Chem., Wash., D.C., 1094 p. Bryant. J., T. R. Green, T. Gurusaddaiah, and C. A. Ryan. 1976. Proteinase inhibitor II from potatoes: Isolation and characterization of its protomer components. Bio- chemistry 15:3418-3424. BUSHUK, W., AND I. HLYNKA. 1960. Disappearance of bromate during baking of bread. Cereal Chem. 37:573-576. Cuq, J. L., M. Provansal, F. Guilleux, and C. Cheftel. 1973. Oxidation of methionine residues of casein by hydrogen peroxide. J. Food Sci. 38:11-13. Dassow, J. A., M. Patashnik, and B. J. Koury. 1970. Characteristics of Pacific hake, Merluccius Table 7.— Percent of amino acid in hydrolysate of ground Pacific whiting muscle. Amino acid Non- 0.5% Na2HPGv 0.5% K2HPO«- para- Nontreated H202 + 0.025% Ha02 f 0.025% sitized parasitized KBr03 treated KBr03 treated Aspartic acid 94 9.5 9.6 9.6 Threonine 4.5 49 46 46 Serine 48 5.0 5.0 50 Glutamic acid 13.6 13.6 13.8 13.8 Proline 3.3 34 3.4 36 Glycine 7.2 70 7.0 7.0 Alanine 8.8 84 8.7 8.5 Valine 5.6 5.5 5.6 55 Methionine 26 2.7 26 2.7 Isoleucine 4 2 4.2 4.2 4.2 Leucine 7.6 7.6 7.7 76 Tyrosine 2 2 2.2 1.9 2.2 Phenylalanine 2 8 2.8 2.8 2.8 Histidine 1.6 1.6 16 1.6 Lysine 7.7 7.8 78 7.8 Arginine 4.0 3.9 4.0 4.0 4Spinelli, J. 1980. Injection of aqueous additives into fish by high-pressure injection. Paper presented at Pacific Fish- eries Technologists meeting, Astoria, Oreg., 3/16-19/80. Northwest and Alaska Fisheries Center, Natl. Mar. Fish. Serv., NOAA, 2725 Montlake Blvd. E., Seattle, WA 98112. productus, that affect its suitability for food. In Pacific hake, p. 127-136. U.S. Fish Wildl. Serv., Circ. 332. Deisseroth, A., and A. L. Dounce. 1970. Catalase: Physical and chemical properties, mech- anism of catalysis, and physiological role. Physiol. Rev. 50:319-375. Hass, G. M., R. Venkatakrishnan, and C. A. Ryan. 1976. Homologous inhibitors from potato tubers of serine endopeptidases and metallocarboxypeptidases. Proc. Natl. Acad. Sci., U.S. 73:1941-1944. James, A. L., and J. E. McCrudden. 1976. Whitening of fish with hydrogen peroxide. Pro- ceedings: The production and utilization of mechanical- ly recovered fish flesh (minced fish) 7/8 April 1976, p. 54- 55. Interox Chemicals (U.K.) Ltd., Luton, Bedford- shire, Minist. Agric, Fish., Food, Torry Res. Stn. Lowry, O. H., N. J. Rosenbrough, A. L. Farr, and R. J. Randall. 1951. Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193:265-275. Melville. J. C, and C. A. Ryan. 1972. Chymotrypsin inhibitor I from potatoes. Large scale preparation and characterization of its subunit components. J. Biol. Chem. 247:3445-3453. Nakatani, H., and K. Katagiri. 1979. Foodstuffs with phosphate peroxide additive. U.S. Patent Office. Patent No. 3,545,892. Pintauro, N. D. 1974. Food additives to extend shelf life. Noyes Data Corp.. Park Ridge, N.J., 400 p. Price, R. J., and J. S. Lee. 1970. Inhibition of Pseudonwnas species by hydrogen peroxide producing Lactobacilli. J. Milk Food Technol. 33:13-18. Ryan, C. A., G. M. Hass, and R. W. Kuhn. 1974. Purification and properties of a carboxypeptidase inhibitor from potatoes. J. Biol. Chem. 249:5495-5499. Sims, G. G., C. E. Coshan, and W. E. Anderson. 1975. Hydrogen peroxide bleaching of marinated her- ring. J. Food Technol. 10:497-505. Spackman, D. H., W. H. Stein, and S. Moore. 1958. Automatic recording apparatus for use in the chro- matography of amino acids. Anal. Chem. 30: 1 190-1206. Tsen, C. C. 1968. Oxidation of sulfhydryl groups of flour by bromate under various conditions and during the breadmaking process. Cereal Chem. 45:531-538. 286 FEEDING HABITS OF STOMIATOID FISHES FROM HAWAIIAN WATERS Thomas A. Clarke1 ABSTRACT Stomachs were examined from over 2,800 specimens of stomiatoids collected near Hawaii. Small Vinciguerria nimba ria ate mostly small copepods and ostracods, while large fish appeared to switch to large amphipods and small euphausiids. The remaining planktivorous species, sternoptychids and small gonostomatids, fed primarily on large calanoid copepods and small euphausiids. All of these appeared to feed by active, visual searching, and preferred prey were probably more visible than other zooplankton in appropriate size ranges. Diets and preferences of the planktivorous stomiatoids were similar to or identical with those of one or more species of myctophids which share the same habitat. The large gonostomatids ate micronekton but appeared to feed in the same manner as the small individuals and species. The species from six other families, which appear to be morphologically adapted to ingest rela- tively large prey, did in fact feed mostly on prey 20% of their body length or longer. Only two species ate zooplankton as well. Most species with chin barbels were nearly or exclusively piscivorous, and those without barbels ate few or no fish. The barbel and analogous structures appear to be used pri- marily to attract and aid in the capture of relatively large fish. Apparent preferences for certain types of prey by the piscivorous species indicate that interspecific differences in barbel features are related to dietary specialization. Based on feeding incidence and estimates of stomach evacuation time, the piscivorous stomiatoids appear to consume a large fraction of the standing crop of plank- tivorous fishes each year. Stomiatoid fishes are important components of the micronekton in most tropical and temperate oceanic areas (e.g., Maynard et al. 1975). Most species occur in the upper 1,000 m and undertake diel vertical migrations (Clarke 1974 and others cited therein). They include both small, plank- tivorous species and generally larger forms with certain morphological features apparently re- lated to capture of relatively large prey. Little is known of the feeding habits of these fishes and, consequently, of their role and impor- tance in the pelagic food web. Diets of a few planktivorous species have been reported, but usually from few specimens and without identifi- cation of prey beyond major taxa. Clarke (1978) showed that some planktivores feed while at depth during the day. Knowledge of the prey of nekton-eating species has consisted mainly of in- cidental reports scattered throughout the litera- ture rather than systematic investigations of large numbers of specimens. This paper presents results of examination of stomach contents of over 70 species of stomia- toids from an extensive series of collections near ■Department of Oceanography and Hawaii Institute of Ma- rine Biology, P.O. Box 1346, Kaneohe, HI 96744. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80, NO. 2. 1982. Hawaii in the north central Pacific Ocean. Almost all the species are vertical migrators; the abundant, nonmigrating species of Cyclothone, Sternoptyx, and Argyropelecus (which are the subjects of separate studies by other investiga- tors) are not included. Diets of the planktivorous species are compared with estimates of prey abundance in appropriate depth ranges in order to determine whether composition and apparent preference are similar to those of cooccurring, nonstomiatoid planktivores which feed in the upper layers at night (Clarke 1980). Data from the nekton-eating stomiatoids allows considera- tion of preference, feeding methods, and the impact of these predators on the planktivorous micronekton in the community. METHODS Specimens for this study were collected ca. 20 km west of the island of Oahu, Hawaii (ca. lat. 21°20-30'N, long. 158°20-30'W) in waters 2,000- 4,000 m deep. Previous studies in this area have considered the vertical distribution and certain other aspects of the ecology of stomiatoids (Clarke 1974) and the feeding chronology of five species (Clarke 1978). Other investigations in the 287 FISHERY BULLETIN: VOL. 80, NO. 2 area have been summarized by Maynard et al. (1975). Over 2,800 specimens of nine families were examined. Based upon preliminary results, mor- phology, and the literature, the species were separated into two groups, each of which was treated differently. Members of the Photichthyi- dae, Sternoptychidae, and Gonostomatidae were considered planktivores; and those of the Astro- nesthidae, Chauliodontidae, Idiacanthidae, Mel- anostomiatidae, Stomiatidae, and Malacostei- dae as nekton-eating species. All specimens of planktivorous species were taken with a 3 m Isaacs-Kidd midwater trawl which terminated in a 1 m diameter cone of ca. 3 mm mesh netting with a ca. 2 1 nonfiltering cod end bucket. Towing procedures were the same as described in Clarke (1980). The trawl was low- ered to a given depth as rapidly as possible, towed for 2-3 h at ca. 2 m/s, and retrieved as rap- idly as possible. A time-depth recorder of the appropriate range was attached to the trawls; depth records were accurate to 2-4% of the depth fished. In addition to night tows at 70-170 m described in Clarke (1980), specimens were also taken from day tows at 400-800 m and night tows at 225-250 m made in September 1973 and November 1974 (Table 1). During some of the deeper tows, the trawl changed depth by as much as 50-100 m during the "horizontal" portion of the tow. Since the most abundant planktivores were known to feed during the day (Clarke 1978), zoo- plankton were sampled at 400-500 m during the day (Table 1) with opening-closing 70 cm diame- ter bongo nets (505 yum mesh). The nets were low- ered closed, opened for 0.5-1 h atca. 1 m/s ship's speed, then closed, and retrieved. Time-depth re- corders attached to the nets indicated vertical movement of up to 100 m during the open por- tions of the tows. Volume sampled by each net was estimated from the mouth area, duration of the open portion of the tow, and an estimated speed of 1 m/s. All material was preserved immediately after capture and held in ca. 4% formaldehyde/sea- water. Except for certain trawl samples where large numbers of Vinciguerria nimbaria were caught and only individuals with obviously full stomachs were selected, all specimens of each species considered were measured (standard length, SL, to the nearest millimeter) and stom- achs examined. Intact prey items were identi- fied, counted, and measured to the nearest 0.1 mm (prosome length for copepods, total length without telson for malacostracans, and total length or maximum dimension for other prey). Identifiable remains among partially digested material were recorded. Any remains of chae- tognaths (the only gelatinous prey found) were counted as intact since they are probably de- graded much more rapidly than other prey types. Items in the mouth or esophagus were not counted; their limbs and bodies were not com- pressed, indicating that they had been taken after capture. Otherwise, there was no evidence of postcapture ingestion by the fishes. Most prey types found intact in the stomach were also re- corded as digested remains that had almost cer- tainly been eaten well before capture, and, conversely, several types of abundant zooplank- ton were rarely or never found in the stomachs, as would be expected if the fish were feeding in- discriminately in the net. There was no evidence that food was regurgitated during or after cap- ture; I found no everted stomachs and no digested remains in the esophagus. Zooplankton from the bongo net samples were counted from either the entire sample (euphausi- ids and other relatively large types) or 1/16-1/32 aliquots taken with a Folsom plankton splitter. For both plankton and intact prey items, eu- phausiids and most copepods (with the exception of unidentifiable copepodites, which were fairly common in all the plankton samples) were identi- fied to species. Ostracods (mostly Conchoecia TABLE 1.— Dates, local (Hawaiian Standard) times, and depths of tows with 3 m Isaacs-Kidd midwater trawl and 70 cm bongo plankton nets off Oahu, Hawaii. Times for trawls are for the period at depth; total times including descent and ascent are in parentheses. Times for bongos are for the open period only. Depth figures are the ranges during "horizontal" portions of tow or modal depth if the range was <20 m. Date Time Depth (m) Trawls: 25 Sept 1973 1523-1723 (1500-1750) 400 9 Nov. 1974 1540-1740 (1535-1802) 400-450 25 Sept. 1973 0748-0954 (0721-1028) 450-500 25 Sept. 1973 1148-1348 (1115-1435) 525 11 Nov. 1974 0818-1118 (0736-1154) 550-600 9 Nov. 1974 0808-1108 (0730-1132) 550-650 26 Sept 1973 0820-1020 (0742-1120) 600 9 Nov. 1974 1230-1430 (1155-1500) 600-650 12 Nov. 1974 0756-1000 (0722-1100) 650 (briefly to 800) 26 Sept. 1973 1227-1427 (1142-1550) 700-800 10-11 Nov. 1974 2303-0100 (2250-0115) 250 11 Nov. 1974 0155-0505 (0145-0515) 225 Bongos: 14 Sept. 1973 0930-1033 400-425 14 Nov. 1974 0808-0908 400-425 14 Sept. 1973 1103-1135 425-525 14 Sept 1973 1241-1311 550 288 CLARKE: FEEDING HABITS OF STOMIATOID FISHES spp.) and amphipods were not further identified, and other prey types were identified only to major taxa. Prey types of the same genus or of similar size, pigmentation, etc. were often lumped for convenience of presentation of re- sults. Densities of zooplankton (Table 2) were calculated from the counts (corrected for any subsampling) and estimated volumes filtered; however, since these are based on so few samples, they can be considered as only rough estimates of prey abundance at the depths where the fishes were caught. Furthermore, the densities of types under 1.0 mm long are underestimated due to mesh escapement; for most of these, densities are probably about 4-5 times higher than estimated from the samples (Clarke 1980). The nekton-eating species were much less abundant than the planktivores, and their feed- ing incidence and number of prey per fish were lower; consequently, in order to gather as much data as possible I examined specimens from a wide variety of trawl samples taken between 1969 and 1978. These included both horizontal and oblique samples in the upper 1,200 m— mostly either above 350 m at night or deeper dur- ing the day. Almost all were taken with a 3 m Isaacs-Kidd trawl towed at ca. 2 m/s. The termi- nal section was of fine (333 yum) plankton mesh for about two-thirds of the samples. For a few rare species I also took material from collections with a 5 m Isaacs-Kidd, a 3 m Tucker, or a 2/3 Cobb pelagic trawl. Data from the more abun- dant fishes were grouped by arbitrary size classes or by time of capture. For the latter, "day" included all tows started and completed between sunrise and sunset plus a few dusk tows which were completed after sunset but fished at or near the day depths of the fishes. Similarly, "night" included tows taken wholly between sun- set and sunrise plus a few dawn tows that fished at or near night depths of the fishes. Specimens were identified, measured, and classified into one of four categories: Damaged — the stomach ruptured or lost during capture, Empty — stomach completely empty or with only a trace of unidentifiable remains, Remains — prey completely disintegrated but identifiable to major taxon, Intact — prey in one piece or a few large pieces. Sizes (standard length of fishes, length without telson of crustaceans, and mantle length of squids) of all intact prey items were re- corded. Depending upon size of the item and de- gree of digestion, the accuracy of these measure- ments was an estimated ±1-5 mm. Relative length of the prey items, as percentage of stan- dard length of the predators, was used for pre- sentation. Intact crustaceans and many of their remains could be identified to genus or species, but only a fraction of the intact fishes could be unquestionably identified. Where a fish prey could not be identified positively, a probable identification could be often given based on a process of elimination. Because of their photo- phores, myctophids and some stomiatoids could be identified as such at more advanced stages of digestion than other fishes; in most cases where an item was clearly not a myctophid, it was in good enough condition to be more precisely iden- tified. There was little evidence of postcapture inges- tion of large items. A few very fresh items, i.e., those without a coating of stomach mucus or with the limbs not flattened against the body, were not counted. Most of these items were still partly in the esophagus and were usually types not found as digested remains in the same predator spe- cies, e.g., a euphausiid in an otherwise piscivo- rous species. As with the planktivores, there was no evidence of postcapture regurgitation of prey by nekton-eating species. Most of the nekton-eating species proved to eat only small nekton (prey >10 mm long). Zooplank- ton (usually copepods) were very rarely found in their stomachs— always in near-perfect condi- tion and never as digested remains. Certain spe- cies of these fishes, however, appeared to eat both small and large prey, and zooplankton were rou- tinely found in their stomachs. In spite of the fact that many specimens of these species were taken by trawls with a fine mesh terminal section, there was little evidence that the data were biased by postcapture ingestion. As with the strictly planktivorous species, the types of prey found intact included only a narrow range of the types collected in the cod end of the trawl rather than a mixture as would be expected from indis- criminate ingestion in the net, and digested re- mains of the same types of prey were also re- corded for these species. Finally, as will be shown below, the incidence of small items in the stomachs decreased with size of the fish; this would not be expected if these species were for some reason prone to ingestion after capture. (At towing speeds of less than ca. 1.5 m/s, post- capture ingestion of both large and small items appears to be a serious problem. During the course of this study, I examined specimens from several tows taken at 1.0-1.5 m/s. Zooplankton— 289 FISHERY BULLETIN: VOL. 80, NO. 2 co o> 1-2 u — "S s .fa X 5 W c cc a! Q LO a V CO. 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[^ s t; CD CD CO CO ■c x: o o 3 3 LU Uj CO ^1 CO co CO <0 CO S E S SEE CD CD CO E E E o o o L*. h» W 3 3 3 CD CD CD a S a 3; S; S; E E g, EE5 CO CO Q. CL a 'VI A CD Cl co CL to to "> . 3 3 to cl "O "O CD to CD Q. -Q -Q ^ (^ CO to 2 2 X 3 ^ to 2 2 S Q.CL-S CD CD CD CO 3 *C 290 CLARKE: FEEDINC HABITS OF STOMIATOII) FISHES up to 10-12 assorted copepods and ostracods, all apparently recently ingested — were found in several stomachs of fishes that otherwise had eaten only relatively large items. I also found several apparently freshly ingested euphausiids and sergestid shrimps in stomachs of fishes that otherwise appeared to be strictly piscivorous. Specimens from these slow tows were not in- cluded in the data presented here.) Estimates of biomass and relative abundance of vertically migrating fishes in the study area and of feeding incidence of the nekton-eating stomiatoids were made from catches of a series of oblique 3 m Isaacs-Kidd trawl tows taken at approximately monthly intervals between Au- gust 1977 and November 1978. A time-depth re- corder and a flowmeter were mounted on the trawl for all tows. All fishes were identified, spe- cies were grouped by taxa and known or prob- able feeding habits, and wet weights of each group determined for each sample. All nekton- eating stomiatoids from the series were exam- ined and are included in the results below. The 58 night tows in this series fished between the surface and ca. 350 m and covered the night- time depth range of all vertically migrating spe- cies. The relative abundances of the different taxonomic and trophic groups were calculated based upon total numbers from all the night tows. Biomass (wet weight) per unit area of each group was calculated as in Maynard et al. (1975) for each sample. The overall mean of all samples and all seasons was used as the estimated aver- age biomass. The 28 day tows covered the day depth ranges of the vertically migrating species (ca. 350-1,000 m), but for various reasons it was not possible to reliably estimate volume filtered (and therefore biomass per unit area) from these tows. The numbers of nekton-eating stomiatoids and of prey species in the catch and the numbers of prey found in the stomachs of the stomiatoids from both day and night tows were used to esti- mate feeding incidence relative to the numerical standing crop of prey species. RESULTS Photichthyidae Vinciguerria nimbaria (Table 3) from three samples within its day depth range were divided into two size groups (16-25 mm and over 25 mm SL). Catches of three of the six size-depth groups were high, and only fish with visually apparent full stomachs were selected for examination (Table 3, columns 3, 5, 6). All fish of the other groups were examined, but total numbers of in- tact prey were still quite low for these. Overall the most frequent items in the stom- achs were small copepods and ostracods. Oncaea spp. were the dominant prey in most size-depth groups, and in all samples Oncaea— especially the small forms — were more frequent in the diets of the smaller fish than in those of the large. Be- yond this, however, the diet composition varied between groups without much apparent relation to size or depth, e.g., Clausocalanus spp. and Pleuromamma gracilis were important fractions of the prey of the small fish from 400 m and both size groups from 450 to 500 m; candaciids and Scolecithrix danae were taken by most groups, but decidedly more frequently (as percentage of prey items) by the large fish from 400 m; the fre- quency of ostracods varied among the groups from 3% to 42% of the total items. Some of this variability was undoubtedly a consequence of small sample sizes from three groups, but part resulted from large numbers of certain prey types occurring in only one or a few of the fish from a given size-depth group. Exam- ples include (see appropriate column of Table 3): All 7 P. gracilis from 1 of 6 fish with prey (col- umn 1); all 5 amphipods from 1 of 3 fish (column 2); 4 of 5 Undinula spp. from 1, 4 of 5 Sapph irina spp. from another, and all 11 pelecypod larvae from another out of 18 fish (column 3); 13 of 41 Clausocalanus spp. in 1 and 34 of 73 P. gracilis in 3 others out of 20 fish (column 5); 14 of 15 Scole- cithrix danae in 1 and 24 of 34 P. gracilis in 2 others out of 9 fish (column 6). The presence or absence of only one or two fish such as these had an important effect on percentages of certain items in the estimated diet of a size-depth group. Vinciguerria nimbaria over 30 mm SL had eaten considerably larger items more frequently than smaller fish. The only large day-caught specimen (37 mm) contained remains of another fish, a 3.0 mm amphipod and two Nematobrach- ion spp., each ca. 15 mm long. Ten specimens over 30 mm were taken in a night tow at 70 m. Most items in the stomachs of these fish were on the borderline between "intact" and "remains" and difficult to count similarly to those from the day specimens, but it was clear that euphausi- ids—mostly Stylocheiron spp.— were the most frequent items and that small copepods were much less important than in the smaller fish. Re- mains of six to nine Stylocheiron each were found 291 FISHERY BULLETIN: VOL. 80, NO. 2 Table 3.— Numbers of intact items of different prey types from stomachs of Vinciguerria nimbaric i and V. poweriae from several depth s and times. Remains of types not found intact are denoted by ' 'r"; in column seven (V. nimbaria. Night, 70 m), numbers of nearly intact remains (see text) are given in parentheses. V. nimbaria V. poweriae Day Night 70 Day 400-300 23-29 Night Depth (m) 400 400-450 450-500 225-250 Size (SL, mm) 17-25 26-30 16-24 26-30 17-25 26-30 31-39 20-34 No examined 14 8 18 13 20 9 10 11 16 No. w/intact prey 6 3 18 4 20 9 0 8 7 No. of intact prey 54 33 270 31 437 192 0 57 17 No of prey type: Neocalanus spp. — — — — 1 1 r(4) — — Nannocalanus minor — — — — — 1 — — — Undinula spp. — — 5 — 1 1 — — — Clausocalanus spp. 3 — 1 — 41 13 — — — Euchaeta spp — 1 — — — 4 r(2) — — Aetideidae — — — — — 2 r(1) — — Scolecithnx danae — 5 3 1 2 15 — — — Scolecithricidae <1 0 mm 1 — — 1 2 2 — — — Scolecithricidae >1.0 mm — 1 — ■ — 5 1 — 2 — Pleuromamma abdominalis — — — r 3 1 — 1 — Pleuromamma spp CIV, CV — — 1 — 8 2 — — — Pleuromamma gracilis 7 r 5 1 73 34 — — r Lucicutia spp. <1.3 mm 3 r 3 — 20 9 — — 1 Helerorhabdus spp — — 1 — 2 1 — — — Augaptilidae — — — — — 1 — — — Candacia spp 1 1 2 — 4 6 r(1) 3 r Paracandacia spp — 7 2 — 1 3 r(13) 1 2 Unident calanoid — 1 — — 6 2 r(5) — — Corycaeus spp — 1 10 — 11 1 r(1) — — Oncaea mediterranea 9 2 66 6 82 13 r(2) 6 5 Oncaea conilera 10 2 43 4 55 17 — 7 — Oncaea venusta 1 — 19 1 7 4 — 3 3 Oncaea spp <0.6 mm 13 2 29 — 67 24 — 3 1 Sapphirina spp — — 5 1 — 1 rd) — — Aegisthes spp — — — — — 1 — — — Euphausia spp — r r — 6 2 — 2 — Stylocheiron spp. — — — — — r r(28) r r Nematobrachion spp. — — — — — — — 1 r Euphausiid larva — — 1 — 3 4 r(1) — — Caridean larva — 1 — — — 1 — — — Amphipod <2.0 mm — 1 4 — 2 — — 1 — >2.0 mm — 4 3 1 4 4 r(46) — — Ostracod <1.0 mm 2 — 27 4 16 9 — 5 2 >1.0 mm 4 1 20 9 14 8 r(9) 16 3 Gastropod larva — — 8 — 1 1 — 6 — Pelecypod larva — — 11 — — — — — — Heteropod {Atlanta spp ) — 1 1 — — — — — — Chaetognath — 1 — — — 1 r(1) — — Fish larva — 1 r 2 — 2 r(2) r r in four of the large V. nimbaria. Amphipods were also apparently important items in the diet of these large fish, but similar to the above exam- ples, about 38 of the approximately 46 amphi- pods recorded were eaten by only 2 of the 10 fish. Vinciguerria poweriae was taken in small numbers in the same day tows as V. nimbaria and at night at 225-250 m (Table 3). Both the inci- dence of fish with intact prey and the number of prey per fish were lower at night, indicating that, like V. nimbaria (Clarke 1978), V. poweriae feeds during the day. The items and remains found in stomachs of both groups indicate that V. poweriae's diet is generally similar to that of V. nimbaria of the same sizes. The lower per- centages of Oncaea spp., higher percentages of ostracods, and less diversity may have been an artifact of small sample size. Sternoptychidae Valenciennellus tripunctulatus and Danaphos oculatus (Table 4) were taken in day tows with and slightly deeper than the Vinciguerria spp. The small Valenciennellus tripunctulatus — mostly from the shallower tows— had eaten some Oncaea spp., ostracods, and small (1.0-1.5 mm) calanoids, but most of their prey and all of those of the larger fish were medium to large cala- noids. Few prey were found in D. oculatus, but with the exception of a small scolecithricid and remains of an ostracod, all were large calanoids. Gonostomatidae The diet of Gonostoma atlanticum (Table 5) from day tows consisted of essentially the same 292 CLARKE: FKKDINC HABITS OF STOMIATOII) FISIIKS TABLE 4.— Numbers of intact prey from stomachs of ValrtiricnnrllNs tripiuictii- latu8 from day samples at four different depths and of Danaphos oculatus com- bined from four different day samples. Remains of types not found intact are denoted by "r." Danaphos Valenciennellus tripunctulati JS oculatus Depth (m) 400 400-450 450-500 525 400-600 Size (SL, mm) 22-30 23-29 28-31 29-34 28-40 No. examined 11 10 3 4 21 No. w/intact prey 11 10 3 4 10 No. of intact prey 84 44 7 34 21 No. of prey type: Neocalanus spp. — 1 — — — Eucalanus spp 3 — — 1 — Clausocalanus spp. 4 1 — 1 — Aetideidae <2.0 mm 4 — — 2 3 >2.0 mm 10 3 1 — 8 Euchaeta media 12 4 2 6 5 Scolecithricidae <1.0 mm 4 2 — — 1 >1.0 mm 3 1 1 9 — Pleuromamma xiphias 11 11 1 12 3 Pleuromamma xiphias CV 9 1 — — — Pleuromamma abdominalis 3 2 2 1 — Pleuromamma abdominalis CV 1 — — — — Pleuromamma gracilis 6 — — — — Heterorhabdus papilliger 4 1 — — — Heterorhabdus spp. 2 — — — — Candacia longimana — — — 1 1 Oncaea conifera 2 5 — — — Oncaea spp <0 6 mm — 1 — — — Corycaeus spp — 1 — — — Ostracod <1.0 mm — 2 — — — 1.1-1 9 mm 1 3 — — r Unident. calanoid 5 4 — 1 — Chaetognath — 1 — — — Table 5.— Numbers of intact prey from stomachs of four species of gonostomatid fishes taken day and night and combined from two or more samples within given depth ranges. In this table, a few stage V copepodites of Pleuromamma xiphias and P. abdominalis are included with adults. Prey types not found as intact items are denoted by "r." Additional remains from fish of column seven (225-250 m depth) included a penaeidean shrimp and a large Metridia sp. Data for Gonostoma elongatum and G. ebelingi over 120 mm SL are in Table 6. Gonostoma atlanticum Gonostoma elongatum Gonostoma Day ebelingi Diplopho Day + s taenia * Day N ight Day 400-800 34-78 N ight night Depth (m) 400-525 170-250 110-170 29-88 225-250 93-120 400-500 34-77 525-650 94-117 400-650 + 90 Size (SL. mm) 22-45 i 46-65 25-44 46-54 53-93 103-171 No examined 34 29 26 9 24 15 17 9 21 9 14 No. w/intact prey 25 21 7 4 6 9 2 7 4 8 9 No. of intact prey 74 46 10 5 22 18 3 20 9 13 19 No. of prey type: Neocalanus spp. — — — — 1 — — — — 1 — Undinula sp. — — — — — — — — — 1 — Eucalanus spp. 1 — — — — — — — — — — Aetideidae 2 2 — 1 4 — — 2 3 — — Euchaeta media r 1 — 1 — — — 1 — — — Scottocalanus spp r 2 1 2 r — — — 4 — — Amallothrix spp. 2 1 — — — — — — — — — Pleuromamma xiphias 33 10 1 — 11 15 2 5 r 2 2 Pleuromamma abdominalis 8 3 2 — — 1 — — — 4 — Pleuromamma gracilis — 1 — — — — — — — — — Lucicutia spp 1 — 1 — — — — — — — — Candacia longimana 6 3 1 r 2 — r r — — — Unident calanoid 1 — 2 1 — — — — — — — Oncaea spp 3 — — — 1 — — 6 — — — Euphausia spp. 13 14 2 — — 1 r 1 — 5 4 Stylocheiron spp. 2 — — r r r r r — — — Nematoscelis spp — 6 — — — — — — 1 — — Nematobrachion sp. — — — — — — 1 — — — — Thysanopoda aequalis — 3 — r 1 — — 1 — — 2 Thysanopoda spp — — — — — — r — — r 1 Euphausnd larva — — — — — — — — — — 1 Ostracod 1 — — — — 1 — 4 1 r — Amphipod — — — — 2 — r — — — 7 Fish 1 — — — r — r r _ 2 293 FISHERY BULLETIN: VOL. 80. NO. 2 types of copepods eaten by the sternoptychids plus small (8-12 mm) species of euphausiids. The euphausiids were over twice as frequent and, among the copepods, P. xiphias and P. abdomi- nalis much less important in the diet of the larger of the two size groups of fish. Gonostoma atlanticum appears to feed by day (Clarke 1978); as expected, the remains and few intact prey items found in night-caught specimens were similar to those from day-caught fish. Gonostoma elongatum were divided into three size groups. Specimens <90 mm SL from both day and night tows (Table 5) contained mostly large copepods, the majority of which were P. xiphias. Euphausiids or their remains were found in several specimens; only one, a Thysano- poda aequalis, was over 10% of the fish's length. Intermediate-sized G. elongatum (93-120 mm SL) were taken only at night, and most stomachs contained only digested remains. The frequency of euphausiids in the diet appeared higher than in the small fish, and one plus the remains of two others were over 10% of the fish's length. Gonos- toma elongatum over 120 mm (Table 6) had eaten large prey in all but two cases. Relative sizes of most measurable items were about 10%, but val- ues ranged from 3.8% to 27% (excluding two cope- pods and a somewhat suspicious pyrosome). Penaeidean shrimps and euphausiids were the most frequent items and remains, but fish were taken by several and squid by two of the large specimens. Limited data for G. ebelingi and Diplophos taenia indicated that both diet and differences between size groups were similar to those of G. elongatum, but there were some differences in important prey types. Data for G. ebelingi came exclusively from day tows. Small fish (Table 5) had eaten small zooplankton— Oncaea spp. and ostracods — as well as the larger P. xiphias and euphausiids; the intermediate-sized individuals had eaten only large zooplankton. The largest fish (Table 6) had eaten only fish and crustaceans over 10 mm long; the relative sizes of intact items were 11-24%. Diplophos taenia (Table 5) were mostly from day tows. Small fish had eaten med- ium to large copepods and Euphausia spp. The large fish contained few copepods or their re- mains; most prey were small euphausiids or the large (5-6 mm) amphipod Vibilia spp. The two largest fish examined had eaten myctophids. One of the myctophids (Lampanyctus sp.) and a T. tricuspidata were relatively large (29 and 22%, respectively), but all other items were <10%. Astronesthidae Astronesthes indicus under 60 mm SL fed mostly on copepods and ostracods (Table 7). Small prey types, especially Oncaea spp., were more frequent in diets of fish under 30 mm SL. Of the two species of scolecithricid copepods eaten, the smaller Scolecithrix danae(ca.. 1.5 mm prosome length) was more frequent in the diet of the fish under 30 mm than in the 31-60 mm fish, but the larger Scottocalanus spp. (over 3 mm PL) were more frequent in the larger fish. Euphausi- ids were only slightly more frequent in the diet of the 31-60 mm fish than in that of the smaller ones; remains of euphausiids, including five in one fish, were found only in the 31-60 mm group. The few individuals over 60 mm SL (Table 6) were mostly empty; only a myctophid and fish re- mains were found. The smallest individual of A. "cyaneus" (15 mm SL) had eaten small zooplankton, but those 20-47 mm SL (Table 6) had eaten only Euphausia spp. — some up to almost one-half their own length. Fish remains were found in two of the three larger fish examined. The small and inter- mediate-sized A. splendidus had eaten a few copepods and a small euphausiid, but all other prey of all sizes were relatively large— an aver- age of 41% of SL— and all but two were fish (Table 6). Small A. "similis" (Table 6) contained only fish remains; the large individuals contained fish and a single euphausiid whose relative length was considerably less than those of the fishes eaten. (See Clarke 1974, regarding differ- ences between the two provisionally identified species and A. cyaneus and A. similis.) The items found in Heterophotus ophistoma (Table 6) were unique in several respects, but the significance of these cannot be assessed from the insufficient data here. One of the small speci- mens contained squid remains — otherwise found in only two specimens of G. elongatum. The four large specimens contained two sergestids, a Ster- noptyx sp. — the only nonmigrating fish found in any stomiatoid, and remains of a Parapandalus sp. — the only adult caridean shrimp found. All of these items were relatively smaller than prey of most other nekton-eating species. Chauliodontidae Chauliodus sloani (Table 6) had eaten mostly fish; only those <120 mm had taken crusta- ceans—mostly euphausiids— frequently. The 294 CLARKE: FEEDING HABITS OF STOMIATOII) FISHES Table 6.— Summary of stomach analyses for nekton-eating stomiatoids. See text for definition of categories. Under "Time" (first column): D = day, N = night, B = both combined. Under "Remains recorded" (last column): e = euphausiid, s = sergestid, c = un- identifiable crustacean, m = myctophid, f = unidentifiable fish, sq = squid. See text for explanation of groups of unidentified Eustom ias spp. Relative I engths of prey No % of undamaged specimens in % of predator SL Time SL (mm) specimens (damaged) Empty Remains only Intact items (No. of items) Remains Family/species Fish Crustaceans recorded Gonostomatidae: Gonostoma elongatum D 138-207 11(0) 64 9 27 13-20(2) 10-13(3) e.sq' N 126-210 10(0) 10 40 60 13-17(2) 6-27(6) e.c.f.sq2 Gonosloma ebelingi D 121-143 19(0) 58 32 11 — 11-24(3) e.c.m.f Astronesthidae: Astronesthes indicus B 64-152 20(2) 83 11 6 29(1) — f Astronesthes "cyaneus" B 15-47 30(0) 60 23 17 — 24-48(6) e.c3 B 114-164 3(0) 33 67 0 — — m,f Astronesthes splendidus B 22-39 31(1) 53 23 23 32-63(5) 31-41(2) e.m.f B 41-58 17(0) 76 6 18 41-44(2) — e.m.f5 B 66-95 14(0) 57 7 36 21-64(5) — m Astronesthes "similis" B 23-68 27(1) 73 27 — — — m.f B 98-122 5(0) 40 20 40 25-41(2) 8(1) f Heterophotus ophistoma B 35-70 8(1) 86 14 — — — sq B 141-320 4(0) 25 25 50 7(1) 6-11(2) c Chauliodontidae: Chauliodus sloani D 20-60 43(4) 62 18 20 33-45(7) 20(1) e.m.f N 20-60 57(9) 58 23 19 31-63(6) 10-20(2) e.m.f D 61-120 12(2) 50 20 30 21(1) 11-16(3) e.f N 61-120 33(9) 54 25 21 22-42(6) — m.f D 121-255 24(6) 44 22 33 14-33(5) 13(1) f N 121-232 23(11) 50 25 25 14-19(3) — c.f Idiacanthidae: Idiacanthus fasciola D 50-100 55(25) 90 10 — — — m.f N 50-100 73(24) 88 4 8 16-22(4) — f D 101-200 38(6) 72 19 9 17-20(3) — m.f N 101-200 57(8) 78 14 8 9-20(4) — f D 201-375 37(1) 75 14 11 13-23(4) — f N 201-372 102(7) 84 6 9 10-23(8) 4-8(2) f Melanostomiatidae: Thysanactis dentex D 121-167 29(0) 86 — 14 30-48(4) — — N 121-174 51(5) 67 13 20 21-42(5) 14-29(3) f6 Eustomias bifilis D 50-90 40(5) 91 — 9 19-20(3) — — N 50-90 95(2) 85 4 11 17-47(10) — m,f D 91-165 36(5) 74 13 13 8-21(4) — m,f N 91-170 60(2) 91 5 3 15-33(3) — f Eustomias enbarbatus B 56-219 26(3) 78 13 9 16-41(2) — f Eustomias spp. (3,low) B 50-160 46(4) 79 7 14 17-32(6) — f Eustomias longibarba B 66-152 50(3) 79 9 11 24-42(5) 25(1) f Eustomias gibbsi B 61-141 35(3) 91 3 6 34-37(2) — f Eustomias spp. (3. hi) B 55-161 134(7) 83 9 8 17-34(10) — f Eustomias "silvescens" B 60-180 32(1) 68 6 26 23-48(8) — f Eustomias spp. (2) B 60-161 152(0) 80 8 12 17-76(18) 14(1) f Bathophilus kingi B 24-140 3(2) 76 17 7 23-40(3) — f Bathophiius spp. B 26-90 27(3) 67 21 12 45-67(3) — f Photonectes spp B 22-78 14(2) 42 25 33 34-72(4) — f B 132-240 10(0) 90 — 10 26(1) 16(1) — Leptostomias spp B 35-290 31(2) 83 7 10 13-29(3) — f Melanostomias spp B 62-165 8(0) 75 12 12 33(1) — f Stomiatidae: Stomias danae B 42-183 12(0) 75 8 17 24-33(2) — f Malacosteidae: Aristostomias spp. B 33-140 25(8) 71 24 6 35(1) — m.f Photostomias spp B 29-51 37(6) 68 13 19 — 9-30(4) s.c Photostomias sp. 1 B 52-102 73(4) 74 16 10 — 15-28(8) s,c Photostomias sp. 2 B 51-90 54(2) 67 21 12 — 29-42(6) s.c Photostomias sp. 2 B 91-140 38(1) 89 8 3 — 30(1) s.c Small intact items also recorded: 'Euchirella sp. 2Pleuromamma xiphias, candean larva, pyrosome. 3Oncaea spp , ostracod. 4P. xiphias, P. abdommalis, euphausiid larva. 5P. xiphias, Euchirella sp. 6lsopod. fishes eaten by the smallest size group were rela- tively larger (30-63%) than the fishes from the larger C. sloani (14-29% with one exception) or any of the crustaceans (10-20%). Of the 28 fish eaten, 18 were myctophids of at least 5 different genera (Ceratoscopelus, Hygophum, Notolych- wus, Lampcuiyetus, and T ri phot u run); five others were definitely not myctophids and included one and probably a second Vinciguerria nimbaria and what was most likely a Bregmaceros sp. 295 FISHERY BULLETIN: VOL. 80, NO. 2 Table 7. — Summary of stomach analyses of planktivorous sizes of Astronesthes indicus and Thysanactis dentex. For large prey types, the range of relative lengths in percentage of predator length is given in parentheses after the count. Data for larger fishes of both species are in Table 6. Astronesthes indicus Thysanactis dentex Size (SL, mm) 15-30 31 ■60 43-90 91- 120 Time Day Night Day Night Day Night Day Night No. examined (No. damaged) 23(0) 37(1) 43(1) 55(2) 78(1) 104(3) 37(0) 79(5) Percent undamaged: Empty 70 67 86 77 57 44 73 68 Remains only — 3 2 4 10 19 8 8 Intact items 30 31 12 19 32 38 19 24 Intact large items 4 8 2 9 16 21 16 22 No. of prey type: Eucalanus sp. — 1 — — — — — — Aetideidae 3 — — — 8 8 — 2 Scolecithrix danae 3 6 1 2 — — — — Scottocalanus spp. — 1 1 4 1 — — — Pleuromamma xiphias 1 — — — 24 21 2 13 Pleuromamma abdominalis — — — — 5 3 — 3 Other calanoid 6 3 — 5 5 3 — — Oncaea spp 16 9 1 4 — — — — Aegisthes sp. — 1 — — — — — — Euphausia spp 1(21) 2(19-35) 1(14) 4(12-30) 2(7-13) 3(10-13) 1(10) 3(10-11) Nematoscelis sp. — — — — — 1(11) — — Thysanopoda aequalis — 1(21) — — 8(12-19) 18(11-19) 1(10) 4(10-13) Thysanopoda spp — — — 1(30) 1(24) 3(23) 1(22) 3(21-28) Euphausiid larva 3 6 1 1 2 1 — — Decapod larva — 1 — — — 1 — — Sergestes spp — — — — — 2(18-20) — 1(11) Ostracod 21 15 14 8 — 1 — — Fish — — — — 2(23-24) 3(15-36) 3(16-43) 7(18-53) Idiacanthidae All sizes of Idiacanthus fasciola had eaten fish nearly exclusively (Table 6). Of the 23 fish, 15 were myctophids of at least 5 genera (Bolinich- thys, Ceratoscopelus, Diaphus, Lamp any ctus, and Triphoturus). Only one of the others, possibly a stomiatoid, was definitely not a myctophid. The largest prey of all sizes of /. fasciola were about 20% of the predator's length, but the minimum and average relative size of prey were somewhat higher in the small /. fasciola. The only two crus- taceans found were intact, but neither appeared to have been very recently ingested. No crusta- cean remains were found, and the two intact crustaceans were smaller than all (substantially smaller than most) of the fishes eaten. Two other, smaller items — a pyroosome and a copepod — found in /. fasciola were not counted because they showed no sign of digestion or compression. Thus /. fasciola must have occasionally fed in the net and may have ingested the crustaceans there. Whatever the case, crustaceans are certainly a very minor part of the diet. Melanostomiatidae Thysanactis dentex under 120 mm SL had eaten zooplankton as well as large prey (Table 7). The 43-90 mm size group had eaten small eu- phausiids — mostly Thysanopoda aequalis 11- 19% of their length— and large, pigmented cope- pods — mostly Pleuromamma xiphias; however, several relatively larger (15-36% of SL) fishes, Thysanopoda spp., and sergestids were also found. Fish 91-120 mm had eaten copepods and small euphausiids much less frequently; the bulk of the diet was relatively large fish and crusta- ceans. With the exception of a single isopod, the items and remains from fish >120 mm (Table 6) included only relatively large prey: other fishes, a large Thysanopoda spp., and two sergestids. Of the 24 intact fishes from all sizes of Thysanactis dentex, 9 were definitely myctophids of at least 5 different genera (Bolinichthys, Diaphus, Diogen- ichthys, Lampadena, and Triphoturus), and 11 were definitely of other families, including 6 Bregmaceros spp. and 2 Melamphaes spp. Most of the high values of relative size were for the slen- der Bregmaceros spp. The three B. japonicus from the 91-120 mm SL Thysanactis dentex were 45-53% compared with 11-28% for the remaining fishes and large crustaceans. Among the prey from T dentex, over 120 mm SL, the three Breg- maceros sp. (c.f. B. macclellandi) ranged from 39 to 42%, while with the exception of an unidenti- fied fish at 48%, the remaining fish prey were 14- 32%. There were approximately 30 species of Eu- stomias in the collections, many of them either 296 CLARKE: FEEDING HABITS OF STOMIATOID FISHES undescribed or of uncertain status. Eustomias bifilis was the only one for which large numbers were available, and only 4 others were repre- sented by more than 25 specimens (Table 6). The remaining identifiable species were pooled according to pectoral ray and photophore counts along with specimens whose barbels had been damaged and could not be identified to species. Those designated "3, low" were all damaged spec- imens with 3 pectoral rays and 15 or fewer VAL and VAV photophores. Eustomias bifilis and E. enbarbatus were the only other species from the area with the same counts. Those designated "3, hi" included 69 specimens of at least 6 unde- scribed species and 65 damaged specimens, all with 3 pectoral rays and over 15 VAL and VAV photophores — the same counts as for E. longi- barba and E. gibbsi. Those designated "2" in- cluded 6 damaged specimens and 146 others of about 20 species, which, like E. "silvescens," had only two pectoral rays. The 2-rayed species have shorter and generally more ornate barbels than any of the 3-rayed species (cf. illustrations in Morrow and Gibbs 1964). All prey items and remains from the 3-rayed species with low counts were fish. Of 20 intact items from E. bifilis, 11 were the myctophid Bolinichthys loyigipes and 6 were myctophids of at least 3 other genera {Benthosema, Diogenich- thys, and Hygophum). One of the three unidenti- fied items was definitely not a myctophid and was probably a Howella sp. The range of relative size of prey (15-34% of SL) was large, but there was no trend with the size of the predator. One and probably both of the intact fish found in E. enbarbatus were Howella sp. The six intact items from the damaged specimens (most of which were probably the abundant E. bifilis) included three Bolinichthys longipes, a Benthosema, an un- identified myctophid, and an unidentified fish. The prey of E. longibarba, E. gibbsi, and the other species with three pectoral rays and high photophore counts were, with one exception, fish. Of the 17 intact fish, 15 were myctophids includ- ing 7 and probably 8 Bolinichthys longipes and at least 2 other genera (Benthosema and Cerato- scopelus). The median relative size of fish prey for these Eustomias spp. (25%) was significantly higher (P<0.05, Mann-Whitney test, one-tailed probability) than that for the Eustomias spp. with three rays and low photophore counts (20.5%). One specimen of E. longibarba had eaten a large euphausiid, Thysanopoda pectinata. One of the Eustomias spp. with two pectoral rays had eaten asergestid shrimp, but all other prey of this group were fish. These Eustomias spp. appeared to eat fewer and different mycto- phids than did any of the 3-rayed species. Eu- stomas "silvescens" (cf. fig. 106A in Morrow and Gibbs 1964), the most commonly taken species of this group, had eaten three Scopelosaurus spp., three myctophids (two Bolinichthys longipes and a Diaphus), and two unidentified fish. Stomachs of the remaining species contained a total of 18 intact fish: 12 myctophids, 2 Howella sp., and 4 Scopelosaurus spp. (plus 2 more of the latter that were too digested to measure). Five and probably six of the myctophids were Diaphus spp., and only three and probably four were B. longipes. In the 3-rayed species of Eustomias, Diaphus was found only once, and B. longipes was the most common prey. Although data are too few to be certain, some of the 2-rayed species appeared to have diets that were restricted or included high proportions of relatively rare fishes. For one un- described form, all four items were Diaphus spp.; for another, two out of four were Howella sp.; and for a third and fourth, two out of two items and two out of four remains, respectively, were Scopelosaurus spp. The median relative size of prey of the 2-rayed species (27%) was sig- nificantly (P = 0.01) higher than that for the 3- rayed species with low counts, but did not differ from that for the 3-rayed species with high counts. The two crustaceans recorded from Eustomias spp. appear suspicious and indicative of postcap- ture ingestion, especially since no digested crus- tacean remains were found in any of the stom- achs. The two items showed no obvious signs of having been eaten after capture, but neither were they much digested. The only indirect evi- dence that these were actual prey items and not eaten in the net is that I have found both crusta- ceans and their remains in the stomachs of several E. bulbornatus, a species which does not occur in the study area. Since at least one species of the genus appears to eat crustaceans, it is pos- sible that others may do so occasionally. Based upon a limited amount of data (Table 6), the remaining melanostomiatid genera, as well as Stomias danae (Stomiatidae) and the Aristo- stomias spp. (Malacosteidae), are piscivorous. All the identifiable fish eaten by these species were myctophids. All three items from Lepto- stomias spp. were Notolychnus valdiviae. The relative size of prey of the small Photonectes spp. and several of the Bathophilus spp. was high— 297 FISHERY BULLETIN: VOL. 80. NO. 2 over 50% in several cases. The only crustacean found was a partially digested penaeidean shrimp, together with a myctophid, in a large Photonectes sp. Malacosteidae Only 24 items were found in the 100 Malacos- teusniger examined (Table 8). The most frequent items were copepods; these included some small harpacticoids, but most were large aetideids or scolecithridids. Similar-sized Pleuromamma xiphias were conspicuously absent. Two fish (86 and 93 mm SL) had eaten somewhat larger prey, and remains of relatively large prey were found only in the three largest fish examined. The inci- dence of intact prey was much lower in the larger of the two size groups. As indicated in Clarke (1974), two species of Photostomias occur near Hawaii; neither is iden- tical with P. guernei, the only presently recog- nized species. The form designated species 1 here matures at about 60 mm SL and grows to ca. 100 mm SL, while species 2 matures at about 120 mm SL and grows to >150 mm SL. Individuals less than ca. 50 mm SL cannot be reliably separated. The data given in Table 6 are limited to speci- mens that were analyzed after I had learned to separate the species as well as possible; the text below, however, also includes prey identifica- tions and relative sizes from 54 other specimens from earlier collections. These 54 specimens were no longer conveniently available to me after Table 8.— Summary of stomach analyses of Malacosteus niger with list of all items and remains found. % undamaged specimens Size (SL, mm) No. examined (damaged) Empty Remains only Intact items 24-90 44(3) 71 2 27 91-188 56(0) 88 4 9 SL — items or remains: 30 Undeuchaeta plumosa 37 Candacia longimana, Chirundina streets/, aetideid CV, cope- pod remains 61 Undeuchaeta major 70 Oncaea sp 70 remains of 3-4 copepods 71 2 C. streets/, 2 U. major, Euchirella curticauda 80 2 C. streetsi, U. plumosa, Lophothrix sp. 81 aetideid CV 84 Oncaea sp. 85 Oncaea sp 86 Lophothrix sp., Euphausia hemigibba, myctophid (10 mm SL) 87 Sapphirina sp. 93 Nematoscelis tenella 96 Amallothrix sp. 97 Euchirella sp.. remains Scaphocalanus sp. 101 Corycaeus sp 110 Thysanopoda sp. remains 111 Gaetanus kruppi, fish remains 188 fish remains I had learned to separate the species, and could not be identified with certainty from notes taken at the time of examination. Both species ate crustaceans exclusively, and with few exceptions the prey and identifiable re- mains were sergestid shrimps, mostly small Ser- gestes spp. Two large individuals of species 2 had eaten Gennadas spp., and an unidentified small specimen had eaten a Nematobrachion, the only euphausiid found. Aside from the Gennadas occurring only in species 2, there was no evidence of difference in diet between the two species. Ex- cept for a juvenile shrimp eaten by a small fish, relative length of prey was 15-42% of SL with a median of 28.5%. DISCUSSION Vinciguerria nimbaria, V. poweriae, Valenci- ennellus tripunctulatus, Danaphos oculatus, and Gonostoma atlanticum and small G. elongatum, G. ebelingi, and Diplophus taenia were planktiv- orous, i.e., almost all prey were <5-10 mm long. Clarke (1978) showed that four of these species feed primarily by day, and the limited data here indicated that Vinciguerria poweriae does also. The majority of the diets of V. n imbaria and V. poweriae <30 mm SL consisted of small cope- pods and ostracods. Vinciguerria nimbaria >30 mm SL appeared to feed mostly on substantially larger prey — amphipods and small euphausiids, but large calanoid copepods were not important at any size. In the western Pacific, V. nimbaria, apparently smaller than the smallest size group covered here, were also reported to feed mostly on small copepods and ostracods (Ozawa et al. 1977). Certain prey types found in stomachs of V. nimbaria, e.g., Scolecithrix danae, Paracandacia spp., Oncaea venusta, Stylocheiron spp., were either absent or very rare in the daytime plank- ton samples, but most were present at moder- ately high densities within the nighttime depth range of V. nimbaria (Clarke 1980). Based on diel changes in state of digestion of prey, Ozawa et al. (1977) concluded that V. nimbaria fed at sunset and at sunrise; their evidence for feeding at sunrise is indirect and equivocal. Clarke's (1978) data do not preclude feeding during the upward migration at sunset, but give no indica- tion of feeding at night or sunrise. Thus, while some of the prey types not present in the plankton by day may have been taken at sunset, it seems unlikely that any would remain intact until late 298 CLARKE: FEEDINC. HABITS OF STOMIATOID FISHES afternoon (when two of the day trawls were made) the next day. Vinciguerria nimbaria could conceivably undertake short, irregular excursions to shallower water during the day, or alternatively, may have a strong preference for rare, but perhaps vulnerable "stragglers" from populations with shallower centers of abun- dance. For several prey types, most of the items re- corded were found together in one or a few of the fish examined. This indicates that V. nimbaria often feeds on patches or aggregations of certain prey types. My earlier observation (Clarke 1978) that V. nimbaria stomachs tend to be either quite full or nearly empty throughout the day is also indicative of encounters with patches of prey. Since patchiness would increase the variability of encounter rates by both individual fish and the plankton nets, this might explain why some prey types were poorly represented by the few plank- ton samples as well as the large apparent differ- ences in diet between small samples of fish. Wherever and however V. nimbaria feeds, it clearly showed preference for certain prey types. Some types which were abundant in the zoo- plankton samples, e.g., Oncaea spp., Clausocal- anus spp., small ostracods, were eaten frequently by fish <30 mm SL; but many other types, e.g., Eucalanus spp., scolecithricids (except Scoleci- thrix danae), Metridia spp., large Pleuromamma spp., and chaetognaths, also abundant were either absent or poorly represented in the diet. The types poorly represented in the diet were mostly either larger, less pigmented, or more translucent than those frequently eaten, regard- less of whether the latter were rare or abundant in the plankton. The diet and apparent prefer- ences of small V. nimbaria are most similar to but not identical with myctophids such as Ben- thosema suborbital and Bolinichthys longipes which feed on small zooplankton (Clarke 1980). Vinciguerria nimbaria >30 mm SL showed apparent preference for Stylocheiron spp. and amphipods, both of which were rather uncom- mon within the day depth range. In contrast to both the remaining planktivorous stomiatoids and several myctophids which also feed on large zooplankton (see below), V. nimbaria ignored the large calanoids which were fairly abundant at the deeper end of its depth range (Table 2). The diets of the remaining planktivorous sto- miatoids were nearly restricted to large cala- noids and small euphausiids. The cope pods eaten were fairly abundant within the day depth ranges of the fishes (Table 2), but were appar- ently preferred over similar-sized Eucalanus spp., augaptilids, and chaetognaths which were also fairly abundant. The latter types are very translucent compared with the types eaten and probably less detectable visually. The Gonosto- ma spp. and D. taenia have relatively smaller eyes than V. nimbaria (data given in Grey 1964). Thus, the apparent preferences of these gono- stomatids may result from their being poorly equipped to detect small, translucent, or other- wise less visible prey. (The sternoptychid species both have relatively large eyes, but they are tubular and directed upward, and are difficult to compare with the others.) The diets of the planktivorous stomiatoids ex- cept Vinciguerria spp. were not only similar to each other but to those of three common mycto- phids {Lampanyctus nobilis, L. steinbecki, and Triphoturus nigrescens), which also have rela- tively small eyes (Clarke 1980). Limited data on diet from Clarke (1978) indicates that the abun- dant myctophids of the Lampanyctus niger spe- cies group also feed similarly. Thus, although they feed at different depths and times, several coexisting species of fishes are utilizing the same resources and apparently feeding selectively for the same reasons; conversely, a relatively few species of large zooplankton — particularly P. xiphias and Euphausia spp. — are supporting a large fraction of the planktivorous fishes. Cer- tain small zooplankton, e.g., Oncaea spp. and P. gracilis, also appear to be heavily grazed by Vin- ciguerria and several other fishes from the same area (Clarke 1980), but overall there is less inter- specific overlap in diet and more evidence of dif- ferent feeding mechanisms among species which eat small zooplankton. Gonostoma elongatum, G. ebelingi, and D. tae- nia appear to be essentially planktivores that consume some large prey simply because they reach larger sizes than do the other planktivor- ous stomiatoids. All three have well-developed gill rakers, none have large fangs, and the car- diac portions of the stomach are not notably elon- gate. Similarly, to the small individuals, the large specimens usually contained several rela- tively small prey; relative size of most items was ca. 10% of SL with few over 20%. Most of the prey were crustaceans, euphausiids and sergistid shrimps, but some fish and squid were taken. The only evidence of selectivity was the repeated occurrence of the relatively uncommon amphi- pod, Vibilia spp., in D. taenia. 299 FISHERY BULLETIN: VOL. 80, NO. 2 The remaining species— of six families— all appear basically adapted for capture and inges- tion of relatively large prey. All have large fangs, none have well-developed gill rakers, and in most the cardiac portion of the stomach is elongate and, in some species, obviously capable of dis- tension to accommodate prey over one-half the predator's body length. All these species except Malacosteus danae have eaten relatively large prey (usually at least 20% of SL) at all sizes and most of them exclusively such items. There was rarely more than one prey item in a stomach. Juvenile Thysanactis dentex and Astronesthes spp. — especially A. indicus — were the only fishes of this group that routinely ate zooplankton. Those consumed by small A. indicus were ostra- cods and small copepods, generally similar to the diet of Vinciguerria nimbaria. The juvenile T. dentex, which were larger than the planktivorous stages of A. indicus, had eaten mostly large cala- noids and small euphausiids, essentially the same eaten by similar-sized Gonostoma spp. In both species, however, the incidence of relatively large prey was as high in the small planktivorous stages as in the sizes which ate only large prey. Thus, rather than changing with growth from small to large prey (but of the same range of rela- tive size), these species appear to prey on an in- creasingly narrower range of relative sizes of prey. Most of the nekton-eating stomiatoids were principally or exclusively piscivorous. The Pho- tostomias spp. were the only ones that never ate fish. The relatively large prey of juvenile A indi- cus and A. "cyaneus" were euphausiids, but there was limited evidence that adults of both species are piscivorous. The smallest size group of Chauliodus sloani and all sizes of T. dentex had eaten some relatively large euphausiids or serge- stids; usually these were relatively smaller than the fishes eaten. Otherwise, crustaceans were either a minor or suspect part of the diet. The systematic examinations of fairly large numbers of specimens by Beebe and Crane (1939), Legand and Rivaton (1969), and Borodu- lina (1972), and many other isolated reports in the literature generally agree that species of the six families considered as nekton-eating here eat primarily or exclusively relatively large prey which are usually fish. The only well-documented exception is Tactostoma macropus, which ap- pears to eat only euphausiids and sergestids (Borodulina 1972). Notes by Fitch and Laven- berg (1968) indicate that off California several congeners of piscivorous Hawaiian species rou- tinely eat crustaceans and that one, Bathophilus flemingi, eats "small crustaceans almost exclu- sively." The discrepancies may be artifacts due to differences in towing speed (not given by Fitch and Lavenberg and most other studies). The same types of differences were observed between specimens from the same area collected at speeds of over or under ca. 1.5 m/s (see Methods). There was evidence of selectivity by the preda- tors among the potential prey fishes. All but one of the fishes identified from stomachs were ver- tically migrating species; in particular, the non- migrating Cyclothone and Sternoptyx, which are abundant within the day depth ranges of the predators, were absent from the diets of all pred- ators except Heterophotus ophistoma. Other stomiatoids, particularly the abundant Vinci- guerria spp., were underrepresented, and the abundant myctophids of the L. niger complex were absent. Based on the relative abundances of different migrating fishes in the study area (Table 9), several species of predators took cer- Table 9.— Relative abundance and estimated average biomass (wet weight) of vertically migrating fishes based on data from 58 oblique trawls taken at night near Oahu, Hawaii, in 1977- 78. Total number of fishes caught was 14,084. Relative abun- dance is expressed as percent of total myctophids, the domi- nant group. Relative al Dundance as % of total myctophids Average biomass Species Numbers Biomass (gm/103/m2) Stomiatoids: Small planktivores 1.2 5.4 Vinciguerria spp 130 Others 2.8 Gonostoma spp , Diplophus taenia 7.6 18 1 808 Nekton-eating species 15.9 664 Astronesthes spp 0.7 Chauliodus sloani 04 Idiacanthus fasciola 9 1 2 Thysanactis dentex 0.9 Eustomias spp. 08 Photostomias spp 06 Others 0.6 Myctophids: 100 4555 Lampanyctus "niger" complex 13.0 Lampanyctus spp (others) 25.6 Ceratoscopelus warmingi 14.2 Diaphus spp 12.6 Notolychnus valdiviae 12.0 Triphoturus nigrescens 5.1 Benthosema suborbital 5.1 Bolinichthys longipes 34 Others 89 Other planktivores: 62 276 Melamphaeidae 3.7 Bregmaceros spp. 1.8 Cheilodipteridae, Notosudidae, etc. 0.9 Other nekton-eating species: 4.5 20.2 Eels 0.5 Iniomi. Trichiuroids, Chiasmodontidae, etc. 1.3 :um CLARKK: FKKDINC HABITS OF STOMIATOII) FISIIKS tain prey species much more frequently than would be predicted by random nonselective feed- ing. Examples include nonmyctophids, particu- larly Bregmaceros spp., in the diet of Thysanactis dentex; Bolinichthys longipes in Eustomias bifi- lis; Howella spp. in E. enbarbatus; Diaphusspp., Howella spp., and Scopelosaurus spp. in the Eustomias spp. with two pectoral rays; and Noto- lychnus valdiviae in Leptostomias spp. The prob- ability of drawing at random, e.g., two Howella spp. or two Scopelosaurus spp. out of two fish from the fauna is very low. The relative sizes of fish prey for most species of predators were 20-30% of SL. Many of the val- ues over 30% were for relatively slender prey such as Bregmaceros or Scopelosaurus. Only the Bathophilus and Photonectes spp. and small Chauliodus sloani appeared to take prey >30% routinely. The values for /. fasciola were mostly <20%; this species is, however, so slender that the relative size in terms of head length or body weight would be more like those for the other species. If the weights of predator and prey were both similarly related to the cube of the length, then 20-30% relative length gives a value of 0.8-2.7% of body weight per item. If anything, this is prob- ably an underestimate of average prey size, since the predators are for the most part slenderer than their prey. Also the stomiatoids seem to be softer bodied than most of their prey and may have a higher water content (cf. Blaxter et al. 1971); this would mean that relative prey size in terms of dry weight is higher. Borodulina (1972) gives lengths (SL ?) and wet weights of 14 fish prey and stomiatoid predators. The relative lengths of prey were 12-52% and relative weights 0.1-2.8%. The latter are probably underestimates of relative weight since some losses of prey weight must have occurred even in specimens still intact enough to be measured. With the exceptions of A. indicus and T. den- tex, all species with chin barbels fed exclusively or nearly so on relatively large fish. The barbel is rudimentary in C. sloani, which was also pisciv- orous except at the smallest sizes, but C. sloani has an elongated first dorsal ray with a light organ on the tip. Of the other nekton-eating spe- cies without barbels, fish were absent from the diets of the Photostomias spp. and eaten only by the largest M. niger and A. "cyaneus." The large gonostomatids also lack a barbel. Fish were less frequent than large crustaceans in their diets and were relatively smaller than fishes eaten by the predators with barbels. Tactostoma macro- pus, the only melanostomiatid known to eat pri- marily crustaceans (Borodulina 1972), has the smallest and most rudimentary barbel in the family. Although there are no directly supportive data or citations, it is undoubtedly true that in the open ocean, crustaceans far outnumber fishes at lengths <15-20 mm; for lengths >25-35 mm the opposite is probably true. It is also probably true that a fully metamorphosed fish is a faster swim- mer than a similar-sized crustacean and, other things being equal, more likely to evade capture when attacked by a predator. Thus a predator which preferred items 20-30% of its length and actively searched for prey would have a diet simi- lar to those of A. indicus and A. "cyaneus." The small predators would encounter crustaceans much more frequently and probably capture those encountered more frequently than they would fish, while the large predators would almost be forced into piscivory due to the relative rarity of appropriate-sized crustaceans. If the predator preferred prey only 10% of its body length, the diet would resemble those of the large Gonostoma spp., where even the largest individ- uals (100-200 mm) would still encounter more crustaceans than fish in the appropriate size range. Most of the fishes with barbels must either re- ject crustaceans encountered or feed other than by active search. A plausible and likely hypoth- esis (which has been suggested by others) is that they are "passive" and use the luminescent bodies in the barbel to attract prey. Bertelsen (1951) developed a similar hypothesis for the ceratioid angler fishes. Since several of the prey fishes are not known to be bioluminescent them- selves, it is most probable that the barbel mimics food of the prey species — most of which appear to be primarily visual feeders (see above) — rather than a conspecific of the prey. The large crusta- ceans apparently are not similarly attracted; this is not surprising in view of their very different eyes and probably different diet and feeding be- havior. Thus the barbel may be an adaptation for attracting and perhaps aiding in capture of rela- tively large fish. This mechanism could allow these stomiatoids to subsist on relatively large prey whose densities are quite low (on the order of 1/m2 of sea surface, see Maynard et al. 1975) with less energy expenditure than would be re- quired for active search and capture. Further- more, assuming the findings of Pandian (1967) 301 FISHERY BULLETIN: VOL. 80. NO. 2 are generally true, the fish, which appear to be preferentially attracted, would be more effi- ciently digested and converted than crustaceans. Chin barbels (and the first dorsal ray of Chau- liodus) are not fully developed until after meta- morphosis; for most species covered here, the smallest specimens examined (Tables 6, 7) are roughly the size at which the barbel appears fully developed. The Astronesthes spp. are quite small at metamorphosis, and it is not surprising that they apparently eat some of the zooplankton encountered regardless of whether or not they possess a barbel. Likewise, newly metamor- phosed C. sloani would be expected to encounter so many more appropriate-sized crustaceans than fish that it would include some of the former in its diet. Bertelsen (1951) has similarly sug- gested that juvenile ceratioids eat some items as a result of visual detection and capture rather than by use of their lures. (The Bathophilus and Photonectes spp. are almost as small at metamor- phosis as C. sloani, but, perhaps because they can handle relatively larger prey, appear to feed in the passive mode immediately after acquiring a barbel.) Astronesthes indieus, however, continues to feed like the barbelless A. "cyaneus" i.e., as would be predicted for an actively searching spe- cies, until at least up to ca. 60 mm. Astronesthes indieus is unique in that the barbel is not fully developed shortly after metamorphosis but changes considerably as the fish approaches adult size (Gibbs 1964); consequently, it may not begin to feed passively until later. Thysanactis dentex has a well-developed bar- bel, metamorphoses at rather large size, and appears to capture fish as frequently as the other species with barbels; but it also feeds on zoo- plankton until it is fairly large and includes rela- tively large crustaceans in its diet at all sizes. It thus appears to feed as an actively searching visual predator as well as by using the barbel. In spite of the advantages suggested for passive feeding, T. dentex is obviously successful at com- bining both methods; except for Idiacanthus fasciola, it is by far the most common species of the barbelled stomiatoids in the study area (Table 9). Assuming that the above hypotheses are valid, then evidence for selective feeding by some spe- cies indicates that interspecific differences in barbel morphology and, perhaps, methods of de- ployment have evolved to specialize in attraction of a restricted type of prey, i.e., some of the spe- cies may be analogous to devoted aficionados of fly fishing in Homo sapiens. Although even the "general ist" T. dentex showed some evidence of preference for certain fishes, most evidence of re- stricted diets was from Eustomias, which is the most speciose genus considered and also has the most varied and ornate barbels. If sufficient data become available, it would be pertinent to com- pare the degree of preference in Eustomias with, e.g., Bathophilus or Aristostomias, in which all the species have similar and rather plain bar- bels. Regardless of whether the barbel is used or not, the advantages of specialization in diet, such as increased efficiency of capture, must be great. The overall density of prey in the study area is low compared with other oceanic areas, and much current ecological theory (e.g., Schoener 1971; Werner and Hall 1974) would predict broad diets rather than restriction to a single prey type such as Scopelosaurus spp., whose den- sity is <1% of the already low total fish density. The Photostomias spp. have no obvious fea- tures that would predict a diet restricted almost totally to sergestids. Though they lack a barbel, this would not explain the total absence of fish from the diet. The absence of caridean shrimps from their diet, as well as from those of the other species, may be related to stouter exoskeleton and heavier spines in these shrimps than in ser- gestids, but there are no such features to suggest why the very abundant large euphausiids and penaeid shrimps are also nearly completely ignored. Photostomias must either be able to attack and detect only sergestids or have some method of luring only them into proximity. Malacosteus niger is the only "nekton-eating" predator which does not vertically migrate (Clarke 1974). Zooplankton densities within most of its depth range are low both day and night, but by day it overlaps with several abundant ver- tically migrating fishes as well as sergestids (Walters 1977) and large euphausiids (Hu 1978). Since this species is apparently well adapted for ingestion of large prey, has one of the largest gapes of all stomiatoids (Morrow 1964), and is so poorly adapted for small prey — no gill rakers or floor to the mouth, it is all the more perplexing that it had eaten so few relatively large items. It appears to subsist on a rather odd assortment of copepods. Among the nekton-eating species, there were few differences between day- and night-caught fish in the incidence of intact prey, and none of the differences were sufficiently large to allow any inference about feeding chronology. There 302 CLARKE: FEEDING HABITS OF STOMIATOII) FISHES is some indirect evidence for night feeding. Most of the predators are found with their prey both day and night; however, some prey, the Bregmaceros and Melamphaes spp., occur well below their predators during the day (Clarke and Wagner 1976) and could only have been eaten at night or during migration. The absence of nonmigrating species in the diets also indi- cates less or no feeding during the day. Finally, if the lures of these predators are used to attract fish which are themselves actively searching for prey, the high frequency of species which feed in the upper layers at night and the low frequency of day-feeding, but vertically migrating, stomia- toids also indicates night feeding by the preda- tors. The average biomass of the nekton-eating stomiatoids in the study area was a substantial fraction of that of their prey (Table 9) and indi- cates that they are probably an important source of mortality to the prey species. An estimate of the stomiatoids' impact on the prey populations can be made from the catch and stomach content data from the 1977-78 series of oblique trawl tows and estimates of stomach evacuation time. The entire series of tows caught 17,543 vertically migrating planktivorous fish of the types eaten by the stomiatoids: Myctophids, exclusive of the Lampanyctus niger complex, plus other non- stomiatoid planktivores. The same tows caught 822 nekton-eating stomiatoids, exclusive of Pho- tostomias spp. A minimum of 111 fishes or fish remains were found in the stomachs of these predators. If the totals from this extensive series of samples are taken as representative of the average state in the study area, then on the aver- age the nekton-eating stomiatoids consume 0.63% of the prey numbers over a period of time equal to that required to evacuate the stomach. This estimate is likely to be low because both feeding incidence of the predators and their numbers relative to the prey are probably under- estimated. There were 107 stomiatoids whose stomachs were ruptured, and any prey they might have contained are not included. In fact, it is possible that individuals with distended stom- achs were more susceptible to damage during capture and consequently, that the incidence of prey in the damaged specimens might have been higher than in the undamaged ones. The num- bers of both predators and prey caught by the trawls are both negatively biased due to avoid- ance of the net, but there is evidence that the larger stomiatoids, especially Astronesthes spp., are much better avoiders than the small plankti- vores (Clarke 1973, 1974). Unless there was a dif- ference in bias between stomiatoids with full and empty stomachs, this would also result in an underestimate of the percent of the prey popula- tion consumed. There are no available data to directly esti- mate the time required to evacuate the stomach for these fishes, but studies of other fishes fed comparable sized meals indicate that evacuation time is no longer than 4 d and probably less. Evacuation times determined at temperatures similar to those encountered by the stomiatoids at night (15°-25°C) are mostly less than a day (Pandian 1967; several studies summarized by Magnuson 1969); at temperatures similar to those of the day depths (4°-5°C) values are 2-4 d (Tyler 1970; Popova and Sytina 1977). If evacuation time were 4 d, the annual consumption by stomiatoids would be 57.5% of the average standing crop of prey (0.63% X 365/4); if the time were 1 d, con- sumption would be 2.3 times the standing crop. Although annual production by vertically mi- grating planktivorous fishes probably exceeds the average standing crop (Clarke 1973), the esti- mated consumption by piscivorous stomiatoids indicates that the latter account for a large and possibly predominant share of the former's pro- duction. Though stomiatoids appear to be the most abundant piscivores, consumption of the migrators by other, similar-sized predators, e.g., scopelarchids, chiasmodontids, trichiuroids, eels, and squids, is also likely to be substantial. The migrating planktivorous fishes, in turn, appear to be the dominant group of plankton con- sumers in the tropical open ocean (Clarke 1973; Maynard et al. 1975). Together, these indicate that a large fraction of primary production is eventually channeled into small predators, smaller than the average planktivore in many other parts of the ocean, rather than into large, commercially harvestable species. ACKNOWLEDGMENTS I am indebted to many people who assisted in collection and sorting of the samples from which these fishes were taken and also to the crew of the RV's Teritu, Moana Wave, and Kana Keoki. K. Gopalakrishnan identified most of theeuphausi- ids and decapods and capably taught me how to identify the remainder. This research was sup- ported by NSF GA-38423, NSF OCE 77-09202, and the Hawaii Institute of Marine Biology. 303 FISHERY BULLETIN: VOL. 80, NO. 2 LITERATURE CITED Beebe, W„ and J. Crane. 1939. Deep-sea fishes of the Bermuda Oceanographic Expeditions. Family Melanostomiatidae. Zoologica 24:65-238. Bertelson, E. 1951. The ceratioid fishes. Dana Rep. Carlsberg Found. 89, 276 p. Blaxter, J. H. S., C. S. Wardle, and B. L. Roberts. 1971. Aspects of the circulatory physiology and muscle systems of deep-sea fish. J. Mar. Biol. Assoc. U.K. 51:991-1006. Borodulina, 0. D. 1972. The feeding of mesopelagic predatory fish in the open ocean. J. Ichthyol. 12:692-703. Clarke, T. A. 1973. Some aspects of the ecology of lanternf ishes (Mycto- phidae) in the Pacific Ocean near Hawaii. Fish. Bull., U.S. 71:401-434. 1974. Some aspects of the ecology of stomiatoid fishes in the Pacific Ocean near Hawaii. Fish. Bull., U.S. 72:337-351. 1978. Diel feeding patterns of 16 species of mesopelagic fishes from Hawaiian waters. Fish. Bull., U.S. 76:495- 513. 1980. Diets of fourteen species of vertically migrating mesopelagic fishes in Hawaiian waters. Fish. Bull., U.S. 78:619-640. Clarke, T. A., and P. J. Wagner. 1976. Vertical distribution and other aspects of the ecol- ogy of certain mesopelagic fishes taken near Hawaii. Fish. Bull., U.S. 74:635-645. Fitch, J. E., and R. J. Lavenberg. 1968. Deep-water teleostean fishes of California. Univ. Calif. Press, Berkeley, 155 p. Gibbs, R. H., Jr. 1964. Family Astronesthidae. In Y. M. Olsen (editor), Fishes of the western North Atlantic. Part 4, p. 311-350. Mem. Sears Found. Mar. Res., Yale Univ., 1. Grey, M. 1964. Family Gonostomatidae. In Y. M. Olsen (editor), Fishes of the western North Atlantic. Part 4, p. 78-240. Mem. Sears Found. Mar. Res., Yale Univ., 1. Hu, V.J. M. 1978. Relationships between vertical migration and diet in four species of euphausiids. Limnol. Oceanogr. 23:296-306. Legand, M., and J. Rivaton. 1969. Cycles biologiques des poissons mesopelagiques de l'estde l'Ocean Indien. Troisieme note: Action predatrice des poissons micronectoniques. Cah. O.R.S.T.O.M., ser. Oceanogr. 7:29-45. Magnuson, J. J. 1969. Digestion and food consumption by skipjack tuna (Katsuwonus pelamis). Trans. Am. Fish. Soc. 98:379- 392. Maynard, S. D., F. V. Riggs, and J. F. Walters. 1975. Mesopelagic micronekton in Hawaiian waters: Faunal composition, standing stock, and diel vertical migration. Fish. Bull., U.S. 73:726-736. Morrow, J. E., Jr. 1964. Family Malacosteidae. In Y. M. Olsen (editor), Fishes of the western North Atlantic. Part 4, p. 523-549. Mem. Sears Found. Mar. Res., Yale Univ., 1. Morrow, J. E., Jr., and R. H. Gibbs, Jr. 1964. Family Melanostomiatidae. In Y. M. Olsen (edi- tor), Fishes of the western North Atlantic. Part 4, p. 351- 511. Mem. Sears Found. Mar. Res., Yale Univ., 1. Ozawa, T., K. Fujh, and K. Kawaguchi. 1977. Feeding chronology of the vertically migrating gonostomatid fish, Vinciguerria nimbaria (Jordan and Williams), off southern Japan. J. Oceanogr. Soc. Jpn. 33:320-327. Pandian, T. J. 1967. Transformation of food in the fish Megalops cypri- noides. I. Influence of quality of food. Mar. Biol. (Berl.) 1:60-64. Popova, O. A., and L. A. Sytina. 1977. Food and feeding relations of Eurasian perch (Perca fluviatilis) and pikeperch (Stizostedion lucio- perca) in various waters of the USSR. J. Fish. Res. Board Can. 34:1559-1570. Schoener, T. W. 1971. Theory of feeding strategies. Annu. Rev. Ecol. Syst. 2:369-404. Tyler, A. V. 1970. Rates of gastric emptying in young cod. J. Fish. Res. Board Can. 27:1177-1189. Walters, J. F. 1977. Ecology of Hawaiian sergestid shrimps (Penaeidea: Sergestidae). Fish. Bull., U.S. 74:799-836. Werner, E. E., and D. J. Hall. 1974. Optimal foraging and the size selection of prey by bluegill sunfish (Lepomis macrochirus). Ecology 55:1042-1052. 304 DESCRIPTION OF LARVAE OF THE GOLDEN KING CRAB, LITHODES AEQUISPINA, REARED IN THE LABORATORY Evan Haynes1 ABSTRACT Larvae of golden king crab, Lithodes aequispina, were reared in the laboratory from Stage I through Stage V (glaucothoe). Each of the five larval stages is described and illustrated. Zoeae of L. aequ ispina are distinguished from zoeae of L. maja and L. anta rctica by the number of telsonic setae and the length of the posterolateral spines on somites 2-5. The glaucothoe of L. aequispina are dis- tinguished from glaucothoe of L. maja and L. antarctica by the terminal configuration of the carapace spines. Zoeae of L. aequispina are distinguished from zoeae of Paralithodes spp. by number of telsonic setae and by setation of the antennal flagellum. Morphological differences be- tween larvae of Lithodidae and Paguridae are greater than previously believed. Information on the larval stages of the genus Lithodes is meager — only the larvae of Lithodes maja (Linnaeus) from the North Atlantic Ocean and larvae of L. antarctica (Jacquinot) from the South Pacific Ocean have been described (Sars 1890; MacDonald et al. 1957; Campodonico 1971). In this paper, I describe larvae of the golden king crab, L. aequispina (Benedict), from the North Pacific Ocean and compare them with larvae of L. maja, L. antarctica, and Para- lithodes spp., and with larvae of the subfamily Pagurinae (family Paguridae). METHODS An ovigerous L. aequispina releasing larvae was collected from waters of southeastern Alaska (lat. 58°41.5'N, long. 135°05'W) during a National Marine Fisheries Service trawling survey. The specimen was caught 9 March 1979 at 292 m. Bottom water temperature was 2.3°C. The female was placed in about 2, 500 1 of filtered seawater at 2.3°C. Hatching resumed immedi- ately, and the first samples were taken about 10 min later. No prezoeae were seen. The samples were preserved in a 5% solution of Formalin2 and seawater. About 4 h after hatching, 10 larvae were trans- ferred to each of 30 250 ml jars containing about 200 ml of filtered seawater at 6.8°C. The jars were checked daily for exuviae, and a few larvae ■Northwest and Alaska Fisheries Center Auke Bay Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 155, Auke Bay, AK 99821. 2Reference to trade names does not imply endorsement by National Marine Fisheries Service, NOAA. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80. NO. 2. 1982. were preserved every other day. The individuals and cast skins of various stages provided a con- tinuous sequence of stages. Seawater in the holding containers was changed every other day, and the larvae were fed plankton daily that was strained through a 0.333 mm mesh. The density of food was controlled only to the extent that a few food items remained in the container at the end of each feeding period. Terminology, methods of measuring, tech- niques of illustration, and nomenclature of ap- pendages follow Haynes (1973, 1976). Setation formulae are the number of setae per segment from the distal segment to the proximal segment. For clarity in the illustrations, setules on setae are usually omitted, but spinulose setae are shown. A minimum of five larvae of each stage was used to verify segmentation and setation. Only those morphological characteristics useful for readily identifying each stage are given. STAGE I ZOEA Mean total length of Stage I zoeae (Fig. 1A), 7.3 mm (range 6.8-7.7 mm, 20 specimens). No chromatophores; internal thoracic area orange — coloration same throughout all larval stages. Rostrum slightly sinuate, without teeth, about three-fourths length of carapace. Posterolateral spines on carapace. Eyes sessile. Antennule (Fig. IB).— First antenna, or anten- nule, with unsegmented, tubular basal portion (peduncle) and two distal, conical projections. 305 FISHERY BULLETIN: VOL. 80, NO. 2 Left Right 0.25 mm 0.25 mm Figure 1.— Stage I zoea of Lithodes aequispina: A, whole animal, right side; B.antennule, dorsal; C, antenna, ventral; D, mandibles (left and right); E, maxillule, ventral; F, maxilla, dorsal; G, first maxilliped, lateral; H, third maxilliped, lateral; I. pereopods 1-5, Peduncle with simple seta terminally. Larger projection with two aesthetascs subterminally, four aesthetascs and two simple setae terminally. Smaller projection with aesthetasc and simple seta terminally. Antenna (Fig. 1C).— Second antenna (antenna) with inner flagellum (endopodrte) and outer antennal scale (exopodite). Naked flagellum un- segmented, slightly shorter than scale (scale length includes spine). Antennal scale unjointed 306 distally, fringed with 10 heavily plumose setae along terminal and inner margins; prominent spine distally on outer margin. Ventral surface of protopodite with spinulose spine at base of flagellum, naked spine at base of scale. Shape and spination of protopodite same as in later zoeal stages except fewer spinules on spinulose spine. Mandibles (Fig. ID).— With unsegmented palps in all larval stages. Incisor process of left man- HAYNES: DESCRIPTION OF GOLDEN KINO CRAB LARVAE L J 0.5 mm 0.5 mm L J 1 .0 mm lateral; J, abdomen and telson, dorsal; K, minute seta of telson, ventral. 0.25 mm dible a tooth; right mandible with diserrate incisor process. Anterior margins of each man- dible with three or four small teeth between incisor and molar processes. Neither mandible with subterminal tooth on molar process in any larval stage. Maxillule (Fig. IE).— First maxilla (maxillule) with coxal endites, basial endites, and endo- podite. Coxopodite (proximal lobe) two-seg- mented, distal segment with plumose seta and six spines: four spines spinulose, two simple. Basipodite (median lobe) with two spinulose spines terminally, simple seta subterminally. Endopodite originates from lateral margin of basipodite. Endopodite three-segmented with three setae terminally and one seta distally on second segment. Maxilla (Fig. IF).— Second maxilla (maxilla) with platelike exopodite (scaphognathite). Exo- podite with 11 long, evenly spaced plumose setae along outer margin. Future location of proximal expansion indicated by small lobe. Endopodites unsegmented in all larval stages; in Stage I, setation formula of endopodite 3, 1, 3. Basipodite and coxopodite bilobed. Basipodite with four setae on distal lobe, five setae on proximal lobe; coxopodite with four setae on distal lobe, six setae on proximal lobe. First maxilliped (Fig. 1G).— Most heavily setose of natatory appendages. Unsegmented proto- podite with 10 setae. Endopodite distinctly five- segmented; setation formula 4, 3, 1, 2, 3. Exo- podite a partially segmented long, slender ramus with four terminal natatory setae. Second maxilliped. — Essentially same as first maxilliped except endopodite four-segmented. Third maxilliped (Fig. 1H).— Endopodite and exopodite undeveloped, naked; exopodite two- segmented. Pereopods (Fig. II). — Poorly developed, without exopodites in all larval stages; segmentation may be indistinct. 307 FISHERY BULLETIN: VOL. 80, NO. 2 Pleopods (Fig. 1 A).— Absent on first somite in all larval stages; in Stage I, present on somites 2-5 as distinct buds. Pleopod 6 absent until Stage III. Abdomen and telson (Fig. 1A, J).— Abdomen with five somites and telson (somite 6 fused with telson until Stage IV). Somites 2-5 with pair of posterolateral spines, four short spines along posterior margin, pair of hairs near dorsopos- terior margin. Telson slightly emarginate posteriorly, with 11 + 11 (rarely 10 + 11) densely plumose setae. Ninth pair of setae on telson longest, almost one-third telson width. All setae jointed with the telson except ninth pair; ninth pair fused with telson. Minute plumose seta between setal pairs 10 and 11 (Fig. IK). Except outer pair of setae, setae with setules. Setules along terminal margin between bases of setae. Without uropods in all larval stages. Anal spine absent in all larval stages. STAGE II ZOEA Mean total length of Stage II zoeae, 7.5 mm (range 7.0-8.0 mm, 10 specimens). Rostrum and carapace same shape as in Stage I. Eyes stalked. Antennule (Fig. 2A).— Large plumose seta and three small simple setae at distal joint of unseg- mented peduncle. Antenna (Fig. 2B).— Two-segmented flagellum extends slightly beyond plumose setae of scale. Antennal scale with 9 (rarely 10) heavily plumose setae along terminal and inner mar- gins. Mcmdibles. — Essentially same as in Stage I except with a few more teeth along anterior margin and palp slightly larger. Maxillule. — Same as in Stage I except tip of basi- podite somewhat more rounded. Maxilla.— Scaphognathite (Fig. 2C) with 20 (sometimes 21) plumose setae along inner and outer margins; proximal expansion distinct, naked. Endopodite, basipodite, or coxopodite same as in Stage I except coxopodite occasionally with five setae on proximal lobe. Maxillipeds. — Similar to Stage I maxillipeds, but exopodites of maxillipeds two-segmented; pairs 1, 2, and 3 with 9, 9, and 8 natatory setae, respectively. Pereopods (Fig. 2D, pereopod 1).— Chelae of pereopod 1 similar to pereopod 1 of adult but without spines, setae, or teeth. Pereopods 2-5 same as in Stage I except longer and pereopod 5 four-segmented. 0.5 mm L 0.5 mm 0.25 mm 0.25 mm Figure 2.— Stage II zoea of Litkodes aequispina: A, antennule, dorsal; B, antenna, ventral; C, maxilla (scaphognathite), dorsal; D, pereopod 1, lateral. 308 HAYNES: DESCRIPTION OF GOLDEN KIN(J CRAB LARVAE Pleopods, — Pleopods 2-5 bilobed, unsegmented, without setae, about one-third height of somites. Abdomen and telson. — Abdomen same shape and spination as in Stage I. In Stages II-IV, telson with 12 + 12 (rarely 11 + 12) densely plumose setae; tenth setal pair longest (about one-fourth telson width), fused with telson. Telson fused with somite 6. STAGE III ZOEA Mean total length of Stage III zoeae, 7.6 mm (range 7.4-8.4 mm, 10 specimens). Rostrum (Fig. 3A) more styliform than in Stages I and II, about one-half carapace length, with short spine and minute hair at base. Lateral margin of carapace indented just posterior to eye. Antennule.— Inner projection and peduncle two- segmented; outer projection three-segmented. Antenna.— Inner flagellum of antenna five-seg- mented; terminal segment with four or five simple setae and small, distinct spine at tip. Mandibles.— Essentially same as in Stage II. Maxillule. — Basipodite with two or three addi- tional short, blunt spines compared with Stages I and II. Maxilla. — Scaphognathite with 23 plumose setae along inner and outer margins; naked proximal expansion slightly longer than in Stage II. Maxillipeds. — Essentially identical to Stage II maxillipeds except naked endopodite of third maxilliped five-segmented; exopodite with nine natatory setae. Pereopods (Fig. 3B, pereopod 1).— Essentially identical to Stage II except chelae of pereopod 1 slightly narrower than in Stage II; protopodite usually with five spines. Pleopods. — Lengths of pleopods 2-5 about equal to heights of somites; pleopod 6 small, nonfunc- tional. Telson (Fig. 3C). (rarely 11 + 12). -With 11 + 11 plumose setae Figure 3.— Stage III zoea of Lithodes aequispina: A, carapace, lateral; B. pereopod 1, lateral; C. telson, ventral. STAGE IV ZOEA Mean total length of Stage IV zoeae, 6.8 mm (range 6.3-7.4 mm, six specimens). Rostrum (Fig. 4A) about four-tenths carapace length. Carapace markedly more spiny than in Stage III. Antennule. — Outer projection four-segmented, with about 14 aesthetascs; distal and penulti- mate segments each with long seta and two short setae. Antenna (Fig. 4B). — Antennal flagellum eight- segmented, about 1.3 times length of scale. 309 FISHERY BULLETIN: VOL. 80, NO. 2 L 1 .0 mm J 0.5 mm 0.25 mm Figure 4.— Stage IV zoea of Lithodes aequispina: A, carapace, lateral; B, antenna, ventral; C, third maxilliped, lateral; D, pereopod 1, lateral; E, pereopod 2, lateral; F, pereopod 5 (terminal segments), lateral. Terminal spine of antennal scale somewhat curved. Maxillule and mandibles. — Essentially identical to Stage III. Pleopods. — Pleopods 2-5 about 1.4 times height of somites. Pleopods without setae; pleopod 6 unsegmented, about one-third length of telson, with two (sometimes three) short setae terminal- ly. Maxilla.— Scaphognathite with about 45 plu- mose setae along inner and outer margins. Maxillipeds (Fig. 4C, third maxilliped).— No change in maxillipeds from Stage II except endopodite of third maxilliped with four simple setae on penultimate segment. Exopodite with eight or nine natatory setae. Pereopods (Fig. 4D, pereopod 1; E, pereopod 2; F, pereopod 5).— Dactylopodite of chela of pereopod 1 with teeth. Pereopods 2-5 adult in shape. Propodite of pereopod 5 setose. Abdomen and telson. — Dorsoposterior spines on somites 2-5 reduced in size, often absent on somite 2. Telson jointed with somite 6; with 11 + 11 plumose setae (rarely 12 + 12). STAGE V (GLAUCOTHOE) Mean total length of Stage V larvae, 5.9 mm (range 5.2-6.3 mm, eight specimens). Glaucothoe characteristically spinous (Fig. 5A, J, K). Eye stalk with one anterior spine, three dorsal spines. Antennule (Fig. 5B).— Adult in form. 310 HAYNES: DESCRIPTION OF GOLDEN KINO CRAB LARVAE Figure 5.— Stage V (glaucothoe) of Lithodes aequispina: A, carapace, dorsal; B, antennule, dorsal; C, antenna, ventral; D, mandible (left), anterior; E, maxillule, ventral; F, maxilla, dorsal; G, first maxilliped, lateral; H, second maxilliped, lateral; I, third maxilliped, lateral; J, first maxilliped (chela), lateral; K, abdomen and telson, lateral; L, telson, dorsal. Antenna (Fig. 5C). — Eleven-segmented flagel- lum more setose than in Stage IV. Scale a small projection with short spine terminally. Proto- podite with spine ventrally. 311 FISHERY BULLETIN: VOL. 80, NO. 2 Mandible (Fig. 5D).— Mandible grooved, with- out spines or teeth. Palp curved, naked. Maxillule (Fig. 5E).— Coxopodite and basipodite more rounded than in zoeal stages. Coxopodite and naked endopodite unsegmented. Maxilla (Fig. 5F).— Proximal expansion of scaphognathite somewhat bulbous. Endopodite without setae. Basipodite bilobed with five or six short setae on each lobe. Coxopodite bilobed with short seta on distal lobe. First maxilliped (Fig. 5G).— Smaller, less developed than in zoeal stages. Endopodite and exopodite curved posteriorly; unsegmented endopodite without setae. Two-segmented exo- podite with two minute spines at tip. Second maxilliped (Fig. 5H). — Endopodite curved posteriorly, smaller and less developed than in Stage IV. Exopodite with five natatory setae. two zoeal stages and the glaucothoe; Sars (1890) described the prezoea, first zoeal stage (both obtained from known parentage), and last zoeal stage (obtained from plankton). (The term "inter- mediate stage" in Sars' figure legend refers to the first zoea [MacDonald et al. 1957].) Sars' figures of the prezoeal telson and of Stage I are shown by Gurney (1942). The only other pub- lished description of Lithodes larvae known to me is that of L. antarctica larvae described from specimens reared in the laboratory (Campodoni- co 1971). Larvae of L. aequispina, L. antarctica, and L. maja can be distinguished (see Table 1). In general, larvae of L. maja have fewer stages and are more developed for a given stage than larvae of L. aequispina and L. antarctica. In Stage I L. maja, the eyes are stalked, and the telson and somite 6 are jointed. In contrast, the eyes of L. aequispina and L. antarctica are not stalked until Stage II, and the telson and somite 6 are not jointed until Stage IV in L. aequispina and Stage Third maxilliped (Fig. 51). — Posteriorly curved endopodite with numerous setae. Exopodite with five natatory setae. Pereopods. — Chelae (Fig. 5J) of pereopod 1 typi- cally adult, more spinous and setose than in Stage IV. Right chela slightly larger than left chela. Pereopods 2-4 typically adult in shape and spination. Pereopod 5 same as in Stage IV. Pleopods.— Pleopods 2-5 setose, about 2.5 times height of somites. Endopodites with a few cincinnuli. Pleopod 6 with four setae terminally that extend considerably beyond telson. Abdomen and telson (Fig. 5K, L).— Pair of dorso- posterior spines on somites 1-5. Somites 2-5 with pair of dorsoanterior spines and three pairs of posterolateral spines. Somite 6 with pair of dor- soanterior spines. All somites with hairs; one hair usually near each spine. Terminal margin of telson indented, with a few minute spines or setae. COMPARISON OF LARVAL STAGES WITH DESCRIPTIONS BY OTHER AUTHORS All the larval stages of L. maja have been described. MacDonald et al. (1957) described the Table 1.— Morphological characteristics for distinguishing between larvae of Lithodes aequispina, L. antarctica, and L. maja. ? = no information available. Characteristic L. aequispina L. antarctica L maja No of stages 5 4 3 Stage 1: eyes sessile sessile stalked peduncle of antennule unsegmented partially segmented 3-segmented antennal flagellum unsegmented partially segmented 5-segmented telson and somite 6 not jointed not jointed jointed pairs of telsonic setae1 11 9 8 or 9 longest pair of telsonic setae jointed with telson no yes no Stage II: peduncle of antennule unsegmented partially segmented 3-segmented telson and somite 6 not jointed not jointed jointed endopodite of third maxilliped unsegmented unsegmented 5-segmented pleopods uniramous buds biramous biramous pairs of telsonic setae' 11 9 8 or 9 longest pair of telsonic setae jointed with telson no yes no Stage III: pairs of telsonic setae' 11 9 — longest pair of telsonic setae jointed with telson no yes — Glaucothoe tips of spines on most single carapace bifid bifid toothed spine on rostral 6 small spines 3 small spines spine bifid. complex terminally terminally no small spines terminally natatory setae on exopodites of second and third maxillipeds 5, 5 7, 7 ? 'in addition to a minute setal pair 312 IIAYNKS: DESCRIPTION OF C.OLDKN KING CRAB LARVAE III in L. antarctica. The peduncle of the antennuleand endopodite of the third maxilliped of Stage II L. maja are segmented, butareunseg- mented in Stage II L. aequispina and L. antarctica. Among genera of the family Lithodidae, larvae of L. aequispina are most similar morpho- logically to larvae of the genus Paralithodes. Zoeae of L. aequispina can be readily distin- guished from Paralithodes zoeae (Sato 1958) by the number of telsonic setae and by the setation of the antennal flagellum. In L. aequispina zoeae, the telson has 1 1 pairs of setae in all stages, and the antennal flagellum is setose beginning in Stage III; whereas, in Paralithodes zoeae, the telson has nine or fewer pairs of setae, and the antennal flagellum is naked. In the glaucothoe, the carapace spines of L. aequispina are markedly larger and more spinous than in the glaucothoe of Paralithodes. Formerly, zoeae of the family Lithodidae were considered similar morphologically to those of the subfamily Pagurinae (family Paguridae), because zoeae of Lithodidae differ only in the reduction or disappearance of the uropods (Gurney 1942; MacDonald et al. 1957). Zoeal development of L. aequispina and L. antarctica varies somewhat from the pattern of develop- ment of the other known larvae of the family Lithodidae, as summarized by Gurney and MacDonald et al. Zoeae of the Pagurinae have the following characterstics: the antennal flagellum has fewer than three setae in all stages; the telson has six pairs of setae in Stage I and seven pairs in Stages II-IV; and the exo- podites of the maxillipeds have 7, 7, 6 setae in Stage II, 7 or 8 setae in Stage III, and 8 setae in Stage IV. Zoeae of L. aequispina have an antennal flagellum that is setose beginning in Stage III; the telson has 11 pairs of setae in all stages; and the exopodites of the maxillipeds have 9, 9, and 8 setae in Stage II and 9, 9, and 9 setae in Stages III and IV. Zoeae of L. antarctica differ from zoeae of the Pagurinae by having in all zoeal stages nine pairs of telsonic setae and eight setae on each exopodite of the maxillipeds. The glaucothoe of the Paguridae and Lithodidae are similar to the adults and, thus, readily distin- guished from each other. LITERATURE CITED Campodonico, I. 1971. Desarrollo larval de la centolla Lithodes antarctica Jacquinot en condiciones de laboratorio. (Crustacea Decapoda, Anomura: Lithodidae). An. Inst. Patagonia 2(1-2):181-190. Gurney, R. 1942. Larvae of decapod Crustacea. Ray Soc. (Lond.) Publ., 306 p. Haynes, E. 1973. Descriptions of prezoeae and Stage I zoeae of Chionoecetes bairdi and C. opilio (Oxyrhyncha, Oregoniinae). Fish. Bull.. U.S. 71:769-775. 1976. Description of zoeae of coonstripe shrimp, Pandalus hypsinotus, reared in the laboratory. Fish. Bull.. U.S. 74:323-342. MacDonald, J. D.. R. B. Pike, and D. I. Williamson. 1957. Larvae of the British species of Diogenes, Pagurus, Anapagurus and Lithodes (Crustacea, Decapoda). Proc. Zool. Soc, Lond. 128:209-257. Sars, G. 0. 1890. Bidrag til Kundskaben om Decapodernes Forvandlinger. II: Lithodes- Eupagurus- Spiropagurus - Galathodes - Galathea - Munida - Porcellana - (Nephrops). Arch. Math. Naturv. 13:133-201. Sato, S. 1958. Studies on larval development and fishery biology of king crab, Paralithodes camtschatica (Tilesius). [In Jpn., Engl, summ.] Bull. Hokkaido Reg. Fish. Res. Lab. 17:1-102. 313 THE SEASONAL CYCLE OF GONADAL DEVELOPMENT IN ARCTICA ISLAND1CA FROM THE SOUTHERN NEW ENGLAND SHELF1 Roger Mann2 ABSTRACT The seasonal cycle of gonadal development of the ocean quahog, A rctica itlandica, on the Southern New England Shelf was investigated by collectingadultclams at regular intervalsfrom September 1978 to May 1980 from a 36-50 m depth transect, preparing histological sections of the gonadal tis- sue, and examining these microscopically for stages of development. Hydrographic measurements made concurrently with the clam collections included temperature, conductivity, dissolved oxygen, and pH. Morphologically ripe specimens were present from March through October, but predomi- nated from May through September. A prolonged spawning period from May through November is indicated, spawning being most intense from August through November. Multiple annual spawn- ings at both the individual and population level were evident. After an assessment of the hydro- graphic conditions in the area it was hypothesized that larval survival is probably greatest during the months of October and November, which is the time of the breakdown of the intense seasonal thermocline and before the onset of low winter seawater temperatures. Ocean quahog, Arctica islandica (= Cyprina islandica), is a large pelecypod that occurs in European waters from the White Sea to Spain (Jensen 1902; Loven 1929; Zatsepin and Filatova 1961; Punin 1978) and in American coastal wa- ters from Newfoundland to Cape Hatteras (Nicol 1951; Merrill and Ropes 1969; Ropes 1978). The species supports an active fishery in the Middle Atlantic region and has been the subject of much recent study (Murawski and Serchuk 1979; Thompson, Jones, and Dreibelbis 1980; Thomp- son, Jones, and Ropes 1980; Ropes and Murawski 1980). In the Middle Atlantic region the greatest concentrations of A. islandica are found in depths of 25-61 m with the mean depth of occur- rence increasing from 39 m off Long Island to 52 m off Virginia and North Carolina (Merrill and Ropes 1969; Ropes 1978). The seasonal temperature structure of the waters of the Middle Atlantic region was first comprehensively described by Bigelow (1933) and has subsequently been the subject of many investigations and reviews (Walford and Wick- lund 1968; Colton and Stoddard 1973; Bumpus 1973; Beardsley et al. 1976; Williams and Gods- hall 1977). Two important features are evident: An intense summer thermocline that builds in May and persists until September, and a "pool" ■Contribution No. 4715 from Woods Hole Oceanographic In- stitution. 2Woods Hole Oceanographic Institution, Woods Hole, MA 02543. of cold water (annual temperature range 2°- 13°C), surrounded on both the inshore and off- shore sides by warmer water, that develops on the continental shelf below the thermocline dur- ing the spring, summer, and early fall months (Ketchum and Corwin 1964; Bowman 1977). The cold pool of bottom water in the summer months overlies much of the depth range occupied by A. islandica. Maximum water temperatures on the sea floor in the depth range occupied by A. islan- dica occur in September and October (Bigelow 1933), and a strong relationship exists between the 16°C bottom isotherm for October and the in- shore distribution limit of A. islandica (Bigelow 1933, figs. 49, 60; Merrill and Ropes 1969, fig. 2). Loosanoff (1953) described the reproductive cycle of A. islandica based upon specimens col- lected regularly from commercial catches at Point Judith, R.I., from March to November (a complete annual cycle was examined but not re- ported). Following histological preparation and microscopic examination of the specimens, Loosanoff concluded that histological "Spawn- ing begins near the end of June or early in July when the water temperature is approximately 13.5°C." The conclusion was based on tempera- ture data inferred from earlier observations by Merriman and Warfel (1948). Loosanoff (1953) also concluded that spawning continued through August, and that approximately 50% of A. islan- dica examined were totally spent by early Octo- ber. The larvae of A. islandica have been reared Manuscript accepted September 1981. FISHERY BULLETIN: VOL. 80, NO. 2. 1982. 315 FISHERY BULLETIN: VOL. 80. NO. 2 to metamorphosis by Landers (1976) and Lutz et al. (in press). Landers (1976) reported that fertilization and early cleavage were obtained at 10°, 15°, and 20°C; however, embryos only survived to the veliger stage at the two lower temperatures, and to metamorphosis at 10°- 12°C. The cultures reared by Lutz et al. (in press) were maintained to metamorphosis at tempera- tures ranging from 9° to 13°C; but none of these investigators defined the maximum tem- perature at which metamorphosis could be effected. After reviewing data on seasonal water tem- perature structure in the Middle Atlantic Bight and the reproductive biology of A. islandica re- ported by Loosanoff ( 1953) and Landers (1976). certain inconsistencies were evident. It has long been suspected that bivalve larvae can partially control their position in the water column by swimming (Carriker 1961; Wood and Hargis 1971; Cragg and Gruffydd 1975). If A. islandica spawn in July, then larvae swimming upwards to the regions of highest primary productivity, and hence phytoplankton food, would encounter both an intense thermocline at 20-30 m depths and surface temperatures in excess of 20°C. Both temperature conditions would be either deleteri- ous to growth or even lethal according to Landers (1976). Therefore, it would appear appropriate to hypothesize that spawning in October or Novem- ber would be more congenial to larval survival because, after the fall thermocline breakdown and subsequent vertical mixing of the water col- umn, vertical movement of the larvae would not be limited by an intense thermocline. Further- more, any temperature stratification that did exist at this time would have widely spaced verti- cal isotherms and thus form only weak barriers to horizontal dispersion. A need was evident to simultaneously assess the reproductive cycle of the adult A. ishindica and hydrographic conditions affecting it and larval survival. This study describes the game- togenic cycle of adult A. islandica, based on microscopic examination of histological prepa- rations from individuals collected regularly from several depths over a 2-yr period, and con- current physical data collected during the same period. METHODS AND MATERIALS Fourteen collections of A. islandica were made at intervals of 4-8 wk from September 1978 to May 1980 at depths ranging from 27 to 50 m in the vicinity of Block Island, R.I. Stations at27-30 m depth (Station A) were north and east of Block Island (lat. 41°19'N, long. 71°34'W and lat. 41° 13'N, long. 71°32'W, respectively). Stations at 36, 42, and 48-50 m (Stations B-D, respectively) were on a transect directed due south at long. 71° 31'W at lat. 41°11'N, 41°03'N, and 41°01'N, re- spectively. Specimens were collected with a com- mercial hydraulic clamdredge(blade width 1.54 m, pump pressure 5.63-7.0 kg/cm2, 7.5 cm diame- ter ring size; tows of 5-min duration) during the period September 1978-August 1979 and with a nonhydraulic clam dredge (blade width 0.62 m; 5.0 cm diameter ring size; tows of 20-30 min dur- ation) during September 1979-June 1980. Both dredges were selective for clams larger than the diameter of the rings. The clams were opened on board the vessel and either the soft tissues removed whole, or a section of tissue approximately 1 cm2 excised from the surface of the midventral region. The tissues were preserved in Bouins fixative for 24-48 h, rinsed in water for 6 h, and stored in 70% ethanol. Histological preparation of tissue sections in- cluded embedding in paraffin, sectioning at 7 ju, staining with Delafield's hematoxylin, and coun- terstaining with eosin Y by the procedure of Humason (1962). A minimum of 15 specimens was examined from the midventral samples col- lected on each collection date. An additional five specimens of whole animals from each collection date were examined in tissue excised from each of the dorsal, midventral, and ventral regions in order to assess the uniformity of development throughout the gonadal tissue. Slide prepara- tions were examined microscopically for evi- dence of gametogenesis and spawning (Holland 1972), and each was classified into one of five categories of gonadal condition, by the criteria of Holland and Chew (1974) as follows: Early active: Male: Many follicles: spermatogonia and spermatocytes numerous, no sperma- tozoa. Female: Oogonia arising from stem cells along the follicle; no free oocytes. Nuclei stain darker than cytoplasm. Late active: Male: Follicles contain predominantly spermatids and spermatozoa. Female: Both free and attached oocytes pres- ent. Oocytes have nuclei that stain 316 MANN: CONADAL DEVKLOl'MENT IN ARCTICA ISLANDICA lighter than cytoplasm and a distinct nucleolus. Ripe: Male: Follicles filled with spermatozoa in swirling patterns. Female: Predominantly free oocytes with dis- tinct nucleus and nucleolus. Partially spent: Male: Follicles disorganized and often empty. Some full follicles remaining. Female: Follicles disorganized. Some mature ova remaining, some undergoing cy- tolysis. Spent: Male: Follicles disorganized and empty, few spermatozoa remaining. Female: Follicles disorganized and empty, few ova remaining. The report of Loosanoff (1953) was used for comparison throughout the procedure. The clas- sification of gonadal development into stages is, by definition, qualitative. A quantitative option of describing female gonadal development as a function of mean ova diameter was considered inapplicable in the present study because ova were often elongated or otherwise nonspherical in shape, especially during development from oogonia to oocytes. Hydrographic measurements were made at each station on each collection date. A vertical profile, from surface to bottom at 5 m intervals, was made of temperature and conductivity using either a model 6D or S8000 Hydrolab Water Quality Analyser (Hydrolab Corporation, Austin, Tex.)3 and the conductivity measurements were converted to salinity. On six occasions these data were supplemented by vertical profiles of dis- solved oxygen content and pH measured with the same instrument. RESULTS Hydrographic Observations Figure 1 depicts the seasonal temperature structure of the water column at Stations A-D. No marked differences were recorded between the 2 yr of the study; hence data have been pooled. An intense seasonal thermocline was initiated in April-May and reached a maximum intensity at 3Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. between 20 and 30 m depths in August. Surface waters cooled during the fall months of Septem- ber and October. A uniform temperature struc- ture throughout the water column was evident from November through April. The intense nature of the thermocline and its relationship to depth at sample stations (A-D) is illustrated in Figure 2 for August 1979. Maxi- mum bottom temperatures recorded at Stations A-D, respectively, were 15.4°, 14.0°, 12.9°, and 12.6°C, and they occurred earliest at the two shallower stations. Salinity values recorded during the study agreed well with those reported previously by Ketchum and Corwin (1964). Surface to bottom salinities increased from 30.907.. to 32.087.. dur- ing July at Station A and from 31.597..to 32.857.. at Station D. Salinities were highest but rela- tively stable throughout all depths and stations during the winter months (all values ranged from 32.307.. to 33.527.,). Dissolved oxygen data were in general agree- ment with those summarized for the Middle Atlantic region by Williams and Godshall (1977). Surface waters to 20 m depth were at or within 10% of saturation throughout the year. A gradual decline in percentage saturation was evident be- low the seasonal thermocline from April to late August (Fig. 3A). This was most obvious imme- diately adjacent to the sediment-water interface where a minimum dissolved oxygen level of 65% saturation was recorded at Station D in August 1979. Concurrently pH also decreased reaching a minimum of 7.9 (Fig. 3B) at the sediment-water interface at all stations in August 1979. Gonadal Observations A rctica islandica is dioecious. Out of 669 speci- mens, hermaphroditism was found in only 2 indi- viduals which contained spatially separate de- veloping male and female follicles (Fig. 4). Serial sectioning indicated that gonadal maturation occurred initially in tissues at the dorsal extrem- ity of the gonadal mass and progressively later moving toward the ventral extremity (Fig. 5). Multiple spawnings in the same animal during one annual cycle, originating from tissues in a similar spatial sequence, were suggested by the presence of spent follicles in dorsal sections, while follicles in the ventral sections of the same specimen were in late active or ripe condition. No evidence was found of a second maturation of spent, dorsal gonadal follicles following spawn- 317 FISHERY BULLETIN: VOL. 80, NO. 2 Figure 1.— Seasonal changes in seawa- ter temperature at 10 m intervals at Sta- tions A-D during September 1978-May 1980. For simplicity 2 yr of data have been pooled and are presented on a sin- gle annual cycle. I l^l I I I I I I 1 L ,o - LJ f\ /^\ - /> /^\ / A / /7> \ - M ^ \ \ * * /, ,, i i i i i JFMAMJJASOND JFMAMJJASOND MONTH O SURFACE • 10 m A 20 m A 30 m D 36 m O 40 m ■ 42 m ♦ 48 m * ALL DEPTHS STATION 10 20 ft. Uj 30 40 50 TEMPERATURE °C AUGUST 31 , 1979 DISSOLVED OXYGEN^ % SATURATION 90 70 50 I 1 1 1 1 1 r- » 10 15 41°13' 41011' 41" 09' 4V07' 41°05' 41°03' 41°or LATITUDE °N Figure 2.— Water column temperature structure along the transect from Stations A to D, 31 August 1979, illustrating the intense thermocline and its intersection with the bottom. Figure 3.— Vertical profiles of percentage saturation of dis- solved oxygen and pH at Station D for April (o) and August (•). 318 ^ 20 P~ 25 Si 30 35 h 40 45 48 • ' • 9 • 9 Y cm PH 8 20 810 80 I 1 1 1 1 1 B MANN: CONADAI, DKVKI.OI'MKNT IN ARCTIC A ISLANDICA *m ""># **i. S ft* - * SEr^ Vie Figure 4.— Midventral sections of hermaphrodite Arctica inland ica collected at Station A, 2January 1980. A. Section illustrating spatially separate male (B) and female (C) gonadal tissue. Scale bar 1 mm. B. Expanded view of male gonadal tissue illustrating spent male follicle. Scale bar 50 n. C. Expanded view of female gonadal tissue illustrating degenerating ova. Scale bar 50 p. ing during one annual cycle in either of the two years when observations were made. Gonadal maturation, then, probably occurs only once per year in each individual clam. The mean diameter of the ova taken from histological sections of ripe female clams was 52.4 /x (n = 59 ova). This com- pares with a value of 66.3 /i ( n = 22 ova) obtained from unfertilized eggs stripped from ripe, live animals. The disparity between preserved and live material in the present instance is probably 319 FISHERY BULLETIN: VOL. 80. NO. 2 * B .... "T;*:' •■ 9 ' ■ . /t";) i .■ ■„-■■ — * D ' W- i .mm. V • • ■ .; y- *B ■ '♦Vfejj FuaiRE 5.— Sequential development of gonadal material in the dorsal-ventral plane in Arctica islandica. A. Female, dorsal sec- tion, spent gonadal tissue. Scale bar 100 ji. B. Female, midventral section, partially spent gonadal tissue. Scale bar 100 p. C. Female, ventral section, ripe gonadal tissue. Scale bar 100 p. Preparations A-C from one clam. D. Male, dorsal section, ripe spermatozoa. Scale bar 10 /u. E. As for D except scale bar 50 m- F. Male, ventral section, late active development. Scale bar 100 n. Preparations E and F from one clam. Both clams from Station I), 15 June 1979. 320 MANN: CONAOAL DEVELOPMENT IN ARCTICA ISLANDICA 1978 1979 1980 □ EARLY ACTIVE □ LATE ACTIVE ■ RIPE □ SPENT El PARTIALLY SPENT Figure 6.— Seasonal changes in gonadal development by sex in Arctica island ica for the period September 1978- May 1980; all stations pooled. due to shrinkage during fixation and subsequent dehydration in alcohol. Both values are consider- ably lower than the diameter of 85-90 ju reported by Loosanoff (1953); however, these latter values were for fertilized eggs. Individual spermatozoa measured 6 n in length in both fixed and live preparations. Table 1 summarizes observed gonadal condi- tions in midventral sections taken from A. islan- dica at all stations during the study. Data are pooled for shallow (A and B) and deep (C and D) stations, respectively, due to the similarity of annual bottom temperature changes at these sites (Figs. 1, 2). Gonadal condition data are pooled for all stations and are presented graphic- ally in Figure 6. Several major features were evi- dent. Early active development in the male clams first occurred in early February and con- tinued through May. Late active male develop- ment began in late February and remained evi- dent until June. Most ripe males occurred from May through September and partially spent male clams were found from May through No- vember and during January 1979. Eight percent of the female clams were in early active stage in May 1979. Two percent of the female clams were in late active stage in June and August 1979. Gametogenesis in the female clams began earlier in the year of 1980 than in 1979, with 12% of the females in early or late active stage in February 1980, and 10% in late active stage in both March and April 1980. Ripe females were present from May through October. The small proportion of early and late active females recorded during February to June in comparison to the larger equivalent proportion (31-93%) of males sug- gested that the duration of the period required to attain ripeness is shorter in the female clams. The onset of spawning activity in both sexes was marked by a substantial increase in the pro- portion (to over 30% of total in both males and females) of partially spent animals and contin- ued during the spawning period. Completely spent individuals were greatest from August through November, although some were found as early as May and June. In the female clams only partially spent and spent individuals were present year-round, the former being particu- larly abundant during August and September, and the latter being most abundant from Novem- ber through March. A prolonged spawning per- iod from May through November was indicated even though levels were low during the period May through July. 321 FISHERY BULLETIN: VOL. 80, NO. 2 Table 1.— Numbers of Arctica islandica in each gonadal development stage by date for the period September 1978-May 1980: Data are pooled for shallow (A, B) and deep (C, D) stations, respectively. Stage description: EA, early active; LA, late active; R, ripe; PS, partially spent; S, spent. Station d 9 Date EA LA R PS S n EA LA R PS S n 9/78 A + B C + D 2 3 4 2 6 4 13 1 2 1 2 1 4 1 7 6 13 11/78 A + B C + D 3 8 9 4 5 12 17 2 5 1 10 5 17 6 1/79 A + B C + D (') 2 3 5 4 11 15 3/79 5/79 A + B C + D A + B C + D 3 8 7 6 2 10 12 24 1 1 5 3 8 8 13 13 6/79 A + B C + D 1 11 20 27 27 11 3 4 54 50 1 11 10 16 23 17 12 44 46 8/79 A + B C + D 1 14 10 14 14 8 2 36 27 1 5 1 8 21 10 6 23 29 9/79 A + B C + D 1 4 4 1 1 6 5 1 3 3 1 5 3 11/79 A + B C + D ,1 . 2 4 6 2 7 9 1/80 A + B C + D (') 14 14 1 13 14 2/80 A + B C + D (') 12 1 1 14 1 1 4 10 16 3/80 A + B C + D (') 7 4 4 15 1 2 7 10 4/80 A + B C + D ,2, 3 10 1 6 20 2 2 17 21 5/80 A + B C + D 1 4 3 2 3 2 7 8 2 4 3 3 3 5 10 Total 349 318 'Dredging prevented by bad weather. 2No collection due to gear failure. A total of 667 A. islandica were of separate sexes and the observed ratio of this sample was 1 :0.91 . These data are not significantly different from a 1:1 sex ratio. This analysis omits the two hermaphrodites. Recently, Thompson et al. (1980b) have described the advanced age for sex- ual maturity in A. islandica, and Ropes and Murawski (1980) have examined the size and age at sexual maturity of A. islandica collected from a depth of 53-55 m south of Long Island, N.Y. They found that individual A. islandica&s large as 47 mm in length had undifferentiated gonads and males began producing germinal cells at a smaller size and younger age than females. Small individuals were rare in the presentstudy. Arctica islandica caught with the hydraulic dredge ranged from 70 to 1 10 mm in shell length, but were predominantly (84% of total) from 80 to 100 mm. The smallest specimen caught in the nonhydraulic dredge measured 62 mm in length, but most specimens (80% of total) were 80-100 mm. A record relating the length of each clam examined to its gonadal development was not kept in the present study; therefore a relation- ship between sex and length cannot be described. The present data on sex ratio differ from those of Jones ( 1980), who observed a sex ratio of 1 :0.72 in a sample of 320 A. islandica of >75 mm individ- ual length which were collected from offshore New Jersey during the period April 1977-March 1979. DISCUSSION Data describing water column physical char- acteristics are in general agreement with pre- vious work in illustrating the seasonal, intense thermocline, and indicate that mixing across this phenomena is small during the summer months. Partial oxygen depletion below the thermocline during the summer is probably strongly related to biological activity. The minor differences in gonadal development in A. islandica between stations is, at first, sur- prising considering the fact that the inshore, shallower stations (A and B) were consistently warmer than the offshore, deeper stations (C and D) (Figs. 1, 2, 6); however, an assessment of go- 322 MANN: (iONADAI, DKVKLOPMKNT IN ARCTICA ISLANDICA nadal condition is subject to the following in- herent inadequacies. First, a continuous game- togenic process is being described in discrete stages. Second, it is difficult to consistently ob- tain a midventral section that is a representative mean of the cline of gonadal developmental stages within one animal. Third, sample collec- tions were relatively infrequent considering the small differential in bottom temperatures be- tween the stations and the comparatively high rate of change of bottom temperature during the summer months (Fig. 1). It is probable that these three factors effectively combined to mask any depth-dependent difference in gonadal develop- ment. Morphologically ripe specimens were present from March through October, but predominated from May through September. Although no mor- phologically ripe specimens were found in De- cember or January — in contrast to the data of Loosanoff (1953) — the presence of partially spawned animals at this time, followed by the first appearance of early gametogenic stages in February and March, supports Loosanoffs hy- pothesis that no significant "resting" or "indif- ferent" period occurs in the annual gametogenic cycle. The sequential ripening of gonadal folli- cles from the hinge (dorsally) towards the foot (ventrally), in a manner similar to that described for Mija arenaria by Coe and Turner (1938), was not described by Loosanoff (1953). No examples of the "atypical" sperm development described by Loosanoff ( 1953) were observed in the present study. The present data are, however, not in com- plete agreement with the recent statement in Thompson, Jones, and Dreibelbis (1980), with respect to A. islandica, that "All individuals spawned once and once only in each of the two years studied." Jones (1980) is quoted as the source of documentation substantiating this statement. This is somewhat surprising in that, like the present study, Jones (1981) found some sequential gonadal development and the pres- ence of a large proportion of partially spent indi- viduals of both sexes in samples collected in the late summer and fall months. Both of these obser- vations support the conclusion that individual specimens spawn at least once per annual repro- ductive cycle. It is relevant to speculate on the nature of the proximal stimuli (sensu Baker 1938) of gameto- genesis and spawning in A. islandica, given the present physical and biological data, based on the extensive discussion of the subject by Baker (1938) and Giese and Pearse (1974). Arctica islandica initiated gametogenesis in February when water temperature is lowest. This is in con- trast to the more intensively studied intertidal species which either cease gametogenesis during the period of lowest temperature, e.g., Mytilus edulis in Northern Europe (Chipperfield 1953), or initiate gametogenesis only with rising water temperatures and at the time of the phytoplank- ton spring bloom, e.g., Ostrea edulis and Crassos- trea gigas (Walne and Mann 1975). Ansell (1974), Gabbott (1975), and Mann (1979a, b) found that the initiation of gametogenesis in bivalves is often preceded by a period of accumulation of carbohydrate reserves which are subsequently used as a predominant respiratory substrate during gametogenesis and that this period of accumulation usually coincides with a period of high primary productivity and food availability. The author can find no data on seasonal phyto- plankton productivity for the region immediately east and south of Block Island; however, substan- tial data are available for the lower Narragan- sett Bay (Hitchcock and Smayda 1977; Pratt 1965; Smayda 1957), Block Island Sound (Riley 1952b), and Long Island South (Smayda 1976). Lower Narragansett Bay is characterized by an intense winter (January to March) diatom bloom and a smaller, late summer to autumn (July to October) bloom (Smayda 1976). Block Island and Long Island Sounds exhibit a more classical spring and autumn bloom (Hitchcock and Smayda 1977; Smayda 1976). It is not unreason- able to suggest that phytoplankton from the autumn and winter blooms in Narragansett Bay are washed into Block Island Sound (Riley 1952a), and that, because of the vertically well- mixed nature of the water column at this time, both they and the phytoplankton from the classi- cal spring and autumn blooms become available to A. islandica. Phytoplankton was probably made available by wind and storm events similar to those which effect the mixing and distribu- tion of chlorophyll in the New York Bight and Georges Bank, as described by Walsh et al. (1978). In turn these blooms may be a potential food source for storage metabolism in A. islan- dica during the late fall, winter, and early spring months prior to and coincident with the initial stages of gametogenesis. Specimens collected throughout this period had both bright green digestive glands and a well-developed crystalline style indicative of active feeding on phytoplank- ton. 323 FISHERY BULLETIN: VOL. 80, NO. 2 The precise nature of the spawning stimulus to A. islandica remains open to discussion. Loosa- noff (1953) suggested that spawning was initi- ated at a water temperature of approximately 13.5°C; however, the data of Figures 1 and 6 indi- cate that absolute temperature per se is probably not the ultimate spawning stimulus. Further- more, laboratory experiments to induce spawn- ing by temperature shock alone have proved both inconsistent and usually unsuccessful (Loosanoff 1953; Landers 1976; Lutzetal. in press). Indeed, A. islandica has proven to be a very difficult species to spawn in laboratory systems. It also fails to respond to salinity and pH changes, the addition of suspension of sex products (Loosanoff 1953; Landers 1976), and the more recent meth- od of Morse et al. (1977) involving exposure to alkaline seawater (pH = 9.1) and hydrogen per- oxide (range of concentrations 2.5 — 5 X 10"3 M) (Lutz et al. in press). While these methods of stimulating spawning have generally been very successful with many intertidal and shallow water species (Loosanoff and Davis 1963; Morse et al. 1977) which experience short-term (e.g., tidal) environmental fluctuations, their inappli- cability to A. islandica is, perhaps, not surpris- ing considering the fact that the deep, infaunal habitat of the species is comparatively well damped from short-term environmental fluctua- tions. Spawning occurred from May through November in field populations of A. islandica, and was heaviest during late August to October and at the time of the fall thermocline break- down. Changes in bottom temperature coinci- dental with spawning occurred, but the rate and magnitude were small (Fig. 1). Clarke4 recorded a prolonged spawning season for A. islandica. His studies of A. islandica, which were collected from a similar temperature regime to the pres- ent study in depths of 20 m off Seabrook, N.H., indicated some spawning from June through October with the greatest intensity from August to October. The prolonged nature of the spawn- ing season in field populations reinforces the conclusion that while a specific, absolute temper- ature may be an important spawning stimulus, it is probably effective only in conjunction with changes in other stimuli, such as increases in percentage saturation of oxygen, pH, and food availability. Spawning stimuli other than temperature have been reported by Ansell et al. (1978), who found a close correlation in the Clyde Sea area between an abrupt increase in bottom dissolved oxygen levels following a seasonal thermocline breakdown and spawning activity in the infaun- al bivalve Nuculana minuta. The fate of larval A. islandica spawned prior to the thermocline breakdown also remains open to discussion. The observations of Landers (1976), Wood and Hargis (1971), and Cragg and Gruffydd (1975) suggest that larvae in the early stages of development swim upwards and that substantial larval mortalities are probable from early spawnings, since, at least, temperatures too hot for survival would be encountered. To complete development successfully larvae spawned in June would have to remain below an intense thermocline through which little mixing occurs. This appears improbable. The inference is that a period exists during which the survival of larvae is limited by hydrographic events and that the larvae of A. islandica do not freely move throughout the entire depth of the water column until after the breakdown of the summer thermo- cline. Furthermore, the low winter water tem- peratures recorded in the Middle Atlantic Bight may also effectively depress continued develop- ment of larval stages spawned late in the fall months. Therefore the period during which the larvae of A. islandica survive to metamorphosis may be considerably shorter (approximately 2 mo, October and November) than that during which the adults are capable of spawning (7 mo, May to November). ACKNOWLEDGMENTS It is a pleasure to thank Rodman E. Taylor, Jr. for his continued and enthusiastic assistance throughout this program, John W. Ropes for critical reading of the manuscript, and Elaine M. Lynch for editorial assistance. Special thanks are also due to R. Ferrara of the F.V. Albert Quito and A. D. Colburn of the RV Asterias for much patience during field operations. This work was supported by NOAA Office of Sea Grant Contracts No. 04-8-MO1-149 and NA 79AA-D-00102, and the Andrew W. Mellon Foundation. LITERATURE CITED 4P. Clarke, Benthic Biologist, Normandeau Associates, Bed- ford, NH 03102, pers. commun. May 1978. Ansell, A. I). 1974. 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Oceanogr. 23:659-683. Williams, R. G., and P. A. Godshall. 1977. Summarization and interpretation of historical physical oceanographic and meteorological information for the Mid Atlantic Region. NOAA Center for Exper- imental Design and Data Analysis, Final Rep. to Bureau of Land Management Oct. 1977, 306 p. Wood, L., and W. J. Hargis, Jr. 1971. Transport of bivalve larvae in a tidal estuary. 4th Eur. Mar. Biol. Symp., p. 29-44. Zatsepin, V. I., and Z. A. Filatova. 1961. The bivalve mollusc, Cyprina islandica (L), its geographic distribution and role in the communities of benthic fauna. Trans. Inst. Oceanogr. Acad. Sci. USSR 46:201-216. 326 REGENERATION OF NITROGEN BY THE NEKTON AND ITS SIGNIFICANCE IN THE NORTHWEST AFRICA UPWELLING ECOSYSTEM Terry E. Whitledge1 ABSTRACT Nitrogen and phosphorus excretion rates were measured for octopus and six species of fish in the northwest Africa upwelling region near lat. 21°40'N. The nekton excretion rates ranged from 0.44 to 4.61 /ig NHVN/mgdry weight per day and the whole body C:N (by atoms) of the specimens was 4. 85. The calculated nitrogen turnover time in the well-fed specimens was about 65 days. The estimated rates of ammonium regeneration over the shelf (<200m) for all the nekton wasabout3mg-at/m2per day which was 27% of the phytoplankton ammonium uptake requirements. On the slope (>200m) the nekton regenerated 1.8 mg-at/m2 per day which was 11% of phytoplankton ammonium uptake. The ammonium production by bacterioplankton. zooplankton, nekton, and sediments accounted for 226% of the ammonium utilized in the nearshore shelf region and 83% in the offshore region. Ammonium is an important source of nitrogen for phytoplankton growing in the sea. Estimates of nutrient uptake using 15N tracer experiments have indicated that ammonium regeneration may be responsible for 44 to 83% of nitrogen utilized by phytoplankton in the North Pacific gyre (Eppley et al. 1973) and up to 50% in the Peru upwelling system (Dugdale and Goering 1970). The source of ammonium in the marine environment may be recycled through any of several animal groups. Ammonium regenera- tion in Long Island Sound was found to be pre- dominantly from zooplankton and benthos (Har- ris 1959), while in Georgia coastal waters, phosphate regeneration (and presumably am- monium regeneration) was produced by zoo- plankton that are large enough to be sampled adequately by nets (Pomeroy et al. 1963). The regeneration of nitrogen by zooplankton has been examined in several coastal upwelling ecosystems. The red crab, Pleuroncodes plan i pes, copepodites, and adult Acartia regenerated about 16% of total phytoplankton nitrogen up- take (Whitledge in press) in the Baja California upwelling system while zooplankton in the Peru upwelling ecosystem regenerated about 15% of total nitrogen uptake (Whitledge 1978). In the northwest Africa upwelling region off Cape ■Oceanographic Sciences Division, Department of Energy and Environment, Brookhaven National Laboratory, Upton, 33.7 -2>2>fiT NY 11973. Manuscript accepted October 1981. FISHERY BULLETIN: VOL. 80. NO. 2. 1982. Blanc (Fig. 1), the zooplankton were shown to re- cycle 33% of nitrogen productivity over the shelf (Smith and Whitledge 1977). The focus in most regeneration studies has been zooplankton because fish and benthic orga- nisms have relatively smaller biomasses in many oceanic areas. However, the biomass of the anchoveta in the Peru upwelling ecosystem was estimated to be 15 times greater than the zoo- plankton biomass (Dugdale and Goering 1970), and the fish regenerated 22% of the phytoplank- ton total nitrogen uptake and 59% of the ammo- nium uptake (Whitledge 1978). Since the fish in the Peru upwelling system produce a significant quantity of recycled nitrogen, another major fishing area, the northwest Africa upwelling system, was studied to examine the relative im- portance of nutrients regenerated by fish in com- parison with that by zooplankton (Smith and Whitledge 1977), benthic processes (Rowe et al. 1977), and bacterioplankton (Watson 1978). In addition, the biology of many species of fish has not been investigated with respect to changes of nitrogen excretion rates over time and under various conditions so an attempt was made to in- crease our understanding of this elimination process. METHODS Near-bottom fish specimens of Diplodus sene- galensis, Pegellus couperi, Cantharus cantharus, and Pomadasys incisus were captured in bottom 327 FISHERY BULLETIN: VOL. 80, NO. 2 30' 22 00' 30' 21° 00' LAT 2I°42.2'N ■+-A LONG 18° 09 2' W LAT 21° 02 N -▼LONG 18° 19. 5 W \5 18° Figure 1.— Station locations in the upwelling region off northwest Africa. 328 WHITLEDGE: REGENERATION OF NITROGEN BY NEKTON trawls. The fish were transferred immediately to a holding tank aboard the RV Atlantis II and were maintained as long as a week with daily feeding. Specimens were held at least 6 h before experiments were initiated. Excretion measure- ments were collected on several specimens after the holding tank had been cleaned, rinsed with ethyl alcohol, flushed, and filled with seawater. The tank was covered with black polyethylene sheeting to reduce light and to prevent contami- nation by particulate matter. After the animals were placed in the tank and the experiment was initiated, water samples were collected every 10 min for periods of up to 3 h. Most of the experi- ments were started in the late evening so the temperature of the experimental tanks was within 1°-2°C of ambient surface seawater. There was no heating effect by sunlight so the temperature ranged from 14.5° to 16°C for all the experiments with <0.5° change in tempera- ture during any of the experiments. "Fresh" specimens were examined within 12 h of cap- ture. Specimens that had been starved for 1 and 2 d were used to estimate nonfeeding excretion rates. After all water samples had been col- lected, the specimens were blotted on towels and weighed. The animals were subsequently dried in a circulating oven at 70°C until a constant dry weight was obtained. The whole dried fish were ground into a powder for determination of per- centage body nitrogen and carbon. Excretion samples were analyzed for ammo- nium, urea, nitrate, silicate, phosphate, dis- solved organic nitrogen, and dissolved organic phosphorus. The samples were freshly run and were filtered through a 0.45 jum glass-fiber filter to remove particulate matter. The chemical methods used were similar to those described by Freiderich and Whitledge ( 1972) except for urea and dissolved organic nitrogen and phosphorus which were determined by the methods of DeManche et al. (1973) and Armstrong et al. (1966). RESULTS Excretion Measurements Eight excretion experiments were performed on a total of five species of demersal fish. In addi- tion, excretion measurements were taken from two blue sharks, Prionace glauca, and several octopi, Octopus vulgaris. The typical tank con- centrations of nitrogen compounds measured during the experiments are shown in Figure 2. The rate of ammonium excretion was approxi- mately twice as large as the rate for urea. The rate of excretion for ammonium was more nearly linear than that for urea, although the nonlin- earity for urea is probably within the precision limits of the method. The sum of ammonium and urea represents the identified nitrogen excretion in the experiments. The difference between this sum of ammonium and urea and total nitrogen excretion (as measured after ultraviolet irradia- tion) is probably composed of organic nitrogen compounds such as dissolved amino acids, tri- methylamine oxide (Grollman 1929; Wood 1958), or creatine (Whitledge and Dugdale 1972). All experiments conducted showed a nearly linear increase in ammonium concentrations over the short duration of the experimental periods. Like- wise the increases in urea and total excreted nitrogen were nearly linear but were more var- iable than ammonium. A summary of all nitrogen excretion experi- ments is shown in Table 1. Well-fed demersal species such as Diplodus senegalensis excreted from 1.03 to 1.44 nS NH4-N/mg dry weight per 6.0 0) - 4.0 D I < rr o o o 2.0 - — <$y ^y/ &/ ,o/ / / «V / 200 m was estimated by acoustic mea- surements to be about 80 g wet weight/m2 and was thought to be composed of jack mackerel, Trach >< rus symmetricus (Thorne et al. 1977). Just offshore of the shelf break concentrations as large as 105 g wet weight/m2 of fish were occa- sionally observed. Demersal fish biomass was smaller than found on the shallow shelf region and was estimated to be 3.3 g wet weight/m2 from bottom trawls (Haedrich et al. 1976). It should be noted that biomass estimates ob- tained from the acoustic survey for the pelagic populations and the trawl sampling for demersal nekton were often highly variable (Thorne et al. 1977). Several of the most abundant nekton spe- cies (e.g., Sardinella spp.) were migrating through the study area and a considerable amount of commercial fishing was occurring so the mean biomass values used in regeneration calculation are an attempt to use a reasonable value that was the best estimate of the nekton biomass assessment investigators. Regeneration Rates Regeneration rates were calculated from nek- ton biomass and fish excretion data for the shelf «200 m) and slope region (>200 m) in the north- west Africa upwelling area. These regions were considered separately because of large differ- ences in both the fish and zooplankton popula- tions in these two areas. The sum of ammonium regeneration rates calculated for pelagic fish over the shelf amounts to 2.87 mg-at/m2 per day (Table 3) while demersal fish regeneration rates were 0.09 mg-at/m2 per day for a total of 2.96 mg- at/m2 per day. The anchovy excretion rates were estimated from Engraulis ringens and E. mor- dax values (Whitledge 1978) and Plesionika spp. excretion rates were estimated using values for small sizes of Pleuroncodes planipes, a pelagic crab endemic to the eastern tropical Pacific. The ammonium regeneration rates for the slope region were dominated by T. symmetricus (1.80 mg-at/m2 per day) while demersal fish con- tributed only 0.04 mg-at/m2 per day. The jack mackerel excretion rate used in the calculation was obtained from specimens examined in the eastern Pacific region (McCarthy and Whitledge 1972). Table 3.— Regeneration of ammonium by fish over the shelf and slope areas of northwest Africa upwelling ecosystem. Ammonium Regeneration excretion rate rate Wet wt Dry wt fjg N/mg mg-at N/m2 g/m2 g/m2 dry wt per day per day Shelf (<200 m) Pelagic Sardine 32 8 46 2.63 Anchovy 8 2 '1.7 0.24 Demersal Sparids and flatfish 2.2 0.55 1 23 005 Cephalopods 10 0.17 071 0.01 Shrimp 1.4 022 220 003 Total 446 1094 296 Slope (>200 m) Pelagic Horse mackerel 80 20 1 26 1.80 Demersal Sparids 1.6 0.4 1.23 004 Total 81.6 204 1.84 Estimated from Engraulis ringens and E. mordax rates 2Estimated from Pleuroncodes planipes rates. DISCUSSION The significance of nutrient regeneration by fish is most apparent when the ammonium re- generation rates are compared with phytoplank- ton uptake rates measured by 15N-labeled nitrate and ammonium. The mean ammonium and ni- trate uptakes are estimated to be 11 and 10 mg- at/m2 per day for the shelf region (Maclssac and Dugdale2). The ammonium regeneration rate for 2Jane J. Maclsaac and Richard C. Dugdale, University of Southern California, Los Angeles, CA 90007, pers. commun. June 1977. 332 WHITLEDGE: REGENERATION OF NITROGEN BY NEKTON the fish totals 2.96 mg-at/m2 per day (Table 4), which is about 26.9% of the ammonium used by phytoplankton and 14. l%of total inorganic nitro- gen utilized. Results of zooplankton regeneration experi- ments obtained at the same time showed varia- tions related to size of the organisms and depth of water. Smaller zooplankton were most abundant and had largest excretion rates inshore while the largest zooplankton biomass was located just off- shore of the shelf break where the larger zoo- plankton with smaller excretion rates were found (Smith and Whitledge 1977). The mean ammonium regeneration rate calculated from zooplankton that were separated into four size classes of 102, 223, 505, and 1,000 Mm was 4.7 mg- at/m2 per day over the shelf, which is about 42.7% of the ammonium used in primary production and 22.4% of total inorganic nitrogen uptake. The release of ammonium from the sediments off northwest Africa was estimated by placing bell jars on the bottom in the shallow inshore re- gion (25 m) where divers could collect initial and final samples using plastic bottles (Rowe et al. 1977). The mean ammonium release rate from the two locations was 5.64 mg-at N/m2 per day. This value represents 0.23 Mg-at/1 per day if mix- ing occurred over the entire water column in the nearshore region. The ammonium content of pore water in the upper few centimeters and at the seawater-sediment interface was quite large in the two nearshore stations compared with samples collected at 50 and 200 m. Likewise the gradients of ammonium production at the sedi- ment-water interface was shown to decrease from MOO /xg-at/1 per cm at 25 m to <40 /ug-at/1 Table 4.— Nitrogen budget for northwest Africa upwelling ecosystem. per cm offshore of the shelf break. So using the concentration of ammonium in pore water and sediment-water interface gradients as indica- tors of ammonium flux from the sediments, the sediments were estimated to be releasing about 5.6 and 1.9 mg-at/m2 per day at water depths of 50 and 200 m. These sediment-release values would provide 78.9% of ammonium used in pri- mary production and 24.2% of the total inorganic nitrogen uptake over the inner shelf. A smaller portion of productivity evidently sinks to the sediments hence smaller benthic release rates are observed. The input to the water column from the sedi- ments nearshore at depths of 30 m or less are probably very significant in creating and main- taining a high concentration of ammonium found in the shallow waters (Fig. 5) that are often discolored due to a large air-derived suspended load. The ammonium-release rates from the sedi- ment are larger than nearshore pelagic regen- eration rates and the large aeolian sediment load (Sarnthein and Walger 1974; Rowe et al. 1977; Milliman 1977) was presumably large enough to inhibit phytoplankton nutrient uptake as a result of light attenuation and to discourage large bio- masses of zooplankton (Codispoti and Friederich 1978). It is therefore probable that the primary productivity not eaten by the small-sized zoo- plankton falls to the bottom, so an appreciable quantity of ammonium is placed in the water col- umn by zooplankton excretion and particulate organic matter decomposition on the bottom. 41 STATIONS 44 42 63 4364 10- Ammonium regeneration Percent of Percent of 20 mg-at/m2 ammonium nitrate p lus E I per day uptake ammonium uptake Shelf' 30 Baclerioplankton 05 7 2 1- CL UJ Zooplankton 7.82 104 33 Fish 2.96 39 13 Q 40 Benthic sediments 5.64 75 24 Total 16.92 225 72 Offshore2 50 Bacterioplankton 4.43 27 20 Zooplankton 5.35 33 24 Fish 1.84 11 8 60 Benthic sediments 1.88 12 8 Total 13.50 83 60 3 • ^ ^ • , *• • 3.0 / — • • / • • • >V • — • 2.0 . J • \ • • Jc ~ 2.0 *iv • X^i.o * • • ^y • _ • • \_/C - i i i 1 i 'Phytoplankton ammonium uptake = 7.5 mg-at/m2 per day. Phytoplankton nitrate uptake = 16.0 mg-at/m2 per day 2Phytoplankton ammonium uptake = 16.2 mg-at/m2 per day. Phytoplankton nitrate uptake = 6.2 mg-at/nr per day. Source for footnotes 1 and 2: Dugdale and Maclsaac, unpubl. results 25 20 15 IO 5 0 DISTANCE OFFSHORE (km) Figure 5.— Distribution of ammonium (pg-at/l) observed in a transect of stations across to shelf at lat. 21°40'N. 333 FISHERY BULLETIN: VOL. 80, NO. 2 Bacterioplankton studies in the northwest Africa upwelling ecosystem (Watson 1978) esti- mated the phytoplankton biomass in the water column to be much larger than bacterial biomass at stations <350 m water depth. The bacterial biomass in the sediments, however, was higher nearshore and lower offshore. The water column contained only 8% of the bacterial biomass on the inshore stations, so the bacteria are probably re- cycling only about 0.5 mg-at N/m2 per day in- shore. The offshore region has about 73% of the bacterial biomass in the water column compared with the sediments, so the bacterioplankton may regenerate as much as 4.4 mg-at/m2 per day in the deeper waters of 200 m or greater. The bac- terial processes that were occurring in the sedi- ments were estimated from bell jar experiments (Rowe et al. 1977). The inshore bottom ammo- nium release rates (5.64 mg-at/m2 per day) include bacterial, meiofaunal, and chemical pro- cesses occurring in the sediments, so these values were used rather than the purely bacterial rates of Watson (1978). The difference between the bell jar and bacteria-only rates is about 5.1 mg-at/m2 per day. This difference is quite high to explain as a chemical rate so meiofaunal rates evidently are quite important. In offshore waters the sedi- ment release rates are much lower than inshore based on near-bottom ammonium gradients and decreased ammonium pore water concentra- tions. The sparids in this study, Mediterranean Sea reef fish (Whitledge 1972), and the nearshore and bottom fish of British Columbia( Wood 1958) have apparently much smaller weight-specific ammonium excretion rates than fish such as the Peruvian anchovy, northern anchovy, jack mackerel, and sardinella. The increased meta- bolic rate needed by mackerels and clupeoids is probably a result of their large energy demands resulting from continuous swimming. Low metabolic rates in sluggish mammals have been shown to be related to their relatively infrequent movements (Whittow 1977) compared with highly active animals of similar body weight. As a result it could be predicted that respiration or excretion rates for fish should be related to both their body weight and index of locomotion such as swimming speed or daily swimming time. The total amountof ammonium regenerated in the upwelling ecosystem off northwest Africa has spatial variability which cannot be ignored. Nevertheless, regeneration in organisms from bacterioplankton through benthos (Table 4) is estimated to recycle significantly large amounts of nitrogen in the ecosystem and easily produce all of the ammonium used in primary produc- tivity. In some shallow locations ammonium is produced in large quantities and biological up- take is reduced such that high concentrations of ammonium are often observed in the very near- shore water. ACKNOWLEDGMENTS This work was supported mainly by National Science Foundation Grant OCE-78-05737 as a component of the United States IDOE Coastal Upwelling Ecosystems Analysis (CUEA) Pro- gram. The analysis was also partially supported by the United States Department of Energy under Contract No. DE-ACO2-76CH00016. LITERATURE CITED Armstrong, F. A. J., P. M. Williams, and J. D. H. Strick- land. 1966. Photo-oxidation of organic matter in sea water by ultra-violet radiation, analytical and other applications. Nature (Lond.) 211:481-483. Blackburn, M., and W. Nellen. 1976. Distribution and ecology of pelagic fishes studied from eggs and larvae in an upwelling area off Spanish Sahara. Fish. Bull., U.S. 74:885-896. Codispoti, L. A., and G. E. Friederich. 1978. Local and mesoscale influences on nutrient varia- bility in the northwest African upwelling region near Cabo Corbeiro. Deep-Sea Res. 25:751-770. DeManche, J. M., H. Curl, Jr., and D. D. Coughenower. 1973. An automated analysis for urea in seawater. Limnol. Oceanogr. 18:686-689. Dugdale, R. C, and J. J. Goering. 1970. Nutrient limitation and the path of nitrogen in Peru current production. Anton Brunn: Rep. 4, p. 5.3- 5.8. Tex. A&M Press. DURBIN, A. G., AND E. G. DURBIN. 1975. Grazing rates of the Atlantic menhaden Brevoortia tyra n n ux as a function of particle size and concentration. Mar. Biol. (Berl.) 33:265-277. Eppley, R. W., E. H. Renger. E. L. Venrick, and M. M. Mullin. 1973. A study of plankton dynamics and nutrientcycling in the central gyre of the North Pacific Ocean. Limnol. Oceanogr. 18:534-551. Friederich, G. O., and T. E. Whitledge. 1972. AutoAnalyzer procedures for nutrients. In S. P. Pavlou (editor), Phytoplankton growth dynamics: Chemostat methodology and chemical analyses, p. 38-60. Dep. Oceanogr. Univ. Wash., Spec. Rep. 52. Grollman, A. 1929. The urine of the goosefish {Lophius piscatorius): its nitrogenous constituents with special reference to the presence in it of trimethylamine oxide. J. Biol. Chem. 81:267-278. 334 WIIITI.KDCK: RKCKNKRATION OF NITROCKN BY NEKTON Haedrich. R. L.. M. Blackburn, and J. Brulhet. 1976. Distribution and biomass of trawl-caught animals off Spanish Sahara, West Africa. Matsya 2:38-46. Harris, E. 1959. The nitrogen cycle in Long Island South. Bull. Bingham Oeeanogr. Collect.. Yale Univ. 17:31-65. McCarthy, J. J., and T. E. Whitledge. 1972. Nitrogen excretion by anchovy (Engravlis mordax anil E. ringens) and jack mackerel {Trachwrus sym- metricus). Fish. Bull., U.S. 70:395-401. MlI.UMAN. J. D. 1977. Effects of arid climate and upwelling upon the sedimentary regime off southern Spanish Sahara. Deep-Sea Res. 24:95-103. Pandian, T. J. 1970. Intake and conversion of food in the fish Limanda limanda exposed to different temperatures. Mar. Biol. (Berl.) 5:1-17. Pomeroy, L. R., H. M. Mathews, and H. S. Min. 1963. Excretion of phosphate and soluble organic phos- phorus compounds by zooplankton. Limnol. Oeeanogr. 8:50-55. Rowe, G. T., C. H. Clifford, and K. L. Smith, Jr. 1977. Nutrient regeneration in sediments off Cap Blanc, Spanish Sahara. Deep-Sea Res. 24:57-63. Sarnthein, M„ and E. Walger. 1974. Der aolische sandstrom aus der W-Sahara zur Atlantikkuste. Geol. Rundsch. 63:1065-1087. Smith, S. L., and T. E. Whitledge. 1977. The role of zooplankton in the regeneration of ni- trogen in a coastal upwelling system off northwest Africa Deep-Sea Res. 24:49-56. Thorne, R. E.. O. A. M athisen. R. J. Trumble, and M. Black- burn. 1977. Distribution and abundance of pelagic fish off Spanish Sahara during CUEA Expedition JOINT-I. Deep-Sea Res. 24:75-82. Walsh, J. J., and S. O. Howe. 1976. Protein from the sea: A comparison of the simu- lated nitrogen and carbon productivity of the Peru up- welling ecosystem. In B. C. Patten (editor), Systems analysis and simulation in ecology, Vol. IV, p. 47-61. Acad. Press, N.Y. Watson, S. W. 1978. Role of bacteria in an upwelling ecosystem. In R. Boje and M. Tomczak (editors), Upwelling ecosys- tems, p. 139-154. Springer-Verlag. Berl. Whitledge, T. E. 1972. Excretion measurements of nekton and the regen- eration of nutrients near Punta San Juan in the Peru upwelling system derived from nekton and zooplankton excretion. Ph.D. Thesis, Univ. Washington, Seattle, 115 p. 1978. Regeneration of nitrogen by zooplankton and fish in the northwest Africa and Peru upwelling ecosystems. hi R. Boje and M. Tomczak (editors), Upwelling ecosys- tems, p. 90-100. Springer-Verlag, Berl. In press. The role of nutrient recycling in upwelling eco- systems. /» R. T. Barber and M. E. Vinogradov (edi- tors), Bioproductivity of upwelling ecosystems. Else- vier, Amsterdam. Whitledge, T. E., and R. C. Dugdale. 1972. Creatine in seawater. Limnol. Oeeanogr. 17:309- 314. Whittow, G. C. 1977. Night shift for sloths and other sluggards. Nat. Hist. 86(l):66-72. Wood, J. D. 1958. Nitrogen excretion in some marine teleosts. Can. J. Biochem. Physiol. 36:1237-1242. 335 THE ATLANTIC STURGEON, AC1PENSER OXYRHYNCHUS, IN THE DELAWARE RIVER ESTUARY Harold M. Brundage III and Robert E. Meadows' ABSTRACT Records of Atlantic sturgeon, Acipenser oxyrhynchus, captured in the Delaware River estuary from 1958 through 1980 were obtained from the literature, unpublished data, and logs maintained by commercial fishermen who took Atlantic sturgeon incidental to their operations for other species. During the period reviewed, there were 130 Atlantic sturgeon reported captured; 64 in commercially fished gill nets and 66 incidental to fishery and ecological studies. Atlantic sturgeon were most abundant in Delaware Bay (river km 0-55) in spring and in the lower tidal river (river km 56-127) during summer. This seasonal distribution appeared similar to that described for the Hudson River estuary. Atlantic sturgeon between 800 and 1,300 mm total length were relatively more abundant in the Delaware River estuary than had been reported in other estuaries, suggesting utilization of the Delaware system during a greater portion of the life cycle. The Atlantic sturgeon, Acipenser oxyrhynchus, inhabits large estuaries and Atlantic coastal waters from Labrador to eastern Florida; a southern subspecies, A. o. desotoi, occurs throughout the Gulf of Mexico (Vladykov and Greeley 1963). The Delaware River estuary, historically one of the major spawning and nursery areas for the Atlantic sturgeon, once supported the largest and most profitable sturgeon fishery on the Atlantic coast (Ryder 1890). The fishery in the Delaware River estuary was extremely short lived, however, and followed a pattern of rapid decline observed in most other estuaries. The commercial fishery, which began in the mid- 19th century and expanded rapidly after 1870 as smoked sturgeon and caviar gained acceptance, declined precipitously about 1900 and virtually collapsed by 1905 as the population declined (see Ryder 1890; Cobb 1900; Murawski and Pacheco 1977). Overfishing of adults on the spawning grounds combined with late maturity appears principal- ly responsible for this decline, although destruc- tion of benthic food organisms by coal silt pollu- tion and general deterioration of water quality and destruction of juvenile Atlantic sturgeon by American shad, Alosa sapidissima, fishermen probably contributed. Little is known of the present status of the Atlantic sturgeon in the Delaware River estuary. 'Ichthyological Associates, Inc., 100 South Cass Street, Middletown, DE 19709. Manuscript accepted October 1981. FISHERY BULLETIN: VOL. 80. NO. 2. 1982. As a preliminary step towards an assessment all available recent records of Atlantic sturgeon capture in the estuary were compiled. Reliable, quantitative data were found for the period 1958 through 1980. Most records were obtained from the substantial body of published and unpub- lished data generated by recent fishery and ecological studies. Further information was ob- tained via personal communication with the staffs of the Delaware River Anadromous Fishery Project of the U.S. Fish and Wildlife Service, the Delaware Division of Fish and Wildlife, and Ichthyological Associates, Inc. In addition, during spring 1979 and 1980, three commercial gill netters who had previously worked with the authors maintained logs of Atlantic sturgeon captured incidental to their operations for other species. Some 25 other fishermen were interviewed to obtain their im- pressions of Atlantic sturgeon occurrence and abundance. Inherent in this approach was the premise that representative trends might become apparent when a body of incidental records and anecdotal accounts are considered together. Apparent trends must be interpreted cautiously, however, since sampling gear and effort varied considerably between and within years. To aid in the delineation of spatial-temporal trends the estuary was divided into three regions based on physiography and salinity regime. "Delaware Bay" extends from the mouth (river km 0) to the vicinity of the Leipsic River (river km 55), is shaped like a flattened funnel and has 337 FISHERY BULLETIN: VOL. 80. NO. 2 extensive shoals along the New Jersey shore (Fig. 1). The estuary narrows considerably at about river km 56 to form the "lower tidal river" which extends to Marcus Hook, Pa. (river km 127). The "upper tidal river" extends to the fall line just north of Trenton, N.J. (river km 222). Delaware Bay is generally polyhaline (18- 30 7..), the lower tidal river mesohaline to oligohaline (0.5-187..), and the upper tidal river limnetic (0.0-0.57..) (Tudor 1980). These zones of salinity may be displaced considerably, however, depending upon freshwater flow, tidal stage, and local meteorological conditions. RESULTS From 1958 to 1980 there were 130 documented captures of Atlantic sturgeon in the Delaware River estuary (Table 1, Fig. 1); 68 in Delaware Figure 1. — Locations of recorded captures of Atlantic sturgeon in the Delaware River Estuary, 1958-80. Seasons are defined as winter— December through January; spring — March through May; summer— June through August; fall — September through November. Records- for which precise capture locations are not known are also given. PENNSYLVANIA DELAWARE CITY TRENTON A WINTER U SPRING O SUMMER D FALL 10 20 PICKERING DELAWARE Additional Records (j) Delaware Bay , Q] Lower Delaware Bay ATLANTIC OCEAN Table 1.— Recorded captures of Atlantic sturgeon, Acipenser oxyrfujnchus, in the Delaware River estuary. November 1958-July 1980. Salin- To al River ity Temp length Date Area km 7„ CO Method of capture No. (mm) Source 14 Nov. 1958 Lower Delaware Bay — — — 9 1 m trawl 1 508 deSylva et al 1962 Sept. 1967 Harbor of Refuge. Del. 3 — — 9 1 m trawl 1 — Daiber and Wockley 1968 Oct. Joe Flogger Shoal, Del. 42 — — 9.1 m trawl 1 — Daiber and Wockley 1968 31July 1968 Liston Point, Del. 77 28 cm gill net 5 814, 1 1,165, 1,431 143, 1,193 IA, Inc.,' Middletown, Del. 1 Aug. Liston Point 77 28 cm gill net 5 680, 1 1.172, 1,431 157. 1,323 IA, Inc., Middletown 9Aug Liston Point 77 — — 28 cm gill net 1 889 IA, Inc., Middletown Mar -Apr 1969 Little River, Del. 45 — — 13-14 cm gill net 5 — DRBAFP2 unpubl. data 28 Sept 1971 Delaware Point, Del. 72 3.5 22.0 4.9 m trawl — IA, Inc., Middletown 20 June 1972 Artificial Island, N.J. 79 30 22.0 4.9 m trawl — IA, Inc., Middletown 24 Sept 1973 Newbold Island. N.J. 203 — — 4.9 m trawl 196 IA, Inc., Middletown Mar -Dec. 1974 Burlington Island, N.J. 190 — — Cooling water intake — DRBAFP unpubl data 23 May Artificial Island 79 1.0 20 1 4.9 m trawl 340 IA, Inc , Middletown Aug Bordentown. N.J 206 — — 4.9 m trawl — DRBAFP unpubl data 8 May 1975 Artificial Island 79 5.0 175 14 cm gill net 700 IA, Inc , Middletown 19 May Artificial Island 82 1.5 19.0 8 cm gill net — IA, Inc , Middletown 10-1 1 June Newbold Island, N.J. 200 — — 4.9 m trawl 3349 Martin Marietta Corp., 1976 Oct -Dec. Delaware Power Plant 163 — — Cooling water intake — DRBAFP unpubl data 24 Mar 1976 Artificial Island 79 0 86 8 cm gill net 765 IA, Inc , Middletown 10 May Fishing Creek. N.J 75 5.0 16.0 14 cm gill net 550 IA, Inc , Middletown 17 Mar 1977 Little River 45 — — Gill net 1,117 Dovel 1979 4Apr Appoquinimink River, Del 82 — — 4.9 m trawl 591 IA, Inc , Middletown 13Apr. Little River 45 — — Gill net 457 Dovel 1979 12 May Artificial Island 86 50 16.0 4.9 m trawl 519 IA. Inc . Middletown June Pea Patch Island, Del 98 — — Gill net — DRBAFP unpubl. data 27 June Artificial Island 82 70 24.2 8 cm gill net 720 IA, Inc., Middletown 21 July Artificial Island 82 5.0 28.0 8 cm gill net 680 IA, Inc . Middletown 18 Mar 1978 Bowers Beach, Del 38 — — Gill net — Dovel 1979 22 Mar Little River 45 — — Gill net 2 — Dovel 1979 23 Mar Bowers Beach 38 — — Gill net — Dovel 1979 27 Mar Little River 45 — — Gill net — Dovel 1979 30 Mar Fowler Beach. Del 15 — — Gill net — Dovel 1979 3 Apr Little River 45 — — Gill net — Dovel 1979 338 BRUNDAGE and MEADOWS: ATLANTIC STURGEON IN DELAWARE RIVER ESTUARY Table 1.— Recorded captures of Atlantic sturgeon, Acipvnuern.njrh nucha.-*. Continued. n the Delaware River estuary, November L958-July 1980.- Date Area River km Salin- ity 7.. Temp (°C) Method of capture Total length No. (mm) Source 7 Apr Little River 8 Apr Del Haven, N J 15 Apr Little River 22 Apr. Cohansey River, N.J. 29 Apr Del Haven May Little River 3 May Del Haven 6 May Delaware Bay 10 July Harbor of Refuge 24 July Artificial Island 24 July Elsinboro Point, N J 24 July Artificial Island 15Aug Burlington Island 17Aug. NE of Harbor of Refuge 24Aug. Artificial Island 28 Aug Burlington Island 6 Sept Burlington Island 20 Sept. Artificial Island 16Apr. 1979 Old Bare Shoal, Del 16Apr. Hope Creek, N J 20 Apr Hope Creek 20Apr Kitts Hummock, Del. 22 Apr Kitts Hummock 23Apr Kitts Hummock 24 Apr Kitts Hummock 25 Apr. Port Mahon, Del. 25 Apr Kitts Hummock 25 Apr Hope Creek 26 Apr. Port Mahon 26Apr Kitts Hummock 29Apr Port Mahon 29 Apr Port Mahon 30Apr Kitts Hummock 1 May Port Mahon 2 May Port Mahon 3 May Port Mahon 6 May Port Mahon 9 May Port Mahon 11 May Port Mahon 12 May Port Mahon 21 May W of Joe Flogger Shoal 22 May Offshore Smyrna River. Del. 22 May Ship John Shoal 12 June Hope Creek 21 June W of Joe Flogger Shoal 22 June Ship John Shoal 1 2 July Smyrna River July Ship John Shoal 9 Aug N of Pea Patch Island 25 Sept. Bowers-Pickering Beaches, Del Sept. Ship John Shoal 22 Oct Harbor of Refuge Oct. Fourteen Ft Bank. Del 1 Nov Offshore Prime Hook Beach, Del. 2 Nov Artificial Island 16 Feb 1980 Artificial Island 24 Mar Pickering Beach. Del 25 Mar Pickering Beach 26 Mar Pickering Beach 29 Mar Pickering Beach 8Apr. Artificial Island 22Apr Pickering Beach May Old Bare Shoal, Del. 6 May Artificial Island 19May Blake Channel 28 May Artificial Island 24 June Reedy Island Dike, Del. 10 July Sunken Ship Cove. N J 16July Artificial Island 17 July Offshore Smyrna River 24July Artificial Island 31 July Artificial Island 45 — — Gill net 1 — Dovel 1979 17 — — Gill net 1 — Dovel 1979 45 — — Gill net 1 — Dovel 1979 61 8.0 170 4.9 m trawl 760 IA, Inc , Middletown 17 — — Gill net 1 — Dovel 1979 45 — — Gill net 2 Dovel 1979 17 — — Gill net 1 — Dovel 1979 — — — Gill net 2 Dovel 1979 3 — — Hook and line 1,524 Del. Dep. Fish and Wildl. 80 40 270 4 9m trawl 1 604 IA, Inc , Middletown 92 40 27.5 4 9m trawl 1 678 IA. Inc , Middletown 82 7 0 27 6 4.9 m trawl 518 IA. Inc , Middletown 190 — — 4.9 m trawl 157 IA. Inc , Absecon, N J 1 29.0 25.2 4.9 m trawl 1 2,000 IA, Inc , Middletown 82 5.0 27.7 4.9 m trawl 1 690 IA, Inc , Middletown 190 0 25.0 4.9 m trawl 175 IA, Inc.. Absecon 190 0 25.0 4.9 m trawl 175 IA, Inc . Absecon 80 70 234 4.9 m trawl 1 648 IA, Inc.. Middletown 17 — — 9 1 m trawl 1 855 Smith 1980 78 — — 14 cm gill net 760 Commercia fisherman 78 — — 14 cm gill net 890 Commercia fisherman 41 — — 13 cm gill net 1 610 Commercia fisherman 41 — — 10-13 cm gill net 2 900. 1,030 Commercia fisherman 41 — — 13 cm gill net 2 830, 980 Commercia fisherman 41 - — 13 cm gill net 2 865, 880 Commercia fisherman 47 — — 10 cm gill net 584 Commercia fisherman 41 — — 13 cm gill net 660 Commercia fisherman 78 — — 14 cm gill net 914 Commercia fisherman 47 — — 13 cm gill net 570 Commercia fisherman 41 — — 13 cm gill net 685 Commercia fisherman 47 — — 13 cm gill net 1,067 Commercia fisherman 47 — — 13 cm gill net 580 Commercia fisherman 41 — — 13 cm gill net I > 711, 865 Commercia fisherman 47 — — 13 cm gill net 810 Commercia fisherman 47 — — 13 cm gill net ! I 720, 940 Commercia fisherman 47 — — 13 cm gill net 890 Commercia fisherman 47 — — 13 cm gill net 880 Commercia fisherman 47 — — 13 cm gill net 810 Commercia fisherman 47 — — 13 cm gill net 914 Commercia fisherman 47 — — 13 cm gill net 965 Commercia fisherman 42 20.0 167 9.1 m trawl 860 Smith 1980 71 13.0 183 9.1 m trawl ; > 935. 1.117 Smith 1980 58 17.0 18 1 9 1 m trawl 955 Smith 1980 77 — — Dead on surface 889 IA, Inc , Middletown 42 240 19.6 9 1 m trawl 960 Smith 1980 58 16.0 20.8 9.1 m trawl > 1,190, 750 Smith 1980 71 120 24.8 4.9 m trawl 960 IA, Inc., Middletown 58 170 25.2 9 1 m trawl 815 Smith 1980 101 1.0 28 1 4.9 m trawl 128 IA, Inc., Middletown 38-44 — — Gill net 1,090 Commercia fisherman 58 18.0 227 9 1 m trawl 1 1,150 Smith 1980 3 — 13.2 4.9 m trawl 1 810 IA, Inc . Middletown 34 25.0 14 7 9 1 m trawl 875 Smith 1980 7 27.0 11.3 9 1 m trawl 1 1,100 Smith 1980 80 6.0 15.0 Cooling water intake t 936 IA, Inc . Middletown 80 100 05 Cooling water intake 1 692 IA, Inc.. Middletown 44 — — Gill net 1 760 Commercia fisherman 44 — — Gill net 1 457, 760 457. 1,066 Commercia fisherman 44 — — Gill net 1 1,220 Commercia fisherman 44 — — Gill net 1 1.524 Commercia fisherman 80 1 0 9.5 Cooling water intake 1 3750 IA, Inc.. Middletown 44 — — Gill net 1 760 Commenca fisherman 17 270 15.6 9 1 m trawl 1 1.010 Del Dep. F sh and Wildl 80 40 170 Cooling water intake 1 689 IA, Inc., Middletown 40 180 175 4.9 m trawl 1 927 IA, Inc , Middletown 80 7.0 21 0 Cooling water intake 1 942 IA, Inc , Middletown 84 — — Dead on surface 1 620 1A, Inc., Middletown 80 — — Dead on beach 1 1.010 IA, Inc . Middletown 80 — — Cooling water intake 1 3637 IA, Inc.. Middletown 71 14 0 25.3 9 1 m trawl 1 1,035 Del Dep. F sh and Wildl 80 100 280 Cooling water intake 1 1,015 IA, Inc.. Middletown 80 8.0 280 4.9 m trawl (surface) 1 1,230 IA, Inc . Middletown 'Ichthyological Associates, Inc 2Delaware River Basin Anadromous Fishery Project. 3Converted from fork length 339 FISHERY BULLETIN: VOL. 80, NO. 2 Bay, 53 in the lower tidal river, and 9 in the upper tidal river. A total of 64 specimens were captured in commercially fished gill nets, most as a bycatch of operations for American shad, and weakfish, Cynoscion regalis. The remaining 66 specimens were taken incidental to various fishery and ecological investigations; 23 by 4.9 m bottom trawl, 17 by 9.1 m bottom trawl, 12 by experimental gill net, 9 at industrial cooling water intakes, 1 by 4.9 m surface trawl, 1 by hook and line, and 3 were dead on the water's surface or on shore. In Delaware Bay Atlantic sturgeon were taken from March through November (Fig. 2). Catch was greatest during March through May (14-23/mo), low during July through August (1/mo), and increased somewhat during Septem- ber through November (2 or 3). The spring peak was composed largely of specimens captured in 1979 and 1980 by the cooperating commercial gill netters who logged incidental Atlantic sturgeon captures while fishing shallow waters off of Kitts Hummock (river km 41) and Port Mahon (river km 47), Del., in 1979 and Pickering Beach (river km 44), Del., in 1980. Their records reflect 27 specimens taken during 20 April-14 May 1979 and 8 during 24 March-22 April 1980. Additionally, all 18 Atlantic sturgeon reported from Delaware Bay by Dovel (1979) were taken during March-May (see Table 1). Although this abundance pattern may be biased by the greater fishing effort expended during spring relative to other seasons, essentially all other commercial gill netters interviewed reported the highest frequency of incidental sturgeon capture during spring. Most Atlantic sturgeon taken in the gill net fishery are apparently below marketable size and are released. Records indicate that survival in gill nets was very high if the nets were tended daily. In the lower tidal river Atlantic sturgeon were taken from February through September and in December (Fig. 2); most during July (16), al- though moderate numbers (6-10) were taken from April through August. Eleven specimens were taken in late July and early August 1968, by two part-time commercial gill netters purposely fishing for Atlantic sturgeon. These men fished, typically for a 2-wk period in summer, between Delaware City (river km 98) and Liston Point (river km 77), Del., during the late 1940's through the early 1970's. They employed essentially traditional methods, as described by Cobb (1900), and drifted 9 X 572 m, 28 cm cotton mesh 10 0 20 10 K Ul CD I 0 z 25 15 UPPER TIDAL RIVER (n = 7) I 1 LOWER TIDAL RIVER (n=53) -1 1 1 1 1 I r- DELAWARE BAY (n = 63) J F M ' A ' M MONTHS Figure 2.— Number of Atlantic sturgeon captured monthly in three regions of the Delaware River estuary, 1958-80. gill nets along the bottom from about 1 h before to about 1 h after low tide (Beck2). These were, to the best of our knowledge, the last successful commercial efforts directed specifically at Atlantic sturgeon. Although the above men- tioned 11 specimens are the only quantitative accounting of their catch available, anecdotal accounts indicate considerable success with as many as 191 specimens taken in a 2-wk period (Beck 1973). In the upper tidal river, Atlantic sturgeon were captured in June (1), August (4), and September (2) (Fig. 2). Only one specimen was taken in the Wilmington, Del., to Philadelphia, Pa. (river km 114-170), reach. In this region mean dissolved oxygen concentrations approach zero during summer and are typically below 5 ppm during May through October (Freiders- dorff et al. 1978). This fish was taken sometime during October-December 1975, when oxygen concentration was considerably higher. Available data showed that Atlantic sturgeon occurred over a wide range of water temper- ature (0.5°-28.1°C) and salinity (0.0-29.0 V..). The varying availability of temperature and salinity data by region, however, precludes further dis- cussion. Values were available for 62% of the specimens captured in the lower tidal river but -Robert A. Beck, Department of Natural Resources and Environmental Control Divisionof Fish and Wildlife, P.O. Box 1401, Dover, DF 19901, pers. commun. December 1978. 340 BRUNUAGE and MEADOWS: ATLANTIC STURGEON IN DELAWARE RIVER ESTUARY only 10% of those from Delaware Bay and 22% of those taken in the upper tidal river. Length data were available for 97 Atlantic sturgeon. Reported fork length (FL) for 1 1 speci- mens were converted to total length (TL) with the relationship FL = 0.878 TL -6.551, r =0.999, calculated from measurements of 19 specimens. Total length ranged from 457 to 2,000 mm (X = 885 mm; n = 45) for specimens taken in Delaware Bay, from 128 to 1,431 mm (X= 863 mm; n = 48) in the lower tidal river, and from 157 to 196 mm (X= 176 mm; n = 4) in the upper tidal river (Fig. 3). Based on age-length data for the Hudson River estuary (Dovel 1979), the probable age of specimens taken in Delaware Bay ranged from 0+ to ca. 20+ and from 0+ to ca. 14+ in the lower tidal river. Only age 0+ specimens were taken in the upper tidal river. No individuals in spawning condition were reported. 5 r CE UJ m Z> 0 10 rf UPPER TIDAL RIVER (n=4) 1 ' ■ 1 ' ■ ' 1 ' ' ' 1 ' ' ' 1 LOWER TIDAL 5 I- ' r-T'L RIVER (n = 48) r~l n^ ^^ j. — ««, — . 0 1 ' i 1 1 1 1 1 r i I r i ■ ■ • // • 10 • 5 . DELAWARE BAY (n = 45) 0 +_ U ^_ ~Ln i ' 100 400 700 1000 1300 1600 1 OTAL L EN GTH (m m) Figure 3. — Length-frequency distributions of Atlantic sturgeon captured in three regions of the Delaware River estuary, 1958-80. DISCUSSION Despite the limitations imposed by reliance on incidental catch records, a number of generali- zations regarding the Atlantic sturgeon in the Delaware River estuary can be made. The data strongly indicate that there is a viable population of Atlantic sturgeon in the Delaware system which utilizes different regions of the estuary to varying degrees depending on season and life stage. A definite pattern of seasonal movement within the estuary can be inferred. In early spring substantial numbers of juvenile Atlantic sturgeon occurred in the shallow waters of Delware Bay; later in spring, abundance increased in the lower tidal river and this upstream movement continued through early summer. This is similar to the pattern described by Dovel (1979) for the Hudson River, i.e., juvenile Atlantic sturgeon overwinter in the deeper waters of the lower estuary and move up- stream and inshore in spring in response to in- creasing water temperature. However, in the Delaware River estuary, juvenile Atlantic sturgeon ranged to the the fall line at Trenton, whereas in the Hudson River they were found only to river km 145 (Kingston, N.Y.), some 100 km below the limit of tidal intrusion. During summer, Atlantic sturgeon were most abundant in the lower tidal portion of the Dela- ware River and probably use this region as a foraging ground. Numbers in this reach de- creased somewhat during August, the month of maximum water temperature. Dovel (1979) reported that Hudson River Atlantic sturgeon seek cooler waters during summer and may move south before water temperature peaks. In the present study, however, no such movement to Delaware Bay during August was evident, although numbers in the bay increased slightly in September. Abundance in the Delaware system decreased in the upper and lower tidal river in September and increased somewhat in Delaware Bay during September through November, suggest- ing a return to overwintering areas. Some indi- viduals may have left the estuary at that time to overwinter in the nearshore ocean. Interviews conducted in 1978 and 1979 with commercial trawl fishermen operating out of Ocean City, Md., indicate that Atlantic sturgeon are commonly taken near the mouth of Delaware Bay in fall. Most of these fish are small, ranging from 0.6 to 1.5 m long, with occasional captures of larger individuals of 2.5-3.5 m. Evidence on occurrence of older juveniles in the Delaware system disagrees with reports from other systems. Murawski and Pacheco (1977) reported that these fish emigrate from the estuary when they reach 760-915 mm long and do not return for a number of years until mature. Dovel (1979) found that Atlantic sturgeon be- tween about 800 mm (ca. age 5) and 1,300 mm TL (ca. age 12) were rare in the Hudson River estuarv and inferred that these individuals re- 341 FISHERY BULLETIN: VOL. 80, NO. 2 mained at sea. However, in the Delaware River estuary Atlantic sturgeon between 800 and 1,300 mm were common and composed 62% of the measured specimens from Delaware Bay and 48% of those from the lower tidal river. It is possible that the Delaware River estuary is utilized during a greater portion of the Atlantic sturgeon's life cycle then is the Hudson. This may be associated with the relatively unimpacted condition of Delaware Bay and the lower Dela- ware River as compared with the heavily indus- trialized and degraded lower Hudson River estuary. It is also possible that an Atlantic sturgeon which has left the Hudson River may utilize other estuaries, including the Delaware system, during this portion of its life. Recapture of tagged Hudson River sturgeon in the Delaware River and more distant estuaries (Dovel 1979) may substantiate this view. No specimens in spawning condition were re- corded from the Delware River Estuary; most reported were probably immature. Most Atlan- tic sturgeon captured in the Delaware River estuary were <112 cm TL minimum for mature males and <200 cm for mature females reported by Dovel (1979). Larger mature specimens are almost certainly present in the estuary but are not vulnerable to the small-mesh gear typically fished by commercial fishermen and fishery biologists. Even though spawning location could not be ascertained it is perhaps signficant that the smallest specimen recorded (128 mm) was taken near Pea Patch Island, Del. (river km 101), an area historically described (Borodin 1925) as a principal spawning area for Atlantic sturgeon. This compilation of incidental catches and a substantial body of anecdotal information sug- gests that Atlantic sturgeon may be far more abundant in the Delaware River estuary than commercial catch statistics and the impressions of other fishery scientists indicate (Hoff3). The reported scarcity of Atlantic sturgeon may be more the result of not fishing the appropriate gear in the right locations at the right times or of not monitoring fishermen who are. A more definitive status evaluation will require quanti- tative investigation to determine population size, mortality rate, age-specific fecundity, age at 'James G. Hoff, Biology Department. Southern Massachu- setts University, North Dartmouth. MA 02747. pers. commun. July 1980. See also, Hoff. J. G. 1980. Review of present status of the stocks of the Atlantic sturgeon. Acipenser oxyrhynchus (Mitchill). Southeastern Massachusetts Univ.. North Dartmouth, 136 p. first reproduction, and spawning time and loca- tion. In any event, the value of incidental capture records and anecdotal accounts should be recog- nized and continued monitoring of available sources is advisable. The potential for restora- tion of the stock is high, based on the lack of industrial development in the lower estuary and the fact that as yet undammed, the Delaware River still features relatively natural run-off and river flow patterns. Pollution abatement programs, particularly those involved with improvement of dissolved oxygen levels in the Chester to Philadelphia reach will undoubtedly enhance this potential. ACKNOWLEDGMENTS We are grateful to Victor J. Schuler and Alan W. Wells of Ichthyological Associates, Inc., for their critical reading of the manuscript. Joseph Miller of the U.S. Fish and Wildlife Service, Richard J. Seagravesof the Delaware Division of Fish and Wildlife, and Robert G. Howells of Ichthyological Associates, Inc., supplied collec- tion data for several specimens. We also thank Robert G. Howells for drafting the figures and Holly J. Jones for assistance with manuscript preparation. LITERATURE CITED Beck, R. A. 1973. Sturgeon— alive and well. Del. Conserv. 17(2):4- 6. Borodin, N. 1925. Biological observations on the Atlantic sturgeon (Acipenser sturio). Trans. Am. Fish. Soc. 55:184-190. Cobb, S. N. 1900. The sturgeon fishery of the Delaware River and Bay. Rep. U.S. Comm. Fish. 1899:369-380. Daiber, F. C, and R. C. Wockley. 1968. Annual Dingell-Johnson Report, 1967-1968. Univ. Del., Newark, 35 p. deSylva, D. P., F. A. Kalber, Jr., and C. N. Schuster, Jr. 1962. Fishes and ecological conditions in the shore zone of the Delaware River estuary, with notes on other species collected in deeper waters. Univ. Del. Mar. Lab., Inf. Ser., Publ. 5, 164 p. Dovel, W. L. 1979. Biology and management of shortnose and Atlan- tic sturgeon of the Hudson River. Final Rep., 53 p. Freidersdorff, J. W., L. Lofton, and R. C. Reichard. 1978. Performance report Delaware River Basin anad- romous fishery study. U.S. Fish Wildl. Serv., Rosemont, N.J., 34 p. Martin Marietta Corporation. 1976. Monitoring fish migration in the Delaware River. Final Report - March 1976. Martin Marietta Corp., Baltimore. 86 p. 342 BRUNDAGE and MEADOWS: ATLANTIC STURGEON IN DELAWARE RIVER ESTUARY Ml'RAWSKI, S. A., AND A. L. Pacheco. 1977. Biological and fisheries data on Atlantic sturgeon, Acipenser oxyrhynchus. Sandy Hook Lab. Tech. Ser. Rep. 10, 69 p. National Marine Fisheries Service, Highlands, N.J. Ryder, J. A. 1890. The sturgeons and sturgeon industries of the east- ern coast of the United States, with an accountof experi- ments bearing upon sturgeon culture. Bull. U.S. Fish Comm. 8:231-329. Smith, R. W. 1980. Marine fish populations in Delaware Bay and selected shore zone areas. Final Rep., Doc. No. 40- 05/80/03/3, Del. Dep. Fish Wildl., 70 p. Tudor, R. A. 1980. The Delaware River Estuary. In V. J. Schuler (editor), An ecological study of the Delaware River near Artificial Island 1968-1976: A summary, p. 3-9. Ichthyological Associates, Inc., Middletown, Del., 303 P- Vladykov, V. D., and J. R. Greeley. 1963. Order Acipenseroidei. In Fishes of the western North Atlantic, Part three, p. 24-60. Mem. Sears Found. Mar. Res., Yale Univ. 343 LARVAL DEVELOPMENT OF LABORATORY-REARED ROSYLIP SCULPIN, ASCELICHTHYS RHODORUS (COTTIDAE) Ann C. Matarese1 and Jeffrey B. Marliave2 ABSTRACT Larvae which hatched from egg masses collected at southwest Vancouver Island, Canada, were identified as Ascelichthys rhodorus and were successfully reared through transformation. A devel- opmental series from yolk-sac larvae through newly settled juveniles (5.9-17.6 mm SL) is described and illustrated. Larvae hatch at approximately 6.0 mm SL and the yolk is absorbed by 6.5 mm SL. Notochord flexion begins between approximately 8.8 and 9.0 mm SL and is usually completed by 11.0 mm SL. Transformation to the juvenile stage begins between 12.0 and 13.0 mm SLand is com- plete in most of our larger specimens (15.0-16.0 mm SL). Ascelichthys rhodorus larvae possess the following distinguishing characters: 1) pigment patterns along the ventral body and gut, 2) a pointed snout and moderately slender body as compared to other cottids, and 3) four prominent preopercular spines. A series of larvae is examined for meristic struc- tures, including fin ray, vertebral and caudal development, and sequence of bone ossification. All structures except the caudal complex are ossified in our largest specimen ( 17.6 mm SL). Head and preopercular spination is discussed. Minimum egg incubation time was 24 days (10°C); the minimum spawning period was 25 days. Larvae were examined for swimming behavior; older larvae maintained a relatively high speed schooling behavior throughout the planktonic phase. Settlement of juveniles started at 55-60 days, with ambivalence over reentry to the plankton until about 90 days, when settlement became perma- nent. The rosylip sculpin, Ascelichthys rhodorus, is a small (11-15 cm) intertidal and subtidal cottid species distinguished by smooth skin, a low spin- ous dorsal fin, the absence of pelvic fins, and a single hooked preopercular spine (Hart 1973). Little is known of its biology and development or its relationships within the family Cottidae (Howe and Richardson 19783). The geographic range of A. rhodorus extends from Moss Beach, Calif., northward to Sitka, Alaska (Miller and Lea 1972), and localized populations are com- monly found throughout this range (Howe and Richardson footnote 3). We provide here the first published descrip- tion of the larvae of A. rhodorus with notes on the development and behavior of the species in the aquarium environment. 'Northwest and Alaska Fisheries Center Seattle Labora- tory, National Marine Fisheries Service, NOAA, 2725 Mont- lake Boulevard East, Seattle, WA 98112. 2Vancouver Public Aquarium, P.O. Box 3232, Vancouver, B.C. V68 3X8 Canada. 3Howe, K., and S. L. Richardson. 1978. Taxonomic re- view and meristic variation in marine sculpins (Osteichthys: Cottidae) of the northeast Pacific Ocean. Final Rep., NOAA NMFS Contract No. 03-78-MO2-120. 1 January 1978 to 30 Sep- tember 1978, Northwest and Alaska Fisheries Center, Na- tional Marine Fisheries Service, NOAA, 2725 Montlake Blvd. East, Seattle, WA 98112. Unpubl. rep. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80, NO. 2. 1982. MATERIALS AND METHODS Egg Collection and Laboratory Rearing On 23 March 1979, nine unidentified egg masses were collected from under boulders on a cobble beach, at the 0.9 m tide level, at Jordan River (southwest Vancouver Island, Canada; lat. 48°25'20"N, long. 124°03'30"W). The egg masses were incubated in flowing seawater of about 10°C and 27'/.. salinity at the Vancouver Public Aquarium. Only three tanks were available for rearing larvae, so some larvae that hatched on different dates were mixed. Rearing tanks were of 1,000 1 volume, with inflow rates of over 1 tank volume/day. Newly hatched Artemia salinn nauplii were fed in excess numbers to larvae once daily. Larvae were killed and preserved (3% Formalin4 with sodium borate buffered sea- water of 157.. salinity) at weekly intervals until settlement from the planktonic stage started at 55-60 d. All preserved specimens were from two rearing tanks, one with a single sibling group and the other with a mixture of larvae from two separate hatching dates (Table 1). Surviving 4 References to trade names do not imply endorsement by the National Marine Fisheries Service, NOAA. 345 FISHERY BULLETIN: VOL. 80, NO. 2 Table 1.— Age and sibling relationships for Ascelichthys rho- dorus larvae used for descriptions. Tank Date killed (1979) Age (days) Relationship1 1 26 Mar 3 1 1 9 Apr 14/17 2 1 13 Apr 18/21 2 Not reared 17 Apr <1 — 2 17 Apr 8 1 1 17 Apr 22/25 2 1 26 Apr 31/34 2 2 1 May 22 1 1 1 May 36/39 2 1 1 May 36/39 2 1 9 May 44/47 2 2 23 May 44 1 1 23 May 58/61 2 '1 = siblings, all one age. same source. 2=2 sibling groups, mixed age, different source. juveniles from both tanks were reared to matur- ity at the Vancouver Public Aquarium. Taxonomic Specimens Measurements The following measurements were made on 64 unstained larvae of A. rhodorus (5.9-15.8 mm SL) using an ocular micrometer in a stereomicro- scope: Standard length (SL)— Snout tip to notochord tip prior to development of caudal fin, then to posterior margin of hypural bones. Head length (HL)— Snout tip to posterior mar- gin of opercle. Snout to anus length— Distance along body mid- line from snout tip to a vertical line through center of anal opening. Body depth at pectoral— Vertical distance from dorsal to ventral body margin at pectoral fin base. Meristic Structures A total of 49 larvae was cleared and stained for observation of various meristic structures and sequence of bone ossification. The following size ranges inadvertently were not preserved and are not represented in our discussion: 9.5-10.0 mm SL and 11.5-12.5 mm SL. Bone terminology fol- lows Richardson and Washington (1980). Specimens were stained using alizarin red and alcian blue (Dingerkus and Uhler 1977). Struc- tures were considered ossified even if only slightly stained with alizarin red. Counts on stained larvae were made of dorsal fin spines and rays, anal fin rays, left pectoral fin rays, caudal fin rays, branchiostegal rays, and abdominal and caudal vertebrae (including the terminal ural centrum). Counts of caudal fin rays in juvenile and adult A. rhodorus were made from radio- graphs of six specimens (46-101 mm SL) from the collections in the College of Fisheries, Uni- versity of Washington, Seattle. Twenty adult specimens (57-99 mm SL) were also cleared and stained for examination of the caudal fin. The problems and inconsistencies of head spination terminology in cottid larvae have been discussed by Richardson and Washington (1980). We follow their terminology by using names pro- posed for Sebastes spp. (Richardson and Laroche 1979). Head spines for A. rhodorus larvae were examined on cleared and stained specimens in order to determine the origin of the spines. Illustrations of larvae were made with the aid of a camera lucida. IDENTIFICATION OF ASCELICHTHYS RHODORUS The eggs of A. rhodorus range from 1.7 to 2.0 mm in diameter. Larvae hatch at approximately 6.0 mm SL and the yolk is absorbed by 6.5 mm SL. Notochord flexion begins between approxi- mately 8.8 and 9.0 mm SL and is usually com- plete by 11.0 mm SL. Transforming larvae (about 12.0-13.0 mm SL) were distinguished by a combination of characters including changes in pigmentation and ossification of fin rays. Our largest specimens (15.0-18.0 mm SL) were newly settled and exhibited increased juvenile pigmen- tation. The work of Richardson (1981) attempts to organize the cottid genera from the northeast Pacific that have been divided into phenetic groupings based on larval characters. In the northeast Pacific, larvae of 25 of 40 genera are described and most of the genera can be placed in 6 groups. Several genera are ungrouped (e.g., Enophrys, Gymnocanthus, and Myoxocepha- lus). The present study indicates that Ascelichthys is most similar to the genera of Richardson's Group 2 (Paricelinus, Triglops, Icelus, Chitono- tus, and Icelinus) which all possess the following characters: 1) moderately slender body form; 2) pointed snout; and 3) four prominent preopercu- lar spines. Most members of this group also have postanal ventral midline melanophores some- times extending along the caudal fin base. Although Richardson considers Group 2 coher- 346 MATARESE and MARLIAVE: LARVAL DEVELOPMENT OF ROSYLIP SCULPIN ent, some differences are found among the gen- era in degree of gut pigmentation, head spina- tion, number and position of postanal ventral melanophores, and myomere counts. In degree of gut pigmentation, A. rhodorus larvae have a moderate intensity of melano- phores; the gut is not as dark as Pa ricelinus but is darker than Chito>wtus. Ascelichthys rhodorus do not have as many head spines as some mem- bers of Group 2 (e.g., Triglops and Paricelinus), possessing only parietal and nuchal spines and lacking spines in regions of the postocular, post- temporal-supracleithrum, opercle, and cleith- rum. There is much variation among Group 2 genera in the number of ventral melanophores ranging from none in some species of Triglops to over 40 in Chitonotus( Richardson and Washing- ton 1980). Larvae of A. rhodorus are most similar to larvae of Paricelinus in ventral pigmentation by having approximately 20-30 melanophores in preflexion larvae and approximately 15-20 me- lanophores in postflexion larvae. Myomere counts may also be useful in distinguishing A. rhodorus larvae. Myomere counts for A. rhodorus are most similar to those reported for Chitonotus and Icelinus«40). Triglops, Icelus, and Pariceli- nus have >40 myomeres (Howe and Richardson footnote 3). The absence of pelvic fins in A. rhodorus does not distinguish the early larvae since in most cot- tids the pelvic fins are the last fins to develop. However, in larger postflexion specimens the lack of pelvic fins does help to distinguish the species. DEVELOPMENT OF ASCELICHTHYS RHODORUS Pigment Patterns A total of 35 larvae was examined for changes in larval pigmentation (Fig. 1). The following discussion describes general trends in melano- phore distribution. In the head region, pigment on early preflex- ion larvae is usually scattered dorsally over the head and nape; posterior to the eye, heavy inter- nal pigment occurs at the base of the brain (Fig. 1 A). With development, pigment increases in the area of the head, snout, mouth, operculum, and internally around the brain (Fig. 1B-E). A dis- tinct patch of melanophores occurs at the jaw angle, first appearing between 6.0 and 8.0 mm SL and then becoming less prominent as larvae begin to transform (>12.0 mm SL). After 6.0 mm SL, pigment appears on the underside of the mouth along the median cartilage between the dentaries and urohyal (Fig. 1C). In the abdomi- nal region, early larvae have a distinctly pig- mented gut with large, stellate melanophores covering most of the abdominal cavity (Fig. 1A- C). Melanophores are also present on the isthmus and pectoral fin base of early larvae (Fig. IB, C). With development, the external pigment cover- ing the gut becomes more internal than external with only a few melanophores visible on the over- lying skin (Fig. ID). An average of about 15 melanophores ( N = 12, range 11-22) line the ventral body midline in 0-8 d (6.1-7.9 mm SL) A. rhodorus larvae, beginning well posterior to the anus at about myomeres 11- 15 (Fig. 1A-C). These ventral melanophores show much variation in size and spacing among individual specimens. In general, the spacing be- tween melanophores decreases from anterior to posterior with the last few spots appearing close together. The size of melanophores does not fol- low any pattern although usually the first 2 or 3 anterior spots are larger than the posterior ones. In preflexion larvae between 22 and 36 d (8.8-9.5 mm SL), the ventral melanophores extend fur- ther forward beginning at about the fifth myo- mere posterior to the anus and increase in number to over 20 (N= 11, range 23-28). Melano- phores in the anterior half of the ventral midline pigment (about the first 12 spots) are more widely spaced and occur in the area where the anal fin is forming. In larger postflexion larvae at 44 d ( 10.2 mm SL), 15-20 (N = 25, range 9-22) ventral midline melanophores are present with the pigment beginning just posterior to the anus (Fig. ID, E). The anterior melanophores along the developing anal fin are larger and are be- coming more diffuse as they extend into the fin. Transforming specimens have fewer ventral spots, usually about 10 (N — 23, range 8-13), with most of them more internal than external (Fig. IF). In these specimens, melanophores posterior to the completely developed anal fin appear more or less as a single row whereas those along the anal fin are aligned in a double row. In the tail region posterior to the ventral midline row of melanophores a group of caudal melanophores occurs near the tail tip on the early larvae (Fig. 1A). As the caudal fin develops, these melano- phores begin to align in the area where the hy- pural bones are forming and in some specimens mav extend onto the caudal fin (Fig. IB, D). 347 FISHERY BULLETIN: VOL. 80, NO. 2 6.2 mmSL B 9.0 mm SL 11.0 mm SL 15.2 mm SL Figure 1.— Larval stages of Ascelichthys rhodorus showing changes in pigmentation: A. 6.2 mm SL; B. 9.0 mm SL; C. 9.0 mm SL (ventral view); D. 11.0 mm SL; E. 11.0 mm SL (ventral view); F. 15.2 mm SL. 348 MATARESE and MARLIAVE: LARVAL DEVELOPMENT OF ROSYLIP SCULPIN Little pigment is added until the onset of trans- formation, except on the head, nape, and in the dorsal, anal, and caudal finfolds. Pigmentation changes occurring at the beginning of transfor- mation are visible as early as 44 d after hatching (10.0-11.0 mm SL) but are not consistently visible until the 47th day (13.0 mm SL). During trans- formation A. rhodorus larvae show a rapid in- crease in pigmentation of all areas of the head and nape, and on the anterior dorsal body surface over the gut. A few melanophores appear in the dorsal portion of the postanal body becoming patches of pigment in the upper region dorsally and laterally (Fig. IF). Melanophores also ap- pear in the posterior caudal peduncle area. Early juveniles of the transformed, newly settled A. rhodorus have small, densely concentrated me- lanophores on the entire head, and several spots on the overlying skin over the gut cavity in addi- tion to internal melanophores (Fig. IF). The juveniles also have internal pigment along the notochord, and several distinctive groups of me- lanophore patches in the postanal body region along the upper body and in the caudal peduncle area. Dorsal body pigment on the largest speci- mens (17.0 mm SL) occurs in about five patches located under the posterior portion of the first dorsal fin, at the anterior, posterior, and center of the second dorsal fin, and in the posterior cau- dal area. Morphology (Tables 2, 3) Head length of A. rhodorus as a proportion of standard length increases with development and becomes almost one-third the standard length in early juveniles. Head length increases from 21.3% SL in preflexion larvae to 25.4% SL in lar- vae undergoing flexion. Values for head length continue to increase to 29.5% SL in postflexion larvae and 31.1% SL in transforming specimens. The head length of adult rosylip sculpin is slightly larger than our postflexion and trans- forming larvae; adult head lengths are generally about 37% SL (Hart 1973). Eye diameter as a proportion of head length decreases with development. Preflexion larvae have diameters over half the size of the head (50.8% HL), decreasing to 36.6% HL in trans- forming larvae. Eye diameter continues to de- crease in adult rosylip sculpin, usually measur- ing about 25% HL (Hart 1973). Snout to anus length as a proportion of stan- dard length increases with development. Snout Table 2.— Morphometries (in millimeters) of larvae and juve- niles of Ascelichthys rhodorus. Approximate interval of noto- chord flexion is between dashed lines and interval of transfor- mation is between solid lines. Age' (days) Standard length Head length Eye diameter Snout to anus length Body depth at pectoral 0 5.9 1.2 0.7 2.0 1.2 0 6.2 1.2 0.7 2.0 1.2 0 62 1.3 0.7 2.0 1.3 0 6.3 1.3 0.7 20 1.2 0 63 1.3 0.7 2.0 1.2 0 6.3 1.3 07 2.0 1.2 0 63 1.3 0.7 2.0 1.2 0 63 1.3 0.7 2.0 1.2 0 63 1.3 0.7 2.0 1.3 0 64 1.3 0.7 22 1.2 8 5.4 1.0 0.6 2.0 1.2 8 58 1.2 07 1.8 1.1 8 6 1 1.4 0.6 2.2 13 8 68 1.5 07 24 1.1 8 6.9 1.6 0.7 24 1.1 8 7.1 1.5 0.7 2.2 1.2 8 7.1 16 0.7 2.6 1.2 8 72 1.5 0.7 2.3 1.2 8 72 1.7 0.7 2.4 1.1 8 76 1.8 0.7 2.7 1.3 8 7.9 1.8 — 2.5 1.3 22 8.5 2.2 0.9 3.3 1.9 22 8.5 2.1 0.9 3.1 19 22 8.5 2.1 0.9 3.3 1.8 22 8.8 2.5 0.9 3.6 2.0 22 8.9 2.1 0.9 3.4 1.9 22 " 8.9 2.1 0.9 3.6 2.0 22 90 25 0.9 3.4 2.0 22 9.0 2.3 0.9 3.4 2.1 22 10.5 3.0 1.0 4.6 25 36/39 8.5 21 0.9 3.0 1.8 36/39 85 2.0 0.9 3.3 1.7 36/39 86 2.2 0.9 3.3 1.9 36/39 86 2.2 0.9 3.5 18 36/39 8.8 2.2 0.9 3.3 1.9 36/39 8.8 2.1 0.9 3.5 2.0 36/39 8.8 2.1 0.9 3.5 1.9 36/39 8.9 2.2 0.9 3.5 2.0 36/39 95 25 — 3.9 2.1 36/39 95 2.4 0.9 3.6 2.0 44 10.1 2.8 1.0 4.5 2.6 44 10.1 29 1.1 4.5 2.2 44 10 .1 3.0 1.1 4.5 2.4 44 10.2 3.0 1.1 46 24 44 10.3 3.0 1.1 4.5 2.6 44 10.5 3.0 1.1 4.7 2.4 44 10.5 3.3 1.2 4.9 2.6 44 10.9 3.4 1.2 5.3 2.6 44 11.0 3.4 1.2 5.2 2.5 44 11.0 3.1 1.2 4.9 2.6 44/47 12.8 3.8 1.5 6.1 3.3 44/47 13.0 3.9 1.5 65 3.6 44/47 13.3 3.7 1.5 6.5 3.7 44/47 13.3 40 1.5 6.4 3.6 58/61 13.3 3.9 1.6 6.5 3.8 58/61 13.8 49 1.7 7.0 34 58/61 168 48 1.7 8.5 3.9 58/61 16.0 52 1.7 8.2 4.2 58/61 17.6 5.1 1.8 9.1 48 58/61 13.0 4.0 1.5 6.3 29 58/61 13 1 4.0 1.6 6.3 29 58/61 14.0 49 1.6 7.0 3.2 58/61 15.0 5.0 1.7 7.7 3.4 58/61 15.8 5.2 1.7 7.8 3.9 'Two ages separated by a slash Indicates a mixed age group, different sibling groups (see Methods). length to anus length increases from one-third the standard length (33.2% SL) in preflexion lar- vae to 39.0% SL in larvae undergoing flexion. 349 FISHERY BULLETIN: VOL. 80, NO. 2 Table 3.— Body proportions of larvae and juveniles of Ascelichthys rhodorus. Values given for each body proportion are expressed as percent of standard length (SL) or head length (HL): mean, stan- dard deviation, and range. Body proportion Preflexion Flexion Postflexion Transforming Sample size Standard length (mm) Head length/SL Eye length/HL Snout to anus/SL Body depth at pectoral tin base/SL 21 6.5±0.6 (5-8) 21.3±1.4 (18-24) 50.8±6.4 (38-60)' 33.2±2.0 (31-37) 18.5±1.9 (15-22) 19 8.9±0.5 (8-11) 25.4±1.6 (24-29) 40 5±3.6 (30-45)2 39.0±2 0 (35-44) 22 0+0.9 (20-24) 10 10.5±0.4 (10-11) 29.5±1.3 (28-31) 36.6+1.1 (35-39) 45.4±1.6 (44-49) 23.8±1.2 (22-26) 14 14.3+1.6 (13-18) 31.1 ±2.4 (28-36) 36.6±3.0 (33-41) 49.6±1.3(48-52) 25.2±2 3 (22-29) 'Sample size 2Sample size 20 17. Values for snout length to anus length continue to increase in postflexion larvae to 45.4% SL and to almost half the body length (49.6% SL) in trans- forming larvae. Body depth at the pectoral fin base increases only slightly with development. Preflexion lar- vae have a body depth of 18.5% SL and values in- crease to 25.2% SL in transforming larvae. Adult body depths are usually about 28% SL (Hart 1973). Meristic Structures (Table 4) The following discussion of the development of meristic structures describes only general trends, as specimens show much variation in the sequence of bone ossification and our collection does not include all size ranges. Variation occurs frequently in the size of larvae with respect to the development of meristic structures. In general, the development of meristic characters appears dependent on size rather than age. Different growth rates as seen in standard length differ- ences among individuals and between tanks are also reflected in the development of meristic structures (Tables 1, 4). Oral Region Branchiostegals are the first meristic struc- tures to develop as ossification occurs as early as 6.8 mm SL. The full complementof six branchios- tegals (seven in a few specimens) is not consis- tently ossified until the larvae are 9.0 mm SL. Gill arches are stained blue by 9.0 mm SL and most begin to ossify between 8.8 and 9.5 mm SL. Ossification of gill rakers is complete by 13.3 mm SL. Axial Skeleton Abdominal and caudal centra begin to form 350 between 8.8 and 9.0 mm SL, and development proceeds from anterior to posterior with the first signs of ossification occurring in larvae between 8.8 and 9.5 mm SL. Abdominal centra are com- pletely ossified in 10.2 mm SL larvae. Caudal centra begin to ossify in 10.0 mm larvae and ossi- fication of the completed vertebral column ap- pears in 12.8 mm SL larvae. Neural and haemal spines begin to ossify in larvae between 8.8 and 10.2 mm SL. All neural spines in the abdominal area are ossified by 10.2 mm SL, and the remaining neural spines in the caudal area are complete by 12.8-13.3 mm SL. Haemal spines took up red stain in our 10.2 mm SL larvae but are not completely ossified until 12.8-13.3 mm SL. Ossification of both neural and haemal spines proceeds anterior to posterior with the last neural and haemal spines asso- ciated with the caudal complex the last to ossify. Fin Development In general, all fins except caudal fin rays begin to ossify at 10.2 mm SL. Dorsal spines and pec- toral fin rays are completely ossified by 12.8 mm SL, and dorsal and anal fin rays are fully ossified in 13.3 mm SL specimens. The caudal complex begins to ossify with the hypural bones in larvae between 12.8 and 13.3 mm SL. The following description is based on our available specimens although our largest juvenile (17.6 mm SL)does not have the full com- plement of ossified caudal fin rays. The caudal fin is associated with a complex of 4-5 centra (1 ural and 3-4 preural centra), 3-4 neural and 3-4 haemal spines, 3 epurals, 1 super- ior hypural (H Y 4-5), 1 inferior hypural (H Y 1-3), and 1 pair of uroneurals (Fig. 2). Caudal fin rays total 31-37 of which 10-13 are superior secondary fin rays and 8-11 are inferior secondary fin rays. Principal caudal fin rays supported by the hy- pural bones number 13 (6 are supported by the MATARESE and MARLIAVE: LARVAL DEVELOPMENT OF ROSYLIP SCULPIN > T3 C cci tn 01 c -a o> j=. OS -a c CD 01 O) -O C OJ -a o u 3 o c > -S c .£ — CO" o C to X a) o a> D. qj < XI . cfi CO ■ — o .2 o ct) ■s I cc o => «g ,E- t/3 *3 C -C CIS .S *■> 05 c > 3 0) T3 C c8 > 3 OS 0) I u < C3 O o, <1> re u CD c_ 01 HI O > o o a >• cj CO CD "- a. Ol CO < "O co t: — TJO) t c c E to OJ c- 55 i i i i i i i I i I I i i i i I i i i i i i i i I I I i i I I ! 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CD - = £*« ,« CO CO 05 »» m a> cd i= C)J£ O CO CO c Is* i-o + 351 FISHERY BULLETIN: VOL. 80, NO. 2 B HY 1 HY 2-3 HY 1-3 HY4 HY 5 7.2 mm SL HY4 8.5 mm SL 8.7 mmSL HY 13 10.0 mm SL 13.0 mm SL 16.0 mm SL HY 4 5 HY1-3 62.0 mm SL 352 MATARKSK anil MARLIAVE: LARVAL DEVELOPMENT OK ROSYLIP SCULPIN superior hypural and 7 are supported by the in- ferior hypural). Ahlstrom5 generalized that all members of the family Cottidae probably have a total of 12 principal caudal rays, 6 supported by the superior hypural and 6 supported by the in- ferior hypural. Verification of this principal fin ray count came from counts on 20 adult speci- mens acquired for this study, 19 of which actu- ally had a 6+7 count. Richardson6 has also ob- served a number of exceptions to a 6+6 count in other members of the family Cottidae. A symmetrical fin fold surrounds the tip of the notochord in newly hatched specimens 6.0 mm SL. In 7.2 mm SL larvae, a thickening is visible ventral to the notochord (Fig. 2A). By 8.5 mm SL, the ventral thickening is differentiated into three cartilaginous plates (Fig. 2B). The anterior plate represents hypural 1 (parhypural ) followed by a larger plate presumably representing the fusion of hypurals 2 and 3. Posterior to hypurals 2 and 3, a third plate represents hypural 4. A few caudal fin rays are also visible by 8.5 mm SL. In slightly larger larvae of 8.7 mm SL the urostyle is just beginning to undergo notochord flexion, and the unossified hypural 1 has fused with hy- purals 2 and 3 forming the inferior hypural plate (Fig. 2C). Also in 8.7 mm SL larvae, differentia- tion of hypural 5, and epurals 1 and 2 is visible (Fig. 2C). In larvae undergoing notochord flex- ion (10.0 mm SL) unossified hypurals 4 and 5 have begun fusing to form the superior hypural plate (Fig. 2D). We did not detect fusion of a sixth hypural bone during the formation of the super- ior hypural plate. If a sixth hypural bone de- velops late in the larval period as it does in the phylogenetically related blackgill rockfish, Se- bastes melanostomus, (Moser and Ahlstrom 1978), it was not evident in the juveniles or adults we examined. The first appearance of unossifed epural 3 also occurs in specimens about 10.0 mm SL (Fig. 2D). Ossification proceeds rapidly once the larvae have undergone notochord flexion. By 5E. H. Ahlstrom, Southwest Fisheries Center, National Ma- rine Fisheries Service, NOAA, La Jolla, CA 92038, pers. com- mun., class notes, 1971. (Deceased.) 6S. L. Richardson, Gulf Coast Research Laboratory, East Beach Drive, Ocean Springs, MS 39564, pers. comnnun. Febru- ary 1981. Figure 2.— Development of the caudal fin of Ascelichthys rho- dorus: A. 7.2 mm SL; B. 8.5 mm SL; C. 8.7 mm SL; D. 10.0 mm SL; E. 13.0 mm SL; F. 16.0 mm SL; G. 62.0 mm SL. EP = epural; HS = haemal spine; HY = hypural; NC = notochord; NS = neural spine; PU = preural centrum; U = ural centrum; UR = uroneural. Ossified elements are stippled. 13.0 mm SL, the ural centrum and all preural centra are ossified (Fig. 2E). The single ural cen- trum is not fused to the first preural centrum. Hypural bones, neural and haemal spines, and caudal fin rays have also begun ossifying in 13.0 mm SL specimens (Fig. 2E). By 16.0 mm SL, a completely ossified pair of uroneurals is visible dorsad to the urostyle (Fig. 2F). All three epurals have begun to ossify, thus completing the caudal complex except for a few unossified secondary caudal fin rays. This caudal complex of a 16.0 mm SL early juvenile resembles in all details that of a 62.0 mm SLadult(Fig.2G). In a number of specimens abnormalities of the last neural and haemal spines were observed, e.g., double neural spines from the first preural centra (Fig. 2E) and a large flattened haemal spine (Fig. 2G). Spination Four similar-sized preopercular spines are ossified on specimens 8.8-9.0 mm SL(Fig. IB). In 10.2 mm SL larvae the upper preopercular spine is larger than the lower three (Fig. ID). After transformation the three lower spines are no longer visible, leaving only the prominent upper spine (Fig. IF). The single hook shaped spine is visible on our largest specimens, appearing very similar to the single, recurved spine for which the adults are commonly known. On specimens 8.8-9.0 mm SL, one small, pari- etal spine isevident(Fig. lB).Thisspine remains prominent and is joined by a nuchal spine in 10.2 mm SL larvae (Fig. ID). The parietal and nuchal spines are no longer visible in larvae >12.8 mm SL(Fig. IF). REPRODUCTIVE BEHAVIOR AND LARVAL REARING Egg masses of A. rhodorus were found wedged in irregular spaces among rocks under larger boulders, but the eggs adhered only to other eggs, not to rock surfaces. No egg masses were found under boulders lying on sand, shell, gravel, or solid rock surfaces. The egg masses were taken only in a narrow band at the low water level, which was the lowest tidal level dur- ing March and early April 1979. This cobble beach had been repeatedly searched for fish eggs during lower tides before and after the period of the vernal equinox, i.e., in December, January, April, May, and June of previous years, but this kind of egg was only found during the moderate 353 FISHERY BULLETIN: VOL. 80, NO. 2 low tides of the vernal equinox. In April 1981, A. rhodorus eggs were found in the same area, but about half were dead while the remainder all hatched upon return to the laboratory. Perhaps the protracted exposure to air in April killed many of the earlier embryonic stages; an in- crease in embryonic temperature tolerance with development has been documented for another intertidal cottid, Clinocottus acuticeps (Marliave 1981a). Considering a relatively dense spawning of about one mass/3 m2 found in March 1979, and the lack of egg masses at other times, this species might be characterized by a brief spawning sea- son. Superficially, A. rhodorus eggs resembled Hexagrammos spp. eggs in size (about 2.0 mm) and color, although there were far fewer eggs per mass. As with Hexagrammos spp., newly spawned eggs were a semitranslucent blue to purple, grading toward opaque white toward the egg center (personal observation by J. B. Marli- ave). Eggs with advanced embryos, showing guanine eye pigment, appeared brown overall, due to melanophores overlying dark olive yolk material. All egg masses were incubated and hatched in the laboratory; none were used for egg counts but some egg diameter measurements were taken. Hatching occurred on March 23 (1 mass) and 26 (1 mass) and on April 9 (3 masses) and 17 (4 masses). This range of hatching dates indicated a minimum spawning period of 25 d. The collection and final hatch dates indicated a minimum egg incubation period of 24 d at 10°C. During the planktonic larval stage, larvae of A. rhodorus displayed relatively high-speed schooling behavior and a marked tendency to- ward startle responses. It is of note that both this species and another common northeastern Pa- cific Ocean fish, Trichodon trichodon (Marliave 1981b), are rare or unknown from plankton sam- ples and school soon after hatching in the con- fines of a tank. Unlike T. trichodon, however, A. rhodorus larvae do not school immediately upon hatching but develop schooling behavior within 2 wk of hatching. Ascelichthys rhodorus larvae do not swim as fast as those of T. trichodon; A. rho- dorus cruised at 2.5-7.5 body lengths/s at 2 wk of age, at 3-10 body lengths/s at 4 wk, and at 2.5-9.0 body lengths/s at 6 wk, with usual speeds close to 5 body lengths/s. From hatching onward, the A. rhodorus larvae were very easily disturbed, either by physical interference from other types of zooplankton, by movements of observers, or by abrupt changes in lighting. Startle responses were characterized by rapid bursts of undirected swimming which, in older larvae, effected the breakdown of schools. After 2 wk, larval A. rhodorus schooled near the surface at all ages except for those larvae in tanks with larval shrimp, Pandalus danae. The P. danae occupied the surface layers and A. rho- dorus schooled off the tank bottom until the P. danae settled from the plankton, after which A. rhodorus schooled near the surface. This pattern occurred successively in two separate tanks; no shrimp were present in the third tank. Thus, the vertical distribution of the A. rhodorus larvae was modified by the presence of other planktonic organisms. Settlement to the bottom started at 55-60 d of age (14-18 mm SL) and schooling generally ceased. However, for unknown reasons all larvae in a tank would temporarily resume schooling from time to time. Between 60 and 90 d, there was a gradual increase in the proportion of set- tled larvae with no observed difference in feed- ing behavior between settled and schooling fish. By 90 d of age, the majority of juveniles were per- manently settled and no further schooling was noted. Among cottids, protracted ambivalence about settlement from the plankton has been observed in Gilbertidia sigalutes (Marliave 1981c). After initial settling was observed, substrate trays containing sand, gravel, and pebbles were placed in the tanks to determine substrate pref- erences of the larvae (Marliave 1977), but the trays were avoided. Larval A. rhodorus never settled against vertical surfaces, as is typical of a variety of other cottids which lack discreet sub- strate preferences (personal observation by J. B. Marliave). Settlement was typically on open bot- tom throughout the month of ambivalence be- tween settlement and reentry to the plankton. ACKNOWLEDGMENTS Laboratory rearing was conducted at the Van- couver Public Aquarium (Vancouver, B.C., Can- ada). We thank the following at the Northwest and Alaska Fisheries Center Seattle Laboratory of the National Marine Fisheries Service: Bev- erly Vinter who assisted in identifying and illus- trating the larvae; Bernie Goiney for technical assistance; Arthur Kendall for review of the manuscript; and Jean Dunn for helpful discus- sions on caudal fin development and review of the manuscript. Kevin Howe, College of Fisher- 354 MATARKSK and MARLIAVE: LARVAL DKVKLOI'MKNT OK ROSYLIP SCULI'IN ies, University of Washington, provided adult specimens and taxonomic advice. Sally L. Rich- ardson, Betsy B. Washington, and Joanne L. Laroche reviewed an earlier version of the manu- script and provided many useful suggestions. LITERATURE CITED DlNGERKUS, G., AND L. D. UHLER. 1977. Enzyme clearing of alcian blue stained whole small vertebrates for demonstration of cartilage. Stain Technol. 52:229-232. Hart, J. L. 1973. Pacific fishes of Canada. Fish. Res. Board Can., Bull. 180, 740 p. Marliave, J. B. 1977. Substratum preferences of settling larvae of ma- rine fishes reared in the laboratory. J. Exp. Mar. Biol. Ecol. 27:47-60. 1981a. High intertidal spawning under rockweed, Fucus distiehus, by the sharpnose sculpin, Clinocottus acuti- ceps. Can. J. Zool. 59:1122-1125. 1981b. Spawn and larvae of the Pacific sandfish, Trieho- don trichodon. Fish. Bull., U.S. 78:959-964. 1981c. Vertical migrations and larval settlement in Gilbertidia sigalutes, F. Cottidae. In R. Lasker and K. Sherman (editors), The early life history of fishes, II, Vol. 178, p. 349-351. Rapp. I'.-V. Reun. Cons. Int. Explor. Mer. Miller, D. J., and R. N. Lea. 1972. Guide to the coastal marine fishes of California. Calif. Dep. Fish Game, Fish Bull. 157, 235 p. Moser, H. G., and E. H. Ahlstrom. 1978. Larvae and pelagic juveniles of blackgill rockfish, Sebastes melanostomus, taken in midwater trawls off southern California and Baja California. J. Fish. Res. Board Can. 35:981-996. Richardson, S. L. 1981. Current knowledge of larvae of sculpins (Pisces: Cottidae and allies) in northeast Pacific genera with notes on intergeneric relationships. Fish. Bull., U.S. 79:103-121. Richardson, S. L., and W. A. Laroche. 1979. Development and occurrence of larvae and juve- niles of the rockfishes Sebastes crameri, Sebastes pinni- ger, and Sebastes helvomaeulatus (Family Scorpaenidae) off Oregon. Fish. Bull., U.S. 77:1-46. Richardson, S. L., and B. B. Washington. 1980. Guide to the identification of some sculpin (Cotti- dae) larvae from marine and brackish waters off Oregon and adjacent areas in the northeast Pacific. U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circ. 430, 56 p. 355 A BEAK KEY FOR EIGHT EASTERN TROPICAL PACIFIC CEPHALOPOD SPECIES WITH RELATIONSHIPS BETWEEN THEIR BEAK DIMENSIONS AND SIZE Gary A. Wolff1 ABSTRACT A method of identifying the beaks and estimating body weight and mantle length of eight common species of eastern tropical Pacific cephalopods is presented. Twenty specimens were selected from each of the following species: Symplectoteuthis oualaniensis, Dosidiem gigas, Ommastrephes bar- tramii, Onychoteutkis banksii, Abralwpsis affinis, Pterygwteuthis giardi, Liocranchia reinhardti, and Loligo opalescens. Seven dimensions measured on the upper beak and five dimension^ measured on the lower beak are converted to ratios and compared individually among the species using an analysis of variance procedure and Tukey's to. Significant differences (a<0.05) observed among the species' beak ratios means, in addition to structural characteristics, are used to construct artificial keys for the upper and lower beaks of the eight species. Upper and lower beak dimensions are used as independent variables in a linear regression model with mantle length and body weight ( log trans- formed). Two equations are given for estimating the length and weight for each species from the upper or lower beak. One uses the rostral length dimension because of its durability and the second uses a dimension derived from a stepwise regression procedure. The importance of cephalopods as prey is well documented for whales (Gaskin and Cawthorn 1967; Clarke et al. 1976; Clarke 1977), seals (Aus- tin and Wilki 1950; Laws 1960), seabirds (Ash- mole and Ashmole 1967; Imber 1978), tunas (Pinkas et al. 1971; Matthews et al. 1977), tunas and porpoise (Perrin et al. 1973), and sharks (Clarke and Stevens 1974; Tricas 1979). Due to the rapid digestion of the softer body parts, how- ever, the cephalopod's beak is often the only iden- tifiable structure remaining in these predator's stomachs as evidence of feeding on cephalopods. Consequently, the accuracy of specific identifica- tions and estimates of cephalopod biomass con- sumed by these predators often suffers. Two methods have generally been used to ap- proach the problem of characterizing cephalo- pod beaks. A descriptive method was used most notably by Clarke (1962, 1980), Mangold and Fioroni(1966), and Pinkas etal. (1971). Families, genera, and occasionally species were identified from structural characteristics of the beak. A biometric method was used by Wolff (1977) and Wolff and Wormuth (1979) to separate two spe- cies of ommastrephid squid with beak dimen- sions. It was suggested that the method could be 'Department of Oceanography, Texas A&M University, Col- lege Station, TX 77843; present address: Environmental Engi- neering, Texas A&M University, College Station, TX 77843. Manuscript accepted October 1981. FISHERY BULLETIN: VOL. 80, NO. 2, 1982. expanded to include other species of cephalo- pods. This study presents a key based on structural and biometric differences among the beaks of eight species of cephalopods. The species of ceph- alopods examined were: Symplectoteuthis oua- laniensis (Lesson), Dosidicus gigas (d'Orbigny), Ommastrephes bartramii (Lesueur), Onychoteu- this banksii (Leach), Abraliopsis affinis (Pfeffer), Pterygioteuthis giardi Fischer, Liocranchia reinhardti (Steenstrup), and Loligo opalescens Berry. Regression equations of body weight and mantle length from beak dimensions are also presented. MATERIALS AND METHODS The cephalopods for this study were obtained from Southwest Fisheries Center, National Ma- rine Fisheries Service, and Invertebrate Collec- tion, Scripps Institution of Oceanography, La Jolla, Calif. Twenty specimens of each species were selected in the maximum mantle length range available. Table 1 shows the ranges for mantle length and body weight and collection locations for the cephalopods. The buccal masses were removed, after the specimens were mea- sured and weighed, and placed in a solution saturated with sodium borate and trypsin (8 g trypsin/1 sodium borate solution) for 6 to 10 d. 357 FISHERY BULLETIN: VOL. 80, NO. 2 Table 1.— Mantle length (ML) ranges, body weight ranges, and collection locations for the species (nla = specimens collected in the Pacific but spe- cific location not available). ML Weight Number range range of Species (mm) (g) specimens Lat. Long. Symplectoteuthis 130-290 79-927 1 00° 33' S 111°14' W oualaniensis 2 03° 25' S 110°31' W 2 06° 49' S 86°14' W 1 05° 12' S 91°49' W 1 08° 09' S 100°3V W 1 05° 46' S 102°31' W 1 00° 26' S 109° 28' W 1 01°15' S 112°5V W 2 02°40' S 116-1V W 1 oo°or s 118°03' W 2 00° 46' S 105°35' W 1 02°52' S 97°21' W 3 07°19' S 94°24' W 1 05° 14' S 83°32' W Dosidicus 196-321 191-842 2 00° 33' S 111-14' W gigas 3 02°52' S 97-21' W 3 07° 49' S 81°38' W 3 05° 14' S 83°32' W 1 01°46' S 108°58' W 2 00° 26' S 06° 49' S 11°38' S 06°00' S 04° 30' S 11°30' S 05°02' S 02°52' S 11°44' S 109°28' W 86°14' W 87°13' W 96° 16' W 89°16' W 93°18' W 91°49' W 97°21' W 83° 56' W Ommastrephes 85-165 11-118 4 30° 03' N 156°1 1' W bartramii 2 30°08' N 135°02' W 5 24° 18' N 155°00' W 9 28°1V N 155-17' W Onychoteuthis 40-130 3-67 2 13°00' N 132-00' W banksii 1 nla 1 25°10' N 121°22' W 10 13°49' N 118°59' W 3 18°00' N 113°00' W 3 00° 28' N 105-53' W Abraliopsis 19-26 0.5-4.3 5 24°06' N 109°37' W all in is 6 nla 7 11°3V N 131°08' W 2 05°42' N 86°53' W Pterygioteuthis 16-30 0 3-14 1 05°02' S 91°49' W giardi 2 11°44' S 83°56' W 2 10°24' N 107°46' W 2 06°30' N 139°00' W 2 00°04' N 127°47' W 2 00° 20' N 120°21' W 9 01°21' N 130°47' W Liocranchia 23-125 1-24 1 00° 30' N 96° 50' W reinhardti 3 18°32' N 119-51' E 1 32°34' N 117-29' W 1 12°40' N 112-46' W 14 13°49' N 118°59' W Loligo 80-153 12-49 7 34° 00' N 120°10' W opalescens 6 26° 30' N 114-50' W 7 33° 29' N 117-47' W The beaks were then removed from the buccal masses and placed in 40% isopropyl alcohol. Beak dimensions were measured with vernier calipers or an occular micrometer. Seven dimen- sions were measured on the upper beak of each specimen: length of the rostrum (RL), rostral tip to inner margin of wing (RW), length of hood (HL), width of the wing (WW), wing to crest length (WCL), jaw angle width (JW) and length of the crest (CL). Five dimensions were mea- sured on the lower beak of each specimen: rostral tip to inner posterior corner of lateral wall (RC), rostral tip to inner margin of wing (RW), length of the rostrum (RL), length of the wing(WL), and jaw angle width ( JW) (Fig. 1 ). These dimensions were transformed to ratios to remove the dimen- sionality. Comparisons among species' beak ratios were made with a one-way classification analysis of variance procedure (ANOVA). The ratios were normally distributed and the ratio 358 WOLFF: BEAK KEY FOR EIOHT CEI'HALOPOD SPECIES side view rw top view LjwJ LOWER UPPER Figure 1.— Dimensions measured on the upper and lower beak. transformation met the criteria for validity as described by Anderson and Lydic (1977). Tukey's (u procedure was used to test for significant dif- ferences (a<0.05) among 21 ratio means from the upper beak and 10 ratio means from the lower beak for each species. This procedure in- volves the computation of a confidence interval from the formula: a» = qa (p, Mi) s?, where w is a range for the treatment means with a given probability level (a<0.05), q is the studentized range, p is the number of treatments, m is the error degrees of freedom and sj is the standard error of the treatment means (Steel and Torrie 1960). Simple linear regressions were calculated to express the relationship between a beak dimension and the mantle length and log trans- formed body weight. An AMDAHL 470 V/6 computer2 performed the majority of computa- tions. RESULTS The results of the ANOVA procedure are sum- marized in Tables 2 and 3. The species' means are ranked and the standard error of the treat- ment mean for each ratio is given. These tables form the basis for the construction of the biomet- 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. ric portion of the beak key. Combinations of de- scriptive characteristics and significant beak ratios are used to identify the eight species of cephalopods. Separate keys are provided for the upper and lower beak. The ratio values presented in the key are mid- points between species' means and often greatly exceed the stated significance level (a<0.05) as indicated by the confidence interval for the spe- cies' means which follows in parentheses. Addi- tional descriptive characteristics and alternate beak ratios are given to corroborate the initial identification. Figures 3-10 show upper and lower beaks for each of the species. A few of the alternate ratios in the upper and lower beak key have species' means which are not significantly different. These ratios can be considered reliable since Hartley (1955) suggested that the experi- mentwise error rate could be relaxed consider- ably below the standard a<0.05 level due to the conservative nature of Tukey's w procedure. Additional alternate ratio values can be deter- mined from Table 2 to distinguish species if the ratios in the key are not satisfactory (e.g., dam- aged beak). The descriptive characteristics fol- low a slightly modified version of Clarke's termi- nology (1962, 1980) with several additions as shown in Figure 2. This key should be used with caution on specimens which are greatly outside the size range of this study. 359 FISHERY BULLETIN: VOL. 80, NO. 2 Table 2.— Upper beak ratio means (?) and standard error of the treatment means (s,) (co = 4.3os (8, 152) Sx), So = Sympkctoteuthis oualaniensis, Dg = Dosidicus gigas, Ob = Ommas- trephes bartramii, Obnk = Onychoteuthis banksii, Aa = Abraliopsis affinis, Pg = Pterygio- teuthis giardi, Lr = Liocranchis reinhardti Lo = Loligo opalescens. s, Ratio Spec :ies 0.0130 RL/RW So Dg Ob Obnk Aa Pg Lr Lo X 0.766 0682 0.606 0599 0 592 0 580 0.523 0.485 0.0051 RL/HL So Aa Dg Obnk Pg Ob Lr Lo X 0354 0 345 0.335 0316 0313 0.309 0 290 0.246 0.0351 RL/WH So Aa Dg Obnk Pg Ob Lr Lo X 1.507 1.341 1.282 1.190 1.151 1.111 0941 0863 0.0058 RL/WCL So Dg Ob Aa Pg Obnk Lr Lo X 0.358 0.354 0.319 0 306 0287 0287 0261 0.211 0.0148 RL/JW Obnk So Dg Aa Ob Pg Lr Lo X 1.349 1.215 1.161 1.128 1.061 1.042 0.963 0936 0.0038 RL/CL So Dg Ob Aa Pg Obnk Lr Lo X 0.288 0.280 0.252 0.234 0226 0.218 0.211 0.177 0.0136 RW/HL Aa Lr Pg Obnk Ob Lo Dg So X 0.585 0.557 0.542 0528 0.510 0.509 0.491 0463 0.0571 RW/WW Aa Obnk Pg So Dg Ob Lr Lo X 2254 1.980 1.979 1.968 1.878 1.831 1.799 1.757 0.0141 RW/WCL Ob Dg Aa Lr Pg So Obnk Lo X 0526 0.519 0518 0502 0 496 0467 0 452 0.435 00532 RW/JW Obnk Lo Aa Lr Pg Ob Dg So X 2.257 1.955 1.916 1.851 1 806 1.758 1.705 1.586 00190 RW/CL Ob Dg Lr Aa Pg So Lo Obnk X 0.416 0 411 0405 0396 0391 0376 0.365 0364 0.0751 HL/WW So Aa Dg Obnk Pg Ob Lo Lr X 4253 3.870 3827 3756 3.660 3594 3460 3.244 0.0095 HL/WCL Dg Ob So Pg Lr Aa Obnk Lo X 1 058 1.033 1.010 0917 0901 0884 0.856 0855 0.0593 HL/JW Obnk Lo Dg Ob So Pg Lr Aa X 4.277 3 846 3.474 3453 3431 3332 3.324 3279 0.0061 HL/CL Dg Ob So Lr Pg Lo Obnk Aa X 0.837 0.817 0813 0.728 0722 0.718 0689 0.677 0.0055 WW/WCL Ob Lr Dg Pg Lo So Aa Obnk X 0 288 0.280 0.277 0.253 0.249 0.238 0232 0230 00309 WW/JW Obnk Lo Lr Ob Pg Dg Aa So X 1.148 1.135 1.036 0 966 0922 0910 0.861 0 811 0.0045 WW/CL Ob Lr Dg Lo Pg So Obnk Aa X 0.228 0.226 0.219 0210 0 199 0.192 0.185 0.178 0.0785 WCL/JW Obnk Lo Aa Lr Pg So Ob Dg X 5.014 4.516 3.719 3 693 3642 3 399 3342 3284 0.0038 WCL/CL Lo Lr So Obnk Dg Ob Pg Aa x 0841 0808 0806 0805 0.791 0791 0788 0767 00033 JW/CL Dg Ob So Lr Pg Aa Lo Obnk X 0241 0.238 0.238 0.219 0.218 0.207 0 188 0 162 Table 3.— Lower beak ratio means (x) and standard error of the treatment means (sr). s. Ratio Species 0.0138 RC/RW Lo Dg Pg Aa Ob So Obnk Lr X 1.235 1 232 1.213 1 209 1.200 1 199 1 186 1 142 0.0509 RC/RL Lo Lr Pg Obnk Ob Aa Dg So X 4058 3580 3424 3222 2967 2960 2807 2783 00221 RC/WL Dg So Ob Aa Obnk Pg Lo Lr X 1 829 1 756 1.700 1.689 1.644 1.552 1.526 1.513 0879 RC/JW Lr Lo Aa Ob Pg Dg Obnk So X 4402 4025 3852 3673 3525 3.357 3.341 2 996 0.0504 RW/RL Lo Lr Pg Obnk Ob Aa So Dg X 3 289 3 139 2828 2722 2475 2459 2323 2 280 0.0148 RW/WL Dg So Ob Aa Obnk Lr Pg Lo X 1.485 1 465 1.418 1 398 1.387 1.327 1.280 1 236 00729 RW/JW Lr Lo Aa Ob Pg Obnk Dg So X 3867 3258 3 179 3 066 2918 2822 2.727 2500 00115 RL/WL Dg So Ob Aa Obnk Pg Lr Lo X 0653 0632 0.577 0575 0512 0.457 0.425 0.380 0.0274 RL/JW Aa Ob Lr Dg So Obnk Pg Lo X 1 308 1 243 1 235 1 197 1.077 1.037 1.032 0 996 00597 WL/JW Lr Lo pg Aa Ob Obnk Dg So X 2.911 2641 2.296 2284 2.168 2039 1.838 1.709 360 WOLFF: BEAK KEY FOR EIOHT OEPHALOPOD SPECIES OUTER hood POSTERIOR INNER (c) rostrum rostrum jaw angle — shoulder wing base ANTERIOR jaw angle insertion anterior margi ( produced) Figure 2.— Descriptive characteristics of the upper and lower beak; (a) deeply recessed jaw angle, (b) moderately recessed jaw angle, (c) jaw angle not recessed, (d) pigment stripes on inner surface of rostrum and crest, (e) hood deeply notched at crest, (f ) hood slightly notched at crest, (g) upper beak characteristics, (h) lower beak characteristics. la. lb. 2a. 2b. KEY TO THE UPPER BEAK *Alternate beak ratio **Alternate beak ratio CI greater than the difference between the species means. Jaw angle deeply recessed Jaw angle not deeply recessed Prominent groove at jaw angle Groove absent at jaw angle 6 2 3 4 361 FISHERY BULLETIN: VOL. 80, NO. 2 3a. RL/JW >1.24 (CIos = 1.349±0.032); *HL/JW >3.78 (CIos = 4.277+0.127); *RL/HL <0.33 (CIos = 0.316±0.011) Onychoteuthis banksii Jaw angle slightly recessed; anterior-posterior groove at jaw angle % of RL (Fig. 2); wing base inserted % down anterior margin of lateral wall; pigment changes with growth shown in Figure 3. Figure 3.— The upper (U) and lower (L) beak of Onychoteuthis banksii(\ - ML = 40 mm, URL =0.11 cm, LRL = 0.12 cm; 2 - ML = 84 mm, URL = 0.195 cm, LRL = 0.191 cm; 3 - ML = 130 mm, URL =0.24 cm, LRL = 0.24 cm). 3b. RL/JW <1.24 (CIos = 1.128+0.032); *HL/JW <3.78 (CIos = 3.279+0.127); *RL/HL >0.33 (CIos = 0.345+0.011) Abraliopsis affinis Jaw angle slightly recessed; anterior-posterior groove at jaw angle 0.301 (CI05 = 0.313±0.01 1); *RL/CL >0.218 (CI05 = 0.226+0.008) Pterygioteuthis giardi Jaw angle not recessed; wing base inserted just above base of anterior margin of lateral wall; pigment changes with growth shown in Figure 5. FIGURE 5.— The upper and lower beak of Pterygioteuthis giardi (1 - ML = 16 mm, URL = 0.03 cm, LRL = 0.03 cm; 2 - ML = 22 mm, URL = 0.05 cm, LRL = 0.05 cm; 3 - ML = 30 mm, URL = 0.06 cm. LRL = 0.05 cm). 2mm 363 FISHERY BULLETIN: VOL. 80, NO. 2 5a. RL/HL>0.268(CIo5 = 0.290+0.011); *RL/CL >0.194 (CIos = 0.211+0.008); *JW/CL >0.204 (CIos = 0.219+0.007) Liocranchia reinhardti Jaw angle not recessed; wing base inserted % down anterior margin of lateral wall; pigment changes with growth shown in Figure 6. FIGURE 6.— The upper and lower beak of Liocranchia rein- hardtid - ML = 23 mm, URL =0.03 cm, LRL = 0.03 cm; 2 - ML = 67 mm, URL =0.08 cm, LRL = 0.09 cm; 3 - ML = 125 mm, URL = 0.15 cm, LRL = 0.15 cm). 5b. RL/HL<0.268 (CIos = 0.246+0.011); *RL/CL <0.194 (CIos = 0.177+0.008); *JW/CL <0.204 (CIos = 0.188+0.007) Loligo opalescens Jaw angle not recessed; wing base inserted just above base of anterior margin of lateral wall; pigment changes with growth shown in Figure 7. 2mm Figure 7.— The upper and lower beak of Loligo opalescens (1 - ML = 80 mm, URL = 0.09 cm, LRL = 0.11 cm; 2 - ML = 117 mm, URL = 0.12 cm, LRL = 0.13 cm; 3 - ML = 153 mm, URL = 0.21 cm, LRL =0.18 cm). 364 WOLFF: BEAK KEY FOR EIGHT CEPHALOPOD SPECIES 6a. RL/JW M.lll (CI05 = 1.161±0.032) 7 6b. RL/JW 0.60 cm; pigmentation in lateral wall is absent in beaks with URL <0.60 cm; other pigment changes with growth shown in Figure 8. 1 1 2 mm Figure 8.— The upper and lower beak of Ommastrephes bar- ^ramu (1- ML =85 mm, URL=0.15cm,LRL = 0.15 cm; 2- ML = 140 mm. URL = 0.28 cm, LRL =0.31 cm; 3 - ML = 165 mm, URL = 0.40 cm, LRL = 0.41 cm). 7a. HL/CL >0.825 (CI05 = 0.838+0.013); *RL/HL <0.344 (CIos = 0.334+0.011); **RL/ JW<1.188 (CIos = 1.161+0.032) Dosidicus gigas Jaw angle deeply recessed; wing base inserted x/2 way down anterior margin of lateral wall; two pigment stripes extend from the inner surface of the rostrum posteriorly onto the inner surface of the crest (Fig. 2)3; ridges and grooves more prominent than 3Rancurel, P. 1980. Note pour servir a la connaissance de Symplectoteuthisoualaniensis(Lesson 1830) (Cephalopoda, Oegopsi- da) : Variations ontogeniques du bee superieur. Cahiers de L'Indo-Pacifique 2(2):21 7-232. 365 FISHERY BULLETIN: VOL. 80, NO. 2 pigment stripe in beaks with URL >0.60 cm; pigment changes with growth shown in Figure 9. 2mm Figure 9.— The upper and lower beak of Dosidicus gigas (1 - ML = 196 mm, URL = 0.46 cm, LRL = 0.41 cm; 2 - ML =237 mm, URL = 0.57 cm, LRL = 0.55 cm; 3 - ML = 321 mm, URL = 0.79 cm, LRL = 0.75 cm). 7b. HL/CL <0.825 (CIos = 0.813+0.013); *RL/HL >0.344 (CI05 = 0.354+0.011); *RL/JW >1.188 (CI05 = 1.215+0.032) Symplectoteuthis oualaniensis Jaw angle deeply recessed; wing base inserted l/2 down anterior margin of lateral wall; two pigment stripes present as in D. gigas (Fig. 2); ridges and grooves more promi- nent in beaks with URL >0.50 cm; pigment changes with growth shown in Figure 10. i 1 2mm 366 WOLFF: BEAK KEY FOR EIGHT CEPHALOI'OD SPECIES Figure 10.— The upper (see bottom of p. 366) and lower beak of Sympleetoteuthis oualaniensis (1 - ML = 130 mm, URL = 0.35 cm, LRL = 0.33 cm; 2 - ML = 188 mm, URL = 0.55 cm, LRL = 0.50 cm; 3 - ML = 290 mm, URL = 0.76 cm, LRL = 0.70 cm). KEY TO THE LOWER BEAK la. lb. 2a. 2b. 3a. 3b. 4a. 4b. 5a. 5b. Ridge or fold on lateral wall Ridge or fold absent on lateral wall. 2 3 RL/JW M.173 (CIos = 1.308+0.059); *RC/RL <3.091 (CI05 = 2.96+0.122) Abraliopsis affinis Jaw angle not recessed; no hood notch at crest; anterior-posterior ridge or fold on lateral wall4 (Fig. 2); pigment changes with growth shown in Figure 4. RL/JW <1.173 (CIos = 1.037+0.059); *RC/RL >3.091 (CIos = 3.222+0.122) Onychoteuthis banksii Jaw angle not recessed; no hood notch at crest; prominent anterior-posterior ridge on lateral wall (Fig. 2); pigment changes with growth shown in Figure 3. Jaw angle strongly recessed Jaw angle slightly or not recessed 6 4 RL/JW M.134 (CIos = 1.235+0.059); *RW/JW >3.565 (CIos = 3.87+0.157) Liocranchia reinhardti Jaw angle slightly recessed; no hood notch at crest; pigment changes with growth shown in Figure 6. RL/JW <1.134 (CIos = 1.032+0.059) 5 RC/RL >3.741 (CIos = 4.058+0.122); *RL/WL <0.418 (CIos = 0.380+0.033) Loligo opalescens Jaw angle not recessed; no hood notch at crest; anterior margin of lower wing often pro- duced; pigment changes with growth shown in Figure 7. RC/RL <3.741 (CIos = 3.424+0.122); *RL/WL >0.418 (CIos = 0.457+0.033) Pterygioteuthis giardi Jaw angle not recessed; no hood notch at crest; pigment changes with growth shown in Figure 5. 4A ridge or fold on the lateral wall of the lower beak is characteristic in many cephalopod species (e.g., Histioteuthis spp.). 367 FISHERY BULLETIN: VOL. 80, NO. 2 6a. RL/WL >0.604 (CI05 = 0.632+0.033) 7 6b. RL/WL <0.604 (CIos = 0.577±0.033); **RC/RL >2.890 (CI05 = 2.97+0.122) Ommastrephes bartramii Jaw angle recessed; no hood notch at crest (Fig. 2); pigment changes with growth shown in Figure 8. 7a. RL/JW >1.137 (CI05 = 1.197+0.059); **RC/JW >3.175 (CIos = 3.360+0.189) ....... Dosidicus gigas Jaw angle recessed; the hood is deeply notched at the crest (Fig. 2); pigment changes with growth shown in Figure 9. 7b. RL/JW <1.137 (CI05 = 1.077+0.059); **RC/JW <3.175 (CI05 = 2.990+0.189) Symplectoteuthis oualaniensis Jaw angle recessed; the hood is moderately notched at the crest (Fig. 2); pigment changes with growth shown in Figure 10. The wet body weight and mantle length values for each species were used in linear regression equations to establish a relationship with a beak dimension. The regression equation has the form: y — a + bx, where ij = weight or mantle length, a = # intercept, b = slope of the regression line, and x — beak dimension. Initially a stepwise procedure, based on r2 values, was used to deter- mine if combinations of beak dimensions would improve the estimate. Adding more than one in- dependent variable to the regression equations did not substantially increase the r2 values of the body weight and mantle length equations. The upper and lower beak of each species is represented by a pair of equations for mantle length and a pair of equations for body weight (Tables 4, 5). The firstsetof equations represents the best single independent variable equation derived from the stepwise regression procedure. The second set of equations retains the durable RL dimension of the upper and lower beak as the independent variable for all eight species. For the body weight equations all values were trans- formed to natural logarithms before regression. DISCUSSION The research on cephalopod beak ratios was initiated to determine whether species could be separated and identified by comparing different beak dimensions. Once this had been established, the primary use of such a technique was consid- ered to be stomach content analysis. The condi- tion of beaks removed from preserved, identified specimens is ordinarily much better than that of specimens removed from a predator's stomach. Therefore, other beak characteristics, in addi- tion to maximum separation between species' means, were considered when the beak ratios for the key were selected. The selection was based on a dimension's durability under mechanical and chemical action, the effect such action would have on the accuracy of the beak dimension's measurement, and the ability to separate the ratio means at a given confidence level (a =0.05). Consequently, small dimensions with easily Table 4.— Regression equations and r2 values for mantle length and body weight, upper beak regression equations in centimeters, asterisk indicates best regres- sion based on r2. Species Mantle len gth (mm) r2 Body weight (g) r2 Symplectoteuthis 'ML = -2.17 + CL 105.2 0.95 •In W = 3.7 + ln CL 3.1 0.98 oualaniensis ML = -10.9 f RL 382 2 0.81 In w = 7.6 + In RL 32 095 Dosidicus 'ML = 658 + CL 86.2 095 •In w = 4.3 + ln CL 2 23 0.97 gigas ML = 41.1 + RL 346 8 0.87 In w = 7.3 + In RL 254 0.91 Liocranchia 'ML = -5.4 + JW 804 7 096 •In IV = 7.2 + In JW 2 34 088 reinhardti ML = -3.2 + RL 806 9 094 In w = 7.0 + In RL 2.22 0.87 Abraliopsis •ML = 4 1 + CL 63.7 093 •In w = 3.3 + In CL 2.86 090 alii n is ML - 9 1 + RL 216.1 087 In w = 6.0 + In RL 2.2 0.85 Onychoteuthis •ML = -22.1 + CL 127.6 092 •In W = 9.4 + In RL 38 0.93 banksii ML = -31.0 + RL 641.0 087 In w = 9.4 + In RL 3.8 0.93 Pterygioteuthis ■ML = 2.1 + RW 230.9 0.76 ■In w = 3.8 + In CL 2 75 0.87 giardi ML = 7.3 +■ RL 289.8 062 In w = 5.8 + ln RL 2.04 0.83 Ommastrephes •ML = 42.4 + HL 95 8 099 •In w = 3.7 + In CL 2.4 098 bartramii ML = 51.4 + RL 282 4 094 In w = 6.7 + In RL 2.15 0 96 Loligo •ML = -5.7 + CL 153 5 094 •In w = 6.0 + ln RW 2.25 0.80 opalescens ML = 422 + RL 542.7 079 In w = 5.7 + In RL 121 0.65 368 WOLFF: BEAK KKY FOR EIGHT CEPHALOPOD SPECIES Table 5.— Regression equations and r2 values for mantle length and body weight, lower beak regression equations in centimeters, asterisk indicates best regression based on r2. Species Mantle length (mm) r* Body weight (g) f2 Symplectoteulhis •ML = -11.93 + RC 115.4 096 •In W = 4.7 + ln AC 3.2 098 oualaniensis ML = 6 98 + RL 392 .5 093 In W = 7.8 + In RL 3.0 096 Dosidicus 'ML = 680 + WL 207.7 095 'In W = : 4.97 + In AC 2.3 095 gigas ML = 44.2 + RL 357 9 084 In W = 7.4 + In RL 2.48 091 Liocranchia •ML = 0.85 + JW 956.8 094 •In W = 7.76 + In JW2 3 088 reinhardti ML = -1 09 + RL 802 2 0.89 In w= 6.7 + In RL 2 1 0.80 Abraliopsis •ML = 63 + RC 111 095 •In w = 3.8 + ln RC 2.5 0.91 aft in is ML = 9.8 + RL 192 8 088 In w = 5.5 + In RL 2.1 0.81 Onychoteuthis •ML = -22.5 + RC 177.7 0.93 •In w = 4.7 + In AC 3.5 094 banksii ML = -289 + RL 610.0 0.95 In w = 9.1 + In RL 3.7 089 Pterygioteuthis •ML = 23 + RC 121.9 0.76 •In w= 45 + In AC 2 7 092 giardi ML = 6.2 + RL 331.6 041 In w= 7.6 + ln RL 2.6 0.70 Ommastrephes ■ML = 44.6 + RC 103.5 099 •In w = 4.4 + In AC 2.3 099 barlramii ML = 527 + RL 276.1 096 In w= 6.6 + ln RL 2.07 098 Loligo 'ML = 6.0 + AW 240 9 0.87 •In w = 4.4 + In RC 1.95 0.76 opalescens ML = 32.4 + RL 607.8 0.74 In w= 6.0 + ln RL 1.4 058 damaged margins (e.g., RW, WW upper beak) were excluded from consideration when con- structing the key, even though they might show very good separation between species' means when used in a ratio (e.g., RL/RW upper beak). Larger dimensions which have easily damaged margins (e.g., CL/HL) can still provide a reliable dimension within the variability of the sample simply because the eroded margin represents less of the overall dimension compared with the smaller dimension with similar properties. Accurately determining which cephalopods are abundant in an area and which of these might be important in a predator's diet are diffi- cult problems to solve. The abundance of a spe- cies in a trawl sample is not necessarily an accu- rate reflection of its relative abundance in the field (Wormuth 1976) or in a predator's stomach (Clarke 1977). In an attempt to reduce this sampling bias the cephalopods in this study were chosen on the basis of their abundance in trawl samples (Young 1972; Okutani 1974), in collec- tions using alternate sampling devices (e.g., dip nets and jigs (Wormuth 1976)), and in stomach content studies of cephalopod predators in the same area (Pinkas et al. 1971; Perrin et al. 1973). The eastern tropical Pacific is the area for which these beak characterizations were con- structed. In many cases, large, pelagic cephalo- pod predators in this area will contain a large percentage of the species described in this study. As one moves away from this area, however, less can be said about the potential usefulness of this key, since the species composition and morpho- logical characteristics, including beak dimen- sions, can change. As an example, 28 specimens of O. bartramii from the Gulf of Mexico and northwestern Atlantic have an upper rostral length to jaw width ratio mean (RL/JW) of 1.22 (CI05 = ±0.02); considerably greater than the eastern tropical Pacific mean of O. bartramii (x = 1.06, CI05 = ±0.03). This higher ratio value also holds for three specimens from southeastern Australia. Such geographical variation in species with disjunct distributions is not uncommon and has been noted in other body measurements for O. bartramii by Young (1972). Additional measure- ments must be made on remaining cephalopod species in this key, particularly those with dis- junct distributions, before this key can be reliably used outside the eastern tropical Pacific area. There will be cephalopods in the stomachs of predators which are not included in this work. In order to reduce misidentifications, therefore, full use should be made of the alternate ratio means, the beak figures, and the descriptive characteristics. In most beaks, the dimensions which resulted in the best regression equations for mantle length and body weight were those that were close to the overall length of the beak (CL, HL, RC). In badly damaged beaks, however, these dimensions are often in poor conditon. The pairs of regression equations for each of the eight spe- cies represent an effort to increase the flexibility of estimating the size of a cephalopod. The re- gression equations which use the RL dimension variable will give less accurate estimates, but can be used in all but the most severely damaged beaks, as the RL is a very durable dimension. ACKNOWLEDGMENTS I thank J. H. Wormuth and A. D. Hart, Texas A&M University, for providing many helpful 369 FISHERY BULLETIN: VOL. 80, NO. 2 suggestions during the course of this research and in the review of this manuscript. I also thank C. F. E. Roper, National Museum of Natural His- tory, and W. F. Perrin, Southwest Fisheries Cen- ter, National Marine Fisheries Service, NOAA, for their early encouragement and help in ini- tiating the research; D. Au, Southwest Fisheries Center, and B. Lee, San Francisco State Univer- sity, for supplying many of the specimens and body measurements; and H. G. Snyder, Scripps Institution of Oceanography, for locating the re- mainder of the specimens and arranging for their loan. This research was supported by con- tract 03-7-208-35284 from the National Oceanic and Atmospheric Administration and grant DAR 7924779 from the National Science Foun- dation. LITERATURE CITED Anderson, D., and R. Lydic. 1977. On the effect of using ratios in the analysis of vari- ance. Biobehav. Rev. 1:225-229. ASHMOLE, N. P., AND M. J. ASHMOLE. 1967. Comparative feeding ecology of sea birds of a tropi- cal oceanic island. Peabody Mus. Nat. Hist., Yale Univ., Bull. 24, 131 p. Austin, 0. L., and R. Wilki. 1950. Japanese fur sealing. Nat. Resour. Sect. Rep. Tokyo, 129 p. Clarke, M. R. 1962. The identification of cephalopod "beaks" and the relationship between beak size and total body weight. Bull. Br. Mus. (Nat. Hist.) Zool. 8:420-480. 1977. Beaks, nets, and numbers. Symp. Zool.Soc.Lond. 38:89-126. 1980. Cephalopoda in the diet of sperm whales of the southern hemisphere and their bearing on sperm whale biology. Discovery Rep. 37:1-324. Clarke, M. R., N. Macleod, and O. Paliza. 1976. Cephalopod remains from the stomachs of Sperm whales caught off Peru and Chile. J. Zool. (Lond.). 180: 477-493. Clarke, M. R., and J. D. Stevens. 1974. Cephalopods, blue sharks and migration. J. Mar. Biol. Assoc. U.K. 54:949-957. Gaskin, D. E.. and M. W. Cawthorn. 1967. Squid mandibles from the stomachs of sperm whales (Physeter catodon L.) captured in the Cook Strait region of New Zealand. N.Z. J. Mar. Freshwater Res. 1:59-70. Hartley, H. O. 1955. Some recent developments in analysis of variance. Commun. Pure Appl. Math. 8:47-72. Imber, M. J. 1978. The squid families Cranchiidae and Gonatidae (Cephalopoda: Teuthoidea) in the New Zealand region. N.Z. J. Zool. 5:445-484. Laws, R. M. 1960. The southern elephant seal (Mirounga leonina Linn) at South Georgia. Nor. Hvalfangst-Tidende 49: 466, 468-476, 520-524, 526-536, 539-542. Mangold, K., and P. Fioroni. 1966. Morphologie et biometrie des mandibules de quel- ques cephalopodes mediterraneens. Vie Milieu 17(Ser. A):1139-1196. Matthews, F. D., D. M. Damkaer, L. W. Knapp, and B. B. COLLETTE. 1977. Food of western North Atlantic tunas (Thunnas) and lancet-fishes (Alepisaurus). U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-706, 19 p. Okutani, T. 1974. Epipelagic decapod cephalopods collected by mi- cronekton tows during the EASTROPAC Expeditions, 1967-1968. (Systematic Part). Bull. Tokai Reg. Fish. Res. Lab. 80:29-118. Perrin, W. F., R. R. Warner, C. H. Fiscus, and D. B. Holts. 1973. Stomach contents of porpoise, Stenella spp., and yellowfin tuna, Thunnus albacares, in mixed-species aggregations. Fish. Bull., U.S. 71:1077-1092. Pinkas, L., M. S. Oliphant, and I. L. K. Iversen. 1971. Food habits of albacore, bluefin tuna, andbonitoin California waters. Calif. Dep. Fish Game, Fish Bull. 152, 105 p. Steel, R. G. D., and J. H. Torrie. 1960. Principles and procedures of statistics, with spe- cial reference to the biological sciences. McGraw-Hill, N.Y., 481 p. TRICAS, T. C. 1979. Relationship of the blue shark, Prionace glauca, and its prey species near Santa Catalina Island, Califor- nia. Fish. Bull., U.S. 77:175-182. Wolff, G. A. 1977. Morphometry and feeding habits of two ommastre- phid squid. M.S. Thesis, Texas A&M Univ., College Station, 61 p. Wolff, G. A., and J. H. Wormuth. 1979. Biometrie separation of the beaks of two morpho- logically similar species of the squid family Ommastre- phidae. Bull. Mar. Sci. 29:587-592. Wormuth, J. H. 1976. The biogeography and numerical taxonomy of the oegopsid squid family Ommastrephidae in the Pacific Ocean. Bull. Scripps. Inst. Oceanogr., Univ. Calif. 23, 90 p. Young, R. E. 1972. The systematics and areal distribution of pelagic cephalopods from the seas off southern California. Smithson. Contrib. Zool. 97, 159 p. 370 MOVEMENT AND SPEED OF DOLPHIN SCHOOLS RESPONDING TO AN APPROACHING SHIP D. Au AND W. Perryman1 ABSTRACT Eight dolphin schools of the species Stenella attenuata, S. longirostris, and S. coeruleoalba were approached by ship and observed from a helicopter in the eastern Pacific to study their response to the vessel. All schools swam away from the projected track of the aproaching ship. Their movement, relative to the ship, followed paths that curved around the ship. Average swimming speeds while avoiding the ship varied from 5.1 to 8.8 knots. In some cases avoidance apparently began at 6 or more miles away from the ship. The effect of this behavior on shipboard censusingof dolphins is discussed. In the eastern tropical Pacific, tuna fishermen encircle with purse seine nets schools of certain small cetaceans, mainly spotted and spinner dolphins, Stenella attenuata and S. longirostris, to capture the yellowfin tuna, Thunnus albacares, with which they are associated (Perrin 1969, 1970). The resulting incidental kill of dolphins has led the National Marine Fisheries Service to study the status of these cetacean populations, as required by the Marine Mammal Protection Act of 1972. Data collected from commercial fishing boats and research vessels are important in determining the distribution and abundance of the dolphins. In the areas of intensive "porpoise fishing," dolphins are apparently learning from their experience with nets and fishing vessels. The animals are recaptured with purse seines fre- quently enough to have possibly learned to posi- tion themselves within the net to better facilitate their own release (Pryor and Kang2). More im- portantly, they may also have developed various behaviors to avoid detection by a fishing vessel and to reduce their chances of capture (Pryor and Kang footnote 2; Stuntz and Perrin3). Dolphin schools, especially of the spotted and spinner dolphin species, commonly swim rapidly away from approaching ships. This behavior is 'Southwest Fisheries Center La Jolla Laboratory, National Marine Fisheries Service, NOAA, La Jolla, CA 92038. 2Pryor, K., and I. Kang. 1980. Social behavior and school structure in pelagic porpoises (Stenella attenuata and S. longirostris) during purse seining for tuna. Southwest Fish. Cent. Admin. Rep. LJ-80-11C. 3Stuntz, W. E., and W. F. Perrin. Learned evasive behavior by dolphins involved in the eastern tropical Pacific purse seine fishery. (Abstr.) Third Conference on the Biology of Marine Mammals, Seattle, Wash., October 7-11, 1979. _ 3-)l~^ Manuscript accepted October 1981. FISHERY BULLETIN: Vol. 80, NO. 2, 1982. our usual observation when studying dolphins from research ships. In November 1976 we conducted a study to describe ship-avoidance behavior of dolphins. The purpose was to quantitatively describe school trajectories around an approaching ship and to evaluate the effect on shipboard censusing of dolphins. This study also allowed us to measure the swimming speeds of the schools and to make observations on school structure and behavior. METHODS AND MATERIALS We conducted this study from the NOAA Ship Surveyor, a 300-ft (91.4 m) steam-powered research vessel, and its Bell4 204 helicopter. We worked in the study area, the vicinity of Clipperton Island (lat. 10°15'N, long. 109°10'W) in the eastern Pacific, for 9 d (26 November to 4 December 1976). During six of these days, we made observations from the helicopter, flying twice daily in a crossing pattern ahead of the ship's track (Fig. 1). This enabled us to detect dolphin schools ahead of the ship and to follow the sequence of events leading to avoidance or the detection of the school by the shipboard observers. The 2.5-h flights began in mid- morning (ca. 0900 h) and early afternoon (ca. 1330 h) to take advantage of the best lighting conditions for aerial observations and photo- graphy. Air speed was about 80 kn (1 kn = 1.85 km/h) at altitudes between 1200 and 1800 ft (366- 4Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 371 FISHERY BULLETIN: VOL. 80. NO. 2 SHIP Figure 1.— Path of helicopter in front of ship during search phase of study. 549 m). Maximum altitude was determined by the cloud ceiling. During each flight, two scientific observers aboard the ship searched independently with 20 X 120 mm binoculars for dolphins. The observers were not in com- munication with the helicopter and were gener- ally unaware of its position because of its range and because of their visual concentration on the sea surface. The ship's speed was between 11 and 13 kn. Once a school was located, the helicopter re- mained near the school to serve as a radar target to fix the position of the dolphins relative to the vessel. Each time the helicopter passed over the school, we signaled the deck officer aboard ship via radio to record our radar range and bearing. These measurements from the ship were taken at successive time intervals to enable tracking the movement of the school. There was no indication to us that the helicopter affected school behavior. Indeed, the schools usually appeared to be swimming calmly throughout the tracking, until the ship approached to within a mile of the dolphins. During this tracking phase, ship course changes were minimized in order to determine how closely the school would pass the approaching vessel if not pursued. In some cases the ship was turned so its projected track would pass near the school, but course changes were minimal thereafter. The shipboard radar used was a Decca-RM 1630. Its rated accuracy is to within 300 yd (274 m) of range at a distance of 10 nmi (18.5 km) and to within 1° of angular bearing. The radar measurements were made by a trained deck officer. At the end of the tracking phase the ship approached closely or followed each school until the observers aboard had completed their esti- mates of school size and species composition. Meanwhile, we continued to take aerial photo- graphs (35 and 70 mm still and 16 mm movie) and notes on school size and behavior that had begun when the school was first sighted. The movements and speeds of the schools as de- scribed below do not refer to this last phase of the operation. School movement and speed were calculated whenever possible from relative motion plots since such plots portray the situation as seen from a ship. Required information for each plot includes the time interval between radar fixes, the course and speed vector of the ship, and the relative motion vector of the school, as deter- mined by the radar ranges and bearings (the method is described by Bowditch 1966). These data were then used to construct vector triangles which were solved to get school speed vectors. Distance (range) was measured in nautical miles (nmi) and speed in knots (kn). The results were checked by plotting the sequential, absolute positions of the vessel and school from the data on vessel speed and data on range and bearing of ship to helicopter (school). School movement was measured from this absolute plot, and speed determined from the time interval between fixes to give results that should be the same as those obtained from the relative motion plots. When the ship made a course change, disrupting the relative position analysis for that time interval, the absolute position plot was the only solution. A hypothetical example of a relative motion plot is presented in Figure 2. The ship is at the center (0) of the polar plot, proceeding straight ahead (000° or top of plot). Sequential radar ranges and bearings, from the moving ship to a dolphin school, are obtained at 0800, 0815, ..., and 0900 h. These fixes are plotted, and the line connecting them shows the relative motion of the school that is passing around to the right of the ship. The actual swimming vectors of the school, which produce this relative motion, can be ob- tained by solving vector triangles such as that shown at the center of the plot. For example, the 372 All ami I'KRRYMAN: MOVEMENT AND SI'EEl) OF DOLl'HIN SCHOOLS 000°, the school's swimming vector (OD) is obtained by vector subtraction as shown. In this case the swimming vector is 7.5 kn, heading 060°, and is the average swimming velocity be- tween 0830 and 0845 h. Notice that the relative motion line is defined by ranges and bearings while the triangle at the center is composed of speed vectors, where, for convenience, 10 kn is defined as having magnitude 0 to 2 on the mile scale. RESULTS Figure 2.— Example of relative motion plot and calculation of school swimming vector. relative motion between 0830 and 0845 h is equivalent to a relative velocity vector of 9.1 kn heading 134°. Projecting this vector (SD) onto the ship's vector (OS), which is 10 kn heading Vessel Avoidance We were able to follow eight dolphin schools with the ship and helicopter (Table 1). The species were the spotted dolphin, the spinner dolphin, and the striped dolphin, S. coeruleoalba. All eight schools continuously adjusted their Table 1.— Summary of dolphin schools observed from helicopter. School Species Date and position Local time (h) Initial Range (nmi) Speed (kn) School' size Behavior relative to distance from ship2 1 Stenella 11-26-76 attenuata / 11°54'N V07°13'W + Stenella longirostris Stenella 11-27-76 coeruleoalba / 8°27'N \107°07'W Stenella attenuata Stenella attenuata I 10°00'N \ V108°01'W/ / 9°30'N \ \109°39'W/ 0950 5.6 5.8 100 At 3.5 mi ship changes course and school increases speed to 8 3 kn. Between 1.9 and 2.6 mi school veers 40° to right across ship's path; as ship's path is crossed, school alters course again to head directly ahead of ship. At 2 mi school is in 2 groups running very purposefully with little intraschool deviations. Cruising smoothly at 5-6 kn with little splashing during most of vessel approach; strong evasive maneuvers at 100 m by group closest to ship. Two species incompletely mixed; many adults and juveniles in school. 0938 6.2 4.3 50 School initially "porpoising" gently as a loose aggregation, moving away to ship's right. At ca. 6.0 mi ship changes course; school veers 108° to left, acceler- ating to 5.8 kn At ca. 5.0 mi school turns left again, still moving away at ca. 5.5 kn. At ca. 3.3 mi ship changes course and school accelerates to 6.3 kn temporarily. Between 2.0 and 3.0 mi school turns more to left; still running smoothly at 5.5 kn with little splashing. As ship passes 2.0 mi to right of school, it veers sharply left, con- tinuing on almost opposite course as ship Individuals bunching up at 18 mi. At times school composed of 4 groups. At 1.5 mi school speed is 8.3 kn. At 0 9 mi school running smoothly ahead of ship; a portion breaks off to right at ca. 100 m distance 0935 5 2 6 4 15 School initially seen under ca 100 feeding boobies (Sula sp .). moving away from ship At ca. 4.3 mi school accelerates to 7.8 kn then slows to 6.2 kn. At 3 5 mi school turning to right. Between 2 0 and 3.0 mi school swimming smoothly at ca. 5.0 kn; birds flying, rafting, or diving; most working ahead of school; later they form 2 large rafts behind school. By 1.5 mi school speed has increased to 7.2 kn. As school passes to left of ship at ca 1.5 mi, it accelerates to 13 kn and veers to left. Birds have ceased feeding inside of 2 mi distance. School begins strong evasive maneuver at ca. 1/4 mi distance. 323 6 2 3 8 350 Initially detected as bird target by radar Between 4 2 and 4 9 mi school changes course sharply away from ship, increasing speed to 4.6 kn, then slowing to 2.9 kn. At 3.0 mi much splashing in running school; some long, flat leaps seen. School becoming more scattered Birds toward rear of school; later are scattered over school. At ca 3 2 mi ship makes 90° turn to left; school veers 94° to left and increases speed; much running leaps seen; by 3.0 mi school speed is 6.5 kn. Between 2 5 and 3 0 mi main group in school turns toward ship; moments later they reverse their course again. 373 FISHERY BULLETIN: VOL. 80. NO. 2 directions of swimming, by small increments, so that the distance between the school and the ship's projected track tended to increase contin- uously with time. The schools were either already proceeding on courses directed away from the ship when first sighted or made sharp course changes away from the vessel soon after. Several schools were moving off at relatively high speed when first seen. All the schools were evidently avoiding the ship. The behavior that indicated avoidance is summarized in Table 2 for each school. It appeared that avoidance be- havior sometimes had begun when the school was still 6 or more nautical miles away from the ship. Sufficient positioning data were collected from six of these schools to prepare diagrams of their movement relative to the approaching ship (Figs. 3, 4). The first school, school 1, is not plotted because frequent course changes by the ship during its tracking made relative move- FlGURE 3.— Relative movement plots of five schools (nos. 2, 3, 4, 6, 7), showing the apparent motion as seen by a shipboard observer. Dotted lines are by dead reckoning. ment difficult to portray. The path of relative movement of any of these schools, drawn by connecting the sequential series of radar fixes of the school as the ship moved forward, does not Table 1.— continued. School Species Date and position Local time (h) Initial Range (nmi) Speed (kn) School' size Behavior relative to distance from ship2 Stenella 12-2-76 attenuata / 9°39'N ^109°48'W + Stenella longirostris 0953 Stenella attenuata 12-3-76 ca. °31'N °30'Wj 1032 / 9°31'N \ \110°30'wJ Stenella attenuata + Stenella longirostris I 10°00'N \ \110°30'W / 1440 Stenella coeruleoalba 12-2-76 r 10°27'N 1 ,110°01'W< 1420 At 2.5 mi individuals begin to bunch up; school in form of large arc with some scattered animals on the sides; birds no longer feeding At 1 6 mi school is again scattered. Within 0 5 mi parts of school breaking away from ship's path; birds rafting nearby. 5.8 ca 2 6 300 Initially seen with many birds ahead and to right of school. School speed is ca. 2.6 kn. At 3.3 mi school changes course sharply away from ship and speed accel- erates. Animals running with compact ranks at rear of school; few birds over school now. At 3.0 mi school running smoothly at ca. 8.4 kn. At 2.2 mi individuals appear confused, going in various directions within oval shaped school At 2.0 mi a group temporarily heads toward ship before reversing course; school speed is 9 3 kn. At 06 mi many circuitous movements seen among small subgroups School passes to ship's left; all individuals uniformly running from ship at 8-9 kn; birds rafting ahead Ship turns toward school at ca. 0.5 mi; school splits ahead of ship at ca 200 m; each dolphin species goes to different side of ship 6.9 ca. 10.0 40 School initially seen as running, oval mass moving off at ca 10 0 kn with much splashing. At 6.5 mi school is in 2 groups moving smoothly in arc with little splashing At 5.7 mi school is in 2 groups moving smoothly at 8 5 kn At 5.1 mi school is composed of a dense and a scattered section, many direction changes among subgroups School speed is down to 7 0 kn At 4.5 mi school is scattered; composed of 3 large groups; many direction changes seen; speed is ca. 90 kn again Between 3.5 and 4.0 mi school speed decreases to 7.6 kn then increases to 9 3 kn as school begins passing to ship>'s left. 36 8.8 150 Initially swimming smoothly at ca. 8.8 kn with little splashing, scat- tered individuals at rear of school. At ca. 3.0 mi school still holding similar course with speed of ca. 7.0 kn; 50-70 birds over school At 2.4 mi ship changes course and school also changes course and in- creases speed; birds scattered over the scattered school. At 1.4 mi school running smoothly in loose groups, going ca 6.0 kn At <1.0 mi smoothly running school is scattered by ship. 0 9 65 A leaping, loosely aggregated school at 0 9 mi At 0.7 mi school running with increasing speed as ship turns toward school At 1/4 mi school forming an arc ahead of ship Estimated from aircraft, distances and behavior from radar ranging and bearing, interpolation of movement trajectories, and field notes. Distances in nautical miles. 374 AU and l'KRKYMAN: MOVEMENT AND SPEED OF DOI.IMllN SCHOOLS TABLE 2. — Range and behavior when vessel avoidance was first seen. School number Species Range (nmi) Behavioral indication of vessel avoidance 1 S attenuata 56 S longiroslris 2 S coeruleoalba ca. 6.0 3 S attenuata 52 4 S attenuata ca 4 6 5 S attenuata 33 S. longirostris 6 S attenuata 69 7 S attenuata 3.6 S. longirostris 8 s. coeruleoalba 0.9 School rapidly swimming away from ship at 5.8 kn when first sighted from helicopter As ship turned toward this school, the animals accelerated from 4.3 to 5 8 kn and turned away from the ship School rapidly swimming away from ship at 6.4 kn when first sighted from helicopter. School made sharp course change away from ship and ac- celerated to 4.6 kn. School turned away from ship and accelerated from 2.6 to 8 4 kn. School moving away from ship at high speed (ca. 10 kn) when first sighted from helicopter. School moving away from ship at high speed (8.8 kn) when first sighted from helicopter School leaping away from ship when first sighted from helicopter Figure 4. — Relative motion plot of school 5, showing its apparent motion as seen by a shipboard observer. Small arrows show actual school velocities at various distances. Note heading reversal shown at 1.5 mi. represent the actual swimming directions of the school, but rather the resultant of the swimming velocity of the school and the movement of the vessel. The ship's position remains at the center of each diagram, and swimming direction is depicted relative to the ship's heading, which is toward the top of the page. The plots therefore show the apparent motion of the schools as seen by an observer aboard the ship. A break in the relative motion line for a school represents a course change by the ship. The relative movement of five schools (schools 2, 3, 4, 6, and 7) are depicted in Figure 3 where, for clarity, swimming speed vectors and the times of radar fixes are not included. It is important to realize however, that along each relative motion line the school is generally swimming away from the oncoming ship. We have extrapolated parts of the movements of schools 2 and 3, based upon our observations of their activity. The movement of each of the five schools is depicted as though moving relative to the same ship heading (000°). These schools are described in two groups. The first group (schools 2, 3, 4, and 6 in Figure 3) was initially located between 5 and 7 nmi from the ship. After some initial adjustments in heading, the schools' swimming directions re- mained relatively constant. The resultant paths of the dolphin schools thus veered from the track line at a nearly constant angle after this initial period. Assuming that the schools would remain approximately on the same course and extending their lines of relative movement, it appeared that these schools would have passed no closer than 2.4 nmi from the ship, had it remained on the same course. School 4 exhibited additional notable behavior that is not shown in Figure 3. When the school had passed abeam, the ship was turned towards the school. Five minutes later, at a range of about 2.5 nmi, a large section of the school turned and headed toward the ship in a tightly aggregated group. Within a minute this section reversed course again and rejoined the original school. The second group (schools 2, 3, and 7 in Figure 3) consists of schools that were between 2.6 and 3.7 nmi away, either when first sighted (school 7) or after the ship had turned toward the school at the end of an initial tracking period (schools 2 and 3). The lower and separated segments of the latter schools' tracks represent the relative movements after the ship had turned. These schools were then within 0.4 nmi of the ship's projected track. Even so schools 2 and 3 subsequently came no closer than 1.4 nmi to the ship. School 7, by its initial projected trajectory, would have come no closer than 1.5 nmi, but after the ship turned toward it, its new resultant path would have taken it about 0.7 nmi from the ship. 375 FISHERY BULLETIN: VOL. 80. NO. 2 School 5 behaved quite differently from the others. Both relative movement, time of radar fixes, and swimming speed vectors are shown for this school (Fig. 4). The swimming speed vectors, shown as arrows attached to the relative motion line between various time and distance intervals, are drawn proportional to the calculated swimming speeds (Table 3). School 5 was probably feeding when the bird flock associated with it was first detected on the ship's radar at a distance of 5.8 nmi. The distance and bearing plots of the birds indicated erratic movement. Later, in the tracking-by-helicopter phase, the first two ranges and bearings showed the school moving at only 2.6 kn. The inferred feeding behavior from this is consistent with the feeding behavior described by Norris et al. (1978), as well as other observations by us in the eastern Pacific. At a closer range of about 3.3 nmi from the ship, the school's behavior changed radically as it altered course by 97° to the right and increased its speed to 8.4 kn, turning on a course that would have taken it 2.0-2.5 nmi abeam of the passing ship. Between 2.3 and 3.0 nmi the school again shifted course, this time by 70° to the left, and increased its speed to 9.4 kn. When this school reached a point about 0.5 nmi from the track line and 2.3 nmi from the ship, its behavior changed again. Individuals and subgroups within the school began swimming in many different directions, making large changes in course heading. Suddenly the main body of the school turned nearly 180° and swam toward the ship at high speed (~9 kn). After closing to within 1 nmi of the ship, the school reversed itself again, and thereafter swam rapidly away from the vessel. This type of "error" in choice of avoidance heading was only seen in schools 4 and 5, which were both relatively large schools (300- 350 individuals estimated). School Speed While avoiding the ship, the speeds of the first seven schools varied between 2.5 and 13.1 kn, with average speeds between 5.1 and 8.8 kn (Table 3). The eighth school was too close to the ship for ranging measurements by radar. There was no apparent difference in swimming speeds among the three species observed. Substantial variation in speed occurred in all seven schools. Schools 1, 2, 3, and 4 swam at speeds that aver- aged between 5 and 7 kn. Schools 6 and 7 had the Table 3.— School swimming speed vectors. Time Range1 Speed2 School (h) (nmi) Bearing' Course2 (kn) 1 0950 5.6 088° 1015 3.6 105 128.2° 58 1022 3.3 107 128 6 8.3 1030 26 104 126.3 5.7 1035 19 112 166.7 5.3 1042 1.4 115 114.5 62 1049 08 110 100.0 6.8 1101 0.7 310 092.0 4.0 3x=6.0 2 0938 6.2 016 0942 5.9 026 118.3 4.3 0952 49 026 010.6 5.8 1000 3.7 017 330.7 5.5 1006 29 008 324.6 6.3 1013 1.8 352 304.6 5.5 1019 1.5 320 315.2 83 1028 2.0 255 285.2 5.7 1033 3.0 230 216.5 5.6 1045 2.5 212 2236 6.0 1051 2.0 200 2290 5.9 1104 0.9 179 1828 6.3 x=5.9 3 0935 52 295 0940 4.7 297 3009 6.4 0943 4.4 299 3089 6.5 0947 4.1 301 2988 7.8 0953 3.5 308 3166 6 2 0959 3.1 320 326.2 78 1006 28 340 335.1 62 1016 2.9 019 354.2 5.0 1023 2.0 010 337.0 "4.9(1017-1023) 1029 1.6 353 005.0 6.6 1032 1.5 335 334 5 72 1035 1.8 296 2640 13.1 x=7.1 4 0823 62 333 0829 4.9 333 0865 38 0835 4.2 330 3495 4.6 0841 3.2 318 261.9 29 0845 3.0 305 2825 6.5 0857 32 256 2632 5.2 0915 1.6 255 2658 6.2 "x=5.1 (0835-0915) 5 5 1001 4.3 356 1006 3.3 354 264.2 26 1011 3.0 357 001.2 84 1017 2.3 339 2908 9.4 1022 0.6 334 1484 93 1027 0.5 268 314.7 7.9 4 x= 8.8 (1011-1027) 6 1032 69 281 1038 6.5 278 273.6 10.0 1050 5.7 277 279.2 85 1056 5.1 277 284.4 7.0 1102 47 273 2620 9.2 1108 4.3 270 270.1 8.8 1112 39 271 2974 7.6 1121 3.4 258 2533 93 x=8.6 7 1440 36 167 1446 3 2 170 182.4 88 1452 26 177 199.1 6.6 1458 21 191 215.3 7.5 1505 1.4 197 175.6 60 1508 1.0 205 164.6 25 1519 1.1 240 2420 11.5 x=7.2 'Range and bearing of school from ship at times appropriate to the speed calculation If notable, behavior at these and other times are re- ported in Table 1. 2Speed vectors pertain to time intervals ending at times listed unless otherwise indicated Calculations are from relative or absolute plots in- volving ship motion. 3Mean school speed refers to times when school is responding to ship 4Time interval for this calculation. 5This school was actually sighted at 0953. but measurements did not begin until 1001 376 AU and PERRYMAN: MOVEMENT AND SPEED OF DOLPHIN SCHOOLS highest initial speeds, 10.0 and 8.8 kn, respec- tively, and had average speeds of 8.6 and 7.2 kn, respectively. Both were moving with the waves in a Beaufort 4 seastate(l 1-16 kn wind) and were probably utilizing the forward momentum of the swell as described by Lang (1975). The speed of school 5 was also high ( >8 kn) after the first 5 min that it was observed. Its average speed while actively avoiding the ship was 8.8 kn. This higher sustained speed may have been related to its level of excitement that was evident in its apparently confused state, when it turned toward and then away from the ship (Table 1, Fig. 4). Schools 3 through 7 showed some tendency for increased speeds as the ship drew nearer. Swimming Behavior and School Structure Field descriptions of each school, and later study of the aerial movie and still photographs, revealed no obvious indication of dominant, or leading, individuals or subgroups. The schools were seen to progress in an almost amoeboid fashion with subgroups of two to five individuals striking off in different directions or accelerat- ing to higher speeds, then drifting back to the main body of the school if not followed by others in the school. Although individuals and sub- groups within a school were constantly changing course, sometimes abruptly, the heading of the main body of the school remained nearly constant or changed slowly. The schools ap- peared as loose aggregations of individuals and small subgroups, most proceeding along similar headings. Individualistic rather than coordi- nated movements were the general feature of these schools. The schools appeared to be one- layered, i.e., groups of animals were not swimming beneath others. As the vessel closed to within 2 nmi of the schools, the subgroups within the schools were seen to be increasingly oriented in lines abreast. Animals in the rear third of a school could be seen swimming faster than those ahead. The result was that the width of a school in the direction of its swimming axis narrowed as the distance between ship and school decreased. DISCUSSION Our first impression from the observed school behavior and structure was that the dolphins were not noticeably disturbed by the vessel's presence. Only at a distance of less than a mile did bunching or compaction of the relatively dis- persed individuals and small subgroups become common and did the schools obviously appear to be running, i.e., in flight (Table 1). Radical, evasive maneuvers were not regularly seen until the last 200 m of distance between ship and school. Examination of the relative motion plots and the consecutive vectors of swimming speed and course made it clear, however, that the dolphins were actually avoiding the ship much earlier, sometimes beginning at distances approaching the horizon for a shipboard ob- server. Though ship-avoidance behavior should not be surprising, considering the extent of "porpoise fishing," in the study area, it is a behavior not easily studied from a surface platform. These observations have important implications relative to population studies of dolphins, especially those conducted from ships. Because a shipboard observer sees a dolphin school increasingly in profile view as distance increases, an understanding of its structure and behavior is helpful for proper interpretation of its characteristics. A travelling school appears to be a loose aggregation of relatively widely sep- arated individuals or subgroups of 2-5 animals. Rather than being made up of relatively few, tight subgroups of various sizes, as observed for spotted dolphins in a purse seine (Norris et al. 1978), most of the animals in these schools appeared to be swimming independently, as individuals or in pairs. This school configuration appeared typical all during vessel avoidance, except at radial distances of less than a mile from the ship. The schools we observed remained incon- spicuous to the shipboard observers because they swam smoothly, without much splashing, at speeds that averaged 6.8 kn. Even at swimming speeds of 7-9 kn, the animals often broke the water surface with little commotion and swam most of the distance between breaths just under the surface. Bursts of higher speed, with attendant long leaps (2-3 body lengths) and large splashes, occurred only temporarily. The swimming speeds presented in Table 3 pertain to these pelagic dolphins when swim- ming in the cruising mode, i.e., moving smoothly with little splashing for sustained periods. The higher observed speeds of 7-9 kn are still in the upper range for prolonged cruising speeds of smaller dolphins (Webb 1975). That this must be so is indicated by the fact that research ships 377 FISHERY BULLETIN: VOL. 80. NO. 2 moving at 10 kn can always closely approach these dolphins, provided that the schools can be followed. Evidently school speeds greater than that of the ship can be maintained only temporarily. Dolphins that do break into the "running," or leaping swimming mode, must be exceeding a certain "crossover speed." This is the swimming speed above which a leaping locomo- tion becomes more efficient. It is calculated to be somewhat in excess of 10 kn (Au and Weihs 1980). Thus several lines of evidence indicate that cruising speeds are <10 kn, as we in fact measured. Dolphins of course are capable of temporary higher speeds than reported here. Top burst speeds as high as 14.5 kn have been measured for Tursiops truncatus (Lang and Norris 1966) and 21.4 kn for S. attenuata (Lang and Pryor 1966). Because the faster, leaping locomotion produces much splashing, dolphins that avoid ships by moving away more slowly at cruising speed obviously are more difficult to detect from the ships. The initial avoidance probably pro- ceeds at cruising speed because the dolphins are not yet highly alarmed at the distances at which detection of the ship and evasion begins. The evasive behavior of dolphins perhaps has its most important implication relative to school density studies conducted from ships. In par- ticular the line-transect method (Seber 1973; Burnham and Anderson 1976), which can be employed for absolute density estimation of schools, may be affected. An important require- ment of the method is that the schools do not move, or move randomly or little, relative to the speed of the observer. However, schools are evidently capable of avoidance movements at speeds approaching that of the ship. Therefore positions of schools relative to the ship and prior to movement that are required to describe the probability of sighting a school cannot be obtained if there is movement. Only if the school trajectories were known could the observed positions be corrected. The probability of sighting is usually obtained from the distribu- tion of perpendicular distances that are a transformation of the relative positions of sighted schools. Laake( 1978) and Burnham etal. (1980) emphasized that when school movement occurs, both the probability functions describing detectability and the altered animal distribution are completely confounded in the distribution of observed perpendicular distances. School move- ment also violates the critical assumption that all schools initially on the track line will be seen. Therefore, line transect methods for absolute density estimation usually cannot be used when avoidance movements occur. It is easy, however, to understand how avoid- ance behavior reduces the probability of sighting a school from a ship. Without movement this probability would be (Burnham and Anderson 1976) ll g(x)dx where w is the half width of the swath being searched, which could be the horizon distance, and g(x), the detection function, is the probability of sighting a school that is initially at perpen- dicular distance x from the track line. The function, g(x), is monotonically decreasing from 1 on the trackline (#(0) = 1). Therefore, schools avoiding a ship by effectively moving farther abeam must obtain a value to g(x), say g(x)1, that is less that that at its initial distance x. These reduced values, g(x)1, replace the original values of g(x) at all initial perpendicular distances where avoidance movements began. The area under this altered detection curve (i.e., the plot of g{x)x against x), which determines the new probability of sighting a school from the track, is accordingly reduced. Reasonable models of the detection function and how it is altered by avoidance behavior can be constructed to show that this reduction can be considerable. If dolphins do obtain lower g(x) values from their avoidance trajectories, the behavior would be advantageous. This seems entirely possible considering that the schools can cruise at speeds approaching that of many research ships (Table 3) and apparently can detect and continue to sense a ship from considerable distance. Evidence of the latter are the distances at which avoidance behavior was apparent (Table 2) and the near simultaneous changes in school course or speed following course changes by the ship. Such changes occurred at 3.5 mi in school 1, at 6.0 and 3.3 mi in school 2, at 3.2 mi in school 4, and at 2.4 mi in school 7 (Table 1). With significant reduction in sighting prob- ability possible from avoidance, it would be useful to empirically determine the actual probabilities, g(x)1, or to model this behavior. We expect, however, that the specifics of avoidance trajectories as well as the probabilities would 378 All ami I'KRRYMAN: MOVEMENT AND SI'KKD OF DOI.I'IIIN SCHOOLS vary greatly with species, populations and their experience, and the specific behavioral activity of the school when encountered. The type of ship involved and environmental conditions may also affect avoidance behavior. ACKNOWLEDGMENTS We thank our numerous reviewers, shipboard mammal observers Frank Ralston and Dale Powers, and the officers and crew of the NOAA Ship Surveyor. Special thanks to helicopter pilot Lt. William Harrigan who skillfully maneu- vered over the schools and maintained communi- cation with the ship, and to Lorraine Prescott who patiently typed the manuscript. LITERATURE CITED All, D., AND D. Weihs. 1980. At high speeds dolphins save energy by leaping. Nature (Lond.) 284:548-550. BOWDITCH, N. 1966. American practical navigator. U.S. Navy Oceanogr. Off. Publ. 9, 1524 p. U.S. Gov. Print. Off., Wash., D.C. BURNHAM. K. P., AND D. R. ANDERSON. 1976. Mathematical models for nonparametric infer- ences from line transect data. Biometrics 32:325-336. Burniiam, K. P., D. R. Anderson, and J. L. Laake. 1980. Estimation of density from line transect sampling of biological populations. Wildl. Monogr. 72, 202 p. Laake, J. L. 1978. Line transect estimators robust to animal move- ment. M.S. Thesis, Utah State Univ., Logan, 55 p. Lang, T. G. 1975. Speed, power, and drag measurements of dolphins and porpoises. In T. Y. T. Wu, C. J. Borkaw, and C. Brennen (editors), Swimming and flying in nature, Vol. 2, p. 553-572. Plenum, N.Y. Lang, T. G., and K. Pryor. 1966. Hydrodynamic performance of porpoises (Stenella attenuata). Science (Wash., D.C.) 152:531-533. Lang, T. G., and K. S. Norris. 1966. Swimming speed of a Pacific bottlenose porpoise. Science (Wash., D.C.) 151:588-590. Norris, K. S., W. E. Stuntz, and W. Rogers. 1978. The behavior of porpoises and tuna in the eastern tropical Pacific yellowfin tuna fishery-preliminary studies. Available Natl. Tech. Inf. Serv., Springfield, Va., as PB 283970, 86 p. Perrin, W. F. 1969. Using porpoise to catch tuna. World Fish. 8:42-45. 1970. The problem of porpoise mortality in the U.S. tropical tuna fishery. Proc. 6th Annu. Conf. Biol. Sonar and Diving Mammals, p. 45-48. Stanford Res. Inst, Menlo Park, Calif. Seber, G. A. F. 1973. The estimation of animal abundance and related parameters. Hafner Press, N.Y., 506 p. Webb, P. W. 1975. Hydrodynamics and energetics of fish propulsion. Fish. Res. Board Can., Bull. 190, 158 p. 379 THE STRAIT OF GEORGIA HERRING FISHERY: A CASE HISTORY OF TIMELY MANAGEMENT AIDED BY HYDROACOUSTIC SURVEYS Robert J. Trumble,1 Richard E. Thorne,2 and Norman A. Lemberg1 ABSTRACT A stock assessment program which combines hydroacoustic biomass estimates with midwater trawl sampling, spawning escapement estimates, and daily catch reporting has provided a timely method of managing an intensively fished, Pacific herring population in Puget Sound, Wash. Since 1976, these techniques have been implemented through the spawning season to estimate adult herring biomass, and to set quotas consistent with the biomass. The estimates become available for manage- ment use less than a day following completion of an acoustic-trawl survey, which allows for in-season adjustments in fishing. Acoustic-trawl surveys carried out at regular intervals during the spawning season monitored declines of prespawning adult herring biomass; the declines corresponded to cumulative increases of catch and spawning escapement. After full recruitment to the fishery, the sum of catch, escape- ment, and acoustic-trawl estimates provided a point estimate of total available adult herring. Within a season, these point estimates varied less than 15%. This stability is a check on the accuracy of acoustic surveys, and confirms that accuracy is sufficient for management purposes. Management of virtually all fisheries requires information on the abundance of the resource with which to set catch quotas, limit effort, or determine stock condition. The effectiveness of fishery management is often hampered by the need to make decisions based on stock assess- ment requiring long time periods or doubtful assumptions, or both. Fisheries on the west coast of the United States and Canada for sac-roe (egg skein) of Pacific herring, Clupea harengus pallasi, have a need for rapid management response. The herring migrate from offshore waters to subtidal and intertidal spawning grounds. The fish are harvested just prior to spawning and the sac-roe is subsequently prepared as a caviar product. Total allowable harvests can be taken in very short times, from minutes to days, and prolonged fishing time easily leads to overharvest. An ob- jective of sac-roe herring management is to obtain real time estimates of abundance prior to and during the fishery so that quotas compatible with abundance may be established. Spawning escapement goals must be met without losing the opportunity to catch harvestable fish. Traditional methods of determining abun- 'Washington Department of Fisheries, M-l Fisheries Center WH-10, University of Washington, Seattle. WA 98195. fisheries Research Institute WH-10, University of Wash- ington. Seattle, WA 98195. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. 80, NO. 2, 1982. dance or setting fishing rates are inadequate for the short-duration sac-roe herring fisheries. Catch per unit effort (CPUE), virtual population analysis/cohort analysis (VPA), or yield per recruit (Y/R) provide postharvest information, and often with lags of several years. Problems with effort standardization and harvesting aggregated fish (CPUE), the need for independ- ent estimates of highly variable recruitment (VPA), and sexual maturity being reached after maximum cohort biomass (Y/R) make these methods difficult to apply to in-season sac-roe herring management even without the timeli- ness factor. Sac-roe herring management relies heavily on catch records and on spawning escapement estimates. Even though these values ultimately combine to estimate total abundance, they are too late for in-season estimates and in-season management modifications. Abundance esti- mates before and during the spawning/fishing season can be obtained by use of hydroacoustic techniques, as are used in Washington, Alaska, and British Columbia. Successful management of the sac-roe herring fishery in the Strait of Georgia, Wash., requires timely information on the abundance of the fishable stock during the fishing season. A fleet composed of purse seiners and gill netters has the capacity to harvest the available quota within 1 381 FISHERY BULLETIN: VOL. 80, NO. 2 to several days. In addition, allocation to treaty Indian fishermen is required by Federal Court rulings (the Boldt decision), which established separate treaty and nontreaty quotas. Biologists representing Washington State, participating tribes, and the University of Washington agreed that a target quota should be 20% of the total estimated population biomass (Trumble 1980). The application of hydroacoustic techniques offered timeliness in the Strait of Georgia herring stock assessment program (Thorne 1977a) when combined with midwater trawling, analysis of catch records, and spawning ground surveys. This paper presents results of applica- tion of these techniques during 1976-79 to the management of the fishery. METHODS AND MATERIALS The concept of the sac-roe herring stock assessment program is to estimate the biomass of adult herring in prespawning condition, and add to this the biomass of adult herring removed by spawning or being caught. Hydroacoustics pro- vided estimates of total pelagic fish biomass, and midwater trawl sampling provided species com- position data to identify prespawning adults; the combination of hydroacoustics and midwater trawling will be referred to as "acoustic-trawl." Spawning ground surveys provided estimates of spawning escapement, and catch records tracked the success of the fishery. Catch and escapement estimates provide a postfishery check on the accuracy of the acoustic data, and in conjunction with acoustic-trawl surveys, a series of in-season estimates of the total biomass of mature herring. Acoustic Survey Equipment and Methods The hydroacoustic data acquisition system consisted of a modified 105 kHz Ross3 200A echosounder, an interface amplifier that re- duced the signal frequency from 105 kHz to 5 kHz, a Sony TC-377 tape deck which recorded the 5 kHz data on magnetic tape, and an oscilloscope to monitor system operation. The transducer produced a 7% degree full angle beam at the half power (-3dB) points. The modifications of the system include an internal 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. calibration oscillator to monitor and measure system gain (Thorne et al. 1972; Nunnallee 1973). The echosounder transmitted a pulse length of 0.6 m s. The echosounder and transducer were periodically calibrated at the Applied Physics Laboratory, University of Washington. Normal- ly, calibration occurred at the beginning and end of each field season. The acoustic data from the magnetic tapes was processed with a digital echo integration system implemented on a PDP 11/45 computer (Thorne 1977 b). A mean target strength of -33 dB/kg was used by the program to scale the integrator data to estimates of fish density. This value was originally established on the basis of both comparisons with net tows and in situ target strength measurements (Thorne 1977a) and the value still appears to be reasonable. Although considerable information has been obtained on the dependence of target strength on fish length (FAO 1978; Thorne in press), the variation in mean fish lengths in the Strait of Georgia is insufficient to warrant using a length-dependent variable instead of a constant for the target strength scaling factor. Herring typically range from 18 to 24 cm SL, and compose 70-90% of the biomass in the acoustic-trawl surveys. During 1976 and 1977, the University of Washington's 12 m RV Malka was used as the acoustic platform, with a hull-mounted trans- ducer. Subsequently, the acoustic program chartered a 10 m gill net vessel and used an over- the-side pole-mount for the transducer. Acoustic surveys were conducted during April and May (and to the first part of June 1976) in order to bracket the spawning migration of the herring (Lemberg 1978). The surveys were conducted between Point Roberts and Lummi Island on a standardized trackline which had 10 transects, each about 8 km in length (Fig. l).The surveys were typically conducted at twice weekly intervals around the peak of the migration, and less frequently during the early and late stages of the run. During the day, herring normally aggregate in tight schools at depths of 40 m or more. At night, the schools disperse and form widespread layers 5-10 m thick at depths of 10-30 m; herring density decreases such that many fish are distinguishable as individual targets. Until actively ready to spawn, herring remain in water deeper than 20 m. The survey area encompassed the prespawning holding area, bounded by the 8- 10 fathom contours on the inside, and the 50-60 382 TRUMBLE ET AL.: STRAIT <)E GEORGIA HERRINC FISHERY Figure 1.— Strait of Georgia standard track line pattern (....)• Solid lines and 10-fathom contour (--•) define survey subareas (from Lemberg 1978). fathom contours on the outside. Spawning occurs on adjacent shorelines. The surveys were conducted at night when the herring were less patchily distributed and further off bottom. Transects were evenly spaced and designed for maximum mileage during hours of darkness. At about 0.5 h per transect, plus turn around and set up time between transects, each survey required the approxi- mately 6 h of darkness. Data were integrated for density (kg/m3) at preselected depth intervals for each transect; depth interval densities were accumulated for a depth zone, usually 5-40 m below the surface to calculate an average density (kg/m2) for each transect. Extrapolation of average density to the surface area represented by each transect, summed over all transects, provided biomass estimates. The acoustic estimates of maturing adult herring biomass were available the after- noon following each survey. Midwater Trawling Procedures The midwater trawl sampling was done from chartered 20-24 m commercial fishing trawlers simultaneously with the acoustic surveys. This procedure has two advantages in addition to synopticity. First, the vessel requirements for the acoustic vessel are less demanding so that a smaller, less expensive vessel could be used. Second, it was possible to direct the towing 383 FISHERY BULLETIN: VOL. 80, NO. 2 operation from the acoustic vessel on the basis of target abundance from the echograms in an attempt to approximate optimal sampling allocation (Cochran 1977). The net employed was a four panel midwater trawl with 9.2 m headrope and footrope and 9.2 m sides designed to open 6.1 m vertically and horizontally; meshes tapered from a 7.6 cm stretch mesh in the wings to a 1.27 cm stretch mesh cod end liner. Head rope floats and chain on the foot rope were used to aid the vertical opening. Trawl doors were metal, V-type, and weighed 31 kg; 55 m dandylines extended from the doors to the side panels. Trawl depth was monitored with a bathykymograph and in 1977, by third wire telemetry to one of the trawl doors. A typical survey included three to five 30-60 min tows. The number of tows was limited by hours of darkness. Catches were sorted on board by major species, normally herring, dogfish, cod, and smelt, and by incidentals; each species aggregate was weighed separately. Two sub- samples of herring were collected from each tow. One subsample was processed on board to determine maturity (prespawning, spent, and immature). The other was returned to the laboratory for length, weight, age, sex, and sexual maturity data. Spawning Ground Surveys The herring lay adhesive eggs on lower intertidal and upper subtidal vegetation. The biomass of herring which have spawned can be estimated from the intensity and extent of spawn deposition in conjunction with fecundity, sex ratio, and average weight data (Hourston et al. 1972). The basic procedure is to sample vegetation along the shoreline and note the intensity (number of egg layers) of deposition. A spawning ground survey crew used a small (4-5 m) boat with outboard motor to maneuver nearshore, and a grappling rake to retrieve vegetation at 350-500 m spacing along the spawning grounds. Observations on spawning intensity and extent are then converted to an estimate of the spawning escapement (Trumble et al. 1977; Meyer and Adair 1978). The survey intensity during the spawning period is typically twice weekly for each of four major spawning areas in the Strait of Georgia. During the 2-mo period (April-May) that encompasses the ex- tremes of the spawning period, 15-20 spawning ground surveys are conducted for each of the four areas. The objective to maximize number of sur- veys to reduce the time between spawn deposition and survey is limited by available personnel. Catch Records The Washington Department of Fisheries has a computerized data retrieval system for pre- liminary catch statistics. Telephone reports of daily estimated catch (soft data) are required from each buyer by noon of the day following the catch. These telephone reports are replaced and updated when fish receiving tickets (hard data) arrive. Management during the fishery used both soft and hard data; this report used final data. Summary reports of daily and cumulative landings by treaty and nontreaty fishermen, and totals for the combined fleet, are available through the catch data retrieval system. RESULTS A point estimate of sac-roe herring abundance was made the day following each hydroacoustic survey by incorporating cumulative spawning escapement estimates and cumulative catch up through the date of each hydroacoustic survey. This procedure assumed that acoustic-trawl estimates represent maturing adult fish remain- ing to spawn, while cumulative catch and escape- ment account for adult fish removed from the spawning population. The point estimates should be similar once the stock has fully recruited to the area, and will then represent total biomass; as acoustic estimates decline through the season, compensating increases in catch and escapement occur. 1976 Surveys The total acoustic biomass estimates in the study area during 1976 ranged from an initial value of 1,920 tons 5-8 April to a peak of 21,000 tons on 21-22 April (Table 1). Trawl catches were predominately herring (about 90% by weight). However, a large proportion of the herring biomass was often either juvenile or spawned out fish. Only 58% of the total biomass estimates was maturing herring at the time of the peak estimate. The acoustic-trawl estimates of matur- ing herring increased from 1,480 tons during the first survey on 5-6 April to a maximum of 12,240 on 21-22 April, and decreased to 0 tons on the last survey, 3-4 June (Fig. 2). 384 TRUMBLE ET AL.: STRAIT OF GEORGIA HERRING FISHERY Table 1. — Results from hydroacoustic-midwater trawl surveys in the Strait of Georgia, Wash, (weights in short tons), 1976. Maturing Juvenile adult or spent Miscella- % Date Total herring herring neous spawners 4/5-6 1,920 1,480 440 — 77.1 4/13-14 7,030 4,030 2.150 850 57.3 4/21-22 21.100 12,240 6,360 2.500 580 4/27-28 10,940 8370 1.400 1,170 76.5 5/5-6 7.050 3,460 2,170 1.420 49.1 5/19-20 4,530 1.460 1.830 1.240 32.2 6/3-4 2,090 0 990 1,100 0 5 10 15 20 25 30 5 April IO 15 20 25 30 4 May June Figure 2.— Biomass estimates of adult roe-herring in the Strait of Georgia, 1976. Fifty-nine spawning ground surveys were con- ducted between 8 April and 8 June. The total spawning biomass from these surveys was estimated to be 9,590 tons (Fig. 2). The fishery extended from 25 April to 23 May with a total catch of 2,190 tons. The highest point estimate of total adult herring biomass, on 21-22 April, was slightly over 14,000 tons and was predominately from the acoustic-trawling data. The last estimate, 11,800 tons, was from the spawning escapement esti- mate plus the total catch. The average of the five estimates between 21-22 April and 3-4 June was 12,700 tons. The fishery harvested 17.4% of the maturing adult biomass, well within the 20% limit. 1977 Surveys Fish abundance in the study area in 1977 fol- lowed the general pattern of 1976, building up to a peak and then declining as the herring moved inshore to spawn. The total acoustic biomass esti- mates in the study area ranged from a peak value of 10,090 tons on 25-26 April to a minimum value of 3,410 tons on 17-18 May (Table 2). The trawl catches were again predominately herring. The proportion of maturing adult herring ranged from 69% to 84% of the total catch during the first half of the survey period when the acoustic-trawl estimate composed the major component of the total biomass; later in the season proportions de- creased. The acoustic-trawling estimate of spawn- er herring reached a peak of 7,900 tons (Fig. 3). Seventy-seven spawning ground surveys were conducted from 7 April to 9 June. The estimated spawning escapement was 8,800 tons (Fig. 3). The fishery extended from 11 April to 12 May with a total catch of 2,300 tons. The timing of the migration differed slightly from 1976. Significant amounts of spawning and substantial catches occurred before the peak of the acoustically measured biomass. Consequent- ly, the first total biomass point estimate after presumably full recruitment, 11,300 tons, included substantial inputs from the spawning ground surveys and catch data, as well as the acoustic (Fig. 3). The last estimate was 11,100 tons, composed of the 8,800 ton spawning escape- ment estimate and the 2,300 ton catch. The mean of the final catch plus escapement and the five surveys from presumably full recruitment was 11,040 tons. The harvest rate reached 20.8% for 1977. Table 2.— Results from hydroacoustic-midwater trawl surveys in the Strait of Georgia, Wash, (weights in short tons), 1977. Date Total Maturing adult herring Juvenile or spent herring Miscella- neous % spawners 4/5-6 4,530 3,130 1,210 190 69.1 4/12-13 4,340 2,990 1,060 290 689 4/18-19 7.480 6,280 710 490 839 4/21-22 7.700 5,770 1,230 700 74.9 4/25-26 10,090 7.900 1,430 760 78.3 4/28-29 8,950 5.000 3,160 790 559 5/3-4 9.600 4.260 1.610 3.730 44.4 5/10-11 3.560 2,060 1,070 430 57.9 5/17-18 3.410 550 1.960 900 16.1 IO 15 20 25 30 5 April IO 15 20 25 30 4 May June Figure 3.— Biomass estimates of adult roe-herring in the Strait of Georgia, 1977. 385 FISHERY BULLETIN: VOL. 80, NO. 2 1978 Surveys Herring abundance estimated through the 1978 season showed considerably more variabil- ity than in other years of the surveys (Fig. 4, Table 3). As expected, abundance was low at the time (11-12 April) of the first acoustic-trawl survey. The following week, 16-22 April, acoustic-trawl estimates of maturing adult herring increased to approximately 13,400 tons in each of two surveys, and the total estimate exceeded 16,000 tons. For the next three surveys, 24 April-1 May, acoustic-trawl estimates of maturing adult herring biomass in the survey corridor dropped considerably, and correspond- ing total abundance declined to 10,000-11,000 tons. On 4-5 and 8-9 May estimates of total maturing herring increased to 13,000 tons; these latter estimates included 3,500-6,000 tons from acoustic surveys. The highest biomass estimate occurred just after complete immigration when the estimate comprised mostly acoustic data. The original high values, midseason low values, and inter- Table 3. — Results from hydroacoustic-midwater trawl surveys in the Strait of Georgia, Wash, (weights in short tons), 1978. Date Total Maturing adult herring Juvenile or spent herring Miscella- neous % spawners 4/11-12 6,340 5,450 700 190 860 4/17-18 17,420 13,450 2,540 1,430 77.2 4/20-21 17,420 13,410 3,670 340 77.0 4/24-25 9,100 6,380 1,850 870 70.1 4/26-27 8,820 6,250 1,870 700 70.9 5/1-2 7,310 4,350 1,930 1,030 59.5 5/4-5 9,700 5,960 2,780 960 61.4 5/8-9 6,400 3,650 2,330 420 57.0 18- 16- '\TOTAL 14- 12- § IO- 3 o \ACOUSTIC TRAWL »-° ■B e CUMULATIVE SPAWNING ESCAPEMENT CUMULATIVE CATCH .-•-•" 5 IO 15 20 25 30 5 IO 15 20 25 30 4 April May June FIGURE 4.— Biomass estimates of adult roe-herring in the Strait of Georgia, 1978. mediate values at the end of the season were com- posed of at least two similar estimates, which suggests that the changes represent actual occurrences. The final spawning escapement estimate, based on 67 spawning ground surveys was 8,840 tons. Total catch was 2,120 tons. Cumulative escapement plus catch equaled 10,960 tons. Mean value of the eight population estimates made from the time of completed immigration to the survey area was 12,700 tons. The 16.7% harvest rate, lowest of this 4-yr series, was due to a reduced quota during the midseason period of low abundance estimates. 1979 Surveys Total all-species acoustic abundance estimates (Table 4) increased from a normal low value of about 3,000 tons in mid-April to a peak of 8,150 tons following presumed full recruitment on 27 April. By the end of the season, estimates were less than 3,000 tons. Maturing adult herring comprised 50-70% of acoustic biomass until the last survey of the season. Early season estimates of 1,000-2,000 tons of adult herring increased to about 5,600 at the peak, and declined to 890 tons on 7-8 May. Seventy-two spawning ground surveys con- ducted during 1979 provided an escapement esti- mate of 8,040 tons. Total harvest was 1,920 tons. Variation in 1979 seasonal abundance esti- mates for adult (spawner) herring showed a pattern similar to those observed in 1976 and 1977: biomass increased rapidly early in the season, and remained fairly constant for the duration of sampling (Fig. 5). From the time of full recruitment, total adult herring estimates ranged from 8,000 to 10,000 tons. As in 1977, con- siderable spawning and catch occurred prior to the peak acoustic estimate, and added consider- ably to the first estimate following presumed full Table 4.— Results from hydroacoustic-midwater trawl surveys in the Strait of Georgia, Wash, (weights in short tons), 1979. Date Total Maturing adult herring Juvenile or spent herring Miscella- neous % spawners 4/11-12 3.840 2.340 1,460 40 609 4/16-17 2.680 1,290 1.370 20 48.1 4/19-20 4,410 2,530 1,530 300 585 4/23-24 5.270 3.330 1,730 210 632 4/26-27 8,150 5.590 2.200 360 686 4/30-5/1 5,750 4,110 1,520 120 71.5 5/3-4 2.510 1,390 1.080 40 55.4 5/7-8 2.870 890 820 1,160 31.0 386 TRUMBLE ET AL.: STRAIT OF GEORGIA HERRING FISHERY Table 5.— Stock assessment summary, U.S. Strait of Georgia sac-roe herring, 1976-79. 10 15 20 25 30 April 10 15 20 25 30 4 May June Figure 5.— Biomass estimates of adult roe-herring in the Strait of Georgia, 1979. recruitment. Average estimate of total adult herring biomass was 8,950 tons. The fishery harvested 21.8% of this estimated biomass in 1979. DISCUSSION AND CONCLUSIONS The combination of techniques applied in the management of the sac-roe herring fishery provides a timeliness and accuracy greater than any single technique. The catch records are ob- tained rapidly, but by themselves have little management value. CPUE data are difficult to evaluate in a timely manner and has question- able application in a mixed gill net and purse seine fishery on schooling fishes whose migration patterns and timing vary annually; consequent- ly, CPUE data are not used in the sac-roe herring fishery. The spawning ground surveys provide escapement data, but are not timely for in-season management of the fishery. Conceivably the excess biomass could be harvested after escape- ment goals have been met, but this approach forces the fishery to the end of the season when fish are younger, smaller, and less valuable than early in the season. The hydroacoustic-trawling data provide the single most useful information for in-season management. The estimates of potential spawn- ing biomass are available for management decisions by the end of the day following the nighttime survey. The acoustic-trawl data have provided good agreement with the other measure of biomass. The average of the weekly total run size estimates from the sum of all three data sources have varied from 1% to 14% of the final estimate from the catch and spawner escapement estimate (Table 5). In all 4 yr the peak acoustic-trawling estimate in conjunction with these data has provided a Average of Total Total Catch + full recruitment Year catch escapement escapement point estimates1 1976 2,190 9,590 11,780 12,700 1977 2,300 8,800 11,100 11.040 1978 2,120 8,840 10,960 12,700 1979 1.920 8.040 9,960 8,950 'This estimate consists of the average of acoustic-trawl plus cumulative escapement plus cumulative catch point estimates from the time of full re- cruitment through the final catch plus escapement estimate. reasonable and timely estimate of total run size. However, the estimate of total run size obtained using the peak acoustic-trawl estimate was higher than the final estimate for all years ex- cept 1979, and higher than all in-season point estimates. Variability (random or unsystematic factors) may contribute to the result, but in general the high sampling power of acoustics and the fairly uniform distribution of the herring render this component inconsequential (Saville 1977), and 95% confidence intervals calculated from the acoustic data are typically on the order of ±10%. Variability associated with the trawling data for species composition is probably more important, but is difficult to in- corporate. Combined acoustic-trawling variance estimation procedures have been developed for other studies (Thomas 1979; Thomas et al. 1979); however, they were not applied in this study since we were more concerned with the sources of potential error (systematic factors or bias). Three sources of bias may contribute to the ob- served differences between the peak acoustic- trawling estimate and the final estimate. The acoustic estimates may be biased high because of the target strength assumption, but the acoustic techniques may underestimate later in the run when the fish move into shallow water just prior to spawning. Studies by other investigators indi- cate that a value of —32 dB/kg (which would result in a 20% lower estimate) may be more reasonable (Nakken and Olsen 1977; FAO 1978) than the —33 dB/kg value used. Alternatively, the estimates from spawning ground data could be biased to the low side. Clearly more information on target strength is needed to confidently establish the accuracy of the acoustic technique as a measure of fish biomass. The reasonable agreement with the sum of the spawning escapement estimates and catch is reassuring, but the spawning escape- ment estimates are also subject to bias and un- certainty, and the exploitation rate has been too consistent to give much insight into the magni- 387 FISHERY BULLETIN: VOL. 80, NO. 2 tude and direction of potential bias in these two estimators. In spite of the present uncertainties in the accuracy of both the spawning escapement and the acoustic-trawl estimates, the results are well suited to the current management plan of the fishery. The objective of present management procedures is to maintain the population at recent historical levels through a combination of a biologically reasonable exploitation rate and a minimum escapement level. The accuracy of the acoustic techniques probably already exceeds our understanding of optimal exploitation rates. Thus, while improvements are conceivable and may be dictated by future developments in the fishery, the present procedures provide a sound interim approach with timeliness which has been rarely achieved in fishery management. ACKNOWLEDGMENTS Collection and analysis of catch records and acoustic, trawl, and spawning ground data was conducted and financed primarily by the Marine Fish Program of the Washington Department of Fisheries. Supplemental funds and personnel have been provided by the Fisheries Assistance Office of the U.S. Fish and Wildlife Service and by the Lummi, Swinomish, Nooksack, and Suquamish Indian Tribes which participate in the fishery. This analysis was partially supported by the Washington Sea Grant Program under the National Oceanic and Atmospheric Administra- tion, U.S. Department of Commerce. LITERATURE CITED Cochran, W. G. 1977. Sampling techniques. 3ded. Wiley, N.Y.,428p. Fao. 1978. Report of the meeting of the working party on fish target strength, FAO/ACMRR ad hoc group of experts on the facilitation of acoustics research in fisheries. ACMRR: 9/78/Inf. 14. 27 p. FAO. Rome. HOURSTON, A. S., D. N. OUTRAM, AND F. W. NASH. 1972. Millions of eggs and miles of spawn in British Col- umbia herring spawning 1951 to 1970. (Revised, 1972.) Fish. Res. Board Can. Tech. Rep. 359, 164 p. Lemberg, N.A. 1978. Hydroacoustic assessment of Puget Sound herring, 1972-1978. Wash. Dep. Fish. Tech. Rep. 41, 43 p. Meyer, J. H., and R. A. Adair. 1978. Puget Sound herring surveys including observa- tions of the Gulf of Georgia sac-roe fishery, 1975-1977. U.S. Fish Wildl. Serv., Olympia, Wash., 71 p. Nakken, 0., and K. Olsen. 1977. Target strength measurements of fish. Rapp. P.- V. Reun. Cons. Int. Explor. Mer 170:52-69. Nunnallee, E. P., Jr. 1973. A hydroacoustic data acquisition and digital data analysis system for the assessment of fish stock abun- dance. Univ. Wash. Fish. Res. Inst. Circ. 73-3, 48 p. Saville, A. (editor). 1977. Survey methods of appraising fishery resources. FAO Fish. Tech. Pap. 171, 76 p. Thomas, G. L. 1979. The application of hydroacoustic techniques to determine the spatial distribution and abundance of fishes in the nearshore area in the vicinity of thermal generating stations. In Proceedings of Oceans '79, IEEE conference of engineering in the ocean environ- ment, p. 61-73. IEEE, N.Y. Thomas, G. L., L. Johnson, R. E. Thorne, and W. C. Acker. 1979. Techniques for assessing the response of fish assemblages to offshore cooling water intake systems. Fish. Res. Inst. Tech. Rep. FRI-UW-7927, 110 p. Univ. Wash.. Seattle. Thorne, R. E. 1977a. Acoustic assessment of Pacific hake and herring stocks in Puget Sound, Washington and southeastern Alaska. Rapp P.-V. Reun. Cons. Int. Explor. Mer 170:265-278. 1977b. A new digital hydroacoustic data proscessor and some observations on herring in Alaska. J. Fish. Res. Board Can. 34:2288-2294. In press. Assessment of population abundance by echo integration. Proceedings of SCOR Working Group 52, symposium on assessment of micronekton, April 1980. Biol. Oceanogr. J. Thorne, R. E., E. P. Nunnallee, and J. H. Green. 1972. A portable hydroacoustic data acquisition system for fish stock assessment. Wash. Sea Grant. Publ. 72-4, 14 p. Trumble, R. J. 1980. Herring management activities in Washington state. In B. R. Melteff and V. E. Wespestad (editors), Proceedings of the Alaska herring symposium, p. 91- 113. Alaska Sea Grant Rep. 80-4. Trumble. R. J., D. Penttila, D. Day, P. McAllister, J. Boettner, R. Adair, and P. Wares. 1977. Results of herring spawning ground surveys in Puget Sound, 1975 and 1976. Wash. Dep. Fish. Prog. Rep. 21, 28 p. 388 NOTES EFFECTS OF LONG-TERM MERCURY EXPOSURE ON HEMATOLOGY OF STRIPED BASS, MORONE SAXATILIS The striped bass, Morone saxatilis, is found along the shore of the heavily populated Atlantic coast of North America; hence, it is subjected to considerable domestic and industrial pollution. Even higher pollutant concentrations may be encountered when the fish migrate into rivers to spawn. Because of the availability of the species, its value to both commercial and sport fisheries, and its normal habitat in many areas where pol- lution is a problem, the striped bass may be a particularly appropriate indicator species for pollution studies. In spite of these factors, in- formation about sublethal effects of metal on striped bass is limited; even the response of the species to mercury, perhaps the most widely studied heavy metal, has received little attention in the literature. That fish accumulate mercury from water has been demonstrated both in the laboratory and in the wild. Pentreath (1976). in a study of accumu- lation, distribution, and retention of mercury, found a gradual uptake and slow loss of :03mercury in the plaice, Pleuronectes platessa, during laboratory exposures up to 90 d. Olson et al. (1973) showed that the rainbow trout, Salmo gairdneri, accumulates mercury through the gills. Our laboratory demonstrated uptake of mercury into the winter flounder, Pseudopleuro- nectes americanus, during a 60-d laboratory exposure (Calabrese et al. 1975). Mercury analyses on fish taken from their natural envi- ronment corroborate the laboratory findings: An increasing mercury concentration correlated with increasing weight has been demonstrated in the pike, Esox lucius; the bluefish, Pomatomus saltatrix; the blue hake, Antimora rostrata; and the striped bass(Johnelsetal. 1967; Alexander et al. 1973; Cross et al. 1973). The sensitivity of striped bass to pollution in general has been reported by a number of inves- tigators. Raney (1952) noted that, although the striped bass had formerly used as spawning areas most of the large rivers along the Atlantic coast of the United States, the species had virtually disappeared from many of these areas, notably the Delaware, Connecticut, and Roanoke Rivers; he attributed its disappearance to gross pollution. Chittenden (1971) also attributed the lack of striped bass in the Delaware River to gross pollution and suggested that a major limiting factor was the river's very low oxygen content. An earlier study in our laboratory demonstrated sublethal responses of the striped bass to mercury. Juvenile striped bass were ex- posed to 5 and 10 parts per billion (ppb) mercury for periods ranging from 30 to 120 d. Measure- ments of gill-tissue oxygen consumption showed changes whose magnitude and direction varied with length of exposure (Dawson et al. 1977). The present study was undertaken to deter- mine the nature and extent of physiological dis- turbance to striped bass caused by mercury exposure using a variety of hematological tests. Variables related to the oxygen-carrying capacity of the blood, such as hemoglobin and hematocrit, were considered important because of earlier indications that mercury exposure affects respiration (Dawson et al. 1977), because of the suggestion that low oxygen levels eliminate striped bass from certain polluted environments (Chittenden 1971), and because of evidence that mercury affects these measure- ments in other fish (Calabrese et al. 1975; Dawson 1979). In addition, because my earlier work indicated that mercury disrupts osmo- and ion-regulation in winter flounder(Dawson 1979), I included these aspects of plasma chemistry in the present study. Methods Exposure Striped bass were obtained from the Edenton National Fish Hatchery, U.S. Fish and Wildlife Service, Edenton, N.C., where they had been reared in freshwater. Upon arrival at the North- east Fisheries Center Milford Laboratory, they were placed directly into flowing Milford Harbor seawater and allowed to acclimate for 2 wk prior to exposure. Throughout the acclima- tion and the exposure period the fish were fed Purina Trout Chow1 ad libitum, daily. The fish 1Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. FISHERY BULLETIN: VOL. 80, NO. 2, 1982. 389 were exposed in 80 1 glass aquaria filled to 60 1 with sand-filtered seawater by a proportional- dilution apparatus (Mount and Brungs 1967). The dilutor controlled the intermittent delivery of mercury-treated and control water at a flow rate of 1 1 to each tank every 3 min throughout the test period. This provided a flow of 480 1/tank per d and an estimated 90% replacement time of 7 h (Sprague 1969). Mercury, as mercuric chloride, was added at concentrations of 5 and 10 ppb. The concentrations are nominal concentra- tions of the metal ion in solution, not including the background level, which was below 0.3 ppb. The fish were exposed for 60 d and then removed for testing. Each tank contained 5 fish, for a total of 15 fish at each mercury concentration and 15 controls. The fish averaged 17.1 cm long (range 13.1-19.0) and 59.3 g (range 22.7-79.3). The expo- sure ran from late November 1976 to January 1977. The temperature ranged from a high of 8°C at the beginning of the exposure period to a low of 0°C at the termination of the exposure. Salinity during the exposure period averaged 27.07.. and ranged from 26.0 to 29.67.. with the exception of 1 d when it fell to 207... Hematology Blood was collected from each fish by cardiac puncture using a 3 ml plastic syringe and a 22- gage needle. The sample was transferred gently into an 8 ml glass vial containing 150 units of dried ammonium heparinate as an anticoagu- lant. Microhematocrits (packed red cell vol- umes) were determined following centrifugation for 5 min at 13,500 X g. Hemoglobin concentra- tions were determined by the cyanmethemoglo- bin method using the Hycel reagent; absorbance was read on a Bausch and Lomb Spectronic 20 spectrophotometer at 540 nm. Erythrocytes were counted in a hemacytometer using Natt- Herricks diluting fluid (Natt and Herrick 1952) at a 1:200 dilution. Within 4 h after collection, the remaining blood sample was centrifuged at 12,000 X g for 4 min and the plasma frozen for later determination of osmolality, protein, sodium, potassium, and calcium. Plasma sodium, potassium, and calcium concentrations were measured with a Coleman 51 flame photo- meter. Plasma protein was determined by the Biuret method as modified by Layne (1957). Plasma osmolalities were determined on an Advanced 3L osmometer using a 0.2 ml sample. Samples were pooled as necessary to obtain a 0.2 ml volume. The effect of the added heparin on the osmolality was negiligible. Three indices were computed from the measured values: mean corpuscular volume in cubic micrometers/cell = Hct/RBC X 10, mean corpuscular hemoglobin in picograms/cell = Hb/RBC X 10, and mean corpuscular hemoglobin concentration in grams/ 100 ml packed red cells = Hb/Hct X 100. All data were analyzed using Student's t-test. Results Control fish had a mean hematocrit of 47%, a hemoglobin concentration of 8.7 g/100 ml, and a red cell count of 4.10 X 106 cells/mm3 (Table 1). These values resemble those reported by other investigators: Courtois (1976), using striped bass of similar size acclimated to cold seawater, re- ported a mean hematocrit of 46 and a hemo- globin of 8.4. More recently, Westin (1978) reported a hematocrit of 47.9, a hemoglobin of 9.11, and a red cell count of 3.79 for adult striped bass during the spawning season. The effects of mercury on the erythrocyte component of the blood were pronounced (Table 1). Hematocrit, hemoglobin, and RBC all decreased following mercury exposure. In each case the response was significantly greater at the higher mercury concentration. The reduction in hemoglobin was proportional to the reduction in red cell count: About 10% in the 5 ppb-exposed animals and about 25% in the 10 ppb-exposed animals. This is reflected in the lack of change of the mean corpuscular hemoglobin and indicates that the lowered hemoglobin concentration in exposed fish is the result of a lower number of circulating erythrocytes and not of a smaller quantity of hemoglobin in each cell. The de- Table 1.— Effects of 60-d exposure to mercuric chloride on erythrocytes of striped bass (means ± SE with ranges in parentheses). Test Controls 5 ppb 10 ppb Hematocrit, 47±1.3 36±1 2" 26±1.6" % packed cells (38-56) (30-47) (17-36) Hemogloblin, g/100 8.7±0.05 7.8±0.13" 6.6±032" ml whole blood (7.8-99) (7 2-8.9) (4.9-8.8) Red blood cells, 4.10±0.106 382±0.106 3.03 ±0.180" 106 cells/mm3 (3.69-4.81) (3 19-4.45) (2.10-4.57) Mean corpuscular vol- 115.2±3.70 96.6±3.69" 862±358" ume, /ym3/cell (96-147) (69-118) (65-114) Mean corpuscular hemo- 21.4±0 52 20.3+054 21.9±0 73 globin, pg/cell (18.5-25.9) (166-23.4) (18.7-290) Mean corpuscular Hb concentration, g/100 18.7±0.44 21.8±057" 25.6±0.58"" ml packed red cells (17.0-21.6) (18.9-27.3) (22.8-28.8) Number of samples 14 15 13 "Significantly different from controls at 0.005 level, '"Significantly dif- ferent from controls at 0.001 level. 390 creases in hematocrit were greater proportion- ately: 23% and 45% of the control value in the 5 and 10 ppb-exposed groups. The greater decrease in hematocrit represents not only a lower number of red cells but, in addition, a smaller mean volume in red cells of exposed ani- mals, reflected in the significantly lower mean corpuscular volume for exposed animals. Exposure to mercury also affected the osmo- and ion-regulatory capacity of the striped bass (Table 2). There was no significant difference be- tween 5 ppb-exposed fish and controls in any of the five plasma chemistry variables measured. In the 10 ppb-exposed animals, the plasma sodium and the osmolality increased to 238 mEq/1 and 462 mOsm. Plasma calcium dropped to 3.98 mEq/1 in the 10 ppb-exposed group, significantly lower than the control value of 4.52. Although the mean calcium concentration in the 5 ppb-exposed fish was even lower, because of the greater variability in that group, it was not significantly different from that of controls. There was no significant difference between controls and 10-ppb-exposed fish in plasma pro- tein or potassium. Table 2.— Effects of 60-d exposure to mercuric chloride on plasma chemistry of striped bass (means ± SE with ranges in parentheses). Plasma samples were pooled as necessary to ob- tain volume of material required. Test Controls 5 ppb 10 ppb Na, mEq/1 195±2.6 198±2 1 238±6.2" K, mEq/1 (180-202) 6.57±0.799 (174-204) 5.19±1.088 (210-262) 5.00±0.588 Ca, mEq/1 (3.00-9.60) 4.52±0.135 (2.20-980) 3.90±0.303 (240-900) 398±0.146 Protein, g/100 ml (4.00-530) 3.70±0.218 (298-580) 3.51±0.016 (326-4.74) 3.34±0446 Osmolality. mOsm (3.14-4.58) 354±10.8 (3.05-4.15) 369±6.9 (238-5.18) 462±11.8*' Number of samples (321-395) 8 (346-398) 8 (435-519) 10 "Significantly different from controls at 0.05 level, "Significantly dif- ferent from controls at 0.001 level. Discussion Mercury had a major disruptive influence on the hematology of the striped bass, affecting both the red cell component of the blood and the plasma chemistry. Mercury had similar effects on winter flounder in an earlier study (Dawson 1979). In general, the changes demonstrated in winter flounder paralleled those of striped bass although the magnitude of change was smaller in the winter flounder in spite of higher mercury concentrations, namely, 10 and 20 ppb. The one exception was that the mean corpuscular volume increased in winter flounder and decreased in striped bass. The greater sensitivity to mercury in striped bass may represent a real species dif- ference or may simply reflect the smaller size of the striped bass used. The alterations in plasma sodium and osmolal- ity following mercury exposure may be caused by gill-tissue damage. Meyer (1952) found de- creased uptake and increased loss of sodium in the gills of mercury-exposed goldfish in freshwater. Olson et al. (1973) found ultrastruc- tural damage in rainbow trout gills following mercury exposure. Renfro et al. (1974) demon- strated mercury uptake by the gill of the killifish, Fundulus heteroclitus, in freshwater and con- comitant inhibition of sodium uptake. Our labo- ratory has demonstrated mercury uptake from seawater into the gills of winter flounder (Cala- brese et al. 1975). At least two sites of mercury accumulation have been described which could account for changes in the red cell component of the blood. Olson et al. (1973) and Pentreath (1976) reported the uptake of mercury into the blood of rainbow trout and plaice which could lead to direct cell damage. Perhaps more relevant are reports of mercury accumulation in the kidneys of teleosts; this would very likely affect renal hemopoiesis and, hence, such variables as hematocrit, hemo- globin, and RBC. Olson et al. (1973) reported a high mercury concentration in the kidney rainbow trout following a 24-h exposure. Pen- treath (1976) reported that, following a 60-d exposure of the plaice to 203Hg, the kidney was among the organs highest in 203Hg. Hematology is a valuable tool for assessing a variety of stresses in fish. Its main limitation lies in the lack of information about the normal range of values in fish. Wedemeyer and Yasutake (1977) have noted that, in general, hematological measurements show a greater variation in fish than in many other animals. Fish are subjected to a wide range of tempera- ture, salinity, and nutrient availability, all of which are likely to be reflected in their hematology. Courtois (1976) has demonstrated hematological changes in striped bass exposed to varying conditions of temperature and salinity. Bridges et al. (1976) have demonstrated signifi- cant seasonal variation in winter flounder hematology. Hesser (1960), Blaxhall and Daisley (1973), and Wedemeyer and Yasutake (1977) have attempted to standardize and interpret 391 hematological tests as applied to fish. The gradual accumulation of the necessary back- ground information should make fish hematol- ogy an even more useful tool in the future. Acknowledgments The author thanks the Edenton National Fish Hatchery for the striped bass used in this study and Rita S. Riccio for her critical reading and typing of this manuscript. Literature Cited Alexander, J. E., F. Foehrenbach. S. Fisher, and D. Sullivan. 1973. Mercury in striped bass and bluefish. N.Y. Fish Game J. 20:147-151. Blaxhall, P. C, and K. W. Daisley. 1973. Routine hematological methods for use with fish blood. J. Fish Biol. 5:771-781. Bridges, D. W., J. J. Cech, Jr., and D. N. Pedro. 1976. Seasonal hematological changes in winter flounder, Pseudopleuronectes americanus. Trans. Am. Fish. Soc. 105:596-600. Calabrese, A., F. P. Thurberg, M. A. Dawson, and D. R. Wenzloff. 1975. Sublethal physiological stress induced by cad- mium and mercury in the winter flounder, Pseudo- pleuronectes americanus. In 3. H. Koeman and J. J. T. W. A. Strik (editors), Sublethal effects of toxic chemicals on aquatic animals, p. 15-21. Elsevier Sci. Publ., Amsterdam. Chittenden, M. E., Jr. 1971. Status of the striped bass, Morone saxatilis, in the Delaware River. Chesapeake Sci. 12:131-136. Courtois, L. A. 1976. Hematology of juvenile striped bass, Morone saxatilis (Walbaum), acclimated to different environ- mental conditions. Comp. Biochem. Physiol. 54A:221- 223. Cross, F. A., L. H. Hardy, N. Y. Jones, and R. T. Barber. 1973- Relation between total body weight and concen- trations of manganese, iron, copper, zinc, and mercury in white muscle of bluefish {Pomatomus saltatrix) and a bathyl-demersal fish Antimora rostrata. J. Fish. Res. Board Can. 30:1287-1291. Dawson, M. A. 1979. Hematological effects of long-term mercury ex- posure and subsequent periods of recovery on the winter flounder, Pseudopleuronectes americanus. In W. B. Vernberg, A. Calabrese, F. P. Thurberg, and F. J. Vernberg (editors), Marine pollution. Functional re- sponses, p. 171-182. Acad. Press, N.Y. Dawson, M. A., E. Gould, F. P. Thurberg, and A. Calabrese. 1977. Physiological response of juvenile striped bass, Morone saxatilis, to low levels of cadmium and mercury. Chesapeake Sci. 18:353-359. Hesser, E. F. 1960. Methods for routine fish hematology. Prog. Fish-Cult. 22:164-171. Johnels, A. G., T. Westermark, W. Berg, P. I. Persson, and B. Sjostrand. 1967. Pike (Esox lucius L.) and some other aquatic organ- isms in Sweden as indicators of mercury contamination in the environment. Oikos 18:323-333. LAYNE, E. 1957. Spectrophotometric and turbidimetric methods for measuring proteins. III. Biuret methods. In S. P. Colowick and N. O. Kaplan (editors), Methods in enzymology. Vol. Ill, p. 456-461. Acad. Press, N.Y. Meyer, D. K. 1952. Effects of mercuric ion on sodium movement through the gills of goldfish. (Abstr.) Fed. Proc. 11:107-108. Mount, D. I., and W. A. Brungs. 1967. A simplified dosing apparatus for fish toxicology studies. Water Res. 1:21-29. Natt, M. P., and C. A. Herrick. 1952. A new blood diluent for counting the erythrocytes and leucocytes of the chicken. Poultry Sci. 31:735-738. Olson, K. R., P. O. Fromm, and W. L. Frantz. 1973. Ultrastructural changes of rainbow trout gills ex- posed to methyl mercury or mercuric chloride. (Abstr.) Fed. Proc. 32:261. Pentreath, R. J. 1976. The accumulation of inorganic mercury from sea water by the plaice, Pleuronectes platessa L. J. Exp. Mar. Biol. Ecol. 24:103-119. Raney, E. C. 1952. The life history of the striped bass, Roeeus saxatilis (Walbaum). Bull. Bingham Oceanogr. Collect., Yale Univ. 14:5-97. Renfro, J. L., B. Schmidt-Nielsen, D. Miller, D. Benos, and J. Allen. 1974. Methyl mercury and inorganic mercury: uptake, distribution, and effect on osmoregulatory mechanisms in fishes. In F. J. Vernberg and W. B. Vernberg (editors), Pollution and physiology of marine organisms, p. 101-122. Acad. Press, N.Y. Sprague, J. B. 1969. Measurement of pollutant toxicity to fish. I. Bio- assay method for acute toxicity. Water Res. 3:793-821. Wedemeyer, G. A., and W. T. Yasutake. 1977. Clinical methods for the assessment of the effects of environmental stress on fish health. U.S. Fish Wildl. Serv., Tech. Pap. 89, 18 p. Westin, D. T. 1978. Serum and blood from adult striped bass, Morone saxatilis. Estuaries 1:126-128. Margaret A. Dawson Northeast Fisheries Center Milford Laboratory National Marine Fisheries Service, NO A A Milford, CT 061,60-6^99 392 RAPID AND SPONTANEOUS MATURATION, OVULATION, AND SPAWNING OF OVA BY NEWLY CAPTURED SKIPJACK TUNA, KATSUWONUS PELAMIS This study was designed to test a hypothesis, for- mulated on the basis of preliminary observa- tions, that skipjack tuna, Katsuwonus pelamis, captured in Hawaiian waters during their breed- ing season and maintained alive would ovulate spontaneously within a few hours after capture. If such did occur, and on a consistent and predict- able basis, this would be of practical value in attempts to spawn these fish in captivity. Methods These investigations took place at the Kewalo Research Facility of the National Marine Fish- eries Service Honolulu Laboratory. Six deliver- ies of live skipjack tuna were received from two commercial fishing vessels during June and July 1980, within the normal spawning season of the species in Hawaiian waters (Brock 1954; Matsu- moto 1966). The fish had been caught by stan- dard pole-and-line methods and transported to the receiving dock of the laboratory in baitwells. Upon delivery they were transferred to circular tanks, 7.3 m diameter by 1.1 m deep, provided with continuous flow of seawater. Time of cap- ture for all groups was between 1500 and 1700; time elapsed between capture and delivery to the laboratory ranged from 3.5 to 8 h, with a mean of 5.5 h. Sea temperatures at the capture sites were not measured, but were probably between 25° and 30°C. Water temperatures in the holding tanks were about 25° to 26°C. With all except the first group, a siphon and straining net were used to sample water continuously from the holding tanks to detect the release of their slightly buoy- ant, pelagic ova. For the last four of the six groups, we arranged also to receive specimens fished from the same school but refrigerated on ice immediately after capture. All the specimens were between 40 and 50 cm in fork length (FL) and 1.4 to 2.2 kg; tunas larger than this are diffi- cult to keep alive in the baitwells of these vessels (about 145 by 165 by 130 cm deep on the vessel which delivered five of the six groups). Skipjack tuna of this size are between 1 and 2 yr old and are probably in their first spawning season (Brock 1954; Yoshida 1971). We determined gonadal maturation states of specimens at various specified times following their capture, either through biopsies on live spe- cimens or through postmortem dissections. Unless a specimen is already running ripe, neither its sex nor gonadal maturity can be de- termined through external appearances. Biop- sies involved extraction of gonadal tissue by catheterization through the urogenital pore of restrained, unanesthetized fish. Ova were teased free from unpreserved, fresh or refrigerated ovarian tissue, immersed in a 0.9% saline solu- tion, and the diameters of 25 from each of the largest and second largest developing groups were measured with an ocular micrometer. Also, since we were interested primarily in the occur- rence and progress of ovulation, we classified females into the following four categories: Un- ovulated — ripe ova not present in ovarian lumen, developing ova enclosed within follicles; ovulat- ing— some ripe ova present in ovarian lumen but not easily stripped from females, follicles contain large, preovulatory ova 0.80 to 1.0 mm in diame- ter; ripe— ovarian lumen filled with large quan- tities of ova which can be easily stripped from females; spent — few residual ova present in ovar- ian lumen, follicles with relatively small ova of <0.5 mm diameter. Results Responses of each sex remained constant among the six groups. Testes of males sacrificed after 7 to 8.5 h appeared identical to those sacri- ficed and refrigerated on capture. All males had testes that were mature, white, and firm and had thick, viscous milt in the sperm ducts. None yielded milt when moderate stripping pressure was applied. To fertilize ova stripped from fe- males, we had to squeeze milt directly from testes dissected from sacrificed males. Observations on all six groups of female skip- jack tuna received from 8 June to 31 July are summarized in Table 1. None of the 16 specimens killed and refrigerated on capture was in an ovu- latory state. The maturing ova in the largest modal group averaged 0.59 to 0.64 mm in 14 of these females and 0.74 mm in another, while the remaining individual had relatively immature ovaries (Table 2). Nine females which died in transit to the laboratory were placed in refriger- ation. Times of death had not been recorded by the fishing crews, but were <5 h after capture in all cases. None of these females had yet ovulated, and the ova in their largest developing modal groups averaged from 0.60 to 0.93 mm in diame- FISHERY BULLETIN: VOL. 80. NO. 2. 1982. 393 Table 1.— Ovulatory status of skipjack tuna at different times following capture during June and July 1980. Time No. Unovulated Ovulating Ripe Spent Refrigerated immediately after capture 16 16 Captive females, 0-5 h after capture' 9 9 Captive females, 5-6 h after capture 13 1 Captive females, 7-8.5 h after capture 12 3 Captive females, 1 5-65 h after capture 20 12 0 19 'Refrigerated after dying in transit to the laboratory; individual times of death not known, but <5 h after capture in all cases. could be completed within 8 h after capture and occurred even in females that were so seriously traumatized that they died within a few hours after this time. Unless manually stripped, the ripe females released ova into the holding tank, and by the next day, 15 to 24 h after capture, were in a spent condition. Spawning behavior was not observed to occur. Instead, their behavior was invariably abnormal, as is typical for skip- jack tuna during their first days in captivity, with individuals swimming aimlessly about the holding tanks. The ovulated ova, both those released spontan- eously into the tanks and those stripped from Table 2.— Mean sizes (mm)1 of ova in largest and second largest modal group of developing ova in skipjack tuna killed and refrigerated immediately after capture, or refrigerated after dying in transit to the laboratory. Date 31 July Refrigerated on capture Died in transit No 15July 4 21 July 7 22 July 3 Largest group 0.62 0.62 Second group No Time (h)2 Largest group 0.62 Not measured 061 Not measured 0.59 Not measured 0.60 Not measured 060 042 0.60 0.39 0.60 0.40 0.59 0.41 0.59 0.40 0.60 0.39 0.59 0.40 022 0.10 0.64 0.41 0.74 0.44 0.41 043 'Standard deviations 0.02-0.04 2Time between capture and death <45 <5 Second group 0.84 0.44 0.93 0.43 076 0.44 0.69 0.44 072 0.42 0.70 0.42 0.72 0.45 067 0.41 060 0.41 ter (Table 2). Of those kept alive, all but 1 of the 13 specimens examined 5 to 6 h after capture were ovulating but not yet ripe, while 8 of 12 examined after 7 to 8.5 h were ripe. Such ripe in- dividuals yielded about 100,000 to over 150,000 ova when stripped. All but 1 of the 20 specimens examined 15 to 65 h after capture were spent. On all five occasions when the holding tanks were monitored for the presence of spawned ova, large numbers of ova were evident by the morning fol- lowing delivery. These observations clearly demonstrated that female skipjack tuna caught and kept alive dur- ing this time of year rapidly underwent the final stages of ovarian maturation and then ovulated ripe ova into the ovarian lumen. This response ripe females, were normal in size and appear- ance. They were spherical, transparent, aver- aged about 1.0 mm in diameter, and had a single oil globule about 0.24 mm in diameter. The fertil- ization rate of ova stripped from females about 8 h following their capture was only about 40% to 50%; this may reflect the quality of the ova or the small amounts of viscous milt squeezed from the dissected testes. The embryos hatched in about 30 to 31 h at 25° to 26°C and started feeding on the third day after hatching. Although they fed actively on rotifers, Brachionus sp., and copepod nauplii, we were not able to rear any beyond the 12th day. Numerous investigators have described the multimodal size distribution of developing ova in 394 the ovaries of maturing tunas. All of the ova in the most advanced modal group (about 0.60 mm or larger in these specimens) appeared to under- go final maturation and ovulation during this response but the second largest modal group seemed not to be affected. Ovaries from "control" specimens killed and refrigerated on capture and from those that died within 5 h contained an advanced modal group of maturing ova, as previ- ously described, and a second, smaller modal group in which the ova averaged between 0.39 and 0.44 mm in diameter (Table 2). Ovaries from fully ovulated, ripe females and from recently spent females contained a residual modal group of similar, unovulated ova that averaged 0.39 to 0.49 mm in diameter (Table 3). These latter observations support the common assumption that in species with multimodal size distribu- tions of developing ova, only the most advanced modal group will mature and be ovulated' for a given spawning. Table 3.— Mean sizes (mm)1 of ova in largest modal group of unovulated ova in ripe or recently spent skipjack tuna. Date Hours after capture Status Ova diameter 28 June 8 Ripe 0.46 8 Ripe 046 17 July 46 Spent 0.43 46 Spent 0.40 21 July 7 Ripe 0.43 22 July 20.5 Spent 0.42 25 Spent 0.39 23 July 232-39 Spent 0.40 32-39 Spent 043 32-39 Spent 049 31 July 26.5-15 Spent 0.45 'Standard deviations 0 02-0.04 2Found dead in holding tanks, time interval since last seen alive. Discussion This rapid ovarian maturation, ovulation, and spawning appears to be a unique response to cap- ture not previously reported. The trigger to this response is not known but appears related to stresses associated with capture and confine- ment. Witschi and Chang (1959) earlier con- cluded that ovulation of vertebrates could be facilitated by stress, but there has been a lack of direct evidence to support this conclusion. In- direct evidence for such a relationship within teleosts is suggested by ovulatory responses of certain species to treatment with corticosteroids (Hirose 1976; Sundararaj and Goswami 1977) and with epinephrine (Jalabert 1976), both of which have been reported to increase rapidly in serum concentrations following such stresses as handling and increased temperature (Mazeaud et al. 1977; Strange et al. 1977; Cook et al. 1980). The handling associated with being hooked, transported in crowded baitwells, transferred to shore tanks, and confined is obviously stressful and often fatal to newly captured skipjack tuna. Thermal stress may occur when they are con- fined in warm surface waters and prevented from returning to cooler depths after feeding. Many additional aspects of this postcapture ovulatory response are not yet understood. Sev- eral aspects would be of particular interest: 1) the state of ovarian maturation that would be prerequisite for rapid egg development in fe- males; 2) the seasonal availability of responsive females; 3) whether the time to complete ovula- tion, about 7 to 8 h in this study, will vary depend- ing on such factors as water temperature, ovar- ian maturation, or time of day the fish are caught; and 4) whether this apparent response to acute stress is entirely an artificially produced anomaly, or whether it does have some relation to their natural spawning biology. Past efforts to rear tunas in captivity (briefly reviewed by Kaya et al. 1981) had not heretofore resulted in dependable spawning procedures for any species. However, the occurrence and pre- dictability of the ovulatory response to capture have now been applied to establish a routine pro- cedure for spawning skipjack tuna at the Kewalo Research Facility. Additional spawnings have thus been accomplished during the summer of 1981, the second season of trials, and the response has been observed also in a second species of tuna — kawakawa, Euthynnus affinis. It would be of interest to determine whether other species will undergo a similar response to stresses of cap- ture and confinement. Acknowledgments These observations were made possible through a research contract from the National Marine Fisheries Service to the senior author and through the administrative support and en- couragement provided by Richard S. Shomura, Director of the Honolulu Laboratory of the Na- tional Marine Fisheries Service Southwest Fish- eries Center. Literature Cited Brock, V. E. 1954. Some aspects of the biology of the aku, Katsuwonns pelamis, in the Hawaiian Islands. Pac. Sci. 8:94-104. 395 Cook, A. F., N. E. Stacey, and R. E. Peter. 1980. Periovulatory changes in serum Cortisol levels in the goldfish, Carassius auratus. Gen. Comp. Endocri- nol. 40:507-510. Hirose, K. 1976. Endocrine control of ovulation in medaka (Oryzias latipes) and ayu (Plecoglossiis altivelis). J. Fish. Res. Board Can. 33:989-994. Jalabert, B. 1976. In vitro oocyte maturation and ovulation in rain- bow trout (Sal mo gairdneri), northern pike (Esox lucius), and goldfish (Carassius auratus). J. Fish. Res. Board Can. 33:974-988. Kaya, C. M., A. E. Dizon, and S. D. Hendrix. 1981. Induced spawning of a tuna, Euthynnus a/finis. Fish. Bull., U.S. 79:185-187. Matsumoto, W. M. 1966. Distribution and abundance of tuna larvae in the Pacific Ocean. In T. A. Manar (editor), Proceedings, Governor's Conference on Central Pacific Fishery Re- sources, p. 221-230. State of Hawaii. Mazeaud, M. M., F. Mazeaud, and E. M. Donaldson. 1977. Primary and secondary effects of stress in fish: Some new data with a general review. Trans. Am. Fish. Soc. 106:201-212. Strange, R. J., C. B. Schreck, and J. T. Golden. 1977. Corticoid stress responses to handling and temper- ature in salmonids. Trans. Am. Fish. Soc. 106:213-218. Sundararaj, B. I., and S. V. Goswami. 1977. Hormonal regulation of in vivo and in vitro oocyte maturation in the catfish, Heteropneustesfossilis (Bloch). Gen. Comp. Endocrinol. 32:17-28. Witschi, E., and C. Y. Chang. 1959. Amphibian ovulation and spermiation. In A. Gorbman (editor), Comparative endocrinology, p. 149- 160. Wiley, New York. Yoshida, H. O. 1971. The early life history of skipjack tuna, Katsuwonus pelamis, in the Pacific Ocean. Fish. Bull., U.S. 69:545- 554. Calvin M. Kaya Southwest Fisheries Center Honolulu Laboratory National Marine Fisheries Sennce, NOAA Honolulu, HI 96812 Present address: Department of Biology Montana State University Bozeman, MT 59717 Andrew E. Dizon Sharon D. Hendrix Thomas K. Kazama Martina K. K. Queenth Southwest Fisheries Center Honolulu Laboratory National Marine Fisheries Service, NOAA Honolulu. HI 96812 ESTIMATING AND MONITORING INCIDENTAL DOLPHIN MORTALITY IN THE EASTERN TROPICAL PACIFIC TUNA PURSE SEINE FISHERY Each year the purse seine fishery for yellowfin tuna, Thunnus albacares, in the eastern tropical Pacific is responsible for the incidental kill of thousands of small cetaceans,1 primarily dol- phins or "porpoise." Yellowfin tuna are often associated with small cetaceans in this region and fishermen have used this association since 1959 to catch tuna(McNeely 1961; Perrin 1969; Fox 1978). During the purse seining operation, cetaceans encircled with yellowfin tuna by the net may become entangled and accidentally drown. In such cases, the fishermen retain the tuna and discard the cetaceans at sea. The Marine Mammal Protection Act of 1972 requires the tuna fishery to be managed so that the dolphin populations are maintained at spe- cific population levels and that incidental mor- tality be reduced to insignificant levels. The National Marine Fisheries Service (NMFS) has the responsibility of monitoring the dolphin mor- tality and of assessing the impact of dolphin mortality on dolphin populations. NMFS carries out research on the abundance and distribution of dolphins, their biology, the level of incidental mortality, and methods for reducing incidental mortality. Beginning in 1971, the NMFS regularly placed observers on purse seiners to collect data on the incidental mortality of dolphins. Prior to 1974, however, only a few observers were hired to collect data; the amount of data collected, therefore, is too small to produce a precise esti- mate of total incidental mortality. Most estimates from this period place the total at about 300,000 to 500,000 animals/yr. Estimates for 1974 and 1975, which are more precise, are 140,000 and 157,000 animals killed, respectively, for the U.S. fleet (Smith2). After a U.S. District Court ruling in 1976, the NMFS set an annual quota of 78,000 animals for 'Dolphin, in this paper, is used as a general term referring to all small cetaceans impacted in the fishery. Mortality or kill refers to dolphin mortality incidental to the catch of yellowfin tuna. The unit of fishing effort "set" is defined as a single deployment of a purse seine net around an aggregation of dol- phin or tuna. Tuna catches are expressed in the unit short tons, as it is the most common form in which these statistics are re- ported. 2Smith, T. D. Report of the status of porpoise stock work- shop. Southwest Fish. Cent. Adm. Rep. LJ-79-41, 120 p. 396 1976 as the maximum allowable kill by the U.S. tuna fishery. Methods for monitoring the mortal- ity levels, and projecting when the quota would be reached during the year, were required. A yellowfin tuna quota(175,000-195,000 short tons) managed by the Inter-American Tropical Tuna Commission (IATTC), around which the tuna fishermen planned their fishing operations, was also in effect and had to be incorporated into the procedure. In this paper, we describe statistical methods which have been used to estimate the annual incidental dolphin mortality for the U.S. fleet during the year and at the end of the year since 1976. This estimative procedure has been used also for foreign fleets by IATTC since 1979 (Allen and Goldsmith 1981). Methods The data sources used to monitor and estimate incidental dolphin mortality were the scientific observer program of the NMFS and the logbook records of the IATTC. The NMFS observer program provides data on discarded dolphins. Trained technicians were placed aboard a random sample of U.S. tuna ves- sels to collect data of various types, including number of dolphins killed in a set, amount of tuna caught, species of tuna, fishing location, vessel capacity, and duration of trip. The IATTC maintains a logbook system where- by it collects data on type of set, fishing locations, tonnage of catch, species of tuna, vessel carrying capacity, and other information that are recorded in logbooks by fishermen. Three mortality rates were used to estimate total dolphin mortality. They were obtained by dividing the total observed kill of dolphins by the total observed number of dolphin sets (kill-per- set), by the total observed number of days-at-sea (kill-per-day), and by the observed total catch of yellowfin tuna associated with dolphin (kill-per- ton). Estimation Procedures Three estimation procedures were used in this study. The first procedure was based on kill-per- day statistics to monitor the dolphin mortality during the year; the second was based on kill- per-ton combined with kill-per-day to project the closure date; and the third was based on kill-per- set to estimate the total mortality at the end of the year. The kill-per-day and the kill-per-set methods were based on stratified ratio estimators. Trips from which the dolphin set data were taken, were stratified according to fishing locality, ves- sel carrying capacity, yellowfin tuna catch, gear type, and fishing time. The fishing locality and time were directly related to the I ATTC's yellow- fin tuna regulatory system, which includes 1) an annual quota on yellowfin tuna catch within the Commission's yellowfin regulatory area(CYRA) (Fig. 1), 2) season closure to enforce the quota on yellowfin tuna catch, and 3) a "last trip" allo- cated at season closure to each vessel that fished during the open period (Table 1). Kill-Per-Day Method The kill-per-day method requires all trips to be stratified according to gear type, vessel carrying capacity, and fishing time; this method was de- veloped to monitor kill during the season. The year was divided into three periods, each desig- nating a trip type. Trip-type 1 included all vessel Figure 1.— The major part of the Inter-American Tropical Tuna Commission Yellowfin Regulatory Area (Courtesy of IATTC). 397 days through the IATTC season closure date (1 January through 26 March); trip-type 2 included all vessel days approximately corresponding to the "last trip" (27 March through 4 July); and trip-type 3 contained all vessel days after 4 July. This stratification of time was used to preclude overlapping trips. When a trip crossed a stratum boundary, it was assigned to more than one strat- um. For example, for a trip lasting from 1 March to 5 May, the days from 1 March to 26 March would be assigned to trip-type 1, and days from 27 March to 5 May assigned to trip-type 2 (Table 1). and -2 cov(X,Y) X{ Y, where s,2 su = nxv - xy j_ Wj — 1 XiYa- Yf Hi — 1 S(XU - X,) ( YtJ - Y{) Table 1.— Layout of stratification of vessel trips (sets) for kill- per-day and kill-per-set methods. Kill-per-day method with maximum 30 strata: 15 for each gear type NMFS Trip 1 Trip 2 vessel 1 Jan -26 Mar 27 Mar -4 July class open1 regulated Trip 3 5 July-end of fishing open2 regulated I III Kill-per-set method with maximum 32 strata IATTC vessel class Successful sets Unsuccessful sets Inside CYRA Outside CYRA Inside CYRA Outside CYRA 'Trips trips." Hast not subject to IATTC season closure Most of them were "last trips" or trips made outside of CYRA The statistical formulation for dolphin mortal- ity estimation according to a stratified ratio esti- mator is as follows (Cochran 1977): For the ith stratum, i = 1 /, let N, = total number of vessel trips nt — number of observed trips Xij = kill for the jth observed trip j = 1, . . ., 71 i Y,j = days-at-sea for the jth observed trip r, = kill-per-day sr, = the approximate sample standard error of r, (kill-per-day) Mj = total number of days-at-sea T, = estimated total kill then r, = XXij I XYa j (1) cov(X,Y) n , • — 1 r,M, T = (IT,) = Zr,M, Sr2 = ZM? S* The ratio estimator (r,) and its approximate sample variance (s,2,) are unbiased only under certain conditions (Cochran 1977). Alternative variance formulas have been suggested to cor- rect the bias (Royall and Eberhardt 1975; Royall and Cumberland 1981). We chose the commonly used variance formula (s 2) in our procedure be- cause the results of a simulation study showed that the bias of the ratio estimator and the ap- proximate variance is negligible (Lo3). The simu- lation study was based upon the empirical dol- phin mortality data collected in 1977. Beginning on 30 June 1976, NMFS observers radioed their mortality counts to a shore base each month (starting in 1977, estimates were made biweekly). Data from this source were used to estimate cumulative mortality and to pro- ject the date when the annual quota would be reached. Combined Kill-Per-Day and Kill-Per-Ton Method The method using combined kill-per-day and kill-per-ton was developed to project at the end of 3Lo, N. C. H. Simulated results of a commonly used ratio estimator applied to incidental dolphin mortality by U.S. tuna purse seiners in the eastern tropical Pacific. Manusc. Southwest Fisheries Center La Jolla Laboratory, National Marine Fisheries Service, NOAA, La Jolla, CA 92038. 398 each month the date on which the quota would be reached. It included two procedural steps: 1. A series of cumulative dolphin mortality esti- mates for each future month was made by summing the current total mortality, based on kill-per-day statistics, and the projected mortality for future months, based on kill- per-ton statistics. To calculate the projected cumulative mortality in future month m, we denote, at the end of month h, Th = the estimated current total mortality from the observed data by kill-per- day method T,„j, = the projected cumulative mortality at the end of month m based upon T„ Um = the tonnage of yellowfin tuna catch in month m Um = the historical monthly tonnage aver- age of yellowfin tuna catch Zw = observed kill-per-ton weighted by number of vessels of two gear types. We then have 1 m.h l z 1 m-\,h H" U „i ' ^W = 1 m-l.h "T Um ZiW Th +{ (! *) for m = h + l, h + 2 12 l30% in the megalopa. During starvation, biomass declines in an exponential pattern. Larvae of all stages die, when ca. 40 to 60% of their living substance and energy is lost. The C :N ratio suggests that protein serves as the main source of energy; in the final phase, presumbaly, lipids are also catabolized. Weight-specific energy and probably also metabolism decrease in a hyperbola-shaped curve. Advanced rearing techniques developed in the last three decades have greatly increased our knowledge of autecology and physiology of meroplanktonic marine larvae. However, there is little quantitative information on growth, energetic needs, and reserves. Within the literature on decapod larvae, there are numerous data on size increments from one developmental stage to the next (Rice 1968), but few on biomass production. Since size is fairly constant in each particular instar, this informa- tion represents only a rough measure of actual growth patterns. A number of authors have investigated bio- chemical or energetic aspects of larval develop- ment in decapod crustaceans: Reeve (1969), Mootz and Epifanio (1974), Frank et al. (1975), Sulkin et al. (1975), Logan and Epifanio (1978), Morgan et al. (1978), Anger and Nair (1979), Capuzzo and Lancaster (1979), Omori (1979), Dawirs (1980), Stephenson and Knight (1980). These studies, however, mainly concentrated on 'Biologische Anstalt Helgoland, Meeresstation, D-2192 Helgoland, Federal Republic of Germany. 2 Zoologisches Institut der Universitat Kiel, Olshausenstr. 40 - 60, D-2300 Kiel 1, Federal Republic of Germany. Manuscript accepted December 1981. FISHERY BULLETIN: VOL 80, NO. 3, 1982. gross differences among larval stages rather than on changes within single instars. Thus, bio- mass was either considered practically constant in each stage, or it was interpolated by means of (mostly exponential) regression equations describing growth from the first to the last larval instar. The present paper attempts to analyze actual growth patterns within stages of the spider crab, Hyas araneus. Growth achieved in the laboratory under optimal food conditions (as in this paper) probably represents only one end of the scope in which development is possible, rather than a typical expression of it. The other end is char- acterized by the poorest food level still allowing minimal growth. Anger and Dawirs (1981) dis- cussed the potential ecological role of starvation in a variable environment. They showed that larvae of Hyas araneus are well adapted to this condition. In the present study diminution and growth rates were estimated from frequent samples of starved and fed larvae. They constitute a further step toward a better understanding of larval ecology and energetics in North Sea species as required in a joint research project! Anger and 419 y/f-v/y FISHERY BULLETIN: VOL. 80, NO. 3 Nair 1979; Dawirs 1979, 1980; Anger and Dawirs 1981). MATERIALS AND METHODS Ovigerous Hyas araneus were dredged from a deep channel near the island of Helgoland (North Sea) during early winter in 1978-79 and 1979-80. After hatching, the zoeae were isolated in vials and maintained individually at 12°C. Food (a mixture of freshly hatched Australian Artemia sp. nauplii and the rotifer Brachionus plicatilis) and filtered seawater were changed every second day. The methods of obtaining and rearing the larvae have been described in detail by Anger and Dawirs (1981). For determination of wet weight, larvae were caught individually with pen-steel forceps, briefly rinsed in water from an ion exchanger, blotted for about 10 s on filter paper, and trans- ferred to preweighed silver cartridges. All weight measurements were carried out on an Autobalance AD-2 (Perkin-Elmer)3 to the nearest 0.1 m£- The techniques and equipment used for obtaining dry weight (DW), carbon (C), nitrogen (N), and hydrogen (H) content of larvae and young crabs were the same as described by Anger and Nair (1979) and Dawirs (1980): deep freezing, vacuum drying, weighing, and com- bustion in aC-H-N analyzer (Model 1106, Carlo Erba Science). Only rinsing of the material (see above) was added as an initial step. This standard procedure was adopted to remove pos- sible adherent salt and thus to increase the accuracy of the measurements. Comparison of test measurements, however, did not show signif- icant differences (Anger and Nair 1979). Energy estimates (J) were obtained from carbon values by applying the N-corrected regression equation given by Salonen et al. (1976). Statistical procedures were the same as referred to in detail by Anger and Dawirs (1981). In regression equations, intercept (6) and slope (m) are given; in addition, correlation coeffi- cients (r) and their level of significance (P) for deviation from zero are provided. For logarith- mic transformations, In (= loge) was applied. All statistical tests were two-tailed. In May 1979, a first series of 46 analyses com- prising 123 individually reared zoea-1 larvae (Z- 1) of Hyas araneus was carried out to compare 3Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. their growth patterns with those previously ob- served by Anger and Nair (1979) in commonly reared zoeae. This set of data showed unsatisfac- torily high variation, and high mortality pre- vented a larger number of analyses. For this reason, in February 1980 another set of 92 analyses comprising 110 prezoeae, 274 Z-l, and 30 early Z-2 was obtained (Table 1). The data for later stages given in Table 2 had been obtained in March and April 1979 (112 samples, 149 individuals). RESULTS Larval Growth Fresh weight (FW) values fluctuated around constant levels in all larval stages without clear increase in a single stage (Tables 1, 2). This steplike growth pattern did not allow any analysis of actual body growth during larval in- stars. The gain in total live weight (FW) from the prezoea to the freshly metamorphosed crab was ca. 770%. It was 640% in DW, and only ca. 470% in C, N, and H. The absolute increase during larval development is shown in Figure 1. During the extremely short, nonfeeding prezoea stage there was no gain in C, N, H, and energy. Molting to the Z-l resulted in a minor loss of organic constit- uents (cast cuticle) and in some uptake of water and salt (Table 1; Fig. 1). During the following instars there was an appreciably absolute in- crease in all parameters considered. It was generally strongest in the second zoeal stage and, surprisingly, weakest in the megalopa. The values shown in Figure 1 for Z-l, Z-2, and magalopa form a straight line when arranged in a semilogarithmic scale. This indicates that growth from stage to stage followed an exponen- tial pattern during this period. The different growth patterns in wet weight (steplike) and DW (gradual) were caused by a combination of these two patterns in the water content of the larvae; during each molt, it suddenly increased, and then it gradually de- creased during the molt cycle. This decrease could be expressed as a power function in all larval instars: In (% H20) = b + m In (t + 1), where b is approximately the logarithm of the initial water content, m is the slope, and t is the time (days from the beginning of a particular stage). All r's for these fitted curves were significantly different from zero (P<0.001). The rate of de- 420 ANGER and DAWIRS: ELEMENTAL COMPOSITION OF HYAS ARANEUS be "3 •5 u crt .2 * ■m > 1_ OJ ^ • o S > in -: -H y< /. ^ 0j C 3 be g o -* C 0) §§ ■fi-8 01 O g «1 IS o > 21 a* .S £ ° . «- C * ^ P Q E C 3 *J c § c "3 c« £ _; >> S s- — "O en . 0) (—• co £ 6 fc Si s- +J d _c be o 0) S- is 01 — £ OJ 3 !_ c Is, bc^ > c « o s t> a: u co. < CD i- O) O S CO CO >- o >- >- T rOrlD CD CM CO CD CD CM CD CD «> d r-- 'j CO r- cp en CM CO CD *- CO CO CO CD r-^ d f o d d d d • t- lO I ^ CO I CO CO I cr d 00 CM CD CD I- ■» CO CO r- CM ^ in r- CO ^-r-;^cp ^T-i-Cp co ddr^csi coo cod cbddd r- tJ- co r- »- CO CO CO o t- f o oo o tod oid to "> "■> CO O^ COO COCNf-Cp h- i- CO CO O C\J CO CO T- TT O CO CO O I- CO CO i- oq ^-_i^ in in d oS d in o c\j o o cnj ■» d co in t- co m t^- co oo cm r~ »- r- * in co r- cm in n in cq co CO d ^- CM co m co co enco loddoi CD OJ CO *- r-' d t^ d cm co o m r» d ^ d q *- en - <- o uo id en o m o cm o *r o T- OCOOCM T CM N CO d * 6 in' r co 6 co d r- co ^t co cm cp co in o d d cp ^- o> m Lodsd CNJ t- TJ- ^r cooso r- i- O) T- in d d d en in cm cm o>p o> co in d »- d cm d CM T- in d '- O NO w 'fl mo ^ d ■>t CO c\j d co *- in o in c\j in d »-' d ■- d co o in »- in t- cm in cp ^r cm m d ci d d -r- cm t^- co ^r m >- o cnj d d d d Olr-OOJ 7- t- it d d d in d co o cm co ■r^ d ^ d 00 OCNJCOCO ■"ti-OlCO co oo co in CO CM O in t- r^ cm co CM m co o o> T- CO O) CO CO CNJ O *» 1- CO CO cnj m in O) cnj d d >- co co CO i-CO aco d d d cm d co o co o d d d d d d C-- y- t- CM ^'diod oo »- in -^ m in O y- ^O CO t- od "-6 o o i m ■" m »- co oo o o o f' d »-' o r^ cm do * " O *- CO r- COO d d d d -a- d oi in oi co r^dcoV CD »- O CO o d d d CD y- 00 CM d o d d d d co a> m o i- o |x HH Ix -H IX -H l> -H lx -H lx -H I* -H IX -H lx -H I* -H IX -H g> en 5- — 3 ^ 3 £- 3 I 1 o H I o 5 o E o CO "O c c CO c 2 421 FISHERY BULLETIN: VOL. 80. 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CM ^ d CM odt-o ri c> <6 d •<» o r^ O o o o !■ a> CO t CO CO ■* f O) *" IX +| IX W lx -HI* -H Ix -h lx -H IX -H IX -H IX -H lx -H lx -H y) en 3 3^ £ 3 £ 3 (6rf) (%) ■o 5 a 0) a> CO >. CO c CO > T3 C 5 3 o Z c E 3 LL 5 I o z I o -5 — ) c 2 422 ANGER and DAWIRS: ELEMENTAL COMPOSITION OF HYAS ARANEUS 450 1 400- 350- O) 300 v 250H "5 C 200 150J 100- 50- other constituents [C^\ hydrogen yy-::< i-ii! nitrogen carbon m® Essaa Stage of development IMW 1 I Figure l.—Hyas araneus. Initial dry weight, carbon, nitrogen, and hydrogen content in the prezoea (PZ), zoeal stages (Z-I, Z-II), megalopa (M), and first crab stage (C). 423 FISHERY BULLETIN: VOL. 80, NO. 3 crease gradually declined during larval develop- ment (Tables 1, 2). This trend was reflected by decreasing m of fitted regression curves: —0.074 in the Z-l, -0.045 in the Z-2, and -0.031 in the megalopa. In Figure 2 only the first regression (Z-l) is shown as the most accurately measured example (the curve for starved zoeae given in the same graph will be discussed below). Growth in zoeal stages can also be described as a power function of t: In y = b + m In (t + 1), where y is any measure of biomass except FW (DW, C, N, H, J). The lvalues were almost identical with the logarithms of the initial biomass measure under consideration, the m values varied be- tween 0.29 and 0.48 (Table 3). The fitted curves describe the actual growth patterns until late premolt was reached. In this very advanced period in the Z-l stage (days 12 and 13), growth ceased or even switched to a slight loss. These last values were not included in the Z-l regressions. The fitted growth curves were converted to percentage values of early postmolt levels, so that direct comparison of relative increase rates became possible (Fig. 3; Z-l curves for 1980 values only). In zoeae the individual energy content (J) re- vealed the strongest increment, DW the weakest. The rate of increase in N was similar to that in DW, whereas C and H increased at a higher rate during individual growth (Table 3). A compari- son of the biomass values in first zoeae obtained in two different seasons and years shows that the 1979 larvae were not only less viable (see above), but also showed lower initial biomass (reflected by lower b values in all regression equations describing growth) and lower growth rates (re- flected by m values), especially in C, H, and J. TABLE 3.— Parameters of regression equa- tions for individual growth in larval stages of Hyas araneus: In y = 6 + m ■ In (t + 1). t= time (d); r = correlation coefficient; df = degrees of freedom; dry weight (DW), car- bon (C), nitrogen (N), hydrogen (H) in /ug. and energy contents (J). Stage y b m r df Zoea 1' DW 4 164 0.300 0924 44 Zoea 1 DW 4.228 0.385 0989 64 Zoea I' C 2918 0370 0873 44 Zoea 1 C 3.107 0.451 0.994 64 Zoea I1 N 1.495 0.331 0 839 44 Zoea 1 N 1.604 0.384 0979 60 Zoea I1 H 1.016 0354 0.833 44 Zoea I H 1.164 0.475 0.994 62 Zoea I1 J -0.511 0.377 0870 44 Zoea 1 J -0.292 0.479 0990 64 Zoea II DW 4986 0.290 0.938 44 Zoea II C 3.858 0.354 0934 44 Zoea II N 2.449 0.305 0.938 44 Zoea II H 1.961 0350 0925 44 Zoea II J 0.457 0381 0927 44 '1979 observation (all others from 1980) megalopa • = H «=N •=C U 8 12 16 Age (days) Figure 2.— Hyas araneus. Water content (% fresh weight) in Z- 1 larvae fed and starved for different lengths of time. 20 24 Figure 3. — Hyas araneus. Growth patterns [dry weight (DW), energy contents (J), carbon (C), nitrogen (N), and hydrogen (H) per individual] in all larval stages expressed as percentage of early postmolt levels. Solid curves: fitted by equations (see text); dotted curves: fitted by eye. 424 ANGER and DAWIRS: ELEMENTAL COMPOSITION OF HYAS ARANEUS However, due to high variation among the 1979 samples, these differences were not statistically significant. In May 1979, eight Z-2 of H. araneus were isolated from a plankton sample and analyzed for comparison. The results (Table 4) compared favorably with those of late laboratory-reared Z- 2 larvae (Table 2), although C and H values were slightly higher in the field-caught larvae. It becomes obvious from Figure 3 (lower graph) that growth in the megalopa was quite different from that in the zoeal stages. Since variation among analyses (see Table 2) was rather high, calculation of fitted growth curves was not considered useful and, therefore, only the assumed pattern was displayed in the diagram as an eye-fitted curve. A surprising de- crease in all parameters was found during the last third of the megalopa stage. As a result, young crabs contained only little more organic substances than young megalopae (Fig. 1). From the above results, approximate average daily energy gains per individual (J/d per ind.) can be calculated. In the 1979 Z-l larvae a value of 0.08 was estimated. This compares favorably with the data reported by Anger and Nair (1979). They found 0.06 (their figures —0.4 and 0.6 on page 51 are erroneous; they should read —0.04 and 0.06), based on C contents, and 0.07 to 0.11, based on biochemical composition (excluding and including chitin, respectively). Since the 1980 larvae grew better (see above), their daily energy gain was higher: 0.16 J/d per ind. In the second zoeal stage a value of 0.22 was found (Fig. 1). In the megalopa it was similar (0.20) until day 16, when it dropped to —0.34 until Table 4.— Ranges and arithmetic means (J) for Hyas araneus zoea-2 from Helgoland plankton in May 1979. Four analyses comprising eight individuals. For explanation of abbreviations see Table 1. Range X FW (M) 1,162-1.292 1.220 DW ipg) 304-346 322 H20 (%) 72.6-74.4 73.6 C (%) 35.0-36.9 35.7 (pg) 106.7-1274 115.2 N (%) 7.60-773 7.67 (pg) 23.1-26.7 24.7 H (%) 5.23-5.51 5.36 to) 15.9-19.0 17 3 C/N 4.53-4.77 4.66 J/ind. 3.67-4.49 4 00 J/mg DW 12.1-13.0 12.4 metamorphosis; on the average, a weak gain (0.02 J/d per ind.) resulted. The weight-specific energy content (J/mg DW) followed a cyclic pattern (Fig. 4). Due to salt uptake, it decreased during molt, and then it in- creased again during growth. From instar to instar there was a conspicuous decreasing trend. It was related to a decrease in the percentage of organic substances, expressed as maximum sum of the C, N, and H portions (upper part of Fig. 4). The ratio between single elements can be used as an index for biochemical composition. Changes in the C:N ratio mainly indicate shifts in the relative amounts of lipids (plus carbo- hydrates) and proteins (plus free amino acids) (Fig. 5). There were no major differences found during the molt cycles. In all larval stages there was an initial increase, followed by a decline. 4 8 12 16 20 24 28 32 36 40 44 48 60- 16 prezoea 16 prezoea 15 §55] z Deo -1 15 £ zoea- II 14 zoea- I jkJL zoea- II X50- 14 Q 13 Jr 45; ' ■ : ' ■ ' ' ' ' ' ' i me ga! Dpa 13 E "■ 12 \ 1 megalo pa crab •12 11 V \ i •11 10 t 1 moult 1 moult 1 1 moult > i meta morpho ft SIS ' ' 10 12 16 20 24 28 32 Day after hatching 36 40 44 48 FIGURE 4.— Hyas araneus. Changes in weight-specific energy during larval development; vertical lines: 95% con- fidence intervals of the means. Upper right: Maximum sum of carbon (C), nitrogen (N), and hydrogen (H) in all larval stages. 425 FISHERY BULLETIN: VOL. 80, NO. 3 Figure b.—Hyas araneus. C:N (car- bomnitrogen) ratio in larvae fed and starved for different lengths of time. 8 10 12 U 16 18 20 22 Age (days) Certainly the buildup of the chitin cuticle, and perhaps also the disproportionately strong storage of lipids, contributed to the increase. The subsequent decrease in the C:N ratio suggests that more proteins than other organic constitu- ents were accumlated later. This trend was best visible in the Z-l and megalopa stages; in the latter it was followed by a new increase begin- ning on day 16. This period was identical with that of decreasing biomass (Fig. 3). The curves given in Figure 5 for starved larvae will be dis- cussed below. TheC:H ratio remained fairly constant within stages, and it did not differ much among larval instars. The mean values and 95% confidence intervals (weight-based) were 6.67+0.08 in the Z- 1 (1980), 6.64±0.26 in the Z-2, and 6.49+0.11 in the megalopa. In field-caught Z-2 larvae and in young crabs mean ratios of 6.66 and 6.67 were found. The ratios in the Z-l and megalopa stages were statistically different from each other (P<0.01). There was also a significant difference (P — 0.002) between the figures in the Z-l from 1979 (6.86+0.09) and from 1980 (see above). The growth patterns described in Figure 3 do not consider losses due to shedding of exuviae. In order to determine the approximate amount of organic substances cast during molts, occasional analyses of exuviae were carried out (Table 5). Wet weight and DW measurements did not provide useful results, because the amount of water and salt inside the cast could not be accurately determined. The composition of the exuviae corresponded closely to that of its main component, chitin. Deviations from the theoreti- cal atomic ratio C:N:H =9:1:14 can partly be explained by analytical inaccuracies (see 95% confidence limits in the megalopa), partly by other biochemical components of exuviae, or by slight chemical changes before sampling and analyzing the casts (partial decomposition). The amount of organic matter lost during zoeal molts was far lower than during meta- morphosis to the crab: 4 to 5% versus 19% in N, 6 to 9% versus 29% in both C and H (Table 5). Assuming an energy content of ca. 18 J/mg dry organic exuvial matter (after Winberg 1971, somewhat corrected for protein compounds) and a C content of ca. 45% (according to the molecular formula of chitin), then the energy losses should be ca. 0.23 J in the Z-l, 0.29 in the Z-2, and 1.61 in the megalopa. These estimates correspond to ca. 9, 7, and 34% of total body energy levels in late premolt in these stages. Compared with average daily energy fixation rates (see above), these figures mean losses of ca. 1.3 to 1.4 d in the zoeal stages, and ca. 8 d in the megalopa. Preliminary experiments were carried out to Table 5.— Composition [carbon (C), nitrogen (N), hydrogen (H)] of larval exuviae of Hyas araneus and percentage of pre- molt matter cast at ecdysis. n - number of analyses, AT = number of exuviae analyzed. C N (pg) H (jjg) Weight ratio Atomic ratio n N Zoea-I % cast 585 9 067 5 092 9 8.7:11 4 10:1:19 1 15 Zoea-ll % cast 7.20 6 1 10 4 1 10 7 6.6:1:1 8114 1 10 Megalopa % cast X ± 40 56 4.07 29 5.46 0.62 17 6.39 056 29 7.511. 2 9116 7 7 426 ANGER and DAWIRS: ELEMENTAL COMPOSITION OF HYAS ARANEUS determine food consumption in the Z-l stage using Artemia salina nauplii as prey. The average values found were near 20 /ug C/d per ind. or 0.8 to 0.9 J/d. Gross growth efficiency therefore should be about 10 to 20%. The amount taken up by the larvae (3 d old) corresponded to ca. 55% of their own body C and to ca. 36% of their own DW. In light of the experimental conditions, we consider this near the maximum level. Loss of Biomass During Starvation F W of starving larvae did not show significant changes (Tables 6 to 8). Also water content could not always be measured with sufficient accuracy to detect clear trends. In the Z-l and in the megalopa, first a slight decrease and later a con- spicuous increase of water content occurred. The latter trend was linear in the Z-l (Fig. 2); it could Table S.—Hyas araneus losses in starved Z-l larvae. For explanation of abbreviations see Table 1. Time (d): 0 2 4 6 8 10 12 13 14 15 16 17 FW X 493 538 522 501 534 533 532 557 547 577 584 589 iug) ± 10 16 27 20 16 29 38 14 28 52 35 39 DW X 65 80 79 77 74 73 71 73 70 70 66 68 ifjg) ± 1 2 3 3 3 2 2 3 1 2 1 4 HjO (%) 868 85.1 84 9 84.6 86.2 86.4 866 86.9 87.2 87.8 88 6 884 C (%) X 35.1 27.5 25.8 24.7 24.6 23.2 22.8 22.0 22.2 21 7 22.1 21.4 ± 03 04 03 0.2 03 0.4 06 03 0.3 04 03 1.0 (^9) X 22 9 21.9 204 19.0 18.2 16.8 16.2 16.1 15.6 15.3 14.6 146 ± 03 0.2 0.7 07 0.8 05 0 8 08 02 05 04 07 N (%) X 8.1 62 58 5.57 5.3 5.0 48 4.72 4.7 46 48 48 ± 0.1 0.1 0.1 004 0.2 0.2 02 0.05 0.1 0.1 01 0.2 lM9) 7 53 4.91 46 43 3.9 3.6 3.4 3.4 3.30 326 3.16 33 ± 0.1 004 0.1 02 0.2 0.1 02 0.1 006 007 003 0.1 H (%) X 5.0 3.82 355 3.60 3.33 3.27 3.15 3.11 317 33 32 30 ± 0.1 0.05 0.05 0.04 004 0.07 0.11 0.06 002 03 01 04 (A»9) X 3.3 3.05 2.8 28 25 24 2.2 2.3 2.23 22 2.1 2 1 ± 0.1 002 0.1 0.1 0.1 0.1 0.1 0.1 0.02 0 1 0.1 0 1 C/N X 431 4.47 4.47 4.43 4.63 4.62 4.75 4.67 474 4.70 4.64 4,43 ± 0.03 004 0.04 006 0.12 0.10 0.11 0 09 0.07 0.05 0.11 0.05 J/ind. X 0.79 069 062 0.57 0.55 0.50 0.48 0.47 0.45 0.44 0.42 042 ± 0.01 0.01 002 0.02 0.02 0.01 002 0 02 0.01 0.02 0.01 0.02 J/mg DW X 12.1 8.6 7.9 7 4 7.4 6.8 67 64 65 63 64 6.1 ± 0.2 0.3 0.1 0.1 0.1 0.2 02 0.1 0.1 0.1 0.1 04 n (analyses) 10 5 5 5 5 5 5 5 5 5 5 3 N (individuals) 50 25 25 25 25 25 25 25 25 25 25 13 Table l.—Hyas araneus losses in starved Z-2 larvae. For explanation of ab- brevations see Table 1. Time (d): 0 4 '4 8 '8 12 '12 16 20 FW x 1 ,150 2.422 1,219 1,184 1,176 1,034 1,022 929 1,240 (**g) ± 308 349 68 102 67 144 — 263 474 DW x 172 174 195 145 170 154 172 153 131 (V9) ± 28 14 15 17 24 12 — 17 14 HaO (%) 85.0 928 840 87.8 85.5 85.1 83.2 83.5 89.4 C (%) x 36.5 29.9 30.4 28.2 27.2 26.7 26.6 25.5 22.2 ± 2.7 12 1.9 1.4 1.7 2.2 — 1.4 2.1 iUQ) x 628 52.1 59.6 40.8 465 41.1 45.6 39 0 290 ± 11.2 60 8.1 56 9.0 5.6 — 5.9 5.4 N (%) x 84 64 70 63 64 6.1 6.3 56 55 ± 03 03 07 08 0.3 0.1 — 03 04 (pg) * 14.4 11.1 13.5 9.1 10.9 97 10.9 8.6 72 ± 19 1.3 2.2 1.9 19 0.9 — 09 1.3 H (%) x 5.7 4.3 42 39 3.7 38 3.8 3.7 3.1 ± 03 02 04 0.4 0.3 0.4 — 02 04 g) x 17.8 12.0 10.5 12.6 10.2 9.8 ± 3.4 2.5 2.7 4.5 3.7 4.7 C/N X 44 46 4.5 4.5 4.4 4.5 ± 0.2 0.2 0 1 0.2 0.3 0.5 J/ind. X 4.1 2.6 2 1 24 2.1 19 ± 0.8 05 0.5 09 0.8 0.8 J/mg DW x 12.4 7.9 6.9 6.8 6.8 6.7 ± 1.0 03 0.4 0.5 0.6 04 n (analyses) 9 5 5 5 5 3 be expressed by the statistically significant regression equation: %H20 = 83 + 0.32 t (r = 0.959; P<10'4), where t = time (days from hatching). This effect was visible by eye: larvae, which had starved for a long time, acquired an increasingly bloated appearance like those ex- posed to a hypotonic medium. DW tended to decrease during starvation, but due mostly to high variation among parallel determinations, only in the Z-l stage could a statistically significant trend be found between days 2 and 17 (Fig. 6): DW (Mg) = 82 - 0.85 t (r = 0.966; P<10"5). The decreases in C, N, H, and J during t followed an exponential pattern: In y = b + mt, where y is any measure for biomass (C, N, H in ng) or energy (J). To allow direct comparison, fitted curves were again converted to percentage values and shown in Figure 6 (only Z-l stage as an example). For the other stages similar curves were obtained (Table 9). The slope parameters (= regression coefficients, m, in the log-trans- formed equations) were not statistically signifi- cantly different from each other. The 6 values were very close to the logarithms of the initial figures for biomass. In all three larval instars the energy content (J/ind.) dropped more drastically than C, N, and H contents (Table 9). In the Z-l there was also a slightly stronger decline in N as compared with C and H (Fig. 6). The maximal losses observed shortly before starvation death of the larvae 428 FISHERY BULLETIN: VOL. 80, NO. 3 ? 4 6 S 10 12 14 16 6 S 10 12 Age (days) U 16 Figure 6.—Hyas araneus. Loss patterns [dry weight (DW), energy content (J), carbon (C), nitrogen (N), and hydrogen (H) per individual] in starved Z-l larvae. Solid lines: fitted by equations (see text); dotted curve: fitted by eye. Table 9.— Parameters of regression equations for loss of individual biomass in starved larval stages of Hyas araneus: In y = b+ mt; t = time (d). For further explanation see Table 3. Stage y 6 m r df Zoea 1 C 3.127 -0.028 -0.986 61 Zoea 1 N 1.653 -0.032 -0.984 61 Zoea I H 1 167 -0 027 -0.972 61 Zoea I J -0.285 -0.037 -0.981 61 Zoea II C 4.082 -0.033 -0.868 ?5 Zoea II N 2.548 -0.029 -0.836 25 Zoea II H 2 166 -0.036 -0.843 25 Zoea II J 0.698 -0.041 -0.886 ?5 Megalopa C 4.663 -0.028 -0 634 32 Megalopa N 3 181 -0.030 -0.673 32 Megalopa H 2.748 -0.029 -0.608 3? Megalopa J 1.268 -0.038 -0.698 32 were ca. 36 to 46% in the Z-l, 45 to 58% in theZ-2, and 43 to 51% in the megalopa. The average daily energy loss per individual increased from the first to the last larval stage. If converted to weight-specific figures, a weak opposite trend became visible. This means that increasing reserves became available during the progress of development, and weight-specific metabolism tended to decrease somewhat. However, the above average values are only rough estimates, since the loss patterns are nonlinear (see above), but they do reflect general differences among stages (Table 10). The decrease pattern in weight-specific energy contents of starved larvae (within stages) followed a hyperbola: In J/mg DW = b + m In (t + 1), where t = time (days), 6 is close to the logarithm of the initial value, and m is the slope. ANGER and DAWIRS: ELEMENTAL COMPOSITION OF HYAS ARANEUS Table 10.— Average daily energy loss in starved larval stages of Hyas araneus (estimated from carbon-hydrogen-nitro- gen values). J = energy contents; DW = dry weight. Stage J/d per ind J/d per mg DW Zoea I Zoea II Megalopa 002 0.07 0.11 0.35 032 028 The b values of the fitted curves were ca. 2.5, the m's were -0.20 (Z-2) to -0.23 (Z-l); and the r's varied between -0.964 (P<0.002; Z-2) and -0.992 (P<1010; Z-l). Using the conversion factor 20.19 J/ml O2 given by Brody (1945), approximate figures for oxygen consumption could be estimated from the energy values in Tables 6 to 8. In all stages there was apparently a drastic reduction in respira- tion rate during the first few days of starvation (Table 11). For comparison of the stages, again average values were computed (from values in Table 10). Corresponding to the weight-specific energy values (see above), from which they were derived, a weak decreasing trend became apparent (Table 11). The C :N ratio (Fig. 5) did not follow a uniform pattern in starved larvae. In the Z-l stage a long period of gradual increase was followed by a short period of rapid decrease. This suggests that protein was catabolized at a higher rate than other constituents during most of the starvation period; only in the premortal phase, wereN-poor substances (most probably lipids) apparently used as the main energy source. In the Z-2 and in the megalopa variation was too high to discern clear trends. In the former instar the C:N ratio also showed a drop at the end suggesting some similarity with the Z-l, whereas in the latter stage apparently it did not change at all. The C:H ratio was practically constant in all larval instars. It was in most cases significantly lower in fed than in starved larvae. The mean values and 95% confidence intervals (by weight) were 6.67±0.08 versus 7.07±0.012 in the Z-l (P<105), 6.64±0.26 versus 6.98±0.30 in the Z-2 Table 11.— Weight-specific respiration rates {jx\ 02/h per mg dry weight) in relation to the time of starvation of Hyas araneus. Days of starvat ion Stage 2 4 8 >8 X1 Zoea 1 Zoea II Megalopa 3.6 07 1.6 2.3 0.3 04 0.5 0.2 073 0.66 059 'Computed from Table 10 data (not significant), and 6.49±0. 11 versus 6.80±0.28 in the megalopa (P = 0.014). There was a similar statistically significant difference (P = 0.002) between the C:H ratios found in Z-l larvae in May 1979 (6.86±0.09) and in February 1980 (6.67±0.08). DISCUSSION Larval growth has been measured and de- scribed in a number of different ways. Incre- ments in zoeal body size obey the general rules summarized by Rice (1968), who calculated an average growth factor of 1.29 for brachyurans. From the figures given by Christiansen (1973) for H. araneus, factors of 1.26 to 1.30 can be derived, depending on the distance measured. A factor of 1.3 is also obtained, if size is assumed to be pro- portional to the cube root of DW. As pointed out by Rice (1968), the megalopa can hardly be included in those considerations because of its different shape. It is generally accepted that FW is a poor measure of actual biomass. Its determination is inaccurate and thus yields highly variable re- sults. Moreover, it does not change in an orderly manner during the molt cycle and therefore, it must be regarded as insensitive to changes in organic matter. This is caused by changes in the water content. It is difficult to understand why a number of authors described biochemical and physiological changes in developing crustacean larvae on a wet weight basis, and so severely reduced the value of their information. We suggest that FW or Formalin wet weight never be used as a reference base in such studies, but only as a source of additional information (e.g., for water content of tissues). D W is a far better measure of biomass, although it is influenced by inorganic salts. Unfortunate- ly, different drying methods (temperatures and times) are used by different investigators. Ash- free DW should improve the accuracy in physio- logical studies, if used as a basic unit. However, again drying and combustion temperatures and times are not uniformly applied. Elemental composition, especially C content, can be used as a reliable expression of living organic substance. Inorganic C does not play a signficant role in marine planktonic organisms (Curl 1962) and therefore C is also a measure of energy equivalents (Salonen et al. 1976). C-based energy estimations apparently tend to be some- what lower than those calculated from bio- 429 FISHERY BULLETIN: VOL. 80, NO. 3 chemical composition (Anger and Nair 1979); comparison of both methods with direct calo- rimetry in identical material should be worth- while. However, the J values given in this paper compare favorably with those reported else- where for decapod larvae (e.g., Cummins and Wuycheck 1971; Mootz and Epifanio 1974; Logan and Epifanio 1978; Capuzzo and Lan- caster 1979; Dawirs 1980; Stephenson and Knight 1980). The interpretation of changes in the relative chemical composition of larvae (C:N, C:H) leads to interesting assumptions about physiological processes, but there is a need for complementary biochemical investigations. Such analyses are planned for future studies as an extension of the present results. So far, our figures compare favorably with those given in the literature (Childress and Nygaard 1974; Ikeda 1974; Omori 1979; Dawirs 1980). Ikeda (1974) investigated a large number of zooplankton species, and he found that C:N (by weight) is in most cases 3 to 5, whereas C:H is mostly 6 to 7. Growth (any measure except size and FW) during larval development in decapod Crustacea usually follows — at least for some period — an exponential pattern, if gain from stage to stage is considered (Reeve 1969; Mootz and Epifanio 1974; Logan and Epifanio 1978; Johns and Pechenik 1980; Stephenson and Knight 1980). This also holds true for the zoeal stages of Hyas araneus. Interpolation of biomass values within single stages from such exponential curves yields poor correspondence of predicted and ob- served data, because growth within stages follows different patterns. In both zoeae it could be described most accurately by power func- tions, whereas exponential regressions do not fit as well. At the end of the molt cycle, however, such parabola-shaped fitted growth curves lose their applicability. This final period probably corresponds to the stages D2 to D4, during which molt is prepared by separating the epidermis from the old cuticle (Freeman and Costlow 1980). Possibly, there is no more significant food uptake during this phase of body reconstruction (Anger and Dawirs 1981). In the megalopa, another growth pattern was found. The period of body reconstruction and of presumed inability to take up food preceding metamorphosis appears to be much longer in this stage. The daily energy loss per individual was three times higher during this time as opposed to megalopae starved from the beginning. This contrast suggests that a final fasting period is a normal part of the development program, not considered starvation, and thus not counter- balanced by reduced metabolism. This assump- tion is supported by a number of observations in other decapod megalopae (Mootz and Epifanio 1974; Schatzlein and Costlow 1978; Dawirs 1980; for recent review see Anger and Dawirs 1981). The duration of the megalopa stage is much more variable than the zoeal instars. This fact may be related to the ecological role of the megalopa which is to select a biotope suitable for adult life. The capacity to delay selection should be related to the amount of reserve accumulated prior to the change in energy balance. This strategy is in contrast to that observed by Pechenik (1980) in gastropod larvae. These do not cease to grow with the onset of metamorphic competence, and their capability to delay meta- morphosis appears to be related to the preceding growth rate. More detailed investigations on the nutritional and ecological needs of the megalopa stage are necessary for a better understanding of this critical phase in benthic recruitment. All these complicated changes of biomass as well as their extent (two- to threefold increases within single stages) suggest that the use of "characteristic" values for particular instars ap- plied in energy budgets and other energetic considerations must lead to very rough figures. Another complicating factor is annual or seasonal variation in initial biomass of hatching larvae and in their growth rate. Since viability also appears to be related to this kind of variation, future studies will have to examine its degree and significance. The same holds true for possible systematic differences between labora- tory-reared larvae and those obtained from wild plankton. Several authors (Knight 1970 and earlier papers; Rice and Provenzano 1970; Ingle and Rice 1971) observed higher growth rates in naturally grown developmental stages of different decapod species. Only a small part of the organic matter accumulated during the zoeal stages is lost in exuviae. This is much different in the megalopa. More than three times more matter and energy was found in its cast exoskeleton than in both zoeae combined. These and other striking dis- similarities between zoea and megalopa larvae underline their different roles. The former accumulate energy-rich substances taken from the pelagic food web, and they are responsible for dispersal of the species. The latter stage, which 430 ANGER and DAWIRS: ELEMENTAL COMPOSITION OF HYAS ARANEUS often crawls on the bottom, presumably will test suitable benthic habitats, before it goes through metamorphosis at a selected site. It appears that a rigid exoskeleton is advantageous as a pro- tective means in the evolution of benthic crustaceans, whereas in pelagic species and stages it is probably disadvantageous for energetic reasons (increasing swimming energy). The preliminary determinations of feeding rates on Artemia sp. nauplii yielded almost the same values (in C per day) as observed by Anger and Nair (1979) using Polydora ciliata larvae as prey. This confirms that the amounts in the above data are correct, but further studies con- sidering the whole molt cycle in each larval stage will be necessary for comparisons with the growth measurements of the present investiga- tion. The feeding rates observed in the Z-l of H. araneus as well as larval DW are similar to those found by Mootz and Epifanio (1974) in the Z-4 stage of Menippe mercenaria. Measuring the loss of organic matter and energy during starvation bears the same technical problems as measuring growth. FW, apart from its inaccuracy, is practically constant even during long-term starvation. This masking of changes in organic constituents is again caused by changes in water content. We assume that the underlying mechanism is some kind of starvation edema. Due to degradation of amino acids, the osmotic pressure in the hemolymph must decrease, and consequently water may pas- sively enter body tissues. The water lost in the hemolymph might be replaced by seawater. This assumption would explain the observed net in- crease in body volume, water, and ash contents of starving larvae (Ikeda 1971, 1974; Mayzaud 1976). Instrusion of inorganic salts replacing degraded organic ions presumably is responsible not only for increasing ash portions, but also for the low degree of loss in DW. The latter observa- tion means that DW can also be used in energetic studies of starving zooplankton to a limited degree, because it does not reflect actual losses in organic matter and energy. Losses in C, N, H, and individual J's followed an exponential pattern with a weak curvature. The maximum possible losses until death amounted to ca. 40 to 60% of initial values, de- pending on the parameter and larval stage under consideration. These observations correspond to those by Anger and Nair (1979) and Dawirs (unpubl. data) on starved larvae of H. araneus and Carcinus maenas, respectively. Ikeda(1974) reported reductions in biomass of other zoo- plankton down to 20%. Our figures also become higher if chitin is excluded from these calcula- tions. Anger and Dawirs (1981) found that feeding after initial starvation in Z-l larvae of H. araneus is successful only if a certain time (point- of-no-return, PNR) is not exceeded. Comparing this time span with the above biomass data, the actual limits of starvation resistance are already reached when 25 to 30% of organic matter (C,N,H) or 30 to 35% of individual energy are lost. Beyond this PNR another ca. 10% loss in all these parameters is possible, before the larva dies, re- gardless of eventual food availability. Fifty per- cent of the larvae already reach this limit (PNR50) when only ca. 20% of the organic sub- stance or ca. 25% of energy is lost. The PNR values for the other stages have not yet been determined. Another finding reported by Anger and Dawirs (1981) is that relatively short initial feed- ing periods suffice for zoeae of H. araneus to suc- cessfully reach the next stage (Z-2 or megalopa), regardless of further food availability. Convert- ing these time spans to biomass data, a sur- prising agreement in both zoeal stages is found: 50% of the larvae reach this "point-of-reserve- saturation" (PRS50), when they have gained ca. 70% N, 90% C and H each, and ca. 95% energy (re- lated to early postmolt levels). If food is contin- ually available, considerable further accumula- tion of organic matter and energy will take place (see above), but this additional reserve will not be needed before the next stage is reached. If no prey is available during this period (presumably premolt) the next stage will be significantly pro- longed, thus revealing a certain dependence on reserves accumulated during the preceding zoeal stage. Anger and Dawirs (1981) suggested that sterols (precursors of the molting hormone, ecdysterone) may play a crucial role in this phenomenon. It is doubtful that energetics alone can explain the early appearance of the PNR, since the actual losses in organic body substance are rather low at that time. We assume that an irreversible damage in some hormonal or enzymatic system is involved in ecdysis. The weight-specific metabolic rate is a major factor deciding the maximal survival time under starvation (Ikeda 1974). It is far lower in starved as compared with fed zooplankton (see, e.g., Ikeda 1977 and earlier papers cited therein; 431 FISHERY BULLETIN: VOL. 80, NO. 3 Mayzaud 1976; Logan and Epifanio 1978; Capuzzo and Lancaster 1979). The hyperbola- shaped decrease pattern in weight-specific energy (see above) is in accordance with that described by Mayzaud (1976) for respiration rates in starved zooplankton. There is an initial acclimation period with strongly decreasing metabolic rate, followed by more or less constant values. Our estimates for oxygen consumption follow this pattern, and their amounts compare favorably with literature data, if starvation and relatively low temperature (12°C) are taken into account (for review see Schatzlein and Costlow 1978). In a low temperature range, high Qio values are to be expected. This assumption is confirmed by extremely long survival times observed by Anger and Dawirs (1981). These figures of starvation resistance as well as our calculations of weight-specific respiration rates fit the quan- titative relationship between these two para- meters described by Ikeda (1974). The metabolism of starved H. araneus larvae is mainly based on protein degradation (Anger and Nair 1979). According to the literature, this is a general feature in crustaceans (e.g., Mayzaud 1976; Ikeda 1977 and earlier papers; Capuzzo and Lancaster 1979). Our observations on changes in the C:N ratio suggest that during the final (premortal) period of long-term starva- tion, lipids also become important as a last reserve. However, at this time the larva is already doomed to die, regardless of eventual food availability, since the PNR has been ex- ceeded (Anger and Dawirs 1981). The amount of reserve and proportions of metabolic pathways apparently are also subject to annual and seasonal variation, possibly even to differences among different parts of one brood (e.g., Regnault 1969; Pandian and Schumann 1967; Pandian 1970; Pandian and Katre 1972; Anger and Dawirs 1981). Those changes may also explain differences between daily energy losses in starved zoeae estimated by Anger and Nair (1979) and in the present study. Future in- vestigations will have to examine the amount and significance of such natural variation super- imposed on the response patterns of decapod larvae in different feeding conditons. ACKNOWLEDGMENTS This paper is a contribution to research project "Experimentelle Okosystemanalyse" sponsored by Bundesministerium fur Forschung and Technologic Bonn, West Germany (Grant No. MFU-0328/1). We are grateful to our colleagues W. Greve, M. Janke, F. Schorn, and E. Wahl for providing food organisms. J. Ufer operated the C-H-N analyzer, and B. Lammel made the drawings. Our thanks are also due to J. Markham for correcting the manuscript. The second author is indebted to Studienstiftung des Deutschen Volkes, Bonn - Bad Godesberg, for financial support. LITERATURE CITED Anger, K., and R. R. Dawirs. 1981. Influence of starvation on the larval development of Hyas araneus (Decapoda, Majidae). Helgol. Wiss. Meeresunters. 34:287-311. Anger, K., and K. K. C. Nair. 1979. Laboratory experiments on the larval development of Hyas araneus (Decapoda, Majidae). Helgol. Wiss. Meeresunters. 32:36-54. Brody, S. 1945. Bioenergetics and growth. Reinhold, N.Y., 1023 p. Capuzzo, J. M., and B. A. 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Press, Long., 175 p. 433 A MULTISPECIES ANALYSIS OF THE COMMERCIAL DEEP-SEA HANDLINE FISHERY IN HAWAII Stephen Ralston1 and Jeffrey J. Polovina2 ABSTRACT In the Hawaiian Islands 13 species of bottom fish are commonly harvested in the commercial deep- sea handline fishery. These are all high-level carnivores, including snappers, jacks, and a species of grouper, which are sought in water depths ranging from 60 to 350 m. Cluster analyses performed on the Hawaii Division of Fish and Game commercial catch report data suggest the existence of three bottom fish species groups which apparently segregate on the basis of depth distribution. These groups seem to be stable through time and similar among differing geographic localities. Two measures of fishing effort, catch-records and fisherman-days, were compared to determine which is more suitable for use in stock-production analyses. Fisherman-days was selected because, among other reasons, it repeatedly demonstrates a stronger negative correlation with catch per unit effort. Application of the Schaefer stock-production model to this multispecies fishery on a species-by- species basis provides an inadequate description of productivity. When catch statistics are aggregated according to the three cluster analysis species groups the results are much improved. In this regard consistently significant results and production estimates were obtained from the Maui- Lanai-Kahoolawe-Molokai bank, a region which presently accounts for about half of the total Hawaii catch. No significant interaction among the cluster groups was detected. When all 13 bottom fish species are analyzed together, the results are in agreement with the preceding analysis. Examining the aggregation process suggests that the model based on the intermediate level of aggregation (cluster groups) explains slightly more of the variation in total catch than does the model which treats all 13 species together. We estimate the annual maximum sustainable yield of the commercial deep-sea handline fishery around the Maui-Lanai-Kahoolawe-Molokai bank to be 106 metric tons or about 272 kg/nmi of 100- fathom isobath. Because recreational catch is unaccounted for these figures are considered lower bounds for the gross production obtainable from this type of fishery although currently the commercial fishery is operating close to this maximum-sustainable-yield level. Effective management programs for tropical fisheries are difficult to achieve (Pauly 1979). Often attempts at managing these fisheries are based on the application of inappropriate models to sparse data. Both deficiencies are due in part to the multiplicity of fish species inhabiting tropical environments. This great diversity (Sale 1977; Talbot et al. 1979) makes it difficult to compile adequate data for all species of interest. The Hawaiian Islands, which straddle the Tropic of Cancer, possess a relatively impover- ished tropical ichthyofauna, yet between 600 and 700 species are known from this region (Gosline and Brock 1960). Coupled with high diversity, 'Fisheries Research Institute, College of Fisheries, University of Washington, Seattle, Wash.; present address: Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 3830, Honolulu, HI 96812. 2Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 3830, Honolulu, HI 96812. Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80, NO. 3, 1982. many tropical countries lack a refined statistical system for the acquisition and storage of fisheries data. In concert these two limitations impose severe restrictions on the quantity and quality of data which are currently available for the analysis and management of tropical fisheries (Pope 1979). Furthermore, classical fisheries models thus far developed have been directed toward the management of temperate and boreal stocks (Food and Agriculture Organ- ization of the United Nations (FAO) 1978). These models usually treat species as independent management units. It has become apparent that such an approach is often inadequate when ex- trapolated to the tropics where community dynamics become increasingly important (Pauly 1979). The multispecies approach to managing fisheries exploitation in complex ecosystems has only recently acquired a substantive base in the literature. Early work by Larkin (1963, 1966) 435 FISHERY BULLETIN: VOL. 80, NO. 3 evaluated the consequences of Lotka-Volterra competition and predator-prey systems on optimum exploitation strategies. Paulik et al. (1967) examined the problem of maximizing the yield from a fishery composed of mixed stocks, each with a unique spawner-recruit curve. A large body of descriptive work has documented the successional nature of changing catch composition which is often characteristic of increasing exploitation in a multispecies fishery (e.g., Regier 1973). Several recent multispecies investigations present highly sophisticated eco- system models that require numerical solution and/or dynamic simulation, as well as numerous parameter estimates (Parrish 1975; Andersen and Ursin 1977; Laevastu and Favorite 19783). An alternative to this latter approach simply treats multispecies fisheries as though they behave as would a single species stock and evaluates production by application of the total biomass Schaefer model (TBSM) (Pope 1979). Brown et al. (1976) estimated total finfish pro- duction in the northwest Atlantic in this manner, as did Brander (1977) for demersal fish and shellfish in the Irish Sea. A review of this approach shows that "these overall Schaefer models generally seem to fit the data rather better than the fits experienced with their component stocks" (FAO 1978). Among the possible reasons for this are 1) the TBSM really presents a more realistic representation of multi- species fisheries than does summing the yields of individual stocks, 2) the better fit results from some type of averaging process, 3) artifacts in the method of fitting and/or shifts in preference between species within a fishery may result in a better fit when total biomass is evaluated (FAO 1978; Pauly 1979; Pope 1979). Several authors have issued the caveat that a thorough under- standing of trophic relations is fundamental to managing any multispecies fishery and that such considerations may easily invalidate the application of the TBSM (May et al. 1979; Pauly 1979). This paper estimates the productivity of deep- dwelling bottom fish stocks around the main islands of the Hawaiian Archipelago using stock- production methods. The fishery for these stocks is conducted in offshore waters ranging in depth from 60 to 350 m where a variety of species, prin- cipally snappers of the Family Lutjanidae, abound. In addition to providing preliminary productivity estimates for this fishery, an exam- ination of the performance of the TBSM at various levels of species aggregation is under- taken. This latter analysis provides a quasi- quantitative means of evaluating the applicabil- ity of the TBSM to the Hawaiian offshore handline fishery. SOURCES OF DATA AND DESCRIPTION OF THE FISHERY In the State of Hawaii, all fishermen who sell a portion of their catch must be licensed as com- mercial fishermen by the Hawaii Division of Fish and Game (HDFG). There is no licensing requirement for recreational fishing. New com- mercial licenses are issued every fiscal year and once licensed, fishermen are required to submit a monthly catch report whether or not they have fished. These monthly catch reports require from each fisherman entries on the days and areas in which he fished, the types of fishing gear used, the number of individuals and pounds of the different species landed, and the dollar value of the catch. Incomplete reporting is thought to be common and raises the question of bias in the data (Ralston 19794). Perhaps more serious is the omission of any direct measure of fishing effort or fishing power in the information concerning bottom fish obtained from these reports. Monthly catch reports are coded, keypunched, and stored on magnetic tape for future use by H DFG. These data are the basis of this study and currently span the 20-yr period 1959 to 1978 inclusive, comprising some 600,000 records. While the date are voluminous, the extent of non- reporting by recreational fishermen and of in- complete or underreporting by commercial fishermen is unknown. The complete HDFG data account for all types of commercial fishing in the State of Hawaii; therefore, only those catch records which list deep-sea handline fishing gear were used in this study. This reduced the data to one-fourth its original size and defined the scope of the fishery. Although the name suggests otherwise, the fishing gear is primarily hydraulic or electric 3Laevastu, T., and F. Favorite. 1978. Numerical evalua- tion of marine ecosystems. Part 1. Deterministic bulk biomass model (BBM). NWAFC Process. Rep., Natl. Mar. Fish. Serv., NOAA, Seattle, Wash., 22 p. (Unpubl. rep.) 4Ralston, S. 1979. A description of the bottomfish fisher- ies of Hawaii, American Samoa, Guam, and the Northern Marianas. A report submitted to the Western Pacific Region- al Fishery Management Council, Honolulu, 102 p. (Unpubl. rep.) 436 RALSTON and POLOVINA: COMMERCIAL DEEP-SEA HANDLINK FISHERY although some manual equipment remains in use. The fishery mainly exploits 13 categories of fish species (Table 1). Confusion concerning the taxonomy of species in the family Carangidae prohibits a more detailed classification of these forms although Pseudocaranx dentex and Caranx ignobilis probably account for the majority of ulua landed in Hawaii. While P. dentex is abundant in the Northwestern Hawaiian Islands, it is apparently uncommon around the main high islands (Uchida5). Further confusion is apt to result from the findings of Anderson (1981), who recently revised the genus Etelis and changed the names of both Hawaiian species. In addition, two hogfish species are frequently taken, Bodianus bilunulatus and B. vulpinus, although the former species seems to inhabit somewhat shallower depths than the latter. Of those species listed, most are caught almost exclusively with deep-sea handline gear. The exceptions are ta'ape, ulua, and a'awa which are commonly taken by several other methods (e.g., inshore handline, purse seine, gill net, etc.) (Ralston footnote 4). Catches of these species reported here include only those portions taken in the offshore handline fishery. In descending order the dominant species in the fishery by weight are the opakapaka, ulua, uku, onaga, hapu'upu'u, and kahala (Ralston Tabus 1.— Principal species of fish landed in the Hawaiian offshore handline fishery. Common Average Family Species name weight (kg) Lutjanidae Aphareus rutilans Lehi 3-8 Aprion virescens Uku 2-8 Etelis coruscans Onaga 2-8 E carbunculus Ehu 0.5-2 Lutjanus kasmira Ta'ape 05 Prislipomoides fila- Opakapaka 1-6 mentosus P. sieboldii Kalekale 0.5 P. zonatus Gindai 0.5-2 Carangidae Caranx and Caran- goides spp. Ulua 1-10 Seriola dumerili Kahala 3-10 Serranidae Epinephelus quernus Hapu'upu'u 3-10 Labridae Bodianus spp. A'awa 1-3 Scorpaenidae Pontinus macrocephala Nohu 1-2 5R. N. Uchida, Southwest Fisheries Center Honolulu Labor- atory, National Marine Fisheries Service, NOAA, Honolulu, HI 96812, pers. commun. November 1980. footnote 4). These species taken together ac- counted for 86% of the total catch by weight in 1978, nearly all of which was marketed in Hawaii as fresh fish. Total landings from the fishery have remained relatively constant from 1959 to 1978, showing a slight increase in recent years, although higher catches were briefly re- ported during the late 1940's and early 1950's (Fig. 1) (Ralston footnote 4). Most of these species are highly prized and in recent years have averaged close to $5.00/kg ex-vessel. In the past about 85% of the catch of deep dwelling bottom fish has been made around the main Hawaiian Islands in contrast to the un- inhabited Northwestern Hawaiian Islands (Grigg and Pfund 1980). Catches from the latter area have increased remarkably in the last 2 y r, as larger, more seaworthy vessels have entered the fishery. Nonetheless, the lack of sufficient data 200 150 V) z o K O {0 against the alter- native hypothesis that p<0 where p is the popula- tion correlation coefficient between CPUE and/. Even though a negative correlation between CPUE and effort is expected in a situation where catch and effort are completely unrelated random variables, the degree of spurious correlation due to this effect will be small if the main cause of variation in CPUE is varying stock abundance (Gulland 1974). Correlations were computed between these two variables, using both measures of fishing effort for each species group-bank combination (3X4 = 12). Additional correlations were computed for the total aggregated catch from each of the four banks (1 X 4 = 4), resulting in 16 comparisons of the two measures of effort (Table 4). Comparisons which might be based on treating species as independent stocks are in- appropriate here because the two measures of effort become equal in this limiting case. One means of evaluating the effectiveness of these two measures is to compare the signs of the cor- relation coefficients (r) and the magnitudes of the coefficients of determination (>-2) for each. It 440 RALSTON and POLOVINA: COMMERCIAL DKKP-SKA HANDLINK FISHKRY Table 4.— Comparisons of correlations of CPUE and fishing effort if) for two different measures of/. The total aggregate incorporates all 13 species. Bank' Unit of fishing effort Catch-records Fishermai r i-days Group r r2 r2 1 Hawaii 0 095 0.01 -0.128 002 MLKM -0358 0.13 2-0.503 025 Oahu -0.153 0.02 -0259 0.07 KNK 0 180 003 -0.111 0.01 II Hawaii -0.111 0.01 -0 120 0.01 MLKM -0379 0.14 2-0.769 0.59 Oahu +0285 008 +0 293 0.09 KNK +0.481 023 +0237 0.06 III Hawaii -0 187 003 -0015 000 MLKM -0240 006 2-0.502 0.25 Oahu -0 362 0.13 2-0.390 0.15 KNK -0 308 0 09 2-0.395 0.16 Total aggregate Hawaii -0.150 0.02 -0334 0.11 MLKM 2-0.463 0.21 2-0.878 0.77 Oahu 2-0 465 022 2-0.521 0.27 KNK +0.395 0.16 -0.165 0.03 'MLKM = Maui-Lanai-Kahoolawe-Molokai KNK= Kauai, Niihau, and Kaula Rock Significant at P = 0.05 level, one-tailed test, df 18. is apparent that in 13 of the 16 possible compari- sons, fisherman-days showed a stronger negative correlation with CPUE than did catch-records. Based on these results we conclude that fisherman-days predicts the behavior of CPUE more precisely than catch-records. Use of this measure also eliminates repeated counting of effort statistics when more than one species in a group is caught on a particular day and has greater intuitive appeal as well. For these reasons we conclude that fisherman-days is the best measure of fishing effort available at present. It is worth noting that these two different measures of effort are approximately linear in their relationship to one another, imply- ing that the superiority of fisherman-days over catch-records as a measure of effort is probably due to a smaller residual variance of instanta- neous fishing mortality (F) on the former statistic than on the latter. Stock Production Analyses In this section the Schaefer model is applied to the deep-sea handline data in which the catch is aggregated at three different levels. At the first level a single-species Schaefer model is fitted to each species separately. Next, the TBSM is fitted to each of the three species groups delimited by the cluster analysis. In the final section the total aggregated catch of all 13 species taken together is analyzed with the TBSM. Fisherman-days was used as the measure of fishing effort throughout, but equilibrium approximation (Gulland 1972) was not attempted because no information was available concerning the longevity of these species and a previous appli- cation of this method to the data had shown little improvement in the results (Ralston footnote 4). When each species is treated independently there are 52 separate analyses (4 banks with 13 species each). In only two of these regressions of CPUE on /is the null hypothesis /?>0, where j3 is the slope of the regression, rejected in favor of the alternative hypothesis /3<0. Both involved the MLKM bank where opakapaka (t = -2.91, df = 18) and uku (t = -1.82, df = 18) demonstrated significant inverse regressions in which respec- tively, 32% and 16% of the total variation in CPUE were explained. The significance of these two re- gressions can easily be attributed to the Type I error and consequently nothing can be concluded from these results concerning the productivity of these fishes. The fit of the TBSM to the data is much improved when the three species groups are con- sidered. The model was applied to the HDFG data 12 times; once for each species group and bank combination. Significant results (P = 0.05, one-tailed test) were obtained in 5 of the 12 appli- cations of the model (Table 5). The three analyses from the MLKM bank were significant in every case and those for Group III were significant in three out of the four regressions tested. The ob- servation that the results from the remaining banks and species groups are not significant is not so disturbing because 56% of all bottom fish landings are harvested from the MLKM bank (Table 2). An estimate of the maximum sustain- able yield (MSY) and optimum effort was then computed for each of the five significant com- binations, as well as a standardized measure of productivity, calculated as the sustainable yield of bottom fish per nautical mile of 100-fathom isobath. Assuming logistic growth of the stocks the catchability coefficient was estimated using the computer program PRODFIT (Fox 1975). The t value in the table refers to the test of the null hypothesis that the slope of a regression is zero or positive. Pope (1979) has proposed an interactive model to describe multispecies fisheries in which total yield is depicted as the sum of the yields of individual species with additional terms to account for community interactions. In the simple two-species case the equation describing surplus production (Y) is: 441 FISHERY BULLETIN: VOL. 80. NO. 3 Table 5.— Significant applications of the total biomass Schaefer model to the Hawaii Division of Fish and Game data set where species have been aggregated according to cluster analysis species groupings. Species MSY2 Opti mum effort MSY/nmi Catchability rvalue Bank' group (kg/yr) (fisherman -days) 100-fathom iso bath coefficient (df = 18) MLKM 1 23,000 480 60 0.00180 -2.47 II 48,800 662 125 0.00062 -5.11 III 31,900 396 82 0.00120 -2.46 Oahu III 1,900 119 12 0.00280 -1.74 KNK III 4,800 84 25 0.00600 -1.77 'MLKM = Maui-Lanai-Kahoolawe-Molokai KNK = Kauai, Niihau, and Kaula Rock. 2MSY = maximum sustainable yield. Y = aiN\ + CU2N2 - + (d + c2)NiN2 6i7vV 62M2 (1) where M and N2 refer to the population sizes of species one and two and a\, c^, 61, 62, Ci, and C2 are model parameters (Pope 1979). This model is the sum of two single-species surplus production models with the additional term (ci + c2)NiN2 to account for the interaction between the two species. Depending upon the signs of c\ and C2 the equation models predation, competition, or mutualism. More importantly, the sum of these two parameters determines the impact of the interaction on the sustainable yield of the system. The question of whether significant interac- tion occurs among the cluster-analysis species groups was examined by considering the MLKM bank alone. The regressions of all three cluster groups were highly significant from this region and further treatment of these data is therefore considered appropriate. In the three-species version of Equation (1) there are three terms involving the sum of c parameters. In this analysis a species group (I, II, or III) is treated as though it were a single species and the a and b parameters necessary to evaluate the equation were taken from the independently calculated regressions of Table 5. A nonlinear regression routine (SAS Institute 1979, program NLIN) was employed to estimate the sums of the various c parameters for the MLKM bank (Table 6). It is apparent that these sums do not differ significantly from zero and hence there is no evidence for. significant inter- action among groups. This result further Table 6.— Tests of whether interaction between cluster analysis species groups have a significant effect on total bottom fish yield from the Maui-Lanai-Kahoolawe-Molokai bank. Term Parameters Evaluated value 95% confidence limits (c, + c2) N,fV2 (c2 + c3) N2N3 (c, + c3) /v,N3 (C1 + c2) (c2 + c3) (c + c3) 0.242 0.185 -0 868 (-0.244, 0.728) (-0 284. 0.654) (-2.365. 0.629) supports the classification of species into independent assemblages for use in an aggre- gated treatment of the data. In the final analysis all species were treated as a single group and the TBSM was applied to the total aggregate. Of the four possible regressions of CPUE on /, both the MLKM and Oahu banks yielded significant results (Table 7). Similar computations were performed for these sites as had been done previously. In addition the regres- sion of total bottom fish CPUE on / for the MLKM bank and the corresponding catch curve (catch versus effort) were plotted (Fig. 3). It is reassuring to note that the sum of the three- species group MSY's from this bank, calculated from the preceding analysis, amounts to 103,700 kg/yr. This estimate compares favorably with the present result (a difference of about 2%) though the two figures were computed somewhat inde- pendently. A comparison of MSY/nmi 100- fathom isobath between these two banks reveals the Oahu value to be substantially less than the MLKM value. Although this may in actuality represent differences in habitat quality and pro- ductivity between these banks, there is the pos- sibility that the difference is at least partially due to a difference in the extent of unreported recreational fishing pressure between the banks. The results of the stock-production analysis for the MLKM bank provide statistically acceptable regressions, yet the estimates of production are Table 7. — Significant applications of the total biomass Schaefer model to the Hawaii Division of Fish and Game data set where all species have been grouped into one total aggregate. Bank MSY2 (kg/yr) Optimum effort (fisherman-days) MSY/nmi, 100-fathom isobath Catchability coefficient t value (df = 18) 'MLKM = Maui-Lanai-Kahoolawe-Molokai. 2MSY = maximum sustainable yield. MLKM' Oahu 106,000 15,700 901 424 272 105 000080 000168 -7.77 -2.59 442 RALSTON ami POLOVINA: COMMERCIAL DKhT-SKA HANDLINK FISHERY 240 — 200 V < n x. IbO o JC 111 120 I- < - o o a. 2 I r~ ! — f" 1 13 INDEPENDENT SPECIES (n-52) LL n n ljj 3 CLUSTER ANALYSIS SPECIES GROUPS (n-12) _□ . □ J L n n n TOTAL AGGREGATE (n = 4) "4 -.2 0 +.2 + .4 +.6 CORRELATION COEFFICIENT (r) +.8 Figure 4.— Frequency distributions of correlation of co- efficients between CPUE and fishing effort based on three levels of species aggregation. cause only 2 out of the 13 single-species regres- sions were signficant, it is not appropriate to use the single-species results in our comparison of the effects of aggregation. Table 4 presents the correlation coefficients between CPUE and effort for each of the three cluster groups and the total aggregate. At first glance it appears that for the MLKM bank the TBSM applied to the total group fits substantially better (r2 = 0.77 for fisherman-days) than the TBSM applied to any of the three species groups (r2 = 0.25, r2 = 0.59, and r2 = 0.25). However, an examination of the correlations between fishing effort for the three cluster groups reveals that these variables are highly correlated (Table 8). Grunfeld and Griliches (1960) have cogently argued that increased colinearity of independent variables can lead to an increase in the goodness of fit (r2) when data have been aggregated. This deceptive gain in the explanatory power of an aggregated independent variable prevents a direct compari- Table 8.— Correlations of fishing effort (fisherman- days) if) among cluster analysis species groups. Group effort 12 13 n f2 1.000 0.943* 1.000 0.900* 0.940* 1.000 'Significant P = 0.01. df =78. 444 RALSTON and POLOVINA: COMMERCIAL DEEP-SEA HANDLINE FISHERY son of the coefficients of determination obtained from different levels of grouping. Thus it is improper to compare the goodness of fit for the grouped analysis to that for the total aggregate without correcting for this bias. They suggest that a more appropriate and direct way of comparing the effect of these two levels is to compare the proportion of variance in the total catch explained by the predicted total catch from the two levels of aggregation. We must use catch rather than CPUE as the dependent vari- able because the sum of the CPUE values pre- dicted from each of the grouped models will not predict total CPUE. When annual catch (C) rather than CPUE is used the Schaefer model becomes annual catch explained by the sum of the three species groups model is r2 defined as: C = af-bf + E (2) where a and 6 are constants, /is fishing effort in fisherman-days, and E is a normal random vari- able with mean 0 and finite variance. In the case when catch and effort are aggregated into the three species groups there will be three equations of the form of Equation (2) based on the grouped annual catch (C,) and grouped annual effort (/) for i = 1, 2, 3. For the completely aggregated TBSM there will be a single equa- tion of the form of Equation (2) with total annual catch {TC) and total annual effort (77). In all four equations the nonlinear regression coeffi- cients a and b can be estimated with the 20 yr of annual data from 1959 to 1978. We can then use these coefficients to obtain predicted group annual catches (Cl}) for groups i = 1,2, 3 and years j = 1, 2, ...,20, and the predicted total annual catches (TQ) for years j = 1, 2, ...,20 given the corresponding effort statistics. We now have two estimates of total annual catch based on either TCj from the fully aggregated TBSM or Cv + C2j + C3j from the three species groups regressions. We can compare these two levels of aggregation based on their accuracy in predicting TC. This is done by defining SSg to be the sum of squares of TCj— &j — Ckj— Csj for j = 1, 2 20, or the deviations of the grouped predicted catch from the observed total, and defining sg2 — SSg/19. Let SS, be the sum of squares of TCj — TCj, j = 1, 2 20, or the deviations of the predicted total catch of the completely aggregated TBSM from the observed total catch. Finally let s2 = SS,/19 and sT<2 be the sample variance of the total annual catch. Then the proportion of the variance of the total 2 _ 1 -Sg/sre (3) and the proportion of the variance in the total annual catch explained by the TBSM is r,2 defined as: rf = 1 - s?/stc2 (4) For the MLKM bank we determine r2 - 0.14 and rg2 = 0.18. Thus the increased level of data aggregation going from treating the fishery as three separate groups to one total group does not in fact improve the fit of the catch curve although this appeared to be the case when the r2 for the TBSM applied to the total group was compared to the r2 values for the TBSM applied to each of the three cluster groups (Table 4, Fig. 4). As outlined previously these coefficients of deter- mination, as calculated above, refer to the pre- diction of catch from effort data, for which the fit is substantially poorer than the fit of CPUE on effort. A consideration of statistical aggregation theory has shown that the classification of bottom fish species into cluster groups results in slightly better predictions of total bottom fish catch than does analysis of the total aggregate. Since superior performance is achieved at an intermediate level of aggregation, it is possible to discount the undesirable effects of "averaging" which have troubled previous investigators (FAO 1978; Pauly 1979; Pope 1979). Further- more, the lack of significant interaction among the species groups (Table 6) suggests that this particular application of the TBSM to the Hawaiian offshore handline fishery is appro- priate. Even though the separation of data from the MLKM bank into three species groups produced only a marginally better fit than the total aggregate model and the extra computations which are necessary were extensive (e.g., clustering), some advantage can be gained by splitting the fishery up into the groups listed in Table 3. Not only is the biological realism of the stock-production analysis enhanced but interest- ing patterns are also allowed to emerge. Notice, for example, that while the estimate of MSY for Group I from the MLKM bank is less than that for Group III from the same bank (Table 5), the fishing effort required to reach that figure is 445 FISHERY BULLETIN: VOL. 80, NO. 3 substantially greater, in spite of the fact that the catchability coefficient for Group I is greater than for Group III. This apparent contradiction can be understood when estimates of carrying capacity and instantaneous growth rate are com- puted for the two groups. Ricker (1975) showed that the virgin shock biomass (Boo) is equal to a/q and the intrinsic rate of natural increase (r) is equal to aq/b, where q is the catchability co- efficient and a and b are the intercept and slope, respectively, of the regression of CPUE on effort. Using these equations the estimate of virgin biomass for Group I at the bank is much less than for Group III whereas the intrinsic rate of natural increase for Group I is nearly double that of Group III, hence, the disparity in catchability coefficients. This manner of evaluating the growth dynamics of the fishery implies that if fishing were to stop abruptly, Group I would recover to pristine levels much sooner than either Group II or III. Thus, this analysis would predict that a form of succession would occur around the MLKM bank if fishing were cur- tailed as a new equilibrium point was ap- proached. Although there is little hope of manip- ulating the system to test this particular prediction of the model, this type of heuristic calculation can provide valuable insights con- cerning the consequences of different manage- ment programs. Pope (1979) has shown that in a multispecies fishery an increase in the colinearity of effort values among species or groups will result in a more parabolic-shaped yield curve. Conse- quently, he argues that if fishing pressure is exerted in such away that the fishing mortalities of the various species remain in constant ratio to one another, then the use of the TBSM is a real- istic management option. He points out though, that it cannot be concluded that an MSY esti- mated by application of the model to actual data is anywhere near the global maximum of the system. These considerations bear directly on this study because of the high correlations of fishing effort among the three species groups. Even though MSY from the MLKM bank is estimated to be 106 t/yr it is quite possible that a substantially larger yield could be sustained if it were possible to alter the ratios of fishing mortality among the species groups. This pos- sibility is not unrealistic because these groups seem to be for the most part spatially separated. In principle then, appropriate management action could reduce fishing effort on one group while simultaneously increasing that on another, but at present it is impossible to speculate about what the global MSY of the MLKM bank might be. One of the least realistic aspects of the TBSM is its inability to adequately model trophic dynamics (Pauly 1979). The addition of Lotka- Volterra interaction terms to the model (Pope 1979) is a relatively simplistic attempt to deal with this problem. Pauly (1979) argued that the surplus-yield of fish predator-prey systems may be overestimated by the TBSM because of "prudent predation" by top carnivores. This theory (Slobodkin 1961) would propose that fish predators optimally harvest their fish prey, leaving little or no remaining latent productivity of the prey species for man to utilize. These argu- ments must impose group selectionist reasoning and suffer as a result. Nevertheless, the TBSM assumes that total stock size is greatest in a virgin state, a condition which need not be satis- fied if limitation is internally imposed (May etal. 1979). Fortunately these considerations do not detract from the value of the present analysis. The six dominant species in the fishery (opakapaka, ulua, uku, onaga, hapu'upu'u, and kahala) are all high-level carnivores and occupy a similar trophic position. No predator-prey re- lationship is known to exist between any of the 13 species listed in Table 1, although extensive gut content analyses of all life history stages are currently unavailable. Thus, some of the objec- tionable aspects of the TBSM have been minimized by not including species from differ- ent trophic levels within the same analysis. Predator-prey relationships in a fisheries context are poorly understood at present and will probably require a more dynamic construct than the TBSM is capable of offering (May et al. 1979; Pauly 1979). SUMMARY Examining the HDFG catch report data shows that the commercial deep-sea handline fishery in the Hawaiian Islands is a multispecies fishery composed principally of 13 species of bottom fish, 6 of which comprise 86% of total landings. Snap- pers (Lutjanidae), jacks (Carangidae), and a species of grouper (Serranidae) dominate the catch, all of which are high-level carnivores. In the main high islands of the Hawaiian Archipelago (see Figure 2) three bottom fish 446 RALSTON and POLOVINA: COMMERCIAL DEEP-SEA HANDLING FISHERY species groups are recognized based on cluster analyses which measure the tendencies of the various species to appear with one ar. >ther in the catch. These groups seem to segregate on the basis of depth distribution, providing convenient biological assemblages for aggregating catch statistics. Application of the Schaefer stock-production model to this fishery on a species-by-species basis provides an inadequate description of produc- tivity. When species are aggregated into the cluster groups and analyzed with TBSM, the results are much improved. In this regard con- sistently significant results and production esti- mates were obtained from the MLKM bank, a region which presently accounts for half of the State of Hawaii's catch. No significant inter- action among these groups was detected. When all 13 species are analyzed together, the results are in agreement with the preceding analysis. Based on TBSM applied to the MLKM bank, we estimate the annual MSY of the commercial deep-sea handline fishery to be 106 1 or about 272 kg/nmi of 100-fathom isobath. Because recrea- tional catch is unaccounted for, these figures are considered lower bounds for the gross produc- tion obtainable from this type of fishery although currently the commercial fishery is operating close to this MSY level. By examining the effect of aggregating catch statistics we show that the production models based on the intermediate level of catch aggre- gation (cluster groups) together explain slightly more of the variation in the total catch than does the production model based on the total aggre- gate catch in spite of a higher coefficient of deter- mination resulting from the latter analysis. High correlations of fishing effort among cluster groups account for this nonintuitive result. Application of the Schaefer stock-production model to catch and effort data aggregated over species can be a useful tool for the analysis of a multispecies fishery. The appropriate level of aggregation will depend on biological and geo- graphic factors. ACKNOWLEDGMENTS This work is the result of research sponsored in part by the University of Hawaii Sea Grant College Program under Institutional Grant No. NA79AA-D-00085 from NOAA Office of Sea Grant, Department of Commerce, and consti- tutes journal contribution UNIHI-SEAGRANT- JC-81-08. We would like to thank John L. Munro for his early encouragement to undertake this study and Roy Mendelssohn, who suggested employing aggregation theory to examine our results. Darryl T. Tagami helped with much of the computer work. LITERATURE CITED Andersen, K. P., and E. Ursin. 1977. A multispecies extension to the Beverton and Holt theory of fishing, with accounts of phosphorus circula- tion and primary production. Medd. Dan. Fisk.- Havunders. (N.S.) 7:319-435. Anderson, W. D., Jr. 1981. A new species of Indo-west Pactific Etelis (Pisces: Lutjanidae), with comments on other species of the genus. Copeia 1981:820-825. Brander, K. M. 1977. The management of Irish Sea fisheries - A review. G.B. Minist. Agric. Fish. Food Fish. Lab. Leafl. 36, 40 p. Brock, V. E., and T. C. Chamberlain. 1968. A geological and ecological reconnaissance off western Oahu, Hawaii, principally by means of the re- search submarine "Asherah." Pac. Sci. 22:373-394. Brown, B. E., J. A. Brennan, M. D. Grosslein, E. G. Heyerdahl, and R. C. Hennemuth. 1976. The effect of fishing on the marine finfish biomass in the Northwest Atlantic from the Gulf of Maine to Cape Hatteras. Int. Comm. Northwest Atl. Fish. Res. Bull. 12:49-68. Dixon, W. J. (editor). 1977. BMD biomedical computer programs, P-series. Univ. Calif. Press, Los Angeles, 880 p. FAO 1978. Some scientific problems of multispecies fisheries. Report of the expert consultation on management of multispecies fisheries, Rome, 20-23 September 1977. FAO Fish. Tech. Pap. 181, 42 p. Fox, W. W., Jr. 1975. Fitting the generalized stock production model by least-squares and equilibrium approximation. Fish. Bull., U.S. 73:23-37. Gosline, W. A., and V. E. Brock. 1960. Handbook of Hawaiian fishes. Univ. Hawaii Press, Honolulu, 372 p. Grigg, R. W., and R. T. Pfund (editors). 1980. Proceedings of the Symposium on Status of Re- source Investigations in the Northwestern Hawaiian Islands, April 24-25, 1980, University of Hawaii. Honolulu, Hawaii. Sea Grant Misc. Rep., UNIHI- SEAGRANT-MR-80-04, 333 p. Grunfeld, Y., and Z. Griuches. 1960. Is aggregation necessarily bad? Rev. Econ. Statist. 42:1-13. GULLAND, J. A. 1972. Population dynamics of world fisheries. Wash. Sea Grant Publ. 72-1, Univ. Wash., Seattle, 336 p. 1974. The management of marine fisheries. Univ. Wash. Press, Seattle, 198 p. Hawaii Department of Land and Natural Resources. 1979. Hawaii fisheries development plan. Department of Land and Natural Resources, State of Hawaii, 297 p. 447 FISHERY BULLETIN: VOL. 80, NO. 3 LARKIN, P. A. 1963. Interspecific competition and exploitation. J. Fish. Res. Board Can. 20:647-678. 1966. Exploitation in a type of predator-prey relation- ship. J. Fish. Res. Board Can. 23:349-356. May, R. M., J. R. Beddington, C. W. Clark, S. J. Holt, and R. M. Laws. 1979. Management of multispecies fisheries. Science (Wash., D.C.) 205:267-277. Munro, J. L. 1978. Actual and potential fish production from the cor- raline shelves of the Caribbean Sea. In H. B. Stewart, Jr. (editor), Cooperative investigations of the Caribbean and adjacent regions — II. Symposium on progress in marine research in the Caribbean and adjacent regions, held in Caracas, 12-16 July 1976. Papers on fisheries, aquaculture and marine biology, p. 301-321. FAO Fish. Rep. 200. Parrish, J. D. 1975. Marine trophic interactions by dynamic simula- tion of fish species. Fish. Bull., U.S. 73:695-716. Paulik, G. J., A. S. Hourston, and P. A. Larkin. Exploitation of multiple stocks by a common fish- J. Fish. Res. Board Can. 34:2527-2537. 1967. ery. Pauly, D. 1979. Theory and management of tropical multispecies stocks: A review, with emphasis on the Southeast Asia demersal fisheries. ICLARM Stud. Rev. 1, 35 p. Pope, J. 1979. Stock assessment in multispecies fisheries, with special reference to the trawl fishery in the Gulf of Thailand. South China Sea Fish. Develop. Coord. Programme, SCS/DEV/79/19, 106 p. Regier, H. A. 1973. Sequence of exploitation of stocks in multispecies fisheries in the Laurentian Great Lakes. J. Fish. Res. Board Can. 30:1992-1999. RlCKER, W. E. 1975. Computation and interpretation of biological statistics of fish populations. Bull. Fish. Res. Board Can. 191, 382 p. Rothschild, B. J. 1977. Fishing effort. In J. A. Gulland (editor). Fish population dynamics, p. 96-115. Wiley, Lond. Sale, P. F. 1977. Maintenance of high diversity in coral reef fish communities. Am. Nat. 111:337-359. SAS Institute. 1979. SAS user's guide. 1979 ed. Statist. Anal. Syst., 494 p. Slobodkin, L. B. 1961. Growth and regulation of animal populations. Holt, Rinehart, and Winston, N.Y., 184 p. Strasburg, D. W., E. C. Jones, and R. T. B. Iversen. 1968. Use of a small submarine for biological and oceanographic research. J. Cons. 31:410-426. Talbot, F. H., B. C. Russell, and G. R. V. Anderson. 1979. Coral reef fish communities: unstable, high- diversity systems? Ecol. Monogr. 48:425-440. 448 DEVELOPMENT AND APPLICATION OF AN OBJECTIVE METHOD FOR CLASSIFYING LONG-FINNED SQUID, LOLIGO PEALEI, INTO SEXUAL MATURITY STAGES William K. Macy III1 ABSTRACT An objective method of classifying long-finned squid, Loligo pealei, by their sexual maturity was developed using cluster and discriminant analysis techniques. The resulting system recognizes four developmental stages and employs a maximum of only five easily measured morphometric parame- ters. Such a system is easy to use and is suitable for large-scale field studies with relatively untrained help. The value of determining clearly recognized reproductive stages is demonstrated by an appli- cation of the method. Each summer schools of long-finned squid, Loli- go pealei Lesueur, 1821, move into shallow coastal waters from Delaware Bay to Cape Cod to spawn (Verrill 1882; Haefner 1964; Summers 1968, 1971). During the colder months, however, the squid are found only offshore, concentrated in canyon mouths along the continental slope (Sum- mers 1967, 1969; Vovk and Nigmatullin 1972; Serchuk and Rathjen 1974). While the size/age composition of the species has been relatively well described by Verrill (1882), Summers (1967, 1968, 1969, 1971), Tibbetts (1975, 1977), and Mesnil (1977), many details of its reproduc- tive cycle, particularly during the offshore peri- od, remain unclear (see Summers 1969, 1971; Vovk 1972; Arnold and Williams-Arnold 1977; Mesnil 1977). From such studies it appears that L. pealei lives only 12-18 mo on average, and that like most squid it dies after spawning (Arnold and Williams-Arnold 1977). Details of the repro- ductive biology and population structure of such a short-lived species, with only two year classes at most, are especially important in the develop- ment of prudent stock management programs. Unfortunately, no single method for character- izing the reproductive state of individuals of this species has been employed to date. A number of classification methods have been employed for a variety of squid species, which reflect both interspecific differences and differ- ing requirements of the investigators using them (Tinbergen and Verwey 1945; Mangold-Wirz 1963; Fields 1965; Hayashi 1970; Vovk 1972; •Narragansett Mussel Co., 146 Main Street, North Kings- town, RI 02852. Holme 1974; Ikehara et al. 1977; Durward et al. 1978; Juanico 1979; Hixon 1980). Many of these methods are slow because of the large number of variables required or the need for sample weigh- ing or microscopic examination. Some methods also rely mainly on subjective distinctions. From 1975 through 1978, ecological studies concerning the population structure, movement patterns, and feeding habits of L. pealei were conducted (Macy 1980). During the first year of the study, the Vovk (1972) method for classifying squid into one of five stages of sexual maturity was used with length-frequency data to charac- terize changes in the population reproductive structure over time. While the Vovk method was useful, in practice squid were often encountered which could not be readily classified. This report concerns the development and application of a new, faster, and more objective maturity classifi- cation system. The method was then successfully employed to classify large numbers of squid throughout the remainder of the study referred to above. METHODS From late April through November each year, squid were collected on an approximately bi- weekly basis throughout the inshore study area located in the southern part of the West Passage of Narragansett Bay, R.I. (inset Fig. 1). A bal- loon-type otter trawl (Oviatt and Nixon 1973), towed at ca. 4.6 km/h, was used. To insure ran- domness and adequate size-class representation, samples of at least 100 squid each were randomly selected from the pooled catch of duplicate 20- Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80. NO. 3, 1982. 449 FISHERY BULLETIN: VOL. 80, NO. 3 Figure 1.— Inshore and offshore sampling locations on the coast and continental shelf of New England. The study area in lower Narragansett Bay is indicated by shading in the inset. Depths in meters. tissue. Frequently, the length of typical sperma- tophores can be determined while still within Needham's sac or the penis. Mantle width (MW, Table 1), a measure of mantle circumference, was defined as the distance across the widest part of the mantle when opened flat to form a rough isosceles triangle. Mantle thickness (MT) was measured at the thickest portion along the midventral incision. All weight measurements were blotted fresh or live weights (e.g., wet weight, WW, and gonad weight, GW) and were recorded to the nearest 0.01 g if <120 g or to the nearest 0.1 g if >120 g, on a top-loading digital balance. The relative abundance of spermato- phores in Needham's sac (ASN), in the penis (ASP), of eggs in the ovary (AEO), or in the ovi- duct (AEOV) were scored on the basis of "none," "a few," or "many" present. In females, a distinc- tion was also made between immature and ma- ture eggs (Table 1). The four variables — ASN, ASP, AEO, and AEOV — were purposely scored on this nonquantitative basis to avoid time-con- suming enumeration. After completing the above length measurements and abundance esti- mates, the complete reproductive tracts, includ- ing gonadal products (Table 1), were dissected out and weighed (GW). From the tabulated raw data the various proportional indices (GI, MWI, MTI, TLI, SPI, NGI, and AGI (see Table 1)) were then computed. min trawl tows. The selected squid were bagged and placed in chilled containers for transporta- tion to the laboratory, where they were either immediately examined or were quick-frozen at — 25°C for storage. Additional frozen samples of 100-500 squid each were obtained from the Na- tional Marine Fisheries Service, Woods Hole, Mass.; from offshore surveys by the French vessel Cryos conducted during November-December 1975 and 1976; and from the Russian vessel Argus during November 1977 and March 1978 (Fig. 1). Only the 1976 Narragansett Bay and Cryos sam- ples were used to develop and verify the classifica- tion system described here. The new system was then used to classify the 1977 and 1978 samples. For analysis, squid were opened midventrally to expose internal organs and allow sexing. Twenty characters were then determined (Table 1). Length measurements were made to the near- est millimeter using a ruler along the greatest dimension, taking care not to stretch the organ or Table 1.— The initial 20 input parameters tested for classi- fying squid into maturity stages. See Figure 3 for organ iden- tification. Mantle length, cm = DML = dorsal mantle length Wet weight, g = WW = total live weight Mantle width, cm = MW Mantle thickness, cm = MT Gonad weight, g = GW' Gonad index = GW/WW = GI Mantle width index = MW/DML = MWI Mantle thickness index = MT/DML = MTI Males: Testis length, cm = TL Spermatophore length, cm = SPL2 Abundance of spermatophores in Needham's sac = ASN3 Abundance of spermatophores in penis = ASP3 Testis length index = TL/DML = TLI Spermatophore length index = SPL/DML = SPI Females: Nidamental gland length, cm = NGL Accessory gland length, cm = AGL Abundance of eggs in ovary = AEO4 Abundance of eggs in oviduct = AEOV3 Nidamental gland index = NGL/DML = NGI Accessory gland index = AGI/DML = AGI 'For females: (nidamental + accessory + oviducal glands) + ovary/ oviduct + eggs. For males: testis + (Needham's sac +spermatophoric organ + penis). 2Length of an average spermatophore excluding tail (= cap thread), scored as "0" if not present or if visible only as a round speck 3Scored on a 1-3 scale, where 1 = none, 2 = "a few," 3 = abundant. 'Scored on a 1 -5 scale, where 1 = none, 2 = "a few" immature, 3 = many immature, 4 = "a few" mature, 5 = many mature. 450 MACY: CLASSIFYING LONG-FINNED SQUID INTO SEXUAL MATURITY STAGES Statistical analyses were performed using the Biomed Computer Programs P-Series (BMDP) (Brown 1977) on an Itel AS-5R computer2 of the University of Rhode Island Academic Computer Center. The initial data matrix consisted of the 20 variables listed in Table 1 , from 675 males and 693 females randomly selected from the 1976 Cryos offshore and 1976 Narragansett Bay in- shore samples. After standardization of the vari- ables, principal components analysis (BMDP program 4M) (Morrison 1976) was employed to group variables and to determine their impor- tance in accounting for observed variance. Clus- ter analysis (BMDP 2M) was then used with the Euclidean-distance metric as the amalgamation algorithm to group cases (Anderberg 1973). Finally, stepwise linear discriminant analysis (BMDP 7M) (Anderson 1958) was used with dif- ferent variable combinations to generate a series of functions which best discriminated between the groups identified in the cluster-analysis stage. A goal of 95% or better overall correct clas- sification of individuals was set. RESULTS Development of the Discriminant Functions The initial cluster analysis revealed only two major groupings for each sex. Further examina- tion, however, suggested that the major clusters consisted of different size-based groupings of mature and immature individuals. Spent squid (using the Vovk (1972) scale) did not group to- gether. Weight variables— WW, GW, and GI (Table 1) — were then dropped from the data matrix because it was known that length mea- sures correlate well with their respective weight counterparts and because principal components analysis had not indicated any particular advan- tage to using one variable type or the other. Clus- ter analysis was then rerun using the remaining 17 variables. Four clusters of developmental stages could then be recognized, corresponding to "ripe/spent," "nearly mature," "advanced im- mature," and "immature" (barely sexable). Sev- eral size-based subgroups were still evident within the major clusters. After scoring the squid on a 1-4 scale based on the cluster results, subsequent discriminant analysis produced moderately good separation of the four groups. Efforts were then focused on improving class separation and reducing the number of variables required. First, those cases which were suspect- ed to be misclassified based on posterior prob- ability and Mahalanobis D2 statistics (Lachen- bruch and Mickey 1968) were corrected. By this time a rather clear picture of the characteristics of each stage had been formed, and thus inspec- tion of the raw data was often sufficient to deter- mine if reclassification was warranted. Using different combinations of variables in the dis- criminant analyses, the number of variables was further reduced by retaining only those which improved classification accuracy, as indicated by a pseudojackknife test (see BMDP documen- tation; Lachenbruch and Mickey 1968). Best results were obtained with the following input variables: MW and MWI, SPL or AGL, API or AGI, TLI or NGI, and ASP or AEOV (Tables 1, 2). In males 94.6% correct classifica- tion (Table 2) was obtained using only the three most important variables, SPI, MWI, and TLI (determined by their order of entry into the step- wise analysis), while 96.6% of the females were correctly classified using the first four varia- bles—AEO, AGI, MWI, and NGI. Stage 2 squid were incorrectly classified 19% in males and 10.7% in females, but other squid were correctly grouped in at least 90% of the cases. A plot of the Table 2.— Classification of Loligo pealei into stages of sexual maturity using linear discriminant functions. The variables to be measured are listed below with their coefficients or weight- ing factors for each maturity stage. To classify an individual, construct four linear equations, one for each stage, using the measured values and the appropriate coefficients and constant and solve. The equation resulting in the largest value indicates the stage into which the individual has been assigned. 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. Stage 1 2 3 4 Variable: Males: SPI -949.083 -838.030 -972.007 596.250 MWI 112.680 88 635 92.161 16472 TLI 7.445 65.620 133.984 130.547 Constan t -49.822 -39.961 -60.416 -35921 94 6% correctly classified Females: AEO 9.695 9 440 13.297 28915 AGI -71.476 82 104 233.148 282733 MWI 98.606 83.025 67.263 76.922 NGI -26.426 -10.377 54.122 35.443 Constan t -46.310 -37.240 -49.256 -105.526 96 6% correctly classified Example: Assume squid is male Then, Y(1)=- 949 083 X SPI + 112.680 X MWI + 7.445 X TLI - 49 822 Y(4) = 596 250 X SPI + 16.472 X MW I + 130.547 XTLI - 35.921, where SPI, MWI, TLI are the actual values for the squid in question. 451 FISHERY BULLETIN: VOL. 80, NO. 3 mean values of the first and second canonical variates for each stage (Anderson 1958) (Fig. 2) shows that stages 1-4 follow a logical sequence from immaturity to ripeness. The first two ca- nonical variates are the orthogonal pair of linear combinations of the variables which best dis- criminates between the groups. Mean values for the final discriminant function variables are listed in Table 3. Typical DML's for each of the sex-stage groups have also been included for ref- erence. CANONICAL VARIABLE 1 Figure 2. — Canonical variates for each stage of sexual matur- ity evaluated at the stage or group means for each sex. Trajec- tories between subsequent stages are indicated by arrows. The Classification Process To determine the stage of maturation of a squid, the sex must first be determined. If this cannot be done by visual inspection, the squid is considered juvenile (stage 0). Otherwise, DML and MW, plus TL and SPL for males, or NGL, AGL, and E 0 V for females, should then be deter- mined. From these four or five parameters the appropriate indices needed (Table 2) can be cal- culated. As indicated in Table 2, a set of four lin- ear equations is then constructed by combining the measured parameter values with the ap- propriate discriminant function coefficients (weighting factors) and constant listed for each stage. The equation with the largest solution in- dicates the stage into which the squid should be placed. Thus, once the raw data have been mea- sured and recorded, the actual classification can be done at a later date using even a simple hand calculator. If the raw data are stored on a com- puter-readable medium, as was done in this study, the process is particularly efficient. To investigate the broader applicability of the classification, additional squid from the 1976 Narragansett Bay and Cryos samples were clas- sified. The discriminant analysis was then per- formed on these new data to see if the same four stages were identifiable. Over 98% of theindivid- Table 3.— Typical mean values (1 SD) of selected maturity stage vari- ables of Loligo pealei, listed by sex and stage of development. With the exception of mantle length values (DML), which are from a much larger pooled sample from 1976 to 1978. the reproductive character means are those of the 1976 Narragansett Bay and Cryos samples used to compute the final discriminant functions listed in Table 2. Variable coding fol- lows that of Table 1. Stag e 1 2 3 4 Variable: Males: TLI (%) 116 (3.62) 19.0 (3.70) 30.7 (3.73) 30.3 (4.45) MWI (%) 85 8 (6 90) 71.7 (7.51) 78 0 (8 74) 532(11.71) SPI (%) 0 0 0 3.6 (0 93) n 131 119 42 383 DML (cm) 7 1 (2.17) 111 (3.25) 108 (4.67) 18.6 (8.03) n 506 610 159 708 Females: AEO 1.0 1.0 18 4.7 AGI (%) 0 2.6(1.00) 5.2 (2.62) 57 (1.27) MWI (%) 83 6 (7 98) 74.7 (8 09) 65.0(11.12) 61.4 (925) NGI (%) 7.8 (3.23) 114 (4.86) 24.0 (3.74) 25.8 (4.24) n 243 124 64 262 DML (cm) 7.8 (2 24) 114 (3.09) 13.6 (4.47) 14.3 (3.99) n 947 467 155 498 Juveniles: MWI (%) 97.3(10.24) n 1,857 DML (cm) 4.6 (1.13) n 1.887 452 MACY: CLASSIFYING LONG-FINNED SQUID INTO SEXUAL MATURITY STAGES uals of both sexes were correctly grouped, and the new discriminant functions did not differ appreciably from the original ones. Thus the method was shown to be internally consistent (precise). Accordingly, during 1977 and 1978 only the four or five measurements necessary for classification purposes were routinely taken. The Four Maturity Stages A description of the general characteristics of each of the four maturity stages of L. pealei fol- lows. Figures 3a and b illustrate the important morphometric changes indicated by the discrim- inant analysis results. Stage 0: These juvenile squid lack visible go- nads (Fig. 3a) and are very broad for their length. Stage 1: In females (Fig. 3a) the nidamental glands appear as thin white streaks, averaging 8% of DML (Table 3). In males the testis appears as a pale oval body, about 11% of DML, and is frequently obscured by the stomach and cae- cum. Stage 2: Both the nidamental glands and tes- tis have almost doubled in length, to 11% and 19% DML, respectively, and the accessory and ovi- ducal glands of females or the spermatophoric organ/Needham's sac complex of males becomes evident. The ovary appears as a fine-grained band of tissue. Stage 3: This is a transitional stage between immaturity and maturity. The NGI and AGI have approximately doubled again (24% and 5% DML), and the translucent white immature ova give the ovary a distinctly granular appearance ( AEO = 2 or 3). TheTLI averages31% DML(Fig. 3b; Table 3), and immature spermatophores may be visible as small white specks in Needham's sac ( ASN = 2). No gametes can be found in the penis or oviduct, however. Stage 4: In these mature squid (Fig. 3b), much of the mantle cavity is occupied by the bulging ovary and oviduct or by the testis. Ripe eggs fill the oviduct and appear as amber spheres 1-2 mm in diameter (AEO>3, AEOVM). Elon- gate mature spermatophores (ca. 5 mm long) are visible both in Needham's sac and in the penis (ASN, ASP>1). Immature ova are also found beneath the ripe eggs in the ovary, and usually the spermatophore receptacle is packed with spermatophores. A few virgin females were seen, however. An Application of the Method Insights into the usefulness and relevance of the new classification system can be provided by a brief examination of several findings of the overall population study of which this was a part (Macy 1980). Vovk ( 1972) distinguished between ripe/mature squid and spent squid, but through- out 1975 when the Vovk method was routinely employed, no spent squid were positively identi- fied. Subsequent statistical analysis also failed to make this distinction. Laboratory observations (Macy 1980), however, suggest a reasonable ex- planation: Isolated females spawned repeatedly over 2-3 wk, but still contained significant num- bers of immature eggs; neither sex ceased feed- ing after mating; and no evidence of nutrient depletion was found. Thus no truly spent individ- uals might be expected. Maturing squid, on the other hand, were abun- dant in late winter prior to the onset of inshore migrations. In the March 1978 Argus samples, stage-3 squid constituted 35-40% of the popula- tion, while only 8% of the females and 21% of the males had yet reached maturity (stage 4). About 1 mo later (late April) large mature squid began to arrive and spawn in Narragansett Bay. By late July most spawning activity was completed, but already stage-1 individuals from early spawnings were becoming numerically domi- nant. By the time of arrival offshore, in late fall and early winter (Cryos and Argus 1977 sam- ples), fewer than 6% of either sex were mature or maturing, but over 50% of the population was composed of stage-2 squid. These early winter stage-2 squid seem to repre- sent two distinct age/maturity groups: Smaller developing young of the year, and larger and pre- sumably older squid whose gonads appear to be resorbing or regressing. The 1976 Cryos sample, for example, consisted of three groups of males with modal lengths of 8.2, 11.6, and 19.1 cm. Only 4.5% of these males (n — 287) were mature (stages 3, 4), but 71.4% were at stage 2. The modal size of the stage-2 squid lay between 10 and 12 cm, but individuals ranged from 8 to 23 cm. The remain- ing stage-1 squid had a modal length of only 8-9 cm. Regressing stage-2 individuals belonged to both the 11.6 and 19.1 cm size classes. Their go- nads had the coloration and approximate length of more mature individuals, but were distinctly thin and lacked eggs or spermatophores of any size. 453 FISHERY BULLETIN: VOL. 80, NO. 3 a O (juvenile) cm Figure 3.— Squid of each stage of maturity illustrating those morphometric changes which the discriminant analysis showed to be important, a. Juvenile and immature squid (stages 1, 2). b, Maturing and mature or ripe squid (stages 3, 4). The diagrams are drawn to scale using the mean values of the morphometric characters given in Table 3 for each sex-stage 454 MACY: CLASSIFYING LONG-FINNED SQUID INTO SEXUAL MATURITY STAGES b. [ 1 cm combination. S = stomach; C = caecum; NG = nidamental glands; T = testis; AG = accessory glands; OG = oviducal gland; 0 = ovary; N= Needham's sac/spermatophoric organ complex; SP =spermatophores; E =egg mass (mature); OV =oviduct; P = penis. Digestive tracts are not shown in stages 3 and 4 (Fig. 3b). 455 FISHERY BULLETIN: VOL. 80, NO. 3 DISCUSSION A classification system should have two major attributes: It should be objective and easy to em- ploy, and it should be biologically meaningful. The major impediment to satisfying both con- cerns appears to be the high degree of variability which exists within and between populations of L. pealei. This species has a wide geographic range, from the coast of South America to Nova Scotia (Cohen 1976), and thus populations living in different parts of the range are exposed to dif- ferent and varying environmental conditions (temperature, salinity, photoperiod, and food availability) throughout their respective annual cycles. Such environmental variation is mani- fested by both spatially and temporally varying growth rates, which result in the presence of multiple cohorts within a year class (Summers 1968, 1971; Mesnil 1977; Lange and Johnson 1979), and by differences in the timing of inshore movement and gonad maturation (Hixon 1980; Macy 1980). Thus it is evident that samples used to construct a sexual development classification should at least reflect both the inshore and off- shore portions of the range. This was done (Fig. 1). The Vovk (1972) classification, however, was based only on offshore collections, and as a result probably included relatively few spawning indi- viduals and young of the year in early develop- ment. Summers (1968, 1969, 1971), on the other hand, sampled both inshore and offshore, but dis- tinguished only between mature and immature individuals. Objectivity and Utility of the Multivariate Approach The multivariate approach to the classifica- tion problem is appropriate and objective when geographic (environmental) variability of un- known magnitude is superimposed on the usual random variation among individuals, producing the observed age or size and reproductive struc- ture of the population or species. This is true because the analytical approach used here can effectively integrate the information and pro- vide a simple numeric classification rule. Growth rates for L. pealei have only been esti- mated from modal size progressions (Summers 1971; Mesnil 1977), and hence the age of an indi- vidual or cohort can only be roughly estimated. Since multiple cohorts occur even within a small area (Narragansett Bay), mean and standard de- viation values of morphometric characters, such as of DML or GW, have limited value for discrim- ination because of the large variability range of individuals (i.e., multimodality). It is known, for example, that considerable variation exists in the age or size of L. pealei at spawning (Haefner 1964; Summers 1971; Macy 1980). Standardiza- tion by the use of ratio parameters or indices may provide a partial solution to the variability prob- lem. In the interest of speed and ease of measure- ment, a set of nominal variables to assess the relative abundance of eggs or spermatophores (ASN, ASP, AEO, AEOV; Table 1) was used in addition to the ratio or interval variables (MWI, TLI, SPI, NGI). The "none," "some," "many" rating scale is not strictly objective, but such coarse evaluations can be done reliably with little training and have proved to be valuable dis- criminators. Theoretically it is possible to de- velop an entirely objective classification system. In practice, a somewhat more subjective ap- proach usually proves necessary. What other in- vestigators have found important in distinguish- ing different maturity groups, such as gonad to body weight ratios (Hayashi 1970), must certain- ly influence the initial selection of variables to be measured. The investigator must also decide how detailed a classification is desired and what addi- tional parameters may be required. Repeated use of the exploratory technique of cluster analy- sis followed by stepwise discriminant analysis, as employed here, provides a way of learning how many groups may be present and how to "best" identify them using only those variables which can be shown to significantly aid discrimi- nation. But, at this stage too, the researcher must at least roughly determine the basis for case clus- tering (by size, color, sexual development, etc.). Biological Relevance and Accuracy Statistically accurate and precise results may prove meaningless in reality. Thus the most im- portant verification of the classification scheme is the demonstration of biological relevance in the appropriate context. In each of the 2 yr when the system was routinely employed, a predictable and logical progression of sexual development from hatching to spawning was observed. More- over, the findings which resulted from this appli- cation of the method are reasonable and have significant, broader implications. 456 MACY: CLASSIFYING LONG-FINNED SQUID INTO SEXUAL MATURITY STACKS Laboratory studies confirm evidence from the field that spent squid cannot be reliably distin- guished from spawning squid, even though the majority of samples (Narragansett Bay) were taken on the spawning grounds during the peak of reproductive activity. Hixon (1980) was also unable to find spent L. pealei or arrow squid, L. plei, in the Gulf of Mexico, and he too document- ed multiple spawning by L. pealei. Furthermore, it has been shown histologically (Burukovski and Vovk 1974) that egg development is highly asyn- chronous among individuals, and that a series of eggs at different stages of development in the ovary is typical. Prolonged spawning by poorly synchronized individuals of a population would tend to extend spawning over time, and may well account for the lack of reports of dead or dying squid of this species on the spawning grounds. Stage-3 individuals, particularly males, were poorly sampled during 1976 (Table 3). This was expected since only fully mature individuals move inshore in large numbers, and reproduc- tive development ceases or regresses in late fall. These animals show the first obvious signs of ap- proaching maturity: Developing eggs and sper- matophores may be visible, and the nidamental and accessory glands of females and the testes of males (Table 3) have reached sizes comparable to those of fully mature squid. The stage may be of short duration, since gonad development appears to be rapid offshore, with large squid, especially males, maturing faster than the smaller ones (Summers 1969; Macy 1980). In the March 1978 Argus samples, large numbers of stage-3 squid were identified, and it is unfortunate that other late winter or early spring offshore samples were not available to better document the latter stages of maturation. The relatively low classification accuracy of the method for stage-2 squid (81% for males) probably is due to the wide size range of these in- dividuals in the fall and early winter, and to the unusual gonad development of the larger indi- viduals. Sexual regression by gonad resorption to a neutral or inactive state, though relatively common in bivalve molluscs (Sastry 1979), ap- pears to be rare in cephalopods. Regression has been suspected in L. pealei (Summers 1971; Vovk 1972; Arnold and Williams-Arnold 1977) and possibly also in European common squid, L. vulgaris (Tinbergen and Verwey 1945), however. The phenomenon could explain why only a few of even the largest squid (20 cm and larger DML), thought to be in their second year (Summers 1971; Mesnil 1977), are mature in the lute fall and early winter offshore samples. Lacking a re liable means of aging this species, it is not cur- rently possible to prove that the larger "re- gressed" squid are in factolder than their smaller developing stage-2 counterparts. It is also pos- sible that sexual maturation merely halts at the onset of winter and resumes again in January or February prior to onshore migrations. This hy- pothesis does not explain why the gonads appear to be shrinking, nor would it account for the pres- ence of both very large and small squid at the same stage of development. Unfortunately, L. pealei has not been held sufficiently long in cap- tivity to confirm either supposition. Comparisons with Other Classification Methods The main assets of the classification method presented here are its objectivity and its ease and speed of use. To be sure, the development took considerable time, especially interpretation of early cluster analyses, but the basic strategy is relatively straightforward and does have inter- nal accuracy checks. If a more detailed break- down of the maturation process were desired, e.g., to examine details of gametogenesis, the same analysis techniques could be applied to ob- jectively identify and separate the various phases. Thus the methodology should be appli- cable to a wide range of biological problems. When compared with several other classifica- tion systems, the advantages of the present meth- od become more evident. Two basic classes of sys- tems exist. Those used by Tinbergen and Verwey (1945), Holme (1974), Juanico (1979), and Hixon (1980) are mainly qualitative, in that the pres- ence or absence of one or more characters, con- siderations of color or texture, and estimation of relative sizes or gamete abundance are used. The other group of classification schemes, typified by those of Mangold-Wirz (1963), Hayashi (1970), Vovk (1972), and Durward et al. ( 1978) are quan- titative methods. These schemes may employ one or more subjective judgments or estimates, but rely mainly on objective characters such as rela- tive organ lengths or weights, egg diameters, or spermatophore lengths (absolute or relative) to distinguish successive maturity stages. Both types of classification systems are of value, but only the latter group will be discussed further because their methods are more objective and 457 FISHERY BULLETIN: VOL. 80, NO. 3 perhaps more suitable for large-scale applica- tions. There are obvious similarities between this classification and that of Vovk (1972), and it ap- pears that, except for stage-5 spent squid, the maturity stages are comparable in both systems. It should be reiterated, however, that the stage characteristics and average parameter values given in this report (Fig. 3a, b; Table 3) were identified after the classification functions had been determined, whereas in the Vovk system the stage indicators form the basis for classifica- tion. The offshore squid sampled by Vovk also appear to have been larger by at least 3-5 cm at each stage than those used in this study. Thus, NGL indices in the Vovk study are 6.4-25% great- er than those given in Table 3. A TLI, surpris- ingly, was not used. Vovk did employ hectocoty- lus length, but in L. pealei the hectocotylized arm may be difficult to identify, particularly in small males, and, more important, may be lost or dam- aged during trawl capture of squid. These and other smaller differences between the methods appear to result mainly because Vovk did not sample the actively spawning inshore popula- tion. His method generally works well for experi- enced personnel, but dissection and weighing of the reproductive tracts and weighing the whole squid take more time and equipment than may be available in the field. At least two more char- acters must be recorded for each sex as well. Two simple but objective classifications were developed for Japanese squid, Todarodes pacifi- cus (Hayashi 1970) and for female short-finned squid, Illex illecebrosus (Durward et al. 1978). Hayashi computed a numerical index, M, equal to the weight of Needham's sac (NW) divided by NW plus the testis weight, or to the oviduct weight (odW) divided by odW plus the ovary weight. If the computed value of M is <0.5, equal to 0.5, or between 0.5 and 1.0, the squid is consid- ered immature, mature, or spent, respectively. Since spent L. pealei are at least rare, the system reduces to a two-stage classification which offers no obvious advantage over the immature-mature distinction used by Summers (1968). The dissec- tion and weighing of the two tissues are addi- tional drawbacks. Durward et al. (1979) used data initially ob- tained from six /. illecebrosus which matured in captivity but had not spawned to develop a five- stage maturity scale for females. These investi- gators showed (by scatter plots and regression analyses) that relative NGI's correlated well with identifiable stages of ovarian development. Thus only two parameters, DML and NGL, were needed for classification. As Durward et al. have pointed out, the critical values of the NGI for Illex for the first four stages are very similar to those for Loligo (Table 3). However, in L. pealei NGI ranked last of four variables in importance (Table 2), and even the most significant variable (AEO) alone yielded only 77.8% correct classifi- cation accuracy. This simple and objective classi- fication for Illex is now widely used ( Amaratunga and Durward 1979). ACKNOWLEDGMENTS This research was funded in part by an NSF Grant for Improving Doctoral Dissertations. The author gratefully acknowledges the vital com- puter and boat time provided by the University of Rhode Island and the Graduate School of Oceanography, the able drafting of Betsy Wat- kins, and the assistance of S. B. Saila during the field studies and preparation of the manuscript. LITERATURE CITED Amaratunga, T., and R. D. Durward. 1979. Standardization of data collection for the short- finned squid, Illex illecebrosus. ICNAF Sel. Pap. 5, p. 37-41. Anderberg, M. R. 1973. Cluster analysis for applications. Acad. Press, N.Y., 359 p. Anderson, T. W. 1958. An introduction to multivariate statistical analy- sis. John Wiley & Sons, N.Y., 374 p. Arnold, J. M., and L. D. Williams-Arnold. 1977. Cephalopoda: Decapoda. In A. C. Giese and J. S. Pearse (editors), Reproduction of marine invertebrates, Vol. IV, p. 243-290. Acad. Press, N.Y. Brown, M. B. (editor). 1977. BMDP-77 Biomedical computer programs P-ser- ies. Univ. California Press, Berkeley, 880 p. BURUKOVSKI, R. N., AND A. N. VOVK. 1974. Some questions of oogenesis in the Northern Amer- ican squeed (Loligo pealei Les.) from the Georges Sand- bank. Arkh. Anat. Gistol. Embriol. 66:44-50. Fish. Mar. Serv. (Can.), Transl. Ser. 3711. Cohen, A. C. 1976. The systematics and distribution of Loligo (Cepha- lopoda, Myopsida) in the western North Atlantic, with descriptions of two new species. Malacologia 15:299- 367. Durward, R. D., T. Amaratunga, and R. K. O'Dor. 1978. Maturation index and fecundity for the female squid Illex illecebrosus. Fish. Mar. Serv. (Can.), Tech. Rep. 833, p. 24.1-24.10. Fields, W. G. 1965. The structure, development, food relations, repro- duction, and life history of the squid Loligo opalescens 458 MACY: CLASSIFYING LONG-FINNKD SQUID INTO SKXUAL MATURITY STACKS Berry. Calif. Dep. Fish Game, Fish Bull. 131, 108 P- Haefner, P. A., Jr. 1964. Morphometry of the common Atlantic squid, Loligo pealei, and the brief squid, Lolliguneida brevis in Dela- ware Bay. Chesapeake Sci. 5:138-144. Hayashi, Y. 1970. Studies on the maturity condition of common squid— I. A method of expressing the maturity condi- tions by numerical values. [Engl, abstr.] Bull. Jpn. Soc. Sci. Fish. 36:995-999. Hixon, R. F. 1980. Growth, reproductive biology, distribution and abundance of three species of Loliginid squid (Myopsida, Cephalopoda) in the northwest Gulf of Mexico. Ph.D. Thesis, Univ. Miami, Coral Gables, 249 p. Holme, N. A. 1974. The biology of Loligo forbesi Steenstrup (Mollusca: Cephalopoda) in the Plymouth area. J. Mar. Biol. Assoc. U.K. 54:481-503. Ikehara, K., S. Kasahara, I. Okachi, T. Shimizu, and M. Hamabe. 1977. Contributions of biological information useful for development of inshore squid fishery in the Japan Sea. I. Ecology and maturity process in Loligo edulis budo WAKIYA et ISHIKAWA fished in the waters around the Oki Islets in the western Japan Sea. [Engl, abstr.] Bull. Jpn. Sea Reg. Fish. Res. Lab. 28:29-49. JUANICO, M. 1979. Contribuicao ao estudio da biologia dos Cephalo- poda Loliginidae do Atlantico sul occidental, entre Rio de Janiero e Mar del Plata. Ph.D. Thesis, Univ. Sao Paulo, Sao Paulo, Brazil, 102 p. Lachenbruch, P. A., and M. R. Mickey. 1968. Estimation of error rates in discriminant analysis. Technometrics 10(1):1-11. Lange, A. M. T., and K. L. Johnson. 1979. Dorsal mantle length — total weight relationships of squid (Loligo pealei and Illex illecebrosus) from the northwest Atlantic off the coast of the United States. ICNAF Res. Doc. 79/II/4, 13 p. Macy, W. K. 1980. The ecology of the common squid Loligo pealei Lesueur, 1821 in Rhode Island waters. Ph.D. Thesis, Univ. Rhode Island, Kingston, 249 p. Mangold-Wirz, K. 1963. Biologie des cephalopods benthiques et necto- niques de la Mer Catalane. Vie Milieu, Suppl. 13:1-285. Mesnil, B. 1977. Growth and life cycle of squid, Loligo pealei and Illex illecebrosus, from the Northwest Atlantic. ICNAF Sel. Pap. 2, p. 55-69. Morrison, D. F. 1976. Multivariate statistical methods. McGraw-Hill, N.Y., 415 p. Oviatt, C. A., and S. W. Nixon. 1973. The demersal fish of Narragansett Bay: an analy- sis of community structure, distribution and abundance. Estuarine Coastal Mar. Sci. 1:361-378. Sastry, A. N. 1979. Pelecypoda (excluding Ostreidae). In A. C. Giese and J. S. Pearse (editors), Reproduction of marine inver- tebrates, Vol. V, p. 113-292. Acad. Press, N.Y. Serchuk, F. M., and W. F. Rathjen. 1974. Aspects of the distribution and abundance of the long-finned squid, Loligo pealei, between Cape Hatteras and Georges Bank. Mar. Fish. Rev. 36(1): 10- 17. Summers, W. C. 1967. Winter distribution of Loligo pealei determined by exploratory trawling. Biol. Bull. (Woods Hole) 133: 489. 1968. The growth and size distribution of current year class Loligo pealei. Biol. Bull. (Woods Hole) 135:366- 377. 1969. Winter population of Loligo pealei in the mid- Atlantic Bight. Biol. Bull. (Woods Hole) 137:202-216. 1971. Age and growth of Loligo pealei, a population study of the common Atlantic coast squid. Biol. Bull. (Woods Hole) 141:189-201. TlBBETTS, A. M. 1975. Squid fisheries (Loligo pealei and Illex illecebrosus) off the northwest United States, ICNAF Subarea 5 and Statistical Area 6. ICNAF Res. Doc. 75/60, 34 p. 1977. Squid fisheries (Loligo pealei and Illex illecebrosxis) off the northeastern coast of the United States of Ameri- ca, 1963-74. ICNAF Sel. Pap. 2, p. 85-109. TlNBERGEN, L., AND J. VERWEY. 1945. Zur biologie von Loligo vulgaris Lam. Arch. Neerl. Zool. 7:213-286. Verrill, A. E. 1882. Report on the cephalopods of the northeastern coast of America. U.S. Comm. Fish and Fish., pt. 7, Rep. Comm., 1879:211-450. Vovk, A. N. 1972. Method of determining maturing stages in gonads of the squid Loligo pealei. Zool. Zh. 51:127 132. Fish. Res. Board Can., Transl. Ser. 2337. Vovk, A. N., and Ch. M. Nigmatullin. 1972. Biology and fisheries of common cephalopods of the Atlantic. Tr. Atl. Nauchno-Issled. Inst. Rybn. Khoz. Okeanogr. 42:22-54. (Available Natl. Tech. Inf. Serv., Springfield, Va. as TT 72-50101.) 459 BIOENERGETICS AND GROWTH OF STRIPED BASS, MORONE SAXATILIS, EMBRYOS AND LARVAE Maxwell B. Eldridge, Jeannette A. Whipple, and Michael J. Bowers1 ABSTRACT Fluctuations in year class size of striped bass are known to be related to development and survival in the early life stages. Bioenergetic aspects of growth and development of striped bass embryos and larvae were determined in the laboratory to discover some of the physiological needs and processes of these stages from fertilization to metamorphosis. Energy was provided by endogenous (yolk and oil globule) and exogenous (Artemia sp.) sources. Initial amounts of yolk and oil varied significantly among eggs from seven different females, and these differences were reflected in different patterns of consumption and growth. Feeding larvae consumed their endogenous oil at rates related to exogenous food intake. Daily food rations of larvae from the onset of feeding to metamorphosis were estimated for field and laboratory conditions. Rations increased with size and age of the larvae. Wild larvae were estimated to have daily rations substantially greater than those of cultured larvae. Energy outputs were measured in growth and oxygen consumption. Egg size (total dry weight) directly influenced early periods of growth, but later compensatory growth, seen in more rapid growth in larvae from smaller eggs, made up for initial differences. Growth and food consumption were linearly related and, again, different growth characteristics were seen in each batch of fish. Embryos and prefeeding larvae had the highest Qo2, while metabolism on a weight-specific basis increased with tissue dry weight and was best described by a power function. Gross caloric conversion efficiencies were highest from fertilization to initial feeding. Feeding larvae used their resources at levels under 20% and their conversion efficiencies did not appear to correlate with food concentration. In an energy budget model, striped bass embryos and larvae given the highest food density con- sumed yolk energy at constant rates until totally absorbed. Oil globule consumption fluctuated in relation to growth and nonassimilation, rising sharply after first feeding then declining as food in- take increased. Metabolism fluctuated according to developmental stage, rising with the onset of active feeding. Nonassimilation steadily increased as larvae relied more on exogenous food. Striped bass, Morone saxatilis, populations have fluctuated historically throughout their ranges, but in recent years they have declined consis- tently and unexplainably, especially on the west coast of the United States. Present estimates place the population of the San Francisco Bay/ Delta estuary at 33% to 40% of its 1960 peak abun- dance and it is forecasted to decline further (Stevens 1980). Despite availability of consider- able information on striped bass (Pfuderer et al. 1975; Rogers and Westin 1975; Horseman and Kernehan 1976; Setzler et al. 1980), factors that control or influence these fluctuations and de- clines are not known. Field researchers con- cluded from 20 yr of data collection that year class size directly correlates with survival and growth during the first 60 d of life and this, in turn, is controlled by environmental conditions— principally the interrelated factors of fresh- water flow, water diversion, and food supply (Stevens 1977a, b; Chadwick 19792; Stevens 1980). To determine the direct causal mechanisms operating between these environmental condi- tions and early life stage growth and survival, we conducted a series of laboratory experiments over a 6-yr period. Our working hypothesis was that a combination of inherent and environmen- tal factors determined the ability of striped bass embryos and larvae to meet metabolic require- ments for successful growth and survival to the pivotal age of 60 d. These factors involve a vari- ety of physiological, morphological, and behav- ioral functions, and are controlled and/or limited by environmental conditions. Whole organism 'Southwest Fisheries Center Tiburon Laboratory, National Marine Fisheries Service, NOAA, Tiburon, CA 94920. Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80, NO. 3. 1982. 2Chadwick, H. K. 1979. Striped bass in California. Pre- pared for U.S. Environmental Protection Agency, Region II, 27 p. 461 FISHERY BULLETIN: VOL. 80, NO. 3 bioenergetics was selected as our approach be- cause it represents these functions in an inte- grated and comprehensive fashion. Bioenergetics of adult fishes has been studied for some time (Ivlev 1939a, b; Winberg 1956; Warren and Davis 1967; Brett and Groves 1979). As interest in fish eggs and larvae grew, knowl- edge gained from studies of adults was applied toward research on early life stage energetics (Toetz 1966; Laurence 1969, 1971, 1977; Cooney 1973). Most of these publications are concerned with the critical period when larvae begin active feeding and change from endogenous to exoge- nous energy sources (May 1974b). Other re- searchers have used bioenergetic studies to assess the effects of pollutants or other environ- mental conditions on larvae (Laurence 1973; Eldridge et al. 1977). Our early research on striped bass embryos and larvae has already been reported (Eldridge et al. 1981). Emphasis was on factors associated with food and feeding of larvae and how they re- lated to mortality, point of no return, develop- ment, and, to a limited extent, energetics. The research presented here is a detailed analysis of the energy sources, endogenous and exogenous, and their influence on energy outputs in the early life stages of striped bass. MATERIALS AND METHODS Energy Input Determinations Component analyses of eggs prior to fertiliza- tion were done on eggs from seven different fe- males used for embryo and larval studies and on 34 ripe fish collected at random from natural spawning areas. All eggs came from fish from the Sacramento River, Calif. Three replicates of 25 eggs each were weighed fresh after brief blot- ting on absorbent filter paper, then dried to con- stant weights at 60°C and reweighed to yield water contents and total dry weights. Yolks and chorions were dissected from Formalin3-pre- served eggs with microdissection tools; they then were dried and weighed to the nearest 0.1 ng. These amounts were then subtracted from the total weight to provide oil weights. Total lipid contents were obtained by 2:1 chloroform-meth- anol extraction in micro-Sohxlet apparatus. Our procedure for caloric determinations of yolk and 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. oil involved whole egg homogenization followed by centrifugation to separate yolk, oil, and chor- ion membrane components. Yolk and oil were then aspirated into dishes, oven dried to constant weights at 60°C, and bombed according to stan- dard microbomb calorimetric methods. Esti- mates of tissue and Artemia caloric contents were made from homogenates of whole animals, the larvae being sampled after complete oil glob- ule consumption. All caloric contents are ex- pressed as calories per gram ash-free dry weight. All measurements of yolk and oil volume and lengths were done with ocular micrometers in dissecting microscopes. All measurements and determinations were performed at least in dupli- cate and, if possible, in triplicate. Eggs from seven different females were fertil- ized artificially according to methods of Bonn et al. (1976). Eggs were incubated in McDonald jars. After hatching, larvae were transferred to hemispherical 8 1 acrylic plastic containers held in water tables to stabilize temperature. Initial stocking densities were approximately 150 lar- vae/container. In three of the seven batches, lar- vae were reared to the age when feeding begins, 7 d after fertilization (D-7). The remaining four batches were reared to 29 d after fertilization (D- 29). During the process we attempted to dupli- cate natural water quality conditions as much as possible. Temperatures were maintained at 18°C, and oxygen content was at or near satura- tion throughout the experiments. Photoperiod and light qualities were kept close to natural. Sa- linities were zero from fertilization to D-4, 1.0 %<• from D-5 to D-13, and 3%« from D-14 to D-29. Each day containers were cleaned and new water and food were added. An endemic small (1- 2 /jm) green phytoplankter (Nephroselmus sp.) was also added in concentrations of 102-103/ml. Larvae began feeding consistently on D-7, at which time they were given newly hatched, live Artemia salina nauplii (San Francisco Bay Brand). The range of initial food concentrations was selected to include the estimated natural zooplankton densities (0.003 to 0.010/ml (Daniel 1976)) and the concentrations used in other striped bass research. Initial concentrations were 0.00, 0.01, 0.10, 0.50, 1 .00, and 5.00 Artemia/ ml. To estimate daily exogenous food rations of lar- vae we used the following formula: daily food ration = (average stomach contents)( hours of active feeding)/digestive time. Detailed studies 462 ELDRIDGE ET AL.: BIOENERGETICS AND GROWTH OF STRIPED BASS on diel feeding patterns and evacuation rates of larvae in our experimental systems were con- ducted in the early stages of this study and were presented in Eldridge et al. (1981). Because lar- vae in all food concentrations consumed their food within 10 h after food was first introduced, we selected 10 h/d for use in the above formula. We found that sampling larval stomachs 1 h after food introduction was most representative of average stomach contents during the active feeding periods. A minimum of 10 larvae was dissected and the stomach contents were quanti- fied for each food ration estimate for each experi- ment. Evacuation rates of food ingested by lar- vae which were feeding continuously ranged from 1 .5 to 5.5 h with an overall average of 3.3 h. Times of 100% evacuation were combined for dif- ferent-aged larvae and used in this study (Table 1). Table 1.— Average times (h) required for Ar- temia nauplii to pass through the digestive tracts of continuously feeding striped bass lar- vae. Age (days after fertilization) Food concentration {Artemia/m\) 0.01 0.10 0.50 100 5.00 9-16 17-24 25-29 3.3 2 5 2.5 4.0 2.8 2.5 3.5 3.5 3.7 4.5 4.0 35 2.3 4.0 3.0 Energy Output Determinations Growth of embryos and larvae was measured by carefully removing all yolk and oil globules from Formalin-preserved specimens, rinsing the remaining tissues in distilled water, drying at 60°C, and weighing to the nearest 0. 1 ng. Mea- surements were in duplicate with 3 to 5 speci- mens per sample. Standard lengths of larvae were measured to the nearest 0.1 mm with an ocular micrometer. Duplicate measurements of 20 larvae each were done. Preserved specimens were measured as soon as possible. The entire set of samples from each experiment required an average of 8 wk to process. Oxygen consumption was used as a measure of "routine" metabolism (Fry 1971) and was mea- sured with standard manometric techniques using a differential microrespirometer. At least five replicate samples (from 5 to 50 animals/sam- ple depending on age and size) were taken at each test period. Sampling occurred at D-0.5, -1.0, -2.0, -4.0, and on each even day until D-30 (time measured from time of fertilization). RESULTS Energy Inputs Endogenous Sources Initial sources of energy for striped bass em- bryos and early larvae are yolk and oil, the latter contained in a single large globule. The relative composition of these egg components was found to vary considerably between the seven different females used in rearing experiments (Table 2). Oil accounts for most of the variability in dry weight, whereas yolk is more variable in mea- surements of volume. Caloric contents of these two energy sources were consistent, which indi- cates that variability of total energy in the egg results from differences in absolute amounts of oil, yolk, or both, rather than differences in the energy content of those materials. Eggs from different females contained widely ranging Table 2.— Dry weights, volumes, and caloric contents of striped bass eggs and egg components at time of fertilization. Three replicates of 25 eggs each were used for dry weights, three replicates of 20 eggs each for volumes, and two replicates of approximately 50 mg (dry weight) were used for caloric content determinations. Mean volume (mm3) Caloric content Experi- ment no Mean dry weight (mg) yolk oil total yolk oil chorion total yolk oil cal/g 5,687 cal/egg 0 648 cal/g 9,223 cal/egg 1.383 cal/egg 1 0.114 0.150 0.022 0286 0.67 0.21 2031 2 0089 0.137 0.023 0.249 0.65 020 5.720 0.509 9,360 1.282 1.791 3 0.131 0089 0.028 0.248 0.57 0.13 5,622 0736 9,133 0.813 1.549 4 0 106 0.251 0.016 0.373 0.52 0.21 5,641 0 596 9,869 2477 3.073 5 0 118 0 189 0.014 0.321 0.20 0.17 5.635 0.665 9,627 1.819 2.484 6 0089 0 128 0.014 0231 038 0.18 5,635 0.502 9,738 1.247 1 749 7 0 083 0.115 0.012 0210 062 0.14 5,625 0467 9,655 1.110 1.577 0 104 0.151 0.018 0.274 0.516 0.177 5,652 0.589 9.515 1.447 2.036 SE 0.018 0054 0 006 0.057 0.170 0.033 37 0 100 278 0.546 0.558 Range 0089- 0089- 0.012- 0.210- 020- 0.13- 5.641- 0 467- 9.133- 0.813- 1.549- 0.131 0.251 0.028 0.373 0.67 0.21 5,720 0.736 9.869 2.477 3.037 C.V. 17.3 35.6 33.0 20.8 33.0 184 0.7 16.9 2.9 37.7 27.4 463 FISHERY BULLETIN: VOL. 80, NO. 3 amounts of yolk and oil (coefficients of variation 27% and 25% for yolk and oil, respectively) and little «3%) difference was found in energy con- tents. The oil globule accounted for an average 55% of the dry weight and 71% of the total energy of the egg. Yolk accounted for 38% of dry weight and 29% of energy. The two sources combined provided an average 2.036 cal/egg. Yolk contained an average 5,652 cal/g, which agrees with Phillips' (1969) estimate of 5,660 cal/g gross energy for digested protein. Lipid extraction analyses of yolk from three of the seven spawned females showed that only 3.8% of dry weight was lipid material. Embryos and larvae from the seven different females consumed their yolks linearly (Fig. 1). At hatching an average 58% of the original yolk energies remained, and they were totally utilized between D-6 and D-7, the time when active feed- ing began. Analyses showed no significant dif- ferences in yolk utilization rates but highly significant differences in intercepts (P<0.01), further indication of the differences in original yolk reserves. Initial oil energy contents per egg ranged from 0.8 to 2.5 cal (Table 2) and differed significantly between batches (P<0.05). An average 86% of these initial amounts remained at hatching and 71% was present on D-7. Analyses of covariance indicated that the utilization rates from fertiliza- tion to feeding (Fig. 2) also were significantly different (P<0.05). With the exception of one batch, embryos and larvae consumed their oil energies so that approximately the same amounts of energy remained on D-7. The rates at which oil globule calories were utilized and the ages at complete oil energy absorption (D-20 to D-29) appeared related to 0.8 Si! 0.6- O < O >- 04- 02- FEEDING I food concentration (Fig. 3). Starved larvae and those in 0.01 Artemia/m\ concentrations con- served oil, whereas those fed progressively higher concentrations consumed energy at faster rates. Analyses of covariance showed significant differences in oil consumption among batches within each food concentration. Tests of food con- centrations and oil consumption within batches showed all to have highly significant differences (P<0.01) in intercepts, and two of the four batches had significant slope differences (P<0.05). Exogenous Sources Larvae in all experiments began active feed- ing 5 d after hatching. Average stomach con- tents, presented as the average number of in- gested Artemia and their equivalent calories, are presented in Table 3. These data were further used to calculate daily food rations (Table 4). With some exceptions, larvae increased their exogenous energy intake in direct relation to food availability and age in all food concentra- tions except 0.01 Arte?nia/m\. Larvae in this low concentration showed no particular trend. Energy Outputs Growth Embryonic and prefeeding larval growth, measured in assimilated tissue calories, differed significantly among the seven batches (P<0 .01). 2.5-1 2.0 LU 5 1.5- O —J < u =i 1.0- O 0.5 oJ HATCHING FEEDING DAYS AFTER FERTILIZATION DAYS AFTER FERTILIZATION Figure 1.— The consumption of yolk calories by seven differ- ent batches of striped bass embryos and larvae cultured under identical conditions. Figure 2.— The consumption of oil globule calories by seven different batches of striped bass embryos and prefeeding lar- vae. 464 ELDRIDGE ET AL.: BIOENERGETICS AND GROWTH OF STRII'EI) BASS IS) LU ex. o < EXPERIMENT NO. 4 10 15 20 25 DAYS AFTER FERTILIZATION Figure 3.— The consumption of oil globule calories by striped bass larvae from four different batches (experiments 4-7) fed six dif- ferent food concentrations (0.00 to 5.00 Artemia/ml). 465 FISHERY BULLETIN: VOL. 80, NO. 3 Table 3.— Average stomach contents and their corresponding caloric equiva- lents of striped bass larvae feeding at different food concentrations from 9 to 29 d after fertilization. Presented as number of food organisms/number of calories per larva. Age (days after fertilization) Food co icentrations (no. Artemia/m\) 001 0.10 050 1 00 5.00 9 005/0 001 0.15/0.001 540/0052 430/0041 7.60/0.073 11 0/0 0.85/0.008 7.50/0072 11.70/0 112 2.80/0.027 13 1.50/0 014 3.30/0.032 920/0088 18 40/0.177 9.890/0.094 15 0.05/0.001 4.10/0.039 23 10/0222 24.00/0231 10.20/0.098 17 0.15/0.001 8.40/0.081 27.10/0260 39.40/0.39 18.60/0.179 19 0/0 12 50/0.120 29.50/0.283 33 30/0320 2460/0.236 21 0.15/0.001 13.00/0 125 26.10/0.251 40.00/0.384 33.70/0.324 23 4.16/0040 1420/0.136 47 40/0.456 35.90/0.345 53.00/0.509 25 1.10/0.001 57.20/0.550 17.00/0 163 83.10/0.799 59.40/0.571 27 0.25/0.002 470/0.045 65 40/0628 60.20/0.579 7240/0.696 Table 4.— Estimated daily food ration (number of Artemia consumed by one larva in 24 h/equivalent calories consumed in 24 h) of striped bass larvae at differ- ent ages feeding at different food densities. Age (days after fertilization) Prey densities (Artemia/m\) 0.01 0 10 050 1.00 5.00 9 0.2/0001 04/0004 15.4/0.148 9.6/0092 19.0/0 183 11 0/0 2.1/0.020 21.4/0 206 26.0/0.250 7.0/0067 13 4.6/0044 83/0.079 26.3/0253 40.9/0393 24.5/0.235 15 0.2/0.001 10.3/0.099 66.0/0 634 53.3/0.513 25.5/0.245 17 0.6/0.006 305/0.294 77.4/0.744 112.6/1 082 82.7/0.794 19 0/0 45.5/0.437 84.3/0810 95 1/0914 109 3/1.051 21 06/0.006 47.3/0.454 74.6/0.717 114 3/1.098 149.8/1.439 23 16.6/0 160 51 6/0.496 135.4/1 301 102.6/0.986 235.6/2.264 25 1.0/0.010 18.8/0 181 176.8/1.699 150.5/1.446 241.3/2.319 29 11.6/0.111 58.8/0.565 194.3/1.867 2888/2.775 410.0/3.940 Greater differences were seen in the intercepts than rates, and this, in turn, seemed related to the initial egg sizes (total dry weights). Descrip- tive equations for assimilated tissue calories of the different experiments are in Table 5. Daily growth coefficients (Laurence 1974) to hatching and to first feeding correlated well with initial egg size. The rate of growth from fertilization to hatching age (avg. Gw= 1.872) was three times that to feeding age (avg. Gw= 0.647). Standard lengths at hatching (3.9±0.6 mm), and especially at first feeding (5.8±0.3 mm) (Table 5), also correlated well with initial egg size. Smaller standard deviation of D-7 larvae than of newly hatched larvae (coefficients of var- iation 5% vs. 15%) suggests larval lengths con- verged with age. Growth characteristics of feeding larvae were unique to each batch within each food concentra- tion as was found in earlier stages. Examples are given in Figures 4 and 5 which present growth in tissue calories and standard lengths of larvae fed the high food ration (5.0 Artemia/ ml). Within each batch, growth was linearly re- lated to food concentration (Fig. 6). Differences in overall growth are again apparent. Experi- ment 7 larvae grew fastest. Larval length-weight relations were exponen- Table 5.— Best descriptive equations (y = tissue calories, x = days after fertilization), initial egg dry weights, standard length, and growth coefficients of striped bass embryos and prefeeding larvae. Experi- ment Initial egg size (fjg) Best fit growth equation (tissue cal) Standard errors of estimate Standa rd ler gths (mm) Daily instantaneous growth coefficients' at hatch ng at feeding to hatchi ng to feeding 1 286 y = 0.159359 (x0578582 0.0480 4.7 5.5 1.966 0.624 2 249 y = 0.107496 (x0847936 0 0653 40 5.6 1.844 0.630 3 248 y = 0 133695 (x°860384 00446 4.7 5.7 1.733 0.694 4 373 y = 0.139619 (x0732'74 00537 3.2 61 2.172 0.715 5 321 y = 0 190165 (x0767B" 0.0537 32 6 1 2.172 0715 6 231 y = 0090892 (x°82885:> 00187 3.6 5.9 1.763 0633 7 210 y = 0 115968 (x0692893 00763 3.7 5.4 1 733 0580 'Daily instantaneous growth coefficients grams. loge W/days after fertilization where W = dissected tissue dry weight in micro- 466 ELDRIDGE ET AL.: BIOENERGETICS AND GROWTH OF STRIPED BASS 15-| S '0 O < I 10 15 20 25 DAYS AFTER FERTILIZATION 30 Figure 4.— Growth of four batches of feeding striped bass lar- vae measured in calories of assimilated tissue from first feed- ing (D-7) to D-29. tial for all fish groups (Fig. 7). Experiment 7 lar- vae were the heaviest per unit length and did nut attain the lengths that other larvae did. All lar- vae put on weight rapidly after reaching a stan- dard length of about 8 mm. Oxygen Consumption Metabolic rates of embryos and larvae are pre- sented in Figure 8. Embryos and prefeeding lar- vae had the highest Qo2's. After feeding began oxygen consumption stabilized and remained constant for the duration of the experimental period. On a weight-specific basis oxygen con- sumption increased with tissue dry weight and was best described by a power function (Fig. 8), although the relationship appears almost linear. o z < o z < 12-, 10- 6- 10 15 20 25 DAYS AFTER FERTILIZATION 30 Figure 5.— Growth of four batches of feeding striped bass lar- vae measured in standard lengths from first feeding (D-7) to D-29. 020-, o 0.15 O- 0.10- Z £ < o zu < 005 -i ' 1 0.5 1.0 FOOD CONCENTRATION NUMBERS (ml"1 ) Figure 6.— Instantaneous growth coefficients of four batches of feeding striped bass larvae that fed on six different food concentrations (0.00 to 5.00 Artemia/m\). Utilization Efficiency Gross caloric conversion efficiencies were highest from fertilization to initial feeding, fol- lowed closely by efficiencies during the embry- onic period (Table 6). Only in larvae from the highest food concentration did conversion effi- ciencies remain at elevated levels. Larvae feed- ing at the other food concentrations used their resources at levels under 20%, and their conver- sion efficiencies did not appear to correlate with food concentration. Starved larvae had the low- est efficiency and demonstrated negligible growth after D-7. Table 6. — Mean gross caloric conversion efficiencies (in per- cent) for striped bass embryos, prefeeding larvae, and larvae feeding at different prey concentrations. To To initial feeding Food concentrations (Artemia/m\) to 29 d after fertilization hatching 0.00 0.01 0 10 0.50 1.00 5.00 37.7 43.8 150 190 13.9 17.3 18.7 31.9 DISCUSSION Energy Inputs Striped bass eggs were found to be high in energy content and to vary considerably in size. Undoubtedly the high proportion of lipids (found mostly in the oil globule) makes the striped bass egg one of the most energy-rich of fish eggs. At 7,808 cal/g striped bass eggs exceed the caloric values of eggs from freshwater, anadromous, and marine fishes which normally range from 5,386 to 6,238 cal/g (Hayes 1949; Smith 1957, 467 FISHERY BULLETIN: VOL. 80, NO. 3 3.0-, 2.5- ~ 2.0H E 2 1.5- O 5 >- Q 1.0- 0.5- oJ Experiment 4 Y=0.00170543e r=0.97 (0.680339X) Experiment 5 Y=0.00600652e<0533521X> r = 0.96 (0.652494X) Experiment 6 Y=0.00236324e r = 0.93 Experiment/ Y=0.00121027e(° 796209X> r= 0.89 (0.631929X) Combined Y=0.0028787e r= 0.92 STANDARD LENGTH (mm) Figure 7.— Assimilated tissue dry weights and corresponding standard lengths of four batches of striped bass larvae. 1958; Fluchter and Pandian 1968; Blaxter 1969). Egg size variability was not unexpected as eggs are reported to vary within and among a variety of fish species (Clupea harengus, Blaxter and Hempel 1963; Sardinops caerulea, Lasker 1962; Trachurius symmetricus, Ware 1975; Theilacker 19804). It appears from studies of embryos and larvae with large oil globules that the energy from the oil is important to larval growth and survival, and the influence of this energy source is present 4Theilacker, G. H. 1980. A review of pelagic larval fish behavior and physiology. Presented at Institute del Mar del Peeru (IMARPE) Workshop, April 21-May 5, 1980. for long periods. In this study and that of Rogers and Westin (1981), striped bass larvae retained their oil energy reserves for extended periods, especially when starved. This is not common in fishes although similar retention of the oil glob- ule was noted in Bairdiella ieistia (May 1974a) and Leuresthes tenuis (May 1971; Ehrlich and Muszuski in press). The oil globule also seemed to help striped bass larvae avoid or prolong the typical point-of-no-return, the time of irrever- sible starvation (Eldridge et al. 1981). In a re- view of larval fish physiology, Theilacker (1980) concluded that in addition to egg size and acti- vity, egg lipid level relates most to larval resili- ence. 468 ELDRIDGE ET AL.: BIOENERGETICS AND GROWTH OF STRIPED BASS 6 4 o "5. y=00276310 r = 097 0721444 20 15 10 a. O 5^ 500 1000 1500 TISSUE DRY WEIGHT (ng) y = 000436581 + (00159775/x) r-088 10 20 30 DAYS AETER FERTILIZATION Figure 8.— Oxygen consumption of striped bass embryos and larvae plotted against assimilated tissue dry weight (above) and age (below). In an attempt to compare our laboratory de- rived estimates of daily food ration with those from wild striped bass larvae we obtained stom- ach content data of 1,468 field-caught larvae (sized to 11.9 mm SL) spawned from 1971 to 1973. The summarized data of Table 7 show wild larvae were smaller (4.0 to 4.9 mm) than labora- tory larvae (6.1 mm) at the time of first feeding. This is possibly due to differences in preserva- tion methods. When wild larvae attained sizes of 7.0 to 7.9 mm, over 75% were feeding. This agrees with our laboratory observation that over 80% of the 2-wk-old and older larvae (>7.0 mm SL) fed actively in food concentrations of 0.50 Artemia/ ml and greater. The overall average of feeding incidence for wild larvae was 70.5%. Wild larvae also displayed preference for cladocerans, Cy- clops sp. and Eurytemora sp., which, together, accounted for 89% of all food consumed. Other studies of striped bass from east coast nursery areas showed that the largest part of the larval diet consisted of small Crustacea and microplank- ton (Meshaw 1969; Humphries and Cumming 1972). Using these data we calculated daily caloric rations, according to the previously described formula, for each size category of wild larvae (Table 7). Caloric equivalences for the different food types were obtained from the literature (Richman 1958; Cummins 1967; Clutter and Theilacker 1971; Laurence 1976; Sitts 1978). In- Q..2 00 o u bo -2 .£; u 4) ■s >> cB j» -O o "55 ^* 4) j_ 3 CB ■33 BJ ■v c cb c/i 1) O. c 4 E cB 3 .2 8 U -t_> o « 13 i2 o a, lH at co > t> '5 . E w o o to to c/3 o 4) c C « — CO N fed m CO - .2 * c -s . -_- 0 TO O) C7) U > ca " — *- c O 0 » 0 CO (0 ■O CD >. c —> ro — O •=, E (0 «- cj to B«" LU O , *- 16 c - c 0 1- calo equ vale CO ■D 0 2 en Q- — a> 5 Q- 0 0 0 (O (O "O 8-5 -o =1 E LU 4> 1 . O • CO 0 c "O (0 ca «- — CO O 0 0% w 13 0 £ O a ■ co O K a) >. Z E CO •c C-F, C= — u 5 -a ™ 5 0 E #00 to _ 11 arva size m S -1 E '"— ' Or OlOS . 1 1 co m oj tj o < I I >- •- m c\j to i oddf-N'- CD^OWSCBO)^ ^O^IOCMCOOLO COCOOi'-tDOCDT- Oi-^-c\JCNJc\ico-»* h^C7>r^T^CDCDO)C7> 00*>»-l/>COt7>C3CO '-cvjcocO'^-Tj-mto o 0 o o d o 000 pooooooo oddddoddd 000000000 00000000 00000000b 000000000 000000000 OOO'-OCMI^SS *-cDcooc\jc\jogco obdOT-^^^^ OOOOOO*---'- '-0>0'-'^COCSJCO OO'-'-'-t-CNJCM dddodddd 000000000 ^(DlfiSCDSnO) O 03 03CJ)CT)03C7)03CJ)q^: cd^idcdr^cdd'-'- ooooopppp co ^incDNCooiOT- 469 FISHERY BULLETIN: VOL. 80, NO. 3 formation on natural feeding duration was taken from Miller,5 which showed that wild larvae feed 24 h a day but feed more intensely during crepus- cular periods. Evacuation rate was set at 5 h, a compromise between our estimate of 3.3 h for larvae fed Artemia at 18°C and the estimate of 1 1 to 12 h made by McHugh and Heidinger (1977) for larvae given Artemia and held at 25°C. Daily caloric rations for wild larvae range from 0.646 cal for smaller larvae to 4.151 cal for 11.0 to 11.9 mm SL larvae. These rations are higher than those of laboratory larvae. Except for the largest cultured larvae, rations were usually one-half the field larvae rations. Thus within equivalent size categories wild larvae appear to have daily rations substantially greater than those of cul- tured larvae. Other estimates of daily rations of striped bass larvae range widely. Miller (foot- note 5) concluded that field-caught larvae (6.8 to 9.2 mm SL) consumed rations equivalent to 0.159 cal for rotifers or up to 2.958 cal for cladocerans. Doroshev (1970) estimated daily intake of labora- tory-reared larvae to be 9.704 to 29.112 cal, con- sisting of Cyclops nauplii or small copepods. Our average calculated daily estimates for the differ- ent food concentrations for the 29-d experimental period fall within Miller's estimates of wild lar- vae (Table 8). Table 8. — Mean daily caloric rations of striped bass larvae given five different food densities from D-7 to D-29. Food density Mean overall daily caloric ration (Arlemia/m\) (calories/larva per d) 0.01 0035 0.10 0.439 0.50 0802 1.00 0.823 5.00 1 313 Energy Outputs Our results suggest that there is compensatory growth in embryos and larvae that offsets initial egg size differences. The size ranges are not as broad in newly hatched larvae and larvae at first feeding (D-7) (seen in Table 5) as they are in the eggs. Likewise, initial egg size corresponds bet- ter to the size ranking of larvae at hatching age than it does to larvae at feeding age. The mean instantaneous growth coefficient during the 2-d embryonic period was 1.872 with a coefficient of 5Miller, P. E., Jr. 1978. Food habit study of striped bass post yolk-sac larvae. The Johns Hopkins University, Chesa- peake Bay Institute, Spec. Rep. 68, Ref. 78-8. variation (C. V.) of 8.5% (Table 5). From hatching to first feeding it was 0.647 with a decreased C.V. of 7.0%, an indication of narrowing diversity. Further compensatory growth was seen in tissue weights and standard lengths of feeding larvae (Figs. 4, 5), and convergence of sizes was seen in all food concentrations above 0.10 Artemia/m\. Weights were similar on D-25 and lengths on D- 27. In the two higher food concentrations, sizes converged by D-17. Compensatory growth was documented years ago in salmon fry (Hayes and Armstrong 1942), so this is not necessarily unique to striped bass. Theilacker (in press) more recently found that growth rates of jack mackerel larvae varied with egg size. Growth of feeding striped bass larvae was clearly tied to exogenous food consumption as seen in Figure 6. This relation is well established in other larval fishes (O'Connell and Raymond 1970; Saksena and Houde 1972; Laurence 1974; May 1974a; Houde 1977; Taniguchi in press). Growth rates of our larvae, especially those in the higher food concentrations, are similar to findings with other populations of striped bass (Rogers et al. 1977). The most comparable study (Daniel 1976) included continuous introduction of Artemia for 10 d in concentrations of 0.004 to 0.030 nauplii/ml. Twenty-five days after hatch- ing larvae grew to an average standard length of 8.5 mm. Fish used in the present study were longer than Daniel's in the two higher food con- centrations and smaller in the three lower con- centrations. As in our study, Daniel's larvae also grew directly in relation to food density. Tissue weights of Daniel's fish fed the 0.008 and greater Artemia/ml concentrations approximated those of our fish fed concentrations of 0.005 and above. Our larvae that fed at 5.0, however, were all heavier than Daniel's larvae. Lai etal.( 1977) also cultured California striped bass larvae but in varying salinities. Larvae of comparable age feeding on Artemia (densities unreported) were similar to our larvae from the 0.50 nauplii/ml. Larvae from our higher densities were larger. Oxygen consumption measurements varied directly with size, age, and temperature. Be- cause temperature was held constant in all tests, age and size were the most influential factors affecting oxygen consumption, and these factors produced distinctive patterns. The high meta- bolic rates (Qo2's) demonstrated by embryos and newly hatched larvae were probably the results of the activity accompanying hatching and of the high metabolic needs associated with rapid tis- 470 ELDRIDGE ET AL.: BIOENERGETICS AND GROWTH OF STRIPED BASS sue growth and differentiation. These needs re- mained high into the period of feeding transfor- mation and then leveled off to nearly constant rates after D-10. Similar patterns have been seen in other fishes (Smith 1957; Blaxter 1969). The relation of oxygen consumption to weight is usu- ally described in a log-log transformation with a slope approximating 0.8 (Winberg 1956). Our slope of 0.72 shows that our equation describes the weight-metabolism relation up to the final size encountered. Laurence (1977) found winter flounder metabolism profoundly changed after metamorphosis resulting in a curvilinear pat- tern described best by a third degree polynomial equation. It is likely that striped bass would show similar tendencies when measured further along in development. Reviews (Blaxter 1969; Eldridge et al. 1977) show that efficiencies during the strictly endoge- nous energy period of embryos and prefeeding larvae ranged from 40% to 70%. Our findings with striped bass tended toward the low side of this range. Micropterus salmoides was most similar to striped bass, with efficiencies of 35.2% to hatching and 43.9% to feeding (Laurence 1969). Like those of striped bass, the eggs of M. salmoides also possess large oil globules, and their larvae have similar predatory behavior. Gross growth efficiencies of aquatic consumers in general normally fluctuate between 15% and 35% (Welch 1968). Efficiencies of larval and post- larval fishes have also been found to be within this range (Ivlev 1939a; Laurence 1973, 1977). Ivlev (1945) believed postembryonic stages were restricted to efficiencies <35%, and fish nor- mally have decreasing efficiencies with age (Parker and Larkin 1959; Theilacker footnote 4). All our efficiency values support these conclu- sions. Whether feeding or not, our older larvae had lower conversion efficiencies, probably re- sulting from increased metabolic demands asso- ciated with greater activity. All organisms must balance input and output energies to successfully survive, grow, and ulti- mately reproduce. The essential relations between input and output energies and the equa- tion which balances them have been well dis- cussed by several authors (Winberg 1956; War- ren and Davis 1967; Warren 1971; Wiegert 1976). This paper presents data that make up the basic parameters of an energy budget. The basic relation of these components can be presented in: where Qi = input energies, whether endoge- nous, exogenous, or a combina- tion of the two Qw = waste energy Qa — growth energy Qm = metabolic energy. All but Qw have been studied by us, and the effects of food density and initial egg size have been discussed. In Figure 9 we present a graphic- model of the energy budget of striped bass em- bryos and larvae fed the high ration diet (5.0 Artemia/mX). This model approximates that of Laurence (1977) except that we include input energies of yolk and oil, and we present the rela- tions against time as rates (i.e., calories con- sumed or expended per 24 h period per organ- ism). When the energy budget is presented in these terms, some distinctive patterns emerge. Yolk provides a constant energy input until it is ex- hausted on or about D-7. Oil is used rapidly at first, then more slowly until yolk energy is no longer available and the animal initiates feed- ing. At this time, the larva increases its use of oil 10 < 10 o < O > D Z */» — cc o t o.i \ \ A S vcar • Yolk I i _1_ T" 6 12 18 24 DAYS AFTER FERTILIZATION 30 Qi = Qw+QG + Q M Figure 9.— Energy budget of input calories (yolk, oil. and food) and output calories (growth, metabolism, and nonassimilation) presented in calories per individual embryo or larva per day. 471 FISHERY BULLETIN: VOL. 80, NO. 3 until exogenous feeding becomes established, after which it gradually decreases consumption of oil until oil energy is depleted. An initial adjustment to exogenous energy intake is fol- lowed by a continuously increasing exogenous input concomitant with decreased reliance on oil energy. Growth showed an interesting pattern that suggested it is closely linked to oil energy prior to feeding and to exogenous food energy after initiation of feeding. Growth rates declined steadily to D-6 and increased abruptly there- after. Metabolism increased steadily during incuba- tion and hatching. After the energy consuming hatching process it decreased slightly to the on- set of feeding. After D-7, increasing activity associated with feeding resulted in continuously increasing metabolism. Nonassimilation is the energy remaining after metabolism and growth are subtracted from the total energy input. When energy input is endoge- nous, nonassimilation comprises poor utilization and/or redeposition of yolk and oil into other tis- sues. Nonassimilation of exogenous food is mostly due to undigested food. In this model non- assimilation fluctuated with oil input energy and growth to first feeding. It increased during adjustment to feeding and declined when both oil and food calories were available. As Artemia be- came the main energy source nonassimilation in- creased. Poor digestion in older larvae in the form of nearly intact Artemia in the intestines was seen commonly, especially in the high food rations. The bioenergetics model and its parameters are presently being used to measure various abiotic and biotic stresses, including pollutants. It promises to be a useful method for assessing the effects of these factors. ACKNOWLEDGMENTS Many individuals, to whom we are indebted contributed to the research in this paper. We especially wish to thank Michael D. Cochran and Donald E. Stevens, and their colleagues, of the California Department of Fish and Game, for continuous support and assistance in our work. LITERATURE CITED Blaxter, J. H. S. 1969. Development: eggs and larvae. In W. S. Hoar and D. J. Randall (editors), Fish physiology, Vol. Ill, p. 177- 252. Acad. Press, N.Y. 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Striped bass (Morone saxatilis) monitoring tech- niques in the Sacramento-San Joaquin Estuary. In W. Van Winkle (editor), Proceedings of the conference on assessing the effects of power-plant-induced mortality on fish populations, Gatlinburg, Tenn., May 3-6, 1977, p. 91-109. Pergamon Press, N.Y. 1977b. Striped bass (Morone saxatilis) year class strength in relation to river flow in the Sacramento-San Joaquin Estuary, California. Trans. Am. Fish. Soc. 106:34-42. 1980. Factors affecting the striped bass (Morone saxa- tilis) fisheries of the West Coast. Presented to Fifth Annual Mar. Rec. Fish. Symposium, March 1980, Bos- ton, Mass. Taniguchi, A. K. In press. Survival and growth of spotted seatrout (Cy- 473 FISHERY BULLETIN: VOL. 80, NO. 3 noscion nebulosus) larvae in relation to temperature, prey abundance and stocking density. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178. ' Theilacker, G. H. In press. Effect of feeding history and egg size on the morphology of jack mackerel, Trachurus symmetricus, larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178. Toetz, D. W. 1966. The change from endogenous to exogenous sources of energy in bluegill sunfish larvae. Invest. Indiana Lakes Streams 7:115-146. Ware, D. M. 1975. Growth, metabolism and optimal swimming speed of a pelagic fish. J. Fish. Res. Board Can. 32:33-41. Warren, C. E. 1971. Biology and water pollution control. W.B.Saun- ders Co., Phila., 434 p. Warren, C. E., and G. E. Davis. 1967. Laboratory studies on the feeding, bioenergetics, and growth of fish. In S. D. Gerking (editor), The bio- logical basis for freshwater fish production, p. 175-214. J. Wiley and Sons, N.Y. Welch, H. E. 1968. Relationships between assimilation efficiencies and growth efficiencies for aquatic consumers. Ecol- ogy 49:755-759. Wiegert, R. G. (editor). 1976. Ecological energetics. Dowden, Hutchinson, and Ross., Inc., Stroudsburg, Pa., 457 p. Winberg, G. G. 1956. (Rate of metabolism and fishes.) [In Russ.] Nauch. Tr. Imeni V.I. Lenina, Minsk, 253 Can. Transl. Ser. 194, 239 p.) food requirements of Belorussk. Gos. Univ. p. (Fish. Res. Board 474 STOCK AND RECRUITMENT RELATIONSHIPS IN PANULIRUS CYGNUS,* THE COMMERCIAL ROCK (SPINY) LOBSTER OF WESTERN AUSTRALIA G. R. Morgan,2 B. F. Phillips,3 and L. M. Joll* ABSTRACT r Abundance of the breeding stock, level of settlement of the puerulus stage, juvenile densities and recruits to the fishery for Panulirus cygnus from 1969 to 1979 are examined. A dome-shaped relationship between the index of abundance of the breeding stock and subsequent puerulus settlement indicates that stock-dependent effects during the planktonic larval stages apparently control the level of puerulus settlement. However, density-dependent relationships (characterized by more asymptotic relationships between the various life history stages) dominate after settlement of the puerulus on the coastal reefs and control the level of recruitment to the fishery and eventually to the breeding stock. The relationship between the settlement of the puerulus stage and the catch rates of the recruits entering the fishery 4 years later is adequately described by a Ricker's stock-recruitment curve as is the level of puerulus settlement to the subsequent abundance of the breeding stock. The relationship between the level of puerulus settlement and the later abun- dance of juveniles at various ages is not clear and possible reasons for this are suggested. The significance of the stock-dependent relationship between breeding stock and puerulus and the density-dependent relationship between puerulus and breeding stock in maintaining recruitment to the fishery is discussed. The importance of understanding the stock-re- cruitment relationship in exploited fish popula- tions has been recognized for many years and has been the subject of several workshops and sym- posia (e.g., Parrish 1973), as well as a great deal of research. While the importance of such rela- tionships in exploited invertebrate stocks has been equally recognized, quantitative data, par- ticularly for crustaceans, has been virtually non- existent (Hancock 1973). Like many fish species, crustaceans in general and spiny (rock) lobsters in particular, pass through several distinct stages in their life his- tory and, as Hancock (1973) pointed out, a proper understanding of the overall stock-recruitment relationship can be gained only by considering the relationship between successive stages over a number of years. Hancock's belief is reinforced by the studies of Larkin et al. (1964) and Paulik (1973) who, having considered the theoretical 'The western rock lobster is referred to as P. longipes or P. longipes cygnus in some of the literature quoted; these are synonymous with P. cygnus. department of Fisheries and Wildlife, 108 Adelaide Ter- race, Perth, 6000, Western Australia. 3CSIRO, Division of Fisheries Research, P.O. Box 21, Cro- nulla, N.S.W. 2230 Australia. 4CSIRO, Division of Fisheries Research, P.O. Box 20, North Beach, W.A. 6020 Australia. Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80. NO. 3, 1982. forms of a stock-recruitment relationship in- volving such multistage life histories, showed that several stable equilibrium points can exist in the overall spawning stock-recruitment curve, depending on the relationships existing between the various life history stages. The western rock lobster, Panulirus cygnus George, the object of an important fishery in Western Australia (Morgan and Barker 1979) passes through several major stages during its life history. These include a series of phyllosoma larvae, a puerulus stage, and juvenile and adult stages. After a planktonic life of 9-11 mo (Chittle- borough and Thomas 1969; Phillips et al. 1979), the surviving phyllosoma larvae metamorphose into a puerulus stage and settle between Septem- ber and January each year in shallow coastal areas. The younger juveniles concentrate on shallow limestone reefs to depths of 10 m, with some larger juveniles to 20 m. At about 4 or 5 yr of age (i.e., 4 or 5 yr from hatching) juveniles mi- grate from the shallow reef areas onto the conti- nental shelf into depths of 30-150 m where ma- turity is reached, mating takes place, and the life cycle is completed. Chittleborough and Phillips (1975) reported that, based on the data available at that time, in- dices of year-class strengths obtained from the 475 W- HYU. FISHERY BULLETIN: VOL. 80, NO. 3 puerulus at settlement and those derived from measurements of density of juveniles of P. cygnus aged 2 or 3 yr were consistent. However, they found survival to recruitment into the fishery did not mirror the pattern of year-class strength at or soon after settlement. The purpose of this paper is to examine the changes that take place in the abundance of the various stages in the life history of P. cygnus including data on puerulus settlement and juvenile density and to investi- gate their interrelationships. METHODS The abundance of the several stages in the life history of P. cygnus has been measured by vari- ous methods over a number of years. The meth- ods used have reflected the practical problems of sampling the different stages and have included catch and fishing effort data from the commer- cial fishery for the adult stage, collectors com- posed of artificial seaweed to catch the puerulus stage, and mark and recapture studies of the juveniles using baited traps. All ages and year classes referred to in this paper relate to the year of hatching and so include the 9-11 mo larval phase. For example, the 1969 year class was hatched in January-February 1969 and settled as puerulus larvae between September 1969 and January 1970. Abundance of the Breeding Stock The western rock lobster is confined to the western coast of Australia from approximately North West Cape to Cape Naturaliste (Fig. 1). The majority of the commercial catch is taken between lat. 28° and 32°S (Sheard 1962). The coastal fishery operates from 15 November to 30 June of the following year although prior to 1978 the coastal season concluded on 14 August each year. The Abrolhos Islands fishing season which extended from 15 March to 14 August prior to 1978, now also ends on 30 June. The abundance of the breeding stock (i.e., those females carrying external eggs) has been measured since 1966 from research logbook data supplied on a voluntary basis from about 200 boats or 25% of the commercial rock lobster fleet. In addition to catch, fishing effort, and fishing locality information separated into four depth categories, i.e., 0-10, 10-20, 20-30, and over 30 fathoms, each fisherman records his daily catch of numbers of spawning female rock lobsters. 20° S 2V 28' 32' 36' North West Cape Indian Ocean Abrolhos Islands':. Rat Is/* Rottnest /s. Garden Is. Cape Naturaliste 108° E 112' 116' 720° FIGURE 1.— Location of the sites mentioned in the text. However, these data are not available from the Abrolhos Islands for December, January, and February since this area is closed to commercial fishing at this time each year. Consequently, comparable data on the breeding stock had to be obtained from research vessel cruises to each of the four island groups of the Abrolhos during January and February 1979. Sixty commercial wire beehive pots without escape gaps were set each day for a total of 20 d on the fishing grounds where the greatest concentration of spawning females is to be found. The pots had previously been calibrated in the Garden Island area (Fig. 1) by comparison with commercial catch rates of spawning females. During the comparison, catch rates of spawning females were low (mean of 0.05 animals/pot) and the variances relatively large so it is not surprising that no significant difference (at the 5% level) could be detected be- tween the catch per pot lift of spawning females by the research vessel's pots and the catch per pot lift of spawning females by commercial fish- ermen's pots. However, additional calibration of the research vessel's pots would add confidence to this conclusion. 476 MORGAN ET AL.: STOCK AND RECRUITMENT RELATIONSHIPS IN PANUURUS CYGNUS Abundance of the Puerulus Stage Phillips (1972) showed that the last larval stage, the puerulus, of P. cygnus could be cap- tured using collectors composed of artificial sea- weed moored at the surface within the protection of the coastal reefs. Subsequent studies by Phil- lips and Hall (1978) have shown that the catches from these collectors provide a measure of the relative strength of settlement from year to year. All collectors used in this study were as de- scribed by Phillips (1972). The collectors were checked monthly after each new moon period when most puerulus settled. All settlement took place at the puerulus stage. The western rock lobsters were removed from the collectors either as puerulus or after they had molted into very small postpuerulus juveniles. Since the plank- tonic period is 9-11 mo, settlement occurs be- tween September of the year of hatching and the following January. Abundance of Juveniles Density of age groups (ages 2-7 yr) has been measured on shallow test reefs at Garden Island (since 1965) and Seven Mile Beach (since 1970), using the single census trap-mark-recapture method described by Chittleborough (1970). These test reefs are adjacent to the collectors used to catch the puerulus stage. Abundance of Recruits to the Fishery During late November of each year, large numbers of immature, newly molted, pale col- ored rock lobsters migrate into deeper water from the shallow water inshore reefs (which are generally inaccessible to fishermen) where they have spent the previous 4 or 5 yr. This offshore movement normally lasts through December and in all lasts about 6 wk. Since they are newly molted, their food requirements are high (Chit- tleborough 1975) and consequently their catch- ability by baited pots is high (Morgan 1974). During this migration the fishermen catch large quantities of these animals which are locally known as the "whites" (George 1958). Although a small number of animals undergo two or per- haps three "white" phases in their life cycle, the "white" phase generally occurs only once during an individual's lifetime (George 1958), and this enables the migrating "whites" to be equated with the recruits to the fishery. Estimates of the abundance of the potential emigrants from the shallow reefs have been made by Chittleborough (1970), although a better measure of their abundance is available from the catch rate (measured as the catch per pot lift) of the commercial fishery during November and December when practically all of the commer- cial catch consists of "white" rock lobsters. Infor- mation on catch and fishing effort for November and December each year has been taken from the fishermen's monthly returns, which are com- pleted as a condition of the fishing license by all fishermen. RESULTS Since there have been several customs adopted in the designation of year classes in P. cygnus (e.g., Chittleborough 1970; Morgan 1977) a sum- mary of the convention used in this paper will enable the various relationships presented below to be followed more easily. The convention used and the major events in the life history of P. cygnus are as follows: Hatching of eggs Settlement of puerulus larvae Juveniles on inshore reefs Migration of "whites" to offshore areas Maturity and first breeding November, December year x — 1, January, February, and March year x, with midpoint taken as 1 Janu- ary of year x. September year x to Janu- ary year x + 1. Year x + 1 to x + 4 and x+5 (ages 1 to 4 or 5). November and December year x + 4 and x + 5, with the majority being x + 4. January and February year x + 6 and x + 7, with the majority being x + 6. Stock Definition Based on similarities in catch rates from the commercial fishery, Morgan (1977) concluded that although some population parameters such as growth rates, size at first maturity, etc. varied between localities, the western rock lobster could, as a first approximation, be considered as a single, genetically coherent, unit stock. This view is reinforced by the studies of Phillips et al. (1979) who demonstrated the wide dispersal of 477 FISHERY BULLETIN: VOL. 80, NO. 3 the phyllosoma larvae in the eastern Indian Ocean. Consequently, in the following analyses a single stock has been assumed, although latitudi- nal differences in some population parameters have necessitated a simple division of the fishery into areas north of lat. 30°S and south of lat. 30°S. The Breeding Stock From the research logbook information, it was evident that spawning rock lobsters were con- centrated in the 20-30 fathom depth range with an average of 89. 9% of the total catch of spawning females each year being taken in this depth range during the period 1966-80. Year-to-year variation was small with the percentage ranging from 86.4% in 1971 to 92.1% in 1967. In addition, the majority of spawning female rock lobsters (average of 81.4% for the period 1966-79) were captured during January and February each year with, again, little year-to-year variation. Accordingly, the catch per pot lift of spawning females taken in 20-30 fathoms in January and February each year has been used as a basis for the calculation of an index of abundance of spawning females. No adjustment for soak time was made since catch per pot lift has been shown to be independent of soak time (Morgan 1977). The use of catch per pot lift data as an index of abundance assumes, of course, that catchability remains constant from year to year. Morgan (1974) has shown that catchability varies during a year in response to molt condition, water tem- perature, and water salinity. Year-to-year varia- tion in catchability of spawning P. cygnus fe- males for January and February is likely to be small, since it would be expected that these ani- mals would be in an intermolt condition, and year-to-year temperature and salinity variation on the spawning grounds in January and Febru- ary is small (Morgan and Barker 1979). The average size of the spawning females var- ies with locality, being larger in southern areas (Morgan and Barker 1979). Average size infor- mation on spawning females has been collected on a regular basis since the 1971-72 season from commercial vessels fishing out of the ports of Dongara, Jurien Bay, Lancelin, and Fremantle (Fig. 1). These data have been previously pre- sented in a series of annual reports on the fishery (e.g., Morgan and Barker 1979). Occasional col- lections of size composition data of spawning fe- males were made prior to the 1971-72 season, particularly at Jurien Bay and Lancelin (B. K. Bowen, unpubl. data). These two sources of data have been used to calculate the average size of spawning female P. cygnus for various years. The relationship between size and fecundity (Morgan 1972) has then been used to calculate the number of eggs produced by a spawning fe- male rock lobster of this average size. Panulirus cygnus spawns only once per year in most areas in the wild (Morgan 1980b). Data on the catch rates of spawning female P. cygnus taken in 20-30 fathoms in January and February each year, the mean size of these spawning females, and the resultant fecundity are shown in Table 1, separated into two areas: north of lat. 30°S and south of lat. 30°S. Index of Abundance of Spawning Stock The most appropriate index of spawning suc- cess in P. cygnus is the number of first stage phyl- losoma larvae released during the hatching peri- od. However, since it has not been possible to measure phyllosoma abundance directly, an in- direct measure, utilizing the abundance and fecundity of the spawning females, is necessary. Thus the total number of first stage phyllosoma larvae released is approximately equal to (total number of spawning females) X (their average fecundity). The number of spawning females in each of the two coastal areas (north and south of lat. 30°S) may be estimated from their catch rate (a mea- sure of density) multiplied by the area of the spawning grounds. The area of the spawning grounds for coastal localities north and south of lat. 30°S is given in Table 2. Thus, for example, a measure of the total number of spawning females north of lat. 30°S in 1966 is given by 0.44 (from Table 1) X 6,690 (from Table 2) = 2,943.6. It should be noted that this measure gives a rela- tive, not an absolute, figure for the numbers of spawning females since a knowledge of the catch- ability coefficient per unit area, q, would be necessary to convert catch rate (c/g) into absolute numbers (N) by using the relationship c/g qX N where A = area of the spawning grounds. Catchability has been measured at the Abrol- 478 MORGAN ET AL.: STOCK AND RECRUITMENT RELATIONSHIPS IN PANULIRUS CYGNUS TABLE 1.— Catch (numbers) per pot lift of spawning female Panulirus cygnua taken in 20-30 fathoms in January and February each year (c/g), the mean size of the spawning females (S) (in millimeters carapace length), and the resultant fecundity at this size (F), for two coastal areas. The method of calculation of the index of abundance of the breeding stock (I. A. S.) is explained in the text. NA = Not yet available. Coastal areas north Coastal areas south All coastal All coastal and of lat. 30° S of lat 30' S areas Abrolhos areas Year c/g S (mm CL) F c/g S (mm CL) F IAS. (X 107) IAS. (X 107) 1966 044 0.53 174 198 1967 0.61 92.2 321.710 0.33 179 204 1968 050 902 302,110 065 205 234 1969 0.49 028 146 166 1970 0.40 0.34 136 155 1971 0.23 0.23 84 96 1972 0.48 929 328,570 0.16 104.3 440,290 125 143 1973 022 90.5 305,050 0.15 104 6 443,230 69 79 1974 0.12 91.3 312,890 0.08 106 4 460,870 37 42 1975 0.14 94.5 344,250 0.13 105 0 447,150 49 56 1976 0.16 93.5 334,450 0.13 104 0 437,350 54 62 1977 0.24 920 319,750 016 1039 436,370 75 86 1978 024 928 327,850 0.11 104.6 443,230 67 76 1979 0.27 NA 0.17 NA 83 95 1980 0.19 NA 0.11 NA 56 64 Table 2.— Comparison of egg production estimates for coastal areas north and south of lat. 30°S and the Abrolhos Islands area for 1979. Abrolhos North of lat 30°S South of lat. 30°S Total Area of spawning grounds from Admiralty charts (km2) (A) 840 6,690 3,500 11,030 Average size of spawners 74 94 105 (mm carapace (research (Morgan and (Morgan and length (B)) cruise data) Barker 1979) Barker 1979) Fecundity (from Morgan 1972) (C) 143,300 339,300 447,150 Catch per pot lift of 1.16 0.27 0.17 spawning females (from research (from fishermen's (from fishermen's (D) vessel) log books) log books) Relative numbers A X D (E) 974 1,906 595 Egg production X 107, EXC(F) 13.99 61.29 26.60 101.88 Percentage egg production 14% 60% 26% 100% hos Islands (Morgan 1974) but it has not been considered necessary to introduce additional assumptions by converting relative to absolute numbers. From Table 1, it is apparent that for each area the average size of spawning female P. cygnus has remained approximately constant for the years for which data are available, although significant differences are apparent between the two coastal areas. Consequently, the mean value of the yearly average sizes for each area has been taken and used to calculate average fecundity for the years 1966-80 using the relationship given by Morgan (1972). These values are north of lat. 30°S, CL 92mm (fecundity 319,750) and south of lat. 30°S, CL 105 mm (fecundity 447,150). Calcu- lation of an index of abundance of the spawning stock for each coastal area each year can now be made while summation for each year gives the index for all coastal areas. These are as follows: North of lat. 30°S: Catch rate X 6,690 X 319,750. South of lat. 30°S: Catch rate X 3,500 X 447,150. All coastal areas: Catch rate (north of lat. 30°S) X 6,690 X 319,750 + catch rate (south of lat. 30°S) X 3,500 X 447,150. Annual indices of abundance of the spawning stock for all coastal areas are shown in Table 1. It should be noted that this is a more refined index than that used by Morgan (1980a). During the research vessel cruises in the Abrolhos Islands area in January and February 1979, the average catch per pot lift of spawning females was 1.16 or about six times that of coastal areas. However, as shown in Table 2, the small geographical area and the smaller average size of spawning female P. cygnus reduces the appar- ent importance of the Abrolhos Islands area, both in terms of the number of spawning females 479 FISHERY BULLETIN: VOL. 80, NO. 3 and their egg production, when compared with the coastal areas. The Abrolhos Islands area, therefore, contrib- uted only about 14% of total egg production in 1979. No data on the catch rates of spawning fe- males at the Abrolhos Islands are available for years other than 1979, so it has had to be assumed that the Abrolhos Islands area contributed 14% of the total egg production in each year from 1966, although year-to-year variation in the geo- graphical distribution of settling puerulus lar- vae will no doubt change this value to some extent. The index of abundance of the spawning stock for all coastal and Abrolhos Islands areas has therefore been estimated by multiplying the coastal index for each year by 1.14. These values are also shown in Table 1. Abundance of Puerulus Stage The relative densities of settlement of the puerulus stage (expressed as the mean number per collector settling between September and January at Rat Island (Abrolhos Islands), Seven Mile Beach, Jurien Bay, and Garden Island) are given in Table 3. The data for the different sites have been pooled as an unweighted arithmetic mean and expressed as the mean number of puerulus settling on the collectors, to provide an annual index of settlement. Abundance of Juveniles Estimated densities of various year classes at Garden Island and Seven Mile Beach were calcu- lated as described by Chittleborough and Phil- lips (1975) (Table 4). Abundance of Recruits to the Fishery The catch per pot lift of "white" rock lobsters taken during November and December has var- ied during the years 1964-78 (Table 5) and has re- sulted in similar variations in total catch from the fishery (Table 6). The Relationships Spawning Stock and Puerulus Settlement Since the peak of puerulus settlement each year occurs from September to January (Phillips and Hall 1978) and is the result of spawning in the previous January and February (Chittlebor- ough and Phillips 1975), the settlement of pueru- Table 3.— Mean number of puerulus settling per collector. — = not measured. Year of Index annual Rat Seven Mile Jurien Garden hatching settlement Island SE Beach SE Bay SE Island SE 1969 9.7 — 15.2 190 4.2 1.07 — 1970 22.4 '358 894 35.0 2.72 17.8 5.00 0.8 0.85 1971 388 47.5 3.12 67.3 500 34.7 4.50 2.5 1.90 1972 35.7 688 390 33.7 3.14 396 3.12 0.8 0.85 1973 71.4 73.8 6.07 83.2 4.74 117.4 10.96 11.0 3.06 1974 126.3 130.8 883 159.8 1248 2096 2204 5.1 2.55 1975 73.2 105.8 8.60 97.3 6.03 79.6 6.07 10.2 2.25 1976 72.3 1068 7.09 114.3 7.77 656 5.67 26 0.81 1977 68.4 112.8 785 860 7.01 722 681 2.4 060 1978 114.5 1826 19.33 182.8 1169 82 4 6.53 10.2 2.59 1979 71.0 102.5 7.42 76.2 4.28 944 16.74 11.0 2.67 Table 4.- 'Converted from two collectors to a different set of four collectors to ensure compatability with later samples -Estimates of year-class strength (no./ha) for juvenile western rock lobsters on nursery reefs (in January). — measured; NA = not yet available. not Age (yr) 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 Garden Island 2 — 3.800 4,400 1.400 500 1,200 700 150 1,500 2,600 404 1,932 1,246 2,381 957 1,340 3 3,245 1,070 3,324 317 265 875 537 92 971 1,200 274 1.053 765 969 630 1,300 4 921 810 730 174 195 685 333 60 448 813 149 646 311 638 611 NA 5 697 178 401 128 152 424 217 28 304 443 91 366 205 618 NA NA Seven Mile Beach 2 — — — — — 6.200 6,100 5,100 12.100 1 1 ,767 29.869 9,952 5,449 40,163 29.503 3 — — — — — 5,779 3,825 2,318 2.135 7,591 5,460 4.316 5,012 2,828 6.145 4,986 4 — — — — 3.540 1,461 978 1.339 3,522 789 2,174 2,598 433 1,039 NA 5 — — — — — 1,352 616 613 621 509 397 1,127 397 73 NA NA 480 MORGAN ET AL.: STOCK AND RECRUITMENT RELATIONSHIPS IN PANULIRUS CYCNUS Table 5.— Catch (kg) per pot lift of rock lobsters taken by the commercial fishery during November and December for the years 1964-79. Year Catch (kg)/pot lift Year Catch (kg)/pot lift 1964 1 300 1972 1.057 1965 1 344 1973 0.674 1966 1.352 1974 0997 1967 1.713 1975 1.115 1968 1.304 1976 1.079 1969 0973 1977 1.238 1970 1.001 1978 1.443 1971 1.029 1979 1.364 Table 6.— Total catch for the western rock lobster fishery. Total catch Total catch Season (kg < 106) Season (kg - 106) 1965-66 8.120 1973-74 6780 1966-67 8635 1974-75 8.877 1967-68 9853 1975-76 8731 1968-69 8078 1976-77 9 281 1969-70 6918 1977-78 10742 1970-71 8013 1978-79 11.429 1971-72 8.171 1979-80 10698 1972-73 6 809 INDEX OF SPAWNING STOCK Figure 2.— The Flicker (1958) stock-recruitment model, to- gether with 95% confidence limits. The model is fitted to data on the index of abundance of spawning Panulirus cygnus and the resultant level of settlement of the puerulus stage. The year shown is the season of hatching of the larvae. lus in year x (plus January of year x + 1) may be compared directly with the index of abundance of the spawning stock (I.A.S.) in year x. The Ricker (1958) stock-recruitment relation- ship of R - AS exp(-BS), where R = recruit- ment, S = stock size, A = coefficient of density- dependent survival, and B = coefficient of den- sity-independent mortality, was fitted using the method of Cushing and Harris (1973). The rela- tionship is shown in Figure 2 and provides a good fit to the observed data (proportion of sum of squares explained is 0.775). Estimates of A and B with their standard errors (SE) are A = 7.645, SE = 2.193 and B = 0.026, SE = 0.004. Puerulus and Juvenile Densities The relationship between puerulus and juve- nile densities is not clear. In contrast to the state- ment of Chittleborough and Phillips (1975) that puerulus settlement is a good indicator of subse- quent juvenile density, the additional data avail- able for Seven Mile Beach (Table 7) indicate that the correlation between puerulus settlement and the subsequent density of 2-yr-old juveniles is poor ( r = 0.359, P>0.05). Neither do the data give an acceptable fit to a Ricker ( 1958) stock-recruit- ment curve. The same conclusion is reached from examination of Garden Island data (Tables 3, 4) ( r = 0.528, F>0.05). For example, relatively high settlement of puerulus at Seven Mile Beach in 1974 and 1977 (Table 7) when total juvenile den- sity was also high gave rise to very poor and very high densities, respectively, of 2-yr-olds. Beyond 2 yr of age, however, density-dependent mortal- ity is evident. At both Garden Island and Seven Mile Beach there was a significant (P<0.001) Table 7. — Level of puerulus and subsequent juvenile densities of Panulirus cygnus in January and mortality rates at Seven Mile Beach, Western Australia. — = not measured; NA = not yet available; arrows connect individual year classes. Year of hatching Puerulus mean no settling/ collector Age in years of juveniles arising from puerulus 2 No /ha 3 No. /ha 4 No. /ha 5 No. /ha Juveniles present on reef at time of puerulus settlement Total no. /ha 2-5 yr Mortality rate/yr of animals aged > 3 yr 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 10.231 15.829 21.310 39.472 15.566 13.032 46.716 36.478 NA 0863 0466 0768 1 934 0 686 0 657 1 879 1 780 NA 481 FISHERY BULLETIN: VOL. 80, NO. 3 correlation between total density of juveniles on the test reefs and annual mortality rate. Puerulus Settlement/Juvenile Densities and Recruitment to the Fishery Chittleborough and Phillips (1975) examined the relationship between the density of larger juveniles on the coastal reefs during the latter part of the year and the success of the commer- cial white fishery in adjacent waters. They found that, although density-dependent mortality dur- ing the juvenile phase ensures reasonably con- stant recruitment to the fishery over a wide range of initial year-class strengths, in some years the level of puerulus settlement may be in- adequate (i.e., below the holding capacity of the shallow-water reefs), and poor recruitment to the fishery may result. They reported that from the data available at that time only the incidence of particularly poor year classes could be used to predict the relative success of the "white" fishery, i.e., to forecast poor future recruitment to the fishery. Thus, as reported by Hancock (1971), follow- ing the low settlement of puerulus larvae on the collectors in 1969-70 (the hatchings of January- March 1969) and low density of early juveniles, it was predicted by Chittleborough and Phillips in 1971 (Anonymous 1974) that low catch levels would be likely in 1972-73 and even lower levels likely at the opening of the 1973-74 season (i.e., the "whites" of November and December 1973). This prediction was borne out by the catches of these 2 years (Anonymous 1974), the white sea- son of 1973 being the poorest on record, particu- larly in the Fremantle area (reflecting trends observed in the Garden Island research area). It was pointed out by Chittleborough and Phil- lips (1975) that the appearance of a very strong settlement, such as that resulting from the hatch- ings of 1974 at Seven Mile Beach, did not neces- sarily mean that a high level of recruitment to the fishery could be predicted for the 1977-78 and 1978-79 seasons. The preceding year classes were relatively strong so that the year class of 1974 faced intense competition and high mortal- ity while on the "nursery" reefs. Nevertheless, the 1978 "white" catch rate was the second high- est on record. Figure 3 shows that in fact a good relationship does exist between the level of settlement of the puerulus and the subsequent catch rate (mea- sured as the catch per pot lift) of the "whites" 4 yr later. (Proportion of sum of squares accounted for is 0.574.) The relationship is well described by a Ricker (1958) stock-recruitment curve, fitted by the method of Cushing and Harris (1973). Parameter estimates and their standard errors (SE) are A = 0.048, SE = 0.0066 and B = 0.012, SE = 0.0018. A similarly good relationship is achieved by using the puerulus settlement data from Seven Mile Beach only; this is to be expected because of their close correlation with the annual index of settlement (r = 0.966, P<0.01). Since the "whites" catch contributes about 40% of the total catch of any one season, it follows from Figure 3 that there should also be a good relationship between the level of puerulus settle- ment in year x and the total commercial catch rate of the season beginning in November, year x + 4, despite the inevitable confusion of year classes in catches taken after December (i.e., af- ter the "whites") each season. The total commer- cial catches for 1965-66 to 1978-79 are shown in Table 6. The influence of the poor white catch rate of 1973 and the high white catch rate of 1978 on total catches of these years can be clearly seen. Puerulus Settlement and Subsequent Spawning Stock Whereas the relationships between the other stages in the life history of P. cygnus are not influ- enced by the effects of fishing mortality, the rela- PUERULUS SETTLEMENT Figure 3.— The Ricker (1958) stock-recruitment model, to- gether with 95% confidence limits. The model is fitted to data on the index of the annual level of puerulus settlement and sub- sequent catch rates of Pa nut iriis cygnus at recruitment into the fishery 4 yr later. The year shown is the season of hatching of the larvae. 482 MORGAN ET AL.: STOCK AND RECRUITMENT RELATIONSHIPS IN PANl'UltUS CYdNI'S tionship between puerulus settlement and the subsequent spawning stock will inevitably be confused by the effects of variable amounts of fishing pressure on the commercial stocks be- tween the time the rock lobsters are recruited to the fishery as whites and the time that they be- come mature. In addition, the mature females will be subjected to fishing pressure when they are not carrying eggs. When they are carrying eggs, the fishermen are required by law to re- turn these mature females to the sea. This fishing pressure on the mature and im- mature stocks will lead to a reduction in the abundance of the spawning females compared with their potential abundance if there was no fishing pressure. Moreover, the degree of reduc- tion will be a function of the fishing effort (/) since Nt = N0e{M">f)t where Nt = numbers present at time t No — numbers present at time 0 M = instantaneous natural mortality rate q = catchability coefficient. If the growth rate of P. cygnus is considered (Morgan 1977), it will take approximately 1 yr in coastal areas north of lat. 30°S for female rock lobsters to grow from the legal minimum length of 76 mm to the average size of a mature female of 92 mm (Table 1) and approximately 2 yr in areas south of lat. 30°S to grow from 76 mm to the average size of a mature female of 105 mm. Therefore, as a first approximation and neglect- ing the apparently small influence of the Abrol- hos Islands area, it will be assumed that female P. cygnus are subjected to fishing pressure for an average of 1.5 yr during their life in the fishery. The indices of abundance of the spawning stock for all areas (Table 1) can now be adjusted to take into account the probable effects of fishing pres- sure by assuming the index for any year, i, is not only a result of puerulus settlement in previous years but has been reduced by the effect of fish- ing effort in year (i - 1) and one-half the fishing effort in year {i — 2). Using the effective fishing effort data given by Morgan (1979) and Hancock (1981), a relative index, R.I., for later years can be calculated so that it takes into account the effects of fishing effort prior to maturity. This will be given by R.I. (/) = I.A.S.(i)/exp (- 20.21,28 SEP. n=1424 8 MAR 1978; n=262 70 90 110 130 STANDARD LENGTH (mm) 30 50 70 90 110 130 150 170 190 210 230 TOTAL LENGTH (mm) Figure 3.— Monthly length frequencies (moving averages of three)of C. hoMms captured off Port Aransas. Group identity (ID) often is not clear where spawned groups meet. 491 AUG FISHERY BULLETIN: VOL. 80, NO. 3 1 OCT 1977; n = 628 14,15 JUN. MAY77? n = 329 70 90 110 130 STANDARD LENGTH (mm) 30 50 70 90 110 130 150 TOTAL LENGTH (mm) 170 190 210 230 Figure 4.— Monthly length frequencies (moving averages of three) of C. nothus captured off Freeport. Group identity (ID) often is not clear where spawned groups meet. of most large individuals off Port Aransas in fall 1977 is not certain. Greatest or most successful spawning occurs during late summer. Many fish 25-65 mm SL were taken at 11 , 12, and 29 m off Port Aransas in late September (August77 group in Figure 3). This August-spawned group was collected at widely separated locations and formed a princi- pal mode off Port Arnasas through early Decem- ber. Fish of this size also formed a dominant mode off Freeport from October through Decem- ber (August77 group in Figure 4). Similarly, a group hatched in September formed a principal mode off Port Aransas and Freeport during November and December (September group in Figures 3, 4). In contrast to these late summer groups, fish hatched in late spring did not form dominant modes. Gonad maturity data suggest that C. nothus spawns from May through September in agree- ment with the spawning season indicated by length frequencies. Gravid or ripe females were 492 DeVRIES and CHITTENDEN: SPAWNING TO MORTALITY OF SILVER SEATROUT Figure 5.— Length frequencies (moving averages of three) of C. nothus captured off Freeport, Tex., 6-15 January 1974, by depth. Frequencies were reanalyzed from Chittenden and McEachran (1976, fig. 10). Group identity often is not clear where spawned groups meet. 70 id 30 110 130 150 170 TOTAL LENGTH (mm) 190 210 230 50 70 90 110 130 150 STANDARD LENGTH (mm) 170 190 captured during late May, June, and late Sep- tember (Fig. 6), and other females 130 mm SLor larger were in the late developing stage. Some males had large gonads from May through Sep- tember, and running ripe males were captured off Freeport in June and off Port Aransas in Sep- tember. Females were only in the developing and resting stages in November and December, and no large females were captured from Febru- ary through April. 20 -i < o J EZZ42 O 5 n=23 = "bfEj n=7 10-i ^T" 1 1 — I w Xtt^/A l 1 i n=17 UJ z 2 ^5- or. :1 & n=24 O "1 n=2 10 -L -Ft- rnS n=15 \fl ,,,r,rv ' 4 ' 51 61 7 n=1 3 4 5 6 7 8 through July 1978, but the comparatively few in- dividuals of the 1976 year class appeared only in October and November (Fig. 4). Cynoscion nothus reached 130-190 mm SL at age I. Fish of the dominant August and Septem- ber spawned groups averaged 145-150 mm SL at 11 mo, although individuals ranged from 125 to 170 mm SL (Table 2). Similarly, the few survi- vors of the May groups were 130-190 mm SL at 11-14 mo. These observed sizes at age agree with the mean back-calculated length of 156 mm SL presented later. Growth increments varied between months. The August and September spawned groups grew fastest in June and September, averaging about 25-30 mm SL/30 d (Fig. 7). Growth of re- cently hatched young steadily decreased from October to December and was smallest during the December-March period when increments averaged 5 mm SL/30 d. Growth increments then steadily increased to about 15-20 mm SL/30 d from March to June. The apparent pattern of greatest growth during the warm months and slowed growth during winter might be mislead- ing. We have no growth data for the late summer period when the August-September groups MATURITY STAGE Figure 6.— Monthly maturity stages of female C. nothus. Ma- turity stages are 3) early developing, 4) late developing, 5) gravid, 6) ripe, 7) spawning/spent, and 8) resting. Growth and Age Determination by Length Frequency Only one year class of C. nothus occurred or dominated in any 1 mo. Fish of the 1976 and 1977 year classes occurred off Port Aransas during June, July, and August 1977 (Fig. 3). These were the only months when two year classes were clearly evident, although the comparatively few large individuals of uncertain identity in Sep- tember-October 1977 probably were of a second year class. Only the 1976 and 1977 year classes occurred off Freeport from October 1977 40n >. n o co CO E20H E O DC O I - Sen?7 A„g-Sep77 modes (Pol Q - Sep /Aug-Sep lower limit □ - Aug-Sep77 midranges V Aug Sep , modei V AugSep^rrudrangei A AugJ7 modei IPorl Aransas) A - Aug77 model (FreepcMl 0 Sep77 '"O'1" ,P°" Afansasl ^ - Sep . modes (Frecpon) Jan Feb Feb Mar — J— Mar Apr Apr May — 1— May Jun - 1- Jul Aug fcug Spr: — r~ Sep Oct —I 1 Oct Nov Nov Dec -I Dec Jan PERIOD WHEN GROWTH OCCURRED Figure 7.— Monthly growth increments of C. nothus. Unad- justed growth increments (Table 2) were adjusted to growth/ 30 d. 493 FISHERY BULLETIN: VOL. 80, NO. 3 would have spawned. Growth from July through September could have been high as the apparent pattern suggests, or it might have slowed down and/or ceased as these fish matured and spawned. Age Determination Using Scales Silver seatrout can be aged using scales, although few fish had scales with either an annu- lus or false annulus. Only 38 of 1,483 fish (2.6%) had an annulus, and no fish had more than one. Only 41 fish (2.8%) had a false annulus, and they included 5 fish with an annulus. These percent- ages overemphasize the frequency of annuli and false annuli because the stratified sampling used to select specimens for intensive processing also selected all the large fish which would most likely show these marks. Repeated examination suggests that age de- termination of C. nothus is consistent. We had 90% agreement in a second reading of scales from 225 fish, which included 123 fish >150 mm SL and all 38 fish first determined to have an annu- lus. The second reading identified an annulus in 45 specimens, including 30 of the 38 fish (79% agreement) first determined to have an annulus. The eight fish for which an annulus was not con- firmed were collected in May and June about when the annulus forms; their scales had small marginal increments after an indefinite clear 1 Apr n=1 La May n=14 ^ <£>_ L\- T 1 Jun n=13 o5l 2 L i 1 — Jul n=1 Hi O 5" LU CC 5- 5- ^r Aug n=1 1 Sep n=4 -^ Oct n=1 _^_ i 1 Nov n=2 /\ 1^ -i r* 1 1 10 30 MARGINAL INCREMENT (mm*42) zone, and secondary radii and/or cutting over were not distinct. The second reading was done without knowing sizes or collection dates. This would minimize agreement between readings. May-spawned C. nothus form an annulus from April (or earlier) to June when they reach 130- 190 mm SL and 1 yr of age, but time of annulus formation may vary between spawned groups and is not clear for August- or September- spawned fish. Marginal increments were small- est from April to June and generally increased thereafter (Fig. 8), suggesting the first annulus forms from April (or earlier) to June. The small- est fish with an annulus was 139 mm SL and most exceeded 150 mm SL. The proportion with an annulus increased with increasing size, per- centages being 16% at 150-159 mm SL (n = 55), 24% at 160-169 mm SL (n = 54), 60% at 170-179 mm SL (n = 10), and 100% at 180 mm SL and greater (n = 6). The proportion of the fish >150 mm SL with an annulus (Fig. 9) was significantly higher in May and June, when most of these large fish were May-spawned, than it was in Sep- tember and November, when most were August- or September-spawned. Fish with an annulus in the period August-November all exceeded 170 mm SL and probably were survivors of the May7e group; those without an annulus then were 150- 170 mm SL and probably August- or September- spawned. Back-calculated lengths agree with length fre- quencies. Lengths at age I back-calculated using the Lee method (Lagler 1956) varied from 132 to 176 mm SL in comparison to 130-190 mm SL based on length frequencies. The mean back- calculated length was 156 mm SL with 95% con- fidence limits of 153-159 mm. 30 > o z LU o LU cc QC 10 □ Without an annulus 0 With an annulus Ds a 9 _Ea. ra 0. cc Q- < < 2 z 3 o < o o > o z MONTH CAPTURED Figure 8.— Monthly marginal increments for C. nothus with one mark. Figure 9.— Histogram showing by month the number and per- centage of C. nothus>l50 mm SL with and without an annulus. 494 DeVRIES and CHITTENDEN: SPAWNING TO MORTALITY OF SILVER SEATROUT Maximum Size, Life Span, and Mortality Silver seatrout off Texas are small fish whose maximum life span (tL) is about 1-1.5 yr. The largest of the 17,820 specimens that we captured were only 190 mm SL (230 mm TL). Almost 90% of the C. nothus captured off Port Aransas were <110 mm SL(Fig. 10), 99.1% were<160mm SL, and 99.9% were <180 mm SL. Off Freeport, 85% were <110 mm SL, 99% were <160 mm SL, and 99.9% were <180 mm SL (Fig. 11). All C. nothus disappeared off Texas when they were slightly older than age I (Table 3). The total annual mortality rate of C. nothus in the gulf off Texas approaches 100% and has a best estimate of 99.83%. Values of total annual mortality (1 — S) in each of the 9 mo from October 1977 through July 1978 off Freeport were 100% based on the expression S = N,/N0 where 5 = rate of survival and No and N, are the number of fish in consecutive year classes 0 and t. Only one year class was present off Freeport in those months so that N, = 0. For the same reason, 1 — S was 100% off Port Aransas in each of the 4 mo from Febru- ary through May 1977, during November and December 1977, and during March 1978. Mor- tality estimates were 98% and 99.9% for Septem- ber and October off Port Aransas, assuming that fish >140 and >150 mm SL were from the older year class. For June, July, and August, 1 — S could not be estimated from the Port Aransas data, because the younger year class had just hatched and was incompletely recruited. How- ever, if the predominant group in August had hatched in spring 1977, then 1 — S would ap- proach 100% in that month also. Following the first procedure of Robson and Chapman (1961), we calculated an average value of 1 — S = 99.83% by pooling the identifiable No and N, values for each month. Distribution and Availability Larger C. nothus seem more susceptible to trawling during the day. Few fish >100 mm SL were taken in night collections at 11, 18-24, and 29-31 m (Fig. 12), but many were taken in day collections at 7, 13-15, and 18-24 m. Large silver seatrout almost disappeared dur- ing winter. Fish >120 mm SL from the May77- and August-September76 spawned groups were common during November off Port Aransas (Fig. 3) and during October and November off Freeport (Fig. 4), but very few were captured 110 130 150 TOTAL LENGTH (mm) Figure 10.— Length frequency (moving averages of three) and cumulative percentage of all C. nothus collected off Port Aran- sas, Tex., February-December 1977. STANDARD LENGTH Figure 11.— Length frequency (moving averages of three) and cumulative percentage of all C. nothus collected off Freeport, Tex., October 1977-July 1978. from December through March. The larger spe- cimens of the August77-spawned group also dis- appeared about December, which may be why the August- and September-spawned groups were not distinct thereafter. Many large fish were again taken in May or June. Total Weight- and Girth- Standard Length and Standard Length-Total Length Relationships Regression and related analyses for total weight-standard length, girth-standard length, and standard length-total length relationships are presented in Table 4. All regressions were 495 FISHERY BULLETIN: VOL. 80. NO. 3 Table 4.— Analyses of total weight-standard length, girth-standard length, and standard length-total length relationships for C. nothus. Lengths and girths are in millimeters and weights are in grams. Corrected Corrected Residual total total Equation n MS SSx SSy X y log,o TW = -4.7582 + 3.0077 logio SL 2,451 00014 6375 580.16 1 .9056 0.9733 G = 6.64 + 0.63 SL 2,451 12.87 2,429,280 996,341 86.0 608 SL = -7.48 + 1.54 G 2,451 31.37 996,341 2.429,280 60.8 860 SL = -3.76 + 0.84 TL 303 7.48 587,667 420.074 101.5 81.8 TL =4 98 + 1.18 SL 303 10.46 420,074 587,667 81.8 101.5 significant ata =0.01. Coefficients of determina- tion (100 r2) were 97% for girth-standard length relationships but 99% for total weight-standard length and standard length-total length relation- ships. All relationships were based on fish whose standard length range was 26-188 mm. DISCUSSION Spawning Our findings on C. nothus reproduction agree with the limited literature. The finding of spawn- ing from May to late October is consistent with reports of 1) fish about 35-40 mm TL (26-30 mm SL) or smaller from June to December (Hilde- brand and Cable 1934; Hoese 1965; Christmas and Waller 1973; Mahood 1974), 2) ripe individ- uals in mid-May (Miller 1965) and throughout August (Gunter 1945; Hildebrand 1954), and 3) late-developing specimens in August and Sep- tember (Mahood 1974). Our finding of peak spawning in late summer agrees with Gunter (1945) and Chittenden and McEachran (1976), and with the dominance of a late summer- spawned group in Mahood (1974, fig. 13). The small size at maturity is consistent with Miller's (1965) report of running ripe females only 135- 140 mm TL (110-114 mm SL), although the small- est fish that Mahood (1974) collected in late- developing or spent condition was 205 mm TL (168 mm SL). Our finding of May-, August-, and September-spawned groups is similar to the spring peak and late summer or fall peak of reproduction reported for C. nothus (Mahood 1974) and for C. arenarius (Shlossman and Chit- tenden 1981). The latter workers suggested that the spawning periodicity of C. arenarius was timed to coincide with the two major periods of rising sea level in the northern Gulf of Mexico each year when surface currents could transport eggs and/or larvae to inshore or estuarine nurs- eries. Spawning of C. nothus in the Gulf of Mexi- co probably is timed also to take advantage of such current transport. We have observed that C. nothus exhibits two distinct peaks of spawning within the August-September major spawning period. It is not yet clear 1) whether multiple- spawned group production consistently occurs within the late summer reproduction period, which would imply spawning keyed to regu- lar intraperiod cues, or 2) whether multiple- spawned group production in the late summer period reflects irregular happenstances such as the increased survival and recruitment that could occur if reproduction at times coincided with unusually favorable current transport (Hjort 1914, 1926; Nelson et al. 1977), or if a criti- cal larval period (Marr 1956; May 1974) irregu- larly coincided with an unusually great food supply. Growth and Age Determination Our estimates that C. nothus in the northern Gulf of Mexico reach 130-190 mm SL and aver- age 150 mm or more when they disappear at age I agree with Chittenden and McEachran (1976) and Chittenden (1977) that C. nothus reaches 120-150 mm SL (150-185 mm TL) at age I. Gun- ter's (1945) estimate that fish 75-110 mm SL (93- 138 mm TL) taken in May were about 1 yr old is low and may have been based on fish that actu- ally would not have reached age I until the major spawning period of August-September. None of these cited workers, though, recognized the mul- tiple-spawned group composition of this species and their estimates of age could be in error. Our estimates for C. nothus agree with estimates for C. nebulosus of 157-165 mm SL at age I (Pearson 1929; Moody 1950; Tabb 1961), although lower estimates of 116 and 130 mm SL have been re- ported (Klima and Tabb 1959; Moffett 1961). The growth of C. nothus also agrees with estimates for C. regalis of 143-180 mm SL at age I (Merri- ner 1973). Seasonal growth of August-September spawned C. nothus appears comparable to that of C. nebulosus and C. regalis. Pearson (1929) found 496 DeVRIES and CHITTENDEN: SPAWNING TO MORTALITY OF SILVER SEATROUT 30- > O z LU 3 o LU cc LL 7 m (D); n=1348 10 collections 70 90 110 130 STANDARD LENGTH (mm) 190 30 50 70 90 110 130 150 170 TOTAL LENGTH (mm) 190 210 230 Figure 12.— Pooled length frequencies (moving averages of three) of C. nothus collected by day (D) and night (N) off Port Aransas, Tex., at each depth. a similar seasonal growth pattern for C. nebu- losus from Texas, but he did not calculate monthly increments. Estimates of monthly growth for C. regalis at age 0 are about 30-55 mm TL during the summer (24-45 mm SL) and about 10 mm TL-in October (Welsh and Breder 1923; Hildebrand and Cable 1934; Pearson 1941). Scales can be used to age C. nothus, but age de- 497 termination would probably be as accurate from intensive length frequencies alone. The long spawning season and multiple-spawned group compositions complicate age determination. Exact age determination may be difficult for the few fish age II or older. The few fish of these ages might not be distinct in length frequencies and a spawned group probably could not be assigned. Growth and mortality estimates for C. nothus should be based upon individual spawned groups to avoid misinterpretation. Maximum Size, Life Span, and Mortality The largest specimen of C. nothus that we cap- tured (190 mm SL = 230 mm TL) is similar to the maximum sizes typically reported (Hildebrand and Cable 1934; Gunter 1945; Hildebrand 1954; Christmas and Waller 1973; Chittenden and McEachran 1976). The only published records of fish much >190 mm SL include a specimen 315 mm SL (380 mm TL) from the Gulf of Mexico off Mississippi (Franks et al. 1972), a few specimens to 259 mm SL (312 mm TL) from industrial fish catches in the gulf (Thompson 1966), and Ma- hood's (1974) report of two fish 255 mm SL (308 mm TL) from the Atlantic Ocean off Georgia. Net avoidance and/or behavioral change to a midwater life-style probably does not explain the absence of C. nothus >190 mm SL off Texas, be- cause we collected many C. arenarius to 283 mm SL. Large C. nothus apparently do not occupy water deeper than 46 m off Texas, because twice monthly day and night collections at 55-100 m in the period June 1979- August 1980 have not cap- tured larger fish (Chittenden, unpubl. data). The absence of large C. nothus off Texas might indi- cate movement to rough, normally untrawled substrate or possibly a spawning or postspawn- ing movement to the northcentral gulf. Large C. nothus to 225-250 mm SL occur in deep water in the northcentral gulf (E. Gutherzand B. Rohr ), but the comparative percentage of these large fish needs further study. Based on our data and the published literature, however, it appears that C. nothus does not exist in significant num- bers at sizes >190 mm SL. Even Mahood's(1974) data indicate that only 4% of his specimens were >188 mm SL. 6E. Gutherz and B. Rohr, Fishery Biologists, Southeast Fisheries Center Pascagoula Laboratory, National Marine Fisheries Service, NOAA, Pascagoula, MI 39567, pers. com- mun. January 1981. FISHERY BULLETIN: VOL. 80, NO. 3 The maximum life span of C. nothus is only 1- 1.5 yr off Texas, although it might be as long as 2 yr in the northcentral gulf or off the southeast United States. A value of ti. = 1-1.5 yr seems reasonable for Texas waters because fish >160- 180 mm SL (the average size at age I) made up 188 mm SL were age II fish. The high mortality rate that we have found explains why few C. nothus had an annulus. Most fish probably die before or while a mark forms on the scales. Distribution and Availability The disappearance of large C. nothus that we found during winter agrees with Mahood (1974, table 8), who reported only six specimens (of 947 fish) >130 mm SL (160 mm TL) from October through April, and with Hildebrand and Cable (1934), who reported no C. nothus captured off Beaufort Inlet, N.C., during winter although they were rather common in summer. The dis- appearance of large C. nothus during the colder months and their subsequent reappearance in spring probably reflects an offshore overwinter- ing movement of large fish. This interpretation is supported by 1) reanalysis of Chittenden and McEachran's (1976, fig. 10) data on distribution of C. nothus in mid-January (Fig. 5) which indi- cates that fish > 140 mm SL were most abundant in deep water, and 2) Miller's (1965) report that large C. noth us occurred in deep water from Feb- ruary through April. 498 DeVRIES and CHITTENDEN: SPAWNING TO MORTALITY OF SILVER SEATROUT General The production of several spawned groups over a broad time period in each annual spawn- ing season is extremely important to the popula- tion dynamics of C. nothus. This species is short- lived and appears little more than an annual crop whose abundance could fluctuate greatly from year to year. However, the multiple-spawned group structure would buffer against population instability just as a multiple year class structure buffers population size in longer lived species. The multiple-spawned group feature may aver- age over a longer period each year the effects of environmental variation on spawning success, may dampen fluctuations in annual spawning success associated with environmental extremes, and may stabilize population sizes. Similarly, the effects of fishing would be averaged over a greater number of spawned groups in 1 yr, so that the multiple-spawned group structure might minimize the possibility of recruitment overfishing. In that event, stock assessments based on dynamic pool models and growth over- fishing would be more valid. Many features of the population dynamics of C. nothus — short life span, high mortality rate, and rapid turnover of biomass — are similar to those in the Atlantic croaker, Micropogonias un- dulatus, of the Carolinean Province (White and Chittenden 1977; Chittenden 1977). This sup- ports the suggestion (Chittenden and McEachran 1976; Chittenden 1977) that the abundant species of the white and brown shrimp communities in the gulf have evolved towards a common pattern of population dynamics. Because of their similar population dynamics, the implications of Chit- tenden's (1977) simulations on croaker could serve as a first approximation of the effects of harvesting C. nothus, so that this species also should have a great biological capacity to resist growth overfishing. ACKNOWLEDGMENTS We are much indebted to the Texas Parks and Wildlife Department, and particularly the crew of the RV Western Gulf(T. Cody, K. Rice, Capt. D. Perez, and D. Majorando), for allowing the senior author to participate in cruises aboard the RV Western Gulf and for all their cooperation and assistance. P. Shlossman and Captains H. Forrester, J. Forrester, and M. Forrester also assisted greatly with field collections. J. Merri- ner, R. Noble, K. Strawn, and T. Bright reviewed the manuscript and made many very helpful suggestions. Financial support was provided, in part, by the Texas Agricultural Experiment Station and by the Texas A&M University Sea Grant College Program, supported by the NOAA Office of Sea Grant, U.S. Department of Commerce. LITERATURE CITED Alverson, D. L., and M. J. Carney. 1975. A graphic review of the growth and decay of popu- lation cohorts. J. Cons. Int. Explor. Mer 36:133-143. Bagenal, T. B., and E. Braum. 1971. Eggs and early life history. In W. E. Ricker (edi- tor), Methods for assessment of fish production in fresh waters, p. 166-198. Blackwell Sci. Publ.. Oxf. Chittenden, M. E., Jr. 1977. Simulations of the effects of fishing on the Atlantic croaker, Micropogon undulatus. Proc. Gulf Caribb. Fish. Inst. 29:68-86. Chittenden, M. E., Jr., and J. D. McEachran. 1976. Composition, ecology, and dynamics of demersal fish communities on the northwestern Gulf of Mexico continental shelf, with a similar synopsis for the entire Gulf. Texas A&M Univ., Sea Grant Publ. TAMU-SG- 76-208, 104 p. Christmas, J. Y., and R. S. Waller. 1973. Estuarine vertebrates, Mississippi. In J. Y. Christmas (editor), Cooperative Gulf of Mexico estua- rine inventory and study. Mississippi, p. 320-434. Gulf Coast Res. Lab., Ocean Springs. Miss. Dahlberg, M. D. 1972. An ecological study of Georgia coastal fishes. Fish. Bull., U.S. 70:323-353. Franks, J. S., J. Y. Christmas. W. L. Siler. R. Combs. R. Waller, and C. Burns. 1972. A study of the nektonic and benthic faunas of the shallow Gulf of Mexico off the state of Mississippi as re- lated to some physical, chemical and geological factors. Gulf Res. Rep. 4:1-148. GlNSBURG, I. 1929. Review of the weakf ishes (Cynoscion) of the Atlan- tic and Gulf coasts of the United States, with a descrip- tion of a new species. Bull. U.S. Bur. Fish. 45:71-85. 1931. On the difference in the habitat and the size of Cynoscion arenarius and C. nothus. Copeia 1931: 144. Guest, W. C, and G. Gunter. 1958. The sea trout or weakf ishes (genus Cynoscion) of the Gulf of Mexico. Gulf States Mar. Fish. Comm. Tech. Summ. 1, 40 p. Gulland, J. A. 1969. Manual of methods for fish stock assessment. Part I. Fish population analysis. FAO Man. Fish. Sci. 4. 154 P- Gunter, G. 1938. Seasonal variations in abundance of certain estua- rine and marine fishes in Louisiana, with particular reference to life histories. Ecol. Monogr. 8:313-346. 1945. Studies on marine fishes of Texas. Publ. Inst. Mar. Sci. Univ. Tex. 1:1-190. 499 FISHERY BULLETIN: VOL. 80, NO. 3 Gutherz, E. J., G. M. Russell, A. F. Serra, and B. A. Rohr. 1975. Synopsis of the northern Gulf of Mexico industrial and foodfish industries. Mar. Fish. Rev. 37(7):1-11. HlLDEBRAND, H. H. 1954. A study of the fauna of the brown shrimp (Penaeus aztecus Ives) grounds in the western Gulf of Mexico. Publ. Inst. Mar. Sci. Univ. Tex. 3:229-366. 1955. A study of the fauna of the pink shrimp (Penaeus duorarum Burkenroad) grounds in the Gulf of Cam- peche. Publ. Inst. Mar. Sci. Univ. Tex. 4 (Part 1): 169- 232. HlLDEBRAND, S. F., AND L. E. CABLE. 1934. Reproduction and development of whitings or kingfishes, drums, spot, croaker, and weakfishes or sea trouts, family Sciaenidae, of the Atlantic coast of the United States. [U.S.] Bur. Fish., Bull. 48:41-117. HlLDEBRAND, S. F., AND W. C. SCHROEDER. 1927. Fishes of Chesapeake Bay. Bull. U.S. Bur. Fish. 43:1-366. Hjort, J. 1914. Fluctuations in the great fisheries of northern Eur- ope viewed in the light of biological research. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 20, 228 p. 1926. Fluctuations in the year classes of important food fishes. J. Cons. Int. Explor. Mer 1:5-38. Hoese, H. D. 1965. Spawning of marine fishes in the Port Aransas, Texas area as determined by the distribution of young and larvae. Ph.D. Thesis, Univ. Tex., Austin, 144 p. Klima, E. F., and D. C. Tabb. 1959. A contribution to the biology of spotted weakfish, Cynoscwn nebulosus, (Cuvier) from northwest Florida, with a description of the fishery. Fla. Board Conserv., Mar. Res. Lab. Tech. Ser. 30, 25 p. Lagler, K. F. 1956. Freshwater fishery biology. 2d ed. Wm. C. Brown Co., Dubuque, Iowa, 421 p. Mahood, R. K. 1974. Seatrout of the genus Cynoscwn in coastal waters of Georgia. Ga. Dep. Nat. Res., Contrib. Ser. 26, 36 p. Marr, J. C. 1956. The "critical period" in the early life history of ma- rine fishes. J. Cons. Int. Explor. Mer 21:160-170. Massman, W. H. 1963. Annulus formation on the scales of weakfish, Cy- noscwn regalis, of Chesapeake Bay. Chesapeake Sci. 4: 54-56. May, R. C. 1974. Larval mortality in marine fishes and the critical period concept. In J. H. S. Blaxter (editor), The early life history of fish, p. 3-19. Springer- Verlag, N.Y. Merriner, J. V. 1973. Assessment of the weakfish resource, a suggested management plan, and aspects of life history in North Carolina. Ph.D. Thesis, North Carolina State Univ., Raleigh, 201 p. Miller, J. M. 1965. A trawl survey of the shallow Gulf fishes near Port Aransas, Texas. Publ. Inst. Mar. Sci. Univ. Tex. 10: 80-107. MOFFETT, A. W. 1961. Movements and growth of spotted seatrout, Cy- noscion nebulosus (Cuvier), in West Florida. Fla. Board Conserv., Mar. Res. Lab. Tech. Ser. 36, 35 p. Moody, W. D. 1950. A study of the natural history of the spotted trout, Cynoscion nebulosus, in the Cedar Key, Florida, area. Q. J. Fla. Acad. Sci. 12:147-171. Moore, D., H. A. Brusher, and L. Trent. 1970. Relative abundance, seasonal distribution, and species composition of demersal fishes off Louisiana and Texas, 1962-1964. Contrib. Mar. Sci. Univ. Tex. 15:45- 70. Nelson, W. R., M. C. Ingham, and W. E. Schaaf. 1977. Larval transport and year-class strength of Atlan- tic menhaden, Brevoortia tyrannus. Fish. Bull., U.S. 75:23-41. Pearson, J. C. 1929. Natural history and conservation of redfish and other commercial sciaenids on the Texas coast. Bull. U.S. Bur. Fish. 44:129-214. 1941. The young of some marine fishes taken in lower Chesapeake Bay, Virginia with special reference to the gray sea trout, Cynoscion regalis (Bloch). U.S. Dep. Inter., Fish Wildl. Serv., Fish. Bull. 50:79-102. Perlmutter, A., W. S. Miller, and J. C. Poole. 1956. The weakfish (Cynoscion regalis) in New York waters. N.Y. Fish Game J. 3:1-43. Robson, D. S., and D. G. Chapman. 1961. Catch curves and mortality rates. Trans. Am. Fish. Soc. 90:181-189. ROYCE, W. F. 1972. Introduction to the fishery sciences. Acad. Press, NY., 351 p. Shlossman, P. A., and M. E. Chittenden, Jr. 1981. Reproduction, movements, and population dynam- ics of the sand sea trout, Cynoscion arenarius. Fish. Bull., U.S. 79:649-669. Swingle, H. A. 1971. Biology of Alabama estuarine areas— cooperative Gulf of Mexico estuarine inventory. Ala. Mar. Resour. Bull. 5, 123 p. Tabb, D. C. 1961. A contribution to the biology of the spotted sea- trout, Cynoscion nebulosus (Cuvier) of east-central Flor- ida. Fla. Board Conserv., Mar. Res. Lab. Tech. Ser. 35, 24 p. Tesch, F. W. 1971. Age and growth. In W. E. Ricker (editor), Meth- ods for assessment of fish production in fresh waters, p. 98-130. Blackwell Sci. Publ., Oxf. Thompson, M. H. 1966. Proximate composition of Gulf of Mexico indus- trial fish. U.S. Fish Wildl. Serv., Fish. Ind. Res. 3(2): 29-67. Welsh, W. W., and C. M. Breder, Jr. 1923. Contributions to life histories of Sciaenidae of the eastern United States coast. Bull. U.S. Bur. Fish. 39: 141-201. White, M. L.. and M. E. Chittenden, Jr. 1977. Age determination, reproduction, and population dynamics of the Atlantic croaker Micropogonias undu- latus. Fish. Bull., U.S. 75:109-123. 500 CYCLOGRAPSVS INTEGER H. MILNE EDWARDS, 1837 (BRACHYURA, GRAPSIDAE): THE COMPLETE LARVAL DEVELOPMENT IN THE LABORATORY, WITH NOTES ON LARVAE OF THE GENUS CYCLOGRAPSUS Robert H. Gore and Liberta E. Scotto1 ABSTRACT rT The complete larval development of Cyclograpsus integer, a small sesarmine grapsid crab, is de- scribed and illustrated from larvae reared in the laboratory. Cyclograpsus integer attains five, and often six, zoeal stages plus one megalopal stage. Temperature affects both duration of larval devel- opment and number of larval stages. At 25°C, the megalopal stage was attained in 26-27 days from fifth stage zoeae and 31-32 days from sixth stage zoeae, while metamorphosis at 20°C occurred in 53-55 days from sixth stage zoeae. The zoeal and megalopal stages of C. integer are compared to all known cultured species of the genus and morphological differences are noted. Cyclograpsus integer zoeae may be distinguished from both other species in the genus and other species in the family by its antennal morphology, being the only species with the type A antenna(i.e.,theexopodite about equal in length to the protopodite). Megalopae of this species may be distinguished from other species in the genus by the formation of the frontal region and the terminal setation of the telson. Other poten- tially useful zoeal morphological characters are discussed regarding both the taxonomicand phylo- genetic position of C. integer. The sesarmine genus Cyclograpsus is cosmopoli- tan, containing at least 16 species, 13 of which occur in the Indo-West Pacific region (Griffin 1968). Cyclograpsus integer, one of four species in the genus occurring in the New World and the only one known from the western Atlantic, is quite widespread with records from western and eastern Africa, and localities in the Indo-West, eastern central, and northern west Pacific Ocean (Monod 1956; Griffin 1968; Manning and Hol- thuis 1981). Although Rathbun (1918) listed the Peruvian and South American species Cyclo- grapsus cinereus Dana, 1851 as being the eastern Pacific analog to C. integer, Griffin (1968) noted that Cyclograpsus escondidensis Rathbun, 1933, an eastern Pacific species known only from Cen- tral America, was closer to C. integer than to any other member of the genus. In the same study, Griffin described Cyclograpsus sanctaecrucis, a new species from Santa Cruz Island in the south- western Pacific Ocean, stating that "Except in the presence of a lateral notch on the carapace, [this] species most closely resembles C. integer." Thus, Cyclograpsus integer appears similar to at 'Smithsonian Institution, Fort Pierce Bureau, Ft. Pierce, FL 33450. Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80, NO. 3. 1982. least two other species in the genus from the Pacific Ocean. The larvae of members of the genus are not well known, and the complete larval develop- ment has been determined for only two New World species at present. Costlow and Fagetti (1967) described and illustrated the complete de- velopment of C. cinereus from Chile, and in a sub- sequent paper Fagetti and Campodonico (1971) recorded the development of a species from Juan Fernandez Islands which they identified as Cyclograpsus punctatus H. Milne Edwards, 1837. Griffin, however (1968), suggested that specimens of Cyclograpsus from those islands are actually referable to Cyclograpsus lavauxi H. Milne Edwards, 1837, stating that C. puncta- tus is restricted to South Africa. To add to this confusion, Wear (1970) described and illustrated the first zoeal stages of two New Zealand species, Cyclograpsus insularum Campbell and Griffin, 1966, and C. lavauxi. But a comparison of his illustrations of the latter species with the first zoeal stage figured by Fagetti and Campodonico shows substantial differences in the number and position of chromatophores, appendage pro- cesses, and segmentation of the maxillule, sug- gesting that notable variation occurs between eastern and western Pacific populations of C. 501 FISHERY BULLETIN: VOL. 80, NO. 3 lavauxi, if Fagetti and Campodonico's species was misidentified. These differences raise the possibility that the New Zealand (Wear 1970) and Chilean (Fagetti and Campodonico 1971) forms of C. lavauxi are subspecies, assuming that Griffin is correct in restricting C. punctatus to South Africa. On the other hand, the Chilean specimens may indeed have been correctly iden- tified as C. punctatus, thus accounting for the observed differences in the larvae, as well as reinstating the Juan Fernandez Islands as the westernmost zoogeographical boundary for the species. Until further data are available, we will consider Fagetti and Campodonico's species to be correctly identified as C. punctatus, so that we may compare the morphological features of this species with others in the genus. The aforementioned confusion, and the wide- spread occurrence of C. integer, as well as its close morphological relationship to C. escondi- densis, its Central American analog, all illus- trate the importance of determining the larval development of these species. Accomplishing this would facilitate identification of their re- spective larvae in the plankton and also allow comparisons of morphological features in zoeal and megalopal stages. The latter stages provide a means of elucidating phylogenetic relation- ships both intra- and intergenerically among the Grapsidae. Accordingly, in this paper we describe and illustrate the complete larval devel- opment of Cyclograpsus integer and compare salient characters shared by the zoeae and mega- lopae in C. punctatus, C. cinereus from the New World, and C. lavauxi and C. insularum first zoeae from the Indo-West Pacific. MATERIALS AND METHODS Three ovigerous females (carapace width 7.0, 9.3, 10.4 mm) were collected among medium- sized cobbles in the high intertidal zone at Bod- den Town, Grand Cayman Island, on 15 July 1980. Following previous methodology (Gore 1968), the crabs were maintained in 19 cm diame- ter glass bowls filled with seawater (34 %o) and fed Artemia spp. nauplii daily until hatching occurred on 25, 28, and 29 July 1980 (largest to smallest female, respectively). A total of 192 lar- vae were cultured in eight 24-compartmented polystyrene trays, one larva per compartment. The eight trays were maintained in controlled temperature units in a diel fluorescent light cycle of 12 h light, 12 h dark. A total of 144 larvae (72 at each temperature) were cultured at 20° and 25°C (±0.5°C). Another 48 larvae were main- tained at 15°C (±0.5°C). Seawater (34-36 %.) was changed and the larvae were fed Artemia nauplii daily. All dead larvae, molts, and representative live specimens were preserved in 70% ethanol. Descriptions and illustrations were made with the aid of dissecting stereomicroscope and com- pound microscope with camera lucida attach- ments, using specimens from all three hatches. Measurements are the arithmetic mean of all specimens examined in a given stage. Carapace length was measured from the base of the ros- trum to the posterior margin of the carapace, lateral view in zoeae and dorsal view in mega- lopae. Carapace width in the latter was mea- sured dorsally across the widest part of the cara- pace. In all descriptions, setal formulae progress distally. The first 4 zoeal stages are denoted as ZI to ZIV. One series of fifth zoeal stages (ZVu; ulti- mate) molted directly to megalopa stage; another (ZVp; penultimate) molted to a sixth (Z VI) stage. The morphological differences in these two forms are noted in the text. A complete larval series and/or their molts is deposited in the National Museum of Natural History, Washington, D.C. (USNM 184669); the Allan Hancock Foundation, University of South- ern California, Los Angeles (AHF 2328-1); the British Museum (Natural History), London (1981-447); the Rijksmuseum van Natuurlijke Historie, Leiden (D-34220); the Museum Na- tional d'Histoire Naturelle, Paris (M. N.H.N. - B7294, 7295); and the Indian River Coastal Zone Museum, Fort Pierce, Fla. (IRCZM 89:5096). The adult females are divided among the Na- tional Museum of Natural History, the Indian River Coastal Zone Museum, and the Paris Museum. RESULTS OF THE REARING EXPERIMENT Temperature not only influences the duration of larval development within stages, but also affects the number of zoeal stages attained (Table 1, Fig. 1). At the warmer temperature (25°C) either 5, or occasionally 6, zoeal stages occurred. However, the single first crab stage was reached after 37 d in the laboratory by a megalopa which molted from a stage V zoea. Of 3 other stage V zoeae that molted to stage VI, only 2 eventually reached megalopa and none sur- 502 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOGRAPSUS INTEGER Table 1.— Duration in days of larval and postlarval stages in Cyclograpsus integer &t two laboratory-culture temperatures. (Mean based only on larvae attaining next stage.) Tempera- ture (°C) Stage Minimum Mean Mode Maximum Number molting to next stage (or dying in molt) 25 Zoea 1 5 6.6 6 11 44 II III 4 4 43 4 4.2 4 6 6 22 (+2) 18 IV 4 42 4 5 14 Zoea V-Megalopa Zoea V-VI 4 4 52 6 40 4 6 4 5 (+2) 3 Zoea Vl-Megalopa Megalopa (V) Megalopa (VI) 6 11 All died in 6.0 6 stage after 1 day 6 2 1 0 20 Zoea 1 II 9 7 10.9 10(13)' 9.2 8 14 (21)' 17 21 (+1) 14 III 6 7.3 8 9 13 IV 7 79 8 9 10 Zoea V-Megalopa Zoea V-VI No fifth 6 stage zoeae molted to 7.7 7-8 megalopa 12 9 Zoea Vl-Megalopa Megalopa 11 18 11.7 12 21.7 12 25 6(+1) 3 'Died in stage Figure 1.— Percent survival and duration of larval stages in Cyclograpsus integer reared under laboratory conditions. N = number of larvae cultured at each tempera- ture; * = combined stages; u = ultimate stage; p = penultimate stage. [See text] DAYS IN STAGE 503 FISHERY BULLETIN: VOL. 80, NO. 3 vived to first crab stage. The time period of 37 d may well be a reasonable reflection of what takes place in the plankton, because at 25°C in the lab- oratory a hypothetical zoea passing through the minimum duration for each stage could conceiv- ably attain first crab stage in as few as 32 d (5 stages) or 38 d (6 stages) after hatching. The variation in duration of each zoeal stage at 25°C (except for the first zoea) was rather low, comprising no more than 2 d. Stage I, however, could last from 5 to lid, although most individ- uals molted to stage II between 6 and 7 d after hatching. A single zoea that remained in stage I for lid also molted to stage II, but died the fol- lowing day. A comparison of the values in Table 1 with the survival graph (Fig. 1) shows that mor- tality was quite high on the days just prior to, and during, the ecdysial period in stage I, but as development progressed the mortality subse- quently fell. These results are similar to others obtained in our laboratory with brachyuran and anomuran larvae, and indicate that the more mature zoeal stages have a greater survival potential. This might be a result of one or a com- bination of factors, including the type, quality, and amount of food consumed, the genetic make- up of the parents, or a response by the larvae to unfavorable physical conditions in the labora- tory (see Bookhout and Costlow 1970; Knowlton 1974; Gore et al. 1981, for summaries of the vari- ous hypotheses). At 20°C, both within-stage and overall devel- opmental duration were more variable. Ex- tended zoeal durations and the production of a sixth zoeal stage were both noted at the cooler temperature. Larvae remained in stage I 9-14 d before proceeding with further development. Most larvae molting to stage II did so 10 d after hatching. However, a larger component of zoeae died than survived during this ecdysis, most dying at day 14, with 3 zoeae lasting until day 21. It would seem that whatever general effect the lower temperature has on zoeal stages cannot be overridden after about 12-13 d in the first stage, so that the larvae eventually die if they have not molted by this time. Once stage II was reached, most zoeae were capable of continuing their de- velopment with relatively little mortality com- pared to that seen in stage I (Fig. 1). Modal values of within-stage developmental time were generally twice that seen at 25°C. The rearing data also show that the megalopal stage was at- tained following 6, rather than 5, zoeal stages, approximately 53-55 d after eclosion. Another 18-25 d were required before the first crab stage was reached. Thus, a minimum of 73 d was re- quired after hatching to complete development, even though an extrapolation from the minima in Table 1 suggests that a hypothetical zoea might possibly reach first crab stage in as few as 64 d after hatching at 20°C. Extended develop- mental times such as these are not necessarily detrimental if the larvae can avoid predation and find sufficient and suitable food. Such longer periods of development could aid in the dispersal of the larvae, thereby accounting, at least in part, for the wide distribution of the adults of this spe- cies. However, at the lower temperature of 15°C, all of the 48 larvae remained in stage I up to 12 d before dying. This high mortality suggests very unfavorable conditions for the survival of this species. Cyclograpsus integer, along with some species of Sesarma, is among the few Sesarminae, and among still fewer Varuninae and Plagusiinae (Wilson 1980; Wilson and Gore 1980) known to have extra larval stages. The species presently stands alone in the genus in having this feature, but joins an increasingly large group of brachy- uran (and anomuran) crustaceans in which an additional larval stage occurs either at lower, or perhaps suboptimum, temperatures (Sandifer 1973; Knowlton 1974; Scotto 1979; Gore et al. 1981). The studies just cited follow classic inves- tigations by Costlow et al. (1960), Bookhout (1972), and Bookhout and Costlow (1974) in which temperature and salinity were manipu- lated and the effects on survival, duration, and number of larval stages were observed. The data in all these studies add to a large body of circum- stantial evidence from the plankton (e.g., alleged substages, morphological variants, oversized larvae, etc.) which suggests that additional lar- val stages may be an integral part of a decapod crustacean's larval potentiality in nature, and not just an artifact observed during laboratory culture of the species. Whether extra stages occur commonly, or only rarely, they are still classifiable as a response to change in conditions, and as such constitute an evolutionary adapta- tion toward survival. Description of the Larvae First Zoea Carapace length: 0.38 mm; 5 specimens exam- ined. 504 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOGRAPSUS INTEGER Carapace (Fig. 2A, a).— Smooth, globose, dorsal spine short, slightly curving posteriorly, rostral spine stout, bluntly rounded, ventrally directed; no lateral spines present in this stage. A medio- dorsal knob (Fig. 2a) midway between bases of dorsal and rostral spines with 5 integumental sensilla arranged as illustrated, these present in all stages. Posterolateral margin of carapace in- distinctly and irregularly dentate; ventrolateral margin produced into a blunt V-shaped process. Paired setae posterolateral^ to base of dorsal spine in all stages. Eyes unstalked. Abdomen and Telson (Fig. 2B).— Five somites; first naked, second, third, and fourth with paired lateral knobs (fourth smallest) directed anter- iorly, ventrally, and laterally respectively, these also with bluntly rounded posterolateral process; fifth somite with bluntly rounded posterolateral process. Pair of posterodorsal setae on somites 2-5 in all stages. Telson rectangular with pair of short, minutely hairy, furcae, 6 spines in be- tween, each armed with rows of spinules. Shal- low median notch present. Antennule (Fig. 2C). — Conical rod directed an- teriorly, flanking rostral spine, with 4 aesthe- tascs of varying size. Antenna (Fig. 2D). — Biramous; protopodite and exopodite spinelike processes approximately equal in length, both armed with 2 rows of spin- ules; exopodite with a simple seta one-third dis- tance from base. Mandibles (Fig. 2E).— Asymmetrically scoop- shaped process; incisor process with 1 large tooth anteriorly as well as posteriorly, 3 bluntly rounded denticles in between, plus 3 similarly on posterior edge of right mandible, 2 on left; molar process irregularly dentate, a large rounded tooth on the posterior angle. Maxillule (Fig. 2F). — Endopodite 2-segmented, setal formula progressing distally 1,5 (4 termi- nal plus 1 subterminal); basal endite with 5 stout setae, coxal endite with 4 stout, 1 thinner seta. Additional pubescence as illustrated. Maxilla (Fig. 2G).— Endopodite irregularly bi- lobed, each with 2 setae; basal and coxal endite bilobed, setal formula proximally to distally 5,4 and 4,3, respectively. Scaphognathite with 4 plumose setae on outer margin, distal portion tapering to setose apical process. Other pubes- cence as illustrated. Maxilliped 1 (Fig. 2H).— Coxopodite naked; basi- podite with 9 ventral setae, progressing distally 2,2,3,2; endopodite 5-segmented, setal formula 2,2,1,2,4+1 (Roman numeral = dorsal setae), third segment with several minute hairs on dor- sal surface; exopodite indistinctly 2-segmented, 4 terminal natatory setae. Maxilliped 2 (Fig. 21).— Coxopodite naked; basi- podite with 4 ventral setae, progressing distally 1,1,1,1; endopodite 3-segmented, setal formula 0,1,5+1; exopodite indistinctly 2-segmented, 4 natatory setae. Color. — Overall golden-brown under refracted light, abdomen colored more intensely than cephalothorax. Cornea black under refracted, iridescent blue under reflected light. Grouped brown and orange chromatophores appear as fol- lows: carapace, 4 interocular, 1 at base of dorsal spine, 1 at position of posterodorsal knob, 2 at future position of lateral spines, 4 along posterior margin, 3 at posteroventral angle; appendages, 1 on mandibles, 1 each on antennular and antennal protopodites, 2 on each maxillipedal basipodite; abdomen, 1 pair ventromedially on first somite, second through fifth somites with 1 pair antero- ventrally and 1 pair posteroventrally; telson with 1 pair anteriorly and 1 pair posteriorly at base of each set of 3 spines. Second Zoea Carapace length: 0.50 mm; 5 specimens exam- ined. Carapace (Fig. 3A).— Enlarged, pair of ventrally curved lateral spines now present. Dorsal and rostral spines both elongated, thinner, ends more tapered than first stage. Pair of interocular and 1 posterolateral seta now present. Posterodorsal knob midway between base of dorsal spine and posterior edge of carapace more prominent. Eyes stalked. Abdomen and Telson (Fig. 3B).— Similar in shape and armature to first stage with addition of single long dorsal seta on posteromedial edge of first somite. Antennule (Fig. 3C).— As in first stage but with 6 unequal aesthetascs. 505 FISHERY BULLETIN: VOL. 80, NO. 3 Figure 2. — First zoeal stage of Cyclograpsus integer. (A) Lateral view; (a) anterodorsal view; (B) abdomen and telson (in dorsal view as illustrated here and throughout all stages); (C) antennule; (D) antenna; (E) mandible; (F) maxillule; (G) maxilla; (H) maxilli- ped 1; (I) maxilliped 2. 506 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCI.OdKAI'SUS INTECEK Figure 3.— Second zoeal stage of Cyclograpsus integer. (A) Lateral view; (B) abdomen and telson; (C) antennule; (D) antenna; (E) mandible; (F) maxillule; (G) maxilla; (H) maxilliped 1; (I) maxilliped 2. 507 FISHERY BULLETIN: VOL. 80. NO. 3 Antenna (Fig. 3D).— Similar in form and arma- ture to first stage, with addition of minute hair on exopodite opposite of simple seta one-third from base. Mandible (Fig. 3E).— Increased in size, shape and armature similar to first stage. Maxillule (Fig. 3F).— Endopodite and coxal en- dite setation unchanged. Basal endite now with 5 stout, 3 thinner setae plus 1 long plumose seta on basal margin. Maxilla (Fig. 3G).— Endopodite, basal, and coxal endite setation unchanged. Scaphogna- thite with 5 long, thin, plumose setae proximally, 3 stout plumose setae on distal margin. Maxilliped 1 (Fig. 3H).— Coxopodite with 1 ven- tral seta. Basi- and endopodite setation un- changed. Exopodite with 6 natatory setae. Maxilliped 2 (Fig. 31).— Coxo-, basi-, and endo- podite setation unchanged. Exopodite now with 6 natatory setae. Color. — Overall darker golden brown than first stage. Color much more intense at dorsal spine, fifth somite, and telson. Lateral spines, rostrum, maxillipedal endo- and exopodites transparent. Deep golden hue around base of dorsal spine. Other chromatophore color and position as in first stage. Third Zoea Carapace length: 0.70 mm; 5 specimens exam- ined. Carapace (Fig. 4 A).— Zoea much enlarged, dor- sal, rostral, and lateral spines elongate, 2 pair of interocular setae, posterodorsal knob more prominent, posterolateral margin now with 4 or 5 setae placed as illustrated, irregular denticula- tion ventral to setae present here and in all stages. Posterodorsal margin of carapace with 3 setae. Abdomen and Telson (Fig. 4B). — Sixth abdomi- nal somite now present, with small bluntly rounded posterolateral process. First somite with 3 dorsomedial setae, middle the longest. Paired lateral knobs on second and third somites enlarged, posterolateral processes on somites 2- 5. Telson with interfurcal setal formula now 4+4, innermost pair the shortest. Antennule (Fig. 4C). — Unchanged in form from second stage, with 4 unequal aesthetascs. Antenna (Fig. 4D).— Similar to second stage, exopodite now slightly shorter than protopodite. Mandible (Fig. 4E).— Similar in form and arma- ture to second stage. Maxillule (Fig. 4F).— Endopodite and basal endite armature unchanged, 1,5 and 8+1 pro- cesses basally, respectively. Coxal endite with 5 setae plus 1 long plumose seta on basal mar- gin. Maxilla (Fig. 4G).— Endopodite 2,2, as before, basal endites 5,4, coxal endites now 5,3. Scaphog- nathite setae increased to 10 thinner plus 6 stout distal setae, separated by sparse hairs as illus- trated. Maxilliped 1 (Fig. 4H).— Coxo- and basipodite setation unchanged. Endopodite setal formula now 2,2,1 plus spine replacing dorsal setae, 2, 4+1. Exopodal natatory setae 8. Maxilliped 2 (Fig. 41).— Coxo-, basi-, and endo- podite setation unchanged. Exopodite with 8 natatory setae. Color. — Now appearing ocherous orange. Dorsal spine, abdomen, and telson darkest. Lateral spine with orange coloration on ventral surface. Orange chromatophores: at base of rostral spine, another midway to tip; on 2 or 3 basipodite of maxillipeds. Sixth somite and telson each with pair of orange-brown chromatophores medio- ventrally. Other chromatophore pattern re- mains as in first stage. Fourth Zoea Carapace length: 0.80 mm; 5 specimens exam- ined. Carapace (Fig. 5A).— Similar in form to third stage, elongate dorsal spine now with 5 setae on anterior margin as illustrated. Posterodorsal border now with 4 setae, posterolateral margin with 6. V-shaped process on ventrolateral mar- gin less blunt than previous stages. 508 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOGRAPSUS INTEGER A,B 0.5mm i ii i i i H,l 0.25mm E-G 0.1mm C,D 0.1mm Figure 4.— Third zoeal stage of Cyclograpsus integer. (A) Lateral view; (B) abdomen and telson; (C) antennule; (D) antenna; (E) mandible; (F) maxillule; (G) maxilla; (H) maxilliped 1; (I) maxilliped 2. 509 FISHERY BULLETIN: VOL. 80, NO. 3 A,B 1.0mm C-G 0.25mm H,l 0.25mm ■ Figure 5.— Fourth zoeal stage of Cyclograpsus integer. (A) Lateral view; (B) abdomen and telson; (C) antennule; (D) antenna; (E) mandibles; (F) maxillule; (G) maxilla; (H) maxilliped 1; (I) maxilliped 2. 510 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOGRAPSUS INTEGER Abdomen and Telson (Fig. 5B).— Pleopod and uropod buds now present on somites 2-5 and 6, respectively. First somite now with 5 middorsal setae. Antennule (Fig. 5C).— Conical rod with 5 termi- nal plus 2 subterminal aesthetascs. Antenna (Fig. 5D). — Armature and form similar to previous stage. Endopodal bud now present, less than one-half length of protopodal process. Mandible (Fig. 5E).— Similar to third stage with addition of 1 bluntly rounded tooth on posterior edge of incisor process. Maxillule (Fig. 5F).— Endopodite setation un- changed, basal endite now with 11 or 12 setae, coxal endite with 8 setae, 3-5 plumose setae on basal margin, placed as illustrated. Maxilla (Fig. 5G).— Setal formulae on endopo- dite 2,2; basal endites 6,5; coxal endites 7,3. Scaphognathite with 17-21 thinner setae, plus 5 or 6 stouter distal setae. Maxilliped 1 (Fig. 5H).— Coxopodite now with 2 ventral setae. Basipodite setation unchanged. Endopodite now with 2,2,1 plus 1 spine, 2,5+1. Exopodal natatory setae 9. Maxilliped 2 (Fig. 51).— Coxo-, basi-, and endo- podal setation unchanged. Exopodite now with 9 natatory setae. Color.— Ocherous orange; additional orange and brown chromatophores appear together as fol- lows: 1 each posterior to eyestalks, 1 anteromedi- ally on somites 2-4, a pair anteroventrally on somites 5 and 6, 1 anteroventral plus another medioventral pair on telson, and 1 each at base of lateral spine. Fifth Zoea (Ultimate) Carapace length: 1.2 mm; 3 specimens exam- ined. Carapace (Fig. 6A).— Similar to previous stage, dorsal spine elongate, posterodorsal border with 4 setae, posterolateral margin with 8 setae. Abdomen and Telson (Fig. 6B).— First somite with 6 or 7 middorsal setae, all other morphologi- cal features similar to fourth stage. Pleopod buds elongate, all now with endopodites. Antennule (Fig. 6E).— Endopodal bud present laterally below 2 tiers of aesthetascs, 5 unequal terminal aesthetascs plus 1 seta, and 6subtermi- nal aesthetascs. Basal region swollen, unseg- mented. Antenna (Fig. 6F).— Endopodal bud now three- fourths length of protopodal process. Exopodal spine remains shorter than protopodite. Mandible (Fig. 61).— Palp bud present on anter- ior surface. Incisor and molar form and arma- ture as in fourth stage. Maxillule (Fig. 6J).— Endopodal setation un- changed. Basal endite with 15 or 16 setae, coxal endite with 10-13 setae, 3 additionally on basal margin. Maxilla (Fig. 6K).— Endopodite unchanged. Setae of basal endites 8,8, coxal endites 11,4. Scaphognathite with 31-33 marginal setae. Maxilliped 1 (Fig. 6L).— Coxopodite now with 3 ventral setae. Basi- and endopodite setation un- changed. Exopodite now with 11 natatory setae. Maxilliped 2 (Fig. 6M).— Coxo-, basi-, and endo- podal setation unchanged. Exopodite now with 12 natatory setae. Maxilliped 3 (Fig. 6N).— Rudimentary trilobed, unsegmented naked process. Color. — Similar to previous stage. Numerous additional brown and orange chromatophores appear especially on anterior region of cephalo- thorax and sixth abdominal somite and telson. Tips of maxillipedal exopodites now with orange hue. On day before metamorphosis to megalopa, ultimate fifth stage zoea has very dark brown cephalothorax with innumerable spidery brown and orange chromatophores interspersed. Dor- sal spine and abdomen vermilion. Coalesced orange and brown chromatophore occur poster- iorly on the eyestalk. Fifth Zoea (Penultimate) Carapace length: ined. 1.1 mm; 3 specimens exam- 511 FISHERY BULLETIN: VOL. 80, NO. 3 Figure 6.— Fifth (ultimate, A, B, E, F, I-M, penultimate, C, D) and sixth (G, H) zoeal stages of Cyclograpsus integer. (A) Lateral view; (B) abdomen and telson; (C, E, G) antennule; (D, F, H) antenna; (I) mandible; (J) maxillule; (K) maxilla; (L) maxilliped 1; (M) maxilliped 2; (N) maxilliped 3. 512 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOCRAPSUS INTEGER Remarks. — The penultimate fifth stage zoea molted to a sixth stage before metamorphosing to megalopa. Only morphological features differ- ing significantly from the ultimate fifth stage, which molts directly to megalopa, are discussed below. Antennule (Fig. 6C). — No endopodal bud present, 5 terminal plus 4 subterminal unequal aesthe- tascs present. Antenna (Fig. 6D).— Endopodal bud only one- half length of protopodal process, other arma- ture and processes similar. Mandible. similar. -No palp present, other armature Abdomen. — Pleopod buds without endopodites, less elongate and developed. Sixth Zoea Carapace length: 1.3 mm; 3 specimens exam- ined. Remarks.— The sixth stage zoea appear similar in form and armature to the ultimate fifth stage. Only morphological characters which may be used to distinguish between the two stages are discussed below. Carapace. — Little inflated, posterodorsal border with 6 setae. Abdomen and Telson. — First somite with 8 or 9 middorsal setae, pleopod buds more elongate. Antennule (Fig. 6G). — Aesthetascs arranged in tiers as illustrated, progressing distally 2,2,4,4. Antenna (Fig. 6H). — Endopodal bud obscurely segmented, five-sixth length of protopodal pro- cess. Mandible. — Palp more elongate. Maxillule. — Basal endite with 18 setae, coxal endite with 12 setae, basal margin with 3 or 4 plumose setae. Maxilla. — Basal endites with 9,8, coxal with 12,4 setal formulae. Scaphognathite with 34-37 mar- ginal setae. Maxilliped /.— Coxopodite with 4 or 5 ventral setae. Basipodite setal formulae variable from 9 to 11 ventral setae, exopodite with 12 or 13 nata- tory setae. Maxilliped £— Coxopodite naked or with 1 seta ventrally, endopodite setation variable either 0,1,5+1 or 1,1,5+1. Exopodite with 13 or 14 nata- tory setae. Maxilliped 3.— Trilobed as in fifth stage, may have 1 seta on each lobe. Color.— Similar to fifth stage, innumerable spi- dery brown and orange chromatophores, entire maxillipeds now orange brown. Megalopa Carapace length X width: specimens examined. 1.45 X 1.25 mm: 7 Remarks. — Megalopae molting from both fifth and sixth zoeal stages are similar in form and arma- ture. Morphological characters distinguishing megalopae, which molted from ZVI, are placed in brackets under the appropriate headings. Carapace (Fig. 7A, B).— Cephalothorax sub- quadrate, laterally inflated. Smooth surface cov- ered with hairs as illustrated, plus innumerable setae on posterior and posterolateral borders. Frontal region developed into ventrally de- flexed, bluntly rounded rostrum with distinct median cleft, appearing as U-shaped sinus viewed dorsally. Anterolateral margins of cara- pace produced into 2 indistinctly rounded lobes. Eyes large, projecting laterally. Abdomen and Telson (Fig. 7A, a, E-I).— Somites 1-5 with bluntly rounded posterolateral pro- cesses, somite 6 much broader than long; all with setae as illustrated; telson semicircular, no pos- terior marginal setae, 2 pairs medially, others as illustrated. Pleopods well developed, with vari- able setation 16-19, 20 or 21, 19-22, 22 [19-21, 21, 22, 22], all endopods with 3 hooked setae termi- nally. Uropods with 10 or 11 exopodal plus 1 pro- topodal seta [11 or 12 plus 1]. Pereopods (Fig. 7A, C, D).— Chelipeds well de- veloped, somewhat inflated, unarmed, equal, shorter than walking legs, gape of chelae irregu- larly serrated, setae on remaining articles as 513 FISHERY BULLETIN: VOL. 80, NO. 3 Figure 7.— Megalopa stage of Cyclograpsus integer. (A) Dorsal view; (a) telson; (B) rostrum (anterolateral view); (C) left cheliped; (D) second pereopod dactyl; (E) first pleopod; (F) second pleopod; (G) third pleopod; (H) fourth pleopod; (I) uropod. Scale lines = 0.5 mm. 514 GORE an<1 SCOTTO: LARVAL DEVELOPMENT I »F CY( 7 OGRAPSl 'S INTEGER illustrated. Second to fourth pereopods elongate, similar, each with distoventral tooth on propodus and 4 ventral teeth on dactyl. Fifth pereopod dactyl with 3 [3 or 4] long pectinate setae (= brachyuran feelers). Antennule (Fig. 8A).— Biramous, peduncle 3- segmented, extremely enlarged, bulbous basal segment with 2 or 3 [3-5] setae, middle segment much smaller ovoid, with 2 or 3 [3 or 4] setae, dis- tal segment larger than middle, expanded dis- tally, naked. Flagellar lower ramus 1-segmented, 3 terminal, 1 subterminal setae; upper ramus 4- segmented, tiered aesthetascs usually arranged (0)(6), (6, plus 1 lateral seta), (5, plus 1 terminal seta). Antenna (Fig. 8B).— Peduncle with 2-4 distal setae; flagella with setation 1,2,0,0,2-3, 0,5,3,3, [1,2,0,0,4,0,4-5,3,3-4]. Mandible (Fig. 8C).— Incisor process smooth, spatulate; molar process elongate, tubular; palp 2-segmented with 0,9 setae. Maxillule (Fig. 8D).— Endopodite irregularly shaped, with 4 distal, 2 or 3 lateral setae; basal endite with 12 spines, 12-14 setae [25-29], coxal endite with 8 spines plus 2 rows of about 9 or 10 processes each [32] arranged in tiers as illus- trated. Basal margin with 4 [3-5] long setae. Maxilla (Fig. 8E).— Endopodite unsegmented, 2 [3] setae on lower lateral margin. Basal endites with 9-11, 12-14, [10-12, 13-16] processes, coxal endites with 7, 18-20 [8 or 9, 20-22] processes. Scaphognathite with 61-62 marginal setae plus 5 laterally on the blade as shown [70-72 plus 5]. Maxilliped 1 (Fig. 8F).— Exopodite 2-segmented, with 2 distal, 4 terminal setae. Endopodite irre- gularly shaped, unsegmented, 4-8 setae scat- tered over length. Basal endite with 13-17 [15- 17], coxal endite with 17-20, setae. Epipodite with 9 or 10 [13-18] long, aesthetascoid processes. Maxilliped 2 (Fig. 8G). — Exopodite 2-segmented, 2 lateral, 4 terminal setae. Endopodite 5-seg- mented setation progressing distally 3-7, 1, 1, 3 or 4, 6 or 7. Epipodite with 4-7 distal, 1 proximal, aesthetascoid processes, [9-11, plus 1]. Protopo- dite setae not determined. Maxilliped 3 (Fig. 8H). — Exopodite 2-segmented with 5 or 6 proximal, 4 or 5 terminal setae; endo- podite 5-segmented setae progressing distally 16-18, 12 or 13, 8-10, 10 or 11, 6 or 7 [18-20, 13,8- 12, 9-12, 8], protopodite with 21 or 22 [22-26] setae, epipodite with 21-26 aesthetascoid pro- cesses distally plus 8or9setaeproximally [30-32, plus 8-11]. Color. — Innumerable spidery orange and brown chromatophores completely covering cephalo- thorax, abdomen, pereopods, eyestalks, and all feeding appendages. DISCUSSION Zoeal Stages The complete larval development of <20% of the known species of Cyclograpsus has been studied, and zoeal stages within the genus will be difficult to identify in the plankton. Larvae of the genus are unusual in several respects; therefore, some morphological and developmental charac- ters may yet prove to be of aid in identification. For example, in at least two species (('. integer and C. cine reus) lateral carapace spines are lack- ing in the first stage, but appear in all later stages (Costlow and Fagetti 1967). Within the genus, some form of armature occurs on the ven- trolateral carapace margin, either as spines, small teeth, setae, or a combination of these. In general, teeth or spines occur in the early stages and are replaced by setae as development pro- ceeds. The number and time of appearance of these processes seems to be species specific (Table 2; and summary in Fagetti and Campo- donico 1971). In addition to the ventrolateral processes, later larval stages of all species of Cyclograpsus studied to date bear some form of setation of spination on the posterior middorsal margin of the carapace above the insertion of the abdomen. In C. cinereus, this takes the form of paired spines in the second and subsequent zoeal stages (Costlow and Fagetti 1967); in C. puncta- tus, a similar situation appears in the third and later stages (Fagetti and Campodonico 1971). whereas in C. integer, 3 setae appear in the third and subsequent stages. Unfortunately, the characters noted above are not restricted to Cyclograpsus but are shared, at least in part, among zoeae of several other genera in the four grapsid subfamilies. For instance, several genera in the Grapsinae, Varuninae. and Sesarminae have zoeal stages which lack lateral 515 FISHERY BULLETIN: VOL. 80, NO. 3 F-H 0.25mm i i ii Figure 8.— Megalopa stage of Cyclograpsus integer. (A) Antennule; (B) antenna; (C) mandible; (D) maxillule; (E) maxilla; (F) maxilliped 1; (G) maxilliped 2; (H) maxilliped 3. 516 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOGRAPSUS INTEC.F.K ""3 u X ft to > 3 o eo* t- etS o o CO ft E o c , I a> c ! 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CD >• CD |-E?=1 £ 1 "|o2 5 ft 2 5 S S S 8 £ S» "B I 5> S CO CO --co g CO g 5 ■2 — = ^ > N CO CO CO CO CD CD CD CO O O O o N N N M *-3 CO CO CO CO CD CD CD CD O o O O rsl M N rsi O 0) _ = ~ > > *g c o CO CO CO CO CD O CD O % CD O — tsi N N N tsi CO CD o N CO o tsi O CO CO & CD co O — N 6 _ CO — 3 CO CO CD c o — N 517 FISHERY BULLETIN: VOL. 80, NO. 3 carapace spines. No first stage grapsine zoeae, no Sesarma (Sesarminae), nor Acmaeopleura (or possible Gaetice) larvae in the Varuninae have these spines (see summary in Wilson 1980). Moreover, Pachygrapsus zoeae (Grapsinae), like some larvae in Cyclograpsus, apparently lack lateral spines in the first, but possess these in subsequent, zoeal stages (Schlotterbeck 1976; Bourdillon-Casanova 1960). On the other hand, all known plagusiine larvae have lateral spines from the first stage onward (Wilson 1980). Setation or spination on the ventrolateral cara- pace margin is another widely shared feature among grapsid genera. Examples include Brachynotus (Bourdillon-Casanova 1960), Hemi- grapsus (Kurata 1968), and Cyrtogr a ps :us (Scelzo and Lichtschein de Bastida 1979) in the Varuni- nae, Sesarma (Baba and Miyata 1971) in the Ses- arminae, Leptograpsus (Wear 1970) in the Grap- sinae, and Plagusia (Wilson and Gore 1980) in the Plagusiinae. In many instances, however, carapace and telson spine formulae differ sub- stantially from that seen in larvae of Cyclograp- sus, thereby allowing at least provisional separa- tion among these zoeae. Regarding middorsal carapace setation, many descriptions of brachyuran larvae either fail to note its occurrence or do not allow judgment to be made because of undetailed illustrations. A gen- eral perusal of the literature available on grap- sid larvae (Wilson 1980) shows that, in addition to Cyclograpsus, only a few sesarmine genera had this feature indicated, including Chasmag- nathus (Boschi et al. 1967), Helice (Baba and Moriyama 1972), and in the Varuninae Hemi- grapsus (Hart 1935) and Cyrtograpsus (Scelzo and Lichtschein de Bastida 1979). Several other studies provide suitably detailed illustrations which suggest that this character may be more or less widespread among the zoeae of these sub- families. However, these setae are apparently absent in plagusiine and grapsine larvae, as far as can be ascertained from the literature. Be- cause these setae usually do not appear until later zoeal stages (ZIII and beyond) their useful- ness as an identifying character is somewhat limited. One other carapace feature that seems note- worthy, at least for the genus Cyclograpsus, is the pterygostomian region of C. integer, this re- gion is produced into a triangular, toothlike prominence in the first stage, which becomes more sharply pronounced as development pro- ceeds. In C. cinereus, this prominence is always bluntly rounded until the last stage, when it be- comes more acute. In C. punctatus the promi- nence develops very slowly and apparently never becomes acute. Only the first zoeal stages are known in C. lavauxi and C. insularum (Wear 1970) and the prominence is not well developed in either, being similar to that seen in C. puncta- tus. Although the toothlike prominence is seen to some extent in other grapsid zoeae, it does not appear to be quite as prominent, based on the illustrations provided in several studies. The type of antenna has always been consid- ered an important classification feature in brachyuran larvae (Aikawa 1929). Most brachy- uran larvae have a type B antenna (i.e., exopod about 0.5-0.75X the length of the protopodal spine). This type is widely present throughout the Grapsidae, being found predominantly in the Sesarminae and Varuninae, but seen in only iso- lated instances in either the Grapsinae or Plagu- siinae. Nearly all Grapsinae have a type C an- tenna (exopod substantially reduced in size to the protopodal spine), an advanced character also shared for the most part among the known larvae of plagusiine genera (see summary in Wilson 1980). All Cyclograpsus larvae possess a type B an- tenna, with the exception of C. integer, which has a type A antenna (exopod and protopod about equal). The type A antenna is considered to be primitive (Aikawa 1929). The larvae of C. integer are even more remarkable in having the anten- nal protopodal spine and exopod both armed along their respective lengths with rows of teeth, in a manner similar to that seen in Eriocheir zoeae (Varuninae; Aikawa 1929), and reminis- cent of some antennae exhibited by larvae in sev- eral xanthid genera (e.g., Scotto 1979). In other Cyclograpsus zoeae, the exopod is entire, and only the protopodal spine is so armed. Cyclograp- sus integer is thus noteworthy for two exceptions: 1) an antenna of a form (i.e., doubly armed) rarely noted within the Grapsidae, and 2) an an- tenna type (A) found in no other zoeae of any genus in the Grapsidae. Rice (1980) summarized the available knowl- edge on the Grapsidae in a major paper dealing with brachyuran zoeal classification. In attempt- ing to delineate useful features among the four subfamilies of grapsid crabs, he suggested that the known zoeae of the Varuninae and Sesarmi- nae might be distinguished from the Grapsinae and Plagusiinae by always having a well-devel- oped antennal exopod at least half as long as the 518 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOGRAPSUS INTEGER spinous (protopodal) process (i.e., type B) and bearing at least 10 medial setae on the basis of the first maxilliped. Wilson (1980) subsequently demonstrated that Ewihirogra/psus larvae (Var- uninae) have extremely shortened antennal exo- pods (type C) plus only 8 basipodal setae, and therefore are more allied to Grapsinae and Plag- usiinae larvae than to those of the Sesarminae or other Varuninae. As noted above, C. integer also refute Rice's suggestion in regard to the Sesar- minae, by having a type A antenna and by bear- ing 9 (instead of 10) basipodal setae. Larvae of C. cinereus also have 9 basipodal setae on maxilli- ped 1, but these occur in a grouping different from that seen in C. integer, C. lavauxi larvae have 6 and C. insularum have 12 setae (Table 2). As to other features for distinguishing among the larvae of Cyclograpsus, setation and arma- ture of abdominal somites can be useful. Begin- ning with the second (C. integer), third (C. ciner- eus), or fourth zoeal stage (C. punctatus), nonpaired, usually elongate or spinelike setae are found on the posterodorsal margin of the first abdominal somite. As development proceeds these setae either increase in number (1, 3, 5, in C. integer stages), or remain unchanged (3, C. punctatus; 5, C. cinereus). Somite armature shows similar diversity, with a hooklike spine or knob on the second (C. cinereus), second and third (C. punctatus, C. lavauxi), or second through fourth somites (C. integer, C. insularum first zoea). Regrettably, neither of these charac- ters are specific for Cyclograpsus larvae because they occur in other brachyuran zoeae and are seen, for example, in the Goneplacidae(Carc*'»o- plax, Lee and Hong 1970; Tritodynamia, Bouc- quet 1965), as well as several other families less closely related to the Grapsidae (Lebour 1928, fig. 5, p. 483). The telsons in Cyclograpsus zoeae all seem referrable to Aikawa's (1929) type B (i.e., with- out supernumerary lateral spines, and typically brachyuran in shape). The telson formula of 1+3 (= furcal spine, plus movable spiny seta; Gore 1979) changes in stage III to 1+4 in C. integer, C. cinereus, and C. punctatus; the latter species, however, adds an additional medial pair of setae in stage V, becoming 1+5. Table 2 provides a summary of all of these features. Megalopal Stage The megalopae of the three Cyclograpsus spe- cies in which complete development is known differ substantially from one another and should prove more easily separable than their respec- tive larvae. The frontal region bears a strongly deflexed rostral spine in C. punctatus (Fagetti and Campodonico 1971), has a ventrally deflexed. bluntly rounded rostrum with a median cleft in C. integer, and is only slightly produced and without a rostral spine in C. cinereus (Costlow and Fagetti 1967). Other easily observed char- acters not requiring dissection include terminal setation on the telson, aesthetascs on the anten- nule, exopodal setae of the third maxillipeds, pleopods, and uropods. These, plus characters requiring some dissection to observe, are sum- marized in Table 3. None of the megalopal stages in any of the three species considered resembles the juvenile or adult crabs. Moreover, they do not exhibit easily noticeable differences from many other brachyuran megalopae, let alone grapsid mega- lopae. In general, lack of rostral spines, or with the rostrum only poorly developed, usually de- flexed, and unarmed, is seen in many grapsid postlarvae. Many of the species have the lower ramus of the antennule appearing as a 1-seg- mented, simple, palplike process (as in Chasmag- nathus, Helice, Cyrtograpsus, and others, Cost- low and Fagetti 1967), or even reduced to a simple seta (Sesarma; Costlow and Bookhout 1962). But because of the paucity of descriptions there is little use in attempting further classifi- cation at this time. In the discussion above we have demonstrated that several suggestions proposed by Rice (1980) for classifying grapsid larvae can no longer be considered useful. Although the distinctions among the larvae of the subfamilies Grapsinae and Varuninae, and Varuninae and Sesarminae have become blurred, we nonetheless reiterate the value of Rice's classification attempt, and draw special attention to his key to the brachy- uran families based on zoeal characters. By using the characters he proposed, one may still arrive within the Grapsidae using the key, pro- vided that the subfamilial headings are disre- garded. Rice's couplet 26 may then be modified to read as follows: 26. Carapace without lateral spines in all zoeal stages • • 27 Carapace usually with lateral spines in all zoeal stages or without only in first zoeal stage 28 519 FISHERY BULLETIN: VOL. 80, NO. 3 Table 3.— Comparison of selected megalopal characters in three species of Cyclograpsus. C. integer C. cinereus C. punctatus Cephalothorax Numerous hairs dorsally Dorsally naked1 Dorsally naked' Front Bluntly rounded. Slightly produced. Strongly deflexed ventrally deflexed without rostral rostral spine medially cleft rostrum spine Telson processes 0 terminal, 3 lateral, 3 terminal, 3 lateral, 9 terminal, 8 dorsal 2 pairs dorsally 2 pairs dorsally (6 transversely) Antennular (0)(6)(6,+1 seta) (0)(3)(4,+1 seta)(5) (0)(4)(4,+2 setae) aesthetascs (5.+1 seta) (4, +3 setae) Antennal flagella 9 articles 11 articles 9 articles Mandibular palp 0,9 setae 0.9 setae 0,7 setae Maxlllule Basipod 24-26 processes [25-29] 21 processes ca. 24 processes Coxopod 28-30 processes [32] 11 processes 16 processes Basal margin 4 setae [3-5] No data 2 setae Maxilla Endopod 0, +2 lateral setae 2, +1 lateral setae 1,1+4 lateral setae Scaphognathite 61-62 marginal setae [70-72] ca. 70 marginal setae ca. 65 marginal setae Maxilliped 3 Exopod 5-6 proximal, 4-5 distal 3 proximal, 5 distal 2 proximal, 5 distal setae setae1 setae' Pleopods Exopod setae 16-22 [19-22] 17-20 15-16 Uropod setae 1 protopodal, 10-11 1 protopodal, 10 1 protopodal, 8 exopodal [11-12] exopodal exopodal 'Data interpolated from illustrations, no specific description given zoeal stage VI. : megalopal stage obtained from We look to future studies that will provide de- scriptions of several common genera in the Grap- sinae (e.g., Geograpsus, Goniopsis), Sesarminae (Metapograpsus), as well as to additional studies on larvae of previously known genera in the Plagusiinae {Plagnsia, Percnon), and Varuninae (Euchirograpsus, Cyrtograpsus, and the as yet unknown zoeae of Glyptograpsus). All have the potential for providing further clarification of relationships among the Grapsidae. ACKNOWLEDGMENTS We thank S. Dillon Ripley, Smithsonian Insti- tution, Washington, D.C. for providing travel funds to collect the specimens used in this report. Paula M. Mikkelsen aided in field collecting and in maintaining the ovigerous females and larvae in the laboratory. LITERATURE CITED AlKAWA, H. 1929. On larval forms of some Brachyura. Rec. Ocean- ogr. Works Jpn. 2:17-55. Baba, K„ and K. Miyata. 1971. Larval development of Sesarma (Holometopus) de- haani H. Milne Edwards (Crustacea, Brachyura) reared in the laboratory. Mem. Fac. Educ, Kumamoto Univ. 19:54-64. Baba, K., and M. Moriyama. 1972. Larval development of Helice tridens uniana Rath- bun and H. tridens tridens De Haan (Crustacea, Brachy- ura) reared in laboratory. Mem. Fac. Educ, Kuma- moto Univ. 20:49-68. Bookhout, C. G. 1972. The effect of salinity on molting and larval devel- opment of Pagurus alatus Fabricus reared in the labora- tory. Fifth Europ. Mar. Biol. Symp., p. 173-187. Bookhout, C. G., and J. D. Costlow, Jr. 1970. Nutritional effects of Artemia from different loca- tions on larval development of crabs. Helgolander wiss. Meeresunters. 20:435-442. 1974. Larval development of Portunus spinicarpus reared in the laboratory. Bull. Mar. Sci. 24:20-51. Boschi, E. E., M. A. Scelzo, and B. Goldstein. 1967. Desarrollo larval de dos especies de Crustaceos Decapodos en el laboratorio. Pachycheles haigae Rodrigues da Costa (Porcellanidae) y Ckasmagnathus granulata Dana (Grapsidae). Bol. Inst. Biol. Mar., Mar del Plata 12, 46 p. Bocquet, C. 1965. Stades larvaires et juveniles de Tritodynamia at- lantica (Th. Monod) (=Asthenognathm atlanticus Th. Monod)et position systematiquedececrabe. Cah. Biol. Mar. 6:407-418. Bourdillon-Casanova, L. 1960. Le meroplancton du Golfe de Marseille: les larves de crustaces decapodes. Recueil Trav. Stn. Mar. En- doume 30, 286 p. Costlow, J. D., Jr., and C. G. Bookhout. 1962. The larval development of Sesarma reticulatum Say reared in the laboratory. Crustaceana 4:281-294. Costlow, J. D., Jr., C. G. Bookhout, and R. Monroe. 1960. The effect of salinity and temperature on larval de- velopment of Sesarma ci)terettm(Bosc)re3Lred in the lab- oratory. Biol. Bull. (Woods Hole) 118:183-202. Costlow, J. D., Jr., and E. Fagetti. 1967. The larval development of the crab, Cyclograpsus cinereus Dana, under laboratory conditions. Pac. Sci. 21:166-177. Fagetti, E., and I. Campodonico. 1971. The larval development of the crab Cyclograpsus punctatus H. Milne Edwards, under laboratory condi- 520 GORE and SCOTTO: LARVAL DEVELOPMENT OF CYCLOCRAPSl N INTEGER tions (Decapoda Rrachyura, Grapsidae, Sesarminae). Crustaceana 21:183-195. GORE, R. H. 1968. The larval development of the commensal crab Pol i/ou y.r gibbesi Haig, 1956 (Crustacea: Decapoda). Biol. Bull. (Woods Hole) 135:111-129. 1979. Larval development of Galathea rostrata under laboratory conditions, with a discussion of larval devel- opment in the Galatheidae (Crustacea Anomura). Fish. Bull.. U.S. 76:781-808. Gore, R. H., C. L. Van Dover, and K. A. Wilson. 1981. Studies on Decapod Crustacea from the Indian River region of Florida. XX. Micropanope barbadensis (Rathbun, 1921 ): the complete larval development under laboratory conditions (Brachyura, Xanthidae). J. Crust. Biol. 1:28-50. Knowlton, R. E. 1974. Larval developmental processes and controlling factors in decapod Crustacea, with emphasis on Caridea. Thalassia Jugosl. 10:138-158. KURATA, H. 1968. Larvae of decapoda Brachyura of Arasaki , Sagami Bay — II. Hemigrapsus sanguineus (de Haan) (Grapsi- dae). Bull. Tokai Reg. Fish. Res. Lab. 56, p. 161-165. LeBour, M. V. 1928. The larval stages of the Plymouth Brachyura. Proc. Zool. Soc. Lond. 1928:473-560. Lee, B. D., and S. Y. Hong. 1970. The larval development and growth of decapod crustaceans from Korean waters. I. Carcinoplaxvestitus (de Haan) (Goneplacidae, Brachyura). Publ. Mar. Lab.. Busan Fish. Coll. 3:1-11. Manning, R. B., and L. B. Holthuis. 1981. West African Brachyuran crabs (Crustacea: Deca- poda). Smithson. Contrib. Zool. 306, 379 p. Monod, Th. 1956. Hippidea et Brachyura ouest-africains. Mem. Inst. Fr. Afr. Noire 45, 674 p. Rathbun, M. J. 1918. The grapsoid crabs of America. U.S. Natl. Mus. Bull. 97, 461 p. Rice. A. L. 1980. Crab zoeal morphology and its bearing on the i sification of the Brachyura. Trans. Zool. Soc Lond. (1980)35:271-424. Sandifer, P. A. 1973. Effects of temperature and salinity on larval devel- opment of grass shrimp. Palaemoru tes vulgaris ( Deca- poda, Caridea). Fish. Bull., U.S. 71:115-123. Scelzo, M. A., AND V. Lichtschein de Bastida. 1979. Desarrollo larval y metamorfosis del cangrejo Cyrtograpsus altimanus Rathbun, 1914 (Brachyura. Grapsidae) en laboratorio, con observaciones sobre la ecologia de la especie. Physis 38(94):103-126. SCHLOTTERBECK, R. E. 1976. The larval development of the lined shore crab, Packygrapsus crassipes Randall, 1840 (Decapoda Brachyura, Grapsidae) reared in the laboratory. Crus- taceana 30:184-200. Scotto, L. E. 1979. Larval development of the Cuban stone crab, Me- nippe nodifrons (Brachyura, Xanthidae), under labora- tory conditions with notes on the status of the family Menippidae. Fish. Bull., U.S. 77:359-386. Wear, R. G. 1970. Life-history studies on New Zealand Brachyura. 4. Zoea larvae hatched from crabs of the family Grapsidae. N.Z. J. Mar. Freshwater Res. 4:1-35. Wilson, K. A. 1980. Studies on Decapod Crustacea from the Indian River region of Florida. XV. The larval development under laboratory conditions of Euchirograpsus atneri- canus A. Milne Edwards, 1880 (Crustacea Decapoda: Grapsidae) with notes on grapsid subfamilial larval characters. Bull. Mar. Sci. 30:756-775. Wilson, K. A., and R. H. Gore. 1980. Studies on Decapod Crustacea from the Indian River region of Florida. XVII. Larval stages of Plagusia depressa (Fabricius, 1775) cultured under laboratory conditions (Brachyura: Grapsidae). Bull. Mar. Sci. 30: 776-789. 521 REPRODUCTION, MOVEMENTS, AND POPULATION DYNAMICS OF THE LONGSPINE PORGY, STENOTOMUS CAPRINUS K1 Paul Geoghegan3 and Mark E. Chittenden, Jr.4 ABSTRACT Stenotomus caprinus mature at 90-125 mm TL as they approach age I. Spawning occurs once a year in a discrete period of 50-80 days duration from January through April with peak activity in Febru- ary or March. The male-female sex ratio was 1:1.21 in the spawning period. Spawning occurs in waters deeper than 27 m, and its timing coincides with the periodicity of onshore surface currents in the northern Gulf of Mexico. These currents probably transport eggs and larvae inshore to nursery areas <27 m deep where recruitment occurs. Young-of-the-year gradually disperse as they mature to waters 36-55 m deep where age I and II fish are most abundant. Stenotomus caprinus are most vulnerable to trawling at night. Growth in length is fastest in their first 8 months but slows greatly as they mature and divert energy towards reproduction. Stenotomus caprinus averaged 1 10-135 mm TL at age I, 130-155 mm at age II, and 160 mm at age III. Maximum size is about 200 mm TL and maximum lifespan typically is 2.5-3 years. Total annual mortality rate is 83-99%, butpostspawning survival, mortality rates, and lifespan vary greatly between year classes. Total weight-total length, length-length, and girth-total length relationships are presented. The population dynamics of S. caprinus appear quite different from those of S. ehrysops, and the genus Stenotomus may show zoo- geographic change at Cape Hatteras, N.C. Stenotomus caprinus, the longspine porgy, ranges in the Gulf of Mexico (Gulf) from Cam- peche Bank, Mexico, to Apalachee Bay, Fla., (Caldwell 1955) and occurs rarely in the Atlantic to North Carolina (Dawson5). It is very abundant at depths of 40-110 m and is the dominant fish in the brown shrimp community (Hildebrand 1954; Chittenden and McEachran 1976; Chittenden and Moore 1977). Stenotomus caprinus makes up a significant portion of the catch in the industrial fishery of the north central Gulf (Roithmayr 1965; Gutherz et al. 1975). Despite its abundance, little is known about this species. Its life history is known from gen- eral faunal studies such as Miller (1965), Moore et al. (1970), and Franks et al. (1972), although Henwood et al. (1978) described its food habits. Only Caldwell (1955), Henwood (1975), Henwood et al. (1978), and Dawson (footnote 5) have made 'Based on a thesis submitted by the senior author in partial fulfillment for the M.S. degree, Texas A&M University. 2Technical Article 17149 from the Texas Agricultural Ex- periment Station, College Station, TX 77843. :iDepartment of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Tex.; present address: Com- monwealth of Massachusetts, Division of Marine Fisheries, Cat Cove Marine Laboratory, 92 Fort Avenue, Salem, MA 01970. department of Wildlife and Fisheries Sciences, Texas A&M University. College Station, TX 77843. 5Dawson, R. A systematic revision of the sparid genus Ste- notomus. M.S. Thesis in prep., The College of Charleston, Charleston, S.C. Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80. NO. 3, 1982. studies specifically directed at 5. caprinus. This paper describes maturation and spawn- ing seasonality, movements and spawning areas, growth and sizes at age, mortality and lifespan, merits of age determination by scales and length-frequency analysis, length-length, total weight-total length, and girth-total length rela- tionships for S. caprinus. METHODS AND MATERIALS Stenotomus caprinus were collected monthly along a transect in the Gulf off Freeport, Tex., (Fig. 1) from October 1977 through March 1980 aboard a chartered shrimp trawler using double rigged 10.4 m shrimp trawls with 4.4 cm stretched cod end mesh and a tickler chain. Sta- tions were occupied at depths of 5, 9, 13, 14, 16, 22, 24, 27, 36, 47, 55, 64, 73, 82, 86, and 100 m. Collections were made during the day through September 1978; thereafter, a day and night cruise were usually made each month. The 22 m depth range was primarily occupied after Octo- ber 1978, and depths >47 m were first occupied in June 1979. Two tows of 10 min bottom time were made at each depth except that 1 tow was made prior to October 1978, 8-12 tows were made at 14 m, and 24 tows usually were made at 22 m. All S. caprinus were separated from the catch, measured for total length, fixed in 10% Forma- 523 FISHERY BULLETIN: VOL. 80, NO. 3 Figure 1.— Location of sampling areas with transect indicating stations occu- pied off Freeport, Tex. 5 10 15 20 25 NAUTCAL MLES lin,6 and later preserved in 70% ethanol. For the Table l.— Description of gonad maturity stages assigned to Stenotomus caprinus. period October 1978 to March 1980, 300 fish each month were selected by stratified random sam- pling to determine total length (TL), fork length (FL), standard length (SL), girth (G) at the fourth dorsal spine, total weight(TW), and ovary maturity stage and to take scale samples, except that only total weight, total length, sex, gonad weight, and ovary maturity stage were deter- mined from October 1979 to March 1980. Female and immature fish were assigned gonad matur- ity stages (Table 1) similar to Kesteven's system (Bagenal and Braum 1971). Scales were taken below the lateral line near the tip of the pectoral fin following procedures for S. chrysops (Dery and Rearden7), and cellulose acetate impressions were examined using a scale projector. Supplemental collections were made aboard the FRS Oregon II (NMFS) from 10 April to 1 May 1980 in the north central Gulf at depths of 9-91 m between long. 91°31' and 92°00'W (Rohr et al.8). Stenotomus caprinus were selected from Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 7Dery, L., and C. Reardon. 1979. Report of the State-Fed- eral scup (Stenotomus chrysops) age and growth workshop. Woods Hole Lab. Ref . 79-57, 10 p. Northeast Fisheries Center Woods Hole Laboratory, National Marine Fisheries Service, NOAA, Woods Hole, MA 02543. »Rohr, B. A., A J. Kemmerer, and W. H. Fox, Jr. 1980. FRS Oregon II Cruise 106 4/10-5/1/80. Cruise Report, 12 p. Southeast Fisheries Center Pascagoula Laboratory, National Marine Fisheries Service, NOAA, P.O. Drawer 1207, Pasca- goula, MS 39567. Stage Description Immature Maturing virgin Early developing 4 Late developing 5 Gravid 6 Ripe 7 Spent/resting Gonads barely or not visible. Gonads very small, sexes not distinguishable. Sexes distinguishable but individual eggs are not visible. Eggs opaque, ovaries extending along <90% of gut cavity. Ovaries extend along 90% or more of lateral wall of gut cavity, < 50% of eggs translucent. Ovaries extend 90% or more of lateral wall of gut cavity, >50% of eggs translucent. Ovaries barely extend along lateral wall of gut cavity, flaccid with few small eggs. Similar in appearance to Stage 3, but occurs in fish large enough to have already spawned. the catch without randomization procedures and measured in fork length. Year class identities were indicated by speci- fying the years in which the fish hatched. Age was determined by analysis of length frequen- cies, e.g., the Petersen method (Lagler 1956; Tesch 1971). The superior merits of this proce- dure for S. caprinus are noted in the section on Age Determination Using Scales. Size descrip- tions for each year class and each cruise (Table 2, Fig. 2) were based on major portions of fre- quency distributions cited. Boundaries between groups are indicated in Table 2 and Figure 2; mortality and growth calculations were based on groups defined by these boundaries. Arithme- tic means were used to describe central tenden- cies for each year class and each cruise because length frequencies within year classes were 524 GEOGHEGAN and CHITTENDEN: REPRODUCTION, MOVEMENTS OF LONGSPINE PORGY approximately normally distributed. Hatching dates of 15 February and 15 March were assigned to the 1978 and 1979 year classes, respectively, to estimate their growth and ages. Descriptions of spawning periodicity and growth assume that S. caprinus reach 20-30 mm TL 1-2 mo after hatch- ing. This assumption and assigned hatching dates seem reasonable because: 1) Stenotomus caprin us average 13-14 mm TL/30d growth dur- ing their first 8 mo of life (Fig. 3); 2) the slope and elevation of the regression of ovary weight on total length for the 1979 year class was greatest in mid-March (Fig. 4, Table 3) and back calcu- lated length of this year class was —5.26 mm TL at 0 d of age (Fig. 5). A hatching date of 15 Febru- ary was assigned to the 1978 year class because this year class recruited about 1 mo earlier in 1978, although gonad data are lacking for this period. There appears to be no published data on size at early age other than our findings. Our interpretations of the life history of S. caprinus obviously apply best to the area off Freeport, Tex., but they probably apply to much broader areas in the Gulf, judging from the agreement of our findings with the general pub- lished data on this species. MATURATION AND SPAWNING SEASONALITY Results Stenotomus caprinus mature at 90-125 mm TL as they approach age I. Sex could be determined by eye at 90 mm TL as many fish entered the Early Developing stage ( Fig. 6). Fish entered the Late Developing, Ripe, and Gravid stages at 100- 125 mm TL. These data are supported by the extrapolated .r-intercepts of ovary weight on total length which were 80-100 mm TL during the January-April spawning period (Fig. 4, Table 3). Our estimates of size at maturity agree with the mean sizes at age I given later. Little somatic growth occurs after S. caprinus enters the later stages of gonad maturation (Fig. 6). Mean sizes of fish approaching age I were 1 10 mm TL in the Early Developing, 113 mm in the Late Developing, 115 mm in the Gravid and Ripe, and 118 mm in the Spent/Resting stages. Stenotomus caprinus spawn once a year in a discrete period from January through April. This period is indicated by collections off Texas of fish that were 30-40 mm TL in April 1978. 20- 50 mm in May 1979, and 20-40 mm in February- March 1980 (Fig. 2), and by the capture of fish 20-80 mm TL in late April 1980 in the north cen- tral Gulf (Fig. 7). No spawning occurs from May through December, because the smallest fish collected in that period belong to year classes hatched before May. Peak spawning occurred in March and early April in 1979 and from Janu- ary through March 1980 as indicated by the in- creased slopes and elevated ovary weight-total length regression lines in those periods (Fig. 4, Table 3). The sharply defined and readily fol- lowed length-frequency modes for each year class indicate that spawning occurs in one dis- crete period each year. Gonad maturity data support a January-April spawning period and indicate that virtually all S. caprinus spawn at 12 mo of age. Fish in Gravid or Ripe stages occurred only in the period Janu- ary-April, and Spent/Resting stage fish ap- peared immediately thereafter (Fig. 8). Virtually all spawning occurs in the period January-April and few fish delay spawning until age II because extremely few fish were in the Immature, Matur- ing Virgin, or Early Developing stages in that period. The spawning period probably spans about 50- 80 d within the January-April interval, assum- ing larger fish were spawned before smaller ones, and all fish grew at the same rate as noted later. The spawning period duration was ap- proximated from growth increments and size ranges (expressed as 99% confidence limits for observations) of the 1978 and 1979 year classes in June and July (Table 2), their first months of full recruitment. The mean 99% confidence limit for observations in the June-July period was 22.19 mm in 1978 and 40.27 mm in 1979, and respec- tive mean daily growth was 0.45 mm/d and 0.50 mm/d. Calculated lengths of spawning periods were 49 din 1978 (22. 19 mm ^0.45 mm/d) and 82 d in 1979 (40.85 mm -s- 0.50 mm/d). These esti- mates suggest that the successful spawning pe- riod is much shorter than the January-April interval indicated by length compositions and gonad data. Stenotomus caprinus exhibited a sex ratio of 1.00 male to 1.21 females. This ratio was ob- served in 1 ,506 fish examined during the spawn- ing period and differs significantly from Ll(x2 = 13.01, a =0.05, df = 1). Discussion Our findings agree with the limited literature on Stenotomus reproduction. Previous workers 525 FISHERY BULLETIN: VOL. 80, NO. 3 10 5 1Ch 5 ./v 1 OCT 77 DAY N = 92 C/f=92 77 0 76 1 3 DEC 77 DAY 1 N = ?43 C/f = 48 6 77 I , 20 FEB 78 DAY \-r/\rJ\ N = 6)C/(=15 3 ^T- 1 **^ I 1 21 MAR 78 DAY N=7 C/f= 1 4 14 APR 78 DAY N = 73 C/f=4 6 1 8 MAY 78 DAY N = 1 C/(=0 2 14 JUN 78 DAY N = 305 C/f=610 15 JUL 78 DAY N = 781 C/l = 86 8 15 SEP 78 DAY N=134 C/f = 11 2 OCT 78 NIGHT N = 238 C/l=19 8 1 DEC 78 NIGHT N = 667 C/f = 25 7 3 DEC 78 DAY N = 900 C/f=33 3 24 FEB 79 DAY N=112 C/f = 3 5 12 MAR 79 NIGHT N = 1516 C/l = 44 6 78 I -, 77,2 , r- — > 1 160 200 30 20 10 10 5 20-1 15 10 5 5i 20n 15 10 5 \ 12 MAR 79 NIUHT N=1516 C/f=44 b 78,1-.— 77 2— t 5 APR 79 NIGHT N=1139 C/f = 33 5 20 APR 79 DAY N = 242 C/f=7 1 79 0- 14 MAY 79 NIGHT N = 478 C/f = 14 1 6 JUN 79 NIGHT N=1205 C/f = 31 7 78.1-«-77.2-t 79 0 78,1 i 21 JUN 79 DAY N = 246 C/f = 8 2 5-9 JUL 79 NIGHT N=295 C/f = 7 4 -78 1- 77 2 T JX^ , 79 0 1 772 19-22 JUL 79 DAY /f = 2 3 •—/\-?8 1- J N = 66 C/l 22-25 AUG 79 DAY N = 214 C/l = 6 3 22-25 SEP 79 DAY -79.0-A _ _78.l_77.2 N = 439C/f=119 40 120 160 200 TOTAL LENGTH (mm) Figure 2.— Monthly length frequencies (moving averages of three) of Stenotomus caprinus off Freeport, Tex. Bars in each panel 526 GEOGHEGAN and CHITTENDEN: REPRODUCTION, MOVEMENTS OF LONGSPINE I'ORGY 20n 22-25 SEP 79 DAY N = 439 C/f = 1 1 9 2-6 OCT 79 NIGHT N = 5146 C/f=131.9 " 15-18 NOV 79 DAY 1 N=248 C/f=6 2 79,0 1 ►I- 1 , 78,1-^77,2-, i , | r , *r ^nin — ■ < 1-4 DEC 79 NIGHT N=1133 C/f=28 3 79.0 77.2 r , 78.1 ►*, 200 15 10 5 30 n 20 10H 80 0 T ^~ 14-19 DEC 79 DAY N=315 C/f-7 9 79 0 3-6 JAN 80 NIGHT N = 853 C/l = 23 7 60- 4-11 FEB 80 NIGHT N=1066 C/f = 24 2 45- il l\ " 3 30 ►—79 l—i — A I\78.2.m 15 •80. Oi ftj I A, 1 ■ i '-i ^"T 15-20 FEB 80 DAY N = 386 C/f=107 5-8 MAR 80 NIGHT N=724 C/(=18 1 78 2, h77 3-, 19-23 MAR 80 DAY N = 464 C/l=10 3 120 200 TOTAL LENGTH (mm) indicate the size range of a; year class. The first two digits within a bar indicate the year class: the last digit is age in years: e.g.. 7*. I represents the 1978 year class when age I. C/f indicates number of individuals per 10-min tow. 527 FISHERY BULLETIN: VOL. 80, NO. 3 Table 2.— Growth data (mm TL) for Stenotomus caprinus from the Gulf off Freeport, Tex. Increments with an asterisk (*) were adjusted to growth per 30 d and plotted in Figure 3. Night and day cruises are indicated by N and D. Observed size ranges delineate year class boundaries used in growth and mortality calculations. 95% 99% Unadjusted Observed Mean confidence confidence growth Collection size range length limits of limits of increment date n (mm) (mm) s2 the mean observations (mm) 1977 Year Class 1 Oct 1977, D 92 85-120 100.5 54.1 990-102.0 81.3-119 4 5 Nov 1977, D 0 — — — — — — 3 Dec. 1977, D 242 103-157 127.6 123.3 126.2-1290 99.0-156.2 +27.1 20 Feb. 1978, D 61 113-157 134.4 125.0 131 6-137.2 105.6-163.2 +6.8 21 Mar. 1978, D 7 119-150 132.0 116.0 122.4-141.6 94.3-169.7 -2.4 14 Apr. 1978, D 66 95-157 135.9 115.2 133.3-138.5 108.3-163.5 +3.9 8 May 1978, D 1 120 120.0 0 120 0 120 0 -15.9 14 June 1978, D 0 — — — — — 15 July 1978, D 0 — — — — — 15 Sept 1978, D 0 — — — — — 11 Oct. 1978, N 0 — — — — — 1 Dec. 1978, N 3 136-155 145 3 82.3 1286-1620 92.3-198.3 +25.3 13 Dec 1978. D 12 136-147 141.2 11.1 139.1-143.3 131.0-151 .4 -4.1 24 Feb. 1979, D 0 — — — — — 12 Mar. 1979, N 15 146-182 155.8 99.2 150.3-161.3 126.4-185.2 +14.6 5 Apr. 1979, N 7 151-165 156.4 22.3 152.2-160.6 139.9-172.9 +0.6 20 Apr. 1979, D 0 — — — — — 14 May 1979, N 0 — — — — — 6 June 1979, N 10 145-166 154.6 40.9 150.1-159 1 134.3-174.9 -1.8 21 June 1979, D 0 — — — — — 5 July 1979, N 1 165 165 0 0 165.0 165.0 +11.4 19 July 1979, D 3 145-157 153 0 37.0 141 8-164.2 117 5-188.5 -12.0 22 Aug. 1979, D 3 146-159 151.7 44.3 139.5-163.9 112.8-190.6 -1.3 22 Sept. 1979, D 2 146-148 147.0 2.0 110.1-183.9 133.1-160.9 -4.7 2 Oct. 1979, N 4 145-160 153.0 38.7 144.4-161.6 124.4-181.6 +6.0 16 Oct. 1979, D 19 145-167 151.7 34.3 148.9-154.5 134.9-168.5 -1.3 3 Nov. 1979, N 6 144-161 149.8 38.2 143.6-150.0 126.9-172.7 -19 15 Nov. 1979, D 5 144-164 152.4 56.3 143.8-161.0 122.1-182.7 +2.6 1 Dec. 1979, N 12 144-153 1487 7.9 1469-150.5 140.1-157.3 -3.7 14 Dec. 1979, D 4 150-164 157.6 19.7 151.3-163 7 137.1-177.9 +8.8 3 Jan. 1980, N 8 154-170 161 .5 20 3 156.8-165.2 146.4-176.6 -4.0 16 Jan. 1980, D 1 164 164 0 0 164.0 164.0 +2.5 4 Feb. 1980, N 2 155-157 1565 0.5 154.3-158.7 149.5-163.5 -7.5 15 Feb 1980, D 4 156-165 162.2 17.6 155.4-1680 142.9-181.5 +5.7 5 Mar. 1980, N 4 154-175 164.5 77.7 152.3-176.7 116.1-205.1 +2.3 19 Mar. 1980, D 3 155-158 156.7 1.3 154 6-158.8 150.0-163.4 -7.8 1978 Year Class 14 Apr. 1978, D 7 29- 40 32.3 11.9 29.2- 35.4 20.2- 44.4 8 May 1978, D 0 — — — — — 14 June 1978, D 305 50- 76 64.9 19.5 64 4- 65.4 53.5- 76.3 +32.6' 15 July 1978, D 781 51- 93 79.0 17.6 78.7- 79.3 68.2- 89.8 +14.1* 15 Sept. 1978, D 134 78-111 98.7 25.4 97 8- 996 85.7-111.7 +19.7' 11 Oct. 1978, N 238 93-131 109.2 35.8 108 4-110.0 93.8-124.6 +10.5' 1 Dec. 1978. N 664 98-135 114.3 28.2 113.9-114.7 100.6-128.0 +5.1* 13 Dec. 1978, D 888 100-135 117.8 26.9 1 17.5-1 18.1 104.4-131.2 +3.5* 24 Feb. 1979, D 112 107-133 121.8 40.9 120.6-123.0 105.3-138.3 +4.0' 12 Mar. 1979, N 1.501 96-145 120.7 65.1 120.3-121.1 99 9-141.5 -1.1* 5 Apr. 1979, N 1,132 98-150 121.4 64.9 120.9-121.9 100.6-1422 +7.0* 20 Apr. 1979, D 241 110-146 123.5 39.7 122.7-124.3 107.3-139.7 +2.1* 14 May 1979, N 389 100-138 1198 33.7 118 9-120 7 104.8-134.8 -3.7* 6 June 1979, N 988 100-144 119.5 48.9 119.4-119.6 101.5-137.5 -0.3* 21 June 1979, D 135 100-143 121.7 47.3 120.5-1229 104.0-139.4 +2.2* 5 July 1979, N 73 101-145 121.4 59.2 120 9-121.9 101 6-141 2 -0.3* 19 July 1979. D 46 110-144 122.2 342 120.5-123.9 106.4-1380 +0.8* 22 Aug. 1979, D 202 105-145 124.4 42.3 123.5-125.3 107 6-141 2 +2.2' 22 Sept. 1979, D 190 110-145 125.6 30.4 124.8-1264 111.4-139.8 +1.2* 2 Oct. 1979, N 209 110-144 124 7 50 5 123.7-125.7 106.4-143.0 -0.9* 16 Oct. 1979, D 212 113-144 127.6 38.7 126 8-128.4 111.6-143.6 +3.6* 3 Nov. 1979, N 410 116-143 127.3 359 126 7-127 9 111 9-142 7 -0.3* 15 Nov. 1979, D 88 116-143 128.6 37.9 127.3-129 9 112.7-144.5 +1.3* 1 Dec. 1979, N 608 116-143 129.0 45.1 128.5-129.5 111.7-146.3 +0.4* 14 Dec. 1979, D 175 116-149 131.9 71.9 130.6-133.2 110.1-153 7 +2.9* 3 Jan 1980, N 647 116-153 131.6 48 3 131 1-132.1 113.7-149.5 -0.3* 16 Jan 1980, D 418 116-155 131.4 548 130.7-132.1 112.3-150 5 -0.2* 4 Feb 1980. N 769 116-154 131.3 54.0 130 8-131 6 112.4-150.2 -0.1* 15 Feb. 1980, D 153 120-155 132.2 44.1 131.2-133 4 115.2-1494 +1.0* 5 Mar. 1980, N 464 120-153 133 9 44.0 133.3-134 5 1168-151 0 +1.6* 19 Mar 1980, D 234 120-154 133.7 536 1328-1346 114 8-152.6 -0.2' 528 GEOGHEGAN and CHITTENDEN: REPRODUCTION. MOVEMENTS OF LONGSPINE PORGY Table 2.— Continued. 95% 99% Unadjusted Observed Mean confidence confidence growth Collection size range length limits of limits of increment date n (mm) (mm) s2 the mean observations (mm) 1979 Year Class 14 May 1979, N 89 22- 49 27.6 10.5 26 9- 28.3 19.3- 35.9 6 June 1979, N 207 29- 69 43.7 59 0 42.7- 44.7 23 9- 63.5 + 16. T 21 June 1979, D 111 35- 74 50 8 44.3 50.2- 51 4 33.7- 67.9 t7 r 5 July 1979, N 220 30- 76 55.0 74.1 73.0- 75 2 32.8- 77,2 +4.2* 19 July 1979, D 17 40- 80 69 2 76.9 64.7- 73.7 46.6- 91.8 +14.2* 22 Aug. 1979, D 9 63- 81 72.9 33.1 688- 77.2 58 1- 87.7 +3 7- 22 Sept 1979, D 247 58-102 83 3 78.8 77.7- 79.9 60.4-106.2 +104- 2 Oct 1979, N 4,933 58-109 83.7 24.3 83.6- 83.8 71.0- 96 4 +0.4* 16 Oct 1979, D 363 70-112 89 4 509 88 7- 90.1 71.0-1078 +5.7* 3 Nov. 1979, N 355 72-115 96 8 36.5 96 2- 97.4 81 2-112.4 +7.4* 15 Nov. 1979, D 155 87-115 100 4 18.0 99 7-101.1 89 5-111.3 +3.6* 1 Dec. 1979, N 525 88-115 100 5 21.3 100.1-1009 886-112.4 +0.1* 14 Dec. 1979, D 136 91-115 102.6 15.9 101.9-1033 92 3-112.9 +2.1* 3 Jan 1980, N 198 91-115 104 6 178 104.0-105.2 93.7-115.5 +2.0* 16 Jan 1980, D 138 94-115 104.1 16.4 103.4-1048 93.7-114.5 +0.5* 4 Feb 1980, N 223 91-115 105.7 23.3 105.1-106.3 93.3-118.1 +1.6* 15 Feb. 1980, D 223 96-119 107.3 25.3 106.6-1080 94.3-120 3 + 1.6* 5 Mar 1980, N 243 98-119 109 4 17.7 108 9-110.0 986-1202 +2.1* 19 Mar 1980, D 225 96-119 107.7 274 107 0-1084 94 2-121.2 -1.7* proposed a spring or late winter-early spring spawning period (Hildebrand 1954; Miller 1965; Chittenden and McEachran 1976) based on the captures of fish 106-159 mm TL with well-devel- oped gonads in February (Hildebrand 1954) and fish 31-89 mm TL in early May and June (Cald- well 1955; Miller 1965). Henwood's (1975) histo- logical studies indicated spawning from Novem- ber through April, but our data indicate little or no spawning before January. Our finding that 30r rr O 2 • 7979 YEAR CLASS • • • • • • • '. . ' * • ■ ..■■..■■ .1 . T. . I . . 1 ... 1.. . i FEB MAR APR MAY JUN JUL AUG SEP OCT NOV 0EC JAN EE8 MAR Age 0 0 16 46 76 106 137 168 198 229 259 290 321 350 381 AGE (days) Table 3.— Analyses of the monthly regressions of ovary weight ( Y) in grams on total length (X) in mil- limeters for female Stenotomus caprinus, Decem- ber 1978-March 1980. Regressions were significant ( at a = 0.05) except on 1 1 October 1978, 6 June 1 979. 19 July 1979, 22 August 1979, and 22 September 1979. Cruise n 100 r2 Equation 1 Dec 1978 144 23 70 Y = -0.963 + 0.010 X 24 Feb. 1979 41 17 89 Y = -0.913 + 0.016 X 12 Mar. 1979 168 37.35 Y = -3 096 + 0.038 X 5 Apr. 1979 109 48.18 Y = -3.295 + 0.036 X 20 Apr 1979 84 7.00 Y = -0 496 - 0 008 X 14 May 1979 110 23.26 Y = -0.166 f 0.002 X 5 July 1979 24 36.97 Y = -0.333 + 0.004 X 2 Oct. 1979 79 41.52 Y = -0.352 + 0 004 X 16 Oct. 1979 53 1058 Y = -0.109 + 0.002 X 3 Nov. 1979 89 47 78 Y = -0.232 - 0.003 X 15 Nov. 1979 65 58 86 Y = -0.564 + 0.007 X 1 Dec. 1979 68 71.36 Y = -1 486 + 0 016X 14 Dec. 1979 83 62.26 Y = -1.450 + 0.016 X 3 Jan. 1980 97 51.04 Y = -1.613 + 0.020 X 16 Jan 1980 85 82 36 Y = -2.329 + 0.026 X 4 Feb. 1980 93 73.57 Y = -3.132 + 0 036X 15 Feb. 1980 79 59 02 Y = -1.962 + 0.024 X 5 Mar 1980 81 4807 Y = -2.203 + 0.028 X 19 Mar. 1980 64 69 22 Y = -2.148 + 0.026 X 5 o rr z o 7978 YEAR CLASS Figure 3.— Monthly growth incre- ments for the 1978 and 1979 year classes of SU notomus caprinus. Unad- justed growth increments (Table 2) were converted to growth per ,30 d. Negative growth was rounded to 0. FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV 0EC JAN FEB MAR Age 0 Age I 0 13 43 74 104 135 166 196 227 257 288 319 347 378 408 439 469 500 531 561 592 622 653 684 713 744 775 AGE (days) 529 FISHERY BULLETIN: VOL. 80, NO. 3 FIGURE 4.— Monthly ovary weight- total length regressions for Stenotomus caprinus. The length of each line shows the observed size range. i eg > a. < > o 20 15 00 5 APR 79 120 130 140 TOTAL LENGTH (mm) 150 1979 YEAR CLASS Y=-5 257+0.644X-0 0009x! 1 100r2=97. 69 ' 95% conscience — limits tor Mean * observations -► Range 20 6C I00 140 180 220 260 300 340 380 £ AGE (days) £ 15 I 15 I 15 1 15 1 15 1 15 I 15 1 15 1 15 1 15 1 15 1 15 1 15 ' 15 MAR APR Z 160 < o SEP 0C1 NOV COLLECTION DATE FEB MAP 80 7978 YEAR CLASS Y=34.747+0.310x-0.0002x2 100r2 = 80.03 95% confidence limits tor observations Range 200 AGE (days) 10 1 15 1 15 1 15 1 15 1 15 1 15 1 15 1 15 1 15 1 15 1 15 1 15 1 15 I 15 1 15 1 15 1 15 1 15 I 15 I 15 1 15 1 15 1 15 1 15 I 15 I 15 MAR APR MAY JUN JUL AUG SEP 0C1 NOV OEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FES MAR APR COLLECTION DATE Figure 5.— Mean observed and pre- dicted sizes at age for the 1978 and 1979 year classes of Stenotomus capri- nus. Mean sizes at age (Table 2) were regressed on age after assigned hatch- ing dates of 15 February and 15 March for these respective year classes. Re- gressions were significant at a =0.05. virtually all S. caprinus spawn at 12 mo of age has not been reported, nor has the discrete and short duration of spawning been recognized. Sex ratios have not been reported for 5. caprinus, although 1:1 and 1:1.26 male to female ratios have been reported for its congener S. chrysops (Smith and Norcross 1968; Morse 1978). The pat- tern of spawning in S. caprinus is several months earlier in timing but similar to S. chrysops which spawns once a year from May through August 530 GE0GHEGAN and CHITTENDEN: REPRODUCTION. MOVEMENTS OF LONGSI'INE I'OKGY with greatest spawning in June (Bigelow and Schroeder 1953; Finkelstein 1969a). 10 12 9 6 3-I Immature n = 604 Maturing Virgin n = 150 Early Developing n=142 TOTAL LENGTH (mm) Figure 7.— Length frequency (moving averages of three) of Stenotomus caprinus captured in the north central Gulf aboard the Oregon II, 10 April-1 May 1980. Probable ages and year class identities are indicated. MOVEMENTS, SPAWNING AREAS, AND DIEL VARIATION IN CATCH Results o- Late Deve oping z 6- n = 64 ._ LU I 3 /)h < m hi u. u Eo> i-£ 1 ii lOO in E °> 00 r- 0. LU CO z 7i n co I 9 1 ^ o o E<*> o O O o ID o m o 2 3 5 C H c ■g tr. a> C4 T by depth for Sf rowth. C/f indie O "a? 6t f 1 V r* u A0N3nD3dd a) be CIS J- cp > a be c > o E o c 0) 3 a- a> c a> J I w OS O 533 FISHERY BULLETIN: VOL. 80, NO. 3 perse to deeper water. Our finding that age-I and age-II fish show no size-depth gradient and are mixed throughout 27-100 m depths has not been reported but agrees with Moore's (1964) finding that average weight did not increase in waters deeper than 64 m. Our findings that S. caprinus is most vulner- able to trawling at night has not been reported, although similar behavior has been recorded for S. aculeatus (Powles and Barans 1980). Fritz (1965) found that S. chrysops made up a greater percentage of the catch at night, although Smith and Norcross (1968) reported crepuscular catches were greatest. Henwood et al. (1978) sug- gested that S. caprinus actively feeds during the day. These fish might be inactive and near the bottom at night, and thus more vulnerable to trawling. AGE DETERMINATION USING SCALES Results Stenotomus caprinus cannot be aged readily using scales. Scales from 2,342 fish were exam- ined for annuli using criteria of Dery and Rear- den (footnote 7) which include cutting over, ir- regular spacing, and breaking of circuli. Marks similar to annuli were occasionally observed, but these marks varied greatly between scales from the same fish and between fish of the same size, age by length-frequency analysis, and date of capture. Annuli frequently were not apparent on fish that must have been age II or III according to length-frequency analysis, although one im- portant criterion for valid use of the scale method (Lagler 1956; Tesch 1971) is that this procedure should agree with ages determined from length frequencies. Discussion Our finding that it is difficult to age S. capri- nus using scales agrees with Henwood (1975). In contrast, several authors have used scales suc- cessfully to age S. chrysops (Finkelstein 1969a; Hamer 19799); although this becomes difficult beyond age III (Smith and Norcross 1968). Stenotomus caprinus are best aged using 9Hamer, P. 1979. Studies of the scup, Stenotomus chry- sops, in the Mid-Atlantic Bight. N.J. Div. Fish, Game, Shell- fish., Necote Creek Res. Stn., Misc. Rep. 18m, 66 p. length frequencies, particularly if, as in the pres- ent study, there is a long-term set of data from cruises made close together in time. Under these conditions age determination by length-fre- quency analysis may be obvious, as we found. Length-frequency analysis would be less reliable if cruises were several months apart in time, be- cause year class frequencies could merge after age I as our data indicate. The superior merits of age determination by length-frequency analysis are not surprising for S. caprinus because 1) this species spawns once ayear in a discrete period, 2) within year class frequencies appear normally distributed, and 3) growth of large and small fish within a year class is uniform as evidenced by the observed constant variance. In addition, length- frequency analysis generally is most clear for younger ages (Lagler 1956; Tesch 1971), and S. caprinus only lives a few years (see section on Mortality and Postspawning Survival). AGE DETERMINATION AND GROWTH USING LENGTH- FREQUENCY ANALYSIS Results No more than four year classes of S. caprinus were present at any time off Texas and only one or two predominated. These year classes repre- sented young-of-the-year and ages I, II, and III (Fig. 2). Only one year class predominated in any month from October 1977 through April 1979, although two year classes often were captured. The 1977 year class predominated initially in this period but virtually disappeared at age I after the 1978 year class recruited. Three year classes usually were captured after the 1979 year class recruited in May. In contrast to the virtual disappearance of the 1977 year class, the 1978 year class remained abundant at age I after the new year class recruited. As a result, two year classes (1978 and 1979) were equally predomi- nant from May 1979 through March 1980. Four year classes were present after the 1980 year class recruited in February, but only the 1978 and 1979 year classes predominated. Minor qualifications should be noted to the designation of the 1977 year class. The group identified as the 1977 year class in the period December 1977-April 1978 may contain mem- bers of the 1976 year class. This is suggested be- cause 1) the size range offish in that period may be too broad for one year class; 2) apparent 534 GEOGHEGAN and CHITTENDEN: REPRODUCTION. MOVEMENTS OF LONGSPINE PORGY growth between October and December 1977 is high when compared with the same period in other years; and 3) size at age I is comparatively large for the 1977 year class. The 1977 and 1978 year classes were difficult to distinguish after December 1978, so that the 1977 year class there- after may include fast growing members of the 1978 year class. Stenotomus caprinus growth varied between year classes, but sizes averaged 110-135 mm TL at age 1, 130-155 mm at age II, and 160 mm at age III. Observed mean sizes at age I, based on pooled data from February and March (Table 2), were 134.2 mm TL for the 1977 year class (range 113- 157 mm), 120.8 mm for the 1978 year class (range 96-145 mm), and 107.5 mm for the 1979 year class (range 91-119 mm). These sizes at age I agree with regression predictions (Fig. 5) of 114.8 mm TL for the 1978 year class and 110.0 mm for the 1979 year class. Observed mean size at age II was 132.5 mm TL for the 1978 year class (range 116-155) (Table 2), which closely agrees with a regression prediction of 128.6 mm (Fig. 5). The few survivors of the 1977 year class aver- aged 155.8 mm TL (range 146-182) at age II and 160.8 mm at age III (range 154-175 mm) (Table 2). Many fish approached the maxima in the size ranges at age cited for each year class, and the ranges at age appeared constant between collec- tions indicating uniform growth (Table 2). Possible error in assigned hatching dates would have little effect on our estimates for mean sizes at age because 99% confidence intervals of observations were constant within the following periods (Table 2): December 1977-April 1978 for the 1977 year class; December 1978-June 1979 for the 1978 year class; and December 1979- March 1980 for the 1979 year class. Stenotomus caprinus grow rapidly in their first 8 mo, but growth slows greatly as they ma- ture and appears negligible after maturity. The 1978 and 1979 year classes showed a rapid, almost linear decline in monthly growth incre- ments during their first 8 mo (Fig. 3). Growth of the 1978 year class averaged 13.62 mm TL/30 d from 15 February through early October 1978, and the 1979 year class averaged 12.66 mm/30 d from 15 March to early November 1979, ignor- ing the regression effect. In contrast, the 1978 year class grew only 13 mm TL in its second year; and the 1977 year class grew only 23 mm in its second year and 4 mm in its third year. This growth pattern may result in gradual merging of year class size compositions after age I as indi- cated by the 1978 and 1979 year classes (P^ig. 2). The small amount of growth after maturity seems to occur primarily during the late spring- early fall interim between reproductive activi- ties (Fig. 3). Very little growth occurred in the January-April spawning period when the 1978 year class averaged 0.83 mm TL/30 d in that pe- riod in 1979 and 0.80 mm/30 d in 1980. Size at age I varies between S. caprinus year classes, but growth is not obviously density de- pendent. No simple relationship was apparent for the 1977-79 year classes (Fig. 10) between mean size at age I and their index of year class strength, calculated as tcJXfi where 5/,- is the total number of tows and Sc, is the total catch at age I for each year class at depths of 27-47 m. Fish of the weak 1979 year class averaged smaller at age I (107.5 mm TL) than the strong 1978 year class (120.8 mm), a pattern not consis- tent with density dependent growth. Growth of the 1979 year class might have been depressed by interaction with the strong 1978 year class, but no density dependent relationship was apparent even when a pooled index of population strength was substituted for the 1979 year class strength index. 140 100 1977 * E E 130 ■ — ' i- LU o < H 120 < LU N W z 110 7979 Pooled < • • LU 1978 * 25 50 75 100 INDEX OF YEAR CLASS STRENGTH Figure 10.— Relationship between mean sizes at age I and year class strength for Stenotomus caprinus off Freeport, Tex. Indices of individual year class strength are indicated by stars and the pooled index by solid circle. Discussion Our findings on growth are largely new be- cause the growth of S. caprinus has not been described previously. Sizes at age I agree with Chittenden and McEachran's (1976) suggestion 535 FISHERY BULLETIN: VOL. 80, NO. 3 that 5. caprinus reaches 90-123 mm TL at age I. Back-calculated lengths of S. chrysops are 120- 155 mm TL at age I and 182-213 mm at age II (Finkelstein 1969a; Hamer footnote 9). Sizes at age I appear to be similar in these species, but S. chrysops is much larger at age II. Our growth data and the constant size noted in later gonad maturity stages (Fig. 6) indicate that S. caprinus markedly diverts energy from somatic growth to gonadal development as it matures. The differ- ent sizes of these congeners at age II probably reflect this drastic diversion of energy in S. ca- prinus. MAXIMUM SIZE AND LIFESPAN Results The maximum size typically reached by S. caprinus is about 200 mm TL. The largest fish collected off Texas (n = 22,924) was 182 mm TL, and the largest specimen collected in the north central Gulf (n — 1,576) aboard the Oregon II was 193 mm TL. The maximum lifespan of S. caprinus typically appears to be 2.5-3 yr. In the period October 1977-March 1980, 99% of the specimens captured off Texas were <146 mm TL, and 99.5% were <149mm(Fig. 11). Many age II fish captured off Texas were as large as 155 mm TL. The largest fish collected was age II when captured in March 1979, or age III if it was a member of the poorly defined 1976 year class (Fig. 2). These data indi- cate that a value of ti = 2.5-3 yr is reasonable for this Beverton-Holt model parameter (Gulland 1969). This estimate is supported by data from the north central Gulf (Fig. 7) in which 99% of the fish were <172 mm TL and 99.5% were <176 mm. Fish of these sizes were age II or III in the north central Gulf (Fig. 7). Discussion The maximum sizes reported herein are slightly larger than the maximum size reported by Hildebrand (1954), Caldwell (1955), and Chit- tenden and McEachran (1976). The only pub- lished record of S. caprinus much larger than 200 mm TL is that of Franks et al. (1972) who captured a specimen 256 mm TL in the north central Gulf. The apparent larger size of individ- uals at given percentages of the catch in the north central Gulf might reflect growth differ- ences between areas, or the nonrandom sub- 58CN 80 120 160 TOTAL LENGTH (mm) 200 Figure 11.— Length frequency (moving averages of three) and cumulative percent frequency of all Stenotomus caprinus col- lected off Freeport, Tex., October 1977-March 1980. sampling from the Oregon //catch which would probably select larger fish. Values of ti would vary from year to year due to variation in post- spawning survival noted later. MORTALITY AND POSTSPAWNING SURVIVAL Results Stenotomus caprinus has a total annual mor- tality rate of about 83-99% on a time-specific basis. Time-specific total annual mortality rates (1 — S) were calculated from the expression S = N(/No where S = rate of survival, and N, and No are the numbers of fish collected at age each cruise in depths of 18-100 m. The pooled esti- mate, using Heincke's procedure (Ricker 1975) was 98.95% comparing the 1977 and 1978 year classes and individual rates generally exceeded 98%. These values probably overestimate 1 — S, because the 1978 year class was stronger than the 1977 year class (Fig. 10). The pooled estimate comparing the apparent 1976 and 1977 year classes was 99.79%. The pooled estimate compar- ing the 1978 and 1979 year classes was 84.94% which may be fortuitous because it included one data set (October 1979) for which an exception- ally large number of fish from the 1979 year class were captured. A minimum pooled mortality estimate for the 1978 and 1979 year classes is 40.73%, if the exceptional October 1979 data set is excluded. This is probably a large underesti- mate because the 1979 year class was so much weaker than the 1978 year class. Realistic esti- mates could not be calculated in most instances comparing the 1978 and 1979 year classes be- cause N, exceeded iV0, which largely reflects the much greater strength of the 1978 year class (Fig. 10). Time-specific mortality estimates made from Chittenden and McEachran's (1976) 536 GEOGHEGAN and CHITTENDEN: REPRODUCTION, MOVEMENTS OF LONGSPINE PORGY raw data were 99% for late September 1973 (S = 5/435) and 83% for January 1974(5 = 395/2,468). Pooled cohort-specific estimates of 1 - S were 99.23% for the 1977 year class and 83.36% for the 1978 year class using Heincke's procedure. The different mortality rates for these year classes are consistent with theoretical mortality rates given later, and the greater postspawning survi- val of the 1978 year class. Postspawning survival of S. caprinus, total annual mortality rates, and maximum lifespan varies greatly between years and year classes. The 1977 and apparently 1976 year classes rarely appeared after they spawned at age I (Fig. 2). In contrast, many members of the 1978 year class survived after spawning at age I and spawned again at age II. White and Chittenden (1977) suggested somatic weight variation as a factor in the survival of the Atlantic croaker, Micropogonias undulatus. Somatic weight of fe- male S. caprinus did not change in a regular monthly pattern, and regression elevations dif- fered widely in consecutive months (Fig. 12, Table 4). Discussion Both time-specific and cohort-specific esti- mates indicate that the total annual mortality rate of S. caprinus is about 83-99%, depending on postspawning survival. Lower values in this range agree with theory (Royce 1972:238) that total annual mortality is 78-84% if the maximum age is 2.5-3 yr as observed. Higher values are consistent with theoretical annual rates of 90- 100% given the 1-2 yr lifespan observed for some year classes. Variation in postspawning survival might not- be due to somatic weight changes because of the lack of a regular monthly pattern and the wide variation in regression elevations between adja- cent months, although our somatic weight re- gressions are based primarily on the 1978 and 1979 year classes which did not disappear after spawning. TOTAL WEIGHT-TOTAL LENGTH, GIRTH-TOTAL LENGTH, AND LENGTH-LENGTH RELATIONSHIPS Regression and related analyses for total weight-total length, girth-total length, and length-length relationships are presented in Table 5. Table 4.— Analyses for the monthly regressions of somatic weight (V) in grams on total length (X) in millimeters for fe male Stenotomus caprinus, October 1978-March 1980. All re- gressions were significant at a = 0.05. Collection date n 100 r2 Equation 11 Oct 1978 53 86 01 Y = 50 789 + 0 699 X 1 Dec. 1978 144 87 44 Y = 71 240 - 1.323 X + 0 008 X2 24 Feb 1979 41 7888 Y = -32 009 + 0 506 X 12 Mar. 1979 168 94.57 Y = 73 409 1 361 X \ 0 008 X2 5 Apr 1979 109 97.15 Y = 59.722 1 234 X 1 0 008 X2 20 Apr 1979 84 80 36 Y = 234 333 - 4.095 X 0 020 X2 14 May 1979 110 84.32 Y = 68 022 - 1 327 X + 0 008 X2 6 June 1979 56 92.71 Y = -69.449 + 0 843 X 21 June 1979 49 7044 Y = -34.932 + 0 539 X 5 July 1979 24 91 41 Y = 137.564-2.44 X + 0013 X' 19 July 1979 20 60.11 Y = -48.541 f 0.663 X 22 Aug. 1979 70 8001 Y = 186 455 3,150 X * 0015 X2 22 Sept. 1979 82 6832 Y = -38 548 + 0.584 X 2 Oct 1979 79 95.62 Y = 71.630 + 1.233 X t 0.007 X2 16 Oct. 1979 53 88 69 Y = 44 643 + 0.631 X 3 Nov 1979 89 93.90 Y = -37.481 +0.578 X 15 Nov 1979 65 95.70 Y = 4.819-0.237 X + 0 004 X2 1 Dec 1979 37 68 44 Y = -30 428 + 0 508 X 14 Dec. 1979 82 96.32 Y = -43.178 +0 609 X 3 Jan. 1980 96 95 34 Y = 35 286 - 0.762 X + 0 006 X2 16 Jan. 1980 86 97 36 Y = 35.576 - 0.795 X + 0 006 X2 4 Feb 1980 93 97 57 Y = 20 722 - 0 526 X + 0.005 X2 15 Feb. 1980 79 96.23 Y = 20.382 - 0 506 X + 0 005 X2 5 Mar. 1980 80 83.65 Y = -38.256 + 0.565 X 19 Mar. 1980 64 79.38 Y = -49 710 + 0 662X Total length-total weight regressions for adult males and females were not significantly differ- ent in slope (F = 0.029, df = 1,657, a = 0.05) or in adjusted means (F= 1.63, df = 1,658, a =0.05) so that one pooled regression equation was pre- sented for them. Calculated slopes varied signifi- cantly from 0 = 3.0 (t = 13.2, df = 1,682, a = 0.05) except when data for immatures, males, and fe- males were pooled (t = 0.197, df = 2,792, a = 0.05). GENERAL DISCUSSION Stenotomus caprinus, which inhabits the warm temperate Gulf, exhibits markedly differ- ent population dynamics from Stenotomus chry- sops, which primarily inhabits the cold temper- ate Atlantic north of Cape Hatteras, N.C. Our data and the literature agree that for S. capri- nus: 1) spawning occurs in one discrete period a year with peak spawning in February or March; 2) all individuals reach maturity and spawn at 90-125 mm TL as they approach age I; 3) maxi- mum size typically is about 200 mm TL, but most fish are much smaller; 4) maximum lifespan is 2.5-3 yr; 5) total annual mortality rate is 83-99%, but postspawning survival, total annual mortal- ity rates, and lifespan vary between year classes; and 6) average sizes are 110-135 mm TL at age I, 130-155 mm at age II, and 160 mm at age III. In contrast, S. chrysops north of Cape Hatteras 1) 537 FISHERY BULLETIN: VOL. 80. NO. 3 60 50 ai 40 60 50 3 40 I o LU § 30 o H < 2 o ?n U) 10 12 MAR 79 6 JUN 79 OCTOBER 1978-SEPTEMBER 1979 5 JUL 79 22 AUG 79 I o LU 5 30 a i- < 2 o ?0 (/) 1 DEC 78 — ■ 5 ^Pfl 79 m 11 OC7" 78 22 SEP 79 79 JUL 79 21 JUN 79 5 APR 79 20 APR 79 14 MAY 79 14 FEB 79 90 100 110 120 130 TOTAL LENGTH (mm) OCTOBER 1979-MARCH 1980 15 FEB 80 16 OCT 79 140 150 160 16 JAN 80 4 FEB 80 3 JAN 80 / / 1Q MAR 80 OV 79 / /y' //^/0C1 79 5 MAR 80 1 DEC 90 100 110 120 130 TOTAL LENGTH (mm) 140 150 160 Figure 12.— Monthly somatic weight-total length regressions for Stenotomus caprinus. The length of each line shows the observed size range. spawns in the period May-August with peak spawning in June (Bigelow and Schroeder 1953; Finkelstein 1969a); 2) reaches maturity at age II at 182-213 mm TL (Finkelstein 1969a, b; Hamer footnote 9); 3) reaches a maximum size of ap- proximately 480 mm TL (Hamer footnote 9); 4) has a maximum lifespan of 15 yr (Finkelstein 1969a); 5) apparently has a much lower total an- 538 GEOGHEGAN and CHITTENDEN: REPRODUCTION, MOVEMENTS OF LONGSPINE POROY Table 5.— Analyses of total length-total weight (A), length-length (B), and total length-girth (B) relationships for Stenotomus capriyius. Lengths and girths are in millimeters and weights are in grams. All regressions were significant at a = 0.05. See Methods and Materials for symbols. Residual Observed TL mean Corrected total SS Means of range (not transformed) Relation Equation n 100 r3 square for both variables variables A. All fish Logu >TW = 2.793 99 32 00017 Log TW = 705.12 Log TW = 1 .28 21-182 -4 85 + 3 05 Log,0TL Log TL = 75 17 Log TL = 2.01 Adult fish Logu ,TW = 1.683 9051 00010 Log TW = 18.27 Log TW = 1 .50 91-182 -4 13 + 2.71 Log,0TL Log TL = 2.25 Log TL = 2 08 Observed range Residual Corrected Mean of for dependent mean total SS for dependent variable (not Relation Equation n 100 r2 square dependent variable variable transformed) B SL-TL SL = 0.41 +0.76 TL 2.776 99 26 3.55 1 ,326,361 .42 81 88 21-182 TL-3L TL = 0.26 + 1.31 SL 2,776 99 26 6.10 2,280,443.91 116.86 21-182 SL-FL SL = 0.85 + 0 11 FL 2,421 97.12 4.01 337,068 73 81 88 26-182 FL-SL FL = 2.90 + 1.14 SL 2.421 97 12 540 453.813.15 104.88 26-182 FL-TL FL = 1.99 +0.88 TL 2,402 97 36 4 98 452,54920 104.88 26-182 TL-FL TL = 093 + 1.11 FL 2,402 97.36 624 567,821 45 116.86 26-182 TL-G TL = 8.27 + 0.94 G 2.792 98 00 16.32 2,286,24929 107.26 21-182 G-TL G = -6.54 + 1.04 TL 2.792 98 00 18.17 2,545,01998 105.50 21-182 nual mortality rate, theoretically 26% based on a 15-yr lifespan (Royce 1972:238); and 6) averages 120-155 mm TL at age I, 183-213 mm at age II, and 232-257 mm at age III (Finkelstein 1969a; Hamer footnote 9). The basic pattern of population dynamics characteristics enumerated for 5. eaprinus is similar to that reported from the Gulf for Micro- pogonias undulatus (White and Chittenden 1977), Cynoscion nothus (DeVries and Chitten- den 1982), C. arenarius (Shlossman and Chitten- den 1981), and Peprilus burti (Murphy 1981). These findings give additional support to the suggestions (Chittenden and McEachran 1976; Chittenden 1977) that the abundant species of the white and brown shrimp communities in the Gulf have evolved a common pattern of popula- tion dynamics that stresses small size, short life- span, high mortality rates, and rapid turnover of biomass, especially when compared with conge- ners or conspecifics north of Cape Hatteras. The intrageneric variation in Stenotomus sup- ports the suggestion of White and Chittenden (1977) that zoogeographic variation in life histor- ies and population dynamics occurs at Cape Hat- teras. Unfortunately, the meager information published from the Atlantic coast south of Cape Hatteras does not permit enumeration of popula- tion dynamics of Stenotomus from that area. However, our findings on Stenotomus are consis- tent with the intrageneric variation in popula- tion dynamics within the genus Cynoscion at Cape Hatteras (Shlossman and Chittenden 1981), and are similar to the zoogeographic vari- ation reported for M. undulatus (White and Chit- tenden 1977). This zoogeographic variation in population dynamics characteristics has impor- tant management implications, because Carolin- ean Province fish should be less sensitive to growth overfishing than their congeners or con- specifics north of Cape Hatteras. ACKNOWLEDGMENTS We are much indebted to M. Burton, T. Craw- ford, T. Fehrman, R. Grobe, M. Murphy, J. Pa- vela, M. Rockett, J. Ross, P. Shlossman, B. Slingerland, G. Standard, H. Yette, and Cap- tains H. Forrester, J. Forrester, M. Forrester, P. Smirch, and A. Smircic for assistance in field collections and data recording. R. Darnell, E. Klima, K. Strawn, J. Pavela, and J. Ross re- viewed the manuscript. E. Gutherz and B. Rohr made it possible to use data from the NMFS groundfish survey 106. R. Case wrote and assist- ed with computer programs. Financial support was provided, in part, by the Texas Agricultural Experiment Station and by the Texas A&M Uni- versity Sea Grant College Program, supported by the NO A A Office of Sea Grant, Department of Commerce. LITERATURE CITED Bagenal, T. B., AND E. Braum. 1971. Eggs and early life history. In W. E. Ricker (edi- tor), Methods for assessment of fish production in fresh waters. 2d ed., p. 166-198. Blackwell Sci. Publ., Oxf.. Engl. BlGELOW, H. B., AND W. C. SCHROEDER. 1953. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv.. Fish. Bull. 74, 577 p. Caldwell, D. K. 1955. Distribution of the longspined porgy, Stenotomus 539 FISHERY BULLETIN: VOL. 80, NO. 3 caprinus. Bull. Mar. Sci. 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Galtsoff (coordinator), Gulf of Mexico, its origin, water, and marine life, Vol. 55, p. 101-118. U.S. Dep. Inter., Fish Wildl. Serv., Fish. Bull. 89. Miller, J. M. 1965. A trawl study of the shallow Gulf fishes near Port Aransas, Texas. Publ. Inst. Mar. Sci., Univ. Tex 10:80- 108. Moore, D. 1964. Abundance and distribution of western Gulf bot- tomfish resources. In Biological Laboratory, Galves- ton, Tex., fishery research for the year ending June 30, 1963, p. 45-47. U.S. Fish Wildl. Serv., Circular 183. Moore, D., H. A. Brusher, and L. Trent. 1970. Relative abundance, seasonal distribution, and species composition of demersal fishes off Louisiana and Texas, 1962-1964. Contrib. Mar. Sci., Univ. Tex. 15:45- 70. Morse, W. W. 1978. Biological and fisheries data on scup, Stenotomus chrysops (Linnaeus). U.S. Dep. Commer., NOAA, NMFS, Sandy Hook Lab., Tech. Ser. Rep. 12, 41 p. Murphy, M. D. 1981. Aspects of the life history of the Gulf butterfish Peprilus burti. M.S. Thesis, Texas A&M Univ., College Station, 77 p. Powles, H., and C. A. Barans. 1980. Groundfish monitoring in sponge-coral areas off the southeastern United States. Mar. Fish. Rev. 42(5): 21-35. Ricker, W. E. 1975. Computation and interpretation of biological sta- tistics of fish populations. Fish. Res. Board Can. Bull. 191, 382 p. ROITHMAYR, C. M. 1965. Industrial bottomfish fishery of the northern Gulf of Mexico, 1959-63. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 518, 23 p. Royce, W. F. 1972. Introduction to the fishery sciences. Acad. Press, N.Y., 351 p. Shlossman, P. A., and M. E. Chittenden, Jr. 1981. Reproduction, movements, and population dynam- ics of the sand seatrout, Cynoscion arenarius. Fish. Bull., U.S. 80:649-669. Smith, N. P. 1975. Seasonal variations in nearshore circulation in the northwestern Gulf of Mexico. Contrib. Mar. Sci., Univ. Tex. 19:49-65. Smith, W. G., and J. J. Norcross. 1968. The status of the scup (Stenotomus ch rysops) in win- ter trawl fishery. Chesapeake Sci. 9:207-216. Tesch, F. W. 1971. Age and growth. In W. E. Ricker (editor), Meth- ods for assessment of fish production in fresh waters, 2d ed., p. 98-130. Blackwell Sci. Publ., Oxf., Engl. White, M. L., and M. E. Chittenden, Jr. 1977. Age determination, reproduction, and population dynamics of the Atlantic croaker, Micropogonias undu- latus. Fish. Bull., U.S. 75:109-123. 540 VERTICAL MIGRATION AND ITS EFFECT ON DISPERSAL OF PENAEID SHRIMP LARVAE IN THE GULF OF CARPENTARIA, AUSTRALIA Peter C. Rothlisberg1 ABSTRACT i Penaeid shrimp larvae in the Gulf of Carpentaria, Australia, sampled over discrete depths and time intervals showed a day-night pattern of vertical distribution. The magnitude of the migrations in- creased with larval development. The patterns of vertical distribution were variable and depended strongly on light penetration. Vertical migratory behavior of larvae was linked to currents at var- ious depths. Daily and fortnightly extrapolations of larval displacement showed that vertical migra- tion generally enhanced horizontal advection but the distances and directions were dependent on the current regime and the vertical distribution pattern. It was estimated that larvae could beadvected from 70 to 100 km, far enough to traverse the distance from the known spawning grounds to estuar- ine nursery grounds. Results of this short-term study indicate that differential advection on a seasonal scale may be responsible for the temporal and spatial recruitment patterns of postlarvae observed in the Gulf of Carpentaria. Vertical migration is widespread among marine and freshwater Crustacea (Russell 1925; Bain- bridge 1961). The migration is often periodic and can vary from diurnal and tidal through to sea- sonal and ontogenetic periodicity. Almost as diverse as the organisms involved are the prob- able environmental cues that elicit the response and adaptive advantages attributed to this be- havior (Bainbridge 1961; Enright 1977; Pearre 1979). Undoubtedly animals have adopted verti- cal migratory behavior for a variety of immedi- ate and long-term biological advantages (Vino- gradov 1968). Most of the adaptive advantages of vertical mi- gration that have been suggested usually apply to animals that live in relatively deep water with temperature, pressure, light, food, and predator abundance gradients. Shallow-water holoplank- tonic and meroplanktonic animals also undergo vertical migrations, however. Because the verti- cally migrating animal is exposed to different current regimes at different depths (Hardy 1936, 1953), the behavior has been invoked to aid maintenance of position within estuaries (Bous- field 1955; Graham 1972; Weinstein et al. 1980; Wooldridge and Erasmus 1980) and on continen- tal shelves (Walford 1938). It has also been sug- gested that timed vertical migration enhances ■Division of Fisheries Research, CSIRO Marine Laborator- ies, P.O. Box 120, Cleveland, Qld. 4163, Australia. Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80, NO. 3. 1982. horizontal displacement up an estuary (Carriker 1951; Wood and Hargis 1971; Sandifer 1975; Big- ford 1979; Sulkin et al. 1980), alongshore (Long- hurst 1968; Efford 1970), or onshore (Woodman- see 1966; Penn 1975; Rimmer and Phillips 1979), often against the prevailing currents. In no in- stance, however, have these mechanisms been demonstrated by monitoring both the vertical behavior and the in situ current regimes simul- taneously. Dispersal, during the pelagic larval phase, is the most likely mechanism that brings postlar- val and juvenile penaeid shrimp into shallow- water coastal and estuarine nursery areas from their offshore spawning grounds (Kirkegaard 1975). Evidence of vertical migration of penaeid larvae, which might enhance the onshore move- ment, is mixed and inconclusive. In the study by Eldred et al. (1965) the larval vertical distribu- tion patterns were variable between species, but appeared to be consistent in the study by Temple and Fischer (1965). A change in behavior from photopositive to photonegative with develop- ment was reported by Racek (1959), while a gradual increase in vertical migratory ability, without a phase change, has been seen in other studies (Temple and Fischer 1965; Jones et al. 1970). Most noticeable have been the variable pat- terns in vertical distribution with varying envi- ronmental conditions in studies with repeated sampling (Temple and Fischer 1965; Jones et al. 1970). Nevertheless, based on an idealized larval 541 FISHERY BULLETIN: VOL. 80. NO. 3 behavior and limited knowledge of current re- gimes, Penn (1975) hypothesized that larvae of Penaeus latisulcatus, off Western Australia, were capable of moving onshore against prevail- ing currents during certain times of the year. In this study I attempted to test Penn's (1975) hypothesis by intensively sampling the changes in vertical distribution of penaeid larvae while simultaneously monitoring currents and other environmental parameters in the water column. I hoped to gain insight into the following: the on- togeny of vertical migratory behavior, the envi- ronmental factors that control the larval be- havior, the current regimes and how they change with depth, and the advective consequences to the larvae resulting from vertical migration through this variable current field. Staples (1979), studying the postlarvae of Pe- naeus merguiensis in the Gulf of Carpentaria, found discrete temporal and spatial patterns of postlarval recruitment into the rivers around the gulf. These patterns could not be explained en- tirely by the distribution of adults and the timing of spawning. He proposed that the temporal and spatial patterns of recruitment were caused by the different fates of larvae arising from two peaks of spawning (spring and autumn). While seasonal changes in the direction of larval advec- tion were suggested, little was known about cur- rent regimes in the gulf (Cresswell 1971) and nothing known about how these currents would affect the distance and direction of penaeid lar- val dispersal. This study was, therefore, in- tended to provide insight into the mechanisms and pathways of larval dispersal and to help ex- plain the variable timing and magnitude of post- larval recruitment. MATERIALS AND METHODS Discrete depth sampling was conducted re- peatedly at two locations (Fig. 1) during survey cruises in the Gulf of Carpentaria (Rothlisberg and Jackson 1982). These locations were <30 m in depth and close to known concentrations of adult penaeid shrimp. The ship was anchored on station and a7.6cm(3in)centrifugalpump(Fig. 2), driven by a 6 kW (8 hp) aircooled gasoline en- gine, was used to pump water from depth. The end of the 10.2 cm (4 in) intake hose was clamped to a weighted wire fed through a meter block. The full length of the hose, in 9.2 m (30 ft) quick coupled lengths, was deployed, regardless of the sampling depth, to prevent variable friction 142°E Figure 1.— Station numbers and locations for discrete depth sampling (stars) in the Gulf of Carpentaria, Australia. Figure 2. — Schematic of pump, water discharge, and filtering system: A) 10.2 cm (4 in) intake hose; B) 7.6 cm (3 in) self- priming centrifugal pump with 6 kW (8 hp) gasoline engine; C) 7.6 cm (3 in) outlet hose; D) quick coupling; E) spinner drum; F) tripod; G) 142 ^m mesh plankton net. effects. Water from the pump was discharged through a 7.6 cm (3 in) diameter hose tangen- tially into a drum (spinner) mounted on a tripod. Upon loss of velocity the water drained gently through a 56 cm diameter plankton net (142 /im mesh) suspended beneath the spinner. The outlet hose was coupled to the spinner in such a manner that it could be inserted and withdrawn quickly to allow precisely timed pumping intervals. The pumping rate (up to 1,000 1/min) was monitored with timed fills of a container of known volume. The water column was divided into four strata, and the inlet placed at the center of the stratum. The pump was brought to speed, the outlet hose inserted in the spinner, and the stratum sampled 542 ROTHLISRERG: VERTICAL MIGRATION OF PENAEID SHRIMP LARVAE for a 15-min interval. After 15 min the outlet hose was quickly withdrawn, the pump speed re- duced, and the hose inlet lowered to the next stra- tum for 5 min of flushing before the next 15-min sample was taken. The four strata were there- fore sampled in a 75-min pumping series which was initiated every 2 h and continued for 24-36 h. At the same time that the pump inlet was be- ing deployed astern on the main wire, a Lerici current meter (Frassetto 1967), modified for deck readout of current velocity, was deployed amidship on the hydrographic wire. Fifteen- minute records at each depth stratum were ob- tained simultaneously with plankton samples. All current meter records were annotated on a strip chart recorder in the deck readout unit. To link the vertical distribution of the shrimp larvae to the current vectors at depth, the median level of larval vertical distribution was calculated (Cronin and Forward 1979) for each of the larval substages at each 4-h time interval and assigned to one of the four depth strata. The intermediate (2-h) larval distributions were in- terpolated from the 4-h time series. The current vectors for each 2-h time interval, associated with the depth stratum (levels 1-4) to which the median larval depth corresponded, were added progressively over 24 h for each larval substage (Fig. 7b, c). In addition to the median larva, three other hypothetical behavior patterns were mod- elled: 1) a nonmigratory surface dwelling ani- mal; 2) a nonmigratory near-bottom dwelling animal; and 3) a larva (12:12 larva, Figs. 7, 8, 9) that followed the behavior pattern dictated by Penn's (1975) hypothesis, i.e., it moved the full height of the water column on a strict 12:12 day: night cycle for the entire length of the larval life. A photometer, with both deck and submersible cells, was used to measure the ambient and sub- marine irradiance (/iW/cm2). Irradiance levels were recorded at 2 m intervals at the start of every 2-h pumping series during daylight. The meter was not sensitive enough to record vari- able levels of moonlight or starlight. Tempera- ture profiles were obtained with both a bathy- thermograph and water sampled from the pump outlet. Plankton biomass (settled volume) from dis- crete depth samples was obtained by settling the fixed sample (10% formaldehyde, sodium tetra- borate buffer) for 4 h in Imhoff cones (Rothlis- berg and Jackson 1982). The samples were then transferred to 2% 2-phenoxy ethanol for preser- vation and subsequent microscopic examination. For economy and expediency, only every other sampling series (4-h) was examined. Nosubsam- pling scheme was employed. Numbers of larvae in each sample were standardized to numbers per cubic meter based on the calibrated pump- ing rates. RESULTS Ontogeny of Vertical Migration From sampling done on 22 and 23 March 1977 north of Groote Eylandt (Station 210), early lar- vae (zoeal stages 1-3) were seen to move up into the water column only at night (Fig. 3). This movement was very limited and rarely extended more than one-half the distance to the surface. By day they were almost totally restricted to the bottom stratum of the water column sampled. The mysis stages extended the range of their nighttime excursions to the full water column without completely abandoning the lower part of the water column at night. They too returned almost completely to the bottom stratum by day. Postlarval numbers in the samples were too few to make generalizations, but they did appear to ZOEA 1 0 5 10 15 20 !!■ ■ilii ■!■!!■ MYSIS 1 POSTLARVA BIOMASS 0 5 10 15 20 V/cm2 ,1 12 16 20 24 4 8 12 12 16 20 24 4 8 12 TIME OF DAY 12 16 20 24 4 8 12 Figure 3.— Relative larval abundance (percent) by substage and depth stratum, vertical distribution of settled plankton volume (percent), and vertical profiles of submarine irradi- ance (/iW/cm2) for 22-23 March 1977 at Station 210 north of Groote Eylandt. The dark horizontal bar indicates night. 543 FISHERY BULLETIN: VOL. 80, NO. 3 extend the mysis pattern further by almost com- pletely abandoning the lower parts of the water column by night but still returning by day. Variations in the Pattern of Vertical Distribution High light penetration was characteristic of the station occupied on 22 and 23 March 1977 (Fig. 3). Conditions were calm, isothermal, and clear with a secchi disc depth of 16 m in the 22 m water column and penetration of the 1,000 /uW/ cm2 isolume to 20 m. Under these conditions, movement of the larvae away from the deepest stratum occurred only at night and almost all stages (first zoea (Zl) through third mysis (M3)) returned to the bottom stratum during daylight. On 6 and 7 May 1977 (Station 310), though sea state and wind conditions were comparable with the previous sampling session, increased turbid- ity limited the 1,000 /iW/cm2 isolume penetra- tion to only 10 m or about half of the water col- umn (Fig. 4). This change in light penetration paralleled marked changes in the vertical distri- bution of all larval stages. During daylight, early larval stages (zoea 1-3) were not confined to the bottom stratum. The day-night differences in vertical distribution, though present, were less distinct than in the previous case, and these early larval stages were seen even at the surface at night. The day-night pattern for mysis stage larvae was even less distinct. Though spread throughout the water column, they appeared to be slightly more concentrated at or near the sur- face at night. Postlarval (PL) numbers were again low, and they were near the surface dur- ing the entire diel period. They were more abun- dant in the surface stratum during the night. At the station east of Mornington Island on 27 and 28 March 1977 (Station 270) the wind and sea conditions were extremely calm but light penetration was even more diminished than in the previous two cases. On this occasion the 1,000 juW/cm2 isolume penetrated only about one-third of the water column (Fig. 5). Further changes in the patterns of larval distribution were seen. Early larval stages were concentrated in the middle two depth strata with nighttime move- ments to the surface. The mysis stage larvae were also predominantly in the middle part of ZOEAl ZOEA 1 0 7 14 21 28 MYSIS 1 MYSIS 1 0 5 10 15 20 POSTLARVA 4 8 12 16 20 24 4 BIOMASS I 4 8 12 16 20 24 4 TIME OF DAY pW/cm2xl02 4 8 12 16 20 24 4 Figure 4.— Relative larval abundance (percent) by substage and depth stratum, vertical distribution of settled plankton volume (percent), and vertical profiles of submarine irradi- ance (/xW/cm2) for 6-7 May 1977 at Station 310 north of Groote Eylandt. The dark horizontal bar indicates night. 0 7 14 21 28 POSTLARVA BIOMASS 22 2 6 10 14 18 22 22 2 6 10 14 lb 22 22 2 6 10 14 18 22 TIME OF DAY Figure 5. — Relative larval abundance (percent) by substage and depth stratum, vertical distribution of settled plankton volume (percent), and vertical profiles of submarine irradi- ance (^W/cm2) for 27-28 March 1977 at Station 270 east of Mornington Island. The dark horizontal bar indicates night. 544 ROTHLISBERG: VERTICAL MIGRATION OF PENAKII) SHRIMP LARVAE the water column by day but spread out to both the surface and the bottom strata at night. Again the postlarval numbers were low and little day- night patterning was evident. No postlarvae were caught at any time in the surface stratum and were near the bottom both day and night. Of concern was possible day-night variation in larval abundance due to avoidance of the inlet hose and/or larval distribution outside the range of the sampler. Of particular concern was the possibility that during the day larvae were on or near the bottom below the hose inlet at its low- est extent. To test statistically for a temporal variation in larval abundance, the larval num- bers were initially combined over all depths within a sampling time interval and then a square root transformation was applied. A sine curve was fitted to estimate gradual rather than abrupt day-night changes in larval numbers. Postlarval numbers were too low to include in the analysis. Time alone was highly significant for the total number of larvae and significant at lower levels for three of six larval substages (Table 1 ). The high level of significance of the sta- tion-time interaction for all but the Z2 larvae in- dicates that the small diel variation in abun- dance was variable between sampling occasions. Inspection of the data showed that the peak abun- dances varied by stage, location, and time of day and that there was no systematic difference in catchability which would bias the interpretation of the diurnal patterns shown previously. To add confidence to the diagrammatic inter- pretation (Figs. 3-5), further analysis, using an arc-sine transformation of the proportional lar- val abundances by depth also, showed that the abundances at the four depth strata were quite variable from one date to the next. This was indi- cated by the high degree of significance of the station effects at almost all depths (Table 2). The abundances of larvae in the surface stratum (level 1) showed the most consistent relationship with time of day, with larvae rarely at the sur- face by day, on any cruise, and increasing in abundance at the surface by night. Further, the station-time interaction at depth (e.g., level 3) was significant for most larval stages and sub- stages, indicating a high degree of station-to-sta- tion variation in the depth of peak abundance. Table 2.— Summary of analysis of variance of proportional larval abundance at four discrete depths. An arc-sine transfor- mation was applied to the percentages. F-ratios Stage/ Station-time Error sub- Station Time interaction mean stage Level (2, 11 df) (2, 11 df) (4. 11 df) square Zoea 1 7.53" 5.29* 2.56+ 0.03293 2 17.01'" 0.72 2.15 002167 3 4.56' 0.60 649" 002906 4 22.68*" 2.31 2.10 0 04125 Mysis 1 7.33' 16.11"' 0.76 0 02179 2 10.55" 1.94 846" 0.01277 3 768** 2.58 335+ 001925 4 14.89*** 1.25 9.27" 0.03075 Z1 1 1.25 0.13 2.10 003876 2 10.61" 0.78 091 004839 3 3.84+ 0.59 7.31" 003953 4 12.74" 2.12 3.27 + 005937 Z2 1 6.65* 7.42" 2.23 0.04838 2 17.53" 0.46 1.59 002760 3 8.85" 1.03 5.56' 003270 4 30.46"' 348+ 0.97 005877 Z3 1 11.05" 6.43* 2.38 0.3573 2 9.99" 0.27 1.09 003112 3 4.03* 1.89 4.10' 004522 4 14.00*" 0.47 1.22 0.09720 M1 1 913" 16.15" 0.35 001989 2 13.82*" 0.27 5.78" 001714 3 4.26* 1.90 3.39* 002365 4 40.92'" 2.24 21.86*" 0.01289 M2 1 2.50 4.97* 111 006961 2 206 0.34 1.07 008163 3 3.31 + 0.20 3.02 + 0.05118 4 5.70* 1.06 2.44 0.10437 M3 1 4.85* 9.31" 0.80 0 05065 2 1.21 0.16 2.27 009051 3 3.74+ 1.01 924" 0 03211 4 2.22 1.51 213 0.16646 — p / I J X »— o 12.5m — l. — Z_._ -r n 17.5m j / ? ^^T OO 04 "- 7.5n I »— Q. HI a 12.5m \ i_ \ v " * ^ ^~r^ 4 >~J N 17. 5m •*■■ y' 1 1 — < **-■«- '-. , ,^, :20cm sec"' 3.5m w 10.5r X t— Q- LU Q V~7 V^ °; . / I 1 / ' 06 10 14 18 22 ~ x. I lit.. //// J | 17.5m -y * — -^ 1 1 L * — ^ N TTT 24.5m -* — . v — A_ S ,. rr^ -*— *- •— — • T 20 cm sec" Figure 6.— Mean 2-h current vectors at four depths and three stations: A) Station 210, 22-23 March 1977 north of Groote Eylandt; B) Station 310, 6-7 May 1977 north of Groote Eylandt; C) Station 270, 27-28 March 1977 east of Mornington Island. the time of slack water (e.g., Fig. 6a, 1200; 6b, 0000). This apparent increase is believed to be an artifact of the time lag in sampling with the mi- grating current meter. Short-term wind events can also be detected at the surface stratum (Fig. 6b, 2.5 m; 1800-2200). Time lag and wind events alone, however, cannot explain all the variation in the current vectors. Other anomalous current vectors at depth (e.g., Fig. 6a, 1000, 17.5 m; 0800, 7.5 m) represent short-term nontidal perturba- tions of unknown origin. Over the 24-h sampling period at Station 210, the net displacement (measured as a straight line from the origin to the end of the progressive vec- tor) was quite variable for migratory and non- migratory animals. Surface-dwelling animals would have been displaced to the northwest, near-bottom dwelling ones to the south, and the 12:12 larva almost due west. The net drift of the 12:12 larva was considerably less than either of the nonmigratory animals. The larval move- ments (Fig. 7b, c) based on sampled vertical dis- tributions would have closely paralleled the bot- tom currents in this case because so much of their time was spent in the lower parts of the water column. The slight differences in displacement direction and distance between substages reflect the differences in depth distribution. Because of their wider excursions, the postlarvae were ex- posed to more of a mixture of the bottom and sur- face currents and therefore approached the 12:12 larva in direction of advection during that larval stage. To calculate an approximate total dis- placement over the whole of the larval phase, the 24-h picture was extrapolated by making several assumptions. Firstly, the larval life span was set at 14 d with 2 d for each larval substage (Zl, Z2, Z3, Ml, M2, M3, PL). Secondly, within each sub- stage the same vertical migratory behavior pre- vailed on both days. Thirdly, the current regime, seen during the 24-h sampling period, was con- stant over the 14-d larval life. By doubling the length of the daily resultant vectors for each lar- val substage and adding them progressively, the 2-wk displacement is approximated (Fig. 7d). The calculation of absolute distances is not pre- cise because of the nature of the assumptions, especially the third. The period of sampling was, however, between neap and spring tides so the tidal currents would have been moderate and a reasonable approximation of mean velocities over the tidal cycle. Under these criteria, the median larva would have been displaced about 69 km (37 nmi), the 12:12 larva 25 km (13 nmi), 546 ROTHLISBERG: VERTICAL MIGRATION OF PENAEID SHRIMP LARVAE Surface Scale a.b.c Figure 7.— Progressive vector diagrams for horizontal advection, based on 2-h median larval distributions and currents at Station 210, north of Groote Eylandt on 22- 23 March 1977. a) Advection over 24 h of a larva spend- ing 12 h of daylight at the bottom stratum and 12 h of night at the surface (dotted line), a nonmigratory ani- mal at the surface (solid line), and a nonmigratory animal near the bottom (dashed line); b)zoeal substages 1-3 (solid, dashed, dotted lines, respectively); c) mysis substages 1-3 and postlarvae (solid, dashed, dotted, dot- dashed lines, respectively); d) 14-d extrapolation of daily resultant vectors: nonmigratory surface (dashed line); nonmigratory bottom (dashed line); 12:12 surface bottom larva (dotted line); median larva (solid line). 547 FISHERY BULLETIN: VOL. 80, NO. 3 and the surface and near bottom nonmigratory animals 62 km (34 nmi) and 72 km (39 nmi), respectively. The larvae were displaced to the southwest from the sampling station north of Groote Eylandt. This trajectory would have taken them in the general direction of Groote Eylandt or the coastal rivers in the Limmen Bight, southwest of Groote Eylandt. Greater dis- tances could be attained if the pelagic postlarval stage was maintained through several instars before metamorphosing to the benthic-living juvenile shrimp. Procedures for approximating displacement distance and direction on the other two sampling occasions were similar but the resultant dis- placements were quite different because of the different vertical distribution patterns seen on each occasion. At Station 310, north of Groote Eylandt, submarine irradiance was reduced and the vertical distribution of the larval substages was more varied (Fig. 4). Consequently, the hori- zontal displacements of individual larval sub- stages (Fig. 8b, c), though dominated by the bottom currents (Fig. 6b), were quite varied. The hypothetical 2-wk displacement was again in the same direction as the bottom current (Fig. 8d), but the distance was enhanced by the fact that larvae were further off the bottom in their nightly excursions for slightly higher propor- tions of the time. Total horizontal displacement over the 2-wk larval period, up to and including 2 d of postlarval life, would be about 75 km (40 nmi). The direction of advection of the median larva in this case is to the northwest. The 12:12 larva would have been displaced seawards to the central Gulf of Carpentaria. Analysis of the larval migratory patterns (Fig. 5) and the current regime (Fig. 6c) at Station 270 east of Mornington Island showed yet another pattern of displacement (Fig. 9). Here, because there were large numbers of larvae in the upper part of the water column both night and day, the displacement would have been in the direction of the surface currents (Fig. 9a, b, c). Slight deflec- tion away from the surface direction was seen in older larvae (M 1-PL) as more of them moved into the lower part of the water column (Fig. 9d). The displacement distance over the 2-wk period would have been 98 km (53 nmi). All advection was to the west, with the 12:12 larva going to the southwest towards the coast and the median larva heading west-northwest, away from the coast, in the general direction of the surface cur- rents. DISCUSSION While it is widely thought that changes in light intensity are the primary environmental cues that initiate and control the diel vertical migra- tions in aquatic animals (Ringelberg 1964; Thor- son 1964; Boden and Kampa 1967; Hutchinson 1967; Segal 1970; Buchanan and Haney 1980), there have been cases in which the timing of the migration was not strictly in phase with changes in light intensity, possibly because of changes in subsurface light and/or feeding history and strategy of the animals (Enright and Honegger 1977; Bohrer 1980). In shallow-water coastal environments, factors affecting light penetra- tion and therefore vertical distribution of ani- mals are numerous and subject to rapid change. Turbulence with concomitant turbidity caused by both wind and tidally induced currents, river and coastal runoff, and rapid phytoplankton growth would be the more significant causes of light reduction. It is these short-term changes in submarine irradiance that are probably respon- sible for some of the conflicting reports about whether or not penaeid larvae migrate vertical- ly. The first mention of differential vertical dis- tribution of penaeid larvae is by Racek (1959), sampling off the eastern Australian coast. His sampling was not strictly stratified, he pub- lished no supportive data, and the conclusions are probably drawn from a combination of field and laboratory observations. He stated that nau- plii as well as first and second protozoeae (= zoeae) were strongly attracted to bright light. I saw no evidence of this in our field collections but have observed it under artificially high light in- tensities in the laboratory. There may be some threshold light intensity at which point penaeid larvae shift their behavior from photonegative to photopositive similar to that described for the larvae of Uca pugilator (Herrnk'md 1968). From his field sampling, Racek found that late proto- zoeae and early mysis stages rose to the surface at night and sunk to lower strata during day- light. The vertical distribution of late mysis and postlarvae were not mentioned in Racek's brief account. In the study by Eldred et al. (1965), the day- night pattern of vertical distribution was neither persistent within nor consistent among genera. For Penaeus duorarum only postlarvae were dis- cussed. Pooled samples were dealt with, so little information about station-to-station variation 548 ROTHLISBERG: VERTICAL MIGRATION OF I'ENAEII) SHRIMP LARVAE b Z3 Y : / / J'YCl Figure 8.— Progressive vector diagrams for hori- zontal advection, based on 2-h median larval distri- butions and currents at Station 810, north of Groote Eylandt on 6-7 May 1977. a) Advection over 24 h of a larva spending 12 h of daylight at the bottom stra- tum and 12 h of night at the surface (dotted line), a nonmigratory animal at the surface (solid line), and a nonmigratory animal near the bottom (dashed line); b) zoeal substages 1-3 (solid, dashed, dotted lines, respectively); c) mysis substages 1-3 and post- larvae (solid, dashed, dotted, dot-dashed lines, re- spectively); d) 14-d extrapolation of daily resultant vectors: nonmigratory surface (dashed line); non- migratory bottom (dashed line); 12:12 surface bot- tom larva (dotted line); median larva (solid line). M3 Ml pL t N *> •• <>' SURFACE 40 km i 1 Scale d 549 FISHERY BULLETIN: VOL. 80, NO. 3 Surface Figure 9.— Progressive vector diagrams for horizontal advection, based on 2-h median larval distributions and currents at Station 270, east of Mornington Island on 17-28 March 1977. a) Advection over 24 h of a larva spending 12 h of daylight at the bottom stratum and 12 h of night at the surface (dotted line), a nonmigratory animal at the surface (solid line), and a nonmigratory animal near the bottom (dashed line); b) zoeal substages 1-3 (solid, dashed, dotted lines, re- spectively); c) mysis substages 1-3 and postlarvae (solid, dashed, dotted, dot-dashed lines, respectively); d) 14-d extrapolation of daily resultant vectors: nonmigratory surface (dashed line); nonmigra- tory bottom (dashed line); 12:12 surface bottom larva (dotted line); median larva (solid line). 10 km Scale a,b,c 0 M3 SURFACE \ \ Z3 Z2 Z\ \ 40 km Scale d 18 cm). These plastic corers were also used to subsample Smith-Mclntyre grabs collected on two cruises in July and September 1979 at the same site. Samples were preserved in 10% buffered Forma- lin and stained with rose bengal. The fauna was extracted from the sediments (well-sorted fine sand) by shaking and decanting followed by three rinses. A 38.5 /jm sieve was used to retain the fauna. Harpacticoid copepods and nematodes were identified to species and enumerated. RESULTS The data for all four flatfish species are sum- marized in Table 1. A total of 422 guts from re- cently settled fish (17-88 mm SL) were examined, only 16 of which were empty (4%). The guts of an additional 40 late stage IV and early stage V P. vetulus larvae (sensu Shelbourne 1957) were also examined. These metamorphosing individuals, ranging in size from 16 to 18 mm SL, all had empty stomachs and intestinal tracts. The 13 prey categories identified (Table 1, top) were placed into three broad groupings based on the size of individual food items and their typical location within the habitat. Small benthic prey were composed of palps from the surface deposit- feeding polychaete Magelona sacculata, juvenile bivalves (predominantly Tellina modesta and occasionally Siliqua patula), siphon tips cropped from tellinid clams, harpacticoid copepods (mainly Halectinosoma spp. and a few Thomp- sonula hyaenae and Rhizothrix curvata), free- living nematodes (Theristus sp. and Mesacan- thion sp.), and tube feet from the sand dollar Dendraster excentricus. These food items were on the order of 0.5-1.5 mm long. Larger benthic prey were amphipods (predominantly Ampelisca spp. and Eohaustoris sp.), cumaceans, decapods (juvenile Cancer magister, pinnotherid crabs, and Callianassa calif omiensis), and polychaetes (Nephtys sp., Glycinde armigera, Magelona sac- culata, Thalenessa spinosa, and Spiophanes bom- byx). These prey were usually juveniles measur- ing 1.5-4 mm in their largest dimension. Species identifications were difficult for this latter group because of their immature status and ten- dency to fragment after being eaten. Examina- 557 FISHERY BULLETIN: VOL. 80, NO. 3 Table 1. — Summary of data collected for English sole, Parophrys vetulus; butter sole, Isopsetta isolepis; speckled sanddab, are the number of fish out of the total examined which had empty guts. The two values listed for each prey category are average No tows Length Small benthic prey Harpac- Species and exam- No. fish range Magelona Juvenile Tellinid ticoid Dendraster date ined examined (mm) palps bivalves siphons copepods Nematodes tube feet English sole 12 May 1977 1 12(1) 18-29 0 08 (0.64) 0.42 (0.91) 0.22 (0 73) 0.22 (0 82) - (0.18) 23 June 1977 1 16(0) 19-48 0.01 (0.19) - (0.19) 0.18 (0 56) 0.42 (0.69) — (006) 12 June 1978 1 3(0) 22-24 0 04 (0.33) 0 88 (1.0) 0.04 (0.66) 0.02 (0.33) 15 June 1978 1 5(0) 20-25 0 59 (1.0) 0.17 (0.80) 0.14 (1.0) 0 05 (0.40) 13 July 1978 2 14(0) 19-46 0.46 (0.89) 0.24 (0.83) 0.08 (0.33) 0.18 (0.70) — (0.06) 25 July 1978 1 12(0) 24-84 0 09 (0.75) 0.01 (0.08) 0 17 (0.42) 0 40 (0.67) 5 Sept. 1978 1 3(0) 45-58 1.0 (1.0) 14 Nov 1978 1 5(0) 18-21 099 (1.0) 23 Jan. 1979 4 24(2) 17-34 0.72 (0.94) 0.05 (0.25) — (0.06) 0.13 (0.52) 22 Mar. 1979 2 20 (0) 19-35 0.02 (0.50) 0 80 (1.0) 0.02 (0 36) 0.14 (0.90) 18 Apr. 1979 2 27(1) 19-38 0.10 (0 50) 0.20 (0 73) 0.17 (0.61) 0.23 (0.67) — (0.22) 29 May 1979 4 37(5) 18-42 0.07 (0 24) 0.20 (0 25) 0.24 (0.38) 0.20 (0.41) 0.05 (0.19) 30 June 1979 2 23(1) 18-61 0.01 (0.50) — (0.09) 0.14 (0.75) 0.61 (0.75) 19 July 1979 3 10(0) 27-62 0.20 (0.25) 0.30 (0.79) 8 Aug. 1979 2 11 (0) 30-87 0.26 (0.19) 0.03 (0 06) 0 03 (0.19) 24 Sept. 1979 2 13(0) 46-82 002 (0.07) 0.10 (0.35) Total 235 (10) x 1979 0.11 (0.27) 0.22 (0.41) 0.06 (0 20) 0.16 (0.57) 0.01 (0 05) 0.08 (0 09) Butter sole 23 June 1977 1 6(1) 18-23 0.01 (0.20) 0.25 (0.80) 0.47 (0.80) 15 June 1978 1 16(0) 19-30 0 62 (0.87) 0.13 (060) 0.01 (0.13) 0.01 (0.27) 0.05 (0.47) 25 July 1978 1 16(0) 22-31 0,44 (0.75) 006 (0.12) 0.24 (0.82) 0.13 (0.57) 29 May 1979 3 14(2) 17-35 0.04 (0.10) 0.15 (0.50) 0.25 (0.62) 0.17 (0.63) 0.11 (0.25) 30 May 1979 1 4(0) 49-60 0 03 (0 25) 0.03 (0.25) 19 July 1979 3 7(0) 21-88 — (0.08) 0 38 (0.58) 0.11 (0.33) 8 Aug. 1979 4 9(1) 24-34 0.02 (0 38) 0 43 (0.50) - (013) 0.47 (0.58) Total 72 (4) x 1979 0 02 (0.12) 0.25 (0 46) 006 (0.19) 0.20 (0.45) 0.03 (0.06) Speckled sanddab 23 June 1977 1 4(0) 34-44 041 (0.75) 0 13 (0 25) 25 July 1978 1 5(0) 41-65 22 Mar. 1979 1 10(0) 29-39 0.08 (0.10) 0.01 (0.10) 0.10 (0 10) 18 Apr. 1979 1 10(0) 29-38 29 May 1979 2 14(0) 33-50 0.13 (0.13) 30 June 1979 1 7(0) 30-52 19 July 1979 2 11 (1) 35-70 24 Sept. 1979 3 15(0) 38-70 Total 76(1) x 1979 0.02 (0.02) 0.01 (0.02) — (0.02) 0.02 (0 02) Sand sole 22 Jan. 1979 2 6(0) 30-38 18 Apr. 1979 1 3(0) 29-55 19 July 1979 2 6(0) 29-50 8 Aug 1979 2 13(0) 31-52 24 Sept. 1979 2 11 (1) 30-48 Total 39(1) X1979 tion of the meiofaunal cores revealed that all the organisms classified as "benthic" occurred in the upper 1 cm of sediment. Prey items which were never found in benthic samples were defined as "pelagic" and consisted of mysids (mainly Neo- mysis kadiakensis), calanoid copepods (Pseudo- calanus sp.), and veliger larvae. This distinction between benthic and pelagic organisms is some- what arbitrary, since some of these species are mobile epibenthic forms which probably occur both in the sediments and the overlying water. Adequacy of the sample sizes used in deter- mining food habits of the flatfish species was assessed using several techniques. The guts of 16 Parophrys vetulus (19-48 mm SL) and 16 /. iso- lepis (19-33 mm SL) were examined from each of two tows. These two species were selected be- cause they fed on a much broader spectrum of prey than Citharichthys stigmaeus or Psettiehthys melanostictus and hence are subject to greater sampling error. The cumulative number of prey categories encountered, expressed as a function of sample size, is shown in Figure 2. For both English sole and butter sole, after seven or eight fish had been examined, no new food categories were found. After examining only four fish, 75% of all food items had been collected. This qualita- tive consistency among guts is also reflected in the high frequency of occurrence (Table 1) for most prey. Quantitatively, the composition of gut 558 H0GUE and CAREY: FEEDING ECOLOGY OF 0-AGE FLATFISHES Citharichthys stigmaeus; and sand sole, Psettichthys melanostictus. Numbers in parentheses under the heading "No. fish examined" numerical percent composition and average frequency of occurrence (in parentheses). " — " indicates prey item <0.01. Large benthic prey Pelagic prey Species and date No tows exam- ined No. fish examined Length range (mm) Amphi- pods Cumacea Decapods Poly- chaetes Mysids Calanoid copepod Veliger larvae English sole 12 May 1977 12 (1) 18-29 0.03 (0 27) - (009) 001 (0 18) 23 June 1977 16(0) 19-48 0.15 (0 63) 0 24 (0 44) 12 June 1978 3(0) 22-24 0.01 (0 33) 0.01 (0 33) 15 June 1978 5(0) 20-25 0.02 (0 40) 0 04 (0 60) 13 July 1978 2 14 (0) 19-46 0 02 (0 40) 0.01 (0.36) 0 02 (0 42) 25 July 1978 12 (0) 24-84 0.18 (0 25) 0 04 (0.25) 0.03 (0.10) 0.04 (0 08) 5 Sept 1978 3(0) 45-58 14 Nov 1978 5 (0) 18-21 0.01 (0.20) 23 Jan 1979 4 24 (2) 17-34 0 08 (0 52) 002 (0.14) — (0.06) 22 Mar 1979 2 20 (0) 19-35 0.03 (0.60) — (0.30) - (010) 18 Apr 1979 2 27 (1) 19-38 0.25 (0 62) 0 04 (0.35) — (003) — (009) 29 May 1979 4 37 (5) 18-42 0.03 (0 19) 0 03 (005) 0.17 (0.17) 0.02 (0.16) - (0.13) 30 June 1979 2 23 (1) 18-61 0.18 (0 54) 0.05 (0.25) — (0.09) — (009) 19 July 1979 3 10(0) 27-62 0.33 (0.70) 0.15 (0.50) 0.01 (0.08) 8 Aug. 1979 2 11 (0) 30-87 0.45 (0 86) 0.21 (0.81) 0.01 (0 13) — (033) 0.01 (006) 24 Sept 1979 2 13 (0) 46-82 0.29 (0.90) 0.41 (0.84) 0.18 (0 57) — (009) Total 235 (10) x 1979 0 21 (062) 0.11 (0.41) 0.02 (0.06) 0.03 (0.14) - (0.07) Butter sole 23 June 1977 1 6(1) 18-23 0.07 (0 80) 0.20 (0.20) 15 June 1978 1 16 (0) 19-30 0.02 (0.33) 0.01 (0 20) 0.16 (0.87) 25 July 1978 1 16(0) 22-31 0.03 (0 25) 0.05 (0 38) 0.05 (0.38) — (0.06) 29 May 1979 3 14 (2) 17-35 0.04 (0.21) 0.03 (0.16) 0.03 (0.16) 0.05 (0.33) 30 May 1979 1 4(0) 49-60 0.32 (1.0) 026 (1.0) 0.29 (1.0) 0.07 (0.25) 19 July 1979 3 7(0) 21-88 0.21 (0 58) 004 (0.17) 0.18 (0.33) 0 08 (0 08) 8 Aug. 1979 4 9(1) 24-34 0.07 (0.54) 0.01 (063) - (0.13) Total 72(4) x 1979 0.16 (0 58) 0.09 (0 49) 0 12 (0.33) 0.03 (0 10) 0.03 (0.14) Speckled sanddab 23 June 1977 1 4 (0) 34-44 0.20 (0 50) 0.13 (0 25) 0 11 (0.25) 0.03 (0 25) 25 July 1978 1 5 (0) 41-65 1.0 (1.0) 22 Mar 1979 1 10(0) 29-39 0.08 (0 30) 0.01 (0.10) 0.72 (0.80) 18 Apr 1979 1 10 (0) 29-38 0.20 (0 20) 0.52 (0.60) 0.03 (0.10) 0.25 (0.30) 29 May 1979 2 14 (0) 33-50 0.25 (0.43) 0.30 (0.53) 0.32 (0.53) 30 June 1979 1 7 (0) 30-52 0.03 (0.57) - (0.05) 0.01 (0.29) 0 96 (1.0) 19 July 1979 2 11 (1) 35-70 0 04 (0.20) 0.96 (1.0) 24 Sept 1979 3 15 (0) 38-70 0.14 (0 52) 0.08 (0.25) 0.20 (0.52) 0.59 (0.86) Total 76(1) x 1979 0.12 (0.37) 0.10 (0.17) 0.09 (0.24) 0.63 (0.75) Sand sole 22 Jan 1979 2 6(0) 30-38 10 (1.0) 18 Apr. 1979 1 3(0) 29-55 1.0 (1.0) 19 July 1979 2 6(0) 29-50 1.0 (1.0) 8 Aug. 1979 2 13(0) 31-52 0.03 (0.17) — (0.13) 069(0.80) 0.28(0 40) 24 Sept 1979 2 11 (1) 30-48 1.0 (1.0) Total 39(1) 71979 0.01 (0.03) 0.80 (0.83) 0.14 (0 13) 0.06 (0 08) ii--A-6-6--A--rj— g — 6— g--g — • P. VETULUS a--a I. ISOLEPIS I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 NO. FISH Figure 2. — Cumulative number of prey categories sampled as a function of sample size for Parophrys vetulus and Isopsetta isolepis. Each data point represents the mean of two separate trawl collections. Vertical bars are ±1 standard deviation. contents varied little among individuals of a spe- cies within a trawl. For each species studied, food items from fish caught in the same trawl tended to have the same rank order of numerical abun- dance. This consistency of results was statistic- ally significant; the null hypothesis of inde- pendence among prey rankings was rejected (Friedman's nonparametric randomized block ANOVA, P<0.005; Gibbons 1971). On several sampling dates the number of fishes available for study was small, e.g., Parophrys vetulus on 5 September 1978 (three fish), /. isolepis on 30 May 1979 (four fish). The small within-sample vari- ability of these species, however, indicates that such small sample sizes will not unduly bias de- 559 FISHERY BULLETIN: VOL. 80, NO. 3 termination of the major food items consumed. As is apparent from Table 1, P. vetulus feeds on a wide variety of benthic animals. Juvenile bi- valves, harpacticoid copepods, Magelona palps, and amphipods are particularly abundant in English sole guts. On most sampling dates, the frequency of occurrence of these four prey in the diet of English sole was high, although typically only one or two items dominated the diet numeri- cally. Occasionally a food item which was usually rare became a major component in the guts of English sole, such as free-living nematodes on 25 July 1978 or echinoid tube feet on 30 June 1979. The diet of /. isolepis was very similar to that of P. vetulus, with the exception that butter sole fed to a greater extent on mysids and decapods. Ci- tharichthys stigmaeus fed equally on large epi- benthic crustaceans (amphipods, decapods, cumaceans) and pelagic prey. Polychaetes were totally lacking in the diet. Psettichthys melano- stictus consumed mysids almost exclusively; only on 8 August 1979 were other pelagic prey found in the guts of this species. Average H' diversity of food consumed per sampling date in 1979 was 1.38 for English sole, 1.47 for butter sole, 0.81 for speckled sanddabs, and 0.14 for sand sole. The similarity in diets of these four species was com- pared by computing the percent similarity index (PSI; Whittaker 1960) based on the average 1979 proportions of prey consumed by each species (Table 2). Two of these paired comparisons, Parophrys vetulus-I. isolepis and C. stigmaeus- Psettichthys melanostictus, indicate similarities exceeding 50%. In the case of the speckled sand- dab and the sand sole, this dietary overlap is based on their common utilization of one food category, mysids. English and butter soles share a wide variety of prey which were consumed in very similar proportions, e.g., 29 May 1979. Observations of 20-25 mm Parophrys vetulus feeding in laboratory aquaria revealed two basic types of foraging behavior. In the first, fish re- mained motionless on the bottom and then peri- odically lunged forward 1-2 cm, striking at ob- jects located on the surface of the sediment. In Table 2.— Percent similarity of prey consumed by English sole. Parophrys vetulus; butter sole, Isopsetta isolepis; speckled sanddab, Citharichthys stigmaeus; and sand sole, Psettichthys melanostictus, based on the average 1979 diets shown in Table 1. the second, fish slowly raised their heads above the bottom then rapidly thrust forward, causing the upper few millimeters of sediment to billow into suspension. Parophrys vetulus would then strike in rapid succession at small objects pre- sumably temporarily displaced from the bottom. Neither type of behavior predominated; both were detected in all of the individuals observed. After monitoring these responses for several hours, fish were sacrificed and the guts exam- ined. Harpacticoid copepods dominated the diet of these fish. Shifts in prey preference as a function of fish size (age) were observed in English sole. The average diets of all P. vetulus less than and greater than 35 mm SL were computed using the 1979 data and then compared (Table 3). The dra- matic difference in prey of these two size classes is apparent. Smaller fish (17-35 mm SL) con- sumed small prey almost exclusively, while larger fish (35-82 mm SL) only occasionally in- gested these small items, choosing instead amphi- pods and cumaceans. Isopsetta isolepis showed a similar shift in the preferred size of prey as stan- dard length increased from 30 to 40 mm. Four- teen butter sole (17-35 mm SL) caught on 29 May 1979 fed predominantly on small food items, while the gut contents of four larger fish (49-60 mm SL) caught 1 d later were composed of am- phipods, cumaceans, and decapods (Table 1). A similar distinction was found in fish collected on 19 July 1979. Neither C. stigmaeus nor Psettich- thys melanostictus altered the taxonomic com- position of their diet within the size ranges of fish we examined, although, as with English and but- ter soles, larger fish ate larger prey. The guts of all four species were generally <25% full in the morning before 0900 h. Stomach fullness gradually increased during the late morning and afternoon. The correlation between Table 3.— Mean numerical proportions of dominant prey items in the guts of Parophrys vetulus less than and greater than 35 mm SL. Species P. vetulus I. isolepis C. stigmaeus I. isolepis 077 C. stigmaeus 0.29 039 P. melanostictus 001 0.05 0.64 SL <35 mm SL >35 mm Small benthic prey Magelona palps 0.28 0.03 Juvenile bivalves 029 0.01 Tellinid siphons 0.13 0.01 Harpacticoid copepods 0.16 008 Total 0.86 013 Large benthic prey Amphipods 0 08 046 Cumaceans 003 0.30 Decapods 0.01 004 Polychaetes 0.0 0.06 Total 0.12 0.86 560 HOGUE and CAREY: FEEDING ECOLOGY OF 0-AGE FLATFISHES the time of capture (ranging between 0830 and 1800 h) and average gut fullness for English sole was significant; r = 0.49, P = 0.05. On 22 March 1979 two otter trawl hauls were made, one at 1000 and another at 1800 h. Guts of 10 English sole ranging in size between 19 and 35 mm SL were examined from both trawls. The diets of both groups of fish were the same, but the fish collected at 1800 h had an order of magnitude more food items in their guts than the earlier collection: 90% full, 198±56 SD items, vs. 10% full, 18±17 SD items. Isopsetta isolepis, C. stig- maeus, and P. melanostictus showed similar daily trends. Sufficient numbers of English sole of the same size were collected on 23 January and 29 May 1979 to compare the similarity of diets within and between replicate trawls. The PSI was used to quantify the proportion of food items found in common for each possible pair of fish collected on a sampling date. Mean similarity values were then obtained by averaging the PSI values for the fish within the same trawl and for fish col- lected in different trawls. Comparing replicate samples obtained at the same depth (Table 4), the average PSI for fish guts within the same trawl in both January and May, as well as the mean PSI between fish in different trawls in January, were approximately the same, 50%. The simi- larity between two trawls at the same depth in May, though, is very low (3%). Table 4 (bottom) also shows a comparison of within-trawl and between-trawl similarity, where trawls were collected at different depths (20 m and 30 m). Again the within-trawl affinities are high in both January and May, as is the between-tow similarity in January. The average PSI in May for fish from different depths is low. The in- creased between-trawl variability in food habits noted on 29 May was a general feature observed in all late spring and early summer replicate col- lections of Parophrys vetulus. For example, on 13 Table 4.— Average percent similarity of index of Parophrys vetulus diets within and between replicate trawls on 23 Janu- ary and 29 May 1979. Repli cates at same Replicates at different depth depths Within Between Within Between trawl trawl trawl trawl 23 January 1979 20 m 53% 53% 20 m and 30 m 71% 66% 29 May 1979 10 m 50% 3% 20 m and 30 m 65% 12% July 1978, trawls were made at 15 m and 20 m. Magelona palps numerically comprised 72% of the English sole diet at 15 m butonly 19% at 20 m, while juvenile bivalves and harpacticoid cope- pods combined to form 19% of the prey consumed at 15 m and 63% at 20 m. The diet of recently settled English sole changed continually among sampling months. Comparing similar-sized fish (17-35 mm SL) caught in 1979 (Fig. 3) reveals that dominant food items on a numerical basis varied from Magelona palps (November 1978, January 1979), juvenile bivalves (March 1979), bivalve siphons (April and May 1979), to juvenile bivalves and harpacticoid copepods (July 1979). Examination of samples collected in 1977 and 1978 showed that the sequence of changes noted in 1979 does not repeat each year. Magelona palps, which in 1979 were never a dominant item in the diet of P. vetulus after January, were numerically the most abundant food on two sampling dates in the summer of 1978. Other between-year differences exist, e.g., 5 September 1978 and 24 September 1979, but it is impossible to determine whether these differences are real or a result of spatial variability in diet combined with insufficient sampling. The apparent increased equitability of prey items shown in Figure 3 for April and May rela- tive to January and March does not indicate that spring and summer diets of individual fish are more diverse than in winter. Instead, the differ- ence is an artifact of the spatial variability pre- viously noted, being generated by averaging the data for all fish caught in different tows. The average dietary diversity {FT ) of an individual fish on 23 January 1979 (0.43±0.35 SD, n = 24) was not significantly different from that on 29 May 1979 (0.37 ±0.41 SD, n = 32). The only seasonal data currently available on the abundance of benthic organisms at Moolach Beach are for nematodes and harpacticoid cope- pods. Nematodes are very abundant {x = 1,050 • 10 cm"2), but quantitatively, with the exception of one sampling date, are not significant in the diet of the fish species we studied. Harpacticoids are important in the diets of English and butter soles, yet are not abundant at the study site. Their average density for the eight sampling dates between July 1978 and September 1979 was 12.2±4.0 SE • 10 cm"2. Only the larger spe- cies found in the 0-1 cm depth increment were present in fish guts. Halectinosoma spp. com- prised more than 80% of all harpacticoid prey. 561 FISHERY BULLETIN: VOL. 80, NO. 3 Seasonally, Halectinosoma ranged in abundance from a mean of 6.8 • 10 cm'2 between May and September (n - 5) to zero from October to March (n — 3). Their period of maximum density coin- cides with their maximum occurrence in the diet of 17-35 mm SL English sole (Fig. 3). NOVEMBER 10 T 075 ■■ ■■ 050 ■■ .. 0.25 - MAG. BIV. SIR HAR. APRIL rrrr: &£&* MAG. BIV. SIR HAR. JANUARY ■ rrn MAG. BIV. SIP. HAR. \-\J MAY 075 ■ - 0-50 • ^ 025 ■ ••••••: • • ■.*.* ■ *..* • °.v • ■ HIIIU1! •••••••.•••.••' ^^ -- + -■ ■••.••••••••• -44-: '..•:■„•:•:.•:•;.• H MAG. BIV. SIP. HAR. MAG. BIV. SIR HAR. JULY MAG. BIV. SIR HAR. FIGURE 3.— Seasonal change in food habits of Parophrys vetuliui <35 mm SL between November 1978 and July 1979. Vertical bars indicate average proportion of Magelona palps (Mag.), juvenile bivalves (Biv.), clam siphons (Sip.), and harpacticoid cope- pods (Har.) in the diet. 562 HOGUE and CAREY: FEEDING ECOLOGY OF 0-AGE FLATFISHES DISCUSSION The diet of recently settled English sole is a function of size, location of capture, and season (Tables 1, 3, 4). Both the within-year and be- tween-year differences in diet noted for P. vetu- lus are similar to changes documented for other pleuronectid species (Macer 1967; Edwards and Steele 1968) and are probably related to tem- poral changes in density of prey organisms. Steele et al. (1970) concluded that variations in predation on Tellina siphons and polychaetes by young plaice, Pleuronectes platessa, were a result of changes in both the absolute and relative abundances of these prey over time. The observed relationship between seasonal changes in har- pacticoid copepod abundance and the utilization of these prey as food by English sole is the only direct evidence we have to support this conten- tion. However, the juvenile bivalves {Tellina and Siliqua) consumed by Parophrys vetulus were all young of the year which are known to have tem- porally variable recruitment (Jones5), suggest- ing that seasonal availability of this food item is also not constant. Moreover, Oliver et al. (1980) seasonally sampled the nearshore macrobenthos in a region of Monterey Bay, Calif., which was very similar to Moolach Beach in terms of physi- cal environment and fauna present. Their results indicate that the abundance of amphipods and such polychaetes as Magelona sacculata vary both within and between years. English sole at Moolach Beach probably alter their diet over time in accordance with similar temporal changes in the density of these larger prey spe- cies, but additional benthic data obtained con- currently with fish collections are necessary to substantiate this conclusion. The marked differences between summer and winter spatial variability in English sole diets (Table 4) are thought to be related to changes in both the abundance and spatial distribution of prey. During the winter, intense storm activity along the Oregon coast produces large waves which continually disturb and mix the sediments of the inner continental shelf (Komar et al. 1972). The meiobenthos has been shown to become ran- domly distributed during these periods within small areas (1 m2) and only slightly aggregated on larger scales (Hogue 1982). Small benthic prey fed upon by 0-age English sole would most 5H. R. Jones, School of Oceanography, Oregon State Univ., Corvallis, OR 97331, pers. commun. likely be affected by this vigorous physical mix- ing in much the same way as the meiofauna. As a result, English sole feeding at either the same depth or different depths may consume similar prey in the winter (Table 4, January) because prey organisms are more evenly distributed within the study area compared to other times of the year. Such a distribution, when coupled with the numerical dominance of one food item, would increase the similarity of food items available for consumption throughout the region. During the late spring and summer the physical disruption of sediment is minimized and the spatial distri- bution of the meiofauna becomes increasingly aggregated (Hogue 1982). Distinct differences in the species composition and abundance of nema- todes and harpacticoids have been found at loca- tions only 250 m apart. During this period there is little similarity in diets of English sole from replicate trawls (Table 4, May). In the spring and summer, P. vetulus may be opportunistically ex- ploiting different prey which are densely aggre- gated in different sectors of the Moolach Beach site. Seasonal changes in the spatial distribution of prey items may also alter the rate at which prey are consumed. Experiments with fish feeding in aquaria (Ivlev 1961) have shown that an increase in the degree of aggregation of food sources has the same effect on the rate of food consumption as an increase in the concentration of food. Results of Tinbergen et al. (1967) suggest similar rela- tionships between the spatial distribution of prey and predation. Fish commencing their benthic feeding in the late spring and summer at Moo- lach Beach may benefit energetically from the increased aggregation of benthic organisms dur- ing this period relative to that found during the winter. The consumption of parts of macrobenthic organisms, e.g., Magelona palps and tellinid clam siphons, rather than whole individuals by English sole <35 mm in length is probably re- lated to the maximum size of food items capable of being captured and ingested by these fish. We measured the mouth size of 30 mm P. vetulus and found that prey greater than about 2 mm in their largest dimension are too large to be consumed by such small fish. Siphons and palps are appar- ently the only portion of larger prey which are available for ingestion by fish <35 mm SL. As fish grow larger than 35 mm, small food items are neglected in favor of polychaetes, amphi- pods, and cumaceans which yield far more en- 563 FISHERY BULLETIN: VOL. 80, NO. 3 ergy per individual item. Two fortuitous conse- quences of this size-dependent predation may be important. First, the dietary overlap between small juveniles and larger fish is minimized, thus conserving food stocks for recently settled individuals. Second, both siphons and palps are capable of being regenerated. By consuming only parts of benthic organisms, food sources are not destroyed and may be cropped again in later months by other individuals following regenera- tion. This may be particularly important in the case of English sole because juveniles are contin- uously recruited to the bottom over a 9-mo period (Krygier and Pearcy footnote 2). The four pleuronectiform fishes we studied form a trophic continuum, ranging from gener- alists feeding upon numerous benthic prey (P. vetulus) to specialists relying on a few pelagic food items {Psettichthys melanostictus). Isopsetta isolepis and C. stigmaeus are intermediate in their position on the continuum. Few published results exist with which to compare ours. Cailliet et al. (1979) investigated the food habits of Par- ophrys vetulus, C. stigmaeus, and Psettichthys melanostictus at an ocean station in Monterey Bay. The fish they examined were all larger than the ones for which we have data, but the same basic trends emerge. They found that English sole was a generalist, eating a wide variety of benthic food items; sand sole relied almost totally on mobile crustaceans for food; and speckled sanddab fed on pelagic and epibenthic Crustacea and occasional infaunal worms and molluscs. Wakefield (footnote 3) has studied the adult food habits of these three species as well as those of /. isolepis collected at the Moolach Beach site. Although the specific food items ingested differ for recently settled juveniles and adults at this site, the basic modes of feeding, e.g., infaunal generalist or pelagic specialist, remained un- changed at Moolach Beach as the youngest juve- niles mature to adults. The greatest similarity among diets is between those of Parophrys vetulus and /. isolepis. Both of these benthophagous species have similar mouths with small, asymmetrical jaws and small incisor teeth. Both complete metamorphosis and com- mence benthic feeding at the same size (18-20 mm SL). Qualitatively there is no difference in their diet, although quantitatively butter sole occasionally feed more heavily on mysids. Com- paring fish of the same size (17-35 mm SL) on 29 May 1979, P. vetulus and /. isolepis fed on the same prey items in the same proportions. If food should be limiting for these two species, then in the absence of subsequent shifts in food prefer- ence the potential exists for competitive inter- action. While observing the feeding behavior of P. vetulus in the laboratory, several butter sole were placed in the aquaria along with the Eng- lish sole. Isopsetta isolepis were observed to bite the fins of P. vetulus and pursue them around the tank. These were casual observations which were only replicated over a 2-d period. Should this aggressive behavior be substantiated by fur- ther work, then interference competition be- tween P. vetulus and /. isolepis in the Moolach Beach area seems likely. On the whole, however, English and butter soles do not settle at the same time or place. Parophrys vetulush&s a protracted benthic recruitment period, settling to the bot- tom between November and July in estuarine and coastal waters <30 m deep (Krygier and Pearcy footnote 2). Isopsetta isolepis, on the other hand, has a restricted settling period (May- August) yet occurs over a broader depth range (9-60 m)(Krygier and Pearcy footnote 2). If inter- specific interactions were occuring between English and butter soles, it is likely that they would be limited to regions of overlap like Moo- lach Beach in the summer months. ACKNOWLEDGMENTS We wish to thank E. Krygier, W. Pearcy, and A. Rosenberg for making available to us their collections of fish. C. D. Mclntire, C. B. Miller, W. G. Pearcy, G. Boehlert, and W. W. Wakefield have read and commented on the manuscript. This work is a result of research sponsored by the Oregon State University Sea Grant College Pro- gram supported by NOAA, Office of Sea Grant, U.S. Dep. of Commerce, under grant NA79AA- D-00106. LITERATURE CITED Cailliet, G., B. S. Antrim, and D. S. Ambrose. 1979. Trophic spectrum analysis of fishes in Elkhorn Slough and nearby waters. In S. J. Lipovsky and C. A. Simenstad (editors), Gutshop '78 fish food habits studies. Proc. Second Pac. Northwest Tech. Workshop, October 10-13, 1978, p. 118-128. Univ. Wash. Press, Seattle. CUSHING, D. H., AND J. G. K. HARRIS. 1973. Stock and recruitment and the problem of density dependence. Rapp. P.-V. Reun. Cons. Perm. Int. Ex- plor. Mer 164:142-155. Edwards, R., and J. H. Steele. 1968. The ecology of 0-group plaice and common dabs at 564 HOGUE and CAREY: FEEDING ECOLOGY OF 0-AGE FLATFISHES Loch Ewe. I. Population and food. J. Exp. Mar. Biol. Ecol. 2:215-238. Gibbons, J. D. 1971. Nonparametric statistical inference. McGraw- Hill Inc.. N.Y., 306 p. Hayman, R. A., and A. V. Tyler. 1980. Environment and cohort strength of Dover sole and English sole. Trans. Am. Fish. Soc. 109:54-70. HOGUE, E. W. 1982. Seasonal changes in the abundance and spatial dis- tribution of a meiobenthic assemblage on the open Ore- gon coast and its relationship to the diet of 0-age flat- fishes. Ph.D. Thesis, Oregon State University, Cor- vallis. Ivlev, V. S. 1961. Experimental ecology of the feeding of fishes. Yale Univ. Press, New Haven, 302 p. Komar, P. D., R. H. Neudeck, and L. D. Kulm. 1972. Observations and significance of deep-water oscil- latory ripple marks on the Oregon Continental shelf. In D. J. P. Swift, D. B. Duane, and O. H. Pilkey (editors), Shelf sediment transport: Process and pattern, p. 601- 619. Dowden, Hutchinson, & Ross, Inc., Stroudsburg, Pa. Laroche, J. L., and S. L. Richardson. 1979. Winter-spring abundance of larval English sole, Parophrys vetulus, between the Columbia River and Cape Blanco, Oregon during 1972-1975 with notes on occurrences of three other pleuronectids. Estuarine Coastal Mar. Sci. 8:455-476. Laroche, W. A., and R. L. Holton. 1979. Occurrence of 0-age English sole, Parophrys vetu- lus, along the Oregon coast: an open coast nursery area? Northwest Sci. 53:94-96. Macer, C. T. 1967. The food web in Red Wharf Bay (North Wales) with particular reference to young plaice (Pleuronectes platessa). Helgolander wiss. Meeresunters. 15:560- 573. Oliver, J. S., P. N. Slattery, L. W. Hulberg, and J. W. Nybakken. 1980. Relationships between wave disturbance and zona- tion of benthic invertebrate communities along a sub- tidal high-energy beach in Monterey Bay, California. Fish. Bull., U.S. 78:437-454. Paloheimo, J. E., and L. M. Dickie. 1966. Food and growth of fishes. III. Relations among food, body size, and growth efficiency. J. Fish. Res. Board Can. 23:1209-1248. Pearcy, W. G., and D. Hancock. 1978. Feeding habits of Dover sole, Microstomus pacifi- cus; rex sole, Glyptocephalus zackirus; slender sole, Ly- opsetta exilis; and Pacific sanddab, Citharichthys sordi- dus, in a region of diverse sediments and bathymetry off Oregon. Fish. Bull., U.S. 76:641-651. Pearcy, W. G., M. Hosie, and S. L. Richardson. 1977. Distribution and duration of pelagic life of larvae of Dover sole, Microstomus pacificus; rex sole, Glypto- cephalus zachirus; and petrale sole, Eopsetta jordani, in waters off Oregon. Fish. Bull., U.S. 75:173-183. Pielou, E. C. 1969. An introduction to mathematical ecology. Wiley- Interscience, N.Y., 286 p. Richardson, S. L., and W. G. Pearcy. 1977. Coastal and oceanic fish larvae in an area of up- welling off Yaquina Bay, Oregon. Fish. Bull., U.S. 75: 125-145. Rosenberg, A. A. 1981. Growth of juvenile English sole, Parophrys vetulus, in estuarine and open coastal nursery grounds. M.S. Thesis, Oregon State University, Corvallis. Shelbourne, J. E. 1957. The feeding and condition of plaice larvae in good and bad plankton patches. J. Mar. Biol. Assoc. U.K. 36: 539-552. Steele, H. J., A. D. McIntyre, R. R. C. Edwards, and A. Trevallion. 1970. Interrelations of a young plaice population with its invertebrate food supply. Symp. Brit. Ecol. Soc. 10: 375-388. TlNBERGEN, N., M. IMPEKOVEN, AND D. FRANCK. 1967. An experiment on spacing-out as a defence against predation. Behaviour 28:307-321. Whittaker, R. H. 1960. Vegetation of the Siskiyou Mountains, Oregon and California. Ecol. Monogr. 30:279-338. 565 PRESSURE SENSITIVITY OF ATLANTIC HERRING, CLUPEA HARENGUS L., LARVAE1 David R. Colby,2 Donald E. Hoss,2 and J. H. S. Blaxter3 ABSTRACT Larval Atlantic herring, Clupea harengus harengus L., are known to change their vertical distribu- tion by day and night, but it is not clear if they can sense their depth by perception of hydrostatic pressure. Two experiments were designed to test whether herring larvae would respond to imposed pressure changes by making appropriate compensatory vertical movements and whether such ability could be related to the development of the bulla system (stage I, bulla absent; stage II, bulla liquid-filled; stage III, bulla gas-filled). In the first experiment, pairs of larvae were exposed to a fixed sequence of pressure changes (&P) from ±13 cm H20 to ±66 cm H20. Members of simul- taneously tested pairs tended to be influenced by one another when responding to pressure change. The response of stage-I larvae tended to first increase and then decrease over a20-min test period for a given AP. Stage-II and stage-Ill larvae showed better performances in compensating for imposed pressure changes than did stage I. Larvae exposed to a sudden pressure increase of 5 atm (atmos- pheres) (5,000 cm H20) before the experiment did not perform as well as those not so exposed, but the differences were not statistically significant. A second experiment tested the response of individual larvae to randomized sequences of pressure changes. Stage-Ill larvae moved most frequently to compensate for the pressure changes, but stage-I and stage-II larvae also responded to changes in pressure. Both experiments show that herring larvae of all three stages compensate for applied pressure changes by moving up when pressure is increased and down when it is decreased, but that they rarely move sufficiently far in the vertical plane to fully compensate. Larval fish are known to change their vertical distribution diurnally. Although this behavior is probably controlled by changes in light inten- sity, it is not clear whether hydrostatic pressure perception is important in limiting or controlling the depths reached at different stages of the ver- tical migration cycle. A few workers (e.g., Qasim et al. 1963) have shown that fish larvae can re- spond to pressure changes; in particular, Bishai (1961) and Blaxter and Denton (1976) have shown that Atlantic herring, Clupea harengus harengus L., larvae are pressure sensitive. The most likely site for a pressure receptor is a gas-filled structure, such as a swim bladder, which, if compliant, undergoes large changes in volume during vertical movements (10 m change of depth being equivalent to 1 atmospheric pres- sure). However, clupeoids, together with some other groups such as mormyrids, have gas-filled bulla. In herring the bulla appears to be sensitive to pressure changes (Allen et al. 1976; Denton 'Contribution No. 82-11B, from the Southeast Fisheries Cen- ter Beaufort Laboratory, National Marine Fisheries Service, NOAA, Beaufort, N.C. Southeast Fisheries Center Beaufort Laboratory, National Marine Fisheries Service, NOAA, Beaufort, NC 28516. 3Dunstaffnage Marine Research Laboratory, Oban, Scot- land. Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80, NO. 3. 1982. and Blaxter 1976). In herring the prootic bulla has two parts: one filled with gas, the other with perilymph. The two parts are separated by an elastic membrane. This membrane responds to pressure changes, driving the perilymph in or out of a fenestra, which is situated close to the utriculus of the inner ear. The gas-filled part of the bulla is also connected to the swim bladder by a very narrow gas duct. This connection allows the prootic membrane to adapt to slow changes of pressure. If the pressure increases, the mem- brane bows in and being elastic tends to return to its resting position. The swim bladder wall is compliant and the pressure differential created along the gas duct causes gas to flow into the bulla from the swim bladder. If the pressure de- creases, the membrane bows outward (into the perilymph space) and gas flows from the bulla back to the swim bladder. In the fully functional system described above the bulla may respond to hydrostatic pressure changes, but because the system adapts in 15-30 s, there will be no perception of absolute pres- sure. In the very early larval stages of herring (from hatching to 18 mm TL) no bulla is present; the bulla appears at about 18 mm and usually is filled with gas by 26 mm. The swim bladder is not fully formed until 35 mm or more (Blaxter 567 FISHERY BULLETIN: VOL. 80, NO. 3 and Denton 1976). One would predict that her- ring larvae up to 18 mm would have little or no pressure sensitivity. As the bulla becomes filled with gas but before the swim bladder develops, we would expect very high sensitivity to absolute pressure (no adaptation being possible) and her- ring larvae from 26 to 35 mm would be in this category. Larger larvae would retain sensitivity to pressure change, but the development of the adaptation mechanism would prevent its being an absolute sense. One also would predict that herring larvae with gas-filled bullas but no swim bladders would be especially vulnerable to large pressure changes that could cause the mem- brane to burst. Hoss and Blaxter (1979) have shown that herring larvae do appear to be espe- cially vulnerable to large, rapid pressure changes at about this stage of the life history. Blaxter and Hoss (1979) followed the develop- ment of the adaptation mechanism, measured its time constant, and have shown that adaptation usually does not develop until a length of >30 mm. This paper describes a detailed analysis of pressure sensitivity in herring larvae, using the hypothesis that a larva will swim up to compen- sate for increasing pressure and down to com- pensate for decreasing pressure and that this is due in part to the development of the bulla sys- tem. In the two experiments to be described, par- ticular attention was paid to measuring changes in sensitivity during the development of the bulla-swim bladder system. In addition, the effect of a large, rapid pressure change on subse- quent pressure sensitivity also was investigated in one experiment. MATERIALS AND GENERAL METHODS Herring were reared from fertilized eggs, using the techniques of Blaxter (1968). The tem- perature during development increased from about 7°C near hatching to 12°C, 4 or 5 mo later. The pressure sensitivity experiments were con- ducted in a constant temperature room at 9°- 10°C, using the apparatus of Blaxter and Denton (1976). This apparatus consisted of a Plexiglas4 cylinder 80 cm high and 7 cm in diameter, the transparent wall being marked on the outside to give 16 equal sections numbered 1-16. The sur- 4Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. face was designated 0, the bottom as 17. This allowed an observer to record the position of a larva in the cylinder at any given instant with a number from 0 to 17. The pressure in the cylinder could be changed by a preset amount by opening a two-way tap at the top, which exposed the water surface to atmospheric pressure or to posi- tive or negative pressures in a gas reservoir. Each larval herring was anesthetized after it was tested and the developmental stage of its bulla (stage I, no bulla; stage II, bulla liquid- filled; stage III, bulla gas-filled) was ascertained. A complication arose that the bulla does not be- come instantaneously filled with gas and may contain only a few or many bubbles. Pressure sensitivity is more likely to be high if the bulla is full of gas. At least 10 larvae of each developmen- tal stage were used. EXPERIMENT I Design Pairs of larvae of approximately equal length and stage of development were tested simulta- neously. After a 2-3 min acclimation period at atmospheric pressure, 10 observations on the position of each fish were made at 15-s intervals. The pressure was then changed and the observa- tions were repeated at the new pressure. The pressure sequence selected was based upon prior research (Blaxter and Denton 1976) and involved changing the pressure from atmos- pheric to each of the following pressures four times: ±13, ±39, and ±66 cm H20 (1 cm H20 = 0.001 atm), for a total of 480 observations and 47 changes of pressure (Fig. 1). This fixed sequence of increasing pressure differentials was chosen to avoid the potential danger of larvae becoming overstimulated initially at the higher pressures. Earlier evidence (Blaxter and Denton 1976) indi- cated that larvae moved upwards to compensate for increased pressure and downwards to com- pensate for decreased pressure, and the extent of vertical movement was correlated with the ex- tent of pressure change (AP) applied. Large pressure changes early in the sequence might not only block responses to smaller subsequent pres- sures but might also cause earlier fatigue. There- fore, pressure changes were not randomized and an experiment commenced regardless of larval distribution in the water column. Approximately half the larvae used in Experiment I were pre- exposed for 1 min to an abrupt pressure increase 568 COLBY ET AL: PRESSURE SENSITIVITY OF ATLANTIC HERRING 66 39 13 ATM -13 CM I E o ^^ LU DO CO CO UJ cc a. -39 -66 Mnjw 66 i 39 ■ n 13 ATM -13 IF i JUL 1 -39 j -66 i i 1 J 1 20 40 60 80 100 120 TIME (minutes) Figure 1.— The upper figure depicts the fixed pattern of pres- sure changes to which pairs of larval herring were exposed in Experiment I. The lower figure shows an example of one of the randomized sequences of pressure changes to which a larval herring was exposed in Experiment II. An independently ran- domized sequence was drawn for each larval herring tested. of 5 atm (5,000 cm H2O) before the onset of the regular pressure series to determine if this abrupt AP would impair subsequent pressure sensitivity differently in the different develop- mental stages. These are referred to as treated larvae, whereas those not preexposed are re- ferred to as control larvae. Results vertical direction to compensate for the change in pressure; -, if it moved in the opposite direc- tion; and nr, if it showed no net change in its ver- tical position. We have used these assigned scores in the analyses to follow. Larvae not responding were treated as if they had moved in the non- compensatory direction, so the analyses are con- servative. The scoring technique allows one to evaluate the frequency with which a fish, con- tending with a dynamic pressure regime, moved correctly, i.e., moved in the appropriate vertical direction to compensate for the imposed pressure change. A separate analysis of variance of the number of compensatory responses was calculated for each treatment group, using only the data for members of homogeneous pairs to determine whether the paired larvae tend to respond to- gether. The intraclass correlation coefficients ranged from 0.91 to 0.92 for the two stage-I groups to 0.20 and 0.32 for the two stage-Ill groups, respectively (Table 1 ). Thus for the least, well-developed fish (stage I) the variation among members of a pair was only one-ninth as great as the variation between average values for pairs of fish, i.e., the two members of a pair tended to re- spond together as a unit. The stage-II control group was an exception to this general pattern. For that group the variation among members of a pair was greater than the variation among pairs, suggesting that the members of a pair tended to move away from one another as pres- sure within the cylinder was changed. The lack of independence in the responses of fish tested simultaneously invalidates use of the data for mixed pairs (i.e. .pairs of fish of different developmental stages) and requires that we con- sider pairs of larvae as the experimental unit in testing hypotheses about the average perfor- mances. An analysis of variance of data for homo- Although pairs of larvae selected for simultan- eous testing were judged visually to be of equal length, the developmental status of their bulla systems was evaluated only after they were sub- jected to the pressure tests and was sometimes found to differ (Table 1). A total of 480 locations within the cylinder were recorded for each herring tested. We aver- aged 10 locations of a larva during a 2.5-min test at a given pressure to obtain a more concise sum- mary of the response pattern. We then assigned a score to the larva for each 2.5-min series: +, if its average position indicated it had moved in the Table 1.— Numbers of herring larvae, numbers of pairs of lar- vae of the same developmental stage, and intraclass correlation coefficients for fish tested in Experiment I. Control Preexposed to 5 atm (treated) Stage 1 Number of individuals 9 8 Number of homogeneous pairs Intraclass correlation coefficient 4 0.92 4 0.91 Stage II Number of individuals 15 11 Number of homogeneous pairs Intraclass correlation coefficient Stage III Number of individuals 4 -0.42 10 4 0.41 11 Number of homogeneous pairs Intraclass correlation coefficient 2 0.20 4 0.32 569 FISHERY BULLETIN: VOL. 80, NO. 3 geneous pairs disclosed that stage-I fish moved vertically to compensate for the imposed pres- sure changes less often than those possessing a more developed bulla system (Table 2). No advan- tage for fish possessing gas-filled bullas rather than liquid-filled bullas was detected. Although there was a consistent tendency for herring pre- viously exposed to 5 atm to move vertically to compensate less frequently than those not so exposed, this tendency was not statistically sig- nificant. The overall intraclass correlation co- efficient was 0.67, implying that the average variation among pairs within a treatment group was twice that between members of a pair. The hypothesis testing reported above ignores the fact that a larval herring could respond in three ways to the 47 changes in pressure; it could move vertically to compensate, it could move ver- tically in the opposite direction, or it could simply maintain its current position within the cylinder. A plot of the data for pairs of larvae shows that nonresponse to changing pressure was more frequent for stage-I larvae than for the more developed fish (Fig. 2). Two pairs of larvae in particular, one for the stage-I control group and one from the stage-I treated group, are clearly outliers, showing no response during 49% and 86% of the trials, respectively. If these two pairs are dropped from the analysis, then the dif- ferences reported above are no longer significant and the means are 27.7 and 25.2, respectively (in- stead of 23.8 and 19.8) and are close to those for the corresponding stage-II groups (Table 2). A plot of moving averages of the percentage of compensatory responses against the sequential series of pressure changes reveals that the stage- I herring exhibited a rather consistent pattern of Table 2. — Analysis of variance of number of com- pensatory moves of fish during pressure sensitivity tests, and table of means: I = bulla absent, II = bulla liquid filled, III = bulla gas filled. Source df Mean square F Preexposure 1 4547 049 Developmental stage 2 314.26 3.40 II versus III 1 88.05 0.95 I versus II and III 1 540.47 585" Interaction 2 2848 0.31 Experimental error 16 92 44 508" Sampling error 22 1820 Intraclass correlation coefficient = 0.67 Average number of compensatory moves per fish: Control Preexposed to 5 atm Stage I 23.8(51%) 19.8 (42%) Stage II 28.9(61%) 26.1 (56%) Stage III 32 2 (68%) 30.5 (65%) CO LU > O > rx o < co z LU Q- o o u. O rx LU CO Z o Bulla Absent 90 . Bulla Liquid-filled 80 A Bulla Gas-filled 70 . A 60 "A A\ 50 • \ • o \ 40 0 • A 30 V \ 20 10 / / / 1 .... / \ i i i i i j — i i\ ■P<0.05; "P<0.001. 10 20 30 40 50 60 70 80 90 NUMBER OF ANTICOMPENSATORY MOVES Figure 2.— Total numbers of compensatory vertical move- ments of a pair of herring plotted against the corresponding number of anticompensatory movements for that pair. The dashed line indicates the evenly divided response expected under the null hypothesis. Nonresponse is indicated by the ver- tical (or horizontal) distance from the hypotenuse. Control and preexposed pairs are not plotted separately. Arrows indicate two outliers. response over the 20 min test period for a given AP, especially for the larger AP's (Fig. 3). Per- formance improved at the onset of a new incre- ment or decrement of pressure and then fell off as the test continued, only to improve when the next increment or decrement was used. The other two developmental stages showed a rela- tively high initial frequency of compensation that rapidly decreased, then subsequently in- creased until the test of the final pressure change. Discussion The results in Figures 2 and 3 clearly show that some larvae are responsive to pressure. However, the relatively small sample size, the correlation in the behavior between members of a pair simultaneously tested, and the relatively high variation in response among experimental units within a given treatment group reduced our ability to distinguish differences in the re- sponse to changes in pressure of herring of dif- ferent developmental stages. Additional prob- lems in interpreting the first experiment arose from the evidence that tests of a given pressure 570 COLBY ET AL.: PRESSURE SENSITIVITY OF ATLANTIC HERRINC in ui > o >■ H I* co in z _ 111 o % • O a 2 > zi o a. 68 64 60 56 52 48 44 40 36 32- Bulla Gas-filled '■/ Bulla Liquid-filled .m - l/V 1 l. v l/\ \/ \ Bulla Absent ■13 J_ _L ■13 +39 -39 ►66 -66 Figure 3.— Moving averages of the percentage of correct ver- tical movements for the three developmental stages of herring in the first experiment. Data for control and preexposed her- ring are not plotted separately. change were too long and that the test series as a whole was too protracted as well. The fixed na- ture of the pressure series, while reducing the chance that larvae would be overstimulated if initially exposed to higher pressure changes, confounded possible differences in response to different pressure changes with habituation to the stimulus or possible learning effects. A sec- ond series of experiments was designed there- fore to reduce or eliminate some of these prob- lems. EXPERIMENT II Design The major features of the second design were: Table 3.— Analysis of variance of the number of compensatory responses of herring in the second experiment and table of means: I = bulla absent, II = bulla liquid filled, III = bulla gas filled. Source df Mean square Developmental stage 2 62.9394 5.86" I versus II 1 0 4091 0 030 I and II versus III 1 125.4697 1168" Experimental error 30 10.7394 Average number of compensatory responses per fish: Stage I 14 18 (62%) Stage II 13.91 (60%) Stage III 18.18 (79%) "P<001. 1) a single factor, developmental stage of the bulla system; 2) all herring tested individually; 3) an independently randomized test sequence for each fish; 4) each pressure change tested twice; 5) shorter duration of the test series (Fig. lb) (the larvae were subjected to 23 changes of pressure rather than 47 as in the first experi- ment); and 6) experiments started when herring were at the center of the test column. Eleven her- ring of each developmental stage were tested. Results As in the first experiment, average positions within the test cylinder were calculated for each pressure change. Vertical movements, as indi- cated by successive differences in these averages, were then scored as compensatory, anticompen- satory, or no response. Analysis of variance of the number of scores indicated that herring with gas-filled bullas compensated more frequently than herring having either liquid-filled bullas or no bullas at all (Table 3; Fig. 4). The stage-Ill herring on the average moved vertically to com- pensate 79% of the time compared with 60% and 62% for stage-II and stage-I herring, respectively. However, in Figure 4 we show that even several stage-I larvae achieved relatively high scores, suggesting that a different test of the hypothesis might be based upon classifying larvae into two o Bulla Absent . Bulla Liquid-filled S 20l- V^ ,»du * Bulla Gas-filled > O > oc o t- < 09 z III Q. O O XL UJ m 2 4 6 8 10 12 14 16 18 20 22 2 pi* NUMBER OF ANTICOMPENSATORY MOVES Figure 4.— Total numbers of compensatory vertical move- ments by individual herring in Experiment II plotted against the number of anticompensatorymoves. (See legend for Fig. 2.) 571 FISHERY BULLETIN: VOL. 80, NO. 3 categories: 1) those that made more compensa- tory movements than one would expect by chance, and 2) those that did not. In Experiment II, each herring was exposed to a random sequence of 23 changes in pressure. If we regard nonresponse as noncompensatory, then the binomial distribution provides a basis for classifying the larvae into two groups, those that moved in the compensatory direction more frequently than one would expect by chance, and those that did not. Under the null hypothesis the probability that a herring would make 16 or more compensatory shifts in vertical position is <0.05. Using this criterion, we classified 5 of the stage-I larvae, 4 of the stage-II larvae, and 10 of the stage-Ill larvae as having made more com- pensatory vertical movements than one would expect by chance. A chi-square test showed that the stage-Ill larvae more frequently compen- sated for the imposed pressure change than the two earlier stages (chi-square = 7.69, df = 2, P<0.03). This implies that the bulla system con- tributes to the larval herring's hydrostatic pres- sure perception only after it contains gas. Because the average position of a larval her- ring was determined for each pressure level, we could calculate the average vertical distance it moved for each change in pressure. The average distances moved for the 19 successful fish were regressed against the corresponding change in pressure (Fig. 5). The lines for stage-I and stage- II larvae nearly coincide and their slopes are about half that of the regression for stage-Ill herring. The greatest departure from these lines, fitted through the origin, is for the stage- Ill herring at the -66 cm H2OAF. They failed to move downward in the column as much as their performance at other pressure changes would predict. We note that even the stage-Ill herring moved only about 17% of the distance re- quired to compensate fully for an imposed pres- sure change. Discussion The average proportion of tests in which a lar- val herring moved vertically to compensate was higher in the second experiment than in the first. This was probably due to the shorter duration of the trials and the test series which should have reduced any effects of habituation or fatigue. However, the random nature of the pressure changes in the second experiment may also have contributed to the enhancement of the response. E o Q > o LU O CO O —I < o a. LU > LU O < cr LU > < +20 oBulla Absent Full Compensation • Bulla Liquid-filled / + 15 ABulla Gas-filled 1 A + 10 1 1 Stage III V +5 0 - 1 1 \- Stage H Stage I i-^1 -5 -10 - ***^ /■ . i ° y i - s * / / / -15 / / / 1 i i -66 -39 -13 0 +13 +39 +66 CHANGE IN PRESSURE (cm H20) Figure 5.— Average vertical distances moved by herring lar- vae to compensate for changes in pressure. Both of the experimental designs employed in this investigation yielded information. The first design revealed that when two herring are tested simultaneously, the response of each is influ- enced by the presence of the other. It also re- vealed that the response of a herring to a repeated pressure change tends to increase and then de- crease over a 20-min period. The second design provided a more satisfactory test of the null hypothesis that a herring's response to pressure change is independent of the developmental stage of the bulla system and also confirmed an implication from the first experiment: namely, that even before the full development of the bulla system, herring are capable of detecting changes in pressure of the magnitude used in this investi- gation. Finally, the second experiment demon- strated that herring possessing a gas-filled bulla system will exhibit a markedly improved per- formance when compared with less mature lar- vae. In very few instances did the larvae move a sufficient vertical distance to fully compensate for the imposed pressure change— a similar find- ing to that of Blaxter and Denton (1976). Even the stage-Ill larvae, on the average, only moved 17% of the distance to compensate fully. This is partly a statistical artifact of the manner in which we measured a larva's response. We re- 572 COLBY ET AL.: PRESSURE SENSITIVITY OF ATLANTIC HERRING corded its position at 15-s intervals over the 2.5- min period of a given AP and then averaged those 10 values. Thus, unless a larva either over- compensated or fully compensated during the first 15 s, its average position during the 2.5-min test would necessarily not be at the level of com- pensation. The vertical and horizontal limits of the appa- ratus also probably impeded vertical progress of larvae in some instances, because the position of the larva within the apparatus at the initiation of a change in pressure determined the potential vertical distance the larva could move to com- pensate; this would be most important as a source of bias at the larger AP's. Still another possible explanation for the in- complete nature of the compensation may lie in the artificiality of the experiment. Fish are not normally subjected to abrupt hydrostatic pres- sure changes as they swim with a vertical com- ponent. It is difficult to design an experiment to show a hydrostatic pressure sense in a free swim- ming vertically moving fish larva. Gibson5 has shown, however, that the activity of juvenile plaice (which lack a swim bladder) varies regu- larly during sinusoidal changes of hydrostatic pressure of amplitudes of about 50 cm H2O re- peated over a 4-h period, thus demonstrating sensitivity to slow changes of pressure in a fish without a swim bladder. The site of pressure sensitivity in the herring larvae has not been identified, but it seems to be related to the bulla because sensitivity is en- hanced when the bulla is full of gas. It is possible that abrupt changes of pressure applied to the top of a column of water might generate particle displacements in the water that could be per- ceived by neuromast organs. We do not believe this is a likely explanation of the observed pres- sure sensitivity in stage-I and stage-II larvae, however, because in some experiments the pres- sure change was applied over about 5 s, which reduced any resonant effects in the apparatus, but was equally successful in causing correct re- sponses. Because the swim bladder serves as a gas reser- voir for the bulla, the bulla cannot provide per- ception of absolute pressure for a juvenile or an adult herring. However, in the larva the develop- ment of the gas-filled bulla precedes that of the 5R. N. Gibson, Principal Scientific Officer, Dunstaffnage Marine Research Laboratory, P.O. Box No. 3, Oban, PA34 4AD, Argyll, Scotland, pers. commun. March 1979. swim bladder and therefore the bulla may tem- porarily serve as a depth indicator ( Blaxter et al. 1981), permitting a larva to limit the maximum depth reached during vertical movements ini- tiated by changes in light intensity. Having a mechanism to limit the maximum depth of verti- cal migration may enable a larva to maintain its position in the water column. This could be of adaptive value similar to that described for an- chovy by Hunter and Sanchez (1976), in that it may serve to keep larvae together and facilitate the development of schooling. A depth indicator might also serve as an energy-saving mechanism if it enables a larva to maintain its position in that portion of the water column where food is most abundant. In conclusion, we have found that herring lar- vae display pressure sensitivity both before and after the bulla system has developed, although it is enhanced in larvae with a gas-filled bulla. The threshold of sensitivity was not determined but lies below 13 cm H2O (1 cm Hg). For a herring larva near the sea surface this observation im- plies that pressure sensitivity is <1.3% of the ambient pressure. Prior treatment of larvae to 5 atm pressure did not significantly impair sensi- tivity. LITERATURE CITED Allen, J. M., J. H. S. Blaxter, and E. J. Denton. 1976. The functional anatomy and development of the swimbladder-inner ear-lateral line system in herring and sprat. J. Mar. Biol. Assoc. U.K. 56:471-486. BlSHAl, H. M. 1961. The effect of pressure on the survival and distribu- tion of larval and young fish. J. Cons. Cons. Int. Explor. Mer 26:292-311. Blaxter, J. H. S. 1968. Rearing herring larvae to metamorphosis and be- yond. J. Mar. Biol. Assoc. U.K. 48:17-28. Blaxter, J. H. S„ and E. J. Denton. 1976. Function of the swimbladder-inner ear-lateral line system of herring in the young stages. J. Mar. Biol. Assoc. U.K. 56:487-502. Blaxter, J. H. S., E. J. Denton, and J. A. B. Gray. 1981. The auditory bullae-swimbladder system in late stage herring larvae. J. Mar. Biol. Assoc. U.K. 61:315- 326. Blaxter, J. H. S., and D. E. Hoss. 1979. The effect of rapid changes of hydrostatic pressure on the Atlantic herring Clupea harengus L. II. The re- sponse of the auditory bulla system in larvae and juve- niles. J. Exp. Mar. Biol. Ecol. 41:87-100. Denton, E. J., and J. H. S. Blaxter. 1976. The mechanical relationships between the clupeid swimbladder, inner ear and lateral line. J. Mar. Biol. Assoc. U.K. 56:787-807. 573 FISHERY BULLETIN: VOL. 80, NO. 3 Hoss, D. E., AND J. H. S. Blaxter. vae of the northern anchovy, Engraulis mordax. Fish. 1979. The effect of rapid changes of hydrostatic pressure Bull., U.S. 74:847-855. on the Atlantic herring Clupea harengus L. I. Larval survival and behaviour. J. Exp. Mar. Biol. Ecol. 41: Qasim, S. Z., A. L. Rice, and E. W. Knight-Jones. 75-85. 1963. Sensitivity to pressure changes in teleosts lacking Hunter, J. R., and C. Sanchez. swim-bladders. J. Mar. Biol. Assoc. India 5:289- 1976. Diel changes in swim bladder inflation of the lar- 293. 574 FEEDING ECOLOGY OF SOME FISHES OF THE ANTARCTIC PENINSULA Robert A. Daniels2 ABSTRACT Feeding ecology of 19 species of Antarctic fishes is examined. All species are carnivorous; the most important prey are amphipods, polychaetes, and isopods. Seven of the species examined (Notothenia neglecta, N. gibberifrons, N. nudifrons, N. larseni, N. kempi, Trematomus seotti, and T. bernacehii) are feeding generalists with diets varying with size of fish, season, and locality of capture. Seven other species (Trematomus newnesi, Pleuragramma antarcticum, Cryothenia peninsulae, Artedidraco skottebergi, Harpagifer bispinis, Prionodraco evansii, and Parachaenichthys charcoti) are specialists, feeding predominantly upon prey either from a single taxon or from very few taxa. Five species {Notothenia rossii, Trematomus eulepidotus, Cryodraco antarcticus, Pagetopsis maeropterus, and Chaenocephalus aceratus) were not well represented in the samples, but a qualitative description of their diet is included. The fishes studied consume a wide variety of food types and use several feeding behaviors. Based on field and laboratory observations, most species are ambush predators. However some species use an indiscriminant slurp method, grazing, or a search and capture form of feeding. Some species switch feeding behaviors seasonally or with locality. Diet similarity is high only in morphologically similar species. Where a high degree of diet similarity occurs, overlap in distribution tends to be low. Although most species are high-level carnivores and at least some occur sympatrically, direct competition for food among the species does not appear to exist. This partitioning of food resources adds to the complexity of the structure of Antarctic communities. The position of these fishes in the Antarctic trophic structure should be further examined and considered before extensive exploitation is begun. Feeding ecology in Antarctic fishes has, until recently, attracted little attention. Richardson (1975) described the diets of four species of fish found along the Antarctic Peninsula and discussed diet overlap. In a thorough study, Targett (1981) examined the trophic structure of five demersal fish communities off Antarctic and sub-Antarctic islands. Permitin and Tarverdiyeva (1972, 1978) examined degree of diet similarity among 10 fishes from the sub- Antarctic island, South Georgia, and in noto- theniids and channichthyids collected from the South Orkney Islands, an archipelago north of the Antarctic Peninsula. Moreno and Osorio (1977) examined diet changes with depth in one species, and Wyanski and Targett (1981) reported on diets of nine harpagiferids. Others (Arnaud and Hureau 1966; Holloway 1969; Arnaud 1970; Hureau 1970; Everson 1970; Permitin 1970; Meier 1971; Yukov 1971; DeWitt and Hopkins 1977; Moreno and Zamorano 1980; Duarte and Moreno 1981) described one com- ponent of the diet of various fishes, the diet of one ■Science Service Journal Series No. 337, New York State Museum, Albany, N.Y. 2New York State Museum, Biological Survey, Cultural Education Center, Room 3132, Albany, NY 12230. Manuscript accepted December 1981. FISHERY BULLETIN: VOL. 80, NO. 3, 1982. species or qualitative descriptions of stomach contents. This study examines several aspects of feeding ecology of Antarctic fishes, including seasonal, spatial, and size-related changes. With increasing interest in the exploitation of Antarctic resources (Lyubimova et al. 1973), the need to understand the feeding ecology of these fishes and their position in Antarctic communi- ties has become important. STUDY AREA The Antarctic Peninsula reaches north from the continent to lat. 63°18'S, long. 55°02'W. Its west coast is flanked by numerous islands which create many bays, inlets, straits, and small coves. Weather conditions and longevity and distribu- tion of fast and brash ice vary along the penin- sula seasonally, yearly, and with area. Water temperatures at Palmer Station (lat. 64°46'S, long. 64°04'W) fluctuate approximately 2°C from 0°C; salinities range from 32.2%« to 33.5%o except immediate to shore and in surface waters during the spring thaw; dissolved oxygen remains near saturation at 6-10 cc/1; pH ranges from 7.9 to 8.5 (Krebs 1974; Showers et al. 1977). Primary productivity varies greatly along the peninsula (Krebs 1974) and in the Antarctic in 575 FISHERY BULLETIN: VOL. 80, NO. 3 general (El-Sayed 1968) through the year. The composition of the sea bed varies among mud, rubble, and bedrock. Mud bottoms, consisting of glacial flour and diatomaceous oozes, are most common and are found in most straits, bays, and large inlets. Rubble bottoms, composed of heter- ogeneous mixtures of gravel, cobbles, and boulders, are generally found in small, pro- tected, nearshore coves. Rock cliffs are common along coastal areas and on many submerged mounts. Each bottom type supports a distinctive fauna (Lowry 1969; DeLaca 1976; Kauffman 1977; Daniels and Lipps 1982). Approximately 40 species of fish are found off the Antarctic Peninsula (DeWitt 1971). Table 1 provides a brief description of the species included in this study. METHODS Fish used in this study were collected at 11 sites from Terra Firma Islands, Margurite Bay (lat. 68°42'S, long. 67°32'W) to Low Island (lat. 63°25'S, long. 62°10'W) using otter and Isaacs- Kidd trawls, long lines, barrel nets, mud grabs, and hand nets used by scuba divers between 27 January and 28 December 1975 (Fig. 1). Samples were taken at most sites in February or March; a second collection was taken in December at four sites. In areas adjacent to Palmer Station, fish were collected at monthly intervals from January to December. Fish were preserved immediately in 4% buffered formaldehyde solution; preservative was injected into the stomach cavities of larger specimens. Most species did not regurgitate stomach contents when placed in preservative. However, most channichthyids everted their stomachs when caught; therefore, these species are not included in the analysis and only a qualitative description of their diets is presented. A total of 1,609 stomachs of 19 species were examined. Each of the major Antarctic families is represented: 12 nototheniids, 2 harpagiferids, 2 bathydraconids, and 3 channichthyids. Speci- mens were later measured (standard length Table 1. — Distribution and morphometric data of fishes collected off the Antarctic Peninsula, 1975. Norman (1940) and DeWitt (1971). Information on ranges from Relative Adult Probable abundance Basic body size range Position Species Distribution habitat in samples shape (SL mm) of mouth Nototheniidae Notothenia neglecta circumpolar rubble-algae common bullheadlike 200-300 terminal Notothenia gibberifrons Antarctic Pen. South Georgia Scotia Ridge mud abundant bullheadlike 200-300 subterminal Notothenia nudifrons Antarctic Pen South Georgia Scotia Ridge rocky cliff, mud abundant fusiform 100-150 terminal Notothenia larseni Antarctic Pen. South Georgia Scotia Ridge column, bentho-pelagic abundant fusiform 100-150 terminal Notothenia rossii circumpolar rubble-algae rare bullheadlike 200-300 terminal Notothenia kempi Antarctic Pen. pelagic, bentho-pelagic rare fusiform 150-300 slightly supraterminal Trematomus scotti circumpolar pelagic, bentho-pelagic abundant fusiform 100-150 terminal Trematomus newnesi circumpolar pelagic, bentho-pelagic common fusiform 150-200 supraterminal Trematomus bernacchii circumpolar rubble-algae common builheadlike 150-250 terminal Trematomus eulepidotus circumpolar rubble-mud rare fusiform 150-250 supraterminal Pleuragramma antarcticum circumpolar pelagic common fusiform 100-150 supraterminal Cryothenia peninsulae Antarctic Pen pelagic rare fusiform 100-150 slightly supraterminal Harpagiferidae Artedidraco skottsbergi circumpolar mud rare bullheadlike 75-100 terminal Harpagiter bispinis Antarctic Pen. South Georgia Falkland Is. rubble-algae common bullheadlike 75-100 terminal Bathydraconidae Prionodraco evansii circumpolar mud rare wedgelike 100-125 terminal Parachaenichthys charcoti Antarctic Pen. Scotia Ridge rubble-algae rare wedgelike 200-250 terminal Channichthyidae Cryodraco antarcticus circumpolar pelagic rare wedgelike 100-150 terminal Pagetopsis macropterus circumpolar pelagic rare wedgelike 100-150 terminal Chaenocephalus aceratus Antarctic Pen. South Georgia Scotia Ridge mud rare wedgelike 200-300 terminal 576 DANIELS: FKKDING ECOLOGY OF ANTARCTIC FISHES g George I. Q„Joinville I. 0 100 200 km Figure 1.— Antarctic Peninsula showing sites where major collections of fish were made, 1975: Low Island (1), Dallmann Bay (2), The Sound, Melchior Islands (3), Port Lockroy (4), Arthur Harbor, site of Palmer Station (5), Peltier Channel (6), Paradise Harbor (7), Argentine Islands (8), Adelaide Island (9), Square Bay (10), and Terra Firma Islands (11). (SL)), weighed, and dissected. Stomachs were removed, opened, and all contents flushed onto petri dishes. Prey items were sorted, counted, and assigned a point volume (Hynes 1950). One point is approximately equivalent to an isopod Munna sp. with an approximate volume of 0.25 ml and approximate dimensions of 15 X 5 X 3 mm; one point was also approximately equivalent to 2 mg dry weight. To test the accuracy of the estimated volumes, the contents of 60 stomachs of Harpagifer bispinis were assigned a point volume, volume was measured by displacement, and the contents were dried and weighed. There was little difference between the three measure- ments (Friedman's Test, 0.29-23 individ- uals (x = 17). Where possible, at least 20 individ- uals were examined. When a sufficient number of specimens was collected, the sample was seg- regated by size of fish, season, or area of capture. These subsamples were then compared using a X test for association (Remington and Schork 1970). Fullness indices, measures of feeding in- tensity (Windell 1971), were calculated for each subsample, and significance was determined by Wilcoxon sum of ranks test (paired samples) or Kruskal-Wallis x2 test (3 or more samples) (Langley 1970). Mean prey size was calculated by dividing total volume per taxon by total num- ber of prey items consumed. Percentage diet similarity by number and volume was deter- mined using: S= 100(1 -% X\p„- pw\) where p„ and pyi are the proportions of the diets of species x and y respectively of prey item i (Lin- ton et al. 1981; Abrams 1980; Schoener 1970). Diet diversity was examined by the number of taxa found in the diet of each species (P) and diversity index H = — Sp,ln(p), where p, — the proportion of the ith species in the sample (Shan- non and Weaver 1949). RESULTS Feeding Behaviors Fishes were observed using variations of four basic behaviors: ambush feeding, bottom slurp- ing, water column feeding, and grazing. Ambush feeding was observed most frequently in the field. Harpagifer bispinis, Notothenia neglecta, Trematomus bernacchii usually, and N. gibber- ifrons, on occasion, perched among rocks or partially buried themselves in soft mud and waited for a prey organism to approach. As the prey neared, the fish lunged and then engulfed the item. Treatment of the prey after capture de- pended upon its relative size and morphology. If possible, the item was swallowed whole. Ex- ceptions to this were scaleworms. In the labora- tory, I observed H. bispinis capture a scaleworm on 16 occasions, pull it into its mouth, spit it out, immediately pull it into its mouth again, and re- peat the process several more times (x = 6, range = 2-16). This procedure successfully removed all scales from the worm before the fish actually consumed it. This process apparently occurred in the wild since scales are rarely found in H. bispinis stomachs although scaleworms are an important part of its diet (below). If the prey item was too large to engulf whole, it was eaten in parts. I observed N. neglecta capturing fish one- third to one-half as long as itself on five occasions in laboratory tanks. The predatory N. neglecta pulled the prey fish T. bernacchii or N. nudifrons into its mouth, usually head first, retreated to a protected area, and began to digest that part of the fish in its mouth and stomach. This process took up to 12 h during which time the predator was quiescent. Large prey items taken from the stomachs of N. neglecta commonly showed signs of differential digestion, which indicates that this method of feeding occurs in the wild. Fish using ambush feeding tended to be largely car- nivorous and preyed upon relatively large, motile organisms. Fishes were observed to take only moving organisms. On many occasions in the lab- oratory, H. bispinis ignored stationary amphi- pods close to its mouth and readily visible. When the amphipod moved, it was consumed. Often movement consisted only of a twitching antenna. The slurp feeding method was observed most frequently in N. gibberifrons which swam over mud bottoms, sucked up and sifted through large quantities of mud, and consumed the organisms encountered (Daniels and Lipps 1978). Mud and small rocks were also swallowed and passed through the gut. Fish using this method usually fed upon sedentary or slow-moving invertebrates and rarely consumed plant matter. Bacteria ad- herent to mud may also have been an important part of their diet. Water column feeding was characteristic of the pelagic P. antarcticum, juvenile T. newnesi, and, on occasion, demersal forms like N. neglecta. 578 DANIELS: FEEDING ECOLOGY OF ANTARCTIC FISHES Pleuragramma antarcticum was observed under fast ice in schools of several thousand individuals on three occasions. Individuals darted about and frequently approached the ice-water interface where they appeared to bite at and consume small amphipods {Nototropis sp.). Individual juvenile T. neumesi also entered the water col- umn under an ice cover or during other periods of low light intensity. These fish generally were found in shallow-water brown algae, Desmeristia anceps, beds except when ice was present and light conditions were favorable. They then left the beds individually and occupied the water column where they fed on the undersurface of the ice, or the substrate or in the column. On one occasion, one large N. neglecta (400 mm SL) en- tered the water column and ate several P. antarc- ticum from a school before returning to a rock outcropping. Fishes using this feeding method usually fed upon motile invertebrates, such as eupausiids, pteropods, and amphipods, or other fishes often associated with the pelagic or cryopelagic communities. Grazing, although never observed, appeared to be an important feeding method in some spe- cies, most notably TV. neglecta, during spring and summer. Individuals were collected with large sheets of macroalgae (e.g., Phyllogigas grandi- folius, Iridaea obovata, or Desmeristia spp.), solitary, epiphytic diatoms (Trigonium acticum, Cocconeis imperatrix, Amphora sp., Grammato- phora sp., Licmophora sp., and Achnanthes sp.), and epibenthic diatoms (Biddulphia anthropo- morpha, Melosira sol, Amphora sp., Grammato- phora sp., Licmophora sp., Achnanthes sp., and Isthmia sp.) in their stomachs. It was inferred from stomach contents that fishes commonly switched from one feeding method and/or foraging area to another with season. Notothenia neglecta ambushed prey from rock outcroppings and algae beds through much of the year. During the spring and summer plankton blooms, however, some individuals be- gan to search for food on homogeneous mud bot- toms away from any protective rock crannies, as evidenced by large numbers of mud-bottom iso- pod Serolis polita in some stomachs in Decem- ber. During spring and summer, individual N. neglecta cropped macroalgae and harvested diatom mats from mud and gravel bottoms. Noto- thenia gibberifrons used the slurp feeding meth- od to forage in more northern areas but am- bushed its prey in southern areas (Daniels and Lipps 1978). Diets Diets varied among the 14 species examined so that fishes could be ranked from specialized feeders to feeding generalists (Tables 2, '.I, 4). Seven species were generalists (high P and H) and seven species were specialists (low Pand //). Generalists consumed a variety of organisms which were phylogeneticly and morphologically distinct. Specialists preyed upon organisms with similar morphologies or in the same prey taxon. There appeared to be two types of specialists: in one group, Cryothenia peninsulae, Harpagifer bispinis, Artedidraco skottsbergi, and Parachaen- ichthys charcoti, the diet consisted largely of organisms from one prey taxon; while in the second, Trematomus newnesi, Pleuragramma antarcticum, and Prionodraco evansii, relatively few prey taxa were consumed in approximately equal numbers. Although quantitative data on food availability were not collected, generalists also appeared to be feeding opportunists that ate the most abundant available prey. Individuals in the generalist species also tended to be general- ists. Individual N. neglecta commonly consumed prey from 5 to 10 taxa (87% of sample) and most of the available prey in the algae beds of Arthur Harbor (Lowry 1969) were found in stomachs of N. neglecta. Specialists tended to be more selec- tive. In the rubble bottom community where H. bispinis was collected, gastropods, small echino- derms, and errant polychaetes were abundant, yet, except for the scaleworms, which became seasonally important, were rarely found in H. bispinis stomachs. Individuals in the specialist species also tended to be specialists; 91% of the H. bispinis examined had consumed prey from one or two taxa. Amphipods were the prey item most fequently taken by fish (Tables 2, 3, 4). However, they were the most important component by volume in only H. bispinis and A. skottsbergi. Polychaetes were also frequently consumed and were an important part of the diet of N. nudifrons, N. larseni, T. scotti, and A. skottsbergi by both number and volume. Isopods, gastropods, and pelecypodsalso occurred consistently, but were relatively minor components in most diets. Other taxa were im- portant dietary items for only particular species or at particular times of year. Euphausiids, Euphausia superba and E. chrystallorophias, dominated the diets of N. larseni, T. scotti, T. neumesi, T. bernacchii, Pleuragramma antarc- ticum, and C. peninsulae by number and volume. 579 FISHERY BULLETIN: VOL. 80, NO. 3 Table 2.— Diets by percentage frequency of occurrence, number, and point volume and diet diversity by number of taxa consumed (P) and diversity index (H) of fishes of the genus Notothenia collected off Antarctic Peninsula, 1975. See text for explanation of terms. N. neglecta N. g, •bberifrons N. nudilrons N. larseni N. kempi Freq Freq Freq. Freq Freq. (%) No Vol. (%) No. Vol <%) No Vol. (%) No Vol (%) No Vol. Number examined 173 339 164 278 18 Foraminifera <1 <1 <1 28 4 <1 <1 <1 <1 4 2 <1 6 2 1 Ponfera <1 <1 <1 4 <1 <1 Coelenterata <1 <1 <1 <1 <1 <1 <1 <1 <1 Ctenophora 2 <1 <1 <1 <1 <1 Nemertea 10 <1 6 4 <1 1 <1 <1 <1 <1 <1 1 Nematoda 7 1 <1 3 1 <1 Bryozoa 1 <1 <1 <1 <1 <1 Brachiopoda <1 <1 <1 Oligochaeta <1 <1 <1 Polychaeta, sedentary 65 21 27 errant 21 <1 2 21 2 9 43 22 45 18 10 12 44 19 31 Mollusca Gastropoda 75 10 4 15 2 1 12 4 3 1 <1 <1 11 7 4 Pelecypoda 6 <1 <1 38 8 6 1 <1 <1 <1 <1 <1 Scaphopoda 3 <1 <1 Cephalopoda 1 <1 <1 <1 <1 <1 <1 <1 <1 Arthropoda Crustacea Amphipoda 94 84 21 54 51 19 66 56 31 39 36 12 22 25 17 Isopoda 15 1 7 7 1 3 23 8 7 5 3 1 28 25 20 Cumacea 9 2 1 1 <1 <1 3 3 <1 17 7 8 Euphausiacea 6 <1 4 6 <1 5 2 <1 1 30 27 54 11 4 9 Ostracoda 3 <1 <1 7 <1 <1 7 2 <1 <1 <1 <1 Copepoda 15 1 <1 3 <1 <1 1 <1 <1 17 9 4 Pycnogonida 1 <1 <1 2 <1 5 7 2 4 <1 <1 <1 Echmodermata Asteroidea <1 <1 <1 Echinoidea <1 <1 <1 <1 <1 <1 <1 <1 <1 Holothunoidea 3 <1 <1 1 <1 1 Crinoidea 1 <1 <1 4 1 5 <1 <1 <1 Ophiuroidea 9 2 8 <1 <1 <1 1 <1 <1 Chordata Tunicata <1 <1 <1 2 <1 1 1 <1 <1 3 <1 <1 6 2 1 Pisces 13 <1 28 <1 <1 3 1 2 2 Egg mass 3 1 1 2 3 7 Macroalgae 80 21 12 2 3 <1 3 1 Diatoms 12 3 Miscellaneous <1 3 <1 2 5 Taxa (P) 24 28 18 22 9 Diversity (H) 1 99 2.31 1.53 1.61 1.88 Fish are a major part of the diet of N. neglecta and Paracfiaenichthys charcoti by volume but were unimportant by number. Changes with Locality In N. gibberifrons, N. larseni, T. scotti, and H. bispinis, the diets of individuals of a similar size group caught at the same time of year but in dif- ferent localities showed significant differences in the prey taken (Fig. 2) and in the amount of food consumed (Table 5). In each species, approx- imately the same number of prey taxa were con- sumed, but only in H. bispinis were the taxa identical. The other species consumed not only different amounts from each taxa, but also dif- ferent types of prey. This change in diet is most dramatic in N. gibberifrons (Fig. 2). Individuals from the more northerly Peltier Channel tended to consume sedentary invertebrates such as sedentary annelids, clams, and cumaceans which are often found buried up to several centimeters in the mud. Individuals from the samples of the southern Terra Firma Islands tended to con- sume motile, rubble-bottom organisms, such as errant polychaetes, amphipods, and fish. Ontogenetic Changes Sample sizes were large enough in six species to compare differences in diet with fish size. Within each species, individuals collected from the same locality at the same time but of differ- ent size tended to consume prey from the same taxa, but the relative importance of each taxon by volume varied significantly (x2, P<0.02)(Figs. 3, 4). In all species mean prey size, mean number of prey items consumed, and number of different prey types consumed increased with fish size. Diet diversity showed no size-related change in any species except in T. bernacchii (Table 6). 580 DANIELS: FEEDING ECOLOGY OF ANTARCTIC FISHES Table 3.— Diets by percentage frequency of occurrence, number, and point volume and diet diversity by number of taxa consumed (P) and diversity index (//) of fishes of the genera Trematomus, Pleuragramma, and ( 'ryothemia collected off Antarctic Peninsula, 1975. See text for explanation of terms. T. scotti T newnesi T. bernacchii P. antarcticum C. penmsulae Freq. Freq Freq. Freq Freq. (%) No Vol (%) No. Vol (%) No Vol (%) No. Vol (%) No. Vol. Number examined 146 37 76 17 18 Foramlnifera 3 13 2 Coelenterata <1 <1 <1 Nemertea 5 2 2 12 <1 23 Nematoda 2 <1 <1 Brachiopoda <1 <1 1 Polychaeta, sedentary 23 29 16 4 <1 4 17 6 4 errant 36 14 18 11 6 6 22 2 10 3 2 2 6 1 ■ 1 Mollusca Gastropoda 4 2 1 6 3 1 12 1 4 Pelecypoda 8 3 <1 3 <1 <1 Arthropoda Crustacea Amphipoda 29 19 6 47 33 23 72 89 26 7 5 2 6 1 <1 Isopoda 4 3 <1 6 3 1 18 3 12 Cumacea 7 5 <1 33 53 10 Euphausiacea 35 13 48 35 53 68 8 4 2 40 24 69 100 92 95 Ostracoda <1 <1 <1 1 <1 <1 Copepoda 1 <1 <1 Pycnogonlda 3 1 1 1 <1 <1 Echinodermata Holothurloidea <1 <1 <1 Cnnoidea <1 <1 <1 Ophiuroidea 4 2 1 Chordata Tunicata 1 <1 <1 1 <1 3 Pisces 1 <1 <1 7 3 3 Egg mass <1 1 <1 Macroalgae 2 1 16 3 Miscellaneous 2 12 Taxa (P) 20 5 14 6 4 Diversity (H) 1.60 0.84 1.97 079 0.33 Table 4.— Diets by percentage frequency of occurrence, number, and point volume and diet diversity by number of taxa consumed (P) and diversity index (H) of harpagiferids and bathydraconids collected off the Antarctic Peninsula, 1975. See text for explanation of terms. Artedidraco Parachaenichthys sc :ottsbergi Harpagiler bispinis Freq Prionodraco evansii Freq. Charcot! Freq Freq (%) No. Vol. (%) No. Vol. (%) No Vol. (%) No Vol Number examined 17 237 21 12 Foraminifera 6 3 <1 Polychaeta, errant 47 25 47 27 4 16 28 7 19 Mollusca Gastropoda 4 <1 <1 Pelecypoda 1 <1 <1 Arthropoda Crustacea Amphipoda 59 61 46 88 88 79 24 19 29 38 72 8 Isopoda 12 10 5 24 5 4 Cumacea 38 65 31 Euphausiacea 19 8 21 50 22 15 Ostracoda 2 <1 <1 Pisces 25 6 76 Egg mass 6 1 <1 Macroalgae 8 <1 13 1 Taxa (P) 4 8 4 4 Diversity (H) 088 0.68 1.53 072 Seasonal Changes Changes in diet in N. neglecta and H. bispinis were monitored at monthly intervals in Arthur Harbor through the year. Notothenia neglecta showed a significant seasonal diet change (x2 = 727, df = 104, P<0.01); these fishes switched from being omnivores in the austral spring and summer to a carnivorous diet through autumn and winter. Notothenia neglecta also consumed a large variety of organisms, including individuals from several different microhabitats such as isopod Serolis polita and nemertean worm Lineas corrugatus from mud bottom areas, 581 FISHERY BULLETIN: VOL. 80. NO. 3 Notothenia gibberifrons Terra Firma Island n=20 Peltier Channel n=30 Brabant Island n=24 Notothenia larseni Argentine Island n=30 Brabant Island n=29 Low Island n=27 Trematomus scotti KEY SP - Sedentary polychaete EP - Errant polychaete Am - Amphipod P - Pycnogonid O - Ophiuroid K - Krill I - Isopod * - Other Terra Firma Island n=24 Square Bay n=26 Argentine Island n=33 Harpagifer bispinis Argentine Island n^20 Port Lockroy n=23 Paradise Harbor n-25 Arthur Harbor n-25 Figure 2.— Changes in feeding associated with locality of capture in four notothenioid fishes. Fishes used in comparisons are similar in size and were taken during the same season. 582 DANIELS: FEEDING ECOLOGY OF ANTARCTIC FISHES Table 5.— Changes in diet by locality of capture in fishes of similar size and taken during the same sea- son off the Antarctic Peninsula, 1975. Ax2 test for association was used to examine changes in the volume of each taxon consumed; a Kruskal-Willas x2 test was used to examine changes in feeding inten- sity (fullness index). Area n SL (mm) Range (mm) No. taxa consumed Vol ume Fullness i ndex Species x2 P X x3 P Nolothema Peltier Chan 30 146 106-217 13 68 gibberifrons Terra Firma Is 20 123 100-146 13 8? Brabant 1. 24 134 87-260 12 393 1 <0.01 7.5 85 <0.05 N. larseni Brabant 1. 29 120 70-150 4 8.1 Low 1. 27 114 84-152 8 6.6 Argentine Is 30 113 72-162 10 2246 -0 01 24 20.2 <0.01 Trematomus Terra Firma Is. 24 69 45-90 7 70 SCOttl Square Bay 26 98 61-137 9 49 Argentine Is. 33 99 63-126 15 1049 <0.01 6.9 15.8 -"001 Harpagifer Argentine Is. 20 71 58-80 6 44 bispims Port Lockroy 23 67 43-82 5 84 Paradise Harbor 25 68 57-88 5 55 Arthur Harbor 25 70 51-85 5 42.1 <0.01 8.2 14 1 <001 Table 6.— Size-related changes in diet in Antarctic fishes, Antarctic Peninsula, 1975. Fish in each species were collected at the same time from the same locality. Size SL Mean no. Mean prey size No. taxa X range Species Capture group n (mm) (mm) items/stomach (vol. /item) consumed Mean H Notothema Arthur Harbor 1 10 80 71-90 138 09 7 0.5 neglecta December 1 8 199 165-231 82 0 45 8 0.8 1 1 9 292 258-313 370 12.8 12 0.6 Notothema Peltier Chan 1 14 80 49-99 58 0.6 10 08 gibberifrons February 1 I 20 129 116-148 80 1.2 13 08 II I 20 193 163-217 109 18 15 09 Notothema Dalmann Bay I 28 50 32-65 4.7 02 10 0.7 nudifrons December 1 I 16 116 93-153 4.3 07 11 07 Notothema Low 1. I 16 94 82-105 27 1.8 4 0.3 larseni March 1 I 19 139 113-157 24 3.7 7 05 Trematomus Argentine Is. I 18 84 63-99 30 1.6 11 0.5 SCOttl March 1 I 17 121 108-144 27 3.3 13 0.8 Trematomus Arthur Harbor I 13 69 60-78 15.0 0.5 4 0 1 bernacchii June 1 I 14 138 107-160 31.4 2.7 8 03 II I 14 200 180-233 10.1 8.1 10 0.7 krill and Pleuragramma antarcticum from the pelagic and cryopelagic communities, limpet Patinigera polaris from rocky cliffs, and a large number of organisms from rubble-bottom areas, the habitat from which this species was most fre- quently collected. Harpagifer bis pin is consumed prey from the same taxa through the sampling period, but the importance of each taxon differed (x2 = 149, df = 21, P<0.01). The significance re- sults from a midwinter peak in abundance of scaleworms. This species consumed organisms from the rubble-bottom community which con- sisted largely of the amphipods Bovallia gigantea, Eurymera monticulosa, the scaleworm Har- mothoe spinosa, and the isopods, Munna sp. and Cymodocea antarctica. Differences in diet of similar-sized individuals of Notothenia gibberifrons, N. nudifrons, N. larseni, and T. scotti collected at the same locality at different times of year were signifi- cant in the relative importance of each prey taxon, but tended to show no significance in the amount of food consumed (Table 7). In all four species individuals tended to consume prey from the same number of taxa. Spring samples tended to contain individuals of a smaller size than late summer samples. Dietary Similarity Diets were >60% similar in 17 species pairs by number and in 11 species pairs by volume (Table 8). Similarity in diet by number of prey items consumed is greater due to the large number of amphipods taken by most fishes. A high percentage similarity by volume, a value more indicative of the importance of each food type, was obtained for morphologically similar species such as the two harpagiferids, A. scottsbergi 'and Harpagifer bispinis, and the pelagic-benthope- lagic complex of N. larseni, T. scotti, T. newnesi, Pleuragramma antarcticum, and Cryothenia peninsulae. Species that were generalists showed 30-60% similarity in diet with other 583 Notothenia neglecta FISHERY BULLETIN: VOL. 80. NO. 3 71-90mm n-10 165-23 1mm n-8 258-3 13mm n=9 Notothenia gibberifrons 49-99mm n=l4 11 6- 148mm n=20 l63-217mm n=20 Notothenia nudifrons KEY SP - Sedentary polychaete EP - Errant polychaete Am - Amphipod G - Gastropod L - Lamellibranch P - Pycnogonid C - Cumacea F- Fish Al - Algae I - Isopod E - Echinoid * - Other 32-65mm n=28 93-153mm n=l6 Figure 3.— Size-associated changes in feeding in three Notothenia spp. collected at the same locality on the same day. generalists and <30% similarity with the more specialized feeders. Generalists were often collected at sites with other generalists and spe- cialists. The tendency among specialized feeders was one of low percentage similarity in both diet and distribution. Other Species Four N. rossii, morphologically similar to N. neglecta, consumed prey from six taxa. Amphi- pods were most important by number (81%); krill (31%) and demersal fish (51%) were important by volume. Krill was the most important component by number and volume in the diets of five T. eulepidotus, seven Pagetopsis macro pterus, and eight Cryodraco antarcticus. These species con- sumed prey from relatively few taxa and were exclusively carnivorous. Trematomus eulepidotus, morphologically similar to T. scotti, in addition to the pelagic krill, also consumed cumaceans which are typically associated with mud bottoms. The channichthyids, P. macropterus and C. antarcticus also consumed fish, such as 584 DANIELS: FEEDING ECOLOGY OF ANTARCTIC FISHES Notothenia larseni 82-105mm n=l6 Trematomus scotti 113-157mm n=19 KEY SP - Sedentary polychaete EP - Errant polychaete Am - Amphipod P - Pycnogonid L - Lamellibranch O - Ophiuroid T - Tunicate K - Krill I - Isopod * - Other 63-99mm n=18 108-144mm n=17 Trematomus bernacchii 60-78mm n=13 107-160mm n=14 180-233mm n=14 Figure 4.— Size-associated changes in feeding in three nototheniids collected at the same locality on the same day. the pelagic Pleuragramma antarcticum and the demersal N. nudifrons. In one Pagetopsis mac- ropterus collected in Margurite Bay, both species of krill found in the area were present. The stomachs of 42 Chaenocephalus aceratus were examined and found to be empty. DISCUSSION Antarctic fishes show great variety in the type of prey consumed and the behavior used to cap- ture prey. Yet all occupy a similar position in the community, that of a high-level carnivore. Of the 19 species included in this study, all consumed actively moving prey frequently and, with the exception of N. gibberifrons, active prey dom- inated diets. Although the diets of the prey are poorly known, at least some, like Bovallia gigantea, Harmothoe spinosa, and Sterechinus neumayeri, are themselves high-level carnivores (Bone 1972; Brand 1976). In this study the nototheniids show the great- est diversity in both diets and feeding behaviors although a high degree of similarity in diet 585 FISHERY BULLETIN: VOL. 80, NO. 3 Table 7.— Seasonal dietary changes in fishes of sim ilar size collected at the same locale off the Antarctic Peninsula. 1975. A \* test for association was used to examine changes in the volume of each taxon con- sumed. A Wilcoxon sum of ranks test was used to examine changes in feeding intensity. SL Range (mm) No. taxa Vol' jme Fi illness index Species Area Date n (mm) consumed x2 P X R P Notothenia Peltier Chan. Summer 30 146 106-217 13 68 gibberifrons Spring 49 138 100-229 13 31 3 <0.01 6.0 1,301 <0.30 Brabant 1. Summer 25 134 87-260 12 7.5 Spring 22 123 106-167 9 1146 <0.01 2.1 294 <0.01 Notothenia Low 1 Summer 20 107 72-140 8 5.6 nudifrons Spring 34 95 47-127 5 80.9 <001 5.8 500 <0.74 Notothenia Low 1. Summer 27 114 84-152 8 66 larseni Spring 25 99 90-142 9 66.7 <0.01 95 544 <0.08 Brabant 1. Summer 29 120 70-150 4 8.1 Spring 30 86 60-126 5 279 <0.01 22 735 <0.04 Trematomus The Sound Summer 8 112 88-134 5 64 scotti Spring 7 101 85-114 5 109.4 <0.01 3.4 47 <0.20 Table 8.— Percentage diet similarity by number of prey items consumed (upper triangle) and point volume (lower triangle) in fishes taken off the Antarctic Peninsula, 1975. co c CO CO to ^ M fc o CO £ a r^ 5) o CO ■c 2 o _ 1 * C ttl 2 o c o-S o * Q> CO o> c o) .o Q3 CO ^Q- t w co-Q - 0> m ° 2 2 2 2 2 K- l~ i~ Q. O •cj: I CL a N neglecta 58 63 46 33 26 37 89 5 8 61 86 18 71 N. gibberifrons 39 — 61 52 34 51 39 56 13 14 57 55 24 51 N. nudifrons 36 42 — 58 58 44 46 64 10 3 87 66 27 54 N. larseni 28 40 31 — 52 49 67 43 38 29 41 44 37 60 N. kempt 34 40 61 39 — 48 41 32 20 6 56 35 37 29 T. scotti 19 42 30 70 38 — 45 32 27 23 36 27 20 32 T newnesi 28 31 32 72 34 62 — 43 32 56 42 41 33 55 T. bernacchii 52 37 50 27 42 34 39 — 10 5 66 93 25 77 P. antarcticum 16 11 6 61 22 61 79 18 — 26 10 7 67 30 C. peninsulae 3 11 3 55 10 53 70 12 76 — 2 2 10 23 A skottsbergi 28 31 67 25 53 25 30 41 5 2 — 70 27 61 H bispinis 27 33 52 26 38 23 30 41 4 2 66 — 24 72 P evensii 25 34 49 46 53 46 50 38 35 23 49 44 — 28 P charcoti 39 16 9 25 17 21 23 12 20 16 9 8 23 — among similar species is often present. Results from other studies, using fewer species, are similar (Permitin and Tarverdiyeva 1972, 1978; DeWitt and Hopkins 1977; Richardson 1975; Moreno and Osorio 1977; Moreno and Zamorano 1980). This high diversity is attributable to diet changes with size of fish, capture locality, and season. The harpagiferids, bathydraconids, and chan- nichthyids tend to be more specialized than the nototheniids in both their choice of prey and in the method used to obtain it. Results for Har- pagifer bispinis can be compared to those of Meier (1971), Richardson (1975), and Wyanski and Targett (1981). In all cases, H. bispinis was shown to consume amphipods overwhelmingly. Artedidraco skottsbergi consumed polychaetes and amphipods; similar results were reported by Wyanski and Targett (1981). No comparable data are available for the bathydraconids or the channichthyids examined in this study. How- ever, the diets of the five channichthyids exam- ined by Permitin and Tarverdiyeva (1972, 1978) show them to be specialized feeders and, with the exception of C. aceratus, planktivorous; my re- marks regarding the diets of P. macropterus and Cryodraco antarcticus corroborate these find- ings. The high degree of dietary similarity that I ob- served among certain fishes and the similarity of diets reported by Permitin and Tarverdiyeva (1972, 1978), and Richardson (1975) do not necessarily imply interspecific competition over food, but do suggest a complex trophic structure not normally associated with communities of high latitudes (Cushing 1975). The benthic fishes studied use a wide variety of mechanisms to assure a constant food supply. For the general- ists, these include switching prey types and feeding strategies; the specialists consume prey types which are themselves capable of maintain- ing stable populations either by switching food by becoming inactive (Dearborn 1967) or by possessing a reproductive biology which in- 586 DANIELS: FEEDING ECOLOGY OF ANTARCTIC FISHES eludes high fecundity and long mean generations (Cushing 1975). These stabilization mechanisms provide a constant source of food despite dis- balanced primary production. With this con- stant and relatively abundant food source, com- petition, which requires a limiting resource (Larkin 1963), does not appear to be common among Antarctic fishes. The fact that high diet similarity is observed argues against competi- tion over a limited food resource as a major factor structuring Antarctic fish associations (Zaret and Rand 1971; Tyler 1972). Where competition may be important, e.g., in the pelagic-bentho- pelagic fish association, the major prey item is krill, which is abundant. However, this abun- dance may be temporary and of recent origin. This would obscure the importance of competi- tion in structuring Antarctic associations and points to the need for further study. The position of fishes in the trophic structure of Antarctic communities is also not well under- stood. All are carnivorous and many are second or third level carnivores. Whether or not these fishes are themselves consumed in large num- bers by the abundant birds and mammals of the Antarctic is poorly known. Some birds consume small species or juveniles of large species (Wat- son 1975) and several species of seals are re- ported to consume fish (Dearborn 1965; Stone- house 1972). However, the species consumed and the relative importance of fish in the diets of these predators remain unknown. It does appear that such predators do not have much of an impact on the large benthic fish populations, since the fishes are extremely slow growing and long lived (Emerson 1970). Thus the impact of heavy and unaccustomed predation (fishing) on this system could be very disruptive. Before ex- tensive exploitation begins, the life history of the organisms to be harvested should be understood. ACKNOWLEDGMENTS I thank P. B. Moyle, J. H. Lipps, and T. E. DeLaca for assistance given during the study and the preparation of the manuscript. I also thank D. Laine, W. 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Daniels, and D. Laine. 1977. Marine biology at Palmer Station, 1975 austral winter. Antarct. J. U.S. 12:22-25. Stonehouse, B. 1972. Animals of the Antarctic: the ecology of the far south. Holt, Rinehart & Winston, N.Y., 171 p. Targett, T. E. 1981. Trophic ecology and structure of coastal Antarctic fish communities. Mar. Ecol. Prog. Ser. 4:243-263. Tyler, A. V. 1972. Food resource division among northern, marine, demersal fishes. J. Fish. Res. Board Can. 29:997- 1003. Watson, G. E. 1975. Birds of the Antarctic and sub-Antarctic. Am. Geophys. Union Antarct. Res. Ser., 350 p. WlNDELL, J. T. 1971. Food analysis and rate of digestion. In W. E. Ricker (editor), Methods for assessment of fish produc- tion in fresh waters, 2d ed., p. 215-226. IBP (Int. Biol. Programme) Handb. 3. Wyanski, D. S., and T. E. Targett. 1981. Feeding biology of fishes in the endemic Antarctic family Harpagiferidae. Copeia 1981:686-693. Yukov, V. L. 1971. The range of Dissostichus mawsoni Norman and some features of its biology. J. Ichthyol. 11:8-18. Zaret, T. M., and A. S. Rand. 1971. Competition in tropical stream fishes: support for the competitive exclusion principle. Ecology 52:336- 342. 588 THE EARLY LIFE HISTORY OF THE PACIFIC HAKE, MERLUCCIUS PRODUCTUS Kevin M. Bailey1 ABSTRACT The early life history of Pacific hake. Merluccius product us, is described from laboratory and field studies. At ambient temperatures (11°-13°C) egg hatching takes about 100-120 hours; complete absorption of the yolk takes about 150-200 hours. Respiration rates for first feeding larvae at 12°C are 4.8-6.8 jul/mg per hour. Growth rates for at least the first 20 days are slow compared with other larvae in the California Current. First-feeding hake larvae require a daily ingestion of about 0.13 calories. In this study I present information on the early life history of Pacific hake, Merluccius produc- tus, including rates of development, starvation, growth, and metabolism. I have also used sam- ples from Ahlstrom (1959) and others to examine the vertical distribution of eggs and larvae by size class. My objectives in examining these life history processes are to 1) evaluate the hypothe- sis that the availability of food directly after com- plete yolk-sac absorption is the critical factor in survival of larval Pacific hake and 2) to deter- mine the relative length of time Pacific hake are in egg and yolk-sac stages and are most vulner- able to invertebrate predators. The early life history of Pacific hake repre- sents an interesting contrast to other fishes that spawn off the coast of California, including the northern anchovy, Engraulis mordax, and the Pacific mackerel, Scomber japonicus. Compared with these other species the early life history of Pacific hake has been little studied. It is known that hake larvae live below the mixed layer in colder water, and that first-feeding larvae have large mouths, so they can feed on a wide spec- trum of food particles (Ciechomski and Weiss 1974; Sumida and Moser 1980). Both the anchovy and mackerel have been subject to intensive in- vestigation as models of the causes of egg and larval mortality. Eggs and larvae of both anchovy and mackerel are found within the warm upper mixed layer (Ahlstrom 1959). Compared with hake larvae, anchovy and mackerel have rela- tively small mouths at first feeding; thus, the size 'College of Fisheries, University of Washington, Seattle. WA 98195. of ingested food particles is restricted (Hunter 1980). At least for first-feeding anchovy larvae, it has been shown that the availability of food of the proper size and in adequate densities is impor- tant to survival (Lasker 1975). The results of the present study, in particular the determination of the food requirements of hake larvae may indi- cate important differences in the survival strate- gies of these three fishes. METHODS Development and Growth All laboratory experiments in this study were conducted using eggs collected at Port Susan, Wash. This stock is reproductively isolated from the Pacific hake spawning off the California coast (Utter 1969), but I am assuming that tem- perature-specific rates of metabolism of larvae hatching from Port Susan eggs are similar to the rates for larvae hatching from eggs spawned in the California Current because 1) egg size is the same, 2) temperature-dependent hatching times are the same (see results this study), and 3) growth to age 2 is the same (Kimura and Milli- kan 1977). Eggs were collected with a 500 /urn mesh meter net (equipped with a cod end designed to capture live zooplankton) and returned to the laboratory at 5°-10°C. Eggs and larvae were reared in fil- tered seawater in 1-4 1 jars containing 50 ppm each penicillin G potassium and streptomycin sulfate. Egg hatching experiments were done with 3 replicates of 10-20 eggs/1. Percent hatch- ing was checked every 12 h. The eggs used in these experiments were without visible embryos Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80. NO. 3, 1982. 589 FISHERY BULLETIN: VOL. 80, NO. 3 and were assumed to be about 12 h old. The time to 50% hatching was determined by interpolation from the linear regression of percent hatching (y) against time (x). Confidence intervals on the 50% hatch time were calculated from the predic- tion of x from y as: C.L. = x + byAyi - y) D + H, where D — byx — t (o.o5,n-2> Sb , and H t (0.05, n -2) ~D~ n x2 Time to 50% yolk-sac absorption was determined similarly. Survival of yolk-sac larvae appeared to increase substantially under lighting in the cold rooms, which raised temperatures in these experiments to 10.5°C in the 8°C room and to 13.7°C in the 12°C room. The 15°C room was con- sistently lighted. After hatching at temperature, postyolk-sac larvae were removed, placed in new jars, and observed to determine time to starva- tion. Growth was examined by counting daily incre- ments on otoliths. For verification of otolith in- crements as daily marks, larvae were reared in the laboratory without antibiotics in a 12-h light- dark cycle. Larvae were fed Artemia salina nauplii and natural zooplankton strained through a 216 ^im mesh net at a concentration of about 1 animal/ml. Field-caught specimens were obtained from several cruises off the Cali- fornia coast in 1977, 1978, and 1979. Both labora- tory-reared and field-caught specimens were preserved in 80% ethanol. Larvae were measured (standard length) and otoliths were removed under a dissecting microscope fitted with a po- larizing filter. Otoliths were mounted on a glass slide in protex or euparal, and rings on the oto- liths were counted at 600-1000X magnifica- tion. Larval dry weights (preserved in 80% ethanol for otolith investigations and in 3% Formalin2 for respiration investigations) were determined on a Cahn 25 Electrobalance after rinsing the larvae in distilled water and subsequently drying them for 24 h at 60°C. Weight loss due to preservation was determined by comparing weights of sub- 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. samples of fresh-frozen larvae and preserved larvae, all hatching from the same cohort of eggs. Shrinkage in length was determined by measur- ing anaesthetized larvae before preservation and then again after 2-3 wk of preservation in 80% ethanol or 3% Formalin. Shrinkage due to preser- vation delay and death in a wet cod end during or after a plankton tow was simulated by anaesthe- tizing and measuring larvae, and then placing them on seawater-wetted paper towels for spe- cific time periods. Larvae were then preserved in Formalin. These preservation effects were tested only on first-feeding larvae. Growth, egg development, and yolk-sac ab- sorption data were fitted with a Gompertz curve using a least-squares nonlinear curve fitting pro- gram (SPSS). The Gompertz growth function was selected because it is a flexible nonlinear function commonly used in studies of larval fish (Zweifel and Lasker 1976). Metabolic Rates Respiration rates of larvae were measured using a micro-Winkler technique (Carritt and Carpenter 1966). Experiments were conducted in 30 ml glass stoppered jars, at densities of 2-3 larvae/jar, in dim light for 11-14 h. Larvae in fil- tered seawater were acclimated to temperatures for 12 h. After the experiments were completed and oxygen fixed, jars were kept for 2-10 d at 8°C in the dark before titrating. Experiments were designed to include 3-5 replicates per tem- perature; however, when bubbles formed during the experiment (a constant problem at 15°) sam- ples were discarded. Vertical Distribution Samples from vertical series of tows taken in 1954 and 1955 were reported by Ahlstrom (1959). I sorted and measured these samples to examine size-related vertical distribution. Pacif- ic hake larvae from an additional three vertical series taken in 1969 were sorted and measured. Since there were no apparent day-night differ- ences, all hauls, day and night, were combined. Nonstandardized data consisting of raw num- bers per haul, uncorrected for volume of water filtered, were used since more detailed informa- tion did not exist for many hauls. Data on num- bers of larvae caught per haul were classified into the depth interval where most of the tow took place. 590 BAILEY: EARLY LIFE HISTORY OF PACIFIC HAKE RESULTS Development Times Egg hatching time shows a marked response to temperature (Fig. 1 ). Time for 50% hatching of eggs collected at Port Susan ranges from 3.5 d at 15°C to 4.5 d at 12°C (coastal temperature range at 50 m depth is 11°-14°C) and 6.5 d at8°C (the approximate temperature at Port Susan). Also shown in Figure 1 are the mean hatching times of eggs collected off California that were report- ed by Zweifel and Lasker (1976). The time from hatching to complete absorp- tion of the yolk sac is also temperature dependent (Fig. 2). The time for 50% of the sample larvae to completely utilize their yolks is 9.7 d at 10°C, 6.4 d at 12°C, and 4.2 d at 15°C. I was notable to rear 160.0 60.0 8-0 9.0 10-0 11.0 12-0 TEnPERATURElt) 13-0 14.0 15-0 Figure 1.— Effect of temperature on time to 50% eggs hatch- ing for Pacific hake, and 95% confidence intervals. Small solid circles are hatching times from Zweifel and Lasker ( 1976). Data was fitted to a Gompertz curve: Y = 484.00 * exp(-2.89 * (1 - exp( -0.0623 * X))). 240.0 208.0 176.0 144.0 1 ~\ T 112.0 i i i i — i. — T i 8.0 9.0 10.0 11.0 12.0 TEttPERflTURE(t) 13.0 14.0 15-0 FIGURE 2.— Effects of temperature on 50% time to complete yolk-sac absorption for Pacific hake larvae and 95% confidence intervals. Data was fitted to a Gompertz curve: Y= 1,269.52 * exp(-108.82 * (1 - exp( -0.0016 * X))). larvae to yolk-sac absorption at 8°C. At 8°C, 8-12 d old larvae still had considerable yolk supplies and no functional mouth. A well-developed mouth normally formed after 4 d at 12°C and after 3 d at 15°C. Both the mean and the maximum length of time to starvation after complete utilization of the yolk decreased with increasing temperature (Table 1). A nonparametric analysis of variance (Kruskal-Wallis; Conover 1971) indicates that temperature has a significant effect on the time to starvation (P<0.01). The variance in the mean time to death was large in these experiments due to death occurring not only from starvation, but from other causes such as being trapped in the surface film. These early nonstarvation deaths were excluded from the analysis. Table 1.— Starvation experiments. Tempera- ture (°C) Mean time to starvation (h) Standard deviation 1 00% starva- tion (h) No. of larvae 8 12 15 251 0 200.2 150.0 656 29.1 178 318 235 168 Growth Rates Larvae were reared in the laboratory beyond the yolk-sac stage (±1 d) to verify otolith incre- ments as daily marks. Increments begin to be added 1-2 d before complete yolk-sac absorption, perhaps coinciding with the onset of feeding; after yolk absorption, 1 ring is apparently added each day (Fig. 3). Rings on these otoliths were much fainter than those of field-caught speci- mens, possibly due to poor feeding, lighting, or other rearing conditions in the lab. Postyolk-sac larvae grown in the laboratory survived up to 10 n 10 9 8 CD 7|- t— z _ LU 6 o= 5 <_) z - 4 3 2 1 0 5 6 HCE OflYS 10 11 Figure 3.— The daily addition of increments by laboratory- reared postyolk-sac Pacific hake larvae. 591 FISHERY BULLETIN: VOL. 80, NO. 3 d beyond the expected starvation date, but I was not able to maintain larvae much older than this. The growth of field-caught larvae collected off California and stored in 80% ethanol was deter- mined by otolith aging. Readings to 30 incre- ments appear to clearly represent daily deposi- tion of increments. However, after roughly 30 increments, dark bands appearing on the otoliths were separated by several inner rings and it was difficult to distinguish which were daily incre- ments. R. Methot (Southwest Fisheries Center, National Marine Fisheries Service, La Jolla, Calif.) who read many of these otoliths from large larvae, felt that the larger bands were the daily marks. For the large otoliths I read, I fol- lowed this assumption. The growth of Pacific hake larvae in length (not corrected for preservation effects) was fitted with a Gompertz curve (Fig. 4); however, a straight line provides a better fit for larvae <20 d old (Fig. 4, insert). Pacific hake larvae grow slowly in length for at least the first 30 d of post- hatching life and then grow rapidly. Growth in weight was examined by determin- ing a length-weight relationship for larvae (Fig. 5a) and then combining this information with the age-length relationship described above (Fig. 5b). The weights used were from larvae pre- served in 80% ethanol and uncorrected for pres- • 50 .50 :-1.00 -1.50 -2.00 + + .50 .75 1 .00 LOG LENGTH trim 1.25 Figure 5.— Growth in weight of Pacific hake larvae, a. length-weight relationship of larvae off California (dry weights are from larvae preserved in ethanol), b. age-weight relation- ship. B.O 6.0 + + # + 40-0 2.0 ''+ +++. *-<%»*+> tff+ 0 S.O 10.0 IS.O Ztl.O 30.0 INCREMENTS + t/ 20.0 p$ fa r + \T+ 10.0 n 00* &+*+ ?+ + ' 25.0 50.0 75.0 100.0 INCREMENTS (DAYS) 125.0 150.0 Figure 4.— The growth of larvae caught off southern California determined from otolith increments. A Gompertz curve was fit to the data, Y = 1.72 * exp(3.15 * (1 - exp(-0.02624 * X))). Insert: daily growth for the first 20 d was fit better with a straight line: Y = 2.75 + 0.16X 592 BAILEY: EARLY LIEE HISTORY OF PACIFIC HAKE ervation effects. Increase in weight also appears to be slow for at least the first 30 d of posthatch- ing life. Weight loss of fi rst- feeding larvae due to pres- ervation in 80% ethanol was 57.8%, probably due mostly to loss of lipids and soluble proteins; weight loss in 3% Formalin was 24.1% (Table 2). Shrinkage in length of first-feeding larvae preserved in Formalin was 8.9%; shrinkage of larvae preserved in ethanol was 3.6% (Table 3). Shrinkage due to delay in preservation was ex- amined. Larvae in the 9-min delayed group de- creased 17% in length, while those in the 29-min group decreased 40% in length. Most larvae, and especially larger larvae, probably do not die dur- ing the tow, and I have observed that in Puget Sound most larvae are alive after capture with a jar-type cod end. However, after a typical CalCOFI tow it probably takes an average of 5-10 min to remove and wash the cod end before preserving the larvae. I estimate that in routine sampling surveys small Pacific hake larvae probably shrink 9-20% in length due to handling. Shrinkage of large larvae was not tested and is probably different. Table 2. — Weight loss due to preservation, determined by comparing fresh-frozen larvae to preserved larvae. Dry weights in milligrams. Live 80% ethanol 3% Formalin Mean dry-weight (mg) 0.083 0 035 0.063 Standard deviation 0 007 0 004 0 006 No. of larvae 5 5 5 % of live weight 100 0 42.2 75.9 o 0.4 IO M I2 I3 TEMPERATURE (°C) Figure 6.— The effect of temperature on mean respiration rates (/xl/animal per h) (if Pacific hake larvae of different stages. Vertical bars are ±1 standard deviation. respiration rates for first-feeding larvae are 4.8- 6.8 ^1/mg-dry wt per h. These respiration rates were determined in 30 ml bottles, which did appear to slightly impair the swimming activity of larvae. Consequently, these rates are consid- ered to be within the range between routine and active metabolism. The dry weights reported in Table 4 are of Formalin-preserved larvae, un- corrected for weight loss due to preservation. With the correction, weight specific rates would be 25% lower. Vertical Distribution Table 3.— Shrinkage in standard length of first-feeding lar- vae due to preservative and related to delay in time of preser- vation, determined by comparing standard lengths of live lar- vae with preserved larvae. Three larvae per treatment; lengths are in millimeters. Ethanol 80% Forma lin Preservative: 3% 3% 3% 3% Minutes delay Mean live length Mean fixed length % length loss 0 4.44 4.28 36 0 4.63 422 89 9 4.52 3.73 17.5 16 4.46 3.70 17.0 29 452 2 71 40 1 Metabolic Rates Respiration rates for Pacific hake larvae in- crease as a function of temperature and size (Fig. 6; Table 4). The experimental temperatures rep- resent the range encountered by hake larvae within the spawning region. At 12°C, the mean temperature larvae experience off California, Ahlstrom (1959) noted that Pacific hake eggs (and also most unsized hake larvae) were aggre- gated near the base of the mixed layer. From my analysis, most small larvae <8 mm were caught in the 50-100 m depth interval (Fig. 7), which corresponds to Ahlstrom's observations. Larger larvae were caught deeper; however, large lar- vae near the surface may be more able to avoid capture. An analysis by Lenarz (1973) indicates that larger larvae are probably able to avoid plankton nets in daytime. Large larvae, >12 mm, appear to be close to the surface later in the year (May-June), and have been caught at depths of only 25-50 m in nighttime plankton tows (A. Alvarino3). From my own observation in June 3 A. Alvarino. Southwest Fisheries Center La Jolla Labora- tory, National Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 92038, pers. commun. June 1979. 593 FISHERY BULLETIN: VOL. 80, NO. 3 Table 4.— Summary of respiration experiments. Dry weights are of Formalin preserved larvae, uncorrected for weight loss due to preservation. Mean Mean li\l //I/ Tempera- length weight Repli- Larvae/ animal mg-dry wt ture (° C) Experiment (mm) (mg) cates jar per h SD per h 8 a. yolk sac — — 3 3 0 170 0044 447 b yolk sac 3.49 0038 3 5 0 185 0.072 4.87 c. 1st feeding 3.81 0.049 2 2 0271 — 5.53 d 1st feeding 3.97 0055 4 3 0260 0083 4.73 e. feeding 395 0.068 3 1 0.402 0244 5.91 f. feeding 3.97 0.070 2 1 0.426 — 6.09 12 a. yolk sac — — — — — — — b. yolk sac 349 0.038 4 3 0.261 0027 6.87 c. 1st feeding 3.81 0.049 3 2 0.332 0 066 678 d. 1st feeding 3.97 0055 3 3 0 265 0052 482 e feeding — — — — — — — f. feeding 3.97 0070 2 2 0.549 — 7.84 15 a. yolk sac — — — — — — — b. yolk sac 349 0038 4 3 0 460 0.126 12.11 c. 1st feeding 3.81 0049 3 3 0.467 0080 953 d 1st feeding 3.97 0.055 4 3 0345 0041 6.27 e feeding — — — — — — — f. feeding — — — — — — — 0 - 10 50 51 - I00 uj 101 - 200 Q 20! - 300 0 1(0 % 0 % k0 <1> li-8 8-12 >12 LARVAL SIZE CLASS(MM) Figure 7.— The vertical distribution of Pacific hake larvae off the California coast shown as the percent of larvae within each depth interval by size class. Sample numbers are 1174, LT 4 mm; 1051, 4-8 mm; 19, 8-12 mm; 5, GT 12 mm; total sample of 2,249 larvae. 1979, large larvae were also caught in midwater trawls near the surface in nighttime. In contrast to eggs and larvae off the Califor- nia coast, which are found at midwater, Pacific hake eggs and larvae in Puget Sound are located near the bottom of the water column. This is shown in Figure 8 for animals sampled at Port Susan (maximum depth, 110 m). This trend was also observed for animals collected at Dabob Bay (maximum depth, 175 m); the majority of eggs and larvae were found in the bottom 25 m of the water column. The difference in vertical distri- bution between eggs off California and eggs in Puget Sound may be explained as follows. The water at a reference level of 100 m is less saline (29.3%o) and less dense (1.0228) in Puget Sound than water off the California coast (33.6 %o 1.0258). Off California, eggs are spawned at 200- 500 m depth, are relatively buoyant compared < 0-1)0 > 20 - 1)0 1)0 - 75 75 - 110 EARLY STAGE LATE STAGE YOLK-SAC EGGS EGGS LARVAE LARVAE < 5™ti LARVAE > 5™n EGG/LARVAL STAGE Figure 8.— The vertical distribution of Pacific hake eggs and larvae at Port Susan, Wash., shown as the percent of eggs or larvae within each depth interval by developmental stage or size class. Sample numbers: early stage eggs, 2,845; late stage eggs, 1,147; yolk-sac larvae, 409; larvae LT 5 mm, 31 ; larvae GT 5 mm, 12; total sample of 4,444. with the surrounding water, and rise upward to a level of equal buoyancy. Eggs in Puget Sound are spawned near bottom (Thorne 1977). Assum- ing that they are about the same density as the California eggs, these eggs are relatively less buoyant in the less dense water of Puget Sound, and therefore remain near the bottom. DISCUSSION Compared with eggs and larvae of other fishes in the California Current system, rates of devel- opment, growth, and metabolism of Pacific hake eggs and larvae are slow. These factors may be indicative of survival tactics (Hunter 1980), and differences could reflect the relative importance of certain environmental conditions, such as food abundance and predation pressure, in larval sur- 594 BAILEY: EARLY LIFE HISTORY OF PACIFIC HAKE vival. Hunter (1980) contrasted several types of life history tactics for larvae of marine fishes. He indicated that in relatively cold water, where metabolic costs are low, a tactic of slow growth, feeding on large prey, and passive hunting may be common. This does appear to be the strategy of Pacific hake larvae. This tactic is quite differ- ent from that of high metabolism, fast growth, and active hunting demonstrated by other lar- vae, such as Pacific mackerel and to a lesser ex- tent northern anchovy. Larvae of Pacific hake are located in colder water than larvae of Pacific mackerel and northern anchovy (Ahlstrom 1959) and compared with these other species the growth of Pacific hake larvae is slow (Fig. 9). Metabolic rates are difficult to compare because of different experimental techniques, but as a lower limit (due to the restrictive container size), 3-5 d old Pacific mackerel larvae require about 0.411 Ml-02/animal per h at 19°C (Hunter and Kimbrell 1980). This compares with 0.265 Ml-02/ animal per h for first-feeding Pacific hake larvae at 12°C from this study. I have calculated the energetic requirements of a first-feeding Pacific hake larva based on the routine metabolic rate at 12°C (the ambient tem- perature off the California coast) and growth in weight for larvae caught in the field, after cor- recting for preservation effects (Table 5). These values were converted to calories assuming val- ues of 1 /j1-02 =0.005 cal and 1 mg-dry weight of TABLE 5.— Caloric requirement of first-feeding Pacific hake larvae from growth and metabolism. Mackerel Anchovy Hake Figure 9.— Comparative growth of field-caught Pacific hake larvae (at 11°-14°C; this study), field-caught anchovy larvae (13°-16°C; Methot and Kramer 1979), and laboratory-reared Pacific mackerel larvae (19°-20°C; Hunter and Kimbrell 1980). Respiration rate at 12°C - 0 30 /yl/animal per h Length Weight Corrected (mm) (mg) weight (mg)' Growth day 4 3 412 0 0440 0.0694 day 5 3 577 0.0512 0.0808 Weight gain 0 011 mg/d = 0 0550 calories2 Respiration = 7.20 /j\/d = 0.0360 calories3 00910 calories Daily ration = Metabolism f Growth t Nonassimilated + Egestion Daily ration x 0.7 = Metabolism + Growth Daily ration = 0 130 calories 'Corrected for preservation effects. 25 003 cal/mg-dry wt tissue (Laurence 1977). 30 005 cal//jl-Q2 (Laurence 1977). larval fish tissue = 5.003 cal (Laurence 1977). The average first-feeding hake larva thus re- quires 0.091 cal/d to maintain and grow. This value is likely to be an underestimate of the cal- oric requirement due to an undetermined amount of energy needed to attack, capture, and digest prey animals. Estimates of assimilation coefficients range from 0.8 (Healy 1972; Dagg 1976) to 0.5 ( Vlymen 1977). Assuming an assimi- lation coefficient of 0.7, as suggested by Ware (1975) and Laurence (1977), Pacific hake larvae would need to ingest 0.130 cal/d to satisfy meta- bolic and growth costs. Although this seems to be a reasonable estimate, significant errors may arise from the factors used for length-weight conversion, preservation effects, and from the assumed assimilation coefficient. I would sug- gest a more thorough examination of these fac- tors in future experiments. Using Sumida and Moser's( 1980) report on the stomach contents of 3-4 mm Pacific hake larvae (Table 6), I calculated an estimate of daily ration that can be compared with the above estimate. Several approximations are necessary in this calculation, including 1) a feeding period of 12 h, 2) a digestion time, which I assume to be 5 h— ranges for other species are 3-8 h for herring (Werner and Blaxter 1980) and 2-4 h for Pacific mackerel (Hunter and Kimbrell 1980), and 3) a value of 5.2519 cal/mg-dry wt for copepods (Laurence 1976). The daily ration can then be calculated as: Daily ration = Stomach content weight X Feeding period/Digestion time (Feign- baum 1979; Laurence 1977). For small Pacific hake larvae the daily ration thus calculated is 0.129 cal, which compares very closely with the previous estimate. Hunter and Kimbrell (1980) calculated that 3-5 d old Pacific mackerel larvae require 0.143 cal/d to maintain and grow, based on the weight 595 FISHERY BULLETIN: VOL. 80, NO. 3 Table 6.— Average daily ration of 3-4 mm Pacific hake larvae (data from Sumida and Moser 1980, table 1). Number prey/stomach in- cludes those with empty guts. Total Prosome Dry Dry weight/ Prey length length weight No. prey/ stomach organism (mm)1 (mm)2 (mg)3 stomach (mg) Adults Clausocalanus 1.15 0.70 0006 0.38 0.00228 Paracalanus 1.0 0.57 0.004 0.29 0.00116 Calocalanus 1.0 0.57 0.004 0.08 0.00032 Oithona 0.95 0.52 0 003 0.03 0.00009 Calanoid unid 1.04 0.60 0004 009 0.00036 Disintegrated 1 04 0.60 0.004 0.08 0.00032 Copepodites Calanus sp. 1.50 1.00 0.050 0.02 0.00100 Oithona 0002 0.03 000006 Calanoid 0002 1.09 0.00218 Cyclopoid 0002 0.03 0.00006 Disintegrated 0002 0.21 0.00042 Nauplii 0.001 2.00 0.00200 Eggs 0.0005 1.06 0.00056 001025 Calories per stomach = 0.01025 mg X 5.2519 cal/mg-dry wt4 = 0.05383 cal Calories in stomach x Feeding period (FeJgenbaum 1979; Daily ration Digestion time Laurence 1977) 0 0538 X 12 0.129 cal/d. 'From Brodskii 1967, Fulton 1968 2From Total length = 1.16 x prosome length f 0.34; Fulton 1968 3From Vidal 1978; Feigenbaum 1979. "5.2519 cal/mg-dry weight conversion for copepods (Laurence 1976). gain of laboratory-reared larvae and metabolic rates at 19°C. As they note this must be a lower limit. Assuming the same assimilation coeffi- cient that I used for hake, 0.7, mackerel would need to ingest 0.204 cal/d to satisfy this ration requirement. First-feeding hake larvae have very large mouths compared with either mack- erel or anchovy (Fig. 10), so they may feed on a wide size range of planktonic animals (including adult copepods); hake larvae could satisfy daily rations by capturing 25 nauplii or 15 small cope- podites or 6 small calanoid adults or 1 Calanus adult. In contrast, both first-feeding mackerel and anchovy require a smaller size range of food particles (Hunter 1980). At least for anchovy, their survival depends on finding patches of small food organisms, such as the dinoflagellate, Gymnodinium (Lasker 1975). To satisfy its ration requirement a first-feeding Pacific mackerel larva would have to capture 4,000 Gymnodinium cells, 240 rotifers, or 39 copepod nauplii. It seems evident that they require high density patches of prey for successful feeding, whereas hake larvae may not require such dense patches of food for successful first-feeding. From the results of this study, I infer that the first feeding of Pacific hake larvae is not as im- portant to their survival as it is for Pacific mack- erel and also for northern anchovy. This concept is supported by 1) the lower daily ration of hake larvae due to temperature-dependent activity and growth, 2) larger food items in the diet of hake larvae which provide more calories per prey item, 3) the relatively longer starvation time for hake larvae, i.e., they take 6-12 d to starve after complete yolk utilization, whereas anchovy take only about 4 d (Lasker et al. 1970), and 4) the abil- ity of hake larvae to feed while still having yolk reserves (Sumida and Moser 1980). In addition, there is evidence of high energy wax esters in eggs of Merluccius (Mori and Saito 1966); thus larvae may have a longer safety period to find food. This concept does not exclude the possibil- ity of a critical starvation period occurring later in larval or postlarval life, when stored energy reserves are exhausted and energetic demands are greater. Predation may be relatively important as a factor influencing survival of Pacific hake lar- vae. Egg and yolk-sac stages of marine fish appear to be the stages most vulnerable to preda- tion (Theilacker and Lasker 1974; Hunter 1980). Because of the colder temperatures that Pacific hake eggs and larvae inhabit, and resulting growth and development rates that are slow compared with Pacific mackerel (Hunter and 596 Q 5» O BAILEY: EARLY LIFE HISTORY OF PACIFIC HAKE 1.6 1.4 — 1.2 e e x 1.0 .8 .6 A .2 r Scomber y £". ringens £. mordax J L J L 2 4 6 8 10 12 14 16 18 20 22 24 26 LENGTH (mm) Figure 10.— Mouth sizes of larvae of hake, mackerel, anchovy, and cod by length class (Hunter 1980). Kimbrell 1980) and northern anchovy (Zweifel and Lasker 1976), Pacific hake spend a longer time in vulnerable stages. Consequently, preda- tion pressure on hake eggs and larvae may be high. ACKNOWLEDGMENTS I thank W. Wooster, D. Gunderson, M. Till- man, and two reviewers for editing and com- menting on the manuscript. I further thank R. Methot for instruction in reading otoliths and J. Yen, J. Hunter, and R. Francis for helpful dis- cussions. G. Moser, E. Ahlstrom, and A. Alva- rino provided the vertical series samples, and J. Yen, G. Stauffer, and P. Smith provided oppor- tunities for field sampling. Financial support was given by the Northwest and Alaska Fisher- ies Center. LITERATURE CITED Ahlstrom, E. H. 1959. Vertical distribution of pelagic fish eggs and lar- vae off California and Baja California. U.S. Fish Wildl. Serv., Fish. Bull. 60:107-146. Brodskii, K. A. 1967. Calanoids of the far eastern seas and polar basins of the USSR. (Trans, from Russian by A. Mercado.) Isr. Program Sci. Transl., Jerusalem, 440 p. Carritt, D. E., and J. H. Carpenter. 1966. Comparison and evaluation of currently employed modifications of the Winkler method for determining dissolved oxygen in seawater; a NASCO report. J. Mar. Res. 24:286-318. ClECHOMSKI, J. D. DE, AND G. WEISS. 1974. Estudios sobre la almentacion de larvas de la mer- luza, Merluccius mertuccius Hubbsi y de la anchoita, Engraulis anchoita en el mar. Physis Rev. Asoc. Argent. Cienc. Nat. Buenos Aires 33:199-208. Conover, W. J. 1971. Practical nonparametric statistics. Wiley, N.Y., 462 p. Dagg, M. J. 1976. Complete carbon and nitrogen budgets for the car- nivorous amphipod, Calliopius laeviusculus (Kroyer). Int. Rev. Ges. Hydrobiol. 61:297-357. Feigenbaum, D. 1979. Daily ration and specific daily ration of the chae- tognath Sagitta e?>flata. Mar. Biol. (Berl.) 54:75-82. Fulton, J. 1968. A laboratory manual for identification of British Columbia marine zooplankton. Fish. Res. Board Can. Tech. Rep. 55, 141 p. Healy, M. C. 1972. Bioenergetics of a sandy goby (Gobius minutus) population. J. Fish. Res. Board Can. 29:187-194. Hunter, J. R. 1980. The feeding behavior and ecology of marine fish larvae. In J. E. Bardach (editor), The physiological and behavioral manipulation of food fish as production and management tools. Int. Cent. Living Aquat. Res. Man- age., Manila. Hunter. J. R., and C. A. Kimbrell. 1980. Early life history of Pacific mackerel. Scomber 597 FISHERY BULLETIN: VOL. 80, NO. 3 japonicus. Fish. Bull., U.S. 78:89-101. KlMURA, D. K., AND A. R. MlLLIKAN. 1977. Assessment of the population of Pacific hake (Mer- luccius productus) in Puget Sound, Washington. Wash. Dep. Fish. Tech. Rep. 35, 46 p. Lasker, R. 1975. Field criteria for survival of anchovy larvae: the relation between inshore chlorophyll maximum layers and successful first feeding. Fish. Bull., U.S. 73:453- 462. Lasker, R., H. M. Feder, G. H. Theilacker, and R. C. May. 1970. Feeding, growth, and survival of Engraulis mor- dax larvae reared in the laboratory. Mar. Biol. (Berl.) 5:345-353. Laurence, G. C. 1976. Caloric values of some North Atlantic calanoid copepods. Fish. Bull, U.S. 74:218-220. 1977. A bioenergetic model for the anaysis of feeding and survival potential of winter flounder, Pseudopleuro- nectes americanus, larvae during the period from hatching to metamorphosis. Fish. Bull., U.S. 75:529- 546. Lenarz, W. H. 1973. Dependence of catch rates on size of fish larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 164:270- 275. Methot, R. D., and D. Kramer. 1979. Growth of northern anchovy, Engraulis mordax, larvae in the sea. Fish. Bull., U.S. 77:413-423. Mori, M., and T. Saito. 1966. The occurrence and composition of wax in mullet and stockfish roes. Bull. Jpn. Soc. Sci. Fish. 32:730- 736. SUMIDA, B. Y., AND H. G. MOSER. 1980. Food and feeding of Pacific hake larvae, Merluc- cius productus, off southern California and Baja Cali- fornia. Calif. Coop. Oceanic Fish. Invest. Rep. 21:161- 166. Theilacker, G. H., and R. Lasker. 1974. Laboratory studies of predation by euphausiid shrimps on fish larvae. In J. H. S. Blaxter (editor), The early life history of fishes, p. 287-300. Springer- Verlag, N.Y. Thorne, R. E. 1977. Acoustic assessment of Pacific hake and herring stocks in Puget Sound, Washington and southeastern Alaska. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 170:265-278. Utter, F. M. 1969. Transferrin variants in Pacific hake (Merluccius productus). J. Fish. Res. Board Can. 26:3268-3271. Vidal, J. 1978. Effects of phytoplankton concentration, tempera- ture, and body size on rates of physiological processes and production efficiencies of the marine plankton cope- pods, Calanus pacificus Brodsky and Pseudocalanus sp. Ph.D. Thesis, Univ. Washington, Seattle, 200 p. Vlymen, W. J. 1977. A mathematical model of the relationship between larval anchovy (E. mordax) growth, prey microdistribu- tion and larval behavior. Environ. Biol. Fishes 2:211- 233. Ware, D. M. 1975. Growth, metabolism and optimal swimming speed of pelagic fish. J. Fish. Res. Board Can. 32:33-41. Werner, R. G., and J. H. S. Blaxter. 1980. Growth and survival of larval herring (Clupeahar- engus) in relation to prey density. J. Fish. Res. Board Can. 37:1063-1069. ZWEIFEL, J. R., AND R. LASKER. 1976. Prehatch and posthatch growth of fishes— a gen- eral model. Fish. Bull., U.S. 74:609-621. 598 THE BIOLOGY OF THE WHITE PERCH, MORONE AMERICANA, IN THE HUDSON RIVER ESTUARY D. W. Bath and J. M. O'Connor1 ABSTRACT White perch, Morone americana, are found throughout a 250 km region in the Hudson River from Manhattan north to Albany, New York. They represent a dominant species in most portions of the river, although they are of little importance in the commercial fishery. Life history information was determined for more than 7,500 white perch collected from a 15 km region of the Hudson River be- tween Haverstraw and Bear Mountain, New York. Annulus formation began by the first week in May and was completed by the end of July. Maxi- mum age for both male and female white perch was 7 years. Most of the growth occurred in the first 3 years for both males and females, and represented 78% of the length attained by the seventh year. Most fish were sexually mature by their second year. The length-weight relationship observed for Hudson River white perch was Log W= -4.743 + 3.093 Log L. The mean fecundity was 50,678 eggs per female, with a range of 15,726-161,449. The white perch, Morone americana (Gmelin), inhabits rivers, bays, and estuaries of the Atlan- tic coast from Nova Scotia to South Carolina (Hildebrand and Schroeder 1928; Bigelow and Schroeder 1953; Leim and Scott 1966). The spe- cies has been introduced to freshwater lakes and reservoirs through migration, stocking, and by being landlocked in impoundments (Bigelow and Schroeder 1953; Mansueti 1961; Woolcott 1962). White perch has been reported in Lake Ontario (Sheri and Power 1969), Lake Erie (Lar- sen 1954; Trautman 1957), and the waters of Quebec (Scott and Christie 1963; Leim and Scott 1966). Most recently it has been introduced into the waters of Nebraska (Hergenrader and Bliss 1971). White perch is found throughout a 250 km re- gion in the Hudson River from Manhattan north to Albany, N.Y. It represents a dominant species in most portions of the river (McFadden2), al- though it is of little importance in the commer- cial catch (Sheppard3). The species is particu- larly abundant in the Hudson River from Nyack north to Catskill, N.Y. (Perlmutter 1967). With the exception of a fecundity study (Holsapple and Foster 1975), no life history infor- mation for white perch in the Hudson River has been published. Site-specific data for white perch populations are available in reports (Ray- theon Co.4; Lawler, Matusky and Skelly Engi- neers5, 6; Texas Instruments Inc.7). The present study was carried out to investigate the life his- tory of white perch in the Hudson River estuary over a 15 km section, from Haverstraw to Bear Mountain, N.Y. This section of the Hudson River is a very stressful environment owing to frequent changes in salinity: On an annual basis, the re- gion experiences one to several transitions be- tween limnetic and oligohaline conditions (Abood 1974). The white perch is one of the high- ly adaptable species that can tolerate these changes. Along with the hogchoker, Trinectes maculatus, it is a dominant year-round resident of this portion of the Hudson region. 'New York University Medical Center, Department of En- vironmental Medicine, Laboratory for Environmental Studies, 550 First Avenue, New York, NY 10016. 2McFadden, J. T. 1978. Influence of the proposed Corn- wall pumped storage project and steam electric generating plants on the Hudson River Estuary with emphasis on striped bass and other fish populations. Rep. for Consolidated Edison Co. of N.Y., Inc., 1179 p. 3D. J. Sheppard, New York State Department of Environ- mental Conservation, 50 Wolfe Road, Albany, NY 12223, pers. commun. March 1980. Manuscript accepted December 1981. FISHERY BULLETIN: VOL. 80, NO. 3, 1982. 4Raytheon Co. 1971. Indian Point ecological survey re- port II, January-June 1970. Submarine Signal Div., Ports- mouth, R.I., 165 p. 5Lawler, Matusky and Skelly Engineers. 1974. Hudson River aquatic ecology studies at Roseton and Danskammer Point. Vol. III. Fish. Rep. to Central Hudson Gas and Electric Corp., N.Y., 114 p. 6Lawler, Matusky and Skelly Engineers. 1974. Hudson River aquatic ecology studies— Bowline Point and Lovett Gen- erating Stations. Vol. IV, 445 p. 7Texas Instruments Inc. 1974. Hudson River ecological study in the area of Indian Point. 1973 Annu. Rep. to Consol- idated Edison Co. of N.Y., Inc., 426 p. 599 FISHERY BULLETIN: VOL. 80. NO. 3 MATERIALS AND METHODS We collected white perch at seven beach sein- ing stations, nine trawling areas, and one experi- mental mesh gill net location between Haver- straw and Bear Mountain, N.Y., on the Hudson River from April through November 1970 (Fig. 1). Beach seine collections were made with a 30.4 m by 2.4 m seine (9.5 mm square mesh) or a 15.2 m by 1.5 m seine (6.5 mm square mesh), each with a central bag of 6.5 mm square mesh. The large seine was set from shore with the aid of a boat and retrieved in a semicircle. The 15.2 m seine was handhauled by pulling the seine paral- lel to the shore in water ~1.2 m deep. The large seine was fished in water ~2.4 m deep. Bottom and surface trawls were made with a 7.6 m semiballon trawl, constructed with a 38.1 mm stretch mesh nylon body, with a 31.8 mm stretch mesh nylon cod end rigged with an inner liner of 6.5 mm stretch mesh nylon. Trawl doors were 1.1 m in length and 0.46 m in width. Tow Bear Mt. Bridge Peekskill N Albany Catskill Sougerties Kingston 32 Newburgh x Bear Mt Stony Point- Hoverstrow Nyack' Manhattan OKm Stony Point Trawling Sites a Seining Sites • Gillnet Sites Figure 1.— Region of Hudson River from which white perch were collected. 600 BATH and O'CONNOR: BIOLOGY OF WHITE PERCH IN HUDSON RIVER ESTUARY speed for trawling was about 3.4 km/h. Details of the towing procedure are described in Rathetal. (1979). The gill net was an experimental type with four panels of varying mesh size. The net mea- sured 30.4 m by 1.8 m and contained 7.6 m each of 12.7, 25.4, 38.1, and 76.2 mm stretch mesh mono- filament line. It was hung from 9.5 mm braided, polycore float line, with a bottom lead-coreline. All fish collected at each site were immediate- ly labeled and preserved in 10% Formalin8 and returned to the laboratory for analysis. Each fish was measured (standard length (SL)) to the nearest millimeter, weighed to the nearest 0.1 g, and the sex was determined. A subsample of 310 fish was measured for fork length (FL) and total length (TL) to determine regression equations for comparison of Hudson River white perch 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. populations with data from other river systems. Mature ovaries and testes were removed from selected individuals, weighed, and preserved in 10% Formalin. The ovaries were later transfer- red to (iilson's fluid for fecundity analysis! Ricker 1968). Stomachs were removed from randomly selected fish and preserved in 10% Formalin for later food analysis. Scales for age analysis were re- moved from behind the left pectoral fin (Rounse- fell and Everhart 1953), cleaned, pressed, and sealed between glass microscope slides. The scales were read within 6 mo of the collection date. RESULTS Time of Annulus Formation Annulus formation began by the first week in May and was completed in all age groups by the end of July (Table 1). Younger fish (age groups 1 and 2) completed the annulus by the end of June. Table 1.— Percentage of aged white perch, Morone americana, with a new annulus and with a given number of circuli beyond the new annulus during a given period. Date collected Age (winters of life) No. spec Percent with new annulus Percent with noted no. of circuli beyond new annulus 1-2 3-4 5-6 7-8 >8 May 22- 1 June 2 2 (incl.) 3 4 5 >5 June 9- 1 June 16 2 (incl.) 3 4 5 >5 June 19- 1 June 30 2 (incl.) 3 >3 July 1- 1 July 17 2 (incl ) 3 4or5 >5 July 24- 1 July 30 2 3 or 4 >4 Aug. 1- 1 Aug. 15 2 3 4 or 5 >5 Aug. 17- 1 Aug. 31 2 3 >3 Sept- 1 Oct. 2 3 >3 11 73 64 9 36 50 50 0 36 39 39 0 14 29 29 0 14 0 0 0 31 0 0 0 7 100 14 14 20 70 45 15 17 47 41 0 14 43 22 14 13 39 31 8 21 0 0 0 5 100 0 0 7 100 29 14 8 50 50 0 9 33 33 0 3 100 0 0 8 100 0 25 17 88 24 35 6 83 67 16 5 20 0 0 4 100 0 0 10 100 0 0 7 100 43 57 2 100 100 0 10 100 0 0 21 100 0 0 9 100 0 11 12 100 8 17 2 100 50 50 15 100 0 0 4 100 0 0 6 100 0 0 6 100 0 17 15 100 0 0 5 100 0 0 6 100 0 0 2 100 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29 14 29 0 10 0 0 0 6 0 0 0 7 0 0 0 0 0 0 0 0 0 0 0 0 40 20 40 57 0 0 0 0 0 0 0 0 0 0 0 0 0 0 100 13 50 13 0 29 0 0 0 0 0 0 0 0 0 0 0 0 0 0 100 0 20 20 60 0 0 0 0 0 0 0 0 0 0 0 100 0 10 14 76 33 33 11 11 58 17 0 0 0 0 0 0 0 0 0 100 0 25 0 75 17 50 0 33 67 17 0 0 0 0 0 100 0 0 0 100 0 17 17 67 0 100 0 0 601 FISHERY BULLETIN: VOL. 80, NO. 3 White perch of age groups 3 and older completed the annulus ~2 wk later. Length-Frequency and Age Distribution During May and June, there were three modes in the length-frequency data, with peaks at 65.0- 69.0, 105.0-109.0, and 140.0-144.0 mm (Figs. 2, 3). These peaks represent the 1-, 2-, and 3-yr age groups. From July to November the length fre- quencies ranged from 10.0-14.0 mm to 200.0- 204.0 mm (Fig. 4). The prominent mode at 50.0- 54.0 mm represents young-of-the-year fish (Fig. 5). Growth The relationship between anterior scale radius and standard length for white perch from all age groups was L = 32.64 + 45.56 {R), where L = standard length in millimeters and R = scale radius in millimeters. The coefficient of deter- mination (r2) was 0.88 (Fig. 6). The standard lengths at the various annuli were back-calculated and the growth histories were constructed for each year class, along with growth increments for each age group (Tables 2, 3). The most rapid growth occurred in the first 3 yr of life, and accounted for 78.0% of the total growth at the maximum size observed. Subse- quent average growth increments were uniform among year classes, but considerably smaller (Fig. 7). Similar growth histories were compiled for each year class for both male and female white perch (Tables 4-7). Females grew slightly larger in TL than males of the same age (Fig. 8). Length Conversions We calculated the relationship between total length, fork length, and standard length mea- surements taken on a subsample of 310 white perch, ranging in size from 30.0 mm to 182.0 mm SL. A linear regression was computed to obtain conversions between the three methods so that we could compare growth rates among the dif- ferent white perch studies. (Fig. 6). The relation- ship between total length and standard length was SL = -1.05 + 0.81 TL, r2 = 1.0; the relation- ship between fork length and standard length was SL = -0.99 + 0.86 FL, r2 = 1.0. Length -Frequency Distribution Total #Fish = 1959 (May- June 1970) Male = *- Female = Total = ?; ^r 0* 0 1.0 2.0 3.0 40 Scale Radius (mm) 5.0 Figure 6.— Relationship between scale radius and standard length of white perch from the Hudson River between Nyack and Bear Mountain, N.Y. r* = 0.88. 1964 1965 1966 1967 Year Class 1968 1969 Figure 7.— Graphic representation of the growth histories of year classes of white perch from the Hudson River between Nyack and Bear Mountain, N.Y., 1963-69. 12 3 4 5 Age Group FIGURE 8.— Mean calculated standard lengths (mm) and incre- ments of growth for each year of life of white perch from the Hudson River between Nyack and Bear Mountain, N.Y. Male Males Log W= -2.262+ 1925 Log X Females Log W= -4.738+ 3099 Log X 1 1 hi 10 100 1000 Standard Length (mm) Figure 9. — Length-weight relationships of male and female white perch from the Hudson River between Nyack and Bear Mountain, N.Y. For males, r2 = 0.706; for females, r2 = 0.965. 605 FISHERY BULLETIN: VOL. 80, NO. 3 fecundity data for May and June (Fig. 10). The egg-to-length relationship was Y- l,697.08e002 X, where Y = number of eggs per fish and X = length, r2 = 0.39. The white perch analyzed had a Table 3.— Growth history of the white perch in the Hudson River between Haverstraw and Bear Mountain, N. Y., 1963-69. Growth increment for i idicated year of life period 1 2 3 4 5 6 7 1963 69 2 1964 71.9 50.0 1965 68.9 50.7 30.9 1966 70.2 50.3 28.2 14.1 1967 69.4 51.4 29.2 134 120 1968 71.7 54.1 290 15.8 107 9.7 1969 73.4 549 30.4 17.0 13.5 9.6 82 mean fecundity of 50,678 eggs/female with a range of 15,726-161,449. The relationship between ovary weight and total body weight for 243 female white perch of known age collected from May to October is shown in Table 8. The changes in the ratio of ovary weight to body weight expressed as a per- centage shows that spawning took place during June and was completed by July. Thereafter the ovaries are refractory and do not regain their weight until prior to the succeeding spawning season. The occurrence of the spawning season is further substantiated by the occurrence of white perch eggs and larvae in ichthyoplankton during June and July collections from the Hudson River Table 4.— Calculated growth of white perch males in the Hudson River between Haverstraw and Bear Mountain, N.Y., 1963-69. Year No. Calculated standard I ength (mm) at er d of year class 1 2 3 4 5 6 7 1963 2 669 115.2 142.3 156.8 1693 1797 189.1 1964 11 68 .2 117.2 144.9 157.0 1685 178.9 1965 32 665 114.3 140.2 1552 167.2 1966 37 693 1194 1466 1626 1967 54 686 121.6 152 5 1968 63 706 1262 1969 21 79.4 Weighted means 70.0 121.2 1472 1588 1676 179 0 189 1 Increment 70.0 51.2 26.0 11,6 88 11.4 10 1 Percent of total growth 37.0 27.1 13.8 6 1 4.6 6.0 5.3 No. 220.0 1990 136 0 820 45 0 13 0 20 Table 5.— Growth history of the white perch males in the Hud- son River between Haverstraw and Bear Mountain, N.Y., 1963-69. Growth Growth increme nt for indicated yea ' of life period 1 2 3 4 5 6 7 1963 669 1964 682 483 1965 665 490 27.1 1966 693 47.8 277 145 1967 686 50.1 25.9 12 1 12.5 1968 70.6 53.0 27 2 150 11.5 104 1969 700 556 30.9 16.0 120 104 9.4 (Lauer et al. 1974). Sex Ratio Of the 2,600 mature fish collected, 1,209 were males and 1,442 were females, giving an overall sex ratio of 0.83 to 1.0 in favor of females. This phenomenon has been observed for other fish populations in which females attain an older age Table 6.— Calculated growth of white perch females in the Hudson River between Haverstraw and Bear Mountain, N.Y., 1963-69. Year No. Calculated sta idard ength ( mm) at end of year class 1 2 3 4 5 6 7 1963 10 696 120.1 151 9 166.2 177.6 1876 195 8 1964 25 732 1244 151.4 1658 175.6 1856 1965 29 70.4 121.9 1528 170.1 1838 1966 41 70.6 1232 1546 171 7 1967 67 70.5 1256 1562 1968 98 73.0 1286 1969 35 788 Weighted means 724 125.6 1542 1693 179.6 186 2 1958 Increment 72.4 53.2 286 15.1 103 66 96 Percent of total growth 369 27 2 14 6 7.7 52 34 49 No. 3050 270.0 1720 1050 640 350 10.0 606 BATH and O'CONNOR: BIOLOGY OF WHITE PERCH IN HUDSON RIVER ESTUARY Table 7.— Growth history of white perch females in the Hud- son River between Haverstraw and Bear Mountain, N.Y., 1963-69. Growth Growth increment for year of life period 1 2 3 4 5 6 7 1963 69 6 1964 73.2 50.5 1965 70.4 51 2 31 8 1966 70.6 51.5 279 14.3 1967 70.5 526 309 14 4 11 4 1968 73 0 55.1 31 4 173 98 100 1969 72.4 55.6 306 17 1 137 100 82 o to en en I60 - • / / / I40 - May + June / Y = 1697.08e002X / - rl=0.39, r=0.62 ^>/ 120 • . / / / . / 100 / / 80 / / • / 60 • • • • / ' / j • • / ' * " 40 • * • . - / / • / • * • ^s I • 20 • • • • • • n i i • • i i i i i i i 100 120 140 160 180 200 STD Length (mm) Figure 10.— Relationship between fecundity and standard length in female white perch collected during May and June from the Hudson River between Nyack and Bear Mountain. N.Y. Table 8. — Mean ovary weight expressed as percentage of body weight. Age May June July August Septem ber October 2 4.0 3.6 1.1 0.5 0.4 1.1 3 4.7 4.3 18 04 06 07 4 7 1 40 1 0 0.5 — 1.8 5 59 39 1 5 08 — — 6 59 4 1 06 — — — 7 78 30 — 0.5 — — Total no of fish 243 than males (Elrod and Hassler L969). Chi square analysis of data from individual collections showed the difference to be significant ( x2 1 32. 1 : P<0.001). During May and June the population consisted of 70.1% mature males and females and 29.9% immature fish. From July to November the population consisted of 40.6% mature males and females and 59.4% immature fish. The change observed in the population between mature and immature individuals was due to the recruitment of young-of-the-year fish into the population sampled by our gear. DISCUSSION The growth and reproductive characteristics of white perch from the Hudson River compare favorably with data from other riverine systems. The maximum age attained in the Hudson River is about 7 yr, and maximum size is about 200 mm. Other data from the Hudson River (Lawler, Matusky and Skelly Engineers footnote 6; Texas Instruments Inc. footnote 7) show maximum age to be 7 and 9 yr, respectively, with a maximum size of from 200 to 222 mm. White perch from the Connecticut River, Conn. (Marcy 1976; Marcy and Richards 1974) attained a maximum age of about 8 yr, but grew to a maximum size of more than 280 mm. Wallace (1971) and Miller (1963) studied brackish water segments of the Dela- ware River estuary white perch populations and reported maximum ages of 8 and 10 yr, respec- tively. However, Wallace obtained a maximum size (~175 mm) smaller than found in Miller's (~257 mm) and smaller than in other riverine populations. White perch from the Patuxent River, Md., and the Roanoke River, N.C., had a greater maximum age, up to 10 yr; however, the size attained at 7 yr is approximately the same as in the Hudson River, from 190 mm to 205 mm (Conover 1958; Mansueti 1961). In Figure 11 we have plotted calculated standard lengths by age groups for white perch from five riverine sys- tems. A similarity of growth rates for most pop- ulations is obvious except for the Connecticut River where perch grow more rapidly through- out their life span. Such rapid growth is more characteristic of white perch in freshwater im- poundments than of riverine populations (Thoits 1958). The rapid growth of perch in the Connecticut River may be attributed to a longer growing sea- son; the onset of annulus formation occurs nearly 2 mo earlier than in the Hudson River. However, 607 FISHERY BULLETIN: VOL. 80, NO. 3 280 240 e 200 e C 160 1 120 c/5 80 40 0 X- o Connecticut River (Marcy) Hudson River (Bath) Delaware River (Miller) Patuxent Estuary (Mansueti) Delaware River (Wallace) Roanoke River (Conover) ± J_ _L _L _L 4 5 6 Age Group 8 10 Figure 11.— Mean calculated standard lengths for white perch based on present and other studies. this rapid growth rate estimate could be an arti- fact. Data from more recent year classes (1963- 65) show lower rates of growth than observed from the 1959 through 1962 year classes (Marcy and Richards 1974). The Connecticut River pop- ulation may be expanding rapidly and respond- ing to increased population size with reduced rates of growth (Mansueti 1961). White perch populations from south of the Hudson River show earlier onset and completion of the annulus. In the Chesapeake region, an- nulus formation begins in April (Mansueti 1961). In the estuarine portions of the Delaware River (Wallace 1971), the timing of annulus formation was shown to be complete by mid-June to early July. Lawler, Matusky and Skelly Engineers (footnote 5) reported that annulus formation in white perch from the Newburgh, N.Y., region of the Hudson River began in May and was com- pleted by early July, essentially the same time observed in the present study. In Lake Ontario (Sheri and Power 1969) annulus formation was completed in July. The Connecticut River white perch (Marcy and Richards 1974) were anoma- lous in the apparent phenological trend of annulus formation, beginning in late March with com- pletion during mid-May. This anomaly may be due to slightly higher average seasonal tempera- tures in the Connecticut River compared with those in the Hudson and Delaware Rivers, or it may be related to the fact that Marcy and Richards' ( 1974) studies were apparently carried out on a rapidly expanding population. The basic reproductive potential for white perch, expressed as fecundity, appears to vary among the estuarine and freshwater populations studied. In estuarine and tidal rivers, fecundity values are similar throughout the range. White perch from the Roanoke River and Albemarle Sound, N.C., for example, had a mean fecundity of ~56,000 eggs/fish for age groups 3 and 4 (range 20,000-90,000; Conover 1958). Thoits (1958), in a generic study of white perch, estimated fecun- dity at 40,000 eggs/female. Hudson River fish fall close to this mean, with fecundity from three independent studies given as 21,000-135,000 (age groups 3 and 4; Holsapple and Foster 1975), 39,000-116,000 (Lawler, Matusky and Skelly Engineers footnote 6), and 16,000-161,000 with a mean of ~51,000 eggs/ female in the present study. Variations in the data are most likely re- lated to numbers of females sampled and the dif- ficulty of obtaining fecundity data from a species which spawns over an extended period of time (Thoits 1958; Mansueti 1961; Taub 1969). Freshwater lake populations of white perch may produce more eggs than similar groups in estuarine and tidal river systems. Au Clair (1956) 608 BATH and O'CONNOR: BIOLOGY OF WHITE PERCH IN HUDSON RIVER ESTUARY estimated the fecundity of white perch from Sebasticock Lake, Maine, at 164,000 eggs/ female. Taub (1969), studying white perch from Quabbin Reservoir, Mass., gave a mean fecundity value of 271,000 eggs/ female for age groups 3 and 4 (range 190,000-321,000). These fecundities, which are at least double that found in riverine populations, may be related to environmental factors such as food supply, sample size, time of capture, or technique used (Taub 1969). Growth data for these populations show that the in- creased fecundity is primarily related to an in- creased growth rate for white perch in lacustrine systems, and attainment of a greater size for mature females (Thoits 1958; Taub 1969). The white perch does not contribute substan- tially to the commercial fishery of the Hudson River and has declined sharply from the 590 1 (1.3 million lb) observed for the New York Bight re- gion in the 1901 statistics (McHugh and Ginter 1978). Sheppard9 reported that for the Hudson River the average catch between 1913 and 1964 was -19,073 lb, ranging from 2,249 to 60,522 lb. The average commercial catch during 1965-74 was 1,600 lb. However, the species has ecological impor- tance in cycling nutrients within estuarine food webs and thus contributes to populations of com- mercially important marine and anadromous fisheries. The juvenile white perch in the Hudson River are prey for yearling and older striped bass, Morone saxatilis; adult white perch; and presumably other species such as the bluefish, Pomatomus saltatrix (Bigelow and Schroeder 1953; Texas Instruments Inc. footnote 7, 197610). The adaptability of the species to waters of dif- ferent quality and chemical characteristics, and the high plasticity of fecundity and growth rate under various conditions (e.g., brackish waters vs. freshwater impoundments) suggest potential importance of white perch as highly suited to temperate zone aquaculture. ACKNOWLEDGMENTS Robert Koski kindly provided white perch for analysis. Scale analyses were verified by Dale Wallace, and Lois Peters assisted with statistical 9Sheppard, D. J. 1976. Valuation of the Hudson River fishery resources: past, present and future. Bur. Fish., N.Y. Dep. Environ. Conserv., Albany, 50 p. 10Texas Instruments Inc. 1976. Predation by bluefish in the Lower Hudson River. Consolidated Edison Co. of N.Y., Inc., 32 p. analyses. The assistance of Alfred Perlmutter was invaluable throughout the project in provid- ing specimens and many helpful comments on the manuscript. We thank Gordon Cook for graphics, and Eleanor Clemm and Toni Moore for typing of the manuscript. The research was supported in part by the Consolidated Edison Co. of New York, Inc., and in part by the National Institute of Environmental Health Sciences, Grant ES00260 to the New York University Medical Center, Department of Environmental Medicine, Laboratory for Environmental Studies. LITERATURE CITED Abood, K. A. 1974. Circulation in the Hudson estuary. Ann. N.Y. Acad. Sci. 250:39-111. Au Clair, R. P. 1956. The white perch, Morone americana (Gmelin), in Sebasticook Lake, Maine. M.S. Thesis, Univ. Maine. Orono, 60 p. Bath, D. W., J. A.Hernandez, T. Rippolon, andG. McCarkv. 1979. Technique for simultaneous sampling of plankton- ic fish eggs and larvae at three depths. Prog. Fish-Cult. 41:158-160. Bigelow, H. B., and W. C. Schroeder. 1953. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv., Fish. Bull. 53, 577 p. CONOVER, N. 1958. Investigation of the white perch, Morone ameri- cana (Gmelin), in Albemarle Sound and the lower Roanoke River, North Carolina. M.S. Thesis. North Carolina State Univ.. Raleigh, 58 p. Elrod, J. H., and T. J. Hassler. 1969. Estimates of some vital statistics of northern pike, walleye, and sauger populations in Lake Sharpe, South Dakota. U.S. Dep. Inter.. Bur. Sport Fish. Wildl., Tech. Pap. 30, p. 3-17. Hergenrader, G. L, and Q. P. Bliss. 1971. The white perch in Nebraska. Trans. Am. Fish. Soc. 100:734-738. Hildebrand, S. F., and W. C. Schroeder. 1928. Fishes of Chesapeake Bay. U.S. Bur. Fish., Bull. 43(1), 366 p. HOLSAPPLE, J. G., AND L. E. FOSTER. 1975. Reproduction of white perch in the lower Hudson River. N.Y. Fish Game J. 22:122-127. Larsen, A. 1954. First record of the white perch (Morone americana) in Lake Erie. Copeia 1954:154. Lauer, G. J., W. T. Waller, D. W. Bath, W. Meeks. R. Heffner. T. Ginn, L. Zubarik. P. Bibko. and P. C. Storm. 1974. Entrainment studies on Hudson River organisms. In L. D. Jensen (editor), Proceedings of the Second En- trainment and Intake Screening Workshop, p. 37-82. The Johns Hopkins University Cooling Water Research Project, Rep. 15. LE Cren, E. D. 1951. The length-weight relationship and seasonal cycle in gonad weight and condition in the perch (Perca flunatilis). J. Anim. Ecol. 20:201-219. 609 FISHERY BULLETIN: VOL. 80, NO. 3 Leim, A. H., and W. B. Scott. 1966. Fishes of the Atlantic coast of Canada. Fish. Res. Board Can., Bull. 155, 485 p. Mansueti, R. J. 1961. Movement, reproduction and mortality of the white perch, Roccus americanus, in the Patuxent Estuary, Maryland. Chesapeake Sci. 2:142-205. Marcy, B. C, Jr. 1976. Fishes of the Lower Connecticut River and the ef- fects of the Connecticut Yankee Plant. In D. Merriman and L. M. Thorpe (editors), The Connecticut River Eco- logical Study, The impact of a nuclear power plant, p. 61-113. Am. Fish. Soc, Wash., D.C. Marcy, B. C, Jr., and F. P. Richards. 1974. Age and growth of the white perch Morone ameri- cana in the lower Connecticut River. Trans. Am. Fish. Soc. 103:117-120. MCHUGH, J. L., AND J. J. C. GlNTER. 1978. Fisheries. Mesa New York Bight Atlas Monograph 16. New York Sea Grant Institute, Albany, N.Y., 129 p. Miller, L. W. 1963. Growth, reproduction and food habits of the white perch, Roccus americanus (Gmelin), in the Delaware River estuary. M.S. Thesis, Univ. Delaware, Newark, 62 p. Perlmutter, A., E. E. Schmidt, and E. Leff. 1967. Distribution and abundance of fish along the shores of the lower Hudson River during the summer of 1965. N.Y. Fish Game J. 14:47-75. RlCKER, W. E. (editor). 1968. Methods for assessment of fish production in fresh waters. Int. Biol. Prog. Handb. 3, 313 p. Blackwell Sci. Publ., Oxford, Engl. ROUNSEFELL, G. A., AND W. H. EVERHART. 1953. Fishery science: its methods and application. John Wiley & Sons, Inc., N.Y., 444 p. Scott, W. B., and W. J. Christie. 1963. The invasion of the lower Great Lakes by the white perch, Roccus americanus (Gmelin). J. Fish. Res. Board Can. 20:1189-1195. Sheri, A. N., and G. Power. 1969. Annulus formation on scales of the white perch, Morone americanus (Gmelin), in the Bay of Quinte, Lake Ontario. Trans. Am. Fish. Soc. 98:322-326. Taub, S. H. 1969. Fecundity of the white perch. Prog. Fish-Cult. 31:166-168. Thoits, C. F. 1958. A compendium of the life history and ecology of the white perch, Morone americana (Gmelin). Bull. Mass. Div. Fish Game 24:1-16. Trautman, M. B. 1957. The fishes of Ohio. Ohio State Univ. Press, Co- lumbus, 683 p. Wallace, D. C. 1971. Age, growth, year class strength, and survival rates of the white perch, Morone americana (Gmelin) in the Delaware River in the vicinity of Artificial Island. Chesapeake Sci. 12:205-218. Woolcott, W. S. 1962. Infraspecific variation in the white perch, Roccus americanus (Gmelin). Chesapeake Sci. 3:94-113. 610 IDENTIFYING CLIMATIC FACTORS INFLUENCING COMMERCIAL FISH AND SHELLFISH LANDINGS IN MARYLAND1 Robert E. Ulanowicz,2 Mohammed Liaquat Ali,3 Alice Vivian,4 Donald R. Heinle,5 William A. Richkus,6 and J. Kevin Summers6 ABSTRACT In five of the seven most important commercial fisheries of Maryland an appreciable portion of the annual variations in catch can be linked with past fluctuations in the physical environment. The harvest figures were compared with appropriate annual characterizations of 40 years of daily environmental records using a variation of the stepwise multiple linear regression technique. The criterion for entry of a term into the regression was how well the given variable improved the pre- diction of a randomly chosen independent subset of catch figures. The identification of spurious predictor variables becomes less probable under this criterion. The results should help in the organization of further research and management concerning these species and may afford esti- mates of catches 1 or more years into the future. Annual population levels of commercially har- vested fish and shellfish usually fluctuate widely over the years. Such variation is often attributed to the influence of important environmental var- iables, such as water temperature, upon spawn- ing success (Sissenwine 1978). Environmental variables may directly affect the mortality rates of prerecruits or indirectly exert influence by altering the abundance of forage or predators. Many other aspects of the ecosystem may also alter population levels (Cushing 1975); however, exact causative mechanisms in most fisheries are seldom known. Year-to-year fluctuations in the abundance of exploited species will determine in part the magnitude of annual harvest of those species. But the relationship will not be completely deter- ministic, since landings will also be influenced by socioeconomic factors (e.g., prices and costs as they affect effort) as well as biological factors un- related to exploitation (Ricker 1978). Despite •Contribution 1235, Center for Environmental and Estua- rine Studies of the University of Maryland. 2University of Maryland, Chesapeake Biological Labora- tory, Solomons, MD 20688. 3University of Maryland, Chesapeake Biological Labora- tory, Solomons, Md.; present address: Senior Scientific Officer, Fisheries Campus Chandpur, P.O. Baburhat, Dist Comilla, Bangladesh. 4University of Maryland, Chesapeake Biological Labora- tory, Solomons, Md.; present address: 517 Flag Harbor Drive, St. Leonard, MD 20685. 5University of Maryland, Chesapeake Biological Labora- tory, Solomons, Md.; present address: CH2M Hill, 1500 114th Ave. SE., Bellevue, WA 98004. 6Martin Marietta Corporation, Environmental Center, Bal- timore, MD 21227. these many complicating factors, significant cor- relations between various environmental vari- ables and commercial landings of various species have been found in a number of fisheries. Dow (1977), for example, showed that temperature correlates well with the landings of 24 species of finfish, Crustacea, and mollusks off the coast of Maine. Sutcliffe( 1972) found freshwater input to St. Margaret's Bay to be a good indicator of fish- eries production, possibly because of the stimula- tion of production caused by the nutrients in the runoff water. However, in neither case were the observed relationships demonstrated to help in predicting harvests, nor were the specific mech- anisms responsible for the observed relation- ships rigorously delineated. In contrast, a regres- sion model of brown shrimp landings off North Carolina, using temperature and salinity as in- dependent variables, was found to be a reason- ably accurate predictor of future landings (Hunt et al.7). Hunt's model has proven to be a useful management tool for this fishery, helping fisher- men to decide how to gear up for the coming sea- son.8 Multiple linear regression has likewise been employed to explain variations in catch (e.g., Flowers and Saila 1972; Driver 1976). Only Manuscript accepted January 1982. FISHERY BULLETIN: VOL. 80, NO. 3, 1982. 7Hunt, J. H., R. J. Carroll, V. Chinchilli. and D. Franken- burg. 1979. Relationship between environmental factors and brown shrimp production in Pamlico Sound, North Caro- lina. Completion Report for Project 2-315-R, North Carolina Department of Natural Resources, Morehead City, N.C., 37 p. 8M. W. Street, Chief, Fisheries Management Section, Divi- sion of Marine Fisheries, North Carolina Department of Nat- ural Resources and Community Development, P.O. Box 769, Morehead City, NC 28557, pers. commun. April 1981. 611 FISHERY BULLETIN: VOL. 80, NO. 3 in the former instance, however, was there an attempt to validate the regression using indepen- dent data. Thus, the value of correlative or regression models of fisheries is twofold: First, significant correlations can serve to guide research into identifying the causes of annual variation in catch; secondly, if validated, such models may forecast harvest in cases where more detailed de- terministic models cannot be developed for lack of information. The issue of model validation is especially im- portant. Correlational models which best regress to the available data are often not the best predic- tors (Saila et al. 1980). In an effort to overcome this difficulty we have employed an amended version of stepwise regression analysis which does not rely solely on overall good ness-of- fit, but rather identifies those variables most likely to provide good predictions of data points not used in the actual regression. To our knowledge multiple correlational mod- els of the relationships between environmental variables and commercial landings in the Mary- land portion of Chesapeake Bay have not been attempted in an algorithmic fashion. Because most of the dominant species reproduce in Mary- land waters, the influence of environmental variation on harvest of these species may be par- ticularly strong. Thus, we have developed multi- variate regressions of the landings of major commercial species, using as predictors those environmental variables considered to have bio- logical significance for the species being exam- ined. Although measures of catch per unit effort (CPUE) would have been preferable as indica- tors of stock size, adequate effort data were not available. The results provide valuable insight into factors which may contribute to determining the population dynamics of these species and may also prove to be of value in establishing man- agement practices. SPECIES ADDRESSED AND DATA AVAILABLE Seven dominant species in Maryland landings were selected for analysis. American oyster, Crassostrea virginica; blue crab, Callinectes sapidus; soft shell clam, Mya arenaria; and striped bass, Morone saxatilis, were chosen be- cause they are the four species which yield the greatest dollar value to the Maryland economy. Menhaden, Brevoortia tyrannus, and alewife, Alosa pseudoharengus and A. aestivalis arbi- trarily combined, were selected because they have been dominant in number of pounds har- vested. The bluefish, Pomatomus saltatrix, was included because its harvest has increased dra- matically in recent years, and there was interest in determining if this increase might be related to environmental variation. A 33-yr record of annual catch data for 24 com- mercial species was available from records maintained by the Chesapeake Biological Lab- oratory and the NO AA Current Fisheries Statis- tics series. These records report the total Mary- land landings (Chesapeake Bay and Atlantic Ocean) for each year. The Chesapeake Bay por- tion of the harvest heavily dominates the catches of the chosen species (85% or more of total). Be- cause of the difficulty in obtaining sufficient information to separate Bay catch from the State total, the total was assumed to be representative of Chesapeake Bay. ANNUAL CHARACTERIZATIONS OF ENVIRONMENTAL DATA The environmental variables for which long- term records exist are water temperature, air temperature, salinity, and precipitation. All four have potential relevance to the levels of commer- cial harvest. Cross correlative relationships among these variables would be accounted for in the stepwise multivariate regression procedure employed in the analysis (discussed below). Daily recordings of these variables exist for a period exceeding 40 yr as taken from the Chesapeake Biological Laboratory pier at the mouth of the Patuxent estuary in Solomons, Md. Because this location is central to the Maryland portion of Chesapeake Bay, these data were assumed to be characteristics of conditions in the bay as a whole. Gaps in air temperature and precipita- tion from 1960 onwards were filled by data taken at the nearby Patuxent River Naval Air Test Center in Lexington Park, Md. While catch figures represented the total land- ings for a season, environmental data existed with much finer temporal resolution. Our goal was to pair each annual catch figure with a value of an environmental property which might be representative of the effect that variable had on the stock during the year the daily readings were accumulated. One straightforward way of char- acterizing a year is to calculate the annual average of the variable in question. The stock, 612 ULANOWICZ ET AL.: IDENTIFYINC. CLIMATIC FACTORS INFLUENCING MARYLAND LANDINGS however, may be more sensitive to shorter term deviations from this average. In an effort to quantify these deviations we devised four differ- ent ways of treating each of the original four time series to yield 26 annual series of environmental data. The first of these methods, calculating the annual average, has already been mentioned. But the annual mean conveys little information on the cumulative amount of stress or benefit ex- perienced by the populations because of the ex- treme high or low values of environmental vari- ables. To portray the cumulative effects of these deviations, we defined variables analogous to the degree-days of agricultural science. Here the effect of a variable is assumed to be manifested only when its value goes beyond a certain "bias- level." If, for example, the organism is assumed to be cold stressed when the water temperature falls below 4°C, then 3 successive days of 1°C water temperature will contribute 9 degree-days towards the index of cold stress. For each of the four variables recorded, a high and a low bias level were chosen so that when conditions exceeded these bounds at Solomons, we estimated that there were significant regions throughout the Maryland section of the Chesa- peake Bay where fish and shellfish were prob- ably stressed (or benefited) by the large excur- sions from the norm. These bias levels are shown in Table 1. Of course, the fishery might be responding to individual episodes of stress, rather than the yearly cumulative value. We, therefore, elected to measure the lengths of the longest episodes during a year that a variable was beyond the bias values. These episodes were intermediate time- scale phenomena (on the order of 1 to several weeks), and we wished to avoid contamination from high frequency events. For example, salin- ity may have remained above 16.2 ppt for all of a 28 d period, save on the 15th day when it dropped to 16.1 ppt. To characterize the episode as 14 d in duration would clearly be erroneous. To avoid such contamination we chose a "gap-interval" for Table 1.— Parameters used in calculating cumulative variables and episodes. Variable High bias Low bias Salinity 16.2 V, 10.5V. Water temperature 26.5°C 4°C Air temperature 30°C 0°C Precipitation 3 cm/d' 0 cm/d 'This value becomes 0.01 cm/d in calculating rain episodes, i.e., any day it rains is counted each variable ranging from 3 to 5 d. If the vari- able went beyond the bias level for a duration not exceeding the gap interval, the episode was not terminated, although the days on which the lapse occurred were not tallied in the episode length. Thus, the episode of high salinities men- tioned above would be counted as 27 d. Finally, the possibility remains that the stocks might be acutely affected by short-term, intense stresses. We felt this eventuality would be re- flected in the annual extremes of each variable. These four operations, when applied to the four daily time series, yielded 26 annual time series of interest. (Cumulative and extreme low precipi- tations are uniformly zero by definition, and pro- vide no information.) These series constituted the possible "predictor vectors" from which those yielding the best multiple regressions would be chosen. The values for the 26 variables calcu- lated for the years 1938-76 are listed in Ulano- wicz, Caplins, and Dunnington (1980). REGRESSION METHODOLOGY In most fish stocks, year class size is considered to be established by the juvenile stage (Cushing 1975). For example, oyster spat set (analogous to juvenile stages of finfish) is a good indicator of spawning success (Galtsoff 1964). Thus, recruit- ment (and subsequently harvest) is often corre- lated to those conditions in the past which helped determine the level of juvenile success. In popu- lations where all individuals in a year class are recruited into the fishery at the same age, and annual landings consist primarily of a single year class, a significant correlation might be obtained when the environmental variable in question was lagged against landings by the number of years equivalent to the age at recruit- ment. For most species harvested in Maryland, re- cruitment is not simultaneous for all members of a year class; landings in 1 y r may consist of mem- bers of several or many year classes. Thus, envi- ronmental characteristics important to estab- lishing year class strength may be partially correlated with landings recorded over several years, and vice versa. In order to account for such extended partial recruitment, stepwise regres- sions were employed, allowing the contribution of a given environmental variable to be assessed by successively lagging that independent vari- able by annual increments so as to encompass the lifespan of most of the stock being fished, i.e., 613 FISHERY BULLETIN: VOL. 80, NO. 3 harvests are regressed against conditions during the same year, 1 yr ago, 2 yr ago, etc. In the case of species which do not spawn in Maryland and where environmental conditions in the Chesapeake Bay would not influence year class size (i.e., menhaden and bluefish), any sig- nificant correlations arising would either be the result of how the Chesapeake Bay environmental conditions influence the availability of the spe- cies to Maryland fishermen, or how its con- ditions might be correlated with critical condi- tions at the remote spawning site. Oysters and striped bass, being the longer lived of the species of interest, were regressed against conditions as long ago as 9 yr in the past. Conditions affecting the remaining species were investigated over the past 5 yr. As mentioned in the introduction, we wished to limit our attention to those variables which are most likely to be good predictors of future har- vests. In conventional stepwise regression, that variable which increases the goodness-of-fit by the greatest amount (usually measured by R2, the percentage of the variance explained by the model) is included as the next variable in the re- gression equation. We chose instead to enter that variable which improved the model prediction of independent data points by the greatest amount. To implement this alternate criterion we ran- domly chose 25% of our data to be reserved for testing. At each step in the regression all of the remaining variables were entered in turn into a least squares multiple regression using the re- maining 75% of the data (employing subroutine GLH from the Univac9 STAT-PAK library). The coefficients derived for each entry were then used to see how well they would predict the test values of the dependent variable. That variable whose inclusion generated the greatest improve- ment in fitting the test data (as measured by the sum of the squares of the deviations) was entered into the prediction equation. Ivakhnenko et al. (1979) suggested that one should continue to include terms until the predic- tion can no longer be improved. It became appar- ent during the first few runs, however, that with six or eight degrees of freedom in the test data, statistically insignificant improvements in pre- dicting the independent data were occurring. Accordingly, no variable was added to the pre- diction equation when its F-to-enter statistic 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. (calculated on the fit to the test data) dropped below 3.5. This somewhat low level of confidence (a little below 90%) was chosen so as not to ex- clude potential predictors early in the screening process. It should also be pointed out that be- cause of the small number of points in the test data, a relatively large percentage of the error in the test data must be explained to meet this F-to- enter criterion (40-60% in our trials). By separating test and regression data in a random manner, it was always possible that by chance the set of test data chosen for any single run was unduly influenced by high or low pro- duction years. Such bias in the test data could result in a predictor accurate only under particu- lar circumstances. Hence, it was necessary to run several (and in the later stages of the screen- ing process, many) trials with different ran- domly chosen sets of test data. Presumably, the predominance of any single sequence of predic- tor vectors among the various trials would be an indication that the associated model might be a robust tool for forecasting. Once the functional form of the best predictor has been chosen, the parameters of this equation are redetermined using the full data set. The sequence of searches outlined above should provide a necessary (although not suffi- cient) test for prediction formulae. RESULTS AND DISCUSSION To facilitate easy recognition of the environ- mental variables in the regression equations that are to follow, we adopt a two-letter, one-digit code to designate each of the 260 possible predic- tor vectors. The first letter will be either A, C, E, or X according to whether the processed variable represented an annual average, cumulative de- viation, episode, or extremum, respectively. The second letter will designate air temperature, water temperature, daily precipitation, or salin- ity by T, W, P, or S, respectively. When it is necessary to distinguish between high or low de- viations of these variables, the low values will be designated by writing the second letter in the lower case. Finally, the digit will designate the number of years lag behind the harvest figures. As examples, Cs3 would indicate cumulative low salinity 3 yr in the past, whereas EW2 would de- note the longest episode of high water tempera- tures 2 yr ago. After the field of predictor variables for each fishery had been narrowed to five or fewer, 1,000 614 ULANOWICZ ET AL.: IDENTIFYING CLIMATIC FACTORS INFLUENCING MARYLAND LANDINGS Monte Carlo trials were run for each species using different random combinations of test data. In five of the seven species considered, pairs of two variables were identified frequently enough to warrant their being cited as potential predictor formulae in Table 2. In one case (blue crab) no variables appeared often enough in the trials to warrant reporting a predictor equation. By contrast several sequences of oyster predic- tors appeared often, but no sequence predomi- nated in the trials. About five separate sequences appeared with almost equal frequency. Hence, no formula for oysters is cited. In the clam regression, Cwl appeared as the primary predictor in over 50% of the trials. In roughly 20% of these instances CS2 was included as secondary predictor. No predictor was chosen 12% of the time. When the two selected variables In Maryland, soft shell clams spawn in spring and fall (Pfitzenmeyer 1962). However, the spring set each year is almost totally eradicated because of predation by benthic feeding fish and crabs which migrate onto Maryland clam grounds each spring and leave each fall (Holland et al.11). Factors influencing the strength of the fall set (which occurs from October through De- cember) and the ensuing survival of juveniles have not been identified. It appears that these factors are the ones most likely to have the great- est effect on the magnitude of commercial clam landings. Since Maryland is near the southern "Holland, A. F., N. K. Mountford. M. Hiegel, D. Cargo, and J. A. Mihursky. 1979. Results of benthic studies at Calvert Cliffs. Final Report to Maryland Power Plant Siting Pro- gram. Ref. No. PPSP-MP-28. 229 p. Martin Marietta Labor- atories, Baltimore, Md. Table 2.— Potential predictors of landings (in metric tons) of designated species; see text for code to predictor variables. Multiple Species Regression fl2 F df Soft clam, Mya arenaria H, = 372.4 + 13.56Cw1 + 3.765CS2 0.60 11.1 22 Menhaden, Brevoortia tyrannus Hm = 888.4 + 45.99Ep5 - 9.126CT4 0.53 11.1 30 Bluefish, Pomatomus sal tat hx H„ = -48.20 + 1.948Ep5 + 0.1693Cs2 0.60 14.8 29 Alewives, Alosa aestivalis and A. pseudoharengus H. = 3.344 - 24 19Ep3 + 93.80Xt2 0.51 10.5 30 Striped bass, Morone saxatilis H, = 7,414 - 446.5AT3 + 2.435CH 0.45 8.3 30 were finally regressed against the entire data set, 60% of the total variance was explained, 49% by Cwl alone. Environmental data were avail- able to assess the predictive value of this equa- tion for the year 1977. As can be seen in Figure 1, this projected value has a large deviation from the recorded measure, but this deviation falls within the range of errors in the hindcast. Interpretation of this equation in terms of causality is complicated by the absence of effort data. For example, the effects of the rise in number of licensed clammers (from 3 in 1952 to 100 in 1957 to 200 in 1979 [Richkus et al.10]) on catch cannot be accounted for, and they may have been substantial. Still, the strong correla- tion between cumulative low water temperature lagged 1 yr and catch suggests a causal relation- ship. I0Richkus, W. A., J. K. Summers, T. T. Polgar, and A. F. Hol- land. 1980. A review and evaluation of fisheries stock man- agement models. Martin Marietta Laboratories, Baltimore, Md., 177 p. 03 O z □ z < 2 < 2000- 1000- i i I i | I I I — I | I I — I I | I I i i | i — n- 1950 1960 1970 YEAR 1980 Figure 1.— Maryland soft clam landings in metric tons from 1952 to 1977 (solid line) and landings predicted using the re- gression model (dotted line) (Table 2). (Landings for 1977 did not enter into the derivation of the model.) Environmental fac- tors were a cumulative low deviation in water temperature (with a 1-yr lag behind the harvest figure), and a cumulative high deviation in salinity (with a 2-yr time lag). 615 FISHERY BULLETIN: VOL. 80, NO. 3 boundary of the geographical range of soft-shell clams (Manning12), cold water temperatures may, in some unexplained way, enhance the sur- vival of a previous year's set. Manning and Dunnington (1956) showed that Maryland clams grow at a rapid rate, achieving legal size (2 in, 5.1 cm) at an age of 16 to 22 mo. Hence clams spawned in the fall of one year would enter the commercial fishery during the spring 2 yr later. Extreme low water tempera- tures generally occur in January or February of each year and during some years coincide with periods of high salinities. Thus, both variables in the regression model could be exerting an effect on juvenile clams from set to the age of 6-7 mo, when they are approximately 0.5 cm (0.2 in) in size. Low water temperature may delay move- ment of predators into Maryland waters, permit- ting juvenile clams to grow to a less vulnerable size. High salinities during the juvenile life stages could also favor growth and rapid matur- ation of clams. The remaining four regressions are composed of variables which are less readily explained. The two terms entering the menhaden regres- sion have 4 and 5 yr lags (Table 2). But menhaden which make up Maryland landings are of ages 2 and 3, with almost no 4-yr-old fish taken (Merri- ner13). Thus, any causal mechanism suggested by the regression would have to be a second genera- tion response, remembering that menhaden do not become sexually mature until ages 3 or 4. Ep5 appeared as the most important predictor in 37% of the trials with CT4 following as a second- ary predictor in 23% of those cases. Menhaden catch is depicted in Figure 2. Juvenile bluefish use Chesapeake Bay as a nur- sery area and there is the possibility that a dis- tinct Chesapeake Bay stock of bluefish exists (Kendall and Walford 1979). Bluefish, being a marine species, are generally not found in low salinity waters, and their distributions can be well defined by salinity patterns (Lippson et al. 1980). Thus, the precipitation variable entering the regression (Table 2) may reflect diminished nursery habitat caused by high precipitation, re- sulting in a decline of harvestable fish in future 5000 12Manning, J. H. 1957. The Maryland soft-shell clam in- dustry. Study Report 2, 25 p. Maryland Department of Re- search and Education, Solomons, Md. 13J. V. Merriner, Chief, Division of Fisheries, Southeast Fisheries Center Beaufort Laboratory, National Marine Fish- eries Service, NOAA, Beaufort, NC 28516, pers. commun. Sep- tember 1980. Figure 2.— Actual (solid line) and predicted (dotted line) catches in metric tons of menhaden, 1946-76, based on the re- gression model in Table 2. Environmental factors were an episode of low daily precipitation (with a 5-yr time lag behind the harvest figure), and cumulative high deviation in air tem- perature (4-yr time lag) which had a negative effect. years. However, age composition of Maryland bluefish catch is unknown, and the particular lags in the regression are not readily explained. Bluefish harvests are illustrated in Figure 3. Ep5 appears as the primary predictor in 56% of the trials run with Cs2 following in 23% of those instances. It is noteworthy that the same variable (Ep5) appears as the most useful predictor of both menhaden and bluefish. Both species are coastal spawners, and it is entirely possible that 250 1980 Figure 3.— Predicted (dotted line) and recorded (solid line) weights of bluefish landings in metric tons, 1947-76, based on the regression model in Table 2. An episode of low daily pre- cipitation (5-yr time lag), and cumulative low deviation in salinity (2-yr time lag) were the environmental factors. 616 ULANOWICZ ET AL.: IDENTIFYING CLIMATIC FACTORS INFLUENCING MARYLAND LANDINGS the same causal mechanism is affecting the catches of both fishes. Both species included in landings asalewives, A. pseudoharengus and A. aestivalis, areanadro- mous, tributary spawners in Maryland (Hilde- brand and Schroeder 1927). Thus, poor spawn- ing success could readily be related to low freshwater runoff caused by low precipitation. However, the age of first spawning of these spe- cies is from 3 to 5 yr, with the majority spawning at 4 or 5 ( Davis et al.14). The regression (graphed in Fig. 4) suggests the possibility that recruit- ment in Maryland occurs at a younger age, but data on the age distribution of the catch are un- available to confirm or refute this suggestion. The other variable entering the alewife regres- sion (Table 2) is lagged by 2 yr. Since fish taken in a given year would have been present in the Atlantic Ocean 2 yr before being harvested, this correlation is difficult to explain in a causal man- ner. Ep3 is the major predictor in 50% of the trials and is followed by Xt2 in 20% of those cases. The least significant of all the predictors cited is the one for striped bass (see Fig. 5). Both terms show a favorable correlation with cold air temperatures over a season. Cold seasons are "Davis, J., J. V. Merriner, W. J. Hoagman, R. H. St. Pierre, and W. L. Wilson. 1971. Annual Progress Report, Anadro- mous Fish Project. Proj. No. Va. AFC7-1, 106 p. Virginia Institute of Marine Science, Gloucester Point, Va. 01 a z Q z 1000 — 2000 Q Z I I I I 1940 l"..|.. ■■!■■■■ I 1960 YEAR I I I | I 1 1 1970 1980 Figure 5.— Predicted (dotted line) and tabulated (solid line) landings in metric tons of striped bass from 1944 to 1976, based on the regression model in Table 2. Environmental factors were high annual average air temperature (3-yr time lag) (negative effect) and cumulative low air temperature (1-yr time lag). conducive to greater amounts of ice formation along river edges. The scouring from ice floes contributes high quality detritus to the riverine system to supplement the food source for zoo- plankton, in turn providing the larvae with abundant food (Heinle et al. 1976). Boynton et al.15 have previously remarked that year class success correlates jointly with cold winters and high runoff. The chosen variables did not domi- nate the trials heavily. AT3 was the major pre- dictor in only 33% of the trials, one-third of which were accompanied by the variable Ctl. Xs4 ap- peared as the major predictor almost as often (25% of the time there was no major predictor), but did not result in a significant correlation with the full data. An examination of the power spectra of the errors of the five models ( using subroutine POW- DEN in Univac STAT-PAK) revealed no appre- ciable differences from the spectral pattern of random noise. CONCLUDING REMARKS Perhaps the most significant observations to be made from this exercise involve the compari- son of the results reported herein with those re- ported previously from a conventional search for Figure 4.— Annual landings (solid line) in metric tons of ale- wife, 1944-76, as compared with predicted values (dotted line), based on the regression model in Table 2. Environmental fac- tors were an episode of low daily precipitation (3-yr time lag) (negative effect) and an extremum of low air temperature (2-yr time lag). 15Boynton, W. R.. E. M. Setzler, K. V. Wood, H. H. Zion, M. Homer, and J. A. Mihursky. 1976. Potomac River fisheries program ichthyoplankton and juvenile investigations. Ref. No. 77-169CBL, 328 p. Center for Environmental and Estua- rine Studies, Solomons, Md. 617 FISHERY BULLETIN: VOL. 80, NO. 3 predictors using the same data (Ulanowicz, Ali, and Richkus 1980). The major predictors cited in the previous work were either identical to, or qualitatively similar to, the initial variables selected by the more usual analysis. In that earlier work up to seven terms appeared in one regression equation (F-to-enter criterion of 4.0), and R2 values ranged as high as 0.86 with four variables. Despite having dropped the F-to-enter criterion below the90% confidence level, the joint criterion that the variables chosen also be reason- ably good "internal predictors" appears to have resulted in a more stringent combined test for selecting variables. Fewer spurious predictors are likely to appear using the new criteria. Although the regression with the full set of data will not be as tight as might otherwise be pos- sible, there is less likelihood that predictions on independent data will be wildly in error. In the words of Ivakhnenko et al. (1979), the "fan of pre- dictions" has been narrowed. When the number of possible predictor vectors is large compared with the number of observa- tions (as it is in this study), there is concern that multiple regression R2 values can be in- flated (Rencher and Pun 1980). Fortunately, the method described herein does not rely on R2 values alone. Before a variable is chosen for fur- ther consideration, it must explain a significant fraction of the variance in several randomly assembled groups of test data. To see how well this might screen against including spurious variables, the search procedure for the men- haden predictor was rerun with the yearly obser- vations randomly scrambled. Out of 28 possible trials with the original data, at least one variable was added in exactly half the trials (with an aver- age F-to-enter of 9). In all but 2 of those 14 suc- cesses the first variable entered was identical (Ep). By contrast, only 5 successful trials were recorded with the scrambled data (average F-to- enter was 5), although one variable did appear in 3 of those successful trials. Nonetheless, there is an evident decrease in the frequency and num- ber of variables with successful F-to-enter ratios in the trials with scrambled data. The only spe- cies studied giving results nearly as poor as the scrambled data was blue crab, and those find- ings were disregarded. Unfortunately, the results of the present anal- ysis must still be viewed with caution. Although the possibility of identifying a spurious correla- tion as a predictor has been decreased, it cannot be totally eliminated. The fact that substantial portions of the variability in landings of all the species considered can be explained by a few en- vironmental variables suggests the important role which environmental conditions play in de- termining stock size. However, our inability to interpret many of these relatinships in a causal manner reflects both a lack of knowledge of mechanisms influencing fish population dynam- ics as well as an unfamiliarity with the auto and cross correlative relationships between the vari- ables introduced into the regression process. (Because the procedure employed was stepwise, true causal variables may have been displaced in the regressions by spurious variables which by chance were closely correlated. No detailed anal- ysis of the independent variable data sets was performed to address this issue. More analyses would be required to fully account for this possi- bility.) Despite these limitations, the analyses appear to have been fruitful, particularly in the case of the soft clam. As for the other species, the value of the models will be determined when sufficient data are available to assess their predictive value for future landings. Only then can it be ascer- tained whether any chosen predictor was spuri- ous or reflected some unknown causal relation- ship between environmental variation and stock dynamics. Meanwhile, the terms appearing in the regressions may engender new research projects into the mechanisms determining the sizes of these important fisheries stocks. ACKNOWLEDGMENTS This work is a result of research sponsored in part by the NOAA Office of Sea Grant, Depart- ment of Commerce, under grant no. 04-7-158- 44016. Mohammed Liaquat Ali's internship at the Chesapeake Biological Laboratory was jointly sponsored by the Directorate of Fisheries, Government of Bangladesh, and the World Bank. Alice Vivian was supported by the Envi- ronmental Protection Agency's Chesapeake Bay Program, Eutrophication Project, grant no. Sub R806189010. William A. Richkus and J. Kevin Summers were supported under a contract to the Martin Marietta Environmental Center from the Coastal Resources Division, Maryland Tide- water Administration. Edward Houde and Mar- tin Wiley provided comments helpful in revising the manuscript. The Computer Science Center of the University of Maryland donated some of the computer time used in this project. The authors 618 ULANOWICZ ET AL.: IDENTIFYING CLIMATIC FACTORS INFLUENCING MARYLAND LANDINGS would like to thank the journal referees for sug- gesting the separation of data into regression and verification subsets and the scrambling of the criterion vector to check for spurious predic- tors. LITERATURE CITED Cushing, D. H. 1975. Marine ecology and fisheries. Camb. Univ. Press, Camb., 278 p. Dow. R. L. 1977. Effects of climatic cycles on the relative abundance and availability of commercial marine and estuarine species. J. Cons. Cons. Int. Explor. Mer 37:274-280. Driver, P. A. 1976. Prediction of fluctuations in the landings of brown shrimp (Crangon crangon) in the Lancashire and West- ern Sea Fisheries District. Estuarine Coastal Mar. Sci. 4:567-574. Flowers. J. M., and S. B. Saila. 1972. An analysis of temperature effects on the inshore lobster fishery. J. Fish. Res. Board Can. 29:1221-1225. Galtsoff, P. S. 1964. The American oyster, Crassostrea rirginica Gme- lin. U.S. Fish Wildl. Serv., Fish. Bull. 64:1-480. Heinle, D. R., D. A. Flemer, and J. F. Ustach. 1976. Contributions of tidal marshlands to mid-Atlantic estuarine food chains. In M. L. Wiley (editor), Estua- rine processes. Vol. II. Circulation, sediments, and transfer of material in the estuary, p. 309-320. Acad. Press, N.Y. HlLDEBRAND, S. F., AND W. C. SCHROEDER. 1927. Fishes of Chesapeake Bay. Bull. U.S. Bur. Fish. 43(1), 366 p. IVAKHNENKO, A. G., G. I. KROTOV, AND V. N. VlSOTSKY. 1979. Identification of the mathematical model of a com- plex system by the self-organization method. In E. A. Halfon (editor). Theoretical systems ecology, p. 325-352. Acad. Press, N.Y. Kendall, A. W.-, and L. A. Walford. 1979. Sources and distributions of bluefish, Pomatomus saltatrix, larvae and juveniles off the east coast of the United States. Fish. Bull., U.S. 77:213-227. Lippson, A. J., M. S. Haire, A. F. Holland, F.Jacobs, J.. Jen- sen. R. L. Moran-Johnson, T. T. Polgar, and W. A. Rich- KUS. 1980. Environmental atlas of the Potomac estuary. Johns Hopkins Univ. Press, Bait., Md., 279 p. Manning, J. H., and E. A. Dunnington. 1956. The Maryland soft shell clam fishery: A prelimi- nary investigation report. Proc. Natl. Shellfish. Assoc. 46:100-110. Pfitzenmeyer, H. T. 1962. Periods of spawning and setting of the soft-shell clam, Mya arenaria, at Solomons, Maryland. Chesa- peake Sci. 3:114-120. Rencher, A. C and F. C. Pun. 1980. Inflation of R2 in best subset regression. Techno- metrics 22:49-53. RlCKER, W. E. 1978. Computation and interpretation of biological sta- tistics of fish populations. Dep. Environ. Fish. Mar. Serv., Ottawa, Bull. 191. Saila, S. B., M. Wigbout, and R. J. Lermit. 1980. Comparison of some time series models for the analysis of fisheries data. J. Cons. Cons. Int. Explor. Mer 39:44-52. Sissenwine, M. P. 1978. Is MSY an adequate foundation for optimum yield? Fisheries (Bethesda) 3(6):22-42. SUTCLIFFE, W. H., JR. 1972. Some relations of land drainage, nutrients, partic- ulate material, and fish catch in two eastern Canadian bays. J. Fish. Res. Board Can. 29:357-362. Ulanowicz, R. E., M. L. All and W. A. Richkus. 1980. Assessing harvests of pelagic and invertebrate fisheries of northern Chesapeake Bay in terms of envi- ronmental variations. Int. Counc. Explor. Sea Code C. M. 1980/H:43, 8 p. Ulanowicz, R. E.. W. C. Caplins, and E. A. Dunnington. 1980. The forecasting of oyster harvest in central Chesa- peake Bay. Estuarine Coastal Mar. Sci. 11:101-106. 619 AERIAL SURVEYS FOR MANATEES AND DOLPHINS IN WESTERN PENINSULAR FLORIDA A. Blair Irvine,1 John E. Caffin,2 and Howard I. Kochman1 ABSTRACT Low altitude aerial surveys were conducted to count West Indian manatees, Trichechns manatus, and bottlenose dolphins, Tursiops truncatus, in western peninsular Florida. A total of 554 manatees was observed in 297 groups. Most of the manatees (58.5%) were sighted in the Collier-Monroe Counties in shallow, brackish inshore areas. A total of 1,383 bottlenose dolphins was observed in431 herds, including 700 (in 146 herds) in the Gulf of Mexico, 491 (in 185 herds) in bays, and 192 (in 100 herds) in marsh-river habitats. West Indian manatees, Trichechus manatus, and bottlenose dolphins, Tursiops truncatus, occur in rivers, estuaries, and coastal areas in Florida (Moore 1953; Layne 1965; Hartman 19743; Irvine and Campbell 1978). Manatees are dis- persed throughout Florida waters during the summer, but concentrate around warmwater sources in winter (Hartman footnote 3; Irvine and Campbell 1978). Aerial surveys indicate that bottlenose dolphins are also well dispersed in coastal waters of Florida (Odell 1976, 1979; Leatherwood 1979; Odell and Reynolds 19804). However, localized distribution patterns and seasonal changes in distribution and abundance have only been documented in a few areas for manatees (Odell 1976, 1979; Irvine et al. 19785; Shane 19806) or dolphins (Odell 1976, 1979; 'Denver Wildlife Research Center, Gainesville Field Sta- tion, 412 NE. 16th Ave., Room 250, Gainesville, FL 32601. 2Denver Wildlife Research Center, Gainesville Field Sta- tion, Gainesville, Fla.; present address: U.S. Forest Service, P.O. Box A.D., Umilla, FL 32702. 3Hartman, D. S. 1974. Distribution, status, and conserva- tion of the manatee in the United States. Report to U.S. Fish and Wildlife Service, National Fish and Wildlife Laboratory, Wash., D.C. National Technical Information Service PB 81 140725. 'Odell. D. K., and J. R. Reynolds III. 1980. Distribution and abundance of the bottlenose dolphin, Tursiops truncatus, on the west coast of Florida. Report to the U.S. Marine Mam- mal Commission, Wash., D. C. National Technical Informa- tion Service PB 80-197650. 5Irvine, A. B., M.D.Scott, and S.H.Shane. 1978. A study of the West Indian manatee, Trichechus manatus, in the Banana River and associated waters, Brevard County, Florida. U.S. Fish and Wildlife Service, National Fish and Wildlife Laboratory, Final Draft Contract Report to John F. Kennedy Space Center, NASA, Kennedy Space Center, FL 33899. Con- tract No. CC 63426A, KSC-DF-112. 6Shane. S. H. 1980. Manatees (Trichechus manatus) in Brevard County, Florida: Abundance, distribution and use of power plant effluents. Report to Florida Power and Light Co., P.O. Box 13100. Miami. FL 33101. Contract No. 61552- 86540. Shane and Schmidly 19787; Irvine et al. 19798). The distribution of manatees and dolphins in various habitat types and salinities in Florida also is unclear. More information is needed to serve as a basis for sound conservation and management deci- sions because manatees and dolphins are pro- tected by the Marine Mammal Protection Act of 1972; manatees are also protected by the En- dangered Species Act of 1973. Southwestern Florida, encompassing Everglades National Park (ENP; Monroe County) and the Ten Thou- sand Islands (Collier-Monroe Counties), is of particular interest because this area has been relatively unaffected by human development. Abundance, habitat use, and herd size informa- tion is therefore of interest for comparison with more developed areas. We conducted a series of aerial surveys from July to December 1979 to examine the distribu- tion and relative abundance of manatees and dolphins from Bayport, Hernando County (lat. 28°32'N, long. 82°39'W), Fla., south to Flamin- go Ranger Station (ENP), Monroe County (lat. 25°08'N, long. 81°02'W), Fla. METHODS Surveys were conducted during five periods: 24 through 29 July, 6 through 11 and the 17th of Manuscript accepted December 1981. FISHERY BULLETIN: VOL. 80, NO. 3 1982. 7Shane, S. H., and D. J. Schmidly. 1978. The population biology of the Atlantic bottlenosed dolphin, Tursiops truncatus, in the Aransas Pass area of Texas. Report to U.S. Marine Mammal Commission, Wash., D.C. National Technical In- formation Service PB 283-393. 8Irvine, A. B., M. D. Scott, R. S. Wells, J. H. Kaufmann, and W. E. Evans. 1979. A study of the movements and activities of the Atlantic bottlenosed dolphin, Tursiops truncatus, in- 621 FISHERY BULLETIN: VOL. 80, NO. 3 September, 2 through 8 October, 2 through 8 November, and 3 through 9 December 1979. Weather permitting, surveys were conducted on consecutive days in a chartered Cessna9 172 aircraft at an airspeed of about 160 km/h and an altitude of about 150 m. The final day of the Sep- tember survey was postponed until 17 Septem- ber because of adverse weather caused by Hur- ricane Frederic. The flight on 6 December was shortened, and flights scheduled for 7 and 8 December were cancelled due to inclement weather. The cancellation of those flights pre- vented December coverage of Charlotte Harbor and associated rivers, all of the Caloosahatchee and Orange Rivers, and the area from Estero Bay (Lee County) south to the Broad River (Mon- roe County) in ENP. The Whitewater Bay area of ENP was surveyed on 9 December 1979. After the July surveys, an extra survey day was added to the schedule, and daily coverage was redis- tributed to shorten flights in south Florida. Daily surveys lasted from 2 h 25 min to 6 h 21 min (x = 3 h 52 min). Flights usually began between 0730 and 0800 h. The right door of the aircraft was removed to increase visibility on the 7 September flight and on all flights in subsequent months. One observer was seated in the right front and another in the left rear. Sighting locations of all manatees and dolphins were noted on charts of each earea by the forward observer. Comments were dictated into a cassette tape recorder, or noted directly on the chart. Calves were defined as small manatees or dolphins closely associating with larger animals of approximately twice their size (after Irvine and Campbell 1978). Dolphins or manatees with- in an arbitrary distance of about 100 m of con- specifics were counted as being in the same "herd" or group. Use of the term "herd" to de- scribe social aggregations of dolphins is well established in the literature by Norris and Dohl (1980), but "herds" of manatees are not known to occur (Hartman 1979; Reynolds 1981). Flight routes were marked on maps of the en- tire western Florida study area to facilitate con- sistent coverage on successive surveys. The routes were selected to cover probable manatee habitat (Hartman footnote 3; Irvine and Camp- bell 1978). Survey routes generally followed the 2 m bottom contour. The deepwater shipping channel was also surveyed in Tampa Bay. Pilots used the route maps to navigate, leaving the ob- servers free to scan for animals. The plane de- viated from the route only to investigate sight- ings and to count or photograph animals. Areas surveyed included 1) bays and estuaries; 2) the Caloosahatchee River to the Ortona Lock in July and to Moore Haven on other surveys; 3) canals, bayous, rivers, and creeks (>1 m deep) up to 25 km inland; 4) the Intracoastal Waterway (ICW); 5) coastal areas to 0.5 km offshore, or to depths of about 2 m where shoals extended well offshore (Pasco and Hernando Counties). Sighting locations on the flight record charts were categorized into three habitat types: 1) off- shore: the Gulf of Mexico, 2) bay-estuary: bays, estuaries, and large rivers with direct access to the Gulf of Mexico, and 3) marsh-river: complex marsh habitats (Leatherwood and Platter10), in- land bays (Monroe County), and narrow rivers. Using criteria from Remane and Schlieper (1971), salinity at each sighting location was sub- sequently classified as fresh «0.5%osalt), brack- ish (0.5 to 30%osalt), or marine (>30%osalt) based on available reports (E.P.A.11; Wang and Raney 197912; U.S. Department of Commerce 1973; Weinstein et al. 1977; Schmidt and Davis 197813). Offshore habitats were always catego- rized as marine, even though salinities in some areas might have been influenced by tide and freshwater runoff from recent storms. Relative survey effort was estimated as the percentage of total flight time in each habitat and salinity type. Patterns of relative abundance and mean herd or group size were evaluated using chi-square and analysis of variance (ANOVA) procedures (Sokal and Rohlf 1969). Multiple comparisons among means were analyzed with Duncan's eluding an evaluation of tagging techniques. Report to U.S. Marine Mammal Commission, Wash., D. C. National Techni- cal Information Service PB 298 042. 9Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 10Leatherwood, S., and M. F. Platter. 1979. Aerial assess- ment of bottlenose dolphins off Alabama, Mississippi and Louisiana. In D. K. Odell, D. B. Siniff, and G. H. Waring (edi- tors), Tursiops truncatus assessment workshop, p. 49-86. Re- port to U.S. Marine Mammal Commission, Wash., D.C. National Technical Information Service PD 291 161. "E.P.A. Water Quality Information Storage System (STQRET), 401 M. Street, SW., Wash., DC 20460. 12Wang,J. C.S., and E.C. Raney. 1971. Distribution and fluctuations in the fish fauna of the Charlotte Harbor Estuary, Florida. Charlotte Harbor Estuarine Studies. Mote Marine Laboratory, 1600 City Island Park, Sarasota, FL 33577. "Schmidt, T. W., and G. E. Davis. 1978. A summary of estuarine and marine water quality information collected in Everglades National Park, Biscayne National Monument and adjacent estuaries from 1879 to 1977. U.S. National Park Service, South Florida Research Center, P.O. Box 279, Home- stead, FL 33030. Report T-519. 622 IRVINE ET AL: AERIAL SURVEYS FOR MANATEES AND DOLPHINS Multiple Range Test (Steel and Torrie 1960). A square root transformation (\J herdsize + 0.5) was applied to the counts to make them suitable for parametric analysis (Steel and Torrie 1960). Computations were performed with programs of the Statistical Analysis System (Helwig and Council 1979) at the University of Florida, Gainesville, Fla. RESULTS Manatees Two hundred and ninety-seven groups of manatees, totaling 554 individuals, were ob- served during 121.8 survey hours (Fig. 1). Num- bers sighted (Table 1) and average number of individuals per groups (Table 2) varied by county and month. Total numbers of manatees sighted increased from September to November, but the total per county consistently increased only in Monroe County. Total counts were not statistically compared among counties because habitat type, weather, and amount of survey area were not equivalent. Ninety-four percent of the groups sighted con- sisted of one to four animals (Fig. 2). Group sizes were not observed with equal frequency, and more than half of the 297 sightings were of single animals (P<0.005; chi-square). However, 367 (66.2%) of the 554 manatees sighted were in groups. Pooled samples of all counties indicated that group size-frequency distributions did not vary significantly between months (F>0.80; chi- square). Mean group size for the pooled sample of all sightings was 1.9 (SE = 0.12). A subset of data, including only those counties with sightings in each month (Monroe, Lee, and Sarasota Coun- ties ), was analyzed as a two-way ANOVA. This analysis provided no evidence of a month by county interaction (P>0.85), indicating that any pattern of monthly variation in group size was comparable for those three counties. Monthly variation in average group size, analyzed as a separate one-way ANOVA for each county, was significant (P<0.05) only in Hillsborough County, due to high December counts at warmwater effluents. Numbers of manatees sighted were not pro- portional to the amount of survey time in each habitat type or salinity (F<0.005; chi-square). Pooled samples from all counties indicated that numbers of manatees sighted per month varied significantly by salinity and habitat (P<0.0005; chi-square). Except in December, substantially more manatees were sighted in marsh-river hab- itats than in other habitat types, and most were in brackish water (Table 3). From 51 to 100 manatees, representing 54.3 to 75.7% of those sighted on July to November sur- veys and 58.5% overall, were observed in Monroe and Collier Counties (Table 1). Manatees were consistently sighted in Whitewater Bay, Cheva- lier Bay, and in the Lopez River (ENP, Monroe County), but the largest concentrations were found in Collier County from Marco Island to Chokoloskee. Manatees may have been over- looked if they were not near the surface or creating surface wakes or mud trails because of water turbidity (estimated visibility 0-0.5 m). A maximum of two manatees per survey was sighted in Charlotte Harbor (Charlotte County; Fig. 1 ) and small numbers of manatees were con- sistently sighted in Pine Island Sound, Matlacha Pass, San Carlos Bay, in the lower reaches of the Table 1.— Numbers of manatees and bottlenose dolphins observed, by county, during aerial surveys in western peninsular Florida from July to December 1979. C = calves. Manatees Bottlenose dolph ins County July Sept. Oct. Nov. Dec. July Sept. Oct. Nov Dec. Charlotte 4 5 6 0 '1 13+1C 22+1C 11+1C 1 '12+2C Collier 41 49+2C 63+1 C 49 (2) 9 20 11 29+1C (') De Soto 0 0 0 0 (2) 0 0 0 0 (2) Glades 0 0 0 1 (2) 0 0 0 0 (2) Hendry 0 0 0 2+2C (2) 0 0 0 0 (2) Hernando 0 0 0 0 0 4 0 7 8 0 Hillsborough 16 3 0 0 47+3C 30+2C 17+2C 17 0 3 Lee 15 17 + 1C 7 26 + 1C '12 34 37 + 1C 100+1C 32 '62+3C Manatee 6 0 3 4 0 8+2C 6 44+3C 13 44+1C Monroe 9+1C 10 20 48+3C '28 15 35+2C 26+1 C 66 '28+4C Pasco 0 0 0 0 1 2 17 + 1C 27 119+3C 59+3C Pinellas 0 0 0 0 7 56+1C 36+3C 39 73+2C 33+1 C Sarasota 2 6 11 14+1C 6 12 + 1C 60+4C 23+1 C 6 9 Total 93+1 C 90+3C 110+1C 144+7C 102+3C 183+7C 250+14C 305+7C 347+6C 250+14C 'Incomplete survey 2Not surveyed 623 FISHERY BULLETIN: VOL. 80, NO. 3 Figure 1. — Locations and numbers of manatees sighted during 1979 aerial surveys in western pen- insular Florida. Symbols: triangle = July, open square = September, open circle = October, solid circle = November, solid square = December, c = calf. Multiple sightings in localized areas are sum- marized. - 28° ► 26° 82° 624 IRVINE ET AL: AERIAL SURVEYS FOR MANATEES AND DOLPHINS _ 3 •-a JO O) F ci2 o O ra a! O T3 I* _o L. cS o c 0) Q. C > 3 0> c8 c 3 B 3 o £°- -° OS l u w a; -F -° .9 E to a; co o c /S 2« -£•2 o o> to o c o -a c Rt CO 0> c ea £ o o> 3 o u he a> be ct fc. > CM U Q.2 E § 3" CO o ~. ^ ,*. CO , . CM°2° I I — CO — ,-. — CM O CO CD 00 CO CO CM y_ CM O) r- CD co co r"-* -it co o lo _^ f^ _ co _ cm co *— ^ lo '*_;CM^;cDr^C0"o)„C0_O)"'l CNiScoSoiS^C^SoiSco'S., CD CO LO ' ^ „ I I o in Tt in tj- cd co ^Slh-coScviSbS^-CcNiS. CD^O^toOo'cNj'"' LcNJ ° ^ SoCuSC^S N. CO r- cb o • o I I o ~ 1- CO ^ .- *- o 0) ri in ■ o CO I I ""* ~; LO "4 "~- ' : ■" ^ o v o> " co • co2icN2.^c^°^^co-s^^ ^~ CM — O) — 7- f*- CM TT i- Tt 05 y- co ** ai cd o -"i" o *— C\J C\J LO LO CNJ TT "~- -r^l^ir>-^o,i;LO_-coco- - T— -O O O CO ■ r— -CM CO i- CO a> co co , , CM° CNjS. CNJ CO -T- r- co en co ^ ^^rr£co2.coC^°CNJ^cNi2.cNj£ cm t — co a> *- ■* in i>. — i- P P I ^* ■» i£ ■* P " *-" T O •,- I co "~ co "" cd 2 m ■" o ." "> ^ - " ur,2i-2.cNi2.^°^^coCcN,2. O ',' ^ „ „ _ V 2§ ' 2X5 X ,5 I I o ,- o _; LO ^cm° I I I CNJ I I o I I o o D w >. C O CD en CO T3 r CO -5 o CD a> O Q O I I T 00 CNJ S - ° 1- CNJ CO ■^•" — o o .« to „ r^ A en A, cnj CD - O i LO - CNJ ■ CNJ ~ CD | I I — CNJ CO CNJ >- CO O CD " I I o • o co CO co in c 0) m a T c CO aj "1 CM c en DO n c n o o c c (0 CD E t o °o _ to 5 I Slo-O £ Ol D Si ' o o n CD CD O o to to o CO ■S f 3 X> — co c; "> _ 2 o o _to CD CD c CO c o u CO CS "53 c eg to cozz i _l 2 5 CL CL CO 625 FISHERY BULLETIN: VOL. 80, NO. 3 190 r 180 s D Z 60 50 40 30 - 20 10 l~l n :j—i r i~i 123456789 GROUP SIZE 15 25 Figure 2.— Group size-frequency distribution of manatees sighted during aerial surveys from July through December 1979. A few manatees were consistently sighted be- tween Charlotte Harbor and Tampa Bay. The animals were sighted in Lemon Bay, Roberts Bay, and Little Sarasota Bay, and were often near the channel of the ICW. North of Sarasota County, manatees were pri- marily sighted in rivers emptying into Tampa Bay, including the Hillsborough, Alafia, Mana- tee, and Little Manatee Rivers. Our observations in Hillsborough and Manatee Counties may have been hampered in September by cloud cover and in October by turbid waters resulting from re- cent flooding. Manatees were observed near warmwater refuges described by Hartman (footnote 3) only during the December flights. A total of 40 mana- tees was sighted at the two warm effluents of the Gibsonton Phosphate Plant in the Alfia River (Hillsborough County). Eight manatees were sighted in the Big Bend Power Plant effluent (Hillsborough County), and a cow and calf were observed just offshore of the effluent. Five mana- tees were observed at the P. L. Bartow Plant effluent (Pinellas County), and two manatees were observed near the intake canal. A single manatee was sighted in the intake canal of the Anclote Power Plant (Pasco County). A maximum of three calves per county was sighted on any survey. Total percentage of calves sighted ranged from 0.9 to 4.9% on different surveys. Caloosahatchee River, and in Estero Bay (Lee County). Manatees were sighted in the Upper Caloosahatchee River (Glades and Hendry Coun- ties) only in November. Manatees were not sighted near the warmwater refuge in the Orange River, Lee County (Hartman footnote 3), but the area was not surveyed in December when ambient air and water temperatures were coldest. Bottlenose Dolphins Four hundred and thirty-one herds, totaling 1,383 bottlenose dolphins, were observed. The total number of dolphins sighted increased from July to November, but fluctuated in most coun- ties with no obvious trends (Table 1). Sightings were common in interior bays and rivers in ENP Table 3.— Manatee and bottlenose dolphin sightings in different habitat-types and estimated salinities. Manatees Bottlenose dolphins Habitat-type Salinity Habitat-type Salinity Off- Bay- Marsh- Fresh Brackish Salt Off- Bay- Marsh- Fresh Brackish Salt shore estuary river (<0.5%.) (0.5-30 %„> (>30%„) shore estuary river (<0.5%.) (0.5-30%.) (>30%. ) Mean group or herd size 1.29 2.38 1.69 1.93 1.85 1.93 4.79 265 1.92 0 2.19 3.97 (±SE) (0.13) (034) (0.10) (0.35) (0.14) (0.21) (0.70) (019) (0.19) (0.14) (0.44) No. of groups or herds 14 85 198 14 240 43 146 185 100 0 184 247 No. of animals 18 202 334 27 444 83 700 491 192 0 403 980 (percent) (3.2) (365) (603) (4.9) (80 1) (150) (50.7) (35.5) (13.9) (29.1) (709) Percent of survey time 17.7 44.3 380 8.9 50.1 41.0 177 44.3 38 0 8.9 50.1 41.0 626 IRVINE ET AL: AERIAL SURVEYS FOR MANATEES AND DOLPHINS and well into Tampa Bay. In the Charlotte-Lee Counties area, dolphins were common in the Gulf of Mexico, around Pine Island, and occasionally in the lower Caloosahatchee River. Most coastal sightings were within 0.5 km of the beach. Dolphin herd sizes were not sighted with equal frequency (Fig. 3); most sightings (56%) con- sisted of two or more animals (P<0.005; chi- square). Mean herd size for the pooled sample of all sightings was 3.2 dolphins/herd (SE = ± 0.26). Effects of county and month on average herd size in counties with sightings in each month (Table 2) were analyzed as a two-way ANOVA. The county by month interaction was significant (P<0.0005), indicating that monthly variations in dolphin herd sizes were not comparable among counties. A separate one-way ANOVA for each county indicated that monthly variation in herd size was significant (P<0.05) only in Lee County, due to a high December mean. Pooled sightings from all counties indicated that herd size-fre- quency distributions varied significantly be- tween months (P<0.001; chi-square), with fewer single dolphins and more large groups (>4) sighted in July and December. Numbers of dolphins observed were not pro- portional to the amount of survey time in differ- ent habitats and salinities (P<0.005; chi-square). More animals were observed off the beach and in saltwater (Table 3), but monthly trends were not apparent. Dolphins were not sighted in fresh- water. Pooled samples from all counties where sightings occurred indicated that numbers of dolphins sighted per month varied significantly by habitat and salinity (P<0.001). Most dolphins were sighted offshore in Pinellas and Sarasota Counties; more animals were in bay-estuary than in other habitats in Lee County; and most were in marsh-river habitats in Collier and Monroe Counties. A maximum of 5.3% calves was observed dur- ing both the September and December surveys. A high of 12.5% calves was sighted in Monroe County in December, but this total may not be representative because relatively few dolphins were sighted in the area during the abbreviated surveys (Table 1). DISCUSSION Manatees are usually sighted in small groups when away from warm water refuges. Eighty- six percent of the sightings during aerial surveys by Odell (1979) and 89% of the sightings by Hart- man (1979) were of one to four manatees. Our results and those from other surveys (Hartman 1979; Odell 1979; Reynolds 1981) indicate that the greater percentage of manatees sighted are found in groups, but one is the most common group size. Although Hartman (1979) suggested that manatees are "essentially solitary," solitary manatees are nevertheless a minority of the total numbers sighted. Odell (1979) sighted from 0 to 71 manatees 2 Z O 40 - QoQn nnnnr, a> l-l [-1 l—l n I— l,;(l I ;H-t;lf-l ,;■!-! 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 27 30 44 72 HERD SIZE FIGURE 3.— Herd size-frequency distribution of bottlenose dolphins sighted during aerial surveys from July through December 1979. 627 FISHERY BULLETIN: VOL. 80, NO. 3 during transect surveys conducted from July to December 1973 through 1976 in Monroe and Collier Counties. Hartman (footnote 3) sighted 45 manatees in Monroe and Collier Counties during a summer survey; Irvine and Campbell ( 1978) re- ported observing 163 manatees during a 1976 winter survey of the same area. Although abun- dance reports by different authors are not com- pletely comparable because of variability among survey methodologies, results of our study clear- ly support previous reports that southwestern Florida is a center of manatee abundance (Moore 1951; Hartman footnote 3; Irvine and Campbell 1978). Southerly shifts in the distribution of mana- tees in Florida during the fall were predicted by Moore (1951) and Hartman (footnote 3). Al- though total counts in Monroe and Collier Coun- ties generally increased during fall surveys, the significance of this trend is unclear. Increased sightings may correlate with changes in mana- tee abundance, but could also indicate that the animals are for some reason more easily ob- served in that season. In any event, a southerly autumn shift in distribution cannot be conclu- sively shown based on our data. The preponderance of manatee sightings in brackish water and marsh-river habitats occur- red in the areas of Collier and Monroe Coun- ties, which are characterized by that combina- tion of habitat and salinity. Inland bays in ENP and Ten Thousand Islands area of Collier County were classified as "marsh-river" habitat because access to the Gulf of Mexico is restricted by relatively narrow or shallow channels. Although the survey results may be general indicators of habitat use, they should be viewed with some caution because all habitat types were not sur- veyed equally, and local salinities may have varied seasonally due to runoff from rainfall. Irvine and Campbell (1978) reported the relative frequencies of manatee sightings in fresh, brack- ish, and salt water as 19.1, 42.5, and 38.3%, re- spectively, during winter surveys, and 35.2, 34.9, and 29.6% during a summer survey of the entire state. In contrast, 80% of the manatees sighted in our surveys were in brackish water (Table 3). The few sightings in Charlotte Harbor are noteworthy because manatees are often sighted by residents in this area (Moore 1951; Hartman footnote 3), and 36 manatees were counted in Charlotte Harbor during a summer aerial sur- vey by Hartman (footnote 3). Manatee use of the Bartow and Anclote power plants has not been specifically reported, but two sightings mapped by Irvine and Campbell (1978) were at these plants. We sighted few manatee calves (4.9% maxi- mum per survey) compared with other surveys. Calves made up 5.2% of the animals sighted by Odell (1979) in Collier and Monroe Counties in 1973 through 1976, but during a 1976 winter sur- vey of the same area, 10.4% of the manatees sighted were calves (Irvine and Campbell 1978). Leatherwood (1979) counted 9.9% calves in the Indian and Banana Rivers in eastern Florida, and Irvine and Campbell (1978) reported overall calf percentages of 9.6% in winter and 13.4% in summer from surveys of the entire state. Odell (1979) suggested that the tendency of calves to stay close to their mothers might result in fewer calf sightings in turbid waters, but this hypo- thesis has not been verified. Too few calves were sighted in our study to indicate seasonal repro- ductive trends. The dolphin sightings are of particular inter- est due to the paucity of information on T. truncatus in nearshore areas of western penin- sular Florida. The sightings were not analyzed for abundance and density estimates (see dis- cussion by Leatherwood et al. 1978), because flight routes were designed to optimize manatee sightings and were not flown as straight lines. Our observations can, however, provide informa- tion on dolphin herd size and habitat use. Average herd size (3.2 dolphins/herd) was con- siderably smaller than herd sizes reported from other aerial surveys in nearshore areas. In coastal waters of Alabama, Mississippi, and Louisiana, herd sizes averaged 25.2 dolphins with herd size in marshlands averaging 16.7 (Leatherwood and Platter footnote 10). Sub- groups contained a mean of 5 dolphins in sounds and 3.8 dolphins in marshes (Leatherwood and Platter footnote 10). Barham et al. (1980) re- ported that herd sizes averaged 6.95 dolphins in Texas, and Leatherwood (1979) reported herds averaging 8.20 dolphins in eastern Florida. In primarily estuarine areas of western Florida, group size (equivalent to herd size as used here) was 4.8 dolphins/group (Irvine et al. 1981). Differences between observed herd sizes have been attributed to the influence of geography and habitat on dolphin groups structure (Leath- erwood and Platter footnote 10), with largest groups found offshore (Wells et al. 1980). How- ever, criteria for defining "herds" or "subgroups" are rarely reported, and could influence differ- 628 IRVINE ET AL: AERIAL SURVEYS FOR MANATEES AND DOLPHINS ences in reported results. During our surveys we often encountered several herds within a few kilometers of each other, after not seeing dol- phins for distances of 20 km or more. Although such assemblages may have been dispersed sub- groups of a larger herd, they did not meet our arbitrary criteria for defining a "herd." Our spatial definition of herd may be unsatisfactory if bottlenose dolphins, like some other cetaceans, maintain acoustic contact over many kilometers (Payne and Webb 1971). Acoustic contact among free ranging groups of T. truncatus, however, has not been demonstrated, and we know of no more appropriate basis for defining herds from aerial sightings. The proportion of dolphin calves noted during our surveys (5.3%) is low when compared with other reports. Leatherwood (1979) observed 8.1- 10.1% calves during aerial surveys in eastern Florida in August, while Irvine et al. (footnote 8) reported a maximum of 11% from May to July during surface surveys near Sarasota, Fla. Shane and Schmidly (footnote 7) noted that calves constituted 7.6% of all dolphin sightings during surface surveys near Port Aransas, Tex., and Barham et al. (1980) sighted 9.3% calves from the air in the same area. Leatherwood14 observed 7.7% calves in 1974 and 7.9% calves in 1975 near the mouth of the Mississippi River. Our calf counts may be lower because we only counted very small animals; calves may grow to 2 m long within the first year (Leatherwood foot- note 14) and therefore large calves may not have been distinguished as such. SUMMARY AND CONCLUSIONS Most of the manatees (58.5%) were located in the Everglades National Park (Monroe County) and Ten Thousand Islands (Collier County) areas, and most (80.1%) were in brackish water. Because these areas are relatively undisturbed by human development, they have great value as locations to protect and study the endangered manatee. Dolphins were well dispersed in the survey area. Fifty -one percent were sighted in the Gulf "Leatherwood, S. 1977. Some preliminary impressions on the numbers and social behavior of free swimming bottle- nosed dolphin calves {Tursiops truncatus) in the northern Gulf of Mexico. In S. H. Ridgway and K. W. Benirshke (editors), Breeding dolphins: Present status, suggestions for the future, p. 143-167. National Technical Information Service PB 273 673. of Mexico, 49% were in brackish water, and none were located in freshwater. Seasonal movement patterns and reproductive trends based on calf sightings of both dolphins and manatees are unclear. While the survey re- sults are valuable as indicators of relative abun- dance, they are not useful to estimate total abun- dance because the percentage of animals not observed is unknown. ACKNOWLEDGMENTS This research was supported by the Bureau of Land Management under contract to the Nation- al Fish and Wildlife Laboratory (MOU-AA551- MU9-19). Jean Duke and C. R. Smith partici- pated in several survey flights. We thank James Kushland and Sonny Bass for assistance with flights over the Everglades National Park; Tom Fritts, Steve Leatherwood, James Powell, Tom O'Shea, Galen Rathbun, and Susan Shane made constructive comments on earlier versions of the manuscript. Esta Belcher prepared the illustra- tions and Luanne Whitehead typed the manu- script. LITERATURE CITED Barham, E. G., J. C. Sweeney, S. Leatherwood, R. K. Beggs, and C. L. Barham. 1980. Aerial census of bottlenose dolphin, Tursiops truncatus, in a region of the Texas coast. Fish. Bull., U.S. 77:585-595. Hartman, D. S. 1979. Ecology and behavior of the manatee Trichechus manatus in Florida. Am. Soc. Mammal. Spec. Publ. 5, 153 p. Helwig, J. T., and K. A. Council (editors). 1979. SAS users guide. SAS Inst. Inc., Raleigh, N.C. Irvine, A. B., and H. W. Campbell. 1978. Aerial census of the West Indian manatee, Tri- checus manatus, in the southeastern United States. J. Mammal. 59:613-617. Irvine, A. B., M. D. Scott, R. S. Wells, and J. H. Kaufmann. 1981 . Movements and activities of the Atlantic bottlenose dolphin, Tursiops truncatus, near Sarasota, Florida. Fish. Bull., U.S. 79:671-688. Layne, J. N. 1965. Observations on marine mammals in Florida waters. Bull. Fla. State Mus., Biol. Sci. 9:131-181. Leatherwood, S. 1979. Aerial survey of the bottlenosed dolphin, Tursiops truncatus, and the West Indian manatee, Trichechus manatus, in the Indian and Banana Rivers, Florida. Fish. Bull., U.S. 77:47-59. Leatherwood, S., J. R. Gilbert, and D. G. Chapman. 1978. An evaluation of some techniques for aerial cen- suses of bottlenosed dolphins. J. Wildl. Manage. 42: 239-250. 629 FISHERY BULLETIN: VOL. 80, NO. 3 Moore, J. C. 1951. The range of the Florida manatee. Q. J. Fla. Acad. Sci. 14:1-19. 1953. Distribution of marine mammals to Florida waters. Am. Midi. Nat. 49:117-158. NORRIS, K. S., AND T. P. DOHL. 1980. Structure and functions of cetacean schools. In L. H. Herman (editor), Cetacean behavior: Mechanisms and processes, p. 211-261. John Wiley and Sons, N.Y. Odell, D. K. 1976. Distribution and abundance of marine mammals in south Florida: preliminary results. In A. Thorhaug and A. Volkes (editors), Biscayne Bay: past/present/ future, p. 203-212. Univ. Miami Sea Grant Prog. Spec. Rep. 5. 1979. Distribution and abundance of marine mammals in the waters of the Everglades National Park. In R. M. Linn (editor), Proceedings of the First Conference on Scientific Research in National Parks, New Orleans, La., 9-12 November 1976. U.S. Dep. Inter., Natl. Park Serv. Trans. Proc. Ser. 5(1):673-681. Payne, R., and D. Webb. 1971 . Orientation by means of long range acoustic signal- ing in baleen whales. Ann. N.Y. Acad. Sci. 188:110-141. Remane, A., and C. Schlieper. 1971. Biology of brackish water. 2d ed. Wiley Inter- sci., N.Y., 372 p. Reynolds, J. E., III. 1981. Aspects of the social behavior and herd struc- ture of a semi-isolated colony of West Indian manatees, Trichechus manatus. Mammalia 45:17-48. SOKAL, R. R., AND F. J. ROHLF. 1969. Biometry. The principles and practices of statistics in biological research. W. H. Freeman and Co., San Franc, 776 p. Steel, R. D. G., and J. H. Torrie. 1960. Principles and procedures of statistics, with special reference to the biological sciences. McGraw- Hill Book Co., N.Y., 481 p. U.S. Department of Commerce. 1973. Surface water temperature and density-Atlantic Coast North and South America. U.S. Dep. Commer., NOAA, Natl. Ocean Surv. Publ. 31-1, 109 p. Weinstein, M. P., C. M. Courtney, and J. C. Kinch. 1977. The Marco Island estuary: a summary of a physico- chemical and biological parameters. Fla. Sci. 40:97- 124. Wells, R. S., A. B. Irvine, and M. D. Scott. 1980. The social ecology of inshore odontocetes. In L. H. Herman (editor), Cetacean behavior: Mechanisms and processes, p. 263-317. John Wiley and Sons, N.Y. 630 NOTES EFFECT OF SEASON AND LOCATION ON THE RELATIONSHIP BETWEEN ZOOPLANKTON DISPLACEMENT VOLUME AND DRY WEIGHT IN THE NORTHWEST ATLANTIC1 Biomass or "standing stock" is a routinely mea- sured index of abundance for studies of the inter- actions between trophic levels in the oceanic food web. Zooplankton biomass is usually reported as quantity of zooplankton per unit volume of water. Measures of quantity currently in use in- clude displacement volume (Frolander 1957; Sutcliffe 1957; Yentsch and Hebard 1957; Tran- ter 1960; Ahlstrom and Thrailkill 1963), wet weight (Nakai and Honjo 1962), dry weight (Lovegrove 1966), and carbon (Curl 1962; Piatt et al. 1969). These measures can be applied to a spe- cies at a specific developmental stage, to the en- tire population, or to all members of the commu- nity combined. Carbon and dry weight have been considered preferable because variability caused by interstitial and intracellular water is eliminated by either technique (Ahlstrom and Thrailkill 1963). They are not, however, practi- cal measures in some investigations because spe- cialized equipment is required and the tech- niques' destructive nature prevents further analysis of the sample. Measurement of displace- ment volume and wet weight are nondestructive, rapid, and use simple techniques which provide indexes of abundance, but do measure total mat- ter, including water. As an alternative, conversion factors or tables of "equivalents" have been used to transform dis- placement volume or wet weight into carbon or dry weight (Bsharah 1957; Menzel and Ryther 1961; Piatt et al. 1969; Be et al. 1971; Le Borgne 1975; Wiebe et al. 1975). However, plankton sam- ples represent aggregations of organisms at a particular time and place which change accord- ing to season, geographical location, and local environmental conditions. For these reasons, and because many conversion factors were calcu- lated with data produced by outdated techniques, the accuracy of interconversions between bio- mass measures has been questioned (Lovegrove 1966; Piatt et al. 1969; Beers 1974). Recently, Wiebe et al. (1975) provided conversion factors based on data collected from different oceanic areas over several years in order to account for seasonal and geographical variation in samples. This study explores whether a conversion equation based on data from numerous samples collected in contiguous areas during different seasons can account for sample variability and more accurately convert between biomass mea- sures than equations derived from smaller and smaller subsets of data. Unlike previous studies, an intense sampling strategy provided the means to derive equations to convert between displacement volume and dry weight for sam- ples from both broad and restricted geographic areas and for different seasons. Interconversion accuracy was verified with subsequent samples by comparing estimated values with field mea- surements. In addition, the relative variability and the values of both measures were compared in order to determine which index is more useful for these types of studies. Materials and Methods Plankton samples were collected by the Na- tional Marine Fisheries Service Northeast Fish- eries Center in conjunction with the Marine Re- sources Monitoring Assessment and Prediction (MARMAP) program (Sherman 1980). Sampling was conducted six times a year in 1977 and 1978 off the northeast coast of the United States in three adjacent areas: Gulf of Maine (GOM), Georges Bank (GB), and Southern New England (SNE). Sampling locations are shown in Figures 1 and 2. Paired 61 cm diameter bongo samplers fitted with 0.505 mm and 0.333 mm mesh nets were towed obliquely through the water column at a speed of 1.5-2.0 kn. Maximum sampling depth was 200 m or 5 m from the bottom in shal- lower areas, and tow duration was 5-15 min. A flowmeter was strung inside the bongo frame to measure the volume of water filtered. Plankton samples from the 0.333 mm mesh nets were used in this analysis. Samples were preserved in 5% buffered Formalin2 for at least 6 mo before anal- 'MARMAP Contribution MED/NEFC 81-8. FISHERY BULLETIN: VOL. 80, NO. 3, 1982. 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 631 01 o> > '- D en < s OS c o CO c« o> to 01 o Oi 3 3 s- u C 03 w C _o OS o _o bo c "5. E 03 CO u os D a 632 74* 72* 70* 68* 66* 1 1 1 1 1 " " ^i) °ALBATR0SS IV 78-02 AjjK«** •DELAWARE II 78-02 3 — T-t SO. NEW ENGLAND V GEORGES BANK LATE WINTER J I I 74* 72* 70* 68* 66 • 1 1 ^ALBATROSS IV 1 1 78-04 1 JnwV ' 1/ ♦ARGUS 78-04 / ' • • \ /- f 1 • • • \ < WLF — / • • • • • • v*" OF MAINE /• * • r-, ID \ • D \ X V * i V* • • V5" D^&j »7\x tw ia^-~ • va. ?'. • • T ~ w*" • • • • \ • •yV* « i«^* — '1 K* * i \ • ^) seorges BANK J \^ • 50 /V£"»f ENGL AND — l 1 1 1 1 A//Z7 SPRING 1111 - 44* - 42« 40* 74* 72° 70* 68" 66° 1 1 1 •ALBATROSS 1 78- 1 07 ^wft^ 6ULF ( ^ J^Z\ OF \ -Ti \maine^\ _°ALI0T 78 -01 r • / • I* • • • \y . • • . \ - *-.• • • \ • • X •^•y • •- / ^ GEORGES / ^^ • a^ \ BANK 50. i NEW ENGLAND - EARLY SUMMER - 1 1 1 1 ii i i- 76° 72 44° - 40* - 38° 1 1— BEL0G0RSK 78-01 GULF OF MAINE GEORGES BANK LATE SUMMER -1 I I 1_ BEL0G0RSK 78 SO. NEW ENGLAND EARLY - MID AUTUMN J I i i i 74* 72* 70* 68# 66* 1 1 1 1 1 -BEL0G0RSK78-04£1%) associated with the par- ticular equation, expressed as percent of total numbers. Cope pods are broken down into major species (>1%) with their abundance expressed as percent of total copepod numbers (in parentheses). Zooplankton data from Sherman et al. (1978, 1979). Season Late winter Early spring Midspring Late spring Early summer Midsummer Midautumn Late autumn Regression equation Variance of slope Log (DW) = -0.795 + 0.725 Log (DV) Log (DW) = -1 079 + 0.963 Log (DV) Log (DW) = -1.103 + 0.929 Log (DV) Log (DW) = -1.663 + 1.312 Log (DV) Log (DW) = -1 939 + 1.541 Log (DV) Log (DW) = -1.795 + 1.379 Log (DV) Log (DW) = -1.190 + 0.976 Log (DV) Log (DW) = -1.251 + 1.109 Log (DV) 21 27 55 30 30 53 27 30 0903 0.00810 0.951 000348 0929 0.00348 0956 0.00532 0969 0.00980 0.900 000757 0.907 000672 0.956 0.00360 Late spring Late winter B Early spring Midspring Copepoda 88.6 P. minutus (87.8) C. finmarchicus ( 6.2) C. typicus ( 3.0) Chaetognatha 8.6 Copepoda P. minutus C. finmarchicus T. longicornus C. typicus Cirri pedia 88.2 96 (75.1) ( 8.5) ( 6.2) ( 5.4) Copepoda 91.5 C. finmarchicus (55.3) P. minutus (28.8) M. lucens ( 3.0) A. longiremus ( 1 9) C. typicus ( 1.3) Chaetognatha 42 Cladocera 14 Copepoda 88 4 P. minutus (44 3) C. finmarchicus (37.2) T. longicornus (117) M. lucens ( 2.3) Chaetognatha 6.3 Cladocera 3.0 Early summer Midsummer Midautumn Late autumn 91.8 Copepoda 91.3 I Copepoda 662 Copepoda 75.6 P. minutus (33.9) C. typicus i :59.8) C. typicus i 70.1) C. finmarchicus (27.8) C. finmarchicus I ;19.8) A. clausi i : 5.1) C. typicus (19.0) P. minutus i : 5.2) A. tonsa i : 4.0) T. longicornus (11.6) M. lucens i : 3.1) P. minutus i : 3.4) M. lucens ( 1.2) Cladocera 23.6 P. parvus i : 3.2) Chaetognatha 7.E i Chaetognatha Thaliacea Amphipoda 45 1.7 1.6 C. minor Cladocera Chaetognatha i 21.3 10 : 2.2) Copepoda C. typicus P. parvus P. minutus Chaetognatha 5.5 (60.6) (15.3) (11.0) Table 4.— A) The recommended geometric mean regressions for interconversion between displacement volume (DV) and dry weight (DW) in the Georges Bank area; and B) the relative abundance of the major taxa (>1%) associated with the particular equa- tion, expressed as percent of total numbers. Copepods are broken down into major species (>1%) with their abundance expressed as percent of total copepod numbers (in parentheses). Zooplankton data from Sherman et al. (1978, 1979). A Variance Season Regression equation N r of slope Late winter-early spring Log (DW) = -1.195 + 1.059 Log (DV) 39 0.908 000518 Midspring Log (DW) = -1.324 + 1.119 Log (DV) 37 0989 0.00372 Late spring-early summer Log (DW) = -1.360 + 1.159 Log (DV) 40 0.954 0.00314 Midsummer-late summer Log (DW) = -1.403 + 1.176 Log (DV) 36 0891 0.00828 Early autumn Log (DW) = -1.662 + 1.296 Log (DV) 18 0949 00104 Midautumn Log (DW) = -1.349 + 1.070 Log (DV) 20 0.945 0.00941 Late autumn (1977) Log (DW) = -1.210 + 1.091 Log (DV) 20 0914 0.0111 Late autumn (1978) Log (DW) = -1.509 + 1.215 Log (DV) 14 0950 0.0129 Late winter-early spring Midspring B Late spring-ea rly summer Midsummer Copepoda 80 7 Copepoda 89.7 Copepoda 76.6 Copepoda 893 P. minutus (55.6) C. finmarchicus (79.8) C. finmarchicus (42.8) C. typicus (53.1) C. finmarchicus (37.1) P. minutus (16.9) P. minutus (36.1) C. hamatus (16.6) C. typicus ( 2.6) M. lucens ( 2.5) C. hamatus (11.7) C. finmarchicus (10.2) M. lucens ( 1.8) Chaetognatha 2.3 C. typicus ( 5.1) P. minutus ( 8.9) Chaetognatha 6.9 Ostracoda 15 M. lucens ( 1.5) P. parvus ( 5.6) Cirri pedia 4.9 Cirripedia 1.3 T. longicornus ( 1.3) M. lucens ( 3.7) Amphipoda 4.8 Amphipoda 1.1 Chaetognatha 6.7 Chaetognatha 4.9 Pelecypoda 1.7 Coelenterata Cladocera Decapoda 56 4.1 3.1 Cladocera 1.8 Early autumn Midautumn Late autumn (1977) Late autumn (1978) Copepoda 95 1 Copepoda 94 5 Copepoda 86.6 Copepoda 89.8 C. typicus (50.1) C. typicus (64.6) C typicus (57.0) C. typicus (51.1) P. minutus (198) C. finmarchicus (10.2) P. minutus (280) P. parvus (19.9) C. hamatus (18.4) C. hamatus ( 8.7) C. finmarchic us ( 4.3) C. finmarchicus (11.0) C. finmarchicus ( 2.5) P. parvus ( 5.7) C. hamatus ( 3.8) P. minutus ( 7.9) M. lucens ( 2.0) P. minutus ( 5.6) P. parvus ( 2.2) C. hamatus ( 6.1) P. parvus ( 1.9) M. lucens ( 1.3) M lucens ( 1.7) Chaetognatha 8.7 Pelecypoda 1.7 Chaetognatha 2.3 Pelecypoda 69 Chaetognatha 1.3 Amphipoda 14 Chaetognatha 5.5 iYM Table 5.— A) The recommended geometric mean regressions for interconversion between displacement volume (DV) and dry weight (DW) in the Gulf of Maine area; and B)the relative abundance of the major taxa(>l%) associated with the particular equa- tion, expressed as percent of total numbers. Copepods are broken down into major species (>1%) with their abundance expressed as percent of total copepod numbers (in parentheses). Zooplankton data from Sherman et al. (1978, 1979). A Variance Season Regression equation N r of slope Late winter-early spring Log (DW) = -1.168 + 1.156 Log (DV) 25 0.956 0.00504 Midspring Log (DW) = 1.169 + 1.106 Log (DV) 37 0.954 0.00314 Late spring-early summer Log (DW) = -1 035 + 1.080 Log (DV) 47 0949 0.00260 Midsummer Log (DW) = -1.470 + 1.377 Log (DV) 28 0.966 0.00476 Late summer Log (DW) = -1 .079 + 1 .089 Log (DV) 22 0949 0.00846 Midautumn (1977) Log (DW) = -1.201 + 1.242 Log (DV) 23 0977 0.00339 Midautumn (1978) Log (DW) = -1.343 + 1.304 Log (DV) 24 0957 0.0129 Late autumn Log (DW) = -1.576 + 1.419 Log (DV) 44 0.935 0.00608 Late winter-early spring Midspring B Late spring-early summer Midsummer Copepoda 96 3 Copepoda 93 5 Copepoda 94.0 Copepoda 97.5 C. linmarchicus (63 .7) C. linmarchicus (86 7) C. linmarchicus (83.5) C. linmarchicus (79.9) M. lucens (18.9) P. minutus ( 8.0) P. minutus (10.3) P. minutus (10.0) P. minutus (13.6) M. lucens ( 5.0) M. lucens ( 4.6) M. lucens ( 4.2) Oithona sp. ( 1.7) Amphipoda 5.0 A. longiremis ( 1-1) C. typicus ( 4.2) Amphipoda 1.3 Cladocera 4.8 A. longiremis Cladocera ( 1.3) 1.1 Late summer Midautumn (1977) Midautumn (1978) Late autumn Copepoda 99.2 Copepoda 99 0 i Copepoda 98.9 Copepoda 99 1 C. linmarchicus (47.3) C. linmarchicus (51 3) C. typicus (39.1) C. typicus (37.0) C. typicus (42.0) C. typicus (29.3) C. linmarchici JS (34.6) C. linmarchicus (28.3) P. minutus ( 7.7) P. minutus (114) P. minutus (17.9) P. minutus (21.4) M. lucens ( 3.5) A longiremis ( 1.5) P. parvus ( 4.7) P. parvus ( 2 6) P. parvus ( 1.3) M. lucens A. longiremis ( 4.5) ( 1.1) bined and a new regression equation calculated. These equations, and the equations showing sig- nificant differences between years, are the rec- ommended equations for conversion between the biomass measures (Tables 3-5). Choice of which regression to use should be based on area, season, and species composition. Confidence limits can be calculated for any predicted dry weight or dis- placement volume by using the method outlined by Ricker (1973) or Wiebe et al. (1975). A listing of values for predicting dry weights and dis- placement volumes within 95% confidence limits is given in Table 6. The limitations of the method for the area under study are as follows. The presence in sam- ples of organisms such as salps, jellyfish, and doliolids, which have a high displacement vol- ume to dry weight ratio due to a greater reten- tion of intracellular water, can significantly affect the accuracy of dry weight estimates (Wiebe et al. 1975). This was also observed in our data, but only on rare occasions were these or- ganisms encountered. Chaetognaths were also mentioned by Wiebe et al. as organisms that could alter the biomass relationship. Since they are common, but not dominant, components of the plankton throughout the year in our sampling areas, the seasonal regressions account for their continuous presence and are therefore appli- cable to samples where they are present. This study revealed two additional situations in which sample composition caused a deviation in the bio- mass relationship. Twenty samples collected during late winter 1977 from the GOM and GB contained high concentrations of diatoms, pri- marily Rhizosolenia sp. and Thalassiosira sp., and microzooplankton not normally captured by 0.333 mm mesh nets. The samples resembled thick "pea soup" and many hours were required for draining in order to obtain a displacement volume reading. Since their dry weight to dis- placement volume ratios were very low com- pared with other samples collected during the same period, the samples were eliminated from the general analysis and a separate regression calculated (r = 0.962) for them (Table 1). The second situation was observed in autumn 1978 when the siphonophore population increased dramatically, especially off SNE and in the GOM. Since these delicate colonial aggregations are easily fragmented during collection, their abundance could not be measured quantitatively. For these samples, displacement volume to dry weight ratios were disproportionally high be- cause of the intracellular water retained by their nectophores. The regression line calculated with data only from siphonophore-dominated samples was significantly different (P<0.05) in both 637 Table 6.— Values needed to calculate 95% confidence limits for predicted dry weights (DW) and displacement volumes (DV) from the equations in Tables 3-5. For an explana- tion of symbols and the methods used, one should consult Ricker (1973) or Wiebe et al. (1975). Prediction of DW Prediction of DV Area/season f95 X' Ix'2 Sy'x'2 r xy'2 Sxy2 Southern New England Late winter 2.05 1 329 4.384 0.0156 0.775 4.067 0.0168 Early spring 2.08 0.945 1.894 0.0154 -0.110 0996 0.0292 Midspring 2.01 1 598 8.156 0.0281 0.478 9.250 0.0248 Late spring 2.04 1.915 2.025 0.0107 0.850 3484 0.00622 Early summer 2.04 1.683 0.694 0.00671 0.655 1.651 0.00282 Midsummer 2.01 1.706 2.614 00205 0.577 4.973 0.0108 Midautumn 2.05 1.334 1.147 0.00780 0.117 1.092 00081 Late autumn 2.05 1.347 1.588 0.00568 0.121 1.648 0.00545 Georges Bank Late winter-early spring 2.02 0.962 3.363 0.0194 0.122 4.073 0.0173 Midspring 2.03 1.783 3.361 000309 0.671 4.918 0.00228 Late spring-early summer 2.02 1.892 5938 0.0189 0.833 7.972 00141 Midsummer-late summer 203 1.615 1.730 0.0145 0.497 2391 0.0105 Early autumn 2.10 1.471 0652 0.00678 0 284 1 .0952 0.00403 Midautumn 2.09 1.150 0655 0 00615 0256 0.748 0.00539 Late autumn (1977) 209 1 393 1.088 0.0119 0.310 1 2935 000997 Late autumn (1978) 2.15 1.492 0.767 0.00949 0 198 1.133 0.00676 Gulf of Maine Late winter-early spring 2.06 1.045 1.261 0 00630 0041 1.685 0.00471 Midspring 2.03 1.571 2.037 0 00641 0.568 2491 0.00524 Late spring-early summer 2.01 1.695 3.009 0.00772 0.796 3 508 0.00662 Midsummer 2.05 1.675 0.977 000470 0.836 1.851 000252 Late summer 2.12 1.396 1 738 0.00985 0.423 2.059 000832 Midautumn (1977) 2.07 1 708 1.446 0.0049 0.920 2230 0.00317 Midautumn (1978) 2.16 1 501 0.232 000302 0.614 0.395 0.00177 Late autumn 2.01 1 592 2552 0.0154 0683 5.147 0.00766 slope and elevation from all other seasonal lines and had a high rvalue (Table 2). Since the occur- rence of siphonophores in large numbers has been reported in our sampling areas (Sumner 1911; Rogers etal. 1978), this predictive equation should be useful for future occurrences of this phenomenon. A coefficient of variation (cv) was calculated for each group of displacement volume and dry weight measures in order to compare the relative variability between the two indexes. As expected, both indexes were highly variable, with cv's averaging 54.3% (31.6-133.5%) and 65.4% (33.4- 147.8%) for displacement volume and dry weight, respectively. Surprisingly, of the 36 data sets, 31 exhibited higher cv's for dry weight than for dis- placement volume. A two-tailed variance test was used to determine whether this difference was significant (Lewontin 1966) for the paired displacement volume-dry weight values. Only GOM late autumn (1977) displacement volumes had a significantly (P<0.05) lower cv than the corresponding dry weights. When all values were combined, however, and a single cv calcu- lated for each index, displacement volumes were significantly (P<0.05) less variable. This was un- expected, because water retained interstitially and intracellularly should increase variability among displacement volumes. It appears, then, that displacement volume is a more consistent and more reliable measure of plankton standing stock than dry weight. Zooplankton standing stock for 1977 and 1978 in each area is plotted in Figure 3A-C. The mea- sures are juxtaposed in order to reveal whether any discrepancies exist between the two pat- terns. For SNE and GB the two indexes of abun- dance follow strikingly similar patterns. In the GOM, however, the dramatic midautumn in- crease in dry weight for 1977 is not equally re- flected by the displacement volume curve. Cala- nus finmarchicus dominated these samples (Sherman et al. 1978) and further examination revealed that they were stage V copepodites, the condition in which they overwinter. Comita et al. (1966) showed that C. finmarchicus collected from the Bute Channel, England, reach their weight and caloric maxima in autumn and early winter, with stage V individuals having the high- est values. The impact these overwintering pre- adults had on the dry weight measures was confirmed by plotting the seasonal mean dry weight-displacement volume ratios for all three areas (Fig. 4). GOM autumn ratios were highest for both years, 17.4% and 13.4%, respectively. Furthermore, samples dominated by C. fin- marchicus had higher ratios than samples from shallower stations where the copepods Pseudo- 638 Figure 3.— Changes in median displacement vol- umes and dry weights for A) Southern New England, B) Georges Bank, and C) Gulf of Maine waters. Dashed lines represent intersurvey peri- ods. Similar abundance trends are portrayed by both indexes, but discrepancies in magnitude be- tween measures occur for Georges Bank summer samples and throughout the year in the Gulf of Maine. Displacement volumes are from Sherman et al. (1977, 1978). E O O o o O > LU LlI o < _l Q. < Q LlI 120 100 80 60 40 ■ 20 • 0 - 120 - 100 80 60 40 20 0 - 120 100 80 60 40 20 0 SOUTHERN NEW ENGLAND DISPLACEMENT VOLUMEK^^ DRY ^\ / WEIGHT \ £ *. 5 t~ i i i i i r~i i I i i r~i n m i r GEORGES BANK h \ \ DRY \ '■ *" WEIGHT l DISPL ACE MEN T " - * VOLUME h I I I I I I I I I I I I © i i i i I I I I I ! GULF OF MAINE DRY WEIGHT /A. y/ V 10 -8 - 6 - 4 - 2 - 0 I I i i i i I I I II II I I I I I I I I ! I I JFMAMJJ AS0MDJF MAMJJ A S 0 N D -10 -6 6 4 2 0 — 12 — 10 8 6 4 — 2 — 0 fO E O O E >- rr Q Q LlI 1977 1978 o o E en O I- >- tr o < 14 - 12 10 - 8 - GULF OF MAINE SOUTHERN NEW ENGLAND i i i i i i i i i i i i i i ! i i i : i i i i FMAMJJASONDJFMAMJJASOND 1977 1978 winter and represent a substantial biomass underestimated by displacement volumes. Autumn increases in dry weight were not ob- served for GB or SNE, though both areas sup- port large populations of Calanus in the spring and summer. In general, overwintering Calanus remain in deep water and do not migrate ver- tically (Marshall and Orr 1955). The only concen- trations of preadult Calanus found in these areas were at a few stations located near or below the 100 m contour line during late autumn. These samples had higher dry weight-displacement volume ratios than Calanus free stations. The G0M is able to support a large population of over- wintering Calanus in deepwater basins. Figure 4.— Seasonal changes in dry weight/displacement vol- ume ratios for the three sampling areas. Points are placed at the midpoints of the survey cruises. Gulf of Maine samples have higher values throughout the year. calanus minutus or Centropages typicus were abundant. The preadult Calanus apparently store lipid reserves for survival through the Discussion The linear relationship between displacement volume and dry weight is affected by the sea- sonal changes in species composition and age structure which occur throughout the year in zooplankton communities. Accurate intercon- version between them is possible only with a ser- 639 ies of seasonal equations that are restricted to a specific area. A single general conversion equa- tion derived from samples from a widespread area cannot provide estimates of abundance with sufficient accuracy to describe the variation in abundance and community composition neces- sary for detailed studies of trophic structure and community composition. The findings presented here are generally consistent with those of pre- vious investigators (Lovegrove 1966; Piatt et al. 1969; Beers 1974), with the exception of Wiebe et al. (1975). It should be recognized that the latter approach (Wiebe et al. 1975) has utility in com- paring disparate data sets from different geo- graphical areas and seasons. It is necessary to recognize the limitations of each approach and select according to the intended use of the data. Previous reports have recommended dry weight determinations over displacement vol- umes because both interstitial and intracellular water is eliminated from the sample, removing bias caused by gelatinous organisms (Ahlstrom and Thrailkill 1963; Beers 1974). Further, since only organic and inorganic substances remain in the sample, dry weight should provide informa- tion regarding the potential food value of the plankton standing stock. However, the high cor- relation found between displacement volume and dry weight (r = 0.925, 442 df) implies that both measures provide equivalent assessments of standing stock and potential food value. In two of the three areas investigated, GB and SNE, both measures portray identical ascending and de- scending trends in biomass with maximal and minimal points closely correlated (Fig. 3). In addition, variability, though high for both tech- niques, is higher for dry weight. Discrepancies between the two measures ap- pear, however, when one examines GOM data. Standing stock is underestimated by displace- ment volume because samples there have high dry weight to displacement volume ratios (Fig. 4). As a consequence, when biomass is compared between the GOM and GB or SNE, each index gives a different interpretation of between-area differences (Fig. 5). For example, in autumn 1977, mean dry weight for the GOM was five times higher than for SNE, but mean displace- ment volume was only twice as high. This phe- nomenon is attributed to the life history of C. finmarchicus in the GOM. Dry weight values re- ported by other investigators from different areas are also more readily comparable than dis- placement volumes because Lovegrove's tech- 160 - I- Z 140 - w — . uj E izo - a o 100 - 80 - 60 40 20 < o E o o E a < UJ 2 ® DISPLACEMENT VOLUME GEORGES BANK SOUTHERN NEW ENGLAND i i i i i I i — rm — i i i i i t DRY WEIGHT GEORGES BANK GULF OF MAINE / SOUTHERN NEW ENGLAND I I I I I I 1 I I I I 1 JFMAMJJASONDJFMAM JJASOND 1977 1978 Figure 5.— Trends in plankton abundance for the three areas in 1977 and 1978 as measured by A) displacement volume, and B) dry weight. Each measure gives a different interpretation of between-area differences in biomass, especially in the Gulf of Maine. nique (1966) for measuring them has been widely accepted, while techniques for measuring dis- placement volumes vary, especially in the at- tempt to remove interstitial water (Wiebe et al. 1975). Thus, for studies comparing standing stock between different sea areas, and for other advantages previously mentioned, dry weight is the preferred measure. Summary This report has provided a series of season- and area-specific equations for the interconversion of zooplankton displacement volume and dry weight. In addition, interconversion equations for samples with large amounts of phytoplank- ton and siphonophore fragments have been cal- culated. However, dry weights should be mea- sured directly on samples containing organisms with large amounts of intracellular water be- cause they drastically affect the biomass rela- 640 tionship. It is our experience, however, that these organisms are abundant only on rare occasions in the MARMAP study area. The predictive equations should assist investigators assessing zooplankton standing stock on the continental shelf of the Northwest Atlantic. General conversion factors at best yield only gross estimates, thus investigators should be aware of the limitations imposed by these values. A decision must be made by the investigator as to what level of accuracy is acceptable on the basis of what the data is to be used for. Further break- down of the data into smaller subsets than area and season is possible, but the result would be an unwieldy number of equations sensitive to minute changes in trophic conditions. However, one can conclude from this study that effective displacement volume to dry weight conversion equations must to some extent take into account seasonal and areal variations in community com- position. Given these considerations, the data presented here show no increase in variability in- herent in displacement volume over dry weight biomass measures. Displacement volume pro- vides a simple, easily routinized, rapid and non- destructive method of representing biomass, which is appropriate for processing the large numbers of samples typical of survey sampling programs. Acknowledgments I am indebted to J. R. Green for his guidance throughout the study and to D. Busch who greatly improved the manuscript. Gail Santoro typed the final manuscript and Lianne Arm- strong drafted the figures. Literature Cited Ahlstrom, E. H., and J. R. Thrailkill. 1963. Plankton volume loss with time of preservation. Calif. Coop. Oceanic Fish. Invest. Rep. 9:57-73. Be, A. W. H., J. M. Forns, and 0. A. Roels. 1971. Plankton abundance in the North Atlantic Ocean. In J. D. Costlow, Jr. (editor), Fertility of the sea 1:17-50. Gordon and Breach Sci. Publ., N.Y. Beers, J. 1974. Biomass. In H. F. Steedman (editor), Laboratory methods in the study of marine zooplankton, Vol. 35, p. 352-354. J. Cons. Bsharah, L. 1957. Plankton of the Florida Current. V. 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Bull, U.S. 76:281-284. Sherman, K. 1980. MARMAP, a fisheries ecosystem study in the Northwest Atlantic: Fluctuations in ichthyoplankton- zooplankton components and their potential for impact on the system. In F. P. Diemer. F. J. Vernberg, and D. Z. Mirkes (editors), Advanced concepts in ocean mea- surements for marine biology, p. 9-37. Belle W. Baruch Institute for Marine Biology and Coastal Research, Univ. S.C. Press. Sherman, K., C. Jones, and J. Kane. 1979. Zooplankton of continental shelf nursery and feed- ing grounds of pelagic and demersal fish in the north- west Atlantic. Int. Counc. Explor. Sea CM. 1979/L:27. Sherman, K., L. Sullivan, and R. Byron. 1978. Pulses in the abundance of zooplankton prey of fish on the continental shelf off New England. Int. Counc. Explor. Sea CM. 1978/L:25. Snedecor, G. W., and W. G. Cochran. 1967. Statistical methods. 6th ed. Iowa State Univ. 641 Press, Ames, 593 p. Steedman, H. F. (editor). 1976. Zooplankton fixation and preservation. Monogr. Oceanogr. Methodol. 4, 350 p. The UNESCO Press, Paris. Sumner, F. B., R. C. Osburn, and L. J. Cole. 1911. A biological survey of the waters of Woods Hole and vicinity. Sect. 1— Physical and zoological. Bull. U.S. Bur. Fish. 31:1-442. SUTCLIFFE, W. H., Jr. 1957. An improved method for the determination of pre- served plankton volumes. Limnol. Oceanogr. 2:295- 296. Tranter, D. J. 1960. A method for determining zooplankton volumes. J. Cons. 25:272-278. Wiebe, P. H., S. Boyd, and J. L. Cox. 1975. Relationships between zooplankton displacement volume, wet weight, dry weight, and carbon. Fish. Bull., U.S. 73:777-786. Yentsch, C. S., and J. F. Hebard. 1957. A gauge for determining plankton volume by the mercury immersion method. J. Cons. 22:184-190. Zar, J. H. 1974. Biostatistical analysis. Prentice-Hall, Engle- wood Cliffs, N.J., 620 p. Joseph Kane Northeast Fisheries Center Narragansett Laboratory National Marine Fisheries Service, NOAA South Ferry Road, Narragansett, RI 02882. ESTIMATION OF EQUILIBRIUM SETTLEMENT RATES FOR BENTHIC MARINE INVERTEBRATES: ITS APPLICATION TO MYA ARENARIA (MOLLUSCA: PELECYPODA) It is generally agreed that marine invertebrates possessing planktotrophic larval stages experi- ence extremely high mortality during the early stages of their life history. In the settlement of benthic invertebrates, mortality occurs during three critical phases: 1) fertilization, 2) the free- swimming pelagic stage, and 3) the early post- larval attachment period. Since egg loss, larval recruitment, and early postlarval mortality may often be the limiting steps in the development and maintenance of marine benthic communi- ties, it is of interest to ecologists to be able to make direct estimates of settlement rates in such populations. It is often difficult, however, to obtain reason- able estimates of early life history stage mortal- ity rates. The earliest attempt to determine such rates was made by Thorson (1966). Based on the standing crop of a population of Venus (= Mer- cenaries mercenaria, he estimated that approxi- mately 98.6% of the clams died during the post- larval period (stage 3) and that loss prior to this was probably much heavier. More recently, Muus (1973), in a study of 11 species of bivalves in the Oresund, Denmark, found postlarval mor- tality rates (stage 3) of 67-100% for all species; whereas Gledhill (1980) calculated larval mor- tality rates (stage 2) of 99.38% and 99.99% for two populations of Mya arenaria in Gloucester, Mass. None of these estimates, however, take into account the heavy mortality that occurs during stage 1, thereby overlooking the substantial loss occurring during the fertilization process itself. In an attempt to overcome the difficulty in estimating early survival parameters empiri- cally, Vaughan and Saila (1976) developed an in- direct method using the Leslie matrix for deter- mining mortality rates during the first year of life for the Atlantic bluefin tuna, Thunnus thynnus, assuming an equilibrium population. By expanding their treatment, as suggested by Van Winkle et al. (1978), it is possible to divide age class 1 into particular stages, thereby mak- ing the model appropriate for cases dealing with animals possessing more complex life cycles (i.e., those which include egg, larvae, postlarval juve- niles, etc.). In the case of benthic invertebrates with free-swimming larval stages, this method can be used to calculate mortality rates during settlement for any species population for which demographic parameters are available. Such theoretical estimates are of special interest for two reasons. First, the equilibrium settlement rate (r.s) value can be compared with field-deter- mined estimates; second, the value may be useful in the prediction of future age structures in natural populations. This paper describes the indirect method for estimating the settlement rate based on age- specific fecundity and survivorship rates and discusses its application to a commercially im- portant species of bivalve, Mya arenaria. Results Leslie Matrix Matrix methods for analyzing age-structured populations were developed by Leslie (1945, 642 FISHERY BULLETIN: VOL. 80, NO. 3, 1982. 1948) and subsequently used in numerous studies of human and animal populations. In the present setting, the Leslie matrix takes the form: L(r„) CLi 02 a3. . . a»-i a-,, rxbi 0 0 . . .0 0 0 b2 0 . . .0 0 0 0 0 6»-i 0. Here, a, is the number of female eggs produced annually by a female Mya arenaria in class i(age i — 1 to i), and 6, is the probability of a clam in class i — 1 surviving to class i for fe2. The sur- vivorship from age-class 1 to age-class 2 (P„ in the notation of Vaughan and Saila (1976)) has been divided into two factors, rs and 6i. The fac- tor r, is the settlement rate, or the probability that an egg will develop into a clam with a 2 mm shell length (0-2 mo of age); 6i is the probability that a clam with a 2 mm shell length will survive the remainder of the year (about 10 mo). The intrinsic growth rate is an increasing function of the settlement rate, r.,. Therefore, the equilibrium value, r., , 0■■< biaz + 616203 + ... + 6162 ... 6/,-iO„ 'This age class represents clams 2-29 9 mm in shell length Discussion In his classic work on marine invertebrate communities, Thorson (1950) stated the defini- tive "number of eggs and larvae produced per pair of adult animals per lifetime to maintain the population is. ..one pair of larvae." More simply, to remain at equilibrium, a replacement rate of one must be maintained. For a population of Mya 643 arenaria possessing the life history statistics given above, 1 out of about 790,000 eggs pro- duced during the lifetime of an individual must survive to ensure continuance of the population. However, variable recruitment and high post- larval mortality tend to be the general rule among temperate and boreal marine inverte- brates, especially the bivalves. At the Jones River in Gloucester, the tidal flat received a heavy set of young Mya arenaria in 1973 (Brous- seau 1978a, b). Based on crude estimates of stock density, age-specific fecundity, and the density of the resultant spatfall, the settlement rate was 0.0498%, or about 34 times larger than the cal- culated r.,eq. During the two subsequent years, on the other hand, this site received only a lim- ited spatfall, which, coupled with high postlarval mortality, resulted in settlement rates of 0.0%. Under such fluctuating conditions, therefore, the settlement history of a population takes on added significance. In addition to being of theoretical interest, determination of the equilibrium settlement rate for a commercially important species may be of value in its harvesting management as well. Although the impact of repeated exploitation is difficult to assess given the uncertainties of en- vironmental conditions, continued harvesting on tidal flats receiving annual settlement rates below equilibrium may prove to be extremely harmful to the resident population. Literature Cited Brousseau, D. J. 1978a. Spawning cycle, fecundity, and recruitment in a population of soft-shell clam, Mya arenaria, from Cape Ann, Massachusetts. Fish. Bull., U.S. 76:155-166. 1978b. Population dynamics of the soft-shellclam Mya arenaria. Mar. Biol. (Berl.) 50:63-71. Gledhill, C. 1980. The influence of established infauna on recruit- ment of the soft-shell clam, Mya arenaria L. M.S. Thesis, Univ. Massachusetts, Amherst, 40 p. Leslie, P. H. 1945. On the use of matrices in certain population mathe- matics. Biometrika 33:183-212. 1948. Some further notes on the use of matrices in pop- ulation mathematics. Biometrika 35:213-245. Muus, K. 1973. Settling, growth and mortalityof young bivalves in the Oresund. Ophelia 12:79-116. Thorson, G. 1950. Reproductive and larval ecology of marine bottom invertebrates. Biol. Rev. (Camb.) 25:1-45. 1966. Some factors influencing the recruitment and establishment of marine benthic communities. Neth. J. Sea Res. 3:267-293. Van Winkle, W., D. L. DeAngelis, and S. R. Blum. 1978. A density-dependent function for fishing mortality rate and a method of determining elements of a Leslie matrix with density-dependent parameters. Trans. Am. Fish. Soc. 107:395-401. Vaughan, D. S., and S. B. Saila. 1976. A method for determining mortality rates using the Leslie matrix. Trans. Am. Fish. Soc. 105:380-383. Diane J. Brousseau Department of Biology Fairfield University Fairfield, CT 061,30 Department of Mathematics Fairfield University Fairfield, CT 061,30 Jenny A. Baglivo George E. Lang, Jr. GROWTH OF JUVENILE RED SNAPPER LUTJANUS CAMPECHANUS, IN THE NORTHWESTERN GULF OF MEXICO1 The red snapper, Lutjanus campechanus, has re- ceived considerable attention in the past due to its importance as a commercial and sport fish in the Gulf of Mexico. Most published material deals with the fishery and is summarized in Carpenter (1965). Few major papers have dealt with the natural history of red snapper. Moseley (1965) reported on growth, reproduc- tion, and food habits of red snapper taken by trawl and handline off the Texas coast. He deter- mined age and growth rate from scales by assuming that growth checks were produced during the spawning season. Bradley and Bryan (1975) also sampled red snapper along the middle Texas coast with trawl and hook and line. They were unable to distinguish age classes by length frequencies and attributed that to an ex- tended spawning season. Futch and Bruger (1976) used otolith readings to determine age and growth of red snapper off the coast of Florida. This paper presents new information on growth of young snapper and relates that infor- mation to their occurrence on an artificial reef. 'University of Texas Marine Science Contribution No. 519. 644 FISHERY BULLETIN: VOL. 80. NO. 3. 1982. Study Area and Methods The artificial reef, composed of three sunken World War II liberty ships, is located approxi- mately 29 km offshore (lat. 27°35'N, long. 96°54'W) from Port Aransas, Tex., in 33 m of water. Red snapper were collected from the reef with fish traps in March, May, July, September, November, and December 1979. The rectangu- lar traps (1.8m X 1.2m X 0.6m) were made of 1.25 cm reinforcing bar covered with 3.4 cm mesh plastic coated wire. The entrance cone had an initial opening of 60.9 X 45.7 cm terminating in a 90° downturn with a 25.4 cm diameter entrance port. During each sampling period, five traps were baited with fish scraps and set on the bottom around the reef for 24 h. All red snapper captured in traps were measured in standard and total lengths and placed in a flowing sea- water live box onboard ship. Snapper which were in good condition after 1 h on board ship were tagged with numbered internal-anchor tags and released over the artificial reef. Small red snappers (<160 mm) were collected from the south Texas outer continental shelf during 1975 through 1977 with a 10.7 m "flat trawl" with 4.45 cm stretch mesh in the body and 2.5 cm stretch mesh in the bag. From 1975 to June 1976 a 9.5 mm stretch mesh liner was used inside the bag. Trawl sampling depths ranged from 10 m to 132 m. Seventy-two trawl samples were taken in 1975, 222 in 1976, and 294 in 1977. All trawls were made at a speed of about 2 kn for 15min,(Fordetailsof sampling sites and procedures see Flint 1981.) Results Growth The smallest fish taken in the trawl samples were generally 20-29 mm (Table 1). Juveniles <40 mm were caught in August, September, and October, and eight individuals of this size were taken in June 1976. Two year classes can be identified in the length-frequency table (Table 1) and followed for 12-18 mo. The smallest fish taken in traps at the ship reef were 100-110 mm. Snapper <100 mm could escape through the mesh. Length-frequency histograms for combined trawl and trap data are shown for each month (Fig. 1). Two cohorts, age group 0 and age group I, are apparent in the data and a third cohort, age group II, may be present in the March and July data. Recruitment of small snapper (<40 mm) into the population occurred primarily in June and July as evidenced by the modal size of the age 0 year class in August, September, and October. Limited recruitment of small fish continued into October. Length-frequencies of snappers cap- tured in June through December were distinctly bimodal. Modal size classes for age I fish were 110 mm in June and 130 mm in July. Modal size classes for age 1+ fish were 150 mm in December Table 1.— Length-frequency distribution of red snapper caught in trawl samples. The number of individuals of each size class in each month is shown. No samples were taken in months with an asterisk (*). 1974 1975 1976 1977 Length D J F* M" A M J* J" A S o- N- D" J* F M A M J J A S O N D J F M A M J J A S O N D 10-19 1 20-29 2 12 6 30-39 1 4 1 1 5 40-49 1 7 1 3 12 6 1 2 3 50-59 2 8 1 1 11 1 7 1 1 11 10 60-69 5 1 3 1 11 1 3 3 1 1 24 11 1 70-79 4 4 4 4 6 4 7 8 26 20 1 1 80-89 1 1 1 1 1 3 3 1 13 3 3 1 5 27 16 2 90-99 2 2 6 2 2 2 9 4 1 2 4 5 2 100-109 1 2 2 1 1 4 2 2 1 110-119 1 2 2 5 2 1 1 120-129 1 1 1 3 130-139 1 3 1 140-149 1 2 1 150-159 1 1 1 160-169 1 1 1 170-179 3 1 2 1 2 180-189 3 190-199 1 5 200-209 1 3 210-219 1 220-229 2 230-239 1 645 50- 40- 30- 20 10 40- 30 20 10 30 20 10 _rz£ JAN N:2 FEB N-34 MAR N:23 &s >- Z> o 40- 30- 20- 10- 20- 10- 30- 20- 10- JZ^ APR NUl MAY N = 41 JUN NZ19 30- 20- 10 AUG N-29 2 0- 10- SEP N = 364 30- 20- 10- OCT NH02 20- 10- n£L NOV Ni42 20- 10- DEC N = 62 -i — i — r~n — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i iii — i — i — i — i — i — i — i — i — ; — i — i — i — 10 30 50 70 90 110 130 150 170 190 210 230 250 270 290 310 330 350 LENGTH CLASS (mm) FIGURE 1.— Size distribution of young red snapper from pooled trawl and fish trap collections. and 190 mm in March. It appears that age II snapper were 210-230 mm in July although few fish of that age class were caught. Tagging Numbered, internal-anchor tags were placed in 267 red snapper between 117 and 350 mm (mean = 192 mm) on the ship reef in July, Sep- tember, and November 1979. Sportfishermen re- turned 28 tags and our fish trap sampling pro- duced seven additional returns (13% total return rate). All fish were recaptured from the ship reef. The longest "free time" for any fish in our study was 92 d except for one fish which was tagged and recaptured twice over a 1 12-d period. 646 Sixty-three percent of the recaptures were within 30 d of release. No fish were recaptured after 11 December 1979 despite continued fishing effort on the ship reef during the winter and spring of 1980. Measurements from the seven fish recaptured by our own sampling yielded growth rates of 0.12-0.55 mm/d (mean = 0.29 mm/d). Based on age determination from our length-frequency plots, these represent growth rates of age 1+ snapper. Lengths of recaptured red snapper re- ported by sportfishermen were not considered accurate enough to use for growth determina- tions. Discussion Bimodal size distributions of red snapper caught in trawls and traps indicate that juve- nile red snapper grow more slowly than pre- viously thought. Moseley (1966) presented the first detailed account of growth rates for snapper using scale annuli for age determination. He assumed that growth checks were produced during the spawning period rather than during a midwinter slow growth period, an assumption confirmed by later workers (Futch and Bruger 1976). Moseley (1966) found that fish with one spawning check averaged 250 mm and deter- mined a growth rate of about 90 mm between spawnings (about 0.25 mm/d). He proposed that red snapper grow 200-230 mm during their first year. Bradley and Bryan (1975) cited other un- published data from Texas which indicated an initial growth check on scales at about 200 mm fork length and a mean growth rate of 60 mm/yr between formation of the first and the fifth rings. Futch and Bruger (1976) determined that maturity is probably reached after the second year (age 11+) in Florida. Their data also indicated that the first growth check (on otoliths) generally occurred on snapper of about 200 mm. A slower growth rate could be inferred from otolith, scale, and vertebrae aging by Bortone and Hollingsworth (1980) who found that snapper with one growth check averaged 163 mm and snapper with two growth checks averaged 197 mm. Small sample size (46) and one sampling date (17 October) may have influ- enced their results. That snapper mature at age 11+ (Futch and Bruger 1976) and produce growth checks as a result of spawning activity suggest that fish with a single annulus are not age 1+ as Moseley (1966) suggested but are age II+. Our data are consistent with this hypothesis. The dis- tinct bimodality in length frequencies of snapper <220 mm during June through December (Fig. 1) indicates the presence of two year classes within this size range. We propose that red snapper grow to 110-130 mm during the first year and attain a size of 220-230 mm the second year. It is at this size (age II) that they apparently reach sexual maturity (Camber 1955; Futch and Bruger 1976). This growth rate is consistent with established postspawning growth rates of 60 (Bradley and Bryan 1975) to 90 mm/yr (Moseley 1966) between the first and fourth or fifth spawnings. Red snapper >160 mm were uncommon in our trawl samples. Bradley and Bryan (1975) also collected few snapper between 150 mm and 220 mm in trawl or hook and line catches. Numerous fish of this size were trapped at the ship reef in July and September. Tagging data indicated that 130-250 mm (age I and early age II) snapper were abundant on the ship reef from July through September and some remained there through November or December. The absence of tag returns after December indicates that the fish present there all summer and fall either moved away, presumably to deeper water (Moseley 1966; Bradley and Bryan 1976) or had suffered substantial mortality. Fable (1980) found essentially no movement in 17 returns from 299 tagged red snapper in 60 m of water off the Texas coast. Conclusions 1. We suggest that growth rates of juvenile red snapper during the first 2 yr are slower than previously reported. Our data indicate snapper attain a length of 110-130 mm the first year and 200-230 mm the second year. 2. Juvenile snapper <150 mm were common in trawl samples throughout most of the year. 3. Snapper 130-250 mm were common on the artificial reef from July through December. Tagging studies indicated the snapper remain around the artificial reef during the summer and fall but none were captured there or elsewhere after December. Acknowledgments We would like to thank the captain and crew of the RV Longhorn for their competence and assistance in doing the field work. Special thanks 647 go to our colleagues Steve Rabalais and Rick Kalke for their invaluable assistance in the field. This manuscript benefited from the critical re- views by Dr. Checkley, J. Holt, and N. Rabalais and from reviews of an earlier draft by two re- viewers. This work was supported by the Bureau of Land Management Contract AA550-GTG-17 and the Texas Coastal and Marine Council, Con- tract IAC (78-79)-2183 and IAC (80-8D-0044 to the University of Texas. Literature Cited BORTONE, S. A., AND C. L. HOLLINGSWORTH. 1980. Aging red snapper, Lutjanus campechanus, with otoliths, scales, and vertebrae. Northeast Gulf Sci. 4:60-63. Bradley, E., and C. E. Bryan. 1975. Life history and fishery of the red snapper (Lutjanus campechanus) in the northwestern Gulf of Mexico: 1970-1974. Proc. Gulf Caribb. Fish. Inst. 27:77-106. Camber, C. I. 1955. A survey of the red snapper fishery of the Gulf of Mexico, with special reference to the Campeche Banks. Fla. State Board Conserv. Tech. Ser. 12, 64 p. Carpenter, J. S. 1965. A review of the Gulf of Mexico snapper fishery. U.S. Fish Wildl. Serv., Circ. 208, 35 p. Fable, W. A., Jr. 1980. Tagging studies of red snapper (Lutjanus campechanus) and vermilion snapper (Rhomboplites aurorube>is) off the south Texas coast. Contrib. Mar. Sci. 23:115-121. Flint, R. W. 1981. Introduction. In R. W. Flint and N. N. Rabalais (editors), Environmental studies of a marine ecosystem, south Texas outer continental shelf, p. 3-14. Univ. Texas Press, Austin. Futch, R. B., and G. E. Bruger. 1976. Age, growth, and reproduction of red snapper in Florida waters. In H. R. Bullis and A. C. Jones (editors), Proceedings: Colloquium on snapper-grouper fishery resources of the Western Central Atlantic Ocean, p. 165-184. Fla. Sea Grant Program Rep. 17. Moseley, F. N. 1966. Biology of the red snapper, Lutjanus aya Bloch, of the northwestern Gulf of Mexico. Publ. Inst. Mar. Sci. Univ. Tex. 11:90-101. Scott A. Holt Connie R. Arnold The University of Texas Marine Science Institute Port Aransas Marine Laboratory Port Aransas, TX 7837S AN ASSOCIATION BETWEEN A PELAGIC OCTOPOD, ARGON AUTA SP. LINNAEUS 1758, AND AGGREGATE SALPS Biologists working in the epipelagic zone of the ocean have reported that representatives of numerous planktonic taxa seem to be closely associated with gelatinous zooplankton, includ- ing hyperiid amphipods (Madin and Harbison 1977; Harbison et al. 1977; Laval 1980), gammarid amphipods (Vader 1972), isopods (Barham and Pickwell 1969), decapods (Shojima 1963; Thomas 1963; Trott 1972; Bruce 1972; Herrnkind et al. 1976), cyclopoid copepods (Heron 1973), mysids (Bacescu 1973), cirripedes (Fernando and Ramamoorthi 1974), and fish (Mansueti 1963; Janssen and Harbison in press). Some symbionts in these groups are morpho- logically adapted to feed principally on the host and/or on the food material which the host col- lects, while others seem to associate more inter- mittently with gelatinous zooplankton, depen- dent on their nutritional state and that of the gelatinous hosts. Accordingly, symbioses may range from specific, structural associations to temporary or casual associations. In this note we report a previously undescribed association between a cephalopod and a plank- tonic gelatinous herbivore. While conducting re- search scuba studies of gelatinous zooplankton in the western Gulf of Mexico, we collected juvenile pelagic octopods of the genus Argonauta sp. Linnaeus 1758, in association with aggregate generation salps (Pegea socia (Bosc 1802)). The salp chains were composed of 40-60 indi- viduals, each approximately 10 cm in apical/ basal length. Individuals within the aggregate generation of Pegea socia (Bosc 1802) are uni- formly covered with fine reticulated gold pig- mentation and contain orange nucleii. The in- dividuals each have four noticeable body muscles forming two x-shaped groups. Within each group, the pair of muscles are not fused dorsally. Endostyle bands of each individual are slightly arched. Two juvenile octopods, a male and female with mantle lengths 8.4 mm and 6.7 mm, respectively, were collected from separate chains at a depth of 5-10 m at lat. 26°21'N, long. 95°45'W, on 26 February 1981. The males and females of Argonauta sp. have eight circumoral append- ages, none of which are filiform. The body is not flattened, has no fins and no aquiferous pores on the head. The dorsal arms of the female are not 648 FISHERY BULLETIN: VOL. 80. NO. 3, 1982. connected by a deep web and have broad ter- minal expansions modified for secretion of an external shell of egg case when mature. The left third arm of the male is hectocotylized, autono- mous, and coiled up in a sac beneath the left eye. The octopods were first noted inside the branchial cavity of one of the aggregate salps, attached by their tentacles to that individual's pharynx wall; however, they both left their hosts during our capture of the salps in quart jars. We found only one octopod per salp chain, though the salps had many hyperiid amphipods (Vibilia armata Bovallius 1887), cyclopoid copepods (Sappharina angusta Dana 1852), and fish in association. We found no morphological damage to the individual aggregate salps which had hosted the octopods. The association of juvenile octopods with salp aggregates may afford a source of food (com- mensal amphipods), flotation, transportation, and/or camouflage to the octopods. Examination of Formalin'-preserved gut contents from these octopods was inconclusive, however, since neither octopod had fed recently and only un- identifiable, residual solids remained in the gut. It is improbable that the octopod was seeking protection by attaching to the salp chain, since moving out from the host was an immediate re- action to in situ visual stimuli and/or local per- turbations. We thank C. E. Lea and G. J. Denoux for their identification of the octopods and copepods, respectively. Identification of the octopods was based on generic characteristics described by Voss (1956). Salps were classified as Pegea soda (Bosc 1802) as described by Madin and Harbison (1978). Amphipod identification was based on body shape, eye structure, and character of pereiopods as described by Bowman and Gruner (1973) for genus and Dick (1970) for species. Copepods were identified by body shape, seg- mentation, and appendage characteristics as described by Owre and Foyo (1967). Research scuba operations were supported by the National Science Foundation, grant OCE78-22481. Literature Cited Bacescu, M. 1973. A new case of commensalism in the Red Sea: the myside Idiomysis tsumamali n. sp. with the coelen- 1 Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. terata M contact us and Cassiopea. Rev. Roum. Biol. Ser. Zool. 18:3-7. Barham, E. G., and G. V. PlCKWELL. 1969. The giant isopod Anuropsus: A scyphozoan symbiont. Deep-Sea Res. 16:525-529. Bowman, T. E., and H.-E. Gruner. 1973. The families and genera of Hyperiidea (Crustacea: Amphipoda). Smithson. Contrib. Zool. 146, 164 p. Bruce, A. J. 1972. An association between a pontoniinid shrimp and a rhizostomatous scyphozoan. Crustaceana 23:300-302. Dick, R. I. 1970. Hyperiidea (Crustacea: Amphipoda). Keys to the South African genera and species, and a distribution list. Ann. S. Afr. Mus. 57:25-86. Fernando, A. S., and K. Ramamoorthi. 1974. Rare occurrence of Conchoderma virgatum (Spengler, 1790) (Cirripedia— Lepadomorpha) on a scyphozoan medusa. Curr. Sci. (Bangalore) 43:126. Harbison, G. R., D. C. Biggs, and L. P. Madin. 1977. The associations of Amphipoda Hyperiidea with gelatinous zooplankton— II. Associations with Cnidaria, Ctenophora and Radiolaria. Deep-Sea Res. 24:465- 488. Heron, A. C. 1973. A specialized predator-prey relationship between the copepod Sapphirina angusta and the pelagic tunicate Thalia democratic. J. Mar. Biol. Assoc. U.K. 53:429-435. Herrnkind, W., J. Hlusky, and P. Kanciruk. 1976. A further note on phyllosoma larvae associated with medusae. Bull. Mar. Sci. 26:110-112. Janssen, J., and G. R. Harbison. In press. Fish in salps: The association of squaretails (Tetrogonurus spp.) with pelagic tunicates. J. Mar. Biol. Assoc. U.K. Laval, P. 1980. Hyperiid amphipods as crustacean parasitoids associated with gelatinous zooplankton. Oceanogr. Mar. Biol. Annu. Rev. 18:11-56. Madin, L. P.. and G. R. Harbison. 1977. The association of Amphipoda Hyperiidea with gelatinous zooplankton — I. Associations with Salpidae. Deep-Sea Res. 24:449-463. 1978. Salps of the genus Pegea Savigny 1816 (Tunicata: Thalicea). Bull. Mar. Sci. 28:335-344. Mansueti, R. 1963. Symbiotic behaviors between small fishes and jelly fishes, with new data on that between the stromateid Pepritus alepidotus, and the scyphomedusa, Ckysaora quinquecirrha. Copeia 1963:40-80. Owre, H. B., and M. Foyo. 1967. Copepods of the Florida Current. Fauna Caribaea; Number 1. Crustacea, Part 1: Copepea. Inst. Mar. Sci., Univ. Miami, 137 p. Shojim, Y. 1963. Scyllariid phyllosomas' habit of accompanying the jelly-fish. Bull. Jpn. Soc. Sci. Fish. 29:349-353. Thomas, L. R. 1963. Phyllosoma larvae associated with medusae. Nature (Lond.) 198:208. Trott, L. B. 1972. The portunid crab Charybdis feriatus (Linnaeus) commensal with the scyphozoan jellyfish Stomolophus nomurai (Kishinouye) in Hong Kong. Crustaceana 23:305-306. 649 Vader, W. 1972. Associations between gammarid and caprellid amphipods and medusae. Sarsia 50:51-56. VOSS, G. L. 1956. A review of the cephalopods of the Gulf of Mexico. Bull. Mar. Sci. Gulf Carrib. 6:85-178. P. T. Banas D. E. Smith D. C. Biggs Department of Oceanography Texas A&M University College Station, TX 7781>3 fied by the author using scuba). Based on its con- struction, the purse seine used in waters >30 m by both NMFS and OSU was assumed to fish to about 24 m deep.2 Personnel of NMFS, fishing in waters >30 m, collected seven juvenile wolf eels in 1980 (232 sets) between Copalis Head, Wash., and Til- lamook Bay, Oreg. These fish ranged in length from 430 to 506 mm SL. One of these juvenile wolf eels had been tagged on 24 October 1978 off Doyle Island near Port Hardy, British Columbia (Fig. 1), by personnel of the Canadian Department of Fisheries and Oceans (Bailey3). The tag was applied inciden- tally to a purse seine tagging operation for chum MIGRATION OF A JUVENILE WOLF EEL, ANARRHICHTHYS OCELLATUS, FROM PORT HARDY, BRITISH COLUMBIA, TO WILLAPA BAY, WASHINGTON Juvenile wolf eels, Anarrhichthys ocellatus, were rarely reported off the Washington-Oregon coast prior to 1979. One 87 mm juvenile was col- lected by midwater trawl in 1962, 80 km off Newport, Oreg. (Wakefield 19801). Another juvenile of 468 mm standard length (SL) was caught in 1969 (51 sets) by personnel of the Northwest and Alaska Fisheries Center, Nation- al Marine Fisheries Service (NMFS), while purse seining for juvenile salmonids in shallow marine waters (<30 m in depth) adjacent to the mouth of the Columbia River. While purse seining for juvenile salmonids in these same waters, no wolf eels were caught in either 1978 (49 sets) or 1980 (67 sets) by NMFS, but in 1979 (109 sets), 19 specimens between 467 and 531 mm SL were collected. Oregon State University (OSU) personnel caught 113 juve- niles during a 10-d purse seine cruise for juvenile salmonids in 1979 (56 sets) between the Colum- bia River and Coos Bay, Oreg., in waters >30 m. These fish ranged in size from 281 to 610 mm SL (Wakefield 1980). The purse seine used in waters <30 m deep fished to a depth of about 6 m (veri- 'Wakefield, W. W. 1980. Occurrence and food habits of pelagic Anarrhichthys ocellatus juveniles collected off the Oregon coast during June, 1979. Paper presented at Sixtieth Annual Meeting of the American Society of Ichthyologists and Herpetologists at Texas Christian University, Fort Worth, Texas, June 15-20, 1980. 2J. Jurkovitch, Fishery Biologist, Northwest and Alaska Fisheries Center, National Marine Fisheries Service, NOAA, 2725 Montlake Blvd. E., Seattle, WA 98112, pers. commun. February 1981. 3D. D. Bailey, Chief, Salmon Services, Department of Fish- eries and Oceans-Pacific Region, 1090 West Pender St., Vancouver, British Columbia V6E 2P1, pers. commun. August 1980. 125° W CANADA Recapture _^_q location Willapa Bay WASHINGTON Tillamook |r Bay * i; C-olumbia River OREGON Coos Bay - X 50° N 45° Figure 1.— Location of tagging (Port Hardy, B.C.) and recap- ture (Willapa Bay, Wash.) sites of a juvenile wolf eel. 650 FISHERY BULLETIN: VOL. 80, NO. 3, 1982. salmon, Oncorhynchus keta. Only one wolf eel was tagged and its length was not recorded (Gould4). The juvenile was recaptured on 12 July 1980, 23 km off Willapa Bay, Wash., and was 502 mm long (Fig. 1). Distance traveled from tagging location to recapture site was about 593 km in 628 d. Approximate average move- ment was 0.94 km/d. Information about the early life history of wolf eels has been sparse. Kanazawa (1952) and Marliave (1978) both observed a change to adult characteristics of pigmentation and dentition at lengths between 500 and 600 mm SL. Marliave, who has reared wolf eels at the Vancouver Public Aquarium in British Columbia, placed the juvenile-adult changeover at the end of the first year of life. He also noted that the fish, by the age of 3 mo, had begun to prefer the bottom except when feeding. Shelter seeking and territoriality became evident between 4 and 5 mo of age and about 200-400 mm long. At the end of 15 mo the fish ranged from 600 to 950 mm in length with a mean of just under 700 mm. The tagged juvenile specimen has provided the first evidence of a difference in early life history of wild wolf eels compared with aquarium- reared fish with regard to juvenile behavior, growth rate, and length of time in the juvenile phase. This wolf eel possessed juvenile charac- teristics of coloration and dentition and was a minimum of 2+ yr in age. It was pelagic and be- low the lower end of the growth range attained by aquarium fish in 15 mo. There have been no reports in the literature documenting migratory behavior of this species. Adult wolf eels are known to exhibit strong ter- ritoriality and attraction to some type of struc- ture as shelter. Also a strong homing instinct exists even though a considerable amount of ter- ritory is covered while feeding away from shelter (Hulberg and Graber 1980). Ayres, a fish inhabiting the eastern North Pacific Ocean. Calif. Fish Game 38:567-574. Marliave, J. G. 1978. Laboratory culture of wolf eels. Annu. Proc. Am. Assoc. Zool. Parks Aquar., p. 160-167. David R. Miller Northwest and Alaska Fisheries Center National Marine Fisheries Service, NOAA 2725 Montlake Blvd. E. Seattle, WA 98112 Literature Cited Hulberg, L. W., and P. Graber. 1980. Diet and behaviorial aspects of the wolf-eel, Anar- rhichthys ocellatus, on sandy bottom in Monterey Bay, California. Calif. Fish Game 66:172-177. Kanazawa, R. H. 1952. Variations in the wolf eel, Anarrhichthys ocellatus 4A. Gould, Biologist, South Coast Division, Department of Fisheries and Oceans-Pacific Region, 1090 West Pender St., Vancouver, British Columbia V6E 2P1, pers. commun. December 1980. 651 INFORMATION FOR CONTRIBUTORS TO THE FISHERY BULLETIN Manuscripts submitted to the Fishery Bulletin will reach print faster if they conform to the following instruc- tions. These are not absolute requirements, of course, but desiderata. CONTENT OF MANUSCRIPT The title page should give only the title of the paper, the author's name, his affiliation, and mailing address, including ZIP code. The abstract should not exceed one double-spaced page. In the text, Fishery Bulletin style, for the most part, follows that of the U.S. Government Printing Office Sti/le Manual. Fish names follow the style of the Amer- ican Fisheries Society Special Publication No. 12, A List of Common and Scientific Names of Fishes from the United States and Canada, Fourth Edition, 1980. Text footnotes should be typed separately from the text. Figures and tables, with their legends and head- ings, should be self-explanatory, not requiring refer- ence to the text. Their placement should be indicated in the right-hand margin of the manuscript. Preferably figures should be reduced by photog- raphy to 5:V4 inches (for single-column figures, allowing for 50% reduction in printing), or to 12 inches (four double-column figures). 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The accuracy of the literature cited is the responsibility of the author. Abbreviations of names of periodicals and serials should conform to Serial Sources for the BIOSIS Data Base. (Chem ical Abstracts also uses this system, which was developed by the American Standards Associa- tion.) Common abbreviations and symbols, such as mm, m, g, ml, mg, °C (for Celsius), %, 7... and so forth, should be used. Abbreviate units of measure only when used with numerals. Periods are only rarely used with abbreviations. We prefer that measurements be given in metric units; other equivalent units may be given in paren- theses. FORM OF THE MANUSCRIPT The original of the manuscript should be typed, double-spaced, on white bond paper. Please triple space above headings. We would rather receive good duplicated copies of manuscripts than carbon copies. The sequence of the material should be: TITLE PAGE ABSTRACT TEXT LITERATURE CITED TEXT FOOTNOTES APPENDIX TABLES (Each table should be numbered with an arabic numeral and heading provided) LIST OF FIGURES (Entire figure legends) FIGURES (Each figure should be numbered with an arabic numeral; legends are desired) ADDITIONAL INFORMATION Send the ribbon copy and two duplicated or carbon copies of the manuscript to: Dr. Carl J. Sindermann, Scientific Editor Fishery Bulletin Northeast Fisheries Center Sandy Hook Laboratory National Marine Fisheries Service, NOAA Highlands. NJ 07732 Fifty separates will be supplied to an author free of charge and 100 supplied to his organization. No covers will be supplied. Contents — continued BATH, D. W., and J. M. O'CONNOR. The biology of the white perch, Morone americana, in the Hudson River estuary 599 ULANOWICZ, ROBERT E., MOHAMMED LIAQUAT ALI, ALICE VIVIAN, DONALD R. HEINLE, WILLIAM A. RICHKUS, and J. KEVIN SUMMERS. Identifying climatic factors influencing commercial fish and shellfish landings in Maryland 611 IRVINE, A. BLAIR, JOHN E. CAFFIN, and HOWARD I. KOCHMAN. Aerial surveys for manatees and dolphins in western peninsular Florida 621 Notes KANE, JOSEPH. Effect of season and location on the relationship between zoo- plankton displacement volume and dry weight in the northwest Atlantic 631 BROUSSEAU, DIANE J., JENNY A. BAGLIVO, and GEORGE E. LANG, JR. Estimation of equilibrium settlement rates for benthic marine invertebrates: Its application to Mya arenaria (Mollusca: Pelecypoda) 642 HOLT, SCOTT A., and CONNIE R. ARNOLD. Growth of juvenile red snapper, Lutjanus campechanus, in the northwestern Gulf of Mexico 644 BANAS, P. T., D. E. SMITH, and D. C. BIGGS. An association between a pelagic octopod, Argonauta sp. Linnaeus 1758, and aggregate salps 648 MILLER, DAVID R. Migration of a juvenile wolf eel, Anarrhichthys ocellatus, from Port Hardy, British Columbia, to Willapa Bay, Washington 650 nctr* ccio r\no ^TOFc - issue: $4.5(1 domestic and $5.65 foreign. s\i*3 1982 ice. jVV Hc^JVlass, [ Contents— continued Notes BOEHLERT, GEORGE W., W. H. BARSS, and P. B. LAMBERSON. Fecundity of the widow rockfish, Sebastes entomelas, off the coast of Oregon 881 BABINCHAK, JOHN A., DANIEL GOLDMINTZ, and GARY P. RICHARDS. A comparative study of autochthonous bacterial flora on the gills of the blue crab, Callinectes sapidus, and its environment 884 LE BOEUF, BURNEY J., MARIANNE RIEDMAN, and RAYMOND S. KEYS. White shark predation on pinnipeds in California coastal waters 891 SCHLOTTERBECK, ROBERT E., and DAVID W. CONNALLY. Vertical strati- fication of three nearshore southern California larval fishes (Engraulis mordax, Genyonemus lineatus, and Seriphus politus) 895 LIBBY, DAVID A. Decrease in length at predominant ages during a spawning migration of the alewife, Alosa pseudoharengus 902 GOLDBERG, STEPHEN R. Seasonal spawning cycle of the longfin sanddab, Citharichthys xanthostigma (Bothidae) 906 ROBINSON, GARY R. Otter trawl sampling bias of the gill parasite, Lironeca vulgaris (Isopoda, Cymothoidae), from sanddab hosts, Citharichthys spp 907 INDEX, VOLUME 80 911 Notices NOAA Technical Reports NMFS published during the first 6 months of 1982 The National Marine Fisheries Service (NMFS) does not approve, recommend or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to NMFS, or to this publication fur- nished by NMFS, in any advertising or sales promotion which would indicate or imply that NMFS approves, recommends or endorses any proprietary prod- uct or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or pur- chased because of this NMFS publication. IN MEMORIAM Thomas A. Manar 1912-1982 Thomas Alonzo (Lon) Manar, former Chief of the Scientific Publications Staff (now the Scien- tific Publications Office), died at his home in Encinitas, Calif., on 26 August 1982 after a heart seizure. Lon Manar was a journalist, newspaper- man, science writer, and editor in the best tradi- tions of his craft. As the Chief of the Scientific Publications Staff in Seattle, Wash., from 1970 to 1974, he set the style and format for a re- vamped U.S. Fishery Bulletin. The early years of the Marine Fisheries Review also reflected his flair for innovative and creative journalism. In 1974 his superior service and unique talents were recognized with the award of a Bronze Medal by the U.S. Department of Commerce. A graduate in journalism from the University of Oklahoma, Mr. Manar joined the Scripps In- stitution of Oceanography as scientific editor in 1951 after a stint as a meteorologist in the U.S. Army during World War II and as a newspaper- man in Oklahoma. In the early 1960's he set up the public information office at the University of California, San Diego when the campus was de- veloping. In 1965, following the death of his wife, Ruth, Mr. Manar left the University for a position with the Federal Government as Chief of Publication Services for the Bureau of Commercial Fisheries Biological Laboratory in Honolulu, Hawaii; until 1970 he lived and worked in Honolulu. His last position before retirement was as an editor and consultant with the Southwest Fisheries Center of the National Marine Fisheries Service, NOAA, in La Jolla, Calif. Mr. Manar was a man of wide interests and enthusiasm — art, music, reading, nature photog- raphy. After his retirement he traveled exten- sively in this country and abroad. He is survived by a sister, Maurine Manar of Encinitas. While Mr. Manar was not a fishery biologist, he understood scientists and their needs. Many manuscripts arrived on his desk in shambles and emerged as examples of good scientific writing. Those of us who benefited from his talents are grateful; the Fishery Bulletin has benefited the most. 653 QUALITATIVE AND QUANTITATIVE NUTRIENT REQUIREMENTS OF FISHES: A REVIEW1 Mark R. Millikin2 ABSTRACT Qualitative and quantitative protein, amino acid, lipid, fatty acid, carbohydrate, vitamin, and min- eral requirements are summarized for salmonids and warmwater fish species. Special emphasis is placed upon amino acid, vitamin, and mineral requirements of fishes, since recent research with these nutrients has contributed to a better understanding of fish physiology and nutritional require- ments. Protein requirements of fishes briefly stated are as follows: 30 to 55% dietary protein depen- dent upon age and feeding habit and dietary essential amino acids which include arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Dietary lipid concentrations as high as 12 to 24% have demonstrated sparing action of protein for growth rather than energy utilization in fishes. Essential fatty acids for fishes usually include linolenic acid or an elongated form in the 114 g (Na- tional Research Council 1977; Andrews 1977). Table 2.— Quantitative protein requirements of several fish species. Initial Protein Study Rearing mean requirement, duration temperature Species weight % dry diet (wk) (°C) Criteria' Reference Salmo gairdneri 69 40 10 16-27 G.FC.BP Satia (1974) 1.3 45 10 10 G.FC Halver et al. (1964) 61.0 42 22 8-12 G.BP Austreng and Refstie (1979) 0.7 40 32 15 G.FC Cho et al. (1976) 6.5-7.0 240-45 10 9-125 G.PER.FC Zeitoun et al (1973) Oncorhynchus kisulch 14.5 40 10 6.5-10.5 G Zeitoun et al (1974) O. tshawytscha 1.5 55 10 15 G DeLong et al (1958) 1.5 40 10 8 G DeLong et al (1958) O. nerka 1.15 45 10 10 G.FC Halver et al (1964) Micropterus salmoides ? 40 2-8 23 G.FC Anderson et al. (1981) M. dolomieui ? 45 4-9 20.5 G.FC Anderson et al. (1981) Morone saxatilis 2.25 355 6 24.5±2 G,FC Millikin (1982) 1.41 47 10 205 G,FC Millikin (in press) Pleuronectes platessa 14.5 50 12 15 G Cowey et al. (1972) Fugu rubnpes 2.0 50 3 25-26 G.FC Kanazawa et al (1980b) Anguilla japonica 3.1 44.5 8 25 G.BP Nose and Arai (1972) Tilapia zilli 1.65 35 3 24-26 G Mazid et al. (1979) T. aurea 04 336 12 26-29 G Davis and Stickney (1978) Ictalurus punctatus ? 35 26 ? G.FC Lovell (1972) 10-25 35 8 28 G.PER Murray et al. (1977) Chanos chanos 004 40 4 25-28 G.FC Lim et al. (1979) Ctenopharyngodon idella 0.15-0.20 41-43 6 22-23 G.PER Dabrowski (1977) Cypnnus carpio 5.8 38 4 ? G Ogino and Saito (1970) Chrysophrys aurata 26 38 16 ? G,FC Sabaut and Luquet (1973) 'G = growth, FC = feed conversion, BP = body protein, PER = protein efficiency ratio. 2Protein requirement increased from 40 to 45% as salinity increased from 10 to 20%o. 'Highest protein concentration examined. ing to Rumsey (1978), protein sources generally have higher metabolizable energy values than carbohydrate sources for salmonids. Thus, in many dietary protein requirement studies, fishes were probably offered higher metabolizable en- ergy values in the high protein diets compared with the low protein diets. Since fish fed low pro- tein diets may have had less available energy, additional protein may have been shunted for metabolic requirements other than growth. Many of the quantitative protein requirements, listed in Table 2, may be overestimated values due to this shift in utilization of protein in low protein diets (Rumsey 1978). Therefore, protein- energy studies examining several energy concen- trations within each of several dietary protein concentrations provide better estimates of quan- titative dietary protein requirements of fishes. Dietary protein concentration requirements The higher protein concentrations in these two ranges produce better growth of channel catfish fingerlings and subadults, whereas the lower protein concentrations provide better protein conversion (weight protein fed -r weight gain) (Andrews 1977). Increased water temperature has variable effects on the minimal protein or energy require- ment for maximal growth rate of fishes. For ex- ample, chinook salmon fingerlings require 40% protein at 8°C and 55% protein at 15°C (DeLong et al. 1958). Striped bass fingerlings (initial mean weight = 1.4 g) require 47% protein at 20.5°C, while additional dietary protein is re- quired (about 55%) at24.5°C for maximal growth of slightly larger fingerlings (initial mean 4Nutrient content of diets is expressed as percentage of the diet on a dry weight basis, unless otherwise noted. 657 FISHERY BULLETIN: VOL. 80, NO. 4 weight = 2.2 g) (Millikin in press and 1982, re- spectively). In separate studies with rainbow trout fingerlings, 35% dietary protein provided as good a growth rate as 40 or 45% protein within any of several temperature regimes (National Research Council 1981). Fingerlings (mean ini- tial weight = 2.0 g) fed either 35, 40, or 45% pro- tein grew equally well within any one tempera- ture regime (9°, 12°, 15°, and 18°C) over a 16-wk period (Slinger et al. 1977, cited in National Re- search Council 1981). Slightly larger rainbow trout (mean initial weight = 3.45 g) also grew equally well when fed 35, 40, or 45% dietary pro- tein within any one of three temperature regimes (9°, 12°, or 18°C) over a 24-wk period (Cho and Slinger 1978, cited in National Research Council 1981). Growth rates were progressively higher at each successive increase in rearing temperature, regardless of dietary protein concentration, ex- cept for 18°C in the second study. Increased feed consumption of lower protein diets occurred when rainbow trout were reared at higher tem- peratures and probably satisfied higher protein requirements at elevated water temperatures (National Research Council 1981). Chinook salm- on fry (0.4 g) require 53% dietary protein (dry weight basis) combined with 16% dietary lipid (dry weight basis) when reared at 5° or 12°C based upon weight gain and survival rates (Fow- ler 1980, 1981). However, growth rates were two to three times more rapid for chinook salmon fry reared at 12°C. Changes in salinity may alter protein require- ments of anadromous or euryhaline species. Rain- bow trout fingerlings require 45% protein for optimal growth at 20%o compared with a 40% protein requirement at 10%<> (Zeitoun etal. 1973). Since a salinity of 10%ois almost isotonic with in- ternal fluids (9%0) of rainbow trout fingerlings, the higher dietary protein requirement for rain- bow trout reared in a salinity of 20%c. suggests that the higher dietary protein concentration may assist in osmoregulation in a hypertonic ex- ternal environment for this species (Zeitoun et al. 1973). Conversely, coho salmon, O. kisutch, smolts require 40% protein in 10 and 20%«. Although maximum weight gain occurred at 40% protein in both salinities, maximum protein retention occurred at 40% protein in 10%« and 50% protein at 20%» (Zeitoun et al. 1974). The authors con- cluded that the hyperosmotic environment (20 %<>) did not stress coho salmon smolts in the same manner as previously shown with smaller rain- bow trout fingerlings. Also, underyearling rain- bow trout (mean weight = 70 g) require more dietary arginine (1.2% of the diet) when reared in freshwater than in those individuals reared in 20%o (1.0% arginine of the diet) (Kaushik 1977, cited in Poston 1978). Further work is necessary to more firmly establish whether protein require- ments change with salinity for specific life stages of various anadromous or catadromous fish spe- cies. AMINO ACIDS Qualitative and Quantitative Requirements Examination of qualitative amino acid require- ments of fishes has often been based upon growth and feed efficiency in long-term feeding studies. Typically, one of several amino acids is removed singly from a well-defined formula diet which is assumed to be nutritionally complete (i.e., posi- tive control), to determine if significant reduc- tion in weight gain occurs in fish fed the selected, amino acid-deficient diets compared with growth of fish fed the control diet. Thereafter, any group of fish fed a diet determined to be deficient in an amino acid, as indicated by reduced growth and feed efficiency, is separated into two subgroups: One subgroup is retained on the amino acid-defi- cient diet (control diet minus one amino acid), whereas the other subgroup is fed the control diet. Reduced growth rate or cessation of growth in fish fed the amino acid-deficient test diet ver- sus the control diet is considered to be confirma- tion of a dietary requirement for the specific amino acid being tested. On the basis of such amino acid feeding studies, several fish species have been found to require the same 10 amino acids (arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) as essential dietary con- stituents. Species requiring dietary inclusion of these amino acids include chinook salmon (Hal- ver et al. 1957); rainbow trout (Shanks et al. 1962); sockeye salmon, O. nerka (Halver and Shanks 1960); channel catfish (Dupree and Hal- ver 1970); Japanese eel, Anguilla japonica, and European eel, Anguilla anguilla (Arai et al. 1972b); common carp (Nose et al. 1974); red sea bream, Chryxophrys major (Yone 1975); and red- belly tilapia, Tilapia zilli (Mazid et al. 1978). Qualitative amino acid requirements of plaice, Pleuronectes platessa, and sole, Solea solea, were investigated, using intraperitoneal injections of uniformly labelled - 14C-glucose into individuals 658 MILLIKIN: NUTRIKNT REQUIRKMKNTS OF FISHES of the two fish species (Cowey etal. 1970). Forma- tion of radioactive labelled aspartic acid, glu- tamic acid, cysteine, serine, glycine, alanine, and proline over a 6-d period implied that sufficient amounts of these amino acids can be produced by underyearling plaice and sole through inter- mediary metabolism, thus suggesting dietary nonessentiality of those specific amino acids. On the other hand, arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, thre- onine, and valine were not incorporated from (U - 14C) - glucose, thus implying dietary essentiality. Although the authors suggested that metabolic requirements for tyrosine were provided from hydroxylation of ingested phenylalanine, this still needs to be tested. Possible essentiality of tryptophan was not examined, thereby leaving the status of this amino acid unresolved for the plaice and sole. Quantitative amino acid requirements deter- mined for several fish species are generally based on weight gain, feed efficiency, and sometimes free amino acid plasma levels of individuals fed graded concentrations of a particular amino acid (Table 3). In addition to those values listed in Table 3, coho salmon have been shown to require 2.4% arginine of the dry diet (6.0% of the dietary protein), 0.7% histidine of the dry diet (1.7% of the dietary protein) (Klein and Halver 1970), and 0.2% tryptophan of the dry diet (0.5% of dietary protein) (Halver 1965). Many similarities exist between species in individual quantitative amino acid requirements when expressed as a percent of dietary protein (Table 3). Amino acid composition of eggs and larval stages for a given species has been shown to be a good guideline for estimating quantitative amino acid requirements of fry and fingerling stages. For example, diets formulated to contain the amino acid composition of Atlantic salmon eggs promoted better growth of Atlantic salmon fin- gerlings than use of an amino acid pattern based on the National Research Council's (1973) recom- mendations for salmonids (Ketola 1980). Ketola (1980) also observed the same pattern of acceler- ated growth in rainbow trout fry fed diets formu- lated on the basis of egg amino acid composition of that species compared with the National Re- search Council's (1973) recommendations. In a separate study, rainbow trout fingerlings were fed a diet containing soybean meal as the sole protein source or the same diet supplemented with amino acids (leucine, methionine, lysine, valine, and threonine) to provide a dietary essen- tial amino acid profile similar to rainbow trout eggs. Improved weight gain occurred in rainbow trout fingerlings fed the amino acid supple- mented diet, thereby suggesting the similarity between amino acid profiles of rainbow trout eggs and dietary amino acid requirements of rainbow trout fingerlings (Rumsey and Ketola 1975). Amino Acid Availability A significant contribution to channel catfish diet formulation recently came from an exten- sive investigation of true amino acid availability (corrected for metabolic fecal amino acids) and apparent amino acid availability (digestibility) values of various feedstuffs commonly incorpo- rated into commercial catfish diets (Wilson et al. Table 3.— Quantitative dietary amino acid requirements for several fish species. Amino acid Channel catfish2 Chinook salmon3 Japanese eel4 Common carp5 Arginine 4 3 (1.0) 6.0 (2.4) 4.5 (1.7) 4.2 (1.6) Histidine 1.5 (0.4) 1.8 (0.7) 2.1 (0.8) 2.1 (0.8) Isoleucine 2.6 (0.6) 2.2 (0.9)6 4.0 (1.5) 2.3 (0.9) Leucine 3 5 (0.8) 3.9 (1.6)6 5 3 (2.0) 34 (1.3) Lysine 5.1 (1.2) 5.0 (2.0) 5.3 (2.0) 5.7 (2.2) Methionine 2.3 (0.6)7 4.0 (1.6)8 5.0 (1 9)8 3.1 (1.2)9 Phenylalanine 5.0 (1.2)'° 5.1 (2.1)6" 5.8 (2.2)" 6.5 (2.5)" Threonine 2.3 (0.5) 2 2 (0.9) 4.0 (1.5) 3.9 (1.5) Tryptophan 0.5 (0.1) 0 5 (0.2) 1.1 (0.4) 0.8 (0.3) Valine 3 0 (0.7) 3.2 (1.3) 4.0 (1.5) 3 6 (1.4) 'Expressed as percentage of dietary protein with requirement as percentage of dry diet in parentheses. 2Based upon 24% dietary protein (Robinson et al. 1980a) 3Based upon 40% dietary protein unless otherwise noted (National Research Council 1973). 4Based upon 37.7% dietary protein (Nose and Arai Unpubl. data, cited in Cowey and Sargent 1979) 5Based upon 38 5% dietary protein (Nose 1979) 6Based upon 41% dietary protein (National Research Council 1973) 7ln the absence of cystine which can replace 50 to 60% of methionine requirement (Harding et al. 1977). 'Methionine + cystine. 9ln the absence of cystine. '"Phenylalanine + tyrosine requirement. Tyrosine can replace ca. 50% of phenylalanine (Robinson et al. 1980a). "in the absence of tyrosine. 659 FISHERY BULLETIN: VOL. 80. NO. 4 1981). Results generally suggested that reason- able agreement occurs between average appar- ent amino acid availability and protein digesti- bility values of any one specific protein source. However, individual amino acid availabilities were quite variable within and among various feed ingredients tested. Also, apparent amino acid availability values were considerably less than true amino acid availability values for feed ingredients containing relatively low protein content (e.g., 9 to 19%), such as rice bran, rice mill feed, wheat middlings, and corn. Lysine Dietary lysine requirements for fishes range from 5.0 to 6.8% of the dietary protein. In addi- tion to the quantitative lysine requirements listed in Table 3, rainbow trout fry require 6.8% lysine and lake trout, Salvelinus namaycush, fry re- quire 6.0% lysine as a percentage of total dietary protein (Ketola 1980). Robinson et al. (1980b) re- ported a dietary lysine requirement of 5% of the dietary protein for channel catfish fed an ade- quate dietary protein concentration (30%); thus confirming a dietary lysine requirement (5.1% of the dietary protein) for channel catfish fed a marginal dietary protein concentration of 24% (Wilson et al. 1977). Excessive dietary lysine in the presence of marginal or adequate dietary arginine concentrations did not depress growth or feed efficiency of channel catfish, nor did ex- cessive arginine depress growth or feed efficien- cy of channel catfish in the presence of marginal dietary lysine concentrations (Robinson et al. 1981). This is in contrast to lysine-arginine an- tagonisms reported for several terrestrial spe- cies (Maynard and Loosli 1969). Lysine deficiency in fish may conceivably re- sult in depressed rates of collagen formation. Hydroxylysine has been shown to be a constituent of collagen in several fish species (Mehrle5). Fin rot occurred in rainbow trout fed a lysine-defi- cient diet containing corn gluten meal as the sole protein source (Ketola 1979a). Supplementation of a combination of lysine, arginine, histidine, isoleucine, threonine, tryptophan, and valine to the corn gluten meal diet resulted in improved survival, increased growth, and prevention of severe caudal fin erosion. At the same time, 5Paul M. Mehrle, Columbia National Fisheries Research Laboratory, U.S. Fish and Wildlife Service, Columbia, MO 65201, pers. commun. December 1981. removal of lysine from the amino acid mixture in the corn gluten meal supplemented diet in- creased mortality, reduced growth, and resulted in caudal fin erosion of rainbow trout. Methionine Quantitative dietary methionine requirements for several fish species have been shown to de- pend upon dietary cystine concentration, since cystine can substitute for a portion of the methi- onine requirement. This is the result of the con- version of methionine to cystine being a common pathway of intermediary metabolism in many terrestrial animals (Maynard and Loosli 1969) as well as fish (National Research Council 1973). Rainbow trout fingerlings require 0.6% methio- nine (1.7% of the dietary protein) and 0.45% cys- tine (1.29% of the dietary protein), a total sulfur amino acid requirement of 1.05% of the diet (2.99% of dietary protein). This is based upon growth and feed efficiency as demonstrated by feeding studies, using a factorial design of 0.3 to 0.75% methionine and 0.04 to 0.6% cystine (Page 1978). Excessive cystine for rainbow trout (e.g., 0.6%) did not partially satisfy methionine re- quirements in methionine-deficient diets (0.3 and 0.45% methionine) based on weight gain and feed conversion. Chinook salmon require 0.5 to 0.6% dietary methionine (1.3 to 1.5% of the dietary pro- tein) in the presence of 1.0% dietary cystine, whereas 1.6% methionine did not produce maxi- mum growth in the presence of 0.05% dietary cystine (Halver et al. 1959). Channel catfish re- quire 0.56% dietary methionine (2.34% of the die- tary protein) in the absence of cystine, while 60% of the methionine requirement is replaceable with cystine (Harding et al. 1977). Methionine deficiency has been shown to re- sult in cataractogenesis in lake trout fingerlings and rainbow trout fingerlings. After 12 wk, rain- bow trout fingerlings (initial mean weight = 1.5 g) fed 0.6% methionine plus 0.3 or 0.45% cystine did not develop any cataracts (Page 1978). Lower dietary methionine content (0.3 or 0.45%) com- bined with dietary cystine content ranging from 0.04 to 0.6% produced varying degrees of cata- racts in rainbow trout. In another study, lake trout fingerlings were fed methionine-deficient diets (0.36% methionine = 0.96% of the dietary protein) containing soybean protein isolate as the sole protein source (40% of the diet). After 8 wk, lake trout fingerlings showed only initial signs of opacification of subcapsular areas (Pos- 660 MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES ton et al. 1977). However, after 16 wk, 100% of lake trout fed 0.36% dietary methionine devel- oped bilateral lenticular cataracts, while none of the individuals fed the control diet containing 1.2% dietary methionine (3.27% of the dietary protein) had cataracts. Attempts to supplement suboptimal dietary concentrations of methionine plus cystine with dietary taurine or inorganic sulfate have proven unsuccessful with channel catfish fingerlings and rainbow trout fingerlings. Channel catfish fingerlings fed dietary taurine or inorganic sul- fate as a partial replacement for methionine had reduced growth rates (Robinson et al. 1978), whereas rainbow trout fingerlings had reduced growth and developed cataractogenesis (Page et al. 1978). The absence of cataractogenesis in me- thionine-deficient channel catfish may be the result of the relatively shorter duration of this study (8 wk) compared with a 16-wk study on lake trout (Poston et al. 1977). Another explana- tion for the absence of cataract formation in channel catfish may be due to the slightly larger initial size of channel catfish (mean weight = 7.7 g) compared with lake trout (mean weight = 5 g). Either of these factors may have produced a slower turnover rate of amino acids in channel catfish. According to a summary by Poston et al. (1977), insufficient methionine often results in reduc- tions in sulfhydryl group concentrations, and lens glutathione synthesis also decreases rapidly during formation of most cataracts. The authors speculated that lens glutathione possibly pro- tects the lens sulfhydryl groups from oxida- tion. Tryptophan Tryptophan deficiency symptoms have been described in rainbow trout; sockeye salmon; brook trout, S. fontinalis; and channel catfish. Tryptophan deficiency in rainbow trout and sock- eye salmon has resulted in scoliosis (Shanks etal. 1962; Halver and Shanks 1960, respectively). In a separate study with rainbow trout, hyperemia, scoliosis, and abnormal deposition of calcium occurred in kidney and bony plates surrounding the notochord and sheath of fish fed tryptophan- deficient diets (Kloppel and Post 1975). The authors suggested that hyperemia might be at- tributed to a lack of serotonin resulting from a deficiency of its precursor, tryptophan. In dis- cussing scoliosis, Kloppel and Post (1975) noted that tryptophan is a major component of proto- collagen, a supposed precursor of collagen. How- ever, the absence of scoliosis in channel catfish fingerlings fed tryptophan-deficient diets (Wil- son et al. 1978), compared with studies on sal- monids, probably resulted from a slower growth rate of channel catfish because of a larger initial mean weight (12.5 g). Quantitative tryptophan requirements have been shown to be similar for three different sal- monid species and channel catfish. Almquist- type plots of growth responses indicated dietary tryptophan requirements of 0.15 to 0.25% of the diet (0.4 to 0.6% of dietary protein) for chinook salmon and 0.20 to 0.25% of the diet (0.5 to 0.6% of dietary protein) for sockeye salmon and coho salmon (Halver 1965). Channel catfish finger- lings fed a tryptophan-deficient diet (0.05%) for 8 wk had significantly poorer weight gain and feed efficiency than individuals fed diets containing as low as 0.12% tryptophan (0.5% of dietary pro- tein) (Wilson et al. 1978). Wilson et al. (1978) sug- gested that the lower dietary tryptophan require- ment of fishes compared with that of terrestrial animals may be due to an inability of fish to con- vert tryptophan to niacin, thus reducing the metabolic need of tryptophan in fishes as com- pared with terrestrial species. Growth rate of brook trout and the low ratio of two enzyme activities (3-hydroxyanthranilic acid oxygenase to picolinic acid carboxylase) concerned with an intermediate of the conversion pathway of tryp- tophan to niacin indicated that dietary trypto- phan is not an efficient niacin precursor for this species (Poston and DiLorenzo 1973). Addition- ally, a low ratio of the two liver enzyme activities exists in lake trout, rainbow trout, Atlantic salm- on, and coho salmon compared with terrestrial vertebrates (Poston and Combs 1980). LIPIDS Optimal Dietary Lipid Concentrations and Protein-to-Energy Ratios Optimal dietary lipid concentrations for inclu- sion in formulated feeds for fishes involve con- sideration of several factors. The minimal die- tary lipid concentration that maximizes dietary protein available for growth rather than energy (i.e., protein sparing) may be excessive for diet incorporation if fish are being cultured as a lean product for human consumption, or if freezer storage space is unavailable to retard develop- 661 FISHERY BULLETIN: VOL. 80. NO. 4 ment of oxidative rancidity of the diets. However, if fish are being hatchery cultured for release into natural waters, high body lipid composition may be beneficial as an energy source during acclimation to natural food (Wedemeyer et al. 1980). Also, feeds that contain the minimal die- tary lipid concentration required for maximal protein sparing action for a particular species are relatively cost-effective. Protein sparing action of various dietary lipid concentrations has been examined for several fish species. Channel catfish fingerlings (mean initial weight = 1.25 g) cultured at 26.7° to 32.2°C and fed 35% protein diets grew faster on 8% die- tary lipid, either as beef tallow or corn oil, than on 4% of either dietary lipid source (Dupree 1969a). Dietary lipid concentrations of 16% corn oil or beef tallow reduced growth rate and pro- tein deposition of channel catfish compared with 8% dietary lipid. Therefore, maximal protein sparing action occurred at <16% of either die- tary lipid source but >8% dietary lipid. In a sep- arate study, larger channel catfish fingerlings (initial mean weight = 7.0 to 7.5 g), cultured at 30°C and fed 25% protein diets containing either 5, 8, 12, 15, or 20% bleached menhaden oil, had maximal weight gain and protein deposition when fed 25% protein with 15% lipid (Dupree et al. 1979). Channel catfish fingerlings (either 0.5 or 1.0 g initial mean weight in separate experi- ments) reared at 28°C grew faster when fed 35% protein plus 12% lipid, rather than 5% lipid com- bined with 25 or 35% protein or 12% lipid com- bined with 25% protein (Murray etal. 1977). Con- versely, when channel catfish reared at 23°C were fed 25 or 35% protein combined with 5 or 12% lipid, 5% lipid plus 25 or 35% protein was sufficient for maximal weight gain and food con- version, probably due to lower metabolic require- ments. Channel catfish with initial and final mean weights of 14 and 100 g, respectively, re- quired 35% protein and 12% lipid, whereas sub- adults weighing 114 to 500 g required 25% pro- tein and 12% lipid when reared at 27°C (Page and Andrews 1973). Protein-to-energy ratio require- ments of channel catfish fingerlings (initial mean weight = 7.0 g) as a function of protein deposition were found to be 88 mg protein/kcal between dietary energy concentrations of 275 to 341 kcal/100 g when reared at 26.7°C (Garling and Wilson 1976). However, maximal weight gain occurred in fish fed 32 to 36% protein. There- fore, for the most cost-effective feed, the optimal dietary protein concentration for channel catfish fingerlings reared at 26.7°C is between 24 and 32%, when considering weight gain, feed effi- ciency, and protein deposition. Rainbow trout fingerlings (initial mean weight = 4.8 g) reared at 12.2°C over an 18-wk period had equally good growth rates when fed 35% protein and 24% lipid as individuals fed 44 or 53% protein, each com- bined with either 8, 16, or 24% lipid. This indi- cated a minimal dietary lipid concentration of 24% for maximal protein sparing action and an optimal protein-to-energy ratio of 73 mg protein/ kcal (Lee and Putnam 1973). Conversely, a study evaluating three dietary protein concentrations (33, 39, and 44%) combined with 22% lipid in each of three forms (22% herring oil, 14.6% herring oil plus 7.4% lard, or 11% herring oil plus 11% lard) in a 3 X 3 factorial showed that better growth was obtained in rainbow trout fingerlings (initial mean weight = 5.4 g) fed 44% protein and 22% lipid, regardless of the ratio of herring oil to lard when reared at 1 1.5°C over a 14-wk period ( Yu et al. 1977). Protein efficiency ratios and protein retention values were similar, regardless of die- tary protein concentration and lipid source com- binations fed to rainbow trout fingerlings. The contradictory results of these two studies in the minimal dietary protein required (35% protein plus 24% lipid versus 44% protein plus 22% lipid) for maximal growth of rainbow trout fingerlings can be partially explained by differences in die- tary fiber concentrations. A low dietary fiber concentration (6.5%) was incorporated in diets containing 36, 44, or 53% protein plus 24% lipid, whereas a high dietary fiber concentration (22.4%) was incorporated in diets containing 36, 44, or 53% protein plus 8% lipid (Lee and Putnam 1973). However, in the study by Yu et al. (1977), dietary fiber concentrations were held constant at 11.2% in all diets. Therefore, variable dietary fiber concentrations in the first study may have differentially affected amino acid absorption rates or feed utilization. Successive increases in dietary lipid concentration of 7, 11, or 16% in 30% protein diets or 9, 15, or 21% lipid in 40% protein diets resulted in increased weight gain and im- proved feed conversion of rainbow trout finger- lings (initial mean weight =2g) within each dietary protein concentration when reared at 11°C (Reinitz et al. 1978b). Minimal dietary pro- tein and lipid concentration requirements were not determined, since the highest dietary protein (40%) plus lipid (21%) combination that was eval- uated also produced maximal growth and opti- mal feed conversion ratios for rainbow trout fin- 662 MII.LIK1N: NUTRIENT REQUIREMENTS OF FISHES gerlings. A separate study demonstrated that about 35% protein combined with either 23 or 27% dietary lipid provided better growth of rain- bow trout fingerlings than 36% dietary protein combined with 14% dietary lipid (Reinitz and Hitzel 1980). However, the two high lipid concen- tration diets did not produce better growth rates of rainbow trout fingerlings than a 35% protein, 18% lipid diet. C. E. Smith et al. (1979) reported that rainbow trout brood stock fed high energy, high protein diets (16% lipid plus 48% protein or 17% lipid plus 49% protein) produced a greater volume of larger eggs than did fish fed diets low and intermediate in energy and protein (6% lipid plus 36% protein or 9% lipid plus 42% protein). However, considerable variation in protein (i.e., amino acid profiles) and lipid (i.e., fatty acid profiles) sources used between diets in this study makes interpretation of the data difficult. Striped bass fingerlings reared at20.5°C and fed 37, 47, or 57% protein with 7, 12, or 17% lipid in a 3X3 factorial design showed maximal protein sparing action of lipid for growth when fed 12% lipid combined with 47% dietary protein or 17% lipid combined with 57% protein (Millikin in press). Juvenile turbot, Scophthalmus maximus, fed 35% protein combined with 3, 6, or 9% lipid plus 9 or 18% carbohydrate attained best growth and feed conversion when fed the diet containing 35% protein, 9% carbohydrate, and 9% lipid (Adron et al. 1976). Possibly, additional dietary lipid would have further spared protein for growth rather than energy. Also, a diet contain- ing 35% protein, 9% carbohydrate, and 9% lipid produced similar growth and feed conversion of turbot when compared with a diet containing 55% protein, 9% carbohydrate, and 3% lipid. Juve- nile blue tilapia, Tilapia aurea, with initial and final mean weights of 2.5 and 7.5 g, respectively, require about 56% protein and 460 kcal/100 g diet (123 mg protein/kcal) while fish >7.5 g re- quired 34% protein and 320 kcal/100 g diet (109 mg protein/kcal) for maximum growth (Winfree and Stickney 1981). Essential Fatty Acids Inclusion of either linolenic acid (18:3o>3) or a more highly unsaturated fatty acid in the a>3 series in the diet of rainbow trout is essential. Rainbow trout fingerlings fed diets containing 1% 18:3cu3 as a supplement to 7.8% corn oil dou- bled their weight gain compared with individ- uals fed 10% corn oil as the sole dietary lipid source (Lee et al. 1967). Castell et al. (1972a) de- termined that 1% 18:3co3 or ethyl linolenate pro- duced larger rainbow trout than 1% linoleic acid (18:2oj6) or ethyl linoleate. Additionally, 1% 18: 3o»3 prevented essential fatty acid deficiency symptoms (e.g., fin erosion, heart myopathy, shock syndrome, and swollen, pale livers), while as much as 5% 18:2a>6 did not cure such symptoms (Castell et al. 1972b). Dietary linolenic acid's essentiality and growth enhancing ability for rainbow trout was confirmed in another study, wherein 1% methyl linolenate plus 4% methyl laurate (C 12:0) provided maximal growth and prevention of fatty acid deficiency symptoms compared with fish fed 5% methyl laurate (Wa- tanabe et al. 1974). Rainbow trout fingerlings fed either 0.5% 20:5a;3 or 0.5% 22:6o>3 had better growth rates than individuals fed 0.5% 18:3a>3 in diets containing 5% total lipid, thereby showing a higher essential fatty acid efficiency of 20:5co3 and 22:6cu3 at low dietary concentrations of these fatty acids (Takeuchi and Watanabe 1977). How- ever, it is unknown whether evaluation of higher dietary concentrations (e.g., 1 to 3%) of each of these fatty acids would have produced similar differences in essential fatty acid efficiencies in terms of growth and feed efficiency of rainbow trout fingerlings. Yu and Sinnhuber (1972) found that 1% dietary 18:3cu3 or 1% docosahexae- noic acid (22:6cw3) provided similar growth rates in rainbow trout fingerlings. No higher dietary concentrations of either fatty acid were studied, nor were total dietary lipid concentrations >2% (dry diet basis) examined. The essentiality of 18: 3o»3 for rainbow trout was further substantiated in a 34-mo feeding study in which fingerlings fed 1% ethyl linolenate plus 5% ethyl laurate grew to maturity and produced viable offspring which in turn had normal growth rates (Yu et al. 1979). Incorporation of 1.5% ethyl linoleate to a lipid mix of 1% ethyl linolenate plus 3.5% ethyl laurate did not confer any additional advantage in growth rate, percent fertile eggs, or percent viable fry for rainbow trout compared with indi- viduals fed the 1% ethyl linolenate diet. Closely related species such as coho salmon and rainbow trout have different quantitative dietary requirements for 18:3a>3 administered as the triacylglycerol, trilinolenin. Coho salmon fin- gerlings required 1 to 2.5% trilinolenin for maxi- mum growth and feed efficiency when fed die- tary trilinolenin concentrations ranging from 0 to 5%. High dietary trilinolein concentrations (>1%) in the presence of the optimal trilinolenin 663 FISHERY BULLETIN: VOL. 80, NO. 4 concentrations fed to coho salmon fingerlings re- sulted in reduced growth rate and feed efficiency values (Yu and Sinnhuber 1979). On the other hand, rainbow trout fingerlings had best growth rates and feed efficiency when fed higher trilino- lenin concentrations combined with low trilino- lein concentrations (5% trilinolenin plus 0% trili- nolein or 3% trilinolenin plus 1% trilinolein) (Yu and Sinnhuber 1976). In a separate study, rain- bow trout fingerlings fed a diet sufficient in 18: 3cu3 (1% ethyl linolenate) actually had better growth rates and feed efficiency than fish fed 1% ethyl linolenate plus 1.5% ethyl linoleate (Yu and Sinnhuber 1975). Dietary supplements of 5% ethyl linoleate to feeds containing 0.1, 0.5, or 1% ethyl linolenate markedly reduced growth and feed efficiency of rainbow trout finger- lings. Chum salmon, 0. keta, fed 5% dietary lipid as either 5% methyl laurate, 4% methyl laurate plus 1% 18:2oj6, 4% methyl laurate plus 1% 18:3o>3, or 3% methyl laurate plus 1% 18:2o>6 and 1% 18:3to3, showed best weight gain and feed efficiency when offered the 3% methyl laurate plus simul- taneous supplements of 1% 18:2cu6 and 1% 18:3o»3 (Takeuchi et al. 1979). Also, simultaneous sup- plementation of 18:2w6 (1%) and 18:3o;3 (1%) pro- duced slightly better weight gain of chum salmon fingerlings than 4% methyl laurate plus 1% of a highly unsaturated fatty acid mix (containing 26.5% 20:5a>3 plus 42.1% 22:6a>3). However, mini- mal dietary requirements of 18:2a;6 or 18:3a>3for optimal growth rate of chum salmon fingerlings were not determined. Dietary supplements of either methyl linoleate or methyl linolenate at 0.5 or 1.0% concentrations provided better growth of Japanese eel finger- lings than a fat-free diet or 7% methyl laurate (T. Takeuchi et al. 1980). However, contradictory results in two separate studies by these investi- gators prevent any conclusions regarding mini- mal requirements of 18:2oj6 and 18:3co3 for this species. Common carp fry and fingerlings have demon- strated better growth when fed diets containing highly polyunsaturated fats (e.g., cod liver oil) than those containing 5% methyl laurate (Wata- nabe 1975a, b). Intermediate growth rates oc- curred in common carp fry fed either 1% methyl linoleate or 1% methyl linolenate plus 4% methyl laurate over a 22-wk period (Watanabe et al. 1975a), whereas 1% methyl linoleate or 1% methyl linolenate did not improve growth of common carp fingerlings over an 18-wk period (Wata- nabe et al. 1975b). High variability exists among various fish spe- cies in ability to elongate and desaturate dietary 18-carbon fatty acids to 20- or 22-carbon fatty acids. Several marine species appear to have lower enzymatic elongation-desaturation capa- bilities than freshwater fishes. Administration of (1 — 14C) 18:3a>3 to individuals of red sea bream; black sea bream, Mylio macrocephalus; opaleye, Girella nigricans; striped mullet, Mugil cephalus; and rainbow trout indicated that only rainbow trout exhibited appreciable radioactiv- ity in 22:6c«3 of body lipids (Yamada et al. 1980). Therefore, it was concluded that marine species have limited ability to elongate and desaturate 18:3w3, resulting in dietary essentiality of eico- sapentaenoic acid (20:5a>3) or 22:6a>3 and non- essentiality of 18:3oj3. In another study, injec- tions of (1 — 14C) 18:3(o3 into two individuals of each of several fish species resulted in inten- sive incorporation of 18:3o>3 into 20:5ai3 and 22: 6cu3 in rainbow trout, while very low percent bioconversion of 18:36 as well as elevated 22:6^3 concentrations in individuals fed 1% 18:3a;3, sug- gesting an ability of rainbow trout to elongate and desaturate linoleic and linolenic acid. Also, rainbow trout, fed a fat-free diet or 5% oleic acid (18:1oj9) as the sole dietary lipid, accumulated high body lipid concentrations of eicosatrienoic acid (20:3w9), an indicator of essential fatty acid deficiency in terrestrial animals. Furthermore, comparison of dietary fatty acid composition and initial and final body fatty acid composition of rainbow trout in another feeding study, suggests the ability of this species to elongate and desatu- rate 20:5tu3 into 22:6a»3 (Castledine and Buckley 1980). Cowey et al. (1976) concluded thatturbot lack the necessary microsomal desaturases to effectively convert 18:lcu9, 18:2co6, or 18:3oj3 into polyunsaturated fatty acids for deposition in neutral fats or phospholipids based upon growth and body lipid composition. Also, 1% dietary 18: 3w3 or 1% arachidonic acid (20:49. Additionally, 1% cod liver oil plus 4% 18:lco9 produced better growth rates of turbot than all other dietary treatments (Cowey et al. 1976). Simultaneous supplementation of 0.45% 18:2o>6 and 0.45% 18: 3a>3 as the only dietary constituents of the o»6 and o»3 series did not increase the level of 20:5w3 or 22:6tu3 liver triglycerides in underyearling plaice (Owen et al. 1972). Growth studies of red sea bream indicated that a 2% dietary polyunsatu- rated fatty acid mix (38% 20:5^3, 1.4% 22:5^6, and 33.4% 22:6o»3) promoted significantly better weight gain than fish fed up to 4.2% dietary methyl linolenate (Fujii and Yone 1976). It was concluded that 18:3a>3 is not essential for red sea bream, since this species has little, if any, capa- bility to elongate and desaturate 18-carbon fatty acids to 20- and 22-carbon fatty acids, based upon body fatty acid composition. Specific qualitative and quantitative essential fatty acid requirements have not been deter- mined for channel catfish fry (Yingst and Stick- ney 1979) and channel catfish fingerlings (Na- tional Research Council 1977; Stickney 1977). Nevertheless, growth rates of channel catfish in several studies comparing various lipid sources (e.g., beef tallow, menhaden oil, safflower oil, and corn oil) have consistently been high in indi- viduals fed menhaden oil as the chief dietary lipid (Stickney and Andrews 1971, 1972; Murray et al. 1977; Dupree et al. 1979; Yingst and Stick- ney 1979, 1980). Typically, menhaden oil con- tains a large amount of fatty acids of the tu3 family (Stickney 1977), especially the polyun- saturated fatty acids (e.g., 3% 18:3w3, 17% 20:5a>3, and 13% 22:6w3). Therefore, w3 fatty acids may be essential for channel catfish, especially in the fry and early fingerling stages. Unlike most fish species studied, Tilapia zilli, fingerlings require 1% 18:2cw6 or 20:4a>6 for opti- mal weight gain as opposed to fatty acids of the w3 series (Kanazawa et al. 1980a). However, this same species has a greater relative ability to elon- gate and desaturate 18:3w3 to 20:5a>3 and 22:6a>3, than to elongate and desaturate 18:2cu6 to 20:4co6 (Kanazawa, Teshima, and Imai 1980). In a review of lipid requirements of fishes, Castell (1979) discussed differences in fatty acid composition of fishes due to salinity, tempera- ture, diet composition, depth, seasonal variation, and reproductive stage; requirements, metabo- lism, and functions of dietary fatty acids for fishes are also discussed. CARBOHYDRATES Carbohydrates are included in formulated feeds for fish primarily as a low cost source of energy to spare dietary protein for growth rather than energy. Protein sparing action of dietary carbohydrate was demonstrated in brook trout fed marginal concentrations of dietary protein (28 or 32%) with optimal protein-to-calorie ratios of 75 mg protein/kcal (Ringrose 1971). Maximal dietary carbohydrate concentrations that can be fed to fish without reducing growth rate depend upon whether the fish species is car- nivorous, omnivorous, or herbivorous. For exam- ple, maximal dietary dextrin concentrations that did not reduce growth rate were 10% for yel- lowtail, Seriola quinqueradiata, 20% for red sea bream and 30% for common carp (Furuichi and Yone 1980). Rainbow trout subadults can be fed 38% wheat meal or 41% cooked wheat (17 to 25% of dietary metabolizable energy) without dele- terious effects on growth (Edwards et al. 1977). Similarly, rainbow trout fed 32% wheat meal or 21% wheat meal plus 13% glucose (15 and 26% metabolizable energy of the diet) did not have significant differences in growth rate (Refstie and Austreng 1981). However, dietary Cerelose6 concentrations as low as 14%, substantially in- creased liver glycogen concentrations of rainbow trout compared with fish fed 0 or 7% dietary Cerelose (Hilton 1982). Additionally, low rearing temperatures (10° vs. 15°C) for rainbow trout resulted in increased liver glycogen concentra- tions. Therefore, Hilton (1982) suggested that stocking rainbow trout with high liver glycogen concentrations into natural waters could result in impaired liver function. Incipient lethal levels of waterborne copper were reported to be lower for rainbow trout fed higher concentrations of available carbohydrate, probably as the result of impaired liver function from high liver glycogen content (Dixon and Hilton 1981). Digestibility of carbohydrates is generally in- versely related to molecular complexity. Thus, monosaccharides are more available nutrition- ally to fishes than are disaccharides, which in turn are more available than are polysaccha- rides. Relative growth rates of chinook salmon fingerlings fed 20% carbohydrate were as fol- lows: glucose > sucrose > fructose > maltose > dextrin > potato starch > galactose (Buhler and 6Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 665 FISHERY BULLETIN: VOL. 80, NO. 4 Halver 1961). Brook trout fingerlings (initial mean weight = 1.6 g) fed 14% glucose, galactose, or fructose over a 20-wk period had better growth rates when fed 14% glucose or fructose (McCart- ney 1971). Rainbow trout fingerlings had better growth rate, feed conversion, and protein effi- ciency when fed 30% glucose concentrations com- pared with 30% raw corn starch or 15% glucose plus 15% cellulose (Bergot 1979a). Dietary glu- cose concentrations as high as 30% doubled plasma glucose 6 h after the first meal, while normal plasma glucose concentrations were at- tained 24 h later (Bergot 1979b). Channel catfish fingerlings can utilize 2.25 g of dextrin in place of 1 g of lipid for growth equally well within die- tary lipid concentrations of 5 to 12.5% and digest- ible carbohydrate concentrations of 5.6 to 22.5% (Garling and Wilson 1977). Dietary fiber is not required by fishes and is considered to be a nonnutrient bulk component in fish diets. According to Leary and Lovell (1975), dietary cellulose in excessive amounts probably decreases absorption of essential nutri- ents by physical obstruction of enzymes and in- creased rate of passage through the digestive system. Obstruction of enzyme activity may re- sult from ingested fiber chelating metal ions serving as cofactors of enzymes. Dietary cellu- lose concentrations as high as 8% did not inhibit growth of channel catfish, whereas 14% dietary cellulose depressed growth. No similar studies have been conducted with salmonids or other fish species to evaluate maximum tolerable, dietary fiber concentrations. Cellulase activity in stomachs of several fish species and intestinal portions of stomachless Cyprinidae was positively correlated with amount of detritus consumed (Prejs and Blasz- czyk 1977). Microflora ingested along withdetri- tal material is probably responsible for the cellu- lase activity in fish; however, further research should examine sources of cellulase activity, espe- cially in herbivorous species. VITAMINS Qualitative vitamin requirements of fishes (National Research Council 1973, 1977) and their biochemical and physiological functions are gen- erally similar to requirements and functions demonstrated for terrestrial animals. Early qualitative vitamin requirement studies of fishes usually consisted of long-term feeding trials (e.g., 14 to 24 wk) in which laboratory cultured salmonids were fed a positive control diet (i.e., assumed to be nutritionally complete) or that same diet omitting one of several vitamins (McLaren et al. 1947; Halver and Coates 1957; Coates and Halver 1958). Growth, survival, be- havior, internal organ appearance, blood physi- ology, and histopathology were often examined to describe deficiency symptoms. Also, fish fed a vitamin-deficient diet were often divided into two subgroups during the course of the study. One subgroup remained on the vitamin-deficient diet while the recovery subgroup was fed the complete diet to detect positive responses such as accelerated growth rate and disappearance of deficiency symptoms. More recently, biochemical criteria such as activities of specific enzymes requiring a given vitamin for coenzyme formation have been used to determine qualitative and quantitative vita- min requirements of fishes (C. E. Smith et al. 1974; Cowey 1976). According to C. E. Smith et al. (1974), biochemical defects in the form of re- duced enzyme activity allow detection of pre- clinical vitamin deficiencies. A review of vitamin requirements of fishes was presented by Halver (1979). Thiamine Essentiality of dietary thiamine has been veri- fied for brook, brown {Salmo trutta), and rainbow trout (McLaren et al. 1947; Phillips and Brock- way 1957), chinook salmon (Halver 1957), coho salmon (Coates and Halver 1958), channel cat- fish (Dupree 1966), rainbow trout (Kitamura et al. 1967a; Aoe et al. 1969), Japanese eel (Arai et al. 1972a), red sea bream (Yone 1975), and turbot (Cowey et al. 1975). Thiamine deficiency symp- toms commonly observed in many of these fish species include anorexia, poor growth, depig- mentation, and loss of equilibrium. Hemorrhage and congestion of fins has been noted in thiamine- deficient Japanese eel (Hashimoto et al. 1970; Arai et al. 1972a) and thiamine-deficient com- mon carp (Aoe et al. 1969). Quantitative thiamine requirements have been determined for turbot and channel catfish. Cowey et al. (1975) detected optimal erythrocyte transketolase (thiamine pyrophosphate serves as coenzyme) activity in turbot fed 2.6 mg thiamine/ kg dry diet, whereas maximal growth occurred at dietary thiamine concentrations >0.6 mg/kg dry diet. Therefore, in addition to growth rates, functional evidence such as enzyme activity also 666 MII.I.IKIN: NUTRIENT REQUIREMENTS OK KISIIKS provides additional useful information for esti- mating quantitative vitamin requirements. Channel catfish fingerlings require a minimal dietary thiamine concentration of 1 mg/kg dry diet based upon maximal weight gain, feed effi- ciency, and prevention of thiamine deficiency symptoms such as anorexia, poor growth, dark coloration, and higher mortality (Murai and Andrews 1978a). Hematocrit values of channel catfish were unaffected by dietary thiamine con- centrations ranging from 0.1 to 20.1 mg/kg dry diet. It is unknown why channel catfish and com- mon carp require lower dietary concentrations of thiamine compared with salmonids. Omnivo- rous fish would seemingly require higher amounts of thiamine for oxidative decarboxyla- tion of pyruvate and the transketolase reaction of the pentose phosphate shunt, due to the ability of herbivores and omnivores to metabolize higher dietary carbohydrate concentrations than car- nivorous fish such as salmonids (Murai and An- drews 1978a). Riboflavin Dietary essentiality for riboflavin has been re- ported for rainbow trout (McLaren et al. 1947), brook, brown, and lake trout (Phillips and Brock- way 1957), chinook salmon (Halver 1957), Atlan- tic salmon (Phillips 1959a), channel catfish (Du- pree 1966), common carp ( Aoe et al. 1967a; Ogino 1967), rainbow trout (Kitamura et al. 1967a; Poston et al. 1977; L. Takeuchi et al. 1980), Japa- nese eel (Arai et al. 1972a), and red sea bream (Yone 1975). Rainbow trout (mean initial weight = 5.9 g) fed riboflavin-deficient diets developed bilateral corneal and lenticular lesions after 11 and 15 wk of the experimental period (Poston et al. 1977). Further evaluations of cataract forma- tions induced from riboflavin deficiency in rain- bow trout fingerlings confirmed no retinal dam- age according to histopathological examinations (Hughes et al. 1981a). Fin necrosis, snout erosion, and spinal deformation also occurred in ribo- flavin-deficient rainbow trout (Poston et al. 1977). In a separate study, rainbow trout finger- lings ( initial mean weight = 1.5 g) fed riboflavin- deficient diets displayed anorexia, poor growth, high mortality rate, lesion of fins, and cataract formation during an 8-wk study (L. Takeuchi et al. 1980). Common carp fingerlings fed ribofla- vin-deficient diets showed anorexia, poor growth, high mortality rate, and hemorrhage of skin and fins (L. Takeuchi et al. 1980). Murai and Andrews (1978b) reported 100% occurrence of "short body dwarfism" due to shortening of individual verte- brae in riboflavin-deficient channel catfish after 20 wk. These authors speculated that abnormal vertebral growth may be related to hypothyroid- ism which in turn may be caused by riboflavin deficiency. Quantitative riboflavin requirements have been determined for common carp, rainbow trout, and channel catfish. In several different studies, riboflavin requirements of carp finger- lings apparently declined with increasing fish size based on growth rate and liver riboflavin content. Common carp fingerlings with an initial mean weight equalling 1.5 g required 20 mg riboflavin/kg dry diet over a 6-wk period (Aoe et al. 1967a). Slightly larger carp fingerlings (ini- tial mean weight = 2.8 g) required 10 mg ribofla- vin/kg dry diet over a 6-wk period (Ogino 1967), whereas individuals with an initial mean weight equalling 3.4 g required 5 to 7 mg riboflavin/kg dry diet (L. Takeuchi et al. 1980). Rainbow trout with an initial mean weight of 7 g required 12.2 mg riboflavin/kg for maximal growth, whereas 18.2 mg riboflavin/kg were required for satura- tion of head and posterior kidney tissue (Wood- ward 1982). However, larger rainbow trout fin- gerlings (initial mean weight = 11.2 g) required 3 mg riboflavin/kg dry diet according to growth, food conversion, and mean erythrocyte glutathi- one reductase activity coefficient or 12 mg ribo- flavin/kg dry diet for maximal liver riboflavin content (Hughes et al. 1981b). Rainbow trout fingerlings (initial mean weight = 1.5 g) required 4 mg riboflavin/kg dry diet based upon growth rate and feed efficiency and 6 mg riboflavin/kg dry diet based on liver riboflavin content (L. Takeuchi et al. 1980). Channel catfish fingerlings require 9 mg riboflavin/kg dry diet for maximal growth and 3 mg riboflavin/kg dry diet to pre- vent occurrence of short body dwarfism (Murai and Andrews 1978b). Pyridoxine Dietary essentiality of pyridoxine has been re- ported for rainbow trout (McLaren et al. 1947), brook, brown, and lake trout (Phillips and Brock- way 1957), chinook salmon (Halver 1957), Atlan- tic salmon (Phillips 1959a), coho salmon (Coates and Halver 1958), common carp (Ogino 1965), channel catfish (Dupree 1966), rainbow trout (Kitamura et al. 1967a), yellowtail (Sakaguchi et 667 FISHERY BULLETIN: VOL. 80, NO. 4 al. 1969), Japanese eel (Arai et al. 1972a), red sea bream (Yone 1975), turbot (Adron et al. 1978), and gilthead bream, Spams aurata (Kissil et al. 1981). Coates and Halver (1958) mentioned sev- eral pyridoxine deficiency symptoms for coho salmon including nervous disorders, hyperirri- tability, poor appetite, indifference to light, and rapid occurrence of postmortem rigor mortis. Halver (1957) reported the following additional pyridoxine deficiency symptoms for chinook salmon: ataxia, edema of peritoneal cavity, color- less serous fluid, blue-green coloration on dorsal surface, and excessive flexing of opercles. Clini- cal signs of pyridoxine deficiency in rainbow trout include hyperirritability, nervous dis- orders, erratic and rapid swimming, flexing of opercles, greenish-blue coloration, and tetany, just before death (C. E. Smith et al. 1974). Pyri- doxine-deficient rainbow trout displayed normo- cytic, normochromic anemia, indicating that pyridoxine has a function in maintenance of normal erythropoiesis in this species (C. E. Smith et al. 1974). Also, rainbow trout fed pyridoxine- def icient diets for 7 d had lower aspartate amino- transferase activity in white muscle, whereas liver aspartate and alanine aminotransferase activity was reduced after 28 d (Jurss 1978, 1981). Pyridoxine deficiency symptoms in channel cat- fish fingerlings included nervous disorders, er- ratic swimming, opercle extension, and tetany (Dupree 1966). Andrews and Murai (1979) con- firmed a pyridoxine requirement for channel catfish fingerlings, reporting that fish fed pyri- doxine-deficient diets displayed anorexia, ner- vous disorders, tetany, and blue-green coloration on the dorsal surface. No anemia was detected in pyridoxine-deficient individuals, whereas a mi- crocytic, normochromic anemia was observed in channel catfish fed 20 mg/kg or greater of pyri- doxine. Chinook salmon fingerlings fed a high protein diet (65%) require about 15 mg pyridox- ine/kg diet for optimal growth and disease re- sistance to Vibrio anguillarum (Hardy et al. 1979). Quantitative pyridoxine requirements are known for channel catfish, red sea bream, gilt- head bream, turbot, and common carp. Channel catfish fingerlings require a minimum of 4.2 mg pyridoxine/kg dry diet for maximal growth (An- drews and Murai 1979). Red sea bream required a minimum of 5 to 6 mg pyridoxine/kg dry diet for maximal glutamic oxaloacetic transaminase activity and maximal glutamic pyruvate trans- aminase activity (Yone 1975). A minimum of 2 to 5 mg pyridoxine/kg dry diet is required for maximal weight gain and pyridoxine liver con- tent of red sea bream (Yone 1975). Kissil et al. (1981) reported optimal dietary pyridoxine con- centrations for gilthead bream as a function of growth (1.97 mg pyridoxine/kg dry diet) and liver alanine aminotransferase activity (3.0 to 5.1 mg pyridoxine/kg dry diet). Pyridoxine deficien- cy symptoms in gilthead bream included hyper- irritability, erratic swimming behavior, poor food conversion, retarded growth, and high mor- tality. Turbot fed pyridoxine concentrations of 1.0 mg/kg dry diet up to 30 mg/kg had similar growth rates, whereas individuals fed 0.26 or 0.50 mg pyridoxine/kg dry diet had reduced weight gain (Adron et al. 1978). Liver alanine aminotransferase activity and muscle and liver aspartate aminotransferase activity increased with higher dietary pyridoxine concentrations up to 2.5 mg/kg dry diet. Therefore, a dietary pyridoxine concentration of 2.5 mg/kg dry diet satisfied both maximal growth and liver aspar- tate aminotransferase activity for turbot. Com- mon carp fingerlings required 5.4 mg pyridox- ine/kg dry diet for maximal growth rate and prevention of deficiency symptoms (Ogino 1965). Niacin Niacin has been shown to be an essential die- tary constituent for rainbow trout (McLaren et al. 1947), brook and brown trout (Phillips and Brockway 1957), lake trout (Phillips 1959b), chi- nook salmon (Halver 1957), channel catfish (Du- pree 1966), common carp ( Aoe et al. 1967c), Japa- nese eel (Arai et al. 1972a), brook trout (Poston and DiLorenzo 1973), and red sea bream (Yone 1975). Hemorrhage and lesions of the skin have been reported in niacin-deficient channel catfish (Andrews and Murai 1978) and Japanese eel (Arai et al. 1972a). Dietary requirements for maximal growth include 28 mg niacin/kg dry diet for common carp (Aoe et al. 1967c) and 14.4 mg niacin/kg dry diet for channel catfish finger- lings (Andrews and Murai 1978). Pantothenic Acid Essentiality of dietary pantothenic acid has been demonstrated for rainbow trout (McLaren et al. 1947), brown, brook, rainbow, and lake trout (Phillips and Brockway 1957), Atlantic salmon (Phillips 1959a), chinook salmon (Halver 668 MILLIKIN: NUTRIENT REQUIREMENTS OF EISHES 1957), coho salmon (Coates and Halver 1958), channel catfish (Dupree 1966), rainbow trout (Kitamura et al. 1967a), Japanese eel ( Arai et al. 1972a), and red sea bream (Yone 1975). Most of these species fed pantothenic acid-deficient diets displayed mucous covered gills, anorexia, re- duced weight gain, and "clubbed gills." Quantitative pantothenic acid requirements have been determined for channel catfish fry (250 mg/kg dry diet) and channel catfish finger- lings (10 mg/kg dry diet) (Murai and Andrews 1975 and 1979, respectively) and common carp fingerlings (40 mg/kg dry diet) (Ogino 1967). Murai and Andrews (1975) suggested that the relatively high dietary pantothenic acid require- ments of channel catfish fry might be partially due to higher rates of micronutrient losses in small feed crumbles (high surface to volume ratio) fed to fry compared with larger feed par- ticles fed to fingerlings. Ascorbic Acid Ascorbic acid has several important physio- logical functions in fishes and is the vitamin most sensitive to processing and storage losses in fish formula feeds. Therefore, extensive re- search has been conducted on qualitative and quantitative ascorbic acid requirements for fishes. Ascorbic acid is a cofactor of an enzyme which is involved in hydroxylation of proline and lysine during collagen formation, thereby con- tributing to bone and skin formation. Ascorbic acid also has a role in iron metabolism and de- toxification of organic pollutants such as toxa- phene and polychlorinated biphenyls during ac- cumulation in the liver. Qualitative dietary ascorbic acid requirements have been reported for rainbow trout (McLaren et al. 1947; Kitamura et al. 1965; Hilton et al. 1978; Sato et al. 1978; John et al. 1979), brook trout (Poston 1967), coho salmon and rainbow trout (Halver et al. 1969), yellowtail (Sakaguchi et al. 1969), Japanese eel (Arai et al. 1972a), chan- nel catfish (Lovell 1973; Wilson and Poe 1973), red sea bream (Yone 1975), mrigal, Cirrhina mrigala (Mahajan and Agrawal 1980a), and snake head, Channa punctatus (Mahajan and Agrawal 1979). Ascorbic acid deficiency symp- toms in coho salmon and rainbow trout include reduced growth, distorted and twisted filament cartilage of the gill arches, acute lordosis and scoliosis, and eventual dislocation of vertebrae (Halver et al. 1969). Other physiological changes in ascorbic acid-deficient rainbow trout include low hematocrit values (Hilton etal. 1978; John et al. 1979), and high plasma levels of triglycerides and cholesterol (John et al. 1979). Halver (1972b) reported that the rate of repair of experimentally induced wounds in salmonids is directly related to the amount of ascorbic acid intake. Rainbow trout fed ascorbic acid-deficient diets for 18 wk displayed impaired collagen formation in the skin according to an in vitro radioisotopic method with labeled proline (Yoshinaka et al. 1978). Brook trout fingerlings fed ascorbic acid-defi- cient diets over a 34-wk period developed scoliosis and/or lordosis, increased mortality rate, and in- ternal hemorrhaging (Poston 1967). Scorbutic channel catfish experienced lordosis, scoliosis (and ultimately, broken back), hemorrhage with- in the vertebral column, and brittle vertebrae (Wilson and Poe 1973). Also, these investigators reported reduced serum alkaline phosphatase activity (65% lower), lower vertebral collagen content (42% less on a dry basis), and less hydroxy- proline in the collagen of scorbutic channel cat- fish. Wilson and Poe (1973) speculated that re- duced serum alkaline phosphatase activity may indicate reduced bone formation from lower osteoblastic activity. In addition to the aforemen- tioned common ascorbic acid deficiency symp- toms (e.g., lordosis, scoliosis, hemorrhage along spinal column, and poor growth), channel catfish had increased susceptibility to pathogenic bac- terial infestation (Aeromonas liquefaciens) and occasional formation of hemivertebrae (Lovell 1973). Also, Halver et al. (1975) reported hyper- plasia of nuclei of eye support cartilage in salmo- nids deficient in ascorbic acid. Vertebral collagen percentages of 24.5% or less and liver ascorbic acid concentrations of 50 /ig/g or less occurred in ascorbic acid deficient channel catfish finger- lings with an initial mean weight equalling 22 g (Lovell and Lim 1978). In contrast, channel cat- fish fingerlings fed sufficient ascorbic acid had 26% or greater vertebral collagen and 65 ng or greater ascorbic acid/g of liver tissue. In a sepa- rate study, Lim and Lovell (1978) reported the following ascorbic acid deficiency symptoms in smaller channel catfish fingerlings (initial mean weight = 2.3 g): 1) anorexia after 9 wk, 2) scolio- sis, lordosis, and darker pigmentation after 10 wk, and 3) lower hematocrit values after 18 wk. Also, liver ascorbic acid concentrations of 30 \xgjg and vertebral collagen percentages of 25% or less occurred in ascorbic acid-deficient channel cat- fish in this smaller size range. Snake heads with 669 FISHERY BULLETIN: VOL. 80, NO. 4 ascorbic acid deficiency had an elevated liver cholesterol content after 150 d, in addition to the occurrence of scoliosis, lordosis, and decreased ascorbic acid concentrations in blood and kidney (Mahajan and Agrawal 1979). Ascorbic acid de- ficiency in fish from the same study resulted in normochromic, normocytic anemia after 120 d and normochromic, macrocytic anemia between 180 and 210 d (Agrawal and Mahajan 1980). Using 45Ca as a tracer, snake heads had reduced absorption of calcium from surrounding water by gills and skin and lower muscle and bone cal- cium content when fed an ascorbic acid-deficient diet for 210 d (Mahajan and Agrawal 1980b). Since distortion of gill filaments from cartilage malformation often occurs in ascorbic acid-defi- cent fish, decreased calcium absorption through the gills may have resulted from the ascorbic acid deficiency (Mahajan and Agrawal 1980b). Channel catfish (initial weight slightly >5 g), fed either 670 or 5,000 mg of ascorbic acid/kg dry diet, did not receive any additional advantages in weight gain or backbone collagen concentration (Mayer et al. 1978). However, channel catfish ex- posed to increasingly higher concentrations of toxaphene were at least partially protected from growth retardation, vertebral development anomalies, and skin integrity problems, when higher dietary ascorbic acid concentrations were consumed. For instance, the no-effect toxaphene concentration on skin integrity (e.g., mucous cell numbers and epidermal thickness) was <37 ng/1 for channel catfish fed 63 or 670 mg ascorbic acid/kg dry diet, while the no-effect toxaphene concentration was between 68 and 108 ng/1 for fish fed 5,000 mg ascorbic acid/kg dry diet (Mayer et al. 1978). Methods to measure rupture (the force level causing specimen failure) and elastic limit (the force level above which perma- nent structural damage occurs in a test speci- men) according to Hamilton et al. (1981a) were used to evaluate effects of ascorbic acid deficiency on bone strength of channel catfish (Hamilton et al. 1981b). Channel catfish fingerlings (initial weight = 4 to 5 g) fed diets containing no ascorbic acid had significant reductions in length and weight after 150 d. Also, after 150 d, fish fed no supplemental ascorbic acid had reductions of 10% in backbone collagen and 16% in hydroxy- proline concentration in collagen. Additionally, in channel catfish fed no supplemental ascorbic acid, 24% less force was required to cause perma- nent damage of vertebral centra (elastic limit) and failure of vertebral centra (rupture) occurred at 16% less force than in individuals fed 500 mg ascorbic acid/kg dry diet. Quantitative ascorbic acid requirements have been determined for several fish species. Rain- bow trout (initial mean weight = 0.3 g) require 100 mg ascorbic acid/kg dry diet and coho salm- on (initial mean weight = 0.4 g) require about 50 mg ascorbic acid/kg dry diet based upon blood and anterior kidney ascorbic acid concentrations and growth rate (Halver et al. 1969). The mini- mal level of ascorbic acid in the blood of coho salmon and rainbow trout accompanying normal growth and survival rate is 35 Mg ascorbic acid/g blood. Hilton et al. ( 1978) reported a lower ascor- bic acid requirement (40 mg/kg dry diet) for larger rainbow trout (initial mean weight = 6.7 g), based upon growth, feed conversion, survival rate, and serum iron levels. Andrews and Murai (1975) estimated that channel catfish fingerlings (initial mean weight = 2.3 g) require 50 mg ascor- bic acid/kg dry diet over a 28-wk period based on growth, feed conversion, and absence of ascorbic acid deficiency symptoms. Channel catfish fin- gerlings (initial mean weight = 2.3 g) required 30 mg ascorbic acid/kg dry diet over a 22-wk period for maximal growth, whereas 60 mg ascorbic acid/kg (the next highest experimental concentration) was sufficient to prevent distor- tion of gill filament cartilage and promote re- generation of skin and muscle in experimentally inflicted wounds after 10 d (Lim and Lovell 1978). Mahajan and Agrawal (1980a) concluded that mrigal fry and fingerlings require about 700 mg ascorbic acid/kg dry diet based upon growth, survival rates, and percentage occurrence of skeletal deformities. Several sources of dietary ascorbic acid have been evaluated for relative nutritional value for channel catfish and rainbow trout. Channel cat- fish fingerlings (initial mean weight = 7.9 g) fed equimolar concentrations of 25 mg i.-ascorbic acid (uncoated or ethylcellulose coated) or dipo- tassium L-ascorbate 2-sulfate dihydrate (AS) per kg dry diet over a 20-wk period did not show sco- liosis, whereas 42% of the fingerlings fed a diet containing <5 mg ascorbic acid/kg dry diet had scoliosis (Murai et al. 1978). Maximal weight gains and feed efficiency of channel catfish var- ied with dietary ascorbic acid sources. Only 50 mg of ethylcellulose coated or uncoated L-ascor- bic acid were required for maximal growth and feed efficiency, while 200 mg of L-ascorbate-2- sulfate dihydrate were required for similar in- crements of weight gain. Generally, growth 670 MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES reached a maximum when blood L-ascorbic acid concentrations reached 7 Aig/ml (Murai et al. 1978). Rainbow trout which were considerably younger (0.3 g) than channel catfish from the previous study, required about 80 mg of dipotas- sium ascorbic-2-sulfate (DAS)/kg dry diet over a 20-wk period to avoid ascorbic acid deficiency symptoms in the majority of fishes, and 160 mg DAS/kg dry diet to achieve normal growth (Hal- ver et al. 1975). Choline Dietary essentiality of choline has been demon- strated for rainbow trout (McLaren et al. 1947), brook and brown trout (Phillips and Brockway 1957), lake trout (Phillips 1959b), chinook salm- on (Halver 1957), coho salmon (Coates and Hal- ver 1958), channel catfish (Dupree 1966), rainbow trout (Kitamura et al. 1967a), common carp (Ogino et al. 1970a), Japanese eel (Arai et al. 1972a), and red sea bream (Yone 1975). Choline deficiency symptoms in fish include poor growth and feed efficiency, anorexia, fatty livers, and hemorrhagic areas in kidneys, liver, and intes- tine. Quantitative choline requirements have been estimated for common carp fingerlings and lake trout fingerlings. Ketola (1976) examined rela- tive growth rates of lake trout fed an unsupple- mented diet (30 mg choline/kg dry diet) compared with equimolar supplements of aminoethanol, dimethylaminoethanol, methylaminoethanol, be- taine-HCl, and choline (equivalent to 2,600 mg choline/kg dry diet). Lake trout fed the unsupple- mented diet and aminoethanol and betaine sup- plements had reduced growth rates and high liver fat content. It was concluded that since betaine, a source of labile methyl groups, did not affect growth or liver fat content, any metabolic function of choline in regulation of liver fat in lake trout is unrelated to transmethylation. In a separate feeding study, a quantitative dietary choline requirement of 1,000 mg/kg dry diet was determined for lake trout fingerlings (Ketola 1976). Common carp require an estimated mini- mal dietary choline-Cl concentration of 2,000 mg/kg dry diet based upon slightly reduced growth and fatty livers in individuals fed cho- line-deficient diets (Ogino et al. 1970a). The pos- sible role of methionine as a methyl donor and its relative efficiency in preventing fatty liver and hemorrhagic degenerations of kidneys of choline- deficient fish has not yet been investigated. Folic Acid and Cyanocobalamin Qualitative folic acid requirements have been demonstrated for brook, brown, and rainbow trout (Phillips and Brockway 1957), chinook salmon (Halver 1957), coho salmon (Coates and Halver 1958), channel catfish (Dupree 1966), rainbow trout (McLaren etal. 1947; Kitamura et al. 1967a), Japanese eel (Arai et al. 1972a), and rohu, Labeo rohita (John and Mahajan 1979). However, common carp fingerlings (mean initial weight = 2.5 g) fed several folic acid concentra- tions (0 to 15 mg/kg diet) over 16 wkdid not show differential responses in growth, feed conversion, folic acid liver content, and erythrocyte counts (Aoe et al. 1967b). Folic acid deficiency symptoms in chinook salmon include poor growth, anorexia, anemia, lethargy, dark coloration, and megaloblastic erythropoiesis (Halver 1957), while coho salmon displayed poor growth and anorexia (Coates and Halver 1958). Channel catfish fed folic acid-defi- cient diets displayed lethargy, anorexia, and in- creased mortality (Dupree 1966). Anemia in coho salmon fed folic acid-deficient diets was macro- cytic with poikilocytosis of erythrocytes and a reduction in number of the erythrocytes (Smith and Halver 1969). Clinical folic acid deficiency symptoms in coho salmon in the same study in- cluded reduced growth, pale gills, exophthalmia, dark coloration, and distended abdomens with ascites fluid. These authors suggested that blood cell formation in fish is very sensitive to folic acid deficiency because of the importance of folic acid in incorporation of nucleotides into deoxyribo- nucleic acid. Phillips (1963) detected anemia (type was not reported) in brook trout fingerlings fed folic acid-deficient diets after 9 wk. Qualitative cyanocobalamin requirements have been demonstrated for chinook salmon (Halver 1957) and channel catfish (Dupree 1966). Halver (1957) reported growth retardation and reduced hemoglobin concentrations and erythro- cyte numbers in chinook salmon fed a cyanoco- balamin-deficient diet for 16 wk. Channel catfish fed cyanocobalamin-deficient diets displayed growth retardation after 36 wk (Dupree 1966) or lower hematocrits after 24 wk (Limsuwan and Lovell 1981). Limsuwan and Lovell( 1981) demon- strated that intestinal microorganisms synthe- sized about 1.4 ng of cyanocobalamin/g body weight per day. Lack of differences in growth, hemoglobin concentration, and erythrocyte num- bers in fish fed either 21.8 ng cyanocobalamin/g 671 FISHERY BULLETIN: VOL. 80, NO. 4 diet or 1.8 ng cyanocobalamin/g diet suggested that cyanocobalamin requirements are margi- nal for channel catfish (initial mean weight = 7.1 g) over a 24-wk period. However, channel cat- fish fry and early fingerling stages may have demonstrated a cyanocobalamin requirement under similar conditions. The effects of feeding folic acid-deficient or folic acid plus vitamin Bi2(cyanocobalamin)-defi- cient diets have been examined with brook trout (Phillips 1963) and rohu (John and Mahajan 1979). During the time interval between 9 and 15 wk of a feeding study, anemia was more pro- nounced in brook trout fed a diet deficient in both vitamin Bi2 and folic acid than in individuals fed a diet deficient in folic acid only. Lethargy, mus- cular loss, and poor growth rate were accentu- ated in rohu fed a diet concurrently deficient in folic acid and cyanocobalamin, compared with fish fed diets deficient in either folic acid or cyanocobalamin, singly. Megaloblastic anemia occurred in rohu fed a folic acid-deficient diet, a cyanocobalamin-deficient diet, and a diet defi- cient in both vitamins (John and Mahajan 1979). Biotin Qualitative dietary requirements for biotin have been demonstrated for brook, brown, and lake trout (Phillips and Brockway 1957), chinook salmon (Halver 1957), coho salmon (Coates and Halver 1958), goldfish, Carassius auratus (Tomi- yama and Ohba 1967), common carp (Oginoetal. 1970b), Japanese eel (Arai et al. 1972a), channel catfish (Robinson and Lovell 1978), and lake trout (Poston and Page 1982). Biotin deficiency symptoms generally occurring in salmonids in- clude anorexia, poor growth, and depressed liver acetyl CoA carboxylase and pyruvate carbox- ylase (Poston and Page 1982). Biotin deficiency signs include spastic convulsions, fragmentation of erythrocytes, and muscle atrophy in chinook salmon (Halver 1957), depigmentation in chan- nel catfish (Robinson and Lovell 1978), abnormal synthesis of liver fatty acids and high liver glyco- gen content in brook trout (Poston and McCart- ney 1974), pale-colored gills often with a mucous coating, protruding beyond the operculum in rainbow trout (Castledine et al. 1978), and high rates of deposition of glycogen in kidney tubules and short, thick gill lamellae in lake trout (Pos- ton and Page 1982). Biotin has been shown to be important in af- fecting growth and acetyl CoA carboxylase ac- tivity in fish. Lake trout fingerlings required a minimum of 0.1 mg biotin/kg dry diet for opti- mal growth rate and a minimum of 0.5 mg bio- tin/kg dry diet for optimal swimming stamina (Poston 1976a). Acetyl coenzyme A carboxylase activity has been shown to be fully activated in livers of rainbow trout containing >3.3 ^g bio- tin/g liver (Castledine et al. 1978). Dietary biotin concentrations of 8 mg/kg dry diet enhanced liver pyruvate decarboxylase activity in channel catfish fingerlings (Robinson and Lovell 1978), whereas 6 mg biotin/kg dry diet increased acetyl CoA carboxylase and pyruvate decarboxylase activities in brook trout fingerlings (Poston and McCartney 1974). Common carp fingerlings re- quire 1 mg biotin/kg dry diet for maximal weight gain and biotin liver content (Ogino et al. 1970b). Since biotin-containing lipogenic and gluco- neogenic enzymes or both may have low activity in biotin-deficient trout, increased liver glycogen concentrations and altered liver fatty acid com- positions may result (Poston and McCartney 1974; Poston 1976a). High concentrations of liver glycogen were reported in biotin-deficient lake trout (Poston 1976a; Poston and Page 1982) and rainbow trout (Castledine et al. 1978). Altered liver fatty acid composition occurred in biotin-deficient brook trout (Poston and McCart- ney 1974) and rainbow trout (Castledine et al. 1978). Liver lipid concentrations did not vary be- tween channel catfish fed 0% or 8 mg biotin/kg dry diet over a 22-wk period (Robinson and Lovell 1978). Biotin-deficient diets resulted in larger liver size in brook trout compared with individ- uals fed sufficient dietary biotin (6 mg/kg dry diet) (Poston and McCartney 1974), whereas the presence (8 mg/kg dry diet) or absence of dietary biotin did not affect liver size in channel catfish (Robinson and Lovell 1978). Inositol Qualitative requirements for inositol have been reported for rainbow trout (McLaren et al. 1947), brook, brown, and rainbow trout (Phillips and Brockway 1957), chinook salmon (Halver 1957), coho salmon (Coates and Halver 1958), common carp (Aoe and Masuda 1967), Japanese eel (Arai et al. 1972a), and red sea bream (Yone 1975). General inositol deficiency symptoms in- clude poor feed digestibility and utilization, anorexia, reduced growth, and distended abdo- mens (Halver 1972a). Skin lesions occurred in common carp fed inositol-deficient diets and in- 672 MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES eluded the following physiological and morpho- logical changes: hemorrhage around the base of the dorsal fin, loss of skin mucosa, and "slough- ing off of scales and fins (Aoe and Masuda 1967). Quantitative inositol requirements are avail- able only for common carp and red sea bream. Common carp require 4 g inositol/kg dry diet for maximal weight gain, feed conversion, and pre- vention of skin lesions (Aoe and Masuda 1967). Red sea bream require between 550 and 900 mg inositol/kg dry diet in direct proportion to die- tary glucose concentrations of 10 to 40% (Yone 1975). Currently, quantitative inositol require- ments for salmonids are based upon dietary con- centrations (250 to 400 mg/kg dry diet) that were included in the control diets used to determine qualitative vitamin requirements of chinook salmon (Halver 1957). Vitamin A Vitamin A has been shown to be an essential dietary constituent for channel catfish (Dupree 1966), rainbow trout (Kitamura et al. 1967b), common carp (Aoe et al. 1968), goldfish (Jones et al. 1971), and brook trout (Poston et al. 1977). General physiological functions of vitamin A in fish include a role in maintaining normal growth rate, pigmentation, and vision. Long-term feed- ing studies have consistently yielded various eye malformations (e.g., popeye, cataracts, hermor- rhage) in fish fed vitamin A-deficient diets. Rain- bow trout fed no supplemental vitamin A in a semipurified diet developed corneal pitting and homogeneous clouding, thickening of the corneal epithelium, and degeneration of the retina (Pos- ton et al. 1977). However, growth during the 22- wk period was similar regardless of dietary vita- min A content (0% vs. 10,000 International Units (IU) vitamin A/kg dry diet). Brook trout of a smaller initial weight (0.15 g) than the rainbow trout fingerlings (5.9 g) grew significantly faster over a 20-wk period when fed 10,000 IU vitamin A/kg dry diet compared with 0% vitamin A (Pos- ton et al. 1977). Pronounced eyeball protrusions and dermal depigmentation occurred in brook trout fed vitamin A-deficient diets. Histopatho- logical examinations of eyes of salmonids have shown that lens damage does not occur in vita- min A-deficient fish (Poston et al. 1977). Vitamin A deficiency symptoms in channel catfish include depigmentation, opaque and protruding eyes, atrophy, and death (Dupree 1970). Vitamin A- deficient goldfish developed exophthalmos, loss of scales, anorexia, and eventual mortality (Jones etal. 1971). Conversion efficiency of /3-carotene to vitamin A has been examined indirectly for channel cat- fish and brook trout. Dupree (1966) indicated that 12 mg /?-carotene/kg dry diet (equal to 20,000 IU of vitamin A/kg dry diet) were insufficient to prevent popeye in channel catfish fed vitamin A- deficient diets, whereas 450 IU of vitamin A/kg dry diet were sufficient to prevent occurrence of popeye in channel catfish fed diets devoid of /3- carotene. These results suggested an inefficient conversion rate (if any) of /3-carotene to vitamin A in channel catfish (Dupree 1966). In a separate study, channel catfish fingerlings (mean initial weight = 2.25 g) fed 1,000 IU vitamin A acetate had optimal weight gain and no occurrence of popeye or other vitamin A deficiency symptoms (Dupree 1970). Poston etal. (1977) demonstrated indirectly that brook trout can convert dietary /3-carotene into vitamin A with conversion effi- ciency being greater at 12.4°C than at 9°C. Indi- viduals fed 6 mg /3-carotene/kg dry diet (10,000 IU vitamin A activity/kg for many terrestrial animals) without supplemental vitamin A did not develop depigmentation or pronounced eye- ball protrusion. However, brook trout fed 10,000 IU vitamin A palmitate/kg dry diet without sup- plemental /3-carotene grew significantly better than fish fed 6 mg /3-carotene/kg dry diet. Addi- tionally, brook trout fed 0.6 mg /3-carotene/kg dry diet (1,000 IU vitamin A activity) during the same experimental period developed pronounced eyeball protrusion at either 9° or 12.4°C. Vitamin D Qualitative requirements for cholecalciferol have been determined for channel catfish and rainbow trout. Lovell and Li (1978) demonstrated the essentiality of dietary cholecalciferol for channel catfish fingerlings via greater weight gain and bone mineralization (total body ash, phosphorus, and calcium) in individuals fed 500 IU cholecalciferol/kg dry diet compared with 0% dietary cholecalciferol. Hypervitaminosis was not detected since dietary cholecalciferol concen- trations as high as 1,000,000 IU/kg dry diet did not suppress body weight gain nor body fixation of calcium and phosphorus. Barnett et al. (1979a) established the essentiality of cholecalciferol for rainbow trout fingerlings using two dietary con- centrations (0% vitamin D3 compared with 1,000 IU/kg dry diet). These investigators found that 673 FISHERY BULLETIN: VOL. 80, NO. 4 symptoms of cholecalciferol deficiency included decreased weight gain and feed efficiency, marked increase in plasma triiodothyronine (T3) levels, lethargy, anorexia, increased lipid con- tent of white muscle and liver, and clinical signs of tetany. Further study of cholecalciferol defi- ciency in rainbow trout indicated occurrence of tetany of the epaxial musculature (white muscle fibers) and changes in muscle ultrastructure, while red muscle fibers constituting the lateral line musculature appeared to be normal (George et al. 1979). These changes were interpreted as being indicative of disruption of calcium homeo- stasis. Bone ash, calcium and phosphorus, alka- line phosphatase, plasma calcium, and plasma magnesium were similar in rainbow trout fed either 1,000 IU cholecalciferol/kg dry diet or 0% cholecalciferol. Possibly, feeding dietary chole- calciferol concentrations >1,000 IU/kg to rain- bow trout fingerlings would have influenced cal- cium, phosphorus, or magnesium content of bone or plasma. Plasma T3 concentrations of rainbow trout were unaffected by calcium supplementa- tion of vitamin D-deficient diets and plasma and skeletal calcium levels were unaffected by a lim- ited range of dietary vitamin D content (0 to 1,000 IU cholecalciferol/kg dry diet) (Leather- land et al. 1980). Relative efficacy of dietary ergocalciferol com- pared with dietary cholecalciferol was examined in channel catfish fingerlings (Andrews et al. 1980) and rainbow trout fingerlings (Barnett et al. 1979b; Leatherland et al. 1980). Dietary con- centrations of 1,000 IU/kg or less promoted simi- lar growth rates when identical amounts of ergo- calciferol and cholecalciferol were fed to channel catfish. Comparison of identical dietary concen- trations of cholecalciferol and ergocalciferol above 1,000 IU/kg (2,000 to 20,000 IU/kg) re- sulted in greater weight gain of fingerlings fed cholecalciferol. Based upon weight gain, channel catfish fingerlings (initial mean weight = 2.3 g) require dietary cholecalciferol at greater concen- trations than 1,000 IU/kg dry diet, but <4,000 IU/kg dry diet (Andrews et al. 1980). Slightly larger channel catfish (initial mean weight = 6.0 g) require dietary cholecalciferol at greater concentrations than 1,000 IU/kg dry diet, but <2,000 IU/kg dry diet. Hypervitaminosis oc- curred in channel catfish fed 50,000 IU/kg of ergocalciferol or cholecalciferol as evidenced by reduced weight gain and feed efficiency. How- ever, vertebral bone ash was not affected by vari- ous dietary ergocalciferol or cholecalciferol con- centrations. Leatherland et al. (1980) reported that an inverse relationship between T3, a growth stimulating hormone, and dietary vitamin D concentration (cholecalciferol or ergocalciferol) existed in rainbow trout fingerlings. They specu- lated that hypersecretion of T3 in fish fed vitamin D-deficient diets may be a compensatory re- sponse. Cholecalciferol concentrations of 200 or 800 IU/kg promoted slightly better growth of rainbow trout than identical concentrations of ergocalciferol (200 or 800 IU/kg). Also, 800 IU of cholecalciferol/kg was the only dietary vitamin D concentration which significantly reduced T3 concentrations of fish compared with those fed a vitamin D-deficient diet. Barnett et al. (1979b) reported that rainbow trout fingerlings require between 1,600 and 2,400 IU of cholecalciferol/kg dry diet and that cholecalciferol is three times more effective than ergocalciferol in promoting weight gain. Vitamin E Vitamin E has been established as an essential dietary component for chinook salmon (Woodall et al. 1964), brown trout (Poston 1965), channel catfish (Dupree 1969b; Murai and Andrews 1974), Atlantic salmon (Poston et al. 1976), com- mon carp (Watanabe et al. 1970a; Watanabe and Takashima 1977), and rainbow trout (Cowey et al. 1981a). Vitamin E deficiency symptoms in channel catfish include poor growth, reduced food conversion, exudative diathesis, muscular dystrophy, depigmentation, fatty livers, anemia, and atrophy of pancreatic tissue (Murai and An- drews 1974). Dietary supplementation of dl-«- tocopherol (25 to 100 mg/kg) fed to channel cat- fish fingerlings removed all of these deficiency symptoms, whereas an antioxidant, ethoxyquin (125 mg/kg), did not significantly improve hematocrit levels or reduce incidence of muscu- lar dystrophy. Vitamin E deficiency symptoms in chinook salmon included poor growth, exoph- thalmia, ascites, anemia, clubbed gills, epicar- ditis, and ceroid deposition in the spleen (Woodall et al. 1964). Brook trout fingerlings fed vitamin E-deficient diets had reduced growth rates, in- creased mortality, and lower microhematocrit values than did fish fed a diet containing 500 mg of m.-a-tocopherol acetate/kg dry diet (Poston 1965). Atlantic salmon fed vitamin E-deficient diets displayed anemia, pale gills, anisocytosis, poikilocytosis, exudative diathesis, dermal depigmentation, muscular dystrophy, and in- 674 MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES creased carcass fat and water content (Poston et al. 1976). Vitamin E has been shown to be important in reproductive physiology of fishes. Adult female common carp (initial mean weight = 100 g) fed a vitamin E-deficient diet for 17 mo displayed re- duced weight gain, lower gonadosomatic index, apparent muscular dystrophy (degenerative epaxial muscles), higher muscle water content, lower muscle protein content, and lower concen- trations of yolk granules and yolk vesicles in oocytes compared with individuals fed 700 mg a-tocopherol/kg dry diet (Watanabe and Taka- shima 1977). Also, developing ovaries of common carp fed vitamin E-deficient diets had altered polar lipid fractions in the form of lower concen- trations of 20:4co6, 20:5a»3, and 22:6a»3 and higher concentrations of 18:lco9 and 20:3a»9. Quantitative vitamin E requirements of fishes depend upon interaction of several factors: 1) Dietary concentration of polyunsaturated fatty acids, 2) dietary selenium concentration, 3) die- tary concentrations of proxidants and antioxi- dants, 4) diet storage temperature, and 5) length of diet storage. Woodall et al. (1964) reported that a dietary vitamin E concentration of 5 to 30 mg a-tocopherol combined with 5% herring oil provided satisfactory growth of chinook salmon and prevented the occurrence of clinical defi- ciency symptoms in this species. Common carp fingerlings (initial mean weight = 1.6 g) required about 100 mg a-tocopherol/kg dry diet in order to maintain maximal growth rate and feed effi- ciency (Watanabe et al. 1970b). Slightly larger common carp fingerlings (initial mean weight = 6.4 g), fed 100 mg or less of DL-a-tocopheryl ace- tate/kg dry diet concurrently with 5% dietary methyl linoleate as the sole lipid component, dis- played apparent muscular dystrophy and had less weight gain than did fish fed 300 mg dl- tocopheryl acetate/kg dry diet plus 5% methyl linoleate (Watanabe et al. 1977). Also, common carp fed 10 or 15% methyl linoleate plus 100 mg DL-a-tocopheryl acetate, had significantly less weight gain and higher occurrence of muscular dystrophy than fish fed 2 or 5% methyl linoleate plus 100 mg DL-a-tocopheryl acetate. Rainbow trout fingerlings (initial mean weight = 0.9 g) fed a diet containing 15% pollock liver oil (in the form of methyl esters) displayed general vita- min E deficiency signs (anorexia and reduced growth), after 6 wk (Watanabe et al. 1981). Diets supplemented with 50 mg a-tocopherol/kg dry diet prevented anorexia and promoted growth rates equal to those fish fed 100, 300, or 500 mg a-tocopherol/kg dry diet. However, the minimal requirement may be slightly <50 mg a-tocopher- ol/kg dry diet. Larger rainbow trout fingerlings (initial mean weight = 10 g) require 20 to 30 mg Di.-a-tocopheryl acetate/kg dry diet when fed 1% 18:3w3 plus 13% palmitic acid (Cowey et al. 1981a). Dietary vitamin E concentrations <20 mg DL-a-tocopheryl acetate/kg dry diet resulted in higher molar ratios of polyunsaturated fatty acid to tocopherol in rainbow trout livers. Also, in vitro ascorbic acid-stimulated peroxidation in mitochondria and microsomes was significantly higher in rainbow trout fed low dietary vitamin E concentrations (e.g., 0 and 5 mg DL-a-tocopheryl acetate/kg dry diet). Furthermore, these investi- gators suggested that the vitamin E requirement for rainbow trout is undoubtedly proportionally higher with increasing dietary concentrations of unsaturated fatty acids. Supplementary dietary concentrations of either 33, 66, or 99 IU of DL-a- tocopheryl acetate/kg dry diet added to 20 mg of dietary a-tocopherol/kg dry diet, produced equal growth rates, feed efficiency, and whole body percentage protein, lipid, and moisture of rain- bow trout fingerlings fed 12% dietary lipid (Hung et al. 1980). In another study, diets con- taining 24 mg of a-tocopherol/kg dry diet com- bined with about 12% dietary lipid, which in- cluded 7.5% dietary, unoxidized herring oil, prevented vitamin E deficiency in rainbow trout fingerlings (Hung et al. 1981). Vitamin K Dietary supplementation of vitamin K for sal- monids has proven beneficial in increasing hematocrit values of brook trout (Poston 1964) and lake trout (Poston 1976b), whereas vitamin K supplementation of diets fed to channel catfish did not enhance blood clotting time or hemoglo- bin concentrations (Murai and Andrews 1977). Growth of each of the aforementioned species was unaffected by dietary vitamin K supplemen- tation. A dietary concentration of 1 mg menadi- one dimethylpyrimidinol bisulfite/kg dry diet was sufficient to provide normal coagulation and packed cell volume of lake trout blood (Poston 1976b). Murai and Andrews (1977) concluded that channel catfish have an extremely low, if any, dietary vitamin K requirement, since indi- viduals fed a diet devoid of vitamin K had similar weight gain, blood clotting times, prothrombin times, and hematocrit values to individuals fed 675 FISHERY BULLETIN: VOL. 80, NO. 4 up to 1.2 mg menadione sodium bisulfite/kg dry diet. MINERALS Calcium and Calcium-to-Phosphorus Ratios Initial investigations indicated that calcium uptake in fish is primarily through imbibition and gill absorption rather than from dietary sources (Podoliak 1961; Simmons 1971). Never- theless, since calcium and phosphorus are both major components of fish bone and scales, die- tary calcium-to-phosphorus ratios were exam- ined by several investigators to determine if any interactions occur between calcium and phos- phorus, which might result in altered bone ash, calcium, and phosphorus content. Dietary cal- cium did not affect growth and feed efficiency of common carp (Ogino and Takeda 1976), channel catfish (Lovell 1977), and rainbow trout (Ogino and Takeda 1978). However, in a separate study with channel catfish, 1.5% dietary calcium in- duced maximal weight gain, whereas lower and higher dietary calcium concentrations produced less weight gain (Andrews et al. 1973). Optimal growth and feed conversion occurred in channel catfish fingerlings fed a 1.5:1 ratio of calcium to phosphorus (Andrews et al. 1973) and optimal feed efficiency and serum inorganic phosphorus were observed in red sea bream fed a 1:2 ratio of calcium to phosphorus (Sakamoto and Yone 1973). The difficulty in determining whether die- tary calcium-to-phosphorus ratios are nutrition- ally significant in fish may be complicated by dietary factors such as magnesium and vitamin D or use of suboptimal calcium water concentra- tions in various studies. Based on the few species studied, it is unknown whether salinity deter- mines if dietary calcium-to-phosphorus ratios are important dietary factors. Optimal dietary calcium-to-phosphorus ratios have been reported for one marine species (red sea bream) and one freshwater species (channel catfish), while no optimal ratios were reported for common carp or rainbow trout. Phosphorus Dietary essentiality of phosphorus has been verified for channel catfish (Andrews et al. 1973; Lovell 1978), Atlantic salmon (Ketola 1975a), red sea bream (Yone 1975), common carp (Ogino and Takeda 1976), and rainbow trout (Ogino and Takeda 1978). Deficiency symptoms in channel catfish include reduced growth, poor feed effi- ciency, low bone ash, and low hematocrit levels (Andrews et al. 1973), and reduced weight gain, bone ash, and bone phosphorus content (Lovell 1978). Red sea bream fed phosphorus-deficient diets contained lower vertebral ash, calcium, and phosphorus and more brittle bone structure (Yone 1975). Common carp and rainbow trout fed diets deficient in phosphorus had reduced calcium, phosphorus, and ash content of whole body and vertebrae (Ogino and Takeda 1976; Ogino and Takeda 1978, respectively). Also, Ogino and Takeda (1976) reported deformity of the frontal bone of the cranium of common carp and spondylolisthesis, brachyospondylie, and synostosis of vertebrae in phosphorus-deficient individuals. Based on examination of limited sources of phosphorus, dietary phosphorus requirements have been reported as 0.4% or 0.42 to 0.47% for channel catfish (Gatlin et al. 1982; Lovell 1978, respectively), 0.6% inorganic phosphorus supple- mented to a diet containing 0.7% phosphorus from plant sources for Atlantic salmon (Ketola 1975a), 0.68% for red sea bream (Yone 1975), 0.6 to 0.7% for common carp (Ogino and Takeda 1976), and 0.7 to 0.8% for rainbow trout (Ogino and Takeda 1978). Supplementation of 0.4 to 2% monosodium, monocalcium, or dicalcium phos- phate to diets containing 0.55 to 0.65% available phosphorus did not improve growth or feed effi- ciency of rainbow trout fingerlings (initial mean weight = 21 g) over an 18-wk period (Reinitz et al. 1978a). Generally, inorganic phosphorus in formulated feeds is more digestible or available for fishes than organic forms of phosphorus occurring in soybean meal and fish meal (Ketola 1975a, b; Lovell 1978). Magnesium Magnesium is an essential constituent of bone in fish and is interrelated with calcium metab- olism. Whole body and vertebral calcium content were inversely related to dietary magnesium concentration in common carp (Ogino and Chiou 1976) and rainbow trout (Ogino et al. 1978), whereas whole body and vertebral phosphorus content were unaffected by dietary magnesium in the same species. Sakamoto and Yone (1979) concluded that marine fishes have very low (if 676 MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES any) dietary magnesium requirements, since 12 versus 66 mg magnesium/ 100 g diet fed to red sea bream did not differentially affect growth, vertebral magnesium content, or vertebral cal- cium content. Quantitative dietary magnesium requirements for rainbow trout (0.06 to 0.07%) and carp (0.04 to 0.05%) were established based upon one dietary calcium concentration and one calcium and mag- nesium concentration in ambient water in each study (Ogino et al. 1978; Ogino and Chiou 1976, respectively). Cowey (1976) reported that exces- sive dietary calcium (2.7%) in relation to dietary magnesium (0.04%) was accompanied by renal nephrocalcinosis in rainbow trout, while 0.1% magnesium fed to rainbow trout along with 2.7% calcium resulted in normal renal calcium con- centrations. Further increases in dietary cal- cium concentrations to 4% required dietary mag- nesium concentrations of 0.1%, rather than 0.06% magnesium to prevent renal calcinosis (Cowey et al. 1977). Therefore a direct interrelationship was established between dietary calcium and magnesium fed to rainbow trout in freshwater (Cowey 1976). bow trout fed 1 mg zinc/kg dry diet (Ogino and Yang 1978). Although carboxypeptidase activity was not tested, lower activity of this zinc-contain- ing enzyme could explain lower protein digesti- bility (Ogino and Yang 1978). Ketola (1979b) determined that laboratory diets containing 40% white fish meal (60 mg zinc/kg dry diet) caused bilateral cataracts in rainbow trout, possibly as a result of excesses of other minerals in white fish meal (calcium, phosphorus, sodium, or potas- sium). Supplementation of 150 mg zinc/kg dry diet to the laboratory diet containing 40% white fish meal and 60 mg zinc/kg dry diet resulted in normal growth rates and prevented cataract for- mation in rainbow trout. Common carp, fed 1 ppm dietary zinc in the presence of 10 jug zinc/1 rearing water over 12- and 16-wk periods in sep- arate studies, had high mortality rates, reduced growth rate, and had fin and skin erosion (Ogino and Yang 1979). No cataract formations were re- ported in zinc deficient common carp, however. Common carp fingerlings required between 15 and 30 ppm of dietary zinc for optimal growth. Iron Manganese Common carp and rainbow trout fingerlings have been found to have higher growth rates when fed 12 to 13 mg manganese/kg dry diet ver- sus 4 mg manganese/kg dry diet (Ogino and Yang 1980). Manganese-deficient rainbow trout displayed abnormal curvature of the backbone and malformation of the tail. Zinc Zinc has been shown to be an essential trace element for rainbow trout in separate studies (Ogino and Yang 1978; Ketola 1979b) and com- mon carp (Ogino and Yang 1979). Dietary zinc concentrations of 15 and 30 mg/kg dry diet fed over an 8-wk period in the presence of 1 1 ;ug zinc/1 of rearing water promoted satisfactory growth of rainbow trout, while 5 mg zinc/kg dry diet produced slightly slower growth rates (Ogino and Yang 1978). In the same study, rainbow trout fingerlings fed 1 mg zinc/kg dry diet had poor growth, high mortality (46% vs. 0% in other treatments), high incidence of cataracts (49% vs. 0% in other treatments) and high incidence of fin erosion (86% vs. 0% in other treatments). Protein digestibility was appreciably reduced in rain- Dietary iron is essential for fishes to maintain normal hemoglobin content, hematocrit value, and mean corpuscular diameter. Hypochromic, microcytic anemia occurred in red sea bream (Yone 1975) and common carp (Sakamoto and Yone 1978b) as well as anisocytosis in red sea bream fed iron-deficient diets. Control diets fed to red sea bream and common carp, which pre- vented these iron deficiency symptoms, contained 1.2 g ferric citrate/kg dry diet and 199 mg iron/ kg dry diet, respectively. A minimal dietary iron concentration of 150 mg/kg diet is required to prevent iron deficiency symptoms such as low mean corpuscular diameter and low blood iron content in red sea bream (Sakamoto and Yone 1978a). Copper Dietary copper requirements have been inves- tigated for channel catfish, common carp, and rainbow trout. Copper requirements, if any, for fingerling channel catfish are <1.5 mg/kg dry diet (Murai et al. 1981). Channel catfish fed 9.5 mg copper/kg dry diet while reared in water con- taining 0.33 ng copper/1 for 16 wk grew signifi- cantly slower than individuals fed diets contain- ing only 3.5 mg copper/kg dry diet. Further 677 reductions in weight gain occurred in channel catfish fed diets containing 17.5 or 33.5 mg cop- per/kg dry diet compared with those individuals fed 9.5 mg copper/kg dry diet. Also, a slight re- duction occurred in the number of erythrocytes and hematocrit levels in channel catfish fed 33.5 mg copper/kg dry diet resulting in slight anemia. Murai et al. (1981) suggested that since fish can absorb copper from the surrounding water, ab- sorption of environmental copper may result in lower dietary copper requirements than that re- quired by most terrestrial animals. Common carp fingerlings fed 0.7 mg copper/kg dry diet had lower weight gain than individuals fed 3.0 mg copper/kg dry diet (Ogino and Yang 1980). In contrast, no differential growth response oc- curred in rainbow trout fingerlings fed either 0.7 or 3.0 mg copper/kg dry diet (Ogino and Yang 1980). Selenium Selenium is an essential dietary constituent for Atlantic salmon and rainbow trout. Poston etal. (1976) demonstrated dietary essentiality of sele- nium for Atlantic salmon fry and fingerlings. Deficiency of dietary selenium suppressed gluta- thione peroxidase activity, while supplements of both vitamin E (500 IU DL-a-tocopheryl acetate/ kg) and selenium (0.1 mg/kg dry diet) prevented muscular dystrophy. However, no minimal die- tary selenium requirement nor minimal seleni- um concentration causing toxicity was deter- mined for Atlantic salmon. Dietary selenium concentrations as low as 0.07 mg/kg dry diet pre- vented selenium deficiency symptoms (i.e., de- generation of liver and muscle) in rainbow trout fingerlings concurrently fed 400 IU vitamin E/ kg dry diet while reared in water containing 0.4 isg selenium/1 (Hilton etal. 1980). Since selenium is a component of glutathione peroxidase, it is of interest that maximal plasma glutathione per- oxidase activity was obtained at a dietary sele- nium concentration of 0.15 to 0.38 mg/kg dry feed. On the other hand, selenium toxicity oc- curred in rainbow trout fed dietary selenium concentrations of 13 mg/kg of dry diet, causing reduced growth and feed efficiency and uncoordi- nated spiral swimming behavior 12 to 24 h be- fore death. Hilton et al. (1980) emphasized the importance of reporting dietary vitamin E con- centrations and water borne selenium concen- trations when investigating dietary selenium re- quirements of fish. FISHERY BULLETIN: VOL. 80, NO. 4 Iodine Iodine has been shown to have a role in thyroid metabolism in fishes similar to that occurring in terrestrial animals. Woodall and LaRoche(1964) examined dietary iodide requirements of chinook salmon fed 0.1 to 10.1 mg iodide/kg diet during an initial 6-mo study and an additional 9-mo study. After 6 mo, no significant differences oc- curred in growth, feed efficiency, and body com- position. However, iodine stored in the thyroid glands of chinook salmon fed 0.1 mg iodide/kg dry diet equaled only 40% of the iodide in indi- viduals fed higher iodide concentrations (0.6, 1.1, 5.1, and 10.1 mg iodide/kg dry diet). The authors concluded that the minimal dietary iodide re- quirement of chinook salmon fingerlings was about 0.6 mg iodide/kg dry diet based upon the iodide content in thyroid glands. Additionally, they recommended a higher dietary iodide re- quirement for advanced parr (1.1 mg iodide/kg dry diet) and speculated that smoltification may be accompanied by increased thyroid activity. Increased thyroid activity has been demon- strated in several salmonids during the parr- smolt transformation (Wedemeyer et al. 1980). SUMMARY AND RECOMMENDATIONS 1) All fish species examined thus far in feeding studies require the same dietary essential amino acids (arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine). 2) Optimal dietary lipid concentrations for maximal protein sparing action in most fish species range from 12 to 24%. 3) Qualitative essential fatty acid require- ments and ability to elongate and desatu- rate fatty acids such as linoleic and linolenic acids are highly variable among fishes, in- dicating a need for more species-specific research. 4) Relative protein sparing action of carbo- hydrates and lipids is also highly variable among fish species, necessitating more spe- cies-specific research in place of approxi- mating metabolic capabilities of an un- studied species based upon knowledge of other species. 5) Extensive research is needed to determine 678 MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES nutrient requirements for the striped bass and several coolwater fish species that sup- port important commercial or recreational fisheries, or both. 6) A better understanding of the effects of high dietary fiber on fishes is necessary to evaluate the amount of interference of fiber with enzyme action, changes in transit time of ingested feed in the digestive tract with varying dietary fiber concentrations and effects of dietary fiber on nutrient absorp- tion of fishes. 7) Calcium and magnesium requirements in fishes should be further examined for indi- vidual species reared in different calcium and magnesium concentrations or salinities to further determine relative nutritional importance of dietary and water absorption routes of these minerals. 8) Phosphorus requirements of fishes need to be evaluated in conjunction with calcium and magnesium requirements to determine optimal dietary ratios of each macrominer- al. 9) Knowledge of requirements of fishes for trace elements such as selenium, copper, iron, and zinc is rare, thereby warranting additional research. 10) Better definition of quantitative nutrient requirements of brood stock of various spe- cies is necessary to ensure better quality eggs and fry. 11) Regarding better standardization of indi- vidual fish nutrition experiments, panelists from a recent fish nutrition workshop have recommended that measurements for me- tabolizable energy values for experimental diets and digestibility values for macronu- trients should be monitored and reported. This is especially important in studies eval- uating dietary protein concentration re- quirements and optimal protein to energy requirements of fishes. Metabolism cham- bers used by Smith (1971, 1976) are the pre- ferred method. ACKNOWLEDGMENTS I am grateful to Gary Rumsey, Hugh Poston, George Ketola, Lowell Sick, Jeanne Joseph, and Paul Bauersfeld for critical review of the manu- script and to Sandra West for typing the manu- script. LITERATURE CITED Adron, J. W., A. Blair, C. B. Cowey, and A. M. Shanks. 1976. Effects of dietary energy level and dietary energy source on growth, feed conversion and body composition of turbot (Scopkthalmus maximus L.). Aquaculture 7: 125-132. Adron, J. W., D. Knox, C. B. Cowey, and G. T. Ball. 1978. Studies on the nutrition of marine flatfish. The pyridoxine requirement of turbot {Scopkthalmus maxi- mus). Br. J. Nutr. 40:261-268. Agrawal, N. K., and C. L. Mahajan. 1980. Hematological changes due to vitamin C deficiency in Channa punctatus Bloch. J. Nutr. 110:2172-2181. Anderson, R. J., E. W. Kienholz, and S. A. Flickinger. 1981. Protein requirements of smallmouth bass and largemouth bass. J. Nutr. 111:1085-1097. Andrews, J. W. 1977. Protein requirements. In R. R. Stickney and R. T. Lovell (editors), Nutrition and feeding of channel cat- fish, p. 10-13. South. Coop. Ser., Bull. 218. Andrews, J. W., and T. Mural 1975. Studies on the vitamin C requirements of channel catfish (Ictalurus punctatus). J. Nutr. 105:557-561. 1978. Dietary niacin requirements of channel catfish. J. Nutr. 108:1508-1511. 1979. Pyridoxine requirements of channel catfish. J. Nutr. 109:533-537. Andrews, J. W., T. Murai, and C. Campbell. 1973. Effects of dietary calcium and phosphorus on growth, food conversion, bone ash and hematocrit levels of catfish. J. Nutr. 103:766-771. Andrews, J. W., T. Mural and J. W. Page. 1980. Effects of dietary cholecalciferol and ergocalciferol on catfish. Aquaculture 19:49-54. AOE, H., AND I. MASUDA. 1967. Water-soluble vitamin requirements of carp— II. Requirements for p-aminobenzoic acid and inositol. Bull. Jpn. Soc. Sci. Fish. 33:674-680. Aoe, H., I. Masuda, T. Mimura, T. Saito, and A. Komo. 1968. Requirement of young carp for vitamin A. Bull. Jpn. Soc. Sci. Fish. 34:959-964. Aoe, H., I. Masuda, T. Mimura, T. Saito, A. Komo, and S. Kitamura. 1969. Water-soluble vitamin requirements of carp — VI. Requirement for thiamine and effects of antithiamines. Bull. Jpn. Soc. Sci. Fish. 35:459-465. Aoe, H., I. Masuda, T. Saito, and A. Komo. 1967a. Water-soluble vitamin requirements of carp — I. Requirement for vitamin B2. Bull. Jpn. Soc. Sci. Fish. 33:355-360. Aoe, H., I. Masuda, T. Saito, and T. Takada. 1967b. Water-soluble vitamin requirements of carp — V. Requirement for folic acid. Bull. Jpn. Soc. Sci. Fish. 33:1068-1071. Aoe, H., I. Masuda, and T. Takada. 1967c. Water-soluble vitamin requirements of carp— III. Requirements for niacin. Bull. Jpn. Soc. Sci. Fish. 33: 681-685. Arai, S., T. 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Carbohydrate in rainbow trout diets: Effects of the level and source of carbohydrate and the number of meals on growth and body composition. Aquaculture 18:157-167. 1979b. Effects of dietary carbohydrates and of their mode of distribution on glycaemia in rainbow trout (Salmo gairdmri Richardson). Comp. Biochem. Phys- iol. 64A: 543-547. Buhler, D. R., and J. E. Halver. 1961. Nutrition of salmonoid fishes. IX. Carbohydrate re- quirements of chinook salmon. J. Nutr. 74:307-318. Castell, J. D. 1979. Review of lipid requirements of finfish. In J. E. Halver and K. Tiews (editors), Finfish nutrition and fishfeed technology, Vol. I, p. 59-84. Heenemann, Berl. Castell, J. D., D. J. Lee, and R. 0. Sinnhuber. 1972a. Essential fatty acids in the diet of rainbow trout (Salmo gairdneri): lipid metabolism and fatty acid com- position. J. Nutr. 102:93-100. Castell, J. D., R. O. Sinnhuber, D. J. Lee, and J. H. Wales. 1972b. 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Slinger, and H. S. Bayley. 1976. Influence of level and type of dietary protein, and of level of feeding on feed utilization by rainbow trout. J. Nutr. 106:1547-1556. Coates, J. A., and J. E. Halver. 1958. Water-soluble vitamin requirements of silver salmon. U.S. Fish. Wildl. Serv. Spec. Sci. Rep. Fish. 281, 9 p. Cowey, C. B. 1976. Use of synthetic diets and biochemical criteria in the assessment of nutrient requirements of fish. J. Fish. Res. Board Can. 33:1040-1045. 1979. Protein and amino acid requirements of finfish. In J. E. Halver and K. Tiews (editors), Finfish nutrition and fishfeed technology, Vol. I, p. 3-16. Heenemann, Berl. Cowey, C. B., and J. R. Sargent. 1972. Fish nutrition. Adv. Mar. Biol. 10:383-492. 1979. Nutrition. In W. S. Hoar, D. J. Randall, and J. R. Brett (editors), Fish physiology. Volume VIII: Bioener- getics and growth, p. 1-69. Acad. Press, N.Y. Cowey, C. B., J. W. Adron, and A. Blair. 1970. Studies on the nutrition of marine flatfish. 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Studies on the nutrition of marine flatfish. The effect of different dietary fatty acids on the growth and fatty acid composition of turbot (Scophthalmus maxi- mus). Br. J. Nutr. 36:479-486. Cowey, C. B., J. A. Pope, J. W. Adron, and A. Blair. 1972. Studies on the nutrition of marine flatfish . The pro- tein requirement of plaice (Pleuronectes platessa). Br. J. Nutr. 28:447-456. Dabrowski, K. 1977. Protein requirements of grass carp fry (Cteno- pharyngodon idella Val.). Aquaculture 12:63-73. Davis, A. T., and R. R. Stickney. 1978. Growth responses of Tilapia aurea to dietary pro- tein quality and quantity. Trans. Am. Fish. Soc. 107: 479-483. DeLong, D. C, J. E. Halver, and E. T. Mertz. 1958. Nutrition of salmonoid fishes. VI. Protein require- ments of chinook salmon at two water temperatures. J. Nutr. 65:589-599. Dixon, D. G., and J. W. Hilton. 1981. Influence of available carbohydrate content on tol- erance of waterborne copper by rainbow trout, Salmo gairdneri Richardson. J. 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Am. Fish. Soc. 99: 90-92. Edwards, D. J., E. Austreng, S. Risa, and T. Gjedrem. 1977. Carbohydrate in rainbow trout diets. I. Growth of fish of different families fed diets containing different proportions of carbohydrate. Aquaculture 11:31-38. Fowler, L. G. 1980. Starting diets for chinook salmon fry. Prog. Fish- Cult. 42:165-166. 1981. Protein and energy relation of starting diets for chinook salmon fry. Prog. Fish-Cult. 43:151-153. Fujii, M., AND Y. Yone. 1976. Studies on nutrition of red sea bream— XIII. Effect of dietary linolenic acid and 3-highly unsatu- rated fatty acids in marine fishes and rainbow trout. Bull. Jpn. Soc. Sci. Fish. 46:1231-1233. Yingst, W. L., Ill, and R. R. Stickney. 1979. Effects of dietary lipids on fatty acid composition of channel catfish fry. Trans. Am. Fish. Soc. 108:620-625. 1980. Growth of caged channel catfish fingerlings reared on diets containing various lipids. Prog. Fish-Cult. 42: 24-26. YONE, Y. 1975. Nutritional studies of red sea bream. Proc. First Int. Conf. Aquaculture Nutr., p. 39-64. Yoshinaka, R., M. Sato, and S. Ikeda. 1978. In vitro formation of collagen in skin of ascorbic acid-deficient rainbow trout. Bull. Jpn. Soc. Sci. Fish. 44:1147-1150. YU, T. C, AND R. O. SlNNHUBER. 1972. Effect of dietary linolenic acid and docosahexaeno- ic acid on growth and fatty acid composition of rainbow trout (Salmo gairdneri). Lipids 7:450-454. 1975. Effect of dietary linolenic and linoleic acids on growth and lipid metabolism of rainbow trout (Salmo gairdneri). Lipids 10:63-66. 1976. Growth response of rainbow trout (Salmo gaird- neri) to dietary 6 fatty acids on growth and feed conversion efficiency of coho salmon (On- corhynchus kisutch). Aquaculture 16:31-38. YU, T. C, R. O. SlNNHUBER, AND J. D. HENDRICKS. 1979. Reproduction and survival of rain bow trout (Salmo gairdneri) fed linolenic acid as the only source of essen- tial fatty acids. Lipids 14:572-575. YU, T. C, R. O. SlNNHUBER, AND G. B. PUTNAM. 1977. Use of swine fat as an energy source in trout rations. Prog. Fish-Cult. 39:95-97. Zeitoun, I. H., J. E. Halver, D. E. Ullrey, and P. I. Tack. 1973. Influence of salinity on protein requirements of rainbow trout (Salmo gairdneri) fingerlings. J. Fish. Res. Board Can. 30:1867-1873. Zeitoun, I. H., D. E. Ullrey, J. E. Halver, P. I. Tack, and W. T. Magee. 1974. Influence of salinity on protein requirements of coho salmon (Oncorhynchus kisutch) smolts. J. Fish. Res. Board Can. 31:1145-1148. 686 ANALYSIS OF DOUBLE-TAGGING EXPERIMENTS Jerry A. Wetherall1 ABSTRACT Statistics arising from double-tagging experiments may be applied to estimate tag-shedding prob- abilities directly, to estimate parameters of underlying theoretical shedding models, or to estimate mortality rates free of tag-shedding bias. Simple maximum likelihood estimators of tag retention rates, along with their asymptotic vari- ances, may be derived assuming conditional multinomial sampling models. If specific models of shedding are of interest, limitations of existing theory may be reduced by assuming the Type II shedding rate is time-dependent. In the more realistic models and their simpler precursors, parame- ters may be estimated by least squares or by maximum likelihood methods. Complications arising in the direct maximization of the conditional likelihood may be circumvented by use of iteratively reweighted Gauss-Newton algorithms available in standard statistical software packages. Simple diagnostic plots may be helpful in model selection. When a sequence of double-tagged cohorts is released, recapture statistics may be treated sepa- rately or combined to estimate common shedding rates, but a more general linear model may be used to fully exploit the structure of the experiment and to estimate both common parameters and those unique to each cohort. When recapture times are unknown but the experiment spans a sufficiently long period, the ratio of constant Type II tag-shedding rate to constant Type II total mortality rate may be estimated. Under similar circumstances, but with exact recapture times known for each fish, maximum like- lihood estimates of both parameters may be computed. If only the Type II mortality rate is of interest, it may be estimated free of tag-shedding bias by simple linear regression of appropriate double-tagging statistics, if Type II shedding and Type II mortality are constant during the experiment. The estimation of fishing mortality rate, exploi- tation rate, and population size through mark and recapture experiments is often complicated by the incidental shedding or loss of marks. Fail- ure to account for tag shedding may lead to biased parameter estimates. Thus a well-designed tag- ging experiment will incorporate some provision for estimating shedding rates and computing correction factors. The approach usually taken is to release a group, or perhaps several groups of double- tagged fish, and then to estimate shedding rates using information on the number of fish returned in a sequence of recapture samples still bearing both tags and on the number of returns with only one tag remaining. A variety of statistical meth- ods and estimation procedures have been devel- oped. Papers by Beverton and Holt (1957), Gul- land (1963), Chapman et al. (1965), Robson and Regier (1966), Chapman (1969), Bayliff and Mo- brand (1972), Seber (1973), Laurs et al. (1976), Arnason and Mills (1981), Kirkwood (1981), and Seber and Felton (1981) are particularly note- worthy. In recent years attention has focused pri- marily on the regression methods developed by Chapman et al. (1965) and extended first by Bay- liff and Mobrand (1972) and most recently by Kirkwood (1981). Despite the extensive literature on double-tag- ging there is need for an integration of existing thought and for development of new ideas and statistical methods. Accordingly, this paper sur- veys basic tag-shedding theory and the most widely used analytical techniques, and describes a variety of new models and estimation proce- dures. Left unaddressed are several important aspects of planning double-tagging experiments. These are the subject of a companion paper by Wetherall and Yong (1981). TAG LOSS IN SINGLE-TAGGING EXPERIMENTS 'Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 3830, Honolulu, HI 96812. To establish a context for later derivations we begin by reviewing the process of tag loss in a population of single-tagged fish. In such a popu- Manuscript accepted April 1982. FISHERY BULLETIN: VOL. 80. NO. 4. 1982. 687 FISHERY BULLETIN: VOL. 80, NO. 4 lation, losses may be caused by fishing mortality or recapture, natural mortality, tagging mortal- ity (mortality induced by the application or presence of the tag), permanent emigration, or by tag shedding. In addition, recaptured tags are considered "lost" if not detected in the catch and recovered, or, when recovered, if not returned or reported. bined effects of fishing mortality, F(x), natural mortality, M(x), instantaneous tag shedding, L(x), and remaining losses, G(x). The usual as- sumptions are that the Type II losses operate in the manner of independent Poisson processes with constant rates and that the recovery and reporting rates also are constant. Under these conditions the model takes the familiar form E{r) = 77AUO)| F + X ) (l - expHF + X)A,)) (< exp(-(F + X)t)) (1) ') Beverton and Holt(1957) recognized twokinds of losses, which they designated Type I and Type II (these are called Type A and Type B by Ricker 1975). Type I losses are those which, in effect, re- duce the number of tags initially put out. They result from the pulse of tagging mortality and tag shedding occurring immediately after re- lease (or in a relatively brief period following release) and from the nonrecovery and nonreport- ing of tag recaptures. Type II losses are those happening steadily and gradually over an ex- tended period following release of the tagged fish. These relations may be stated more succinctly in a simple mathematical model. Let E(r,) denote the expected number of returns of tags recap- tured in the ith time interval following the re- lease of iY,(0) single-tagged fish. Then where 17 X TT P I M + L + G. A variety of estimation schemes based on this equation have been developed, notably by Paulik (1963). These have been reviewed along with other mark-and-recapture approaches by Cor- mack (1968) and Seber (1973). The importanceof assumptions on Type I and Type II losses in these procedures depends on which parameters are of central concern in the experiment. In fisheries applications the parameter most often focused on is the fishing mortality rate, F. Paulik's single- release regression model with constant A, for estimating F and the exploitation rate, n=(F/(F + M)) [1 - exp(-(F+ M)A)] stems directly from Equation (1). In this situation, if Type I losses are present the model will estimate -qF rather than E(r,) = n p NS(Q) / F{u) J(u) exp (- / H(x) dx)du u \ 0 / where t, A, 1 - TV 1 ~ P time at the beginning of in- terval i length of time interval i probability that a tag is lost due to immediate tagging mortality probability that a tag is shed immediately following re- lease instantaneous fishing mor- tality rate at time u probability that a tag recap- tured at time u is not re- covered and reported (a Type I loss) H(x) = total instantaneous rate of Type II tag loss at time x. Here H(x) represents the unspecified com- F(u) 1 - { (u) F. Subsequent estimates of X will be too large. Further, estimates of the exploitation rate will be negatively biased, and if these are used along with Ns(0) to estimate total population sizes, such estimates will be inflated. Of course, this is the general effect of Type I losses on Petersen esti- mates. If Type II tagging mortality or Type II tag shedding occur, the estimate of F'from this sin- gle-release model will not be affected, but the estimate of n will be less than the true exploita- tion rate of the unmarked population. Sometimes all recaptures are made during subintervals of equal length imbedded and ir- regularly spaced within the total recapture peri- od (e.g., in a salmon fishery with a complex pat- tern of open and closed periods). In this case, Paulik shows that the single-release model based on Equation (1) will give estimates of Fand X 688 WETHERALL: ANALYSIS OF DOUBLE-TAGGING EXPERIMENTS which are unaffected by Type I losses, and in fact will yield an estimate of 77 as well as the usual estimates of F and X. Since the conditions re- quired for this scheme will not often be encoun- tered, it will usually be necessary to conduct a multiple-release experiment, with at least one preseason release, in order to obtain separate estimates of F, X, and 77. Models appropriate to this situation have also been extensively devel- oped by Paulik (1963). However, even in the multiple-release models the Type II tagging mortality and Type II shed- ding will generate an underestimate of the true exploitation rate. Thus while the problems im- posed by Type I losses may be circumvented by more elaborate experimental designs, the unde- sired effects of Type II losses remain. Two reme- dies are possible: 1) The single-tagging may be supplemented with a double-tagging experiment and other special studies to estimate Type II components and determine correction factors, or 2) double-tagging may be used exclusively to esti- mate mortality rates unaffected by Type I and Type II shedding. Both strategies are treated be- low. We note here that even when tag shedding and mortality are not the chief concerns of a tag- ging experiment, double-tagging is often em- ployed simply to increase expected recovery rates (e.g., Hynd 1969; Bayliff 1973). MODELS OF DOUBLE-TAGGING We restrict our attention to the case where members of the population are marked with two tags differing in position of attachment and pos- sibly type (call these Type A and Type B). We assume the burden of carrying both tags is equal to the stress of carrying either one alone. Fur- ther, we assume that the probabilities of loss are the same for each tag of a specified type and inde- pendent of the status of the other tag. Suppose a cohort of fish is double-tagged at time 0. For any fish still alive at time t, the probability that the Type A tag has been shed can be stated as nA(0 --■- 1 - pa0a(O where #a(0 = exp can be dropped, i.e., the common probability of shedding by time t is >(— JLa(u) duj. An analogous expression exists with respect to tag B. Where shedding rates are assumed to be the same for tag Types A and B the subscripts il(t) = 1 ■- Pg{t). (2) If we set L(u) = L(constant), Equation (2) em- bodies the assumptions of Bayliff and Mobrand (1972)— Type II shedding is a simple Poisson process with an identical constant rate for each tag, so that each tag has the same probability of shedding by time t. Moreover, in due course all surviving fish will have shed both tags as long as L>0, i.e., ft(oo) - 1. The validity of this particular set of assump- tions has recently been challenged by results of tag-shedding studies with northwest Atlantic bluefin tuna, Thunnus thynnus, (Baglin et al. 1980) and with southern bluefin tuna, T. mac- coyii, (Kirkwood 1981). In the former case, it was found that the Type II shedding rate increased with time. In Kirkwood's analysis it was appar- ent that the Type II rate decreased markedly over time. Therefore, it clearly would be advan- tageous to construct a model permitting time- dependent Type II shedding rates. Kirkwood approached this problem by attacking the com- mon assumption of uniform shedding probabili- ties among all fish in the cohort. Instead, he con- sidered the Type II shedding rate for each tag applied to be constant over time, but further as- sumed that the rate for each tag was a random variable with specified probability density. In this light, the deterministic model at Equation (2) is replaced by the expectation J(t) = E[fl(t)] — 1 — p E[g{t)]. The average time-varying shed- ding rate at time t may now be defined as *(t) E{g(t) ■ L] E{g(t)} where the expectations are taken with respect to the probability density of L. Following standard principles of reliability theory, this may be re- duced to nn = - d\nE{g(t)} dt Under Kirkwood's assumptions V(t) will de- crease with time as long as there is variation in shedding rate among tags, i.e., there will be a continuous culling of tags with relatively high shedding probabilities. This concept is clearly an 689 FISHERY BULLETIN: VOL. 80. NO. 4 attractive alternative to the Bayliff-Mobrand model. Problems in which the instantaneous loss rate is treated as a random variable arise in a variety of contexts ranging from bioassay to analysis of labor turnover in corporations. Because of its unimodality and mathematical tractability, the distribution often selected to describe this varia- tion is the gamma distribution with mean A and variance k2/b (e.g., see Bartholomew 1973:186 or McNolty et al. 1980). As Kirkwood (1981) showed, for the tag-shedding problem, this choice leads to J(t) = 1 - p b + kt, (3) so that nt) bk b + kt The Bayliff-Mobrand model is now seen as a special deterministic case; when b — °°, J(t) — 1 - p exp(— kt) and ^(0 — k. Kirkwood con- sidered a further elaboration of Equation (3) by assuming only a fraction of the tags, <5, will have a nonzero probability of shedding; the remainder are regarded as permanently attached. In this event the expected probability of shedding by time t is J(t) = 8 1-P b + kt, (4) While this approach significantly advances the realism and flexibility of tag-shedding the- ory, it fails to account for the apparent increase in average shedding rate as observed in the Atlantic bluefin tuna. Thus, although permitting variation in shedding rate among tags, it still considers the rate for each tag to be constant over time. This condition is not apt to hold. As Kirkwood (1981) himself pointed out, plastic dart tags may become so firmly imbedded and overgrown by tissue as time passes that the probability of shed- ding approaches zero. This is most apt to occur in species which grow slowly, such as the southern bluefin tuna. On the other hand, it is well known that various metallic tags may corrode with time and their shedding probabilities increase. Plas- tic tags also deteriorate. Accordingly, consider the Type II shedding rate to be a function of time, L(t). A relatively simple model for this situation is L{t) = a + fit{y~l\ permitting a wide variety of forms for the instan- taneous shedding process. In general, all three parameters of this model could be specified as random variables. Thus with a > 0, /3 > 0, and — oo < y < oo the probability of shedding might increase over time for some fish in a cohort, de- crease for others, and be constant for the remain- der. However, to simplify the analysis assume here that y is fixed and identical for all members of the cohort. Now if a and fi are independently distributed as gamma random variables we have J(t) and = 8 1 - Pi bk_ b + kt b + kt yc + ye it yc + gf yc + tjt' y-V (5) where the new symbols are £ , the expected value of )8, and c, the reciprocal of the squared coeffi- cient of variation of p. Hence, if between-tag var- iability in a and /3 approaches zero, J(t) - 5<1 - p exp kt + £ty y and V(t) - A + Ztly~u. In the basic model at Equa- tion (4), for tags still in place at time t the condi- tional probability of shedding in the interval (t, t + dt) is independent of t. In the extended model at Equation (5), this conditional probability may also increase or decrease with t depending on 7- While elaboration of the tag-shedding equa- tions in this manner is straightforward, it is doubtful whether a very clear discrimination be- tween such parameter-laden models is possible given the usual recapture statistics. Distinctions between the extended models are reduced by the integration of the shedding processes over sev- eral recapture periods and are further obscured by sampling variation. However, on the basis of these conceptual models of the tag-shedding process we can now write the well-known equations describing the expected number of tags of a specified type still attached at time t. For N,t(0) fish initially double- tagged with Types A and B tags, let S(t) = w ■ exp (-\z(u)di) 690 WETHERALL: ANALYSIS OF DOUBLE-TAGGING EXPERIMENTS be the probability of survival to time t, where 1 — 7r = probability of immediate mortality and Z(n) = H(u) — L(u) is the time dependent instan- taneous death rate. Then the expected number of fish bearing a single tag of Type A at time t is N*(t) = Nd(0) S(t) JB(0(1 - Mt)). An analogous expression may be written for Ns(t), and if the two tags are considered identical, the subscripts A and B may be dropped to yield NM) = mt) + NB(t) = 2NA0) S(t) J(t) (1 - J(t)), the expected number of fish still bearing a single tag at time t. The expected number of double-tagged fish at time t when A and B types are differentiated is Nd(t) = Nd(0) S(t)(l - Mt))(l - Mt)) or when no distinction is made between A and B types, Nd(t) = Nd(0) S(t)(l - J(t)f. In any event, the total number of fish expected at time t with one or two tags remaining is N.(t) = Ns(t) + Nd(t). The processes described above are not directly observable, so inferences about the shedding rates must be made on the basis of catch statis- tics. When recapture effort is exerted during a time interval we assume it is applied continu- ously. During a period of length A, beginning at time t, the expected number of recaptures of tagged fish in category j is therefore n+&i E{rjr) = / F(u) Nj(u) du (6) The standard procedures for estimating shed- ding rate parameters, and many of those to be described shortly, rely on a sequence of ratios of the estimated or observed number of recaptures from the various categories during successive fishing periods. It is clear from the equations above that such ratios will be functions of r, and the shedding parameters only, and independent of Fj, N(l(0) and any parameters of the survival function S(r(). Further, the ratios will be unaffected by non- recovery or nonreturn as long as these processes operate at constant levels with respect to re- captures during a given time interval and at the same rates for each tagged fish category. Throughout this paper we assume this is so. However, this latter condition is one which could be violated easily, particularly if catches are not inspected carefully for tag recaptures. Where fish are handled individually there may be no difference in recovery rates between single- and double-tagged fish. Otherwise, recovery rates may be greater in double-tagged individuals. Once tagged fish are recovered, there may be further problems with respect to return rates. Laurs et al. (1976) in a study of shedding rates in North Pacific albacore, T. alalunga, and Myhre (1966) in experiments with Pacific halibut, Hip- poglossus stenolepis, allowed for the possibility that a certain proportion of double-tagged recov- eries would be misreported as having only a single tag. [For example, a fisherman might pocket one of the tags as a souvenir, or one tag might be simply lost after recapture.] where j = A, B, s, d, ■ . To complete the integral at Equation (6) it has been customary to make two key assumptions at this juncture (Chapman et al. 1965). First, we as- sume the fishing mortality rate, F(u), is a step function constant within each recapture inter- val, i.e., F(u) = F, for t,< u < t, + A, Second, we assume the average value of N:(u) during the in- terval is approximately equal to Nj{t, + A,/2). [This approximation is generally quite good for A, of 1 yr or less. If Nj(u) is linear over the interval the relation is exact regardless of A,.] Under these conditions the set of recapture equations becomes E(rfi) = F% A, Nj(Ti) where r, = t, ■ + A, /2 . (7) ESTIMATION OF SHEDDING RATES AND PARAMETERS In the analysis of tag-shedding data a broad range of objectives may be pursued, and these give rise to a variety of estimation problems and approaches. Fundamentally, of course, the analyst wishes to correct systematic bias in esti- mates of basic population parameters caused by tag loss. There are several ways to do this. Where concurrent single-tagging and double-tagging experiments are conducted, information on shed- ding rates from the double-tagging may be used to compute adjustment factors, which in turn are applied to recoveries from the primary single- tagging study. Thus in single-tag estimation pro- cedures based on Equation (1), for example, r, would simply be replaced by 691 FISHERY BULLETIN: VOL. 80, NO. 4 r = r k -i (8) where m, estimated from double-tagging, is the probability that a tag will still be attached at time rr If returns from the double-tagging ex- periment are too few to provide an estimate of k, for each recapture interval, interpolation is necessary. In any event, in this approach only minimal assumptions need be made about the manner in which shedding occurs. In most treatments of tag shedding, however, a specific model is postulated for the shedding process. Once the parameters of such a model are estimated, appropriate adjustments for tag shedding are made either to the single-tag recov- ery data, as above, or directly to estimated popu- lation parameters. A third strategy is to conduct the experiment entirely with double-tagged fish, and to estimate mortality rates and other popula- tion parameters directly, in such a way that no corrections are necessary. These various approaches are discussed now in greater detail, assuming a continuous recapture process. For situations in which tagged fish are recaptured once at most, but only in point sam- ples, some estimation procedures are given by Seber (1973) and Seber and Felton (1981). For multiple-recapture models of the Jolly-Seber type, again with point sampling, the reader should consult Arnason and Mills (1981). Estimating Adjustment Factors for Single-Tag Recoveries Here we estimate xt, the probability of tag re- tention at time t,, the midpoint of the ith recap- ture period. We assume the shedding probabili- ties for each tag are identical and independent of the status of the other tag, and that recovery and reporting rates are the same for recaptured fish bearing either one tag or two. Under these condi- tions the number of double-tag recoveries, rdi, is proportional to k,2 and the number recovered with only a single tag remaining, rs.,, is propor- tional by the same factor to 2k, (1 — k{). Of the total number of recoveries from the double-tagging experiment in the ?th period, the proportion bearing two tags is therefore "it, — 2 - K Maximum likelihood (ML) estimates of the k, are 692 now easily derived. We assume the conditional distribution of rdl, given (rd, + rsi), is binomial with parameter Pdi. The likelihood of the /th re- capture sample is thus Zi = n\ «i Ki irxi rd,\ rsl\J\2 - Ki/ \ The ML estimator of k, is easily found: 2rdi Ki r, + 2r, si di (9) This result is also given by Seber (1973) under somewhat different assumptions. The asymptotic variance of k1 is Ou . - k,-(1 - *,-) (2 - K,f 2r, (10) As usual, numerical estimates are computed by inserting k4 in place of *,. Note that k, has a small negative statistical bias. In fact, using a Taylor series expansion it may be shown that E(k,) - «i [l - (1 - Ki) (2 2rn «L~\ Bias increases with time out, i.e., as k, decreases, and is inversely related to the total number of re- captures. When k, ■ = 0.5 and r.% — 10, the negative bias in k, is <4%. Note further that since the likelihood function is conditioned on r,, inferences based on Equa- tions (9) and (10) apply strictly only to the par- ticular experimental outcome being studied, and not to the broader class of results which might be obtained in replications of the experiment. Pro- viding that the approximation in Equation (7) is valid, a more complicated unconditional model would yield the same estimate of «,, but the vari- ance of Ki would be greater, reflecting the sto- chastic nature of the mortality and recapture processes which lead to the r(. Since our interest is in estimating shedding rates and not mortality rates, as a rule we consider only the simpler con- ditional likelihoods. Above we have assumed the two tags are iden- tical insofar as shedding rates are concerned. When they are subject to different shedding rates another set of estimators is required. Where A and B tags are identified, the number of A- WETHERALL: ANALYSIS OF DOUBLE-TAGGING EXPERIMENTS type recaptures, rAi, is proportional to ka,(1 - kHi ) while rsi is proportional to kb,(1 — ka,). The num- ber of double-tagged recaptures is proportional to KAi kb, . We assume the number of recaptures in the three classes are trinomial given Ka% + >'n, + rdi, with conditional probabilities Pm = B, di 1 '"(I ~ KA,)(1 "- KB,) ' These assumptions lead to the ML estimates and KA,(1 — KB/) 1 - (1 - KA,) (1 - K'B,(1 — KA,) KB,) 1 " (1 ■" Kki) {I - KA, KB, KB,) 'di «A, rB, + r and kb, = rd, di rA, + ^di Estimating Parameters of Specific Models Regression Methods Despite the directness and simplicity of the general adjustment procedure outlined above, most double-tag analyses have aimed at unravel- ing specific underlying mechanisms of the tag- shedding process. The probability of tag reten- tion, k,, is then seen as a continuous function of time and a vector of model parameters, 6, to be estimated from the recapture data. In the termi- nology established above, k( =1 —J(t,). Thus if k, or some transformation of k, is plotted against r, the form of an appropriate shedding model may be revealed. In fact, this is the approach adopted in much of the recent tag-shedding literature, and various weighted regression procedures have been developed to handle the parameter estimation. The general formulation of these is: find 6 such that S(6) = S w.Uj,-/^))2 ,=i is minimum. In the two-parameter Bayliff-Mo- brand model y; = ln/c,-, where k, is given in Equa- tion (9), and /, (0) = lnp — Lr . In the four-param- eter Kirkwood model Vi = 1 ~ "i Me) = 6 ,6 + At, In both cases the authors suggest setting h; = r.i. This is not optimal in a statistical sense, but is clearly preferable to equal weighting. It should be noted further that neither the Bayliff- Mobrand model nor the Kirkwood model is based on an explicit consideration of error structure for the observations. For example, there is consider- able support in the literature for a multiplicative error in the recapture process, i.e., r„ = E(rs,) exp(csi) and rdi = E(rdi) expi^,) and in this case the algebra leads one to the nonlinear model 2r0 Jin) 1 " J(r) + e, where e, has mean 0 and variance alr Appropri- ate weights for this model are Wi _2 'si 'di r-i The regression models discussed here have as- sumed that recaptures are obtained from a single cohort of tagged fish. However, it is often the case that several lots of tagged fish are released at dif- ferent times, so the recaptures in a particular in- terval may come from different cohorts. In this event the analysis may be applied to each of the m cohorts separately, provided these are fairly large. When multiple releases are made but the individual cohorts are small, so that relatively few recaptures are expected from each cohort, the usual procedure is to assume mortality rates and shedding rates are constant and identical for each group and to simply aggregate the recap- ture statistics from the several releases. Let the recapture intervals be of equal length, A, and let r\,j and rdl] denote the number of single-tagged and double-tagged fish from the jih cohort re- captured during the ith interval following that cohort's liberation. Employing the Bayliff-Mo- brand linear regression model, one can estimate lnp and L in the usual manner as £ = {x1 w xr x1 w y (11) where /? = [lnp L]T X = {x,j} is the augmented data matrix 693 FISHERY BULLETIN: VOL. 80. NO. 4 Y = such that xn — 1 for all i and Xi2 = -a - 1/2) A [yi] is the vector of dependent vari- ables with elements m-i 2 2 r, y, = In* i=i di] X rsij + 2 1 r, (12) rfii Here IT is a matrix of statistical weights, and m,- is the number of cohorts for which recapture sta- tistics are available in the ith postrelease inter- val. The symbol T denotes the matrix transpose. If sufficient recaptures are obtained to analyze each cohort separately (say r.tJ > 10) but a com- mon shedding rate is assumed, several alterna- tive approaches are available. First we can treat the separate releases as partial replicates of the same experiment and construct the dependent variables as the logarithms of the geometric means of individual statistics for each cohort. Thus to estimate lnp and L we use Equation (11) as before but now set A second approach when the shedding rates are constant and the vv- are sufficiently large is to treat returns from each of the m releases sepa- rately and then average the individual estimates. Thus the overall estimate of L, for example, would be L = X.wj Lj where Lj is the estimated slope from the linear regression of Vv 2rdi In rSy + 2rdij on r,. Here the individual estimate of L from the j'th cohort is given a weight Wj inversely propor- tional to its relative variance. In practice we sub- stitute the statistic Wi -2 m Z o M l y< = X In 2r, dij „ + 2^ (13) Although as an estimator of ln/c, Equation (13) usually has slightly greater negative bias than Equation (12), such bias is negligible and the approach taken in Equation (13) has the advan- tage that statistical weights may be calculated empirically for cases where w; > 2. In particu- lar, define the tth diagonal element of W as 2-i Wu — rriiim, — 1) where y, is given by Equation (13), and let u% = 0 for i =&j. When some of the m, are equal to 1, then the wn may be computed using the delta method as w-n = m, m I / TSy{rsjj -- rdtJ) *dij\rsij + 2rdlJ) -i on the assumption that the rdij and rSij are comple- mentary binomial variables. o'i being the estimated variance of L, computed in the jth regression. For the regression analysis itself, appropriate statistical weights for the yv- would be proportional to ~-2 _ r,i,j (rslJ + 2rdij)2 Finally, the variance of L may be estimated as = I 3=1 * rl ~2 Wj o~ [jl \| A third approach is to assume that the set of regression estimates from the m cohorts are sam- pled from an underlying but unspecified stochas- tic process which, with respect to the estimation of Type II shedding rate, has mean L and vari- ance o\. The regressions of ytJ on r, are unweight- ed, and empirical estimates of L and a~ are given very simply by L = 2 Lj/m and ~ 2 °1 2 (Lj - Lf/m(m j=i / - 1), 694 WETHERALL: ANALYSIS OF DOUBLE-TAGGING EXPERIMENTS where L, is the regression estimate correspond- ing to the jth cohort. A shortcoming of many double-tag analyses is that attention has been focused on estimating constant p and L despite the existence of multiple- release statistics. In fact the multiple-release ex- periment permits a more elaborate assessment of shedding processes, with the level of detail determined by specific characteristics of the experimental design. To illustrate this, consider an experiment with six recapture periods of equal length, A. Two cohorts of double-tagged fish are released, at the beginning of the first and fourth periods. We assume there is a unique Type I shedding rate associated with each cohort, and that the Type II shedding rate is the same for each group but is a function of time following release. Specifically, we assume the latter rate is constant for two recapture intervals following the release of any cohort, may then change to another constant level for two more periods, and so on. The recapture statistics from the experiment may be arrayed as follows: Release group 1 2 Recapture interval: 2 3 4 5 rsu Tsl2 Vd\2 r sl3 ^13 VsU rdU rs21 rd2l rsl5 rdl5 Vs22 Vd22 6 Vsl6 rd\e Vs23 Vd23 Note that m\ = m2 = m3 = 2 and ra4 = wis = me = 1. The parameter vector p = [lnpi lnp2 Li L2 L3] T may now be estimated from Equation (11) with Y as given in Equation (13) and the data matrix defined as X = 1/2 1/2 -A/2 0 0 1/2 1/2 -3 A/2 0 0 1/2 1/2 -2 A -A/2 0 1 0 -2 A -3 A/2 0 1 0 -2 A -2 A -A/2 1 0 -2 A -2 A -3 A/2 As usual, the covariance matrix of (5 is estimated by V = (XTWX)-\ With a little imagination this general linear model can easily be adapted to accommodate a wide variety of multiple-release experimental designs. Standard analysis of covariance tech- niques may be applied to test the associated hypotheses concerning /3. Maximum Likelihood Methods As an alternative to the least squares methods we now describe some ML procedures for esti- mating the model parameters in the single-re- lease case. Given the total number of recaptures in the tth period we again assume the numbers falling in the various classes are multinomially distributed. Thus when the A and B tags are identical there are just two classes, and the num- bers in each are binomial variables with condi- tional expectations E(rdl) = r, Pn di = r.A — r,- 1 -An) 1 +J(Ti) [1 - An) A 1 -At,) and E(rsi) = r.( (1 - Pdi). Assuming further that the statistics for successive periods are mutually independent, the joint likelihood function for the double-tag recovery data {rdl rd2, ..., rdn] given {r.\, r.2, ..., rn} is >=i\rdil rsi\/ pdrw - pdi) rgi (14) where Pdi is a function of r, and the vector of parameters to be estimated, 6. When the A and B tags are not identical, the recaptures are partitioned into three disjoint classes, and the numbers in each are trinomial with expectations Jb(tv) (1 - Ja(t,)) and E{rAl) = 1 - JB(7V) JA(Tt) '' ^^ E(rJ = Mn) (1 - Mr,)) . 1 -Mr,) Mr,) **"** B' E(rdt) = (1 - Mr,)) (1 " Jb(t,)) 1 - JB(r,.) Mr,) = r, (1 - PA, - PBi). 695 FISHERY BULLETIN: VOL. 80, NO. 4 Now the joint conditional likelihood of the re- capture sample is £ = n i\»a.-! ra,]- rdi] IPa,^ Pb/Bi X (1 - PAl - PBi) rdi In either case, once the underlying model and the corresponding elements of 8 are identified, the ML estimates of 8 may be computed by maxi- mizing X directly using a variety of iterative search procedures. In some situations the deriva- tives of X with respect to 8 are easily derived, but even then only numerical solutions are possible. For example, when A and B tags are identical and J{t,) = 1 — p(exp(— Lt,-)), the ML estimates of p and L are found by solving the system of equations 0 = X n C, and 0 = X a where Q = (1 + Pdi) (rdi - Pdl n) 1 - p di = J(r,r{rti (I ~ J(r,-)\ ' \1 +J(ri)) = J(T,yl{rd, - E(rdi)}. The asymptotic covariance matrix of L and p may then be derived in the usual manner by in- verting the corresponding negative information matrix / = 2 rl A i=l 1 " n n - X r, D, - X Di __ ^ 1=1 p 1=1 where A = r.f Pd> (1 + Pd,f 1 - Pdi Explicit analytical solutions are possible when there is only a single recapture period centered at r and the model is reduced to a one-parameter function of either the Type I or Type II shedding rate, i.e., either J(t) = 1 — exp(— Lr) or J(t) = 1 — p. In this event the ML estimate of L (with p = 1) is 2rd L = \n +2rd with asymptotic variance estimated by rs (rs + rd) (15) '2 _ o~ r2rd (rs + 2rdY or when shedding is a function of p only (with L = 0) and /\ 2rd p - rs + 2rd -2 . rs 2rd (16) a^ — P (r, +2rrf) 3 • In the case of identical A and B tags a con- venient alternative to direct maximization of the likelihood function is to fit the recapture data to their expectations using an iteratively re- weighted Gauss-Newton algorithm. To accom- plish this one may use routines available in cer- tain standard statistical software packages, e.g., BMDP2. Specifically, we find an admissible value of 8 which minimizes the sum of squares S'= X Wi[rdi - E{rdi)f. i=i Since the rdi are assumed to be binomial (i.e., of "regular exponential" form), minimizing S' with a Gauss-Newton routine is equivalent to maxi- mizing the likelihood of Equation (14) provided the weights used are the reciprocals of the vari- ances of the rdi and are recomputed at each itera- tion based on the current parameter values ( Wedderburn 1974; Jennrich and Moore 1975; Jennrich and Ralston 1978). In this case the weights must be fv, = [r, Pdi (1 - Pdl)]'\ where Pdi is the function Pdl evaluated at the current parameter estimates. Asymptotic standard er- rors for the parameter estimates are also com- puted by the BMDP routine. A similar device may be used when a distinc- tion is made between A and B tags. Given rA, + rdi we assume rd, is binomial with expectation EB(rdl) = (rAl- + rlh) (1 ■- Jb(r,)). Analogously, 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 696 WETHERALL: ANALYSIS OF DOUBLE-TAGGING EXPERIMENTS EA(rdi) = (rB, + rdt) (1 - Ja(t,)). Thus an itera- tively reweighted Gauss-Newton algorithm mini- mizing S'B = 2 wBi (rdi - EB(rd,)Y' 1=1 with wBi = wBi = [(rAi + rdi) JB(r,)(l - Jb(t,))]'1 is used to compute ML estimates of shedding pa- rameters for the B class of tags. A parallel pro- cedure gives ML estimates of parameters for the A class. Note that the two sets of parameter esti- mates are not independent. Unknown Recapture Times A tacit assumption in the foregoing procedures is that the time between release and recapture for each returned fish is known to "interval accu- racy," and that exact recapture time information is available for only a fraction of the recoveries, so that all recoveries are grouped into the n time intervals to permit estimation. This will often be the case. However, in some fisheries it is conceiv- able that only the crudest sort of information is available on recapture times. For estimation purposes, all that is known is rd and rs, the total number of recaptures in each class over the ex- perimental period (0, T). When T is relatively small, say 1 yr or less, then estimation of a single Type I or Type II shedding parameter is possible, as in Equation (15) or (16). In an experiment of longer duration this is not feasible. However, it is possible under certain circumstances to estimate the ratio of the Type II shedding rate to other Type II losses. Let fishing be constant, contin- uous, and uniform at an instantaneous rate F. Assume further that the total instantaneous mor- tality rate is a constant, Z, and that shedding of tags occurs at an instantaneous rate L. If there are no Type I losses, the ratio of E(rg) to E(rd) in a double-tagging experiment approaches 2L x Z + L as T — °°. Thus if L = aZ, a moment estimator of a is provided by x a = 2 - x and if one has an estimate of Z which has a syste- matic bias due to Type II shedding, say Z\ then a corrected estimate may be obtained, i.e., Z' = Z\\ +a)-1. This method may also be used where single- tagging and double-tagging experiments are run concurrently. Then if A^(0) fish are released double-tagged and M(0) with single tags, let r'd and r'g be recaptures from each group still bear- ing the initial complement of tags. Under the same assumptions as above this leads to a r/AUO) ~ rJAE(O) 2riNs(0) - r,'N,(0) 1 < d < 2. riNM —^ , 0<-<2 (17) 2rd - rs rd Exact Recapture Times Turning now to the other end of the spectrum, under ideal conditions it is possible that the exact time out will be known for each fish returned. When exact recapture times are available for all fish the returns from a single-tagging experi- ment may be analyzed using ML procedures first developed by Gulland (1955) and later elabor- ated by Chapman (1961) and Paulik (1963). These rest on the assumption of binomial recap- ture probabilities based on constant Type II loss rates and on a resulting conditional recapture time distribution which is truncated negative exponential. Chapman et al. (1965) extended the same concepts to returns of fish initially double- tagged and still retaining both tags upon recap- ture, and showed that the difference between the estimated total Type II loss rate in a double-tag- ging experiment and the corresponding total Type II loss rate in a single-tagging study yielded an estimate of L. They noted that this is the best estimate of L possible using only the recapture information from a single-tagging experiment and from fish put out and returned with two tags. Left open was the possibility of combining this information with recapture times for fish initial- ly double-tagged but returned with only one tag still attached. For this class of fish the distribu- tion of recapture times is more complicated. We now consider an exact recapture time mod- el for an experiment based exclusively on fish initially double-tagged. Suppose JVrf(0) double- tagged fish are released at time 0. Over the course of the experiment, terminating at time T, a total of rd fish are recaptured and returned with both tags intact, and rs with only a single tag remain- ing. In addition, for each tagged fish returned 697 FISHERY BULLETIN: VOL. 80, NO. 4 we assume the exact recapture time is known, i.e., we know {tsl, ts2, .... tsrs} and {tdi, td2, ..., tdrd\. Let *«/ = Pr {fish is returned with both tags intact in (0, T)} and /s <*>/"( 1 - 4>s s = 2/ F(m) S(m) J(m) (1 - «/(m)) dw and 4>rf = / f\u) S(u) (1 - J(u)f du. Further, the conditional probability densities for recapture times are f,(t) = m = 2F(t) S(t) J(t)(l - J(t))/$a 0 < t < T 0 otherwise f F\t) S(t)(l - J(t)?/*d 0 < t < T 0 otherwise. The joint likelihood function for the observed numbers of single- and double-tag recoveries and the respective sets of recapture times may now be written as rs rd Z = Pr{rd, rs\. n Mtsd n fd(td!). i=i i=i For specified forms of F{u), S(u), and J{u) com- putation of ML estimates may now be contem- plated, although the form of £ is apt to be exceed- ingly complex in most situations. For example, taking the most elementary case, assume that J(u) = 1 - exp(-Lu), S(u) = exp[-(M + F)u] and F(u) = FtorO. Under these conditions the log-likelihood becomes In Z = K + r. InF + (NAO) - r. ) X lnh -(' 2LF2 W (F + M + L)(F + M +2L) - (F H- M) T. - L(Ta + 2Td) rs + 1 ln(l - exp(-Lf„-)) i=i where K is a function of the observations only, rs T = S t 1=1 rd Td = z tdi, T = Ts + Td, and r = rs + rd. Using numerical methods this may now be maxi- mized as a function of F, M, and L in the usual manner to yield ML estimates of these parame- ters, as well as asymptotic variance estimates. A simpler approach which yields information on Z — F + M and L is to condition the likelihood of rd and rs on the total number of recaptures, r, i.e., Pr {rd, rs} = 3>.s $d Jd rs\ rdll\d \ 4>,- + $d This gives the log-likelihood In X = K' + r. {ln(Z + L) + ln(Z + 2L) - ln(Z + 3L)} - ZT - L(T + T.) rs + S ln(l - exp(-L^)) (18) i=i where K' is independent of Z and L. Differentiating Equation (18) with respect to Z and L and setting the derivatives to zero one finds that the ML estimates of Z and L satisfy, among other relations, the equation T. r 1 + 1 Z + L Z + 2L Z + SL Combining this with the result at Equation (17) leads immediately to a solution for Z, i.e., 698 WETHERALL: ANALYSIS OE DOUBLE-TAGGING EXPERIMENTS r. Z=T 1 + 1 1 + a 1 + 2a 1 + 3a whence L — a Z. Estimating Mortality Rates by Double-Tagging All Fish In most of the preceding sections we assumed the basic purpose in double-tagging was to pro- vide auxilliary information on shedding rates which could then be applied to correct recapture statistics or mortality rate estimates obtained in a primary single-tagging experiment. An attrac- tive alternative is to use double-tagged fish en- tirely and to estimate the mortality rates and other vital parameters in such a way that no bias corrections are necessary. If exact recapture times are recorded, the ML model just discussed is appropriate. When recapture data are grouped into n time intervals of length A, centered at times r(, a convenient context for developing this approach is the single-tagging regression model suggested by Chapman (1961) and discussed fur- ther by Cormack (1968) and Seber (1973). This takes the form In r> h A, = \n[qpNA0)] -Qfl ~ Xt, + e, (19) where f, = the nominal fishing effort during period i f,' = 2 fj Aj H — — the estimated J=1 nominal effort up to time n q = the catchability coefficient c, = a random error term. In this particular model one obtains estimates of q and X, and, since Ns(0) is known, an estimate of p as well. However, in the presence of Type II shedding the exploitation rate for any period will be underestimated, i.e., hidden in X will be the term L. The usual Drocedure would be to correct X by subtracting L, where L is obtained in an in- dependent double-tagging experiment. Instead, if we apply the model directly to recapture statis- tics from a double-tagging experiment (AUO) fish initially double-tagged) we will obtain an estimate of X unaffected by Type II losses and in need of no corrections. This is accomplished by substituting the dependent variable + 2rdi 2A, f, 2rrfl- n, + 2r, (20) Further, it now transpires that the estimate of the regression intercept term is free of Type I shedding effects, i.e., one will estimate \n[qN,i(0)] rather than \n[qpNd(0)]. If we assume r,( and rtl, are complementary bi- nomial variables given r.it and that r, is Poisson, then approximately correct weights for the re- gression employing Equation (20) are Wi (n, +2rrf,-)2 rdi, When effort statistics are not available so that a constant fishing mortality rate must be as- sumed, or when there is a linear dependence be- tween the two independent variables f ,' and r, , then separate estimates of q and X are not pos- sible using the single-tag model of Equation (19) unless Type I errors are absent. Nor is p esti- mable. Instead, one may only regress ln(rj/A,) on t, to yield estimates of ln[pFM(0)] and (F + X). But when the model is applied to a double-tag- ging experiment under the same restrictions, it is still possible to estimate both q and X un- affected by shedding. Note that the dependent variable of Equation (20) from the double-tagging experiment is anal- ogous to the one of Equation (19) appropriately corrected for tag shedding, as in Equation (8). In both cases the recaptures rdi and r,., are assumed to be point samples taken exactly at t,. Thus while in the example above k, = p exp(— Lr,), the correction procedure of Equation (8) and the method outlined here are independent of assump- tions on the manner of tag shedding (cf. Seber 1973:281), provided the recapture intervals are reasonably small (say 1 yr or less). SUMMARY AND CONCLUSIONS The aim of this paper has been to extend the theory and methodology of estimating tag-shed- ding rates through double-tagging. Attention was focused on the situation most commonly en- countered in fishery applications, wherein two identical tags are placed on each member of an 699 FISHERY BULLETIN: VOL. 80, NO. 4 experimental cohort, tagged fish are recaptured at most once in a fishery which is essentially con- tinuous, and the time at liberty is known exactly for only a fraction of the recapture sample. The regression models studied by Chapman et al. (1965), Bayliff and Mobrand (1972), and Kirk- wood (1981) were extended to permit the Type II shedding rate for each tagged fish to be a func- tion of time. Both deterministic and stochastic versions were presented and previously pub- lished models were shown to be special cases. If all tags are subject to the risk of shedding, i.e., if 6 = 1, and if data are available from several recapture periods, a simple plot of In*, against t, will reveal whether the average Type II shed- ding rate, V(t), is constant; if it is, the relation- ship will be linear. In this event the most parsi- monious model consistent with the data will be the deterministic model based on a constant Type II shedding rate, L. In addition, if the points suggest a negative intercept on the ordi- nate the Type I retention rate, p, may be added to the parameter set. One may then carry out the parameter estimation using either the Bayliff- Mobrand linear regression model, or the non- linear regression of ln(r,,/2rrf() on r(, depending on which error structure is assumed. However, since the plot of In*, versus r, is approximately linear even with multiplicative error in the re- capture process, it probably makes little differ- ence which estimation method is used as long as proper statistical weights are incorporated. If 8 = 1 and the plot of In*, versus r, is nonlin- ear, one of the more complicated tag-shedding models is called for. A trend which is concave downward suggests that y(t) is increasing with time and points to the stochastic model of Equa- tion (5) or its deterministic counterpart. On the other hand, upward concavity could be explained either by a model in which the Type II shedding rate decreased with time or by Kirkwood's(1981) hypothesis, or by a combination of the two as in Equation (5). Another useful diagnostic plot is 1 — k, against r-. These are the variables considered in Kirk- wood's nonlinear model. When L is constant the plotted points will be traced by a line analogous to a von Bertalanffy growth curve with asymp- tote 8 and location parameter p, and they should indicate which of these two parameters to in- clude in the model and how much precision to ex- pect in the resulting estimates. (In passing, it is worth mentioning that if 8 is to be estimated jointly with L, a longer experiment is required to ensure high precision in the parameter estimates than if L alone is being estimated.) The treatment of recaptures from double-tag- ging experiments with multiple cohorts was dis- cussed in the context of the Bayliff-Mobrand model. Alternative methods of combining infor- mation from several cohorts to estimate common shedding parameters were proposed, and a gen- eral linear model approach was suggested for situations where more elaborate structural as- sumptions are made. A full numerical evaluation of these procedures remains to be done. As an alternative to the least squares regres- sion methods usually employed, some new ML procedures were presented. These are more diffi- cult to use than the regression techniques, but offer advantages in some situations. For exam- ple, when only two recapture periods are possible one cannot compute the precision of regression estimates in the Bayliff-Mobrand model, but standard errors in the equivalent ML model are still estimable. The most promising method for deriving ML estimates in the general case may be the iteratively reweighted Gauss-Newton algorithm. Indeed, if one has access to the right computer software (such as the BMDPAR and BMDP3R programs supplied by BMDP) this approach is nearly as easy to use as the simple Bayliff-Mobrand linear regression method. A sensible procedure would be to first study the diagnostic plots suggested above for the regres- sion analysis, and then fit the selected model using an iteratively reweighted least squares algorithm. The estimation procedures discussed above are applicable when data are grouped by recap- ture interval. For situations in which the exact time at liberty is known for each recapture an unconditional ML model was developed. This may be applied not only to estimate shedding rates but also to estimate mortality rates un- affected by shedding. However, in its general form the likelihood function is rather compli- cated and only numerical solutions would be pos- sible in most situations. Analytical estimators for L and Z were derived for a simplified condi- tional likelihood. Besides the more stringent data requirements this model requires the extra assumption of constant mortality rates during the experiment. In the final section it was shown that through double-tagging it is possible to estimate mortal- ity rates free of tag-shedding biases even when the recapture data are available only to interval- 700 WETHERALL: ANALYSIS OF DOUBLE-TAGGING EXPERIMENTS accuracy, and without resort to the usual concur- rent single-tagging experiment. The model was developed in the simple context of a fixed Type II shedding rate, but the principle applies to more complicated shedding processes as well. If the burden imposed by the second tag can be ne- glected, it therefore seems advantageous to dou- ble-tag all fish. In any case, when shedding is ap- preciable the greater overall recovery rates from double-tagging make the exclusive use of double- tagged fish a proposition well worth considering. LITERATURE CITED Arnason, A. N., and K. H. Mills. 1981. Bias and loss of precision due to tag loss in Jolly- Seber estimates for mark-recapture experiments. Can. J. Fish. Aquat. Sci. 38:1077-1095. Baglin. R. E., Jr., M. I. Farber, W. H. Lenarz, and J. M. Mason, Jr. 1980. Shedding rates of plastic and metal dart tags from Atlantic bluefin tuna, Thunnus thynnus. Fish. Bull., U.S. 78:179-185. Bartholomew, D. J. 1973. Stochastic models for social processes. John Wiley & Sons, 411 p. Bayliff, W. H. 1973. Materials and methods for tagging purse seine- and baitboat-caught tunas. [In Engl, and Span.] Inter-Am. Trop. Tuna Comm. Bull. 15:465-503. Bayliff, W. H., and L. M. Mobrand. 1972. Estimates of the rates of shedding of dart tags from yellowfin tuna. [In Engl, and Span.] Inter-Am. Trop. Tuna Comm. Bull. 15:439-462. Beverton, R. J. H., and S. J. Holt. 1957. On the dynamics of exploited fish populations. Fish. Invest. Minist. Mar. Fish. Minist. Agric, Fish. Food. (G.B.), Ser. II, 19, 533 p. Chapman, D. G. 1961. Statistical problems in dynamics of exploited fish- eries populations. Proc. Berkeley Symp. Math. Stat. Probab. 4:153-168. 1969. Statistical problems in the optimum utilization of fisheries resources. Bull. Int. Stat. Inst. 42:268-293. Chapman, D. G., B. D. Fink, and E. B. Bennett. 1965. A method for estimating the rate of shedding of tags from yellowfin tuna. [In Engl, and Span.] Inter- Am. Trop. Tuna Comm. Bull. 10:333-352. Cormack, R. M. 1968. The statistics of capture-recapture methods. In H. Barnes (editor). Oceanography marine biology annual review 6:455-506. George Allen and Unwin, Ltd., Lond. GlJLLAND, J. A. 1955. On the estimation of population parameters from marked members. Biometrika 42:269-270. 1963. On the analysis of double-tagging experiments. Int. Comm. Northwest Atl. Fish. Spec. Publ. 4:228- 229. Hynd, J. S. 1969. New evidence on southern bluefin stocks and mi- grations. Aust. Fish. 28(5):26-30. Jennrich, R. I., and R. H. Moore. 1975. Maximum likelihood estimation by means of non- linear least squares. Am. Stat. Assoc. Proc. Stat. Corn- put. Sect., p. 57-65. Jennrich, R. I., and M. L. Ralston. 1978. Fitting nonlinear models to data. Health Sci. Comput. Facil., Univ. Calif., Los Angeles, BMDP Tech. Rep. 46, 71 p. Kirkwood, G. P. 1981. Generalized models for the estimation of rates of tag shedding by southern bluefin tuna (Thunnus mac- coyii). J. Cons. Cons. Inst. Explor. Mer 39:256-260. Laurs, R. M., W. H. Lenarz, and R. N. Nishimoto. 1976. Estimates of rates of tag shedding by North Pacific albacore, Thunnus alalunga. Fish. Bull., U.S. 74:675- 678. McNolty, F., J. Doyle, and E. Hansen. 1980. Properties of the mixed exponential failure process. Technometrics 22:555-565. Myhre, R. J. 1966. Loss of tags from Pacific halibut as determined by double-tag experiments. Int. Pac. Halibut Comm. Rep. 41, 31 p. Paulik, G. J. 1963. Estimates of mortality rates from tag recoveries. Biometrics 19:28-57. RlCKER, W. E. 1975. Computation and interpretation of biological sta- tistics of fish populations. Fish. Res. Board Can. Bull. 191. 382 p. Robson, D. S., and H. A. Regier. 1966. Estimates of tag loss from recoveries of fish tagged and permanently marked. Trans. Am. Fish. Soc. 95: 56-59. Seber, G. A. F. 1973. The estimation of animal abundance and related parameters. Hafner Press, N.Y., 506 p. Seber, G. A. F.. and R. Felton. 1981. Tag loss and the Petersen mark-recapture experi- ment. Biometrika 68:211-219. Wedderburn, R. W. M. 1974. Quasi-likelihood functions, generalized linear models, and the Gauss-Newton method. Biometrika 61:439-447. Wetherall, J. A., and M. Y. Y. Yong. 1981. Planning double-tagging experiments. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SWFC-13, 44 p. 701 FOUR NEW SPECIES OF SQUID (OEGOPSIDA: ENOPLOTEUTHIS) FROM THE CENTRAL PACIFIC AND A DESCRIPTION OF ADULT ENOPLOTEUTHIS RETICULATA Lourdes Alvina Burgess1 ABSTRACT Four new species of Enoploteuthis (E. obliqua, E. oetolineata, E. jonesi, and E. higginsi) are described, illustrated, and compared. Adults of E. reticulata Rancurel 1970 are described for the first time. A key for all the species is provided. Cephalopods are important fisheries resources in the Pacific Ocean. Thus, clarification of cephalopod systematics, particularly from areas where they are not thoroughly known such as the central Pacific, is important. Because enoplo- teuthid squids are deepwater animals that are not easily accessible or profitable to fish, they are not at present generally exploited commercially. In Toyama Bay, Sea of Japan, however, the enoploteuthid squid Watasenia scintillans (Berry 1911) is fished regularly in the spring and early summer when swarms of this species migrate to the surface to spawn (Sasaki 1914). Cephalopods also play important roles in marine food webs. They are the principal food of many marine mammals, fishes, and some birds. Reintjes and King (1953) found that 26% of the aggregate total volume of the stomach contents of yellowfin tuna, Thunnus albacares, captured in the central Pacific consisted of cephalopods. King and Ikehara (1956) showed that as much as 33% of the food of the bigeye tuna, T. obesus, were squids, including Enoploteuthis sp. Berry (1914) reported on the cephalopods col- lected on board the U.S. Fish Commission steamer Albatross from the Hawaiian area; the collection included enoploteuthid squids but none of them of the genus Enoploteuthis. Species of Enoploteuthis from Hawaiian waters and the central Pacific are described here for the first time and compared with all the known spe- cies of Enoploteuthis in the world. Four new species of pelagic squids belonging to the genus Enoploteuthis, together with some 'Southwest Fisheries Center Honolulu Laboratory, Nation- al Marine Fisheries Service, NOAA, Honolulu, Hawaii; present address: T. F. H. Publications, Inc., 21 1 West Sylvania Avenue, Neptune, NJ 07753. adults of E. reticulata, were identified during the examination of the large collection of cepha- lopods at the Honolulu Laboratory, Southwest Fisheries Center of the National Marine Fish- eries Service (NMFS), Honolulu, Hawaii (form- erly Bureau of Commercial Fisheries Biological Laboratory, Honolulu). The squids were taken from various areas of the central Pacific on several research vessels operated by the Honolulu Laboratory from 1953 to 1970. The fishing gear was either a modified Cobb trawl, a 10-ft Isaacs-Kidd trawl, or a Nanaimo trawl. The depth of fishing generally was between 50 and 100 m; most of the fishing was done at night. Details on the capture of the cephalopods re- ported on here, including all holotypes and para- types, are available from the original cruise re- ports and logs on file at the Honolulu Laboratory. Type specimens are deposited in the cephalo- pod collections of the Division of Mollusks, U.S. National Museum of Natural History (USNM), Smithsonian Institution. The terminology of the anatomical parts, mea- surements, and indices conform to those general- ly used for squids and in particular to those listed and defined by Roper (1966): ML = mantle length, CH = club hooks, CS = club suckers, MWI = mantle width index, HWI = head width index, FLI = fin length index, FWI = fin width index, ALI = arm length index, and TLI = ten- tacle length index. As in Roper (1966) the arm length is measured from the first basal hook (or sucker) to the tip of the arm. The ranges and means of indices given in the descriptions were computed from measure- ments of the male and female specimens listed in Tables 1 to 5. This is not applicable to indices in- Manuscript accepted April 1982. FISHERY BULLETIN: VOL. 80. NO. 4. 1982. 703 FISHERY BULLETIN: VOL. 80, NO. 4 eluded in the remarks on immature individuals; not all their measurements are presented in the tables. The following abbreviations which appear in the list of material refer to the research vessels: HMS = Hugh M. Smith, CHG = Charles H Gilbert, and TC = Townsend Cromwell. A + sign after numbers in the text and tables indicates a missing mantle or arm tip, or lost suckers. FAMILY ENOPLOTEUTHIDAE PFEFFER 1900 Genus Enoploteuthis Orbigny 1848 Diagnosis: Enoploteuthids with numerous light organs on mantle, head, and arms; single row of small light organs on ventral surface of eyeball; two rows of hooks on tentacular club; buccal connectives DDVD2; fins lateral; and mantle projecting posteriorly as free "tail." Type species: Loligo leptura Leach 1817; Hoyle 1910:409, by elimination. Enoploteuthis obliqua n. sp. (Figs. 1, 2A; Table 1) Enoploteuthis sp. (No. 2), Okutani 1974: figures 12c, d, f. Holotype: Male, ML 55 mm, TC-48, Stn. 11, 11°47'N, 144°47'W, 31 March-1 April 1970, 50 m, USNM 729722. Paratypes: 1 female, ML 50 mm, TC-46, Stn. 9, 11°49'N, 144°51'W, 14 October 1969, 50 m, USNM 577605. 1 male, ML 41 mm, TC-46, Stn. 9, 11°49'N, 144°51'W, 14 October 1969, 50 m, USNM 729713. 1 male, ML 58 mm, TC-48, Stn. 19, 11°34'N, 144°54'W, 3-4 April 1970, 50 m, USNM 729688. Other material: 5 specimens, ML 12-17 mm, TC-43, Stn. 10, 12°03'N, 144°55'W, 8 May 1969, 50 m. 16 specimens, ML 5-18 mm, TC-43, Stn. 14, 11°56'N, 144°56'W, 10 May 1969, 50 m. 5 specimens, ML 12-17 mm, TC-43, Stn. 22, 07°41' N, 145°01'W, 13 May 1969, 50 m. 1 female (from Alepisaurus stomach contents), ML 50 mm, TC-44, equatorial central Pacific, July- August 1969, 10-100 m, USNM 729716. 2 spec- 2D = dorsal; V = ventral. imens, ML 5 and 10 mm, TC-44, Stn. 16, 11° 51'N, 144°41'W, 11 July 1969, surface. 1 specimen (from Alepisaurus stomach contents), ML 27 mm, TC-44, Stn. 17, 11°N, 144°W, 10 July 1969. 2 specimens, ML 12 and 17 mm, TC-44, Stn. 18, 11°53.2'N, 144°49.3'W, 11 July 1969, 100 m. 1 male, ML 37+ mm, 4 specimens, ML 12-20 mm, TC-44, Stn. 24, 07°32.9'N, 145°58'W, 13 July 1969, 50 m. 1 specimen, ML 13 mm, TC- 44, Stn. 32, 07°31.5'N, 144°50.2'W, 17 July 1969, 50 m. 1 specimen, ML 12 mm, TC-44, Stn. 54, 00°01.8'N, 145°08.8'W, 28 July 1969, 50 m. 4 specimens, ML 6-11 mm, TC-47, Stn. 16, 12°02'N, 144°54'W, 23 January 1970, 50 m. 3 specimens, ML 7-10 mm, TC-48, Stn. 16, 11°45' N, 144°46'W, 2-3 April 1970, 20 m. 1 female, ML 40+ mm, TC-48, Stn. 19, 11°34'N, 144°54'W, 3-4 April 1970, 50 m. Description: The mantle is muscular except for the thin-walled posterior end (tail) consisting of a gelatinous alveolar material. The mantle is widest (MWI 29.1 -.52. 4-34.1) at the anterior edge and tapers into a blunt end. The anterior ventral margin is slightly excavated forming low, pointed lateral angles on each side. The dorsal margin is extended anteriorly into a median rounded lobe. The fins are wider (FWI 62A-69.5-73.2) than their lengths (FLI 52.0-59.0-64.0). They are attached anteriorly at about the midpoint of the mantle length. The anterior margin of each fin forms a rounded lobe. The lateral angles (72°) of the fins are rounded. The posterior margins are straight and are fused to the mantle separately, except for a point (difficult to see) near the tip of the mantle where they join. The funnel is large, triangular, and has a broad base. The funnel-mantle locking cartilage is straight, the ends are rounded but the anterior end is slightly narrower; the median groove is shallow. The funnel organ of the holotype is large (9 mm long). The dorsal pad has an inverted V- shape with a slender papilla anteriorly and with prominent ridges on the limbs; each limb is about 2.5 mm wide. The ventral pads are oval and elongated (7 mm long, 3 mm wide). The head is nearly square in cross section and narrower than the mantle (HWI 21.8-26.0-29.3). The funnel groove has a distinct edge on each side. The edges continue posteriorly to form the first pair of nuchal folds which bears the small olfactory papillae. The second and third nuchal folds are crescentlike membranes on each side 704 BURGESS: FOUR NEW SPECIES OF SQUID ENOPLOTEUTHIS Table 1.— Measurements (in millimeters) and counts of Enoploteuthis obliqua. missing mantle or arm tip, or lost suckers. TC = RV Townsend Cromwell; + = a Cruise: TC-48 TC-48 TC-46 TC-44 TC-46 TC-44 TC-44 TC-44 Station: 19 11 (Holotype) 9 9 24 24 18 Sex: Male Male Female Female' Male Male ? ? Mantle length 58 55 50 50 41 37+ 20 17 Mantle width 19 16 17 16 14 13 9 9 Head width 17 12 14 12 11 8 5.5 7 Fin length 34 32 31 32 21 17 7 8 Fin width 36 38 36 35 30 22 10 12 Arm length Right 1 29 25+ 25 26 20 17+ 9 10 Right II 31 + 24 26 27 21 17 + 12 11 Right III 28+ 26 24 30 20 21 + 11 9+ Right IV 31 27+ 25 31 20 20+ 10 9 + Left IV 32 27 25 31 22 22 10 Arm hooks/suckers Right 1 18/24 20/24 23/26 20/22 20/23 10/18 16/— 18/12 Right II 22/20 21/25 24/24 22/20 20/18 20/— 17/— 18/13 Right III 23/— 22/24 24/20 22/16 21/20 20/— 15/— 17/— Right IV 28/16 30/21 32/15 31/15 30/14 28/— 18/— 26/— Left IV 28/16 31/16 31/12 31/19 30/18 29/14 17/— 28/— Tentacles right/left Tentacle length — 47/53 32/— 45/41 29/30 31/— 12/- 14/— Club length — 9+/10 8.5/— 13/13 11— 11— 3.5/— 3.5/— Club hooks Right (dorsal/ventral)- left (dorsal/ventral) — 4/4-4/5 4/5 — 4/5-4/5 3/5-4/4 — 1/— Club suckers right/left Distal suckers — — /13 17/— 14/14 11/— 11/— Carpal suckers — 5/3 5/— 5/5 5/5 4/4 3/4 5/— 'From stomach of Alepisaurus. of the neck that are connected to each other posteriorly by a narrow membranous ridge. The third dorsal fold extends dorsally as a mem- branous ridge, but the ridge does not reach the midline of the head. Dorsal and ventral ocular "windows" are present and the latter easily allows a count of the nine eye photophores on the ventral side of the eyeball. The eye opening is a large, wide, transverse oval with a deep sinus (Fig. 1 F). The buccal membrane completely hides the buccal mass and surrounding lips. Eight slender supports are joined by slender connectives to the arms in the order DDVD (i.e., all are attached to the dorsal side of the arms except the third pair which are attached to the ventral side of arm III). The inner surface of the buccal membrane is rugose, but without papillae; the lappets are delicate and pointed. The membrane is purple and does not appear much darker than most parts of the body. The chromatophores are small and are scattered evenly on both the supports and the membrane. The arms are subequal, slender, and much shorter than the mantle length (ALI: I, 48.8- 50.2-52.0; II, 43.6-50.2-54.0; III, 47.3-5L0-6O.O; IV, 48.8-55.2-62.0). They taper gradually to slender tips. The swimming keels are low and poorly developed on the dorsal arms, and they are mainly confined to the distal third of these arms. The swimming keel of arm III is wider than the arm at its greatest width. The lateral membrane or tentacular sheath along arm IV is narrow; it is about half of the arm width proxi- mally and it extends to the tip of the arm. Protec- tive membranes are developed on the ventral side of all arms, but decrease in size in the follow- ing order: III, II, I, IV. The dorsal protective membranes on all the arms are low; on arm IV the trabeculae are not evident. The right ventral arm of the male is hectocoty- lized. The protective membrane on the medial side of this arm (Fig. 1J) is expanded into an un- dulating membrane that extends from the eighth pair of hooks to the tip of the arm. The dor- sal protective membrane is slightly developed. In the males small tubercles or conical papillae are present between the bases of the hooks and bases of all arms. All the arms bear two rows of alternating strong hooks, each (Fig. IE) completely enclosed in a membranous sheath. The distalmost hook is about half the length of the largest one. In both sexes, arm IV has the most hooks. The distal part of each arm is occupied by two rows of suckers with wide apertures and slender stalks. The inner sucker ring bears seven or eight prominent truncated teeth on the distal margin but the proximal margin is smooth (Fig. IB). The outer ring has numerous pegs (Nixon and Dilly 1977). 705 FISHERY BULLETIN: VOL. 80. NO. 4 706 BURGESS: FOUR NEW SPECIES OF SQUID ENOPLOTEUTHIS The suckers decrease in diameter distally, be- come globular in shape, and have only three or four blunt teeth. The tentacles are shorter than the mantle (TLI 62.1-79.2-96A), very delicate and slender. The stalk is laterally compressed, about a third of the width of arm III. The club is not expanded (Fig. IK). The carpus bears a series of four or five suckers and four, five, or seven pads, and the whole cluster is bordered by a very low ridge on each side. The manus in- cludes a dorsal row of three or four sheathed hooks and a ventral row of four or five slightly larger similarly sheathed hooks (Fig. ID). These two rows are very close to each other. Marginal suckers are absent. A medial sucker or two may be present in series with the hooks distally. The largest club hook is smaller than any of the arm hooks. The dactylus of the club is occupied by 11 to 17 suckers that are also arranged in two rows. They have long stalks and wide openings. The distal margin of the inner sucker ring bears six or seven slender blunt teeth and the outer sucker ring has numerous pegs (Fig. 1C). Protective mem- branes are absent. The aboral keel or dorsal membrane is narrow and, at most, about half the length of the club. The tip of the club is rounded and bears a short hoodlike membrane that conceals one or two of the suckers there. There are two types of light organs on the in- tegument: Large dark ones with pearly white centers and small white ones with very narrow outer pigmented rings. These photophores range in size from small (0.2 mm) to large (0.4 mm), and they are randomly interspersed with each other. The most distinctive feature of this species is the unique arrangement of the mantle photophores. Some of the rows are slanting or oblique (Fig. 1A), instead of the usual straight longitudinal rows described in most other Enoploteuthis species. Two median longitudinal rows (two to three photophores in width), separated by an Figure I.— Enoploteuthis obliqua (A-F, K, and L from fe- male paratype, ML (mantle length) 50 mm; other body parts are from specimens as listed.) A, Ventral aspect; B, Dorsal arm sucker; C, Tentacular sucker; D, Tentacular hook, oral and lateral aspects; E, Dorsal arm hook, oral and lateral as- pects; F, Eye and surrounding area; G, Mandibles: upper (1), lower (2), male, ML 37 mm; H, Dorsal arm sucker, ex- Alepisaums female, ML 50 mm; I, Radular teeth, male, ML 37 mm; J, Hectocotylus, male, ML 41 mm; K, Tentacular club; L, Eye light organs; M. Section of spermatophore, male holotype, ML 55 mm. intervening space lacking photophores, extend from the anterior edge of the mantle to the pos- terior tail. Photophores on the posterior part of the mantle are scattered, those on the anterolat- eral part are arranged in four oblique rows on each side of the median longitudinal rows. Ex- cept for the most posterior row, the oblique rows radiate from the anterior edge of the mantle. The edge of the mantle is lined by a transverse row in which the photophores are closer to each other ventrally than dorsally. A few isolated photo- phores are present on the dorsal surface of the mantle, none are present on the surface of the fins. The tail has a single row on each side; a few photophores occur on the ventral side, but none are present on the dorsal side. Six groups of photophores occur on the funnel: Two broad rows separated by a narrow midline space on the ventral side; a short row of six or seven light organs on each lateral margin (one or two photophores are present in the space be- tween these rows posteriorly); and a group of photophores on each side of the bridles on the dorsal side of the funnel. There are two patches of light organs, sep- arated by a narrow space, in the apical region of the funnel groove. Six rows are recognizable on the ventral surface of the head, three rows on each side of a narrow midline space devoid of photophores. A row (two or three closely set photophores in width) along the lateral edge of the funnel groove extends anteriorly with in- creased numbers of photophores medial to each eye. It then bifurcates into two branches: one branch extends along the ventral aboral border of arm IV to a point opposite the last arm hook, the other branch continues distally along the base of the tentacular sheath to the tip of arm IV. The next lateral row of the head photophores ex- tends from near the first nuchal fold anteriorly, although a short gap occurs opposite the lens of the eye at the ventral window, along the head and onto the edge of the tentacular sheath where it continues to near the tip of arm IV. The lateral- most row of the head extends from between the second nuchal fold to the posterior margin of the eye; it continues as a single row of closely set photophores along the edge of the eyelid ven- trally to the ventral edge of the optic sinus (Fig. IF). The dorsal edge of the eyelid is devoid of light organs. From the dorsal edge of the optic sinus the row proceeds along the base of the swimming keel of arm II almost to the tip of the arm. Some small white photophores occur near 707 FISHERY BULLETIN: VOL. 80, NO. 4 the eye region between the median and lateral- most rows. Nine light organs occur in a single row on the ventral side of the eyeball (Fig. 1L). The termi- nal photophores are larger and are separated by a wide space from a row of seven much smaller ones that lie adjacent to one another. The teeth of the radula are long and slender (Fig. II); the rachidian has distinct cusps on each side. The first lateral teeth are the shortest. The mandibles of a young male (ML 40 mm) have distinct growth lines on the wings. The rostrum is heavily pigmented; the edges are sharp and the tip of the upper mandible is very pointed (Fig. Id). The gular plate of the lower mandible is strengthened by three stout ribs (Fig. 1G2). The gladius has a strong rachis which is rounded anteriorly and thickened medially. The thin vanes are widest at about the midpoint of the total length. The rounded posterior cone is shallow and thin. A single spermatophore was found in the spermatophoric sac of the holotype (ML 55 mm), and its measurements are given below: Spermatophore segment Entire spermatophore Spiral filament Cement body Sperm reservoir Length (mm) 11.5 4.5 1.5 5.5 The spiral filament is slightly sculptured at the aboral end by some irregular ridges. The cement body has a small collar at the oral end (Fig. 1M). A few spiral turns are visible behind the spermatophore cap. of an Alepisaurus) exhibits certain features not observed in other specimens of the same or near- ly the same size. The arm and tentacular hooks have flattened processes (Fig. 1H). Further- more, this specimen shows a slight variation in the arrangement of photophores: some photo- phores occur on the median space of the mantle. The closest species to E. obliqua is E. leptura (Leach 1817) from the Atlantic. Both obliqua and leptura have slender tentacles and clubs. There are few suckers (<20) arranged in two rows on their clubs. However, obliqua has fewer tentacu- lar hooks (at most 9) while leptura has more (6- 12). The carpal cluster is elongate and without prominent ridges in both species. Their sperma- tophores show similar characteristics: very little sculpture in the spiral filament and one small collar on the cement body. The specific name obliqua reflects the arrange- ment of the mantle photophores. The oblique ar- rangement of light organs on the mantle was de- scribed earlier by Okutani (1974). His three im- mature specimens (ML 23.8-25.8 mm) from the EASTROPAC collection and a fourth specimen from the invertebrate collection of the Scripps In- stitution of Oceanography are all referable to E. obliqua, His material was collected in the eastern Pacific. Distribution: Equatorial regions of the central and eastern Pacific. Enoploteuthh octolineata n. sp. (Figs. 3, 2C; Table 2) Holotype: Female, ML 71 mm, HMS-47, Stn. 58, 02°56'N, 150°03'W, 4 November 1958, 212 m, USNM 577607. Young individuals: Small specimens (ML 6.0- 20.0 mm) are easily separated from other species of Enoploteuthis by the unique oblique rows of photophores on the mantle. Early development of the oblique rows are shown in Figure 2Aa and b in specimens ML 7 and 9 mm, respectively. Arm hooks are formed early; six to nine hooks are already present in the arms at ML 6.0 mm. But tentacular hooks appear much later; a ML 17 mm specimen has one tentacular hook and an- other (ML 20 mm) has none at all. Only two rows of suckers are present on the club. Remarks: A female specimen tentatively as- signed to this species (from the stomach contents Paratypes: 1 female, ML 75 mm, TC-43, Stn. 52, 00°01'N, 145°03'W, 28 May 1969, 50 m, USNM 729721. 1 female, ML 56 mm, TC-46, Stn. 37, 03°23'N, 145°04'W, 26 October 1969, 50 m, USNM 729720. 1 male, ML 46 mm, TC- 48, Stn. 50, 03°29'N, 144°58'W, 17-18 April 1970, 50 m, USNM 729708. Other material: 1 specimen, ML 10 mm, HMS- 47, Stn. 51, 00°44'S, 149°46'W, 2 November 1958, 576 m. 1 specimen, ML 25 mm, HMS-47, Stn. 58, 02°56'N, 150°03'W, 4 November 1958, 212 m. 1 specimen, ML 15 mm, CHG-89, Stn. 5, 02°40'N, 157°31'W, 28 July 1966, 120-240 m. 1 specimen, ML 15 mm, TC-43, Stn. 12, 12°11'N, 708 BURCESS: FOUR NEW SPECIES OF SQUID ENOPLOTEUTHIS y< A #«■■ ,,-4 ?«s*2 ^w; \, Figure 2.— Ventral aspect of mantle and head of immature Enoploteuthis specimens. A, E. obliqua: ML 7 mm (a), ML 9 mm(b); B, E. reticulata: ML 13 mm (a), ML 26 mm (b); C, E. octolineata: ML 10 mm (a). ML 26 mm (b); D and F. E. jonesi, ML 17 mm: E and G, E. higginsi, ML 15 mm. 145°11'W, 9 May 1969, 20 m. 1 specimen, ML 20 mm, TC-43, Stn. 26, 07°33'N, 144°50'W, 15 May 1969, 50 m. 3 specimens, ML 19-30 mm, TC-43, Stn. 38, 03°30'N, 145°06'W, 20 May 1969, 50 m. 2 specimens, ML 21 and 40 mm, TC-43, Stn. 42, 03°32'N, 144°59'W, 22 May 1969, 50 m. 1 specimen, ML 24 mm, TC-43, Stn. 48, 00°04'N, 145°07'W, 26 May 1969, 50 m. 2 specimens, ML 20 and 22 mm, TC-43, Stn. 52, 00°01'N, 145°03' W, 28 May 1969, 50 m. 1 specimen, ML 26 mm, TC-44, Stn. 26, 07°14.8'N, 144°58.8'W, 14 July 1969, 20 m. 1 specimen (from Alepisaurus stomach contents), ML 28 mm, TC-44, Stn. 44, 03°49.9'N, 145°18'W, 22 July 1969, 50 m. 1 specimen, ML 20 mm, TC-44, Stn. 56, 00°15.2'N, 144°43.9'W, 29 July 1969, 50 m. 1 specimen, ML 25 mm, TC-44, Stn. 68, 03°39'S, 144°54.5'W, 3 August 1969, 75 m. 1 specimen, ML 36 mm, TC-46, Stn. 41, 03°19'N. 145°03'W, 28 October 1969, 50 m. 2 specimens, ML 14 mm, TC-46, 709 FISHERY BULLETIN: VOL. 80. NO. 4 Table 2.— Measurements (in millimeters) and counts of Erwploteuthis octolineata. HMS =RV Hugh M. Smith; TC = RV Townsend Cromwell; + = missing arm tips and lost suckers. Cruise: HMS-47 TC-43 TC-46 TC-48 TC-48 TC-44 HMS-47 TC-43 Station: 58 (Holotype) 52 37 50 92 26 58 12 Sex: Female Female Female Male ? ? ? ? Mantle length 71 75 56 46 33 26 25 15 Mantle width 26 27 21 18 13 11 13 6 Head width 24 21 16 14 10 10 12 5 Fin length 50 52 38 30 19 15 15 7 Fin width 54 56 42 32 23 20 20 8 Arm length Right 1 43 49 28+ 32 23 16 15 8 Right II 42 46 32 '32 24 16 18 8 Right III 42 50 31 38 25 18 17 7 Right IV 42 52 38 33 25 16 16 9 Left IV 45 54 35 31 25 18 16 — Arm hooks/suckers Right 1 21/36 23/26 20/23+ 20/— — 21/25 16/14 16/12 Right II 22/32 22/24 21/21 18/— 22/— 22/22 21/— 16/14 Right III 25/27 24/28 22/22 21/18 20/— 21/24 23/— 15/11 Right IV 29/25 34/38 32/25 29/23 28/10+ 30/22 21/— 18/10 Left IV 30/30 32/34 31/26 29/20 + 26/12 29/27 29/12 — Tentacles right/left Tentacle len gth 75/80 70/70 53/— 43/44 39/37 15/16 25/— 13/— Club length 19/18 — 14/15 12/13 10/9 5/5 5/— 4/- Club hooks (Right (dorse il/ventral)- left (dorsal/ventral) 4/5-4/6 — 6/5 4/6-4/6 5/5-4/6 4/5 — 4/5-4/6 5/5 — — Club suckers right/left Distal suckers 16/17 — 14/14 14/16 10/— — /19 — — Carpal sucki 3rs 3/5 6/4 6/5 5/6 4/— 6/4 3/— — 'Length of left arm. Stn. 45, 03°29'N, 144°54'W, 30 October 1969, 50 m. 1 female, ML 56 mm, TC-46, Stn. 47, 03°23' N, 145°04'W, 31 October 1969, 115 m. 2 speci- mens, ML 16 and 20 mm, TC-47, Stn. 45, 03°28' N, 144°59'W, 3-4 February 1970, 50 m. 1 speci- men, ML 39 mm, TC-48, Stn. 35, 07°18'N, 144° 47'W, 11-12 April 1970, 50 m. 1 female, ML 49 mm, TC-48, Stn. 50, 03°29'N, 144°58'W, 17-18 April 1970, 50 m. 1 specimen, ML 33 mm, TC- 48, Stn. 92, 00°08'N, 145°00'W, 28 April 1970, 50 m. Description: The mantle (MWI 36.0-.i7. .5-39.1) is cylindrical and tapers gradually toward the end of the blunt tail. Ventrally the anterior edge of the mantle is only slightly excavated and the lateral angles are pointed and low. The anterior dorsal lobe is rounded and also low. The fin lengths are more than half of the mantle length (FLI 65.2-f5S.O-70.4) and the com- bined width of both fins is less than the mantle length (FWI 69.6-75.9-76.1). The anterior mar- gins project into rounded lobes near their ante- rior attachments. The lateral angle (about 70°) is rounded and the posterior margin is slightly convex. The funnel is large; its length equals its width. The funnel-mantle locking cartilage is simple; its anterior end is slightly narrower and more pointed than the rounder posterior end. The fun- nel valve is a wide semilunar flap; its anterior edge reaches the edge of the funnel opening. The head (HWI 28.0-30.2-33.8) is narrower than the mantle, almost square in cross section, slightly rounded on the top, and is deeply ex- cavated on its posteroventral surface to form a large funnel groove. The dorsal and ventral ocular "windows" are distinct. The eye opening has a deep sinus (Fig. 3G). Three nuchal folds lie on each side of the head; the closest fold to the funnel bears at its posterior end the tonguelike olfactory papilla. These nuchal folds are united to each other by a narrow posterior membrane, although this membrane does not reach the dorsal midline. The buccal membrane is purple and the eight supports are joined by connectives to the arms in the order DDVD. The membrane is pig- mented more heavily than the supports. The lappets are delicately pointed, and the inner sur- face of the buccal funnel is very rugose but lacks papillae. The arms are subequal and shorter than the mantle (ALI: I, 60.6-65.2-69.7; II, 57.1-61.8-69.6; III, 55.4-6(5.0-82.6; IV, 59.2-66. 7-72.0). They are nearly square at their bases and taper into fine points. Arms I and II have very low keels; arm I is keeled to about half its length and arm II to 710 BURGESS: FOUR NEW SPECIES OF SQUID ENOPLOTFA'THIS Figure 3.—Enoploteuthis octolineata. (A-E, G, I, and J from female paratype, ML (mantle length) 75 mm; other body parts are from specimens as listed.) A, Ventral aspect; B, Tentacular hook; C. Tentacular sucker; D, Dorsal arm sucker; E, Dorsal arm hook, oral and lateral aspects; F. Mandibles: upper (1), lower (2), male, ML 25 mm; G, Eye and surrounding area; H, Radular teeth, ML 25 mm; I, Tentacular club; J, Eye light organs. 711 FISHERY BULLETIN: VOL. 80. NO. 4 about one-third. The swimming keel of arm III is about as wide as the arm. The tentacular sheath is narrow, about half the width of arm IV near the base. The dorsal and ventral protective mem- branes are developed on all the arms and extend to the arm tips. The ventral membranes are wider on arm III, although they do not reach the top of the hooks. The protective membranes of arm IV are very narrow, except those on the hectocotylus of the male. The ventral protective membrane of right arm IV (hectocotylus) of the immature male paratype (ML 46 mm) is slightly enlarged into a narrow undulating membrane, about' 1 mm wide, op- posite the eighth and ninth pairs of hooks. The dorsal protective membrane is very narrow. The arm hooks (Fig. 3E) are biserial and are completely covered by sheaths. Arm IV is slightly longer than the other arms, and has the greatest number of hooks. The suckers on the distal part of the arms can be separated into two types. The distalmost suckers are markedly re- duced in size, are globular in shape with small apertures, and lack teeth. The proximal suckers have long stalks and wide openings. The inner rings of these suckers have eight to nine large pointed teeth distally, very irregular, smaller teeth proximally, and a wide shelf at the bottom half. The outer ring bears numerous pegs (Fig. 3D). The tentacles are weakly developed, about as long as the mantle (TLI 93.3-0&4-112.7) and very narrow (only about one-third of the width of arm III). The cross section is almost triangular. The club is also narrow (Fig. 31). The aboral keel ex- tends from opposite the second hook to the tip of the club. Protective membranes are absent, but a short hoodlike membrane is present at the blunt tip. The carpal cluster is composed of a series of three to six smooth-ringed suckers and three to five rounded pads which are biserially arranged in an elongate patch. One of the paratypes (ML 75 mm) has two additional suckers on the stalk located a short distance from the right carpal cluster (such suckers not present in other speci- mens); corresponding pads, if any, were not seen on the opposite tentacle due to damage. The manus has a total of 9 to 11 sheathed hooks and an occasional sucker in the distal part. These alternating dorsal and ventral hooks are only slightly separated medially. Hooks on the dorsal row are smaller. The hooks (Fig. 3B) resemble the arm hooks in structure, except for the rela- tively narrower bases of club hooks and their relatively smaller size. The few (16 or 17) distal suckers on the dactylus are also biserial. They have long stalks and wide openings; the inner rings have about 10 sharp teeth distally, a series of smaller denticulations proximally, and an inner shelf at the proximal bottom part(Fig. 3C). The outer ring bears pegs. There are two types of skin photophores: Very dark ones with whitish centers and white ones with very thin outer black rings (in preserva- tion). The smallest is about half the size of the largest, but intermediate sizes occur. Both types appear randomly interspersed. On the ventral side of the mantle there are eight distinct rows separated by spaces wider than the rows them- selves. A continuous midline space is present from the anterior of the mantle to the tail (Fig. 3A). Four parallel rows of varying widths lie on either side of this space. The first and second lateral rows extend from the excavated part of the mantle to the tail. The third row extends from opposite the lateral angle of the mantle to the tip of the mantle, occurring along the lateral margins of the tail as a single row of evenly spaced photophores. The photophores of these rows tend to disperse at the posterior end, par- ticularly the second row, and the rows become slightly intermingled, but each row remains rec- ognizable. The fourth or lateralmost row is com- posed of widely spaced light organs forming a single line that becomes somewhat irregular op- posite the region of the fins. Small photophores are dispersed on the dorsal side of the mantle, but there are none on the fins or on most of the tail except for the lateral row mentioned above and a few very small ones ventrally. A transverse row that has fewer and more widely separated photo- phores dorsally runs along the edge of the mantle. Four narrow rows of photophores separated by wide spaces are present on the ventral half of the funnel. There are two additional rows on the dorsal side, one on each side of the bridles. There are eight separate rows of photophores on the ventral half of the head, four rows on each side of a wide median space. The first row lateral to the midline space originates anterior to the bridle within the apex of the funnel groove and continues directly to the ventral aboral side of arm IV and ends just beyond the distalmost arm hook. The second lateral row begins at the pos- terior end of the funnel groove and runs along the edge of the groove, over the ventral part of the head, and proceeds anteriorly along the base of 712 BURGESS: FOUR NEW SPECIES OF SQUID ENOl'LOTKUTHIS the tentacular sheath to the tip of arm IV. The third row extends anteriorly from the base of the first nuchal fold but is interrupted by the window of the eye, and subsequently divides. One branch unites with the second row at a short dis- tance from the base of the ventral arm. The other branch continues laterally along the edge of the tentacular sheath to the tip of arm IV. The fourth row begins opposite the second nuchal fold and proceeds to the posterior margin of the eye open- ing and runs along the edge of the eyelid ventral- ly to the optic sinus (Fig. 3G). The dorsal half of the eyelid has no light organs. From the upper edge of the optic sinus the fourth row continues along the base of the swimming keel of arm III to almost opposite the last arm hook. An additional short arc-shaped row of very small white photo- phores, set far apart, lies between the third and fourth rows on the posteroventral eye region. This short row is inconspicuous and can easily escape detection. The light organs on the eyeball vary from 9 to 10. The large terminal photophores are sepa- rated by a space from a series of eight or seven adjacent round to oval smaller light organs (Fig. 3J) of varying dimensions. The radula has seven long, slender, slightly curved teeth in each transverse row. The rachid- ian tooth has pointed cusps, one on each side. The lateralmost teeth are longest (Fig. 3H). The mandibles are strong and heavily pig- mented. The rostrum of the upper mandible is very pointed and the edges are sharp (Fig. 3Fi). The lower mandible has three distinct ridges (Fig. 3F2). In a specimen ML 25 mm the wings of both halves are transparent. The gladius is featherlike and the rachis is thickened into a rounded ridge dorsally. The vanes are fragile and narrow. The cone is thin and narrow, but rounded posteriorly. The thickened edge of the vanes described by Roper (1966, fig. 14) in E. anapsis is only slightly indi- cated here. There are no spermatophores in the largest male paratype (ML 46 mm). The hectocotylus is not fully developed; the lappet is only 1 mm wide and there are no tubercles on the inner surface of the arms. Numerous sperm reservoirs are present in one of the females (ML 75 mm). These are about 6 mm long and are attached in two areas: on the inner wall of the mantle (opposite the midpart of each funnel retractor muscle) and in the concave inner wall of the retractor muscles themselves. The same female is gravid; the diameter of an egg taken from the ovary is slight- ly <1 mm. Young individuals: Immature specimens (ML 10-30 mm) have six to eight rows of light organs on the mantle. These rows first appear as a series of elongate patches of large photophores sepa- rated by spaces which later develop smaller photophores (Figs. 2Ca, b). At ML 10 mm, all the arms have hooks. The club has two rows of suckers ancf no hooks. Five of the suckers are set apart proximally and presumably become carpal suckers. At ML 15 mm there are three hooks on the club; by ML 20 mm the club has eight hooks. The tentacles of these immature individuals are shorter than the mantle (TLI 5O.O-0S4-86.7). The light organs of the eye do not develop simultaneously: some of the smaller individuals have only seven or eight (the two terminal photophores and five or six inner ones). Remarks: The most distinctive feature of this species is the eight well-defined rows of photo- phores, separated by wide spaces, on the mantle. In some respects this species resembles E. leptura in the shape of the fins and the structure of the clubs and tentacles. However, the latter species has only seven rows of photophores on the mantle, one of which arises from either of the most median pair of rows and does not reach the mantle. This feature is also found in juveniles. The arrangement of the photophores on the head also differs. The third lateral row is unbranched in E. leptura. Distribution: Central Pacific, equatorial wa- ters. Based on sampling for the present collec- tion, E. octolineata does not seem to occur in the Hawaiian area. Enoploteuthh jonesi n. sp. (Figs. 4, 2D, F; Table 3) Holotype: Male, ML 47 mm, TC-7, Stn. 12, off Milolii, Hawaii, 16 August 1964, 9-13 m, USNM 729717. Paratopes: 1 male, ML 35 mm, CHG-89, Stn. 24, 14°55.1'S, 164°02'W, 10 February 1966, 90- 130 m, USNM 729699. 1 female, ML 82 mm, TC-7, Stn. 12, off Milolii, Hawaii, 16 August 1964, 9-13 m, USNM 577608. 1 female, ML 40 mm. TC-32, Stn. 28, 20°58.6'N, 158°33.7'W, 25 July 1967, 92-122 m, USNM 729707. 713 FISHERY BULLETIN: VOL. 80, NO. 4 Other material: Stn. 14, 06°06 1966, 70-80 m. 89, Stn. 29, 04 1966, 120-135 m. 89, Stn. 31, 01 1966, 90-150 m. Stn. 37, 20°59 1967, 55-123 m. Stn. 39, 20°59 1967, 63-101 m. Stn. 46, 20°57 1967, 77-118 m. 1 male, ML 27 mm, CHG-89, .9'S, 157°44.2'W, 3 February 1 specimen, ML 22 mm, CHG- °05'S, 167°51'W, 14 February 1 specimen, ML 17 mm, CHG- °01'S, 168°06'W, 15 February 1 specimen, ML 11 mm, TC-32, .l'N, 158°12.7'W, 15 August 1 female, ML 30 mm, TC-32, .6'N, 158°29.3'W, 15 August 1 female, ML 35 mm, TC-32, .6'N, 158°28.7'W, 18 August Description: The mantle is long, cylindrical, and narrow (MWI 24.4-54.5-40.7). The width at the edge is only slightly greater than that at the middle and the sides taper into a blunt tail. The mantle is muscular except for the tail which is thin-walled and translucent, yet very firm. The ventral anterior excavation of the mantle is shallow and the lateral angles and middorsal projection are low and blunt. Each fin is triangular and their combined width is about three-fifths to four-fifths of the mantle length (FWI 65.9-74.0-80.0). The fins are shorter than their combined width (FLI 62.9- 67.5-70.0). The anterior margin is rounded and the posterior margin is slightly concave. The lateral angles are sharp, about 75°. The funnel is triangular with a broad base. The funnel-mantle locking cartilage is simple and typical of the genus. The groove is shallow and it spreads out toward the more rounded posterior end of the cartilage. The funnel organ is large; the dorsal pad has a papilla and well- developed ridges; the ventral pads are oval with pointed anterior ends. The semilunar funnel valve is wide and its anteriormost edge does not reach the edge of the funnel opening. The head is nearly square in cross section, as long as it is wide, and nearly as broad as the mantle (HWI 25.6-50.9-37.5). Both dorsal and ventral ocular "windows" are distinct. The eye opening is a wide oval (triangular when con- stricted) and has a moderately deep sinus. The three crescentic nuchal folds are prominent. The olfactory papilla is tonguelike and arises from the nuchal fold nearest to the funnel. The funnel groove is moderately deep and the sides of this excavation are steep. The buccal funnel has eight stout supports connected to the arms in the order DDVD. The lappets are pointed; the inner wall of the buccal membrane is very rugose and carries papillae. Both membrane and supports are covered with small fine chromatophores, but the membrane appears darker. The arms are of moderate length ( ALI: I, 40.0- 45.4-50.0; II, 43.9-45.5-51.9; III, 47.6-5i. 5-59.2; Table 3.— Measurements (in millimeters) and counts of Enoploteuthis jonesi. TC = RV Townsend Cromwell: CHG RV Charles H. Gilbert; + = lost suckers. Cruise: TC-7 TC-7 TC-32 CHG-89 TC-32 CHG-89 CHG-89 CHG-89 Station: 12 12 (Holotype) 28 24 39 14 29 31 Sex: Female Male Female Male Female Male ? ? Mantle length 82 47 40 35 30 27 22 17 Mantle width 20 14 15 13 11 11 10 9 Head width 21 13 15 11 9 9 8 65 Fin length 56 32 28 23 21 17 14 105 Fin width 54 34 32 25 24 20 18 14 Arm length Right 1 35 23 16 15 15 13 '9 8 Right II 36 24 19 17 15 14 115 9 Right III 39 23 20 17 16 16 12 10 Right IV 46 28 22 20 15 15 13 11 Left IV 46 28 21 19 15 15 — — Arm hooks/suckers Right 1 26/41 20/48 21/— 19/30 17/22 14/18 '15/16 11/19 Right II 27/32 23/38 22/— 16/20 18/18 18/18 17/18 14/14 Right III 28/36 21/28 22/— 22/22 17/15 20/18 18/16 14/21 Right IV 31/15 21/10 23/— 25/9 21/15 21/21 19/— 22/20 Left IV 31/22 28/38 25/— 26/16 21/18 21/12 + 19/— — Tentacles right/left Tentacle length — /86 61/— 65/68 43/— 51/46 48/51 42/42 23/27 Club length — /20 15/— 15/15 12/- 11/11 11/11 9/9 7/7 Club hooks Right (dorsal/ventral)- left (dorsal/ventral) — 7/7 7/7 — 6/7-6/7 7/6 — 7/7-6/7 — 7/6 7/7 — 6/6-5/7 Club suckers right/left Distal suckers — /68 64/— 72/52 + 70 64/72 — /64 72/- 68/64 Carpal suckers — /4 4/— 3/4 4/- 3/4 — /4 3/— 4/4 'Length or count of left arm. 714 BURGESS: FOUR NEW SPECIES OF SQUID ENOPLOTEUTHJS Figure i.—Enoplotevthisjonesi (A-F, I, and J from male holotype. ML(mantle length) 47 m; other body parts are from specimens as listed.) A. Ventral aspect; B, Dorsal arm hook, oral and lateral aspects; C, Dorsal arm sucker; D, Tentacular hook; E, Tentacular sucker; F, Hectocotylus; G, Mandibles: upper (1), lower (2), ML 27 mm; H. Radularteeth, ML27mm; I.Eyelight organs; J, Tentacular club. 715 FISHERY BULLETIN: VOL. 80, NO. 4 IV, 50.0-55.0-59.6). Arm IV is longest in both sexes. The arms are nearly square in cross section and they taper distally into fine delicate tips. The keels of arms I and II are confined mainly to the distal halves of the arms. The swimming keel of arm III is as wide as the arm at its midpoint. The lateral membrane (or tentacu- lar sheath) of arm IV is moderately wide and extends to the tip of the arm. Dorsal and ventral protective membranes are present in all the arms. The ventral membrane is more developed than the dorsal, particularly on arm III. In the males the right arm IV is hectocotylized. The ventral protective membrane on this arm forms a very wide lappet that extends from about the middle half, opposite the sixth pair of hooks, to about four-fifths of the arm length. Distally the membrane is much narrower and tapers to the arm tip (Fig. 4F). The dorsal protective membrane is slightly modified: a small tongue- like flap is developed opposite the distal end of the larger medial lappet. In addition, the males have numerous conical tubercles at the bases of the oral surface of all the arms and between the bases of all the hooks. The biserial and regularly arranged hooks are completely sheathed by membranes (Fig. 4B). The distal arm suckers have long stalks. Each inner ring has eight teeth on its distal half and none on the smooth proximal half (Fig. 4C). The outer rings bear pegs all around. The suckers are progressively smaller distally; the distal suckers assume a globular shape, have small apertures, no teeth, and no outer rings. The tentacles are longer than the mantle (TLI 104. 9- .7 53.3-188.9) and are about twice the length of the longest arm. The stalk is oblong in cross section near the base, very muscular, and almost as thick as arm III. The proximal partof the club is as narrow as the stalk or only slightly ex- panded. The club becomes unusually narrow in the distal one-third (Fig. 4J). The tip is blunt. The aboral keel is about one-half of the club length. A semilunar membrane is present on the ventral or oral side; it extends between the carpal area and the fourth pair of hooks. Protec- tive membranes are developed on the ventral side but are rudimentary dorsally. Protective membranes are absent on the dactylus. The carpal cluster consists of three or four smooth- ringed suckers and several rounded pads in a compact round cluster together with some ir- regular grooves and ridges. There are 13 or 14 robust hooks in two rows on the club. The ventral row includes a series of greatly enlarged hooks. The hooks (Fig. 4D) are enclosed by membranes but the tips are exposed. These hooks have very broad bases and are set in rounded shallow ex- cavations. Marginal suckers are absent. Twelve to 18 transverse rows of 4 small suckers per row occupy the narrow dactylus. About 12 of these suckers at the tip are slightly larger than the im- mediately preceding transverse row, thus forming a cluster at the tip of the club. All the club suckers have smooth inner rings (Fig. 4E). The pegs on the outer ring are moderately long and may hide the smooth edge of the inner ring from view. The integumentary photophores occur in different sizes ranging from about 0.2 to 0.4 mm. A photophore may appear dark or very pale, depending on the extent of pigmentation. Many of the larger photophores are heavily pigmented, except for a small central area. Most of the smaller photophores are pale because pigmen- tation is confined to the periphery in the form of a very thin dark ring. Intermediate conditions be- tween these extremes occur. At first glance the photophores on the mantle appear scattered at random, but on closer examination one can recognize four multiserial, ill-defined rows: two rows on each side of a very narrow midline space that extends from the anterior opening of the mantle to the tail and bounded laterally by a broad zone of photophores (Fig. 4A). Each row consists of large and small photophores set near each other; smaller and whiter ones occupy the central part of the row, while the larger and more conspicuously darker ones are located mostly on the outer area of the row. These rows become more difficult to distinguish posteriorly. A single row of evenly spaced photophores extends along the lateral margins of the tail. Numerous photophores occupy the ventrolater- al surface and some single photophores, gener- ally small ones, are scattered on the dorsal sur- face of the mantle, except near the midline. The edge of the mantle is lined by a single row of photophores; the photophores are spaced pro- gressively farther apart toward the dorsal mid- line. The funnel has six groups of photophores: Two rows separated by a midline space on the ventral side; a short row on each lateral side; and two dorsal rows, one on each side of the bridle. A small triangular cluster of photophores is situated in the apex of the funnel groove. A space in the ventral midline of the head is broken by a 716 BURGESS: FOUR NKW SPECIES OF SQUID l-.Wori.OTh'lTIIIS short row of two or three photophores that bi- furcates at the fork of the ventral arms; each branch continues along the ventral aboral side of arm IV to almost the tip. A row of closely set photophores runs along the edge of the funnel groove and divides near the apex of the groove into two branches, each with photophores in single file. The branches reunite near the base of arm IV. The row continues distally along the base of the tentacular sheath to the tip of the arm. The third lateral row on the head begins anterior to the first nuchal fold, has a gap at the window of the eye, and then continues and splits into two branches: A medial branch that continues ante- riorly and ends near the base of arm IV at the midline of the tentacular sheath and a lateral branch that extends along the edge of the tentac- ular sheath and terminates about the level of the last hook on arm IV. The lateralmost row on the head also starts at the first nuchal fold, continues along the nuchal crest, and turns toward the posterior eyelid where it runs along the ventral edge to the optic sinus. The row begins again on the dorsal edge of the optic sinus, continues along the base of the swimming keel of arm III, and stops at about three-fifths of the arm length. The dorsal eyelid lacks photophores. There are nine irregularly spaced photophores on the ventral part of the eyeball (Fig. 41). The posteriormost light organ is larger than the anteriormost which in turn is larger than the re- maining seven light organs. The latter are slightly different from each other in size and shape. The teeth of the radula are long (lateralmost teeth are longest), blunt, and slightly curved (Fig. 4H). Of the seven teeth only the rachidian tooth has small lateral cusps. The upper mandible of a small specimen (ML 30 mm) has distinct growth lines on the wings (Fig. 4Gi). The riblike ridges on the gular plate of the lower mandible are well developed (Fig. 4G2). The gladius is feather-shaped. The rachis is blunt anteriorly and forms a strong ridge dorsally through its length. The vanes are narrow, widest at about a third of the length of the gladius. The posterior end is curved inward ending in the cone. The largest female (ML 82 mm) is gravid; the ovaries are distended and extend to the posterior part of the mantle cavity. The eggs are opaque and about 1 mm in diameter. None of the males have spermatophores. Young individuals: Immature individuals (ML 11-22 mm) have relatively wider mantles (MWI 45.5-57.0-72.1) than adults. At ML 11 mm the arms have the following armature: 1 to 3 suckers proximally, 7 to 12 hooks, and 15 to 20 suckers distally. The tentacles are distinctly longer than the mantle (TLI 172.7). The club has three hooks along with nine biserial suckers on the manus. Two of the suckers are slightly set apart (future carpal suckers). Four rows of minute suckers are located on the dactylus. At ML 17 mm the arms have no proximal suckers, 12 to 18 hooks, and 19 to 21 distal suckers. The club resembles that of the adult, except that two marginal suckers are present on the dorsal distal side of the manus and although there are already four carpal suckers, the carpus is still not com- pletely developed. The photophores on the mantle are not distinctly arranged into rows, except for two medialmost rows which are sep- arated by a narrow space (Fig. 2D). The rows on the head are each composed of photophores in single file (Fig. 2F). The number and position of the rows agree with those of the adult. Remarks: Adults of this species resemble superficially E. chuni Ishikawa 1914 from Japan, but they are easily distinguished by the photophore pattern of the head and arms. Enoploteuthis chuni has seven rows of photo- phores on the head (including the rows passing along the ventral eyelids) (pi. XX, fig. 1, Sasaki 1920), whereas jonesi has six rows. There is a distinct midventral multiserial row on the head of chuni, whereas the ventral midline of jonesi is a clear space, except for two or three single photophores near the fork of the ventral arms anteriorly. Some rows of photophores on the head divide and reunite in jonesi, a condition absent in chuni. The row of photophores at the base of the swimming keel of arm III reaches the tip of the arm in chuni, but in jonesi, the same row ends slightly beyond one-half to three-fifths of the arm length. These observations were confirmed by T. Okutani of the Tokai Regional Research Laboratory (presently with the National Science Museum, Tokyo) who kindly examined speci- mens of E. chuni from Suruga Bay and com- pared them with illustrations of E. jonesi sent to him. In addition, there are more distal club suckers in chuni (90) than in jonesi (64-72) and these suckers are toothed in chuni and smooth in jonesi. The counts and measurement of E. jonesi 111 FISHERY BULLETIN: VOL. 80. NO. 4 overlap those of E. anapsis Roper, 1964 from the tropical Atlantic and Caribbean. These species exhibit the following differences: 1) The midline space on the mantle in jonesi continues uninter- rupted to the tail, but this space in anapsis has some scattered photophores near the tail; 2) the row that traverses the window on the ventral side of the head is bifurcate in jonesi whereas it is single in anapsis. The tentacles and clubs of anapsis are relatively longer than those of jonesi. The distal club suckers are more numerous in jonesi (64-72) than in anapsis (40-50). This species is named after Everet C. Jones, former fishery biologist at the Honolulu Lab- oratory. It was under the supervision of E. C. Jones that the specimens collected during some of the cruises reached me in good condition. Distribution: Central Pacific, Hawaiian wa- ters, and equatorial region. Enoploteuthis higginisi n. sp. (Figs. 5, 2E, G; Table 4) Enoploteuthis species B, Young 1978: figure 9B. Holotype: Male, ML 37 mm, Teritu, Stn. 6 off Waianae, Oahu, September 1969, 110 m, USNM 729710. Paratypes: 1 male, ML 35 mm, CHG-89, Stn. 11, 06°04.9'S, 157°36.9'W, 2 February 1966, 140-200 m, USNM 729714. 1 female, ML 53 mm, TC-32, Stn. 22, 21°02'N, 158°29.7'W, 21 July 1967, 67-117 m, USNM 729723. 1 female, ML 45 mm, TC-32, Stn. 56, 21°22.4'N, 158° 14.6'W, 23 August 1967, 97-179 m, USNM 577609. Other material: 1 specimen, ML 27 mm, HMS- 47, Stn. 51, 00°44'S, 149°46'W, 2 November 1958, 576 m. 1 specimen, ML 12 mm, CHG-51, Stn. 164, 16°44'N, 169°16'W, 14 February 1961, 100 m. 1 specimen, ML 12 mm, CHG-51, Stn. 172, 19°21'N, 169°20'W, 15 February 1961, 0-100 m. 1 specimen, ML 16 mm, CHG- 89, Stn. 29, 04°05'S, 167°51'W, 14 February 1966, 120-135 m. 1 specimen, ML 11 mm, CHG- 89, Stn. 30, 02°59'S, 167°51'W, 15 February 1966, 100-125 m. 1 male, ML 46 mm, TC-32, Stn. 23, 21°00.2'N, 158°30.1'W, 22 July 1967, 17-25 m. 1 female, ML 60+ mm, TC-32, Stn. 28, 20°58.6'N, 158°33.7'W, 25 July 1967, 8-60 m. 1 female, ML 30 mm, 2 specimens, ML 12 and 19 mm, TC-32, Stn. 33, 20°58.8'N, 158° 28.4'W, 13 August 1967, 83-99 m. 1 female, ML 32 mm, 1 specimen, ML 22 mm, TC-32, Stn. 37, 20°59.1'N, 158°12.7'W, 15 August 1967, 55- 123 m. 1 male, ML 30 mm, 2 females, 37 and 40 mm, TC-32, Stn. 38, 20°58.7'N, 158°27.9'W, 15 Table 4.— Measurements (in millimeters) and counts of Enoploteuthishigginsi. TC =RV Townsend Cromwell; CHG : RV Charles H. Gilbert; + = missing mantle tip and lost suckers. Cruise: TC-32 TC-32 TC-32 TC-32 Teritu CHG-89 TC-32 CHG-51 Station: 28 22 23 56 6 (Holotype) 11 56 172 Sex: Female Female Male Female Male Male Female ? Mantle length 60 + 53 46 45 37 35 29 22 Mantle width 24 20 18 14 14 13 13 11 Head width 20 17 13 14 15 12 11 10 Fin length — 39 30 34 27 23 20 15 Fin width 58 42 38 34 30 30 24 21 Arm length Right 1 42 32 25 26 20 20 '13 15 Right II 24 36 27 25 20 21 '15 12 Right III 48 33 28 28 21 20 '15 12 Right IV 51 37 28 31 23 23 19 11 Left IV 53 34 32 33 23 — 17 13 Arm hooks/suckers Right 1 26/22 25/34 19/- 25/22 20/16 24/16 16/19 16/20 Right II 29/27 26/34 22/— 25/20 22/16 23/20 17/20 18/20 Right III 32/28 28/33 22/- 25/22 22/20 22/20 18/23 16/21 Right IV 28/28 26/21 25/— 29/20 22/2 + 26/14 + 22/23 18/6 Left IV 28/26 27/20 27/— 29/22 26/16 — 20/23 20/7 Tentacles right/left Tentacle length — 108/117 110/— — /92 41/41 60/— — /48 34/27 Club length — 17/17 16/— -/16 11/11 11.5/— — /9 — Club hooks Right (dorsal/ventral)- left (dorsal/ventral) — 5/6-5/6 4/6 — — 6/6 5/6-5/6 5/6 — — 4/6 — Club suckers right/left Distal suckers — 68/68 — -/60 60/60 72/— — /64 — Carpal suckers — 3/3 3/— — /3 3/2 3/— -/3 — 'Length or count of left arm 718 BURGESS: FOUR NEW SPECIES OF SQUID ENOPLOTEITIUS August 1967, 8-25 m. 1 male, ML 46 mm, TC- 32, Stn. 41, 20°58.9'N, 158°29.1'W, 16 August 1967, 59-122 m. 1 female, ML 37 mm, TC-32, Stn. 44, 21°00.1'N, 158°29.1'W, 18 August 1967, 72-118 m. 1 female, ML 47 mm, TC-32, Stn. 45, 20°58.1'N, 158°28.7'W, 18 August 1967, 12-31 m. 2 specimens, ML 27 and 28 mm, TC-32, Stn. 46, 20°57.6'N, 158°28.7'W, 18 August 1967, 77-118 m. 1 female, ML 35 mm, TC-32, Stn. 48, 20°59.7'N, 158°27.7'W, 19 August 1967, 60-104 m. 1 female, ML 29 mm, TC-32, Stn. 56, 21°22.4'N, 158°14.6'W, 23 August 1967, 97-179 m. Description: The muscular mantle is slender (MWI 31.1-37.S-44.8) and conical; the translu- cent tail is slender and ends bluntly. The ventral anterior edge of the mantle is not deeply ex- cavated and the lateral angles are pointed, but low. The dorsal anterior lobe is low. The fins are triangular, wide (FWI 15.6-81.2- 85.7), and long (FLI 65.2-704-75.6). The anterior margin near its attachment is a rounded lobe, but more laterally it appears straight. The lateral angles (about 75°) are rounded at the tip. The slightly concave posterior margins join the mantle independently, but the union of both fins (close to the tip of the mantle) is indistinct. The funnel is triangular and wide at the base. The funnel valve is a wide semicircular flap. The funnel organ is large; an anterior papilla and thick lateral ridges are present. The funnel- mantle locking cartilage is simple with a shallow groove. The anterior part of the cartilage is slightly narrower than the posterior end. The head is as wide as the mantle (H WI 28.3- 34.0-40.5). The eye opening is a wide oval with a deep anterior sinus. The funnel groove is moderately deep and the lateral sides continue posteriorly as sharp ridges. The ventral ocular "windows" are translucent. The three nuchal folds are very prominent. The tongue-shaped olfactory organ is attached to the first fold closest to the funnel. The second and third folds are united to each other posteriorly and the third fold on each side continues as a much reduced fold toward the dorsal midline. The buccal membrane has a DDVD attach- ment to the arms. Numerous folds and broad tonguelike papillae occur on the inner surface of the membrane. The external surface is densely supplied with small purplish chromatophores so that it is darker than most parts of the body. The arms are slender but muscular, nearly square in cross section at the base and finely pointed at their tips. The arms are moderate in length (ALI: I, 44.8-5.4.3-60.4; II, 51.7-53.0-67.9; III, 51.7-53.5-62.3; IV, 58.6-65.5-73.3). Arm IV is longest in both sexes. The swimming keels are developed to about one-half of arm I distally, two- thirds of arm II distally, and complete in arm III where they are as wide as the arm at the mid- section. The lateral membrane (tentacular sheath) of arm IV is wide and reaches to the tip of the arm. Dorsal and ventral protective mem- branes are developed on all the arms of both sexes. They are widest on arm III and least developed on arm IV, except on the hectocotyl- ized arm of the male. The right ventral arm of the male is hectocotyl- ized. The protective membranes of this arm are modified. At about the middle half of the arm opposite the sixth pair of hooks, the ventral pro- tective membrane becomes enlarged into a wide undulating flap that is reduced abruptly about three-fourths of the arm length and continues distally to the tip of the arm as a much narrower membrane. The dorsal protective membrane, on the contrary, is only slightly modified. A short semilunar flap is present opposite the distal end of the larger ventral flap (Fig. 5F). Numerous conical papillae are scattered on the oral surface of the arms of males between the bases of the hooks and on the bases of the arms. The arms have biserial hooks proximally and biserial suckers distally. The hooks (Fig. 5E) are strongly attached and completely enclosed by sheaths. About half of the suckers at the tips of the arms have long stalks and wide openings. The distal half of the inner rim of the sucker has seven to eight teeth; the two middle teeth are narrower than the lateral teeth; a shelf is visible on the proximal half (Fig. 5B). The outer ring bears numerous pegs. The remaining suckers gradually become smaller distally, assuming a globular shape with smaller openings that lack teeth and outer rings. The robust tentacles are much longer than the mantle (TLI 1 1 0. 8- i £0.3-239.1). The stalk near the base is almost square in cross section and as stout as arm III. The carpus and manus of the club are wide but the dactylus is quite narrow (Fig. 5G). The carpal cluster is compact and it includes three smooth-ringed suckers (very rarely two suckers) and several rounded pads and some elongate ridges and grooves; these are arranged in an oval cluster. Ten to 12 very robust, sheathed hooks are present in two rows 719 FISHERY BULLETIN: VOL. 80, NO. 4 \ -- — „ : t "\ / i i r Figure 5.—Enoploteuthis higginsi. (A-E, G, and I from female paratype, ML (mantle length) 45 mm; other body parts are from specimens as listed.) A, Ventral aspect; B, Dorsal arm sucker; C, Tentacular sucker; D, Tentacular hook, oral and lateral aspects; E, Dorsal arm hook, oral and lateral aspects; F, Hectocotylus, male holotype, ML 37 mm; G, Tentacular club; H, Mandibles: upper (1), lower (2), female, ML 37 mm; I, Eye light organs; J, Radular teeth, female, ML 37 mm; K, Section of spermatophore, male, ML 46 mm. 720 BURGESS: FOUR NEW SPECIES OF SQUID KNOPLOTKUTHIS on the manus. The ventral row includes a few large curved hooks, the largest hook is about one- fifth larger than the largest arm hook. The hooks have broad bases (Fig. 5D) and fit into shallow depressions on the club. The distal club suckers are arranged in four longitudinal rows (between 15 and 18 suckers in each row). The inner rings of these suckers are smooth but are surrounded by an outer ring with broad pegs that can be mis- taken for teeth of the inner ring (Fig. 5C). A few suckers in the distal part of the dactylus are slightly enlarged and form a cluster there at the blunt end of the club. The dorsal or aboral keel is well developed and extends from opposite the third dorsal hook to the blunt end. A smaller semilunar membrane lies on the oral or ventral side of the club. It extends from opposite the distal half of the carpal cluster to opposite the second or third ventral hook. Protective mem- branes are poorly developed but recognizable. The integumentary photophores range in size from about 0.2 mm to about 0.4 mm with varying degrees of pigmentation. Some are very dark with small pearl gray centers, others are lighter with varying widths of peripheral pigmentation. Those with very thin dark rings appear palest or almost white. The photophores on the ventral surface of the mantle appear to be distributed at random (Fig. 5A). They are concentrated on the ventral surface except at the tail and gradually become widely scattered toward the dorsal sur- face. A single row extends along each lateral margin of the tail. The free edge of the mantle opening is lined by a transverse row where the photophores are farther separated dorsally. There are no photophores on the fins, or on most of the ventral area of the tail. Two rows of photophores separated by a median space are present on the ventral surface of the funnel. A shorter row or patch occurs on each of the lateral margins and a wider strip is found on each of the dorsolateral surfaces of the funnel. The distribution of the photophores on the head is rather intricate. A small cluster lies in the apical region of the funnel groove. The ventral midline of the head is not totally clear of light organs, as a few isolated ones may be present. A very short row of three to four photophores in single file on the ventral midline (near the bases of arm IV) splits into two at the fork of the arms; each branch then continues along the ventral aboral edge of arm IV, ending a short distance from the distal tip of the arm. A row of photophores begins near the first nuchal fold, follows the curve of the funnel groove, and at a point near the apex of the funnel groove it splits into a wider medial branch and a narrower lateral branch. These branches reunite near the base of arm IV and the combined row proceeds anteriorly along the base of the tentacular sheath to the tip of arm IV. The next lateral row begins anterior to the first nuchal fold, is interrupted by a gap at the window of the eye, continues for a short distance, and divides into two short branches; each branch then extends to the edge of the tentacular sheath independently. A row of single photophores runs along the edge of the tentacular sheath and stops a short distance from the tip of arm IV. The lateralmost row on the head extends from the first nuchal fold along the nuchal crest, then anteriorly to and along the ventral margin of the eyelid, and ends at the ventral edge of the optic sinus. The row begins again on the dorsal edge of the optic sinus, con- tinues along the base of the swimming keel of arm III, and terminates at about one-half the length of the arm. Two or three isolated small photophores occur in the area surrounding the ventral part of the eye opening; one photophore is usually located directly lateral to the window. There are nine light organs on the ventral part of the eyeball. The terminal organs are much larger and slightly separated from seven smaller, closely set, light organs (Fig. 51). The radular teeth (seven teeth in a series) are long and slender. The outermost lateral teeth are longest while the innermost lateral teeth are shortest. The rachidian tooth has cusps. The three median teeth are almost straight while the two outermost lateral teeth are slightly curved (Fig. 5J). The upper mandible (Fig. 5Hi) has a pointed rostrum with very sharp edges and the lower mandible (Fig. 5H2) has three well-developed ribs on the gular plate. The gladius is feather shaped and the midrib is low and rounded. The cone is narrow and rounded at the extreme end. The vanes start to broaden at about one-third of the length and reach their greatest width at about half of the length. The lateral edges of the gladius appear slightly thickened when held against a strong light. Spermatophores from a male (ML 46 mm) are about 14 mm in total length. The cement body is slightly greater than half the length of the sperm reservoir and has two collars at the oral end (Fig. 721 FISHERY BULLETIN: VOL. 80. NO. 4 5K), the anterior much smaller than the poste- rior. The aboral part of the spiral filament is supplied with numerous intricate diamond- shaped depressions separated by thickened ridges. Two to four turns are present behind the cap. A spermatophore examined has the follow- ing measurements: Spermatophore segment Length (mm) Entire spermatophore Sperm reservoir Cement body Spiral filament 13.8 5 2.8 6.0 Some eggs taken from the ovary of the female paratype (ML 53 mm) measured about 1.2 mm each. Young individuals: Small individuals (ML 11- 16 mm) have relatively wider mantles (MWI 56.3-5P.4-63.6) and the photophores on the mantle are scattered (Fig. 2E) as they are in the adult. At ML 15 mm all the rows of photophores on the head correspond to those of the adult with respect to number and position (Fig. 2G). The most medial row consists of several photophores set close to each other as in the adult. All other rows are composed of a single line of photo- phores. At ML 12 mm the tentacles are robust and longer than the mantle (TLI 108.3), more than the length of the arm. The club has two carpal suckers, four hooks on the ventral side of the manus among a group of 16 suckers (pre- sumably future hooks), some marginal suckers, and numerous quadriserially arranged suckers on the dactylus. The aboral keel is also developed. The arms bear between 12 and 14 hooks and a sucker at the base of one of the dorsal arms. Thirteen or 14 suckers occupy the distal part of arms I, II, and III, and 24 suckers on arm IV. At ML 16 mm there are still 4 club hooks and 2 carpal suckers, but the arm hooks have increased (18 on arm IV) as have the distal suckers. At ML 19 mm, 16 to 19 hooks are observed on the arms and 6 to 7 on the club along with an increased number of distal arm suckers and club suckers. At this stage three carpal suckers are present as in the adult. Remarks: The species can be easily confused with E. jonesi; counts and measurements overlap and both species can be found in the same trawl hauls. However, a close examination of the material reveals a series of minor but consistent characteristics that separate one from the other even at a small size (ML 10 mm). At comparable sizes the tentacles and clubs are similar in struc- ture, but jonesi has 13 or 14 club hooks and usually 4 carpal suckers while higginsih&s 11 or 12 club hooks and usually 3 carpal suckers. Both have long tentacles, but they are relatively longer in higginsi. Discrete longitudinal arrangement of photo- phores on the mantle is wanting in higginsi while a median space and identifiable rows are found in jonesi. The arrangement of photophores on the head also shows some differences: 1) The row closest to the midline is multiserial in higginsi whereas it is simple in jonesi; 2) isolated photo- phores occur in the midline area of the head and in the space near the eye in higginsi but are absent in jonesi; 3) the row directly anterior to the window is bifurcate in both species but in higginsi both branches extend to the tentacular sheath whereas in jonesi only the lateral branch does; and 4) the row of photophores on arm III is incomplete in both species, but in higginsi the row rarely extends more than 50% of the arm length (45-52% of arm length, 11 specimens) and in jonesi the row is more than half the arm length (56-85% of arm length, 18 specimens). Enoploteuthis higginsi, like E. jonesi, shares many characteristics with E. chuni and E. anapsis (see remarks section of E. jonesi), but the scattered distribution of photophores on the mantle is distinctive of higginsi. Rows do not occur on the mantle in any stage of development in higginsi. At ML 10 mm, or smaller, the rows are already evident in anapsis (Roper 1966, figs. 22, 23). Specimens captured in Hawaiian waters which were labeled Enoploteuthis sp. B and reported in Young (1978) also belong to this species (R. E. Young3). This enoploteuthid squid is named after Bruce E. Higgins, former fishery biologist at the Honolulu Laboratory under whose leadership most of the material was collected during cruise 32 of the RV Townsend Cromwell in Hawaiian waters. Distribution: Central Pacific, Hawaiian, and equatorial regions. 3R. E. Young, Department of Oceanography, University of Hawaii, Honolulu, HI 96822, pers. commun. 3 March 1980. 722 BURGESS: FOUR NKW SPKCIFS OF SQUID ICXOl'LOTEUTHIS Enoploteutbis reticulata Rancurel 1970 (Figs. 6, IB; Table 5) Enoploteuthis reticulata Rancurel 1970: figures 31-37 (incorrect spelling reticula in figures 31- 33). Enoploteuthis sp. (No. 1), Okutani, 1974: figures 12a. b. e. Enoploteuthis sp. A. Young 1978: figures 9B, 10A. Material examined: 1 male, ML 130 mm (regurgitated by a porpoise) CHG-7, 20°42.7'N, 157°50'W, 3 February 1953. USNM 729718. 1 male, ML 117 mm. HMS-30, Stn. 3, 28°38.5'N. 161°20.3'W, 16 July 1955, 100 m. 1 specimen, ML 26 mm, TC-7, Stn. 5. off Waianae, Oahu, 12 August 1964, 60-100 m. 1 female, ML 35 mm, TC-32, Stn. 3. 21°22.5'N, 158°13.5'W, 13 July 1967, 15-25 m. 1 specimen, ML 13 mm, TC-32, Stn. 4, 21°20.9'N, 158°13.1'W, 13 July 1967, 75- 107 m. 1 specimen, ML 18 mm, TC-32, Stn. 6, 21°21.7'N, 158°13.3'W, 14 July 1967, 83-124 m. 1 female, ML 45 mm, TC-32, Stn. 9, 21°21.5'N, 158°13.5'W, 15 July 1967, 17-25 M. 2 females, ML 39 and 62 mm, TC-32, Stn. 15, 21°20.3'N, 158°12.2'W. 17 July 1967. 16-30 m, USNM 729691. 1 specimen, ML 30 mm, TC-32, Stn. 28. 20°58.6'N, 158°33.7'W, 25 July 1967, 92-122 m. 1 male, ML 46 mm, TC-32, Stn. 29, 20°59.5'N, 158°31.5'W, 26 July 1967, 8-60 m. 1 male, ML 71 mm, TC-.'^, Stn. 31, 20°59.6'N, 158°29.3'W, 13 August 1967. 80-121 m, USNM 577606. 1 specimen, ML 32 mm, TC- 32, Stn. 46, 20°57.6'N, 158°28.7'W, 18 August 1967, 77-1 18 m. 1 male, ML 50 mm, TC-32, Stn. 48, 20°59.7'N, 158°27.7'W, 19 August 1967, 60- 104 m. Description: The mantle is almost circular in cross section and is very muscular; the tail is thin and translucent. The mantle is widest at the opening (MWI 27 A-32.3-W .1) and the sides con- verge gradually toward the saccate tail. The anterior ventral margin is very slightly exca- vated and the lateral angles are pointed, but low. The dorsal evagination of the mantle is a rounded and low lobe. The fins are about three-fifths of the mantle length (FLI 62.4-^.7-67.7) and are moderately wide (FWI 59.8-^.^-82.6). They arise at about the anterior third of the mantle length. The anterior margin projects as a rounded lobe near its attachment and then extends laterally, and together with the almost straight posterior margin, a rounded angle (about 72°) is formed. The posterior margins are each joined to the mantle separately leaving a small gap between them. The funnel is triangular and almost as wide as Table 5.— Measurements (in millimeters) and counts of Enoploteuthis reticulata. CHG = RV Charles H. Gilbert; HMS = RV Hugh M. Smith; TC = RV Townst nd Cromwell; + - missing arm tips and lost suckers. Cruise: CHG-7 HMS-30 TC-32 TC-32 TC-32 TC-32 TC-7 TC-32 Station: 3 31 15 29 28 5 6 Sex: Male Male Male Female Male 9 ? ? Mantle length 130 117 71 62 46 30 26 18 Mantle width 38 32 22 23 17 12 11 10 Head width 31 30 19 17 13 12 8 8 Fin length 88 73 43 42 30 16 15 9 Fin width 85 70 48 44 38 20 18 14 Arm length Right 1 65 58 '45 35 28 17 15 12 Right II 65 65 '46 43 + 30 19 15 13 Right III 70 '60 '47 34 + 30 18 16 12 Right IV 69 65 45 38 33 18 17 13 Left IV 72 66 48 40 31 19 17 13 Arm hooks/suckers Right 1 26/— 24/8 + '21/24 21/20 20/15 20/11 21/14 21/14 Right II 24/— 24/19 '23/24 26/16 20/18 18/10 21/12 20/15 Right III 24/— 24/22- '24/15 24/14 22/13 20/11 22/11 21/14 Right IV 32/— 34/17 33/20 28/11 29/9 27/12 30/9 30/10 Left IV 31/— 33/19 33/35 31/12 26/13 27/12 28/10 30/9 Tentacles right/left Tentacle length 120/126 93/115 76/68 80/60 47/49 22/28 20/20 — /16 Club length 20/20 21/21 16/16 — /14 14/14 8/8 6/6 5 — /5 Club hooks Right (dorsal/ventral)- left (dorsal/ventral) 5/5-4/5 5/6-5/6 6/6-7/5 5/5-5/5 5/6-4/5 5/5-5/5 4/5-5/5 — 3/5 Club suckers right/left Distal suckers — 10/8 10/8 — 11/8 8/— 10/9 — /8+ Carpal suckers 5/4 4/6 6/6 5/5 5/5 4/6 5/7 -/6 'Length or count of left arm. 723 FISHERY BULLETIN: VOL. 80, NO. 4 it is long. The funnel-mantle locking cartilage is simple. The anterior end is slightly pointed and narrower than the posterior end. The groove is shallow and wider posteriorly. The funnel organ has a papilla on the anterior end of the dorsal component (inverted V-shape), is small, and has wide ridges on the lateral limbs. The ventral components are oval but have pointed anterior ends. The funnel valve is broad and its rounded anterior edge reaches the level of the funnel opening. The head is almost square in cross section, slightly rounded at the top, and narrower than the mantle (HWI 23.8-26.-4-28.3). The ventral excavation is moderately deep and well marked by sharp lateral edges. The three nuchal folds on each side of the head are very prominent. The first nuchal fold bears a tonguelike olfactory papilla at its posterior end. The second and third folds are crescentic folds with broad anterior ends and are united to each other posteriorly by a narrow membrane. From the posterior end of the third fold a narrow membranous ridge extends toward the dorsal midline but does not quite reach it. In large specimens the nuchal crest connects the three folds to each other and to the midline, so that three oval areas are formed on each side of the head posteriorly. The eye opening is wide and has a deep sinus. Both dorsal and ventral ocular "windows" are easy to recognize, particularly in specimens that have been preserved longer. The buccal membrane has eight stout supports with connectives attached to the arms in the order DDVD. The lappets are pointed and the inner surface of the buccal membrane is rugose and lacks papillae. The membrane is darker than the supports; small chromatophores are present in both structures. The arms are moderate in length; the ventral arms, which are longest, are shorter than the mantle length (ALL I, 49.7-56.1-63.4; II, 50.0- 58.9-G5.2; III, 51.3-5SU-66.2; IV, 53.1-61.7-11.1). Weak keels extend along the distal third of arm I, along the distal half of arm II, and from the base to the tip of arm III. In the largest specimen the swimming keel of arm III is slightly wider than the arm width. The tentacular sheath along arm IV is narrow, about half of the arm width near the base, and reaches the tips of the arms. The protective membranes are developed on borders of all arms, but are more strongly developed on the ventral borders. This is particularly so on arm III, although the ventral membrane is never wider than the height of the hooks. The trabeculae and the membranes are very distinct even at the tips of the arms. The right ventral arm of the male is hectocotyl- ized (Fig. 6B). The ventral protective membrane on this arm is enlarged into an undulating lappet, which extends from near the 9th or 10th pair of hooks to the arm tip, although it becomes progressively reduced in width distally. The membrane is deeply notched at about two-thirds of its length so that two semilunar flaps of un- equal lengths are formed. The dorsal protective membrane is less developed than the ventral pro- tective membrane even in the area opposite the enlarged lappet. In addition, the males have numerous conical tubercles distributed on the oral surface, at the bases of all the arms, and on the areas between the bases of the hooks. The arm hooks are large (Fig. 6E), arranged in two alternate rows, and enclosed by sheaths. The ventral arms of both sexes bear the most hooks. None of the hooks are unusually enlarged or re- duced in either sex. The distal part of each arm has two rows of suckers. The proximal suckers in this region have long stalks and the inner rings of these suckers have seven or eight large blunt teeth (middle two teeth broadest) distally and smooth proximally (Fig. 6C). The outer ring has long pegs. The most distal pairs of suckers (with about three teeth) are much reduced in size, carried on short stalks, and have small openings. The tentacles are generally about the length of the mantle (TLI 79.5-iO(U-129.0). The stalk is slender, only about one-third of the width of arm III. The sides are compressed and the cross section is almost triangular. The club is narrow (Fig. 61). The carpus includes between four and seven smooth-ringed suckers and corresponding pads arranged in an elongated series which is limited on both sides by a narrow ridge. The manus includes a dorsal row of four to seven sheathed hooks and a ventral row of five or six slightly larger hooks. The hooks (Fig. 6F) have narrow bases. The largest hooks are not bigger than any of the largest arm hooks. Marginal suckers are absent and any sucker present along the rows of hooks in young specimens certainly represents an undeveloped hook. The dactylus has 8 to 11 suckers arranged in two rows. They have long stalks and wide openings. The sucker rings bear teeth; six or seven short teeth distally and six or seven very blunt teeth proximally (Fig. 6D). The outer ring has many short pegs. The tip of the club is blunt with a short over- 724 BURGESS: FOUR NEW SPECIES OF SQUID ENOPLOTEUTHIS Figure &.—Enoploteuth is reticulata Rancurel. (A, C-F, and J from female, ML (mantle length) 62 mm; other body parts are from specimens as listed.) A, Ventral aspect; B, Hectocotylus, male, ML 71 mm; C, Dorsal arm sucker; D. Tentacular sucker; E, Dorsal arm hook, oral and lateral aspects; F, Tentacular hook, oral and lateral aspects; G, Mandibles: upper (D. lower (2), male, ML 50 mm; H, Radular teeth, male, ML 50 mm; I, Tentacular club, male, ML 117 mm; J, Eye light organs; K. Section of spermatophore, male, ML 117 mm. 725 FISHERY BULLETIN: VOL. 80. NO. 4 lapping hood which conceals a few of the suckers at the tip. The aboral keel is also narrow and extends from opposite the second hook to the lateral side of the hooded tip. Protective mem- branes are not developed on either side. The photophores range in size from 0.2 to 0.4 mm. The dark or light appearance of each photophore is caused by the extent of pigmenta- tion. The majority of the small ones are white owing to pigmentation confined only to the periphery of the photophores. The photophore pattern of the mantle is distinctive. It can be described briefly as the combined effect of about six ill-defined longitudinal rows and four oblique rows to produce a netlike or reticulated pattern (Fig. 6A). The photophores are scattered irregu- larly in the posterior region of the mantle, except on the tail where a single row extends on each side to the tip of the tail. The ventral area of the saccate tail lacks photophores. A single trans- verse row in which the photophores are farther apart dorsally lies along the anterior edge of the mantle. A few small photophores are distributed on the dorsal surface of the mantle. The fins lack photophores. Two longitudinal rows, separated by a midline space, occur on the ventral surface of the funnel. A short row (connected to the ventral row pos- teriorly) is located on each side of the funnel and a long row of photophores is found on the dorso- lateral side, close to each bridle. The photophore pattern on the ventral side of the head is observed best in smaller specimens. Two clusters, separated by a narrow midline space, lie in the apex of the funnel groove. A clear space occupies the ventral midline of the head. Eight main rows of photophores (four rows on each side of the midline space) are present. The first or most medial row begins at the posterior end of the funnel groove, extends anteriorly to the ventral aboral side of arm IV, and reaches almost to the tip of this arm. The second row branches out from the first row near the apex of the funnel groove, extends parallel to the first row and joins it at a point near the base of arm IV, at about the same level as the anterior margin of the eye. At the base of arm IV the width of the second row is increased by addi- tional photophores, and as the row continues along the base of the tentacular sheath distally it is gradually reduced to a single series of photo- phores which reaches the tip of the arm. A very short row or cluster of photophores occurs be- tween the first and second rows at a short distance beyond the base of arm IV, but in older individuals this short row tends to lie closer to the second row and may be difficult to distinguish. The third lateral row extends from opposite the first nuchal fold anteriorly (interrupted by a gap at the window of the eye) to the base of arm IV where it merges with the second row. A branch continues further along the edge of the tentacu- lar sheath almost to the tip of arm IV. The fourth or most lateral row extends from the second nuchal fold to the posterior margin of the eye and passes along the edge of the ventral eyelid to the ventral edge of the optic sinus. The row begins again on the dorsal edge of the optic sinus and continues along the base of the swimming keel of arm III to a short distance from the tip. An arclike row of small white photophores, spaced widely, lies along the ventral region of the eye be- tween the third and fourth rows of photophores. Nine light organs, arranged in a single row, are present on the ventral side of the eyeball. The terminal organs are much larger than the seven, closely spaced, interior light organs and are set apart from them. The interior organs are not of uniform size (Fig. 6J). The seven radular teeth are blunt and slightly curved. The rachidian has low lateral cusps (Fig. 6H). The mandibles are strong; the rostrum of the upper mandible is pointed and the edges are sharp (Fig. 6G1). The gular plate of the lower mandible is reinforced by three stout ribs (Fig. 6G2). At ML 45 mm the wings of both halves are already well pigmented. The gladius is thin with a low rounded midrib. The vanes are narrow and widest at about the middle. The cone is thin-walled and as wide and rounded as the anterior end of the gladius. The spermatophores are large. The cement gland has a large swelling at the aboral end (Fig. 6K). The aboral end of the spiral filament, anterior to the cement gland, is plain except for some longitudinal ridges. Two or three spiral turns behind the cap are present. Measurements from two specimens are given below: Length (mm) Spermatophore ML 130 mm il 4L 71 ■: segment specimen specim Entire spermatophore i 28 14 Spiral filament 12 6.2 Cement gland 3 1.8 Sperm reservoir 13 6 726 BURGESS: FOUR NEW SPECIES OF SQUID KSOPLOTEUTHIS Young individuals: At ML 13 mm the photo- phores on the mantle are arranged as small clusters of large photophores distributed in a definite pattern (Fig. 2Ba). There are a few small and large photophores on the head, arms, and funnel, and they are aligned in areas that cor- respond to the adult pattern. At this stage there are 17 to 21 arm hooks and 7 to 11 distal arm suckers. The tentacles are shorter than the mantle (TLI 84.6) and weak. On the club a single hook, along with 16 suckers in two rows, is devel- oped; however, the carpal area is not yet differ- entiated. At ML 18 mm, 20 or 21 hooks and 14 or 15 distal suckers are present on each of arms I, II, and III, and 30 hooks and 9 distal suckers are present on arm IV. On the club, 6 carpal suckers are set apart from 8 hooks (biserial) on the manus and about 13 suckers on the dactylus. At ML 26 mm the photophore pattern of the mantle appears more complex. First, additional photo- phores develop between the clusters whereby four oblique rows are present; and second, six longitudinal rows of indistinct small white photophores are present (Fig. 2Bb). This pattern, although not as complicated, resembles that of the adult. At this stage the clubs have 9 or 10 hooks, 9 or 10 distal suckers (biserial), and 5 to 7 carpal suckers. A ML 45 mm female has an oviducal gland 2.0 mm long, and at ML 46 mm the right ventral arm of the male is already hectocotylized, although the lappet is still very narrow and the tubercles on the arm bases are minute. There is no indication of spermatophores in the still undeveloped genital system. However, a ML 50 mm specimen has spermatophores. Remarks: The present material can be as- signed with confidence to E. reticulata (Rancurel 1970). The photophore patterns of the mantle, head, and arms, and characteristics of the tentacles and clubs are very close, and hook counts (arms and clubs) overlap. Differences in measurements are not considered to be signifi- cant. Okutani (1974; 51, fig. 12a, b, e) described and illustrated a specimen, labeled n. sp. (No. 1) in his paper on the cephalopods collected at lat. 17°53'S, long. 126°18'W during the EASTRO- PAC Expedition. 1967-68; I have examined this particular specimen deposited in the U.S. National Museum; it is E. reticulata. Enoploteuthis sp. A of Young (1978) belongs to E. reticulata described here (R. E. Young foot- note 3). The reticulated pattern is not unique. A similar pattern has been described for E. galaxias Berry, 1918. However, these two species differ in a number of basic features. Ex- cept for the mantle photophores, the pattern of the light organs in galaxias is unlike that of reticulata; there is a median row present in the head of galaxias flanked by three lateral rows, or a total of seven rows. A median row is absent in reticulata. I have examined the type of E. galaxias deposited at the Australian Museum, Sydney, Australia. Unfortunately, the specimen has darkened considerably and the photophore pattern is no longer recognizable with an ordinary microscope. The tentacles and clubs are very different. The tentacular stalk in galaxias is as stout as the arms, but in reticulata the stalk is only a third of the arm width. The club of galaxias has an expanded carpus, whereas in reticulata the carpus is very slender. The carpal suckers and pads in galaxias are arranged in a compact oval area, but in reticulata they are biserially arranged lengthwise in a narrow area. The suckers of the dactylus in galaxias are quadriserially arranged and quite numerous (38-43), whereas they are biserially arranged and very few (8-11) in reticulata. Lastly, the rachidian tooth of galaxias has no cusps, but that of reticulata does. The present collection data and those from the literature show that E. reticulata occurs over a wide area of the Pacific, Hawaiian waters in- cluded, from lat. 28°38.5'N to 22°58'S and from long. 164°04'E to 126°18'W. GENERAL DISCUSSION Since the description of Loligo leptura by Leach (1817) and the subsequent designation of this species as the type of the genus Enoploteuthis Orbigny, 1848 by Pfeffer (1900), only five other valid species have been described: E. chuni Ishikawa 1914; E. galaxias Berry 1918; E. anapsis Roper 1964; E. theragrae Taki 1964; and E. reticulata Rancurel 1970. (See summary of history, synonymy, and generic diagnosis in Roper 1966.) Enoploteuth is dubia Adam 1960 was described from a single specimen captured in the Gulf of Aqaba, Red Sea. However, Adam in his remarks was not certain that it was an Enoploteuthis. With more material and information several years later, he removed the species from Enoploteuthis (Adam 1973). 727 FISHERY BULLETIN: VOL. 80. NO. 4 Enoploteuthis theragrae was described from seven specimens found in the stomach contents of two codfish, Theragra chalcogramma, captured in 1957 and 1962 from two localities in the Japan Sea. These specimens probably are allied to E. chuni. Except for the mantle photophores (six in rows for theragrae and eight in rows for chuni) all other diagnostic characters are shared by both species (M. Okiyama4). GEOGRAPHIC DISTRIBUTION Enoploteuthis anapsis and E. leptura are widely distributed in the Atlantic. Enoploteuthis leptura is known from the Gulf of Guinea (type locality), Madeira, Cape Verde Islands, the southern Straits of Florida (Roper 1966), and east of Bermuda (Roper 1977). Enoploteuthis anapsis is recorded from parts of the western Atlantic in the Gulf of Mexico and Caribbean Sea, from the mid- Atlantic, Madeira, St. Helena, and South Equatorial Current (Roper 1966), and east of Bermuda (Roper 1977). Enoploteuthis chuni was first described from Toyama Bay, Sea of Japan, and Sasaki (1920) re- ported it later, again from Toyama Bay and farther south from Bungo Strait. Shimomura and Fukataki (1957) recorded it again from the sea of Japan together with Wataseniascintillans in the stomach contents of Alaskan pollock. Okutani (1967) listed an adult specimen from Sagami Bay on the Pacific side of Japan and some larval stages later (1968), also from the Pacific side of Japan. The first and only record of E. theragrae is from the Sea of Japan in 1964. Enoploteuthis galaxias is known only from the type locality, off Gabo Island to Everard Grounds, Victoria, Australia. Enoploteuthis reticulata was described from specimens taken by midwater trawl and from stomach contents of Alepisaurus ferox caught in areas of the southwest Pacific, approximately between lat. 22° and 18°S and long. 164°E and 133°W. The present material extends the dis- tribution to lat. 21°N in the Hawaiian area and Okutani's specimen (1974, Enoploteuthis sp. No. 1) to the southeast Pacific at lat. 17°S, long. 126°W. The genus Enoploteuthis was first reported from the central Pacific by King and Ikehara (1956) in their study of the food and feeding 4M. Okiyama, Tokyo University, Tokyo, Japan, pers. commun. 26 November 1970. habits of the yellowfin tuna and bigeye tuna. They found a total of 36 specimens of Enoploteu- this in the stomach contents of these fishes. There are no other previous records of the genus from the central Pacific. The station data of the present material show that E. obliqua ranges approxi- mately from lat. 11°N to 5°S and long. 81° to 144°W; E. octolineata from lat. 7°N to 3°S and long. 144° to 157°W; E. jonesi from lat. 20°N to 14°S and long. 157° to 168°W; and E. higginsi from lat. 21°N to 4°S and long. 149° to 169°W. Of the five species found in the central Pacific, namely, obliqua, octolineata, jonesi, higginsi, and reticulata, the last three species range to areas close to the Hawaiian Islands whereas obliqua and ocfo/meata do not (Fig. 7). Based on available records, reticulata has the widest range; it is found in the southwest Pacific, Hawaiian area, and southeast Pacific. Collections made between September 1969 and November 1974 by the University of Hawaii include specimens of E. reticulata and E. higginsi (Young 1978). BATHYMETRIC DISTRIBUTION The genus Enoploteuthis is rare in collections, and, except for E. anapsis (Roper 1966), E. higginsi, and E. reticulata (Young 1978), few depth records are available. Useful depth data are available for only two specimens of E. leptura studied by Roper (1966). These specimens were taken from depths between 0 and 170-300 m. Enoploteuthis anapsis is represented by 25 specimens taken from depths between 33 and 600 m at night and a single specimen from very deep waters, 2,000 m, during the day. Roper and Young (1975) mentioned the capture of an E. anapsis specimen in a closing net at 90 m, off Bermuda at night. Depth records are not included in the original description of E. chuni; however, the Albatross specimens reported by Sasaki (1920) came from the stomach of a fish captured from deep water, about 857 m. Okutani (1967, 1968) reported an adult from a depth of 700 m and two larval stages from the surface. The only known specimens of E. galaxias (four specimens) were captured at depths between 288 and 450 m. The present material, except for that from two tows at 240 and 576 m, came from depths between the surface and 179 m. Depth data and other pertinent records are listed in Table 6 for 131 specimens of obliqua, octolineata, jonesi, 728 BURGESS: FOUR NKW SPECIES OF SQUID F.NOI'LOTEVTHIS 130° 140° 150° 160° "170° 180° 170° 150° 150° 140° 130° 120° 110° 100° 90° 80° 70° Figure 7.— Distribution of Enoploteuthis species in the Pacific. higginsi, and reticulata. Most of the specimens (93.1%) were taken between the surface and 150 m, and the greatest number of these (48. 1%) came from a depth of 50 m. A majority of the specimens (70.2%) were collected at night between 1900 and 0400. A limited number of specimens (8.4%) came from the few tows made during the day. Enoploteuthis higginsi and E. reticulata captured off Oahu, Hawaii, were taken close to the surface (50-100 m) at night and much deeper (500-600 m) during the day (Young 1978). Species of Enoploteuthis are undoubtedly mesopelagic forms (200-1,000 m day habitat) that make diel vertical migrations as has been demonstrated for E. a napsis by Roper ( 1966) and for two other Enoploteuthis by Young (1978). RELATIONSHIPS The Pacific species of Enoploteuthis fall into two natural groups allied either to E. anapsis or E. leptura along the same characters that separate these two Atlantic species (see Roper 1966). Apparently, there are two species com- plexes within the genus: Species that tend toward the development of larger clubs and long and muscular tentacles, and those species that exhibit the opposite trends. Additional features of the former complex are: many suckers in four rows on the clubs, large hooks, and oval to round carpal apparatus. These are features common to galaxias, chuni, theragrae, anapsis, jonesi, and higginsi. Within this group, anapsis, jonesi, and higginsi all have the semilunar membrane on the club while galaxias and theragae are illustrated in the literature without it. Both Berry (1918) and Taki (1964) do not mention the semilunar membrane in their species descriptions. I have seen the holotype of galaxias, but I could not verify the presence of the membrane because of the poor 729 FISHERY BULLETIN: VOL. 80. NO. 4 Table 6.— Bathymetric data of Enoploteuthis species: obliqua, octolineata, jonesi, higginsi. and reticulata. TC = RV Tvwnsend Cromwell; HMS = RV Hugh M. Smith; CHG = RV Charles H. Gilbert. Cruise Station No of Mantle Depth Time no no. specimens length (mm) Sex (m) 24 h Month Enoploteuthis obliqua TC-48 19 58 M 50 — April TC-48 11 55 M 50 — March TC-46 9 50 F 50 1945-0230 October TC-44 i - 50 F — — July-August TC-46 9 41 M 50 1945-0230 October TC-48 19 40 + F 50 — April TC-44 24 37 + M 50 1933-0245 July TC-44 17 1 1 27 — — — July TC-44 24 4 12-20 — 50 1933-0245 July TC-43 14 16 5-18 — 50 1945-0235 May TC-43 22 5 12-17 — 50 2017-0237 May TC-43 10 5 12-17 — 50 1943-0239 May TC-44 18 2 12-17 — 100 1947-0253 July TC-44 32 1 13 — 50 1937-0303 July TC-44 54 1 12 — 50 1932-0238 July TC-47 16 4 6-11 — 50 1930-0250 January TC-48 16 3 7-10 — 20 — April TC-44 16 2 55-10 — 0 1059-0129 July Enoploteuthis octolineata TC-43 52 75 F 50 1940-0244 May HMS-47 58 71 F 212 2013-2153 November TC-46 47 56 F 115 1939-0240 October TC-46 37 56 F 50 1934-0236 October TC-48 50 49 F 50 — April TC-48 52 46 M 50 — April TC-43 42 21-40 — 50 1942-0235 May TC-48 35 39 — 50 — April TC-46 41 36 — 50 1935-0230 October TC-48 92 33 — 50 — April TC-43 38 19-30 — 50 1944-0240 May TC-44 44 1 1 28 — — 1935-0237 July TC-44 26 26 — 20 1934-0243 July TC-44 68 25 — 75 1932-0235 August HMS-47 58 25 — 212 2013-2153 August TC-43 48 24 — 50 1943-0240 May TC-43 52 20-22 — 50 1940-0244 May TC-43 26 20 — 50 1945-0235 May TC-44 56 20 — 50 1933-0235 July TC-47 45 16-20 — 50 2000-0200 February TC-43 12 15 — 20 1945-0226 May CHG-89 5 15 — 120-240 2058-2332 July TC-46 45 14 — 50 1934-0234 October HMS-47 51 10 — 576 2013-2158 November Enoploteuthis jonesi TC-7 12 82 F 9- 13 1926-2056 August TC-7 12 47 M 9-13 1926-2056 August TC-32 28 40 F 92-122 1952-0152 July CHG-89 24 35 M 90-130 2053-2246 February TC-32 46 35 F 77- 118 1951-0151 August TC-32 39 30 F 63-101 1053-0153 August CHG-89 14 27 M 70-80 0258-0445 February CHG-89 29 22 — 120- 135 2038-2231 February CHG-89 31 17 — 90-150 2040-2233 February TC-32 37 11 — 55- 123 0354-0954 August Enoploteuthis higginsi TC-32 28 60+ F 8-60 1952-0152 July TC-32 22 53 F 67-117 1952-0152 July TC-32 45 47 F 12-31 1143-1743 August TC-32 41 46 M 59- 122 1151-1751 August TC-32 23 46 M 17-25 0403-1003 July TC-32 56 45 F 97- 179 1952-0152 August TC-32 38 2 37-40 F 8-25 1144-1744 August TC-32 44 37 F 72- 118 0353-0953 August Teritu 6 37 M 110 — September TC-32 48 35 F 60- 104 1155-1755 August CHG-89 11 35 M 100-200 0254-0445 February TC-32 37 32 F 55- 123 0354-0954 August TC-32 38 30 M 8-25 1144-1744 August TC-32 33 30 F 83-99 1950-0150 August TC-32 56 29 F 97- 179 1952-0152 August TC-32 46 2 27-28 — 77- 118 1951-0151 August HMS-47 51 27 — 576 2013-2153 November TC-32 37 22 — 55- 123 0354-0954 August TC-32 33 2 12-19 — 83-99 1950-0150 August CHG-89 29 16 — 120- 135 2038-2231 February CHG-51 164 12 — 0- 100 2105-2323 February 730 BURGESS: FOUR NEW SPECIES OF SQUID ENOPLOTEUTHIS Table 6.— Continual. Cruise Station No. of Mantle Depth Time no. no. specimens length (mm) Sex (m) 24 h Month CHG-51 172 1 12 — 0-100 2100-2250 February CHG-89 30 1 11 — 100-125 0603-0745 February Enoploteuthis reticulata CHG-7 2 1 130 M — daylight February HMS-30 3 I 117 M 100 2105-2315 July TC-32 31 71 M 30-121 0354-0954 August TC-32 15 62 F 16-30 0352-0952 July TC-32 48 50 M 60-104 1155-1755 August TC-32 29 46 M 8-60 0343-0755 July TC-32 9 45 F 17-25 0354-0954 July TC-32 15 39 F 16-30 0352-0952 July TC-32 3 35 F 12-15 0355-0955 July TC-32 46 32 — 77-118 1951-0151 August TC-32 28 30 — 92-122 1952-0152 July TC-7 5 26 — 60-100 2023-2156 August TC-32 6 18 — 83-124 0354-0954 July TC-32 4 13 — 75-107 1146-1747 July From stomach of Alepisaurus. 2Regurgitated by a porpoise condition of the specimen. Enoploteuthis gal- axias, chuni, and theragrae have a midventral row of photophores on the head flanked by two lateral rows which extend (without branching) to the ventral arms. These three species are found in the western Pacific: chuni and theragrae from Japan and galaxias from Australia. The re- maining species of this complex, anapsis, jonesi, and higginsi, are very similar: All have distal club sucker rings without teeth; all have an in- complete midventral row of photophores on the head (represented by a short anterior segment near the base of the ventral arms and by a tri- angular patch of photophores in the apex of the funnel groove); the first lateral row of photo- phores on the head is divided and reunited before extending to the ventral arms; and all have an incomplete photophore row on arm III. The longitudinal rows of photophores on the mantle are easily recognized in anapsis and jonesi, but not in higginsi. Enoploteuthis leptura, octolineata, obliqua, and reticulata comprise the other species com- plex. They all have thin, slender, and short tentacles, clubs without semilunar membranes, few club suckers that lie in two rows, and a continuous midventral space on the head. Enoploteuthis octolineata and E. leptura are similar in that both have distinctly separated first and second lateral rows of photophores on the head, and lack a triangular patch of photo- phores in the apex of the funnel groove although each of the first lateral rows continues into the groove. Both species also have distinct and well- spaced mantle and funnel photophores. Enoplo- teuthis reticulata and E. obliqua also show similarities. The photophore pattern on the head, arms, and funnel have basically the same arrangement: Two small clusters of photo- phores, separated by a narrow space, are present in the apex of the funnel groove and, except for the continuous midventral space, single photo- phores are present posteriorly in the spaces between the funnel photophore rows. Thus, the rows are not completely separated. However, the mantle photophore pattern of each species is distinct: oblique in one and reticulate in the other. Enoploteuthis reticulata and E. galaxias have similar patterns of mantle photophores, but their head photophore patterns and some features of the clubs differ. The reticulate pat- tern on the mantle is probably an independently developed trait. The spermatophores of E, higginsi and E. anapsis are both intricately sculptured, while those of E. leptura, E. obliqua, and E. reticulata are simple. Since the spermatophores of the other species are undescribed, it remains to be seen if the sculptured type are only associated with the first species complex and the simple type with the second complex. The important characters (except photophore pattern) of these two complexes are listed in Table 7. KEY TO THE SPECIES OF ENOPLOTEUTHIS (ADULTS, WORLDWIDE) 1. Tentacular stalk and club narrow, suckers on dactylus few and in two rows; carpal cluster elongate; semilunar mem- brane absent 2 731 FISHERY BULLETIN: VOL. 80, NO. 4 CD , , i - i. >- CO P ra ^ - »- c c c c 0) 0) CD CD CO CO CO 01 .O .Q .O -Q Q. CO CO Q. O. D. CO CO CO CO £ j_ -d -a 2? -c CD CD ■9 5 3 CD CO ■*"* O o u„„- CO CO c c c CD CD CD CD CD 3 E — . "O "O CO CO CO T c c xi n n r^ r- o m 3 3 co co co h- CD CO O jd & +_. c si CO CO CO CO CO CO .0 CN C\J U) S i-N ^r c m r*- r*- T T V V "a E o o oo Jooo O) CO C TT CD CO O i- 00 CO 1- T- i- o ^"o en *r c\j CN CM i- r- i~ f- 3 o ° -*~ o °z O) t- O CM O O CO CO 00 O) a. T- 1- T- 1- T- c«j 13 75 C a! O to > o _ ,_ _- CO CO CO a. e Q.Q- ^ o CO §8s! CD CD CD CD CO CO CO CO CJ) Q) CT 0> C C C C s — 3 - o 3 CO R° U £ 2 O O O O O CD CD CD CD •2 -£ "§' <^> co in C7) ^T ^-» CO, X O CO t^ O) *- o r^ cS Q. £ »S s cb n m co en P ^. CJ) CM o c Tf o »- N CO CO CD CD CN r- CO — t- i- CJ> CSJ r- CM a> o> r- *- c £ O CO CO O C7) CO o ^- m co o o cd oi OS CM CO CO ^T O CD CN CT> CO (- c i- O CO CO O r- co co r^ cj) cd a) t— t— t— r- t— s o «3 1 1 E a CO CO O t S CD O) CO O CO w _i 5 CO 5 to s co m 't ^t s m co ^t < E 3 cd E CO °>. \ in X E N N 0(0 WO rr o co m co CD oo co co r- co co Tf miON 5 li- X X CD Q) Q. "q. <0 CO E q> £ CO 03 30 cm. Thirty percent of the largest worms displayed no sign of sexual development. Single eggs of 50 n diameter were first observed in the coelom from October to November. These eggs entered a rapid growth phase between August and December and attained a maximum diameter of from 183 y. (1967) to 194 ^ (1968) at time of spawning during April and May. Maturation could take as long as 18-20 months or as little as 12 months. The numbers of eggs laid by sandworms were found to vary between 0.05 (16 cm worm) and 1.3 million eggs (54 cm worm). The onset of spawningoccurred when the surface water temperature was between 7.0°C (1968) and 8.1°C (1967) and when the bottom water temperature was between 6.7°C (1968) and 7.6°C (1967). During both years, spawning occurred 4 days after full moon during the period of spring tides. Scuba observations revealed that male spawners emerged from the mud about 3 hours after high water. At the peak of spawning, densities of epitokes may reach 1 worm/m2. Male spawners are readily consumed by herring gulls, Larus argentatus. The sandworm, Nereis virens Sars, commonly occurs on the Atlantic coast from Virginia north- ward to the Arctic region. It is also found in Ice- land. Norway, Ireland, and the North Sea to France (Pettibone 1963). Nereis virens is known to inhabit coarse and fine muddy sand, mussel beds, and the roots of decaying marsh and eelgrass (Pettibone 1963). The sandworm population in the Sheepscot River study area at Wiscasset, Maine (lat. 44°N, long. 70°40'W), inhabits a gray, silty clay which is mod- erately burrowed and contains shell fragments, mica flakes, and 2% organic carbon (Reynolds et al. 19752). The mean tidal amplitude in this re- gion is 2.9 m. Ecologically, sandworms occupy an important position in the food web of other invertebrates, fish, and shorebirds. They have been harvested commercially for bait along the Maine coast for more than 40 years, with landings of 26.9-38.1 million worms/yr and a landed value of $0.5-1.1 'Maine Department of Marine Resources Research Labora- tory, West Boothbay Harbor, ME 04575. 2Reynolds, L., J. Bowman, and E. Kelly. 1975. Unpub- lished summary of sediment size, x-radiography. chemistry, and mass physical properties of six cores and two grabs from Maine. LJ.S. Naval Oceanographic Office, Washington. D.C. million reported between 1966 and 1980 (NMFS 1966-80). Previous research on Maine sandworms in- cluded studies on digging (Ganaros 19513) and dispersion (Gustafson 1953; Dean 1978). Although intensive harvesting qualifies the sandworm for management considerations, only reports by Glidden (1951)4 and Dow and Creaser (1970) con- tain life history information pertinent to man- agement of sandworm populations in Maine. The present study was undertaken to provide life his- tory information for a sandworm population in the Sheepscot Estuary at Wiscasset, Maine. It also includes some information on subjects not previously investigated or which differ from findings reported from other geographical loca- tions. Other studies on the life history and reproduc- tion of Nereis virens include Brafield and Chap- man (1967) and Bass and Brafield (1972) in the Thames Estuary at Southend, England; Sveshni- kov ( 1955) in Rugozerski Bay near the White Sea, Bull. 3Ganaros, A. 1951. Commercial worm digging. Dep. Sea Shore Fish., Augusta, Maine, 6 p. 4Glidden, P. E. 1951. Three commercially important polychaete marine worms from Maine. Rep. Dep. Sea Shore Fish., Augusta, Maine, 25 p. Manuscript accepted April 1982. FISHERY BULLETIN: VOL. 80. NO. 4. 1982. 735 FISHERY BULLETIN: VOL. 80, NO. 4 Russia; and Snow and Marsden (1974) at Brandy Cove, St. Andrews, New Brunswick, Canada. Materials and Methods All sandworms were collected in the vicinity of a small intertidal mud flat at Wiscasset, Maine, closed to commercial digging. Within this area, a section running parallel to the low-water mark and measuring 91 m X 24 m was used for experi- mental purposes. Differences in tidal height be- tween the upper and lower extremities of this experimental area were about 22 cm. Monthly, three 1 m2 sample plots were randomly chosen and dug within the experimental site. The sam- pling device consisted of a 1 m2 frame with deep walls (45 cm) that could be pushed into the mud to prevent escape. Within each plot, the surface ooze was removed with a dustpan to a depth of 2-3 cm and deposited within a square framed recep- tacle constructed of 1 mm mesh fiberglass screen. The receptacle was then partially immersed in the river and carefully agitated to remove sedi- ment. The remaining debris and worms were poured into a plastic container and transported to the laboratory. Small portions of debris, to- gether with seawater, were deposited in dissect- ing trays and dispersed with a needle probe. The contents were thoroughly searched and all small sandworms, swimming or hiding among the debris, were removed with forceps. Clumps of deeper and firmer mud were removed from the sampling device in the field to the maximum depth of burrowing activity (about 30 cm) and carefully broken by hand to remove the larger worms intact. These worms were also trans- ported to the laboratory in plastic buckets. All sandworms were acclimated to high salin- ity water (about 32%0) at the laboratory prior to immersion in anesthetic (7.5% MgCb). Lengths were obtained using a V-shaped measuring trough containing ample anesthetic to cover the worms. Coelomic fluid was withdrawn with the aid of capillary pipettes, and sex was determined by microscopic examination of the contents. Egg diameters were measured with an ocular mi- crometer and without a cover slip. Usually 10 eggs were measured from each worm. The rela- tionship of sandworm length to numbers of eggs laid was corrected for transformation bias fol- lowing the methodology of Bradu and Mundlak (1970). Worms used in the study to determine the per- cent of mature males and females and immature females in each length increment were obtained during February (prior to spawning) from pooled samples dug independently of the regular monthly sample. The distinction between ma- ture and immature females was made after examining eggs in the coelomic fluid; large eggs from mature worms would be spawned in April or May, and small eggs would be spawned ap- proximately 1 yr later. We were unable to make a distinction between mature and immature males. Sandworms designated "nonspawners" include worms of all sizes that have not spawned and whose coelomic contents present no clue about sexuality. "Spent" worms include both males and females that have spawned and are deteriorating and approaching death. Female sandworms used for egg counts were anesthetized, measured, and preserved. The worms were then split lengthwise and washed thoroughly to remove as many eggs as possible. Next, the body was chopped into 1 cm pieces, im- mersed in seawater, and stirred magnetically. After three or four changes of water, most eggs were dislodged. Egg samples were diluted in 0.1-2.7 1 seawater, depending upon size of the worm and numbers of eggs present. Two 1 ml ali- quots were withdrawn from this mixture during agitation, placed on Sedgwick-Rafter5 counting cells, and the number of eggs counted under the 10X objective. The mean value was then multi- 5Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. cc 3 < CC CL TEMP (SURFACE) & & TEMP(BOTTOM> • • SALINITY (SURFACE] □ □ SALINITY (BOTTOM ) 30 28 26 ° >- 24 222 20 18 16 I I I I I I I I I I I NDjJFMAMJJASO 1966 I 1967 Figure 1.— Summary of temperature and salinity data col- lected from the Sheepscot River near the Wiscasset closed area between November 1966 and October 1967. 736 CREASERand CLIFFORD: LIFE HISTORY STUDIES OF SANDWORM plied by the dilution factor to obtain the final egg count. Hydrographic data were usually obtained shortly after the collection of worm samples. Mean monthly water temperature was calcu- lated from 25 thermister recordings collected in situ at 30-min intervals at hydrographic stations occupied for 12 h. Mud temperature records were collected in situ by digging a shallow hole in the mud flat and inserting a thermometer hori- zontally at a depth of about 10 cm. Water sam- ples used in salinity analysis were obtained using a 1 1 water sampler. Water samples of 5 ml were analyzed for salinity by the Knudsen method. Sandworms were captured during spawning using scuba techniques or dip nets. RESULTS Salinity and Temperature of the Study Area The salinity and temperature regime of the river water at the study area during the period November 1966-October 1967 is summarized in Figure 1. During these studies, surface salinity varied between 17 and 29%o, surface tempera- ture between -1° and 15°C, bottom salinity be- tween 24 and 29%o, and bottom temperature be- tween -1° and 14°C. Length Frequency Preliminary digging in the Wiscasset closed area indicated that sandworms were most abun- dant in the region of the low-water mark. Within this region, significant variations in both abun- dance and size were recorded for three randomly selected 1 m2 plots dug from one tidal height during one time period. Because of this variation, digging more than 1 sample plot/mo was desir- able. We elected to dig and combine the results of 3 randomly selected plots/mo because the com- bined results produced fairly consistent length- frequency trends between months. Considerable breakage of all sizes of sandworms was encoun- tered during handling and processing. During agitation, the presence of sharp shells and debris in the upper layer of organic ooze resulted in additional breakage of juvenile sandworms prevalent there. Some unavoidable bias has therefore resulted in the numbers of juvenile worms reported. Length-frequency results for all whole worms collected during August, Sep- tember, and October are shown in Figure 2. Sandworms captured varied in length between <1 and 31 cm. Numbers of whole individuals captured during these months varied between 546 and 701. Figure 2 indicates some recruit- ment of small individuals into the sampled popu- lation during the summer. Additional length-fre- quency information collected during this study is presented in Creaser and Clifford (1981)6. The August-October 1967 length-frequency data, when combined to produce sufficient num- ber, was analyzed by the method of Harding (1949), as explained by Cassie( 1950), to determine the number of assumed age modes. Although five assumed modes and linear growth were detected by this analysis, there is considerable overlap in length at age; the results are therefore question- able until they can be verified against other aging techniques. 6Creaser, E. P., and D. A. Clifford. 1981. Life history studies of the sandworm Nereis virens Sars, in the Sheepscot Estuary, Maine. Maine Department Marine Resources Re- search Laboratory, Res. Ref. Doc. 81/16. 37 p. N = 546 AUG 1966 10 15 20 25 LENGTH, CM Figure 2.— Monthly length frequency distributions for three combined plots dug from the Wiscasset closed area. 737 FISHERY BULLETIN: VOL. 80, NO. 4 Proportions of male, female, and nonspawning sandworms of various lengths are shown in Fig- ure 3. There is an increase in numbers of mature males and females with increasing size. Worms >30 cm show a preponderance of mature females over mature males. More than 30% of the largest worms showed no sign of sexual development. Oocyte Development The results of oocyte growth studies are pre- sented in Figure 4A, and water temperatures associated with these data are shown in Figure 4B. Eggs of about 50 ^ were first observed in the coelom in October-November. Diameter in- creased from 80 to 160 m during the rapid-growth phase which occurred between August and De- cember. Prior to spawning, the rate of egg growth decreased. Maximum mean egg diame- ters obtained were 183 /x (1967) and 194 M (1968). A Student's t-test revealed a significant differ- ence between these mean diameters (t = 4.65910; P<0.05; 14 df). Spawning occurred in April and May during a 4-5 wk period, and few egg-bearing worms were found after the beginning of June. The maturation of gametes required 18-20 mo, or as little as 12 mo, depending upon when the eggs were ovulated into the coelom. Annual spawning, together with a maximum development period of 18-20 mo, accounted for the presence of two gen- eral egg sizes in sandworms inspected between October-November and April-May. Eggs ap- proaching spawning size varied the least in di- ameter (the smallest standard deviation) (see Figure 4A). During the period of rapid egg growth, both mud and bottom river tempera- tures were decreasing (see Figure 4B). Numbers of Eggs Laid The numbers of eggs laid by sandworms of various lengths are recorded in Figure 5. The range varies between about 0.05 and 1.3 million eggs for worm lengths of 16 and 54 cm, respec- tively. Environmental Conditions During Spawning Spawning first occurred in the Wiscasset re- gion on 28 April 1967 and 17 April 1968. A sum- mary of hydrographic conditions associated with spawning on 2 May 1967 and 19 April 1968 is presented in Table 1. Table 1 shows that mean surface-water temperatures of 7.0°C (1968) and 8.1°C (1967) and bottom water temperatures of 6.7°C (1968) and 7.6°C (1967) were associated with the onset of spawning. During both years, initial activity in the Wiscasset area occurred 4 d after full moon during the period of spring tides. The stage of the tide during which spawn- ing activity occurs was investigated on 23 April 1968, using scuba techniques. During a series of six dives beginning just after high water (08:28 100 N=1453 □ = NON- SPAWNER [^%j : MALE (MATURE) UJ u 80 z p=l : FEMALE (MATURE) LLI 2) I FEMALE (IMMATURE) U60 O — i— LU 40 u LU 20 _ m 1 1 1 I 5.0-9 9 10.0- M 3 15.0-19 9 20.0— Zt .9 2! 0 7 1.9 3( .0 3< l.'l 3! 0 3 19 LENGTH ,CM Figure 3.— Proportions of male, female, and nonspawning sandworms of various lengths col- lected prior to spawning during February 1967. 738 CREASERand CLIFFORD: LIFE HISTORY STUDIES OF SANDWORM o IE 5 (15) (1) » 40 20 0 (3) (2: (101(101 112*11) (181 i: NUMBERS OF WORMS INSPECTED _i 1 i_ OND JFMAMJ JASOND J FMAMJJ 1966 1967 IB) 1968 O :MEAN MUD TEMPERATURE A FROM 3 AREAS OF WORM FLAT 0NDJFMAMJJAS0NDJFMAMJ J I9S6 1967 1968 Figure 4.— (A) Oocyte growth occurring simultaneously in two groups of Wiscasset sandworms at different stages of maturation (lines fitted by eye). (B) Monthly mean mud and bottom water temperature from the Sheepscot River at Wis- casset. Table 1.— Summary of temperature and salinity associated with sandworms spawning at Wiscasset, Maine, on 2 May 1967 and 19 April 1968. 2 May 1967 1030-1430 h 19 April 1968 0730-1200 h Temp. (°C) Salinity Ay Temp. (°C) Salinity (%o) Ay Surface if ± 1 SE Range Bottom if ± 1 SE Range 8.1±0.3 68-9 1 7.6±0.2 6.6-84 19 98± 0.38 18.51-21.58 23.18+ 0.43 21 24-2532 9 9 9 9 7.0+0.2 5.8-7.8 6.7+0.2 5.3-8.0 23.55± 0.25 2275-2508 25 .34+ 0.26 2380-26 09 10 10 10 10 EST) and ending just before low water (14:34 EST), no spawning worms were observed until about 3 h after high water (Table 2). Although the possible role of water temperature in initiat- ing spawning cannot be completely eliminated, 13l N 50 1.2 1.1 1.0 .9 0 8 V -.6 CO o O .5 LU 4 .3 .2 11- E 0464 L25523 0 5 10 15 20 25 30 35 40 45 50 55 60 ANESTH LENGTH, CM Figure 5.— Number of eggs produced as a function of sand- worm length. the tidal-condition results in Table 2 are consis- tent with numerous visual observations on spawning activity in the Wiscasset area over many years. Spawning Characteristics Nearly all sandworms captured during spawn- ing were males. Females were only rarely en- countered in the latter part of the spawning sea- son. Scuba observations revealed that male sandworms emerge from the mud anterior-end Table 2.— Data collected during scuba investigation of tidal conditions between high water and low water at onset of spawn- ing activity on 23 April 1968. Temperature (°C) Salinity (%o) No. worms collected Surface Bottom Surface Bottom Time Tide of height dive (m) (High water 0828 h EST) 0910- 3.4 7.3 6 1 24 24 26 64 0930 1010- 2 9 7 6 6 5 25 12 26 24 1028 1103- 2.1 8 1 7 7 24 87 24 74 1123 1200- 1.2 8 8 8.2 24 61 24 69 1222 1305- 06 9.4 9.1 25 16 25 26 1335 1400- 0.5 11.2 10 4 24.72 24 98 1410 (Low water 1434 h EST) 0 0 0 127 118 96 0 0 0 0 0 0 739 FISHERY BULLETIN: VOL. 80. NO. 4 first. These free-swimming spawners displayed two characteristic types of swimming behavior: 1) Swimming more or less in a straight path (with occasional tumbling and back swimming) with typical lateral undulations of the body, and 2) swimming in circles typically 10-15 cm in diame- ter. Spawning worms appeared to be distributed randomly over the flats. During peak spawning, the density of worms observed swimming near the surface of the mud was about 1 worm/m2. All male spawners collected in the Wiscasset area were definitely epitokous individuals, having undergone morphological changes. Mature fe- male sandworms dug from the flats were typi- cally dark green, males that had just emerged to spawn were lighter green, and males that were "spawned out" but still swimming were a dark, bluish green. Some male sandworms may spawn during more than one tide. Numerous male sand- worms were observed burrowing back into the flats during scuba dives. None, however, bur- rowed deeply into the mud. The reproductive strategy of the sandworm qualifies it as a "mono- telic" species, i.e., it breeds once in its lifetime, all gametes are released in one or two large batches, and the spent animals die immediately or shortly afterwards without developing more gametes (Clark cited in Stancyk 1979). Some nearly "spent" individuals were observed to contain large numbers of a parameciumlike ciliate. Predation During receding tides in the Wiscasset vicinity during April, an increasing number of herring gulls, Larus argentatus Pontoppidan, circling the flats, anticipated the ensuing spawning activ- ity of Nereis virens. At the height of spawning, thousands of gulls could be observed feeding on male spawners. DISCUSSION AND CONCLUSIONS Salinity and Temperature of the Sandworm Habitat The salinity and temperature regime encoun- tered by Nereis virens in other geographical areas is incomplete. Brafield (1968)7 indicated that water and interstitial salinity encountered 7A. E. Brafield, Department of Biology, Queen Elizabeth College (University of London), Campden Hill Road, London, England, pers. commun. 1968. by the Southend, England, sandworm popula- tion varied between 28-32%o and 27.5-31.5%0. and water temperature varied between 3.2°C (Janu- ary) and 22.5°C (August). The Wiscasset popula- tion is subjected to more estuarine salinity condi- tions and cooler water temperatures than in England. The temperatures recorded for Brandy Cove, New Brunswick, by Snow (1972) are very similar to the temperatures recorded in Figures 1 and 4B. Length-Related Observations The concave nature of the length-frequency data presented in Figure 2 is consistent with a highly variable recruitment pattern resulting from larval mortality and intense predation soon after settlement (Warwick cited in Coull 1979). The absence of sexual products in the coelom of a proportion of the largest sandworms (see Fig. 3) appears to be characteristic of the species. Both Snow and Marsden (1974) and Brafield and Chapman (1967) have made similar observa- tions. The fate of these large nonspawners is not known. They possibly emigrate to subtidal or downriver habitats or succumb to natural or dig- ging mortality without spawning. Considerable variation exists in the maximum size of Nereis virens reported from different geo- graphical locations. The largest individual re- ported in Figure 2 was 31 cm. Sandworms of 70- 75 cm (anesthetized length) have been dug from the Back River in Boothbay, Maine (lat.43°54' 15" N, long. 69°40' W). Sveshnikov (1965) reported catching epitokous individuals 45 cm in length and also reported that the heteronereid form of N. virens reached a length of 90 cm along the coast of England and 1 m in Japan. Khlebovich (1963) reported mature individuals reaching 38.5 cm in the White Sea. The sex ratio of Nereis virens collected prior to spawning varies with geographical location. In our studies, the sex ratio of small potential spawn- ers was approximately 1 female: 1 male, whereas the sex ratio of individuals >30 cm was approxi- mately 2 females: 1 male. There is no reason to believe that these changes in sex ratios with size result from nonspawners (in February) becom- ing sexually mature by spawning onset in April. Our observations reveal that the maturation rate of both eggs (see Figure 4A) and sperm requires considerably more than 2 mo. The change in sex ratio may indicate that larger potential males are more disposed to either free-swimming in the 740 CREASER and CLIFFORD: LIFE HISTORY STUDIES OF SANDWORM water or exposing themselves on the surface of the mud, and are therefore subject to greater natural mortality through predation. The free- swimming habits of Nereis virens (especially at night) have been well documented (Crowder 1923; Gustafson 1953; Dean 1978). Brafield and Chapman (1967) reported that by the onset of spawning, males and females occurred in about equal numbers. Snow (1972), on the other hand, reports a 3:1 ratio of males to females prior to spawning. Oocyte Development Some similarities exist between our studies of oocyte development (see Figure 4 A) and those of Brafield and Chapman (1967) and Snow and Marsden (1974). Brafield and Chapman (1967) reported that ovulation occurred in February or March at 50 n and the oocyte diameters increased from 80 /j. to 160 p. during the period of rapid growth between September and December. The increase in oocyte diameters to 170-180 n prior to spawning required about 14 mo. Snow (1972) re- ported that the smallest eggs found free in the coelom of Nereis virens measured 10 /i in diame- ter. The eggs usually remained in clumps until they measured 25 m and appeared singly above 50 m- Snow and Marsden (1974) stated that the rapid-growth phase began in September, and their egg growth figure showed that this ex- tended at least until December. They stated that maturation required 1-2 yr, depending upon the time of year when the eggs were produced. Ova measured 210-240 /j. when spawned in May. The standard deviation for oocyte diameters recorded in both the present study and that of Brafield and Chapman (1967) reveals that small oocytes are more variable in size than large oocytes. The large standard deviation for small oocytes results from ovulation occurring over a long period. Eventually, the maturation rate of oocytes produced late in this period accelerates so that all oocytes mature at a certain size at the same time (Clark cited in Stancyk 1979). Similar observations have been recorded for Nereis diversicolor Muller (Clark and Ruston 1963). Oocyte development in Nereis virens follows the typical sigmoid growth curve. Similar obser- vations have been recorded for all or part of the oocyte maturation processes in Arenicola marina Linnaeus (Howie 1964 pers. commun. cited in Clark 1965), Nereis diversicolor (Clark and Ruston 1963), and Glycera dibranchiata Ehlers (Creaser 1973). Although no length measurements were ob- tained for the sandworms used in Figure 4A, it was generally evident to us that no relationship existed between size of the adult and size of the eggs; potential spawners of all sizes at one time possessed eggs of similar size. Numbers of Eggs Laid Sandworms >37 cm long were not found in the Wiscasset closed area (Creaser and Clifford foot- note 6). However, a few larger worms, up to 54 cm long, were captured adjacent to the closed area after extensive digging, and egg counts from these as well as the more typical sizes were included in this study. Sandworms contained considerably fewer eggs than were found in simi- lar-sized bloodworms, Glycera dibranchiata, col- lected from the same closed area but higher on the flat (Creaser 1973). The relatively large num- bers of eggs produced (0.05-1.3 million), however, are consistent with the observation that macro- fauna species generally produce large numbers of gametes (Thorson 1950 cited in Coull 1979). Environmental Conditions During Spawning Clark and Olive (1973) reported that "In the family Nereidae, sexual maturation and epitoky are caused by a decline in the rate of production of a cerebral hormone." Clark (1965) suggested that changes in the secretion rate of cerebral hormone might be controlled by environmental conditions or by some feedback mechanism. A distinction is made between (a) necessary envi- ronmental conditions and (b) specific environ- mental signals (Clark cited in Stancyk 1979). Results of the present study suggest that a water temperature of about 7°-8°C might be one of the necessary environmental conditions re- quired to initiate spawning. This hypothesis is strengthened by the fact that Snow and Marsden (1974) successfully fertilized Nereis virens ova and reared the young in the laboratory at 7°C. Sveshnikov(1955) recorded that surface temper- ature varied between 8.9° and 9.5°C at time of spawning in the White Sea. Some investigators (Thorson 1946; Korringa 1957) have reported that a rise in seawater temperature triggers spawning in a number of marine organisms. Bass and Brafield (1972) induced premature spawn- 741 FISHERY BULLETIN: VOL. 80, NO. 4 ing in Nereis virens with an artificial rise in tem- perature from ambient (5°C) to 22°C over a 10-h period. The specific environmental signals required to initiate spawning may be associated with the phase of the moon and the stage of tide. Our obser- vations of initial spawning activity shortly after full moon are in partial agreement with Pettibone ( 1963) who reported that the spawning activity of Nereis virens on the New England coast centered around both full and new moon. Brafield and Chapman (1967), Bass and Brafield (1972), and Snow and Marsden (1974) have reported that swarming coincided with the time of new moon. The sandworms at Wiscasset spawn during the second half of the outgoing tide through the first part of the incoming tide. Pettibone (1963) re- ported similar observations from Barnstable, Mass. Bass and Brafield (1972) reported swarm- ing in the Thames population only during periods of day and night high tides. Our only observation of some exceptionally large Nereis virens swarm- ing at high water occurred in the Damariscotta River, Maine, in the vicinity of Fort Island (lat. 43°53'30" N, long. 69°31'30" W). Spawning Characteristics Some of the characteristics of spawning Nereis virens recorded by different investigators are summarized in Table 3. Nereis virens has been described as atokous (Brafield and Chapman 1967; Snow and Marsden 1974) and epitokous (Gustafson 1953; Sveshnikov 1955; Khlebovich 1963). Clark (1961) reported that the structural modification associated with epitoky may be subtle and consist only of an elon- gation of the setae, modification of the sense organs, and reconstruction of the musculature. According to this description, spawning individ- uals captured in the vicinity of Wiscasset were obviously epitokes; the same morphological changes recorded in England by Bass and Bra- field (1972) for adult males were observed in the Wiscasset population. There is no reason to doubt that Nereis virens display different reproductive characteristics in different geographical loca- tions. Dales (1950) reported that nereids are well known for displaying variable reproductive habits within a given species. ACKNOWLEDGMENTS We extend our appreciation to Clement Walton and Christy Adams for their assistance in the collection of data used in this research. Special thanks are also due to David Sampson for assist- ance in the analysis of data, James Rollins for Table 3. — Some characteristics of spawning Nereis virens recorded by different investigators. Location of Location of Male swimming behavior Color of Fate after Investigators spawning males spawning females during spawning spawners spawning Bass and Brafield males in free- believed females spawned observed circular swimming 4% of males deep worms swarmed sev- (1972) swimming in burrows in both vertical and horizon- red with white lines eral times before be- swarms tal plane; anterior portion of marking margin of coming spent butdie gravid worm becomes rigid. anterior segments; a few were creamy white after spawning Brafield and Chapman males in free- believed females spawned females lime green worms die after (1967) swimming swarms in burrows or possibly spent short period swarm- ing at surface males milky green spawning Clark (1961) males often dominate breeding swarms of nereids swimming in tight circles is common to all swarming nereids Snow and Marsden males in free- believed females spawned survival after spawn- (1974) swimming swarms in burrows ing is highly unlikely Our observations males in free- believed females spawned 2 types: 1) swimming in females dark green individual worms swimming in burrows; some evidence straight lines is characteris- males pale green sometimes spawn on swarms that they emerge from tic of new spawners that becoming darker more than one tide mud to die after spawning have just emerged from the as worms become but die after spawn- mud; 2) circular swimming spawned out ing of spent or nearly spent indi- viduals caused by anterior portion curved downward and worm tipped on side when swimming 742 CREASER and CLIFFORD: LIFE HISTORY STUDIES OF SANDWORM photographic services, and Vicki Averill for typing. This research was conducted by the Maine Department of Marine Resources Research Lab- oratory, West Boothbay Harbor, Maine, in co- operation with the United States Department of Commerce, National Marine Fisheries Service, and was financed under Public Law 88-309, Project 3-16-R. LITERATURE CITED Bass. N. R., and A. E. Brafield. 1972. The life-cycle of the polychaete Nereis virens. J. Mar. Biol. Assoc. U.K. 52:701-726. Bradu, D., and Y. Mundlak. 1970. Estimation in lognormal linear models. J. Am. Stat. Assoc. 65:198-211. Brafield. A. E., and G. Chapman. 1967. Gametogenesis and breeding in a natural popula- tion of Nereis virens. J. Mar. Biol. Assoc. U.K. 47:619- 627. Cassie, R. M. 1950. The analysis of polymodal frequency distributions by the probability paper method. N.Z. Sci. Rev. 8:89- 91. Clark, R. B. 1961. The origin and formation of the heteronereis. Biol. Rev. (Camb.) 36:199-236. 1965. Endocrinology and the reproductive biology of polychaetes. Oceanogr. Mar. Biol. Annu. Rev. 3:211- 255. Clark, R. B., and P. J. W. Olive. 1973. Recent advances in polychaete endocrinology and reproductive biology. Oceanogr. Mar. Biol. Annu. Rev. 11:175-222. Clark, R. B., and R. J. C. Ruston. 1963. The influence of brain extirpation on oogenesis in the polychaete Nereis di versicolor. Gen. Comp. Endo- crinol. 3:529-541. COULL, B. C. 1979. Marine benthic dynamics. Library in Marine Science, No. 11. Press. Georgetown, S.C., 451 p. Creaser, E. P., Jr. 1973. Reproduction of the bloodworm (Glycera dibran- chiata) in the Sheepscot estuary, Maine. J. Fish. Res. Board Can. 30:161-166. Crowder. W. 1923. Dwellers of the sea and shore. MacMillan Co., N.Y., 333 p. Belle W. Baruch Univ. So. Carolina Dales, R. P. 1950. The reproduction and larval developmentof AV/v/.s (I i versicolor. O. F. Muller. J. Mar. Biol. Assoc. U.K. 29:321-360. Dean, D. 1978. Migration of the sandworm Nereis virens during winter nights. Mar. Biol. (Berl.) 45:165-173. Dow, R. L., and E. P. Creaser, Jr. 1970. Marine bait worms, a valuable inshore resource. Atl. States Mar. Fish Comm. Leafl. 12, 4 p. Gustafson, A. H. 1953. Some observations on the dispersion of the marine worms Nereis and Glycera. Maine Dep. Sea Shore Fish. Fish Circ. 12. Harding, J. P. 1949. The use of probability paper for the graphical anal- ysis of polymodal frequency distributions. J. Mar. Biol. Assoc. U.K. 28:141-153. Khlebovich, V. V. 1963. Biology of Nereis virens (Sars) in the Kandalakska Bay of the White Sea. Tr. Kandalakshkoga Gos. Zapov. 4:250-257. Korringa, P. 1957. Lunar periodicity. Mem. Geol. Soc. Am. 67(1): 917-934. National Marine Fisheries Service. 1966-1980. Monthly current fisheries statistics— Maine landings. U.S. Dep. Commer., Natl. Mar. Fish. Serv., NOAA, Wash., D.C. Pettibone, M. J. 1963. Marine polychaete worms of the New England re- gion. I. Families Aphroditidae through Trochochaeti- dae. U.S. Natl. Mus., Bull. 227, 356 p. Snow, D. R. 1972. Some aspects of the life history of the Nereid worm Nereis virens (Sars) on an intertidal mud flat at Brandy Cove. St. Andrews, N.B. M.S. Thesis, McGill Univ., 161 p. Snow, D. R., and J. R. Marsden. 1974. Life cycle, weight and possible age distribution in a population of Nereis virens (Sars) from New Brunswick. J. Nat . Hist. 8:513-527. Stancyk, S. E. 1979. Reproductive ecology of marine invertebrates. Belle W. Baruch Library in Marine Science, No. 9. Univ. So. Carolina Press, Columbia, S.C., 283 p. Sveshnikov, V. A. 1955. Reproduction and development of Nereis virens Sars. Dokl. ANSSSR Zool. 103:165-167. Thorson, G. 1946. Reproduction and larval development of Danish marine bottom invertebrates, with special reference to the planktonic larvae in the sound (0resund). Medd. Dan. Fisk. Havunders. Ser. Plankton 4(l):l-523. 743 DIET OVERLAP BETWEEN ATLANTIC COD, GADUS MORHUA, SILVER HAKE, MERLUCCIUS BILINEARIS, AND FIFTEEN OTHER NORTHWEST ATLANTIC FINFISH Richard W. Langton1 ABSTRACT Diet overlap calculated as the percentage similarity between the diets of Atlantic cod, Gadus morhua, silver hake, Merluccvus bilinearis, and 15 other finfish species was computed from stomach contents data collected in the northwest Atlantic between Cape Hatteras, North Carolina, U.S.A., and western Nova Scotia, Canada, from 1973 through 1976. Since crustaceans are preyed on by both Atlantic cod and silver hake and most of the 15 other groundfish species representing members of the Rajiformes, Perciformes, Gadiformes, and Pleuronectiformes, completely dissimilar diets occur very rarely. Although the overlap values are quite variable, the greatest overlap, with few excep- tions, occurs among the gadiform fishes themselves rather than between the gadids and species from the three other ordinal taxonomic levels. Furthermore, Atlantic cod and silver hake show a size dependent shift in diet (at 60-70 cm for Atlantic cod and 20-25 cm for silver hake) from crustaceans to fish so that, generally, the major overlap levels are for the smaller size classes of fish. Overlap levels are discussed in relation to the prey species the predators share and also in terms of their usefulness in identifying potential trophic linkages between northwest Atlantic finfish. The traditional way of identifying fish is by recognizing individual species as discrete taxo- nomic units. Although the species concept is fun- damental to any biological work, fishery biolo- gists have been considering other means of grouping species. These are usually attempts to lump species in an ecological sense and they often depend on the fishes' diet. These feeding niche groupings may then be related to the morphol- ogy and size of the fish or the prey. Food related size classes for fish have, for example, been iden- tified by Parker and Larkin (1959), Paloheimo and Dickie (1965), and Tyler (1972). These classes are referred to as threshold lengths or feeding stanzas. Grouping of fish based on gut morphol- ogy alone has been explored extensively for flat- fish by deGroot (1971), while prey size grouping was developed by Ursin (1973) and applied to northwest Atlantic fish by Hahm and Langton (19802). More recently, scientists on the west coast of the United States have been looking at Pacific fish assemblages (Gabriel and Tyler 1980) and have proposed the idea of an Assem- blage Production Unit (Tyler et al. in press). The 'Department of Marine Resources, Marine Resources Lab- oratory, West Boothbay Harbor, ME 04575. 2Hahm, W., and R. Langton. 1980. Prey selection based on predator/prey weight ratios for some northwest Atlantic fish. Int. Counc. Explor. Sea, CM. 1980/L:62, 9 p. Assemblage Production Unit is defined as a geo- graphically limited natural production system of interacting organisms, in which all production is trophically linked. The key to all these schemes of species indepen- dent linkages is a complete understanding of whatever criteria are used to group like animals. In the present paper, fish predators have been grouped by species in 5 cm size classes and the diet of each 5 cm length group described quanti- tatively as a percentage weight of the total stom- ach contents for each group. Diet overlap has then been calculated for each species-size class combination and the overlap levels related to actual diet composition. Although diet overlap calculations have their limits (discussed in Lang- ton and Bowman 1980), as do any other methods of data reduction, this paper offers one way of evaluating real and/or potential trophic linkages between northwest Atlantic finfish. METHODS Stomachs were collected from both demersal and pelagic fish by personnel at the Northeast Fisheries Center Woods Hole Laboratory, as part of a multispecies food-habit study conducted from 1973 through 1976. The sampling area cov- ered the continental shelf waters from Cape Hatteras. N.C., to the Canadian coast of Nova Manuscript accepted April 1982. FISHERY BULLETIN: VOL. 80, NO. 4. 1982. 745 FISHERY BULLETIN: VOL. 80, NO. 4 Scotia. Details of this food-habit survey were de- scribed in an International Council for the Ex- ploration of the Sea document and will not be re- peated here (Langton et al. 19803). Diet overlap, expressed as the percentage simi- larity between diets, was calculated according to the formula of Shorygin (Ivlev 1961) and has been described in several other papers as a means of evaluating the diet of northwest Atlan- tic finfish (Langton and Bowman 1980; Grosslein et al. 1980) although there are other methods of indexing like diets (Lipovsky and Simenstad 1978). The calculation is quite simple and is done by summing the smaller value, as a percentage weight in the present case, for all prey shared by the two predators. The computed value ranges from 0 to 100%, with 0% representing no diet overlap and 100% representing identical diets. The final overlap value is sensitive to the taxo- nomic level at which the prey was identified and for this paper the finest taxonomic breakdown available was used, i.e., prey identified to species whenever possible. Because of the sensitivity of this overlap measure to the taxonomic break- down of prey, statistical methods of evaluating absolute overlap values are not practical. Instead, the values have been classified as low, 0-29%; medium, 30-60%; or high, >60% for the purpose of discussion. The computation of diet overlap was auto- mated and the actual computer program checked by running diet overlap for any one predator against itself. In this case the computer gener- ates a value of 100% overlap for fish in the same size class and then a mirror image of values on each side of the 100% line. This is shown graph- ically in Figure 1 where Atlantic cod is plotted three dimensionally versus Atlantic cod. The plotting program only considered size classes up through class 25 (125 cm maximum fork length), but by truncating the output at this level little data was eliminated (a total of 5 cod out of 1,714 examined, for example). In fact, since the fish were taken randomly from the catch, the major- ity of the samples came from the most frequently occurring size classes which, even for Atlantic cod, did not approach this maximum size. Fur- thermore, size classes that did not include a sam- ple size of at least 10 fish were eliminated before the data were plotted since very small samples would not necessarily be representative of the size class. This study concentrates on two of the major fish predators in the northwest Atlantic, silver hake and Atlantic cod, and on the questions of their diet overlaps with 15 other finfish species. The food habits information presented is limited to an explanation of the prey shared by the preda- tors which results in the observed overlap values. Detailed descriptions of the diet of the fish col- lected by the Northeast Fisheries Center are in preparation or have been given elsewhere. Die- tary information on the northwest Atlantic Gadi- formes and Pleuronectiformes can, for example, be found in Langton and Bowman (1980, 1981), Bowman and Bowman (1980), and Durbin et al. (1980)4 while data on fish from other taxa are described in Edwards and Bowman (1979) and Grosslein et al. (1980). RESULTS Atlantic Cod — Little Skate Atlantic cod, Gadus morhua Linnaeus, and lit- tle skate, Raja erinacea Mitchell, show relatively little similarity in diet (Fig. 2A). The maximum value of 48% was found for the overlap between size class 3 (11-15 cm) Atlantic cod and size class 3 little skate. The prey shared by these predators are primarily small crustaceans, in particular amphipods such as Unciola. Unfortunately, slightly more than 10% of the diet of each of these fish was unidentifiable with a resulting increase in the overlap values. As can be seen from Figure 2A, apart from the peak of 48%, medium levels of dietary overlap exist between Atlantic cod 11-20 cm (size classes 3 and 4) and little skate up to 45 cm total length (size class 9). Medium overlap values again occur between little skate 36-55 cm (size classes 8-11) and Atlantic cod 31-65 cm (size classes 7-13). This overlap can generally be at- tributed to the preponderance of a variety of crustaceans in the diet of both predators. For larger Atlantic cod the overlap values with little skate are extremely low, primarily because of a 3Langton, R., B. North, B. Hayden, and R. Bowman. 1980. Fish food habit studies-sampling procedures and data process- ing methods utilized by the Northeast Fisheries Center, Woods Hole Laboratory, U.S.A. Int. Counc. Explor. Sea, CM. 1980/ L:61, 16 p. 4Durbin, E., A. Durbin, R. Langton, R. Bowman, and M. Grosslein. 1980. Analysis of stomach contents of Atlantic cod (Gad us morhua) and silver hake (Merluccius bilinearis) for the estimation of daily rations. Int. Counc. Explor. Sea, CM. 1980/L:60 (revised), 21 p. 746 LANGT0N: DIET OVERLAP BETWEEN SEVENTEEN NORTHWEST ATLANTIC PINKISH VV*C (5 CM LENGTH CLASSES) FIGURE 1.— Three dimensional plot of the diet overlap of Atlantic cod versus Atlantic cod; the same data set. Presented here is an example of the graphics output from diet similarity calculations. The peak represents 100% overlap for the same 5 cm length class of fish with a mirror image of values on either side of the peak. shift in the diet of Atlantic cod from crustaceans to fish. Atlantic Cod — Redfish Atlantic cod and redfish, Sebastes marinus (Linnaeus), generally show low levels of diet overlap (Fig. 2B). There were, however, some medium overlap values occurring between the smaller Atlantic cod and redfish. The peak value of 49% occurred between redfish 16-20 cm (size class 4) and Atlantic cod 6-10 cm (size class 2) which was primarily the result of predation on pandalid shrimp Dichelopandalus leptocerus. Unfortunately, few of the redfish stomachs ex- amined in this size class contained prey (2 out of 21 examined) so this peak may be artificially high, although in the other cases where medium overlap levels were found, pandalid shrimp were generally consumed by both predator species. Atlantic Cod — Longhorn Sculpin The pattern of diet overlap between Atlantic cod and longhorn sculpin, Myoxocephalus octo- decemspinosus (Mitchill), shows low to medium overlap values over much of the size range of both species. The values do decrease, however, between the larger Atlantic cod (>61 cm, size class 13) and smaller longhorn sculpin (<16 cm, size class 3) (Fig. 2C). The peak value of 38% occurred between two different predator size classes, and in both instances the single most im- portant prey contributing to this overlap was the 747 FISHERY BULLETIN: VOL. 80, NO. 4 RAJIFORMES PERCIFORMES 20 15 CM LENGTH CLASSES) FIGURE 2.— Three dimensional plot of the diet overlap of Atlantic cod with selected rajiform and perciform fishes. 748 LANGTON: DIET OVERLAP BETWEEN SEVENTEEN NORTHWEST ATLANTIC EINFISII pandalid shrimp Dichelopandalus leptocerus, although a large variety of other crustaceans contributed to both of the predator's diets. Atlantic Cod — Scup Overlap between the diet of Atlantic cod and scup, Stenotomus chrysops (Linnaeus), is at a low level (Fig. 2D), and the low values represent a broad array of prey, principally crustaceans, that constitutes the forage base of these two predators. The only trend in these values is that they are at their lowest for large Atlantic cod (>80 cm) and all size classes of scup. This is the result of the larger Atlantic cod's piscivorous habits. Atlantic Cod — Butterfish The Atlantic cod and butterfish, Peprilustria- ca nth us (Peck), show very low diet overlap levels, the maximum being 19% for 11-15 cm (size class 3) fish of both species. There was, however, rela- tively more overlap between the smaller Atlantic cod (<45 cm) and all sizes of butterfish sampled (Fig. 2E). Atlantic Cod — White Hake The diet of white hake, Urophycis tenuis (Mitchill), shifts from crustaceans such as eu- phausiids, shrimp, and mysids when they are small (<=50 cm) to primarily fish for the larger white hake. This parallels the change in the Atlantic cod's diet with size. The result is a vary- ing degree of dietary overlap across all size classes of fish examined (Fig. 3A). Low levels occurred between the smaller white hake and the larger size classes of Atlantic cod and vice versa. Intermediate levels, values in the 30-50% range, are found in clusters which are the result of a variety of shared prey types. Some of these val- ues in the 40 and 50% range depend upon the fish components in the diet. In particular, silver hake and herring, Clupea harengus, together with un- identified fish are the most commonly occurring prey that these predators share. The greatest overlaps observed were between 21-25 cm (size class 5) Atlantic cod and several larger size classes of white hake (36-85 cm, size classes 8- 17) (Fig. 3A). This high overlap is somewhat arti- ficial since it is the result of unidentified fish prey in both predators' diets. It does, however, amplify the importance of fish prey to these pred- ators. Atlantic Cod — Red Hake Atlantic cod and red hake, Urophycis chuss (Walbaum), have low to intermediate levels of diet overlap. The lowest values occur between small red hake and large Atlantic cod (Fig. 3B). These small red hake prey quite heavily on crus- taceans while the larger Atlantic cod have shifted their habits from crustacean prey to fish. The diet of red hake does, however, include more fish prey as the predators themselves grow, so that the overlap values between the larger size classes of red hake and Atlantic cod remain at an inter- mediate level. Atlantic Cod — Spotted Hake Atlantic cod and spotted hake, Urophycis regia (Walbaum), have diets which overlap at low to intermediate levels (Fig. 3C). The prey that they have in common is primarily crustaceans but may also include some fish. The cluster of inter- mediate values occurring between 11-25 cm (size classes 3-5) Atlantic cod and 11-30 cm (size classes 3-6) spotted hake is, for example, the re- sult of predation on crustaceans such as Mega- nyctiphanes, Dichelopandalus, Crangon, Unci- ola, and other less significant taxa, while the intermediate overlap peaks between 31-35 cm spotted hake and Atlantic cod are due to fish predation. Atlantic Cod — Pollock Atlantic cod and pollock, Pollachius rirens (Linnaeus), show low to intermediate levels of d iet overlap over all size classes of both predators examined. Both of these species are crustacean/ fish predators, relying more heavily on fish as they increase in size. For the smaller pollock, the euphausiid Meganyctiphanes norvegica and the shrimp Pasiphaea multidentata were the major components of the diet while the Atlantic cod re- lied on a much broader variety of prey. For the larger fish of both species a variety of pisces were included in the diet, some of which was not read- ily identifiable at any lower level than simply fish flesh. The problem in identifying fish re- mains generated two artificial peaks in overlap 749 FISHERY BULLETIN: VOL. 80, NO. 4 GADIFORMES 15 CM. LENGTH CLASSES) Figure 3.— Three dimensional plot of the diet overlap of Atlantic cod with selected gadiform fishes. 750 LANOTON: DIET OVERLAP BETWEEN SEVENTEEN NORTHWEST ATLANTIC FINEISH between Atlantic cod of size class 5 and pollock of size classes 10 and 14 as seen in Figure 3D. Atlantic Cod — Haddock Haddock, Melanogrammus aeglefinus (Lin- naeus), is primarily benthic in its feeding habits with the result that its diet is similar to Atlantic cod's only when the Atlantic cod are also feeding on the benthos. Consequently, the degree of diet overlap between these two predators is highest for the smaller animals, as can be seen in Figure 3E. The diversity of prey that both these preda- tors consume reduces the computed overlap val- ues. The relatively low maximum values, 47% being the highest for 16-20 cm (size class 4) Atlan- tic cod and 11-15 cm (size class 3) haddock, make it difficult to identify any particular species of prey that gives rise to the observed intermediate levels of overlap. Atlantic Cod — Ocean Pout Ocean pout, Macrozoarces a mericanus( Schnei- der), are fairly specific in their predatory habits, and these habits do not overlap with those of Atlantic cod to any extent (Fig. 3F). A single prey species, the sand dollar, Echinarachnius pa rma, accounts for most of the diet of ocean pout although amphipods were also present in many of the fish stomachs examined. Atlantic Cod — American Plaice The diets of Atlantic cod and American plaice, Hippoglossoides platessoides (Fabricius), over- lap at. quite low levels, the highest value being 33% for 26-30 cm (size class 6) Atlantic cod and 21-25 cm (size class 5) American plaice. Ameri- can plaice prey on a variety of benthic animals but, as they grow larger, they rely more on echin- oderms than crustaceans and polychaetes. This is reflected in the diet overlap plot (Fig. 4A); the larger size classes of American plaice (>45 cm) have extremely small overlap with Atlantic cod because of predation on the sand dollar. Atlantic Cod — Witch Flounder Little diet overlap occurs between Atlantic cod and witch flounder, Glyptocephalus eynoglossus (Linnaeus), with all of the calculated values be- ing 30% or less (Fig. 4B). Witch flounder are benthic predators with polychaete worms being of major importance as prey although they do consume crustaceans and other invertebrates. It is the crustacean component of the diet which accounts for these low levels of overlap with the Atlantic cod. Atlantic Cod — Yellowtail Flounder The diets of Atlantic cod and yellowtail floun- der, Limanda ferruginea (Storer), overlap at generally low levels (Fig. 4C). There is only one cluster of intermediate levels involving yellow- tail flounder from a single size class (class 3, 11- 15 cm) which reflects the occurrence of pandalid shrimp Dichelopandalus leptocerus in both pred- ators' diets. As with many other species, a reduc- tion in the level of overlap occurs as the disparity in fish size increases. For yellowtail flounder this is quite apparent when compared with the larger Atlantic cod because the large Atlantic cod are primarily piscivorous. However, this reduction is not as noticeable for large yellowtail flounder and small Atlantic cod since the benthic habits of yellowtail flounder change little as the fish in- crease in size. Atlantic Cod — Fourspot Flounder Atlantic cod and fourspot flounder, Paralich- thys oblongus (Mitchill), show low and intermedi- ate levels of diet overlap (Fig. 4D) which is pri- marily a result of predation on crustaceans. The single most important crustacean prey was the pandalid shrimp Dichelopandalus leptocerus which makes up from 17% to 30% of the diet of 21- 30 cm fourspot flounder and 3% to 40% of the diet of 6-45 cm Atlantic cod. Silver Hake — Little Skate The pattern of diet overlap between silver hake, Merluccius bilinearis (Mitchill), and little skate is shown in Figure 5A. Generally, overlap levels are low but medium levels range up to a high of 44% between small silver hake 1-15 cm (size classes 1-3) and little skate 11-45 cm total length (size classes 3-9). This degree of overlap can be attributed to the crustaceans in each of these predators' diets with the sand shrimp, Crangon septemspinosa, being of particular im- portance. For larger silver hake the diet overlap with little skate is insignificant since these larger hake prey on fish while little skate of all sizes prey primarily on benthic crustaceans. 751 FISHERY BULLETIN: VOL. 80, NO. 4 PLEURONECTIFORMES 20 15 CM LENGTH CLASSES) Figure 4.— Three dimensional plot of the diet overlap of Atlantic cod with selected pleuronectiform fishes. Silver Hake — Redfish High levels of overlap occur between 16-20 cm (size class 4) silver hake and 11-45 cm (size classes 3-9) redfish (Fig. 5B). The peak value is 75% for 31-35 cm (size class 7) redfish and these smaller silver hake. Most of this overlap is due to predation on the euphausiid Meganyctiphanes norvegica, which accounted for 60% and 63% of the diet of these 16-20 cm silver hake and 31-35 cm redfish, respectively. The other high overlap values between these two predators can also be attributed to euphausiids making up more than 50% of the diets. Medium levels of overlap, 30- 42%, were found for other size silver hake and redfish. Once again Meganyctiphanes norvegica was a major dietary item but in some cases Di- chelopandalus leptocerus also contributed sig- nificantly. For the larger silver hake (>35 cm, greater than size class 7) there was little, if any, diet overlap. These large silver hake prey heavily on fish while redfish are predominantly crusta- cean predators. Silver Hake — Longhorn Sculpin Intermediate diet overlap values occur be- tween silver hake ranging from 6 to 15 cm in length (size classes 2-3) and most of the size classes of longhorn sculpins examined (Fig. 5C). This overlap is due to both predators' reliance on crustaceans such as Crangon septemspinosa, Dichelopandalus leptocerus, and Neomysis amer- icana. For the larger silver hake, those that are primarily piscivorous, there is virtually no over- 752 LANGTON: DIET OVERLAP BETWEEN SEVENTEEN NORTHWEST ATLANTIC FINFISH RAJIFORMES PERCIFORMES (B) $**«** (5 CM LENGTH CLASSES) Figure 5.— Three dimensional plot of the diet overlap of silver hake with selected rajiform and perciform fishes. 753 FISHERY BULLETIN: VOL. 80. NO: 4 lap or, at least, extremely low levels of overlap with longhorn sculpin. Silver Hake — Scup Silver hake and scup both prey on crustaceans, but they share few prey species in common so that diet overlap values are quite low (Fig. 5D). There is a trend for the overlap values to decrease when comparing larger silver hake and scup which mirrors the shift towards fish predation by these larger silver hake. Silver Hake — Butterfish The diets of silver hake and butterfish overlap at very low levels, the highest value being 17% which was the result of predation on the squid Loligo (Fig. 5E). Generally, the butterfish is more planktonic in its predatory habits than the silver hake which is reflected in the low overlap values. Silver Hake — Atlantic Cod Silver hake and Atlantic cod are generally found to have low to intermediate levels of diet overlap and very few values that are >60% (Fig. 6A). All of the high values are the result of un- identified fish remains forcing up the computed overlap values. Both of these predators become more piscivorous as they grow larger, but this size-specific dietary shift is not reflected in an obvious change in the level of diet overlap. In other words, the smaller fish share crustacean prey species such as euphausiids while the larger predators both prey on a number of different spe- cies of fish. Silver Hake — White Hake There is a clear pattern of overlap when com- paring the diets of silver and white hake (Fig. 6B). The diets of the larger fish of both species do not overlap with the smaller fish of the opposite species. In other words, the diet of small silver hake has little in common with the larger white hake and vice versa. The explanation for this is a size dependent change in diet for both predators. When small, they both rely on crustaceans, such as euphausiids, and then gradually shift to fish as the predator grows. For example, the high value, 74% between 16-20 cm (size class 4) silver hake and 31-35 cm (size class 7) white hake results from over 50% of either of these predators feed- ing on Meganyctiphanes norvegica. For compari- son, the other high value, 75%, for 41-45 cm (size class 9) silver hake and 66-70 cm (size class 14) white hake, is the result of fish predation on such fish as silver hake, clupeids, and other unidenti- fiable fish remains. Silver Hake — Red Hake The diet overlap between silver and red hake ranges from 0% to intermediate levels as high as 56%. The general pattern is increasing overlap with increasing predator size up to 26-30 cm (size class 6) and then leveling off or decreasing slight- ly between the larger fish (Fig. 6C). The peak value, occurring between 26-30 cm silver hake and 41-45 cm (size class 9) red hake, can be ex- plained by predation on fish, Die he lop and al us leptoeerus, and other invertebrates. Silver Hake — Spotted Hake Silver and spotted hake show, for the most part, intermediate to high levels of diet overlap between similar size fish (Fig. 6D). Peak values of 60% and 70% occur, for example, between 11- 20 cm (size classes 3-4) and 16-25 cm (size classes 4-5) silver and spotted hake, respectively. These peaks are the result of a reliance by both preda- tors on Meganyctiphanes norvegica, Dichelopan- dalus leptoeerus, and Crangon septemspinosa. The intermediate overlap values are also, how- ever, a reflection of predation on fish, especially for the larger silver and spotted hake. Silver Hake — Pollock High diet overlap values exist between silver hake 16-20 cm (size class 4) and pollock 16-65 cm (size classes 4-13). Two prey categories are re- sponsible for these high levels, Meganyctiphanes norvegica and unidentified fish remains. Medi- um levels of overlap between these two predators are common for most size classes except for silver hake below 10 cm. Overlap between these small- er silver hake and all sizes of pollock falls into the lower overlap category. There are also extremely low values between small pollock and large sil- ver hake (Fig. 6E). Silver Hake — Haddock Silver hake and haddock show little similarity in their diets and the resulting diet overlap val- 754 LANOTON: DIET OVERLAP BETWEEN SEVENTEEN NORTHWEST ATLANTIC PINKISH GADIFORMES (A) FIGURE (L— Three dimensional plot of the diet overlap of silver hake and selected gadiform fishes. Poui 15 CM LENGTH CLRSSES) 755 FISHERY BULLETIN: VOL. 80, NO. 4 ues are all quite low (Fig. 6F). Even with these low values, there is an obvious trend; the higher values occur between the smaller individuals of these two predators which reflects the depen- dance of small silver hake and haddock on crus- tacean prey. Silver Hake — Ocean Pout The diets of silver hake and ocean pout are mutually exclusive so that there is an extremely small degree of diet overlap (Fig. 6G). The only prey that they share in common are amphipods, but again, this is at a very low level. Silver Hake — American Plaice Silver hake and American plaice show very low levels of dietary overlap (Fig. 7A). Despite the lack of diet similarity, a pattern does emerge when comparing these two predators. The larger size classes of both species show virtually no over- lap, while what similarity does exist occurs be- tween silver hake and American plaice <40 cm. The diet of these larger individuals is quite spe- cific, fish for silver hake and echinoderms for American plaice, so little overlap is to be ex- pected, while the smaller individuals of both spe- cies prey on invertebrates. Silver Hake — Witch Flounder Silver hake and witch flounder share little prey in common with resulting low levels of diet overlap. The only exception to these low levels is a high peak (66% and 67%) between 16-20 cm (size class 4) silver hake and 11 -20 cm (size classes 3-4) witch flounder (Fig. 7B). A single prey species, PLEURONECTIFORMES fV-OU* 15 CM LENGTH CLASSES) Figure 7.— Three dimensional plot of silver hake and selected pleuronectiform fishes. 756 LANGTON: DIET OVERLAP BETWEEN SEVENTEEN NORTHWEST ATLANTIC FINFISH Meganyctiphanes norvegica, is responsible for this since it alone accounts for >63% of each pred- ator's diet. Similarly, the smaller peaks in the figure are also the result of having euphausiids as a common prey item. Silver Hake — Yellowtail Flounder Silver hake and yellowtail flounder have, for the most part, low levels of dietoverlap (Fig. 7C). The few intermediate levels that do occur are, in all but one instance, related to yellowtail floun- der that are 11-15 cm in length (size class 3) which have preyed on Crangon septemspinosa, Diehelopandalus leptocerus, or small unidenti- fied fish. The one exception is for 6-10 cm (size class 2) yellowtail flounder and silver hake. These fish preyed primarily on Crangon septem- spinosa, Neomysis americana, and amphipods with a resulting diet overlap of 39%. Even with these low overlap levels an overall pattern is apparent; the greatest overlap occurs between the smaller size classes of both species. Silver Hake — Fourspot Flounder The diets of silver hake and fourspot flounder overlap at low to intermediate levels (Fig. 7D). The highest value, 54%, occurs between 6-10 cm (size class 2) silver hake and 16-20 cm (size class 4) fourspot flounder. The peak, as with most of the other intermediate values, is the result of predation on crustaceans such as Crangon sep- temspinosa, Neomysis americana, and Diehelo- pandalus leptocerus. DISCUSSION The diet overlap comparisons presented here are one way to simplify fish food habits data and to identify real or, at least, potential pathways of energy exchange. As with any method of data re- duction, however, certain compromises have to be accepted which must be kept in mind when discussing the results. The limitations of per- centage similarity calculations have been de- scribed by several authors (Day and Pearcy 1968; Moyle 1977; Keast 1977; Langtonand Bow- man 1980; MacPherson 1981)and these limits in- clude both biotic and abiotic factors. Such factors as the taxonomic level of prey identification, the actual quantity of prey consumed (especially since percentage similarity is a relative measure of dietary constituents), predator/prey distribu- tion and abundance, and temporal factors that influence both predator and prey behavior all have to be considered in evaluating the meaning of diet overlap data. The present data consider the entire northwest Atlantic as a single homogeneous ecological sys- tem since all the available data were grouped by species for the diet overlap calculations. This is a first attempt to examine size-specific finfish predation in the northwest Atlantic and, without more extensive basic biological information on finfish and invertebrate community structure, there was no reason to subdivide the data set. The research survey cruises on which the fish stom- achs were collected were, however, planned for discrete geographic regions (e.g., Gulf of Maine, Georges Bank) and employed stratified random sampling based primarily on depth dependent strata (Grosslein 1969; Clark and Brown 1977). If the research survey catch data were analyzed statistically, using techniques such as cluster analysis, to identify fish species associations or assemblages, then there may be justification for subdividing the data set. Such methods have been utilized recently to identify northwest Pa- cific finfish assemblages (Gabriel and Tyler 1980; Tyler et al. in press) and have been used, to a limited degree, for northwest Atlantic fishes (Tyler 1972, 1974; Knight and Tyler 1973). What- ever techniques are employed the basic problem is the same: defining what constitutes an eco- logically homogeneous system. From the figures presented, it is clear that completely dissimilar diets occur very rarely. This raises the question of the significance of diet overlap and whether such measures are indica- tive of resource competition. The limits of diet overlap calculations have been dealt with briefly above and the significance of any given numeri- cal value for diet overlap has also been men- tioned. Diet overlap has some value as an indi- cator of potential energy flow pathways but it is not an absolute measure of trophic linkages. The overlap values are obviously indicators of co- existence rather than competition, especially since overlap values have been observed to de- crease rather than increase when resources are limited (Zaret and Rand 1971; Keast 1978; Mac- Pherson 1981). The ideas of competition versus coexistence have been considered for gadoid fishes by Jones (1978). Jones pointed out some of the more subtle distinctions between the diets of three gadoid species which, on cursory examina- tion, appear to overlap. For example, although 757 FISHERY BULLETIN: VOL. 80, NO. 4 both haddock and Atlantic cod from the same trawl haul preyed on juvenile Sebastes, they were preying on different-sized juveniles and, in gen- eral, Jones observed that Atlantic cod tended to consume larger prey than haddock of the same size. This type of detailed stomach contents anal- ysis, together with observations on fish feeding behavior in the laboratory and in situ, is the type of biological information necessary for accu- rately defining what constitutes an ecologically homogeneous system, or, more importantly, an energetically coupled unit within the system. There are some general patterns to the overlap values which may indicate real, or at least poten- tial, trophic linkages. In comparing Atlantic cod with six other gadids, for example, the overlap levels generally are at their lowest between the larger cod (greater than size class 10, >50 cm) and the smaller size classes of the other preda- tors (Fig. 3). This reflects the shift in the Atlantic cod's feeding habits from being primarily a crus- tacean predator to a piscivore with an increase in body size. In effect, Atlantic cod occupy differ- ent, size-specific, feeding niches which corre- spond to these other predators only when both species are small and more dependent on crusta- cean prey. For silver hake (Fig. 6) the pattern is similar but silver hake are a smaller fish than Atlantic cod and switch to a piscivorous habit at a smaller size. In addition to this pattern, there is also a noticeable shift in overlap between silver hake, the three other hake species, and pollock. The overlap with the smaller size classes of silver hake is low or even decreases slightly as the four other gadid species increase in size. Conversely, overlap is highest for the larger silver hake and these four gadids. This is a result of predation on many different species of crustaceans by all these predators and a shift towards fish preda- tion as they grow. In comparing both Atlantic cod and silver hake with the one rajiform and the four perci- form fish species, the overall pattern of diet over- lap is the same. The larger Atlantic cod and silver hake show a decreasing level of overlap with the smaller size classes of these other finfish preda- tors (Figs. 2, 5). Atlantic cod and silver hake do not show a similar pattern of diet overlap when compared with the four pleuronectiform species of finfish (Figs. 4, 7). With the three pleuronectid species (Fig. 4A-C) the highest levels of overlap with Atlantic cod occur between the smaller size classes of all three species while the lowest levels occur between the larger size classes. This is similar to changes in overlap observed for the perciform species. For the one bothid (Fig. 4D) a size-dependent shift in overlap is not readily apparent. The overlap values for silver hake and flatfishes are at a maximum, albeit low overall, for the smaller individuals of the three pleuro- nectids (Fig. 7A-C) but, like the Atlantic cod, are fairly constant over all size classes of the one bothid species examined (Fig. 7D). This pattern of diet overlap with the pleuronectids may be at- tributed to the crustacean/fish shift in diet for the Atlantic cod and silver hake, and either little change in the flatfish diet or, as with American plaice, a change in diet to one that does not in- clude much, if any, fish prey. Atlantic cod and silver hake are crustacean/ fish predators with a size-dependent shift in predation from crustaceans to fish as these pred- ators grow. In the present data the shift to fish predation for Atlantic cod occurs at about 60-70 cm and for silver hake at about 20-25 cm. These sizes are not absolute and depend very much on the availability of prey. Daan (1973), for exam- ple, observed a difference in North Sea cod feed- ing habits when comparing samples from the northern and southern North Sea. Crustaceans predominated in the stomachs of the larger speci- mens from the southern region while their northern counterparts had already shifted over to a piscivorous habit. In the northwest Atlantic a similar, but less obvious, shift was observed in the diet of cod when compared over a 10-yr peri- od (Grosslein et al. 1980). When the finfish bio- mass was low (1973-76 vs. 1963-66), crustaceans were slightly more important as prey although the general impression resulting from studying the two data sets was a fairly constant pattern of predation over time. The diets of Atlantic cod, and presumably most of these other predators, are fairly stable although there is an apparent degree of fine tuning that depends upon the avail- ability of prey and other controlling factors in the environment. In summary, assuming that the diets of Atlan- tic cod and silver hake are reasonably stable over time, and that the same is true for the 15 other predators examined, then the pattern of overlap described above suggests that the greatest over- all potential for interaction exists between the smaller stages of the two gadids and the other predators. Furthermore, the greatest overlap, with few exceptions, occurs among the gadiform fishes themselves rather than between the gadids and the other ordinal taxonomic levels. 758 LANGTON: DIKT OVERLAP BETWEEN SEVENTEEN NORTHWEST ATLANTIC EINFISH This observation may not only be reassuring to the taxonomist but is also of significance to fish- ery biologists in their attempts to identify eco- logical units. It suggests that future food habit studies should be directed towards the juvenile, or at least smaller, stages of closely related spe- cies if the goal is to understand how finfish co- exist by partitioning food resources in the marine environment. ACKNOWLEDGMENTS My sincerest thanks go to the people who helped generate the diet overlap data described in this paper: Bill Freund, Woods Hole Oceanographic Institution, wrote the computer program that automated the diet overlap calculations; Jacki Murray and John Hauser, Northeast Fisheries Center, modified the program and generated most of the data; Jean Garside and Margaret Hunter, Department of Marine Resources, devel- oped the three dimensional plotting program and generated the figures for the paper. LITERATURE CITED Bowman, R. E., and E. W. Bowman. 1980. Diurnal variation in the feeding intensity and catchability of silver hake (Merluccius bilinearis). Can. J. Fish. Aquat. Sci. 37:1565-1572. Clark, S. H., and B. E. Brown. 1977. Changes in biomass of finfishes and squids from the Gulf of Maine to Cape Hatteras, 1973-74, as deter- mined from research vessel survey data. Fish. Bull., U.S. 75:1-21. Daan, N. 1973. A quantitative analysis of the food intake of North Sea cod, Gadus morhua. Neth. J. Sea Res. 6:479-517. Day. D. S., and W. G. Pearcy. 1968. Species associations of benthic fishes on the conti- nental shelf and slope off Oregon. J. Fish. Res. Board Can. 25:2665-2675. DeGroot, S. J. 1971. On the interrelationships between morphology of the alimentary tract, food and feeding behaviour in flat- fishes (Pisces: Pleuronectiformes). Neth. J. Sea Res. 5: 121-196. Edwards, R. L., and R. E. Bowman. 1979. Food consumed by continental shelf fishes. In H. Clepper (editor), Predator-prey systems in fisheries management, p. 387-406. Sport Fishing Inst, Wash., D.C. Gabriel, W. L., and A. V. Tyler. 1980. Preliminary analysis of Pacific coast demersal fish assemblages. Mar. Fish. Rev. 42(3-4):83-88. Grosslein, M. D. 1969. Groundfish survey program of BCF Woods Hole. Commer. Fish. Rev. 31(8-91:22-30. Grosslein, M. D., R. W. Langton, and M. P. Sissenwine. 1980. Recent fluctuations in pelagic fish stocks of the Northwest Atlantic, Georges Bank region, in relation to species interactions. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 177:374-404. IVLEV, V. S. 1961. Experimental ecology of the feeding of fishes. Yale Univ. Press, New Haven, 302 p. Jones, R. 1978. Competition and co-existence with particular ref- erence to gadoid fish species. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 172:292-300. KEAST, A. 1977. Diet overlaps and feeding relationships between the year classes in the yellow perch (Perca flavescens). Environ. Biol. Fishes 2:53-70. 1978. Trophic and spatial interrelationships in the fish species of an Ontario temperate lake. Environ. Biol. Fishes 3(1):7-31. Knight, W., and A. V. Tyler. 1973. A method for compression of species association data by using habitat preferences, including an analysis of fish assemblages on the southwest Scotian Shelf. Fish. Res. Board Can. Tech. Rep. 402, 15 p. Langton, R. W., and R. E. Bowman. 1980. Food of fifteen northwest Atlantic gadiform fishes. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF- 740, 23 p. 1981. Food of eight northwest Atlantic pleuronectiform fishes. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-749, 16 p. Lipovsky, S. J., and C. A. Simenstad (editors). 1978. "Gutshop 78" fish food habits studies. Proceed- ings of the Second Pacific Northwest Technical Work- shop, 222 p. Washington Sea Grant Publication, Divi- sion of Marine Resources, University of Washington, Seattle, WA 98195. MacPherson, E. 1981. Resource partitioning in a Mediterranean demer- sal fish community. Mar. Ecol. Prog. Ser. 4:183-193. Moyle, P. B. 1977. In defense of sculpins. Fisheries (Bethesda) 2: 20-23. Paloheimo, J. E., and L. M. Dickie. 1965. Food and growth of fishes. I. A growth curve de- rived from experimental data. J. Fish. Res. Board Can. 22:521-542. Parker, R. R., and P. A. Larkin. 1959. A concept of growth in fishes. J. Fish. Res. Board Can. 16:721-745. Tyler. A. V. 1972. Food resource division among northern marine, demersal fishes. J. Fish. Res. Board Can. 29:997-1003. 1974. Community analysis. In R. O. Brinkhurst. Chap- ter 5, The benthos of lakes, p. 65-84. St. Martin's Press, Inc., N.Y. Tyler, A. V., W. L. Gabriel, and W. J. Overholtz. In press. Adaptive management based on structure of fish assemblages of northern continental shelves. Can. J. Fish. Aquat. Sci. Ursin, E. 1973. On the prey size preference of cod and dab. Dan- nish Inst. Fish. Mar. Res. 7:85-98. Zaret. T. M., and A. S. Rand. 1971. Competition in tropical stream fishes: support for the competitive exclusion principle. Ecology 52:336- 342. 759 THE RELATIONSHIP OF WINTER TEMPERATURE AND SPRING LANDINGS OF PINK SHRIMP, PENAEUS DUORARUM, IN NORTH CAROLINA1 William F. Hettler and Alexander J. Chester2 ABSTRACT Spring landings of pink shrimp in North Carolina were highly correlated with water temperature during the previous winter. The strongest relation was found between landings and the average water temperature of the two coldest consecutive weeks of each year ( r2 = 0.82). Following the cold winters of 1977, 1978, 1980, and 1981, when temperatures averaged below 5°C, landings were <160,000 kg. Following the warm winters of 1965, 1974, and 1975, when temperatures averaged above 8°C, landings were >450,000 kg. Changes in water temperature through the year were de- scribed by a sine-cosine curve in which minimum temperatures generally occurred during the 5th week and maximum temperatures occurred during the 31st week of the year. Weekly mean air temperatures were linearly related to water temperatures (r2 = 0.97) over the entire range of data, but they were not useful as proxy data for predicting pink shrimp landings (r2 - 0.50) because the air-water relation was more variable at low temperature. Local rainfall did not have a significant effect on shrimp landings. Temperature is a critical environmental factor influencing metabolism, growth, reproduction, distribution, and survival of animals (Kinne 1963). Local abundance may be affected by mi- gration or death in response to extreme devia- tions from temperatures to which the animal is adapted. The effect of such temperature ex- tremes is expected to be more severe for a popu- lation at the limit of its geographic range, par- ticularly when temperature is known to be a factor limiting north-south distribution (Wil- liams 1969a). For species whose life cycle is completed in 1 yr, or in fisheries where reliance on annual re- cruitment is heavy (Loucks and Sutcliffe 1978), temperature records may be useful as a predic- tor of landings. A cause-and-effect relationship between harvest and temperature may be more obvious for species with one year class than for long-lived species whose landings are compli- cated by multiple year-class contributions (Nor- cross and Austin 1981). Penaeid shrimp, which have an annual life cycle, have no significant con- tribution from other year classes to compensate for a reduction in biomass caused by unfavorable temperatures. 'Contribution No. 82- 12B of the Southeast Fisheries Center, National Marine Fisheries Service, NOAA. Southeast Fisheries Center Beaufort Laboratory, National Marine Fisheries Service. NOAA, Beaufort, NC 28516-9722. Shrimp mortality in the southeast United States due to cold has been reported by Gunter and Hildebrand (1951), Lindner and Anderson (1956), and Lunz (1958). Of the three species of Penaeus that occur in North Carolina waters, only pink shrimp, Penaeus duorarum Burken- road, overwinter in shallow estuaries (Williams 1955a) and, therefore, would be more likely to suffer from abnormally cold winter tempera- tures than either brown shrimp, P. aztecus, or white shrimp, P. setiferus. Pink shrimp have an annual life cycle in which the adults spawn off- shore during early summer and postlarvae and juveniles utilize the estuaries, where several en- vironmental factors can affect distribution and survival. These factors include temperature, sa- linity, substrate, debris cover, and seagrass spe- cies and density (Costello and Allen 1970; Grady 1971; Gunter 1950, 1961; Williams 1955a, 1958, 1969b). Peak recruitment of postlarvae into North Carolina estuaries occurs from July to September (Williams 1969b). Juveniles that overwinter in the estuary migrate towards the sea as adults, primarily in May and June, and be- come the object of a trawl and channel net fishery located in the mouth of the Neuse River, south- western Pamlico Sound, Core Sound, Bogue Sound, and in the ocean between Beaufort Inlet and Bogue Inlet (Williams 1955b). The primary purpose of this study was to in- vestigate the relationship between winter tern- Manuscript accepted March 1982. FISHERY BULLETIN: VOL. 80. NO. 4. 1982. 761 FISHERY BULLETIN: VOL. 80, NO. 4 peratures and spring landings of pink shrimp in North Carolina to determine if temperature could be used as a predictor of landings. Several recent harsh winters (Diaz and Quayle 1980; Ingham 1979) provided an opportunity to com- pare landings over a range of temperatures. This relationship may serve to focus attention on the importance of temperature extremes in under- standing ecosystem productivity. We also ana- lyzed available water and air temperatures to model the annual temperature in the lower New- port River estuary, to compare the weekly mean temperatures of each year with the annual model, and to test the use of air temperature as proxy data for periods when no water temperatures were available. Finally, we examined the effect of local winter rainfall on pink shrimp landings. METHODS Temperature records were analyzed from the Newport River estuary, which is centrally lo- cated within the North Carolina pink shrimp nursery and fishing grounds, the "Carteret- Onslow Area" of Williams (1955b) (Fig. 1). This estuary, had been the site of several studies con- ducted by our laboratory during which tempera- tures were routinely monitored at one or more locations, but the entire time-series of tempera- ture records had not been analyzed. Seawater temperatures were obtained from recordings made at Pivers Island near Beaufort, N.C., at the mouth of the Newport River estuary beginning in 1962. From 1962 until 1968, rec- ords were kept on the island's north channel, and from 1968 to the present, records were kept on the east channel. These locations are <400 m apart. From 1968 to mid-1974, continuous rec- ords either were not kept or were inadvertently lost. Thus, complete continuity from 1962 to 1981 was not possible. Seawater temperature was recorded continu- ously on 7-d circular charts. Recordings since 1974 were calibrated (±0.1°C) with a precision mercury thermometer. The accuracy and preci- sion of pre-1974 records could not be determined. Weekly means from 1962 to mid-1974 were cal- culated by averaging hourly readings during each 7-d cycle. Weekly means from mid-1974 to 1981 were calculated by using a compensating polar planimeter. The planimeter method per- mitted rapid integration of the entire weekly temperature record into a single temperature by converting the mean radius of the area encom- passed by the temperature cycle to the equiva- lent weekly mean temperature. Daily air temperatures and monthly precipita- tion totals were recorded at the National Weather Service observation station in Morehead City, N.C., 6.2 km west of Pivers Island, and were pub- CORE SOUND PIVERS ISLAND v Q< GUE OUN .»\^ 77° OO'W h Figure 1. — Pink shrimp nursery area (indicated by hatched lines). Pivers Island was point-source of water tem- perature data. 762 HETTLER and CHESTER: WINTER TEMPERATURE AND SPRING LANDINGS OF PINK SHRIMP lished by NOAA Environmental Data and Infor- mation Service, National Climatic Center, Ashe- ville, N.C. Weekly mean air temperatures were calculated by averaging daily maximum and minimum records. Rainfall records for Decem- ber, January, and February were totalled for each winter. The commercial landings of pink shrimp (kilo- grams of abdomens) were obtained from records published by the U.S. Department of Commerce (North Carolina Shrimp Landings, Current Fisheries Statistics series) (Table 1). Landings from late winter through July of each year com- prised the portion of the fishery considered by our hypothesis to be influenced by severe over- wintering conditions, primarily extensive peri- ods of low temperatures and, possibly, reduced salinities. Landings after July were excluded be- cause, in late summer, size and weight decreased, reflecting recruitment of postwinter juveniles into the estuary. RESULTS AND DISCUSSION Annual Temperature Cycle in the Newport River Estuary Weekly mean water temperatures in the New- port River estuary displayed a basically sinus- oidal annual pattern (Fig. 2). Actually there ap- peared to be a slight distortion in the seasonal sine relationship whereby vernal warming pro- ceeded at a slower rate than autumnal cooling. Available data from 1962 to 1981 were used to mathematically define the annual temperature cycle according to the following least-squares, multiple regression equation: Tw = a + bi SIN 2jrW 52 + b2 COS 2jtW 52 where Tw was the mean weekly temperature for week W, a was an intercept reflecting the overall average yearly temperature, and b\ and b2 were regression coefficients controlling the timing and amplitude of annual minimum and maxi- mum temperatures. The derived equation (Fig. 2) was an adequate representation of the annual cycle of tempera- ture in the Newport River estuary (R2 = 0.93) and helped illustrate several aspects of the plotted data. Minimum temperatures tended to occur during the 5th week of the year (early February); maximum temperatures occurred during the 31st week (mid-August). Winter temperatures were characterized by greater week-to-week variability than summer temperatures. In gen- eral, the fitted curve consistently overestimated winter temperatures. This trend arose from an apparent asymmetry of the minimum and maxi- mum temperatures about the yearly mean. That Table 1.— Landings of pink shrimp in North Carolina compared with various combinations of winter water temperature data collected at Pivers Island, N.C, and air temperature and rainfall data collected at Morehead City, N.C. Air temperature biweekly periods corre- sponded with the coldest two consecutive weeks used for water temperature. Landings Average water temperature (°C) Average coldest Coldest Total Feb -July two con- biweekly rainfall (kg, heads Coldest secutive air temp. (cm, Dec - Year off) Dec -Mar Jan. -Feb week weeks <°C) Feb.) 1962 365,390 8.5 8.1 6.2 7.0 8.5 203 1963 70,237 7.5 7.0 5.9 6.0 5.5 34.4 1964 274,298 8.1 8.3 6.1 6.2 3.2 39.7 1965 452,246 9.9 9.7 7.1 8.4 — 18.0 1966 150,080 9.0 8.2 4.3 5.2 2.9 27.2 1967 387,773 9.0 89 69 7.6 8.9 33.7 1968 266,781 — — — — — 27.7 1969 321,693 — — — — — 21.2 1970 91.968 — — — — — 32.8 1971 353,767 — — — — — 31.7 1972 205,667 — — — — — 41.1 1973 330,455 97 8.7 4.7 56 3.6 35.5 1974 518,670 12.1 126 79 91 8.8 493 1975 497,163 11.6 11.6 10.2 10.6 8.4 34.7 1976 367.671 10.6 9.6 6.0 7.6 4.4 26.7 1977 13.272 6.4 4.9 2.8 3.1 1.0 28.2 1978 15,567 6.9 6.2 35 3.8 4.6 37.8 1979 293.432 8.8 7.6 5.6 5.6 3.8 47.6 1980 157,781 8.4 8.2 38 48 4.8 29.9 1981 134,626 78 7.0 3.7 4.9 2.8 36.7 r2 0790 0.804 0.720 0.822 050 0.003 763 FISHERY BULLETIN: VOL. 80, NO. 4 30i- O o UJ tr g 20 < tr UJ Q. UJ DC UJ < 10- / \* 4C • /• \ 7 1* J \ • / \* / #\ / \ # £/ \ • \ • • \ * / • \*» / • • • \ • • J* • Va •/ / I* /* \ * \ • • 1969 1970 1971 1972 ' 1973 1974 1975 | | J_ _L i I I 30r- YEARS Figure 2.— Newport River estuary (Pivers Island) weekly mean water temperatures. Fitted line represents the least squares /2ttW\ / 2nW\ determined equation: Th = a + b\ sin I I + o2 cos I J, where Tie is the mean weekly temperature for week W, a = 17.88, 61 = -5.20, and 62 = -7.94 (R2 = 0.93). 764 HETTLER and CHESTER: WINTER TEMPERATURE AND SPRING LANDINGS OF PINK SHRIMP is, winter lows were displaced farther from the mean than were summer highs. As a group the years 1962-67 were cooler in the summer and warmer in the winter than 1974-81. Lower temperatures during cold months re- flected a series of very cold winters in the mid- 1970s (Diaz and Quayle 1980). An analysis of covariance showed that the average yearly tem- perature of the 1962-67 year group was signifi- cantly different (P<0.05) from the 1974-81 group. Either a systematic calibration bias was introduced by different observers, thermo- graphs, and recording locations, or tempera- tures were actually more extreme in the latter year group. Calibration bias does not satisfac- torily explain how both high and low tempera- ture extremes could occur, but a climate phe- nomenon can be cited. According to R. G. Quayle, NOAA National Climatic Center, Asheville, N.C., the 1962-67 winters were less variable in daily temperature means than the 1973-81 win- ters. For example, the January and February monthly mean air temperatures at Wilmington, N.C., and Cape Hatteras, N.C., were not differ- ent between the two year-groups, but the stan- dard deviations of the monthly means were sig- nificantly different at both stations between year-groups (Table 2). Thus, our recorded de- pressions in weekly winter temperatures in the 1973-81 group probably reflect more extreme actual fluctuations. Table 2. — Comparison of means and standard devia- tions of January and February air temperatures at two North Carolina coastal stations for year-groups 1962-67 and 1973-81. Air temperature (°C) Year- Wilmington Cape Hatteras group X SD X SD 1962-67 Jan. 7.67 1.51 7.56 1.17 Feb. 8.44 1.73 7.06 1.16 1973-81 Jan. 7.94 3.74 7.61 3.26 Feb. 8.00 3.10 6.83 3.20 Air- Water Temperature Relation Close thermal coupling between air and water has been found in shallow estuaries. Roelofs and Bumpus (1953) reported that water temperature in Pamlico Sound showed a seasonal cycle closely related to air temperature. Lindner and Ander- son (1956), documenting a winter kill of white shrimp in south Atlantic and Gulf of Mexico waters of the United States, also referred to a close relationship between air temperature and surface water temperature. Smith and Kierspe (1981) presented a model of air-water heat ex- changes in a shallow estuary and suggested that their model could reduce the need for in situ in- strumentation while providing for close approxi- mation of daily average temperatures. For the purpose of using air temperatures as proxy data for missing water temperatures (1968-72, Table 1), we decided to examine the re- lation between local air and water temperatures (Fig. 3). Although air temperature fluctuations were accompanied by a predictable shift in water temperatures over the entire range (r2 = 0.97), at water temperatures below 12°C the rela- tionship was not as useful ( r2 = 0.68). We believe that water temperatures rather than air temper- atures are required for acceptable predictions of fishery yields in estuaries. 3 2r 26 3 < tr 20 ■saP' .... '-I." _L _L 8 14 20 AIR TEMPERATURE (°C) 26 32 Figure 3.— Correlation of Morehead City, N.C., average weekly air temperatures with Newport River estuary (Pivers Island) average weekly water temperatures over 339 consecu- tive weeks from 1974 to 1981. (Intercept = 2.21. slope = 0.96, r2 = 0.97.) For points below a water temperature of 12°C. r2 = 0.68; and this relationship is not considered useful for predic- tive purposes during winter. Relationship Between Temperature, Rainfall, and Pink Shrimp Landings The February through July pink shrimp land- ings were considered a dependent variable to be plotted against various combinations of winter temperature data (Table 1). Landings were re- gressed on average winter water temperature from December through March (r2 =0.79), aver- age temperature in January and February ( r2 = 0.80), average temperature of the coldest week 765 FISHERY BULLETIN: VOL. 80, NO. 4 (r2 = 0.72), and average temperature of the two coldest consecutive weeks (r2 = 0.82). All rela- tionships were significant (P<0.01). If the aver- age temperature of the two coldest consecutive weeks was <6°C, then shrimp landings were be- low average (Fig. 4). Although average winter temperatures (De- cember-March) and average monthly tempera- tures (January plus February) each accounted for significant portions of the variance in annual landings, the strongest relationship was found between landings and the average of the two coldest consecutive weeks. This may arise be- cause, as Williams (1969b) stated, averages do not adequately represent extremes since they dampen the duration and intensity of the cold. Using a process of expressing temperature in heating degree days, Williams (1969b) postu- lated that the catch of all species of penaeid shrimps of a given year in North Carolina may depend on net heating degree days during the coldest preceding 6 mo (November-April). He found the poorest catches in cold years (1958, 1961, and 1963) for all three species combined and further suggested that warm years may be as beneficial as cold years are deleterious. The role of temperature on activity and osmo- regulation of pink shrimp has been documented (Williams 1955a, 1960). The lower temperature for activity under experimental conditions was about 14°-16°C; complete cessation of activity was noted below about 10°C. Below 8.8°C, osmo- regulatory ability was impaired. Pink shrimp may survive periods of winter cold by burying deeply into the substrate, and Fuss and Ogren (1966) reported that below 14°C, shrimp remain buried, abandoning the usual pattern of noctur- nal emergence. Laboratory experiments showed pink shrimp to be more tolerant to combinations of low salinity and low temperature than brown shrimp, and this may explain the occurrence of pink shrimp in North Carolina estuaries during the winter (Williams 1960). In contrast, fall and midwinter brown shrimp immigrants do not survive cold weather as well. The usual recruit- ment period for brown shrimp postlarvae is Feb- ruary and March; for white shrimp it is June through September (Williams 1965). Because osmoregulation is impaired at low temperatures, we considered that low salinity could increase mortality caused by low tempera- tures. Although salinity records were not avail- able, we compared local rainfall measurements with pink shrimp landings from 1962 to 1981. landings (kfl)= 75648(T| - 213044 r2=0 82 s - 1 2 3 4 5 6 7 8 9 10 11 12 AVERAGE OF THE TWO COLDEST CONSECUTIVE WEEKS TEMPERATURE (°C) Figure 4.— Relation of pink shrimp landings in North Caro- lina to the average water temperature of the two coldest con- secutive weeks in the Newport River estuary. Numbers by dots represent year of landings. (Actual landings of 198,000 kg were predicted to be 165,200 kg, based on the coldest average biweekly period temperature in 1982 of 5.0°C.) We found no correlation between rainfall and landings (r2 = 0.003) (Table 1). Further, rainfall added no significant contribution to the explana- tion of variance in landings data when it was in- cluded with temperature as a predictive variable (multiple R2 = 0.826). Both the driest (18.0 cm in 1965) and wettest (49.3 cm in 1974) winters oc- curred in years when landings were very large, approximately 500 metric tons. Williams ( 1969a) also found no significant relationship between rainfall and total catch of all shrimp species. However, Hunt et al.3 reported that salinities >10%o and temperatures >20°C during April and May are necessary for good brown shrimp harvests in North Carolina. Similarly, Gunter and Hildebrand (1954) found a strong correla- tion of total rainfall and white shrimp catch in Texas. Deviations from the shrimp landings-temper- ature relationship may, in part, be due to the process of estimating landings. Errors may in- clude improper species identification by fish dealers, lack of accuracy in estimated weight landed, and incomplete landing coverage. The direct trading of shrimp to private individuals by numerous part-time fishermen, plus the rec- reational landings, neither of which is reported, undoubtedly causes an underestimate of total 3Hunt, J. H., R. J. Carroll. V. Chinchilli, and D. Franken- berg. 1980. Relationship between environmental factors and brown shrimp production in Pamlico Sound, North Caro- lina. N.C. Dep. Nat. Resour. Community Dev. Div. Mar. Fish. Spec. Sci. Rep. 33, 29 p. 766 HETTLKR and CHESTER: WINTER TEMPERATURE AND SI'RINC LANDINGS OF PINK SHRIMP landings (Caillouet and Koi 1980). On the other hand, because of increased demand and higher prices for shrimp, fishing effort is probably more intensive in recent years. We did not consider effort in our analysis because reliable data were not available. Williams (1969b) concluded that pounds landed almost paralleled his calculated catch-effort index and therefore that actual har- vest data satisfactorily represented annual pro- ductivity independent of effort. Another source of variability to be considered, the annual varia- tion in the recruitment of postlarvae, was dis- missed because Williams (1969b) and Williams and Deubler (1968) found no relation between densities of penaeid shrimp postlarvae and sub- sequent landings. Similarly Lindner and Ander- son (1956) found that a severe cold kill of adult white shrimp in 1940 had no effect on the next year's landings. A number of complications in relating catch and climate were listed by Austin and Ingham (1979). In our study, which began with a concep- tual model of an organism and its relation to a physical parameter, some of the following sug- gested complications were mitigated: 1) A causal relationship of temperature to production was biologically appropriate, because the life history and temperature tolerance of pink shrimp are known; 2) the use of proxy data (air temperature instead of water temperature) was avoided; 3) major variations in the shrimp landings are probably due to cold kill of overwintering shrimp caused by cold-water temperatures (r2 = 0.82); 4) while the quality of the biological data (landings) cannot be judged, the length of the time series (15 yr) is probably adequate; 5) an in- terest does exist among fishery biologists and managers in using environmental data and rela- tionships for predictive, explanatory, or model- ing purposes; 6) although environmental data were point source, landings were from a geo- graphical area (<100 km radius) sufficiently re- stricted so as not to have masked biota-environ- mental relations. ACKNOWLEDGMENTS We thank Dennis Spitsbergen, North Carolina Division of Marine Fisheries, for information on the distribution of juvenile pink shrimp and on the spring shrimp fishery. Robert Quayle, NOAA National Climatic Center, Asheville, N.C., kindly furnished air temperature data. David Peters, James Waters, William Schaaf, and William Nicholson of the Southeast Fisher- ies Center Beaufort Laboratory reviewed an earlier revision of the manuscript. LITERATURE CITED Austin, H. M., and M. C. Ingham. 1979. Use of environmental data in the prediction of ma- rine fisheries abundance. In Climate and fisheries: Proceedings from a workshop on the influence of envi- ronmental factors on fisheries production, p. 93-98. Center for Ocean Management Studies, University of Rhode Island, Kingston, R.I. Caillouet, C. W., and D. B. Koi. 1980. Trends in ex-vessel value and size composition of annual landings of brown, pink, and white shrimp from the Gulf and south Atlantic coasts of the United States. Mar. Fish. Rev. 42(12): 18-27. Costello, T. J., and D. M. Allen. 1970. Synopsis of biological data on the pink shrimp Penaeus duorarum dvararum Burkenroad, 1939. FAO Fish. Rep. 57:1499-1537. Diaz, H. F., and R. G. Quayle. 1980. An analysis of the recent extreme winters in the contiguous United States. Mon. Weather Rev. 108:687- 699. Fuss, C. M., Jr., and L. H. Ogren. 1966. Factors affecting activity and burrowing habits of the pink shrimp, Penaeus diwrarum Burkenroad. Biol. Bull. (Woods Hole) 130:170-191. Grady, J. R. 1971. The distribution of sediment properties and shrimp catch on two shrimping grounds on the continen- tal shelf of the Gulf of Mexico. Proc. Gulf Caribb. Fish. Inst. 23:139-148. Gunter, G. 1950. Seasonal population changes and distributions as related to salinity, of certain invertebrates of the Texas Coast, including the commercial shrimp. Publ. Inst. Mar. Sci., Univ. Tex. 1(2):7-51. 1961. Habitat of juvenile shrimp (family Penaeidae). Ecology 42:598-600. Gunter, G., and H. H. Hildebrand. 1951. Destruction of fishes and other organisms on the south Texas coast by the cold wave of January 28 - Feb- ruary 3, 1951. Ecology 32:731-736. 1954. The relation of total rainfall of the state and catch of the marine shrimp {Penaeus setiferus) in Texas wa- ters. Bull. Mar. Sci. Gulf Caribb. 4:95-103. Ingham, M. C. 1979. Marine environmental conditions off the Atlantic and Gulf coasts of the United States, January 1977- March 1978. Mar. Fish. Rev. 41(5-6):35-47. KlNNE, O. 1963. The effects of temperature and salinity on marine and brackish water animals. I. Temperature. Ocean- ogr. Mar. Biol. Annu. Rev. 1:301-340. Lindner, M. J., and W. W. Anderson. 1956. Growth, migrations, spawning and size distribu- tion of shrimp Penaeus setiferus. U.S. Dep. Inter., Fish Wildl. Serv., Fish. Bull. 56:555-645. Loucks, R. H., and W. H. Sutcliffe, Jr. 1978. A simple fish-population model, includingenviron- 767 FISHERY BULLETIN: VOL. 80. NO. 4 mental influence, for two western Atlantic shelf stocks. J. Fish. Res. Board Can. 35:279-285. LUNZ, G. R. 1958. Pond cultivation of shrimp in South Carolina. Proc. Gulf Caribb. Fish. Inst. 10:44-48. Norcross, B. L., and H. M. Austin. 1981. Climate scale environmental factors affecting year class fluctuations of Chesapeake Bay croaker Micropo- gonias undulatus. Va. Inst. Mar. Sci. Spec. Sci. Rep. 110, 78 p. ROELOFS, E. W., AND D. F. BUMPUS. 1953. The hydrography of Pamlico Sound. Bull. Mar. Sci. Gulf Caribb. 3:181-205. Smith, N. P., and G. H. Kierspe. 1981. Local energy exchanges in a shallow, coastal la- goon: Winter conditions. Estuarine Coastal Shelf Sci. 13:159-167. Williams, A. B. 1955a. A contribution to the life histories of commercial shrimps (Penaeidae) in North Carolina. Bull. Mar. Sci. Gulf Caribb. 5:116-146. 1955b. A survey of North Carolina shrimp nursery grounds. J. Elisha Mitchell Sci. Soc. 71:200-207. 1958. Substrates as a factor in shrimp distribution. Limnol. Oceanogr. 3:283-290. 1960. The influence of temperature on osmotic regula- tion in two species of estuarine shrimps (Penaeus). Biol. Bull. (Woods Hole) 119:560-571. 1965. Marine decapod crustaceans of the Carolinas. U.S. Fish Wild!. Serv., Fish. Bull. 65:1-298. 1969a. Penaeid shrimp catch and heat summation, an apparent relationship. FAO Fish. Rep. 57:643-656. 1969b. A ten-year study of meroplankton in North Caro- lina estuaries: Cycles of occurrence among penaeidean shrimps. Chesapeake Sci. 10:36-47. Williams, A. B., and E. E. Deubler. 1968. A ten-year study of meroplankton in North Caro- lina estuaries: Assessment of environmental factors and sampling success among bothid flounders and penaeid shrimps. Chesapeake Sci. 9:27-41. 768 SEASONAL ABUNDANCE, COMPOSITION, AND PRODUCTIVITY OF THE LITTORAL FISH ASSEMBLAGE IN UPPER NEWPORT BAY, CALIFORNIA Larry G. Allen1 ABSTRACT This study was designed to characterize the littoral fish populations by 1) composition and principal species, 2) diversity and seasonal dynamics, 3) productivity, and 4 ) important environmental factors. Monthly samples (January 1978 to January 1979) obtained with four quantitative sampling methods at three stations in upper Newport Bay yielded 55,561 fishes from 32 species which weighed 103.5 kg. The top five species made up over 98% of the total number of individuals. One species, Aikerinops affix is, predominated in numbers (76.7% of all fishes) and biomass (79.8%). This dominance was reflected in the low overall H' diversity values for numbers (H'N = 0.89) and bio- mass (H'h = 0.84). Number of species, number of individuals, and biomass were greatest during the spring and summer. Quantitative clustering of species based on individual samples revealed five species groups which reflected both microhabitat and seasonal differences in the littoral ichthyofauna. Species Group I was made up of five resident species— A. affinis, Fund ul us parvipinnis, Clevelandia ios, Gillichthys mirabilis, and Gambusia affinis. Species Groups II-VI were composed of summer and winter periodics and rare species. The mean annual production (9.35 gdry weight/ m2 determined by the Ricker production model) of the littoral zone fishes was among the highestof reported values for comparable studies. This high annual production was mainly the result of the rapid growth of large numbers of juveniles that utilized the littoral zone as a nursery ground. Young-o{-the-yea.r Atherinops affinis contributed 85% of this total production. Canonical correlation analysis indicated that temperature and salinity together may influence littoral fish abundance. These two abiotic factors accounted for 83% of the variation in the abun- dances of individual species. Emigration from the littoral zone, therefore, seems to be cued by seasonal fluctuations in temperature and salinity. I propose that this offshore movement forms an important energy link between the highly productive littoral zone and local, nearshore marine environment. Semienclosed bays and estuaries are among the most productive areas on Earth, ranking with oceanic regions of upwelling, African savannas, coral reefs, and kelp beds (Haedrich and Hall 1976) in terms of animal tissue produced per year. Bays and estuaries harbor large stocks of nearshore fishes and are important feeding and nursery grounds for many species of fish, in- cluding commercially important ones. However, the high productivity of fishes is accompanied by low diversity (Allen and Horn 1975) which prob- ably reflects the stressful ecological conditions in bays and estuaries and the high physiological cost of adaptation to them (Haedrich and Hall 1976). The few studies that have dealt with pro- 1 Department of Biological Sciences, University of Southern California, Los Angeles, Calif.: present address: Department of Biologv. California State University, Northridge, CA 91330. ductivity in estuarine fishes were summarized by Wiley et al. (1972) and Adams (1976b). Utilization of temperate embayments by juve- nile and adult fishes is markedly seasonal with high abundances corresponding to the warmer, highly productive months of spring through autumn. Seasonal species typically spend one spring-autumn period in the shallows of a bay growing at an accelerated rate in the warm, highly productive waters (Cronin and Mansueti 1971). Most studies to date dealing with composition and temporal changes of bay-estuarine fish populations have been conducted on the Gulf of Mexico and Atlantic coasts of the United States where estuaries are larger and more numerous than those on the Pacific coast (e.g., Bechtel and Copeland 1970; Dahlberg and Odum 1970; Der- ickson and Price 1973; McErlean et al. 1973; Oviatt and Nixon 1973; Recksiek and McCleave Manuscript accepted March 1982. FISHERY BULLETIN: VOL. 80, NO. 4, 1982. 769 FISHERY BULLETIN: VOL. 80, NO. 4 1973; Haedrich and Haedrich 1974; Targett and McCleave 1974; Livingston 1976; Moore 1978; Shenker and Dean 1979; Orth and Heck 1980). Although quantitative in nature, many of these investigations suffer from the inefficient (Kjel- son and Johnson 1978) trawl sampling gear used and the high mobility of most fishes. Adams (1976a, b) used dropnet samples to accurately assess the density and productivity of the fishes of two North Carolina eelgrass beds. Weinstein et al. (1980) used a combination of block nets, seines, and rotenone collections to derive accu- rate quantitative estimates of fishes in shallow marsh habitats in the Cape Fear River Estuary, N.C. Previous investigations of fishes in Newport Bay have included a species list (Frey et al. 1970), a general species account (Bane 1968), two indi- vidual species accounts (Fronk 1969; Bane and Robinson 1970), and two studies on the popula- tion ecology of the fauna based on juveniles and adults (Posejpal 1969; Allen 1976). An assess- ment of the ichthyoplankton and demersal fish populations during 1974-75 (Allen and White in press) is the most comprehensive work to date. Despite these studies, a substantial component of the ichthyofauna, the littoral fishes of the upper bay (0-2 m depth from mean higher high water), had not been adequately sampled. In a study of the demersal ichthyofauna of Newport Bay dur- ing 1974-75 (Allen 1976), I found that three— Atherinops affinis, Fundulus parvipinnis, and Cymatogaster aggregata — of the five most numer- ous species were the ones that occurred in the shallow water over the mudflats which cover about 60-70% of the surface area of the upper bay reserve. Despite their high numerical ranking, the relative abundances of these littoral species were underestimated because sampling was car- ried out almost exclusively by otter trawls in the deeper channels of the upper bay. The recogni- tion of this gap in our knowledge served as the impetus for the present study. The main purposes of this study were to char- acterize the littoral ichthyofauna of upper New- port Bay quantitatively by 1) composition and principal species, 2) diversity and seasonal dy- namics, 3) productivity, and 4) key environ- mental factors that are influencing this fish assemblage. SHEILMAKE* ISLAND LOWER BAY Figure 1.— Map of upper Newport Bay, Orange County, Calif., with the locations of the three sampling stations. METHODS AND MATERIALS Study Area Newport Bay (lat. 33°37'30"N, long. 117° 54' 20"W) is located in Orange County, Calif., 56 km southeast of Los Angeles and 140 km north of the Mexican border (Fig. 1). The upper portion is the only large, relatively unaltered bay-estuarine habitat in California south of Morro Bay (lat. 34.5°N). The low to moderately polluted lower portion, commonly called Newport Harbor, has been severely altered by dredging activities, landfills, and bulkheads to accommodate more than 9,000 boats. The study area, the upper two- thirds of the upper bay, is bordered almost com- pletely by marsh vegetation and mudflats. The California Department of Fish and Game pur- chased and set aside this area as an ecological reserve in 1975. Three stations, about 0.5 km in length, were spaced evenly along the shore of the upper New- port Bay (Fig. 1). Sampling was stratified based on prior information on the uniqueness of the fish fauna of the three areas (Allen 1976). This design also allowed thorough coverage of the study area. Each station was situated on a littoral (inter- tidal) mudflat area adjacent to marsh vegetation 770 ALLEN: LITTORAL FISH ASSEMBLAGE and was divided into 10 numbered sections of equal size. Selection of the section sampled each month was random in order to satisfy statistical assumptions and minimize the impact of sam- pling on any particular section from month to month. Each station included a tidal creek or pool (panne) which was sampled on the marsh islands. Sampling Procedures Monthly samples were taken at the three sta- tions during the 13-mo period from January 1978 to January 1979 for a total of 39 station samples. Sampling was carried out within ±3 h of daytime neap high tide to minimize tidal level effects. Two days were usually required to sample three stations, stations 1 and 2 the first day and station 3 the second. Four types of sampling gear were employed at each station as follows: 1) A 15.2 mX 1.8 mbagseine(BS) with 6.4 mm mesh in the wings and 3.2 mm mesh in the 1.8 X 1.8 X 1.8 m bag was used twice at each station. Hauls were made by setting the net parallel to and 15 m off the shore at a depth of 1-2 m. The BS was then hauled to shore using 15 m polypropy- lene lines attached to 1.8 m brails on each end of the net. Each haul sampled an area of 220 m2. 2) A 4.6 m X 1.2 m small seine (SS) with 3.2 mm mesh was pulled 10 m along and 2 m from the shore (at a depth to 1 m) and pivoted to shore. Two hauls were made in the inshore area and one haul in the panne at each station. Each haul sam- pled an area of 62.4 m2. [One exception to the sampling routine occurred at station 3 panne in April 1978 when no sample was taken due to a dry panne.] 3) A 2.45 X 2.45 X 1.0 m dropnet (DN) with 3.2 mm mesh was used to sample the water column and bottom at 0.5-1.5 m depth. The DN was sus- pended from a 5.0 X 5.0 X 1.0 m aluminum pipe frame, released by pins at each corner. Two 19 1 plastic buckets were attached to each corner of the frame for flotation. The net and frame were maneuvered into position, anchored, and left un- disturbed for 10 min. After release the DN was pursed by the chain line and hauled to shore by nylon line. The DN sampled an area of 6.0 m2. 4) A small, square enclosure (SE) was used in conjunction with an anesthetic (quinaldine mixed 1:5 with isopropyl alcohol) with the intent of sampling small burrow inhabiting fishes, especially gobies. The SE was constructed of heavy duck material mounted on a 1.0 X 1.0 X 1.0 m collapsible frame of 25.0 mm PVC pipe and sampled 1.0 m2 of bottom. The SE was set at three randomly chosen positions in an undis- turbed portion of each station section at a depth of 0.5-1.0 m. The bottom of the SE was forced into the upper few centimeters of substrate and the quinaldine mixture added to the enclosed water column. The enclosed volume and shallow sub- strate was then thoroughly searched for 10 min using a long-handled dip net of 1.0 mm mesh. A detailed comparison of the effectiveness of these four methods is the subject of a separate paper (Horn and Allen2). Ten samples were taken at each of the three stations each month (2 BS samples, 3 SS samples, 2 DN samples, 3 SE samples) for a total of 30 samples/mo and 289 samples over the study (minus one SS haul in April 1978 at station 3). Catches were either frozen on Dry Ice3 or pre- served in 10% buffered Formalin. Specimens >150 mm SL were injected abdominally with 10% buffered Formalin. Subsamples of frozen specimens were oven dried (40°C) for 48-72 h for dry weight determination. Mean dry weights were based on a minimum of 20 individuals/size- class of each common species at each station each month. Data on six abiotic factors were recorded or determined for each station: temperature, salin- ity, dissolved oxygen, sediment particle size, depth of capture (by individual samples), and distance into the upper Newport Bay from the Highway 1 bridge (see Fig. 1). Production Estimation Production is the total amount of tissue pro- duced during any given time interval including that of individuals which do not survive to the end of that time interval (Ivlev 1966). Productiv- ity is the rate of production of biomass per unit of time (Wiley et al. 1972). Production of a fish stock 2Horn, M. H., and L. G. Allen. Comparison of methods for sampling shallow-water estuarine fish populations. Manu- scr. in prep. California State University, Fullerton, Fuller- ton. CA 92634. 3Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 771 FISHERY BULLETIN: VOL. 80, NO. 4 is the product of the density of fish and the growth of the individuals (Ricker 1946). An HP9100A program was developed with the aid of Joel Weintraub (California State Univer- sity, Fullerton) to calculate the production of each recognizable size-class of the common spe- cies, those which were collected in at least 2 con- secutive months at each station. The model used was that proposed by Ricker (1946) and modified by Allen (1950) and is calculated as follows: where G = P = GB log, w2 - log, Wl At is the instanta- neous coeffi- cient of growth; B Z = Bi(J:-z-l) G-Z is the average biomass over the time interval; -(log, N2 - log, Ni) At is the instan- taneous coef- ficient of population change of the immediate sampling area (station) attributable to mortality and migration; B is the biomass density of fishes at t\\ wu W2 are the mean weights of individuals at time t\ and fo; and N\, N2 are the numbers of fishes present at h and t%. G—Z is the net rate of increase in biomass during At (1 mo). The model assumes that production data need not be corrected for immigration and emigration of fishes in and out of the sampling area, pro- vided the density and growth by size-class are estimated frequently enough to accurately assess the abundance and growth of fishes actually in the sampling area (Chapman 1968). In the present study, growth increments were estimated from length-frequency data for fishes from all three stations each month for each size- class. The length data, therefore, were represen- tative of the entire population of the size-class in the upper Newport Bay and served to minimize the effects which localized movements into and out of a particular station have on monthly growth values. The average weight, w, of a size- class per month was calculated as follows: 1) Dry weight equivalent for the median length in a size interval (5 mm intervals) was determined using standard length to dry weight curves for each common species; 2) the proportion (range 0-1) of individuals represented in the size interval was multiplied by the dry weight equivalent for the interval; 3) the products were then summed for all size intervals contained within the particular size-class of the species yielding an average weight, w. This method proved to be more accu- rate than simply taking the mean length of the entire size-class and determining the dry weight equivalent. The "best estimate" of biomass density {B) for each discernible size-class was determined in the following manner: 1) The biomass density (wet weight) derived from the method (BS, SS, DN, or SE) shown to be most effective at sampling the particular species was used. Table 1 lists the spe- cies with corresponding collecting gear ranked by their effectiveness at capturing the species. This list is based on a comparative study of the sampling methods (Horn and Allen footnote 2); 2) if, as in a few cases, the biomass estimated was inordinately high, due to a large catch in one replicate sample, the estimate defaulted to the next gear type in the rank order; 3) the biomass estimate in wet weight was converted to a dry weight (DW) equivalent by a conversion factor determined for each species and entered into the production model as B\ (g DW/m2). Production is the total of all positive values for size-classes dur- ing a time period (1 mo in this case) at each sta- tion. Negative values were due to sampling error and emigration and were not included in produc- tion estimates. Large individuals (>100 mm SL) of Mugil cephalus were not included in production esti- Table 1.— Methods for best estimate of spe- cies densities ranked by effectiveness (Horn and Allen text footnote 2). BS = bag seine; SS = small seine; DN =dropnet; SE =square enclosure. Species Methods ranked by effectiveness At her mops allinis Fundulus parvipmnis Clevelandia ios Anchoa compressa Gambusia allinis Cymatogaster aggregala Gillichthys mirabilis Anchoa delicatissima Mugil cephalus Engraulis mordax Leuresthes tenuis Ouielula ycauda llypnus gilberti Syngnathus spp Hypsopsetta guttulala Lepomis macrochirus Lepomis cyanellus All other species BS, SS SS, BS SE. SS, DN BS, SS, DN SS, BS BS, DN, SS SS, SE, BS BS, SS SS, BS BS, SS BS, SS DN, SS DN. SS SS, DN SS, DN BS. SS BS, SS BS, SS 772 ALLKN: LITTORAL FISH ASSKMHLACIK mates because quantitative estimates of densi- ties could not be obtained for the large members of this mobile species. Data Analysis Cumulative Species Curve The cumulative number of species in Febru- ary (low fish density) and June (high fish density) was plotted against the number of samples taken in order to assess the adequacy of sampling. Two random sequences were used for the arrange- ment of the 30 samples taken each month by the four methods. Each method sampled a unique subhabitat within the littoral zone. Cumulative species curves (reflecting presence/absence) were based on a combination of methods to in- sure that all possible species occupying the lit- toral zone at a particular time were represent- ed. Diversity Both the Shannon- Wiener information func- tion (Shannon and Weaver 1949) and species richness were used as measures of diversity for pooled station and upper bay samples. The Shan- non-Wiener index reflects both species richness and evenness in a sample. factors— temperature (TEMP), salinity (SAL), dissolved oxygen (DO), distance into the upper bay from the Highway 1 bridge (DSTUPB), aver- age particle size of the sediment (APRTSZ), and depth of capture (DPTHCAP); the second in- cluded only temperature and salinity to deter- mine the amount of variation these two factors accounted for alone. RESULTS Temperature and Salinity Patterns Water temperatures of the littoral zone at all three stations increased steadily during the peri- od January-June from 14°-15°C to 26°-28°C( Fig. 2). The temperatures remained high (>25°C) throughout the summer months and then de- clined gradually until November. Between No- vember and December the temperature dropped sharply at each station. Temperatures in the pannes were generally higher than the tempera- 30 20 10 Station 1 /,»--" ' ^ NX Cluster Analysis and Canonical Correlation The Ecological Analysis Package (EAP) de- veloped by R. W. Smith was used at the Univer- sity of Southern California Computer Center to determine species associations (cluster analysis), species abundance correlations to abiotic factors (multiple regression subprogram), and possible effects of abiotic factors on individual species abundance (canonical correlation). The cluster analysis utilized the Bray-Curtis index of dissimilarity (Clifford and Stephenson 1975). This index allowed quantitative cluster- ing without assuming normality in the sampled population. A square-root transformation of spe- cies counts was done to counter the tendency of this index to overemphasize dominant species. Canonical correlation analysis was used to de- termine whether and to what extent abiotic fac- tors interacted with individual species abun- dances in the 39 station samples over the study period. Two separate canonical correlation anal- yses were made: The first run included six abiotic V o o 3 o a a. E e Station 2 30 / V 20 ^^^^ 10 Panne Inshore Station 3 -- /' - \ / ""*" — """^ — /^-* * I i i 30 20 10 J78FMAMJ J AS ONDJ79 Months Figure 2.— Month-to-month variation (January 1978-January 1979) in water temperature (°C) for the alongshore area and panne at each of the three sampling stations. (* - panne dried- up.) 773 FISHERY BULLETIN: VOL. 80. NO. 4 tures along the shore especially in the summer months (July-September). Salinity varied more than temperature (Fig. 3) due to rainfall and periodic runoff from sur- rounding urban areas. In general all stations had low salinities during January through March 1978, a period of heavy rainfall. After May 1978, salinities remained high (between 25 and 32 ppt) with decreases in June 1978 (stations 1 and 3, un- known cause), September 1978 (all stations due to heavy rainfall), and January 1979 (station 3 due to rainfall). Panne salinities at station 1 were consistently low (usually <6 ppt) indicating a constant freshwater input. The pannes at sta- tions 2 and 3, however, usually had salinities equal to or higher than the alongshore area due to evaporation. Total Catch Sampling during the 13-mo period yielded 55,561 individuals of 32 species that weighed a total of 103.5 kg (Table 2). Station 1 40 30 20 10 Station 3 i i i 1 i 1 1 1 i 1 1 1 J78FMAMJJ ASONDJ79 Months Figure 3.— Month-to-month variation (January 1978-Janu- ary 1979) in salinity (ppt) for the alongshore area and panne at each of the three sampling stations. (* = panne dried-up.) Atherinops affinis greatly predominated in numbers (76.7%) and biomass (79.9%). Fundulus parvipinnis ranked second in both numbers (12.1%) and biomass (7.6%), followed in order by Gambusia affinis (5.5% numbers), Clevelandia ios (2.4% numbers), and Anchoa com pressa (1.2% numbers). These five species accounted for 98% of the total number of individuals and 96% of the total biomass (Table 2). The skewed distribution of number of individuals among species was re- flected in the relatively low overall H' diversity values of 0.89 for numbers (H'N) and 0.84 for bio- mass {H'h). The vast majority of individuals of most species were either young-of-the-year or juveniles. Station 1— A total of 13,859 individuals repre- senting 19 species was collected during the year. The catch totaled 22.7 kg. All three of these totals were the lowest of those from the three stations. Overall H' diversity for numbers was 1.17 and for biomass, 0.89. Atherinops affinis ranked first in numbers (55.2%) and biomass (76.7%) but was less abundant here than at stations 2 and 3. Gam- busia affinis (20.6%) and Fundulus parvipinnis (19.1%) were common at this station especially in the panne. Station 2— The greatest number of individuals (24,813) and biomass (42.9 kg) were collected at this site. Although 27 species were captured, over 90% of these individuals were from one spe- cies, Atherinops affinis. The large number of attached eggs and small (<20 mm) fish caught in July (52% of all A. affinis) indicated that this area was a breeding site for A. affinis. Fundulus par- vipinnis (4.4%) was second in numerical rank. H' for numbers (0.49) and biomass (0.70) were low. Station 3— A total of 16,889 fishes belonging to 23 species were obtained at this station. Ather- inops affinis made up 74.4% of the individuals and 78.8% of the 37.9 kg total biomass. Other im- portant species in order of decreasing numerical abundance were Fundulus parvipinnis (17.6%), Clevelandia ios (3.4%), Cymatogaster aggregata (1.3%), and Anchoa compressor (1.3%). Overall, Hh and H'u were 0.87 and 0.85, respectively. Cumulative Species Curves Cumulative species curves from February and June (Fig. 4) reached an asymptote before 20 samples (about 66% of total samples), indicating 774 ALLEN: LITTORAL FISH ASSEMBLAGE OJ OJ a 3 C cfl I 00 3 C Ed £ xf oS 3 o a a; z s_ CD a. a. 3 o CD C o CD -C 03 en a E o IS C C -a c 3 -O cS _>> -C c o H m < E- CO 111 O) o IT) ■* o CO o m co CM o O CM a> ■ in tt m - o r^ a> co co CO ▼- CO CM c\i t^ CO MOO O r- a> CO CM CO »-' CM ■st CM ■» O 00 i- CO CO' T-CvJi-TtTtCOCOCMO ■<* m CD O) CMCMr^CMCOCOO)COO *- a> cm ai o> co ^t- m cm co i- m i- o cr> i- CMIOlOOSi-NNt- CMCOlOO'-fl'-'- CO rP)i- '-SEOt-OWONIO aJoc\jcba>'-o TT m co in co co >- •st i- m CM OO"- CO i- co CO CO t- CO CM O) CM r- irios CM CM CM O O CM *- m co co O) r- co O CM CO CO lD r^ co ■<* o> V i^O O lO O i- l- CM CM CO CM CO CO CO rr ro CO CM CO CD co en *~ m h- co o> co ■- r~ *T ■» CM co a> o r- r- i- in 2 c co c Us si" a w 2 ^ O 3 w C C ~ 3 <0 s ? s * £ 3 § 5 <(u.OO o CO CO 2> "o CD CO (0 ;» ci v. - m O J? 2 3 CD C « 0 _3 V) ~Ss 3 C (0 <0 co 5; ? ™ fc c O D) a c c\jf^oinccico m-i- cDOioco^cDTr^cNjt- --^(Ocb^coN^iridNdcbdcD'joddj "3" i- CO LO CO ^t CO o SO'tOCOOMn'tOtOOMO^CO'-T-i-ri-r-T-r-r-^^^^r;^^ CD^m-^-OjTfCOCOC\J(N^^OOpOOOOOOOOOOOOOOOpO devi^evj^oooodooddoododdddddddoooooo 0) o E 0) u Q o z *- CM h~ *3" "o to co d cm d J) co in oj co co o co TT 00 C\J CM t- m co d X3 E CD Q d> CO 00 O CM CO ■^t CO 00 CM r- m tj- tj- Tj- CO r- t- Cm" r^ O CO CM CO CO *~ d d d d ^ i*~ *- co c\j *- o co qiDi- i- ■«T Cm" CM CO O CO ■*!" O CM CO CO CO O CO CMO-^fcOT-cppr^ ddd'-ddo'- OCNJOO-^UOt-CMI^ CO CO CO d cm" cm r^ oo t- c\j o cm m r- r-- o r- CM C\J CO d co co in d c\j t^ 3 £ o CM W J 03 < CM t- T ^ 00 CDOfl CO CO i- O CM CO co in - o iA 03 IB IB ~ tO 3 ■C O to C 3 ^ C3 oo CM CO CO o O OO co co d in oo I- CO d r— oo t- d CM T- oo co *- i>- rr d o t- uo d "D Q) (0 3 -c cb to 0) c 3 14) for the entire spring-summer period from May to August 1978. Richness then decreased through the fall, reaching its lowest point of six species in December 1978. Diversity H' values fluctuated in a pattern opposite to that of species richness. H'\ decreased during the summer from a high in May of 1.76 to a low in June of 0.44. H'B also de- creased sharply in summer but unlike H'\ con- tinued to decline for the remainder of the study. Both the number of individuals and biomass be- gan to increase dramatically during May 1978 and reached peaks of 21,907 individuals and 21.7 kg in June. Both numbers and biomass decreased in August with number of individuals increasing again in September. Biomass declined once again in September during a period of rainfall and then increased in October. In the months from October 1978 to January 1979 a rapid de- cline in both numbers and biomass was evident and was especially pronounced from November to December. A greater number of individuals (992-579) and much greater biomass (4,692-597 g) was obtained in January 1979 than in January 1978. Species Associations Cluster analysis based on individual samples yielded five species groups which, upon further 2.0 x 1.0 ° » 10 Z o> a § 6 C . O ' O H Diversity Number of Species zJS cT 16 o X ~~ 12 in E a en B c Number of Individuals o> Biomass 1 1 1 ! J78 F M A M J J A S O N D J 79 Months Figure 5.— Monthly variation (January 1978-January 1979) in total number of species, diversity H' (for numbers, Hn, and biomass, HB), number of individuals and biomass (g) for fishes collected by all methods at stations 1-3 combined in the littoral zone of upper Newport Bay. 777 FISHERY BULLETIN: VOL. 80, NO. 4 examination, reflected both spatial (microhabi- tat) and seasonal differences in the littoral ich- thyofauna (Fig. 6). Group I was a loosely associated group of the five resident species (maintain populations year round in littoral zone) which could be further di- vided into three subgroups. Subgroup A had only one member, Atherinops affinis, an abundant schooling species. Clevelandia ios and Gillich- thys mirabilis which comprised subgroup B are burrow-inhabiting gobiids of the shallows and pannes. Subgroup C included two species, Fun- dulus parvipinnis and Gambusia affinis, which inhabited pannes and other high intertidal areas. Clevelandia ios, G. mirabilis, and F. par- vipinnis are residents of salt marshes in Cali- fornia and other west coast estuaries and are probably the species most threatened by altera- tions of these habitats. Group II consisted of three midwater school- ing species— Anchoa compressa, A. delicatis- sima, and Cymatogaster aggregata — most of which were caught mainly from January to August. Group III was made up of three distinctly sea- sonal, benthic species: Two gobiids, Quietula ycauda and Ilypnus gilberti, and a cottid, Lep- tocottus armatus, which was relatively rare dur- ing 1978 compared with previous years (pers. obs.). Group IV included an engraulid, Engraulis mordax; syngnathids, Syngnathus spp. (includ- ing S. auliscus and S. leptorhynchus); and the pleuronectid, Hypsopsetta guttulata. These spe- cies were seasonally present in mid- to late sum- mer. Members of this group were only loosely associated (> 80% distance). Group V was composed of four species which were collected at times of low salinities. Lepomis macrochirus and juveniles of Mugil eephalus were sampled together early in the year (Janu- ary-March 1978). Lepomis cyanellus and Leures- thes tenuis were found together only in Septem- ber. Group VI included 12 rare species, most of which could be considered summer periodics in the littoral zone in 1978. These were Umbrina roncador, Urolophus halleri, Paralichthys cali- fornicus, Mustelus californicus, Cynoscion nobil- is, Acanthogobius flavimanus, Sphyraena argen- tea, Girella nigricans, Symphurus atricauda, Porichthys myriaster, Morone saxatilis, and Seriphus politus. Members of the species groups identified in the dendrogram (Fig. 6) are illustrated in dia- % DISTANCE 140 120 100 80 _!_ 60 40 _L_ 20 {1 Q d Atherinops affinis Clevelandia ios i Gillichthys mirabilis J Fundulus parvipinnis l Gambusia affinis J Anchoa delicatissima Cymatogaster aggregata Anchoa compressa Quietula ycauda Ilypnus gilberti Leptocottus armatus Engraulis mordax Syngnathus spp. Hypsopsetta guttulata Mugil eephalus Lepomis macrochirus Lepomis cyanellus Leuresthes tenuis }A III IV Figure 6.— Dendrogram of the clustering of littoral fish species by individual samples taken at stations 1-3 in upper Newport Bay, five species groups (Roman numerals) are recognized according to the Bray-Curtis index of dissimilarity (% distance). A, B, and C are subgroups of species Group I. 778 ALLEN: LITTORAL FISH ASSEMBLAGE grams (Figs. 7-9), depicting occurrences in the alongshore area or panne during three different time periods (January-March 1978, April-Sep- tember 1978, and October 1978-January 1979). Only species with >5 individuals during each time segment were included in the diagrams. These diagrams illustrate the high degree of sea- sonality within this fish assemblage. During the January-March 1978 period of heavy rainfall, members of three species groups (I, II, and V) were present in relatively low abun- dances (Fig. 7). A halocline existed at station 3 during this period, and Atherinops affinis was collected only seaward of the halocline at this sta- tion. Representatives of group V, Mugilcephalus juveniles and Lepomis macrochirus, were found associated with very low salinities. Large M. cephalus were observed in both the channel and littoral areas during most of the year. The spring-summer period of April-Septem- ber 1978 was characterized by increased water temperatures and salinities, accompanied by in- creased numbers of species and individual fishes (Fig. 8). Green algal beds, composed primarily of Enteromorpha sp., Chaetomorpha linum, and Ulva lobata, developed along the shore of the entire upper bay, and served as a nursery area for large numbers of juvenile fishes. All species groups, except V, were represented during this time. Juveniles of Atherinops affinis occurred in large numbers in the shallows with juvenile Cymatogaster aggregata also being abundant at station 3. Young-of-the-year F. parvipinnis were very abundant in the pannes, especially at sta- tions 1 and 3. By October the extensive algal beds had dis- appeared. The October 1978-January 1979 peri- od was marked by decreased number of species and abundance (Fig. 9). The only common spe- cies were members of group I (residents) with a few juvenile M. cephalus representing group V. Productivity Annual production (mean of three stations by month) of the entire upper Newport Bay was 9.35 g D W/m2 per year (Table 3). Young-of-the-year Atherinops affinis contributed 85.1% to total pro- duction followed by Anchoa compressa (4.9%) and Fundulus parvipinnis (4.2%). Productivity was highly seasonal with the spring-summer period (April-September) ac- counting for 75.9% of the total annual production (Table 3, Fig. 10). Productivity, which was very co- ca o Q. 2 C B c t- B s t- ja e8 SS 3 -C C .£ * .§? u a-. *b "3 2 c C3 E c I III _: x < _ o co ■& o c ^^CVJfflffl^^OCMOOtOCgO r- in CO ■<* O ■comco.-o,-oocNj,-o *-CNcoo^rt-oooooo^-o Oh-000000000000 f~ in o ■* CO i- r- O o ci CO o o o o CD d cnj co *- m "* co co r~ a> o T o CO r- o o r-'dcio r-~ cnj co -*r CNJ O) in to in o co co o t- — •- o o o o in d d d d *t co co m ,- o CD CNJ Oi CO CD CNJ r~ co o ^r co o CD i- O O O O d d d d d d on o r-~ l- Tt a) CNJ ■^r o co m cnj co co o co ^ o in to o ■- o o o cnj q o d o d d d d d ■>»■ CO d o o o o d "~ o o CO o o o o o CO a> o d o d o o o o CO o o o CNI CNJ d d uo i- cnj o> O O ■r- O O i- O O i- ■<* CNJ CNJ Cnj O »- O O 1" in -^ o o o o d d i- ^r cnj o o o o o o o o o d do o d o o d in co cnj o o •<<- o o — o o o co o o co o o o o d d a) o o o co ^ £ 8 C £ ° CO CO » t. Q. o <2 C C 5 1 c c CO 5 CO O CO CO = ! "5 3 §5 LL U X 2 x » *- O ^ co a « = o *i- "£ cb x co a-o r- CO CO =: o. o co ■c o ^ o o » - .c = °- ? o * ^^ c Ot5< co O) CD CO CO °> 3 ' CO ,; 3 3 O 0) <0 OujO lit 3 fc C COO CL Q. 5 X. CD ^ =: -j 0) ^> £} °~ C <° C CO Sen 779 FISHERY BULLETIN: VOL. 80. NO. 4 re o> >. o 6> c 3 o >. 3 "re -c a o> o en 3 >-. !c o o u E E o a « a a> >. E ? c o> 5 § e/> E c a re a re re in 3 ■Q E re O * 0< 3 o 5 E '-a es .r c r- T3 > o o > z '£ '— ~z It I a — 3 = O c c a X! c be E o Q J3 c C ~G N OJ S Q o bt oi C *-> ~ bt 03 °C c 3 *■* -a X Si c/: 1 3 o " £ "rt x ^ OJ X ZJ -«^ C c •— '"* z. cfl 0) - 3 -*J ~ o '> o> c — c _o ~ Ol 4-3 ifl s- Al - - o -x •f. a! a o 01 — p. o> 0) o Sm V ■f. a: «*-. o b*h O U] 5 E s- et-i o> •_ c - "oi / s- > c bt I "~ ri 1 0) C o *-» o 1 ■/. ' ! l_ - ™ t-^ o • — c t— ( ■I. Is D 00 c C9 t> r" E < 780 ALLEN: LITTORAL FISH ASSKMBLACK (0 0) >. •2 c o •2 3 _3 X <0 6> c 3 ■2 -o <0 *— «» o 5) o E i <0 Q. O •2 c t— 3 3 3 c (0 J= 3 O "5 5 <0 s_ "3 .5. > 3 ■Q o J*. o o 3 c Ui c 3 u. <0 a E <0 <5 a -j o r o\ % is a TO CD k_ ;>. (0 (0 ■•— a> a> TO 9 >■ 2 E o 10 to to E to 6> c 3 Q. o 6> •«■ 6> Km 33 m O a. c <0 c a TO o >s (A 3 3 O E o u CJ to TO 1— •n 3 •C o a o >« V) "55 ■o c _C0 "55 TO <0 e c c **- <0 o ■c u (0 o ■c a> hs. O) O) (0 c Cn C is JO 3 ■*— ■*— 10 c o 0) TO 3 1 «*" ^ c O d O o> s c o c o V a 1) L. CO CD c o s x "e CT5 Si 0) © -° a. S j. §.«« II be a c a E =» 3 '£. - S- IS I =: - 0) [— S_ »- V 3 a be a. ;- 3 •i- "8.5 01 93 .n •- f c be o e -a 'S * 2 £ CO w a .2 .£ — - be "S.S L. 3 C O c o> CO 0) t- a a *- cu .2 -2 *-> __ E J* E °» t- be l. - 00 ta as 3 781 FISHERY BULLETIN: VOL. 80, NO. 4 CD e >. o 6> o >» w 3 "5 ■c a a o CO a c 3 O >> •!2 c c s. CO a c o c o c o 05 E J- o s- O oi 3 C C4 —3 00 t- a> •_ a> -O O O O be c 3 -a >> o a 0> Z (-< 0> tt a 3 o O) c o «« .Sf (1) cfl be c cS c CO a nj .2* _c o. 0) o c c a> en 01 Ih a 0) u o '-£ a) £ £ eS Ih be a Q I ai w OS O 782 ALLEN: LITTORAL FISH ASSEMBLAGE Z ~ § 1 S ul 2 i* FMAMJJASONDJ MONTHS (1978 ■ 1979) Figure 10.— Monthly variation in mean production ( x± 2 SE, g DW/m2) of the littoral fishes from three stations in upper Newport Bay (February 1978-January 1979). low from February to May 1978, increased rap- idly from June to a peak in August (5.2 g DW/ m2). Monthly production then declined drastic- ally in September, a period of heavy rainfall dur- ing which many of the larger young-of-the-year Atherinops affinis emigrated from the study area. Production increased in October but then showed a steady decline to zero in December, a time of a sharp decrease in mean water tempera- ture in the upper bay. Relationship of Abiotic Factors to Fish Abundance and Distribution Temperature was found to have a significant, positive correlation (P<0.01, df = 37) with num- ber of species (r = 0.42), number of individuals (r = 0.48), and biomass (r = 0.54) when station totals were considered. Similarly, salinity was significantly correlated with number of individ- uals (r = 0.36) and biomass (r = 0.64) (Table 4). Temperature was the factor which yielded the highest number of significant correlations (6) with individual species, followed by salinity, dis- solved oxygen, distance into the upper bay, and depth of capture, each with four (Table 4). An analysis of intercorrelations among abiotic factors yielded three significant (P<0.05, df = 37) positive relationships: 1) Temperature and salinity (r = 0.48); 2) temperature and dissolved oxygen (r = 0.53); and 3) dissolved oxygen and distance into the upper bay (r = 0.32). According to canonical correlation analysis, the six abiotic variables accounted for 93% of the variation in individual species abundances along the first canonical axis (Table 5). A second run indicated that 83% of the variation in species abundances could be accounted for by tempera- ture and salinity alone. This finding strongly implies that interactive effects of temperature Table 4. — Correlation coefficients (r)of individual species numbers and of total number of species, number of individuals, and biomass with six environmental factors. TEMP = temperature, SAL = salinity, DO = dissolved oxygen, DSTUPB = distance into upper Newport Bay from Highway 1 bridge, APRTSZ = average particle size of sediments. DPTHCAP = depth of capture. Abiot c factors Species TEMP SAL DO DSTUPB APRTSZ DPTHCAP Alhennops alfinis 055" 0.57" 0.21 0.00 -0.12 0.23 Fundulus parvipinnis 0.18 0.15 -0.3T 0.00 -0.06 0.03 Anchoa compressa 0.38- 0.21 0.35* -0.01 0.05 0.24 Clevelandia ios 0.43" 0.22 0.08 -0 09 -0.16 0.23 Mug/7 cephalus -0.62" -0.29 -0.10 0.11 0.26 0.02 Gillichthys mirabitis 0.25 -0.22 0.44" 0.31* 0.01 0.00 Anchoa delicatissima 0.10 0.08 -0.22 -0.22 0.05 -0.02 Gambusia alfinis 0.21 -0.25 0.16 0.58" -0.07 -0.02 Hypsopsetta guttulata 030 0.21 0.43" 026 -0.10 0 28 Cymatogaster aggregata 0.14 028 -0.01 -0.34- 0.01 0.14 Ouietula ycauda 0.46" 035* 0.19 -0.16 0.01 oss- llypnus gilberli 0.39- 0.31' 0.23 -0.10 0.11 o.ss- Lepomis macrochirus -0.29 -0.44* -0.23 0.10 0.09 0.04 Lepomis cyanellus 006 -0.27 -0.29 0.16 -0.20 005 Engraulis mordax 0.22 0.16 0.00 0.13 -0.07 033- Leuresthes tenuis 0.16 0.14 -0 09 -0.15 0 10 -0.01 Leptocottus armatus 0.29 0.13 0.38 -0 09 -0.01 0.05 Syngnathus spp. 0.53 0.23 0.35 0.08 -0.07 0.33' Species totals (by station) No. of species 0.42" 0.05 — — — — No. of individuals 0.48" 0.36- — — — — Biomass 0.54" 064" — — — — significant at 0.05 level, significant at 0.01 level. 783 FISHERY BULLETIN: VOL. 80, NO. 4 Table 5. — Summary of two canonical cor- relation runs of individual species abun- dances against environmental variables. Axis R2 df Run No. 1 (6 environmental; 18 species) 1 0.93 0.96 212.9* 126 2 0.84 0.92 144.1* 102 3 0.73 0.85 96.3 80 Run No. 2 (temperature, salinity only, 18 species) 1 0.83 0.91 77.8" 36 2 0.61 0.78 26.5 17 * = significant at 0.01 . and salinity were important in influencing spe- cies abundance. The 18 most common species were ordinated along temperature and salinity axes using sim- ple correlation values (r) as an index of relative influence of these two factors (Fig. 11). Thirteen of the 18 species were positioned in the upper right quadrant indicating that they were all positively correlated with temperature and sa- linity. Three species, Gambusia affinis, Gillich- thys mirabilis, and Lepomis cyanellus, located in the upper left quadrant correlated positively Sspp. Ac* Aa ._ I • Qy ig ,Gm La» •Hgj •Em ] • Ca Fp. . Lt Ad I j i i i --i-- — ; ! 1 ; 1 1 1 1 — .6 .5 .4 -.3 .2 .1 0 .1 .2 .3 .4 .5 .6 Correlation Coefficient (r) with Salinity Figure 11.— Ordination of 18 common species of the littoral zone of upper Newport Bay on correlation coefficients (r) for temperature (y-axis) and salinity (x-axis). Dashed lines indi- cate 0.05 significance levels. Aa-Atherinopsaffin is, Ac- A nchoa compressa, Ad-Anchoa delicatissima, Ca-Cymatogaster aggre- gate!, Ci-Clevelandia ios, Em-Engraulis mordax, Fp-Fundulus parvipinnis, Ga-Gambusia affinis, Gm-GUlichthys mirabilis, Hg-Hypsopsetta guttulata, Ig-Ilypmis gilberti, La-Leptocottus armatus, hm-Lepomis macrochirus, Lt-Leuresthes tenuis, Mc- Mugil cephalus, Qy-Quietula ycauda, Sspp- Syngnathus spp. with temperature, but negatively with salinity. The lower left quadrant includes two species, Lepomis macrochirus and Mugil cephalus, with negative temperature and salinity influences. No species were positioned in the negative tem- perature, positive salinity quadrant probably be- cause this situation rarely occurred in the littoral zone in 1978. DISCUSSION Composition, Diversity, and Seasonal Dynamics The ichthyofauna of the littoral zone in upper Newport Bay was numerically dominated by a few, low trophic-level species (five species ac- counted for >98% of all specimens collected), a situation similar to that found in many estuarine fish populations (Allen and Horn 1975). Atherin- ops affinis is an opportunistic feeder and has been characterized as both a herbivore/detriti- vore (Allen 1980) in upper Newport Bay and a low-level carnivore (Fronk 1969; Quast 1968). The second most abundant fish, Fundulus parvi- pinnis, is a low-level carnivore that feeds on small crustaceans and insects (Allen 1980; Fritz 1975). Gambusia affinis, Clevelandia ios, and Anchoa compressa are, likewise, low-level carni- vores, feeding mainly on insects, benthic micro- invertebrates, and zooplankton (Allen 1980). Large individuals of Mugil cephalus were not sampled effectively, but probably constituted a significant proportion of biomass within these fish assemblages. Adult M. cephalus fed mainly on detritus and pennate diatoms (Allen 1980). This essentially herbivorous diet closely matches that described by Odum (1970) for M. cephalus. The overall H' diversity values (H'x range, 0.42-1.76; overall 0.89) for the littoral zone were comparable to values derived from other studies of bay-estuarine fish faunas and to other studies in Newport Bay. Haedrich and Haedrich (1974) derived values of 0.33-1.03 for Mystic River Es- tuary, Mass.; Stephens et al. (1974) presented in- dices of 0.65-2.08 for Los Angeles Harbor, Calif.; Allen and Horn (1975) published values of 0.03- 1.11 for Colorado Lagoon, Alamitos Bay, Calif.; and Quinn (1980) calculated values of 0.21-2.59 (overall 1.9) for Serpentine Creek in subtropical Queensland. Using otter trawl data, I calculated #; values of 0.20-1.96 (overall 0.98) for the upper Newport Bay in 1974-75 (Allen 1976). The con- current bimonthly portion of this study (Horn 784 ALLEN: LITTORAL FISH ASSEMBLAOE and Allen 1981) obtained a bimonthly range for numbers of 0.48-2.17 (overall 1 .05) when the deep- er channel areas were also sampled. The rela- tively wide range of H'\ values in all of the above studies reflects the differential utilization of these embayments by fishes on a seasonal basis. At the same time, the low overall diversity re- flects dominance both in numbers and biomass by a few species. The seasonal usage has the effect of increasing annual diversity, although only one or two species dominate numerically at any one time. The H' values for biomass (H'n range 0.23-1.55; overall 0.84) were fairly close to those for numbers and, again, mainly reflected the dominance of A. affinis (~80%). In all, 26 of the 32 reported species had young-of-the-year fishes, making up a significant portion of their populations. Fluctuations in juvenile population levels had a substantial effect on the littoral fish populations. Juvenile recruitment plus the im- migration of adult fishes presumably for repro- duction or for exploitation of high productivity in warmer months were the principal causes for seasonal changes in the ichthyofauna. These ac- tivities reflect the widely recognized function of bay-estuarine environments as spawning and nursery grounds (Haedrich and Hall 1976). The general pattern of increased number of species and numbers of individuals during the late spring through fall period in upper Newport Bay has been observed in many other studies of temperate bay-estuarine fishes (e.g., Pearcy and Richards 1962; Dahlberg and Odum 1970; Allen and Horn 1975; Adams 1976a). Several studies of estuarine fish populations have, in addition, de- tected summer depressions in abundance be- tween peaks in spring and fall in other estuaries (Livingston 1976; Horn 1980) and in lower New- port Bay (Allen 1976). Studies of subtropical estuarine fish popula- tions have shown a trend in seasonal abundances that is 6 mo out of phase with the above observa- tions. Fish abundances were highest during the winter months (November-March) in the Hui- zache-Caimanero Lagoon of Mexico due to increases in members of both demersal and pe- lagic fishes (Amezcua-Linares 1977; Warburton 1978). This coastal lagoon system is subject to a narrower range of temperatures over the year (18.3°-27.9°C) than most temperate systems. However, the Mexican system undergoes wide variation in salinity, especially during the rainy season from July to October (see section Influ- ence of Abiotic Factors). Species Associations Species groupings were subject to strong sea- sonal influence and bore a striking resemblance to the classification scheme of Atlantic nearshore fish communities proposed by Tyler (1971). Ac- cording to Tyler's classification the Atlantic nearshore fish communities can be divided into regular and periodic components. Periodic com- ponents can be winter seasonals, summer season- al, or occasionals. The upper Newport Bay fish assemblage had regulars (group I) and periodics (groups II-V). The "anchovy" group (II), the "goby" group (III), and the " Engraulis-Hypsop- setta" group (IV) were all summer seasonals. Group V had both winter seasonals in Mugil cephalus and Lepomis macrochirus and summer seasonals in Lepomis cyaneilus and Leuresthes tenuis. The latter group, however, could best be characterized by the affinity of its components to lower salinities rather than to a particular time of year. The occasional component was repre- sented by the 12 species of group VI which also occurred in the summer. Thus Tyler's classifi- cation may have a broader application than he originally proposed, and perhaps holds true for many estuarine ichthyofaunas. Species Densities and Productivity Density estimates for some species of littoral fishes are particularly difficult to obtain. Such species include small, burrow-inhabiting fishes of the family Gobiidae and other small benthic fishes such as killifishes, flatfishes, and sculpins which escape under a seine or through the mesh of various nets. This study attempted to obtain density values for all littoral fishes, especially for the elusive species listed above. By setting up the procedure for choosing the "best estimate" of density from among four different sampling methods, actual densities of the species have been more closely approximated. If the biomass density of Atkerinops af finis for the entire study is calculated by dividing its total biomass by the total area of coverage by all four sampling gears, a biomass density of 3.3 g/m2(or about 0.83 g DW/m2) is obtained. This density value is lower than the estimate of 1.16 g DW/m2 derived through the best estimate process (Table 6). In this particular case, most densities were mean values of six bag seines which were very effective (99%) at capturing A. affinis (Horn and Allen footnote 2). Biomass density for the gobiid, 785 FISHERY BULLETIN: VOL. 80, NO. 4 Table 6.— Grand mean estimate of bio- mass density (g DW/m2) for common spe- cies in the littoral zone (excluding panne) over the 13-mo period (January 1978-Janu- ary 1979) from the best estimate criteria. Species Xg DW/m2±1 SE Athennops alfinis (adult) A. affinis Fundulus parvipinnis Gambusia affinis Clevelandia ios Anchoa compressa Cymatogaster aggregata Gillichthys mirabilis Anchoa delicatissima Mugil cephalus Quielula ycauda llypnus gilberti Hypsopsetta guttulata Engraulis mordax Lepomis macrochirus Lepomis cyanellus 0.1043±0.0602 1.1590±0.2573 0.1064±0.0223 0.001 5±0 0028 0.0261 ±0.01 17 0.1195±0.0493 0.0167 ±0.0158 0.01 31 ±0.0035 0.0077+0.0053 0.0024+0.0018 0.0029±0.0025 0.0021 ±0.0021 0.0043±0.0035 0.0019±0.0018 0.0006+0.0005 0.0003+00001 1.5688 g DW/m2 Clevelandia ios, determined by total area cover- age was 0.013 g/m2 (about 0.003 g DW/m2). The value based on best estimate (using square enclo- sures and small seine estimates) was about 10 times higher at 0.03 g DW/m2. This large dis- crepancy is due to the low efficiency of the bag seine for capturing this species. Since the bag seine covered the largest area of any of the sam- pling gears (220 m2), its addition to the density determination for C. ios led to the large under- estimate. The total biomass density of all species by total area was 4. 13 g/m2 (or about 1.02 g DW/ m2) which again was lower than the best estimate grand mean density of 1.57 g DW/m2. Average standing stock for the upper bay spe- cies during 1978 was 784 kg DW, based on an estimate of 50 ha of habitable littoral zone in upper Newport Bay. This is equivalent to 3,136 kg (wet weight) or 6,899 lb of fish. By the same procedure, the average standing stock of A. affinis was 631.6 kg DW and that of C. ios, 13.1 kg DW. The annual production of 9.35 g DW/m2 for the upper Newport Bay littoral zone in 1978 ranked among the highest values recorded for studies with comparable production determinations of production models (Table 7). The Newport Bay production estimate in 1978 was surpassed only by the estimate for Fundulus heteroclitus (Meredith and Lotrich 1979), an es- tuarine species of the east coast of the United States. Fundulus heteroclitus represented a very efficient energy link between the marsh and the littoral zone in their study. However, as Mere- dith and Lotrich pointed out, the production value may be an overestimation due to the under- estimation of the area of marsh utilized by the fish. The value 4.6 g DW/m2 obtained by Adams (1976b) for fishes inhabiting east coast eelgrass beds, which are acknowledged as highly produc- tive areas, is half the estimate for the littoral zone of upper Newport Bay. Short food chains have been implicated as the primary reason for high production in estuarine fish communities (Adams 1976b), a contention which is supported by the findings of this study. Young-of-the-year Atherinops affinis accounted for 85% of the annual production and formed a direct link through their herbivorous/detritivor- ous diet to the high primary productivity of this estuarine system. The remaining, numerically important species of the littoral zone were low- level carnivores. There is little doubt that this assemblage represents an example of "food chain telescoping" as described by Odum (1970). Even though the fish production in the littoral zone of upper Newport Bay was high compared with most comparable studies, the value pre- sented here is undoubtedly an underestimate. The largest species of the system, adult Mugil cephalus, was not represented in the production estimates due to inadequate sampling. Inclusion of this species would have substantially increased the production value. It is unlikely, however, that productivity of adult M. cephalus could approach that of juvenile Atherinops affinis which were responsible for 85% of the annual fish produc- tion. Influence of Abiotic Factors The positive correlations between tempera- ture and total abundance, biomass and number of species, and between salinity and total abun- dance and biomass indicate the general impor- Table 7.— Comparison of annual fish production (P) for ma- rine or estuarine studies with comparable production determi- nations. Wet weights were converted by multiplying by 0.25. Values are for all species except where noted. Estimated annual P Study (g DW/m2) Locale and habitat Delaware salt marsh creek {Fundulus heteroclitus) Newport Bay littoral zone Mexican coastal lagoon Cuban freshwater lagoons No. Carolina eelgrass beds Bermuda Coral Reef Texas lagoon (Laguna Madre) English Channel pelagic and demersal fishes Georges Bank commercial fishes Meredith and Lotrich (1979) 10.2 present study 9.4 Warburton (1979) 8.6 Holcik (1970) 62 Adams (1976b) 4.6 Bardach (1959) 4.3 Hellier (1962) 3.8 Harvey (1951) 10 Clarke (1946) 0.4 786 ALLEN: LITTORAL FISH ASSEMBLAGE tance of these factors to this assemblage. Indi- vidual correlations between abiotic factors and species abundances likewise emphasized the im- portance of temperature and salinity. The corre- lations between individual species abundances and dissolved oxygen as well as distance into the upper Newport Bay could be due to the intercor- relations of both dissolved oxygen and distance with temperature. Intercorrelations among factors can confound the interpretation of relationships and introduce redundancy in multivariate analyses. The rela- tionship between dissolved oxygen and distance into the upper Newport Bay is intuitive consider- ing its shallow depths. The positive relationship between temperature and dissolved oxygen was probably due to photosynthesis by green algae during the summer. Winter rainfall in the basic- ally Mediterranean climate of southern Califor- nia was responsible for the positive correlation between temperature and salinity found in New- port Bay. This relationship is by no means abso- lute, as evidenced by the low salinities encoun- tered during the tropical rains of September 1978 when temperatures were high. The results of the second canonical correlation analysis indicate that interaction between tem- perature and salinity explained most of the vari- ability in species abundance in this system. The correlation between these two abiotic factors probably inflated the R2 value slightly, but does not negate the overall findings. Ordination of in- dividual species by correlation coefficients with temperature and salinity underscores the influ- ences of these factors on individual species. Fur- thermore, the substantial decrease in numbers of A. affinis at station 1 and the somewhat smaller decrease at station 3 during September rains (low salinity) and relatively high temperatures also illustrate this temperature-salinity inter- action. I propose that an important consequence of temperature-salinity influence found in the present study is the transfer of biomass and, therefore, energy from the littoral zone to the adjacent channel and ultimately to local offshore areas via migration of fishes. This mechanism for energy transfer was best illustrated by the apparent emigration of a large portion of the 0- age class A. affinis from the littoral zone from September to December 1978. The transfer also included the biomass produced by essentially all of the periodic species. Weinstein et al. (1980) reached a similar conclusion in their study of the fishes in shallow marsh habitat of a North Caro- lina estuary. An extensive mark and recapture study should be planned to test this hypothesis in the future. Seasonal fluctuations of temperate bay-estua- rine fish populations may have several causes, but temperature and salinity seem frequently to be the underlying factors. The pattern of in- creased number of species and individuals with increased temperature in temperate bays and estuaries has been reviewed by Allen and Horn (1975). Recently the large-scale influence of sa- linity on bay-estuarine fish populations has been demonstrated by Weinstein et al. (1980) for Cape Fear River Estuary, N.C. Unfortunately, any salinity interaction with temperature was not in- vestigated or discussed in the above study. Studies of subtropical estuaries (Amezcua- Linares 1977; Warburton 1978; Quinn 1980) in- dicate that salinity may have greater influence on fish populations, since annual temperature ranges are narrower than in temperate bays and estuaries. In each of the above studies on sub- tropical estuaries, increased abundances cor- responded to the season of low rainfall and there- fore high salinity. Blaber and Blaber (1981) con- cluded that turbidity and not temperature and salinity was the single most important factor to the distribution of juvenile fishes in subtropical Moreton Bay, Queensland. However, Blaber and Blaber ( 1981) did not present statistical evidence to support this contention. The most important environmental factors influencing tropical estu- arine (eelgrass) ichthyofaunas are more difficult to identify (Weinstein and Heck 1979; Robertson 1980) and probably include biotic factors such as prey availability, competitors, predators, as well as abiotic factors. Biotic interactions are un- doubtedly important in temperate estuarine sys- tems including upper Newport Bay. However, their overall influence on the system is probably swamped by large fluctuations in the physical environment. Fluctuations in rainfall and temperature re- gimes during a year and from year to year can have marked effects on the ichthyofauna of estu- aries. Moore (1978) has identified long-term (1966-73) fluctuations in summer fish popula- tions in Aransas Bay, Tex. He found that diver- sity values (H' range of 1.38-2.13) were quite variable from year to year probably as a result of major climatological changes (an unusually wet year; a drought and two hurricanes). These changes in diversity values were probably caused 787 FISHERY BULLETIN: VOL. 80, NO. 4 by changes in abundance within a set of resident estuarine species and of periodic species. In 1978 the ichthyofauna of upper Newport Bay was subjected to rainfall twice that of a "nor- mal" year (70.9 cm for 1978; mean 28.1 cm). The specific effects of this increased precipitation are difficult to assess due to a lack of data from pre- vious years but some guarded comparisons can be made. Population densities of Atherinops affinis were lower in 1974-75 than those encoun- tered during 1978 (Allen 1976). Also Cymato- gaster aggregata, Clevelandia ios, and Leptocot- tus armatus occurred in lower numbers in 1978 than in previous years (Horn and Allen 1981). These discrepancies point out the strong year- to-year fluctuations that occur in the fish popula- tions of upper Newport Bay. This conclusion is in complete agreement with the findings of Moore (1978) and sheds doubt on the possibility of com- pletely characterizing a "normal" year in many estuaries because of unpredictable annual varia- tions in climate. ACKNOWLEDGMENTS This paper represents a portion of my disserta- tion research completed at the University of Southern California. For their support and guid- ance I wish to thank my dissertation committee members: Basil Nafpaktitis, Jon Kastendiek, Robert Lavenberg, Kenneth Chen, and, espe- cially, Michael Horn. A number of people deserve my thanks for participating in the sampling pro- gram over the 13-mo period; they are Gary Devian, Frank Edmands, Terry Edwards, Den- nis Hagner, John Hunter, Paul Kramsky, Marty Meisler, Margaret Neighbors, Linda Sims, Vic Tanny, Jr., Carol Usui, Brian White, and Craig Wingert. Special thanks go out to Russell Bell- mer (U.S. Army Corps of Engineers), Jack Fan- cher (U.S. Fish and Wildlife Service, USFWS), Peter Haaker (California Department of Fish and Game), Katie Heath, Jeff Jones, Marie Har- vey, and Wayne White (USFWS) for their help in carrying out the field work. I thank Ed DeMar- tini and Michael Horn for offering helpful com- ments on the manuscript. Financial support for this research was pro- vided by a contract from the California Depart- ment of Fish and Game to California State Uni- versity, Fullerton (M. H. Horn, Principal Investi- gator). A 3-mo extension was generously funded by the Orange County Fish and Game Commis- sion. LITERATURE CITED Adams, S. M. 1976a. The ecology of eelgrass, Zostera marina (L.), fish communities. I. Structural analysis. J. Exp. Mar. Biol. Ecol. 22:269-291. 1976b. The ecology of eelgrass, Zostera marina (L.), fish communities. II. Functional analysis. J. Exp. Mar. Biol. Ecol. 22:293-311. Allen, K. R. 1950. The computation of production in fish populations. N.Z. Sci. Rev. 8:1-89. Allen, L. G. 1976. Abundance, diversity, seasonality and community structure of fish populations in Newport Bay, California. M.A. Thesis, California State Univ., Fullerton, 108 p. 1980. 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Soule and M. Oguri (editors), Marine studies of San Pedro Bay, California, Part IV, Environ- mental field investigations. Allan Hancock Found. Publ., USC-SG-6-72:l-42. Targett, T. E., and J. D. McCleave. 1974. Summer abundance of fishes in a Maine tidal cove with special reference to temperature. Trans. Am. Fish. Soc. 103:325-330. Tyler, A. V. 1971. Periodic and resident components in communities of Atlantic fishes. J. Fish. Res. Board Can. 28:935-946. Warburton, K. 1978. Community structure, abundance and diversity of fish in a Mexican coastal lagoon system. Estuarine 789 FISHERY BULLETIN: VOL. 80, NO. 4 Coastal Mar. Sci. 7:497-519. Weinstein, M. P., S. L. Weiss, and M. F. Walters. 1979. Growth and production of some important species 1980. Multiple determinants of community structure of fish in a Mexican coastal lagoon system. J. Fish Biol. in shallow marsh habitats. Cape Fear River Estuary, 14:449-464. North Carolina, U.S.A. Mar. Biol. (Berl.) 58:227-243. Weinstein, M. P., and K. L. Heck, Jr. Wiley, J. L., T. S. Y. Koo, and L. E. Cronin. 1979. Ichthyofauna of seagrass meadows along the 1972. Finfish productivity in coastal marshes and estu- Caribbean coast of Panama and in the Gulf of Mexico: aries. In Proceedings of the Coastal Marsh and Estu- composition, structure and community ecology. Mar. ary Management Symposium, Louisiana State Univ., p. Biol. (Berl.) 50:97-107. 139-150. 790 CYCLIC COVARIATION IN THE CALIFORNIA KING SALMON, ONCORHYNCHUS TSHAWYTSCHA, SILVER SALMON, 0. KISUTCH, AND DUNGENESS CRAB, CANCER MAGISTER, FISHERIES Louis W. Botsford,1 Richard D. Methot, Jr.,2 and James E. Wilen3 ABSTRACT There are apparent cyclic fluctuations in the catch record of both northern and central California salmon fisheries. They are of the same period and strength as well-known cycles in crab catch but of different phase. Statistical characteristics of this covariation, as reflected in estimates of auto- and cross-correlation functions, change following the decline of the central California Dungeness crab fishery. Analysis of a likely cause of this phenomenon, a greater delay in switching of effort from crab to salmon during years of high crab catch, indicates that this mechanism is not present. Phase differences between salmon and crab cycles imply constraints on remaining potential causes, but a cause of the cyclic covariation has not been established. Regular patterns in fishery catch records reflect underlying mechanisms that can provide the basis for broader understanding, better predic- tion, and consequently better management of the fishery. Cyclic fluctuations in the northern Cali- fornia Dungeness crab catch have been a topic of research for the past 10 yr. We document here cyclic fluctuations in the northern California salmon catch (Fig. 1) of the same frequency but different phase. Coastwide fluctuations in Dungeness crab catch were originally attributed tooceanograph- ic causes (Anonymous 1965). Peterson (1973) demonstrated a statistical relationship between coastal upwelling and crab catch. Botsford and Wickham (1975) concluded from estimates of the appropriate cross- and auto-correlation func- tions that, while crab catch was indeed cyclic and upwelling was correlated with crab catch after a lag of 1 or 2 yr, upwelling itself was not cyclic, hence was not the source of the cycles. Botsford and Wickham (1978) later showed that interage, density-dependent mortality could be the cause of the observed cycles, and derived new stability results that indicated size-selective fishing could decrease population stability, and thereby in- 'Department of Wildlife and Fisheries Biology. University of California. Davis, CA 95616. 2Bodega Marine Laboratory. P.O. Box 247. Bodega Bay, Calif.; present address: Southwest Fisheries Center La Jolla Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla. CA 92038. 3Division of Environmental Studies, University of Califor- nia, Davis. CA 95616. crease the propensity for cyclic fluctuations. They cited two known potential interage, den- sity-dependent mechanisms, cannibalism and an egg-predator worm, and are conducting field samples of these. On the basis of a disparity be- tween the period of observed cycles and the peri- od of cycles produced by a model that included cannibalism, McKelvey et al. (1980) claimed that cannibalism could not cause the cycles. Botsford (1981) pointed out that the observed disparity was not new, but had been noted by Botsford and Wickham (1978), and critically analyzed the rea- soning used by McKelvey etal. (1980) in drawing a new conclusion. In summary, the cause of cycles in the northern California Dungeness crab Dungeness crob Totol salmon Silver salmon 3 O x X 2 o < < in 80 Manuscript accepted April 1982. FISHERY BULLETIN: VOL. 80, NO. 4. 1982. Figure 1.— Total landings (kg) in the northern California crab and salmon fisheries for the years 1940-76. 791 FISHERY BULLETIN: VOL. 80, NO. 4 catch record is still not known and research in this area is continuing. In contrast to the considerable research atten- tion attracted by cyclic fluctuations in crab catch, fluctuations in the salmon catch record have, to our knowledge, not been previously iden- tified as cyclic. Yet, as seen in Figure 1, these apparently periodic fluctuations in salmon catch have a peak amplitude of about ±0.5 of the mean value. While abundance is predicted each year as part of the management process, these predic- tions have not taken advantage of this regular pattern that accounts for about two-thirds of the peak catch. An understanding of the underlying cause of cycles in salmon catch has great poten- tial for improved predictive ability and better salmon management. There are many possible causes of the observed similar cycles in the salmon and crab fisheries. There may be a direct biological interaction be- tween the two species that by itself gives rise to cycles. Alternatively, one may vary cyclically and a direct biological interaction may cause the other to follow it. As another class of possibilities the two processes need not necessarily be directly related but may both be under the influence of a third process (e.g., environmental factors). A third class of possible causes of the observed co- variation is some sort of economic linkage be- tween the two fisheries. Since many fishermen fish both species, abundance and effort in one could affect effort in the other. METHODS AND DATA Our approach to eliminating unlikely causes of the observed covariation from the many possible causes is based on interpretation of estimated auto- and cross-correlation functions (also called correlograms). This statistical technique has been useful in interpretation of cycles in wildlife populations (Moran 1949; Finerty 1980) and is a recommended initial step in time series analysis (Jenkins and Watts 1968; Box and Jenkins 1970). However, there are few useful results on statisti- cal significance of estimated correlation func- tions. We use a simple form of a method described by Bartlett (1946). If individual points in a time series are independent and identically distrib- uted, an estimate of the correlation between them is Gaussian with mean zero and variance 1/N where N is the total number of samples on which the estimate is based. In the following analysis we show 5% error limits on plots of cor- relation functions. The occurrence of values of correlation greater in magnitude than this limit more frequently than 1 in 20 indicates a "non- random" process. This approach is somewhat limited in that it focuses on single points rather than the pattern of the estimated correlation function as a whole. If samples in each series are not independent, the significance of both cross- and auto-correla- tion functions will be overestimated (Granger and Newbold 1974). A suggested solution to this problem in estimating cross-correlations is to prewhiten (i.e., remove correlation between sam- ples) each series by fitting an ARM A model (Box and Jenkins 1970) to the series, then compute cross-correlations between the residuals. We have not taken this approach for two reasons: 1) Computed correlations based on the residuals actually underestimate significance of results (Box and Pierce 1970; Durbin 1970) and 2) pre- whitening may actually remove correlations of real interest. With regard to the latter, some auto-correlation within each series exists be- cause of known physical processes (e.g., the fact that catch is the result of fishing several age classes causes intraseries correlation). Removal of this intraseries correlation would reduce the chance of detecting real interseries correlation (e.g., correlation stemming from a causal mech- anism that involved catch). Removal of intraser- ies correlation on the basis of known physical mechanisms will provide more meaningful re- sults; however, it will require further studies of effort dynamics and life histories in both the salmon and crab fisheries. In the meantime, as a simple exploration of the possibility of "spurious" results, we also present correlograms computed from first-differenced data (first-differencing is the process of replacing the data point xt at time t with the difference xt — .r(_i). First-differencing reduces intraseries correlation and has been shown to greatly reduce the incidence of spurious interseries correlation (Granger and Newbold 1974). Correlation results of first-differenced data can be interpreted as the correlation be- tween changes in each series. Also, in all correla- tions presented, a linear trend has been removed from the series. Salmon data for these analyses are from month- ly catch records collected and published by the California Department of Fish and Game (1954- 78). The northern California salmon catch con- sists of landings at Crescent City, Eureka, and Fort Bragg. The central California catch is from 792 BOTSFORD ET AL.: CYCLIC COVARIATION IN CALIFORNIA FISHERIES San Francisco and Monterey. The unit of salmon catch is kilograms of dressed fish with heads on. Crab catch (kilograms) was summarized by season rather than calendar year so that a sea- son's catch includes catch from November and December of the previous year. The geographic breakdown of crab catch was the same as the salmon catch. Seasonal distribution of crab catch and effort was available only from 1952 to 19764 for a northern California region which included an average of 93% of the total northern California catch. In addition to crab catch data, we have also used recent estimates of preseason legal abundance (Methot and Botsford 1982). These estimates were computed from the decline in catch-per-unit-effort within each season accord- ing to the Leslie method. Gotshall( 1978) also esti- mated preseason legal abundance for the years 1967-72 using the Leslie method. His results for those years are essentially the same as those used here. McKelvey et al. (1980) also estimated pre- season legal abundance, but used a method that depended on the estimated total number of pots in the fishery and annual catch. Since the rela- tionship between these variables can change from year to year in this fishery, we did not use their estimates. We present first the statistical characteristics of cyclic fluctuations in the northern California salmon and crab catch records as reflected in estimates of their auto- and cross-correlation functions. We then examine characteristics of each of the two salmon species in the fishery. The northern California salmon fishery is composed of king (or chinook) salmon, Oneorhynchus tsha- wytscha, which originate primarily in coastal rivers of northern California and Oregon, and silver (or coho) salmon, 0. kisutch, which origi- nated primarily in coastal rivers of northern California and Oregon in the 1950's, but depend increasingly on hatchery production in Oregon in the 1960's and 1970's (Pacific Fisheries Man- agement Council 1978). We then compare the characteristics of the northern California fishery to the central Cali- fornia fishery which differs in two respects: 1) It includes a period of protracted decline in the crab fishery and 2) it involves salmon stocks that originated in the Sacramento and San Joaquin River systems (Pacific Fisheries Management Council 1978). The central California crab fish- ery declined near 1960 and has remained at a low level since then. Putative causes of this decline and continued low level include an increase in sea temperature (Wild 1980), a predatory worm (Wickham 1979), and an increase in individual growth rate (Botsford 1981). We compare char- acteristics of the northern California fisheries with the central California fishery both before and after the decline. We then examine a specific potential cause of the observed covariation. The most obvious and perhaps the most parsimonious explanation of the observed covariation in catch records is switching behavior of fishermen. The proposed hypothesis is simply that, during years of high crab abundance, more fishermen continue to fish for crab rather than beginning to fish for salmon when the salmon season opens. The legal crab season opened in December and continued at least through June in the years of interest. The salmon season opened in April or May, depend- ing on year and species. Although most of the crab catch is landed early in the season, crab and salmon seasons do overlap, thus providing an opportunity to switch. The possibility that this mechanism is responsible for the observed be- havior is examined here from three points of view: 1) A comparison of catch during overlap- ping and nonoverlapping segments of the salmon season, 2) analysis of changes in mean date of the salmon catch, and 3) calculation of the relation- ship between salmon catch and crab catch per delivery during May and June. RESULTS Northern California Total Catch Estimates of the auto-correlation function for both total northern California Dungeness crab landings and total northern California salmon landings for the years 1940 to 1976 are of the form that would arise from cyclic processes of period 9 or 10 yr (Fig. 2). They both fall to a sig- nificant negative value of correlation then rise to a significant positive value of correlation.5 The auto-correlation of crab abundance is not shown "Annual Market Crab-Statewide Reports, California Depart- ment of Fish and Game. 1952-77. 5Estimates of the same functions for the time period 1952 to 1976 imply that crab is more cyclic (dropping to 0.7 then in- creasing to 0.8) while salmon is less cyclic (dropping to -0.3 then increasing to 0.4). In this analysis, as in the raw data (Fig. 1), salmon catch appears to be more cyclic in earlier rather than later years, while the crab catch appears to be more cyclic in later years. 793 FISHERY BULLETIN: VOL. 80, NO. 4 LAG (years) Figure 2.— An estimate of the autocorrelation functions for northern California total salmon and crab catch data (Fig. 1). Dotted lines are 0.05 error limits (see text). i.o 0 5- 0.0 o I- < cr_ or o o If) in O or u -05 -1.0 •15 Northern Salmon i salmon catch lags 1 crab catch . ! 1940-1976 ■10 -5 0 LAG (years) 10 Figure 3.— An estimate of the cross-correlation function be- tween northern California total salmon and crab catch data (Fig. 1). A positive lag corresponds to salmon following crab. but is essentially the same as the auto-correlation of catch (i.e., decreases to significant negative values at 4 and 5 yr, then increases to significant positive values at 10 yr). The auto-correlation functions computed from first-differenced crab and salmon catch series have the same form but are lower in absolute values. The first negative peak is just barely sig- nificant in both, whereas the positive peak of about 10 yr is significant only for the crab catch series. An estimate of the cross-correlation between total northern California salmon and crab catch is of the form that would arise from two cyclic, covarying processes with a period of 9 or 10 yr and a constant lag of about 4 yr (salmon leading crab) (Fig. 3). Decreasing amplitude of the cor- relation function with increasing lag is caused by the increasing amplitude of crab catch. The im- plications of Figure 3 are that crab catch is nega- tively correlated with salmon catch 1 or 2 yr later and salmon catch is positively correlated with crab catch 3, 4, and 5 yr later. The same cross-correlation computed for the years for which crab abundance estimates are available (1952-76) is essentially the same as Fig- ure 3. The cross-correlation computed using pre- season abundance instead of catch also is quite similar. First-differencing all three cross-cor- relation functions reduces the amplitude of the function somewhat. The correlation at positive lag is no longer significant and correlation at negative lag is significant only at a lag of —5 yr (except for first-differenced preseason abun- dance which is not quite significant). The values of cross-correlation for the various versions of these time series are summarized in Table 1. Northern California Catch by Salmon Species Because of differences in life history between the two species and the fact that increasing num- bers of silver salmon originate in hatcheries, comparison of the relative contributions of each species to the cyclic covariation with crab could provide a clue to the underlying cause. Neither of the estimated auto-correlation functions for king and silver salmon appear as cyclic as the auto- correlation of combined salmon catch (Fig. 4). From this figure king salmon appears somewhat Id or or O <_> o h- < 0 5 00 •0 5 10 4 6 LAG (years) 10 Figure 4.— An estimate of the autocorrelation functions for northern California king salmon and silver salmon catch data (Fig. 1) for the years 1952-76. 794 BOTSFORD ET AL.: CYCLIC COVARIATION IN CALIFORNIA FISHERIES T DO CD CC I CM O O i- 1 en r~- o> in O T" 1 1 CO i- CO CO 1 1 i- o in in i- o 1 1 m o O CM 1 to i- o o T O) 00 o o CO f T i CO CO i- o o in T T O CM CO i- O) o> CM t- O r- CM O o in *t CO in cm r- o 1 oo in o o i- CM ^f CM O CO O i- 1 1 O 00 CM O 1 CO CO CO o in en CO o O CO »- o CM -"J" CM O h- O CM O r- o CM i- CM Q CM CO CO o in ■»■ CO CM col t- ■ i- o r^ cm *~ T CO t- r- CM CO i- O CO T? CD T CM CM CO CO o ir> in CM O 1 1 co in i- o 1 1 in i- T" O 1 1 i- CO O i- 1 CO CM I- CM 1 1 CO r- o o 1 O) CO CM O 1 1 O) CO O i- o CM T ■*r| in tIcm 1 1 CM 00 ■* CM 1 1 ool 00 ■t CO 1 1 00 CO CO CM 1 1 CM i- CO CM 1 1 cd -- t o r-\ r*- ml i- o>| in Ol T- col CO CM P"- CM r- 1 ■ o o oo h- i- O) CM O 1 1 O) CT> T? ml co ml cm I 1 cmIco co co 1 1 CO CO 1 1 O) CO 1 1 *r|r^ m|co 1 1 m o> ■^ r- 1 1 r-~ h- -» CM 1 1 m t- CM O 1 1 Tlcnl co in| 1 1 ol ml oi m 1 1 col in col T* 1 1 ,-| CM I-. ■* 1 1 1 — 1 -^3" 1 1 ol m oo ^r 1 1 r-~ oi ■G CM 1 1 col o| col *t\ 1 1 cm| o m in 1 1 o>| in ml cm 1 1 CO O) TT CM 1 1 ool 00 col ■<* 1 1 ool m CO •>» 1 1 O i- CO CM 1 1 O u. O"- Ou-Ou- Oli- Ou- Oli- O a o o o o o o o z o z o z o z o z o O u- o o o O o o o b b b E E en c CD > b E CO CO CO CO CO CO CO CO en CO 00 00 MT CO 00 00 n n ~A a n n n n n CO CO CO CO CO CO CO CO CO o CD O CO CD C >. ■O CO < LU cyclic while silver salmon is less so. The latter may be due to the shorter time record for silver salmon. First-differencing decreases the value of the peak of negative correlation in king salmon to an insignificant level but the pattern is pre- served. Estimates of cross-correlation between crab catch and catch of each salmon species appear similar to the correlation between crab catch and total salmon catch (Fig. 5). Again, the observed characteristics seem to be stronger in the king salmon rather than the silver salmon records. First-differencing of the crab and salmon series reduces correlation values so that the positive correlation at a negative lag remains significant for king salmon only (Table 1). i o o < tr o o 00 00 o tr o 0.5 - 0.0 - -0.5 - -1.0 i Northern California 1 salmon catch ags crab i catch K inq 1 Silver \ 1 1 V i A \ * i \ \ \ \ \ \ / / // // \\ N / / \ \ / \ \ / - \ \ \ \ \ *- - 1 // - 1 1 1 i -15 ■10 -5 0 LAG (years) 10 15 Figure 5.— An estimate of the cross-correlation function be- tween northern California crab catch and king salmon and sil- ver salmon for the years 1952-76. Central California Total Catch Because of differences between the central California crab fishery (Fig. 6) and the northern California crab fishery, comparison of charac- teristics of covariation between salmon and crab in northern California with that in central Cali- fornia provides some basis for determining the underlying cause of the covariation in northern California. We can narrow the range of possible causes by determining whether the covariation under discussion here exists both before and after the decline of the crab fishery in 1961. This investigation is, however, somewhat hampered by the extremely short time series that result from bisecting these records. For the predecline period (1940-61), the auto- 795 FISHERY BULLETIN: VOL. 80, NO. 4 Dungeness crab Total salmon Silver salmon 2 5 Figure 6.— Total landings (kg) in the central California crab and salmon fisheries for the years 1940-76. correlation functions of salmon and crab catch are virtually the same as in northern California. Salmon and crab fall to —0.37 and —0.59, respec- tively, (the latter is significant at 0.05) at 4 yr, then increase to +0.43 and +0.54, respectively, (neither significant at 0.05) at 10 yr. First-dif- ferencing decreases the strength of both the posi- tive and negative peaks of auto-correlation in both of these series. The estimated cross-correla- tion between salmon and crab catch in the early period is also similar to that in northern Califor- nia except for a shift in the negative lag direction near zero lag (Fig. 7). The correlation at zero lag has a significant negative value in central Cali- fornia whereas it is not significant in northern i o LlI rr rr o o CO CO O li o 0 5- 00 - -0 5 •1.0 \ , ] Central Col iforiri'a "V /| isalmon lags efab / / rr-L |--J>I962- 1976. '.■*"' - i ""■?— -\— -j.— — "" i 1 _ \ * / j! \ ' n ' i i / > ,'\ j \ \ i i / * \" / i \ > / 1 / 1 l. ' \ / \ i \ 1 - J I . / VI / i ' \ /. >i ^^ ^-. * •.' - / : \ \ -10 -5 0 5 LAG ( years) 10 15 Figure 7.— Estimates of cross-correlation functions between central California Dungeness crab and total salmon catch, both before and after the decline in 19(51. Outer significance levels apply to the period after the decline. California. This shift would correspond to a negative relationship between crab and salmon, with salmon following crab more closely in cen- tral than in northern California. After first- differencing each series the positive correlation peak at negative lag disappears but the negative correlation at zero lag remains (Table 1). For the postdecline period (1962-76). the auto- correlation function for crab catch appears cyclic, as it was before the decline, but the period of the cycles has apparently decreased (Fig. 8). The auto-correlation function for salmon de- creases to a significant negative value at 3 yr, but shows no clear cyclic tendency for greater lags. First-differencing decreases this first peak by about 0.1 for both series. The cross-correlation estimate for the postdecline period is similar to the northern California relationship for negative lags (i.e., crab following salmon), but is not simi- lar for zero and positive lags (Fig. 7). Both of these latter estimates are for a low number of data points, hence interpretation for large lags is risky (note that the outer significance levels in Figure 7 are for the later period correlation). After first-differencing only the positive correla- tion at negative lag remains significant (Table 1). LAG (years) Figure 8.— An estimate of autocorrelation functions for cen- tral California Dungeness crab and total salmon catch for the years following the decline in crab catch (i.e., 1962-76). Switching Effort Between Species If the cyclic nature of salmon catch is caused by fishermen fishing salmon only when crab are not abundant, then cycles in salmon catch should be determined by salmon catch in the part of the 796 BOTSFORD ET AL.: CYCLIC COVARIATION IN CALIFORNIA FISHERIES season that overlaps the crab season. In other words, salmon catch should appear to be much more cyclic early in the season than late in the season. Salmon catch for the months of April through June and the period from July through September are shown in Figure 9.6 The only readily apparent feature of this plot is the in- creasing trend of early season catch. Estimates of the auto-correlation functions of early and late season salmon catch are shown in Figure 10. Neither of these appears as smoothly *The same analysis as that presented here was performed with a bisecting; date of 31 May rather than 30 June with no dif- ference in the results. 20 I 5 - x I- < ° I 0 z o < CO -i 0.5 - < 00 1 Northern California ■ April - June July- September I I 50 55 60 65 YEAR 70 75 80 Figure 9.— Total salmon catch (kg) in northern California in the early part of the season (April-June) and the late part of the season (July-September) for the years 1952-76. Northern California Salmon Catch April - June July- September. _ -1.0 10 12 LAG (years) Figure 10.— Estimates of the autocorrelation functions for the early (April-June) and late (July-September) parts of the sea- son. cyclic as the total catch. However, since they both decrease to negative values then increase to ap- proximately the same positive value at a 10-yr lag, one does not appear more cyclic than the other. Estimates of the cross-correlation between total crab catch and early salmon catch and be- tween total crab catch and late salmon catch are shown in Figure 11. There is very little differ- ence between these functions for each time peri- od and they are quite similar to the same function for total annual catch. The only difference be- tween the two species is a slightly more pro- nounced pattern of correlation for early rather than late season to the right of the origin (i.e., where salmon follows crab). After first-differ- encing only the positive correlation at a lag of —5 remains (Table 1). From Figures 10 and 11 we can conclude that the cyclic nature of salmon catch is not contained entirely in the early, overlapping part of the sea- son. A second, though not independent, means of testing the proposed hypothetical mechanism is to examine the mean data of salmon catch. If crab abundance determined salmon catch early in the salmon season, mean date of the salmon catch would increase with crab catch. The cor- relation between mean date of salmon catch and total crab catch was not significant (r — —0.022 with linear trend subtracted from mean date of salmon catch). Thus this test also yields a nega- tive result. A third consequence of the proposed mecha- o h- < or or o <_> CO co O rr <_> 0 5 00 - -0 5 -1.0 Northern California salmon catch logs crab April - June July- September •15 -5 0 LAG (years) 15 Figure 11.— Estimates of the cross-correlation functions be- tween Dungeness crab catch and total salmon catch early in the season (April-June) or total salmon catch late in the season (July-September). 797 FISHERY BULLETIN: VOL. 80, NO. 4 nism is a relationship between catch per delivery of crab and salmon catch. If fishermen continue to fish crab when crab is abundant, then there would be a relationship between catch per crab delivery and salmon effort in months of overlap between the two fisheries. This relationship would show up in salmon catch provided it was not occluded by fluctuations in salmon abun- dance. The value (v) per delivery of crab catch was computed for the months of May and June each year as follows: PW CPID where P W CPI D market price total weight landed in the months of May and June consumer price index number of deliveries in the months of May and June. For the years 1952 to 1976 there is no significant relationship between salmon catch during May and June and value of each crab delivery (r = 0.31). DISCUSSION Interpretation of the correlation functions computed here is somewhat subjective. Since, as described earlier, significance levels do not hold rigorously, they can be interpreted only in a rela- tive sense. Correlations from the first-differenced data can supplement interpretations of the raw (except for detrending) data. First-differencing removes intraseries correlation, hence empha- sizes changes between adjacent points in a series. Cross-correlations computed from first-differ- enced series are more sensitive to the timing of changes, and less sensitive to sustained high and low values. The lag between recurring changes in specific directions in each series must remain constant in order to produce a high cross-correla- tion. Significant correlations that do not remain high following first-differencing should not necessarily be regarded as spurious, rather they may stem from variables that are highly auto- correlated (e.g., abundance or catch as compared with age-class sizes). On the other hand signifi- cant correlations that remain high following first-differencing probably stem from variables with less intraseries correlation. Computed cross- and auto-correlations sup- port the existence of cyclic covariation between crab and salmon catch in northern California. The fact that the negative correlation at a lag of +2 (Fig. 3) is no longer significant after first-dif- ferencing (Table 1) implies that it probably arose from the extended periods of high constant crab catch and low constant salmon catch (Fig. 1). These same characteristics appear to be pres- ent when each salmon species is considered indi- vidually. They are, however, weaker in the king salmon and weaker still in silver salmon. The shorter length of the silver salmon time series may be responsible for the latter. The analysis of central California data is more informative, although it too is constrained by shorter series. Early catch records in central California resemble northern California records in some respects. The auto-correlations of both salmon and crab are the same and the cross-cor- relation function has the same general shape except that the peak at negative lag is at —3 yr and the peak at positive lag in northern Califor- nia is at a lag of zero (Figs. 3, 7). This negative correlation at 0 lag is quite apparent in Figure 6. The most striking departure from the northern California situation is the substantial decline of the positive peak at negative lag and the persis- tence of the negative peak at 0 lag following first- differencing (Table 1). This implies that changes in crab and salmon that are in the same direction are less regular than changes in the opposite di- rection. Following the decline in crab catch in central California the auto-correlation functions show weaker cycles of shorter period for the crab and the existence of a cyclic pattern for salmon is questionable. The cross-correlation function is similar to the predecline case but shifted to more negative lags. This could occur, for example, if two cyclic processes retained their shape but were shifted in time with respect to each other. After first-differencing the positive peak at negative lags persists yet the negative peak is diminished in magnitude by half. The postde- cline period is similar to northern California in this respect but differs in having a negative cor- relation at a lag of —2. The observed differences in lag value of points of significant correlation raise the question of whether the northern California crab or salmon fishery lags its central California counterpart. The cross-correlation between northern Califor- nia and central California salmon catch for the period 1940 to 1976 has a significant positive 798 BOTSFORD ET AL.: CYCLIC COVARIATION IN CALIFORNIA FISHERIES peak at +1 and +2 yr that remains significant at +1 yr after first-differencing. The same char- acteristics are present, though less strong, when the predecline and postdecline periods are con- sidered individually. This lag of 1 or 2 yr between northern California and central California salm- on catch is commensurate with the shift in the point of negative correlation for the predecline situation (Fig. 7). The cross-correlation between crab catches at the two locations does not show significant results nor do higher correlations persist after first-differencing. We can consider the implications of observed correlations for three classes of possible mecha- nisms. The first class of mechanisms involves cyclic environmental factors which indepen- dently drive the cycles in each species. Differ- ences in life history between the two species could be responsible for the phase difference be- tween the two cyclic processes. In the second class of mechanisms, one species is cyclic because of environmental factors or an endogenous mech- anism within the population and the second spe- cies is cyclic because of some linkage to the first species. The third possibility requires neither species to be inherently cyclic. Rather, a biologi- cal interaction between the two species results in cyclic behavior in both (e.g., as in a classical predator-prey system). The computed correla- tion functions place constraints on specific tim- ing of the mechanisms in each of these classes. These can be compared with known life history characteristics and suspected interactions to eliminate some possibilities. The life histories of the two species follow simi- lar temporal patterns. The eggs of Dungeness crab and fall-run king salmon hatch in midwin- ter. The pelagic crab larvae drift for several months then settle as first crabs during April and May. The salmon fry remain in streams for several months then enter the ocean in late spring through summer. Some adult crabs enter the fishery 3 yr after hatching but most are caught at age 4. King salmon first enter the fish- ery about 2% yr after hatching, and most are caught at 3% yr and some are caught 4% yr after hatching. That there was no significant positive cross- correlation between the two catch records at 0 lag indicates that a cyclic environmental factor which drives the cycle of one species through an effect on one age-class cannot also affect the same age-class of the other species. This implies, for example, no direct interaction between the 0 age classes of the two species. This is to be expected since most crab larvae have settled before salm- on smolts begin entering the nearshore pelagic environment. The positive cross-correlation, which indicates that good (bad) salmon catches are followed 3 to 5 yr later by good (bad) crab catches, may be a re- sult of a cyclic environmental factor which affects early salmon survival in 1 yr and similarly af- fects larval crab survival 3 to 5 yr later. This environmental factor need not affect exactly the same age class in both species. For example, a positive effect on growth and survival of matur- ing salmon in their penultimate year at sea and a simultaneous positive effect on ovary develop- ment in female crab could increase salmon catch in the following year and crab catch 4 to 6 yr later through increased egg production in the follow- ing year. Salmon have been observed to prey heavily on pelagic crab megalopae (Orcutt 1978). If this mechanism is considered as increased larval crab mortality when salmon are abundant, it does not fit the conditions implied by the correla- tions. However, if abundant crab megalopae lead to a good crab year class while increasing the growth and survival of adult salmon, then the observed cross-correlation would result. A mech- anism by which salmon were more available to the fishery during years of high crab larval abundance could also cause the observed covari- ation. The negative cross-correlation indicates that good (bad) crab catches are followed 1 to 2 yr later by bad (good) salmon catches. That this does not persist following first-differencing is commensurate with it being a result of fluctua- tion in an auto-correlated series (e.g., abundance) rather than a less auto-correlated series (e.g., re- cruitment). The mechanism which is a priori the most likely cause of this observation was the one investigated in detail in this paper: the cycle in salmon catch is actually a cycle in fishing effort for salmon and that this cycle is driven by the highly cyclic crab catch. The conclusion resulting from analyses of the hypothesis of behavioral switching by fishermen is that an immediate response to crab abundance is not a likely cause. The strongest evidence for this was the comparison of the cyclic nature of early with late season salmon catch. The other two analyses are less powerful because both the availability of salmon and the variation in wea- ther conducive to salmon fishing introduce vari- 799 FISHERY BULLETIN: VOL. 80. NO. 4 ability in April and May salmon catch. The con- clusion drawn from the comparison of early versus late season catch, however, rests on ob- serving the cyclic nature in the late season catch regardless of its cause. While we have concluded that an immediate behavioral response is not a likely cause, other related possibilities remain. The observed covari- ation could be caused by an inherently cyclic crab fishery and a negative response of effort in salmon throughout the salmon season (rather than solely in the months of overlap). Further elucidation of the economic question awaits re- sults of an ongoing study of microeconomic be- havior of fishermen. Consideration of the life histories of the species and the timing of events implied by the lags in correlation admits the possibility of direct inter- action and dependence of both cycles on environ- mental factors. Oceanographic conditions have been suggested as causes of fluctuations in other fisheries. Wild (1980) recently proposed that a change in sea surface temperature in the late 1950's reflects a change in the marine environ- ment that is responsible for the decline in the central California Dungeness crab fishery. He also suggested that changes in sea surface tem- perature were related to fluctuations in the northern California crab catch record. However the actual values of correlation between these processes are not significant. Southward et al. (1975) presented data on cyclic fluctuations in sea temperature and covarying changes in fish population parameters over the past 50 yr in the English Channel. Though the observed changes in lags and sen- sitivity to first-differencing may not be related to the causal mechanism, the nature of the covaria- tion between salmon and crab catch does appear to have changed following the decline in central California crab landings. This change is not ex- plained by fishermen switching between species, but could stem from Wild's (1980) proposed change in oceanographic conditions. The de- crease in the period of the cycles in crab abun- dance following the decline is of some interest with regard to the issue of the cause of the decline itself. One of the possible causes of a decrease in period of the cycles is an increase in individual growth rate. This increase in growth rate is a necessary component of one of the potential causes of the decline (Botsford 1981) but is diffi- cult to demonstrate because of the paucity of samples before the decline. Possible effects of internal population dynam- ics on the observed behavior are worthy of exam- ination. An interage, density-dependent mecha- nism has been cited as a potential cause of the cycles in crab abundance (Botsford and Wick- ham 1978, 1979). A similar mechanism could be operating on salmon abundance if the several stocks in the fishery were in synchrony. Peter- man (1978) found positive correlations in smolt- to-adult survivorship between several groups of Pacific salmon populations. Populations that are not density-dependent but reproduce only in their final year have also long been known to fluctuate in a cyclic fashion (Bernardelli 1941; Leslie 1945). However, the period of the cycles is equal to the age of reproduction rather than twice the mean age of reproduction as it is in the stock-dependent recruitment case (Ricker 1954; Botsford and Wickham 1978). The methods used here could prove useful in other fisheries problems. While time-series tech- niques have been applied to fishery problems, the primary goal has been a final model of the fishery rather than a search for causal relation- ships. The latter approach, the one taken here, has the advantage of leading to models that are based on known causal mechanisms rather than correlations of unknown causal mechanisms. Since the nature of these mechanisms could change significantly (possibly because of a change in fishing policy itself), a policy that is cognizant of them will fare better than one that relies on a statistical description from the past. Another analytical time-series technique that we have not used here is the computation of cau- sality as defined by Granger (1969). His special definition of causality is based on whether addi- tion of data from past time on one variable de- creases the error with which another variable can be predicted. The investigations performed here are in the same spirit but do not result in a single quantitative measure of causality. While we have demonstrated here a potentially important statistical relationship, we have not uncovered the underlying cause. The ultimate cause, however, is worth pursuing. Its discovery and quantitative description could put salmon and crab management on a firmer basis by sup- plying greater predictive ability. Management could then respond to abundance on a firmer, predictive basis rather than a trial-and-error basis. 800 BOTSFORD ET AL.: CYCLIC COVARIATION IN CALIFORNIA FISHERIES ACKNOWLEDGMENTS The authors would like to acknowledge the contribution of J. Fletcher who pointed out the possible cyclic covariation of the two catch rec- ords. We would also like to thank W. A. Gardner and R. Mendelssohn for their reviews and com- ments. This work is a result of research sponsored by NOA A Office of Sea Grant, Department of Com- merce, under Grant #NOAA-M0M84 R/F52. LITERATURE CITED Anonymous. 1965. [Discussion following the report on Dungeness crabs.] Pac. Mar. Fish. Comm., 16th and 17th Annu. Rep., p. 38-39. Bartlett, M. S. 1946. On the theoretical specification and sampling prop- erties of autocorrelated time-series. J. R. Stat. Soc. Lond. Suppl. 8(1):27-41. Bernardelli, H. 1941. Population waves. J. Burma Res. Soc. 31:1-18. BOTSFORD, L. W. 1981. The effects of increased individual growth rates on depressed population size. Am. Nat. 117(l):38-63. BOTSFORD, L. W., AND D. E. Wickham. 1975. Correlation of upwelling index and Dungeness crab catch. Fish. Bull., U.S. 73:901-907. 1978. Behavior of age-specific, density-dependent models and the northern California Dungeness crab (Cancer magister) fishery. J. Fish. Res. Board Can. 35:833- 843. 1979. Population cycles caused by inter-age, density- dependent mortality in young fish and crustaceans. In E. Naylor and R. G. Hartnoll (editors), Cyclic phenomena in marine plants and animals, p. 73-82. Proceedings of the 13th European Marine Biology Symposium, Perga- mon, N.Y. Box, G. E. P., and G. M. Jenkins. 1970. Time series analysis; forecasting and control. Holden-Day, San Franc, 553 p. Box, G. E. P., and D. A. Pierce. 1970. Distribution of residual autocorrelations in auto- regressive-integrated moving average time series mod- els. J. Am. Stat. Assoc. 65:1509-1526. California Department of Fish and Game. 1954-78. California marine fish landings. Calif. Dep. Fish Game. Durbin, J. 1970. Testing for serial correlation in least-squares re- gression when some of the regressors are lagged depen- dent variables. Econometrica 38:410-421. FlNERTY, J. P. 1980. The population ecology of cycles in small mammals. Yale Univ. Press, New Haven, 234 p. GOTSHALL, D. W. 1978. Relative abundance studies of Dungeness crabs, Cancer magister, in northern California. Calif. Fish Game 64:24-37. Granger, C. W. J. 1969. Investigating causal relations by econometric mod- els and cross-spectral methods. Econometrica 37:424- 438. Granger, C. W. J., and P. Newbold. 1974. Spurious regressions in econometrics. J. Econ. 2:111-120. Jenkins, G. M., and D. G. Watts. 1968. Spectral analysis and its applications. Holden- Day, San Franc, 525 p. Leslie, P. H. 1945. On the use of matrices in certain population mathe- matics. Biometrika 33:183-212. McKelvey, R., D. Hankin, K. Yanosko, and C. Snygg. 1980. Stable cycles in multistage recruitment models: An application to the Northern California Dungeness crab (Cancer magister) fishery. Can. J. Fish. Aquat. Sci. 37:2323-2345. Methot, R. D., Jr., and L. W. Botsford. 1982. Estimated preseason abundance in the California Dungeness crab (Cancer magister) fisheries. Can. J. Fish. Aquat. Sci. 39:1077-1083. MORAN, P. A. P. 1949. The statistical analysis of the sunspot and lynx cycles. J. Anim. Ecol. 18(1):115-116. Orcutt, H. G. (compiler). 1978. Dungeness Crab Research Program. Report for the year 1978. Calif. Dep. Fish Game, Mar. Resour. Admin. Rep. 78-16, 24 p. Pacific Fisheries Management Council. 1978. Fishery management plan and environmental im- pact statement for commercial and recreational salmon fisheries of the coasts of Washington, Oregon and Cali- fornia. Pac. Fish. Manage. Counc, 158 p. Peterman, R. M. 1978. Testing for density-dependent marine survival in Pacific salmonids. J. Fish. Res. Board Can. 35:1434- 1450. Peterson, W. T. 1973. Upwelling indices and annual catches of Dunge- ness crab, Cancer magister, along the west coast of the United States. Fish. Bull., U.S. 71:902-910. Ricker, W. E. 1954. Stock and recruitment. J. Fish. Res. Board Can. 11:559-623. Southward, A. J., E. I. Butler, and L. Pennycuick. 1975. Recent cyclic changes in climate and in abundance of marine life. Nature (Lond.) 253:714-717. Wickham, D. E. 1979. Carcinonemertes errans and the fouling and mor- tality of eggs of the Dungeness crab, Cancer magister. J. Fish. Res. Board Can. 36:1319-1324. Wild, P. W. 1980. Effects of seawater temperature on spawning, egg development, hatching success, and population fluctua- tions of the Dungeness crab, Cancer magister. Calif. Coop. Oceanic Fish. Invest. Rep. 21:115-120. 801 SWIMMING KINEMATICS OF SHARKS1 P. W. Webb- and Raymond S. Keyes3 ABSTRACT Video-tape recordings were made of locomotor movements of six species of free-swimming sharks. The following kinematic parameters were measured, normalized where appropriate with total body length (L): tail-beat frequency (/), specific tail-beat amplitude (A/L), specific wavelength of the propulsive wave (A/L), specific stride length (S/L), and the rate of change of A/L with position along the body. These parameters were measured over a range of swimming speeds up to 3.9 m/s (4 L/s) for one species, the blacktip shark, Carcharhinus melanopterus. Data were obtained only over a narrow- range of low swimming speeds for the other species, because they could not be induced to swim at high speeds. For the blacktip shark, /increased with speed, but A/L, A/L, and, hence, S/L all de- creased as speed increased. Among the six species, A/Land S/L tended to be larger for more fusiform species, while A/L and /, at a given speed, appeared to be lower. This implies swimming move- ments of more fusiform species generated more thrust per beat than elongate species and/or the swimming drag was lower. The pattern of amplitude changes along the body length of sharks was intermediate between that observed for elongate and fusiform teleosts. Thrust and swimming efficiency can be improved when discrete fins interact, as between the dorsal and caudal fins of sharks. For this to occur, a phase difference of >0.5 n must occur between the vortex wake shed at the trailing edge of an anterior fin and the leading edge motion of a more posterior fin, which interacts with the upstream vortex sheet. The variations in swimming kine- matics with speed, the differences among the species studied, and the conservative nature of body form in sharks probably function to increase thrust and efficiency by such interaction between median fins. Most studies on fish locomotion have concen- trated on bony fish, especially teleosts. As a re- sult, modern ideas on fish locomotor functional- morphology are dominated by knowledge of only one of the major groups of fish. However, there are many unique features among cartilaginous fish that suggest they have exploited some differ- ent biomechanical possibilities. Sharks appear to swim like elongate teleosts, but in contrast they have discrete, often widely spaced median fins more typical of fusiform teleosts. Lighthill (1970) and Sparenberg and Wiersma( 1975) have shown that this combination provides an oppor- tunity for median fins to interact in such a way that thrust and Froude efficiency (the ratio of useful work to total work of the propellor system) are improved. If shark locomotion were to utilize flow inter- actions between median fins to hydromechanical advantage, they would have to swim somewhat differently from teleosts. For example, teleosts 'Contribution No. 8104-SD from Sea World, San Diego, Calif. 2Southwest Fisheries Center La Jolla Laboratory, National Marine Fisheries Service, NOAA, La Jolla, Calif.; present address: School of Natural Resources, University of Michigan, Ann Arbor, MI 48109. 3Sea World, San Diego, CA 92109. modulate tail-beat frequency with speed, but sharks might also have to vary other kinematic parameters, such as the length of the propulsive wave and tail-beat amplitude. Therefore, the fol- lowing experiments were performed to deter- mine how swimming kinematics and phase dif- ferences between fin motions varied with speed for six species of sharks. While difficulties were encountered in obtaining data over a wide range of speeds, the results suggest that sharks vary swimming kinematics to utilize interactions be- tween median fins, as postulated by Lighthill (1970). METHODS Observations were made on six species of free- swimming sharks (Fig. 1). Three species, the bull shark, Carcharhinus leucas; lemon shark, Negaprion brevirostris; and nurse shark, Gingly- mostoma cirratum, were approximately 2-2.5 m in total length. They were contained in the public display at Sea World, San Diego, Calif., described by Weihs et al. (1981). Specimens of the other three species were smaller; Pacific blacktip shark, Carcharhinus melanopterus (total length, L = 0.97±0.5 m; X ± 2SE; N = 7); bonnethead, Manuscript accepted February 1982. FISHERY BULLETIN: VOL. 80, NO. 4. 1982. 803 FISHERY BULLETIN: VOL. 80, NO. 4 ▲ Ginglymostoma c/rratum nurse shark Sphyrna tiburo bonnethead shark A Triakis semifasciata leopard shark Carcharhinus melanopterus blacktip shark □ Negaprion brev/rostris lemon shark O Carcharhinus leucas bull shark Figure 1.— Drawings (not to scale) showing the longitudinal body form of the six species of sharks for which swimming kinematic data were obtained. The symbols are used through most of the following figures. Sphyrna tiburo (L = 0.93+0.09 m; N = 5); and leopard shark, Triakis semifasciata (L = 0.98+ 0.11 m; N = 5). The three smaller species were part of a second public display in an outside pool at Sea World. This pool was approximately oval in shape, 9 m long, 5.5 m wide, and 0.3 m deep. Small individual sharks were also observed in a small rectangular tank, 2.5 m long, 1.2 m wide, and 0.3 m deep. This tank had a transparent bot- tom. The water temperature in all three facilities was the same and constant at 24.5°C. Thomson and Simanek ( 1977) have shown that most sharks fall into one of four functional-morphology groups. Group 1 includes sharks with stream- lined, fusiform, deep bodies; a narrow caudal peduncle with lateral flukes (streamlining); and a high aspect ratio tail. This group is represented by large pelagic species, such as Lamna which were unavailable for study. Group 2 is similar to group 1, but lacking the deep body and stream- 804 WEBB and KEYES: SWIMMING KINEMATICS OF SHARKS lined caudal peduncle. Carcharhinus leucas, C. melanopterus, and S. tiburo represent group 2. Group 3 includes sharks with a low aspect ratio tail, making a small angle to the horizontal, and a less fusiform body, represented by G. cirratum, T. semifasciata, and N. brevirostris. Group 4 in- corporates the squaloid sharks, e.g., Centrolepis, which were not available. Swimming movements were recorded on video tape. Recordings were made above the free sur- face of the public display facilities. Surface rip- ples were small compared with the images of the sharks and were therefore ignored. To avoid sur- face problems, observations in the rectangular tank were made from below through the trans- parent bottom. Surface ripples did not deleter- iously affect measurement accuracy because no differences in data from the public facilities and the rectangular tank could be found. Swimming records were obtained for as wide a range of speeds as possible. In most cases, normal variation in motor behavior due to the operation of the park was exploited. For the large sharks, observations were made before the display opened, during normal hours, and during feed- ing. Because of the possibility of injury leading to mortality, other invasive methods to induce higher speeds were not used. Similar procedures were employed for the smaller sharks. Under- water concussions, induced by dropping heavy objects (fluid-filled metal kegs), and visual stim- uli were used to induce higher speeds in these sharks. Tactile stimuli were also employed to generate a range of speeds in the rectangular tank. Video tape was analyzed "frame-by-frame," using manual advance to resolve movements to within 1/60 s (17 ms). Because a large length range was used, kinematic observations were normalized, for convenience, with respect to total length, L, measured from the tip of the nose to the tip of the tail. Specific swimming speed (speed/L), specific amplitude (amplitude/L), and tail-beat frequency (/) were measured for periods of steady swimming of two or more tail beats. The speed of the propulsive wave (c) was calculated from the backward displacement of wave crests, and specific wave-length (k/L) was calculated from e/Lf. RESULTS Representative swimming movements for three of the species of sharks are illustrated in Figure 2. The body was bent into a wave that travelled backwards over the body at a speed greater than the swimming speed. The ampli- tude increased caudally to reach maximum val- ues at the trailing edge (the tip of the caudal fin). In general, the form of propulsive movements was similar to that of other fish, as originally described by Gray (1933). Kinematic parameters varied among the six species and with swimming speed. In practice, it proved extremely difficult to induce the sharks to swim over a wide speed range. This is consis- tent with experiences of Johnson (1970) with the brown shark, Carcharhinus plumbeus{= C. mil- berti), and Brett and Blackburn (1978) with the spiny dogfish, Squalus acanthias. Hunter and Zweifel (1971) reported kinematic data for a sin- gle leopard shark, Triakis henlei, swimming in a water tunnel, but the speed range is not given. Only the blacktip sharks swam over a speed range large enough to permit examination of the relationships between kinematics and speed. Data for the other species was therefore simply averaged (Table 1 ). The sharks also did not swim at very low speeds. Tail-beat frequency increased linearly with speed (Fig. 3 A), as found for other species of sharks and for teleosts (see Johnson 1970; Hunter and Zweifel 1971; Webb 1975; Aleyev 1977). How- ever, frequencies increased at a higher rate with speed than observed for other fish. Mean specific speeds and tail-beat frequencies varied among the six species of sharks. Compared with the slope of the blacktip shark relationship, more elongate species (e.g., nurse shark; group 3 of Thomson and Simanek 1977) tended to have high- er tail-beat frequencies at a given specific speed than more fusiform fish (e.g., bull shark; group 2 of Thomson and Simanek 1977) (Fig. 3B; Table 1 ). Specific amplitude of the blacktip shark de- creased with increasing speed (Fig. 3C) and hence was inversely related to tail-beat fre- quency. Specific amplitudes varied from 0.06 to 0.21 among species, with the more fusiform sharks having lower values (Fig. 3D). With the exception of the bull shark, mean specific swim- ming speeds were greater for the more fusiform species. Thus, for the interspecific data, specific amplitude decreased with specific speed, similar to the intraspecific observations on blacktip sharks. Among teleosts, both tail-beat amplitude and frequency may increase together at very low speeds (Bainbridge 1958; Webb 1971, 1973). However, over most of the speed range, caudal 805 FISHERY BULLETIN: VOL. 80. NO. 4 0-3 0-4 0-5 06 0-7 \ [A k Carcharhinus >i - oo o $m X H < or 0-8 0-6 0-4 0-2 0 -0-2 -0-4 - Anguilla 0- \J A \ A fusiform \ / \ / " * sharks ^teleosts \ y^ — / V # ->* A J* \ — 0 A/ \ / Ax • A ^ ■ — /• • — — _ s. sharks - i.'/i— *- — t "^_ A • * r ■ _• is Anguilla i J A 1 1 1 1 1 1 1 l 1 1 0 0-2 0-4 0-6 08 10 (nose) LOCATION ALONG BODY (tail) Figure 6.— The relationship between the rate of change of am- plitude along the body length and the position along the body in some fishes. The data for fusiform teleosts (solid hexagons linked by solid lines) were taken from Bainbridge (1963) for dace, Lewiscus leuciscus, and bream, Ambramis brama. Data for Anguilla (open hexagons linked by a solid line) were taken from Gray (1933). Data for the sharks (see key in Fig. 1) were taken from Figure 2; the dotted line was fitted by eye through the data for sharks. 808 WEBB and KEYES: SWIMMING KINEMATICS OF SHARKS (1926), and has been more recently updated by Lindsey (1978). The definition of common loco- motor patterns, or modes (Lighthill 1975), for undulatory swimming movements of the body and caudal fin are based on the number of one- half wavelengths contained within the body length and the pattern of increasing amplitude along the body. The elongate eel, Anguilla, is definitive for the anguilliform mode where the body contains more than one-half wavelength within the body length, and often one or more complete waves. The lateral amplitude of body movements rises early and is large over most of the body length. Jacks, in the family Carangidae, are representative of the carangiform mode where the body length contains less than one-half wavelength, and lateral displacements increase rapidly over the posterior third or half of the body. Breder (1927) used the term "sub-carangi- form mode" for fish with wave patterns of the anguilliform mode and amplitude changes simi- lar to the carangiform mode. So far, detailed studies of fusiform teleosts have been on sub- carangiform swimmers. The six species of shark are also subcarangi- form swimmers according to these definitions; the body contained more than one-half of a wave (Table 1, Fig. 5) and the amplitude of body move- ments increased predominantly over the poster- ior half of the body (Fig. 6). However, the maxi- mum rate of increase in amplitude occurred over the third quarter of the body, intermediate be- tween the situation for elongate and fusiform teleosts. Therefore, although the sharks swam in the subcarangiform mode, they were more eel- like than fusiform teleosts. This is consistent with the unaided visual impressions of shark swimming. Among teleosts, trends in swimming kinemat- ics from the anguilliform mode towards carangi- form modes are associated with changes in body form from an elongate, flexible body to a more fusiform, less flexible body. This is coupled with a larger caudal fin depth increasingly separated from the body by a narrow caudal peduncle, a morphology defined as narrow necking (Light- hill 1975). The same trends are seen in the six species of sharks studied here (Fig. 1, Table 1). The more fusiform species were those with longer propulsive wavelengths and a larger tail depth swimming in a more carangiform mode than the elongate sharks. In terms of the classifi- cation of shark functional morphology by Thom- son and Simanek(1977), group 1 is most carangi- form and groups 3 and 4 are most anguilliform. Group 1 representatives were not studied here. The two factors of increasing wavelength and caudal fin depth in the carangiform swimmers are known to increase thrust and Froude effi- ciency (Lighthill 1975). However, thrust is re- duced by a decrease in tail-beat amplitude. Among the sharks, increasing wavelength and tail depth were found with smaller amplitudes. Thus, the more fusiform, more carangiform spe- cies show features that would both enhance and decrease performance. Stride length increased in these more fusiform sharks so that overall the larger wavelength and deeper caudal fins must generate more than enough thrust, perhaps more efficiently, to offset reduced amplitudes. The details of kinematic movements appear very different for sharks compared with bony fish. In the teleosts that have been studied to date (see Hunter and Zweifel 1971; Aleyev 1977) tail- beat frequency is the major kinematic variable with speed, and over most of the range of swim- ming speeds, it is the only variable. In contrast, the blacktip shark modulated all three of the kinematic variables that influence thrust: tail- beat frequency, tail-beat amplitude, and the length of the propulsive wave. Teleosts vary one morphological parameter with speed that would also affect thrust. This is the depth of the caudal fin trailing edge (Bainbridge 1963; Webb 1971) to vary the mass of water accelerated by propul- sive movements (see Alexander 1968; Lighthill 1975). The skeleton of shark fins is based on car- tilaginous ceratotrichia, rather than bony rays, which cannot be individually controlled. As a result, shark fins lack the flexibility to substan- tially modify fin depth during swimming. The differences in locomotor kinematics with speed of the sharks illustrated by the blacktip shark, compared with teleosts, may be related to hydrodynamic interactions between the median dorsal fins and the caudal fin. This interaction was first described by Lighthill (1970) and has been developed in detail using hydromechanical theory for inviscid fluids by Sparenberg and Wiersma (1975). A vortex sheet is shed by the trailing edge of any sharp fin or body edge. This vortex sheet travels downstream, but it also has a lateral velocity component determined by the motion of the trailing edge; i.e., the wake follows a sinusoidal path (see illustrations in Rosen 1959; Aleyev 1977). The vortex sheet carries momen- tum determined by the motions and dimensions of the body and fin at the fin trailing edge. 809 FISHERY BULLETIN: VOL. 80, NO. 4 The momentum carried in the vortex sheet will contribute to instantaneous thrust, and if there is no downstream fin to influence the flow, this momentum will contribute to the mean thrust and power of the fish (Wu 1971; Newman and Wu 1973). However, when there is a down- stream re-entrant fin (i.e., a second downstream median fin spanning the flow from the anterior fin) the vortex sheet will impinge on the leading edge of that fin. If the gap between the fins is small, there is little difference between the mo- tion of the incident vortex sheet and the motion of the leading edge of the downstream fin. Then the mean strength of the vortex sheet shed by the downstream fin is determined by the motion of that fin, with no significant contribution from the upstream vortex sheet from the anterior fin, i.e., the upstream fin has no effect on the wake eventually shed by the fish. In this case, the inter- action between median fins does not influence mean thrust. Lighthill (1970) showed that a different situa- tion can occur when the gap between median fins is large. Under these circumstances, there may be a large enough phase difference between the motion of the incident vortex sheet and the down- stream fin, so that the momentum shed upstream is not annihilated by the second fin. Then, the work done by the anterior fin against the momen- tum shed by its trailing edge together with that due to an increased incident velocity at the down- stream fin increase total power output and im- prove efficiency (Lighthill 1975:80-84; Sparen- berg and Wiersma 1975). The phase difference in the motion of the trail- ing edge of one fin located at a position ai, along the body, and the leading edge of a second more posterior fin at position a2, is 27r(a2 — ai)/X where \ is the length of the propulsive wave. However, the vortex sheet travels downstream at the mean speed, U, of the fish, while the body undulation travels backwards at a speed c, greater than U. Therefore, the phase difference, 4>, in the motions of the vortex sheet shed by the anterior fin and the leading edge of a posterior fin is given by (Lighthill 1975, equation 28): ♦—("KM- (1) Sharks typically have three median fins, the first and second dorsal fins and the caudal fin. Thomson and Simanek (1977) have analyzed sev- eral morphological features of 56 species of sharks and show that the second dorsal fin is characteristically small compared with the first dorsal fin, especially in pelagic species. In addi- tion, the second dorsal fin would only be partly re-entrant to most of the vortex sheet shed by the upstream fin because of the posterior taper of the body. Therefore, it seems likely that the second dorsal fin has relatively little effect on the flow between the other two fins during steady cruis- ing. Thomson and Simanek's observations also indicate that the caudal fin depth is typically greater than or equal to that of the trailing edge of the first dorsal fin, as required to maximize the interaction. Therefore, <£ was calculated for interactions between the first dorsal fin and the caudal fin of the blacktip, bonnethead, and leop- ard sharks (Table 2; Fig. 7). 4> was close to, or >0.57r, as required for the interaction hypothe- sized by Lighthill (1970). A single record for the dogfish, Acanthias vulgaris, in Gray (1933) also gives a value of = 0.52tt (Webb 1975). For 0-9 0-8 0-7 9 0-6|- 6 S °'5~ ta 0-4- 0-3- 0-2 0-1 4- :.+ _L 0 12 3 4 U/L- SPECIFIC SWIMMING SPEED (L.s-1) Figure 7.— The relationship between the phase difference (see Equation (1)) and specific swimming speed for three species of sharks. Vertical and horizontal bars are ±2SE. The key to symbols is in Figure 1. Table 2.— Separation, (a2 - «i)/L, between the trailing edge of the first dorsal fin (aO and the mean position of the leading edge of the caudal fin («2>, and phase difference ($) between their movements for three species of sharks. was calculated from data in this table and in Figures 3 and 4 using Equation (1). Species (a2-a,)/L (X±2SE) (n radians) Leopard shark 0.48 0.55±0.20 Bonnethead shark 0.50 0.48±0.08 Blacktip shark 0.47 0.51 ±0.05 810 WEBB and KEYES: SWIMMING KINEMATICS OF SHARKS blacktip shark, was of the order of 0.57T over the range of swimming speeds studied. In Equation (1), a\ and a2 are constants, and therefore, / or X can be varied at any speed to keep (p>0.5n. However, such changes also affect thrust. For example, if A varies with speed, com- pensatory changes in tail-beat frequency and/or tail-beat amplitude must occur to balance thrust and drag at a given speed. The blacktip shark modulated both. Therefore, the modulation of wavelength, amplitude, and frequency with speed can be explained in terms of mechanical advantages from an interaction between widely spaced median fins. It should also be noted that the early rate of increase of amplitude along the body in sharks, occurring near the first dorsal fin, might increase the strength of the vortex sheet. This could enhance thrust, perhaps more than would occur with patterns of increasing amplitude seen in fusiform teleosts. Adaptive flow interactions between median fins as suggested by Lighthill (1970) apply to the established flow patterns of a steadily swimming fish. Therefore, the common body form and kine- matic patterns of sharks appear to be adapta- tions for cruising. Some sharks, analogous in form to tuna (group 1 of Thomson and Simanek 1977), are obviously highly specialized for cruis- ing (Lighthill 1975; Lindsey 1978), but the pres- ent observations suggest that other sharks are also specialized through the utilization of other principles, exploiting more anguilliform propul- sion and a more elongate, flexible body. The dis- tribution of the median fins along the body is very similar among sharks (Thomson and Sima- nek 1977). This suggests that such cruising adap- tations are relatively common. Furthermore, sharks are frequently negatively buoyant, when continuous forward motion is important in swim- ming free from the bottom. This argues for the importance of cruising in the routine behavior of sharks, and hence the importance of any mecha- nisms to enhance thrust and efficiency in steady swimming. Comparative observations on teleosts also sug- gest that in general, sharks are specialized in cruising. Experimental studies have shown that optimal design for transient swimming patterns (angular and linear acceleration) differs from, and is largely exclusive of, that for steady swim- ming such as cruising (see review by Webb in press). In teleosts, optimal morphological fea- tures for steady swimming include a small area anterior to a deep high aspect ratio tail propel- ling a fairly rigid body. For maximum accelera- tion, depth (and hence area) should be large over the whole length of a flexible body. Bony fish can achieve some compromise because of their flex- ible fins, but in general design for unsteady acceleration activity appears most important (Webb 1982). Compromises are excluded for sharks because they do not have collapsible fins. In addition, the separation of the median fins re- duces the area of the body available to generate large forces for acceleration. Some sharks, e.g., the horn shark, Heterodontus francisci, have somewhat enlarged median fins that suggest a greater importance of acceleration. In general, a more posterior location of the first dorsal fin is associated with larger area fins, as in Ginglymo- stoma cirratum that could similarly improve acceleration. In this case the more posterior loca- tion of the first dorsal fin may be at the cost of reducing below 0.57T. However, the body and fin form typical of sharks (Thomson and Sima- nek 1977) probably provides for poor accelera- tion performance. In conclusion, sharks appear to have exploited their different structural capacities to specialize for cruising when swimming. ACKNOWLEDGMENTS This work was completed while P. W. Webb was an NRC/NOAA Research Associate on leave from the University of Michigan. I am indebted to R. Lasker and J. R. Hunter for their hospital- ity. The authors thank Sea World for providing specimens and facilities. LITERATURE CITED Alexander, R. McN. 1968. Animal mechanics. Univ. Washington Press, Seattle, 346 p. Aleyev, Y. G. 1977. Nekton. Junk, The Hague, 435 p. Bainbridge, R. 1958. The speed of swimming of fish as related to size and to the frequency and amplitude of the tail beat. J. Exp. Biol. 35:109-133. 1963. Caudal fin and body movement in the propulsion of some fish. J. Exp. Biol. 40:23-56. Breder, C. M., Jr. 1926. The locomotion of fishes. Zoologica (N.Y.) 4:159- 297. Brett, J. R., and J. M. Blackburn. 1978. Metabolic rate and energy expenditure of the spiny dogfish, Squalus acanthias. J. Fish. Res. Board Can. 35:816-821. 811 FISHERY BULLETIN: VOL. 80, NO. 4 Gray, J. 1933. Studies in animal locomotion. I. The movement of fish with special reference to the eel. J. Exp. Biol. 10: 88-104. Hunter, J. R., and J. R. Zweifel. 1971. Swimming speed, tail beat frequency, tail beat am- plitude, and size in jack mackerel, Trachurus symmetri- cus, and other fishes. Fish. Bull., U.S. 69:253-266. Johnson, C. S. 1970. Some hydrodynamic measurements on sharks. Nav. Underwater Cent. Tech. Rep. 189, 13 p. Lighthill, M. J. 1970. Aquatic animal propulsion of high hydromechani- cal efficiency. J. Fluid Mech. 44:265-301. 1975. Mathematical biofluiddynamics. SIAM, Phila., 281 p. LlNDSEY, C. C. 1978. Form, function, and locomotory habits in fish. In W. S. Hoar and D. J. Randall (editors), Fish physiology, vol. VII, p. 1-100. Acad. Press, N.Y. Newman, J. N., and T. Y. Wu. 1973. A generalized slender-body theory for fish-like forms. J. Fluid Mech. 57:673-693. Rosen, M. W. 1959. Water flow about a swimming fish. U.S. Navy Ordinance Test Stat. Tech. Publ. 2289, 96 p. SPARENBERG, J. A., AND A. K. WlERSMA. 1975. On the efficiency increasing interaction of thrust producing lifting surfaces. In T. Y.-T. Wu, C. J. Bro- kaw, and C. Brennen (editors), Swimming and flying in nature, vol. 2, p. 891-917. Plenum Press, N.Y. Thomson, K. S., and D. E. Simanek. 1977. Body form and locomotion in sharks. Am. Zool. 17:343-354. Wardle, C. S. 1975. Limit of fish swimming speed. Nature (Lond.) 255:725-727. Wardle, C. S., and J. J. Videler. 1980. How do fish break the speed limit? Nature (Lond.) 284:445-447. Webb, P. W. 1971. The swimming energetics of trout. 1. Thrust and power output at cruising speeds. J. Exp. Biol. 55:489- 520. 1973. Effects of partial caudal-fin amputation on the kinematics and metablic rate of underyearling sockeye salmon (Oncorhynchus nerka) at steady swimming speeds. J. Exp. Biol. 59:565-581. 1975. Hydrodynamics and energetics of fish propulsion. Bull. Fish. Res. Board Can. 190, 158 p. 1982. Locomotor patterns in the evolution of actino- pterygian fishes. Am. Zool. 22:329-342. Weihs, D., R. S. Keyes, and D. M. Stalls. 1981. Voluntary swimming speeds of two species of large carcharhinid sharks. Copeia 1981:219-222. Wu, T. Y. 1971. Hydrodynamics of swimming fishes and cetace- ans. Adv. Appl. Math. 11:1-63. 812 POPULATION BIOLOGY OF CHUM SALMON, ONCORHYNCHUS KETA, FROM THE FRASER RIVER, BRITISH COLUMBIA Terry D. Beacham1 and Paul Starr2 ABSTRACT Population biology of Fraser River chum salmon, Oncorhynchus keta, was investigated. Mean age of chum salmon during the run declined from 3.98 years in October to 3.78 years in December in the 1970s. Females were more abundant than males in 4-year-old chum salmon, but males were more abundant than females in 3- and 5-year-old chum salmon. Fecundity of females was 3,250 eggs/ female at a standard length of 58.0 cm and did not vary among years sampled. Fry tended to mi- grate downstream earlier when the previous winter had been warm than when it was cold. Egg- to-fry survival was correlated with rainfall, air temperature, and number of eggs deposited. Mean age of return of a brood year was positively correlated with its abundance. The return to escapement ratio for even-numbered brood years was inversely correlated with the abundance (catch plus escapement) of the previous brood year, which suggests that marine survival of chum salmon may be density-dependent. The return to escapement ratio for odd-numbered brood years was positively correlated with early downstream migration of chum salmon fry relative to pink salmon, 0. gor- buscha, fry and with increased chum salmon spawning escapements relative to those of pink salmon. Stocks of chum salmon, Oncorhynchus keta, in British Columbia and Alaska have fluctuated considerably in abundance (Hoar 1951; Wickett 1958; Hunter 1959; Helle 1979). These fluctua- tions have been attributable to variability in freshwater and marine survival, and have been related to climatic factors such as rainfall (Wick- ett 1958) and to population density or predation on fry (Hunter 1959). Chum salmon in British Columbia return to spawn in their natal streams mainly as 3- and 4-yr-olds, and to a lesser extent as 5-yr-olds. The mean age of returning adults tends to be greater for stocks from northern British Columbia than from southern British Columbia (Pritchard 1943; Ricker 1980). Chum salmon tend to spawn later in the fall than other species of Oncorhynchus, and the fry migrate downstream in the spring, within a few days after emerging from spawning beds. The chum salmon stocks of the Fraser River have supported commercial fisheries in John- stone Strait, the Strait of Georgia, and the Fraser River for many years (Palmer 1972) (Fig. 1). Annual catches of chum salmon were extensive ■Department of Fisheries and Oceans, Fisheries Research Branch, Pacific Biological Station, Nanaimo, B.C., Canada V9R 5K6. department of Fisheries and Oceans, Field Services Branch, 1090 West Pender Street, Vancouver, B.C., Canada V6E 2P1. Manuscript accepted April 1982. FISHERY BULLETIN: VOL. 80. NO. 4, 1982. in Johnstone Strait during 1951-54, ranging from 0.7 to 2.0 million fish, and in the Fraser River, ranging from 274,000 to 479,000 fish. However, the annual contribution of Fraser River chum salmon to the Johnstone Strait catch is unknown before 1964. Catches of chum salmon declined substantially during 1965-69, ranging from 23,000 to 649,000 fish in Johnstone Strait (an estimated 0 to 228,000 Fraser River chums), and 10,000 to 196,000 fish in the Fraser River. Catches have continued to vary widely in the 1970s. Fraser River chum salmon have thus shown marked fluctuations in abundance, and these fluctuations have not been satisfactorily account- ed for. It is not currently possible to identify stocks of Fraser River chum salmon, so for pur- poses of the analysis, Fraser chum salmon were treated as a unit stock. This paper describes the population biology of Fraser River chum salmon and results of studies on the causes of variability in the number of returning adults. MATERIALS AND METHODS Estimates of abundance of returning adult and downstream migrating fry were derived by different sampling methods. Fry were enumer- ated during 1965-81 on the lower Fraser River near Mission City (Fig. 1) using techniques pre- viously described by Todd (1966) and Bailey 813 FISHERY BULLETIN: VOL. 80, NO. 4 VANCOUVER ISL Figure 1.— Areas in British Columbia where Fraser River chum salmon are caught in the commercial fish- ery. Inset shows areas in the lower Fraser River where fry and returning adults were sampled. (19793). Briefly, the sampling procedure con- sisted of suspending traps at various depths from the surface to 3.7 m (12 ft) from either side of a boat travelling at a constant velocity relative to the water for 15-min periods. Samples were taken in this manner between 0500 and 1300 h. Preliminary sampling had established that chum fry migrated past Mission City were most active during this period. Sampling occurred during this period, 5 d a week from beginning of March to end of May. Daily sampling was con- tinued for 24 h 2 or 3 d/ wk so that estimates of the daily proportion of fry migrating during the stan- dard shift (0500 to 1300 h) could be made, and daily totals of chum fry migrating past Mission City calculated. Sampling was also performed at different sites across the 527 m (1,725 ft) width of the Fraser River at Mission City. The depth and 3Bailey, M.D. 1979. Enumeration of salmon in the Fraser River. Unpubl. manuscr., 122 p. Department of Fisheries and Oceans. cross-sectional area of the river were known at each sampling site, as well as the area sampled by the fry traps, so that, by extrapolation, the number of fry migrating downstream daily could be estimated. Abundance of chum salmon fry used in the present analysis was taken from Bailey (footnote 3), as were the dates when 50% of the chum and pink, O. gorbuscha, salmon fry were estimated to have migrated past the sam- pling site. Weekly mean lengths (mm) of fry were determined in 1978. Sex ratios, age composition, length-at-age, and fecundity of adult chum salmon arriving at the river mouth were derived from test fishing con- ducted at Cottonwood Drift from 1962 to 1979 and Albion from 1978 to 1979 (Fig. 1). A 274 m (150-fathom) long, 60-mesh deep gill net having 16.9 cm (6% in) mesh was set for a standard 30- min drift twice a day during the slack period of the lowest tide of the day. Smaller fish may have avoided capture on account of gill net selectivity (McCombie and Berst 1969; Todd and Larkin 814 BEACHAM and STARR: POPULATION BIOLOGY OF CHUM SALMON 1971), which could possibly bias adult age com- position, sex ratios, and fecundity estimates. However, we believe that any bias present was not of sufficient magnitude to mask trends in abundance of individual brood years. Daily test fishing 5 d/wk was usually conducted from late September until mid-December, although sam- pling within this period was not conducted when the commercial fishery was operating in the river. Ages of chum salmon were determined from scales. Bilton and Ricker (1965) and LaLanne and Safsten (1969) have outlined the methodology of using scales for aging chum salm- on. Lengths were recorded as either fork length or postorbital-hypural length to the nearest mil- limeter. Fecundity was determined by direct counts of the number of eggs in both ovaries. Age composition in the escapement was assumed to be the same as that in the test fishery. Escape- ment was estimated during the 1960s by visual counts on spawning beds, by test fishing, and by a tagging program (Palmer 1972), whereas in the 1970s, escapement was estimated from visual counts and test fishing only. Total returns for a brood year included the catch plus escape- ment. Fraser River chum salmon are taken by the fishery which operates near the river mouth, and by fisheries in Johnstone Strait, the Strait of Georgia, and at Point Roberts in the United States. The proportion of Fraser River chum salmon in the Johnstone Strait fishery was esti- mated seasonally based on the tagging studies reported by Palmer (1972). Since the fishery in the Strait of Georgia exploits mixed stocks of chum salmon, it was not possible to estimate the contribution of Fraser River chum salmon in this fishery, although it is small compared with the catch in Johnstone Strait. Catches in the Fraser River, as well as 100% of the catches off Point Roberts, and the Fraser River contribution to Johnstone Strait were summed to estimate the total annual catch of Fraser River chum salmon. Although not all chum salmon caught off Point Roberts, 20 km south of the Fraser River mouth, may be bound for the Fraser River, any overesti- mation of the Fraser River contribution to the Point Roberts catch is compensated for by under- estimation of the Fraser River contribution to the Strait of Georgia catch. Escapements of pink salmon used in the present study were those listed in the annual report of the International Pacific Salmon Fisheries Commission for 1979 (Anonymous 1980). RESULTS Marine Growth High-seas scale and tagging studies have indi- cated that chum salmon from British Columbia and Alaska range from lat. 45°N to 60°N and from long. 130°W to 180° in the North Pacific Ocean (Shepard et al. 1968). Specific distribu- tions of Fraser River chum salmon were not available. However, the effect of variability in ocean water temperatures on growth rate was in- vestigated by comparing the mean monthly tem- perature from March through August (major part of growing season) at Station P (lat. 50°N, long. 145°W) and mean length-at-age of return- ing adults. Fork lengths of returning adults dur- ing 1960-69 were taken from Palmer (1972) and were converted to postorbital-hypural lengths by the regressions: Males: H = 1.08 FL - 219 (N = 100, r = 0.72) Females: H = 1 .00 FL - 130 ( N = 100, r = 0.89) where FL = fork length in millimeters and H — postorbital-hypural length in millimeters. These regressions were derived from chum salmon taken by the Fraser River commercial fishery in 1962 and 1963. Postorbital-hypural lengths of re- turning adults during 1970-78 were derived from the test fishery at Cottonwood Drift. For the period of 1960-78, mean lengths-at-age of 4- yr-old chum salmon were correlated with water temperature at Station P during the penultimate growing season for males (r = 0.49, n — 19, P<0.05) and females (r = 0.44, n = 19, P<0.06). However, there was no correlation for mean length-at-age and water temperature at Station P during the penultimate growing season for age-3 fish (males: r = 0.17, n = 19, P>0.10; fe- males: r = —0.08, n = 19,P>0.10)orintheyearof return and mean length-at-age for age-3 fish (males: r = 0.17, P>0.10; females: r = 0.10, F>0.10). The relatively stable mean length-at- age for returning age-3 chum salmon is undoubt- edly due to selectivity of the sampling gear, with possibly only the larger age-3 fish susceptible to capture in a 16.9 cm mesh gill net. Age Composition and Sex Ratios of Returning Adults The mean monthly age composition of chum salmon migrating upstream during the years 815 FISHERY BULLETIN: VOL. 80, NO. 4 1970-79 indicated that the proportion of age-5 fish in the run decreased from October through December, whereas the proportion of age-3 fish increased (Table 1). Age-4 chum salmon com- prised about 74% of the run in each month, while age-3 comprised 24% of the run in December but only 14% in October. Sex ratios were variable among ages, with more male chum salmon returning at age 3 (X2 = 23.7, df = 1, P<0.01) and age 5 (X2 = 10.7, P<0.01 ) than did females (Table 2). More female chum salmon returned at age 4 than did males (X2 = 70.6, P<0.01). Since the mean age of chum salmon in the run decreased through time, and sex ratios vary with age, the sex ratio of the run may also vary through time. However, an appli- cation of the sex ratios by age in Table 2 to the age compositions in Table 1 shows that sex ratios of the total run were nearly the same each month (52.9% females in October, 53.1% in November, and 52.9% in December). Table 1.— Percentage age composition by month (Octo- ber-December) of chum salmon sampled in the Fraser River test fishery, 1970-79. Sample sizes are in paren- theses. Age October November December 3 4 5 13.7 (326) 74.3 (1,826) 12.0 (304) 21.7 (715) 74.3 (2,443) 4 0 (132) 23.8 (307) 73.4 (947) 2.6 (36) Total 100.0 (2,456) 100.0 (3,290) 100 0 (1,290) Mean age (yr) 3.98 3.82 378 Table 2.— Sex ratios (males:females) of age-3, -4, and -5 chum salmon sampled in the Fraser River test fishery, 1960-79. Age: 3 4 5 Ratio Sample size 1.19 3,172 0.79 5.378 1.30 626 Fecundity Fecundity was determined from samples of chum salmon taken in 1966, 1968, and 1978 with females ranging in postorbital-hypural length from 50 to 66 cm. Females sampled in 1978 were generally larger than those in 1966 and 1968 (Table 3). A two-way analysis of covariance with sampling year and age as factors and length as a co-variate (co-variate was accounted for before factors were tested) indicated that there was no significant difference in fecundity (F) among years (F= 0.92, df = 2 and 228, P>0.05) or among ages (F = 2.66, P>0.05). The mean fecundity for all samples was 3,250 eggs/female (Table 3). The relationship between fecundity and length of 234 females sampled was described by: loge F = 2.8659 + 0.8193 loge L (r = 0.29) (1) where F = fecundity and L = postorbital-hypural length in millimeters. The regression was signifi- cant (F = 20.1, P<0.01), but accounted for about only 9% of the variability in fecundity (Fig. 2). Most of the females sampled were between 54 and 63 cm in length, and with high variability in fecundity within this short length range, little of the variability in fecundity could be accounted for by the regression. Table 3. — Number of females sampled, mean length (cm), mean age (yr), and mean fecundity of chum salmon from the Fraser River. SE = standard error of mean. Year: 1966 1968 1978 Total n 109 76 49 234 Length 574 57.9 59.5 58.0 SE of length 0.2 0.3 0.4 0.2 Age 390 389 3.90 3.90 Fecundity 3,227 3,276 3,261 3,250 SE of fecundity 395 466 60.1 277 Age: 3 4 5 n 26 194 2 Length 55.8 58.1 58.3 SE of length 06 0.2 1.3 Fecundity 3,292 3,246 3,091 SE of fecund ity 836 28.4 2879 Fry Migrations and Survival The major portion of the downstream migra- tion of chum salmon fry passed the Mission City sampling site from mid-March to the end of April. Usually 50% of the fry had passed the sam- pling site between April 13th and the 23d (Fig. 3), although 50% of the fry have passed the sam- pling site as early as April 3 (1976 brood year) and as late as May 3 ( 1971 brood year). About 80% of the chum salmon fry migrate downstream at a length of <40 mm. However, the proportion of fry >40 mm long during the downstream migra- tion tends to increase with time. By the second week of May 1978, 20% of the fry were >43 mm long and weighed 1.0 g, which suggests a period of freshwater rearing for these fry. Linear regression was used to determine the relationship of air temperature (T), determined as the mean of monthly air temperatures at the Abbotsford airport from December through February, to timing of the fry migration (F), 816 BEACHAM and STARR: POPULATION BIOLOOY OF CHUM SALMON 47 45- 43- 41- 39- 37- O 35 O 01 c 33 0) ^ 3H 0) E Z 29 27 25 23 50 -i — 54 — i — 58 1 52 54 56 58 60 Orbital - hypural length (cm) — i — 62 64 66 FIGURE 2.— The relationship between fecundity and length in female chum salmon sampled from the test fishery in 1966, 1968, and 1978. 817 FISHERY BULLETIN: VOL. 80, NO. 4 Marc h Apr i May Figure 3.— Mean time of chum fry downstream migrations on theFraser River, 1965-80. Dotted lines indicate 95% confi- dence limits. measured as the days from April 1 to the date of 50% migration. Abbotsford airport is located near many major chum salmon spawning areas (Fig. 1). The model fitted was: 25.53 r : _n„. (n rrd .444 15) T = R = E = mean monthly air temperature at Abbotsford airport from Decem- ber through February total rainfall in cm at Abbotsford airport from November through January number of eggs deposited X106. The analysis yielded: Variable Coefficient SE t T -7.62 2.51 -3.03 T/R 615.90 130.42 4.72 T/E 4,369.52 1,375.07 3.18 TIRE -266,517.54 77,530.32 -3.44 Constant 5.99 (2) The regression was significant (R2 = 0.77, F = 10.75, df = 4 and 13, P<0.01), and the correlation matrix for the model is shown in Table 5. The in- dividual factors of rainfall (r = —0.28) and egg numbers (r = —0.005) were not significantly cor- related with egg survival, but their interactions with temperature were. Egg survival tended to increase during drier winters, but if these drier winters were also relatively cold, then egg survi- val was lowered. If the winter was both relatively dry and warm, then egg survival was good, as was the case for the 1976 brood year (Table 4). and the regression was significant (r = 0.61, P<0.05) (Fig. 4). Fry tend to migrate down- stream earlier following a warmer winter than following a colder winter, presumably because warmer temperatures accelerate egg develop- ment. Based on estimates of the number of migrating fry and egg deposition (Table 4), egg-to-fry sur- vival varied from 6% to about 35% in the 1961-78 brood years. Multiple regression was used to de- termine the relationship of rainfall, egg num- bers, air temperature, and their interactions on variability in egg survival. The model fitted through stepwise regression was: S=aT+bTX— + c TX — + d T R E 1 1 X — X — + e R E where S = % egg to fry survival 818 (3) 28 o 12 12 3 4 Mean monthly temperature (Dec- Feb.) (°C) Figure 4.— Median date of downstream chum fry migration versus mean monthly temperature from December through February as measured at the Abbotsford airport. BEACHAM and STARR: POPULATION BIOLOGY OF CHUM SALMON Table 5.— Correlation matrix for theoKK-to-fry survival model. Variables are listed in the text. c E ■- CD 3 Q. < to »-■ — ■ CD _ 5 O — C« 3 >- o < a* *23 z o co ° E IE I* C/) en 0 ■D . O co O Qj ^ocococomcomcoT-T)-cM «f 'J(D©0)i-t-i/)COCDSOt-tJ; T i-CNJocococsi^csjco^^cvi'^ ^ (bcococooiiriioco^Trsoico cocor^o>r^CNjCNjcococococoin 5 a3 CD CO CO CD CO 01 If) o O CO O) CO CM oo CM CO O) co CO CO CO CO CO CO ■<* T CO CO co CO CM f CO f^ in CO CO O CD CO o O CM CNJ CM o ^r ■t CM T CO •<* NC\JO)OOin^oscpoo)co^ uScbco^^t^r^cbi-cbcb^oS C\J CNJ i- t- m O) h- ^T r- r- r- o *- oi ^t CD tt in in m go CO CM h- 0> o r- CD CD CD 00 00 ■*? o> m co m n to CO OlfilDNO)OmO)'tNN^^)

r- cbroOi-T-NcotDcosi-piJif) cb cb co *- CM CM v- T-CNJCMr-i- t-oroi-onNs^onno cd CJ)i-CO'tNC\I^t(DCMT-(Ot-ir) o Oi-OCVJr-r-OOJr-r-O'-O l^ cO'-CNjcnoooo^-oicDCNjr-T-o m cbcbcbcrJoSinihcri'^-^r^oSco o cocor^Oh-CMCMcococococoin *- cMTj-i-cNjincTicooD^incocNjcD cnj lfilT)CO'-'-CONSOI/)in'-i- i-CO^ti-i-'* cT>^incNJcT>cTioincDcbcNJotb cm i*^ in rr o o> couocotpncNjomTj-NCMinco uSc\JTrc^c\iihoScNr-~ooodcT)0 o cm ro »- f co co ^r co CT) cvjiuomcnNtDNO^inoco »- r*- ^u)coinco(DinoN^sncM cm *- cm co p in cNjCNJr^^r^c6crJr^oo^tco- ocin i SO)^^UO(DCOSSS(DCOt- Tt o »- CO N CD CNjCNjco-^-cOh-cocNjcDm'^-oco o> 'f o co co in ooooooooooooo o ooocoo OOOincOOO'-CDOCOCD'- CO CJ) CO CNJ o o cooqcoo)i/)(00)coioo)coin ^ co co o co s co o r- m a) cd cm cm co in cm" co o *- m o i- oo co cotJ)Ocoonoo)ONi,ninO)wi-N(Os t-^i-CM»-CO(M'-i-COCMCM »- CO CNJ CM *- ooooooooooooo o ooooo ooooooooooooo o ooooo OOOOOOOOi-^f^-h-O CO CO N CO CD N tj-" o" ^r in in o cm cm" o" co" co a> co in" m" oo" co' cd n-* tDCO'-CNJCOCO'-CNIOOmsm CD co co co co w »-r-c\JcOt-^c\icocococoiOTr m cm m uo Tf n '-CMCO^mcDSCOOO'-CMCO Tf UO (DN CO O) CDCDCDCOCOCDCDCDCDSNNN r- r-- r-- h- h- h- 0)0) O") O) CT> O) Varia ble S T T/R TIE TIE X Ft s 1 00 052 073 022 029 T 1.00 0.80 066 0.60 77ft 1.00 049 0.64 TIE 1.00 093 T/EXR 1.00 There was a slight tendency for egg survival to decline with increasing numbers of eggs de- posited and this effect was enhanced by a cold winter. Thus spawning escapement (egg deposi- tion), rainfall, and temperature interact to pro- duce variable freshwater survival. Fry-to-adult survival was inversely correlated with egg-to-fry survival (r = —0.62, n = 14, P<0.05), which sug- gests a density-dependent response of chum salmon fry survival. Age of Return Total returns from the 1961 through the 1974 chum salmon brood years have ranged from 180,000 to 1,930,000 fish (Table 4). The propor- tion of the brood year returning at age 3 has ranged from 4% to about 42%. To determine if the mean age at maturity from a brood year was de- pendent upon the total number of adults pro- duced from that brood year, we regressed mean age at maturity (in years) on total return (Fig. 5). This regression produced: Mean age = 3.67 + 1.923 X 10"7 Returns (n = 14) (4) where r — 0.63 ( P<0.05). The mean age at matur- ity of a brood year increased as did the total num- 200 400 600 800 1000 1200 1400 1600 1800 2000 Tolo I cecums (» I0*3) Figure 5.— Mean age of return of a brood year of chum salmon versus its abundance. 819 FISHERY BULLETIN: VOL. 80, NO. 4 ber of returning adults, which suggests that if the timing of returns is size dependent, then den- sity-dependent growth may occur during the ocean residence of chum salmon. Pink salmon re- turn to the Fraser River in abundance in odd years, but return in negligible amounts in even years. The mean age at maturity and number of returning chum salmon adults tended to be higher in even brood years than in odd ones (Fig. 5), so that pink salmon may indirectly influence mean age at maturity of chum salmon through an effect on survival of chum salmon. The proportion of a brood year returning at age 3, 4, and 5 is frequently of importance in pre- dicting annual returns. For Fraser River chum salmon, the percentage age composition of the re- turns from a brood year is related to the mean age of return of the brood year as follows: % age 3 = 321.56 - 78.26 mean age (r2 = 0.93) (5) % age 4 = -141.68 + 56.20 mean age (r2 = 0.63) (6) % age 5 = -79.88 + 22.06 mean age (r2 = 0.50). (7) If the returns from a brood year can be predicted, then the mean age of return of a brood year can be obtained from Equation (4) and applied to Equations (5)-(7) in order to obtain numbers re- turning at each age. Return to Escapement The ratio of total returns for a brood year to escapement (R/S) has varied from 0.8 to 4.0 for the 1961 through 1974 brood years. The available evidence suggests that for escapements below 850,000 adults, egg-to-fry and fry-to-adult survi- vals will generally be large enough to allow the number of returning chum salmon to remain above replacement levels (Fig. 6). However, only the 1968 escapement was above 600,000 adults, so further information on the R/S ratio for escape- ments >500,000 adults is required in order to evaluate the effect of varying escapements on chum salmon survival. There was no evidence to indicate a decline in recruits per spawner at escapements >500,000 fish, and thus the optimal escapement is uncertain. Optimal escapements will not be established with confidence until de- clines in recruits per spawner (or density-depen- dent mortality) is observed at high spawning stock sizes. 2000 ' 68 1 8 00 • 1600 ' .69 1 400 .64 72 O 12 0 0" '74 a t 1 000 ■ tr .66 800 • .73 600 .65 .62 .70 400 .75 .67 61 ^^ ^/t\ 200 0 ^/ 63 100 200 300 400 500 600 700 800 900 Spowners ( * 103 ) Figure 6.— Total return versus numbers of spawners for the 1961-75 brood years of Fraser River chum salmon. Fry-to-adult survival has been variable, rang- ing from 0.3% to 2.4% (Table 4). The average sur- vival for the even brood years was 1.53%, whereas survival for the odd brood years was 0.85%. The effect of fry abundance on variability in fry-to- adult survival was investigated for odd brood years by summing the estimated numbers of chum salmon and pink salmon fry, and for even brood years by assuming that the number of pink salmon fry produced was negligible. The data suggested that chum salmon fry survival tended to increase when the abundance of chum and pink salmon fry decreased (Fig. 7). This relation- ship can be expressed by: % survival = 0.73 + 46.53 Fry abundance (millions) (r = 0.52) (8) for the 1961-75 brood years. All of the fry-to- adult survivals for the odd brood years, except for the 1965 and 1969 brood years, were below 1.0%, whereas all of the fry-to-adult survivals for the even brood years were above 1.0%, with the 1964 and 1968 brood year fry survival being higher than the rest. Some of the variability in fry-to-adult survival was due to the timing of the downstream fry mi- gration. The higher survival of the 1965 and 1969 brood year fry when compared with other odd 820 BEAC'HAM and STARR: POPULATION BIOLOGY OF CHUM SALMON J.O- 68 6 4 2.0< 65 .69 66 LO- .70 75 67_73 .72 .74 .71 CI 50 100 150 200 250 300 350 400 450 500 Number of pink and chum fry 1 .10 ) I 3 5 7 9 II 13 15 17 19 21 23 25 27 29 I 3 5 April Moy Figure 7.— Fry-to-adult survival for chum salmon versus total abundance of pink and chum salmon fry. The abundance of pink fry from even-numbered brood years was assumed to be negligible. brood years may be accounted for by the early downstream migration, and the same condition may apply to even brood years (Fig. 8). With fry-to-adult survivals of Fraser River chum salmon generally lower in odd brood years than in even ones, odd- and even-numbered brood years were separated in a further analysis of var- iability in the returns to spawners relationship. The R/S ratio for even brood years was inversely related with the total number of returning adults of the previous odd brood year (Fig. 9). This rela- tionship was determined through regression and is described by: Figure 8.— Fry-to-adult survival of chum salmon versus medi- an date of downstream migration. ^ = 1.367 + St 0.3867 R (n = 7) (9) «-i where Rt = total returns for even-numbered brood year St = spawning escapement producing that brood year Rt-i = total returns of previous brood year in millions and the correlation between Rt/S, and \/R,.x was significant (r = 0.91, P<0.01). This equation can be rearranged to give a prediction of total num- ber of returning adults in year t, given escape- ment and total return of the previous brood year. The above suggests that survival of chum salmon in the marine environment is dependent upon the abundance of conspecifics in the previous brood year. Marine survival may thus be density-de- 2 4 6 8 10 12 14 16 Returns of previous broodyeor ( x I 0 ) Figure 9.— Ratio of returns/spawners for even-numbered brood years of Fraser River chum versus chum abundance in previous brood year. pendent, and interbrood year interactions, pos- sibly through competition for food, may affect marine survival of chum. Pink salmon have been implicated in the pres- ent study as impacting population dynamics of Fraser River chum salmon during odd brood 821 FISHERY BULLETIN: VOL. 80, NO. 4 years. Multiple regression was used to describe the effect of pink salmon on chum salmon fry sur- vivals by: £ = a L + h{D) + c S P (10) where R S P D total returns from a given brood year spawning escapement of chum salmon that produced a given brood year spawning excapement of pink salm- on in same brood year median time of downstream pink salmon fry migration minus median for chum salmon fry in days regression constant. The analysis yielded: Variable Coefficient SE S/P 13.268 4.928 2.69 D 0.136 0.034 3.93 Constant -1.469 CHUM ESCAPEMENT / PINK ESCAPEMENT The regression was significant (F = 9.60, df = 2, and 3, P<0.05) and accounted for 85% of the vari- ation in R/S in odd brood years (R = 0.92). The chum salmon R/S ratio increases the earlier that chum salmon fry migrate downstream relative to pink salmon fry (Table 6). If chum salmon es- capement is 10% of that of pink salmon, then the time of the median downstream migration of chum salmon fry must be at least 9 d earlier than that of pink salmon fry if the chum salmon spawners are just to replace themselves (R/S = 1.0) (Fig. 10). However, if chum salmon escape- Table 6.— Dates when 50% of the fry were estimated to have migrated downstream and estimated spawning es- capements for odd-numbered brood years, 1965-77. Spawni ig escapements Brood Date of 50% fry Chum migration Pink (*10J) year Chum Pink 1965 11 April 2 May 185.0 1.191.1 1967 17 April 24 April 212.0 1.831.4 1969 15 April 24 April 3900 1.529.5 1971 3 May 5 May 3567 1.803.8 1973 19 April 16 April 4530 1,754.1 1975 15 April 23 April 235.3 1,367.3 1977 20 April 25 April 538.8 2.387.8 Figure 10.— Contour plot for returns/spawners for odd-num- bered brood years of Fraser River chum in relation to timing of pink and chum fry migrations and relative spawning escape- ments of pink and chum. Contour lines of R/S = 1.0, 2.0, 3.0, and 4.0 are plotted. ment is 30% of the pink salmon escapement and chum salmon fry still have a 9-d advantage over pink salmon fry, then the R/S ratio for chum salmon will be between 3.0 and 4.0, as happened for the 1969 brood year (Fig. 10). The chum salmon R/S ratio will still be between 3.0 and 4.0 if the chum salmon escapement is 15% of the pink salmon escapement, provided the chum salmon fry have at least a 19-d advantage over the pink salmon fry, similar to the 1965 brood year (Fig. 10). DISCUSSION Mean lengths at maturation for 4-yr-old chum salmon in the present study were found to be sig- nificantly correlated with oceanic water temper- atures in the penultimate growing season but not in the final one. Helle (1979) found that oceanic 822 BEACHAM and STARR: POPULATION BIOLOGY OF CHUM SALMON environmental factors during the final ocean year strongly influenced length at maturity of chum salmon from Olsen Creek, Alaska. The causes of the different results of the two studies are uncertain, but may in some way be related to the timing of the attainment of a threshold length for spawning. The fecundity of Fraser River chum salmon (3,250 eggs/female) reported in the present study was greater than that reported by Foerster and Pritchard (1936) for Fraser River chum salmon (2,943 eggs/ female), for Nile Creek chum salmon (2,726 eggs/female) (Neave 1953), and for Hook- nose Creek chum salmon (2,083-3,097 eggs/fe- male) (Hunter 1959). Only a few of the mean fecundities listed by Bakkala (1970) for North American and Asian chum salmon were greater than that of Fraser River chum salmon. How- ever, size and age compositions of chum salmon sampled for fecundity in the former studies were unavailable, and it may be that larger sized chum salmon were sampled in the Fraser than in other areas because smaller females may have avoided the test fishery. In chum salmon, males have been reported to predominate in the early part of the run and fe- males in the later part (Gilbert 1922; Henry 1954). In the present study, sex ratios as mea- sured by the test fishery remained relatively con- stant during the fall upriver migration. This result was probably due to differences in run timing of stocks in the Fraser River, so that stocks in different stages of completeness of the run were sampled at the same time, and thus temporal shifts in sex ratios may have been ob- scured. Freshwater and marine survival of Fraser River chum salmon have varied about sixfold and fivefold, respectively. Rainfall and gravel permeability have been implicated in variable freshwater survival elsewhere, with higher rain- fall in the fall (except in flood years) and looser, more permeable gravel resulting in higher sur- vival (Wickett 1958). Freshwater survival of chum salmon in Hooknose Creek was inversely related to the total number of pink and chum salm- on eggs deposited (Hunter 1959). The present study indicated that freshwater survival of Fraser River chum salmon was inversely related to the amount of winter rainfall, and that much of the variability in freshwater survival was at- tributable to interactions among temperature, rainfall, and egg abundance. Mortality among young fry has been suggested to be a major influence in determining the abun- dance of returning adults from a brood year of pink or chum salmon (Neave 1953; Hunter 1959; Parker 1965). Egg-to-fry survival in Fraser River chum salmon was largely dependent upon physical environmental fluctuations, whereas fry-to-adult survival may be dependent upon chum and pink salmon abundance. The effects of favorable or unfavorable environmental condi- tions during incubation appear to be compen- sated for by density-dependent responses of sur- vival during the marine life history stage of chum salmon. Density-dependent survival dur- ing the marine residence period has been sug- gested for several Oncorhynchus species, with possible interactions within and among brood years (Peterman 1978). The present study indi- cated that for even brood years of Fraser River chum salmon, marine survival may be inversely associated with the abundance of the previous brood year, which suggests that the number of returns from a brood year is not determined until the mixing of underyearlings and older chum salmon in the ocean. Although early fry mortal- ity is undoubtedly heavy in chum salmon, as it is in other marine fish, and although it has been suggested that the determination of year-class abundance occurs soon after hatching in marine fishes (Cushing and Harris 1973), some evidence does suggest that year-class abundance is not de- termined in the first year of life of marine fishes (Ponomarenko 1973; Lett et al. 1975). The present study indicated that the mean age of returns of a brood year increased with brood year abundance. Similar observations have been reported by Birman (1951) for chum salmon in the Amur River in the Soviet Union and Helle (1979) for chum salmon in Olsen Creek in Alaska. This result implies that growth during ocean residence is density-dependent, as has been re- ported in other marine fishes (Sonina 1965; Palo- heimo and Kohler 1968; Templeman etal. 1978). Competition for food may be one of the mecha- nisms of this density-dependence. The present study also indicated that higher marine water temperatures were accompanied by increased growth rates, as indicated by annual variability in size of returning 4-yr-old chum salmon. The present study suggests that there may be competition between chum and pink salmon fry in the Fraser River estuary or Strait of Georgia. Phillips and Barraclough (1978) found that chum salmon fry in the Strait of Georgia near the Fra- ser estuary were larger in 1967 and 1969 when 823 FISHERY BULLETIN: VOL. 80, NO. 4 pink salmon fry abundance would be low than those in 1966 and 1968 when pink salmon fry would be abundant. When chum and pink salmon fry migrated at similar times, chum salmon fry-to-adult survival was lower than when chum salmon fry migrated earlier than pink salmon fry. Pink salmon grow faster than do chum salm- on (Ricker 1964), and this faster growth rate may allow them to outcompete chum salmon fry for food. The influence of pink salmon on egg-to- fry survival of chum salmon was not examined, but we expect it would be minimal relative to en- vironmental influences as pink salmon spawn earlier in the Fraser River than do chum salmon. The present study suggests some areas that need to be explored further. Interspecific inter- actions between pink and chum salmon fry may be investigated by marking and varying the size and time of release of chum salmon fry in years when pink salmon fry are present and measuring rates of adult returns for these sets of fry, similar to the studies of Fraser et al. (1978) for chum on the Big Qualicum River and Bilton (1978) for coho salmon, Oncorhynchus kisutch. ACKNOWLEDGMENTS We are indebted to those who sampled and aged the salmon caught in the test fishery and sampled the fry during their downstream migra- tions. Tom Bilton provided the data used to con- vert chum fork lengths to postorbital-hypural length. M. C. Healey and B. E. Riddell made many helpful suggestions which improved the manuscript. The manuscript was prepared with the assistance of the staff at the Pacific Biologi- cal Station. LITERATURE CITED Anonymous. 1980. Annual report 1979. International Pacific Salm- on Fisheries Commission, New Westminster, B.C., 57 P- Bakkala, R. G. 1970. Synopsis of biological data on the chum salmon, Oncorhynchus keta (Walbaum) 1792. U.S. Fish Wildl. Serv., Circular 315, 89 p. Bilton, H. T. 1978. Returns of adult coho salmon in relation to mean size and time of release of juveniles. Fish. Mar. Serv. Tech. Rep. 832, 73 p. Bilton, H. T., and W. E. Ricker. 1965. Supplementary checks on the scales of pink salmon (Oncorhynchus gorbuscha) and chum salmon (O. keta). J. Fish. Res. Board Can. 22:1477-1489. BlRMAN, I. B. 1951. (Qualitative characteristics of the stocks and dy- namics of abundance of autumn chum salmon of the Amur River.) Izv. Tikhookean. Nauchno-Issled. Inst. Morskogo Rybn. Khoz. Okeanogr. (TIRNO) 35:17-31. Fish. Res. Board Can., Transl. Ser. 103. CUSHING, D. H., AND J. G. K. HARRIS. 1973. Stock and recruitment and the problem of density dependence. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 164:142-155. FOERSTER, R. E., AND A. L. PRITCHARD. 1936. The egg content of Pacific salmon. Biol. Board Can., Prog. Rep. Pac. Biol. Stn. 28:3-5. Fraser, F. J., D. D. Bailey, and M. J. Wood. 1978. Big Qualicum River salmon development project (Vol. Ill): Experimental rearing of chum salmon juve- niles (Oncorhynchus keta) in fresh water (1968-1970). Fish. Mar. Serv. Tech. Rep. 752, 22 p. Gilbert, C. H. 1922. The salmon of the Yukon River. U.S. Bur. Fish., Bull. 38:317-332. Helle, J. H. 1979. Influence of marine environment on age and size at maturity, growth, and abundance of chum salmon, Oncorhynchus keta (Walbaum), from Olsen Creek, Prince William Sound, Alaska. Ph.D. Thesis, Oregon State Univ., Corvallis, 129 p. Henry, K. A. 1954. Age and growth study of Tillamook Bay chum salmon (Oncorhynchus keta). Fish Comm. Oreg., Con- trib. 19, 28 p. Hoar, W. S. 1951. The chum and pink salmon fisheries of British Co- lumbia, 1917-1947. Fish. Res. Board Can., Bull. 90, p. 1-46. Hunter, J. G. 1959. Survival and production of pink and chum salmon in a coastal stream. J. Fish. Res. Board Can. 16:835- 886. LaLanne, J. J., AND G. Safsten. 1969. Age determination from scales of chum salmon (Oncorhynchus keta). J. Fish. Res. Board Can. 26:671- 681. Lett, P. F., A. C. Kohler, and D. N. Fitzgerald. 1975. Role of stock biomass and temperature in recruit- ment of southern Gulf of St. Lawrence Atlantic cod, Gadus morhua. J. Fish. Res. Board Can. 32:1613-1627. McCombie, A. M., and A. H. Berst. 1969. Some effects of shape and structure of fish on selec- tivity of gillnets. J. Fish. Res. Board Can. 26:2681- 2689. Neave, F. 1953. Principles affecting the size of pink and chum salmon populations in British Columbia. J. Fish. Res. Board Can. 9:450-491. Palmer, R. N. 1972. Fraser River chum salmon. Can. Fish. Serv., Pac. Reg., Tech. Rep. 1972-1, 284 p. Paloheimo, J. E., and A. C. Kohler. 1968. Analysis of the southern Gulf of St. Lawrence cod population. J. Fish. Res. Board Can. 25:555-578. Parker, R. R. 1965. Estimation of sea mortality rates for the 1961 brood-year pink salmon of the Bella Coola area, British Columbia. J. Fish. Res. Board Can. 22:1523-1554. 824 BEACHAM and STARK: POPULATION BIOLOGY OF CHUM SALMON PETERMAN, R. M. 1978. Testing for density-dependent marine survival in Pacific salmonids. J. Fish. Res. Board Can. 35:1434- 1450. Phillips, A. C, and W. E. Barraclough. 1978. Early marine growth of juvenile Pacific salmon in the Strait of Georgia and Saanich Inlet, British Colum- bia. Fish. Mar. Serv. Tech. Rep. 830, 19 p. PONOMARENKO, V. F. 1973. On a probable relation between age composition and spawning stock and abundance of the year classes of cod in the Barents Sea. Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer 164:69-72. Pritchard, A. L. 1943. The age of chum salmon taken in the commercial catches in British Columbia. Fish. Res. Board Can., Prog. Rep., Pac. Coast Stn. 54:9-11. Ricker, W. E. 1964. Ocean growth and mortality of pink and chum salmon. J. Fish. Res. Board Can. 21:905-931. 1980. Changes in the age and size of chum salmon (Oneo- rhynchus keta). Can. Tech. Rep. Fish. Aquat. Sci. 930, 99 p. Shepard, M. P., A. C. Hartt, and T. Yonemori. 1968. Salmon of the North Pacific Ocean— Part VIII. Chum salmon in offshore waters. Int. North Pac. Fish. Comm., Bull. 25, 69 p. Sonina, M. A. 1965. Relationship between the growth rate and popula- tion density of haddock in the Barents Sea. Int. Comm. Northwest Atl. Fish. Spec. Publ. 6:565-570. TEMPLEMAN, W., V. M. HODDER, AND R. WELLS. 1978. Age, growth, year-class strength, and mortality of the haddock, Melanogrammus aeglefinus, on the south- ern Grand Bank and their relation to the haddock fish- ery of this area. Int. Comm. Northwest Atl. Fish. Res. Bull. 13:31-52. TODD, I. S. 1966. A technique for the enumeration of chum salmon fry in the Fraser River, British Columbia. Can. Fish Cult. 38:3-35. Todd, I. S., and P. A. Larkin. 1971. Gillnet selectivity on sockeye (Chworhynchiisnerka) and pink salmon (O. yorbuxcha) of the Skeena River sys- tem, British Columbia. J. Fish. Res. Board Can. 28: 821-842. WlCKETT, W. P. 1958. Review of certain environmental factors affecting the production of pink and chum salmon. J. Fish. Res. Board Can. 15:1103-1126. 825 TROPHIC PATTERNS AMONG LARVAE OF FIVE SPECIES OF SCULPINS (FAMILY: COTTIDAE) IN A MAINE ESTUARY Joanne Lyczkowski Laroche1 ABSTRACT The food habits and trophic relationships of larvae of five species of marine cottids — Myoxocephalus aenaeus, M. octodecemspinosus, M. scorpius, Triglops murrayi, and Hemitripterns americanus — were examined and compared during winter and early spring when they cooccur at peak abundance in the Damariscotta River estuary, Maine. Overall feeding incidence was high with <14% of the larvae in any species having empty guts. Larvae of all five species began to feed before yolk absorp- tion was complete. Among the five species, M. aenaeus and M. octodecemspinosus were most similar in mouth size, prey size, and dominant prey— adult Microsetella norvegica in January and February (winter) and Balanus nauplii in March (early spring). Mouth size, prey size, and dominant prey in early spring (Bal aim* nauplii) of Myoxocephalus scorpius were similar to the other species of Myoxocephalus, but the most frequently ingested prey in winter was the centric diatom, Coscinodiscus sp. Triglops murrayi larvae had relatively larger mouths and ingested somewhat larger prey than similar-sized Myoxocephalus larvae, feeding primarily on adult Pseudocalanus minutus in both winter and early spring. Although mouth sizes of//, americanus and T. murrayi larvae were similar, the diet of H. americanus was composed almost exclusively of fish larvae, primarily other cottids. The high incidence of ingestion of Balanus nauplii by Myoxocephalus and T. murrayi in early spring may indicate some degree of density-dependent food utilization by those larvae. Yet other prey, adult Temora longicumis and epibenthicharpacticoidcopepods, appeared to be preferred over other presumably more abundant zooplankton. Percent diet overlap was greatest among the three species of Myoxocephalus and, except between M. aenaeus and M. octodecemspinosus, was lower in winter when mean plankton volume (an ap- proximate measure of food supply) was low. Observed differences in vertical distribution resulting in partial spatial segregation of M. aenaeus and M. octodecemspinosus larvae may reduce competi- tion for food between the two species, thus allowing the consistently high degree of dietary overlap between them. Prey size (maximum carapace width) at first feeding ranged from 100 to 375 /im among the three species of Myoxocephalus and >800 /xm for H. americanus. There was no dramatic change in prey types or sizes with increasing larval size. Larvae of the five species of cottids were found to most closely resemble hake (genus Merluccius) in prey size relationships. There have been relatively few detailed descrip- tions of the food habits of marine fish larvae de- spite the reputed importance of starvation as a primary cause of mortality in the sea (Hunter 1976). Our generalized concept of early feeding ecology in marine fishes is based mostly on highly fecund species whose larvae hatch from small planktonic eggs at 2-3 mm in length with undeveloped eyes and mouths( Arthur 1976; Last 1978a, b; Sumida and Moser 1980). Little is known of trophic relations among larvae of fishes such as the cottids which deposit relatively few, large, demersal eggs and whose planktonic lar- vae hatch at sizes ^5 mm, in a relatively ad- vanced stage of development with pigmented 'Gulf Coast Research Laboratory, East Beach Drive, Ocean Springs, MS 39564. Manuscript accepted June 1982. FISHERY BULLETIN: VOL. 80, NO. 4. 1982. eyes and functional mouths (Laroche 1980). Fishes with widely divergent ontogenies would be expected to also have different early trophic relations, whose comparisons may yield further insights into processes controlling survival in the sea. The kinds of food used in most laboratory studies of foraging behavior, feeding efficien- cies, and growth of fish larvae are usually organ- isms which are easily cultured in quantity but are not natural larval fish prey, or which are known size fractions of wild plankton whose spe- cies composition is only approximately known. Laboratory results, based solely on unnatural and/or single prey, or prey described by size only, may have little relevance to the real situa- tion in the sea. It is not unreasonable to suspect that different kinds (and sizes) of prey may sig- 827 FISHERY BULLETIN: VOL. 80, NO. 4 nificantly affect the feeding and growth of fish larvae. For these reasons, there is a need for addi- tional detailed descriptions of natural prey so that laboratory studies can be designed to inves- tigate the effects of these prey organisms on larval fish behavior, metabolism, and growth. This study was undertaken to examine and compare the food habits and trophic relation- ships of the larvae of five species of marine cot- tids — Myoxocephalus aenaeus, M. octodecemspi- nosus, M. scorpius, Triglops murrayi, and Hemi- tripterus americanus— during winter and early spring when they cooccur at peak abundance in the Damariscotta River estuary, Maine. Data are presented on feeding incidence, diet composi- tion, diet overlap, larval mouth size, and prey size. Trophic patterns are examined with respect to possible interspecific competition and the in- fluence of relative prey abundance and morphol- ogy on foraging. Aspects of the feeding ecology of these larvae are compared with the early feeding ecology of other marine fishes. MATERIALS AND METHODS Larvae used in diet analyses were collected in surface and bottom tows of a 1 m, 360 nm mesh conical plankton net which was mounted atop a 1.3 m wide X 45.7 cm high Blake trawl (a type of beam trawl). Although larvae were collected throughout the Damariscotta River, a drowned river valley opening into the Gulf of Maine and located on the central Maine coast, most speci- mens were captured in the middle basin of the estuary (Laroche 1980). Myoxocephalus (M. ae- naeus, M. octodecemspinosus, and M. scorpius) and T. murrayi larvae were collected, for the most part, on these dates in 1973: 22 January; 6, 20, 21 February; and 5, 6, 19, 20 March. From 26 to 30% of larvae of the four species used in diet analyses were taken in surface tows and 70 to 74% were taken in bottom tows. Larvae of H. americanus were rare in collections; therefore, all specimens collected during the period Janu- ary-April 1972-74 were used in diet analyses. Prior to preservation in 10% Formalin2 in the field, an unquantified amount of MS-222 (tri- caine methanesulfonate) was added to each sam- ple. The sample was gently swirled as the anes- thetic dissolved larvae became inactive. This procedure eliminated defecation and/or regurgi- tation subsequent to capture. Before removal of the gut, standard length (SL, to nearest 0.1 mm) and upper jaw length (i.e., distance from symphysis to posterior mar- gin of maxillary along the ventral aspect, to nearest 0.01 mm) were measured using an ocular micrometer in a stereomicroscope. Jaw length rather than gape was used as a measure of poten- tial size of the mouth opening because jaw length was not affected by whether the mouth was opened or closed at the time of preservation and could, therefore, be measured more consistently and precisely. Larvae were placed in a cavity of a double-depression glass slide, and the entire gas- trointestinal tract from esophageal sphincter to anus was gently pulled intact from the abdomi- nal cavity. At this time the presence or absence of yolk was noted, and an estimate was made of the quantity of yolk present: one-fourth, one-half, three-fourths of abdominal cavity full or only a remnant remaining. The gut was placed in the other, water-filled cavity of the slide, and the gastric and pyloric regions were teased apart separately using two fine probes. The presence or absence of food items in each of these regions was noted. Food items were identified to the lowest taxon possible and counted except for undigestable prey remains, such as setae, and unrecognizable debris. Pseudocalanus eggs, which were prob- ably ingested with the brooding females, and small diatoms (in March samples only) were like- wise not counted. Maximum body width or di- ameter of most food items was measured. Larvae were grouped into arbitrarily chosen size intervals, based on overall size distributions, to facilitate intra- and interspecific diet compari- sons. Percent frequency of occurrence (%FO) and percent of total number (%A0 of prey ingested by larvae in each size group were calculated for each food category. An estimate of the relative importance of each food category was obtained by multiplying %FO by %N. Diet overlap was measured using the Schoener index (1970): a = 100 [1 - 0.5 i /px 1=1 vjl 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. where pxi = proportion (percent by number) of food category i in the diet of species x; pyi = pro- portion (percent by number) of food category i in the diet of species y\ and n = the number of food 828 LAROCHE: TROPHIC PATTERNS AMONG LARVAE OF SCULPINS (COTTIDAE) categories. Percent by volume or weight is, in most cases, more useful than %Nor %FO in mea- suring diet overlap. However, for predators like larval Myoxocephalus and T. murrayi whose prey are similar in size (Fig. 1), calculation of the Schoener index using %N and %FO produces a relatively unbiased estimate of diet overlap (Wallace 1981). Settled volumes of the ichthyoplankton sam- ples were measured by displacement method in either a 100 or 250 ml graduated cylinder after large jellyfish and macrophytic algae or other large plant debris were removed. RESULTS Feeding Incidence The percentage of cottid larvae with empty guts ranged from 0 to 13 depending on the spe- cies, with T. murrayi having the lowest overall incidence of empty guts and H. americanus the highest (Table 1). Only M. aenaeus and M. scor- pius had equal or higher percentages of empty guts in January and February than in March. In addition to this high incidence of feeding, many larvae examined had begun to feed before yolk absorption was complete (Table 1). A remnant of yolk (often sizeable) was found attached to or closely associated with the liver in feeding larvae over a wide size range: 5.3-9.5 mm SL in M. aenaeus; 7.2-11.5 mm SL in M. octodecemspino- sus; 7.5-10.4 mm SL in M. scorpius; 8.5-12.0 mm SL in T. murrayi; and 12.0-15.9 mm SL in H. americanus. Among the three species of Myoxocephalus lar- vae with three-fourths of the abdominal cavity filled with yolk (N = 33), about 80% had food in their guts. The number of food items found in these larvae ranged from 1 to 4 in M. aenaeus, 2 to 12 in M. octodecemspinosus, and 1 to 21 in M. scorpius. No yolk-sac larvae of T. murrayi were Fiih Larvae Decapod Zoeae Temora Pseudocalanus Tisbe Turbellana Balanus Harpacticus Coscinodiscus Microsetella Prey Width (micront) -I 1 1 1 1 1 1 // 1- Hemitnpterus americanus Triglops murrayi Myoxocephalus scorpius H 1- — I 1 1 1 1 U — I— 160 240 320 400 480 560 640 720 800 880 1260 Body Width (microns) Figure 1.— Range in maximum body width (microns) of the major prey ingested by larvae of five species of cottids in the Damariscotta River estuary, Maine. collected. Of the seven H. americanus larvae with prominent yolk sacs, only two had empty guts. Each of the other larvae contained one food item. Diet Composition Gut contents were examined of 147 M. aenaeus, 5.3-9.5 mm SL; 106 M. octodecemspinosus, 7.2- 12.4 mm SL; 87 M. scorpius, 7.5-13.4 mm SL; 58 T. murrayi, 8.5-18.1 mm SL; and 24 H. ameri- canus, 12.0-16.2 mm SL (Tables 2-10). Percent number of Coscinodiscus sp. was calculated only Table 1.— Incidence of Myoxocephalus, Triglops, and Hemitripterus larvae with empty guts, and those with both food and a remnant of yolk present. (A/ = number of larvae examined.) January-February March Species N % empty % with yolk + food N % empty % with yolk + food Myoxocephalus aenaeus M. octodecemspinosus M. scorpius Triglops murrayi 18 31 18 22 6 0 11 0 January-Apri 94 100 89 73 129 75 69 36 6 5 0 3 75 66 91 6 Hemitripterus americanus 24 13 83 829 FISHERY BULLETIN: VOL. 80, NO. 4 Table 2. — Summary of food habits of 18 Myoxocephalus aenaeiis larvae captured on 22 January and 6 February 1973. %FO = percent frequency of occurrence (FO) among larvae containing food; %N = percent of the total number (TV) of food items ingested by larvae in that size group. Size range (mm) 5.3-6.4 6.5-7.4 Food item FO %FO W %/V FO %FO N %/V Balanus nauplii 1 7.1 1 0.8 Calanoid copepods: Temora longicomis 1 7.1 3 25 Harpacticoid copepods: Microselella norvegica 3 75.0 9 81.8 14 100.0 104 85.2 Tisbe spp. 2 14.3 2 1.6 Unidentified. Adults and copepodites 1 7.1 1 0.8 Coscinodiscus sp 1 25.0 2 182 7 50.0 11 9.0 Total no. food items 11 122 Number larvae examined 4 14 Number larvae empty 1 0 Table 3.— Summary of the food habits of 129 Myoxocephalus aenaeus larvae captured on 5, 6, 19, and 20 March 1973. %FO = percent frequency of occurrence (FO) among larvae containing food; %JV = percent of the total number (.V) of food items ingested by larvae in that size group. Size rar ige (mm I 5.5-6.4 6.5-7.4 7.5-8.4 8.5-9.5 Food item FO %FO N %/V FO %FO N %/V FO %FO N %/V FO %FO N %/V Balanus nauplii 12 100.0 34 61.8 43 93.5 158 57.5 37 88.1 115 426 20 952 90 54.9 Calanoid copepods: Temora longicomis 3 6.5 4 1.5 9 21.4 16 5.9 4 190 5 3.0 Harpacticoid copepods: Microsetella norvegica 4 33.3 9 16.4 24 52.2 47 17.1 23 54.8 51 18.9 13 61.9 12 7.3 Tisbe spp. 10 21.7 13 4.7 10 23.8 20 7.4 5 23.8 9 5.5 Harpacticus spp. 2 4.3 2 0.7 13 31.0 17 6.3 6 28.6 9 5.5 Zaus sp. 2 4.3 2 07 3 7.1 4 1.5 Unidentified: Adults and copepodii tes 5 10.9 6 2.2 3 7.1 4 1.5 1 4.8 2 1.2 Unidentified copepod nauplii 1 2.2 1 0.4 1 4.8 25 15.2 Turbellana 3 25.0 4 7.3 13 28.3 19 6.9 12 28.6 23 8.5 4 19.0 7 4.3 Ostracoda 2 4.3 2 0.7 Unidentified invertebrate eggs: Single 1 83 7 12.7 7 152 21 7.6 2 4.8 13 4.8 Sacs 1 8.3 1 1.8 6 14.3 7 2.6 4 19.0 5 3.0 Coscinodiscus sp. 3 25.0 — 10 21.7 — 10 23.8 — 7 33.3 — Setae 2 167 — 5 10.9 — 11 26.2 — 3 14.3 — Unrecognizable debris 5 41.7 — 13 28.3 — 20 47.6 — 12 57.1 — Total no. food items 55 275 270 164 Number larvae examined 17 49 42 21 Number larvae empty 5 3 0 0 in January-February and not in March when barnacle nauplii were the principal prey of lar- vae, because it is likely that some proportion of these diatom cells were released from the guts of Balanus nauplii during digestion. Cells ^25 yum in diameter were found inside undigested Ba- lanus nauplii taken from the guts of cottid lar- vae. Flatworms (Turbellaria) ingest diatoms whole (Jennings 1957) and these may also have contributed Coscinodiscus cells. Most of the calanoid and harpacticoid copepods ingested by cottid larvae were adults and, for Temora longi- comis, mostly females. Bundles of setae of un- determined origin seemed to accumulate in the guts of cottid larvae. The most likely sources of these are the appendages of Microsetella and Balanus nauplii. Diet Comparisons Relative importance of each prey taxon was estimated from the product of %FO and %N. Ma- jor prey (%FO X %N>100) of only similar-sized larvae were ranked according to this value and compared for seasonal as well as inter- and intra- specific differences (Tables 11, 12). In general, the same trophic patterns were present among larvae in size groups not included in these com- parisons (Tables 2-10). In January and February the dominant prey of 830 LAROCHE: TROPHIC PATTERNS AMONO LARVAE OF SCULPINS (COTTIDAE) Table 4. — Summary of the food habits of 31 Myoxocephalus octoiiecemsfjinoxus larvae captured on 22 January and 6 February 1973. %FO = percent frequency of occurrence (FO) among larvae containing food; %7V = percent of the total num- ber (JV) of food items ingested by larvae in that size group. Size rar ige (mm; I 7.2-8.4 8.5-9.4 Food item FO %FO N %/V FO %FO N %/V Balanus nauplii 2 28.6 2 1.7 Calanoid copepods: Temora longicomis 7 29.2 8 25 7 100.0 28 23.3 Harpacticoid copepods: Microsetella norvegica 24 100.0 284 89.3 7 100.0 65 542 Tisbe spp. 2 83 2 06 Harpacticus spp. 2 83 2 0.6 Unidentified: Adults and copepodites 3 12.5 3 09 2 28.6 3 2.5 Unidentified copepod nauplii 2 8.3 3 0.9 1 14.3 2 1.7 Ostracoda 1 4.2 1 03 Unidentified invertebrate eggs: Single 2 28.6 20 16.7 Coscmodiscus sp 3 12.5 15 4.7 Setae 1 4.2 Total no. food items 318 Tio Number larvae examined 24 7 Number larvae empty 0 0 both M. aenaeus and M. octodecemspinosus was Microsetella norvegica, while Coscinodiscus sp. dominated the diet of Myoxocephalus scorpius larvae. Coscinodiscus sp. cells are bright green in color and the digestive tracts of M. scorpius larvae observed in the field before preservation appeared to be this same color. Unlike similar- sized M. octodecemspinosus and M. scorpius, Triglops murrayi larvae fed primarily on adult Pseudocalanus mi nut us and calanoid copepod- ites. which were largely digested but most re- sembled, and probably were, immature Pseudo- calanus. There appeared to be no distinct change in dominant prey types as larvae grew within the size ranges examined. The largest M. octodecem- spinosus and M. scorpius larvae ingested more kinds of prey than smaller larvae, but the reverse was true for T. murrayi. In March, the overwhelmingly dominant prey of all three species of Myoxocephalus were Ba- lanus nauplii. Microsetella ranked second in importance among 7.5-9.5 (9.4) mm SL Myoxo- cephalus aenaeus and M. octodecemspinosus lar- vae, but was replaced by adult Temora longi- comis in 9.5-12.4 mm SL M. octodecemspinosus. No other prey of M. scorpius larvae at any size approached the importance of Balanus nauplii which were nearly the exclusive prey of this spe- cies in March. Mean number of nauplii per M. scorpius larva ranged from 12 to 16 depending on larval size, whereas the range in mean num- ber for the other two species of Myoxocephalus was only 3-8 nauplii/larva. As in January and February, Pseudocalanus dominated the diet of T. murrayi larvae in four of six size groups. Balanus nauplii ranked second in importance in four size groups, and ranked first in the largest size group. Other fish larvae, primarily M. aenae- us, were nearly the exclusive prey of all H. amer- icanus larvae examined. Up to four prey larvae were found in the gut of a single H. americanus larva, and a 13 mm SL rockgunnel, Pholis gun- nellus, larva was found coiled up inside the gut of a 13 mm SL specimen. There was no dramatic change in prey types ingested among the five species with increasing larval size. Only the change in the second-ranked prey of M. octo- decemspinosus larvae from Microsetella to Temora may have been related to increased size. The most important seasonal change in diet among cottid larvae was replacement of Coscino- discus sp. and, to a lesser extent, Microsetella by Balanus nauplii. Barnacle nauplii also became a relatively important component of the diet of T. murrayi larvae in March but Pseudocalanus continued to dominate the diet of larvae in most size groups. Diet Overlap Diet overlap was measured among larvae of four species of cottids (H. americanus excluded because of its obviously unique diet), using the Schoener index (1970) which describes the rela- tive amount of dietary overlap between species pairs on a scale of 0 = no overlap to 100 = com- 831 FISHERY BULLETIN: VOL. 80, NO. 4 cj C a> •~ 3 CJ o cj c 0) 3 a a- 3 a> o «- bo C 4> 5 N f-l -3 0) ^ co > . u CO eS c- — 5 >> rH X! 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C o o 0) CD Q. c I O S"2 CD C Q D -O £1 E E z z ^ c« >>T i- be S I * i S^ S § as c a H 2! p >> s- g Si g M g 8 s c £ - 0 p c 1 » ai 2^ a) a> X3 e« ft — tflO to — r, cu «5 t« S CO . 6 ^v C1J as js OS'S w ft o £ < Z a. -h — "C-gfe; CM o i2 53 ■■5 a 53 5C -^ CO T3 t> O OS £ "-1 -Si o g 3 .. CO to '• 2 be ^H J= •- w 2 ■§ EH t- u CO | CO co I co o o d d i- ■»! in as | O) n CO CU o o o N CD (0 > d c o Q. ffl a CO U CD o 1- □ LL 3 E CD CD E E 3 3 z z CO _J Eco E E _ co E 800 mm for H. americanus (Sumida and Moser 1980; de Ciechomski and Weiss 1974). Among fish larvae that ingest 50-100 ^m wide prey at first feeding, there is usually a distinct and often dramatic increase in prey size with development. This is seen typically as a change from a diet of copepod eggs and nauplii to one of advanced copepodites and adults. No dramatic increase in prey size or progression in prey types occurs in cottid and hake larvae. Hunter (1980) recently attempted to categorize marine fish larvae into distinct ecological roles based on those behavioral and physiological traits primarily associated with feeding. Two distinct groups, engrauliform and scombriform, based on extensive field and laboratory observa- tions of northern anchovy and Pacific mackerel larvae, emerged from his analyses. Cottid larvae share some scombriform traits such as relatively large mouths and prey. Similarities in feeding posture, maneuverability, and swimming speed may be inferred because of features in body shape shared by cottid and Pacific mackerel lar- vae. These larvae, however, would be expected to differ significantly in rates of metabolism and growth because of the different environmental temperature regimes they inhabit: 14°-21°C for highest abundances of Pacific mackerel (Kramer 1960) and 0°-4°C for cottid larvae (Laroche 1980). In this regard, cottid larvae more closely resemble hake larvae which inhabit deeper, colder oceanic waters than either anchovy or Pacific mackerel. Hunter (1980) suggested that hake larvae may belong to a third trophic group characterized by reliance on large prey, a fea- ture already shown to be shared with cottid lar- vae, and slow metabolism and growth. Although growth rates have not been estimated for cottid larvae, increases in monthly median lengths of ^1 mm (Laroche 1980) and relatively stationary modes in length-frequency distributions during winter and spring in the Damariscotta River estuary (Townsend 1981) may be explained, in part, by slow growth rates. Despite some apparent similarities, there are notable differences in the early life histories of hake and the five species of cottids: for example, egg size, 0.98 vs. 1.5-4 mm; size at hatching, 2.4 vs. 5-12 mm; and stage of eye and mouth develop- ment at hatching, partial vs. complete. The sig- nificance of differences such as these in further distinguishing ecological roles among fish larvae will be better understood only after the early feeding ecology of more species has been investi- gated. ACKNOWLEDGMENTS The following individuals are gratefully ac- knowledged for their significant contributions to this study. Wayne A. Laroche and Paul C. Jensen guided and assisted me in the field; John Konecki, Gilbert Jaeger, Paul Montagua, and William T. Peterson patiently taught me the taxonomy of in- vertebrate taxa; Joseph J. Graham generously supplied sampling gear and laboratory equip- ment, and the numerous discussions on larval fish ecology and taxonomy with him and Stanley R. Chenoweth were invaluable; Hugh H. DeWitt and Bernard J. McAlice provided long-term sup- port and counsel; Wayne A. Laroche, Percy L. Donaghay, and William T. Peterson read the manuscript and suggested useful ways to im- prove it. LITERATURE CITED Arthur, D. K. 1976. Food and feeding of larvae of three fishes occurring in the California Current, Sardinops sagax, Engraulis mordax, and Trachurus symmetricus. Fish. Bull., U.S. 74:517-530. Beyer, J. E. 1980. Feeding success of clupeoid fish larvae and stochas- tic thinking. Dana 1:65-91. Blaxter, J. H. S. 1965. The feeding of herring larvae and their ecology in relation to feeding. Calif. Coop. Oceanic Fish. Invest. Rep. 10:79-88. Blaxter, J. H. S., and G. Hempel. 1963. The influence of egg size on herring larvae (Clupea harengus L.). J. Cons. Cons. Int. Explor. Mer 28:211- 240. Crisp, D. J. 1962. The planktonic stages of the cirripedia Balanus balanoides (L.) and Balanus balanus (L.) from north temperate waters. Crustaceana 3:207-221. de Ciechomski, J. D., and G. Weiss. 1974. Estudios sobre la alimentacion de larvas de la mer- 839 FISHERY BULLETIN: VOL. 80. NO. 4 luzza, Mertuccius merluccius hubbsiy de la anchoita, En- graulis anchoita en el mar. Physis. Rev. Asoc. Argent. Cienc. Nat. 33:199-208. 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Early life history of the sea raven, Hemitripterus villosus, (Hemitripterinae, Cottidae) in the Japan Sea. [In Jpn., Engl, abstr.] Bull. Jpn. Sea Reg. Fish. Res. Lab. 27:1-10. SCHOENER, T. W. 1970. Nonsynchronous spatial overlap of lizards in patchy habitats. Ecology 51:408-418. Sherman, K., and K. A. Honey. 1971. Seasonal variations in the food of larval herring in coastal waters of central Maine. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 160:121-124. Shirota, A. 1970. Studies on the mouth size of fish larvae. [In Jpn., Engl, abstr.] Bull. Jpn. Soc. Sci. Fish. 36:353-368. Sumida, B. Y., and H. G. Moser. 1980. Food and feeding of Pacific hake larvae, Merluc- cius produetus, off southern California and northern Baja California. Calif. Coop. Oceanic Fish. Invest. Rep. 21:161-166. Townsend, D. W. 1981. Comparative ecology and population dynamics of larval fishes and zooplankton in two hydrographically different areas on the Maine coast. Ph.D. Thesis, Univ. Maine, Orono, 282 p. Wallace, R. K., Jr. 1981. An assessment of diet-overlap indexes. Trans. Am. Fish. Soc. 110:72-76. Weatherly, A. H. 1972. Growth and ecology of fish populations. Acad. Press, N.Y., 293 p. Zaret, T. M., and A. S. Rand. 1971. Competition in tropical stream fishes: support for the competitive exclusion principle. Ecology 52:336- 342. 840 FOOD HABITS OF JUVENILE SALMON IN THE OREGON COASTAL ZONE, JUNE 1979 William T. Peterson,1 Richard D. Brodeur,2 and William G. Pearcy2 ABSTRACT Euphausiids, hyperiid amphipods, crab larvae, and fishes were the important prey identified from stomachs of 408 juvenile salmon collected in a purse seine along the Oregon coast in J une 1979. Food habits of juvenile salmon differed among species. About 95% of the weight and numbers of prey of chum salmon consisted of euphausiids and hyperiids. Euphausiids and hyperiids were numerically the most abundant prey items of juvenile coho and chinook salmon, but, on a weight basis, over half the stomach contents consisted of fishes. Variability in food habits was high for both juvenile coho and chinook salmon. Fishes from only 2 of 45 station pairs (coho) and 3 of 28 (chinook) had diet similarities >75%. The statistical relation- ship between weight of euphausiids and weight of fishes in stomachs for coho and chinook juveniles showed a strong tendency for both species to contain large amounts of either fishes or euphausiids, but not both simultaneously. Diet overlap between coho and chinook juveniles was high overall, but low between the same 20 mm size classes of these same species. Euphausiids were eaten in equal numbers throughout the 100-200 mm coho size range; euphausiids were not eaten by chinook <180 mm fork length. Hyperiids were mainly eaten by 180-220 mm coho and by 140-180 mm chinook. Fishes were con- sumed mainly by juveniles of both species >160 mm. Based on estimated zooplankton standing stocks, an average (160 mm) coho salmon would have to search and consume all prey in a minimum volume of about 2-8 m3 per day to fill its stomach. The average abundance of juvenile coho, as determined from purse seining, was 1 smoltper 11,500 m3,or about 1,440-5,760 times the minimum search volume. These data are related to the question of whether food limitation exists for juvenile salmonids in the sea. Our knowledge of the ecology of salmon in the ocean, especially during early juvenile life, is scant compared with our understanding of the freshwater phase of salmon life. The first few months that juvenile salmon spend at sea have been identified as a critical period when year- class success may be affected (Gunsolus 19783; Walters et al. 1978; Healey 1980). Basic studies of abundance and distribution, growth, mortality, and feeding habits of young salmon during their first few months at sea are needed to evaluate how the ocean environment and the density of juvenile salmon affect the production of adult salmon. This paper contributes new information on ■School of Oceanography, Oregon State University, Corval- lis, Oreg.; present address: Marine Sciences Research Center, State University of New York-Stony Brook, Stony Brook, NY 11794. 2School of Oceanography, Oregon State University, Corval- lis, OR 97331. 3Gunsolus, R. T. 1978. The status of Oregon coho and recommendations for managing the production, harvest, and escapement of wild and hatchery-reared stocks. Intern, rep., 59 p. Oregon Department of Fish and Wildlife, Clackamas Laboratory, 17330 S.E. Evelyn Street, Clackamas, OR 97015. Manuscript accepted April 1982. FISHERY BULLETIN: VOL. 80. NO. 4. 1982. feeding habits of juveniles of three species of salmon off the Oregon coast: coho, Oncorhynchus kisutch; chinook, O. tshawytscha; and chum, O. keta, salmon. The authors describe the food habits of each species, variability in food habits among fishes collected at different stations, diet overlap between coho and chinook, and speculate on the impact of foraging juvenile coho on zoo- plankton populations in coastal waters. METHODS Fish were collected in a purse seine 457 m long X 30 m deep, constructed of 32 mm stretch mesh with 30 meshes of 127 mm mesh along the bottom of the net. The maximum volume of water en- compassed by a round haul set that fished to 10 m depth was calculated to be no more than 1.5 X 105m3. A total of 56 purse seine sets were made between 18 and 29 June 1979 in three regions of the Oregon coastal zone: Off the Columbia River (northern Oregon), off Newport (central Ore- gon), and in the vicinity of Coos Bay (southern Oregon) (Fig. 1). A total of 509 salmonids <35 cm FL (fork length) (henceforth called juveniles) 841 FISHERY BULLETIN: VOL. 80, NO. 4 125 NEWPORT -FL 44-46 • • • 'SIUSLAW R. 44c 43c Figure 1.— Location of the 56 purse seine sets made by the FV Flamingo (FL), 18-29 June 1979. Three geographical regions were arbitrarily defined as northern (FL 1-24), central (FL 25-46), and southern (FL 47-56). were collected in the sets. Stomach contents of 220 juvenile coho, 147 juvenile chinook, and 41 juvenile chum salmon were examined. Whole fish <35 cm FL were preserved at sea, after slitting the body cavity, in a 5-15% Forma- lin4-seawater mixture. In the laboratory, all juvenile salmonids were identified to species, measured (fork length), and stomachs removed. Relative stomach fullness was visually estimated on a scale of 0-3 (where 0 = empty; 1, 2, and 3 = fullness in thirds; distended stomachs = 3). State of digestion was noted as one of three subjective categories: Well-digested, partially digested, or fresh. Due to the possibility of differential diges- tion times of prey items, categorization of state of digestion probably has little meaning except for the "fresh" category. Food items were identified to the lowest pos- sible taxonomic level and enumerated. Crusta- ceans and fishes were also identified to develop- mental stage. Standard length of all fish prey was measured as well as total length of most of the invertebrate taxa from the coho salmon stom- achs. Euphausiid lengths were measured from the posterior edge of the eye socket to the tip of the telson. Stomach contents of all salmonids were sorted into major taxonomic groups, damp- dried on absorbent paper, and weighed to the nearest 0.01 g. RESULTS Occurrence and Abundances of Prey Taxa Table 1 lists the average abundances of major taxa of prey in salmonid stomachs and the aver- age length and length ranges of fishes examined. Euphausiids, amphipods, and crab larvae were the most numerous taxa in the stomachs of juve- niles of all three species. Fishes were the only other major taxa found in all juvenile salmon. Numbers of fish per stomach were low. On a weight basis, fishes were the most important prey for juvenile coho and chinook, followed by eu- phausiids (Table 2). Chum stomachs contained mostly euphausiids and amphipods. Based on percent frequency of occurrence of prey in stomachs, euphausiids occurred in 85% of all chum stomachs, 63% of coho stomachs, and about 50% of chinook and steelhead stomachs (Table 2). Amphipods also ranged in frequency of occurrence from 56 to 32% among these same species. The occurrence of fishes, on the other hand, ranged from 10% of the chum stomachs to 69 and 71% in coho and chinook stomachs, respec- tively. 4Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 842 PETERSON ET AL.: FOOD HABITS OF JUVENILE SALMON Table 1.— Average number of prey in individual stomachs of juvenile chum, coho, and chinook salmon. A more detailed tax- onomic breakdown is given in Table 3. Prey category Chum Coho Chinook Euphausiids 44.4 36.9 71.9 Amphipods 30.8 28.0 22.9 Fishes 1.2 4.0 4.2 Crab larvae 2.0 13.5 99 Copepods 1.6 6.5 3.2 Molluscs — 10.6 1.7 Barnacle cyprids — 4.5 — Shrimp larvae — 3.0 1.3 Number of stomachs 41 220 146 Number of empty stomachs 5 22 14 Average length of salmonid (mm) 124 164 208 Range In length (mm) 102-144 94-134 89-308 Table 2.— Average wet weight (in grams) of major prey groups found in juvenile chum, coho, and chinook salmon stom- achs. Numbers in parentheses are percentages of salmon stom- achs containing the specific prey item. Average weight of stomach contents is for fish with food in their stomachs. Weights of salmon are wet weights calculated from mean lengths using the length-weight equations of Healey (1980). Ch urn Coh 0 Chin ook Prey category Wt. % Wt. % Wt. % Euphausiids 0.22 (85) 0.35 (63) 0.63 (51) Amphipods 0.04 (56) 0.20 (43) 0.12 (31) Fishes 0.07 (10) 0.73 (69) 1.04 (71) All others 0 04 (7) 0.12 (88) 0.46 (70) Average weight of stomach contents (g) 0.28 0.93 1.30 Average weight of salmon (g) 23.5 55.3 140.7 Stomach contents as % body weight 1.2 1.7 0.9 Total weight of stomach contents of each of the three species of juvenile salmon reflects the size of the fishes sampled (Table 2). Weights of stom- ach contents expressed as percent of total body weight are similar, however, averaging about 1.3%. Frequencies of occurrence and average abun- dances of specific prey taxa for each of the three juvenile salmon are shown in Table 3 and are re- ferred to in the following discussion of the diets for each of the species. Chum Salmon The diet of chum salmon consisted mainly of the euphausiid Thysano'essa spinifera and the hyperiid amphipod Hyperoche medusarum. Mean numerical abundances of T. spinifera per chum stomach collected from northern, central, and southern Oregon were 30.1, 149.7, and 3.7, respectively; abundances of hyperiids were 2.9, 104.8, and 17.5, respectively. Both these prey were most common in chum salmon stomachs collected off central Oregon, but sample sizes were so small that it is difficult to attach any real significance to these differences. Coho Salmon A total of 19 invertebrate and 13 fish taxa were identified from coho stomachs (Table 3). Major prey items were juvenile euphausiids (T. spini- fera, average length about 9.0 mm), unidentified hyperiid amphipods (average length about 4.5 mm), and various fishes (most between 25 and 30 mm long). The most frequently occurring fish identified from the juvenile coho stomachs were Pacific sand lance, Ammodytes hexapterus; juve- nile rockfishes, Sebastes spp.; and larval or juve- nile stages of several species of flatfishes, clupe- ids, and osmerids. Average length of the prey euphausiid, T. spinifera, was directly related to length of the juvenile coho predator. The slope of the regres- sion line (Fig. 2) was significantly different from zero (r = 0.46, 28 df, P-0.01), indicating that coho between 100 and 210 mm long eat progres- sively larger euphausiids. Juvenile coho fed on a broad spectrum of fish prey sizes, but, again, larger fish often consumed larger prey. Coho 141-180 mm long fed mainly on fish that were 11-30 mm long, whereas 181-200 mm coho con- sumed mostly larger fishes, ranging from 21 to 40 mm long (Table 4). However, the regression of lengths of whole prey fishes on lengths of juvenile coho, 94-220 mm, was not significantly different from zero. Relationships between size of coho and num- bers and sizes of prey were studied for 87 juve- 100 1 50 200 COHO LENGTH (mm) Figure 2.— The relationship between coho length and mean euphausiid prey length. 843 FISHERY BULLETIN: VOL. 80, NO. 4 Table 3.— Frequency of occurrence (f/n %) and average abundance {x) of prey found in stomachs of juvenile chum, coho, and chinook salmon. Ch urn Coho Chinook Prey taxa f/n % X f/n % X f/n % X Euphausiids Thysanoessa spimlera (9 mm) 83 44.1 56 2.0 53 80.9 T. spinifera (22 mm) 2 2.0 15 22 5 19 Euphausia pacifica (18 mm) 2 1.0 8 2.0 3 14.5 Unidentified 10 12.7 5 4.3 Amphipods Parathemisto pacifica 15 1.2 8 1.6 Hyperoche medusarum 34 46.7 20 42.2 Pnmno macropa 2 1.0 Unidentified Hyperndae 15 7 8 44 30.1 19 35.7 Gammandae (Atylus tndens) 11 5.0 12 2.1 Fishes Ammodytidae Ammodytes hexapterus 10 1.2 30 24 32 2.0 Pleuronectiformes Isopsetta isolepis 1 1.0 Cithahchthys spp. 1 1.3 Psettichthys melanostictus 1 1.0 Unidentified flatfish 8 1.8 32 78 Hexagrammidae 3 1.6 Gadidae 1 1.3 2 1.3 Cottidae 11 1.8 Hemilepidotus spp. 3 4.8 Unidentified 3 1.6 Clupeidae 6 3.1 3 2.2 Osmeridae 5 3.2 3 30 Scorpaenidae Sebastes spp. 15 3.5 8 1.4 Unidentified and Digested 10 2.5 45 3.1 48 1.7 Crab Larvae Cancer magister megalopae 16 4.2 9 1.8 Cancer spp. megalopae 16 0.6 Pinnotheridae zoeae 10 4.7 3 19.2 Pinnotheridae megalopae 12 16.2 Pagundae zoeae 3 2.0 Copepods Calanus cristatus 6 8.1 1 12.0 C. marshallae 4 2.0 Eucalanus bungii 4 1.0 Epilabidocera longipedata 1 1.0 Unidentified 12 1.6 3 1.0 Molluscs Limacina helicina 7 106 2 1.7 Cephalopods 1 10 Miscellaneous Arthropods Juvenile Crabs 4 14.0 Decapod shrimp mysis 2 2.0 6 2.5 6 1.0 Pandalus jordani zoeae 4 10 3 1.3 Barnacle cyprids 2 1.0 7 4.4 Mysids 3 1.2 2 1.3 Insects 2 1.0 2 1.2 1 1.0 Chaetognatha Sagitta elegans 2 5.0 1 1.0 Polychaetes Tomoptens sp. 1 6.5 Table 4. — Frequency distribution of lengths of fish prey found in stomachs of juvenile coho salmon of various length IS. Standard Number length nf Length of fish prey (mm) of coho (mm) coho 0-10 11-20 21-30 31-40 41-50 51-60 >60 81-100 1 1 1 101-120 3 3 1 121-140 36 3 7 10 1 4 141-160 66 27 35 4 4 1 1 161-180 70 8 69 80 28 21 2 181-200 30 5 25 23 3 4 201-220 7 7 1 1 nile coho with stomachs full of fresh material to minimize the problem of differential digestion rates of various prey items. No statistically sig- nificant differences (PX).05) were found be- tween length of coho and either number of euphausiids, total number of prey items, or num- 844 PETERSON ET AL.: FOOD HABITS OF JUVENILE SALMON bers of fishes. Significantly greater numbers of hyperiid amphipods occurred, however, in larger than in smaller coho (Fig. 3). Average weight of fishes in stomachs also increased with length of juvenile coho. Total weight of stomach contents was related to length of juvenile coho (weight of prey = —1.0 + 0.016 X length of coho, r = 0.43, P<0.01). The relationship between the two food groups most important to juvenile coho was investigated by plotting weights of euphau- siids versus weights of fishes in the stomachs for each of the 87 coho. This plot was divided into quadrants by drawing lines parallel to the abscissa and ordinate at the median values of euphausiid and fish weight. The numbers of data points in each quadrant are shown in a 2 X 2 con- tingency table (Table 5). The x2 of 12.5 was highly significant (P<0.01, 1 df), indicating a strong tendency for juvenile coho to contain large amounts by weight of either fishes or euphausi- ids, but not both at the same time. Of these 87 coho, 26% contained only fishes and 21% only euphausiids. This trend may be a result of active selection of one type of prey or a result of prey Table 5.— Contingency table comparing weight of fish and euphausiid prey found in the stomachs of 87 juvenile coho salmon. Euphausiid prey (g) <0.24 -0.24 Fish prey (g) >0.48 <0.48 31 13 13 30 patchiness. The latter explanation may be more plausible, since stratification of these two prey groups in the stomachs was evident in those indi- viduals containing both prey items. Variability in the composition of stomach con- tents of coho salmon was often high among the 10 stations where at least six fish were analyzed per station (Table 6). For example, juvenile euphausi- ids were the most numerically abundant prey taxa at four stations (2, 3, 12, and 29); hyperiid amphipods at four other stations (10, 27, 28, and 39); and fishes and crab larvae at one station each. The differences in feeding habits among stations were compared by calculating similarity indices for all possible station pairs. We used the percent similarity index (PSI = 1 min P{), where ioo JUVENILE EUPHAUSIIDS HYPERIIDS "I i '""I i 1 r IOO 140 180 220 260 300 FISHES -f™p^l | H I I I ! IOO 140 180 220 260 300 i r 220 260 300 SIZE CLASS OF SALMONID (mm) FIGURE 3.— Average abundance of juvenile euphausiids and hyperiids and average weight of fish prey occurring in the stomachs of each 20 mm size class of juvenile coho and chinook salmon. The averages are taken over only those stomachs in which prey items occurred. The numbers at the top of the leftmost figure denote the sample size in each 20 mm size class. 845 FISHERY BULLETIN: VOL. 80, NO. 4 Table 6.— Sampling data and percent of total numbers of major prey items found in juvenile coho stomachs off the Oregon coast (only at those stations where six or more juvenile coho were taken). Includes only those prey taxa comprising 2% or more of the total number of prey items. Northern Oregon Central Oregon Station 1 2 3 10 12 22 27 28 29 39 Time of day 0630 0900 1000 1730 0800 1500 0930 1130 1300 0900 Day in June 18 18 18 19 20 21 23 23 23 27 Water depth (m) 40 77 102 66 77 130 55 77 73 55 Distance from shore (km) 11.8 19.4 25.9 13.3 19.1 33.3 10.0 16.3 27.0 9.4 Number of coho examined 33 14 16 32 37 30 8 6 11 8 Average length of coho (mm) 158 175 158 154 158 163 165 161 157 193 Percent of coho with empty or nearly empty stomachs 58 79 69 25 8 20 12 33 0 0 Thysanoessa spinilera (juveniles) 8.9 68.3 41.4 6.3 93.4 12.1 9.8 2.6 53.5 3.4 Hyperiid amphipods 20.1 22.5 26.9 36.0 13.0 39.7 89.9 30.7 94.0 Fishes 42.0 29 8.4 10.7 6.0 84 29.3 Crab megalops 16.5 26.1 Crab zoea 4.0 24.0 Pteropods 9.2 Calanus cristalus 6.5 4.9 Cancer magister megalops 4.9 17.0 4.9 Gammand amphipods 6.2 7.7 T. spinilera (adult) 16.6 2.1 Barnacle cyprids 3.1 93 22 Euphausia pacifica 9.5 3.1 Total number of prey items 169 378 227 364 2,516 1,135 174 306 1,745 1,326 Pi is the proportion of the ith taxa (based on num- bers of individual prey) in a stomach (Whittaker 1960), and PSI between a pair of stations is calcu- lated by summing the smaller (minimum) P/s for all food items. Similarity was generally low (<50%) among stations. Only 6 of the 45 possible pairings showed similarities >66% (stations 2-3, 2-12, 2-29, 3-29, 10-27, and 28-39), and only two pairs had a similarity >75% (2-29 and 28-39). Some of this variability among stations may be related to the geographical regions sampled. For example, the numerical percentage of euphausi- ids averaged 45.5% for coho caught near the Columbia River plume (stations 1-22) compared with 17.4% off the central Oregon coast (stations 27-39, Table 6). Fishes occurred in the diets at all stations and made up 14% of the total prey num- bers in the Columbia River area, whereas they were a significant part of coho diets at only one of four stations off Newport. Amphipods occurred more frequently in the stomach contents off Newport, averaging 63.6% of the total number, compared with 20.1% in coho from the Columbia River plume. The copepod, Calanus cristatus, and pteropod, Limacina helicina, were impor- tant components of the diets of only those juvenile coho caught off the central Oregon coast. An additional component of among-station variabil- ity may be attributed to differences in diet be- tween inshore and offshore stations. Coho taken within 12 km of shore contained a greater pro- portion of fishes at two of three stations, while those captured offshore contained more euphau- siids. Chinook Salmon Thirty taxa were identified from the stomachs of juvenile chinook. Major prey items were juve- nile euphausiids (T. spinifera), hyperiid amphi- pods (mostly Hyperoche medusarum), pinnother- id crab larvae, and various fishes (Table 3). The most frequently identified fishes were flatfish and Pacific sand lance larvae, both occurring in 31% of the stomachs. Juvenile scorpaenids were third, occurring in only 7% of the stomachs. Chinook salmon with stomachs full of fresh food {n = 42) were studied to test the hypothesis that weight of euphausiids and weight of fish prey in stomachs were independent, using the same procedure as with coho. The x2 from the contingency table (Table 7) was significant at the 0.07 level. Hence there is a tendency for chinook to eat either euphausiids or fishes, but this in- verse relationship is not as strong as for juvenile coho salmon. The weight of stomach contents in- creased with size of juvenile chinook salmon. The slope of the regression (weight of prey = —4.2 + 0.032 X length of chinook, over the range of 100- 200 mm) was significantly different from zero (r = 0.66, P<0.05). Table 7.— Contingency table comparing weight of fish and euphausiid prey found in the stomachs of 42 juvenile chinook salmon. Euphausiid prey (g) = 0.0 0 0 Fish prey (g) >0.67 <0.67 14 7 7 14 846 PETERSON ET AL.: FOOD HABITS OF JUVENILE SALMON Based on the percent by number, euphausiids and fishes were more important in the diet of chinook collected off the Columbia River than off the central Oregon coast (Table 8). As with coho, between-station variability was high. Only three station pairs had high similarities in diet (PSI >90%: 11-12, 11-14, and 12-14) mainly due to the high proportions of T. spinifera consumed at these stations. salmonids of both species increased in length, they consumed larger fish, but coho between 140 and 330 mm consumed larger fish on the average than chinook of the same size. Juvenile chinook also consumed more pleuronectid larvae and fewer scorpaenids than coho. Chinook ate very few pteropods and no barnacle cyprids while these taxa occurred in about 10% of the coho stomachs (Table 3). Diet Overlap Similarity (PSI) was calculated as before to study diet overlap among species of juvenile salmon at four stations where at least eight indi- viduals of two or more salmon species occurred. Diets were similar (PSI >66%) at three of these stations. At station 12, chum, coho, and chinook juveniles ate 94.7, 93.4, and 90.9% euphausiids, respectively, by number; at station 27, coho and chinook ate nearly equal proportions of hyperiids and fishes; and at station 39, coho and chinook ate 94.0 and 91.3% hyperiids, respectively. Diets were dissimilar at station 1. This dietary overlap among cooccurring spe- cies of juvenile salmonids suggests that a poten- tial exists for competition, should food be limit- ing. This potential was highest among different size classes of juvenile coho and chinook salmon but was reduced among similar-sized fishes (Fig. 3). Euphausiids were eaten most often by coho 100-200 mm long, but not by chinook <180 mm. The opposite pattern is seen with hyperiid am- phipods: Small chinook (<180 mm) ate more hyperiids than similar-sized coho. As juvenile DISCUSSION Fishes, euphausiids, hyperiid amphipods, and crab larvae were the most important prey for juvenile salmon off Oregon. Other published studies dealing with the diet of juvenile salmo- nids in the ocean show basically the same result, although there are notable differences. Manzer (1969) concluded that juvenile chum salmon from Chatham Sound, British Columbia, were planktivorous, feeding mostly on larvaceans (Oikopleura spp.) and unidentified copepods, and that coho were piscivorous, feeding mostly on Pacific herring and sand lance. Healey (1980) found that juvenile chum salmon from Saanich Inlet also fed predominantly on larvaceans and copepods, but individuals caught in more open waters of Georgia Strait ate euphausiids, amphi- pods, and fishes, as found off Oregon in this study. Juvenile coho studied by Healey contained 34% fishes (by volume) in Georgia Strait and 3% in Saanich Inlet, appreciably less than the 70% re- ported by Manzer in Chatham Sound. Healey concluded that chinook and coho from Georgia Strait had very similar food habits. Fresh et al. Table 8.— Sampling data and percent of total numbers of major prey items found in juvenile chinook stomachs off the Oregon coast (only at those stations where six or more individual chinook were taken). Includes only those prey taxa comprising at least 2% of the total number of prey items. Northern Oregon Central Oregon Station Time of day Day in June Water depth (m) Distance from shore (km) Number of chinook examined Average length of chinook (mm) Percent of chinook with empty or nearly empty stomachs Thysanoessa spinifera (juveniles) Hyperiid amphipods Fishes Crab megalops Pteropods Euphausia pacilica T. spinifera (adults) At y I us tridens Calanus cristatus Unidentified items Total number of prey items 1 8 11 12 14 18 0630 1415 1915 0800 1055 1000 18 19 19 20 20 21 40 38 68 77 71 73 11.8 11.1 17.2 19.1 18.9 176 8 9 12 14 13 14 147 208 239 253 211 245 50 11 8 36 15 29 97.2 90.9 98.9 228 68.1 5.4 30.1 25.3 8.3 45.7 2.5 2 1 10.9 61.5 2.5 2.1 4.3 3.2 2.5 39 185 1,906 277 1,846 92 27 39 43 0930 0900 0410 23 27 28 55 55 57 10.0 9.4 9.3 19 11 6 183 164 178 47 27 17 46.4 37.8 91.3 23.7 19.9 13.4 7.9 7.5 31.6 12.4 291 987 97 847 FISHERY BULLETIN: VOL. 80, NO. 4 (1981) reported that juvenile chum from near- shore pelagic habitats of Puget Sound fed on euphausiids, crab larvae, and gammarid amphi- pods on a weight basis; coho fed largely on larvae of decapod crustaceans; and chinook fed on eu- phausiids. The qualitative range in variability of diet present during our 2-wk sampling period was similar to that found by the above authors from various months, years, and geographical loca- tions. At some times and locations, euphausiids were dominant prey; at others, amphipods and fishes. This variability suggests that juvenile salmon are opportunistic, feeding on abundant prey available at a particular time and place. The main prey items of our juvenile salmon comprise three general size groups: 1) Fishes having an average length of 29 mm, 2) euphausi- ids and Cancer magister megalopae, ranging in length from 7 to 10 mm, and 3) hyperiid amphi- pods between 4 and 6 mm.The fact that juvenile salmonids ate large numbers of euphausiids agrees with what is known about the abundances of various-sized planktonic prey sampled in coastal waters of Oregon during period years (Table 9). Over the range of 7-10 mm, euphausi- ids were the most abundant prey item. Shrimp larvae and C. magister megalopae were abun- dant only during limited periods, usually only June. The predominant euphausiid eaten was T. spinifera, a neritic species. Euphausia pacifica, although a more abundant species of euphausiid in the North Pacific, is more oceanic and is not Table 9.— Abundance of salmonid prey aver- aged from plankton samples collected during June and July at stations located 1, 3, 5, and 10 mi off Newport, Oreg. Zooplankton are aver- aged over the years 1969-72 (Peterson and Miller 1976); crab larvae over the years 1969-71 (Lough 1975, 1976); and larval fish from 1971 only (Richardson and Pearcy 1977). Plankton tows are step-oblique through the entire water col- umn, during daytime, using a 0.2 m diameter bongo net (0.24 mm mesh) for zooplankton and a 0.7 m bongo net (0.5 mm mesh) for fish larvae. Prey taxa Average no./m3 Pinnotheridae megalopae 0.1-1 Cancer magister megalopae 1-8 Pagurus megalopae 10-20 Calanus cristatus 2.3 C. marshallae (C5 + females) 50 Pteropods 14.3 Hyperiid amphipods 3.6 Decapod shrimp mysis 19.2 Chaetognaths 11.7 Thysanoessa spinifera 6.8 Larval fish 1-2 common in shallow shelf waters (Hebard 1966; Peterson and Miller 1976; Youngbluth 1976) and was found in low numbers in our salmonid stom- achs. Juvenile salmonids collected off Oregon fed predominantly on subadult individuals, possibly because adult euphausiids migrate into deeper waters during the day (Alton and Blackburn 1972) when salmon presumably feed. Subadult euphausiids are abundant in the upper 20 m of the water column during both day and night (Peterson5). The large numbers of hyperiid amphipods and the paucity of copepods in the diet of juvenile salmon were surprising. Hyperiids are neither abundant in Oregon coastal waters nor are they particularly large compared with other more common planktonic taxa (Table 9). The average length of the amphipods (4.5 mm) is not much greater than Calanus marshallae (stage 5 cope- podites and females, 3.0-4.0 mm TL (total length)). The ratio of amphipods to C5 C. mar- shallae abundance was 1:14 in plankton samples (Table 9) but 4 : 1 in the stomachs of juvenile coho. Frequency of occurrence in juvenile coho stom- achs was 44% for amphipods compared with only 6% for Calanus. Similarly, the copepod C. cris- tatus (8 mm TL), with an average abundance about the same as hyperiids, was seldom eaten. Length alone may not be adequate for assessing size-selective predation in juvenile salmon. Okada and Taniguchi (1971) found that the upper size limit of prey may be determined by prey width. This may be relevant because hyperi- ids are generally much broader at their widest dimension than copepods of the same length. One hypothesis to explain the high selectivity of amphipods by juvenile coho salmon concerns their peculiar swimming behavior and pigmen- tation. In the laboratory, hyperiids caught in coastal waters were extremely active swimmers (Peterson6). Most species have a large, heavily pigmented (black) compound eye, which could increase their detection by a visual predator, as shown for freshwater fish (Zaret and Kerfoot 1975). Copepods, on the other hand, lack the visual contrast of amphipods and are less active swimmers, generally swimming upwards and 5W. T. Peterson, Marine Sciences Research Center, State University of New York-Stony Brook, Stony Brook, NY 11794, unpubl. data, 1977. 6W. T. Peterson, Marine Sciences Research Center, State University of New York-Stony Brook, Stony Brook, NY 11794, pers. obs. 1978. 848 PETERSON ET AL.: FOOD HABITS OF JUVENILE SALMON then sinking passively through a portion of the water column. Another explanation for the presence of large numbers of hyperiids in salmonid guts is that juvenile salmon may pick them from the surface of medusae. The predominant hyperiid con- sumed by chinook and chum salmon was Hyper- oche medusarum, a species known to live on the exumbrellar surface of medusae (Bowman et al. 1963; Harbison et al. 1977). The host may be easy for salmon to locate, particularly the large Chrys- aora fuscescens (bell diameter of several tens of centimeters), which were very numerous in our purse seine samples. Larval fishes were the other important prey item. Information on their distribution and abun- dance is limited to sampling done in 1971-72. Data given in Table 9 are from Richardson and Pearcy (1977) for larvae captured at stations within 2-28 km from shore. Abundances were 200-400 larvae/10 m2, or 1-2 larvae/m3, assuming they are all distributed only within the upper 20 m of the water column. To investigate the question of food limitation, estimates are needed of salmonid feeding rates, salmonid abundance, prey abundance, and prey population growth rates. Feeding and digestive rates can be inferred from field data, if there is pronounced diel periodicity in stomach fullness or state of digestion (Eggers 1977; Lane et al. 1979), but we have no evidence for this in our lim- ited study. Thus, whereas estimates of stomach fullness were obtained from this study, feeding rates were estimated from other studies. The average weight of food in full juvenile coho stom- achs ( 1 .5 g wet weight) is equivalent to about 2.6% of the 55 g body weight of an average juvenile coho (160 mm long) (from Healey 1980). Walters et al. (1978, fig. 6) showed that the maximum ration of juvenile sockeye salmon weighing 55 g is slightly <3% of body weight per day. On the other hand, Brett (1971) found that the maxi- mum daily intake of food was 7-8% of body weight for a 50 g sockeye salmon. Therefore, we assume that juvenile coho fill their stomachs between 1 and 3 times per day on the average. Averaged over the 2-wk period in June 1979, the average 160 mm juvenile coho contained 37 euphausiids, 28 amphipods, and 4 fish (Table 1). In order to locate this quantity of food, this salm- on would have had to search a minimum of ap- proximately 5.4 m3 of water for the euphausiids, 7.8 m3 for the amphipods, and at least 4.0 m3 for the larval fish. This assumes that all prey avail- able to plankton nets are also fully available to juvenile salmon, and that annual differences are minor. Considering the well-known problems of zooplankton sampling variability and the fact that samples from different years are being com- pared, the agreement on water volume searched by salmon to locate each prey item seems quite good. The maximum abundance of juvenile salmo- nids in any one purse seine was 123 fish, and the average number of fish in sets in which at least 5 fish were caught was 26. The mean abundance in these 16 sets was 17 fish/105m3. Juvenile coho abundances were about one-half as great, 8.7 fish/105m3, or 1 fish/11,500 m3. If a juvenile coho fills its gut once per day, it needs to eat all prey in about 4-8 m3 water/d. Thus, as a rough average, one individual would consume at least 4/1 1,500- 8/1 1,500 (or 0.03-0.07%) of the available prey per day. Should this individual coho fill its gut three times each day, it would consume up to 0.1-0.2% of the standing stock of prey per day. Coho and chinook combined would consume aboutO.2-0.4% of available prey per day. If growth rates of prey population equal or exceed these loss rates, predation by juvenile coho and chinook alone will not reduce standing stocks of prey. Unfortu- nately, estimates of these vital parameters are lacking. Walters et al. (1978) examined the effect of food limitation on juvenile salmon growth and survival using a computer simulation model. In- put variables included 1) zooplankton distribu- tion, abundance, and production rates; 2) ration, growth, and mortality of young salmon in rela- tion to body size; and 3) timing of arrival of smolts at sea and rate of migration along the coast in relation to zooplankton production cycles. They tentatively concluded that juvenile salmonids were not food-limited, but rather predator-limited. This conclusion rests on a cru- cial assumption of the availability of zooplankton prey, which may be in error. Their estimates of zooplankton production and mortality and fish consumption (their table 3, columns 5, 6, and 7) were calculated using estimates ofthebiomass of zooplankton within a 20-400 m water column, de- spite their assumption that salmon forage only in the upper 20 m of the water column. They as- sumed that zooplankton prey removed by salmon during the day will be replaced from deepwater zooplankton populations at night. Since the sur- face biomass is enhanced by diel vertical migra- tions mainly at night and juvenile salmonids are 849 FISHERY BULLETIN: VOL. 80, NO. 4 thought to be daylight or crepuscular feeders (see Bailey et al. 1975; Godin 1981 and references therein), they may never encounter this night- time increase in zooplankton abundance. The studies of Healey (1980) and Simenstad et al. (19807) both suggest that food availability may affect the abundance of juvenile salmon. They found that fewer salmon remained in Georgia Strait (British Columbia) and Hood Canal (Washington), respectively, when feeding conditions were poor. Obviously, the question of ocean limitation of salmon production cannot be resolved until much more is learned about the ecology of juvenile salmon and their competitors in the coastal zone. Substantially more informa- tion is needed on the abundance and availability of prey in near-surface waters, as well as on feed- ing, growth rates, and migration patterns of juvenile salmon. ACKNOWLEDGMENTS This research was made possible by funding provided by the Oregon Department of Fish and Wildlife (ODFW), Pacific Marine Fisheries Commission, Oregon State Sea Grant College Program, Oregon Aqua-Foods Inc., Crown Zel- lerbach Inc., and Anadromous Inc. We are in- debted to the Northwest and Alaska Fishery Cen- ter of the National Marine Fisheries Service for the loan of the purse seine. James Lichatowich, Thomas Nickelson, and Jay Nicholas (ODFW), Charles Simenstad (University of Washington), and two anonymous reviewers made helpful comments on the manuscript. LITERATURE CITED Alton, M. S., and C. J. Blackburn. 1972. Diel changes in the vertical distribution of the euphausiids, Thysanoessa spinifera Holmes and Eu- phausia pacifica Hansen, in coastal waters of Washing- ton. Calif. Fish Game 58:179-190. Bailey, J. E., B. L. Wing, and C. R. Mattson. 1975. Zooplankton abundance and feeding habits of pink salmon, Oncorhynchus gorbuscha, and chum salmon, Oncorhynchus keta, in Traitors Cove, Alaska, with specu- lations on the carrying capacity of the area. Fish. Bull., U.S. 73:346-861. 7Simenstad, C. A., W. J. Kinney, S. S. Parker, E. 0. Salo.J. R. Cordell, and H. Buechner. 1980. Prey community structure and trophic ecology of outmigrating juvenile chum and pink salmon in Hood Canal, Washington. Final rep. (1977-79) No. FRI-UW-8026, 113 p. University of Washington, Fisheries Research Institute, Seattle, WA 98195. Bowman, T. E., C. D. Meyers, and S. D. Hicks. 1963. Notes on associations between hyperiid amphipods and medusae in Chesapeake and Narrangansett Bays and the Niantic River. Chesapeake Sci. 5:141-146. Brett, J. R. 1971. Satiation time, appetite, and maximum food in- take of sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Board Can. 28:409-415. Eggers, D. M. 1977. Factors in interpreting data obtained by diel sam- pling of fish stomachs. J. Fish. Res. Board Can. 34:290- 294. Fresh, K. L., R. D. Cardwell, and R. R. Koons. 1981. Food habits of Pacific salmon, baitfish, and their potential competitors and predators in the marine waters of Washington, August 1978 to September 1979. Wash. Dep. Fish. Prog. Rep. 145, 58 p. Godin, J.-G. J. 1981. Daily patterns of feeding behavior, daily rations, and diets of juvenile pink salmon (Oncorhynchus gor- buscha) in two marine bays of British Columbia. Can. J. Fish. Aquat. Sci. 38:10-15. Harbison, G. R., D. C. Biggs, and L. P. Madin. 1977. The associations of Amphipoda Hyperiidea with gelatinous zooplankton.— II. Associations with Cnidaria, Ctenophora, and Radiolaria. Deep-Sea Res. 24:465- 488. Healey, M. C. 1980. The ecology of juvenile salmon in Georgia Strait, British Columbia. In W. J. McNeil and D. C. Hims- worth (editors), Salmonid ecosystems of the North Pacific, p. 203-229. Oreg. State Univ. Press, Corval- lis. Hebard, J. F. 1966. Distribution of Euphausiacea and Copepoda off Oregon in relation to oceanographic conditions. Ph.D. Thesis, Oregon State Univ., Corvallis, 85 p. Lane, E. D., M. C. S. Kingsley, and D. E. Thornton. 1979. Daily feeding and food conversion efficiency of the diamond turbot: an analysis based on field data. Trans. Am. Fish Soc. 108:530-535. Lough, R. G. 1975. Dynamics of crab larvae (Anomura, Brachyura) off the central Oregon coast, 1969-1971. Ph.D. Thesis, Oregon State Univ., Corvallis, 229 p. 1976. Larval dynamics of the Dungeness crab, Cancer magister, off the central Oregon coast, 1970-71. Fish. Bull., U.S. 74:353-376. Manzer, J. I. 1969. Stomach contents of juvenile Pacific salmon in Chatham Sound and adjacent waters. J. Fish. Res. Board Can. 26:2219-2223. Okada, S., and A. Taniguchi. 1971. Size relationship between salmon juveniles in shore waters and their prey animals. Bull. Fac. Fish., Hokkaido Univ. 22:30-36. Peterson, W., and C. Miller. 1976. Zooplankton along the continental shelf off New- port, Oregon, 1969-1972: distribution, abundance, sea- sonal cycle and year-to-year variations. Oreg. State Univ. Sea Grant College Prog. Publ. ORESU-T- 76-002, 111 p. Richardson, S. L., and W. G. Pearcy. 1977. Coastal and oceanic fish larvae in an area of up- welling off Yaquina Bay, Oregon. Fish. Bull., U.S. 75: 125-145. 850 PETERSON ET AL.: FOOD HABITS OF JUVENILE SALMON Walters, C. J., R. Hilborn, R. M. Peterman, and M. J. Youngbluth, M. Stalky. 197b\ Vertical distribution and die! migration 0f eu- 1978. Model for examining early ocean limitation of Pa- phausiids in the central region of theCaliforniaCurrent. cific salmon production. J. Fish. Res. Board Can. 35: Fish. Bull., U.S. 74:925-9:'>(i. 1303-1315. Zaret, T. M., and W. C. Kerfoot. WHITTAKER, R. H. 1975. Fish predation on Bosmina longirostris: Body-size 19(>o. Vegetation of the Siskiyou Mountains, Oregon and selection versus visibility selection. Ecology 56:232- California. Ecol. Monogr. 30:279-338. 237. 851 SPAWNING AND LARVAL DEVELOPMENT OF THE HOGFISH, LACHNOLAIMUS MAXIMUS (PISCES: LABRIDAE) Patrick L. Colin1 ABSTRACT Spawning of the hogfish, Lachnolaimus maxim/us, along a reef-sand interface near the insular shelf edge off southwestern Puerto Rico was observed over a period of 20 months by scuba diving. Eggs were collected and returned to the laboratory for hatching. Male-female ratio was about 1:10. Males patrolled elongate territories, which did not change during the 20 months, during the afternoon. Males initiated spawning by a courtship display using the prolonged dorsal fin spines and other fins. If the female responded, an elaborate process, termed the spawning rush, occurred during which the gametes were released. A male spawned with one female at a time, but often spawned with several females during an afternoon. Peak spawning was from December to April. There was no evidence that spawning was influenced by current speed or direction or by lunar or tidal periodicity. Eggs were planktonic, about 1.2 mm in diameter, lacked visible pigment, and hatched in 23 hours at 25.5°C. They were preyed on extensively by yellowtail snappers, Ocyurus chrysurus. Larvae, which survived in the laboratory up to 50 days, lacked a distinct transformation to juveniles but gradually acquired pigment and juvenile form after 13 days. Free-swimming postlarvae formed mucous bubbles at night. The hogfish, Lachnolaimus maximus (Wal- baum), is the largest tropical western Atlantic labrid, reaching about 11 kg (Randall and Warmke 1967); adults are conspicuous members of many reef communities. A highly prized food- fish, it is taken incidentally with other fishes, particularly by spear or hook and line. It is a protogynous hermaphrodite, but there are no primary males. Color patterns are distinc- tive between sexes. Males, which are more highly pigmented, have a dark reddish brown mask on the head. Also of the same hue are the base and first soft rays of the dorsal fin, the base of the rays in the lunate caudal fin, the pelvic fins, and the leading edge of the anal fin. The color of these darkened areas varies in intensity, depending on the nervous state of the male. The pectoral fins are yellow and there is an elongate spot on each side of the body. Females lack the reddish brown darkening, but possess a black spot about the size of the eye at the posterior base of the dorsal fin. The first three dorsal fin spines are greatly prolonged in males, much more than in females. Males also have filaments on the anal fin, soft dorsal fin, and margins of the caudal fin. The snout is longer in males and has a concave profile. 'Mid-Pacific Research Laboratory, c/o Hawaii Institute of Marine Biology, P.O. Box 1346, Kaneohe, HI 96744. Although various aspects of its biology, such as food habits (Reid 1954; Randall and Warmke 1967; Davis 1976) and growth (Davis 1976), have been well documented, little has been published on spawning or early life history. While scuba diving on a shelf-edge coral reef off southwestern Puerto Rico to study reef fish spawning, I en- countered a large spawning population of hog- fish. I was able to observe the courtship display and spawning rush over a 20-mo period from De- cember 1977 to July 1979. I also was able to col- lect large numbers of fertilized eggs, which were returned to the laboratory and hatched. A large number of larvae were kept alive up to 30 d, while smaller numbers were maintained to 50 d. I was able, therefore, to describe and illustrate in some detail the development of larvae from hatching through the juvenile stage. METHODS Observations of Courtship and Spawning The site was visited 154 d during the 20 mo. From December through March, when spawn- ing was high, visits were daily, if possible, but during the summer, visits were usually weekly. Males and females were observed both at close range and also from the maximum distances pos- sible. The presence of observers had less effect on Manuscript accepted February 1982. FISHERY BULLETIN: VOL. 80, NO. 4. 1982. 853 FISHERY BULLETIN: VOL. 80. NO. 4 the behavior of males than females, but no dis- turbance was noted if the observer moved no closer than about 4-8 m. Only during early phases of the spawning rush would rapid move- ments by a diver cause the female to abort the spawning rush. Once the spawning rush had reached an advanced point, however, the obser- ver could approach quickly without interrupt- ing. Fish frequently observed seemed to become accustomed to the observers. Motion pictures (16 mm) were made of differ- ent aspects of spawning behavior. These were analyzed frame-by-frame to determine the dura- tion of each act and the orientation of the fish during the rapid spawning rush. Collection and Rearing of Eggs Eggs were collected with fine mesh dip nets (sold as "brine shrimp nets") 10 by 15 cm with mesh openings of about 100 ju in diameter. After some practice, an observer could follow a pair on their spawning run and quickly locate the dif- fuse cloud of gametes when they were released. The cloud was either constantly observed or squirted with ink mixed with seawater from a plastic bottle to provide a reference mark. About 45 s to 1 min were needed to assure fertilization. After that time, eggs were collected by passing the net through the water where the eggs oc- curred. In one smooth motion, the net was then everted into a plastic bag and the bag was filled with water from the area where the gametes occurred, in hope of obtaining more sperm in the water and thereby increasing the chances of fer- tilization. Eggs collected before 45 s had elapsed generally were not fertile. Since the ability to see the cloud of gametes decreases with each second, the collection of planktonic eggs with a small hand net is a contest between the time required for fertilization and the ability of the collector to discern the location of the eggs. Although the ink helps to locate the eggs, it quickly disperses or tends to rise or sink because of the differences in density. I found it valuable to remain about 0.5- 1.0 m away from the cloud, once it had been located, and focus on sediment particles, opaque eggs, or larger zooplankton rather than trying to follow the rapidly dispersing cloud. If the bag is clear plastic, the eggs, once inside, can be seen easily. It helps to face the sun (underwater) and backlight the eggs by blocking out the sun di- rectly to the eyes with a hand behind the bag. The eggs in the bags were transported to the laboratory in buckets partially filled with sea- water, and were released into aerated closed- circuit 80 1 aquaria within about 90 min of being collected. Rearing methods followed Houde and Tanaguchi (1977). The aquarium was constantly illuminated by a twin 20-watt fluorescent lamp. A culture of Chlorella was introduced at hatch- ing. Later larvae were fed wild zooplankton col- lected with 53 n mesh nets. Temperatures were maintained at 25°-27°C. Selected eggs and larvae were preserved in 3% Formalin2. Larvae were illustrated from pre- served specimens by a camera lucida attachment on a dissecting microscope. The Study Site The study site was located on the insular shelf edge 16 km ESE of La Parguera, Puerto Rico (approximate position: lat. 17°54'N, long. 66°57'W). It is typical of most reefs off the south coast of Puerto Rico and the Virgin Islands (Mac- Intyre 1972; Adey et al. 1977). It is an elevated ridge about 100-150 m wide, paralleling the actual shelf break, and has a rocky substrate with abundant coral, particularly on the sea- ward and inshore flanks. Minimum depth is about 16 m. Near the study area the seaward por- tion slopes gently to about 18-19 m depth, then plunges downward at an angle of about 60° to oceanic depths. The inshore side slopes down- ward at about 10° until it meets a nearly level sandy-rubble plain. This slope, termed the "moat slope," is where most spawning activity by L. maximus was observed. Water temperatures varied between 24° and 27°C, visibility between 50 and 10 m. The area is within the trade wind belt of the Atlantic tropics and is consistently exposed to easterly winds of moderate force (Glynn 1973). Waves usually con- sisted of a small wind produced chop associated with larger swells. Wave heights of 1-2 m were common, but seldom exceeded 2 m. Complete calms would occasionally occur, most often dur- ing winter. These calms were associated with lee-shore conditions on the southwestern coast and occurred only a few percent of the time. Cur- rents were generally east to west, paralleling the shelf edge, but occasionally they were completely reversed or ran strongly off or onto the shelf. Clearest water occurred when strong southeast- -Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 854 COLIN: SPAWNING AND LARVAL DEVELOPMENT OF HOGFISH erly winds drove oceanic water up onto the shelf edge and also produced rough conditions. The most turbid water was either associated with calms, when the normal wind-driven flow from offshore was eliminated, or when large amounts of rain fell on Puerto Rico, particularly during the summer-fall wet season. OBSERVATIONS Spawning Groups of L. maximus Males established a territory along the moat- moat slope interface and defended it against the intrusion of other males. The territory was un- usual in being very elongate along the moat-moat slope axis, but not ranging far either over the sandy moat or up the moat slope. Males patrolled their territory during the afternoon, passing from one extreme of the sand-reef border to the other without changing direction except as inter- rupted by spawning rushes with females. Three territories that I closely examined each encom- passed about 100 m of the moat-moat slope inter- face. The turning points at either end remained consistent over the entire 20 mo. During active spawning periods, generally 2-3 min, were re- quired for one "pass" if no spawning occurred. An estimated 10-15 females occurred with each male during the afternoon. Although I found some evidence that females may remain with the same male during any one day, I could not de- termine if they changed males at other times. Time and Conditions of Spawning Active spawning was observed from Decem- ber through April, but I could not be sure if spawning also occurred in other months when low water visibility often made observations dif- ficult. Males, however, continued to patrol their territories during the afternoon and were occa- sionally seen to court females, but no spawning was seen. In any event, it is certain from direct observation that spawning during winter and spring must be at least an order of magnitude above any that may occur during summer and fall. Davis (1976) reported that peak spawning, based on gonad indices, of Florida Keys hogfish is probably in February and March, although some spawning may be occurring in other months. Gonad indices were consistently low from May through August. There is no evidence for lunar periodicity. Dur- ing peak spawning periods, spawning rushes occurred on all phases of the moon and spawning proceeded day after day with no apparent change over the lunar cycle. Spawning began in midafternoon, but the exact time of initiation was never observed. Hog- fish were spawning by 1.5 h before sunset and continued to spawn until 15-30 min before sun- set. Males began to patrol more slowly as sunset approached, and the frequency of spawning rushes decreased quickly. Females seemed to leave the spawning area, or at least were not visible, by about 15 min before sunset. Males con- tinued to patrol slowly until about sunset, then left the immediate area of the sand-reef inter- face. During the season of active spawning, current speed or direction, surge on the bottom, and water clarity seemed to have little effect on spawning behavior. Rushes were observed under nearly all conditions encountered. Water tem- peratures ranged between 24° and 26°C. Day length was short, being near the annual mini- mum of about 11 h near the start of peak spawn- ing in December and about 12.5 h by April. Spawning Behavior A female often indicated her readiness to spawn by moving up in the water column on approach of a male; otherwise, a male would actively court females encountered on his patrol. If a female was seen near the bottom, a male would swim quickly towards her, shifting from pectoral sculling to caudal fin swimming in a burst of speed, and then dive towards her exhibit- ing a courtship display. This consisted of erect- ing the three long anterior spines of the dorsal fin and shaking the posterior two of these rapidly back and forth at about 8-10 cycles/s. The pos- terior portion of the dorsal fin, the upper and lower caudal fin margins, and the pelvin fins were also agitated at a similar rate. Often the male would swoop above the female and dive rapidly towards her while displaying. If no re- sponse was elicited, the male would move quickly on to another female or resume patrolling. The spawning act was part of an elaborate process termed the spawning rush, which could be initiated by the male actively courting the female or by the female simply rising up in the water column as the male approached on his patrol. The rush required 10-25 s total time from the time the fish left the vicinity of the substrate. 855 FISHERY BULLETIN: VOL. 80. NO. 4 On the basis of hundreds of observations and the complete filming of 12 rushes, the spawning rush may be broken down into six distinct periods: 1) Pectoral swim up, 2) tail swim, 3) swim alongside and tilt, 4) release, 5) circle and display, and 6) swim down (Fig. 1). 1) Pectoral swim up— A male approaching from some distance a female which was up above the bottom would swim upward at an angle of 10°-20° towards the female, using concurrent sculling of the pectoral fins, usually of 2.0-2.5 beats/s. The dorsal and anal fins were folded against the body. As he approached the female, who rose slowly at a steeper angle to match his ascent, the male began to turn laterally and shifted to the second type of swimming. 2) Tail swim— The male folded the pectoral fins against his body and began undulating the caudal fin and posterior portion of his body at about 4 beats/s. Pelvic fins were usually about one-half extended. The female continued to rise slowly as the male approached her from behind. This stage lasted about 2-5 s. 3) Swim alongside and tilt— The male, using the tail only, continued swimming and came for- ward alongside the female, who was still moving forward. Their bodies were close together, the male slightly behind the female with his snout about even with her eye (Fig. 2). Once alongside, the male angled the dorsal portion of his body outward at about 15°-20° from the female. This took 0.5-1.5 s. During this phase, the male and female turned laterally 90°-180° in the direction of the female. 4) Release — At the end of the turn to initiate gamete release, the male started swimming for- ward more rapidly than the female. As he over- took her, he bent his body laterally towards her, then broke in the opposite direction. At this time the gametes of both sexes appeared to be re- leased. The cloud could usually be seen, but the exact moment of release was difficult to deter- mine. In some cases the male, when he turned toward the female, was sufficiently far forward to actually cross slightly into her path. The sharp break away from the female was accomplished by a sharp flick of the caudal fin. This also served Figure 1.— Idealized spawning sequence of Lacknolaimus maximum under conditions where the female meets the male in mid- water. The male (right) approaches and initiates the "pectoral swim up" action (1) followed by "tail swim" (2-3) when approaching the female. The lateral turn in "swim alongside and tilt" towards the female (4-5) is followed by the "release" of the gametes (6). "Circle and display" (7-8) precedes "swim down" (9). In this case the male is illustrated as returning in the direction opposite that when spawning was initiated, but this is not always the case. Often the male will continue patrolling in the same direction. 856 COLIN: SPAWNING AND LARVAL DEVELOPMENT OF HOGFISH FIGURE 2.— Photograph of spawning pair of Laehnolaimus maximus with the smaller female in front of the male. The fish are turning laterally in the "swim alongside and tilt" action just prior to release of the gametes. Photo by C. Arneson at the study site. to create a turbulent eddy where the gametes had been released to aid in their mixing. 5) Circle and display — When the male broke sharply away from the female, she also turned away, but not as sharply. Both started downward, the male doing a 180° lateral turn while descend- ing. When laterally exposed to the female he initiated a display similar to that used in court- ship. The three dorsal spines were erected, the last two shaken. The soft portion of the dorsal and anal fins, the upper and lower margins of the caudal fin, and the pelvic fins were agitated at a rate of 8-10 times/s. This display continued for 1- 3 s as the male approached the female and they continued down. 6) Swim down — The male separated from the female and swam downward at a steep angle. She did likewise. He may quickly approach another female and engage in courtship behavior or he may simply rise into the water column if another female is ready to spawn. Occasionally he will court the female he has just spawned with after they have returned to near the substrate, but I have never seen a female spawn two times in rapid succession. In many instances it was possible to observe the gamete cloud after it had been released. The movements of the fish, particularly the male, produce an area of turbulence where the gam- etes are thoroughly mixed. On occasion the actual sperm cloud was also faintly visible. With- in 15-20 s after release, the gametes will occupy a volume near 1 m3. There are usually several hun- dred or more eggs released per rush. In some instances no egg cloud could be found, even though the usual procedures for locating it were followed and the observer arrived within a few seconds to the region in which the eggs should have been. It is possible, but not yet proven, that eggs are simply not released on some rushes. Yellowtail snappers, Ocyurus chrysurus, were active predators on the eggs immediately after release. One to as many as ten yellowtail snap- pers would converge on the egg cloud 1-2 s after eggs had been released and would pick individual items, presumably eggs, from the water. This occurred in about 20-40% of rushes. Generally if yellowtail snappers observed a pair of L. maxi- mus rising to spawn, they would attempt to locate and eat the eggs. On occasion individuals 857 FISHERY BULLETIN: VOL. 80, NO. 4 would follow pairs of L. maximus so closely that the spawning rush would be interrupted, causing both the male and female to return to the sub- strate. Yellowtail snappers were much more abun- dant at the actual insular shelf edge than at the hogfish spawning area. At the shelf edge they formed loose aggregations of from several hun- dred to several thousand individuals feeding on zooplankton high above and beyond the shelf edge. Only a relatively few were found near the moat-moat slope interface, some 100 m away, but these few influenced the reproductive success of L. maximus. Gonad indices of both sexes vary considerably during the year (Davis 1976) in a pattern consis- tent with my observations. Gonad indices of males for each month ranged from about 0.14 to 0.20 (gonad weight as a percentage of body weight) for December to April and from 0.0 to slightly less than 0.10 for June to August. The in- dices were relatively low compared with those for other Caribbean labrids (Warner and Robertson 1978) but on a level with those of terminal males (both primary and secondary) of some other spe- cies. Lachnolaimus maximus is monandric (no primary males) (Davis 1976) and haremic, and the low gonad indices of males are consistent with the data for larger Caribbean labrids of Warner and Robertson (1978). Males are close to an order of magnitude heavier than other "large" Caribbean labrid males (Halichoeres radiatus and Bodianus rufus) and two orders of magni- tude above those of smaller species. Although the gonad indices are low compared with those of other species, the actual gonad is large. The rela- tive size between large and small labrids may not be very important. Males observed in the present study spawned repeatedly each afternoon during the active season. While data for an entire after- noon were not available, I estimated that at least some males engaged in 50-100 spawning rushes/ afternoon and that they were capable of fertiliz- ing each group of eggs released. The female-male ratio among adults also seems higher than in most other Caribbean lab- rids. Davis (1976) reported a ratio of 13:1 in the 724 individuals he sampled, which is close to the estimated 10:1 ratio that I observed. Warner and Robertson (1978), however, reported a ratio of only 3:1 or less for most species. The spawning location, about 100 m from the insular shelf edge rather than at the edge itself, appears contrary to some of the concepts put for- ward by Johannes (1978). It is true that many reef fishes producing planktonic eggs often move considerable distances to be able to release eggs at insular shelf edges where they may be trans- ported offshore. Hogfish, however, rarely move long distances to spawn. Adults can easily range to the shelf edge for spawning and some individ- uals probably remain along the shelf edge at night after spawning ceases. The potentially heavier egg predation by yellowtail snapper at the shelf edge may help restrict hogfish spawn- ing to more inshore areas. In addition, hogfish are typically found on the sandy margins of reefs where they feed largely on sand-dwelling mol- luscs (Randall and Warmke 1967) and the moat- moat slope interface area provides both reef shel- ter and open sand. Territories held by males may also represent feeding areas, whereas the actual shelf edge near the spawning area has little sand, and consists mostly of rock and coral. EGG AND LARVAL DEVELOPMENT Eggs are 1.2 mm in diameter and have a single oil globule 0.17 mm in diameter. They float and lack any visible pigment. They hatched 23 h after fertilization at 25.5°C. Larvae were reared at about 26°C but the tem- perature could not be closely controlled. When hatched, the larvae had little pigment. Scattered melanophores occurred in the head region and in a line on the dorsal margin of the body (Fig. 3a). They did not orient until about 24 h after hatch, but the eyes were still unpigmented at that stage (Fig. 3b). A line of melanophores along the ven- tral surface of the body began to develop at this time. Sometime between 24 and 36 h posthatch the eyes became pigmented. First food was added 31 h after hatch. Larvae seemed to be making feeding strikes by about 42 h posthatch (Fig. 3c). At this stage the amount of pigment along the ventral surface of the body increased and was plainly visible to the unaided eye. The black pigment increased daily until 7-8 d post- hatch and then remained stable. At 7 d posthatch feeding with Artemia salina was initiated. At this time pigment cells were visible on the tip of the lower jaw and on the lower margin of the gill cover. By 10 d posthatch the fin rays had begun to develop, the pelvic fin buds were apparent, and notochord flexion had occurred. Gas bladder inflation occurred 10 d posthatch (Fig. 3e) in 10-20% of the larvae. Larvae without the bladder inflated would swim with the tail 858 COLIN: SPAWNINO AND LARVAL DK.VKLOPMKNT OF HOOFISII 1mm Figure 3.— Larval stages of Lacknolaimus maximus. a, At hatch; b, 24 h posthatch; c, 42 h posthatch; d, 7d posthatch; e, 10 d posthatch. 859 FISHERY BULLETIN: VOL. 80, NO. 4 down at an angle of 20°-30° while those with the bladder inflated would swim with the tail slightly up. By 12-13 d the bladders of nearly all larvae had been inflated. At 13 d posthatch the first traces of the juvenile color pattern began to appear (Fig. 4a) with the development of three pigmented lobes on the base of the anal fin. Widely scattered brown chromatophores appeared on the body, but showed no discernible pattern. At this point the full complement of dorsal, anal, and caudal fin rays had been developed, but the pectoral rays did not seem fully developed. The pelvic fins con- sisted of only a slight bulge and the first three spines of the dorsal fin were elongated compared with those more posterior. At this stage the fish were considered to be postlarvae. At 17 d the body had a distinct brown and white color pattern (Fig. 4b) with the first three dorsal spines elongated. At this stage there was little difficulty identifying the postlarvae as L. maximus. The postlarvae did not orient to the bottom of the rearing tank, but remained free- swimming. The lights of the rearing tank were extinguished for the first time overnight at 17 d posthatch. Over one-half of the larvae formed 2 mm Figure 4.— Larval stages of Lachnolaimus maximus. a, 13 d posthatch; b, 17 d posthatch; c. 25 d posthatch. 860 COLIN: SPAWNING AND LARVAL DEVELOPMENT OF HOOFISH mucous bubbles around themselves that night while floating free in the water near the surface. None rested on the bottom. Such behavior is known in other labrids but had been previously unknown for L. maxim us or among free-floating individuals. Adults have been observed many times at night with no mucous bubble formation. Bubble formation has not been previously noted for "nonbenthic" labrids. The concept of bubble formation as an antipredator device is supported by its occurrence in postlarvae. Most larvae broke free of the bubbles within seconds after lights were turned on. At 17 d posthatch, postlarvae tended to stay under material floating on the surface of the water (mostly discarded clumps of mucous bub- bles and Artemia cysts). Several would stay under a single clump at the surface. No aggres- sive interactions were noted. Larvae were white and brown, the colors and pattern closely resem- bling that of Sargassum, which may serve as shelter for postlarvae carried into offshore waters. Ten 18-d posthatch postlarvae were put into an 80 1 aquarium with a white sand substrate. Some individuals rested on the bottom the first night, while others remained in the water column, all in mucous bubbles. By 34 d posthatch the fish ori- ented strongly to the bottom. Little is known of the early life history of juve- niles. Roessler (1964), who reported them from Thalassia beds, found some correlation in abun- dance with density of the bed. The larvae reared in the present study were maintained until about 50 d posthatch, but after about 30 d began dying without obvious cause. They were maintained either in bare aquaria or with a white sand bot- tom and were never exposed to a Thalassia com- munity. They were fed a combination of Artemia and wild zooplankton. In their natural environ- ment there may be a diet shift to microinverte- brates at an age when they began dying. Larvae did not undergo a quick metamorpho- sis but gradually began to acquire brown and white pigment of juveniles about 13 d posthatch. While still free-swimming the larvae and post- larvae became highly pigmented, which would seem to be a distinct disadvantage in open water. These pigmented young seemed to shelter be- neath any floating objects in the rearing aquar- ium, particularly the shards of their discarded mucous bubbles, which were brown in color. While there are no reports in the literature, their coloration would serve to conceal them in float- ing Sargassum and potentially other floating marine plants. Quick development and the lack of a distinct metamorphosis implies that perhaps the optimum survival strategy to the juvenile stage would be an inshore transport of eggs and larvae and retention of juveniles near the spawn- ing location. Unless associated with floating objects or plants, large L. maximus larvae would be at a distinct disadvantage in the pelagic realm. The life history of L. maximus implies that the postlarvae become benthic in an inshore location near sea grass beds and subsequently move to offshore reefs (Davis 1976). From the present study there seems no control of spawning condition which would produce an inshore dis- persal of eggs (currents, winds, tides, or wave action) and except for seasonal differences, it seems eggs are simply broadcast randomly with- out the influence of environmental conditions which would influence their ultimate destina- tion. ACKNOWLEDGMENTS Major equipment was provided by two grants (OCE 76-02352 and OCE78- 25770) from the Divi- sion of Ocean Sciences, National Science Foun- dation, to the author. Much of the operational support was provided by two grants from the Na- tional Geographic Society. Ileana Clavijo and Charles Arneson participated in most of the field work. Charles Arneson provided Figure 2. Two journal reviewers provided valuable criticism of the manuscript. LITERATURE CITED Adey, W. H., I. G. MacIntyre, and R. Stuckenrath. 1977. Relict barrier reef system off St. Croix: Its implica- tions with respect to late Cenozoic coral reef develop- ment in the western Atlantic. Proc. Third Int. Coral Reef Symp., Miami. 2:15-22. Davis, C. 1976. Biology of the hogfish in the Florida Keys. M.S. Thesis, Univ. Miami, Coral Gables, 86 p. Glynn, P. W. 1973. Ecology of a Caribbean coral reef. The Pontes reef- flat biotope: Part I. Meteorology and hydrography. Mar. Biol. (Berl.) 20:297-318. Houde, E. D., AND K. Tanaguchi. 1977. Methods used for rearing marine fish larvae at the Rosenstiel School of Marine and Atmospheric Sciences. Report to Environmental Protection Agency. Johannes, R. E. 1978. Reproductive strategies of coastal marine fishes in the tropics. Environ. Biol. Fishes 3:65-84. MacIntyre, I. G. 1972. Submerged reefs of eastern Caribbean. Bull. 861 FISHERY BULLETIN: VOL. 80, NO. 4 Am. Assoc. Pet. Geol. 56:720-738. Randall, J. E., and G. L. Warmke. 1967. The food habits of the hogfish (Lachnolaimus maxi- mus), a labrid fish from the western Atlantic. Caribb. J. Sci. 7:141-144. Reid, G. K., Jr. 1954. An ecological study of the Gulf of Mexico fishes, in the vicinity of Cedar Key. Florida. Bull. Mar. Sci. Gulf Caribb. 4:1-94. ROESSLER, M. 1964. A statistical analysis of the variability of fish popu- lations taken by otter trawling in Biscayne Bay, Florida. M.S. Thesis, Univ. Miami, Coral Gables, 126 p. Warner, R. R., and D. R. Robertson. 1978. Sexual patterns in thelabroid fishes of the western Caribbean, I: The wrasses (Labridae). Smithson. Con- trib. Zool. 254, 27 p. 862 BIOLOGY OF THE WHITEBONE PORGY, CALAMUS LEUCOSTEUS, IN THE SOUTH ATLANTIC BIGHT1 C. Wayne Waltz, William A. Roumillat, and Charles A. Wenner2 ABSTRACT Whitebone porgy, Calamus leucosteus, were taken in trawl surveys over reef and nonreef habitats in the South Atlantic Bight in depths of 11 to 88 m. Larger individuals were taken in greater depths. Twelve age groups can be identified with sectioned otoliths and nine using scales. Annulus formation for otoliths and scales occurs between June and July. Von Bertalanffy growth equations of Lt = 331 [l _el>™,.*2«39o1J from otoliths and Lf = 362 [l- e-02611«'t03973] from scales suggest that attainment of maximum size for this species is similar to reports for other reef species. The fork length-weight relationship for C. leucosteus can be described by W— 0.00004 FL2907. The whitebone porgy is a protogynous hermaphrodite: younger, smaller fish are predominately females, and older, large fish are mostly males. Sexual transition most commonly occurs between ages II-IV and fork lengths 18-25 cm. Peak spawning occurs in May with total fecundity ranging from 30,400 to 1,587,400 eggs. The fecundity-weight relationship can be described by F = 10.29438 WIJB62. Regional landings data are not available for C. leucosteus; however, it was the third and fourth most abundant species by weight from trawler landings in South Carolina during 1979 and 1980. The whitebone porgy, Calamus leucosteus, occurs from the Carolinas south to the Florida keys and throughout the Gulf of Mexico (Fischer 1978). Although more abundant and more frequently encountered in or near sponge-coral habitats at depths from 10 to 100 m (Fischer 1978; Powles and Barans 1980), individuals are sometimes taken from predominantly sandy bottoms (Wenner et al. 1979). This species is of commercial importance to trawl fishermen, but little information is available on its life history. The purpose of this paper is to present data on age, growth, reproductive biology, distribution, and relative abundance of C. leucosteus in the South Atlantic Bight. MATERIALS AND METHODS Distribution and relative abundance were determined from seasonal (fall 1973 to winter 1977) stratified random otter trawl surveys (Grosslein 1969) from Cape Fear, N.C., to Cape Canaveral, Fla. Sampling was conducted from the RV Dolphin with a 3/4 scale version of a Yankee No. 36 otter trawl (Wilk and Silverman 1976) towed for 0.5 h at 6.5 km/h. Most specimens (~98%) used for analysis of age, 'MARMAP Contribution No. 190 and Contribution No. 141 of the South Carolina Marine Resources Research Institute. 2South Carolina Wildlife and Marine Resources Depart- ment. P.O. Box 12559. Charleston. SC 29412. growth, and reproductive biology were collected with otter trawls (3/4 Yankee No. 36, 40/54 fly net, University of Rhode Island high rise trawl (Hillier 1974)) from 1975 to 1980. The remainder were caught with baited fish traps and hand- lines. Fish were weighed (nearest gram) and measured (nearest mm total length [TL], fork length [FL], and standard length [SL]). Sagittae and scales from beneath and/or just behind the posterior edge of the pectoral fin below the lat- eral line were removed and stored dry. Impres- sions of several scales from each fish were made on clear acetate sheets with a model C Carver Laboratory Press3 (1,547-1,687 kg/cm2, 65.5°C, 5-10 min). Readability was reduced in large oto- liths due to clouding of the central area and crowding of the rings along the outer margin; opaqueness also increased in all otoliths with storage time. These problems were corrected by preparing dorsal-ventral cross sections (~0.4 mm thick) on a plane perpendicular to the ante- rior-posterior axis through the center of the nu- cleus with a Buehler Isomet low speed saw. Aging structures were analyzed using trans- mitted light on a microprojector at 40X. Scale measurements were made on a line through the center of the scale from the focus to the outer edge, whereas otolith measurements were taken from the center of the nucleus to the outer Manuscript accepted February 1982. FISHERY BULLETIN: VOL. 80. NO. 4. 1982. 3Reference to trade names does not imply endorsement by the National Marine Fisheries Service. NOAA. 863 FISHERY BULLETIN: VOL. 80. NO. 4 margin along the ventral edge of the sulcus acousticus. Two independent readings were made on each. Most analyses were performed using the Sta- tistical Analysis System (Helwig and Council 1979). A FORTRAN program based on Poole (1961) gave back-calculated length at age. The von Bertalanffy growth equation (Bertalanffy 1938) was fitted to mean back-calculated fork length at age using parameters derived from Walford lines obtained by least square linear re- gressions (Everhart et al. 1975). All regression equations other than the regressions of radial measurement on fork length are the functional regressions of Ricker (1973, 1975). Sex and reproductive condition of most fish were determined by histological examination of the gonads, which were fixed in formal-alcohol solution (Humason 1972). Tissues were prepared for embedding by passage through an Autotech- nicon Duo Model 2A Automatic Tissue Proces- sor. Gonads were embedded in paraffin, sectioned at ~7/n with a rotary microtome, stained with Harris' hematoxylin and counter- stained with eosin Y. The first 200 slides were read by two individuals, then, following agreement on interpretation, the remaining sections were viewed by a single observer. Sex and maturity codes were formed by modifying Moe (1969) and Mercer (1978) and applying the four part index of Hilge (1977). The sex codes include hermaphrodite recognition and, when used with the maturity stages, give an accurate and objective estimate of reproductive status. Sexes were identified as undifferentiated, male, female, simultaneous hermaphrodites, male- predominating hermaphrodite, and female- predominating hermaphrodite. Maturity was classed as follows: Class Testicular state Ovarian state Immature little or no spermato- small, basophilic cyte development oocytes Ripening from gonads with a from relatively few primary and sec- acidophilic ondary spermatocytes oocytes through through those where large yolky oocytes lumen filled with spermatozoa Ripe predominance of predominance of (running) spermatozoa, little yolk filled oocytes, active spermato- few hydrated eggs genesis present Spent no spermatogenic nonspawned mature activity, some eggs becoming residual sperm atretic present in tubules Resting some mitotic predominately with regeneration of small basophilic spermatogonia oocytes, few traces of atretic activity Transi- resting testicular resting ovarian tissue tional tissue with with testicular ovarian tissue in tissue in active active develop- development. ment Terminology used in histological descriptions of gonadal development follows Hyder (1969) and Combs (1969). Fecundity estimates were obtained from developing ovaries which were weighed (nearest gram) and placed in Gilson's solution (Humason 1972). Following digestion of the connective tissue and external tunic, the eggs were washed and stored in 50% isopropyl alcohol. Eggs were diluted to 1 1, and three to four 1 ml subsamples were removed from a well-mixed suspension, placed in gridded petri dishes, and counted at 12X. The mean of the individual counts ex- panded to the 1 1 volume was used to estimate total fecundity. Histological examination re- vealed that eggs of diameter <0.15 mm were re- tained in spent ovaries without signs of atresia, while larger unshed oocytes atrophied. Eggs >0.15 mm were considered potential gametes for the impending spawn and were the only ones in- cluded in the fecundity estimates. RESULTS Distribution and Abundance Calamus leucosteus occurred in 94 of 575 stratified random otter trawl tows in depths <110 m during research survey cruises from 1973 to 1977. This species was taken in depths of 11 to 88 m from lat. 28 °50'N to 34°36'N (Fig. 1). Although whitebone porgies were caught over the sandy bottom of the open shelf habitat, they were more frequently taken in trawl tows that contained sponges and corals, indicative of iso- lated patch reefs. Calamus leucosteus was found in 58% of the 67 trawl tows containing live bottom organisms and 1 1% of the open shelf tows during the surveys from 1973 to 1977. During the spring of 1978, otter trawl sampling in shallow water (18-42 m) sponge-coral habitat from Florida to North Carolina collected C. leucosteus in 43 of 57 tows. Thus, C. leucosteus may be found in reef and nonreef habitats in the South Atlantic Bight. Seasonal catch/tow values indicated that C. leucosteus moved into warmer offshore waters 864 WALTZ ET AL.: BIOLOGY OF THE WHITEBONE PORGY 73* \ 7«« 34' 33° 75 32 30° 76 29 28 27 77° 28° 27° 79° 78° Figure 1.— Locations where whitebone porgy, Calamus leucosteus, were taken during stratified random trawl surveys from 1973 to 1977. 865 FISHERY BULLETIN: VOL. 80, NO. 4 during winter months, when inshore waters of the South Atlantic Bight have their annual minimum values (Table 1). They were absent in 55 trawl tows made during winter in the 9-18 m depth zone and showed variable frequencies of occurrence in other seasons in comparable depths. A trend for an increase in modal length with increasing trawl depth was apparent (Fig. 2). All specimens <24 cm FL were encountered in depths <56 m. Table 1.— Catch/tow values from whiteboneporgies, Calamus leueosteus, from stratified random research surveys from 1973 to 1977. >h = number of trawl tows which contained C. leueosteus: n = total trawls in depth zone. Depth zone (m) Season Catch/tow 9-18 19-27 28-55 56-110 Winter x catch/tow number 0 4.0 2.0 0 7 x catch/tow weight (kg) 0 1.23 1.07 0.43 n,ln 0/55 13/50 9/66 4/42 Spring x catch/tow number 0.3 1.4 0 3 1.3 x catch/tow weight (kg) 0 03 0.55 0.10 103 n,ln 2/22 5/20 4/28 4/18 Summer x catch/tow number 4.3 2.6 3.1 0.6 x catch/tow weight (kg) 1.12 1.02 1.65 0.43 n,/n 9/48 10/50 16/66 5/41 Fall x catch/tow number 2.7 2.6 0.8 0.6 x catch/tow weight (kg) 0.82 1.08 0.24 0.52 n,/n 4/18 4/18 3/19 2/14 30 20 IO 0 40 IO a U. 40 -| O ir 30 9-l8m x = 2l n = 252 i i i l9-27m 1=24 n= 406 III!. I .11, III! I.I 20 - CD 2 => Z IO 0 20 10 28-55m * = 26 n= 363 ,.1. . ..Illlllll ll 56-IIOm 3= 30 n = 86 i i i i | i i i i | i i i i | i i i i | i i i I ) I 5 10 15 20 25 30 FORK LENGTH (cm) I ! 1 | I I m |m i I | I I M | 35 40 45 50 FIGURE 2.— Length-frequency distribution of Calamus leu- eosteus by depth zone for 3/4 Yankee trawl caught specimens (1973-77). Age and Growth Life history information was obtained from 1,732 fish collected from 1975 to 1980. Age deter- minations were attempted for 1,664 pairs of oto- liths and 1,679 scale samples, and of these, 80% of the otoliths and 45% of the scales showed discern- ible rings. There was a 62.8% 1:1 agreement in ages obtained from both scales and otoliths from 760 individuals. Mean marginal increments by month for scales and otoliths were examined to determine the time of annulus formation (Fig. 3). Samples were combined by month regardless of the year of capture. Mean marginal increments should approach zero at the time of annulus formation; this occurs in June on scales and in July on otoliths. Fork lengths increased with increasing age as shown by scales and otoliths (Table 2); however, this progression was obscured in older age groups by smaller sample sizes. In general, average fork lengths derived from scale age and otolith age were similar for the first few years, then fish aged by otoliths tended to be smaller- then those aged by scales. Fish given identical ages using both scales and otoliths showed average fork lengths at age similar to those derived by scales alone. The relationships of fork length to otolith and scale radius were best described by the equations logFL = 1.041 +0.844 log OR n= 1,320 r2 = 0.70 5 4 § 3H z => 2 o (133) (166) (71) I 0 35-i 30- tr 25 o z - 20-| _i I 15- 1 I0J (94) SCALES (252) O (l) O O All ages • • Ages l-ll -I 1 1 1 1 1 1 1 1 1 1 I JFMAMJJASOND MONTHS Figure 3.— Mean marginal increments for otoliths and scales by month for Calamus leueosteus. Number in parentheses = sample size. 866 WALTZ ET AL.: BIOLOGY OF THE WHITEBONE PORGY Table 2.— Mean observed fork length, number and standard deviation (SD) by age for otoliths, scales, and individuals given identical ages by scales and otoliths of Calamus leucosteus. Otoliths Scale; Otolith-sca No. FL les Age No. FL SD No FL SD SD 0 34 111 22.4 24 98 182 16 96 17.9 1 174 153 25.6 122 143 23.4 98 144 22.6 II 319 201 23.5 238 191 22.1 183 194 205 III 172 225 23.2 145 225 22.0 93 225 20.1 IV 138 248 22.5 73 256 28.9 41 247 200 V 155 263 26.3 77 284 30.8 29 280 27.7 VI 109 280 27.2 54 314 290 10 314 199 VII 73 284 31.6 18 312 33.5 6 295 44.0 VIII 57 279 32.0 6 345 293 — — IX 34 289 26.1 2 313 66.4 — — — X 25 290 31.5 — — — — — — XI 26 301 33.0 XII 8 309 26.9 FL = -36.713 + 1.176 SR n = 757 r2 = 0.82 the best value of Lx by using several trial values of Lx and regressing In (Lx - L) against t, where L = mean back-calculated fork length and t = age (Ricker 1975). The straightness of this line is sen- sitive to changes in Lx and the L^ that pro- duced the straightest line was Lx = 331 for oto- liths and L^ = 362 for scales. Values of K = 0.1731, to = -2.6390 for otolith ages and K = 0.2611, h = —0.3973 for scale ages were obtained. The theoretical growth equations derived from these values were Otoliths L, = 331 [l - e-0"31(t+2.6390) j scales L, = 362 [l-e-o.26ii- *^e ■*-±j O e?X*j. 2./* C^jg&W* FIGURE 5.— Histological sections of Calamus leucosteus gonads. A, immature female; B, developing female; C, spent female; D, transitional gonad. AT = atretic oocyte, T = testicular tissue. 869 FISHERY BULLETIN: VOL. 80, NO. 4 1?**W '• V ••"* ' 4» t **d»> ■* * g M # - i ... V ■H*. "v, D Figure 6.— Histological sections of Calamus leucosteus gonads. A, developing male; B, developing male with residual oocytes in testes; C, developing female with inactive testicular tissue present; D, simultaneous development in both ovarian and testicular tissue. IT = inactive testicular tissue, RO = residual oocyte, S = spermatozoa, T = testicular tissue. 870 WALTZ ET AL.: BIOLOGY OF THE WHITEBONE PORGY 100 90- eo 70 60 50- 40 30 o 20 < *?• •'Y\ .■*■* »--* -f t W '»-».. 100 90 80 - 70 60 - 50 -40 30 - 20 I 0 .*-»-«« I00-, 90- 80 70 60- 50- 40 30- 20- I 0 T I i | i I I i | I I r i i — i — i — i — r 15 20 2 5 30 SIZE CLASS (cm) • • female » 4 transitional * — v. 00 90 80 70 60 50 r- 40 30 20 I 0 -i i 1 1 1 1 1 "1' — 15 yr is 21.5 yr. Specific fecundity Age (yr) N (eggs/g) SE 5 1 151.4 — 6 3 254.0 37.0 7 6 2729 31.4 8 3 2733 6.7 9 5 355.3 26.9 10 12 374.7 27.9 11 14 444.9 22.6 12 6 423.4 38.2 13 5 476.8 22.5 14 1 516.1 — >15 8 447.4 7.8 The length-fecundity and weight-fecundity re- lationships described in the present study differ significantly from data presented by Phillips (1964; analysis of covariance, P<0.01). The 20 fish in his study were collected from 1957 to 1959 in California. We converted the total length measurements in Phillips to fork length using the total length-fork length relationship in Len- arz4 and plotted mean values by 1 cm length in- tervals for comparison with data from the present study (Fig. 2). Values are similar through approximately 40 cm FL, but at greater lengths the values from Phillips are more variable and generally lower than fecundity determined in the present study. Similarly, data on mean weight-specific fecundity was lower; MacGregor (1970) calculated a value of 288 eggs/g from Phil- lips' (1964) data. As stated above, the mean from the present study was 389 eggs/g. The weight- fecundity regression from Phillips(1964)ischar- acterized by a lower slope. The lines intersect near 1,000 g and Phillips' estimate at 2,000 g is 67.5% of that predicted by the regression from the present study. Gunderson et al. (1980) noted a similar pattern of generally lower fecundity at greater lengths when comparing their data for S. goodei and S. flavidus with that of Phillips (1964). Since the methods in the present study are most similar to those of Gunderson et al. (1980), methodological differences could explain the different results. Geographic differences, however, may also be involved. Gunderson et al. (1980) noted increased fecundity at length for S. goodei in northern as compared with southern geographic regions. Clear differences are also apparent in the length at 50% maturity for sev- eral species of Sebastes, with maturity occurring earlier in southern areas. Barss and Echeverria (footnote 3), for example, noted that the length and age at 50% maturity for S. entomelas females are 38 cm FL and 7 yr off Oregon and 32 cm FL and 5 yr off California. Thus reproductive char- acteristics within species may differ between areas. It is probable that & entomelas spawns only once per year. While MacGregor (1970) noted evidence of multiple spawning in three species of Sebastes, these species were generally character- ized by lower weight-specific fecundity than ob- served for S. entomelas. Furthermore, the lack of a secondary mode of oocytes and the distinct, relatively short spawning season noted by Barss and Echeverria (footnote 3) in both Oregon and California samples indicate a single spawning per year for this species. Estimates of fecundity from the four samples of S. entomelas with fertilized ovaries were be- low values predicted from the weight-fecundity relationship; the percent of expected fecundity decreased with increasing developmental stage of embryo (Table 2). These specimens had no signs of extrusion of embryos during capture, but it cannot be ruled out. Raitt and Hall (1967), however, noted that egg counts from fertilized Table 2.— Percentage of nonviable eggs and reduc- tion in fecundity in the ovaries of four specimens of fertilized Sebastes entomelas. The percent non- viable eggs was determined in four subsamples of 300 eggs. Expected fecundity was determined from the weight-fecundity relationship. 4Lenarz, W. H. 1980. Aging and growth of widow rock- fish. Unpubl. manuscr. Southwest Fisheries Center Tibu- ron Laboratory, National Marine Fisheries Service, NOAA, Tiburon, CA 94920. % nonviable Fecundity Ovarian stage eggs (±2 SE) (% expected) Newly fertilized 0.4 (0.17) 87 Late high blastula 1.0 (0.81) 62 Late high blastula 3.2 (0.79) 56 Eyed embryos 0.4 (0.17) 38 883 specimens of S. marinus were below those of non- fertilized specimens and suggested that the dif- ference was related either to incomplete fertili- zation or to presence of nonviable eggs which are subsequently resorbed after fertilization. MacGregor (1970) observed undeveloped or un- fertilized oocytes from the same batch as devel- oping embryos in all species of Sebastes exam- ined, but these accounted for only 0.06% of the egg count in 5. paucispinis. In S. entomelas, this percentage was higher (Table 2). Moreover, since the percentage of expected fecundity decreases with later developmental stage, resorption of nonviable embryos may occur throughout the gestation period. Because estimated and realized fecundity may differ, Gunderson (1977) sug- gested that fecundity estimates of S. alutus be considered tentative. Foucher and Beamish (1980) have made similar suggestions concern- ing fecundity of the oviparous Pacific hake, noting that nonviable oocytes could contribute to overestimates of fecundity. In the genus Sebastes it would thus be interesting to determine fecun- dity in various stages of developing and fertilized ovaries in a shallow living species which could be captured with no fear of extrusion-related reduc- tions in counts of fertilized eggs or embryos. Acknowledgments This work was supported by Contract Number 81-ABC-00144 from the National Marine Fish- eries Service, Northwest and Alaska Fisheries Center, Seattle, Wash. We thank the fishing in- dustry in Newport, Oreg., for cooperation with sampling and catch information and R. L. Dem- ory and W. H. Lenarz for their helpful comments on the manuscript. We also thank W. H. Lenarz for supplying ages for the specimens from this study and Karen Dykes for typing the drafts of the manuscript. Literature Cited Al.VERSON, D. L., A. T. Pruter, and L. L. Ronholt. 1964. A study of demersal fishes and fisheries of the northeastern Pacific Ocean. H. R. MacMillan Lecture Series on Fisheries. Inst. Fish. Univ. B.C., Vancouver, 190 p. Bagenal, T. B., and E. Braum. 1968. Eggs and early life history, hi W. E. Ricker (edi- tor). Methods for assessment of fish production in fresh waters, p. 159-181. Int. Biol. Programme Handb. 3. Foucher, R. P., and R. J. Beamish. 1980. Production of nonviable oocytes by Pacific hake (Merluccius productus). Can. J. Fish. Aquat. Sci. 37: 41-48. Gunderson, D. R. 1977. Population biology of Pacific ocean perch, Sebastes alutus, stocks in the Washington-Queen Charlotte Sound region, and their response to fishing. Fish. Bull., U.S. 75:369-403. Gunderson, D. R., P. Callahan, and B. Goiney. 1980. Maturation and fecundity of four species of Sebas- tes. Mar. Fish. Rev. 42(3-4):74-79. Gunderson, D. R, and T. M. Sample. 1980. Distribution and abundance of rockfish off Wash- ington, Oregon, and California during 1977. Mar. Fish. Rev. 42(3-4):2-16. MacGregor, J. S. 1970. Fecundity, multiple spawning, and description of the gonads in Sebastodes. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 596, 12 p. Phillips, J. B. 1964. Life history studies on ten species of rockfish (genus Sebastodes). Calif. Dep. Fish Game, Fish Bull. 126, 70 p. Raitt, D. F. S., and W. B. Hall. 1967. On the fecundity of the redfish, Sebastes marinus (L.). J. Cons. 31:237-245. George W. Boehlert Oregon State University Marine Science Center Newport, OR 97365 Oregon Department of Fish and Wildlife Newport, OR 97365 Oregon State University Murine Science Center Newport, OR 97365 W. H. Barss P. B. Lamberson A COMPARATIVE STUDY OF AUTOCHTHONOUS BACTERIAL FLORA ON THE GILLS OF THE BLUE CRAB, CALLINECTES SAPIDUS, AND ITS ENVIRONMENT1 The bacterial flora of blue crabs, Callinectes sapidus, has been previously enumerated and identified by examining blue crab hemolymph (Tubiash et al. 1975; Sizemore et al. 1975; Col- well et al. 1975). Other studies on live blue crabs •Contribution No. 82-17C of the Southeast Fisheries Center Charleston Laboratory, National Marine Fisheries Service, NOAA, P.O. Box 12607, Charleston, SC 29412-0607. 884 FISHERY BULLETIN: VOL. 80, NO. 4, 1982. have been concerned with the presence of specif- ic human or fishery pathogens in the hemo- lymph, necrotic tissue, or gill material (Rosen 1967; Williams-Walls 1968; Krantz et al. 1969; Cook and Lofton 1973; Johnson 1976). The state- ment of Tubiash et al. (1975) that the hemolymph of most healthy blue crabs contains a natural or autochthonous bacterial flora has been chal- lenged, and it has been suggested that further experiments using minimally stressed crabs would be needed to substantiate that statement (Johnson 1976). This study was designed to determine, season- ally, the natural Vibrio, fecal coliform, and aero- bic, heterotrophic bacterial populations on blue crabs from environments that differed in salin- ity and influx of urban and industrial pollutants. These microbial populations were also compared with those found in intertidal oysters (Cras- sostrea virginica), waters, and sediments col- lected simultaneously with the crabs. Blue crab gills were chosen as a suitable substrate for microbiological investigations because they have direct contact with the environment and are easily sampled and processed for enumeration of their bacterial flora. Materials and Methods Two South Carolina areas, Charleston harbor and St. Helena Sound, an estuary 35 mi south of Charleston, were surveyed during a 22-mo pe- riod between August 1979 and May 1981 (Fig. 1). Within each area, two sampling stations were selected, representing mean salinities of 10%o and 25%0. The Charleston harbor sampling stations were Foster Creek, salinity 10%o, a tributary to the Wando River, which, along with the Ashley and Cooper Rivers, forms Charleston harbor; and Shutes Folly Island, salinity 25%o, situated near the center of Charleston harbor. The oyster beds in both sites are closed to harvest- ing because fecal coliform levels, monitored in the water column and oyster meats by the South Carolina Department of Health and Environ- mental Control, exceed safe limits for harvesting areas. Foster Creek receives negligible industri- al pollution, whereas the Shutes Folly Island sta- tion receives a moderate-to-heavy influx of industrial pollutants. The St. Helena Sound stations were the Ashepoo River at Mosquito Creek, salinity 10%o, and St. Helena Sound at the mouth of Rock Creek, salinity 25%o. Shellfish beds at these stations are open to harvesting, with no discernible influx of urban, industrial, or commercial pollutants. Each station was sampled on a quarterly basis to coincide with the highest and lowest temperatures in the water column and during the middle of the two transitional periods in water tempera- tures. Blue crabs were captured in commercial-type crab pots baited with fresh fish heads. The crab pots were harvested from 4 to 24 h after being set, dependent on the seasonal rate of blue crab capture. Intertidal oysters and sediments from the oyster beds were collected manually at low tide. Two hundred grams of the top centimeter of sediment were removed with sterile tongue de- pressors and placed in sterile containers. Sur- face water samples (1 m below the surface) were collected with a Niskin2 sterile bag sampler (General Oceanics, Miami, Fla.) at the site of blue crab collections. All sediment, water, and oyster samples were immediately cooled with ice. Blue crabs were maintained at their in situ temperature by placing them in a thermally in- sulated container. All samples were analyzed within 4 to 8 h. During a survey, two to four rep- resentative composite samples of blue crab gills (dependent on seasonal activity of blue crabs), three oyster composites, and two samples each of sediment and surface water were collected and analyzed for each sampling station. A composite gill sample contained gills from 10 to 12 crabs. Since mature female blue crabs migrate to higher salinities, male blue crabs dominated the population at 10%o salinity and females at 25%o salinity. Whenever possible, blue crabs above the legal harvesting size for South Carolina, 127 mm, were sampled. Each survey was completed within 4 d. For monitoring purposes, tempera- ture and salinity of the surface water were mea- sured, using a YSI Model 33 Salinity-Conduc- tivity-Temperature meter (Yellow Springs In- strument Co., Yellow Springs, Ohio). Preparation of oyster and water samples for analyses followed standard procedures (Ameri- can Public Health Association 1970, 1976). Cara- paces of the blue crabs were cracked vertically with a blow from a stainless steel knife. The knife did not penetrate into the gut or organs. The carapace was then removed by pulling up on the lateral spines (Fig. 2). Exposed gills were aseptically removed with forceps and placed in 2Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. 885 [-, LfirrTt^ **m — -/A » J Im.\ * ft if if I SCALE \ 10 0 MMIiiiiMiIm ^^Tr?^^ ■Jr ,-j£^^& «'»'» SAHTt€ */vt* 0t *^SF 4 SOUTH SAHTWC *IV£* t Illl ■ out 1*11 Mtlltll » Vi T iff"* ^^-FoUtf Cr»tk ,ii(ii n«S ^7^0 J^ , OfMHLISTOH *4*0O* ^^ /Jftr^^thut** Felly Island i£ |W 5ro*{j /*tfr • «>*r* eoisTo nivgtt vSK? ^n\ ' ^ " ~ Aah«poo Riv«r c 'i ^SST ftj J6«/r* tDISTQ KIVC* •^ J M£LtmA SCUMO •i^XS^^^rj f s C &2*fef*$ *o#r *orsu tovmc t h 1 ^fS^^t ti^'mi; \ CJiWOmr JOMtf BIOHGi* ^fek^i— -bJ^T" Figure 1.— Map of coastal South Carolina showing location of sampling stations. 886 FIGURE 2.— Photograph of blue crab with section removed from vertically cracked carapace. sterile containers. The blue crab gills were ho- mogenized in a blender for 2 min at high speed and further prepared for bacterial analysis fol- lowing the standard procedure for oysters. Blue crab gills and oysters were analyzed on a wet- weight basis (50 g), but sediments were analyzed on a volume-to-volume basis (50 ml) because of the great differences in sediment densities found in the environment. The initial dilution was made by volume displacement of the diluent by the sediment in a calibrated container as pre- viously described (Babinchak et al. 1977). All dilutions were made using sterile 0.1% peptone (Difco Laboratories, Detroit, Mich.) saline solu- tion (1.5% NaCl). Total viable, aerobic, heterotrophic bacterial counts for all samples were determined, using the spread-plate technique and a modification of a low-nutrient, artificial seawater plating med- ium (ASWLN) of Litchfield et al. (1975) con- taining the following ingredients per liter of half-strength artificial seawater (Rila Marine Mix, Teaneck, N.J.): 0.5 g peptone (Difco), 0.5 g yeast extract (BBL Microbiology Systems, Cockeysville, Md.), 0.1 g sodium glycerophos- phate (MCB Manufacturing Chemist, Inc., Cin- cinnati, Ohio), and 20 g agar (BBL). Three repli- cates of each dilution were plated, and the inoculated plates incubated at 20°C for 14 d. Fecal coliform counts in all samples were esti- mated by the three-tube most-probable-number (MPN) procedure prescribed for seawater and tissues (American Public Health Association 1970, 1976). Lauryl sulfate tryptose broth (BBL) was used in the presumptive test, with confirma- tion in EC broth (BBL) incubated at 44.5°C in a circulating water bath. Vr6Wo-like organisms were enumerated on thiosulfate citrate bile salts agar (TCBS; BBL) using the spread-plate technique for all samples. Fifteen to thirty colonies, representing all coloni- al types, as determined with oblique or darkfield illumination through a stereomicroscope, were picked only from the blue crab gill-inoculated TCBS plates. The cultures were purified and then characterized biochemically using the API 20E system (Analytab Products, Inc., Plainview, N.Y.). 887 Results During the initial survey, it was noted that many intermolt blue crabs had dark brown or mahogany-colored gills which contrasted with the light-colored gills of recently molted crabs. The light- and dark-colored gill material was subsequently divided and analyzed separately. The microbiological data from 61 blue crab gill samples collected during five quarterly sur- veys were analyzed statistically using a general- ized analysis of variance (ANOVA) employing the maximum likelihood approach. The depen- dent variables for analysis were the microbial counts on the blue crab gills; independent vari- ables were urban and industrial pollution, salin- ity, season, gill color, and their pairwise inter- actions. In Table 1, the P-values resulting from the analysis of variance indicated that season, gill color, and the interaction of pollution and season affected the total Vibrio and aerobic, heterotrophic bacterial counts. Fecal coliform counts were not significantly affected by any of the variables investigated. Graphically displayed in Figure 3 is the effect of season and gill color on total Vibrio and aero- bic, heterotrophic bacterial counts. Dark gills had consistently higher counts, and the counts showed a similar pattern with season. Surprisingly, the absence of urban fecal pol- lution had no significant impact on fecal coliform counts in blue crab gills (Table 1). Blue crab gills obtained from St. Helena Sound, a pristine area, yielded high fecal coliform counts, whereas in- tertidal oysters and waters sampled concurrent- ly were relatively free of contamination (Table 2). To confirm the identity of the fecal coliforms found in St. Helena Sound, 90 bacteria were isolated from positive EC broth MPN tubes, checked for their Gram reaction, and analyzed Table l.—P values resulting from generalized ANOVA of crab gill data. The hypothesis that a factor has an effect on microbial counts in blue crab gills is accepted when P<0.05. P-values, dependent variables Independent variables Heterotrophs Vibrio Fecal coliforms Pollution 0.748 Salinity 0.549 Season 0.030 Gill color 0001 Pollution - salinity 0.916 Pollution - season 0.001 Pollution - gill color 1 Salinity - season 1 Salinity - gill color 1 Season - gill color 1 0.233 0207 0015 0.001 1 0.036 1 1 1 1 0.304 0.211 0.355 0.312 6- 5- • HETEROTROPHS DARK GUIS ■ HETEROTROPHS LIGHT GUIS a VIBRIOS OARK GILLS D VIBRIOS LIGHT GILLS NOV T 9 7 9 EEB I980 MAY I980 AUG I960 NOV I980 Figure 3. — Average total Vibrio and heterotrophic bacterial counts per gram of light and dark crab gill tissue from all samples collected from the St. Helena Sound area. biochemically with the four reactions which con- stitute the IMViC differential test (American Public Health Association 1976). The sources for the bacterial isolates were blue crab gills (35), water (26), sediment (15), and oysters (14). Ninety-four percent of the isolates were identi- fied as typical Escherichia coli and 6% as typical Enterobacter aerogenes. Twenty fecal coliforms isolated from blue crab gills were also tested with the API 20E system, and all identified as E. coli. Representative samples of blue crab stomach contents analyzed in parallel with the Table 2.— Distribution of fecal coliforms in samples collected from St. Helena Sound area. Fecal coliforms/100 g' Nov Feb. May Aug. Nov Sample 1979 1980 1980 1980 1980 Intertidal oysters 21 12 12 21 160 Water 80 5 2 16 12 Sediment 430 340 60 19 90 Blue crab gills 2.000 4,300 230 4,300 210 '100 ml of water and sediment samples 888 corresponding gill tissues gave significantly lower heterotrophic counts. Dark blue crab gills harbored the same hetero- trophic bacterial populations found in the sedi- ments (Fig. 4). Similar results with total Vibrio populations were obtained in these areas. As shown in Figure 4, oysters and water contained lower heterotrophic counts. Only 10 to 30% of the TCBS bacterial isolates from individual samples of light and dark gills could be identified to genus and species using the API identification system. Aeromonas spp. made up 28% of those TCBS isolates identifed. D SEDIMENT » Gill ■ OYSTER • WATER - 5- 1 1 1 1 1 — NOV 1979 FEB 1980 MAY 1980 AUG 1980 NOV 198 Figure 4. — Average heterotrophic bacterial counts per gram of sample collected quarterly from Foster Creek. Discussion Common external features which distinguish blue crabs with brown to mahogany gills are rust-spotted exoskeletons and, occasionally, at- tached barnacles and algae. These conditions are not considered abnormal for late intermolt crabs. Johnson (1977) has also described a viral disease in which blue crabs displayed similar diagnostic signs: failure to molt, a brown-spotted exoskeleton, and gills that were often red-brown. Sections made from dark gills collected during the survey showed that these gills were, to vary- ing degrees, fouled by a layer of bacteria and mucus (P. T. Johnson3). Observations of similar- ly fouled gills of rock crabs, using scanning elec- tron microscopy, showed large numbers of bac- teria residing on the gill tissue, similar to those found on blue crab gills in this study using bac- terial enumeration procedures (F. Thurberg4). These enumeration data suggest that the gills of blue crabs provide an ecological niche for the growth and physiological activity of hetero- trophs, Vibrio spp., and related organisms, equivalent to that described for sediments and zooplankton (Kaneko and Col well 1975 a, b, 1978). The high fecal coliform population found in our pristine area would indicate that gill surfaces also provide a protective ecological niche much like that reported for marine sediments, where high fecal coliform populations can accumulate and persist even in ecosystems where influx of fecal coliforms is low (Rittenburg et al. 1958; Van Donsel and Geldreich 1971; Babinchak et al. 1977). Urban and industrial pollution did not have an effect on total Vibrio and aerobic, heterotrophic bacterial counts on blue crab gills. Since these two microbial populations are indigenous and dependent on nutrient levels for growth, indus- trial and domestic pollution would not necessar- ily have shown an effect over the pristine areas sampled. The vast marshlands which drain into the St. Helena Sound area (Tiner 1977) would introduce large natural levels of dissolved and particulate organic material and other nutrients which could support the high bacterial levels observed. The low rates of identification by the API 20E system can be attributed primarily to the high percentage of clinical bacterial isolates which form the API data base. Even some of our posi- tive identifications are now in question, because marine isolates identified as Aeromonas spp. with the API system are known to be Group F vibrios (Seidler et al. 1980). This group of Vibrio- like organisms has been associated with diar- rheal illness, although the epidemiology of the disease has not been well-defined. 3P. T. Johnson, Northeast Fisheries Center, National Marine Fisheries Service, NOAA, Oxford, MD 21654, pers. commun. 1981. 4F. Thurberg, Northeast Fisheries Center, National Marine Fisheries Service, NOAA, Milford, CT 06460, pers. commun. 1981. 889 The data obtained in this study establish blue crab gills as excellent surfaces for enu- merating the blue crab's natural adherent bacterial population. Bacterial quantitation, which is difficult to achieve with other crab surfaces, is easily accomplished with gills. Suc- cession of bacterial species and the possible influence of environmental contaminants in the bacterial colonization of blue crab gills are also conveniently accommodated by the molting process. The freshly molted gill sur- faces can be compared with gills that have been exposed to the environment for extended periods. Gill surfaces may provide a model system for monitoring biological or chemical pollutants based on observable changes in the autochthonous bacterial populations of blue crab gills. Acknowledgments The authors thank L. Ng for statistical analy- sis of the data and V. Ward and D. Green for their technical assistance. Literature Cited American Public Health Association. 1970. Recommended procedures for the examination of sea water and shellfish. 4th ed. Am. Public Health Assoc, Inc., Wash., D.C. 1976. 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Adsorption of Vibrio parahaemolyticus onto chitin and copepods. Appl. Microbiol. 29:269-274. 1975b. Incidence of Vibrio parahaemolyticus in Chesa- peake Bay. Appl. Microbiol. 30:251-257. 1978. The annual cycle of Vibrio parahaemolyticus in Chesapeake Bay. Microb. Ecol. 4:135-155. Krantz, G. E., R. R. Colwell, and E. Lovelace. 1969. Vibrio parahaemolyticus from the blue crab Cal- linectes sapidus in Chesapeake Bay. Science (Wash., D.C.) 164:1286-1287. Litchfield, CD., J. B. Rake, J. Zindulis, R. T. Watanabe, and D. J. Stein. 1975. Optimization of procedures for the recovery of heterotrophic bacteria from marine sediments. Mi- crob. Ecol. 1:219-233. Rittenberg, S. C, T. Mittwer, and D. Ivler. 1958. Coliform bacteria in sediments around three marine sewage outfalls. Limnol. Oceanogr. 3(1):101- 108. Rosen, B. 1967. Shell disease of the blue crab, Callinectes sapidus. J. Invertebr. Pathol. 9:348-353. Seidler, R. J., D. A. Allen, R. R. Colwell, S. W. Joseph, and O. P. Daily. 1980. Biochemical characteristics and virulence of en- vironmental group F bacteria isolated in the United States. Appl. Environ. Microbiol. 40:715-720. Sizemore, R. K., R. R. Colwell, H. S. Tubiash, and T. E. Lovelace. 1975. Bacterial flora of the hemolymph of the blue crab, Callinectes sapidus: Numerical taxonomy. Appl. Mi- crobiol. 29:393-399. Tiner, R. W., Jr. 1977. An inventory of South Carolina's coastal marshes. S.C. Mar. Resour. Cent. Tech. Rep. 23, 33 p. Tubiash, H. S., R. K. Sizemore, and R. R. Colwell. 1975. Bacterial flora of the hemolymph of the blue crab, Callinectes sapidus: Most probable numbers. Appl. Microbiol. 29:388-392. Van Donsel, D. J., and E. E. Geldreich. 1971. Relationships of salmonellae to fecal coliforms in bottom sediments. Water Res. 5:1079-1087. Williams-Walls, N. J. 1968. Clostridium botulinum type F: Isolation from crabs. Science (Wash., D.C.) 162:375-376. John A. Babinchak Daniel Goldmintz Gary P. Richards Southeast Fisheries Center Charleston Laboratory National Marine Fisheries Service, NOAA P.O. Box 12607. Charleston, SC 29M2-0607 890 WHITE SHARK PREDATION ON PINNIPEDS IN CALIFORNIA COASTAL WATERS White sharks, Carcharodon carcharias, prey on various fishes, sea turtles, whales, dolphins, and on several species of pinnipeds (Allen 1880; Elli- ot 1881; McCormick and Allen 1963; Davies 1964; Nishiwaki 1972; Ellis 1976; Ainley et al. 1981; MeCosker 1981). Data on pinnipeds preyed upon by sharks in California waters are meager and many aspects of the predator-prey relationship are unknown. Four types of evidence indicate that sharks prey on pinnipeds: 1) Pinniped remains in the stomachs of dead sharks, 2) observation of seals with injuries inflicted by large sharks, 3) obser- vation of shark attacks on seals, and 4) the pres- ence of sharks near seal rookeries at a time when seals are present. We report evidence of the first two kinds regarding shark predation on north- ern elephant seals, Mirounga angustirostris, and harbor seals, Phoca vitulina. Methods Five white sharks caught in southern Califor- nia waters in 1975 and 1976 and two white sharks that washed ashore in central California in 1977 and 1978 were examined. The fresh dead sharks were weighed, measured, and their sex determined. Stomachs were dissected out and contents identified, and in some cases, weighed and measured (Table 1). From 1968 to 1980, shark-bitten elephant seals on Ano Nuevo Island and the adjacent Ano Nuevo Mainland in central California were counted, photographed, and identified individu- ally, and their behavior was monitored. This was accomplished during daily censuses conducted each breeding season from December to mid- March and during weekly censuses conducted during the remainder of the year. Only seals with fresh wounds judged by their pink or bloody appearance to be less than a few days old were in- cluded in the sample. This gives us confidence that our subjects were injured near the study area. We did not census animals with old scars or healed injuries, whose origins were difficult to ascertain. Shark injuries were differentiated from other wounds, caused by boat propellers or intraspecific fighting, by their oval shape and the jagged serrations caused by the predator's sharp teeth. Both slight and serious wounds were included. Slight wounds consisted of superficial tooth punctures or scrapes across the skin; seri- ous wounds involved deep bites and tears. Seri- ously wounded seals had large flaps of flesh exposed or chunks of flesh missing. The di- mension of bites was measured on a few dead seals. We marked and followed 11 females who sus- tained moderate to severe shark wounds when pregnant just before arriving on the island to give birth. Their pups were marked at birth and the pair was observed until the filial relationship ended. Northern elephant seal females give birth within a week after arriving on the rookery. A female nurses her pup daily for about 4 wk before weaning it and returning to sea (Le Boeuf et al. 1972). A similar search for shark-bitten harbor seals, which breed at Ano Nuevo Island and numerous Table 1.— Stomach contents of white sharks collected off the California coast from 1975 to 1978. Specimens 1-5 were collected by Sea World of San Diego, no. 6 by K. Skaug and M. Riedman, and no. 7 by an anonymous fisherman. Specimen number Date of collection Location Sex Total length (m) Weight of shark (kg) Stomach contents 1 24 June 1975 8 km northeast of Santa Catallna Island F 39 623 7 2 1 Aug. 1975 110 m west of Laguna Beach F 2.4 138 8 3 6 Sept 1975 Near Anacapa Island F 4.9 1.428.8 4 7 Sept 1975 113 km southeast of Anacapa Island F 50 1.560.4 5 13 June 1976 West end of Catalina Island F 5.5 1.882.4 6 3 Feb 1977 Ano Nuevo Bay F 4.7 ? 7 25 Sept 1978 1.6 km offshore near Aptos M 3.9 540 Anterior portion of stomach contained har- bor seal remains (18.2 kg). Posterior stomach held unidentified pinniped. A 4-in patch of pinniped pelage Harbor seal, well digested. Skull and posterior portion of a juvenile ele- phant seal, plus large amounts of fur and digested material. Nearly digested Bulk suggested a large animal, probably a marine mammal. Approximately one-third of a recently eat- en 4-yr-old male elephant seal. The head of a harbor seal FISHERY BULLETIN: VOL. 80. NO. 4. 1982. 891 other locations along the California coast, was not conducted. Results Table 1 summarizes data obtained from the stomachs of seven great white sharks examined shortly after they washed ashore dead or were captured at sea. Four points are worth noting: 1) Six stomachs contained seal remains, three of harbor seals and two of northern elephant seals. 2) Large prey was consumed. On the basis of tooth annuli and head and proboscis size, we estimate that specimen no. 6 (Fig. 1) con- tained the remains of a male elephant seal, 4 to 5 yr old. Intact, this seal would have measured approximately 3 m in length and weighed 450 to 680 kg. 3) The dimensions of the barely digested mate- rial in four of the shark stomachs indicate that the prey had been consumed in large 4) pieces. For example, the stomach of one spe- cimen contained the entire head, unmarred and severed cleanly at the neck. Both hind- flippers and the tail were covered with hair and still attached to a segment of the sac- rum. Also included were both foreflippers, one attached to a large piece of flesh con- taining the shoulder, a large portion of the midsection including six vertebrae, and several pieces of flesh and fur in various stages of decomposition. The elephant seal material weighed about 225 kg. Six of the seven sharks were females. The majority of the shark-injured elephant seals were observed during the winter breeding season. Only two recently bitten animals were observed on Ano Nuevo Island in spring, despite the larger number of animals present at this time compared with the breeding season (Le Boeuf and Bonnell 1980). Fewer than three victims per breeding season were observed from 1968 to 1976. From 1976 to Figure 1— A moribund great white shark (Specimen No. 6 in Table 1) that washed ashore near Ano Nuevo Point shortly after having consumed approximately one-third of a young male northern elephant seal. 892 1980, 44 elephant seals with shark-inflicted in- juries were observed (Table 2). Most of the ele- phant seals bearing recent shark wounds were adults. Males incurred the highest injury rate. Even the largest adult bulls, measuring more than 4.9 m and weighing between 1,800 and 2,700 kg were observed with shark bites (see Fig- ure 2a). This may be due to the male habit of spending more time in the water near the rook- ery during the breeding season than females. Table 2.— Shark-bitten northern elephant seals observed on Ano Nuevo Island and the Ano Nuevo Mainland. Adult Adult Juve- Year males females niles Pups Total 1976 3 3 1977 3 4 1 8 1978 1 7 1 9 1979 5 1 1 7 1980 16 1 17 Total 25 16 2 1 44 Shark bites were located on diverse areas of the body but rarely on the head (Fig. 2). Possibly, frontal attacks were less successful or head bit- ten seals simply did not survive the encounter. In many cases, large pieces of blubber were missing or hung loosely from the animal. Some seals lost a foreflipper or hindflipper and in one case most of the proboscis. Some animals were bitten several times. The majority of injured seals survived and re- cuperated rapidly. Infected wounds were rarely observed. Only three elephant seals died on the island or on the mainland following shark injury. In September 1976, an S^-mo-old female was found dead with numerous deep lacerations and teeth marks covering her body. In December 1977, a 1-wk-old pup washed up with its entire sacral region amputated just below the umbili- cus. In February 1978, a large 7-yr-old male died on the island's main breeding beach from mas- sive shark wounds incurred within the previous 24 h. The most serious wounds consisted of two large oval chunks of flesh missing from the left side of the thoracic region (Fig. 2e). The bites measured 61 and 69 cm wide, 61 cm high, and 30 cm deep. No bite penetrated the body cavity al- though some muscle was removed and a rib was partly exposed. Most female elephant seals bitten by sharks shortly before giving birth failed to wean their pups successfully. One female gave birth to a stillborn and returned to sea immediately. Seven females either abandoned their pups shortly after parturition or they were unable to care for them adequately. Four of these pups died; the eventual status of the other three pups could not be determined. The three females who were suc- cessful in weaning their pups appeared to have sustained the least serious injuries. All injured females remained in the harem for a much short- er period than normal. No injured female was observed to copulate, as uninjured females do, just before returning to sea. Thus, most injured females not only failed to produce a pup during the year of injury, but if they failed to copulate, they did not reproduce in the subsequent year as well. Discussion The data on stomach contents of white sharks presented in this paper is conclusive evidence that this shark preys on elephant seals and har- bor seals in southern and central California wa- ters. We hypothesize that shark-inflicted injuries to northern elephant seals at Ano Nuevo were caused primarily by white sharks. This hypothe- sis is supported by: 1) Data from a white shark that washed ashore at Ano Nuevo Bay whose stomach contained the remains of an elephant seal (Table 2). 2) Observation of white sharks in the area. Twice during the summer of 1970 seal re- searchers saw white sharks measuring about 4.5 m from a dinghy 100 m south of the island. Party boat operators and fisher- men reported seeing white sharks in this area several times during the last decade. Anglers report that white sharks occasion- ally attack large lingcod, Ophidon elonga- tus, when they are caught on hook and line; the sharks surface and circle boats, espe- cially when fishing stops (Miller and Col- lier 1980). 3) An observed white shark attack of a northern elephant seal near Ano Nuevo Island. This occurred on 1 February 1981. 4) The large size of shark bites. This indicates that they were caused by large sharks. White sharks may also be responsible for injuries to elephant seals on other rookeries in California (Ainley et al. 1981) and in Mexico (Townsend 1885; B. Le Boeuf, pers. obs.). 893 . 'I- * * »«« - ^£*t*m. BBMBB^ *,j^*^?rtMtLj. ' fL -* • ^ss* » \ B^_Hkt^ Figure 2.— A variety of shark-inflicted wounds observed on elephant seals and sea lions at Ano Nuevo. A crescent shaped wound (a) and toothprints (b) on adult male elephant seals. A crescent bite on the dorsal posterior of an adult female elephant seal (c) and a large imprint of both jaws on an adult female with a blind left eye (d). Two large chunks of flesh bitten off the left side of an adult male elephant seal who subsequently died from his wounds (e). A California sea lion bearing a recently inflicted shark injury (f). The results of this study support and augment those of Ainley et al. (1981) on South Farallon Island near San Francisco, Calif. They found that white sharks were responsible for most of the shark attacks observed on pinnipeds in the waters surrounding the island during the period September 1970 to February 1979. Northern ele- phant seals were attacked more frequently than harbor seals and sea lions, and shark-bitten fe- male elephant seals exhibited low reproductive success. Shark attacks on elephant seals of Ano Nuevo Island and South Farallon Island (Ainley et al. 1981) appear to be increasing, but more data 894 based on continued monitoring is necessary to confirm this point. Periodic increases in shark attacks of the magnitude found in these two studies may be related to several possible factors: The well-documented increase in elephant seals (Le Boeuf and Bonnell 1980), an increase in abun- dance of sharks, or to one or a few relatively inept predators at work. Acknowledgments We thank Sea World of San Diego for permit- ting us to use data from their shark collecting expeditions; Walter Ward for bringing the beached shark to our attention and for providing measurements; Keith Skaug, C. Leo Ortiz, Rob- ert Gisiner, and Anne Hoover in acquiring and examining shark stomach contents; and Jack Ames, Ellen Chu, Daniel Miller, and Breck Tyler for comments on the manuscript. This study was supported in part by the National Science Foun- dation grant BNS 74-01363 402 to B. J. Le Boeuf. mals of the sea: Biology and medicine, p. 3-204. Charles C. Thomas, Springfield, 111. Townsend, C. H. 1885. An account of recent captures of the Cal ifornia sea- elephant, and statistics relating to the present abun- dance of the species. Proc. U.S. Natl. Mus. 8:90-93. Burney J. Le Boeuf Center for Coastal Marine Studies and Crown College University of California, Santa Cruz Santa Cruz, CA 95064 Marianne Riedman Center for Coastal Marine Studies University of California, Santa Cruz Santa Cruz, CA 95061, Sea World 1720 South Shores Road San Diego, CA 92109 Raymond S. Keyes Literature Cited Ainley, D. G., C. S. Strong, H. P. Huber, T. J. Lewis, and S. H. Morrell. 1981. Predation by sharks on pinnipeds at the Farallon Islands. Fish. Bull.. U.S. 78:941-945. Allen, J. A. 1980. History of North American pinnipeds: A mono- graph of the walruses, sea-lions, sea-bears and seals of North America. Gov. Print. Off.. Wash., D.C., 785 p. Davies, D. H. 1964. About sharks and shark attack. Brown, Davis, and Piatt Ltd., Durban, 237 p. Elliott, H. W. 1881. The seal-islands of Alaska. Gov. Print. Off., Wash., D.C., 176 p. Ellis, R. 1976. The book of sharks. Grossett and Dunlap, N.Y., 320 p. Le Boeuf. B. J., and M. Bonnell. 1980. Pinnipeds of the California islands: abundance and distribution. In D. Power (editor), The California Islands: Proceedings of a Multidisciplinary Symposium. Santa Barbara Museum of Natural History, Santa Bar- bara, Calif. Le Boeuf, B. J., R. J. Whiting, and R. F. Gantt. 1972. Perinatal behavior of northern elephant seal fe- males and their young. Behaviour 43:121-156. McCormick, H., and T. Allen. 1963. Shadows in the sea. Chilton Books, Phila., 415 p. McCosker, J. E. 1981. Great white shark. Science 81 2(6):42-51. Miller. D. J., and R. S. Collier. 1980. Shark attacks in California and Oregon. 1926-1979. Calif. Fish Game 67(2):76-104. Nishiwaki, M. 1972. General biology. In S. H. Ridgway (editor). Mam- VERTICAL stratification of three NEARSHORE SOUTHERN CALIFORNIA LARVAL FISHES (ENGRAULIS MORDAX, GENYONEMUS LINEATUS, AND SERIPHUS POLITUS) Length measurements of larval fish are most fre- quently used in describing life stages (Moser and Ahlstrom 1974), and the subsequent develop- ment of population estimates (Kumar and Adams 1977). Field and laboratory observations are used to construct growth models of larval fishes, which are useful in predicting rates of growth under various environmental conditions (Hunter 1976). When combined with observations of lar- val abundance and distribution, length measure- ments can be indicators of both larval and adult ecology. Larval length-frequency data provide information about adult distribution and abun- dance, spawning periodicity, food preferences, and behavioral transitions that occur during de- velopment (Gj^saetor and Saetre 1974; Tanaka 1974). Larval length-frequency distributions of three species of fish were determined in conjunction with a study of the effects of a power plant off- shore cooling water intake on local nekton popu- lations. The three species chosen [northern an- FISHERY BULLETIN: VOL. 80, NO. 4, 1982. 895 chovy, Engraulis monto (Engraulididae); white croaker, Genyonemus lineatus (Sciaenidae); queenfish, Seriphus politus (Sciaenidae)] are among the most abundant adult fishes in the area, and are important links in the local trophic structure. The northern anchovy is important as forage for larger fishes and is fished commer- cially for manufacture of fish meal and oil. While the two sciaenid species have less commercial value, both are important as forage for larger species. Materials and Methods Samples were collected as part of a program of preoperational environmental studies at San Onofre Nuclear Generating Station (Fig. 1). In the area near the generating station (designated "treatment"), two transects extended over depths of 8 to 11 m and 12 to 15 m. Transects were also located in a "reference" area 5.8 km northwest. The two areas are similar in bottom topography and in the presence of a kelp bed just south of the outer transects. Each transect was 760 m in length. The two treatment transects and the two reference transects were each separated by 150 m. Monthly collections were made every 30±2 d from March 1978 through July 1979. Results for March through July samples for 1978 and 1979 are presented as mean values for the 2 yr com- bined. Three vertical water column levels were sam- pled. The neuston was sampled, using a Manta net (Brown 1979). This net has a rectangular mouth (86 cm X 15 cm) and is designed to sample the upper 14 cm of the water column. The net fil- tered a volume of approximately 100 m3 during each tow. Midwater samples were taken with paired opening-closing 60 cm diameter circular bongo SANTA BARBARA LOS ANGELES PACIFIC OCEAN / SAN ONOFRE 1 NUCLEAR GENERATING STATION ^o *S METERS 0 500 IOOO 2000 DEPTH IN FEET Figure 1.— Location of sampling sta- tions offshore San Onofre Nuclear Gen- erating Station ("treatment") and San Mateo Point ("reference"). Inset locates the area in relation to southern Califor- nia. 896 nets(McGowan and Brown 1966) towed obliquely through the entire midwater column (about 0.5 m below the surface to 1.0 m above the bottom). Each side of the paired net filtered a volume of about 200 m3/tow. Samples from the epibenthos were collected using an Auriga1 net specially designed for sam- pling over rock-cobble bottoms. The net has a rectangular mouth, 0.5 m X 2.0 m, and filtered about 800 m3 during each tow. Each net was equipped with two flowmeters for volume determinations. Mesh size of each net was 0.333 mm, to facilitate collection of both eggs and larvae (Bolin 1936). Four replicates were collected by each gear at night at each of the four transects. Due to shrinkage of the larvae during preser- vation (4% buffered Formalin-seawater), lengths of the individuals at hatching were smaller than those observed for unpreserved specimens (Thei- lacker 1980), ranging from 1.9 mm for white croaker to 2.5 mm for northern anchovy. The fish were considered to become juveniles after the de- velopment of adult fin rays and spines, which was taken as a length of 30 mm for all three spe- cies. Larvae were divided into 10 size classes of 3 mm each. Results Engraulis mordax The major spawning period for northern anchovy was observed to be from December through May (Fig. 2). Length-frequency distri- butions in neuston samples indicated a pattern of high concentrations of small larvae during heavi- est spawning periods (March and December 1978), followed by months of relatively even dis- tributions from 0 to 15 mm. Larger larvae ap- peared and often became the major larval com- ponent in the neuston 2 to 3 mo after heavy spawning periods. Midsize larvae (12 to 18 mm) were often observed in reduced numbers in com- parison with smaller or larger larval sizes. Low spawning activity during late summer was re- flected in reduced numbers of larvae in neuston samples. Midwater collections of northern anchovy were characterized by larval concentrations in 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service. NOAA. the 6 to 18 mm size range, with abundance of 0 to 6 mm larvae fluctuating with spawning activity of adults. Except in the heavy spawning months of March and December 1978, midsize larvae generally outnumbered 2.5 to 6 mm larvae and composed the majority of midwater larvae taken. Significant numbers of larvae >21 mm were taken in the midwater samples only at the end of the main spawning season. Collections of northern anchovy from epiben- thic samples indicate consistent dominance of the distribution by 6 to 18 mm larvae during most months, with distributions shifted toward larger larvae during midsummer months. Over- all concentrations in epibenthic samples were consistently the highest among the three levels. Genyonemus lineatus The major spawning period for white croaker was from December to May (Fig. 3). Larvae taken in the neuston were generally low in abun- dance and rarely larger than 6 mm, while mid- water concentrations were also generally re- stricted to 0 to 6 mm larvae. Larvae were observed in these levels mainly from December through April. Most white croaker larvae were taken in epibenthic samples, especially late in the spawning season. In contrast to the upper two levels, larvae were relatively abundant from October through June. While small larvae were frequently taken in epibenthic samples during the major spawning months, the epibenthos was generally dominated by larvae in the 3 to 12 mm size range. Larvae >15 mm were rarely taken. Seriphus politus Queenfish, like white croaker, is highly sea- sonal in its spawning habits, with the main spawning period extending from March to Sep- tember (Fig. 4). Significant numbers of larvae were taken in neuston collections only in March and April, and were restricted to 0 to 6 mm size classes. Midwater collections followed a similar trend, although slightly larger larvae persisted through September. The majority of queenfish larvae were taken in epibenthic samples, with numbers of individuals in each size class decreas- ing from 0 to 3 mm through 15 to 18 mm groups. As was observed in white croaker samples, indi- viduals >18 mm were rarely collected. 897 IO2 O 3 6 9 12 15 IB 21 24 •4 27 30 O 3 6 18 21 24 27 30 O 3 6 9 12 15 ?4 27 30 § 10 \ / CO -J p S IO2 ■O 1 * I / ^ IO2 S io JULY TDlh Jimi 1 AUGUST Neuston SEPTEMBER . i;i i ...I I rT-u_ Epibenthic d_ OCTOBER n :j^:La aa 0 3 6 9 12 15 18 18 21 24 27 30 0 3 15 18 21 24 27 30 0 3 6 9 24 27 30 IO2 IO I 103 IO2 10 I IO2 10 I NOVEMBER :lk jsfcf:™) 1 i. DECEMBER JANUARY Lfcaram. : '■■■ ':•: ': : Epibenrhic in FEBRUARY I iJTTSm^ 3 6 9 12 15 18 21 24 27 30 0 3 6 9 12 15 18 21 24 27 30 0 3 6 9 12 15 18 21 24 27 30 0 3 6 9 12 15 18 21 24 27 30 STANDARD LENGTH (mm J FIGURE 2.— Mean monthly concentrations of 10 larval size classes of northern anchovy. Engraulis mordax, in three water column levels, March 1978-February 1979. Each monthly value represents a mean of 4 replicates from each of 4 transects (total replicates = 16). Discussion In preliminary studies near San Onofre from August 1977 through February 1978, signifi- cantly greater numbers of larvae were observed in all three water column levels at night com- pared with daytime collections. Sampling was restricted to nighttime beginning in March 1978. 898 10* 10 I 10* IO I ,o3 IO 10 I IO2 10 I IO* 10 I lot- 10 MARCH B — _ APRIL ~ MAY NO Genyonemus in Somples F'™ ■ m JUNE NO Genyonemus in Samples JiL 9 12 15 IO 21 & 27 30 O 3 6 9 12 15 18 21 24 27 30 O 3 6 9 12 15 18 21 24 27 30 O 3 6 9 12 15 B 21 24 27 30 ^ \ 0.05) based on a x2 test from a 1 : 1 ratio (Table 1 ). This ratio had been previously shown to be con- sistent from 1977 to 1979 in the Damariscotta River (Libby 1981). In analyzing length with time, I was more con- cerned with similarities between the slopes of lines comparing males and females than in dif- -Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. mean length varied daily, the compared length distribution in each sample was less variable. Bartlett's test of homogeneity demonstrated no significant differences between the residual var- iances ( x2 = 3.59, df = 1 , P>0.05). A t-test of sig- nificance of slope (t equals a ratio of the slope to its standard error) applied to the pooled regres- sion coefficient showed that the slope (—0.36) was significantly different from zero (t = 9.36, df = 707, P<0.05). The influx of male and female alewives into the river follows a similar pattern regardless of their size differences. Ages through- out the 1979 and 1980 samples ranged from 3 to 8 yr for 234 males and 3 to 9 yr for 259 females and from 4 to 7 yr for 361 males and 3 to 7 yr for 344 females, respectively. 903 Age distribution from the 1979 and 1980 samples Age: 3 1+5 6 7 8 9 Total 1979 Males 5 134 79 11 4 1 - 234 Females 1 115 116 22 3 1 1 259 1980 Males — 116 221 22 2 — — 361 Females 2 93 211 32 6 — — 344 Age by time regressions for the 1980 data were computed for each sex and an analysis of covari- ance(Table3) revealed no significant differences between the slopes. The pooled regression like the pooled length by time regression, showed a significant slope (—0.02) at the 5% level. These two nonzero slopes (length by time and age by time) are evidence of changes in mean size and mean age throughout this alewife migration. The slope of the length trend (—0.36) is greater and significantly different from the age trend slope (—0.02) at the 5% level. The daily age com- position of alewives moving to their spawning ground is a result of the fish schooling by size. Lengths were separated into respective age categories for both years and regressions were computed of the age-length relation over time for each sex (Fig. 2). This was not done for ages three and seven through nine because of the small sam- ple size. Ages four, five, and six were predomi- nant, constituting over 95% of all the fish in the samples. All regressions produced negative slopes, although regressions A and B in 1979 and C and D in 1980 (Fig. 2) proved their slopes to be nonsignificant from a zero slope. An analysis of covariance applied to all regres- sions in each year showed no significant differ- ences between slopes (Tables 4, 5). Apparently Table 3.— Analysis of covariance of age by time regressions for male and female aiewives and test for nonzero pooled slope. Damariscotta River, 1980. Treatment Regression coefficient df Residual SS Mean square Males -0.016 359 115.755 Females 0021 342 137.007 within 701 252.872 0.36 Pooled ■0.019 702 253.127 Difference between slopes 1 0.365 0.37 Comparison of slopes Test of pooled slope coefficient 'F = SB = 1.01, df = 0.02 SE = 701 2P 0.003 = 0.32 t = B/SE = 7.49 1F test, ratio of mean square of difference between slopes to mean square of difference within slopes. Calculated probability, not significant at the 5% level. 3Pooled slope coefficient. 325 320- 3I5- 3IO — 305 x I- o i2! 300 I979 -2^2!H£I3 N-22 -® 6^ O 295 290 285 280 _i 1_ 15 20 25 30 35 x H o 10 15 20 DAYS 25 30 35 Figure 2.— Regressions of length at age with time from the 1979 and 1980 Damariscotta River alewife fishery. the nonsignificant slopes still contributed to the homogeneity of the combined slopes producing significant 1979 and 1980 pooled regression slopes of —0.24 and —0.21, respectively. These results show, along with the previously observed decrease in length with time and age with time of this alewife migration, that the length of fish at age also decreases with time. The fish that arrive 904 Table 4.— Analysis of covariance of length by time regression by age and sex for alewives and test for nonzero pooled slope. Damariseotta River, 1979. Regression Residual Mean Treatment coefficient df SS square Male age 4 -0.25 132 12,772.315 5 -0.04 77 9.186.425 6 -0.42 9 269.782 Female age 4 -0 29 113 11.810 600 5 -0.35 114 11,923 360 6 -0 08 20 996 642 within 465 46.959 124 100.10 Pooled -0 24 470 47,503000 Difference between slopes 5 543.876 108.7 Comparison of slopes 'F = 1.07, df = 465 2P = 0.63 Test of pooled slope coefficient 3e = f = 0.24 SE = 0.05 B/SE = 4.59 'F test, ratio of mean square of difference between slopes to mean square of difference within slopes. Calculated probability, not significant at the 5% level. 3Pooled slope coefficient. applied to each observed age frequency against the age-length key expected frequency, for each day sampled, indicated no significant differences between observed and expected age frequencies in the 1980 data. The magnitude of this decreas- ing trend in length at age may vary from year to year and stock to stock, but it is present and should be taken into account when investigating a migratory stock of alewives. Acknowledgments I thank David B. Sampson for his help and re- view of this paper, Sherry Collins for her assist- ance in data collecting, and James Rollins for drafting the figures. Literature Cited Table 5.— Analysis of covariance of length by time regres- sions by age and sex and test for nonzero pooled slope. Damari- seotta River, 1980. Regression Residual Mean Treatment coefficient df SS square Male age 4 -0.19 114 7.819.279 5 -0.22 219 10,575.189 6 -0.01 20 835.044 Female age 4 -0.08 91 5.926.716 5 -0.24 210 14,708.805 6 -0.41 30 1,699.554 within 683 41,564.587 60 86 Pooled -0.21 688 41,824 344 Difference between slopes 5 259757 51.95 Comparison of slopes 'F = 0.854, df = 683 2P = 0.49 Test of pooled slope coefficient JB f = -0.21 SE = 0.03 = B/SE = 6.15 'F test, ratio of mean square of difference between slopes to mean square of difference within slopes. Calculated probability, not significant at the 5% level 'Pooled slope coefficient earliest are not only the largest of the migrating stock but also of the age groups. The change in length at age is a source of bias in determining the age composition of the ale- wife harvest if a pooled age-length key were used. Westrheim and Ricker (1978) studied biases connected with application of an age- length key to stocks with different age composi- tions. Using an age-length key derived from pooled length subsamples will introduce bias in computing age composition of an anadromous alewife run. The pooled age-length key assumes homogeneity, but lengths at age change through- out the migration period. Such bias may, how- ever, dwell within the range of acceptable error of 5% of the expected age frequencies. Chi square Cooper, R. A. 1961. Early life history and spawning migration of the alewife (Alosa pseudoharengus). M.S. Thesis, Univ. Rhode Island, Kingston, 58 p. KissiL, G. W. 1974. Spawning of the anadromous alewife, Alosa pseu- doharengus, in Bride Lake, Connecticut. Trans. Am. Fish. Soc. 103:312-317. Libby, D. A. 1981. Difference in sex ratios of the anadromous alewife, Alosa pseudoharengus, between the top and bottom of a fishway at Damariseotta Lake, Maine. Fish. Bull., U.S. 79:207-211. Watson, J. E. 1965. A technique for mounting and storing herring oto- liths. Trans. Am. Fish. Soc. 94:267-286. Westrheim, S. J., and W. E. Ricker. 1978. Bias in using an age-length key to estimate age- frequency distributions. J. Fish. Res. Board Can. 35: 184-189. David A. Libby Department of Marine Resources Marine Resources Laboratory West Boothbay Harbor, ME 04575 905 SEASONAL SPAWNING CYCLE OF THE LONGFIN SANDDAB, CITHARICHTHYS XANTHOSTIGMA (BOTHIDAE) This note contains the first description of the sea- sonal spawning cycle of the longfin sanddab, Citharichthys xanthostigma. This fish is common off southern California, but rare north of Santa Barbara and occurs at depths from 2 to 201 m (Miller and Lea 1976). Methods Fish were collected by otter trawl off the coast of southern California at depths of 45-64 m from San Clemente (lat. 33°20'N, long. 117°38'W) to Huntington Beach (lat. 33°40'N, long. 118°00'W). Collections were made during January-Decem- ber 1978. Only females were examined. Speci- mens were immediately slit along the abdomen and placed in 10% Formalin1. Ovarian histologi- cal sections from 137 C. xanthostigmawere cut at 8 fim and stained with iron hematoxylin. Season- al gonosomatic indices (ovary wt/fish wt X 100) were calculated from preserved fish. Ovaries were classified histologically into four stages (Table 1). Table 1.— Monthly distribution of body sizes (SL) and stages in Citharichthys xanthostigma spawning cycle, January-De- cember 1978. Regressed Previ- Vi- or tello- tello- Spawn- Range regressing genic genic ing Month N (mm) (%) (%) (%) (%) January 12 127-162 8 0 0 92 February 17 107-162 0 6 6 88 April 14 144-190 79 0 0 21 May 17 115-180 82 0 0 18 June 20 110-181 95 0 0 5 July 21 137-210 100 0 0 0 October 18 116-190 44 28 28 0 December 18 115-160 17 17 11 55 Results Most C. xanthostigma spawn in winter (Table 1). At this time the majority of females contain yolk-filled oocytes (>290 Mm in diameter) and gonosomatic indices reach their highest values (Fig. 1). Females were in spawning condition in December. The presence of mature (yolk-filled) 60-| 8 50 5 40- O O ^ 3 0 I 20 o 1 0- 12 I 18 ) 20 17 21 18 rr I I — I 1 1 1 1 1 1 1 — JAN FEB APR MAY JUN JUL OCT DEC Month Figure 1.— Seasonal gonosomatic indices for Citharichthys xanthostigma. Vertical line = range; horizontal line = mean; rectangle = 95% confidence interval. Sample size above each month. oocytes from an incipient spawning, and of post- ovulatory follicles which are remnants of the follicular walls of recently spawned oocytes (Hunter and Goldberg 1980), and of maturing oocytes for a subsequent spawning in the same ovary indicated that C. xanthostigma spawns more than once each season. The number of spawnings per season is unknown, however. Post- ovulatory follicles were similar to those of other teleost fishes (Hunter and Goldberg 1980). The smallest mature ( ripe) female measured 107 mm SL (standard length); the largest, 181 mm SL. Miller and Lea (1976) reported this species may reach 250 mm TL (total length). The incidence of spawning females decreased in spring. At this time most females contained regressed ovaries (Table 1 ) consisting of primary oocytes (53 jum) or regressing ovaries in which oocytes in various stages of vitellogenesis were undergoing atresia. Ovaries from fish taken dur- ing July were regressed, and gonosomatic indices were reduced (Fig. 1). Ovarian activity for the new spawning cycle began during autumn. This was apparent in October (Table 1 ) when previtel- logenic females containing slightly enlarged, vacuolated oocytes (118 jum) and vitellogenic fe- males (yolk deposition in enlarging oocytes) were present. Discussion 'Reference to trade names does not imply endorsement by the National Marine Fisheries Service. NOAA. My data have shown C. xanthostigma is a win- ter spawner in southern California. Spawning 906 FISHERY BULLETIN: VOL. 80. NO. 4, 1982. times in other California flatfishes are variable with a tendency toward winter. Fitch and Laven- berg (1971) reported the following spawning periods: Platichthys stellatus, November-Febru- ary; Microstomus pacificus, November-March; Citharichthys sordidus, July-September; Para- lichthys californicus, February-July. Goldberg (1981) reported summer spawning in Symphurus atricauda and summer-fall spawning (Goldberg 1982) in Hippoglossina stomata. Spawning in Citharichthys stigmaeus occurs April- September (Ford 1965). Pleuronichthys verticalis which was investigated by Fitch (1963) and Goldberg (1982) and Glyptocephalus zachirus which Frey (1971) reported on were in spawning condition through- out the year. Such year-round spawning is un- common among California flatfishes. Acknowledgments I am grateful to M. Heinz and T. Pesich (Or- ange County Sanitation District, Marine Labora- tory) and R. Sewell (Orange County Board of Education, Marine Studies Institute) for assist- ance in obtaining specimens. This study was aided by a Whittier College faculty research grant. Literature Cited Fitch, J. E. 1963. A review of the fishes of the genus Pleuronichthys. Los Ang. Cty. Mus. Contrib. Sci. 76:1-33. Fitch, J. E., and R. J. Lavenberg. 1971. Marine food and game fishes of California. Univ. Calif. Press, Berkeley, 179 p. Ford, R. E. 1965. Distribution, population dynamics and behavior of a bothid flatfish, Citharichthys stigmaeus. Ph.D. The- sis, Univ. Calif., San Diego, 243 p. Frey, H. W. (editor). 1971. California's living marine resources and their utili- zation. Calif. Dep. Fish Game, 148 p. Goldberg, S. R. 1981. Seasonal spawning cycle of the California tongue- fish, Symphurus atricauda (Cynoglossidae). Copeia 1981:472-473. 1982. Seasonal spawning cycles of two California flat- fishes, Pleuronichthys verticalis (Pleuronectidae) and Hippoglossina stomata (Bothidae). Bull. Mar. Sci. 32: 347-350. Hunter, J. R, and S. R. Goldberg. 1980. Spawning incidence and batch fecundity in north- ern anchovy, Engraulis mordax. Fish. Bull., U.S. 77: 641-652. Miller, D. J., and R. N. Lea. 1976. Guide to the coastal marine fishes of California. Calif. Dep. Fish Game, Fish Bull. 157, 249 p. (Rev. publ. by Div. Agric. Sci., Univ. Calif., Richmond). Stephen R. Goldberg Department of Biology Whittier College Wfiittier. CA 90608 OTTER TRAWL SAMPLING BIAS OF THE GILL PARASITE, URONECA VULGARIS (ISOPODA, CYMOTHOIDAE), FROM SANDDAB HOSTS, CITHARICHTHYS SPP. Lironeca vulgaris (Crustacea, Isopoda, Cymo- thoidae) is a common parasite infesting the gill chambers of many marine fish species from the California coast. Both male and female isopods reside in the gill chambers of sanddab hosts. Aspects of the ecology of this parasite and host specificity are given in Brusca (1978, 1981) and Keusink (1979). Both authors discuss the propensity of isopods, particularly males, to abandon hosts in otter trawls, which may cause false host records. Further, if host abandonment occurs during the trawling operation then esti- mates of prevalence (no. of infested hosts/total no. of hosts), relative parasite density (total no. of parasites/total no. of hosts), and mean parasite intensity (total no. of parasites/no. of infested hosts) will be biased. During a study of the inter- actions between L. vulgaris and two sanddab hosts, Citharichthys stigmaeus and C. sordidus, I analyzed the efficiency of traditional otter trawl collecting methods. Prevalence, relative parasite density, and mean parasite intensity were com- pared for samples of a host population gathered by otter trawls and divers utilizing scuba. Methods Speckled sanddabs, Citharichthys stigmaeus, and Pacific sanddabs, C. sordidus, were collected from a site about 0.5 km west of Goleta Point, Santa Barbara County, Calif., just seaward of an extensive bed of giant kelp, Macrocystis pyrifera. The depth was 16 m and the substrate consisted of fine sands and silts with occasional stands of the brown alga, Pterygophora California, and patches of eelgrass, Zostera marina. FISHERY BULLETIN: VOL. 80, NO. 4. 1982. 907 On 6 November 1979, five consecutive otter trawls of 10-min duration each were taken. The 3.7 m otter trawl was equipped with a cod end of 1.8 cm square mesh. Immediately following re- trieval of the catch, sanddabs were sorted and placed in sealed plastic bags. Any L. vulgaris wandering about the catch were also retained. After the last trawl, four scuba divers entered the water and collected sanddabs by hand net, attracting fish with bait (sea urchin roe). Fish were transferred to sealed plastic bags. Speci- mens were collected in this manner for approxi- mately 40 min. All fish and isopods collected by both methods were sexed and measured within the next day. Host sex, total length to the nearest 0.1 cm, and number of parasitic isopods harbored were de- termined. Isopod total length was measured to the nearest 0.1 mm. Isopod sex was determined by several criteria: 1) Differential allometric re- lationship of width to length (Montalenti 1941), 2) presence of penes in males, 3) asymmetry of females, i.e., body twisted to the right or left (Brusca 1978), and 4) presence of oostegites in gravid females. Manca and aegathoid stages (see Brusca 1978) were lumped as juveniles. 15 10 OTTER TRAWL • N = 56 >- O 1 z LU o 15 LU ^^ rip D Uninfested ^ Infested 6 7 8 9 10 12 13 14 SCUBA L N = 73 6 7 8 9 10 11 12 13 14 FISH LENGTH (cm) Results and Discussion Otter trawl catches consisted only of flatfish, and sanddabs comprised most of the catch. Size- frequency histograms for sanddab hosts collected by otter trawls and scuba divers were not signifi- cantly different (Fig. 1, Kolmogorov-Smirnov test, P>0.05). Inspection of these histograms in- dicates that divers are able to sample small fish more efficiently. Consequently, important infor- mation regarding the acquisition of isopod para- sites by young fish may not be obtained when sampling with otter trawls. A comparison of the percent of fish infested with L. vulgaris reveals a highly significant disparity between the two sampling methods. In the trawl, 21 out of 56 hosts (37.5%) were infested versus 54 out of 73 hosts (73.9%) in the diver sample (chi-square = 17.449, P<0.005). Size-frequency histograms for all isopods re- covered by both collecting methods were signifi- cantly different (Fig. 2, Kolmogorov-Smirnov test, P<0.05). If only male isopods were consid- ered, the difference was very significant (P< 0.01) while for female isopods there was no dif- ference (P>0.05). Apparently male L. vulgaris abandon hosts in otter trawls prior to retrieval of Figure 1. — Comparison of size-frequency histograms for Ci- tharickthys spp. collected by otter trawl and divers utilizing scuba. Size distributions of sanddab hosts were similar (Kol- mogorov-Smirnov test, P>0.05) but the percentage of hosts harboring parasitic isopods was significantly different (chi- square test, P<0.005). the catch. This was especially evident for small males (Fisher exact test, P = 0.0057; small males <10.6 mm vs. large males >10.6 mm). Large males may also leave their hosts since a majority of large male isopods were unassociated with hosts in the trawl sample (13 out of 17 males, see Figure 2). In one trawl sample a pod of male iso- pods was found in the cod end indicating that these individuals did not have sufficient oppor- tunity to escape. Female isopods have feeble crawling abilities (Brusca 1978) and do not ap- pear to abandon hosts in trawls. Relative parasite density in the diver sample was significantly higher (1.2 isopods per fish) than otter trawl samples (0.4 isopods per fish) (£-test, P<0.001) as was mean parasite intensity with 1.6 and 1.1 isopods per infested host, respec- tively (f-test, P<0.001). In conclusion, otter trawls consistently under- estimate prevalence, relative parasite density, and mean parasite intensity of L. vulgaris popu- 908 10 > o z LU D o LU OTTER TRAWL N =38 10u n n D Juveniles E3 dd on Fish □ Unattached dd ^ no on Fish H Unattached ^ nn 3.4 6.6 9.8 t 13.0 16.2 19.4 SCUBA N = 85 5- n 6.6 9.8 13.0 16.2 ISOPOD LENGTH (mm) 19.4 M.A. Thesis, San .lose State Univ., San Jose, Calif. MONTALENTI, G. 1941. Studi sull' ermafroditismo dei Cimotoidi. — I. Emetka audouinii (M, Edw.) e Anilocra physodes (L.). Publ. Stn. Zool. Napoli 18:337-394. Gary R. Robinson Department of Biological Sciences I diversity of ( 'alifornia Santa Barbara, Calif. Present address: Charles Darwin Research Station Santa Cruz lata ml, Galapagos Casilla 58-39, Guayaquil, Ecuador Figure 2.— Comparison of size-frequency histograms for the gill parasite, Lironeca vulgaris, from sanddab hosts collected by otter trawl and scuba divers. Size distributions of isopods were significantly different between the two samples (Kolmo- gorov-Smirnov test, P<0.05). Small male isopods were notably absent and several isopods were unattached to sanddab hosts in the otter trawl sample. lations on C. stigmaeus and C. sordidus. This bias is caused by the abandonment of hosts, particu- larly by small male isopods. Shorter trawling times may reduce the amount of bias. However, when accuracy is desired, scuba is the preferred sampling method. Acknowledgments S. Anderson, D. Richardson, B. Harman, and S. Karl Kindly provided diving and trawling assistance. A. Kuris, R. Warner, G. Wellington, B. Victor, and M. Schildhaeur provided valuable comments on the manuscript. Literature Cited Brusca, R. C. 1978. Studies on the cy mothoid fish symbionts of the east- ern Pacific (Crustacea: Cymothoidae). II. Systematics and biology of Lironeca vulgaris Stimpson 1857. Occas. Pap. Allan Hancock Found., New Ser. 2:1-19. 1981. A monograph on the Isopoda Cymothoidae (Crus- tacea) of the eastern Pacific. Zool. J. Linn. Soc. Lond. 73:117-199. Keusink, C. 1979. Biology and natural history of the fish parasite Lironeca vulgaris (Crustacea: Isopoda: Cymothoidae). 909 INDEX Fishery Bulletin Vol. 80, 1- 1 Acipenser oxyrhynchus—see Sturgeon, Atlantic Acipenser transmontanus — see Sturgeon, white Aerial surveys for manatees and dolphins in western peninsular Florida, by A. Blair Irvine, John E. Caffin, and Howard I. Kochman 621 Africa, northwest upwelling ecosystem regeneration of nitrogen by nekton 327 Age and growth of a pleuronectid, Parophrys vetulus, during the pelagic larval period in Oregon coastal waters, by Joanne Lyczkowski Laroche, Sally L. Richardson, and Andrew A. Rosenberg 93 Age and growth of larval Atlantic herring, Clupea harengus L., in the Gulf of Maine-Georges Bank region based on otolith growth increments, by R. Gregory Lough, Michael Pennington, George R. Bolz, and Andrew A. Rosenberg 187 AINLEY. DAVID G., HARRIET R. HUBER, and KEVIN M. BAILEY. Population fluctuations of Cali- fornia sea lions and the Pacific whiting fishery off cen- tral California 253 Alewife decrease in length at predominant ages during spawning migration 902 ALL MOHAMMED LIAQUAT-see ULANOWICZ et al. ALLEN, LARRY G., Seasonal abundance, composi- tion, and productivity of the littoral fish assemblage in upper Newport Bay, California 769 Alosa pseudoharengus — see Alewife Analysis of double-tagging experiments, by Jerry A. Wetherall 687 Anarrhichthys ocellatus — see Eel, wolf Anchovy, northern vertical stratification off southern California 895 ANGER, KLAUS, and RALPH R. DAWIRS, Ele- mental composition (C, N, H) and energy in growing and starving larvae of Hyas araneus (Decapoda. Majidae) 419 Antarctic Peninsula feeding ecology of some fishes 575 Arctica islandica—see Quahog, ocean Argonata sp. association between, and aggregate salps 648 ARNOLD, CONNIE R.-see HOLT and ARNOLD Ascelickthys rhodorus—see Sculpin, rosylip (An) association between a pelagic octopod, Argonauta sp. Linnaeus 1758, and aggregate salps, by P. T. Banas. D. E. Smith, and D. C. Biggs 648 Atlantic Bight, Middle ocean quahog growth 21 Atlantic, northwest zooplankton effect of season and location on relationship be- tween displacement volume and dry weight 631 Atlantic, western North whale, humpback feeding behavior 259 Atlantic Bight, South porgy, whitebone biology 863 Atlantic Ocean, western tuna, bluefin reproductive biology 121 (The) Atlantic sturgeon, Acipenser oxyrhynchus, in the Delaware River estuary, by Harold M. Brundage III and Robert E. Meadows 337 AU, D., and W. PERRYMAN. Movement and speed of dolphin schools responding to an approaching ship 371 Australia Gulf of Carpentaria effect of vertical migration on dispersal of penaeid shrimp larvae 541 Australia, Western lobster, rock stock and recruitment relationships 475 Avoidance of towed nets by the euphausiid Nematosce- lis megalops, by P. H. Wiebe, S. H. Boyd, B. M. Davis, and J. L. Cox 75 BABINCHAK, JOHN A.. DANIEL GOLDMINTZ. and GARY P. RICHARDS, A comparative study of autochthonous bacterial flora on the gills of the blue crab, Call i in eti s sapid us. and its environment 884 BAGLIN, RAYMOND E., JR.. Reproductive biology 911 of western Atlantic bluefin tuna 121 BAGLIVO, JENNY A. -see BROUSSEAU et al. BAILEY, KEVIN M., The early life history of the Pacific hake, Merluccius productus 589 BAILEY, KEVIN M.-see AINLEY et al. BANAS, P. T.. D. E. SMITH, and D. C. BIGGS, An association between a pelagic octopod, Argonauta sp. Linnaeus 1758, and aggregate salps 648 BARANS, CHARLES A.— see MANOOCH and BARANS BARSS, W. H.-see BOEHLERT et al. Bass, striped bioenergetics and growth of embryos and larvae energy inputs 462, 463, 467 energy outputs 463, 464, 470 utilization efficiency 467 effects of long-term mercury exposure on hematol- ogy 389 BATH, D. W., and J. M. O'CONNOR, The biology of the white perch, Morone americana, in the Hudson River estuary 599 BEACHAM, TERRY D., and PAUL STARR. Popu- lation biology of chum salmon, Oncorhynchus keta, from the Fraser River, British Columbia 813 (A) beak key for eight eastern tropical Pacific cephalo- pod species with relationships between their beak dimensions and size, by Gary A. Wolff 357 BIGGS, D. C— see BANAS et al. (The) biology of the white perch, Morone americana, in the Hudson River estuary, by D. W. Bath and J. M. O'Connor 599 Biology of the whitebone porgy, Calamus leucosteus, in the South Atlantic Bight, by C. Wayne Waltz, William A. Roumillat, and Charles A. Wenner 863 Bioenergetics and growth of striped bass, Morone saxa- tilis, embryos and larvae, by Maxwell B. Eldridge, Jeannette A. Whipple, and Michael J. Bowers 461 Biscayne Bay, Florida interrelation of water quality, gill parasites, and gill pathology of some fishes 269 BLAXTER, J. H. S.-see COLBY et al. BOEHLERT, GEORGE W., W. H. BARSS, and P. B. LAMBERSON, Fecundity of the widow rockfish, Sebastes entomelas, off the coast of Oregon 881 BOLZ, GEORGE R.-see LOUGH et al. Bonnethead swimming kinematics 803 912 BOTSFORD, LOUIS W., RICHARD D. METHOT, JR., and JAMES E. WILEN, Cyclic covariation in the California king salmon, Oncorhynchus tshawytscha, silver salmon, O. kisutch, and Dungeness crab, Cancer magister, fisheries 791 BOWERS, MICHAEL J. -see ELDRIDGE et al. BOYD, S. H.— see WIEBE et al. British Columbia salmon, chum population biology, Fraser River 813 BRODEUR, RICHARD D.— see PETERSON et al. BROUSSEAU, DIANE J., JENNY A. BAGLIVO, and GEORGE E. LANG, JR., Estimation of equilibrium settlement rates for benthic marine invertebrates: Its application to Mya arenaria (Mollusca: Pelecynoda) . 642 BRUNDAGE, HAROLD M.. Ill, and ROBERT E. MEADOWS, The Atlantic sturgeon, Acipenser oxyrhynchus, in the Delaware River estuary 337 BURGESS, LOURDES ALVINA, Four new species of squid (Oegopsida: Enoploteuthis) from the central Pacific and a description of adult Enoploteuthis retic- ulata 703 CAFFIN, JOHN E.-see IRVINE et al. Calamus leucosteus— see Porgy, whitebone California, central sea lion, California population fluctuations and Pacific whiting fishery 253 California, southern croaker, white development of eggs and larvae off coast 403 Newport Bay seasonal abundance, composition, and productivity of littoral fish assemblage 769 salmon, coho phenotypic differences among hatchery and wild stocks 105 shark, white predation on pinnipeds in coastal waters 891 vertical stratification of nearshore larval fishes anchovy, northern 895 croaker, white 895 cjueenfish 895 Callinectes sapid it* — see Crab, blue Cancer magister— see Crab, Dungeness ( 'archarhinus leucas—see Shark, bull Carcharhinus melanopterus — see Shark, Pacific black- tip Carcharodon carcharias — see Shark, white CAREY. A. ('... JR.— see HOGUE and CAREY CARTER. GARY R.— see HAIN ct al. CASEY. JOHN G.— see PRATT et al. Cephalopods Pacific, eastern tropical beak key with relationships between beak dimen- sions and size 357 Cetaceans tagging techniques for small cetaceans freeze brands 137, 140 natural marks 139, 140 radio tags 136, 139 Roto tags 140 spaghetti tags 139, 140 visual tags 136, 140 CHESTER, ALEXANDER J.— see HETTLER and CHESTER CHITTENDEN. MARK E.. JR.-see DeVRIES and CHITTENDEN; GEOGHEGAN and CHITTENDEN Citkarickthys cornutus larval development and occurrence cephalic spination 47 characters, distinguishing 39 counts 37 developmental terminology 37 fin and axial skeleton formation 44 identification 38, 39 morphometries 37, 41 occurrence 47 pigmentation 40 specimens 36 teeth 47 transformation 47 Citkarickthys gymnorkinus larval development and occurrence cephalic spination 56 characters, distinguishing 51 counts 37 developmental terminology 37 fin and axial skeleton formation 54 identification 38. 51 morphometries 37, 54 occurrence 56 pigmentation 51 specimens 36 teeth 56 transformation 56 Citkarickthys spilopterus larval development and occurrence cephalic spination 62 characters, distinguishing 57 counts 37 developmental terminology 37 fin and axial skeleton formation 61 identification 38, 57 morphometries 37, 59 occurrence 62 pigmental ion specimens teeth transformation Citkarickthys xanthostigma—see Sanddab, longfin CLARKE. THOMAS A.. Feeding habits of stomi- atoid fishes from Hawaiian waters 57 36 62 62 287 CLIFFORD, DAVID A.-see CREASER and CLIFFORD Clupea harengus—see Herring. Atlantic Cod. Atlantic diet overlap between, and other northwest Atlantic finfish butterfish 749 flounder, fourspot 751 flounder, witch 751 flounder, yellowtail 751 haddock 751 hake, red 749 hake, spotted 749 hake, silver 754 hake, white 749 plaice, American 751 pollock 749 pout, ocean 751 redfish 747 sculpin, longhorn 747 scup 749 skate, little 746 COLBY. DAVID R.. DONALD E. HOSS. and J. H. S. BLAXTER. Pressure sensitivity of Atlantic herring, Clupea harengus L., larvae 567 COLIN, PATRICK L.. Spawning and larval develop- ment of the hogfish, Lachnolaimus maximus (Pisces: Labridae) 853 Columbia River Hanford. Washington snout dimorphism in white sturgeon 158 (A) comparative study of autochthonous bacterial flora on the gills of the blue crab, Callinectes sapidus, and its environment, by John A. Babinchak, Daniel Gold- mintz, and Gary P. Richards 884 CONKLIN, ROBERT B.-see PRATT et al. CONNALLY, DAVID W.— see SCHLOTTERBECK and CONNALLY CONOVER, DAVID O., and STEVEN A. MURAW- SKI. Offshore winter migration of the Atlantic silver- side, Menidia menidia COX, J. L.— see WIEBE et al. Crab, blue comparative study of autochthonous bacterial flora on gills and environment 145 884 913 Crab, Dungeness cyclic covariation in California fisheries California, central, total catch 795 California, northern catch by salmon species 794 total catch 793 switching effort between species 796 Crab, golden king larval description comparison of larval stages with descriptions by other authors 312 stage I zoea 305 stage II zoea 308 stage III zoea 309 stage IV zoea 309 stage V (glaucothoe) 310 Crab, spider elemental composition and energy in growing and starving larvae biomass loss during starvation growth Crab — see also Cyclograpsus integer 427 420 CRASS, DENNIS W., and ROBERT H. GRAY, Snout dimorphism in white sturgeon, Acipenser trans- montanus, from the Columbia River at Hanford, Washington 158 CREASER, EDWIN P.. and DAVID A. CLIFFORD, Life history studies of the sandworm. Nereis virens Sars, in the Sheepscot Estuary, Maine 735 Croaker, white eggs and larvae off southern California coast comparison with similar species 413 distribution 415 embryonic development 404 fin development 410 head spination 411 ossification 411 pigmentation 407 proportions 413 yolk-sac larvae morphology 407 yolk-sac larvae pigmentation 405 vertical stratification off southern California 895 Cyclic covariation in the California king salmon, Oncorhynchus tshawytscha, silver salmon, O. kisutch, and Dungeness crab, Cancer magister, fisheries, by Louis W. Botsford, Richard D. Methot, Jr., and James E. Wilcn 791 Cyclograpsus integer H. Milne Edwards, 1S37 (Brachyura, Grapsidae): The complete larval develop- ment in the laboratory, with notes on larvae of the genus Cyclograpsus, by Robert H. Gore and Liberta E. Scotto 501 Cyclograpsus integer larval development in laboratory fifth zoea (penultimate) 511 fifth zoea (ultimate) 511 first zoea 504 fourth zoea 508 megalopa 513 rearing experiment results 502 second zoea 505 sixth zoea 513 third zoea 508 Cynoscion nothussee Seatrout, silver DANIELS, ROBERT A.. Feeding ecology of some fishes of the Antarctic Peninsula 575 DAVIS, B. M.-see WIEBE et al. DAWIRS. RALPH R.-see ANGER and DAWIRS DAWSON, MARGARET A., Effects of long-term mercury exposure on hematology of striped bass, Morone sitxutilis 389 DEAN, J. M.— see RADTKE and DEAN Decrease in length at predominant ages during a spawning migration of the alewife, Alosa pseudoharen- gus, by David A. Libby 902 Delaware Rivet- Atlantic sturgeon in estuary 337 Description of larvae of the golden king crab, Lithodes aequispina, reared in the laboratory, by Evan Haynes 305 Development and application of an objective method for classifying long-finned squid, Loligo pealei, into sexual maturity stages, by William K. Macy III 449 Development of eggs and larvae of the white croaker, Genyonem us litieatiis Ayres (Pisces: Sciaenidae), off the southern California coast, by William Watson 403 Development of the vertebral column, fins and fin sup- ports, branchiostegal rays, and squamation in the swordfish, Xiphias gladius, by Thomas Potthoff and Sharon Kelley 161 DeVRIES, DOUGLAS A., and MARK E. CHITTEN- DEN, JR., Spawning, age determination, longevity, and mortality of the silver seatrout, Cynoscion nothus, in the Gulf of Mexico 487 Diet overlap between Atlantic cod. (hid its morhua, silver hake, Merluccius bilinearis, and fifteen other northwest Atlantic finfish, by Richard W. Langton . 745 Distribution, abundance, and age and growth of the tomtate, Haemulon aurolineatum, along the south- eastern United States coast, by Charles S. Manooch III and Charles A. Barans 1 DIZON, ANDREW E.-see KAYA et al. Dolphin, bottlenose Florida, western peninsular aerial surveys 621 914 Dolphin mortality estimating and monitoring incidental in eastern tropical Pacific combined kill-pcr-day and kill-per-ton method... 398 estimation procedures 397 kill-per-day method 397 kill-per-set method 399 Dolphin schools movement and speed, responding to an approaching ship school speed 376 swimming behavior and school structure 377 vessel avoidance 373 (The) early life history of the Pacific hake, Merluccius productus, by Kevin M. Bailey 589 Eel, wolf migration from Port Hardy, British Columbia, to Willapa Bay, Washington 650 (The) effect of protease inhibitors on proteolysis in parasitized Pacific whiting, Merluccius productus, muscle, by Ruth Miller and John Spinelli 281 Effect of season and location on the relationship be- tween zooplankton displacement volume and dry weight in the northwest Atlantic, by Joseph Kane . . 631 Effects of long-term mercury exposure on hematology of striped bass, Morone saxatilis, by Margaret A. Dawson 389 ELDRIDGE, MAXWELL B.. JEANNETTE A. WHIPPLE, and MICHAEL J. BOWERS, Bioener- getics and growth of striped bass, Morone saxatilis, embryos and larvae 461 Elemental composition (C, N, H) and energy ingrowing and starving larvae of Hycis araneus (Decapoda, Maji- dae), by Klaus Anger and Ralph R. Dawirs 419 Engraulis mordax—see Anchovy, northern Enoploteuthis spp. — see Squid Estimating and monitoring incidental dolphin mor- tality in the eastern tropical Pacific tuna purse seine fishery, by Nancy C. H. Lo, Joseph E. Powers, and Bruce E. Wahlen 396 Estimation of equilibrium settlement rates for benthic marine invertebrates: Its application to Mya urinaria (Mollusca: Pelecynoda), by Diane J. Brousseau, Jenny A. Baglivo, and George E. Lang, Jr 642 Etropus crossotus larval development and occurrence cephalic spination 67 characters, distinguishing 63 counts 37 development terminology 37 fin and axial skeleton formation 67 identification 38, 62 morphometries 37, 64 occurrence 67 pigmentation 63 specimens 36 teeth 67 transformation 67 Eubalaena glacialis — see Whale, right (An) evaluation of techniques for tagging small odontocete cetaceans, by A. B. Irvine, R. S. Wells, and M. D. Scott 135 Fecundity of the widow rockfish, Sebastes entomelas, off the coast of Oregon, by George W. Boehlert, W. H. Barss, and P. B. Lamberson 881 Feeding behavior of the humpback whale, Megaptera novaeangliae, in the western North Atlantic, by- James H. W. Hain. Gary R. Carter, Scott D. Kraus, Charles A. Mayo, and Howard E. Winn 259 Feeding ecology of 0-age flatfishes at a nursery ground on the Oregon coast, by E. W. Hogue and A. G. Carey, Jr 555 Feeding ecology of some fishes of the Antarctic Penin- sula, by Robert A. Daniels 575 Feeding habits of stomiatoid fishes from Hawaiian waters, by Thomas A. Clarke 287 Finfish, northwest Atlantic diet overlap between Atlantic cod 745 silver hake 745 Fish Maryland commercial landings identifying climatic factors influencing 611 Fish assemblage, littoral seasonal abundance, composition, and productivity in upper Newport Bay, California abiotic factors, influence 786 catch, total 774 cluster analysis and canonical correlation 773 composition, diversity, and seasonal dynamics . . . 784 cumulative species curve 773, 774 diversity 773 production estimation 771 productivity 779 relationship of abiotic factors to fish abundance and distribution 783 sampling procedures 771 seasonal abundance and diversity 777 species associations 777, 785 species densities and productivity 785 study area 770 temperature and salinity patterns 773 Fish muscle trimethvlamine estimation 157 915 Fishery, deep-sea handline multispecies analysis of commercial, in Hawaii aggregation effects 444 clustering 439 data sources and fishery description 436 fishing effort 438, 440, 443 stock production analyses 441 Fishes Biscayne Bay, Florida interrelation of water quality, gill parasites, and gill pathology 269 feeding ecology along Antarctic Peninsula dietary similarity 583 diets 579 feeding behaviors 578 study area 575 nutrient requirements, qualitative and quantitative amino acid availability 659 ascorbic acid 669 biotin 672 calcium 676 calcium-to-phosphorus ratios 676 carbohydrates 665 choline 671 copper 677 cyanocobalamin 671 fatty acids, essential 663 folic acid 671 inositol 672 iodine 678 iron 677 lysine 660 magnesium 676 manganese 677 methionine 660 niacin 668 optimal dietary lipid concentrations and protein- to-energy ratios 661 pantothenic acid 668 phosphorus 676 protein 656 pyridoxine 667 ribloflavin 667 selenium 678 thiamine 666 tryptophan 661 vitamin A 673 vitamin D 673 vitamin E 674 vitamin K 675 zinc 677 stomiatoid, feeding habits in Hawaiian waters Astronesthidae 294 Chauliodontidae 294 Gonostomatidae 292 Idiacanthidae 296 Malacosteidae 298 Melanostomiatidae 296 Photichthyidae 291 Sternoptychidae 292 Flatfishes Oregon coast feeding ecology of 0-age at nursery ground 555 Food habits of juvenile salmon in the Oregon coastal zone, June 1979, by William T. Peterson, Richard D. Brodeur, and William G. Pearcy Four new species of squid (Oegospsida: Enoploteuthis) from the central Pacific and a description of adult Eno- ploteuthis reticulata, by Lourdes Alvina Burgess . . . Fundulus heteroclitus—see Mummichog Gadus morhua—see Cod, Atlantic Genyonemus lineatus — see Croaker, white GEOGHEGAN, PAUL, and MARK E. CHITTEN- DEN, JR., Reproduction, movements, and population dynamics of the longspine porgy, Stenotomus cap- Georgia., Strait of herring fishery case history of timely management aided by hydro- acoustic surveys GIBSON, D. M., A note on the estimation of trimethy- lamine in fish muscle Ginglymostoma cirratum — see Shark, nurse GOLDBERG, STEPHEN R., Seasonal spawning cycle of the longfin sanddab, Citharichthys xantho- stigma (Bothidae) GOLDMINTZ, DANIEL— see BABINCHAK et al. GORE, ROBERT H., and LIBERTA E. SCOTTO, Cyclograpsus integer rl. Milne Edwards, 1837(Brachy- ura, Grapsidae): The complete larval development in the laboratory, with notes on larvae of the genus Cyclo- grapsus GRAY. ROBERT H.-see CRASS et al. 841 703 523 381 157 906 501 Growth during metamorphosis of English sole, Paro- phrys vetulus, by Andrew A. Rosenberg and Joanne Lyczkowski Laroche 150 Growth of juvenile English sole, Parophrys vetulus, in estuarine and open coastal nursery grounds, by Andrew A. Rosenberg 245 Growth of juvenile red snapper, Lutjanus campecha- nus, in the northwestern Gulf of Mexico, by Scott A. Holt and Connie R. Arnold 644 Growth of the ocean quahog, Arctica islandica, in the Middle Atlantic Bight, by Steven A. Murawski, John W. Ropes, and Fredric M. Serchuk 21 Gulf of Carpentaria, Australia shrimp larvae, penaeid effect of vertical migration on dispersal 541 Gulf of Mexico seatrout, silver 916 spawning, age determination, longevity, and mortality 487 snapper, red growth of juvenile 644 Haemulon aurolineatum — see Tomtate HAIN. JAMES H. W., GARY R. CARTER, SCOTT D. KRAUS, CHARLES A. MAYO, and HOWARD E. WINN, Feeding behavior of the humpback whale, Megaptera novaeangliae, in the western North Atlantic 259 Hake, Pacific early life history development and growth 589 development times 591 growth rates 591 metabolic rates 590, 593 vertical distribution 590, 593 Hake, silver diet overlap, between other northwest Atlantic finfish butterfish 754 cod, Atlantic 754 flounder, fourspot 757 flounder, witch 756 flounder, yellowtail 757 haddock 754 hake, red 754 hake, spotted 754 hake, white 754 plaice, American 756 pollock 754 pout, ocean 756 redfish 752 sculpin, longhorn 752 scup 754 skate, little 751 Hanford, Washington Columbia River snout dimorphism in white sturgeon 158 Hawaii fishery, deep-sea handline multispecies analysis, commercial 435 fishes, stomiatoid feeding habits 287 HAYNES, EVAN, Description of larvae of the golden king crab. Lithodes aequispina, reared in the laboratory 305 HEINLE. DONALD R.-see ULANOWICZ et al. Hem itripterus a merican us trophic patterns among larvae in estuary 827 HENDRIX, SHARON D.-see KAYA et al. Herring, Atlantic age and growth of larval based on otolith growth increments growth curve compared with other field studies . 196 laboratory-reared larvae 191 larval growth 194 otolith growth 192 pressure sensitivity 567 Herring fishery Strait of Georgia, timely management acoustic survey equipment and methods 382 catch records 384 1976-79 surveys 384-386 spawning ground surveys 384 trawling procedures, midwater 383 HETTLER, WILLIAM F., and ALEXANDER J. CHESTER, The relationship of winter temperature and spring landings of pink shrimp, Penaeus duo- rarum, in North Carolina 761 HJORT, R. C, and C. B. SCHRECK, Phenotypic dif- ferences among stocks of hatchery and wild coho salm- on, Oneorhynehu* kisutch, in Oregon, Washington, and California 105 Hogfish courtship and spawning observations 853 egg and larval development 858 egg collection and rearing 854 spawning behavior 855 spawning groups of L. maximus 855 study site 854 time and conditions of spawning 855 HOGUE. E. W.. and A. G. CAREY, JR.. Feeding ecology of 0-age flatfishes at a nursery ground on the Oregon coast 555 HOLT, SCOTT A., and CONNIE R. ARNOLD. Growth of juvenile red snapper, Lutjanus campecha- nus, in the northwestern Gulf of Mexico 644 HOSS, DONALD E.-see COLBY et al. HUBER. HARRIET R.-see AINLEY et al. Hudson River estuary perch, white biology Hyas araneus—see Crab, spider 599 Identifying climatic factors influencing commercial fish and shellfish landings in Maryland, by Robert E. Ulanowicz, Mohammed Liaquat Ali, Alice Vivian, Donald R. Heinle, William A. Richkus, and J. Kevin Summers 611 Increment formation in the otoliths of embryos, larvae, and juveniles of the mummichog, Fundulus hetcro- clitus, by R. L. Radtke and J. M. Dean 201 (The) interrelation of water quality, gill parasites, and gill pathology of some fishes from south Biscayne Bay, Florida, by Renate H. Skinner 269 917 Invertebrates benthic marine equilibrium settlement rates 642 IRVINE. A. B., R. S. WELLS, and M. D. SCOTT, An evaluation of techniques for tagging small odontocete cetaceans 135 IRVINE, A. BLAIR, JOHN E. CAFFIN, and HOWARD I. KOCHMAN, Aerial surveys for man- atees and dolphins in western peninsular Florida .... 621 JOLL, L. M.-see MORGAN et al. JOYCE, GERALD G., JOHN V. ROSAPEPE. and JUNROKU OGASAWARA, White Dall's porpoise sighted in the North Pacific 401 KANE, JOSEPH, Effect of season and location on the relationship between zooplankton displacement vol- ume and dry weight in the northwest Atlantic 631 Katsuwonus pelamis — see Tuna, skipjack KAYA, CALVIN M., ANDREW E. DIZON, SHARON D. HENDRIX, THOMAS K. KAZAMA, and MAR- TINA K. K. QUEENTH, Rapid and spontaneous maturation, ovulation, and spawning of ova by newly captured skipjack tuna, Katsuwonus pelamis 393 KAZAMA, THOMAS K.-see KAYA et al. KELLEY, SHARON-see POTTHOFF and KELLEY KEYES, RAYMOND S.— see LE BOEUF et al; WEBB and KEYES KNIGHT. MARGARET, and MAKOTO OMORI, The larval development of Sergestes similis Hansen (Crustacea, Decapoda, Sergestidae) reared in the lab- oratory 217 KOCHMAN, HOWARD I.— see IRVINE et al. KRAUS, SCOTT D.-see HAIN et al. Lachnolaimus maximus — see Hogfish LAMBERSON, P. B.-see BOEHLERT et al. LANG, GEORGE E.. JR.-see BROUSSEAU et al. LANGTON, RICHARD W., Diet overlap between Atlantic cod, Gadus morkua, silver hake, Merluccius bilinearis, and fifteen other northwest Atlantic fin- fish 745 LAROCHE. JOANNE LYCZKOWSKI, Trophic pat- terns among larvae of five species of sculpins (Family: Cottidae) in a Maine estuary 827 LAROCHE, JOANNE LYCZKOWSKI, SALLY L. RICHARDSON, and ANDREW A. ROSENBERG, Age and growth of a pleuronectid, Parophrys vetulus, during the pelagic larval period in Oregon coastal waters LAROCHE, JOANNE LYCZKOWSKI- BERG and LAROCHE -see ROSEN- Larval development of Citharickthys cornutus, C. gym- norhinus, C. spilopterus, and Etropus crossotus (Bothi- dae). with notes on larval occurrence, by John W. Tucker, Jr Larval develoment of laboratory-reared rosylip scul- pin, Asceliehthys rhodorus (Cottidae), by Ann C. Matarese and Jeffrey B. Marliave (The) larval development of Sergestes similis Hansen (Crustacea, Decapoda, Sergestidae) reared in the lab- oratory, by Margaret Knight and Makoto Omori . . . 93 35 345 217 LE BOEUF. BURNEY J.. MARIANNE RIEDMAN. and RAYMOND S. KEYES, White shark predation on pinnipeds in California coastal waters 891 LEMBERG, NORMAN A. -see TRUMBLE et al. LIBBY, DAVID A., Decrease in length at predomi- nant ages during a spawning migration of the alewife, Alosa pseudoharengus 902 Life history studies of the sandworm. Nereis virens Sars. in the Sheepscot Estuary. Maine, by Edwin P. Creaser and David A. Clifford 735 Lironeca vulgaris otter trawl sampling bias of. from sanddab host . . . 907 Lithodes aequispina — see Crab, golden king LO, NANCY C. H.. JOSEPH E. POWERS, and BRUCE E. WAHLEN, Estimating and monitoring incidental dolphin mortality in the eastern tropical Pacific tuna purse seine fishery 396 Lobster, rock stock and recruitment relationships in Western Australia breeding stock 478 breeding stock abundance 476 index of abundance of spawning stock 478 juvenile abundance 477, 480 juvenile densities and recruitment to the fishery . 482 puerulus and juvenile densities 481 puerulus settlement and subsequent spawning stock 482 puerulus stage abundance 477, 480 recruits to fishery abundance 477, 480 spawning stock and puerulus settlement 480 stock definition 477 Loligo pealei — see Squid, long-finned Long Island, New York shark, white, observations off 153 LOUGH. R. GREGORY, MICHAEL PENNINGTON, 918 GEORGE R. BOLZ.and ANDREW A. ROSENBERG, Age and growth of larval Atlantic herring, ('lupin karengus L.. in the Gulf of Maine-Georges Bank region based on otolith growth increments Lutjanus campechanus—see Snapper, red 187 MACY. WILLIAM K.. III. Development and appli- cation of an objective method for classifying long- finned squid, Loligo pealei, into sexual maturity stages 449 Maine sculp ins trophic patterns among larvae of five species in an estuary 827 Sheepscot Estuary sandworm, life history studies 735 Manatee, West Indian Florida, western peninsular aerial surveys 621 MANN. ROGER. The seasonal cycle of gonadal development in Arctica islandica from the Southern New England shelf 315 MANOOCH, CHARLES S.. III. and CHARLES A. BARANS, Distribution, abundance, and age and growth of the tomtate, Haemulon aurolineatum, along the southeastern United States coast 1 MARLIAVE-see MATARESE and MARLIAVE Maryland fish and shellfish commercial landings climatic factors 611 Massachusetts whales, right Cape Cod waters 875 MATARESE, ANN C, and JEFFREY B. MARLI- AVE, Larval development of laboratory-reared rosylip sculpin, Ascelichthys rhodorus (Cottidae) 345 MAYO, CHARLES A.— see HAIN et al. MEADOWS. ROBERT E.— see BRUNDAGE and MEADOWS Megaptera novaeangliae—see Whale, humpback M, nidia menidia—see Silverside, Atlantic Mercury exposure bass, striped effects of long-term on hematology 389 Merluccius bilinearis—see Hake, silver Merluccius product us— see Hake, Pacific: Whiting, Pacific METHOT. RICHARD D.. JR. -see BOTSFORD et al. Migration of a juvenile wolf eel, Anarrhichthys ocel- latus, from Port Hardy. British Columbia, to Willapa Bay. Washington, by David R. Miller 650 MILLER. DAVID R.. Migration of a juvenile wolf eel, Anarrhichthys ocellatus, from Port Hardy. British Columbia, to Willapa Bay, Washington 650 MILLER. RUTH, and JOHN SPINELLI, The effect of protease inhibitors on proteolysis in parasitized Pacific whiting. Merluccius productus, muscle 281 MILLIKIN. MARK R., Qualitative and quantitative nutrient requirements of fishes: A review 655 MORGAN. G. R., B. F. PHILLIPS, and L. M. JOLL. Stock and recruitment relationships in Panulirus chunks, the commercial rock (spiny) lobster of Western Australia 475 Morone americana—see Perch, white Moron* saxatilis—see Bass, striped Movement and speed of dolphin schools responding to an approaching ship, by D. Au and W. Perryman . . 371 (A) multispecies analysis of the commercial deep-sea handline fishery in Hawaii, by Stephen Ralston and Jeffrey J. Polovina 435 Mummichog otolith increment formation age estimation of wild fish 210, 213 effect of temperature and body growth on otolith formation 210, 213 embryological formation 204, 206, 211 light effect on increment formation 206, 212 removal, preparation, and inspection 204 MURAWSKI, STEVEN A., JOHN W. ROPES, and FREDRIC M. SERCHUK, Growth of the ocean qua- hog, Arctica islandica, in the Middle Atlantic Bight . 21 MURAWSKI, STEVEN A. -see CONOVER and MURAWSKI Mi/a armaria equilibrium settlement rate estimation 642 Myoxocephalus aenaeus trophic patterns among larvae in estuary 827 Myoxocephalus octodecemspinosus trophic patterns among larvae in estuary 827 Myoxoceph a I us scorpi us trophic patterns among larvae in estuary 827 Negaprion brevirostris—see Shark, lemon Nekton regeneration of nitrogen in northwest Africa up- welling system excretion measurements 329 919 nekton biomass 331 regeneration rates 332 Nematoscelis megalops avoidance of towed nets 75 Nereis virens — see Sandworm North Carolina shrimp, pink relationship of winter temperature and spring landings 761 (A) note on the estimation of trimethylamine in fish muscle, by D. M. Gibson 157 Observations of right whales, Eubalaena glacialis, in Cape Cod waters, by William A. Watkinsand William E. Schevill 875 Observations on large white sharks, Carckarodon carcharias, off Long Island, New York, by Harold L. Pratt, Jr., John G. Casey, and Robert B. Conklin 153 Offshore winter migration of the Atlantic silverside, Menidia menidia, by David 0. Conover and Steven A. Murawski 145 OGASAWARA, JUNROKU-see JOYCE et al. OMORI, MAKOTO-see KNIGHT and OMORI Oncorhynchus kctn—see Salmon, chum Oncorhynchus kisutch—see Salmon, coho; Salmon, silver Oncorhynchus tshawytscha—see Salmon, chinook; Salmon, king Oregon flatfishes feeding ecology of O-age at nursery ground 555 rockfish, widow fecundity off coast 881 salmon, coho phenotypic differences among hatchery and wild stocks 105 salmon, juvenile food habits in coastal zone, June 1979 841 sole, English growth during metamorphosis 150 Otter trawl sampling bias of the gill parasite, Lironeca vulgaris (Isopoda, Cymothoidae), from sanddab hosts, Cithariehthys spp., by Gary R. Robinson 907 Pacific, central squid four new species 703 Pacific, eastern tropical cephalopods beak key with relationships between beak dimen- 920 sions and size 357 dolphin mortality estimating and monitoring incidental in tuna purse seine fishery 396 Pacific, North white Dall's porpoise sighted 401 Panulirus cygnus—see Lobster, rock Parophrys vetulus—see Sole, English PEARCY, WILLIAM G.-see PETERSON et al. Penaeus duorarum—see Shrimp, pink PENNINGTON, MICHAEL-see LOUGH et al. Perch, white biology in Hudson River estuary growth 602 length conversions 602 length-frequency and age distribution 602 length-weight relationship 604 reproduction 604 sex ratio 606 time of annulus formation 601 PERRYMAN, W.— see AU and PERRYMAN PETERSON, WILLIAM T., RICHARD D. BRO- DEUR, and WILLIAM G. PEARCY, Food habits of juvenile salmon in the Oregon coastal zone, June 1979 841 Phenotypic differences among stocks of hatchery and wild coho salmon, Oncorhynchus kisutch, in Oregon, Washington, and California, by R. C. Hjort and C. B. Schreck 105 PHILLIPS, B. F.-see MORGAN et al. Phocoenoides dalli—see Porpoise, Dall's Pinnipeds California coastal waters predation by white shark 891 POLOVINA, JEFFREY J. -see RALSTON and POLOVINA Population biology of chum salmon, Oncorhynchus keta, from the Fraser River, British Columbia, by Terry D. Beacham and Paul Starr 813 Population fluctuations of California sea lions and the Pacific whiting fishery off central California, by David G. Ainley, Harriet R. Huber, and Kevin M. Bailey 253 Porgy, longspine reproduction, movements, and population dynamics age determination and growth using length- frequency analysis 534 age determination using scales 534 maturation and spawning seasonality 525 mortality and postspawning survival 536 movements, spawning areas, and diel variation in catch 531 size, maximum, and lifespan 536 total weight-total length, girth-total length, and length-length relationships 537 Porgy, whitebone biology in South Atlantic Bight age and growth 866 distribution and abundance 864 reproduction 868 South Carolina commercial landings 871 Porpoise, Dall's white, sighted in North Pacific 401 Port Hardy, British Columbia eel, wolf migration of juvenile from, to Willapa Bay, Wash- ington 650 POTTHOFF, THOMAS, and SHARON KELLEY, Development of the vertebral column, fins and fin sup- ports, branchiostegal rays, and squamation in the swordfish. Xiph ids {/hull us 161 POWERS, JOSEPH E.-see LO et al. PRATT, HAROLD L„ JR., JOHN G. CASEY, and ROBERT B. CONKLIN, Observations on large white sharks, Carcharodon carckarias, off Long Island, New York 153 Pressure sensitivity of Atlantic herring, Clupea karengus L., larvae, by David R. Colby, Donald E. Hoss, and J. H. S. Blaxter 567 Quahog, ocean growth in Middle Atlantic Bight field studies 23 length-weight studies 28 mark-recapture studies 24 shell banding studies 26 southern New England shelf seasonal cycle of gonadal development 315 Qualitative and quantitative nutrient requirements of fishes: A review, by Mark R. Millikin 655 Queenfish vertical stratification off southern California 895 QUEENTH, MARTINA K. K.— see KAYA et al. RADTKE, R. L.. and J. M. DEAN, Increment forma- tion in the otoliths of embryos, larvae, and juveniles of the mummichog. Fundulus heteroclitus 201 RALSTON. STEPHEN, and JEFFREY J. POLO- VINA, A multispecies analysis of the commercial deep-sea handline fishery in Hawaii 435 Rapid and spontaneous maturation, ovulation, and spawning of ova by newly captured skipjack tuna, Katsuwonus pelamis, by Calvin M. Kaya. Andrew E. Dizon. Sharon D. Hendrix, Thomas K. Kazama, and Martina K. K. Queenth 393 Regeneration of nitrogen by the nekton and its signifi- cance in the northwest Africa upwelling ecosystem, by Terry E. Whitledge 327 (The) relationship of winter temperature and spring landings of pink shrimp. Prune us duomrum, in North Carolina, by William F. Hettler and Alexander J. Chester 761 Reproduction, movements, and population dynamics of the longspine porgy, Stenotomus caprinus, by Paul Geoghegan and Mark E. Chittenden. Jr 523 Reproductive biology of western Atlantic bluefin tuna, by Raymond E. Baglin, Jr 121 RICHARDS. GARY P.-see BABINCHAK et al. RICHARDSON, SALLY L.-see LAROCHE et al. RICHKUS, WILLIAM A.-see ULANOWICZ et al. RIEDMAN, MARIANNE— see LE BOEUF et al. ROBINSON, GARY R.. Otter trawl sampling bias of the gill parasite. Lironecu vulgaris (Isopoda, Cymothoi- dae), from sanddab hosts, Citharichthys spp 907 Rockfish, widow fecundity off Oregon coast 881 ROPES, JOHN W.— see MURAWSKI et al. ROSAPEPE, JOHN V.— see JOYCE et al. ROSENBERG, ANDREW A.. Growth of juvenile English sole, Parophrys vetulus, in estuarine and open coastal nursery grounds 245 ROSENBERG, ANDREW A., and JOANNE LYCZ- KOWSKI LAROCHE. Growth during metamorpho- sis of English sole, Parophrys vetulus 150 ROSENBERG, ANDREW A.-see LAROCHE et al.: LOUGH et al. ROTHLISBERG. PETER C, Vertical migration and its effect on dispersal of penaeid shrimp larvae in the Gulf of Carpentaria, Australia 541 ROUMILLAT, WILLIAM A.-see WALTZ et al. Salmon, chinook food habits of juvenile in Oregon coastal zone, June 1979 diet overlap 847 occurrence and abundance of prey taxa 846 Salmon, chum food habits of juvenile in Oregon coastal zone, June 921 1979 diet overlap 847 occurrence and abundance of prey taxa 843 population biology from Fraser River, British Columbia age composition and sex ratios of returning adults 815 age of return 819 fecundity 816 fry migrations and survival 816 marine growth 815 return to escapement 820 Salmon, coho food habits of juvenile in Oregon coastal zone, June 1979 diet overlap 847 occurrence and abundance of prey taxa 843 phenotypic differences among hatchery and wild stocks, U.S. Pacific coast characters, morphological 107, 108 electrophoresis 107 environmental data 107 isozyme gene frequencies 110 life history 107, 110 sampling 106 statistics 108 stock similarity 113 stream systems and wild stocks similarity 117 Salmon, king cyclic covariation in California fisheries California, central, total catch 795 California, northern catch by salmon species 794 total catch 793 switching effort between species 796 Salmon, silver cyclic covariation in California fisheries California, central, total catch 795 California, northern catch by salmon species 794 total catch 793 switching effort between species 796 Sanddab otter trawl sampling bias of Lironeca vulgaris 907 Sanddab, longfin seasonal spawning cycle 906 Sandworm life history study in Sheepscot Estuary, Maine eggs, numbers laid 738, 741 environmental conditions during spawning .... 738, 741 length frequency 737, 740 oocyte development 738, 741 predation 740 salinity and temperature of study area 737, 740 spawning characteristics 739, 742 SCHEVILL, WILLIAM E.-see WATKINS and SCHEVILL CONNALLY, Vertical stratification of three near- shore southern California larval fishes (Engraulis mor- dax, Genyonemus lineatus, and Seriphus politus) 895 SCHRECK, C. B.-see HJORT et al. SCOTT, M. D.— see IRVINE et al. SCOTTO. LIBERTA E.— see GORE and SCOTTO Sculpin, rosylip larval development axial skelton 350 egg collection and laboratory rearing 345 fin development 350 identification 346 measurements 346 morphology 349 oral region 350 pigment patterns 347 reproductive behavior and larval rearing 353 spination 353 Sculpins trophic patterns among larvae in a Maine estuary diet comparisons 830 diet composition 829 diet overlap 831 feeding incidence 829 mouth size, larval, and prey width 836 Sea lion, California California, central population fluctuations and Pacific whiting fishery 253 Seasonal abundance, composition, and productivity of the littoral fish assemblage in upper Newport Bay, California, by Larry G. Allen 769 (The) seasonal cycle of gonadal development in Arctica islandica from the Southern New England shelf, by Roger Mann 315 Seasonal spawning cycle of the longfin sanddab, Citharichthys xanthostigma (Bothidae), by Stephen R. Goldberg 906 Seatrout, silver spawning, age determination, longevity, and mor- tality in Gulf of Mexico age determination using scales 494 distribution and availability 495, 498 growth and age determination 496 growth and age determination by length fre- quency 493 maximum size, life span, and mortality 495. 498 spawning 489, 496 total weight- and girth-standard length and stan- dard length-total length relationships 495 Sebastt's rutomclaa—see Rockfish, widow SCHLOTTERBECK. ROBERT E., and DAVID W. SERCHUK, FREDRIC M.-see MURAWSKI et al. 922 Sergestes si mil is larval development nauplius I 218 nauplius II 218 nauplius III 218 nauplius IV 223 postlarva 1 238 postlarva II 238 protozoea I 223 protozoea II 223 protozoea III 225 zoea I 231 zoea II 234 Seriphus politus—see Queenfish Shark, bull swimming kinematics 803 Shark, lemon swimming kinematics 803 Shark. leopard swimming kinematics 804 Shark, nurse swimming kinematics 803 Shark, Pacific blacktop swimming kinematics 803 Shark, white observations off Long Island, New York 153 predation on pinnipeds in California coastal waters 891 Sharks swimming kinematics 803 Shellfish Maryland commercial landings identifying climatic factors influencing 611 Shrimp, pink relationship of winter temperature and spring land- ings in North Carolina air-water temperature relation 765 annual temperature cycle in Newport River Estuary 764 relationship between temperature, rainfall, and landings 765 Shrimp larvae, penaeid effect of vertical migration on dispersal in Gulf of Carpentaria, Australia consequences of vertical migration 545 ontogeny of vertical migration 543 pattern variations of vertical distribution 544 Silverside, Atlantic migration, offshore winter 145 SKINNER, RENATE H„ The interrelation of water quality, gill parasites, and gill pathology of some fishes from south Biscayne Bay, Florida 269 SMITH, I). E.-see BANAS et al. Snapper, red ( rulf of Mexico growth of juvenile 644 Snout dimorphism in white sturgeon, Acipenser transmontanu8, from the Columbia River at Hanford. Washington, by Dennis W. Crass and Robert H. ( tray 158 Sole, English age and growth in Oregon coastal waters field and laboratory procedures 94 increment formation 95 spawning and rearing procedures 94 statistical procedures 95 growth during metamorphosis 150 growth in estuarine and open coastal nursery grounds 245 Spawning, age determination, longevity, and mortal- ity of the silver seatrout, Cynoscion nothus, in the Gulf of Mexico, by Douglas A. DeVries and Mark E. Chittenden, Jr 487 Spawning and larval development of the hogfish, Lach- nolaimus maximus (Pisces: Labridae), by Patrick L. Colin 853 Sphyrna tiburo — see Bonnethead SPINELLI, JOHN-see MILLER and SPINELLI Squid Enoplotcuth is reticulata adult description 723 four new species from the central Pacific bathymetric distribution 728 Enoploteuthis higginsi 718 Enoploteuth is jonesi 713 Enoplotcuth is obliqua 704 Enoploteuthis octolineata 708 geographic distribution 728 key to species of Enoploteuthis 731 relationships 729 Squid, long-finned objective method for classifying into sexual matur- ity stages application 453 biological relevance and accuracy 456 classification process 452 comparisons with other classification methods . . . 457 discriminant functions development 451 maturity stages, four 453 multivariate approach, objectivity and utility 456 STARR, PAUL— see BEACHAM and STARR Stenotomus caprinus—see Porgy, longspine Stock and recruitment relationships in Panulirus cyg- nus, the commercial rock (spiny) lobster of Western Australia, by G. R. Morgan, B. F. Phillips, and L. M. Joll 475 923 (The) Strait of Georgia herring fishery: A case history of timely management aided by hydroacoustic surveys, by Robert J. Trumble, Richard E. Thorne, and Norman A. Lemberg 381 Sturgeon, Atlantic Delaware River estuary 337 Sturgeon, white Columbia River at Hanford, Washington snout dimorphism 158 SUMMERS, J. KEVIN— see ULANOWICZ et al. Swimming kinematics of sharks, by P. W. Webb and Raymond S. Keyes 803 Swordfish development anal fin 169 anal fin pterygiophores 171 branch iostegal rays 179 caudal fin 172 caudal fin supports 172 dorsal fin 165 dorsal fin pterygiophores 166 pectoral fin 162 pectoral fin supports 163 squamation 181 vertebral column 175 Tagging experiments analysis of double-tagging adjustment factor estimation for single-tag recov- eries 692 models 689 mortality rate 699 parameter estimation of specific models 693 shedding rate and parameter estimation 691 tag loss in single-tagging experiments 687 Tagging techniques cetaceans, small odontocete 135 THORNE, RICHARD E.-see TRUMBLE et al. Thunnus thynnus—see Tuna, bluefin Tomtate distribution, abundance, and age and growth along southeastern U.S. coast age and growth 3, 10, 15 distribution and relative abundance 1, 4, 14 length-weight and fork length-total length re- lationships 4, 13 management 16 mortality estimates 4, 13 spawning 4, 13, 16 Triakis xcmifnsciata—see Shark, leopard Triclnrliiis nianatus—see Manatee, West Indian Trimethylamine estimation in fish muscle Trophic patterns among larvae of five species of sculpins (Family: Cottidae) in a Maine estuary, by Joanne Lyczkowski Laroche TRUMBLE, ROBERT J., RICHARD E. THORNE, and NORMAN A. LEMBERG, The Strait of Georgia herring fishery: A case history of timely management aided by hydroacoustic surveys 157 827 381 TUCKER, JOHN W., JR., Larval development of Citharichthys cornutus, C. gymnorhinus, C. spilopterus, and Etropus crossotus (Bothidae), with notes on larval occurrence 35 Tuna, bluefin reproductive biology of western Atlantic egg diameter heterogeneity 126 fecundity estimates 131 gonosomatic index 123 morphology, gross 123 ova size 123 ovary histology 126 sex composition 123 Tuna, skipjack rapid and spontaneous maturation, ovulation, and spawning of ova by newly captured 393 Tursiops truncatua—see Dolphin, bottlenose ULANOWICZ, ROBERT E., MOHAMMED LIA- QUAT ALL ALICE VIVIAN, DONALD R. HEINLE, WILLIAM A. RICHKUS, and J. KEVIN SUMMERS. Identifying climatic factors influencing commercial fish and shellfish landings in Maryland TrigUyps murrayi trophic patterns among larvae in an estuary . 827 Vertical migration and its effect on dispersal of penaeid shrimp larvae in the Gulf of Carpentaria, Australia, by Peter C. Rothlisberg Vertical stratification of three nearshore southern Cali- fornia larval fishes (Engraulis mordax, Genyonemus lineatus, and Seriphus politus), by Robert E. Schlot- terbeck and David W. Connally VIVIAN. ALICE-see ULANOWICZ et al. WAHLEN, BRUCE E.-see LO et al. WALTZ, C. WAYNE, WILLIAM A. ROUMILLAT. and CHARLES A. WENNER. Biology of the white- bone porgy, Calamus lewcosteus, in the South Atlantic Bight Washington salmon, coho phenotypic differences among hatchery and wild stocks 611 541 895 863 105 924 WATKINS. WILLIAM A., and WILLIAM E. SCHEVILL, Observations of right whales, Kubalae- na glacialis, in Cape Cod waters 875 WATSON. WILLIAM, Development of eggs and larvae of the white croaker, GenyonemuslineatusAyres (Pisces: Sciaenidae), off the southern California coast 403 WEBB, P. W„ and RAYMOND S. KEYES, Swim- ming kinematics of sharks 803 WELLS. R. S.-see IRVINE et al. WENNER, CHARLES A. -see WALTZ et al. WETHERALL, JERRY A. Analysis of double- tagging experiments 687 Whale, humpback feeding behavior in western North Atlantic behavioral strategies 265 bubbling behaviors 261 circular swimming/thrashing 260 inside loop behavior 261 lunge feeding 260 prey species 266 Whale, right observations in Cape Cod waters 875 WHIPPLE, JEANNETTE A.— see ELDRIDGE et al. White Dall's porpoise sighted in the North Pacific, by Gerald G. Joyce, John V. Rosapepe. and Junroku Ogasawara 401 White shark predation on pinnipeds in California coastal waters, by Burney J. Le Boeuf. Marianne Riedman. and Raymond S. Keyes 891 Whiting, Pacific fishery off central California population fluctuations of California sea lions and 253 protease inhibitors on proteolysis in parasitized muscle blended fish 282, 283 diabasic phosphate peroxides 284 effect of inhibition on texture 282, 285 enzyme inhibitors 282 fillet treatment 286 frozen storage effect 285 ground fish 282, 283 hydrogen peroxide 284 oxidative effect on amino acids 282, 285 potassium bromate 284 preparation of ground fish blocks for storage 282 test for presence of peroxides or bromates 283 WHITLEDGE, TERRY E.. Regeneration of nitrogen by the nekton and its significance in the northwest Africa upwelling ecosystem 327 WIEBE, P. H.. S. H. BOYD, B. M. DAVIS, and J. L. COX. Avoidance of towed nets by the euphausiid Nt matoscelis megalops 75 WILEN. JAMES E.-see BOTSFORD et al. Willapa Bay. Washington eel, wolf migration of juvenile from Port Hardy, British Columbia, to 650 WINN, HOWARD E.— see HAIN et al. WOLFF, GARY A., A beak key for eight eastern tropical Pacific cephalopod species with relationships between their beak dimensions and size Xiphias gladius — see Swordfish Zalophus californianus — see Sea lion, California Zooplankton Atlantic, northwest effect of season and location on relationship be- tween displacement volume and dry weight 357 631 925 NOTICES NOAA Technical Reports NMFS published during first 6 months of 1982 C ircular 442. Proceedings of the Sixth U.S.-Japan Meeting on Aquaculture, Santa Barbara, California. August 27-28, 1977. By Carl J. Sinder- mann (editor). March 1982, iii + 66 p. [Five articles are published in this paper.] 443. Synopsis of the biological data on dolphin-fishes, Coryphaena hip- purus Linnaeus and Coryphaena equiselis Linnaeus. By Barbara Jayne Palko, Grant L. Beardsley, and William J. Richards. April 1982, iv + 28 p., 15 figs., 10 tables. 445. Sharks of the genus Carcharhinus. By J. A. F. Garrick. May 1982, vii + 194 p., 83 figs., 91 tables. Special Scientific Report — Fisheries 753. Factors influencing ocean catches of salmon, Oncorhynchus spp., off Washington and Vancouver Island. By R. A. Low, Jr. and S. B. Mathews. January 1982, iv + 12 p., 6 figs., 7 tables. 754. Demersal fish resources of the eastern Bering Sea: Spring 1976. By Gary B. Smith and Richard G. Bakkala. March 1982, vi + 129 p., 92 figs., 68 tables. 755. Annotated bibliography and subject index on the summer flounder, Paralichthys dentatus. By Paul G. Scarlett. March 1982, iii + 12 p. 756. Annotated bibliography of the hard clam (Mercenaria mercenaria). By J. L. McHugh, Marjorie W. Sumner, Paul J. Flagg, Douglas W. Lip- ton, and William J. Behrens. March 1982, iii + 845 p. 757. A profile of the fish and decapod crustacean community in a South Carolina estuarine system prior to flow alteration. By Elizabeth Lewis Wenner, Malcolm H. Shealy, Jr., and Paul A. Sandifer. March 1982, iii + 17 p., 8 figs., 5 tables. Some NOAA publications are available by purchase from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402. Individual copiesof NOAA Technical Reports (in limited numbers) are available free to Federal and State Government agencies and may be obtained by writing to User Services Branch (D822), Environ- mental Science Information Center, NOAA, Rockville, MD 20852. INFORMATION FOR CONTRIBUTORS TO THE FISHERY BULLETIN Manuscripts submitted to the Fishery Bulletin will reach print faster if they conform to the following instruc- tions. These are not absolute requirements, of course, but desiderata. CONTENT OF MANUSCRIPT The title page should give only the title of the paper, the author's name, his affiliation, and mailing address, including ZIP code. The abstract should not exceed one double-spaced page. In the text, Fishery Bulletin style, for the most part, follows that of the U.S. Government Printing Office Style Manual. 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Sindermann, Scientific Editor Fishery Bulletin Northeast Fisheries Center Sandy Hook Laboratory National Marine Fisheries Service, NOAA Highlands, NJ 07732 Fifty separates will be supplied to an author free of charge and 100 supplied to his organization. No covers will be supplied. Contents — continued Notes BOEHLERT, GEORGE W., W. H. BARSS, and P. B. LAMBERSON. Fecundity of the widow rockfish, Sebastes entomelas, off the coast of Oregon 881 BABINCHAK, JOHN A., DANIEL GOLDMINTZ, and GARY P. RICHARDS. A comparative study of autochthonous bacterial flora on the gills of the blue crab, Callinectes sapidus, and its environment 884 LE BOEUF, BURNEY J., MARIANNE RIEDMAN, and RAYMOND S. KEYS. White shark predation on pinnipeds in California coastal waters 891 SCHLOTTERBECK, ROBERT E., and DAVID W. CONNALLY. Vertical strati- fication of three nearshore southern California larval fishes (Engraulis mordax, Genyonemus lineatus, and Seriphus politus) 895 LIBBY, DAVID A. Decrease in length at predominant ages during a spawning migration of the alewife, Alosa pseudoharengus 902 GOLDBERG, STEPHEN R. Seasonal spawning cycle of the longfin sanddab, Citharichthys xanthostigma (Bothidae) 906 ROBINSON, GARY R. Otter trawl sampling bias of the gill parasite, Lironeca vulgaris (Isopoda, Cymothoidae), from sanddab hosts, Citharichthys spp 907 INDEX, VOLUME 80 911 Notices NO A A Technical Reports NMFS published during the first 6 months of 1982 f1Df~\ cni nna MM. WHOI LIBRARY H 1 U7 C