M8L U.S. Department of Commerce Seattle, Washington Volume 93 Number 1 January 1995 Fishery Bulletin Contents *Jfc'&**j*. Cceanr 15 Companion articles JAN 9 1995 Woods Hci; Barlow, Jay The abundance of cetaceans in California waters. Part I: Ship surveys in summer and fall of 1991 Forney, Karin A., Jay Barlow, and James V. Carretta The abundance of cetaceans in California waters. Part II: Aerial surveys in winter and spring of 1991 and 1992 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, recom- mends, or endorses any proprietary product or pro-prietary material men- tioned here-in, or which has as its pur- pose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NMFS publication. Articles 27 Bruce, Barry D. Larval development of King George whiting, Sillaginodes punctata, school whiting, Sillago bassensis, and yellow fin whiting, Sillago schomburgkii (Percoidei: Sillaginidae), from South Australian waters 44 Carls, Mark G., and Charles E. O'Clair Responses of Tanner crabs, Chionoecetes bairdi, exposed to cold air 57 Cortes, Enric Demographic analysis of the Atlantic sharpnose shark, Rhizoprionodon terraenovae. in the Gulf of Mexico 67 Ellis, Denise M., and Edward E. DeMartini Evaluation of a video camera technique for indexing abundances of juvenile pink snapper, Pristipomoides filamentosus. and other Hawaiian insular shelf fishes 78 Finnerty, John R., and Barbara A. Block Evolution of cytochrome b in the Scombroidei (Teleostei): molecular insights into billfish (Istiophoridae and Xiphiidae) relationships Fishery Bulletin 93 1 1), 1995 97 Kornfield, Irv, Austin B. Williams, and Robert S. Steneck Assignment of Homarus capensis (Herbst, 1 792), the Cape lobster of South Africa, to the new genus Homarinus (Decapoda: Nephropidae) 1 03 Milton, David A., Steven A. Short, Michael F. O'Neill, and Stephen J. M. Blaber Ageing of three species of tropical snapper (Lutjanidae) from the Gulf of Carpentaria, Australia, using radiometry and otolith ring counts 1 16 Natanson, Lisa J., John G. Casey, and Nancy E. Kohler Age and growth estimates for the dusky shark, Carcharhinus obscurus, in the western North Atlantic Ocean 1 27 Rickey, Martha H. Maturity, spawning, and seasonal movement of arrowtooth flounder, Atheresthes stomias, off Washington 1 39 Schmid, Jeffrey R. Marine turtle populations on the east-centrai coast of Florida: results of tagging studies at Cape Canaveral, Florida, 1986-1991 Notes 1 52 Benetti, Daniel D., Edwin S. Iversen, and Anthony C. Ostrowski Growth rates of captive dolphin, Coryphaena hippurus, in Hawaii 1 58 Canino, Michael F, and Elaine M. Caldarone Modification and comparison of two fluorometric techniques for determining nucleic acid contents of fish larvae 1 66 Laidig, Thomas E., and Stephen Ralston The potential use of otolith characters in identifying larval rockfish (5eo<3sfe5 spp.) 1 72 Matsuura, Yasunobu, and Roger Hewitt Changes in the spatial patchiness of Pacific mackerel. Scomber japonicus, larvae with increasing age and size 1 79 Riley, Cecilia M., G. Joan Holt, and Connie R. Arnold Growth and morphology of larval and juvenile captive bred yellowtail snapper, Ocyurus chrysurus 1 86 Secor, David H., T. Mark Trice, and Harry T. Hornick Validation of otolith-based ageing and a comparison of otolith and scale-based ageing in mark-recaptured Chesapeake Bay striped bass, Morone saxatilis 191 Szedlmayer, Stephen T, and Jeffrey C. Howe An evaluation of six marking methods for age-0 red drum, Sciaenops ocellatus 1 96 Wiley, David N., Regina A. Asmutis, Thomas D. Pitchford, and Damon P. Gannon Stranding and mortality of humpback whales, Megaptera novaeangliae, in the mid-Atlantic and southeast United States, 1 985-1 992 207 Awards Abstract. — A ship survey was conducted in summer and fall of 1991 to estimate the abundance of cetaceans in California waters be- tween the coast and approximately 555 km (300 nmi) offshore. Line- transect methods were used from a 53-m research vessel. Approxi- mately 10,100 km were searched, and 515 groups of cetaceans were seen. The estimated abundances and coefficients of variation (in pa- rentheses) of the most common small cetaceans are the following: 226,000 (0.28) short-beaked com- mon dolphins, Delphinus delphis; 78,400 (0.35) Dall's porpoises, Pho- coenoides dalli; 19,000 (0.41) striped dolphins, Stenella coeruleo- alba; 12,300 (0.54) Pacific white- sided dolphins, Lagenorhynchus obliquidens; 9,470 (0.68) long- beaked common dolphins, Delphinus capensis; and 9,340 (0.57) northern right whale dolphins, Lissodelphis borealis. The estimated abun- dances (and CV's) of the most com- mon large cetaceans are 2,250 (0.38) blue whales, Balaenoptera musculus; 935 (0.63) fin whales, Balaenoptera physalus; 756 (0.49) sperm whales, Physeter macrocephalus; and 626 (0.41) humpback whales, Megap- tera novaeangliae. Estimates are also made for other species and for higher-level taxa that could not be identified to species. The abundance of cetaceans in California waters. Part I: Ship surveys in summer and fall of 1991 Jay Barlow Southwest Fisheries Science Center National Marine Fisheries Service. NOAA RO. Box 271. La Jolla. California 92038 Manuscript accepted 31 May 1994. Fishery Bulletin 93:1-14 ( 1995). The abundance of cetaceans in Cali- fornia waters is poorly known for the majority of species found there. For small cetaceans, quantitative estimates of abundance with statis- tical confidence limits are available only for common dolphins, Delphi- nus delphis (Dohl et al., 1986) and for harbor porpoise, Phocoena phocoena (Barlow, 1988). For large cetaceans, such estimates are avail- able for gray whales, Eschrichtius robustus (Reilly, 1984; Buckland et al., 1993a); humpback whales, Meg- aptera nov aeangliae (Calambokidis et al., 1990a, 19931), and blue whales, Balaenoptera musculus.1 Estimates have been made for some of the other species (Dohl et al.2,3), but these estimates are more than 10 years old, and most lack informa- tion on statistical precision. Many, and perhaps all, cetaceans in California waters are vulnerable to entanglement and death in gillnet fisheries. A program is now in place to estimate the incidental mortality of cetaceans in the Cali- fornia gillnet fisheries (Lennert et al., in press). It is difficult, however, to assess the impact of gillnet mor- tality on cetacean populations with- out knowing population sizes. Co- ordinated ship and aerial surveys were initiated recently to estimate the abundance of all cetacean spe- cies in the region of California gillnet fisheries. To evaluate the ef- fect of seasonality on cetacean abun- dance, surveys were designed to cover both cold-water months (Feb- Apr) and warm-water months ( Jul- Nov). A ship survey was conducted during the warm-water period of 1991; an aerial survey was conducted during the cold-water periods of both 1991 and 1992. Results from the ship survey are reported here; population estimates from the aerial surveys are reported in a companion paper (Forney et al., this issue). Field methods A line-transect survey was con- ducted from 28 July to 5 November 1991 with the 53-m National Ocean- ographic and Atmospheric Admin- 1 Calambokidis, J., G. H. Steiger, and J. R. Evenson. 1993. Photographic identification and abundance estimates of humpback and blue whales off California in 1991-92. Final Contract Rep. 50ABNF100137, sub- mitted to the Southwest Fish. Sci. Cent., P.O. Box 271, La Jolla, CA 92038, 40 p. 2 Dohl, T. P., K. S. Norris, R. C. Guess, J. D. Bryant, and M. W. Honig. 1978. Cetacea of the Southern California Bight. Part II of Summary of marine mammals and sea- bird surveys of the Southern California Bight area, 1975-78. Final Rep. to the Bu- reau of Land Management, 414 p. [NTIS Rep. No. PB81248189.] 3 Dohl, T. P., R. C. Guess, M. L. Duman, and R. C. Helm. 1983. Cetaceans of central and northern California, 1980-83: status, abundance, and distribution. Final report to the Minerals Management Serv., Con- tract No. 14-12-0001-29090, 284 p. 1 Fishery Bulletin 93(1). 1995 istration (NOAA) vessel McArthur to assess the abun- dance of cetaceans in California waters. Primary cruise tracks were drawn for a unifirm survey of the 814,900 km2 area between the 18-m (10-fathom) isobath and approximately 555 km (300 nmi) offshore (Fig. 1). Primary observation team The basic survey method was that which was devel- oped and used to estimate the abundance of small cetaceans in the eastern tropical Pacific (Holt and Powers, 1982; Holt, 1987; Holt and Sexton, 1989; Wade and Gerrodette, 1993). The primary observa- tion team consisted of three observers who searched from a viewing height of 10 m above the sea surface: two observers searched with 25x pedestal-mounted binoculars; the third observer searched with unaided eye, and (occasionally) 7x binoculars, and also served as data recorder. Observers rotated among these three duty stations every 1/2 hour, and two observer teams alternated work and rest periods every two hours. Sighting effort was maintained from dawn to dusk whenever weather conditions allowed, and searching covered the entire region from directly in front of the vessel to 90 degrees left and right and Figure 1 Transect lines (thin solid lines) completed during the survey. The bold polygon indicates the limit of the main study area. out to the horizon. Data were recorded on a lap-top computer that had direct input from the ship's GPS (Global Positioning System) navigation system. Re- corded data included sighting conditions (sea state, cloud cover, sun position, etc.), observer positions, the beginning and end of effort, and information per- taining to sightings. When a sighting was made, all observers were made aware of the animals' location. The perpendicu- lar distance from the trackline to the center of the group was estimated from the initial bearing and distance. The initial bearing of a cue (a blow, a splash, or a sighting of animals) was measured relative to the bow of the vessel by means of a calibrated collar on the base of the yoke of the 25x binoculars. The initial distance was typically estimated from a cali- brated reticle scale in the oculars of both the 25x and 7x binoculars with the formula derived by Smith ( 1982) and was calibrated by using radar-measured distances to inanimate objects (Barlow and Lee, 1994). If a shore horizon was closer than 11.1 km (6 nmi), distance was estimated by comparison with the radar-measured distance to shore. Occasionally, for very close animals seen only by the third observer, sighting distances and angles were estimated by eye. If a cue turned out to be a cetacean, effort was inter- rupted and the ship was typically diverted towards the animals in order to obtain esti- mates of species composition and group size. The vessel was not typically diverted for ce- taceans that were greater than 5.55 km (3 nmi) perpendicular distance from the trackline. Species identification was made collec- tively by the team, but quantitative estimates of species composition and group size were made independently by each observer. For estimation purposes, a group was defined as a collection of closely associated individuals (typically within several body lengths of each other) that exhibited cohesive behavior. In the field, however, a single distant sighting might prove to be two behaviorally distinct groups upon closer inspection. In such cases, when it was impossible to determine which was the original group sighted, both groups were pooled to estimate group size and spe- cies composition. For mixed-species groups, species composition was recorded as an observer's estimate of the percentage of each species present in the group. The observers recorded species composition and group-size data in confidential personal notebooks, and the data were transcribed at the end of the day into the computer data record by the cruise leader. Barlow. Abundance of cetaceans in California waters: ship surveys Species identification Observers attempted to classify all the species present in a group to the lowest possible taxonomic level (one member of each team was a cetacean iden- tification expert with at least nine months of at-sea survey experience on prior marine mammal surveys). Several higher taxonomic groups were used in cases where species identification was not possible. These higher groups were beaked whales of the genus Mesoplodon; unidentified sei or Bryde's whales; uni- dentified beaked whales (including members of the genera Mesoplodon and Ziphius); unidentified large whales (including members of the species group "large whale" in Table 1 as well as the genera Esch- richtius and Eubalaena); unidentified baleen whales (including members of the genera Balaenoptera, Megaptera, Eschrichtius, and Eubalaena); unidenti- fied small whales (including members of the species groups "small whales" and "large delphinids" in Table 1 ); unidentified delphinoids (including members of the species groups "small delphinids," 'large delphinids," and "cryptic species" in Table 1); and unidentified cetaceans (which could include any of the species listed above or in Table 1). The number of sightings identi- fied to these higher taxonomic levels is relatively small, and these animals were not included in the abundance estimates for individual species. Conditionally independent observer In addition to the primary observation team, a fourth observer was on duty 81% of the time and looked for cetaceans that were missed by the primary team. This conditionally independent observer was sta- tioned immediately next to the other observers, searched with 7x binoculars and unaided eyes, and did not reveal the presence of cetaceans until after they were clearly missed by the primary observation team (i.e. after they had passed abeam of the vessel or were bow-riding). Nine different people served as independent observers during the survey, and all worked irregular schedules that overlapped with both primary teams. Independent observers did not work more than two consecutive hours. When a sighting was made by the independent observer, that person maintained their normal behavior so as to avoid drawing the attention of the primary observer team. Initial bearing and distance were estimated by eye or with the aid of reticles in the ocular of 7x binocu- lars and a hand-held protractor. After a group was clearly missed by the primary team, the independent observer announced the presence of the animals to the data recorder and gave the initial bearing and distance. Typically the vessel was diverted towards the group, and species composition and group size were estimated by the primary observation team. Analytical methods Cetacean abundance was estimated from survey data with line-transect methods (Buckland et al., Table 1 Number of groups of cetaceans which contained members of the indicated species and species groups. The sum of all species in a group may be greater than the total for that group because the latter contains mixed-species groups. Totals do not include off-effort sightings. Species group and No. of species sightings Small delphinids 285 short-beaked common dolphin, Delphi nus delphis 123 long-beaked common dolphin, Delphinus capensis 6 unclassified common dolphin, Delphinus spp. 8 striped dolphin, Stenella coeruleoalba 24 Pacific white-sided dolphin, Lagenorhynchus obliquidens 12 northern right whale dolphin, Lissodelphis borealis 16 unidentified delphinoid 21 Cryptic species 132 harbor porpoise, Phocoena phoeoena 32 Dall's porpoise, Phocoenoides dalli 97 pygmy sperm whale, Kogia breviceps 3 Large delphinids 37 bottlenose dolphin, Tursiops truncatus 16 Risso's dolphin, Grampus griseus 29 killer whale, Orcinus orca 5 Large whales 127 sperm whale, Physeter macrocephalus 13 Baird's beaked whale, Berardius bairdii 1 Bryde's whale, Balaenoptera edeni 1 Bryde's or sei whale, Balaenoptera edeni or B. borealis 2 fin whale, Balaenoptera physalus 22 blue whale, Balaenoptera musculus 49 humpback whale, Megaptera novaeangliae 13 unidentified baleen whale 9 unidentified large whale 22 Small whales 48 unidentified beaked whale 7 mesoplodont beaked whale {Mesoplodon spp.) 5 Cuvier's beaked whale, Ziphius cavirostris 14 minke whale, Balaenoptera acutorostrata 4 unidentified small whale 11 unidentified cetacean 8 Fishery Bulletin 93(1). 1995 1993b). The basic equation for estimating abundance, N, for grouped animals with line transect is given by N- AnSf(O) 2Lg(0) (1) where A = size of the study area; n = number of sightings; S = mean group size; fiO) = sighting probability density at zero per- pendicular distance; L = length of transect line completed; and g(0) = probability of seeing a group directly on the trackline. Ideally, S, /10), and g(0) would be estimated sepa- rately for each species. However, the presence of mixed-species groups and small sample sizes required pooling for the estimation of/10) andg(O). The param- eter /(0) was estimated with the Hazard rate model (Buckland, 1985). This model was fitted by maximum likelihood with ungrouped perpendicular distances. Perpendicular distances were estimated from bearing and radial distance estimates made by observers. Pooling and stratification for estimating f (0) Pooled /T0)'s were estimated for five species groups: "small delphinids," "large delphinids," "small whales," "large whales," and "cryptic species." The five species groups were defined to include all of the species seen on the survey (Table 1) and were based on patterns of species cooccurrence in groups and on similarities in the physical and behavioral attributes that affect sightability from a ship. As an example, bottlenose dolphins, Tursiops truncatus, were never seen in a single-species group but were seen with Risso's dolphins, Grampus griseus, 13 times, with striped dolphins, Stenella coeruleoalba, one time, and with sperm whales, Physeter macrocephalus , three times. Bottlenose dolphins were pooled together with Risso's dolphins because they were seen most fre- quently with that species and because their sighting characteristics are more similar to Risso's dolphins (medium body size, prominent dorsal fin, occasional low puffy blow, small to medium group size) than to the other two species with which they were seen. Because killer whales, Orcinus orca, were never seen with other species but share the same sighting char- acteristics, these were also included in the species group "large delphinids." The other four groups are "small delphinids" which are of small body size (2-3 m) and are found in medium to large groups; "small whales" which are of medium body size (4-10 m), typically show no blow, often surface inconspicuously, and are typically found in small groups; "large whales" which are of large body size (10-30 m), al- most always show a conspicuous blow, and are found in small to medium groups; and "cryptic species" which are small (1.5—4.0 m), show no blow, typically surface inconspicuously, and are found in small groups. The assignment of higher-than-species taxa to species groups is given in Table 1. In estimating /10) for each species group, I explored stratification by two factors that are likely to affect sightability: sea state and group size. To avoid esti- mating more parameters than are justified by the data, I chose the most parsimonious stratification model by minimizing Akaike's Information Criterion (AIC) (Akaike, 1973), defined as 2 multiplied by the number of parameters used to estimate f\ 0) minus 2 multiplied by the sum of the log-likelihoods of the fitted values of/tO). Sea state was subjectively strati- fied into calm (Beaufort 0-2) and rough ( Beaufort 3- 5), based on the obvious degradation in sighting con- ditions that occurs with the presence of whitecaps at Beaufort 3. I stratified by group size by first finding the group size that divided the data into two samples with approximately the same number of sightings in each. If this stratification resulted in a lower AIC, I explored further stratification into three samples of approximately equal size. The above approach to stratification resulted in different strata for each species group. For small delphinids, AIC was minimized by stratifying group size into the categories 1-20, 21-100, and >100. For large delphinids, optimal stratification was with group size categories of 1-20 and >20. For large whales, AIC was minimized by using group size strata of 1-3 and >3. Because "cryptic species" and "small whales" were seldom seen in rough conditions, I estimated abundance for these species by using only data from calm conditions and did not explore strati- fication by sea state. Group size stratification re- sulted in higher AIC values for "cryptic species" and "small whales," so these groups were not stratified by group size. Sea-state stratification was not cho- sen on the basis of AIC values for any species group. In stratification by group size, estimates of den- sity in the various strata are added together to give an overall density. The equation for estimating abun- dance of each species k is therefore given by Nt 1 7 = 1 AnhkShkfhk(0) 2Lgjk(0) (2) where A = size of study area; Barlow. Abundance of cetaceans in California waters: ship surveys lj,k Jj-k = number of sightings of species k in group size stratum,/'; = mean group size of species k in group size stratum j; f k(0) - sighting probability density at zero per- pendicular distance for group size stra- tum./ of the species group to which spe- cies k belongs; L = length of transect line completed; and g k(0) = probability of detecting a group directly on the trackline for group size stratum j of the species group to which species k belongs. Perpendicular distance truncation Sightings of distant groups add little to the estima- tion of trackline density and can introduce bias. Buckland et al. (1993b) recommend truncating to eliminate at least the most distant 5% of all sightings. In the current study, groups of cetaceans were typi- cally not pursued for species identification and group size estimation if they were farther than 5.5 km (3 nmi) from the trackline. Therefore, by survey design, perpendicular distances must be truncated at no more than 5.5 km. I used a truncation distance of 3.7 km (2 nmi) for "small delphinids," "cryptic spe- cies," "large delphinids," and "small whales," which eliminated 8.8%, 2.4%, 4.6%, and 12.8% of all groups (respectively). A truncation distance of 5.5 km was used for "large whales," which eliminated 10.9% of groups. Group-size estimation The estimation of group size for cetaceans is diffi- cult and can lead to bias in the estimation of abun- dance. To avoid bias, correction factors were devel- oped for individual observers. The estimates of four of the six primary observers on the present survey had been previously calibrated by means of aerial photographic estimates to represent "true" group size.4 The "best" estimates of two of these four were found to indicate group size with accuracy and did not require any correction factors. The other two re- quired correction factors, and, for one, correction fac- tors varied significantly from one year to the next. A helicopter was not available to make aerial photo- graphic estimates of group size on the present sur- vey, so correction factors for individual observers were estimated indirectly by comparison with the two 4 Gerrodette, T. D., and C. Perrin. 1991. Calibration of shipboard estimates of dolphin school size from aerial photographs. Admin. Rep. LJ-91-36, available from Southwest Fish. Sci. Cent., P.O. 271, La Jolla, CA 92038. 73 p. observers who, in the previous study, did not require correction. Linear regression was used to compare one obser- ver's estimates of group size to another's for the sub- set of groups that were estimated by both. Group sizes were log10-transformed to normalize variances. For the two observers who did not require a correction factor in the previous study,4 the slope of the regres- sion was 1.009 (SE=0.017), indicating that, relative to each other, the observers were still estimating group size consistently. Correction factors for the other four observers were based on the slope and in- tercept of the regression of their "best" estimates against the mean of "best" estimates of the two who did not need calibration. The group size for each species in a group was es- timated as the average of all observers' corrected estimates of the size of the group multiplied by the average of all observers' estimates of the percentage of that species present (if in a mixed-species group). Probability of detecting trackline groups Estimating the probability that a group on the transect line will be seen, g(0), is fraught with diffi- culties (see Buckland et al. [1993b] for a review of previous attempts). In the context of bias from missed groups of marine mammals, it is useful to think in terms of the dichotomy proposed by Marsh and Sinclair ( 1989): bias can result from groups that were available to be seen but were not (perception bias) and from groups that were not available to be seen either because they did not surface or because they surfaced behind a swell (availability bias). I will make a minimum estimate of perception bias based on data collected by the conditionally independent observer and on the approach given in the Appendix. Because the sample of sightings made by independent observ- ers is small (only 37 cetacean groups), f2(0) in Equa- tion 7 was estimated for all cetaceans pooled with- out stratification by group size or sea state. Perpen- dicular distance data were fitted with the Hazard rate model to estimate f2(0). (Groups are only avail- able to the independent observer if they were missed by the other observers; therefore the distribution of perpendicular distances need not be monotonically decreasing. In this case, however, it was, and a more general model is not likely to have performed better than the Hazard rate model.) The analytical vari- ances of /"j(O) and f2(0) (from the information matrix method) were used in estimating the coefficient of variation ofg^O) from Equation 8, and the variances of n1 and n2 were estimated by assuming a Poisson distribution. Consideration of availability bias is deferred to the Discussion section. Fishery Bulletin 93(1), 1995 Coefficients of variation and confidence intervals Coefficients of variation (CV) and confidence inter- vals (CI) of the abundance estimates are based on the bootstrap method (Efron, 1977; Buckland et al., 1993b). The sightings associated with consecutive segments of search effort were combined to form a set of subsamples of 139 km (75 nmi) of search effort (corresponding to approximately one day of survey effort).5 I drew subsamples randomly with replace- ment from this set of effort segments, and a pseudo- population size was estimated by using the same group size stratification as was used for the actual abundance estimates. For each bootstrap sample, the probability of detecting trackline groups, g(0), was estimated as a random number between 0 and 1 drawn from the probability distribution of a bino- mial ratio with a mean and coefficient of variation equal to the estimated values. This process was re- peated 1,000 times, and the CV of the estimated population size was calculated as the standard error of the 1,000 pseudo-population sizes divided by the estimated population size. Bootstrap 95% confidence intervals on the population estimates were based on the 25th and 976th ranked estimates from the boot- strap samples. Log-normal 95% confidence intervals were based on the method given by Buckland et al. (1993b) and used the bootstrap estimate of CV. Results During the survey approximately 10,100 km of searching effort were completed (Fig. 1), and 515 cetacean groups were seen during the sampling ef- fort. Tracklines included 2,386 km in calm sea states (Beaufort 2 or less) and 7,696 km in rough sea states (Beaufort 3-5). During the survey, 18 cetacean spe- cies were identified (as well as at least one species that could only be identified to genus) (Table 1 ). More detailed data summaries for this survey are pre- sented by Hill and Barlow (1992), including the po- sitions and school sizes of all on- and off-effort sightings of cetaceans and pinnipeds, maps showing the distribution of sightings for each species, distri- butions of perpendicular distances for each species, patterns of association in mixed-species groups, sum- maries of searching effort completed under various conditions, and sighting rates of individual observ- ers. The fit of the probability density functions to 5 Barlow, J. 1993. The abundance of cetaceans in California wa- ters estimated from ship surveys in summer/fall 1991. Admin. Rep. LJ-93-09, available from Southwest Fish. Sci. Cent., P.O. Box 271, La Jolla, CA 92038, 39 p. the distributions of perpendicular distances are il- lustrated by Barlow.5 Group-size estimation Group-size correction parameters, the slopes and intercepts (in parentheses) of log10-transformed re- gressions, were 0.922 (0.03), 1.022 (-0.03), 0.886 (0.07), and 0.777 (0.11) for the four observers who required correction. Three of these observers appear to have underestimated group size, in some cases by a large amount (a group of 500 would have been, on average, estimated as 328, 534, 283, and 152 by these four observers, respectively). Probability of detecting trackline groups Independent observers searched a total of 8,190 km. Approximately 7% of groups were detected only by the independent observer; however, all groups that were detected only by the independent observer were groups of less than 20 individuals and accounted for only 0.7% of the individuals that were seen on the survey. Of all groups that had less than 20 animals and were seen while the independent observer was on duty, 347 were seen by the primary observers, and 40 were seen by the independent observer. Abundance estimation With estimated values of/(0) and ^(0) (Table 2), den- sity and abundance were calculated for 19 cetacean species and 9 higher taxonomic categories (Table 3). Common dolphins were the most abundant cetaceans by a large margin. Of the two recently recognized common dolphin species (Heyning and Pen-in, 1994), the short-beaked variety was much more abundant than the long-beaked variety. Blue whales were the most abundant species of large whale. Discussion Distribution The distributions of cetaceans seen during this sur- vey (Figs. 2—6) are in general agreement with the results of other studies in this area (Leatherwood et al., 1982; Dohl et al., 1986; Smith et al., 1986; Barlow, 1988; Forney et al., this issue; Dohl et al.2,3). How- ever, the observed distribution of some species con- tradicted results of previous studies. Striped dolphins were seen rather commonly in mixed groups with short-beaked common dolphins in southern and cen- tral California between 185 and 555 km (100-300 Barlow: Abundance of cetaceans in California waters: ship surveys Table 2 Estimated values of flO) andg(O) for each ( )f the species group stratifications which were chosen jn the basis of Akaike's [nforma- tion Criterion (AICl minimization. Truncation distances for estimating f[ 0 1 are 5.5 km for large whales and 3.7 km for all other species. Sample sizes include the total number of groups seen by the primary team, n, the number of groups seen by the primary team when an independent observer was on duty, n ,, and the number of groups seen by the independent observers but not by the primary team, n.2. NA indicates information that is not available because it could not be estimated. CV is the coefficient of variation. Primary observers Secondary observers Primary observers Number of si ghtings flO) CV f{0) CV CV Main stratum and substrata n "i n2 km'1 flO) km-1 A0) giO) giO) Small delphinids (3.7 km truncation) group size 1-20 67 58 9 1.258 0.249 1.864 0.147 0.770 0.137 group size 21-100 58 51 0 0.944 0.336 1.864 0.147 1.000 NA group size 101+ 47 44 0 0.283 0.193 1.864 0.147 1.000 NA Cryptic species (3.7 km truncation) calm seas 102 78 14 1.574 0.199 1.864 0.147 0.787 0.103 Large delphinids (3.7 km truncation) group size 1-20 15 14 1 0.504 0.306 1.864 0.147 0.736 0.391 group size 21+ 17 17 0 0.352 NA 1.864 0.147 1.000 NA Large whales (5.5 km truncation) group size 1-3 87 81 3 0.696 0.278 1.863 0.146 0.901 0.073 group size 4+ 26 22 0 0.256 NA 1.863 0.146 1.000 NA Small whales (3.7 km truncation! calm seas 23 19 1 0.614 0.488 1.864 0.147 0.840 0.218 nmi) from shore. Although striped dolphins were known to inhabit this area (Leather- wood et al., 1982), their frequency of occur- rence was much greater than expected. Blue whales were seen primarily in southern Cali- fornia between 92 and 370 km (50-200 nmi) offshore. In previous years, this species was seen commonly in central California between the coast and 92 km (50 nmi) offshore (Calambokidis et al., 1990b). One species was surprising in its absence: short-finned pilot whales, Globicephala macrorhynchus, were previously common in southern California, es- pecially around the Channel Islands in winter (Leatherwood et al., 1982). (Note: one group of pilot whales was seen and photographed by independent researchers between San Fran- cisco and Monterey on 2 November 1991.6) Abundance Abundance estimates from this study are also in general agreement with previous esti- 6 Jones, P. A, and I. D. Szczepaniak. 1992. Report on the seabird and marine mammal censuses conducted for the long-term management strategy (LTMS), August 1990 through November 1991, for the U.S. Environmental Protection Agency, Region IX, San Francisco. July 1992. 42' : C*pe Mendocino 40' \ ® X X 38' X**® «* I S«n Francisco X o ) u ® # x V 36' \ CO 8 » * * j Pcfci!Conc*pCfcin 34' PACIFIC X X CO 9 >-* * * 1. A & X It a x „ x * x xx CP» 8 xx 9* 30' 132" 130' 128' 126' 124' 122" 120' 118" Longitude Figure 2 Locations of on-effort sightings of short-beaked common dolphins (x), long-beaked common dolphins (O), unidentified common dolphins (A), and striped dolphins ( ). Scientific names are given in Table 1. Fishery Bulletin 93(1). 1995 Table 3 Number of groups seen (n ), mean group size (S), density of individuals , abunda rice estimates (N), 95% confidence intervals (CI) on those estimates, and coefficients of variation (CV) for al species and higher taxa that were identified. Density estimates are based on lengths of transect given in the text and estimates of/tO) andg(O) given in Table 2. Mean group size includes only the indicated species and can therefore be less than the minimum of the group size category (which is defined based on the total number of all species present). Scientific names are given in Table 1. Number Mean Animal Pop. Boot strap Log-normal Lower Upper Lower Upper of groups group size density size 95% 95% 95% 95% Species strata n S km2 N CV CI CI CI CI Small delphinids short-beaked common dolphin 3.248 225,821 0.279 143,026 419,911 132,139 385,918 group size 1-20 25 11.0 0.261 group size 21-100 52 44.7 1.274 group size 101 + 39 267.3 1.713 long-beaked common dolphin 0.136 9,472 0.683 0 27,029 2,817 31,842 group size 1-20 1 11.8 0.011 group size 21-100 0 0.0 0.000 group size 101+ 4 190.2 0.125 common dolphin (unclassified) 0.148 10,286 0.815 573 37,007 2,539 41,664 group size 1-20 6 5.4 0.031 group size 21-100 1 15.1 0.008 group size 101 + 1 661.5 0.109 striped dolphin 0.273 19,008 0.412 8,234 45,864 8,755 41,267 group size 1-20 2 7.7 0.015 group size 21-100 5 29.3 0.080 group size 101 + 14 77.6 0.178 Pacific white-sided dolphin 0.177 12,310 0.537 1,888 27,965 4,590 33,010 group size 1-20 7 11.5 0.076 group size 21-100 3 46.2 0.076 group size 101 + 2 75.4 0.025 northern right whale dolphin 0.134 9,342 0.567 2,125 21,488 3,322 26,272 group size 1-20 10 9.9 0.094 group size 21-100 3 9.4 0.015 group size 101 + 2 75.7 0.025 unidentified delphinoid 0.052 3,603 0.462 1,180 6,197 1,521 8,536 group size 1-20 17 3.2 0.052 group size 21-100 0 0.0 0.000 group size 101+ 0 0.0 0.000 Cryptic species harbor porpoise' 31 5.0 0.758 52,743 0.682 0 147,905 15,714 177,026 Dall's porpoise 69 3.3 1.127 78,422 0.354 33,462 150,487 40,026 153,649 pygmy sperm whale 2 1.3 0.013 870 0.796 0 2,741 220 3,433 Large delphinids bottlenose dolphin 0.022 1,503 0.481 499 3,819 615 3,674 group size 1-20 4 2.8 0.004 group size 21+ 10 8.3 0.017 Risso's dolphin 0.122 8,496 0.415 4,236 21,676 3,890 18,555 group size 1-20 12 8.3 0.039 group size 21+ 16 25.2 0.082 killer whale 0.004 307 1.196 0 2,340 48 1,947 group size 1-20 3 3.7 0.004 group size 21+ 0 0.0 0.000 Large whales sperm whale 0.011 756 0.493 211 1,537 303 1,886 group size 1-3 4 1.2 0.002 group size 4+ 9 6.6 0.009 Barlow: Abundance of cetaceans in California waters ship surveys Table 3 (Continued) Number Mean Animal Pop. Boot strap Log-normal Lower Upper Lower Upper of groups group size density size 95% 95% 95% 95% Species strata n S km-2 N CV CI CI CI CI Baird's beaked whale 0.001 38 1.025 0 127 7 203 group size 1-3 0 0.0 0.000 group size 4+ 1 3.7 0.001 Bryde's whale 0.001 61 1.078 0 242 11 339 group size 1-3 1 1.9 0.001 group size 4+ 0 0.0 0.000 Bryde's or sei whale 0.001 63 1.093 0 232 11 355 group size 1-3 2 1.0 0.001 group size 4+ 0 0.0 0.000 fin whale 0.013 935 0.635 130 2,607 299 2,925 group size 1-3 17 1.4 0.011 group size 4+ 4 4.7 0.003 blue whale 0.033 2,250 0.381 899 4,131 1,093 4,632 group size 1-3 36 1.6 0.026 group size 4+ 13 3.3 0.007 humpback whale 0.009 626 0.411 196 1,133 289 1,359 group size 1-3 7 1.8 0.006 group size 4+ 3 7.3 0.003 unidentified baleen whale 0.003 214 0.631 26 530 69 665 group size 1-3 5 1.2 0.003 group size 4+ 1 2.1 0.001 unidentified large whale 0.009 629 0.470 167 1,306 262 1,508 group size 1-3 15 1.3 0.009 group size 4+ 0 0.0 0.000 Small whales unidentified beaked whale 3 3.5 0.019 1,322 0.892 0 4,541 295 5,921 mesoplodont beaked whale 2 1.0 0.004 250 0.834 0 746 60 1,040 Cuvier's beaked whale 7 1.9 0.023 1,621 0.823 186 5,555 396 6,637 minke whale 4 1.1 0.008 526 0.971 0 2,244 106 2,596 unidentified small whale 5 1.0 0.009 645 0.767 127 2,061 170 2,446 unidentified cetacean 3 1.7 0.009 620 0.879 0 2,026 141 2,731 ' More precise estimates for harbor porpoise are recently available in Barlow and Forney (1994). mates (Dohl et al., 1986; Barlow, 1988; Calambokidis et al., 1990a; Dohl et al.23). This is the first cetacean survey in California waters to include the region between 277 and 555 km (150-300 nmi) offshore. The studies of Dohl et al.2-3 included only the inshore 185 km (100 nmi) of the present study area, making di- rect abundance comparisons difficult. The mark-re- capture population estimates of blue and humpback whales by Calambokidis et al. (1990, a and b) were based on individuals sighted near the coast. Further- more, the estimates of Dohl et al.2-3 do not have as- sociated statistical confidence intervals. Hence, ac- curate comparisons with previous studies can be made only for the more coastal species and mean- ingful statistical tests of differences can be made for even fewer species. Direct comparisons with the 1991 and 1992 aerial surveys (Forney et al., this issue) are planned for future publications. The abundance of harbor porpoise estimated for 1984 and 1985 was approximately 9,576 (CV=0.51) (Barlow [1988] his regions 1-4), which is smaller than the present estimate of 52,700 (CV=0.68). This dis- crepancy may be due to the inappropriate design of the present survey for a coastal species such as har- bor porpoise. Humpback whale abundance in central California was estimated as 338 based on aerial surveys from Au- gust to November of 1980-83 (Dohl et al.3); however, this estimate does not include a correction factor for submerged whales. Based on mark-recapture methods, the abundance of humpback whales in 1991 and 1992 was estimated to be 581 (CV=0.03).1 This estimate is Fishery Bulletin 93(1). 1995 42' x3"««x \ 1 40' ^i» f Cape Mendocino 38' x X o SrV *%\^ft»*w Latitude X J *] Point Conception 34' A 4 ^ -. Loe ^^V__Ari9eto6 PACIFIC OCEAN V 1 32' \ A 30' *■* 132' 130' 128' 126' 124' 122' 120' 118' Longitude Figure 3 Locations of on-effort sightings of Dall's porpoise (x ), northern right whale dolphins ( ), and Pacific white-sided dolphins (O). Scientific names are given in Table 1. 42 O *1 1 a, ( Cape Mendocino 40' A \ \ ° ) 38' & *-A H V\ \ San Francisco N, Latitude CO a r A\ \ ' *\ 34' | Point Conception O A -oS-X-*"*01" PACIFIC a '*-& \ OCEAN * * \ 32' AA 30' ' 132' 130' 128' 126' 124' 122' 120' 118' Longitude Figure 4 Locations of on-effort sightings of killer whales (O), Risso's dolphins (A), and bottlenose dolphins (x). Scientific names are given in Table 1. very close to the present estimate of 626 and is well within its 95% confidence interval. For two species, new estimates of abun- dance appear to be substantially different from previous estimates. For the late 1970's, the combined summer and fall estimate of common dolphin abundance was 57,270 (CV=0.17) (Dohl et al., 1986). Although the methods used were very different and the area surveyed was smaller in that study, es- timates for other small cetaceans are simi- lar in the two studies. A large increase in common dolphin abundance is likely. This could have resulted as an effect of the 1991— 92 El Nino. Although there were no surface temperature manifestations of El Nino in the study area at the time of the survey, it is pos- sible that common dolphins were moving into California waters from farther south as a result of El Nino changes there. Since 1980, a decline has been noted in the abundance of the northern stock of common dolphins south of 30°N (Anganuzzi et al., 1993), and those authors hypothesize that this could have been caused by a general northward move- ment of that stock. This interpretation is con- sistent with the increases noted here, but the magnitude of the decrease in the south (from approximately 500,000 in 1980 to approxi- mately 100,000 in 1991 [Anganuzzi et al. 1993]) is greater than the entire estimated population in California waters. The abundance of blue whales, based on the current line-transect data (2,250), is also much higher than recent estimates made from individual-identification mark-recap- ture techniques (904 based on left-side pho- tographs and 1,112 based on right-side pho- tographs).1 Although some mark-recapture estimates may be biased low because of geo- graphic heterogeneity in habitat use by indi- vidual whales (Hammond, 1990), the meth- ods used for mark-recapture should have minimized those effects.1 South of the present study area, the abundance of blue whales was estimated to be 1,415 (CV=0.24) based on line- transect ship surveys in the eastern tropical Pacific from 1986 to 1990 (Wade and Ger- rodette, 1993). The latter study included sightings made along the coast of Baja Califor- nia (which probably belong to the California feeding population) as well as sightings made near the Costa Rica Dome and along the Equa- tor (which are likely to be part of a different population; Reilly and Thayer [1990]). Barlow: Abundance of cetaceans in California waters, ship surveys I I 42 ' ° 1 Of Cape Mendocino 40 38' x \ San Francisco N Latitude 5> Ox |> A 0\ o \ 34' *^\ Point Conception >yO *^ *— -. LO. PACIFIC ©x^x,, ^ , J%. OCEAN #*##* • \ X X ^ 32" 30 x x * o x ^ x 132' 130' 128' 126' 124' 122' 120' 118' Longitude Figure 5 Locations of on-effort sightings of fin whales ( ), humpback whales (O), blue whales (x), and sperm whales ( ). Scientific names are given in Table 1. Probability of detecting trackline groups The probability of detecting a trackline group of ani- mals,^), varied between 0.74 and 1.0 (Table 2 ). The data clearly indicated that small groups are much more likely to be missed than are large groups. This is intuitively obvious and justifies stratifying by group size when estimating ^(0) values. The fraction of trackline harbor porpoise seen in calm seas has been estimated previously to be 0.78 (with five ob- servers on a similar platform in California, Barlow [1988] and 0.70 (with six observers in the Gulf of Maine, Palka [1993]). The higher value ofg(0) esti- mated here for "cryptic species" with only three ob- servers (0.81) may be due to the inclusion of Dall's porpoise which may be easier to see or may simply be an artifact of small sample size. These estimates of the fraction of animals seen include only animals that were available to be seen. Availability bias is likely to be large for species such as beaked whales, which have extremely long dive times, and harbor porpoise and Dall's porpoise, which have shorter dive times but seldom are seen more than 0.5 km from the ship and may therefore remain submerged during the entire time they are within visual range. Correcting for availability bias is more difficult than for perception bias. Attempts that have been made so far have involved detailed modeling of the surfacing behavior of the animal and the searching behavior of the researchers (Doi, 1971, 1974; Barlow et al., 1988; Stern, 1992; Kasamatsu and Joyce7). In addition, there are still problems with estimating perception bias because the methods used here assume that all animals are equally available to be seen if they sur- face. Heterogeneity in sightability (e.g. ani- mals that splash vs. animals that do not) gen- erally will result in an underestimate of the fraction missed. Additional work is needed to obtain complete estimates of the fraction of trackline animals seen for all species. Previous studies of Dall's porpoise have shown that attraction to the vessel is a greater problem for estimating the abun- dance of this species than are missing trackline animals (Turnock and Boucher8). Turnock and Quinn (1991) estimated a cor- rection factor of 0.2378 (CV=0.3391) to ad- just Dall's porpoise abundance estimates for ship surveys (effectively then, g0=4.2). That study was based, however, on a design that used only one observer who searched with 7x binoculars and unaided eyes. In the present study, very few Dall's porpoise ap- peared to be attracted to the vessel; of those sighted in calm conditions and used for abundance estimation, only 10% (9 of 88) of the Dall's porpoise groups approached the vessel to "ride the bow wave," and 89% (78 of 88) were exhibiting a "slow roll" sur- facing behavior at the time they were first sighted. Because attraction to the vessel was less than in other studies and because most Dall's porpoise were sighted before showing any apparent reaction to the vessel (perhaps because 25x binoculars were used), the magnitude of bias is probably less than that es- timated by Turnock and Quinn ( 1991). Statistical precision An attempt was made to account for most sources of sampling error in the bootstrap estimates of confi- dence intervals and coefficients of variation. How- ever, several sources of variation could not be easily included. The process of selecting a stratification 7 Kasamatsu, F., and G. G. Joyce. 1991. Abundance of beaked whales in the Antarctic. Int. Whaling Comm. working paper SC/43/012. 8 Turnock, B. J., and G. C. Boucher. 1990. Population abundance of Dall's porpoise, Phocoenoides dalli, in the western North Pacific Ocean. Int. Whaling Comm. working paper SC/42/SM10. 12 Fishery Bulletin 93(1), 1995 40" 38 ■£ 36' 34" 30' 132' 120' 118' Longitude Figure 6 Locations of on-effort sightings of beaked whales of the genus Mesoplo- don (...), Cuvier's beaked whales (O), Baird's beaked whales ( ), and unidentified beaked whales (x). Scientific names are given in Table 1. model by minimizing AIC would have been too time consuming to include in the bootstrap procedure; hence, precision estimates are contingent on the cho- sen models being approximately correct. Variability in estimating mean group size was included implic- itly in the Monte Carlo sampling, but it was assumed that the group size estimate for any given group was accurate. Pooling of data to estimate /10) and g(0) introduces a bias (to the extent that individuals dif- fer within a pooled group) which is not accounted for in precision estimates. All of these factors would tend to result in precision being overestimated. Overall, coefficients of variation are likely to be too small and true confidence intervals are probably wider than those reported. Acknowledgments This survey could not have been accomplished with- out the diligent work of many people, including the officers and crew of the RV McArthur. S. Hill served as cruise coordinator. The six primary observers were W. Armstrong, S. Benson, J. Cotton, D. Everhardt, M. Lycan, and R. Mellon. The independent observ- ers included E. Archer, K. Forney, S. Hill, S. Kruse, M. Lowry, V. Philbrick, B. Taylor, and P. Wade (and J. B.). The ship-board data log- ging software was written by J. Cubbage (and J. B.). Observer training was provided by S. Hill, A. Jackson, W. Perryman, and R. Pit- man. Data were edited and archived by A. Jackson and K. Wallace. Sighting distribu- tions were plotted with software written by T Gerrodette. The survey design was im- proved by thoughtful suggestions from T Gerrodette and D. DeMaster. This manu- script was improved by helpful suggestions from S. Buckland, K. Burnham, J. Calam- bokidis, J. Carretta, K. Forney, T Gerrodette, J. Laake, R. Brownell, P. Wade, and two anonymous reviewers. Literature cited Akaike, H. 1973. Information theory and an extension of the maximum likelihood principle. In B. N. Petran and F. Csaaki (eds.), International symposium on information theory, 2nd ed., 1451 p. Akadeemiai Kiadi, Budapest, Hungary. Anganuzzi, A. A., S. T. Buckland, and K. L. Cattanach. 1993. Relative abundance of dolphins associated with tuna in the eastern Pacific Ocean: analysis of 1991 data. Rep. Int. Whaling Comm. 43:459^165. Barlow, J. 1988. Harbor porpoise (Phocoena phocoena ) abundance es- timation in California, Oregon and Washington: I. Ship surveys. Fish. Bull. 86:417-432. Barlow, J., and K. A. Forney. 1994. An assessment of the 1994 status of harbor porpoise in California. U.S. Dep. Commer., NOAA Tech. Memo. NMFS. NOAA-TM-NMFS-SWFSC-205, 17 p. Barlow, J., and T. Lee. 1994. The estimation of perpendicular sighting distance on SWFSC research vessel surveys for cetaceans: 1974 to 1991. U.S. Dep. Commer., NOAA Tech. Memo. NMFS. NOAA- TM-NMFS-SWFSC-207, 46 p. Barlow, J., C. Oliver, T. D. Jackson, and B. L. Taylor. 1988. Harbor porpoise (Phocoena phocoena ) abundance es- timation in California, Oregon and Washington: II. Aerial surveys. Fish. Bull. 86:433-444. Buckland, S. T. 1985. Perpendicular distance models for line transect sampling. Biometrics 41:177-195. Buckland, S. T., J. M. Breiwick, K. L. Cattanach, and J. L. Laake. 1993a. Estimated population size of the California gray whale. Mar. Mamm. Sci. 9(3):235-249. Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993b. Distance sampling: estimating abundance of biologi- cal populations. Chapman and Hall, London, 446 p. Barlow: Abundance of cetaceans in California waters: ship surveys Burnham, 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. Calambokidis, J., J. C. Cubbage, G. H. Steiger, K. C. Balcomb, P. Bloedel. 1990a. Examination of population estimates of humpback whales in the Gulf of the Farallones, California. Rep. Int. Whaling Comm., Special Issue 12:325-333. Calambokidis, J., G. H. Steiger, J. C. Cubbage, K. C. Balcomb, C. Ewald, S. Kruse, R. Wells, and R. Sears. 1990b. Sightings and movements of blue whales off cen- tral California 1986-88 from photo-identification of individuals. Rep. Int. Whaling Comm., Special Issue 12: 343-348. Dohl, T. P., M. L. Bonnell, and R. G. Ford. 1986. Distribution and abundance of common dolphin, Del- phinus delphis, in the Southern California Bight: a quan- titative assessment based on aerial transect data. Fish. Bull. 84:333-343. Doi, T. 1971. Further development of sighting theory on whales. Bull. Tokai Reg. Fish. Res. Lab. 68:1-22. 1974. Further development of whale sighting theory. In W. E. Schevill (ed. ), The whale problem: a status report, p. 359-368. Harvard Univ. Press, Cambridge, MA. Efron, B. 1977. Bootstrap methods: another look at the jack- knife. Ann. Statistics 7:1-26. Forney, K. A., J. Barlow, and J. Carretta. 1995. The abundance of cetaceans in California waters. Part II: Aerial surveys in winter and spring of 1991 and 1992. Fish. Bull. 93:15-26. Hammond, P. S. 1990. Heterogeneity in the Gulf of Maine? Estimating humpback whale population size when capture probabili- ties are not equal. Rep. Int. Whaling Comm., Special Is- sue 12:135-140. Heyning, J. E., and W. F. Perrin. 1994. Evidence for two species of common dolphins (genus Delphinus ) from the eastern North Pacific. Contrib. Nat. Hist. Mus. Los Angeles Co. 442, 35 p. Hill, P. S., and J. Barlow. 1992. Report of a marine mammal survey of the California coast aboard the research vessel McArthur July 28- November 5, 1991. U.S. Dep. Commer, NOAA Tech. Memo. NOAA-TM-NMFS-SWFSC-169, 103 p. Holt, R. S. 1987. Estimating density of dolphin schools in the eastern tropical Pacific Ocean using line transect methods. Fish. Bull. 85:419^134. Holt, R. S., and J. E. Powers. 1982. Abundance estimation of dolphin stocks involved in the eastern tropical Pacific yellowfin tuna fishery deter- mined from aerial and ship surveys to 1979. U.S. Dep. Commer., NOAA Tech. Memo. NOAA-TM-NMFS-SWFC- 23, 95 p. Holt, R. S., and S. N. Sexton. 1989. Monitoring trends in dolphin abundance in the east- ern tropical Pacific using research vessels over a long sam- pling period: analyses of 1986 data, the first year. Fish. Bull. 88:105-111. Leatherwood, S., R. R. Reeves, W. F. Perrin, and W. E. Evans. 1982. Whales, dolphins, and porpoises of the eastern North Pacific and adjacent Arctic waters: a guide to their identification. U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circular 444, 245 p. Lennert, C, S. Kruse, M. Beeson, and J. Barlow. In press. Incidental marine mammal bycatch in California gillnet fisheries. Rep. Int. Whaling Comm., Special Issue. Marsh, H., and D. F. Sinclair. 1989. Correcting for visibility bias in strip transect aerial surveys of aquatic fauna. J. Wildl. Manage. 53:1017-1024. Palka, D. 1993. Estimates of g(0) for harbor porpoise groups found in the Gulf of Maine in August 1991. Ph.D. diss., Univ. California, San Diego. Reilly, S. B. 1984. Assessing gray whale abundance: a review. In M. L. Jones, S. L. Swartz, and J. S. Leatherwood (eds.), The gray whale, Eschriehtius robustus. Acad. Press, 624 p. Reilly, S. B., and V. G. Thayer. 1990. Blue whale {Balaenoptera musculus) distribution in the eastern tropical Pacific. Mar. Mamm. Sci. 6(4):265-277. Smitb, R. C, P. Dustan, D. Au, K. S. Baker, and E. A. Dunlap. 1986. Distribution of cetaceans and sea surface chlorophyll concentrations in the California Current. Mar. Biol. 91:385-402. Smith, T. D. 1982. Testing methods of estimating range and bearing to cetaceans aboard the RVD.S. Jordan. U.S. Dep. Commer., NOAA Tech. Memo. NOAA-TM-NMFS-SWFC-20 [avail, from National Tech. Information Serv., Springfield, VA 22161], 30 p. Stern, S. J. 1992. Surfacing rates and surfacing patterns of minke whales (Balaenoptera aeutorostrata ) off central California, and the probability of a whale surfacing within the visual range. Rep. Int. Whaling Comm. 42:379-386. Turnock, B. J., and T. J. Quinn II. 1991. The effect of responsive movement on abundance es- timation using line transect sampling. Biometrics 47:701- 715. Wade, P. R., and T. Gerrodette. 1993. Estimates of cetacean abundance and distribution in the eastern tropical Pacific. Rep. Int. Whaling Comm. 43: 477-494. 14 Fishery Bulletin 93fl), 1995 Appendix "S =nmf(0)5. (5) To estimate the total fraction of trackline groups missed owing to perception bias requires that the survey be designed with two teams of completely in- dependent observers. To be independent, both teams would have to search simultaneously, not notifying or cueing each other until a group of animals had passed abeam of the vessel and were clearly missed by the other team. This approach was deemed infea- sible because of the need to approach groups to esti- mate group size and species composition. If the ves- sel was not turned until after all groups had passed abeam, a very large percentage of those groups would not be relocated. The probability of relocation would depend on group size and species composition. These factors would add considerably to the difficulty in interpreting such survey data. Instead, the survey was designed to use a single, conditionally independent observer who was aware of sightings made by the primary team, but who did not reveal the presence of a group until that group was clearly missed by the primary team. Data from the conditionally independent observer are used to make an estimate of the probability that the primary survey team detected a trackline group. The expected number of groups, n, seen very close to the transect line, say within distance 8, can be estimated as na g(x)h(x)dx 0 ' (3) n5 = g(x)h(x)dx where nm is the total number of groups seen within the truncation distance co, g(x) is the probability of seeing a group that is at perpendicular distance x, and h(x) is the probability that a group will be at perpendicular distance x (usually assumed to be 1.0 for primary observers at all x). As 5 approaches zero distance, the above equation can be reexpressed as ns nag(0)h{0)8 g{x)h(x)dx (4) which, from the line-transect definition of /TO) (Burnham et al., 1980), can be simplified to The probability of a trackline group being seen by the primary observers can be expressed as £l(0)= '1,S "is + n2S I g2(0) (6) where the subscript 1 refers to sightings made by the primary observers and subscript 2 refers to sightings missed by the primary observers but seen by the independent observer. Combining Equations 5 and 6 and simplifying results in Sl(0): llca A<0) nlolk(0) + n2lJ2(0)/g2(0) (7) Because there were three primary observers and only one independent observer, gx(0) should be greater than or equal tog2(0). Thus Si(0) fi(0) (9) (10) CV2(n1J + CV2(n2(O) + CV2{f1(0)) + CV2{k(0)). (11) Abstract. Two aerial line- transect censuses of cetaceans were conducted along the California coast during March-April 1991 and February-April 1992. The two sur- veys were designed to provide a combined estimate of cetacean abundance for winter and spring (cold-water) conditions; they com- plemented a summer and fall ship survey in 1991. The study area (264,270 km2) extended about 278 km ( 150 nmi ) off the coast of south- ern California, and 185 km (100 nmi) off the coast of central and northern California. A primary team of two observers searched for cetacean species through bubble windows that allowed an unob- structed view to the sides and di- rectly beneath the aircraft. A third, conditionally independent observer searched through a belly window and reported animals that were missed by the primary team. Ap- proximately 7,069 km and 5,973 km were searched in 1991 and 1992, respectively, resulting in 253 sightings of at least 18 cetacean species (some animals could only be identified to higher taxa). Esti- mates of abundance and coeffi- cients of variation (in parentheses) for the most common small ceta- ceans are the following: 306,000 (0.34) common dolphins, Delphinus spp.; 122,000 (0.47) Pacific white- sided dolphins, Lagenorhynchus obliquidens; 32,400 (0.46) Risso's dolphins, Grampus griseus; and 21,300 (0.43) northern right whale dolphins, Lissodelphis borealis. Abundance estimates (and CV's) for the most common whales are the following: 892 (0.99) sperm whales, Physeter macrocephalus; 392 (0.41) beaked whales, genera Meso- plodon and Ziphius; 319 (0.41) humpback whales, Megaptera novae- angliae; and 73 (0.62) minke whales, Balaenoptera acutorostrata. The abundance of cetaceans in California waters. Part II: Aerial surveys in winter and spring of 1991 and 1992 Karin A. Forney Jay Barlow James V. Carretta Southwest Fisheries Science Center National Marine Fisheries Service. NOAA RO. Box 271, La Jolla, California 92038 Manuscript accepted 31 May 1994. Fishery Bulletin 93:15-26 (1995). California coastal waters are a pro- ductive and highly variable oceano- graphic region with a diverse ma- rine fauna. Coastal fisheries, prima- rily gillnet fisheries, cause the inci- dental death of a variety of marine mammal species (Barlow et al., in press). However, the impact of this mortality can only be evaluated if estimates of population size are available for the affected species. In the late 1970's and early 1980's, abundance estimates were obtained based on aerial surveys,1-2 but esti- mates of precision were not ob- tained for most species. Because of the age and uncertainty of these es- timates, the National Marine Fish- eries Service conducted aerial and shipboard surveys during 1991 and 1992. Based on evidence of season- ality in the abundance and distri- bution of some cetaceans (Leather- wood and Walker, 1979; Dohl et al., 1986), separate abundance esti- mates were obtained for winter and summer conditions. Two aerial sur- veys (March-April 1991 and Febru- ary-April 1992) were completed during cold-water conditions, and one ship survey (July-November 1991) was conducted during warm- water conditions (Barlow, this is- sue). The survey periods were cho- sen based on climatic atlases of the California coast which show that, on average, March and April have the coldest, and September and October the warmest sea-surface tempera- tures (U.S. Navy, 1977). Standard line-transect methods (Burnham et al., 1980; Buckland et al., 1993a) were used from both platforms. Pre- liminary abundance estimates were calculated after completion of the first aerial survey in 1991 (Forney and Barlow, 1993), but confidence limits were large. In this paper, we present combined abundance estimates for the 1991 and 1992 aerial surveys. Survey methods The methods used during the 1991- 92 aerial surveys are described in detail by Forney and Barlow (1993) and Carretta and Forney (1993), and only a summary is presented below. The study area (264,270 km2) 1 Dohl, T. P., K. S. Norris, R. C. Guess, J. D. Bryant, and M. W. Honig. 1978. Cetacea of the Southern California Bight. Part II of Summary of marine mammal and sea- bird surveys of the Southern California Bight area, 1975-1978. Final Report to the Bureau of Land Management, 414 p. [NTIS Rep. PB81248189.] 2 Dohl, T. P., R. C. Guess, M. L. Duman, and R. C. Helm. 1983. Cetaceans of central and northern California, 1980-1983: status, abundance and distribution. OCS Study MMS 84-0045. Minerals Management Ser- vice contract No. 14-12-0001-29090, 284 p. 15 16 Fishery Bulletin 93(1). 1995 encompasses California waters out to a distance of 185-278 km (100-150 nmi) from the coast and roughly a depth of 3,000-4,000 m (Fig. 1). It was defined on the basis of the distribution of fisheries that are known to take marine mammals and does not reflect a distributional boundary for any marine mammal population. Surveys were conducted along transect lines forming two nearly uniform, overlap- ping grids (Fig. 1). The resulting overall grid lines were spaced 41^46 km (22-25 nmi) apart. The loca- tion of the transect grid was chosen without refer- ence to specific areas or topographical features. To avoid potential differences in regional coverage, an attempt was made in each year to complete all transects of the first grid, providing coarse coverage of the entire study area, before beginning the second grid. However, in both years, poor weather conditions prevented the completion of both survey grids. In 1991, 85% (5,326 km) of transect grid 1 and 27% (1,739 km) of grid 2 were completed, and in 1992, jjrto 41°- - / / f — 1 Cape Mendocino 40°- 39°- .., ■ V__ / 7\ San Francisco "'-. 38°- \""/~— -— V ^-J? '- ■ \L_/ ~~7V California \ 37°- Latitude CO 1 35°- \7 / 7\Ft Conception 34°- \ / ^ ^r^"^ 7 P\ Los Angeles Pacific ^^\r~^~~L 7 ^^X 33°- Ocean X. 7~^~7^-----^'/-ZL 32°- 31°- Tn° JU | i | ■ | i | ■ | i | ' | i | ' | 127° 126° 125° 124° 123° 122° 121° 120° 119° 118° 11 7° Longitude Figure 1 Study area with two overlapping transects grids. The solid line represents grid 1, the dotted line grid 2. 81% (5,065 km) of transect grid 1 and 14% (890 km) of grid 2 were completed. The relative proportions of survey effort in different sea state and cloud cover conditions were similar for the two years (Table 1). The survey platform was a twin-engine turbo-prop DeHavilland Twin Otter, flown approximately at an altitude of 213 m (700 ft) and an airspeed of 165-185 km/h (90-100 knots). All cetacean and sea turtle sightings were recorded, but because of the high den- sities of pinnipeds near rookeries, these species were recorded only when seen farther than 10 km from land. Two "primary" observers searched through bubble windows on the left and right sides of the air- craft. These windows allowed observers to view to the side and directly beneath the aircraft with at least 10° of overlap between sides. To achieve higher sight- ing efficiency near the transect line, observers searched for cetaceans only out to a declination angle of 12° (1,004 m perpendicular distance). An addi- tional "secondary" observer monitored the trackline area out to 55° declination angles (on both sides) through a round 45-cm ( 18- in) viewing hole in the belly of the air- craft and reported sightings missed by the primary team. A fourth person re- corded all sighting, effort, and environ- mental data. To minimize observer fa- tigue, all observers rotated between these four active positions and one resting position roughly every 30 min- utes. All observers had previous experi- ence in identifying cetacean species from aerial or shipboard platforms, or both. All survey data were recorded on a laptop computer connected to a LORAN or GPS (Global Positioning System) navigational receiver, providing a con- tinuous record of position (updated every few seconds), altitude, air speed, and survey conditions. Environmental conditions, such as Beaufort sea state, percent cloud cover, and glare, were updated whenever changes occurred. Conversation in the aircraft was re- corded on a central cassette recorder as a backup to the computer record. Observers also recorded individual sighting information into personal notebooks. Surveys were conducted only in Beaufort sea states 0-4. Following the methods described in Forney and Barlow ( 1993) and Carretta and Forney (1993), the aircraft circled for each sighting to obtain species iden- tifications and school size estimates Forney et al.: Abundance of cetaceans in California waters: aerial surveys 17 Table 1 Survey effort (in km) stratified by sea state and percent cloud cover. Beaufort sea state Cloud cover 0 and 1 2 Total 1991 0-24 25-49 50-74 75-100 Total 1992 0-24 25-49 50-74 75-100 Total 212 26 45 76 359 406 0 2 78 913 66 58 129 1,166 933 8 43 251 486 1,235 1,932 96 331 980 3,338 1,349 141 192 758 2,440 1,346 85 241 532 4,403 273 676 1716 2,205 7,069 1,220 113 47 433 1,813 3,908 262 284 1,519 5,973 Both years combined 0-24 25-49 50-74 75-100 Total 618 26 47 154 845 1,846 74 101 380 2,401 3,280 2,566 8,311 238 199 536 523 288 960 1,737 965 3,235 5,778 4,018 13,042 (each observer made a confidential record of best, high, and low estimate into a personal field notebook). Any additional schools sighted while the aircraft was di- verted from the transect were recorded as 'off-effort' sightings. Only sightings made during active searches on predetermined transect lines Con-effort') were in- cluded for abundance estimation. The secondary obser- ver only reported sightings missed by the primary observer team; these secondary sightings were used to estimate the fraction of animals missed on the transect line. Analytical methods Stratification Because we were not able to complete both grids in all regions of the coast, the study area was divided into four a posteriori geographic areas to approximate uni- form coverage within each stratum (Fig. 2). Environ- mental conditions such as sea state and percent cloud cover were recorded throughout the survey, as they have been shown to influence cetacean sighting rates (Holt and Cologne, 1987; Forney et al., 1991). However, be- cause of the small number of sightings made during each combination of environmental conditions, it was not possible to evaluate their effect quantitatively. Because of the difficulty in identifying beaked whales to species level during aerial surveys, only a combined abundance estimate was obtained for this group. In the preliminary analyses of the 1991 aerial survey data, Forney and Barlow ( 1993) assigned other unidentified species based on a 'nearest identified neighbor' ap- proach. In the analyses presented here, unidentified cetacean sightings were treated separately as either 'unidentified dolphin or porpoise,' 'unidentified small whale,' or 'unidentified large whale,' because they rep- resented only a small fraction of the total animals seen. The small number of sightings for each species made it necessary to pool distributions of perpendicu- lar sighting distances for line-transect calculations. Forney and Barlow (1993) created preliminary spe- cies groups based on considerations of school size, body size and behavior, and pooled distributions for groups that were not statistically different from one another. The same procedure was used for this analy- sis, resulting in the same three species/group-size categories: 1 ) small cetacean groups with 1-10 animals; 2) small cetacean groups with more than 10 animals; and 3) medium and large cetaceans (Table 2). Table 2 Estimates of flO) and g(0), and number of sightings (n) for the three species/group-size categories used in the analysis. Small cetaceans Group size n /t0) g(0) 1-10 > 10 99 53 4.70 2.85 0.67 0.85 Species Harbor porpoise, Phocoena phocoena Dall's porpoise, Phocoenoides dalli Pacific white-sided dolphin, Lagenorhynchus obliquidens Risso's dolphin, Grampus griseus Bottlenose dolphin, Tursiops truncatus Common dolphins Delphinus delphis and D. capensis Northern right whale dolphin, Lissodelphis borealis Medium and large cetaceans Group size n f{0) giO) 1-22 57 2.49 0.95 Species Killer whale, Orcinus orca Small beaked whales, Ziphius cavirostris and Mesoplodon spp. Sperm whale, Physeter macrocephalus Right whale, Eubalaena glacialis Gray whale, Eschrichtius robustus Minke whale, Balaenoptera acutorostrata Blue whale, B. musculus Fin whale, B. physalus Humpback whale, Megaptera novaeangliae Fishery Bulletin 93| 1995 42" 39° - -a B 36° 35° 34° 33° 32° 31°- 30° Pacific Ocean 127° 126° 125° 124° 123° 122° 121° 120° 119° 118° 117° 127° 126° 125° 124° 123° 122° 121° 120° 119° 118° 117° Longitude Longitude Figure 2 Completed transects (solid lines) for 1991 and 1992, and a posteriori geographic strata (separated by broken lines) used in the analysis. Area numbers are shown in circles. Abundance estimation Line transect methods (Burnham et al., 1980; Buck- land et al., 1993a) were applied to estimate abun- dances separately for each species in each stratum: Nh yyA nij,k \j,k /}<0) 2L,gj(0) (1) where Ni = lu,k 'ij.k estimated total number of animals of species k in the study area; number of sightings of species k in area i and species/group-size category,/'; average group size of species k in area i and species/group-size category J, calculated as the total number of animals in all groups di- vided by the number of groups sighted; /"■(0) - the probability density function evaluated at zero perpendicular distance for species/group- size category j; giO) = the probability of detecting a group of ani- mals on the transect line for species/group- size category j ; L = the length of transect surveyed in area i (in km); and A- = the size of area i (in km2). Values for/(0) were obtained for each species/group- size category by fitting the distribution of all per- pendicular sighting distances (primary and second- ary; measured in km) to the Hazard rate model with the statistical software program HAZARD (Buckland, 1985). A value for ^(0) was estimated fol- lowing the methods described in Forney and Barlow ( 1993 ), but because of small sample sizes, it was not possible to estimate the variance ing(0). This should result in a downward bias in the variance of the abun- dance estimates, but bias in the abundance estimates themselves will be reduced. The lengths of transect lines flown, L- (and total sizes, A-), for the four areas are 3,715 km (46,300 km2) for area 1; 2,831 km (63,772 km2) for area 2; 4,461 km (120,108 km2) for area 3; and 2,035 km (34,090 km2) for area 4. Variance estimation Variance in estimated abundance was calculated with bootstrap techniques applied to the complete data Forney et al.: Abundance of cetaceans in California waters: aerial surveys 19 set. The data were subdivided by area into effort seg- ments of equal length, and the segments were then drawn randomly with replacement until the total number of kilometers actually surveyed in each area was reached. This process was replicated 1,000 times. Forney and Barlow (1993) demonstrated that the choice of segment lengths between 5 km and 20 km did not influence the resulting estimates of precision. In this analysis we also performed bootstrap simula- tions for 50 km and 100 km segments and again found that segment length did not affect estimates of vari- ance. For the bootstrap analysis, we chose a segment length of 50 km, which roughly reflects the degree of sampling variability for these surveys (i.e. the dimen- sion of actual gaps in the sampling grid in Figure 2). Each of the 1,000 bootstrap replicates was treated and analyzed as a separate survey: sightings were first stratified into the three species/group-size cat- egories given above. Individual values for n and s were calculated, and/10) was estimated with the pro- gram HAZARD. The estimated value of g(0) was treated as a correction factor known without error. The variance, coefficient of variation, and 95% confi- dence intervals were obtained from the distribution of the 1,000 bootstrap abundance estimates with stan- dard formulae. Because the bootstrap method (Buck- land, 1984) of obtaining confidence intervals can re- sult in the lower 95% confidence intervals being smaller than the actual number of animals seen (or even zero) we also calculated log-normal confidence intervals based on the bootstrap coefficient of variation. Results Detailed results of the survey, including sighting in- formation and plots of sighting locations for all spe- cies sighted are presented elsewhere (Carretta and Forney, 1993). Results relevant to the analyses pre- sented in this paper are given below. A total of 253 cetacean sightings were made (Fig. 3): 213 on effort (while actively searching), and an additional 40 off effort (24 while in transit, 8 beyond 12° declination angle, 7 while circling over another group of animals, and 1 by an off-effort observer). Twenty eight on-ef- fort sightings could not be positively identified to the 42° 38°- T3 3 36° -I 35°- 34° 33° 32° 31° 30° Pacific Ocean , 1 , 1 , 1 , 1 1 1 1 1 1 1 1 1 1 1 1 127° 126° 125° 124° 123° 122° 121° 120° 119° 118° 117° Longitude 42" 38° 37° 0) "O 2 36° 33° 32° 31°- 30 Pacific Ocean . 1 . 1 1 1 1 1 1 F ' 1 ■ 1 ' 1 ' I ' 127° 126° 125° 124° 123° 122° 121° 120° 119° 118° 117° Longitude Figure 3 Locations of all 253 cetacean sightings made during the 1991 and 1992 surveys. The 213 on-effort sightings (used in the abun- dance estimation) are shown by diamonds, and the 40 off-effort sightings (e.g. made while circling or in transit) are shown with plus signs. 20 Fishery Bulletin 93(1), 1995 species level. Four of these sightings were identified as ziphiid whales, for which a combined abundance estimate was calculated. The remaining 24 sightings were treated separately in the analyses. 300 400 500 600 700 Perpendicular distance 800 900 1000 0 100 200 300 400 500 600 700 800 900 1000 Perpendicular distance 300 400 500 600 700 Perpendicular distance 800 900 1000 Figure 4 Distribution of perpendicular sighting distances (100-m intervals; solid line) and Hazard model fit (dotted line) for (A) small cetaceans in groups <10, (B) small cetaceans in groups >10, and (C) medium and large cetaceans. The Hazard model provided adequate fits to the perpendicular distance distributions for the three species/group-size categories (Fig. 4). Estimates of f\0) andg(O) are given for each group in Table 1. Al- though the full transect grid was not completed in either year because of poor weather, the resulting estimates of abundance (Table 3) are the most precise that have been produced to date for this area and sea- son. CVs range from 0.24 to 0.49 for small cetaceans and from 0.35 to 1.11 for large cetaceans. Discussion Comparisons with previous abundance estimates Our abundance estimates (Table 3) can be compared directly with estimates based on 1975-83 aerial sur- veys,12 which are likely to have similar biases. The estimate of 8,460 Dall's porpoise, Phocoenoides dalli, is similar to previous aerial survey estimates of 3,000-4,000 in winter and spring.1-2 The current es- timate of 122,000 Pacific white-sided dolphins,3 Lagenorhynchus obliquidens, is greater than the com- bined estimates of 26,000 (spring) to 33,500 (winter) for central and northern California2 and 5,300 ( Jan- Jun) for southern California.1 Our estimate of 21,300 northern right whale dolphins is less than the com- bined estimates of 29,000 (spring) to 61,500 (winter) for central and northern California2 and 5,900 ( Jan- Jun) for southern California.1 The prior studies do not give estimates of statistical precision for any of the above species, but given the CVs of our estimates, the above differences are not likely to be statistically significant. In contrast to the species above, common dolphins, Delphinus spp., appear to be much more abundant at present than during the period 1975—83. The cur- rent winter estimate (306,000; CV=0.34) is more than an order of magnitude larger than the previous value of 15,488 (CV=0.36; Dohl et al., 1986), and the 99% log-normal confidence limits for these two estimates do not overlap. Preliminary comparisons (Barlow, unpubl. data) of 1979 and 1980 ship surveys with the 1991 ship survey (Barlow, this issue) also show a significant increase in common dolphin abundance. Based on these two separate lines of evidence for winter and summer conditions, the abundance of common dolphins in California appears to have in- 3 Although estimates for Pacific white-sided dolphins based on the combined 1991 and 1992 survey data are over twice the preliminary estimate of 46,000 from only the 1991 data (Forney and Barlow, 1993), the new estimate lies well within the 95% confidence limit of the previous value. Forney et al.: Abundance of cetaceans in California waters: aerial surveys 21 Table 3 Number of groups seen, mean group size, density of individuals , and abundance estimates for cetaceans in the entire California study area, and subdivided by geographic stratum (See Fig. 2). Coefficients of variation (CV) and 95% confidence intervals (CI) for the overall abundance estimates are also given. Unid.=unidentified. Bootstrap CI Log-normal CI Animal Population Species and Number of Mean group density size Lower Upper Lower Upper area groups size km"2 N CV 95% 95% 95% 95% Harbor porpoise' 18 1.2 0.0060 1,599 0.345 664 2,915 829 3,085 Area 1 0 0.0 0.0000 0 Area 2 0 0.0 0.0000 0 Area 3 10 1.0 0.0079 949 Area 4 8 1.4 0.0191 650 Dall's porpoise 38 3.1 0.0320 8,460 0.240 5,203 13,361 5,320 13,453 Area 1 9 4.0 0.0342 1,582 Area 2 2 4.5 0.0112 716 Area 3 19 2.6 00395 4,744 Area 4 8 3.0 0.0416 1,418 Pacific white-sided dolphin 21 151.6 0.4605 121,693 0.466 35,404 261,524 51,041 290,144 Area 1 5 24.6 0.0573 2,654 Area 2 7 69.4 0.2945 18,779 Area 3 7 237.1 0.6218 74,678 Area 4 2 457.0 0.7505 25,583 Risso's dolphin 19 47.6 0.1225 32,376 0.456 10,255 65,984 13,812 75,891 Area 1 14 28.5 0.2029 9,396 Area 2 1 8.0 0.0100 636 Area 3 4 124.3 0.1860 22,343 Area 4 0 0.0 0.0000 0 Bottlenose dolphin 8 17.9 0.0123 3,260 0.487 618 6,783 1,320 8,052 Area 1 7 20.3 0.0684 3,165 Area 2 0 0.0 0.0000 0 Area 3 1 1.0 0.0008 95 Area 4 0 0.0 0.0000 0 Common dolphins 27 514.9 1.1568 305,694 0.340 124,730 539,319 159.864 584,552 Area 1 22 592.7 5.8769 272,101 Area 2 4 176.0 0.4161 26,535 Area 3 1 157.0 0.0588 7,058 Area 4 0 0.0 0.0000 0 Northern right whale dolphin 31 18.9 0.0807 21,332 0.428 9,151 42,629 9,548 47,658 Area 1 18 12.3 0.1378 6,381 Area 2 4 56.5 0.1395 8,895 Area 3 6 11.8 0.0341 4,091 Area 4 3 22.7 0.0577 1,966 Killer whale 2 1.0 0.0002 65 0.689 0 133 19 220 Area 1 0 0.0 0.0000 0 Area 2 1 1.0 0.0005 30 Area 3 1 1.0 0.0003 35 Area 4 0 0.0 0.0000 0 Beaked whales2 8 1.9 0.0015 392 0.408 151 774 182 845 Area 1 0 0.0 0.0000 0 Area 2 3 1.0 0.0014 89 Area 3 2 1.5 0.0009 106 Area 4 3 3.0 0.0058 197 Sperm whale 3 10.0 0.0034 892 0.990 0 2,798 176 4,506 Area 1 0 0.0 0.0000 0 Area 2 2 14.5 0.0134 857 22 Fishery Bulletin 93(1). 1995 Table 3 (Continued) Bootstrap CI Log-normal CI AniTTlfll Po*^>'l atinn Species and Number of Mean group .\I1L Lllill A V density size Lower Upper Lower Upper area groups size km"2 N CV 95% 95% 95% 95% Area 3 1 1.0 0.0003 35 Area 4 0 0.0 0.0000 0 Northern right whale 1 1.0 0.0001 16 1.110 0 59 3 95 Area 1 1 1.0 0.0004 16 Area 2 0 0.0 0.0000 0 Area 3 0 0.0 0.0000 0 Area 4 0 0.0 0.0000 0 Gray whale3 25 4.2 0.0108 2,844 0.347 1,187 5,270 1,469 5,507 Area 1 12 3.4 0.0145 669 Area 2 0 0.0 0.0000 0 Area 3 11 5.3 0.0170 2,043 Area 4 2 3.0 0.0039 132 Minke whale 3 1.0 0.0003 73 0.616 0 181 24 223 Area 1 1 1.0 0.0004 16 Area 2 0 0.0 0.0000 0 Area 3 1 1.0 0.0003 35 Area 4 1 1.0 0.0006 22 Blue whale 1 1.0 0.0001 30 0.990 0 100 6 149 Area 1 0 0.0 0.0000 0 Area 2 1 1.0 0.0005 30 Area 3 0 0.0 0.0000 0 Area 4 0 0.0 0.0000 0 Fin whale 2 1.5 0.0002 49 1.012 0 57 9 254 Area 1 2 1.5 0.0011 49 Area 2 0 0.0 0.0000 0 Area 3 0 0.0 0.0000 0 Area 4 0 0.0 0.0000 0 Humpback whale 8 1.6 0.0012 319 0.407 114 622 148 688 Area 1 1 1.0 0.0004 16 Area 2 0 0.0 0.0000 0 Area 3 2 1.5 0.0009 106 Area 4 5 1.8 0.0058 197 Unid. large whale 5 1.2 0.0006 160 0.457 40 348 68 376 Area 1 1 2.0 0.0007 33 Area 2 0 0.0 0.0000 0 Area 3 3 1.0 0.0009 106 Area 4 1 1.0 0.0006 22 Unid. small whale 3 1.0 0.0003 68 0.676 0 188 20 226 Area 1 2 1.0 0.0007 33 Area 2 0 0.0 0.0000 0 Area 3 1 1.0 0.0003 35 Area 4 0 0.0 0.0000 0 Unid. dolphin or porpoise 15 4.4 0.0180 4,766 0.331 2,050 8,368 2,533 8,966 Area 1 2 1.5 0.0028 132 Area 2 5 4.2 0.0223 1,419 Area 3 7 5.7 0.0258 3,096 Area 4 1 2.0 0.0035 118 1 More appropriate estimates for harbor porpoise are recently avai able in Barlow and Forney ( 1994). (See D iscussion section.) 2 This category includes beaked whales of the genus Mesoplodon and Cuvier's beaked whale, Ziphius cavirostris. No Baird's beaked whales, Berardius bairdii , were seen during the surveys. 3 A more accurate estimate of the entire population of California gray whales is presented in Buckland et al., 1993. (See Discus- sion section.) Forney et al. ; Abundance of cetaceans in California waters: aerial surveys 23 creased dramatically since the early 1980's. The causes of this increase are not known, but it is pos- sible that long-term oceanographic changes (Roemmich, 1992; Roemmich and McGowan, 1994) have resulted in a shift in the distribution of com- mon dolphins into this area. This hypothesis is con- sistent with the observed decline in population size of the northern common dolphin south of our study area (Anganuzzi and Buckland, 1994). Similarly, an apparent decrease in abundance was seen in short-finned pilot whales, Globicephala macrorhynchus . This species was commonly seen in the Southern California Bight on surveys during the late 1970's and early 1980's,1'2 but only one off-effort sighting of four animals was made during our surveys. Our estimate of 304 humpback whales is roughly half the recent estimate obtained from photo-identi- fication studies.4 This is quite surprising because humpback whales, Megaptera novaeangliae , in the California feeding population are expected to be in waters off Mexico during the winter and spring sea- son. However, it is possible that some animals had already moved north into California at the time of the sightings. Alternatively, the sighted animals may have been part of the southeastern Alaska feeding population that migrates southward to breed in Mexi- can waters in spring (Baker et al., 1986). Previously published estimates for harbor porpoise, Phocoena phocoena (Barlow, 1988; Barlow et al., 1988; Barlow and Forney, 1994) and gray whales, Eschrichtius robustus (Reilly, 1984; Buckland et al., 1993b), are substantially higher than the estimates presented here. This is probably because the defined study area is not appropriate for the range of these animals. Gray whales have a much larger range and migrate through California waters (southward and then northward) from roughly November to May. Our estimate represents that portion of the population which was migrating through California in March and early April. Harbor porpoise are limited to a narrow coastal band, and our transect lines only over- lapped with this region at specific points. More appro- priate abundance estimates for harbor porpoise are pub- lished in Barlow (1988) and in Barlow and Forney (1994). Comparisons with 1991 ship surveys Although a statistical comparison between these winter and spring aerial survey estimates and the 1991 summer and fall ship survey estimates (Barlow, this issue) is precluded at this time because of dif- ferences in the sizes of the two study areas, a few patterns are noteworthy. Despite the differences in seasonal timing and areal coverage, estimates of abundance are very similar for several species. Simi- lar estimates of abundance were obtained for total common dolphins (306,000 vs. 246,000), northern right whale dolphins, Lissodelphis borealis (21,300 vs. 9,340), bottlenose dolphins, Tiirsiops truncatus (3,260 vs. 1,500), and sperm whales, Physeter macrocephalus (892 vs. 756) (aerial vs. ship esti- mates, respectively). More disparate estimates were obtained for Pacific white-sided dolphins ( 122,000 vs. 12,300), Risso's dolphins, Grampus griseus (32,400 vs. 8,500), harbor porpoise (1,600 vs. 52,700), Dall's porpoise (8,460 vs. 78,400), and total beaked whales, Ziphius cavirostris and Mesoplodon spp. (392 vs. 3,230). It may be important to note that all cases in which the ship estimates are substantially larger than the aerial estimates are for species which spend a large fraction of their time diving (harbor porpoise, Dall's porpoise, and beaked whales). Such species could be more easily missed by aerial observers owing to avail- ability bias. In the case of Pacific white-sided dol- phins and Risso's dolphins, the winter and spring aerial estimates may be larger because of a seasonal movement of animals out of Oregon and Washington in winter.5 Additional analyses, which account for differences in geographic extent of the aerial vs. ship surveys, are planned in the future. Bias There are several sources of potential bias in this study. First, abundance estimates may be biased low because animals are missed by aerial observers (per- ception bias; Marsh and Sinclair, 1989). This is most likely to be a problem with poor observation condi- tions (high sea state or overcast conditions, or both). We have attempted to estimate the magnitude of perception bias in this study through the use of a conditionally independent observer and have cor- rected abundance estimates to reduce this effect. A second source of downward bias, availability bias (Marsh and Sinclair, 1989), is introduced because animals that are submerged when the aircraft passes overhead are not available to be seen. This effect is 4 Calambokidis, J., G. H. Steiger, and J. R. Evenson. 1993. Pho- tographic identification and abundance estimates of humpback and blue whales off California in 1991-92. Final Contract Re- port 50ABNF100137 to Southwest Fish. Sci. Cent., RO. Box 271, La Jolla, CA 92038, 67 p. 5 Green, G. A., J. J. Braeggeman, R. A. Grotefendt, C. E. Bowlby, M. L. Bonnell, and K. C. Balcomb III. 1992. Cetacean distribu- tion and abundance off Oregon and Washington, 1989-1990. Ch. 1 in J. J. Brueggeman (ed.), Oregon and Washington ma- rine mammal and seabird surveys. Minerals Management Ser- vice Contract Report 14-12-0001-30426 prepared for the Pacific OCS (Outer Continental Shelf) Region. 24 Fishery Bulletin 93(1). 1995 expected to be smallest for species which tend to oc- cur in large groups, such as common dolphins, and largest for species which spend relatively little time at the surface, such as porpoise, beaked whales, and sperm whales. Dive studies (Barlow et al., 1988) may provide information on the magnitude of availability bias, but each species requires a separate assessment of the average proportion of time it spends at the sur- face (and hence is 'available'), and adequate estimates are not currently available for most species in Cali- fornia waters. Rough estimates can be made for Dall's porpoise and humpback whales based on prior stud- ies. Dall's porpoise have similar sighting character- istics to those of harbor porpoise (both have a small body size and generally are found in small groups); thus, assuming that dive patterns are similar and applying the correction factor of 3.1 (CV=0.17) for harbor porpoise,6 one would obtain a corrected esti- mate of approximately 26,200 Dall's porpoise. Based on a very small sample, a correction factor of 2.7 has been estimated for humpback whales.7 This would yield a corrected abundance estimate of 861 humpback whales. Clearly, given the magnitude of these correc- tion factors, availability bias can be substantial. Potential upward bias in line-transect analysis can result if factors other than distance to the trackline affect the probability of seeing a school. School size has been shown to affect the probability of detection (Drummer, 1985; Holt and Sexton, 1989), and this can lead to an upward bias in the abundance esti- mate (Quinn, 1985; Drummer and McDonald, 1987; Buckland et al., 1993a). To counteract this effect, we have stratified small cetacean sightings by group size and estimated abundances separately for small and large groups of the same species. This is an artificial separation, but it reduces potential biases that are due to large variation in group size within a single species, such as common dolphins or Pacific white- sided dolphins. Within each stratum, correlations of perpendicular sighting distance with group size are weak and not significant at oc=0.05 (r=0.195 for small cetaceans in groups of 1—10 animals; r=0.169 for small cetaceans in groups of greater than 10 animals; and r=0.183 for whales in groups of all sizes). 6 Calambokidis, J., J. R. Evenson, J. C. Cubbage, P. J. Gearin, and S. D. Osmek. 1993. Development of a correction factor for aerial surveys of harbor porpoise. Draft Final Contract Report to the National Marine Mammal Laboratory, NMFS, NOAA, 7600 Sand Point Way NE, BIN C-15700, Seattle, WA 98115. 36 p. 7 Calambokidis, J., G. H. Steiger, J. C. Cubbage, K. C. Balcomb, and P. Bloedel. 1989. Biology of humpback whales in the Gulf of the Farallones. Final report for Contract CX-8000-6-0003 to Gulf of the Farallones National Marine Sanctuary, NOAA, Fort Mason Center, Bldg. 201, San Francisco, CA 94123, 93 p. In summary, we have attempted to correct for per- ception bias by estimating the fraction of animals missed during these surveys and have minimized potential upward bias with a poststratification by school-size range. However, species-specific availabil- ity bias cannot currently be estimated, and overall our abundance estimates are likely to be biased downward. Precision Estimation of variance for line-transect abundance calculations can be difficult. We have attempted to include most of the sources of sampling error in the bootstrap procedure, which reestimates n, s, and/10) (in Eq. 1) for each replicate. Our analysis revealed that the choice of segment length used for the boot- strap did not affect the resulting estimates of preci- sion within the range of appropriate segment lengths for this study (5-100 km; longer segments would not be appropriate because surveys extended only 100-150 km offshore). However, potential heterogeneity due to the pooling of different species and group sizes for esti- mation of /(0) andg(0) was not accounted for in preci- sion estimates. Furthermore, we did not include the variance ing(0) or in the estimation of group size for each school encountered (however, the variance in the estimated mean group size for the survey was included in the bootstrap procedure). Thus, the coefficients of variation for the abundance estimates (Table 3) are likely to be underestimated and the confidence inter- vals are likely to be too narrow. Considerations for future aerial surveys Two species of common dolphins, short-beaked and long-beaked, are recognized in California waters (Rosel, 1992; Dizon et al., 1994; Heyning and Perrin, 1994). Although clear differences in color pattern, size, and beak length exist between these two forms, it is not currently possible to differentiate them dur- ing aerial surveys; therefore the abundance estimate here is a combined estimate. Unless reliable means of identifying the two species from the air are devel- oped, aerial surveys will not be adequate for future assessments requiring separate estimates of short- beaked and long-beaked common dolphins. Similarly, it was difficult to distinguish between the smaller species of beaked whales during our aerial surveys. The estimates presented for the beaked whales as a group are therefore a combined estimate for Ziphius cavirostris and Mesoplodon spp. All unidentified beaked whale sightings could be narrowed down to these two genera. The only other beaked whale species known to occur in this region, Berardius bairdii, can be readily distinguished based Forney et al.: Abundance of cetaceans in California waters: aerial surveys 25 on its size and was not sighted during this survey. It is likely that the categorization of "small beaked whales" will be necessary on future aerial surveys. The survey grid used here was not designed for species which are restricted to a narrow coastal re- gion. Harbor porpoise are found primarily in waters inshore of the 50-fathom (92-m) isobath (Barlow, 1988). Two distinct populations of bottlenose dolphins are found in California; the inshore form is found only within about 1 km of shore (Hansen, 1990; NMFS8). All of the bottlenose dolphins seen during this aerial survey were at least several miles from the main- land; therefore our estimate is assumed to represent the population of offshore animals. Precise estimates of abundance for harbor porpoise and inshore bottle- nose dolphins will require dedicated aerial surveys designed for those species. Work is currently in progress on both of these projects.8 Acknowledgments Funding for this project was provided by the Office of Protected Species, U.S. Department of Commerce. The aircraft was provided by the NOAA Aircraft Operations Center. We express special thanks to the pilots: T O'Mara, J. Vance, P. Wehling, and M. White. We are grateful to the meteorological staff of the National Weather Service for their valuable assis- tance in planning flights. Observers were D. Ever- hart, S. Kruse, C. LeDuc, R. LeDuc, and M. Lycan (also J. B., J. V. O, and K. A. F). Survey design was improved by comments from D. Ainley, H. Braham, S. Buckland, K. P. Burnham, D. DeMaster, D. Goodman, T Gerrodette, L. Hansen, W Hoggard, D. Palka, and T Polacheck. Data recording software was developed by J. Cubbage (and J. B.). An earlier draft of this manuscript was reviewed by the participants of the Status of California Cetacean Stocks Work- shop in March- April 1993; we thank all for their ef- forts and reviews. The submitted manuscript was reviewed by J. Calambokidis, R. Hobbs, and an anonymous reviewer. Surveys were conducted under Marine Mammal Protection Act permit 748 and per- mits GFNMS-01-92 and CINMS-01-92 from the Na- tional Marine Sanctuary Program. Literature cited Anganuzzi, A., and S. Buckland. 1994. Relative abundance of dolphins associated with tuna in the eastern Pacific Ocean: analysis of 1992 data. Rep. Int. Whaling Comm. 44:361-366. 8 National Marine Fisheries Service, Southwest Fisheries Sci- ence Center, unpublished data. Baker, C. S., L. M. Herman, A. Perry, W. S. Lawton, J. M. Straley, A. A. Wol man. G. D. Kaufman, H. E. Winn, J. D. Hall, J. M. Reinke, and J. Ostman. 1986. Migratory movement and population structure of hump- back whales (Megaptera novaeangliae) in the central and eastern North Pacific. Mar. Ecol. Prog. Ser. 31:105-119. Barlow, J. 1988. Harbor porpoise, Phocoena phocoena, abundance es- timates in California, Oregon and Washington: I. Ship surveys. Fish. Bull. 86:417-432. 1995. The abundance of cetaceans in California waters. Part I: Ship surveys in summer and fall of 1991. Fish. Bull. 93:1-14. Barlow, J., and K. A. Forney. 1994. An assessment of the 1994 status of harbor porpoise in California. U.S. Dep. Commer., NOAA Tech. Memo. NOAA-TM-NMFS-SWFSC-205, 17 p. Barlow, J., C. Oliver, T. D. Jackson, and B. L. Taylor. 1988. Harbor porpoise, Phocoena phocoena, abundance es- timates in California, Oregon and Washington: II. Aerial surveys. Fish. Bull. 86:433-444. Barlow, J., R. W. Baird, J. E. Heyning, K. Wynne, A. M. Manville II, L. F. Lowry, D. Hanan, J. Sease, and V. N. Burkanov. In press. A review of cetacean and pinniped mortality in coastal fisheries along the west coast of the U.S. and Canada and the east coast of the USSR. Rep. Int. Whal- ing Comm. (Special issue.) Buckland, S. T. 1984. Monte Carlo confidence intervals. Biometrics 40:811-817. 1985. Perpendicular distance models for line transect sampling. Biometrics 41:177-195. Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993a. Distance sampling: estimating abundance of biologi- cal populations. Chapman and Hall, New York, 446 p. Buckland, S. T., J. M. Breiwick, K. L. Cattanach, and J. L. Laake. 1993b. Estimated population size of the California gray whale. Mar. Mamm. Sci. 9:235-249. Burnham, 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. Carretta, J. V., and K. A. Forney. 1993. Report of the two aerial surveys for marine mam- mals in California coastal waters utilizing a NOAA DeHavilland Twin Otter aircraft, March 9-April 7, 1991 and February 8-April 8, 1992. U.S. Dep. Commer, NOAA Tech. Memo. NOAA-TM-NMFS-SWFSC-185, 77 p. Dizon, A. E., W. F. Perrin, and P. A. Akin. 1994. Stocks of dolphins (Stenella spp. and Delphinus delphis) in the eastern tropical Pacific: a phylogeographic classification. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 119, 20 p. Dohl, T. P., M. L. Bonnell, and R. G. Ford. 1986. Distribution and abundance of common dolphin, Del- phinus delphis, in the Southern California Bight: a quan- titative assessment based upon aerial transect data. Fish. Bull. 84:333-343. Drummer, T. D. 1985. Size-bias in line transect sampling. Ph.D. diss., Univ. Wyoming, Laramie, 143 p. Drummer, T. D., and L. L. McDonald. 1987. Size-bias in line transect sampling. Biometrics 43:13-21. 26 Fishery Bulletin 93(1), 1995 Forney, K. A., D. A. Hanan, and J. Barlow. 1991. Detecting trends in harbor porpoise abundance from aerial surveys using analysis of covariance. Fish. Bull. 89:367-377. Forney, K. A., and J. Barlow. 1993. Preliminary winter abundance estimates for ceta- ceans along the California coast based on a 1991 aerial survey. Rep. Int. Whaling Comm. 43:407-415. Hansen, L. J. 1990. California coastal bottlenose dolphins. In S. Leath- erwood and R. R. Reeves (eds.), The bottlenose dolphin, p. 403—420. Academic Press, San Diego. Heyning, J. E., and W. F. Perrin. 1994. Evidence for two species of common dolphins (genus Delphinus) from the eastern North Pacific. Contrib. Sci. (Los Angel.) 422. Holt, R. S., and J. Cologne. 1987. Factors affecting line transect estimates of dolphin school density. J. Wildl. Manage. 51:836-843. Holt, R. S., and S. N. Sexton. 1989. Monitoring trends in dolphin abundance in the east- ern tropical Pacific using research vessels over a long sam- pling period: analyses of 1986 data, the first year. Fish. Bull. 88:105-111. Leatherwood, S., and W. A. Walker. 1979. The northern right whale dolphin Lissodelphis bo- realis Peale in the eastern North Pacific. In H. E. Winn and B. L. Olla (eds.), Behavior of marine mammals: cur- rent perspectives in research. Vol. 3: Cetaceans, p. 85- 141. Plenum Press, New York-London. Marsh, H., and D. F. Sinclair. 1989. Correcting for visibility bias in strip transect aerial surveys of aquatic fauna. J. Wildl. Manage. 53:1017-1024. Quinn, T. J., II. 1985. Line transect estimators for schooling popula- tions. Fish. Res. 3:183-199. Reilly, S. B. 1984. Assessing gray whale abundance: a review. In M. L. Jones, S. L. Swartz, and J. S. Leatherwood (eds.), The gray whale, Eschrichtius robustus, p. 203-223. Academic Press, Orlando. Roenunich, D. 1992. Ocean warming and sea level rise along the south- west U.S. coast. Science 257:373-375. Roemmich, D. H., and J. A. McGowan. 1994. A long term decrease in zooplankton off California. Paper presented at the 1994 Ocean Sciences Meeting in San Diego, California, February 21-25, 1994. Abstract 0111-6 published in Supplement to EOS, Transactions, American Geophysical Union Vol. 75, No. 3, January 18, 1994. Rosel, P. E. 1992. Genetic population structure and systematic relation- ships of some small cetaceans inferred from mitochondrial DNA sequence variation. Ph.D. diss., Univ. California, San Diego, 191 p. U.S. Navy. 1977. U.S. Navy marine climatic atlas of the world. Vol. II: North Pacific Ocean. NAVAIR 50-1C-529. U.S. Govern- ment Printing Office, Washington, D.C. 20402. Abstract. The larval develop- ment of Sillaginodes punctata, Sillago bassensis, and Sillago schomburgkii is described based on both field-collected and laboratory- reared material. Larvae of the three species can be separated based on a combination of pigment and meristic characters, including extent and appearance of dorsal midline pigment, lateral pigment on the tail, presence or absence of pigment above the notochord tip, myomere number, extent and tim- ing of gut coiling, and size at flex- ion. The most useful meristic char- acter across the range of specimens was number of myomeres. Sillagi- nodes punctata with 42-45 myo- meres are easily distinguished from Sillago schomburgkii with 36-38, and from S. bassensis with 32-35. The timing of gut coiling and its subsequent effect on anus position differed both among the three species examined here and from that previously reported for sillaginid larvae in general. Timing of gut coiling and extent of anus migration are not useful characters for the identification of temperate Australian sillaginids at the fam- ily level but are useful on a specific level. Possible implications of the development of the gut to diet are discussed. Based on the presence of larvae, all three species spawn in South Australian waters. No larvae of a fourth sillaginid species, S. flin- dersi, were found during the study. South Australia is the western dis- tributional limit for S. flindersi and it does not appear to spawn in the area. Larval development of King George whiting, Sillaginodes punctata, school whiting, Sillago bassensis, and yellow fin whiting, Sillago schomburgkii (Percoidei: Sillaginidae), from South Australian waters Barry D. Bruce South Australian Department of Fisheries GPO Box 1625. Adelaide. South Australia 5001 Present address. CSIRO Division of Fisheries, GPO Box 1 538. Hobart. Tasmania. Australia 700 1 Manuscript accepted 15 June 1994. Fishery Bulletin 93:27-43 (1995). The perciform family Sillaginidae (whiting and sand smelts) consists of three genera, three subgenera, and thirty-one species of small to moderately sized fishes found pri- marily in shallow coastal waters of the Indo-Pacific (McKay, 1992). Sillaginids are highly valued food fishes in many tropical and temper- ate waters. The Sillaginidae are re- lated to the Percidae, Sciaenidae, and, to a lesser extent, the Haemu- lidae (McKay, 1985) although their sister group is yet to be determined (McKay, 1992). The most speciose of the three sillaginid genera (Sillago) includes twenty-nine species. The remaining two genera, Sillaginodes and Sillaginopsis, are monotypic. The taxonomy of the family is approach- ing stability; only a few species re- main undescribed (McKay, 1992). Two genera and thirteen species of sillaginids are found in Austra- lian waters. Four species inhabit the waters off South Australia: the King George or spotted whiting, Sillaginodes punctata; yellow fin whiting, Sillago schomburgkii; western school whiting, Sillago bassensis; and eastern school whit- ing, Sillago flindersii. The latter two species were, until recently, con- sidered subspecies of S. bassensis (McKay, 1992). All four species are widely distributed in southern Aus- tralia and form the basis for impor- tant commercial fisheries across their range (McKay, 1985; Kailola et al., 1993; May and Maxwell1). The adult and juvenile biology of each of the four species has previ- ously been documented by several authors (Scott, 1954; Gilmour, 1969; Lennanton, 1969; Robertson, 1977; Weng, 1983, 1986; Burchmore et al., 1988; Jones2; Jones et al.3), but very little is known of their early life his- tory and neither the eggs nor the larvae of any of the four species have previously been described. In 1986, the South Australian Department of Fisheries began an ichthyoplankton program to inves- 1 May, J. L., and J. G. H. Maxwell. 1986. Field guide to trawl fish from temperate waters of Australia. CSIRO Division of Fisheries Res., Hobart, Tasmania, 492 p. 2 Jones, G. K. 1979. Biological investigations on the marine scale fishery in South Aus- tralia. South Australian Dep. Agric. and Fisheries Rep., 72 p. 3 Jones, G. K., D. A. Hall, K. L. Hill, and A. J. Stamford. 1989. The South Australian marine scale fishery: stock assessment, economics, management. South Australian Dep. Fisheries Green Paper, 186 p. 27 28 Fishery Bulletin 93(1), 1995 tigate the larval ecology of commercially important fishes of South Australian waters. An important pre- requisite of any such program is the ability to make an accurate identification of larvae to species. This paper details the development of Sillaginodes punctata, Sillago schomburgkii, and S. bassensis lar- vae collected during this study. Materials and methods Specimens were obtained from plankton and beach seine samples collected between March 1986 and March 1991 aboard the research vessel MRV Ngerin in coastal waters and at various inshore nursery ar- eas off South Australia. Details of sampling locations and procedures are described in Bruce (1989). Briefly, larvae were obtained from stepped oblique tows with 70-cm-diameter bongo nets fitted with 500-micron mesh. Postsettlement (refer to definition below) lar- vae and juveniles were captured with a fine mesh beach seine (7 m x 1.8 m, 2-mm mesh) as well as by dipnetting and diving. The field-collected series of Sillaginodes punctata was supplemented with lar- vae reared in the laboratory at West Beach, Adelaide. All field-collected specimens used for description were fixed in a 10% formalin-seawater solution buff- ered with sodium tetraborate (borax) and were later transferred to a 5% solution buffered with sodium B-glycerophosphate (0.5 g per 1,000 mL). Reared lar- vae were fixed immediately in the 5% solution. Reared S. punctata were used for illustration when possible because of their superior condition. Some pigment differences were apparent between reared and field-collected larvae largely as a result of ex- pansion or contraction of melanophores. Melano- phores of field-collected larvae were generally less expanded than reared specimens. Reared larvae were typically greater in length than similarly developed field-collected material owing to increased shrink- age in the latter. Similar shrinkage effects have been previously reported for a variety of species (Theilacker, 1980; Hay, 1981; Bruce, 1988). Unless specified, devel- opment at length refers to field-collected material. Representative series of S. punctata and Sillago bassensis are deposited with the I.S.R. Munro Fish Collection, CSIRO, Hobart Tasmania. Too few S. schomburgkii larvae were collected to allow a com- plete analysis and all are currently held in a collec- tion maintained by the author at CSIRO Division of Fisheries, Hobart, Tasmania. Developmental terminology and body measure- ments follow Leis and Trnski (1989). The term "postsettlement" is used to describe newly settled individuals prior to the acquisition of scales and ju- venile colour patterns, after which they are referred to as juveniles. Body length measurements (BL) are measured as notochord length, NL (i.e. from the snout tip to the end of the notochord), in preflexion and flexion larvae, and standard length, SL (i.e. from the snout tip to the posterior margin of the superior hypural elements), in postflexion larvae and juve- niles. Body depth is taken at two points. Body depth at pectoral (BDp) is equivalent to "body depth" as defined by Leis and Trnski ( 1989), that is, as "the vertical distance between body margins (exclusive of fins) through the anterior margin of the pectoral fin base." Body depth at anus (BDa) is defined as the vertical distance between body margins (exclusive of fins and, initially, the gut) through the midpoint of the anal opening. BDa includes the gut only after overlying musculature has developed. Sillaginodes punctata eggs were measured with a Zeiss photomi- croscope III fitted with an ITC 510 video camera and linked to an Apple Macintosh SE computer via an HEI 582A video coordinate digitizer. Egg dimensions are reported to the nearest micron. Larvae were measured to the nearest 0.1 mm with a dissecting microscope fitted with an ocular micrometer. Postsettlement larvae and juveniles were measured to the nearest 0.1 mm with vernier calipers. Meristic counts were made on S. punctata and Sillago bassensis specimens cleared and stained with alcian blue and alizarin red-S following Potthoff (1984). Insufficient specimens of S. schomburgkii were available for clearing and staining and therefore all meristics were taken from unstained material. Descriptions are based primarily on the detailed examination of a representative series of specimens; however, comments on pigment and meristic vari- ability stem from the routine examination of all lar- vae collected. The number of specimens examined in detail, the size range covered, and the museum ref- erence numbers (for lodged material) are provided under each species account. Results Identification Larvae were identified to family level from larval sillaginid characters reported in the literature. Silla- ginid larvae are elongate and have 30-^t4 myomeres (Johnson, 1984; Miskiewicz, 1987; Leis and Trnski, 1989). The gut typically reaches to greater than 55% body length in preflexion larvae. The anus is reported to migrate anteriorly during development (often dur- ing flexion) as a result of coiling of the anterior sec- tion of the gut, thus shortening the preanal length Bruce Larval development of Sillagmodes punctata. Sillago bassensis, and Sillago schomburgku 29 (Leis and Trnski, 1989). Sillaginids have a charac- teristic series of melanophores along the dorsal and ventral midlines (particularly prominent in small larvae) and generally have pigment located on the angle of the lower jaw. Three types of sillaginid larvae were found during this study. Specific identity of two of the types (S. schomburgkii and Sillaginodes punctata) was estab- lished by comparing vertebral counts and fin meristics of postflexion larvae to those of adult and juvenile specimens. Smaller larvae were linked by establishing a developmental series based on the extent and appearance of dorsal midline pigment, lateral pigment on the tail, presence or absence of pigment above the notochord tip, myomere number, extent and timing of gut coiling, and size at flexion. The identity of S. punctata was also confirmed by comparison to reared larvae. Though clearly separating Sillaginodes punctata from Sillago schomburgkii, fin meristics and verte- bral counts overlap in the other two South Austra- lian sillaginid species (S. bassensis and S. flindersi), thus making the specific separation of their larvae difficult. Sillaginid larvae from southern Tasmania (where only S. flindersi are found) and larvae be- lieved to be S. flindersi from New South Wales (NSW) coastal waters were compared to the third sillaginid larval type collected in South Australia in order to ascertain its identity. The NSW and Tasmanian (re- ferred to herein as eastern) specimens were highly similar but differed from the South Australian type with respect to two pigment characters. First, east- ern specimens had a single prominent, elongate mel- anophore located below the level of the pectoral fin base and overlying the cleithrum that was absent in South Australian material (Fig. 1). Second, eastern specimens developed external lateral midline pig- ment on the tail at an earlier size (7.2 mm) than did South Australian material (14.8 mm). Two sillaginids are known from Tasmanian waters: Sillaginodes punctata and Sillago flindersi (Lastetal., 1983). Only S. flindersi is known to spawn in Tasmanian waters. The eastern form was thus identified as S. flindersi and the South Australian specimens as S. bassensis. Insufficient material was available across the full size range to render an adequate description of the lar- val development of S. flindersii, and thus this spe- cies is not treated in further detail here. The most useful meristic character separating the three South Australian larval types was number of myomeres. Sillaginodes punctata with 42-45 myomeres are easily distinguished from Sillago schomburgkii with 36—38 and S. bassensis with 32— 35. Meristic details for these three species and S. flindersi are listed in Table 1. Descriptions King George whiting [Sillaginodes punctata Cuvier 1829), Figure 2 Material examined — 75 specimens, 2.0-30.5 mm BL (CSIRO L587-01, L587-02, L587-03, L587-04, L587-05, L587-06; L588-01; L589-01). Larval development — The pelagic eggs of S. punctata are spherical and have an unsegmented yolk and smooth chorion. Late stage eggs are 839- 935 microns in diameter (mean 880, n=25) and have a single oil droplet 246-263 microns in diameter (mean 255, n=25). Reared larvae hatched at 2.00- 2.15 mm (mean 2.07, re=24) at 16.5-18.7°C. The tim- ing of fertilization was not recorded as spawning oc- curred in brood stock tanks overnight. Estimates for incubation period are 48-60 hours. The temperature of the spawning tank was 16.5°C and fertilized eggs were transferred to a 90-liter tank held at 18.0-18.7°C for subsequent incubation, 24 hours prior to hatching. Newly hatched larvae have a posteriorly located oil droplet and adopt a head-down position in rear- ing containers. Yolk absorption was complete in reared larvae by 3.5 mm (8 days), although the small- Figure 1 Detail of head and trunk pigment of (A) Sillago bassensis and (B) Sillago flindersi. Myomeres have been omitted for clarity. Position of cleithrum is indicated by a dotted line. Arrow indicates characteristic melanophore overlying cleithrum in S. flindersi. 30 Fishery Bulletin 93(1), 1995 Table 1 Selected early life history features useful for identifying sillaginid larvae ( sizes are in mrr ). Size at Size at Completion first lat. first of Size at Size at midline dorsal Size at fin Number of Species gut coiling flexion pigment banding settlement formation6 myomeres Dorsal fin Anal fin Pectoral fin Sillaginodes punctata' 21.0-24.0 5.7-7.0 8.0 6.5-7.0 15.0-18.0 C,P1,A,D2+D1,P2 42^5 XlI-XIII+I,25-27 11,21-24 13-15 Sillago bassensis' 4.1-7.5 4.8-6.5 14.0 12.0-13.0 12.0-13.0 C,P1,A,D1+D2,P2 32-35 X-XII+1, 16-19 11,18-20 15-16 Sillago schomburgkii' >5.1<10.17 4.8-? 2.7 <10.1 12.0-13.0 8 36-38 X-XJI+1, 19-22 11,17-20 15-16 Sillago nliata2'3 <5.0 4.0-5.6 5.3 6.5 15.5 CAD2,D1,P1,P2 30-34 XJ+1,16-18 11,15-17 15-17 Sillago maculata2 8 4.6-6.5 3.3 10.6 8 C,PU,D2,D1,P2 33-36 XI-XII+1,19-21 11,19-20 15-17 Sillago sihama4 5.9 5.9 5.9 9.0 8 8 33-34 XI+1,20-23 11,21-23 15-17 Sillago japonica5 <7.6 <7.6 7.6 7.6 11.5 8 35-37 XI+1,21-23 11,22-24 15-17 ' This study. 2 Miskiewicz, L987. 3 Munro, 1945 4 Uchida et al. , 1958. 5 Mito, 1966 (as Sillago japonicus ); Kinoshita 1988. 6 Based on all elements present ar d ossified, C = caudal PI = pectoral, P2 = pelvic A = anal, Dl = first dorsal D2 = second dorsal. 7 No specimens between 5.1 and 10.1 mm were available. Coiling of the gut had not commenced in the 5.1-mm specimen but had been completed in the 10.1-mm specimen. * Data not available. est field-collected larvae (2.9 mm) had already com- pleted yolk absorption. Larvae are elongate (BDp=ll-16% BL) and have 42^45 myomeres (17-21 abdominal + 23-27 candal). Body depth at anus increases slightly from 7% to 9% BL during development. Other body proportions re- main relatively constant (Table 2). The gut is ini- tially straight and differentiates into defined fore, mid and hind gut sections by 3.7 mm. The gut exhib- its some convolution but does not coil during the lar- val phase. The midgut becomes rugose by approxi- mately 5.0 mm and remains so, although overlying musculature obscures this feature in postsettlement larvae larger than 21.0 mm. The gut begins to coil in postsettlement larvae of 21.0 -24.0 mm and is com- plete by 26.0 mm. Coiling of the gut proceeds with- out migration of the anus and is achieved by elonga- tion and anterior looping of the midgut. Conse- quently, body proportions do not show a significant change in preanal length which remains at 50—52% BL. The gas bladder is first visible in reared larvae by 3.5 mm (5 days) and is prominent and inflated in 86% of field-collected larvae (random subsample, n=50; all larvae collected at night) and all postsettlement lar- vae collected (all postsettlement larvae collected dur- ing day). The gas bladder has its origin at myomeres 2-5 in preflexion larvae but migrates posteriorly dur- ing development to myomeres 13-18 by 18.7 mm. The snout is initially slightly concave in profile, but after flexion, this gradually changes to straight or slightly convex. The eye is round. The mouth ini- tially reaches to below the eye, but is short of the eye in postflexion larvae. Six to eight small villiform teeth are present on the premaxilla by 5.8 mm. The num- ber of teeth increases to 10-12 by late flexion (6.5- 7.0 mm). There are no head spines. Scales are first present around the gut and lateral midline by approximately 27.5 mm. The development of fins in larval and juvenile S. punctata is summarized in Table 1. Completion of fin development occurs in the following sequence: caudal; pectoral; anal and second dorsal (almost si- multaneously); first dorsal; and pelvic. The rays of the caudal fin are present just prior to flexion in larvae of 5.6 mm. Flexion commences by 5.7-6.0 mm and is usually complete by 7.0 mm. Pec- toral fin buds are present in reared larvae as slight swellings on the body above the anterior margin of the oil droplet by 3.1 mm (2 days post hatch). Incipient rays are first visible by 7.5 mm and commence ossifi- cation by 8.5 mm. A full complement of 13-15 pectoral rays is present by 11.5 mm. Anal and second dorsal fin anlagen appear during flexion (5.8 mm). Distinct bases are present by 7.0 mm, incipient rays by 7.2 mm, and ossification commences by 8.0 mm. The anal and sec- ond dorsal fins complete development by 13.0 mm. The Bruce: Larval development of Sillagmodes punctata, Sillago bassensis. and Sillago schomburgku Figure 2 Development of Sillaginodes punctata. (A) 2.1 mm; (B) 2.9 mm; (C) 3.1 mm; (D) 3.5 mm; (E) 3.6 mm; (F) 4.2 mm; (G) 5.8 mm; (H) 6.5 mm; (I) 8.5 mm; (J) 12.0 mm; (K) 18.7 mm postsettlement; (L) 22.4 mmlpostsettlement: myomeres omitted for clarity). A-I are reared specimens, J-L are field-collected specimens. first dorsal fin anlage is present by 6.2 mm. Distinct bases are present by 7.6—8.6 mm and ossification of spines has commenced by 8.5—8.9 mm. The first dorsal fin completes development by 13.1 mm. Pelvic fins first appear as slight swellings on either side of the gut in 9.2-mm larvae. Well-developed buds are present by 13.0 mm, incipient rays form shortly thereafter. The pelvic fin does not complete development until 20.0-21.5 mm. Larval pigment — The oil droplet is well pigmented with large stellate melanophores from at least 24 32 Fishery Bulletin 93(1), 1995 hours prior to hatching until yolk exhaustion. Newly hatched larvae have melanophores scattered over the body. Melanophores appear on the ventral and ante- rior regions of the yolk sac by 2.8 mm and pigment also appears within the finfold (both dorsal and anal) between myomeres 25—32 in reared larvae (not appar- ent in field-collected larvae — probably owing to finfold damage). Finfold pigment disappears by 3.5 mm. Initially, melanophores are scattered over the snout but they disappear by 3.5 mm. Pigment appears at the angle of the lower jaw and is retained throughout the larval period. Melanophores are typically present on the lower jaw, ventrally on the gular membrane, and internally below the otic capsule. Further pigment does not form on the head until after settlement. The dorsal surface of both the gut and the gas bladder are covered with melanophores during development. A linear series of discrete melanophores is present on the ventral midline of the gut in preflexion and flexion lar- vae. Ventral melanophores disappear from the hindgut by 10.0 mm and this region then remains unpigmented. Concurrently, the remaining 5—8 melanophores be- tween the cleithral symphysis and the hindgut become elongate and are retained in postsettlement larvae. Bruce: Larval development of Sillagmodes punctata. Sillago bassensis, and Sillago schomburgkit 33 Figure 2 (continued) By 4.0 mm, pigment on the dorsal surface of the trunk and tail coalesce to form 11-18 discrete, evenly placed melanophores that extend in a linear series posteriorly from the nape to within about 4 or 5 myomeres from the notochord tip. The dorsal sur- face of the notochord tip has 0-3 melanophores (most commonly 1 or 2) and when present they are useful in separating preflexion Sillaginodes punctata from Sillago bassensis and S. schomburgkii, both of which lack pigment dorsally on the notochord tip. The dor- sal series of melanophores on the trunk and tail gradually disappears by the end of flexion (6.5-7.0 mm), excepting those between myomeres 31-40, which become prominent and may extend laterally over the body surface when expanded. Lateral mid- line pigment develops in this area during late flex- ion and is retained throughout the postflexion stage. Dorsal pigment gradually redevelops in postflexion larvae as a series of discrete bands, each comprising 3 or 4 pairs of stellate melanophores. Postsettlement lar- vae have 4—6 such bands which subsequently increase in number to 8-10 as juvenile pigmentation develops. Ventral pigment on the tail in newly hatched lar- vae is initially scattered but coalesces to form a se- 34 Fishery Bulletin 93(1). 1995 Table 2 Body proportions of larvae of Sillaginodes punctata ( expressed as a percentage of body length), d = damaged; g = gas bladder not visible; — = character not yet formed. Specimens between dotted lines were undergoing flexion. Pre -gas - Vent to Body length Pre-anal Pre-dorsal bladder Head Snout Eye anal fin Body depth Body depth (mm) length fin length length length length diameter length at pectoral at anus 3.1 51.6 37.1 22.5 6.4 9.7 12.9 8.1 3.2 53.1 — 23.4 18.7 3.1 6.2 — 10.9 6.2 3.3 51.5 — 28.8 24.2 6.1 9.1 — 15.1 9.1 3.6 51.3 — 22.2 19.4 4.1 8.3 — 11.1 5.5 3.7 51.3 — 24.3 21.6 4.1 8.1 — 12.2 6.8 4.1 47.5 — 24.4 19.5 3.7 7.3 — 12.2 6.1 4.2 50.0 — 23.8 19.0 2.3 7.1 — 11.9 7.1 4.3 55.8 — 32.5 23.2 4.6 9.3 — 16.2 9.3 4.7 51.1 — 34.0 23.4 4.2 8.5 — 14.9 8.5 5.0 50.0 — 30.0 24.0 5.0 8.0 — 13.0 8.0 5.3 52.8 — 32.1 22.6 3.7 7.5 — 13.2 8.5 5.4 50.0 — 29.6 20.4 1.8 7.4 — 13.0 7.4 5.7 47.3 — 31.6 22.8 5.3 7.0 — 12.3 7.9 5.9 45.8 — 28.8 18.6 5.1 6.8 — 11.9 6.8 6.0 48.3 60.0 31.6 23.3 6.7 6.7 — 13.3 8.3 6.2 50.0 31.4 21.0 4.0 6.4 6.4 12.1 8.1 6.3 47.6 50.8 33.3 23.8 6.3 6.3 4.2 11.1 7.9 6.4 51.6 46.9 32.0 20.3 6.2 6.2 — 12.5 7.8 6.5 47.7 49.2 33.1 23.8 6.1 d 6.9 12.3 7.7 6.6 47.0 — 30.3 22.7 5.3 6.1 6.6 10.6 7.5 6.8 50.0 48.5 30.9 20.6 5.9 6.6 — 12.5 8.1 7.0 51.4 52.3 34.3 21.4 d d — 11.4 10.0 7.2 54.1 50.0 37.5 23.6 5.7 7.6 0.7 11.1 8.3 7.6 52.6 53.9 34.2 22.3 5.3 7.2 2.6 11.8 7.9 8.4 52.3 40.4 40.4 21.4 5.9 7.1 0.0 12.5 10.7 9.3 52.3 30.1 39.7 21.5 6.4 6.4 1.6 10.7 9.1 10.3 52.4 31.1 40.8 21.3 5.8 6.8 0.5 11.1 9.7 12.0 50.0 27.5 39.2 21.7 6.7 5.0 0.6 10.0 9.2 13.1 49.6 27.5 40.4 19.8 5.3 5.3 0.7 9.2 8.4 15.7 50.9 27.4 40.8 19.1 5.7 d 0.0 10.2 11.5 16.1 50.9 26.7 41.0 19.2 5.0 5.6 0.0 9.9 9.9 18.2 51.1 27.5 40.6 20.3 6.0 6.0 0.5 9.9 10.4 18.7 49.2 25.7 38.0 19.8 5.3 5.9 1.1 9.6 9.1 ries of closely spaced melanophores extending to the notochord tip by 3.6 mm. Preflexion larvae have 2—4 melanophores ventrally on the notochord tip. Dur- ing flexion, melanophores between myomeres 23-38 become more prominent (similar to the dorsal series). The ventral series of melanophores on the tail be- comes gradually obscured by overlying musculature (excepting the prominent region between myomeres 32-38) in postflexion larvae. Paired external melano- phores develop ventrally on the tail in larvae greater than 8.5 mm and by settlement stage, approximately one pair per myomere is present. This ventral series forms a regular pattern of expanded and contracted melanophores in postsettlement specimens, match- ing the banding pattern of the dorsal series. School whiting [Sillago bassensis Cuvier, 1 829), Figure 3 Materials examined— 40 specimens, 2.3-17.2 mm BL (CSIRO L586-01— 10 specimens). Larval development — The smallest S. bassensis larva examined was 2.3 mm BL. At this size the mouth and gut are functional, the eyes are pig- mented, a gas bladder is present, and yolk absorp- tion is complete. Larvae are elongate (BDp= 13-20% BL) and have 32-35 myomeres ( 11-15+19-23). Body depth at anus increases slightly from 8-12% BL during develop- ment. Other body proportions remain relatively con- stant (Table 3). The gut forms a convoluted tube in the smallest specimen and is already differentiated Bruce Larval development of Sillaginodes punctata, Sillago bassensis, and Sillago schomburgkn 35 Figure 3 Development of Sillago bassensis. (A) 3.2 mm; (B) 4.4 mm; (C) 4.8 mm; (D) 5.9 mm; (E) 7.2 mm; (F) 11.2 mm; (G) 12.7 mm (postsettlement). into fore, mid, and hindgut regions. The midgut be- comes rugose by 3.0 mm and remains so, although overlying musculature obscures this feature prior to settlement. The gut begins to coil in preflexion lar- vae by 4.1 mm. Coiling proceeds without migration of the anus and is achieved by elongation and ante- rior looping of the midgut (Fig. 4). Consequently, body proportions do not show a significant change in preanal length which remains at 47—48% BL. Coil- ing of the gut is completed in postflexion larvae (7.0- 7.5 mm). The gas bladder has its origin at myomeres 2-8 in preflexion larvae but migrates posteriorly during development to myomeres 5-10 in postflexion larvae. The gas bladder is inflated and prominent in 90% of field-collected larvae (random subsample n=40; all larvae were collected at night). 36 Fishery Bulletin 93|1). 1995 The snout is initially slightly concave in profile, but after flexion, this gradually changes to straight or slightly convex. The eye is round. The mouth ini- tially reaches to below the center of the eye but ex- tends only to the anterior margin of the eye in postflexion larvae. Four to six small villiform teeth are present on the premaxilla by 4.7 mm. The num- ber of teeth increases to 7 or 8 during flexion (4.8- 6.5 mm). Head spination is only weakly developed. A single minute preopercular spine is present by 7.8 mm but is not visible after settlement (12.5 mm). A weak posttemporal ridge is present by 7.2 mm and is retained; however, no posttemporal spines develop. The single opercular spine is first visible by 12.7 mm and is retained in juveniles. Scales develop after settlement and are first vis- ible around the gut and lateral midline of the tail by approximately 16.0 mm. The development of fins in larval and juvenile S. bassensis is summarized in Table 1. Completion of fin development occurs in the following sequence: caudal; pectoral; anal, first dorsal and second dorsal fins (almost simultaneously); and pelvic. The rays of the caudal fin are present just prior to flexion in larvae of 4.4 mm. Flexion commences by 4.8-5.0 mm and is complete by 6.8 mm. Pectoral fin buds are present in the smallest specimen (2.3 mm), incipient rays form during flexion (5.8-6.0 mm), and a full complement of 15 or 16 rays is present by 10.0 mm. Anal-fin and second-dorsal-fin anlagen appear during flexion. Distinct bases are present by 6.5—7.0 mm, incipient rays by 6.8-7.1 mm, and ossification of posterior rays has regularly commenced by 7.2 mm. Ossification of dorsal and anal elements proceeds anteriorly and both fins complete development by 10.0-10.5 mm. The first dorsal fin anlage is present by 7.0 mm. Distinct bases are present by 7.5-8.0 mm and ossification of spines has commenced by 8.0-8.5 mm. Development of the first dorsal fin is complete by 10.0-10.5 mm. Pelvic fin buds are present in 7.0- 7.2 mm larvae below the pectoral fin bases. Develop- ment of the pelvic fin is complete by 12.5 mm. Larval pigment — S. bassensis larvae were the least pigmented of the three sillaginid species examined. Pigment on the head in preflexion larvae is lim- ited to the angle of the lower jaw and internally to Bruce: Larval development of Sillagmodes punctata. Sillago bassensis, and Sillago schomburgkri 37 Table 3 Body proportions of larvae of Sillago bassensis (expressed as a percentage of body len gth). d = i iamaged; g = gas bladder not visible; — = character not yet formed. Specimens between dotted lines were undergoing flexion. Pre-gas- Vent to Body-length Pre-anal Pre-dorsal bladder Head Snout Eye anal fin Body depth Body depth (mm) 2.3 length fin length length length length diameter length at pectoral at anus 56.5 _ g 23.9 4.3 8.6 17.4 6.5 3.1 48.4 — 27.4 24.2 d d — 16.1 8.1 3.4 44.1 — 23.5 19.1 5.9 7.3 — 14.7 5.9 3.7 51.3 — 28.4 d 4.1 8.1 — 16.2 8.1 3.8 47.4 — 25.0 22.4 3.9 9.2 — 17.1 6.6 4.1 51.2 — 29.3 26.8 6.1 8.5 — 18.3 8.5 4.2 52.4 — 29.8 26.2 7.1 8.3 — 19.0 10.7 4.3 46.5 — g 23.2 5.8 7.0 — 13.9 6.9 4.4 52.3 — 34.1 28.4 6.8 9.1 — 20.4 11.4 4.5 50.0 — g 24.4 4.4 7.7 — 15.5 8.9 4.6 44.6 — 28.2 23.9 6.5 8.7 — 14.1 7.6 4.7 44.7 — 29.8 22.3 6.4 7.4 — 12.8 6.4 4.8 54.2 36.4 29.2 6.2 8.3 2.1 18.7 12.5 4.9 44.9 — 29.6 22.4 5.1 8.2 — 13.3 8.2 5.3 47.2 — 33.0 26.4 7.5 7.5 — 15.1 8.5 5.5 50.9 38.1 g 30.9 9.1 9.1 0.0 20.9 12.7 5.7 50.9 — 31.6 29.8 8.8 8.8 0.0 17.5 10.5 5.8 44.8 56.9 56.9 25.9 6.9 7.7 0.6 13.8 7.7 5.9 49.1 55.9 g 27.1 8.5 8.5 2.5 18.6 11.0 6.3 46.0 47.6 33.3 26.2 6.3 7.9 0.8 14. 8.7 7.7 49.3 54.5 32.5 25.3 7.8 7.8 0.0 18.8 13.6 7.9 45.6 53.2 32.9 25.3 6.3 7.6 2.5 13.9 8.9 8.9 51.7 38.2 34.3 28.6 7.8 7.8 0.0 18.5 16.3 9.6 47.9 33.3 37.5 25.0 7.3 8.3 0.0 14.6 12.5 10.1 44.5 30.7 g 22.8 4.9 7.9 0.9 14.8 10.9 10.2 45.1 31.3 g 24.5 5.9 8.3 1.0 14.7 10.8 11.3 46.9 33.6 33.6 28.3 7.1 8.0 0.0 16.8 13.3 Figure 4 Morphology of the gut in Sillago bassensis (ventral view of pigment omitted). (A) 2.9 mm; (B) 4.2 mm; (C) 5.5 mm. 38 Fishery Bulletin 93(1), 1995 below the otic capsule. Melanophores are irregularly present ventrally on the gular membrane. Additional pigment on the head does not develop until after settlement. Melanophores then develop immediately anterior to and above the eye as well as on the snout and lower jaw. Larger specimens quickly develop a cap of melanophores over the mid and hindbrain. Pigment on the dorsal surface of the gut consists of 2-7 approximately evenly spaced melanophores in preflexion larvae. This reduces to 2 or 3 just prior to flexion. In postflexion larvae, internal pigment over the gut is restricted to above the gas bladder. Ventral pigment on the gut consists of a midline se- ries of 8-14 melanophores extending from just ante- rior to the cleithral symphysis to the anus in both preflexion and flexion larvae. One to two additional melanophores are usually present either side of this series below the level of the pectoral fin base (76% of larvae, random subsample «=25), forming a diamond pattern when viewed ventrally (Fig. 5). Preflexion larvae have 10-18 discrete, evenly placed melanophores that extend in a dorsal linear series on the trunk and tail to within 1-3 myomeres of the notochord tip. The dorsal surface of the noto- chord tip remains unpigmented throughout devel- opment. The dorsal series of melanophores gradu- ally disappears during flexion (4.9—6.5 mm). Postflexion larvae have 0-3 melanophores (most com- monly 0) below the bases of the second dorsal fin. Dorsal pigment redevelops after settlement as a se- ries of discrete bands each comprising 3-6 pairs of stellate melanophores. The first of these bands de- velops immediately below the posterior-most second dorsal fin rays, 5 or 6 additional bands subsequently Figure 5 Ventral pigment on the gut: (A) Sillaginodes punctata, 4.7 mm; Sillago schomburgkii, 4.4 mm; (C) Sillago bassensis, 4.1 mm. (B) develop anteriorly, and a single band developes pos- teriorly on the caudal peduncle by 20.0 mm. Lateral midline pigment on the tail does not form until after settlement, although some internal pigment may be present over vertebrae between myomeres 25-30 after 11.0 mm. A single row of 14—19 melanophores is present along the ventral midline of the tail in preflexion lar- vae. This ventral row is gradually obscured by over- lying musculature during flexion. Paired external melanophores subsequently develop ventrally on the tail in postflexion larvae, approximately one pair per myomere. After settlement, this ventral series forms a regular pattern of expanded and contracted mel- anophores producing a similar banding pattern to the dorsal series. One to two (most commonly 2) mel- anophores are present ventrally on the notochord tip in preflexion larvae. These are retained in postflexion larvae and, with additional melanophores, form a band of pigment over the caudal-fin ray bases. Yellow fin whiting [Sillago schomburgkii Peters 1865), Figure 6 Material examined — 16 specimens, 2.7-18.7 mm BL. Larval development — The smallest S. schomburg- kii examined was 2.7 mm. At this size the mouth and gut are functional, the eyes are pigmented, a gas blad- der is present, and yolk absorption is complete. Larvae are elongate (BDp= 14-18% BL) and have 36-38 myomeres (15-17+20-22). Body depth at anus increases from 8 to 16% BL during development. Other body proportions remain relatively constant (Table 4). The gut forms a convoluted tube in the smallest specimen and is already differenti- ated into fore, mid and hindgut regions. The midgut becomes rugose by 4.4 mm and re- mains so, although overlying musculature obscures this feature prior to settlement. The gut has not begun coiling in the largest flex- ion-stage larva available (5.1 mm). Coiling of the midgut has begun in the 10.1-mm larva and is well developed in all postsettlement larvae. Insufficient specimens were available to further document the timing of gut coil- ing. Coiling of the gut proceeds without mi- gration of the anus and is achieved by elon- gation and anterior looping of the midgut. Consequently, body proportions do not show a significant change in preanal length which remains at 51-53% BL. The gas bladder has its origin at myomeres 1-8 in preflexion lar- vae and is inflated and prominent in all larvae collected during night tows. The gas bladder is inconspicuous in larvae caught during the day. Bruce: Larval development of Sillaginodes punctata, Sillago bassensis, and Sillago schomburgkn 39 D Figure 6 Development of Sillago schomburgkii. (A) 2.7 mm; (B) 4.4 mm; (C) 5.0 mm; (D) 10.1 mm; (E) 13.0 mm (postsettlement). 40 Fishery Bulletin 93(1), 1995 The snout is initially slightly concave in profile, but after flexion this gradually changes to straight or slightly convex. The eye is round. The mouth ini- tially reaches below the eye but is short of the eye in postflexion larvae. Four to six small villiform teeth are present on the premaxilla by 4.4 mm. The num- ber of teeth increases from 10 to 12 during flexion (from 4.8 to greater than 5.1 mm). Head spination is only weakly developed. One to two preopercular spines are discernible in postsettlement larvae. A weak posttemporal ridge with 1 or 2 small spines is developed in the 10.1-mm postflexion larva and is present in all postsettlement larvae examined. The single opercular spine is not visible in the 10.1-mm larva but is present in postsettlement larvae and is retained in juveniles. Scales develop after settlement and are first vis- ible around the gut and lateral midline by 17.2 mm. Insufficient numbers of specimens were available to document the full sequence of fin development or the completion of flexion in S. schomburgkii. The rays of the caudal fin are present in flexion larvae of 4.8 mm. Flexion commences by 4.8 mm. Pectoral fin buds are present in the smallest speci- men (2.7 mm) and incipient rays form during flex- ion. Rays of the pectoral fin have commenced ossifi- cation in the 10.1-mm postflexion larva. A full comple- ment of 15 or 16 pectoral fin rays is present in the smallest postsettlement larva (12.7 mm). Anal-fin and second-dorsal-fin anlagen appear during flexion. Full complements (spines and rays) of the anal fin and both dorsal fins are present in the 10.1-mm speci- men. The pelvic fin has commenced development in the 10.1-mm larva and has completed development by 12.7 mm. Larval pigmentation — Pigment on the head in preflexion S. schomburgkii larvae is limited to the angle of the lower jaw and internally to the base of the otic capsule. One or two melanophores are also present ventrally on the gular membrane, increas- ing to three during flexion. Additional melanophores develop on the snout tip, scattered over the lateral surface of the head, and a cap of pigment forms over the mid and hindbrain in postflexion larvae. Pigment on the dorsal surface of the gut and gas blad- der consists of 8—10 approximately evenly spaced melanophores. Scattered internal melanophores gradu- ally spread over the lateral walls of the gut in post- flexion larvae. Ventral pigment on the gut consists of a midline series of 8-14 melanophores extending from just anterior of the cleithral symphysis to the anus (Fig. 5). Preflexion larvae have 15-22 discrete, evenly spaced melanophores that extend in a dorsal linear series from the nape to within 2-5 myomeres of the notochord tip. The number of dorsal melanophores decreases to 13 by 5.0 mm. A series of three discrete dorsal bands consisting of 3-5 paired stellate mel- anophores has replaced this dorsal series in the 10.1 mm postflexion larva. Lateral midline pigment in S. schomburgkii larvae is the most pronounced of all three species examined and is present on the tail in the smallest larva (2.7 mm) as 2 or 3 elongated mel- Table 4 Body proportions of larvae of Sillago schomburgkii (expressed as a percentage of body length), d = damaged; g = gas bladder not visible; — = character not yet formed. Specimens between dotted lines were undergoing flexion. Pre-gas- Vent to Body length Pre-anal Pre-dorsal bladder Head Snout Eye anal fin Body depth Body depth (mm) length fin length length length length diameter length at pectoral at anus 2.7 53.7 24.1 20.4 3.7 9.2 14.8 6.3 3.3 51.5 — 25.7 21.2 5.1 9.1 — 15.1 7.6 3.6 48.6 — g 25.0 6.1 8.3 — 13.9 8.3 3.7 50.0 — g 24.3 5.4 8.1 — 16.2 9.4 3.8 51.3 — 25.0 22.4 2.6 7.9 — 14.5 7.9 3.9 52.3 — 28.2 22.3 6.4 7.7 — 15.4 7.7 4.0 51.2 — g 25.0 7.5 7.5 — 17.5 9.0 4.3 52.3 — g 22.1 5.8 8.1 — 15.1 9.3 4.4 53.4 — 28.4 22.7 5.7 8.4 — 14.8 7.9 4.8 53.1 31.2 25.0 6.2 8.3 15.6 10.4 5.0 53.0 — 34.0 25.0 7.0 9.0 8.0 18.0 11.0 10.1 52.5 34.6 g 27.7 8.9 6.9 2.0 17.8 15.8 13.6 49.3 32.3 g 27.2 7.3 8.1 3.6 16.9 14.7 17.2 53.5 36.0 g 30.2 9.3 8.1 2.9 17.4 14.5 Bruce: Larval development of Sillagmodes punctata, Sillago bassensis, and Sillago schomburgkn 41 anophores in the vicinity of myomeres 24-26. Lat- eral midline pigment spreads both anteriorly and posteriorly as a linear series of elongated myomeres during development. By 10.1 mm, lateral midline pigment consists of 18 stellate and approximately evenly spaced melanophores extending from the pec- toral fin to the caudal peduncle. Internal pigment along the vertebrae is visible in the 10.1-mm post- flexion larva but is most pronounced in post- settlement larvae as clusters of melanophores located over every 2-5 vertebrae. A single row of 16-18 melanophores is present along the ventral midline of the tail in preflexion lar- vae. This ventral row is gradually obscured by over- lying musculature during flexion. Paired external melanophores (approximately one pair per myomere) subsequently develop ventrally on the tail in post- flexion larvae, approximately one per myomere. Two to three (most commonly three) melanophores are present ventrally on the notochord tip in preflexion larvae. These are retained in postflexion larvae and form a band of pigment over the caudal-fin ray bases. Discussion Egg or larval development, or both, have been de- scribed for only four other species of sillaginid lar- vae: Sillago japonica (Kamiya, 1925; Ueno and Fujita, 1954; Ueno et al., 1958; Mito, 1966 — as Sil- lago japonicus; Ikeda and Mito, 1988; Kinoshita, 1988; Oozeki et al., 1992); Sillago sihama (Gopinath, 1946; Uchida et al., 1958; Ikeda and Mito, 1988; Kino- shita, 1988); Sillago maculata (Miskiewicz, 1987; Kinoshita, 1988); and Sillago ciliata (Munro, 1945; Miskiewicz 1987; Tosh4). In addition, Miskiewicz (1987, p. 62) reported a series of unidentified sillaginid larvae which, based on pigment on the lat- eral wall of the gut below the pectoral fin base, were almost certainly Sillago flindersi. Characters useful for the identification of tropical sillaginid larvae at the family level and similarity of sillaginid larvae to those from other families have been considered in detail by Leis and Trnski (1989) and Miskiewicz ( 1987). Although most of the charac- ters discussed by these authors also apply to the tem- perate species considered here, an exception was the timing of gut coiling. Leis and Trnski ( 1989) reported that the gut of tropical sillaginid larvae commenced coiling during notochord flexion and was accompa- nied by the anterior migration of the anus. In the South Australian species, coiling of the gut com- menced prior to flexion in S. bassensis, after settle- ment in Sillaginodes punctata, and had not yet com- menced in the largest flexion larva available for Sillago schomburgkii (although coiling of the gut was present in a 10. 1-mm postflexion larva ). In all cases, coiling of the gut proceeded without migration of the anus and was achieved by anterior looping of the midgut. The implications of these variations are un- clear but suggest that, although useful on a specific level, the timing of gut coiling and migration of the anus are not useful characters for the identification of temperate sillaginids at the family level. The significance of gut coiling may relate to shifts in diet. Robertson (1977) reported a dietary shift in postsettlement Sillaginodes punctatus (-punctata) in Westernport Bay (Victoria) between November and December, a shift from harpacticoid copepods, gammarid amphipods, and mysids to larvae of the ghost prawn Callianassa australiensis, polychaetes, and juvenile crabs. Robertson correlated this dietary shift with increasing body size and mouth gape as well as with the availability of C. australiensis lar- vae. However, from his length-frequency data, this period also corresponds to the size range during which postsettlement S. punctata undergo gut coil- ing. Alternatively, because evacuation rates are be- lieved to decrease after gut coiling (Arthur, 1976, and references within; Young5), perceived changes in diet may be confounded by increased food retention times. Stomach contents were not analyzed during this study; they provide a valuable topic for further re- search. Despite seasonal sampling over five years, larvae of only three of the four sillaginid species with adult distributions extending to South Australia were lo- cated during this study. The lack of Sillago flindersi larvae suggests either that this species does not spawn in South Australian waters, that sampling frequency was too course to detect the presence of larvae of this species, or that S. flindersi larvae be- have differently from other sillaginid species and are less prone to capture (e.g. epibenthic and neustonic). Sillago flindersi larvae are frequently encountered in similar sampling regimes in coastal waters of east- ern Australia6 and in Tasmanian waters (author's pers. observ.) and thus it seems unlikely that a lack of their larvae in South Australian samples repre- sents an artifact of sampling or that their behavior is fundamentally different from other sillaginid larvae. 4 Tosh, J. R. 1903. Notes on the habits, development etc. of the common food fishes of Moreton Bay. Queensland Marine Dep.: Marine Biologist's Report. 5 Young, J. W. CSIRO Div. Fisheries, GPO Box 1538 Hobart, Tas- mania, Australia 7001. Personal commun., 1993. 6 Miskiewicz, A. G. Sydney Water Board, PO Box A53, Sydney South, NSW, Australia 2000. Personal commun., 1993. 42 Fishery Bulletin 93(1), 1995 South Australian waters represent the western distributional limit of S. flindersi in southern Aus- tralia (McKay, 1992; Gomon et al., 1994; Kailola et al., 1993). Spawning times for S. flindersi vary throughout its range; a summer spawning is recorded for Victorian populations (Hobday and Wankowski7). No data are available on either the reproductive con- dition of S. flindersi or on the presence or absence of juveniles in South Australian waters. However, on the basis of a lack of larvae, I suggest that spawning does not occur in South Australia and that the west- ern limit of S. flindersi comprises fish recruited from eastern populations. Acknowlegments I would like to thank G. K. Jones, S. A. Shepherd, A Miskiewicz, J. M. Leis, and A. J. Butler for their help- ful comments on the manuscript. Thanks are also due to A. R. Knight, R. Hudson, R. Moehring, and D. A. Short for their help in collecting and processing plankton samples. 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. 74:517-529. Bruce, B. D. 1988. Larval development of blue grenadier, Macruronus novaezelandiae (Hector), in Tasmanian waters. Fish. Bull. 86:119-128. 1989. Studying larval fish ecology: an aid to predict future catches. SAFISH 13(4):4-9. Burchmore, J. J., D. A. Pollard, M. J. Middleton, J. D. Bell, and B. C. Pease. 1988. Biology of four species of whiting (Pisces: Sillaginidae) in Botany Bay, New South Wales. Aust. J. Mar. Fresh- water Res. 39:709-727. Gilmour, A. J. 1969. The ecology of King George whiting Sillaginodes punctatus (Cuvier and Valenciennes) in Westernport Bay, Victoria. Ph.D. thesis, Monash Univ., Australia. Gopinath, K. 1946. Notes on the larval and post-larval stages of fishes found along the Trivandrum coast. Proc. Indian Natl. Sci. Acad. 12(1):7-21. Gomon M. F, C. J. M. Glover, and R. H. Kuiter. 1994. The fishes of Australia's south coast. State Print, Adelaide, Australia, 992 p. Hay, D. E. 1981. Effects of capture and fixation on gut contents and body size of Pacific herring larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:395-400. 7 Hobday, D. K., and J. W. J. Wankowski. 1987. School whiting Sillago bassensis flindersi: reproduction and fecundity in east- ern Bass Strait, Australia. Victorian Dep. Conserv., Forests and Lands, Fisheries Div. Int. Rep. 153, 24 p. Ikeda, T., and S. Mito. 1988. Pelagic fish eggs. In M. Okiyama (ed.), An atlas of the early stage fishes in Japan, p. 999-1083. Tokai Univ. Press, Tokyo. Johnson, G. D. 1984. Percoidei: development and relationships. In H. G. Moser, W. J. Richards, D. M. Cohen, M. F. Fahay, A. W. Kendall Jr. , and S. L. Richardson ( eds. ), Ontogeny and sys- tematics of fishes, p. 464-498. Am. Soc. Ichthyol. Herpetol., Spec. Publ. 1. Jones, G. K. 1980. Research on the biology of the spotted ( King George ) whiting in South Australian waters. SAFIC 4:3-7. Kailola, P. J., M. J. Williams, P. C. Stewart, R. E. Reichelt, A. McNee, and C. Grieve. 1993. Australian fisheries resources. Bureau of Rural Sciences, Fisheries Res. and Develop. Corp., Canberra, Australia, 422 p. Kamiya, N. 1925. Description of pelagic fish eggs and their larvae in Tate- yama Bay. J. Imperial Fish. Inst. 21: 71-85. [In Japanese.] Kinoshita, I. 1988. Sillaginidae. In M. Okiyama (ed.), An atlas of the early stage fishes in Japan, p. 449-452. Tokai Univ. Press, Tokyo. Last, P. R., E. O. G. Scott, and F. Talbot. 1983. Fishes of Tasmania. Tasmanian Fisheries Develop- ment Authority, Hobart, Australia, 563 p. Leis, J. M., and T. Trnski. 1989. The larvae of Indo-Pacific shore fishes. Univ. New South Wales Press, 371 p. Lennanton, R. C. J. 1969. Whiting fishery — Shark Bay. Fishing Industry News Service. W. Aust. Dep. Fish. Wildl. 2(1):4-11. McKay, R. J. 1985. A revision of the fishes of the family Sillaginidae. Mem. Queensl. Mus. 22: 1-73. 1992. FAO species catalogue. Vol. 14: Sillaginid fishes of the world. FAO, Rome., 87 p. Miskiewicz, A. G. 1987. Taxonomy and ecology of fish larvae in Lake Macquarie and New South Wales coastal waters. Ph.D. thesis, Univ. New South Wales. Mito, S. 1966. Fish eggs and larvae. In S. Motoda (ed.), Illustra- tions of the marine plankton of Japan, Vol. 7. Soyosha, Tokyo, 74 p. [In Japanese.] Munro, I. S. R. 1945. Postlarval stages of Australian fishes — No. 1. Mem. Queensl. Mus. 12:136-153. Oozeki, Y., P. Hwang, and R. Hirano. 1992. Larval development of the Japanese whiting, Sillago japonica. Jpn. J. Ichthyol. 39:59-66. Potthoff, T. 1984. Clearing and staining techniques. In H. G. Moser, W. J. Richards, D. M. Cohen, M. F. Fahay, A. W Kendall Jr., and S. L. Richardson (eds.), Ontogeny and systematics of fishes, p. 35-37. Am. Soc. Ichthyol. Herpetol., Spec. Publ. 1. Robertson, A. I. 1 977. Ecology of juvenile King George whiting Sillaginodes punc- tatus (Cuvier and Valenciennes) (Pisces: Perciformes) in West- ern Port, Victoria. Aust. J. Mar. Freshwater Res. 28:35-43. Scott, T. D. 1954. The life history of the spotted whiting, Sillaginodes punctatus (Cuvier and Valenciennes) in South Australia. M.Sc. thesis, Univ. Adelaide, Australia. Bruce: Larval development of Sillaginodes punctata, Sillago bassensis, and Sillago schomburgkn 43 Theilacker, G. H. 1980. Changes in body measurements of larval northern anchovy, Engrauhs mordax, and other fishes due to han- dling and preservation. Fish. Bull. 78:685-692. Uchida, K., S. Imai, S. Mito, S. Fujita, M. Ueno, Y. Shojima, T. Senta, M. Tahaku, and Y. Dotu. 1958. Studies on the eggs, larvae and juveniles of Japanese fishes. Series 1: Second laboratory offish biology. Fish. Dep. Fac. Agric, Kyushu Univ., Fukuoka, Japan. [In Japanese.] Ueno, M., and S. Fujita. 1954. On the development of the egg of Sillago sihama (Ferskal). Jpn. J. Ichthyol. 3:118-120. Ueno, M., T. Senta, and S. Fujita. 1958. Sillago sihama (Ferskal). In Kyushu University eds., Second laboratory of fisheries biology: studies on the eggs, larvae and juveniles of Japanese fishes. Shyuk- ousha, Fukuoka. [In Japanese.] Weng, H. T. 1983. Identification, habitats and seasonal occurrence of juvenile whiting (Sillaginidae) in Moreton Bay, Queens- land. J. Fish Biol. 23:195-200. 1986. Temporal distribution of whiting (Sillaginidae) in Moreton Bay, Queensland. J. Fish Biol. 29:755-764. Abstract. Female and sublegal-size male Tanner crabs, Chionoecetes bairdi, are often caught incidentally in the males- only fishery for this species. Effects of low air temperature during the winter fishery on juvenile and fe- male adult crabs and on the devel- oping eggs brooded by the females were simulated in the laboratory by exposing crabs to cold air (-20 to +5°C) up to 32 minutes; controls were not exposed. Exposure was expressed as degree-hours (°h), the product of temperature (°C) and time (hours). Severe exposure caused death: median lethal expo- sure stabilized at -3.3 + 0.8°h for juveniles and —4.3 ± 0.5°h for adults after 16 days. Exposure also re- duced vigor (measured by righting ability), caused pereiopod auto- tomy, and depressed adult feeding rates and juvenile growth. Expo- sures causing one-half the crabs to cease righting were —1.2 ± 0.3°h for juveniles and -2.1 ± 0.3°h for adults (measured immediately af- ter exposure). Mean pereiopod au- totomy ranged up to 44% for juve- niles exposed to -2°h, and up to 10% for adults exposed to -10.6°h. Ecdysis of juveniles was not af- fected, but exposed juveniles fre- quently shed additional pereiopods with the molt. Prompt return of incidentally caught Tanner crabs to the sea when temperatures are be- low freezing should reduce adverse effects of cold aerial exposure. Responses of Tanner crabs, Chionoecetes bairdi, exposed to cold air Mark G. Carls Charles E. O'Clair Auke Bay Laboratory, Alaska Fisheries Science Center National Marine Fisheries Service, NOAA 1 1305 Glacier Highway Juneau, Alaska 99801-8626 Manuscript accepted 23 May 1994. Fishery Bulletin 93:44-56 (1995). Tanner crabs, Chionoecetes bairdi Rathbun, 1893, are the target of a large commercial pot fishery and are an important commercial spe- cies in Alaskan waters (Otto, 1989). Landings of C. bairdi rose to a peak of 57,923 metric tons (t) in 1978, then declined to 5,390 t in 1987; landings increased to 23,507 t in 1990. 1 Current Alaska fishing regula- tions require release of small (<139- mm carapace width) male and all female C. bairdi. Commercial fish- ery openings in recent years have generally ranged from November through April,2 when minimum daily air temperatures can drop to -21°C.3 The amount of time inciden- tally captured crabs remain on deck varies, ranging from a few minutes during pot fishing to hours in some trawling operations (Stevens, 1990). Exposure to cold air during fishing operations may be detrimental to individual crabs (Carls and O'Clair, 1990), exposed egg clutches, and possibly — with sufficient fishing pressure — to the population. Regu- lations also require that Tanner crabs caught incidentally by multi- species trawling operations in the eastern Bering Sea be returned to the sea, but these regulations may be ineffective because of poor survival (22 + 3.6% for C. bairdi) of the culled crabs (Stevens, 1990). Here we report the responses of juvenile and adult female Tanner crabs and their offspring exposed to cold air. Our objectives were to determine the effects (immediate 1 Kruse, G. Alaska Dep. Fish and Game, Div. Commer. Fish., Juneau, AK 99802. Pers. commun., July 1992. 2 ADF&G (Alaska Department of Fish and Game). 1989a. Report to the Alaska Board of Fish- eries. Southeast Alaska and Yakutat (Re- gion 1) 1988/89 shellfish fisheries. Regional Information Rep. No. 1J89-01. ADF&G, Div. Commercial Fisheries, Juneau, AK. 1989b. Westward region shellfish report to the Alaska Board of Fisheries. ADF&G Regional Information Rep. No. 4K89-3. ADF&G, Div. Commercial Fisheries, Westward Regional Office, 211 Mission Rd., Kodiak, AK 99615, 325 p. 1989c. Prince William Sound management area shellfish report to the Alaska Board of Fisheries. ADF&G Regional Informa- tion Rep. No. 2C89-03. ADF&G, Div. Commercial Fisheries, Central Region, 333 Raspberry Rd., Anchorage, AK 99581, 55 p. 1989d. Cook Inlet area shellfish manage- ment report to the Alaska Board of Fish- eries, 1988-89. Regional Information Rep. No. 2H89-03. ADF&G, Div. Com- mercial Fisheries, 333 Raspberry Rd., Anchorage, AK 99581, 75 p. 1989e. Synopsis of the Montague Strait ex- perimental harvest area 1985-1988. ADF&G Regional Information Rep. No. 2C89-04. ADF&G, Div. Commercial Fish- eries, Central Region, 333 Raspberry Rd., Anchorage, AK 99581, 21 p. 1989f. Report to the Board of Fisheries Norton Sound red king crab fishery (sum- mer fishery only). ADF&G Regional In- formation Rep. No. 3N89-05. ADF&G, Div. Commercial Fisheries, Central Re- gion, Juneau, AK, 14 p. 3 NOAA. 1987. Local climatological data, monthly and annual summaries with com- parative data. U.S. Dep. Commer., Na- tional Climatic Data Center, Asheville, NC 28801. 44 Carls and O'Clair: Responses of Chionoecetes bairdi to cold air 45 and long-term) of exposure to cold air on 1) survival; 2) sublethal responses, including righting response, limb autotomy, feeding rate, ecdysis (juveniles), and growth; and 3) reproductive responses including egg survival, zoeal production, zoeal viability, and subse- quent egg extrusion and viability of the extruded clutch. Methods Experimental crabs were collected with crab pots. Juvenile crabs (both sexes) were collected in Auke Bay, Alaska (lat. 58°21'N, long. 134°41'W) on 14 and 19 January 1988. Ovigerous females were captured near Eagle River (lat. 58°31'N, long. 134°48'W) and Lena Point (lat. 58°24'N, long. 134°47'W) in Favorite Channel, Alaska, on 11 February 1988. In the laboratory, carapace length (distance from the posterior margin of the right ocular orbit to the midpoint of the posterior margin of the cara- pace) was measured to the nearest millime- ter. Carapace width was subsequently esti- mated by regressing carapace widths and lengths of Tanner crabs measured at a later date.4 Live weight was measured to the near- est 0.1 g. Juvenile crab weights ranged from 26 to 229 g (* = 109 ±14 g), and carapace lengths ranged from 35 to 64 mm (3c=49 ±2.3 mm) (Fig. 1). Estimated juvenile cara- pace widths (for both sexes) ranged from 46 to 74 mm (width=-0.237 + 1.318 x length, r2=0.994, rc=145). The immature condition of males was determined solely by body size. Adult female crab weights ranged from 182 to 553 g ( x = 329 ± 8 g), and carapace lengths ranged from 65 to 96 mm (x=80 ±1.0 mm) (Fig. 1). Estimated female carapace widths ranged from 85 to 124 mm (width=1.746 x 1.274 x length, r2=0.995, n=70). Crabs were maintained in 500-L tanks at ambient seawater temperatures (6.0-6.9°C for juveniles, 5.3-6.0°C for adults) until ex- posure to test air temperatures; after expo- sure they were returned to the same tanks for 32-35 days of observation (4.7-6.7°C for juveniles, 4.7-5. 2°C for adults). A subset of 40 female crabs was retained for an addi- tional three months of observation. Crabs were exposed in a modified chest freezer divided by a vertical baffle into two compartments of unequal size (Carls and O'Clair, 1990). Infrared heat lamps were placed in the smaller compartment for temperature control. To ensure uniform temperatures, a small fan (in the center bottom of the baffle) drew air from the exposure chamber into the small chamber at 45 ± 5 cm/sec. Return air circulated over the baffle into the exposure chamber. Temperatures were measured with a thermistor located in the exposure area near the fan and were regulated manually by switching the heat lamps on or off. Temperatures were con- trolled to ±0. 1°C after the chamber had cooled to the desired temperature. Crabs were exposed to cold air on the plywood bottom of the exposure chamber. Juvenile crabs were randomly placed in six groups with 10 crabs per group and were exposed to cold air on 21 and 25 January (about one week after capture). Exposure temperatures ranged from -5.0 to -20.0°C; exposure durations were 0, 12, 16, or 24 minutes to yield 0, -1.0, -1.5, -2.1, -4.0, and -8.0°h exposures (Table 1). The lengths (F5 54=0.06, P>0.99) and 25 r ~n ~\ 20 T 200 260 320 380 Wet weight (grams) Ik _r_r 500 40- 30- 10- Adult females Juveniles dcuxi 30 17/ Tilm rl i i 50 60 70 Carapace length (mm) n Figure 1 Chionoecetes bairdi length and weight frequencies. Adult female frequencies may not be directly comparable to juvenile frequencies because they were taken from a different locality. 4 r^O.99. Stone, R. NMFS Auke Bay Lab., Juneau, AK 99801-8626. Unpubl. data, May 1992. 46 Fishery Bulletin 93(1), 1995 Table 1 Temperature and duration of exposure of Chionoecetes bairdi to cold air. The number of crabs exposed (n) is also indicated. Controls were not exposed to air. SE = standard error. Air temperature Exposure (Celcius) time mean SE (minutes) Degree-hours n Juveniles — — 0 0.00 10 -5.0 0.02 12 -0.99 10 -7.5 0.05 12 -1.50 10 -10.2 0.24 12 -2.05 10 -15.0 0.03 16 -4.00 10 -20.0 0.07 24 -8.02 10 Adults 5.1 0.12 8 0.683 7 5.0 0.01 32 2.672 7 — — 0 0.000 31 -3.2 0.21 4 -0.211 8 -3.1 0.04 8 -0.411 8 -3.1 0.06 16 -0.813 8 -3.0 0.03 32 -1.621 8 -8.2 0.19 4 -0.544 8 -8.1 0.11 8 -1.075 8 -8.1 0.06 16 -2.149 8 -8.1 0.03 32 -4.299 7 -13.1 0.18 4 -0.875 8 -12.9 0.08 8 -1.720 8 -13.0 0.03 16 -3.472 7 -13.0 0.02 32 -6.933 8 -20.3 0.34 4 -1.353 8 -20.1 0.15 8 -2.676 8 -18.4 0.08 16 -4.899 8 -19.9 0.04 32 -10.597 8 weights (F554=0.02, P>0.99) of the crabs did not dif- fer significantly between treatments. Change in ju- venile crab body weight was estimated from initial and final measurements (32 d). Female crabs were randomly placed in 20 groups (including controls) in a complete 4 (temperature) by 5 (length of exposure) design, with 7 to 8 crabs per group. Treatment temperatures ranged from -3.1 to -20.3°C and exposure duration ranged from 0 (controls) to 32 minutes (Table 1). Two additional groups were tested at 5°C for 8 and 32 minutes (Table 1). The crabs did not differ significantly in length (F21U9=1.13, P=0.324) or weight (P.21 149=1.36, P=0.149) between treatments. Exposure took place 16 and 17 February (about six days after capture). Observation continued through 22 June. Mortality and limb autotomy were monitored daily. Crabs were judged dead when scaphognathite move- ment stopped. Generally, dead crabs were rechecked the following day before they were removed from test tanks. The number of legs missing on each crab was counted and autotomized legs were removed from the tanks. Righting response (the time it took a crab to right itself when placed on its back underwater), which we considered to be a measure of vigor, was timed to the nearest 0.01 second immediately after aerial ex- posure and 1, 2, 4, 8, 16, 24, and 32 days thereafter. Crabs that could not right themselves after 2 min- utes were recorded as "not righting" and were placed upright in the tank. A subset of 40 female crabs randomly selected from the entire exposure range was used for reproductive observations. The crabs were isolated 32 days after exposure in covered 70-L tanks that overflowed into 19-L buckets containing conical 363-u mesh nets de- signed to trap zoeae. Flow rates were approximately 1.5 L/minute; 95% turnover time was 2.3 hours and water temperatures ranged from 5.2 to 5.9°C during this period (23 March-11 May). Feeding rates were measured before and after the zoeal hatch while the 40 ovigerous females were in- dividually isolated. Mussels, Mytilus trossulus, were fed ad libitum to crabs during each feeding period. Live mussels were cut in half and drained tissue- side down on paper towels for five minutes, weighed, then placed in the tanks. Twenty-four hours later the remaining food was removed, drained, and weighed as before. At each feeding, four food portions were placed as controls in tanks without crabs. Con- sumption was corrected for the mean weight changes in the control portions. Feeding observations were repeated every 1 to 3 days, from 41 to 60 and from 85 to 98 days after exposure. Zoeae were collected daily, rinsed from the nets, concentrated in a known volume, and subsampled with a 5- or 10-mL Hensen-Stemple pipette (Carls and O'Clair, 1990). Subsamples, which contained a minimum of 200 zoeae, were preserved in 5% forma- lin and counted later; the occasional large subsample was divided with a Folsom plankton splitter before being counted. After zoeal hatching, all debris from each tank bottom was preserved to determine the number of dead eggs and zoeae. Responses of the crabs were related to aerial ex- posure, expressed as the product of air temperature (°C) and length of time in air (hours), i.e. degree-hours (°h). In a similar experiment, Carls and O'Clair ( 1990) demonstrated the usefulness of this technique for interpreting responses to aerial exposure in adult king crabs, Paralithodes camtschaticus. Because the responses of the Tanner crabs to exposure (in °h) were similar in form to those of the king crabs over identi- Carls and O'Clair: Responses of Chionoecetes bairdi to cold air 47 cal treatment ranges (0-32 minutes, -20 to +5°C; see Results section) and could be described by the same types of simple linear or nonlinear models, we used the same technique here. Regression techniques and logit analysis were used to relate response variables to exposure (Berkson, 1957; BMDP, 1983). We compared median lethal re- sponses with log-likelihood ratio tests (Fujioka, 1986). Multiple regression was used to test for dif- ferences in the slopes of regression lines and to ad- just for covariates (Kleinbaum and Kupper, 1983). The relation of selected response variables to one another was tested with parametric correlation. Af- ter one-way analysis of variance, comparisons of treatment means were made with Tukey's or Dunnett's a posteriori multiple comparison tests and judged significantly different if P<0.05. Proportional data were arcsine transformed. Reported error ranges are ±95% confidence limits. Results Mortality Below -1 to -3 degree hours, exposure to cold air killed crabs. Almost all mortality occurred 1-2 days after exposure; in groups where more than half the crabs died, mortality always reached 50% within 2 days. Mortality was inversely related to exposure and increased rapidly below -l°h for juveniles and below -3°h for adults (logistic regressions [large P- values indicate good fits], PJuvenile=0.959, Padul=0.882; Fig. 2). Nearly all deaths occurred within 8 days af- ter exposure; no crabs died after day 16. For juve- niles, calculated median lethal exposures rose from -7.7 ± 3.4°h 1 day after exposure to -3.3 ± 0.8°h 16 days after exposure, and for adults from -7.2 ± 1.6°h to -4.3 ± 0.5°h over the same time period (Table 2). Righting response The speed with which crabs righted themselves when placed on their backs was inversely related to expo- sure (Fig. 3A). The response was most clearly de- scribed by the percentage of crabs not righting within two minutes (logistic regressions, P=0.799 [n=6] for juveniles; P=0.978 [ra=22] for adults; Fig. 3B). Per- centages of crabs not righting increased sharply be- low — 1.0°h for juveniles and below -2.2°h for adults, and crabs ceased righting entirely after exposure to <-4.0°h for juveniles and <-6.9°h for adults (Fig. 3B). Median exposures causing one-half the crabs to cease righting (EC50) were -1.2 ± 0.3°h for juveniles and -2.1 ± 0.3°h for adults, measured immediately after exposure; values declined to —1.6 ± 0.3°h for juve- niles and -3.8 ± 0.5°h for adults measured 32 days after exposure (Table 3). The percentage of crabs unable to right themselves immediately after expo- sure was significantly correlated with cumulative mortality (PJuvenile=0.003, r' venile = 0.91, n=6; P . „<0.001,r^7,=0.67,/i=22) and, therefore, could adult ' adult > serve as a predictor of death. Righting times tended to improve (decrease) dur- ing the first eight days after exposure, but this re- covery was generally not statistically significant. ^k *"^N juveniles mortality o o \ \ \o \ Percent o \ ° \ ° \ 20- \ X^D adults \. □ x"s$2| 0- 1 ' 1 ' 1 ' 1 ■ 1 ' 1 -10 -8 -6 -4 -2 0 Degree- hours Figure 2 Cumulative percent mortality (P) of juvenile and adult female Chionoecetes bairdi, observed 32 days after emersion, as a function of exposure (°h): P/llMnifcj=100 / (1 + e<3 74 + x ■14x°h)), -Padu„=100 / (1 + e<6 42 + 1.48x°h)) 48 Fishery Bulletin 93(1), 1995 Righting times of juvenile crabs from all exposures tended to decrease over time (Fig. 4). The righting times of adult crabs exposed to <-2.2°h generally showed little evidence of recovery. Median exposures causing one-half the crabs to cease righting also gen- erally declined, but 95% confidence bars overlapped. Pereiopod autotomy Exposure to cold air caused pereiopod autotomy. Ju- venile pereiopod losses increased from 0 to -2°h but declined towards the most severe exposure (-8°h), possibly because early mortality precluded autotomy (Fig. 5A). Juvenile crabs often dropped legs or chela during aerial exposure, but losses also continued af- ter exposure (Fig. 5B), often during ecdysis (Fig. 6). Adult crabs autotomized fewer pereiopods than ju- veniles; as with juveniles, loss was most frequent immediately after exposure. Loss of pereiopods in adults was directly related to severity of exposure (P<0.001, r2=0.85, n=19; Fig. 5A). Autotomy was cor- related with mortality in adult crabs (P<0.001, r2=0.81, n=19) but not in juveniles (P=0.621, r2=0.07, n=6). Autotomy was also correlated with the percent- age of adult crabs not righting as measured immedi- ately after exposure (P<0.001, r2=0.81, n=22). Ecdysis Juvenile crabs began molting 22 January and con- tinued through 21 February. Molt timing was not correlated with exposure (r2=0.09). Juveniles exposed 100- 80- — W-ii- \ juveniles \ B A 60 -I o\ o fa I 40- i i i \ 20- adults \ X I I V \ o- odcrofflso o o I 1 1 1 1 1 1 ' 1 ' 1 1 1 ' -10 8 Degree-hours Figure 3 Righting times of juvenile and adult female Chionoecetes bairdi capable of righting (A), and percentage not righting (B) observed 32 days after emersion as functions of exposure (°h). Percentages not righting were 100/(1 + e'6235 + > 651 * °h>) for adults and 100/(1 -h>(4701 * 2858 * °h)) for juveniles. Error bars are ±1 standard error. The ability of the single surviving -4.9°h adult crab improved over time; its righting time 32 days after exposure was similar to that of controls. Carls and O'Clair Responses of Chionoecetes bairdi to cold air 49 Table 2 Degree-hours caus ng death (LC) in Chionoecetes bairdi exposed to cold air, estimated with logit analysis. The LC number indicates the percentage of crabs affected e.g. LC50 is the median lethal degree-hours. The error term (CI) is the estimated 95% confidence interval. Day LC10 LC30 LC50 LC70 LC90 CI Juveniles 1 -0.9 -5.1 -7.7 -10.4 -14.6 3.4 2 -1.0 -4.6 -6.8 -9.0 -12.6 2.6 4 -1.3 -3.9 -5.5 -7.1 -9.7 1.7 8 -1.3 -2.9 -3.9 -4.8 -6.4 1.1 16 -1.3 -2.5 -3.3 -4.0 -5.2 0.8 32 -1.3 -2.5 -3.3 -4.0 -5.2 0.8 Adults 1 -3.1 -5.6 -7.2 -8.8 -11.3 1.6 2 -2.8 -5.2 -6.7 -8.2 -10.6 1.5 4 -2.6 -4.8 -6.2 -7.5 -9.7 1.3 8 -3.0 -4.0 -4.6 -5.1 -6.1 0.6 16 -3.2 -3.9 -4.3 -4.8 -5.5 0.5 32 -2.8 -3.8 -4.3 -4.9 -5.8 0.6 to cold air frequently lost pereiopods during ecdysis; losses increased from 0 to — 4°h. The only crab ex- posed to -8°h that attempted to molt lost no limbs, but died during ecdysis (Fig. 6). Feeding rates Feeding rates of adult female Tanner crabs were sig- nificantly depressed by exposure to cold air (PANOVA<0.001). In general, adult females exposed to <— 2.7°h (62% of the median lethal exposure) ate sig- nificantly less than did controls (Tukey test). Feed- ing rates measured shortly before zoeal hatching (41 to 60 days after exposure) were significantly less (P<0.05) for all crabs than feeding rates after zoeal hatching (85-98 days after exposure), but the slopes (feeding rate/exposure) before and after hatching did not differ (multivariate regression, P>0.50; Fig. 7). The frequency of feeding also increased significantly after zoeal hatching (P<0.001) and was significantly related to aerial exposure before and after larval hatching (P/mrar<0.001). The most severely treated crabs (-4.9°h) did not eat before zoeal release but ate 57% of the time after release. Weight change Change in weight of juvenile crabs was reduced by exposure to cold air. Wet weights of juvenile crabs that did not molt declined with increasing exposure severity (P=0.002, r2=0.42, n=20; Fig. 8). The weight Table 3 Effective degree-hours causing cessation of i -ighting (EC) in Chionoecetes bairdi exposed to cole air, estimated with logit analysis. The EC number indicates the percentage of crabs affected; EC50 is the median effective degree-hours. The error term (CI) is the estimated 95% confidence interval. Day EC10 EC30 EC50 EC70 EC90 CI Juveniles 0 -0.2 -0.8 -1.2 -1.6 -2.2 0.3 1 -0.7 -1.2 -1.5 -1.7 -2.2 0.3 2 -0.6 -1.1 -1.5 -1.8 -2.3 0.3 4 -0.5 -1.1 -1.4 -1.7 -2.2 0.3 8 -1.1 -1.4 -1.7 -1.9 -2.3 0.3 16 -0.9 -1.3 -1.6 -1.9 -2.4 0.3 24 -0.8 -1.4 -1.7 -2.1 -2.6 0.3 32 -0.9 -1.3 -1.6 -1.9 -2.4 0.3 Adults 0 -1.3 -1.8 -2.1 -2.5 -3.0 0.3 1 -2.0 -2.7 -3.1 -3.5 -4.1 0.4 2 -1.8 -2.4 -2.8 -3.2 -3.8 0.4 4 -2.3 -2.8 -3.1 -3.4 -3.9 0.4 8 -2.1 -2.7 -3.0 -3.4 -4.0 0.4 16 -2.2 -2.7 -3.1 -3.5 -4.0 0.4 24 -2.2 -2.9 -3.4 -3.8 -4.6 0.5 32 -2.4 -3.3 -3.8 -4.3 -5.1 0.5 increment of juvenile crabs that molted also declined with decreasing exposure (Fig. 8). This trend was not significant until an outlier at -2.0°h was removed (P=0.021, r2=0.56, n=9). Pereiopod autotomy prob- ably influenced these weight outcomes. The weight changes of juvenile crabs that did not molt were cor- related with righting response measured immedi- ately after exposure (P=0.018, r2=0.88, «=5, Y=a + bx3). Changes in weight of adult crabs were not cor- related with exposure (P>0.07, r2=0.08, rc=44). Reproduction Exposure of ovigerous female crabs to cold air gen- erally did not affect the eggs or subsequently released zoeae unless the female died; all eggs died if the fe- male died. Timing of initial zoeal release (20 April ± 1 day), duration of release (11+1 day), and median release date (26 April ± 1 day) did not vary with ex- posure (r2=0.04, n=44; Fig. 9). Zoeae placed in sepa- rate containers for two days were not significantly affected by exposure prior to hatching (P=0.425, r2=0.02, «=43), and 87 ±3% continued swimming through the test period. Larval mortality, measured as the percentage of zoeae that sank to tank bottoms and died (0.4 ±0.2%), did not vary with exposure (^=0.03, n=44). Zoeal mortality (2 ±2%) during swim- ming tests was not correlated with exposure (r2=0.09). 50 Fishery Bulletin 93(1), 1995 The percentage of eggs that hatched may have been slightly affected by exposure, but our results were inconclusive (P„„M„„„_ „„ =0.036, but P, . , regression:arcsin lack of ^•cO.OlO, and ^=0.10). The percentage of eggs hatch- ing in the -5.3°h treatment differed significantly from the control (Dunnett's test), but the difference was minor (99.1% versus 99.8% hatching). Egg extrusion may have been influenced by expo- sure, but the data were inconsistent. Elapsed time between larval hatching and subsequent egg extru- sion tended to be prolonged by exposure, but the re- sponse was variable (PHnea =0.005, Plack O^,=0.719, r2=0.19, rc=41). Egg extrusion generally occurred two days (median) after zoeal release but ranged from 0 to 18 days; only crabs in the two most severe treat- ments (<—4.3°h) exceeded nine days. The date of ex- Juveniles Adults 60 50- 40- 30- 20 10 0 60 control JiBDQ Q- T ^ I ' I ' I ' I - control I ' I I ' ' I ' 1 i ' i ' r 50 40 j§ 30- 20 10-1 0 60 -1.5 °h I ' I I ' I ' I I ' I ' I ' I ' I I ' I -2.0 °h 24 32 0 Days after exposure Figure 4 Righting times of juvenile and adult Chionoecetes bairdi as a function of time in days after emersion. Error bars are ±1 standard error. trusion (4 May ±7 days) may also have been changed by exposure, but again the statistical results were incon- elusive (P^ar=0.011, P*^ ^=0.700, r^O.16, n=41). Exposure did not affect the percentage of Tanner crabs extruding eggs (93%, Plinea =0.730, r^O.03, ra=6). Discussion Extreme exposure to cold air was lethal to Tanner crabs. It is also possible that thermal shock caused when the crabs were returned to water following expo- sure was also damaging. Following sublethal exposure, crabs exhibited a slowed righting response, autotomy of pereiopods, depressed feeding rates (adults), and weight loss or reduced weight gain (juveniles). Temperature and duration of treat- ment were both critical factors in de- termining how aerial exposure affected Tanner crabs. In a similar experiment with king crabs, the response of crabs to exposure was clearly observed when exposure was defined as the product of temperature and the length of exposure time (Carls and O'Clair, 1990). The use of this composite variable worked well with the current data set. However, our approach may not be generally appli- cable (for discussion see Carls and O'Clair, [1990]). Design of this experiment precluded independent analysis of temperature and time factors. However, either fac- tor may be predicted as a function of the other. For example, at -10°C, 10% of juvenile crabs may be killed by an 8- minute exposure, and 50% may be killed by a 20-minute exposure. Similarly, a 10-minute exposure would impair right- ing in 50% of juvenile crab at -7°C. Pre- dicted times and temperatures were calculated from degree-hours causing death (LC) or from effective degree-hours causing cessation of righting (EC) esti- mates (Tables 2 and 3); temperature multiplied by time (units are Celcius and hours) matched the LC or EC esti- mates. Predictions of adult and juvenile Tanner crab response are summarized in Figure 10 and Appendices. In our ex- ample (Fig. 10), short-term effects are predicted by ability to right immedi- ately after exposure; impaired crabs may be subject to increased predation at this time. Long-term effects are pre- -1.6 "h -2.2 "h Carls and O'Clair: Responses of Chionoecetes bairdi to cold air 51 &U- : A 40 -_ ,11 " Juveniles / 30 ~ / 20 ~ i 1 t 1 1 1 1 1 1 1 1 1 { ii 10 -j < i t i Adults \ 0- 1 ' 1 "" 1 i i B juveniles only -10 -8 -6 -4 Degree-hours -2 -2.0 °h -4.0 °h -1.5 °h -10 °h I ' I 24 Days after exposure 50 40 30 ■20 = -10 control l-1 — T 32 Figure 5 Percent of total pereiopod loss by juvenile and adult female Tanner crabs as a function of exposure I A) and as a function of time for juveniles (B). Error bars are ±1 standard error. dieted by mortality after exposure-induced death ceased. Mortality of adult Tanner crabs was significantly greater below -3°h and vigor was reduced below -2°h compared with control crabs. Exposures that are this severe probably occur infrequently on the fishing grounds except during winter in the north- ern Gulf of Alaska and the Bering Sea. Data are lacking on the time incidentally captured crabs remain on deck before being released, but dura- tion probably varies widely. Larger vessels employ- ing assembly-line techniques may process crabs more rapidly than do smaller vessels. Poor handling of culls combined with prolonged exposure may fur- ther reduce survival of incidentally caught crabs. Crabs captured incidentally during trawling are probably stressed more than those caught in pots. Stevens ( 1990) reported trawl tows ranging up to 6.4 hours and retention times of Tanner crabs up to 17 hours; the median lethal holding time for Tanner crabs was 8.3 hours. Net type influenced survival, and injuries were present in a greater pro- portion of dead than of live crabs (Stevens, 1990). 100- -e -4 Degree- hours Figure 6 Limb loss by juvenile Chionoecetes bairdi at ecdysis as a func- tion of exposure: percent loss=-8.856 + 4,756.960 e"° 629 * (0h * 10). Error bars are ±1 standard error. Numbers molting in each group were 4, 4, 2, 6, 1, and 1 for controls through -8°h, re- spectively. 52 Fishery Bulletin 93(1). 1995 -2- T" -5 -4 ~ i ' r~ -3 -2 Degree hours Figure 7 Feeding rates (milligram food/gram crab weight/day) of adult female Chionoecetes bairdi before (F =4.556 + 1.071 pre x °h) and after (Fpos,=12.161 + 1.255 x °h) zoeal hatching as a functions of exposure (°h). Error bars indicate 95% CI. 100- 80- 60- S 40- 20 0- -20- did not molt -3 -2 Degree- hours Figure 8 Changes in wet weight of juvenile Chionoecetes bairdi as a function of exposure. Weights of crabs that molted versus those that did not were treated separately. Error bars are ±1 standard error. Mortality and injury due to aerial exposure have been reported for other commercially harvested de- capod crustaceans. For example, king crabs were af- fected by exposure to cold air, but were less sensitive than Tanner crabs (Carls and O'Clair, 1990). The western rock lobster, Panulirus cygnus, was signifi- cantly affected by >15 minutes exposure to warm air (27-35°C); recapture rates were lower than for un- exposed controls, and the probability of mortality due to predation rose (Brown and Caputi, 1983). We do not know what physiological mechanism(s) caused the abnormal events during ecdysis that of- ten resulted in death. O'Brien et al. (1986) induced apolysis (the separation of integumentary tissues from the exoskeleton during proecdysis) in several species of brachyurans by packing crabs in ice. Apolysis occurred within one hour in most cases and was not caused by death (O'Brien et al., 1986). O'Brien et al. (1986) did not observe ecdysis in their experimental crabs; therefore, the effect of apolysis on the timing, duration, and success of ecdysis in crabs is not known. In the present experiment, al- though mortality occurred during ecdysis in juvenile crabs, the timing of ecdysis was not affected. Evaporative water loss during exposure probably did not contribute significantly to the effects we ob- served. The fact that warmer exposures, such as the 32-minute exposure at +5°C, caused little or no ef- fect supports this supposition. Similar observations were made for king crab (Carls and O'Clair, 1990). In a study by Taylor and Whiteley (1989), the lob- ster Homarus gammarus vulgaris, which rarely comes in contact with air in its natural environment, was exposed to air at 15°C for up to 14 hours. Water loss, inferred from the constancy of most hemolymph ion concentrations, was minimal (Taylor and Whiteley, 1989). Oxygen delivered to H. gammarus tissues was substantially reduced, and C02 accumu- lated, but levels returned rapidly to normal after a 14-hour exposure. Lactate levels increased, but el- evation of bicarbonate ions increased the buffering capacity of the hemolymph. Because exposures did not exceed 32 minutes, it is unlikely that reduced oxygen directly caused Tanner crab mortality in our experiment. However, at low air temperatures, gills may have been damaged by frost, thus impairing respiratory gas, metabolite, and ion exchange after the crabs were returned to the water. The ability of crabs to right themselves proved to be a sensitive measure of crab viability. Righting response data collected immediately after exposure correlated strongly with less-immediate responses such as mor- tality and growth. Pereiopod loss also impaired righting. Pereiopod autotomy in adult crabs was a function of exposure. Mortality may have influenced the au- totomy response curve for juvenile crabs: during se- vere exposure, crabs apparently died before autotomy could take place. Aerial exposure reduced weight gain in juvenile crabs and caused weight loss in juveniles that did not molt. However, wet weights of the adult crabs (all anecdysial) did not vary with exposure. This ab- Carls and O'Clair: Responses of Chionoecetes bairdi to cold air 53 control 80- ■ O 60- °to 40- ■ \ O 20- cy* ° a* o - g^Nd 0- O 09B0 i i i i l i i 100- 80- 60- 40- 20- 100- 80- 60- 40- 20- o o o o -3.5 "h CK %°v o \ i i i I | i , , , 1 . i i I i i -I — I — I — r- -2.1 °h o - earoaoBO T — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — T 100 ~r 110 r 120 T 130 100 1 I ' ' 110 T"1" 120 Julian day -4.3 "h -4.9 °h 130 Figure 9 Zoeal production (number of zoeae per gram female Chionoecetes bairdi) as a function of time. Curves were fit with smoothing techniques (4253HI (Velleman and Hoaglin, 1981). Units are in °h. sence of weight changes in the adults is puzzling because feeding rates were significantly depressed by exposure. Growth of adult western rock lobsters was reduced by exposure (Brown and Caputi, 1985). Body size, shape, and volume may be important factors in predicting crab response to cold-air expo- sure. Results of the present experiment support this hypothesis: smaller crabs (juveniles) were more sen- sitive to exposure than were larger crabs (adults). Additionally, adult Tanner crabs were more sensi- tive to exposure than were larger king crabs (Carls and O'Clair, 1990), but unknown interspecific fac- tors may have influenced this difference. An experi- ment involving a broad size range of conspecific in- dividuals is needed to test whether sensitivity to ex- posure is size-dependent in crabs. Surprisingly, aerial exposure did not measurably af- fect the developing larvae of exposed females unless the female died. Surviving crabs produced normal zoeae. Moreover, the timing of larval release, larval swimming ability, and viability were not affected by exposure. Longer-term larval responses, such as sur- vival past the first molt and zoeal growth, were not examined. Exposure may have reduced hatching suc- cess (by <1%) of the Tanner crab larvae and possibly may have affected the timing of egg extrusion, but these responses did not vary strongly. Schlieder (1980) re- ported a 13% reduction in hatching success in the stone crab, Menippe mercenaria, compared with controls when the crabs were exposed to air at 27-33°C for two hours. Hatching success was reduced further by a five- hour exposure and by autospasy (Schlieder, 1980). 54 Fishery Bulletin 93(1), 1995 In summary, although environmental conditions as severe as those tested are uncommon on the fish- ing grounds during fishing operations (except in the central and northern Bering Sea), low-temperature aerial exposure during fishing operations can ad- versely affect incidentally captured crabs. Exposure to cold air reduced crab vigor and feeding rates, caused limb autotomy, and killed the crabs in severe situations. Progeny died if exposure to cold air killed females brooding them, otherwise larvae were not measurably affected. Prompt return of incidentally caught Tanner crabs to the sea, especially during ex- tremely cold weather, should reduce adverse effects of exposure to cold air. Adults, Death ////I 50- II 40- / 30 ~. JJIJ 20 ~ yyy/J 90^^^/ 10- =*5?io-^'^ 'I"""1"! -30 -20 -10 0 -30 -20 -10 0 Temperature (Celcius) Temperature (Celcius) Figure 1 0 Predicted time in minutes required to cause death or impair righting of juvenile and ovigerous female Chionoeeetes bairdi following expo- sure to cold air. Mortality predictions are based on cumulative mor- tality through day 16; no deaths were observed in the ensuing 16 days. Righting predictions are based on responses immediately after exposure; there was a tendancy for righting times to improve after exposure, but improvements were generally not statistically significant. Acknowledgments We thank Tyrus Brouillette for his technical assistance during this experiment and the reviewers who im- proved this manuscript with their helpful suggestions. Literature cited Berkson, J. 1957. Tables for the maximum likelihood estimate of the logistic function. Biometrics 13:28-34. BMDP. 1983. Statistical software [1983 printing with additions], W. E. Dixon (ed.). Univ. Calif. Press, Berkeley, 735 p. Brown, R. S., and N. Caputi. 1983. Factors affecting the recapture of undersize western rock lobster Panulirus cygnus George returned by fish- ermen to the sea. Fish. Res. (Amst.) 2:103-128. 1985. Factors affecting the growth of undersize western rock lobster, Panulirus cygnus George, returned by fishermen to the sea. Fish. Bull. 83:567-574. Carls, M. G., and C. E. O'Clair. 1990. Influence of cold air exposures on ovigerous red king crabs (Paralithodes camtschatica) and Tanner crabs (Chionoeeetes bairdi) and their offspring. In Proc. int. symp. king and Tanner crabs, Nov. 1989, Anchorage, Alaska, p. 329- 343. Alaska Sea Grant College Program, Univ. Alaska, Fairbanks, AK 99775-5040. Fujioka, J. T. 1986 Log-likelihood ratio tests for comparing dose-response data fitted to the logistic function. U.S. Dep. Commer., NOAA Tech. Memo. NMFS F/NWC-96, 25 p. Kleinbaum, D. ('•., and L. L. Kupper. 1983. Applied regression analysis and other multivariable methods. Duxbury Press, Bos- ton, MA, 556 p. O'Brien, J. J., D. L. Mykles, and D. M. Skinner. 1986. Cold-induced apolysis in anecdysial brach- yurans. Biol. Bull. 171:450-460. Otto, Robert S. 1989. An overview of eastern Bering Sea king and Tanner crab fisheries. In Proc. int. symp. king and Tanner crabs, Nov. 1989, Anchorage, Alaska, p. 9-26. Alaska Sea Grant College Program, Univ. Alaska, Fairbanks AK 99775- 5040. Schlieder, R. A. 1980. Effects of desiccation and autospasy on egg hatching success in stone crab, Menippe mercenaria. Fish. Bull. 77:695-700. Stevens, B. G. 1990. Survival of king and Tanner crabs cap- tured by commercial sole trawls. Fish. Bull. 88:731-744. Taylor, E. W., and N. M. Whiteley. 1989. Oxygen transport and acid-base balance in the haemolymph of the lobster, Homarus gammarus, during aerial exposure and resubmersion. J. Exper. Biol. 144:417-436. Wilt-man, P. F., and D. C. Hoaglin. 1981. Applications, basics, and computing of exploratory data analysis. Duxbury Press, Boston, MA, 354 p. Carls and O'Clair: Responses of Chionoecetes bairdi to cold air 55 Appendix Table 1 Predicted time in minutes required to cause death of the listed percentage of adult Chionoecetes bairdi at indicated temperatures (°C). Calculations are based lethal responses (LC10, LC30, . . . LC90) estimated on day 16. Temperature -1.0 10% 189 30% 50% 233 260 70% 90% 288 332 Temperature 10% 30% 50% 70% 90% -16.0 12 15 16 18 21 -2.0 95 116 130 144 166 -17.0 11.1 13.7 15.3 16.9 19.5 -3.0 63 78 87 96 111 -18.0 10.5 12.9 14.5 16.0 18.4 -4.0 47 58 65 72 83 -19.0 9.9 12.3 13.7 15.2 17.5 -5.0 38 47 52 58 66 -20.0 9.5 11.6 13.0 14.4 16.6 -6.0 32 39 43 48 55 -21.0 9.0 11.1 12.4 13.7 15.8 -7.0 27 33 37 41 47 -22.0 8.6 10.6 11.8 13.1 15.1 -8.0 24 29 33 36 41 -23.0 8.2 10.1 11.3 12.5 14.4 -9.0 21 26 29 32 37 -24.0 7.9 9.7 10.9 12.0 13.8 -10.0 19 23 26 29 33 -25.0 7.6 9.3 10.4 11.5 13.3 -11.0 17 21 24 26 30 -26.0 7.3 9.0 10.0 11.1 12.8 -12.0 16 19 22 24 28 -27.0 7.0 8.6 9.6 10.7 12.3 -13.0 15 18 20 22 26 -28.0 6.8 8.3 9.3 10.3 11.9 -14.0 14 17 19 21 24 -29.0 6.5 8.0 9.0 9.9 11.4 -15.0 13 16 17 19 22 -30.0 6.3 7.8 8.7 9.6 11.1 Appendix Table 2 Predicted time in minutes required to cause death of the listed percentage of juvenile Chionoecetes baird i at indicated tempera- tures (°C). Calculations are based lethal responses (LC10, LC30 , . . . LC90) estimated on day 16. Temperature 10% 30% 50% 70% 90% Temperature 10% 30% 50% 70% 90% -1.0 81 152 196 241 311 -16.0 5.1 9.5 12.3 15.0 19.5 -2.0 41 76 98 120 156 -17.0 4.8 8.9 11.5 14.2 18.3 -3.0 27 51 65 80 104 -18.0 4.5 8.4 10.9 13.4 17.3 -4.0 20 38 49 60 78 -19.0 4.3 8.0 10.3 12.7 16.4 -5.0 16 30 39 48 62 -20.0 4.1 7.6 9.8 12.0 15.6 -6.0 14 25 33 40 52 -21.0 3.9 7.2 9.3 11.5 14.8 -7.0 12 22 28 34 44 -22.0 3.7 6.9 8.9 10.9 14.2 -8.0 10 19 25 30 39 -23.0 3.5 6.6 8.5 10.5 13.5 -9.0 9 17 22 27 35 -24.0 3.4 6.3 8.2 10.0 13.0 -10.0 8 15 20 24 31 -25.0 3.2 6.1 7.8 9.6 12.5 -11.0 7.4 13.8 17.8 21.9 28.3 -26.0 3.1 5.8 7.5 9.3 12.0 -12.0 6.8 12.7 16.4 20.1 26.0 -27.0 3.0 5.6 7.3 8.9 11.5 -13.0 6.2 11.7 15.1 18.5 24.0 -28.0 2.9 5.4 7.0 8.6 11.1 -14.0 5.8 10.8 14.0 17.2 22.2 -29.0 2.8 5.2 6.8 8.3 10.7 -15.0 5.4 10.1 13.1 16.0 20.8 -30.0 2.7 5.1 6.5 8.0 10.4 56 Fishery Bulletin 93(1). 1995 Appendix Table 3 Predicted time in minutes required to impair righting response of the listed percentage of adult Chionoecetes bairdi at indicated temperatures (°C). Calculations are based on righting responses (EC 10, EC30, . . . EC90) estimated immediately after exposure. Temperature 10% 30% 50% 70% 90% Temperature 10% 30% 50% 70% 90% -1.0 79 109 129 148 179 -16.0 4.9 6.8 8.0 9.3 11.2 -2.0 39 55 64 74 89 -17.0 4.6 6.4 7.6 8.7 10.5 -3.0 26 36 43 49 60 -18.0 4.4 6.1 7.2 8.2 9.9 -1.0 20 27 32 37 45 -19.0 4.1 5.8 6.8 7.8 9.4 -5.0 16 22 26 30 36 -20.0 3.9 5.5 6.4 7.4 8.9 -6.0 13 18 21 25 30 -21.0 3.7 5.2 6.1 7.0 8.5 -7.0 11 16 18 21 26 -22.0 3.6 5.0 5.9 6.7 8.1 -8.0 10 14 16 19 22 -23.0 3.4 4.8 5.6 6.4 7.8 -9.0 9 12 14 16 20 -24.0 3.3 4.6 5.4 6.2 7.5 -10.0 8 11 13 15 18 -25.0 3.1 4.4 5.1 5.9 7.2 -11.0 7.1 9.9 11.7 13.5 16.3 -26.0 3.0 4.2 5.0 5.7 6.9 -12.0 6.5 9.1 10.7 12.3 14.9 -27.0 2.9 4.0 4.8 5.5 6.6 -13.0 6.0 8.4 9.9 11.4 13.8 -28.0 2.8 3.9 4.6 5.3 6.4 -14.0 5.6 7.8 9.2 10.6 12.8 -29.0 2.7 3.8 4.4 5.1 6.2 -15.0 5.2 7.3 8.6 9.9 11.9 -30.0 2.6 3.6 4.3 4.9 6.0 Appendix Table 4 Predicted time in minutes required to impair righting response of the listed percentage of juvenile Chionoecetes bairdi at indi- cated temperatures (°C). Calculations are based on righting responses (EC 10, EC30, . . EC90) estimated immediately after exposure. Temperature 10% 30% 50% 70% 90% Temperature 10% 30% 50% 70% 90% -1.0 13 49 71 93 129 -16.0 0.83 3.05 4.45 5.84 8.07 -2.0 7 24 36 47 65 -17.0 0.78 2.87 4.19 5.50 7.59 -3.0 4 16 24 31 43 -18.0 0.74 2.71 3.95 5.19 7.17 -4.0 3.3 12.2 17.8 23.4 32.3 -19.0 0.70 2.57 3.75 4.92 6.79 -5.0 2.7 9.8 14.2 18.7 25.8 -20.0 0.66 2.44 3.56 4.67 6.45 -6.0 2.2 8.1 11.9 15.6 21.5 -21.0 0.63 2.33 3.39 4.45 6.15 -7.0 1.9 7.0 10.2 13.4 18.4 -22.0 0.60 2.22 3.23 4.25 5.87 -8.0 1.7 6.1 8.9 11.7 16.1 -23.0 0.58 2.12 3.09 4.06 5.61 -9.0 1.5 5.4 7.9 10.4 14.3 -24.0 0.55 2.04 2.97 3.90 5.38 -10.0 1.3 4.9 7.1 9.3 12.9 -25.0 0.53 1.95 2.85 3.74 5.16 -11.0 1.2 4.4 6.5 8.5 11.7 -26.0 0.51 1.88 2.74 3.60 4.96 -12.0 1.1 4.1 5.9 7.8 10.8 -27.0 0.49 1.81 2.64 3.46 4.78 -13.0 1.0 3.8 5.5 7.2 9.9 -28.0 0.47 1.74 2.54 3.34 4.61 -14.0 0.9 3.5 5.1 6.7 9.2 -29.0 0.46 1.68 2.45 3.22 4.45 -15.0 0.88 3.26 4.74 6.23 8.60 -30.0 0.44 1.63 2.37 3.12 4.30 Abstract. The Atlantic sharpnose shark, Rhizoprionodon terraenovae, is a small coastal spe- cies caught in recreational fisher- ies and as bycatch in the shrimp trawl and longline fisheries in the Gulf of Mexico. Demographic analyses incorporating the best available information on validated age and growth, age at maturity (tmat), maximum age (tmax), repro- ductive habits, and age-specific natural mortality and fecundity were performed. An initial set of three life history tables based on input parameters tma=4, tmax=10, constant age 1+ survivorship (S=0.657), and varying first year survivorship (So=0.432, scenario 1; So=0.512, scenario 2; So=0.657, sce- nario 3 or best case scenario) yielded net reproductive rates (i?0) ranging from 0.844 to 1.284, a gen- eration length (G) of 5.8 years, and instantaneous rates of population change (r) ranging from -0.029 to 0.044. Further simulations were performed to test the sensitivity of the computed demographic param- eter values to modifications in vari- ous input biological parameter val- ues (scenarios 4 through 14). Over- all, manipulations of biological pa- rameters mx, tmaV and tmax caused large variations in demographic parameters r, >), where #=0.359, Lx=108, and fo=-0.985. Number of offspring was further divided by two, because the natality func- tion (mx) at age represents the number of female off- spring per female parent and sex ratios at birth are 1:1 and parturition is annual (Parsons, 1983). Reports of unusually large litter sizes in tropical populations of R. terraenovae were also incorporated in some of the analyses that follow by doubling fecundity at age (m ). *=o The finite or annual rate of change (er) was then calculated from the refined values of r. In addition, the theoretical population doubling or halving time in years «x2) assuming a stable age distribution was com- puted as (In 2)/r or (In 0.5)/r, respectively (Krebs, 1985). The initial set of analyses, consisting of three differ- ent scenarios, was run by using the most reliable input biological parameters: t =10, tmat=A, mr=baseline age- specific natality, and S=0.657. In scenario 1, first year natural mortality was arbitrarily doubled (M=0.42 x 2=0.84) or So=0.432. In scenario 2, a value of So=0.512 was obtained from the Leslie matrix algorithm by as- suming an equilibrium (or stationary) population (Vaughan and Saila, 1976). Thus, the following equa- tion was solved for So after assuming r=0: i-i i=i ("•*!«■*) llSJ 7 = 1 1 Parsons, G. Univ. Mississippi, MI 38677. Personal commun.. 1993. where m is fecundity at age, I is the oldest age group in the population ( 10 years), and S; is survival from age j to y+l. In scenario 3, (referred to as the best case scenario), S0 was assumed to be equal to survivor- ship in the following years (So=S=0.657=e-° 42). For this best case scenario, the stable age distribution (C^) was calculated according to Krebs ( 1985) and plotted. In a second set of analyses, the input biological or life history parameters (t .,t ,m,S,S) were var- J r mat1 max1 x1 ' o ied to test the sensitivity of the resultant demographic parameters (R , G, r, and tK2). These sensitivity analy- ses measured the percentage change of the output de- Cortes: Demographic analysis of Rhizoprionodon terraenovae 59 mographic parameter of interest relative to the best case scenario. In the case of ^x2, sensitivity was assessed by calculating a multiplication factor that measures the number of times the population doubling time changes relative to the best case scenario (example: if ^=15.7 in the best case scenario and 4.1 in the altered state, then the multiplication factor [mf]=15. 7/4. 1=3.8, i.e. t^ has been shortened 3.8 times in the altered state). Based on the results from the initial set of analy- ses (scenarios 1 through 3), the existing knowledge of life history traits in R. terraenovae, and the re- sults from the FMP (er=1.91), input parameter val- ues were manipulated in the direction that would be favorable to population increase and should thus be regarded as optimistic scenarios. The following varia- tions, relative to the best case scenario, were applied: doubling mx (mx=2; scenario 4); reducing tnmt by 1 year (tmat=3; scenario 5) and by 2 years (tmat=2; sce- nario 6); reducing tmat by 1 year and doubling mx (tmat=3, mx=2; scenario 7); reducing tmat by 2 years and doubling mx (tmat-2, mx=2; scenario 8); increas- ing S0 by 10% (So=0.723; scenario 9) and by up to 50% (°So=0.985; scenario 10); increasing S by 10% (S=0.72°3; scenario 11) and by up to 50% (S=0.985; scenario 12); doubling tfuax (tmax=20 [note that S and S will also vary, since they depend on tmax\; scenario 13); and an extreme manipulation that was under- taken to approximate the FMP value of er=1.91 (equivalent to an r of 0.647), where tmat was reduced by 1 year, mx was doubled, and S and So set at 95% (t ,=3, m =2, S=S =0.95; scenario 14). mat ' x ' o ' A third set of simulations was run incorporating the estimated mean instantaneous fishing mortal- ity rate from 1986 to 1989 (F=0A28), as used in the stock assessment of small coastal species (Parrack2) on which the FMP for sharks of the Atlantic Ocean is based, to demonstrate the effect of exploitation and various age-at-first-entry scenarios. Fishing mortal- ity (F) was added to natural mortality (M) in the survivorship function lx = NQ(e~[M+F]x), with F initially starting at age 0, then sequentially up to age 9. Arep, the minimum age at which individuals can first enter the fishery and still allow the population to replace it- self (r>0) was calculated by noting the age at which the intrinsic rate of increase (r) becomes zero or positive. These simulations were run first under scenarios 1 through 3, and then under scenarios 4 through 14. Results The initial set of life history tables yielded net re- productive rates per generation (R0), ranging from 0.844 to 1.284, a generation length (G) of 5.8 years, and intrinsic rates of population change (r), ranging from -0.029 to 0.044 (Table 1 ) depending on the value of first year survivorship (S0) used. In scenario 1 (S =0.432), the results indicated that the population would decrease at a rate of 2.9% per year and would halve about every 24 years. Halving times are indi- cated by negative values in the tx2 column. In sce- nario 2 (S =0.512), r is equal to 0 by definition. Un- der the best case scenario (scenario 3; S =0.657), the 2 Parrack, M. L. 1990. A preliminary study of shark exploi- tation during 1986-1989 in the U.S. FCZ. Contrib. MIA- 90-493, NOAA, NMFS, SEFC, Miami, FL 33149, 23 p. Table 1 Simulations of the Gulf of Mexico population of the Atlantic sharpnose shark, Rhizoprionodon terraenovae, under three scenarios that use input parameter values representing the best biological information available. Only natural mortality is included in these analyses. First year survival rates (S0) were obtained as follows: So=0.432 (scenario 1 ) was obtained by doubling the natural mortality value computed from Hoenig's ( 1983) relationship between mortality rate and maximum age; So=0.512 (scenario 2) was computed from the Leslie matrix algorithm (see text) assuming an equilibrium population (Vaughan and Saila, 1976). The third line (in italics) represents the best case scenario (scenario 3; So=S=0.657). Input parameter values' Computed parameter values2 Scenario 'mat t max mx s sa Ro G r er **2 1 4 10 \3 0.657 0.432 0.844 5.762 -0.029 0.971 -23.9 2 4 10 1 0.657 0.512 1.000 5.762 0. 1.000 — 3 4 10 1 0.657 0.657 1.284 5.762 0.044 1.045 15.7 1 'ma;=aee at maturity; fmal=maximum age; m .^age-specific natality; S=survivorship after the first year of life; So=survivorship for the first year of life. 2 fl0=net reproductive rate per generation; G=generation length, in years; r=intrinsic rate of population change refined through the Euler equation (see text); er=finite rate of population change; ^^theoretical doubling (positive values) or halving ( negative values) time in years assuming a stable age distribution. 3 "1" indicates baseline age-specific natality. 60 Fishery Bulletin 93(1), 1995 population increased at 4.5% per year and doubled about every 16 years. The predicted stable age distribution (Cj for the best case scenario (Fig. 1) suggested that about 80% of the population was composed of immature indi- viduals. Because of the lack of data on sizes and ages at first capture in the recreational and commercial 2 3 4 5 6 7 8 Age Class ( years ) Figure 1 Predicted stable age distribution of the Atlantic sharpnose shark, Rhizoprionodon terraenovae , under the best case scenario presented in Table 1, assuming geometric growth (with r=0.044) and constant age-specific mortality and fer- tility rates. fisheries, the actual proportion of the population sub- ject to fishing is unknown. Likewise, no size or age com- position of this population is available from surveys, precluding any comparisons with the theoretical C . Results of the sensitivity analyses indicated that doubling age-specific natality, mx, had a distinct ef- fect (a 286% increase) on the population's rate of in- crease, r (scenario 4), and would allow the popula- tion to double in only 4.1 years or 3.8 times faster than in the best case scenario (Table 2). Generation length, G, remained the same, while net reproductive rate per generation, Ro, increased 100% (Table 3). Decreasing age at maturity, tmat, by one year (sce- nario 5) produced a smaller change in r, tx2, and Ro (Tables 2 and 3) than doubling mx, but decreased G by 12% (Table 3). Further decreasing tmat by another year (scenario 6) produced almost the same values of r and tx2 as those obtained in scenario 4 (Table 2), although Ro increased only 5% and G decreased by 20%. The combined effect of decreasing tmat and dou- bling mx together (scenarios 7 and 8) produced in- creases in r up to near 700% and tx2 values up to 8 times shorter than in the best case scenario (Table 2). Under scenarios 7 and 8, Ro also increased by up to more than 200%, while G decreased by up to 20%. Increasing first year survivorship, So, by 10% (sce- nario 9) yielded a value of r 39% higher and a value of tx2 1.4 times shorter than in the best case scenario (Table 2), affected Ro very little (a 10% increase only), and had no effect on G (Table 3). A further increase Table 2 Simulations of the Gulf of Mexico population of Rhizoprionodon terraenovae to test the sensitivity of computed population rate of increase and doubling time to input biological parameter values. Input val jes were manipulated in scenarios 4 through 14; the best case scenario (BC; top row) is shown in italics to facilitate comparison All other symbols are as defined in Table 1. Scenario Input parameter values Computed parameter values tmal t max mx S So r % change of r1 «x2 mP BC 4 10 1 0.657 0.657 0.044 15.7 4 4 10 23 0.657 0.657 0.170 286 4.1 3.8 5 3 10 1 0.657 0.657 0.111 152 6.2 2.5 6 2 10 1 0.657 0.657 0.168 282 4.1 3.8 7 3 10 2 0.657 0.657 0.265 502 2.6 6.0 8 2 10 2 0.657 0.657 0.356 709 1.9 8.3 9 4 10 1 0.657 0.723 0.061 39 11.4 1.4 10 4 10 1 0.657 0.985 0.117 166 5.9 2.7 11 4 10 1 0.723 0.657 0.123 179 5.6 2.8 12 4 10 1 0.985 0.657 0.378 759 1.8 8.7 13 4 20 1 0.811 0.658 0.228 418 3.0 5.2 14 3 10 2 0.950 0.950 0.634 1,341 1.1 14.3 ; % change of r relative to the best case scenario 2 Multiplication factor indicating the number of times t^ has been shortened relative to the best case scenario 3 "2" indicates baseline age -specific natality values have been doubled. Cortes: Demographic analysis of Rhizopnonodon terraenovae 61 Table 3 Simulations of the Gulf of Mexico population of Rh zoprionodon terraenovae to test the sensitivity of computed net reproductive rate per generation and generat on len gth to input biological parameter values Input values were manipulated in scenarios 4 through 14 the best case scenario (BC top row) is shown in italics to facilitate comparison. All other symbols are as defined in Table 1. Scenario Input parameter values Computed parameter values *mul t max m, S So «o % change of Ro' G % change of G' BC 4 10 1 0.657 0.657 1.28 5.76 — 4 4 10 22 0.657 0.657 2.57 100 5.76 0 5 3 10 1 0.657 0.657 1.72 34 5.06 -12 6 2 10 1 0.657 0.657 1.34 5 4.58 -20 7 3 10 2 0.657 0.657 3.43 168 5.06 -12 8 2 10 2 0.657 0.657 4.08 219 4.58 -20 9 4 10 1 0.657 0.723 1.41 10 5.76 0 10 4 10 1 0.657 0.985 1.92 50 5.76 0 11 4 10 1 0.723 0.657 2.05 60 6.06 5 12 4 10 1 0.985 0.657 11.66 809 7.20 25 13 4 20 1 0.811 0.658 4.99 290 8.30 44 14 3 10 2 0.950 0.950 29.6 2,212 6.7 16.3 ' % change of R and G relative to the best case scenario. 2 "2" indicates baseline age-spec fie natality values have been doubled. in S up to 50% (scenario 10) had a more distinct effect on r (166% increase), tx2 (2.7 times shorter), and R0 (50% increase), but did not affect G (Tables 2 and 3). Increasing age 1+ survivorship (S) by 10% (scenario 11) had a similar effect on all the demo- graphic parameters to increasing So by 50% (scenario 10; Tables 2 and 3), whereas increasing S by 50% (scenario 12) had a very profound effect on all the demographic parameters, increasing r by 759%, shortening tx2 by almost 9 times (similar to scenario 8), increasing Ro by over 800% and lengthening G by 25% (Tables 2 and 3). Doubling longevity (tmax) to 20 years (scenario 13) also markedly affected r (418% increase), tx2 (5 times shorter), and Ro (290% increase), and produced the largest value of G (8.3 or a 44% increase) in all sce- narios (Tables 2 and 3). Finally, the extreme manipulations of scenario 14 (reducing tmat to 3 years, doubling mx, increasing S and So to 95%, with a tmax of 10 years) produced a 13- fold increase in r, a value of t x2 more than 14 times shorter, a 22-fold increase in Ro and only a 16.3% increase in G (Tables 2 and 3). For all simulations, population doubling time (tx2) was lessened and generation length (G) was the de- mographic parameter less sensitive to changes in input biological parameter values. With the estimated mean fishing mortality from 1986 to 1989 (F=0.428) added to natural mortality starting at each age interval from 9 to 0, RQ and r were progressively reduced as F was progressively started closer to age-0 (Table 4). In scenarios 1 (So=0.432) and 2 (So=0.512), r was always negative and became increasingly so as simulated fishing started earlier in the life of R. terraenovae. Only by using best case scenario (scenario 3) values could the population be made to replace itself or grow by ma- nipulating age at first capture. When fishing pres- sure was applied between 6 and 5 years of age or about 97 cm total length (TL) the population was able to replace itself. Generation length remained the same under the three scenarios but progressively decreased as fishing mortality included progressively earlier ages. Theoretical halving time also progres- sively shortened as fishing started at younger ages, whereas in the best case scenario doubling time in- creased as age at first capture dropped from 9 to 6 years. The effect of added fishing mortality on survivor- ship can be identified as a progressive decrease in percentage survival as fishing starts progressively earlier in the lifespan of the shark (Fig. 2). Age-spe- cific reproduction also decreases significantly as fish- ing mortality is applied at progressively earlier ages (Fig. 3). When the estimated mean fishing mortality from 1986 to 1989 (F=0.428) was added to natural mor- tality in scenarios 4 through 14 (Table 5), A , the earliest age at which sharks can first be captured to 62 Fishery Bulletin 93(1), 1995 3 4 5 6 7 Age Class ( years ) Figure 2 Survivorship curves for Rhizoprionodon terraenovae un- der the survival conditions presented in Table 1 for the best case scenario (S=S =0.657) and fishing mortality as in Table 4 (F=0.428), starting at three different ages (1, 5, and 8 years). 3 4 5 6 7 Age Class ( years ) Figure 3 Age-specific reproduction for Rhizoprionodon terraenovae under the survival conditions presented in Table 1 for the best case scenario (S=So=0.657) and fishing mortality as in Table 4 (F=0A28), starting at three different ages (1, 5, and 8 years). Table 4 Simulations of the Gulf of Mexico population of Rhizoprionodon terraenovae under the three same scenarios as in Table 1 but with estimatec mean fishing mortality from 1986 to 1989 (F=0.428 [Parrack2]) added to natural mortality starting at different ages. All symbols are as defined in Table 1. Computations based on the following first year survival rates: scenario 1 (S0 =0.432); scenario 2 (S0= 0.512); and scenario 3 (best case So=0.657) Age at first capture Demographic parameter 9 8 7 6 5 4 3 2 1 0 Scenario 1 R0 0.83 0.81 0.77 0.71 0.62 0.49 0.32 0.21 0.14 0.09 G 5.70 5.60 5.45 5.27 5.06 4.86 4.86 4.86 4.86 4.86 r -0.03 -0.04 -0.05 -0.07 -0.09 -0.14 -0.23 -0.31 -0.38 -0.46 er 0.97 0.96 0.95 0.94 0.91 0.87 0.80 0.74 0.68 0.63 'x2 -21.7 -18.2 -14.4 -10.7 -7.4 -4.9 -3.1 -2.3 -1.8 -1.5 Scenario 2 R0 0.99 0.96 0.91 0.84 0.73 0.58 0.38 0.25 0.16 0.10 G 5.71 5.60 5.45 5.27 5.06 4.86 4.86 4.86 4.86 4.86 r -0.00 -0.01 -0.02 -0.03 -0.06 -0.11 -0.19 -0.27 -0.35 -0.43 er 1.00 0.99 0.98 0.97 0.94 0.90 0.82 0.76 0.70 0.65 0). 2 "2" indicates baseline age-specific natality values have been doubled. allow for full population replacement (r >0) given the fishing mortality, became progressively smaller as the value of r increased (see Table 2 for reference). Increasing S0 by 10% (scenario 9) allowed for an age at first capture of 5 years, while doubling mx (sce- nario 4), reducing t t to 3 years of age (scenario 5), increasing S0 by 50% (scenario 10), or increasing S by 10% (scenario 11) all had the same effect of allow- ing for an age at first capture of 4 years (90 cm TL) compared with 6 years (99 cm TL) under the best case scenario. Reducing t by 2 years (scenario 6) or increasing £ to 20 years (scenario 13) both al- lowed for an A of 3 years (82 cm TL), while reduc- ing tmat by 1 year and doubling mx (scenario 7) al- lowed an A of 2 years. Under the most extreme manipulations, which included reducing tmat by 2 years and doubling mx (scenario 8), increasing S by 50% (scenario 12), and reducing tmat to 3 years, dou- bling mx, and setting S and So at 95% (scenario 14), an age at first capture of 1 year (55 cm TL; scenarios 8 and 12) and of 0 years (32 cm TL) could be applied in a given year. Discussion These demographic analyses using the best available information indicate that the Gulf of Mexico popula- tion ofR. terraenovae may be very vulnerable to fish- ing pressure. Results showed that, based on known life history parameters, the population's intrinsic rate of increase was, at best, only r=0.044, equating to a finite rate of er=1.045, which is much lower than the rate estimated for "small coastal" species in the stock assessment used to develop the FMP for sharks of the Atlantic Ocean (er=1.91). Furthermore, compa- rable rates to the FMP values were only obtained after extreme manipulations of the input life history parameters, which diverged too widely from observed life history parameters to be realistic. For example, one of the possible scenarios that would yield an es- timate of er of 1.91 implies that age at maturity has to be decreased from 4 to 3 years, fertility doubled, and survivorship increased by almost 50% relative to the most optimistic initial scenario, i.e. the best case scenario, resulting in estimates of 29.6 for Ro, 6.7 for G, and 1.1 for tx2. This means that, in the absence of fishing, the population would almost double every year. Rhizoprionodon terraenovae is the main species caught in the Texas recreational shark fishery and is also caught by the headboat and other recreational fisheries in the Gulf of Mexico. More importantly, it represents a significant bycatch in the shrimp trawl fishery operating in the Gulf of Mexico and to a lesser extent in the longline reef fish and shark fisheries, and in the gillnet fishery in the same area. The lack of data on the age and size at which individuals of R. 64 Fishery Bulletin 93(1). 1995 terraenovae first enter these fisheries, as well as the relative proportions of each age and size group rep- resented, preclude a more detailed analysis at this time. However, the demographic analysis represent- ing the best case scenario indicated that under the present fishing level R. terraenovae should not enter the fishery until individuals reach about 97 cm TL or almost 6 years of age if the population was managed to just replace itself. There is evidence that smaller ani- mals are being caught in the various fisheries, but the proportions of each age class are unknown. The biological parameters incorporated in sce- narios 1 through 3 represent the best, most reliable information available. Data on age and growth were taken from a tetracycline-validated laboratory study (Branstetter, 1987) which indicated that females mature entering their fifth year of life (age-4) and that maximum age is between 8 and 10 years. In another study (Parsons, 1985), female maturity was estimated at between 2.4 to 3.9 years. However, this study used only males and mean lengths for age classes, which, as pointed out by Branstetter (1987), affected the von Bertalanffy parameters. The possi- bility of earlier female age at maturity and even longer lifespan was incorporated in several of the demographic analyses (scenarios 5, 6, 7, 8, 13, and 14), which evidently yielded more liberal results on which more risk-prone management decisions could be based. The unpublished information on fertility at age was derived from a study on the reproductive biology of R. terraenovae (Parsons, 1983) and relates female to- tal length to number of uterine eggs or embryos for 78 specimens. Parsons ( 1983) also noted that tropical popu- lations of R. terraenovae had been reported to have as many as 12 embryos. This possibility was taken into account by doubling fertility at age in several analyses (scenarios 4, 7, 8, and 14), which again produced more optimistic estimates of population parameters. The age, growth, and reproduction information used in this study was based on animals collected in the northern central and western Gulf of Mexico. The extent to which this information is applicable to the entire population or whether there are different stocks in the Gulf with different age, growth, and reproductive capabilities is not known. For example, I recently examined an 82-cm-TL pregnant female with 3 embryos, measurements which fit nicely the regression equation of Parsons (1983), but which would result in a back-calculated age of 3 years with the von Bertalanffy growth function, although the female could have been older, e.g. age 4, owing to variability in size at age, which is not uncommon in sharks (Kusher et al., 1992, and references therein). The most important and also the most difficult parameter to estimate is natural mortality (M). The value of M used in this study was taken from Hoenig's ( 1983) relationship between longevity and total mor- tality for virgin or lightly exploited stocks. The as- sumption that Z could be approximated to M, or that no fishing mortality occurred during the period for which growth parameters for this species were de- rived, may have been violated. However, the possi- bility of lower natural mortality values was incorpo- rated in several analyses (scenarios 9 through 14). While Hoenig's equation represents a shortcut and obvious simplification of reality, the lack of catch and effort data, or age or size composition for stocks of this species precludes calculation of any other esti- mates of M at this time. Lack or inappropriateness of both fishery and biological data may explain why several other researchers have used the same ap- proach to estimate natural mortality in shark popu- lation studies. Except for age-0 Negaprion brevir- ostris (Manire and Gruber, 1993), no actual age-spe- cific estimates of natural mortality are available for any shark species. The value derived for M (0.42) in this study is equivalent to an annual survivorship of 0.66, which is low when compared with survival estimates for other species of sharks. Values derived from Hoenig's (1983) regression equation include 0.82 for the an- gel shark, Squatina californica, (Cailliet et al., 1992); 0.85 for N. brevirostris (Hoenig and Gruber, 1990); 0.87 for Triakis semifasciata (Smith and Abramson, 1990; Cailliet, 1992); and 0.90 for Carcharhinus plumbeus (Hoff, 1990). Grant et al. (1979) derived a value of 0.90 for the Australian school shark, Galeorhinus australis, using cohort analysis, and Walker ( 1992) used a value of 0.82 in a dynamic pool fishery simulation model of the gummy shark, Mustelus antarcticus, which was also obtained through cohort analysis. The lower survivorship value for R. terraenovae may be due to the smaller size of this species which would make it more sus- ceptible to predation by other sharks, especially at early ages, since pups are born at about only 30 cm TL in coastal waters about 10 m deep (Castro, 1993). The very high estimate of F (0.428) used in this study was derived from a shark stock assessment that is the basis for the recently implemented (26 April 1993) FMP for sharks of the Atlantic Ocean. However, the accuracy of this estimate, based on a 4-year catch-and-effort time series, is uncertain, and the demographic analyses undertaken in this study indicate that R. terraenovae is vulnerable to high removal levels in the early years of life. It is also possible that the age, growth, and repro- ductive data used in this study are only representa- tive of the population at a time when fishing pres- sure was not as high as it is at present. Potential Cortes: Demographic analysis of Rhizopnonodon terraenovae 65 Table 6 Life history parameters for severa species of sharks compared to the best case scenario for Rhizoprionodon terraenovae in the Gulf of Mexico. Species R0 G r er 100 m separating adjacent stations, successive video deployments were likely indepen- dent, because the greatest distance offish attraction to the bait was only 48 to 90 m. This estimate was based on average maximum bottom current speeds of 0.1 to 0.2 m/s respectively (Bathen, 1978), a soak time of 10 minutes, and a swimming speed for opakapaka of 0.6 m/s (or approximately 3 body lengths (BL) per second, where one BL=20 cm; Videler, 1993). Depths of all video and longline sets were determined by depth sounders aboard the re- search vessels, and positions were determined by GPS (Global Positioning System) or sighting com- pass, as Loran-C capabilities were unavailable. Longlines were deployed approximately perpen- dicular to depth contours. Bottom longline operations used modified Kali longlines,6 each with 30 individu- 6 Shiota, P. M. 1987. A comparison of bottom longline and deep- sea handline for sampling bottom fishes in the Hawaiian Ar- chipelago. Honolulu Lab., Southwest Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, Honolulu, HI 96822-2396. Southwest Fish. Cent. Admin. Rep. H-87-5, 18 p. Ellis and DeMartmi. Video camera sampling of Pristipomoides filamentosus abundance 69 21.6 21.5 Figure 1 Area of operations off Kaneohe Bay, Oahu, for video and longline sur- veys for opakapaka, Pristipomoides filamentosus. Stations for video and longline in 1992 are midpoints identified by solid circles. Area of video coverage in 1993 is enclosed within the dotted lines and stations are midpoints identified by hollow circles. ally weighted and buoyed 3-m PVC droppers. Drop- pers were attached along the main line about 18 m apart. A 9.07-kg test, hard monofilament branch leader and a 3.63-kg test, hard monofilament hook leader were used. Each dropper had five leaders with size-12 Izuo circle hooks (AH style), for a total of 150 hooks per longline set. Stripped squid was used as bait. The standard soak time was 30 minutes, and three to four sets were completed each day. Two separate, 8-mm video camera assemblies were used for the video operations. Each video camera was equipped with a No. 1 diopter magnification lens and a wide angle zoom lens with a red filter for underwa- ter correction. Camera focus, sensitivity, and white balance were manually adjusted, but an automatic aperture setting was used. The focus distance for both video cameras was fixed at 2.13 m, and the focal length of the lens was set at 11 mm. Each video cam- era was enclosed in an underwater housing and se- cured in a weighted frame (Fig. 2). A single, 15-cm long bait container was positioned 60 cm in front of the camera lens and mounted on a PVC rod. The bait container held a single (=0.5-kg) mackerel (Scomber sp.) and one whole squid (Loligo sp.) tie-wrapped to the outside, both of which were changed after each deployment. The camera assemblies were manually 70 Fishery Bulletin 93(1). 1995 Figure 2 Baited video camera assembly with bait container positioned 60 cm in front of the camera lens. for each video sequence, three indices of abundance were scored for each spe- cies taped: maximum number (MAXNO); time to first appearance (TFAP); and total duration in sequence (TOTTM). The MAXNO index was de- termined as the peak number of a spe- cies visible at any one time (maximum interval one second) during a deploy- ment. Fork length (FL) to the nearest 0.1 centimeter (cm) was recorded for fish caught on the longline. The FL of opakapaka observed on video was esti- mated and rounded to the nearest 5 cm by comparing fish swimming in the plane of the bait container with the known size of the container. Statistics An average maximum number offish re- corded for data collected in 1992 was cal- culated for each of nine sequences (three video stations) by using a mean weighted by the duration of each occurrence: lowered to the bottom and marked by a buoy; later they were raised to the surface by outboard engine power. Cameras were allowed to rest on the bottom for a standard interval of 10 minutes before retrieval. The duration and number of video camera deploy- ments to be used on the ship cruise were estimated on the basis of three earlier pilot deployments of the video assembly from small craft. These prior tests indicated that about 10 minutes were required to deploy and retrieve the camera assembly. The time to first appearance (TFAP) of opakapaka from the three pilot stations was 227 ± 300 sec (mean ± 1 stan- dard deviation of the data [SD]) after bottom con- tact. A bottom time of 10 minutes was chosen to ac- commodate likely extremes and also to allow 6 deploy- ments per 2-h tape (20 min per deployment x 6 deploy- ments). With two cameras, 12 deployments per day could be made without changing tapes. The maximum number of longline sets was limited to four per day, based on three camera deployments per longline set. Types of data Species presence, total number of individuals per species, and the number of hooks lost were recorded for each longline set. Species presence and duration of squid bait attachment to the bait container (BTM) were recorded for each video sequence. In addition, £*„ Nh Aw (1) N where Xw=the weighted average maximum num- ber of fish, rc=total number of occurrences, Xh= maxi- mum number of fish seen in the hth occurrence, N/i=duration (s) of the hth occurrence, and N=YNh= 600 s. Video indexes were calculated as means (of up to 3 deployments) to standardize for multiple deploy- ments per station. Video indices were derived in two logarithmic forms — mean of logs (ML), ]Tln(x,+l) ML = -^ (2) and log of means (LM), LM = In + 1 (3) where ac- = individual datum for a variable (i.e., the value for the variable MAXNO, TFAP, or TOTTM for each deployment at a station) and /i=number of de- ployments per station. The longline index consisted of log-transformed individual set data [In (catch + Ellis and DeMartmi. Video camera sampling of Pristipomoides filamentosus abundance 71 1)]. The number of stations where each species was caught or seen was also tallied for each gear type. For nonzero mean data collected in 1993, the best form of the video index (LM\ see Results section), was calculated as follows: (4) 7 \" LM' = ln x*. .=1 n V /_ where x - individual datum for MAXNO and rc=number of deployments per station. A matrix of Pearson's correlation coefficients was calculated for 1992 data (SAS, 1987) with the log- transformed variables to detect interrelationships among all the video and longline indices. Spearman's rank correlations were also calculated and compared. Multiple linear regression (SAS, 1987) was used to estimate the effect of competition between opakapaka and puffers for longline hooks on the basis of the fol- lowing model: Y = p1X1 + p2X2+e, (5) where F=ln (opakapaka video MAXNO), Xj=ln (no. hooks lost + no. puffers caught), andX2=ln (number of opakapaka caught). The model was run as a for- ward regression without an intercept and with an entry level for significance equal to P<0.10. The pre- cision (repeatability) of video and longline was de- scribed by the coefficient of variation (V, Sokal and Rohlf, 1981; Zar, 1984): V = f-^-|xl I mean , (6) where SD is the standard deviation. Longshore station and relative depth effects for 1993 data were analyzed by using standard para- metric and nonparametric procedures (SAS, 1987). Sample size and power analysis We evaluated video and longline data in a power analysis for the £-test of means. Specifically, we esti- mated the sample sizes required to detect a twofold change in abundance by using either sampling method. Skalski and McKenzie (1982) set a prece- dent for use of the criterion of twofold change in en- vironmental monitoring studies; annual variations much larger than this are typical for marine fishes (Hennemuth et al., 1980; Francis, 1993). The effect size (ES) was calculated as follows: ES = 0.693 SD (7) where 0.693= I ± twofold difference in x I for the natu- ral log ( x ) and SD is the standard deviation. Cohen (Tables 2.3.4 and 2.4.1, 1988) was consulted for the requisite sample sizes. The ES for each gear was evaluated at 13=0.20, power (1-J3)=0.8, and a2=0.05. For the 1993 data, ES was also evaluated at a2=0.1. Results and discussion Sample composition The mean time to first appearance (TFAP) of opakapaka for 1992 video tapes with opakapaka present (all islands included) was 203 ±165 (SD) sec- onds. The total time (TOTTM) of opakapaka during a deployment averaged 122 ± 133 seconds. The maxi- mum number (MAXNO) of opakapaka appeared on tape at approximately 354 (±153) s, based on the nine video sequences for which the weighted average MAXNO ( X w) was calculated. These data confirm our initial choice of a 10-min bottom time. In 1992, only windward Oahu data were used for comparisons and statistical analyses, because the opakapaka measures from Maui and Kauai included large percentages (92% and 67%) of "double-zeros" (zero longline catch, zero fish recorded). Catches of P. filamentosus also were greatest for the windward Oahu site; 54 of the 58 juvenile opakapaka were longlined off windward Oahu. Puffers were preva- lent at windward Oahu and at Maui. Both longlined and video-recorded opakapaka were juvenile size (13 to 21 cm FL, and 15 to 25 cm FL, respectively; Kikkawa, 1984; Moffitt and Parrish4). Frequency of occurrence data and total number of species differed between longline catches and video records (Fig. 3). Puffers ranked first in abundance and opakapaka second in both the longline and video data. Video cameras recorded the presence of opakapaka and puffers more often than did the longlines (Fig. 3). Video tapes also recorded a greater diversity of species (Table 1), suggesting greater ac- curacy of the video system. Fish that were not caught by the longline but were seen on video included reef- associated species (e.g. pennant butterflyfish, Heniochus diphreutes, and whitesaddle goatfish, Parupeneus porphyreus, sharks {Carcharhinus sp.), and rays (Dasyatis sp.). Longlines also undersampled the lizardfish, Trachinocephalus myops (Fig. 3), a major component of this deep-water, soft-bottom fish assemblage.5 No major differences in species compo- sition occurred in video surveys from 1992 and 1993. 1 992 video-longline relations The MAXNO index for opakapaka and puffers was highly correlated with the total duration on film 72 Fishery Bulletin 93(1), 1995 15 O a 0} Ih S-, o o O I G o -t-> CB -♦-> 6 2 10 TORQ = FILA = PORP ■ SHRK DASY TRAC SCOU SERI HENI KASM | video V/A longline Torq-uiganer florealis Pristipomoides filamsntosus = Parupeneus porphyreus = Carcharhinus ap. = Dasyatis sp. ■ Trachinocepfialus myops = unidentified Scombndae ■ Soriola dume-iiii = Hemochus diphreutes = Lutjanus kasmira J I Liu TORQ FILA PORP SHRK DASY TRAC SCOM SERI HENI KASM SPECIES Figure 3 Frequency of occurrence of ten common species on video camera deployments and longline sets conducted during 1992 off windward Oahu (re = 15 stations). Refer to Table 1 for common names. Table 1 Total numbers of fish seen ar d caught at 15 video and longline stations located off windward Oahu during 1992. Total number for a fish taxon for video stations is the sum of the maximum numbers seen on 38 films. Total number for longline stations is the number of fish caught. Species Common names Video Longline Torquigener florealis Bleeker's balloonfish 221 80 Pristipomoides filamentosus Pink snapper (opakapaka) 94 54 Heniochus diphreutes Pennant butterflyfish 25 — Parupeneus porphyreus Whitesaddle goatfish 10 — unidentified Scombridae Tuna or mackeral 6 — Trachinocephalus myops Lizardfish 5 — Carcharhinus sp. Shark 4 — Sphyrna sp. Hammerhead shark 4 — Seriola dumerilii Amberjack 3 — Dasyatis sp. Stingray 3 — Chaetodon miliaris Milletseed butterflyfish 3 — unidentified teleosts Bony fish 2 — Parupeneus pleurostigma Sidespot goatfish 1 — Sufflamen fraenatus Bridle triggerfish 1 — Canthigaster rivulata Maze toby 1 — Parupeneus sp. Goatfish 1 — Lutjanus kasmira Bluestripe snapper •3 Ellis and DeMartini: Video camera sampling of Pristipomoides filamentosus abundance 73 (TOTTM) and time to first appearance (TFAP) of the respective species (Table 2, LM form). The duration of squid bait (BTM index) was significantly corre- lated with the MAXNO index and the other video indices for opakapaka but was more strongly corre- lated with the MAXNO index for puffers (Table 2). Videos indicated that puffers were usually respon- sible for the removal of the squid bait; a direct rela- tionship between puffer numbers and the rate of bait disappearance was evident. Spearman's rank corre- lations mirrored the parametric correlations. After log-transformation, the data pairs were ap- proximately bivariate normal. Among all the video indices, MAXNO was best correlated with InCPUE (LLNO) for opakapaka (Table 2). The ML and LM forms of the MAXNO video index were compared separately with the longline CPUE, and the LM form provided a slight but consistently better Pearson's correlation than did the ML form for both opakapaka and puffers. Therefore, the LM form of the MAXNO index was used for all further parametric compari- sons and analyses. The MAXNO-CPUE relationship was approxi- mately linear (Fig. 4A), and its residual plot showed Table 2 Correlation between log-transformed mean video indices (LM) and log-transformed longline catch per unit of effort (InCPUE) from the 1992 windward Oahu site (n=15 sta- tions). Pearson correlation coefficients (r) are displayed above their respective P- values (Prob> \R\ , Ho. Rho=0) for Pristipomoides filamentosus and Torquigener florealis. MAXNO = maximum number seen on tape; TOTTM=total duration of a species an tape; TFAP=time to first appear- ance of a species; BTM=duration of external squid bait; and LLNO=longline CPUE. TOTTM TFAP BTM LLNO Pristipomoides filamentosus MAXNO 0.9665 -0.9143 -0.5748 0.7855 0.0001 0.0001 0.0250 0.0005 TOTTM -0.8500 -0.5681 0.7285 0.0001 0.0271 0.0021 TFAP 0.5729 -0.6467 0.0256 0.0092 BTM -0.2982 0.2803 Torquigener florealis MAXNO 0.9465 -0.5770 -0.6654 0.5365 0.0001 0.0243 0.0068 0.0392 TOTTM -0.6030 -0.5902 0.5932 0.0173 0.0205 0.0198 TFAP 0.5141 -0.1143 0.0499 0.6851 BTM -0.5193 0.0473 neither discernible pattern nor slope (P=1.0, Fig. 4B). If all double-zero data are deleted, the correlation between video MAXNO and longline CPUE loses sig- nificance (r=0.55, P=0.08, n = ll). However, the double-zero data were retained in subsequent analy- ses because there was no a priori reason to believe they did not represent real absences. The observed magnitude of hook loss ( x =32%) in- dicates that longline CPUE is fundamentally inac- curate and biased for sampling this habitat and spe- cies assemblage. Apparently, most hook loss occurred when puffers bit through the leader above the hook. Hook competition is often a problem with longlines when hooked fish begin to saturate available hooks (Rothschild, 1967). Removal of hooks has a similar effect. A multiple linear regression with two descrip- tive variables, a puffer factor (Xj) equal to the num- ber of hooks lost plus puffer catch and opakapaka catch (X2), was run to determine the effect of puffers on the relation between longline CPUE and the video MAXNO index for opakapaka. X: and X2 were first determined to be uncorrected (r2=0.02, P=0.62). The model (Eqn. 5) for the multiple regression was forced through the origin, because neither sampling device could record the presence offish in its absence. The total variation in the opakapaka video index ex- plained by the model was 87% (i?2=0.87, P<0.001). Opakapaka longline CPUE explained 83% of the varia- tion (^=0.83, P<0. 001), and the puffer factor explained an additional 4% of the variation (^=0.04, P=0.07). The latter observation suggests that the puffer factor might strongly influence video-longline relations for opakapaka at times of relatively high puffer abundance. Precision for longline and video cameras was sepa- rately examined. For both opakapaka and puffers, cameras had nominally but consistently better pre- cision (V=81% and 48%) than did longline CPUE (V=91% and 71%). 1 993 video statistics The MAXNO video index did not differ between shal- low and deep positions (Student's r=0.27, P=0.79; Kruskal-Wallis x2=0.09, P=0.76) in May 1993 (Fig. 5). The mean MAXNO data lack a monotone trend over stations (P=0.5), even though raw MAXNO values were atypically large at several stations 20 - o 0 15 - O 9 1 O 10 - i 1 ii CI 0 p p o O i I 5 - ? ( I p II • II • O • 0 0 8 ( ) c > II • • 0 o 1 » • 0 0 • 0 0 5 10 15 20 Station Figure 5 Scatterplot of maximum number of opakapaka observed (MAXNO) for shallow and deep positions and their mean by stations for data collected during May 1993. Stations are ordered in geographic sequence from farthest southeast (sta. 1) to farthest northwest (sta. 18). Means with component data hidden represent coincident shallow and deep values. 1992) observed that, although time of arrival of the first fish (TFAP) was strongly related to estimated fish densities, the maximum number offish seen at a station (MAXNO) either was unrelated or inversely related to densities. Our observation that MAXNO was highly correlated with an abundance estimate (CPUE ) may at first seem contradictory to these prior findings. However, there are important differences between our methods and those of previous studies: previous deep-sea work operated in unproductive depths >2,000 m and cameras recorded data for at least 11 hours per station, whereas our study was limited to productive depths <100 m for which a rela- tively short soak time ( 10 min) was sufficient. In the deep-sea studies, all bait was open to consumption. The partly internal bait of our system created a res- ervoir of odor that persisted for the soak duration in most cases; puffers removed all bait in only 3 out of 75 deployments. Differences in rates of bait consump- tion between the two deep-sea stations and result- ing variations in bait attractiveness may have con- tributed to the disparity between MAXNO and fish density in the deep-sea studies. The MAXNO and TFAP indices in our study were highly correlated (Table 2). This correlation suggests that the greater the density, the faster the fish ar- rive at the bait. These data agree with the observa- tions of Priede et al. ( 1990), where fish arrived at the camera faster at the station with presumed higher densities. Since the MAXNO and TFAP indi- ces were both significantly correlated with CPUE in our study (Table 2), the MAXNO index was chosen as the best index of abundance because it had the better correlation. A persistent bait source and short soak time may have contributed to this stronger cor- relation. In the future, the use of MAXNO as an in- dex of abundance should be reevaluated separately for each species and application. Conclusions Video cameras provide an accurate tool for sampling juvenile opakapaka, and the video MAXNO variable provides a relatively precise and accurate index of abundance. Based on 1993 data for a series of two camera deployments per station, minima of 17 to 22 pairs of deployments (34-44 sets) per study area would be necessary to detect a twofold change in ju- venile opakapaka numbers (at TRICHIURIDAE SCOMBRIDAE } - SCOMBRIDAE XIPHHDAE ISTIOPHORIDAE Scombrini Gasterochisma Grammatorcynus Scomberomorus + Acanthocybium V Sardini Thunnini Figure 1 Two phylogenetic hypotheses for the scombroid fishes based on morphological evidence. The studies of (A) Johnson (1986) and (B) Collette et al. (1984) are examples of the scombrid- subgroup and the scombrid-sister group hypotheses of billfish (Istiophoridae and Xiphiidae) relationships. Johnson ( 1986) considered billfishes a subgroup of the family Scombridae most closely related to the wahoo, Acanthocybium solandri. Collette et al. ( 1984 ) placed the billfishes as a sister group to the Scombridae. Both hypotheses propose that billfishes and scombrids share a common ancestor to the exclusion of other scombroids. An alternative hypothesis for billfish relationships is that billfishes are not scombroids. This hypothesis has never been depicted explicitly in the form of a cladogram (Gosline, 1968; Nakamura, 1983; Potthoff et al., 1980; Potthoff et al., 1986). al. (1984) study and several additional characters (Fig. 1). Like Collette et al., Johnson proposed that billfishes and scombrids compose a monophyletic group, but he regarded billfishes as a subgroup of the Scombridae. A critical piece of evidence support- ing this hypothesis that billfishes are a derived group within scombrids is the presence of cartilaginous in- terconnections between gill filaments in billfishes and the scombrid Acanthocybium solandri. Based largely on this proposed synapomorphy, Johnson placed Istiophoridae and Xiphiidae as derived scombrids and Acanthocybium as their sister group. This association has been suggested by others (Lutken, 1880; Fraser-Brunner, 1950). However the position of billfishes in Johnson's study was only weakly supported because of homoplasy. For ex- ample, five of the ten character-state transitions that support billfish monophyly on Johnson's cladogram are reversals. We will refer to the Johnson hypoth- esis as the scombrid subgroup hypothesis. Other workers have proposed that billfishes are not scombroids. In 1986, Potthoff et al. published a study of bone development in scombroids in which they discussed scombroid phylogeny They concluded that billfishes are not scombroids because of their lack of resemblance to other scombroids in vertebral number and osteological development. They sug- gested that these characters indicate billfish affini- ties to the percoids. This hypothesis has been sug- gested in previous studies (Potthoff et al., 1980; Nakamura, 1983). We will refer to this hypothesis as the nonscombroid hypothesis. It is evident from the morphological studies that there has been a great deal of homoplasious mor- phological evolution in billfishes. Therefore, it is dif- ficult to reconstruct the evolutionary relationships of this group based on morphology alone. In an at- tempt to derive additional, independent data on scombroid intrarelationships and, in particular, to address the position of billfishes, we compiled a mo- 80 Fishery Bulletin 93(1), 1995 lecular data set that consists of DNA sequences from the mitochondrial gene cytochrome b. This gene codes for a functionally conserved protein that should fa- cilitate sequence alignment over ancient divergences. Additionally, it has been used to examine both in- traspecific genealogy (Finnerty and Block, 1992) and much deeper phylogenetic questions such as the ori- gin of the mammalian orders (Irwin et al., 1991). The initial scombroid radiation probably occurred in the Paleocene epoch (Bannikov, 1985; Carroll, 1988). Therefore, cytochrome b sequence should be phylo- genetically informative about divergences within the suborder. The analysis presented in this paper builds on our earlier molecular study (Block et al., 1993). However, we have improved on the previous study in several ways which allow us to directly test the competing hypotheses of billfish relationships. First, we have obtained sequences from additional outgroups. The inclusion of presumably more distant outgroups per- mits us to address the question of scombroid mono- phyly. This is important because the nonscombroid hypothesis of billfish relationships argues that the Scombroidei is not a monophyletic group. Second, we include sequence information from the scombrid Acanthocybium, a taxon which is integral to the scombrid subgroup hypothesis. Third, we utilize sta- tistical tests to directly compare different hypoth- eses of billfish relationships. Finally, we emphasize character-state changes that accrue relatively slowly in order to minimize the effects of phylogenetic noise. Materials and methods Samples Partial cytochrome 6 sequences (590 base pairs) were obtained from 75 individuals representing 34 spe- cies of perciform fishes: 30 scombroid species and four putative outgroup taxa (Sphyraena, Coryphaena, Mycteroperca, and Morone; Table 1). We included Sphyraena based on the placement by Johnson ( 1986) of this taxon as the most primitive member of the Scombroidei. Several percoid taxa (Coryphaena, Mycteroperca, and Morone) were included because of the suggestion by some authors that billfishes are percoids (Gosline, 1968; Potthoff et al., 1980; Nakamura, 1983; Potthoff et al., 1986). Published cytochrome b sequences from two cypriniform fishes obtained from Genbank were used to root the phylo- genetic analysis (Crossostoma lacustre [Tzeng et al., 1990] and Cyprinus carpio [Chang, 1994]). We veri- fied the outgroup status of the cyprinids by first con- ducting a phylogenetic analysis using published se- quence from the sturgeon Acipenser transmontanus, a holostean, to root a parsimony analysis. We at- tempted but were unable to obtain full length se- quences (590 base pairs) from two fixed and preserved specimens of Scombrolabrax heterolepis possibly be- cause of DNA degradation in these specimens. DNA extraction DNA was obtained from frozen tissue samples of the mitochondria-rich "heater tissue" (found in Istio- phoridae, Xiphiidae, and Gasterochisma melampus; Block, 1986), red muscle, white muscle, or liver. Di- gestion of 0.1-0.6 g tissue was performed in ten vol- umes of extraction buffer containing 100 mM Tris CI (pH 8.0), 10 mM EDTA, 100 mM NaCl, 0.1% SDS, 50 mM DTT, and 0.7 mg/mL proteinase K. Digestion proceeded for 2-4 hours at 41°C. The homogenate was extracted twice with equal volumes of phenol (pH 8.0), once with 1:1 phenol/chloroform, and once with chloroform. The final extract was precipitated with 1/9 volume of 3M sodium acetate (pH 5.2) and 2.5 volumes of 100% ethanol. DNA amplification and sequencing The polymerase chain reaction (PCR) was used to am- plify a 700 base pair region of cytochrome b. A 305 base pair segment (not including primers) was generated by using published oligonucleotide sequences (Kocher et al., 1989). We amplified an overlapping, 425-bp region farther downstream with primers L15079 (5- GAGGCCTCTACTATGGCTCTTACC-3') or L15080 (5- CGAGGCCTTTACTACGGCTCTTACCT-3) and H15497 (5'-GCTAGGGTATAATT GTCTGGGTCGCC- 3). Double stranded amplification was performed in a 100-uL volume containing 50 mM KC1, 10 mM Tris- HC1 (pH 8.3), 1.5-3.0 mM MgCl, 200 ^M of each dNTP, each primer at 1 mM, 1 |j,g of template DNA, and 2 units of Amplitaq DNA polymerase (Perkin- Elmer/Cetus). Most templates were amplified through thirty cycles of PCR [1 minute denaturation (92-95°C), 1 minute annealing (40-50°C), and 3 min- utes extension (72°C)] on an Ericomp thermal cycler. Alternatively, PCR was performed on a DNA Ther- mal Cycler 480 (Perkin-Elmer) with the following temperature cycling regime: 5 cycles of 1 minute de- naturation at 95°C, 1 minute primer annealing at 40°C, 1:30 ramp to 72°C, and one minute extension at 72°C, followed by 25-35 cycles with an annealing temperature of 45°C. An 18-pL aliquot of the double stranded product was run by means of electrophore- sis through a IX TBE 1% agarose gel (Sea Plaque, FMC) at 5 V/cm for 45 minutes. A single stranded template was produced by asymmetric PCR (Gyl- Finnerty and Block: Evolution of cytochrome b in the Scombroldei 81 Table 1 Partial cytochrome b sequences (590 base pairs) were obtained from 34 perciform fishes, including 30 scombroid species. Pub- lished cytochrome b sequences were also obtained from Genbank for two cypriniform fishes. Order and suborder' Family and species Common name n Locales2 Perciformes:Scombroidei Istiophoridae Istiophorus platypterus sailfish 2 A,P Makaira indica black marlin 2 I Makaira nigricans blue marlin 8 A,P Tetrapturus albidus white marlin 2 A Tetrapturus angustirostris shortbill spearfish 2 P Tetrapturus audax striped marlin 3 P Tetrapturus belone Mediterranean spearfish 2 M Tetrapturus pfluegeri longbill spearfish 1 A Xiphiidae Xiphias gladius broadbill swordfish 6 A,P Scombridae Acanthocybium solandri wahoo 3 A Scomberomorus cavalla king mackerel 1 A Scomberomorus maculata Spanish mackerel 2 A Gasterochisma melampus butterfly mackerel 3 T Auxis thazard frigate mackerel 2 P Euthynnus affinis kawakawa 2 P Euthynnus alletteratus little tunny 2 A Katsuwonus pelamis skipjack tuna 2 P Thunnus alalunga albacore tuna 2 P Thunnus albacares yellowfin tuna 2 P Thunnus maccoyii southern bluefin tuna 2 T Thunnus obesus bigeye tuna 2 P Thunnus thynnus northern bluefin tuna 2 A Sarda chiliensis eastern Pacific bonito 1 P Sarda sarda Atlantic bonito 2 A Scomber scombrus Boston mackerel 2 A Scomber japonicus chub mackerel 2 P Gempylidae Gempylus serpens snake mackerel 2 P Lepidocybium ftavobrunneum escolar 2 P Ruvettus pretiosus oilfish 2 A Trichiuridae Trichiurus lepturus scabbard fish 3 A Perciformes:Percoidei Coryphaenidae Coryphaena equiselis pompano dolphin 2 P Serranidae Mycteroperca interstitialis yellowmouth grouper 1 A Percichthyidae Morone saxatilis striped bass 1 P Perciformes:Sphyraenoidei Sphyraenidae Sphyraena sphyraena Atlantic barracuda 1 A Cypriniformes Balitoridae Crossostoma lacustre hillstream loach Tzeng et al., 1992 Cyprinidae Cyprinus carpio carp Chang et al., 1994 ' Eschmeyer, 1990. 2 A=Atlantic ocean; P=Pacific Dcean; I=Indian ocean; T= Tasman sea; M=Mediterranean Sea. 82 Fishery Bulletin 93[1), 1995 lensten and Erlich, 1988) carried out in a 100-uL volume containing the same reactants as the initial PCR but using 10 uL of the dissolved gel band and reducing one primer concentration 100-fold. The product was washed by centrifugal dialysis with ster- ile water in Centricon microconcentrators (Amicon) to remove excess dNTP's. Sequencing was performed with the Sequenase kit (United States Biochemical, Cleveland, Ohio) by using the limiting primer from the asymmetric PCR reaction. Data from eight spe- cies were obtained by directly sequencing double- stranded PCR products. The template was purified prior to sequencing (either directly from the PCR reaction mix or following excision of the appropriate band from low-melt agarose) with Magic PCR Preps (Promega). Sequencing was performed with the Sequenase kit according to the specifications of Casanova et al. ( 1991 ). Sequences from Mycteroperca and Morone was obtained after first cloning the PCR products in pGEM t- vector (Promega) according to the manufacturer's instructions. Transformation was carried out by using XL-1 blue cells. Two positive clones were selected for each PCR product. Double- stranded sequencing (Sequenase 2.0) was performed following alkaline denaturation as recommended by the manufacturer. Sequence was obtained from both strands of the amplified fragment for all individuals. Analysis Sequences were aligned by using the Mac Vector pro- gram (IBI Biotechnologies). Maximum parsimony analysis was performed with PAUP 3.1. (Swofford, 1991). Neighbor-joining (Saitou and Nei, 1987) and UPGMA dendograms were constructed with Phylip 3.5 (Felsenstein, 1993). The strength of support for various nodes was assessed by using the bootstrap analysis (Felsenstein, 1985). Specific conditions for each analysis are contained in the figure legends. Competing phylogenetic hypotheses were com- pared by using the "enforce topological constraints" option of PAUP 3.1. This option allowed us to deter- mine the length difference between the most parsi- monious trees that support each hypothesis. The cla- distic permutation test for monophyly and nonmonophyly (Faith, 1991) was then used to ascer- tain whether the more parsimonious hypothesis is significantly better than the competing hypothesis according to the criterion of parsimony. The test was performed as follows. The actual length difference between trees supporting the two opposing hypoth- eses was obtained. Then 99 permuted data sets were constructed from the original data set by randomly shuffling the character states for each character. We then obtained the length difference between trees supporting the two opposing hypotheses for each permuted data set. If the actual length difference was matched or exceeded fewer than 5 times in all 100 data sets (the original data set plus 99 permuted data sets), then the more parsimonious hypothesis was considered to be significantly better than the less parsimonious hypothesis. This corresponds to a to- pology-dependent permutation tail probability, or T- PTP, of less than or equal to 0.05. The effects of character weighting on parsimony analysis were assessed by EOR weighting (Thomas and Beckenbach, 1989; Knight and Mindell, 1993): each type of nucleotide substitution was weighted according to the ratio of its expected number of oc- currences divided by its observed number of occur- rences, or EOR. There are six types of nucleotide substitutions if we disregard the direction of change: A«G, CoT, G<=>T, G<=>C, A»T, and A<=>C. The ob- served number of each substitution type was obtained through pairwise sequence comparisons. Pairwise comparisons were performed between sets of sister species (sister species were identified through an initial unweighted phylogenetic analysis; see Fig. 2). Sister-species comparisons were used for two reasons. First, within a clade, sister species will tend to rep- resent relatively recent speciation events. This recency lessens the chance that multiple substitu- tions have occurred at the same site and that more recent substitutions obscure older ones. Second, all comparisons between pairs of sister species are mu- tually independent. Therefore, if we restrict our com- parisons to sister species, we cannot count the same base substitution twice. We modified the method of Knight and Mindell ( 1993) to derive the expected number of substitutions in each class. This method accounts for differences in the frequencies of the four nucleotides that greatly influence the expected frequency of each substitu- tion type. For instance, if guanine residues are very rare, then substitutions of other nucleotides for gua- nine will also be rare. The L-strand base composi- tion of cytochrome b in scombroid fishes is strongly skewed (Table 2), as it is in other groups examined (for example, Irwin et al., 1991). Cytosines and thy- midines each compose nearly 30% of the total nucle- otide population whereas guanines compose less than 16%. In order to incorporate knowledge of the base composition into our derivation of the expected num- ber of each substitution type, we proceeded as fol- lows. First, the average frequency of each nucleotide (/) was obtained for all species used in the pairwise sequence comparisons. Second, the observed num- ber of each substitution type (S0(i -j), where i and./ represent two different nucleotides, was obtained by summing the results from all pairwise comparisons of Finnerty and Block: Evolution of cytochrome b in the Scombroidei 83 hliophorus platyplerus Makaira nigricans Tetrapturus albidus Tetrapturus audax Tetrapturus angustirosrns Tetrapturus pfluegeri Tetrapturus belone Makaira indica Xiphias gladius Thunnus alalunga Thunnus albacares Thunnus maccoyii Thunnus thynnus Thunnus obesus Katsuwonus pelamis Euthynnus affinis Euthynnus alletleratus Auxis thazard Sarda chiliensis Sarda sarda Scomberomorus cavalla Scomberomorus maculata Acanthocybium solandri Scomber japon icus Scomber scombrus Gasterochisma melampus Gempylus serpens Ruvettus pretiosus Lci'idticxhmm flavohrunneum Trichiurus lepturus Istiophoridae Xiphiidae Scombridae Gempylidae Tnchiuridae Cor\phaena equiselis Mycteroperca interstitialis Morone saxatilis Sphyraena sphyraena Crossostoma lacustre Cyprinus carpio Figure 2 Phytogeny of the Scombroidei based on an unweighted analysis of 248 phylogenetically informa- tive nucleotide sites. The cladogram depicted is a strict consensus of four equally parsimonious trees identified by using a heuristic search procedure on the program PAUP 3.1. (Swofford, 1991): TBR (tree bissection and reconnection) branch swapping was performed on 10 starting trees generated through random stepwise addition of taxa. Crossostoma and Carpio were specified as the outgroup. Length, consistency index, and retention index are the following: L=1595, CI=0.317, RI=0.539. Circled numbers at nodes indicated the percentage of trials in which a given partition between taxa is supported in 1,000 replications of the bootstrap analysis (Felsenstein, 1985). Only nodes supported in >50% of bootstrap replications are indicated. sister species. The expected number of each of the six substitution types (S^ -|)was then derived as follows: iE[i^j -Ifi fj)(S0[total])/3- We divide by three because three types of base sub- stitutions are possible for each base, and we are in- terested in obtaining an expectation for one of them. For example, the expected number of A<=>T substitu- tions equals the average frequency of A's (0.23) plus 84 Fishery Bulletin 93(1), 1995 Table 2 Nucleotide substitutions by type determined through where i and./ represent two different nucleotides, were taxa. The expected substitutions for each type, SEUolal], and f- are the frequency of nucleotides i andy. Average C=0.32. pairwise alignments. The observed substitutions for each type, calculated by summing the results from 8 pairwise comparisons were calculated according to the formula S£(Ma;|=(/)+/')(S0,Ma;|)/3, >ase frequencies for the 16 species are as follows: G=0.16, A=0.23, of sister where f T=0.29i TRANSVERSIONS Pairwise comparison Substitution Types TRANSITIONS A»G CoT GoT GoC AoT \»C Total Tetrapturus audax vs. Tetrapturus albidus 0 0 0 1 1 0 2 Tetrapturus angustirostris vs. Tetrapturus pfluegeri 7 1 0 0 0 0 8 Makaira nigricans vs. Istiophorus platypterus 1 21 0 0 1 0 23 Euthynnus affinis vs. Euthynnus alletteratus 5 27 0 0 3 3 38 Thunnus thynnus vs. Thunnus maccoyii 4 3 0 0 1 0 8 Scomberomorus maculata vs. Scomberomorus cavalla 13 38 1 1 8 11 72 Sarda sarda vs. Sarda chiliensis 6 15 0 3 0 2 26 Scomber japonicus vs. Scomber scombrus 25 35 2 5 6 6 79 Total observed substitutions 61 140 3 10 20 22 256 Expected substitutions (see Methods section) 33.28 52.05 38.40 40.96 44.37 46.92 256 Expected/observed ratio (EOR) 0.55 0.37 12.80 4.10 2.22 2.13 the average frequency of T's (0.29) multiplied by the total number of substitutions (256) divided by three, or 44.37 (Table 2). The weights used for each substitution type (Table 2) are the ratios of expected substitutions divided by observed substitutions for that substitution type, rounded to the nearest integer (expected divided by observed ratios, or EOR's). All EOR's less than one were rounded to one. Weights were entered into PAUP 3.1. (Swofford, 1991) in the form of a step matrix. Results Sequence evolution and interfamilial relationships Molecular data sets, such as the cytochrome b se- quences presented in this study, are known to encom- pass subsets of characters that evolve at different rates. Subsets of data that differ in their evolution- ary rates will also differ in their phylogenetic utility. Character state changes that accrue very rapidly should permit resolution of very recent divergences. However, these rapid character state changes can provide false inferences about distant relationships because of homoplasy The likelihood of reversals and independent acquisitions is high if a particular site is evolving rapidly because there are only four pos- sible character states (G, A, T, and C) and only six possible types of character state change (A<=>G, CoT, GoT, GoC, AoT, and AoC). Therefore, in order to make an accurate reconstruction of the earliest branching events in scombroid history, we should emphasize slowly evolving character state changes. In an effort to best utilize the phylogenetic infor- mation from both slowly and rapidly evolving char- acter state changes, our phylogenetic analysis pro- ceeds in several discrete steps. We begin with an unweighted analysis of all informative nucleotide sites. This analysis is strongly influenced by nucle- otide substitutions that accrue rapidly and should be most informative concerning recent speciation events. We then attempt to improve our resolution of more ancient divergences by giving greater weight to less frequent types of nucleotide substitutions. We conclude with a phylogenetic analysis based on the inferred amino acid sequences. The amino acid se- quences evolve very slowly and should provide our most reliable estimates of the earliest splits between lineages. In each instance, the phylogenetic analy- sis is preceded by a discussion of the evolutionary varia- tion in the character subset under consideration. Unweighted nucleotide analysis A 590-base pair fragment of the cytochrome b gene, representing positions 134 through 723 of the hu- man cytochrome b sequence, was aligned across all Finnerty and Block: Evolution of cytochrome b in the Scombroidei 85 1 Istiophorus platypterus 2 Makaira nigricans 3 Makaira indica 4 Tetrapturus albidus 5 Tetrapturus audax 6 Tetrapturus angustirostris 7 Tetrapturus belane 8 Tetrapturus pfluegeri 9 Xiphias gladius 10 Acanthocybiun solandri 11 Sccmberamorus cavalla 12 Sccnteranorus maculata 13 Gasterochisma melampus 14 Auxis thazard 15 Euthynnus affinis 16 Euthynnus alletteratus 17 Katswonus pelamis 18 Thunnus alalunga 19 Thunnus albacares 20 Thunnus maccoyii 21 Thunnus obesus 22 Thunnus thynnus 23 Sarda chiliensis 24 Sarda sarda 25 Scomber japonicus 26 Scomber scombrus 27 Gempylus serpens 28 Lepidccybium flavobrunneum 29 Ruvettus pretiosus 30 Trichiurus lepturus 31 Sphyraena sphyraena 32 Coryphaena equiselis 33 Morane saxatilis 34 Myctoperca interstitialis 20 40 60 80 100 120 TCCTTACACocrmTLi'iaxTATGCACTACACCTCAGACATCCc^^ A Y T A R .A..T. .A..T. A. .A. .A. .T..A .T. ..C.T. ..G. .R. .A.T. .. .A.T.G. .T .TG... ..G.C. .C C G. .A. ... AT. A T. .A. .A. -T. .C... .C.T. . .G. ..A.T.G. ..G.. .AGT... .TG. ..A.T... .TG.C. . .G.T. . .G.T. A. .C. A. . . A. X .A. .T. C. .T..T. ..T..A. ,T. . .G. .C T. .T. .T .A .A .A. .T. .C. .C.T. .C..C.T. G.RC T.X. .A. .A. .A. .A. .A. .C.C. .C.T. TG.. .A.T. TG...A.T. .G.A.A.T. .G.C. .G.C. .G.C. .C.T. .C.T. .A.T. .A.T. .TG.C. ..G.C. T. .T. .T. .A..C.TT .A. .C.T. ..T. A. .C.T. ..A. C. .T..C. CC .T..CC CC .A..T..A .A T C C.C. .CC. .CC.( .T X. .T. .A. .T. .A. .T. C C.C. .A. .A. .A. .A. .C.T. .C.T. TG.. .A.T. YG...A.T. A.T. .G.C. .G.C. .G.C. .C.T. .C. C .T. .C G..CC G..CC C.C. C.C. .T..C A.. .A. .A. .T..T. .A. .A ..C.T. .GC.C. .TG...A.T. .TG.T.AGT. . A. A. .C. C .T. .A. .T. CC • R..CC C.C .A. C.C .A. A. .C.T. ..A A. .C.T. . .A A. .C.T. . .A C. .C.T. ..T C.T. .TG. . .A.T G.C. .A C.T A. .T. .C .C.T. . .T C T. ..T C.CT...T. A A A .T. .T. . .C.T. .TG. . .A.T G.C. .A. .C C. .T G T T A. .C CCC. .C .A T T A. .C.T... A A. .C.T. ..A T. .C.T. . .T A. .C.T. . .A A. .TG.T. .T C A A. .C.T. . .A T. .C CC C.C.T..G T..C.T A. .C.T. .A .C -T. .C. .T. .G.C .GAC .GC.C . .G. . .A.T A AC. .A. .C T. .T. .A. -C .A. .C .CC< .CC( .C A. .C... .A. .T. .T..A. .A .C.C .C... TG.T. A.T. .G.7.A.T. .TG.C .TG.C .A. .C. .A..C. .C. • A. .C. C. .T..CC .C.C. A. G. .C.A. .A. X. C. T..CCI CC' .A T.X... -A A.. C.A ..C.T. .QG. .. .G.T.A.T.T. . .CA.A.T... T..T G. .A AC. .T..TGAC. .T...C.T. .T.X. X.A. C A A T..C..A. .T..T .G..A. .T..T. .T.G .T.A. X. X..C CC G..C G .G..A. -AA.C .A. X .A. .A. .A. .T.X. .. ..T.C.T. T. .T C. -T A. -T. . . .T. .A. X A. .T. .A T C. .CCC X. . . AA.T. .T. X. . .AC . .A. .T. .ACA T. X. .T.X T. 240 260 280 CCGCCTTajICGaCT3uT3raCICOCCTGAGGACAAAT TT X CG C X C r . .TCA. T X C . .TCA. T X c T ■3 1 i; Figure 3 Alignment of partial cytochrome b sequence (590 base pairs) across 34 species of perciform fishes and two species of Cypriniformes. Nucleotide position 1 is equivalent to position 134 of the human cytochrome b gene. Intraspecific polymorphism is indicated as follows: R=A/G, Y=C/T, M=A/C, S=C/G, K=G/T, W=A/T, H=A/T/C, D=A/G/T. Ambiguities are indicated by '?' thirty-six species included in the analysis (Fig. 3). No deletions or insertions were detected. Overall, 293 nucleotide positions are variable; 248 were poten- tially phylogenetically informative. As expected for a protein coding sequence, the degree of nucleotide variability differs according to codon position (Table 3). The third position is most variable and the sec- ond position is least variable. Differences in nucle- otide variability at the three codon positions are due to the fact that many third position substitutions are silent, whereas many second position substitutions result in nonconservative amino acid replacements. The differences in substitution rates between codon positions becomes more apparent when we compare 86 Fishery Bulletin 93(1), 1995 1 RT ..T.. c ..T.. ..T.. A. ..T. . ..T.. .A. ..T. . .A. T G..C.C. ..T. . A r T . .c. . .T.. . .C. A A T T 11 G. A T .C r T .T. A A A A ..G ..T.. ..C. A A T T T r. .A CT.C .CG. .. CC 12 A. A T G r .c. A A G r .T. A ..G C A T A A r CT.C. .CG.C. C ..G r. A A r O AT.C. A .CG. .. 17 G. .A. ..A. .T. .C .c. .c. .T. .A. .A. .A. .A. A. -A.CT .CC.C. ..G .T .A. .A. .c. .T. ..c. .A AT.C. .CG.C. .C. 18 G. ..A. .T. .c .T. .c. .A. .A. .A. .T. .T. .A.cr .CC.C. .TO ..G. .T .A. .A. .c. .T. .T. .T. ..c. .A AT.C. .A. .CG.C. .C. 20 G. T A T .c T .c. A r. A A .T. .A.cr ..C.C. .TO T A A r T ..c. .A AT.C. A .CG.C. r 21 G. .T. . .A. .T. .c .T. .c. .T. .A. .A. .A. .T. .A.cr .CC.C. .TG .T. .A. .A. .c. .T. .G.. ..c. .A AT.C. .A. .CG.C. .c. 23 G. r. T .c r .c. r A A r A .A.cr .CC.C. ..G ..G. .T. .A. .c. .T. CT.C. .A. .03... ..T 24 0 r. T .c c .c. r A A A ■y .A.cr .CC.C. ..G ..G. .T. .A. .c. .T. .Y. .T. .G.. . .c. CT.C. .G. .03... ..T 25 G. ..G. .c. .A. .c .G. .A. .A. .T. .T.cr .AC.C. .TG.G. . ..C. .A. .A. .c. .T. AT.C. .A. .CG.C. .CC 26 G. A r T .c. .A. r A A T .A A ...CA .AC.C. .TG ..T.. ..G. A A c T T .G. T r. ..c. T. AT.C. ..G... rr 27 G. A r. r .c. .TT.A. T A r .T. G ...c. TAC... .TG.G.. C .T A .A c ..T.A. T r ..c. .G AT.C. T .03... TOC.T. ..G ..T.. C A A T CT.C. .C.C. r 29 G. A .c r T .c. A G r G .G.C. TQC.T. . .G.G.. ..T. . ..c. A A c ..c. AT.. . ..G.C. C 30 A. .T.. .A. . . .c. .C. .c. .T. .A. .T. .T. .G. .TA.T. .A.CA .AC.C. .AG . .c. .A. .A. .c. .T. .A. . .CA.T AT... .A. .CG.C. .c ..T. T T A T T .T. T T Y 33 A. T T G A .A. .T r .TT.AT.A. T r .T. A G. .. .CC... .T A T .A. A . .c. .T CT.C. A ..G.C. r 440 460 480 500 520 540 560 580 1 CTGCTATGACTCTAATCCACCTCCTrTTCClOCACGAAACAaG^ 2 C. .A C Ft. .A A. .G G T C .C. .R. .C. .A. .A .GC... .G..G. A. .G..A. .C. .A. .C. .A. .GC... .G. .G. .G..G. .G. .C. .G. .C. 9 TA..CGCA. .CA 10 .A..C. .A. .AA 11 TC A. .AA 12 TG..C. .A. .AA 13 TG..C. .A. .AA 14 .A A 15 .A A. .AA 16 -A A. .AA 17 .A..C AA 18 .A. .C AA 19 .A.. 20 .A.. 21 .A.. 22 .A.. 23 TA. . 24 TA..C..A..AA 25 TG..AGCA..AA 26 TA. .GGCAG.G. 27 .A. .A AA 28 .A AT. A. 29 TG. .A. .A. .AA 30 TA..03CT..A. 31 T. .G.G.C.CC 32 TG..A.CT...T 33 GCC. .C. 34 .A..CT.T. .AC T. .T. TC. .. • A .A. .A. TC.T A. .G..T..G. .C. .C. .C A. .CC.C. .T C C. .T. .C A.TC. .AY TA.T C. .C T A.TA. .AC A.T C G. .T..A. .C.C .C. .C T C. .C A.T... A. .C AAT. . .A. TC.T A A T T. .T T. . .AC. .GT. . .TA C C TC.G. .T. .A. .C. .T. .T. .T C A.TC. .CC.C A C C TC A A G. .C. .A. .T. .T T. . .A A.T. .C.C C. .T. ..C C.C. AAT. .AC C.C.T.T. ..CT. .C.C. AAT. OCT A A C. .A A.TC. GC.G. .T. . .A.T C C .T A. .T T C.C. .C .C. .AAT. T.A TC.T A A C .? A.T. . .AC A C C .C A C.T. .C AAT. T.A TC A T C. .A Y. .Y. .A.T. . .A A.T. .G. .C C .C A C.T. .C. .C. .AATT. A TC.T. T T T. .T. .A.TC. .A A.T C .C.T. .C.TGAT. . . .AA.TC.T T T T T. .A.TC. -A . . .AA . . .AA . ..AA TC.T. . . . TC.T. .T. TC.T. . . . TC.T TC.T. . . . TC.T. . . . TC T T A.. .G..A.. .A. .A.. T. .T. .A.TC. .A .. .A.T. . T. .T. .A.TC .A .. .A.T. . T .T. .A.TC. .A .. .A.T. . .A.TC. .GC . . .A.T. . . .C. -A.T. . .ACG.. . . .A . .C. .A.T.. .CC . -TA.T. . . .C. . .A. .T C. . . .T. .T T A.T. . .CC TA.T C. . X. .C. . .C..G. . T.. T.. A.. .T. -G. . ...C.T C.TGAT... G . ..C.T C.TGAT.. .G ...C.T C.TGAT... G . ..C.T C.TGAT... G . .TC.T. .A. .C. .AATT. .G ..TC.T. .A AATT. .G ...C.T..C T. ..C TA.G. .T C.C .C TT. .C. .T. .A T T... . .T..A..T A..T . . .A .03... CA. CA. . -CCTCA. .CCCACG. .GG.G.CA. . .G.G.CA. . .G.A.CA. . .G.A.CA. . .G.A.CT. . .G.G.CA. ..G.A.CA. . .G.A.CG. . .G.A.CA. . .G.A.CA. .TO.. .CA. .TG...CA. .CG.A.C. T. .A. -CG .03T .CGT.A. . .TG . .G.T.. . .T3 .TO .CG.T. .T 03 CG .CG .03 .03 .03.. . .G.G .TT. . ..T ..T ..T ..T ??? ..T TC T..A. .C T..T..G..C T T C.C A C C. .C T C GAT. . .AG.G C ..GG..??? GC.A A A A. .T A.T. . .CC.C A C A TC A. ,C .T.TA. .A A.C G CC.T G T T A.T. . .AC.C TA C C T. .G T CG. .C AAT. . .C. . .G. . -CA. -T T .C.T. .T C G. .C C.T GCTA. .ACT A. . -T. . .C C T. -T. .T. .T T. . .C.T. .A AATTA.A. .C. .OCT. . .C . .A.T CG.T AA.C A G A. .C ACT3. .ACT A. . .T. . .C .G. .C A. A. A CG. .C TA. .G. .C. .C.C .C. . .C. .TAG. .G. . . -T. -A. .A T G. .T. .C .C .T T CC T. . .T.C OC.C A T. .T TC.ACT. .C . .A. A.T. . .GT.G3. ,CTT. .C. -A. . . CT.A TT.G T C TEA. .OCT T. .T.T. . .C CC T T G T G. -C. -A. . -G.C . .G G T TT T T GTT. . .C CT3. .GC.T T C.C A T. .A. .T T. .TC A A G. .C .CCA. -C .A. . . Figure 3 (continued) the inferred number of substitutions (Table 3). For example, if a nucleotide site is twofold variable, i.e. if two bases occur at that position in an alignment of all species, then at least one base substitution has occurred at that position during the evolutionary his- tory of the species concerned. Likewise, if a position is threefold variable, at least two substitutions have occurred, and so on. By this approximation, the 293 variable positions have experienced at least 521 sub- stitutions, and substitutions at the third position outnumber substitutions at the first and second po- sitions by nearly 4 to 1 and by more than 12 to 1, respectively. Figure 2 presents a phylogeny of the Scombroidei based on an unweighted parsimony analysis of all informative nucleotide sites. In this cladogram, only the relationships among recently diverged taxa are strongly supported. There is support for the mono- phyly of genera within the family Scombridae (Thunnus, Euthynnus, Sarda, Scomber, and Scorn- Finnerty and Block: Evolution of cytochrome b in the Scombroidei 87 Table 3 Variable sites in the cytochrome 6 nucleotide alignment (Fig. 2) according to codon position. Variable sites are fur- ther characterized according to how many nucleotide states are present: 2 states=twofold variable, 3 states=threefold variable, fourstates=fourfold variable. Total sites Variable sites A) twofold variable sites B) threefold variable sites C) fourfold variable sites Minimum inferred substitutions = [(A) + 2(B) + 3(C)] Phylogenetically informative variable sites Codon position 1 2 3 Total 196 197 197 590 72 29 192 293 50 27 69 146 15 2 49 66 7 0 74 81 101 31 389 521 42 18 188 248 beromorus), and for the monophyly of the family Istiophoridae. Interrelationships within the family Istiophoridae and the genus Thunnus are well resolved. No other nodes are supported by more than fifty per- cent of bootstrap replicates (Felsenstein, 1985). Fur- thermore, there is a substantial polychotomy. Weighted nucleotide analysis The lack of resolution in the unweighted nucleotide analysis is not entirely unexpected. From Table 3, we can surmise that many nucleotide sites have in- curred multiple substitutions and therefore the like- lihood of convergent substitutions or reversals is high. In order to minimize the confounding effects of these homoplasious base substitutions, we have weighted infrequent substitution types more heavily using a modification of the method of Knight and Mindell (1993). If we disregard the direction of char- acter change, we can place all nucleotide substitu- tions into six classes : A<=>G, C<=>T, G<=>T, G<=>C, A<=>T, and A<=>C. Through pairwise sequence comparisons we obtained observed counts for each of these sub- stitution types (Table 2; also see Methods section). We observe a nearly 50-fold difference between the most common (Cc=>T) and the least common (G<=>T) substitution types. Then, from the total number of observed substitutions and the observed frequency of each base, we derived the expected number of oc- currences for each substitution type. The ratios of expected occurrences to observed occurrences for each substitution type (EOR's) were then used to weight the six types of base substitutions. The result of this weight- ing scheme is that substitution types that occur less frequently than expected are weighted more heavily. A phylogeny based on EOR weighting of nucleotide substitutions is presented in Figure 4. It retains all of the strongly supported nodes that appear in the unweighted topology. In addition, the weighted to- pology contains three more basal nodes that are strongly supported by the bootstrap analysis (>50%): the node uniting Gempylidae, Scombridae, and Trichiuridae, the node uniting Xiphiidae and Istiophoridae, and the node uniting Auxis and Euthynnus. This suggests that the character weight- ing scheme has accomplished its goal to some extent: we have retained the phylogenetic signal from rap- idly evolving substitutions while emphasizing the phy- logenetic signal from slowly evolving substitutions. According to the weighted cladogram (Fig. 4), all scombroids fall into two clades. The billfishes com- prise one clade consisting of a monophyletic Istiophoridae and its sister group, Xiphiidae. All other scombroids (Gempylidae, Scombridae, and Trichiuridae) fall into a separate clade. This major split within the suborder Scombroidei is in agree- ment with our previous study (Block et al., 1993). However, in contrast with our previous study, the use of character weighting and the inclusion of more distant outgroups leads to the result that the subor- der Scombroidei is not monophyletic. On the most parsimonious tree, Sphyraena and Coryphaena share a common ancestor with the gempylid-scombrid- trichiurid clade to the exclusion of billfishes, though this node does not receive particularly strong sup- port from the bootstrap analysis. This result indi- cates some support for the hypothesis that billfishes are not scombroids. More importantly, the cladogram excludes the possibility that billfishes and scombrids comprise a monophyletic group within the Scombroidei, as required by the scombrid subgroup and scombrid sister group hypotheses. In summary, the weighted analysis agrees with the nonscombroid hypothesis and conflicts with the scombroid subgroup and scombroid sister group hypotheses. Amino acid analysis Amino acid substitutions occur far less frequently than nucleotide substitutions owing to the strong functional constraints on many regions of the mol- ecule. Cytochrome b is a component of the electron transport chain and spans the inner mitochondrial membrane. The portion of the gene sequenced in this study encodes 195 amino acids corresponding to resi- dues 46 through 240 of the human cytochrome b (Fig. 5). 88 Fishery Bulletin 93|1). 1995 Isliophorus platypterus Makaira nigricans Tetraphtrus albidus Tetrapturus audax Tetrapturus anguslirostris Tetrapturus pfluegeri Tetrapturus belone Makaira indica Xiphias gladius Xiphiidae Thunnus alalunga Tlumnus albacares Thunnus maccoyii Thunnus thynnus Thunnus obesus Katsuwonus pelamis Euthynnus affinis Euthynnus alletteratus Auxis thazard Sarda chiliensis Sarda sarda Scombridae + Gempylidae Scomber japonicus Trichiuridae Scomber scombrus Trichiurus lepturus Scomberomorus cavalla Scomberomorus maculata Acanlhocybium solandri Ruvettus pretiosus Lepidocybium flavobrunneum Gasterochisma melampus Gempylus serpens Sphyraena sphyraena Coryphaena equiselis Morone saxatilis Mycteroperca interstitialis Crossostoma lacustre Cyprinus carpio Figure 4 Phytogeny of the Scombroidei based on a weighted, maximum parsimony analysis of informative nucleotide sites. The six types of nucleotide substitutions are weighted according to the ratio of their expected occurrence to their observed occurrence (see Table 3). Weights used for each sub- stitution type are the following: A«=>G=1, CoT=l, Gt=>T=13, GoC=4, A<=>T=2, and AoC=2. Crossostoma and Carpio were specified as the outgroup. The tree depicted is the single most parsimonious topology identified in a heuristic search: TBR branch swapping was performed on 10 starting trees generated through random stepwise addition of taxa. Tree length is 2,348 steps. PAUP 3.1. was unable to derive consistency and retention indices for the cladogram that incorpo- rated the weighting scheme. Circled numbers at nodes indicate the percentage of trials in which a given partition between taxa is supported in 1,000 replications of the bootstrap analysis (Felsenstein, 1985). This fragment spans four transmembrane domains and includes part of the region implicated as the outer membrane redox reaction center (Howell and Gilbert, 1988; Howell, 1989; Fig. 6). In a comparison of the inferred peptide sequences across the 36 species in- cluded in this study, 134 (69%) of the 195 amino acid residues are invariant, 34 (17%) occur in 2 amino acid states, and 27 (14%) occur in 3 or more states. Fmnerty and Block: Evolution of cytochrome b in the Scombroidei 89 Carpio Crossostcira Myctoperca Morcne Coryphaena Sphyraena Xiphias Istiophoridae (8) Thunnus (5) Euthynnus (4*) Sarda (2) Sccrrbertmorus c. Scorrberonrtrus m. Acanthocybium C^sterochisra Scxrrber japonicus Scarber scarbrus Gerrpylus Lepidocybium Ruvettus Trichiurus Carpio Crossostcira Myctoperca Morone Coryphaena Sphyraena Xiphias Istiophoridae (8) Thunnus {5} Euthynnus (4*) Sarda (2) Scccrbertmorus c. Scarberomorus m. Acanthocyiun Gastercchisma Sconber japonicus Scomber sccnbrus Genpylus Lepidocybium Ruvettus Trichiurus Alignment of in otide sequences gies) and the a sequence withi among the gen< studies are un 1993). 10 20 30 40 50 60 70 80 90 LTuLFIAMHYTSDISTAFSSViraCRI^^ I.. I SP. . -M. ... P.VES. LOO 110 Tyrmr .t .qAVPVMTwr 120 130 140 150 160 170 180 190 X^WlTOa^SVINAXLTOFFAFBFLLPFVIAAOTIEIi^^ .1 AAL.I... .IP AAV.VG. . .IP V. ..TVL.VL. . .1 AAL.IG.. .1 T AVL.V. .S .1 T AVL.M3.. Figure 5 ferred amino acid sequences. The amino acid sequences were inferred from the nucle- presented in Figure 3 by using the translation option of Mac Vector (IBI technolo- nimal mitochondrial genetic code. There was no variation in inferred amino acid i the family Istiophoridae, within the genus Thunnus, within the genus Sarda, nor traAuxis, Euthynnus, and Katsuwonus. Conserved positions identified by previous ierlined in the query sequence, Carpio (Howell and Gilbert, 1988; Esposti et al., This level of variability in amino acid sequence is very similar to that reported in a study of placental mammals, a group whose divergence times are prob- ably comparable to scombroids (Irwin et al., 1991). Much of the variation in scombroid cytochrome b occurs in the transmembrane portion of the molecule and represents substitutions between hydrophobic residues (leucine, isoleucine, and valine). The larg- est stretches of invariant residues (21 and 17) occur in a region implicated as part of the Qo redox reac- tion center (Howell and Gilbert, 1988; Howell, 1989; Fig. 6). All of the functionally constrained sites iden- tified by previous studies are conserved throughout the fishes included in this study (see Fig. 5; Howell and Gilbert, 1988; Esposti et al., 1993). Figure 7 presents a parsimony analysis based on 38 informative amino acid sites. The amino acid se- quences do not provide information about more re- cent speciation events because they evolve very slowly, but they contain important evidence about the relationship of billfishes to other scombroids. The amino acid analysis shares two important similari- ties with the weighted nucleotide analysis: first, Scombridae, Gempylidae, and Trichiuridae comprise a clade, and second, Sphyraena and Coryphaena share a common ancestry with this Scombridae- Gempylidae-Trichiuridae assemblage to the exclusion of the billfishes (Xiphiidae and Istiophoridae). The node uniting Sphyraena with the scombrid-gempylid- trichiurid clade is one of the more strongly supported nodes according to the bootstrap analysis. Therefore, cytochrome b amino acid substitutions support the non- scombroid hypothesis and conflict with the scombrid subgroup and scombrid sister group hypotheses. 90 Fishery Bulletin 93(1). 1995 NHj COOH Figure 6 Variability in amino acid sequence superimposed over a structural model for cyto- chrome b (Howell, 1989). Hypervariable residues, present in three or more amino acid states, are indicated by solid circles. Variable residues, present in two states, are indicated by open circles. The amino acids present at invariant residues are specified on the diagram. Residue 1 of this fragment is equivalent to the forty-sixth residue from the amino terminal of the protein in humans. The strength of the evidence that billfishes are not scombroids can be emphasized by directly examining the amino acid characters that are informative about this issue. Of the 38 informative amino acid sites, no sites unite billfishes and other scombroids to the ex- clusion of other perciforms, whereas eight sites unam- biguously separate billfishes from all other scombroids, i.e. sites where all billfishes possess one character state and all other scombroids possess some other character state (characters 12, 14, 15, 16, 113, 117, 140, and 169; Fig. 5). At all of these sites, billfishes share the same character state as one or more of the percoid fishes. Furthermore, at three of these eight sites (15, 16, and 169), Gempylidae, Scombridae, and Trichiuridae share a common state with Sphyraena to the exclusion of all other species in the study As this character analysis emphasizes, the amino acids are consistent with the hypothesis that billfishes are not scombroids and that Sphyraena is the sister group of a clade consisting of Gempylidae, Scombridae, and Trichiuridae. Intrafamilial relationships Within the family Istiophoridae (Istiophorus, Makaira, and Tetrapturus), cytochrome b nucleotide sequence provides a particularly well resolved and strongly sup- ported phylogenetic signal. This is probably due to the recency of the istiophorid radiation. The maximum se- quence divergence between any two species within this clade is less than five percent. We have performed a more in depth analysis of the interrelationships of istiophorids using the exhaustive search option of PAUP 3.1 (Swofford, 1991). Use of the exhaustive search op- tion guarantees identification of the most parsimoni- ous tree. The topology of this tree is identical to the topology of the istiophorid clade within the more inclu- sive scombroid phylogeny (Fig. 8, cf. Fig. 2). Neighbor- joining and UPGMA analyses produce an identical to- pology. Computer simulations suggest that agreement between these three methods should increase our con- fidence in a phylogenetic hypothesis (Kim, 1993). Finnerty and Block: Evolution of cytochrome b in the Scombroidei 91 / Sarda // Auxis-Euthynnus-Katsuwonus /// Thunnus /y^^ Gasterochisma VI n O ■^^ ifa / Scomberomorus cavalla Scomberomorus maculata 3 a CL V n + /%. (84) <^ /^ \^v O 1 rMK \\ / Acanthocybium T3 y\\\ \^\ Lepidocybium El n ,/ \\\ \^ Gempylus + H T); V=nucleotide transversions (C/T<=>A/G). Within the Istiophoridae transitions outnumber transversions 54 to 6. Neighbor-joining (Saitou and Nei, 1987) and UPGMA den- drograms produced with Phylip 3.5 (Felsenstein, 1993) have the same topology. Distance trees were constructed by using Kimura's (1980) two parameter genetic distance, and by assuming a tran- sition to transversion bias of 9:1. of cytochrome b does not support the monophyly of the genus Makaira. The black marlin, Makaira indica, appears to be the sister group of a clade con- taining all other istiophorids, while the blue marlin, M. nigricans, is sister group of the sailfish, /. platypterus. The most parsimonious tree that contains a monophyletic Makaira is six steps longer than the shortest tree overall (158 ver- sus 152), and on the most parsimonious tree, the M. nigricans-I. platypterus node is strongly supported by bootstrap analysis (85%). Cytochrome b provides good resolution of the relationships of the genera of the tribe Thunnini (Auxis, Euthynnus, Katsuwonus, and Thunnus). According to the nucleotide data the nine Thunnini species sequenced in this study com- prise two clades, one consisting of the genus Thunnus and one containing the other genera: Auxis, Euthynnus, and Katsuwonus. This dis- tinct split in the Thunnini was proposed by Kishinouye in 1923 and is consistent with the mor- phological hypothesis of Collette et al. (1984). Support for the monophyly of the Thunnus clade is particularly robust; however, the relation- ships within the genus cannot be resolved with- out the inclusion of both Thunnus tonggol and Thunnus atlanticus which were not sequenced in this study. The number of substitutions sepa- rating T. thynnus from T. maccoyii (<0.5% se- quence divergence) are small considering their status as separate species. Discussion Interfamilial relationships and the limits of the Scombroidei Throughout this analysis, we have focused on the long-standing controversy over the limits of the Scombroidei and, particularly, whether billfishes are scombroids. Cytochrome b appears to be informative on this issue. In the two phy- logenetic analyses that emphasize the more slowly evolving characters (see Figs. 4 and 7), the most parsimonious tree topology is clearly most consistent with the hypothesis that bill- fish are not scombroids: in each case, one or more nonscombroids share a common ancestry with the scombrid-gempylid-trichiurid clade to the exclusion of billfishes (Table 4). Therefore, according to the criterion of parsimony, the nonscombroid hypothesis is superior to the scombrid subgroup and to the scombrid sister group hypotheses. However, in our opinion, the Finnerty and Block: Evolution of cytochrome b in the Scombroidei 93 most parsimonious trees alone do not constitute suf- ficient evidence to reject these unfavored hypotheses. The question we must ask is the following: How unparsimonious are these hypotheses? In comparing the tree topologies that support each competing hypotheses (Table 4), it is clear that our data refute the notion that billfishes share a com- mon ancestor with the Scombridae to the exclusion of other scombroids (Gregory and Conrad, 1937; Berg, 1940; Fraser-Brunner, 1950; Collette et al., 1984; Johnson, 1986). For example, the shortest trees sup- porting a billnsh-scombrid clade are 13% longer than the minimum-length tree based on inferred amino acid sequence (Table 4). According to the cladistic permutation test for nonmonophyly (Faith, 1991), this length difference constitutes significant evidence against the monophyly of scombrids plus billfishes. The condition that billfishes and scombrids comprise a monophyletic group is a requirement of both the scombrid subgroup and scombrid sister group hypoth- eses. Therefore, according to the cytochrome b data, we reject these two hypotheses. The cytochrome b data clearly support the third hypothesis, that billfishes are not scombroids, though not as strongly as they refute the first two hypoth- eses. According to the inferred amino acid sequences, the shortest tree that supports scombroid monophyly places billfishes as sister group to all other scom- broids and is nearly 3% longer than the most parsi- monious tree overall (145 versus 141 steps). This length difference alone does not constitute signifi- cant evidence against the monophyly of the Scom- broidei according to a cladistic permutation test for nonmonophyly (see Methods section; Faith, 1991). However, as previously mentioned, there are three amino acid characters that unite scombrids, gempylids, and trichiurids with Sphyraena to the exclusion of billfishes (amino acids 15, 16, and 169). There are no characters that unite scombrids, gempylids, and trichiurids with billfishes to the ex- clusion of the putative outgroups. Our study is con- sistent with the hypothesis that billfishes are most closely related to some percoid lineage (Nakamura, 1983; Potthoff et al., 1986). The question of which taxon is most closely related to billfishes remains unanswered. On the basis of this evidence, we sup- port a conservative definition of the Scombroidei, including only the families Scombridae, Gempylidae, Table 4 Comparison of three competing hypotheses of billfish (Istiophoridae and Xiphiidae) relationships based on inferred amino acid sequences from cytochrome 6. 'na' = not applicable. Characteristics of tree which would support hypothesis Hypothesis I: Scombrid subgroup II: Scombrid sister group III: Nonscombroid Scombridae + billfishes are Billfishes are sister group of a a monophyletic group monophyletic Scombridae Acanthocybium is the sister group of billfishes Billfishes do not compose part of a monophyletic group with any other scombroid taxon or taxa Does the most parsimonious tree support the hypothesis? No No Yes If the answer to B is no, how much longer is the shortest tree which does support the hypothesis? 13.5% 13.0% (160 steps vs. 141 steps) (159 steps vs. 141 steps) na Based on the increase in tree length, can we reject the underlying hypothesis with statistical significance? Yes Yes (T-PTP = 0.01) (T-PTP = 0.01) na 1 The topology dependent permutation tail probability ( T-PTP; Faith, 1991) was used to determine the difference. Values of T-PTP<0. 05 were considered significant. See Methods section. significance of the length 94 Fishery Bulletin 93(1), 1995 and Trichiuridae (Cuvier and Valenciennes, 1832; Gosline, 1968; Potthoffet al., 1986). How can these inferences from molecular data be reconciled with the morphological data? We believe that this is an instance where molecular data comple- ment morphological data well. Cytochrome b provides an unambiguous phylogenetic signal that billfishes are genetically distant from other scombroids. In contrast, the existing morphological data does not clearly discriminate between a number of hypoth- eses. The number of character reversals in morpho- logical phylogenies that classify billfishes as scom- broids indicates that there have been many ho- moplastic changes in the billfish lineage. According to the morphological evidence, either billfishes are scombroids and have undergone several reversals to the primitive state, such as their low number of ver- tebrae, or billfishes are not scombroids but have evolved many convergent similarities to scombroids, such as their paired lateral caudal keels. Many of the morphological characters that unite billfishes to other scombroids, particularly to Scom- bridae, may be adaptations for continuous swimming, and are therefore of questionable phylogenetic value. These include hypurostegy, the projection of the cau- dal fin-ray bases anteriorly to cover the hypurals (Col- lette et al., 1984; Johnson, 1986), fusion of the hypurals (Collette et al., 1984; Johnson, 1986), and inter- filamentar gill fusion (Johnson, 1986). Hypurostegy and interfilamentary gill fusion are known to have evolved convergently in nonscombroid taxa (Luvarus imperialis [Leis and Richards, 1984]; and Amia calva [Bevelander, 1934]). The molecular data presented here provide a phylogenetic signal that is indepen- dent of convergent morphological adaptations that might confound phylogenetic analysis. There has been convergent evolution in the molecular characters, but unlike many of the morphological characters men- tioned, this convergent evolution does not appear to be the result of strong selection: most amino acid substi- tutions exchange amino acids with similar size, charge, and degree of polarity. Therefore, when compared with the existing morphological data, the phylogenetic sig- nal in the molecular data is less likely to have been obscured by similar selective pressures acting upon distantly related lineages. Istiophorid phylogeny Historically, there have been numerous disagree- ments over the number of species within the Istiophoridae and their interrelationships (Goode, 1882; Jordan and Evermann, 1926; LaMonte and Marcy, 1941; Nakamura, 1983). This is evidenced by the synonymies for many istiophorids, e.g. the Medi- terranean spearfish, Tetrapturus belone, has also been assigned to Istiophorus (Ben-Tuvia, 1953) and Makaira (Tortonese, 1958). The most thorough treat- ment of billfish systematics to date is a phenetic analysis conducted by Nakamura (1983). Nakamura recognized 11 species of istiophorid billfishes in three genera, including the designation of separate Atlan- tic and Indo-Pacific species for blue marlin (Makaira nigricans and M. mazara) and sailfish (Istiophorus albicans and /. platypterus). The molecular evidence presented here agrees with Nakamura ( 1983) in supporting the monophyly of the genus Tetrapturus, and within this genus, clades con- sisting of audax + albidus and pfluegeri + angus- tirostris + belone. Cytochrome b does not support the recognition of separate Atlantic and Pacific species of blue marlin and sailfish. Previous results (Finnerty and Block, 1992) identified substantial overlap in the cytochrome b haplotypes found among Atlantic and Pacific populations of blue marlin. The sailfish sample in this study includes one Atlantic specimen and one Pacific specimen that differ at only two sites among 590 (0.3%). We infer from the cytochrome b data (Block et al., 1993; and this study) a nonmono- phyletic Makaira and support for a clade consisting of the blue marlin (Makaira nigricans) and the sail- fish (Istiophorus platypterus). Based on the cytochrome b data, istiophorid tax- onomy at the generic level is not concordant with phylogeny. It is premature to suggest taxonomic re- vision of istiophorid genera, but we believe it is im- perative to obtain more molecular data, particularly from nuclear genes, to determine whether the infer- ences presented here can be corroborated. Further- more, we recognize the need for an extensive cladis- tic analysis of istiophorid relationships based on ad- ditional morphological data. Another taxonomic is- sue raised by this study concerns the number of valid Tetrapturus species. An extensive genetic survey of several populations from each species is required to determine the number of evolutionarily independent or reproductively isolated lineages within this genus. Relationships within the genus Thunnus The systematics of the genus Thunnus have been well studied owing to the commercial importance of tu- nas and interest in physiological specializations as- sociated with the evolution of endothermy Collette (1978) suggested a taxonomic subdivision of the ge- nus reflecting a split between tropical species (sub- genus Neothunnus: blackfin tuna, Thunnus atlan- ticus, longtail tuna, Thunnus tonggol, andyellowfin tuna, Thunnus albacares) and species that inhabit cooler waters (subgenus Thunnus: bluefin tuna, Finnerty and Block: Evolution of cytochrome b in the Scombroldei 95 Thunnus thynnus, southern bluefin tuna, Thunnus maccoyii, albacore, Thunnus alalunga, and bigeye tuna, Thunnus obesus). According to this hypothesis, the primitive condition for the genus Thunnus is a tropical distribution, and the cold water tunas com- pose a monophyletic group united by specializations that allowed them to exploit cooler temperate or deep waters. The nucleotide analyses presented in Fig- ures 2 and 4 are not consistent with this hypothesis. The cytochrome b phylogeny groups a tropical spe- cies, the yellowfin tuna, Thunnus albacares, with two species adapted for extremely cold water, the blue- fin tuna and southern bluefin tuna (Thunnus thynnus and Thunnus maccoyii). However, it is premature to draw conclusions about relationships within the ge- nus Thunnus until data are obtained from two tropi- cal species not included in this study, Thunnus atlanticus and Thunnus tonggol. Acknowledgments We thank A. Stewart, J. Kidd, A. Borisy, S. Eng, S. Malik, D. Wang, F. Manu, and V. Master for techni- cal assistance. We are indebted to C. Proctor, P. Grewe, G. DeMetrio, P. Davie, J. Pepperell, K. Dickson, B. Collette, and F. Carey for tissue samples. B. Collette, D. Johnson, J. Graves, and M. Westneat provided valuable assistance on the project and con- structive comments on the manuscript. This research was supported by NSF grant IBN8958225 to B. A. B. and NEH molecular biology training grant IBN8958225 and a Sigma Xi Grant-in-aid of Research to J. R. F. Literature cited Bannikov, A. F. 1985. Fossil scombrids of the USSR. Tr. Paleontol. Inst. Akad. Nauk SSSR 210:59-90. Ben-Tuvia, A. 1953. Mediterranean fishes of Israel. Bull. Sea Fish. Sta. Haifa 8:1-40. Berg, L. S. 1940. Classification of fishes both recent and fossil. Tr. Zool. Inst. Akad. Nauk SSSR 5<2):87-517. [In Russian.] Bevelander, G. 1934. The gills of Amia calva are specialized for respira- tion in an oxygen deficient habitat. Copeia 1934:123-127. Block, B. A. 1986. Structure of the brain and eye heater tissue in mar- lins, sailfish, and spearfishes. J. Morphol. 190:169-189. Block, B. A., J. R. Finnerty, A. F. R. Stewart, and J. Kidd. 1993. Evolution of endothermy in fish: mapping physiologi- cal traits on a molecular phylogeny. Science 260:210-214. Carroll, R. L. 1988. Vertebrate paleontology and evolution. 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Abstract. — Three species of nephropid lobsters have been rec- ognized in the genus Homarus: the American and European lobsters, H. americanus and H. gammarus of the northwestern and northeast- ern Atlantic, respectively, and the Cape lobster of South Africa, H. capensis, few specimens of which have been studied until recently. Analysis of new specimens allows reconsideration of the systematic status of this species and a subse- quent transfer to a monotypic new genus Homarinus. Far smaller than its northern relatives, with a maximum observed carapace length of 47 mm, the Cape lobster has first chelae adorned with a thick mat of plumose setae and less abundant setae on the carapace, tail fan, and abdominal pleura, whereas these setae are absent in Homarus. Relative length and shape of the carpus on pereopod 1, tooth pattern on cutting edges of first chelae, shape of the linguiform rostrum, large size of oviducal openings, and structure of male pleopods differ from corresponding features in Homarus. Comparative analysis of DNA from the mito- chondrial 16s rRNA gene demon- strated considerable sequence di- vergence of the Cape lobster (9.7%) from its putative congeners. The magnitude of this estimate relative to that between the two North At- lantic species (1.3%) further sug- gests that taxonomic revision is warranted. Assignment of Homarus capensis (Herbst, 1 792), the Cape lobster of South Africa, to the new genus Homarinus (Decapoda: Nephropidae) Irv Kornfield Department of Zoology and Center for Marine Studies University of Maine, Orono. Maine 04469 Austin B. Williams National Marine Fisheries Service Systematics Laboratory National Museum of Natural History. Smithsonian Institution Washington, DC 20560 Robert S. Steneck Department of Oceanography and Ira C. Darling Center University of Maine, Walpole, Maine 04573 Manuscript accepted 25 September 1994. Fishery Bulletin 93:97-102 (1995). Until now, three species of neph- ropid lobsters have been recognized in the genus Homarus Weber, 1795 (see Holthuis, 1991)://. americanus H. Milne-Edwards, 1837, the north- western Atlantic American lobster; H. gammarus (Linnaeus, 1758), the northeastern Atlantic-Mediterra- nean European lobster; andH. cap- ensis (Herbst, 1792), the South Af- rican Cape lobster. All are found in cool or cold temperate waters, and the North Atlantic species range into subarctic waters. The northern H. americanus and H. gammarus are well-known, abundant, and eco- nomically valuable species, but the southern H. capensis has long been problematic because only a few specimens (13 males, 1 female) were known to exist in collections (Barnard, 1950; Wolff, 1978; Hol- thuis, 1991). Gilchrist (1918) had seen only three specimens and re- marked (p. 46) that "it is a very rare species, and is not even known to Cape Fishermen." Kensley (1981) recorded its distribution in the Cape Province as Table Bay to East Lon- don, and recent new collections ex- tend the range to Transkei (Kado et al., 1994). Regardless of its rarity, sufficient specimens of the Cape lobster, liv- ing and preserved, are now avail- able for analysis of its distribution, morphological, and genetic at- tributes, and systematic status. Results of our studies indicate that this species should be removed from Homarus and placed in a genus of its own; this paper provides sup- porting evidence for this action and offers supplementary descriptive information on the species. Homarinus, new genus Figs. 1-4 Type species — Homarus capensis (Herbst, 1792) by present designa- tion and monotypy. Description — Carapace moderately compressed, narrower than deep, sparsely setose, middorsal carina barely evident on gastric region, ob- solescent on thoracic region posterior to deep cervical groove. Rostrum 97 98 Fishery Bulletin 93(1), 1995 Figure 1 Homarinus capensis (Herbst). Living male, carapace length 3.41 cm, photographed in an aquarium in Sea Fisheries Research Institute, Cape Town, South Africa, by Robert Tarr. (a) Left lateral; (6) dorsal. Kornfield et al.: Cape lobster taxonomy 99 a b d i— 2 — / Figure 2 Male pleopods (pi); mesial views of pi 1 (slight lateral folds on tips not shown in these views), and mesial views of appendix masculina on mesial ramus of pi 2: (a and 6) Homarinus capensis, left (USNM 251452); (c and d) Homarus americanus, right (USNM 13952); (e and f)H. gammarus, right (USNM 2085). Scale is 1 mm; bar 1 applies to c through f\ bar 2 applies to a and 6. linguiform in dorsal view, broad at base where mar- gins coalesce with orbits, margins bearing 4-6 small spines and gradually tapering anteriorly to rather abruptly pointed or narrowly rounded tip, reaching distal 1/3 of penultimate article of antennular peduncle, shallow dorsal concavity running its entire length. Telson and uropods with thick fringe of plumose setae on distal margin and with scattered non- plumose long setae dorsally on these appendages and sixth abdominal segment. Telson as wide at base as long, with lateral margins slightly sinuous and subparallel bearing obsolescent spines and rugae, each side ending in fixed posterolateral spine; ter- minal margin beyond spine broadly convex; distal 1/3 of surface bearing obsolescent transverse rugae. Uropods broadly subovate, sparsely setose on dorsal surface; mesial ramus broadest near posterior mar- gin with width about 0.73 length, row of obsolescent lateral marginal spines ending in fixed posterolat- eral spine; lateral ramus with width about 0.72 length, diaresis well behind midlength bearing row of fixed but irregularly worn spines ending in stron- gest spine at posterolateral angle. Chelae of first pereopods with thick coat of long plumose setae on upper surface of palm, overhang- Figure 3 Homarinus capensis (Herbst), tail fan (from figure in H. Milne-Edwards, 1851). ing extensor margin and distributed a distance along fixed finger; similar setae on mesial surface of car- pus and ventral surface of merus. Fingers not gap- ing; those of major chela with crushing teeth (often worn) opposed from near base to about midlength 100 Fishery Bulletin 93(1). 1995 Ha Hg He Ha Hg He Ha Hg He Ha Hg He Ha Hg He Ha Hg He Ha Hg He Ha Hg He ggtcgcaaacttttttgtcgatatgaactctcaaaataaataacgctgtt 5 0 atccctaaagtaacttaaatttttaatcaacaancaanggatcanttaca 100 . ca.c.a . t. . cacnnnnnnaaatatctctgtattttaaatttaaacagttacnnaaatta g t c....t..a....a..t tatcatcgtcgccccaacgaaataattntagtatataaataatattaaac c ...t ac.c g t.. tttcaactcatctaattatatactaaattattaagctttatagggtctta . . .t ..a...t g.a tcgtccctttaaaatatttaagccttttcacttaaaagtcaaattcaatt c . . tg . a . tttgtgtttgagacagtttgcttcttgtccaaccattcatacaagcctcc 150 200 250 300 350 ac.t.t. aattaagagactaatgactatgctaccttc 380 . g. nn. Figure 4 Partial sequence for the mitochondrial 16s rRNA gene. Sequences for Homarus americanus (Ha), H. gammarus (Hg), and Homarinus capensis (He) have been deposited with GenBank Accession Numbers U11238, U11246, and U11247 respectively. Dots indicate nucleotides identical with Ha; letters indicate nucle- otide substitutions at the homologous sites. Sites marked 'n' have unresolved nucleotides. ing form -inus, resembling. The gen- der is masculine. Homarinus capensis (Herbst, 1 792), new combination Synonymy— Holthuis (1986:243, fig. 1) gave an exhaustive synonymy for Homarus capensis, and a later (1991:59) less inclusive account. These treatments are so recent and readily available that reiteration here would be unnecessarily redun- dant. Succeeding reference to the species follows. Homarus capensis. — Kado, Kittaka, Hayakawa and Pollock, 1994:72, figs. 2, 3, 4. followed by row of intermittent noncrushing moder- ate conical teeth with 4-6 smaller ones in intervals between them; minor chela with latter pattern of noncrushing teeth on cutting edge of each finger; tips of fingers on each chela curved toward each other and crossing. Carpus of major chela elongate; anterior margin with two prominent spines and smaller ones between, palmar condyle subcircular and flattened, with sug- gestion of spines or tubercles on its anteromesial margin; dorsomesial margin strongly tuberculate and partly obscured by setae; shorter dorsolateral mar- gin also tuberculate but less prominently so; strong low spines on mesioventral margin. Merus bearing subdistal anterolateral spine, well-separated sharp tubercles on mesiodorsal margin, and mesioventral row of fairly uniform small tubercles. Minor chela with similar but less developed orna- mentation; merus with acute spines and spiniform tubercles. Etymology — The name Homarinus is derived from French homard, lobster, and the adjectival combin- Material — Cape Province, South Af- rica. USNM 251451. 16, East Lon- don?, R. Melville-Smith, 92-RMS-O, Nov 1992, regurg., dismembered, carapace length (cl) 26.5 mm, short carapace length (scl) 21 mm, abdo- men length (abdl) 33.0 mm. USNM 251452. 1 6 , southwest Dassen Island [33°26'S, 18°05'E], regurgitated from Sebastichthys capensis, badly crushed and partly dismembered, R.S. Steneck, 92-D-2, 1 Dec 1992, cl 32 mm, scl 25.5 mm. USNM 251453. 19, Still Bay [34°23'S, 21°27'E], dismembered, R. Melville- Smith, RMS7, abdl 45 mm. USNM 251454. 1 9 , Still Bay, regurg., R. Melville-Smith, RMS8, 5 mm, abdl 47 mm. Additional specimens reported to us by R. Melville- Smith, Sea Fisheries Institute, Cape Town: 1 6 , North Dassen Island, tide pool, RSS, 92-D-l, 3 Feb 1992; 19 . Port Alfred, RMS 1; 18, Houghham Park, Algoa Bay; 1 8 , Dassen Island, west side, RMS 3; 1 6 , Cape St. Francis, RMS 4; 18, Cintsa Reef, East London, RMS 5; 1 6 , Sunday's River mouth, RMS 6; 2 6 , Cape St. Francis, RMS 9 and 10; 1 9 , Haga Haga, Transkei coast, RMS 11. Description — As for genus with addition of the fol- lowing details. Abdominal pleura well developed, with rounded angles; pleuron of segment 1 small; pleuron of seg- ment 2 broad, overlapping first and third pleura; pleura 3^t-5 with antero ventral angle rounded, pos- terolateral angle subrectangular; pleuron of segment 6 rounded ventrally, posterolateral angle rounded and confluent with anterolateral angle of telson. Kornfield et al.: Cape lobster taxonomy 101 Telson with dorsal setae distributed in 3 longitu- dinal tracts, central and submarginal on either side; central tuft proximally in midline and another near each anterolateral corner; sparse similar setae on abdominal pleura; lateral ramus of uropod with ven- tral submarginal row of setae laterally. Eyes with distal edge of cornea slightly exceeding level of basicerite tip; this tip reaching to midlength of narrowly rounded antennal scale exceeded by its very strong anterolateral spine (rarely doubled) reaching distal edge of penultimate article in anten- nular peduncle; latter falling short of distal margin of terminal article in antennal peduncle. Epistome with median anterior spine closely flanked at either side by shorter rounded spine. Cheliped of pereopod 1 having fixed finger with narrowed extensor margin set off by shallow submar- ginal groove. Palm with compound row of low for- ward pointing spines and tubercles on flexor surface, similar development on extensor edge originating at carpal condyle and running along proximal margin of palm, across its basal end, and distally for a dis- tance along palm. Oviducal opening on coxa of pereopod 3 oval; its axes 1.3 x 1.8 mm on measured female noted below. Pleopod 1 with distal article broader than shaft and hollowed mesially, forming flattened tubular opening when appressed to opposite member, tip ir- regularly rounded. Pleopod 2 with appendix masculina on mesial aspect of endopod bearing tuft of strong setae at apex. Uropods with protopodite bearing 2 strong spines overhanging proximal end of mesial and lateral ra- mus respectively. Variation — There is minor variation in development of spines, tubercles, etc., among the two females and two males examined. According to Stebbing (1900), sides of the rostrum may have 5, 6, or 7 spines on the margin. Density of setae on exoskeletal parts is subject to considerable variation, owing perhaps to recency of molting, age, or abrasion after preservation. Color — Color of a living animal is shown in Figure 1. Published records summarized by Holthuis (1986) indicate that color may depart considerably from that shown here: coral-red to tawny or reddish yellow, which may have resulted from postmortem changes; or, in the fresh state, "of a rather dark olive colour, not dissimilar to that of the Northern lobster" Gilchrist (1918:45). Molecular characterization — Comparative analysis of a portion of the 16s ribosomal RNA gene from mitochondrial DNA (mtDNA) was conducted by using standard protocols (Kocher et al., 1989). Mito- chondrial DNA's purified by CsCl ultracentrifugation (Lansman et al., 1981) were amplified by PCR with the conserved primers 16sar and 16sbr of Palumbi et al. (1991). Following asymmetric amplification (Homarus americanus and H. gammarus) or cycle- sequencing (Homarinus capensis), DNA's were manu- ally sequenced by the dideoxy chain-termination method of Sanger et al. (1977). Aligned sequences are presented in Figure 4. Sequence divergence be- tween taxa was estimated by using the two-param- eter method of Kimura (1980). Sequence divergence between Homarus americanus and H. gammarus was 1.3%, whereas average divergence between these two species and Homarinus capensis was 9.7%. The 16s rRNA gene is one of the most slowly evolving regions of the mtDNA molecule (Xiong and Kocher, 1994); this conservative property makes it particularly use- ful for comparative studies among distantly related taxa. Though there is no formal recognition of equiva- lence between levels of sequence divergence and taxo- nomic rank (Hillis and Moritz, 1990), it is clear that the relative magnitude of divergence can be a useful taxonomic indicator (Avise, 1994). The magnitude of sequence differentiation that we observed between H. capensis and the two North Atlantic taxa strongly suggested the existence of two discrete clades. Mo- lecular divergence reinforced our conclusions from the reexamination of the morphology of these species. Remarks — Morphological differences between Homarinus capensis and the two species of Homarus are clear cut. Perhaps the most obvious differences are that Homarinus capensis has a dense coat of se- tae on the outer surface of the palms and on other articles of the chelipeds (PI), and scattered setae distributed over the carapace, tail fan, sixth abdomi- nal segment, and pleurae of the remaining abdomi- nal segments; Homarus americanus and H. gam- marus are smooth and glabrous. The telson of Ho- marinus has subparallel sides and its exposed sur- face bears many obsolescent transverse rugae (Fig. 3); the telson of Homarus species has sides converg- ing toward the tip, giving a subtriangular shape. First pleopods are more elongate and slender in Homarus species than in Homarinus (Fig. 2). The two species of Homarus attain large size (Wolff, 1978), whereas Homarinus capensis appears to be much smaller at maturity. No ovigerous females of H. capensis have been found, but openings of the oviducts are at least twice the size of those on com- parably sized specimens of the species of Homarus (see Kado et al., 1994). This suggests that there are fewer eggs with accelerated larval development in Homarinus capensis relative to slower larval devel- 102 Fishery Bulletin 93(1). 1995 opment from smaller more numerous eggs in Homarus species (Kado et al., 1994). Acknowledgments Our conclusions converged independently from two viewpoints. A. B. W. and other carcinologists have long understood grounds for generic separation of the Cape lobster from Homarus on the basis of morphol- ogy. I. K. and R. S. S. concluded this on the basis of genetic divergence and were well into their analysis before forces were joined. A. B. W. drafted the sys- tematic section and assembled the jointly produced text. Keiko Hiratsuka Moore rendered drawings of the pleopods. G. C. Steyskal provided advice on the choice of a new generic name. The manuscript was critically reviewed by W. Glanz, R. B. Manning, and T. A. Munroe. We are indebted especially to colleagues at the Sea Fisheries Institute, Cape Town, South Africa, who helped us in this study; Roy Melville- Smith provided materials and information, and Rob- ert Tarr photographed the living specimen of Cape lobster. George M. Branch, University of Cape Town, provided logistic support and aided in specimen ac- quisition. Yan Kit Tarn and Alex Parker provided sequence data. R. S. S. was supported by grants from the South African Foundation of Research Develop- ment, the Visiting Scholar Fund, and the Student Fund for Visiting Scholars of the University of Cape Town. Molecular work was supported by NOAA Sea Grant (NA90AAD-SG499) and NSF (EHR-9108766 and OCE-9203342). 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Ill: Tech- niques and potential applications. J. Mol. Evol. 17: 214-226. Linnaeus, C. 1758. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differ- entiis, synonymis, locis, ed. 10, 1, iii + 824 p. Laurentii Salvii, Holmiae, Stockholm. Milne-Edwards, H. 1837. Histoire naturelle des Crustaces, comprenant 1'anatomie, la physiologie et la classification de ces animaux, Vol. 2, 532 p. Librairie Encyclopedique de Roret, Paris. 1851. Observations sur le squelette tegumentaire des Crustaces decapodes, et sur la morphologie de ces animaux. Ann. Sci. Nat., Paris (3, Zool.)16:221-291, pis. 8-11. Palumbi, S., A Martin, S. Romano, W. O. McMillan, L. Stice, and G. Grabowski. 1991. The simple fool's guide to PCR, v. 2.0. Special pub- lication of the Univ. of Hawaii Dep. Zoology and Kewalo Marine Laboratory, 23 p. Sanger, F., S. Nicklen, and A. R. Coulson. 1977. DNA sequencing with chain-terminating inhib- itors. Proc. Nat. Acad. Sci. (USA) 74:5463-5467. Stebbing, T. R. R. 1900. South African Crustacea. Mar. Investig. South Af- rica 1:14-66, pis. 1-4. Weber, F. 1 795. Nomenclator entomologicus secundum entomologiam systematicum ill. Fabricii, adjectis speciebus recens detectis et varietatibus.... C. E. Bohn, Chilonii [Kiel] et Hamburgi, viii + 171 p. Wolff, T. 1978. Maximum size of lobsters (.Homarus) (Decapoda, Nephropidae). Crustaceana 34:1-14, pis. 1-2. Xiong, B., and T. D. Kocher. 1994. Phylogeny of the sibling species of Simulium venustum and S. verecurdum (Diptera: Simuliidae) based on sequences of the mitochondrial 16s rRNA gene. Mol. Phyl. Evol. 3:293-303. Abstract. — A radiometric age- ing method was used to resolve con- flicting results from ageing tropi- cal lutjanids based on annual ring counts in whole and sectioned otoliths. The number of rings de- tected in sectioned otoliths of Lut- janus erythropterus, L. malabar- icus, and L. sebae from unexploited populations in the Gulf of Carpentaria, Australia, were 1.6 to 2.4 times the number found in whole otoliths. To obtain an inde- pendent estimate of age, we mea- sured 210Pb/226Ra radioactive dise- quilibria of both whole and cored otoliths. As all species had high lev- els of 226Ra, they could be aged with relative accuracy by this method. Samples of whole otoliths and cores with a similar ring count had simi- lar radiometric ages. In samples whose sectioned and whole-otolith ages differed by more than 4 years, the whole otolith ring count agreed better with the radiometric age (for an uptake activity ratio i?=0.0). This result stands in marked con- trast to the radiometric age valida- tion of section counts for slow-grow- ing, long-lived fish inhabiting tem- perate to subtemperate waters. In this region, all species lived less than 10 years and grew to a maxi- mum size of up to 600 mm SL. They reached a similar length in one year, but L. erythropterus grew faster than the other two species thereafter. The sexes had the same growth rates. Our results were similar to those found for these spe- cies elsewhere and suggest that in tropical fishes, such as lutjanids, rings observed in sectioned otoliths and other hard parts may not be formed annually. Where possible, ages derived from counts in these structures should be verified by independent methods. Ageing of three species of tropical snapper (Lutjanidae) from the Gulf of Carpentaria, Australia, using radiometry and otolith ring counts David A. Milton CSIRO Division of Fisheries Marine Laboratories. RO. Box 1 20 Cleveland. Queensland 4 1 63, Australia Steven A. Short Environmental Radiochemistry Laboratory ANSTO. Private Mail Bag 1 Menai. NSW. 2234. Australia Present address: Kmgett Mitchell and Assoc. RO. Box 33-849. Auckland. New Zealand Michael F. O'Neill Stephen J. M. Blaber CSIRO Division of Fisheries Marine Laboratories. RO. Box 1 20 Cleveland. Queensland 4 1 63. Australia Manuscript accepted 18 August 1994. Fishery Bulletin 93:103-115 (1995). Tropical fishes can be difficult to age because many species do not deposit annual rings in their hard parts (Longhurst and Pauly, 1987). Lutjanids, which are highly valued commercial fishes in the tropical Indo-Pacific region, often have ring patterns in their hard parts that are difficult to interprete (e.g. Davis and West, 1992). The age and growth of many lutjanid species have been well studied and the results of these studies have formed the basis of age-structured stock assessments upon which the management of these fisheries is based (e.g. Sains- bury, 1988). In the western Pacific, Lutjanus malabaricus has been the most widely studied lutjanid, as it is the main catch of trawl and line fisher- ies in northern Australia, adjacent Indonesian waters, and in the South China Sea. The reported maximum age (up to 10 yr ) and growth param- eters differ both between regions (Lai and Lui, 1974, 1979) and within one area (northern Austra- lia: Lai and Lui, 1979; Chen et al., 1984; Edwards, 1985; McPherson and Squire, 1992). These studies estimated age from growth rings in vertebrae (Lai and Lui, 1979; Chen et al., 1984; Edwards, 1985) or in whole otoliths (McPherson and Squire, 1992). The latter method may underestimate the age of longer-lived species because of the difficulty of distinguishing all the growth rings (Casselman, 1974). The timing of formation of annual growth rings in Lutjanus from northern Australia has not been fully verified. Several authors (Lai and Lui, 1974, 1979; Chen et al., 1984; Yeh et al., 1986; Davis and West, 1992) have concluded that the outer ring is probably deposited 103 104 Fishery Bulletin 93(1), 1995 annually, but the season when this ring is formed varies between studies and species. Such ambigu- ities cast doubt on the validity of the conclusions and suggest that differences in the estimated growth rate and age of Lutjanus populations may be related to problems of interpretation rather than to biological differences. A radiometric method has recently been used suc- cessfully to estimate the age of long-lived fishes (Bennett et al., 1982; Fenton et al., 1991). This method uses the known decay rates of isotopes of Radium-226 (226Ra) and Lead-210 (210Pb) in bony parts to estimate the age of fish. It does not rely on operator interpretation to estimate age and there- fore is particularly useful for ageing long-lived spe- cies where the growth rings are often not clearly de- fined (Casselman, 1974). The objectives of the present study were 1) to esti- mate the age and growth of Lutjanus malabaricus, L. erythropterus, and L. sebae from the Gulf of Carpentaria by counting rings in whole and sectioned otoliths; and 2) to use the 210Pb/226Ra radiometric ageing method to make an independent age estima- tion of the same fish. S'U«m T AUSTRALIA > • • 10" 0 • • J • • • • • / ~~ef,"E Figure 1 Map of the Gulf of Carpentaria showing the distribution and relative abundance of Lutjanus erythropterus, L. malabaricus, and L. sebae during a systematic survey in November 1990. Materials and methods Sampling Most samples of Lutjanus erythropterus, L. mala- baricus, and L. sebae were collected during a sys- tematic survey of the Gulf of Carpentaria between long. 136° and 142°E in November 1990. Two similar random-sampling surveys were made across the northern Gulf of Carpentaria (north of lat. 14°30'S) in November 1991 and January 1993. Samples of Lutjanus malabaricus were also collected during a survey of eight areas in the Gulf of Carpen-taria by the commercial trawler Clipper Bird in June 1990 (Fig. 1). Details of survey design, trawl gears, and trawl durations are given in Blaber et al.(1994). Commercial-sized Lutjanus malabaricus (1-3 kg) were obtained from fish retained for sale after the June 1990 survey. During the systematic survey in November 1990, all specimens of the three target species of lutjanids were retained for ageing studies. In November 1991 and January 1993, only fish from length classes underrepresented in previous samples were processed. All fish were measured (standard length [SL] in mm), weighed (±1 g), and sexed, and both sagittae were removed, dried, and stored in la- belled bags for future analysis. Radiometry Radioanalysis requires about 1 g of sample material; therefore, fish were pooled to obtain the necessary sample weight. For juveniles, up to four otoliths were required to obtain this weight. Otoliths used for radioanalysis were chosen in two ways. First, for each species, otoliths from juvenile, maturing, and ma- ture fish that had the same sectioned-otolith ages, similar otolith weights, and similar sizes, and came from the same region of the Gulf of Carpentaria were pooled for radioanalysis. Second, otoliths of the same whole-otolith age and from fish of similar size were abraded with a mechanical sander to a central core approximating the weight (see Table 2), length, and shape of the otolith of a fish whose whole-otolith age was 3 (otolith length=11.6 ± 0.7 for L. erythropterus; 12.7 ± 0.4 for L. malabaricus; and 11.4 ± 0.4 for L. sebae). The exception was sample 2490 for which otoliths were ground to a core age of 2 (weight 0.156 ± 0.005 g; otolith length 9.2 ± 0.16 mm; n=92). The otolith nucleus at the center of the cores was located by examining intact otolith morphology and by sec- tioning other samples (Campana et al., 1990). This age is less than the age at sexual maturity for all species. Milton et al.: Ageing of Lutjanus erythropterus. L malabancus. and L sebae 105 The method of radioanalysis of the otoliths is de- tailed in Fenton et al. (1990, 1991). It involves mea- suring the specific activity of 226Ra:210Pb by alpha- spectrometry. Because of the extremely small spe- cific activities measured (0.01-0.1 dprn-g"1 for Polo- nium-210 [210Po]), cleanliness is of the utmost im- portance in the analytical procedure. Every item of laboratory ware that contacted the otolith solutions and otoliths was chemically decontaminated in al- kaline 0.05M Na4EDTA(pH 10.5). The otoliths were washed and rinsed several times in this solution, then washed several times in 0.1M HC1 (<10 s) and fi- nally washed twice in water. Our analyses of 210Pb, via its short-lived daugh- ter-proxy 210Po, and 226Ra were made with high-reso- lution alpha-spectrometers according to the meth- ods of Fenton et al. (1990). The mean 210Po reagent blank was 0.0071 ± 0.0012 dpm. Recovery of 210Po was always at least 90% and instrument background counts (for 208Po and 210Po) were less than one countd-1. 226Ra was analyzed by a direct alpha-spec- trometry method and chemical yield was measured by gamma spectrometry of a Barium-133 (133Ba) tracer (Fenton et al., 1990, 1991). Mean activity of the 226Ra blanks was 0.0174 ± 0.0026 dpm, which was lower than in previous studies (e.g. Bennett et al., 1982; Fenton et al., 1991) owing to careful con- trol of reagents. Recovery of 226Ra (as estimated by the recovery of 133Ba tracer) was greater than 85% for all samples. (l-e-' --). XT\\ l-(l-R) (l-e-) XT \ -X(t-T) (2) where all parameters are the same as in the previ- ous model, except T, which is the estimated age of the otolith core. A linear mass growth model was assumed only up to the age of the core. The initial uptake 210Pb/226Ra activity ratio was generally as- sumed to be i?=0.0. This is the most conservative value, and so radiometric age estimates derived with this value must overestimate the maximum possible age of the sample. The above equations were solved numerically by a Newton-Raphson iteration method (Fenton et al., 1991). Stable element analysis The levels of lead and barium in otoliths are pre- sumed to act as stable equivalents of 210Pb and 226Ra and so can be used to assess the uptake of the radio- active isotopes and to normalize the radiometric data (Fenton and Short, 1992). Therefore, the concentra- tions of stable lead, barium, strontium (Sr), and cal- cium (Ca) in each otolith sample were measured for an aliquot of each dissolved otolith solution used in the radiometric analysis. Each solution was analyzed by inductively coupled plasma mass spectrometry for lead and barium and by inductively coupled plasma atomic emission spectrometry for strontium and calcium. Data analysis The ages of whole otoliths were calculated on the basis of a single constant (linear) growth rate by the equation originally derived by Bennett et al. (1982): A=l-(1-R) 1 It (1) where A=the ratio of the activity of 210Pb to 226Ra activity at time t (210Pb/226Ra)t; i?=ratio of 210Pb to 226Ra at the time of deposition [(210Pb/226Ra)0]; and >.=decay constant for 210Pb (0.03114 yr_1). Assump- tion of a single linear mass growth rate produces radiometric ages that are greater than those that would result from assumption of an exponential (non- linear) rate, the bias always favoring a higher value (Campana et al., 1993). It should be understood that using this assumption (linear mass growth of the otolith) will produce age estimates that always over- estimate the real age. For otolith cores, ages were calculated from Smith et al.'s (1991) equation: Otolith ageing Pairs of otoliths from each fish were cleaned of ex- cess tissue, dried at 60°C for 24 h, weighed (± 0.1 mg) and measured along the longitudinal axis with dial calipers (± 0.05 mm). One otolith of each pair was embedded in polyester resin and cross-sectioned with a diamond saw (Augustine and Kenchington, 1987). Thin sections (approximately 200 |im) of each otolith were bonded to microscope slides with thermo- plastic cement. Each section was polished on both faces with 800-grit wet-and-dry carborundum paper before being examined with a video-enhanced light microscope attached to a microcomputer with pre- cise distance-measuring software. The rings (pre- sumed annuli) were counted and the distance be- tween them measured along the dorsal axis adjacent to the sulcus, where they were most clearly distin- guishable. In whole otoliths, the rings were counted against a strong background point light source. Counts of rings in all whole and sectioned otoliths were made independently by two readers. When the ring counts differed, the otoliths were reexamined by both readers. If the counts still differed by more 106 Fishery Bulletin 93(1), 1995 than one, the data were discarded (<5% of all otoliths). If counts differed by one, the higher value was chosen (10% of otoliths). The relative frequency of these discrepancies was similar for all species. Data analysis The length-at-age data were fitted to the repara- meterized von Bertalanffy growth curve of Francis (1988). This method has the advantage that the pa- rameters estimated are independent and can be com- pared directly between species and populations. Most previous studies of lutjanid age and growth have fitted the von Bertalanffy growth equation to data on length at age (e.g. Lai and Lui, 1979; Manooch, 1987; Davis and West, 1992). However, the estimated parameters Lm, K, and tQ either do not have direct biological meaning (e.g. Knight, 1968; Schnute and Fournier, 1980; Ratkowsky, 1986) or are extrapo- lations from the data (Ratkowsky, 1986). Francis (1988) extended the equation of Schnute and Fournier (1980) to derive a new set of parameters Lv L2, and L3 (his L, I , and lw), which correspond to the length at the lower, middle, and upper limits of any arbitrarily defined age range, such that: Lt=L1+(L3-L1)(l-r2{t^/u"^))/a-r2), (3) where r = (L3—L2)/(L2—L1); Lt is the mean length of a fish at age t; and Lv L2 and L3 are the length at the lower, middle, and upper limits of two arbitrary ages 0 and w. By fitting a curve of this form, extrapola- tions beyond the data are avoided, as the three fit- ted parameters are chosen from within the range of the data and hence can be directly compared with the results of previous studies. In this study, we set 0 = 1 ring and w = 6 rings for each species. This equation has the advantage that the age range to be examined can be chosen by the investigator, rather than having to be the largest and smallest age classes found, as required by the Schnute and Fournier ( 1980) equation. These param- eters (Lj, L2, and L3) can also be expected to have similar properties to those of Schnute and Fournier (1980) and not to show the high negative correlation between Lx and K (Francis, 1988). All parameters were estimated by an iterative least-squares method (SAS NLIN procedure with the Marquardt option; SAS, 1989). Vaughan and Kanciruk (1982) found that this procedure consis- tently showed the least bias in parameter estimates, converged rapidly, and provided more precise esti- mates than did standard linear techniques. A mea- sure of goodness-of-fit was obtained by calculating an r2 value from the residual and the explained sums of squares derived from the least-squares regression. Relationship of ring counts in whole and sectioned otoliths with radiometric ages The estimated age from ring counts in whole and sectioned otoliths used in the radiometry were com- pared for all species by two methods. First, the rela- tionship between radiometric age and whole and sec- tioned otolith ages of the same fish were plotted. If the slope of the relationship was not significantly different from 1, the results of the two methods were considered to be in close agreement. Second, the two ageing methods were compared with the radiomet- ric ages with a Wilcoxon matched-pairs ranks test (Conover, 1980). The two hypotheses tested were 1) that whole otolith ring counts underestimated true age (radiometric age) or 2) that sectioned otolith ring counts overestimated true age. Results Radiometry Lutjanus erythropterus— The specific activity of 226Ra and the 210Pb/226Ra activity ratio differed among the three samples of L. erythropterus (Tables 1 and 2). The activity ratio was highest in the cored sample (0.118 ± 0.031; Table 2). Ring counts in whole otoliths were linearly related to otolith mass (Fig. 2A) and ring count in sectioned otoliths, though the relationship was significantly weaker CP<0.05). Radiometric age estimates were calculated on the basis of a single constant (linear) growth rate for otolith mass, which removes the need to include the mass growth rela- tion in the radiometric age calculation (Eq. 1). Un- der the assumption of a constant growth model, ra- diometric age estimates were most similar to those obtained from the ring counts in whole otoliths (Table 2). The match was best for the cored otolith sample where model assumptions are less stringent (sample 2673). Lutjanus malabaricus — The specific activity of 226Ra in L. malabaricus otoliths differed among samples and among size classes (Tables 1 and 2). The 210Pb/ 226Ra activity ratios ranged from less than 0.027 to 0.212 and varied to a similar degree in cored and whole-otolith samples (Table 2). Otolith weight was linearly related to the number of rings in whole otoliths (Fig. 2B), and this relationship was stron- ger than that for counts from sectioned otoliths Milton etal.: Ageing of Lutjanus erythropterus, L malabaricus, and L sebae 107 Table 1 Elemental composition of otoliths of three species of Lutjanus used in the radiometric analysis. Whole = whole otoliths used; cored = otoliths cored to age 3+ (L. erythropterus ) or 2+(L. malabaricus and L. sebae ). Numbers in parentheses represent repeated analyses of a sa mple in which several otoliths of similar whole and sectioned age had been combined. 226Radium 210Lead Lead Barium Pb/Ba Strontium Calcium Sr/Ca Whole/or dpm-g-1 dpm-g"1 (Pb) (Ba) mass (Sr) (Ca) mass Species Sample cored (± la) (± la) (ppm) (ppm) ratio (ppm) (ppm) ratio L. erythropterus 2065 Whole 0.2277 ± 0.0132 0.0174 ±0.0047 0.08 18.7 0.004 2,800 395,000 0.0071 2066 Whole 0.1623 ± 0.0087 0.0070 ± 0.0035 0.19 11.5 0.016 2,720 398,000 0.0068 2673 Cored 0.1331 ± 0.0087 0.0157 ± 0.0040 0.66 9.2 0.071 — — — L. malabaricus 2062(2) Whole 0.2390 ±0.0111 -0.0025 ± 0.0045 0.27 8.2 0.033 2,915 462,000 0.0063 2063 Whole 0.0728 ± 0.0066 0.0067 ± 0.0042 3.49 6.5 0.537 3,330 470,000 0.0071 2063(2) Whole 0.0582 ± 0.0049 -0.0010 ± 0.0025 0.22 13.4 0.016 1,990 321,000 0.0062 2063(3) Whole 0.0916 ± 0.0053 0.0072 ±0.0017 0.55 4.8 0.114 2,240 399,000 0.0056 2064 Whole 0.2118 ±0.0164 0.0173 ± 0.0024 2.28 5.8 0.390 3,000 395,000 0.0076 2438 Whole 0.1014 + 0.0064 0.0068 ± 0.0036 0.41 5.3 0.080 2,005 426,000 0.0047 2439 Whole 0.2942 ± 0.0141 0.0133 ± 0.0043 0.06 7.5 0.008 2,250 415,000 0.0054 2440 Whole 0.1080 ±0.0068 0.0135 ± 0.0029 0.18 6.2 0.029 2,910 438,000 0.0067 2489 Cored 0.1678 ± 0.0088 0.0356 ± 0.0055 <0.09 6.7 <0.014 2,160 407,000 0.0053 2490 Cored 0.1219 ±0.0078 0.0180 ± 0.0037 <0.09 6.2 <0.014 2,040 416,000 0.0049 L. sebae 2068 Whole 0.1036 ± 0.0064 0.0139 ± 0.0034 3.13 8.7 0.360 2,360 396,000 0.0060 2069 Whole 0.1046 ±0.0058 0.0312 ± 0.0037 1.38 8.1 0.170 2,510 398,000 0.0063 2070 Whole 0.0460 ± 0.0042 0.0100 ±0.0023 0.46 5.0 0.092 — — — 2647 Cored 0.2143 ±0.0114 0.0373 ± 0.0049 0.50 11.5 0.043 — — — 2648 Cored 0.1756 ± 0.0099 0.0458 ± 0.0052 0.66 9.4 0.071 — — — Table 2 Results of radiometric and direct ageing otoliths of Lutjanus malabaricus, L. erythropterus and L sebae from the Gulf of Carpentaria. Radiometric ages were calculated by using a constant growth rate model and by using R = 0.0 (where R = initial 210Pb:226Ra activity ratio at time of deposition). All errors n radiometric age estimates expressed at la level (n = number of otoliths in sample). SE = Standard error. Numbers in parentheses represent repeated analyses of a sample in which several otoliths of similar whole and sectioned age iad been combined. Mean length Mean otolith Whole Sectioned 210pb.226Ra Radiometric Species Sample n (mm)± SE mass (g) ± SE otolith age otolith age activity ratio age L. erythropterus 2065 3 316 ±2 0.3315 ± 0.0186 3 3 0.076 ±0.021 5.1 ± 1.5 2066 2 364 ±- 0.3875 ± - 3.3 6 0.043 ± 0.022 2.8 ± 1.5 2673 3 368 ±7 0.4750 ± 0.0507 4 9 0.118 ±0.031 5.5 ±1.1 L. malabaricus 2062(2) 2 310 ± - 0.4852 ± - 3 3 <0.027 (95% CD <1.8 (95% CD 2063 2 350 ± - 0.5775 ± - 4 6 0.092 ± 0.058 5.7 +4.3,-4.0 2063(2) 2 348 ±- 0.6170 ±- 4 6 <0.069 (95% CD <4.6 (95% CD 2063(3) 3 346 ±7 0.6118 ±0.0133 4 6 0.079 ± 0.019 0.8 ±0.8 2064 3 443 ± 7 1.5591 ± 0.0493 6.7 14 0.082 ±0.013 5.6 ± 0.9 2438 4 250 ±2 0.2517 ± 0.0063 3 3.5 0.067 ± 0.036 4.5 +2.6,-2.5 2439 1 650 2.1155 9 13 0.045 ± 0.015 3.0 ± 1.0 2440 1 560 2.1111 7 19 0.125 ±0.028 8.8 + 2.2,-2.1 2489 4 455 ± 10 1.6185 ± 0.1349 9 13 0.212 ±0.035 8.7+1.5,-1.4 2490 5 422 ±7 1.1055 ± 0.0501 8 8 0.148 ±0.032 6.1 ± 1.2 L. sebae 2068 4 222 ± 5 0.2429 ± 0.0261 2 3 0.134 ±0.034 9.5 + 2.7,-2.6 2069 2 304 ±- 0.6152 ±- 3.5 7 0.298 ± 0.039 24.2 +4.2,-3.9 2070 2 399 ±- 1.5658 ± - 5.5 15 0.217 ± 0.054 16.4+5.1,-4.6 2647 3 400 ± 15 1.4462 ± 0.0184 5 12.3 0.174 ±0-023 7.1 ± 1.0 2648 2 462 ±- 2.1000 ±- 7 15.5 0.261 ± 0.033 11.2+1.5,-1.4 108 Fishery Bulletin 93(1). 1995 "l-5-i l erythropterus 6 8 10 Number of rings Figure 2 The relationship between otolith weight and the number of rings counted in whole otoliths of (A) L. erythropterus, (B) L. malabaricus, and (C)L. sebae. (P<0.05). Under the assumption of a constant mass growth model, radiometric age estimates were again most similar to those found for whole otolith ring counts. The match was best for samples of cored otoliths (2489, 2490) where assumption of a mass growth model is almost absent (Table 2). Lutjanus sebae — The specific activity of 226Ra and the 210Pb/226Ra activity ratio varied less between samples in L. sebae than in the other species (Tables 1 and 2). As with the other species, otolith weight was linearly related to the ring counts of whole otoliths; therefore, a single constant growth rate was assumed in interpre- tation of the radiometric data (Fig. 2C). The radiomet- ric age estimates of intact otolith samples of juveniles (2068, 2069, 2070), based on the assumption of no allogenic 210Pb uptake in the otoliths (R=0.0), were higher than the ring counts for both sectioned and whole otoliths (Table 2). Samples 2068 and 2069 were prob- ably subject to high rates of allogenic 210Pb uptake, as indicated by the high stable Pb/Ba mass ratios (Table 1). Radiometric ages of both sets of cored otoliths were most similar to the age estimates based on whole otolith counts. However, both these samples (2647 and 2648) had very low stable Pb/Ba mass ratios (Table 1). Mod- elled radiometric ages of L. sebae samples (both whole and cored) for different values of R indicate that R - 0. 10 best matches the ring count of whole otoliths (Table 3). Lead.'Barium ratios The stable lead:barium ratios of all samples were plotted against radiometric age assuming an initial activity ratio/? = 0.0 (Fig. 3). Neither L. malabaricus nor L. erythropterus showed an increase in the ratio with increasing age. However, in four of the five L. sebae samples radiometric age increased rapidly with increasing stable lead (Fig. 3). Otolith ageing Lutjanus erythropterus — The growth curves of L. erythropterus based on ring counts in whole otoliths 30- A L sebae • L. malabaricus n L. erythropterus >: 20- 0.3) (Table 4) and lived to a similar age. Lutjanus malabancus — The growth curves express- ing the best fit of length-at-age data from both sec- tioned otoliths and whole otoliths show significant differences (P<0.05) in the estimated growth rates (Fig. 4B). More rings were counted in sectioned otoliths than in whole otoliths from the same fish (Fig. 6B), but were linearly related (whole otolith count=0.64 x (sectioned otolith count) + 0.79; r2=0.81, 1,869 =3614.7, P<0.001). Growth parameters of the reparameterized von Bertalanffy equation of male and female L. mala- baricus did not differ except for L3; this parameter was larger in males (P<0.05). Not all fish collected were sexed, but the growth parameters of the com- bined equation differed from that obtained from the subsets that were sexed (Table 4). Lutjanus sebae — Ages based on counts of sectioned and whole otoliths differed significantly in L. sebae over 350 mm SL (P<0.05; Fig. 4C). More rings were detected in the otoliths of these fish when they were sectioned than when examined intact, although the number of rings detected by the two methods were linearly related (Fig. 6C; whole otolith count=0.50 x (sectioned otolith count) + 0.19; r2=0.80, F1 140=546.0, P<0.0001). The growth parameters of the reparameterized von Bertalanffy equation were similar for both sexes (Table 4). Lutjanus sebae were larger at one year (Lx) Table 4 Growth parameters (SL ± SE) of the reparameterized von Bertalanffy growth equations for Lutjanus malabaricus, L. erythropterus, and L. sebae ( 1-6 rings) from the Gulf of Carpentaria (r2 = nonlinear i estimate of goodness-of-fit). Species Sex n LjiSE L2±SE L3±SE r2 L. erythropterus both 172 75.40 ± 11.67 335.21 ± 2.73 457.12 ± 10.01 0.93 females 61 75.03 ± 17.57 346.66 ± 5.07 477.29 ± 15.64 0.95 males 30 86.06 ± 22.0 337.47 ± 4.50 468.66 ± 18.55 0.94 L. malabaricus both 878 78.09 ± 2.99 298.94 + 1.72 424.92 ± 1.37 0.95 females 159 195.37 ± 27.37 329.09 ± 4.31 423.19 ±2.70 0.70 males 73 100.63 ± 15.50 313.62 ± 6.91 442.67 ± 4.54 0.92 L. sebae both 144 122.27 ± 3.22 287.28 ± 2.18 451.501 3.27 0.97 females 14 99.92 ± 17.84 277.43 ± 8.58 443.96 ± 7.54 0.99 males 9 113.50 ± 3.98 284.83 ± 5.30 461.10 ±4.41 0.99 Fishery Bulletin 93(1), 1995 A bUU- L erythropterus 400- \Tu 300- 200- D /W [ ] \ - whole otolith 100- 0- { - sectioned otolith Figure 4 Plot of the mean length-at-age (±) range and the growth curves of the three species oiLutjanus based on ring counts in whole and sectioned otoliths. than were other species (P<0.05). However, at six years of age (L3) they were about the same size as L. erythropterus but were larger than L. malabaricus (P<0.05). Relationship of ring counts in whole and sectioned otoliths with radiometric ages There was a significant linear relationship between both whole and sectioned otolith ring counts and ra- diometric age (Fig. 7; P<0.001 in both cases). The slopes of the lines of best fit differed (/}=1.04 ± 0.11; r2=0.84 for whole otolith ring counts and /?=1.83 ± 0.06; r2=0.87 for sectioned otolith ring counts). Be- cause the initial activity ratios of the L. sebae samples (R) were obviously greater than 0.0 in at least the whole otolith samples, these were not included in the analyses. There was no significant difference between whole otolith ring counts and radiometric ages for all spe- cies combined (T=53.5; P>0.30, re=15) or for L. malabaricus (T=17.5; P>0.15, rc=10). However, for all species combined we found that the sectioned ring counts were significantly greater than the radiomet- ric age of the same fish (T=6.5; P<0.001, ra=15). The sectioned ring counts of L. malabaricus were also greater than the radiometric ages (T=2; P<0.005, n=10). Discussion This is the first study to use 210Pb/226Ra activity ra- tios to verify the age of relatively short-lived tropi- cal fishes. Previous studies that have used these ra- tios to estimate age have focussed on species that live to at least 70 years (Bennett et al., 1982; Campana et al., 1990; Fenton et al., 1991). In the Lutjanidae, natural levels of 226Ra in the otoliths were high, which helped to minimize the variances in the 210Pb/"226Ra activity ratio and hence the errors in the age estimates. Radiometry provided strong evidence that the rings counted in whole otoliths were the best estimate of the true age of the three lutjanids studied. The radiometric methods we used tend to overes- timate age because the assumptions concerning the otolith mass growth model and rate of incorporation of allogenic 210Pb were conservative. The only con- ceivable mechanism that would lead to underesti- mation of ages radiometrically would be a signifi- cant loss of radon (222Rn) from otoliths during growth (West and Gauldie, in press). Radon is the daughter of 226Ra and the only gas- eous precursor of 210Pb in the decay chain. Its mean lifetime is only 4.8 x 105 seconds, and its effective (physical) diffusivity in otoliths would be about 0.5 x 10"12 m2-s_1. Radon diffusion out of otoliths would be further retarded by adsorption to organic matter (Wong et al., 1992). Simple calculations based on the known microstructure of otoliths (Campana and Neilson, 1985) and on the existing data on radon emanation (Morawska and Phillips, 1993) show that significant loss of radon from otoliths is extremely unlikely, as previously suggested from empirical stud- ies (Fenton and Short, 1992). Milton et al.: Ageing of Lutjanus erythropterus, L maiabancus. and L. sebae 1 1 Figure 5 Photographs of an otolith of a 270-mm L. erythropterus showing the discrepancy between the number of rings seen by examining (A) the intact otolith (2 rings) and (B) after sectioning (5 rings). Scale=l cm. Fishery Bulletin 93(1), 1995 Why ages derived from whole and sectioned otoliths were significantly different remains unclear. The differences in ring counts increased with the size of the fish, and the slope of the regression (whole vs. sectioned ring count) was steepest for the fastest- growing species, L. erythropterus. The otoliths were large (up to 30 mm long, and weighing 3 g), so the daily rings during periods of reduced or variable growth of younger fish were still relatively widely spaced. Thus, what would appear as a diffuse, single hyaline zone in a whole otolith examined against reflected light may have appeared in section as a group of hyaline and opaque zones. These problems 14 - A L. erythropterus 12- o 0 10- ooo o o 8- o o o o 6- ooo ooo 4- oooo ooo 2- ooo o o 0 - * i ' i • i ■ i 0 2 4 6 8 Sectioned otolith ring count -* -» ro 3 Ol O Ol o 03 IOOO P- IOOOOOO 0) ooooooo ST ooooooo 0 g oooooooo ooooooooo o ooooooooo oo ooooooo o o oo o ooo o 0 2 4 6 8 10 20- c L. sebae 15- 10- 5- o- lOOOOO oooooo ooooooo oooooo ooooo oo oooo oo oo o 1 1 1 1 . 1 I 1 1 0 2 4 6 8 10 Whole otolith ring count Figure 6 Plot of the relationship between whole and sec- tioned otolith ring counts of the three species of Lutjanus. in otolith interpretation were most marked in L. erythropterus and led to the greatest discrepancy in ring counts. Studies of the age and growth of Lutjanus mala- baricus from northern Australia and the South China Sea used ring counts in vertebrae (Lai and Liu, 1974, 1979; Edwards, 1985), sectioned otoliths (Chen et al., 1984), and whole otoliths (McPherson and Squire, 1992). Their estimates were similar to the estimates we obtained from whole-otolith ageing, although L. malabaricus from the Great Barrier Reef appear to grow much faster and live at least one year less than those found in other areas (McPherson and Squire, 1992). However, the previous studies and our study provide different estimates of the von Bertalanffy growth parameters Lx and K (Table 5). These differ- ences may have major impacts on age-structured fish- ery models (e.g. yield per recruit) that use these pa- rameters to estimate optimal yield. Lutjanus erythropterus and L. sebae from the Gulf of Carpentaria grew at similar rates to those reported from other parts of northern Australia (Ju et al., 1988; McPherson and Squire, 1992) and elsewhere within their range (Druzhinin and Filatova 1980; Yeh et al., 1986; McPherson and Squire, 1992). However, the growth of L. sebae in the Gulf of Carpentaria did not decline as they approached the maximum age ob- served. This may have been caused by an error in the ring count in otoliths of older fish or because the older age classes were not caught in the trawls. The maximum size of L. sebae in Australian waters has been reported to be between 1.0 and 1.4 m (Allen, 12- 10- Slope = 1.04 ±0.11 - y S r2 = 0.84 / c 8- D O ° fi- o> 6 c ir 4" o / A / □ • X • A* / • L malabancus whole • S ± • A L erythropterus whole 2" / O L malabancus cores ./ Q L sebae cores / A/- erythropterus core 0" ( ) 2 4 6 8 10 12 Radiometric age (yr) Figure 7 The relationship between radiometric age (yr) and whole otolith ring counts of all samples (except L. sebae whole otolith samples). Milton etal.: Ageing of Lutjanus erythropterus. L. malabancus. and L sebae 13 Table 5 Von Bertalanffy growth parameters of tropical Lutjanus from northern Australia and elsewhere within their range (W=whole otoliths; S=sectioned otoliths; V=vertebrae; U=urohyal; Sc =scales). Species Locality Sex Method K Lx Maximum age Reference L. erythropterus Gulf of Carpentaria Both W 0.30 565 6 Present study Great Barrier Reef F w 0.44 500 7 McPherson and Squire (1992) M w 0.41 500 7 McPherson and Squire (1992) Northwest Shelf Both V 0.21 603 7 Juetal. (1988) L. malabaricus Arafura Sea Both V 0.17 707 10 Edwards (1985) Both V 0.12 790 8 Lai and Lui (1979) Gulf of Carpentaria Both w 0.22 592 9 Present study N.W. Australia Both V 0.13 768 8 Lai and Lui (1979) Both V 0.25 715 10 Chen etal. (1984) S. China Sea Both V 0.14 790 11 Lai and Lui (1974) Great Barrier Reef F w 0.23 696 7 McPherson and Squire ( 1992) M w 0.18 820 7 McPherson and Squire ( 1992) Vanuatu Both s 0.31 600 — Brouard and Grandperrin (1984) L. sebae Gulf of Aden Both Sc 0.16 660 11 Druzhinin and Filatova (1980) Gulf of Carpentaria Both w 0.06 1483 9 Present study N.W. Australia Both V 0.13 678 10 Yeh etal. (1986) Great Barrier Reef F w 0.18 851 8 McPherson and Squire (1992) M w 0.15 736 8 McPherson and Squire (1992) L. vittus N.W. Australia F u 0.37 267 7 Davis and West (1992) M u 0.22 346 8 Davis and West (1992) 1985; Grant, 1985) or 16 to 22 kg (Grant, 1985; Allen and Swainston, 1988), which is much greater than we recorded (5 kg). This species may, therefore, live more than 10 years. Indeed, large L. sebae (over 800 mm) from the Great Barrier Reef are known to live on deep coral reefs at depths greater than 60 m1; the deepest part of the Gulf of Carpentaria is only 55 m. This sug- gests that fish may move from this region as they grow. Our radiometric ageing results have several im- portant implications beyond the verification of the age structure of each species. First, they demon- strated that for species that have a high otolith 226Ra specific activity, 210Pb/226Ra activity ratios can be used to age fish as young as 3 years with accuracy. Previously these radioisotopes have only been used to age long-lived species (>10 yr; Bennett et al., 1982; Campana et al., 1990; Fenton et al., 1991). Other radioisotope pairs (228Th:228Ra) have been used to age short-lived tropical species (Campana et al., 1993), but these are only useful for fish up to 5 years old because of the short half-life of Th-228. Second, for relatively short-lived species, radiomet- ric ageing of whole otoliths and cores using a single- phase linear model of otolith mass growth rate gave similar results. Campana et al. (1990) and Smith et 1 Williams, D. Australian Institute of Marine Science, PMB No. 3, Townsville 4810, Queensland, Australia. Personal commun., 1993. al. (1991) argued that new material accreting to the outer surface of the otolith may not accrete 226Ra in similar specific activities to the juvenile (t=0). This would invalidate the use of a simple otolith mass growth model to interpret the radiometric data for otoliths of postjuvenile fish. However, even with a single-phase linear mass growth model (a two-phase model would have reduced the age estimates), we were able to verify that the ring counts in whole otoliths were a more accurate measure of the true age than counts from sectioned otoliths (in accord with core radiometric ages). However, we agree with Smith et al. (1991) that otoliths should be cored for radiometric ageing, if possible, which would avoid the use of an otolith mass growth model. The third point that arises from our analyses re- lates to the ratio of allogenic to radiogenic lead in Lutjanus otoliths. We set the uptake activity ratio value at zero (R=0.0) because higher values would have lowered the age estimates (e.g. Smith et al., 1991). However, from the stable lead/barium ratios and the high age estimates of two of the L. sebae samples (2068 and 2069) it appears that, at least for this species, the juveniles may be taking up more allogenic 210Pb than the adults (Fenton and Short, 1992). There was no systematic increase in the Pb/ Ba mass ratios of L. malabaricus and there is insuf- ficient data for L. erythropterus to be conclusive (Fig. 1 14 Fishery Bulletin 93(1), 1995 3). However, for lutjanids it appears that a Pb/Ba mass ratio <0.2 probably indicates that the assump- tion of a low initial activity ratio (R) is valid, whereas the three samples where the Pb/Ba mass ratio is 0.3- 0.6 indicate that the assumption of low R may be invalid. The Pb/Ba ratios are, therefore, a useful test of the validity of the low R assumption. Finally, this appears to be the first instance where radiometric methods are more consistent with whole- otolith ages rather than sectioned-otolith ages. All previous radiometric studies offish from temperate and subtemperate waters have verified section counts (Bennett et al., 1982; Campana et al., 1990; Fenton et al., 1990, 1991; Smith et al., 1991). The metabolic effects of the annual cycle of inorganic and organic deposition in otoliths may be more pronounced in these environments resulting in clear annuli in otoliths offish from more temperate regions. Conclusions This study has shown that radiometry using 210Pb/ 226Ra activity ratios in both whole and cored otoliths can accurately estimate the ages of fish as young as 3 years. Stable leadibarium mass ratios were used to identify samples that may invalidate the assump- tion of constant uptake of allogenic lead (i?=0). For the lutjanids examined, ring counts in sectioned otoliths were shown to overestimate fish ages. Meth- ods such as marginal increment analysis do not verify that the ageing method used is accurate unless the pattern is demonstrated to be consistent for all age classes. This indicates that tropical fish should be aged by two independent methods where possible to help minimize possible ageing errors. Acknowledgments We thank John Salini, David Brewer, and Ted Wassenberg for coordinating otolith collection and Robert Chisari for meticulously performing the ra- diochemical alpha source preparations. Gwen Fenton and Chris O'Brien made constructive comments on an earlier draft of the manuscript. This project was partly funded by the Australian Fishing Industry Research and Development Council (FRDC grants 88/90 and 29/91). Literature cited Allen, G. R. 1985. FAO species catalogue. Vol. 6: Snappers of the world. FAO, Rome, 208 p. Allen, G. R., and R. Swainston. 1988. The marine fishes of north-western Australia. W. A. Museum, Perth, 201 p. Augustine, ()., and T. J. Kenchington. 1987. A low-cost saw for sectioning otoliths. J. Cons. Int. Explor. Mer 43:296-298. Bennett, J. T., G. W. Boehlert, and K. K. Turekian. 1982. Confirmation of longevity in Sebastes diploproa (Pi- sces: Scorpaenidae) from 210Pb/226Ra measurements in otoliths. Mar. Biol. 71:209-215. Blaber, S. J. M., D. T. Brewer, and A. N. Harris. 1994. The distribution, biomass and community structure of fishes of the Gulf of Carpentaria, Australia. Aust. J. Mar. Freshwater Res. 45:375-396. Brouard, F., and R. Grandperrin. 1984. Les poissons profonds de la pente recifale externe a Vanuatu. Notes et documents d'Oceanographie No. 11. ORSTROM Port- Vila, Vanuatu, 131 p. Campana, S. E., and J. D. Neilson. 1985. Microstructure of fish otoliths. Can. J. Fish. Aquat. Sci. 42:1014-1032. Campana, S. E., H. A. Oxenford, and J. N. Smith. 1993. Radiochemical determination of longevity in flyingfish Hirundichthys affinis using Th-228/Ra- 228. Mar. Ecol. Prog. Ser. 100:211-219. Campana, S. E., K. C. T. Zwanenberg, and J. N. Smith. 1990. 210Pb/226Ra determination of longevity in redfish. Can. J. Fish. Aquat. Sci. 47:163-165. Casselman, J. M. 1974. Analysis of hard tissues of pike Esox lucius with spe- cial reference to age and growth. In T B. Bagenal (ed. ), The ageing offish, p. 13-27. Unwin Brothers, Ltd., England. Chen, C. Y., S. Y. Yeh, and H. C. Liu. 1984. Age and growth of Lutjanus malabaricus in the north west shelf off Australia. Acta Oceanogr. Taiwan 15:154-164. Conover, W. J. 1980. Practical nonparametric statistics. John Wiley and Sons, New York, 493 p. Davis, T. L. O., and G. J. West. 1992. Growth and mortality of Lutjanus vittus from the north west shelf of Australia. Fish. Bull. 90:395-404. Druzhinin, A. D., and N. A. Filatova. 1980. Some data on Lutjanidae from the Gulf of Aden. J. Ichthyol. 39:8-14. Edwards, R. R. C. 1985. Growth rates of Lutjanidae (snappers) in tropical Australian waters. J. Fish Biol. 26:1-4. Fenton, G. E., D. A. Ritz, and S. A. Short. 1990. 210Pb/226Ra disequilibria in otoliths of blue grenadier Macruronus novaezelandiae: problems associated with ra- diometric ageing. Aust. J. Mar. Freshwater Res. 41: 467-473. Fenton, G. E., S. A. Short, and D. A. Ritz. 1991. Age determination of orange roughy, Hoplostethus atlanticus (Pisces: Trachichthyidae), using 210Pb:226Ra disequilibria. Mar. Biol. 109:197-202. Fenton, G. E., and S. A. Short. 1992. Fish age validation by radiometric analysis of otoliths. Aust. J. Mar. Freshwater Res. 43:913-922. Francis, R. I. C. C. 1988. Are growth parameters estimated from tagging and age-length data comparable? Can. J. Fish. Aquat. Sci. 45:936-942. Grant, E. M. 1985. Guide to fishes. Dep. Harbours and Marine, Bris- bane, 896 p. Milton et al.: Ageing of Lutjanus erythropterus, L malabancus. and L sebae I 15 Ju, D. R., S. Y. Yeh, and H. C. Liu. 1988. Age and growth of Lutjanus altifrontalis in the waters off northwest Australia. Acta Oceanogr. Taiwan 20: 1-12. Knight, W. 1968. Asymptotic growth: an example of nonsense disguised as mathematics. J. Fish. Res. Board Can. 25:1303-1307. Lai, H. L., and H. C. Liu. 1974. Age determination and growth of Lutjanus sanguineus in the South China Sea. J. Fish. Soc. Taiwan 3:39-57. 1979. Age determination of Lutjanus sanguineus in the Arafura Sea and northwest shelf. Acta Oceanogr. Taiwan 10:160-171. Longhurst, A. R., and D. Pauly. 1987. Ecology of tropical oceans. Acad. Press, London, 407 p. McPherson, G. R., and L. Squire. 1992. Age and growth of three dominant Lutjanus species of the Great Barrier Reef inter-reef fishery. Asian Fish. Sci. 5:25-36. Manooch, C. S. 1987. Age and growth of snappers and groupers. In J. J. Polovina and S. Ralston (eds.), Tropical snappers and grou- pers: biology and fisheries management, p. 329- 373. Westview Press, Boulder. Morawska, L., and C. R. Phillips. 1993. Dependence of the radon emanation coefficient on radium distribution and internal structure of the material. Geochim. Cosmochim. Acta 57:1783-1797. Ratkowsky, D. A. 1986. Statistical properties of alternative parameter- izations of the von Bertalanffy growth curve. Can. J. Fish. Aquat. Sci. 43: 742-747. Sainsbury, K. 1988. The ecological basis of multispecies fisheries, and management of a demersal fishery in tropical Australia. In J. Gulland (ed.), Fish population dynam- ics, p. 349-382. Wiley, Chichester, England. SAS (SAS Institute, Inc). 1989. Non-linear regression. In SAS user's guide: statis- tics, p. 575-606. SAS Inst., Inc., Cary, NC. Schnute, J., and D. Fournier. 1980. A new approach to length-frequency analysis: growth structure. Can. J. Fish. Aquat. Sci. 37:1337-1351. Smith, J. N., R. Nelson, and S. E. Campana. 1991. The use of Pb-210/Ra-226 and Th-228/Ra-228 disequilibria in the ageing of otoliths of marine fish. In P. J. Kershaw and D. S. Woodhead (eds), Radionuclides in the study of marine processes, p. 350-359. Elsevier, London. Vaughan, D. S., and P. Kanciruk. 1982. An empirical comparison of estimation procedures for the von Bertalanffy growth equation. J. Cons. Int. Explor. Mer 40:211-219. West, I. F., and R. W. Gauldie. In press. Determination of fish age using 210Pb:226Ra disequilibrium methods. Can. J. Fish. Aquat. Sci. 51. Wong, C. S., Y. P. Chin, and P. M. Gschwend. 1992. Sorption of radon-222 to natural sediments. Geo- chim. Cosmochim. Acta 56:3923-3932. Yeh, S. Y, C. Y. Chen, and H. C. Liu. 1986. Age and growth of Lutjanus sebae in the waters off northwestern Australia. Acta Oceanogr. Taiwan 16:90-102. Abstract. — Age and growth of the dusky shark, Carcharhinus obscurus, was estimated from bands in the vertebral centra of 122 individuals and from length-fre- quency data from 341 individuals. The von Bertalanffy growth func- tion parameters from the vertebral analysis were considered more ro- bust (L =373, #=0.038, <0=-6.28, male; zT=349, #=0.039, *0=-7.04, female). Comparison of male and female growth curves generated from vertebral data indicate a sta- tistically significant difference; however, these differences are due primarily to larger sizes attained by adult females. Estimates of age at maturity indicate that dusky sharks follow the typical carchar- hinid pattern of slow growth and late age at maturity. The size at maturity is reported at 231 cm FL and 235 cm FL for males and fe- males, respectively. These lengths correspond to approximately 19 years for males and 21 years for fe- males. The oldest fish aged from ver- tebrae was a 33+ year-old female. Age and growth estimates for the dusky shark, Carcharhinus obscurus, in the western North Atlantic Ocean Lisa J. Natanson John G. Casey Nancy E. Kohler Narragansett Laboratory, Northeast Fisheries Science Center National Marine Fisheries Service, NOAA 28 Tarzwell Drive Narragansett, Rhode Island 02882-1 199 Manuscript accepted 15 July 1994. Fishery Bulletin 93:116-126 (1995). Sharks have become increasingly important in U.S. commercial fish- eries in the western North Atlantic Ocean in recent years. U.S. landings of large coastal sharks, represented primarily by several species in the family Carcharhinidae, increased from 135 to 7,122 metric tons (t) from 1979 to 1989 (Anon., 1993). Musick et al. (1993) reported that annual recreational catches are es- timated to be 35,000 U.S. tons and related annual mortality is over 10,000 U.S. tons (9,074 1). As a group, sharks tend to exhibit slow growth, late age at maturity, and low fecun- dity (Holden, 1973). As a conse- quence of these life history charac- teristics, recruitment in sharks is directly dependent on stock size (Holden, 1973). This direct relation- ship means that elasmobranchs may not be able to recover readily from overexploitation (Holden, 1973). The dusky shark, Carcharhinus obscurus, is part of the species com- plex presently managed under the Secretarial Shark Fisheries Manage- ment Plan (FMP) for the Atlantic Ocean (Anon. 1993). Currently, dusky sharks are harvested in commercial fisheries off the southeastern United States and in the Gulf of Mexico. Rec- reational fishermen off the northeast- ern United States also catch dusky sharks (Casey and Hoey, 1985; Musick et al., 1993). The shark FMP (Anon. 1993) details the need for ac- curate life history information on in- dividual species taken in the shark fishery. Proper management at the species level requires specific infor- mation on age and growth. The dusky shark is a common coastal pelagic species with a world- wide distribution in temperate and tropical waters (Compagno, 1984). In the western North Atlantic, it ranges from as far as Banquereau Bank off Nova Scotia, Canada, to southern Brazil, including the Gulf of Mexico and Caribbean Sea (Hoey, 1983; Compagno, 1984). Tagging studies show dusky shark move- ments from southern New England to Yucatan, Mexico (Casey et al.1; Hoey, 1983). Age and growth studies of large sharks are difficult because many species are highly migratory, mak- ing them available for only short seasonal periods, and different ele- ments of the population segregate spatially by size and sex (Hoenig and Gruber, 1990). In addition, the large size attained by adults makes them difficult to sample. Recent lit- erature has discussed the benefits of growth and longevity estimates attained from tag and recapture 1 Casey, J. G., H. L. Pratt Jr., and C. E. Stillwell. 1980. The shark tagger summary. Newsletter of the Coop. Shark Tagging Program. U.S. Dep. Commer., Northeast Fish. Sci. Cent., Natl. Mar. Fish. Serv., 28 Tarzwell Rd., Narragansett, RI, 02882-1199. 116 Natanson et al.: Age and growth estimates for Carcharhmus obscurus I 17 studies (Casey and Natanson, 1992). These data are not available for the dusky shark nor is validation of vertebral band periodicity. Previous attempts to age the dusky shark were based on limited data and were inconclusive (Lawler, 1976; Hoenig, 1979; Schwartz, 1983). We have attempted to strengthen age esti- mates of C. obscurus by using vertebral band counts together with marginal increment analysis and by us- ing comparisons with length-frequency data. With the von Bertalanffy growth function thus derived, we esti- mate age at maturity and longevity for this species. Materials and methods Data and vertebral samples from dusky sharks were obtained between 1963 and 1993 from research cruises, sport fishing tournaments, and commercial shark fishermen from Cape Cod, Massachusetts, to off the east coast of Florida. Vertebral samples were taken in all months except January, March, and November. Length measurements Total and fork lengths were measured to the nearest centimeter (cm) for each specimen. Fork length (FL) was measured from the tip of the snout to the fork of the tail. Total length (TL) is defined as the distance from the snout to a point on the horizontal axis in- tersecting a perpendicular line extending downward from the tip of the upper caudal lobe to form a right angle (Kohler et al.2). All lengths used are fork lengths unless otherwise noted. FL can be converted to TL by using the regression equation: FL = 0.8352 (TL) -2.2973. [r2 = 0.99, n = 167] Vertebral samples Vertebral samples were taken from above the bran- chial chamber. Sections of vertebral columns were trimmed of excess tissue and then frozen or preserved in 70% ethanol (Casey et al., 1985). Two vertebrae from each specimen were processed histologically following Casey et al. (1985), with the exception of the use of RDO (DuPage Kinetics) for decalcification. All vertebral sections were cut sagit- tally through the focus to a thickness of 80-100 mi- crons, stained with Harris hematoxylin, and mounted in glycerin jelly (Humason, 1972). Bands in the vertebra were counted from an im- age projected on a Summagraphics MM-1812 digi- tizing tablet (Skomal, 1990). Measurements from the focus to growth bands at points along the internal corpus calcareum were digitized directly into an IBM PC-XT computer. The radius of each centrum was measured from the focus to the distal margin of the intermedialia along the same diagonal as the band measurements. Annual growth marks were defined following Casey et al. (1985) for the sandbar shark, Carcharhinus plumbeus, where the annual mark is defined by a wide translucent zone that traverses the intermedialia and continues into the corpus calcareum as an opaque band. Vertebral sections from 171 dusky sharks were prepared. Bands in the same centrum section were counted at least once by each of four investigators to verify that the band counts were repeatable. Sections were considered unreadable if bands could not be discerned in accordance with the above definition. If two readers considered the section unreadable, the sample was eliminated from the final analysis. Counts were accepted if two or more readers agreed. The individual ring measurements for all readers in agreement were then averaged. If two readers agreed on one count and two on another for the same specimen, the higher count was accepted. Specimens where there was no initial agreement were recounted until two of the investigators reached a consensus or the sections were discarded. The relationship between vertebral radius (VR) and FL was calculated to determine the most appro- priate method for back calculation of the size-at-age data (Ricker, 1969). The FL to VR relationship was linear but did not pass through the origin. There- fore, the Lee method was considered more appropri- ate (Ricker, 1969): I - a + (b x s), where / = the length of fish when the vertebra was obtained; a = the intercept on the length axis; b = the slope of the line; and s = the total vertebral radius. A von Bertalanffy growth function (VBGF) was fit- ted to the data by using the following equation (von Bertalanffy, 1938): Lt=L„(l-e-k«-<°>), 2 Kohler, N. E., J. G. Casey, and P. A. Turner. Length-weight re- lationships for 13 Atlantic sharks. Unpubl. manuscr. where Lt = predicted length at time t\ Lx= mean asymptotic fork length (of the fish); K = a growth rate constant (yr_1); and t0 = the theoretical age at which the fish would have been zero length. 118 Fishery Bulletin 93(1), 1995 Growth in length data were analyzed by using FISHPARM, an IBM PC compatible program (Prager et al., 1987), which implements Marquardt's algo- rithm for nonlinear least squares parameter estima- tion (Marquardt, 1963). Bernard's (1981) multivariate analysis for compar- ing growth curves was employed to test the hypoth- esis that male and female vertebral growth curves were the same. This method also determines which of the von Bertalanffy parameters are the most sta- tistically significant cause of any differences in growth. Marginal increment analysis Validation, the confirmation of the temporal mean- ing of the growth increment (Brothers, 1983), is dif- ficult to attain for large pelagic species and was at- tempted by using marginal increment analysis. The marginal increment ratio (MIR) (Skomal, 1990) was calculated by using the following equation: MIR = (VR - Rn)/(R„ - Rn^), where VR = the vertebral radius; Rn = the last complete band; and Rn_1 = the next to last complete band. Mean MIR was plotted against month to locate peri- odic trends in band formation. The MIR relates the edge formation to the width of the previous completed band, which corrects for differences in band width between small and large fish. Length frequency Length-frequency distributions were analyzed by us- ing Shepherd's (1987) model. The sample was sepa- rated by sex and calculations were made at 3-cm in- tervals. Initial values of Lm and K, based on biologi- cal parameters obtained from the literature (Springer, 1960; Compagno, 1984) were entered into the pro- gram which was then rerun until the highest score function was attained. The LM and if associated with this score function were used to calculate tQ by using the following equation: tQ = t + (UK) (\n[Lx - Lt]/LJ, where t0 = 0 (birth); Lt = mean size at birth; K = the von Bertalanffy growth constant; and Loo= the mean asymptotic fork length. Longevity Estimates of longevity were obtained by using tag and recapture data. Data on eight recaptured dusky sharks at liberty for greater than 10 years were ex- amined. Age at tagging was assigned from the size estimate provided at the time of release. This esti- mated age was based on growth curves derived from vertebrae. The number of years at liberty were then added to estimate age at recapture. Results Vertebral samples Of the 171 processed vertebra, 36 (21.0%) were con- sidered unreadable. Initial agreement by two or more readers was reached on 89 specimens. The remain- ing 50 sections were recounted by two of the investi- gators. A consensus was reached on 37 of those re- counted and the rest were discarded as unreadable. Six were then eliminated for having no information on sex. The remaining 120 (70.2%) consisted of 53 male and 67 female specimens ranging in size from a 73 cm FL neonate to a 296 cm FL adult female. The FL-VR regression showed a linear relationship: FL = 12.82(VR) + 24.99 [n = 114; r2 = 0.99] . The FL to VR relationship was significantly differ- ent between the sexes for all fish combined (ANCOVA, P<0.05). However, this was due to three large females whose removal from the analysis al- tered the curves and showed the males and females to be statistically indistinguishable (P<0.05) (Fig. 1). We chose to use the combined relationship without those three samples. Back-calculated as compared with empirical length-at-age data show a smaller estimated size for fish of younger ages, when calculated from the ver- tebrae of the older fish, indicating the presence of a slight Lee's phenomenon for both sexes (Table 1). Lee's phenomenon was more pronounced in females and increased with age. The MIR data showed a distinct, periodic trend of increasing increment growth from April through June (female) or July (male); after this peak there was a slight decrease and apparent leveling (Fig. 2). The decrease in incremental growth is not large enough to indicate a double band formation. The graph suggests that an annual winter band is formed between September and April. This band can be vis- ible by February in males; no data were available for females. The time of annulus formation cannot Natanson et al.: Age and growth estimates for Carcharhinus obscurus 300 - 250 g 200 _c ? 150 o _i £ 100 - 50 -■ • ••» Large females not used for regression calculation 10 15 Radius (mm) 20 25 Figure 1 Relationship between vertebra] radius (cm) and fork length (cm) for male and female dusky sharks, Carcharhinus obscurus. be further established owing to a lack of winter samples. January was used as the month of band formation for the assignment of age classes (Casey et al., 1985). Back-calculated length at first band (80.2 cm FL male; 85.8 cm FL female ) corresponded closely to the known size at birth of 85-100 cm TL (Castro, 1983; Compagno, 1984). The first winter band would have formed after approximately six months growth (as- suming January deposition and spring parturition), and the following bands represented annual growth (Branstetter, 1987). The oldest female in the sample was 33+ years and the oldest male, 25+ years. The parameters of the VBGF determined from the back-calculated data were similar to known life his- tory characteristics except that the predicted L^ for males was higher than that for females (Table 2). Those samples that were neonates with no visible birthmark were excluded from the VBGF analysis. Therefore, only 114 samples (47 male and 67 female) were included in the final calculations. The tQ and if values appear simi- lar between the sexes (Table 2). However, the male and female growth curves are significantly different (P<0.05) based on Bernard's ( 1981) multivariate analysis (Table 3). The results indicated that the differences were caused by the t0 and Lx values (in order of significance). The reported size at maturity for the dusky shark is 231 cm FL and 235 cm FL for males and females, respectively. These lengths correspond to 19 years for males and 21 years for females based on the ver- tebral growth curves (Table 4). Length frequency Length observations from a total of 208 female and 133 male dusky sharks were used to calculate von Bertalanffy parameters by using length-frequency analysis. Samples were obtained from 1961 to 1987 for the months May through November. Because of small yearly sample sizes, data for all years were combined by month. A comparison of the VBGF parameters from the length-frequency analysis [LF] with those derived from vertebral analysis (Table 2) shows that the Lm and t0 values from the vertebral analysis for females were lower than those derived from the length-frequency analysis, and that the K value for females was basi- cally the same for both data sets. The length-frequency analysis for males results in a lower L^ than that from the vertebral analysis and in higher t0 and K values. The VBGF differences in both sexes are not large and both curves indicate late age at maturity (males: 25 yr [LF], 19 yr [vertebral]; females: 16 yr [LF], 21 yr [ver- tebral]) and slow growth (males: if =0.049 [LF], 0.038 [vertebral]; females: #=0.040 [LF], 0.039 [vertebral]) (Fig. 3). The von Bertalanffy parameters for the sexes combined are shown for comparison (Table 2). Longevity Tagging records from NMFS Cooperative Shark Tag- ging Program show that 6,067 dusky sharks were tagged and 131 recaptured between 1962 and 1992. 120 Fishery Bulletin 93(1), 1995 Table 1 Back-calculated and observed size-at-age data for male and female dusky shark Carcharhinus obscurus. Male Ring( age in years) Birth 6 months 0 1 2 3 4 5 6 7 8 Back-calculated X 80.2 87.3 94.1 103 113.9 124.4 132 140.5 149.7 157.7 163.8 SD 5.6 5.5 6.2 7 9.2 10.6 10.7 11.7 12.7 12.6 10.5 n 47 34 30 28 25 21 20 20 19 17 Observed X 87.7 100.5 123.5 116.7 124.5 138 148 173.5 164 SD 5.1 53. 2.1 5.5 4.9 0 0 0.7 7.9 n 13 4 2 3 4 1 1 2 3 Male Ring( age in years) 9 10 11 12 13 14 15 16 17 18 19 Back-calculated X 161.7 179.2 188.6 196.1 202.4 209.8 216.1 220.5 226.5 232.3 237.9 SD 11.6 12.3 10.4 11.8 11.7 13.5 13 11.4 11.7 12.4 12.5 n 14 13 11 10 10 10 10 9 9 8 8 Observed X 172 177.5 177 233 245 260.5 SD 0 2.1 0 0 0 9.2 n 1 2 1 1 1 2 Male Ring (age in years) 20 21 22 23 24 25 26 27 28 29 30 Back-calculated X 246.4 252.6 254.9 256.6 252.6 255.2 SD 14.5 13.2 15.1 16.1 0 0 n 6 6 4 3 1 1 Observed X 256.5 256 263.5 265 SD 3.5 0 9.2 0 n 2 1 2 1 1 female Ring (age in years) Birth 6 months 0 1 2 3 4 5 6 7 8 Back-calculated X 85.8 92.3 99.3 107.4 118.8 128.6 136.2 143.7 150.5 157.8 164.8 SD 5.1 4.5 5 6.3 8.4 9.4 9.5 8.5 8.8 9.4 9.9 n 67 55 52 50 48 45 41 38 35 33 33 Observed X 91.8 104.3 106.5 107 122.3 134.8 138.3 161 154.5 SD 4.5 7.2 6.4 2.8 3.8 16.8 26 12.5 3.5 n 12 3 2 2 3 4 3 3 2 Natanson et al.: Age and growth estimates for Carcharhinus obscurus 121 Table 1 (continued) Female Ring (age in years) 9 10 11 12 13 14 15 16 17 18 19 Back-calculated X 171.5 178.8 186.3 192.9 199.8 206.2 212.4 216.7 222.6 228.4 233.4 SD 10.2 9.6 10.8 10.9 12.4 12.9 13.3 10.5 11.6 12.3 12.6 n 33 30 28 28 28 28 28 27 27 27 27 Observed X 183 190 262 281 SD 15.5 9.9 0 0 n 3 2 1 1 Female Ring (age in years) 20 21 22 23 24 25 26 27 28 29 30 Back-calculated X 237.9 242.1 246 149.8 252.9 256.4 258.6 262.9 265.4 266.2 265.1 SD 12.3 12.1 12.5 12.2 12.6 13.5 11.9 13.3 11.8 15.2 12.7 n 26 24 23 22 20 16 15 13 9 5 4 Observed X 253.4 263 284 156.5 161.5 274 266.5 272 270.8 281 262 SD 14.8 0 0 2.1 9 0 16.3 10.5 6.5 0 0 n 2 1 1 2 4 1 2 4 4 1 1 Female Ring (age in years 1 31 32 33 34 35 36 37 38 39 40 41 Back-calculated X 267.9 277.1 291.4 SD 15.2 16.6 0 rc 3 2 1 Observed X 269 269 276 SD 0 0 0 rc 1 1 1 Eight of these fish were at liberty from 10.1 to 15.8 years. Estimated ages at tagging were based on the vertebral growth curve and ranged from birth to 27 years. The best example of longevity came from a dusky shark that was tagged at an estimated 27 years (260 cm FL) and was recaptured 12 years later at an estimated age of 39 years (Table 5). Discussion In the present study, vertebral data and length-fre- quency data were independently analyzed to derive estimates of von Bertalanffy growth parameters for the dusky shark. Because of the differences between the methods and their sensitivity to the data used to calculate the VBGF parameters, each method pro- duced slightly different growth curves and, therefore, different estimates of age at maturity and longevity (calculated based on maximum reported size). The length-frequency estimates obtained from the dusky shark data are probably somewhat biased owing to limitations of the data and properties of the length- frequency model (Majkowski et al., 1987; Shepherd 122 Fishery Bulletin 93(1). 1995 et al., 1987; Natanson, 1990). As a slow-growing, long-lived species, the dusky shark may have over- 1.2 MALE 1 OH = 0.8 /\ Z 0.6 < W 04 / V" 02 r^* J FMAMJ JASOND MONTH n= 0 001 64 11 13 54 00 12 FEMALE or 5 0.8 y\ Z 0.6 < W 04 J 02 J FMAMJ JASOND MONTH n= 0 001 517 16 22 20 00 Figure 2 Mean vertebral marginal increment ratios (MIR) by month for each of four readers for the dusky shark, Carcharhinus obscurus. Number of samples used to calculate the means for each month are located below the figure. lapping lengths at age which may obscure length modes and bias the estimates of model parameters (Rosenberg and Beddington, 1987; Shepherd et al., 1987). The vertebral method is therefore considered the more robust method and the length-frequency parameters are used for comparison only. Yoccoz (1991) has brought up questions as to the validity of judging biological significance based on statistical tests. He suggests that statistical signifi- cance is not necessarily indicative of biological sig- nificance; this appears to be the case with the dusky shark. The statistically significant differences shown between male and female dusky shark vertebral growth curves may not reflect biological differences. Examination of the length-at-age data suggests that biologically the differences between male and female vertebral curves are small. The age and size at ma- turity differ by only two years and five centimeters for males and females (Table 4). Females are pre- sumed to grow ultimately to a larger size than males. This means that either growth slows in males after maturity or that males do not live as long as females. The vertebral VBGF derived in this study is very similar to the curve attained by Hoenig (1979) for combined sexes for the ages under consideration (birth to 33 years) but is different from data presented by Lawler (1976) and Schwartz (1983). Hoenig's ( 1979) parameter values for the VBGF have a slightly higher Lro and t0 and lower K than parameters de- rived from vertebral analysis in the present study (Table 2). Lawler (1976), using vertebral analysis to determine the age of female dusky sharks, obtained VBGF-parameter values markedly different from the present study (Table 2). The Lx in his study is more than twice as large as the Lx reported here and his lvalue suggests a much slower growth rate. These two factors combine to make Lawler's (1976) curve appear as a straight line from birth to 34 years. Table 2 The von Bertal, dusky sharks ai Parameters inffy para id Lawler meters derived in this study compared to those derived in Hoenig's (19791 's (1976) study of female dusky sharks, Carcharhinus obscurus. study of male and female Male Female Combined L„ K t0 n £» K 200 kg/hr) in spring and fall at depths of 183-365 m and decreased in winter, while above 183 m CPUE was highest (about 50- 150 kg/hr) in July-August but dropped to at or near 0.0 kg/hr in November-March. There was no appar- ent seasonal trend in CPUE at depths >366 m. The proportion of mature females at each macro- scopic maturity stage varied seasonally (Fig. 3). Be- cause spring discards included fish that were the Rickey: Maturity, spawning, and seasonal movement of Atheresthes stomias 131 Market n = 2,167 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Discard n = 185 014 012 0.10 0 08 0.06 0.04 0 02 000 15 20 25 30 35 40 45 50 55 60 65 70 75 60 Survey n = 351 15 20 25 30 35 40 45 SO 55 60 65 70 75 Length (cm) Figure 2 Length-frequency distributions of arrowtooth flounder by sample category. Dark bars = males; clear bars = females. same size as fish in winter market samples, discard and market samples were pooled by common month and by keeping years separate. Throughout the year, samples almost always included large spent/resting females that did not show signs of ovarian recrudes- cence. Gravid females first appeared consistently in September 1991. The proportion of developing, gravid, and spent females stayed relatively constant through November. In December the first ripe/run- ning fish and a substantial increase in the propor- tion of spent females were seen. The next available sample was March 1992 when all the mature females were in the spent/resting stage. Developing females reappeared the following May, and their proportion increased into the fall. In 1992, the first gravid and ripe/running fish were seen in November. Length at 50% maturity calculated from survey data was 28.0 cm for males and 36.8 cm for females (Table 5). Estimates of L50% from pooled market and discard ("commercial") data were lower for males and higher for females than estimates from survey data, although confidence intervals for L50% overlapped. For females, seasonal estimates of L5m varied widely. The greatest L5Q% (>41 cm) was seen before spawn- ing (May-August) and the lowest (<37 cm) during spawning (September-December). Parameters for the logistic function were compared with a likelihood- ratio test (Kimura, 1980). Estimates from commer- cial data were significantly different from survey estimates for both females (x2=145.490, P«0.001; Fig. 4) and males (x2=79.383, P«0.001). In a com- parison of years, logistic curves fit to September- December 1991 (commercial) and September-Novem- ber 1992 ( survey) data were significantly different (like- lihood-ratio test, x2=143.257,P«0.001) although again confidence intervals for L5QC/c overlapped. Ovarian tissue samples were analyzed histologi- cally from 111 female arrowtooth flounder collected late December 1991 during spawning. Each of the five macroscopic maturity stages was represented and no two macroscopic stages showed the same fre- quency distribution of oocyte types (Fig. 5). Chroma- tin nucleolar, perinucleolar, and atretic oocytes were present in all the sampled ovaries. In ovaries of im- mature fish, none of the oocytes had progressed be- yond the perinucleolar stage. Vitellogenic or yolked oocytes were prevalent in developing and gravid stage ovaries, and hydra ted oocytes were seen frequently in gravid and ripe/running stage ovaries. Oocytes with cortical alveoli were most frequently seen in spent/resting ovaries. Atresia was more prevalent in all the ovarian stages of spent/resting fish than in immature fish (Table 6). The percent occurrence of a atretic oocytes was lowest in ovaries from developing fish and high- est in ovaries from spent/resting fish. Beta atresia was most common in spent/resting ovaries but also occurred in developing, gravid, and immature ova- ries. All the immature and 43.8% of the spent/rest- ing females had perinucleolar stage ovaries. Postovulatory follicles (POF) were present in ovaries from all macroscopic stages except immature. POF were most frequently seen in ripe/running ovaries and were common in gravid and spent/resting ova- ries; whereas 7 of 29 developing females examined for histology had ovaries with POF. Postovulatory follicles were also present in 7 of 21 spent/resting 132 Fishery Bulletin 93(1). 1995 162 79 300 148 165 172 104 41 50 36 0.4 0.2 - 0.0 H — V — V — H1 — *V — 4 H H — 4 f — H f — V — V — H Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov 1991 rj> <3 1992 [> H Developing £ Gravid Ripe/Running [~ H Spent/Resting Figure 3 Proportions of mature female arrowtooth flounder at each macroscopic maturity stage by month. Number of females listed at top. Table 4 Washington commercial bottom trawl catch rates (kg/hr) of arrowtooth flounder, Atheresthes stomias, by depth interval based on the minimum depth recorded for each tow. n = number of tows. Year Month 1- -182 m 183- -365 m 366-547 m 547+ m n kg/hr n kg/hr n kg/hr n kg/hr 1991 July 1,644 155.7 176 184.0 31 44.6 9 134.5 August 1,391 54.5 179 130.6 21 3.0 5 0.0 September 1,362 14.5 187 157.6 54 27.7 7 0.0 October 860 11.8 274 231.7 56 64.3 4 0.0 November 210 0.0 95 20.3 37 22.7 3 0.0 December 187 0.0 126 8.9 82 35.8 7 0.0 1992 January 221 0.1 120 14.9 82 8.9 18 11.0 February 596 0.0 240 10.7 61 12.2 37 0.4 March 883 0.3 201 19.5 178 39.8 85 8.9 April 462 7.4 155 53.9 110 68.5 31 1.7 May 829 16.3 232 228.2 63 71.0 40 0.0 June 1,131 19.0 174 344.1 38 16.4 90 0.5 July 1,246 53.4 134 50.8 13 1.7 82 1.5 females with perinucleolar-stage ovaries. One 41.0- cm gravid female had no POF and 6.3% of its oocytes were hydrated. All other gravid females had POF. Overall mean oocyte diameters (/im) and standard deviations were as follows: perinucleolar 79.6 ± 34.9 (n=420); cortical alveoli 185.4 ± 23.4 (n=220); vitellogenic 722.9 ± 73.9 (n=290); and hydrated 940.6 ± 206.8 (n=170) (Fig. 6). Chromatin nucleolar stage oocytes were not measured because they never rep- resented the most advanced stage present in an ovary. Mean diameter of perinucleolar oocytes in spent/resting females was about 10 /im greater than that in the immature females (Student's £-test, P<0.003). Some of the variance in hydrated oocyte size Rickey. Maturity, spawning, and seasonal movement of Atheresthes stomias 133 Table 5 Parameter estimates for the logistic model' of proportion mature at length (cm ), length at 50% mature, and 95% confidence intervals, for arrowtooth flounder, Atheresthes stomias from 1991- -92 Washington commercial (pooled market and discard) 1992 Washington survey, and 1972- -75 Oregon data (See Footnote 3 in the text). For females, results are also given for Washi ngton commereial data grouped by months in relation to the spawning season. Sex and stratum a b R2 L50% 95%CIforL50% n Males Washington-survey 24.990 -0.893 0.968 28.0 27.6-28.4 144 Washington-commercial 33.264 -1.197 0.968 27.8 27.5-28.1 424 Oregon 17.397 -0.615 0.971 28.3 27.8-28.8 218 Females Washington-survey 19.891 -0.540 0.971 36.8 36.3-37.3 207 Washington-commercial 20.874 -0.559 0.984 37.4 37.0-37.7 1,928 Oregon 15.056 -0.352 0.989 42.8 42.4-^13.2 1,628 Females2 Jul-Aug 1991 (before) 13.050 -0.281 0.390 46.5 43.2-49.7 298 Sep-Dec 1991 (during) 14.800 -0.410 0.945 36.1 35.5-36.7 887 Mar-Apr 1992 (after) 61.111 -1.568 0.991 39.0 38.8-39.1 239 May-Jul 1992 (before) 18.194 -0.438 0.928 41.6 40.6^2.6 504 1 PL = l/(l+eta+w->). 2 No samples obtained in January-February 1992. can be attributed to distortion of hydrated oocytes that occurs during histological processing. Gonosomatic indices (GSI) for immature and spent/resting fish remained fairly constant across seasons, whereas GSI for developing or gravid fish varied considerably over time, reflecting ovarian recrudescence (Table 7). Individual GSI for im- mature fish ranged from 0.0017 to 0.0154 (aver- age 0.0055), and individual spent/resting GSI ranged from 0.0037 to 0.0259 (average 0.0135). GSI for ripe/running fish (n=4; L =47.8) was not calculated because loss of eggs in handling pre- cluded accurate gonad weights. From histologi- cal analysis, hydrated oocytes and POF were found in "developing" females, indicating some misclassification of spawning females. Because of suspected misclassification, developing and gravid GSI data were pooled by month. GSI for develop- ing or gravid fish showed a rapid increase from about 0.03 in August 1991 and 0.02 in July 1992 to 0.06 in September of both years; the highest an- nual mean GSI occurred in December 1991 and No- vember 1992. The highest individual GSI was 0.2201 in November 1992 for a 38-cm gravid female. 1.0 0.8 0) TO E 0.6 o "g 0.4 Q. O ^0.2 0.0 TftKP*aHBl*ffi- 15 20 25 30 35 40 45 50 55 60 65 Fork Length (cm) -- Commercial^*- Survey Oregon Figure 4 Maturity distributions and logistic curves for female arrowtooth flounder calculated from pooled 1991-92 market and discard (commercial) data, 1992 survey data, and 1973-75 data from Oregon (see Footnote 3 in the text). Discussion The progression of gonad maturity stages, increase in GSI, and the appearance of gravid females show that arrowtooth flounder spawn during fall-winter off Washington. Spawning begins as early as Sep- tember, extends at least through December, and is completed by March. This coincides with the spawn- ing season for Atheresthes evermanni in the western 134 Fishery Bulletin 93(1), 1995 Table 6 Percent occurrence of oocytes in each oocyte developmental stage in arrowtooth flounder, Atheresthes stomias, by macroscopic and microscopic maturity stages. Percent occurrences of atresia and postovulatory follicles (POF) among all oocyte structures also included. Microscopic stage reflects the most advanced oocyti 3 type present, n = number of females, L = mean FL in cm; oocyte-stage 1 = chromatin nucleolar; stage 2 : = perinucleolar; stage 3 = cortical alveoli , stage 4 = vitellogenic; stage 5 = hydrated; and POF = postovulatory follicle. Samples were collected late December 1991. Oocyte developmental stage Atresia Macroscopic Microscopic stage stage n L (cm) 1 2 3 4 5 a P POF Immature Perinucleolar 17 35.7 19.0 81.0 0.0 0.0 0.0 11.5 1.3 0.0 Developing Vitellogenic 26 43.0 2.4 20.7 0.1 76.8 0.0 3.6 0.9 0.5 Developing Hydrated 3 39.7 1.0 20.6 0.0 77.0 1.4 6.6 0.9 0.9 Gravid Hydrated 15 40.4 3.1 25.5 0.2 47.0 24.1 7.2 0.9 7.1 Ripe/Running Hydrated 2 59.0 3.3 39.6 0.0 1.1 56.0 7.2 0.0 26.8 Spent/Resting Perinucleolar 21 48.2 15.8 84.2 0.0 0.0 0.0 21.7 7.3 5.4 Spent/Resting Cortical alveoli 26 61.8 14.5 76.1 9.4 0.0 0.0 20.1 10.2 2.9 Spent/Resting Hydrated 1 42.0 6.3 34.4 0.0 34.4 25.0 16.7 0.0 7.1 Developing Gravid Ripe/Running Spent/Resting □ Postovulalory follicle □ Beta atretic Alpha atretic Alpha Hydrat Vitellogenic □ Cortical alveoli □ P •'"nucleolar □ Chromatin nucleolar Figure 5 Proportion of arrowtooth flounder oocytes assigned by histological criteria to ovarian de- velopmental stages according to macroscopic maturity stage of the whole ovary. Samples were collected late December 1991. Number of females is listed at top. Bering Sea reported by Pertseva-Ostroumova ( 1960). Hirschberger and Smith (1983) found some spawn- ing arrowtooth flounder during spring and summer months in the Gulf of Alaska, but their survey data were insufficient to define the spawning season with any certainty. The appearance of translucent oocytes is usually taken as an indication that spawning is imminent (hours or days) (West, 1990), although there are no laboratory data to indicate the speed at which arrowtooth flounder oocytes ripen and are ovu- lated. Gravid females were first seen in September 1991 coincident with an increase in GSI. A similar increase in September GSI was seen in 1992, but the first gravid females were observed in November, sug- gesting that the start of arrowtooth flounder spawn- ing may vary from year to year. Histological results show arrowtooth flounder are batch spawners, where one female spawns repeat- Rickey. Maturity, spawning, and seasonal movement of Atheresthes stomias 135 Table 7 Arrowtooth flounder, Atheresthes stomias, monthly mean fork length ( L , in cm) and mean gonosomatic index (GSI) and standard deviation (SD) for females selectively sampled for GSI by macroscopic maturity stage. July 1991-July 1992 samples were col- lected shoreside; September-November 1992 samples were collected at sea. Year Month mmature Developing/Gravi d Spent/Resting n L GSI SD n L GSI SD n L GSI SD 1991 July 1 48.0 0.0056 22 63.3 0.0277 0.0096 20 61.1 0.0164 0.0021 August 3 48.0 0.0080 0.0035 10 60.4 0.0290 0.0082 2 63.5 0.0120 0.0028 September 9 42.8 0.0064 0.0020 46 65.1 0.0587 0.0249 15 53.9 0.0163 0.0047 October 10 39.4 0.0051 0.0006 40 61.0 0.0738 0.0246 6 56.7 0.0120 0.0066 November 3 41.7 0.0045 0.0003 20 55.7 0.0883 0.0223 2 54.5 0.0051 0.0003 December 14 36.3 0.0048 0.0018 33 47.0 0.1160 0.0332 11 45.7 0.0070 0.0060 1992 March 10 35.9 0.0045 0.0017 0 — — — 10 49.5 0.0126 0.0015 April 6 40.5 0.0051 0.0013 0 — — — 20 55.3 0.0114 0.0035 May 9 36.6 0.0048 0.0030 1 67.0 0.0140 — 21 65.4 0.0135 0.0026 June 4 44.5 0.0067 0.0009 20 61.9 0.0171 0.0042 20 64.4 0.0151 0.0030 July 5 41.0 0.0071 0.0034 17 57.8 0.0215 0.0046 18 53.8 0.0145 0.0031 September 18 29.2 0.0063 0.0042 28 55.6 0.0615 0.0292 0 — — — October 10 35.9 0.0049 0.0017 10 46.0 0.0567 0.0303 0 — — — November 10 30.0 0.0056 0.0041 11 46.4 0.1004 0.0487 0 — — — edly over a protracted spawning season, as are Pacific halibut, Hippoglossus stenolepis (St-Pierre, 1984), and Dover sole, Microstomus pacificus (Hunter et al., 1992). Size frequencies of oocyte stages (Fig. 6) show distinct populations of oocytes that indicate a group-synchro- nous pattern of development. Postovu- latory follicles were found in "developing" females, those with no visible translucent oocytes, evidence that these fish had re- cently spawned and that macroscopic examination of ovaries could not separate all spawning from nonspawning fish. In September 1991, early in the spawning season, gravid mean GSI was signifi- cantly greater than developing GSI (Student's t-test, P«0.001), but by No- vember and December there was essen- tially no difference between mean GSI for developing and gravid females (Student's f-test, November P<0.105, December P<0.841); the highest mean GSI was ob- served in December. Under the macroscopic matu- rity definitions used, females progress from imma- ture to the developing stage, then cycle between "de- veloping" and "gravid" as successive batches of oo- cytes ripen and are ovulated. The ripe/running stage corresponds then only to the last and perhaps larg- est batch of oocytes, suggesting that by December spawning was near completion for some females. 0.25 0.20 c o ■C 0.15 o Q. O CL 0.10 + 0.05 0.00 Perinucleolar l \ V Cortical alveoli Vitellogenic 1 i ft a l\ k Hydrated Li „iA fl.,^/\,iflJ ■;„,,, LiiXU,mi^A,M mrA 150 300 450 600 750 900 1050 1200 1350 1500 1650 Oocyte diameter (microns) Figure 6 Size-frequency distributions of arrowtooth flounder oocyte developmen- tal stages from ovaries collected late December 1991. Proportions were calculated separately for each oocyte type. Spent/resting females were seen year-round, evi- dence that adult arrowtooth flounder may not spawn every year. Of particular concern is whether small, resting mature fish were misclassified as immature, and vice versa, since errors will bias estimates of size at ma- turity. Immature male arrowtooth flounder were dif- ficult to identify and errors undoubtedly occurred, 36 Fishery Bulletin 93(1), 1995 but there was not enough auxiliary information to quantify them. Macroscopically immature females examined for histology did not show signs of recent spawning, and all were microscopically staged as perinucleolar. Out of 48 spent/resting females exam- ined for histology, 43.8% also had perinucleolar ova- ries. Seven of these had POF, direct evidence of prior spawning. Of the remaining 14, atretic structures were more than twice as common as in immature females. Hunter et al. (1992) used atresia to distin- guish immature from uncertain maturity in Dover sole ovaries defined as inactive but concluded that microscopic examination of oocytes in histological sections may not identify all mature, postspawning females. Relatively high rates of atresia may indi- cate that fish have finished spawning (Wallace and Selman, 1981), but this alone is insufficient to sepa- rate mature from immature fish because atresia can be brought on by stresses not necessarily associated with spawning, such as starvation, pollution, or other environmental conditions (Wallace and Selman, 1981; Hunter and Macewicz, 1985; Hunter et al., 1992). Because histological criteria could not differ- entiate all mature from immature females and be- cause other microscopic evidence of prior spawning such as ovarian wall thickness (Burton and Idler, 1984) was not available, the degree of misclassi- fication of mature vs. immature females staged mac- roscopically could not be determined. Histological processing is known to cause shrink- age of oocytes (West, 1990); therefore oocyte diam- eters determined from processed tissue sections should be considered an index rather than an abso- lute measurement of oocyte size. For arrowtooth flounder, Pertseva-Ostroumova (1960) reported whole egg diameters are about 2.5-3.5 mm. Matarese et al. (1989) lists A. stomias egg diameter as approxi- mately 3 mm, three times the mean diameter of ripe oocytes determined in this study. Seasonal bathymetric migrations are a familiar pattern in flatfish. Dover sole, Microstomas pad ficus, petrale sole, Eopsetta jordani, and English sole, Pleuronectes vetulus, migrate seasonally across depths (Alverson et al., 1964), and Dover sole tend to reside at deeper depths at older ages (Hunter et al., 1990). Kabata and Forrester (1974) sampled arrowtooth flounder off Vancouver Island in May- June 1968 and found increasing length with depth, and a drop in abundance below 420 m (230 fm) con- sistent with these results. Trends in arrowtooth flounder catch rates by depth and season (Table 4) indicate arrowtooth flounder move offshore in win- ter. Arrowtooth flounder were common in shallow water (<183 m) in summer, when the average size of landed fish was large. In winter, smaller numbers and sizes of arrowtooth flounder were caught in deeper water; whereas several hundred tows were reported in shallow water with virtually no arrowtooth flounder. Large, mature, presumably spawning arrowtooth flounder may have moved out of the range of the trawl fishery, possibly to deeper water or north into Canadian waters. However, tar- geted arrowtooth flounder trips are rare and inde- pendent estimates of the amounts of arrowtooth flounder discarded from trawl catches are high, from nearly 76% off Oregon and Washington (Barss and Demory, 1985) to over 80% in the Gulf of Alaska.1 Large volumes of discards and catch unreported in logbooks may obscure trends in distribution; they certainly result in underestimates of arrowtooth flounder CPUE. Hosie (1976) states that arrowtooth flounder spawn off central Oregon from December through March at about 200 fm. Hirschberger and Smith (1983) reported spawning arrowtooth floun- der at depths of over 350 m (191 fm) in the Gulf of Alaska. The full extent of the spawning depth range inhabited by arrowtooth flounder has not been de- termined, but in this study in 1991 gravid females were found in commercial tows out to 512 m (280 fm) and ripe/running females at 475 m (260 fm). In 1992 gravid and ripe/running females were found at 399 m (218 fm). Since these results also suggest that in winter the bulk of the population was in water as deep or deeper than 366 m, it is likely that the ma- jority of arrowtooth flounder off Washington spawn at depths exceeding 366 m (200 fm). To examine trends in length at maturity over time, I fitted logistic curves to Oregon trawl survey data from the 1970's3 to compare with results from Wash- ington (Table 5). The Oregon survey covered the area from Newport, Oregon, south to Cape Blanco and included FL and maturity for 218 male and 1,628 female arrowtooth flounder. Macroscopic criteria used to distinguish mature from immature fish were identical in both studies. Washington maturity samples were collected in all months except Janu- ary and February. All months except July, August, and November were represented in the Oregon data. Arrowtooth flounder in the present study matured at a smaller size than those collected off Oregon, and likelihood-ratio tests (Kimura, 1980) showed sample nonlinear regressions for Oregon were significantly different when compared with both Washington sur- vey data (male x2=:74.555, P<<0.001; female X2=137.922, P«0.001) and commercial data (male X2=80.539,P«0.001; female x2=147.920,P«0.001). Distribution of female maturities across lengths (Fig. 4) suggests that female arrowtooth flounder are maturing at a smaller size than they were off Or- egon in the early 1970's, or that there are latitudinal Rickey: Maturity, spawning, and seasonal movement of Atheresthes stomias 137 differences in size at maturity. However, differences between results for Oregon and the present study could be explained by differences in sampling distri- butions across months, or by different interpretations of maturity codes by different observers; therfore they may not represent a biological change. Size-selectivity and areal or bathymetric sampling biases are critical to estimates of L509l (Welch and Foucher, 1988; Trippel and Harvey, 1991). Predicted length at maturity may be biased if fish are size-seg- regated by area or depth (e.g. if immature fish do not migrate to spawning depths while targeted com- mercial trawl fisheries typically operate where large fish are most likely to be found in quantity, i.e. the spawning grounds). Smaller arrowtooth flounder were not well represented in commercial landings. Size selectivity in commercial fisheries occurs either through net selection (a lesser problem in the trawl survey) or through size-selective targeting and dis- carding. Net avoidance by larger fish may also be a factor. In the extreme case of male arrowtooth floun- der, estimated L5m was below the size range of fish in market samples though well within the size range of fish in commercial discards and survey catches. Because the trawl survey sampled the widest size range of arrowtooth flounder over a fairly large area and depth range prior to peak spawning in 1992, size- at-maturity estimates from the trawl survey repre- sent the best available. Hunter et al. (1992) estimated size at maturity for female Dover sole and found samples taken during the spawning season yielded higher estimates of L50% than did samples taken before spawning. They at- tributed this to the presence of postspawning females with "highly regressed" ovaries that were histologi- cally indistinguishable from immature females, and they concluded that estimates of length or age at first maturity should always be conducted prior to the onset of spawning, when such females are rare. I found the opposite seasonal pattern in length at maturity for female arrowtooth flounder; lowest L50% was estimated from commercial samples collected in the fall during spawning, and highest L509c was esti- mated from months preceding spawning. Market samples collected in summer (before spawning) tended to underrepresent smaller arrowtooth floun- der and yielded extremely high estimates of female length at maturity. In the case where sampling is limited to commercial trawl fisheries, it may be pref- erable to pool year-round sampling data to generate estimates of L5Q% if fish are moving in and out of range of the trawl fleet, rather than to attempt to narrow the sampling window to just prior to spawn- ing as suggested by Hunter et al. (1992). This in- volves the explicit trade-off of some assumed increase in the misclassification of small fish with the signifi- cant bias caused by a seasonal inability to obtain representative samples of the entire size or bathy- metric range of a population. Perhaps coincidentally, female length-at-maturity curves generated from the year-round commercial data and the survey data were strikingly similar (Fig. 4), although statistically the curves were different. Acknowledgments Thanks go to Marion Larkin and the crew of the FV Larkin for their gracious assistance. Jack Tagart and Han-lin Lai advised on sampling design and statis- tical analyses, and Nancy Tonjes arranged routine sampling. I thank Ken Weinberg, Mark Wilkins, and other participants in the 1992 NMFS surveys for their assistance and cooperation, and the anonymous reviewer whose thoughtful comments vastly im- proved the manuscript. This paper is funded in part by a grant from the National Oceanic and Atmo- spheric Administration. Literature cited Alverson, D. L., A. T. Pruter, and L. L. Ronholt. 1964. A study of demersal fishes and fisheries of the north- eastern Pacific ocean. H. R. MacMillan lectures in fisheries. Univ. British Columbia, Vancouver, B.C., Canada, 190 p. Barss, W. H., and R. L. Demory. 1985. Observations on retention and discard of groundfish from a limited sampling of Oregon trawl vessels in 1982. Oregon Dep. Fish Wildl. Info. Rep. 85-7, 15 p. Burton, M. P., and D. R. Idler. 1984. The reproductive cycle in winter flounder, Pseudo- pleuronectes americanus (Walbaum). Can. J. Zool. 62:2563-2567. Gunderson, D. R., P. Callahan, and B. Goiney. 1980. Maturation and fecundity of four species of Sebastes. Mar. Fish. Rev. 42(3-4):74-79. Hart, J. L. 1973. Pacific fishes of Canada. Fish. Res. Board Can. Bull. 180, 740 p. Hirschberger, W. A., and G. B. Smith. 1983. Spawning of twelve groundfish species in the Alaska and Pacific coast regions, 1975-81. U.S. Dep. Commer., NOAATech. Memo. NMFS F/NWC:44, 50 p. Hosie, M. J. 1976. The arrowtooth flounder. Oregon Dep. Fish Wildl. Info. Rep. 76-3, 4 p. Hunter, J. R., and B. J. Macewicz. 1985. Rates of atresia in the ovary of captive and wild north- ern anchovy, Engraulis mordax. Fish. Bull. 83:119-136. Hunter, J. R., J. L. Butler, C. Kimbrell, and E. A. Lynn. 1990. Bathymetric patterns in size, age, sexual maturity, water content, and caloric density of Dover sole, Micro- stomas pact ficus. CalCOFI Rep. 31:132-144. 138 Fishery Bulletin 93(1). 1995 Hunter, J. R., B. J. Macewicz, N. C. Lo, and C. A. Kimbrell. 1992. Fecundity, spawning, and maturity of female Dover sole Microstomus pacificus, with an evaluation of assump- tions and precision. Fish. Bull. 90:101-128. Kabata, Z., and C. R. Forrester. 1974. Atheresthes stomias (Jordan and Gilbert 1880) (Pi- sces: Pleuronectiformes) and its eye parasite Phrixocephalus cincinnatus Wilson 1908 (Copepoda: Lernaeoceridae) in Canadian Pacific waters. J. Fish. Res. Board Can. 31:1589-1595. Kimura, D. K. 1980. Likelihood methods for the von Bertalanffy growth curve. Fish. Bull. 77:765-776. Mahoney, R. 1973. Laboratory techniques in zoology. John Wiley & Sons, New York, NY, 360 p. Matarese, A. C, A. W. Kendall Jr., D. M. Blood, and B. M. Vinter. 1989. Laboratory guide to early life history stages of north- east Pacific fishes. U.S. Dep. Commer., NOAATech. Rep. NMFS 80, 652 p. Pertseva-Ostroumova, T. A. 1960. (Reproduction and development of the species of the genus Atheresthes Jordan et Gilbert [Pleuronectidae, Pisces]). Zool. Zhur. 39(11):1659-1669. [In Russian with English summary.] Ranck, C. L., F. M. Utter, G. B. Milner, and G. B. Smith. 1986. Genetic confirmation of specific distinction of arrowtooth flounder, Atheresthes stomias, and Kamchatka flounder, A. evermanni. Fish. Bull. 84:222-226. Seber, G. A. F. 1982. The estimation of animal abundance and related pa- rameters, 2nded. MacmillanPubl.Co.,Inc.,NewYork,654p. St-Pierre, G. 1984. Spawning locations and season for Pacific halibut. Int. Pac. Halibut Comm. Sci. Rep. 70, 45 p. Trippel, E. A., and H. H. Harvey. 1991. Comparison of methods used to estimate age and length of fishes at sexual maturity using populations of white sucker {Catostomus commersoni). Can. J. Fish. Aquat. Sci. 48:1446-1459. Wallace, R. A., and K. Selman. 1981. Cellular and dynamic aspects of oocyte growth in teleosts. Am. Zool. 21:325-343. Welch, D. W, and R. P. Foucher. 1988. A maximum likelihood methodology for estimating length-at-maturity with application to Pacific cod (Gadus macrocephalus) population dynamics. Can. J. Fish. Aquat. Sci. 45:333-343. West, G. 1990. Methods of assessing ovarian development in fishes: a review. Aust. J. Mar. Freshwater Res. 41:199-222. Yamamoto, K. 1956. Studies on the formation offish eggs I. Annual cycle in the development of ovarian eggs in the flounder, Liopsetta obscura. J. Fac. Sci. Hokkaido Univ. Ser. VI, 12:362-373. Yang, M. S. 1988. Morphological differences between two congeneric species of pleuronectid flatfishes: arrowtooth flounder, Atheresthes stomias, and Kamchatka flounder, A. evermanni. Fish. Bull. 86:608-611. Yang, M. S., and P. A. Livingston. 1986. Food habits and diet overlap of two congeneric spe- cies, Atheresthes stomias and Atheresthes evermanni, in the eastern Bering Sea. Fish. Bull. 82:615-623. Abstract. Marine turtle tag- ging records were collected off east- central Florida by a shrimp trawler from May 1986 to December 1991. The data were analyzed to deter- mine species composition, size dis- tribution, seasonal occurrence, movements, morphometries, and growth of 928 incidentally captured turtles. Loggerhead turtles, Ca- retta caretta, were the most fre- quently captured species (83% of total catch), while Kemp's ridley, Lepidochelys kempi, and green turtles, Chelonia mydas, were caught less frequently (12% and 4%, respectively). The loggerhead turtle population consisted of a sea- sonably variable aggregation of subadult and adult turtles. The Kemp's ridley and green turtle populations were composed of sub- adult turtles and were captured primarily during winter months. Kemp's ridley and loggerhead turtles appeared to exhibit a sea- sonal north-south migrational pat- tern along the Atlantic coast. Re- gression equations were developed for the morphometric relationships of each species. Average yearly growth rates and estimates for the von Bertalanffy growth interval equation were calculated for logger- head and Kemp's ridley turtles. These results indicate that the coastal waters of the Cape Cana- veral area provide an important developmental habitat for the three species of marine turtle. Marine turtle populations on the east-central coast of Florida: results of tagging studies at Cape Canaveral, Florida, 1986-1991* Jeffrey R. Schmid Southeast Fisheries Science Center, National Marine Fisheries Service, NOAA 75 Virginia Beach Drive, Miami, Florida 33149 Archie Carr Center for Sea Turtle Research 223 Bartram Hall, University of Florida Gainesville, Florida 3261 I Manuscript accepted 29 August 1994. Fishery Bulletin 93:139-151 (1995). The marine turtle life history is a dy- namic progression of stages which includes oceanic dispersal of the off- spring and utilization of a series of distinct developmental habitats (Carr, 1980; Hendrickson, 1980). The early in-water stages of marine turtle development have not been as extensively studied as the repro- ductive stage of females. Informa- tion concerning the early life histo- ries of threatened and endangered marine turtles is critical in formu- lating conservation and recovery strategies as mandated by the En- dangered Species Act of 1973 and subsequent amendments. Inaccessibility of immature tur- tles in the open ocean is the major factor contributing to the lack of information on the early stages of development. Other than possible current-mediated dispersal sce- narios (Carr, 1986; Collard and Ogren, 1990), little is known about the pelagic stage of marine turtle development. However, information concerning the populations of im- mature turtles foraging in the coastal waters of eastern Florida has been accumulating as a result of data collected through commer- cial fisheries (fishery-dependent) and fishery-independent activities. Fishery-independent capture and tagging efforts have characterized the populations of loggerhead turtles, Caretta caretta, and green turtles, Chelonia mydas, foraging in the northern part of the Indian River lagoon system (Ehrhart and Yoder, 1978; Mendonca, 1981, 1983; Mendonca and Ehrhart, 1982; Ehrhart, 1983). All green turtles collected in the lagoonal habitat were immature, as were almost all of the loggerhead turtles. Aggrega- tions of marine turtles in the Port Canaveral ship channel were first reported in 1978, when two trawl- ers caught unprecedented numbers of loggerhead turtles while search- ing for a concentration of shrimp (Carr et al., 1980). This prompted the National Marine Fisheries Ser- vice (NMFS) to conduct trawl sur- veys of the ship channel from 1978 to 1984 (Butler et al., 1987; Hen- wood, 1987a; Henwood and Ogren, 1987). The surveys provided infor- mation on the seasonal occurrence and movement patterns of subadult and adult loggerhead turtles (Henwood, 1987a), as well as sub- adult Kemp's ridley, Lepidochelys "Contribution MIA-92/93-94 of the Miami Laboratory, Miami, Florida. 139 140 Fishery Bulletin 93(1), 1995 kempi, and green turtles (Henwood and Ogren, 1987) captured in the vicinity of Cape Canaveral. In addi- tion, the results of research conducted in response to incidental mortality of marine turtles due to dredg- ing in the Port Canaveral ship channel were pre- sented at the Cape Canaveral Sea Turtle Workshop (Witzell, 1987). In 1986, the NMFS Panama City Laboratory initi- ated long-term studies of marine turtles found along the northwest (Cedar Keys) and east-central (Cape Canaveral) coasts of Florida (Schmid and Ogren, 1990). The Kemp's ridley turtle was the target species in both study areas. This paper presents the results of NMFS marine turtle studies conducted in nearshore waters of east-central Florida from 1986 to 1991. Information concerning marine turtle species composition, relative abundance, size frequency, seasonal occurrence, move- ments, morphometries, and growth is provided. Materials and methods Data collection A commercial shrimp-fishing vessel was contracted by NMFS, from May 1986 to December 1991, to mea- sure, tag, and release marine turtles incidentally captured during trawling. Fishing effort and location were a function of the sea- sonal abundance of brown shrimp, Penaeus aztecus, and white shrimp, Penaeus setiferus. Trawling was con- ducted between St. Mary's Entrance, 30°43'N, and Sebastian Inlet, 27°52'N (Fig. 1), and was concentrated in the Cape Canaveral area, 28°30'N to 28°15'N, as defined by Henwood ( 1987a). Fishing effort did not extend beyond 24 km off- shore and 25.6 m in depth. The majority of effort occurred less than 8 km offshore and 13.4 m in depth. Trawling gear con- sisted of four 12.2-m or 12.8-m nets (two on each side) for targeting brown shrimp, or two 24.4-m nets (one on each side) for targeting white shrimp. Captured turtles were double tagged on the trailing edge of the fore flippers with #681 Inconel cattle ear tags. Tag- ging information for each turtle included: tag codes, species, date, location of cap- ture, latitude and longitude, depth, gear type, standard straight-line carapace length (SSCL; nuchal notch to posterior end of postcentral), and straight-line carapace width. Carapace length and width were measured to the nearest 0.1 inch with forester's calipers and were converted to metric units for analysis. Kemp's ridley and green turtles were weighed with a 15-kg capacity spring scale. Notes on the condition of the turtle were recorded when the animal was injured or deformed (e.g. missing flip- per, carapace wounds, etc.). NMFS issued Sea Turtle Conservation Regulations on 29 June 1987 (Federal Register, 1987) that re- quired vessels 25 feet (7.6 m) long or longer to use Turtle Excluder Devices (TED's) in the Cape Canaveral area beginning 1 October 1987. Subse- quently, a NMFS permit was issued authorizing the contract vessel to conduct a TED testing program during fishing operations. The testing procedure con- sisted of towing a net(s) equipped with a Morrison soft TED on one side of the boat and a net(s) without a TED on the other side. Pounds of shrimp, marine turtle captures, and total catch (when possible) were recorded for the trawl types. Effort data were available for 1989- 91, including trawl size and type, number of tows and total tow time, and number of days fished. Data analysis The terms "juvenile" and "subadult" used to describe the early stages of the marine turtle life history are St Mary's Entrance : Cape Canaveral Sebastian Inlet Figure 1 Sampling areas for marine turtles (Caretta caretta, Lepidochelys kempi, and Chelonia mydas) off the Atlantic coast of Florida from 1986 to 1991. Schmid: Marine turtle populations of the east-central coast of Florida 141 not well defined. In this study, the term "juvenile" has been reserved for immature turtles in the pe- lagic stage of development. A turtle is considered "sub- adult" when it has recruited to its respective coastal- benthic habitat and "adult" when sexually mature. Loggerhead turtles greater than 80-cm carapace length were considered adult, based on the length frequencies of Cape Canaveral nesting females (Carr, 1986, and references therein) and earlier investiga- tions of Henwood (1987a). Kemp's ridley turtles greater than 60-cm carapace length were considered adult (Pritchard and Marquez, 1973). Monthly trawling effort was calculated and stan- dardized according to Henwood and Stuntz (1985) by using the formula E ( Nets ■ Length V Min { 305 A~60~ where E is the trawling effort in hours towed by a single 30.5-m headrope length net, Nets is the num- ber of nets towed, Length is the headrope length (m) of a net, and Min is the number of minutes fished. Capture records were analyzed to evaluate species composition within the study area, length-frequency distribution of each species, and patterns of seasonal distribution and movements. Linear regression analyses were performed for carapace width on length for loggerhead turtles. The morphometric data for loggerhead turtles were subdivided into a sub- adult group (<80 cm SSCL) and an adult group (>80 cm SSCL) because the carapace dimensions of this species change as the animals mature (Henwood and Moulding, 1987). Carapace width was regressed on length, and weight regressed on length for Kemp's ridley and green turtles. Turtles with carapace wounds or deformities were not included in the analy- ses. Regression residuals for length-weight relation- ships were analyzed graphically to assess the appro- priateness of the straight-line model (Sokal and Rohlf, 1981; Kleinbaum et al., 1988). Curved carapace lengths (CCL) of stranded turtles were converted to straight-line carapace lengths (SCL) by using the following regression equations of Teas (1993): SCL = -1.442 + (0.948 x CCL) for loggerhead turtles; SCL = 0.013 + (0.945 x CCL) for Kemp's ridley turtles. Total straight-line carapace lengths (TSCL) of log- gerhead turtles were converted to standard straight- line carapace lengths (SSCL) with the regression equation of Henwood and Moulding (1987): SSCL = (0.9964 x TSCL) - 0.775. Yearly growth rates were calculated from the formula G = A Length Days 365 where G is the growth rate in cm/yr, ALength is the difference between the recapture length and the ini- tial length, and Days is the number of days out. The von Bertalanffy growth interval equation was fitted to the recapture data with a nonlinear least-squares regression procedure (SAS, 1988). The von Bertalanffy growth interval equation (Fabens, 1965) for recapture is as follows: CL2=a-(a-CL1)ekt, where CL2 is the carapace length at recapture, a is the asymptotic length, CL1 is the length at first cap- ture, K is the intrinsic growth rate, and t is the time in years between captures. Results Trawling effort Monthly trawling effort varied from year to year ( 1989-91 ); however, monthly totals for all three years indicate that the majority of effort occurred from May to December (Table 1). This corresponds to the sum- mer-fall fisheries for brown and white shrimp, the target species during this study. Monthly turtle cap- ture rates were also variable, probably as a result of the combined seasonal fluctuations in trawling ef- fort and turtle abundance. A structured sampling scheme with equal monthly effort would be required to make accurate calculations of monthly changes in turtle abundance. Loggerhead turtle catch per unit of effort (CPUE) ranged from 0.02 turtles/net hour in October 1989 to 1.09 turtles/net hour in August of 1991. Maximum CPUE of 0.25 turtles/net hour was obtained for Kemp's ridley turtles in May 1990 and 0.05 turtles/net hour was obtained for green turtles in January 1989 (Table 1). Species composition A total of 774 (83%) loggerhead, 113 (12%) Kemp's ridley, and 41 (4%) green turtles were captured, tagged, and released during the course of the study. A leatherback turtle, Dermochelys coriacea, was also 142 Fishery Bulletin 93(1), 1995 captured and tagged. Sixty tagged turtles (42 log- gerhead, 15 Kemp's ridley, and 3 green) were recap- tured by the contract vessel. Additionally, 31 recaptures and recoveries (26 loggerhead, 4 Kemp's ridley, and 1 green turtle) were reported by other investigators. Loggerhead turtle, Caretta caretta — Seven hundred and seventy-four loggerhead turtle captures were Table 1 Monthly trawling effort (net hours) and turtle capture rates (turtles/ net hour) for 1989-91. Cc -Caretta caretta, Lk=Lepidochelys kempi, and Cm=Chelonia mydas. Species Year and Effort Total month (net hours) turtles/hr Cc/hr Lk/hr Cm/hr 1989 Jan 77.0878 0.3113 0.2465 0.0130 0.0519 Feb 13.1918 0.2274 0.0758 0.1516 0.0000 Mar 25.9838 0.3079 0.2694 0.0385 0.0000 Apr 41.1742 0.2672 0.1700 0.0971 0.0000 May 103.9350 0.0770 0.0673 0.0096 0.0000 June 123.1230 0.1462 0.0568 0.0650 0.0244 July 70.7558 0.1555 0.1555 0.0000 0.0000 Aug 72.7545 0.1924 0.1787 0.0137 0.0000 Sept 19.9875 0.1001 0.1001 0.0000 0.0000 Oct 49.5690 0.0202 0.0202 0.0000 0.0000 Nov 139.1130 0.1006 0.0719 0.0216 0.0072 Dec 56.3648 0.1242 0.1064 0.0177 0.0000 1990 Jan 27.1830 0.1104 0.1104 0.0000 0.0000 Feb 57.5640 0.2258 0.1737 0.0521 0.0000 Mar 18.3885 0.4894 0.4350 0.0544 0.0000 Apr 23.1855 0.4313 0.3450 0.0863 0.0000 May 15.9900 0.7505 0.5003 0.2502 0.0000 June 31.5802 0.1583 0.1583 0.0000 0.0000 July 147.1080 0.1971 0.1971 0.0000 0.0000 Aug 117.5265 0.0851 0.0851 0.0000 0.0000 Sept — — — — — Oct — — — — — Nov 148.3072 0.1483 0.1079 0.0067 0.0337 Dec 127.5202 0.2666 0.2196 0.0235 0.0235 1991 Jan 28.7820 0.8686 0.7991 0.0695 0.0000 Feb 23.1855 0.2588 0.2588 0.0000 0.0000 Mar 35.9775 0.1946 0.1668 0.0278 0.0000 Apr 21.5865 0.2780 0.2780 0.0000 0.0000 May 92.7420 0.2588 0.2588 0.0000 0.0000 June 33.5790 0.4467 0.4467 0.0000 0.0000 July 35.7776 0.6988 0.6988 0.0000 0.0000 Aug 21.9862 1.0916 1.0916 0.0000 0.0000 Sept — — — — — Oct 43.3089 0.2309 0.2078 0.0231 0.0000 Nov 77.5515 0.0903 0.0903 0.0000 0.0000 Dec 106.7332 0.1031 0.1031 0.0000 0.0000 Total 2,028.60 recorded off the east coast of Florida. Loggerhead turtles captured in Florida ranged from 38.2 to 110.0 cm SSCL (Fig. 2). Eighty percent (n=616) of the log- gerhead turtles captured were subadults and 20% (n-153) were adults. Loggerhead turtles were present year-round in the Cape Canaveral area (Table 2). Total monthly captures were highest during Novem- ber, December, and January; however, yearly cap- tures for these months varied substan- tially. Subadult loggerhead turtles were most abundant during all months, except June, and showed a decrease from April to July as adult abundance increases, probably in response to the nesting sea- son (Fig. 3). Peaks in the relative compo- sition of the adult size class during April and June correspond to the peak densities reported by Henwood (1987a) for males and females, respectively. Sixty-eight tagged loggerhead turtles have been recaptured or recovered since the implementation of this study. Fifty-two (76%) of these turtles were initially tagged by the contract vessel. The remaining six- teen (24%) loggerhead turtle recaptures were tagged by other investigators in Florida and Georgia. 1.2,3,4,5,6,7 Methods of capture included shrimp trawl (69%), beach stranding (22%), pound net (3%), power plant intake canal (3%), nesting fe- male (1%), and SCUBA sighting ( 1%). The amount of time between tagging and re- capture ranged from 1 to 2,499 days. How- ever, 70% (n=45) were recaptured within a year of initial capture. Twenty-six loggerhead turtles (23 sub- adults and 3 adults) initially captured 1 Bolten, A. University of Florida, Archie Carr Cen- ter for Sea Turtle Research, Gainesville, FL, 32611. Personal commun., 1992. 2 Foster, K. National Marine Fisheries Service, Mi- ami Laboratory, 75 Virginia Beach Drive, Miami, FL, 33149. Personal commun., 1994. 3 Guseman, J. University of Central Florida, Depart- ment of Biology, Orlando, FL, 32816. Personal commun., 1992. 4 Henwood, T. National Marine Fisheries Service, Southeast Regional Office, 9450 Koger Boulevard, St. Petersburg, FL, 33702. Personal commun., 1991. 6 Martin, E. Applied Biology, Inc., P.O. Box 974, Jensen Beach, FL, 34958. Personal commun., 1991. 6 Stuntz, W. National Marine Fisheries Service, Pascagoula Laboratory, P.O. Drawer 1207, Pascagoula, MS, 39567. Personal commun., 1991. 7 Teas, W. National Marine Fisheries Service, Mi- ami Laboratory, 75 Virginia Beach Drive, Miami, FL, 33149. Personal commun., 1991. Schmid: Marine turtle populations of the east-central coast of Florida 143 (A 120 110 - 100 90 5 80 H O 70 a 9 60 H 50 40 - 30 20 10 - x = 67.7 cm n = 769 pi . r_.ri-^-.. . 40 50 60 70 Carapace Length (cm) Figure 2 Length frequencies of loggerhead turtles, Caretta caretta, collected along the Atlantic coast of Florida from 1986 to 1991. Table 2 Monthly and yearly trawl captures of loggerhead turtles Caretta caretta. in the r earshore waters of Florida. Dashes indicate trawling effort outside of the study area. Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Total 1986 1 5/— — /5 37 31 44 123 1987 90 47 31 12 5 11/ /3 2 0 201 1988 1 0 16 1 2 0 4 3 2 6 8 15 58 1989 19 1 7 7 7 7 11 13 2 1 10 6 91 1990 3 10 8 8 8 5 29 10 10 10 16 28 145 1991 23 6 6 6 24 15 25 24 — 9 7 11 156 Total 136 64 68 34 47 43/— 69/— 50/- 19/— 66/— 74 104 774 within the Cape Canaveral study area were subse- quently recaptured within this area. Of this total, eleven turtles (9 subadults and 2 adults) were cap- tured and recaptured in the Port Canaveral ship channel. Eight loggerhead turtles captured in the Cape Canaveral area during the winter were recap- tured or recovered in Georgia, North Carolina, and Virginia during the summer and fall (Fig. 4). All these turtles were subadults ranging from 51 to 61 cm cara- pace length. Three tagged loggerhead turtles (two sub- adults and a nesting female) were reported south of Cape Canaveral by fishery-independent sources. There was a stronger correlation between carapace width and carapace length for subadult loggerhead turtles (r=0.9612; n=508) than for adults (r=0.7724; 7i=151). Regression equations were computed for the relationship of carapace width (CW) to length (SSCL) for subadults: CW = 9.0289 + 0.6848 (SSCL); and adults CW = 22.9153 + 0.5052 (SSCL). Fifty-one yearly growth rates were calculated for forty-nine loggerhead turtles. Extrapolating annual growth rates from these data is difficult owing to the 144 Fishery Bulletin 93(1), 1995 90 - 60 - ~ 70 Relative Composition o o o o 1 1 1 1 \i s / ^ Subadult A /\ + Adult 20 - A ^ A 10 - II 1 1 1 1 1 1 1 1 1 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Month Figure 3 Relative composition of subadult and adult loggerhead turtles collected along the Atlantic coast of Florida from 1987 to 1991. small sample sizes, measurement errors, and short- term recaptures. A number of treatments were ap- plied to the growth data in an attempt to control for measurement error. However, no single approach was able to account for all the error. Consequently, growth rates were calculated for 1) all data combined, 2) those tag and recapture data recorded by the con- tracted personnel, and 3) those data with recapture intervals greater than 90 days. A mean growth rate of 5.56 ± 23.91 cm/yr (range: -11.49 to 167.17 cm/yr) was calculated for all loggerhead turtle recaptures. Analysis of the loggerhead turtles tagged and recap- tured by the contract personnel indicated a mean growth rate of 1.00 ± 1.23 cm/yr (range: 0.00 to 4.01 cm/yr). Additionally, a mean growth rate of 2.98 ± 7.12 cm/yr (range: -5.96 to 38.44 cm/yr) was calcu- lated for all loggerhead turtle recaptures greater than 90 days at large, 1.84 ± 1.76 cm/yr (range: -0.23 to 8.08 cm/yr) for all recaptures greater than 180 days at large, and 1.77 ± 1.88 cm/yr (range: -0.23 to 8.08 cm/ yr) for all recaptures greater than 360 days at large. The von Bertalanffy growth interval equation was fitted to each of these data treatments. Estimates of asymptotic length (a) for loggerhead turtles ranged from 96.08 cm to 112.52 cm and estimates of intrin- sic growth rate (K) ranged from 0.0365 to 0.0588 (Table 3). The growth model for captures and recap- tures by the contract vessel had the lowest residual mean square, a criterion commonly used to select the best fit growth model (Dunham, 1978). The estimated parameters for this data treatment (a = 112.52 cm; #=0.0365) are similar to Henwood's (1987b) esti- mated parameters for nonlinear regression of the von Bertalanffy equation (a=110.002 cm; #=0.0313). Kemp's ridley turtle, Lepidochelys kempi— One hun- dred and thirteen Kemp's ridley turtle captures were recorded on the Atlantic coast of Florida. Kemp's rid- ley turtles ranged in size from 21.5 to 60.3 cm SSCL (Fig. 5). Sixty-five percent (n=70) of these turtles were early to mid-subadults (20-40 cm). With the excep- tion of a single adult turtle, the Kemp's ridley turtles caught on the east coast were classified as imma- ture. Kemp's ridley turtles were captured year-round in the Cape Canaveral area (Table 4). Their pres- ence in the Cape Canaveral area appeared to be sea- sonal; 61% (n=69) of the turtles were captured dur- ing the winter months of December to March. How- ever, a relatively large number of Kemp's ridley turtles captured in January and February of 1987 and in March of 1988 contributed significantly to this trend. Captures of Kemp's ridley turtles during the following years did not exhibit a pronounced seasonal pattern. Nineteen tagged Kemp's ridley turtles were recap- tured or recovered. Eighty-nine percent (n=17) of the turtles were recaptured by shrimp trawls, and 11% (n=2) were recovered from beach strandings. With the exception of a single turtle captured in the area Schmid: Marine turtle populations of the east-central coast of Florida 145 A TLANTIC OCEAN Figure 4 Long-distance recaptures and recoveries of tagged loggerhead turtles. Note: Arrows are not intended to indicate routes traveled by tagged turtles; they are a visual aid to differentiate tagging and recap- ture sites. 0=tagging location; X=recapture location. of initial tagging after 615 days at large, all Kemp's ridley turtles were recaptured within a year. Twelve (63%) Kemp's ridley turtles were initially captured in the Cape Canaveral area and subsequently recaptured within this area. Of this total, four turtles were captured and recaptured in the Port Canaveral ship channel. Two Kemp's ridley turtles had multiple recaptures within the Cape Canaveral area, one tagged in November 1986 was caught once in December 1986 and again in May 1987. Another turtle tagged in May 1990 was recaptured twice that September. Six Kemp's ridley turtles exhibited long-distance movements to and from the Cape Canaveral area (Fig. 6). Two of the recaptures were NMFS Galveston Laboratory headstart turtles released offshore of Padre Island, Texas, in May and captured on the Atlantic coast of Florida in February and March, 0.73 and 1.88 years after release.8 Two Kemp's ridley 8 Caillouet, C, Jr. National Marine Fisheries Service, Galveston Laboratory, 4700 Avenue U, Galveston, TX, 77551. Personal commun., 1991. turtles displayed seasonal movements northward. The turtles were originally tagged in the Cape Canaveral area in December and February and sub- sequently recovered in Georgia and South Carolina in July. Another Kemp's ridley turtle exhibited a southerly migration along the Atlantic coast, from Virginia Beach to Port Canaveral.9 There was a strong correlation between carapace width and carapace length (r=0.9953; n = 105) for Kemp's ridley turtles. Regression of carapace width on length resulted in the equation CW = -2.7157 + 1.0288 (SSCL). A straight-line equation was applied to the length- weight data; however, graphical analysis of the re- siduals indicated a curvilinear relationship between the two variables. Power regression was performed through the log-log transformation of weight and length measurements. A strong correlation (r=0.9756; n=88) was calculated for the transformed weight ( WT) to length relationship, regression of these vari- ables resulted in the equation log WT = -8.2837 + 2.8444 (log SSCL). Twelve yearly growth rates were computed for ten Kemp's ridley turtles. A mean growth rate of 8.28 ± 9.81 cm/yr (range: 0.00 to 29.16 cm/yr) was calcu- lated for all Kemp's ridley turtle recaptures. Analy- sis of the Kemp's ridley turtles tagged and recap- tured by the contract personnel indicated a mean growth rate of 6.92 ± 9.36 cm/yr (range: 0.00 to 29.16 cm/yr). A mean growth rate of 8.79 ± 10.32 cm/yr (range: 0.00 to 29.16 cm/yr) was calculated for re- captures greater than 90 days at large and 5.94 ± 1.80 cm/yr (range: 4.26 to 7.84 cm/yr) for recaptures greater than 180 days at large. The von Bertalanffy growth interval equation was fitted to each of these data treatments. Estimates of asymptotic length ranged from 60.66 cm to 77.85 cm and estimates of intrinsic growth rate ranged from 0.0577 to 0.6037 (Table 5). Asymptotic lengths were probably underestimated because of the lack of adult- sized Kemp's ridley turtles in the database. Green turtle, Chelonia mydas — Forty-one green turtles, ranging in size from 24.0 to 55.4 cm SSCL (Fig. 7), were taken from Florida waters. Eighty-one per- cent (n=33) of the green turtles captured off the east coast of Florida were early subadults less than 40 cm SSCL. No adult green turtles were encountered. 9 Keinath, J. Virginia Institute of Marine Science, College of Wil- liam and Mary, Gloucester Point, VA, 23062. Personal commun., 1993. 146 Fishery Bulletin 93(1), 1995 The presence of subadult green turtles in the Cape Canaveral area appeared highly seasonal (Table 6); 73% (ra=30) were captured from November to Janu- ary. As with other turtle species, this pattern resulted from a high number of captures in 1987 and a high monthly variation during other years. Four tagged green turtles were recap- tured during this study. Three turtles were originally tagged by contract per- sonnel in the Cape Canaveral area. The tag codes for the fourth green turtle matched a set of NMFS tags that had been distributed to Fort Lauderdale, Florida. Of the three green turtles tagged at Cape Canaveral, one was ini- tially tagged in January 1987 and then recaptured in April, approximately 68 km to the north. Another green turtle that was initially tagged in the Cape Canaveral area in January 1990 was re- captured in this area the following Oc- tober. A third green turtle was captured off Port Canaveral in September 1990 and found stranded approximately 41 km to the north the following month. There was a strong correlation (r=0.9590; n=39) between carapace width and carapace length for 24 - 22 - 20 - 18 - x = 37,0 cm of Turtles I I ji Number O ro I I 8 6 4 — X ' ! ' . : 2 — 0 — III" II 1 ■'-:'j, '■'■'■'■ ^m , . 55 60 65 70 Carapace Length (cm) Figure 5 Length frequencies of Kemp's ridley turtles, Lepidochelys kempi, collected along the Atlantic coast of Florida from 1986 to 1991. green turtles. Regression of carapace width on cara- pace length resulted in the equation CW = 4.1763 + 0.6847 (SSCL). Table 3 Estimated values of asymptotic length (a ) and intrinsic growth rate ik ) from nonlinear regression of von Bertalanffy growth interval equation for logger- head turtles (one asymptotic standard error in parentheses). Data treatment n a k All recaptures Capture/recapture by contract vessel All recaptures >90 days All recaptures >180 days All recaptures >365 days 51 96.08 cm 0.0586 (7.07) (0.0149) Residual mean square error = 9.1054 17 112.52 cm 0.0365 (24.74) (0.0204) Residual mean square error = 0.4088 33 96.09 cm 0.0588 (8.72) (0.0185) Residual mean square error = 13.8969 24 96.40 cm 0.0569 (7.97) (0.0162) Residual mean square error = 10.8231 19 96.10 cm 0.0573 (8.82) (0.0183) Residual mean square error = 13.5947 Residual analysis of the length- weight relationship indicated the need for curvilinear terms in the re- gression model. A strong correlation (r=0.9587; n=37) was calculated for the log-transformed weight to length relationship, and regression of these variables resulted in the equation log WT = 8.8784 + 2.9815 (log SSCL). There were no growth data available for green turtles owing to the rela- tively low number of recaptures and the lack of data for the recoveries. Discussion The data for this project were col- lected incidentally through the com- mercial shrimp fishery of east-central Florida. Bias in trawling effort oc- Schmid. Marine turtle populations of the east-central coast of Florida 147 Table 4 Monthly and yearly trawl captures of Kemp's ridley turtles, Lepidochelys kempi, in the nearshore waters of Florida. Dashes indicate trawling effort outside of the study area. Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Total 1986 1' 1 0/— — /0 1 1 4 8 1987 13 10 4 1 0 1/— — — — —11 1 2 33 1988 1 0 17' 0 0 0 2 1 1 1 2 2 27 1989 1 2 1 4 1 8 0 1 0 0 3 1 22 1990 0 3 1 2 4 0 0 0 4 1 1 3 19 1991 2 0 1 0 0 0 0 0 — 1 0 0 4 Total 17 16 24 7 6 9/— 21— 21— 5/— 5/— 8 12 113 1 Recapture of a NMFS Galveston Laboratory Headstart Kemp's ridley turtle. MEXICO Figure 6 Long-distance recaptures and recoveries of tagged Kemp's ridley turtles Note: Arrows are not intended to indicate routes traveled by tagged turtles; they are a visual aid to differentiate tagging and recapture sites. 0=tagging location; X=recapture location. curred because amount of effort and location of trawl- ing were a function of shrimp abundance. These fac- tors certainly contributed to the annual, and possi- bly seasonal, variation in turtle captures observed in this study. Restrictions imposed on the shrimping industry during the course of the study also affected data collection. There was a marked reduction in the number of loggerhead captures following NMFS regu- lations issued in June 1987, requiring the use of TED's in the Cape Canaveral area (Federal Regis- ter, 1987). Despite the bias and inconsistencies of data collection, the use of trawl gear allowed access to marine turtle developmental stages not encoun- tered in nesting beach surveys and inshore netting studies. Furthermore, the Cape Canaveral area has a history of trawl studies for general comparison. 148 Fishery Bulletin 93(1). 1995 £12 O 10 - CD M X = 36 0 cm n = 41 M^ 0 10 20 30 40 50 60 70 80 90 100 110 120 Carapace Length (cm) Figure 7 Length frequencies of green turtles, Chelonia mydas, collected along the Atlantic coast of Florida from 1986 to 1991. Trawl surveys conducted by NMFS and the U.S. Army Corps of Engineers from 1974 to 1984 estab- lished that marine turtles, especially loggerhead turtles, aggregate in the Port Canaveral ship chan- nel. Henwood (1987a) reported a loggerhead CPUE of 2.00 to 4.86 turtles/hour from July to October 1980, Table 5 Estimated values of asymptotic length (a ) and intrinsic growth rate (K) from nonlinear regression of von Bertalanffy growth interval equation for Kemp's ridley turtles (one asymptotic standard error in parentheses). Data treatment n a K All recaptures 12 61.11cm 0.0577 (5.43) (0.2176) Residual mean square error = 3.4359 Capture and recapture by 10 60.81 cm 0.5943 contract vessel (5.76) (0.2439) Residual mean square error = 4.1701 All recaptures >90 days 6 60.66 cm 0.6037 (8.04) (0.3549) Residual mean square error = 8.2325 All recaptures >180 days 3 77.85 cm 0.2466 (21.09) (0.1770) Residual mean square error = 1.1478 increasing to 12.05 turtles/hour in November. But- ler et al. (1987) noted that mean CPUE by month was greater than 10 loggerhead turtles/hour from November 1981 to March 1982 and that there were lower CPUE values from April to September 1982. The CPUE values cited from the previous studies are greater than those in the present analysis, which may be attributable to the different objectives of the present study and the former trawl surveys. The CPUE data presented by Henwood (1987a) were collected during trawl surveys designed to re- duce turtle mortality from mainte- nance dredging in the Port Canaveral ship channel. Butler et al. ( 1987) con- ducted surveys of the channel to de- velop methods of estimating logger- head abundance. Marine turtles were the target species in both of these studies. The CPUE values reported in this study should be viewed as rep- resentative of turtles taken in the commercial shrimp fishery of east- central Florida. The data on loggerhead turtles col- lected in the present analysis are similar to the earlier investigations of Henwood ( 1987a). Most of the log- Schmid Marine turtle populations of the east-central coast of Florida 149 Table 6 Monthly and yearly trawl capt jresc f green turtles, Chelonia mydas, in the nearshore waters of Florida. Dashes indicate trawling effort outside of the study arej L. Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Total 1986 1 0/— — — — /O 0 0 2 3 1987 7 1 0 1 0 0/— — /0 0 6 15 1988 0 0 0 0 0 0 0 0 1 0 0 2 3 1989 4 0 0 0 0 3 0 0 0 0 1 0 8 1990 0 0 0 0 0 0 0 0 1 3 5 3 12 1991 0 0 0 0 0 0 0 0 — 0 0 0 0 Total 11 1 0 1 1 3/— 0/— 0/— 2/— 3/— 6 13 41 gerhead turtles captured on the east-central coast of Florida were mid-subadults (50-70 cm), typical of immature loggerhead turtles in the western Atlan- tic Ocean. There was a shift to a larger size class during the spring and summer, a period when repro- ductively active adults immigrate to the nesting beaches of southeast Florida (Henwood, 1987a). At that time, some immature loggerhead turtles emi- grated to foraging grounds as far north as Chesa- peake Bay. Captures of adult loggerhead turtles in the coastal waters of Florida declined by late sum- mer with the end of the nesting season. Conversely, the presence of subadult loggerhead turtles increased with the onset of winter. Kemp's ridley turtles in the northwestern Atlan- tic are transported from their natal beaches in Mexico by major oceanic currents in the Gulf of Mexico (Col- lard and Ogren, 1990). The smallest Kemp's ridley turtles captured on the east coast of Florida coincide with the minimum size class for postpelagic turtles in the Gulf of Mexico (Ogren, 1989). Skeleto- chronological age estimates indicate that these turtles may be two years old (Zug and Kalb, 1989), which may indicate the length of this species' pelagic developmental stage. Recapture data from the present analysis and that of Henwood and Ogren ( 1987) suggest that Kemp's ridley turtles on the Atlan- tic coast overwinter in the Cape Canaveral area and migrate to northern foraging grounds during the sum- mer. The lack of significant numbers of adult turtles in the northwestern Atlantic suggests that Kemp's ridley turtles migrate from the U.S. east coast upon reaching sexual maturity. Recently, a Kemp's ridley turtle cap- tured and tagged on the southeast coast of Florida was observed nesting in the western Gulf of Mexico.10 Relatively low numbers of green turtles have been captured in the Cape Canaveral area. This observa- 10 Martin, E. Applied Biology, Inc., P.O. Box 974, Jensen Beach, FL, 34958. Personal commun., 1994. tion may be the result of this species preference for a habitat other than the Port Canaveral ship channel and adjacent areas of shrimp trawling. Capture data from fishery-independent studies indicate that early subadult (20-40 cm) green turtles inhabit the nearshore reef tracts off the southeast coast of Florida (Ernest et al., 1989; Wershoven and Wershoven, 1989, 1992; Guseman and Ehrhart, 1990). A slightly larger size class of green turtle was captured on the seagrass shoals of the Indian River Lagoon system (Mendonca and Ehrhart, 1982). Seventy-eight percent of the 108 green turtles captured in Mosquito Lagoon were greater than 40-cm carapace length. Furthermore, green turtles captured in the Indian River Lagoon, south of Sebastian Inlet, were significantly larger than those collected on the reefs offshore of Vero Beach (Guseman and Ehrhart, 1990). There are a number of problems with the growth data presented in this paper. Extrapolating yearly growth rates from short-term recaptures amplifies measurement error. Extremely large and negative growth values were usually the result of short inter- vals between capture and recapture. Differences in the measuring techniques used by other investiga- tors was a major source of error when computing growth rates. Length measurements are often re- ported as "straight-line carapace length" when, in fact, there are four possible straight-line carapace lengths: total, standard, notched, and minimum (Pritchard et al., 1983). Standardized methods of measurement, or a definition of the measurement technique and accurate conversions between the vari- ous techniques, are necessary for comparisons be- tween studies (Bjorndal and Bolten, 1988). The growth models presented in this analysis should be interpreted cautiously given the forementioned prob- lems with the database. In conclusion, the results of this study are indica- tive of the importance of east-central Florida as a developmental habitat for three species of marine 150 Fishery Bulletin 93( 1995 turtle. The Cape Canaveral aggregation of logger- head turtles is composed of significant numbers of subadults. Furthermore, the east coast of Florida supports the second largest rookery for this species (Ross, 1982). Subadult Kemp's ridley and green turtles appear to overwinter in the Cape Canaveral area. The eastern seaboard of North America serves as a vital link between the pelagic stage of marine turtle development and recruitment to the coastal- benthic foraging stages. Continued research in coastal waters is essential to the conservation of these threatened and endangered species. Acknowledgments This project was initiated and managed in part by Larry Ogren. I am indebted to Captain Eddie Chadwick and the crew of the FV Mickey Anne for their diligence in the collection of data. Thanks are also due to Wayne Witzell and Nancy Thompson for constructive comments during manuscript prepara- tion; Wendy Teas and Kellie Foster for stranding and tagging reports; Alan Bolten, Charles Caillouet, Jamie Guseman, Tyrrell Henwood, John Keinath, Erik Martin, and Warren Stuntz for recapture infor- mation; Karen Bjorndal for assistance with growth equations and data treatments; and Lisa Gregory for assistance with the Macintosh graphics program SuperPaint. Literature cited Bjorndal, K. A., and A. B. Bolten. 1988. Growth rates of immature green turtles, Chelonia mydas, on feeding grounds in the southern Bahamas. Copeia 1988:555-564. Butler, R. W., W. A. Nelson, and T. A. Henwood. 1987. A trawl survey method for estimating loggerhead turtle, Caretta caretta, abundance in five eastern Florida channels and inlets. Fish. Bull. 85:447^153. Carr, A. 1980. Some problems of sea turtle ecology. Am. Zool. 20:489-498. 1986. New perspectives on the pelagic stage of sea turtle development. 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Population dynamics of sea turtles utilizing shallow coastal waters off Hutchinson Island, Florida. In S. A. Eckert, K. L. Eckert, and T. H. Richardson (compilers), Proceedings of the ninth annual workshop on sea turtle biology and conservation. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SEFC-232:57-59. Fabens, A. J. 1965. Properties and fitting of the von Bertalanffy growth curve. Growth 29:265-289. Federal Register. 1987. 52(1241:24244-24262. Guseman, J. L., and L. M. Ehrhart. 1990. Green turtles on Sabellariid worm reefs: initial re- sults from studies on the Florida Atlantic coast. In T. I. Richardson, J. I. Richardson, and M. Donnelly (compilers), Proceedings of the tenth annual workshop on sea turtle biology and conservation. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SEFC-278:125-127. Hendrickson, J. R. 1980. The ecological strategies of sea turtles. Am. Zool. 20:597-608. Henwood, T. A. 1987a. 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Growth rates of captive dolphin, Coryphaena hippurus, in Hawaii Daniel D. Benetti Rosenstiel School of Marine and Atmospheric Science Division of Marine Biology and Fisheries, University of Miami 4600 Rickenbacker Causeway. Miami, Florida 33149 The Oceanic Institute, Makapuu Point PO. Box 25280, Honolulu, Hawaii 96825 Edwin S. Iversen Rosenstiel School of Marine and Atmospheric Science Division of Marine Biology and Fisheries, University of Miami 4600 Rickenbacker Causeway, Miami, Florida 33 1 49 Anthony C. Ostrowski The Oceanic Institute, Makapuu Point PO. Box 25280, Honolulu, Hawaii 96825 Dolphin, Coryphaena hippurus, also known as mahimahi or dolphin fish, are pelagic, predatory fish dis- tributed in tropical and subtropical regions throughout the world (Johnson, 1978; Palko et al., 1982). They are an important resource, supporting commercial and sport fisheries throughout their range (Oxenford and Hunte, 1986) as well as having considerable potential for aquaculture (Hagood et al., 1981; Szyper et al., 1984; Kraul, 1989, 1991). Gibbs and Collette (1959) and Palko et al. (1982) reviewed the dis- tribution and biology of dolphin, including age and growth data on wild and captive fish. Age and growth of wild (Oxenford and Hunte, 1983) and captive (Uchi- yama et al., 1986) fish have been estimated from daily increments on otoliths and scale annuli (Beards- ley, 1967; Rose and Hassler, 1968), from modal progression in length- frequency distribution (Wang, 1979), and from fish of known age reared in captivity (Hassler and Hogarth, 1977; Hagood et al., 1981; Szyper et al., 1984; Ostrowski et al., 1989, 1992; Iwai et al., 1992). There is considerable variability in the data, reflecting environmental and nutritional differences associated with experimental designs for cap- tive fish, as well as differences in size, age, and origin of wild fish. In this paper, growth rates of dolphin reared in Hawaii are presented and compared with those of captive and wild dolphin from different popu- lations, as well as other teleost spe- cies. The data presented suggest that there are differences in growth rates and morphology between cap- tive and wild dolphin. Materials and methods Fish were reared in captivity at The Oceanic Institute, Hawaii, from eggs obtained from wild Hawaiian broodstock fish (Fjj first genera- tion) maintained at Anuenue Fish- eries, State of Hawaii. Up to 3 months-of-age juveniles were fed a semi-moist (27.86% moisture) manufactured diet (pellet) twice daily (4% of their body weight per day). The diet contained 53.75% crude protein, 21% crude fat, and a caloric content of 5.13 calmg-1 (dry matter basis). Between 3 and 9.5 months, fish were fed to satiation once a day on a mixed diet of ex- truded salmon pellet (Moore-Clarke), frozen squid, and fish. The feed con- version ratio (FCR) is expressed as a ratio between the dry weight of the total amount of food given and the weight gain of live fish. Up to 3 months-of-age juvenile fish were reared in an outdoor cir- cular tank of 18,800 L (4 m diam- eter x 1.5 m water column height). After 3 months, fish were trans- ferred to a 28,000-L tank (6 m di- ameter x 1 m water column height) used for broodstock maintenance. Both tanks had running ambient seawater (25-27°C and 33-35 ppt salinity) at high flow rates (water turnover rate was at 10 tank vol- umes per day) and under constant aeration. The initial population was 48 fish, stocked at approximately 3 fish per m3. Growth data presented correspond to pooled male and fe- male fish periodically sampled dur- ing the period studied (1-9.5 months). Data are of individually sampled fish and are not averages. Small fish (1—3 months) were sampled daily. Sampling frequency of intermediate (3-6 months) and large (6-9.5 months) fish was weekly and bimonthly, respectively, owing to difficulties in handling larger dol- phin and because there were fewer individuals available for sampling. Since dolphin metamorphosis oc- curs during the third week after hatching and one month-old fish are fully developed juveniles (Be- netti, 1992; Kim et al., 1993), all data corresponding to fish from 1 to 9.5 months-old were combined. Manuscript accepted 31 May 1994. Fishery Bulletin 93:152-157 (1995) 152 NOTE Benetti et al.: Growth rates of captive Coryphaena hippurus 153 Results are expressed as: Absolute growth Absolute growth rate Relative growth Relative growth rate Instantaneous growth rate Specific growth rate Length-weight relationship VGBM (length) VGBM (weight) AG = W2- Wj AGR = (W2-W1)/(t2-t1) RG = (W2-W1)/W1 RGR = (W2-Wi)/W1 (t2~t1) IGR = (In W2 - In Wx) / (t2- tj) SGR = (In W2 - In Wx) / {t2-t1)x 100 W = aLb L. = L (1 -Kit-t ;o>) W, = W (l-e-/f,(- § 40- n=103 / ■ Standard r\3 co 0 o 1 1 ss° 10- jfl n S° un i i i i i i . i i i i 0 60 120 180 240 300 3e >0 Age (days) Figure 1 Growth in length of captive dolphin, Coryphaena hippurus, in Hawaii. 154 Fishery Bulletin 93(1). 1995 with caution. The VBGM applied to length-at-age data for captive dolphin in Hawaii is L, = 169.6 cm [l^r0-72,(-°068)] (Fig. 4). The calculated VBGM for weight is Wt = 58.41 kg [l-e-° 72 ,M)068) ]307. The feed conversion ratio (FCR) of juveniles up to three months of age was 1.1 (dry feed/live fish), and averaged 1.6 for the entire period studied. Discussion There have been several reports of growth rates of wild and captive dolphin, as well as of wild caught fish kept in captivity for various periods of time. Beardsley (1971) reported that a wild caught juve- nile kept in captivity grew from one to 35 lb in one year. Schekter (1983) recorded a growth rate of 4.3 kg (from 0.7 to about 5 kg) in 30 days. In Barbados, dol- phin may reach lengths of over 80 cm in 5.5 months and over one meter in less than one year (Oxenford and Hunte, 1986). In Hawaii, they also attain a length of over one meter at the end of the first year (Uchiyama et al., 1986). By applying the length-weight regression of Rose and Hassler (1968) to these data, it would cor- respond to a mass of about 8 kg in one year. The growth rates presented in this study (4.93 kg and 75.8 cm in 9.5 months) are lower than many of those reported for wild and cultured dolphin in the literature. This may be due to the diet fed to the ex- perimental fish. For instance, Kraul (1989) reported growth rates of 2 kg in 6 months and 9 kg in one year for dolphin that were fed fish and squid in tanks in Hawaii, and of 5.4 kg in 8.7 months for fish reared under identical circumstances but fed commercially available pellets (Kraul and Ako, 1993). The data suggest that captive dolphin grow slower than their wild counterparts. Yet, even when they are fed artificial diets, growth rates of captive dol- phin are among the fastest recorded for teleosts. The specific growth rate (SGR) of dolphin reported in this work (4.3%-10 body weightd-1), by Ostrowski et al. (1992) (10.7-13.3% bwd"1), and by Iwai et al. (1992) (9.3-13.0% bw-d-1) are much higher than those of other marine and brackish water fish raised in cap- tivity. For instance, SGR of the common snook, Centropomus undecimalis; barramundi, hates calcar- ifer; hybrid sea bass, Morone spp. ; Nassau grouper, Epinephelus striatus; spotted seatrout, Cynoscion nebulosus; red drum, Sciaenops ocellatus (Tucker, 1989); three species of mullets, Liza ramada (El- Sayed, 1991), Mugil liza, and M. curema (Benetti and Fagundes Netto, 1991); and the common grouper, E. guaza (Fagundes Netto and Benetti, 1984) range from 0.55 to 3.46% of their body weight per day. The absolute growth rate (AGR) in length of wild and captive dolphin vary between 0.1-0.58 cmd-1 6000 5000 40004 -§,3000 5 2000- 1000 Y = 0.087 X 2 • 10.93 X + 321 .62 r ' = 0.98 n = 141 -i — T^ — i 1 1 — ' 1 ' 1 <~ 0 60 120 180 240 300 360 Age (days) Figure 2 Growth in weight of captive dolphin, Coryphaena hippurus, in Hawaii. 5000- W = 0.00836 L 3 07 r2 = 0.98 4000- n= 103 Weight (g) ro co o o o o o o / 1000- J(' U | i | i | ' I ' 1 ' 1 ' 1 ' 1 ' 1 ' 0 10 20 30 40 50 60 70 80 90 Standard length (cm) Figure 3 Length-weight relationship of dolphin, Coryphaena hippurus, reared in captivity in Hawaii. NOTE Benetti et al.: Growth rates of captive Coryphaena hippurus 155 200 Loo 160 •0 72 (1 -0.06B) . 1 LI - 169.6 cm |1 - 8 ' ' ] - r2 = 0.98 __---- Standard length (cm) * CD l\3 ) O O O S / / / / U 0 12 3 4 Age (years) Figure 4 The von Bertalanffy growth model applied to length-at- age data for 1-9.5 month-old captive dolphin, Coryphaena hippurus, in Hawaii. for the first year of life (Oxenford and Hunte, 1983). The AGR value reported in this study (0.227 cmd-1) is well within this range and the 0. 1-0.6 cmd-1 range reported by Brothers et al. (1983) for the Atlantic bluefin tuna, Thunnus thynnus, another pelagic te- leost. Only a few other pelagic teleosts exhibit growth rates comparable to or higher than dolphin. These include the Atlantic blue marlin, Makaira nigricans, and the Atlantic sailfish, Istiophorus platypterus, two of the largest North Atlantic pelagic teleosts. Prince et al. (1991) estimated the AGR of young Atlantic blue marlin from otolith microstructure as 1.66 cmd-1, a value nearly three times higher than that reported for dolphin. From length frequencies of Atlantic sail- fish, de Sylva (1957) estimated a maximum absolute growth rate of 1.10 cmd-1, twice as fast as that re- ported for dolphin. Although the scope of these com- parisons is limited owing to the different age classes of fish, both the blue marlin and Atlantic sailfish exhibit AGR's several times higher than those mea- sured in this work. In this study, the feed conversion ratio (FCR) was 1.6 (dry feed/live fish). Similarly, Kraul and Ako (1993) obtained a FCR of 1.6 with dolphin fed on a commercially available pellet. FCR's of about 1.0 have been reported for dolphin by Ostrowski et al. (1992), Kraul (1989), and Kraul and Ako (1993), indicating that they are efficient in converting the energy in- take from feeds into growth. Relative to other spe- cies, dolphin do not appear to require extraordinary food intake to sustain their high growth rates, simi- lar to blue marlin (Prince et al., 1991). In this study, cultured dolphin were fed 4% (dry feed) of their body weight per day. This feeding rate is commonly used for other fish species in captivity, which invariably ex- hibit slower growth rates and higher FCR. Dolphin appear to exhibit higher energetic efficiency than most other teleosts because they use a proportionally larger portion of the total gross energy ingested for growth and metabolism than for excretion (Benetti, 1992). Although no spawning was observed, the slight trend of decelerated growth after 180 days (Fig. 1) could be due to the onset of maturation, which in captive dolphin generally occurs in 6 months at 50— 55 cm and 2.0-2.5 kg (Kraul, 1991; Ostrowski et al., 1992), but has been observed to occur as early as 3- 4.5 months (Uchiyama et al., 1986). Somatic growth rates in teleosts usually decrease after the onset of maturation (Jones, 1976). For dolphin, however, the linear equation fitted the data for the period studied with the highest coefficient of correlation (r2=0.98). A reason for this may have been the larger sample size during the juvenile stage, when young fish grow very fast. For instance, Hassler and Rainville (1975)1 found that the length-age relationship of larvae and early juvenile dolphin (13—83 days) was exponential. The VBGM's were used to model growth beyond the scope of the data and therefore must be consid- ered speculative. Although the data fitted both VBGM's (length and weight) with a high coefficient of determination (r2>0.98), the asymptotic sizes pre- dicted by the models can not be tested because it has not been possible to keep dolphin alive in captivity for longer than 18 months. In this respect, the age structure of the population should be considered. It is possible that the potential longevity of the Hawai- ian dolphin stock may not exceed this maximum age in captivity (about 18 months). For instance, the lon- gevity of dolphin from Florida was estimated to be 4 years, but only 2% of the population was found to be older than 2 years (Beardsley, 1967), and only 4% in North Carolina (Rose and Hassler, 1968). The maxi- mum life span of the Southern Caribbean dolphin stock does not appear to exceed 18 months, and few individuals of the North Caribbean stock live longer than 2 years (Oxenford and Hunte, 1986). The asymptotic length estimated by the VBGM (1,^=1.69 m) compares well with existing data for wild fish in the literature (Lm=1.89 and 1.53 m for males and females, respectively) (Beardsley, 1967). The es- timated asymptotic weight (^=58. 4 kg), however, is much higher than the maximum weight of 46 kg reported for this species (Florida Sportsman, 1979). 1 Hassler, N. W., and R. P. Rainville. 1975. Techniques for hatch- ing and rearing dolphin, Coryphaena hippurus, through larvae and juvenile stages. Sea Grant Publ. UNC-SG-75-31, 17 p. 156 Fishery Bulletin 93(1). 1995 This may be explained by the higher value of the exponent (6) of the length-weight relationship cal- culated for captive dolphin in this study (3.07) com- pared with wild fish from North Carolina and Florida, 2.58 < b < 2.75 (Rose and Hassler, 1968). Oxenford and Hunte (1986) reported b values of 2.94 for male and 2.84 for female dolphin from Barbados. These differences indicate that dolphin tend to have shorter, deeper bodies in captivity than in the wild. Blaxter (1988) found that fish reared in captivity tend to be shorter and fatter and have a higher condition fac- tor than fish from the wild, possibly because fish are likely to swim less when confined, diminishing the effect of exercise on growth (Jobling 1990; Christ- iansen and Jobling, 1990; Benetti, 1992; Christiansen et al., 1992; Boisclair and Tang, 1993). This is con- sistent with the predictions of the VBGM's in this study, which indicate that it would take longer for dolphin to reach asymptotic length and weight in captivity (6 years) than in their natural environment (4 years or less). Results presented in this study suggest that cap- tive dolphin grow slower and are less streamlined than in the wild. However, morphological and growth disparities of wild dolphin have been attributed to genetic (Oxenford and Hunte, 1986) and environmen- tal (Rose and Hassler, 1968) differences in unit stocks. The larval development of dolphin from the Gulf of Mexico and from the western Pacific Ocean is similar, but both differ from that off Japan (Ditty et al., 1994). Although Benetti (1992) reported no sig- nificant differences between growth rates and devel- opment of dolphin larvae in Hawaii from Fx and F7 generations inbred in captivity, nothing is known about differences in growth during the juvenile and adult stages among offspring from brood fish from other stocks. Acknowledgments We thank Peter Lutz (Florida Atlantic University), Larry Brand (RSMAS, University of Miami), Eirik O. Duerr (The Oceanic Institute), Eric Prince and Victor Restrepo (Southeast Fisheries Science Cen- ter, NMFS, Miami Laboratory), and Syd Kraul (Waikiki Aquarium) for reviewing an early manu- script. The authors also thank two anonymous re- viewers and the Scientific Editor, Ronald Hardy, for comments which greatly improved the original manu- script. We also thank Arietta Venizelos for editorial help, and Thomas Capo for use of laboratory facili- ties (Experimental Hatchery, University of Miami). This work was part of the senior author's Ph.D. dis- sertation, funded by the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq). Partial funding was also provided by U.S. Dept. of Agriculture, ARS, grant 59-91H2-9-218 to the Oce- anic Institute in Hawaii. Literature cited Beardsley, B. L. 1967. Age, growth and reproduction of the dolphin, Coryphaena hippurus, in the straits of Florida. Copeia 2:441-451 1971. Dolphin spectacular. Sea Front. 17:194-201 Benetti, D. D. 1992. Bioenergetics and growth of dolphin, Coryphaena hippurus. Ph.D. diss., Univ. Miami, 196 p. Benetti, D. D. , and E. B. Fagundes Netto. 1991. Preliminary results on growth of mullets (Mugil liza and M. curema) fed artificial diets. World Aquaculture 22 (4):55-57. Bertalanffy, L., von. 1962. 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Modification and comparison of two fluorometric techniques for determining nucleic acid contents of fish larvae Michael F. Canino Alaska Fisheries Science Center National Marine Fisheries Service, NOAA 7600 Sand Point Way NE. Seattle, Washington 981 1 5-0070 Elaine M. Caldarone Northeast Fisheries Science Center National Marine Fisheries Service, NOAA Narragansett, Rhode Island 02882-1 199 The ribonucleic acid (RNA) content and the ratio of RNA to deoxyribo- nucleic acid (DNA) have proven to be reliable indices of the nutritional condition of larval fish (Buckley, 1979, 1980, 1981, 1984; Wright and Martin, 1985; Buckley and Lough, 1987; Clemmesen 1987, 1988; Rob- inson and Ware, 1988; Canino et al., 1991; Richard et al., 1991; Canino, 1994). Cellular RNA content is cor- related with the rate of protein syn- thesis. DNA content, which re- mains relatively constant in so- matic tissues, may be used as an index of cell number (Bulow, 1987). The RNA/DNA ratio, therefore, re- flects the protein synthesizing ca- pability of larval fish and has been used for estimating recent in situ protein growth (see review by Bulow, 1987; Robinson and Ware, 1988; Hovenkamp, 1990; Hoven- kamp and Witte, 1991). Initial methods for determining RNA and DNA concentrations in tissue homogenates, based upon ultraviolet light absorption (Munro and Fleck, 1966; Buckley, 1979), were limited by sample size, requir- ing about 800 /ig dry weight of tis- sue for a single analysis. The re- quirement of pooled samples offish larvae precluded quantitation of variability among individuals. Re- cent development of highly sensi- tive fluorometric techniques for di- rect measurement of nucleic acid contents of marine phytoplankton (Berdalet and Dortch, 1991; Mordy and Carlson, 1991), bacteria (Mordy and Carlson, 1991), and individual fish larvae (Clemmesen, 1988, 1993; Caldarone and Buckley, 1991; Theilacker and Shen, 1993) now provides a greater choice of meth- ods. Several protocols are based upon the fluorescence of the dye ethidium bromide (EB), when bound to nucleic acids. Fluorescence of the nucleic acid-fluorochrome complex is measured before and after diges- tion of RNA by RNase (Karsten and Wollenberger, 1972, 1977; Robinson and Ware, 1988; Clemmesen, 1993), or after sequential additions of RNase and DNase (Bentle et al., 1981). Total fluorescence is then partitioned into DNA and RNA com- ponents and nucleic acid concentra- tions are calculated indirectly by dif- ference after enzymatic degradation. A two-dye fluorometric method for nucleic acid analysis of indi- vidual fish larvae (Clemmesen, 1988) utilized EB to measure total sample fluorescence and the DNA- specific dye, Hoechst dye H33258 (Hoechst), to measure DNA content directly. A recent modification of this method to a single-dye proce- dure yields higher DNA estimates and RNA estimates comparable to the previous two-dye method (Clemmesen, 1993). Both protocols require extraction and purification of crude homogenates before analy- sis. While substances that interfere with sample fluorescence may be reduced or eliminated, the washing and extraction steps of both meth- ods restrict the number of samples that can be processed in a day. Caldarone and Buckley ( 1991) de- veloped a two-dye method for deter- mining nucleic acid contents that was coupled with an automated flow- injection analysis (FLA) system in which EB is used to estimate total nucleic acid content and Hoechst is used to measure DNA. This method has the advantage of combining high sensitivity and sample throughput rate with a simple extraction proce- dure. Unfortunately, an FIA system may be too costly for many laborato- ries. In this paper, we present an adaptation of the FIA method for con- ventional static fluorometric analy- sis (CFA) and compare results using the two procedures. Methods Fish larvae and juveniles from labo- ratory culture and field samples from six species — Atlantic cod, Gadus morhua; inland silverside, Menidia beryllina; haddock, Melanogrammus aeglefinus; tautog, Tautoga onitis; winter flounder, Pleuronectes americanus; and walleye pollock, Theragra chalcogramma — were chosen to provide different species, ages, and nutritional histories for comparison (Table 1). Fish homo- genates, except those of walleye pollock, were prepared by homog- enizing between 1 and 12 previ- ously frozen individuals with deion- Manuscript accepted 23 May 1994. Fishery Bulletin 93;158-165 (1995). 158 NOTE Canino and Caldarone: Fluorometric techniques for determining nucleic acid contents of fish larvae 159 Table 1 Fish species, sample abbreviations, and sources homogenate at each age. (S) = starved. used for methods comparison. Fish sampled at discrete ages provided one Species Sample name Source Age (d) n Atlantic cod Gadus morhua C C(S) lab lab(S) 41-61 41-61 3 3 Inland silverside Menidia beryllina s S(S) lab lab(S) 104-108 104-108 3 3 Haddock Melanogrammus aeglefinus H lab 11,22,44 3 Tautog Tautoga onitis T lab 20 3 Winter flounder Pleuronectes americanus F lab 26,41,57 3 Walleye pollock Theragra chalcogramma P field <60 3 ized, distilled water in an Ultra-Turrax homogenizer (Tekmar Co.) with three 15-second pulses at maximum power (Caldarone and Buckley, 1991). Previously fro- zen walleye pollock larvae were homogenized in prechilled glass homogenizers. Six aliquots of homo- genate were pipetted into 1.5-mL polyethylene vials and immediately frozen at -80°C until analysis of three aliquots by FIA and three aliquots by CFA. Sample extraction procedures followed those out- lined by Caldarone and Buckley ( 1991). Homogenates were extracted in 1% sarcosine (N-lauroylsarcosine), TRIS-EDTA (5.0 mM TRIS-HC1, 0.5 mM EDTA, pH 7.5) buffer for 30 minutes at room temperature, mixed vigorously in a sample vortexer for 10—15 sec- onds, then extracted for another 30 minutes. Aliquots were diluted with TRIS-EDTA buffer to yield a final concentration of 0.1% sarcosine, then centrifuged at room temperature for 5 minutes at 2,500 times grav- ity (x g) for CFA and 12,000 x g for FIA. The super- natant was recovered for estimation of nucleic acid concentrations by FIA or CFA. Sarcosine, like other anionic detergents, fluoresces at excitation and emis- sion wavelengths used in the analyses. To reduce this effect, samples extracted in 1% sarcosine required a 10-fold dilution with TRIS-EDTA buffer before FIA (Caldarone and Buckley, 1991). In the modified CFA procedure, a final sample concentration of 0.0125% sarcosine produced an acceptable background fluo- rescence (blank) value of approximately 5% of the highest nucleic acid standard. Differences in the total sample volumes required by FIA and CFA procedures required modifications to the concentrations of nucleic acid standards, fluo- rochrome reagents, and sample volumes of fish homogenates. Nucleic acid standard ranges and homogenate sample volumes were chosen to encom- pass the typical range of concentrations encountered by each method during routine analysis of individal fish larvae. Working standards of RNA and DNA were prepared as described by Caldarone and Buckley (1991) by serial dilution of previously fro- zen stock solutions with 0.1% sarcosine in TRIS- EDTA buffer. RNA standards (Sigma Chemical Co., St. Louis, MO, Type IV, calf liver) ranged from 1.97 to 17.68 /ig-mL"1 for FIA and from 0.41 to 13.14 /ig-mLr1 for CFA. DNA standards (Boehringer-Mann- heim Corp., Indianapolis, IN, high molecular weight, calf thymus) ranged from 0.16 to 1.52 /ig-mLr1 for FIA and from 0.07 to 2.37 jig-mL"1 for CFA. Estimates of contamination of the calf liver RNA standard by DNA, determined by fluoresecence in Hoechst, was less than 1% by weight. A 100-//L "spike" of homogenate from walleye pollock larvae was added to serial dilu- tions of RNA and DNA standards in order to estimate the recovery efficiencies using the CFA protocol. Fluorochrome working reagents of EB (137.5 ng-mLr1) and Hoechst (25 ng-mLr1) prepared for FIA in TRIS-EDTA buffer according to Caldarone and Buckley ( 1991) were modified by reducing the sodium chloride (NaCl) concentration in the Hoechst reagent from 0.2 N to 0. 1 N and the pH from 7.5 to 7.0. Work- ing dye solutions of 2.0 pg-mL"1 EB and 5.0 /ig-mLr1 Hoechst prepared for CFA at the same pH and NaCl concentration as for FIA provided a sensitive linear response to the standards while maintaining a low background fluorescence. The RNA and DNA concentrations were estimated for each aliquot. In addition, the amount of endog- enous fluorescence (sample fluorescence in the ab- sence of fluorochrome dye) was determined for most homogenate samples (21 for FIA, 17 for CFA) by sub- stituting an equal volume of TRIS-EDTA buffer for the fluorochrome working reagent in the assay procedure. The FIA system for nucleic acid determination is fully described by Caldarone and Buckley (1991). A 50-/iL sample is injected into a reagent stream con- 160 Fishery Bulletin 93(1). 1995 taining one of the fluorochrome dyes. The injected sample is mixed and transported with the reagent to the fluorescence detector which continuously records the fluorescence at 525 nm excitation and 600 nm emission for EB, or 356 nm excitation and 458 emission for Hoechst. The sample fluorescence is displayed as a peak, whose area is proportional to the concentration (Caldarone and Buckley, 1991). Modification of this procedure for CFA required a minimal total volume (sample plus fluorochrome re- agent) of 2 mL in order to be measured accurately by the fluorometer (Shimadzu RF-540 spectro- fluorophotometer, Shimadzu Corp., Kyoto, Japan), which was adapted to use 12x75 mm borosilicate glass test tubes as cuvettes. For all samples, except the homogenates of larval pollock, a 0.1-mL aliquot of extracted sample was combined with 0.9 mL of TRIS-EDTA buffer and 1.0 mL of fluorochrome work- ing reagent (EB or Hoechst). For larval pollock homogenates, a 0.03-mL aliquot was combined with 0.97 mL of TRIS-EDTA buffer prior to addition of 1.0 mL of the fluorochrome reagents. The sample- fluorochrome mixture was incubated at room tem- perature for 15-30 minutes before fluorescence was measured at the same excitation and emission wave- lengths as in the FIA procedure. Initial trials indi- cated that maximum sample fluorescence was ob- tained within 15 minutes and was stable for more than 4 hours at room temperature. Calculations of nucleic acid concentrations were identical for both methods. First, endogenous sample fluorescence was subtracted from total sample EB or Hoechst dye fluorescence. Sample DNA concen- trations were estimated directly from fluorescence in Hoechst dye by using a DNA-Hoechst standard curve. The computed DNA concentration was used to estimate the fluorescence contribution by DNA to the total sample EB-fluorescence by using a DNA- EB standard curve. Fluorescence due to DNA-EB was subtracted from the total sample fluorescence and the remaining fluorescence was assumed to be due to RNA. The RNA concentration was then estimated by using an RNA-EB standard curve. The relationships between mean RNA and DNA con- centration and RNA/DNA ratios of the fish homo- genates predicted by FIA and CFA methods were ana- lyzed by using a geometric mean regression procedure (Ricker, 1984) that describes the linear central trend between two independent estimates of the variate. Results Standard calibration curves indicated that detection limits for CFA are about 0.07 /ig-mL-1 for RNA and 0.03 /igmL-1 for DNA, similar to the values detect- able with automated FIA (Caldarone and Buckley, 1991). The precision of both methods was comparable; mean coefficients of variation, V (standard devia- tion as a percentage of the mean), for triplicate de- terminations from each homogenate averaged 5 to 7% for RNA and 3 to 4% for DNA over a broad range of estimated sample concentrations. Recovery of DNA standards from six replicate "spikes" of larval pollock homogenate with the CFA method averaged 99.5 + 0.9% in Hoechst and 99.2 ± 2.9% in EB, and recovery of "spiked" RNA standards averaged 94.8 ± 6.0% in EB. Mean nucleic acid concentrations and RNA/DNA ratios offish homogenates were generally lower when estimated by CFA relative to FIA (Fig. 1). RNA con- centration was most strongly correlated between the two methods and DNA concentration less so (Table 2). The ratio of RNA to DNA was only moderately correlated between the two methods and provided the poorest basis for comparison. Intermethodological calibration between FIA and CFA results was achieved by the application of regression coefficients (Table 2) to mean nucleic acid concentrations and RNA/DNA ratios estimated by CFA (Fig. 2). Homogenates prepared from larval stages of the gadid species (Gadus morhua, Melanogrammus aeglefinus, and Theragra chalcogramma), tautog, Tautoga onitis, and winter flounder, Pleuronectes americanus, exhibited negligible endogenous fluores- cence, regardless of fluorochrome, over a 3- to 4-fold range of nucleic acid concentrations (Table 3). En- dogenous fluorescence was highest for juvenile in- land silverside and juvenile winter flounder. Discussion Modification of the FIA method described by Caldarone and Buckley (1991) to conventional fluo- rometry produced an assay protocol with comparable Table 2 Geometric mean functional regression coefficients describ- ing mean RNA and DNA concentrations (/jgmL1 homogenate I and RNA/DNA ratios of 24 fish homogenates determined by conventional fluourometric analysis (CFA) regressed upon estimates obtained by flow injection analy- sis (FIA). Variate Y-intercept Slope RNA DNA RNA/DNA -5.318 -1.795 -0.309 0.652 0.991 0.733 0.972 0.808 0.569 NOTE Canino and Caldarone: Fluorometric techniques for determining nucleic acid contents of fish larvae 161 200 0- O c(S) • c - A S (S) A S D F V H ▼ P O T 150 0- .... -V" " 100 0 - 50.0- 00- ^«^t? AATJ T ■-D — i ..T- .-▼" — 1 1 0.0 100 o 150 0 RNA (/ig mL homogenate) - FIA DNA (/tg mL 12 5 15.0 17.5 homogenate) - FIA 25 0 0.0- 8 0- •-- 6 0 - 4 0- 20- - J^ AA- V V T 0.0- ^•-''' 1 — 1 — — i 1 1 2 0 40 60 RNA/DNA -FIA Figure 1 Mean RNA and DNA concentrations and RNA/DNA ratios of 24 crude fish homogenates obtained by flow injection analysis (FIA) versus conventional fluorometric analysis (CFA). Solid line represents a 1:1 correspondence be- tween the two methods. Dashed line is the geometric mean regression be- tween the two estimates. Species abbreviations as in Table 1. sensitivity, precision, and sample throughput. Mean coefficients of variation (Vx) for DNA concentration estimated by FIA and CFA in this study (3 to 4%) are similar to those reported for replicate assays of a pooled fish homogenate using FIA (Caldarone and Buckley, 1991), another two-dye procedure (Clem- mesen, 1988), and a single-dye method (Clemmesen, 1993). In this study, the mean Vx values for RNA con- centration were 3 to 5% higher when determined by FIA and CFA for multiple homogenates than for FIA estimates of a single, pooled homogenate (Caldarone and Buckley, 1991) but are comparable to those re- ported by Clemmesen (1993) for RNA estimates of pooled fish homogenate using a single-dye technique. The RNA and DNA concentrations of fish homogenates were consistently lower when estimated by CFA compared with FIA. Calibration between the two methods by functional regression relationships established a reasonable basis for comparison of results (Fig. 2), although considerable differences in mean es- timated nucleic acid concentrations and RNA/DNA were still evident. We emphasize that sample homo- 162 Fishery Bulletin 93(1). 1995 250.0 150 0 -■ _, 100.0 50.0 O C (S) □ F • C V H A S (S) ▼ p AS O T 50 0 100 0 150 0 200 0 RNA (figmL"' homogenate) - FIA 1 1 1 2 5 5 0 7.5 10 0 12 5 15.0 17 5 20 0 22.5 25.0 DNA (figmL-1 homogenate) - FIA 6 0 8 0 RNA/DNA - FIA Figure 2 Mean RNA and DNA concentrations and RNA/DNA ratios of 24 crude fish homogenates obtained by flow injection analysis (FIA) versus values trans- formed from conventional fluorometric analysis (CFA) by functional regres- sion coefficients in Table 2. Solid line represents a 1:1 correspondence be- tween the two methods. Species abbreviations as in Table 1. genates for this study were chosen from six fish spe- cies and assayed across far greater ranges of age and nucleic acid concentrations than reported previously (Clemmesen 1988, 1993; Caldarone and Buckley, 1991; McGurk and Kusser, 1992) in order to broaden the scope of comparison and statistical inference. A comparative study of FIA and CFA techniques within the more lim- ited range of sample concentrations encountered dur- ing routine processing of individual larvae of a single species would have undoubtedly yielded higher corre- lations between estimates. The FIA and CFA procedures differ primarily in the choice of instrumentation as both use sample extraction by sarcosine. Caldarone and Buckley (1991) reported that nucleic acids in larval fish samples (<200 /ig dry weight) were completely ex- tracted in one hour at room temperature. Sample nucleic acid concentrations of fish homogenates in this study were prepared to be similar to those ob- tained from assays of individual larvae, suggesting that incomplete or differential extraction of homo- genates by sarcosine between FIA and CIA is un- NOTE Canmo and Caldarone. Fluorometnc techniques for determining nucleic acid contents of fish larvae 163 Table 3 Mean endogenous fluorescence' offish homogenates as a percentage of total fluorescence in Hoechst 33258 (Hoechst) bromide (EB) fluorochromes. Samples are from larvae unless otherwise noted. (S) = starved. or ethidium Species Sample name Age (d) Hoechst EB FIA CFA FIA CFA Atlantic cod C Atlantic cod (starved) C(S) Inland silverside (juvenile) S Inland silverside (juvenile, starved) S(S) Haddock H Tautog T Winter flounder F Winter flounder (juvenile) Walleye pollock P 41-61 41-61 104-108 104-108 11 22 44 20 26 41 57 <60 <3 <3 <2 <2 <1 <1 3 3 38 40 33 37 <1 <1 12 12 <3 <3 <3 <3 <3 <3 <2 <2 <2 <2 <2 <2 <1 <1 <1 <1 <1 <1 <2 <2 2 <2 <2 <2 19 14 <1 6 <3 <2 <1 2 ' Endogenous sample fluorescence occurs in the absence of fluorochrome dye. likely. The consistently lower estimates of nucleic acids with the CFA method, relative to the FIA method, implies a lower ratio of fluorescence yield of samples to standards. One possibility is that the ef- fective sample concentration at the detector may be greater in CFA compared with FIA. In FIA, the time between the mixing of dye and sample is precisely controlled but the ratio of dye to sample is unknown. The concentrations of the fluorochrome working re- agents used in FIA were increased ( 14x and lOOx for EB and Hoechst, respectively) in order to saturate the standards for the CFA modification. A higher ef- fective sample concentration at the detector (possi- bly making the samples less available to the dye), coupled with a longer pathlength, may explain the lower fluorescence yield of the CFA samples relative to the standards. The higher correlation between the methods for RNA estimates than for DNA was an unexpected result; RNA content is calculated indi- rectly (total sample fluorescence minus estimated fluorescence due to DNA) and, presumably, is more subject to measurement error than is direct fluoro- metric determination of DNA. Fluorescence by compounds other than nucleic ac- ids represents a potential source of interference in any fluorometric assay. The level of endogenous sample fluorescence should be determined by pre- liminary analyses when a new fish species or devel- opmental stage is being investigated. Crude tissue homogenates exhibit fluorescence characteristics not found in commercial preparations of nucleic acids that appear to be related to tissue type and develop- mental stage of the fish. Caldarone and Buckley (1991) found that winter flounder and American sand lance, Ammodytes americanus, larvae and the nucleic acids used as standards exhibited negligible amounts of endogenous or residual fluorescence, whereas win- ter flounder postlarvae and juvenile muscle and liver had levels ranging from approximately 5 to 55% of total fluorescence in EB or Hoechst dyes. Clemmesen ( 1993) reported endogenous fluorescence values rang- ing up to 40% in Hoechst determinations of the DNA content of herring, Clupea harengus, larvae. In this study, only homogenates of the juvenile inland sil- verside and juvenile winter flounder exhibited high levels of endogenous fluorescence in Hoechst dye or EB (Table 3), providing further evidence of an onto- genetic effect. Gadid larvae, of approximately the same age as the juvenile winter flounder, displayed negligible amounts of endogenous fluorescence, sug- gesting that systematic differences may also exist. Interference in nucleic acid estimation from con- taminants of crude homogenate preparations has been reported previously (Brunk et al., 1979; Mordy and Carlson, 1991; Clemmesen, 1993). McGurk and Kusser ( 1992) compared three fluorescence methods for quantitating nucleic acids in Pacific herring, Clupea pallasi, larvae. Of the three, the method in- corporating the most extensive purification steps (Clemmesen, 1988) resulted in higher estimates of RNA content and RNA/DNA ratios than the other two methods, suggesting that higher yields may have resulted from the elimination of substances interfer- ing with accurate fluorometric quantitation. How- ever, quenching of nucleic acid fluorescence by con- taminants in the samples does not appear to be sig- 164 Fishery Bulletin 93(1). 1995 nificant in either the CFA or FIA techniques using the sarcosine extraction procedure with larval fish. Recoveries of crude homogenate "spikes" added to nucleic acid standards by FIA (Caldarone and Buckley, 1991) and CFA (this study) are similar to those reported for more purified extracts (Clemmesen, 1993). McGurk and Kusser (1992) re- ported higher RNA contents and RNA/DNA ratios for yolk-sac herring larvae analyzed with the Clemmesen method (1988) and suggested that fluoresecence absorbance by yolk components may be reduced by the purification steps in that assay. However, when a homogenate of winter flounder yolk- sac larvae was "spiked" with nucleic acid standards and subjected to FIA with a sarcosine extraction pro- cedure, recoveries of calf thymus DNA standards remained unchanged and those for calf liver RNA standards only declined by 3 to 5% (Caldarone, Unpubl. data). RNA/DNA indices have proven useful as indica- tors of condition in a wide variety of fish species. When coupled with data on water temperature, and calibrated with laboratory-reared larvae, estimates of recent growth in the field can be obtained (Buckley, 1984). However, this study and others illustrate a common problem with the application of fluorescent techniques to estimation of nucleic acid levels in fish and other biosamples, and the need for inter- calibration. Given the disparity in estimates of RNA and DNA contents due to the method of analysis (McGurk and Kusser, 1992; this study) and choice of nucleic acid standards (Caldarone and Buckley, 1991), no direct intermethodological comparisons of data can be made without intercalibration between analytical methods, as done by McGurk and Kusser (1992), Clemmesen (1993), Mathers et al. (1994), and this study. It is inappropriate to compare RNA/DNA ratio values with published data unless the same methods and standards are used. Also, the general- ized growth equation in Buckley (1984) uses RNA/ DNA ratios determined with an ultraviolet light ab- sorption method that cannot be directly applied to ratios determined with other analytical procedures without running an intercalibration between the two methods. Alternatively, the relation between RNA/ DNA, temperature, and growth must be determined for laboratory-reared larvae by using the analytical method of choice before a growth equation can be applied to fish larvae collected in the field. A general assay protocol for FIA and CFA is pre- sented in Figure 3. For this study, fish larvae were pooled and homogenized to provide adequate repli- cates for methods comparison. On a routine basis, individual larvae may be frozen in 1.5-mL micro- centrifuge vials, then extracted in the same vial, re- ducing processing time and errors associated with sample transfer. The actual volumes of 1% sarcosine and TRIS-EDTA buffer may have to be determined empirically depending upon the larval fish size and sample volume required for spectrofluorometric analysis. A trained operator can process approxi- mately 80 samples for RNA and DNA determinations as well as standards in eight hours using CFA and in five hours with FIA. We do not routinely assay replicate sample aliquots or correct for endogenous sample fluorescence when preliminary estimates are less than 3% of total sample fluorescence. The "best" method for nucleic acid analysis of lar- val fish may well be determined by sample size, in- strumentation, the presence of interfering sub- stances, or the need to compare values to previously published data. Flow-injection analysis (Caldarone and Buckley, 1991) is a sensitive, precise assay with a simple extraction procedure and high sample throughput. The modified CFA protocol presented here retains those advantages, extends them to a more inexpensive method using static fluorometry, and pro- vides an intercalibration between the two methods. one larval fish J, add 1% sarcosine in TRIS-EDTA buffer i incubate 30 min at room temperature i vortex vigorously J, incubate 30 min at room temperature vortex vigorously I dilute with TRIS-EDTA buffer si centrifuge S min at 2,500 x g 0- replicate samples of supernatant r FIA Hoechst EB 4 CFA l/N Hoechst EB to spectrofluorometer Figure 3 Generalized flowchart of the sarcosine extraction, flow in- jection analysis (FIA), and conventional fluorometric analy- sis (CFA) procedures. NOTE Canino and Caldarone Fluorometnc techniques for determining nucleic acid contents of fish larvae 165 Acknowledgments The authors thank L. Buckley, G. Theilacker, D. Busch, A. Kendall Jr., and K. Bailey for their helpful comments on earlier versions of the manuscript and three anonymous reviewers for their critical reviews. S. Picquelle provided assistance in the statistical treatment of the data. This study was conducted as part of the Fisheries Oceanography Coordinated In- vestigations (NMFS, Seattle) and the GLOBEC Cod Recruitment Studies (NMFS, Narragansett) and rep- resents FOCI contribution 0195 and GLOBEC con- tribution 0194. Literature cited Bentle, L., S. Dutta, and J. Metcoff. 1981. The sequential enzymatic determination of DNA and RNA. Anal. Biochem. 116:5-16. Berdalet, E., and Q. Dortch. 1991. New double-staining technique for RNA and DNA measurement in marine phytoplankton. Mar. Ecol. Prog. Ser. 73:295-305. Brunk, C. F., K. C. Jones, and T. W. James. 1979. Assay of nanogram quantities of DNA in cellular homogenates. Anal. Biochem. 92:497-500. Buckley, L. J. 1979. Relationships between RNA-DNA ratio, prey density, and growth rate in Atlantic cod (Gadus morhua ) larvae. J. Fish. Res. Board Can. 36:1497-1502. 1980. Changes in ribonucleic acid, deoxyribonucleic acid, and protein content during ontogenesis in winter floun- der, Pseudopleuronectes americanus, and the effect of starvation. Fish. Bull. 77:703-708. 1981. Biochemical changes during ontogenesis of cod (Gadus morhua L.) and flounder (Pseudopleuronectes amerieanus) larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:547-552. 1984. RNA-DNA ratio: an index of larval fish growth in the sea. Mar. Biol. 80:291-298. Buckley, L. J., and R. G. Lough. 1987. Recent growth, biochemical compostion, and prey field of larval haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) on Georges Bank. Can. J. Fish. Aquat. Sci. 44:14-25. Bulow, F. J. 1987. RNA-DNA ratios as indicators of growth in fish: a review. In R. C. Summerfelt and G. E. Hall (eds.), Age and growth in fish, p. 45-64. Iowa State Univ. Press, Ames, Iowa. Caldarone, E. M., and L. J. Buckley. 1991. Quantitation of DNA and RNA in crude tissue extracts by flow injection analysis. Anal. Biochem. 199:137-141. Canino, M. F. 1994. Effects of temperature and food availability on growth and RNA/DNA ratios of walleye pollock Theragra chaleogramma (Pallas) eggs and larvae. J. Exp. Mar. Biol. Ecol. 175:1-16. Canino, M. F., K. M. Bailey, and L. S. Incze. 1991. Temporal and geographic differences in feeding and nutritional condition of walleye pollock larvae Theragra chaleogramma in Shelikof Strait, Gulf of Alaska. Mar. Ecol. Prog. Ser. 79:27-35. Clemmesen, C. 1987. Laboratory studies on RNA/DNA ratios of starved and fed herring (Clupea harengus) and turbot (Scophthalmus maid- mus) larvae. J. Cons. Int. Explor. Mer 43:122-128. 1988. A RNA and DNA fluorescence technique to evaluate . the nutritional condition of individual marine fish larvae. Meeresforsch. 32:134-143. 1993. Improvements in the fluorometric determination of the RNA and DNA content of individual marine fish larvae. Mar. Ecol. Prog. Ser. 100:177-183. Hovenkamp, F. 1990. Growth differences in larval plaice Pleuronectes platessa in the southern bight of the North Sea as indi- cated by otolith increments and RNA/DNA ratios. Mar. Ecol. Prog. Ser. 58:205-215. Hovenkamp, F., and J. IJ. Witte. 1991. Growth, otolith growth, and RNA/DNA ratios of lar- val plaice Pleuronectes platessa in the North Sea 1987 to 1989. Mar. Ecol. Prog. Ser. 70:105-116. Karsten, U., and A. Wollenberger. 1972. Determination of DNA and RNA in homogenized cells and tissues by surface fluorometry. Anal. Biochem. 46:135-148. 1977. Improvements in the ethidium bromide method for direct fluormetric estimation of DNA and RNA in cell tis- sue homogenates. Anal. Biochem. 77:461-470. Mathers, E. M., Houlihan, D. F., and L. J. Burren. 1994. RNA, DNA and protein concentrations in fed and starved herring Clupea harengus larvae. Mar. Ecol. Prog. Ser. 107:223-231. McGurk, M. D., and W. C. Kusser. 1992. Comparison of three methods of measuring RNA and DNA concentrations of individual Pacific herring, Clupea pallasi, larvae. Can. J. Fish. Aquat. Sci. 49:967-974. Mordy, C. W., and D. J. Carlson. 1991. An evaluation of fluorescence techniques for measur- ing DNA and RNA in marine microorganisms. Mar. Ecol. Prog. Ser. 73:283-293. Munro, H. N., and A. Fleck. 1966. The determination of nucleic acids. In D. Glick(ed.), Methods of biochemical analysis, volume 14, p. 423-524. Interscience Pubis., New York. Richard, P., J. P. Bergeron, M. Boulhic, R. Galois, and J. Person-Le Ruyet. 1991. Effect of starvation on RNA, DNA and protein con- tent of laboratory-reared larvae and juveniles of Solea solea. Mar. Ecol. Prog. Ser. 72:69-77. Richer, W. E. 1984. Computation and uses of central trend lines. Can. J. Zool. 62:1897-1905. Robinson, S. M. C, and D. M. Ware. 1988. Ontogenic development of growth rates in larval Pa- cific herring, Clupea harengus pallasi, measured with RNA- DNA ratios in the Strait of Georgia, British Columbia. Can. J. Fish. Aquat. Sci. 45:1422-1429. Theilacker, G. H., and W. Shen. 1993. Fish larval condition analyzed using flow cytometry. In B. T Walther and H. J. Fhyn (eds.), Physi- ological and biochemical aspects of fish development, p. 346-355. Univ. Bergen, Norway. Wright, D. A., and F. D. Martin. 1985. The effect of starvation on RNA:DNA ratios and the growth of larval striped bass, Morone saxatilis. J. Fish Biol. 27:479-485. The potential use of otolith characters in identifying larval rockfish [Sebastes spp.) Thomas E. Laidig Stephen Ralston Southwest Fisheries Science Center National Marine Fisheries Service. NOAA 3 1 50 Paradise Drive. Tiburon, California 94920 Rockfish of the genus Sebastes are commercially important in the northeast Pacific Ocean, where more than 60 valid species are rec- ognized (Eschmeyer et al., 1983). Although morphological and chro- matic characters are used routinely to identify adults of the genus, such traits are frequently ineffective for young of the year, especially larvae. Like most fish, early developmen- tal stages of Sebastes spp. have less pigmentation, fewer hard struc- tures (e.g. fin rays), and show less differentiation when compared with adults. However, an ability to discriminate among the larvae of the many rockfish species is criti- cal to the advancement of early life history studies in this group. A variety of methods have been used to identify larval and juvenile rockfish (Kendall, 1991). Although pigmentation is the most fre- quently used character (Moser et al., 1977; Laroche and Richardson, 1980; Moser et al., 1985; Kendall and Lenarz, 1987), size at extrusion (Moser et al., 1977), meristic counts (Moser et al., 1977), morphometries (Morris, 1956), size at specific life history events (Stahl-Johnson, 1985), time of parturition in conjunction with geographic location (Moser et al., 1977), and electrophoretic pat- terns (Seeb and Kendall, 1991) have all been used to identify lar- val and juvenile rockfish. A problem with many of these techniques, however, is that larval characters often undergo ontoge- netic change. To overcome this problem, the larvae of many species have been reared in captivity and sequentially sacrificed. This is not only technically demanding, expen- sive, and time consuming, but dif- ferences in development between laboratory and wild fish may affect the number, size, and distribution of the attributes under investiga- tion. Thus, permanent identifiable characters would be useful. A static trait, which retained its character- istics throughout early life, would increase our ability to positively identify rockfish larvae. Otoliths, being acellular aragonitic concre- tions, are good candidates to retain features produced during the lar- val stage. Likewise, otoliths have been shown to contain sufficient variation among species (Hecht and Appelbaum, 1982; Akkiran, 1985; Victor, 1987) and stocks (Messieh, 1972; Postuma, 1974; McKern et al, 1974; Neilson et al., 1985; Smith, 1992) to assign with accuracy group membership to individuals. This study investigates the po- tential of using otolith microstruc- ture to assist in the identification of larval rockfish. We assume that no change occurs to early larval otolith microstructure once it is deposited (Brothers, 1984; Steven- son and Campana, 1992). Otolith characteristics (nuclear shading patterns, nuclear radius, and first increment width) produced during the early larval period were de- scribed and measured from late lar- val and pelagic juvenile stage speci- mens of eight species of rockfish: Sebastes auriculatus, S. entomelas, S. flavidus, S. goodei, S. jordani, S. mystinus, S. paucispinis, and S. saxicola. These species were the most numerous rockfish species collected off the central California coast during the study period. Methods Field collections Samples of young-of-the-year pe- lagic juveniles and late larvae were collected with a midwater trawl ( 12 x 12 m) from the National Oceanic and Atmospheric Administration RV David Starr Jordan. From 1983 to 1989 nine cruises were conducted off central California (lat. 36°30- 38°10'N) during the months of April-June. Pelagic juvenile rock- fish were frozen at sea and re- turned to the laboratory for final identification. Wyllie Echeverria et al. (1990) have described cruise sampling methodology in detail. Laboratory procedures Pelagic juveniles were identified to species from external characteris- tics, including pigmentation, fin- ray counts, and gill-raker counts (Laidig and Adams, 1991). The sag- ittal otoliths were removed and af- fixed whole to microscope slides and were prepared for viewing with the methods outlined in Laidig et al. (1991). Otoliths were examined with a video image interfaced with a digi- tizer (Laidig et al., 1991). Distinct reoccurring shading patterns in the Manuscript accepted 15 June 1994. Fishery Bulletin 93:166-171 (1995). 166 NOTE Laidig and Ralston. Use of otolith characters in identifying larval Sebastes spp. 167 nucleus (i.e. the otolith core) were noted for each spe- cies. Increment counts were made beginning at the first clearly defined mark that completely encircled the primordium (see also Penney and Evans, 1985). This "extrusion" check forms at parturition (Ralston, unpubl. data) and defines the outer edge of the nucleus; the distance from the primordium to this mark is the nuclear radius (Fig. 1), and the incre- ment immediately following the extrusion check is the first growth increment. Data analysis The mean radius of the nucleus and the mean width of the first growth increment were compared among species and years. An overall analysis of variance (ANOVA), incorporating separate pairwise £-tests, equivalent to Fisher's least-significant difference, was performed to detect differences in the size of the nuclear radius and the width of the first increment among species and years. We used a two-way facto- rial analysis and calculated least square means (Searle et al., 1980) to evaluate treatment effects among species, years, and the interaction of species and years. A parametric discriminant analysis, as- suming a multivariate normal distribution with pooled covariance matrix, was used to determine the percentage of each species that was correctly classi- fied by nuclear radius and first increment width, alone and in combination with each other. To further evaluate species-specific differences in nuclear radius and first increment width, the data were pooled over years; however, we recognized the difficulty in isolating the effect of species alone. Sebastes auriculatus and S. saxicola were only sampled in one year; therefore they were not included in the annual variation analysis. For comparison, we treated these single-year studies as the pooled data for the other species. A blind test was performed to determine the accu- racy of the otolith characters in distinguishing be- tween the eight rockfish species used in this study. One hundred otoliths representing all eight species (S. auriculatus [n=5]; S. entomelas [n=13]; S. flauidus [n = 15]; S. goodei [n = 14]; S. jordani [n=25]; S. mystinus [n=9]; S. paucispinis [re=ll]; and S. saxicola [n-8]) were given to a reader. No other information (e.g. species, fish length, etc.) about the individual samples was provided. The reader then attempted to identify the correct species of rockfish, using both measured distances and shading patterns. The re- sults of the tentative classification were compared with the actual species identities to determine per- cent agreement. The significance of this result was evaluated against a null multinomial distribution, by assuming assignments at random to species. Figure 1 A Sebastes goodei otolith displaying the characteristic dark inner ring (DIR) around the primor- dium (PR). NE = nuclear edge. 168 Fishery Bulletin 93(1), 1995 Results Seven specific nuclear shading characters were iden- tified (Table 1): 1) the opacity of the primordium; 2) the opacity of the markings inside the nucleus; 3) the opacity of the increments directly outside the nucleus; 4) the opacity of the nuclear edge; 5) the existence of a dark inner band near the nuclear edge; 6) the existence of a light inner band near the nuclear edge; and 7) the existence of a dark inner ring encir- cling the primordium. In some cases, combinations of the shading pat- terns were sufficient to characterize a species. For example, 84% of the otoliths of S. goodei were found to have a dark primordium, a dark nuclear edge, and a dark inner ring surrounding the primordium, while this combination was never found in the other spe- cies examined (Fig. 1). Likewise, in S.jordani, a light penumbra was regularly found (76% occurrence) adjacent to the inner edge of the nucleus, along with a dark primordium and many inner rings (faint mi- crostructure occurring inside the nucleus). In S. paucispinis and S. flavidus, there was usually a dark inner band next to the edge of the nucleus (87% and 73% occurrence, respectively) . No annual variation was observed for the nuclear shading patterns. How- ever, in the remaining species, the shading patterns were too variable to establish consistent identifiable character states that would distinguish species. Annual variations in nuclear radius and the width of the first increment were examined (Fig. 2). An- nual variation in nuclear radius among the species was not significant; however, annual variability in the width of the first increment was significant (P<0.05). In addition, there was a significant inter- action (P<0.05) between year and species. The mean width of the first increment of S. paucispinis, for example, declined from 1984 to 1989, whereas that of S. flavidus increased (Fig. 2A). Sebastes jordani was found to have the largest average nuclear radius (Table 2; Fig. 2B). The rank order for the remaining species, from largest to small- est average nuclear radii, was S. goodei, S. auriculatus, S. paucispinis, S. flavidus, S. entomelas, S. saxicola, andS. mystinus. Individually, the nuclear radii of S. jordani, S. goodei, S. auriculatus, and S. mystinus were significantly different (P<0.05) from all other species and from each other. Sebastes jordani was also found to have the larg- est average first increment of all species studied (Table 2; Fig. 2A). The rank order of the other spe- cies, from largest to smallest average widths of the first increment, was S. paucispinis, S. goodei, S. auriculatus, S. saxicola, S. flavidus, S. entomelas, and S. mystinus. Sebastes jordani and S. paucispinis had significantly larger average first increment widths (P<0.05) than all other species studied (0.97 //m and 0.91 /im, respectively) (Table 2). A discriminant analysis was performed on the clas- sification of species by using nuclear radius and the width of the first increment as predictor variables (Table 3). Sebastes goodei, S. jordani, S. mystinus, and S. paucispinis were correctly identified from 57 to 83% of the time; Sebastes auriculatus and S. flavidus were classified correctly 33.9% and 41.8% of the time, respectively. Although these values are less than 50% correct, they represent the largest single classification for each species. Two species, S. entomelas and S. saxicola, were not often classified correctly (9.5% and 0%, respectively). In a blind test, the reader correctly classified 70 of the 100 otoliths (70% correct; Table 4), demonstrating that otoliths provide useful information in species iden- tification (P<0.001). Greater than 90% of Sebastes Table 1 Observed shading patterns of otolith nuclei for the eight species studied. An F means the attribute was faint, a D means it was dark, and a blank means that it was either variable or did not exist. For the last three attributes, an X means the character was present, aur = S. auriculatus, ent = S. S. paucispinis, and sax = S. saxicola. entomelas, fla = S. flavidus, goo = S. goodei, jor = S. jordani, mys = S. mystinus, pau = Attribute Species aur ent fla goo jor mys pau sax Primordium opacity Inner ring opacity Outer increment opacity Nuclear edge opacity Dark inner band D F F F F F F F X D D D D F F D D D F F F D X Light inner band Dark primordial ring X X X NOTE Laidig and Ralston: Use of otolith characters in identifying larval Sebastes spp. 169 goodei and S. paucispinis were correctly clas- sified, whereas the remaining species showed lower accuracy varying from 56 to 68%. Discussion Otolith characteristics have been shown to vary among species and among stocks. Rybock et al. (1975) and Postuma (1974) used nuclear dimensions to identify differ- ent fish stocks. McKern et al. (1974) used otolith dimensions to separate seasonal stocks of steelhead trout, and Victor ( 1987) used otolith dimensions to separate differ- ent species of pomacentrids and labrids. Postuma (1974) related otolith opacity to nuclear size and compared this relationship between stocks. Messieh (1972) used otolith shape to distin- guish among stocks of herring. Hecht and Appelbaum (1982) and Gago (1993) also used otolith shape to distinguish between species. We have found that otolith characteristics can effec- tively distinguish certain species of Sebastes. Four of the species examined, S. jordani, S. goodei, S. auri- Table 2 Mean nuclear radi us and first increment width of otoliths (all years combined) of Sebastes. SD = standard deviation n = sample size Nuclear First Species n radius (/Jm) SD increment ipm) SD S. auriculatus 56 14.07 1.48 0.82 0.20 S. entomelas 147 11.81 0.94 0.72 0.13 S. flavidus 122 12.09 0.69 0.72 0.16 S. goodei 230 15.15 0.89 0.85 0.17 S. jordani 541 16.96 0.99 0.97 0.23 S. mystinus 106 10.93 1.05 0.65 0.14 S. paucispinis 277 12.20 1.14 0.91 0.18 S. saxicola 12 11.58 0.90 0.73 0.23 d 110 ^ ' \ A 0--N ^**A \ fi 0 10° ---. \ • a.„ fc.C5 0.90 a £ 5 °-80 C^^^»-* ^ •« aJSt^^A n £ 0.70 A \ • E 0.80 ^*» X. 0.50 w Figure 2 Annual variation in average nuclear radius and first increment width for the six species of Sebastes that had multiple year observations, ent = S. entomelas. fla = S. flavidus, goo = S. goodei, jor = S. jordani. mys = S. mystinus, and pau = S. paucispinis. culatus, and S. mystinus, had significantly different nuclear radii from each other and from the other spe- cies examined. Sebastes jordani, S. goodei, S. pauci- spinis, and S. flavidus each had unique shading pat- terns that may help in species identifications. Sebastes jordani and S. paucispinis were correctly classified over 90% of the time in the blind test, displaying the useful- ness of otolith characteristics for identification. The specificity of otolith characters gives research- ers an opportunity to separate larvae using these characters alone. Without otolith data, the separa- tion of S. mystinus larvae from other rockfish larvae is difficult. Although larval S. jordani are relatively easy to identify on the basis of pigmentation (Moser et al., 1977), identifications can be confirmed with a few additional otolith measurements. We suggest from these findings that the difficult task of identifying rockfish larvae can be facilitated in some cases by employing otolith characters in com- bination with more traditional traits like pigmenta- tion. Of the eight species examined, six species (S. auriculatus, S. flavidus, S. goodei, S. jordani, S. mystinus, and S. paucispinis) had distinctive otolith characters that allowed separation from other spe- cies. Many of the larval stages of the more than 60 species of rockfish found in the northeast Pacific Ocean are very similar, and pigmentation alone cannot always reliably separate species. Otolith character examina- tion may be one further method that can aid research- ers in accurately identifying species in this group. Acknowledgments We would like to thank the crew of the RV David Starr Jordon and all the scientists who participated in the collection of samples. We also thank all of the reviewers for their informative comments. 170 Fishery Bulletin 93(1), 1995 Table 3 Discriminant analysis for nuclear radius and first increment width of otoliths for all years each species of Sebastes. aur = S. auriculatus, ent = S. entomelas, fla = S. flavidus, goo mystinus, pau = S. paucispinis, and sax = S. saxicola. combined showing percent classified as = S. goodei, jor = S. jordani, mys = S. Species Classification aur ent fla goo jor mys pau sax aur 33.9 0.0 17.9 23.2 10.7 0.0 12.5 1.8 ent 1.4 9.5 38.8 1.4 0.0 22.5 12.9 13.6 fla 5.7 14.8 41.8 0.0 0.0 11.5 18.9 7.4 goo 23.5 0.0 0.9 59.6 14.4 0.0 1.7 0.0 jor 0.9 0.0 0.0 15.9 83.2 0.0 0.0 0.0 mys 0.9 4.7 6.6 0.0 0.9 72.6 6.6 7.6 pau 7.6 2.5 13.7 4.3 0.7 6.5 57.4 7.2 sax 0.0 8.3 25.0 0.0 0.0 33.3 33.3 0.0 Table 4 Results of blind test showing classification rates of Sebastes by classifications, aur = S. auriculatus, ent = S. entomelas, fla = S = S. paucispinis, and sax = S. saxicola. species category. Bold numbers along the diagonal flavidus, goo = S. goodei, jor = S. jordani, mys = S ndicate correct mystinus, pau Actual Classified as: AUR ENT FLA GOO JOR MYS PAU SAX % Correct AUR 3 2 60% ENT 2 8 1 2 61% FLA 1 9 1 2 1 60% GOO 1 13 92% JOR 2 1 17 3 1 1 68% MYS 1 1 1 5 1 56% PAU 10 1 91% SAX 2 1 5 63% Literature cited Akkiran, N. 1985. A systematic study on Carangidae (Pisces) employing the otolith characters in the eastern Mediterranean. Bilj. Notes Inst. Oceanogr. Ribar., Split. 63:1-9. Brothers, E. B. 1984. Otolith Studies. In W. J. Richards, D. M. Cohen, M. P. Fahay, A. W. Kendall, and S. L. Richardson (eds.), On- togeny and systematics of fishes, p. 50-57. Spec. Publ. 1, Amer. Soc. Ich. Herp. Allen Press, Inc., Lawrence, KS. Eschmeyer, W. N., E. S. Herald, and H. Hammann. 1983. A field guide to Pacific coast fishes of North Amer- ica. Houghton Mifflin Co., Boston, MA, 336 p. Gago, F. J. 1993. Morphology of the saccular otoliths of six species of lanternfishes of the genus Symbolophorus (Pisces: Mycto- phidae). Bull. Mar. Sci. 52(3):949-960. Hecht, T-, and S. Appelbaum. 1 982. Morphology and taxonomic significance of the otoliths of some bathypelagic Anguilloidei and Saccopharyngoidei from the Sargasso Sea. Helgolander Meeresunters 35:301-308. Kendall, A. W., Jr. 1991. Systematics and identification of larvae and juveniles of the genus Sebastes. Environ. Biol. Fishes 30:173-190. Kendall, A. W., Jr., and W. H. Lenarz. 1987. Status of early life history studies of northeast Pa- cific rockfishes. In Proceedings of the international rock- fish symposium; October, 1986, Anchorage, Alaska, p. 99- 128. Univ. Alaska, Alaska Sea Grant Rep. 87-2. Laidig, T. W., and P. B. Adams (eds.). 1991. Methods used to identify pelagic juvenile rockfish (genus Sebastes) occurring along the coast of central California. U.S. Dep. Commer., NOAA Tech. Memo., NOAA-TM- NMFS-SWFSC-166, 180 p. NOTE Laidig and Ralston: Use of otolith characters in identifying larval Setosres spp. 171 Laidig, T. E., S. Ralston, and J. R. Bence. 1991. Dynamics of growth in the early life history of shortbelly rockfish, Sebastesjordani. Fish. Bull. 89:611-621. Laroche, W. A., and S. L. Richardson. 1980. Development and occurrence of larvae and juveniles of the rockfishes Sebastes flavidus and Sebastes melanops (Scorpaenidae) off Oregon. Fish. Bull. 77:901-923. McKern, J. L., H. F. Horton, and K. V. Koski. 1974. Development of steelhead trout (Salmo gairdneri) otoliths and their use for age analysis and for separating summer from winter races and wild from hatchery stocks. J. Fish. Res. Board Can. 31:1420-1426. 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. Morris, R. W. 1956. Early larvae of four species of rockfish, Sebastodes. Calif. Fish Game 42:149-153. 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 compara- tive notes on species of Sebastes and Helicolenus from other oceans. U.S. Dep. Commer., NOAATech. Rep. NMFS Circ. 402, 71 p. Moser, H. G., E. M. Sandknop, and D. A. Ambrose. 1985. Larvae and juveniles of aurora rockfish, Sebastes aurora, from off California and Baja California. In De- scriptions of early life history stages of selected fishes: the 3rd international symposium on the early life history of fishes and 8th annual larval conference, p. 55-64. Can. Tech. Rep. Fish. Aquat. Sci. 1359, 82 p. Neilson, J. D., G. H. Geen, and B. Chan. 1985. Variability in dimensions of salmonid otolith nuclei: implications for stock identification and microstructure interpretation. Fish. Bull. 83:81-89. Penney, R. W., and G. T. Evans. 1985. Growth histories of larval redfish {Sebastes spp. ) on an offshore Atlantic fishing bank determined by otolith incre- ment analysis. Can. J. Fish. Aquatic Sci. 42:1452-1464. Post uma. K. H. 1974. The nucleus of the herring otolith as a racial charac- ter. J. Cons. Cons. Int. Explor. Mer 35:121-129. Rybock, J. T., H. F. Horton, and J. L. Fessler. 1975. Use of otoliths to separate juvenile steelhead trout from juvenile rainbow trout. Fish. Bull. 73:654-659. Searle, S. R., F. M. Speed, and G. A Milliken. 1980. Population marginal means in the linear model: an alternative to least squares means. Am. Statistician 34:216-221. Seeb, L. W., and A. W. Kendall Jr. 1991. Allozyme polymorphism permit the identification of larval and juvenile rockfishes of the genus Sebastes. Environ. Biol. Fishes 30:191-201. Smith, M. K. 1992. Regional differences in otolith morphology of the deep slope red snapper Etelis carbunculus. Can. J. Fish. Aquat. Sci. 49:795-804. Stahl-Johnson, K. L. 1985. Descriptive characteristics of reared Sebastes caurinus and S. auriculatus larvae. In Descriptions of early life history stages of selected fishes: the 3rd interna- tional symposium on the early life history of fishes and 8th annual larval fish conference, p. 65-76. Can. Tech. Rep. Fish. Aquat. Sci. 1359. Stevenson, D. K., and S. E. Campana (eds.). 1992. Otolith microstructure examination and analysis. Can. Spec. Publ. Fish. Aquat. Sci. 117, 126 p. Victor, B. C. 1987. Growth, dispersal, and identification of planktonic labrid and pomacentrid reef-fish larvae in the eastern Pa- cific Ocean. Mar. Biol. 95:145-152. Wyllie Echeverria, T., W. H. Lenarz, and C. Reilly. 1990. Survey of the abundance and distribution of pelagic young-of-the-year rockfishes, Sebastes, off central California. U.S. Dep. Commer., NOAA NMFS Tech. Memo. NOAA-TM-NMFS-SWFC-147, 125 p. Changes in the spatial patchiness of Pacific mackerel. Scomber japonicus, larvae with increasing age and size Yasunobu Matsuura Instituto Oceanografico da Universidade de Sao Paulo Cidade Universitaria, Butantan, Sao Paulo 05508, Brasil Roger Hewitt Southwest Fisheries Science Center National Marine Fisheries Service, NOAA RO. Box 271, La Jolla, California 92038 terpreted in terms of species-spe- cific differences in life history traits such as adult reproductive behav- ior and larval feeding ecology, size, growth, and mortality (Smith, 1973; Hewitt, 1981; Koslow et al., 1985; McGurk, 1987). Insight into the function of patchiness may be im- proved by comparing how patchi- ness changes with age and size for species with different life histories. In this note, we present patchi- ness-at-age and patchiness-at-size curves for Pacific mackerel, Scom- ber japonicus, larvae and compare them with similar curves for other pelagic fish larvae. Several investigators have sug- gested that the spatial patchiness of fish eggs and larvae may be an important factor in the recruitment process (Smith, 1973; Lasker, 1978; Hewitt, 1981; Houde and Lovdal, 1985; McGurk, 1986). Patchiness has been linked to success in for- aging (Hewitt, 1981), ontogeny of schooling behavior (Hewitt, 1981), and predation mortality (McGurk, 1986, 1987). Contagion in the dis- persion of ichthyoplankton has been described for Pacific sardine, Sardinops sagax, eggs (Smith, 1973); northern anchovy, Engraulis mor- dax, and jack mackerel, Trachurus symmetricus, larvae (Hewitt, 1981); haddock, Melanogrammus aegle- finus, eggs (Koslow et al., 1985); sev- eral taxa found in Biscayne Bay including bay anchovy, Anchoa mitchilli, eggs and larvae (Houde and Lovdal, 1985); Atlantic herring, Clupea harengus harengus, larvae (Henri et al., 1985); Pacific herring, Clupea harengus pallasi, larvae (McGurk, 1987); bluefin tuna, Thun- nus maccoyii, larvae (Davis et al., 1990); Brazilian sardine, Sardinella brasiliensis, larvae; and scaled sar- dine, Harengula jaguana, larvae (Spach, 1990). The patchy distribution of fish eggs and larvae is initially intro- duced by the spawning behavior of adult fish. In order to guarantee successful fertilization in a pelagic environment, eggs must be laid when the adults are highly aggre- gated, and spawning and fertiliza- tion must occur almost simulta- neously (Hewitt, 1981). Alternately, demersal spawners may deposit their eggs in batches that incubate on a substrate before releasing a cohort of larvae into the pelagic environment (McGurk, 1987). Thereafter, eggs or hatching larvae, or both, disperse, principally in horizontal directions; distribution patterns during this period are pri- marily influenced by dispersal, dif- fusion, and transport (Smith, 1973). After a few days or weeks, larvae begin to reaggregate, an ac- tivity that becomes more evident in the juvenile stages of most school- ing pelagic fishes. Patchiness-at-age curves for sev- eral species of pelagic schooling fishes have been shown to exhibit a characteristic "U" shape: high initial patchiness, followed by a rapid decline as the eggs or newly hatched embryos, or both, passively disperse, followed by an increase in patchiness as the developing fish begin to aggregate in schools (Hewitt, 1981; McGurk, 1987; Spach, 1990). Patchiness-at-age curves for fish eggs and larvae have been in- Material and methods Data base The data used in this work came from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) ichthyoplankton data base. These data are available from the CalCOFI on-line data system (Anon., 1988). Details of station and ichthyoplankton data were published in a series of CalCOFI ichthy- oplankton data reports (NOAA Tech. Memo., NMFS, SWFSC, numbers 70-88, 92-100, and 102-105). Size- specific catches of Pacific mackerel larvae, collected from 1953 through 1981, were extracted and summa- rized for the analyses reported here. Pacific mackerel larvae were col- lected with 1-m ring nets from 1953 through 1975 and with bongo nets thereafter. Sampling methods and laboratory procedures were de- scribed by Kramer et al. (1972). Out of 23,963 CalCOFI stations sam- pled from 1953 to 1981, plankton samples from 1,011 stations con- tained at least one Pacific mackerel larva. The 1,011 stations where larva were collected were assumed to define the Pacific mackerel's Manuscript accepted 15 June 1994. Fishery Bulletin 93:172-178 (1995). 172 NOTE Matsuura and Hewitt: Changes in the spatial patchiness of Scomber japonicus 173 habitat, and these stations comprised the data set used in the analyses. Size-frequency analysis Frequency distributions of larval catches by size were assembled and a negative binomial model was fit to each distribution. The negative binomial has been used to describe aggregated distributions of ichthyo- plankton (Hewitt, 1981; Zweifel and Smith, 1981; Smith and Hewitt, 1985). The model is specified by the mean (m) and the index of dispersion (k); the variance (o2) is related to m and k as m + ■ m Lloyd's (1967) index of patchiness (P) was used to describe the intensity of the distribution pattern at various larval sizes where P=l + m m The index has been used by several investigators to describe ichthyoplankton patchiness (Smith, 1973; Hewitt, 1981; Houde and Lovdal, 1985; McGurk, 1987) and may be considered as a measure of how many times more crowded an average individual is relative to an individual in a population with the same mean density, but one which is randomly dis- persed. The index is independent of density and the scale of sampling (Pielou, 1977; Hewitt, 1982) which allows comparisons of patchiness between relatively abundant yolk-sac larvae and less abundant older larvae. By substituting the expression for the vari- ance of the negative binomial, P=l + 1 — ' k where k was estimated by using a maximum likeli- hood estimate expression (Bliss and Fisher, 1953; Smith and Hewitt, 1985). The standard error of the sample estimate of patchiness was estimated by fol- lowing Lloyd (1967): se (P),±4 2 Vvar(&)> where var(&) is the sampling variance of k. Adjusting for shrinkage and converting to age Initial size measurements were obtained from lar- vae preserved in 5% buffered formalin. Preserved size was converted to live size by using the shrinkage rate obtained for jack mackerel larvae from Theilacker (1980). To convert from larval size to larval age, we used the growth curve obtained from laboratory reared larvae with water temperature ranging from 16.8 to 19.2°C (Hunter and Kimbrell, 1980): t = In {SLI 3.4432) 0.05968 where t = age in days since hatching (= 0 age), and SL = standard length in live size (mm). The incuba- tion period (from spawn to hatch) was assumed to be 2.3 days. Results and discussion Frequency distributions of larval catches by size are presented in Table 1. The corresponding live sizes, ages, mean abundances per tow, and patchiness pa- rameters are also presented in Table 1. Larvae less than 3.5 mm in length appear to be undersampled in comparison to larger sizes. Pacific mackerel lar- vae grow rapidly through the first two size classes and therefore are vulnerable to capture for a rela- tively short period of time; small larvae are also more likely to be extruded through the meshes of the sam- pling net (Smith and Richardson, 1977). The change in patchiness with age suggests that re- cently hatched Pacific mackerel larvae were highly aggregated and dispersed rapidly until approximately five days after spawning (Fig. 1). Patchiness gradually increased with age until 9.2 days, then decreased slightly and continued to increase with age thereafter. Morphological and behavioral changes of develop- ing Pacific mackerel larvae are summarized in Table 2 and illustrated in Figure 2. Afunctional visual sen- sory organ is formed in Pacific mackerel larvae at 6.0-6.5 mm and completed at approximately 8 mm.1 Although caudal and pectoral fins begin development at 3.5 mm, swimming speed increases rapidly with size only after the pelvic, anal, and dorsal fins are formed at approximately 9.6 mm (Watanabe, 1970; Hunter and Kimbrell, 1980). Hunter and Kimbrell (1980) reported that schooling behavior did not be- gin until 14 mm, although an increase in patchiness at 4.6 mm is apparent from the plankton catches. It may be that the ontogeny of schooling behavior in Pacific mackerel involves a prolonged period of con- tact between larvae that is necessary for the success- ful integration of approach- withdraw and approach- orient behaviors (Shaw, 1960, 1970; Williams and Shaw, 1971). This phenomenon may be statistically recognizable as an increase in patchiness but not visually recognizable as coordinated social behavior. 1 O'Connell, C. Southwest Fisheries Science Center, Nat. Mar. Fish. Serv., NOAA, P.O. Box 271, La Jolla, California. 174 Fishery Bulletin 93(1). 1995 Table 1 Size-specific catch statistics for Scomber japonicus larvae collected during CalCOFI surveys from 1953 through 1981. \ total of 8,396 larvae were caught at 1,011 stations out of a total of 23,963 CalCOFI stations Preserved size (mm Live size (mm) Catch Age since spawn (days) 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.75 6.75 7.75 8.75 9.75 3.10 3.30 3.50 4.00 4.60 5.20 5.70 6.50 7.70 8.50 9.60 10.70 2.3 3.0 3.3 5.0 7.2 9.2 10.7 13.0 15.7 17.5 19.5 21.3 Number of larvae/sample 0 825 671 571 698 774 806 849 836 908 970 980 995 1 93 149 195 143 112 113 90 99 80 26 28 13 2 34 66 81 63 56 35 34 39 9 10 2 2 3-4 28 42 70 52 36 29 23 17 5 3 1 1 5-8 18 31 42 29 18 16 11 15 6 2 0 0 9-16 5 30 27 15 11 8 3 4 2 0 0 0 17-32 4 15 14 10 2 2 1 1 1 0 0 0 33-64 3 4 5 1 1 2 0 0 0 0 0 0 65-128 1 2 4 0 1 0 0 0 0 0 0 0 129-256 0 1 2 0 0 0 0 0 0 0 0 0 Total larvae 709 1,823 2,334 1,088 762 762 350 400 193 67 36 21 Number of samples 1,011 1,011 1,011 1,011 1,011 1,011 1,011 1,011 1,011 1,011 1,011 1,011 Mean per sample 0.701 1.803 2.309 1.076 0.754 0.754 0.346 0.396 0.191 0.066 0.036 0.021 Variance 13.101 67.540 97.629 10.823 13.885 7.421 1.415 1.936 0.933 0.155 0.050 0.036 k 0.092 0.152 0.209 0.189 0.140 0.102 0.139 0.139 0.097 0.048 0.106 0.030 Patchiness 11.91 7.57 5.79 6.30 8.15 10.76 8.21 8.19 11.33 21.98 10.42 34.28 SE (patchiness) 1.09 0.48 0.32 0.44 0.67 0.94 0.91 0.86 1.71 18.42 4.54 39.78 70 60 50 in » 40 c 1 30 0- : l / i 20 10 %*r~^Z^ i / A rrachurus symmetricus icomber japonicus — e— . -^^^ 0 ^B^_^___-*--- _ ( > 5 10 15 20 25 30 35 4 Time since spawn (days) 0 Figure 1 Lloyd's index of patchiness as a function of larval age for Scomber japonicus and Trachurus symmetricus in the California Current region. NOTE Matsuura and Hewitt: Changes in the spatial patchiness of Scomber japonicus 75 5.7mm 8.5mm 18.1mm Figure 2 Developmental stages of Scomber japonicus larvae (from Matarese et al. 1989). Sizes shown are estimated live sizes. Table 2 Behavioral and morphological changes in developing Scomber japonicus larvae. Measurements Live size 3.1 3.3 3.5 4.0 4.6 5.2 5.7 6.5 7.7 8.5 9.6 10.7 11.8 12.9 14.0 15.1 16.2 17.3 Swimming speed (cm/sec)' 0.4 0.6 0.7 0.9 1.0 1.3 1.8 2.1 2.6 3.1 3.7 4.4 5.0 5.7 6.5 7.3 Cannibalism' Schooling' Patchiness sibling cannibalism between 8 and 15 mm oriented 11.9 7.6 5.8 6.3 8.2 10.8 8.2 8.2 11.3 22.0 10.4 34.3 swimming Feeding ability2 Mouth opening and yolk absorption at 4 mm Fin formation2 CF, PF at 3.5 mm PvF, AF, DF at 9.6 mm Visual sensory organ3 developed between 6.5 and 7.7 mm 1 Hunter and Kimbrell (1980). 2 Watanabe (1970); CF = caudal fin, PF = pectoral fin, PvF = pelvic fin, AF = anal fin, DF = dorsal fin. 3 O'Connell (unpub. data). 176 Fishery Bulletin 93(1). 1995 Patchiness-at-age curves for six species (Engraulis mordax and Trachurus symmetricus, Hewitt, 1981; Clupea harengus pallasi, McGurk, 1987; Sardinella brasiliensis and Harengula jaguana, Spach, 1990; and Scomber japonicus, reported here) describe a similar sequence: a high index is observed at the youngest larval ages, a low index is observed at one or two weeks after spawn, and thereafter the index increases suggesting the onset of schooling behavior (Fig. 3). The highest index of patchiness at early lar- val age was observed for S. brasiliensis (P=14.5). This can be attributed to intensive spawning behavior of adult sardine, short incubation time (Matsuura, 1983), and fast larval growth (Yoneda, 1987) rela- tive to the other species. The lowest index of patchi- ness was observed for C. harengus pallasi (P=3.5) collected in a small inlet on the west coast of Vancouver Island, British Columbia; McGurk (1987) noted that this may be a reflection-dispersed prey. Houde and Lovdal (1985) reported that fish larvae in Biscayne Bay, Florida, were only slightly more patchy (P=1.3) than their prey, which was abundant and not aggregated (P=1.06). Henri et al. (1985) also Time since spawn (days) Figure 3 Patchiness-at-age curves for three species from the California Current (Engraulis mordax, Trachurus symmetricus, and Scomber japonicus), two species from southern Brazil (Sardinella brasiliensis and Harengula jaguana), and one species from British Columbia (Clupea harengus pallasi). reported low patchiness values (P=1.63-3.52) for Clupea harengus harengus larvae collected in the St. Lawrence estuary, Quebec. Hewitt (1981) discussed differences in patchiness-at-age curves forE. mordax and T. symmetricus in terms of their prey availabil- ity and foraging strategies. In contrast to T. sym- metricus, E. mordax exhibited an initial high degree of patchiness and slowly dispersed before showing a rapid increase in patchiness at about 18 days of age. Trachurus symmetricus larvae were approximately 1/10 as abundant, exhibited lower initial patchiness, and achieved maximum dispersion at an earlier age. E. mordax depend on small, but abundant, prey; they have poorly developed swimming capabilities and can effectively forage only through a small volume of water. In contrast, T. symmetricus depend on large, but rare, prey items; they have well-developed swim- ming capabilities and are able to search through rela- tively large volumes of water. In comparison to the four clupeoid species, the in- crease in patchiness was observed to occur at an early age for both S. japonicus and T. symmetricus. Scom- ber japonicus and T. symmetricus larvae share simi- lar morphologies and life his- tory traits. Hunter and Kimbrell (1980) noted that Pacific mackerel larvae may be characterized as having fast growth, rapid swimming abilities, high metabolism, a dependence on increasingly larger prey, and a tendency for cannibalism. Sibling can- nibalism may be an impor- tant survival strategy for mackerel larvae, where larger individuals prey on smaller ones. Grave (1981) reported that by the time Atlantic mackerel, Scomber scombrus, larvae were 12 mm long, 83% of the food items in their diet were other mack- erel larvae. High initial dis- persal, followed by aggrega- tion of similar-sized larvae may be mechanisms for re- ducing sibling cannibalism. Although the patchiness-at- age curves for S. japonicus and T. symmetricus are dis- tinct (Fig. 1), the patchiness- at-size curves are almost co- incident (Fig. 4), suggesting that change in patchiness Scomber japonicus Trachurus symmetricus Engraulus mordax Clupea harengus pallasi Sardinella brasiliensis Harengula jaguana NOTE Matsuura and Hewitt: Changes in the spatial patchiness of Scomber japonicus 77 may be a size-dependent phenomenon!. Acknowledgments The senior author received a research fellowship from the Coordenacao de Aperfei- coamento de Pessoal de m'vel Superior (CAPES) dur- ing his stay at the Southwest Fisheries Science Center in La Jolla, where this publi- cation was prepared. This study, like many others on the ecology offish larvae in the California Current, was inspired and encouraged by the late Reuben Lasker. 60 50 Cfl 40 e 30 20 10 -Sb^-5**^ J > — e — Scomber japonicus Trachurus symmetricus \ N 0 ^^***i*^ _L 2 3 4 5 6 7 8 9 10 11 12 Live size (mm) Figure 4 Lloyd's index of patchiness as a function of larval size for Scomber japonicus and Trachurus symmetricus. Literature cited Anon. 1988. CalCOFI on-line data system, user's manual. NOAA, SWFSC, La Jolla, p. 1-9. Bliss, C. I., and R. A. Fisher. 1953. Fitting the negative binomial to biological data and a note on the efficient fitting of the negative binomial. Biometrics 9:176-200. Davis, T. L. O., G. P. Jenkins, and J. W. Young. 1990. Patterns of horizontal distribution of the larvae of southern bluefin (Thunnus maccoyii) and other tuna in the Indian Ocean. J. Plankton Res. 12(6):1295-1314. Grave, H. 1981. Food and feeding of mackerel larvae and early juve- niles in the North Sea. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:454-459. Henri, M., J. J. Dodson, and H. Powles. 1985. Spatial configurations of young herring iClupea harengus harengus) larvae in the St. Lawrence estuary: importance of biological and physical factors. Can. J. Fish. Aquat. Sci. 42 (Suppl. 1):91-104. Hewitt, R. P. 1981. The value of pattern in the distribution of young fish. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:229-236. 1982. Spatial pattern and survival of anchovy larvae: impli- cations of adult reproductive strategy. Ph.D. diss., Scripps Institution of Oceanography, Univ. Calif., San Diego. Houde, E. 1).. and J. D. A. Lovdal. 1985. Patterns of variability in ichthyoplankton occurrence and abundance in Biscayne Bay, Florida. Estuarine Coastal Shelf Sci. 20:79-103. Hunter, J. R., and C. A. Kimbrell. 1980. Early life history of Pacific mackerel, Scomber japonicus. Fish. Bull. 78:89-101. Koslow, J. A., S. Brault, J. Dugas, and F. Page. 1985. Anatomy of an apparent year class failure: the early life history of the Browns Bank haddock Melanogrammus aeglefinus. Trans. Am. Fish. Soc. 114:478-489. Kramer, D., M. Kalin, E. Stevens, J. Thrailkill, and J. Zweifel. 1972. Collecting and processing data on fish eggs and lar- vae in the California Current region. U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circ. 370:1-38. Lasker, R. 1978. The relation between oceanographic conditions and larval anchovy food in the California current: identifica- tion of factors contributing to recruitment failure. Rapp. P.-V Reun. Cons. Int. Explor. Mer 173:212-230. Lloyd, M. 1967. Mean crowding. J. Anim.Ecol. 36:1-30. Matarese, A. C, A. W. Kendall Jr., D. M. Blood, and B. M. Vinter. 1989. Laboratory guide to early life history stages of north- east Pacific fishes. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 80, 652 p. Matsuura, Y. 1983. Estudo comparativo das fases iniciais do ciclo de vida da sardinha-verdadeira, Sardinella brasiliensis, e da sardinha-cascuda. Harengula jaguana , (Pisces: Clupeidae) e nota sobre a dinamica da populacao da sardinha-verda- deira na regiao sudeste do Brasil. Assoc. Professorship thesis, Univ. Sao Paulo. McGurk, M. D. 1986. Natural mortality of marine pelagic fish eggs and larvae: role of spatial patchiness. Mar. Ecol. Prog. Ser. 34: 227-242. 1987. The spatial patchiness of Pacific herring larvae. Environ. Biol. Fish. 20(21:81-89. Pielou, E. C. 1977. Mathematical ecology. J. Wiley and Sons, New York, 385 p. Shaw, E. 1960. The development of schooling behavior in fishes. Physiol. Zoo. 33(2):79-86. 1970. Schooling in fishes: critique and review. In L. R. Aronson et al. (ed.), Development and evolution of behav- ior: essays in memory of T. C. Schneirla, p. 452^180. Free- man, San Francisco. 178 Fishery Bulletin 93(1). 1995 Smith, P. E. 1973. The mortality and dispersal of sardine eggs and larvae. Rapp. P.-V. Reun. Cons. Int. Perm. Explor. Mer 164: 282-292. Smith, P. E., and S. L. Richardson. 1977. Standard techniques for pelagic fish egg and larva surveys. FAO Fish. Tech. Pap. 175, 100 p. Smith, P. E., and R. P. Hewitt. 1985. Anchovy egg dispersal and mortality as inferred from close-internal observations. CalCOFI Rep. 26:97-110. Spach, H. L. 1990. Estudo comparativo da distribuicao espaco-temporal e de padroes de agregacao de ovos e larvas de Harengula jaguana, Sardinella brasiliensis (Clupeidae: Osteichthyes) eEngraulis anchoita (Engraulidae: Osteiththyes) na costa sudeste do Brasil. Ph. D. diss., Univ. Sao Paulo. Theilacker, G. H. 1980. Changes in body measurements of larval northern anchovy, Engraulis mordax, and other fishes due to han- dling and preservation. Fish. Bull. 78:685-692. Watanabe, T. 1970. Morphology and ecology of early stages of lfe in Japa- nese common mackerel, Scomber japonicus Houttuyn, with special reference to fluctuation of population. Bull. Tokai Reg. Fish. Res. Lab. 62:1-283. Williams, M. M ., and E. Shaw. 1971. Modifiability of schooling behavior of fishes: the role of early experience. Am. Mus. Novit. 2448:1-18. Yoneda, N. T. 1987. Criacao em laboraterio de larvas da sardinha-verda- deira, Sardinella brasiliensis e estudo dos incrementos diarios nos otolites. M.S. thesis, Univ. Sao Paulo. Zweifel, J. R., and P. E. Smith. 1981. Estimates of abundance and mortality of larval an- chovies (1951-75): application of a new method. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:248-259. Growth and morphology of larval and juvenile captive bred yellowtail snapper, Ocyurus chrysurus* Cecilia M. Riley G. Joan Holt Connie R. Arnold Marine Science Institute The University of Texas at Austin RO. Box 1267, Port Aransas, Texas 78373 The snappers (Lutjanidae) are ma- jor components of the reef fish fish- ery in the Gulf of Mexico (Naka- mura, 1976), and recent declines in their populations have prompted interest in a number of manage- ment practices including limited catches, size limits, area closures, and additions of artificial reef habi- tat to improve survival of wild stocks (Leis, 1987; Munro, 1987). Studies on the spawning, distribu- tion, larval and juvenile ecology, and stock assessment of new re- cruits are crucial to the develop- ment of management strategies for reef species since little is known about their early life history (Grimes, 1987). During most devel- opmental stages, snapper larvae are pelagic and widely dispersed, limiting the numbers of specimens to be found in taxonomic collections (Munro, 1987). The similarity in size and pigmentation of small lar- val lutjanids (<5 mm) and the pau- city of species-specific details of size at age and morphological develop- ment has made identification of in- dividuals in ichthyoplankton samples difficult (Leis, 1987). Of the fourteen species of snappers that are found in the Gulf of Mexico,1 larval development has been fully described for only three species: red snapper, Lutjanus campechanus , from both laboratory spawned (Rabalais et al., 1980) and wild caught larvae (Collins et al., 1980); gray snapper, L. griseus, from wild eggs reared in the labora- tory (Richards and Saksena, 1980); and vermilion snapper, Rhomboplites aurorubens, from wild preserved specimens (Laroche, 1977). A recent NOAA report by Richards et al.2 summarizes the larval lutjanid de- scriptions listed above and intro- duces some newly available descrip- tive material for several additional species of snappers including some stages of yellowtail snapper, Ocyurus chrysurus. In their report, the yellow- tail snapper is included in the genus Lutjanus, a change suggested as a result of two recent treatments by Loftus ( 1992) and Domeier and Clark (1992). The commercial and recreational importance of snappers has also been recognized by the aquaculture industry, and efforts are underway to culture several of these species in captivity. In this paper we de- scribe the development and growth of laboratory spawned and reared yellowtail snapper. This species is found from Massachusetts through the Caribbean and south to Brazil (Hoese and Moore, 1977). Labora- tory culture allowed us to document growth and development of the critical larval and juvenile stages of yellowtail snapper that will aid identification and ageing of larval snappers collected in the field. We have also included information on the effects of a commonly used pre- servative (ethyl alcohol) on length measurements and pigmentation characteristics of laboratory-cul- tured larvae for purposes of compara- tive use with wild-collected larvae. Materials and methods Young adult Ocyurus chrysurus were collected by hook and line in July 1990 from the Florida Keys and were transported to the laboratory where they were matured and cycled for one year following the methods described by Arnold (1988). Adults began spawning in July 1991 and contin- ued to March 1994. Eggs were stocked at a density of 50/L in fiberglass tanks (300 and 600 L) with internal biofilters. Lar- vae were reared at 27-28°C with 12 hours light at salinities of 33-38 ppt on a diet of zooplankton (col- lected from the Corpus Christi Ship Channel), rotifers (Branchionus plicatilis) and brine shrimp nauplii (Artemia salina). The description of larval devel- opment is based on larvae from multiple spawns of two different groups of broodstock (15 adults/ tank). Larvae were measured live (SL=tip of snout to posterior tip of notochord) to the nearest 0.01 mm on a stereomicroscope equipped with a drawing tube and digitizing * Contribution 907 of the Marine Science Institute, University of Texas at Austin. 1 Lyczkowski-Shultz, J., and B. H. Comyns. 1992. Early life history of snappers in coastal and shelf waters of the northcentral Gulf of Mexico (late summer/ fall months, 1983-1989). Final Rep. to MARFIN, NA90AA-H-MF730. 2 Richards, W. J., K. C. Lindeman, J. L. Shultz, J. M. Leis, A. Ropke, M. E. Clark, and B. H. Comyns. 1994. Preliminary guide to the identification of the early life history stages of lutjanid fishes of the western central Atlantic. U.S. Dep. Commer., NOAA Tech. Memo. NMFS- SEFSC-345, 49 p. Manuscript accepted 29 August 1994. Fishery Bulletin 93:179-185 (1995). 179 180 Fishery Bulletin 93(1). 1995 pad. Drawings were made with a dissecting scope and camera lucida attachment of live, anesthetized larvae before they were preserved in 80% ethyl alco- hol (ETOH). To determine laboratory shrinkage rates, the larvae were remeasured after at least one month in ETOH, and preserved lengths were com- pared to those of the previous, live measurements. Since larvae were drawn from living specimens, no staining or special preparations were required for observation of spines, rays, or other details of morphology. Results Pigmentation and overall development Daily measurements and developmental milestones are presented in Table 1. The pelagic eggs were spherical, averaged 0.96 mm diameter, had a single oil globule, and hatched in 22-24 hours at 27°C. Eggs were essentially transparent, the only pigment ob- served was a series of small chromatophores on the dorsal surface of the embryo (Fig. 1A). After hatch- Figure 1 Early developmental stages of yellowtail snapper, Ocyurus chrysurus, illustrated from live specimens. (A) late embryo egg, 0.96 mm diameter; (B) 2.23 mm SL newly hatched larva; (C) 3.36 mm, 3 days posthatch. Dark arrows indicate location of yel- low chromatophore. ing and through the two day yolk-sac stage, larvae possessed a single unpigmented oil globule in the anterior end of the yolk-sac, an unpigmented finfold, and 24 myomeres. Within 12 hours after hatching (Fig. IB), the dorsal chromatophores of the embryo had migrated to form a series along the ventral sur- face of the body and tail; a single stellate chromato- phore was present on the gut anterior to the anus, and a light scattering of dark pigment was found on the yolk-sac and lateral surfaces of the head. Exog- enous feeding coincided with development of eye pig- mentation, functional jaws, and gas bladder infla- tion at 3.36 mm (age 3 days, Fig. 1C). Pigmentation at this stage included a large dark chromatophore on the ventral surface of the gut, four chromatophores over the dorsal surface of the gut and gas bladder, and a single, dark chromatophore on the ventral tip of the notochord. In live specimens at this stage, we first observed the development of a yellow chromato- phore (indicated by arrow on Fig. 1C) located on the lateral surface of the body at about midgut. Larvae 3.67-3.82 mm (Fig. 2A) showed dramatic develop- mental changes. The development of numerous yel- low chromatophores (indicated on illustrations by solid arrows) scattered on the lateral surfaces of the head, gut, and upper body near the base of the pectoral fin, as well as dark stellate chro- matophores on the hindbrain and on the ven- tral edge of the cleithrum coincided with erup- tion of the pelvic fin buds and the appearance of preopercular spination. Larvae 4. 10^.53 mm (Fig. 2, B-D) were characterized by daily in- creases in the number of dorsal spines and by elongation of the pelvic fins, as well as by an increase in the density of yellow chromato- phores on the lateral head region. Notochord flexion occurred when larvae reached 4.40 mm at 15-16 days posthatch (Fig. 3A) and was fol- lowed by full fin formation. Changes in pigmen- tation consisted primarily of increasingly dense concentrations of yellow pigment on the lateral upper body and head, dark web-like pigment in the membranes of developing fins, and dif- fuse internal pigment over the gut surface (Fig. 3B). The first indication of adult coloration was visible on early juveniles approximately 14.00 mm SL (Fig. 3C) where yellow chromatophores formed a horizontal line through the eye onto the snout and were also interspersed with the dark chro- matophores lining the dorsal and ventral mar- gins of the body at the fin bases. Yellow pigment was also present along the lateral midline of the tail. Near-adult pigmentation was present by 16.00 mm (age 62 days) at which time juveniles were fully scaled (Fig. 3D). NOTE Riley et al. : Growth and morphology of captive Ocyurus chrysurus Figure 2 Developmental stages and mean live lengths of yellowtail snapper. Dark arrows indi- cate location of yellow chromatophores. (A) 3.67-3.82 mm SL, days 7-9 posthatch; (B) 4.10-4.53 mm SL, days 10-11 posthatch; (C) 4.51 mm SL, day 12 posthatch; (D) 4.11 mm SL, day 13 posthatch. Head spination One or two paired, smooth spines on the posterior edge of the preoperculum first occurred in larvae 3.67-3.82 mm (Fig. 2A). Preopercular spination in- creased to four and a supraocular ridge with one spine was present at 4.10 mm (Fig. 2B). At 4.50 mm (Fig. 2C), 5 or 6 elongated preopercular spines were present, the longest of which occurred at the preopercal angle. Larvae at 4.80 mm and 16 days of age (Fig. 3A) had a fully formed supraocular ridge with 4 short, smooth spines and 3 supracleithral spines. A reduction in the length of all head spines began at approximately 6.00 mm, but some short, opercular spines remained on the oldest juveniles. Fin formation The adult meristic complement of O. chrysurus is X+12-14 dorsal, 9 + 8 caudal, I + 5 pelvic, III + 8-9 anal, and 15 or 16 pectoral (Hoese and Moore, 1977). In laboratory-reared larvae, fin development oc- 182 Fishery Bulletin 93(1). 1995 curred in the following sequence: pel- vic and dorsal spines, caudal, dorsal and anal soft rays, pectoral rays (Table 1). The spinous pelvic and dorsal fin for- mation occurred simultaneously at 4. 10 mm. Dorsal and anal fin analage were first visible at 4.51 mm and ray bases were fully formed by 5.35 mm. Caudal flexion and caudal ray formation oc- curred in larvae between 4.40 and 4.75 mm and was followed by development of the soft rays of the dorsal and anal fins (Fig. 3A); additionally, the spines of the dorsal and pelvic fins were strongly serrated. By 6.23 mm SL, all juveniles had the full adult complement of fin spines and rays (Fig. 3B); however, serrated spines, characteristic of larvae, were still present on juveniles 14.66 mm. Growth and shrinkage Laboratory-reared yellowtail snapper showed large variation in size among larvae of the same age (Table 1), and key developmental events were tightly linked to larval size more than to age. Growth rates prior to flexion averaged 0.31 mm/day and decreased to only 0.18 mm/day during the process of transfor- mation to juveniles (4.83-7.00 mm SL, ages 14-28 days). During the last month and a half of recorded development, ju- venile growth averaged 0.25 mm/day. Mean daily lengths of postpreser- vation larvae are listed on Table 1. Shrinkage after preservation was great- est in larvae prior to any fin develop- ment (<4.00 mm), averaging 10.36% through the first 13 days. Larvae with partial fin development (4.83-5.72 mm SL) shrank an average of 9.32%. Once larvae attained complete development of the dorsal and pelvic fins (>5.00 mm); shrinkage was reduced to an average of 7.24% throughout the remaining ju- venile stages examined. Figure 3 Late developmental stages and mean lengths of yellowtail snapper. Dark arrows indicate location of yellow chromatophores. (A) 4.64-4.80 mm SL, days 15-16; (B) 6.23-6.73 mm SL, days 18-28; (C) 14.66 mm SL, day 31, drawn from preserved specimen; (D) 16.05 mm SL, day 62, from preserved specimen. Discussion Ocyurus chrysurus have similar larval characteris- tics to the previously described snappers Lutjanus campechanus (Collins et al., 1980), L. griseus (Richards and Saksena, 1980), and Rhomboplites aurorubens (Laroche, 1977). Preflexion larvae of each of the four species have a series of chromatophores along the ventral midline and have pigment cover- ing the dorsum of the gut and gas bladder. All have NOTE Riley et al.: Growth and morphology of captive Ocyurus chrysurus 183 a CO co ►J do c cd co c 3 * 72 co S co ~ CO •- - cu 2 -° I | "8 c ° ii u C co TJ * — CO w •c « •o & c to co c CO II " NH to z CO a> Pm T3 „ £co I j DO cu cu I* 3 X J= J= J3 X J3 -C X X J2 J3 X X J= i bo bo 00 bo bo bo bo bo bo bo bo bo bo bn X 1 CO co CO CO CO CO CO a CO co 00 CO cd crt cu u u frH u ki L. u fc. u u u ■*-» -u +1 -*-> -*-> -t-> -4J +-> CO CO CO CO CO CO CO CO CO CO to m CO CO CO >> en o o O O O O O o O o o o o o o OS « c a - cd a x cd CO cd o. DO Q DO d a 3 M cd CD 3 o o o o o o o o o o o d 05 d CM o CO 05 05 Si q CM X CN CM d o o LO CO 05 O CO CM t-H rt ,-H CO co co re ct; it in d CO CO 00 CO X CO ~ - — j ~. ~ > o: ~ r z ~ 000000000000505050)050! OOOOOCOCOCOCOCOCO o o o o o O O O CO CO CO LO lo LO CO CO CO I CO Tf 05 CO o t- LO CM CN d d CN 05 co CO co CN CM X CO co CO CO t-H o CO CO CO CO CN 00 CN CO LO LO CN CO o o o o o o o o •-1 ^ T-H CO CO C~ c~ o 05 LO CO CO CO LO o LO 05 r-i la - CO CO o CO i-H LO LO CO d d 05 LO LO r-4 LO d 05 CO co i— i 0- CO o oc CN CN d CO CN CO t-< O) CO d CO CM CO co i-i CM CO •-< CO o CO CM CD LO CM 05 CO CO CN o CM CO CM It CO ■M O O X ■z ,_, CM CO ■* LO CO C~ co 2 l X CO co CM 05 CM CN CO •<* oo CO CO CO T-H LO o CN LO CD LO co -* co 00 CM CO CO CO r~ co CO CO Tj- It It t LO LO LO LO LO CD C~ CO 05 ■* t~ N CM CO CO 00 LO It 05 LO CO CO o LO LO 05 o 00 o o CO T-H CO X CO o X X CO CO CO CO CO CO CO CO CO CO CO CO LO rt LO LO t» ^r 184 Fishery Bulletin 93(1). 1995 large solitary chromatophores on the cleithral sym- physis, gut ventrum, anus, and on the notochord at the point of flexure, and all undergo flexion within a narrow size range of 4.2-5.2 mm SL. There are, however, a few distinctive characteris- tics that can be used to separate the larvae of these species. Immediately following flexion at 4.40 mm, larvae of O. chrysurus andi?. aurorubens (flexion at 4.7 mm, Laroche, 1977) possess large serrations on both the anterior and posterior margins of the dor- sal spines, but these are not present on larvae of L. campechanus (Collins et al., 1980) or L. griseus (Richards and Saksena, 1980). Preopercular spina- tion is also a useful character in that the longest spine (located at the preopercle angle in each described species) is serrated in R. aurorubens but not in L. campechanus, L. griseus (Laroche, 1977), or O. chrysurus (present study). Lyczkowski-Shultz and Comyns1 compared small, preserved larval R. aurorubens and L. campechanus , and found that both species had two dorsal spines and 4 or 5 preopercular spines at 3.3 to 3.9 mm SL. Yellowtail snapper differ in having fewer or no dorsal spines and only three preopercular spines at the same preserved sizes (cor- responding to days 7-11, Fig. 2, Aand B). Lyczkowski- Shultz and Comyns1 also examined pigmentation differences in <4.0 mm larvae and identified a char- acteristic pigment spot in R. aurorubens located on the branchial chamber and visible through the oper- culum; they also observed pigment on the anterior surface of the gut (at the level of the pectoral fin base) inL. campechanus. Larval O. chrysurus of the same size range were devoid of pigment in either of these locations. Larval R. aurorubens (Laroche, 1977) had numerous, dark chromatophores located on both the midbrain and hindbrain regions in all sizes of larvae examined, however, the two species of Lutjanus and O. chrysurus had head pigment only on the hindbrain area. The yellow chromatophores found on live or recently preserved specimens of O. chrysurus are definitive characteristics for identification of this species; unfortunately, this light-colored pigment was not visible after the 30-day preservation period in larvae <7.00 mm SL and would not likely be detected in ichthyoplankton samples preserved in ETOH. The yellow chromatophores were faintly visible on the snout, operculum, and lateral line of the larger pre- served individuals. Larval O. chrysurus can be dis- tinguished from the other described lutjanid species by utilizing combinations of the above characteris- tics including the presence of heavy serrations on both the anterior and posterior margins of the dor- sal spines at the time of flexion, lack of serrations on the longest preopercle spine, reduced number of preopercle spines and dorsal spines at comparable sizes, and lack of internal pigment on the anterior surface of the gut or branchial chamber. Newly hatched and early developmental stages of larval fishes are rarely collected or retained in net samples.3 Those larvae that are collected show sig- nificant handling effects (Theilacker, 1980; Hay, 1981; McGurk, 1985), including distortion and size reduc- tion that result in less than optimal depictions of size at critical stages of development. In contrast, labo- ratory-reared specimens provide more realistic size values and information on age and pigmentation not available to studies with field-caught larvae. The shrinkage rates at each age and phase of morpho- logical development in O. chrysurus are conserva- tive measures because field-collected larvae show additional shrinkage from net damage. In small unossified larvae, reduction in SL as a result of net collection alone increased shrinkage rates of labora- tory-preserved northern anchovy by 19% (Theilacker, 1980) and in Pacific herring by about 8% (Hay, 1981). From these results it is clear that some additional allowance for net shrinkage should be applied to the laboratory-preserved lengths of O. chrysurus when compared to those of field-caught individuals; how- ever, shrinkage rates may be variable between spe- cies; therefore the value to be used is unclear. Shrink- age rates have been shown to decrease with increas- ing age and size of larvae (Theilacker, 1980; McGurk, 1985) and to become equivalent to that of larvae ex- posed to laboratory handling only (e.g. no net dam- age) once larvae are completely ossified. Shrinkage rates of laboratory O. chrysurus also decreased in postflexion larvae, stabilizing at <10% in early juve- niles. Therefore, to make predictions regarding the live size or age of field-collected larval snappers, an additional, though unknown, rate of shrinkage due to net damage should be taken into account in preflexion stages but not in postlarvae and juveniles. The nomenclatural status of the yellowtail snap- per has come under review recently. After describing the morphology of the natural hybrid between O. chrysurus and Lutjanus synagris (Loftus, 1992) and the laboratory-produced hybrids of O. chrysurus and L. synagris (Domeier and Clarke, 1992), the authors of these studies concluded that the morphological and meristic data indicated that Ocyurus is probably not a distinct genus from Lutjanus. The larval morphol- ogy described in this study of O. chrysurus also con- firms the very similar size and developmental char- acteristics of this species with the previously de- scribed members of the genus Lutjanus. 3 Lyczkowski-Shultz, J. Southeast Fish. Sci. Cent. NOAA, NMFS, Pascagoula, MS. Personal commun., Jan. 1994. NOTE Riley et al.: Growth and morphology of captive Ocyurus chrysurus 185 Acknowledgments We would like to thank Joanne Lyczkowski-Shultz and Scott Holt for their comments and suggestions on the original draft of this manuscript. This work was funded in part by Grant NA16RGO457-03 from the National Oceanic and Atmospheric Administra- tion through the Texas Sea Grant College Program. Literature cited Arnold, C. R. 1988. Controlled year-round spawning of red drum Sciaenops ocellatus in captivity. Contrib. Mar. Sci. (Suppl.) 30:65-70. Collins, L. A., J. H. Finucane, and L. E. Barger. 1980. Description of larval and juvenile red snapper, Lutjanus campechanus. Fish. Bull. 77:965-974. Domeier, M. L., and M. E. Clark. 1992. A laboratory produced hybrid between Lutjanus synagris and Ocyurus chrysurus and a probable hybrid between L. griseus and O. chrysurus (Perciformes: Lutjanidae). Bull. Mar. Sci. 50:501-507. Grimes, C. B. 1987. Reproductive biology of the Lutjanidae: a review. In J. Polovina and S. Ralston (eds.), Tropical snappers and groupers: biology and fisheries management, p. 230- 294. Westview Press, Boulder, Colorado. Hay, D. E. 1981. Effects of capture and fixation on gut contents and body size of Pacific herring larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:395-400. Hoese, H. D., and R. H. Moore. 1977. Fishes of the Gulf of Mexico, Texas, Louisiana, and adja- cent waters. Texas A&M Univ. Press, College Station, 327 p. Laroche, W. A. 1977. Description of larval and early juvenile vermilion snap- per, Rhomboplites aurorubens. Fish. Bull. 75:547-554. Leis, J. M. 1987. Review of the early life history of tropical groupers (Serranidae) and snappers (Lutjanidae). In J. Polovina and S. Ralston (eds.), Tropical snappers and groupers: bi- ology and fisheries management, p. 189-237. Westview Press, Boulder, CO. Loft us, W. F. 1992. Lutjanus ambiguus (Poey), a natural intergeneric hybrid of Ocyurus chrysurus (Bloch) and Lutjanus synagris (Linnaeus). Bull. Mar. Sci. 50:489-499. McGurk, M. D. 1985. Effects of net capture on the postpreservation mor- phometry, dry weight, and condition factor of Pacific her- ring larvae. Trans. Am. Fish. Soc. 114:348-355. Munro, J. L. 1987. Workshop synthesis and directions for future research. In J. Polovina and S. Ralston (eds), Tropical snappers and groupers: biology and fisheries management, p. 639-659. Westview Press, Boulder, Colorado. Nakamura, F. I. 1976. Recreational fisheries for snappers and groupers in the Gulf of Mexico. In H. R. Bullis Jr. and A. C. Jones (eds.), Proceedings of the colloquium on snapper-grouper fish- ery resources of the western central Atlantic Ocean, p. 77- 85. Florida Sea Grant Program Rep. 17, Gainsville, FL. Rabalais, N. N., S. C. Rabalais, and C. R. Arnold. 1980. Description of eggs and larvae of laboratory reared red snapper (Lutjanus campechanus Poey). Copeia 1980:704-708. Richards, W. J., and V. P. Saksena. 1980. Description of larvae and early juveniles of labora- tory-reared gray snapper, Lutjanus griseus (Linnaeus) (Pi- sces, Lutjanidae). Bull. Mar. Sci. 30:515-521. Theilacker, G. H. 1980. Changes in body measurements of larval northern anchovy, Engraulis mordax, and other fishes due to han- dling and preservation. Fish. Bull. 78:685-692. Validation of otolith-based ageing and a comparison of otolith and scale-based ageing in mark- recaptured Chesapeake Bay striped bass, Morone saxatilis David H. Secor T. Mark Trice Chesapeake Biological Laboratory Center for Estuarine and Environmental Sciences The University of Maryland System RO. Box 38. Solomons, Maryland 20688-0038 Harry T. Hornick Maryland Department of Natural Resources, Fisheries Division C2 Tawes State Office Building 580 Taylor Avenue, Annapolis, Maryland 21401 Anadromous striped bass, Morone saxatilis, populations in the mid- Atlantic region comprise important commercial and recreational fish- eries (ASMFC1). Stock assessments for these fisheries depend upon age estimates using annular structures of scales (Merriman, 1941; Man- sueti, 1961; Kahnle et al.2; Hornick et al.3). Age estimation for large adults (>91 cm) has been problem- atic owing to the presence of false annuli and to difficulty in interpret- ing narrow annuli in peripheral fields of the scale (Scofield, 1928a; Merriman, 1941; Tiller, 1950; Mansueti, 1961). Recent work on otolith microchemistry to decipher environmental histories of migra- tory striped bass has provided age estimates that were considerably greater than those previously re- ported (Secor, 1992). Longevity of female Chesapeake striped bass was estimated to exceed 31 years based on examination of otolith mi- crostructure (Secor et al.4). An investigation of the rate of annulus formation in the otoliths of Chesapeake Bay striped bass was performed to verify estimates of growth and longevity (Secor et al.4). For otolith microchemistry applications (Secor, 1992), it also was critical to verify that annuli formed at a yearly rate so that sea- sonal patterns in Sr/Ca ratio (ex- posure to varying salinity) could be interpreted. Heidinger and Clod- felter (1987) reported yearly rates of annulus formation in otoliths of striped bass from one to four years in age in a midwest reservoir, but no specific measurements of accu- racy or precision were presented. No other studies have been pub- lished on annulus formation in striped bass otoliths. A mark-recapture study on hatchery-produced striped bass (Rago et al., 1993; Hornick et al.3) provided samples of known-age resident and migratory fish that were 3 to 7 years old. From 1985 to 1992, approximately 5.5 million juvenile striped bass were stocked in Chesapeake Bay tributaries (Rago et al., 1993). All fish were implanted with a binary-coded wire tag which indicated year of origin and provided information on their hatchery source and release date and site. The objective of this study was to verify the rate of annulus formation by comparing annulus counts with the known age of re- captured hatchery fish. A second objective was to compare scale and otolith ages of large striped bass (>91 cm, total length [TL]) to de- termine the accuracy of age esti- mates derived from scales. Methods Known-age study Striped bass otolith ageing tech- niques were verified by using two sets of known-age, coded-wire tagged (CWT) adults. Agroup of 24 CWT fish was obtained from a col- laborative study of migratory striped bass conducted by the Maryland Department of Natural Resources (DNR); the National Marine Fisheries Service; the North Carolina Department of En- 1 ASMFC (Atlantic States Marine Fisher- ies Commission). 1990. Source document for the supplement to the striped bass FMP-Amendment No. 4. Atlantic States Marine Fisheries Commission. Prepared by Versar, Inc., Columbia, MD, 414 p. 2 Kahnle, A. W., D. Stang, K. Hattala, and W. Mason. 1988. Haul seine study of American shad and striped bass spawn- ing stocks in the Hudson River estuary. New York State Dep. of Environmental Conservation, Albany, NY. 3 Hornick, H. T., R. K. Schaefer, D. T. Cosden, K. J. Booth, J. L. Markham, C. B. McCollough, D. M. Goshorn, M. L. Gary, W. S. Barbour, and R. J. Dickinson. 1992. Investigations of striped bass in Chesa- peake Bay. USFWS Federal Aid Perfor- mance Report. Project F-42-R-5. Maryland Dep. Natural Resources, Tidewater Ad- ministration, Fisheries Div., 219 p. 4 Secor, D. H., H. T. Hornick, and J. Mark- ham. Lost and found generations of Chesa- peake Bay striped bass: improvement in year-class representation of Chesapeake Bay striped bass due to the 1985-1991 Maryland striped bass moratorium. Unpubl. manuscr. Manuscript accepted 23 May 1994. Fishery Bulletin 93:186-190 ( 1995). 186 NOTE Secor et al.: Validation of otolith-based ageing in Morone saxatilis 187 vironment, Health, and Natural Resources; and the U.S. Fish and Wildlife Service. Between 6 and 8 Feb- ruary 1993, migratory fish were captured off the North Carolina coast by the crew of the NOAA ves- sel Chapman by means of a 90-ft, 2-seam fish trawl that was towed for a maximum of 30 minutes (Laney and Cole, 1993). A second group of 13 CWT fish was obtained from DNR commercial drift gillnet and poundnet surveys between 5 October 1992 and 23 February 1993. Pound nets and drift nets were lo- cated in shoal areas of the upper Chesapeake Bay, off Kent Island, MD. Fish in the study group had been tagged with bi- nary coded wire tags as age-0+ juveniles. Tags were removed from recaptured fish and decoded by per- sonnel at the U.S. Fish and Wildlife Service labora- tory in Annapolis, MD, to determine their ages. Otoliths were extracted, soaked in 10% sodium hypochlorite solution, rinsed with deionized water, and embedded within a Spurr epoxy (Secor et al., 1991). Transverse sections, approximately 1 mm thick, were then cut through the otolith cores with a Buehler Isomet saw. The sections were mounted on glass slides, polished on 600-grain sandpaper, and polished again on a slurry of 0.3-fum alumina until their surfaces were free of pits and abrasions. Pol- ished sections were viewed under a light microscope, and otolith annuli were counted by two independent readers. Annuli comprised a narrow opaque zone and a wide translucent zone under transmitted light mi- croscopy (magnification at 60 or 150x). Annuli were counted along the sulcal ridge in transverse sections. The otolith ages were compared with each other and with the known age of the fish. Results Known-age study Striped bass collected in pound nets and drift gill nets in Upper Chesapeake Bay were 3- to 7-year-old males and females. The migratory hatchery striped bass from offshore samples tended to be older, rang- ing in age from 4 to 7 years old (Fig. 1). Agreement between known and estimated age for resident striped bass was 100% for both otolith read- ers (rc=13). Exact agreement between estimated and known age for migratory fish (n=24) was 79% and 87% for reader 1 and reader 2, respectively. All mi- gratory fish were estimated to be within one year of their true age. The mean age difference between read- ers for migratory fishes was not significantly differ- ent from 0 (paired £-test: rc=37; P=0.66). The mean absolute difference between ages estimated by reader 1 and known-age, a measure of precision, was esti- mated at 0.13 years. Precision estimated for reader 2 was 0.08 years. Error in age estimates was not re- lated to fish length or age. Scale vs. otolith study Age estimates from scales and otolith sections were not significantly different for fish with otolith-esti- mated ages of 5 to 11 years (Fig. 2; paired £-test: n-30; P=0.41). However, fish with otolith-estimated ages of 22 to 31 years had scale-estimated ages which were, on average, 9 years less than otolith age esti- mates (Fig. 2; paired t-test: n=30; P<0.0001). Scale vs. otolith study Scales and otoliths were sampled from recreational landings of striped bass (>91 cm TL) during the May 1992 Maryland "Trophy Striped Bass Fishery." These fish were assumed to have spawned recently in up- per Chesapeake Bay tributaries. Five additional fish, large females (>100 cm) collected in 1991 and 1992 from the Patuxent and Nanticoke Rivers by DNR for hatchery propagation purposes, were included in the comparisons. Scales and otoliths were aged indepen- dently by a reader at Chesapeake Biological Labora- tory (otoliths) and at DNR (scales). Otoliths were prepared and aged as described above. Scale samples for ageing had been removed from the left side of the fish above the lateral line and below the first dorsal fin. Age was determined from either direct interpre- tation of the scale's annuli or from acetate impres- sions of the scales. Otoliths and scales were coded so that fish length was unknown to readers. 3 4 5 6 7 Age (yr) Figure 1 Age-frequency distribution of known-age striped bass from Upper Chesapeake Bay, Maryland (MD) and coastal North Carolina (NC). 188 Fishery Bulletin 93(1), 1995 Discussion Annulus formation in otoliths and scales We verified age estimates of striped bass from an- nuli observed in sectioned otoliths offish 3 to 7 years old. Annuli precisely and accurately reflected ages in both resident and migratory Chesapeake Bay striped bass. Annulus appearance at 6 and 7 years was similar to that of annuli from otoliths of much older individuals (Fig. 1 in Secor, 1992). Therefore, we believe that annuli also are formed at a yearly rate in older individuals (e.g. >20 years). Tagged hatchery striped bass represent over 5% of the striped bass population which over-winters in coastal wa- ters off North Carolina (Laney and Cole, 1993). Thus, 30 20 10 Scole Age = Otolith Age 10 20 Otolith age (yr) 30 40 i 2 -4 B 10 20 Otolith age (yr) 40 Figure 2 (A) Scale-estimated age vs. otolith-estimated age for Maryland Trophy striped bass (>91 cm TL). Scale age = 4.55 + 0.46 otolith age; rc=45; ^=0.85. For reference, a line corresponding to scale age = otolith age has been plotted. (B) Discrepancy between otolith-estimated and scale-estimated age vs. otolith-estimated age for Maryland Trophy striped bass (>91 cm TL). (Otolith age- Scale age) = -4.55 + 0.54 otolith age; re=45; r*= 0.88. these fish will continue to provide a pool of known- age material to verify age estimates in older fish. In the next decade it will be possible to verify annulus formation in the oldest fish of the population. The timing of annulus formation in otoliths was not quantitatively evaluated; samples among months of the year were insufficient to conduct a marginal in- crement analysis (see Beckmanetal., 1988, 1990, 1991). However, we did consistently observe that samples col- lected during the Maryland Trophy Striped Bass Sea- son in May 1991 and 1992 (see Secor, 1992) contained a newly formed annulus and that no such annulus was observed in otoliths of resident or migratory fish col- lected in February 1993. Therefore, annulus formation probably occurs during the February-April period. This observation agrees with observations on season of an- nulus formation in striped bass scales (Merriman, 1941; Heidinger and Clodfelter, 1987). On the basis of evidence that annuli in otolith ages represent true age in older fish, we believe that scales significantly underestimate age in fish older than 20 years. Scale ages were not signifi- cantly different from otolith ages for fish aged 5 to 11 years, ages that corresponded to fish 91 to 110 cm TL. Scale ages were, on average, 9 years less than otolith ages in fish older than 20 years that corresponded to fish >120 cm TL. Because samples were unavailable for ages 12 to 19 years owing to the scarcity of individuals from these year classes (Secor et al.4), we could not determine the accuracy of scale ages for this period. In a similar study on southeastern U.S. riverine and reser- voir striped bass, Welch et al. ( 1993) observed that scale ages were in good agreement with otolith ages for fish <90 cm TL but that scale ages were significantly lower than otolith ages for fish 90- 10 cm TL. For Sacramento-San Joaquin striped bass, Scofield ( 1928a) found good agreement be- tween age estimates made from either hardpart for the first eight years offish life. Ageing in striped bass stock assessments Errors in ageing can result in large biases in stock assessments and in mismanagement of fishery resources (Beamish and McFarlane, 1983; Richards et al., 1992). Scientists at the turn of the century recognized that otoliths of- ten provide more accurate and precise estimates of age than do other hard parts (Heinke, 1904; Cunningham, 1905; Haempel, 1910). Indeed, early verification of age estimation based on scales of striped bass relied upon comparisons of age estimates with those based on otoliths NOTE Secor et al.: Validation of otolith-based ageing in Morone saxatilis 189 (Scofield, 1928, a and b). However, the popularity and ease of age estimations using scales caused investi- gators to overlook the importance of verifying age- ing methodology (Beamish and McFarlane, 1983). All stock assessments on migratory populations of striped bass currently rely on interpreting annular fea- tures on scales, a largely unvalidated method. Annu- lus formation in scales of striped bass has been veri- fied for fish up to age three (Humphreys and Kornegy, 1985) and four years (Heidinger and Clodfelter, 1987) in nonmigratory striped bass. Our data indicated that annuli in scales may adequately estimate age for fish less than 12 years of age. Thereafter, scales provided a continuous age distribution between 11 and 20 years of age, and otolith ageing indicated an absence offish corresponding to these ages (Fig. 2). Therefore, we in- ferred that otolith-based age determination will pro- vide more accurate estimates after 12 years of age. A major disadvantage of using otoliths for age de- terminations is that fish must be sacrificed. Because large and old members of coastal populations have potentially high reproductive values and may be important contributors to annual recruitments (Rago and Goodyear, 1987; Zastrow et al., 1989; Secor et al., 1992; Cowan et al., 1993), it may be undesirable to sacrifice large numbers of these individuals for stock assessment purposes. An alternative approach would be to correct the age estimates from scales by using an otolith vs. scale calibration curve (Fig. 2). Our reported relationship was somewhat variable (^=0.85), but with additional otolith samples, reliable prediction of age from scale annuli may be possible. Acknowledgments Jim Van Tassel, Jorgen Skjeveland, Rick Schaefer, Jim Markham, Don Cosden, Marty Gary, David Goshorn, and Scott Barbour provided samples of CWT adults. Ken Booth provided samples of CWT adults and aged scale samples for this study. Bunky^ Charter Boat Service provided samples of migratory Chesapeake Bay striped bass. Mike Mangion assisted in interpretation of CWT-tags and annuli in scales, respectively. This research was supported by the U.S. Fish and Wildlife Service Emergency Striped Bass Study (F&W Contract 14-48-0009-92-934 to Chesa- peake Biological Laboratory) and Maryland Depart- ment of Natural Resources. Literature cited Beamish, R.J., and G.A. McFarlane. 1983. The forgotten requirement for age validation in fish- eries biology. Trans. Am. Fish. Soc. 112:735-743. Beckman, D. W., C. A. Wilson, and A. L. Stanley. 1988. Age and growth of red drum, Sciaenops ocellatus, from offshore waters of the Northern Gulf of Mexico. Fish. Bull. 87:17-28. Beckman, D. W., A. L. Stanley, J. H. Render, and C. A. Wilson. 1990. Age and growth of black drum in Louisiana waters of the Gulf of Mexico. Trans. Am. Fish. Soc. 119:537-544. 1991. Age and growth-rate estimation of sheepshead Archosargus probatocephalus in Louisiana waters using otoliths. Fish. Bull. 89:1-8. Cowan, J. H., Jr., K. A. Rose, E. S. Rutherford, and E. D. Houde. 1993. Individual-based models of young-of-the-year popu- lation dynamics. II: Factors affecting recruitment in the Potomac River, Maryland. Trans. Am. Fish. Soc. 122: 439-458. Cunningham, J. T. 1905. Zones of growth in the skeletal structures of Gadidae and Pleuronectidae. In 23rd annual report of Fisheries Board of Scotland, 1905, Part II: Scientific investigations, p. 125-140. Haempel, O. 1910. Ueber das Wachstum des Huchens (Salmo hucho L.). Ein Beitrag zur Altersbestimmung der Teleostier. Int. Rev. Hydrobiol. Hydrogr. 3:136-155. Heidinger, R. C, and K. Clodfelter. 1987. Validity of the otolith for determining age and growth of walleye, striped bass, and smallmouth bass in power plant cooling ponds. In R. C. Summerfelt (ed.), Age and growth offish, p. 241-252. Iowa State Univ. Press, Ames, LA Heinke, F. 1904. Occurrences and distributions of the eggs, larvae and various age-groups of the food fishes in the North Sea. J. Cons. Int. Explor. Mer, General Report, 1902-1904:1-39. Humphreys, M., and J. W. Kornegy. 1985. An evaluation of the use of bony structures for aging Albermarle Sound-Roanoke River striped bass (Morone saxatilis). North Carolina Wildlife Resources Commission Report, Raleigh, NC, 17 p. Kimura. D. K. 1977. Statistical assessment of the age-length key. J. Fish. Res. Board Can. 34:317-324. Laney, R. W., and W. W. Cole. 1993. Tagging summary for mixed striped bass stocks off- shore North Carolina and Virginia. In Abstracts, 1993 striped bass study, striped bass workshop, p. 144-147. Natl. Mar. Fish. Serv., Silver Spring, MD. Mansueti, R. J. 1961. Age, growth and movements of the striped bass, Roccus saxatilis, taken in size selective fishing gear in Maryland. Chesapeake Bay Sci. 2:9-36. Merriman, D. 1941. Studies of the striped bass (Roccus saxatilis) of the Atlantic coast. U.S. Fish Wildl. Serv., Fish. Bull. 50: 1-77. Rago, P. J., and C. P. Goodyear. 1987. Recruitment mechanisms of striped bass and Atlan- tic salmon: comparative liabilities of alternative life histories. Am. Fish. Soc. Symp. 1:402^116. Rago, P. J., H. Upton, and P. I. Washington. 1993. Estimated contribution of hatchery-reared striped bass to commercial and recreational fisheries of Maryland 1991-1992. In Abstracts, 1993 striped bass study, striped bass workshop, p. 177-184. Natl. Mar. Fish. Serv., Silver Spring, MD. 190 Fishery Bulletin 93(1). 1995 Richards, I. J., J. T. Scbnute, A. R. Kronlund, and R. J. Beamish. 1992. Statistical models for the analysis of ageing error. Can. J. Fish. Aquat. Sci. 49:1801-1815. Scofield. E. C. 1928a. Preliminary studies on the California striped bass. Trans. Am. Fish. Soc. 1928:139-144. 1928b. Striped bass studies. Calif. Fish and Game 14:29-37. Secor, D. H. 1992. Application of otolith microchemistry analysis to in- vestigate anadromy in Chesapeake Bay striped bass Morone saxatilis. Fish. Bull. 90:798-806. Secor, D. H., J. M. Dean, and E. H. Laban. 1991. Manual for otolith removal and preparation for mi- crostructural examination. Belle W. Baruch Institute, Univ. South Carolina Press, Columbia, SC, 85 p. Secor, D. H., J. M. Dean, T. A. Curtis, and F. W. Sessions. 1992. Effect of female size and propagation methods on lar- val production at a South Carolina striped bass (Morone saxatilis) hatchery. Can. J. Fish. Aquat. Sci. 49:1778-1787. Tiller, R. E. 1950. A five-year study of the striped bass fishery of Mary- land, based on analyses of scales. Chesapeake Biological Lab. Publ. 85, 30 p. Welch, T. J., M. J. Van den Avyle, R. K. Bet si 11, and E. M. Driebe. 1993. Precision and relative accuracy of striped bass age estimates from otoliths, scales, and anal fin rays and spines. N. Am. J. Fisheries Manage. 13.616-620. Zastrow, C. E., E. D. Houde, and E. H. Saunders. 1989. Quality of striped bass (Morone saxatilis) eggs in re- lation to river source and female weight. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 191:34-^42. An evaluation of six marking methods for age-0 red drum, Sciaenops ocellatus* Stephen T. Szedlmayer Jeffrey C. Howe Department of Fisheries and Allied Aquacultures Auburn University Marine Extension and Research Center 41 70 Commanders Drive, Mobile. Alabama 3661 5 Mark-recapture studies of fishes can reveal valuable information on move- ment, mortality, and growth rate (Parker et al., 1990). Despite the many successful methods that have been developed for adult fish, mark- ing of small juvenile fishes is prob- lematic (Chapman and Bevan, 1990). Age-0 fish are typically too small and delicate for many marking methods. A few methods for marking age- 0 fishes have been developed: coded wire microtags (Thrower and Smoker, 1984; Brodziak et al., 1992; Bumguardner et al., 1992); spray paint marking (Phinney et al., 1967; Pierson and Bayne, 1983); fluorescent staining (Hettler, 1984; Secor et al., 1991a; Szedlmayer and Able, 1992); and external plastic minitags (Floy Tag and Mfg. Co., Inc., Seattle, WA). All of these methods have advantages and dis- advantages based on the attributes of each species. Thus, there is a need to test different marking methods on small size classes of different species to determine the most suitable methods. Two marking methods have been reported for age-0 red drum, Sciae- nops ocellatus: 1) spray paint mark- ing,1 and 2) coded wire microtags (Bumguardner et al., 1992). Fluo- rescent staining is another method that may be useful for age-0 S. ocellatus and has been successfully applied to juvenile red sea bream, Pagrus major (Tsukamoto et al., 1989), and to larval and juvenile striped bass, Morone saxatilis (Secor et al., 1991a). However, it is not possible from these studies to de- termine the most useful marking method for age-0 S. ocellatus. Hence, we examined mortality, mark retention, and growth in age- 0 S. ocellatus that were marked by one of six different methods: 1) coded wire microtags, 2) external plastic minitags, 3) alizarin com- plexone, 4) oxytetracycline dihydrate [OTC], 5) red fluorescent spray paint, and 6) green fluorescent spray paint. Materials and methods We marked 614 cultured age-0 S. ocellatus (mean standard length [SL] ± standard deviation [SD]=67.4 ± 8.7 mm; range=48— 95 mm SL) on 4—5 February 1993. Fish were anesthe- tized with tricane methanol sulfate (50 mg MS222/L seawater), weighed, measured, and randomly assigned to one of the following treatments: red fluorescent paint (red), green fluo- rescent paint (green), external plas- tic tags (plastic), binary coded wire microtags (wire), oxytetracycline- dihydrate (250 mg OTC/L 25 ppt sea- water for 15 h), and alizarin-complex- one (250 mg alizarin/L 25 ppt sea- water for 15 h). Wire tags were injected into the left epaxial muscle with a specially designed hypodermic needle (North- west Marine Technology, Shaw Is- land, WA). The plastic tags (num- bered disk: 0.5x3x7 mm) were at- tached posterior to the dorsal fin with elastic thread sewn through the left and right epaxial muscles. Red and green paints were applied at a pressure of 70 to 100 psi from a distance of 30 to 50 cm (Phinney et al., 1967). Atotal of 614 fish were marked and classified as follows: 100 OTC, 114 alizarin, 100 red, 100 green, 100 plastic, and 100 wire. All fish were held in a 7,570-L closed seawater system, and differentially marked fish were separated by flow through partitions. Ammonia, ni- trite, and nitrate levels were con- trolled with an oyster shell biologi- cal filter (mean ± standard error [SE]: NH3=0.018 ±0.003 ppm; NO2=0.253 ± 0.047 ppm; N03=47.4 ±1.9 ppm). Particulates were re- moved with a sand filter. Salinity was held constant by addition of artificial seasalts or freshwater (mean salinity ± SE=25.0 ± 0.2 ppt). Temperature was held constant with three 1,000-W heaters (mean temperature ± SE=20.8 ± 0.2°C). Fish mortalities were counted and removed daily for 68 days. All fish were fed daily at 5% body weight per day with Zeigler salmon crumbles no. 2 pellet food (Zeigler Bros. Inc., Gardners, PA). At 25, 48, and 68 days, all fish from each treatment were anesthetized, weighed, measured, and food was adjusted for growth to maintain the daily 5% body weight ration. Red and green paint marks were veri- fied with an ultraviolet light (paint was not visible under white light). Fish were considered marked if at least one granule of pigment was observed. Also, when fish were anesthetized and measured, we randomly sacrificed 20 fish from * Contribution 8-944903 of the Alabama Agricultural Experiment Station, Auburn University, Mobile, Alabama 36615. 1 McMichael, Robert H., Jr. Florida Depart- ment of Natural Resources, St. Peters- burg, FL. Personal commun., 1992. Manuscript accepted 29 August 1994. Fishery Bulletin 93:191-195 (1995). 191 192 Fishery Bulletin 93(1), 1995 each treatment: from OTC and alizarin treatments for otolith mark examination, from wire treatments for wire removal, and from other treatments for fu- ture otolith analysis. All samples were preserved by freezing. In estimating percent survival, it was as- sumed that all fish that were sacrificed (alive and healthy at time of sample) would have survived the 68-d experimental period. The actual survival of sac- rificed fish would be lower than 100%, but the differ- ence in survival rate among treatments would be expected to increase if actual survival rates for all fish were known. Whole sagittal otoliths were removed from OTC and alizarin treatments and viewed with an Olympus BH- 2 compound microscope under 100-W ultraviolet light. When fluorescent marks were not visible on whole otoliths, they were sectioned and polished for in- creased resolution (Secor et al., 1991b; Szedlmayer and Able, 1992). Wire tags were located by mak- ing a sagittal incision of the epaxial muscle and examined under a Nikon stereo-microscope. If wire tags were not located by dissection, fish were X-rayed to locate tags. We compared instantaneous mortality rates with analysis of covariance (ANCOVA) and per- cent tag retention with a randomized block analysis of variance (ANOVA) with day as blocks and marking method as the factor (Zar, 1984). We compared standard lengths (SL) and weights over marking method with ANOVA for each sample date. If significant differences (P<0.05) were detected, we compared the means (ANOVA) or slopes (mortality; ANCOVA) with Newman-Keuls range test (Zar, 1984). Results Instantaneous mortality rates (log per- cent survival=-Zrf + Y) for OTC (-Z=0.0013, r2=0.92), alizarin (-Z=0.0014, r2=0.80), and wire (-Z=0.0016, ^=0.78) marking were sig- nificantly less than those for plastic (-Z=0.0023, ^=0.90), red (-Z=0.0025, r2=0.96), and green treatments (-Z=0.0033, r^O.92; Fig.l). Survival curves showed similar patterns with higher mortality in the first 40 days; thereafter mortality was reduced (Fig. 1). Percent mark retention of alizarin, OTC, and wire tags were signifi- cantly greater than those of other treatments. The highest mark reten- tion was observed for OTC- and alizarin-marked fish (100%; Table 1). Wire-marked fish also showed high retention rates (85-100 %). Red-, green-, and plas- tic-marked fish showed significant declines in tag re- tention over the 68 days (Table 1). Mean SL and weight showed no significant differ- ence among treatments on day 1, 25, 48, and 68 (Tables 2 and 3). Growth rates were similar among all treatments: 1.0-1.1 mm SlVd and 0.5-0.6 g wet wt/d (Tables 2 and 3). Discussion Wire tags provided the best overall performance of the marking methods tested over this two-month 100- ^S>^ N^\\ *-^ NjjsS ^ Survival % 00 o \?S>»_ Alizarin3 \ "■---»»_ Wire3 60- Green" ■-. ( ) 10 20 30 40 50 60 70 Day Figure 1 Percent survival of age-0 red drum, Sciaenops ocellatus, marked by six methods. Treatments with different letters were signifi- cantly different (P<0.05). Table 1 Percent mark retention among sample days of age-0 red drum, Sciaenops ocellatus, marked by one of six methods: wire = coded wire microtag; plastic = external plastic tag; red = red fluorescent paint; green = green fluorescent paint; OTC = oxytetracycline dihydrate; and Ali = alizarin complexone. Num- bers in parenthesis are sample sizes. Treatments with different letters are significantly different (P<0.05). Marking method Day OTC Ali" Wire" Red6 Plastic* Green6 25° 48a6 68c 100.0(21) 100.0(20) 90.0(20) 80.5(82) 78.2(78) 42.3(78) 100.0(20) 100.0(20) 100.0(20) 55.8(52) 49.1(53) 39.1(46) 100.0(19) 100.0(21) 85.0(20) 14.8(27) 24.1(29) 16.0(25) NOTE Szedlmayer and Howe: Six marking methods for age-0 Sciaenops ocellatus 193 study. Wire-marked fish showed low mortality and high tag retention compared with those marked by the plastic and paint methods. Also, individual fish are identifiable with wires which can be more useful than batch marking with OTC and alizarin. Of par- ticular interest were the high tag-retention rates of wires (85-100 %). In past studies of wire tags injected in the cheek muscle of age-0 S. ocellatus, consider- able tag loss was shown over the first 114 d: 67.3% tag retention after 24 h, 47% from 2 to 23 d, and 45% Table 2 Mean standard lengths and growth rates of age-0 red drum, Sciaenops ocellatus, marked by one of six methods: wire = coded wire microtag; plastic = external plastic tag; red = red fluorescent paint; green = green fluorescent paint; OTC = oxytetracycline dihydrate; and Ali = alizarin complexone. Treatments were not significantly different (P<0.05). SL=standard length, SE=standard error, n=sample size. Day Measure Mark method Wire Plastic Red Green OTC Ali 1 SL (mm) 65.9 66.9 66.8 67.1 68.9 67.6 SE 0.8 0.9 0.9 0.9 0.9 0.7 n 100 100 100 100 100 114 25 SL(mm) 90.5 91.6 88.8 90.5 90.7 91.6 SE 1.0 1.1 1.1 1.1 1.1 1.0 n 80 78 82 78 88 95 48 SL (mm) 116.7 117.9 112.5 118.1 117.5 114.0 SE 1.3 1.7 2.0 1.6 1.6 1.4 n 57 53 52 46 64 71 68 SL (mm) 131.1 134.7 134.4 134.3 128.7 129.1 SE 2.2 2.9 2.0 2.3 1.8 2.1 n 37 29 27 25 44 50 Growth (mm/d) 1.1 1.1 1.1 1.1 1.0 1.0 r2 0.86 0.83 0.83 0.85 0.80 0.83 Table 3 Mean wei ghts and standard error (SE)of age 0 red drum, Sciaenops ocellatus. marked by one of six methods: wire = coded wire microtag; plastic = external plastic tag; red = red fluorescent paint ; green = green fluorescent paint OTC = oxytetracycline dihydrate ; and Ali = alizarin complexone Treatments were not significantly different (P<0.05) WT= =we ght, n= sample sizes. Day Measure Mark method Wire Plastic Red Green OTC Ali 1 WT(g) 4.9 5.2 5.2 5.2 5.7 5.2 SE 0.2 0.2 0.2 0.2 0.2 0.2 n 100 100 100 100 100 114 25 WT(g) 12.9 13.5 14.0 13.5 13.4 13.1 SE 0.4 0.5 1.1 0.5 0.5 0.4 n 80 78 82 78 88 95 48 WT(g) 30.1 29.5 27.9 28.2 27.8 27.2 SE 1.1 1.3 1.4 1.1 1.1 1.0 n 57 53 52 46 64 71 68 WT(g) 41.9 44.7 45.1 42.2 37.6 38.1 SE 2.1 2.8 2.2 2.5 1.7 2.0 n 37 29 27 25 44 50 Growth (g/d) 0.6 0.6 0.6 0.6 0.5 0.5 r2 0.80 0.77 0.69 0.80 0.74 0.72 194 Fishery Bulletin 93(1). 1995 from 24 to 114 d (Bumguardner et al., 1992). A simi- lar wire tag loss rate was observed in striped bass tagged horizontally in the cheek muscle (22.2-30.7% retention over the first 70 d; Dunning et al., 1990). However, Dunning et al., (1990) also reported that wire retention rates substantially increased when stripped bass were tagged in the snout (63-98.5%), nape (93.8-99.3%), or vertically in the cheek (82.7- 87.0%) over the first 70 days. Also, Klar and Parker (1986) showed 99% tag retention after 90 days if wires were injected into the epaxial muscle of striped bass. Our results agree with the higher tag retention rates reported by Dunning et al., (1990) and Klar and Parker (1986); there was little indication of tag loss in the first days after marking. We suggest that higher wire retention resulted from mark location, because current wires were injected deep (4—5 mm) into the epaxial muscle and had little chance of expulsion. Although wire tags showed the best overall per- formance compared with other tags, the method was the most labor intensive of all methods, because of the required dissection, removal, and reading of wires. If individual growth rates are needed and both personnel and budget are limiting, plastic tags may be useful. Plastic tags can be read directly without harm to the fish, but they also showed significant tag loss compared with other methods and should be limited to short experiments of no more than 25 days. Paint marking methods showed greater mortali- ties and lower retention times compared with other methods but are useful in situations where fish can only be held for short periods (1-2 h, see Weinstien et al., 1984). However, paint marking methods should also be limited to short-term experiments because of significant mark loss after 25 days. If fish movements or survival are the objectives and fish can be held for long (=15 h) marking peri- ods, then OTC or alizarin may be the best marking methods. Both methods showed higher tag retention ( 100%) and lower mortality rates compared with plas- tic minitags or paint methods. Other studies have shown long-term retention for these chemicals: for example, OTC marks in chum salmon, Oncorhynchus keta (Bilton, 1986) and alizarin marks in P. major (Tsukamoto et al., 1989) were both detected two years after marking. Another advantage of OTC and al- izarin staining was that handling was minimal and probably caused the least amount of stress among all the marking methods, as reflected in the lower mortality rates. Therefore, these fluorescent stains would be most suitable for long-term studies where individual growth rates are not needed and for batch marking large numbers of fish, for example prior to release of hatchery reared fish (Tsukamoto et al., 1989;Secoretal., 1991a). One difference in the present study was the use of oxytetracycline-dihydrate instead of oxytetracycline- hydrochloric acid (HCL), as used in other studies. (Hettler, 1984; Tsukamoto and Shima, 1990; Secor et al., 1991a). The dihydrate form of OTC was ad- vantageous in that it did not cause a reduction in pH as observed with the HCL form. This difference may account for the low mortality observed after 15 hours in the OTC bath (i.e. no fish died during the 15-h mark- ing period). One advantage of the alizarin stain over the OTC marker was the ease in detecting the fluores- cent marks. When whole otoliths were examined only 2 of 91 alizarin otoliths needed further cutting and pol- ishing to detect the stain, whereas 23 of 83 OTC otoliths needed sectioning before OTC marks were visible. As indicated by growth rates, fish acclimated well to the closed seawater system. Although we did not have a control group of fish, growth rates in the present study (1.0-1.1 mm SL/d) were similar to or greater than previous studies of unmarked S. ocellatus of similar sizes and temperatures as the current study: 0.8 mm/d from Tampa Bay (Peters and McMichael, 1987), 0.8 mm/d from Charleston Har- bor (Daniel, 1988), and 1.0 mm/d for reared fish in Texas (Colura et al., 1990). Also, we were not attempt- ing to compare growth rates of marked fish with those of wild populations or those of unmarked laboratory fish but rather to determine the most useful tag of the methods tested. Thus, we recommend wire tags when individual marks are needed because of lower mortality and higher mark retention compared with those from plastic minitags. We recommend alizarin when batch- marking methods are needed and individual growth rates are not critical, because of lower mortality and higher retention compared with those from paint methods and because of ease of detecting mark com- pared with OTC marking. Acknowledgments We thank J. Lindstrom and J. Mang for help in rear- ing and sampling S. ocellatus. We thank L. Collins for review of an early draft. This research was funded through a Saltonstall-Kennedy grant USDC- NA27FD0063-01, National Marine Fisheries Service, National Oceanic and Atmospheric Administration. Literature cited Bilton, H. T. 1986. Marking chum salmon fry vertebrae with oxytetra- cycline. N. Am. J. Fish. Manage. 6:126-128. NOTE Szedlmayer and Howe: Six marking methods for age-0 Saaenops ocellatus 195 Brodziak, J., B. Bentley, D. Bartley, G. A. E. Gall, R. Gomulkiewicz, and M. Mangel. 1992. Tests of genetic stock identification using coded wire tagged fish. Can. J. Fish. Aquat. Sci. 49:1507-1517. Bumguardner, B. W., R. L. Colura, and G. C. Matlock. 1992. Long-term coded wire tag retention in juvenile Sciaenops ocellatus. Fish. Bull. 90:390-394. Chapman, L. J., and D. J. Bevan. 1990. Development and field evaluation of a mini-spaghetti tag for individual identification of small fishes. Am. Fish. Soc. Symp. 7:101-108. Colura, R. L., B. W. Bumguardner, A. Henderson- Arzapalo, and J. D. Gray. 1990. Culture of red drum fingerlings. Texas Parks and Wildl. Dep., Manage. Data Ser. 22, Austin, Texas. Daniel, L. B., III. 1988. Aspects of the biology of juvenile red drum, Sciaenops ocellatus, and spotted seatrout, Cynoscion nebulosus (Pi- sces: Sciaenidae) in South Carolina. M.S. thesis, College of Charleston, Charleston, SC. Dunning, D. J., Q. E. Ross, B. R. Friedmann, and K. L. Marcellus. 1990. Coded wire tag retention by, and tagging mortality of, striped bass reared at the Hudson River Hatchery. Am. Fish. Soc. Symp. 7:262-266. Hettler, W. F. 1984 Marking otoliths by immersion of marine fish larvae in tetracycline. Trans. Am. Fish. Soc. 113:370-373. Klar, G. T., and N. C. Parker. 1986. Marking fingerling striped bass and blue tilapia with coded wire tags and microtaggants. N. Am. J. Fish. Man- age. 6:439-444. Parker, N. C, A. E. Giorgi, R. C. Heidinger, D. B. Jester Jr., E. D. Prince, and G. A. Winans (eds.). 1990. Fish-marking techniques. Am. Fish. Soc. Symp. 7. Am. Fish. Soc, Bethesda, MD, 879 p. Peters, K. M., and R. H. McMichael Jr. 1987. Early life history of the red drum, Sciaenops ocellatus (Pisces: Sciaenidae), in Tampa Bay, Florida. Estuaries 10:92-107. Phinney, D. E., D. M. Miller, and M. L. Dahlberg. 1967. Mass-marking young salmonids with fluorescent pigments. Trans. Am. Fish. Soc. 96:157-162. Pierson, J. M., and D. R. Bayne. 1983. Long-term retention of fluorescent pigment by four fishes used in warmwater cultures. Prog. Fish-Cult. 45:186-188. Secor, D. H., M. G. White, and J. M. Dean. 1991a. Immersion marking of larval and juvenile hatch- ery-produced striped bass with oxytetracycline. Trans. Am. Fish. Soc. 120:261-266. Secor, D. H., J. M. Dean, and E. H. Laban. 1991b. Manual for otolith removal and preparation for mi- crostructural examination. Electric Power Res. Inst, and the Belle W. Baruch Inst, for Marine Biology and Coastal Res., Columbia, SC, 85 p. Szedlmayer, S. T., and K. W. Able. 1992. Validation studies of daily increment formation for larval and juvenile summer flounder, Paralichthys dentatus. Can. J. Fish. Aquat. Sci. 49:1856-1862. Thrower, F. P., and W. W. Smoker. 1984. First adult return of pink salmon tagged as emergents with binary-coded wires. Trans. Am. Fish. Soc. 113: 803-804. Tsukamoto, K., and Y. Shima. 1990. Otolith daily increment in sandfish. Bull. Jpn. Soc. Sci. Fish. 56:1083-1087. Tsukamoto, K., H. Kuwada, J. Hirokawa, M. Oya, S. Sekiya, H. Fujimoto, and K. Imaizumi. 1989. Size-dependent mortality of red sea bream, Pagrus major, juveniles released with fluorescent otolith-tags in News Bay, Japan. J. Fish Biol. 35(A):59-69. Weinstein, M. P., L. Scott, S. P. O'Neil, R. C. Siegfried II, and S. T. Szedlmayer. 1984. Population dynamics of spot, Leiostomus xanthurus, in polyhaline tidal creeks of the York river estuary, Virginia. Estuaries 7(4A):444— 450. Zar, J. H. 1984. Biostatistical analysis, 2nd ed. Prentice-Hall, Englewood Cliffs, NJ, 718 p. Stranding and mortality of humpback whales, Megaptera novaeangliae, in the mid-Atlantic and southeast United States, 1985-1992 David N. Wiley Regina A. Asmutis International Wildlife Coalition 70 East Falmouth Highway, East Falmouth, Massachusetts 02536 Thomas D. Pitchford Virginia Marine Science Museum 7 1 7 General Booth Boulevard, Virginia Beach, Virginia 2345 1 Present address: Florida Department of Natural Resources Florida Marine Research Institute, Marine Mammal Section Southwest Field Station, 1 4 1 8-G Market Circle, Port Charlotte, Florida 33954 Damon P. Gannon Plymouth Marine Mammal Research Center RO. Box 1131. Plymouth, Massachusetts 02362 Marine mammal strandings are a result of, or result in, mortality that may be attributed to natural or an- thropogenic factors. As such, strand- ing data can provide insight on spa- tial distribution, seasonal move- ments, and mortality factors pertain- ing to marine mammal populations (Woodhouse, 1991; Mead1). The general distribution and mi- gratory movements of humpback whales, Megaptera novaeangliae, in the western North Atlantic are well known from numerous studies based on the identification of indi- vidual animals and on other tech- niques. Humpbacks feed in high latitude areas during the summer months, including waters of the Gulf of Maine, eastern Canada, West Greenland, and Iceland (Hain et al., 1982; Martin et al., 1984; Perkins et al., 1984; Katona and Beard 1990). In the winter, whales from all populations migrate to breeding grounds in the West Indies (Balcomb and Nichols, 1982; Mattila and Clapham, 1989; Mattila et al., 1989; Katona and Beard 1990). Between these migra- tory end points, little is known of the distribution of the species. In recent years, however, there has been an apparent increase in the frequency of sightings of humpback whales off the mid- Atlantic coast of the United States (Swingle et al., 1993). Furthermore, a considerable number of strandings have been documented along the mid-Atlan- tic and southeast coasts, many in midwinter, a time when the major- ity of humpbacks are thought to be located in tropical waters. In this paper, we analyze data from these strandings, discuss implications regarding distribution and possible spatial segregation by age class, and examine apparent causes of mortality. Methods Study area and period The study covers the coastal area of eastern North America extend- ing from New Jersey(40°28'5N, 74°00'0W) to southern Florida (25°12'N, 80°13'W), consisting of 2,319 km of coastline (Fig. 1). The eight-year period from 1 January 1985 through 31 December 1992 was investigated. Stranding data were obtained from the United States Museum of Natural History, Smithsonian Institution's Marine Mammal Events Program (MMEP). This information was confirmed and augmented by comparison with data from stranding response per- sonnel involved with the Northeast and Southeast Regional Stranding Networks and with data published in newspaper reports. Organiza- tions involved in the regional stranding networks operate under a permit issued by the National Marine Fisheries Service. The names and organizations of inves- tigators responding to specific stranding events are on file. Analyses The following data were recorded for each stranding: date, location, sex, body length, and the presence or absence of body markings that may indicate a possible anthropo- genic cause of mortality (e.g. ship strike or fishery interaction). Stranding incidents among states were compared by using a ratio of the number of strandings in the state to 1 Mead, J. G. 1979. An analysis of cetacean strandings along the eastern coast of the United States. In J. R. Geraci and D. J. St. Aubin (eds.), Biology of marine mam- mals: insights through strandings, p. 54- 68. Report to U.S. Marine Mammal Comm. Contract MM7AC020. U.S. Dep. of Commer, Natl. Tech. Info. Serv. PB-293 890. Manuscript accepted 15 June 1994. Fishery Bulletin 93:196-205 (1995). 196 NOTE Wiley et al.: Stranding and mortality of Megaptera novaeangliae 197 the length of coastline along the state. This is referred to as the stranding incidence ratio (SIR). Length of coastline was calculated from Ringold and Clark ( 1980). *ANJ MD Chesapeake '. Bay VA , CaPe . oa «»\Hatteras * NC "X ->• /"* sc \ 1 Atlantic \^ GA U Ocean \"a \ J \ FL * 1985- 1988 •1989- 1992 .8 Figure 1 Locations of humpback whale, Megaptera nov- aeangliae, strandings from New Jersey to south- ern Florida, 1985 through 1992. Reproductive class was inferred from body-length data. Animals of less than 8 m in length were con- sidered to be dependent, nursing calves (Nishiwaki, 1959; Rice, 1963). We considered newly independent calves to be animals greater than 8.0 m but less than 9.9 m (calculated from Katona et al., 19832). Males between 9.9 m and 11.6 m and females between 9.9 m and 12.0 m were considered sexually immature but not newly independent. Animals greater than 11.6 m (males) and 12.0 m (females) were considered sexually mature (Nishiwaki, 1959; Rice, 1963). The Mann-Whitney [/-test (Sokal and Rohlf, 1981) was used to test for differences between the number of strandings that occurred in the period 1985—88 versus 1989-92. Time periods were chosen to coin- cide with reported changes in observations of live animals in the same region (Swingle et al., 1993). The hypothesis that strandings occurred randomly throughout the study area was tested by chi-square analysis in a 2x2 contingency table (Sokal and Rohlf, 1981). The hypothesis that stranding events were not influenced by season was tested by chi-square analy- sis. Seasons were winter (January-March), spring (April-June), summer (July-September) and fall (October-December). Seasonal groupings were con- structed so that the winter season would approxi- mately coincide with the period of peak humpback occupancy of the breeding grounds, as reported by Mattila and Clapham (1989). The hypothesis that stranding occurrence was not influenced by sex was tested by chi-square analysis in a 2x2 contingency table. Factors relating to mortality were taken from the written reports of on-site stranding response person- nel from the Northeast and Southeast Regional Stranding Networks or, when not available, from the synthesis of such reports contained in the MMER The experience of stranding network response per- sonnel is variable, and factors contributing to death or interpretation of bodily injury can be subject to debate. If on-site investigators recorded references to rope marks, propeller marks, broken bones, large gashes, etc., or directly suggested ship strike or en- tanglement as a potential cause of death, we attrib- uted the death to possible anthropogenic causes. All mortality not suggesting anthropogenic trauma were grouped into a "natural" mortality category. This in- cluded animals that were euthanized but showed no other indications of human interaction. If a necropsy was conducted and no mention was made of body trauma, we assumed natural mortality. Carcasses that were reported to be in advanced stages of de- composition were eliminated from consideration. 2 Calculated as length at birth, 4.5 m; growth rate, 45 cm per month; 12 month growth period = 9.9 m. 198 Fishery Bulletin 93(1), 1995 Results Mortality A total of 38 stranded humpback whales were re- corded between 1 January 1985 and 31 December 1992 (Table 1). One animal (4/14/85) was not included in the analyses because body condition ("mummifi- cation") indicated death or stranding, or both, oc- curred prior to the study period. The number of strandings by year was as follows: 0 in 1985, 2 in 1986, 0 in 1987, 1 in 1988, 3 in 1989, 8 in 1990, 7 in 1991, and 16 in 1992. Significantly more animals stranded during the period 1989 to 1992 (n=34), than from 1985 to 1988 (n=3) (Mann- Whitney U: Z=-2.32, P=0.02). Of the strandings recorded in our database, 92% (34/37) occurred after January 1989. Significantly more strandings occurred along 170 km of coastline between Chesapeake Bay, Virginia, and Cape Hatteras, North Carolina (x2=70.67, df=l, P<0.01), than occurred in the rest of the study area. In this region, which represents 7.3% (170 km/2,319 km) of the coastline within the study area, 43% (16/ 37) of all strandings occurred. A second cluster of strandings occurred along the coast of northern Florida; however, this grouping was not found to be significant (x2=5.98, df=l, P=0.25). The region, which represents 4.7% (110 km/2319 km) of the study area's coastline, contained 13.5% (5/37) of all strandings. The number of strandings per state was highly variable (Table 2). Numerically, the highest number of strandings occurred in North Carolina (n-15), but the incidence of strandings (strandings per kilome- ter of coastline) was greatest in Virginia (SIR=0.055, n=10), followed by North Carolina (SIR=0.031). South Carolina had the lowest incidence of strandings (SIR=0.003, n=l). The stranding incidence ratio for the entire study area was 0.016. All states recorded at least one stranding. There were no significant differences in stranding occurrence by season (x2=4.22, df=3, P=0.24) (Fig. 2). However, only 8% (3/37) of all strandings occurred during the summer (July-September). Strandings oc- curred with the greatest frequency in April (n=6) fol- lowed by February, March, and October (n=5 each), and least in July and August (n=0 each). In 1992 (the most recent year of the study), strandings were spread over a greater number of months than any of the seven previous years. Data on body length were available for 25 animals. Body length indicated all animals were sexually im- mature but none were dependent calves. Sixty-eight percent (17/25) of the animals were considered newly independent calves. Information on gender was avail- able for 26 animals. Fifty percent (13/26) were fe- male and 50% (13/26) were male. Of the 37 animals, an advanced stage of decomposi- tion eliminated 13 from analysis for potential cause of death. Four additional animals were insufficiently examined or information was inadequately reported to determine a cause of death or the presence or ab- sence of injury or scars. Of the 20 remaining ani- mals, 30% (6/20) had major injuries potentially at- tributable to a ship strike and 25% (5/20) had inju- ries consistent with possible entanglement in fish- ing gear. One animal exhibited scars consistent with past entanglement or ship strike, or both, and was emaciated at the time of stranding. Thus, up to 60% (12/20) of the sufficiently inspected animals showed signs that anthropogenic factors may have contrib- uted to or been directly responsible for their death. However, the possibility that some animals sustained body trauma after death can not be ruled out. Unfor- tunately, few animals were sufficiently necropsied to establish an unequivocal cause of death. Discussion These results suggest that stranding of humpback whales along the mid-Atlantic and southeast coastal areas of the United States has increased. All stranded animals were sexually immature and males and fe- males stranded with equal frequency. However, natu- ral mortality may show a gender bias that has been obscured by the high number of deaths potentially due to anthropogenic factors. Strandings occurred throughout the fall, winter, and spring seasons, but few strandings occurred during the summer months. There are several possible explanations for the apparent increase in strandings, including changes I .hi JA FE MA AP MY JU JL AU SP OC NO DE MONTH Figure 2 Humpback whale, Megaptera novaeangliae, strandings by month, 1985 through 1992. NOTE Wiley et al. . Stranding and mortality of Megaptera novaeangliae 199 Table 1 Humpback estimated. whale, Megaptera novaeangliae, strandings. New Jersey to south Florida, 1985-1992. unk = unknown; est = Date Location Sex Length Necropsy Carcass analyses Potential cause of death 14 Apr 85 Carolina Beach, NC 34°02'--" N 078°53'--" W unk unk no old carcass (mummy or skeleton) not included in analyses unknown 15 Feb 86 Cobb Island, VA 37°2-'--" N 075°4---" W F 10.8 m partial fresh, no obvious sign of external trauma or disease natural 07 Mar 86 N. Myrtle Beach, SC 33°48'-" N 078°44'--" W F 11.7 m yes live stranding; euthanized natural 08 Dec 88 St. Johns, FL 29°54'-" N 081°20'--" W(est) unk 7.8 m (est) no advanced decomposition unknown 14 Jan 89 St. Augustine, FL 29°55'3-" N 081°17'3" W F 7.6 m (est) unknown advanced decomposition unknown 18 Sep 89 Monmouth Beach, NJ 40°19'55" N 073°57'17" W unk 8.0 m (est) no entangled in gear, apparently anchored by gear to bottom entanglement 18 Dec 89 Assateague Island, VA 37°50'-" N 075°20'--" W F 8.7 m' yes live stranding, no external injuries noted natural 27 Jan 90 New Smyrna Beach, FL 29°00'0-" N 080°522-" W M 7.9 m yes advanced decomposition unknown 05 Feb 90 Nags Head, NC 35°56'5-" N 075°36'5-" W unk2 11.1 m partial broken jaw bone, head damaged3 ship strike 24 Feb 90 Corolla Beach, NC 36°15'-" N 075°46'-" W unk 9.0 m (est) unknown fresh, insufficient information unknown 24 Mar 90 Sanderling, NC 36°115-"N 075°45'2-" W unk 7.6 m - 8 m (est) no advanced decomposition unknown 01 Apr 90 Virginia Beach, VA 36°4-'~" N 075°5-'--" W F 9.6 m yes fresh, net/line marks on tail stock, right half of fluke had line marks entanglement 19 Jun 90* Virginia Beach, VA 36°56'15" N 076°03'30" W F 8.3 m yes fresh, no evidence of scars or injuries natural 20 Jun 90 Virginia Beach, VA 36°45'15" N 075°5630" W F 8.2 m yes live stranding; euthanized, rope marks on flukes, emaciated entanglement 200 Fishery Bulletin 93(1). 1995 Table 1 (continued) Date Location Sex Length Necropsy Carcass analyses Potential cause of death 19 Nov 90 Norfolk, VA 36°56'00" N 076°11'30" W M 9.5 m no various rope burns, abrasions on tail stock, rope scars on left flipper entanglement 05 Feb 91 St. Johns, FL 29°59'06" N 081°18'48" W M 9.4 m partial moderately decomposed, no external injuries noted natural 02 Mar 91 Bald Head Island, NC 33°55'0-" N 077°56'4-" W M 8.5 m no inaccessible unknown 15 Oct 91 Kill Devil Hills, NC 36°01'--" N 075°39'--" W unk5 9.3 m6 partial no external injuries noted natural 25 Oct 91 Nags Head, NC 35°56'5-" N 075°37,0-" M 9.1 m(est) no no external injuries noted natural 27 Oct 91 Bodie Island, NC 35°46'0-" N 075°29'1-" W unk 10.0 m no advanced decomposition unknown 08 Nov 91 Island Beach State Park, NJ 39°50'00" N 074°0512"W M 9.0 m yes four propeller cuts, one through the occipital condyle, were cause of death vessel strike 25 Dec 91 Carolina Beach, NC 34°01'~" N 077°54'-" W F 9.9 m no insufficient information unknown 03 Jan 92 Salvo, NC 35°20'9-" N 075°21'8-" W M 10.4 m no no external injuries noted natural 30 Jan 92 Oregon Inlet, NC 35°46'5-" N 075°31'9-" W unk unk no inaccessible unknown 14 Feb 92 Virginia Beach, VA 37-01'-" N 076°07'--" W (est) M 8.5 m; yes left eye socket and left mandible fractured, signs of healing from injuries at point of fractures vessel strike 10 Mar 92 Avon, NC 35°20'--" N 075°21'-" W F 10.7 m partial left fluke "scalloped" possibly due to ship strike or entanglement, evidence of healed rope/net scars on caudal peduncle past entanglement or ship strike 19 Mar 92 North Core Banks, NC 35°01'1-" N 076°060-" W M 11.0 m no advanced decomposition unknown NOTE Wiley et al.: Stranding and mortality of Megaptera novaeangliae 201 Date Location Sex 14 Apr 92 St. Johns, FL 29°45--" N 081°10--" W (est) unk 16 Apr 92 Assateague Island, MD F 38°12'~" N 075°08'--" W 18 Apr 92 Southport, NC M 33°42'8-" N 77°55'4-" W 22 Apr 92 Hatteras, NC F 35°11'4-" N 075°46'3-" W 30 Apr 92 Nags Head, NC unk 35°22'--" N 075°29--" W 16 May 92 Ossabaw Island, GA M 31°45'7-" N 081°050-" W 17 May 92 St. Catherines Island, GA unk 31°38'2-" N 081°08'2-" W 22 Sep 92 Prime Hook National Wildlife Refuge, DE F 38°55'--'- N 075°05--" W 28 Sep 92 Assateague Island, VA M 37°53'--" N 075°22'~" W 09 Oct 92 Metompkin Island, VA F 37°46'-" N 075°32'--" W 22 Oct 92 Virginia Beach, VA M 36°46'15" N 075°57'02" W Table 1 (continued) Length Necropsy Carcass analyses Potential cause of death 8.6 m existing length 8.9 m 9.5 m 8.9 m yes yes 9.2 m (est) no > 7.2 m unk partial 8.3 m (est) yes 8.9 m (est)- part of head buried yes 8.7 m 9.1m yes yes advanced decomposition unknown no external trauma, but skull disarticulated, blunt trauma to left side vessel strike advanced decomposition unknown no external trauma, but extensive skeletal damage, "probably struck by boat" vessel strike advanced decomposition inaccessible unknown advanced decomposition advanced decomposition advanced decomposition unknown unknown unknown advanced decomposition "probably boat strike," 3 areas of hemorrhage noted unknown vessel strike "obvious entaglement scars" on leading edge of fluke and around caudal peduncle entanglement 1 Animal towed prior to measurement, therefore measured length may be greater than actual length. 2 Discrepancy in reported gender. Original stranding report stated female. MMEP reported male. 3 Discrepancy in reported body condition. Original stranding report stated broken jaw bone and head damage. MMEP had no report of body condition. 4 Discrepancy in reported date. Original stranding report stated 19 June 1990. MMEP reported 19 May 1990. 5 Discrepancy in reported gender. Original stranding report stated female. MMEP reported as unknown. 6 Discrepancy in reported body length. Original stranding report stated 9.3 m. MMEP reported an estimated length of 660 cm. 202 Fishery Bulletin 93(1), 1995 Table 2 Humpback whale, Megaptera novaeangliae, strandings by state; 1985 through 1992. Number of Kilometers of SIR: Number of strandings State strandings coastline km of coastline Virginia 10 180.6 0.055 North Carolina 15 485.5 0.031 Delaware 1 45.2 0.022 Maryland 1 50.0 0.020 Georgia 2 161.3 0.012 New Jersey 2 209.7 0.010 Florida 5 935.5 0.005 South Carolina 1 301.6 0.003 in observer effort, mortality factors, and whale dis- tribution. That increased observer effort could ac- count for the increase seems unlikely. The size of stranded humpback whales and both the public and media interest in such events results in few carcasses escaping notice. Additionally, strandings of finback whales, Balaenoptera physalus, over the same time period have remained relatively constant (1985 to 1988, n=10; 1989 to 1992, n=9)) (calculated from MMEP, Smithsonian Institution). An increase for this large baleen species might also be expected if the reported humpback change were due solely to in- creased observer effort. If the reported increase in strandings is not an artifact of observer effort, it may be due to an in- crease in factors resulting in mortality, an increase in the number of animals inhabiting the study area, or both. While the tonnage of cargo moving through Atlantic ports in 1989 showed a 9% increase over the mean of the previous four years (calculated from Anon., 1991), the number of vessels using the Chesa- peake Bay area, and probably the rest of the Atlan- tic coast, has decreased because ships capable of car- rying greater tonnage are being used (Pringer3). While a decline in vessel traffic may result in a de- creased risk to whales, it is possible that these larger, faster, deeper draft vessels pose a greater danger than the slower, shallower draft vessels of the past. In addition to commercial shipping, some areas, such as near Chesapeake Bay and northern Florida, are subject to substantial use by military vessels. How- ever, data pertaining to trends in military vessel traf- fic were not available. Evidence also indicates that as much as 25% of the reported mortality may be attributable to inter- action with commercial fishing activ- ity, such as gill netting. North Carolina's coastal sink gillnet fishery expanded dramatically during the 1980's (Ross4). South Carolina, the state with the lowest SIR, banned the commercial use of gill nets in 1987 (with the exception of a tended shad net fishery) (Moran5). However, fish- ing effort in the entire study area is inadequately monitored to determine trends (Read, in press; Bisack6). While changes in shipping and commercial fishing activity may rep- resent increased hazards to animals inhabiting the study area, they seem inadequate to account for the dra- matic change in stranding levels reported. Each of these hazards existed prior to 1989, the period when strandings began to increase. The most likely expla- nation for the reported increase in mortality appears to be increased use of this area by juvenile hump- back whales that are then exposed to such hazards. Although few standardized marine mammal sur- veys consistently cover the study area, anecdotal and published observations point to a recent increase in live sightings of humpback whales in coastal waters of Florida and Georgia (Kraus7), North Carolina (Barrington8), Virginia (Swingle et al., 1993), and Maryland (Driscoll9). Although reliable estimation of the length of free-swimming whales is difficult, there is general agreement among observers that most, if not all, of the animals frequenting the area are small. Changes in humpback whale distribution in rela- tion to changes in prey composition and abundance have been demonstrated elsewhere (Payne et al., 1986; Piatt et al., 1989; Payne et al., 1990), and such a prey shift may account for or be an important fac- 3 Pringer, Captain M. Association of Maryland Pilots, Baltimore, MD 21228. Personal commun., January 1993. 4 Ross, J. L. 1989. Assessment of the sink net fishery along North Carolina's Outer Banks, fall 1982 through spring 1987, with notes on other coastal gill net fisheries. Special Sci. Rep. 50, North Carolina Dep. of Environ., Health and Nat. Resour., Moorehead City, NC, 54 p. 5 Moran, J. South Carolina Wildlife and Marine Resource De- partment, Charleston, SC 29422. Personal commun., Septem- ber 1993. 6 Bisack, K. 1992. Sink gill net fishing activity in the North At- lantic as reflected in the NEFSC weightout database: 1982- 1991. U.S Dep. Commer, NOAA, Natl. Mar. Fish.Serv. North- east Fish. Sci Cent., Woods Hole, MA 02543. Unpubl. manuscr., 4 p. 7 Kraus, S. New England Aquarium, Boston, MA 02 110. Personal commun., March 1993. 8 Barrington, P. North Carolina Aquarium, Fort Fisher, Kuri Beach, NC 28449. Personal commun., April, 1993. 9 Driscoll, C. NMFS, Office of Protected Resources, Silver Spring, MD 20910. Personal commun., March 1993. NOTE Wiley et al.: Stranding and mortality of Megaptera novaeangliae 203 tor in the change in whale distribution suggested here. While data on changes in prey distribution were not available, the first observations of winter feed- ing humpbacks were documented in the nearshore waters of Maryland (deGroot10) and Virginia (Swingle et al., 1993), during the winters of 1991 and 1992. An additional possibility is that the humpback whale population in the western North Atlantic may be increasing and expanding its range such that habi- tats historically occupied are being recolonized. Sev- eral authors (Katona and Beard, 1990; Sigurjonsson and Gunnlaugsson, 1990) have reported numerical increases for this population, although this may be due to increased effort resulting in more accurate estimates of abundance. Humpback whales may have always been present during winter in offshore waters of the study area, but a shift in prey abundance or distribution, or both, may have brought them into areas where death would result in stranding, rather than have caused them to be lost at sea. However, offshore concentra- tions were not detected during 1978-82 aerial sur- veys (CeTAP11) or during 1980-88 ship board sur- veys (Payne et al.12). While juvenile whales can be expected to exhibit higher mortality than adults (Sumich and Harvey, 1986; Kraus, 1990a), the absence of adult animals from the stranding record may provide support for the suggestions of Swingle et al. (1993) that winter or migratory segregation, or both, is occurring. For- aging opportunities on the breeding grounds are rare (Dawbin, 1966; Baraff et al., 1991), and it may be adaptive for some juvenile animals to remain and feed in mid-latitude areas, rather than to migrate with adults. If occupying the breeding grounds is the preferred behavior, individuals remaining in higher latitude areas may be those that failed to obtain suf- ficient resources during the feeding season. Such nutritionally stressed animals may be more suscep- tible to all forms of mortality, natural or anthropo- genic. Nutritionally stressed juveniles and newly weaned calves in particular may be vulnerable to the effects of the parasitic nematode Crassicauda boopis (Lambertsen, 1992). 10 deGroot, G. 1992. A fluke of nature. The Annapolis Capital- Gazette. 10 March, p. 1. 11 CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and North Atlantic areas of the U. S. outer continental shelf. Final Rep. to the Cetacean and Turtle As- sessment Program, Univ. Rhode Island, Bur. Land Manage., Contract AA551-CT8-48. U.S. Dep. Int., Wash., DC, 450 p. 12 Payne, P. M., W. Heinemann, and L. A. Selzer. 1992. A distri- butional assessment of cetaceans in shelf/shelf-edge and adja- cent slope waters of the northeastern United States based on aerial and shipboard surveys, 1978-1988. Natl. Mar. Fish. Serv., Northeast Fish. Sci. Cent,, Woods Hole, MA 02543. Unpubl. manuscr., 108 p. If winter foraging opportunities are sufficient, ju- veniles may delay their return to traditional feeding areas and may eventually occupy new habitat. This may be one mechanism by which a species establishes itself in new areas or reoccupies historic sites. This process may be reflected in the stranding record. There seems to be a progressive trend not only for an increased number of strandings but for strandings to take place in a greater variety of months. A high percentage of animals exhibited signs that anthropogenic interactions could be implicated in their death. However, there are reasons to believe that mortality estimates based on available strand- ing data could under- or overestimate the impact of human interaction. For example, stranded animals on 16 and 22 April 1992 exhibited no external signs of trauma. However, necropsies indicated internal injuries consistent with a ship strike (McLellan13; Thayer14), suggesting that such injuries could have escaped notice during more cursory examinations. The lack of external body trauma on animals which thorough necropsy revealed to have been killed by a ship strike has also been noted for the northern right whale, Eubalaena glacialis (Kraus15). Alternatively, references to rope or net marks did not always specify whether such marks were of re- cent origin or due to past entanglement from which the animal escaped. Baleen whale entanglement does not always lead to immediate mortality (Kraus, 1990a); however, the effect of escaped entanglement on long-term survivorship or reproductive success, or both, is unknown. If rope or net marks noted in the stranding reports were of past origin, they may have been independent of the animal's death or the animal may have succumbed to the long-term effects of past entanglement. Reduced foraging efficiency during the entanglement period may be a factor in- fluencing animals to engage in winter feeding behav- ior, such as that observed in the study area by Swingle et al. (1993). The apparent high rate of interaction with com- mercial fishing and shipping, may be due, in part, to the age class inhabiting the area. Juvenile animals, and newly independent calves in particular, may be more susceptible to ship strikes or fishing gear en- tanglements, or both, owing to a lack of experience with either factor (Lien, in press). Commercial ship- ping and military traffic to and from the Chesapeake Bay passes by much of the area where strandings 13 McLellan, W. James Madison Univ., Harrisonburg, VA 22807. Personal commun., March 1993. 14 Thayer, V. Natl. Mar. Fish. Serv., Beaufort, NC 28516. Per- sonal commun., March 1993. 15 Kraus, S. New England Aquarium, Boston, MA 02110. Per- sonal commun., March 1993. 204 Fishery Bulletin 93(1), 1995 occur most frequently (Virginia and North Carolina), often in water depths of less than 20 m. In Florida, the concentration of strandings occurs in the vicinity of active commercial and military shipping and where ship strikes have been reported to represent a hazard to northern right whales (Kraus and Kenney, 1991). Entanglement in commercial fishing gear has been the most frequently identified anthropogenic cause of injury and death in humpback whales; gillnet-type gear most often was implicated (O'Hara et al., 1986). Coastal gillnet fisheries exist in the study area on a year-round basis, but effort may peak in late winter/ spring (NMFS, 1992; Swingle et al., 1993; Brooks16). Over 2,200 gillnet licenses have been issued for the mid-Atlantic coastal region. However, fishermen may hold more than one permit and some coastal fisher- ies do not require permits (NMFS, 1992). In the study area, coastal gill nets and whales concurrently oc- cupy waters of less than 15 m in depth (observed by RAA and DPG), and whales have been observed trail- ing such gear (Swingle17). The association of young, inexperienced whales with gill nets in shallow waters may increase the potential for entanglement incidents. Since entanglement mortality is inversely related to body size (Lien et al., 1989; Kraus 1990b), juvenile humpbacks may be more susceptible to fatalities. Data contained in this paper suggest that mid-At- lantic and southeast coastal areas of the United States are becoming increasingly important habitat for juvenile humpback whales and that anthropo- genic factors may negatively impact these animals. However, there are a number of factors that suggest caution should be used in interpretation of these data. The site of stranding is not necessarily the site of death, as the body of a large whale can be carried considerable distances by wind and currents before beaching occurs. Cause of death in the stranded ani- mals was rarely determined with certainty and in most cases was inferred from observations of the presence or absence of surface body trauma, not from thorough necropsy by experienced individuals. A greater emphasis should be placed on complete necropsies of stranded animals to determine not only the immediate cause of death but also whether there is an underlying factor in the fatality. This would allow a more reliable investigation into mortality and provide greater ability to evaluate and alleviate the impact of anthropogenic interactions. This is particu- larly important for an endangered species, such as the humpback whale. 16 Brooks, W. Florida Department of Environmental Protection, Jacksonville, FL 32216. Personal commun., September 1993. 17 Swingle, W. Virginia Marine Science Museum, Virginia Beach, VA 23451. Personal commun., March 1992. Acknowledgments The authors thank James G. Mead of the Smith- sonian Institution for access to data contained in the Marine Mammal Events Program. We also thank the many individuals who comprise the Northeast and Southeast Regional Stranding Networks. Phil Clapham, Colleen Coogan, Sharon Young, and two anonymous reviewers provided comments which greatly improved the manuscript. Literature cited Anonymous. 1991. Statistical abstract of the United States 1991. The national data book. U.S. Dep. Commer. 111:636-637. Balcomb, K., and G. Nichols. 1982. Humpback whale censuses in the West Indies. Rep. Int. Whaling Comm. 32:401-406. Baraff, L. S., P. J. Clapham, D. K. Mattila, and R. S. Bowman. 1991. Feeding behavior of a humpback whale in low lati- tude waters. Mar. Mamm. Sci. 7(2):197-202. Dawbin, W. H. 1966. Seasonal migratory cycle of humpback whales. In K. S. Norris (ed.l, Whales, dolphins and porpoises, p. 145- 170. Univ. Calif. Press, Berkeley. Hain, J. H. W., G. R. Carter, S. D. Kraus, C. A. Mayo, and H. E. Winn. 1982. Feeding behavior of the humpback whale, Megaptera novaeangliae, in the western North Atlantic. Fish. Bull. 80:259-268. Katona, S. K., and J. A. Beard. 1990. Population size, migrations and substock structure of the humpback whale [Megaptera novaeangliae) in the western North Atlantic Ocean. Rep. Int. Whaling Comm., Spec. Iss. 12:295-305. Katona, S. K.. V. Rough, and D. T. Richardson. 1983. A field guide to the whales, porpoises and seals of the Gulf of Maine and eastern Canada, Cape Cod to New- foundland. Charles Scribner's Sons, New York, 255 p. Kraus, S. D. 1990a. Rates and potential causes of mortality in North Atlantic right whales (Eubalaena glacialis). Mar. Mamm. Sci. 6:(4):278-290. 1990b. Fishery entanglements of marine mammals in the Gulf of Maine, 1975-1990. In Proceedings of the Stell- wagen Bank Conference, Univ. Massachusetts, April 26- 27, 1990. Kraus S. I)., and B. D. Kenney. 1991. Information on right whales (Eubalaena glacialis) in three proposed critical habitats in U.S. waters of the west- ern North Atlantic Ocean, 65 p. [Available from NTIS, Springfield, VA.] Lambertsen, R. H. 1992. Crassicuadosis: a parasitic disease threatening the health and population recovery of large baleen whales. Rev. Sci. Tech. Off. Int. Epiz. 11(4):1131-1141. Lien, J. In press. Entrapment of large cetaceans in passive inshore fishing gear in Newfoundland and Labrador (1979- 1990). In W. Perrin and G. Donavan (eds.), International NOTE Wiley et al.: Stranding and mortality of Megaptera novaeangiiae 205 Whaling Commission special issue on mortality of ceta- ceans in passive fishing nets and traps. Lien, J., G. B. Stenson, and I. Ni. 1989. A review of incidental entrapment of seabirds, seals and whales in inshore fishing gear in Newwfoundland and Labrador: a problem for fishermen and fishing gear designers. In J. Huntington (ed.), Proceedings of the world symposium on fishing gear and fishing vessel design, p. 67-71. Marine Institute, St. Johns, Newfoundland. Martin, A. R., S. K. Katona, D. Mattila, D. Hembree, and T. D. Waters. 1984. Migration of humpback whales between the Carib- bean and Iceland. J. Mammal. 65:330-333. Mattila, D. K., and P. J. Clapham. 1989. Humpback whales (Megaptera novaeangiiae) and other cetaceans on Virgin Bank and in the northern Leeward Is- lands, 1985 and 1986. Can. J. Zool. 67(9):2201-2211. Mattila, D. K., P. J. Clapham, S. K. Katona, and G. S. Stone. 1989. Humpback whales on Silver Bank, 1984: population composition and habitat use. Can. J. Zool. 67:281-285. Nishiwaki, M. 1959. Humpback whales in Ryukyuan waters. Sci. Rep. Whales Res. Inst. Tokyo 14:49-86. NMFS (National Marine Fisheries Service). 1992. Taking of marine mammals incidental to commer- cial fishing operations; interim exemption for commercial fisheries. NMFS Fed. Reg. Notice 57( 11 ). O'Hara, K., N. Atkins, and S. Iudicello. 1986. Marine wildlife entanglement in North Amer- ica. Center for Marine Conservation, Washington, D.C., 219 p. Payne, P. M., J. R. Nichols, L. O'Brien, and K. D. Powers. 1986. The distribution of the humpback whale, Megaptera novaeangiiae, on Georges Bank and in the Gulf of Maine in relation to densities of the sand eel, Ammodytes americanus. Fish. Bull. 84:271-277. Payne, P. M., D. N. Wiley, S. B. Young, S. Pittman, P. J. Clapham and J. W. Jossi. 1990. Recent fluctuations in the abundance of baleen whales in the southern Gulf of Maine in relation to changes in selected prey. Fish.Bull. 88:687-696. Perkins, J. S., K. C. Balcomb, G. Nichols Jr., and M. Dea villa. 1984. Abundance and distribution of humpback whales (Megaptera novaeangiiae) in west Greenland waters. Can. J. Fish. Aquat. Sci. 41:533-536. Piatt, J. F., D. A. Methven, A. E. Burger, R. L. Mclagan, V. Mercer, and E. Creelman. 1989. Baleen whales and their prey in a coastal environ- ment. Can. J. Zool. 67:1523-1530. Read, A. J. In press. Interactions between cetaceans and gill net and trap fisheries In the Northwest Atlantic. In W. Perrin and G. Donavan (eds.), International Whaling Commission, special issue on mortality of cetaceans in passive fishing nets and traps. Rice, D. W. 1963. Progress report on biological studies of the larger cetaceans in the waters off California. Norsk Hvalfangst- Tid. 52:181-187. Ringold, P. L., and J. Clark. 1980. The coastal almanac for 1980-the year of the coast. W.H. Freeman and Company, San Francisco, 172 p. Sigurjonsson, J., and T. Gunnlaugsson. 1990. Recent trends in the abundance of blue (Balaenoptera musculus) and humpback whales (Megaptera novaeangiiae) off west and southwest Iceland based on systematic sightings records with a note on the occurence of other ce- tacean species. Rep. Int. Whaling Comm. 40:537-51. Sokal, R. R, and F. J. Rohlf. 1981. Biometry, 2nd ed. W. H. Freeman and Co., San Fran- cisco, 859 p. Sumich, J. L., and J. T. Harvey. 1986. Juvenile mortality in gray whales (Eschrichtius robustus). J. Mammal. 67:179-182. Swingle, W. M., S. G. Barco, T. D. Pitchford, W. A. McLellan, and D. A. Pabst. 1993. Appearance of juvenile humback whales feeding in the nearshore waters of Virginia. Mar. Mamm. Sci. 9 (3):309-315. Woodhouse, C. D. 1991. Marine mammal beachings as indicators of popula- tion events. In J. E. Reynolds and D. K. Odell (eds.), Marine mammal strandings in the United States: proceed- ings of the second marine mammal stranding workshop; 3-5 Dec. 1987, Miami, FL, p. 111-116. U.S. Dep. Commer., NOAA Technical Report NMFS 98. Publication Awards, 1 993 National Marine Fisheries Service, NOAA The Publications Advisory Committee of the National Marine Fisheries Service is pleased to announce the awards for best publications authored by NMFS sci- entists and published in the Fishery Bulletin for Volume 9 1 and in the Marine Fisheries Review for Volume 54. Eligible papers are nominated by the Fisheries Science Centers and Regional Offices and are judged by the NMFS Editorial Board. Only articles that significantly contribute to the understanding and knowl- edge of NMFS-related studies are eligible. We offer congratulations to the fol- lowing authors for their outstanding efforts. Fishery Bulletin, Volume 91 Outstanding Publication Ambrose Jearld Jr., Sherry L. Sass, and Melinda F. Davis Early growth, behavior, and otolith development of the winter flounder Pleuronectes americanus. Fish. Bull. 91:65-75. Ambrose Jearld is with Northeast Fisheries Science Center, Woods Hole, Massachusetts. Sherry Sass is with the Division of Marine Fish- eries, Sandwich, Massachusetts. Melinda Davis is with Fort Valley State College, Fort Valley, Georgia. Marine Fisheries Review, Volume 54 Outstanding Publication Thomas K. Wilderbuer, Gary E. Walters, and Richard G. Bakkala Yellowfin sole, Pleuronectes asper, of the east- ern Bering Sea: biological characteristics, history of exploitation, and management. Mar. Fish. Rev. 54(4): 1-18. Thomas Wilderbuer and Gary Walters are with the Alaska Fisheries Science Center, Seattle, Washington. Richard Bakkala is a retired fishery biologist who was formerly with the Alaska Fish- eries Science Center, Seattle, Washington. Honorable Mention Michael H. Prager and Alec D. MacCall Detection of contaminant and climate effects on spawning success of three pelagic fish stocks off southern California: Northern anchovy Engraulis mordax, Pacific sardine Sardinops sagax, and chub mackerel Scomber japonicus. Fish. Bull. 91:310-327. Michael Prager is with the Southeast Fish- eries Science Center, Miami, Florida. Alec MacCall is with the Southwest Fisheries Sci- ence Center, Tiburon, California. Honorable Mention Carl. J. Sindermann Disease risks associated with importation of nonindigenous marine animals. Mar. Fish. Rev. 54(3): 1-10. Carl Sindermann is with the Northeast Fish- eries Science Center, Oxford, Maryland. 207 Superintendent of Documents Subscriptions Order Form Order Processing Code: *5178 Charge your order. It's Easy! □ YES, enter my subscription as follows: To fax yQm orders (202) 512_2233 subscriptions to FISHERY BULLETIN (FB) for $27.00 per year ($33.75 foreign). The total cost of my order is $ . Price includes regular domestic postage and handling and is subject to change. Please Choose Method of Payment: I I Check Payable to the Superintendent of Documents ~^\ GPO Deposit Account H-E (Company or Personal Name) (Please type or print) (Additional address/attention line) (Street address) (City, State, ZIP Code) (Daytime phone including area code) VISA or MasterCard Account I I I I I I Thank you Jor (Credit card expiration date) , , your order! (Purchase Order No.) May we make your name/address available to other mailers? |~ (Authorizing Signature) 11 Mail To: New Orders, Superintendent of Documents P.O. Box 371954, Pittsburgh, PA 15250-7954 U.S. Department of Commerce Seattle, Washington Volume 93 Number 2 April 1995 Fishery Bulletin Contents Marina Biological Laboratory/ Wood* Hot* Oceanographic Institution Library 209 APR 6 1995 Woods Hole, MA 02543 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 furnished by NMFS, in any advertising or sales promotion which would indicate or imply that NMFS approves, recommends, or endorses any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the adver- tised product to be used or purchased because of this NMFS publication. 217 231 254 262 274 290 299 Articles Ahrenholz, Dean W, Gary R. Fitzhugh, James A. Rice, Stephen W. Nixon, and Wilson C. Pritchard Confidence of otolith ageing through the juvenile stage for Atlantic menhaden, Brevoortia tyrannus Bisbal, Gustavo A., and David A. Bengtson Description of the starving condition in summer flounder, Paralichthys dentatus, early life history stages Doyle, Miriam J., William C. Rugen, and Richard D. Brodeur Neustonic ichthyoplankton in the western Gulf of Alaska during spring Epperly, Sheryan P., Joanne Braun, and Alexander J. Chester Aerial surveys for sea turtles in North Carolina inshore waters Felley, James D., and Michael Vecchione Assessing habitat use by nekton on the continental slope using archived videotapes from submersibles Fisher, Joseph P., and William G. Pearcy Distribution, migration, and growth of juvenile Chinook salmon, Oncorhynchus tshawytscha, off Oregon and Washington Helser, Thomas E., and Daniel B. Hayes Providing quantitative management advice from stock abundance indices based on research surveys Norton, Elizabeth C, and R. Bruce MacFarlane Nutritional dynamics of reproduction in viviparous yellowtail rockfish, Sebastes flavidus Fishery Bulletin 93(2), 1994 308 Restrepo, Victor R., and Christopher M. Legault Approximations for solving the catch equation when it involves a "plus group" 315 Rutherford, Edward S., and Edward D. Houde The influence of temperature on cohort-specific growth, survival, and recruitment of striped bass, Morone saxatilis. larvae in Chesapeake Bay 333 Theilacker, Gail H., and Steven M. Porter Condition of larval walleye pollock, Theragra chalcogramma, in the western Gulf of Alaska assessed with histological and shrinkage indices 345 Wade, Paul R. Revised estimates of incidental kill of dolphins (Delphinidae) by the purse-seine tuna fishery in the eastern tropical Pacific, 1959-1972 355 Yano, Kazunari, and Marilyn E. Dahlheim Killer whale, Orcinus orca, depredation on longline catches of bottomfish in the southeastern Bering Sea and adjacent waters 373 Zeldis, John R., Paul J. Grimes, and Jonathan K. V Ingerson Ascent rates, vertical distribution, and a thermal history model of development of orange roughy, Hoplostethus atlanticus, eggs in the water column Notes 386 Carlson, H. Richard Consistent yearly appearance of age-0 walleye pollock, Theragra chalcogramma, at a coastal site in southeastern Alaska, 1 973-1 994 391 Fenton, Gwen E., and Stephen A. Short Radiometric analysis of blue grenadier, Macruronus novaezelandiae, otolith cores 397 Garduho-Argueta, Hector, and Jose A. Calderon-Perez Seasonal depth distribution of the crystal shrimp, Penaeus brevirostris (Crustacea: Decapoda, Penaeidae), and its possible relation to temperature and oxygen concentration off southern Sinaloa, Mexico 403 Hernandez-Garcia, Vincente The diet of the swordfish Xiphias gladius Linnaeus, 1 758, in the central east Atlantic, with emphasis on the role of cephalopods 412 Kohler, Nancy E., John G. Casey, and Patricia A. Turner Length-weight relationships for 1 3 species of sharks from the western North Atlantic 419 Pepin, Pierre An analysis of the length-weight relationship of larval fish: limitations of the general allometric model Abstract. — The periodicity of increment formation and our abil- ity to enumerate increments in sag- ittal otoliths of Atlantic menhaden are evaluated from hatching through a nine-month period. We studied otoliths from one group of field-col- lected larvae that was marked by immersion in oxytetracycline (OTC ) and from a second group that was marked by immersion in alizarin complexone (ALC). Additionally, otoliths from known-age juveniles resulting from an Atlantic menha- den laboratory spawning and rear- ing experiment were examined. We determined that, on the average, larval and juvenile Atlantic men- haden form one growth increment per day. We were able to age juve- nile menhaden reliably up to 200 days old within a confidence inter- val (CI) of about 7 days and up to 250 days old within a CI of about 16 days. We hypothesized that growth rates may have impacted the periodicity of increment formation, as well as our ability to count them accurately. The statistically stron- gest results were obtained from the ALC-marked fish, which were reared outdoors and displayed growth rates (0.67 to 0.95 mm-day-1) similar to higher rates observed for juveniles captured from estuarine nursery areas. The periodicity of increment counts for the ALC-marked fish was less than one per day when growth rates were observed to be less than 0.3 mm-day-1. Increments in otoliths from the known-age and OTC-marked fish, which were reared indoors, had lower contrast than their outdoor-reared counter- parts. Otoliths were sectioned for enumeration on both a transverse and oblique-transverse plane. With minor exception, no differences in age estimation could be attributed to the orientation of the sections. Confidence of otolith ageing through the juvenile stage for Atlantic menhaden, Brevoortia tyrannus Dean W. Ahrenholz Beaufort Laboratory, Southeast Fisheries Science Center National Marine Fisheries Service. NOAA 101 Pivers Island Road, Beaufort, NC 28516-9722 Gary R. Fitzhugh James A. Rice Stephen W. Nixon Department of Zoology, North Carolina State University RO. Box 7617, Raleigh, NC 27695-7617 Wilson C. Pritchard Beaufort Laboratory, Southeast Fisheries Science Center National Marine Fisheries Service, NOAA 101 Pivers Island Road, Beaufort, NC 28516-9722 Manuscript accepted 21 September 1994. Fishery Bulletin 93:209-216 ( 1995). The daily age information obtained from larval and juvenile fish oto- liths is a valuable tool for studies of early life history and factors affect- ing recruitment (Jones, 1992). Daily age information is necessary for backcalculating cohort-specific spawning dates and is the best ap- proach for estimating mortality and growth rates in young fish (Essig and Cole, 1986; Pepin, 1989; Jones, 1992). A prerequisite, however, is the validation of the temporal peri- odicity of otolith increment forma- tion (Geffen, 1992). While the otolith approach to determination of vital rates has successfully been applied to larval fish, use of otoliths for the juvenile stage has been more controversial, often because of ad- ditional requirements of otolith preparation, including sectioning and polishing of otoliths, and be- cause of increased uncertainty in age estimations and back-calcula- tions of size at age (cf. Rice, 1987; Mosegaard, 1990; Jones, 1992). Many validation studies have de- termined that increments are, on average, daily in periodicity (cf. Jones, 1986), but conditions affect- ing a low growth rate, for example, can result in increment periodicity other than a daily one (Geffen, 1992) or can result in difficulty in the detection of daily increments (Campana, 1992). Therefore ageing error commonly increases with age and otolith size as increment widths decrease with decreasing growth rates, resulting in greater uncer- tainty of ages, growth rates, and birthdates (Rice et al., 1985; Rice, 1987; Campana and Jones, 1992). We examined conditions where con- fidence about the assumption of daily ring deposition may be low and what the consequence would be of increased ageing error on age es- timation for Atlantic menhaden, Brevoortia tyrannus. Larger, older otoliths are more difficult to prepare and read. To address this issue, we also exam- 209 210 Fishery Bulletin 93(2). 1995 ined the efficacy of sectioning and polishing juvenile menhaden otoliths on two orientations of transverse planes. Greater attention to otolith preparation can significantly improve ageing accuracy (Campana and Moksness, 1991), and section orientation can affect the ability to read otoliths (Secor et al., 1992). Previous menhaden validation studies have used only a minor amount of otolith processing, and the material has been examined on the sagittal plane. Maillet and Checkley ( 1990 ) and Warlen ( 1992 ) used known-age, lab-spawned and reared larvae, whereas Simoneaux and Warlen (1987) examined the outer- most growth increments of juvenile Atlantic menha- den injected with oxytetracycline (OTC). Maillet and Checkley ( 1990) examined growth/increment forma- tion from hatching through 36 days of age, Warlen (1992) through 41 days of age, and Simoneaux and Warlen (1987) used juveniles (63-98 mm in fork length) with an experimental duration of 7-14 days after marking with OTC. With the exception of one test group (Maillet and Checkley, 1990), results of all studies indicated that, on average, one growth increment was formed daily. However, these approaches have not resulted in a method that will permit precise and accurate ageing of older juvenile Atlantic menhaden otoliths. While Simoneaux and Warlen ( 1987) were able to validate the daily periodicity of increment formation for a short period of time, their otolith processing method could not be used to determine the actual age of the juveniles examined. The periodicity of increment for- mation in otoliths should be validated over the ranges in age and size that can potentially be encountered with unknown-age, field-collected material. We use two of the preferred validation methods, known-age and otolith-marking, to bridge the gap in age and size among the studies of Maillet and Checkley ( 1990), Warlen ( 1992), and Simoneaux and Warlen (1987) and to provide an estimate of the un- certainty in deriving age from older juveniles. Our known-age study provides a continuous validation from first feeding through metamorphosis, to juve- niles up to 9 months old. 52 to 136 days after hatching, then preserved in 70% ethyl alcohol. Oxytetracycline (OTC) marked fish In 1988, larval Atlantic menhaden collected at Pivers Island, Beaufort, North Carolina, were acclimated to 100-L indoor laboratory tanks and immersed on 7 April in OTC by a procedure modified from Hettler ( 1984). Salinity was slowly reduced to 0%c by adding tap (well) water over several hours. A premixed, buff- ered (sodium bicarbonate) stock solution of OTC was added to the tank. The resulting treatment condi- tions were 300 mg-L"1 OTC at pH 6.3. After four hours of immersion, ambient seawater flow was restored; the test solution was thus diluted within an hour and salinity slowly increased. The fish remained in this tank for the duration of the study. Samples of postlarvae and juveniles were taken periodically, 13 to 147 days following treatment, and preserved in 95% ethyl alcohol. Alizarin complexone (ALC) marked fish In 1992 we conducted validation trials with marked fish under high and low feeding rations to examine further the effect of growth rate on increment depo- sition. Larval menhaden were captured with a neus- ton net at Pivers Island, NC, on 1 April 1992 and held at ambient temperatures and salinities until 21 April, then immersed for 14 hours in 100 mg-L-1 ALC buffered with sodium bicarbonate to pH 6.5. After immersion, 1,026 larval menhaden were divided be- tween two 2, 100-L outdoor holding tanks and sampled monthly, May through December. The lar- vae were fed cultured, live Artemia franciscana and increasing additions of dry food until 29 May, when only dry food (Ziegler salmon starter) was added in a ratio of 3 (high food tank) to 1 (low food tank). The amount of dry food initially added for the low food treatment was 25 mLday-1 in April; this amount was increased to approximately 90 mLday-1 by July and held constant after this period. Materials and methods Known-age fish Atlantic menhaden brood stock were held in the labo- ratory and induced to spawn in February 1987 by Hettler 's (1981) methods. Eggs were hatched and larvae were reared under laboratory conditions as described by Warlen (1992). Samples of postlarvae and later juveniles were sampled periodically from Otolith preparation and increment counting Some otoliths from late larvae were mounted whole in a mounting medium (Flo-tex) on glass microscope slides. After increments were counted on the sagit- tal plane, many were removed from the mounting medium and sectioned on one of two planes as de- scribed below. We generally followed the sectioning techniques described in Epperly et al. (1991) and Secor et al. (1992). Our processing techniques for the ALC- Ahrenholz et al.: Otolith ageing of Brevoortia tyrannus 21 marked group were altered: otoliths were dissected from each fish without bleaching (i.e. without a 59c sodium hypochlorite solution to remove tissue) and serial sectioning was used for the transverse sections rather than single cuts with dual blades. Two sec- tioning orientations were used: a transverse section, taken with the primordium (and focus) as the centerline, on a proximal-distal plane 90° to the an- terior-posterior axis, and an oblique-transverse sec- tion on a proximal-distal plane from a posterior and dorsal position through the focus to the anterior ventral(most) portion (Fig. 1). (Some otoliths were also examined on an unsectioned, sagittal plane.) Transverse sections were taken on the right sagitta and oblique sections were taken on the left, with the exception of the 1992 ALC-marked material for which selection of the right or left sagitta was randomized. Resulting sections were then ground and polished according to the methods of Epperly et al. (1991) and Secor et al. (1992). For otolith terminology and in- crement interpretation we followed Pannella ( 1980) and Campana ( 1992). Oxytetracycline and alizarin complexone marks were located with blue light epifluoresence on pre- pared otolith sections and viewed directly on a com- pound microscope or on a video image analysis sys- tem. The OTC-marked increment(s) fluoresced yel- low-green when illuminated with blue light (Fig. 2) and the ALC-marked zone fluoresced orange. The position of each fluorescing mark was fixed with the aid of an ocular micrometer (scope viewing) or with a pointer on the viewing screen; increment counts were made with white or polarized light. Otolith sec- tions viewed on a video monitor were magnified to l,500x. Since only a fraction of a section would fill the screen at this magnification, increment count- ing was done stepwise between distinguishable fea- tures or "landmarks," and counts were summed when interpretation was complete. An additional series of increment counts was performed with the microscope at l,000x and by tallying counts blindly on a hand- held counter. Agreement between the two methods on enumeration generally was better than 95%. Fi- nal counts were means from the two enumeration Figure 1 A whole sagittal otolith from a 39.0-mm (0.481-g) juvenile Atlantic menhaden, Brevoortia tyrannus, is shown to demonstrate the orientation of sectioning for this study. Transverse (dotted lines) and oblique-transverse (dashed lines) sections are displayed. The otolith is oriented with the dorsal edge up and the anterior to the right. 212 Fishery Bulletin 93(2). 1995 methods. Mean counts from the known-age fish were increased by five to estimate time from spawning rather than from first feeding (Warlen, 1992). ALC- marked material was viewed under a microscope at 400-lOOOx, counted with a hand-held counter, and the median of five serial counts was taken. Statistical analysis Regression and analysis of covariance (ANCOVA) computations were conducted with SAS statistical programs (SAS Institute, Inc., 1985). Analysis of co- variance was used to test for common regression B Figure 2 Photomicrographs of juvenile Atlantic menhaden, Brevoortia tyrannus, sagittal otolith sections showing fluo- rescent marks (arrows). (A) Transverse section of otolith from a post-larval fish 12 days after immersion in alizarin complexone solution (ALC). The maximum dimension of this section (dorsal/ventral) is 462 urn. (B) Oblique-trans- verse section of otolith from a juvenile 42 days after im- mersion in oxytetracycline solution (OTC). The maximum dimension of this section ( posterior-dorsal/anterior- ventral ) is 938 urn. parameters (ring count versus known days) for the low and high food treatments and between transverse and oblique-transverse sectioned material for each marking-validation method (Ott, 1977). Mean growth rates were estimated as the slopes of simple linear regressions of length on age. We tested the null hypothesis that growth incre- ments in otoliths of larval and juvenile Atlantic men- haden are formed daily The null hypothesis is ac- cepted if the regression of estimated increment count on known age in days since marking is significant, the slope is not significantly different from one, and the intercept is not significantly different from zero. We also calculated the appropriate statistical power to detect a relatively small difference from a slope of one (Rice, 1987). Student's-^ test was used to test for significance of the slope and intercept. Statistical power to determine a deviation of 0.1 (a=0.05) from a slope of one was estimated for each linear regres- sion (Rice, 1987; Neter et al., 1989). Results Otolith preparations were generally readable for the ranges in sizes and ages for the elapsed times. Known-age fish were sampled at ages 52, 66, 81, 122, 131, 132, and 136 days; they ranged from 10 to 64 mm in fork length. Mean growth for the known age group was 0.55 mm-d-1, with a standard error (SE) of 0.048 over the interval from March to June. OTC- treated fish were sampled 13, 18, 42, 110, and 147 days after treatment; they ranged from 27 to 98 mm in fork length and ranged in estimated age from 62 to 130 days with a mean age of 103 days at marking, resulting in mean growth of 0.49 mm-d-1 (SE=0.011) for the interval April to August. ALC-marked fish were sampled 12, 42, 71, 100, 131, 161, 190, 205, and 237 days after treatment; they ranged from 26 to 175 mm FL and were approximately 70 days old at mark- ing. Mean growth rates of the ALC-marked fish were 0.67 and 0.95 mm-d-1 (SE=0.020 and 0.015) through day 131 postmarking in low and high food tanks re- spectively Growth visibly declined for the interval from day 161 to day 237 postmark and was 0.29 mm-d-1 for both the low and high food treatments (SE=0.037 and 0.195). It was readily apparent from scatter plots that the ALC growth-increment count beyond day 131 (day 161 to day 237) postmark was less than one per day and the variance about an individual sampling date substantially greater. We pooled data up through day 131 postmark from the ALC high and low food treat- ments because tests for homogeneity of the result- ing slopes (P=0.667) and intercepts (P=0.831 ) for age- Ahrenholz et al.: Otolith ageing of Brevoortia tyrannus 213 increment count regressions (transverse sections) revealed that these parameters were not significantly different between treatments. We tested for the homogeneity of slopes for the in- crement count-age regressions between sectioning orientations separately for the known-age experi- ment and both of the marking experiments. None of the slopes were significantly different (P for known age=0.0583, for OTC=0.188, and for ALC=0.667). Tests for differences in intercepts for the same ex- perimental sets revealed none (P for known age=0.345, for OTC=0.082, and for ALO0.526). Therefore we pooled the increment count results within each experiment. We used regressions to compare the results for the known-age and chemically marked otoliths for about the same time duration (i.e. 136 days for known-age fish, 147 days for the OTC group, and 131 days for the ALC group; Table 1, Fig. 3). The intercepts of the three increment-count regressions were not signifi- cantly different from zero, and none of the three slope estimates were significantly different from 1.0 (Table 1). The results for the ALC and the OTC groups had sufficient power (>0. 80) to detect a difference in slope of 0.1 from a value of 1.0. The standard error of the slope was relatively greater for the known-age group, and thus the power estimate was less than that for the ALC and OTC groups (Table 1). We examined the results from day 161 to 237 for the ALC experiment in parallel fashion. A test for homogeneity of slopes for increment count on days postmark revealed a (marginally) significant differ- ence between the sectioning orientations (P=0.044). Estimates of the slopes from separate regressions for the oblique-transverse and transverse sections were significantly different from 1 (P=0.016 andP<0.001). While these observations begin to define limits for applying daily ageing techniques to juvenile Atlan- tic menhaden, they do not reduce the usefulness of the technique over a relatively broad time period. With the minor exception of the period when incre- ment counts were less than daily in the ALC trial, the results for the ALC-marked and OTC-marked test groups were equivalent for either section orientation with slopes near one and with good statistical power to detect a small deviation from one (Fig. 3, Table 1 ). Discussion Atlantic menhaden, on the average, form one growth increment per day through at least an estimable age of 200 days (131 days postmark + approximately 70 days in age at marking) and a size of nearly 150 mm fork length. We could reliably age menhaden up to 200 days old to within about 7 days when juvenile growth rates were high (e.g. above 0.6 mm-d-1 over summer months). At moderate juvenile growth rates (approximately 0.5 mm-d-1), we still detected incre- ments at approximately one per day through a 250 day time period for the OTC fish ( 147 days postmark + an average of 103 days of age at marking), but the variability of an individual age estimate increased in comparison with fish with higher growth rates. For the OTC and known-age test groups respectively, 95% confidence intervals increased to approximately ±16 and 21 d for similar-aged menhaden with slower growth rates (Table 1, Fig. 3). As growth rates de- clined further (below 0.3 mm-d-1), our increment counts declined to less than one per day, and vari- ability in estimated age increased; this may be due to decreases in increment width or to reduced peri- odicity as has been found for starved larval Atlantic menhaden (Maillet and Checkley, 1990). After day 131 postmark (ALC), declining growth rates and an increment periodicity of less than one per day (Fig. Table 1 Least squares linear regression analysis for increment counts from known-age, oxytetracycline (OTC) marked and alizarine (ALC) marked Atlantic menhaden, Brevoortia tyrannus. otolith sections. The null hypotheses tested are that the intercept=0 and the slope=l. (SE=standard error.) Test group n r2 Intercept SE P Slope SE P %Power' 95%CI2 Known-age 37 0.92 -5.853 5.149 0.263 1.036 0.053 0.501 45.1 21 Tetracycline-marked 34 0.97 1.796 2.139 0.407 0.949 0.027 0.068 94.9 16 Alizarine-marked3 84 0.99 0.634 0.701 0.368 0.990 0.008 0.215 >99.9 7 ' Estimate of percent statistical power to detect a deviation of 0.1 from a slope of one at the P = 0.05 level. 2 95% confidence interval (±days) for an age estimate based on individual ring counts. The 95% confidence intervals for indi- vidual age estimates were constant over the range of values used to generate the regression. 3 Through day 131 postmark. 214 Fishery Bulletin 93(2). 1995 3, bottom graph) corresponded with declining tank temperatures (beginning in September; Fig. 4). How- ever, age could still be estimated within about 3 weeks up to 300 days after hatching (230 days post- mark plus about 70 days in age at marking; Fig. 3). If this relationship were consistently repeatable, it would still be a useful tool for estimating ages of older juveniles, even though the age-ring count relation- ship was well below 1:1. However, we suspect that this change was not so much a function of age as it 140 Known -age o o^ 120 '"5 • 100 O sS' 80 • %^ 60 : o 2 40 • 20 160 140 120 100 1 00 1 50 Days postmark Figure 3 Estimated number of otolith growth increments against elapsed time in days (known age) or days postmark (oxytetracycline [OTC] or alizarin complexone [ALC]) of juvenile Atlantic menhaden, Brevoortia tyrannus. Results from oblique-transverse sections (open circles) and trans- verse sections (closed circles) are pooled for the regression lines shown. The regression coefficients are given in Table 1. (Results for the alizarin-complexone trial for days 161- 237, where increment formation rates were less than daily, are shown on the upper right of the bottom graph. Regres- sion parameters for the oblique-transverse (dashed line) and the transverse (solid line) data sets respectively, are r2=0.81 and 0.79, intercept=39.62 and 62.76, and slope=0.73 and 0.52.) was a result of reduced growth rate, possibly in con- junction with declining temperature, which affected our ability to accurately estimate ages. Savoy and Crecco ( 1987 ) also showed that reduced rearing tem- peratures can reduce growth rate and subsequently result in a count-age slope below 1.0 for larval Ameri- can shad, Alosa sapidissima. The growth rates offish treated with ALC (through day 131 post-ALC-mark) are comparable with obser- vations for upper growth rates of juveniles in tidal creeks, spring through fall (0.7 to 0.83 mmd"1; Kroger et al., 1974). The laboratory-reared fish had lower growth rates, but their rates were still greater than those for the ALC fish following postmarking day 131. Therefore it appears that reduced growth rate was a contributing factor for the higher vari- ance of our estimates of the slope of counts versus days for our known-age and OTC test groups. Simi- larly, the variances for the ALC group were highest during the period when increments displayed a less than daily periodicity (Fig. 3). 0 25 i 50 75 100 Day; i 125 150 postmark i 175 i 200 i 225 i 250 i May July Sep. Npv. Dec. Figure 4 (A) Mean fork length of juvenile Atlantic menhaden, Brevoortia tyrannus (error bars represent ±1 standard deviation ),and (B) tank water temperatures for the alizarin complexone rearing trial (see bottom graph on Fig. 3). Ahrenholz et al. : Otolith ageing of Brevoortia tyrannus 215 The otolith sections of the laboratory-reared ma- terial, which includes the OTC fish following mark- ing, generally had less contrast between alternating bands than did field material. Warlen (1988) noted similar results for gulf menhaden. This was not the case for the ALC fish, where contrast more closely resembled field material. OTC and known-age speci- mens were raised indoors in relatively small ( 100 L) containers, as compared with the larger (2,100 L) outdoor containers used for the ALC fish. (All groups were reared in ambient sea water.) Problems in vali- dating otoliths with laboratory-reared fish have been noted for other species (Campana and Moksness, 1991; Toole et al., 1993). Pannella ( 1980) notes that the transition between increments are unclear with respect to chemical or structural changes in some laboratory-reared material. It may be that otoliths from laboratory-reared specimens are less typical because of confounding effects from container size, growth rates, and other aspects of the rearing condi- tions. The poorer contrast may result in lower accu- racy and precision in increment counting, and the slower growth may result in more variable increment counts for a given time period. We obtained detectable OTC and ALC marks in viewing otoliths with the dosages used for immers- ing larvae. Because of the color contrast of the or- ange-against-blue background, ALC was visibly easier to detect under blue light fluoresence than was OTC. ALC has been used for marking eggs and hard parts in fish; it leaves a brilliant mark, does not ad- versely affect growth at low dosages, and does not require dilution procedures as does OTC (Tsukamoto, 1988; Kishiro and Nakazono, 1991). Although we obtained similar results using either oblique-transverse or transverse sections for those periods when increment formation is on the average one per day, one orientation or the other may be pre- ferred for various reasons. The oblique-transverse method of sectioning may be easier to complete in polishing because the primordium and focus can be detected from a greater distance (thickness) when the material is viewed. This reduces processing time and minimizes the number of overground, unusable preparations. On transverse sections of larger or older individuals, or both, the focus is located more by the outline shape than by early optical discovery. However, some investigators using increment measurements for size back calculation or discriminant analysis may pre- fer the transverse section for ease in keeping the same plane of measurement from otolith to otolith. The two section orientations were useful for cross comparisons and interpretation of certain growth zones. Therefore choice of orientation should depend upon the material being examined and the questions being addressed. Acknowledgments The oxytetracycline experiment was conducted by Robert M. Lewis and James F. Guthrie. The known- age fish, obtained from a spawning conducted by William F. Hettler, were kindly provided by Stanley M. Warlen, and were cared for by Sheryan P. Epperly and Ronald M. Clayton. Valerie Comparetta cared for the menhaden from the alizarin complexone rear- ing trial. Many of the marked otoliths were sectioned and polished by Theresa V. Henley and Robin T. Cheshire. Douglas S. Vaughan assisted us with the statistical power computations. This study was par- tially supported by Grant NA16RG0492 from the Coastal Ocean Program, South Atlantic Bight Recruit- ment Experiment (SABRE), of the National Oceanic and Atmospheric Administration to the North Caro- lina Sea Grant College program. Literature cited Campana, S. E. 1992. Measurement and interpretation of the microstruc- ture of fish otoliths. Can. Spec. Publ. Fish. Aquat. Sci. 117:59-71. Campana, S. I'.., and E. Moksness. 1991. Accuracy and precision of age and hatch date esti- mates from otolith microstructure examination. ICES J. Mar. Sci. 48:303-316. Campana, S. E., and C. M. Jones. 1992. Analysis of otolith microstructure data. Can. Spec. Publ. Fish. Aquat. Sci. 117:73-100. Epperly, S. P., D. W. Ahrenholz, and P. A. Tester. 1991. A universal method for preparing, sectioning and polishing fish otoliths for daily ageing. Dep. Commer., NOAATech. Memo. NMFS-SEFC-283, 15 p. Essig, R. J., and C. F. Cole. 1986. Methods of estimating larval fish mortality from daily increments in otoliths. Trans. Am. Fish Soc. 115:34-40. Geffen, A. J. 1992. Validation of otolith increment deposition rate. Can. Spec. Publ. Fish. Aquat. Sci. 117:101-113. Hettler, W. F. 1981. Spawning and rearing Atlantic menhaden. Prog. Fish-Cult. 43:80-84. 1984. Marking otoliths by immersion of marine fish larvae in tetracycline. Trans. Am. Fish. Soc. 113:370-373. Kishiro, T., and A. Nakazono. 1991. Seasonal patterns of larval settlement and daily otolith increments in the temperate wrasse Halichoeres tenuispinis. Nippon Suisan Gakkaishi 56:409-415. Kroger, R. L., J. F. Guthrie, and M. H. Judy. 1974. Growth and first annulus formation of tagged and untagged Atlantic menhaden. Trans. Am. Fish. Soc. 103:292-296. Jones, C. 1986. Determining age of larval fish with the otolith incre- ment technique. Fish. Bull. 84:91-103. 1992. Development and application of the otolith increment technique. Can. Spec. Publ. Fish. Aquat. Sci. 117:1-11. 216 Fishery Bulletin 93(2), 1995 introduction to statistical methods and data Wadsworth Publ. Co., Belmont, CA, 730 p. Maillet, G. L., and D. M. Checkley Jr. 1990. Effects of starvation on the frequency of formation and width of growth increments in sagittae of laboratory- reared Atlantic menhaden Brevoortia tyrannus larvae. Fish. Bull. 88:155-165. Mosegaard, H. 1990. What is reflected by otolith size at emergence? — A reevaluation of the results in West and Larkin ( 1987). Can. J. Fish. Aquat. Sci. 47:225-228. Neter, J., W. Wasserman, and M. H. Kutner. 1989. Applied linear models, 2nd ed. Irwin, Homewood, IL, 667 p. Ott, L. 1977. An analysis. Pannella, G. 1980. Growth patterns in fish sagittae. In D. C. Rhoads and R. A. Lutz (eds.), Skeletal growth of aquatic organ- isms, p. 519-556. Plenum Press, New York. Pepin, P. 1989. Using growth histories to estimate larval fish mor- tality rates. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 191:324-329. Rice, J. A. 1987. Reliability of age and growth rate estimates from otolith analysis. In R. C. Summerfelt and G. E. Hall (eds.), Age and growth of fish, p. 167-176. Iowa State Univ. Press, Ames, IA. Rice, J. A., L. B. Crowder, and F. P. Binkowski. 1985. Evaluating otolith analysis for bloater Coregonus hoyi: do otoliths ring true? Trans. Am. Fish. Soc. 114:532-539. SAS Institute, Inc. 1985. SAS/STAT Guide for personal computers, version 6 ed. SAS Inst., Inc., Cary, NC, 378 p. Savoy, T. F., and V. A. Crecco. 1987. Daily increments on the otoliths of larval American shad and their potential use in population dynamics studies. In R. C. Summerfelt and G. E. Hall (eds.), Age and growth of fish, p. 167-176. Iowa State Univ. Press, Ames, IA. Secor, D. II., J. M. Dean, and E. H. Laban. 1992. Otolith removal and preparation for microstructural examination. Can. Spec. Publ. Fish. Aquat. Sci. 117:19-57. Simoneaux, L. F., and S. M. Warlen. 1987. Occurrence of daily growth increments in otoliths of juvenile Atlantic menhaden. In R. C. Summerfelt and G. E. Hall (eds.), Age and growth offish, p. 443-451. Iowa State Univ. Press, Ames, IA. Toole, C. L., D. F. Markle, and P. M. Harris. 1993. Relationships between otolith microstructure, microchemistry, and early life history events in Dover sole, Microstomias pacifieus. Fish. Bull. 91:732-753. Tsukamoto, K. 1988. Otolith tagging of ayu embryo with fluorescent substances. Nippon Suisan Gakkaishi 54:1289-1295. Warlen, S. M. 1988. Age and growth of larval gulf menhaden, Brevoortia patronus, in the northern Gulf of Mexico. Fish. Bull. 86:77-90. 1992. Age, growth, and size distribution of larval Atlantic menhaden off North Carolina. Trans. Am. Fish. Soc. 121:588-598. Abstract. — The nutritional sta- tus of laboratory-reared summer flounder, Paralichthys dentatus, larvae and early juveniles was as- sessed by morphometric, biochemi- cal, and histological criteria. Con- ditions of food deprivation were imposed on 6-, 16-, and 33-day-old larvae as well as on 60-day-old ju- veniles. Samples of ad-libitum-fed or starved individuals were ana- lyzed with regard to standard length, dry weight, eye diameter to head height ratio, pectoral angle, RNA:DNA ratio, total protein con- tent, histological appearance of se- lected organs, and cell height of the anterior and posterior intestinal mucosae. In general, tolerance to starvation increased with age: 60 h in 6-day-old-larvae, 72 h in 16- day-old larvae, 8 d in 33-day-old- larvae, and 10 d in 60-day-old-ju- veniles. The results of this study demonstrate that morphological criteria are either not good indica- tors of nutritional status (eye:head ratio), good only for larvae (pecto- ral angle), or require extensive cali- bration (standard length and dry weight). They also show that bio- chemical criteria are either not good indicators ( protein content ) or are sensitive to starvation only in juveniles (RNAtDNAratio). Among the histological criteria, thickness of the posterior intestinal mucosa was the most sensitive and consis- tent indicator of starvation in sum- mer flounder larvae and early ju- veniles. The most salient attributes of this histological analysis were sensitivity, objectivity, ease of in- terpretation, and exemption from shrinkage calibration. These re- sults suggest the use of the histo- logical approach in the face of un- certainties associated with the other methods examined. On the other hand, application of either morphological or histological crite- ria is appropriate for an aquacul- ture setting in which age of larvae is known. Description of the starving condition in summer flounder, Paralichthys dentatus, early life history stages Gustavo A. Bisbal Graduate School of Oceanography, University of Rhode Island Narragansett. Rl 02882 Present address. Northwest Power Planning Council 85! S.W Sixth Avenue. Suite 1 100. Portland. OR 97204-1348 David A. Bengtson Department of Zoology, University of Rhode Island Kingston, Rl 02881 Manuscript accepted 1 December 1994. Fishery Bulletin 93:217-230 (1995). It is currently accepted that star- vation and predation are the main agents of marine fish larval mortal- ity (Hunter, 1976; Bailey and Houde, 1989). However, the relative mag- nitudes of the processes controlling prerecruit mortality are, for the most part, either unknown or con- troversial (Pepin, 1988/1989; Miller et al., 1991). Furthermore, these forces may at times operate concur- rently, adding an additional level of complexity. For instance, although intense food limitation of fish lar- vae can be lethal per se, it could also be regarded as a sublethal agent that exposes weakened individuals to selective predation by reducing their growth rates (Laurence, 1985; Houde, 1987; Fogarty et al., 1991), reaction capabilities (Hunter, 1972, 1981), or ability to maintain a pre- ferred depth in the water column (Blaxter and Ehrlich, 1974). Nutritional condition of teleost larvae has been measured and de- scribed in a number of ways. The physical deterioration of larvae re- sulting from experimental condi- tions of food deprivation has been interpreted by means of morpho- metric and gravimetric (e.g. Hempel and Blaxter, 1963; Ishibashi, 1974; Ehrlich et al., 1976), biochemical (e.g. Ehrlich, 1974, a and b; Buckley, 1980, 1982, 1984; Fraser et al., 1987; Clemmesen, 1987; Richard et al., 1991), and histological (e.g. Ehrlich et al., 1976; O'Connell, 1976, 1980; Theilacker, 1978; Mar- tin and Malloy, 1980; Watanabe, 1985; Theilacker and Watanabe, 1989) criteria. In some cases, sev- eral of these techniques were tested concurrently to determine their relative utility as indicators of star- vation (Martin and Wright, 1987; Setzler-Hamilton et al., 1987). Mar- tin and Wright (1987) proposed the combined application of two or three techniques to any given study be- cause of differences in response time of the measure to actual nu- tritional status. The summer flounder, Para- lichthys dentatus, is a temperate paralichthyid flatfish occurring in Atlantic estuaries and continental shelf waters from Nova Scotia to Florida (Rogers and Van Den Avyle, 1983; Able et al., 1990). During 1983-91, the average landings from the commercial and recreational fishery were 11,400 metric tons. Recent surveys revealed that the stock biomass is currently at the lowest average level since the early 1970s which, combined with calcu- 217 218 Fishery Bulletin 93(2). 1995 lated present fishing mortality rates, indicates that summer flounder stocks are overexploited (NMFS, 1993). The decline in the natural fishery, together with recent success in culturing other flatfish spe- cies, such as the Japanese flounder, Paralichthys olivaceus (Sproul and Tominaga, 1992), and the Eu- ropean turbot, Scophthalmus maximus (Person-Le Ruyet et al., 1991), stimulated interest in the develop- ment of technology for the culture of summer flounder. Basic information on the ability to distinguish starving from feeding P. dentatus larvae and juve- niles will be useful for studies of both natural and cultured populations. Studies on the occurrence or frequency of starvation in either field populations or aquaculture operations must be preceded by an ex- perimental study in which specific starvation indi- cators are validated for fish of known nutritional his- tory. Therefore, the aim of our research was to evalu- ate and compare alternative criteria for assessing starvation effects at several stages during the early life history of P. dentatus. We characterize P. dentatus larvae and recently metamorphosed juveniles subjected to conditions of starvation or ad libitum feeding, using biochemical, morphometric, and histological criteria. Materials and methods Adult broodstock P. dentatus were collected from Narragansett Bay, Rhode Island, and Long Island Sound, Connecticut, and were held in laboratory fa- cilities. They were spawned after artificial induction with repeated carp pituitary injections (2.5 mg/kg) during 8 to 12 consecutive days (Smigielski, 1975). The fertilized eggs were distributed in 38-L glass aquaria covered with opaque black plastic. Each tank was filled with UV-treated filtered (1 |im) Nar- ragansett Bay seawater (adjusted to 34 ±\%c salin- ity by brine addition). Antibiotic (200 mg erythro- mycin activity dissolved in 23 liters of water) was added at one time in each tank, and water changes were performed every 2-3 days to maintain water quality. During the first week, the alga, Tetraselmis suecica, was added to the water. No artificial sub- strate was added to the aquaria. Water temperature was maintained at 19 ±1°C throughout the experi- ment. Overhead illumination adjusted to a natural photoperiod and aeration were provided. Hatching began 55 hours after fertilization. Dur- ing the next 4 days the larval digestive system be- came morphologically ready to process external food at the time of mouth opening (Bisbal and Bengtson, in press). Since yolk resorption and mouth opening are almost simultaneous, flounder larvae were fed daily on rotifers, Brachionus plicatilis, cultured on T. suecica (Lubzens, 1987) after day 4. Newly hatched Reference Artemia III nauplii (Collins et al., 1991) were offered for the first time 18 days later, and the rotifer supply was progressively reduced. Settlement to the bottom began on day 45 after hatching. Available literature on the early life stages offish and previous direct observations on flounder cultures directed our interest toward four developmental stages (Al-Maghazachi and Gibson, 1984; Blaxter, 1988; Youson, 1988). The effects of starvation were evaluated at day 6 (early food ingestion, yolk com- pletely resorbed), day 16 (these larvae have positively ingested and processed food at least once or else they would have died within 10 days after hatching), day 33 (at the beginning of metamorphic eye migration), and day 60 (bottom-dwelling juveniles have meta- morphosed) after hatching. At these times, sub- samples of the larvae pool were randomly placed in one of two 5-L tanks (25 larvae/L): one (control group) receiving food ad libitum (i.e. Brachionus or Artemia ); the other (starved group) devoid of food. Although the presence of food in the gut was not systemati- cally recorded, the performance of feeding motions and active swimming were visually confirmed on an individual basis. An extra subsample was processed as described below in order to establish the basal levels of the several parameters measured prior to the initiation of the imposed starvation (time 0). Based on previous observations on the progression of starvation at different age intervals and constant visual monitoring of behavioral changes, each group (control and starved) was sampled at least three times, from the beginning of the experimental expo- sure until the onset of mortality. A larva was consid- ered dead if it did not respond to gentle probing with a glass rod. If that was the case, the larva was cap- tured and placed under the dissecting microscope for a confirmation of its status. At each sampling time the same protocol was followed: 6 to 10 individuals from each group were sampled for histological analy- sis, 10 for morphometric and dry weight measure- ments, and 10 for biochemical analyses. Morphometric measurements consisted of stan- dard length, eye diameter, head height, and the pec- toral girdle angle as defined by Ehrlich et al. ( 1976). Measurements of live larvae were taken under a dis- secting microscope equipped with an ocular microme- ter accurate to 0.7 um. Pectoral angles were traced under a camera lucida and measured on a digitizing pad. Each fish was then rinsed in deionized water and placed in a 60°C oven until a constant dry weight was obtained. Weight was measured, on either a Met- tler AE 240 balance or a Cahn C-31 electrobalance. Samples for biochemical analysis were rinsed in deionized water and individually preserved in Eppen- Bisbal and Bengtson: Starvation in early life stages of Parahchthys dentatus 219 dorf vials in a — 80°C freezer for no more than 45 days until RNA, DNA, and protein determinations were performed. Owing to the extremely small size of the 6-day-old larvae, each determination was performed on samples consisting of two larvae pooled in the same vial. This was the only case where pooling was necessary. Determinations of RNA and DNA were performed according to the methodology described by Bentle et al. (1981) as modified for individual larvae of small size (Nacci et al., 1992). Total protein determination was assessed by a dye-binding assay ( Bradford, 1976) in which bovine serum albumin was the reference standard. Volumes were adjusted to 96-well micro- titration plates and, after completion of the colored reaction, absorbances were read at 600 nm in an EL 312 Bio-Tek automated microplate reader. The fraction of the sample destined for histologi- cal examination consisted of 6 to 10 specimens pre- served in Dietrich's fixative, embedded in paraffin blocks, and completely sectioned every 4—5 pm on a rotary microtome. Light microscopy analysis was per- formed after staining with Cason's trichromic (Cason, 1950). The qualitative histological examination concen- trated on the liver, pancreas, musculature, and in- testinal mucosae. For quantitative purposes, mea- surements of the cell height of the anterior and pos- terior intestinal mucosae were performed as de- scribed by Theilacker and Watanabe (1989). These measurements consisted of the distance from the basal membrane to the tip of the brush border and were obtained under a microscope equipped with an ocular micrometer eyepiece accurate to 0.02 urn. In the anterior intestine, the site for this measurement was the ventral row of cells located just cranial of the intestinal valve complex (see Fig. 6, A and B). A similar measurement on the posterior intestine mu- cosa was performed caudal of the intestinal valve (see Fig. 6, A and B). Control and starved group parameters at each sam- pling time were compared by using Student's Mests. The overall level of significance (a) for each data set was fixed at a nominal value of 0.05. The critical t- value for k number of tests was adjusted through Bonferroni's correction as oik (Sacks, 1978). All values were plotted as arithmetic means and standard errors. Results Morphometry and biochemistry Sampling of 6-day-old larvae was conducted at 24, 48, and 60 hours after initiation of starvation (Fig. 1 ). Mortality in starved larvae began about 60 hours after food deprivation. The mean standard length of starved larvae was lower than their fed counterparts at all sampling times tt18=3.39, P=0.003, at 24 h, Fig. 1A). Mean dry weight (Fig. IB) and the mean eye to head ratio (Fig. 1C) did not differ significantly (dry weight, £18=2.39, P=0.028, at 24 h; eye/head ratio, *18=1.31, P=0.208, at 60 h). The mean pectoral angle of starved larvae decreased relative to the fed larvae after 24 hours (f18=3.53, P=0.002; Fig. ID). Mean RNA:DNA ratios of starved larvae were lower than those of fed larvae «18=2.68, P=0.015, at 60 h; Fig. IE). After 60 hours, mean RNA:DNA ratios had de- creased from an initial value of 3.75 to 2.74 and 2.31 in fed and starved larvae, respectively. Levels of pro- tein remained fairly constant throughout the experi- mental period (Fig. IF). Sampling of 16-day-old larvae was conducted at 24, 48, and 72 hours after initiation of starvation (Fig. 2). Starved 16-day-old larvae began to die after 72 hours. Mean standard length of both groups was not statistically different at any time U18=2.25, P=0.037, at 72 h; Fig. 2A). However, differences in mean dry weight were significant at 72 hours U18=3.04, P=0.007; Fig. 2B). A comparison of the mean dry weight at the beginning of the experiment and that for each group after 72 hours indicates that fed lar- vae incorporated body mass at a daily specific rate of 7.9%/day, whereas starved larvae lost weight at a rate of 10.4%/day. Similarly, the ratio of eye diam- eter to head height became significantly different only after 72 hours of starvation (t18= 4.41, P<0.001; Fig. 2C). Little difference was observed in the mean pectoral angle between the groups until 48 h (f 18=4.59, P<0.001 ) and 72 hours tf 18=8.25, P<0.001; Fig. 2D). For three days, the mean RNA:DNA ratio of fed animals (2.97-2.99) remained near the mean value at time 0 (2.81; Fig. 2E). During the same pe- riod, starved fish showed a steady decline in RNA:DNA ratio to a final value of 1.93, although dif- ferences were only significant at 72 hours (<18=3.47, P=0.003). Mean protein content initially decreased in both groups but became fairly constant and indis- tinguishable between groups thereafter (Fig. 2F). Sampling of 33-day-old larvae was conducted at 24, 72, 120, and 192 hours after initiation of the ex- periment (Fig. 3). Larvae began to die after approxi- mately 8 days of food deprivation. Starved larvae were significantly shorter than fed ones after 72 hours (*18=3.32, P=0.004; Fig. 3A). Daily specific growth in length of fed larvae progressed at a rate of 2.5%/day but remained almost constant in starved fish. Dry weight of fed larvae also increased signifi- cantly relative to starved larvae (Fig. 3B). At the end of the experimental period, the fed larvae had in- 220 Fishery Bulletin 93(2). 1995 0 12 24 36 48 60 Time (h) Figure 1 Summer flounder, Paralichthys dentatus, 6-day-old larvae. Morphometric, gravi- metric, and biochemical changes during ad libitum feeding ( ) or starvation (• ). (A) standard length; (B) dry weight; (C) eye diameter/head height ratio; (D) pec- toral angle; (E) RNA:DNA ratio; (F) total proteins. Symbols represent the arith- metic mean of samples of 9-10 animals ±Standard Error. Asterisks indicate a statistically significant difference between fed and starved groups at a particu- lar sampling time. creased their dry weight by more than 206% of the initial value, whereas the starved group remained unchanged. This weight difference was significant at 72 hours (*18=4.46, P<0.001), 120 hours «18=5.54, P<0.001), and 192 hours (*18=4.06, P<0.001). The eye:head ratio of both groups differed at 192 hours (*18=4.28, P<0.001; Fig. 3C). At 72 hours (*18=5.38, P<0.001), 120 hours (*18=7.89, P<0.001), and 192 hours U18=6.85, P<0.001) the starved group had a lower mean pectoral angle than did the fed group (Fig. 3D). The RNA:DNA ratio showed an initial rise from 2.88 to 3.41 and to 3.26 in fed and starved larvae, respectively (Fig. 3E). After 24 hours, both groups showed a decline, but starved larvae declined to a much greater extent, resulting in significant differences be- tween the two groups at 120 hours (<18=4.85, P<0.001 ) and 192 hours «18=5.18, P<0.001). By day 8, starved larvae had ratios 62.4% lower than those of fed larvae. Mean total protein of starving larvae was also signifi- cantly lower than that in fed fish, a difference detect- able after 192 hours tt18=4.19,P<0.001; Fig. 3F). Samples of 60-day-old metamorphosed juveniles were taken at 72, 144, and 216 hours (Fig. 4). Mor- tality in the starved group began after 10 days. While the mean standard length of both groups was differ- ent at 216 hours (*18=4.01, P<0.001; Fig. 4A), mean dry weights of the starved and fed groups were sig- nificantly different from each other at each sampling time (*18=2.95, P=0.009, at 72 h; Fig. 4B). In 9 days, fed juveniles grew in length at a daily specific rate of 3.1%/day, whereas starved larvae grew at 0.7%/day. During the same time, fed fish gained weight at a rate of 10.1%/day, whereas starved fish lost 1.9% of their body mass every day. The eye diameter to head height ratio in both groups varied in a similar man- ner (Fig. 4C). A significant difference in the shape of the pectoral angle was only detected at 216 hours U18=3.15, P=0.006; Fig. 4D). Mean RNA:DNA ratios Bisbal and Bengtson. Starvation in early life stages of Paralichthys dentatus 221 E £ 5 0) 5.0 ■o CD ? 4.5 ra 55 160 o> 140 a. - 120 O) ■ 80 o 60 36 48 72 0 48 60 130 n> 110 >° DO 2.5 5 D > 30 | 25 "5 o 20 | Time (h) Figure 2 Summer flounder, Paralichthys dentatus, 16-day-old larvae. Morphometries, gravi- metric, and biochemical changes during ad libitum feeding ( ) or starvation ( • ). (A) standard length; (B) dry weight; (C) eye diameter/head height ratio; (D) pec- toral angle; (E) RNA:DNA ratio; (F) total proteins. Symbols represent the arith- metic mean of samples of 9-10 animals iStandard Error. Asterisks indicate a statistically significant difference between fed and starved groups at a particu- lar sampling time. of starved juveniles remained consistently lower than those of fed juveniles at all times (^=3.05, P=0.007, at 72 h; Fig. 4E). During the experimental period, fed fish maintained a mean ratio between 8 and 9. In contrast, the ratio in starved fish dropped from an initial value of 8.49 to a final value of 4.86, a 68% difference from the fed group. Differences in mean total proteins were significant at 72 hours U17=3.46, P=0.003) and 216 hours (i18=2.71, P=0.014; Fig. 4F). Histology The trunk musculature in fed larvae was striated, closely packed, and composed of parallel myofibrils over the lateral surfaces of the notochord (Fig. 5A). However, under starving conditions, the fibrils were not distinguishable and their parallel orientation was disrupted. Further, muscle fibers were widely sepa- rated because of shrinkage of the cells (Fig. 5B). In 6 and 16-day-old larvae, degradation of skeletal muscle was evident after 24 hours of starvation. In 33-day- old larvae and 60-day-old juveniles, this effect was de- tected after 72 and 144 hours of starvation, respectively. Hepatic tissue of fed larvae appeared continuous and compact, composed of hepatic cells organized in typical liver cords (Fig. 5C). The hepatocytes had a bulky cytoplasm with low staining affinity, several vacuolar inclusions, and round nuclei in their cen- ters. Conversely, liver tissue of starving larvae was fractionated and exhibited loss of the cellular cord arrangement and contained wide intercellular spaces (Fig. 5D). The cytoplasm was severely collapsed and deeply stained (there were no vacuolar spaces) and contained heavily pigmented eccentric nuclei of ir- regular shape. Liver deterioration was detected af- ter 24, 48, 120, and 144 hours of food deprivation in 6, 16, 33-day-old larvae, and 60-day-old juveniles, respectively. 222 Fishery Bulletin 93(2), 1995 Q> 8 „ 2500 3 2000 .!? 1500 d> J 1000 0) >, HI 38 36 B 140 <9. 130 a. 120 3 3.5 > 2.5 5 > 400 300 200 100 72 72 120 Time (h) Figure 3 Summer flounder, Parahehthys dentatus, 33-day-old larvae. Morphometric, gravi- metric, and biochemical changes during ad libitum feeding ( ) or starvation ( • ). (A) standard length; (B) dry weight; (C) eye diameter/head height ratio; (D) pec- toral angle; (E) RNA:DNA ratio; (F) total proteins. Symbols represent the arith- metic mean of samples of 9-10 animals ±Standard Error. Asterisks indicate a statistically significant difference between fed and starved groups at a particu- lar sampling time. The acinar arrangement of pancreatic cells was sensitive to starvation. In fed larvae, the typical aci- nar structure was well defined and symmetrical; cells were arranged around central intercellular lumina (Fig. 5E). Under food deprivation, the acinar struc- ture became increasingly disorganized (Fig. 5F). In 6, 16, and 33-day-old larvae, symptoms of pancre- atic degeneration were discernible as early as 24 hours after food deprivation. In 60-day-old juveniles, this ef- fect was detectable after 144 hours of starvation. The intestinal mucosa of fed larvae was continu- ous and uninterrupted. A distinct brush border com- posed of microvilli was evident. The intestinal lu- men was wide and the columnar enterocytes were systematically arranged and deeply folded. Cytoplas- mic vesicles and vacuoles, suggestive of pinocytosis and intracellular protein digestion, were present in varying numbers and sizes (Fig. 6C). In the starved group, the intestinal mucosa was discontinuous, less compact, and had irregular cells and intercellular spacing. The brush border was not smooth and signs of cell sloughing were evident from the necrotic de- bris in the lumen. The enterocytes were shrunken and collapsed resulting in a severe reduction of the entire mucosal thickness. The intestinal lumen was comparatively occluded. Cytoplasmic vesicles were not present (Fig. 6D). The mean cell height of the anterior intestinal mucosa was significantly different between starved and fed groups of all ages. In all cases, these differ- ences were detectable from the first sampling time (*18=2.99, P=0.008, at 24 h in 6-day-old larvae; £18=8.20, P<0.001, at 24 h in 16-day-old larvae; *18=6.06, P<0.001, at 24 h in 33-day-old larvae; and 1 10=H.O, P<0.001, at 72 h in 60-day-old juveniles; Fig. 7, A, C, E, and G, respectively). Differences in the cell height of the posterior in- testinal mucosa of starved and fed groups were also Bisbal and Bengtson Starvation in early life stages of Paralichthys dentatus 223 Time (h) Figure 4 Summer flounder, Paralichthys dentatus, 60-day-old juveniles. Morphometric, gravimetric, and biochemical changes during ad libitum feeding ( ) or starva- tion (•). (A) standard length; (B) dry weight; (C) eye diameter/head height ratio; (D) pectoral angle; (E) RNA:DNA ratio; (F) total proteins. Symbols represent the arithmetic mean of samples of 9-10 animals iStandard Error. Asterisks in- dicate a statistically significant difference between fed and starved groups at a particular sampling time. significant from the first sampling time in 16-day- old larvae (f18=6.86, P<0.001, at 24 h), 33-day-old larvae (f 18=2.87, P=0.010, at 24 h), and in 60-day-old juveniles U10=3.05, P=0.012, at 72 h; Fig. 7, D, F, and H, respectively). In the case of 6-day-old larvae, these differences were significant after 48 hours U18=10.49, P<0.001; Fig. 7B). Discussion In summer flounder, the onset of mortality due to starvation occurred later in older ontogenetic stages, similar to observations made by Ivlev (1961) and Wyatt ( 1972). Response to starvation may depend not only on energy reserves stored in the liver, muscles, and other body tissues but also on more efficient cata- bolic capabilities attained during ontogenesis (Ehrlich, 1974b). Yin and Blaxter ( 1987 ) argued that the relative tolerance to lack of food is the result of reduced energy costs for metamorphosing flounder that increasingly spend more time lying on the bottom. Morphometric, biochemical, and histological mea- surements all showed significant differences between starved and fed summer flounder at some point dur- ing development. The question then becomes the fol- lowing: Which individual measurement or combina- tion is the most useful indicator of nutritional sta- tus as development proceeds? We define usefulness both in terms of ease and practicality of application. Because of the relatively low resistance to starva- tion in younger larvae, it is imperative to select an indicator with the sensitivity to respond quickly to changes in nutritional status. While mean length and dry weight of fed summer flounder showed a steady increase, starving fish shrank or did not grow. Only in 6-day-old larvae did standard length decrease, presumably representing 224 Fishery Bulletin 93(2). 1995 ***» W* Figure 5 Histological comparisons of ad-libitum-fed and starved summer flounder, Paralichthys dentatus, larvae. (A) 16 days after hatch- ing ( DAH ), skeletal musculature, ad-libitum-fed control ( bar=20 um ). ( B ) 19 DAH, skeletal musculature, after 72 hours of starva- tion (bar=35 um). (C) 18 DAH, hepatic tissue, ad-libitum-fed control (bar=25 um). (D) 19 DAH, hepatic tissue, after 72 hours of starvation (bar=20 um). (E) 19 DAH, pancreatic tissue, well-fed control (bar=55 urn). (F) 19 DAH, pancreatic tissue, after 72 hours of starvation (bar=30 um). Bisbal and Bengtson: Starvation in early life stages of Paralichthys dentatus 225 A pi LU LU W X Jf S *■ , ' ».%*.••• Figure 6 Histological comparisons of well-fed and starved summer flounder, Paralichthys dentatus. larvae. (A) 19 days after hatching (DAH), intestinal mucosae at the intestinal valve, ad-libitum-fed control (bar=50 urn). (B) 19 DAH, intestinal mucosae at the intestinal valve, after 72 hours of starvation (bar=60 |im). The arrows indicate the mucosal height in each intestinal segment. (C) 16 DAH, detail of enterocytes showing absorptive inclusions, ad-libitum-fed control (bar=35 urn). (D) 19 DAH, detail of enterocytes showing cellular sloughing into the lumen, after 72 hours of starvation (bar=20 pm). Abbreviations: AI=anterior intestine, IV=intestinal valve, LU=lumen, PI=posterior intestine. The arrows indicate the mucosal height in each intestinal segment. shrinkage of the larvae after yolk absorption. Shrink- age of starved early stage larvae has been reported in herring (Ehrlich et al., 1976) and striped bass (Eldridge et al., 1981). Additionally, large variation in the extent of shrinkage has been reported in pre- served larvae as a consequence of capture and fixa- tion (Theilacker, 1980; Hay, 1981). The time of sam- pling must also be considered to account for changes in dry weight associated with the diurnal rhythms of visual feeders (Arthur, 1976 ). The dry weight of a larva with a full digestive tract will obviously be greater than that of the same larva with an empty digestive tract. Because extensive calibration between laboratory and field experiments is necessary to compare small larvae at the same developmental stage, length and dry weights are not useful indicators of nutritional status. The pectoral angle accurately identified the nutri- tional condition of earlier larval stages. The variabil- ity within each group was low and significant differ- ences were established early in the sampling proto- col. However, these attributes progressively vanished at later stages. The eye length to head diameter ra- tio was not a good indicator of the feeding condition at any stage because of large variability within each group. Ehrlich et al. (1976) found the pectoral angle to be a good indicator of starvation in both herring, Clupea harengus, and plaice, Pleuronectes platessa , but the eye:head ratio was a good indicator in her- ring only. Morphological characteristics are relatively simple to measure, inexpensive, and require little time, but the validity of laboratory-derived criteria is uncer- 226 Fishery Bulletin 93(2). 1995 c w » "? C 3 s £ E .c •E 13 - 0) O Q. in — •- ° ■£. 0) S E ""(UP § E £ o 21 lc 19 A^ 17 - \ 15 \ 13 ■ 11 9 #*--_ . *• *. 15 13 11 D **\ 9 7 *T^ ** Time (h) Figure 7 Anterior and posterior intestinal mucosal cell height in summer flounder, Paralichthys dentatus, during ad libitum feeding ( ) or starvation ( • ). (A-B) 6-day- old larvae; (C-D) 16-day-old larvae; (E-F) 33-day-old larvae; (G-H) 60-day-old ju- veniles. Symbols represent the arithmetic mean of samples of 9-10 animals ±Stan- dard Error. Asterisks indicate a statistically significant difference between fed and starved fish groups at a particular sampling time. tain for populations in nature (O'Connell, 1976; Theilacker, 1986; Fraser et al., 1987; Setzler- Hamilton et al., 1987). Confinement in experimen- tal tanks influences growth rates and morphometries of laboratory-reared larvae (Blaxter, 1975; Arthur, 1976). At present, the applicability of morphometric indices seems more reliable and feasible for reared larvae, where age and historic information are known and feeding can be controlled. Given the inherent problems of laboratory-to-field calibration and the dynamic changes in body propor- tions due to allometric growth and progressive ossi- fication of developing larvae, Theilacker (1978) con- cluded that no single morphological feature can be singled out as a consistent indicator of larval condi- tion. Because some of the variability associated with field-collected larvae is accounted for by differences in age of larvae, interpretation of the data requires the ability to determine age. Ageing of summer floun- der from daily growth ring deposition is difficult on field-collected larvae of mixed age (Dery, 1988, Szedlmayer and Able, 1992). Therefore, the use of Bisbal and Bengtson: Starvation in early life stages of Paralichthys dentatus 221 length as an estimate of age is a coarse alternative when age data are not available. If this is the case, then the analysis should be restricted to a limited size range (Martin and Wright, 1987). Among the biochemical criteria, protein data had the largest associated variability. Similar variation in the protein content of winter flounder, Pleuronectes americanus, larvae has been obtained by Cetta and Capuzzo ( 1982 ). Other studies have shown that pro- tein breakdown is the major source of energy during starvation of herring (Ehrlich, 1974a I and plaice (Ehrlich, 1974b), at least during early larval stages, when lipid reserves are negligible or nonexistent. The RNA:DNA ratio showed less individual vari- ability and provided a more sensitive index to feed- ing condition than did protein. The ratio of total RNA to DNA in tissues has been extensively used as an indicator of recent growth rate and changes in feed- ing levels of various larval fish ( Buckley, 1984; Bulow, 1987). In recent years, the relative ease and sensi- tivity of this analysis have stimulated the develop- ment of several procedural variations of the tech- nique. Thus, discretion should be exercised in directly comparing RNA:DNA values obtained with different methods and standards (Caldarone and Buckley, 1991). In addition, it has been demonstrated that temperature can affect the RNA:DNA ratio in fish larvae (Buckley, 1982, 1984; Buckley and Lough, 1987). In the 6-day-old larvae used in our study, the RNA:DNA ratio declined by about 30% over the 60- hour experiment, even in fed larvae. After that de- cline, which was similar in magnitude to that ob- served in fed winter flounder larvae 4 days after yolk absorption (Buckley, 1980), the mean RNA:DNA ra- tio of fed larvae remained within a narrow range (2.7 to 3.1) for the remainder of the larval period. There- fore, it appears that a mean RNA:DNA ratio of less than 2.7 strongly suggests food limitation in floun- der. The equilibrium RNA:DNA ratio for P. dentatus larvae reared at 14, 16, or 18°C has been reported to be 2.4, 3.1, and 2.6, respectively (Buckley, 1984). Win- ter flounder and striped bass, Morone saxatilis, lar- vae also appear to establish narrow RNA:DNA equi- librium ranges (Buckley, 1980; Wright and Martin, 1985). After metamorphosis, the RNA:DNA ratio of summer flounder increased to between 8.2 and 8.9, whereas that of starved fish was never above 6. A similar increase in RNA:DNA ratio after metamor- phosis has been observed in fed winter flounder (Buckley, 1980). Although RNArDNA ratio and pectoral angle were both able to discriminate fed from starved summer flounder, pectoral angle was more sensitive to star- vation than was the RNA:DNA ratio in larvae, whereas the opposite was true for juveniles. The quick response of RNA:DNA ratio to food depriva- tion noted by Buckley (1980), Wright and Martin (1985), and Martin and Wright (1987) was not ap- parent in summer flounder. An advantage of bio- chemical methods for field use is that larvae dam- aged by sampling gear can still be analyzed (Fraser et al., 1987) and distortions due to chemical fixatives are avoided. We conclude, therefore, that RNA:DNA ratios may be useful as indicators of nutritional limi- tation in summer flounder larvae and juveniles. Histological analyses indicated that food depriva- tion of summer flounder larvae and early juveniles had a marked effect on several internal structures. Starvation was readily manifest in the intestine, fol- lowed in time by changes in the pancreas, liver, and skeletal musculature, as previously seen in other teleost larvae (Umeda and Ochiai, 1975; Ehrlich et al., 1976; O'Connell, 1976, 1980; Theilacker, 1978, 1986; Cousin et al., 1986; Margulies, 1993). The nu- trient shortages that result from food deprivation have an almost immediate manifestation in the in- testinal epithelium. In starved summer flounder, lipid and protein inclusions progressively disap- peared from the intestinal epithelial cells until they were no longer visible, similar to the previous obser- vations of Ehrlich (1974a), Ciullo (1975), Watanabe ( 1985), and Govoni et al. ( 1986). By contrast, Kjorsvik et al. (1991) reported that pinocytic inclusions were visible at all stages of starvation in cod larvae. Mucosal cell height in summer flounder was ex- tremely sensitive to starvation when applied to the posterior intestine, whereas the height of the ante- rior intestinal mucosa varied with increasing size or age, or both. The mean height of the posterior intes- tinal mucosa showed a stable boundary for discrimi- nation of fed and starved individuals (above 10 (im for fed larvae, below for starved) regardless of indi- vidual size or age. This criterion therefore provides the best tool to assess starvation in summer floun- der during the first 60 days of life. Previous investi- gators have noted the utility of histological exami- nation of intestinal mucosa, especially cell height, for determination of starvation (Ehrlich et al., 1976; Theilacker, 1978, 1980; Watanabe, 1985; Umeda et al., 1986; Theilacker and Watanabe, 1989; Kj0rsvik et al., 1991). The discriminating power of the mu- cosal cell height criterion incorporates the well known advantages of other traditional histological evalua- tion procedures. As with the biochemical criteria, specific equipment and some technical proficiency are required to process the samples. One advantage to this criterion is that samples can be preserved on a ship and no subsequent calibration is necessary for shrinkage due to capture or fixation, or for individual size or age. 228 Fishery Bulletin 93(2), 1995 To summarize, this study has demonstrated that 1) morphological criteria were either not good indi- cators of nutritional condition (eye:head ratio), good only for larvae (pectoral angle), or require extensive calibration (standard and dry weight); 2) biochemi- cal criteria are either not good indicators (protein content) or are sensitive only in juveniles (RNA:DNA ratio); and 3) the histological criterion of posterior intestinal mucosa cell height is the most sensitive and consistent indicator of starvation in young sum- mer flounder over the stages examined. Although the current study needs to be applied to field-collected larvae, the laboratory data indicate that the addi- tional time and expense of histological sample prepa- ration and analysis is justified in the face of uncer- tainties associated with the other methods examined. On the other hand, application of either morphologi- cal or histological criteria is appropriate for an aquac- ulture setting in which age of the larvae is known. Acknowledgments This research was supported by the United States Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fish- eries Service, Saltonstall-Kennedy grant number NA-90-AA-H-SK033. The authors thank Doranne Borsay, Sue Cheer, Ken Thomas, and Paul Yevich for their assistance in this study. Robert Bullock and Austin Williams kindly granted access to their fa- cilities and equipment. 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Percentage of starving northern anchovy, Engraulis mordax, larvae in the sea as estimated by histological methods. Fish. Bull. 78:475-489. Pepin, P. 1988/1989. Predation and starvation of larval fish: A nu- merical experiment of size- and growth-dependent survival. Biol. Oceanogr. 6:23-44. Person-Le Ruyet, J., F. Baudin-Laurencin, N. Devauchelle, R. Metailler, J.-L. Nicolas, J. Robin, and J. Guillaume. 1991. Culture of turbot (Scophthalmus maximus). In 3. P. McVey (ed.), Handbook of mariculture, Vol. II: Finfish aquaculture, p. 21-41. CRC Press, Boca Raton, FL. Richard, P., J. P. Bergeron, M. Bouhic, R. Galois, and J. Person-Le Ruyet. 1991. Effect of starvation on RNA, DNA and protein con- tent of laboratory-reared larvae and juveniles of Solea solea. Mar. Ecol. Prog. Ser. 72:69-77. Rogers, S. G., and M. J. Van Den Avyle. 1983. Species profiles: life histories and environmental re- quirements of coastal fishes and invertebrates (South At- lantic ). Summer flounder. U.S. Fish Wildl. 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Effects of starvation on the histological and morpho- logical characteristics of jack mackerel, Trachurus symmetricus, larvae. Fish. Bull. 76:403-414. 1980. Changes in body measurements of larval northern anchovy, Engraulis mordax. and other fishes due to han- dling and preservation. Fish. Bull. 78:685-692. 1986. Starvation-induced mortality of young sea-caught jack mackerel, Trachurus symmetricus, determined with his- tological and morphological methods. Fish. Bull. 84:1-17. Theilacker, G. H., and Y. Watanabe. 1989. Midgut cell height defines nutritional status of labo- ratory raised larval northern anchovy, Engraulis mordax. Fish. Bull. 87:457^169. Umeda, S., and A. Ochiai. 1975. On the histological structure and function of diges- tive organs of the fed and starved larvae of the yellowtail, Seriola quinqueradiata. Jpn. J. Ichthyol. 21: 213-219. Umeda, S., H. Ochi, and A. Ochiai. 1986. The influences of delayed initial feeding on survival, growth and digestive organs in early postlarvae of the jack mackerel, Trachurus japonicus. Report USA Marine Bi- ology Inst., Kochi Univ. 8:45-53. Watanabe, Y. 1985. Histological changes in the liver and intestine of freshwater goby larvae during short-term starvation. Bull. Jpn. Soc. Sci. Fish. 51:707-709. Wright, D. A., and F. D. Martin. 1985. The effect of starvation on RNA:DNA ratios and growth of larval striped bass, Morone saxatilis. J. Fish Biol. 27:479^185. Wyatt, T. 1972. Some effects of food density on the growth and behaviour of plaice larvae. Mar. Biol. 14:210-216. Yin, M. C, and J. H. S. Blaxter. 1987. Feeding ability and survival during starvation of marine fish larvae reared in the laboratory. J. Exp. Mar. Biol. Ecol. 105:73-83. Youson, J. H. 1988. First metamorphosis. In W. S. Hoar and D. J. Randall (eds.), Fish physiology, Vol. XIB, p. 135-196. Aca- demic Press, New York. Abstract. — Species diversity and abundance offish eggs in shelf waters of the western Gulf of Alaska were similar in both surface neuston net tows and subsurface bongo net tows, but a unique group of fish larvae appear to be associ- ated with the neuston in this re- gion. The dominance of larvae of an osmerid, several hexagrammids, cottids, bathymasterids, Anoplo- poma fimbria, Cryptacanthodes aleutensis, and Ammodytes hexap- terus in this group resembles the neustonic assemblage offish larvae found in the California Current region along the U.S. west coast and most of these taxa are consid- ered obligate members of the neus- ton. Several taxa, however, appear to be abundant in the neuston only at night suggesting a facultative association with the neuston through a diel pattern of vertical migration. The facultative association of cer- tain species of larvae with the neus- ton varies with larval size. The distribution patterns ob- served for most taxa of fish larvae in the neuston during this study suggest that during spring, spawn- ing and emergence of larvae into the plankton and subsequently into the neuston take place mainly around Kodiak Island (except along the seaward side) and along the Alaska Peninsula to the southwest. Analysis of multispecies spatial patterns using recurrent group analysis and numerical classifica- tion did not reveal the existence of more than one neustonic assem- blage of fish larvae in the study area. Apart from perhaps Pleuro- grammus monopterygius larvae, which are known to occur through- out the Gulf of Alaska, and to a lesser extent A. fimbria and Hemi- lepidotus hemilepidotus, members of this neustonic assemblage of lar- vae are not commonly found in the oceanic zone. The ecological significance of a neustonic existence for larvae of fish that are primarily demersal spawners in the Gulf of Alaska is considered to be trophic in nature. Neustonic fish larvae seem to be able to exploit to their advantage the unique feeding conditions which exist at the sea surface. Manuscript accepted 25 September 1994. Fishery Bulletin 93:231-253 ( 1995). Neustonic ichthyoplankton in the western Gulf of Alaska during spring Miriam J. Doyle William C. Rugen Richard D. Brodeur Alaska Fisheries Science Center National Marine Fisheries Service. NOAA 7600 Sand Point Way NE. Seattle. WA 981 I 5-0070 The Fisheries Oceanography Coor- dinated Investigations (FOCI) is a long-term cooperative research pro- gram conducted by National Oce- anic and Atmospheric Administra- tion (NOAA) biological and physi- cal scientists to describe processes leading to recruitment variability of commercially important fish and shellfish stocks of the Gulf of Alaska and Bering Sea (Schumacher and Kendall, 1991). To date, most effort has concentrated on walleye pol- lock, Theragra chalcogramma, in the western Gulf of Alaska, specifically in Shelikof Strait and along the Alaska Peninsula. Understanding the dynamics of the spring spawning of this species in Shelikof Strait and the subsequent hatching, drift, growth, and survival of the larvae, in interaction with the physical and bio- logical oceanographic environment, have been the primary goals of FOCI. Ancillary to the information col- lected on the early life history stages of walleye pollock, are data on the distribution and abundance patterns of eggs and larvae of other fishes that spawn in the coastal waters and adjacent deeper waters of the western Gulf of Alaska. These observations can contribute to our understanding of the biology and ecology of fish populations in this region and the relationships be- tween their life history strategies and the environment. Prior to the onset of FOCI inves- tigations in the early 1980's, plank- ton collections in the vicinity of Kodiak Island were generally lim- ited in scope but still yielded infor- mation on species composition and spatio-temporal patterns in abun- dance offish eggs and larvae ( Rogers et al., 1979; Kendall and Dunn, 1985; Kendall et al.1). Based on early FOCI plankton collections, large-scale patterns in the ichthy- oplankton have been documented for a more extensive portion of the continental shelf along the Alaska Peninsula (Rugen and Matarese2; Rugen3). There remains, however, considerable data from the more recent FOCI spring cruises, the analysis of which may improve our understanding of the ecological re- lationships among the fish popula- tions inhabiting this region. * This paper is contribution FOCI-0 187 from the Fisheries Oceanography Coordinated Investigations program of the National Oceanic and Atmospheric Administration. 1 Kendall, A. W., Jr., J. R. Dunn, R. J. Wolotira Jr., J. H. Bowerman Jr., D. B. Dey, A. C. Matarese, and J. E. Munk. 1980. Zooplankton, including ichthyoplankton and decapod larvae, of the Kodiak Shelf. U. S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fish. Sci. Cent., 7600 Sand Point Way NE, Seattle, WA 98115. Proc. Rep. 80-8, 393 p. 2 Rugen, W. C, and A. C. Matarese. 1988. Spatial and temporal distribution and rela- tive abundance of Pacific cod (Gadus macrocephalus ) larvae in the western Gulf of Alaska. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fish. Sci. Cent., 7600 Sand Point Way NE, Seattle, WA, 98115. Proc. Rep. 88-18, 53 p. 3 Rugen, W. C. 1990. Spatial and temporal distribution of larval fish in the western Gulf of Alaska, with emphasis on the pe- riod of peak abundance of walleye pollock. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fish. Sci. Cent., 7600 Sand Point Way NE, Seattle, WA, 98115. Proc. Rep. 90-01, 162 p. 231 232 Fishery Bulletin 93(2). 1995 During the 1970's and 1980's, several investiga- tions of ichthyoplankton in the neuston were con- ducted in the northeast Pacific Ocean, primarily off the coasts of Washington and Oregon but also ex- tending to southern California waters ( Ahlstrom and Stevens, 1976; Shenker, 1988; Brodeur, 1989; Doyle 1992). These studies established that larvae of many fish are abundant at the surface as well as deeper in the water column and that an additional group of species is almost exclusively neustonic. Doyle (1992) identified obligate and facultative members of the neuston among the larvae and juveniles of fish col- lected off Washington, Oregon, and northern Cali- fornia and attributed their association with the neus- ton primarily to the unique trophic conditions that prevail in this environment. Clearly, the neustonic realm is important in the early life history of many fish species (Zaitsev, 1970; Hempel and Weikert, 1972; Moser, 1981; Tully and O'Ceidigh, 1989; Doyle 1992). The level of importance, however, varies with geographical area and local conditions. Rogers et al. (1979), Kendall and Dunn (1985), Kendall et al.1, and Rugen3 identified a unique sur- face component in the ichthyoplankton of the west- ern Gulf of Alaska and concluded that the larvae of several species, mainly hexagrammids and cottids, are primarily neustonic. This finding merits further investigation concerning the ecological significance of a neustonic existence, particularly in this shelf area where there is a dynamic surface zone with a vigor- ous flow field (Reed et al., 1988; Reed and Schu- macher, 1989). The present paper focuses on the neustonic ichthyoplankton in the western Gulf of Alaska. During seven of the spring cruises (1981- 86), neuston as well as subsurface bongo net sam- pling was carried out. Data from these collections were used 1 ) to examine species composition and rela- tive abundance of ichthyoplankton taxa in the neus- ton and to compare these with subsurface ichthyoplankton col- lected concurrently; 2) to iden- tify obligate and facultative members of the neustonic ich- thyoplankton; 3) to investigate diel variation in catches of lar- vae in the neuston; 4) to com- pare size distributions among the neustonic and subsurface larvae; and 5) to describe hori- zontal distribution patterns of the dominant neustonic ich- thyoplankton species and to re- late these to the oceanography of the western Gulf of Alaska. Methods In 1981, the National Marine Fisheries Service (NMFS) initiated studies on the early life history of walleye pollock in the northwestern Gulf of Alaska. These studies included cooperative cruises with the Soviet Pacific Research Institute (TINRO, Vladi- vostok). Although the primary purpose of these cruises was to assess the spatial distribution and abundance of walleye pollock and to understand the dynamics of their planktonic stages, all taxa collected were identified and measured. For the present study, we used data from seven cruises during which both neuston net and bongo net samples were collected at each station. These cruises were conducted during spring months of the years 1981 to 1986 (Table 1). The survey area extended from the Kenai Peninsula ( 145°W), southwest along the Alaska Peninsula and Kodiak Island to Unimak Pass (165°W). The topog- raphy of the study area in the western Gulf of Alaska is characterized by numerous troughs and shallow banks (Fig. 1). The shelf area, as defined by the 200- m isobath, is generally wide (65-175 km) and drops abruptly to depths of 5,000-6,000 m in the Aleutian Trench, which parallels the shelf break (Fig. 1). A detailed description of the physical oceanography of the region is provided by Reed and Schumacher (1986). The neuston was sampled at a total of 898 stations (Table 1). Station locations varied for each cruise because of specific objectives and are given in Dunn and Rugen.4 Neuston net samples were collected with a Sameoto sampler ( Sameoto and Jaroszynski, 1969 ) Dunn, J. R., and W. C. Rugen. 1989. A catalog of Northwest and Alaska Fisheries Center ichthyoplankton cruises, 1965-1988. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fish. Sci. Cent, 7600 Sand Point Way NE, Seattle, WA, 98115. Proc. Rep. 89-04, 197 p. Table 1 Summary of neuston collections by cruise in the western Gulf of Alaska. conducted during spring of 1981 to 1986 Cruise Inclusive dates Number of collections Longitudinal range (°W) 1SH81 5-18 March 1981 130 148-164 2SH81 16-24 April 1981 60 151-159 1CH83 16-31 May 1983 62 154-159 1SH84 17 April-9 May 1984 157 145-159 1P085 29 March-21 April 1985 151 150-158 2P085 16 May-8 June 1985 189 148-168 1GI86 30 March-20 April 1986 149 138-166 Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 233 Gulf of Alaska 169° W 167° 165° 163° 161° 159° 157° 155° 153° 151° 149° 147° 53° 145° Figure 1 Near surface currents and some geographic and bathygraphic features of the western Gulf of Alaska. Currents based on Reed and Schumacher (1986). with a mouth opening of 0.3 m x 0.5 m and with a 0.505-mm mesh net. Ship speed was 2 knots. Stan- dard MARMAP (Marine Resources Monitoring As- sessment and Prediction) oblique tows (Smith and Richardson, 1977) were conducted to sample subsur- face ichthyoplankton with 60-cm bongo samplers fit- ted with 0.505-mm mesh nets. In shelf waters, tows were made to a depth close to the bottom, usually around 5 m above, and in deep water to a maximum depth of approximately 200 m. Calibrated flowmeters in the mouths of the samplers were used to deter- mine the volume of water filtered by each net. Counts offish eggs and larvae were converted to den- sities per 1,000 m3 for neuston collections, as follows: (n)( 1,000 )/[(h)(w )(/)], where n = number of organisms in sample; h = effective fishing height of net opening (0.15 m); w = width of net opening (0.5 m); / = length of tow in meters (calculated from flowmeter). In order to determine the importance of the neustonic layer relative to that of the entire water column, we compared the paired catches of neuston and bongo tows from the same stations following the approach derived by Hobbs and Botsford ( 1992). This approach accounts for the differences in surface area sampled between the neuston tows and the bongo tows. The method solves for the density of larvae per unit area in the ith sample (A.) and the portion of total water column larvae in the neuston ( 9) simul- taneously in an iterative fashion. We first calculated the surface area (in m2) sampled by the neuston (Am) and bongo (A..) net as: Kt = hxwxl 234 Fishery Bulletin 93(2), 1995 and Ah - r ■ xkxI where r - radius of net opening (0.3 m for bongo net); d = depth of water column sampled. The maximum likelihood estimates of A and 6 for k sample pairs are derived as follows: S„,+Sh x=- and ■'ni °fei k 6 = min IX (=1 XA"'^' V i=l where S ■ = number of larvae in the ith neuston sample; Sbj = number of larvae in the j'th bongo sample. This method assumes that the sample pairs are drawn from a population that is distributed randomly in the horizontal plane but stratified vertically (Hobbs and Botsford, 1992). Plankton samples were preserved in the field with a 5% formalin-seawater solution buffered with so- dium tetraborate. Ichthyoplankton were sorted at the Polish Plankton Sorting Center in Szczecin, Poland. All fish eggs and larvae were removed and identi- fied to the lowest possible taxa. Identifications were later verified at the NMFS laboratory in Seattle. Up to 50 larvae per taxon per station were measured to the nearest 0.1 mm standard length (SL). Since sampling patterns and positions were dif- ferent for each cruise, the study area was subse- quently divided into 298 sectors of approximately 215 mi2 (347 km2). Data from stations within each sector were pooled so that average distribution patterns could be determined for the dominant neustonic taxa. The number of tows in each sector over all seven cruises are illustrated by various levels of stippling (Fig. 2). The mean densities of individual taxa were calculated for each sector by dividing the summed i i i i i i i i i i i i i i i i i i i i i i i i , 11 i i i hP^FQ 57 "00 59°00N 55°00 1 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 I I I I I I I I I " 53 "00 165°00W 163°00 161°00 159°00 157°00 155°00 153°00 151°00 149°00 147°00 145°00 Figure 2 Neuston sampling coverage and intensity per sector for all seven cruises combined (1981-86). Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 235 abundance in each sector by the total number of sta- tions sampled within that sector. Cooccurrences of larval fish taxa in the neuston net samples were determined by using recurrent group analysis (Fager, 1957). This analysis identi- fies groups of taxa that occur together relatively fre- quently and considers only joint occurrences and not abundance. The procedure involves two steps: the calculation of indices of affinity for each pair of taxa and the formation of groups of taxa based on a cho- sen minimum index value. The equation for the af- finity index is N, l where/ = the affinity index (range 0-1); Nj = the number of joint occurrences; Na = the number of occurrences of taxon a, the less common taxon; Nb = the number of occurrences of taxon b, the more common taxon. species. The "flexible sorting" strategy was used and a recommended value of -0.25 was chosen as the clus- tering intensity coefficient (Lance and Williams, 1967). To aid in identification of groups from the dendro- grams, the original data sets (species abundance x stations) were rearranged into two-way tables accord- ing to the order that species and stations appeared in the dendrograms. In this manner, it was possible to see how a group of stations was characterized by the occurrence or definitive range of abundance of a particular species or group of species. After the final species and station groups were chosen, the two-way tables were reduced by calculating the mean abun- dance of each species, within the different species groups, for each station group. The station groups were then plotted on maps of the sampling area to aid in the identification of geographically distinct groups of fish larvae. Results For this study, minimum index values for the for- mation of recurrent groups were set at 0.3 and 0.4, respectively, for two separate runs of the analysis. One or both of these values have been chosen previ- ously by other workers who applied this method to ichthyoplankton data (Kendall and Dunn, 1985; Moseretal., 1987). Numerical classification was used to investigate multispecies spatial patterns among the fish larvae in the neuston. It involves grouping similar entities based on numerical data such as, in this instance, species abundance at a range of stations (Clifford and Stephenson, 1975). An agglomerative, hierarchical technique was chosen. Normal and inverse classifi- cations were carried out on the data sets (i.e. both the species and stations were classified into groups). Only the dominant larval fish taxa occurring in >4% of the samples were included in this analysis, as scarce taxa did not contribute significantly to spa- tial patterns overall. The numerical classification was performed on each individual data set from the seven neuston cruises, as well as on data combined for all the cruises (i.e. mean abundance of larval fish spe- cies in each of the previously chosen geographical sectors). The data were log-transformed prior to analysis. The first step in the classification procedure com- prised the calculation of correlation coefficients for each pair of species or stations in a data set. The Bray-Curtis dissimilarity measure was used. An agglomerative, hierarchical sorting strategy pro- duced dendrograms depicting clusters of stations and Taxonomic composition and density A total of 24,327 fish eggs were collected in the neus- ton samples. Eggs of 12 species representing five families were identified from the samples (Table 2). The numerically dominant taxa included the gadid Theragra chalcogramma and several pleuronectids, mainly Errex zachirus, Hippoglossoides elassodon, Microstomas pacificus, and other unidentified Pleuronectidae. Theragra chalcogramma was the only taxon whose eggs occurred in greater than 10% of all the samples. Although the density of Clupea pallasi eggs was relatively high, this taxon occurred in less than 1% of the samples. It is likely that the presence of these demersal eggs in the neuston was due to clumps of eggs breaking off the substrate and floating to the surface. The low diversity and gener- ally low density offish eggs in the neuston (relative to the diversity and density of fish larvae) was in- dicative of the scarcity of species that spawn pelagic eggs in this region. In total, 41,157 specimens of larvae or early juve- niles were caught in the neuston. The taxonomic di- versity and overall density were higher than for the eggs (Table 3). Thirty-five species were identified representing a total of 18 families. Apart from T. chalcogramma and Anoplopoma fimbria, which spawn pelagic eggs close to the bottom, the numeri- cally dominant taxa among the larvae were demer- sal spawners. Among the dominant larvae, the families Hexa- grammidae and Cottidae were best represented. The 236 Fishery Bulletin 93(2). 1995 Table 2 Summary of all fish eggs collected in neuston gear during spring cruises from 1981 to 1986 in the western Gulf of Alaska. Percent Mean occurrence abundance Scientific name Common name (n=895) (no./lOOOm3) Clupea pallasi Pacific herring 0.37 22.83 Theragra chalcogramma walleye pollock 28.12 205.59 Sebastalobus spp. unidentified thornyhead 1.39 1.04 Chirolophis nugator mosshead warbonnet 0.09 0.03 Trachipterus altivelis king-of-the-salmon 0.74 0.16 Eopsetta exilis slender sole 0.09 0.01 Errex zachirus rex sole 6.38 5.50 Hippoglossoides elassodon flathead sole 7.12 10.69 Microstomas pacificus Dover sole 5.46 33.50 Platichthys stellatus starry flounder 1.57 1.22 Pleuronectes asper yellowfin sole 0.09 0.03 Pleuronectes isolepis butter sole 0.37 0.20 Pleuronectes quadrituberculatus Alaska plaice 5.83 12.67 Pleuronectes vetulus English sole 0.46 0.49 Pleuronectidae unidentified flounder 5.83 12.67 Teleost Type A unidentified teleost 4.07 2.07 Teleost Type H unidentified teleost 0.09 0.01 most abundant species by far was the hexagrammid Hexagrammos decagrammus , which was present in 71% of all the samples collected and had a mean den- sity of 234 larvae/1,000 m3 (Table 3). Less abundant were the hexagrammids H. stelleri and Pleurogram- mus monopterygius. The category Hexagrammos spp. was also numerically important. Many of these lar- vae were most likely H. decagrammus, but the con- dition of the specimens made specific identification impossible. The most important taxa among the cottids were Hemilepidotus hemilepidotus, H. jordani, H. spinosus, Hemilepidotus spp., and Myoxocephalus spp. Hemilepidotus hemilepidotus was the third most abundant species overall, present in 20% of the samples with a mean density of 60 lar- vae/1,000 m3. Ammodytes hexapterus was the sec- ond most abundant taxon with a mean density of 148 larvae/1,000 m3 and was present in 14% of the samples. With a mean density of 43 larvae/1,000 m3, Cryptacanthodes aleutensis was ranked as the fourth most abundant larval taxon and it was present in 21% of the samples collected. The remaining larval taxa each were found in less than 10%- of the samples and had a mean density of less than 20 larvae/1,000 m3. Most important among these were Mallotus villosus, Theragra chalcogramma, the hexagrammids and cottids mentioned above, Bathy master spp., and the family Stichaeidae. The rest were scarce, mostly with a mean density of less than 1 larva/1,000 m3 and a percent occurrence of less than 2%. A comparison of the occurrence of dominant taxa of ichthyoplankton in the neuston samples with their occurrence in bongo samples, and estimates of the fraction of each taxon in the neuston, indicate that most of the dominant larval taxa in the neuston were scarce or absent in the subsurface zone (Table 4). In contrast, the dominant taxa of eggs were the same for both neuston and subsurface samples. Theragra chalcogramma eggs were by far the most abundant and accounted for 69%- of all eggs caught in the neus- ton and 95% in the bongo samples. Eggs of pleuro- nectids, mainly of Microstomus pacificus, Hippo- glossoides elassodon, and Errex zachirus, were the only other eggs to be significantly abundant in ei- ther gear, again indicating the paucity of pelagic spawners in this region. The estimated fractions ( 6) of these eggs occurring in the neuston were moder- ately high (9-26%) merely showing that positively buoyant eggs tend to accumulate in the surface layer. The only taxa of larvae well represented in both neuston and bongo samples were T chalcogramma, A. hexapterus, and Bathy master spp. (Table 4). All three occurred in much fewer of the neuston net than the bongo net samples, however. In addition, the frac- tions of these taxa occurring in the neuston were low (<13%) suggesting that they were only occasionally abundant in the neuston. Among the less abundant taxa in the neuston, Mallotus villosus, Stichaeidae, Zaprora silenus, and Myoxocephalus spp. were only slightly better represented in neuston net than in Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 237 Table 3 Summary of all fish larvae collected in the neuston during spring cruises from 1981 to 1986 in the western Gulf of Alaska. Percent Mean occurrence abundance Scientific name Common name (n=895) (no./1000m3i Mallotus villosus capelin 5.83 8.90 Osmeridae unidentified smelt 0.09 0.03 Nansenia Candida bluethroat argentine 0.09 0.01 Oncorhynehus keta chum salmon 0.09 0.01 Bathylagidae unidentified deepsea smelt 0.09 0.01 Stenobrachius leucopsarus northern lampfish 0.09 0.01 Gadus maeroeephalus Pacific cod 0.65 0.15 Theragra chalcogramma walleye pollock 6.75 13.66 Gadidae unidentified gadid 0.56 0.24 Sebastes spp. unidentified rockfish 1.67 2.68 Hexagrammos decagrammus kelp greenling 59.11 194.84 Hexagrammos lagocephalus rock greenling 0.46 0.09 Hexagrammos octogrammus masked greenling 1.85 0.26 Hexagrammos stelleri whitespotted greenling 8.14 1.87 Ophiodon elongatus lingcod 1.76 0.53 Pleurogrammus monopterygius Atka mackerel 3.61 1.76 Hexagrammos spp. unidentified greenling 3.52 5.94 Hexagrammidae unidentified greenling 0.28 0.04 Anoplopoma fimbria sablefish 5.00 15.37 Blepsius bilobus crested sculpin 0.09 0.01 Enophrys bison buffalo sculpin 0.09 0.01 Hemilepidotus hemilepidotus red Irish lord 16.84 50.25 Hemilepidotus jordani yellow Irish lord 5.55 3.63 Hemilepidotus spinosus brown Irish lord 6.38 5.80 Hemilepidotus spp. unidentified Irish lord 3.70 5.47 Leptocottus armatus Pacific staghorn sculpin 0.09 0.01 Myoxoeephalus spp. unidentified sculpin 2.59 1.04 Radulinus boleoides darter sculpin 0.09 0.01 Cottidae unidentified sculpin 0.65 0.10 Agonidae unidentified poacher 0.28 0.04 Cyclopteridae unidentified snailfish 0.37 0.06 Bathymaster spp. unidentified ronquil 4.63 6.68 Chirolophis decoratus decorated warbonnet 0.19 0.05 Chirolophis spp. unidentified warbonnet 0.56 0.16 Lumpenella longirostris longsnout prickleback 0.09 0.02 Stichaeidae unidentified stichaeid 1.57 4.90 Cryptacanthodes aleutensis dwarf wrymouth 17.76 36.13 Cryptaeanthodes giganteus giant wrymouth 1.67 0.53 Zaprora silenus prowfish 2.78 1.09 Ammodytes hexapterus Pacific sand lance 11.75 123.75 Atheresthes stomias arrowtooth flounder 0.19 0.04 Errex zachirus rex sole 0.46 0.08 Hippoglossoides elassodon flathead sole 0.93 0.15 Hippoglossus stenolepis Pacific halibut 1.67 0.48 Mierostomus pacificus Dover sole 0.09 0.01 Platichthys stellatus starry flounder 0.19 0.05 Pleuronectes bilineatus rock sole 0.56 0.12 Pleuronectes vetulus English sole 0.09 0.01 Psettichthys spp. unidentified sole 0.19 0.02 Reinhardtius hippoglossoides Greenland turbot 1.48 0.55 238 Fishery Bulletin 93(2), 1995 Table 4 Comparison of percent occurence and percent of total abundance (based on no ./1000 m3) of the dominant taxa in the neuston and bongo collections and fraction of each taxon occurring in the neustonic layer (6). Taxa ranked in order of percent occurrence in neuston. Neuston Bongo Fraction Percent Percent Percent Percent Taxa occurrence total abundance occurrence total abundance in neuston Eggs Theragra chalcogramma 33.85 69.40 46.90 95.10 0.013 Hippoglossoides elassodon 8.69 3.61 21.06 0.72 0.091 Errex zachirus 7.68 1.86 18.07 0.77 0.155 Pleuronectidae 7.02 4.28 8.54 2.10 0.261 Microstomias paciftcus 6.57 11.31 13.08 0.87 0.209 Larvae Hexagrammos decagrammus 71.16 40.15 4.99 0.22 0.930 Cryptacanthodes aleutensis 21.38 7.44 3.22 0.08 0.861 Hemilepidotus hemilepidotus 20.27 10.35 2.33 0.09 0.890 Ammodytes hexapterus 14.14 25.50 73.84 29.92 0.053 Hexagrammos stelleri 9.80 0.79 0.11 <0.01 0.989 Theragra chalcogramma 8.13 2.82 48.78 46.05 0.009 Hemilepidotus spinosus 7.68 1.19 0.55 0.01 0.932 Mallotus villosus 7.02 1.83 5.10 0.18 0.568 Hemilepidotus jordani 6.68 0.75 0.00 0.00 1.000 Anoplopoma fimbria 6.01 3.17 2.33 0.04 0.689 Stichaeidae 5.79 0.32 2.33 0.10 0.728 Bathymaster spp. 5.57 1.38 17.74 6.47 0.121 Hemilepidotus spp. 4.45 1.13 2.33 0.04 0.638 Pleurogrammus monopterygius 4.34 0.38 0.11 <0.01 0.974 Hexagrammos spp. 4.23 1.22 0.00 0.00 1.000 Zaprora silenus 3.34 0.22 2.55 0.05 0.541 Myoxocephalus spp. 3.12 0.22 1.88 0.08 0.596 bongo net samples perhaps also reflecting a faculta- tive association with the neuston (i.e. concentrated at the surface only during certain hours). However, the high (54-73%) fraction occurring in the neuston suggests a strong association by these species with the surface zone. The remaining dominant taxa of larvae in the neus- ton were absent or scarce in the bongo samples and all except Hemilepidotus spp. had a 0 value of >85% (Table 4). It seems that their association with the neuston was obligative (i.e. permanent presence in the surface zone). These obligative taxa included the hexagrammids and cottids as well as Crypta- canthodes aleutensis and Anoplopoma fimbria. They formed a unique community of fish larvae in the neustonic realm. Most of the dominant taxa of fish larvae that in- habit the subsurface zone of the western Gulf of Alaska were absent or rare in the neuston, includ- ing Gadus macrocephalus and Sebastes spp., and species of Bathylagidae, Myctophidae, Cyclopteridae, Agonidae, and Pleuronectidae (Kendall and Dunn, 1985; Rugen3). Diel variation in catches of larvae To examine diel variation in catches of larvae for both the neuston and bongo samplers, stations were grouped by hour of the day, and mean densities of larvae for each of the 24 hours were calculated. Be- cause of the substantial variability in day length over the 3-month sampling period, it was not possible to assign a specific sunrise and sunset time that could be used for all cruises. For the purposes of this analy- sis, we assumed that the daytime period lasted from 0700 to 1900 hr and the nighttime from 2200 to 0400 hr. The intervening periods of 0400 to 0700 h and 1900 to 2200 h were presumed to have been twilight, including dawn and dusk, respectively. For all neuston catches combined, both the total mean density and the number of hauls in which lar- vae were caught were higher at night than during Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 239 the day (Fig. 3A). This pattern was not apparent for the bongo catches taken from the same stations (Fig. 3B). Some of the highest catches of larvae in the bongo samples were taken during daylight. The ra- tio of night:day catches for the neuston was 9.1:1, whereas it was 1.6:1 for the bongo tows. The high ratio of night:day catches in the neuston may be at- tributed to two factors: 1) vertical migration of lar- vae into the neuston at night and 2) enhanced avoid- ance of the neuston sampler during daylight. One or both of these factors may operate among the species of larvae in the neuston. Diel variation in catches among all the dominant taxa of neustonic larvae suggested a daytime de- crease in density in the neuston. All larvae, except Hexagrammos decagrammus and Theragra chalco- Total Fish Larvae m Neuston Samples B 3 5 7 9 11 13 15 17 19 21 23 Local Time (Hours) Total Fish Larvae in Bongo Samples ° 2000 llllllllllllllllllll 1 3 5 7 9 11 13 15 17 19 21 23 Local Time (Hours) Figure 3 Diel variation in density and occurrence of total fish larvae in (A) neuston samples and (B) bongo samples for all cruises combined (1981-86). Bars represent mean density offish larvae; dashed line represents total number of collections; solid line represents the number of hauls that collected fish gramma, had lowest occurrences in neuston samples during the day (Fig. 4). Sampler avoidance by the larvae during daylight probably contributed signifi- cantly to this pattern. The taxa Hemilepidotus jordani, H. spinosus, Myoxocephalus spp., Bathy- master spp., and Zaprora silenus were absent from neuston samples during most daylight hours but were relatively abundant in twilight or nighttime samples. Because the latter three of these taxa were relatively common in bongo samples (Table 4), indi- cating a facultative association with the neuston, their scarcity in the neuston during the day may have been at least in part due to a diel pattern of vertical migration with larvae moving toward the surface zone at night. This may have also been true for T. chalcogramma and Ammodytes hexapterus whose larvae were extremely abundant in the bongo net samples (Table 4) but abundant in the neuston samples only at night (Fig. 4). Mallotus villosus lar- vae were also relatively common in bongo samples (Table 4), although they were most abundant in the neuston at night (Fig. 4). As expected, catches of T. chalcogramma eggs showed no discernable diel variation in either den- sity or frequency of positive hauls. The large mean densities during two periods of the day are most likely due to spatial variation of egg densities rather than to any biological factor. Length distributions of dominant neustonic taxa Standardized length distributions were plotted for the dominant neustonic taxa (Fig. 5). Comparisons were made with the corresponding length distribu- tions of larvae in the subsurface zone for six of these taxa that were sufficiently represented in the bongo samples. For all these six taxa, greater median lengths were documented for larvae in the neuston than in the bongo hauls, especially in the case of Mallotus villosus and Ammodytes hexapterus. Mallotus villosus seemed unusual in that all larvae caught in both neuston and bongo net samples were >25 mm SL indicating a predominance of postflexion larvae. This is most likely due to species identifica- tion capabilities, as it is not possible to identify small osmerids to species until the pectoral fin rays are completely developed. With the exception of Bathymaster spp., the larvae caught in the neuston were also significantly larger than those caught in the bongo collections (Kolmogorov-Smirnov (K-S) 2- sample tests; allP<0.01). For A. hexapterus, it seemed that only the large postflexion larvae and early ju- veniles (mostly >20 mm SL) migrated into the neus- ton, mainly at night; most A. hexapterus larvae 240 Fishery Bulletin 93(2), 1995 Theragra chalcogramma 7 9 11 13 15 17 19 21 23 Local Time (Houis) Theragra chalcogramma Local Time (Hours) Hexagrammos decagrammus 3 11 13 15 17 IS 21 23 Local Time (Hours) Pleurogrammus monopterygius 9 11 13 15 17 19 21 23 Local Time (Hours) Mallolus villosus 9 11 13 15 17 19 21 23 Local Time (Hours) Ammodytes hexapterus ^3000- / 000 / IS. ^ / / \ ° 2000- \ r / Mean Density v 4 i . i III tIIttT i > cJm 9 11 13 15 17 19 21 23 Local Time (Hours) Hexagrammos stelleri 9 11 13 15 17 19 21 Local Time (Hours) Anoptopoma fimbria S-700 E I 8 --500 -8 > o O -6 °- ^400 c J™ 7 19 21 23 Local Time (Hours) Figure 4 Diel variation in density and occurrence of walleye pollock, Theragra chalcogramma, eggs and individual dominant taxa offish larvae in neuston samples, for all cruises combined (1981-86). Bars represent mean density; solid line represents the percent of hauls that caught larvae. Doyle et at.: Neustonic ichthyoplankton in the western Gulf of Alaska 241 Hemilepidotus hemilepidotus 5 7 9 11 13 15 17 10 21 23 Local Time (Hours) Hemilepidotus spinosus 9 11 13 IS 17 19 21 23 Local Time (Hours) Myoxocephalus spp 3 15 17 IB 21 23 Local Time (Hours) Cryptacanthodes aleutensis 9 11 13 15 17 19 21 23 Local Time (Hours) Hemilepidotus jordani 9 11 13 15 17 19 21 23 Local Time (Hours) Hemilepidotus spp 0 11 13 15 17 19 21 23 Local Time (Hours) Bathymaster spp Local Time (Hours) Zaprora silenus 9 11 13 15 17 19 21 23 Local Time (Hours) Figure 4 (continued) 242 Fishery Bulletin 93(2). 1995 Uallotus villosus n-685 v9^ 45 36 25 15 5 5 15 25 35 45 2025303640465056606670 Cryptacanthodes alautensis 5-3142 35 , , , , o J. 10 o Q. 10 15 20 25 30 35 40 45 SO v J HLu. 0 5 10 15 20 25 30 35 40 45 SO Hemilepidotus jordani n-276 10 15 20253035404550 Hemilepidotus spp. 20j n"38S 15- V Theragra chalcogramma 45 35 25 15 Hexagrammos stelleri 25 15- 10 25 35-, 30- 25- 20- 15- 10- 5- 10 15 20 25 30 36 40 45 50 45 36 25 15- 5 5 15- 25 36 46 5 10 15 20 25 30 35 40 45 60 Ba thymaster spp. n-629 Myoxocephalus spp. 2S-, 20 15- 10 5 0 5 10 15 20 25 10 15 20253035404550 Pleurogrammus monopterygius S 10 15 20 26 30 36 40 45 SO Hemilepidotus hemilepidotus 10 15 20253036404550 5 10 15 20253035404550 Standard length (mm) Hexagrammos decagrammus -ft- i 1 1 1 1 1 1 1 1 r 0 5 10 15 20253036404660 A/nmodytes hexapterus 1*11771 I T n-12607 0 5 10 15 20 25 X 35 40 45 60 25 Anoplopoma limbria 20-| n-1500 15 0 5 10 15 20253035404550 50-, _ Hemilepidotus spinosus n-501 30- 0 5 10 15 20253035404550 40-, Zaprora silenus n-93 30 0 5 10 15 2025X35404550 Figure 5 Length-frequency distributions for the dominant taxa of fish larvae in neuston samples and, where comparable, in bongo samples (open histograms), for all cruises combined (1981-86). caught in the bongo samples were <15 mm SL. In con- trast, larvae of Bathymaster spp. that were common in the neuston at night did not differ significantly in size from those occurring in the bongo samples; all were small, mostly <10 mm SL. Theragra chalcogramma larvae were also relatively small (all < 15 mm but mostly <10 mm SL) both in bongo and neuston catches. Among the remaining neustonic taxa, most larvae caught were >10 mm SL, and length distributions generally displayed one dominant mode within a rela- tively short length interval. The predominant length range for the taxa Hexagrammos decagrammus, Cryptacanthodes aleutensis, Anoplopoma fimbria, Hemilepidotus hemilepidotus, Myoxocephalus spp., Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 243 and Zaprora silenus was 10-20 mm. Hexagrammos stelleri, Pleurogrammus monopterygius, and Hemil- epidotus jordani larvae were larger with predomi- nant length ranges of 15-40 mm, 15-25 mm, and 15-30 mm, respectively. In contrast, larval sizes for the cottids, Hemilepidotus spinosus and Hemil- epidotus spp., were relatively small with a predomi- nant length range of 5-15 mm. Daytime catches of larvae in the neuston were suf- ficient to make diel comparisons in length distribu- tions for only three of the dominant taxa. There was no significant day-night difference in the length dis- tribution of Hexagrammos decagrammus larvae (K- S test; Z=0.07, P>0.05). Theragra chalcogramma lar- vae caught at night (median length=6 mm) were slightly, but significantly, larger (K-S test; Z=1.52, P=0.02) than those caught during the day (median length=5 mm). Day-night differences were much greater for Ammodytes hexapterus larvae for which the median length caught at night was 24 mm and the median day length was 13 mm (K-S test; Z=4.99, P<0.001). Migration of the larger larvae and juve- niles to the surface at night may have been the cause of this difference, but it is also likely that enhanced sampler avoidance during daylight by large larvae and juveniles reduced the daytime median larval length significantly. Horizontal patterns of distribution Patterns of distribution illustrated here for total and individual dominant taxa of neustonic larvae were based on data combined for all cruises. The distribu- tion maps therefore represent general patterns of horizontal distribution for these species during spring in this region and did not take into account day-night, monthly, or interannual differences in catches. The pattern for total fish larvae in the neuston indicated that highest concentrations generally oc- curred to the southwest of Kodiak Island, in Shelikof Strait, and off the northern tip of Kodiak Island (Fig. 6A). Southwest of the Shumagin Islands and north- east of Kodiak Island, high densities of larvae were more scattered. Despite the high intensity of sam- pling seaward of Kodiak Island (Fig. 2), mean larval concentrations tended to be low in this region. Based on data which incorporated sampling during all sea- sons, Kendall and Dunn (1985) and Rugen3 fre- quently recorded high concentrations of various spe- cies of larvae in the neuston seaward of Kodiak Is- land. The apparent scarcity of larvae here may there- fore be characteristic of spring in the sampling area. Larvae of the osmerid Mallotus villosus were taken primarily southwest of Kodiak Island along the Alaska Peninsula as far southwest as the Shumagin Islands (Fig. 6b). They were scarce southwest of the Shumagin Islands and seaward of Kodiak Island and absent in the northeastern part of the sampling area. This pattern is similar to that described by Rugen3 except that the latter study plus Kendall and Dunn's (1985) observations indicated a greater presence of larvae seaward of Kodiak Island. These studies also showed that M. villotus larvae were relatively scarce both in bongo and neuston samples during spring; the main spawning season seems to be late summer through fall (Kendall and Dunn, 1985). Theragra chalcogramma larvae were usually most abundant in the upper 50 m of the water column in the southern Shelikof Strait area and along the Alaska Peninsula during spring (Schumacher and Kendall, 1991). Spawning takes place primarily in the sea valley in Shelikof Strait during late March and early April. Rugen3 has also documented the occurrence of pollock larvae on occasions in large concentrations to the northeast of Kodiak Island. These patterns were reflected in the distribution of pollock larvae in the neuston documented during the present study (Fig. 6C ). The scarcity of larvae within Shelikof Strait may have been due to the low num- ber of samples from that region. Pollock larvae were absent or scarce along the outer shelf and slope indi- cating that most of the larvae in the surface zone were retained on the shelf. Neustonic larvae of Anoplopoma fimbria were most abundant during late spring and summer in the west- ern Gulf of Alaska where they were associated with the shelf edge (Kendall and Dunn, 1985; Rugen3). The general distribution pattern documented here for the spring months showed them to be most abun- dant close to the shelf edge southwest and northeast of Kodiak Island, as well as around the northern and northwestern perimeter of Kodiak Island (Fig. 6D). As with pollock, this species is a pelagic spawner in deep water, and the distribution pattern of larvae suggested that spawning occurred mainly in outer shelf and slope waters, a pattern which is consistent with what is known about the early life history of this species (Kendall and Matarese, 1987; Doyle, 1992). The dominant hexagrammid species whose larvae were abundant in the neuston of the sampling area all spawn in coastal waters (Matarese et al., 1989). In the Gulf of Alaska region, spawning of these spe- cies seems to occur from fall through spring ( Kendall and Dunn, 1985; Rugen3). Larvae of the most abun- dant species, Hexagrammos decagrammus, were found to be dominant in the neuston during most of the year; during the summer months there was a large decrease in density. They were distributed widely throughout the sampling area, but greater concentrations were found in the southwestern re- 244 Fishery Bulletin 93(2), 1995 l'V ,'.^^J Mallotus villosus '*®pr*K Anoplopoma fimbria Figure 6 Distribution maps for total and individual dominant taxa offish larvae in the neuston for all cruises (1981-86). Mean density of a particular taxa is superimposed on each sector in the form of a dot the area of which is proportional to the mean number of larvae/1,000 m3. gion than northeast of Kodiak Island (Rugen3). The same pattern was apparent from the spring data presented here (Fig. 6E). Larvae were most abun- dant to the north of Kodiak Island and to the south- west beyond the Shumagin Islands, whereas densi- ties were lowest to the northeast and offshore of Kodiak Island. Kendall and Dunn ( 1985) documented widespread distribution around Kodiak Island but mainly at nearshore and midshelf stations early in the spawning season during fall. Advection of larvae in the neuston is probably extensive throughout win- ter and spring months in this region. Patterns in seasonal occurrence and spatial distribution of H. stelleri larvae were similar to those for H. deca- grammus (Fig. 6F), and as found in previous studies (Kendall and Dunn, 1985; Rugen3), densities were much lower than those for H. decagrammus. The third dominant hexagrammid species, Pleuro- grammus monopterygius, was also considerably less abundant in the neuston than was H. decagrammus. Although the spawning season appears to extend from fall through spring, maximum densities of these larvae have been recorded during late October in the Kodiak Island region (Kendall and Dunn, 1985). The distribution of P. monopterygius larvae during the spring months of the present study extended from the Kodiak Island region southwest to the Shumagin Island area; most records were in the vicinity of the shelf edge from Kodiak Island to the Shumagin Is- lands (Fig. 6G). Kendall and Dunn ( 1985) and Rugen3 also recorded highest densities of these larvae over the outer shelf and slope in the Kodiak Island re- gion. The former authors also documented fingers of occurrence of these larvae extending shoreward as- sociated with the troughs seaward of Kodiak Island. Although the larvae of this species usually display an offshore and oceanic distribution, spawning is known to take place in shallow water where currents Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 245 TP5^ Hexagrammos stelleh Pleurogrammus monopterygius ~W*\ H Hemilepidotus hemilepidotus Figure 6 (continued) are strong, primarily at 10-30 m depth, following an onshore migration by the mature adult fish during summer (Gorbunova, 1962; Macy et al.5). Gorbunova (1962) describes the oceanic occurrence of P. monopterygius larvae in the Pacific Ocean and Bering Sea and suggests that they migrate out to sea after hatching in shallow water, thus explaining the pri- marily offshore distribution pattern observed for these larvae. The predominant cottid species in the sampling area were members of the genus Hemilepidotus. As with the hexagrammids, these species are inshore coastal dwellers that spawn demersal eggs and have neustonic larvae (Matarese et al., 1989). In the study area, spawning seems to occur from fall through Macy, P. T., J. M. Wall, N. D. Lampsakis, and J. E. Mason. 1978. Resources of the non-salmonid pelagic fishes of the Gulf of Alaska and eastern Bering Sea. Part 1: Introduction, general fish resources and fisheries, and review of literature on non- salmonic pelagic fish resources. Part of Final Report for Con- tracts R7120811 and R7120812, Task A-7, Research Unit 64/ 354, Outer Continental Shelf Environment Assessment Pro- gram, U.S. Dep. Interior, Bureau of Land Management, 355 p. spring; peak densities of larvae occur in the neuston during fall (Kendall and Dunn, 1985). The most abun- dant cottid recorded during the present study was H. hemilepidotus . Highest densities of this species occurred to the southwest of Kodiak Island, extended beyond the Shumagin Islands, and had a tendency to be associated with the mid- to outer-shelf region (Fig. 6H). Larvae were scarce northeast of Kodiak Island. The same pattern of distribution was ob- served for this species by Rugen3 from samples taken during all seasons. The less abundant H.jordani dis- played a similar distribution pattern (Fig. 61) as did Hemilepidotus spp. (Fig. 6K). Hemilepidotus spinosus, however, had a more northerly distribu- tion. Most larvae were caught northeast of Kodiak Island (Fig. 6J), suggesting that this is the main spawning area for this species. Kendall and Dunn ( 1985) found larvae of the cottid Myoxocephalus spp. to be most abundant during sum- mer to the south of Kodiak Island. The samples from the present study yielded low numbers of these larvae; when present they were found in the mid-shelf region 246 Fishery Bulletin 93(2). 1995 F"*3 Hemilepidotus jordani W >so° xr^n Hemilepidotus spinosus ^P^ K Hemilepidotus spp. ^.^"^AJ Myoxocephalus spp. Figure 6 (continued) between Kodiak Island and the Shumagin Islands (Fig. 6L). Spawning may be centered in this region. Three species of bathymasterids belonging to the genus Bathymaster are known to occur in the sam- pling area: B. caeruleofasciatus , B. leurolepis, and B. signatus (Rogers et al., 1979; Rugen3). They are coastal demersal spawners. At the larval stage, it is not possible to identify these to species and they are included here in the taxon Bathymaster spp. The dis- tribution of these larvae during spring was centered southwest of Kodiak Island (Fig. 6M) suggesting that this may be a primary spawning area. Occurrences were scarce northeast of Kodiak Island and south- west of the Shumagin Islands. It seems, however, that spring is a period when Bathymaster larvae are relatively scarce in the neuston. Previous studies have found these larvae to be most abundant in sub- surface samples from May to October with a peak in summer (Kendall and Dunn, 1985; Rugen3). In the neuston, however, larvae did not become abundant until late June. Although Rugen3 found Bathymaster larvae to be most abundant from Kodiak Island to the Shumagin Islands, he also found them to be abun- dant seaward of Kodiak Island, particularly during the summer, as did Kendall and Dunn ( 1985). There may be a northeasterly progression in spawning ac- tivity in the sampling area from spring to summer. The wrymouth Cryptaeanthodes aleutensis is epi- and meso-benthic in shelf and slope waters and spawns demersal eggs during spring and summer (Matarese et al., 1989). Larvae are associated mainly with the neuston (Kendall and Dunn, 1985; Doyle, 1992; Rugen3). The distribution of C. aleutensis lar- vae during the spring months of the present study was associated primarily with Kodiak Island and southwest to the Shumagin Islands (Fig. 6N), simi- lar to that documented by Rugen.3 Densities were higher in the inner- and mid-shelf region than along the shelf edge and slope. The Pacific sand lance, Ammodytes hexapterus, is a pelagic, schooling species common to coastal and shelf waters and it spawns demersal eggs. Its larvae have been found to be facultative members of the neuston along the U.S. west coast where the well- Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 247 *^*1 Cryptacanthodes aleutensis O Ammodytes hexapterus Figure 6 (continued) developed larvae are abundant in the neuston mainly at night ( Doyle, 1992 ). They are common in the neus- ton and subsurface zone in the western Gulf of Alaska from winter to summer (Kendall and Dunn, 1985; Rugen3). Mean larval lengths tended to be greater in the neuston, however, and densities were highest in the neuston during late spring and summer. As with many of the other species, A. hexapterus larvae were most abundant during spring in the mid-shelf area from southern Kodiak Island to the Shumagin Islands (Fig. 60). They were scarce to the northeast and seaward of Kodiak Island and southwest of the Shumagin Islands. Kendall and Dunn (1985) and Rugen3 found them to be more widely distributed in subsurface samples, including high numbers north- east and seaward of Kodiak Island, implying that spawning is widespread throughout the sampling area. Multispecies spatial patterns Three recurrent groups of larval fish taxa were iden- tified by using Recurrent Group Analysis on data from all cruises (Fig. 7). Constituent members of these groups displayed affinity levels of >0.4 with each other. Individual species from these groups were also associated with individual species from other groups, or from outside the groups, at affinity levels of>0.3or>0.4. The largest group contained four taxa, Crypta- canthodes aleutensis , Hemilepidotus hemilepidotus, Mallotus villotus, and Stichaeidae, which frequently occurred together in the same samples. A second group comprising Ammodytes hexapterus and Hexagrammos decagrammus, the two most abundant larval species in the neuston, was connected to Group 1 via individual linkages among all taxa except Stichaeidae. The result, two groups and their asso- ciated weak linkages, suggested the existence of a loosely affiliated assemblage of larval species in the neuston for this region. Pleurogrammus monopterygius and Hemilepidotus spp. belonged to a third recurrent group which did not display any linkages with other species or groups of species. This may reflect the unusual association 248 Fishery Bulletin 93(2), 1995 H. jordani - H. splnosus - Bathymaster spp. A. fimbria — C. aleutensls H. hemilepidotus Mallotus villosus Stlchaeidae Affinity Level 0.40 0.30 Myoxocephalus spp. A. hexapterus H. decagrammus H. stelleri P. monopteryglus Hemilepidotus spp. Figure 7 Results of recurrent group analysis on neuston data (larvae) for all cruises ( 1981-86). Boxes enclose members of recurrent groups that have affinity levels of 0.4 or higher with each other. Lines connect taxa with affinities outside their groups. ill i ' ' ''..'' i i i i i of P. monopterygius larvae with the outer shelf and slope particularly off Kodiak. Hemilepidotus spp. had a similar pattern of distribution. Two species which were in- cluded in the analysis, but did not display significant affinities with any of the other taxa, were Theragra chalcogramma and Zaprora silenus. It seemed that at least in the neuston, T. chalcogramma, which is the dominant larval taxon in this region, had a unique pattern of occurrence, largely dissimilar to the other neustonic larvae. The lack of affinity of Z. silenus with other species was probably due to its infrequent occurrence in these samples. Kendall and Dunn ( 1985 ) and Rugen3 found a variety of recur- rent groups and inter-species linkages among the neustonic fish larvae in the western Gulf of Alaska over four seasons. The species groups and affinities changed seasonally and were inconsistent among two-week random (Fig. 8) but di trends which reflected sampling periods. Similar to the results presented here, T. chalcogramma did not occur among the recurrent groups or associated linkages of spe- cies identified in these studies. Five species groups and eight sector groups (sectors= sampling sectors in Fig. 2) were identified from the agglomerative hierarchical classification of data com- bined for all the cruises (Table 5). The Bray-Curtis dissimilarity coefficient val- ues at which these groups were formed were high ( mini- mum value of 0.63), particu- larly among the sector groups. These indicated that the groupings were weak and that species were only loosely affiliated with each other in terms of density and distri- bution patterns. The distribution of the eight sector groups seemed splayed certain geographical a variety of distribution pat- ii iiii.i.i I I ,'.U' ' A+AJ i TtV*R 4 2 5 8 3 1 192274722 I 7 2 2 8 12 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 I I I I I I I I I Figure 8 Distribution of sector groups resulting from numerical classification of density data for the dominant taxa offish larvae in the neuston, based on all cruises ( 1981-86). A plus sign ( + ) indicates that no fish larvae were caught in that sector. Doyle et al.: Neustonic ichthyoplankton in the western Gulf of Alaska 249 terns among the larval species. Groups 1 and 2 to- gether were characterized by highest densities of most species (Table 5); these sectors were located primarily around Kodiak Island and particularly in the region between Kodiak Island and the Shumagin Islands to the southwest. Total larval abundance was very low in Group-3 sectors (Table 5 1 which were concentrated mainly to the northeast of Kodiak Is- land and to a lesser extent around the Shumagin Islands. Group-4 sectors displayed an offshore dis- tributional trend, mainly seaward of Kodiak Island. Larval abundance was moderately high for this group, enhanced by highest mean density of Hemilepidotus spp. and Pleurogrammus mono- pterygius (Table 5). Most of the sectors in Group 5 were distributed close to Kodiak Island, and the coastal half of the region immediately southwest of Kodiak, along the Alaska Peninsula. Mean larval density was also moderately high for this group; Theragra chalcogramma, Hexagrammos deca- grammus, and Ammodytes hexapterus were the pre- dominant species. Group 6 included only eight sec- tors, five of which occurred close to Kodiak Island and three in the northeastern extremity of the sam- pling area. Mean densities of T. chalcogramma and A. hexapterus were highest for this group (Table 5) owing to their occurrence in extremely high num- bers in one of the sectors (different one for each spe- cies) along the southern half of Kodiak Island (Fig. 5). Hexagrammos decagrammus was the only spe- cies to occur in sectors belonging to Groups 7 and 8 (Table 5) which were scattered randomly through- out the sampling area. This species was unusual in that its distribution was widespread in contrast with the other taxa that were confined primarily to two or three of the sector groups. Discussion Our results indicated that species diversity and den- sity of fish eggs in shelf waters in the western Gulf of Alaska were essentially the same in the surface and subsurface zone. Theragra chalcogramma eggs were exceptionally abundant and, along with eggs of several pleuronectid species, accounted for >90c7c of all eggs taken in both bongo and neuston samples. Except for T. chalcogramma, pelagic eggs tended to be scarce in the neuston where the predominant mode of spawning among fish species is demersal (Kendall Table 5 Two-way coincidence table showing mean density (no./lOOO m3) of dominant larval species among sector groups. Numbers in parentheses are dissimilarity coefficient values at which the groups were formed Values are >1 in certain instances owing to use of the flexible sorting strategy in combining the entities into groups. Sector groups 1 2 3 4 5 6 7 8 Species groups (1.35) (1.05) (1.67) (1.40) (1.42) (1.29) (0.95) (0.79) 1 Hexagrammos stelleri 2.9 0.8 1.8 4.1 0.8 1.4 0.0 0.0 (0.63) Hemilepidotus jordani 3.7 14.6 0.8 1.9 0.0 0.0 0.0 0.0 Bathymaster spp. 65.4 0.1 0.0 0.6 0.0 1.4 0.0 0.0 Cryptaeanthodes aleutensis 171.2 18.6 1.7 0.3 2.0 45.6 0.0 0.0 2 Anoplopoma fimbira 85.4 1.3 3.6 0.1 0.0 0.0 0.0 0.0 (0.76) Hemilepidotus spp. 1.9 14.2 0.2 48.7 0.8 0.1 0.0 0.0 Hemilepidotus spinosus 2.2 7.6 6.7 0.3 0.0 0.0 0.0 0.0 3 Mallotus villosus 18.6 15.0 0.0 6.3 1.0 0.0 0.0 0.0 (0.79) Pleurogrammus monopterygius 1.3 2.5 0.0 13.6 0.1 0.0 0.0 0.0 Theragra chalcogramma 22.3 0.6 0.2 0.8 53.3 298.1 0.0 0.0 4 Hexagrammos spp. 2.9 0.7 4.1 0.2 0.3 0.0 0.0 0.0 (0.98) Hemilepidotus hemilepidotus 55.3 291.1 2.3 22.7 1.2 0.0 0.1 0.0 Sebastes spp. 7.0 1.0 0.0 0.0 0.0 2.1 0.0 0.0 5 Hexagrammos decagrammus 233.3 303.8 32.6 105.7 91.4 0.0 93.0 6.5 (0.90) Ammodytes hexapterus 411.5 3.2 0.5 0.2 19.8 441.1 0.0 0.0 Total (dominant taxa) 1084.9 675.1 54.5 206.5 170.7 789.8 93.1 6.5 250 Fishery Bulletin 93(2), 1995 and Dunn, 1985). In this region, fish eggs in the neus- ton could be considered strays because their accu- mulation at the surface may be attributed to their positive buoyancy rather than to the deposition of eggs in this zone. A similar conclusion has been made regarding the occurrence of fish eggs in the neuston of shelf and oceanic waters off Washington, Oregon, and northern California (Doyle, 1992). In contrast, a unique group of larval fish appeared to be associated with the neuston in the western Gulf of Alaska, and most of the dominant taxa were scarce or absent in the subsurface zone. The dominance of hexagrammids, cottids, an osmerid, Arcop/opoma/ira- bria, bathymasterids, Cryptacanthodes aleutensis, and Ammodytes hexapterus in this group has also been documented for the larval fish component of the neuston in the California Current region along the U.S. west coast (Brodeur et al., 1987; Shenker, 1988; Doyle, 1992). The occurrence of T. chalcogramma larvae in high numbers in the neuston of the west- ern Gulf of Alaska, however, is unique to this region and reflects the overall dominance of this species in the plankton of the study area (Kendall and Dunn, 1985; Schumacher and Kendall, 1991; Rugen3). Among the dominant taxa of fish larvae in the neuston, most were obligate tenants of the surface, despite the predominance of demersal spawning among these taxa. The most important taxa in this group included the hexagrammids, cottids, Anoplopoma fimbria, and Cryptacanthodes aleutensis, and, accord- ing to the general classification scheme for neustonic organisms (Zaitsev, 1970; Hempel and Weikert, 1972; Peres, 1982), they may be considered obligate mem- bers of the neuston. The same taxa of larvae have been identified as obligate neustonic organisms in the plankton off the U.S. west coast (Doyle, 1992). Because of their scarcity in bongonet samples, the dramatic daytime reduction in density of these lar- vae in the neuston samples may have been attrib- uted primarily to light-aided avoidance of the sam- pling gear. The generally large sizes documented (pre- dominantly > 10 mm SL) for these neustonic larvae also contributed to their ability to avoid the neuston net. Theragra chalcogramma, Ammodytes hexapterus, and Bathymaster spp. larvae were unusual among the dominant neustonic taxa in that they were ex- tremely abundant in bongo net samples also; there- fore, their association with the neuston was consid- ered facultative. Their nighttime presence in the neuston suggested a pattern of diel vertical migra- tion with movement upward at dusk and a return to deeper layers during the day. This pattern has been observed for many species of fish larvae and zoo- plankton in many different regions (Zaitsev, 1970; Hempel and Weikert, 1972; Neilson and Perry, 1990). Mallotus villosus, Myoxocephalus spp., and Zaprora silenus larvae, which were well represented in bongo net samples, but abundant in the neuston at night, may also exhibit this pattern of vertical migration. However, with the limited data presented here, it was difficult to verify this migration pattern. Day- time sampler avoidance, particularly by the larger larvae and early juveniles, is likely to have had a confounding influence on the observation of such a pattern. In addition, it is necessary to consider in more detail the diel variation in the vertical distri- bution pattern of the larvae over the entire range of the water column in which they occurred. Kendall et al. (1987, 1994) observed that within the upper 50 m of the water column, T. chalcogramma larvae (size range approximately 7-10 mm SL) un- dergo limited vertical migration on a diel cycle. These larvae were found to be deepest during the day, shal- lowest in the evening, sink slightly at night, and sink more in the morning. Under controlled laboratory conditions, Olla and Davis ( 1990) also observed simi- lar diel periodicity in vertical distribution of T. chal- cogramma larvae; larvae moved downward with day- time light intensity, upward during evening twilight conditions, remained close to the surface at night, and moved downward again in the morning. The T. chalcogramma larvae caught in the neuston, mainly at night, during the present study were predomi- nantly 5-14 mm SL unlike their counterparts in the bongo net samples that were mostly <6 mm SL. This diel pattern of neustonic occurrence for the larger- sized larvae was likely due to the pattern of diel ver- tical migration observed by the above authors. Observations on the vertical distribution of Ammo- dytes hexapterus larvae have also been made in the western Gulf of Alaska (Rogers et al., 1979; Brodeur and Rugen, 1994). Unlike T. chalcogramma larvae, A. hexapterus larvae were found to be deepest in the water column at night and shallowest at dawn and during the day. This apparent migration pattern of nocturnal descent has also been observed for A. personatus larvae off Japan and has been interpreted as advantageous in terms of diurnal feeding and predator avoidance (Yamashita et al., 1985). If this is the normal diel pattern of vertical migration for Ammodytes larvae, the occurrence of high densities of A. hexapterus larvae in the neuston at night, docu- mented during the present study, seems unusual. On examination of length-frequency distributions for these larvae, however, it appears that the pattern of nocturnal descent was prevalent among larvae <20 mm SL (Yamashita et al., 1985; Brodeur and Rugen, 1994), whereas the nocturnal concentration of lar- vae at the surface was restricted to larger larvae and early juveniles (Doyle, 1992; this study). Perhaps Doyle et al Neustonic ichthyoplankton in the western Gulf of Alaska 251 these larger specimens undertake a nocturnal mi- gration into the neuston as has been indicated by data collected off the U.S. west coast (Doyle, 1992). The length-frequency distributions documented for A. hexapterus larvae here, however, suggest that during spring in the western Gulf of Alaska, the well- developed larvae and early juveniles (>20 mm SL) almost exclusively occupied the neuston. Such speci- mens were rare in the bongo net samples where the predominant larval size range was 5-15 mm SL. The scarcity of the large A. hexapterus larvae in the day- time neuston samples in this instance could be at- tributed to light-enhanced sampler avoidance. Brodeur and Rugen (1994) also found that Bathymaster spp. larvae (4-7 mm SL) were deepest in the water column at night in the western Gulf of Alaska and suggest a diel migration pattern of noc- turnal descent similar to A. hexapterus. A similar pattern of downward migration at night has been observed for Bathymaster spp. larvae in the Bering Sea ( Walline6). Their absence from daytime neuston samples during the present study seemed to contra- dict such a pattern of vertical migration. Whereas most of the young larvae may follow the above pat- tern, our data also suggest a facultative association with the neuston by some of these larvae and a night- time occupation of the neuston as a result of migra- tion upward to the surface. This seems feasible as it is apparent from observations by Kendall and Dunn (1985) and Rugen3 in the Gulf of Alaska that Bathymaster spp. larvae become more neustonic with development. Most Bathymaster spp. larvae taken here, both in neuston net and bongo net samples, were <10 mm SL and would not be able to avoid the sampler as did the A. hexapterus larvae found in the neuston during the present study. The facultative nocturnal association with the neuston proposed here for Mallotus villosus larvae does not contradict what is already known concerning vertical distribution patterns for osmerids in the Gulf of Alaska. Haldorson et al. ( 1993) recorded that osmerid larvae in Auke Bay apparently spend most of their time in the mixed layer, rising to the surface at night and returning to relatively shallow depths during the day. Recent investigations on the interaction between the early life history stages of T. chaleogramma and the oceanographic environment in the western Gulf of Alaska indicate that prevailing southwesterly cur- rents transport larvae from the Shelikof Strait re- gion to nursery grounds along the Alaska Peninsula (Kendall et al., 1987; Kim and Kendall, 1989; Hinckley et al., 1991; Schumacher and Kendall, 1991). Although the southwesterly flowing Alaska Coastal Current bifurcates southwest of Kodiak Is- land, most of this water remains on the shelf, thus potentially retaining the majority of fish larvae in the coastal region. Physical features such as plumes and eddies also serve to retain larvae on the conti- nental shelf and transport them southwestward along the Alaska Peninsula (Vastano et al., 1992). Given these current patterns, the distribution pat- terns observed for most taxa of fish larvae in the neuston during this study suggest that springtime spawning and emergence of larvae into the plank- ton (and subsequently the neuston) took place mainly around Kodiak Island (except along the seaward side) and along the Alaska Peninsula to the southwest. A high concentration of larvae over the shelf from Kodiak Island to the Shumagin Islands was the pre- dominant pattern for most species. Despite their oc- currence in the neuston, these larvae were likely re- tained over the shelf and in the coastal zone by the prevailing currents. In contrast, the more offshore distribution patterns observed for A. fimbria, P. monopterygius, and H. hemilepidotus indicate that a significant proportion of these larvae may have been entrained in the Alaskan Stream over the slope and in deep water. Analysis of multispecies spatial patterns using recurrent group analysis and numerical classifica- tion did not reveal the existence of more than one neustonic assemblage offish larvae in the study area. A unique and comparable assemblage of neustonic fish larvae has also been identified off the U.S. west coast and its geographical distribution is essentially confined to shelf and slope waters off Washington, Oregon, and northern California (Doyle, 1992; Doyle7). Apart from perhaps P. monopterygius lar- vae, which are known to occur throughout the Gulf of Alaska (Gorbunova, 1962), and to a lesser extent A. fimbria and H. hemilepidotus, members of the neustonic assemblage offish larvae in the western Gulf of Alaska are likely to be scarce in the oceanic zone. It has been postulated that the primary advantage of a neustonic existence as an early life history strat- egy for certain species of marine fish is the enhanced trophic conditions that prevail in this biotope ( Moser, 1981; Tully and O'Ceidigh, 1989; Doyle, 1992). The suitability of the neuston as a feeding ground for lar- vae is, however, dependent on the ability of larvae to 6 Walline, P. D. 1981. Hatching dates of walleye pollock I Theragra chaleogramma) and vertical distribution of ichthyoplankton from the eastern Bering Sea, June-July 1979. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fish. Sci. Cent., 7600 Sand Point Way NE, Seattle, WA 98115. Proc. Rep. 81-05, 22 p. Doyle, M. J. 1992. Patterns in distribution and abundance of ichthyoplankton off Washington, Oregon, and northern Cali- fornia (1980 to 1987). U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fish. Sci. Cent., 7600 Sand Point Way NE, Seattle, WA, 98115. Proc. Rep. 92-14, 344 p. 252 Fishery Bulletin 93(2), 1995 seek and capture prey. Although surface aggregations of zooplankton are common at frontal and conver- gence zones, the neuston may in general have a re- duced biota, at least during the daytime. The rela- tively large size and well-developed form that char- acterizes most fish larvae occurring in the neuston of the western Gulf of Alaska and elsewhere is possi- bly an adaptive advantage in terms of finding and consuming suitable quantities of food. The data of Kendall and Dunn (1985) and Rugen3 indicate that hexagrammid and cottid larvae (obligate members of the neuston) are abundant in the study area dur- ing all seasons. Given that peak production of cope- pod nauplii, a dominant larval fish food, occurs dur- ing summer in this region (Cooney, 1986), the above larvae are likely to encounter a diminished biota in the neuston during fall and winter months in par- ticular. Because of their relatively large size, how- ever, a wide diversity of prey organisms are likely to be available to them in the neustonic layer and this diversity may compensate for the lower prey densi- ties of copepod nauplii. Acknowledgments This study would not have been possible without the foresight and assistance of Art Kendall of the Alaska Fisheries Science Center. We appreciate the efforts of the crew and scientists aboard the various research vessels that collected the samples and the expert assistance of the staff of the Polish Plankton Sorting Center in sorting and initial identifications of the samples. Susan Picquelle and Rod Hobbs assisted with the data analysis. We thank Art Kendall, Jeff Napp, Morgan Busby, Brenda Norcross, Bruce Wing, and an anonymous reviewer for valuable comments on an earlier version of this manuscript. Literature cited Ahlstrom, E. H ., and E. Stevens. 1976. 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Zimmerman (eds), The Gulf of Alaska: physical environ- ment and biological resources, p. 57-75. Mineral Man- age. Serv. publ. Outer continental shelf study, MMS 86- 0095. U.S. Gov. Print. Off., Washington, D.C. 1989. Transport and physical properties in central Shelikof Strait, Alaska. Cont. Shelf Res. 9:261-268. Reed, R. K., J. D. Schumacher, and A. W. Kendall Jr. 1988. NOAA's Fishery Oceanography Coordinated Investi- gations in the Western Gulf of Alaska. EOS, Transactions of the American Geophysical Union. 69:890-894. Rogers, D. E., D. J. Rabin, B. J. Rogers, K. J. Garrison, and M. E. Wangerin. 1979. Seasonal composition and food web relationships of marine organisms in the nearshore zone of Kodiak Island- including ichthyoplankton, meroplankton (shellfish), zoo- plankton, and fish. Univ. Washington Rep. FRI-UW-7925, 291 p. Sameoto, D. D., and L. O. Jaroszynski. 1969. Otter surface trawl: anew neuston net. J. Fish. Res. Board Can. 26:2240-2244. Schumacher, J. D., and A. W. 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Fish. 51:1-5. Zaitsev, Y. P. 1970. Marine neustonology. Naukova Dumka, Kiev. [Translated from Russian by Israel Program for Scientific Translations, Jerusalem, 207 p. J Abstract. — Aerial surveys for sea turtles conducted in Core Sound and Pamlico Sound, North Carolina, 1989-91, indicated a spring immigration by the turtles into these sounds and a summer- time dispersal followed by emigra- tion in the late fall and early win- ter. Estimates of density in Core Sound were greater than estimates for Pamlico Sound. Core Sound density estimates were comparable to those reported for the lower Chesapeake Bay and those re- ported from offshore pelagic sur- veys in the region. The data were analysed by strip- and line-transect methods, and the choice of analy- sis did not influence the overall conclusions. The abundance of sea turtles in the inshore waters of the Atlantic Coast at densities at least as great as in the ocean indicates the importance of these estuarine habitats for the foraging and devel- opment of immature turtles. Aerial surveys for sea turtles in North Carolina inshore waters Sheryan R Epperly Joanne Braun Alexander J. Chester Beaufort Laboratory, Southeast Fisheries Science Center National Marine Fisheries Service. NOAA Beaufort. NC 285 1 6 Manuscript accepted 25 September 1994. Fishery Bulletin 93:254-261 (1995). Recent studies have demonstrated the importance of inshore waters as developmental and foraging habi- tats for threatened and endangered sea turtles along the Atlantic Coast of the United States (e.g. Medonca and Ehrhart, 1982; Ehrhart, 1983; Lutcavage and Musick, 1985; Kein- ath et al., 1987; Burke et al., 1992, 1993). A study of sea turtles in North Carolina waters used sight- ings reported by the public and documented the importance of Pamlico and Core Sounds for imma- ture loggerhead, Caretta caretta; green, Chelonia mydas; and Kemp's ridley, Lepidochelys kempii, sea turtles (Epperly et al., in press, a). As part of the same study, aerial surveys were employed over a 3-yr period to provide independent quan- titative verification of the impor- tance of Pamlico and Core Sounds as sea turtle habitats. We report the results of the aerial survey work in Pamlico and Core Sounds, part of the largest estua- rine system in the southeast United States. Once aerial survey method- ology was validated in inshore wa- ters, our goals were 1) to obtain in- dependent evidence for the season- ality and distribution patterns of turtles obtained from other sources, 2) to quantify the abundance of sea turtles in the sounds and compare those densities with other areas, and 3) to evaluate the consequences of the application of line vs. strip survey methodology to the data. Materials and methods Aerial surveys of Core and Pamlico Sounds Pamlico and Core Sounds were di- vided into three areas (Fig. 1): Core Sound (34°41'N to 35°00'N), south- ern Pamlico Sound (35°00'N to 35°20'N), and northern Pamlico Sound (35°20'N to 35°48'N). Areas of each were 248 km2, 2,501 km2, and 1,951 km2, respectively. The divisions were, in part, based on geography and on facilitating access to restricted airspace. In Core Sound, each flight surveyed ap- proximately 26% of the total surface area of the sound (32, rarely 33 transects); for both southern and northern Pamlico Sound, approxi- mately 6% of the total area was sur- veyed (8 transects in southern Pamlico Sound and 11 transects in northern Pamlico Sound). Surveys were taken from a Cessna 172 (from a side-viewing platform) at 128 km/ h and at an altitude of 152 m. This altitude was chosen as a compro- mise between areal coverage and the ability to sight smaller turtles on the surface of inshore waters. Surveys were scheduled so that lo- cal apparent noon occurred approxi- mately half-way through the survey. Surveys were undertaken only if winds were less than 28 km/h and seas were less than 0.6 m with no or few whitecaps (e.g. Beaufort Sea State <2). We attempted to perform 254 Epperly et al.: Aerial surveys for sea turtles 255 Cape Hatieras ATLANTIC OCEAN Cape Lookout Figure 1 Core Sound and subareas of Pamlico Sound flown in aerial surveys for sea turtles in North Carolina inshore waters, 1989-91. the surveys monthly beginning in spring 1989 and bimonthly May-November 1990 and 1991. Because it was difficult to obtain military airspace clearance over Pamlico Sound and because the results of the 1989-90 surveys indicated that our effort was best expended in Core Sound (greater sighting rates), the only area surveyed in 1991 was Core Sound. We employed a systematic sampling design. The underlying assumption was that the systematic sample could be treated as a random sample. There was no reason to assume that the number of turtles sighted per transect would be autocorrelated (i.e. we assumed no areal trend in density or correlations between neighboring transect values). As recom- mended by Cochran (1977) and Eberhardt et al. (1979) in order to avoid potential selection biases of systematic sampling, the starting transect for each survey was chosen at random from all possible transects in the survey. Transect lines ran east-west and were spaced equi-distant from the starting transect. On the basis of the maximum known swim- ming speed of a loggerhead turtle (6 km/h, Keinath, 1993), transects were spaced far enough apart so that a turtle could not be sighted twice during any one survey. LORAN was used to maintain position on the prescribed transects. Beginning and ending longitu- dinal coordinates and time were recorded for each transect flown. Two observers on opposite sides of the plane scanned the waters, recording the time (with synchronized watches) and perpendicular angle to each turtle sighted (with handheld clinometers). On the assumption that groundspeed within a transect was constant, turtle positions were calcu- lated by interpolating time and longitudinal coordi- nates and by converting sighting angle and survey altitude to perpendicular distance from the transect. We used both strip- and line-transect theory to analyze the data. First, a histogram of all perpen- dicular sighting distances was constructed, one for Core Sound and one for Pamlico Sound (Fig. 2). From these histograms we empirically determined the strip width over which the probability of sighting a turtle was not reduced by nearness to the plane ( acute view- ing angle; turtles diving to avoid the plane) or by distance from the plane (reduced detection) to be 0.15-0.30 km from the flight line. Observations 35 - 30 Core Sound 25 - ■ 20 ■ || 15 - 10 - tj 5J B o> 0 - O) a> B "5 1 35 E 3 if Hi.. 0.1 0.2 0.3 0.4 0.5 0.6 0.7 z 30 - 25 - Pamlico Sound 20 - 15 - 10 ■III.. . 0.7 0.1 0.2 0.3 0.4 0.5 0.6 Distance from transect (km) Figure 2 Histograms of distances at which turtles were sighted from the line of flight in Core and Pamlico Sound aerial sur- veys, 1989-91. 256 Fishery Bulletin 93(2), 1995 within this strip were then used to calculate ratio- to-size estimates of density ( DR ) for each survey by using a single-stage, sampling approach in which sampled transects were treated as clusters of unequal sizes (i.e. transect lengths varied; Cochran, 1977; Gates, 1979; Jolly and Watson, 1979): D -Y« ""M- the density of turtles on the surface of the sound; and r* = 5>i. i=l the total number of turtles sighted during a survey, where yt = the number of turtles in the ith transect; and n MR = 2_.mi> total area surveyed (km2), 1=1 where mt - the area surveyed in the ith transect (km2); and inverse of one-half the effective strip width (Burnham et al., 1980), mathematically equivalent to the value of the pdf exactly on the flight line (perpendicular distance=0). On the basis of the histograms of sight- ing distances, data were censored such that the prob- ability of sighting a turtle was not reduced by prox- imity to the airplane. Distance data were rescaled such that x=0 at the point data were censored (0.15 km from flight line). Simple, generalized, and non- parametric models were examined with the program TRANSECT (Laake et al., 1979) to derive density estimators from the sighting distance data. Because only small numbers of turtles were seen during most sampling occasions, we could not conduct individual analyses for each survey. Instead, sighting informa- tion was combined for all Core Sound surveys and for all Pamlico Sound surveys, and an overall flO)^ was specified for each of the two water bodies (s). Density for each survey ( DR ) then was estimated as D, fMsYR 2LR where /10) is the overall /CO) for the water body, and is obtained from the TRANSECT program, and LR (km) is the total length of all transects (/.): n = the number of strip transects sampled. Variances of the density estimates, V( DR ), were calculated as follows: it i_A 5>?(A-A?)2 V(DS) = —Jt . i=l nM2 n-1 where N = the total number of strip transects pos- sible; and y D( = — - , the density of turtles in z'th transect; mi and M M — , the average area of a single transect " (km2). For line-transect analyses we used methods de- scribed by Burnham et al. ( 1980). The essential prob- lem in line-transect analysis is to construct a prob- ability density function (pdf) from the set of perpen- dicular distance observations of sighted organisms to estimate fXO). The value of /10) is defined as the H ■'R ~ ^t ■ The estimated variance of the density estimate for each survey was computed as V(DR) = DR (V(YR) | V(f(0)s)) Yr f(0fs The variance of the number of turtles sighted dur- ing a survey V(YR) is V(YR) = fci- **1Mt-$ n-l and the variance of/l0)s is obtained from the pdf so- lution (Burnham et al., 1980). Experiment to evaluate observer bias Four observers participated in the study. An experi- ment was conducted on 29 August 1991 to evaluate the accuracy and comparability of observer sightings Epperly et al.: Aerial surveys for sea turtles 257 and to validate methodology. Two planes, each car- rying two observers positioned on the same side, con- ducted 12 flights over an area where painted ply- wood "turtles" were deployed. Turtle models repre- senting loggerhead turtles of 30, 60, and 90 cm length, were attached to three anchored ground lines. Within an overflight pass, turtles of one size were grouped on a single line. All three lines could con- tain turtle models during any one pass. The number of turtle models of one size and the line on which they were placed during a single pass were chosen at random, but the experiment was constrained such that a total of six turtle models of each size were displayed within every three passes; the actual num- ber of a given size displayed during a pass ranged from 0 to 4. The number, location, and size of the turtle models were unknown to the observers. Alti- tude and speed were identical to that used in the general survey ( 152 m and 128 km/h). The airplane flew on a line 0.10-0.30 km from the models. Analy- sis of variance techniques were used to examine the contribution of observers, turtle model size, and the interaction of observer and model size to the error in the counts. Results and discussion Under the ideal conditions under which the aerial survey experiment was performed, no significant dif- ferences were detected among observers (AN OVA, df=3, P=0.89). Within the range of sizes tested, turtle size was not a significant factor in the observers' ability to sight turtles ( ANOVA, df=2, P=0.24). On average, 97.2% of the actual number of "turtles" were sighted during a pass (range 50-100%). We concluded that interobserver variability was not a major factor and that turtles could be sighted accurately in relatively turbid waters. The experiment did not test for the effect of fatigue on an observer's ability to sight turtles. The inshore waters of temperate latitudes are sea- sonally repopulated with sea turtles. Nearly all sea turtles in Pamlico and Core Sounds, North Carolina, are immature individuals (Epperly et al., in press, a). Based on public reports, there is evidence that turtles immigrate into Core and Pamlico Sounds in the spring, disperse throughout the sounds in the summer, and emigrate from the sounds in the late fall and early winter (Epperly et al., in press, a). Results of the aerial surveys confirm this general Figure 3 Seasonal sea turtle sightings in aerial surveys of Core and Pamlico Sounds, 1989-91. There were no fall surveys of southern Pamlico Sound, and Core Sound was the only area flown during the winter. The Core Sound area is enlarged to the right of each figure. (A) March- May; (B) June-August; (C) September-November; (D) December-February. 258 Fishery Bulletin 93(2), 1995 Table 1 Strip- and line-transect estimates of density for sea turtles excluding leatherbacks, Dermochelys coriacea, on the surface of Core and Pamlico Sounds North Carolina, 1989-91. Strip-transect Line-transect estimates of density estimates of density Total Number of distance Turtles Turtles turtles sighted surveyed per SE per SE Survey within sound' (km) 100 km2 of mean 100 km2 of mean Core Sound 1989 22 May 30 197 30.48 7.62 37.19 11.63 12 Jul 22 203 22.95 5.75 36.00 9.67 16 Aug 10 227 7.35 2.96 12.55 4.85 12 Sep 15 224 19.34 3.69 25.41 7.09 13 Oct 6 217 1.54 1.20 3.75 2.41 6 Nov 5 231 5.78 2.07 7.05 2.91 14 Dec 5 219 6.08 2.85 9.28 4.49 1990 4 Jan 0 216 0 — 0 — 15 Mar 0 219 0 — 0 — 24 Apr 3 212 3.15 1.69 5.76 3.16 3 May 2 204 3.27 1.81 3.99 2.70 6 Jun 2 228 2.93 1.64 3.57 2.73 7 Jul 0 219 0 — 0 — 2 Sep 0 234 0 — 0 — 4 Nov 0 228 0 — 0 — 1991 25 May 2 222 1.50 1.19 1.83 1.59 7 Jul 1 228 1.46 1.17 1.78 1.75 31 Aug 16 212 17.30 5.48 21.11 9.28 3 Nov 6 217 6.15 2.32 11.26 4.97 Northern Pamlico Sound 1989 30 May 1 387 0.86 0.81 0.77 0.67 24 Jul 4 399 3.35 1.73 3.00 1.53 1 Sep 6 393 3.39 2.10 3.04 2.43 29 Sep 14 383 1.74 1.09 2.34 1.25 14 Oct 8 369 4.52 2.39 5.69 2.46 13 Nov 4 367 0.91 0.89 0.81 0.87 1990 24 May 0 392 0 — 0 — 3 Jul 0 392 0 — 0 — 13 Sep 0 259 0 — 0 — 15 Nov 0 368 0 — 0 — Southern Pamlico Sound 1989 29 May 14 523 4.46 1.33 6.30 1.39 15 Jul 14 510 6.53 2.15 7.63 2.59 1990 19 May 1 504 0.66 0.62 0.59 0.54 4 Aug 2 534 0.62 0.58 0.56 0.49 3 Sep 0 512 0 — 0 — 1 All turtles sighted, including those censored in calculations of density. Epperly et al.: Aerial surveys for sea turtles 259 pattern (Table 1; Fig. 3). Volunteer commercial fish- ermen and the general public reported turtles in in- shore waters April-December. Turtles were also sighted in the sounds during April-December aerial surveys. Spring aerial surveys (March-May) indi- cated that turtles were distributed mainly in Core Sound and along the eastern edge of southern Pamlico Sound. Summer (June-August) and fall (September-November) aerial surveys demonstrated that turtles were distributed throughout the sounds. No sea turtles were sighted during fall 1990 aerial surveys, but turtles were reported in the area by the public and by commercial fishermen (Epperly et al., in press, a). Turtles were still present in Core Sound in December 1989, but none was sighted during Janu- ary or March 1990 aerial surveys. Species were generally indistinguishable from the air because of their small size, except for leather- back sea turtles, Dermochelys coriacea, which were sighted only during the December 1989 survey (three individuals). The loggerhead turtle, with a reddish- brown carapace, was the species most often identi- fied. Data from commercial fishermen indicated that the species composition in Pamlico and Core Sounds was 80% loggerhead, 159?- green, and 5% Kemp's rid- ley sea turtles; leatherback turtles infrequently en- ter inshore waters, and hawksbills, Eretmochelys imbricata, are very rare (Epperly et al., in press, a). Nearly all of the turtles measured by fishermen were greater than 30 cm carapace length (measured over the curve) — the smallest model tested and successfully detected in the aerial survey experiment. Density estimates from line- and strip-transect analysis are given in Table 1. The Fourier series es- timator fit the sighting distance data from both sounds well 0.05). Values of/10) differed substantially between the two sounds: /tO)Con?=8.13 (SE=0.75) and/lO)Pam/;co=5.99 (SE=0.52). Confidence intervals for the estimates of /10)s over- lapped at the 95% confidence level but not at the 90% confidence level. The cause of the difference in our ability to sight turtles between the two sounds was not obvious. Observer fatigue could have been a fac- tor. Transects in Core Sound were short (2.7-14.9 km) and observers were able to take frequent breaks between them. Pamlico Sound transects were long ( 13.9-57.1 km in northern Pamlico Sound; 37.5-94.1 km in southern Pamlico Sound), and breaks occurred infrequently. Homogeneity of background could have been another factor. Core Sound waters were rela- tively clear, and bottom structures (channels, seagrass beds, etc.) were usually visible. This het- erogeneous background served to attract observers and to intensify the observers' searches in order to detect turtles. Consequently, the visual sweep of the observers was confined to an area near the flight path. Conversely, the majority of Pamlico Sound waters usually were turbid and presented a homo- geneous background, except for the easternmost por- tion of the sound which was very similar to Core Sound. Line-transect estimates of density in Core Sound averaged 40% greater than estimates derived from strip-transect theory (Table 1). Line-transect esti- mates of density in Pamlico Sound were, on average, 14% greater than strip-transect estimates. Coefficients of variation of strip- and line-transect estimates of den- sity were nearly identical within each sound (67% for strip- and 66% for line-transect estimates for Pamlico Sound; 47% and 54% for strip- and line-transect esti- mates, respectively, for Core Sound) (Table 1). Application of line-transect and strip-transect analyses to the North Carolina aerial survey data requires several assumptions. Strip-transect analy- sis assumes that 1) transect lines are randomly lo- cated, 2) the strip over which all turtles are assumed to be seen and counted, 0.15-0.30 km, remains con- stant during a single survey and from survey to sur- vey, i.e. sighting conditions (distance from plane, size of turtles, sun position and glare, sea state, weather, etc.) do not affect the ability to sight turtles, 3) no turtle is counted more than once in a given survey, and 4) sightings are independent events. In addition to the first, third, and fourth assumptions above, line- transect analysis requires that 1) all turtles on the line (defined as 0.15 km from the flight line) are seen with certainty, 2 ) turtles do not move prior to sight- ing or before distance measurements are made, 3) measurements are taken without error, and 4) the probability density function remains constant dur- ing a single survey and from survey to survey (i.e. the ability to sight turtles does not change). The underlying assumptions of both methodologies are violated in important ways, primarily with re- spect to the ability to sight turtles. For strip-transect analysis, conditions are such that probabilities of sighting individual turtles within the strip are less than one. In addition, these probabilities vary within and among surveys. For line-transect theory, we do not know that all turtles on the line (x=0) are seen. The histogram of sighting distances (Fig. 2) indicates avoidance behavior in response to the aircraft in com- bination with poor downward visibility near the air- plane, but we cannot be sure that locating the line Cr=0) at 0.15 km from the flight line eliminated this effect entirely. In addition, the use of a pooled pdf may not be completely valid, because factors affecting the ability to sight turtles varied over the course of the study. As applied, strip-transect methods assuredly underestimate the density of turtles on the surface of the water. Line-transect methods, however, may over- 260 Fishery Bulletin 93(2), 1995 estimate or underestimate densities depending on the universality of the pdf. A criticism of strip-transect methods is that observations outside the strip are not included in the analysis and, in the study of rare ani- mals, every observation is important (Eberhardt et al., 1979). In this study, however, only 22 of 171 turtles ( 13%) were sighted at distances greater than 0.30 km from the flight line. In the following comparative dis- cussion, the results of strip-transect analysis are cited, but their use does not affect the overall conclusions. Estimated densities of sea turtles on the surface of Core Sound were consistently higher than surface densities for Pamlico Sound (Table 1). Where compara- tive data exist, densities in southern Pamlico Sound were greater than in northern Pamlico Sound. Densi- ties ranged from 0-30.5 turtles/100 km2 in Core Sound to 0-4.5/100 km2 in northern Pamlico Sound and to 0— 6.5/100 km2 in southern Pamlico Sound. Densities gen- erally were highest during late spring through sum- mer. Densities in northern Pamlico Sound tended to peak at least one month later than in southern Pamlico and Core Sounds. The estimated density of sea turtles on the surface of the sounds was quite different among the study years; turtles were more abundant in 1989. The densities reported in this study are surface densities. Sea turtles are estimated to spend 3.8^11% of their time on the surface (Kemmerer et al., 1983; Keinath et al., 1987; Byles, 1989; Byles and Dodd, 1989; Musick et al. * ). Thus, the estimated number of sea turtles on the surface represents a small frac- tion of those actually in the sounds. Because of the large range in proportion of time that monitored- turtles spend on the surface, we did not try to ex- trapolate surface estimates to an estimate of the sub- merged population in the sounds. For comparison purposes, density estimates from studies that made the extrapolation were converted to surface densities. Comparison of density estimates among aerial survey studies is confounded by differences in plat- forms and altitudes. Aerial surveys utilizing aircraft equipped with bubble observation windows (Fritts et al., 1983; Thompson et al., 1991; Shoop and Kenney, 1992; Thompson2; Lohoefener et al.3) af- 1 Musick, J. A., R. Byles, and S. Bellmund. 1983. Mortality and behavior of sea turtles in the Chesapeake Bay. Annual report for the year 1982, NEFC/NMFS Contract NA80-FAC-99994, Virginia Institute of Marine Science, Gloucester Point, VA, 41 p. 2 Thompson, N. B. 1984. Progress report on estimating density and abundance of marine turtles: results of first year pelagic surveys in the southeast U.S. U.S. Natl. Mar. Fish. Serv, Miami, FL, 59 p. 3 Lohoefener, R., W. Hoggard, K. Mullin, C. Roden, and C. Rogers. 1990. Association of sea turtles with petroleum platforms in the North-Central Gulf of Mexico. Report to the U.S. Dep. Inte- rior, Minerals Manage. Serv., Gulf of Mexico Outer Continental Shelf Regional Off., New Orleans, MMS contract 14-12-0001- 30398, OCS study MMS 90-0025, Natl. Mar. Fish. Serv., Pascagoula, MS, 90 p. forded observers a direct and unobstructed view of the flight line, thus maximizing the area sampled and the number of sea turtles observed per transect. Conversely, our study and other studies utilizing side- viewing aircraft (Keinath et al., 1987; Lohoefener et al., 1988; Keinath, 1993; Epperly et al., in press, b) did not have downward visibility directly beneath the plane, thereby minimizing the area sampled and the number of sea turtles observed per transect. Like- wise, differences in altitude could affect the number of sea turtles sighted. Smaller turtles have a de- creased chance of being sighted at higher altitudes. The altitude used in this study, 152 m, is consistent with that of the 1982-84 study of the offshore wa- ters between Cape Hatteras and Key West, Florida (Schroeder and Thompson, 1987; Thompson2), sur- veys of the Chesapeake Bay and adjacent waters (Keinath et al., 1987; Keinath, 1993) and surveys off the northern North Carolina coast (Epperly et al., in press, b). It differs from the 229 m altitude used in the 1983-86 and the 1988-89 surveys of offshore waters of the Gulf of Mexico (Thompson et al., 1991; Lohoefener et al., 1990) and the 1979-81 surveys of the offshore waters between Nova Scotia and Cape Hatteras (Shoop and Kenney, 1992). Lohoefener et al. (1988), collected turtle data during their 1987 red drum surveys of the Gulf of Mexico using altitudes of 305-457 m. Fritts et al. ( 1983) collected turtle data during marine mammal, bird, and turtle surveys of the Gulf of Mexico and eastern Florida using alti- tudes of 91 m and 228 m. Another factor affecting comparability of density estimates is the proportion of suitable habitat sur- veyed in each study. Comparisons of density esti- mates can be made only for surveys with comparable ratios of suitable to unsuitable habitats surveyed. Suitable habitat presumably accounts for all the area surveyed in inshore studies. Offshore studies gener- ally extended well seaward of suitable habitat and in winter included habitat rendered unsuitable by low temperatures nearshore. Because of methodological differences in aerial survey studies, the application of strip- versus line-transect theory, and our inability to reliably correct surface densities for the proportion of the population that was submerged, comparisons of density estimates among studies are nearly impossible. We compare the results of this study only with other studies with comparable methodologies. Our density estimates for Pamlico and Core Sounds, respectively, were comparable to those for the mid- (0-8.5 turtles/100 km2) and lower (0-57.4 turtles/100 km2) Chesapeake Bay, Virginia (Keinath et al., 1987). Densities in Core Sound and the lower Chesapeake Bay were particularly high, comparable to density estimates of sea turtles in offshore waters Epperly et al.: Aerial surveys for sea turtles 261 (0-126.1, Keinath, 1993; 0-12.3 turtles/100 km2, Epperly et al., in press, b). The abundance of sea turtles in the inshore waters of the Atlantic Coast (North Carolina and Virginia), at densities at least as great as in the ocean, indicates the importance of these estuarine habitats for the foraging and devel- opment of immature turtles. Acknowledgments We thank Joseph Smith and Neil McNeill for their dedication as observers during many aerial surveys that were eye-straining and occasionally hazardous, and John Betts, Bob Burrows, Pim Lauret, Karl Marks, Anthony Marsh, Pat Smith, Ron Snoeij, and Fred Swain for their excellent piloting and naviga- tion skills. 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Abstract. — Videotapes of the sea floor were taken from a sub- mersible during dives at two areas on the continental slope off Cape Hatteras and Cape Lookout, North Carolina, in September 1989. We counted demersal nekton, epi- fauna, and environmental features for 1-minute intervals from video transects. Common morphospecies of demersal nekton were identified, and multivariate analyses were performed to find environmental features that related to habitat use by these forms. In both areas, the ocean floor was extensively sculp- tured with holes and mounds, and both small and large sea anemones were commonly observed. Crinoids were seen in Cape Hatteras dives. Small sea anemones were much more abundant off Cape Hatteras, whereas holes and mounds were more densely distributed off Cape Lookout. Rattails, hake, and serge- stid shrimp were common at both locations. Eels were extremely abundant at the Cape Lookout site, whereas eelpouts, flounder, and lizardfish were found only at the Cape Hatteras location. At both lo- cations, analyses of nekton habitat choices showed that habitat selec- tion was related to density of the holes and mounds made by infauna and to density of the epifauna, such as crinoids and the different types of anemones. Hake, squid, serge- stid shrimp, and lizardfish showed the strongest evidence of habitat selection. Analysis of videotapes, originally recorded for other pur- poses, is a cost-effective means for preliminary examination of the problems that may only be ad- dressed by in situ observations. Assessing habitat use by nekton on the continental slope using archived videotapes from submersibles James D. Felley Office of Information Resource Management, Room 23 1 0 A&l Building, Smithsonian Institution, Washington, DC. 20560 Michael Vecchione National Marine Fisheries Service Systematics Laboratory National Museum of Natural History, Washington, DC 20560 Manuscript accepted 29 August 1994. Fishery Bulletin 93:262-273 (1995). Understanding of the ecology of the deep ocean floor has improved sub- stantially since underwater cam- eras have begun recording life at depths beyond which divers may penetrate. Recently, nekton commu- nities on the shelf and slope have been studied by means of underwa- ter cameras carried by remotely operated vehicles (ROVs) and occu- pied submersibles. Such studies have included analyses of environ- mental features (Hecker, 1990b; Levin et al., 1991), spatial distribu- tion of individual species (Vecchione and Gaston, 1986; Wenner and Barans, 1990; Schneider and Haed- rich, 1991), and patterns of habitat use by species assemblages (Rich- ards, 1986; Felley et al., 1989; Auster et al., 1991; Carey et al., 1990). Underwater cameras have allowed questions to be addressed that are intractable to conventional sampling methods (Haedrich and Gagnon, 1991). Though problems with accurate identification of spe- cies and habitat variables are inher- ent to these studies, such studies open an important window to poorly known ecosystems. We used archived videotapes re- corded by the submersible Johnson Sea-Link to investigate patterns of habitat use by demersal and bentho- pelagic nekton on the continental slope off Cape Hatteras and Cape Lookout, North Carolina. From the videotapes, we identified and counted nekton species, and quantified se- lected environmental variables dis- cernible from video images. Using these environmental variables, we identified the habitat where each species was most likely to be found. We used factor analysis to identify patterns of habitat use among the species (Felley and Felley, 1987; Felley et al., 1989) and to determine which environmental variables seemed most important in structur- ing the nekton assemblage of the continental slope off North Caro- lina. We then compared distribu- tional variances of environment and species occurrence to identify those species selecting subsets of avail- able habitats. Materials and methods Video recording Video transects were recorded dur- ing dives by the Johnson Sea-Link II submersible from the RV Edwin Link. Table 1 summarizes latitudes and longitudes, dates, and dive times. These data and videotapes are from NOAA's National Under- sea Research Center at the Univer- sity of North Carolina at Wilming- ton. Time starting and time ending are the beginning and ending points of the videotape section that we 262 Felley and Vecchione: Nekton habitat on the continental slope of North Carolina 263 Table 1 Information on dives at Cape Hatteras and Cape Lookout, North Carolina, from which videotapes were used for analysis of demersal nekton habitat use. "Dive no." is the dentification number we used to request the tapes. "Start time" and "End time" are the beginning and ending points on the vi deotape section used in the analyses (not the launch and recovery times of the dives I. Depths are in m. Start End Date Latitude Longitude time time Start End Dive no. 1989 °N °W (HH:MM) (HH:MM) depth depth Cape Hatteras 2623 14 Oct 35°23' 74°50- 15:37 18:11 853 853 2627 16 Oct 35°38' 74°48' 8:52 10:01 782 573 2629 17 Oct 35°23' 74°51' 7:29 8:24 610 549 2630 17 Oct 35°29' 74°48' 13:16 13:43 511 420 Cape Lookout 2619 12 Oct 34°15' 75°45' 13:40 14:47 903 853 2620 13 Oct 34°14' 75°45' 9:00 9:07 945 843 2621 13 Oct 34°14' 75°46' 16:31 18:28 793 843 used in the analyses (not the launch and recovery times of the dives). The videotapes were recorded as the submersible cruised along the bottom, generally at a speed of 0.5-1 knot (ca. 25-50 cm/sec). The cam- era faced forward and down and was not panned or moved during the recording of videotape sections used for analysis. At times the submersible stopped to deploy experiments or pick up samples and at other times moved away from the bottom. We recorded data from video images only during periods when the sub- mersible was moving and the bottom was clearly vis- ible. During these periods, we quantified environ- mental variables and counted individuals of nekton species during 1-minute intervals. If the submers- ible stopped or moved away from the bottom during an interval, that interval was discarded. We did not start measuring again until the submersible began moving steadily and the bottom was clearly visible. The bottom topography at the Cape Hatteras site was ex- tremely complex, with gullies, walls, and flat expanses. Only videotapes of flat areas were used for the analy- sis. The videotapes of Cape Lookout dives included only broad expanses of flat slope. Environmental variables recorded are listed in Table 2 and included holes, mounds, and tubes. Holes and mounds are indicators of infaunal activity. Holes were generally 1-3 cm in diameter and mounds gen- erally >10 cm in diameter. Tubes were 5-10 cm in length and most often curved, sometimes with both ends touching the substrate. Objects classified as tubes were identified (Schaff1) as those of polycha- etes and foraminifera (Bathysiphon spp.). Further characterization of sediment samples from these dives can be found in Levin ( 1991) and Gooday et al. (1992). Holes, mounds, and tubes were coded as fol- lows: 0 = none visible during the whole interval; 1 = no more than a total of 1 or 2 visible during the whole interval; 2 = 1 or 2 visible at all times during the interval; 3 = several always visible at any time in the interval, but countable; 4 = too many to count in the interval. Category 4 coded those situations where the environmental feature was so densely distributed that individual features were obscured by others nearer the camera. Other coded variables were gas- tropod/echinoderm tracks ( grooves in the substrate), sea grass detritus/Z/ya/moecia tubes, and sargassum detritus. These were coded 1 or 0 for presence or ab- sence in the interval; e.g. a value of 1 was assigned to the interval whenever one or more tracks were observed. Long thin dark objects that appeared to be bits of sea grass detritus might also include tubes of the polychaete Hyalinoecia (Schaff2). Such objects are referred to as "grass detritus" in this study. Finally, we counted raw numbers of small anemones, large anemones, gastropods, and crinoids. Small anemo- nes probably represented Actinauge verrilli and large anemones may be Bolocera sp. (Levin3). Gage and Tyler (1991) give excellent descriptions of epifaunal and infaunal organisms and benthic features simi- lar to those listed above. 1 Schaff. T. Natl. Mar. Fish. Serv., Silver Spring, MD. Personal commun., 1992. 2 Schaff, T. Natl. Mar. Fish. Serv., Silver Spring, MD. Personal commun., 1993. 3 Levin, L. Scripps Institution of Oceanography, La Jolla, CA. Personal commun., 1992. 264 Fishery Bulletin 93(2). 1995 Numbers of individuals of selected demersal nek- ton species were also recorded for each 1 -minute in- terval. This provided a consistent estimate of rela- tive abundance. Nekton included fishes, cephalopods, and macrocrustacea. As no voucher specimens were collected, identifications were made visually with the assistance of specialists familiar with the groups (noted below in the Results section). Most of these forms could be confidently identified only to genus from the videotapes. Data analysis Data from dives at Cape Hatteras and at Cape Look- out were analyzed separately. Cape Hatteras dives spanned a depth range that included two faunal zones (upper and middle slope) identified by Haedrich et al. ( 1980) and Wenner and Boesch ( 1979). In general, these authors found differences between continental slope communities above 700 meters and those below. Thus, Cape Hatteras dives 2629 and 2630 (Table 1) were con- ducted on the upper slope, whereas dive 2623 was con- ducted on the middle slope. Dive 2627 crossed the boundary identified by Haedrich et al. ( 1980). All Cape Lookout dives were conducted on the middle slope. Depth was not included as a variable in the statistical analyses detailed below, because it was not recorded for each 1-minute videotape segment. Potential effects of biotic zonation were investigated separately by com- parison of species distribution with dive depth. Statistical analysis of habitat choice by the identi- fied nekton followed Felley and Felley (1986, 1987) and Felley et al. ( 1989). All statistical analyses were conducted with the SAS program (SAS Institute, 1988). The steps in the analysis were as follows: 1) calculation of species' mean abundances for environ- mental variables; 2) calculation of a correlation ma- trix among species' mean abundances; 3 ) factor analy- sis of the correlation matrix; 4) comparison of vari- ances of sampling units and of numbers of individu- als of a species on the artificial variables (factors) generated by the factor analysis. These steps were accomplished as follows. First, we calculated means of environmental vari- ables for each species as each variable's mean over 1-minute intervals, weighted by the number of indi- viduals of that species seen in each interval. Thus, a species' mean abundance for a variable represented the value of that environmental variable in inter- vals where the species was most likely to be found. The species' mean abundance was considered the species "preference" for the variable, assuming that these nektonic species select their habitat. Second, species' mean abundances for the environ- mental variables were used to construct a correla- tion matrix among the variables. Note that this cor- relation matrix implies standardizing each variable using a "mean of means" and a "standard deviation of means." A high correlation between two variables is seen when species tend to occur in habitats with contrasting values for both of these variables. For example, an analysis might include some species found typically in shallow gravel areas and some preferring deep sandy areas. This analysis would generate a high correlation between such environ- mental variables as depth and substrate particle size. Thus, patterns of habitat use by species are reflected in patterns of interrelations among the variables. This is an analysis of species associations with par- ticular environments, and the data contain no infor- mation about why a particular species is occurring more often in one habitat type than another. Third, factor analysis (principal component analy- sis with Varimax rotation, Mulaik, 1972) was per- formed on the correlation matrix. Factor analysis resolves patterns of interrelationships among vari- ables into a smaller set of composite variables (fac- tors) to which observed variables (species mean abun- dances) are correlated. Sets of interrelated variables correlating highly with a factor are variables reflect- ing similar patterns of habitat use among the spe- cies. Each factor represents a particular trend in habitat use, an axis differentiating among sets of species that are likely to be found in habitats with contrasting conditions for the variables that define the factor. The example above might produce a fac- tor defined by depth and substrate particle size. Species' values, or scores, for a factor can be calcu- lated by using a factor scoring function. Species with contrasting scores are those found most often in con- trasting environments relative to that factor. To con- tinue the example, species more likely to be found in deep water over sandy substrate would have factor scores that contrasted with those of species more of- ten found in shallow water over coarse substrates (i.e. positive vs. negative scores on the factor). Species with intermediate scores may be characteristic of in- termediate environments on that factor, or they may be found over the entire range of environments reflected by a factor (because the species' score is the weighted mean of scores of intervals where it was found). Note that only a subset of the species analyzed in the example may in fact select habitat based on en- vironmental variables related to depth and substrate. Though a trend in habitat use may be identified for a species assemblage, not all species in the assem- blage may select habitat according to that trend. Further analysis is required to determine which spe- cies show evidence of active selection according to a particular habitat trend. Felley and Vecchione: Nekton habitat on the continental slope of North Carolina 265 Fourth, we investigated habitat selection by indi- vidual species by comparing species' variances on each factor with variance of the environment. Envi- ronmental variance on a factor was determined by calculating factor scores for each 1-minute interval. First, the value for each environmental variable in a 1-minute interval was standardized by using the appropriate "mean of means" and "standard devia- tion of means" noted above. Then the scoring func- tion was applied to each 1-minute sampling unit. Environmental variance was then determined as the variance of sampling unit scores. The score of a 1- minute interval was assigned to all individuals of all species seen in the interval. A species' variance was then calculated for each species as the variance of these scores. The procedure of investigating both species and locality scores on multivariate axes cor- responds to Rotenberry and Wiens'4 "synthetic ap- proach" to the study of communities. We compared a species' variance with environmen- tal variance for each factor by using Levene's test (Levene, 1960; Van Valen, 1978). Bonferroni correc- tions for multiple statistical tests were made by us- ing Rice's (1989) method for investigating tables of statistical test results. Rice's method is a correction for inflated type-I error in situations where several 4 Rotenberry, J. T., and J. A. Wiens. 1981. A synthetic approach to principal component analysis of bird/habitat relationships. In D. E. Capen (ed.), The use of multivariate statistics in stud- ies of wildlife habitat, p. 197-208. USDA Forest Serv. Gen. Tech. Rep. RM-87, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO. different tests of significance are made for a particu- lar null hypothesis. Such a series of tests constitute a "table of statistical tests." In this study, a "table" was considered to be all significance tests made rela- tive to a factor, the corresponding null hypothesis being "species variances are not significantly differ- ent from environmental variance with respect to this factor." Active habitat selection by a species was in- ferred when a species' variance was significantly smaller than the observed environmental variance (1-tailed test). This implies that the species was ac- tively selecting a subset of the available environment with respect to that factor. See Felley and Felley ( 1987) and Felley et al. ( 1989) for more details. Results Environments and biota Cape Hatteras — Table 2 presents means of environ- mental variables for flat areas traversed by dives on the slope off Cape Hatteras. Holes and mounds were common environmental features: one to several holes and mounds were in view at almost all times. In gen- eral, intervals where holes were dense also had a large number of mounds. Tubes were variable in oc- currence. Many were seen in dive 2627 but relatively few were seen in dives 2629 and 2630. Grass detri- tus was very common in dives 2627, 2629, and 2630, occurring in almost every interval. Sargassum de- tritus was infrequent in upper slope intervals (dives Table 2 Environmental variables measured on each interval, with means and standard deviations (in parentheses) for each dive at Cape Hatteras and Cape Lookout, North Carolina. Holes, mounds, and tubes were coded as follows: 0=none in the interval; l=no more than 1 or 2 seen in an interval; 2=always 1 or 2 visible throughout an interval; 3=several always visible, but countable; and 4=too many visible to count. Gastropod/echinoderm tracks, and grass and sargassum detritus were coded 1/0 for presence/absence in the interval (only percentages are reported for these variables). Number of individuals were counted for small anemones, large anemones, gastropods, and crinoids. Environmental variables Holes Mounds Grass Sargassum Small Tubes Tracks detritus detritus anemones Large anemones Crinoids Gastropods Cape Hatteras 2623 2627 2629 2630 Cape Lookout 2619 2620 2621 61 35 41 7 36 7 32 1.75 (0.830) 2.63 (0.490) 2.51 (0.506) 2.29 (0.756) 3.36(0.529) 3.28 (0.488) 3.25 (0.440) 1.36 (0.484) 1.66 (0.482) 1.78 (0.571) 1.14(0.378) 2.22 10.485) 2.14 (0.378) 2.25 (0.508) 2.41(1.321) 2.23 (0.942) 0.73 (0.633) 0.57(0.535) 0.25 (0.439) 0.00 (-) 0.25 (0.440) 100.0 45.7 85.4 14.3 16.7 28.6 53.1 47.5 88.6 82.9 100.0 69.4 14.3 62.5 18.0 6.87(6.711) 0.03(0.180) 5.90(15.367) 0.31(0.564) 8.6 25.80(19.954) 0.17(0.382) 0.00 (-) 0.40(0.976) 4.9 1.37(1.577) 4.63(3.006) 4.66(13.190) 0.27(0.449) 0.0 0.00 (-) 0.00 (-) 0.00 (-) 0.00 (-) 38.9 0.33 (0.676) 28.6 0.14 (0.378) 40.6 0.41 (0.560) 0.53 (0.629) 0.43 (0.534) 0.44 (0.619) 0.00 (-) 0.00 (-1 0.00 (-) 0.03(0.167) 0.00 1 -) 0.00 (-) 266 Fishery Bulletin 93(2), 1995 2627, 2629, 2630), but was more common at the middle slope site (dive 2623). Anemones, echinoderms, gastropods, and inverte- brate tracks were common. Epifaunal forms tended to occur in patches. Coefficients of dispersion (CD, Sokal and Rohlf, 1981) were calculated for small anemones, large anemones, crinoids, and gastropods (data in Table 2). Coefficients of dispersion much greater than 1 (indicating clumped distribution pat- terns) were found for small anemones in all Cape Hatteras dives where they were observed. Small anemo- nes were very abundant in dive 2627. For 15 minutes, the submersible traversed a dense aggregation where numbers ranged from 30 to 80 individuals per inter- val. Small anemones were also common (though not as densely distributed) in dive 2629. Large anemones were seen regularly and were relatively dense in dive 2629 (up to 12 in an interval ). Large anemones had a clumped distribution in this dive, indicated by a high CD value. Coefficients of dispersion were very high for crinoids. A dense patch of crinoids appeared in dive 2629, with 4 to 62 individuals per interval for 6 consecutive inter- vals. Another area of dense crinoids appeared in dive 2623, with 7-70 individuals per interval in 10 consecu- tive intervals. In dive 2630, an extremely dense patch of ophiuroids appeared over 4 consecutive intervals (ophiuroids were not included in the statistical analy- sis as they were seen in so few intervals). Cape Lookout — Holes and mounds were very dense; holes were, in fact, too dense to count during some portions of dives 2619 and 2621. As at Cape Hatteras, intervals with high numbers of holes also had large numbers of mounds. Tubes were rarely observed and were not seen in dive 2620. Grass detritus was com- monly seen but was not as frequent as at Cape Hatteras. Conversely, sargassum detritus was quite frequent, occurring in 39-41% of Cape Lookout in- tervals. Epifaunal species were not abundant and were not patchily distributed. Small anemones were not common (fewer than one per interval) and were less abundant than large anemones. No crinoids were seen in the Cape Lookout dives. Demersal nekton species Many nektonic species were observed on the tapes, but only a few appeared in abundance. These were the spe- cies included in analysis of habitat preferences. As no voucher specimens were obtained, identifications were assigned on the basis of species known to be common in the area, after consultations with taxonomic experts (listed in the Acknowledgments section). Table 3 lists the species included in analyses of habitat choice and their mean numbers in particular dives. The eel (Synaphobranchus sp.; Smith5), though rare at Cape Hatteras, was the most abundant form at Cape Lookout. This genus forms an important part of the middle-slope fauna (Markle and Musick, 1974; Haedrich et al., 1980; Sulak6). Eels were always ob- 5 Smith, D. G. National Museum of Natural History, Washing- ton, DC. Personal commun., 1992. 6 Sulak, K. Atlantic Reference Centre, Huntsman Marine Sci- ence Centre, New Brunswick, Canada. Personal commun., 1990. Table 3 Common demersal nekton species identified in upper slope and middle slope dives, North Carolina, an d average num bers of individuals per 1-minute interval seen in each dive (number of intervals are given in Table 2). See text for discussion of the probable identities of these forms and scientific names Species Cape Hatteras dives C ape Lookout dives 2627 2629 2630 2623 2619 2620 2621 Eel — 0.02 0.10 2.17 2.71 1.75 Rattail 2.60 1.12 0.29 1.69 0.61 0.57 0.78 Longfin hake 0.43 0.66 0.57 0.54 0.22 0.14 0.25 Scorpaenid 4.26 0.07 0.57 1.20 — — 0.03 Lizardfish 0.03 0.34 — 0.02 — — — Eelpout 12.43 5.83 1.43 5.43 — — — Flounder 2.14 1.90 0.86 1.25 — — — Species A — 0.15 — — — — — Sergestid shrimp 0.17 0.59 0.86 0.25 0.11 0.29 0.72 Shrimp 0.09 0.02 — 0.07 0.03 — 0.03 Red deepsea crab — — — 0.02 0.06 0.14 0.16 Cancroid crab — 0.07 0.56 — 0.03 0.14 0.03 Shortfin squid 0.06 0.20 — 0.56 — — 0.22 Octopod 0.03 0.05 — 0.03 — — 0.06 Felley and Vecchione: Nekton habitat on the continental slope of North Carolina 267 served swimming slowly slightly above the bottom, maintaining position with low amplitude tail-beats. Individuals identified as rattails represented ei- ther Nezumia bairdi, N. aequalis (Sulak6), or Coryphaenoid.es rupestris, the three species most commonly encountered in the depth range of these dives (Markle and Musick, 1974; Haedrich et al., 1980; Middleton and Musick, 1986). Rattails were common in all dives and were seen both lying on the bottom and maintaining position off the bottom by swimming slowly (with low amplitude tail-beats). The hake commonly observed in the tapes was the longfin hake, Urophycis ehesteri, a common species on the continental slope of the western North Atlan- tic (Markle and Musick, 1974; Haedrich et al., 1980; Wenner, 1983; Sulak6). Hakes were observed in ev- ery dive, normally lying on the bottom. Quite often they were found in depressions, their bodies in a cir- cular or semicircular posture. Scorpaenids were observed in all Cape Hatteras dives but only in dive 2621 at Cape Lookout. The species represented may be Helicolenus dactylopterus (Sulak6). At Cape Hatteras, they were abundant in both the upper slope (e.g. dive 2627) and the middle slope (dive 2623). When seen, they were always ly- ing on the bottom, their bodies often in a semicircu- lar posture. Lizardfish were seen only on the upper slope, most notably in dive 2629, where 14 individuals were ob- served. These may represent Saurida brasiliensis or S. normani (Sulak6). Several different eelpouts were likely present on these tapes, including Lycenchelys verrillii and Lycodes atlanticus (Sulak6). Lycenchelys paxillus is a more northerly species (Markle and Musick, 1974) but may occur on the North Carolina slope. Eelpouts were the most abundant fish at Cape Hatteras, in all dives, but were not seen at Cape Lookout. Indi- viduals tended to be small (<15 cm), with dark blotches, and lay in sinusoidal posture, usually near objects on the bottom (most often small anemones). Small flounders were seen in all dives at Cape Hatteras but were not found at Cape Lookout. There were most likely several species represented, includ- ing Glyptocephalus cynoglossus. This species is an important component of the slope fauna (Markle and Musick, 1974; Haedrich et al., 1980; Sulak6). A fish occurring commonly only in dive 2629 was designated as Species A. This may have been the off- shore hake, Merluccius albidus ( Sulak6). It was light- colored with dark dorsal blotches, of moderate size (<20 cm), had a terete shape, and a relatively large 7 Williams. A. Natl. Mar. Fish. Serv. Systematics Laboratory, Washington, D.C. Personal commun., 1992. head. It was always observed lying on the bottom, its body straight. Most individuals swam away be- fore the submersible got close enough for adequate observation. The eel and the shortfin squid, Illex illecebrosus (see below), also tended to move away from the submersible. Several decapod crustaceans were also observed. Sergestid shrimp were seen in every dive, always off the bottom. Another decapod seen regularly at both Cape Hatteras and Cape Lookout may have been the shrimp Glyphocrangon sp. (Williams7). Wenner and Boesch (1979) found G. sculpta and G. longirostris at depths greater than 1,000 m. These shrimp were most abundant in dives 2623 and 2627. Individuals were seen walking on the open bottom, where their dark coloration and highly reflective eyes made sight- ing these easy. The red deepsea crab, Geryon quinquedens, was not seen in the upper slope dives but was observed in all middle slope dives, walking on the open bot- tom. It was included in analysis of Cape Lookout species but was too rare to be included in the analy- sis of Cape Hatteras species. Wenner and Boesch (1979) found this species throughout the depth range included here. Cancroid crabs were seen at Cape Hatteras and Cape Lookout, in both upper and middle slope dives and likely represent two species. Wenner and Boesch ( 1979) found Cancer borealis and C. irroratus on the slope of the Middle Atlantic Bight and C. borealis farther downslope than C. irroratus. Several cancroid crabs were seen in dive 2630, where they occurred in association with an extremely dense patch of ophiuroids. The shortfin squid was observed at both Cape Hatteras and Cape Lookout, in both upper and middle slope dives. Individuals were usually lying on the bottom but rose off the bottom when disturbed by the submersible. Occasionally schools were seen off the bottom. Small octopods were seen at both Cape Hatteras and Cape Lookout in both upper and middle slope dives. Individuals were small and most often associ- ated with objects on the bottom, including sea anemo- nes, crinoids, and gastropod shells. The species had short arms and was probably Bathypolypus arcticus. Galatheid crabs were very common on the bottom, especially in areas where holes were dense. We did not include them in the analysis, because we found that estimates of their numbers were biased depend- ing on whether the submersible travelled up or down the slope. When travelling upslope, only individuals walking on the bottom were seen. When travelling downslope, the camera was able to look down into holes. Viewed in this way, many (if not most) of the holes were occupied by galatheid crabs. 268 Fishery Bulletin 93(2), 1995 Analysis of habitat preferences Cape Hatteras — Analysis of species' habitat prefer- ences produced three factors (Table 4). Factor 1 was related to species preferences for different types of epifaunal assemblages. Factor 2 was related to dif- ferent amounts of mounds and crinoids and presence or absence of sargassum detritus. Factor 3 was related to density of holes and presence of grass detritus. Factor 1 had high positive loadings for numbers of small anemones, tubes, and gastropods, and a nega- tive loading for numbers of large anemones. This factor differentiated nekton species found more of- ten in intervals with large numbers of small anemo- nes, gastropods, and tubes, from forms more com- mon in areas with few small anemones, tubes, and gastropods (but where large anemones might be found). Species' scores showed that the scorpaenid, rattail, and shrimp were characteristic of areas with large numbers of small anemones and tubes, whereas cancroid crabs, lizardfish, and Species A were not usually found in such areas (Fig. 1). Factor 2 had high positive loadings for density of mounds and number of crinoids. Sargassum detri- tus had a high negative loading on this factor. This factor differentiated between forms found in asso- ciation with crinoids and mounds, and forms found away from such areas, more in association with sar- gassum detritus. Species found more in areas with crinoids and mounds included the eel and lizardfish. Forms found in areas with few crinoids and mounds (but with sargassum detritus) included Species A, squid, octopod, and scorpaenid (Fig. 1). Factor 3 had high loadings for density of holes and presence of grass detritus. Gastropods and crinoids also contributed positively to this factor. Species found more in areas where holes were dense included the lizardfish, flounder, and scorpaenid, while spe- cies not characteristic of such areas included the squid, cancroid crab, and shrimp (Fig. 1). We compared species' and location variances on each of the three factors to determine which species appeared to be selecting subsets of the environment represented by each factor. Figure 2 illustrates the distributions on factor 1 of location scores, squids (a significant variance comparison), and scorpaenids (variance comparison not significant). Habitat selection according to type of epifaunal assemblage (factor 1) was shown for the squid, which preferred areas where neither small anemones nor large anemones were found (Fig. 2). Habitat selec- tion related to mounds and crinoids (factor 2) was demonstrated for the hake. Hakes tended to be found in areas with many mounds and crinoids. Habitat selection with respect to density of holes and grass detritus (factor 3) was demonstrated for the hake, sergestid shrimp, and lizardfish. These three forms all tended to be seen in areas with intermediate num- bers of holes. Cape Lookout — Only five species were observed in enough intervals to include in a factor analysis of their means. These included the rattail, eel, hake, sergestid shrimp, and red deepsea crab. Factor analy- sis of these species produced two factors (Table 4). Factor 1 related to density of holes and mounds, and factor 2 related to types of epifaunal assemblages. Factor 1 had high positive loadings for density of holes, mounds, and tubes. Numbers of gastropods, presence of invertebrate tracks, and presence of sar- gassum debris contributed negatively to this factor. This factor differentiated between species found more often in areas with many holes and mounds and spe- cies not usually found in such areas. The hake and the red deepsea crab were characteristic of areas with many holes, whereas the sergestid shrimp tended to be found where holes, mounds, and tubes were less densely distributed. None of the comparisons be- tween environmental and species variances were sig- nificant. Factor 2 had high positive loadings for number of small anemones and number of large anemones, and for presence of detritus (both grass and sargassum). The hake was the species most characteristic of ar- eas with many anemones and much detritus, whereas the red deepsea crab was most characteristic of ar- eas devoid of epifauna and detritus. None of the com- parisons between environmental and species vari- ances was significant. Discussion Mobile species respond to environmental variables, seeking certain conditions and avoiding others. The assumption that individuals select their environment is central to this analysis, as it is to multivariate analyses of habitat selection in general (James and McCulloch, 1990). Environmental variables affect- ing an individual's habitat choice may include abi- otic variables, the presence and density of other spe- cies, and the presence and density of members of its own species. The individual's response to a variable of importance may be negative (avoidance) or posi- tive (attraction). Together, the habitat choices of all individuals in an area produce the distributional patterns observed by the investigator. We used patterns of species distribution and asso- ciations between species and environmental vari- ables as a guide to understanding the structure of a Felley and Vecchione. Nekton habitat on the continental slope of North Carolina 269 FACTOR SpcA Lzdf Cncb Octo Plsp Find Sqd Elpt Shmp Hake Eel Rati ScrP Large anemones Small anemones. Tubes EPIFAUNA SpcA Octo Sqd Scrp Cncb Shmp Find Plsp Elpt Rati Hake Lzdf Eel Few sargassum debris present Cncb Sqd Shmp r~ MOUNDS. CRINOIDS Many sargassum debris rare Eel SpcA Octo Plsp Elpt Find Rati Hake Scrp Lzdf Sparse HOLES, GRASS DETRITUS Dense -2 0 2 Figure 1 Distribution of species scores on axes representing habitat use by nekton species at Cape Hatteras. Factor 1 represented habitat use according to different epifaunal as- semblages, factor 2 according to density of mounds and crinoids, and factor 3 according to density of holes and presence or absence of grass detritus. Species abbreviations are as follows: Cncb=cancroid crab, Elpt=eelpout, Flnd=flounder, Lzdf=lizardfish, Octo=octopod, Plsp=sergestid shrimp, Ratl=rattail, Scrp=scorpaenid, Shmp=shrimp, SpcA=Species A (possibly offshore hake), Sqd=shortfin squid. poorly known deep-ocean nekton assemblage. Accept- ing the assumption discussed above, we confronted the following methodological questions: 1) which spe- cies to analyze, 2) which environmental variables to measure, and 3) at what scale to sample. Our an- swers to these questions were pragmatic. We quan- tified those forms we felt could be recognized easily and consistently and were consistently visible on the videotape. We measured as many variables as we could quantify visually in an accurate and repeat- able fashion and also included those variables that seemed to be dominant in the environment (e.g. small anemones, holes). We sampled at a spatial scale as- sumed to approximate the area monitored by spe- cies of the assemblage. Although the area viewed in one minute of submersible cruising (a distance of ca. 15-30 m) is doubtless greater than the area moni- tored by an individual at any particular moment, we felt this to be the smallest manageable sampling unit. Shorter intervals (e.g. 30 seconds) required an inor- dinate amount of videotape stopping and starting. Preliminary analyses suggested that increasing the size of sampling units would create problems, includ- ing 1) a much smaller number of samples for the analysis, 2) loss of information in 1/0 coded variables, as these tended to become 1 (environmental attribute present) in all intervals, and 3) loss of information in variables whose scale of change was smaller than the sampling unit. In each case, increasing the size of sam- pling units tended to decrease the measurable associa- tion between a species and particular environmental variables (see also Schneider et al., 1987). Correlations between species occurrence and par- ticular environmental variables were subjected to multivariate analysis to find the patterns of habitat use in this species assemblage. In accordance with James and McCulloch's ( 1990) caveats, we recognize and stress the correlational aspect of this study. Our analysis produced artificial axes that only reflect real trends. These artificial axes provided the data for all further statistical tests. However, our interpre- tations are strictly tied to the real variables repre- sented by the artificial axes. When a factor had high loadings for holes and small anemones, we inferred that one of these variables, or some other variable strongly related to them, was in fact affecting distri- 270 Fishery Bulletin 93(2), 1995 as 3 ■o > C bution of some species in the assemblage. In this way, we attempted to move from our view of the environment to a view more con- cordant with that of the species that live there. Our view was molded by the environmen- tal variables we measured and the species distributions we observed. These high- lighted differences between the Cape Hatteras and Cape Lookout sites, as well as differences between dives at a site. In all dives, the benthic environments included in this analysis had soft substrate, with vis- ible epifauna and evidence of infauna (holes, mounds). Differences between the two dive sites were seen in the species composition and in the spatial distribution of these spe- cies. There were some depth-related pat- terns in species occurrence at the Cape Hatteras location (Cape Lookout dives were all at similar depths). Density of organisms differed greatly be- tween Cape Hatteras and Cape Lookout. Biota was much more dense at Cape Hatteras. Summing all demersal nekton, anemones, gastropods, and crinoids in each interval, we found that Cape Hatteras dives had a mean of 29.0 organisms per interval, whereas Cape Lookout dives had a mean of 4.6 organisms per interval. At Cape Hat- teras, dives 2623, 2627, 2629, and 2630 av- eraged 24.3, 48.7, 23.0, and 5.1 organisms per interval, respectively. At Cape Lookout, dives 2619, 2620, and 2621 averaged 4.2, 4.9, and 5.0 organisms per interval, respec- tively. Schaff et al. (1992) found density of biota at the Cape Hatteras site to be much higher than at other slope localities, includ- ing the Cape Lookout site. They related the high density of biota at Cape Hatteras to nutrient enrichment due to an interaction between the complex topography of the area and upwelling currents. Distribution patterns of sessile epifauna differed at the two sites. At Cape Hatteras, ophiuroids, crinoids, and small anemones showed evidence of clumped distributions. Large anemones showed a clumped distri- bution in dive 2629. There was no evidence of clumped distributions for any sessile or- ganisms at Cape Lookout. At Cape Hatteras, some species were re- stricted to particular depths. Zonation by depth has been documented for slope megafauna (Gardiner and Haedrich, 1978; Rowe and Haedrich, 1979; Hecker, 1990a). The eel and the red deepsea crab were found Scorpaenid 03 £ c Shortfin squid Factor 1 scores Figure 2 Distribution of intervals, shortfin squid, and scorpaenids on an axis representing epifaunal assemblages at Cape Hatteras. Variance of shortfin squid scores was significantly smaller than that of intervals, whereas variance of scorpaenid scores was not significantly differ- ent. This axis is the same as that labeled factor 1 in Figure 1. almost exclusively at middle slope dives (2623 and 2627, Table 3), whereas the lizardfish and Species A were found mostly in the upper slope dives. Most species included in the analysis were found in a range of depths. Felley and Vecchione: Nekton habitat on the continental slope of North Carolina 271 Table 4 Factor loadings of environmental means for benthic megaf iuna from the slope at Cape Hatteras and Cape Lookout, North Caro- lina. The representations below are of principal components rotated to simple structure. Only factor loadings >0.50 are shown. Analysis Factors 1 2 3 Cape Hatteras Large anemones -0.91 Mounds 0.94 Holes 0.94 Small anemones 0.83 Crinoids 0.73 Grass detritus 0.65 Tubes 0.88 Sargassum detritus -0.88 Gastropods 0.54 Gastropods 0.54 Crinoids 0.50 Cape Lookout Holes 0.92 Grass detritus 0.89 Mounds 0.93 Large anemones 0.88 Tracks -0.72 Small anemones 0.91 Tubes 0.93 Sargassum detritus 0.82 Gastropods -0.96 Sargassum detritus -0.52 Although the various areas appeared qualitatively different, analyses of species' habitat preferences showed us that species in both areas were distrib- uted in relation to similar types of benthic features. Some forms were typically seen in areas with dense aggregations of holes and mounds; others were seen in areas with fewer holes and mounds. Thus, at both localities, nekton distributions were related to par- ticular types of infaunal assemblages. Associations with particular epifaunal assemblages were demon- strated by those species found most often in dense patches of small anemones and (at Cape Hatteras) in areas with dense patches of large anemones or crinoids. Analysis of species preferences suggested that in different areas on the continental slope, nek- ton species respond to similar sets of environmental variables. While analysis of species preferences identified broad patterns of habitat selection for a group of spe- cies, analysis of species variances allowed identifi- cation of habitat selection by individual species. Ac- tive habitat selection (occurrence of a species in a subset of available environments) was demonstrated for 4 of the 13 species included in the Cape Hatteras analysis. While habitat selection according to factors 1 and 2 was shown for only one species each, habitat selection according to density of mounds and grass detritus (factor 3) was shown for three species (hake, lizardfish, sergestid shrimp). Note that sergestid shrimp distribution was related to benthic features, although shrimp were always seen hovering 1 to 2 m above the bottom. Such a seemingly counterintuitive result ( a species selecting habitat according to a vari- able that it does not seem to monitor) suggests the need for more study in this environment. For most species at Cape Lookout and for several at Cape Hatteras, small sample sizes made tests of variance equality quite weak. An uncommon species restricted to a particular habitat might be sampled in numbers too low to allow a statistically signifi- cant test. Examples abound in this study. Our analy- ses identified various environmental gradients. Lo- cations with scores at the extremes of the gradients were sampled in low numbers (e.g. Fig. 2). Forms characteristic of these extreme environments were sampled in correspondingly low numbers, unless they happened to be extremely abundant in a few inter- vals. Thus, we found it most difficult to show statis- tically significant habitat selection for those species that were tightly clustered in specific habitat types. Some examples of uncommon forms found in spe- cific habitat types came from dive 2629 (Table 3). The lizardfish was most abundant in this dive, and Species A and the only eels observed on the upper slope were visible during this dive. The dive area had a high diversity of habitats. The submersible passed over areas with many holes and few anemones or other epifauna, areas dense with small anemones, a dense patch of crinoids (from 5 to 50 individuals per interval over 8 intervals), and an aggregation of large anemones (from 4 to 12 individuals over 18 inter- vals). The extreme scores of Species A, cancroid crab, and lizardfish were strongly affected by their high densities in particular habitats seen in dive 2629. Detailed studies of such heterogeneous areas could clarify the environmental variables used by slope species to select their habitats. In this study, we saw patterns of habitat choice by nekton at different scales, from differences along the slope, to species preferences for different habitats 272 Fishery Bulletin 93(2), 1995 within a dive. Most species were found across the range of habitat types identified by the analysis, though they might be most abundant in one specific habitat. Active habitat selection (species variances smaller than environmental variance) was not seen for such species. Other species were found in num- bers too small to allow a powerful test of active habi- tat selection. Despite these qualifications, this study demonstrated trends in habitat selection by slope nekton and suggested hypotheses for further work. At both sites, habitat selection by demersal nek- ton was related to numbers and types of sessile in- vertebrates and to infaunal organisms that created holes and mounds. These are also two of the trends seen by Felley et al. (1989). They found that habitat selection by demersal nekton of a sandy-bottom shelf environment of the Gulf of Mexico was related to presence or absence of large sessile invertebrates (sponges, cnidarians, and small corals) and to pres- ence or absence of holes and mounds. Habitat selec- tion in that study was also related to amount of al- gal cover. Both this study and that of Felley et al. ( 1989) were based on analysis of videotapes originally recorded for other purposes. There may be problems with us- ing such videotapes. The submersible tracks were not arranged as transects; therefore, we had to re- main aware of potential sampling problems (e.g. the submersible crossing and recrossing a particular area, which did not occur on these videotapes). Sam- pling bias might result from the conditions under which we collected data. We had to stop collecting data when the submersible stopped, when it moved away from the substrate, or when it traversed areas of gullies or ridges. Thus our results can be general- ized to only the habitat we did sample — flat areas. Despite such qualifications, archived videotapes are an inexpensive source of data for exploration of ques- tions relating to distribution patterns in deep-sea organisms. Such patterns are difficult to study in the deep sea (Gage and Tyler, 1991). By using archived videotapes, hypotheses can be developed, utility of specific sampling systems assessed, and improve- ments in methods recommended. We feel that con- sistent collection and archiving of video transects is important for extending the usefulness of submers- ible missions. Acknowledgments We would like to thank L. Levin, T Schaff, K. Sulak, and A. N. Shepard for their comments on the manu- script, insights into the dives, and identifications of several invertebrate species. K. Sulak at the Atlan- tic Reference Centre, Huntsman Marine Science Cen- tre, New Brunswick, Canada, examined still photos of several species taken during these dives, and his identifications form the basis of much of our demer- sal nekton species section. A. B. Williams identified a number of decapod crustaceans, and identifications of particular fish species were provided by J. Will- iams, D. G. Smith, and B. B. Collette. Literature cited Auster, P. J., R. J. Malatesta, S. C. LaRosa, R. A. Cooper, and L. L. Stewart. 1991. Microhabitat utilization by the megafaunal assem- blage at a low relief outer continental shelf site-Middle Atlantic Bight, USA. J. Northwest Atl. Fish. Sci. 11:59-69. Carey, A. G., Jr., D. L. Stein, and P. L. Rona. 1990. Benthos of the Gorda Ridge axial valley (NE Pacific Ocean): taxonomic composition and trends in distri- bution. Prog. 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Wash. 3:106-133. Abstract. — Little is known of the early ocean life of juvenile Chi- nook salmon, Oncorynchus tshaw- ytscha. During the summers of 1981 through 1985 we collected juvenile chinook salmon with fine-mesh purse seines in shelf waters off the Oregon and Washington coasts. Most coded- wire tagged (CWT) fish caught in the ocean were yearlings from Columbia River basin hatch- eries. Catch per unit of effort of CWT yearling fish was much higher in the May-June period than in the August-September period, prob- ably, for the most part, because of the migration of these fish out of the sampling area by late summer. CWT subyearling fish were more abundant in late summer than in spring and early summer. A few fish from the Columbia River Upriver Bright stock of fall chinook salmon were recovered many months after release near where they entered the ocean, indicating that northward mi- gration of some smolts from this highly migratory stock may be de- layed for several months following release, or that some individuals of the stock undertake less extensive migrations than others. Subyearling smolts were rare in our catches, de- spite the larger spawning popula- tions producing these smolts than those producing the yearling smolts in this area. Subyearling fish may have been mainly distributed in shallow water inshore of our sam- pling. Our largest catches of small chinook salmon (<130 mm FL) were taken in the low salinity, high-tem- perature waters of the Columbia River plume. CWT fished were usu- ally recovered north of where they entered the ocean, except in May 1982 when southward currents were strong. Average net rate of mi- gration of yearling smolts between the head of the Columbia River es- tuary and ocean capture was 4.1 kmd1. Average growth rate of CWT yearling fish downstream of river km 75 in the Columbia River was 1.05 mmd"1. Average instan- taneous rate of growth in weight of yearling CWT Columbia River fish between hatchery release and cap- ture in the ocean was 0.92% body wtd-1. Manuscript accepted 29 August 1994. Fishery Bulletin 93:274-289 (1995). Distribution, migration, and growth of juvenile chinook salmon, Oncorhynchus tshawytscha, off Oregon and Washington Joseph R Fisher William G. Pearcy Oceanography Administration Bldg. 104 College of Oceanic and Atmospheric Sciences Oregon State University. Corvallis, OR 97331-5503 The Columbia River once produced the largest runs of chinook salmon (Oncorhynchus tshawytscha) in the world (Van Hyning, 1973). Today, runs are only a fraction of the size they were in the late 19th and early 20th century (Chapman, 1986), and a large fraction of the present popu- lation is produced in hatcheries. Although the runs of Columbia River chinook salmon are affected by many factors (e.g. dams, fresh- water habitat depredation, ocean fisheries, etc.), environmental con- ditions during early ocean life also may be important determinants of year-class success for these fish. Little is known of the early ocean distribution, migration, and growth of chinook salmon during their first year in the ocean prior to becoming vulnerable to ocean fisheries. Hartt and Dell (1986) collected juvenile salmon with purse seines over a wide area of the Gulf of Alaska and the Bering Sea in the late 1950's through the early 1970's. Although relatively few juvenile chinook salmon were caught during their sampling (358 fish in 505 sets be- tween 1964 and 1968; their Appen- dix Table Al), subsequent recover- ies of juvenile fish tagged at sea provided information on early ocean migrations of these fish. Four juve- nile fish tagged in the northern Gulf of Alaska in July and August of the fish's first summer in the ocean were recovered in later years in the spring in the Columbia River, indi- cating that some Columbia River spring chinook salmon migrate rap- idly to the north into the Gulf of Alaska during the first three or four months of ocean life (Hartt and Dell, 1986). Miller et al. (1983) caught juve- nile chinook salmon with purse seines in the ocean off southern Washington and northern Oregon during three periods in 1980: late May through early June; July; and late August through early Septem- ber. They sampled in water where the bottom depth was >30 m near the mouth of the Columbia River, a major source of chinook salmon smolts. Marked Columbia River spring chinook salmon (yearling smolts) were caught only during their spring cruise, and only in gillnet sets that opened to the south, suggesting that this stock group migrates rapidly to the north soon after entering the ocean (Miller et al., 1983). Very few fish <130 mm FL were found over water greater than 30 m bottom depth, in contrast to the great numbers of small fish caught in shallow marine waters near the surf zone by Dawley et al.1 1 Dawley, E. M., C. W. Sims, R. D. Ledger- wood, D. R. Miller, and J. G. Williams. 1981. A study to define the migrational characteristics of chinook and coho salmon in the Columbia River estuary and associ- ated marine waters. Coast. Zone and Es- tuarine Studies Div., Northwest Fish. Sci. Cent., NMFS, Seattle WA 98112. 274 Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 275 Hence, they concluded that offshore movement of chinook salmon is size dependent, beginning when the fish are about 130 mm FL (Miller et al., 1983). Healey (1980, 1991) studied juvenile chinook salmon in Georgia Strait, British Columbia. He found that "stream-type" chinook salmon (those spending a year in streams before entering the ocean) were only abundant in marine sampling from about late April to late May, suggesting that these fish migrated out of the protected waters of Georgia Strait soon after leaving fresh water. Conversely, "ocean-type" fish (those entering salt water as small subyearling fish ) were abundant in the protected marine waters of Georgia Strait throughout the summer and early fall. In this study we describe the abundance, distribu- tion, migration, and growth of juvenile chinook salmon collected by purse seine during the spring and summer of 1981-85 in coastal marine waters from northern Washington to southern Oregon. This study extends the temporal and spatial scope of available information on the early ocean life of juvenile chinook salmon off Oregon and Washington. The following para- graphs include a short review of life histories, spatial and temporal patterns of hatchery releases, and sea- ward migrations of different stocks of chinook salmon smolts in the area from northern Washington to north- ern California to aid the reader in the interpretation of the distribution and movement of juvenile chinook salmon in the ocean as presented in this paper. The majority of stocks of chinook salmon found along the coast of North America from northern Washington to northern California return to rivers to spawn in the fall (i.e. are fall-run fish), and their offspring migrate to the ocean as subyearling smolts (ocean- type) in the summer or fall of the same year during which they emerge from the gravel (Nicholas and Hankin, 1988; Healey, 1991). Although stocks that enter the ocean as yearling smolts ( stream-type ) are also found in this region, mainly in large river systems ( e.g. the Columbia River ), they are not as abun- dant as the ocean-type stocks (Healey, 1983, 1991; Nicholas and Hankin, 1988; Table 1, this paper). Most stream-type fish begin their upstream spawning mi- gration in the spring (i.e. are spring-run fish), and the downstream migration of their offspring to the ocean as smolts begins earlier than that of the ocean-type fish (Healey, 1982; Dawley et al., 1985, a and b). Total releases of yearling and subyearling fall and spring chinook salmon from coastal Washington, Columbia River, and coastal Oregon hatcheries av- eraged 138 million fish per year in the two-year pe- riod 1982-83 (Table l2). Of these releases, about 75% were subyearling fall chinook salmon, 14% were subyearling spring chinook salmon, and 11% were yearling spring chinook salmon (Table 1). (A much smaller number of summer, winter, and late fall chinook salmon, not included in Table 1, were also released in these two years). Fish from the Columbia River accounted for over 89% of all hatchery releases of chinook salmon in this area; Columbia River subyearling fall, subyear- ling spring, and yearling spring chinook salmon rep- resented 66%, 12%, and 11% of the total, respectively. Subyearling fall chinook salmon from coastal Wash- ington and coastal Oregon hatcheries represented 6% and 2% of the total release, respectively. Subyearling spring chinook salmon from coastal Oregon hatcher- ies represented 2% of the total release. Most subyearling fall chinook salmon from the Columbia River and coastal Washington hatcheries were released from April through June at a small size (about 4 or 5 g body wt; Table 1). A smaller pro- portion of subyearling fall chinook salmon from these two areas was also released later in the year at a much larger size (Table 1). In contrast, most subyearling fall and subyearling spring chinook salmon from coastal Oregon hatcheries were released in late summer or fall at a large size (averaging roughly 30-60 g; Table 1 ). Releases of yearling Co- lumbia River spring chinook salmon were concen- trated in the April^June period, whereas releases of subyearling Columbia River spring chinook salmon were spread throughout the year. Some of the fish released from hatcheries were marked with coded- wire tags (CWT) from which the release history of the fish could be obtained. In the two years examined, an average of 2.9% of the subyearling, and 6.5 7c of the yearling fish released from January through June in the Columbia River drainage were marked with CWT's. Releases of chinook salmon smolts from Califor- nia hatcheries averaged about 30 million fish per year in 1982 and 1983, most of which were fall chinook salmon.3 Of the California releases about 25 million were small subyearling fish in the spring and about 5 million were large subyearling fish in the fall. Extensive sampling of juvenile salmon in the lower Columbia River (rkm 75) between 1977 and 1983 determined that yearling chinook salmon smolts en- tered the Columbia River estuary (at rkm 75) mainly from April through June and that peak migration 2 This table was compiled from data received in 1994 from the salmonid release data files of the Regional Mark Information System of the Pacific States Marine Fisheries Commission, 45 SE 82nd Drive, Suite 100, Gladstone, OR 97027-2522. 3 Calculated from data supplied in 1994 bv Frank Fisher, Calif. Dep. Fish, and Game (CDFGl, 2440 North Main St., Red Bluff. CA; Gary Ramsden, CDFG, Trinity River Hatchery, Lewiston, CA; and Kim Rushton, Iron Gate Hatchery, 8638 Lakeview Rd. Hornbrook, CA. 276 Fishery Bulletin 93(2), 1995 Table 1 Total number, percent coded-wire tagged fish, and average fish size for hatchery releases of different age and run groups of chinook salmon, Oncorhynchus tshawytscha, for the Columbia River drainage, coastal Oregon, and coastal Washington areas by quarter (average of releases in 1982 and 1983). Total Jan-Mar Apr-Jun Jul-Sept Oct-Dec Columbia River Fall run (subyearlings) 91,049,664 3,595,917 2.1% 1.9 g 77,520,135 3.2% 5.9 g 8,366,243 7.1% 5.8 g 1,567,369 23.5% 24.5 g Fall run (yearlings) 1,317,560 694,978 17.1% 63.0 g 622,582 8.0% 53.9 g 0 0 Spring run (subyearlings) 15,811,195 2,476,963 0% 1.0 g 6,248,487 1.3% 3.4 g 3,606,772 1.5% 12.1 g 3,478,973 8.2% 57.6 g Spring run (yearlings) 14,885,483 2,988,851 14.9% 40.8 g 11,820,322 3.7% 26.2 g 0 76,310 0% 6.6 g Coastal Oregon Fall run (subyearlings) 3,011,633 180,984 0% 0.6 g 40,032 0% 2.5 g 1,312,591 14.8% 34.0 g 1,478,026 23.7% 48.1 g Spring run (subyearlings) 2,758,584 177,518 14.5% 2.9 g 25,134 0% 2.1 g 1,055,342 13.9% 40.3 g 1,500,590 22.5% 58.7 g Spring run (yearlings) 118,731 118,731 41.7% 89.4 g 0 0 0 Coastal Washington Fall run (subyearlings) 8,528,525 0 7,659,325 3.0% 5.3 g 869,200 22.7% 11.7 g 0 Fall run (yearlings) 27,625 0 27,625 49.9% 64.9 g 0 0 Spring run (subyearlings) 43,987 0 0 43,987 0% 10.1 g 0 Spring run (yearlings) 120,575 0 120,575 15.6% 71.2 g 0 0 was in May (Dawley et al., 1985a, Dawley et al.4). Downstream migration of subyearling chinook salmon smolts into the Columbia River estuary took 4 Dawley, E. M., R. D. Ledgerwood, T. H. Blahm, C. W. Sims, J. T Durkin, R. A. Kirn, A. E. Rankis, G. E. Monan, and F J. Ossiander. 1986. Migrational characteristics, biological observations, place somewhat later, mainly from May through July, with a peak in late June or early July (Dawley et al.4). The average length of subyearling chinook 4 (continued) and relative survival of juvenile salmonids entering the Columbia River estuary 1966-1983. Final Res. Rep., Bonneville Power Admin., Div. Fish Wildl., Portland, OR 97208. Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 277 salmon at the time they entered the Columbia River estuary was usually under 100 mm FL, whereas that of yearling chinook salmon was about 130-150 mm FL (Dawley et al., 1985a). Between January and July 1981-83 about eight times as many subyearling fish as yearling fish were caught at rkm 75 (purse and beach seines combined, Dawley et al., 1985a). Dur- ing the same period an average of 2.3% of subyearling fish and 2.5% of yearling fish caught at rkm 75 were CWT'd (calculated from data in Dawley et al., 1985, a and b). Large numbers of subyearling chinook salmon, the mean lengths of which ranged from 91 mm in May to 135 mm in September, were caught in shallow (<4 m water depth) marine waters outside of the river mouth in some years (Dawley et al.1). Most naturally reared chinook salmon from coastal Oregon river systems also enter the ocean as subyearling smolts (Nicholas and Hankin, 1988). Peak abundance of subyearling chinook salmon in Oregon estuaries generally occurs from late June through August (Reimers, 1973; Nicholas and Hankin, 1988). Although peak abundance in estuar- ies is earlier, juvenile chinook salmon are often caught in estuaries in the late fall (Myers and Horton, 1982; Nicholas and Hankin, 1988). By September, subyearling chinook salmon smolts caught in beach seines in the lower estuaries were generally from 100 to 130 mm mean FL (Nicholas and Hankin, 1988). Ocean migrations of stocks originating in north- ern California and in Oregon south of Cape Blanco are limited in extent, and few maturing fish of these stocks are caught outside of the California and Or- egon ocean or freshwater fisheries (Nicholas and Hankin, 1988; Garrison5). However, some northern coastal Oregon and Columbia River stocks (both spring and fall runs) undertake very extensive mi- grations and are caught in large numbers in the ocean fisheries of Alaska and northern British Columbia (Nicholas and Hankin, 1988; Garrison5; Hansen and Johnson6; Howell et al.7; Vreeland8). 5 Garrison, R. L. 1986. Stock assessment of anadromous salmo- nids. Oregon Dep. Fish Wildl., Annual Prog. Rep., Portland, OR 97207, 47 p. 6 Hansen, H. L., and R. L. Johnson. 1987. An evaluation of fish- ery contribution from fall chinook salmon reared in Oregon hatcheries on the Columbia River, coded-wire-tag recovery pro- gram. Oregon Dep. Fish Wildl., Annual Prog. Rep., Portland, OR 97207, 47 p. 7 Howell, P.. K. Jones, D. Scarnecchia, L. LaVoy, W. Kendra, and D. Ortmann. 1985. Stock assessment of Columbia River anadro- mous salmonids. Vol. 1: chinook, coho, chum and sockeye salmon stock summaries. Final Rep., U.S. DOE, Bonneville Power Admin., Div. Fish Wildl., Portland, OR 97208. 8 Vreeland, R. R. 1986. Evaluation of the contribution of chinook salmon reared at Columbia River hatcheries to the Pacific salmon fisheries. Annual Rep., U.S. DOE, Bonneville Power Admin., Div. Fish Wildl., Portland, OR 97208. 127^ 125^ 123° 121° 49l 47^ 45^ 43^ WASHINGTON Columbia R. ASTOfllA 41 39^ i-yPuget Sound Klamath ft. Sacramento ft. / San Joaquin ft. Figure 1 Sampling areas (A, B, C) where juvenile chinook salmon, Oncorhynchus tshawytscha, were collected in purse seines, 1981-85. Sampling sites occupied in 1983 are shown (dots) along with the 40 and 120 m depth contours (dashed lines). Basins which are major sources of chinook salmon in this region are indicated by arrows. Latitudinal extent of sam- pling varied in the different months and years (see Fig. 5). Methods Chinook salmon were collected with a fine-mesh purse seine between May and September, 1981-85, along a series of east-west transects off Oregon and 278 Fishery Bulletin 93(2). 1995 Washington (Fig. 1; Pearcy and Fisher, 1988, 1990). The sampling area was divided latitudinally into three sections (A, B, and C in Fig. 1 ). Additional sam- pling in July 1984 occurred off northern California as far south as 40°32'N and off the west coast of Vancouver Island as far north as 50°26'N, and in May 1985 in a concentrated area off the mouth of the Co- lumbia River. The months sampled in each year are shown in Table 2. The latitudinal range of sampling varied among years and months (Pearcy and Fisher, 1988; see also Fig. 5, this paper). Transects were gen- erally 37 km apart and collecting stations along each transect were 9.3 km apart starting at about the 37 m depth contour and continuing out to 37 or 46 km offshore. Occasionally stations farther offshore were sampled. For this study we considered all chinook salmon less than 401 mm fork length (FL) to be juvenile fish. This was based on the sizes of known age coded-wire tagged (CWT) fish in our catches. This length range included those fish that entered the ocean as year- lings or subyearlings in the same year in which they were caught in the ocean (age 1.0 or age 0.0, respec- tively9) and those that entered the ocean as subyear- lings in the year prior to capture in the ocean ( age 0. I9). 9 The number before the period indicates winters spent in fresh- water after hatching and before migration to the sea, and the number following the period indicates winters spent at sea ( Koo, 1962). Fork length (FL) of most fish was measured at sea to the nearest mm. CWT fish were measured at sea, then frozen, and later weighed in the laboratory. Tags were decoded by personnel at the Oregon Depart- ment of Fish and Wildlife laboratory in Clackamas, Oregon. Growth rates of CWT chinook salmon between re- lease from hatcheries and capture in the ocean were estimated by (FL1 -FLQ)/d; where FLQ = mean length of fish in the tag group at release, FLX = length of the individual fish when caught in the ocean, and d = the number of days between release and capture (d >10). Often only mean weight at release was readily available for a tag group. For these groups we converted mean weight at release to mean FL by using the geometric mean functional relationship (Ricker, 1973) between average weight (g) and aver- age FL (mm) for CWT groups released in California and the Columbia River for which both mean weight and mean length at release were measured: ln(FL) - 0.3122(ln(u;*))+3.8233, n=311, r2=0.94. Average in- stantaneous rates of growth in weight (% body wt/d) between release and ocean capture were estimated by (ln(Wfj)-ln(Wf0))/d; where Wt1 = weight at cap- ture in the ocean, WtQ = average weight at release, and d = the number of days (>10) between release from the hatchery and capture in the ocean (Ricker, 1975). Growth rates of chinook salmon in the Columbia River estuary and in the ocean prior to capture in Table 2 Catch ( i ), mean catch per set (CPUE , in parenth eses), and percentage of coded- ivire tagged fish in the catch of juvenile chinook salmon Oncorhynchut tshawytscha. for different months and years. May June July Aug Sept n % n % n % n % n % Year (CPUE) CWT (CPUE) CWT (CPUE) CWT (CPUE) CWT (CPUE) CWT 1981 68 (1.08) 5.9% 37 (0.55) 2.7% 73 (1.09) 4.1% 51 (0.77) 2.0% — — 1982 217 (3.50) 7.8% 228 (4.07) 7.0% — — — — 15 (0.39) 6.7% 1983 128 (2.32) 5.5% 52 (0.90) 3.8% — — — — 213 (4.18) 0.0% 1984 — — 104 (1.58) 12.5% 72 (1.20) 2.8% — — 59 (0.93) 10.2% 1985 533* (19.04) 15.6% 282 (3.52) 10.3% — — — — — — 1 Late May and early June sampling off the mouth of the Columbia River. Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 279 1981, 1982, and 1983 for individuals from groups of CWT fish sampled 75 km upstream from the ocean (rkm 75) during their downstream migration were estimated by (FL1 - FLQ)/d\ where FL0 = mean FL of the tag group when sampled in the river (from Dawley et al., 1985b), FL^ = length of the individual fish when caught at sea, and d = days (>10) between the date when half the fish in the tag group had passed rkm 75 and the date of capture in the ocean. (See Dawley et al., 1985, a and b; Dawley et al.4 for detailed information on in-river sampling.) Net migration speed of individual CWT smolts in the lower Columbia River estuary, downstream of rkm 75, and in the ocean prior to capture was esti- mated by dividing the distance between rkm 75 and the point of capture in the ocean (straight line seg- ments) by the number of days (>10) between the date when half the fish in the CWT group had passed rkm 75 during downstream migration (Dawley et al., 1985b), and the date when the individual CWT fish was caught in the ocean. In September 1983 we caught a large number of juvenile chinook salmon, none of which were CWT'd. We examined scales from 128 of these fish in order to estimate their size at time of ocean entry and the length of time they had been in the ocean. Scale ra- dii were measured from the focus to what we inter- preted to be the ocean entrance mark (the last abrupt change in circulus spacing, often accompanied by a few narrowly spaced circuli). Fork length offish at ocean entry was backcalculated by using a geomet- ric mean regression (Ricker, 1973) of FL and scale radius for juvenile chinook salmon (length range approximately 100-350 mm FL) caught by us in the ocean (1981-84) and in four Oregon estuaries by the Oregon Department of Fish and Wildlife (FLlmm) = 2.3772 x Scale radius [mmatS8x) + 0.08, n=202,r2=0.88). We roughly estimated the length of time these fish had been in the ocean by dividing their ocean growth (FL at capture minus back-calculated FL at time of ocean entry) by an assumed ocean growth rate of 1.5 mm-d-1; a growth rate common for juvenile coho salmon during their first summer in the ocean (Fisher and Pearcy, 1988 ) and similar to the estimated mean growth rate downstream of rkm 75 of five CWT Columbia River chinook salmon in the same year (this study). Results Catch per unit of effort A total of 2,132 juvenile chinook salmon were caught in 880 purse-seine sets during our ocean sampling 1981-85. A consistent seasonal trend among years in mean CPUE (all sampling areas combined) of ju- venile chinook salmon was lacking (Table 2). In 1982, CPUE was considerably higher in May and June than in September, but in 1983, CPUE in September was higher than it was earlier in May and June. In 1981 and 1984 little change occurred in CPUE between early and late summer. By far the largest CPUE was during latitudinally restricted sampling off the Co- lumbia River mouth in May 1985 (Table 2). Origin and age of CWT fish CWT fish represented 8.7% ( 185) of juvenile chinook salmon caught in purse seines 1981-85. The percent- age of CWT fish during the different cruises ranged from 0.0% in September 1983 to 15.6% in late May 1985 off the mouth of the Columbia River (Table 2). Most CWT fish caught in the ocean originated in the Columbia River basin (Table 3). CWT Columbia River fish represented 92% (170) of all CWT fish caught in the ocean 1981-85. CWT fish from coastal Oregon hatcheries and from coastal Washington hatcheries represented 6.4% (12) and 1.1% (2) of the total catch of CWT fish, respectively. No CWT fish that originated in British Columbia or Puget Sound, Washington, and only one CWT fish that originated in a California hatchery (Klamath R. system) was caught. Most of the CWT fish that we caught in the ocean were released from hatcheries as yearling fish the same year we recovered them in the ocean (age 1.0, Table 3). In addition, two CWT fish caught in the ocean were released from hatcheries as subyearling fish, but overwintered in freshwater before entering the ocean (based on their size and scale characteris- tics at time of capture). Age-1.0 fish represented 90.8% (168) of the catch of CWT fish 1981-85. Sub- yearling fish released from hatcheries in the spring or summer, a few months or less prior to capture in the ocean (age 0.0 at ocean capture), accounted for only 3.7% (7) of the catch of CWT fish between 1981 and 1985. Fish that overwintered in the ocean after being released as subyearlings in the summer, fall, or winter of the year prior to capture in the ocean (age 0.1 at ocean capture) accounted for only 5.4% (10) of the catch of CWT fish 1981-85 (Table 3). Yearling (age-1.0) chinook salmon smolts from the Columbia River basin were the predominant group of CWT fish in the May and June samples in most years. Most of these were spring run fish, but fall run yearling fish were also abundant in May and June 1985, and fall, summer, and mixed stock year- lings were also present in some years (Table 3). Age-1.0 CWT fish from the Columbia River basin (all runs combined) accounted for 4.4%, 5.1%, 5.5%, and 15.5% of the total ocean catch in May 1981, 1982, 280 Fishery Bulletin 93(2), 1995 Table 3 Number of coded-wire tagged (CWT) fish of different stock groups and ages and their percentage of the total catch (in parentheses) of chinook salmon, Oncorhynchus tshawytscha caught during ocean sampling in different months and years, 1981-85. Absence of sampl ng is indicated by — . No CWT fish were caught in September 1983. Year Release area Age Run Month May June July August Sept 1981 Columbia River 1.0 spring 3 (4.4%) 2 (2.7%) 1981 Columbia River 0.0 mixed 1 (2.0%) 1981 Columbia River 0.0 fall 1(1.4%) 1981 Coast of Oregon 1.0 spring 1 (2.7%) 1981 Klamath River 0.1 fall 1(1.5%) 1982 Columbia River 1.0 spring 11(5.1%) 9 (3.9%) 1(6.7%) 1982 Columbia River 1.0 fall 2 (0.9%) 1982 Columbia River 1.0 summer 1 (0.5%) 2 (0.9%) 1982 Columbia River 0.1 fall 2 (0.9%) — — 1982 Columbia River 0.1 mixed 1 (0.4%) 1982 Coast of Oregon 1.0 spring 1 (0.5%) 1982 Coast of Oregon 0.1 fall 2 (0.9%) 1 (0.4%) 1982 Coast of Washington 1.0 spring 1 (0.5%) 1983 Columbia River 1.0 spring 5 (3.9%) 1983 Columbia River 1.0 fall 1 (0.8%) 1983 Columbia River 1.0 summer 1 (0.8%) — — 1983 Columbia River 0.0 spring 1(1.9%) 1983 Coast of Washington 1.0 fall 1 ( 1.9%) 1984 Columbia River 1.0 spring 9 (8.7%) 1984 Columbia River 1.0 fall 2(1.9%) 1 (1.4%) 1984 Columbia River 1.0 summer — 2(1.9%) 2 (3.4%) 1984 Columbia River 0.0 spring 1 (1.4%) 1984 Coast of Oregon 0.1 fall 1 (1.7%) 1984 Coast of Oregon 0.0 spring 3(5.1%) 1985 Columbia River 1.0 spring 50 (9.4%) 5(1.8%) 1985 Columbia River 1.0 fall 23 (4.3%) 17 (6.0%) 1985 Columbia River 1.0 summer 6(1.1%) 1985 Columbia River 1.0 mixed 4 (0.8%) 3(1.1%) — _ — 1985 Columbia River 0.1 fall 2 (0.7%) 1985 Coast of Oregon 1.0 spring 2(0.7%) 1983, and 1985, respectively, and 5.7%, 12.5%, and 7.8% of the total ocean catch in June 1982, 1984, and 1985, respectively (Table 3). These percentages of CWT fish were much higher than those of down- stream migrant yearling chinook salmon entering the Columbia River estuary, which averaged 2.3% CWT fish during the period January^June, 1981-83 (cal- culated from Dawley et al., 1985, a and b), and were comparable to the CWT percentages of hatchery year- ling Columbia River spring and fall chinook salmon released during the period April-June 1982—83 (3.7 and 8.0%, respectively, Table 1). The high proportion of CWT yearling (age 1.0) chinook salmon from the Columbia River basin in the May and June ocean catches indicates that most unmarked fish caught in the ocean during these months probably were also yearling hatchery fish from the Columbia River basin. Five stocks from the Columbia River basin domi- nated our catch of age-1.0 smolts: Snake River sum- mer, Upriver Bright (URB) and Snake River fall chinook salmon, and Cowlitz River and Willamette River spring chinook salmon (Table 4). These stocks are caught in ocean fisheries as maturing fish mainly to the north of Oregon (Howell et al.7). Catch per unit of effort of CWT Fish Some distinct seasonal trends were apparent in the abundance of the different age classes of CWT fish. Age-1.0 fish were most abundant in catches in May Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 281 Table 4 Coded-wire tagged chinook salmon, Oncorhynchus tshawytscha stocks caught during ocean purse-seine sampling, 1981-85. Recovery Number Mean FL Stock group age recovered (mm) Columbia River Fall Chinook Salmon Lower river hatchery 0.0 1 91 1.0 1 147 Upriver Bright 1.0 20 202 0.1 4 292 Snake River 1.0 26 208 Columbia River Summer Chinook Salmon River 1 Snake R. ) 1.0 13 163 Upper Columbia River 1.0 1 189 Columbia River Spring Chinook Cowlitz River 1.0 29 214 Carson NFH 1.0 16 169 Deschutes River 1.0 6 242 0.0 1 124 Willamette River 1.0 34 190 Upper Columbia River 1.0 7 161 0.0 1 138 Rapid River (Snake R.) 1.0 2 152 Mid-Columbia River Mixed 0.0 1 137 0.1 1 355 1.0 7 158 Coastal Oregon Fall Chinook Domsea Inc. (Siuslaw R.) 0.1 2 290 Elk River 0.1 1 316 Rogue River 0.1 1 389 Coastal Oregon Spring Chinook Anadromous Inc. 0.0 3 214 Umpqua River 1.0 4 279 Coastal Washington Fall Chinook 1.0 1 238 Spring Chinook 1.0 1 203 Klamath River Fall Chinook 0.1 1 290 and June, when they dominated the catch of CWT fish. They were much less abundant in July, August, and September. (Table 5). The few age-0.1 fish were also more common in the May— June period than in the July-September period. Conversely, recoveries of C WT subyearling ( age 0.0) fish were mainly in the July-September period (Table 5). Size-frequency distributions Mean FL of age-1.0 CWT fish was 183 mm, 215 mm, 214 mm, and 281 mm in May, June, July, and Sep- tember, respectively, for all years combined (Table 5). Age-0.1 fish were generally larger than the age- 1.0 fish, averaging 294 mm, 310 mm, and 389 mm FL in May, June, and September, respectively (Table 5). Except for three fish caught in September, age- 0.0 fish were considerably smaller than the other two age classes, averaging 124 mm, 115 mm, and 137 mm FL in June, July, and August, respectively (Table 5). Length-frequency distributions (on a catch/set ba- sis) of juvenile chinook salmon are shown for the three standard sampling areas (A, B, and C) for all years combined (Fig. 2, top), for sampling in July 1984 off northern California (CA) and Vancouver Is- land (BO and for sampling off the mouth of the Co- 282 Fishery Bulletin 93(2). 1995 Table 5 Number, catch per unit of effort (CPUE) and fork length (FL) of coded-wire tagged age-1.0, age ■0.0 and age 0.1 chinook salmon, Oncorhynchus tshawytscha, by cruise for all years combined, 1981 -85. Cruise Years Sets Age 1.0 Age 0.0 Age 0.1 n CPUE Mean FL FL Range n CPUE Mean FL FL Range n CPUE Mean FL FL Range May 81-83 180 23 0.13 200 139-302 0 0.00 — 5 0.03 294 270-316 May 85' 28 83 2.96 178 118-261 0 0.00 — — 0 0.00 — — June 81-85 327 56 0.17 215 140-295 1 <0.01 124 — 4 0.01 310 220-355 July 81,84 107 3 0.03 214 206-223 2 0.02 115 91-138 0 0.00 — — Aug. 81 66 0 0.00 — — 1 0.01 137 — 0 0.00 — — Sep. 82-84 152 3 0.02 281 236-340 3 0.02 214 211-217 1 0.01 389 - ' Samp ing restricted tc an area immediately off the Columbia River. lumbia River (CO) in May 1985 (Fig. 2, bottom). For each month and area the effort (number of purse- seine sets) and total CPUE are also shown. The length-frequency distributions of CWT age-1.0 Co- lumbia River fish are shown in black, and lengths of other CWT fish are indicated by letters (Fig. 2). In the May and June samples, most CWT age-1.0 fish from the Columbia River were between 130 mm FL and 250 mm FL. As discussed earlier, from the percentages of CWT fish in the catches, most un- marked fish in this size range were probably also age-1.0 hatchery fish from the Columbia River. On the basis of CWT's and scale characteristics, we con- cluded that larger fish (about 220-400 mm FL) in May and June were a mixture of age-1.0 and age-0.1 fish. CPUE of fish in May was greatest in Area B, which straddles the mouth of the Columbia River, and was about half as great in areas to the south (C) and to the north (A). Relative to May, CPUE in June decreased in Area C, remained about the same in Area B, and increased in Area A. CPUE in June was much higher in the two northern areas than in Area C. Age-1.0 Columbia River fish were much rarer in all areas in the July-September period than in the May-June period, based both on the catches of CWT fish and the length-frequency distributions of un- marked fish. Generally, CPUE of fish between 150 mm FL and 330 mm FL was low in July and August in all areas. In September only a few age-1.0 and age-0.1 fish were caught in Area A. Only one CWT age-1.0 fish (340 mm FL) was caught in Area C in September. The most abundant fish in July and August were less than 150 mm FL (Fig. 2). Catches of these small fish were highest off northern California (CA), the Columbia River (B), and the Washington coast (A). The few CWT fish caught in July and August in this size range were age-0.0 fish from the Columbia River ( Fig. 2 ). The catches in the ocean in July and August of these small fish coincided with the time of peak abundance of subyearling chinook salmon in Oregon estuaries (Nicholas and Hankin, 1988) and with the later half of the peak migration of subyearling chinook salmon in the Columbia River estuary (Dawley et al.4) and was well after the time when most yearling chinook salmon enter the ocean (in May, Dawley et al.4). Therefore, it is most likely that the unmarked fish <150 mm FL caught in the ocean in July and August were age-0.0 fish. Catches of chinook salmon in September in Areas B and C occurred mainly in 1983 and 1984. In Sep- tember 1984, 32 moderately large (range 160—260 mm FL) fish were caught off Oregon (Area C). These were mainly age-0.0 fish released in August from the Anadromous Inc. release facility on Coos Bay (this conclusion was based on associated CWT fish and their percentage of the catch). During September 1983 we caught 207 unmarked juvenile chinook salmon in areas B and C off Oregon. Fish caught in area B were smaller (mean FL=185, ra=35) than those caught to the south in area C (mean FL=227 mm, rc=172; Fig. 2). Estimated mean FL at time of ocean entry backcalculated from scales was 138 mm and 173 mm for fish caught in areas B and C, respectively. Growth while in the ocean averaged 48.5 mm for fish caught in area B and 52.2 mm for fish caught to the south in area C. Dividing by a growth rate of 1.5 mm/d, we estimated time since ocean entry to be just over one month for both these groups. The estimated date of ocean entry of these fish (sometime in mid or late August) indicates that these were subyearling rather than yearling chinook salmon, since both naturally and hatchery produced yearling fish generally enter the ocean in the spring or early summer (see the introduction to this study). Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 283 May June July Aug Sep B J c r 58 3-71 100 200 300 100 200 300 100 200 300 100 200 300 100 200 300 FL (mm) July 1984 May 1985 D Q. U 5 5.80 1.2 0.8 ■ 0.4 ll 0.0 II 3.0 28 19.02 2.5 ' 2.0 In - 1.5 - 1.0 ; \ II Tl CO CA 0.5 0.0 CWT Fish Age ■ Columbia R. 1.0 a Columbia R. 0.0 b Columbia R. 0.1 c Coastal OR 0.0 d Coastal OR 0.1 e Coastal OR 1.0 f Coastal WA 1.0 g California 0.1 100 200 300 FL (mm) 100 200 300 FL (mm) Figure 2 Length-frequency distributions of juvenile chinook salmon, Oncorhynchus tshawytscha, by month and area (A, B, and C in Fig. 1) for all years combined, for July 1984 off northern California (CA) and the west coast of Vancouver Island (BC) and for May 1985 off the mouth of the Columbia River (CO). Total effort (number of sets, in italics) and total catch per unit of effort (CPUE) are indicated for each month and area. The size-frequency distributions of coded-wire tagged (CWT) age- 1.0 Columbia River fish are indicated in black, lengths of other CWT fish are indicated by letters. 284 Fishery Bulletin 93(2). 1995 However, the mean size at ocean entry backcalculated from scales (173 mm FL) of the fish caught in Area C was much larger than the mean sizes of naturally produced fall chinook salmon reported by Nicholas and Hankin (1988) in Oregon estuaries in the late summer (100-140 mm FL by mid-September, de- pending on the river system). Since the estimated average size at time of ocean entry of the fish caught in Area C in September ( 173 mm FL) was much larger than the average size at which age-0.0 wild smolts enter the ocean (Nicholas and Hankin, 1988; Dawley et al.1; Dawley et al.4), it is probable that these fish were released from a hatchery. The only releases in the study area (ex- cluding California) of large smolts in groups not rep- resented by CWT's during the July-August period were from the Oregon Aqua Foods (OAF) saltwater rearing and release facility on Yaquina Bay, Oregon, which is located within 5 km of the ocean. Almost 800,000 unmarked subyearling fall chinook and 55,000 unmarked subyearling spring chinook salmon were released from this facility between 28 August and 5 September 198310, about three weeks before our sampling in the ocean (22-24 September). The mean weight at time of release for these groups ranged from 47 to 57 g for the fall chinook salmon and was 100 g for the spring chinook salmon. From a regression of FL and body weight (this study) we estimated that the mean lengths of these OAF-re- leased fall chinook salmon at time of release ranged from 152 to 162 mm, close to the mean size at ocean entrance (backcalculated from scales) of the fish we caught in Area C in September 1983 (173 mm). If these OAF-released fish were the source of the un- marked fish caught in the ocean in September 1983, then they were in the ocean about three weeks be- fore capture. If fish size at ocean entrance that we backcalculated from scales was accurate, then their growth rate since entering the ocean was slightly over 2 mmd-1, considerably higher than the mean growth rate (1.05 mmd"1) estimated for age-1.0 Columbia River fish downstream of rkm 75 (see below), and about one and a third times that estimated for juve- nile coho salmon, Oncorhynchus kisutch, caught in the ocean in late summer (Fisher and Pearcy, 1988). Inshore-offshore distributions The inshore-offshore distributions of very small fish (<130 mm FL), which were mainly age-0.0 fish, and of larger fish (>130 mm FL) were similar; the me- dian offshore distance of the catch of each size cat- 10 Information obtained from the Pacific States Marine Fishery Commission's salmon release data base. egory was about 13 km (Fig. 3A). However, small fish were strongly associated with warm, brackish wa- ters (mainly the Columbia River plume), whereas larger fish were not (Fig. 3, B and C). Fully 38% of the small fish, but only 2% of the large fish, were caught in waters <17%15°C (Fig. 3C). These data indicate that, at least over the depths sampled (mainly >37m), the smallest chinook salmon juve- niles were much more likely to be found in the warm, low salinity waters of the Columbia River plume than in the colder, more saline adjacent waters. Our largest catches of juvenile chinook salmon in late summer were taken in September 1983. On the basis of their scale characteristics we concluded that these were hatchery subyearling chinook salmon that had been in the ocean about a month (see section on Size-Frequency Distributions). Almost all of these fish were captured within 4 km of the shoreline, in depths of <40 m (Fig. 4). This is a much more restricted in- shore-offshore distribution than was found in general for the juvenile chinook salmon (mainly age-1.0 fish) caught during all months and years of our sampling combined (Fig. 3A). Since daily upwelling indices dur- ing September 1983 at both 42°N and 45°N were al- most all positive (Mason and Bakun, 1986), the re- stricted inshore distribution of juvenile chinook salmon in this month does not appear to have been caused by onshore transport of water. The difference in offshore distribution between this group of large age-0.0 hatch- ery chinook salmon and the mainly age-1.0 fish caught in early summer may be due to behavioral differences between these groups offish; the age-0.0 fish appear to prefer shallower, more nearshore areas. Migration Several trends are apparent in the migrations of CWT juvenile chinook salmon between ocean entry and capture in purse seines (Fig. 5). In 1983, 1984, and 1985 most fish originating in the Columbia River basin were caught north of where they entered the ocean. In May 1982, however, all Columbia River fish were caught south of the river mouth, but by the fol- lowing month most were caught to the north. All but one of the ten tagged chinook salmon originating from coastal Oregon hatcheries were caught north of where they entered the ocean. Thirteen fish were caught more than 190 km north of where they entered the ocean. Seven of these were age-1.0 fish from the Columbia River drainage (three Snake River fall, two Snake River summer, one URB fall, one Deschutes River spring), one was an age- 1.0 fish from a coastal Oregon River system (Umpqua Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 285 100 0 5 10 15 20 25 30 35 40 Distance offshore (km) B 100 80 o 60 40 20 <130 mm FL 15 20 25 30 Surface salinity (°/0O ) 100 80 60 ro 40 20 s 130 mm FL 10 12 14 16 Surface temperature ( C) 18 Figure 3 Cumulative percentages of small (<130 mm FL), large (>130 mm FL) and all lengths of chinook salmon, Oncorhynchus tshawytscha, caught at various (A) distances offshore (km); (B) sea-sur- face salinities (%>); and (C) temperatures (°C) for all months and years of sampling combined. R. spring chinook salmon), and five were age-0.1 fish from coastal Oregon and California hatcheries (two Siuslaw R. fall, one Elk R. fall, one Rogue R. fall, and one Trinity R. (Klamath R. system) fall chinook salmon). The two farthest northward migrations were made by an age- 1.0 spring chinook salmon from the Umpqua River, Oregon, caught 481 km to the north off northern Washington in June 1985, and by an age-0. 1 fall chinook salmon from the Trinity River, California, caught 317 km to the north in May 1981. Speed of migration Average net migration rate of CWT age-1.0 Colum- bia River juvenile chinook salmon between rkm 75 and their ocean capture locations was 4.1 kmd-1 (range 1.1-14.2 kmd1, «=31; 1981, 1982, and 1983 data combined). This net migration rate was equiva- lent to 0.3 body lengths-sec x (where body length is the average between the mean length of the CWT group at rkm 75 and the length of the individual fish at capture in the ocean). Growth of juvenile chinook salmon Estimated mean growth rates of age-1.0 CWT Co- lumbia River juvenile chinook salmon between hatch- ery release and capture in the ocean and between 286 Fishery Bulletin 93(2). 1995 100 ' / 80 Fish A 60 Sets 40 - rcentage O O i i . i i i §. 0 10 20 30 40 50 60 > Distance offshore (km) | 100 ""• E O 80 Fish Sets B 60 40 " 20 0 0 50 100 150 200 250 Depth (m) Figure 4 Cumulative percentages of number of sets (effort) and number of chinook salmon, Oncorhynchus tshawytscha, caught at various (A) distances offshore (km) and (B) bot- tom depths (m), in September 1983. rkm 75 and capture in the ocean were 0.75 mm-d"1 (rc=152) and 1.05 mm-d-1 (n=31), respectively, for all years combined. The higher estimated growth rates for fish downstream of rkm 75 suggest that growth rates offish in the Columbia River Estuary and ocean were higher than growth rates in the areas upstream in the Columbia River. Growth rates between rkm 75 and ocean capture were 0.98 (n=5), 0.98 (n=21), and 1.41 mm-d"1 (n=5) in 1981, 1982, and 1983, re- spectively. Average instantaneous rate of growth in weight of age-1.0 C WT Columbia River juvenile chinook salmon between hatchery release and ocean capture was 0.92% body wt-d-1 (« = 152), for all years combined. Discussion Age-1.0 chinook salmon smolts from the Columbia River basin migrate rapidly to the north after enter- ing the ocean in the spring. Evidence for this rapid northward migration is found in the sharp decrease between early and late summer in CPUE of CWT age-1.0 fish in the area off Oregon and Washington (Table 5); in the much higher CPUE of age-1.0 fish in the area north of the Columbia River than south of the Columbia River in June (Fig. 2); in the low CPUE of age-1.0 fish in late summer (Fig. 2); and in the predominantly northward migrations of CWT Columbia River fish (Fig. 5). These results are con- sistent with those of Miller et al. (1983), who found CWT age-1.0 fish only in their late spring sampling in 1980 off southern Washington and northern Or- egon, and who caught CWT age-1.0 fish only in purse- seine sets that were open to the south (sets that catch northward swimming fish). Our results are also con- sistent with those of Hartt and Dell (1986) who caught juvenile Columbia River spring chinook sal- mon in the northern Gulf of Alaska in August of their first year in the ocean. Only in May 1982 were many CWT age-1.0 Columbia River fish found to the south of the Columbia River (Fig. 5). This was a period of strong northerly winds and southward flowing sur- face currents which may have transported the juve- nile salmon to the south by advection (Pearcy and Fisher, 1988). Unlike age-1.0 chinook salmon, age-1.0 coho salmon were fairly abundant in late summer off the Columbia River mouth and off Washington (Pearcy and Fisher, 1988). The Columbia River is the major source for both of these species in the study area, and yearlings of both enter the ocean at about the same time (April through June). The continued pres- ence in late summer of age-1.0 coho salmon off the Columbia River and Washington coast suggests that they are less migratory than yearling Columbia River chinook salmon during their first summer in the ocean. As maturing fish, these two species of salmon generally also have different ocean distributions. A major part of the ocean catch of several stocks of Columbia River spring chinook salmon occurs far to the north in British Columbia and Alaska ocean fish- eries (e.g. Willamette R. and Klickitat R. stocks); con- versely, Columbia River and coastal Oregon coho salmon stocks are mainly caught in Washington, Oregon, and California ocean fisheries (Garrison5; Howell et al.7). This divergence in the ocean distri- butions of these two species is already apparent in the first few months of their ocean life. On the basis of estimated growth rates of CWT fish, we concluded that both age-1.0 coho and chinook salmon appear to grow at fairly similar rates during the first few months they are in the ocean. Estimated mean growth rates of CWT age-1.0 Columbia River chinook salmon between release and capture in the ocean (0.75 mm-d-1) and between rkm 75 and cap- ture in the ocean (1.05 mm-d -1) were similar to the estimated mean growth rate of juvenile coho salmon Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 287 00 00 ON 00 ON 00 ON 00 ON e S ~c & t. " 8 ^ >* < s <= -c o "S B « z 05 S s 2 -° § 1 CL, * 00 ,2 x c - 0) x > *- 3 03 •- > O. T3 C Si, ° >~ m "t; < ™ & 2 CD ■- w 7 c o> z ■S v. >> 5 o « J3 y « u C c O tB ,H 2 « C MT3 O 1 | e « = 1 288 Fishery Bulletin 93(2), 1995 caught in the ocean in May and June (0.93 mm-d-1, rc=142; Fisher and Pearcy, 1988). Mean growth rates of CWT juvenile coho salmon caught in the ocean in the July-September period were higher (1.43 mm-d-1, n=69) than growth rates in early summer. Unfortu- nately, we caught too few CWT age- 1.0 chinook salmon in late summer to compare their growth rates with those of coho salmon in late summer. Our esti- mates of growth rates of CWT age-1.0 Columbia River chinook salmon based on mean size offish in the CWT group at time of release or during downstream migra- tion may be biased by size-related differences in mor- tality rates or migration rates out of the sampling area. The ratio of age-1.0 to age-0.1 chinook salmon in our ocean purse-seine samples was disproportion- ately high compared with the relative numbers of these two age classes entering the ocean. Although subyearling chinook salmon were much more numer- ous than yearling chinook salmon among down- stream migrating smolts in the Columbia River (Dawley et al., 1985a), and many more subyearling than yearling chinook salmon were released from hatcheries (Table 1), yearling fish predominated in our catches in the ocean. The high catches in the ocean in May and June of age-1.0 fish coincided with the period of peak downstream migration and ocean entry of these yearling fish. However, no similarly large catches of the more numerous age-0.0 fish oc- curred in the June, July, and August ocean samples, following their peak period of downstream migration in the Columbia River. In fact, CPUE of age-0.0 fish during July and August in Areas A and B, was not nearly as great as the CPUE of age-1.0 fish earlier in May and June (Fig. 2). The relatively low numbers of small age-0.0 chinook salmon caught in water >37 m bottom depth support the hypothesis of Miller et al. (1983) that offshore movement of subyearling chinook salmon is size dependent; few fish move offshore until they reach a size of around 130 mm FL. Many of the small age-0.0 fish caught over deep water in July and Au- gust appeared to have been carried offshore in the Columbia River plume, since they were found in waters of high temperature and low salinity (Fig. 3). During June, July, and August large numbers of small age-0.0 chinook salmon may have been present in shallow nearshore waters inshore of our sampling. Subyearling smolts of those stocks caught in ocean fisheries far to the north as maturing fish (e.g. Co- lumbia River Upriver Bright Fall chinook, Howell et al.7) may migrate to the north while they are still in shallow waters near the surf zone and thus may not be available to sampling over deeper water. Even large age-0.0 fish may prefer shallow water habitats. In late summer, when many age-0.0 fish should be quite large, this age class was rare in our samples. Our only large catches of age-0.0 fish (in September 1983) were inshore of 4 km (Fig. 4). The apparent difference in inshore-offshore distri- bution between age-0.0 and age-1.0 chinook salmon suggests that these two age groups are exposed to different environmental conditions in the ocean and that different factors may be critical in determining their survival in the ocean. Small subyearling chi- nook salmon may be more susceptible than yearling chinook salmon to processes affecting the nearshore environment, such as storms that cause heavy surf conditions, concentrations of nearshore predators, or nearshore dredging and other habitat modifications. On the other hand, by staying in shallow nearshore waters, where southward currents in the summer tend to be slower than 15-20 km farther offshore (Kundu and Allen, 1976; Huyer, 1983), the northward move- ment of the small subyearling fish may be facilitated. In contrast to stream-type age-1.0 chinook salmon from the Columbia River, some ocean-type fish may overwinter in areas near where they enter the ocean. We found four age-0.1 CWT fish of the Columbia River URB fall chinook salmon stock, which is har- vested mainly in Alaska and British Columbia ocean fisheries (Howell et al.7), near or south of the Co- lumbia River many months following their release from hatcheries. Apparently, some individuals of this highly migratory ocean-type stock may delay their northward migration for a long period of time. Alter- natively, the extent of the migrations of individuals of this stock may vary. Those that mature at younger ages (jacks for example) may undertake less exten- sive migrations than those that spawn at older age.5 Acknowledgments We thank D. Larden and his crew of the FV Pacific Warwind and the many people who helped during the cruises or in the laboratory, especially A. Chung, R. Brodeur, J. Shenker, W. Wakefield, D. Gushee, C. Banner, J. Long, K. Krefft, and C. Wilson. Helpful comments by two anonymous reviewers are appreci- ated. This research was supported by NOAA, Na- tional Marine Fisheries Service (Grants NA 27FE0162 and NA 37FE0186) and by Oregon State University Sea Grant (Grant No. NA89AA-D-SG108, Project No. R/OPF-33). Literature cited Chapman, D. W. 1986. Salmon and steelhead abundance in the Columbia River in the nineteenth century. Trans. Am. Fish. Soc. 115:662-670. Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 289 Dawley, E. M., R. D. Ledgerwood, and A. Jensen. 1985a. Beach and purse seine sampling of juvenile salmo- nids in the Columbia River estuary and ocean plume, 1977- 1983. Vol. 1: Procedures, sampling effort and catch data. U.S. Dep. Commer, NOAA Tech. Memo. NMFS F/ NWC-74, 260 p. 1985b. Beach and purse seine sampling of juvenile salmo- nids in the Columbia River estuary and ocean plume, 1977- 1983. Vol. 2: Data on marked recoveries. U.S. Dep. Commer., NOAA Tech. Memo. NMFS F/NWC-75, 397 p. Fisher, J. P., and W. G. Pearcy. 1988. Growth of juvenile coho salmon (Oncorhynchus kisutch ) off Oregon and Washington, USA. in years of dif- fering coastal upwelling. Can. J. Fish. Aquat. Sci. 45:1036-1044. Hartt, A. C, and M. B. Dell. 1986. Early oceanic migrations and growth of juvenile Pa- cific salmon and steelhead trout. Int. N. Pac. Fish. Comm. Bull. 46, 105 p. Healey, M. C. 1980. The ecology of juvenile salmon in Georgia Strait, British Columbia. In W. J. McNeil and D. C. Himsworth (eds.), Salmonid ecosystems of the North Pacific, p. 203- 229. Oregon State Univ. Press., Corvallis, OR 97331. 1982. Juvenile pacific salmon in estuaries: the life system. In V S. Kennedy (ed.), Estuarine comparisons, p. 315-341. Acad. Press, NY. 1983. Coastwide distribution and ocean migration patterns of stream- and ocean-type chinook salmon, Oncorhynchus tshawytscha. Canadian Field-Naturalist 97:427-433. 1991. Life history of chinook salmon (Oncorhynchus tshawytscha). In C. Groot and L. Margolis (eds.), Pacific salmon life histories, p. 311-393. Univ. Brit. Columbia Press, Vancouver. Huyer, A. 1983. Coastal upwelling in the California Current. Prog. Oceanogr. 12:259-284. Koo, T. S. Y. 1962. Age designation in salmon. In T S. Y. Koo I ed. i. Studies of red salmon, p. 41-48. Univ. Washington Press. Seattle. Kundu, P. K., and J. S. Allen. 1976. Some three-dimensional characteristics of low-fre- quency fluctuations near the Oregon coast. J. Phys. Oceanogr. 6:181-199. Mason, J. A., and A. Bakun. 1986. Upwelling index update, U.S. west coast, 33°N-48°N latitude. U.S. Dep. Commer., NOAA Tech. Memo. NMFS- SWFC-67, Monterey, CA 93942. Miller, D. R., J. G. Williams, and C. W. Sims. 1983. Distribution, abundance and growth of juvenile salmonids off the coast of Oregon and Washington, Sum- mer 1980. Fish. Res. 2:1-17. Myers, K. W., and H. F. Horton. 1982. Temporal use of an Oregon estuary by hatchery and wild juvenile salmon. In V. S. Kennedy (ed.), Estuarine comparisons, p. 377-392. Acad. Press, New York. Nicholas, J. W., and D. G. Hankin. 1988. Chinook salmon populations in Oregon coastal river basins: description of life histories and assessment of re- cent trends in run strengths. Oregon Dep. Fish Wildl., Info. Rep. 88-1, 359 p. Pearcy, W. G., and J. P. Fisher. 1988. Migrations of coho salmon, Oncorhynchus kisutch, during their first summer in the ocean. Fish. Bull. 86:173-195. 1990. Distribution and abundance of juvenile salmonids off Oregon and Washington, 1981-1985. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 93, 83 p. Reimers, P. E. 1973. The length of residence of juvenile fall chinook salmon in Sixes River, Oregon. Oregon Fish Comm. Res. Rep. 4(2), Oregon Dep. Fish Wildl., Portland, OR 97201, 43 p. Ricker, W. E. 1973. Linear regressions in fishery research. J. Fish. Res. Board Can. 30:409-434. 1975. Computation and interpretation of biological statis- tics offish populations. Bull. Fish. Res. Board Can. 191, 382 p. Van Hyning, J. M. 1973. Factors affecting the abundance of fall chinook salmon in the Columbia River. Oregon Fish Comm. Res. Rep. 4(1), 87 p. Abstract. — Index-based assess- ments, in which research survey indices serve as the primary source of abundance information, are used for many commercially harvested stocks in the Northeast region. Such assessments generally pro- vide advice only on trends in the relative size of the stock, lack a bio- logical reference point or level, and lack a decision framework for drawing statistical inferences about the state of the resource. We present a stochastic simulation technique for inferring population status relative to an index-based reference point. We applied an in- tegrated moving average model to trawl data on Atlantic wolffish, Anarhichas lupus, to derive fitted indices and propose using the lower quartile (25th percentile) of the fit- ted indices as a reference point. From bootstrapping techniques applied to model residual errors we empirically characterized the vari- ance and shape of the parent dis- tributions of both a fitted abun- dance index at any point in time and the lower quartile. Treating these distributions as jointly con- tinuous random variates, we gen- erated the cumulative density func- tion for the condition Priindex < lower quartile). Thus, for any value of the lower quartile, we can deter- mine the probability that the fit- ted index at any point in time lies below that value of the biological reference point. An examination of the joint cumulative probability satisfying this condition is impor- tant because it allows us to ascer- tain quantitatively the likelihood of correctly deciding whether such a stock is below a prescribed thresh- old level. Providing quantitative management advice from stock abundance indices based on research surveys Thomas E. Helser Northeast Fisheries Science Center National Marine Fisheries Service. NOAA 166 Water Street, Woods Hole. MA 02543 Daniel B. Hayes Northeast Fisheries Science Center National Marine Fisheries Service, NOAA 166 Water Street, Woods Hole, MA 02543 Present address: Department of Fisheries and Wildlife 1 3 Natural Resources Building Michigan State University, East Lansing, Ml 48824 Manuscript accepted 31 October 1994. Fishery Bulletin 93:290-298 (1995). Standardized multispecies bottom trawl surveys conducted annually in the spring and autumn by the Northeast Fisheries Science Center (NEFSC, 1993) have been integral to the scientific advice for manag- ers of the northwest Atlantic fish- ery resources. Not only do the sur- veys provide an efficient means of collecting biological and ecological information on a suite of finfish and invertebrates in the Northwest At- lantic, but they also provide the principal means of monitoring changes in population abundance. The trawl surveys use a stratified random sampling design in which stations are allocated to strata roughly in proportion to stratum area and are randomly assigned to specific locations within strata. Generally, the stratified mean num- ber or weight per tow is used as an index of relative abundance (Gross- lein, 1969; Clark, 1979). Such indi- ces of abundance can be quite vari- able because of heterogenous spa- tial distributions (Byrne et al., 1981), year to year changes in catchability (Byrne et al., 1981; Col- lie and Sissenwine, 1983), and natu- ral changes in population abun- dance. As such, the observed time series of abundance indices reflects two sources of random variation: 1) measurement error arising from within and between year survey sampling variability; and 2) true or "process" error arising from actual changes in population abundance. Measurement error in the survey estimates can be filtered from pro- cess variability by using auto- regressive-integrated-moving-aver- age (ARIMA) models (Box and Jenkins, 1976). However, the esti- mation of the parameters of a full ARIMA model for fisheries research surveys is often problematic be- cause of the relative shortness of the time series (Pennington, 1985). Pennington ( 1985) described an ap- proach based on an a priori specifi- cation of an integrated moving av- erage model in which change in population size follows a simple ran- dom walk. Pennington (1986) and Fogarty et al. (1986) have applied this approach to a number of north- west Atlantic species or stocks, such as yellowtail flounder, Pleuronectes ferrugineus. This approach has be- come the standard method for de- riving "fitted" abundance indices used in the Northeast region (NEFSC, 1993). 290 Helser and Hayes: Quantitative management advice based on stock abundance indices 291 While over 400 species of finfish and invertebrates have been caught in NEFSC's bottom trawl survey during 1963-92, 62 species are caught consistently nearly every year (Fig. 1). Roughly half of these 62 species have some economic importance and are therefore assessed by various means (NEFSC, 1993; Fig. 2). For the traditionally important groundfish species, such as Atlantic cod, Gadus morhua, had- dock, Melanogrammus aeglefinus, and yellowtail flounder, adequate data are available to perform a size or age-structured assessment (yield per recruit or Virtual Population Analysis [VPAp. These types 100 -, 90 - 80 -. 70 - 60 50 -| 40 30 20 10 0 Spring survey ■■Liiii.iiiii 5 10 15 20 25 30 Autumn survey 5 10 QLtaLian^QQciDQ 15 20 25 30 Number of years Figure 1 Frequency of the number of years various species (includes over 400 fish and invertebrates) occurring in the North- east Fisheries Science Centers autumn bottom trawl sur- vey since 1963 and spring bottom trawl survey since 1968. Data included up to 1992. of assessments are usually accompanied by biologi- cal reference points based on fishing mortality rates, absolute stock abundance levels, or both, as indica- tors for stock sizes below which long-term yield or productivity may be jeopardized. While survey abun- dance indices are important to "calibrate" results of analytical models for these species and stocks, they serve as the only source of abundance information to assess the status of the majority of stocks in the Northeast region (Fig. 2). Research survey index- based assessments generally provide only qualita- tive advice on the relative size of the stock and typi- cally do not generate reference points commonly used by fishery managers. In this paper, we extend the present procedures of deriving fitted survey abundance indices to inferring population status relative to an index-based refer- ence point in a probabilistic framework through simu- lation. We use Pennington's ( 1985 ) a priori integrated moving average approach to derive fitted survey time series and then characterize trends in population abundance relative to an index-based reference point defined to be the lower quartile (25th percentile) of the fitted time series. Our choice of the lower quartile for a reference point was rather arbitrary. However, the use of an interquartile ( such as the 25th percentile) computed from the data series over a range of years with reasonably high (as well as low) population sizes probably provides a reasonable reference point and would serve as such even as the time series lengthens. We then used a bootstrap procedure to characterize the uncertainty in both the fitted index and the reference 35 n a 20 ST 15 Yield per Age None Index recruit structured Figure 2 Frequency of assessment types performed on 62 species of fish consistly caught each year in the Northeast Fisheries Science Center's autumn and spring bottom trawl survey. 292 Fishery Bulletin 93(2), 1995 point and provide a probabilistic framework within which management decisions may be based. Statistical methods Estimation of abundance indices Bottom trawl surveys have been conducted in the autumn since 1963 and in the spring since 1968 by the Northeast Fisheries Science Center. The surveys are based on a stratified random sampling design and are used to develop time series of abundance indices that are not subject to biases inherent in fish- ery-dependent data. A detailed review of the survey sampling design, methodology, and application has been provided by Grosslein (1969), Clark ( 1979), and Almeida et al. (1986). Following Cochran (1977), the stratified mean catch per tow is expressed as yt -s h=l Nhyh N (1) where N = total area of all strata; Nh = area of stra- tum h; yh = sample mean in stratum h. The true abun- dance of a fish stock can be modeled as a population process with a linear stochastic difference equation of the form time series of survey abundance estimates, yt, are assumed to be directly proportional to the true popu- lation size, zt, and it is further assumed that the sur- vey index is measured with error, that is y, = zt + et (where the et's are iid MO, oe2)), then the survey time series may be represented by 2). The autoregressive parameter, , remains unchanged in Equation 4 while r\ is the new integrated moving average parameter that reflects error in the survey abundance estimates. Appropriate model specifica- tion is determined by examining the autocorrelation and partial autocorrelation functions, by estimating appropriate parameters, and by checking for model adequacy (Box and Jenkins, 1976). However, this formal procedure of specifying and adequately esti- mating parameters is typically hampered by short time series of data such as those from fishery-inde- pendent surveys. Pennington (1985, 1986) has pro- posed an approach based on a priori specification of the model which addresses: 1) the limitation in the length of the survey time series; and 2) changes in the population availability or catchability. Following Pennington (1986), the true population can be rep- resented as 2* =*A-1 + 02^-2 •••QpZt-p -61at_1 -62at_2.--9qat_q, (2) where zt is the population abundance at equally spaced points in time, (B)zt =6(B)at, (3) where B is the backward shift operator, and all other parameters are defined as above in Equation 2. If a zt =zt_lea' or(l-B)lne, (5) Here the a/s represent the process variability or those factors which cause changes in the population from year t—1 to year t (such as recruitment, fishing mor- tality, migrations, etc.). Pennington (1985) demon- strated that if the model (Eq. 5) and the ratio of vari- ances, ae2/oc2, are known, then z. and the variance of the estimator can be estimated. If we again assume the survey index, yt, to be an estimate of the true population abundance, z„ and that the measurement errors of the index are multiplicative, then lny, =lnz, +et. (6) Assuming the e('s are iid MO, a 2) and independent of the at's, then y. can be represented by the inte- grated-moving average model: (l-S)lny, =(l-6B)ct, (7) where the c,'s are iid MO, oc2) and represent the re- siduals generated by fitting the model to the observed data. For the model (Eq. 7) Helser and Hayes: Quantitative management advice based on stock abundance indices 293 4and(l-0)2=4- at at (8) Therefore, fitting the model (Eq. 7) to the observed survey abundance indices provides an estimate of 8 and from Equation 8, an estimate of o2Ja2c. Pen- nington (1986) notes that this approach has several advantages over using the raw indices in that: 1 ) the resulting model variance is more precisely estimated, as survey variance is affected by varying catchability from year to year; and 2) relevant information con- tained in the other years of the survey is used in estimates for a particular year. Further, the fitted survey series is considered to be more precise than the original series (Pennington, 1985, 1986; Fogarty et al., 1986). At this point the fitted index, with suf- ficient length of time, may be used to characterize trends in abundance relative to a chosen reference point. An estimate of the forecast variance of the fit- ted time series can be calculated (Box and Jenkins, 1976), although the reference point (i.e. interquartile) is deterministic. Further, if the time series is short, a correct specification and estimation of the model parameters will be difficult and parametric estima- tion of the variance uncertain. To overcome these constraints, nonparametric methods with boot- strapping techniques (Efron, 1982) were used to es- timate the variances of the fitted index and the ref- erence point as well as to determine the shape of their parent distributions. This approach is particularly useful in making inferences between the observed population level as estimated by the fitted index and the reference point, within a probablistic framework. Bootstrap procedure Once a maximum likelihood estimate of the inte- grated moving average parameter, 8, has been ob- tained from Equation 7, "fitted" estimates of the sur- vey population abundance, yt, with known residual errors are available at equally spaced points in time, such that a-B)\nyt =(1-8)0, = at . (9) where Var(at) = Var[(l-8)ct] = (l-8)2a2 = aa2 (see Eq. 8). The variance of yt is given by transformed survey abundance estimates. For the ith bootstrap replicate, n values of the model residuals were randomly selected with replacement (redefined as c't) and added to the predicted abundance esti- mates (yt) to obtain n new pseudo- values y*. Thus, a particular realization with the same underlying pro- cess was generated, where Vt = Vt + fief (11) Assuming that Equation 7 provides an adequate rep- resentation of the actual population levels of the time series, it can be shown from Equations 8—11 that the bootstrap generated realizations take on the random component because of measurement error, since (from Eq. 8) v[Wt 8a2 = a2 . (12) Conceptually, this random resampling of the residu- als mimicked a hypothetical resampling of the en- tire time series of abundance estimates with random variation generated from measurement error super- imposed on the underlying process variation (i.e. variation in population levels). Random sampling of residuals and generation of n new time-series pseudo- values were repeated m times (i.e. m bootstrap rep- licates were performed). For each ith bootstrap repli- cate, the prespecified integrated moving average model in Equation 7 was again fitted to the n new pseudo-values of the time series by using the same moving average parameter estimate, 8. The n new pseudo-values of the times series and the new fitted values for the m bootstrap replicates are given as and hV^.yv-,^ (13) (14) respectively. The lower quartile corresponding to each of the n new pseudo- values of the m bootstrap repli- cated time series as 9,>9,,9, (15) V(.yt) = a< 2\ al (10) We applied bootstrapping procedures (Efron, 1982) to the vector of residual errors generated by the in- tegrated moving average model (Eq. 7) applied to log- Rather than obtaining new estimates of 6 for the model fitting to each bootstrap replicate, we followed Pennington's ( 1985) suggestion that, given the large variability inherent in marine trawl surveys, a pre- liminary estimate of 8 between 0.3 and 0.4 appears to be an appropriate value for estimating an abun- dance index, and we set the value of 8 to that origi- 294 Fishery Bulletin 93(2). 1995 nally obtained from Equation 7. Finally, to complete the bootstrap replication procedures we made two final calculations; the mean of the lower quartile ob- tained from the n -fitted pseudo- values of the m boot- strap replicates, and the mean-fitted survey abun- dance index for each year. These are given as and i " — 1 v-i -* (16) (17) (=i This resampling process is conditioned on the set of residuals from a fitted model to the observed data, and no distributional assumption is made concern- ing the structure of the error. The sample size of re- siduals for the example given here (25 to 30) should be adequate to characterize the tails of the underly- ing error distribution, and bootstrap estimates of the mean and lower quartile should have converged suf- ficiently as the number of resampled replicates m was performed 1,000 times. As such, the mean and variances generated by these new realizations of the time series for both the fitted index and the refer- ence point, as well as the shape of their parent dis- tributions, provide the necessary information for making inferences about the population. Further, this approach to generating variances and confidence in- tervals is particularly useful because explicit solu- tions to the "normal equations" cannot be derived because of the nonlinear nature of the equations rep- resenting the underlying population process (Rawlings, 1988). Making inferences Decisions made by fishery managers are often based on the state of the resource relative to a chosen man- agement target or reference point. One question that forms the basis of management action is the follow- ing: Given the uncertainty in both the index of abun- dance and the value of the chosen reference point, what is the probability that the index in year t is less than or equal to the reference point? Statements of probability and inferences regarding the state of the resource can be formulated by using the boot- strap generated data in the following manner: Let the fitted index for any particular year ( yt ) and the lower quartile ( q ) generated from m bootstrap rep- lications be random variates Yj and Y2, respectively. In addition, assume that Y, and Y2 are jointly con- tinuous random variates with the density function f(yj,y2)- In practice, we want to determine the P(Yj -i-o : 1.0 ^ n o E o o i -1.6 : 0.8 c CO | -2.0 0.6 c T3 0) o -2.5 - 0.4 C CO _l / \ j-1 Landings W : .a -3.o - 0? •o c ■ 1 ' ' ■ ' ■ 65 70 75 80 85 90 Year Figure 3 Atlantic wolffish, Anarhichas lupus, landings (thousands of metric tons) and spring bottom trawl survey indices (log,[stratified mean number per tow]) from 1968 to 1992. management, or both. Given the data limitations for wolffish, what value will serve as a reasonable refer- ence point or proxy for a level of stock abundance below which the stock may be in jeopardy? For our example we chose the lower quartile of the fitted survey abundance indices for wolffish as a reference point. Admittedly the choice of a computed statistic and the period of years of the survey indices used are rather arbitrary; the situation for each species should be carefully considered and a suitable refer- ence point agreed upon by fishery managers. How- ever, no matter which reference point is used, a simple comparison of a survey index in any given year with a survey-based reference point fails to con- sider the variability in each of these quantities. Results and discussion Estimates of the stratified mean number per tow (transformed by natural logarithms) clearly show declining trends in abundance, and the fitted index derived from time-series analysis appeared to pro- vide a good, and less variable, representation of the observed data (Fig. 4). The maximum likelihood es- timate of the integrated moving average parameter (0) was 0.50 [SE( 0)=O.2O], although it is probably not reliably estimated as indicated by the relatively flat maximum likelihood surface between 0 and 0.6. Survey indices Observed Fitted Year Figure 4 Predicted indices derived from an integrated moving aver- age model fitted to observed Atlantic wolffish, Anarhichas lupus, spring bottom trawl survey indices (loge[stratified mean number per tow]) from 1968 to 1992. Predicted indi- ces are compared to the lower quartile (25th percentile) of 1968-92 fitted indices as an arbitrary chosen reference point. 296 Fishery Bulletin 93(2), 1995 Pennington ( 1985, 1986) noted similar problems and concluded that the relative shortness of the time se- ries of trawl data makes reliable estimation of the moving average parameter difficult. Although Pennington suggested using a value ranging from 0.3 to 0.4 appropriate for many stocks, we used the value of 0.50 because an analysis of the residuals from the model indicated that they were normally distributed (P>0. 10). The fitted estimates of abundance over the entire time series produce an index whose variance is con- siderably less than the variance of the observed se- ries (Pennington, 1986). A comparison of a fitted in- dex to the reference level (i.e. the lower quartile or 25th percentile) derived from the fitted indices should provide a reasonable evaluation of the stock's status because these reflect "true" trends in population abundance from only process variability (the effect of survey variance has been reduced). The fitted in- dices indicate that wolffish abundance has declined since the early 1980's and that by 1990 the index had fallen below the reference point (lower quartile= -1 .90 ) to -2.2 ( Fig. 4 ). In a hypothetical sense, if man- agers of this resource considered the lower quartile of the fitted indices a reasonable reference point, the 1990 index might have triggered some action, al- though it could be argued that the downward trend itself might be cause for concern. However, given the relative closeness of the fitted value of the 1990 in- dex (-2.2) to the reference point (-1.9), as well as the uncertainty in both values, a logical question to ask is: What is the probability that the fitted 1990 index lies below the reference point? Probability statements addressing this question can be derived from the parent distributions of both the fitted indices and reference points from the 1,000 bootstrap replications (Fig. 5). For the wolffish ex- ample, each of these distributions appear log-nor- mally distributed, the 1990 fitted index exhibiting slightly more dispersion about its mean (as would be expected) compared with the reference point (Fig. 5). Both the fitted index and lower quartile means are nearly identical to the expected values (computed from the initial integrated moving average model fit), indicating little or no bias and uncorrelated model residual errors. Thus, for the time series on wolffish, an a priori integrated moving average model specifi- cation appears appropriate to describe the underly- ing population process. For any value of the lower quartile we can state the probability that the fitted 1990 index lies below that value of the reference point using a discrete approximation of Equation 18. This simply repre- sents the area integrated under the joint density 250 200 L? 150 c 100 50 Wolffish spring survey ■ 1990 Index ■ Lower quartile ll -2.8 -2.6 -22 -2.0 Indices (loge [mean number per tow]) Figure 5 Comparison of empirical distributions of the 1990 spring survey index predicted by an integrated moving average (IMA) model fitted to 1,000 bootstrapped generated realiza- tions of the survey time series 1968-92 and the lower quartile (25th percentile) of those predicted indices. The 1,000 realizations of the time series were generated by sampling with replacement the IMA model residual errors and randomly adding these to the predicted survey indices. Helser and Hayes: Quantitative management advice based on stock abundance indices 297 where the value of the fitted index is less than the value of the lower quartile (Fig. 6). The probability that the fitted 1990 index lies below the estimated value of the lower quartile (-1.9) is approximately 60% (Fig. 6). Further, because of the shape of the parent distribution of the lower quartile, the prob- ability that the 1990 index lies below the reference point increases rapidly for higher and higher values of the reference point. For example, the probability that the 1990 index lies below a value of-1.85, which is nearly as likely as the bootstrapped mean (Fig. 5), increases to almost 75% and reaches nearly 85% at a value of -1.8 (Fig. 6). As an alternative to making inferences about the level of the population at only one point in time, fishery managers may wish to con- sider the likelihood of two (or more) consecutive years jointly falling below the value of the reference point. To address this question, we computed the joint prob- ability of the 1990-91 and the 1990-92 fitted survey indices falling below our chosen reference point. The fitted survey indices over the 1990-92 period were as likely as those over the 1990-91 period to be be- low the reference point: approximately a 57% prob- ability that the indices jointly fell below the refer- ence point. This indicates that current population levels (as indexed by the fitted abundance indices) are considerably below the prescribed threshold level if the lower quartile of the fitted time series were Lower quartile Figure 6 Probability that the value of the 1990 spring survey index predicted by an integrated moving average (IMA) model fitted to 1,000 bootstrapped generated realizations of the survey time series 1968—92 lies below the value of the lower quartile (25th percentile) derived from the predicted bootstrapped indices 1968-92. adopted as the acceptable reference point. It should be emphasized that an "acceptable" reference point in this example refers more to choice of the range of years used for computation of the reference than to the choice of the interquartile, specified in this case to be the 25th percentile. We advise using a range of years for the abundance index which represents rea- sonably high population sizes and then using that fixed set of years for computation of the reference point even as the time series lengthens. This would prevent a ratcheting effect where the reference point declines as the abundance index declines, while al- lowing a characterization of the uncertainty in the reference point. In conclusion, this technique represents an ad- vancement for index-based assessments in the pro- vision of quantitative advice for the management of fish populations surveyed by research vessels that are otherwise lacking in data sources. This approach provides an examination of the joint cumulative prob- ability for the condition Priindex in year t, t+l, ... , t+m < lower quartile) and is important because it allows the likelihood of correctly deciding whether or not a stock is below a prescribed threshold abun- dance or reference point to be ascertained quantita- tively. We emphasize that the computation of a ref- erence point from the time-series data is arbitrary and should be based on a series of observations rep- resenting reasonably high as well as low stock abun- dances. Finally, we illustrated these procedures with trawl survey data for wolffish in the natural log scale, which when the data are differenced, produces ho- mogeneity of variance and stationarity of the time series (Nelson, 1973). It should be noted that retransformation back to the linear scale is likely to result in some bias. We did not examine the effects of transformation bias in this study but suggest that these effects be investigated in the future. Literature cited Almeida, F. P., M. J. Fogarty, S. H. Clark, and J. S. Idoine. 1986. An evaluation of precision of abundance estimates derived from bottom trawl surveys off the northeastern United States. ICES Council Meeting 1986/G:91. Bigelow, H. B., and W. C. Schroeder. 1953. Fishes of the Gulf of Maine. U.S. Dep. interior, Fish. Bull, of the Fish and Wildl. Serv, Vol. 53, 577 p. Box, G. E. P., and G. M. Jenkins. 1976. Time series analysis: forecasting and control, revised ed. Holden-Day, Oakland, CA, 375 p. Byrne, C. J, T. R. Azarovitz, and M. P. Sissenwine. 1981. Factors affecting variability of research trawl surveys. Can. Spec. Publ. Aquat. Sci. 58:238-273. Clark, S. H. 1979. Application of bottom trawl survey data to fish stock assessment. Fisheries 4:9-15. 298 Fishery Bulletin 93(2), 1995 Cochran, W. G. 1977. Sampling techniques. John Wiley and Sons, New York, NY, 428 p. Collie, J. S., and M. P. Sissenwine. 1983. Estimating population size from relative abundance data measured with error. Can. J. Fish. Aquat. Sci. 40:1971-1983. Efron, B. 1982. The jackknife, the bootstrap and other resampling plans. SIAM Monograph No. 38. CBMS-NSF Reg. Conf. Ser., Soc. Ind. Appl. Math., Philadelphia, PA, 92 p. Fogarty, M. J., J. S. Idoine, F. P. Almeida, and M. Pennington. 1986. Modelling trends in abundance based on research vessel surveys. ICES Council Meeting 1986/G:92. Grosslein, M. D. 1969. Groundfish survey program of BCF Woods Hole. Comm. Fish. Rev. 31(8-9)22-30. NEFSC (Northeast Fisheries Science Center). 1993. Status of Fishery Resources off the Northeastern United States for 1993. U.S. Dep. Commer., NOAATech. Memo. NMFS-F/NEC-101, 140 p. Nelson, C. R. 1973. Applied time series analysis for managerial fore- casting. Holden-Day, San Francisco, CA, 231 p. Pennington, M. 1985. Estimating the relative abundance offish from a se- ries of trawl surveys. Biometrics 41:197-202. 1986. Some statistical techniques for estimating abundance indices from trawl surveys. Fish. Bull. 84:519-526. Rawlings, R. O. 1988. Applied regression analysis, a research tool. Wadsworth and Brooks, Pacific Grove, CA, 553 p. Abstract. — Nutritional dynam- ics of yellowtail rockfish, Sebastes flavidus, were analyzed from the perspective of temporal changes in tissue composition of liver, muscle, mesentery, and gonad to determine aspects specific to female reproduc- tion. Monthly tissue composition data over an annual reproductive cycle indicated that females accu- mulated greater somatic tissue en- ergy reserves than did males dur- ing the summer and fall months. Maternal lipid and protein reserves were depleted in a reciprocal rela- tion with ovarian growth during the winter. The greatest declines of lipid and protein occurred in me- senteries and muscle, respectively. Females lost approximately 40% more somatic tissue than males during the time interval from ova- rian development to parturition. Lipid was the primary energy source, contributing 74% of the en- ergy lost from somatic tissues for female-specific reproductive pur- poses. Two-thirds of lipid depleted from maternal soma was for adult metabolic maintenance. Of the other one-third, 43% was gained in ovary tissue during development, leaving 57% for reproductive meta- bolic costs. Protein increased 220% in ovaries relative to female-spe- cific somatic protein loss, indicat- ing de novo ovarian synthesis. This study is the first report of compre- hensive tissue composition dynam- ics and allocation to reproduction in a viviparous marine teleost. The analytical design used demon- strated the significance of each tis- sue component and the temporal pattern of allocation to reproduc- tive development. Nutritional dynamics of reproduction in viviparous yellowtail rockfish, Sebastes flavidus Elizabeth C. Norton R. Bruce MacFarlane Tiburon Laboratory, Southwest Fisheries Science Center National Marine Fisheries Service, NOAA 3 I 50 Paradise Drive, Tiburon, CA 94920 Manuscript accepted 17 October 1994. Fishery Bulletin 93:299-307 ( 1995). Maternal nutritional status and the allocation of nutrients into develop- ing young are important factors con- tributing to reproductive success in fish. Previous investigations have shown that nutritional status can influence fecundity and the vitality of offspring (Anokhina, 1959; Rijns- dorp, 1990; DeMartini, 1991; Kjesbu et al., 1991). By determining the temporal patterns of somatic and gonadal tissue components involved in fish nutritional dynamics, we can improve our understanding of en- ergy and nutritional needs for suc- cessful reproduction. Several studies of nutrient dy- namics in fish have used chemical composition analyses of primary body constituents, including lipid, protein, glycogen, water, and ash components, to assess physiological status and the level of available nutritional reserves (Love, 1970; Caulton and Bursell, 1977; Cui and Wootton, 1988). These reserves have been shown to vary by species and interannually in location, quan- tity, and the sequence of allocation into reproductive development (Sargent, 1976; Medford and Mac- kay, 1978; Henderson et al., 1984; MacFarlane et al., 1993). Generally, the principal source of nutritional energy reserve in fish is lipid (Sar- gent, 1976; Sargent et al., 1989). Protein, primarily used in struc- tural development and enzyme syn- thesis, may also be an additional source of energy when lipid reserves are depleted ( Mommsen et al. , 1980; Walton and Cowey, 1982). Many temperate fish species fol- low a similar seasonal pattern of nutrient dynamics, where energy reserves are accumulated in the summer and depleted during the win- ter reproductive period (Shul'man, 1974). The transfer of nutrients from somatic reserves into ovarian growth has been indicated by the reciprocal relationship between the depletion of somatic stores and ova- rian development (MacKinnon, 1972; Dawson and Grimm, 1980; Dygert, 1990). While this general pattern has been documented in oviparous species, little data on nutritional dynamics are available for viviparous teleosts (Wourms et al., 1988). For the marine vivipa- rous genus Sebastes, only changes in tissue lipids have been measured in relation to reproduction (Guille- mot et al., 1985; Larson, 1991; Mac- Farlane et al., 1993). The yellowtail rockfish, Sebastes flavidus, range from San Diego, California, to Kodiak Island, Alaska (Eschmeyer et al., 1983), and are important both commercially and recreationally (Reilly et al.1; Pacific 1 Reilly, P. N., D. Wilson-Vandenberg, D. Watters, J. E. Hardwick, and D. Short. 1993. On board sampling of the rockfish and ling- cod commercial passenger fishing vessel in- dustry in northern and central California . May 1987-December 1991. Calif. Dept. Fish Game Admin. Report. 93-4, 242 p. 299 300 Fishery Bulletin 93(2), 1995 Fisheries Management Council2). Distinctive char- acteristics of the reproductive strategy of yellowtail rockfish (e.g. small testes, copulation months before fertilization, quiescent testes during period of ova- rian development [Eldridge et al., 1991], and nonmigratory behavior [Pearcy, 1992]) allow male nutrient dynamics to serve as adult metabolic con- trols. Consequently, nutritional energy expenditures specific to female reproduction can be estimated by the difference between female and male dynamics. Knowledge of the nutritional dynamics specific to female reproduction may contribute understanding to the causes of interannual variability of larval pro- duction and health (Moser and Boehlert, 1991). The typical nutrient dynamic pattern may be altered by episodic environmental perturbations that impact reproductive output. Phenomena such as El Ninos modulate the duration and intensity of upwelling, thus lowering oceanic productivity and subsequent energy flow (Boje and Tomczak, 1978; Ainley, 1990). In fact, Lenarz and Wyllie Echeverria (1986) sug- gested that the 1983 El Nino adversely influenced fat accumulation and reproduction in yellowtail rockfish. The purpose of the present study was to determine the temporal dynamics of tissue components in so- matic and ovarian tissues in relation to the annual reproductive cycle for yellowtail rockfish. Our objec- tive was to determine the allocation of tissue compo- nents for nutrition and energy committed to female reproductive development. This report presents the first comprehensive nutritional dynamics study on a marine viviparous species. Materials and methods Adult yellowtail rockfish were collected by hook-and- line at depths of 50 to 150 m from Cordell Bank, a marine bank located approximately 20 nautical miles west of Point Reyes, California (38°01'N, 123°25'W ). Specimens were obtained monthly during one repro- ductive cycle from May 1987 to April 1988. Fish were immediately placed on ice and returned to the labo- ratory for analyses. Within 24 hours of capture, ovarian or testicular stage and morphometries were recorded and tissues were excised for proximate and chemical analysis. Tissues removed included liver, gonad, and a section of muscle from the epaxial portion of the fish just 2 Pacific Fishery Management Council. 1992. Status of the Pa- cific coast groundfish fishery through 1990 and recommended acceptable biological catches for 1993: stock assessment and fishery evaluation. Document prepared for the council and its advisory entities. Pacific Fishery Management Council, Port- land, OR. below the spinous dorsal fin. In addition, mesenteric fat deposits attached to the viscera were dissected and weighed. Muscle mass for individual fish was estimated by a regression equation. We regressed muscle weight on body weight minus gonad weight from represen- tative fish spanning the typical total body weight range (800 to 1600 g) for yellowtail rockfish from Cordell Bank. Muscle mass was determined by muscle (g) = 24.51 + 0.433 [body weight (g) - gonad weight (g)]. (r=0.994, P<0.0005) Determinations of water, ash, and protein content were performed on fresh tissues. Samples analyzed for water content were dried at 80°C to a constant weight and cooled in a desiccator prior to weighing. Dried tissues were incinerated for 4 hours at 550°C to measure ash content. Protein concentration was assayed by the Lowrey method (Lowrey et al., 1951) with bovine serum albumin (Sigma Chemical Co., St. Louis, MO) as a standard. Tissue samples for lipid and glycogen determina- tions were stored at -70°C and analyzed within one month of collection. Lipid was extracted in duplicate from 1 to 2 g of liver, gonad, and muscle by the biphasic method of Bligh and Dyer (1959) following homogenization with a Polytron homogenizer (Brinkman Inc., Westbury, NY). Total lipid was quan- tified by automated thin layer chromatography/flame ionization detection (TLC/FID), by using an Iatroscan TH-10 Mark III (Iatron Laboratories Inc., Tokyo, Japan) with T Datascan software (RSS Inc., Bemis, TN). Triplicates of 1 ul were spotted on Chromarods S-III, dried, and scanned by the FID at 3.1 mm/sec, 0.95 kg/cm2 hydrogen pressure and air flow of 2000 mL/min. Peak areas were converted to total lipid weight by using external standards prepared gravi- metrically from lipid extracts of S. flavidus livers. Standard concentrations were attained by evaporat- ing the organic layer to dryness and reconstituting with chloroform to known concentrations ranging from 2 to 70 ug lipid/uL. Chromarods were cleaned with 9N sulfuric acid, rinsed in Milli-Q water and stored in a desiccator between analytical runs. Glycogen content was measured by the anthrone method (Carroll et al., 1956). Values wer^ standard- ized with glycogen from rabbit liver (Sigma Chemi- cal Co., St. Louis, MO). To evaluate variation in tissues and their compo- nents over the reproductive cycle, tissue component concentrations were converted to component masses by determining the product of tissue mass and com- ponent concentration. Since tissue and component masses are a function of fish size, we adjusted the Norton and MacFarlane: Nutritional dynamics of reproduction in Sebastes flavidus 301 data to compensate for size variation. Tissue and component masses were converted to natural loga- rithms [\n(X + 0.01)] and subjected to the general linear model analysis of covariance (ANCOVA) by using the natural log of standard length (In SL) to adjust for individual size differences among monthly samples. The adjusted means and standard errors of tissue and component masses were backtrans- formed by taking their antilogs. ANCOVA also de- termined the statistical significance of tissue and component variation across the reproductive cycle within each sex. We determined differences among specific monthly means by Duncan's multiple con- trast test with a = 0.05. Differences in monthly means between sexes were assessed by Mests. All analyses were performed within the Number Cruncher Sta- tistical Software package (NCSS, Provo, UT). We estimated the contribution of somatic nutri- tional components to female reproduction by deter- mining changes in tissue component masses between the onset of rapid ovarian growth and parturition. The decrease in somatic component quantities from maximal values before December to minimal levels in March was calculated for each tissue for each sex. Likewise, ovarian accumulation of nutritional com- ponents was calculated as the gain in mass from November to maximal values in December or Janu- ary. Since male yellowtail rockfish are sexually qui- escent during this interval (Eldridge et al., 1991), declines in their somatic nutritional components re- flect utilization for adult metabolic maintenance. Differences in net losses of somatic components be- tween males and females were con- sidered estimates of allocations spe- cific to female reproduction. Temporal dynamics Ovarian development was largely synchronous within the yellowtail rockfish population from the onset of recrudescence in May through late vitello- genesis in November, as documented histologically by Bowers (1992) and MacFarlane et al. ( 1993) (Fig. 1). During December, females were in late vitello- genesis and migratory nucleus stages. Since fertili- zation occurred in January, both late oocyte and early embryonic stages were represented. In February, all females were in mid to late gestation. Parturition, or larval release, was completed in March when ova- ries returned to a small, spent condition. In males, testicular development was evident in August and September; in all other months testes were regressed and quiescent (Fig. 1). Copulation appeared to have occurred in September and Octo- ber; sperm were stored in ovaries prior to fertilization. During the annual reproductive cycle, ovarian mass increased 11 -fold from September through De- cember (Fig. 1). The most significant increase oc- curred during late vitellogenesis between November and December. Ovaries reached maximum size by January and retained mass through February. In comparison, testes reached maximum size in Sep- tember and were less than 5% of ovarian mass be- tween December and February. The masses of liver, muscle, and mesenteric fat var- ied significantly (P<0.01) across the annual repro- Results Size variation Monthly mean standard lengths (±SE) for females and males were 36.5 ±0.7 cm and 35.3 ±0.4 cm, re- spectively (Table 1). Differences in length between sexes and among males over the entire study interval were not significant (P>0.05). Be- cause there were differences among monthly mean lengths of females (P<0.01), analysis of covariance eliminated tissue or component mass variation due to size. Table 1 Monthly mean standard length (SL) ± standard error (SE) for female and male yellowtail rockfish, Sebastes flavidus. Female mean lengths with same superscript were not significantly different (P > 0.05). Mean SL for males did not vary significantly among months, and did not differ significantly from females (P>0.05). n = sample size. Month Females Males n SL SE n SL SE May 6 33.0" 0.9 4 37.2 0.6 June 5 37.0a6c 2.2 5 35.9 0.7 July 6 40.5C 1.2 4 37.4 1.7 Aug 5 40.3C 0.8 5 35.0 0.8 Sept 9 35. v'* 1.3 1 32.0 — Oct 5 36.7a6c 1.5 5 34.6 0.8 Nov 6 37406c 1.7 4 37.1 0.9 Dec 5 35. lab 1.6 5 34.7 1.0 Jan 6 37.0a6c 2.3 5 35.6 0.8 Feb 5 32.7° 1.7 5 34.0 0.4 Mar 5 38.261' 1.1 5 34.5 1.5 Apr 5 34.8°* 1.5 5 36.0 0.8 Monthly mean 36.5 0.7 35.3 0.4 302 Fishery Bulletin 93(2). 1995 Vitellogenesis Early / Late / F / Embryo / Spent Figure 1 Annual ovarian reproductive cycle and monthly tissue wet weights for gonad, liver, muscle, and mesenteric fat of yel- lowtail rockfish, Sebastes flavidus. Values are means ±SE in grams adjusted by ANCOVA for variations in fish size. Temporal sequence of ovarian maturation stages are shown in bar across the top; recrudescence or early development (Dev), early and late vitellogenesis, fertilization (F), em- bryogenesis (Embryo), and spent. ductive cycle in both sexes (Fig. 1). These somatic tissues increased in mass during the summer and remained elevated into fall. Females accumulated significantly more mesenteric fat, liver, and muscle than did males (P<0.001). Declines in female somatic tissues in the fall and winter, during late vitellogen- esis and embryogenesis, were inversely related to the accretion of ovarian tissue. Temporal changes of ovarian tissue components followed a pattern similar to ovarian mass (Fig. 2). Protein and lipid increased 22-fold and 7-fold, respec- tively, from vitellogenesis in October to early gesta- tion in January. Although glycogen showed a signifi- cant increase (P<0.001 ), quantities were always small, representing less than 1% of ovarian mass. Ash and water profiles reflected increased ovarian mass. At maximal size, water accounted for about 70% of ovary mass. Fluctuation in the masses of testicular compo- Gonad Figure 2 Monthly lipid, protein, glycogen, ash, and water content in gonad tissues of yellowtail rockfish, Sebastes flavidus, during one reproductive cycle. Values are means ±SE in grams on a wet weight basis. Missing male values are due to small testes size. nents were insignificant compared with ovarian changes. In many cases, testicular quantities were in- sufficient to perform analyses of all constituents. Dynamics of liver components were dissimilar across the reproductive cycle and between sexes (Fig. 3). Lipid and protein increased from late spring into summer in both sexes; the greatest net gain in female lipid was between July and August. In August, lipid was about 40% of liver mass, whereas protein contributed 10—15%. After August, female liver lipid decreased, but protein remained elevated during vitellogenesis until January. Significantly more liver protein was retained in females than in males from October to January (P<0.001 ). Both female and male liver glycogen followed a temporal pattern of a bimodal increase in the spring and sum- mer with a decrease in the winter. The quantity of gly- cogen was only a small portion of total liver weight. Water in female liver accounted for a large portion of retained liver mass relative to males during late sum- mer and fall (September through December). Norton and MacFarlane. Nutritional dynamics of reproduction in Sebastes flavidus 303 Liver Month Figure 3 Monthly lipid, protein, glycogen, ash, and water content in liver tissues of yellowtail rockfish, Sebastes flavidus, during one reproductive cycle. Values are means ±SE in grams on a wet weight basis. Muscle Month Figure 4 Monthly lipid, protein, glycogen, ash, and water content changes in muscle tissues of yellowtail rockfish, Sebastes flavidus, during one reproductive cycle. Values are means ±SE in grams on a wet weight basis. In terms of quantity, protein content and water con- tent were largely responsible for variation in muscle mass (Fig. 4). Protein content in female muscle in- creased 30% from July through November and was significantly greater than that in males (P<0.005). Muscle protein declined significantly in vitellogenic females after November (P<0. 01). Males experienced a gradual decline in muscle protein from July to January. Lipid accounted for less than 5% of muscle mass in both sexes. In the fall, females had greater muscle lipid than males (P<0.05); lipid levels were similar during the other periods. Muscle glycogen and ash content in females and males changed little across the reproductive cycle and did not appear to coincide with other component dy- namics. Also, muscle glycogen content was an order of magnitude lower than liver glycogen. Nutritional energy dynamics By calculating changes in quantities of somatic and gonadal components from the onset of ovarian de- velopment to parturition, a mass balance of nutri- tional energy dynamics relative to the female annual reproductive cycle was constructed (Table 2). Females lost 94 g of somatic tissue from the start of ovarian development through parturition. Virtu- ally all of this loss was lipid (51 g) and protein (41 g). Females lost 27 g, or about 40% more somatic re- serves than did males. Lipid was mobilized from all somatic tissues. From the total lipid loss of 51 g in females, mesenteric fat contributed the most, 21 g, followed by liver and muscle. Mesenteric fat was also the greatest source of lipid loss in males; however, females used approxi- mately 8 g more lipid from mesenteries than did males during the annual cycle. Overall, females lost 17 g more lipid from soma than did males, suggest- ing that about two-thirds of lipid depleted from so- matic stores was used for adult maintenance. Both females and males lost protein, primarily from muscle, during the time interval of ovarian maturation. Females mobilized 37 g of protein from muscle tissue, which was about 10 grams more than 304 Fishery Bulletin 93(2). 1995 Table 2 Mean net chang i in tissue com uonents during annual reproductive cycle of yellow- tail rockfish, Sebastes flavidu i. All values in grams or kilocalories adjusted by ANCOVA for fish size variation Differences (diff) are changes from start of ovarian development to parturition wi th male data as baseline Net gain( + ) and loss(-) indicated. Tissue Sex Lipid Protein Glycogen Total Liver 9 -15.5 -3.4 -1.6 -20.5 6* -10.1 -3.6 -1.2 -14.9 diff -5.4 +0.2 -0.4 -5.6 Muscle 9 -14.6 -37.4 -0.04 -52.0 6 -11.1 -27.6 +0.01 -38.7 diff -3.5 -9.8 -0.05 -13.3 Mesentery 9 3 diff -21.3 -13.1 -8.2 -21.3 -13.1 -8.2 Z soma 9 -51.4 -40.8 -1.6 -93.8 d -34.3 -31.2 -1.2 -66.7 diff(g) -17.1 -9.6 -0.4 -27.1 (kcal) -161.6 -54.2 -1.6 -217.4 Ovary (g) +7.4 +21.2 +0.1 +28.7 (kcal) +69.9 + 119.8 +0.4 + 190.1 Ovary -<-l) Fp-U(eZ^'-D (3) Given known values of Cp t , Cp_lt t , iVp t+1, and M, no unique joint solution exists for the two unknowns, Fpt and Fp_lt in Equation 3. In this study, we use the simplifying assumption that the value of a in a FP,t P-U (4) purposes, we also use the same approach for catch equations not involving a plus group. Range of values examined In order to evaluate the accuracy of the approxima- tions and to develop empirical corrections, we gener- ated 1,000 uniform random values of each param- eter in the following ranges: N , [500, 1,500], N x t [500, 1,500], M [0.05, 1.0], Fp_[ , [0.05, 3.0], a [0.5, 2.0]. These ranges are arbitrary but we felt that they represent realistic extremes: the stock size of the plus group and the preceding age can differ by a factor of 3; the range in M is representative of a wide range in lifespans; the fishing mortality range is extremely wide because our purpose was to find reasonable approximations for a wide range of Fs; and the range in a allows the fishing mortalities of the plus group and the previous age to differ by a factor of 2. Initial approximations Pope's (1972) approximation to Fa t in Equation 1 can be explained as follows. Consider the equations (from Appendices A and B in Pope, 1972) N. a,t Na + U+le Z, (5) is known so that Fp t in Equation 3 can be replaced by ocFp.j (. Now the solution consists of a single fish- ing mortality rate, Fp_h t. Theoretically, one or more a values can be estimated as parameters in an age- structured model. However, estimation of several a values is difficult, particularly for the last years for which catch data are available (Powers and Restrepo, 1992). Thus, in many assessment applications, a values are assumed from a knowledge of the popula- tion and the fishery being examined (Powers and Restrepo, 1992). For example, selectivity studies of the fishing gear may indicate that fish of ages p-1 and older are equally vulnerable, giving a = 1. and N. M a + l,t + l' N„ ZaA1' FaA1- ,Z„ ) (6) Pope (1972) demonstrated that, over a range of fishing and natural mortality values, the function multiplying Ca , in Equation 6 can be reasonably approximated by e,M/21. Making use of this approxi- mation and substituting Equation 5 into Equation 6 gives N. M a+l,t+l' N a+U + l' ,za. Ca,te Mil Approach The approach we follow is similar to that used by Sims ( 1982 ). We first provide simple approximations to Fp_h t, similar to those developed by Pope (1972). On the basis of simulated parameter values, we then empirically estimate correction factors that can be used to improve upon the initial approximations. Finally, we use the corrected approximations as start- ing guesses for Newton's Method (see Sims, 1982), which can be used to obtain a more accurate numeri- cal solution to the catch equation. For comparative which can be solved for Fa t as ^=ln A' CaJ_e-MI2 + 1 a+M+1 (7) We followed a similar approach for the purpose of obtaining an initial analytical approximation to F 1 t in Equation 3. Consider the special case when the fishing mortalities of the plus group and the preceding age are the same (i.e. a=l in Eq. 4, giving F t= F^ ,). Then, the equation analogous to Equation 5 is ob- tained from Equation 2: 310 Fishery Bulletin 93(2), 1995 L1* p,t T ly p-i,t J Ivp,<+iK > and the equation analogous to Equation 6 is zp_ua-e-F»->-) (8) M NpM1eM=NPit-CPtt Fp_u(l-e-z^-) pU Zp_u(\-e-F>-") * Fp_ua-e-z>->>) (9) ~~ Cp-l,t which, using the same approximation given by Pope (1972), becomes Np>t+1 eM = [Np>t + Np_u ] - [Cpit + Cp_u ]eM'2 . Substituting Equation 8 into the last equation re- sults in NpJ+leM =NPiMez-u -[CpJ +Cp_u\e'MI\ which can be solved for the fishing mortality rate as of parameter values; 2) to plot values of the ratio AF I TF against a and M ( parameters usually assumed to be known a priori) and to identify types of func- tions that can adequately describe the observed re- lationship, if any; and 3) to estimate the coefficients of such functions and use them to correct AF so it becomes closer to TF. This empirical approach is simi- lar to the multiple regression approximations sug- gested by Allen and Hearn (1989). For comparative purposes, we also followed the same approach using the approximation given by Equation 7 for a case without a plus group. Newton's Method Sims (1982) suggested the use of Newton's Method for solving F in the catch equation with a desired degree of precision. For Equation 1, the functional equation of interest is f(Fa,ty- Faj(ez°<-1) N, a+l,t+l , FP-U = ln (Cp.t +^p~l,t) -MI2 i NPtt+1 (10) We found that Equation 10 is often a poor approxi- mation for values of a / 1 (see Results section). A much better approximation can be obtained by in- troducing a into the equation as Fp-u=\n (CpAla + Cp_u) uii + ^ NP,M (11) Empirical correction factors In many cases, given the widespread availability of computers, the approximation given by Equation 11 can be used as an adequate starting guess for an it- erative procedure to get a more accurate solution (e.g. see the next section). In some cases, however, it is desirable to improve upon this approximation in or- der to obtain either a better starting guess, or to ob- tain as close as possible to an accurate solution be- cause iterative computations are expensive. The lat- ter is the case of solving multiple catch equations while conducting a cohort analysis on a computer spreadsheet and is the motivation for this study. The empirical approach we used was simple. De- note the approximation in Equation 11 hyAF and the true fishing mortality by TF. Our approach was 1) to generate a large number of plausible combinations and a solution to Fa t is obtained when f(Fa t) = 0. Sims (1982) showed that all requirements for con- vergence were met in order for Newton's Method to converge to that solution. One iteration of Newton's Method (denoted by i) changes the estimate of Fa t as follows: FaAi + l) = FaAi)- f((Fg,tW) r{Fa,td)) (12) with f'(F„t) = - Ca,(ez°'(Fa2l+FaJM + M)-M) Flt (ez°< - 1)2 For the application of Newton's Method to the so- lution to the catch equation involving a plus group, the functional equation of interest is (from Equation 3) f(Fp-Xt)- CpJ(aFp_1J + M) aFp_u(eaF^-+M-l) , Cp_u(Fp_u+M) Fp_Xt(eF^+M-l) P'M and its derivative with respect to F t t xs Restrepo and Legault: Approximations for solving the catch equation f'(Fp.u) = CpJ (eaF^'+M(a2F^u + aFp_uM + M)-M) aF2_u(eaF»^+M -l)2 Cp-U(^u+M^p-u + Fp-u M + M)-M) F*(eF»»+M-l)2 One iteration of Newton's Method proceeds in the same manner as explained above in Equation 12, if the empirically corrected estimates of fishing mor- tality (see previous section) as initial values are used. Although we did not carry out a rigorous analysis of conditions for convergence, as Sims (1982) did, we did not encounter any cases where an iteration did not result in an improvement. Results Table 1 provides some statistics of the ratio AF I TF for the 1,000 random combinations of inputs, with and without a plus group. In each case, the first column provides these statistics for the initial approximation iAF from Equation 7 for the case without a plus group and AF from Equa- tions 10 and 11 for the plus group approximation). The next column provides the statistics for the ratios after an empirical correction function is applied (the coefficients of these correction factors are presented in the fol- lowing subsections). The last two columns give the statistics after one and two iterations of New- ton's Method. Implications of these results are explained in more detail below. tio indicated an overall 3% bias and the largest er- ror was slightly greater than 8%. Visual inspection of a plot ofAF/ TF against M in- dicated that a linear relationship would improve the approximation. We fitted the model AF I TF = a + b M by minimizing the sum of absolute deviations be- tween the observed ratios and those predicted by the model. The parameter estimates were a = 0.9970, and b = 0.0808. Thus the empirical correction to the initial approxi- mation to F was emp-AF = imLAF/(a + bM). (13) Much improvement in the approximation was ob- tained by use of this simple correction function (Table 1, second column, and Fig. 1, middle panel). The larg- est observed error was now 3%, which compares fa- vorably with the errors reported by Pope ( 1972 ) over a much narrower range of fishing and natural mor- tality rates. Application of a single iteration of Newton's Method resulted in virtual conver- Case I: without a plus group The initial approximation pro- vided by Equation 7 (from Pope, 1972) was reasonable, as ex- pected (See Table 1 and Fig. 1, top panel). The mean AF I TFra- Table 1 Summary statistics for 1,000 ratios of the approximated fishing mortality rate to the true fishing mortality rate (AFITF, see text for a description of how the 1,000 realizations were made). Case I represents analyses not using a plus group. Case II represents analyses with a plus group. Sach column corresponds to a different step in the analyses progressing from an initial approximation (two initial approxima- tions are given tor Case II), to an empirically corrected approximation, to the first two iterations of Newton's Method. CV = coefficient of variation. Case I: no plus group Initial Empirical Newton Newton approx. correction iter. 1 iter. 2 (Eq. 7) (Eq. 13) (Eq. 12) (Eq. 12) Mean 1.0350 0.9969 1.0000 1.0000 Median 1.0318 1.0000 1.0000 1.0000 CV 0.0217 0.0069 0.0000 0.0000 Min. 1.0007 0.9700 1.0000 1.0000 Max. 1.0826 1.0046 1.0001 1.0000 Case II: )Ius group Initial Empirical Newton Newton approx. correction iter. 1 iter. 2 (Eqs. 10, 11) (Eq. 14) (Eq. 12) (Eq. 12) Mean 1.1193 1.0663 0.9976 0.9983 1.0000 Median 1.1418 1.0660 1.0000 0.9995 1.0000 CV 0.1805 0.0876 0.0368 0.0028 0.0000 Min. 0.6315 0.7654 0.8778 0.9814 0.9994 Max. 1.6757 1.3493 1.1204 1.0000 1.0000 312 Fishery Bulletin 93(2), 1995 gence to the true F values (Table 1 and Fig. 1, bot- tom panel). •s A -r 1 1 \ / / / / 1 l \ / / / 0 — 1 1 i True F Figure 1 Progression in the approximation to the fishing mor- tality rate for a catch equation not involving a plus group (400 of the 1,000 pairs of approximated and true F are shown). (Top) Initial approximation (Eq. 7); (Middle) approximation after application of empirical correction function (Eq. 13); (Bottom) approximation after one iteration of Newton's Method (Eq. 12). Case II: with a plus group The initial approximations obtained for the plus group problem were rather poor compared with those of the catch equation without a plus group (Table 1, Fig. 2, top panel). This was not unexpected, because the plus group catch equation is not amenable to al- gebraic manipulations that lead to analytical ap- proximations. However, note that the initial approxi- mation from Equation 11 was much better than that from Equation 10: the observed AF I TF ratios indi- cated smaller biases and a tighter approximation overall (see Table 1). (Note: Subsequent statistics and data reported in Table 1 and Figure 2 are based on the approximation given by Equation 11.) In order to find empirical correction factors, we plotted the observed AF I TF ratios against M (for dif- ferent a values) and against a (for different M val- ues) (see Fig. 3). Visual inspection of these figures indicated that 1 ) the relationship between AF I TF and M could be approximated by a linear model; 2) the relationship between AF I TF and a could be approxi- mated by a logarithmic model; and 3) there was an interaction between M and a in terms of explaining variability in AF I TF. Therefore, we fitted the model AF/TF = a0 + &! ln(a) + b2M + b3 aM to the observed ratios, again by minimizing the sum of absolute residuals. The empirical correction fac- tor used was then emp-AF=inU-AFI{aQ+bl\a{a) + b2M + b3aM) (14) with a0 = 0.9951, bt = 0.2053, b2 = 0.0636, and b3 = 0.0161. This empirical correction function provided a sub- stantial improvement in the approximations (Table 1, Fig. 2, middle panel). However, solution errors on the order of 12% were still obtained after the correc- tion. One iteration of Newton's Method was sufficient to reduce the errors to within 2% (Table 1 and Fig. 2, bottom panel) and the second iteration resulted in virtual convergence (Table 1). Restrepo and Legault: Approximations for solving the catch equation 313 ■ ■ ■ i: • : . » . • -^ . sir- • - 1 i i - vi .•Ji,':••' •*• •T7 - r - / 1 \ i / / / i i True F Figure 2 Progression in the approximation to the fishing mor- tality rate for a catch equation involving a plus group ( 400 of the 1 ,000 pairs of approximated and true F are shown). (Top) Initial approximation (Eq. 11); (Middle) approximation after application of empirical correction function (Eq. 14); (Bottom) approximation after one iteration of Newton's Method (Eq. 12). Summary The results of our study indicate that the empirical correction in Equation 13 applied to Pope's (1972) a = 2.0 As V*~°°o o o ~i — ' — i — ' i > i ■ i 0 2 0.4 0 6 0 8 10 U. U. T3 17°C. The influence of temperature on cohort-specific growth, survival, and recruitment of striped bass, Morone saxatilis, larvae in Chesapeake Bay Edward S. Rutherford Chesapeake Biological Laboratory Center for Environmental and Estuanne Sciences University of Maryland, 1 Williams St., Solomons, MD 20688 Present address: Institute for Fisheries Research Michigan Department of Natural Resources 2 1 2 Museums Annex Bldg.. II 09 N University St. Ann Arbor, Ml 48 1 09 Edward D. Houde Chesapeake Biological Laboratory Center for Environmental and Estuarine Sciences University of Maryland, 1 Williams St., Solomons, MD 20688 Manuscript accepted 17 October 1994. Fishery Bulletin 93:315-332 (1995). Landings of anadromous striped bass, Morone saxatilis, along the Atlantic Coast of the United States declined sharply in the 1970's and 1980s owing to overfishing and a series of poor recruitments (Bore- man and Austin, 1985). Indices of striped bass recruitments in the Chesapeake Bay vary more than 100-fold (Schaefer et al.1). Recruit- ment levels are established by the juvenile stage, when seine-survey indices correlate with subsequent commercial catches of adults (Good- year, 1985). Striped bass spawn in Chesa- peake Bay tributaries from April to June, when frequent storms and heavy rainfall cause temperature, river flow, and pH levels to fluctu- ate. Temperatures experienced by eggs and larvae during the two- month spawning season may range from 10 to 29°C and may have dra- matic effects on production, sur- vival, and growth of cohorts. Initia- tion of spawning in Chesapeake Bay tributaries occurs at 12-18°C when temperatures are increasing rapidly (Olney et al., 1991; Setzler-Hamil- ton and Hall, 1991; Setzler Hamil- ton et al.2). Rapid drops in tempera- ture to below 12°C are lethal to striped bass eggs and larvae (Bar- 1 Schaefer, R. K., R. H. Bradford, J. L. Markham, and H. T. Hornick. 1991. Char- acterization of striped bass stocks in Mary- land, p. 1-74. In H. T. Hornick (project leader), Investigation of striped bass in Chesapeake Bay. US Fish and Wildlife Serv. Fed. Aid Proj. F-42-R-3, MD Dep. Natl. Resour., Tidewater Admin., Annapo- lis, MD. Available: Maryland Department of Natural Resources, Tidewater Admin- istration, Tawes State Office Bldg., Taylor Ave., Annapolis, MD 20688. 2 Setzler-Hamilton, E. M., J. A. Mihursky, K. V. Wood, W. R. Boynton. D. Shelton, M. Homer, S. King, and W. Caplins. 1980. Potomac estuary fisheries program, ichthyoplankton and juvenile investiga- tions. 1977 Final Rep. to Maryland Dep. Natl. Resour., Power Plant Siting Program. Univ. of Maryland. Ref. No. [UMCEES]CBL 79-202. Available: University of Maryland Center for Environmental and Estuarine Studies, Chesapeake Biological Labora- tory, 1 Williams St., Solomons, MD 20688. 315 316 Fishery Bulletin 93(2). 1995 kuloo, 1967; Doroshev, 1970; Davies, 1973; Morgan et al., 1981). Temperature also strongly influences the development of striped bass eggs and larvae (Polgar et al., 1976; Rogers et al., 1977; Rogers and Westin, 1981), the generation times and turnover rates of zooplankton prey (Heinle, 1969), and probably the consumption rates of predators. Previous studies on striped bass recruitment vari- ability averaged larval growth and mortality rates over multiple daily cohorts (Polgar, 1977; Dey, 1981; Kernehan et al., 1981; Uphoff, 1989; Setzler-Hamil- ton et al.2; Low3), thereby obscuring relationships with environmental factors. The presence of daily in- crements on otoliths allows accurate estimates of lar- val hatchdates, growth, and survival (Methot, 1983; Crecco and Savoy, 1985; Essig and Cole, 1986; Leak and Houde, 1987; Rice et al., 1987, a and b) and can provide valuable information about processes and factors affecting recruitment. Otolith-based esti- mates of larval growth histories have the potential to detect the subtle changes in growth rate that could cause order-of-magnitude variability in recruitment (Houde, 1987, 1989). We hypothesize that variable striped bass recruit- ments are generated by variable growth and survival rates of cohorts of larvae produced during a two- month period of highly variable environmental con- ditions. In a related paper (Rutherford et al.4), re- sults of a 3-year study of striped bass larval dynam- ics in the Potomac River and Upper Chesapeake Bay indicated that, on an annual basis, mean larval abun- dances and ratios of weight-specific growth to instan- taneous mortality rate (G/Z) are correlated with ju- venile recruitment indices, indicating that recruit- ment level is fixed during the larval stage. In this study, an analysis of daily cohort abundances and vital rates (growth and mortality) of larvae is pre- sented to describe the process of year-class forma- tion in striped bass and to illustrate how a primary variable, temperature, affects cohort-specific growth, survival, and recruitment potential in Chesapeake Bay. Methods Striped bass eggs and larvae were sampled every 3 to 7 days from April to June in the Potomac River (1987-89) and in the Upper Bay (1988 and 1989; Rutherford et al.4; Fig.l). Methods of collecting ichthyoplankton and environmental data are de- scribed briefly below and in more detail by Houde and Rutherford5 and Rutherford et al.4 Eggs and larvae were collected in duplicated ob- lique tows of a paired 60-cm bongo sampler, with 333- and 505-um mesh nets. Larval abundances based upon the 505-um mesh size, 60-cm bongo net samples were adjusted for extrusion of some small larvae by comparing catches with those in a paired, 333-um mesh net. Adjustments for gear avoidance by large larvae were made by comparing 60-cm net catches during daylight with a series of night catches made on the same dates, and by comparing the 60-cm net catches with those in a 2-m2 Tucker trawl at the same stations and dates. The 2-m2 Tucker trawl (700-um mesh) also provided collections of large larvae in late- season surveys. Riverwide abundances of eggs and larvae were estimated by multiplying mean station densities by the river volume which those stations represented. Egg abundances also were estimated and are reported in Houde and Rutherford ( 1992). Densities of zooplankton that were potential prey for striped bass larvae were estimated from pumped water samples taken near-bottom, mid-depth, and at surface and filtered onto a 53-um screen, or taken by vertical lifts of a 20-cm, 53-um mesh plankton net. Temperature, pH, and salinity were measured at all stations on each survey. Conductivity was measured in 1988 and 1989, and turbidity and light were mea- sured in 1987 and 1988. In addition, gauges at dams upstream of the spawning grounds provided continu- ous temperature measurements. Larval ages, hatch dates, and age-frequency dis- tributions were estimated from an analysis of sagit- tal otolith increments, which are deposited daily in striped bass (Jones and Brothers, 1987; Secor and Dean, 1989). Otolith increments were counted at least three times and the mean of the last two counts was used to estimate age. Aged larvae were grouped into 3-day periods (cohorts) based upon their hatch dates. Three-day cohorts were designated because 95% confidence intervals around mean ages indicated a 3-day range. Otolith-aged larvae from represented length classes were used to estimate the proportions of unaged larvae in each 0.5-mm length class that fell within each one-day age class. These 'age-length 3 Low, A. F. 1986. Striped bass egg and larva survey in the Sacra- mento-San Joaquin estuary. California Dep. Fish and Game. Unreferenced report, November 1986. Available: California Department of Fish and Game, Stockton, CA 95205. 4 Rutherford, E. S., E. D. Houde, and R. M. Nyman. Relation of larval stage growth and mortality to recruitment of striped bass, Morone saxatilis, in the Chesapeake Bay. Unpubl. manuscr. 5 Houde, E. D., and E. S. Rutherford. 1992. Egg production, spawning biomass and factors influencing recruitment of striped bass in the Potomac River and Upper Chesapeake Bay. Rep. to Maryland Dep. Natl. Resour., Contract No. CB89-C01-003. Univ. Maryland, Center for Environmental and Estuarine Studies, Ref. No. [UMCEESJCBL 92-017, 313 p. Available: University of Maryland Center for Environmental and Estuarine Studies, Chesapeake Biological Laboratory, 1 Williams St., Solomons, MD 20688. Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 317 "SC- UPPER BAY ESTUARY POTOMAC RIVER ESTUARY Quantico I Morganlown Figure 1 Map of sampling areas and stations on the Potomac River and Upper Chesa- peake Bay, 1987-89. keys' were developed separately for the Potomac River and the Upper Bay in each year, except 1988, from regressions of otolith-derived ages on larval lengths. In 1988, otoliths of the few larvae collected in the Upper Bay were unreadable because of poor preservation; consequently the age-length key for 1988 Potomac River larvae was also applied to Up- per Bay larval catches. Larval growth rates were estimated by using both an "aggregate sample" method and a back-calcula- tion method. In the aggregate sample method, stan- dard lengths and otolith-derived ages of the entire sample of otolith-aged larvae were analyzed for each cohort in each of the areas. Growth rates of larvae were derived from exponential regressions of larval lengths on ages. Exponential models also were fit to the mean back-calculated length at age of larvae to estimate back-calculated, cohort-specific growth rates. We backcalculated fish lengths at age by using the "biological intercept" method (Campana, 1990). This method does not assume that larvae from all cohorts or populations have the same body length and otolith- radius relationship; thus it allows reconstruction of individual growth histories, which was desirable for our analysis. This method, and other back-calcula- tion methods that assume a constant proportional- Fishery Bulletin 93(2), 1995 ity between otolith growth and fish growth (Fraser- Lee, simple regression), will accurately estimate fish length if somatic growth is relatively fast (Secor and Dean, 1989, 1992; Campana, 1990). If somatic growth is slow, otoliths of slow-growing fish may grow rela- tively fast, causing the relationship between fish and otolith growth to be nonlinear and thus bias back- calculated growth-rates (Geffen, 1982; Reznick et al., 1989; Secor and Dean, 1989, 1992; Campana, 1990). To minimize biased estimates of back-calculated lengths at age for 1988 Potomac River larvae, when growth effects were significant and body size and otolith-size relationships were nonlinear, we fol- lowed the recommendation of Campana and Jones (1992) and log^-transformed fish lengths and otolith radii before applying the biological inter- cept method. Larval cohort mortality rates were estimated from the exponential declines in cohort abun- dances at age obtained from 60-cm sampler catches. In 1989, larval mortality rates in the Potomac River and Upper Bay may have been overestimated when only larvae collected in the 60-cm sampler were considered. Striped bass spawned later in 1989 than in 1987 or 1988, and abundances of cohorts hatched in late May prob- ably were under-represented in 60-cm sampler collections that were completed by 1 June. Better estimates of cohort mortality rates in 1989 were obtained by combining larval collections from the 60-cm sampler with those from the 2-m2 Tucker trawl made from late May to mid-June. A "Pareto" model, which assumes that mortal- ity rate declines in relation to age (Lo, 1986), was compared with the linear model, and the model with the lowest residual sum of squares was se- lected to estimate each cohort's mortality rate. The ratio of instantaneous growth-in-weight rate to in- stantaneous mortality rate (GIZ), an index of lar- val production (biomass), was estimated for each cohort. Instantaneous growth-in-weight rates were derived from back-calculated growth-in-length rates by using a length-weight relationship ( Houde and Lubbers, 1986) for striped bass larvae. Abun- dances of cohorts at 8 mm standard length (SL) were estimated to index their potential contribu- tions to recruitment. At 8-10 mm, striped bass larvae reach the postfinfold larval stage (Fritsche and Johnson, 1980; Olney et al., 1983), when de- velopment of fins and increased swimming ability facilitates feeding as well as ability to avoid preda- tors and can result in a decline in mortality rate. Abundances, and growth and mortality rates of larval cohorts were analyzed in relation to envi- ronmental variables by using stepwise multiple regression analysis (SAS, 1988) to identify factors associated with variable recruitments. Results Spawning, egg and larval abundances, and zooplankton densities Striped bass spawned during April and May, gener- ally during periods of rising temperatures (Figs. 2 and 3). The major spawning peak in the Potomac 2000 1500- 1000- c o B 0) o c ro T3 C 3 JO (0 O) O) UJ 12°C. A secondary spawning peak was evident in mid-May of 1989 (Fig. 2). Peak spawning in the Upper Bay occurred in mid to late May when water temperatures rose to >14°C (Fig. 3). Striped bass egg abundances were highest in 1989 and low- est in 1988 (Rutherford et al.4). Egg abundances were nearly an order of magnitude higher in the Upper Bay in 1989 (77.9 eggs-m"2) than in 1988 (8.2 eggs-m"2) but did not differ significantly (P>0.05) among years in the Potomac (25.1 to 73.5 eggs-m"2). Episodic mortalities of striped bass eggs and lar- vae occurred in the Potomac River in each year after spring storms, which caused flood conditions and sharp declines in river temperatures to or below the 12°C lethal limit. In 1987, a storm on 16-17 April and a subsequent temperature drop caused complete 150 100 50 C o 0) o c co ■o c 3 n (0 O) en w 1988 -i 1 r— r r j u 32 28 24 20 16 1 10 20 30 10 April May 20 30 9 June (D 3 ■o (D 0) C (D 1 10 20 30 10 April May 30 9 June Figure 3 Areawide egg abundances ( millions) of striped bass, Morone saxatilis, estimated on each survey date (bars) during the two years of sampling effort in the Upper Bay, 1988-89. Water temperatures recorded at Conowingo Dam during the spawning season also are given (open diamonds). The 12°C critical low temperature, at which 100% egg and lar- val mortality may occur, is indicated by the dotted line. Note that the Y-axis scales change between years. mortality of all striped bass eggs and larvae, effec- tively eliminating >50% of the season's egg produc- tion (Rutherford et al.4). Although no larvae survived that event, relatively minor spawning (Fig. 2) that occurred later, combined with favorable conditions for larval growth and survival, resulted in higher mean larval abundances than those in 1988 or 1989 (Rutherford et al.4). After 20 April 1987, Potomac River temperatures increased steadily and were both warmer and less variable than in 1988 or 1989. Tem- perature profiles in the Upper Bay were similar in both 1988 and 1989 (Fig. 3). In the Upper Bay, the initial order of magnitude difference between years in egg abundance was maintained through the lar- val stage (Rutherford et al.4). Mean densities of zooplankton that were poten- tial prey for larval striped bass cohorts during the first 5-20 days posthatch were highest in the Potomac River in 1987 and in the Upper Bay in 1989 (Fig. 4). Densities of copepod nauplii, Eurytemora affinis, and rotifers (including Brachionus,Asplanchna, Synchaeta, Polyarthra), in particular, which are ini- tial prey of striped bass larvae (Takacs, 1992; Beaven and Mihursky6), were higher in the Potomac River in mid to late May 1987 than in 1988 or 1989. Growth Body length and otolith-radius relationships Lar- val length was strongly correlated with otolith size in each year (Table 1). The best regression relation- ships were linear for most cohorts with adequate sample sizes (n>4) and ranges in body length. Expo- nential models provided better fits for some Potomac River cohorts, and age was a significant covariate of otolith size for two cohorts in 1989 (Table 1). With few exceptions, cohorts hatched early in the season, experienced mean temperatures <17°C dur- ing the first 20 days posthatch, and had relatively larger otoliths per unit body length than did cohorts hatched when temperatures were warmer. Differ- ences in body length-otolith radius relationships among Potomac River striped bass cohorts were sig- nificant in 1989 (ANCOVA; P<0.001), but not in 1987 (ANCOVA; P>0.10) or 1988 (ANCOVA; P>0.20). Growth rates Growth rates of striped bass larval cohorts, estimated by both aggregate and back-cal- culated methods, indicated that growth varied sea- 6 Beaven, M. S., and J. A. Mihursky. 1979. Food and feeding hab- its of larval striped bass: an analysis of larval striped bass stom- achs from 1976 Potomac estuary collections. Ref. No. [UMCEES]CBL 79-045, Chesapeake Biological Laboratory. Available: University of Maryland Center for Environmental and Estuarine Studies, Chesapeake Biological Laboratory, 1 Wil- liams St., Solomons, MD 20688. 320 Fishery Bulletin 93(2). 1995 Potomac River 1 987 200 Cladocera Copepod Adults & Copepodites Copepod Naupln Rotifera Upper Bay 1 988 150 - 1 10 20 30 10 20 30 9 Potomac River 1 988 = 300- Upper Bay 1 989 1 10 20 30 10 20 30 9 Potomac River 1 989 200- 100 1 10 20 30 10 20 30 April May Date Figure 4 Densities of zooplankton taxa estimated on each survey date in the Potomac River, 1987-89 and Upper Bay, 1988-89. Note that Y-axis scales change among years and areas. sonally in each year. Cohorts that hatched late in the season grew relatively fast, had shorter stage du- rations (Fig. 5), and reached larger sizes by 20 days posthatch than did cohorts hatched earlier, which grew in cooler water. Both methods of estimating growth produced similar rates, although estimates from the aggregate method were much less precise (Figs. 5 and 6). Aggregate-sample growth rates of Potomac River larvae differed significantly among 3-day cohorts in 1987 and 1989. Cohort growth rates, after adjusting for age by analysis of covariance, tended to increase as the season progressed (Fig. 5). They ranged from 0.19 to 0.44 mmd ' (mean ±95% CI=0.26 ±0.06 mmd"1) in 1987, from 0.11 to 0.22 mmd"1 (mean=0.18 ±0.04 mmd"1) in 1988, and from 0.12 to 0.53 mmd"1 (mean=0.24 ±0.07 mmd"1) in 1989. The regression fits of growth data were poor for some Potomac River cohorts in 1988. The predicted mean lengths at 20 days posthatch of larval cohorts were variable, ranging from 7.7 to 11.7 mm SL in 1987, from 6.9 to 9.0 mm SL in 1988, and from 4.8 to 11.1 mm SL in 1989. Predicted ages at 8.0 mm SL also varied, ranging from 13.2 to 21.2 days in 1987, from 14.2 to 23.8 days in 1988, and from 14.6 to 31.6 days in 1989 (Fig. 5). Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 321 Table 1 Body length (SL mm (-otolith radius (R, urn) regressions for larval cohorts of striped bass , Morone saxatilis larvae, collected from the Potomac River, 1987- -89 and the Upper Bay, 1989. "A" = Age (days posthatch); SE = standard error, n = sample size. Cohort Hatch Date Regression SE (slope) r2 n P< Potomac River 1987 22 April SL = 6.220 + 0.029R 2 25 April Ln(SL)= 1.907 + 0.003R <0.001 0.99 7 0.001 28 April SL = 6.025 + 0.022R 0.004 0.99 3 0.010 1 May SL = 5.160 + 0.033R 0.001 1.00 5 0.001 4 May SL = 5.922 + 0.024R 0.004 0.95 4 0.050 7 May SL= 5.221 + 0.024R 0.002 0.98 8 0.001 10 May SL = 5.235 + 0.033R 0.003 0.96 9 0.001 13 May SL = 5.057 + 0.032R 0.002 0.95 25 0.001 16 May SL = 4.900 + 0.03 1R 0.002 0.94 21 0.001 19 May SL = 4.856 + 0.036R 0.002 0.97 20 0.001 Potomac River, 1988 12 April - 3 May SL = 4.491 + 0.035R 0.002 0.92 32 0.001 6 May SL = 3.233 + 0.045R 0.003 0.94 9 0.001 9 May SL = 5.919 + 0.026R 0.004 0.88 10 0.001 12 May SL = 4.658 + 0.036R 0.005 0.86 11 0.001 15 May SL = 5.683 + 0.029R 0.012 0.37 12 0.050 18 May SL = 5.693 + 0.030R 0.008 0.51 16 0.001 Potomac River, 1989 17-26 April SL = 6.068 + 0.021R 0.002 0.97 9 0.001 29-April SL = 5.976 + 0.024R 0.002 0.94 10 0.001 2 May SL = 6.531 + 0.021R 0.006 0.76 11 0.001 5MayS SL = 3.13 + 0.18A + 0.01R 0.058, 0.004 0.78 27 0.001 8 May SL = 3.69 + 0.02A + 0.13R 0.002, 0.034 0.97 19 0.001 11 May SL = 5.331 + 0.031R 0.003 0.90 19 0.001 14 May Ln(SL) = 1.914 + 0.003IR) <0.001 0.80 14 0.001 17 May SL = 4.513 + 0.034R 0.003 0.83 25 0.001 20 May SL = 5.027 + 0.029R 0.003 0.77 28 0.001 23-26 May SL = 6.606 + 0.015R 0.005 0.44 14 0.01 Upper Bay, 1989 8 May SL = 3.890 + 0.037R 0.002 0.97 6 0.001 11 May SL = 4.400 + 0.035R 0.001 0.99 6 0.001 14 May SL = 5.058 + 0.031R 0.003 0.95 11 0.001 17 May SL = 5.058 + 0.032R 0.000 0.97 34 0.001 20 May SL = 5.402 + 0.027R 0.002 0.92 50 0.001 23 May SL = 5.146 + 0.028R 0.003 0.91 47 0.001 26 May SL = 4.507 + 0.032R 0.003 0.90 17 0.001 29 May SL = 4.750 + 0.029R 0.003 0.93 14 0.001 1 June SL = 4.211 + 0.038R 0.005 0.97 4 0.050 4 June SL = 3.393 + 0.056R 2 The larval growth rate estimates of Upper Bay cohorts in 1989 did not differ significantly (P>0.25) and ranged from 0.21 mm-d"1 for larvae hatched on 8 May to 0.32 mm-d"1 for larvae hatched on 1 June (Fig. 5). The mean cohort growth rate was 0.25 ±0.03 mm-d" 1. Predicted mean lengths at 20 days posthatch of the 9 cohorts ranged from 7.4 to 10.0 mm. Predicted ages at 8.0 mm SL ranged from 14.8 to 22.1 days (Fig. 5). Back-calculated growth rates of 5-20 days posthatch larval cohorts from the Potomac River ranged from 0.19 to 0.46 mm-d"1 in 1987 (mean=0.27 ±0.05 mm-d"1), from 0.18 to 0.34 mm-d"1 in 1988 (mean=0.23 ±0.04 mm-d"1), and from 0.11 to 0.36 mm-d"1 in 1989 (mean=0.23 ±0.04 mm-d"1) (Fig. 6). Back-calculated growth rates of Upper Bay larvae, available only for 1989, ranged from 0.18 to 0.36 mm-d"1 (mean=0.26 ±0.03 mm-d"1) (Fig. 6). The differences in back-calculated growth rates among cohorts in each year resulted in different pre- dicted lengths at 20 days posthatch. There were 322 Fishery Bulletin 93(2), 1995 Potomac 1987 Potomac 1989 0.6 0.5 0.4 0.3 0.2 0.1 0 35 0.6 30 0.5 25 0.4 20 0.3 15 10 °2 5 0.1 0 0 a ma ~\ i i i i r vo a, r» wi s <-* »s M sa s Potomac 1988 Upper Bay 1989 0.4- 0.3- 0.2- 0.1 0- l \ k^ a ;. ii -30 -20 fl i i ,< L \\ -10 40 0.5 0.3 Cohort Hatch Date ~1 I I I I i I I r : ^h om« » ^m k » T r~ o Cohort Hatch Date D > Figure 5 Cohort-specific, mean growth rates (closed bars, mmd-1) and stage durations (open bars, age (d)) of 8-mm-total-length striped bass, Morone saxatilis, larvae by hatch date in the Potomac River, 1987- 89, and Upper Bay, 1989. Growth rates determined by the aggregate-sample method. Error bars indicate 95% confidence intervals. among-cohort differences of up to 4.8 mm, 3.0 mm, and 4.6 mm in the Potomac in 1987, 1988, and 1989, respectively, and differences of 3.4 mm in the Upper Bay. Maximum among-cohort differences in predicted ages at 8.0 mm were 11, 9, and 21 days in the Potomac River in 1987, 1988, and 1989, respectively, and 10 days in the Upper Bay (Fig. 6). Back-calculated (r2=0.67; Fig. 7) and aggregate- sample (r2=0.62) cohort growth rates were strongly and positively related to the mean water tempera- tures in which larvae grew. A stepwise multiple re- gression analysis indicated that densities of copepod nauplii, a probable prey of first-feeding striped bass larvae, were negatively correlated with larval growth rate, presumably because nauplii densities were higher near the beginning of the spawning season (Fig. 4) when growth rates were lowest. No other environmental variable, including densities of other zooplankton taxa or densities of striped bass eggs, larvae, or Morone spp. larvae ( striped bass plus white perch, M. americana), explained a significant pro- portion of the variance in larval growth rates. Individual growth rate variability Growth histo- ries of larvae within each cohort that presumably had experienced the same suite of environmental conditions indicated that some individuals grew much faster than average. Within a cohort, individual larvae differed by as much as 5.0 mm in length at 20 days posthatch (Upper Bay 1989, cohort hatched 23 May), and by up to 0.33 mmd"1 in growth rate (Up- per Bay 1989, cohort hatched 23 May). The maxi- mum individual growth rate of a 3-day cohort was 68% higher than the mean. Variance (%CV) in lar- val growth rate or lengths at 20 days posthatch within-cohorts did not differ significantly (Kruskal- Wallis; P>0.10) among years. There was no signifi- cant relationship between variance in growth rate within-cohorts and the mean (P>0.20) or variance (P>0.50) in daily temperatures experienced by cohorts. Evidence for size-selective mortality operating on larger individuals was detected in back-calculated growth histories of striped bass larval cohorts exam- ined from the Potomac River, 1987 and 1989, and Upper Bay, 1989. To detect evidence of size-selective mortality, lengths at capture of larval cohorts col- lected early in the spawning season were compared with back-calculated lengths at age of older larvae in the same cohort collected later in the season. For 10 of the 11 cohorts examined from the Potomac River 1987 (z?=5), 1989 (n=4), and the Upper Bay 1989 in-2), mean back-calculated lengths at 10 and 20 Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 323 Potomac 1987 Potomac 1989 Potomac 1988 Upper Bay 1989 Cohort Hatch Date Cohort Hatch Dak' □ > Figure 6 Cohort-specific, mean growth rates (closed bars, mm-cH) and stage durations (open bars, age (d)) of 8- mm-total-length striped bass, Morone saxatilis, larvae by hatch date in the Potomac River, 1987-89, and Upper Bay 1989. Growth rates determined by the back-calculation method. Error bars indicate 95% confidence intervals. days posthatch of surviving larvae collected late in the season were significantly smaller U-test; P<0.001) than lengths at capture of larvae collected earlier, suggesting that within-cohort mortality had acted selectively against larger individuals. There was no significant difference (P>0.50) in mean lengths at age between early and late-captured larvae in the elev- enth cohort. Analysis of back-calculated larval growth histories suggested that in most Potomac River and Upper Bay cohorts in each year, small larvae are able to com- pensate for slow initial growth and obtain the same length at >20 days posthatch as larvae with large initial lengths. Lengths at capture were compared with back-calculated growth rates in the period 5-20 days posthatch and with calculated lengths at 5, 10, 15, and 20 days posthatch. For all cohorts (n=38) in all years, there either was no significant re- lationship between length at capture and their back- calculated lengths at 5 and 10 days posthatch, or the relationship was negative, i.e. within a cohort, some of the smallest-sized larvae at capture had relatively large back-calculated lengths at 5 and 10 days posthatch. For individuals hatched early in the spawning sea- son (in 14 of 15 cohorts), there also was no relation- ship between lengths at capture and back-calculated lengths at 15 and 20 days posthatch. However, lar- vae that hatched later in the season (in 20 of 23 0.5 E £ CO OS o u e - 0.4 - G= -0.09 + 0.02T r2 = 0.67, n = 45 © Potomac River u 1987 • 1988 ° 1989 Upper Bay ° 1989 14 16 18 20 22 24 26 Temperature (°C) Figure 7 Back-calculated growth rates (G, mm-d"1) of striped bass, Morone saxatilis, larval cohorts, in relation to river tem- peratures (T, °C) averaged over the first 20 days posthatch in the Potomac River, 1987-89, and Upper Bay, 1989. Circled data point is an outlier and was not included in the regression. 324 Fishery Bulletin 93(2), 1995 cohorts), when mean water temperatures were rela- tively warm, had within-cohort growth rates and back-calculated lengths at 15 and 20 days posthatch that were positively related to lengths at capture. For example, individual growth rates of Upper Bay larvae hatched on 14 May 1989 were not correlated with their lengths at capture, suggesting that there had been compensation for slow (or fast) growth at earlier ages (Fig. 8). Growth rates of Upper Bay lar- vae hatched on 23 May were positively related to their Hatched 14 May © o ■s « 3 tj "3 U u « pa Hatched 23 May G= - 0.23 + 0.06(L) r2 = 0.95 0.4- a A r q 03- -S Q G Jr 0.2- tyS /J3 0.1- ' 1 ' I ' I I 10 12 Length (mm TL) at Capture Figure 8 Back-calculated growth rates (G, mmd*1) of individual striped bass, Morone saxatilis, larvae in relation to total lengths (TL) at capture for Upper Bay larvae hatched on 14 May and on 23 May 1989. lengths at capture, indicating that initial growth rate differences had been maintained (Fig. 8). Mortality rates Mortality rates of larval cohorts, which were highly variable, were not correlated with initial cohort abun- dance, growth rate, growth rate variability, stage duration, or with any measured environmental fac- tor. Mean mortalities of cohorts from the Potomac River ranged from 21.9 to 23.9% d"1 in 1987-89. Co- hort-specific mortality rates of Potomac River lar- vae ranged from Z = 0.05 to 0.92-d"1 in 1987, from Z = 0.05 to 0.46-d"1 in 1988, and from Z = 0.07 to 0.60-d"1 in 1989 (Fig. 9). Temporal trends indicated that mor- tality rates of Potomac River larvae were high in April, lowest in early May, and apparently highest in late May (Fig. 9). Larval cohort mortality rates in the Upper Bay during 1989 ranged from Z = 0.02 to 0.28-d"1, averag- ing 11% d_1. There was no obvious temporal trend in Upper Bay larval mortality rates (Fig. 9). G/Z ratio The cohort-specific G/Z ratios were variable, but the median values in each year were positively related to apparent year-class strength in the Potomac River. The median ratios were 1.03 in 1987, 0.41 in 1988, and 0.94 in 1989 (Fig. 9). The Upper Bay median G/Z ratio in 1989 was 1.70, a value higher than the Potomac River me- dian ratios because cohort mortality rates generally were lower in the Upper Bay. In the Potomac River, the cohort-specific G/Z ratios in each year were generally highest for cohorts hatched during the last week of April and the first 10 days of May, when growth rates were increasing and mortality rates were lowest (Fig. 9). Productions of late-stage larvae Summed cohort productions of 8-mm-SL larvae were correlated with juvenile recruitment indices in the Potomac River, suggesting that recruitment is essen- tially fixed during the larval stage. Summed cohort productions were 190 million in 1987, 23 million in 1988, and 109 million in 1989. Potomac River indi- ces of juvenile recruitment for those years were 6.4, 0.4, and 2.2, respectively (Schaefer et al.1). Summed production of Upper Bay larval cohorts at 8 mm SL was 47 million in 1989. The Upper Bay's juvenile recruitment index in 1989 was 19.4, a value 1.6 times higher than the long-term mean (Schaefer et al1). Most cohorts with larvae surviving to 8 mm SL were hatched late in the spawning season when egg produc- tion was low or declining (Fig. 10). In the Potomac River, cohort productions of 8-mm-SL larvae were positively Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 325 Potomac River 1987 Potomac River 1989 0.5- 0 Potomac River 1988 Upper Bay 1989 Cohnrl Hatch Dale Cullort Hatch Date Figure 9 Cohort-specific, instantaneous daily mortality rates (Z, •) and G/Z ratios (bars) of striped bass, Morone saxatilis, larvae by hatch date from the Potomac River, 1987-89, and Upper Bay, 1989. Error bars on mortality rates indicate 1 standard error of mean. Scale on Y-axis varies among panels. related to cohort growth rates, and in the Upper Bay to water temperature. The relationships are for the Potomac River, Ln(iV8) = 6.43 + 31.43 (G); (r2=0.22, P<0.01, re=28) for the Upper Bay, Lnl/Vg) = -36.65 + 4.75 (T) - 0.11 (T2); (r2=0.91, P<.001, 72 = 12) where ln(./V8) is the loge-transformed cohort production of 8-mm-SL larvae, G=cohort growth rate ( mm-d"1 ) and T=mean temperature experienced by the cohort from 5-20 days posthatch. In the Potomac River, cohort larval productions at 8 mm SL also tended to be posi- tively correlated with water temperature, but the correlation was not significant (P>0.10). In the Up- per Bay, cohort production at 8 mm SL was not cor- related with cohort growth rate (P>0.50). The relative cohort abundances of larvae collected in the 2-m2 Tucker trawl on the last day of the sam- pling season, standardized to 8-mm-SL productions from cohort-specific stage durations and survival rates, provided another indicator of larval survival and potential recruitment. Tucker trawl catches in the Potomac River on 4-5 June 1987 indicated that surviving cohorts, which potentially contributed to recruitment, were hatched from 22 April to 19 May and that most survivors hatched in the 22-25 April and 4-10 May periods (Fig. 11A). In 1988, Tucker trawl catches on 2-3 June indicated that surviving 8-mm larvae were hatched from 3 May to 30 May and that most hatched during the 18-24 May period (Fig. 11B). The 1989 Tucker trawl index of 8-mm lar- vae on 8-9 June suggested that, while some poten- tial recruits were hatched in every 3-day period from 20 April to 23 May (Fig. 11C), cohorts hatched on 20 April and 14 and 17 May accounted for >809r of the total numbers represented on 8 June. Relative cohort abundances of 8-mm larvae in the Upper Bay on the last sampling day in 1989 ( 14 June) indicated that potential recruits were hatched from 5 May to 4 June (Fig. 11D). More than 80% of these larvae were hatched between 14 May and 1 June. 326 Fishery Bulletin 93(2). 1995 Potomac River 1987 10 20 30 10 20 30 9 April May Potomac River 1988 10 20 30 10 20 30 9 April May Date Potomac River 1989 60 32 -i 50 28 ■ 40 24 ■ 20 ■ 30 16 ■ 20 12 - -l"-^wf* 10 8- 4- j -"ttf&O i ^>i 1 10 20 30 10 20 30 9 April May Upper Bay 1989 10 20 30 10 20 30 April May Date 4(1 30 20 III 0 D< 3 *3 3 m Figure 10 River temperatures at Wilson Bridge (Potomac River) or Conowingo Dam ( Susquahanna River, Upper Bay), percent egg production, and percent estimated abundances by hatch dates of striped bass, Morone saxatilis, larvae at 8.0 mm TL in 3-day cohorts from the Potomac River, 1987-89, and Upper Bay, 1989. Larval abundances at 8.0 mm were estimated from 60-cm net samples in the Potomac River, 1987-88, and from 60-cm net and 2-m2 Tucker trawl catches in the Potomac and Upper Bay, 1989. The dashed line indicates the 12°C critical low tempera- ture at which 100% mortality of egg and yolk-sac larvae may occur. Discussion Temperature, larval survival, and growth Estuarine nurseries of anadromous fishes are dy- namic environments, subject to fluctuating and some- times unpredictable conditions for survival and growth. Striped bass spawn in the freshwater, tidal regions of mid- Atlantic estuaries during the spring months, a transitional season when average tempera- tures are increasing rapidly, but erratically, from 10 to 25°C. Frequent storms and flood conditions can cause temperatures to drop quickly to lethal or near- lethal levels. The unusually wide range of tempera- tures to which striped bass eggs and larvae may be exposed suggest that temperature may be a factor con- trolling growth rate, stage duration, and survival rate. Our results confirmed that temperature affects larval growth rates and stage durations. Except for observed episodic mortalities associated with tem- perature drops to or below the 12°C lethal limit, more subtle, direct effects of temperature on mortality rates could not be demonstrated. Despite episodic mortalities which impacted early-spawned cohorts, favorable temperatures during the latter half of spawning seasons resulted in significant potential recruitment from small cohorts of late-spawned eggs. The relatively good potential recruitments in the Potomac River, 1987, and Upper Bay, 1989, were derived from modest, late-season spawning that pro- duced fast-growing larvae in environments where water temperatures were steadily increasing. The application of otolith-ageing to identify 3-day cohorts and to derive cohort-specific growth and Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 327 Potomac River 1987 as ■a 2 o H 2 2 u as 73 a o H April May Potomac River 1988 a 3 o H 3 e (- 18 24 30 6 12 18 24 30 April May Cohort Hatch Date Potomac River 1989 Upper Bay 1989 17 23 29 5 11 17 23 29 April May Cohort Hatch Date Figure 1 1 Relative abundance of striped bass, Morone saxatilis, larval cohorts by hatch date, col- lected in the 2m2 Tucker trawl from the Potomac River, 1987-89, and Upper Bay, 1989: (A) 4-5 June, 1987; (B) 2-3 June, 1988; (C) 8-9 June, 1989; (D) 14-15 June, 1989. Relative abundance estimates were adjusted for age-specific survival differences among cohorts. mortality rates of striped bass larvae allowed us to examine the larval stage dynamics of a species that develops over a broad temperature range. Past re- search on survival and growth of striped bass larvae has depended upon modal-length analyses, assumed hatch dates, and assumptions about developmental stages and stage-durations to make inferences about early-life dynamics and recruitment potential (Polgar, 1977; Dey, 1981; Uphoff, 1989; Low3). Our otolith microstructure analysis demonstrated that in 1987-89, only a few cohorts contributed significantly to Potomac River and Upper Bay recruitments and that successful cohorts were hatched late in the season, grew relatively fast, and had short larval-stage durations. The critical role of temperature, particularly its potential to cause episodic mortalities and its effect on growth, has been identified in previous research on striped bass. For example, Dey (1981) and Kernehan et al. (1981) argued that year-class fail- ures in the Hudson River and Upper Chesapeake Bay, respectively, were caused by low-temperature events. Positive relationships between mean growth rates of larval striped bass year classes and temperatures have been reported for the Potomac River (Setzler- Hamilton et al., 1980; Martin and Setzler-Hamilton7 ), the Choptank River (Uphoff, 1989), the Hudson River (Dey, 1981), and the Sacramento-San Joaquin Riv- ers (Low3). In our study, it was clear that estimated produc- tions of cohorts at 8 mm SL were positively corre- lated with cohort-specific growth rates. Growth rates, in turn, were strongly and positively correlated with Martin, F. D., and E. M. Setzler-Hamilton. 1983. Assessment of larval striped bass stock in the Potomac estuary. Final report to U.S. National Marine Fisheries Service. Ref. No. [UMCEES1CBL83-55, 37 p. Available: University of Maryland Center for Environmental and Estuarine Studies, Chesapeake Biological Laboratory, 1 Williams St., Solomons, MD 20688. 328 Fishery Bulletin 93(2), 1995 temperature, supporting the conclusion that late- hatched cohorts, which grew faster than average, were the principal contributors to striped bass re- cruitments in 1987-89. Although cohort-specific mortality rates were not significantly related to co- hort growth rates or to any measured variable, the annual median GIZ ratios (i.e. for combined cohorts) were positively correlated with the juvenile recruit- ment index (Rutherford et al.4). This result indicated that, while the relationships between growth and survival of individual cohorts are complex and diffi- cult to demonstrate, the effect of reduced stage du- ration on larval production and on potential recruit- ment did occur and could be discerned when cohorts were aggregated. Chesney's (1993) simulation model of Potomac River striped bass larval dynamics in 1987 predicted good growth and survival of cohorts hatched late in the season when temperatures and prey densities were high. Research on other species of temperate estuarine and freshwater fishes also has demonstrated that survival and recruitment are highest for fast-growing cohorts (Rice et al., 1987a; Crecco and Savoy, 1985; Jennings et al., 1991), sup- porting Cushing's (1973) "single-process" concept, in which fast larval-stage growth enhances recruitment success through shortened stage durations. Differences in mean temperatures between 1987, 1988, and 1989 in the Potomac River may have led to significant differences in production of 8.0-mm- SL larvae, owing solely to effects on stage duration. Egg productions in the Potomac River were approxi- mately 10 billion in 1987 and 1989, and 6.7 billion in 1988 (Houde and Rutherford, 1992). If larval mor- tality rate had been equal in all years (e.g. Z=0.25), then the mean effect on larval growth and stage du- ration of the observed 4.0°C higher mean tempera- ture in 1987, compared with 1988 or 1989, could have accounted for a 3.7-fold greater production of 8.0-mm- SL larvae in 1987 than in 1988, and a 2.6-fold greater production in 1987 than in 1989. Our estimated pro- duction of 8.0-mm-SL larvae in 1987 was 7.8 and 1.7 times higher, while the juvenile recruitment index (Schaefer et al.1) was 16.0 and 2.9 times higher in 1987 than in 1988 or 1989, respectively. Although our results point to temperature as a critical factor and Chesney's (1993) simulation supports this view, other simulation models of major factors thought to influence year-class strengths of Potomac River striped bass suggest that temperature may be less important than maternal size or zooplankton prey abundance (Cowan et al., 1993), or, under special cir- cumstances, than contaminant levels (Rose et al. , 1993 ). Previous studies of striped bass larval growth have suggested that growth rates are correlated with tem- peratures in the spawning areas (Dey, 1981; Uphoff, 1989; Low3). However, most growth estimates were based upon modal analysis of larval lengths and, consequently, may have been inaccurate. Without benefit of otolith-increment analysis, among-cohort variability in growth rates was unevaluated. In the Choptank River of the Chesapeake Bay, Uphoff ( 1989) estimated annual mean growth rates of striped bass larvae to be 0.37-0.56 mmd"1 from 1981 to 1986, on the basis of length-frequency distributions. These rates were higher than our mean estimates in the Potomac and Upper Bay and were higher than growth rates of all except 4 of the 46 cohorts that we analyzed, although temperature ranges and prey densities are similar in these Chesapeake Bay tribu- taries. Larval cohort growth rates that were backcalculated from otolith-aged, juvenile striped bass from South Carolina also were higher (0.35 to 0.68 mmd-1; Secor, 1990) than most of our estimates. However, larvae from South Carolina experience mean temperatures during spawning and larval de- velopment that are 3-5°C higher than temperatures encountered by Chesapeake Bay striped bass (Secor, 1990). Growth rates of Hudson River larvae in 1973- 76, estimated from the weekly seasonal increases in larval mean lengths from a designated, arbitrary hatch date until 15 July, were 0.10 to 0.20 mmd-1 (Dey, 1981). Those rates were lower than our mean rates and generally lower than our individual cohort growth rates, even though mean temperatures en- countered by larvae in the Hudson and Chesapeake estuaries are similar. Mean annual growth rates of larvae in the Sacramento-San Joaquin River system, estimated for the 1968-86 period from modes in length-frequency distributions, ranged from 0.29 to 0.46 mm-d-1 (Low3). These rates are higher, on aver- age, than our mean rates, although many cohorts of Chesapeake Bay larvae grew at rates in this range. Individual growth rate variability Our analysis of individual larval growth histories to detect evidence of growth compensation and size-se- lective mortality may have been compromised some- what by the back-calculation method. Campana's ( 1990) biological intercept method will provide accu- rate estimates of mean back-calculated growth rate even in the presence of a "growth effect" but will tend to linearize individual growth rates and mask growth inflections (Campana, 1990; Secor and Dean, 1992). Campana (1990) demonstrated through simulation analysis that time-varying changes in the body length-otolith radius relationship caused by increas- ing somatic growth rate could result in underesti- mated lengths at earlier ages and overestimated lengths of older larvae, giving the appearance of com- Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 329 pensatory growth by slow-growing individuals and selective mortality against larger individuals within cohorts. If our analysis of size-selective mortality against larger individuals is correct, it may be that larger individuals experienced higher mortality because their faster swimming speeds increased contact rates with predators. Recent experimental studies (Litvak and Leggett, 1992; Monteleone and Houde, 1992; Pepin et al., 1992; Cowan and Houde, 1993) indicate that as larvae grow and encounter different preda- tor fields, their probability of being encountered and eaten by some predators may increase, resulting in a higher mortality rate for larger individuals than for smaller individuals. Effects of selective mortal- ity against smaller individuals may not become ap- parent until later in the larval stage (e.g. Post and Prankevicius, 1987), because it takes time for differ- ences in growth rate to result in significant differ- ences in size that would lower vulnerability to pre- dation (Rice et al., 1993). We had hypothesized that mortality would select against smaller individuals within cohorts, and that cohorts with higher mean growth rates and highly variable growth rates would contribute more poten- tial recruits than cohorts with lower and less vari- able growth rates (Pepin, 1989; DeAngelis et al., 1991; Rice et al., 1993). In our study, although mor- tality rates may have been highest for the largest or fastest-growing individuals, cohorts contributing most to recruitment in each year were those hatched near the end of the spawning season and which had higher but not more variable growth rates than those hatched earlier. For example, in the Potomac River, 1989, late-hatched cohorts grew, on average, nearly twice as fast from 5-20 days posthatch as did early- hatched cohorts. The high productions of late- hatched, fast-growing cohorts suggest that stage duration, by reducing the time that larvae experi- ence high mortalities, is more important than body size alone in determining potential recruitment of striped bass. Prey densities and growth The failure to detect any significant influence of prey density on cohort-specific growth, survival, or abun- dance at 8.0 mm SL was surprising, because mean zooplankton densities were highest in the Potomac River and Upper Bay in years when mean growth rates, GIZ ratios and recruitment indices were high- est (Rutherford et al.4). Laboratory, pond, and model- simulation studies have demonstrated repeatedly that growth and survival of striped bass larvae in- crease as prey density increases (Miller, 1976; Eldridge et al., 1981; Rogers and Westin, 1981; Houde and Lubbers, 1986; Tsai, 1991; Chesney, 1989, 1993; Daniel8). The strong and dominant effect of tempera- ture upon larval growth rate may have obscured ef- fects of prey density at the cohort-specific level. In the Potomac River, 1987, and in the Upper Bay, 1989, when highest growth rates were observed, zooplank- ton densities were highest, increased as the season progressed, and were correlated positively with tem- perature. In the Potomac River, 1988 and 1989, zoo- plankton densities were lower and not significantly correlated with temperature, yet growth rates of striped bass cohorts at similar temperatures did not differ significantly from the cohort rates in 1987, in- dicating that the temperature effect dominated. It is possible that the failure to demonstrate a rela- tionship between temperature-adjusted, cohort-specific growth rates and prey densities was an artifact that resulted from backcalculating growth rates from mostly older larval survivors. Growth rates of these larvae conceivably may have been higher than growth rates of larvae that died (Miller et al, 1988; Pepin, 1989) and may have obscured impacts of low prey densities on growth. Although for most cohorts, back-calculated growth rates and lengths at age of larvae collected early in the season were not significantly lower than rates and lengths at age of larvae caught later, this result might be artifactual, because of the potential bias on back-calculated growth histories caused by nonlinear changes in the otolith-body size relationship. We believe that recruitment level of striped bass in Chesapeake Bay is essentially set by the abun- dances of cohorts that survive to 8.0 mm SL. Rela- tive productions at 8.0 mm SL and abundances in the juvenile surveys conducted 50 to 100 days later were strongly correlated in the Potomac River and Upper Bay (Rutherford et al.4). Other evidence that striped bass recruitment is fixed during the early postlarval stage (8.0-10.0 mm TL) has resulted from research on striped bass in the Choptank River (Uphoff, 1989) and from the Sacramento-San Joaquin system (Low3). Our results demonstrate that not only is recruitment potential fixed by 8.0 m SL but that relatively few daily cohorts contribute significantly to recruitment in most years. The success of particu- lar cohorts is strongly dependent upon the tempera- ture regime that larvae experience between hatch and 8.0 mm SL. Examination of intraseasonal dif- ferences in cohort-specific growth, survival, and pro- Daniel, D. A. 1976. A laboratory study to define the relation- ship between survival of young striped bass (Morone saxatilis) and their food supply. Calif. Dep. Fish and Game, Anadromous Fisheries Branch, Admin. Rep. 76-1, Sacramento, CA, 13 p. Available: California Department of Fish and Game, Anadro- mous Fisheries Branch, Sacramento, CA. 330 Fishery Bulletin 93(2). 1995 duction has provided a clearer picture of the processes influencing striped bass recruitment than could have been obtained solely from analysis of interannual differences in larval vital rates and abundances. Acknowledgments Funding for this research was provided by the Tide- water Administration, Maryland Department of Natural Resources (MDDNR). This paper constituted part of a Ph.D. dissertation by the senior author while at the University of Maryland. The senior author gratefully acknowledges research assistantship sup- port from MDDNR, a fellowship from the Electric Power Research Institute, and travel support from the University of Maryland System's Chesapeake Biological Laboratory, the Optimist Club of Solomons, and the Chesapeake Bay Yacht Club Association. Field and laboratory assistance was provided by Linton Beaven, Cynthia Cooksey, James Cowan, Edward Chesney, Suzanne Dorsey, Kenneth Langley, Lori Linley, Jamie Lovdal, David Lytle, James MacGregor, Doreen Monteleone, Brian Moser, Timo- thy Newberger, Robert Nyman, John Olney, David Secor, Ana Vasquez, Colleen Zastrow, and the Cap- tain and crew of RV Orion. Ichthyoplankton surveys in the Upper Bay in 1989 were conducted for us by MDDNR personnel. Letty Fernandez assisted with word processing, and Colleen Zastrow and Fran Younger assisted with illustrations. Comments by James A. Rice and an anonymous reviewer signifi- cantly improved the manuscript. Literature cited Barkuloo, J. M. 1967. Florida striped bass. Florida Game and Freshwa- ter Fish Comm., Fish. Bull. 4:1-24. Boreman, J., and H. M. Austin. 1985. Production and harvest of anadromous striped bass stock along the Atlantic coast. Trans. Am. Fish. Soc. 114:3-7. Campana, S. E. 1990. 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Relationship between reported commercial landings and abundance of young striped bass in Chesapeake Bay, Maryland. Trans. Am. Fish. Soc. 114:92-96. Heinle, D. R. 1969. Temperature and zooplankton. Chesapeake Sci.l0:186-209. Houde, E. D. 1987. Fish early life dynamics and recruitment variability. Am. Fish. Soc. Symp. 2:17-29. 1989. Subtleties and episodes in the early life of fishes. J. Fish Biol. 35 (Suppl. A):29-38. Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 331 Houde, E. D., and L. Lubbers. 1986. Survival and growth of striped bass, Morone saxatilis, and Morone hybrid larvae: laboratory and pond enclosure experiments. Fish. Bull. 84:905-914. Jennings, S., J. E. Lancaster, J. S. Ryland, and S. E. Shackley. 1991. The age structure and growth dynamics of young-of- the-year bass, Dicentrarchus labrax, populations. J. Mar. Biol. Assoc. (U.S.)71:799-810. Jones, C, and E. B. Brothers. 1987. Validation of the otolith increment aging technique for striped bass, Morone saxatilis, larvae reared under sub- optimal feeding conditions. Fish. Bull. 85:171-178. Kernehan, R. J., M. R. Headrick, and R. E. Smith. 1981. Early life history of striped bass in the Chesapeake and Delaware Canal and vicinity. Trans. Am. Fish. Soc. 110:137-150. Leak, J. C, and E. D. Houde. 1987. Cohort growth and survival of bay anchovy Anchoa mitchilli larvae in Biscayne Bay, Florida. Mar. Ecol. Prog. Ser. 37:109-122. Litvak, M., and W. C. Leggett. 1992. Age and size-selective predation on larval fishes: the bigger-is-better hypothesis revisited. Mar. Ecol. Prog. Ser. 81:13-24. Lo, N. C. H. 1986. Modeling life-stage specific instantaneous mortality rates, and application to northern anchovy, Engraulis mordax, eggs and larvae. Fish. Bull. 84:395^108. Methot, R. D., Jr. 1983. Seasonal variation in survival of larval northern an- chovy, Engraulis mordax, estimated from the age distri- bution of juveniles. Fish. Bull. 81:741-750. Miller, P. E. 1976. Experimental study and modeling of striped bass egg and larval mortality. Ph.D. diss., Johns Hopkins Univ., Baltimore, MD. Miller, T. J., L. B. Crowder, J. A. Rice, and E. A. Marschall. 1988. Larval size and recruitment mechanisms in fishes: towards a conceptual framework. Can. J. Fish. Aquat. Sci: 45:1657-1670. Monteleone, D. M., and E. D. Houde. 1992. Vulnerability of striped bass, Morone saxatilis Waldbaum, eggs and larvae to predation by juvenile white perch, M. americana Gmelin. J. Exp. Mar. Biol. Ecol. 15:93-104. Morgan, R. P., Ill, V. J. Rasin, and R. L. Copp. 1981. Temperature and salinity effects on development of striped bass eggs and larvae. Trans. Am. Fish. Soc. 110:95-99. Olney, J. E., G. C. Grant, F. E. Schultz, C. L. Cooper, and J. Hageman. 1983. Pterygiophore-interdigitation patterns in larvae of four Morone species. Trans. Am. Fish. Soc. 112:525-531. Olney, J. E., J. D. Field and J. C. McGovern. 1991. Striped bass egg mortality, production and female biomass in Virginia rivers, 1980-1989. Trans. Am. Fish. Soc. 120:354-367. Pepin, P. 1989. Using growth histories to estimate larval fish mor- tality rates. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 191:324-329. Pepin, P., T. H. Schaers, and Y. de Lafontaine. 1992. The significance of body size to the interaction be- tween a larval fish iMallotus villosus) and a vertebrate predator {Gasterosteus aculateus). Mar. Ecol. Prog. Ser. 81:1-12. Polgar, T. T. 1977. Striped bass ichthyoplankton abundance, mortality and production estimation for the Potomac River population. In W. Van Winkle (ed. ), Proceedings of a confer- ence on assessing the effects of power plant-induced mortal- ity on fish populations, p. 110-126. Pergamon Press, NY. Polgar, T. T„ J. A. Mihursky, R. E. Ulanowicz, R. P. Morgan II, and J. S. Wilson. 1976. An analysis of 1974 striped bass spawning success in the Potomac Estuary. In M. Wiley (ed.), Estuarine pro- cesses. Vol. 1: Uses, stresses and adaptations to the estu- ary, p. 151-165. Acad. Press, NY. Post, J. R., and A. B. Prankevicius. 1987. Size-selective mortality in young-of-the-year yellow perch (Perca flavescens): evidence from otolith micros- tructure. Can. J. Fish. Aquat. Sci. 44:1840-1847. Reznick, D., E. Lindbeck, and H. Bryga. 1989. Slower growth results in larger otoliths: an experi- mental test with guppies (Poecilia reticulata). Can. J. Fish. Aquat. Sci. 46:108-112. Rice, J. A., L. B. Crowder, and M. E. Holey. 1987a. Exploration of mechanisms regulating larval sur- vival in Lake Michigan bloater: a recruitment analysis based on characteristics of individual larvae. Trans. Am. Fish. Soc. 116:703-718. Rice, J. A., L. B. Crowder, and F. P. Binkowski. 1987b. Evaluating potential sources of mortality for larval bloater [Coregonus hoyi): starvation and vulnerability to predation. Can. J. Fish. Aquat. Sci. 44:467-472. Rice, J. A., T. J. Miller, K. A. Rose, L. B. Crowder, E. A. Marschall, A. S. Trebitz, and D. L. DeAngelis. 1993. Growth rate variation and larval survival: inferences from an individual-based size-dependent predation model. Can. J. Fish. Aquat. Sci. 50:133-142. Rogers, B. A., and D. T. Westin. 1981. Laboratory studies on effects of temperature and delayed initial feeding on development of striped bass larvae. Trans. Am. Fish. Soc. 110:100-110. Rogers, B. A., D. T. Westin, and S. Saila. 1977. Life stage duration in Hudson River striped bass. Univ. Rhode Island Mar. Tech. Rep 31, 111 p. Rose, K. A., J. H. Cowan Jr., E. D. Houde, and C. C. Coutant. 1993. Individual-based modeling of environmental quality effects on early life stages offish: a case study using striped bass. Am. Fish. Soc. Symp. 14:125-145. SAS (SAS Institute, Inc.). 1988. SAS/STAT user's guide, release 6.03 ed. SAS Insti- tute, Inc., Cary, NC, 1,028 p. Secor, D. H. 1990. The early life history of natural and hatchery-pro- duced striped bass, Morone saxatilis (Walbaum). Ph.D. diss., Univ. South Carolina, Columbia, SC, 210 p. Secor, D. H., and J. M. Dean. 1989. Somatic growth effects on the otolith-fish size rela- tionship in young pond-reared striped bass, Morone saxatilis. Can. J. Fish. Aquat. Sci. 46:113-121. 1992. Comparison of otolith-based back-calculation meth- ods to determine individual growth histories of larval striped bass, Morone saxatilis. Can. J. Fish. Aquat. Sci. 49:1439-1454. Setzler-Hamilton, E. M., and L. Hall Jr. 1991. Striped bass. In S. L. Funderburk, J. A. Mihursky, S. J. Jordan, and D. Riley (eds), Habitat requirements for 332 Fishery Bulletin 93(2), 1995 Chesapeake Bay living resources, 2nd ed., p. 13.1- 13.31. Living Resources Subcommittee, Chesapeake Bay Program, Annapolis, MD. Takacs, R. L. 1992. Early life history of Morone saxatilis and M. americana: ecology, feeding biology and larval conditions in three tributaries of Chesapeake Bay. MS thesis, Univ. Maryland, College Park, MD. Tsai, C.-F. 1991. Prey density requirements of the striped bass, Morone saxatilis (Walbaum), larvae. Estuaries 14(2):207-217. Uphoff, J. H., Jr. 1989. Environmental effects on survival of eggs, larvae and juveniles of striped bass in the Choptank River, Mary- land. Trans. Am. Fish. Soc. 118:251-263. Abstract. — Condition of field- caught walleye pollock, Theragra ehalcogramma, larvae was assessed by using a measurement of midgut cell height that reliably diagnosed the nutritional status of laboratory- reared walleye pollock. The midgut cell height was simple to measure on histological sections. Several correction factors were developed for applying the midgut measure- ment to a field study. These in- cluded regressions to characterize change in larval length associated with net collections of various elapsed times and with fixation in several types of preservatives. The response of midgut cell height to field collection procedures also was tested. The field study indicated larval walleye pollock were starv- ing in the Shelikof Strait, Gulf of Alaska, in 1991. At some stations up to 40% of the larvae were in poor condition. Larvae were most vul- nerable to starvation for 2 weeks following the day of first-feeding. Condition of larval walleye pollock, Theragra ehalcogramma, in the western Gulf of Alaska assessed with histological and shrinkage indices* Gail H. Theilacker Steven M. Porter Alaska Fisheries Science Center National Marine Fisheries Service, NOAA 7600 Sand Point Way NE, Seattle. WA 98 1 ! 5 Manuscript accepted 12 September 1994. Fishery Bulletin 93:333-344 ( 1995). In 1986 the Fisheries-Oceanogra- phy Coordinated Investigations (FOCI) program of the Alaska Fish- eries Science Center and the Pacific Marine Environmental Laboratory began studying the biological and physical processes controlling vari- ability in recruitment of walleye pollock, Theragra ehalcogramma, in Shelikof Strait, Gulf of Alaska. Each year, large concentrations of adult walleye pollock aggregate in the Strait and spawn in late March and early April, producing dense patches of eggs at a depth of about 200 m; there is little variation in the tim- ing or location of the spawning ( Kim and Kendall, 1989; Kendall and Picquelle, 1990; Schumacher and Kendall, 1991). After hatching, lar- vae rise to the upper waters where they may be transported along the Alaska Peninsula, off the shelf to the southeast, or be retained in ed- dies (Vastano et al., 1992). It is be- lieved that the area young pollock occupy during the larval stage is important for their survival (Schu- macher and Kendall, 1991 ). Assess- ing the nutritional condition of lar- val pollock collected from different areas in Shelikof Strait should aid in determining whether food avail- ability is one of the factors influenc- ing survival and recruitment. A variety of indices have been ap- plied to examine the nutritional condition of larval fish. However, for most of the indices, the response rate of the variable to changes in feeding is unknown. Thus, it is dif- ficult to apply the index to estimate mortality rates in the field and sub- sequent recruitment variability. Histological analyses have yielded valuable information on larval nu- tritional condition (O'Connell, 1976; Theilacker, 1978; O'Connell and Paloma, 1981; Sieg, 1992). Further- more, starvation-induced mortality rates for histological studies have been estimated by combining the re- sults from histological condition as- sessments with information on growth and starvation rates (Theil- acker, 1986; Theilacker and Wata- nabe, 1989). Using the estimate of starvation-induced mortality rates, attempts have been made to calcu- late the proportion of natural mortal- ity due to starvation mortality (Hewitt et al., 1985; Owen et al., 1989). Preliminary studies on larval wall- eye pollock have revealed that the height of the midgut mucosal cells are sensitive to starvation, decreas- ing in height measurably over time * Contribution FOCI-0191 to NOAA's Fish- eries-Oceanography Coordinated Investi- gations, Seattle, WA 98115. 333 334 Fishery Bulletin 93(2), 1995 as food is withheld. A decrease in the thickness of the intestine during starvation has been noted for other fishes (Kostomarova, 1962; Nakai et al., 1969; Umeda and Ochiai, 1975; Ehrlich et al., 1976; O'Connell, 1976; Theilacker, 1978, 1986; Kashuba and Matthews, 1984; Boulhic and Gabaudan, 1989; Oozeki et al., 1989; Theilacker and Watanabe, 1989; McFadzen et al., 1994), including the Altantic cod, Gadus morhua L. (Yin and Blaxter, 1987), which is closely related to walleye pol- lock. In this study we describe a midgut cell height in- dex for laboratory-reared walleye pollock. Shrinkage of larval fish captured in a net and pre- served aboard ship differs from that observed in the laboratory (Blaxter, 1971; Theilacker, 1980, 1986; Hay, 1981; McGurk, 1985; Jennings, 1991). The amount a larva shrinks may be dependent on size, the duration of handling (time in the net and how soon after death it is preserved), and the type of pre- servative used. Preservative and gear- related (net) shrinkage have been examined for larvae of a vari- ety of fish species (Theilacker, 1980, 1986; Hay, 1981, 1982; Fowler and Smith, 1983; Tucker and Chester, 1984; McGurk, 1985; Radtke, 1989; Kruse and Dalley, 1990; Jennings, 1991; Hjorleifsson and Klein- MacPhee, 1992). Jennings (1991) found that the magnitude of shrinkage differed among species and concluded that a correction factor for each species must be determined. To relate our laboratory observations to the field, we derived shrinkage indices for larval walleye pollock subject to net treatment and several preservatives. To determine the utility of the midgut cell height index in the field, larval walleye pollock were collected in Shelikof Strait, and their nutritional con- dition was assessed from experimental results. Methods Laboratory rearing Adult walleye pollock were collected from Shelikof Strait, Gulf of Alaska, in April of 1990 to 1993. The fish were spawned aboard ship and the fertilized eggs flown to Friday Harbor Laboratories, University of Washington, in 1991 and to the Alaska Fisheries Science Center in 1990, 1992, and 1993. We raised the larvae in 120-L black fiberglass circular tanks with clear plastic covers and used a 16-h daylight cycle. Seawater temperatures were maintained at 6°C which are typical in May in Shelikof Strait when larvae initiate feeding (Kendall et al., 1987). Each year there were two treatments: one tank contained larvae into which prey were added (fed tank), the second contained larvae that were never offered prey (starved tank). Prey consisted of rotifers, Brachionus plicatilis, at 10/mL and copepod nauplii, Acartia sp., at a minimum of 1-2/mL. Rotifers were raised on algal diets of Isochrysis galbana and Pavlova lutheri, which are high in unsaturated fatty acids (Nichols et al., 1989). The dinoflagellate, Katodinium rotun- datum, was also added as prey for the rotifers and copepods. Ammonia levels were low for both treat- ments (<0.4 ppm). We sampled larvae from both the fed and starved tanks every day or every other day. Calibration of midgut cell height For the histological analysis, walleye pollock larvae were preserved in either Bouin's solution which was replaced with 70% ethanol 24 to 48 h later or in Z- Fix (solution of 10% formalin with zinc and buffers added1). Larvae were processed with standard his- tological procedures; they were dehydrated in a bu- tyl alcohol series, embedded in paraffin wax, seri- ally sectioned at 6 pm in the sagittal plane, and stained with hematoxylin and eosin. We measured the mucosal cell height of the anterior dorsal por- tion of the midgut at 400x magnification (Fig. 1 ). This area was chosen because it exhibits little gut folding which can make the midgut cell height measurement too variable to be useful. We measured three to six neighboring cells (with clearly defined nuclei, base- ment membrane, and microvilli) from the top of the basement membrane to the top of the microvilli and recorded the average height. Fixative effects on larval length To determine the shrinkage of larvae placed directly into preservative (laboratory shrinkage), we mea- sured the standard length (SL, tip of upper jaw to end of notochord, to nearest 0.08 mm) of live larvae sampled from the fed tank and placed them individually into Bouin's solution, 5% formalin, Z-Fix, or 95% ethanol. Bouin's solution was changed to 70% ethanol 24 to 48 h later. Final size of larvae was determined one year after preservation. Final size of ethanol-fixed larvae was measured in distilled water; larvae preserved in the other fixatives were measured in the fixative. Net-treatment and subsequent fixative effects on larval length To examine the effect of net treatment on larval length, a larva was sampled from the fed tank and its stan- dard length was measured. It was then placed in a small net and submerged in a tank of 6°C seawater that re- circulated through the net to simulate a towed sam- Anatech, Ltd., Battle Creek, MI. Theilacker and Porter: Condition of Theragra chalcogramma in the Gulf of Alaska 335 y MICROVILLI Figure 1 The location where the midgut cell height measurement was taken in larval walleye pollock, Theragra chalcogramma. The left photomicrograph shows a sagittal section of the midgut and surrounding organs (larva 8 d after hatch, 4.88 mm SL in Bouin's fixative); the right photomicrograph shows the area where midgut cell height was measured (larva 12 d after hatch, 5.68 mm SL in Bouin's fixative). pling net (Theilacker, 1980). The larva was remeasured after 5 minutes. The final measurement was taken at 10, 15, or 20 min, and then the larva was placed into Bouin's, Z-Fix, or 5% formalin. For additional shrink- age due to preservation, larvae were remeasured from 1 month to 1 year after they were preserved. Change in midgut cell height due to fixative and net treatment Two fixatives used to preserve field-collected larvae were compared to determine their effect on the height of the midgut cells. The effect of Bouin's solution and Z-Fix was compared by sampling 10 fish daily from the fed tank and preserving 5 in Bouin's solution and 5 in Z-Fix. To determine whether the height of the midgut cells changed as larval length decreased dur- ing the net shrinkage experiment, one group of 20 larvae was measured and placed directly into Z-Fix while a second group of 20 was measured, net- treated, and then preserved in Z-Fix. Data analysis Data were analyzed by using SAS (SAS, Inc. 1988), SYSTAT (Wilkinson, 1988), and Minitab (Ryan et al., 1985) computer software. Simple linear regression analysis was used to derive equations to adjust lar- val size for shrinkage. ANOVA was used to compare the midgut cell height of starved and fed larvae of the same size. Midgut cell height of starved larvae reared in 1991 and 1993 was compared with midgut cell height of fed larvae reared in 1991 and 1992 (in 1992, no starved larvae were sampled for midgut measurement, and in 1993, midgut was not measured for fed larvae). Years were used as independent treat- ments to avoid pseudoreplication (Hurlbert, 1984). Field collections Larval walleye pollock were collected for histology from stations located throughout the Shelikof Strait, Gulf of Alaska, during two cruises in the spring of 1991 (Fig. 2). The area sampled covered the entire spawning area in the Strait (Kendall and Picquelle, 1990). Collections were made with a 60-cm bongo net equipped with a 333-|am mesh and solid cod end, which were retrieved vertically from 70 m in about 7 minutes. Because larval fish tissues deteriorate quickly owing to autolysis (Theilacker, 1978), the net was not washed following a tow, and larvae were quickly sorted on sea water ice and preserved in Bouin's fixa- tive. Earlier laboratory studies conducted with larval walleye pollock indicated they must be preserved within 12 min at 6°C in order to retain cellular integrity.2 2 Theilacker, G. H., S. M. Porter. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115. Unpubl. data. 336 Fishery Bulletin 93(2), 1995 066 066 ,C=S '*} BUOY '063 Q 109 059 * K 4 154°* Figure 2 Stations in the Shelikof Strait, Alaska, where walleye pol- lock, Theragra chalcogramma, were collected for histologi- cal analysis in April and May 1991. Table 1 Size of fed and starved treatments of 1991 laboratory- reared larval walleye pollock, Theragra chalcogramma. Larvae were reared at 6°C and preserved in Bouin's fixative. Means and standard deviations (SD) are for 5-10 larvae. Days after hatching Laboratory-preserved standard length (mm Fed Starved mean SD mean SD 8' 5.01 0.18 5.01 0.07 9 5.12 0.16 4.93 0.12 10 5.10 0.16 4.98 0.12 11 5.22 0.16 4.93 0.09 12 5.32 0.29 4.91 0.17 13 5.40 0.20 4.90 0.07 14 5.31 0.23 4.93 0.18 15 5.30 0.30 4.80 0.11 16 5.34 0.20 4.91 0.07 17 5.44 0.34 4.82 0.14 19 4.66 0.13 20 4.67 0.09 ' Day of first feeding. The standard length of all field larvae was mea- sured before processing for histology. We processed all larvae from each field sample that were preserved within 12 minutes. Larvae were processed in the same manner as the laboratory-raised pollock, and midgut cell height was measured in the same area to determine their past feeding history. The vertical depth inhabited by most walleye pol- lock larvae less than 10 mm is between 25 and 37 m (Kendall et al., 1994). Thus we estimated that the elapsed handling time from capture to placement into fixative for the average larva was from 6 to 9 min (3 to 4 min in the net retrieved at 10 m/min plus 3 to 5 min to sort and preserve), or an average of 7.5 min- utes. We used 7.5 min as the average handling time to calculate field-collected size. Results Laboratory rearing 1 99 1 Walleye pollock hatched at a mean SL of 3.5 mm (laboratory-preserved size), grew at an average rate of 0.12 mm/d, and at 17 d after hatching averaged 5.4 mm SL (Table 1). Larvae started feeding on av- erage ( 3e +SD) 8 d after hatching (range 7-9 d) at 5.01 ±0.15 mm SL (range 4.56-5.20 mm SL, re=15), and the yolk was completely absorbed about 5 d later. The growth rate from first-feeding on day 8 to 13 d after hatching averaged 0.078 mm/day. Starved larvae decreased in size as food was with- held for 11 d after first feeding (Table 1). The length of starved larvae began to decrease slowly on day 9 after food was withheld for only 1 day. After 8 d of starvation (16 d after hatching), larvae rapidly de- creased in size. Calibration of midgut cell height The height of the midgut cells of larvae sampled from the starved and fed tanks and preserved in Bouin's solution ranged from 5 to 34 |im (Figs. 3 and 4). Cells were largest in prefeeding yolk-sac larvae before mid- gut differentiation was complete and the lumen fully formed. Starving the larvae caused the midgut cells to decrease slowly in height from about 13 urn at first feeding to about 9 urn after starving for 4 days; the average height remained at about 8 urn as food was withheld for an additional 5 days (Fig. 3). We arbitrarily set 11 um to delimit the fed and starved groups be- cause it gave the best division; this cutoff separated 87.2% of the fed larvae and 80.4% of the starved larvae. The height of the mucosal cells of the anterior dor- sal portion of the midgut increased slightly as fed Theilacker and Porter: Condition of Theragra chalcogramma in the Gulf of Alaska 337 larvae grew (Fig. 4). Midgut cell heights of fed larvae were significantly larger ( ANOVA, P=0.006, df=l) than those of starved larvae of equal length (4.50-5.49 mm SL), and the same treatment was not significantly differ- ent between years (ANOVA, P=0.533, df=2; Table 2). Moreover, the difference in midgut cell heights was attained after food was with- held for 1 day (t-test; P<0.01, df=8; mean fed midgut cell height after 1 d of feeding=12.96 ±1.31 p, n=5; mean starved midgut cell height after 1 d of starvation = 9.12 ±0.99 pm, n=5; 1991 rearing data). Midgut cell height was not affected by a net treatment of 7.5 min, the estimated time a larva is handled during field collection. The cell height of fish that were net-treated be- fore being placed into preservative was not significantly different from those placed di- rectly into preservative U-test; P=0.12; df=30). Additionally, midgut cell height was not influenced by preservative type when Bouin's solution was compared with Z-Fix (t- test;P=0.17;df=80). Fixative effects Larval walleye pollock shrank an average of 4.7% in Z-Fix, 13% in Bouin's, and 8% in 5% formalin. There was no measurable shrink- age in 95% ethanol. For live larvae placed directly in Z-Fix, shrinkage was a constant proportion of size (Table 3). Laboratory shrinkage in Bouin's and 5% formalin was not a constant proportion of size; in each case the y-intercept of the regression differed sig- nificantly from zero (P=0.04 for Bouin's, and P=0.001 for 5% formalin). Smaller larvae shrank proportionately more than larger lar- vae in both preservatives (Fig. 5A; Table 3). For example, in using the regression equa- tions in Table 3, the decrease in size of 5- mm-SL larvae preserved in Bouin's was 15% and in 5% formalin was 9%, whereas the decrease in size of 7-mm-SL larvae in Bouin's was 12% and in formalin was 7%. However, there was no observed shrinkage of larvae preserved in 95% ethanol. In fact, the aver- age larva increased slightly in size, about 1% for 5- mm-SL larvae and 3% for 7-mm-SL larvae (Table 3). Net-shrinkage effects Larvae shrank an average of 7% after a 5-min net treatment, 14% after 10 min, 17% after 15 min, and 22% after 20 min; initial sizes ranged from 4.48 to 35 i _ 30 E 3 25 ' £ 20- .c » 15 u §> 10 1 5 o D O o o ° prefeeding a fed * starved ► o □ O O D D D > o n a ° * o ft H 00DDDaDDO D OB D a § DQSD g ° B a a D D a a □ Ha o ■:■ i i d d 1 add d d H A n I A aao a 1 9 1 . ■ * J , * * : o Iff a o a B I 3 3 3 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Days after hatching Figure 3 Midgut cell height of laboratory-reared prefeeding, fed, and starved larval walleye pollock, Theragra chalcogramma, from hatching to 20 d after hatching. Arrow shows day of first feeding °oo A Ef D° O D DD Q □ O a □ CD 0 DoD^ ^EP o^ cPDa° D LKiUULJLyjJ ODD Iq C *,Jf^p£° %* B D a 3.0 3.6 40 4.5 5.0 5.5 6.0 6.5 7.0 7.5 80 8.5 Laboratory - preserved standard length (mm) Figure 4 Midgut cell height of laboratory-reared prefeeding, fed, and starved larval walleye pollock, Theragra chalcogramma, related to labora- tory-preserved standard length in Bouin's fixative. 9.90 mm SL (Table 3), and sizes after net treatment ranged from 3.76 to 9.48 mm SL. Length after net treatment was linearly related to initial standard length (net time=0) for each treatment period (Fig. 5B; Table 3). Analysis of covariance (ANCOVA) showed that it was possible to interpolate a 7. 5-min regression (needed for field procedures; see Field Collections in Methods section; Table 3) between the 5- and 10-min net-shrinkage regressions; the slopes of the two regressions were not significantly differ- ent (P=0.785) and the lines were not coincident (P<0.01). 338 Fishery Bulletin 93(2). 1995 Table 2 Midgut cell height of fed and starved laboratory-rearei Theragra chalcogramma, at 6°C. 1 larval walleye pollock, Size class (mm)7 year Midgut cell height (Jim) Fed Starved P n mean (SD) n mean (SD) 4.50-5.49 1991 34 14.06 (3.62) 57 8.89 (2.23) 0.006 1992 31 14.53 (4.01) 1993 20 8.16 (1.76) 5.50-5.99 1991 13 18.78 (5.68) ' Adjusted to equal Bouin's laboratory preserved size Table 3 Regression equations for adjusting the size of larval walleye pollock, Theragra chalcogramma, exposed to various conditions that cause shrinkage. Shrinkage type Live SL range (mmi Regression equation la) Laboratory shrinkage in Bouin's' lb) Laboratory shrinkage in Z-Fix2-3 lc) Laboratory shrinkage in 5% formalin4 Id) Laboratory shrinkage in ethanol (95%)4 2) Net treatment, 5 min 3) Net treatment, 7.5 min (interpolated) 4) Net treatment, 10 min 5) Net treatment, 15 min 6) Net treatment, 20 min 7a) Shrinkage in Bouin's after net treatment' 7b) Shrinkage in Z-Fix after net treatment3 7c) Shrinkage in 5% formalin after net treatment3 5.27-7.06 47 5.20-7.60 56 4.20-20.00 42 5.80-18.90 42 4.48-9.90 135 4.48-9.90 134 4.48-9.90 97 4.96-9.90 71 5.52-8.24 18 5.36-7.84 35 4.48-8.40 50 live SL = 0.617+1. 033( laboratory preserved SL) 0.88 live SL = 1.047(laboratory preserved SL) 0.99 live SL = 0.344+ 1 .02 1( laboratory preserved SL ) 0.98 live SL = 0.296+0.929( laboratory preserved SL) 0.99 liveSL=0.509+0.994(NLSL5) 0.93 live SL=0.703+0.988(NL SL) live SL=0.974+0.983(NL SL ) 0.90 liveSL=1.26+0.961(NLSL) 0.87 liveSL=2.26+0.841(NLSL) 0.84 NL SL = 1.118(preserved SL) 0.99 NL SL= 1.036(preserved SL) 0.99 NL SL = 1.0971 preserved SL) 0.99 ' Laboratory shrinkage = live larva placed directly into preservative. 2 Z-Fix histological preservative, 10% formalin with aqueous zinc and buffers (see text). 3 In some cases the constant was not significant and was removed from the regression. 4 Data provided by K. M. Bailey, Alaska Fisheries Science Center. 5 NL SL = net live standard length (size after net treatment before preservation). Theilacker and Porter: Condition of Theragra chalcogramma in the Gulf of Alaska 339 4.5 5.5 65 7.5 8.5 10 - minute net treatment standard length (mm) 6 5 § 6.0 i- 5.5- 4.5- 4.0 3.5 4.0 4.5 5.0 55 6.0 6.5 Preserved standard length after 10 - minute net treatment (mm) Figure 5 Size of fed walleye pollock, Theragra chalcogramma, measured live in the laboratory related to (A) their size after preservation in Bouin's fixative, to (B) their live size after a 10-min treatment in a net, and to (C) the size of live larval walleye pollock treated in a net for 10-min (NL SL [see explanation in Footnote 5 of Table 3]) related to their preserved size in Bouin's fixative after the net treatment. Regression equations are found in Table 3. Shrinkage in preservative after net treatment Correction for field-captured size Net-treated larvae shrank an additional 11.8% after being preserved in Bouin's preservative (Table 3). Shrinkage was constant over the size range treated (5.52-8.24 mm SL, re=18; Fig. 5C). Additional shrink- age of net-treated larvae in Z-Fix was 3.6% (5.36— 7.84 mm SL, n=35; Table 3) and in 5% formalin was 9.7% (4.48-8.40 mm SL, n=50; Table 3). The elapsed time from larval collection to preserva- tion and the preservative type determine which two equations in Table 3 are needed to adjust field-col- lected and preserved size to the equivalent live size. To examine the accuracy of the regression equations for estimating the live length of field-collected lar- vae (Table 3), we measured the live size of 20 larvae, 340 Fishery Bulletin 93(2), 1995 net-treated them for 7.5 min to simulate field collec- tion, preserved them in Z-Fix, and remeasured them several months later. The mean net-treated and pre- served SL (4.58 mm ±0.25) was estimated to be 5.39 mm live size from Equations 3 and 7b in Table 3. The observed mean live standard length of the same 20 larvae was 5.46 mm (± 0.21), a difference of 1%. Field distribution of larvae Yolk-sac and first-feeding walleye pollock larvae were collected in the eastern Shelikof Strait in April 1991 (Fig. 2; stations 136-141). The abundance of first- feeding larvae increased from April to May. In May, larvae ranging in size from first-feeding to 7 mm were fairly evenly distributed along the coast, within the Strait, and out the sea valley.3 Some yolk-sac larvae were also found near the Alaska Peninsula and at the exit of Shelikof Strait. Condition of field-captured walleye pollock Larvae were sampled from six stations in late April and from 15 stations in early May (Table 4). The level of starvation ranged from 10 to 17% at 3 of the 6 stations in April and at 7 of the 15 stations in May. However, in May, at 3 stations along the sea valley (018, 059, and 068), the percent starvation ranged from 30 to 40% (Fig. 2; Table 4). Thirty-two percent (/z=17/54) of larvae <5.00 mm SL were classified as starving in the combined April and May samples (Table 5). This category included larvae that were smaller than average at first feed- ing and those that had shrunk from starvation. The percent starving in the first-feeding size category (5.0 to <5.5 mm SL) was 27% (n=12/45), and the number decreased to 12% («=5/41 ) for 5.5 to <6.0 mm SL group and finally to zero for larvae >6.0 mm (Table 5). Discussion The histological analysis showed that the height of the midgut mucosal cells of laboratory-reared wall- eye pollock corresponded to their feeding condition and that significant changes in cell height could be detected after food was withheld for one day. Thus, a simple measurement of midgut cell height discerned larval nutritional condition. To confirm the useful- 3 Bailey, K. M., M. F. Canino, J. M. Napp, S. M. Spring, and A. L. Brown. Two contrasting years of prey levels, feeding condition and mortality of larval walleye pollock (Theragra chalco- gramma) in the western Gulf of Alaska. U.S. Dep. Commer., Natl. Mar. Fish. Serv., Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115. Manuscr. in review. ness of the measurement for assessing the nutritional condition of field-collected larvae, it was necessary to determine the effects of field collection procedures on the midgut measurement. Although one might expect some compression of the fish body and per- haps a change in gut morphology as a larva shrinks, our experiments with walleye pollock showed no change in size of the midgut cells during the net shrinkage experiments. Thus, we felt confident in applying the laboratory calibration to assess the con- dition of sea-caught larvae. Theilacker and Watanabe (1989) also demonstrated that there was no change in the midgut cell height for northern anchovy, Engraulis mordax, held for periods up to 25 min in the net. Additionally, although preservative type af- fected the final size of pollock larvae, the midgut cell height did not differ between two preservative types tested, Bouin's and Z-Fix. Therefore field-collected larval pollock that are to be analyzed for condition may be preserved in either Bouin's or Z-Fix. Since Farris ( 1963) first noted that larval sardine, Sardinops sagax, shrink when preserved in forma- lin, and Ryland (1966) observed that larval plaice, Pleuronectes platessa, collected in the field were smaller at comparable stages of development than were their laboratory-raised counterparts, informa- tion has accumulated on shrinkage of larval fish placed directly into preservatives and during the process of field collection and preservation (Blaxter, 1971; Theilacker, 1980, 1986; Hay, 1981; Tucker and Chester, 1984; Fowler and Smith, 1983; McGurk, 1985; Radke, 1989). The cause of larvae shrinkage is related to the loss of osmoregulatory ability when they die (Parker, 1963). Fish larvae also shrink while they are alive, and this shrinkage may be due to dam- age by the net to the integument, the main osmo- regulatory system in larvae before the gills develop (Holliday and Blaxter, 1960). The amount of shrink- age is directly related to the interval that larvae re- main in a collecting net. Shrinkage differs among fixatives within species because of the ionic strengths of the preserving fluids (Parker, 1963; Hay, 1982; Tucker and Chester, 1984). Why shrinkage is spe- cies specific may be related to differences in osmo- larity (Theilacker, 1980; Jennings, 1991) or to thick- ness of the integument and mucous layer. The shrinkage values found for walleye pollock larvae placed directly into preservative are similar to those in previous studies (reviewed by Jennings, 1991). Shrinkage of walleye pollock in 5% formalin was greater (as a percentage of length) for smaller larvae (9% for 5 mm SL) than for larger larvae (7% for 7 mm SL). These values are within the range of shrinkage values (3-15%) for other fish larvae sum- marized by Hjorleifsson and Klein-MacPhee (1992). Theilacker and Porter. Condition of Theragra chalcogramma in the Gulf of Alaska 341 Table 4 Number of starving walleye pollock, Theragra chalcogramma, larvae assayed for midgut cell height (MGCH) and prey concentra- tions in Shelikof Strait, Alaska, in April and May 1991. n = number larvae assayed or number starving (STVl. Station Date 1991 Time PST' Temp °C2 MGCH(n) SLdnmC3 STV(n) STV (%)4 Prey5 April 1991 136 26 April 0428 3.93 2 4.70 2 — — 137 26 April 1535 3.81 9 4.53-5.30 2 22 — 138 26 April 1706 4.08 8 4.27-5.22 1 13 — 139 26 April 2342 3.92 4 4.10-5.22 0 — — 140 27 April 0047 3.96 7 4.10-5.47 1 14 — 141 27 April 0157 3.71 6 4.10-5.04 1 17 — May 1991 017 2 May 1417 — 14 4.70-5.47 2 14 — 018 2 May 1839 4.15 27 3.93-6.76 8 30 5.00 038 4 May 1309 3.45 6 4.45-5.81 1 17 1.97 053 5 May 1230 — 1 4.19 0 — — 059 5 May 2153 3.78 5 4.70-5.64 2 40 — 066 6 May 1547 — 2 5.30-5.81 1 — — 068 6 May 2006 3.86 10 4.62-5.90 4 40 3.93 082 7 May 1835 4.12 3 4.87-5.04 2 — 3.07 089 8 May 0507 4.21 3 5.73-6.07 0 — 3.67 109 10 May 1349 4.26 14 5.13-6.93 2 14 — 110 10 May 1525 4.28 14 4.36-6.76 2 14 — Buoy 3 12 May 1045 4.14 15 4.79-6.58 0 0 — Buoy 4 12 May 1147 4.15 9 4.96-6.67 1 11 8.53 Buoy 5 12 May 1256 4.10 10 5.56-6.76 1 10 10.54 Buoy 8 12 May 1555 4.27 7 5.22-6.33 1 14 — ' Pacific standard time. 2 Average temperature between 21 and 40 m depth where a majority of walleye pollock larvae are fou ( — = no measurements taken). 3 Preserved standard length (SL) of larvae assayed (SL adjusted to equal Bouin's laboratory preserved 4 Percent of larvae starving at stations where at least 5 larvae were assayed. 5 Number of copepod eggs and nauplii > 150 um/L averaged over 60 m depth (Bailey et al.3). nd (Kendall et al size, Table 3). . 1994) Walleye pollock preserved in 95% ethanol and mea- sured in water showed a slight increase in size, be- tween 1 and 3%. Values in the literature for ethanol shrinkage vary greatly from 0% (Theilacker, 1980) to 14% (Radtke and Waiwood, 1980), possibly because of concentration differences or because fish are of- ten transferred from ethanol into water for measure- ment. The transfer permits rehydration which usu- ally negates the original shrinkage.4 4 Theilacker, G. H. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, Wa 98115. Unpubl. data. 342 Fishery Bulletin 93(2). 1995 Table 5 Histological condition of walleye p chalcogramma, larvae collected in th Alaska in April and May 1991. ollock, Theragra e Shelikof Strait, Midgut cell height Size class SL (mm)' Starving <11 urn n Healthy >11 urn n No. of larvae Percent starving April 1991 <5.00 6 20 26 23 5.00-5.49 1 9 10 10 May 1991 <5.00 11 17 28 39 5.00-5.49 11 24 35 31 5.50-5.99 5 36 41 12 6.00-6.49 0 19 19 0 6.50-6.99 0 17 Total 17 176 0 ' Standard length (SL) adjusted to equal Bouin's labora- tory preserved size. It is not clear why the amount of shrinkage is re- lated to larval size for some fixatives and not for oth- ers. In this study for example, shrinkage was a con- stant proportion of size for larvae preserved in Z- Fix. However, in Bouin's solution and 5% formalin, smaller larvae shrank more than larger ones. The net-treatment experiment showed that shrink- age increased with elapsed time in the net, as in other studies addressing net-capture shrinkage of larval fish (Theilacker, 1980; Hay, 1981; McGurk, 1985). Although our field collections averaged 7.5 min, we included net shrinkage values for up to 20 min in a net for adjusting the size of larvae collected in stan- dard bongo net hauls and MOCNESS tows. The histological criteria demonstrated that a sig- nificant number of larval walleye pollock were starv- ing in the Shelikof Strait, Alaska, in April and May, 1991. These results agree with the 1991 field study of Bailey et al.3 who used biochemical criteria to de- termine condition of walleye pollock collected in the same area of Shelikof Strait. They found that more walleye pollock were in poor condition in 1991 than in 1990. Subsequent larval mortality, determined independently by ageing larvae from sequential cruises spanning 2 to 3 weeks, was also higher in 1991 than in 1990. 3 Concentrations of copepod nau- plii and invertebrate eggs, the main prey eaten by walleye pollock (Canino et al., 1991), were anoma- lously low throughout Shelikof Strait in 1991, aver- aging 6 prey/L, as compared with 38 prey/L in 19903 and >20 prey/L in earlier years (Incze et al., 1990; Canino et al., 1991). Others have shown that condi- tion of wild larvae is associated with food availabil- ity. In particular, Canino et al. (1991) using a bio- chemical index showed that larval walleye pollock in Shelikof Strait inhabiting areas of sparse prey were in poorer condition and had fewer prey in their guts than their counterparts inhabiting areas of high prey density. Likewise, larval haddock, Melano- grammus aeglefinus, and cod, Gadus morhua, a close relative of walleye pollock, were shown to be in poorer condition in well-mixed areas on Georges Bank than in stratified sites where prey levels were higher (Buckley and Lough, 1987). Kashuba and Mathews (1984) showed that poor histological condition of lar- val shad, Dorosoma spp., correlated with low prey levels and with a subsequent abrupt decline in the population. Our results for walleye pollock indicate that the youngest larvae are most vulnerable to starvation. While 29% of the first-feeding walleye pollock (com- bined <5.50 mm SL groups; n=29/99; Table 5) were classified as starving, one week later the number was reduced to 12%, and 2 weeks later it was zero (Table 5). Others also have found that starvation of larval fishes in the sea decreases quickly, usually within 1 or 2 weeks, as fish larvae mature (O'Connell, 1980; Theilacker, 1986; Robinson and Ware, 1988). Resis- tance to starvation increases after larval fish first feed (Hunter, 1972; Blaxter and Staines, 1971), ac- quire the ability to eat more varied prey (Hunter, 1972; Arthur, 1976) and are able to store energy re- serves (Ehrlich, 1974; Fraser, 1989; Hakanson, 1989). We also found patchy areas along the Shelikof Strait sea valley in early May 1991 with large numbers of starving larvae, two to three times the background level. Whether small areas of high mortality affect total recruitment is unknown. Despite arguments to the contrary (Sissenwine, 1984; Peterman et al., 1988) and a general belief that starvation is not a widespread occurrence in the sea (Heath, 1992), evidence from this study shows that starvation does occur and that it is the young stages of walleye pollock that are vulnerable. The advan- tages of the midgut histological assay, rather than one requiring grading of several tissues, is that it takes less time than does an extensive histological background and is a quantitative rather than a quali- tative measure (Theilacker and Watanabe, 1989). Additionally, rates of starvation-induced mortality may be estimated by using the assay and employing laboratory-determined growth rates to determine size and stage durations. Currently, studies are under- way to correlate changes in the physical environment Theilacker and Porter: Condition of Theragra chalcogramma in the Gulf of Alaska 343 with larval histological condition, feeding, growth, prey availability, and independently determined mortality Acknowledgments We thank Debbie Blood, Ric Brodeur, Jay Clark, Nazila Merati, and Matt Wilson for the spawning and care of the pollock eggs aboard ship and for bringing them back to Seattle. We appreciate the assistance of Annette Brown and Stella Spring during the rear- ing phase of this study and of Frank Morado and Linda Cherepow with the histological preparations. We also thank Kevin Bailey for contributing the labo- ratory shrinkage data for ethanol and formalin. Kevin Bailey, Art Kendall, Debbie Siefert, and Gary Stauffer commented on early drafts of the manu- script, and anonymous reviewers offered improve- ments. The University of Washington, Friday Har- bor Laboratory, furnished aquarium space in 1991. Literature cited Arthur, D. K. 1976. Food and feeding of larvae of three fishes occurring in the Califoria Current, Sardmops sagax, Engraulis mordax, and Trachurus symmetricus . Fish. Bull. 74:517-530. Blaxter, J. H. S. 1971. Feeding and condition of Clyde herring larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 160:128-136. Blaxter, J. H. S., and M. E. Staines. 1971. Food searching potential in marine fish larvae. In D. J. Crisp (ed.), Fourth European marine biology sympo- sium, p. 467-485. Univ. Press, Cambridge. Boulhic, M„ and J. Gabaudan. 1989. Histological criteria for determing starvation in lar- vae of Dover sole (Solea vulgaris Quensel) (Abstract). Rapp. P.-V. Reun. Cons. Int. Explor. Mer 191, p. 476. Buckley, L. J., and R. G. Lough. 1987. Recent growth, biochemical composition, and prey field of larval haddock tMelanogrammus aeglefinus) and Atlantic cod (Gadus morhua) on Georges Bank. Can. J. Fish. Aquat. Sci. 44:14-25. Canino, M. F., K. M. Bailey, and L. S. Incze. 1991. Temporal and geographic differences in feeding and nutritional condition of walleye pollock larvae Theragra chalcogramma in Sheliof Strait, Gulf of Alaska. Mar. Ecol. Prog. Ser. 79:27-35. Ehrlich, K. F. 1974. Chemical changes during growth and starvation of larval Pleuronectes platessa. Mar. Biol. 24:39^18. Ehrlich, K. F., J. H. S. Blaxter, and R. Pemberton. 1976. Morphological and histological changes during growth and starvation of herring and plaice larvae. Mar. Biol. 35:105-118. Farris, D. A. 1963. Shrinkage of sardine ( Sardinops caerulae ) larvae upon preservation in buffered formalin. Copeia 1963:185-186. Fowler, G. M., and S. J. Smith. 1983. Length changes in silver hake {Merluccius bilmearis) larvae: effects of formalin, ethanol, and freezing. Can. J. Fish. Aquat. Sci. 40:866-870. Fraser, A. J. 1989. Triacylglycerol content as a condition index for fish, bivalve and crustacean larvae. Can. J. Fish. Aquat. Sci. 46:1868-1873. Govoni, J. J., G. W. Boehlert, and Y. Watanabe. 1986. The physiology of digestion in fish larvae. Environ. Biol. Fish. 16:59-77. Hakanson, J. L. 1989. Condition of larval anchovy (Engraulis mordax) in the Southern California Bight, as measured through lipid analysis. Mar. Biol. 102:153-159. Hay, D. E. 1981. Effects of capture and fixation on gut contents and body size of pacific herring larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 178:395-400. 1982. Fixation shrinkage of herring larvae: effects of sa- linity, formalin concentration, and other factors. Can. J. Fish. Aquat. Sci. 39:1138-1143. Heath, M. R. 1992. Field investigations of the early life stages of marine fish. Adv. Mar. Biol. 28:2-174. Hewitt, R. P., G. H. Theilacker, and N. C. H. Lo. 1985. Causes of mortality in young jack mackerel. Mar. Ecol. Prog. Ser. 26:1-10. Hjorleifsson, E., and G. Klein-MacPhee. 1992. Estimation of live standard length of winter floun- der Pleuronectes americanus larvae from formalin-pre- served, ethanol-preserved and frozen specimens. Mar. Ecol. Prog. Ser. 82:13-19. Holliday, F. G. T., and J. H. S. Blaxter. 1960. The effects of salinity on the developing eggs and lar- vae of the herring. J. Mar. Biol. Assoc. U.K. 39:591-603. Hunter, J. R. 1972. Swimming and feeding behavior of larval anchovy Engraulis mordax. Fish. Bull. 70:812-838. Hurlbert, S. H. 1984. Pseudoreplication and the design of ecological field experiments. Ecolog. Monogr. 54:187-211. Incze, L. S., P. B. Ortner, and J. D. Schumacher. 1990. Microzooplankton, vertical mixing and advection in a larval fish patch. J. Plankton Res. 12:365-379. Jennings, S. 1991. The effects of capture, net retention and preserva- tion upon lengths oflarval and juvenile bass, Dicentrarchus labrax (L.). J. Fish. Biol. 38:349-357. Kashuba, S. A., and W. J. Matthews. 1984. Physical condition oflarval shad during spring-sum- mer in a southwestern reservoir. Trans. Am. Fish. Soc. 113:199-204. Kendall, A. W„ Jr., and S. J. Picquelle. 1990. Egg and larval distributions of walleye pollock. Theragra chalcogramma, in the Shelikof Strait, Gulf of Alaska. Fish. Bull. 88:133-154. Kendall, A. W., Jr., M. E. Clarke, M. M. Yoklavich, and G. W. Boehlert. 1987. Distribution, feeding, and growth of larval walleye pollock, Theragra chalcogramma, from Shelikof Strait, Gulf of Alaska. Fish. Bull. 85:499-521. Kendall, A. W., Jr., L. S. Incze, P. B. Ortner, S. R. Cummings, and P. K. Brown. 1994. Factors relating to the vertical distribution of eggs and larvae of the walleye pollock ( Theragra chalcogramma) in Shelikof Strait, Gulf of Alaska. Fish. Bull. 92:540-554. 344 Fishery Bulletin 93(2). 1995 Kim, S., and A. W. Kendall Jr. 1989. Distribution and transport of larval walleye pollock {Theragra chalcogramma) in Shelikof Strait, Gulf of Alaska, in relation to water movement. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 191:127-136. Kostomarova, A. A. 1962. Effect of starvation on the development of the larvae of boney fishes. Tr. Inst. Morfol. Zhivotn. Akad. Nauk. SSSR 40:4-77. Kruse, G. H., and E. L. Dalley. 1990. Length changes in capelin, Mallotus villosus (Muller), larvae due to preservation in formalin and anhydrous alcohol. J. Fish. Biol. 36:619-621. McFadzen, I. R. B., D. M. Lowe, and S. H. Coombs. 1994. Histological changes in starved turbot larvae (Scophthalmus maximus) quantified by digital image analysis. J. Fish Biol. 44:255-262. McGurk, M. D. 1985. Effects of net capture on the postpreservation morphometery, dry weight, and condition factor of Pacific herring larvae. Trans. Am. Fish. Soc. 114:348-355. Nakai, Z., M. Kosaka, M. Ogura, C. Hayashida, and H. Shimozono. 1969. Feeding habit, and depth of body and diameter of digestive tract of shirasu, in relation with nutritious condition. J. College of Marine Science and Technology, Tokai Univ. 3:23-34. Nichols, P. D., D. G. Holdsworth, J. K. Volkman, M. Daintith, and S. Allanson. 1989. High incorporation of essential fatty acids by the ro- tifer Brachionus plicatilis fed on the prymnesiophyte Pavlova lutheri. J. Mar. Freshwater Res. 40:645-655. O'Connell, C. P. 1976. Histological criteria for diagnosing the starving condi- tion in early post yolk sac larvae of the northern anchovy, En- graulis mordax Girard. J. Exp. Mar. Biol. Ecol. 25:285-312. 1980. Percentage of starving northern anchovy, Engraulis mordax, larvae in the sea as estimated by histological methods. Fish. Bull. 78:475-489. O'Connell, C. P., and P. A. Paloma. 1981. Histochemical indications of liver glycogen in samples of emaciated and robust larvae of the northern anchovy, Engraulis mordax. Fish. Bull. 78:806-812. Oozeki, Y., T. Ishii, and R. Hirano. 1989. Histological study of the effects of starvation on reared and wild-caught larval stone flounder, Kareius bicoloratus. Mar. Biol. 100:269-275. Owen, R. W., N. C. H. Lo, J. L. Butler, G. H. Theilacker, A. Alvariiio, J. R. Hunter, and Y. Watanabe. 1989. Spawning and survival patterns of larval northern anchovy, Engraulis mordax, in contrasting environments — a site intensive study. Fish. Bull. 87:673-688. Parker, R. R. 1963. Effects of formalin on length and weight of fishes. J. Fish. Res. Board Can. 20:1441-1455. Peterman, R. M., M. J. Bradford, N. C. H. Lo, and R. D. Methot. 1988. Contribution of early life stages to interannual vari- ability in recruitment of northern anchovy (Engraulis mordax). Can. J. Fish. Aquat. Sci. 45:8-16. Radtke, R. L. 1989. Larval fish age, growth, and body shrinkage: infor- mation available from otoliths. Can. J. Fish. Aquat. Sci. 46:1884-1894. 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. 929:1-10. Robinson, S. M. C, and D. M. Ware. 1988. Ontogenetic development of growth rates in larval Pacific herring, Clupea harengus pallasi, measured with RNA-DNA ratios in the Strait of Georgia, British Columbia. Can. J. Fish. Aquat. Sci. 45: 1422-1429. Ryan, B. F., B. L. Joiner, and T. A. Ryan Jr. 1985. Minitab handbook, second ed. PWS-KENT Publ. Co., Boston, MA, 385 p. Ryland, J. S. 1966. Observations on the development of larvae of the pla- ice, Pleuronectes platesa L., in aquaria. J. Cons. 30:177-195. SAS (SAS Institute, Inc.). 1988. SAS/Stat users guide, release 6.03 ed. SAS Insti- tute, Inc. Cary, NC, 1028 p. Schumacher, J. D., and A. W. Kendall Jr. 1991. Some interactions between young walleye pollock and their environment in the western Gulf of Alaska. CalCOFI Rep., Vol. 32:22-40. Sieg, A. 1992. A histological study on the nutritional condition of larval and metamorphosing fishes of the genus Vinciguerria (Photichthyidael sampled in two contrasting environ- ments. J. Appl. Ichthyol. 8:154-163. Sissenwine, M. P. 1984. Why do fish populations vary? In R. May (ed.). Ex- ploitation of marine communities, p. 59-94. Springer- Verlag, Berlin. Theilacker, G. H. 1978. Effect of starvation on the histological and morpho- logical characteristics of jack mackerel Trachurus symmetricus larvae. Fish. Bull. 76:403—414. 1980. Changes in body measurements of larval northern anchovy, Engraulis mordax, and other fishes due to han- dling and preservation. Fish. Bull. 78:685-692. 1986. Starvation-induced mortality of young sea-caught jack mackeral, Trachurus symmetricus, determined with his- tological and morphological methods. Fish. Bull. 84:1-17. Theilacker, G. H., and Y. Watanabe. 1989. Midgut cell height defines nutritional status of labo- ratory raised larval northern anchovy, Engraulis mordax. Fish. Bull. 87:457-469. Tucker, J. W., and A. J. Chester. 1984. Effect of salinity, formalin concentration and buffer on quality of preservation of southern flounder tPara- lichthys lethostigma) larvae. Copeia 1984:981-988. Umeda, S., and A. Ochiai. 1975. On the histological structure and function of diges- tive organs of the fed and starved larvae of the yellowtail, Seriola qumqueradiata. [In Jap., Engl, summ.l Jpn. J. Ichthyol. 21:213-219. Vastano, A. C, L. S. Incze, and J. D. Schumacher. 1992. Observation and analysis of fishery processes: larval pollock at Shelikof Strait, Alaska. Fish. Ocean. 1 :20-3 1 . Wilkinson, L. 1988. SYSTAT: the system for statistics. SYSTAT, Inc. Evanston, IL, 822 p. Yin, M. C, and J. H. S. Blaxter. 1987. Feeding ability and survival during starvation of marine fish larvae reared in the laboratory. J. Exp. Mar. Biol. Ecol. 105:73-83. Abstract. — Dolphins (Delphin- idae) have been killed incidentally by the purse-seine fishery for yel- lowfin tuna, Thunnus albacares, in the eastern tropical Pacific since at least 1959. Annual estimates of the number of dolphins killed from each stock are used by the National Marine Fisheries Service in mak- ing management decisions about the population status of affected stocks. Mortality estimates from the period with the greatest kill of dolphins, 1959-72, are important for estimates of the level of deple- tion of these stocks from their unexploited population sizes. A re- definition of the geographical boundaries of offshore stocks of pantropical spotted dolphins, Sten- ella attenuata, makes it necessary to estimate annual kill for these newly defined stocks for 1959-72. I estimated the number of dolphins killed annually from 1959 to 1972 for the northeastern and western/ southern stocks of spotted dol- phins, using the methods of Lo and Smith ( 1986 ). I also revised the es- timates of annual kill for the east- ern and whitebelly stocks of spin- ner dolphins, S. longirostris, by cor- recting minor problems in previous data and analyses. Additionally, I estimated a coefficient of variation (CV) for each stock-specific esti- mate of incidental kill, which had not previously been done. Esti- mates of total kill were similar to previous estimates: 4.9 million dol- phins are estimated to have been killed by the purse-seine fishery over the fourteen year period con- sidered here, an average of 347,082 per year. Nearly all of the fisheries kill of pantropical spotted dolphins was of the northeastern stock, to- taling 3.0 million (211,612 per year). Estimates of kill for the east- ern stock of spinner dolphins were similar to previous estimates, to- taling 1.3 million (91,739 per year). As expected, CVs of the kill for each stock were higher than those previ- ously reported for the total kill. Revised estimates of incidental kill of dolphins (Delphinidae) by the purse-seine tuna fishery in the eastern tropical Pacific, 1959-1972 Paul R. Wade Scnpps Institution of Oceanography University of California, San Diego LaJolla. CA 92093 Southwest Fisheries Science Center* National Marine Fisheries Service. NOAA RO. Box 27 1 , La Jolla. CA 92038 Manuscript accepted 22 September 1994. Fishery Bulletin 93:345-354 (1995). Dolphins (Delphinidae) have been killed incidentally by the purse- seine fishery for yellowfin tuna, Thunnus albacares, in the eastern tropical Pacific (McNeely, 1961) since at least 1959 (Perrin, 1969). Purse seiners catch tuna by locat- ing and capturing dolphin schools, taking advantage of an association between these species (Au, 1991). In spite of attempts to release dolphins alive using a procedure called the backdown (Barham et al., 1977), dolphins are killed when they be- come entangled in the net. Dolphins from several species are killed; the majority represent either pan- tropical spotted dolphins, Stenella attenuata, or spinner dolphins, Stenella longirostris. Several stocks of each species are impacted. Annual estimates of the number of dolphins killed from each stock are used by the National Marine Fisheries Service (NMFS) in mak- ing management decisions about the population status of affected stocks. For example. Wade (1993) used annual estimates of mortality and variance in mortality to con- clude that eastern spinner dolphins, Stenella longirostris orientalis, were likely below 60% of their unex- ploited population size in 1959. This led to the listing of eastern spinner dolphins as a depleted species un- der the U.S. Marine Mammal Pro- tection Act.1 During the period of greatest dolphin mortality, 1959- 72, the kill of spotted dolphins was estimated to be twice that of spin- ner dolphins (Smith, 1983). There- fore, it is also important to investi- gate the management status of stocks of spotted dolphins. Wade (1993) showed that the estimated decline of the eastern spinner dol- phin was mostly due to the early period of high mortality. Thus, esti- mates of incidental kill from 1959 to 1972, along with a measure of their uncertainty, are crucial for assessing whether spotted dolphin stocks are also depleted. Recently, Dizon et al. (1994) es- tablished new geographical bound- aries for the offshore stocks of pantropical spotted dolphins (Fig. 1) on the basis of a reexamination of cranial morphology (Perrin et al., 1994). Estimates of the number of spotted dolphins killed from each stock must be revised to reflect this stock structure. Therefore, my first objective was to estimate annual kill of the northeastern and west- : Address for correspondence. Federal Register Vol. 58, No. 164, August 26. 1993 (58 FR 45066). 345 346 Fishery Bulletin 93(2), 1995 ern/southern stocks of offshore spotted dolphins for 1959-72, by using the methods of Lo and Smith (1986). My second objective was to revise estimates of annual kill for the eastern and whitebelly stocks of spinner dolphin by correcting minor problems in previous data and analyses. My final objective was to estimate variances for these stock-specific mor- tality estimates, which has not previously been done. Background The number of purse-seine sets capturing dolphins ("dolphin sets" or "sets") is known from fishing ves- sel logbooks for every year since 1959 (Punsley, 1983). Data on mortality per set (MPS) of dolphins have been collected by scientists on tuna purse seiners since 1964 (Smith and Lo, 1983). A formal observer program to collect MPS data was started by NMFS in 1971 (Edwards, 1989). Estimates of incidental dolphin mortality were first presented during work- shops2,3 to assess the status of impacted dolphin stocks and were first published by Smith ( 1983). The most recent estimates of dolphin mortality for 1959- 72 are from Lo and Smith (1986). Since 1979, the Inter-American Tropical Tuna Commission (IATTC) has been responsible for esti- mating the number of dolphins killed from each stock (IATTC, 1989). At the request of NMFS, IATTC pro- vided revised estimates of kill for the northeastern stock of spotted dolphin for the years 1979 to 1992. 4 Additionally, they revised the estimates for 1973 to 1978, last calculated by Wahlen ( 1986). IATTC chose not to revise estimates for 1959 to 1972, citing the scarcity of observer data on MPS, the lack of a formal observer program prior to 1971, and potential biases in the data.5 However, the num- bers of sets made during that period are known with high precision (Punsley, 1983). Lo and Smith (1986) presented a method of analysis that should provide accurate estimates of kill for 1959-72, given certain important but reasonable assumptions. Therefore, I used that method to estimate the number of dolphins killed in each stock annually for the years 1959 to 1972. 2 Anonymous, 1976. Report of the Workshop on stock assessment of porpoises involved in the eastern Pacific yellowfin tuna fish- ery. NOAA, Natl. Mar. Fish. Serv., SWFC Admin. Rep. LJ-76-29. 3 Smith, T. (ed.). 1979. Report of the status of porpoise stocks workshop (August 27-3 1, 1979, La Jolla, Ca. ). NOAA, Natl. Mar. Fish. Serv., SWFC Admin. Rep. LJ-79-41, 120 p. 4 Estimates provided to National Marine Fisheries Service by J. Joseph, Director, IATTC, La Jolla, CA, 18 May 1993. 5 Joseph, J., director, IATTC, La Jolla, CA, 17 February 1993, in a letter addressed to Michael Payne at the NMFS Office of Pro- tected Resources, Silver Spring, MD. Lo and Smith ( 1986) estimated the variance of the total kill of dolphins in each year, but uncertainty in prorating that total to individual stocks has not pre- viously been accounted for. In this study, I include uncertainty of the species and stock proportions by bootstrapping the variance estimates (Efron, 1982) instead of using the analytical estimates of Lo and Smith (1986). This procedure allows this source of variance to be correctly included for the first time in assessments of the status of these dolphin stocks. Methods Lo and Smith ( 1986) formulated a model of total dol- phin kill, 7), as: 2 2 2 Tt-ZuzSlj R"jk xtuk , i=\j=\k=\ (i) where Rtijk = estimated mortality-per-set of dolphins in year t and stratum ijk; Xti ■ , = the number of dolphin sets in year t and stratum ijk, and where strata were defined as i = 1 for large vessels (capacity >600 tons), 2 for small (capacity <600 tons); j = 1 for successful yellowfin tuna catch (>l/4 ton); 2 for unsuccessful catch (600 tons, small is <600 tons), and by catch of yellowfin tuna (successful is >l/4 ton, unsuccessful 600 tons carrying capacity) and 2 for small vessels (<600 tons carrying capacity),,/ equals 1 for successful set (>l/4 ton yellowfin tuna) and 2 for unsuccessful set („., R. ■,,■,, and R. respectively. •22- ■ill' "•12" Discussion Nearly all the mortality of spotted dolphins was ob- served in the northeastern stock (Table 4) because very few dolphin sets were located outside the north- eastern area prior to 1969 (Punsley, 1983). The few sets that occurred outside this area prior to 1968 were sets that were not far offshore but were south of the southern boundary of the stock area at 5°N (Punsley, 1983). Consequently, there were few observations of MPS in western/southern area except in the area south of 5°N and north of the Galapagos (Fig. 1). Al- though this should have little effect on the estimates for the northeastern stock, estimates of mortality for the western/southern stock were not based on many actual observations of MPS of spotted dolphins in the western/southern area. There was complete knowledge of the number of dolphin sets within the western/southern area, but the estimates of mortal- ity for that stock are based on the assumption that MPS was the same in both stock areas. Annual mor- tality estimates for the western/southern stock, though relatively small, may therefore be biased. In Wade: Estimates of incidental kill of dolphins by the purse-seine tuna fishery 351 areas corresponding to the western/southern area, MPS rates were as much as 100% greater than those in the area corresponding to the northeastern area during 1973-76 and 1977-78; significant areal dif- ferences were found in 1977-78 (Wahlen, 1986). If similar differences in MPS by area existed during 1959-72, my estimates of mortality for western/ southern spotted dolphins are negatively biased. For the same reason, my mortality estimates for whitebelly spinner dolphins may also have a nega- tive bias. Observations of MPS of whitebelly spinner dolphins came only from the region of overlap with eastern spinner dolphins; no observations of MPS were from the outside region west of 120°W where whitebelly spinner dolphins are known to occur and where significant fishing effort occurred in 1970, 1971, and 1972 (Punsley, 1983). The three trips observed prior to 1971 were not part of an established data collection program and, therefore, may have been biased observations. In 1965 and 1968, two trips with tuna boats were ob- served by scientists, who collected dolphin specimens and also recorded MPS data (Smith and Lo, 1983). These data were not based on random samples, but there is no obvious reason why the data from tuna vessels on which scientists were allowed to collect specimens would tend to have different mortality rates. However, it is not certain a priori in which di- rection bias would have occurred. Data from the third Table 3 Average numbers of dolphins killed (M) in purse seine sets in the eastern tropical Pacific by year for the 20 observed trips between 1964 and 1972, for small (<600 tons carry- ing capacity) and large (>600 tons carrying capacity) ves- sels making successful (>l/4 ton yellowfin tuna) and un- successful ( 51 • 52 42 "' «23r *. • ••5-5 56 -50°N Figure 1 Survey stations of Japan-U.S. cooperative longline surveys in Alaskan waters ( 1980-89). Surveys were not conducted in the Bering Sea (B-II, B-III, and B-IV) during 1980 and 1981 seasons. (•) = stations where killer whales, Orcinus orca, were not encountered; (A) = stations where whales were encountered (stations 10, 19, and 83 killer whales were observed but no depredation occurred). B = Bering Sea, WA = Western Aleutian Islands, EA = Eastern Aleutian Islands, SH = Shumagin Islands, CH = Chirikof Island, KO = Kodiak Island, YA = Yakutat, SE = Southeast Alaska. tification of species and size offish consumed by killer whales; and 4) quantification of the amounts of longline catch lost to killer whales. Materials and methods Stations for the Japan-U.S. longline research sur- vey in Alaskan waters were established by the Na- tional Research Institute of Far Seas Fisheries, Fish- eries Agency of Japan, and the National Marine Fish- eries Service (NMFS), Alaska Fisheries Science Cen- ter. In 1980 and 1981, 76 stations were fished, exclud- ing areas B-II, B-III, and B-IV (29 stations) in the Bering Sea (Fig. 1). Beginning in 1982, the number of stations (which represent 11 major fishing areas) in- creased to 108 to include the additional Bering Sea sta- tions (Sasaki, 1985; Fig. 1). Surveys were conducted between May and September each year (1980-89). Weather permitting, one station was fished per day. The research vessels selected for the surveys were chartered Japanese commercial longline vessels that had been used for previous sablefish and Pacific cod fishing operations in the North Pacific Ocean. The bottom longline was 16 km long and consisted of 160 "hachis" (skates). Each hachi was 100 m long and contained 45 hooks which were spaced 2 m apart. Gangion lengths were 1.2 m. Each hook was baited with squid (total number of hooks=7,200). The hook (standard type: Tara [=cod] no. 18) was 74 mm in length and 21 mm in width. The depth at which fish were caught was estimated by measuring the depth of water under the vessel with an echo sounder at every fifth hachi. The catch was recorded by estimat- ing the numbers of species or species groups for each hachi. The total catch of the major species was weighed to the nearest gram. Total length (TL) or fork length (FL) was measured for each species to the nearest millimeter. Details of the survey meth- ods and longline gear are described in Yano4,5. 4 Yano, K. 1989. Japan-U.S. joint survey for stock assessment of sablefish and Pacific cod resources in 1988. Report of the North- ern Groundfish Section, Japan Scientific Council on the continued on next page Yano and Dahlheim: Depredation of bottomfish on longline catches by Orcinus orca 357 Between 1980 and 1989, stations where killer whales were present were recorded. During vessel surveys in 1988, depredation rates by killer whales were quantified. During the 1988 surveys, as the groundline was retrieved, fish that had been dam- aged or partially consumed by killer whales were iden- tified by remains left on the hook (e.g. heads, lips, or gills ). In addition, head length ( HL ) or maxillary length (ML) measurements were collected for each damaged fish. Head length (mm) was measured from the most anterior point of the snout of the upper jaw to the most distant point of the posterior margin of the operculum. Maxillary length (mm) was measured along the long- est margin on the premaxillary side. Fork length (FL) for sablefish and arrowtooth flounder, Atheresthes stomias, and total length (TL) for Greenland turbot were also measured. Fork length and TL were mea- sured from the tip of the snout to the central point of the caudal fin. The relationships between HL and FL or TL and between ML and FL or TL were calculated by the least-square method following the equation: Y = a + bX, where Y is FL or TL (mm), X is HL or ML (mm), and a and b are constants. Average lengths of damaged and undamaged fish were compared by using £-tests with a significance level of 0.05. To obtain killer whale depredation rates for each station, direct counts were made of the remaining heads, lips, or gills that were brought aboard the research vessel. Empty hooks did not provide evi- dence of killer whale depredation and were not in- cluded in the analysis. Killer whale depredation rates were calculated by two methods. RNT is the depredation rate calculated from the number of fish preyed upon as a percent- age of the total number of fish landed per fishing trip. RNS is the depredation rate calculated from the number of fish preyed upon as a percentage of the number offish landed from the time the whales were first observed to depredate them. The two depredation rates were calculated for each station as RNT (%) = NP/(NT+NP) x 100 and 4 1 continued) Fisheries Resources (GSKi, Tohoku National Fish- eries Research Institute. Hachinohe Branch, 25-259 Shim- omekurakubo, Samemachi. Hchinohe, Aomori 031, Japan, No. 22, p. 145-173. [In Japanese.] 5 Yano, K. 1990. Report on sablefish and Pacific cod resource de- velopmental survey, 1988. Japan Marine Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, JAMARC Rep. S63/No.ll, 195 p. [In Japanese.] RNS (%) = NP/(NS+NP) x 100, where NP is the number of depredated fish, counted by the remaining heads, lips, or gills; NT is the total number offish landed with no evidence of killer whale depredation; and NS is the number of fish landed without any physical evidence of depredation counted from the time the whales were first observed to dep- redate fish (determined by observing heads, lips, or gills on the groundline). Other depredation rates (REA and REY) were ob- tained by averaging the catch rates (number offish per hachi) obtained during the 1980 and 1988 sur- veys. REA is the depredation rate calculated from the average catch rates for all years at each station. REY is the depredation rate calculated from the av- erage catch rates for all stations for each year. The average catch rates (REA and REY) were obtained through the following formula: REA or REY(%) = 100 - (AJB x 100), where A is the average catch rate during whale dep- redation for all years at each station (for REA ) or all stations for each year (for REY), and B is the aver- age catch rate with no killer whale depredation for all years at each station (for REA) or all stations for each year (for REY). We tested for differences in the average catch rates for REA and REY by using the one-way analysis of variance (ANOVA). The annual survey reports of the Japan Marine Fishery Re- sources Research Center (JAMARC) by Inada and Sasaki,6 Onoda and Sasaki,7 Mizogoshi and Sasaki,8 Funato and Sasaki,9 Iwami and Sasaki,10 Fukui and Sasaki,11 Takeda and Sasaki,12 Takeda,13 and Yano5 provided fish catch data for the study. 6 Inada, T., and T. Sasaki. 1981. Report on sablefish and Pacific cod resource developmental survey, 1980. Japan Marine Fish- ery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, To- kyo 102 Japan, JAMARC Rep. S55/No. 18, 156 p. [In Japanese.] 7 Onoda, M., and T. Sasaki. 1982. Report on sablefish and Pa- cific cod resource developmental survey, 1981. Japan Marine Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 1 02 Japan, JAMARC Rep. S56/No.l5, 140 p. [In Japanese.] 8 Mizogoshi, H., and T Sasaki. 1984. Report on sablefish and Pacific cod resource developmental survey, 1983. Japan Marine Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, JAMARC Rep. S58/No.l3, 219 p. [In Japanese.] 9 Funato, K, and T Sasaki. 1985. Report on sablefish and Pa- cific cod resource developmental survey, 1982. Japan Marine Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, JAMARC Rep. S57/No.l3, 191 p. [In Japanese.] 10 Iwami, T, and T Sasaki. 1985. Report on sablefish and Pacific cod resource developmental survey, 1984. Japan Marine Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, JAMARC Rep. S59/No.l2, 223 p. [In Japanese.] 11 Fukui, J., and T Sasaki. 1988. Report on sablefish and Pacific cod resource developmental survey, 1985. Japan Marine continued on next page 358 Fishery Bulletin 93(2). 1995 Monetary losses incurred during fishing operations were calculated from data for product (kg) and from price per kilogram (yen) of sablefish, Greenland tur- bot, and arrowtooth flounder, contained in the annual survey reports of JAMARC by the following formula: Monetary loss (yen and US dollar) = (Average product value) x (depredation rate [RNT, RNS, REY or REA])/100, where average product value is the average of prod- uct values calculated by product per operation and by price per kilogram in each area and each year. Results Stations with killer whales Between 1980 and 1989, killer whales were reported at 25 stations (Fig. 1 ). Eighteen of these stations were in the eastern Bering Sea (B), five stations were near the eastern Aleutian Islands (EA), and one station each was near the Shumagin Islands (SH) and off Kodiak Island (KO). Fishery interactions consistently occurred at several of the sampling locations (Table 1). The highest frequency of killer whale interactions was reported for two areas in the Bering Sea: B-I (stations 31, 32, and 33) and B-II (stations 22, 25, 26, and 27) (Table 1, Fig. 1). Killer whale group size ranged between 4 and 50 animals during the 1988 survey (Table 2). From the 1988 field observations and photographs of killer whales, there appears to be three killer whale groups involved in the Bering Sea fishery interactions (BS1, BS2, and BS3 in Table 2; Yano and Dahlheim14). Depredation by killer whales During the 1988 survey, when killer whales were observed around the vessel, the hooks on the re- 11 (continued) Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, JAMARC Rep. S60/No.l2, 197 p. [In Japanese.] 12 Takeda, Y., and T. Sasaki. 1988. Report on sablefish and Pa- cific cod resource developmental survey, 1986. Japan Marine Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, JAMARC Rep. S6I/N0. 12, 179 p. [In Japanese.] 13 Takeda, Y. 1988. Report on sablefish and Pacific cod resource developmental survey, 1987. Japan Marine Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, JAMARC Rep. S62/No.ll, 191 p. [In Japanese.] 14 Yano, K., and M. E. Dahlheim. Behavior of killer whales, Orcinus orca, during longline fishery interactions in the south- eastern Bering Sea and adjacent waters. Fisheries Science (unpubl. manuscript). trieved groundline frequently contained only fish heads, lips, or gills (Fig. 2), providing evidence that killer whales were responsible for depredation of longline-caught fish. Occasionally, whole fish showed extensive rake marks made by killer whale teeth (Figs. 3 and 4). Whales consumed longline catches of sablefish, Greenland turbot, arrowtooth flounder, and Pacific halibut, the latter remaining whole but show- ing extensive rake marks. Two heads of searcher were also noted. Other species offish caught on longlines but not eaten by killer whales included Pacific cod, grenadier, Coryphaenoides acrolepis, rockfish, Se- bastes spp., walleye pollock, Theragra chalcogramma, and shortspine thornyhead, Sebastolobus alascanus. Depredation rates Killer whale depredation rates calculated by four different methods showed that the rates based on averages of total catch (RE A and REY) were higher than the rates calculated directly from damaged fish (RNT and RNS). Based on our sampling, depreda- tion rates for Greenland turbot were highest, followed by depredation rates for sablefish, arrowtooth floun- der, and Pacific halibut (Table 3). Depredation rates of about 10% or more (based on both RNT and RNS values) were noted for stations 30, 33, 25, 22, and 20. The highest RNT and RNS values were found at station 25 for Greenland turbot and sablefish and at station 22 for arrowtooth flounder. Arrowtooth floun- der typically had lower depredation rates than those calculated for Greenland turbot or sablefish. How- ever, a large number of damaged arrowtooth floun- der (15-72 specimens) were present in the catch at stations 30, 17, 20, 22, and 25. Annual catch rates (total number of fish caught per hachi) of sablefish, Greenland turbot, and arrowtooth flounder for each station in the EA, B-I, B-II, B-III, and SH areas (Fig. 1) were used to calcu- late depredation rates for all years at each station (REA) and for all stations for each year (REY). Twenty-one stations had fishery interactions involv- ing killer whales during the period 1980-88 (Table 4). Depredation rates (REA) calculated from the av- erage fishery catch rates for years with and without killer whale predation showed that the average catch rates of sablefish and Greenland turbot were signifi- cantly lower when killer whales were present than when killer whales were absent (ANOVA, P<0.01). However, for arrowtooth flounder average catch rates were independent of killer whale depredation (ANOVA, P>0.05). In addition average catch of arrowtooth flounder was similar among years regard- less of the presence or absence of whales (Table 4). Depredation rates (REA) calculated from the average Yano and Dahlheim: Depredation of bottomfish on longline catches by Orcinus orca 359 Table 1 Areas and stations where killer whales, Orcinus orca, were encountered (X) during Japan-U.S. cooperative longline surveys (1980 to 1989). B-II and B-III areas were not surveyed (— ) in 1980 and 1981. Asterisks (*) indicate the stations where killer whales were encountered but no depredation occurred. Area' EA EA EA EA EA B-l B-l B-l B-l B-l B-II B-II B-II B-II B-II B-II B-II B-II B-II B-III B-III B-III B-III SH KO Total per St. no. 35 36 37 38 59 30 31 32 33 34 17 18 19 20 22 25 26 27 28 7 10 12 13 65 83 year Year 1980 1981 1982 1983 1984 1985 1986 1987 X X X X X X X 1 X X X X X X X X X X X X X X X 8 X X X X X X X 19882 1989 X X X X X* X X X X X X* X X* 15 X X X X Total per station 1 1 3 1 1 2 6 4 7 2 2 1 1 3 3 6 5 3 1 1 1 2 1 1 1 60 EA = Eastern Aleutian Islands; B = Bering Sea; SH = Shumagin Islands; KO = Kodiak Island, see Figure 1 for areas. Detailed observations of killer whale predation were documented. catch rates for years with and without killer whale pre- dation ranged from 9.2 to 92.4% for sablefish, from 2.2 to 90.4% for Greenland turbot, and from 1.4 to 80.3% for arrowtooth flounder (Table 4). Between-year comparisons (REY) for catches of all species at the same station (except for 1982 of sable- fish) indicate catches were lower in years with killer whale depredation (Table 5). The average catch rates of sablefish and Greenland turbot for stations with killer whale depredation were significantly lower than in stations without depredation (ANOVA, P<0.05). However, the average catch rate of arrowtooth flounder (for stations with killer whale depredation) was not significantly lower than that for stations without killer whale depredation (ANOVA, P>0.05). Depredation rates (REY) calcu- lated from the average catch rates for stations with and without killer whale predation ranged from 33.4 to 84.1% for sablefish, from 53.3 to 82.6% for Greenland turbot, and from 17.0 to 70.8% for arrowtooth flounder (Table 5). REY values calculated from average catch rates for years with and without killer whale depredation were slightly lower than REA values (Table 6). Predation rates based on the average catch landed (REA and REY values) were higher than those rates ( RNT and RNS values) calculated directly from count- ing heads, lips, and gills of fish remains on the deck during the 1988 survey (Table 6). Depredation rate, based on the four different methods of calculations (i.e. RNT, RNS, REY, and REA), suggested that whales took 14-60% of the sablefish, 39-69% of the Greenland tur- bot, and 6-42% of the arrowtooth flounder. Size of fish consumed by killer whales The size of the fish taken by whales was determined by measurements of HL or ML. The relationships 360 Fishery Bulletin 93(2), 1995 Table 2 Stations where killer whales, Orcinus orca, were encountered during the 1988 Japan-U.S. longline research survey. Area' St. no. Date Operating depth (m) Hachi2 Estimated Arrival number when number of time of killer whales whales killer whales arrived Fishing depth of retrieved hachi (m) First hachi number with evidence of killer whale depredation Fishing depth of first hachi number that received killer whale depredation (m) Group3 identified EA 37 17 June 160-744 40-50 13:30 50 380 54 440 ? B-I 30 23 June 144-480 20-30 10:25 68 380 76 390 1,3 B-I 31 27 July 110-820 5-6 12:15 120 550 123 600 2 B-I 33 22 June 122-812 20-30 8:40 1 800 7 780 1,3 B-II 17 14 July 174-980 8-10 11:05 86 210 95 300 1 B-II 18 15 July 133-215 8-10 8:30 8 136 24 137 1 B-II4 19 17 July 150-245 4 13:16 156 238 — — 2 B-II 20 18 July 160-820 8-10 9:30 42 160 117 440 2 B-II 22 28 June 197-680 15-30 8:45 1 680 6 670 1 B-II 25 24 June 430-613 10-20 8:30 1 610 6 610 2 B-II 26 21 July 485-720 15-20 8:10 1 485 31 509 ? B-III 7 08 July 130-155 10-15 10:50 46 145 110 150 2 B-nr* 10 10 July 167-562 — 8:20 1 167 — — ? SH 65 30 July 135-765 6-8 13:08 127 455 133 660 1 KC 83 18 August 360-750 7-8 11:00 65 520 — — ? 1 EA = Eastern Aleutian Islands; B = Bering Sea; SH = Shumagin Islands; 2 A length of groundline equal to 100 m. 3 See Yano and Dahlheim (See Footnote 14 in text). 4 No predation observed at station. KO = Kodiak Island, see Figure 1 for areas Figure 2 Heads, lips, and gills of partially consumed sablefish, Anoplopoma fimbria, Greenland turbot, Reinhardtius hippoglossoid.es, and arrowtooth flounder, Atheresthes stomias, at station 22. Scale represents 300 mm. Yano and Dahlheim: Depredation of bottomfish on longlme catches by Oronus orca 361 Figure 3 Depredated sablefish, Anoplopoma fimbria, at station 33. (A) Whole fish with rake marks made by killer whale teeth; (B) partially consumed fish showing head, lips, and gills. Scale represents 300 mm. 362 Fishery Bulletin 93(2), 1995 Figure 4 Partially consumed Greenland turbot. Rein- hardtius hippoglossoid.es, and arrowtooth flounder, Atheresthes stomias. Scales repre- sent 300 mm. (A) Arrowtooth flounder with rake marks made by killer whale teeth at station 22; (B) damaged Greenland turbot at station 17; (C) head and lips of partially consumed Greenland turbot at station 22. Yano and Dahlheim: Depredation of bottomfish on longline catches by Oranus orca 363 Table 3 Killer whale, Orcinus orca, predation rates for 1988 on sablefish, Anoplopoma fimbria, Greenland turbot, Reinhardtius hippoglossoid.es, arrovvtooth flounder, Atheresthes stomias, and Pacific halibut, Hippoglossus stenolepis. NPF: number of dam- aged fish; RNT(%) = (number of partially consumed fish, ADAnumber of total catch fish) x 100; RNS (%) = (NP)/(number offish (remaining heads, lips, or gills seen) counted from the start of depredation by killer whales) x 100. Area' St. no. Sablefish Greenland turbot Arrowtooth flounder Pacific halibut NPF RNT RNS NPF RNT RNS NPF RNT RNS NPF RNT RNS EA 37 69 14.11 14.53 33 30.00 30.00 1 2.04 5.88 0 0.00 0.00 B-I 30 13 38.24 43.33 3 60.00 60.00 19 14.29 61.29 0 0.00 0.00 B-I 31 7 2.57 17.07 6 14.63 54.55 0 0.00 0.00 0 0.00 — B-I 33 27 9.68 9.93 3 9.09 10.34 0 0.00 0.00 0 0.00 0.00 B-II 17 9 7.38 9.47 7 16.28 17.07 15 3.50 17.65 0 0.00 0.00 B-II 18 1 0.26 0.26 0 — — 3 0.59 0.59 1 0.72 0.72 B-II 20 25 26.04 71.43 27 71.05 77.14 27 7.42 26.21 0 0.00 0.00 B-II 22 8 5.76 6.20 9 37.50 37.50 72 19.46 19.62 0 0.00 0.00 B-II 25 32 62.75 62.75 21 95.45 95.45 15 12.20 12.20 1 8.33 8.33 B-II 26 3 0.64 0.89 11 20.75 23.91 1 8.33 8.33 0 — — B-III 7 0 0.00 — 0 — — 1 0.77 1.64 4 0.57 4.04 SH 65 5 0.28 2.69 0 — — 0 0.00 0.00 0 0.00 — Average 13.98 21.69 39.42 45.11 5.72 12.78 0.87 1.46 1 EA = Eastern Aleutian Is ands; B = Bering Sea; SH = Shumagir Islands, see Figure 1 for areas. Figure 5 Size of partially consumed sablefish, Anoplopoma fimbria. (A) The relationship between head length (HL) and fork length ( FL ); ( B ) the relationship between maxillary length (ML) and fork length (FL). FL = 97.26 * 3.26 x HL (r = 0.975, n = 149) 1000 A •/ . length (mm) 00 O O 5 60° u_ *i •• • • 120 160 200 240 280 Head length (mm) FL = 163 78 * 902 * ML (r = 0 979. n.113) 1000 B Fork length (mm) I 8 • • /* • 40 60 80 100 Maxillary length (mm) 364 Fishery Bulletin 93(2), 1995 Table 4 Average catch rates (number offish ser hachi ) for years with and without killer whale, Orcinus orca, predation ( 1980-88), and calculated REA [REA = 100- - C (%)]. A = predation occurred; B = = no predation occurred; C = A/B x 100 (%) ; AO = average when C>100% are emitted, ind when REA<0 are omittec . Area' St. no. Sablefish Greenland turbot Arrowtooth flounder Frequency2 A B C REA A B C REA A B C REA D ND EA 35 0.20 2.02 9.90 90.10 0.02 0.15 13.33 86.67 0.37 0.24 154.17 -54.17 1 8 EA 36 0.17 0.35 48.57 51.43 0.01 0.04 25.00 75.00 0.31 0.14 221.43 - -121.43 1 8 EA 37 5.41 7.65 70.72 29.28 0.72 1.92 37.35 62.65 0.30 0.36 83.33 16.67 2 7 EA 59 1.90 3.66 51.91 48.09 0.01 0.01 100.00 0.00 0.06 0.20 30.00 70.00 1 8 B-I 30 4.22 6.18 68.28 31.72 0.25 1.32 18.94 81.06 0.73 0.74 98.65 1.35 2 7 B-I 31 3.02 6.63 45.55 54.45 0.46 3.26 14.11 85.89 0.37 0.32 115.63 -15.63 5 4 B-I 32 1.34 6.35 21.10 78.90 0.23 0.37 62.16 37.84 0.20 0.49 40.82 59.18 4 5 B-I 33 2.50 5.45 45.87 54.13 0.19 1.88 10.11 89.89 0.20 0.17 117.65 -17.65 7 2 B-I 34 2.89 8.81 32.80 67.20 0.37 2.09 17.70 82.30 0.81 0.40 202.50 - -102.50 2 7 B-II 17 0.76 5.66 13.43 86.57 0.28 0.86 32.56 67.44 2.68 0.75 357.33 - -257.37 6 1 B-II 18 2.54 2.80 90.71 9.21 — — — — 3.18 0.64 496.88 - -396.88 1 5 B-II 20 2.94 3.58 82.12 17.88 0.32 1.79 17.88 82.12 1.06 1.26 84.13 15.87 3 4 B-II 22 0.53 6.94 7.64 92.36 0.13 1.05 12.38 87.62 1.69 1.09 155.05 -55.05 3 4 B-II 25 1.38 6.34 21.77 78.23 0.08 0.83 9.64 90.36 0.34 0.95 35.79 64.21 4 3 B-II 26 2.25 6.87 32.75 67.25 0.45 0.46 97.83 2.17 0.09 0.06 150.00 -50.00 4 3 B-II 27 4.80 11.09 43.28 56.72 0.68 0.78 87.18 12.82 0.75 0.07 70.09 29.91 4 3 B-II 28 1.91 6.73 28.38 71.62 0.39 0.12 325.00- 225.00 0.39 1.98 19.70 80.30 6 B-III 7 — 0.02 — — — — — — 0.81 0.14 578.57 - -478.57 6 B-III 12 1.03 4.21 24.47 75.53 0.34 2.33 14.59 85.41 0.75 1.42 52.82 47.18 6 B-III 13 1.65 6.06 27.23 72.77 0.23 0.86 26.74 73.26 0.58 0.93 62.37 37.63 6 SH 65 11.36 10.86 104.60 -4.60 — — — — 1.23 0.15 820.00 - -720.00 8 Average 2.64 5.63 43.55 56.45 0.29 1.12 51.25 48.75 0.80 0.64 187.95 -87.95 2.6 5.3 (AO) (40.34) (59.66) (31.09) (68.91) (57.77) (42.23) ' EA = Eastern Aleutian Islands; B = Bering Sea; SH = Shumagin Islands, see Figure 1 for areas. 2 Frequency af sampling. D = = depredation; ND = no depredation between HL and FL and between ML and FL for sablefish, Greenland turbot, and arrowtooth floun- der are shown in Figures 5—7. Length-frequency distributions from the 1988 sur- vey data for sablefish, arrowtooth flounder, and Greenland turbot are shown in Figures 8-10. Each fig- ure depicts three different length-frequency distribu- tions for each species: 1) those for all areas fished (EA, B-I, B-II, B-III, and SH) including stations that had reports of killer whale interference with longline op- erations without estimated length specimens (all ar- eas; Figs. 8A, 9A, and 10A); 2) size distributions of un- damaged fish for all stations (station numbers are pre- sented in Table 3) that reported killer whale depreda- tion (all stations; 8B, 9B, and 10B); and 3) size distri- bution of partially consumed fish and whose estimated length was based on the calculations made through the above formula of HL and ML (partially consumed fish; Figs. 8C,9C, and 10C). Average length of sablefish was 635.7 mm FL for all areas fished, 607.5 mm FL for undamaged fish at stations where killer whale depredation was evident, and 633.1 mm FL for the partially consumed fish (Fig. 8, A, B, and C). Significant differences were found between average lengths of damaged fish and undamaged fish for all stations where killer whale predation was evident (£=19.65, P<0.05). However, no significant differences were found between aver- age lengths of damaged fish and undamaged fish for all areas fished (£=0.43, P>0.05). The average length of damaged fish was significantly larger than that of undamaged fish at stations where killer whale dep- redation was evident (£=19.65, P<0. 05), but the total average length was about equal to that for all areas fished. Average length of arrowtooth flounder was 528.3 mm FL for all areas fished, 506.5 mm FL for sta- tions fished where killer whale depredation was evi- dent, and 575.2 mm FL for fish that were preyed upon. Significant differences were found between average lengths of damaged fish and undamaged fish (£=7.71 and £=10.99, P<0.05). The average size of Yano and Dahlheim: Depredation of bottomfish on longline catches by Orcinus orca 365 Table 5 Average catch rates (number offish per hachi) for stations with and without killer whale, Orcinus orca, depredation (stations indicated in Table 4), and calculated REY [REY=100-C(%)]. A = depredation occurrec ;B = no depredation occurred; 2 =A/B x 100(%);AO = average when C> 100^ are omitted, and when REY<0 are omitted. Year Sablefish Greenland turbot Arrowtooth flounder Frequency A B C REY A B c REY A B C REY D ND 1980 1.11 2.53 43.87 56.13 0.13 0.60 21.67 78.33 0.19 0.25 76.00 24.00 3 7 1981 0.51 3.20 15.94 84.06 0.48 1.24 38.71 61.29 0.19 0.26 73.08 26.92 1 9 1982 5.03 4.50 11.78 -11.78 0.30 1.18 25.42 74.58 0.14 0.48 29.17 70.83 4 17 1983 2.09 4.56 45.83 54.17 0.38 0.92 41.30 58.70 0.39 0.47 82.98 17.02 9 12 1984 2.04 9.49 21.50 78.50 0.12 0.69 17.39 82.61 0.23 0.31 74.19 25.81 3 18 1985 5.16 7.75 66.58 33.42 0.27 0.72 37.50 62.50 0.33 0.60 55.00 45.00 3 18 1986 3.52 6.69 52.62 47.38 0.36 0.77 46.75 53.25 0.47 0.67 70.15 29.85 8 13 1987 1.42 3.75 37.87 62.13 0.40 1.12 35.71 64.29 0.70 1.31 53.44 46.56 7 14 1988 2.18 4.55 47.91 52.09 0.19 0.48 39.58 60.42 1.33 1.18 112.71 -12.71 12 9 Average 2.56 5.22 49.32 50.68 0.29 0.86 33.78 66.22 0.44 0.61 69.63 30.37 5.56 13.00 AO 41.51 58.49 33.78 66.22 64.25 35.75 1 Frequency of sampling. D = depredation; ND = no depredation. partially consumed fish (Fig. 9C) was significantly larger than that reported from all areas fished (Fig. 9A; £=7.71, P<0.05) and for the stations fished where killer whales were present (Fig. 9B; t = 10.99, P<0.05). There was a bimodal length-frequency distribution for Greenland turbot (Fig. 10, A-C). Average length of Greenland turbot was 744.3 mm TL for all areas fished, 730.8 mm TL for the stations fished where depredation occurred, and 756.1 mm TL for the par- tially consumed fish. Significant differences were found between average lengths of damaged fish and undamaged fish for all stations with killer whale dep- redation (£=2.03, P<0.05 ). However, no significant dif- ferences were found between average lengths of dam- aged fish and undamaged fish for all areas fished U=1.08,P>0.05). The average length of damaged fish was significantly larger than that of undamaged fish at stations with killer whale depredation (£=2.03, P<0.05) but the total average length was about equal to that for all areas fished. Monetary loss For the years 1982-88, data were collected on the product yield of each area and operation, unit price per kilogram (commercial price when landed), and product price per operation for sablefish, Greenland turbot, and arrowtooth flounder (Table 7). The aver- age monetary loss in the total catch per operation (using 160 hachi per operation) was estimated to range from ¥96,853.7 ($717.40 [U.S. dollars] @Y135 calculated from RNT) to ¥790,934.2 ($5,858.80 cal- Table 6 Estimated depredation rate C£> calculated by remaining heads, lips, or gills (RNT and RNS) and by averaging the catch rates (REY and REA). Depredation rate Greenland Sablefish turbot Arrowtooth flounder x RNT 13.98 39.42 5.72 19.71 RNS 21.69 45.11 12.78 26.53 REY 58.49 66.22 35.75 53.49 REA 59.66 68.91 42.23 56.93 culated from REAKTable 8). The average overall loss incurred for all years at all stations (Table 9) as a result of killer whale depredation ranged from ¥402,499.6 to ¥4,667,109.6 (from $29,181.50 to $34,571.20). The total product value of the 4-month survey for each year (D in Table 9) ranged from ¥98,812,086.0 to ¥283,932,240.0 (from $731,941.40 to $2,103,201.80) and the product values per opera- tion (yearly total product value/number of stations per each survey, Pin Table 9 ) ranged from ¥950,116.2 to ¥2,629.002.2 (from $7,037.90 to $19,474.10; Table 9). The yearly loss was 0.21 to 2.96% (G in Table 9) of the total product value in survey and 3.80 to 34.22% (H in Table 9) of the product value per sta- tion (per operation). These values suggest that the rate of yearly overall loss is not large (less than 3%) in total product (survey area is extensive, ranging from the Aleutian Islands to Southeast Alaska in Figure 1 ), 366 Fishery Bulletin 93(2), 1995 TL =187.06 + 2-94 x HL (r = 0.972, n.139) A »: ~ V?' 180 220 260 Head length (mm) 01 c 800 a - 700 TL =264 46 + 7 24 x ML (r = 0 959, n = 112) B •V-". •• v •••• 4 ?:: 60 70 90 110 Maxillary length (mm! Figure 6 Size of partially consumed Greenland turbot, Reinhardtius hippoglossoides . (A) The relationship between head length (HL) and total length (TL); (B) the relationship between maxillary length (ML) and total length (TL). but the rate of yearly loss per station (per operation) is relatively large in product per station. Discussion Although killer whales range throughout Alaskan waters (Braham and Dahlheim, 1982), fishery inter- actions are restricted to the Bering Sea and Prince William Sound (Dahlheim2). In the Bering Sea, two areas, B-I and B-II, were repeatedly noted for pre- dation by killer whales on longline-caught fish. De- spite considerable fishing effort in areas outside the Bering Sea, killer-whale-longline interactions have not been reported for most of the western Aleutian Island chain, Alaska Peninsula, Gulf of Alaska, or Southeast Alaska. However, in September 1991 in Glacier Bay National Park, fishermen reported that a small number of halibut showed evidence of tooth rake marks made by killer whales and consequently were unmarketable fish (Matkin15). In Canadian waters, 85% of the commercial harvest of sablefish is taken by pot gear. There have been no reports of killer whales interfering with this pot fishery. There are, however, two isolated accounts of killer whales raiding Pacific halibut longline operations in Hecate Strait, British Columbia (Ellis16). Sablefish longlining operations also range from Washington State to cen- tral California. Records of killer whale interference with this fishery have not been found (Parks17). The only other area within Alaska where killer whales have been reported raiding longline gear is Prince William Sound. Interactions in this area are well documented (Dahlheim2; Matkin3). At least 19 15 Matkin, D. R. Box Gustavus, AK. Pers. commun., October 1991. 16 Ellis, G. Box 215, Station A, Nanaimo, B.C., Canada V9R 5K9. Pers. commun., March 1990. 17 Parks, N. Alaska Fisheries Science Center, 7600 Sand Point Way N.E., Seattle, WA 98115. Pers. commun., May 1990. Yano and Dahlheim: Depredation of bottomfish on longlme catches by Orcinus orca 367 120 160 Head length (mm) a c ± 600 FL = 66 45 * 7 23 x ML (r = 0 978. n=112) B *s^ • *s^ If 1 40 60 80 100 120 Maxillary length (mm) Figure 7 Size of partially consumed arrowtooth flounder, Atheresthes stomias. (A) The relationship between head length (HL) and fork length (FL); (B) the relationship between maxillary length (ML) and fork length (FL). killer whale pods are known to exist within the area but only two pods have been involved in fishery in- teractions. Although killer whales may frequently travel between Prince William Sound and offshore waters of the Gulf of Alaska, fishery interactions have not been reported in the waters adjacent to Prince William Sound. One encounter with killer whales was reported off Kodiak Island during this study but no depredation occurred. Whales probably learned to depredate longline-caught fish by long-term exposure to fishing activities. Accounts of killer whales feed- ing off the discard of fish-processing vessels for a period of over 30 days has been noted in the Bering Sea (Dahlheim, unpubl. data). Active depredation may begin once the whales learn to associate fishing operations with a feeding opportunity. An examination of the yearly catch data suggested that killer whales depredate 39-69% of the Green- land turbot, 14-60% of the sablefish, and 6^2% of the arrowtooth flounder. Whales took the largest fish for each species consumed. Although available, fish species not eaten by killer whales included Pacific cod, grenadier, rockfish, walleye pollock, and short- spine thornyhead. Little is known of the food habits of Bering Sea killer whales. The fish species con- sumed by the whales during this study have not been previously reported in the diet of North Pacific killer whales (Rice, 1968), perhaps because few stomachs were examined. Within- and between-year comparisons of catch rates of sablefish, Greenland turbot, and arrowtooth flounder showed that fewer fish were landed when killer whales were present. Although annual changes in fish biomass and composition by region have been reported (Yano4-5; Sasaki and Yano18), catch rates (for 18 Sasaki, T., and K. Yano. 1990. Report on Japan-U.S. joint longline survey by Tomi Maru No. 88 in the eastern Bering Sea, Aleutian Region, and Gulf of Alaska, 1988. National Re- search Institute of Far Seas Fisheries, 5-7-1 Orido, Shimizu, Shizuoka 424 Japan, 163 p. 368 Fishery Bulletin 93(2). 1995 n = 31339 » 600 c e E u O a 400 B n = 3410 n:91 I 1 501 601 701 Fork length (mm) Figure 8 Length-frequency distribution of sablefish, Anoplopoma fimbria. (A) All areas (see Fig. 1); (B) all stations fished where depreda- tion occurred; (C) calculated length (head length and maxillary length) of partially consumed fish. the 10-year period) were typically lower when killer whales were reported as present. Depredation rates based on average catch rates (REY and RE A values) were higher than those cal- culated from direct counts of damaged fish (RNT and RNS values). Calculated values of RNT and RNS did not consider empty hooks. It is possible that parts of the fish that were preyed upon were pulled off or dropped off the line as it was being retrieved. Thus the rate of predation based on a direct-count method may underestimate the overall rate of depredation. However, RNT and RNS values were used as direct evidence of depredation by killer whales. RNS val- ues indicated that killer whales actively depredate at least 22% of the sablefish, 45% of Greenland tur- bot, and 13% of the arrowtooth flounder. Large num- bers of arrowtooth flounder are found in shallower depths where killer whales do not actively prey on fish, but sablefish and Greenland turbot are found in deeper depths where active depredation has been observed (Yano4). However, a greater number of dam- aged arrowtooth flounder prevailed in the catch (higher RNS values). Depredation rates by killer whales on the U.S. domestic Bering Sea fishery could easily be higher because some vessels (due to overall size and limited range) are forced to fish repeatedly in the same area. If a particular area is in a region of high killer whale density, the vessel may experience continual problems. Reports of killer whales follow- ing vessels over short distances from one fishing area to another have been documented (Onodera19). 19 Onodera, S. Fishing master ofTomi Maru No. 88, 6-3-25 Irifune, Kushiro, Hokkaido 085 Japan. Personal commun., October 1988. Yano and Dahlheim: Depredation of bottomfish on longline catches by Orcmus orca 369 f A n= 999) 301 401 501 601 701 801 901 200 B n= 2402 100 ll. .III ...lb. 401 501 601 701 801 901 n= 110 301 401 501 601 701 801 901 Fork length (mm) Figure 9 Length-frequency distribution of arrowtooth flounder, Atheresthes stomias. (A) All areas (see Fig. 1): (B) all stations fished where depredation occurred; (C) calculated length (head length and maxillary length) of partially consumed fish. Dahlheim2 estimated that the U.S. domestic longline fishery in the Bering Sea incurred an aver- age loss of $2,300 per day during the winter of 1988, similar to the values ($928.90 in RNT and $3,373.50 in REA per operation [per day]) reported for this study. However, losses reported for this study may be underestimated. For example, monetary losses would be greater if the time spent by fishermen trav- eling from one area to another to escape whales was considered. Also the price per kilogram of sablefish is greater than that for larger fish. Since whales were shown to prefer larger fish, the actual monetary losses per operation may be greater than those reported (val- ues based on an average cost/kg). Matkin et al.20 esti- 20 Matkin, C. O., G. Ellis, O. von Ziegesar, and R. Steiner. 1987. Killer whales and longline fisheries in Prince William Sound, Alaska 1986. Alaska Fisheries Science Center, National mated sablefish losses of $34,300 to $55,500 over the entire season for the 1986 Prince William Sound sablefish longline industry. During the 4-month re- search survey, a minimum value (calculated from RNT) of $2,982.00 and a maximum value (calculated from REA) of $34,571.00 was estimated. Acknowledgments We express our sincere appreciation to T. Sasaki (Na- tional Research Institute of Far Seas Fisheries) and M. Kuroiwa (Japan Marine Fishery Resources Re- 20 (continued) Marine Mammal Laboratory, Seattle, Washington, National Marine Mammal Laboratory, 7600 Sand Point Way N.E., Seattle, WA 98115-0070. Unpubl. manuscr., contract 40ABNF6 2262, 18 p. 370 Fishery Bulletin 93(2). 1995 Table 7 Product of each area , product per operation, price per kilogram, and product price per operation for sablefish, Anoplopoma fimbria, Greenland turbot, Reinhardtius hippoglossoid.es, and arrowtooth flounder, Atheresthes stomias. B = product, C = = product per operation (C = B/A), D = price per kilogram, and E = product value aer operation (E=CxD) Sablefish Greenland turbot Arrowtooth flounder No. of operation B C D E B C D E B C D E Year Area' (A) (kg) (kg) (yen) (yen) (kg) (kg) (yen) (yen) (kg) (kg) (yen) (yen) 1982 EA 17 5,300.0 311.8 722 225,094.1 1.306.4 76.8 383 29,432.4 652.3 38.4 158 6,062.6 B-I 5 5,100.0 1,020.0 722 736,440.0 2,101.6 420.3 383 160,982.6 296.5 59.3 158 9,369.4 B-II 14 5,700.0 407.1 722 293,957.1 4,203.2 300.2 383 114,987.5 1,008.1 72.0 158 11,377.1 B-III 9 2,700.0 300.0 722 216,600.0 4,430.4 492.3 383 188,538.1 474.4 52.7 158 8,328.4 X 509.7 722 368,003.4 322.4 383 123,479.2 55.6 158 8,784.8 1983 EA 15 10,172.2 678.1 506 343,142.2 2,369.3 158.0 277 43.753.1 483.9 32.3 155 5,000.6 B-I 5 6,883.0 1,376.6 506 696,559.6 3,145.9 629.2 277 174,281.8 234.4 46.9 155 7,267.3 B-II 14 13,388.5 956.3 506 483,898.6 2,418.4 172.7 277 47,849.4 957.5 68.4 155 10,600.6 B-III 8 3,356.8 419.6 506 212,317.6 2,829.5 353.7 277 97,972.5 564.8 70.6 155 10,943.4 X 857.7 506 433,996.2 328.4 277 90,966.8 54.5 155 8,447.5 1984 EA 17 11,303.0 664.9 865 575,123.2 1,665.8 98.0 417 40,860.4 323.9 19.1 154 2,933.9 B-I 5 7,378.3 1,475.7 865 1,276,445.9 2,068.1 413.6 417 172,482.9 253.0 50.6 154 7,793.0 B-II 14 11,813.2 843.8 865 729,887.0 1,038.5 74.2 417 30,933.7 693.0 49.5 154 7,622.6 B-III 9 5,526.4 614.0 865 531,148.4 2,673.8 297.1 417 123,887.0 541.9 60.2 154 9,271.8 X 899.6 865 778,154.0 220.7 417 92,031.9 44.8 154 6,899.2 1985 EA 17 18,592.8 1,093.7 978 1,069,632.8 1,399.2 82.3 305 25,103.3 405.6 23.9 170 4,063.0 B-I 5 10,614.0 2,122.8 978 2,076,098.4 2,130.6 426.1 305 129,966.6 338.0 67.6 170 11,492.0 B-II 14 13,249.2 946.4 978 925,551.3 1,478.7 105.6 305 32,214.5 1233.7 88.1 170 14,980.6 B-III 9 7,960.5 884.5 978 865,041.0 3,021.0 335.7 305 102,378.3 794.3 88.3 170 15,003.4 X 1,261.8 978 1,234,040.4 237.4 305 72,407.0 67.0 170 11,390.0 1986 EA 16 14,219.0 888.7 737 654,962.7 874.0 54.6 436 23,816.5 266.0 16.6 152 2,527.0 B-I 5 7,759.0 1,551.8 737 1,143,676.6 1,646.0 329.2 436 143,531.2 407.0 81.4 152 12,372.8 B-II 14 9,864.0 704.6 737 519,269.1 1,361.0 97.2 436 42,385.4 1,239.0 88.5 152 13,452.0 B-III 9 10,486.0 1,165.1 737 858,686.9 2,201.0 244.6 436 106,626.2 531.0 59.0 152 8,968.0 X 1,077.5 737 794,117.5 181.4 436 79,090.4 61.4 152 9,332.8 1987 EA 16 13,832.0 864.5 894 772,863.0 1,767.0 110.4 347 38,321.8 990.5 61.9 105 6,500.2 B-I 5 2,223.0 444.6 894 397,472.4 3.021.0 604.2 347 209,657.4 990.5 198.1 105 20,800.5 B-II 14 3,629.0 259.2 894 231,737.6 2,394.0 171.0 347 59,337.0 3,366.0 240.4 105 25,245.0 B-III 9 3,534.0 392.7 894 351,044.0 2,394.0 266.0 347 92,302.0 1,603.8 178.2 105 18,711.0 X 490.2 894 438,238.8 287.9 347 99,901.3 169.7 105 17,818.5 1988 EA 17 13,851.0 814.8 831 677,069.5 2,008.8 118.2 193 22,805.8 1,107.8 65.2 50 3,258.2 B-I 5 4,807.0 961.4 831 798,923.4 744.0 148.8 193 28,718.4 592.1 118.4 50 5,921.0 B-II 14 6,004.0 428.9 831 356,380.3 558.0 39.9 193 7,692.4 6,242.9 445.9 50 22,296.1 B-III 9 6,745.0 749.4 831 622,788.3 2,176.2 241.8 193 46,667.4 2,005.5 222.8 50 11,141.7 X 738.6 831 613,776.6 137.2 193 26,479.6 213.1 50 10,655.0 Minimum 2,223.0 259.2 506 212,317.6 558.0 39.9 193 7,692.4 234.4 16.6 50 2,527.0 Maximum 18,592.8 2,122.8 978 2,076,098.4 4,430.4 629.2 436 209,657.4 6,242.9 445.9 170 25,245.0 Average 8,428.2 833.6 790.4 658,877.4 2,122.3 245.1 336.J 1 82,574.2 1,021.3 95.3 134.9 12,856.0 ; EA = Eastern Aleutian Islands B = Beri ng Sea, see Figure 1 for areas !. Yano and Dahlheim: Depredation of bottomfish on longline catches by Orcmus orca 371 n= 1925 III 801 901 B ,ll n = 265 801 901 .M.I J n= 78 III 601 701 801 Total length (mm) Figure 10 Length-frequency distribution of Greenland turbot, Reinhardtius kippoglossoides. (A) All areas (see Fig. 1); (B) all stations fished where depredation occurred; (C) calculated length (head length and maxillary length) of partially consumed fish. Table 8 Average monetary loss per station ( 1982-88) estimated by depredation rates (RNT, RNS. REY, and REA) for sablefish, Anoplopoma fimbria, Greenland turbot, Reinhardtius hippoglossoides, and arrowtooth flounder, Atheresthes stomias. Total given for all three species. Sablefish Greenland turbot Arrowtooth flounder Total Depredation rate Yen U.S. $ Yen U.S. $ Yen U.S. $ Yen U.S. $ RNT 92,111.1 682.30 32,550.7 241.10 735.4 5.40 125,397.2 928.90 RNS 142,910.5 1,058.60 37,249.2 275.90 1.643.0 12.20 181,802.7 1,346.70 REY 385,377.4 2,854.60 54,680.6 405.00 4,596.0 34.00 444,654.0 3,293.60 REA 393,086.3 2,911.80 56,901.9 421.50 5,429.1 40.20 455,417.3 3,373.50 372 Fishery Bulletin 93(2). 1995 Table 9 Yearly monetary loss per station and overall loss estimated by depredation rate of RNT (minimum value) and RNA (maximum value), and yearly total product value per survey and product values per station calculated from total product value. Year Yearly monetary loss per station (A) No. of depredated stations (B) Overall monetary loss (C=AxB) Yearly total product value in Yen (U.S. $) No. of stations per survey (E) Product Rate of loss value/station per yearly IF=D/E) product in Yen (G=C/DxlOO) (U.S. $) (%) Rate of loss per station product (H=A/Fxl00) (%) Yen U.S.$ Yen u.s.$ 1982 max. min. 100,624.9 308,350.2 745.40 2,284.10 4 402,499.6 1,233,400.8 2,981.50 9,136.30 121,346,699 (898,864.40) 108 1,123,580.5 (8,322.80) 0.33 1.02 8.96 27.44 1983 max. min. 97,015.0 325,174.7 718.60 2,408.70 9 873,135.0 2,926,572.3 6,467.70 21,678.30 98,812,086 (731,941.40) 104 950,116.2 (7,037.90) 0.88 2.96 10.21 34.22 1984 max. min. 145,459.5 530,579.4 1,077.50 3,930.20 3 436,378.5 1,591,738.2 3,232.40 11,790.70 176,102,713 (1,304,464.50) 108 1,630,580.7 (12,078.40) 0.25 0.90 8.29 32.54 1985 max. min. 201,713.2 790,934.2 1,494.20 5,858.80 3 605,139.6 2,372,802.6 4,482.50 17,576.30 283,932,240 (2,103,201.80) 108 2,629,002.2 (19,474.10) 0.21 0.84 7.67 30.08 1986 max. min. 142,728.9 532,212.9 1,057.30 3,942.30 8 1,141,831.2 4,257,703.2 8,458.00 31,538.50 238,057,678 (1,763,390.20) 107 2,224,838.1 (16,480.30) 0.48 1.79 6.42 23.92 1987 max. min. 101,666.1 337,820.0 753.10 2,502.40 7 711,662.7 2,364,740.0 5,271.60 17,516.60 271,467,224 (2,010,868.30) 107 2,537,076.9 (18,793.20) 0.26 0.87 4.01 13.32 1988 max. min. 96,853.7 388,925.8 717.40 2,880.90 12' 1,162,244.4 4,667,109.6 8,609.20 34,571.20 275,277,684 (2,039,094.00) 108 2,548,867.4 (18,880.50) 0.42 1.70 3.80 15.26 Overall max. 96,853.7 790,934.2 717.40 5,858.80 402,499.6 4,667,109.6 2,981.50 34,571.20 0.21 2.96 3.80 34.22 ' Three stations where no depredation was evident. search Center) for their kind cooperation in provid- ing the data from the sablefish and Pacific cod sur- veys between the years 1980 and 1989. We also thank J. J. Long, R. A. Payne, J. W. Stark, D. Bridges, K. Koike, S. Onodera, and the crew of the research vessel Tomi Maru No. 88 for their valuable coopera- tion during the 1988 survey. Annual surveys were supported by the Japan Marine Fishery Resources Research Center (JAMARC), the National Marine Fisheries Service (NMFS-Alaska Fisheries Science Center), and the National Research Institute of Far Seas Fisheries. Janice Waite prepared final tables. Thomas Loughlin, Richard Merrick, and Harold Zenger (NMFS) reviewed the manuscript. Literature cited Braham, H. W., and M. E. Dahlheim. 1982. Killer whales in Alaska documented in the Platforms of Opportunity Program. Rep. Int. Whaling Comm. 32:643-646. Leatherwood, J. S., and M. E. Dahlheim. 1978. Worldwide distribution of pilot whales and killer whales. Naval Ocean Systems Center, Tech. Rep. 443: 1-39. Leatherwood, J. S., D. McDonald, W. P. Prematunga, P. Girton, D. McBrearty, and A. Ilangakoon. 1990. Records of the "blackfish" (killer, false killer, pilot, pygmy killer, and melon-headed whales) in the Indian Ocean Sanctuary, 1772-1976. In S. Leatherwood and G. P. Donovan (eds.), Cetaceans and cetacean research in the Indian Ocean Sanctuary, p. 33-65. United Nations Envi- ronment Programme, Marine Mammal Technical Publica- tion No. 3, Nairobi, Kenya. Rice, D. W. 1968. Stomach contents and feeding behavior of killer whales in the eastern North Pacific. Norsk. Havlf. 57: 35-38. Sasaki, T. 1985. Studies on the sablefish resources of the North Pa- cific Ocean. Bull. Far Seas Fish. Res. Lab., No. 22: 1-108. Si \ asubrainan in m, K. 1965. Predation of tuna longline catches in the Indian Ocean, by killer whales and sharks. Bull. Fish. Res. Stn., Ceylon 17(2):93-96. Abstract. — To enable accurate ageing of orange roughy, Hoplo- stethus atlanticus, eggs caught in egg production surveys for biomass estimation, eggs were cultured at four experimental temperatures, and the results were fitted to a re- gression model of age-at-stage for the culture temperatures used. Water column ascent and descent rates of early stage eggs were esti- mated by using a combination of experimental observation and theory. Young eggs ascended rap- idly (>300 m-day"1), middle-aged eggs approached neutral buoyancy, and the oldest eggs sank rapidly. The ascent and development rate results were combined with data on water column thermal structure to produce a "thermal history model" of orange roughy egg development, enabling the thermal history of eggs to be considered in ageing them as they rise through the stratified layers into the mixed layer. The ascent and descent rates and modelled depth-at-stage were compared with field data on depth distributions of stages from MOC- NESS tows over the North Chatham Rise, New Zealand. For the domi- nant and subdominant egg stages, predictions closely matched the field results. The model therefore provided a robust method for age- ing eggs caught in an egg produc- tion survey for orange roughy. The ontogenetic pattern of buoyancy in the eggs may partially explain the distributions of early juvenile or- ange roughy on the North Chatham Rise. The bias in predicted egg ages, caused by the assumption that temperature of development was constant for eggs below the mixed layer, was shown to be impor- tant in egg production estimation. Ascent rates, vertical distribution, and a thermal history model of development of orange roughy, Hoplostethus atlanticus, eggs in the water column John R. Zeldis Paul. J. Grimes Jonathan K. V. Ingerson MAF Fisheries, Greta Point Box 297, Wellington, New Zealand Manuscript accepted 9 September 1994. Fishery Bulletin 93:373-385 1 1995). Orange roughy, Hoplostethus atlan- ticus (family: Trachichthyidae), are slow-growing, deep water (700- 1,500 m) fish that have been found in large quantities mainly in New Zealand1 and Australia (Kailola et al., 1993). In winter, orange roughy aggregate to spawn near banks, pin- nacles, and canyons, and these ag- gregations attract large amounts of fishing effort. Fisheries for orange roughy began in 1978—79 in New Zealand. The largest fishery is on the Chatham Rise (Fig. 1 ) where re- ported catches reached 13,800 met- ric tons (t) in 1992-93. l The stock assessment for the Chatham Rise fishery is based on stock reduction modelling of biomass in which com- mercial catches, biological param- eters, and time series of relative bio- mass estimates from research trawl surveys are used. The next largest fishery (with reported catches of 9,128 1 in 1992-93 [Field et al., 1994] ) is off the east coast of New Zealand, and a large proportion of the catch is taken from the winter spawning aggregations on the Ritchie Bank (Fig. 1). The stock reduction analy- sis for this fishery prior to 1993-94 was based primarily on catch-per- unit-of-effort data which were highly uncertain and made the bio- mass estimate very uncertain (Field et al., 1994). Consequently, there was a need for a reliable, ab- solute biomass estimate. After reviewing aspects of the bi- ology of orange roughy planktonic eggs and adult fecundity, Zeldis (1993) concluded that both the an- nual egg production method ( AEPM; Saville, 1964 ) and the daily fecundity reduction method (DFRM; Lo et al., 1992) would be feasible for the esti- mation of absolute spawning bio- mass of orange roughy on the Ritchie Bank. Both the AEPM and the DFRM were applied during an egg production survey of Ritchie Bank orange roughy biomass in June-July 1993.2 Because egg production methods rely on calculating egg production rates from estimates of abundance- at-age of planktonic eggs, a means of ageing the eggs is required. This is done by determining ages of iden- tifiable morphological stages of egg 1 Annala, J. (Compiler) 1994. Report from the Special Fishery Assessment Plenary, 17 August 1994: stock assessments and yield estimates for ORH 3B, 24 p. Unpubl. rept. held in MAF Fisheries, Greta Point library, Wellington, N.Z. 2 Zeldis, J., R. I. C. C. Francis, J. K. V. Ingerson, M. Clark, and P. J. Grimes. 1994. A daily fecundity reduction method esti- mate of Ritchie Bank and east coast North Island orange roughy biomass. Draft New Zealand Fisheries Assessment Research Document. MAF Fisheries, Greta Point, Wellington, N.Z. 373 374 Fishery Bulletin 93|2), 1995 -„ Ritchie Bank ' North f »_ ORH Island N u North Chatham Rise ORH r— ^— -^ ^ Chatham Islands Figure 1 Map of New Zealand and Exclusive Economic Zone and location of Chatham Rise and Ritchie Bank orange roughy, Hoplostethus atlanticus, fisheries. development. Embryogenesis and larval development of orange roughy are undescribed, as are the vertical distributions of the eggs and larvae (Zeldis, 1993). Orange roughy produce large eggs (2.32-mm mean diameter) with a large oil droplet (0.60-mm mean di- ameter), suggesting that their eggs would be strongly positively buoyant (Robertson, 1981). Since egg devel- opment rate in teleosts is strongly temperature depen- dent (Pauly and Pullin, 1988; Pepin, 1991), changes in the vertical distribution of orange roughy eggs dur- ing embryogenesis will have a strong effect on their development rate, because they are spawned in ther- mally stratified waters below the mixed layer (Zeldis, 1993). Therefore, in order to estimate egg production for orange roughy accurately, a model was needed which considers the thermal history of an egg when the ob- served stage of development is used to estimate age. To create and test this model, this study had the following objectives: 1) to describe the temperature dependence of egg development rate; 2) to estimate ascent rates of egg stages with experimentation and theory; 3) to combine results on development rate and ascent rate to develop a 'thermal history model' of orange roughy development in the water column; and 4) to test predictions of this model against ob- served vertical distributions of egg stages in the water column. In this study a generalized description of embryol- ogy is used to address these objectives. Photographs of some of the egg and larval stages have been pub- lished (Grimes and Zeldis, 1993), and detailed de- scriptions of orange roughy embryological and lar- val stages will be published separately. Methods Embryological, ascent rate and vertical distribution studies were conducted on the North Chatham Rise (Fig. 1) from 7 to 28 July 1992 with the MAF Fisher- ies RV Tangaroa, a 70-m research stern trawler (voy- age TAN9206). Additional embryological and ascent rate studies were conducted on the Ritchie Bank from 6 June to 8 July 1993 during an egg production sur- vey (Tangaroa voyage TAN9306). Embryology and development rates To study embryology and development rates, orange roughy eggs were cultured under controlled-tempera- ture conditions in a shipboard laboratory. The cul- turing facility had four insulated, plastic 20-L bins, in which plastic jars with mesh tops were submerged to hold the eggs. Each bin had flow-through supplies Zeldis et al.: Development of Hoplostethus atlanticus eggs in the water column 375 of seawater (500 mL-min-1) filtered to 5 microns. Water was cooled to 6°C by a refrigeration system, then heated to desired culture temperatures by aquarium heaters controlled with digital thermistors. The 6°C inlet and heater for each bin were within a central PVC "upwelling stem" driven by an airstone and provided stable culture temperatures during the study (±0.2°C). The jars and bins were disinfected with weak ammonia about every three days. Culture temperatures used were 6, 8, 10, and 12°C, which spanned the temperature range from the depth of spawning to the sea surface in orange roughy spawning areas. The eggs used for the 6°C culture were fertilized from stripped fish (on voyage TAN9306), and the eggs used for the 8, 10, and 12°C cultures were captured from the plankton (on voy- age TAN9206). Growing captured planktonic eggs was generally more successful than starting with stripped eggs and sperm. Only a few hundred strip- fertilized eggs were successfully grown, as opposed to thousands of captured eggs. Strip-fertilizing was most successful when free-flowing, ovulating females and freely expressible males were taken from the wings of the trawl and when cooled seawater and dilute sperm infusions were used with the eggs. The eggs that were selected from the plankton samples for culturing were those that floated in the plankton catches. Eggs were staged by using the criteria and figures for killifish Fundulus heteroclitus from New (1966), in which most relevant features of orange roughy development were identifiable, up to and including New's stage 25. Subsequent stages were defined by the degree the tail was free of the yolk (as a propor- tion of total tail length), and stage 30 was defined as the hatching stage. Stage numbers used in this pa- per are assumed to represent the midpoints of the time periods of the stages. Eggs were sampled from the jars and examined under a binocular microscope every 3 or 4 hours at 6°C, and less frequently (see Fig. 2) at 8, 10, and 12°C, until stage 9 (morula for- mation). The 6°C eggs were sampled more frequently because they were the only culture temperature used on voyage TAN9306 and more time was available to sample and observe eggs. After morula formation, eggs from all temperatures were sampled once or twice a day until stage 19 (blastopore closure) and then once every 1 or 2 days until hatching was im- minent. After examination, the sampled eggs were either replaced in the culture vessels (if they were rare) or more commonly preserved in 49c buffered formaldehyde in seawater. Since the eggs used in the 8°C, 10°C, and 12°C se- ries were caught from the plankton, their absolute ages at the start of their series (at stage 5) were not known. To estimate the absolute ages of the observed stages, the cumulative time up to each stage since stage 5 was regressed against the observed stage for each series for each temperature. This meant all re- gression lines effectively had a common x-axis inter- cept at stage 5, with age = 0. The absolute age at stage 5 for each temperature was estimated by con- tinuing the lines to 0 on the x-axis and taking the absolute values of the resulting negative y-axis in- 200 8°C 150 6°C /^^ age (hours) o o s^ J3^^ ^^^ J^^~^^ 50 0 J^^^ 0 2 4 6 8 10 12 13 14 15 16 17 18 19 20 21 22 23 24 25 stage Figure 2 Orange roughy, Hoplostethus atlanticus, egg development stages at four tempera- tures from culturing experiment with curves fitted from Equation 1. The stage numbers should be interpreted as indicating the midpoint of the period of each stage. 376 Fishery Bulletin 93(2), 1995 tercepts. These predicted y-axis intercepts had small standard deviations (SD) ranging from 1.3 h to 1.5 h, so this source of error in age estimation was con- sidered negligible. The absolute values of the inter- cepts were then added to the cumulative times of all the observations to estimate the absolute ages for each observed stage for each temperature (Fig. 2). The model was then reestimated by using these ab- solute ages (the fitted lines in Fig. 2). The regression model predicted egg age as an exponential function of temperature and a linear function of stage: age = 8.803 e-°158(emP x stage ( 1) The fit had r2 of 0.96. The justification for assuming that egg age was a linear function of stage was as follows. The mean duration of the stages given by New (1966) at 20°C for killifish were 1.0 ±0.35 (1 SD) h for stages <10, 4.1 ±1.14 h for stages 11 and 21, and 9.0 ±1.15 h for stages 22 and 25. Thus, stage durations were simi- lar within each of these stage groups and differed between the groups by the ratios 1.0: 4.1: 9.0. Evi- dently, these ratios also applied to orange roughy development, judging by the linear appearance of the orange roughy age-at-stage data for each tempera- ture (Fig. 2) when the x-axis (stage) was scaled by these ratios for stages 1 to 10, 11 to 21, and 22 to 25, respectively. Thus, to use Equation 1 to estimate age from stage, the input value for stage had to be scaled by these ratios (e.g., the appropriate input value for stage 13 would be (H)(1) + (2M4.1) = 19.2). Orange roughy egg stages from 26 to 30 deviated from that of New (1966) and were not of a consistent length. Therefore, scaling of these stages was not done and ages for stages >26 were not modeled. The justification for assuming that egg age was an exponential function of temperature was that the egg development period for 140 species of pelagic, spherical marine fish eggs was well predicted as an exponential function of temperature and egg size by Pauly and Pullin (1988). Egg ascent and descent rates To estimate egg ascent and descent rates, a gradu- ated, perspex cylinder (7x100 cm) was suspended from the ceiling of a shipboard laboratory; its bot- tom was open in a bucket of seawater and the cylin- der was filled with surface seawater (35.00 ppt sa- linity; see below for the temperatures used). Orange roughy eggs of various stages were introduced at the bottom of the cylinder and, following an initial as- cent of 10 cm (to allow the eggs to reach terminal velocity), subsequent ascent was timed over four to seven 10-cm intervals. Older eggs sank; therefore these were introduced to the top of the cylinder and descent rates were measured by following an initial descent of 10 cm. Means and standard deviations of these rates were estimated from estimators for a two- stage sampling design, weighted for unequal subsample sizes (Eq. 5 in Picquelle and Stauffer [1985]). The water temperature within the cylinder for the experiments on younger eggs (unfertilized, newly fertilized, cell division, and morula-early blastula eggs: stages 0-11 in Fig. 3) was between 6 and 7 de- grees and characteristic of the water column at the depth of the spawners. Since these eggs were very positively buoyant, it was clear (see Results section) that the older of these stages occurred shallower in the water column, so it was necessary to predict how fast they would ascend under the temperature-sa- linity conditions at shallower depths. This was done by using a combination of experimental observation and theory in the following way. First, it was observed that unfertilized and stage- 1 eggs ascended the experimental cylinder at a mean rate of 275 m-day"1 at 6°C and 35.00 ppt (Fig. 3). This ascent rate was used to predict the density of these eggs by using the theoretical relationships in Robertson (1981), the seawater density, and seawa- ter viscosity (Sverdrup et al., 1964) in the cylinder. The predicted density was 1.02488 g-cm-3. To test this theoretical density against experimental determina- tions, the density of unfertilized and stage-1 eggs was measured by diluting the seawater medium (35.00 ppt, 10°C) of the eggs with distilled water until the eggs became neutrally buoyant and by calculating the density of the seawater (1.02425 gem3). The theoretical and experimental densities can be com- pared if the former value (determined at 6°C) is ad- justed to 10°C by using the coefficient of thermal expansion of seawater to account for the decrease in density of the eggs with increase in temperature (taken to be equal in seawater and fish eggs: Coombs et al., 1985). The coefficient of thermal expansion was interpolated from Table 3.1 in Neumann and Pierson (1966) at 35.00 ppt and 8.0°C and atmospheric pres- sure and was 151- 10~6 per 1°C change in tempera- ture. The resulting theoretical density was 1.02428, virtually the same density as determined experimen- tally. This strongly suggests that the theoretically determined density was realistic and that the theory could be used to adapt experimental ascent rates determined at particular temperatures and salinity to various conditions in the oceanic water column. Accordingly, Robertson's (1981) theoretical rela- tionships were used to calculate the density of stage 1-11 eggs from their experimentally determined Zeldis et al.: Development of Hoplostethus atlanticus eggs in the water column 377 600 500 400 300 200 £■ 100 -o (5 0 £ -100 -200 -300 -400 -500 cell division . . „ . . . .. (stgs 5-7) unfertilized (stg 0) 5 i early - mid * gastrula I n = 60 T (stgs 15-17) * morula - early 1 tilastula n = 39 newly (stgs 9-11) )$ fertilized n = 39 (stg 1 ) n = 45 n = 15 mid late embryo (stgs 22-25) h. . ..........---. n = 12 }i Hatching embryo (stg 30) n = 21 -600 Figure 3 Orange roughy, Hoplostethus atlanticus, egg ascent and descent rates in the experi- mental cylinder for groups of egg stages. Points are means ±95% confidence limits, n = total number of determinations in each group. ascent rate (mean of 350 m-day-1; Fig. 3) at 6.0°C and 35.00 ppt in the experimental cylinder. This den- sity (1.02406 g-cm-3) and the coefficient of thermal expansion were then used to estimate the ascent rates (Table 1) for stage 1-11 eggs through the wa- ter column. This was done for depth strata corre- sponding to 1°C increases, from 6.0 (the bottom at 870 m) to 11.25°C (the bottom of the mixed layer at 250 m). The analysis accounted for the change in density of the eggs (via the coefficient of thermal expansion), change in density of the surrounding water (from MOCNESS-CTD data), and change in seawater viscosity, as the eggs ascended the water column. Neither the viscosity or coefficient of thermal expansion were corrected to account for changes in sa- linity and pressure during the ascent ( p. 69 in Sverdrup et al., 1964; Table 3.2 in Neumann and Pierson, 1966) because they both changed less than 5% over the sa- linity and pressure gradients considered here. Ascent rates of early to mid gastrula and mid to late embryo stages (stages 15-25) were estimated in the cylinder at surface temperature (11-12°C) and Table 1 Predicted ascent rates of stage 1-11 eggs of orange roughy, Hoplostethus atlanticus, water column based on relationships between egg density, water column sigma-t anc at various depths and temperatures in the viscosity given by Robertson (1981). Temp. (°C) Depth (m) Salinity (ppt) Sigma-t (gem-3) Viscosity (g sec-1cm-1) egg density (g-cm-3) Ascent rate (m-day-1) 6.0 870 34.40 1.02710 0.0159 1.02406 305.7 7.0 700 34.48 1.02703 0.0156 1.02391 316.9 8.0 550 34.55 1.02694 0.0152 1.02376 330.8 9.0 400 34.65 1.02686 0.0149 1.02361 335.4 10.0 315 34.75 1.02677 0.0146 1.02346 350.8 11.0 265 34.89 1.02671 0.0142 1.02331 360.6 11.25 250 35.00 1.02675 0.0141 1.02327 368.4 378 Fishery Bulletin 93(2), 1995 salinity (35.0 ppt). These conditions emulated sea- water densities that are experienced by eggs at these stages in nature, because the embryos are approach- ing neutral bouyancy and reside primarily within the mixed layer (see Results section). The descent rate of hatching-stage eggs (stage 30) was measured at 9.0°C. These eggs were very nega- tively buoyant and were probably sinking rapidly through the water column. Because surface salinity water was used in the experimental cylinder, the measured descent rate (366 m-day-1) is probably an underestimate for waters below the mixed layer be- cause of decreasing salinity. The measured descent rate of these eggs at 9.0°C and surface salinity were used to predict their density: 1.02707 gem-3. This was then used to predict their descent rates at 9.0°C and 34.65 ppt (the salinity at 9°C in the water col- umn) which was 381 m-day-1. A thermal history model As orange roughy eggs ascend the oceanic water col- umn, it can be assumed that they will develop at the rate governed by their immediate environmental temperature (Pauly and Pullin, 1988). However, their actual stage at any age is determined by an accumu- lating average of their previous and present tempera- tures. A model which enables this "thermal history" of an orange roughy egg to be considered, when the egg's observed stage is used to estimate its age, was created in the following way. First, it was observed that the temperature-at- depth data for the five MOCNESS profiles (Fig. 4) below the mixed layer had three segments for which the depth change per 1°C change was nearly con- stant. These were 870 m to 450 m, 450 to 315 m, and 315 to 250 m (the bottom of the mixed layer). These depth changes were divided by the predicted egg as- cent rates at each of these 1°C depth intervals (Table 1) to determine the amount of time eggs would spend in each of the 1°C temperature strata. Next, a fam- ily of age-at-stage curves was graphed by using Equa- tion 1 from 6.0°C (the near-bottom temperature) to 11.0°C, each curve representing development over an interval of ±0.5°C. Eggs were then "developed" graphically, by moving along the 6.0°C curve until the change in age equalled the amount of time eggs spent in that stratum (in this case 9.4 h, since this stratum was truncated by the bottom at 5.75°C). The point reached was age = 9.4 h, stage = 2.8 (Fig. 5). Then, these stage 2.8 eggs were developed further by "dropping down" to the 7°C curve and moving along it until the change in age was 11.4 h (the length of time required to ascend through the 6.5-7.5°C stra- tum). The point reached was cumulative age = 20.8 h, stage = 6.7, which was the stage the eggs had reached after accounting for development at 7°C and the previous development at 6°C. This procedure was repeated until eggs were aged through to 11.25°C (at 250 m; the bottom of the mixed layer) at cumulative age = 46.0 h. The eggs at this age were in stage 13. Subsequent egg development to stage 26 occurred in Temperature (° C) i 6 7 8 9 10 11 12 100 \ / 200 - / •=■ 3O0 : ^^^—^^^ Depth y^ 600 ; ^^ 700 ■ ^^ 800 /--"' 900 : y Figure 4 Temperature profile in MOCNESS survey area on the north Chatham Rise during TAN9206. Data are mean temperatures in each 1-m depth stratum across the 5 MOCNESS tows. Temperatures from 780 m to 870 m are extrapolated from tempera- tures below 450 m for use in modelling. Zeldis et al.: Development of Hoplostethus atianticus eggs in the water column 379 65 : 60 ; ^ 55 '-_ ^^^ 50 ■ ^^^ 45 : s 40 : Q) 35 : < 30 : 25 ; 20 - 15 : 10 - 5 - 01234567B9 10 11 12 13 14 15 Stage Figure 5 Orange roughy, Hoplostethus atianticus, egg age-at-stage (h) determined from the thermal history model. Dots indicate age-at-stage for each 1°C temperature stra- tum in the water column. Shaded area shows 9560 cm) predators were unusually abundant, often numbering as many as 20-30 sculpins along a 15-20 m length of rocky ledge. They lay in wait on the bottom and after the young pollock appeared, were often seen pursuing and capturing them. Some sculpins appeared so gorged with young pollock that their gut was greatly distended. As the juvenile pollock grew, they moved down the slope into deeper waters. After reaching approxi- mately 10 cm TL by October or November, they were seen less frequently. By then the pollock were inhab- iting waters 30 m or deeper, approaching the limits of normal scuba operations. By December and into winter, the juvenile pollock were seen infrequently 388 Fishery Bulletin 93(2). 1995 Table 1 Survey effort (number of diving days) in Auke Bay and vicinity, Southeast Alaska, to observe juvenile walleye pollock, Theragra chalcogramma, June- December 1973-94. Year Month June July August Sept Oct Nov Dec Total 1973 0 1 1 3 6 6 5 22 1974 3 4 3 2 5 10 6 33 1975 7 9 8 0 0 0 0 24 1976 4 5 13 7 7 7 15 58 1977 10 5 9 9 4 7 5 49 1978 6 7 10 11 8 11 13 66 1979 17 14 14 13 17 14 17 106 1980 16 4 9 15 9 6 10 69 1981 9 4 11 17 17 14 16 88 1982 3 6 14 9 7 4 11 54 1983 16 7 8 9 12 10 8 70 1984 7 2 7 8 6 6 6 42 1985 8 1 4 6 6 7 12 44 1986 5 3 4 5 9 13 15 54 1987 16 17 8 9 15 13 16 94 1988 6 16 10 13 16 11 17 89 1989 9 5 9 10 15 12 15 75 1990 14 14 8 15 5 11 16 83 1991 4 12 8 11 8 15 17 75 1992 6 10 12 6 8 9 13 64 1993 3 3 5 6 8 9 7 41 1994 6 9 3 8 14 4 44 Total 175 158 178 192 202 199 240 1,344 during daylight. During darkness in November and December, they moved into shallows of 9 m or less and became more loosely aggregated; some individu- als remained on the bottom and motionless under a light beam. At dawn the loose aggregations became shoals and moved downslope again to depths >30 m. Discussion The consistent appearance of the age-0 pollock that I observed each year for 22 years at the Auke Bay site agrees during 1986-89 with the earlier appear- ance for those years of pollock larvae observed in Auke Bay by Haldorson et al. ( 1990). They found that little hatching occurred after the major larval cohort appeared and concluded that pollock spawn during the relatively short period when larval feeding conditions are optimal. By July, I observed that the larvae had usually settled out from a planktonic existence and had be- come demersal juveniles. Typically at this time, sea surface temperatures in Auke Bay are near a yearly peak (Bruce et al., 1977), a thermocline has formed around 12 m depth, zooplankton abundance in the upper water column approaches its yearly maximum (Carlson, 1980), and 3—4 cm juvenile pollock feed mostly on the copepod Acartia clausi (Krieger, 1985). Similar to my findings, the sculpin Myoxocephalus sp. is a major predator of age-0 juvenile pollock in the Bering Sea (Smith, 1981). By October, when the young pollock were 8-10 cm TL, they appeared sufficiently motile to evade most bottom-dwelling predators. They moved to deeper water in the fall around the time that, typically, storms mix the surface and mid-water strata, the thermocline breaks down, and sea temperatures de- crease sharply and become nearly uniform through- NOTE Carlson: Yearly appearance of Theragra chalcogramma off southeastern Alaska 389 Table 2 Dates of first sightings and estimated size range of young- of-the-year w alleye pollock, Theragra chalcogramma, in Auke Bay, Southeast Alaska, 1973- -1994. No est. = no esti- mate; TL = total length. Year Date Size range (TL, cm) 1973 2 August 7 1974 11 October 5-6 1975 17 July 3 1976 15 July 3-5 1977 2 August 5-6 1978 19 July 3-4 1979 14 July 3-4 1980 12 August 4-8 1981 27 July 4-5 1982 27 July no est. 1983 10 July 4-6 1984 12 September no est. 1985 28 August no est. 1986 4 November no est. 1987 18 July 3 1988 23 July 4-5 1989 2 July 4-5 1990 14 July 5 1991 17 August 5 1992 7 July 4-6 1993 24 July 3-6 1994 16 July 3-5 Summary Month of first sightings July 14 years August 5 years September 1 year October 1 year November 1 year Total 22 years out the water column ( Bruce et al., 1977). Generally, by this time zooplankton abundance had declined, daylight was greatly reduced (Carlson, 1980), and juvenile pollock feeding had shifted from copepods to larger prey — mainly mysids and euphausiids (Krieger, 1985). The young pollock appeared to move deeper in response to these changing oceanographic and trophic conditions. Each year, this pattern of appearance of juvenile pollock repeated itself with few exceptions and with remarkable predictability; it was generally consis- tent in timing, location, depth, and size of fish. The consistent residency at the same site, around the same time, by young-of-the-year walleye pollock for 22 consecutive years, demonstrates the long-term significance and potential importance of locales such as Auke Bay as nursery grounds for this species. Acknowledgments I wish to thank all my colleagues at the National Marine Fisheries Service Auke Bay Laboratory who helped with this study, particularly M. L. Dahlberg and K. J. Krieger, who also participated underwater. Literature cited Bailey, K. M., and S. M. Spring. 1992. Comparison of larval, age-0 juvenile and age-2 re- cruit abundance indices of walleye pollock, Theragra chalcogramma, in the western Gulf of Alaska. ICES J. Mar. Sci. 49:297-304. Bruce, H. E., D. R. McLain, and B. L. Wing. 1977. Annual physical and chemical oceanographic cycles of Auke Bay, southeastern Alaska. U.S. Dep. Commer., NOAATech. Rep. NMFS SSRF-712, 11 p. Carlson, H. R. 1980. Seasonal distribution and environment of Pacific herring near Auke Bay, Lynn Canal, southeastern Alaska. Trans. Am. Fish. Soc. 109:71-78. FAO (Food and Agriculture Organization of the United Nations). 1993. Yearbook of fishery statistics, 1991. Vol. 72, 654 p. FAO, Rome. Haldorson, L., M. Pritchett, D. Sterritt, and J. Watts. 1990. Interannual variability in the recruitment potential of larval fishes in Auke Bay, Alaska. In D. A. Ziemann and K. W. Fulton-Bennett (eds.), APPRISE— interannual variability and fisheries recruitment, p. 319-356. The Oceanic Institute, Honolulu, HI. Hinckley, S., K. M. Bailey, S. J. Picquelle, J. D. Schumacher, and P. J. Stabeno. 1991. Transport, distribution, and abundance of larval and juvenile walleye pollock {Theragra chalcogramma) in the western Gulf of Alaska. Can. J. Fish. Aquat. Sci. 48:91-98. Kamba, M. 1977. Feeding habits and vertical distribution of walleye pollock, Theragra chalcogramma (Pallas), in early life stage in Uchiura Bay, Hokkaido. Res. Inst. N. Pac. Fish., Hokkaido Univ., Spec. Vol.: 175-197. Kendall, A. W, Jr., and S. J. Picquelle. 1990. Egg and larval distributions of walleye pollock, Theragra chalcogramma, in Shelikof Strait, Gulf of Alaska. Fish. Bull. 88:133-154. Kim, S. 1989. Early life history of walleye pollock, Theragra chalcogramma, in the Gulf of Alaska. In Proceedings of the international symposium on biology and management of walleye pollock, p. 117-139. Alaska Sea Grant Rep. 89-1, Univ. Alaska, Fairbanks. Krieger, K. J. 1985. Food habits and distribution of first year walleye pollock, Theragra chalcogramma (Pallas), in Auke Bay, southeastern Alaska. M.S. thesis, Univ. Alaska, Juneau, 57 p. Krieger, K. J., and B. L. Wing. 1986. Hydroacoustic monitoring of prey to determine hump- back whale movements. U.S. Dep. Commer., NOAATech. Memo. NMFS F/NWC-98, 62 p. Lloyd, D. S., and S. K. Davis. 1989. Biological information required for improved man- agement of walleye pollock off Alaska. In Proceedings of 390 Fishery Bulletin 93(2), 1995 the international symposium on biology and management of walleye pollock, p. 9-31. Alaska Sea Grant Rep. 89-1, Univ. Alaska, Fairbanks. Pritchett, M., and L. Haldorson. 1989. Depth distribution and vertical migration of larval walleye pollock (Theragra chalcogramma). In Proceedings of the international symposium on biology and manage- ment of walleye pollock, p. 173-183. Alaska Sea Grant Rep. 89-1, Univ. Alaska, Fairbanks. Salveson, S. J. 1984. Growth and distribution of first-year walleye pollock, Theragra chalcogramma, in north Stephens Passage, south- eastern Alaska. M.S. thesis, Univ. Alaska Juneau, 59 p. Serobaba, 1. 1. 1974. Spawning ecology of the walleye pollock (Theragra chalcogramma) in the Bering Sea. J. Ichthyol. 14:544-552. Smith, G. B. 1981. The biology of walleye pollock. In D. W. Hood and J. A. Calder (eds.), The eastern Bering Sea Shelf: oceanog- raphy and resources, Vol. 1, p. 527-551. U.S. Dep. Commer., NOAA, Office Mar. Poll. Assessment. Radiometric analysis of blue grenadier, Macruronus novaezelandiae, otolith cores Gwen E. Fenton Department of Zoology. University of Tasmania GPO Box 252C Hobart. Tasmania 7001. Australia Stephen A. Short Environmental Radiochemistry Laboratory, ANSTO Private Mail Bag I, Menai. NSW 2234. Australia Present address: Kmgett Mitchell and Associates PO Box 33-849, Takapuna. Auckland, New Zealand Ra. In addition, otolith cores have been analyzed with ^Th/^Ra to age flying fish, Hirundichthys affinis (Smith et al., 1991; Camp- ana et al., 1993), and silver hake, Merluccis bilinearis (Smith et al., 1991 ). While the isotope pair 228Th/ 228Ra is useful for short-lived fish up to about 5 years (Campana et al., 1993), analysis of 210Pb/226Ra is appropriate for medium-aged to long-lived fish up to about 120 years. In the present study measure- ments of 210Pb/226Ra disequilibria have been conducted on cores of adult female blue grenadier otoliths in an attempt to provide indepen- dent age data for this species. Blue grenadier, Macruronus novae- zelandiae, is a major commercial fish species in the upper continen- tal slope waters of southeastern Australia and New Zealand. An ac- curate knowledge of age and growth rate of this species is required for management of the fishery. Several ageing studies have provided esti- mates of age for blue grenadier (hoki) from New Zealand waters (reviewed by Paul, 1992), with the maximum age ranging from 12 to 15 years. Kenchington and Augus- tine ( 1987 ) examined whole otoliths and thin transverse sections from blue grenadier caught in southeast- ern Australian waters and reported a maximum age of 25 years. How- ever, Kenchington and Augustine ( 1987) were unable to validate their ages for fish >3 years of age. They found that conventional techniques of validating age estimates, such as tagging, modal analysis, marginal increment or edge-type analysis, and back calculation of lengths at age, could not be applied to blue grenadier. The possibility that radiometric analysis offish otoliths, a technique pioneered by Bennett et al. (1982) for ageing fish, might validate the ages of blue grenadier led to a study by Fenton et al. (1990). Unfortu- nately radiometric analysis of 210Pb and 226Ra in whole blue grenadier otoliths was unsuccessful for esti- mating fish ages (Fenton et al., 1990). This was due to an exponen- tial reduction in 226Ra incorpora- tion into the otoliths of blue grena- dier during their life, a reduction that was believed to result from an ontogenetic change in habitat from juvenile to adult fish. Recent advances with radiomet- ric ageing offish indicate that ages can be determined radiometrically from otolith cores (Campana et al., 1990, 1993; Smith etal., 1991). The coring method removes all the lay- ers of otolith growth beyond the earliest year(s) and thus avoids problems of changes in 226Ra or 210Pb uptake patterns in later life. Furthermore, an analysis of otolith cores circumvents the need to model the mass growth rate of otoliths, which is necessary in de- termining age from whole oto- liths (Smith et al., 1991). Radiometric analysis of otolith cores has been successfully used to age redfish, Sebastes mentella (Campana et al., 1990), and split- nose rockfish, Sebastes diploproa (Smith et al., 1991), with 2ioPb/226 Materials and methods Field collection Blue grenadier, Macruronus novae- zelandiae, were collected by bottom trawling (500-850 m depth) during cruises conducted northwest of Sandy Cape off the west Coast of Tasmania by the Tasmanian De- partment Primary Industry, Divi- sion of Sea Fisheries, and the CSIRO Division of Fisheries be- tween 1985 and 1986. Sagittal otoliths were removed and stored dry. This collection of otoliths was used by Kenchington and August- ine to estimate age by annulus counts (1987) and was subse- quently made available for the present study. Otolith morphometries The linear dimensions of blue gren- adier otoliths (maximum length, width, and thickness with respect to the primordia ) were measured to the nearest 0.1 mm with calipers. Otolith weight was also determined for « = 172 blue grenadier otoliths Manuscript accepted 25 September 1994. Fishery Bulletin 93:391-396 (1995). 391 392 Fishery Bulletin 93(2), 1995 from fish previously aged by Kenchington and Au- gustine (1987). The dimensions of otoliths from 1+ fish (ages assigned by Kenchington and Augustine, 1987) were examined and the average linear dimen- sions and weight for a 1+ fish determined. The aver- age otolith dimensions of 1+ fish were selected as the shape of the core to be removed. This core size was chosen 1) because it ensured minimal influence of changing 226Ra (as reported in Fenton et al., 1990); 2) because it represented the minimum core size that could be repeatably isolated (attempts to remove smaller cores, e.g. 0+ dimensions, resulted in the otolith shattering or splitting, and being unusable; and 3) because it fitted the age estimate of 1+ otoliths by Kenchington and Augustine ( 1987) who were able with confidence to validate fish age for individuals under 3 years old. Removal of otolith core Blue grenadier otoliths chosen for coring were se- lected from females collected from the same site, on the same date, and of similar fish length and otolith weight. Cores were removed from the otoliths by sanding the outer layers away by hand (with respect to the primordia) with wet and dry sand-paper (sili- con carbide paper) in progressively finer grades un- til the desired core dimensions were achieved. The mean core dimensions were compared with the mean whole otolith dimensions for 1+, 2+, and 3+ fish. New, wet and dry sand paper was used for each otolith to eliminate the risk of 210Po cross contamination be- tween otoliths. The cores of 2 or 3 fish were pooled to produce the 1-g sample necessary for radiometric analysis. Radiometric analysis Cores were cleaned of adventitious 210Po by exposure to an alkaline H202 solution for 1/2 hour. The analy- sis of 210Pb via its alpha-emitting, short-lived daugh- ter proxy 210Po followed the method we have previ- ously described (Fenton et al., 1991 ), employing high resolution alpha-spectrometry. Polonium-210 was assumed to be in equilibrium with 210Pb in all samples, and 210Pb concentrations were corrected back to the date offish collection. Mean 210Po reagent blank was 0.0071 ±0.0012 disintergrations per minute (dpm-g""1). Recovery of 210Po was invariably >90%. Instrumental background counts (for 208Po and 2I0Po) were less than 1 count per day. Analysis of 226Ra was by a direct alpha spectrometry technique (Fenton et al., 1991). The mean activity of the 226Ra blanks was 0.0174 ±0.002 dpm-g-1. Both 210Po and 226Ra blank values were reduced to lower values than those from previous studies because of tighter quality control of reagents and minor improvements in technique. Stable element analysis The levels of lead (Pb) and barium (Ba) are presumed to act as stable equivalents of 210Pb and 226Ra (Fenton and Short, 1992) and, as such, can potentially be used to assess the uptake of the radioactive isotopes and for normalizing the radiometric data. Therefore the concentrations of stable lead, barium, calcium (Ca), and strontium (Sr) in each otolith core sample were measured. An aliquot of the same dissolved otolith core solution used for 210Pb and 226Ra analysis was analyzed. Lead and barium were analyzed by induc- tively coupled plasma mass spectrometry (ICP-MS) and strontium and calcium by inductively coupled plasma atomic emission spectrometry (ICP-AES). Calculation of fish age Fish age was calculated by using the model proposed by Campana et al. (1990) and described in Smith et al. (1991). The 210Pb/226Ra activity ratio of the otolith core during growth, assuming a constant mass growth model for the period of core formation only, is given by the equation: Adl210 _ Pb =i-a-R) ARa™ XT where A = specific activity (i.e. activity concentra- tion); R - initial activity ratio (i.e. uptake activity ratio); A = decay constant of 210Pb (year-1); T = period of core formation (years). The activity ratio of the core at any subsequent time in the life of the fish is unaffected by mass growth of the otolith and is therefore given by the equation: '/■/, ARa2M 226 ^ ' i-a-R) -IT \ XT -X(t-T) where t= age of the fish (years). The fish age is found by solving for t by the Newton-Raphson iterative method. All radiometric age values are given with an error value of ±1 stan- dard deviation. NOTE Fenton and Short: Radiometric analysis of Macruronus novaezelandiae otolith cores 393 Table 1 Comparison of core dimensions and the otolith dimensions of 0+, 1+, 2+ and 3+ blue grenadier, Macruronus novaezelandiae. Probability (P) values are giver for r-test comparison of the mean core dimensions and mean whole otolith dimensions SD= standard deviation and n is the number of otoliths measured. Core dimension 0+ otolith 1+otolith 2+ otolith 3+ otolith Otolith length (mm) Mean 12.50 7.20 12.26 15.94 18.66 SD 0.20 0.29 0.68 1.37 1.09 n 24 48 38 12 14 P < 0.001 >0.02 <0.001 <0.001 Otolith width (mm) Mean 5.44 3.27 5.40 6.73 7.64 SD 0.14 0.15 0.30 0.69 0.33 n 24 47 38 12 14 P <0.001 > 0.50 <0.001 <0.001 Otolith Thickness (mm) Mean 1.28 0.74 1.25 1.69 1.79 SD 0.05 0.07 0.10 0.04 0.14 n 24 46 38 12 14 P <0.001 >0.10 <0.001 <0.001 Otolith Weight (g) Mean 0.2008 0.0197 0.0961 0.1870 0.2750 SD 0.007 0.020 0.013 0.043 0.030 n 24 57 38 13 14 P «0.001 «0.001 0.50-0.20 «0.001 Results Otolith core dimensions Otolith growth in linear dimensions and weight for juvenile blue grenadier (0+, 1+, 2+, and 3+) was rapid (Table 1). The cores that were removed approximated the linear dimensions of 1+ fish, but they were heavier than the average 1+ fish with a weight that was not significantly different from that of 2+ fish ( £=1.15;P>0.20). The dimensions and weight of 3+ fish otoliths were significantly greater than the isolated core dimensions. Therefore, in view of the core weight our calculation of age assumed that the cores ana- lyzed represented 2 years of growth. Stable element analysis Low levels of both stable lead and barium were found in all the samples (Table 2). Stable lead ranged from 0.269 to 1.78 ppm. Barium levels were low, ranging from 1.50 to 2.28 ppm, consistent with the relatively low 226Ra levels in these blue grenadier otolith cores. The ratio of Pb/Ba was relatively high, ranging from 0.17 to 0.78. From this Pb/Ba data we concluded that there is some allogenic uptake of 210Pb from the en- vironment. However the extent of uptake was diffi- cult to assess given the low levels of Pb and Ba mea- sured. The Sr/Ca ratio ranged between 0.0034 and 0.0042. Radiometric results 210Pb ranged from 0.0040 ±0.0045 to 0.0078 ±0.0025 dpm-g-1 (Table 3). The 226Ra content of the otolith Table 2 Blue grenadier, Macruronus novaezelandiae, stable element data from inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis of otolith core solutions. Sample Pb Ba Pb/Ba Sr Ca Sr/Ca number ppm ppm ppm/ppm ppm ppm ppm/ppm LH 2269 0.749 1.50 0.50 LH 2270 1.78 2.28 0.78 LH2271 0.389 1.57 0.22 LH2272 0.269 1.55 0.17 1590 400300 0.0040 1620 387800 0.0042 1810 448380 0.0040 1920 483570 0.0040 394 Fishery Bulletin 93(2), 1995 Table 3 Blue Grenadier, Macrui •onus novaezelandiae, otolith core radiometric results and ages calculated by using individual 226Ra and mean 226Ra activity ratios. 210pb/226Ra 210pb/226Ra Otolith Otolith activity activity core age core age Mean Mean ratio from ratio (years) from (years) fish otolith 2iopb 226Ra individual from mean individual from mean Sample length mass No. of (dpm- (dpm- 226Ra 226Ra 226Ra 226Ra number (cm) otoliths g-1) g"1) activity ratio activity ratio activity ratio activity ratio LH 2269 95.63 ±0.44 0.5395 6 0.0051 0.0290 0.174 0.227 5.5 (+3.4, -3.0) 7.6 1+5.0,-4.3) ±0.009 ±0.0023 +0.0036 ±0.082 ±0.111 LH 1817 99.3 ±0.52 0.7116 6 0.0040 0.0203 0.197 0.179 6.4 ( + 10.6, -7.9) 5.7 1+9.2,-7.2) ±0.078 ±0.0045 ±0.0042 ±0.225 ±0.205 LH 2270 104.0 ±1.79 0.7136 6 0.0078 0.0179 0.438 0.351 17.9 ( + 10.2, -7.7) 13.3 (+7.1, -5.8) ±0.053 ±0.0025 ±0.0026 ±0.153 ±0.129 LH 2271 107.2 +3.06 0.8896 6 0.0074 0.0222 0.332 0.331 12.3 (+8.2,-6.5) 12.2 (+8.2, -6.5) ±0.073 +0.0031 ±0.0039 ±0.151 ±0.151 LH 2272 110.3 ±1.37 0.9531 6 0.0058 0.0223 0.259 0.259 9.0 1+6.8,-5.6) 9.0 1+6.9,-5.7) ±0.076 ±0.0030 ±0.0039 ±0.142 ±0.143 cores ranged from 0.0179 to 0.0290 dpm-g : and showed a mean value of 0.0223 ±0.0036 dpm-g"1. The 226Ra values found for the cores were consistent with our earlier analysis (Fenton et al., 1990) of whole otoliths (see Discussion section) and further confirmed that the core represents approximately a 2+ fish. In order to select the value of R, the initial activity ratio used in the calculation of age, we examined our previous data for whole otoliths (Fenton et al., 1990) and the stable element analysis of Pb and Ba (dis- cussed above). From the data for a 1+ fish a value of R<0.06 is indicated; however, data for 0+ fish indi- cate R could be as high as 0.1. A value of #=0.05 ap- pears to be the best estimate for the initial activity. If R were as high as 0.1, it would lower the age esti- mate by approximately 9 months. Conversely, if R =0, ages would be higher by 2.6 years. The differ- ence that a lower or higher value makes to the age estimates is well within the error associated with each radiometric age calculated by using R=0.05. Otolith core ages were calculated by using both the individual sample 226Ra value and the mean 226Ra value. This has little effect on the average age of all the cores analyzed (e.g. 10.2 ±5.0 years [with indi- vidual 226Ra] and 9.6 ±3.2 years [with mean 226Ra]), but the maximum age recorded changes from 17.9 (+10.2, -7.7) years (with individual 226Ra) to 13.3 (+7.1, -5.8) years (with mean 226Ra) depending on which radium value is used. Since all individual 226Ra activity ratios are similar within experimental er- ror, it follows that the best age estimates are calcu- lated by using the mean 226Ra activity. Age estimates from annulus counts conducted by Kenchington and Augustine (1987) relative to fish length and otolith weight are plotted together with the radiometric core age estimates in Figure 1. The radiometric analysis of otolith cores are similar to those assigned by Kenchington and Augustine ( 1987 ), although there is some indication that the radiomet- ric ages may be slightly lower. However, the core samples represent the average age of only three fish, the errors associated with the radiometric analyses are large, and limited sample sizes preclude any meaningful statistical analysis. Discussion Radiometric analysis of otolith cores has successfully provided age estimates for blue grenadier, in contrast to the unsuccessful analysis of whole otoliths by Fenton et al. (1990). The average age of the otolith core samples was approximately 10 years for fish 95- 110 cm in length. NOTE Fenton and Short: Radiometric analysis of Macruronus novaezelandiae otolith cores 395 25~ A m 20- c I -c- 15~ an BD It >■. □ • * „ 1 ♦ % ■*-•-! <*> 34.85 ppt) which flows into the area from the southeast; and 3) warm, highly saline (S >34.9 ppt) Gulf of California water (Roden and Groves, 1959; Stevenson 1970; Alvarez-Borrego, 1983). This region experiences upwelling events dur- ing the spring (Roden, 1964; Roden and Groves, 1959; Alvarez-Borrego and Schwartzlose, 1979). The oxy- gen content in the upper 100 m layer is greater than 1 mL/L; be- low 150 m the oxygen concentration falls to less than 0.5 mL/L and at intermediate depths (500-1,100 m) oxygen may be undetectable by the Winkler method (Alvarez-Borrego et al., 1978). 1 Chapa-Saldana, H. 1956. La distribution comercial de los camarones del noroeste de Mexico y el problema de las artes fijas de pesca. Dir. Gral. de Pesca e Industrias Conexas, Sria. de Marina, Mexico, D.F., 87 p. 2 Loesch, H., and Q. Avila. 1966. Obser- vaciones sobre le pesqueria de camarones juveniles en dos esteros de la costa de Ec- uador. Bol. Cient. y Teen. INP del Ecua- dor. 1, 30 p. Manuscript accepted 29 August 1994. Fishery Bulletin:397-402 (1995). 397 398 Fishery Bulletin 93(2), 1995 J. S. A P IAXTLA \ / \ PRESIDIO / BALUARTE TEACAPAN A GUA BRAVA RIVER 23° 30' RIVER RIVER LAGOgjj^COMPlEX j O • _ 0s* o o ° • o • 0 • o o ^^ 0 o • O o • 0 o o o 0.0 0 0 • O 0 o / GULF OF CALIFORNIA 106° 00' \ 0 30 Km 2™ ,06=30 23"°° ,07-00' / \ / \ Figure 1 Study area (1981-86) located off the mouths of the Piaxtla River and the Teacapan- Agua Brava lagoon complex, Mexico. Twenty-nine stations from the CRIP-INP cruise series are denoted by empty circles. Stations from the BIOCAICT series are indicated with solid circles. Seventeen survey cruises were made by the Centro Regional de Investigaciones Pesqueras of the Institute Nacional de la Pesca (CRIP) on board com- mercial shrimp trawlers during the years 1981, 1982, 1984, 1985, and 1986, and four cruises were made by the Universidad Nacional Autonoma de Mexico between November 1985 and August 1986 on board the vessel MARSEP XI (BIOCAICT cruises). On all cruises, a pair of 22.9-m otter trawl nets was used. The nets have a progressively reducing mesh size from 6.4 cm on the body of the net to 3.8 cm at the cod end. Eleven sampling stations of the BIOCAICT series were located on four transects perpendicular to the coast line off the mouths of Piaxtla, Presidio, and Baluarte rivers and off the Teacapan-Agua Brava lagoon complex. Sampling depth varied from 9 to 90 m. Data from the more extensive CRIP cruises were selected to match the location of the BIOCAICT se- ries (Fig. 1). In all BIOCAICT cruises, surface, mid-water, and bottom water samples were taken with 8-L niskin bottles. Temperature was measured in situ with re- versing thermometers to the nearest 0. 1°C. Dissolved oxygen (DO) was determined by using a modifica- tion of the Winkler method (Strickland and Parson, 1972). At each sampling station, shrimps were sorted, identified, and counted for each catch. Color in fresh animals (Chapa-Saldaha1) proved to be a very reli- able character for species identification. CRIP monthly samples from 29 stations within a depth span of 9-80 m were averaged at intervals of 18 m (10 fathoms), except for the initial interval of 9 m (9-18 m), and pooled across years into four bi- monthly periods. The term sample refers to the num- ber of shrimp per twin net haul divided by the num- ber of hours (ind./h) at each station. The first period (April-May) had a total of 87 samples (April 1985, May 1981, 1982 at 29 stations [Fig. 1], distributed in five depth intervals [9-18 m, 19-36 m, 37-54 m, 55- 72 m, and 73-80 m]). June-July had 203 samples (June 1981, 1982; July 1981, 1982, 1984, 1985, and 1986) while August-September had 145 samples (August 1981, 1985, 1986; September 1982, 1985), and there were 87 samples for October-December (October 1981; December 1985, 1986). The sampling periods between June and September had higher NOTE Garduno-Argueta and Calderon-Perez: Depth distribution of Penaeus brevirostris 399 numbers of samples because the CRIP cruises were primarily intended to sample the closed season that, in those years, was imposed for that period. Catch data were averaged by period and depth interval and are reported as mean number of individuals per hour (ind./h ±SE) of trawling. Seasonal abundance data from BIOCAICT cruises, on the other hand, are re- ported for only three depth intervals: 9-15 m, 40-45 m, and 70-90 m. Catch figures were averaged for every 2.0°C interval of temperature and 0.5 mL/L interval of dissolved oxygen within the observed ranges and are presented as the average number of individuals per hectare (ind./ha ±SE). Nonparametric single factor analysis of variance by ranks (Kruskal-Wallis test for tied ranks) was used to test for differences in shrimp abundance between the five depth intervals in each of the four bimonthly periods and between four dissolved oxygen levels. A nonparametric multiple range test (NMRT) was used in cases where Kruskal-Wallis test were significant (0.05). During June- April - May 10.0 5.0 o.o 40.0 rh 9-18 19-36 37-54 55-72 73-80 Depth Interval (m) August -September N. E 20.0 _r±L 9-18 19-36 37-54 66-72 73-80 Depth Interval (m) June-July 30.0 Q. £ 20.0 B 10.0 0.0 16.0 12.0 E e- -c if) 8.0 4.0 9-18 19-36 37-54 65-72 73-80 Depth Interval (m) October- December D 9-18 19-36 37-64 56-72 73-80 Depth Interval (m) Figure 2 Mean abundance (shrimp/h ±SE) of crystal shrimp, P. brevirostris, at five depth intervals. Data combined from CRIP cruises in 1981, 1982, 1985, and 1986. (A) April-May 1981, 1982, and 1985; (B) June-July 1981, 1982, 1984, 1985, and 1986; (C) August-September 1981, 1982, 1985, and 1986; and (D) October-December 1981, 1985, and 1986. Abundance refers to mean number of shrimp caught at stations located within each depth interval in one hour trawling (paired 22.86-m otter trawl). 400 Fishery Bulletin 93(2). 1995 July, higher catches were obtained between 55 and 72 m (22.1 ±8.855), but abundance was also consid- erable at 37-54 m (6.9 ±3.3) (Fig. 2B, Kruskal-Wallis test, P<0.001). Mean abundance was significantly different between depth interval 55-72 m and all other intervals (NMRT, P<0.01), between depth in- terval 37-54 m and the remaining three intervals (NMRT, P<0.01), and was not significantly different between depth intervals 9-18, 19-36, and 73-80. In August-September, red shrimp was found only at depths beyond 55 m (Fig. 2C, Kruskal-Wallis, P<0.025). Mean abundance was significantly differ- ent between depth interval 55-72 m and all other depth intervals (only three categories were consid- ered, as three intervals with zero abundance were regarded as one; NMRT, P<0.005). Abundance be- tween depth intervals 9-18 m, 19-36 m, 37-54 m, and 73-80 m was not significantly different. During the October-December period, P. brevirostris catches were taken mainly at depth intervals 31—40 and 41- 50 m (Fig 2D, Kruskal-Wallis, P>0.05). Although there appears to be a distinct difference in abundance between depth intervals, the test was not significant because the number of zero catches was high (79 cases out of 84), making the sum of ranks very simi- lar in all intervals. The high standard error indicates the extent of data dispersion. These results suggest that although P. brevirostris is generally found at greater depth intervals in the summer and autumn, its presence at mid-depths and shallower waters in spring may be an indication of seasonal changes in bathymetric distribution, i.e. onshore in spring and offshore in summer and autumn. The distribution and abundance of P. brevirostris observed during the BIOCAICT cruises (Fig. 3) were very similar to those described earlier, i.e. the shrimp were mostly distributed in deeper waters except for the capture of some individuals at a depth of 10 m in June 1986 (Presidio and Baluarte transects). In No- vember 1985 (Fig. 3A) and January 1986 (Fig. 3B), most individuals were caught at the deepest stations (70-90 m; 11.47 ±3.99 and 53.07 ±18.01 ind./ha, 20.0 15.0 ro X 10.0 E e_ JZ C 5.0 0.0 2.0 1.5 ro X Q. 1.0 e November 1985 9-15 40-45 70-90 Depth Interval (m) June 1986 9-15 40-45 70-90 Depth Interval (m) January 1986 ro X 80.0 60.0 40.0 E L. $1 20.0 0.0 B 9-15 40-45 70-90 Depth Interval (m) 4.0 August 1986 ro X X 3.0 2.0 1.0 0.0 D 9-15 40-46 70-90 Depth Interval (m) Figure 3 Mean abundance (shrimp/ha ±SE) of crystal shrimp, Penaeus brevirostris, at depth intervals observed during the BIOCAICT cruises in (A) November 1985, and (B) January, (C) June, and (D) August 1986. NOTE GardunoArgueta and Calderon-Perez: Depth distribution of Penaeus brev/rosms 401 respectively), except for a small catch in the former at the 9-15 m depth interval (0.13 ±0.19 ind./ha). In mid-June, very few specimens were collected (0.37 ±0.26 ind./ha), all in the Presidio and Baluarte transects at depths of about 10 m (Fig. 3C). During the summer cruise (August 1986) all individuals were caught at the deeper stations, (>70 m, 1.50 ±0.73 ind./ ha; Fig. 3D). The distribution of P. brevirostris observed during the BIOCAICT cruises, at all the stations, appeared to be limited to a narrow temperature range. The majority of individuals were caught at temperatures between 14.1 and 18.0°C and, although some indi- viduals were also found at about 24.0°C, the average mean abundance at this temperature was rather low (0.1 ind./ha; Fig. 4). Similarly, the main distribution of P. brevirostris appears to be limited to a narrow bottom dissolved oxygen range (Fig. 5). Mean shrimp densities were highest at the DO levels of 0.9-1.5 mL 0,/L while at higher (2.9-4.1 and 4.2-6.0 mL O/L) and lower lev- els (0.1-0.8 mL O^), mean shrimp abundance was lower ( Kruskal-Wallis test, P<0.005 ). Crystal shrimp abundance was significantly higher at the DO inter- val 0.9-1.5 mL/02 than at the other DO intervals (NMRT, P<0.005. Abundance differences among other DO intervals were not significant. The former suggests that P. brevirostris occupies waters with lower oxygen content than do the other members of the genus. Most studies emphasize their distinct avoidance of hypoxic water and the nega- tive consequences of exposure to it. Renaud (1986) found that P. aztecus and P. setiferus were able to detect and avoid hypoxic water below 2 ppm (1.4 mL 02/L) and 1.5 ppm (1.05 mL 02/L), respectively. Broom (1971) found a slightly higher threshold for the latter species (2 ppm, 1.4 mL O^). Rubright et al. ( 1981) and Bassanesi-Poli ( 1987) reported surface oriented movements of P vannamei when dissolved oxygen in culture ponds dropped below 2 mlVL. Egusa andYamamoto( 1961) observed stress in P japonicus for oxygen concentrations below 2 mL/L and evacua- tion of their burrow at a DO level of 0.7 ppm (0.5 mL Og/L). Regarding prolonged effects of hypoxia, Clark (1986) reported that P. latisulcatus showed molt in- hibition and increased mortality under the hypoxic conditions of 2 ppm (1.4 mL O^). The disappearance of P. brevirostris from tradi- tional fishing grounds in the summer may be due to the occurrence of temperature and dissolved oxygen levels outside its tolerable range. The population may move to deeper regions where low temperature and DO conditions, to which they are better adapted, prevail. Calderon-Perez3 found a substantial num- ber of shrimps of this species 120 m deep in June 1992 but none in shallower areas where tempera- ture and DO were higher. Thus, the seasonal variation in depth distribution of P. brevirostris in the eastern Pacific ocean may be due to bathymetric movements which, for most ani- mals (Figs. 4 and 5), seem to be determined by sea- sonal changes in environmental parameters. 3 Calderon-Perez, J. A. 1992. Data from the BIOCAPESS VI cruise on board the B/O (R/O) El Puma, carried out between 24-30 June 1992. Estacion Mazatlan, Institute de Ciencias del Mar y Limnologia, U.N.A.M., apdo. Postal 811, Mazatlan, Sinaloa, Mexico, CP 82000. 11.0 15.0 19.0 23.0 27.0 31.0 Temperature (°C ) Figure 4 Mean abundance (shrimp/ha ±SE) of crystal shrimp, Penaeus brevirostris, in relation to bottom temperature (°C). Vertical lines represent standard error of the mean for each 2°C interval. 10 2.0 3.0 4.0 5.0 60 Dissolved Oxygen (mL/L) Figure 5 Mean abudance (shrimp/ha ±SE) of crystal shrimp, Penaeus brevirostris, in relation to dissolved oxygen (DO) concentration. Vertical lines represent standard error of the mean calculated for each DO interval of 0.5 mL/L. 402 Fishery Bulletin 93(2), 1995 Acknowledgments The authors wish to express their gratitude to the crew and skipper of the Training Trawler MARSEP XI for their enthusiasm and help during the course of the cruises carried out between November 1985 and August 1986. We are very grateful to Sergio Rendon Rodriguez for his invaluable help during the cruises and for processing samples. Thanks are also due to the participants of the Programa Camaron del Pacifico (Pacific Shrimp Program) of the Centro Regional de Investigacion Pesquera, Mazatlan. Literature cited Alvarez-Borrego, S. 1983. Gulf of California. In B. H. Ketchum (ed.), Estuar- ies and enclosed seas, vol. 26, p. 426-449. Alvarez-Borrego, S. and R. A. Schwartzlose. 1979. Masas de agua del Golfo de California. Ciencias Marinas 1:143,163. Alvarez-Borrego, S., J. A. Rivera, G. Gaxiola-Castro, M. J. Acosta-Ruiz, and R. A. Schwartzlose. 1978. Nutrientes en el Golfo de California. Ciencias Ma- rinas 5:53,71. Barreiro, M. T., and L. Lopez-Guerrero. 1972. Estudio de los recursos pesqueros demersales del Golfo de California 1968-1969. II: Camarones. In J. Carranza (ed.), Memorias IV Congreso Nal. de Oceano- grafia, Mexico, D.F., noviembre 1969, p. 345-359. Bassanesi-Poli, A. T. 1987. Analisis de un cultivo de camaron bianco {Penaeus vannamei Boone) en estanques rusticos en San Bias Nayarit, Mexico. Ph.D. diss., U.A.C.P.yP., Universidad Nacional Autonoma de Mexico, 295 p. Broom, J. G. 1971. Shrimp culture. Proc. 1st Annual Meeting World Maricult. Soc. 1:63-68. Calderon Perez, J. A., and C. R. Poli. 1987. A physical approach to the postlarval Penaeus immi- gration mechanism in a Mexican coastal lagoon (Crusta- cea: Decapoda, Penaeidae). An. Inst. Cienc. del Mar y Limnol. Univ. Nal. Auton. Mexico, 14:147-156. Clark, J. V. 1986. Inhibition of moulting in Penaeus semisulcatus (De Haan) by long-term hypoxia. Aquaculture 52:253-254. Cobo, M., and H. Loesch. 1966. Estudio estadistico de la pesca de camaron en El Ec- uador y de algunas caracteristicas biologicas de las especies explotadas. Bol. Cient. y Teen. I.N.P del Ecuador 1:6-24. Edwards, R. R. C. 1978. The fishery and fisheries biology of the penaeid shrimp on the Pacific Coast of Mexico. Oceanogr. Mar. Biol. Ann. Rev. 16:145-180. Egusa, S., and T. Yamamoto. 1961. Studies on the respiration of the "kuruma" prawn Penaeus japonicus Bate. I: Burrowing behavior with spe- cial reference to its relation to environmental oxygen concentration. Bull. Jpn. Soc. Sci. Fish. 27:22-27. Hendrickx, M. E. 1986. Distribucion y abundancia de los camarones Penaeoidea (Crustacea: Decapoda) colectados en las campahas SIPCO (sur de Sinaloa, Mexico) a bordo del B/O "EL PUMA." An. Inst. Cienc. del Mar y Limnol. Univ. Nal. Auton. Mexico. 13:345-368. Hendrickx, M. E., A. M. Van der Heiden, and A. Toledano-Granados. 1984. 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Bull. 67, Ottawa, Canada. Zar, J. H. 1974. Biostatistical analysis. Prentice-Hall, Inc., Engle- wood Cliffs, NJ, 620 p. The diet of the swordfish Xiphias gladius Linnaeus, 1 758, \n the central east Atlantic, with emphasis on the role of cephalopods Vicente Hernandez-Garcia Dpto. de Biologia, Facultad de Ciencias del Mar Univ. de Las Palmas de G. Canaria C.R 35017, Canary Islands, Spain tained from a longline vessel between 1 and 15th March 1991 by using mackerel, Scomber spp., as bait. Zone C Gulf of Guinea (3°09- 0°36'N and 26027'-4°17'W). Fifteen swordfish (standard length [SL] between 140-209 cm) were selected on the basis of the presence of cephalopods in their stomachs. These were taken from catches made by a longliner between May and July of 1991 by using mackerel and squid, lllex sp., as bait. The swordfish Xiphias gladius Linnaeus, 1758, is a mesopelagic teleost with a cosmopolitan distri- bution between 45°N and 45°S lati- tude. It is an opportunistic preda- tor feeding mainly on pelagic ver- tebrates and invertebrates (Palko et al., 1981). The diet of the sword- fish has been studied mainly in the western Atlantic Ocean (Tibbo et al., 1961; Scott and Tibbo, 1968, 1974; Toll and Hess, 1981; Stillwell and Kohler, 1985). Earlier reports reflected the importance of fish in the swordfish diet, but recently Stillwell and Kohler (1985) cited squid as the predominant compo- nent in the diet of swordfish. Azevedo ( 1989) and Moreira ( 1990), reporting from off the Portuguese coast, mentioned fish (principally Micromesistius poutssou ) and cepha- lopods as the main prey groups of swordfish. This finding was cor- roborated by Guerra et al. (1993) from the Northeastern Atlantic where cephalopods were found to be the most important component of the diet. Maksimov (1969) stud- ied the diet of swordfish in the east- ern tropical Atlantic Ocean. Cepha- lopods were a major component of the diet in all areas sampled and although no cephalopod species were identified, the genus Omma- strephes was present among the five genera found in stomach contents. Stomach content analysis is an important tool in ecological and fisheries biology studies. Oceanic vertebrates are often more efficient collectors of cephalopods than any available sampling gear (Bouxin and Legendre, 1936; Clarke, 1966). The purpose of this study was to expand knowledge of the diet of the swordfish from the central east At- lantic Ocean, with special emphasis on the role of cephalopod species. Material and methods Sampling areas and capture methods The stomach contents of 75 sword- fish, Xiphias gladius, were ana- lyzed. Specimens were caught at night in three different areas of the central east Atlantic Ocean (Fig. 1) from the commercial landings of the Spanish fleet: Zone A Strait of Gibraltar (35053'-35042'N and 6°35'-6o30'W). Thirty five swordfish were caught with drift nets (2.5 miles long x 20 m deep) between 10 and 22 Septem- ber 1990. Zone B South of the Canary Is- lands (23°-26°N and 17°-22°W). Twenty-five swordfish were ob- Stomach preservation and analysis In zones A and B, fish were stored in ice. After landing, fish were mea- sured from the tip of the lower jaw to the fork of the tail (SL). During commercial operations the internal organs were removed before the fish were weighed. The stomach contents of each fish, including all hard parts found in the stomach wall folds (otoliths, very small beaks, and lenses), were weighed (in grams) and preserved in 70% ethyl alcohol. Otoliths were also removed from the fish prey. Nema- todes were found in some stomachs in small quantities, but these were assumed to be parasites and were not considered prey. In general, stomach contents showed an ad- vanced level of digestion. A stomach fullness index (SF) was calculated as SF = (wet weight of the stomach con- tent / wet weight of the swordfish without internal organs) x 100. In zone C only cephalopods were preserved frozen. Fish were frozen immediately after capture without internal organs. This material was not included in comparative analy- ses because the main objective was to record the relative proportions of cephalopod species that were preyed upon in this zone. Scomber spp. and lllex sp. were not considered prey from zones B Manuscript accepted 17 November 1994. Fishery Bulletin 93:403-411 (1995). 403 404 Fishery Bulletin 93(2), 1995 Figure 1 Locations of the swordhsh Xiphias gladius fishing grounds in the central east Atlantic Ocean where samples were obtained in 1990-91. and C respectively because they were used as bait. Prey items were identified to the lowest taxonomic category possible. Fish were identified from otoliths and bones (otolith guides of Harkonen ( 1986), Hecht and Hecht ( 1979), and author's collection). Crusta- ceans were classified from external parts of the skel- eton (Zariquiey -Alvarez, 1968). Lower beaks (LB) were used as the primary means for classification of cephalopods, and beak identity was established by methods described by Clarke ( 1962, 1980, 1986a) and supplemented by a collection of cephalopod beaks (in- cluding beaks removed from locally caught cephalo- pods); upper beaks, other morphological characters (Hess and Toll, 1981), and distributional knowledge (Nesis, 1987) were used in some cases as well. Nearly all the beaks collected were fresh. All lower beaks were identified to the lowest taxon possible and the lower rostral length (LRL) or, in the order Sepiida, the hood length (LHL) (defined in Clarke, 1962, 1980) were measured by digital caliper or steroscopic mi- croscope and eyepiece micrometer. Mantle lengths (ML in mm) and weights (W in g) of the cephalopods from which lower beaks came were then estimated from LRL's or LHL's by using relationships published elsewere (Clarke 1962, 1980, 1986a; Perez-Gandaras, 1983; Wolff, 1982 (cited by Clarke, 1986a), Wolff and Wormuth, 1979). Despite the advanced state of digestion of stom- ach contents, an attempt was made to examine the importance of each prey item. Two methods of stom- ach content analysis were used: percent numerical abundance and percent occurrence (Hyslop, 1980). A coefficient of prey numerical frequency, % No. = {Nil Nt) x 100, and a coefficient of prey frequency, % oc- currence = (NsilNsf) x 100 were calculated; where Ni is the number of prey of each group i, Nt is the total number of prey, Nsi is the number of stomachs containing each group i, and Nsf is the total number of stomachs with food. An index of prey numerical importance (Castro, 1993) was also obtained as % importance = (% No. x % occurrence)1'2 x 100. Comparative analysis of degradation of hard structures Free hard structures (otoliths, beaks, and eye lenses) were often found in the stomach contents. To esti- mate the importance of each prey item from the re- fractory or hard structures, it is important to know the rate of degradation by stomach acids. Otoliths (sagittae) from four chub mackerel, Scomber japonicus (18 to 20 cm SL), similar in size to those found in the swordfish stomachs, and five otoliths of blue whiting, Micromesistius poutassou, from head-specimens found in swordfish stomachs were used to determine the rate of otolith degrada- tion. Otolith lengths, taken on the longest axis, were between 3.70 and 4.10 mm for Scomber and between 10.81 and 13.53 mm for Micromesistius. Beaks from eleven Illex coindetii and two Todarodes sagittatus were used, with LRL's between 3.90 and 6.19 mm and 7.53 and 8.41 mm, respectively. Degradation of six eye lenses, three belonging to T. sagittatus and three belonging to fish species, were also analyzed. Hard structures were placed in a hydrochloric acid (HC1) solution (pH=l.l; value lower than the range reported by Jobling and Breiby [1986] for fish in which the digestive process had begun), and the tem- perature was maintained between 18 and 20°C. The experiment was carried out for 48 hours. Old acid solu- tions were replaced with fresh solutions after 24 hours. Cephalopod beak digestion (measured as decreas- ing upper rostral length, lower rostral length, and NOTE Hernandez-Garcia: Diet of Xiphias gladius 405 lower wing length) and eye lens digestion ( measured as decreasing lens diameter) were measured every 12 hours. Otolith digestion (measured as decrease of the longest axis length) was measured at intervals of 12 hours for blue whiting, although the third in- terval was divided into two intervals (measuring each 6 hours). Otolith digestion was measured at inter- vals of 2.5 or 1 hour for the chub mackerel. Results Stomach fullness analysis Data on fish length (SL), weight (W), and stomach fullness (SF) from zones A and B are given in Table 1. Values of SF in zone A were higher than those in zone B. In the latter area four stomachs were empty whereas in zone A all stomachs had contents. nal column (as long as 78.5 cm). It was estimated that otoliths and spines belonged to a total of 476 fish. Blue whiting, Micromesistius poutassou, was the most important prey species by number (37.81%, Table 3). Cephalopods were detected in 17.14% of the stom- achs sampled, and the number of specimens was es- timated as 26 (Table 2). They were always present in those fish with the highest SF. The Omma- strephidae was the most important family by num- ber (35.6%) and Todarodes sagittatus was the pre- dominant species (23.4%). The Histioteuthidae ranked second in importance (21.4%) and Histio- teuthis bonnellii was the dominant species (11.4%, Table 4). Decapods of the order Natantia were found in the stomach contents of two individuals (Table 2), and a large specimen was identified as Acanthephyra purpurea. Stomach contents analysis Zone A The swordfish diet consisted offish, cepha- lopods, and decapods (Table 2). Fish were the most important item by number (93.33%, Table 2), al- though in 20% of the stomachs analyzed fish were represented by only otoliths and bones. Atotal of 832 otoliths were collected. Most bone remains could not be identified. Many of them consisted of a large spi- Zone B In zone B the swordfish diet consisted of cephalopods and fish. Cephalopods represented the most common food item in this area, revealing the highest index of numerical importance (67.89%, Table 2). A group of six pairs of beaks and one free upper beak with the same shape could not be assigned to any family. These were called "Unknown A." A description and sketches of this beak type (Fig. 2) are given in the Appendix. Ommastrephidae was the Swordfish Xiphias gladius data from zones number offish collected in each zone. A and B: Table 1 length (SL) in cm. weight (W) in Kg, and stomach fullness (SF). n is the SL W SF n Range Mean SD Range Mean SD Range Mean SD Zone A 35 103-193 Zone B 25 112-201 142.4 153.3 17.72 24.54 20-132 13-102 56.95 40.40 29.71 24.36 0.1-9.0 0-5.3 2.46 0.75 2.29 1.37 Table 2 Comparison of the dietary importance of the three major forage categories observed in swordfish stomachs from zones A (35 fish) and B (21 fish). Data are given in terms of numerical frequency, frequency of occurrence, and index of numerical importance. Zone A Forage category Zone B Forage category % number % occurrence % importance % number % occurrence % importance Fish Cephalopods Decapod Crustacea 93.33 5.09 1.56 100.0 17.14 5.71 88.78 8.54 2.66 Fish Cephalopods Decapod Crustacea 28.57 71.42 0.0 42.85 76.19 0.0 32.10 67.89 0.0 406 Fishery Bulletin 93(2), 1995 Table 3 Fish species occurring in the diet of the swordfish Xiphias gladius in zones A and B (35 and 9 swordfish stomachs containing fish, respectively) expressed in terms of numerical frequency, frequency of occurrence, and index of numerical importance. Zone A ZoneB Species % number % occurrence % importance Species % number % occurrence % importance Micromesistius poutassou 37.81 80.00 38.61 Diaphus sp. 16.66 22.22 18.35 Scomber japonicus 3.78 22.85 6.53 Thunnus sp. 5.55 11.11 7.49 Caprosaper 2.10 8.57 2.97 Not identified 77.77 77.77 74.16 Lepidopus caudatus 1.47 20.00 3.80 Trachurus sp. 1.26 14.28 2.97 Merluccius merluccius 0.84 5.71 1.53 Thunnus sp. 0.21 2.85 0.54 Not identified 52.52 71.42 43.00 • r\ \ \ Figure 2 Illustration of the characteristic, unidentified, lower beak (called "Unknown A"). Lower rostral length = 3.4 mm. (A) profile of the beak; (B) profile of the anterior part with one side removed to show the shoulder and the anglepoint; (C) top view; (D) outline of the beak showing the positions of sections shown in E and F; (E) three sections of the crest and one lateral wall taken at positions indi- cated in D to show thickening; and (F) two sections of the wing and shoulder region at positions shown in D. Cartilage is indicated by arrows and dotted area. NOTE Hernandez-Garcia. Diet of Xiphias gladius 407 Table 4 Cephalopods in the diet of the swordfish Xiphias gladius from zones A, B, and C (6, 16, and 15 swordfish with cephalopod remains, respectively) Number of cephalopods (n), index of numerical importance (IN), range of lower rostral length (LRL) range of estimated mantle length (ML), and range of estimated body weight (W) in each zone. The percentage by number of each i species in all areas together is also given. The equation used is given under the symbol (A) (a = Clarke, 1962; b = Clarke, 1980; c = Clarke, 1986; d = Perez-Gandaras 1983; e = Wolff and Wormuth, 1979; f = Wolff. 1982). A specimen identified and counted from upper beaks is indicated by an asterisk (*). Broken beaks are indicated by (R). Group or Zone A Zone B Zone C All zones % LRL ML W % LRL ML W % LRL ML W Species n IN (mm) (mm) (g) n IN (mm) (mm) (g) n IN (mml (mm) (g) % A Family Spirulidae Spirula spirula 1 2.6 0.7 20.4 1.0 0.9 c Family Sepiidae Sepia officinalis 1 5.0 4.0 97 34 0.9 d Family Loliginidae Loligo vulgaris 2 3.7 3.9-1.2 286-311 437-542 1.7 c Family Ancistrocheiridae Ancistrocheirus lesueuri 1 5.0 5.6 186 379 1 3.0 - 170 1.7 b Family Octopoteuthidae Octopoteuthis rugosa 1 5.0 12.4 215 401 0.9 b Family Onychoteuthidae Onychoteuthis A 3 6.5 3.2-4.5 166-245 132-466 1 3.0 6.6 373 1,923 3.5 f Onychoteuthis B 1 3.0 3.0 154 105 0.9 f Onychoteuthis C 6 17.2 3.0-1.4 154-243 109-451 5.3 f Family Gonatidae Gonatus sp. ? 1* 5.0 - 0.9 - Family Histioteuthidae Histioteuthis bonnellii 5* 11.4 6.4-7.9 74-88 247-377 4.4 b Histwteuthis dofleini 1 5.0 7.0 128 435 3 8.3 5.4-6.9 95-121 235-435 3.5 bf Histioteuthis A 1 5.0 2.8 48 53 0.9 b Family Brachioteuthidae Brachioteuthis sp. 1 2.6 1.6 48 3 0.9 c Family Ommastrephidae Todaropsis eblanae 2 7.2 R-U R-141 R-189 1.7 d Todarodes sagittatus 7* 23.4 4.4-6.9 172-274 149-517 2' 5.6 6.5 260 448 8.0 ba Ommastrephes bartrami 1 5.0 8.5 303 1,383 3 8.0 4.5-8.1 180-289 185-1,170 3.5 a Sthenoteuthis pteropus 10* 20.6 8.1-12.9 336-531 787-7,508 22* 41.6 5.3-10.8 21M42 375-4,052 28.3 e Ommastrephid species 1 2.6 1.6 - 0.9 - Family Thysanoteuthidae Thysanoteuthis rhombus 4 7.5 3.3-7.6 252-727 670-8,613 4* 11.8 4.2-5.9 351-543 1,402-4,052 7.0 c Family Mastigoteutbidae Uastigoteuthis sp. 1 5.0 5.6 - 0.9 - Family Grimalditeuthidae Grimalditeuthis bomplandi 1 3.0 3.9 0.9 - Family Cranchiidae Teuthowenia megalops 1 5.0 4.1 179 56 0.9 c Teuthowenia sp. 1 3.0 2.8 0.9 - Megalocranchm sp. 2 5.3 5.1-5.4 276-297 1.7 b Family Argonautidae Argonauta sp. 1* 5.0 - 6 13.0 3.8-7.2 6.2 - Unknown A 7* 14.0 3.0-4.4 6.2 - Not identified 2 7.2 - 3 8.0 - 2 5.9 6.2 - 408 Fishery Bulletin 93(2), 1995 most important family by number (36.8%), and the orangeback squid, Sthenoteuthis pteropus, was the most important species (20.6%, Table 4). Eighteen fish were counted from spinal columns and otoliths with an index of numerical importance of 32.10% (Table 2). Fish were found together with cephalopods in 19.0% of the stomachs containing food. In zone A the numbers of free lenses offish and cepha- lopods were similar. However, only 32 cephalopod lenses were found in zone B; fish lenses were not found. Zone C A total of 46 cephalopods were found in stomachs from zone C. The family Ommastrephidae, represented solely by Sthenoteuthis pteropus, was the most important species by number (41.6%) and esti- mated weight (Table 4). The Onychoteuthidae ranked second in importance by number but not by weight. In the combination of all three zones, the Om- mastrephidae, Onychoteuthidae, Histioteuthidae, and Thysanoteuthidae were the most important cephalopod families by number in swordfish diet (67.9%); other families are probably occasional prey. The most important species was Sthenoteuthis pteropus (28.3%, Table 4). The S. pteropus collected were mostly females, as evidenced by their large ML's (females can reach 650 mm ML and males 280 mm ML, Zuev et al., 1985) and by the presence of large oviducts. Moreover of the "Unknown A" species, five cephalopod species (Braehioteuthis sp., Grim- alditeuthis bomplandi, Megalocranchia sp., Octopo- teuthis rugosa, and Spirula spirula) were identified for the first time in swordfish stomach contents. Comparative analysis of hard structure degradation Otoliths (sagittae) of Scomber japonicus were dis- solved after an average time of 6 hours and 47 min- utes (% decrease of otolith length=2.121 + 14.424T, SD=5 min; Fig. 3). Otolith length decreased signifi- cantly over a period of one hour (ANOVA, df=14, P=5.0425 x 10"5). Otoliths of Micromesistius poutassou showed a sig- nificant decrease in length after an interval of 12 hours (ANOVA, df=8, P=1.7605 x 10"2). After 48 hours, they had lost 40%' of their length (% decrease of otolith length=1.932 + 0.843T, Fig. 3) but still maintained their original shape. Lower rostral length and upper rostral length did not differ significantly after 48 hours in acid (ANOVA, df=24, P=0. 95588 and df=24, P=0. 93221, respec- tively). In addition, wing length of the lower beak did not differ significantly after 48 hours (ANOVA, df=24, P=0. 97319). No significant differences were found for fish and cephalopod eye lense diameter af- ter 48 hours (ANOVA, df=4, P=0.50454 and df=4, P=0.89424, respectively). Scomber japonicus % decrease otol'th length = 2 121 + 14 424T t - 0 9697 , -1 : - -• - ". Micromesistius poutassou % decrease otolith length = I 932 + 0 483T ^ = 0 9419 Time (h) Figure 3 Decrease in otolith length of chub mackerel, Scomber japonicus, and blue whiting, Micromesistius poutassou (measured on the longest axis) after immersion in hydrochloric acid (pH=l.l) for 48 hours. NOTE Hernandez-Garcia: Diet of Xiphias gladius 409 Discussion Commercial longline fishing generally lasts for 12- 14 hours and the fish caught can remain alive for many hours (Boggs, 1992); thus digestion of stom- ach contents is continuous. Moreover, regurgitation regularly occurs (Tibbo et al., 1961). This may bias values of stomach fullness. The period of study was limited in each area and sample sizes were not large, precluding statistical analysis. However, the diet of swordfish appeared to show substantial variation between areas. In neritic areas (zone A) swordfish preyed upon pelagic and benthic species offish and squids, whereas in oceanic areas (zone B) they preyed mainly on squids (Table 2). This pattern was also observed by Maksimov ( 1969). In addition, Carey and Robison (1981) showed that in neritic areas sword- fish have a different ecology and migration pattern from that found in oceanic waters. In neritic areas, swordfish are found near the bottom during the day- light, feeding mainly on benthic species (i.e. Capros aper and Merluccius merluccius in this study, Table 3); at night, they move offshore to feed actively on squid and other migrating fauna concentrated near the surface (i.e. Todarodes sagittatus in this study, Table 4). In oceanic waters, swordfish undergo a diel vertical migration reaching about 600 m at noon and ascend- ing to shallow waters at night; they can prey actively on oegopsid squids at both ends of the migration (Carey and Robison, 1981). The mean number of cephalopods per stomach was 0.7 in zone A, similar to data reported by Moreira ( 1990). In zone B (oceanic waters) the mean was 1.8, similar to the value of 2. 1 calculated from data obtained by Guerra et al. (1993). In zone C, the mean number of cephalopds per stomach was 3. Bane (in Fonteneau and Marcille, 1991 ) also showed that cepha- lopod-prey are more important in oceanic waters than inshore for yellowfin tuna, Thunnus albacares. From analysis of degradation, otoliths were strongly eroded by acid; large, thick otoliths dissolved more slowly than small, thin ones. Cephalopod beaks and eye lenses and fish eye lenses were not affected by acid. Fish were the item with the highest index of numerical importance (Table 2) in zone A. However, the value obtained must be treated with caution be- cause the otoliths of Micromesistius poutassou may accumulate owing to the structure of the stomach wall and the time necessary to dissolve them (Fig. 3). The otoliths of Scomber japonicus were not found free, a feature that accords with the results of the analysis of degradation. Therefore, if evaluation offish biomass is based on the presence of otoliths, biomass may be over- estimated for fish with large and dense otoliths (i.e. M. poutassou ). Fish with smaller and weak otoliths may be underestimated as was observed by both da Silva and Neilson (1985) and Jobling and Breiby (1986). However, the rate of degradation of otoliths in this study may be overestimated because the acidity was greater than the value reported in general for fish stomach acids (pH=2. 0—3.0) after the digestive process has begun. Because cephalopod eye lenses and fish eye lenses are not affected by acid, as noted by Clarke (1986b), the number of lenses found in a stomach may be a means of estimating the relative importance of cephalopods and fish in the diet. However, the percentage of occur- rence offish (counted from whole fish and free otoliths) was similar to that obtained by Azevedo (1989) and Moreira ( 1990) in areas nearest to zone A. In zone B, if eye lenses offish and cephalopods are considered, both of which experience a similar rate of digestion, the rela- tive importance offish in the diet is less than what was indicated by data from the otoliths. The importance (based on % number) of Stheno- teuthis pteropus in zone C is not surprising given the large abundance of this species at these latitudes (Voss, 1966; Zuev et al., 1985). The preferred tem- perature range for swordfish is from 25° to 29°C (Ovchinnikov, 1970) which is nearly the same as that for adult squid females (24°-30°C, Zuev et al., 1985). These temperatures are almost constant at these latitudes throughout the year. Around zone C, there is a complex system of currents and frontal zones where there is a high biomass (Blackburn, 1965; Ovchinnikov, 1970): in addition, high swordfish CPUE values have been obtained in these areas by the Spanish fishing fleet (Mejuto et al., 1991) and the Japanese longline fishery ( Palko et al. , 198 1 ). There- fore, the availability of prey may be partially respon- sible for the distribution of swordfish in these waters. Guerra et al. (1993) found that Sthenoteuthis pteropus was the most common species in the sword- fish diet in the Northeastern Atlantic; this species is possibly one of the unidentified ommastrephid spe- cies found by Maksimov (1969). Todarodes sagittatus and Ommastrephes bartrami were also found. These three species ascend to the upper epipelagic layer and feed actively on myctophids and small squid at night (Nigmatullin et al., 1977; author, unpubl. data). During the day, S. pteropus descend to 350 or 400 m (Moiseyev, 1988). These ommastrephids have a high growth rate and their life span is no longer than 1.5 years (Arkhipkin and Mikheev, 1992; Rosenberg et al., 1980; Ishii, 1977). Therefore, squid may be an effi- cient means of energy transfer in oceanic food webs. Acknowledgments Thanks are given to F. J. Portela, Captain of the F/V Manuela Cervera and to J. Gutierrez for providing 410 Fishery Bulletin 93(2). 1995 samples from Zone C. Thanks are also given to the staff of Algeciras Port for their help and for allowing me to examine swordfish stomachs there. I thank Professor Nikolai Potapuskin for his help with the Russian language. Special thanks are given to Carlos Bas and Jose J. Castro for their many suggestions and helpful comments. The author is especially grate- ful to Malcolm R. Clarke for allowing me to use his large collection of beaks, for the many suggestions he offered, and for his review of the manuscript. Literature cited Arkhipkin, A., and A. A. Mikheev. 1992. Age and growth of the squid Sthenoteuthis pteropus (Oegopsida: Ommastrephidae) from the Central-East Atlantic. J. Exp. Mar. Biol. Ecol. 163:261-276. Azevedo, M. 1989. Information on the swordfish fishery in the Portu- guese Continental EEZ. ICCAT Collective Vol. Scientific Papers 32( 2 ):282-286. Blackburn, M. 1965. Oceanography and the ecology of tunas. Oceanogr. Mar. Biol. Ann. Rev. 3:299-322. Boggs, C. H. 1992. Depth, capture time, and hooked longevity of longline- caught pelagic fish: timing bites offish with chips. Fish. Bull. 90:642-658. Bouxin, M. J., and R. Legendre. 1936. La faune pelagique de l'Atlantique au large du Golfe de Gascogne, recueillie dans des estomacs de germons. Ann. Inst. Oceanogr., Vol. XVI:1-102. Carey, F. G., and B. H. Robison. 1981. Daily patterns in the activities of swordfish, Xiphias gladius, observed by acoustic telemetry. Fish. Bull. 79:277-292. Castro, J. J. 1993. Feeding ecology of chub mackerel (Scomber japonicus) in the Canary Islands area. S. Air. J. Mar. Sci. 13:323- 328. Clarke, M. R. 1962. The identification of cephalopod 'beaks' and the re- lationship between beak size and total body weight. Bull. Br. Mus. (Nat. Hist.) Zool. 8:419-480. 1966. A review of the systematics and ecology of oceanic squids. Adv. Mar. Biol. 4:91-300. 1980. Cephalopoda in the diet of sperm whales of the south- ern hemisphere and their bearing on sperm whale biology. Discovery Rep. 37: 1-324. 1986a. A handbook for the identification of cephalopod beaks. Clarendon Press, Oxford. 1986b. Cephalopods in the diet of Odontocetes. In M. M. Bryden and R. J. Harrison (eds.), Research on dolphins, p. 281-321. Clarendon Press, Oxford. da Silva, J., and J. D. Neilson. 1985. Limitations of using otoliths recovered in scats to estimate prey consumption in seals. Can. J. Fish. Aquat. Sci. 42:1439-1442. Fonteneau, A., and J. Marcille (eds.). 1991. Recursos, pesca y biologia de los tunidos del Atlantico Centro-Oriental. ICCAT, Madrid. Guerra, A., F. Simon, and A. F. Gonzalez. 1993. Cephalopods in the diet of the swordfish, Xiphias gladius, from the northeastern Atlantic Ocean. In Okutani et al. (eds.), The recent advances in fisheries biology. Tokai Univ. Press, Tokyo, Japan, p. 159-164. Harkonen, T. 1 986. Guide to the otoliths of the bony fishes of the North- east Atlantic. In Danbiu ApS. biological consultants. Henningsens Alle 58 DK-2900, Hellerup, Denmark. Hecht, T., and A. Hecht. 1979. A descriptive systematic study of the otoliths of the neopterygean marine fishes of South Africa. Part IV: Siluriformes and Myctophiformes. Trans. Roy. Soc. S. Afr. 44:401-440. Hess, S. C, and R. B. Toll. 1981. Methodology for specific diagnosis of cephalopod re- mains in stomach contents of predators with reference to the broadbill swordfish, Xiphias gladius. J. Shellfish Res. 1:161-170. Hyslop, E. J. 1980. Stomach contents analysis-a review of methods and their aplication. J. Fish. Biol. 17:411-429. Ishii, M. 1977. Studies on the growth and age of the squid, Omma- strephes bartrami (Lesueur), in the Pacific off Japan. Bull. Hokkaido Reg. Fish. Res. Lab. 42:25-31. Jobling, M., and A. Breiby. 1986. The use and abuse of otoliths in studies of feeding habits of marine piscivores. Sarsia 71:265-274. Maksimov, V. P. 1969. Pitanie bol'sheglazogo tuntsa (Thunnus obesus Lowe) i mmech-ryby (Xiphias gladius L.) vostochnoi chasti tropichesko i Atlantiki. Trudy Atlanticheskogo nauchno- issledovatel'skogo instituta rybnogo khozyaistva i okeanografii (Trudy AtlantNIRO) XXV87-99. [English Transl.: Bull. Fish. Res. Board Can. Transl. Series No. 2248.] Mejuto, J., P. Sanchez, J. M. de la Serna. 1991. Nominal catch per unit of effort by length groups and areas of the longline Spanish fleet targeting swordfish (Xiphias gladius) in the Atlantic, years 1988 to 1990 combined. ICCAT, Collective Vol. Scientific Papers 39(2):615-625. Moiseyev, S. V. 1988. New data on vertical distribution of the orangeback squid Sthenoteuthis pteropus (Cephalopoda). Resources and biological bases of rational use of commercial inverte- brates. All-USSR Conf., Vladivostok, Abstr. Commun.: p. 89-90. Moreira, F. 1990. Food of the swordfish, Xiphias gladius Linnaeus, 1758, off the Portuguese coast. J. Fish Biol. 36:623-624. Nesis, K. N. 1987. Cephalopods of the world. In L. A. Burgess (ed.), T. F. H. Publications, Neptune City, NL, for the English trans- lation. [Original in Russian.] Nigmatullin, Ch. M., M. A. Pinchukov, and N. M. Toporova. 1977. The feeding of two background species of epipelagic squids of the Atlantic Ocean. In All-union scientific con- ference on the utilization of commercial invertebrates for food, fodder and technical purposes. Abstracts of Reports, p. 58-60. [Original in Russian.] Ovchinnikov, V. V. 1970. Mech-ryba i parusnikovye (Atlanticheski okean). Ekologiya i funktsional (naya morfologiya). (Swordfishes NOTE Hernandez-Garcia: Diet of Xiphias gladius 41 1 and billfishes in the Atlantic Ocean. Ecology and functional morphology.). Nauch-Issled. Inst. Ryb. Kohz. Okeanogr., Kaliningrad, 106 p. [Transl. by Israel Prog. Sci. Transl., 77 p., 1971; avail. U. S. Dep. Commer., Natl. Tech. Inf. Serv., Springfield, VA, as TT71-5001D. Palko, R. J., G. L. Beardsley, and W. J. Richards. 1981. Synopsis of the biology of the swordfish Xiphias gladius Linnaeus. U.S. Dep. Commer, NOAATech. Rep. NMFS Circ. 441. Perez-Gandaras, P. G. 1983. Estudio de los cefalopodos ibericos: sistematica y binomia mediante el estudio morfometrico comparado de sus mandibulas. Tesis Doctoral, Univ. Complutense de Madrid, Madrid. Rosenberg, A. A., K. F. Wiborg, and I. M. Bech. 1980. Growth of Todarodes sagittatus (Lamarck) (Cepha- lopoda, Ommastrephidae) from the Northeast Atlantic, based on counts of statoliths growth rings. Sarsia 66:53-57. Scott, W. B., and S. N. Tibbo. 1968. Food and feeding habits of swordfish, Xiphias gladius, in the western North Atlantic. J. Fish. Res. Board Can. 25:903-919. 1974. Food and feeding habits of swordfish, Xiphias gladius Linnaeus, in the Northwest Atlantic Ocean. In R. S. Shomura, and R. Williams (eds.), Proceedings of the inter- national billfish symposium, Kailua-Kona, Hawaii, 9-2 Au- gust 1972. Part 2: Review and contributed papers. U.S. Dep. Commer., NOAATech. Rep. NMFS SSRF-675: 138-141. Stillwell, C. E., and N. E. Kohler. 1985. Food and feeding ecology of the swordfish Xiphias gladius in the western North Atlantic Ocean with estimates of daily ration. Mar. Ecol. Prog. Ser. 22:239-247. 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. Bull. Fish. Res. Board Can. 130. Toll, R. B., and S. C. Hess. 1981. Cephalopods in the diet of the swordfish, Xiphias gladius, from the Florida Straits. Fish. Bull. 79:765-774. Voss, G. L. 1966. The pelagic mid-water fauna of the eastern tropical Atlantic with special reference to the Gulf of Guinea. In Proceedings of the symposium on the oceanography and fisheries resources of the tropical Atlantic, Adidjan, Ivory Coast, 20-28 Oct., p. 91-99. Wolff, G. A. 1982. A study of feeding relationships in tuna and porpoise through the application of cephalopod beak analysis. Final Tech. Report for DAR-7924779, Texas A&M Univ., 231 p. Wolff, G. A., and J. H. Wormuth. 1979. Biomnetric separation of the beaks of two morpho- logically similar species of the squid family Omma- strephidae. Bull. Mar. Sci. 29:587-592. Zariquiey-Alvarez, R. 1968. Crustaceos Decapodos Ibericos. Investigacibn Pesquera 32:1-510. Zuev, G. V., Ch. M. Nigmatullin, and V. N. Nikolsky. 1985. Nektonic oceanic squids (genus Sthenoteuthis). Mos- cow: Agropromizdat [in Russian, Eng. contents]. Appendix Description of the "unknown A" lower beak Terms and measurement used to describe the char- acteristic beak (the "Unknown A") are the same as those used by Clarke (1980, 1986a). The beak (Fig. 2 (belongs to an unidentified species of oegopsid, and its general shape is similar to the beak oiDiscoteuthis. It is taller than it is long (Fig. 2A) and although five of them had digested wings, the largest beak (lower rostral length=4.4 mm) had a full wing with an isolated spot. The rostrum is distinctly shorter than deep (gl a-0.67, where g is the hood length in the midline and a is the length of the rostral edge visible in pro- file) and narrow (i/j=2.8, where i is the LRL andj is the distance between the jaw angles). There is no hook in the rostral edge, but rather this is sharp- edged and thickened. The crest is short and has a notch in the lateral wall to the side of the crest (Fig. 2, A and C). The hood does not lie close to the crest. The surface of the hood has a very soft fold. The jaw angle is obtuse and a sharp anglepoint is present (Fig. 2B). Jaw angle is obscured from the side by a very low wing fold (Fig. 2, A, B, and F) which is covered by cartilage (dotted area). A distinct lateral wall ridge forms a fin (Fig. 2, E, I), similar to Histioteuthis beaks (type A) described by Clarke (1980). This runs toward the midpoint of the posterior edge of the lateral wall (Fig. 2, E, III). The beaks ofDiscoteuthis lack this ridge. Length-weight relationships for 1 3 species of sharks from the western North Atlantic Nancy E. Kohler John G. Casey Patricia A. Turner Narragansett Laboratory, Northeast Fisheries Science Center National Marine Fisheries Service, NOAA Narragansett, Rl 02882-1 199 The rapid expansion of sport and commercial fisheries for sharks in the western North Atlantic has cre- ated the need to manage the stocks of several species of large sharks. A fishery management plan for sharks within the U.S. exclusive economic zone (EEZ) of the Atlan- tic Ocean (USDOC, 1992) was implemented in 1993. The 39 spe- cies of sharks included in the fish- ery management plan are not man- aged on an individual species ba- sis, but are grouped into three spe- cies groups — large coastal, small coastal, and pelagic. Basic biologi- cal information needed for stock assessment is lacking for many of these Atlantic sharks, including minimum, maximum, and average sizes, as well as length-to-weight and length-to-length relationships. These data are essential for under- standing the growth rate, age struc- ture, and other aspects of shark population dynamics. Size conversions also have a prac- tical value in fisheries. One mea- sure currently in practice at nearly all shark tournaments on the At- lantic coast is the establishment of minimum size limits and usually a minimum weight. Since sizes must be estimated at sea, means for con- verting lengths to weights are es- sential to anglers. Moreover, the National Marine Fisheries Service (NMFS) conducts an extensive At- lantic Shark Tagging Program us- ing volunteer assistance of recre- ational and commercial fishermen. Commercial fishermen generally are more confident in estimating the weight of sharks being released, and recreational fishermen in esti- mating lengths. Conversions are needed to change these estimates into common size units for analysis. Length data on sharks worldwide have been reported as total length (Strasburg, 1958; Stevens, 1975, 1983; Stevens and Wiley, 1986; Stevens and Lyle, 1989), alternate length (Cailliet and Bedford, 1983; Stick and Hreha, 1989), dorsal length (Aasen, 1963, 1966), pre- caudal length (Nakano et al., 1985; Cliff et al., 1989), standard length (Guitart Manday, 1975) and fork length (Mejuto and Garces, 1984; Casey and Pratt, 1985; Berkeley and Campos, 1988). Most studies include formulas to convert their measurements to total length. To- tal length measurements, however, can vary considerably depending on the placement of the caudal fin (Branstetter et al., 1987). Published size relationships for sharks from various regions of the Atlantic Ocean and Gulf of Mexico include studies on the blue shark, Prionace glauca (Aasen, 1966; Stevens, 1975); tiger shark, Galeo- cerdo cuvier (Branstetter, 1981; Branstetter et al., 1987); silky shark, Carcharhinus falciformis (Guitart Manday, 1975; Bran- stetter, 1987; Berkeley and Cam- pos, 1988); bull shark, C. leucas (Branstetter, 1981); spinner shark, C. brevipinna (Branstetter, 1981); night shark, C. signatus (Guitart Manday, 1975; Berkeley and Cam- pos, 1988); oceanic whitetip shark, C. longimanus (Guitart Manday, 1975); finetooth shark, C. isodon (Castro 1993); shortfin mako, Isurus oxyrinchus (Guitart Man- day, 1975; Mejuto and Garces, 1984); white shark, Carcharodon carcharias (Casey and Pratt, 1985); porbeagle shark, Lamna nasus (Aasen, 1963; Mejuto and Garces, 1984); bignose shark, C. altimus (Berkeley and Campos, 1988); big- eye thresher shark, Alopias super- ciliosus (Guitart Manday, 1975); and scalloped hammerhead, Sphyrna lewini (Branstetter, 1987). In re- sponse to the immediate needs of tournament officials and fisher- men, and for management initia- tives, we present length and weight data for thirteen species of large Atlantic sharks collected by the Apex Predator Investigation (API) of NMFS over a 29-year period. Materials and methods Length and weight data were col- lected from sharks caught by rec- reational and commercial fisher- men and biologists along the U.S. Atlantic coast from the Gulf of Maine to the Florida keys during 1961 through 1989. Sharks were caught primarily on rod and reel at sport fishing tournaments and on longline gear aboard research ves- sels and commercial fishing boats. Some data were obtained from sharks that were harpooned or taken in gill nets. Measurements from a large white shark captured off Rhode Island in 1991 were also Manuscript accepted 29 August 1994. Fishery Bulletin 93:412-418 (1995). 412 NOTE Kohler et al.: Length-weight relationships for I 3 species of sharks 413 included in the analysis because of the shark's un- usual size. Data were obtained opportunistically throughout each year but most (88%) were collected in the months of June, July, and August off the north- east United States between North Carolina and Massachusetts. Only lengths and weights measured by the authors and other members of the API or by cooperating biologists are included in this report. Measurements of embryos and fish known to be preg- nant were excluded from the data set. All lengths were measured with a metal measur- ing tape to the nearest centimeter in a straight line along the body axis; the caudal fin was placed in a natural position. Fork length (FL) was measured from the tip of the snout to the fork of the tail. Total length (TL) is defined as the distance from the snout to a point on the horizontal axis intersecting a per- pendicular line extending downward from the tip of the upper caudal lobe to form a right angle. Total weight (WT) of each shark was measured to the nearest pound and converted to kilograms. The majority of the fish were weighed hanging from the caudal peduncle which allowed any water in the stomach, and in some cases stomach contents, to drop out prior to weighing. Many fish were examined in- ternally and, if unusually large amounts of water or contents were found in the stomach or abdominal cavity, the weights were subtracted to obtain a more accurate weight. Fork-total length relationships for 13 species of shark (n =5,065) were determined by the method of least squares to fit a simple linear regression model. Linear regressions of fork-to-total length were cal- culated with their corresponding regression coeffi- cients, sample sizes, and mean lengths. These data were then combined into four family groups: Alopiidae (thresher sharks), Lamnidae (mackerel sharks), Carcharhinidae (requiem sharks), and Sphyrnidae (hammerhead sharks), and linear regres- sions and TL/FL percentages were calculated for each group. An allometric length-weight equation was calcu- lated by using the method of Pienaar and Thomson (1969) for fitting a nonlinear regression model by least squares. The form of the equation is WT=(a)FLh, where WT=total weight (kg), FL=fork length (cm), and a and b are constants. Length-weight relation- ships, mean lengths and weights, and size ranges were determined for 13 species of sharks (rc=9,512). Literature values for maximum fork length and fork length at maturity were also included. The regres- sions of the length- weight equations expressed loga- rithmically were tested for possible significant dif- ferences (P<0.05) between males and females by using an analysis of covariance test for homogeneity of slopes. Fork length is used throughout this report as the basis for all conversions and comparisons. We have found fork length to be a more precise measurement. For comparative purposes, all values published else- where as total lengths were converted to fork lengths by using the species' equations presented in this paper. Minimum sizes at maturity reported here are from published accounts with their original sources refer- enced, with the exception of Alopias vulpinus and Carcharodon carcharias. Minimum size at maturity for the thresher shark and the male white shark were determined by Pratt1 who used the following crite- ria: smallest male with calcified claspers that rotate at the base and smallest gravid female. When con- siderable variation occurred among published ac- counts, traditional sizes at maturity were chosen primarily from Atlantic populations. The maximum sizes and maximum sizes at birth used here are sum- marized in Pratt and Casey (1990). Results and discussion Linear regressions of fork-to-total length were cal- culated for 13 species of shark and four family groups (Table 1). The slopes of the regression lines of the four families decrease with the increasing length of the upper caudal lobe. The mackerel sharks have lunate tails with the upper and lower caudal lobes almost equal in size. The requiem sharks, hammer- head, and thresher sharks have heterocercal tails with the upper lobe longer than the lower. The latter group have very long upper caudal lobes with the fork length approximately 60% of the total length. The fork length represents 92%, 84%, and 77% of the total length for the mackerel, requiem, and ham- merhead sharks, respectively. A total of 9,512 sharks representing 13 species were measured, sexed, and weighed. There were no significant differences in slope or intercept of the length-weight relationships between males and fe- males for any of the species and therefore one equa- tion, calculated with the sexes combined, was used to represent the data for each species (Table 2). Size at maturity for males and females is difficult to determine for pelagic sharks and can vary in dif- ferent parts of the world (Pratt and Casey, 1990). The discrepancy is due, in part, to the use of vari- able criteria in determining a precise length at sexual maturity (Springer, 1960; Clark and von Schmidt, 1965; Pratt, 1979) and thus maturity is often reported 1 H. L. Pratt, National Marine Fisheries Service, Narragansett, RI 02882. Pers. commun., May 1993. 414 Fishery Bulletin 93(2), 1995 Table 1 Fork length (FL)-total length (TL) relationships for 13 species of sharks and four family groups from the western North Atlantic: FL = (a)TL+b. Fork length and total length means and ranges were taken from data presented in this study. Mean Total Mean Fork total length fork length FL = (a)TL+b length range length range Species n (cm) (cm) (cm) (cm) a b r2 Alopiidae 69 0.4882 37.9566 0.8577 Alopias superciliosus 56 312 155-371 192 100-228 0.5598 17.6660 0.8944 (bigeye thresher) A. vulpinus 13 373 291-450 211 168-262 0.5474 7.0262 0.8865 (thresher shark) Lamnidae 324 0.9352 -3.3292 0.9972 Carcharodon carcharias 112 204 122-517 187 112-493 0.9442 -5.7441 0.9975 (white shark) Isurus oxyrinchus 199 171 70-368 157 65-338 0.9286 -1.7101 0.9972 (shortfin mako) Lamna nasus 13 201 119-247 182 106-227 0.8971 1.7939 0.9877 (porbeagle) Carcharhinidae 4561 0.8290 1.1309 0.9963 Carcharhinus altimus 10 174 132-228 148 112-192 0.8074 7.7694 0.9872 (bignose shark) C. falciformis 15 173 90-258 142 73-212 0.8388 -2.6510 0.9972 (silky shark) C. obscurus 148 153 92-330 125 74-277 0.8396 -3.1902 0.9947 (dusky shark) C. plumbeus 3734 123 51-249 103 42-211 0.8175 2.5675 0.9933 (sandbar shark) C. signatus 38 154 72-235 130 60-195 0.8390 0.5026 0.9883 (night shark) Galeocerdo cuvier 44 247 145-375 203 116-318 0.8761 -13.3535 0.9887 (tiger shark) Prionace glauca 572 214 64-337 179 52-282 0.8313 1.3908 0.9932 (blue shark) Sphyrnidae 111 0.7756 -0.3132 0.9868 Sphyrna lewini 111 206 82-278 160 64-216 0.7756 -0.3132 0.9868 (scalloped hammerhead as a size range rather than as a specific length. An individual author's definition of maturity is some- times ambiguous or obscure. The sizes at maturity (Table 2) are from multiple reference sources and therefore may be mixed in definition and criteria. The original published sources should be consulted as the basis for defining sexual maturity among dif- ferent authors. An attempt was made to obtain samples represen- tative of the full size range of each species. The mini- mum, maximum, and mean lengths and weights by species of sharks examined in this study are reported (Tables 1 and 2). A reliable maximum size is difficult to verify. Lengths or weights, or both, for large fish are often reported inaccurately and published ac- counts usually qualify maximum lengths with such words as "probably reach," "possibly to," or "may grow up to." Maximum lengths (FL) reported in Pratt and Casey (1990) are included for comparison with the sizes measured in this study (Table 2). With the ex- ception of the porbeagle and the tiger shark, our data are within 62 cm (2 ft) of published maximum sizes. The porbeagle shark is less common in our study area; fewer specimens were examined (<30), and therefore the full size range of this species is not rep- resented. Although the tiger shark is purported worldwide to grow to 469 cm FL (15.4 ft) (Castro, 1983; Compagno, 1984; Pratt and Casey, 1990), NOTE Kohler et al.: Length-weight relationships for 1 3 species of sharks 415 Table 2 Fork length ( FL l-total weight ( WT ) relationships for the 13 species of sharks from the western North Atlantic WT = (a )FLb. Fork length and weight means and ranges were taken from data presented in this study. The maximum fork length and sizes at maturity for each species were obtained from the literature. Mean Fork Max Fork fork length fork length at Mean Weight WT = (a)FLb length range length maturity weight range Species Sex n (cm) (cm) (cm) (cm) (kg) (kg) a b r2 Alopias Combined 55 190 100-228 270' 99 11-170 9.1069 xlO-6 3.0802 0.9059 supereiliosus Male 34 188 100-221 180' 92 11-150 (bigeye thresher) Female 21 194 123-228 214' 110 23-170 A. vulpinus Combined 88 201 154-262 276'' 122 54-211 1.8821 x 10"4 2.5188 0.8795 (thresher shark) Male 46 197 154-228 1842 116 54-181 Female 41 207 155-262 2262 129 59-211 Carcharodon Combined 125 186 112-493 5553 141 12-1554 7.5763 x 10"6 3.0848 0.9802 carcharias Male 65 203 117-493 3322 208 16-1554 (white shark) Female 59 168 112-310 454'2 69 12-297 Isurus oxyrinchus Combined 2081 172 65-338 3364 63 2-531 5.2432 x 10-« 3.1407 0.9587 (shortfin mako) Male 1007 169 70-260 1795 59 2-210 Female 1054 174 65-338 2585 68 3-531 Lamna nasus Combined 15 185 106-227 329' 83 19-143 1.4823 x 10"5 2.9641 0.9437 (porbeagle) Male 13 180 106-216 159s 77 19-113 Female 2 214 201-227 2046 117 91-143 Carcharhinus Combined 38 151 97-210 235' 42 6-143 1.0160 x 10-6 3.4613 0.8958 altimus Male 12 158 115-205 1827 45 14-99 (bignose shark) Female 26 148 97-210 1907 41 6-143 C. falciformis Combined 85 118 73-212 253" 22 4-88 1.5406 x 10'5 2.9221 0.9720 (silky shark) Male 39 117 73-196 178" 22 4-88 Female 46 119 78-212 186" 22 4-88 C. obscurus Combined 247 162 79-287 3037 69 5-270 3.2415 x lO"5 2.7862 0.9649 (dusky shark) Male 103 136 79-276 23 18 39 5-216 Female 144 181 83-287 235s 90 6-270 C. plumbeus Combined 1548 129 44-201 1987 30 1-104 1.0885 x 10~5 3.0124 0.9385 (sandbar shark) Male 577 115 45-183 1508 20 1-68 Female 961 138 44-201 152« 36 1-104 C. signatus Combined 124 111 60-203 235' 15 3-102 2.9206 x 10-6 3.2473 0.9502 (night shark) Male 69 112 93-195 — 14 8-64 Female 55 111 60-203 1507 16 3-102 Galeocerdo Combined 187 203 92-339 469' 110 5^99 2.5281 x 10-6 3.2603 0.9550 cuvier Male 92 209 95-318 2589 113 7-348 (tiger shark) Female 92 197 92-339 2659 107 5-499 Prionace glauca Combined 4529 195 52-288 320' 52 1-174 3.1841 x 10"6 3.1313 0.9521 (blue shark) Male 3095 205 54-288 183'" 59 1-174 Female 1398 172 52-273 185"> 34 1-140 Sphyrna lewini Combined 390 158 79-243 239" 47 5-166 7.7745 x lO"6 3.0669 0.9255 (scalloped Male 189 166 107-224 139" 53 11-126 hammerhead) Female 199 151 79-243 194" 41 5-166 ' Castro (1983). 2 Pratt (personal commun.). 3 Randall (1987). 4 Pratt and Casey ( 1990). 5 Stevens (1983). 6 Aasen(1961). 7 Compagno(1984). * Springer ( 1960 . 9 Branstetter et al. ( 1987). 10 Pratt (1979). " Branstetter (1987). 12 Casey and Pratt (1985). 416 Fishery Bulletin 93(2). 1995 Atlantic specimens may not attain that size. Our longest tiger shark was 339 cm FL ( 11.1 ft) (Table 2). The maximum reported length examined by Bran- stetter (1981) in a study of tiger sharks in the north central Gulf of Mexico was 346 cm FL (11.4 ft). The maximum reported length for the U.S. Atlantic coast is 391 cm FL (12.8 ft) (Bigelow and Schroeder, 1948). These lengths are more in agreement with individu- als sampled in this study. Specimens from three species of sharks exceeded the maximum reported lengths (Table 2): sandbar shark, shortfin mako shark, and scalloped hammer- head shark. The 211 cm FL (6.9 ft) female sandbar shark in this study (Table 1) was measured by one of the authors (J. Casey) and is the largest measured sandbar reported to date. This fish was caught in September of 1964 by a sport fisherman approxi- mately 10 miles east of Asbury Park, New Jersey. Unfortunately, the fish was not weighed. Two mako sharks measured in this study were longer than the 336 cm FL (11.0 ft) maximum size fish published in the literature. Both of these fish were 338 cm FL (11.1 ft) females caught by sport fishermen south of Montauk Point, New York. One was landed in July of 1977 and weighed 471 kg (1,039 lbs). The other was caught in August of 1979 and weighed 382 kg (841 lbs). The largest scalloped hammerhead (243 cm FL, 8.0 ft; 166 kg, 365 lbs) was measured at a sportfishing tournament in July of 1985 and was caught 36 miles southeast of Highlands, New Jersey. The lower ends of the length-weight curves also compare well with published estimates of size at birth for each species of shark. Pratt and Casey ( 1990) give maximum size at birth in TL for 11 of the 13 species of sharks sampled here and all except the thresher shark are within 40 cm (16 in) of those sizes. Our smallest thresher shark is 64 cm (25 in) larger than the reported birth size. All of the larger fish were female with the excep- tion of the white and the blue shark (Tables 1 and 2). The larger size attained by females is typical of sharks in general (Pratt and Casey, 1983; Hoenig and Gruber, 1990), and thus larger female blue and white sharks very likely occur outside of our western North Atlantic sampling area which only covers a small portion of their extensive oceanic range. Blue sharks have a complex life history cycle and large females are infrequent visitors to the continen- tal shelf and slope waters off North America. The shelf area serves as a mating ground where the catch consists primarily of juvenile males and females, subadult females, and adult males (Casey, 1985). The occurrence of considerable numbers of the larger fe- males (>240 cm, 7.9 ft) is rare in the western North Atlantic, but numerous large gravid females have been reported in the eastern Atlantic from the Medi- terranean Sea and around the Madeira and Canary Islands (Aasen, 1966; Pratt, 1979). The white shark distribution pattern may be as complex as that of the blue shark but is more ob- scure. Although no mature female white sharks were examined, adult females have been reported from the western North Atlantic. Casey and Pratt (1985) de- scribe a 483 cm FL (15.8 ft) fish harpooned off Montauk, New York, in 1964 and a 526 cm FL ( 17.3 ft) female which became entangled in a gill net near Prince Edward Island, Canada, in July, 1983. Else- where, large female white sharks have been reported in the Gulf of Maine (Bigelow and Schroeder, 1948; Skud, 1962), in the Mediterranean Sea (Ellis and McCosker, 1991) and off the west coast of Florida (Springer, 1939). Catching a large white shark of ei- ther sex, however, is an uncommon event. White sharks are likely to occur singly or as scattered, unassociated individuals over vast geographical ar- eas ( Casey and Pratt, 1985 ). Owing to their immense size, they are difficult to catch and are capable of breaking free of most conventional fishing gear. Factors affecting weight Weights of individual sharks of the same length may differ depending on several factors, including the amount of stomach contents, the stage of maturity, the liver weight, and the condition of the shark. The effects of stomach contents on the weight of the fish were minimal in this study. In many instances, the sharks everted their stomachs prior to being weighed. For the bigger fish, when large amounts of food were present, the weight of the stomach contents was sub- tracted to obtain the total body weight. Since not every shark was examined internally, some pregnant fish may have been inadvertently included in the database. Differences in body weight also reflect differences in the condition of an individual. Sharks have large livers which store high energy, fatty acids for buoy- ancy and for use as a food reserve (Bone and Rob- erts, 1969; Oguri, 1990). The weight of this organ is thus a good indicator of the health or condition of a shark (Springer, 1960; Cliff et al., 1989). The liver is the largest organ by weight in the shark and can vary from 2-24% of the body weight depending on the species (Cliff et al., 1989; Winner, 1990). Varia- tion in the liver size accounted for the majority of the weight difference in individuals of the same spe- cies with corresponding lengths. In six of the eight largest white sharks, the liver weights ranged from 14.6-22.7% of the body weight (hepatosomatic index, HSI) (Table 3). The 458 cm (15.0 ft) FL white shark NOTE Kohler et al.: Length-weight relationships for 1 3 species of sharks 417 in this group had the lowest HSI value (14.6%) al- though it was longer than four heavier fish. The dif- ference in body weight between the 458 cm ( 15.0 ft) FL and the 463 cm (15.2 ft) FL fish is 360 kg (793 lbs). When the weights of sharks without livers are compared, the difference between these two fish is reduced to 239 kg (526 lbs). Thus, eliminating the liver accounted for 34% of the weight difference be- tween these two sharks of similar length. The same is true for large mako sharks. The HSI for one of the longest mako sharks (338 cm, 11. 1 ft FL; 382 kg, 841 lbs) was 5.4% as contrasted with 17.9% for the 323 cm (10.6 ft) FL fish weighing 490 kg ( 1,080 lbs). When the two makos are compared without livers, the dif- ference in body weights is reduced from 108 kg (239 lbs) to 41 kg (91 lbs). Acknowledgments The data for this study could not have been collected without the help and cooperation of thousands of fish- ermen who allowed us to measure their shark catches over the last 29 years. The scientists, officers, and crew of several research vessels also assisted in ob- taining specimens during sampling cruises. We are particularly grateful to tournament officials and par- ticipants from New York, New Jersey, Massachusetts, and Rhode Island from whose catches a large part of the data were collected. Further, we would like to thank the past and present members of the Apex Predator Investigation of the National Marine Fish- eries Service, including Chuck Stillwell, Lisa J. Natanson, Ruth Briggs, H. L. Pratt, and Gregg Skomal for their assistance and support. Table 3 Fork length, body and liver weight, and hepatosomatic index (HSI) for large white sharks, Carcharodon car- charias, from the western North Atlantic. Fork (cm) length Whole body weight (kg) Liver weight (kg) HSI (%) 463 1,245 250 20.1 458 885 129 14.6 446 1,261 206 16.3 444 1,320 232 17.6 437 1,084 246 22.7 425 941 179 19.0 Literature cited Aasen, 0. 1961. Some observations on the biology of the porbeagle shark {Lamna nasus [Bonnaterre]). ICES Council Meet- ing 1961/Near Northern Seas Committee, No. 109, 7 p. 1963. Length and growth of the porbeagle [Lamna nasus [Bonnaterre]) in the northwest Atlantic. Fiskeridir. Skr. Ser. Havunder. 13:20-37. 1966. Blahaien, Prionace glauca (Linnaeus) 1758. Fisken. Havet. 1:1-16. Berkeley, S. A., and W. L. Campos. 1988. Relative abundance and fishery potential of pelagic sharks along Florida's east coast. Mar. Fish. Rev. 50(1): 9-16. Bigelow, H. B., and W. C. Schroeder. 1948. Sharks. In J. Tee-Van, C. M. Breder, S. F Hilde- brand, A. E. Parr, and W. C. Schroeder (eds.), Fishes of the western North Atlantic, Part I, Vol. I, p. 59-546. Mem. Sears Found. Mar. Res., Yale Univ. Bone, Q., and B. L. Roberts. 1969. The density of elasmobranchs. J. Mar. Biol. Assoc. U.K. 49:913-937. Branstetter, S. 1981. Biological notes on the sharks of the north central Gulf of Mexico. Contrib. Mar. Sci. 24:13-34. 1987. Age. growth and reproductive biology of the silky shark, Carcharhinus falciformis, and the scalloped ham- merhead, Sphyrna lewini, from the northwestern Gulf of Mexico. Environ. Biol. Fishes 19:161-173. Branstetter, S., J. A. Musick, and J. A. Colvocoresses. 1987. Age and growth estimates of the tiger shark, Galeocerdo cuvieri, from off Virginia and from the north- western Gulf of Mexico. Fish. Bull. 85:269-279. Cailliet, G. M., and D. W. Bedford. 1983. The biology of three pelagic sharks from California waters, and their emerging fisheries: a review. Calif. Coop. Fish. Invest. Rep. 24, p. 57-69. Casey, J. G. 1985. Transatlantic migrations of the blue shark: a case history of cooperative shark tagging. InR.H. Stroud (ed.), World angling resources and challenges: proceedings of the first world angling conference. Cap dAgde, France, Sep- tember 12-18, 1984, p. 253-268. Int. Game Fish Assoc, Ft. Lauderdale, FL. Casey, J. G., and H. L. Pratt Jr. 1985. Distribution of the white shark, Carcharodon carcharias, in the western North Atlantic. Mem. South- ern Calif. Acad. Sci. 9: 2-14. Castro, J. I. 1983. The sharks of North American waters. Texas A&M Univ. Press, College Station, TX, 180 p. 1993. The biology of the finetooth shark, Carcharhinus isodon. Environ. Biol. Fishes 36:219-232. Clark, E., and K. von Schmidt. 1965. Sharks of the central Gulf Coast of Florida. Bull. Mar. Sci. 15:13-83. Cliff, G., S. F. J. Dudley, and B. Davis. 1989. Sharks caught in the protective gill nets off Natal, South Africa. 2. The great white shark Carcharodon carcharias (Linnaeus). South. Afr. J. Mar. Sci. 8:131-144. Compagno, L. J. V. 1984. FAO species catalogues. Vol. 4., parts 1 and 2: sharks of the world. An annotated and illustrated catalogue of the shark species known to date. FAO Fish. Synopsis 125, 655 p. 418 Fishery Bulletin 93(2), 1995 Ellis, R., and J. E. McCosker. 1991. Great white shark. Harper Collins Pubis., New York, 270 p. Guitart Manday, D. 1975. Las pesquerias pelagico-oceanicas de corto radio de accion en la region noroccidental de Cuba. [Short-range marine pelagic fishing of northwest Cuba.] Seria Oceanologica, Oceanographic Institute, Academy of Sci- ences of Cuba. No. 31, p. 3-26. [Translated for the National Science Foundation and the U.S. Dep. Commer., Natl. Oce- anic and Atmos. Admin., Natl. Mar. Fish. Serv., Washington, D.C., by the Agence Tunisienne de Public-Relations, Tunis.] Hoenig, J. M., and S. H. Gruber. 1990. Life-history patterns in the elasmobranchs: implica- tions for fisheries management. In H. L. Pratt Jr., S. H. Gruber, and T. Taniuchi (eds.), Elasmobranchs as living resources: advances in biology, ecology, systematics and status of the fisheries, p. 1-16. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 90. Mejuto, J., and A. G. Garces. 1984. Shortfin mako, Isurus oxyrinchus, and porbeagle, Lamna nasus, associated with longline swordfish fishery in NW and N Spain. International Council for the Explo- ration of the Sea, Council Meeting 1984/G 72:1-10. Nakano, H., M. Makihara and K. Shimazaki. 1985. Distribution and biological characteristics of the blue shark in the central north Pacific. Bulletin of the Fac- ulty of Fisheries, Hokkaido Univ. 36(3):99-113. Oguri, M. 1990. A review of selected physiological characteristics unique to elasmobranchs. In H. L. Pratt Jr., S. H. Gruber, and T Taniuchi (eds.), Elasmobranchs as living resources: advances in biology, ecology, systematics, and status of the fisheries, p. 49-54. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 90. Pienaar, L. V., and J. A. Thomson. 1969. AJlometric weight-length regression model. J. Fish. Res. Board Can. 26: 123-131. Pratt, H. L., Jr. 1979. Reproduction in the blue shark, Prionace glauca. Fish. Bull. 77:445-469. Pratt, H. L., Jr. and J. G. Casey. 1983. Age and growth of the shortfin mako, Isurus oxyrinchus, using four methods. Can. J. Fish. Aquat. Sci. 40:1944-1957. 1990. Shark reproductive strategies as a limiting factor in directed fisheries, with a review of Holden's method of es- timating growth-parameters. In H. L. Pratt Jr., S. H. Gruber, and T. Taniuchi (eds.), Elasmobranchs as living resources: advances in biology, ecology, systematics, and status of the fisheries, p. 97-109. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 90. Randall, J. E. 1987. Refutation of lengths of 11.3, 9.0, and 6.4 m attrib- uted to the white shark, Carcharodon carcharias. Calif. Fish Game 73(3):163-168. Skud, B. 1962. Measurements of a white shark, Carcharodon carcharias, taken in Maine waters. Copeia 1962:659-661. Springer, S. 1939. The great white shark, Carcharodon carcharias (Linnaeus), in Florida waters. Copeia 1939:114-115. 1960. Natural history of the sandbar shark Eulamia milberti. U.S. Fish Wildl. Serv., Fish. Bull. 61(1781:1-38. Stevens, J. D. 1975. Vertebral rings as a means of age determination in the blue shark [Prionace glauca L.). J. Mar. Biol. Assoc. U.K. 20:605-614. 1983. Observations on reproduction in the shortfin mako, Isurus oxyrinchus. Copeia 1983(1):126-130. Stevens, J. D., and J. M. Lyle. 1989. Biology of three hammerhead sharks (Eusphyra blochii, Sphyrna mokarran, and S. lewini) from northern Australia. Aust. J. Mar. Freshwater Res. 40:129-146. Stevens, J. D., and P. D. Wiley. 1986. Biology of two commercially important carcharhinid sharks from northern Australia. Aust. J. Mar. Freshwa- ter Res. 37:671-688. Stick, K. C., and L. Hreha. 1989. Summary of the 1988 Washington/Oregon experimen- tal thresher shark gill net fishery. Wash. Dep. Fish. Prog. Rep. No. 275, 40 p. Strasburg, D. W. 1958. Distribution, abundance, and habits of pelagic sharks in the central Pacific Ocean. U.S. Fish Wildl. Serv, Fish. Bull. 58:335-361. USDOC (U.S. Department of Commerce). 1992. Fishery management plan for sharks of the Atlantic Ocean. NMFS, Wash., DC, 160 p. Winner, B. L. 1990. Allometry and body-organ weight relationships in six species of carcharhiniform sharks in Onslow Bay, North Carolina. M.S. thesis, Univ. North Carolina at Wilmington, Wilmington, NC, 118 p. An analysis of the length-weight relationship of larval fish: limitations of the general allometric model Pierre Pepin Department of Fisheries and Oceans PO. Box 5667. St. John's. Newfoundland, Canada A1C 5X1 Substantial morphological and physiological changes occur during the early ontogeny of fish. After hatching, both shape and size un- dergo significant alterations in as- sociation with yolk absorption and a subsequent increase in muscula- ture. In fish, the larval stage gen- erally consists of a period of rapid growth, which can vary substan- tially in duration within and among species (Sinclair and Tremblay, 1985, Ware and Lambert, 1985; Houde, 1989; Pepin, 1991). Length and weight may increase by factors of approximately 10 and 1,000, re- spectively, over a time interval that often spans less than 10% of a spe- cies' life time. Such high develop- ment rates are associated with high metabolic rates (Giguere et al., 1989) which can lead to substantial variation in condition as a result of fluctuations in food availability (Houde and Schekter, 1980; Werner and Blaxter, 1980). Studies of varia- tions in growth characteristics and condition have been an important keystone in understanding early life history survival (Houde, 1987). Changes in length or weight through time have been used to as- sess the general growth rates of populations. Most often, the model used to describe length-weight re- lationships of fish larvae is a gen- eral allometric function W = aLb, (la) logW = loga + blogL (lb) that can be estimated with minimal computing power, by using least squares, and for which the fit is gen- erally strong (e.g. Laurence, 1978). The latter point may seem reason enough to assume that a general allometric model is an adequate description of the data. However, some inferences derived from this type of information concern varia- tion in condition. For example, de- viations from a general length- weight relationship (e.g. Fulton's ( 1911) index of condition [K=W/L3, where W and L are the weight and length of individuals]) have been used to describe the relative state of health of individuals (e.g. West- ernhagen and Rosenthal, 1981; Checkley, 1984; Ciechomski et al., 1986; Harris et al., 1986; Frank and McRuer, 1989; Drolet et al., 1991). It is therefore necessary to ensure that the model used to describe the length-weight relationship not only provides a strong fit to the data but also that it accurately describes the functional form of that relationship. Zweifel and Lasker (1976) suggest that changes in length or weight of fish larvae through time can be de- scribed by a Gompertz model L = L0e W = W0eK'(1~e ' (2a) (2b) where W is weight, L is length, and a and b are constants. A logarith- mic transformation of Equation 1 leads to a linear relationship where LQ and W0 are the length and weight at time t=0, K and K' are the specific growth rates at time £=0, and a and a' are the rates of decay in growth rates. Only when a=a' does the length-weight relationship reduce to the form shown in Equa- tion lb. Otherwise, the logarithmic length-weight relationship will ex- hibit a degree of nonlinearity (Laird et al., 1968; Zweifel and Lasker, 1976). Barton and Laird (1969) noted that fitting the general allo- metric model is relatively insensi- tive to slight departures from the true time relations for growth in length and weight (i.e. oc^ct'). Con- sequently, a general allometric re- lationship (Eq. lb), with only two parameters, may be considered to provide an adequate description to the data, despite the fact that a more complex model (e.g. a Gom- pertz length-weight relationship) better describes the patterns of growth in length and weight. Al- though the importance of such subtle differences may appear to be minor, consistent departures from a general allometric model can lead to significant bias in predicting or interpreting weight at length. This can be particularly important when trying to model growth during the early life history (e.g. Rose and Cowan, 1993 ) or in estimating size- dependent metabolic processes (e.g. Checkley, 1984; Ki0rboe, 1989; Giguere et al., 1989). Furthermore, there is potential for inaccurate inferences in instances where con- dition is being studied (e.g. W/L3). Westernhagen and Rosenthal ( 1981 ) and Ciechomski et al. (1986) noted a decrease in Fulton's condition in- dex after hatch, followed by an in- crease some time after first feed- ing. Although this pattern may be due to food deprivation, it can also arise because of a developmentally determined nonlinear allometric length-weight relationship (i.e a*ct'). In this study, I present evidence that, despite a strong fit to a gen- eral allometric length-weight rela- Manuscript accepted 9 November 1994. Fishery Bulletin 93:419-426 < 1995). 419 420 Fishery Bulletin 93(2), 1995 tionship (Eq. lb), the use of such a model may be inappropriate for the study offish larvae. Materials and methods Ichthyoplankton samples were obtained during two surveys of Conception Bay (47°45'N, 53°00'W), New- foundland, Canada. Cruises were held during the periods from 27 June 1990 to 15 July 1990 and from 25 September 1990 to 30 September 1990. Sampling was conducted during daylight hours (0700-1900) with a 4-m2 Tucker trawl equipped with panels of 1,000-, 570-, and 333-|am mesh nitex. At each sta- tion, a single oblique tow of approximately 15 min- utes was made at 2 knots ( 1 m-s _1 ). The net was low- ered to 40 m at a rate of approximately 0.25 m-s-1 and retrieved at 0.064 m-s-1. After the net was washed, samples were preserved in 2% buffered form- aldehyde. Within three to six months after collection, ichthyoplankton were sorted and identified to spe- cies or to the lowest taxonomic level possible (Atlan- tic Reference Centre, Huntsman Marine Science Centre, St. Andrews, New Brunswick, Canada). Sorted specimens were stored in 95% ethanol for approximately three years. Sixteen species were used in this analysis. For each species, 20 to 80 larvae were measured and weighted, depending on abundance, gen- eral condition, and the range of sizes available. Larvae were measured to the nearest 0.1 mm by using an image analysis system mounted on a Wild M3C dissecting microscope that was equipped with an S-type mount fitted with a 0.5x objective. Each larva was placed on a preweighted aluminium sheet and dried in an oven at 65°Celsius. After 24 hours, larvae were transferred to a desiccator for no less than 1 hour and no more than 3 hours. Each larva was weighted to the nearest 0. 1 ug by using a Cahn- 31 microbalance. Length-weight relationships of log10-transformed data were evaluated by using two models. In the first instance, a general allometric model of the form log W = a' + b log L + £ , (3) where W and L are weight and length, a' is equal to log(a ) from Equation lb, b is the exponent in Equa- tion 1, and e is error, was fit by using a general lin- ear algorithm (procedure GLM, SAS, 1988). In the second case, a model of the form logW = a" + b"(logL)c'"+£, (4) where W and L are weight and length, respectively, and a", b", and c" are constants, and e is error, was fit by using a nonlinear iterative least squares algo- rithm (procedure NLIN, SAS, 1988). When the value of c" is not significantly different from 1, Equation 4 reduces to the general allometric model (Eq. 3). Equa- tion 3 is a well-recognized and general functional form used in the estimation of length-weight rela- tionships (Ricker, 1975; Zweifel and Lasker, 1976; Cone, 1989). Equation 4 is not a common form (e.g. a Gompertz model; Laird et al., 1968; Zweifel and Lasker, 1976) but represents a first-order increase in complexity over the general allometric model (Eq. 3). I chose not to use the more complex Gompertz length-weight model, which has been used in other studies (e.g. McGurk, 1987) for two reasons. First, a Gompertz model is best suited for data that cover the entire range of sizes for a developmental stage. Such data were not available from the surveys con- ducted as part of this study. Second, preliminary analysis revealed that Equation 4 is numerically more stable than the Gompertz model for the data used in this study. To establish whether there was a significant de- parture from loglinearity (Eq. 3), a second order poly- nomial was fit to the residuals (Y = a + bX + cX2, where Y are the residuals and X is the log-trans- formed length). If the second order coefficient (c) is not significantly different from 0, then there is no departure from loglinearity and all other terms will also not differ from 0. Results Despite the wide variation in the range of informa- tion available for each species considered in this analysis (Table 1), the relationship between length and weight appears to be strong in all instances (Fig. 1 ). Analysis with the general linear allometric model (Eq. 3) shows a very highly significant fit for all spe- cies (Table 1). Evidence of a nonlinearity in the allo- metric relationship between length and weight is apparent in an analysis of the residuals from the general allometric model (Eq. 3). In 10 of 16 species, the second-order polynomial fit to the residuals in relation to log-transformed length was significant (Table 2). The value of c" (Eq. 4) was significantly different from 1 for 11 of the 16 species used in this study (Table 3). In the case of Ammodytes sp., the value of c" indicates an asymptotic relationship. An exponen- tial length-weight relationship of the log-transformed data is indicated in the 10 other species with values of c" significantly different from 1. Fitting Equation 4 to the data resulted in a decrease in residual sum of squares in 14 of the 16 species which averaged NOTE Pepin: An analysis of the length-weight relationship of larval fish 421 Table 1 General characteristics of the length data for the Parameters of the general allometric model (Eq. 3) of observations (n) are also provided. All relationsh of the estimated parameters. 16 species used in this study. Three groups could only be identified to genus, were estimated for the 16 species used in this analysis. The r2, and the number ips are significant at P<0.001. Values in brackets represent the standard error Species Range in length (mm) Median length (mm) Intercept (a') Slope (b) r2 n Ammodytes sp. 7.3-28.6 18.0 -3.41 2.97(0.14) 0.93 37 Aspidophoroid.es monopterygius 6.4-24.9 13.1 -2.83 2.49(0.20) 0.89 20 Clupea harengus 6.8-28.9 9.7 -4.19 3.45(0.11) 0.97 34 Gadus morhua 2.2-12.2 4.8 -2.68 2.65(0.12) 0.92 40 Glyptocephalus cynoglossus 5.6-37.6 10.6 -3.12 2.63(0.18) 0.85 40 Hippoglossoides platessoides 2.7-24.5 7.7 -3.53 3.42(0.10) 0.94 80 Liparis atlanticus 2.8-7.5 4.0 -2.85 3.15(0.10) 0.98 20 Liparis gibbus 5.3-12.5 7.5 -3.01 3.13(0.20) 0.93 20 Lumpenus sp. 9.9-28.8 16.2 -3.11 2.70(0.10) 0.95 36 Mallotus villosus 4.2-24.0 8.5 -3.55 2.79(0.06) 0.98 40 Pleuronectes americanus 2.1-6.2 3.8 -3.08 3.11 (0.16) 0.91 40 Pleuronectes ferrugineus 1.9-14.4 3.6 -3.35 3.54(0.09) 0.97 40 Sebastes sp. 4.4-9.5 7.5 -2.39 2.27(0.19) 0.76 46 Stichaeus punetatus 8.8-22.0 13.5 -3.96 3.71 (0.13) 0.95 40 Tautogolabrus adspersus 3.3-9.3 5.3 -3.73 4.22(0.25) 0.90 59 Ulvaria subbifurcata 4.5-13.3 6.4 -3.23 3.13(0.13) 0.92 50 19% (range: 2-47%). In the cases of Lumpenus sp. and Sebastes sp., the use of Equation 4 resulted in an increase in the residual sum of squares of 15% and 8%, respectively. Although lengths and weights were not corrected for shrinkage, Hay's (1984) and Johnston and Mathias' (1993) studies show that proportional weight loss due to preservation is greater than shrinkage in length and is proportionally greater as size of larvae decreases. If correction factors had been available, the net result would have been to increase the departure from log-linearity. Discussion Despite the apparently strong fit to the general allo- metric relationship between length and weight of larval fish, this analysis clearly shows a consistent nonlinear pattern in the log-transformed data. Al- though the curvature appears subtle, incorrect as- sumptions about model form may cause bias in the prediction of weights from lengths as well as in the interpretation of size-related variations in the physi- cal condition of fish larvae. The significance of such inaccuracies may be minor for some aspects of the early life history (e.g. range of weights based on a mean functional relationship [Houde, 1989]) but may become more important in the calculation of meta- bolic processes (e.g. Checkley, 1984; Ki0rboe, 1989; Giguere et al., 1989). Furthermore, the interpreta- tion of gross measures of condition could also be in- fluenced by the nonlinear nature of the length-weight relationship of larval fish. For example, calculation of Fulton's K, an index of condition, relies on the as- sumption that the general length-weight relationship of organisms follows a linear logarithmic function, specifically an isometric one (i.e. b=3). Increases or decreases in this coefficient are believed to be related to variations in condition. Not only is the general isometric assumption violated in 11 of 16 species (Table 1), but also that of linearity (Table 3). The sig- nificance of a departure from an isometric relationship in the interpretation of measures of condition relative to changes in body shape has been discussed in gen- eral terms by Cone ( 1989) and in relation to larval fish by Laurence (1978). As Ricker (1975) points out, Fulton's K can be used only to contrast individuals of approximately the same length. However, this is only true if the logarithmic length-weight relationship is lin- ear and may not be appropriate when there is a signifi- cant departure from linearity, as shown in this study. 422 Fishery Bulletin 93(2). 1995 10 0 1 Ammodytes sp 10 A. monopterygtus 10 0 1 C. harengus 10 0 1 G. morhua 9 • # • •* t • 0 01 0 01 0 01 0 01 10 100 10 100 10 100 10 100 10 01 G. cynoglossus 10 1 01 //. platessotdes to 1 0 1 L. atlanbeus 10 0 1 L gtbbus t • 1 • • •* r / V* »• £ en 0) 001 0 001 001 0 001 10 0 01 0 001 0 01 0 001 10 10 ' 10 1 10 1 5 10 1 Lumpenus sp 10 M. villosus . P. amencanus 10 P. ferrvgineus / * • 01 001 01 0 01 ■ y 0 1 001 / 01 0 01 ,/ 10 K) 10 1 0 10 i 10 100 10 Sebastes sp .0 S. punctatus 10 T. adspersus 10 U. subbifiircata 01 ; / 01 / 01 0 1 0 01 0 01 001 0 01 10 I 10 10 1 10 10 ' 10 Length (mm) Figure 1 Logarithmic plot of the length-weight data for the 16 species considered in this analysis. Each point represents an individual larva. Ontogenic development is characterized by notable changes in functional morphology that impact mo- tility, foraging ability, and predator avoidance (Blaxter, 1986; Neilson et al., 1986; Olla and Davis, 1992). Developmental changes in body form or com- position can result in differences in proportional growth in terms of length and weight and thus lead to a nonlinear allometric length-weight relationship. Alternatively, nonlinear variation in the length- weight relationship could be considered as evidence of changes in condition induced by some degree of food deprivation within a population of larval fish (e.g. Grover and Olla, 1986; Frank and McRuer, 1989; Drolet et al. , 199 1 ). Under such circumstances, varia- NOTE Pepin: An analysis of the length-weight relationship of larval fish 423 Table 2 Estimated parameters of a second-order polynomial ( Y = a + bX + cXz ) fit to the residuals (Y) from the general allometric model, estimated for the entire data set, in relation to log-transformed length (X). The right-most column provides the significance level of a two-tailed i-test evaluating the hypothesis that c=0. Species a b c P Ammodytes sp. -3.21 5.45 -2.28 0.003 Aspidophoroides monopterygius 0.79 -1.43 0.63 0.54 Clupea harengus 2.79 -4.99 2.17 0.001 Gadus morhua 0.92 -22.62 1.74 0.003 Glyptocephalus cynoglossus 1.96 -3.56 1.57 0.03 Hippoglossoides platessoides 1.19 -2.83 1.59 0.001 Liparis atlanticus -0.48 1.50 -1.13 0.23 Liparis gibbus -2.30 5.11 -2.80 0.15 Lumpenus sp. 1.48 -2.47 1.02 0.26 Mallotus villosus 1.06 -2.19 1.08 0.001 Pleuronectes americanus 0.66 -2.56 2.37 0.05 Pleuronectes ferrugineus 0.80 -2.47 1.67 0.001 Sebastes sp. 3.70 -9.07 5.49 0.01 Stichaeus punctatus 2.57 -4.47 1.92 0.14 Tautogolabrus adspersus -0.79 2.26 -1.58 0.26 Ulvaria subbifurcata 3.93 -9.16 5.23 0.001 Table 3 Parameter estimates for the nonlinear logarithmic length- weight relationship (Eq. 4). Values in brackets represent the asymp- totic standard error of the estimated parameters. An asterisk next to the parameter in column c" denotes that the exponent is significantly different from 1 (two-tailed r-test). The right-most column provides the percent change in residual sum of squares relative to the fit provided by Equation 3. Apositive value indicates an increase in the residual sum of squares whereas a negative value represents a decrease in the residual sum of squares. Species a" b" c" Percent Ammodytes sp. -18.4 18.0 0.19(0.05)* -22 Aspidophoroides monopterygius -1.84 1.52 1.55(0.92) -3 Clupea harengus -1.92 1.15 2.44(0.29)* -47 Gadus morhua -1.78 1.80 1.94(0.33)* -23 Glyptocephalus cynoglossus -1.53 1.02 2.22(0.59)* -11 Hippoglossoides platessoides -2.27 2.11 1.78(0.19)* -21 Liparis atlanticus -4.66 4.87 0.53(0.37) -9 Liparis gibbus -30.6 30.7 0.09(0.51) -9 Lumpenus sp. -1.56 1.18 1.91(0.81) 15 Mallotus villosus -2.39 1.58 1.76(0.23)* -25 Pleuronectes americanus -2.37 2.83 1.80(0.39)* -9 Pleuronectes ferrugineus -2.42 2.58 1.66(0.16)* -47 Sebastes sp. -0.99 0.93 3.80(1.28)* 8 Stichaeus punctatus -1.65 1.42 2.18(0.59)* -6 Tautogolabrus adspersus -8.02 8.24 0.40(0.51) -2 Ulvaria subbifurcata -1.35 1.26 3.41(0.60)* -29 424 Fishery Bulletin 93(2), 1995 tion in condition, or the scatter about the length- weight relationship, should be greatest at the devel- opmental stage most vulnerable to food deprivation (i.e. yolk absorption). However, the pattern of scat- ter about the length-weight relationship shows little evidence of a consistent pattern associated with that stage of the early life history (Fig. 1). It is possible that the majority of larvae undergo a degree of star- vation associated with the period of yolk absorption (e.g. Theilacker, 1986; Drolet et al., 1991; Marguiles, 1993), which would result in a uniform pattern in the deviation from a general allometric length-weight relationship. However, there is also evidence that suggests that only a limited fraction of a larval fish population suffers from substantial food deprivation (O'Connell, 1981; Canino et al., 1991; McGurk et al., 1992). The consistent nonlinear pattern in the length- weight relationship among a suite of species with different life histories, which could result in substan- tial differences in vulnerability to environmental fac- tors (Miller et al., 1988; Pepin, 1991), suggests that developmental processes in the early ontogeny of fishes are important factors governing the form of this relationship. The degree of curvature in the loga- rithmic relationship (c": Eq. 4) is not significantly correlated with size at hatch (r=0.45, P>0.05, n=14; Fig. 2), which may be a measure of vulnerability to 2 3 Length at hatch (mm) Figure 2 The value of c" in relation to the size at hatch for 14 of the 16 species used in this study. The value of c" provides a measure of the curvature in the logarithmic length-weight relationship. Data on size at hatch were obtained from general refer- ence sources detailing fish life history character- istics (Fahay, 1983; Scott and Scott, 1988). Data were unavailable for Aspidophoroides mono- pterygius and Lumpenus sp. starvation (Miller et al., 1988; but see Pepin, 1991). In fact, the positive trend is opposite that expected on the premise that species that produce small lar- vae should be more vulnerable to starvation. Whether physiological processes rather than de- velopmental constraints result in the nonlinear loga- rithmic length-weight relationship described in this study is uncertain. There are a number of approaches that may be indicative of the physiological condition of larval fish (e.g. Theilacker, 1986; Clemmensen, 1988; Fraser, 1989), but they may never the less be highly correlated with morphometric indices of con- dition (e.g. Theilacker, 1978; Harris et al., 1986; Setzler-Hamilton et al., 1987). Furthermore, there may remain considerable uncertainty about the in- terpretation of variation in such condition indices of larval fish (e.g. Bergeron and Boulhic, 1994). To in- terpret variation in length-weight relationships cor- rectly, it is essential that thorough studies be con- ducted to establish the proper functional form and how this may vary under different feeding conditions. Acknowledgments I thank D. Beales and T H. Shears for their techni- cal assistance. Comments by E. Dalley, T Miller, W. Warren, and two anonymous reviewers were helpful in the development of this study. Literature cited Barton, A. D., and A. K. Laird. 1969. Analysis of allometric and non-allometric differen- tial growth. Growth 33:119-127. Bergeron, J. P., and M. Boulhic. 1994. Rapport ARN/ADN et evaluation de l'etat nutritionel et de la croissance des larves de poissons marins: un essai de mise au point experimental chez la sole iSolea solea). ICES J. Mar. Sci. 51:181-190. Blaxter, J. H. S. 1986. Development of sense organs and behaviour of te- leost larvae with special reference to feeding and predator avoidance. Trans. Am. Fish. Soc. 115:98-114. Canino, M. F., K. M. Bailey, and L. S. Incze. 1991. Temporal and geographic differences in feeding and nutritional condition of walleye pollock larvae Theragra chalcogramma in the Shelikof Strait, Gulf of Alaska. Mar. Ecol. Prog. Ser. 79:27-35. Checkley, D. M. 1984. Relation of growth to ingestion for larvae of Atlantic herring Clupea harengus and other fish. Mar. Ecol. Prog. Ser. 18:215-224. Ciechomski, J. D., R. P. Sanchez, G. Alsepeiti, and H. Regidor. 1986. Study of the growth in weight and condition factor of larval anchovy Engraulis anchoita. Rev. Invest. Desarr. Pesq. 5:183-193. NOTE Pepin: An analysis of the length-weight relationship of larval fish 425 Clemmesen, C. M. 1988. A RNA and DNA fluorescence technique to evaluate the nutritional condition of individual marine fish larvae. Meeresforschung Rep. Mar. Res. 32:134-143. Cone, R. S. 1989. The need to reconsider the use of condition indices in fishery science. Trans. Am. Fish. Soc.118: 510-514. Drolet, R., L. Fortier, D. Ponton, and M. Gilbert. 1991. Production offish larvae and their prey in subarctic southeastern Hudson Bay. Mar. Ecol. Prog. Ser. 77: 105-118. Fahay, M. P. 1983. Guide to the early stages of marine fishes occurring in the western north Atlantic Ocean, Cape Hatteras to the south- ern Scotian Shelf. J. Northwest Atl. Fish. Sci. 4, 423 p. Frank, K. T., and J. K. McRuer. 1989. Nutritional status of field-collected haddock (Mela- nogrammus aeglefinus) larvae from southwestern Nova Scotia: an assessment based on morphometric and verti- cal distribution data. Can. J. Fish. Aquat. Sci. 46 (suppl. 1):125-133. Fraser, A. J. 1989. Triacylglycerol content as a condition index for fish, bivalve, and crustacean larvae. Can. J. Fish. Aquat. Sci. 46:1868-1873. Fulton, T. W. 1911. The sovereignty of the sea. Edinburgh and London. Giguere, L. A., B. Cote, and J. F. St. Pierre. 1989. Metabolic rates scale isometrically in larval fishes. Mar. Ecol. Prog. Ser. 50:13-19. Grover, J. J., and B. L. Olla. 1986. Morphological evidence for starvation and prey size selection of sea-caught larval sablefish, Anoplopoma fimbria. Fish. Bull. 84:484-489. Harris, R. K., T. Nishiyama, and A. J. Paul. 1986. Carbon, nitrogen, and caloric content of eggs, larvae, and juveniles of the walleye pollock, Theragra ehalco- gramma. J. Fish. Biol. 29:87-98. Hay, D. E. 1984. Weight loss and change in condition factor during fixation of Pacific herring, Clupea harengus pallasi , eggs and larvae. J. Fish. Biol. 25:421-433. Houde, E. D. 1987. Fish early life dynamics and recruitment varia- bility. Am. Fish. Soc. Symp. 2:17-29. 1989. Comparative growth, mortality, and energetics of marine fish larvae: temperature and implied latitudinal effects. Fish. Bull. 87:471-496. Houde, E. D., and R. C. S. Schekter. 1980. Feeding by marine fish larvae: developmental and functional response. Environ. Biol. Fish. 5:315-334. Johnston, T. A., and J. A. Mathias. 1993. Length reduction and dry weight loss in frozen and formalin-preserved larval walleye, Stizostedion vitreum (Mitchill). Aquacult. Fish. Manage. 24:365-371. Kiorboe, T. 1989. Growth in fish larvae: are they particularly efficient? Rapp. P.-V. Reun. Cons. Int. Explor. Mer 191:383-389. Laird, A. K., A. D. Barton, and S. A. Tyler. 1968. Growth and time: an interpretation of allo- metry. Growth 32:347-354. Laurence, G. C. 1978. Length-weight relationships for seven species of northwest Atlantic fishes reared in the laboratory. Fish. Bull. 76:890-895. Marguiles, D. 1993. Assessment of the nutritional condition of larval and early juvenile tuna and Spanish mackerel (Pisces: Scombridae) in the Panama Bight. Mar. Biol. 115: 317-330. McGurk, M. D. 1987. Age and growth of Pacific herring larvae based on length frequency analysis and otolith ring number. En- viron. Biol. Fish. 20:33-47. McGurk, M. D., A. J. Paul, K. O. Coyle, D. A. Ziemann, and L. J. Haldorson. 1992. Relationships between prey concentration and growth, condition, and mortality of Pacific herring, Clupea pallasi, larvae in an Alaskan subarctic embayment. Can. J. Fish. Aquat. Sci. 50:163-180. Miller, T. J., L. B. Crowder, J. A. Rice, and E. A. Marschall. 1988. Larval size and recruitment mechanisms in fishes: toward a conceptual framework. Can. J. Fish. Aquat. Sci. 45:1657-1670. Neilson, J. D., R. I. Perry, P. Valerio, and K. G. Waiwood. 1986. Condition of Atlantic cod Gadus morhua larvae after the transition to exogenous feeding: morphometries, buoy- ancy and predator avoidance. Mar. Ecol. Prog. Ser. 32:229-235. O'Connell, C. P. 1981. Percentage of starving northern anchovy, Engraulis mordax, larvae in the sea as estimated by histological methods. Fish. Bull. 78:475-489. Olla, B. L., and M. W. Davis. 1992. Phototactic responses of unfed walleye pollock, Theragra ehaleogramma larvae: comparisons with other measures of condition. Environ. Biol. Fish. 35: 105-108. Pepin, P. 1991. The effect of temperature and size on development and mortality rates of the pelagic early life history stages of marine fish. Can. J. Fish. Aquat. Sci. 48:503-518. Ricker, W. E. 1975. Computation and interpretation of biological statistics offish populations. Bull. Fish. Res. Board Can. 191, 382 p. Rose, K. A., and J. H. Cowan. 1993. Individual-based model of young-of-the-year striped bass population dynamics. I: Model description and baseline simulations. Trans. Am. Fish. Soc. 122:415-438. SAS. 1988. SAS/STAT user's guide, release 6.03. SAS Institute, Cary, NC, 1,028 p. Scott, W. B., and M. G. Scott. 1988. Atlantic fishes of Canada. Can. Bull. Fish. Aquat. Sci. 219, 731 p. Setzler-Hamilton, E. M., D. A. Wright, F. D. Martin, C. V. Millsaps, and S. I. Whitlow. 1987. Analysis of nutritional condition and its use in pre- dicting striped bass recruitment: field studies. Am. Fish. Soc. Symp. 2:115-128. Sinclair, M., and M. J. Tremblay. 1985. Timing of spawning of Atlantic herring (Clupea harengus harengus) populations and the match-mismatch theory. Can. J. Fish. Aquat. Sci. 41:1055-1065. Theilacker, G. H. 1978. Effect of starvation on the histological and morpho- logical characteristics of jack mackerel, Trachurus symmetrieus, larvae. Fish. Bull. 76:403-414. 1986. Starvation-induced mortality of young sea-caught jack mackerel, Trachurus symmetrieus, determined with his- tological and morphological methods. Fish. Bull. 84:1-18. 426 Fishery Bulletin 93(2). 1995 Ware, D. M., and T. C. Lambert. 1985. Early life history of Atlantic mackerel {Scomber scombrus) in the southern Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci. 42:577-592. Werner, R. G., and J. H, S. Blaxter. 1980. Growth and survival of larval herring in relation to prey density. Can. J. Fish. Aquat. Sci. 37:1063-1069. Westernhagen, H. von, and H. Rosenthal. 1981. On condition factor measurements in Pacific herring larvae. Helgolander Meeresunters. 34:257-262. Zweifel, J. R., and R. Lasker. 1976. Prehatch and posthatch growth of fish: a general model. Fish. Bull. 74:609-621. Superintendent of Documents Subscription Order Form *5178 I lYES, enter my subscription(s) as follows: subscriptions to Fishery Bulletin (FBj for $27.00 per year ($33.75 foreign). The total cost of my order is $ . Price includes regular shipping and handling and is subject to change. International customers please add 25%. Company or personal name (Please type or print) Additional address/attention line Street address City. State, Zip code Daytime phone including area code Charge your order. It's easy! ffl TO Purchase order number (optional) For privacy protection, check the box below: □ Do not make my name available to other mailers Check method of payment: □ Check payable to Superintendent of Documents □ GPO Deposit Account □ VISA □ MasterCard To fax your orders (202)512-2250 To phone your orders -□ (202)512-1800 (expiration date) Thank you for your order! Authorizing signature Mail To: Superintendent of Documents P.O. Box 371954, Pittsburgh, PA 15250-7954 333 03U 428 mm \rTjnivK\50 mm TL. The second mode appeared at the inner shelf site in late September at sizes >10 mm TL. This group reached an apparent minimum size of 30 mm TL by the fall (Fig. 4). Movement out of the estuary in the fall is indi- cated by the reduction in the number of age 0+ indi- viduals by November-December (Figs. 4-6). This same pattern of movement out of the estuary also was reflected in the catch per unit of effort (CPUE) Able et al.: Early life history of Centropristis striata 433 Centropristis striata 1977-1987 Larvae/ 10 m Larvae/10 m 70 JrW" ' ' '■ "?t .'..'>* kiloaf tpri ^'..'•.■.•:\:.;.-Vr ^£ ' 4? Figure 3 Monthly distribution and abundance of black sea bass, Centropristis striata, larvae in the mid-Atlantic Bight based on NMFS- MARMAP surveys during 1977-87. from trap collections in the Rutgers University Ma- rine Field Station (RUMFS) boat basin in 1992 (Fig. 7). At the same time, catch rates increased dramati- cally, compared with those for summer, on the inner continental shelf off New Jersey (Fig. 8), owing, pre- sumably, to the addition of individuals moving from the estuary as well as to recently settled fishes. Age 0+ individuals were absent in the winter. Catches at Beach Haven Ridge were zero from December through February and few individuals were caught in March (Fig. 7) in 1991 and 1992. Catches increased in April or May, or during both months, depending on the year, and then decreased through the spring and early summer. This same general seasonal pat- 434 Fishery Bulletin 93(3). 1995 Centropristis striata 1977-1987 Larvae/ 10 m2 0 0 1-10 1 1-100 October Larvae/10 m L~J 0 1-10 Figure 3 (continued) September ■■ ...Vr ■?■■ *2 . ' '->•' November tern occurred in the Great Bay estuary between 1988 and 1992 (Fig. 5) and during 1974 (Fig. 6) when most individuals were present from March through May and from August through November and were ab- sent during the winter. Fall otter trawl sampling from the continental shelf off New Jersey (Fig. 8) and from elsewhere in the mid-Atlantic Bight (Fig. 9) collected age 0+ individu- als of the same lengths (3-9 cm TL) as those in the fall estuarine sampling (September and October, Figs. 4-6). These individuals were distributed throughout the inshore portions of the mid-Atlantic Bight (Figs. 8 and 10). Interestingly, the largest col- lections of age 0+ individuals were taken off eastern Long Island, Rhode Island, and off Massachusetts, both north and south of Cape Cod (Fig. 10). These are areas where larvae were virtually absent in ex- tensive collections between 1977 and 1987 (Fig. 3). Able et a!.: Early life history of Centropristis striata 435 CO CO 3 T3 ■> 73 C "o <5 .□ E 3 Z Occur striaU Ridge inner trap s 200 100 0 200 100 0 200 100 0 100 50 0. 50" 25" 0- 50" 25" 0- 50" 25" 0- 50" 25" 22 July - 4 August n = 2S3 □ Beach Haven Ridge (Inner Shelf) ■ Great Bay (Estuary) 5-18 August n = 608 .■ill. q [ — , 19 August - 1 September n = 566 -■III. 2-15 September n = 236 _■■!■. — 16 -29 September n = 145 -■llli 30 September - 13 October n=110 _n_ ■■■■■■ 14 -27 October n = 163 LJrz, _|H|||l. 28 October - 1 0 November n = 50 Hb_ _— =■ 50" 25" 1 1 - 24 November 11 = 6 50" 25" 25 November - 7 December n = 17 uo ,o ,o ,° ,° /° ,° «_° ^.° «r ^ o? <£" £ 4> & A*3' # ° N0 0? op £ T3 C (D E 3 BO [^ TRAWL (1988- 1990); BO 40 Straps (1991); n. 1M ■ TRAPS(1992);n=944 JANUARY 1988-90 n = 0 1991 n = 0 1992 n = 0 JULY 1988-90 n=12 20 1992 n = 14 -V - ' ' FEBRUARY . AUGUST 1988-90 11 = 0 . 1991 n = 0 1992 n =0 198890 n = 32 1991 n=8 1992 n= 194 111. "OHs-.n MARCH 1988-90 n = 0 1991 n = 12 1992 n = 6 ■III Vm~ SEPTEMBER 1988-90 [1 = 35 1991 n=7 1992 n = 125 APRIL 1988-90 n = 0 1991 n = 120 1992 n=213 OCTOBER 1988-90 n = 2 1991 n=3 1992 n=109 MAY 1988-90 n = 0 1991 n= 12 1992 n = 218 .--■I-,-,-, NOVEMBER 1988-90 n = 0 1991 n=3 1992 n = 37 JUNE 1988-90 n = 7 1991 n = 11 1992 n = 20 DECEMBER 1988-90 n = 0 1991 11=0 1992 n=8 * * * *' ^ £ £ £ £ £ # * * * * 1 ol Z 20 1 o CO E 10 z 0 20 10 ■ inner shelf n = 188 £/| ESTUARY ' n = 151 JANUARY shelf n = 0 estuary n = 0 JULY shelf n = 5 estuary n = 2 FEBRUARY shell n = 0 estuary n = 0 AUGUST shell n = 41 estuary n = 4 ..itiiLli .■■ i MARCH shelf n = 3 estuary n = 1 APRIL shelf n = 7 estuary n = 11 SEPTEMBER shell n = 22 estuary n = 45 il. . jam. . OCTOBER B Shelf n = 1 02 -1 estuary n = 3 lllg 1 . Jlllllll... a MAY Rn shelf n = 1 RfjN0 estuary n = 80 NOVEMBER shelf n = 3 estuary n = 1 20 10 JUNE shelf n = 4 estuary n = 4 DECEMBER shelf n = 0 estuary n = 0 Total length (mm) Figure 6 Monthly length frequencies, based on otter trawl collections, of black sea bass, Centropristis striata, from the inner conti- nental shelf in the vicinity of Beach Haven Ridge and Great Bay-Little Egg Harbor estuary during 1974. the time of first spring collections, temperature was approximately 10°C for individuals age 1+ (approxi- mately 9 months old), whereas in the summer tem- perature was approximately 23°C for age 0+ indi- viduals (Fig. 7). In the vicinity of Beach Haven Ridge, the age 0+ individuals first occurred at approximately 15°C and were most abundant when bottom tempera- tures reached 20°C (Fig. 7). Over the continental shelf in the fall, the age 0+ cohort was collected primarily at bottom temperatures of 14-17°C (Fig. 12) and at higher average temperatures of 16-2 1°C in Massa- chusetts inshore waters (Fig. 12). During winter, most individuals were collected at 6-9°C (Fig. 12), a temperature that probably reflects their greater abundance in deeper waters at that time (Fig. 10). In the spring, this same cohort was abundant at 6— 11°C and 15-17°C. In every instance on the conti- nental shelf, with the possible exception of inshore Massachusetts, the fish were found at higher aver- age temperatures than those represented by most of the stations sampled (Fig. 12). Discussion Annual cycle in the early life history Spawning of black sea bass in the mid-Atlantic Bight proceeds from south to north, presumably with warm- ing temperatures. Our interpretation of this geo- graphical pattern is based on extensive collections during 1977-87 and is consistent with that reported for 1966-67 (Kendall, 1972; Kendall and Mercer, 1982). The occurrence of larvae of all sizes in all areas suggests that spawning and development oc- curs throughout most of the mid-Atlantic Bight. In addition, most larvae were <8 mm TL in our conti- nental shelf collections and were similar to those 438 Fishery Bulletin 93(3), 1995 o o 30 - £ 20 <3 Q. E a> 0. KP 0.3, 5- aj 0.0. c 0) Q O 30 o ns ns ns 20. — b — landward D ♦ seaward ■ ^* *^ ■ ns ""^ ns 0.00 1992 1 m beam trawl no. fish = 72 no tows = 309 3 5 6 7 8 9 10 11 12 25 26 27 Station number Figure 1 1 Abundance of age 0+ black sea bass, Centropristis striata, in the Great Bay-Little Egg Harbor estuary during 1992. See text for habitat designations and Figure 2 for locations. 442 Fishery Bulletin 93(3). 1995 1600 30 30 700 Fall Survey 600 A 1967-1991 1400 A Winter Survey 25 z 1992 c Q Station! 1200 3 500 20 f\\J ■ Black &•* Baaa 20 - 1000 Q Stations o 400 CT - 800 15 f\\\i 15 0> O 300 a 5 600 1(J - [vv^\ 10 200 •X-cn 400 Z 5 5 CO n 100 *V\\\\A 200 £ <» CO c o „ 3 c n CD ^0 ^isk 0 ~ 0 i i i r i i i i i T" ~TT ii ii "■ 2 1 5 9 13 17 21 25 29 B 1 5 9 13 17 21 25 29 in IJi -*• *- _ (TO ° 0> fe 0) -«« -3C- -Q (n/l. ■ 1 25 2 J3 1200 CO t CD 3 c E i Maaaachuaotta Fall Survey 3 3 Q Spring Survey BJ Z 1962 - 1891 ^ O" 3 Z 1000 " ^ 1968-1991 {? 80 H Black Sea Baaa 20 o vj H Black Sa« Bui 150 c/> □ Statlona ; g; \\ CO 5 BOO \ B Station o 60 jk \\l 15 u 600 |l 100 I • g 0) cr 0) CO \ 40 ; xM 10 w 400 \ / ; o 50 A . :*l 0) 200 fN .1 20 n ^-SsJ: " s s M 5 P O. CO 0 i i i i i i ( i i i ■ i i w o'i i ' riViVi'i'i'i'iiiinniT i i i i i i i1 1 5 9 13 17 21 25 29 1 5 9 13 17 21 25 29 0 Temperature (°C) Figure 12 Abundance of age 0+ black sea bass, Centropristis striata, relative to bottom temperature in the spring, fall, and winter on the mid-Atlantic Bight continental shelf and off the coast of Massachusetts, based on Northeast Fish. Sci. Cent . and Massachusetts Div. Marine Fisheries bottom trawl surveys (1982-92). studies are warranted to understand the possible significance of the region as a nursery. In southern New Jersey, spawning and nursery areas are somewhat better delineated. The larvae clearly occur on the inner continental shelf off New Jersey (Figs. 3 and 4; Kendall, 1972), but there is no evidence of larvae in estuaries and bays in New Jer- sey (Croker, 1965; Himchak, 1982; Witting3) or Dela- ware (Pacheco and Grant, 1965; Wang and Kernehan, 1979). The apparent absence of larvae in estuaries and the occurrence of larvae and small juveniles (<20 mm TL) at Beach Haven Ridge suggest that settle- ment may initially occur on the inner continental shelf and that some individuals may remain there while some move into estuaries. Larvae 15-17 mm were reported in late July near Hereford Inlet, New Jersey (Allen et al., 1978), but further details are not available. The only other prior reports of small juveniles in New Jersey estuaries are of 25-mm in- dividuals from Great Egg Harbor (Bean, 1888), 20- mm individuals from Raritan Bay (Nichols and Breder, 1927) and 25-35 mm specimens from lower Delaware Bay (Wang and Kernehan, 1979). The oc- currence of juveniles in the York River in Chesapeake Bay (Musick and Mercer, 1977) was based on indi- viduals that may have overwintered on the continen- tal shelf and reentered the estuary as occurs in New Jersey In other Chesapeake Bay habitats black sea bass (some of them 140-165 mm) were more abundant in eelgrass, Zostera marina, both day and night, than in adjacent unvegetated areas (Orth and Heck, 1980). Our observations suggest that suitable summer nursery habitats, either on the continental shelf or in estuaries, are presumably related to the occurrence of some type of bottom structure, such as peat and shell accumulations. This is further substantiated Able et al.: Early life history of Centropnstis striata 443 by the increase in catch rates of black sea bass juve- niles when shell was added to estuarine substrate to improve oyster recruitment (Arve, 1960). Dissolved oxygen also may influence patterns of habitat use because juveniles are intolerant of low levels (Hales and Able, in press a). The similarities in the densi- ties and in sizes attained in the fall by juveniles in the estuary and in the adjacent inner continental shelf suggest that habitat quality is similar for both these areas, if one assumes that size differential pre- dation or movements did not occur at either site dur- ing the sampling period. In summary, these data in- dicate that both estuaries and the inner continental shelf are important as nursery areas and that juvenile black sea bass are not strickly estuarine dependent. Acknowledgments Numerous individuals assisted in the preparation of this manuscript. Rutgers Marine Field Station per- sonnel provided assistance in sampling, particularly Roger Hoden, Chris Wright, Matt Pearson, Lynn Wulff, Rich McBride, Stan Hales, and Rick Laubly. Rose Petrecca provided video images from SCUBA dives, and Dave Witting made data from SCUBA dives available. Don Byrne and Arnold Howe pro- vided data from New Jersey and Massachusetts in- shore trawl surveys, respectively. This work is the result, in part, of research sponsored by NOAA, Of- fice of Sea Grant, Department of Commerce, under Grant No. NA36-RG0505 (Project Nos. R/F-42, R/F- 65). This is Sea Grant Publication Number NJSG- 94-301. Funding was also provided through Rutgers University, Institute of Marine and Coastal Sciences (IMCS), and through NOAA-NURP New York Bight Center. Literature cited Able, K. W., R. Hoden, D. A. Witting, and J. B. Durand. 1992. Physical parameters of the Great Bay-Mullica River Estuary with a list of research publications. Rutgers Univ., Institute of Marine and Coastal Sciences, Tech. Rep. 92-06, 38 p. Alexander, M. S. 1981. Population response of the sequential hermaphrodite black sea bass, Centropristis striata, to fishing. 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Demersal fish surveys are used for two purposes: to detect trends in multispecies communities for environmental assessment and to pro- vide fishery independent stock assess- ments for management. We compared remotely operated vehicle (ROV) and swept-area trawl surveys to evaluate their strengths and weaknesses for these two purposes. ROV abundance estimates tended to be higher and have lower coefficients of variation than did trawl abundance estimates. This trend is greatest for benthic species and par- ticularly so for small, cylindrically shaped fishes. For patchily distributed, off-bottom fishes such as rockfish, Sebastes spp., sablefish, Anoplopoma fimbria, and Pacific whiting, Merluccius productus, the results vary between ROV and trawl estimates. For environ- mental assessment, the ROV estimates are superior because, for most species, abundances are higher and smaller changes can be detected. For fisheries management of commercially impor- tant species, the results are divided. Dover sole, Microstomias pacificus, and thornyheads, Sebastolobus spp., have higher ROV abundance estimates and lower coefficients of variation than the trawl. Sablefish, which exhibit more off- bottom behavior, have higher trawl es- timates at two of three depths. The ROV and trawl provide different types of information not available from other gear. Much of the difference between the two types of surveys stems from the nature of the sampling gear and from the behavior, body shape, and size of the fishes. Population estimates of Pacific coast groundfishes from video transects and swept-area trawls Peter B. Adams* John L. Butler** Charles H. Baxter*** Thomas E. Laidig* Katherine A. Dahlin** W. Waldo Wakefield**** * Tiburon Laboratory, Southwest Fisheries Science Center National Marine Fisheries Service, NOAA 3 I 50 Paradise Drive, Tiburon, California 94920 ** Southwest Fisheries Science Center National Marine Fisheries Service, NOAA PO. Box 271, La Jolla, California 92038 *** Monterey Bay Aquarium Research Institute 1 60 Central Avenue, Pacific Grove, California 93950 **** National Undersea Research Center School of Fisheries and Oceans Sciences University of Alaska Fairbanks, Fairbanks, Alaska 99775 Present address: Institute of Marine and Coastal Science Rutgers University, New Brunswick, New Jersey 08093 Manuscript accepted 13 February 1995. Fishery Bulletin 93:446-455 (1995). Estimates of population abundance are essential to research for under- standing the impact of human ac- tivities on marine demersal fish populations. Traditionally, swept- area trawl surveys have been used to obtain abundance estimates aimed at fisheries management. Recently, environmental surveys, used to monitor the impacts of pol- lution and coastal development, have become more widespread and important. These two types of sur- veys have different goals. Data from fisheries surveys are used as input for predictive models to forecast the results of alternative fisheries man- agement strategies and are usually directed toward either a single spe- cies or a small species group. Envi- ronmental surveys are used to de- tect trends in populations over time, to distinguish those trends from natural variation, and are usually directed at an entire multispecies fish community. Both types of survey population estimates are subject to the prob- lems of bias and precision. Bias is a particular problem for fisheries sur- veys. Fishery stock assessment is based on models that integrate fish- ery catch-at-age data with fishery- independent survey estimates of abundance (Deriso et al., 1985). The catch-at-age data, sampled from the commercial fishery, document the trend of population change result- ing from recruitment of young fish into the population and from re- moval of individuals out of the population due to fishing and natu- ral mortality. The fishery-indepen- dent survey data are used as a mea- sure of either relative or absolute abundance (Doubleday and Rivard, 1981). These survey data are used to calibrate or "tune" the trend ob- 446 Adams et al.: Population estimates of Pacific coast groundfishes 447 tained from the catch-at-age data to determine how close the population is to a threshold value of over- fishing (Kimura, 1989). Survey data also yield valu- able information on migration routes, or biological parameters such as age-at-maturity, fecundity, and feeding. Biased survey estimates can result in very precise estimates of population abundance which are either lower or higher than the true population abundance. For environmental surveys, the problem of preci- sion is the major concern. Here, the goal is to detect a trend in population size, often of all the fish in the habitat, and to distinguish that trend from natural variation in fish populations. Abundance estimates from trawl surveys tend to have very large variances; often means and variances are correlated (see Lenarz and Adams, 1980). Resulting confidence intervals around means range from 50 to 100% for flatfish spe- cies and are greater than 100% for rockfish, Sebastes spp. (Raymore and Weinberg, 1990). As a result, all but the most extreme changes in population size are masked by these large confidence intervals. Meth- ods commonly used to deal with this variability are transformations using the negative binomial (Lenarz and Adams, 1980) or the Delta distribution (Pen- nington, 1986). Data transformed by using these dis- tributions often result in the variance being inde- pendent of the mean; however, the large confidence intervals and low statistical power remain. In this study we examined video transects con- ducted from a remotely operated vehicle (ROV) as an alternative method for making population estimates of demersal fishes and compared these estimates to those from a conventional swept-area trawl survey. Methods Study site The study site off central California lies along a cone- shaped ridge which runs southwest from Santa Cruz, California, and separates Monterey Canyon to the south from Ascension Canyon to the north (Fig. 1). Surface topography of the ridge is smooth and rela- tively unbroken (Greene1). The ridge is composed of sandstone, is covered with mud of pelagic origin, and is characterized by occasional areas of exposed bed- rock. The stations where ROV and trawl operations were conducted were located along the ridge at depths of 200, 400, and 600 m (see Fig. 1). ROV operations ROV operations were conducted by using the Monterey Bay Aquarium Research Institute's ROV Ventana aboard the RV Point Lobos. The ROV was equipped with a Sony DXC-3000 video camera with a 5.5-44 mm zoom lens, illuminated by four 400-W sodium scandium lights. The zoom lens was used only for identification off the transect. Fiber-optic cable was used for viewing and recording images. The ROV was also equipped with a combined dual signal, a global positioning system and sonar system, which recorded the ROV position every 10 seconds. Depth, altitude off bottom, and various camera settings were also recorded. At least three replicate transects were made at each depth. Transects at the 200-m, 400-m, and 600-m depths were sampled (for dates, see Table 1). Because a video transect covering the same total area as a trawl was not practical, a transect length of similar distance covered by a trawl was chosen (approxi- mately 1.8 km or 1 nmi). Strip transects were used rather than line transects because the orientation of the lights produced a very sharp boundary between illuminated width of the transect and the darkness (Burnhametal., 1980; Butler etal., 1991). Transects were made at a speed of approximately 1.8 km/hr (1 knot) parallel to the isobath, interrupted occasion- ally by stops for fish identification or vehicle main- tenance. Transects were made with a camera angle of 30° off the parallel horizon to the bottom and with a camera height averaging 0.7 m off the bottom. Fish were identified from videotapes by two independent viewers, and the response of each fish to the ROV was recorded as follows: 1) strongly attracted (rap- idly moving into the frame); 2) weakly attracted 1 Greene, G. U.S. Geological Service, Pacific Marine Geology, 345 Middlefield Rd., Menlo Park, CA 94025. Personal commun 1992. Table 1 Dates of remotely operated vehicle (ROV) and trawl sam- pling cruises at 200-m, 400-m, and 600-m depth strata off central California. The number in parentheses is the num- ber of transects or trawls occurring during that month. Depth stratum (m) ROV Trawl 200 400 600 Oct 1991 (3) Mar 1991 (1) Oct 1991 (1) Oct 1992 (2) Jul 1991 (1) Sep 1991 (2) Apr 1991 (2) Sep 1991 (3) Jan 1992 (3) Apr 1991 (1) Sep 1991 (3) Jan 1992 (4) Apr 1991 (2) Sep 1991 (4) Jan 1992 (3) 448 Fishery Bulletin 93(3), 1995 TTH si) \ \ \ * \r.\^# \ \ ' / i f ' 1 l 1*'|/')>1' z^* i z / ^Cx -~ — ^ \' k --Oj iM v f\-x i''f-c' — f ( ' ^.---vJi) ;^--^ j i \v 'x VjV esr .' / i il i--- ■ ' i_i_i r~- -^-^ / , i— a ±x. Figure 1 Study site off central California marked for 200-m, 400-m, and 600-m depth comparisons of population estimates from video transects conducted from an ROV survey and from swept-area trawl surveys. (slowly moving into the frame); 3) no response (no movement); 4) weakly avoided (slowly moving out of the frame); and 5) strongly avoided (rapidly moving out of the frame). A time line, at which the fish were counted, was chosen in the center of the viewing area. To determine transect width at the time line, the ROV was transected over a 5-m square grid, and known lengths from the grid were measured on the moni- tor. From these lengths and standard photometric equations (Wakefield and Genin, 1987), the transect width was calculated to be 1.8 m (see Fig. 2). The vertical perspective of the video ranged from a height of 0.7 m at the camera to a visual horizon of 2.4 m in front of the ROV. The number of fish per transect was converted to fish per hectare by dividing the number offish observed by the area covered (transect distance multiplied by transect width). Trawl operations Trawling was conducted on separate cruises on the RV David Starr Jordan. Three trawl surveys were conducted and a sample size of at least three trawls per station was taken per cruise (for dates, see Table 1). During the April 1991 cruise, all three replicates were not completed owing to inclement weather. Par- allel tows were made along the same isobath as the ROV transect at a speed of approximately 3.7 km/hr (2 knots) for 30 minutes, although control of the trawl was not as exact as that of the ROV. The net, an Ab- erdeen high-rise trawl net with a 29-m (96-ft) head- rope, was equipped with 1.5 x 2.1 m steel doors. Trawl openings were not measured; this type of trawl has an average horizontal opening of 13.5 m (see Fig. 2) and an average vertical opening of 5.5 m Adams et al.: Population estimates of Pacific coast groundfishes 449 Figure 2 Sampling dimensions of a remotely operated vehicle (ROV) video transect and a trawl. Draw- ings of gear and sampling volumes are made to scale. (Rose2). On deck, catches were handled with stan- dard protocol (Smith and Bakkala, 1982) and were sorted to species, weighed, and measured. Lengths were measured for either a subsample of 100 fish or the entire catch, if it comprised less than 100 fish. When the catch was greater than 100 fish for a spe- cies, total species number was extrapolated from to- tal species weight by using the average weight per fish from the subsample weight and numbers. Num- bers of species per hectare were expanded by divid- ing the total species number by the area covered (dis- tance traveled by a tow multiplied by the average width of the trawl). Differences in ROV and trawl abundance estimates for individual species at each depth were tested by using £-tests for differences of unpaired log-trans- formed means. A sign test was used to determine whether the number of times that an ROV abundance estimate (or coefficient of variation) was higher than the trawl was greater than would have been expected randomly (i.e. a 50/50 ratio). Statistical power is defined as 1-/J, where P is the probability of failing to reject a hypothesis when it is false, and therefore power is the probability of cor- rectly rejecting a false hypothesis (Peterman, 1990). 2 Rose, C. National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way N.E., BIN C15700, Se- attle, WA, 98115-0700. Personal commun., 1992. The power of the ROV and trawl abundance esti- mates was evaluated by calculating the required sample size to detect a 50% reduction from the log- transformed mean abundance at a fixed level of a (0.05) and at a high level of power (1-/3, 0.80). Com- parisons were made for the commercially important species (Dover sole, Microstomas pacificus; thorny- heads, Sebastolobus spp.; and sablefish, Anoplopoma fimbria) and for a group of other abundant taxa (catsharks, Scyliorhinidae; skates, Rajidae; and eel- pouts, Zoarcidae) at the 400-m depth (the only depth where all of these taxa occurred in both the ROV and the trawl surveys). Results More fish per hectare were observed from the ROV than were captured in the trawl at the 400-m and 600-m depths, whereas more fish were captured in the trawl at the 200-m depth (Fig. 3). However, the differences in the log-transformed total ROV and trawl estimates were only significant at the 400-m and 600-m depths (400 m: <=5.50, P<0.001; 600 m: <=3.28, P=0.011) and not at the 200-m depth (200 m: <=0.32, P=0.713). Numbers captured in the trawl at the 200-m depth were higher owing to a single large catch of two species of rockfish in one trawl. The ROV estimates offish numbers were higher for most indi- vidual species or taxonomic groups that occurred in 450 Fishery Bulletin 93(3). 1995 B 700 600 500 400 300 200 100 0 4) 4) ROV Trawl //V///////////////y 1) 500 o J3 300 100 * / / / / # f £ *" / \f / / y Fish taxa Figure 4 Coefficients of variation of the mean number offish per hectare estimated from an ROV video strip-transect survey and a swept-area trawl survey from (A) the 200-m depth station (ROV, n=3 and trawl, n=8); (B) the 400-m depth station (ROV, n=4 and trawl, n=S); and (C) the 600-m depth station (ROV, n=3 and trawl, n=9). Adams et al.: Population estimates of Pacific coast groundfishes 453 avoided it. Pacific whiting had the strongest response (69%), appearing to be attracted to the ROV. Sable- fish had the next strongest response (62%), but their numbers were low, averaging 3.75 individuals over all depths. Their behavior was variable: some animals swam away, some swam toward the ROV, and some ignored the ROV. Catsharks showed approximately equal numbers responding and not responding, and those that did respond consistently avoided the ROV. Finally, the red octopus, Octopus rubescens, was the most abundant animal counted from the ROV. It was observed from the ROV only at the 200-m depth at numbers of 1,610 per hectare (SE=516.4) and was not captured in the trawls. The ROV red octopus abundance estimates were higher than any fish es- timate from the trawls. Discussion Much of the difference between the ROV and trawl estimates was due to the different mechanical na- ture of the sampling gear and to the body shape and behavior of the fishes. The ROV intensively sampled a narrow area directly in front and extending up a short height off the bottom. The trawl sampled a much wider area, including a larger area off the bot- tom, but with what must have been a great deal of escapement. The result was that ROV abundance es- timates were higher and had lower coefficients of variation for fishes either strongly associated with the bottom or with a body shape and size, or both, that would pass through the mesh ( such as the red octopus). Conversely, animals with highly patchy dis- tributions and off-bottom behavior (catsharks, rock- fish at the 200-m depth) had higher abundance esti- mates from the larger volume trawl. Although both the ROV and trawl estimates were adjusted to the same surface area, there was no adjustment made to reflect the 7.7 times greater off-bottom height sampled by the trawl (Fig. 2). Probably neither method does a particularly good job of estimating off- bottom fishes that are patchily distributed. Visual estimates offish abundance either from submersibles (Uzmann et al., 1977) or from divers (Kulbicki and Wantiez, 1990) are reported to be higher than those from otter trawl estimates for multispecies assess- ments, but the reverse was true in this study for rock- fishes (see also Krieger, 1993). The smaller sample sizes required to detect a 50% reduction of the ROV abundance estimates would improve the ability to detect trends in abundance such that a smaller increment of change would be detectable. The degree on improvement would vary with species. Reductions of the order of 1.3 to 19 times in required sample size are sufficient to increase the ability to detect true changes in population size. Much of the decrease in required sample size (and increase in statistical power) comes from the much higher ROV abundance estimates. If samples are drawn from two populations with similar levels of variation, a 50% decrease in abundance of the larger estimate is much larger and therefore easier to de- tect. Unfortunately, a great deal of variation due to patchiness in fish distribution remains. For an environmental assessment, the ROV esti- mates provide a better overall picture of the commu- nity than do the trawl estimates. While the similar- ity in the presence and absence of species in the' two methods was surprisingly high, the ROV abundance estimates generally tended to be higher and had lower coefficients of variation. Species that were usu- ally in direct contact with the bottom had much higher ROV abundance estimates than did those cap- tured in the trawl. Small, cylindrically shaped fishes (hagfish, poachers, and eelpouts) had particularly large differences between ROV and trawl abundance estimates, probably owing to escapement under the footrope or through the trawl webbing. The most obvious example of escapement or avoidance was that provided by the red octopus, which was more abun- dant in the ROV sampling than any fish, but which was not captured by the trawl. For the commercially important species at these depths (Dover sole, thornyheads, and sablefish), the results were mixed. For Dover sole and thornyheads, ROV abundance estimates were higher and coeffi- cients of variation were lower. For sablefish, abudance estimates were higher for the trawl sam- pling at 200-m and 600-m depths. Although rockfish at the 200-m depth are not commercially important, the trawl estimates for this taxon were higher, and this is likely to be true of commercially important rockfishes. Stock assessment integrates patterns of removals and information on year-to-year variation in recruit- ment from catch-at-age data with mean levels of abundance and longer term trends from survey data (Deriso et al., 1985; Methot, 1990). Using simulations, Kimura (1989) showed that, if survey data are bi- ased, the results can be a precise, but biased, infer- ence regarding the population. The higher ROV abun- dance estimates mean that trawl estimates are bi- ased too low and that there is actually a larger dif- ference between years of low population size and threshold levels of overfishing set by these assess- ments. The risk of overfishing is actually lower than that which was assumed. A more dangerous situa- tion arises when bottom trawl estimates are larger than the ROV estimates, as with rockfish (also see Krieger, 1993). Here the difference between years of 454 Fishery Bulletin 93(3). 1995 low population and threshold levels of overfishing is actually less than that which was realized, a differ- ence that increases the risk of overfishing. ROVs have the ability to identify the degree of species' attraction to or avoidance of the sampling gear. Three species showed a strong response to the ROV: Pacific whiting, sablefish, and catsharks. Pa- cific whiting was the only species that was attracted to the ROV (Table 3). These three species are usu- ally observed off-bottom and in motion, rather than resting in contact with the bottom. Fishes that are commonly in motion should be in a better position to respond quickly to stimuli (motion, light, etc.) around them. Understanding and accounting for fish behav- ior could improve the accuracy of an estimate. For trawl gear, the level of attraction or avoidance is unknown. Anecdotal evidence for attraction (crowd- ing offish between doors suggested by Krieger [1993]) and for avoidance (net sounder readings of rockfish rising up out of the path of the net [Adams3]), have been reported, but there is no simple way of evaluat- ing these phenomena for trawl gear. While the presence of large seasonal or interannual variation in fish numbers could have introduced bias into the estimates, there is no reason to believe this occurred. None of the 20 most common species cap- tured by the three trawl surveys, which covered al- most the entire study period, exhibited a consistent seasonal or overall trend in fish abundance. Also, the consistency of trends in abundance derived from ROVs and trawls from all depths, even though they were sampled at different times, suggests that large varations in abundance were not an important source of bias. However, if this bias had occurred, it would have been a larger problem for the ROV estimates than for the trawl estimates. The ROV samples at depth were taken during one time period, with the exception of the 400-m depth, whereas the trawl samples were taken at all depths during three cruises over nearly the entire time period. Both ROV and trawl surveys contain additional information that may be critical to the goals of an abundance study. ROV surveys provide much biologi- cal information, particularly on habitat and species association. In two instances, we observed feeding behavior. Trawl surveys deliver the fish on deck; for common types of biological studies, such as ageing or food habits, these specimens are critical. In addi- tion, these specimens enable accurate species iden- tification. Identifcation, however, is expected to be- come less of a problem as video technology improves. 3 Adams, P. National Marine Fisheries Service, Tiburon Labora- tory Southwest Fisheries Science Center, 3150 Paradise Dr., Tiburon, CA 94920. Personal commun., 1986. Finally, there is the chronic problem of the low sta- tistical power of tests of these abundance estimates owing to large, associated variances. Since increas- ing the sample size is often not practical, the only alternative is to stratify the sampling more effectively rather than simply on the basis of depth. Better stratification can come only from a greater understand- ing of the biological factors responsible for fish distri- butions. An adequate understanding would include the association offish with microhabitat and the biological behavior of fishes that leads to patchiness. Surveys could then be stratified on the basis of areas where fish are occurring at background levels and in large patches. Trawl surveys have been unsuccessful in achieving such separation. Information gained from the ROV could lead to the biological understanding necessary to achieve more efficient stratification designs. Acknowledgments This work would not have been possible except for the effort of the scientific parties and crews of the RV Point Lobos and of the RV David Starr Jordan. Data for the photogrammetric calibration were kindly provided by Christopher Herald at the Monterey Bay Aquarium. This manuscript gained much from criti- cal reviews by Kenneth Krieger, Richard Methot, David Somerton, and Mark Wilkins. The ideas de- veloped here benefitted greatly from many long con- versations with Mark Wilkins. The ROV portion of this research was supported by a grant from the West Coast Center of the National Underwater Research Program. Literature cited Burnham, K. P., D. R. Anderson, and J. L. Laake. 1980. Estimation of density from line transect sampling of biological populations. Wildl. Monographs 72, 202 p. Butler, J. L., W. W. Wakefield, P. B. Adams, B. H. Robison, and C. H. Baxter. 1991. Application of line transect methods to surveying demersal communities with ROVs and manned submer- sibles. Proceedings of the OCEANS 91 Conference; Ho- nolulu, Hawaii, 1-3 October 1991, p. 689-696. Deriso, R. B., T. J. Quinn, and P. R. Neal. 1985. Catch-age analysis with auxiliary information. Can. J. Fish. Aquat. Sci. 42:815-824. Doubleday, W. G., and D. Rivard. 1981. Bottom trawl surveys. Can. Spec. Publ. Fish. Aquat. Sci. 58, 273 p. K i in ii ra. D. K. 1989. Variability, tuning, and simulation for the Doubleday- Deriso catch-at-age model. Can. J. Fish. Aquat. Sci. 46:941-949. Krieger, K. J. 1993. Distribution and abundance of rockfish determined from a submersible and by bottom trawling. Fish. Bull. 91:87-96. Adams et al.: Population estimates of Pacific coast groundfishes 455 Kulbicki, M., and L. Wantiez. 1990. Comparison between fish bycatch from shrimp trawl- net and visual censuses in St. Vincent Bay, New Caledonia. Fish. Bull. 88:667-675. Lenarz, W. H., and P. B. Adams. 1980. Some statistical considerations of the design of trawl surveys for rockfish ( Scorpaenidae). Fish. Bull. 78:659-674. Methot, R. D. 1990. Synthesis model: an adaptable framework for analy- sis of diverse stock assessment data. Int. North Pacific Fish. Coram. Bull. 50:259-277. Pennington, M. 1986. Some statistical techniques for estimating abundance indices from trawl surveys. Fish. Bull. 84:519-525. Peterman, R. M. 1990. Statistical power analysis can improve fisheries re- search and management. Can. J. Fish. Aquat. Sci. 47:2-15. Raymore, P. A., Jr., and K. L. Weinberg. 1990. 1984 Spring and autumn surveys of Pacific west coast upper continental slope groundfish resources. U.S. Dep. Commer., NOAATech. Memo. NMFS F/NWC-179, 196 p. Smith, G. B., and R. G. Bakkala. 1982. Demersal fish resources of the eastern Bering Sea: spring 1976. U.S. Dep. Commer., NOAATech. Rep. NMFS SSRF-754, 129 p. Uzmann, J. R, R. A Cooper, R. B. Theroux, and R L. Wigley. 1977. Synoptic comparison of three sampling techniques for estimating abundance and distribution of selected megafauna: submersible versus camera sled versus otter trawl. Mar. Fish. Rev. 39(11):11-19. Wakefield, W W., and A. Genin. 1987. The use of a Canadian (perspective grid) in deep-sea photography. Deep-Sea Res. 34:469-478. Abstract. — The impact of preop- tion by staghorn sculpin, Leptocottus armatus, on newly settled Dungeness crab, Cancer magister, in the Washing- ton coastal estuary of Grays Harbor was studied. Staghorn sculpin are known to be generalist, opportunistic feeders, with relatively high food re- quirements for estuarine growth dur- ing warm summer months. During late spring or early summer, vast numbers of crab megalopae reach the estuary and settle on intertidal flats and in subtidal channels. During the next two months the young-of-the-year ( 0+ ) crab population is rapidly reduced by pre- dation, including cannibalism. Crab without appropriate refuge habitat are highly vulnerable to predation by fish, and accordingly survival of young crab is highest in intertidal shell and eel- grass beds. Abundance and summer growth of crab and sculpin within the estuary were documented by monthly trawling surveys (April to August) in 1989. Stomach contents of sculpin were analyzed to characterize the overall summer diet, to note monthly shifts in major prey items within two age classes of sculpin (0+ and 1+), and to contrast sculpin prey consumed in eelgrass with that consumed in shell habitats. The predominant prey species varied across the categories above but generally in- cluded ghost and blue mud shrimp, Neotrypaea californiensis and Upogebia pugettensis, a nereid polychaete (Nereis brandti), juvenile Dungeness crab, Cancer magister, and sand shrimp {Crangon spp.). Some combination of these species composed 85% of the total diet (on the basis of percentage of total Index of Relative Importance; %IRI) across time and between habitats. A com- parison of diets of sculpin collected at ee- lgrass and shell habitats was signifi- cantly different; a strong preponderence of 0+ crab were consumed at the shell habitat. Nereis brandti was the most important prey for 0+ sculpin, whereas Neotrypaea californiensis was the most important for 1+ and older sculpin. The importance of shell as refuge habitat for C. magister and the apparent contradic- tion in the observation that a large num- ber of 0+ crab were taken by sculpin at the shell habitat are discussed. Food habits of estuarine staghorn sculpin, Leptocottus armatus, with focus on consumption of juvenile Dungeness crab, Cancer magister* Janet L. Armstrong David A. Armstrong Stephen B. Mathews School of Fisheries. WH-1 0 University of Washington, Seattle, Washington 98195 Manuscript accepted 23 November 1994. Fishery Bulletin 93:456-470 (1995). Staghorn sculpin, Leptocottus arma- tus, are common in major estuaries throughout their range from Baja California through the Gulf of Alaska (Hart, 1974). Young sculpin inhabit brackish water streams and chan- nels and move down into the estu- ary as they grow larger during their first year. Older juvenile and adult sculpin are broadly distributed throughout estuarine nursery areas utilized by juvenile crab and are known predators of Dungeness crab, Cancer magister, within estu- aries (Reilly, 1983). Staghorn scul- pin have wide gapes and relatively large mouth areas in relation to their size compared with other spe- cies of fish predators commonly found in estuaries during the sum- mer.1,2 They are opportunistic, gen- eralist predators (Jones, 1962; Hart, 1974; Birtwell et al., 1984) and feed heavily on decapod crustaceans such as the yellow shore crab, Hemigrapsus oregonensis, the ghost shrimp Neotrypaea californiensis, and pea crab, Pinnixa sp. (Tasto, 1975; Posey, 1986). Staghorn scul- pin are described as visual preda- tors that move onto estuarine tideflats with the incoming tide (Tasto, 1975); their foraging behav- ior may contribute to the high mor- tality rate of small 0+ crab (Wain- wright et al., 1992). The Grays Harbor estuary, Wash- ington, contains extensive intertidal tracts of eelgrass and shell that serve as critical nursery areas for young-of-the-year (0+) and one- year-old (1 + ) Dungeness crab3 (Gutermuth and Armstrong, 1989; Gunderson et al., 1990; Jamieson and Armstrong, 1991). During high tides in May and June, vast num- bers of crab megalopae reach estu- aries, settle to the benthos, and metamorphose to the first juvenile instar (Jl). Crab settle over broad expanses of the intertidal sandflats Contribution 903 of the University of Washington, School of Fisheries, Seattle, WA 98195. 1 Smith, J. L. 1976. Impact of dredging on the fishes in Grays Harbor. Appendix G in Maintenance dredging and the environ- ment of Grays Harbor, Washington. Final Rep. by U.S. Army Corps of Engineers, Seattle District, 94 p. 2 McGraw, K., and D. A. Armstrong. 1990. Fish entrainment by dredges in Grays Har- bor, Washington. In C. A. Simenstad (ed.), Effects of dredging on anadromous Pacific coast fishes; workshop proceedings, Se- attle, WA, 8-9 Sep. 1988. Washington Sea Grant Program, Univ. Washington, Se- attle, WA 98195, 160 p. 3 Armstrong, D. A., T. C. Wainwright, J. M. Orensanz, P. A. Dinnel, and B. R. Dum- bauld. 1987. Model of dredging impact on Dungeness crab in Grays Harbor, Wash- ington, Final Rep. FRI-UW-8702 to Bat- telle Northwest Laboratories and U.S. Army Corps of Engineers, Seattle, District, Seattle, WA, 167 p. 456 Armstrong et al.: Food habits of Leptocottus armatus 457 and in subtidal channels but within a few weeks can be found only in areas that afford some refuge4 (Dumbauld et al., 1993; Fernandez et al., 1993a). First year survival, based on five years of trawl sur- vey data in the estuary (Gunderson et al., 1990), has been estimated at approximately 89c ( Wainwright et al., 1992). Different assemblages of predators affect survival of Dungeness crab during each phase of their life history (Reilly, 1983; Stevens and Armstrong, 1985; Thomas, 1985). Estuarine and nearshore fishes, wading birds, and older crab are known to prey upon the young crab instars (Stevens et al., 1982; Fernandez et al., 1993b), causing high mortality rates in the summer months (Wainwright et al., 1992). Predation, including cannibalism, is considered to be the prime cause of the rapid decline in crab abun- dance through the summer. Stevens et al. (1982) showed that during years of high 1+ crab abundance, cannibalism can account for a significant portion of 0+ crab mortality. Even early settling 0+ crab are capable of cannibalizing later settlers of the same year class (Fernandez et al., 1993b). However, aside from Reilly's study (1983) in California estuaries, predation by estuarine fish and wading birds has received little attention as a source of crab mortal- ity. Although sea birds are known to take a toll on megalopae5 and on newly settled crab (Mace, 1983), fish and crab predators are more likely to exert the greatest predation pressure on the highly abundant, small instars during settlement and early development. In this study, we discuss the estuarine summer feeding patterns of staghorn sculpin with respect to a broad spectrum of crustacean prey but focus on their possible significance as predators of 0+ C. magister and on the role of refuge habitat on the basis of spatial patterns of predation in the estuary. A tem- poral shift in consumption of certain prey taxa is also discussed as indicative of opportunistic feeding by staghorn sculpins with seasonal patterns of prey abundance or with life history events which make prey more susceptible to predators. Materials and methods Sampling scheme Grays Harbor (46°55'N, 124°05'W) is a major Wash- ington coastal estuary of about 8,545 hectares (Gunderson et al., 1988) marked by numerous subtidal channels. These channels extend across ex- tensive sandflats that become exposed and represent 679c of surface area during spring low tides. Refuge habitat is provided by epibenthic shell exposed from remnant Mya arenaria and Crassostrea gigas bivalve populations and by eelgrass. Shell coverage has been calculated to account for 199c of the total intertidal area,6 whereas eelgrass (Zostera marina and Z. noltii) was reported to cover 42% of the tidal flat area.7 Staghorn sculpin were collected from Grays Har- bor during six sampling trips from April through August 1989. Sampling was timed to coincide with the following periods: April-May prior to the main pulse of annual crab settlement, June (two trips) during recruitment of 0+ crab, and July— August dur- ing the post-settlement summer growth period. Two intertidal sandflat sites located about 10 km apart were routinely trawled at high tide as a means of contrasting diet in two common epibenthic habitats of the estuary: an eelgrass (Zostera spp.) bed in North Bay, and shell piles (Mya arenaria) in South Chan- nel (Fig. 1). In order to ensure reasonable sample sizes of fish for each trip and site (target of «>20), two trawls each were conducted at both an intertidal station (during slack flood tide) and at an adjacent subtidal station (at low slack) within 6 h on the same day, and fish were pooled for analyses of differences in diet over time. Additional subtidal trawls were made as time permitted for a total of 9— 11 trawls per trip. All trawl samples were collected with a 3-m beam trawl (Gunderson and Ellis, 1986) deployed from a 7-m Boston Whaler. The net had an effective fishing width of 2.3 m and a 4-mm codend liner to retain juvenile crab and fish. Trawls in subtidal channels were run for about four minutes at a speed of 3.7 to 5.6 km/h. Distance fished was determined by optical range finder fixes between buoys deployed at the beginning and end of each tow (see Gunderson et al., 1990, for details of trawl procedure); such distances ranged from 200 to 350 m. Intertidal tows were made between two staked points 160 m apart. Distance fished and fishing width of net were used to estimate area swept for calculation of catch per unit of effort (CPUE; number per hectare). Trawl contents were characterized as to type of vegetation (e.g. algae, 4 Armstrong, D. A., L. Botsford, and G. S. Jamieson. 1990. Ecol- ogy and population dynamics of juvenile Dungeness crab in Grays Harbor estuary and adjacent nearshore waters of the southern Washington coast. Rep. to U.S. Army Corps of Engi- neers, Seattle District, Seattle, WA, 140 p. 5 Armstrong, D. Personal observation at Whitcomb Flats sea gull nesting site. Grays Harbor, WA, May 1988. 6 Dumbauld, B. R., and D. A. Armstrong. 1987. Potential mitiga- tion of juvenile Dungeness crab loss during dredging through enhancement of intertidal shell habitat in Grays Harbor, Wash- ington. Final Rep. FRI-UW-8714 to U.S. Army Corps of Engi- neers, 64 p. 7 Smith, J., L. D. R. Mudd, and L. W. Messmer. 1977. Impact of dredging on the vegetation in Grays Harbor. Appendix F in Maintenance of dredging and the environment of Grays Har- bor, Washington. Final Rep. by U.S. Army Corps of Engineers, Seattle District, 94 p. 458 Fishery Bulletin 93(3), 1995 GRAYS HARBOR i , WASHINGTON Westport E eelgrass S shell , * Subtddal Intettidal Figure 1 Grays Harbor, Washington, sampling locations for staghorn sculpin, Leptocottus armatus, and Dungeness crab, Cancer magister, at eelgrass (E) and shell (S) sampling sites. Bold dashed line denotes intertidal trawls and lighter dashed line indicates subtidal channel trawls. eelgrass, terrestrial leaves), shell, and underlying substrate. All fish and crab were sorted from the catch, identified to species, and counted. Crab were measured (carapace width [CW] inside the 10th lat- eral spine), sexed, and returned to the water. Stag- horn sculpin were picked from the catch and killed. Their body wall was slit, and the fish were preserved in 10% formalin in sea water and later transferred to 70% ethanol in the lab for measurement (total length, TL) and stomach content analyses. Length-frequency data for sculpin and crab were used to determine instar and year-class composition. Crab length-frequency histograms by trip were used to establish the presence of the 1989 year class of 0+ crab from first tentative appearance in May, at peak settlement in early June, and at the time of summer growth through August. Size modes for crab instars (juvenile crab 6-40 mm CW) were visually deter- mined from length-frequency histograms (hereafter crab instars 1 through 7 will be referred to as J1-J7 and conform to instar sizes specified by Wainwright and Armstrong [1993] and Dinnel et al. [1993]). Evaluation of size ranges and modes as compared with stage (CW for crab; TL for sculpin, Tasto, 1975) were used to set the upper size limits for 0+ and 1+ age classes each month during the summer. Sculpin gape measurements Sculpin mouth widths (measured for 466 sculpin) were used as an index of mouth gape size. The mouth of a preserved specimen was gently pried open as far as possible and the internal distance from the intersections of upper and lower jaws was measured. Since fish body lengths are more com- monly reported as standard lengths (SL), sculpin total lengths (TL) were converted to standard length for a dis- cussion of mouth gape to body length relationship8: SL = 0.87338 TL - 2.7584 (r2 = 0.995, n = 53). Stomach content analyses Stomach contents of all staghorn sculpin from a trawl were examined up to a total of 20 fish. When catches were higher, the fish were separated into 5- mm size intervals, then proportionally subsampled until a total of 20 fish were selected for stomach analyses. Sculpin were measured (TL), blotted on paper towels, and weighed wet to the nearest 0.1 g. Then their stomachs were removed, blotted, and weighed with and without contents to derive stomach content weight. An estimate of relative stomach fullness was derived by using six categories corresponding to empty, 1/4, 1/2, 3/4 full, full, and "distended." In the latter case, quantity of prey within the stomach re- sulted in pronounced distention of the body wall be- yond the normal lines and curvature of the fish. Sculpin stomachs were analyzed to document the frequency of occurrence of Dungeness crab, the over- all proportion of the diet attributed to major prey categories, and the relationship between sculpin size and size of juvenile crab prey. Food items were generally identified to species unless obscured by digestion. Prey species consumed frequently were analyzed as a distinct prey category, but species that were consumed infrequently were combined to form a more general prey taxon that also included prey items obscurred by digestion. As an example, the amphipod Eogammarus confervicola was recorded as a separate prey category owing to its high frequency of occurrence, but several species of fishes (Gasterosteus aculeatus, Lumpenus sagitta, Cymatogaster aggregata, Leptocottus armatus, Pleuronectes vetulus, and Citharichthys sp.) were consumed infrequently and were thus grouped as "fish." Analysis of stomach content data was done by 8 Williams, G. Pacific Estuarine Research Labs., San Diego State Univ., San Diego, CA. Unpubl. data, 1991. Armstrong et al.: Food habits of Leptocottus armatus 459 calculation of a modified form (Stevens et al., 1982) of the Index of Relative Importance (IRI) (Pinkas et al., 1971; Hyslop, 1980) based on estimated food weight rather than food volume. For a particular prey category, an IRI value was calculated as IRI = (JVC + GOFO, where NC (numerical composition) is the number of a particular prey item divided by the total number of all prey items in that sample multiplied by 100, GC (gravimetric composition) is the combined weight of a particular prey item divided by the total weight of all stomach contents in the sample multiplied by 100, and FO (frequency of occurrence) is the number of stomachs from a sample containing a given prey item divided by the total number offish sampled mul- tiplied by 100. IRI values from all prey categories were summed to derive a grand total IRI value. The relative importance of each prey category was then expressed as a percentage of this total IRI (hereaf- ter referred to as %IRI). Data analysis Sculpin stomach content data were analyzed from four perspectives. First, an overall summer diet for staghorn sculpin was derived by combining all fish from both sites (E and S), inter- and subtidal, across months to determine dominant prey taxa. Second, a temporal comparison of sculpin diets from late spring through summer was made by examination of sculpin stomachs grouped by sampling trip. Third, the ef- fect of sculpin size (and thus age) on diet was inves- tigated for two size groupings derived from length- frequency histograms of sculpin caught during the six trips. Size ranges and age equivalents were set from the literature (Anaheim Bay, CA, [Tasto, 1975]; Yaquina Bay, OR [Bayer, 1985]) to group fish by age class as either 0+ (n=210) or >1+ (n=256). IRI analy- ses were run separately on 0+ and >1+ sculpin to determine whether there were changes in diet com- position based on predator size. Fourth, prey compo- sition of sculpins feeding at different epibenthic habi- tats was compared by examining diets of fish col- lected from the intertidal eelgrass site (n=55) and diet of sculpin caught at the intertidal shell site (rc=44). To compare dietary overlap of sculpin of the two size/age categories or of sculpin collected at the two different habitats (eelgrass vs. shell), Schoener's (1970) index of overlap (S;o) was calculated as yi SIO = 1-0.5 \J= where P • = the proportion of prey i (%IRI) in the diet of sculpin of size x (or from habitat x); = the proportion of prey i (%IRI) in the diet of sculpin of size y (or from habitat y), and j = the number of prey types. An overlap value of Sl0 > 0.6 (Schoener, 1970) was considered significant in this study. Results Overall summer diet A total of 482 staghorn sculpin stomachs were col- lected from April to August 1989, of which 458 had some stomach contents. Sculpins averaged 118 mm TL (range: 61-215 mm TL) during the five-month sampling period (Table 1). Mouth gape width ranged from 13 to 17% of standard length (gape width = 0. 1818 SL-2.6487, r2=0.909; Fig. 2). Average fish length and weight varied by sampling month and were gener- ally greater in April and May when samples were composed primarily of 1+ fish, decreased in June as 0+ sculpin moved into the sampling sites, and in- creased in July and August as individuals grew through summer (Fig. 3; Table 1). Size-frequency data indicated the presence of two modes equivalent to 0+ and 1+ age classes. Young of the year ranged from 60 to 94 mm TL in April and had grown to 75- 119 mm by August (Fig. 3). For purposes of analyses of diet based on size-age composition of sculpin, 118 mm TL was used as the boundary between 0+ and 1+ groups. These size-age categories were corrobo- rated by otolith annuli determinations of a similar size range of staghorn sculpins from Vancouver Island, British Columbia, estuaries by Mace (1983, p. 369). The mean number of individual prey items per sculpin was 3.4, and gut fullness was generally high; 75% of all stomachs examined were rated 50% full or greater whereas fewer than 5% were empty (Fig. 4). Sculpin stomach contents included 23 prey taxa (Armstrong, 1991) which were grouped into 14 prey categories for IRI analyses (Table 2). Principal cat- egories of sculpins' overall summer diet (% IRI) were the polychaete Nereis (Neanthes) brandti (30% IRI), the ghost shrimp Neotrypaea californiensis (27% IRI), sand shrimps Crangon spp. (13% IRI, including C franciscorum, C. nigracauda, and C. stylirostris), juvenile Cancer magister (9% IRI), and the mud shrimp Upogebia pugettensis (6% IRI). Temporal changes in diet Stomach contents were analyzed on a per trip basis to note change in sculpin diet over the course of the 460 Fishery Bulletin 93(3), 1995 Table 1 Summary data for groups of staghorn sculpin, Leptocottus armatus, sampled during monthly trips and for all sculpin combined from April to August 1989 from Grays Harbor, Washington, for stomach content analysis. During each trip all sculpin were caught from both sites, eelgrass and shell habitats, inter- and subtidal trawls combined. SD = 1 standard deviation, TL = total length. Dates Fish size mmTL) Fish wet wl •(g) Mean gape (mm) No. stomachs examined % empty Mean no. prey per sculpin Mean 1SD Range Mean 1SD Range Apr 7-8 113 21 (61-190) 17 11 (2-70) 14.8 111 0 7.1 May 6-7 138 27 (94-215) 36 28 (9-133) 18.9 38 3 2.5 Jun 4—6 108 25 (72-173) 17 14 (3-62) 14.7 62 0 2.7 Jun 18-19 99 19 (70-162) 12 9 (4-55) 12.2 126 4 2.3 Jul 19-20 121 23 (78-169) 21 13 (4-53) 16 61 11 1.4 Aug 15-18 127 28 (84-213) 24 19 (6-102) 16.7 84 8 3.3 Combined grand mean 118 27 (61-215) 20 17 (2-133) 15.6 482 5 3.4 summer. Entry of small sculpin into our sampling areas in June was inferred by the decrease in mean sculpin size and wet weight (Table 1) and supported by exami- nation of length-frequency histograms (Fig. 3). Diet composition changed appreciably from month to month. During the spring, sculpin primarily consumed the gammarid amphipod E. confervicola (46% IRI), Crangon spp. shrimp (24% IRI), and fish (13% IRI) in April (Fig. 5), whereas the nereid polychaete N. brandti (34% IRI), the thalassinid shrimps N. californiensis (45% IRI), and U. pugettensis (12% IRI) were the most abundant prey in stom- achs in May (Fig. 5). Sculpin consumed few crab, reflecting the relative scarcity of 0+ instars in late spring; Jl instars were found in only 5% of sculpin stom- achs in May and represented less than 1% IRI. Minimal settlement of Dunge- ness crab during May was indicated by low catches of 0+ crabs (Fig. 6; only three Jl were caught in 10 trawls). In early June, juvenile Dungeness crab recruited to the estuary (Fig. 6) and became the second most important diet category (24% IRI, Fig. 5). The nereid polychaete N. brandti was first in dietary importance, accounting for 59% IRI, and Crangon spp. shrimp ranked third ( 10% IRI) in early June. The major pulse of 0+ crab settlement had occurred during late May- early June (after the mid-May sampling; Fig. 6) and thus Jl and J2 crab had become readily available prey by the beginning of summer. Nereid polycha- 40- v=0.18;c-2.65 s ^=0.91 b 0/^ 6, 30- •a ? S, 20- a M n=445 bb^/^ 3 O S io- y^ 0 50 100 150 200 Standard length (mm) Figure 2 Staghorn sculpin, Leptocottus armatus, mouth gape width (y) to stan- dard body length (x) relation based on 445 sculpin from Grays Harbor, Washington, April-August 1989. etes continued as the most important prey item through mid-June (88% IRI), whereas C. magister juveniles accounted for only 4% IRI and were con- sumed by 24% of the sculpin examined. During the mid and later part of summer, decapod crustaceans represented the majority of staghorn sculpin diet. In July and August nereid worms were rarely found in stomach contents, but thalassinid shrimp, N. californiensis and U. pugettensis, together totalled 70% IRI in July and 54% IRI in August (Fig. 5). Juvenile crab accounted for 15% and 13% IRI of Armstrong et al.: Food habits of Leptocottus armatus 46! c 'a. "5 u c o C o a o x=80mm ■!■■ APRIL 0.20' 0.15- 0* 1 MAY n=38 i* x'141 mm 1 0.05- 1 II 1. 0+ 1=91 mm ■III ; a S s S 5 S ; EARLY JUNE n=62 IU.il II 0.20 ■ MID JUNE n=\26 0* i* 0.15 x=9J mm i-129mm 0 10- 1 III 0.05' i III .L. ... •:,-,.-.- 0* x-95 mm assssKsss, JULY n=6\ IlLh 3SK8SSS882 = gaSSSSSiK AUGUST n=227 o* x~ 105 mm Length intervals (mm) Figure 3 Staghorn sculpin, Leptocottus armatus, length-frequency histograms and inferred age classes (0+ and 1+ and older) from Grays Harbor, Washington, April-August 1989. Vertical line indi- cates upper size cut-off of 0+ from 1+ sculpin. Mean sizes of the age class are given by x , n = total number offish examined, both age classes combined. sculpin diets during these months and Crangon spp. for 10% and 11% IRI. Sculpin age-class and prey composition Sculpin length-frequency histograms by trip were examined and fish were separated into two age groups based on size (Fig. 3). The diets of 0+ and >1+ sculpin were compared to determine whether there were differences in prey composition based on fish size. Both sculpin age groups had the same propor- tion of empty stomachs (5%) and the same mean number of prey species (3.4) per predator, indicating similar feeding success rates. Small (0+) sculpins primarily consumed N. brandti (50% IRI), N. californiensis (13% IRI), Crangon spp. (11% IRI), C. magister (9% IRI), bivalve siphon tips, and miscella- neous or unidentified crustaceans (5% IRI each; Fig. 7). Larger sculpins consumed less N. brandti and crangonid shrimp (23% and 5% IRI) but more thalassinid shrimp (N. californiensis [31% IRI] and U. pugettensis [12% IRI]) and large gammarid am- phipods (E. confervicola [8% IRI]). Dietary overlap was significant (SIO=0.6). Sculpins over the entire size range sampled (70-215 mm TL) consumed young Dungeness crab (9% of IRI in the summer diet of both 462 Fishery Bulletin 93(3), 1995 ■c e c 120 mm) consumed isopods, crabs, and fish. While juvenile sculpin less than 60 mm TL were not sampled in the present study, no significant diet shift was noted for the two size groups (60-119 mm and >120 mm) of the Grays Harbor prey assemblage, although relative importance of items differed between the size groups. Smaller fish did consume a relatively higher proportion of poly- chaetes, whereas larger sculpins consumed more thalassinid shrimp (Fig. 7). Other studies have shown that adult staghorn sculpins consume crustaceans as a major portion of their diet when they are available. Dinnel et al. ( 1990 ) found that amphipods, isopods, and an assemblage of crab species (including C. magister and Pinnixa spp.) composed a majority (79% IRI) of the August diets of staghorn sculpins from Padilla Bay, Wash- ington. Data presented by Jones (1962) and Boothe (in Tasto, 1975) showed that the majority of stag- horn sculpin diet (92% IRI) consisted of decapod crus- taceans, including Crangon spp., Upogebia puget- tensis, and a crab assemblage of Cancer sp., Hetni- grapsus sp., Pinnixa sp., and Scleroplax sp. Year- round sampling in Anaheim Bay, California, revealed that sculpin consumed primarily decapod crusta- ceans (78% of the diet by weight) including N. cali- 464 Fishery Bulletin 93(3), 1995 3 e o '€ e o. o APRIL 1989 n=786 Mid JUNE 1989 n=l,577 5 10 IS 20 25 30 35 40 45 S0S5 6O65 70 75 80 85 9O951O0 .11 -llll. 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 JULY 1989 n= 1,204 5 10 IS 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 Early JUNE 1989 n=2,089 5 10 IS 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 AUGUST 1989 n=I,937 •lllll «* 5 I0 15 2O25 30 3540 45 50 55 6065 70 75 80 85 9O95100 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 Carapace width (mm CW) Figure 6 Dungeness crab, Cancer magister, length-frequency histograms from Grays Har- bor, Washington, April to August 1989. Note first occurrence of 0+ crab in May ( 6 mm CW) and peak settlement in early June. Summer growth of 0+ crab is evi- dent by 0+ size modes attaining 30-35 mm CW by August. forniensis, H. oregonensis, and pea crabs, Pinnixa spp. (Tasto, 1975). A multi-species assemblage of crab including Pugettia producta, Cancer productus and C. gracilis, Pinnixa spp., Scleroplax granulata (pea crabs), Hemigrapsus nudus, H. oregonensis, and Pagurus spp. accounted for 25—30% of the spring diet (by volume) of staghorn sculpins >100 mm TL in an estuary of Vancouver Island, British Columbia (Mace, 1983). The summer diet of staghorn sculpins from Grays Harbor, Washington, corroborates Tasto's (1975) ob- servation that the diet of staghorn sculpin >70 mm TL consists of crustaceans, especially decapods in- cluding ghost and mud shrimp (N. californiensis and U. pugettensis), sand shrimp (Crangon spp.), and seasonally abundant 0+ Cancer magister. From IRI analysis, it was determined that Dungeness crab represented about 9% of the overall total summer diet of sculpin. Over 30% of all stag- horn sculpin collected during June and 23% during July and August had 0+ Dungeness crab in their stomachs. Two other decapods that composed even greater proportions of the overall sculpin summer diet were Neotrypaea californiensis and Crangon spp. (27% and 13% IRI, respectively). Other prey Staghorn sculpin also consume prey species such as nereid poly- chaetes, fish, and bivalves that are seasonally abundant and readily available (see Gunderson et al., 1990, for list of infaunal and epi- faunal prey in Grays Harbor). These sculpin have relatively plas- tic feeding behavior and their diet changes month to month, fluctu- ating with relative prey abun- dance and accessibility. Despite this plasticity, the majority of this species' diet (85-99% IRI) gener- ally consisted of only 4 or 5 prey species (Fig. 5; Table 2). In April, before crab were available, sculpin consumed amphipods, especially E. confervicola, and Crangon spp. shrimp. Nereid polychaetes and the thallassinid shrimp Neotrypaea californiensis were primary prey in May. Dungeness crab were incor- porated into the diet as they settled in June and were ranked second in IRI im- portance after N. brandti. The late spring or early summer predominance of N. brandti polychaetes in the diet of sculpin was somewhat unexpected because polychaetes have not often been reported as a major diet item by other researchers from Washington (Smith, 1980; Thorn- burgh, 1980; Dinnel et al., 1990), or British Colum- bia (Mace, 1983), although they are mentioned as prey among fish from California (Jones, 1962; Tasto, 1975). The importance of this polychaete during spring and early summer to sculpin in Grays Harbor suggests that adult worm reproductive activity (Bass and Brafield, 1972; Giese and Pearse, 1975; Durchon, 1984) might make them vulnerable to sculpin preda- Armstrong et al.: Food habits of Leptocottus armatus 465 tion at this time of year. We examined well-pre- served specimens of this polychaete from stom- ach contents but found all were immature. High predation on immature stages of N. brandti may indicate worms are leaving their burrows to dis- perse as described by Dean (1978). By July and August, the behavior of the polychaetes may have changed, or their abundance may have declined since worms were rarely observed from stomach contents during those months. Dungeness crab Predation on 0+ Dungeness crab by sculpin is of interest because of the substantial commer- cial value of the C. magister fishery from north- ern California through southeast Alaska (Botsford et al., 1989) and because of the eco- logical implications of this estuarine predator- prey relation that is dependent on the annual arrival of oceanic crab larvae. Estuaries are important nursery grounds for 0+ crab (Cleaver, 1949; Tasto, 1983; Gunderson et al., 1990) and provide refuge by means of several habitats in- cluding eelgrass and epibenthic shell (Stevens and Armstrong, 1985; Gunderson et al., 1990; Jamieson and Armstrong, 1991; Dumbauld et al., 1993). Fernandez et al. (1993a) demonstrated that megalopae and newly settled 0+ C. magister prefer heavy shell habitat over eel- grass, mud with scattered shell, or bare mud. In addition, field tethering of crab in Grays Harbor showed that shell provided the best protection from predation compared with other habitats and that crab tethered with attached hooks were most often attacked by staghorn sculpin. During peak crab settlement in early June, juvenile crab were found in 42% of the sculpin stomachs examined and represented 10% of the total diet by weight (%GC), or 24% of IRI (Fig. 5). At this time crab are highly vulnerable to predation; the small Jl and J2 instars (6-11 mm CW) are very abundant (over 100/m2; Fernandez et al., 1993b), compete for limited refuge habitat, and molt frequently (every 2—3 weeks; Wainwright and Armstrong, 1993). The temporal pattern of 0+ inter- tidal density is consistent with inferences regarding both the rapid predation of much of the 0+ crab popu- lation shortly after settlement and with the relative importance of epibenthic shell as a refuge to ensure some survival of the year class. From early June to July, 0+ density decreased an order of magnitude at both the intertidal shell and eelgrass sites as mea- sured by trawl, but density was generally about three times higher over shell habitat compared with eel- Bivalve siphons 5% Misc. Crustacea ^ 5% /llnN Cancer magister ^H WMk 9% fl Other 7% \ Nereis brandti \ 50% Neotrypaea \\\\\\\ ' \ 'jE^^= calif orniensis \'yyyy,\^-- ■■— 13% V/V/^ Crangon spp. 11% 0+ Sculpin n=217 Eogammarus confervicola 8% y Fish ^4^ Cancer magister 9% Upogebia y/zY/Y/y. pugettensis ^&$& Nereis brandti \ 23% Crangon spp. 'N'Ny Neotrypaea \w califomiensis ,/ 31% > 1+ Sculpin n=265 Staghorn sculpin, Lepto Grays Harbor, Washingt and >1+ sculpin. All data Figure 7 cottus armatus, diet on, expressed as %II were combined from A composition from 'I, by age class; 0+ pril to August 1989. grass habitat (Fig. 10). This difference in density between the two habitats is likely much greater than that indicated by the trawl data. Net efficiency is unknown, but the gear was designed to operate on a fairly uniform sand-mud substrate (Gunderson and Ellis, 1986) and, we assume, is less efficient over the shell habitat compared with eelgrass habitat (al- though much shell is taken in trawls). More impor- tantly, the net "integrates" animals and material along the trawl path and cannot provide distinctions over smaller spatial scales of highly heterogeneous habitat such as intertidal shell. We know from pre- vious intertidal work done in Grays Harbor that 466 Fishery Bulletin 93(3). 1995 '5 a a. i- O 4(1 30" 20- ■ vnr — a o _?_ io- □ D Q n- — i — i — ■ — i — i — i — i — i — i — i — i — J7 J6 J5 „ J4 J3 J2 Jl 60 80 100 120 140 160 180 Sculpin total length (mm) Figure 8 Relationship between body length (TL) of staghorn sculpin, Leptocottus armatus, predators and carapace widths of Dungeness crab, Cancer magister, instars con- sumed. Left axis shows mean sizes of instars J1-J7 (dotted lines) from Wainwright and Armstrong ( 1993). megalopae settle and that Jl instars occur initially on both open tideflats and in refuge materials (e.g. shell, eelgrass) but are absent from the former within several tidal cycles and are virtually never found on open flats thereafter9 (Dumbauld et al., 1993). De- tailed excavation of shell patches at low tide reveal post-settlement densities of Jl in excess of 100/m2, but only a few per m2 in eelgrass (Fernandez et al., 1993a), which suggests that trawl data collected at high tide are likely a substantial underestimate of 0+ crab in shell compared with crab in eelgrass. These observations reflect a paradox indicated by the data. Higher apparent crab consumption was measured among sculpin collected from the shell habitat (77% IRI) than from the eelgrass (5%) (Fig. 9), inconsistent with the notion that shell provides critical refuge habitat for small crab instars. The mean density of 0+ crab from eelgrass intertidal trawl sites decreased by an order of magnitude from 2,455 crab/ha in early June to 280 crab/ha in mid-July (Fig. 10). During the same period, mean 0+ crab density in shell habitat decreased from 9,452 crab/ha to 874 crab/ha, reflecting migration into the channels (Wainwright, 1994) and the impact of predation in- cluding cannibalism (1+ on 0+ instars [Stevens et al., 1982]; early 0+ on later 0+ [Fernandez et al. 1993b] fish on 0+ crab [Fernandez et al. 1993a]). There appears to be a short time period during peak crab settlement when staghorn sculpin eat many small instars, especially those that settle on bare sand or mud- flats. In this respect Dungeness crab survival throughout much of the bay is dependent upon the availability of suitable refuge habitat210 (Fernandez et al., 1993a) as has been found for ju- veniles of other decapod species (Herrnkind and Butler, 1986; Barshaw and Lavalli, 1988; Howard, 1988; Warren, 1990). This pattern may be explained by the short time scale of settle- ment and rapid predation on small instar crab (especially J1-J2). A possible ex- planation for the difference in observed crab con- sumption by sculpin between the two habitats is that crab settlement in eelgrass or on open tideflats is predated very rapidly and depleted from those areas compared with crab settlement in the shell habitat. Pulses of cohorts could be severely reduced in much less time than the interval between sampling trips and thereafter effectively be unavailable to sculpin in certain areas of the estuary because of virtual re- moval. Crab that recruit to areas of extensive shell may provide a more stable and persistent prey basis as the dynamics of small instars (agonistic interac- tions and foraging) make them vulnerable on the exterior of the shell matrix or as they move short distances between shell piles. Predation by sculpin on J1-J4 instars in shell habitats may occur over a longer period, thereby increasing the likelihood that sculpin in our samples contained crab later in the summer, long after they were depleted from less pro- tected areas of open mud and light cover of eelgrass. This would be reflected both in greater numbers of crab consumed and in greater frequency of occurrence Armstrong, D. A., K. A. McGraw, P. A. Dinnel, R. M. Thom, and O. Iribarni. 1991. Construction dredging impacts on Dungeness crab, Cancer magister, in Grays Harbor, Washington, and miti- gation losses by development of intertidal shell habitat. Final Rep. FRI-UW-9110 to U.S. Army Corps of Engineers, Seattle District, Seattle, WA, 63 p. 10 Doty, D., D. A. Armstrong, and B. R. Dumbauld. 1990. Com- parison of carbaryl impacts on Dungeness crab (Cancer magister) versus benefit of habitats derived from oyster cul- ture in Willapa Bay, Washington. Univ. Washington, Fisheries Res. Inst., Seattle, WA. Rep. FRI-UW-9020, 69 p. Armstrong et al.: Food habits of Leptocottus armatus 467 Cancer magister S% Nereis brandti 25% Intertidal Eelgrass n=55 Other Nereis brandti 5% 5% Neotrypaea californiensis 7% Upogebia pugettensis 6% Cancer magister 77% Intertidal Shell «=44 Figure 9 Staghorn sculpin, Leptocottus armatus, diets, expressed as % IRI from intertidal eelgrass and intertidal shell habitats, Grays Har bor, Washington. All data combined, April to August 1989. in sculpin sampled from the shell habitat (higher %NC and %FO in the IRI calculation). Size at which 0+ crab were no longer vulnerable to sculpin predation was hypothesized to be about 25 mm CW (about instar J5) (Reilly, 1983) based on mouth gape width of the most prevalent size sculpin (gape limited predation [Zaret, 1980]). Theoretically, small crab newly settled to the estuary would be available and vulnerable to sculpin predation for much of their first full summer (as J1-J6), whereas 1+ crab resident in the estuary during summer would be too large (50-100 mm CW, Fig. 6; Stevens and Armstrong, 1985; Gunderson et al., 1990) for stag- horn sculpin to consume. These assumptions were confirmed because only J1-J4 (below 25 mm max. CW) were consumed (Fig. 8). Generally there were relatively few sculpin with an es- timated gape width of 25 mm (Fig. 2), thus sculpin were restricted to Jl— J4 crab. Cara- pace width is the larger body dimension of this species of crab, but if attacked from the side (i.e. laterally at the walking legs rather than face-on towards the chelae), then body length (from the posterior of the carapace to the orbit of eyes) could be the limiting dimen- sion with respect to sculpin mouth gape. Based on data of Weymouth and MacKay (1936), the carapace length (CL) of J3, J4, and J5 instars is about 73%, 71%, and 70% of width, respectively. From this perspective, the average size sculpin of this study could possibly consume instars up to J5 with re- spect to length (approximately 18.8 mm CL). Very few sculpin longer than 175 mm TL were caught; even their estimated gape width was only about 24.6 mm, less than the aver- age carapace width of most 0+ crab by Sep- tember (Wainwright and Armstrong, 1993). The six other potential fish predators of 0+ crab found in greatest abundance through- out the summer included juvenile English sole, Pleuronectes vetulus, shiner perch, Cymatogaster aggregata, snake prickleback, Lumpenus sagitta, saddleback gunnels, Pholis ornata, sand sole, Psettichthys melanostictus, and starry flounder, Platichthys stellatus.2 The first five species have relatively small mouths, are most prevalent as juveniles within the Grays Harbor estuary (English sole) or are not documented as being impor- tant crab predators1 (Williams, 1994). Starry flounder may prey on 0+ Dungeness crab both in Grays Harbor1 and San Francisco Bay (Reilly, 1983) but are uncommon as adults in the former estuary (Rogers et al., 1989). The results of this study expand current knowl- edge of staghorn sculpin's diet composition and feed- ing behavior, establish the importance of 0+ Dunge- ness crab as part of the estuarine summer diet of sculpin, and provide a perspective of the potential impact that sculpin predation has on juvenile Dunge- ness crab survival after settlement. Posey (1986) showed that staghorn sculpin predation limits the distribution of ghost shrimp N. californiensis on in- tertidal sandflats and labeled this fish a keystone predator controlling the depth distribution of newly settled ghost shrimp and the expansion of established beds of adult shrimp. Our data demonstrate that staghorn sculpin are a major predator of small 468 Fishery Bulletin 93(3). 1 995 EL. :165-172. Dinnel, P. A., J. L. Armstrong, R. R. Lauth, K. Larsen, D. A. Armstrong, and S. Sulkin. 1990. Fish predation on Dungeness crab in Padilla Bay, Washington. U.S. Dep. Commerce, NOAATech. Rep. Ser. OCRM/MEMD FRI-UW-9001, 69 p. Dinnel, P. A., D. A. Armstrong, and R. O. McMillan. 1993. Evidence for multiple recruitment-cohorts of Puget Sound Dungeness crab, Cancer magister. Mar. Biol. 115:53-63. Dumbauld, B. R., D. A. Armstrong, and T. L. McDonald. 1993. Use of oyster shell to enhance intertidal habitat and mitigate loss of Dungeness crab (Cancer magister) caused by dredging. Can. J. Fish. Aquat. Sci. 50:381-390. Durchon, M. 1984. Perspectives in the physiology of epitokous metamor- phosis in polychaetes. Fortschr. Zool. 29:3-16. Fernandez, M. , D. A. Armstrong, and O. Iribarne. 1993a. Habitat selection by young-of-the-year Dungeness crab, Cancer magister, and predation risk in intertidal habitats. Mar. Ecol. Prog. Ser. 92:171-177. 1993b. First cohort of young-of-the-year Dungeness crab, Can- cer magister, reduces abundance of subsequent cohorts in in- tertidal shell habitat. Can. J. Fish. Aquat. Sci. 50:2100-2105. Giese, A. C, and J. L. Pearse. 1975. Reproduction of marine invertebrates. In P. C. Schroeder and C. O. Hermans (eds.), Vol. Ill: annelids and echiurans. Acad. Press, New York, NY, 213 p. Gunderson, D. R., and I. E. Ellis. 1986. Development of a plumb staff beam trawl for sam- pling demersal fauna. Fisheries Res. 4:35—41. Gunderson, D. R., D. A. Armstrong, Y. Shi, and R. A. McConnaughey. 1988. Patterns of estuarine use by juvenile English sole (Parophrys vetulus) and Dungeness crab (Cancer magister). Int. Counc. Explor. Sea, Early Life History Symposium, No. 68, 18 p. 1990. Patterns of estuarine use by juvenile English sole, Parophrys vetulus, and Dungeness crab (Cancer magister). Estuaries 13:59-71. Gutermuth, F. B., and D. A. Armstrong. 1989. Temperature-dependent metabolic response of juve- nile Dungeness crab Cancer magister Dana: ecological im- plications for estuarine and coastal populations. J. Exp. Mar. Ecol. 126:135-144. Hart, J. L. 1974. Pacific fishes of Canada. Fish. Res. Board Can., Bull. 180, 740 p. Herrnkind, W. F., and M. J. Butler. 1986. 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Seasonality, spatial dispersion patterns and migra- tion of benthic invertebrates in an intertidal marsh- sandflat system of Puget Sound, Washington and their re- lation to waterfowl foraging and for feeding ecology of stag- horn sculpin, Leptocottus armatus. Ph.D. diss., Univ. Washington, Seattle, WA, 177 p. Stevens, B. G., and D. A. Armstrong. 1985. Ecology, growth and population dynamics of juvenile Dungeness crab, Cancer magister Dana, in Grays Harbor, Washington, 1980-1981. In Proc. symp. Dungeness crab biology and management, p. 119-134. Univ. Alaska Sea Grant Publ. No. 85-3. Stevens, B. G., D. A. Armstrong, and R. Cusimano. 1982. Feeding habits of the Dungeness crab, Cancer magister, as determined by the index of relative importance. Mar. Biol. 72:135-145. Tasto, R. N. 1975. Aspects of the biology of Pacific staghorn sculpin, Leptocottus armatus Girard, in Anaheim Bay. In E. D. Lane and C. W. Hill (eds.), The marine resources of Ana- heim Bay, California, p. 135-154. Calif. 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Crustacean Biol. 13:36-50. Wainwright, T. C, D. A. Armstrong, P. A. Dinnel, J. M. Orensanz, and K. A. McGraw. 1992. Predicting effects of dredging on a crab population: an equivalent adult approach. Fish. Bull. 90:171-182. Warren, J. H. 1990. Role of burrows as refuges from subtidal predators of temperate mangrove crabs. Mar. Ecol. Prog. Ser. 67:295-299. Weymouth, F. W, and D. C. G. MacKay. 1936. Analysis of the relative growth of the Pacific edible crab, Cancer magister. Proc. Zool. Soc. Lond., Part 1:257-280. Williams, G. 1994. Effects of habitat modification on distribution and diets of intertidal fishes in Grays Harbor estuary, Washing- ton. MS. thesis, Univ. Washington, Seattle, WA 98195, 53 p. Zar, J. H. 1984. Biostatistical analysis. Prentice Hall, Inc., Engle- wood Cliffs, NJ, 718 p. Zaret, T. M. 1980. Gape-limited predators. Chapter 2 in Predation and freshwater communities, p. 3-32. Yale Univ. Press, New Haven, CT, 187 p. Abstract. As part of the Southeast Florida and Caribbean Recruitment Project (SEFCAR), penaeoid shrimp lar- vae were collected during the spring and summer cruise of the RV Longhorn in the Lower Florida Keys and Dry Tbrtugas from 29 May to 30 June 1991. Larvae of the pink shrimp, Penaeus duorarum, and the rock shrimp, Sicyonia sp., were dis- tributed inshore close to the Dry Tortugas Grounds, whereas larvae of the oceanic shrimp Solenocera sp. showed mainly an offshore distribution. Significant concentrations of Solenocera sp., Sicyonia sp., and P. duorarum lar- vae at the Tortugas transect in early June were found within and above the seasonal thermocline while the cold cyclonic Tortugas Gyre was intensively developed. For Solenocera sp., which spawn on the outer edge of the gyre, high concentrations of larvae were found at the inshore stations of the Tortugas transect in early June, pre- sumably as a result of the cyclonic cir- culation of the gyre followed by onshore Ekman transport. Penaeus duorarum, which spawn in the shallow Tortugas Grounds, showed a mode of zoea II — III progressing to postlarvae I at the Tortugas Grounds during the 15 days in which the drifter Halley recirculated in the interior of the Tortugas Gyre. Re- tention of P. duorarum larvae by the internal circulation of the gyre at the spawning grounds may be an important mechanism for local recruitment of these shrimp to the nursery grounds of Florida Bay. Larval distribution and transport of penaeoid shrimps during the presence of the Tortugas Gyre in May-June 1 99 1 Maria M. Criales Department of Marine Biology and Fisheries Rosenstiel School of Marine and Atmospheric Science University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33 1 49 Thomas N. Lee Department of Meteorology and Physical Oceanography Rosenstiel School of Marine and Atmospheric Science University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149 Manuscript accepted 7 December 1994. Fishery Bulletin 93:471-482 ( 1995). Penaeoid shrimps constitute the sec- ond most valuable segment of the U.S. fishing industry and are argu- ably one of the most valuable groups of marine species in the world. An- nual stocks fluctuate widely and few spawning stock/recruitment rela- tionships have been demonstrated (Garcia, 1983). The penaeid shrimp Penaeus duorarum, or pink shrimp, supports an important commercial fishery in south Florida. Pink shrimp yielded a stable catch of 9.6 million pounds per year from 1960 to 1986 (Klima et al., 1986). How- ever, this catch has declined by more than 50% in the last four years (NMFS1). This fishery is directly dependent on young shrimp that migrate from nursery areas onto the fishing grounds (Nance and Patella, 1989). Animals with short life spans (=2 years), such as pink shrimp, de- pend almost entirely on one year class being recruited during the year. The life history of P. duorarum of the Dry Tortugas (shallow banks located about 100 km west from Key West) involves one oceanic and one estuarine phase (Garcia and Le Reste, 1981). Adults spawn offshore on the Dry Tortugas, where females lay demersal eggs (Fig. 1). The lar- vae undergo several changes in feeding habits and morphology in- cluding five naupliar stages, three zoeal or protozoeal, and three mysid stages. The last mysis undergoes a moult at which time it transforms into a postlarva. The average time required by P. duorarum to reach the first postlarval stage is approxi- mately 20 days at 26°C (Ewald, 1965). The first postlarval stages are still planktonic whereas those that follow are benthic. Postlarvae mi- grate inshore, entering the Florida Bay nursery grounds where they metamorphose to juveniles. When they have reached a length of about 10 cm, they return to the Tortugas spawning area (Allen et al., 1980). Advective processes of P. duorarum and their relation to oceanographic and environmental factors are not fully understood. Research on the larval phase was performed in the mid 1960's. Munro et al. (1968) and Jones et al. (1970) studied the abun- dance and distribution of larvae of P. duorarum on the Tortugas Shelf and in the Florida Keys. These authors 1 Jones, A. Southeast Fish. Sci. Center, Natl. Mar. Fish. Serv., NOAA, 75 Virginia Beach Dr., Miami, FL 33149. Unpubl. data, 1993. 471 472 Fishery Bulletin 93(3), 1995 25.0 24.0 -84.0 -83.0 -82.0 -81.0 -80.0 Figure 1 Location of transects and 1-m2 MOCNESS sampling stations (*) of the South- east Florida and Caribbean Recruitment Project (SEFCAR) cruise LH3, 29 May-30 June 1991 at the Dry Tortugas and Lower Florida Keys. Shaded area indicates spawning area of pink shrimp, Penaeus duorarum, in southeast Florida. Solid lines are the CTD temperatures at 100 m depth in late May 1991. Dashed line indicates the continuation of the Florida Current. hypothesized that P. duorarum larvae migrate from where they are spawned in the Dry Tortugas by means of the Florida Current and return to Florida Bay through passes in the middle Keys. However, they had difficulty in explaining the exact migratory path in light of inconsistencies between the prevailing currents and the abundance of larvae in the pathway to the coast. Penaeoid shrimps other than Penaeus are abun- dant in the Dry Tortugas and may occur in commer- cial catches (Eldred, 1959), but they are of little or no economic value. Such is the case for the rock shrimp, Sicyonia spp., the humpback shrimp, Solen- ocera spp., and the roughneck shrimp, Trachypenaeus spp. Life histories of these species are poorly known, and larval research in the Gulf of Mexico has focused on trends of seasonal distribution (Eldred et al., 1965; Temple and Fisher, 1967; Subrahmanyam, 1971b). The Southeast Florida and Caribbean Recruitment Project (SEFCAR) has investigated the effect of oceanographic processes on plankton and regional recruitment of fishes and other reef species along the continental shelf in southeast Florida. The hydro- graphic conditions in the Straits of Florida are domi- nated by the strong Florida Current. In the south- western part of the Florida Keys, the Florida Cur- rent is highly variable, often associated with mean- ders and gyres (Lee et al., 1992). The Dry Tortugas are located near the turning point where the south- ward-flowing Loop Current swerves abruptly east to enter the Straits of Florida (Gaby and Baig, 1983). A cy- clonic gyre over the slope off the Dry Tortugas with horizontal dimensions of approximately 200 km has been described by Lee et al. (1994). The gyre, which persisted for about 100 days from mid-May to late August 1994, was observed to move eastward to the region of the Pourtales Terrace (Lee et al., 1994). Lee et al. (1992) called this gyre the Pourtales Gyre, and its effect on lobster Scyllarus sp. and shrimp larvae was demonstrated by the high abundance of larvae nearshore in the path of the westward flow of the gyre (Yeung and McGowan, 1991; Criales and McGowan, 1994). The objective of this study is to describe the horizontal and vertical distribution patterns of the three most abundant penaeoid shrimp lar- vae in the Dry Tortugas and lower Florida Keys during the presence of the cyclonic Tortugas Gyre. This work will form a basis for later comparisons with surveys under different hydrographic conditions. Materials and methods Plankton and hydrographic sampling Samples were collected between 29 May and 30 June 1991, as part of the cruise LH3 of the RV Longhorn, by using a 1-m2 MOCNESS (multiple opening-clos- ing net and environmental sensing system [Wiebe et al., 1976]) with 0.333-mm net mesh size. The nine nets of the MOCNESS were towed in an aperture along an oblique path at a speed of approximately 2 m-s'1, and samples from the surface to near the bottom were collected. Net 1 in the set was towed obliquely from the surface down to about 200 m or to the closest multiple of 20 m if the water depth was less than 200 m. Net 2 (deepest) to net 9 (uppermost) sequentially opened or closed at controlled depths of 200-160 m, 160-130 m, 130-100 m, 100-80 m, 80- 60 m, 60-40 m, 40-20 m, and 20-0 m for the deeper stations, and 50-40 m, 40-30 m, 30-20 m, 20-10 m, and 10-0 m, or 45-30 m, 30-15 m, and 15-0 m depth intervals for the shallow stations (<50 m). A flowmeter and conductivity- temperature depth (CTD) sensors were attached to the net frame. The volume of water filtered in each layer varied from 130 to 593 m3, de- pending on the depth strata sampled. Criales and Lee: Larval distribution and transport of penaeoid shrimps 473 The cruise was divided into four legs (fifty-six sta- tions) from west of the Dry Tortugas to Looe Key in the middle Florida Keys (Fig. 1). The sampling data are summarized in Table 1. Stations of leg 1 were repeated in the other three legs. During leg 2, one transect was added at Marquesas and another at Halfmoon. Leg 3 repeated stations of legs 1 and 2 in addition to an upstream transect (Western transect). Leg 4 included a downstream transect (Looe Key) in addition to the Tortugas, Rebecca, NW Patch, and Marquesas transects (Fig. 1). Sampling was carried out continuously depending on the time the ship arrived at the station (Table 1). Samples were taken during the day at 35 stations and at night at the remaining 21 stations. Three moon phases were covered during this cruise. Twenty-six stations were sampled during the full moon, eight during the last quarter, and eight dur- ing the new moon. Three ARGOS satellite-tracked surface drifters were deployed on the northern side of the gyre as part of the physical oceanographic survey. Two sta- tions were sampled on the track of drifter Halley af- ter a 15-day interval (day 1=30 May, day 15=13 June). 0630 h; n=2l, 1=91.4, SD=115.5) stations was not sig- nificantly different tt-test, <54=0.82, P>0.05); therefore day and night data were pooled (Sokal and Rohlf, 1981). To characterize the vertical distribution of the dif- ferent larval stages per species, the depth of the cen- ter of mass (Zm) was calculated (Ropke et al., 1993): Zm=^(PixZi) where Pi is the standardized (no./lOO m3) number of larvae in the ith depth stratum; Z( is the mean sam- pling depth of the ith depth stratum; C- is the con- centration of larvae in 100 m3; andHi is the width of zth depth interval. Day and night stations were sepa- rated to determine any daily vertical larval migra- tion. Differences in Zm between day and night were not significant for any of the three species (P. duorarum t-test, t24=0.63, P>0.05; Sicyonia sp. t-test, £36=0.95; Solenocera sp. t-test, £50=0.28, P>0.05), sug- gesting no daily vertical migration of larvae; there- fore data were pooled. However, this may be biased by the greater number of day stations (35 day, 21 night). Larval identification and standardization Plankton samples were preserved in 4% formalde- hyde-seawater solution and later transferred to 70% ethanol. Aliquot sampling was performed after the similarity of duplicate samples was statistically evaluated U-test, t9=0.04, P<0.05). Each sample was adjusted to a volume of 500 mL, and the penaeoid larvae sorted from five 25-mL aliquots. The mean of the five counts was standardized to the concentra- tion of larvae (no./lOO m3) or to abundance (no./lO m2 of sea surface). No nauplii were caught because the mesh size of the net was too large to retain them. Penaeoid shrimp larvae were identified to genus or species by using existing keys and larval descrip- tions (Heldt, 1938; Pearson, 1939; Gurney, 1943; Dobkin, 1961; Cook, 1966; Heegaard, 1966; Sub- rahmanyam, 1971a). Postlarvae of Penaeus sp. were identified from the keys of Williams (1965) and the morphometric study of Chuensri (1968). Individual stages were separated only for P. duorarum because it was the only species of interest for which larval stages have been described (Dobkin, 1961). The re- maining penaeoid identifications were made to a generic level. Statistical analysis Mean abundance of total larvae caught at day (0631- 2000 h; rc=35, 3c =98.3, SD=111.6) versus night (2001- Results Horizontal distribution and abundance Penaeus duorarum These larvae showed an on- shore distribution concentrated near the Dry Tortugas (Fig. 2). The density ranged from 1.5 to 57.1 larvae/10 m2 represented by 60.3% zoeae, 15% myses, and 24.7% postlarvae. Distribution of zoeae was nearshore; 90% were caught no farther than 25 km offshore from the Dry Tortugas. Myses were distrib- uted a little farther offshore and eastward than zoeae but no more than 45 km from the coast. The trend of distribution of postlarvae was also close to shore; 83% of postlarvae I— III were located inshore at the Tortugas, Halfmoon, NW Patch, and Rebecca transects. The other 17% were found at the offshore stations of Marquesas associated with the Florida Current front, and no postlarvae were captured at the Looe Key transect (Fig. 2). Larval stages in the spawning area at the NW Patch and Tortugas transects showed a progression of ages during the four legs of sampling (Fig. 3). In late May zoeae II— III showed a high concentration (33.8-45.4 larvae/10 m2) at the spawning area, few myses were found at these stations, and no postlarvae were caught. In early June, 15 days after the first sampling, the abundance of myses and postlarvae in- creased. Postlarvae II— III reached their peak of con- 474 Fishery Bulletin 93(3), 1995 Table 1 Station data and abundance (no./102) of penaeoid shrimp larvae during the Southeast Florida and Caribbean Recruitment Project (SEFCAR) cruise LH3, 29 May-30, June 1991. Max- Distance Local Latitude Longitude depth offshore time (h) Moon Penaeus Sicyonia Solenocera Station N W (m) (km) Date (EDT) phases Transect duorarum sp. sp. Legl, 29-31 May 15 24.498 82.904 25 13.28 29 May 1118 day Full Tortugas 12.14 36.43 0.00 17 24.408 82.907 60 25.19 29 May 1242 day Full Tortugas 0.00 0.00 56.09 19 24.317 82.916 200 37.03 29 May 1418 day Full Tortugas 0.00 0.00 3.46 21 24.222 82.902 207 48.65 29 May 1621 day Full Tortugas 0.00 0.00 54.01 23 24.032 82.903 201 73.10 29 May 1754 day Full Tortugas 0.00 0.00 0.00 26 24.570 83.125 40 21.50 30 May 1947 day Full NW Patch 37.87 29.73 20.60 27 24.559 83.141 40 23.99 31 May 2113 night Full NW Patch 41.33 69.10 12.87 Leg 2, 4-7 June 29 24.500 82.916 20 13.28 4 June 1656 day Full Tortugas 19.02 22.83 3.80 30 24.406 82.908 60 25.19 4 June 1816 day Full Tortugas 19.76 54.01 129.26 31 24.317 82.916 202 37.03 4 June 2036 night Full Tortugas 7.05 52.24 191.50 32 24.227 82.912 203 48.65 4 June 2237 night Full Tortugas 0.00 4.04 254.62 36 24.567 83.132 40 22.33 5 June 1946 day L. quarter NW Patch 0.00 32.85 100.29 37 24.357 82.500 48 40.28 6 June 1121 day L. quarter Halfmoon 36.57 200.21 84.40 38 24.229 82.499 167 47.29 6 June 1243 day L. quarter Halfmoon 18.96 35.17 16.64 39 24.103 83.501 197 58.03 6 June 1442 day L. quarter Halfmoon 2.86 9.71 21.62 40 23.972 82.503 200 71.39 6 June 1644 day L. quarter Halfmoon 0.00 10.46 90.89 42 24.226 82.189 198 30.09 6 June 2334 night L. quarter Marquesas 5.28 0.00 16.13 43 24.324 81.194 196 17.47 7 June 0209 night L. quarter Marquesas 0.00 0.00 43.38 44 24.403 82.191 77 7.31 7 June 0409 night L. quarter Marquesas 0.00 0.00 5.12 Leg 3, 12-18 June 45 24.568 83.120 40 20.17 12 June 0914 day New NW Patch 6.45 3.37 24.84 46 24.833 83.359 56 35.80 12 June 1209 day New Western 2.45 0.00 145.05 47 24.634 83.408 57 44.96 12 June 1429 day New Western 0.00 0.00 103.36 48 25.524 83.445 125 57.06 12 June 1631 day New Western 4.27 6.76 564.17 49 24.401 83.483 202 72.29 12 June 1834 day New Western 0.00 0.00 67.77 50 24.280 83.522 200 88.52 13 June 2057 night New Western 0.00 0.00 93.78 51 24.032 82.903 200 72.76 13 June 0225 night New Tortugas 0.00 0.00 428.11 52 24.222 82.902 203 47.84 13 June 0503 night New Tortugas 0.00 0.00 37.43 53 24.317 82.916 202 34.46 13 June 0709 day New Tortugas 15.64 7.89 153.24 54 24.408 82.907 58 24.93 13 June 0859 day New Tortugas 17.74 26.72 95.20 55 24.498 82.904 21 13.58 13 June 0612 day New Tortugas 0.00 5.03 10.74 56 24.524 82.784 17 14.75 13 June 1437 day New Rebecca 16.72 22.94 13.72 62 24.403 82.191 57 2.02 17 June 1422 day New Marquesas 0.00 4.56 5.94 63 24.324 82.194 162 16.29 17 June 1625 day New Marquesas 0.00 2.58 23.66 64 24.226 82.189 162 28.28 17 June 1751 day New Marquesas 2.72 10.16 11.50 65 24.133 82.186 159 42.05 17 June 1924 day New Marquesas 6.95 17.76 6.00 66 23.972 82.503 160 71.39 17 June 2236 night New Halfmoon 0.00 1.95 48.16 67 24.103 82.501 163 58.03 18 June 0107 night New Halfmoon 0.00 0.00 50.30 68 24.231 82.501 164 47.29 18 June 0314 night New Halfmoon 0.00 0.00 41.40 69 24.360 82.501 15 40.28 18 June 0500 night New Halfmoon 0.00 15.09 11.05 70 24.524 82.784 15 14.75 18 June 0638 day New Rebecca 20.14 16.60 1.95 71 24.559 83.141 30 19.89 18 June 0938 day New NW Patch 17.63 0.00 4.64 centration ( 18.9 larvae/10 m2) in mid-June. In late June the peak of zoeae II reoccurred (35.8 larvae/10 m2). Sicyonia sp. Rock shrimp was the second most abundant species after Solenocera sp. The highest densities were located at the NW Patch and Half- moon transects (Fig. 4A). Zoeae represented 31.3% of the catch and myses 68.7%. Zoeae were highly abundant at the NW Patch stations in early May (78.8 larvae/10 m2) and early June (91.1 larvae/10 m2), and myses were distributed in patches with two large peaks, one at the Halfmoon transect (184.8 lar- Criales and Lee: Larval distribution and transport of penaeoid shrimps 475 Table 1 (continued) Max- Distance Local Latitude Longitude depth offshore time (h) Moon Penaeus Sicyonia Solenocera Station N W 0.05). Effect of the Tortugas Gyre on larval abundance and dispersal Abundance and vertical distribution at Tortugas transect A general downward slope of the upper seasonal thermocline (23-27°C) toward shore was present during the four legs at the Tortugas transect (Fig. 5). Solenocera sp., Sicyonia sp., and P. duorarum larvae were highly concentrated above or within the seasonal thermocline. The strength of the seasonal thermocline, which is uplifted in the interior of the gyre, appears to have been a limiting factor for ver- tical migrations of these penaeoid larvae. Solenocera sp. larvae were very abundant at the inshore stations between 25 and 75 m in depth dur- ing leg 2, corresponding with the strongly developed 476 Fishery Bulletin 93(3), 1995 thermocline (Fig. 5). The inshore distribution of Solenocera sp. during this leg was noteworthy be- cause these larvae showed an offshore distribution during the other legs. Penaeus duorarum 24.9 - it 24.4 - : • : a ft ft ft * 23.9- ft ft Zoeae Range 1-32/10 m' 23 4- -83.5 -83.0 -82.5 -82.0 -81.5 -81 .0 24.9 - 24.4- -a • : • • to -1 23 9 - • ft • Myses Range 1-7/10 m' 23 4- -83.5 -83.0 -82.5 -82.0 -81.5 -81 .0 24.9 - ,aA -~ • • •# ° --"^ * 24.4 - • • • • 23.9 - Postlarvae Range 1-9/10 m' ">3 1 -83.5 -83.0 -82.5 -82.0 -81.5 -810 Longitude Figure 2 Horizontal distribution and relative abundance (larvae/10 m2) of the lar- val stages of pink shrimp, Penaeus duorarum, at the sampling stations of the four legs of the LH3 cruise, 29 May-30 June 1991. Symbols are propor- tional in size to the abundance range and are positioned at the sampling stations. The stars = no catch. High larval concentrations of the three species (P. duorarum: 1-40 larvae/100 m3; Sicyonia sp.: 1-22 larvae/100 m3; and Solenocera sp.: 10-60 larvae/100 m3) were found at the Tortugas transect during leg 2 in early June within and above the sea- sonal thermocline between 25 and 75 m in depth (Figs. 5 and 6). Total abun- dances during leg 2 were much higher than those during any other leg for all three species. The abundance of Solen- ocera sp. was twice as great during leg 2, and there were highly significant dif- ferences among legs (ANOVA, P<0.05) (Fig. 6). Drifter circulation Drifter Halley, de- ployed on 30 May on the northern side of the Tortugas Gyre, moved south- southeast for about seven days, then turned back toward the west-northwest for about seven days (Fig. 7). The drifter spent the first 14 days in a tight recir- culation in the interior of the gyre. The position of the drifter upon release ini- tially corresponded with the position of stations 26 and 27. On 13 June, when it broke out of the gyral circulation, the drifter was located at Rebecca transect at station 56. At this point the drifter entered the Rebecca Channel between the Dry Tortugas and Rebecca Shoal where it stayed for about 10 days, un- dergoing tidal excursions of up to 7 km, but with no net through-flow. Relative percentages of the larval stages of P. duorarum at the station where the Halley drifter was released (Stns. 26 and 27) and at the station where this drifter broke out of the gyre circulation (Stn. 56) are plotted in Figure 7. On 30 May at stations 26 and 27, P. duorarum lar- vae showed one mode of zoeae, mainly II-III (84%). After 15 days, on 13 June, one mode of postlarvae I (67.7%) was present at station 56, a station near the departure point. The trajectory of the drifter Halley and the progression of age of P. duorarum larvae over the 15 days that the drifter spent recirculating within the gyre may indicate retention of P. duorarum larvae at the spawning area. Abundance and composition of Sicyonia sp. larvae at the same two locations, stations 26 and 27, and at station 56 of Criales and Lee: Larval distribution and transport of penaeoid shrimps 477 Early June Late June Figure 3 Percentages of the larval stages of pink shrimp, P. duorarum, at the Tortugas and NW Patch transects during the four legs of the cruise LH3, 29 May-30 June 1991. Z = zoeae; M = myses; and P = postlarvae. Rebecca transect showed a similar trend to that de- scribed for P. duorarum: a high concentration of zoeae at the deployment of the drifter (80% zoeae) and 15 days later a dominance of myses (100% myses). Discussion Munro et al. ( 1968), in an examination of abundance and distribution of P. duorarum larvae in southeast Florida, could not reach firm conclusions regarding the path of migration from the Dry Tortugas to Florida Bay because of the inconsistency between the prevailing currents and the abundance of larvae in the pathway to the coast. However, they hypothesized that P.- duorarum larvae may have been advected from where they were spawned in the Tortugas Grounds by means of the Florida Current and then were carried back into Florida Bay by tidal currents through passes in the middle Keys. The conceptual path of larval advection outlined by Munro et al. (1968) was consistent with the general current pat- tern known at that time. More recent oceanographic research on the Straits of Florida has shown a high variability in the Florida Current in the lower Keys and Dry Tortugas associated with meanders and gyres (Lee et al., 1992, 1994). Lee et al. (1994) showed from moored current meter data and surface drifter tracks that a cold, cyclonic gyre formed off the Dry Tortugas in mid-May and continued as a weak coun- terclockwise recirculation about 200 km in diameter Table 2 Mean and standard deviation of the center of mass (Zn ,±SD) of the larval stages of three penaeoid shrimps duri ng the SEFCAR cruise LH3 May^June 1991 Z(m) SD n Solenocera sp. 42.41 20.97 52 Zoea 35.64 20.08 27 Mysis 42.18 20.69 49 Sicyonia sp. 26.85 17.02 38 Zoea 30.14 20.24 14 Mysis 25.19 13.22 36 P. duorarum 18.42 12.14 26 Zoea 15.00 9.13 15 Mysis 15.07 14.04 15 Postlarvae 16.81 18.67 17 until late August. Thus, the presence of the gyre could have acted as a larval retention and recirculation mechanism for the duration of the sampling cruise. Distributions of zoeae and myses of P. duorarum found in this study agree with those of Munro et al. (1968) and Jones et al. (1970) for the Tortugas shelf. However, postlarval distribution in the present study was different; most postlarvae (stages I— III) were lo- cated inshore near the area where they were spawned, rather than offshore as was found by Munro et al (1968). Composition of larval stages at the 478 Fishery Bulletin 93(3), 1995 A Sicyonia sp 24.9- * i • • .-. a .., ais*^ 24.4- 6 « • • ft • ft ft * • 23.9- * ft ft Zoeae ?3 4 - Range 2-42/ 10 m' B 24.9 23 9 -83.5 -830 -82 5 -82 0 -81-5 -81.0 24.9- * 24.4- <> •r • t • <3 • • • • t • 23 9- • • Myses 234- Range 2-99/10 nV -83 5 -83 0 -82 5 -82 0 -815 -810 Solenocera sp. -83 5 -83 0 -82 5 -82 0 -815 -81.0 24.9 - • JJS&SL* *~ 24.4 - • • • ! • • .■5 • • • """ A • • • 23.9- • • • • Myses 73 4 - ' 1 Range 1 -281 /10 m' -83.5 -83.0 -82.5 -82.0 -81.5 -81.0 Longitude Figure 4 Horizontal distribution and relative abundance (larvae/10 m2) of zoeal and mysid stages of (A) the rock shrimp Sicyonia sp. and (B) the humpback shrimp Solenocera sp. for the four legs of the LH3 cruise, 29 May-30 June 1991. The symbols are proportional in size to the abundance range and are positioned at the sam- pling stations. The stars = no catch. Tortugas and NW Patch transects and at the two stations sampled on the track of the drifter Halley showed the same modal progression of zoeae to postlarvae within 15 days. This period corresponds to the time reported by Ewald (1965) for zoeae III to become postlarvae I at 26°C. This time period for larval development from zoeae to postlarvae also agrees remark- ably well with the trajectory time of the drifter recirculating in the interior of the gyre. The tim- ing of the modal progression of larval stages occurring within those 15 days of gyre recircu- lation at the spawning area, as shown by the drifter, may indicate that P. duorarum larvae were recirculating in the interior of the gyre during development. Interestingly, after the drifter broke out of the gyre circulation it moved toward the east and north toward the Florida Bay shrimp nursery grounds, suggesting a local re- cruitment pathway for this species. Retention of P. duorarum larvae at the spawning area by the Tortugas Gyre for some days after hatching may enhance the survival of these larvae because food resources are avail- able in the uplifted nutracline where Lee et al. (1994) found maximum concentrations of chlo- rophyll and copepod nauplii. Furthermore, postlarvae located in the northern (nearshore) portion of the gyre may increase their chance of settling either by escaping the offshore flow on the western side of the gyre entirely or by resisting the offshore flow, thereby drifting to the west rather than being swept offshore (Porch, 1993). Thus, the primary pathway for P. duorarum larvae to reach the nursery areas of Florida Bay may include retention at the spawning area by recirculation in the Tortugas Gyre followed by movement onto the Southwest Florida shelf and Florida Bay by wind and tidal currents. Those larvae that are advected east- ward by the Florida Current may reach the upper and middle Keys. The latter alternative could explain the great number of postlarvae found in the middle Keys by Munro et al. ( 1968) and Roessler and Rehrer (1971). Sicyonia sp. larvae showed a coastal and shal- low distribution. Young zoeae were generally restricted to the inshore stations, indicating that this species may spawn near the Dry Tortugas Grounds. Myses showed the highest concentrations inshore, with a maximum con- centration at the Marquesas transect. Larval stages at the two stations of the drifter showed a similar trend to that off! duorarum. The time of development of S. brevirostris from spawn- Criales and Lee: Larval distribution and transport of penaeoid shrimps 479 ing to the first postlarval stage is approximately 30 days (Cook and Murphy, 1965). Local retention of larvae at the spawning area followed by recruitment into the coastal region may be the migration mecha- nism for this coastal and short-lived species as well. Early-stage zoeae of Solenocera sp. were widely distributed offshore; two main peaks were located at the Western and Tortugas transects at a depth of about 35 m. The age of these zoeae was estimated to be 3 to 5 days in accordance with Heldt's description ( 1938) of the larval development of S. membranacea. These data indicate that this species may have spawned somewhere in the Gulf of Mexico in a loca- tion corresponding to the outer edge of the Tortugas Gyre. Myses showed an offshore distribution in all but the Tortugas transect during leg 2, where most larvae were found inshore. The great concentration of Solenocera larvae at the inshore stations of the Tortugas transect in early June between 25 and 75 m in depth corresponded with the strongly developed Penaeus duorarum Range 1-5/ 100 m T r 0 10 20 30 40 50 60 70 80 Range 1-10/ 100 m \ 1 1 1 — 1 1 1 I- 0 10 20 30 40 50 60 70 80 B Sicyoma sp. Range 1-11 / 100 m"* T r~ 0 10 20 30 40 50 60 70 80 Solenocera sp. Leg 1 Range 1-11 / 100 m' \* T 1 r~ 0 10 20 30 40 50 60 70 80 Range 1-128/ 100 m1 — 1 1 1 -T 1 1 1 0 10 20 30 40 50 60 70 Leg 2 Leg 3 Leg 4 0 10 20 30 40 50 60 70 80 Distance offshore (km) Figure 5 Cross section of Tortugas transect during the four legs showing the vertical distribution and relative concentrations (larvae/100 m3) of the three penaeoid species: pink shrimp, Penaeus duorarum (A); the rock shrimp Sicyonia sp. (B); and the humpback shrimp Solenocera sp. (C), superimposed over the vertical temperature profiles (°C) from the MOCNESS temperatures. Symbols are proportional in size to the abundance range. The stars = no catch. 480 Fishery Bulletin 93(3). 1995 300 270 240 210 > 180 E o C 150 - | J 120 90 - 60 30 0 Penaeus duorarum Sicyonia sp. Solenocera sp LEG1 LEG2 LEG3 LEG4 Figure 6 Mean relative abundance (larvae/10 m2) and standard deviation of the pink shrimp, Penaeus duorarum, the rock shrimp Sicyonia sp., and the humpback shrimp, Solenocera sp., at the sampling stations of the Tortugas transect during the four legs of the LH3 cruise, 29 May- 30 June 1991. (*) = significant differences in mean rela- tive abundance between legs, within species (P<0.05). thermocline as a consequence of the Tortugas Gyre. Criales and McGowan ( 1994) found Solenocera larvae in high abundance (62% of the penaeoid larvae) at an inshore station of Looe Reef transect during the pres- ence of the Pourtales Gyre, whereas few larvae (only 15%) were captured in the absence of the gyre when the Florida Current intruded close to the coast. The combination of the cyclonic gyre circulation and inshore surface Ekman transport convergence should result in a concentration of larvae in the in- terior of the gyre and in an onshore transport in the eastern portion. Onshore Ekman transport is ex- pected to be relatively high in the Lower Keys and Dry Tortugas where prevalent southeast winds fa- vor onshore transport toward the east-west oriented coast. The importance of Ekman transport on recruit- ment has been shown in the Florida Keys for Scyllarus larvae (Yeung and McGowan, 1991) and for other decapod larvae particularly brachyuran larvae in other regions (see Hobbs et al., 1992; McConnaughey et al., 1994). Substantial gaps exist in our knowledge of the life histories of penaeoid shrimps. For example, larval development of Solenocera spp. has not been con- ducted for any of the five western Atlantic species (Perez-Farfante and Bullis, 1973), and larval devel- opment of only one of the seven western Atlantic spe- cies of Sicyonia spp. is known (Cook and Murphy, 1965). As long as our knowledge of the life history and larval development of these species remains lim- ited, further conclusions regarding interactions of recruitment processes with the physical environment will remain uncertain. This research showed the effects of the Tortugas Gyre circulation on dispersal and abundance of local coastal (P. duorarum and Sicyonia sp.) and oceanic (Solenocera sp.) shrimp species. The modal progres- sion of P. duorarum zoeae to postlarvae within the same 15-day period in which the gyre recirculated in the Tortugas region indicates that P. duorarum larvae, in addition to the advective process postulated by Munro et al. ( 1968), may recirculate within the gyre during their development. Retention of larvae by the gyre circulation at the Dry Tortugas, combined with wind driven transport on the southeast Florida shelf, is a plausible recruitment pathway for pink shrimp recruiting to the nursery grounds of Florida Bay. Acknowledgments The authors gratefully acknowledge M. F McGowan for his assistance and design of the biological sam- pling, W. Richards and A. Jones of the Southeast Fish- eries Science Center of Miami for their continuous support during the course of this research, C. Yeung and C. Limouzy-Paris for their cooperation in the preparation of the manuscript and figures, E. Will- iams for analysis of oceanographic data, and the per- sonnel of SEFC AR and crew of the RV Long Horn for making samples and data available. This work forms part of the Southeastern Florida and Caribbean Re- cruitment project (SEFCAR), funded by the National Oceanic and Atmospheric Administration through co- operative agreement No. NA90RAH00075 with the University of Miami. Literature cited Allen, D. A., J. H. Hudson, and T. J. Costello. 1980. Postlarval shrimp (Penaeus) in the Florida Keys: spe- cies, size, and seasonal abundance. Bull. Mar. Sri. 30:21-33. Chuensri, C. 1968. A morphometric and meristic study of postlarval brown shrimp, Penaeus aztecus Ives, pink shrimp P. duorarum Burkenroad, and white shrimp P. setiferus ( Linnaeus ). M.S. thesis, Univ. Miami, Coral Gables, FL, 108 p. Cook, H. L. 1966. A generic key to the protozoean, mysis, and postlar- val stages of the littoral penaeidae of the northwestern Gulf of Mexico. Fish. Bull. 65:437-447. Cook, H. L., and M. A. Murphy. 1965. Early development stages of the rock shrimp, Sicyonia brevirostris Stimpson, reared in the laboratory. Tulane Stud. Zool. 12(4): 109-127. Criales and Lee: Larval distribution and transport of penaeoid shrimps 481 26N ill 25N D 3 24N Stn. 26, 27 May 30 Sep. 21 Stn. 56 *-■& June 13 % -' Halley SEFCAR, May 1991 83W 82W 81W LONGITUDE BOW 40 UJ < > 20 < Stn. 26, 27 B ■ I I _ H 1 1 1 1 1 Zl Zll Z Ml Ml Mil Mill PI Pll Pill PIV Stn. 56 Zll Z III Ml Mil Mill PI Pll Pill PIV Figure 7 (A) Trajectory of the drifter Halley deployed during SEFCAR cruise LH3 on 30 May 1991. Stations 26 and 27 correspond to the location where the drifter was released, and station 56 with the position of the drifter when it broke out of the cyclonic circulation on 13 June 1991. (A) = positions of stations 26, 27, and 56. (B) Percentages of the larval stages of the pink shrimp, Penaeus duorarum, at stations 26, 27, and 56 sampled on the track of drifter Halley. Z = zoeal stages; M = mysid stages; and P = postlarval stages. Criales, M. M., and M. F. McGowan. 1994. Horizontal and vertical distribution of penaeidean and caridean larvae and micronektonic shrimps in the Florida Keys, U.S.A. Bull. Mar. Sci. 54:843-856. Dobkin, S. 1961. Early development stages of pink shrimp, Penaeus duorarum, from Florida waters. Fish. Bull. 61:321-349. Eldred, B. 1959. A report of the shrimps (Penaeidae) collected from the Tortugas controlled area. Florida Board Conserv. Mar. Res. Lab., Spec. Rep. No. 2, 6 p. Eldred, J. W., G. T. Martin, and E. A. Joyce Jr. 1965. Seasonal distribution of penaeid larvae and post- larvae of the Tampa Bay area, Florida Board Conserv. Mar. Res. Lab., Tech. Ser. No. 44, 47 p. Ewald, J. J. 1965. The laboratory rearing of pink shrimp, Penaeus duorarum Burkenroad. Bull. Mar. Sci. 15:436-^149. Gaby, 1)., and S. Baig. 1983. Gulf Stream variability and width. Mariners Weather Log 27:133-134. 482 Fishery Bulletin 93(3), 1995 Garcia, S. 1983. The stock-recruitment relationship in penaeid shrimps: reality of artifacts and misinterpretations? Oceanogr. Trop. 18(l):25-48. Garcia, S., and L. Le Reste. 1981. Life cycles, dynamics, exploitation and management of coastal penaeid shrimp stocks. FAO. Fish. Tech. Pap. No. 203, 215 p. Gurney, R. 1943. The larval development of two penaeid prawns from Bermuda of the genera Sicyonia and Penaeopsis. Proc. Biol. Soc. Lond. (series B) 113:1-16. Heegaard, P. E. 1966. Larvae of decapod Crustacea. The oceanic penaeids Solenocera-Cerataspis-Cerataspides. The Carlsberg Foundation's oceanographical expedition round the world 1928- 30 and previous "Dana" expeditions. Dana Rep. 67, 147 p. Heldt, M. H. 1938. La reproduction chez les crustaces decapodes de la famille des peneides. Ann. Inst. Oceanogr. Monaco, Paris, xviii (2):31-306, 131 figs. Hobbs, R. C, L. W. Botsford, and A. Thomas. 1992. Influence of hydrographic conditions and wind forc- ing on the distribution and abundance of Dungeness crab, Cancer magister, larvae. Can. J. Fish. Aquat. Sci. 49:1379-1388. Jones, A. C, D. E. Dim itriou, J. J. Ewald, and J. H. Tweedy. 1970. Distribution of early developmental stages of pink shrimp, Penaeus duorarum , in Florida water. Bull. Mar. Sci. 20:634-661. Klima, E. F., G. A. Matthews, and F. J. Patella. 1986. A synopsis of the Tortugas pink shrimp fishery, 1960- 1983, and the impact of the Tortugas Sanctuary. North Am. J. Fish. Manage. 6:301-310. Lee, T. N., C. Rooth, E. Williams, M. F. McGowan, M. E. Clarke, and A. F. Szmant. 1992. Influence of Florida Current, gyres and wind-driven circulation on transport of larvae and recruitment in the Florida Keys coral reefs. Cont. Shelf Res. 12(7/8):971-1002. Lee, T. N., M. E. Clarke, E. Williams, A. F. Szmant, and T. Berger. 1994. Evolution of the Tortugas Gyre and its influence on recruitment in the Florida Keys. Bull. Mar. Sci. 54:621-646. McConnaughey, R. A., D. A. Armstrong, B. Hickey, and D. R. Gunderson. 1994. Interannual variability in coastal Washington Dunge- ness crab (Cancer magister) populations: larval advection and the coastal landing strip. Fish. Ocean. 3( l):22-38. Munro, J. L., A. C. Jones, and D. Dimitriou. 1968. Abundance and distribution of the larvae of the pink shrimp (Penaeus duorarum) on the Tortugas Shelf of Florida, August 1962-October 1964. Fish. Bull. 67: 165-181. Nance, J. M., and F. J. Patella. 1989. Review of the Tortugas shrimp fishery from May 1987 to January 1989. U.S. Dep. Commer., NOAATech. Memo. NMFS-SEFS-238, 11 p. Pearson, J. C. 1939. The early life histories of some American Penaeidae, chiefly the commercial shrimp, Penaeus setiferus. Fish. Bull. 49:1-73. Perez-Farfante, I., and H. R. Bullis Jr. 1973. Western atlantic shrimps of the genus Solenocera with description of a new species (Crustacea: Deacapoda: Penaeidae). Smithsonian Contrib. Zool. No. 153:1-33. Porch, C. E., III. 1993. A numerical study of larval retention in the south- ern Straits of Florida. Ph.D. diss., Univ. Miami, 245 p. Roessler, M. A., and R. G. Rehrer. 1971. Relation of catches of postlarval pink shrimp in Ev- erglades National Park, Florida, to the commercial catches on the Tortugas Grounds. Bull. Mar. Sci. 21:790-805. Ropke, A., W. Nellen, and U. Piatkowski. 1993. A comparative study on influence of the pycnocline on the vertical distribution of fish larvae and cephalopod paralarvae in three ecologically different areas of the Ara- bian Sea. Deep-Sea Res. II 40(3):801-819. Sokal, R. R., and F. J. Rohlf. 1981. Biometry. W.H. Freeman and Co., San Francisco, 832 p. Subrahmanyam, C. B. 1971a. Description of shrimp larvae (family Penaeidae) off the Mississippi coast. Gulf Res. Rep. 3(2):241-258. 1971b. The relative abundance and distribution of penaeid shrimp larvae off the Mississippi coast. Gulf Res. Rep. 3 (21:291-345. Temple, R., and C. S. Fischer. 1967. Seasonal distribution and relative abundance of planktonic stage shrimp (Penaeus spp.) in the northwest- ern Gulf of Mexico, 1961. Fish. Bull. 66:323-334. 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. 4:313-326. Williams, A. 1965. Spotted and brown shrimp postlarvae (Penaeus) in North Carolina. Bull. Mar. Sci. 9:281-290. Yeung, C, and M. F. McGowan. 1991. Differences in inshore-offshore and vertical distribu- tion of phyllosoma larvae of Panulirus, Scyllarus, and Scyllarides in the Florida Keys in May-June, 1989. Bull. Mar. Sci. 49:699-714. Abstract. — A total of 707 common dolphins, Delphinus delphis Linnaeus, (376 males and 331 females) taken in Japanese, Korean, and Taiwanese drift nets in the central North Pacific Ocean from February to November 1990 and 1991 were examined. Sex, total length, date, and location of capture were re- corded. Biological samples were col- lected from 152 of the dolphins exam- ined (93 males and 59 females). Ages were determined by counting dentinal layers. Female reproductive status was determined by macroscopic examina- tion of ovaries (n=43). Eight females were mature, two were pregnant, three were resting, two were lactating, and one was of unknown condition. Testes and epididymes were examined for evi- dence of spermatogenesis (rc=70); 21 males were mature. A preliminary es- timate of gestation period was 11.1 months. The sex ratio appeared to fa- vor males; segregation during the sam- pling period may be responsible for dif- ferences from 1.0. Male average age at sexual maturation was estimated to be 10.5 years. The largest sexually imma- ture male was 179 cm; the smallest sexually mature was 182 cm. Mature testis weights ranged from 273.2 g to 1,190 g. Females reached sexual matu- ration at about 8.0 years; estimates of length at sexual maturation were 172.8 and 170.7 cm. Predicted asymptotic lengths for males and females were 188.1 cm and 179.4 cm, respectively. Calving appeared to peak in May and June. Sampling effort moved north- ward through September; infrequent sampling of parturient females and neonates during the projected calving mode suggests they were segregated outside the fishing area at that time. Growth and reproduction of the common dolphin, Delphinus delphis Linnaeus, in the offshore waters of the North Pacific Ocean Richard C. Ferrero William A. Walker National Marine Mammal Laboratory, Alaska Fisheries Science Center National Marine Fisheries Service, NOAA 7600 Sand Point Way, NE, Seattle, Washington, 981 15 Manuscript accepted 12 December 1994. Fishery Bulletin 93:483-494 (1995). The common dolphin, Delphinus delphis Linnaeus, is an oceanic spe- cies widely distributed throughout the tropical and temperate seas of the world. In the western North Pacific Ocean, published accounts have dealt almost exclusively with taxonomy, distribution, and sea- sonal movements (Ogawa, 1937; Nishiwaki, 1967; Kasuya, 1971; Ohsumi, 1972). The common dol- phin has been studied most exten- sively in the eastern North Pacific Ocean where research has focused primarily on species distribution, herd movements, reproductive sea- sonality, stock differences, and be- havior (Norris and Prescott, 1961; Brownell, 1964; Hui, 1979; Evans, 1982; Perrin et al., 1985; Perryman and Lynn, 1993; Heyning and Perrin, 1994; Walker and Cowan1; Walker et al.2). Two morphotypes of common dol- phin, a short-beaked form and a long-beaked form, differing in ros- tral length, overall size, and color pattern, have been described from southern California waters (Banks and Brownell, 1969; Evans, 1975). Heyning and Perrin (1994) de- scribed two species of Delphinus from the eastern North Pacific Ocean, a short-beaked form which is referable to D. delphis Linnaeus and a long-beaked form assigned to the nominal species D. bardaii Dall, 1893. Recent studies of molecular genetics confirm the morphologic findings and support distinction of these two morphotypes of common dolphin as separate species (Rosel et al., 1994). Despite the abundance of D. delphis in the eastern North Pacific Ocean, little biological information on age, growth, and reproductive condition exists in the literature. Ridgway and Green (1967) and Harrison et al. (1972) present go- nadal data for a total of 30 male and 25 female specimens collected over a 16-year period from single strandings or live-capture. Correlations with age were not incorporated in either study. Hui (1979) correlated age, reproductive condition, and flipper bone development and summarized 1 Walker, W. A., and D. F. Cowan. 1981. Air sinus parasitism and pathology in free- ranging common dolphins, Delphinus delphis, in the eastern tropical Pacific. Southwest Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 8604 La Jolla Shores Dr., La Jolla, CA 92038. Admin. Rep. LJ- 81-23C, 19 p. 2 Walker, W. A., F. G. Hochberg, and E. S. Hacker. 1984. The potential use of para- sites Crassicauda (Nematoda) and Nasi- trema (Platyhelminthes) as biological tags and their role in the natural mortality of common dolphins, Delphinus delphis, in the eastern North Pacific. Southwest Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 8604 La Jolla Shores Dr., La Jolla, CA 92038. Admin Rep. LJ-84-08C, 31 p. 483 484 Fishery Bulletin 93 13). 1995 data on age and gonadal condition for 35 male and 52 female specimens. Most of the dolphins examined in this study were collected during purse-seine re- search operations off the southern California coast (Hui, 1973). In the late 1970's, Japan, Taiwan, and the Republic of Korea initiated high-seas driftnet fisheries for fly- ing squid, Ommastrephes bartrami, and large-mesh fisheries for pelagic fish species including albacore tuna, Thunnus alalunga. The majority of squid driftnet fisheries operated from June to November in the central North Pacific Ocean between lat. 34°- 46°N and long. 171°E-147°W, while large-mesh fish- eries operated farther south and west between lat. 29°N-45°N and long. 147°E-150°W from February to November. Delphinus delphis was the most fre- quently killed cetacean in the large-mesh fisheries and was also found regularly entangled in the squid driftnet fisheries (Hobbs and Jones, 1993). Beginning in 1990, under international coopera- tive agreements, biological samples were collected from marine mammals killed in the Japanese and Taiwanese squid and large-mesh fisheries and from marine mammals killed in the Korean squid fishery. Combining the 1990 and 1991 biological samples provided an opportunity to estimate growth and re- productive parameters for D. delphis from the off- shore waters of the North Pacific Ocean. Materials and methods Specimen collection Scientific observers collected biological data from all cetaceans caught in Japanese, Korean, and Taiwan- ese driftnet operations. Soon after arrival on deck, each cetacean was identified, sexed, measured (total length to nearest 1.0 cm), photographed twice (left lateral and ventral), and given an individual speci- men number. When an animal was dissected, the left lower jaw was tagged and frozen intact. For males, the right testis and epididymis were collected whole, tagged, and preserved in 10% formalin. Females were checked for evidence of lactation by longitudinal in- cision through the left mammary gland. The ovaries and uteri for most females were collected intact. The left ovary and entire reproductive tract was tagged and preserved in 10% formalin. If the animal was pregnant with a large fetus or was recently postpar- tum, only the ovaries and a cross section of the left uterine horn were collected. Fetuses were sexed, weighed to the nearest 1.0 g, and measured to the nearest 1.0 cm. Frozen and preserved samples were shipped to the National Marine Mammal Laboratory in Seattle, Washington, for analyses. Age determination Teeth were extracted from the center of the left lower jaw for age determination. Each tooth was decalci- fied and sectioned (24 um) longitudinally on a freez- ing microtome. Tooth-section preparation and den- tinal growth-layer group (GLG) counting procedure followed guidelines developed by Myrick et al. ( 1983) for Stenella spp. Six to eight stained sections from the center of each tooth were mounted on a glass slide and examined under a compound microscope at 40x and lOOx magnification with transmitted light. Dentinal GLG characteristics have been described for Delphinus (Perrin and Myrick, 1981). Annual deposition of dentinal GLG's has been established for tetracycline-marked common dolphins (Gurevitch et al., 1981). We followed these findings and assumed one GLG represented one year of growth. Each tooth was read independently by two read- ers. Ages were recorded to the nearest 0.5 layer ex- cept for animals with less than one complete GLG. In these cases, we estimated the thickness of the in- complete layer to the nearest 0.2 GLG. Predeter- mined limits on reader variability were established following those used for Lissodelphis borealis in Ferrero and Walker (1993). This procedure allowed for a 0.5- layer difference between readings for estimated ages up to 5 years (measured from the median reading), one layer for estimates between 5 and 10 years, and one additional layer for every 5-year interval thereafter. Within these limits, we averaged the two readers' esti- mates to obtain the final age. When readings differed by more than these limits, the tooth was reread. Examination of reproductive organs Males Right testes with epididymides were weighed to the nearest 0.01 g and measured to the nearest 0.1 cm. A 1-cm3 block was removed from the center of each testis; a similar section of epididymis was removed at mid-length, and both were prepared for histological analysis. Paraffin-embedded tissues were sectioned at 6 um, stained with hematoxylin and eosin, and mounted on glass slides. Testes and epi- didymides were examined for evidence of spermato- genesis by using a compound microscope at lOOx with transmitted light. Males were considered mature if sperm were present in testes tubules. Females Ovaries were weighed to the nearest 0.01 g. Maximum diameter of the left uterine horn was Ferrero and Walker: Growth and reproduction of Delphmus delphis 485 measured to the nearest millimeter. Each ovary was sliced transversely into serial sections (=1 mm thick) with a scalpel and examined for the presence of cor- pora lutea and corpora albicantia. Two measure- ments of corpus diameter, taken at right angles, were recorded for well-regressed corpora; three diameters were recorded for larger corpora. Total corpus counts included corpora albicantia and corpora lutea from both the right and left ovaries. Females were classi- fied as sexually mature if at least one corpus was present on either ovary. Corpora were examined externally for indications of regression, including color change (i.e., darken- ing), reduced size and surface furrowing, and were classified by type following Perrin et al. (1976). Results The sample From February to December 1990 and 1991, a total of 707 D. delphis (376 males and 331 females) were examined (see Fig. 1 for approximate collection loca- tions). Sex, length, collection date, and location were recorded for each specimen, and biological samples were collected from 152 of these dolphins (93 males and 59 females). Postnatal growth patterns and the reproductive parameters, average age and average length at sexual matura- tion, were measured by using the por- tion of the dissected sample for which both age and reproductive status were determined (70 males and 43 females). We tested for differences in the length distributions of the total sample and the reproductive sample; no significant dif- ferences were detected (Kolmogorov- Smirnov Test, D=0.18, P>0.05) The total sample (rc=707) was used to examine sex ratios, gestation period, and reproductive seasonality. The spatial and temporal dis- tribution of the total sample reflects the movement of the driftnet fisheries north- ward from February to August, then southward in the fall (Gong et al., 1993; Nakano et al., 1993; Yatsu et al., 1993; Yeh and Tung, 1993; Table 1). Male D. delphis ranged from 0.4 to 27 years in age (n=93): 3% were calves <1 year old (n=3), 23% were yearlings (n=21), and the remainder were >2 years old. Female ages ranged from 0 to 26 years (n=59); one newborn was sampled, 5% were calves <1 year old (n=3), and 32% were yearlings (n = 19). The age distribution of both sexes (Fig. 2) declined intrinsically except between the two youngest age groupings. Males ranged in length from 86 to 211 cm. Females ranged from 81 to 199 cm (Figs. 3 and 4). Stock identification The two recently described species of common dol- phin in the North Pacific Ocean are separable on the basis of cranial morphometries and color pattern (Heyning and Perrin, 1994). To date five cranial speci- mens are available from the driftnet fisheries and of these, one is from an adult animal. The rostral length to zygomatic width ratio for the single adult speci- men (201 cm, male) was 1.36. The mean ratio for adult male short-beaked common dolphin presented in Heyning and Perrin (1994) was 1.37 (SE=0.046). Preliminary comparison of photographs of common dolphins taken in the driftnet fisheries (color pat- tern features are described in Heyning and Perrin [1994]) suggests that our sample more closely re- sembles the short-beaked common dolphin. Further- more, the currently known distribution of both spe- cies of Delphinus presented in Heyning and Perrin (1994) indicates that only the short-beaked form of — rf 8 - 0 A' b °a « . " « ° V * . • * - „ & 3fco« ¥ & /* ° » °# % z* 170°E 180° 170°W 160° Figure 1 Approximate sampling locations of 376 male and 331 female common dol- phin, Delphinus delphis, caught in Japanese, Korean, and Taiwanese drift nets, February to November, 1990 and 1991. 486 Fishery Bulletin 93(3), 1995 Table 1 Number of Delphinus delphis specimens examined from February to December, 1990 and 1991, Japanese, Korean, and Taiwanese drift nets. from latitudes 29°N to 44°N in Month Latitude (in degrees) 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 February 1 9 8 0 0 0 0 0 0 0 0 0 0 0 0 0 March 15 41 92 15 0 0 0 0 0 0 0 0 0 0 0 0 April 0 4 10 103 10 0 0 0 0 0 0 0 0 0 0 0 May 0 0 0 0 0 53 24 0 0 4 0 0 0 0 0 0 June 0 0 0 0 0 0 15 46 59 33 6 8 0 0 0 0 July 0 0 0 0 0 0 0 0 0 2 21 37 2 13 0 0 August 0 0 0 0 0 0 0 0 0 0 1 11 0 5 2 2 September 0 0 0 0 0 0 0 0 0 0 0 0 2 6 0 0 October 0 0 0 0 0 0 0 0 0 0 0 21 12 4 0 0 November 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 December 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 common dolphin extends into the driftnet fisheries area of the central North Pacific Ocean. On the basis of these factors, we pro- visionally assign the Delphinus in our sample to the short-beaked common dolphin D. delphis. Growth Length at birth and gestation period Only two fetuses (65.0 cm and 12.6 cm) and one age-0 neonate (82 cm) were collected; this small sample size limited our ability to calculate a length at birth with the method described by Hohn and Hammond ( 1985) or the modified DeMaster (1978) approach described by Ferrero and Walker (1993). The small sample size of newborns and lack of near-term fetuses also limited esti- mation of the gestation period. However, if we assume that the length of the age-0 neonate ap- proximates the size at birth (82.0 cm) and consider the collection dates and lengths of the two fetuses, then preliminary estimates can be determined. We explored the gestation period parameter in two ways: 1) by using the relationship between fetal length and time described by Hugget and Widdas (1951), and 2) by using the relationship between size at birth and gestation period described for several species of delphinids by Perrin et al. (1977). Following Hugget and Widdas ( 1951), we regressed the lengths (y) of our two fetus specimens and the 10 15 Age (years) Figure 2 Age-frequency distribution of 93 male and 59 female common dolphin, Delphinus delphis, caught in Japanese, Korean, and Taiwanese drift nets, February to November, 1990 and 1991, in the central North Pa- cific Ocean. age-0 neonate (we assumed this animal was recently born given the complete absence of postnatal den- tine) on time, indexed by day of the year of collection (x), in order to estimate the linear phase of growth (t g-t0), where t is the gestation period and tQ is the "nonlinear" phase of growth. The regression equation -57.04 + 0.264* (1) was significant (r2=0.996, P<0.001). The linear growth phase was estimated to be 10.5 months. We did not attempt to estimate the nonlinear phase be- Ferrero and Walker: Growth and reproduction of Delphinus delphis 487 cause an empirical method for doing so is lacking (Perrin and Reilly, 1984). We also used Perrin et al.'s ( 1977) regres- sion equation: Log(y) = 0.1659 + 0.4586 Log(x), (2) substituting x with the length of our age-0 neonate. The D. delphis length at birth es- timate of 82.0 cm approximated the gesta- tion period at 11.1 months. Postnatal growth Growth curves were fit- ted separately for males and females by using a nonlinear least-squares method. The Laird/Gompertz formula (Laird, 1969) was used as a base model for both sexes: L(t) = L0 exp{a[l-exp(-a£)]}, (3) Female D Male I I M il 1 80 90 1 00 110 1 20 1 30 1 40 1 50 1 60 1 70 1 80 1 90 200 Length (cm| Figure 3 Length-frequency distribution of 93 male and 59 female common dol- phin, Delphinus delphis, for which ages were determined. Samples were obtained from Japanese, Korean, and Taiwanese drift nets, Feb- ruary to November, 1990 and 1991, in the central North Pacific Ocean. where L(t) is the length at age t, LQ is the length at birth, t is the age, a is the specific rate of exponential growth, and a is the rate of decay of exponential growth. For both sexes, we fit two Laird/Gompertz curves, one for the sexually mature animals and the other for the sexually immature, in order to minimize the number of positive residuals in the upper curve segment. The low sample size prohibited attempts to it- eratively fit the two curve segments and locate the intersection point. Female growth through age 2 was rapid, with a predicted length at age of 146.4 cm. The predicted asymptotic length was 179.4 cm (Fig. 5). The male growth curve through age 2 was slightly steeper than that portion of the fe- male growth curve, reaching a predicted length at age of 149.8 cm. The predicted asymptotic length was 188.1 cm (Fig. 6). The mean length of females age 16 and older (i.e. those animals likely to have reached maxi- mum size based on the predicted length at age [16 yr] falling on the asymptotic portion of the upper growth curve) was 179.8 cm (n=5, SE=6.76). The mean length of males age 16 and older was 187.1 cm (n=15, SE=5.57). The difference in mean lengths be- tween sexes was significant U-test, one-tailed, P=0.04). Reproduction Sex ratio Sex ratios were estimated for four sub- sets of the aggregate sample of measured animals 80 90 100 110 120 130 140 150 160 170 180 190 200 210 Length (cm) Figure 4 Length-frequency distribution of all common dolphins, Delphinus delphis, examined at sea February-November 1990-91 (376 males and 331 females). Samples were obtained from Japanese, Korean, and Taiwanese drift nets, February to November, 1990 and 1991, in the central North Pacific Ocean. (n=707) to represent progressively older age groups. The predicted length at age from our postnatal growth models (Figs. 5 and 6) were used to separate the sample into four approximate age groups (<1 year, 1 to 10 years, 10 to 15 years, and >15 years) on the basis of length. In addition, we calculated separate sex ratios for the portions of the sample collected north and south of 34°N latitude. The latitudinal break corresponded to a break in the timing of col- lections, splitting February, March, and April sam- pling from the remainder of the year (Table 1). We used the empirical logistic transform method (Cox and Snell, 1989) to estimate sex ratio as 488 Fishery Bulletin 93(3), 1995 8 10 12 14 16 Age (years) 18 20 22 24 26 28 Figure 5 Age at length of female common dolphin, Delphinus delphis, with fitted growth curves (Laird/Gompertz model). The open circles repre- sent mature individuals; the closed circles represent immature indi- viduals. Samples were obtained from Japanese, Korean, and Taiwan- ese drift nets, February to November, 1990 and 1991, in the central North Pacific Ocean. 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Age (years) Figure 6 Age at length of male common dolphin, Delphinus delphis, with fitted growth curves (Laird/Gompertz model). The open circles are mature individuals; the closed circles represent immature individuals. Samples were obtained from Japanese, Korean, and Taiwanese drift nets, Febru- ary to November, 1990 and 1991, in the central North Pacific Ocean. males. Of the sex ratios calculated by using the sample collected from all areas, only the 10 to 15 year-old group ratio (1.792) was significantly different from 1.0 (Exact Bi- nomial Test, P<0.01). When only the por- tion of the sample collected south of 34°N was considered, none of the ratios was sig- nificantly different from 1.0 (P-values were all >0.2). The sample collected north of 34°N yielded a sex ratio significantly different from 1.0 (Exact Binomial Test, P<0.01) in the 10 to 15 year-old group (2.641) (Table 2). Average age at sexual maturation Only preliminary estimates of average age at sexual maturation (ASM) could be calcu- lated owing to the insufficient number of indeterminant age classes represented in the sample. No indeterminant age classes were represented in the female sample. For males we used the DeMaster ( 1978) method which computes the mean age as ASM = £<*(/„-/;_!), (6) a=J where f is the fraction of mature animals in the sample aged a, j is the age of the youngest mature animal in the sample, and k is the age of the oldest immature animal in the sample. Maturity status overlapped one age class in the male sample, where we estimated the variance as var(ASM) = ]£ a=J fad-fa) (Nn - 1) ' (7) where N c aged a. is the total number of animals m + 0.5 ... f + 0.5 where r is the ratio of males to females, m is the number of males, and f is the number of females. The natural logarithm of r is normally distributed with variance, (n + l)(n + 2) var[ln(r)] = (5) n(m+Mf+D where n is the total number of males and females, m is the number of males, and f is the number of fe- Males The preliminary estimate of aver- age age at onset of sexual maturation for males was 10.5 years (SE=0.50). Only at age 10 did both sexually mature and immature specimens appear in the sample. There was a significant linear correlation between testis weight and age among the immature animals (r2=0.83, P<0.01), but the overall increase in testis weight was small (<50 g over 10 years). A linear re- lationship between age and testis weight was not apparent among mature animals (r2=0.15). Testis weight dramatically increased after age 10 (Fig. 7A). The sample contained 21 sexually mature and 50 sexually immature males. The testis weight of the Ferrero and Walker: Growth and reproduction of Delphtnus delphis 489 youngest sexually mature male (10 years) was 370 g; the testis weight of the oldest immature ( 10 years) was 34.6 g. Weights of mature testes ranged from 273.2 to 1,190 g. Females Only a rough approximation of female av- erage age at sexual maturation was determined. The oldest sexually immature female was age 7.2 years, and the youngest sexually mature was 8.5 years. Of the forty-three female reproductive tracts collected, 8 were from mature animals. The youngest sexually mature female had three corpora (Fig. 8A). Of the mature females, three were resting, two were preg- nant, two were lactating and had stage-2 corpora, and one was of unknown status (Table 3). Average length at sexual maturation Calculation of average length at sexual maturation was limited for the male sample because no indeterminant length classes were represented. The female sample was adequate to estimate the parameter. Two methods were used: the DeMaster ( 1978) method, modified to estimate the average length instead of average age, and a logistic regression method. The modification of DeMaster's method, applied to females, used lengths grouped into even intervals as "max LSM= ^hifi-fi-!), (8) '=*mi. where/ is the index ofthe size class with the small- min est mature animal, imax is the index ofthe size class with the largest immature animal, lt is the lower limit ofthe ith size class, and fl is the fraction mature in the z'th size class. The variance estimate on female LSM was ob- tained by modifying the formula of DeMaster (1978) to account for the interval width (w) so that Table 2 Sex ratios for four age groups of Delphinus delphis. Pre- dicted lengths at age from the Laird/Gompertz growth model were used to determine the upper limits for each group (i.e. 125 cm, both sexes <1 year; 171 cm for males and 169 cm for females aged 1 to 10 years; 187 cm for males and 179 cm for females aged 10-15 years). Sex ratios sig- nificantly different from 1.0 (o=0.05) are marked with an asterisk. SE = Standard error. Area and age groups No. of individuals Male Female Sex ratio SE All areas <1 1-10 10-15 >15 South of 34°N latitude <1 1-10 10-15 >15 North of 34°Nlat < 1 1-10 10-15 >15 32 41 0.7831 0.2342 182 161 1.1362 0.1079 90 50 1.7921* 0.1756 71 79 0.8994 0.1630 ude 11 18 0.6216 0.3750 78 72 1.0828 0.1629 39 31 1.2540 0.2388 24 35 0.6901 0.2625 ude 21 23 0.9149 0.2985 105 89 1.1788 0.1437 51 19 2.6410* 0.2649 47 44 1.0674 0.2086 var(LSM) = w^ N.-l (9) where Nt is number of individuals in the ith size class and the interval width (w) was constant. The logistic regression (Cox and Snell, 1989) fits a logistic curve, (u(a)), the probability that a dolphin Table 3 Age, length, corpus count, and reproductive condition for eight mature female Delphinus delphis taken Taiwanese drift nets in the central North Pacific Ocean from February to December, 1990 and 1991. in Japanese, Korean, and Specimen number Collection date Length ( :m) Age (years) Corpus count Reproductive condition RAT 036 23 Sep 90 170 10 1 Pregnant EJW 037 25 Sep 90 172 8.5 3 Unknown RAT 050 3 Oct 90 180 26 8 Resting JAS 045 28 Mar 91 185 16.5 3 Pregnant JAS 062 4 Jun 91 187 22.5 5 Resting JAS 071 7 Jun 91 181 10 7 Lactating JAS 109 26 Jun 91 177 26 6 Lactating JAS 121 17 Jul 91 170 16.5 2 Resting 490 Fishery Bulletin 93(3). 1995 1200 1000 - "5 ~ 800 c a | 600 S3 s 40° 200 0 _» M«l.f*««» 12 16 Age (years) 20 24 28 200 000 B CO o o o 800 o o 0 600 o o 400 o o o 200 0 _ -,— |-Tt' •• V ■•,.,. 110 120 130 140 1 50 1 60 1 70 Length (cm} 180 190 200 210 Figure 7 (A) Scatterplot of age (years) and testis weight (g) for 93 male com- mon dolphin, Delphinus delphis. The open circles represent mature individuals; the closed circles represent immature individuals. Samples were obtained from Japanese, Korean, and Taiwanese drift nets, February to November, 1990 and 1991, in the central North Pacific Ocean. (B) Scatterplot of length (cm) and testis weight (g) for 93 male Delphinus delphis. The open circles represent mature indi- viduals; the closed circles represent immature individuals. Samples were obtained from Japanese, Korean, and Taiwanese drift nets, Feb- ruary to November, 1990 and 1991, in the central North Pacific Ocean. Males Length at sexual maturation could only be suggested by the largest immature male, 179 cm, and the smallest mature male, 182 cm. There was a significant lin- ear correlation between length and indi- vidual testis weight among immature ani- mals (r2=0.61, P<0.0001). Testis weights changed little with length up to the onset of sexual maturity when weights increased greatly (Fig. 7B). No correlation between length of mature animals and testis weights was detected (P>0.4). Females Female average length at sexual maturation based on the DeMaster (1978) method was 172.8 cm (SE=0.56). With the logistic method, female LSM was 170.7 cm (SE=2.74). The smallest sexually mature female measured 170 cm; two corpora were present on the left ovary. The largest sexu- ally immature female was 178 cm (Fig. 8B). Ovulation rate Calculation of ovulation rate followed methods used for Stenella attenuata in Perrin et al. (1976). The aver- age reproductive age ( A ) in interval p was calculated as (11) / p 7 a &, N V i J of length / is mature, to the distribution of mature and immature animals by age: ,16+c (10) 1 + e lb+c where, I is the length of the dolphin and b and c are the slope and intercept of the regression. Average length at sexual maturation is then estimated as the age where \i(a) = 0.50 so that LSM = -c/b. The regression was done by using a maximum like- lihood and iteratively reweighted least-squares al- gorithm (Chambers and Hastie, 1992). The standard error for Li was obtained by transforming the stan- dard error of the linear fit. where a is the percent maturing in the j'th interval, b is the average reproductive age in interval p of females which matured in i, and c is the percent mature in interval p. The average corpus count in each age in- terval was calculated by dividing the sum of corpora counted in interval i by the number of ma- ture females in interval i. We then regressed the aver- age corpus count on the average reproductive age. Ovarian scars numbered from 1 to 8 corpora among mature females. A linear model provided the best fit to the corpus count and average reproductive age data(r2=0.61,P<0.1). Seasonality Evidence of reproductive seasonality was detected by correlating age and length on collec- tion date. From the aged portion of the sample we regressed ages of specimens <0.5 years (n=5) and the day of the year of collection using a linear model that resulted in the equation y= 158.76 + 265.14*, (12) Ferrero and Walker: Growth and reproduction of Delphinus delphis 491 where x is age and y is the day of the year of collection. At age 0.0, the intercept corre- sponds to a date in early June, suggesting the calving mode. Both the slope and the intercepts were significant (P<0.001 and P<0.05, respectively). We also regressed the lengths of speci- mens <115 cm from the overall sample (ti=30) with day of the year. The 115-cm length corresponded to ages slightly older than 0.5 year for both sexes according to the predicted length-at-age relationship from the Laird/Gompertz growth model. We obtained the equation y = -133.44 + 3.435*, (13) where x is the length andy is the day of the year. Substituting 82 cm, our provisional length at birth, for x, the line intercepts a date in mid-May Both the age- and length- based regressions suggest a seasonal peak in mid-May or early June. The lengths and dates of collection for the two fetuses also support this modal peak. The 65-cm fetus collected 28 March 1991 and the 12.6-cm fetus collected 23 September 1990 were projected to reach full-term in late May to early June. Discussion 8 - 7 I 6 5 o 3 o 2 12 16 Age (years) 20 24 28 8 T 7 6 3 2 115 B 125 135 145 155 165 Length (cm) 175 185 195 The structure of the D. delphis sample sug- gested that it was suitable for preliminary estimation of several basic growth and re- production parameters, although our val- ues would be improved with larger sample sizes. With uncertain prospects for collect- ing additional D. delphis samples, owing to the discontinuation of the high seas squid driftnet fisheries and thus any associated sampling programs, we attempted to provide as much quantitative analy- sis as possible; however, we must regard many of our estimates as provisional. In particular, more reliable estimates of ASM and LSM will require more samples in the indeterminant age and length classes. Strong evidence of seasonality in calving made this sample unsuitable for calculation of calving interval, length of lactation, age of weaning, length of resting period, or reproductive rates. Our application of the double Laird/Gompertz growth model is consistent with methods applied in previous growth studies on small cetaceans (Perrin et al., 1976, 1977), although our sample was not large enough to iteratively fit an intersection point between Figure 8 (A) Scatterplot of age (years) and total corpus count for 59 female, common dolphin, Delphinus delphis. The open circles represent ma- ture individuals; the closed circles represent immature individuals. Samples were obtained from Japanese, Korean, and Taiwanese drift nets, February to November, 1990 and 1991, in the central North Pa- cific Ocean. (B) Scatterplot of length (cm) and total corpus count for 59 female Delphinus delphis. The open circles represent mature indi- viduals; the closed circles represent immature individuals. Samples were obtained from Japanese, Korean, and Taiwanese drift nets, Feb- ruary to November, 1990 and 1991, in the central North Pacific Ocean. the upper and lower curves. While our application of the two-stage model suggests a secondary growth surge near the onset of sexual maturation, the mag- nitude and timing of that event should not be con- sidered reliable without further sampling. We attempted to fit a single Laird/Gompertz model to both the male and female data sets, but in both cases we encountered a preponderance of positive residuals at predicted lengths at age >10 years. Using the single curve, we predicted asymptotic lengths for both sexes at least 10 cm lower than any of the observed lengths for mature specimens. Our results from the double Laird/Gompertz model pro- vide predicted length-at-age relationships with com- paratively smaller residuals, distributed both posi- tively and negatively at older ages. 492 Fishery Bulletin 93(3). 1995 Very few neonates, pregnant females with near- term fetuses, or lactating females, were collected even though we found strong evidence for a calving mode during the sampling period. We considered three possible factors to explain the inconsistency: 1) dif- fering entanglement rates by various age and sex strata, 2) temporal disproportion in sampling effort, especially during the projected peak of the calving season, and 3) population segregation. Following the same rationale developed for sam- pling L. borealis in Ferrero and Walker (1993), we did not consider the potential for bias as a result of the sampling method (i.e. incidental take in drift nets) to be a major factor. Delphinus delphis entangle- ments were scattered randomly along the length of the nets. Multiple entanglements were rare. The entanglements, therefore, appear to arise as indi- vidual events rather than as whole school encoun- ters. Consequently, the sample likely reflects the com- position of the population in the area rather than the composition of an individual school. There is also no evidence to assume that neonates or pregnant fe- males avoid entanglement more than other age or sex strata. Regarding the second possibility, the temporal dis- tribution of the sample does not reflect low sampling effort during the late spring and early summer months. The peak in sampling effort occurred in June, and over 75% of that effort was accomplished in March-June. Thus, the absence of neonates and parturient females in the sample did not result from inadequate collection effort at that time. Population segregation appears to be a likely fac- tor in contributing to the small number of neonates and parturient females in our samples, and its effect is reflected in our sampling where collection locations tracked the northerly progress of the fishery. Our only advanced-term fetus was collected at the southern end of the study area in March. As the sampling ef- fort moved northward, the parturient or lactating females and calves probably remained to the south and were unavailable for sampling. The remaining part of the female population appeared to have been represented in the sample. The age and length distributions also reflect the likelihood that a significant portion of the female population was missing from the sample. The sex ratios calculated for specimens collected in areas south of lat. 34°N were not significantly different from 1.0; however, north of 34°N the ratio signifi- cantly differed from 1.0, favoring males in the 10 to 15 year-old age group. Furthermore, in the 15+ age group the sex ratio was not significantly different from 1.0 which is inconsistent with data for other delphinid species characterized by a greater propor- tion of mature females in the population (see Table 8 in Perrin and Reilly, 1984). Our age and length dis- tributions, which suggest a male-dominated ratio, better describe only the part of the D. delphis popu- lation inhabiting the northern portion of the study area during the fishing season. These distributions and the sex ratio, therefore, should not be consid- ered indicative of the overall population structure. Schooling segregation by age, sex, and reproduc- tive status has been demonstrated for numerous spe- cies of delphinid cetaceans (Perrin and Reilly, 1984); Delphinus delphis is among this group. Schooling segregation of D. delphis has been documented in the Black Sea where during calving and early lacta- tion, females occur predominantly in offshore waters (Kleinenberg, 1956; Tomlin, 1957). Our preliminary estimate of 11.1 months for ges- tation is similar to published accounts for the com- mon dolphin. Gestation periods ranging from 10 to 11 months have been reported for D. delphis (Kleinenberg, 1956; Tomlin, 1957; Harrison, 1969). Growth curves for North Pacific D. delphis have not been published and little definitive information on age and length at the onset of sexual maturation is available. Gurevitch and Stewart3 reported that male D. delphis in the eastern tropical Pacific Ocean (central tropical population) reach sexual maturity around 6-7 GLG's, at a mean length of 200 cm. Hui (1979) presented data on Delphinus from southern California where females were reported to attain sexual maturity around 7-14 GLG's, and males be- tween 8 and 12 GLG's. Length at onset of sexual maturation was 165-182 cm for females and 175- 190 cm for males. Our preliminary estimates of age and length at sexual maturation for both sexes fall within the ranges presented in Hui ( 1979). However, comparisons of our findings on the short- beaked D. delphis from the North Pacific transition zone with those from the southern California sample of Hui (1979) are potentially misleading, given re- cent evidence for the occurrence of two sympatric species of common dolphin in the southern Califor- nia area (Heyning and Perrin, 1994). These two spe- cies, D. bairdii and D. delphis, are documented to differ markedly in overall size, and it is possible that Hui's (1979) sample contained members of both these species, accounting for the wide ranges in lengths at sexual maturation. In addition, differences in ages at onset of sexual maturation between our sample 3 Gurevitch, V. S., and B. S. Stewart. 1978. Structure of kill of the common dolphin, Delphinus delphis, from the eastern tropi- cal Pacific in 1977. Final Rep. for Contract 03-78-M02-0101, Southwest Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 8604 La Jolla Shores Dr., La Jolla, CA 92038, 19 p. Ferrero and Walker: Growth and reproduction of Delphinus delphis 493 and those presented in Hui ( 1979) and Gurevitch and Stewart3 may be due to ageing methods. Both these studies employed an early technique of reading undecalcified, thin sections of formic-acid-etched teeth. This method is now considered imprecise for ageing small cetacean teeth (Perrin and Myrick, 1981 ). Perryman and Lynn ( 1993) documented reproduc- tive seasonality differences between three morpho- logically distinct common dolphin populations from adjacent but differing habitats in the eastern North Pacific Ocean. Calving season in the tropical region was year-round. In the temperate regions, which are characterized by a wider range of oceanographic con- ditions, strong evidence of reproductive seasonality was evident. Our sample suggests evidence for a May-June calv- ing peak as well as for schooling segregation of par- turient females in the southern regions of the tran- sition zone, closer to the subtropical domain. Evi- dence for pronounced reproductive seasonality should be anticipated in this region because the North Pa- cific transition zone is characterized by extreme oceanographic conditions, particularly in the north- ern regions adjacent to the subarctic frontal zone (Roden, 1991). Acknowledgments The authors thank Rod Hobbs, Anne York, and Jim Lerczak for statistical advice and assistance with the growth models. Our special thanks go to Jack Cesarone for his preparation of tooth and reproduc- tive tissue samples. Editorial reviews by Howard Braham, Dale Rice, Doug DeMaster, Kim E. W. Shelden, Gary Duker, James Lee, and two anony- mous reviewers helped improve the manuscript. Our sincere appreciation is also extended to the 1990 and 1991 observer teams for their work collecting bio- logical samples on Japanese, Korean, and Taiwan- ese fishing vessels. Literature cited Banks, R. ( '., and R. L. Brownell. 1969. Taxonomy of the common dolphins of the eastern Pacific Ocean. J. Mammal. 50:262-271. Brownell, R. L. 1964. Observations of Odontocetes in central California waters. Norsk Hvalf. - Tid. 53:60-66. Chambers, J. M., and T. J. Hastie. 1992. Statistical models in S. Wadsworth and Brooks, Pacific Grove, CA, 608 p. Cox, D. R., and E. J. Snell. 1989. Analysis of binary data, 2nd ed. Chapman and Hill, London, 236 p. DeMaster, D. P. 1978. Calculation of the average age of sexual maturity in marine mammals. J. Fish. Res. Board Can. 35:912-930. Evans, W. E. 1975. Distribution, differentiation of populations, and other aspects of the natural history of Delphinus delphis Linnaeus in the northeastern Pacific. Ph.D. diss., Univ. Calif., Los Angeles, CA, 145 p. 1982. Distribution and differentiation of stocks of Delphi- nus delphis Linnaeus in the northeastern Pacific. In Mammals of the sea, Volume 4, p. 45-66. Food and Agri- culture Organization of the United Nations. Ferrero, R. C, and W. A. Walker. 1993. Growth and reproduction of the northern right whale dolphin, Lissodelphis borealis, in the offshore waters of the north Pacific Ocean. Can. J. Zool. 71:2335-2344. Gong, Y., Y. S. Kim, and S. J. Hwang. 1993. Outline of the Korean squid gillnet fishery in the North Pacific. In J. Ito, W. Shaw, andR. L. Burgner(eds.), Symposium on biology, distribution and stock assessment of species caught in the high seas driftnet fisheries in the North Pacific Ocean at Tokyo, Japan, 4 to 6 November 1991. Int. North Pac. Fish. Comm. Bull. 53(D:45-70. Gurevitch, V. S., B. S. Stewart, and L. H. Cornell. 1981. The use of tetracycline in age determination of com- mon dolphins. In W. F. Perrin and A. C. Myrick Jr. (eds.), Age determination of toothed whales and sirenians, p. 165- 169. Int. Whaling Comm. Rep. (Special Issue 3). Harrison, R. J. 1969. Reproduction and reproductive organs. In H. T Anderson (ed.), The biology of marine mammals. Acad. Press, New York and London, 551 p. Harrison, R. J., R. L. Brownell Jr., and R. C. Boyce. 1972. Reproduction and gonadal appearances in some odontocetes. In R. J. Harrison (ed.), Functional anatomy of marine mammals, Vol. 1, p. 361-429. Acad. Press, New York and London, 451 p. Heyning, J. E., and W. F. Perrin. 1994. Evidence for two species of common dolphin (genus Delphinus) from the eastern North Pacific. Los Angeles County Mus. Contrib. Sci. 442:1-35. Hobbs, R. ( '., and L. L. Jones. 1993. Impacts of high seas driftnet fisheries on marine mammal populations in the North Pacific. In J. Ito, W. Shaw, and R. L. Burgner ( eds. ), Symposium on biology, dis- tribution and stock assessment of species caught in the high seas driftnet fisheries in the North Pacific Ocean at Tokyo, Japan, 4 to 6 November 1991. Int. North Pac. Fish. Comm. Bull. 53(III):409-434. Hohn, A. A., and P. S. Hammond. 1985. Early postnatal growth of the spotted dolphin, Stenella attenuata, in the offshore eastern tropical Pacific. Fish. Bull. 83:553-566. Hugget, A., St. G. ,and W. F. Widdas. 1951. The relationship between mammalian foetal weight and conception age. J. Physiol. 114:306-317. Hui, C. A. 1973. Age correlations in the common dolphin, Delphinus delphis Linnaeus. Master's thesis, San Diego State Univ., 64 p. 1979. Correlates of maturity in the common dolphin, Del- phinus delphis. Fish. Bull. 77:295-300. Kasuya, T. 1971. Consideration of distribution and migration of toothed whales off the Pacific coast of Japan based upon aerial sight- ing record. Sci. Rep. Whales Res. Inst. (Tokyo). 23:37-60. 494 Fishery Bulletin 93(3). 1995 Kleinenberg, S. E. 1956. Mlekopitauishchenie Chernogo i Azovskogo Morei. (Mammals of the Black Sea and Sea of Azov). Akad. Nauk., Moscow [Translation series No. 4319, Fisheries and Ma- rine Service, Quebec, 1978], 428 p. Laird, A. K. 1969. The dynamics of growth. Research/Develop. 2(X8):28-31. Myrick, A. ( '., Jr., A. A. Hohn, P. A. Sloan, M. Kimura, and D. O. Stanley. 1983. Estimating age of spotted and spinner dolphins (Stenella attenuata and Stenella longirostris) from teeth. U.S. Dep. Commer, NOAA Tech. Memo. NMFS SWFC-30, 7 p. Nakano, H., K. Okada, Y. Watanabe, and K. Uosaki. 1993. Outline of the large-mesh driftnet fishery of Japan. In J. Ito, W. Shaw, and R. L. Burgner (eds.), Sym- posium on biology, distribution and stock assessment of species caught in the high seas driftnet fisheries in the North Pacific Ocean at Tokyo, Japan, 4 to 6 November 1991. Int. North Pac. Fish. Comm. Bull. 53(I):25-38. Nishiwaki, M. 1967. Distribution and migration of marine mammals in the North Pacific area. Bull. Ocean Res. Inst. Univ. (To- kyo). 1:1-64. Norris, K. S., and J. H. Prescott. 1961. Observations on Pacific cetaceans of California and Mexican waters. Univ. Cal. Publ. Zool. 63:291-402. Ogawa, T. 1937. Studies on the Japanese toothed whales, I-rV. Bot. Zool. 4:1936-1937. [English summary.] Ohsumi, S. 1972. Catch of marine mammals, mainly of small cetaceans by local fisheries along the coast of Japan. Bull. Far Seas Fish. Res. Lab., Shimizu, Japan. 7:137-166. Perrin, W. F., and A. C. Myrick Jr. (eds.). 1981. Age determination of toothed whales and sirenians. Int. Whaling Comm. Rep. (Special Issue 3), Cambridge, U.K. Perrin, W. F., and S. B. Reilly. 1984. Reproductive parameters of dolphins and small whales of the family Delphinidae. In W. F. Perrin (ed.), Reproduc- tion in whales, dolphins and porpoises, p. 97-133. Int. Whal- ing Comm. Rep. (Special Issue 6), Cambridge, U.K. Perrin, W. F., J. M. Coe, and J. R. Zweifel. 1976. Growth and reproduction of the spotted porpoise, Stenella attenuata, in the offshore eastern tropical Pacific. Fish. Bull. 74:229-269. Perrin, W. F., D. B. Holts, and R. B. Miller. 1977. Growth and reproduction of the eastern spinner dol- phin, a geographical form of Stenella longirostris in the eastern tropical Pacific. Fish. Bull. 75:725-750. Perrin, W. A., M. D. Scott, G. J. Walker, and V. L. Cass. 1985. Review of geographical stocks of tropical dolphins (Stenella spp. and Delphinus delphis) in the eastern Pacific. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 23, 28 p. Perryman, W. L., and M. S. Lynn. 1993. Identification of geographic forms of common dolphin (Delphinus delphis) from aerial photogrammetry. Mar. Mammal Sci. 9(21:119-137. Ridgway, S. H., and R. F. Green. 1967. Evidence for a sexual rhythm in male porpoises, Lagenorhynchus obliquidens and Delphinus delphis bairdi. Norsk. Hvalf. - Tid. 56:1-8. Roden, G. I. 1991. Subarctic-subtropical transition zone of the North Pa- cific: large scale aspects and mesoscale structure. In J. A. Wetherall (ed. ), Biology, oceanography, and fisheries of the North Pacific transition zone and subarctic frontal zone, p. 1-38. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 105, 111 p. Rosel, P. E., A. E. Dizon, and J. E. Heyning. 1994. Genetic analysis of sympatric morphotypes of com- mon dolphin (genus Delphinus). Mar. Biol. 119:159-167. Tomlin, A. G. 1957. Kitoobrazyne [Cetacea]. Vol. DC. In V. G. Heptner (ed.), Zveri SSSR i prilezhaschikh stran [Mammals of the USSR and adjacent countries]. Zveri vostochnoi Evropy i severnoi Azii Akad. Nauk SSR, Moscow, 756 p. [Transl. Israel Prog. Scient. transl. Jerusalem, 1967, 717 p.] Yatsu, A., K. II ira mat su, and S. Hayase. 1993. Outline of the Japanese squid driftnet fishery with notes on the by-catch. In J. Ito, W Shaw, and R. L. Burgner (eds.) Symposium on biology, distribution and stock assess- ment of species caught in the high seas driftnet fisheries in the North Pacific Ocean at Tbkyo, Japan, 4 to 6 November 1991. Int. North Pac. Fish. Comm. Bull. 53(I):5-24. Yeh, S., and I. Tung. 1993. Review of Taiwanese pelagic squid fisheries in the North Pacific. In J. Ito, W. Shaw, and R. L. Burgner (eds.), Symposium on biology, distribution and stock assessment of species caught in the high seas driftnet fisheries in the North Pacific Ocean at Tokyo, Japan, 4 to 6 November 1991. Int. North Pac. Fish. Comm. Bull. 53(11:71-76. AbStfclCt. Controversy concern- ing the validity and accuracy of recent assessment results for giant bluefin tuna, Thunnus thynnus, led us to ex- amine alternative methods of estimat- ing their abundance. In collaboration with a New England giant bluefin tuna industry group, we tested the feasibil- ity of using commercial spotter pilots and aerial photography as a means of obtaining tuna counts in the Gulf of Maine and adjacent New England wa- ters. Nine commercial spotter pilots photographed a total of 126 schools of bluefin tuna during the summer of 1993, representing 13,973 fish, with a maximum one-day count of 4,894. Three spotter pilots contributed nearly 70% of the total photographic effort. Differences in photographic ability and commercial involvement in the fishery appeared to influence spotter pilot par- ticipation. Aerial photographic surveys may provide a means of obtaining area- specific minimum abundance and dis- tribution data for giant and large-me- dium bluefin tuna. The feasibility of direct photographic assessment of giant bluefin tuna, Thunnus thynnus, in New England waters Molly Lutcavage Scott Kraus Edgerton Research Laboratory, New England Aquarium 195 State Street. Boston, Massachusetts 02109 Manuscript accepted 31 January 1995. Fishery Bulletin 93:495-503 (1995). Stock assessments of the highly migratory northern Atlantic bluefin tuna, Thunnus thynnus, are prima- rily based on age-structured and lumped biomass models derived from landings data and various abundance indices (Scott et al., 1993). These production or CPUE (catch per unit of effort) models pro- vide the framework for interna- tional management of the commer- cially valuable bluefin tuna. A prob- lem with CPUE-derived estimates of stock biomass, however, is that they are affected by changes in fish- ing effort, technology, fish density, and the marketplace (Lo et al., 1992). How accurately recent as- sessment models portray seasonal bluefin abundance in the west At- lantic, a fishery with a 1993 catch of 1,047.2 metric tons of giant tuna (>77 inches straight fork length [SFL]) and of large-medium cat- egory tuna (between 70 and 77 inches SFL), remains controversial (Clay, 1991; Suzuki and Ishizuka, 1991; Safina, 1993). Aerial surveys have been used to obtain relative indices of abundance in fisheries worldwide, including northern anchovy (Engraulis mor- dax), jack mackerel (Trachurus symmetricus), menhaden (Breuoor- tia spp.), mullet (Mugil spp.), and other pelagic fishes (Squire, 1961, 1972, 1993; Williams, 1981; Scott et al., 1989; Lo et al., 1992). Estimates of fish biomass from these surveys are based on appraisals of school size in tonnage per unit of area, or by size of remotely detected signals such as bioluminescence or turbid- ity fields. Visual biomass estimates from aerial survey data are rela- tively easy to construct but are dif- ficult to interpret without ground truth or information on surfacing behavior (Lo et al., 1993). In contrast, direct enumeration of pelagic fish is notoriously difficult. In the 1950's, U.S. fisheries scien- tists attempted to count giant blue- fin tuna migrating along the Bahama Banks (Rivas, 1978) and later un- dertook direct assessment with pho- tographic and video techniques (NMFS1). Despite dedicated search time, very few fish were detected during the survey. More recently, other countries have explored aerial and remote sensing methods as a means of calibrating catch-related indices for tuna species. Since 1990, transect surveys have provided es- timates of regional abundance and recruitment indices for southern bluefin tuna, Thunnus maccoyii, in 1 Anonymous. 1975. A study of the applica- tion of remote sensing techniques for de- tection and enumeration of giant bluefin tuna. Rep of Southeast Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA. Contrib. No. 437. 495 496 Fishery Bulletin 93(3), 1995 the Great Australian Bight (Morgan, 1992; Chen and Polacheck2). Aerial surface-detection radar surveys targeting bluefin tuna and other tunas have been explored by the French in the Mediterranean and tropical South Pacific areas (Petit et al., 1992). Recently, members of the New England commer- cial giant bluefin tuna industry suggested that spot- ter pilots might provide a platform to examine the potential applications and limitations of direct visual assessment of giant and large-medium bluefin tuna. In coastal waters off New England, spotter pilots have located surface schools of giant bluefin tuna that are then targeted for capture by harpoon, hook and line, and purse-seine operations. In 1993, the New England Aquarium (NEA) and East Coast Tuna As- sociation (ECTA) initiated a collaborative project in- volving fish spotter pilots locating and photograph- ing surface schools of bluefin tuna normally targeted by the fishery. Our objective was to determine whether aerial photography could be used to provide information on the relative abundance, schooling char- acteristics, and spatial distribution of bluefin tuna. Methods The present study relied on a simple technical frame- work involving only voluntary participation by com- mercial spotters and the use of two cameras, one to photograph tuna schools (for enumeration) and an- other to document school location. Nine commercial spotter pilots participated in this survey while en- gaged in the 1993 seasonal fishery. All fish spotters flew single engine aircraft (models Cessna 172 and 182, Citabria, SuperCub) and were based on Cape Cod or in lower Maine. Four pilots spotted for sein- ing operations, five were associated with harpoon or general category fishing (hook and line), and at least two participated in all three categories. Bluefin tuna were photographed from 23 July to 13 September, when participating pilots ceased activities because fishing quotas were filled. Each pilot was provided with a hand-held 35-mm camera (Nikon N8008s) and an autofocus zoom lens (70-210 mm, F3.5/4.5, SIGMA Corp.) to photograph tuna schools. Synchronized databacks on cameras (Nikon, MF-21) imprinted date and time directly on exposed film. A second viewfinder camera (Shot- master Ultra Zoom, 38-60 mm, f6.9 lens, Ricoh Corp. ) 2 Chen, S. X., and T. Polacheck. Data analysis of the aerial sur- veys ( 1991-1994) for juvenile southern bluefin tuna in the Great Austrialian Bight. 1994 SBT Recruitment Monitoring Work- shop, Hobart, Tasmania. Available from T. Polacheck, CSIRO, Div. Fisheries, GPO Box 1538, Hobart, Tasmania 7001. was mounted overhead in the aircraft cabin to docu- ment positions from onboard global positioning sys- tem (GPS) or LORAN units located in or below the dashboard. Both cameras had auto advance features and were linked via cable so that they were simulta- neously triggered when pilots depressed a remote shut- ter control. A photographic record of position (in TD Loran lines or lat./long. ) could then be provided for each photographically documented tuna school. A digital clock synchronized with the 35-mm camera databack was mounted near the LORAN/GPS within range of the viewfinder camera. We could then verify sequence linkage between frames of tuna schools and locations if film advance speeds were not perfectly matched. Tuna schools were photographed with color slide film (Ektachrome 400 ASA, Kodak), selected for depth of penetration and contrast characteristics (NMFS, 1975; Lockwood et al.3). Lenses were fitted with a circular polarizing filter or haze filter for glare reduction. Aircraft positions recorded by the viewfinder camera were read directly from developed black and white film (Tri-X 400 ASA, Kodak). Pilots were supplied with labelled film canisters and with stamped and coded direct mailers for color processing, and were instructed to mail the film im- mediately when it was finished. Black and white film was returned directly to us and processed locally. Analysis Processed film was logged with an identification code, and a cursory examination was made on a light table with a film eye loupe. Tuna counts were made by projecting selected slides of schools and by visually counting individual fish. Images were enlarged by projection to a standard size (78 x 52 cm) onto a sheet of drafting-quality tracing paper marked with 10 x 10 cm square gridlines. Positions of clearly identifi- able fish were marked and the total tallied per grid square and per slide frame. Upon completion of the tally, each sheet was labelled with the film identifi- cation code, frame number, time, and total fish count. No attempt was made to estimate the total number offish in the school. Since bluefin tuna are fast-swimming, mobile fish, it was possible for pilots to photograph the same school at slightly different locations on a single day. A school might be difficult to distinguish from adja- cent, similarly sized schools. When photographed by a spotter in close succession, these schools had to have distinctly different spatial configurations or had 3 Lockwood, H. E. Technicolor Graphics Services, Inc., Houston, TX 77058. Lutcavage and Kraus: Feasibility of photographic assessment of Thunnus thynnus 497 to be separated by at least one nautical mile (nmi) in order to be tallied independently. Spotters and fish- ermen reported maximum travel rates of 4-10 knots for bluefin tuna in the study area. With the assump- tion that swimming speeds were 10 knots, similarly sized schools photographed by different pilots on the same day had to be far enough apart so that it was unlikely that schools could have travelled from one location to the other in a given time period. Results The bluefin tuna survey area, fish spotter land bases, and locations of photographed schools are depicted in Figure 1. A total of 126 bluefin tuna schools, rep- resenting a cumulative count of 13,973 fish, were successfully photographed by spotter pilots on 17 days out of a 50-day survey period, for a total of 35 pilot-days. Pilots reported that, to the best of their knowledge, they photographed only giant or large- medium bluefin tuna size categories (>70 inches SFLl, those targeted by the New England fishery. The position of surveyed schools, indicated by TD values or lat./long. on the pilot's navigational sys- tem, was established for 56 schools. Numbers offish counted in schools ranged from 5 to 1,294 individu- als (Fig. 2). Total giant and large-medium tuna counts were >1,000 fish on four survey days, with a maxi- mum count of 4,894 tuna on 8 August (Table 1). A data summary of schools for three high count survey days (8-10 Aug) is given in Table 2. From one to four spotters participated on high- count days, but no more than four pilots photographed fish on any given survey day. Spotters photographed schools from 0900 to 1803 h, but the greatest effort occurred during midday between 1200 and 1600 h (Table 3). Spotters report that slack tide (estimated to Figure 1 Aerial survey area for giant bluefin tuna, Thunnus thynnus, in New England waters, July-September 1993. Land bases of participating spotter pilots are indicated by stars. Filled circles indicate positions of photographed tuna schools. 498 Fishery Bulletin 93(3). 1995 30 CO o 25 o - u <" 20 - o i 15 - E, ,0 z - 5 XI n 1 1 o o o ,- CN if) O O o o «- CM o o o o o o >* m o Individuals counted in school (>) Figure 2 Frequency distribution of counts of giant and large-medium bluefin tuna, Thunnus thynnus, schools photographed by spotter pilots in New England waters, July-September 1993. be within one hour of nearest coastal reference) often provides good conditions for locating fish. There was no discernible relation between lunar cycle or estimated slack tide and timing of greatest survey effort. Surface schooling configurations of bluefin tuna, documented during the survey, included "soldiers" (small school of giants, fish swimming abreast in a parabola or straightline formation, Fig. 3A), "cart- wheels" (spinning wheel-like formations, Fig. 3B), surface sheets (Fig. 3C), and densely packed domes (Fig. 3D). Basking sharks and, less frequently, hump- back, fin, and other whales, were also photographed in association with bluefin tuna schools. Discussion Spotting and survey effort Most of the bluefin tuna were photographed over a four-day period in August by only a few of the par- ticipating pilots, indicating that survey effort was strongly affected by environmental conditions and pilot effort. Fish spotters flew on less than half the survey period, grounded largely by inclement weather. They photographed all sizes of bluefin tuna schools, but small to medium-sized schools (>5 counts <200) were located and photographed most fre- quently. Although initially instructed to document schools of any size, some pilots reported not bother- Table 1 Highest count days for aerial photography of bluefin tuna, Thunnus thynnus, in New England waters, July-September 1993. Date7 Count No. of schools No. of pilots 8 Aug 4,894 24 2 22 Aug 2,517 16 4 9 Aug 1,067 15 2 10 Aug 1,275 7 1 1 Full moon 2 August; new moon 17 August. ing to photograph very small schools, particularly on "good" fishing days. Search and photographic efforts of participating fish spotters varied widely, reflecting differences in commercial involvement in the fishery and in moti- vation. For example, one pilot photographed a mini- mum of 6,767 giant and large-medium bluefin tuna over five days under excellent survey conditions. However, his survey effort in hours represented <10% of the estimated 400 total flight hours he expended in the 1993 season. This result suggests that aerial photography of giant bluefin tuna can be accom- plished with a small team of motivated pilots. In con- trast, a fish spotter in partnership with seining op- erations photographed far fewer fish (467) because his total survey effort was limited to the few days permitted for his boat to achieve its seasonal quota. If all nine participating pilots had undertaken simul- taneous surveys throughout the season, more com- plete documentation might have been achieved. Throughout the survey we maintained frequent phone contact with the pilots in an effort to improve the quality of aerial and position photographs. Al- though we were able to count tuna in the majority of submitted frames, there was clearly a learning curve in the spotters' attempts to take high-resolution pic- tures. Blurring from aircraft vibration and underex- posure were the most frequent problems with tuna school photographs. Unreadable Loran frames more often than not resulted from excessive glare on the digi- tal readout, from improper film advance, or because the pilot had shifted position and had subsequently blocked the camera's view of the Loran. This problem could be eliminated if position were electronically logged each time the spotter photographed bluefin schools. Enumeration analysis In general, we assumed that environmental condi- tions were fairly uniform (low wind and sea states, Lutcavage and Kraus: Feasibility of photographic assessment of Thunnus thynnus 499 Table 2 Summary of photographed bluefin tuna, Thunnus thynnus, schools on three highest count survey days in New England waters, July-September 1993. Date Pilot Count Time Latitude (°N) Longitude (°W) 08 Aug g 57 12:53 41°25' 68°57' 08 Aug g 152 12:59 41°25' 68°56' 08 Aug g 186 13:01 41°25' 68°57' 08 Aug g 284 13:09 41°25' 68°57' 08 Aug g 1039 13:15 41°27' 68°55' 08 Aug g 457 13:17 41°26' 68°57' 08 Aug g 371 13:57 08 Aug f 96 14:09 42°27' 69°30' 08 Aug g 26 14:27 41°28' 68°55' 08 Aug g 499 14:28 41°28' 68°55' 08 Aug g 315 14:37 08 Aug g 300 14:58 41°29' 68°55' 08 Aug g 52 15:03 41°28' 68°56' 08 Aug g 95 15:06 08 Aug g 42 15:09 41°29' 68°56- 08 Aug g 85 15:17 41°28' 68°56' 08 Aug g 107 15:31 41°29' 68°55' 08 Aug f 313 15:34 08 Aug g 26 15:35 08 Aug f 85 15:45 08 Aug g 44 15:46 08 Aug g 69 15:54 08 Aug g 176 16:09 41°29' 68°55' 08 Aug g 18 17:37 41°27' 68°57' 09 Aug g 79 12:53 09 Aug g 60 12:58 09 Aug c 64 13:04 09 Aug g 83 13:12 09 Aug g 51 13:19 09 Aug c 22 13:20 4137 68°50 09 Aug g 78 13:23 09 Aug g 94 13:40 09 Aug c 58 14:06 41°39' 68°44' 09 Aug g 62 14:23 41°35- 68°45' 09 Aug g 13 16:00 41°36' 68°47' 09 Aug c 136 16:10 41°40' 68°42' 09 Aug c 73 16:28 41°41' 68°41' 09 Aug c 123 16:31 41038■ 68°40' 09 Aug c 71 16:42 41°42' 69°03' 10 Aug g 262 12:52 41°33' 68°48' 10 Aug g 54 13:04 41034' 68°48' 10 Aug g 209 15:50 41°04' 70°51' 10 Aug g 286 15:58 40°59' 70°47' 10 Aug g 344 16:07 41°06' 70°56' 10 Aug g 74 16:09 41°05' 70°56' 10 Aug g 46 16:26 41°01' 71O02' ' Latitude and longitude have been rounded to nearest degree and minute. good light levels, minimal glare) when schools were photographed. Altitude varied among spotters but seemed to be less important in producing good records than were sea state and light condition. However, spotters photographing large schools at low altitude were occasionally unable to include the entire school within the frame. We enumerated only clearly dis- cernible individuals in schools and in some circum- stances were able to count fish in at least one tier below the surface tier. With smaller schools, particu- larly in "soldier formation" or in surface-oriented groups, we were able to count all members of the school. 500 Fishery Bulletin 93(3). 1995 Ka r ' V, • Figure 3 Examples of giant bluefin tuna school configurations photographed by fish spotters in the 1993 New England waters aerial census: (A) soldiers; (B) cartwheels; (C) surface sheet; and (D) densely packed dome. Limitations of the data Direct enumeration of giant bluefin tuna from aerial survey involves potential sources of error that must be addressed. These include species and size-class identification, differences in surfacing behavior caused by environmental or biological variables, and redun- dant counts as fish migrate through the study area. In the 1993 feasibility study, we identified and resolved only a few of these issues but nevertheless obtained information vital for improving future aerial surveys. We observed small differences (<1%) in medium- size and large school totals when three different individuals examined and counted bluefin tuna in Lutcavage and Kraus: Feasibility of photographic assessment of Thunnus thynnus 501 projected images. Considering that we could enumer- ate only an undefined portion of the entire school, this source of error was considered negligible. Species identification of small tunas by aerial ob- servers can be difficult (Morgan, 1992), but the like- lihood that spotters would mistake other species for giant or large-medium bluefin tuna targeted in this New England fishery is very slight. Commercially valuable schools of yellowfin tuna are rare north of Nantucket Shoals (Mather, 1962; Roffer, 1987), and experienced fish spotters would be unlikely to mis- take targeted bluefin tuna for the smaller yellowfin tuna. Marine mammals aggregate in groups of sizes com- parable to that of giant bluefin tuna schools. Spot- ters have reported that they can easily distinguish giant and large-medium bluefin tuna from small marine mammals by body shape, tail orientation, and color, but identification is primarily made from swim- ming postures and frequency of dorsal flexure. 502 Fishery Bulletin 93(3), 1995 Table 3 Fish spotter photography effort by time of day in New England waters, July-September 1993. Time of day (h:min) No. 3f schools photographed 09:00-09:55 1 10:00-10:59 3 11:00-11:59 3 12:00-12:59 21 13:00-13:59 30 14:00-14:59 17 15:00-15:59 27 16:00-16:59 17 17:00-17:59 6 18:00-18:59 1 Because we did not have direct altimetry capabili- ties, size classes of bluefin tuna photographed in this survey could be generally documented only as large- medium or giants from spotter estimates alone. Spot- ters undoubtedly photographed, and we subsequently counted, some bluefin tuna below commercial size classes (<70 inches SFL). Catch records indicated that lengths of individuals in a school may vary by several inches, but only 10% of a seine catch is al- lowed to be undersized.4 Because a spotter's survival in the commercial fishing industry depends upon size judgments being made before seine boats expend ef- fort to capture schools, there is a strong selection for accuracy (Williams, 1981; Squire, 1993). Despite confidence in spotter estimates (Squire, 1993), adequate documentation and validation of their ability to judge size or biomass are lacking. Research to define the accuracy of New England blue- fin tuna spotter estimates, or to explore alternative methods of establishing lengths of photographed bluefin tuna, are clearly needed. Future surveys must obtain more specific information on size classes of photographed fish in order to be used as a point of reference for present CPUE-based models that use total length to assign year class (Anonymous, 1986). The majority of bluefin tuna schools were photo- graphed in five areas traditionally fished for giant tuna, including Great South Channel, Wilkinson Basin, Piatt's Bank, and Jeffreys Ledge. This group of areas may reflect the past experience of the spot- ters and their unwillingness to search where fish are not usually found; it may also indicate that giant and large-medium-sized tuna exhibit clumped distribu- tions in New England waters, where oceanic frontal systems, bottom topography, and concentration of 4 Foster, K. Gloucester Laboratory. Natl. Mar. Fish. Serv., NOAA, 30 Emerson Ave., Gloucester, MA 01930. Personal commun., March 1994. prey provide favorable feeding and thermal conditions (Laurs et al., 1984; Maul et al., 1984; Roffer, 1987). Clumped distributions make redundant counts an underlying problem for aerial assessments. Lacking GPS capabilities in 1993, we acknowledge that we may have counted bluefin tuna schools more than once be- cause we had insufficient data to precisely locate all photographed schools. We have learned, however, that a given spotter is unlikely to photograph the same school twice over a period of a few hours. Once a spot- ter directs a boat onto a school, he moves to other areas because circling by boat is believed to force the fish down, rendering them difficult to catch for some time. In future surveys, an algorithm incorporating maxi- mum swimming speeds and surfacing behavior could be used to limit redundant counts. Minimum counts based on daily rather than pooled totals would also re- duce counting problems resulting from residence time and sequential movement offish through the study area. Conclusions In this collaborative study neither we nor the ECTA believe that expended effort was sufficient to derive, on any given day, a minimum count of giant and large-medium bluefin tuna in New England waters. To do so would require not only perfect environmen- tal conditions (noted by pilots and fishers as a "show" day) but also the complete cooperation and coordi- nation of efforts by participating pilots. Given that the feasibility survey started relatively late in the fishing season, the latter was a difficult goal to achieve. A fundamental limitation of aerial assessment is that only fish at or near the surface are accounted for, providing only a minimum estimate of school size. Surveyed schools subsequently captured by seiners might help define relations between aerial counts and total biomass, but this relation was established for only one set in the 1993 season. In this case ( 27 Aug), we counted 32 fish at the surface of a tightly domed school that yielded 125 large giants once captured. Factors that govern schooling behavior and aggre- gation dynamics are poorly documented in bluefin tuna and the tunas in general (Mather, 1962; Clark and Mangel, 1979; Partridge et al., 1983). Mather (1962) described bluefin tuna behavior patterns of "pushing, milling, and smashing" in New England waters. We have noted spatial configurations (domes, cartwheels, surface sheets) and soldier groups (Par- tridge et al., 1983) depicted in photographed schools. Understanding the interplay of ecological and envi- ronmental factors that govern aggregation of giant bluefin tuna would help to define biases in direct assessment efforts. For example, giant bluefin tuna Lutcavage and Kraus: Feasibility of photographic assessment of Thunnus thynnus 503 are believed to exhibit the most rigidly defined spa- tial structures in schooling fishes (Partridge et al., 1983). If relations between the surface structure of schools and total biomass were known, surface counts could be adjusted to include an estimate of biomass. In future studies, on-board data loggers might be used to give accurate records of search effort and survey tracks and possibly to determine fish size through direct altimetry from phototelemetry and GPS data. Hydroacoustic trials, Lidar, or remotely operated vehicle analysis undertaken alongside sein- ing operations may provide additional groundtruth information that would allow derivation of indices of abundance (Petit et al., 1992). In spite of limitations faced in the 1993 feasibility study, this preliminary aerial survey provided infor- mation on counts, distribution, and schooling char- acteristics of giant and large-medium bluefin tuna. Direct photographic surveys to obtain minimum counts of giant bluefin tuna may be a practical method of obtaining real-time measures of their rela- tive abundance in New England waters. Acknowledgments This research was conducted under an agreement be- tween the New England Aquarium and the East Coast Tuna Association (ECTA). The following pilots partici- pated in data collection, served as the backbone of this survey, and provided valuable advice on fishery opera- tions: Marc Avila, John Betzner, Wayne Davis, Jim Gly- man, Roger Hillhouse, Ted Malley, Jonathan Mayhew, Norman St. Pierre, and Trip Wheeler. Richard Ruais, ECTA, and participating boat captains supported and funded the study and contributed organizational sup- port. Grant MacNally served as photo consultant and helicopter pilot for film trials. We thank two anony- mous reviewers for helpful comments on the manuscript. Literature cited Anonymous. 1986. Report of the bluefin working group. Miami, Florida, USA. September 1985. Int. Comm. Conserv. Atl. Tunas, Coll. Vol. Sci. Pap., Madrid 24:11. Clark, C. W., and M. Mangel. 1978. Aggregation and fishery dynamics: a theoretical study of schooling and the purse seine tuna fisheries. Fish. Bull. 77:317-329. Clay, D. 1991. Atlantic bluefin tuna (Thunnus thynnus) (L): a review. In World meeting on stock assessment of bluefin tunas: strengths and weaknesses. Inter-Am. Trop. Tuna Commission Spec. Rep. 7, p. 91-179. Laurs, R. M., P. C. Fiedler, and D. R. Montgomery. 1984. Albacore tuna catch distributions relative to environ- mental features observed from satellite. Deep-Sea Res. 31:1085-1099. l.o., N. C. H., I. D. Jacobson, and J. L. Squire. 1992. Indices of relative abundance from fish spotter data based on delta-lognormal models. Can. J. Fish. Aquat. Sci. 49:2515-2526. Mather, F. J., III. 1962. Tunas (genus Thunnus) of the western North Atlan- tic. Part III: Distribution and behavior of Thunnus species. In Symposium on scombroid fishes, Part 1, p. 1- 16. Symp. Series 1, Marine Biological Association of In- dia. Mandapam Camp., India, 564 p. Maul, G. A., F. Williams, M. Roffer, and F. Sousa. 1984. Remotely sensed oceanographic patterns and vari- ability of bluefin tuna catch in the Gulf of Mexico. Oceanol. Acta 7:469-^179. Partridge, B. L., J. Johansson, and J. Kalish. 1983. The structure of schools of giant bluefin tuna in Cape Cod. Envir. Biol. Fishes 9:253-262. Petit, M., J-M. Stretta, H. Farrugio, and A. Wadsworth. 1992. Synthetic aperture radar imaging of sea surface life and fishing activities. IEEE Trans. Geosci. Rem. Sens. 80:1085-1089. Rivas, L. R. 1978. Aerial surveys leading to 1974-1976 estimates of the numbers of spawning giant bluefin tuna (Thunnus thynnus) migrating past the western Bahamas. Int. Comm. Conserv. Atlantic Tunas Coll. Vol. Sci., paper 7, p. 301-312. Roffer, M. A 1987. Influence of the environment on the distribution and relative apparent abundance of juvenile Atlantic bluefin tuna along the United States east coast. Ph.D. diss., Univ. Miami, Coral Gables, FL, 154 p. Safina, C. 1993. Bluefin tuna in the West Atlantic: negligent manage- ment and the making of an endangered species. Conserv. Biol. 7:229-233 Scott, G. P., M. R. Dewey, L. J. Hansen, R. E. Owen, and E. S. Rutherford. 1989. How many mullet are there in Florida Bay? Bull. Mar. Sci. 44:89-107. Scott, G. P., S. C. Turner, C. B. Grimes, W. J. Richards, and E. B. Brothers. 1993. Indices of larval bluefin tuna, Thunnus thynnus, abundance in the Gulf of Mexico; modelling variability in growth, mortality, and gear selectivity. Bull. Mar. Sci. 53:912-929. Squire, J. L. 1961. Aerial fish spotting in the United States commercial fisheries. U.S. Fish. Wild! Serv., Commer. Fish. Rev. 23:1-7. 1972. Apparent abundance of some pelagic marine fishes off the southern and central California coast as surveyed by an airborne monitoring program. U.S. Fish. Wild]. Serv. Fish. Bull. 70:1005-1019. 1993. Relative abundance of pelagic resources utilized by the California purse-seine fishery: results of an airborne monitoring program, 1962-90. Fish. Bull. 93:348-361. Suzuki, Z., and Y. Ishizuka. 1991. Comparison of population characteristics of world bluefin stocks, with special reference to the West Atlantic bluefin stock. Coll. Vol. Sci. Pap. ICCAT Reel. Doc. Vol. 35, No. 2., p. 240-245. Williams, M. 1981. Aerial survey of pelagic fish resources of South East Australia 1973-1977. CSIRO Div. Fish. Oceanogr. Rep. No. 130. Abstract. — The egg and larval de- velopment of Paralichthys albigutta (gulf flounder) and P. lethostigma (southern flounder) are described from laboratory-reared and field-collected specimens. Paralichthys albigutta eggs and oil globules had a mean diameter of 0.87 mm (range: 0.84-0.90 mm) and 0.18 mm (range: 0.17-0.19 mm), respec- tively. Paralichthys lethostigma eggs and oil globules had a mean diameter of 0.91 mm (range: 0.84—0.96 mm) and 0.18 mm (range: 0.16-0.20 mm), respec- tively. Recently hatched P. albigutta larvae ranged from 1.8 to 2.2 mm in notochord length (NL) and P. letho- stigma from 2.0 to 2.2 mm NL. Pigment on embryos and newly hatched larvae was relatively more developed for P. albigutta. Almost-paired and almost- contiguous ventral midline melano- phores occurred on preflexion larvae of both species and remained throughout the larval stages. Pigment on the max- illary, vomer, dorsum of the mid-brain, lateral surface of the caudal area, lat- eral surface of gut, and extent of pig- ment along the ventral midline of the isthmus were used to separate labora- tory-reared P. albigutta from P. letho- stigma. However, this pigment was less useful in separating field-collected ma- terial. The number of cranial spines appeared to be diagnostic in separat- ing laboratory-reared early-preflexion larvae. Paralichthys lethostigma con- sistently had three cranial spines, whereas P. albigutta had less than three spines. The development of mer- istic characters was considered the most useful character in separating P. albigutta from P. lethostigma because at any given size P. albigutta was generally more developed than P. lethostigma. Egg and larval development of laboratory-reared gulf flounder, Paralichthys albigutta, and southern flounder, R lethostigma (Pisces, Paralichthyidae) Allyn B. Powell Beaufort Laboratory, Southeast Fisheries Science Center National Marine Fisheries Service, NOAA 101 Pivers Island Road, Beaufort, North Carolina 28516-9722 Theresa Henley Beaufort Laboratory, Southeast Fisheries Science Center National Marine Fisheries Service, NOAA 101 Pivers Island Road, Beaufort, North Carolina 28516-9722 Present address: 4824 N. Britton Drive Stillwater, Oklahoma 74075 Manuscript accepted 20 March 1995. Fishery Bulletin 93:504-515 (1995). Four species of the genus Para- lichthys occur in southeastern U.S. coastal waters. Paralichthys squa- milentus (broad flounder) is not commonly encountered and is of little commercial or recreational value. Paralichthys dentatus (sum- mer flounder), P. lethostigma (south- ern flounder), and to a lesser extent P. albigutta (gulf flounder) are com- mon and of great commercial and recreational value (N.C. Div. Marine Fisheries1). Paralichthys dentatus range from Maine to Cape Cana- veral, Florida, and P. albigutta and P. lethostigma range from North Carolina to Texas (Gutherz, 1967). Eggs and larvae of P. dentatus have been described (Smith and Fahay, 1970) whereas those of P. albigutta and P. lethostigma have not. Com- parative taxonomic studies of late larvae and early juvenile (fully formed vertebrae, dorsal, and anal rays) P. dentatus, P. lethostigma, and P albigutta have been reported. Deubler (1958) showed that late- larval-early-juvenile P. dentatus can be distinguished from the other two congenera by differences in pig- mentation of the dorsal and anal fins and in vertebral number. The only characters useful for separa- tion of P. lethostigma and P. albi- gutta were dorsal-ray and anal-ray counts. Woolcott et al. (1968) showed that 100% separation of the three species could be obtained through a combination of anal-ray and vertebral counts. However, these characters must be fully formed in order to be diagnostic. Vertebral counts alone cannot be used to separate P. albigutta and P. lethostigma. The objective of this study is to describe the eggs and larvae of labo- ratory-reared P. lethostigma and P. albigutta to provide diagnostic characters for identification of these paralichthyids in field-collected material. 1 North Carolina Division of Marine Fish- eries. 1992. Assessment of North Carolina commercial finfisheries. Completion Rep. for Job 2-IJ-16. North Carojina Div. Mar. Fisheries, Morehead City, NC 28557. 504 Powell and Henley: Larval development of Paralichthys albigutta and P. lethostigma 505 Methods Adult P. albigutta and P. lethostigma were collected in the early fall during 1991 and 1992 from commer- cial pound nets in Core Sound, North Carolina. Indi- vidual fish were tagged and meristic data (gill-raker and anal-ray counts) were used to confirm identifi- cation (Gutherz, 1967). Spawning was induced with the aid of hormones as described by Smigielski ( 1975). For P. albigutta three different females were fertil- ized by a single male. Females were injected with carp pituitary hormone (2 mg/kg fish) two or three times to promote hydration. Eggs were fertilized on 14 and 19 February 1992. For P. lethostigma, a total of four different males and four different females were spawned. Eggs were fertilized on 17 December 1992, 24 February, and 2 March 1993. Eggs and sperm from both species were manually stripped into 1-L bowls; eggs were fertilized, and embryos incubated in 100-L black-sided tanks. Paralichthys albigutta larvae were reared in uncir- culated, filtered water at a mean temperature of 19°C (range: 14-24°C) and a mean salinity of 30 ppt (range: 28-30 ppt). Paralichthys lethostigma larvae were reared at a mean temperature of 18°C (range: 16- 19°C) and a mean salinity of 32 ppt (range: 23-42 ppt). Rotifers and Artemia nauplii were provided to young (<15 days old) and older (>15 days old) larvae, respectively Only three P. lethostigma larvae were alive after approximately 35 days, limiting the amount of material available for this species. Eggs and larvae were preserved in 10% buffered forma- lin. Counts of meristic characters were obtained from cleared and stained specimens (Potthoff, 1984). All measurements and observations were made with a Wild M5A stereomicroscope equipped with an ocu- lar micrometer. The larval period was separated into preflexion, flexion, and postflexion stages — the three stages as- sociated with the development of the caudal fin be- fore, during, and after the upward flexion of the no- tochord tip. During preflexion and flexion, larval body length was measured from the tip of the snout to the tip of the notochord (notochord length, NL). In postflexion larvae (defined when 6 upper + 7 lower principal rays were formed) body length was mea- sured from the tip of the snout to the base of the hypural plate (standard length, SL). Postflexion larvae and transforming juveniles of P. albigutta and P. lethostigma captured in Onslow Bay off North Carolina during the winter of 1990 and 1991 were used for 1) comparison with labora- tory-reared specimens and 2) illustrations and in- vestigation of pterygiophore patterns. This material also was used to determine the size when meristic characters develop for P lethostigma because material from laboratory-reared specimens was limited for this species. Observations on pterygiophore patterns and meristic characters were made on cleared and stained specimens. Larval material is deposited at the Beau- fort Laboratory under the care of the senior author. Results Eggs and recently hatched larvae Paralichthys albigutta Eggs were spherical and had a mean diameter of 0.87 mm (range: 0.84-0.90 mm, n=44). One oil globule was present and had a mean diameter of 0.18 mm (range: 0.17-0.19 mm, n=44). The yolk was homogenous, the chorion smooth, and the perivitelline space (in live eggs) nar- row (ca. 0.2 mm). Pigment was first observed in the caudal area of embryos just after blastopore closure (Fig. 1A). On embryos from late-stage eggs (from tail twisting to hatching), pigment occurred on the oil globule, sparsely in the head region, and was most B Figure 1 Laboratory-reared eggs and newly hatched larvae of gulf flounder, Paralichthys albigutta: (A) middle stage: left, anterior view; right, posterior view; (B) late stage: left, anterior view; right, posterior view; and (C) 2.2-mm-NL newly hatched yolk-sac larva. 506 Fishery Bulletin 93(3), 1995 developed in the caudal area. In the caudal area, melanophores occurred in the dorsal- and anal-fin folds, dorsal and ventral midlines, and sparsely on the lateral surface (Fig. IB). Recently hatched P. albigutta larvae ranged from 1.8 to 2.2 mm NL. The oil globule was located in the posterior portion of the yolk sac (Fig. 1C). Paralichthys lethostigma P. lethostigma eggs had a mean diameter of 0.91 mm (range: 0.84-0.96 mm, n=154), and the oil globule had a mean diameter of 0.18 mm (range: 0.16-0.20 mm, rc=154). Pigment on embryos from middle-stage eggs (just after blasto- pore closure) was less developed than that observed for P. albigutta (Fig. 2A). Like P. albigutta, pigment on P. lethostigma embryos was only observed in the caudal area. Pigment on embryos from late-stage eggs was less developed than that observed for P. albigutta (Fig. 2B). Pigment was observed only in the caudal area on P. lethostigma embryos. Recently hatched P. lethostigma larvae were similar in size to P. albigutta (range: 2.0-2.2 mm NL). Like P. albigutta, the oil globule was located in the poste- rior portion of the yolk sac (Fig. 2C). B Figure 2 Laboratory-reared eggs and newly hatched larvae of south- ern flounder, Paralichthys lethostigma: (A) middle stage: left, anterior view; right, posterior view; (B) late stage: left, anterior view; right, posterior view; and (C) 2.1-mm-NL recently hatched yolk-sac larva. Fin development Paralichthys albigutta Fins began to develop in the following sequence: dorsal and caudal, anal, pelvic, and pectoral (Table 1). The adult complement of rays (Gutherz, 1967; Woolcott et al., 1968; Fahay, 1983) was attained in the following sequence: principal caudal rays (10 upper + 8 lower), dorsal fin (71-85), anal fin (53-63) and pelvic fin (6), and pectoral fin (10-12) (Table 1). The development of the caudal fin, indicated by a thickening of tissue on the ventral side, began at 5.2 mm NL. Caudal-fin rays (2 upper + 2 lower) were first observed at 5.5 mm NL, indicating the begin- ning of the flexion stage. The rays began to form at the middle of the fin and developed dorsally and ven- trally almost simultaneously. The adult complement of principal caudal rays ( 10 upper + 8 lower) was attained at 6.9 mm SL. Dorsal rays were first observed during early flex- ion (5.5 mm NL, Table 1). Dorsal rays first formed in the head region anterior to the first neural spine. They were accompanied by an extension of the dor- sal-fin fold that appeared as a flap (Fig. 3B). Dorsal- fin development proceeded slowly during the flexion stage and more rapidly during postflexion (Table 1). Development proceeded posteriorly; however, the anteriormost ray was not observed until 6.1 mm SL. The anterior rays in the head region, especially the third ray, were elongated (Fig. 3D). The adult comple- ment of dorsal-fin rays consistently was attained at 7.8 mm SL (Table 1). Anal-fin rays began to form on postflexion larvae at approximately 6.1 mm SL (Table 1). Formation began in the vicinity of the first haemal spine and development proceeded anteriorly and posteriorly simultaneously. Anal-fin-ray development was rapid, and by 7.7 mm SL the adult complement of anal-fin rays consistently was observed (Table 1). Pelvic-fin rays were first observed on postflexion P. albigutta larvae at 6.9 mm SL (Table 1 ). All speci- mens >8.5 mm SL had a completed pelvic fin. The pectoral fin persisted as a large rayless blade throughout flexion and early postflexion (Table 1). Rays began to form at 7.1 mm SL at the dorsal posi- tion of the blade and developed ventrally (Fig. 4). All specimens >8.5 mm SL had the adult complement (10-12 rays) of pectoral fin rays (Table 1). Paralichthys lethostigma Fins began to develop in the following sequence: dorsal, caudal, anal, pelvic and pectoral (Table 2). The adult complement of rays (Gutherz, 1967; Wolcott et al., 1968; Fahay, 1983) was attained in the following sequence: caudal fin (10 up- per + 8 lower), dorsal fin (80-95) and anal fin (63-74), pelvic fin (6), and pectoral fin (11-13) (Table 2). Powell and Henley Larval development of Paratichthys albtgutta and P. lethostigma 507 Table 1 Meristic data from cleared and stained laboratory reared gulf floun der, Paralichthys albigutta. Dashed lines separate preflexion, flexion, and postflexion stage larvae Postflexion was defined as tht stage when 6 upper + 7 lower caudal rays were observed. NL = notochord length SL = standard length. Principal Body length Days after Dorsal-fin Anal-fin Pelvic-fin Pectoral-fin caudal rays (mm) hatching rays rays rays rays (upper + lower) 4.5 NL 18 0 0 0 0 0 5.2 NL 19 0 0 0 0 0 5.5 NL 19 3 0 0 0 2+2 5.7 NL 19 2 0 0 0 2+2 5.7 NL 19 2 0 0 0 2+2 5.8 NL 19 3 0 0 0 3+3 5.8 NL 24 5 0 0 0 6+5 6.1 NL 19 2 0 0 0 3+3 6.4 NL 31 4 0 0 0 5+5 5.9 SL 24 9 0 0 0 7+7 6.1 SL 26 15 4 0 0 9+8 6.3 SL 26 16 14 0 0 9+8 6.8 SL 31 55 34 0 0 9+8 6.9 SL 36 72 54 3 0 10+8 7.0 SL 36 68 50 4 0 10+8 7.1 SL 36 68 50 5 1 10+8 7.2 SL 31 62 43 0 0 10+8 7.7 SL 36 74 57 5 3 10+8 7.8 SL 36 69 54 5 5 10+8 7.8 SL 44 75 54 5 9 10+8 8.0 SL 36 72 55 5 5 10+8 8.2 SL 44 72 51 5 5 10+8 8.5 SL 44 71 54 6 10 10+8 8.6 SL 44 74 56 6 10 10+8 10.2 SL 59 74 58 6 11 10+8 10.7 SL 52 73 54 6 13 10+8 The development of the caudal fin began at 5.4 mm NL and was similar to that of P. albigutta, but cau- dal rays were not observed until 6.5 mm NL. The adult complement of principal caudal rays (10 + 8) was attained at 8.2 mm SL (Table 2). Dorsal rays were first observed on a preflexion specimen but were not consistently observed till early flexion (6.5 mm NL, Table 2). The development of dorsal rays was similar to that observed for P. albi- gutta. Complete development of the dorsal-fin rays occurred at approximately 8.4 mm SL. Anal-fin rays began to form on postflexion larvae at approximately 7.3 mm SL. Development was simi- lar to that observed for P. albigutta. Like P. albigutta, anal-fin-ray development was rapid and the anal fin appeared to be completely formed by approximately 8.4 mm SL (Table 2). Pelvic-fin rays were first observed on postflexion larvae (8.2 mm SL, Table 2). All specimens >9.7 mm SL consistently had a completed pelvic fin. Pectoral-fin rays began to form at 8.4 mm SL at the dorsal position of the blade and developed ven- trally. The largest specimen (11.0 mm SL) still had not attained a completed (11-13 rays) pectoral fin (Table 2). Pigmentation of laboratory-reared specimens Paralichthys albigutta Newly hatched P. albigutta larvae had dendritic melanophores on the dorsal and anal finfolds midway between the anus and noto- chord tip (Fig. 1C). Dorsal and anal midline pigment posterior to the anus was well developed. Melano- phores occurred on the trunk and head, on the oil globule, and on the yolk sac (Fig. 1C). Melanophores were observed on the snout on a one-day old larva (2.8 mm NL) but not on newly hatched larvae. Characteristic pigment on preflexion larvae was almost-paired and almost-contiguous dorsal and ven- tral midline melanophores that remained character- 508 Fishery Bulletin 93(3), 1995 Figure 3 Developmental stages of laboratory-reared gulf flounder, Paralichthys albigutta (C=cranial spines, P=preopercular spines). (A) 3.5-mm-NL preflexion larva, 10 days old; (B) 5.8-mm-NL early flexion larva, 25 days old; (C) 6.2-mm-NL late flexion larva, 21 days old; and (D) 7.1- mm-SL postflexion larva, 31 days old. istic throughout the larval stages (Fig. 3 A). The al- most-paired dorsal and ventral midline melano- phores merged into one row of dorsal and ventral punctate melanophores in the future caudal-fin re- gion. The most posterior melanophores generally were opposite each other. The dorsal midline pigmen- tation extended anteriorly to the forebrain. Melano- phores were first observed on the lateral portion of the caudal region at approximately 3.5 mm NL (Fig. 3A). Embedded notochord pigment extended anteri- orly ventral to the brain and continued through the eye, giving the appearance of a stripe through the eye. Pigment occurred over most of the ventral finfold and more prevalently in the middle one-third of the dorsal finfold. In the gut region of preflexion larvae, mel- anophores occurred along the ventral mid- line, extending anterior of the cleithral symphysis and along the lateral surface of the gut. Melanophores occurred along the dorsal surface of the gut as a continu- ation of ventral midline pigment and gen- erally terminated in a distinct melano- phore at the junction of the operculum (Fig. 3A). In most specimens a distinct mel- anophore occurred on the ventral area of the base of the pectoral-fin blade. In the head region, melanophores occurred on the operculum and on the dorsum of the mid- brain (cranial bump). Pigment was first observed on the dorsum of the cranial bump during early preflexion (2.9 mm NL), but only 20% of the specimens examined (n=10) had a melanophore here at this time. With increasing size the cranial- bump melanophore occurred at a greater frequency, and by 4.0 mm NL all speci- mens had a melanophore in this region. In the lower-jaw region, melanophores oc- curred both along the lower-jaw rami and at the lower-jaw angle (Fig. 3A). A punc- tate melanophore was observed on both sides of the premaxilla or maxilla, or both. This pair of melanophores was first ob- served on early preflexion larvae (2.9 mm NL) and was observed on every laboratory- reared specimen examined. Vomerine pig- ment was first observed on 3.2-mm-NL preflexion larvae and occurred thereafter on all specimens examined. Pigment on flexion larvae was similar to that observed on late preflexion larvae (Fig. 3, B and C). Melanophores occurred on the lateral surface of the body in the caudal area on all specimens. The most anterior melanophore on the dorsal surface of the gut at the junction of the operculum was stellate and was seemingly isolated from the other gut pigmen- tation (Fig. 3, B and C). Pigment occurred along the proximal base of the developing caudal-fin rays. In the late flexion stage (6.4 mm NL), pigment first appeared on the third elongated dorsal ray. Most of the lateral surface of the hind gut was pigmented. The ventro-lateral surface of the mid- and foregut was pigmented (Fig. 3, B and C). On early postflexion larvae (Fig. 3D), pigment was observed on the base of the caudal fin and on the Powell and Henley: Larval development of Paralichthys albigutta and P lethostigma 509 B Figure 4 Developmental stages of transforming, postflexion laboratory-reared gulf flounder, Paralichthys albigutta (P=preopercular spines). (A) 8.2-mm-SL larva, 34 days old; (B) 9.0-mm-SL larva, 45 days old. pelvic fin. Melanophores on the lateral surface of the body in the caudal area began to align with the myosepta. Pigment on the lateral surface of the body increased with increasing size (Fig. 4). The extended third dorsal ray was pigmented, and pigment was scattered on the developing dorsal- and anal-fin rays. This pigment increased in area during development (Fig. 4). Pigment was scattered in no apparent pat- tern medially on the dorsal- and anal-fin ptery- giophores. The anal-fin pterygiophores were rela- tively more pigmented than those on the dorsal fin. Pigment increased in these areas during development (Fig. 4). The characteristic almost-paired, almost- contiguous dorsal and ventral midline pigment was located at the proximal edge (base) of the dorsal- and anal-fin pterygiophores. Pigment in the head region of early postflexion larvae was similar to that of flex- ion larvae (Fig. 3D) but increased in intensity dur- ing development (Fig. 4). During transformation, P. albigutta larval body pigment increased in intensity (e.g. compare Fig. 4, A and B). Melanophores occurred along the entire base of the caudal fin, but most of the fin was not pigmented. A blotchy pigment pattern was observed on the pterygiophores, caudal peduncle, and lateral line from mid-body anterior to the cleithrum. Mel- anophores along the lateral line from mid-body to the caudal peduncle formed a streak of pigment in later transforming larvae (ca. 8.7 mm SL). Numer- ous melanophores on the lateral surface of the cau- dal area were aligned with the myosepta. This pig- ment occurred mainly in the posterior two-thirds of the caudal area and extended more anteriorly in the dorsolateral area (Fig. 4). The dorsal and anal fins were pigmented along the entire length of their base (i.e. proximally). On the medial portion of the dor- sal- and anal-fin rays on earlier (ca. 7.8 mm SL) trans- forming larvae, pigment appeared as blotches on the 510 Fishery Bulletin 93(3), 1995 Table 2 Meristic data from cleared and stained laboratory-reared and field-collected southern flounder, Paralichthys lethostigma. Dashed lines separate preflexion, flexion, and postflexion stage larvae. Postflexion was defined as the stage when 6 upper + 7 lower caudal rays were observed. An asterisk indicates field-collected material. NL = notochord length; SL = standard length. Body length Days after Dorsal -fin Anal-fin Pelvic-fin Pectoral-fin Principal caudal rays (mm) hatching rays rays rays rays (upper+lower) 4.7 NL 20 0 0 0 0 0 4.9 NL 20 0 0 0 0 0 5.4 NL 20 0 0 0 0 0 6.2 NL 31 2 0 0 0 0 6.4 NL 24 0 0 0 0 0 6.5 NL 31 6 0 0 0 5+5 6.6 NL 31 5 0 0 0 4+4 6.8 NL 31 4 0 0 0 4+3 6.9 NL 31 5 0 0 0 6+6 6.9 NL 35 6 0 0 0 6+6 7.0 NL 40 5 0 0 0 5+5 7.1 NL 35 6 0 0 0 6+6 6.7 SL 39 13 0 0 0 7+8 6.7 SL * 13 0 0 0 9+8 6.7 SL * 10 0 0 0 9+8 7.3 SL * 14 13 0 0 7+6 7.3 SL 48 9 0 0 0 7+8 7.8 SL * 68 41 0 0 9+8 8.2 SL * 84 65 5 0 10+8 8.4 SL * 90 71 5 2 10+8 8.7 SL * 90 70 5 2 10+8 9.2 SL 40 82 62 6 0 10+8 9.2 SL * 83 64 6 5 10+8 9.7 SL * 85 67 5 1 10+8 9.8 SL * 87 63 6 2 10+8 9.8 SL * 87 65 6 4 10+8 10.2 SL * 85 64 6 6 10+8 11.0 SL * 86 63 6 9 10+8 anterior and midbody surfaces of the fins and gradu- ally expanded over the medial portion with develop- ment (Fig. 4). Paralichthys lethostigma Newly hatched P. letho- stigma larvae had melanophores on the dorsal and anal finfolds that were concentrated in the middle of the body (Fig. 2C). Dorsal midline pigment was well developed and generally occurred from the anterior portion of the caudal region to the head and snout. There were fewer melanophores on the dorsal and ven- tral midline posterior to the anus (i.e. in the caudal region). Pigment was observed on the oil globule. Like P. albigutta, characteristic pigment on P. letho- stigma preflexion larvae was almost-paired and al- most-contiguous dorsal and ventral midline melano- phores that merged into one row of dorsal and ven- tral melanophores in the future caudal-fin region (Fig. 5A). On very early preflexion larvae (2.8-3.0 mm NL) that still contained vestiges of yolk and oil, the dorsal midline melanophores were continuous over the brain and snout, and the ventral midline melanophores were continuous over the gut. Melano- phores on the lateral portion of the caudal region were not observed on early preflexion larvae (ca. <3.6 mm NL) and were not as well developed on later preflexion larvae compared with P. albigutta larvae (Figs. 3A and 5A). In the gut region of preflexion P. lethostigma, the lateral portion of the gut was typi- cally devoid of pigment (Fig. 5A) and was never as well developed as that observed for P. albigutta (Fig. 3A). Usually, ventral melanophores in the gut region Powell and Henley: Larval development of Paralichthys albigutta and P. lethostigma 5! 1 were not continuous because a gap appeared just anterior to the anus. Regularly, we observed a pair of melanophores located ventrally on each side of the hindgut. The pecto- ral-fin-ray blade was pigmented. Pigmentation of preflexion P. letho- stigma at the base of the pectoral fin and in the head region was simi- lar to that observed for P. albigutta (Figs. 3A and 5A). Pigment on the maxillary and the dorsum of the midbrain (cranial bump) was less frequently observed in preflexion P. lethostigma larvae compared with preflexion P. albigutta larvae. Cra- nial bump pigment was observed on 36% of the specimens and maxillary pigment on 64% of the specimens (rc=25). Pigment on the vomer of preflexion P. lethostigma also oc- curred less frequently (36% of the specimens had this pigment; n-15); however, this pigment was difficult to discern. It was most effectively seen on fresh, cleared and stained material. Ventral pigment on the isthmus, anterior to the cleithrum, did not extend the full length of the isthmus as was observed on pre- flexion P. albigutta (Figs. 3A and 5A). The number of melanophores observed on the operculum (com- monly one) was less than that ob- served for P. albigutta. Pigment on flexion P. lethostigma larvae was similar to that observed on later preflexion larvae (Fig. 5B). Melanophores were observed on the lateral side of the caudal region; however, they were less organized than those observed for P. albigutta, which appeared to be more banded in appearance. During flexion, pigmentation in- creased on the lateral surface of the hindgut. Dorsal finfold pigmentation was sparse and located at midbody. Ventral finfold melanophores occurred along the distal margin and on the finfold surface at midbody. A melanophore was observed at the ven- tral edge of the pectoral-fin blade, and a distinct melanophore was observed at the junction of the dorsalmost portion of the opercle and the anter- iodorsal portion of the gut. This characteristic pig- mentation was observed for both species. Pigmenta- tion along the ventral midline of the isthmus in- D Figure 5 Developmental stages of laboratory-reared southern flounder, Paralichthys lethostigma (C=cranial spines, P=preopercular spines). (A) 3.3-mm-NL early preflexion larva, 9 days old; (B) 6.4-mm-NL late preflexion larva, 24 days old; (C) 7.7-mm-SL postflexion larva, 45 days old; and (D) 9.1-mm-SL transforming postflexion larva, 40 days old. creased to cover the entire isthmus. Like P. albigutta, melanophores were typically observed on the maxil- lary and the dorsum of the midbrain, but vomerine pigment was irregularly observed on flexion P. lethostigma larvae. Pigmentation (1^1 melanophores) occurred on the opercular region posterior to the eye. Melanophores along the edge of the interopercle and subopercle were first observed on flexion larvae. On postflexion larvae (6.4-9.3 mm SL), pigment was observed at the base of the caudal fin and on the pelvic fin (Fig. 5, C and D). Melanophores occurred on the lateral surface of the body, but they were never 512 Fishery Bulletin 93(3). 1995 aligned with the myosepta as was observed for P. albigutta (Figs. 3D, 4, and 5). Other structures and size at transformation Dorsal and anal fin supports The arrangement of pterygiophores in relation to neural and haemal spines may be valuable for separating P. albigutta and P. lethostigma larvae because they share simi- lar vertebral counts (hence similar haemal and neu- ral spine counts), but different dorsal and anal fin- ray counts. The cumulative number of anal-fin-ray ptery- giophores between the first haemal spine (which is associated with the first caudal vertebrae) and haemal spines posterior to the fourth haemal spine appeared to be diagnostic (Table 3). Although there was overlap in counts, there is a fair degree of sepa- ration in the cumulative number of anal-fin ptery- giophores. For example, between haemal spines 1 and 13, from 28 to 31 pterygiophores would aid in identi- fying P. albigutta, whereas >28 pterygiophores would aid in identifying P. lethostigma. As expected, there was a lesser cumulative number of pterygiophores for P albigutta compared with P lethostigma (Table 3). The cumulative number of dorsal-fin ptery- giophores between the first neural spine (which is associated with the first caudal vertebrae) and fol- lowing spines appeared less valuable (Table 3). There was considerable overlap between species. The cu- mulative number of pterygiophores was most valu- able when a considerable number were developed. For example, between neural spines 1 and 27, from 46 to 52 pterygiophores would aid in identifying P. albigutta, whereas >58 pterygiophores would aid in identifying P. lethostigma (Table 3). Cranial spines and preopercle spines Weak, fleshy preopercle spines were observed on both species at all stages, and they decreased in number with in- creasing size (Figs. 3-5). On both species the exact arrangement and number of preopercle spines gen- erally were difficult to discern but were more readily observed in cleared and stained material. Generally, there were four to five minute spines on the inner shelf of the preopercle, a larger spine at the angle of the outer shelf, and one dorsal to the latter on the outer shelf. Preopercle spines were not observed for speci- mens of either species > approximately 8.5 mm SL. Cranial spines may be diagnostic for separating P. albigutta and P. lethostigma preflexion larvae. We consistently observed three cranial spines on P. lethostigma preflexion larvae (2.9-5.4 mm NL). We never observed more than two (zero to two) on P. albigutta preflexion larvae of similar size. However, in most instances spines could be discerned only on cleared and stained material. Cranial spines generally were never observed on postflexion larvae of either species. Paralichthys albigutta began transformation at a smaller size than did P. lethostigma. For P. albigutta, the migrating eye first appeared at the dorsal mid- line at 7.8 mm SL. On all specimens >7.8 mm SL, the eye had migrated at least to the dorsal midline. For P. lethostigma, the migrating eye first appeared at the dorsal midline at 8.7 mm SL. With one excep- tion, the eye had migrated to at least the dorsal mid- line on all larvae >8.7 mm SL. On one field-collected larva of 11.2 mm SL, the eye had barely reached the dorsal midline as described for P. dentatus (Fahay, 1983). Pigmentation and meristic characters clearly identified this specimen as P. lethostigma. Table 3 The cumulative number (range) of pterygiophores between the first neural and haemal spines and other spines (up to neural and haemal spine number 30 and 20, respectively) for gulf flounder, Paralichthys albigutta (n=15 laboratory- reared and 14 field-collected specimens) and southern flounder, P. lethostigma (n=l laboratory-reared and 13 field- collected specimens). P. albigutta P. lethostigma Spine numbers Dorsal fin Anal fin Dorsal fin Anal fin 1-2 2-3 1-3 2-3 2-3 1-3 4-6 3-5 5-6 4-5 1-4 5-8 5-7 7-9 6-8 1-5 6-9 7-9 8-9 9-10 1-6 8-10 9-11 8-10 11-13 1-7 9-12 10-13 10-12 13-16 1-8 11-13 12-15 12-14 15-18 1-9 13-16 14-17 14-16 17-21 1-10 15-18 16-20 16-18 19-23 1-11 16-21 17-22 18-21 22-26 1-12 18-23 19-25 20-23 24-29 1-13 20-25 21-27 23-26 26-31 1-14 22-28 23-29 25-29 28-34 1-15 24-30 25-31 27-31 30-37 1-16 26-33 27-33 30-34 33-39 1-17 28-35 29-36 32-36 34-42 1-18 30-37 31-38 34-38 37-45 1-19 32-40 33-40 36-41 39-48 1-20 34-42 36-42 38-43 43-51 1-21 36-44 40-45 1-22 38^6 42-18 1-23 39-49 44-50 1-24 41-51 46-53 1-25 43-53 48-55 1-26 45-55 51-58 1-27 46-57 53-61 1-28 48-60 55-64 1-29 51-62 58-67 1-30 53-65 60-70 Powell and Henley: Larval development of Paralichthys albigutta and P lethostigma 513 Identification of field-collected material Material collected from Onslow Bay off North Carolina was examined to determine the reliability of pigment patterns established from laboratory-reared mate- rial (Table 4). We examined the extent of pigment along the isthmus, lateral pigment in the caudal area, vomer and maxillary pigment, and the extent of pig- ment on the lateral surface of the gut of field-col- lected material. On the basis of our observations, cau- tion must be used when relating pigmentation of laboratory-reared material to field-collected material. Generally, field-collected specimens had less intense pigmentation than those reared in the laboratory (Figs. 3-6). Our observations of vomer pigment, max- illary pigment, and lateral pigment on the surface of the gut on laboratory-reared larvae were not consis- tently observed on field-collected larvae (Table 4). Pigment on the lateral surface of the caudal area that aligned with the myosepta and ventral midline pig- ment that appeared to migrate dorsally on the lat- eral surface was observed only on P. albigutta larvae (laboratory-reared and field-collected). The presence of this pattern might aid in the separation of P. albigutta from P. lethostigma. However, the absence of this pattern has little value because field-collected P. albigutta may lack lateral caudal pigment (Table 4) and when present may not always be aligned with myosepta. On preflexion and flexion field-collected Paralichthys larvae, we were unable to define two distinct pigment types but were limited in the num- ber of larvae available. Eight early preflexion larvae (approximately 2.6 mm NL) from Onslow Bay were examined for cranial spines, and only two spines or less were observed. We considered these to be P. albigutta on the basis of observations of laboratory- reared material. A collection of material that included early flexion larvae with three cranial spines would be useful 1 ) to verify the presence of three cranial spines in field-collected material and 2) to catego- rize larvae into two types (i.e. three cranial spines vs. < two cranial spines) for a detailed examination of pigment patterns. In addition, the use of otolith characteristics produced during the early larval pe- riod may be useful in facilitating separation of P. albigutta andP lethostigma (Laidig and Ralston, 1995). Identification of field-collected specimens was based on stage of development of meristic charac- ters (Gutherz, 1967) (Tables 1 and 2). Unless field- collected material is cleared and stained and then measured, the stage of development of meristic char- acters may not be a valid diagnostic character. The bodies of field-collected material generally are bent, and measurements taken before and after clearing and staining, which tend to straighten the bodies, may vary by 1 mm (Table 4). This is especially perti- nent when attempting to identify flexion and early postflexion larvae by size at a developmental stage. Two specimens of Paralichthys squamilentus postflexion larvae were tentatively identified from February collections in Onslow Bay. Pigment at the dorsal and ventral midline resembled P. dentatus (Fahay, 1983). One specimen (5.9 mm SL) had 10 postanal melanophores along the ventral midline. Lateral pigment in the caudal area was absent. The Table 4 Selected field-collected specimens used to examine the effectiveness of pigmentation to identify gulf flounder, Paralichthys albigutta, and southern flounder, P. lethostigma , larvae Species identification was determined by relating body length (measured on cleared and stained material) and ray formation. Presence of pigment indicated by a plus sign (+), absence by a minus sign ( -). Pigment Body length Body length Lateral along entire Lateral Specimen (mm) (mm) cleared Caudal Dorsal Anal gut Vomer Maxillary length of caudal Species number preserved and stained rays rays rays pigment pigment pigment isthmus pigment identification 1 5.4 NL 6.2 NL 10 8 0 — — — P. albigutta 2 5.2 NL 5.7 NL 8 5-6 0 — — — — — P. albigutta 3 6.4 NL 7.3 SL 13 13-14 13 — + — — + P. lethostigma 4 5.4 NL 6.0 SL 12 8 0 + — + + + P. albigutta 5 5.6 NL 5.7 NL 11 6-7 0 + + + + + P. albigutta 6 5.0 NL 5.2 NL 0 3 0 — + — — + P. albigutta 7 5.5 NL 6.5 NL 10 8 0 — — — — + Unknown 8 5.0 NL 5.7 NL 4 3 0 + + — — + P. albigutta 9 5.4 NL 5.9 NL 6 3 0 — — — — — P. albigutta 10 5.1 NL 5.7 NL 4-5 3 0 — — — — — P. albigutta 11 7.8 SL 7.8 SL 17 68 41 — — — — — P. lethostigma 12 6.7 SL 6.7 SL 17 10 0 — — — — — P. lethostigma 514 Fishery Bulletin 93(3), 1995 B Figure 6 Field-collected (A) gulf flounder, Paralichthys albigutta, 7.1 mm SL; (B) southern flounder, P. lethostigma, 8.4 mm SL. other specimen (6.2 mm SL), had 12 postanal mel- anophores along the ventral midline. One melano- phore occurred on the lateral portion of the caudal area. We considered these specimens to be P. squa- milentus because they were well developed for their size compared with P. dentatus (Fahay, 1983). Ap- proximately 64 dorsal rays and 55 anal rays were formed. Neither the dorsal nor anal fins were com- pletely formed. One specimen had four well-defined cranial spines and five preopercle spines. The other specimen had three cranial spines and five preopercle spines. Both specimens had 40 vertebrae. Discussion Paralichthys larvae can be separated from other bothid larvae by ventral midline pigment and the caudal formula when the principal caudal rays are formed (Fahay, 1983). Paralichthys dentatus and, tentatively, P. squamilentus larvae can be separated from P. albigutta and P. lethostigma larvae by differ- ences in postanal ventral midline pigment (Fig. 7) and in size at development. Paralichthys dentatus has a maximum of 13 postanal melanophores along the ventral midline that are not uniform in size or spacing (Smith and Fahay, 1970). Tentatively, P. squamilentus has ventral midline pigment similar to P. dentatus. Paralichthys albigutta and P. letho- stigma have approximately 19-31 postanal ventral midline melanophores that are uniform in size and spacing (Fig. 7). Larval P. dentatus can tentatively be separated from larval P. squamilentus by differ- ences in development. At any given size, P. squa- milentus appears to be significantly more developed than the other three Paralichthys species. However, early preflexion larvae might be difficult to separate from P. dentatus because P. squamilentus has only been tentatively described from two postflexion speci- mens (this study). On the other hand, at any given Powell and Henley: Larval development of Paralichthys albigutta and P lethostigma 515 B ~ — ^r^,yv-'%jrvg-jLj-.-^"» Figure 7 Pigmentation on the ventral side of field-collected, postflexion (A) gulf flounder, Paralichthys albigutta (9.1 mm SL), and (B) summer flounder, P. dentatus (9.7 mm SL). size .P. dentatus is the least developed of the four para- lichthids (Fahay, 1983). The best diagnostic character for separating P. albigutta from P. lethostigma is the development of meristic characters, but field-caught specimens must be cleared and stained prior to identification. At any given size, P. albigutta is more developed than P. lethostigma (Tables 1 and 2). The number of cranial spines could be useful in separating preflexion P. albigutta (zero to two spines) from preflexion P. lethostigma (three spines) if field-collected specimens are in concordance with those reared in the labora- tory. Pigmentation on the lateral surface of the hind- gut and caudal area are more developed in P. albigutta compared with P. lethostigma, but these characters may not be as consistent on wild speci- mens (e.g. Table 6). Caution should be used when extrapolating pigment patterns on laboratory-reared material to field-collected materials. Acknowledgments The authors are grateful to Rick Monahan, Robert Kittrell, and Joe Andrews of the NC Division of Ma- rine Fisheries for providing the spawning stock. Sin- cere appreciation is extended to Valerie Comparetta for her outstanding assistance in the spawning and rearing aspect of this study, to Roger Robbins for his technical support, and to Jeanie Fulford for typing the manuscript. William Hettler, Charles Manooch III, and two anonymous reviewers reviewed the manuscript and provided many valuable comments. Literature cited Deubler, E. E., Jr. 1958. A comparative study of the postlarvae of three floun- ders(Para&Artys)inNorth Carolina. Copeia 1958:112-116. Fahay, M. P. 1983. Guide to the early stages of marine fishes occurring in the western North Atlantic Ocean, Cape Hatteras to the southern Scotian Shelf. J. Northwest Atl. Fish. Sci. 4: 1^23. 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. Laidig, T. E., and S. Ralston. 1995. The potential use of otolith characters in identifying larval rockfish (Sebastes spp.). Fish. Bull. 93:166-171. Potthoff, T. 1984. Clearing and staining techniques. In H. G. Moser et al. (eds.), Ontogeny and systematics of fishes, p. 35- 37. Am. Soc. Ichthyol. Herpetol. Spec. Publ. 1. Smigielski, A. S. 1975. Hormone-induced spawnings of the summer floun- der and rearing of the larvae in the laboratory. Prog. Fish- Cult. 37:3-8. Smith, W. J., and M. P. Fahay. 1970. Description of eggs and larvae of the summer floun- der, Paralichthys dentatus. U.S. Fish Wildl. Serv., Res. Rep. 75, 21 p. Woolcott, W. S., C. Beirne, and W. M. Hall Jr. 1968. Descriptive and comparative osteology of the young of three species of flounders, genus Paralichthys. Chesa- peake Sci. 9:109-120. Abstract. — Upwelling and its as- sociated offshore advection of surface waters can affect the recruitment of nearshore organisms. Late-stage pelagic Pacific and speckled sanddabs, Citha- richthys sordidus and C. stigmaeus, were collected with a midwater trawl off cen- tral California during the spring and summer upwelling season. In both spe- cies, otolith size increased linearly with metamorphic development; standard length, however, increased asymptoti- cally. Earlier stages of both species oc- curred shallower in the water column, whereas later stages occurred deeper. The deeper distribution of later stages may have been due to decreased buoy- ancy as a result of increased otolith size and ossification of bony structures co- incident with metamorphosis. Earlier stages of both species were more abun- dant offshore and less abundant in ar- eas of upwelling, whereas later stages were more abundant nearshore regard- less of upwelling. The difference in the horizontal distributions of early and late stages may have been passively driven by different current patterns as a result of the difference in vertical distri- butions between early and late stages. Distribution of pelagic metamorphic-stage sanddabs Citharichthys sordidus and C. stigmaeus within areas of upwelling off central California Keith M. Sakuma Tiburon Laboratory, Southwest Fisheries Science Center National Marine Fisheries Service. NOAA 3 1 50 Paradise Drive, Tiburon, California 94920 Ralph J. Larson Department of Biology, San Francisco State University 1 600 Holloway Avenue, San Francisco, California 94 1 32 Manuscript accepted 27 February 1995. Fishery Bulletin 93:516-529 (1995). Pacific and speckled sanddabs, Ci- tharichthys sordidus and C. stig- maeus, are abundant along the Pa- cific coast of North America (Miller and Lea, 1976). In both species, spawning peaks during the summer months but also occurs at lower lev- els during the remainder of the year; individuals may spawn more than once during a given season (Arora, 1951; Ford, 1965; Goldberg and Pham, 1987; Matarese et al., 1989; Rackowski and Pikitch, 1989). Sanddabs have a long pelagic stage, which may exceed 324 days in speckled sanddabs and 271 days in Pacific sanddabs (Kendall, 1992; Brothers1), and settle at a relatively large size (20 to greater than 39 mm standard length (SL) for Pacific sanddabs and 24 to greater than 36 mm for speckled sanddabs) (Ahl- strom et al., 1984; Matarese et al., 1989). Kramer (1990) noted that flatfish with nearshore nurseries had brief pelagic stages and settled at small sizes, whereas those with less restricted coastal nurseries had longer pelagic stages and settled at larger sizes. Kramer (1990) placed sanddabs in the latter category; however, speckled sanddabs, in par- ticular, have a somewhat restricted bathymetric distribution as settled individuals (usually found at depths of 40 m and less )( Rackowski and Pikitch, 1989; Kramer, 1990). Both species are widely distributed as pelagic larvae (as far as 724 km off- shore for Pacific sanddabs and 320 km offshore for speckled sanddabs) (Rackowski and Pikitch, 1989), but settled individuals occur within a somewhat more restricted coastal region. The existence of late-stage Pacific and speckled sanddabs in midwater trawls conducted off central Califor- nia by the National Marine Fisher- ies Service (NMFS) Tiburon Labo- ratory (Wyllie-Echeverria et al., 1990) provided an opportunity to examine ontogenetic changes in dis- tribution associated with metamor- phosis and settlement of these two sanddabs. In this paper we investi- gated the vertical and horizontal distribution of pelagic-stage sand- dabs, with the general purpose of elucidating the changes that take place at metamorphosis and settle- ment. Because the NMFS collec- tions were made during the spring 1 Brothers, E. B. EFS Consultants, Ithaca, NY 14850. Personal commun., 1993. 516 Sakuma and Larson: Distribution of Cithanchthys sordidus and C stigmaeus 517 and summer upwelling season, when the associated offshore advection of surface waters can adversely affect marine organisms with pelagic life stages (Parrish et al., 1981; Bailey and Francis, 1985; Roughgarden et al., 1988), the effect of upwelling on pelagic-stage sanddabs was also investigated. Methods Data collection Pelagic Pacific and speckled sanddabs were collected in conjunction with the annual juvenile rockfish sur- veys conducted by NMFS Tiburon Laboratory scien- tists aboard the National Oceanic and Atmospheric Administration (NOAA) research vessel David Starr Jordan. Standard stations extending from Point Reyes to Cypress Point (Fig. 1) were sampled with a 26 x 26 m modified Stauffer midwater trawl with a codend liner of 9.5-mm stretched mesh (Wyllie Echeverria et al., 1990). Standard trawling depth was 30 m except at shallow-water stations where trawls were conducted at 10 m. At certain standard stations a series of three depth-stratified trawls (depths=10 m, 30 m, and 110 m) were conducted to determine bathymetric distributional patterns (Fig. 1). As time permitted, additional trawls, both stan- dard depth and depth-stratified, were conducted at nonstandard stations. All trawls were 15 minutes in duration and were completed between the hours of 2100 and 0600. Stations were sampled during a 10-day "sweep" of the survey area. Three replicate sweeps were com- pleted from mid-May to mid-June of each year; in some years one additional sweep was completed in early April. CTD (conductivity, temperature, and depth) casts were made at each trawl sta- tion to obtain temperature and salinity information at depth. Additional CTD casts were made during the day along tracklines interspersed between the trawl station lines (Schwing et al., 1990). Sur- face temperature and salinity were also recorded continuously by a thermo- salinometer aboard the vessel. CTD and thermosalinometer data were used to determine the relation between upwelling and the spatial distributions of the dif- ferent pelagic stages of both sanddabs. Although the annual juvenile rockfish surveys began in 1983, sanddabs were not identified to species before 1987. Therefore, data were analyzed only from the 1987 through 1991 sur- veys. In addition to the May-June surveys in each year, sampling was carried out in April of 1987, 1988, and 1990. Sanddabs were identified and enumer- ated on board the research vessel at sea. In 1990 and 1991, samples were frozen after identification and enumeration and brought back to the labora- tory where standard length (SL) and stage of meta- morphosis were additionally recorded for each speci- men collected. Five metamorphic stages, based on the staging system used by Pearcy et al. ( 1977), were defined as follows: Stage 1 = left and right eyes positioned sym- metrically on both sides of head; Stage 2 = right eye has begun to move dorsally; Stage 3 = upper edge of right eye within close proximity to the top of the right side of the head; Stage 4 = right eye has begun to cross over to the left side of the head; Stage 5 = right eye completely crossed over to left side of the head. 38 I 37 124 Standard Depth i-Strati fied Longitude (°W) Figure 1 Location of standard trawling stations for Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, collected during 1987-91. 518 Fishery Bulletin 93(3), 1995 No stage-1 individuals were collected, probably be- cause their small size allowed them to pass through the net. To determine if metamorphic stage was a more useful character than SL in resolving spatial pat- terns, twenty individuals from each metamorphic stage of each species were randomly selected from the May to June survey of 1991, and their otoliths were removed. The diameter of the largest otolith, the sagitta, was measured with a compound micro- scope connected to a video camera, monitor, digitizer, and computer. Data analysis Statistical analyses were performed by using the program SAS (SAS Institute, Inc., 1988). Abundances were transformed by ln(x+l) to normalize the data. Mean abundances from the April surveys and for each sweep of the May-June surveys were then calculated for all standard stations successfully sampled to de- scribe temporal differences in abundance. Means and ranges of SL's of the metamorphic stages of both sanddab species were calculated by using specimens measured from the April and May- June surveys of 1990 and from the May-June sur- vey of 1991. Mean SL's were calculated separately for the specimens randomly selected for otolith re- moval in order to compare the observed changes in otolith size relative to metamorphic stage with SL. Tukey's studentized range tests were performed to determine if there were significant differences in SL and otolith diameter with metamorphic development. Owing to changes in the width of the net mouth with depth (width=8 m at 10 m depth, 11 m at 30 m depth, and 13.5 m at 110 m depth), abundances for the depth-stratified trawls were adjusted prior to analysis (Lenarz et al., 1991). Abundances for 10-m depth trawls were multiplied by 11/8, abundances for 30-m depth trawls were not adjusted, and abun- dances for 110-m depth trawls were multiplied by 11/13.5. Because of the large spatial variability in abundances and the fact that not all depth-strati- fied trawls sampled every depth (i.e. because of time constraints only the 10 m and 30 m depths were sampled at some stations, and only the 30 m and 110 m depths were sampled at others), differences in abundance with depth, were evaluated by paired comparison f-tests. Pairing was by station; each depth pair available was considered ( 10 m versus 30 m, 30 m versus 110 m, and 10 m versus 110 m). When both observations of a pair were equal to 0, that pair was deleted from the analysis. To determine if there was a seasonal change in depth distribution, analy- ses were performed on all the surveys from 1987 to 1991, the April surveys alone, and the May-June surveys alone. To determine changes in vertical dis- tribution with development, the paired comparisons were also carried out on each of the metamorphic stages, by using data from the April and May-June surveys of 1990 and from the May-June survey of 199 1 . To determine the similarity of horizontal distribu- tions among metamorphic stages, Spearman rank correlation coefficients were calculated for the abun- dances of different stages over standard stations during the 1990 and 1991 surveys. CTD salinity at the surface (average salinity at 3-5 m depth) and at the standard mid-depth of 30 m (average salinity at 28—32 m) from each sweep of the May-June surveys of 1990 and 1991 was contoured by using the Kriging option in the program SURFER (Golden Software, Inc., 1990). Owing to problems with the CTD during the second sweep of the May- June survey of 1991, thermosalinometer data were incorporated into the available CTD data to gener- ate the surface contours. The log-transformed abun- dances of metamorphic stages 2 and 5 were overlaid onto the salinity contours to observe the relation (if any) between the abundances of these two metamor- phic stages and salinity features indicative of coastal upwelling. These two stages had the greatest poten- tial for differences in spatial relations with salinity features, given that stage-2 individuals were not com- petent for settlement, whereas stage-5 individuals were relatively close to settlement. Thermosalinometer data were used to determine trawls conducted in areas of recent upwelling. Schwing et al. (1991) designated recently upwelled water as having surface temperatures less than 10.5°C and surface salinities greater than 33.6 ppt. We used surface salinities greater than 33.6 ppt but surface temperatures less than 11.0°C to allow for marginal surface layer warming during the daylight hours prior to the nighttime trawls. Log-transformed abundances obtained at standard stations from the May-June surveys of 1990 and 1991 were converted to standard scores (log-transformed abundances rescaled for each year so that mean=0 and standard deviation=l) to adjust for year effects, allowing the data from both years to be combined. T-tests were used to compare the mean standard scores of meta- morphic stages in upwelling and non-upwelling ar- eas. Separate analyses were performed for shallow- depth (10-m) trawls and standard mid-depth (30-m) trawls because of the possibility of a depth effect due to metamorphic stage and the fact that upwelling typically affects only the upper 20 m of the water column (Parrish et al., 1981). To increase sample size, trawls at nonstandard stations were included in the analysis. Sakuma and Larson: Distribution of Cithanchthys sordidus and C. stigmaeus 519 Results Overall abundances and seasonal abundance pat- terns of the two sanddab species were variable (Fig. 2). In 1991, the abundance of both species increased monotonically during the May-June sampling period, whereas in 1987 and 1988, catches were relatively high in April but showed a marked decrease by the end of May-June, suggesting that pelagic sanddab abundance frequently declines during the April-June period (Fig. 2). However, catches of Pacific sanddabs in April of 1990 were low relative to May-June, and the May-June catches in 1988 and 1989 did not change monotonically, suggesting interannual varia- tion in seasonal patterns (Fig. 2). Although April- June abundances were variable (Fig. 2), the inter- annual variation in year-class strength of pelagic sanddabs could not be determined without complete seasonal data. In both species, SL increased asymptotically with metamorphic stage (Fig. 3). In addition, the range of lengths within each stage was quite large (Fig. 3). Pacific sanddabs were generally larger than speck- led sanddabs at each metamorphic stage (Fig. 3). Although stage-2 individuals were significantly smaller than individuals of subsequent stages, the mean SL's did not differ significantly among the three later stages (oc=0.05, df=76 for Pacific sanddabs and df=75 for speckled sanddabs). Whereas SL increased asymptotically with metamor- phic development in both sanddabs, otolith diameter showed a linear increase (Fig. 4). In addition, otolith diam- eter increased dramatically with SL (Fig. 5), and mean otolith diameter increased sig- nificantly with each successive stage (a=0.05, df=76 for Pacific sanddabs and df=75 for speck- led sanddabs). It appears that metamorphosis in sanddabs is possible at a range of sizes (30 mm to >50 mm SL in Pacific sanddabs and 25 to 40 mm SL in speckled sanddabs) and that once initiated, there is little growth in length but continued otolith growth (Figs. 3-5). In general, Pacific sanddabs were relatively evenly distrib- uted throughout the water col- umn; there was a slight de- crease in abundance with in- creasing depth (Table 1). Sepa- rate analyses of the April and May-June surveys showed similar results (Table 1). In contrast to Pacific sanddabs, speckled sanddabs were significantly more abundant in shallow and mid-depth trawls than in deep trawls (Table 2). Ana- lyzed separately, the May-June surveys showed a similar pattern to the overall analysis, but the April surveys showed less distinct differences in depth dis- tribution (Table 2). The April surveys showed a trend of decreased abundance in deep trawls relative to shallow and mid-depth trawls, but the differences were not significant (Table 2). Depth distributions differed among the metamor- phic stages of both sanddab species. Stage-2 individu- als of Pacific sanddabs were significantly more abun- dant in mid-depth trawls than in deep trawls, with a trend for increased abundance in shallow trawls ver- sus deep trawls (Table 3; Fig. 6). Although both stage- 3 and stage-4 sanddabs showed a relatively even dis- tribution throughout the water column (with no sig- nificant differences among depths), stage-3 individu- als tended to be less abundant with increased depth, whereas stage-4 individuals tended to be more abun- dant with increased depth (Table 3; Fig. 6). Stage-5 individuals were generally less abundant in shallow trawls and showed a tendency toward increased abundance with increased depth (Table 3; Fig. 6). In speckled sanddabs, stage-2 individuals were significantly more abundant in mid-depth trawls Pacific Sanddabs April May-June - Speckled Sanddabs i 5 S 3 i ■a i (1 5 t \K 1987 1988 1989 1990 1991 1987 1988 1989 1990 1991 Year Figure 2 Means and standard errors of the log-transformed abundances of Pacific and speck- led sanddabs, Citharichthys sordidus and C. stigmaeus, collected at standard sta- tions during April and May-June 1987-91 (means of the three sweeps for the May- June surveys are connected by a line). 520 Fishery Bulletin 93(3), 1995 Pacific Sanddabs GO 50 I" ■o I 30 20 10 Speckled Sanddabs T T f T i" t ! n !' * i" • I" I [ J. Stage 2 Stage 3 Stage 4 Stage 5 Stage 2 Stage 3 Stage 4 Stage 5 Figure 3 Means and ranges of standard lengths of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, in 1990 and 1991 as a function of meta- morphic stage. All specimens measured are represented by dotted lines; those subsampled for otolith removal are represented by solid lines. Standard devia- tions for the specimens selected for otolith removal are shown with thick lines; ranges are shown with thin lines. Pacific Sanddabs Speckled Sanddabs 1,800 1,600 1,400 S 3 1,200 g 1,000 5 I 2 O 600 400 200 T i Stage 2 Stage 3 Stage 4 Stage 5 Stage 2 Stage 3 Stage 4 Stage 5 Figure 4 Means, standard deviations, and ranges of otolith diameters of metamorphic stages of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, collected in 1990 and 1991. Standard deviations are shown with thick lines; ranges are shown with thin lines. Sakuma and Larson: Distribution of Citharichthys sordidus and C stigmaeus 521 Table 1 Paired comparison f-tests of log-transformed abundance (ln(x+D) of Pacific sanddabs, Citharichthys sordidus, from 1987 to 1991 at depth-stratified stations. If both num- bers within a pair were = 0, that pair was deleted from the analysis. Depth pair n Mean diff. SE / P All surveys 10 m - 30 m 57 0.07 0.1723 0.4047 0.6872 30 m - 110 m 63 0.03 0.1358 0.2075 0.8363 10 m- 110 m 39 0.43 0.2122 2.0419 0.0482 April surveys 10 m - 30 m 15 0.11 0.4375 0.2515 0.8051 30 m- 110 m 11 -0.35 0.3193 -1.0889 0.3018 10 m- 110 m 8 0.53 0.5727 0.9192 0.3886 May-June surveys 10 m - 30 m 42 0.06 0.1779 0.3109 0.7574 30 m- 110 m 52 0.11 0.1491 0.7223 0.4734 10 m- 110 m 31 0.41 0.2278 1.7962 0.0825 Table 2 Paired comparison <-tests of log-transformed abundance (ln(x+D) of speckled sanddabs, Citharichthys stigmaeus, from 1987 to 1991 at depth-stratified stations. If both num- bers within a pair were = 0, that pair was deleted from the analysis. Depth pair n Mean diff. SE * P All surveys 10 m - 30 m 54 -0.01 0.1379 -0.1024 0.9188 30 m - 110 m 51 0.62 0.1395 4.4494 0.0001 10 m- 110 m 37 0.69 0.1555 4.4301 0.0001 April surveys 10 m - 30 m 14 0.02 0.3319 0.0499 0.9610 30 m- 110 m 13 0.59 0.3488 1.7036 0.1142 10 m- 110 m 8 0.75 0.3479 2.1487 0.0687 May-June surveys 10 m - 30 m 40 -0.02 0.1484 -0.1675 0.8678 30 m- 110 m 38 0.63 0.1476 4.2666 0.0001 10 m- 110 m 29 0.67 0.1768 3.8038 0.0001 than in deep trawls with a trend for increased abun- dance in shallow trawls versus deep trawls (Table 4; Fig. 6). Stage-3 and stage-4 individuals were most abundant in mid-depth trawls; stage-3 individuals showed a tendency for decreased abundance in shal- low trawls versus mid-depth trawls (Table 4; Fig. 6). Stage-5 individuals were distributed relatively evenly throughout the water column, with a tendency to- ward increased abundance with increased depth (Table 4; Fig. 6). In contrast to Pacific sanddabs, of the four metamorphic stages, only stage-5 individu- als of speckled sanddabs were abundant in the deep trawls (Table 4; Fig. 6). Thus, speckled sanddabs gen- erally occurred shallower in the water column than did Pacific sanddabs (Fig. 6). Within each species of sanddab, abundances of ad- jacent metamorphic stages were correlated over sta- tions (Table 5). However, the correlations decreased among more dissimilar stages, indicating changes in distribution with advancing metamorphosis (Table 5). The only two stages in either species that were not significantly correlated with each other were stages 2 and 5 (Table 5). Results of the correlation analysis provided a substantial basis for overlaying only stage-2 and stage-5 abundances onto the salin- ity contours in Figures 8 and 9. CTD salinity contours showed that many of the patterns at the surface were still noticeable at 30 m (Fig. 7; and Sakuma, 1992). Therefore, only the sur- face salinity contours were used because they pro- Table 3 Paired comparison Mests of log-transformed abundance (ln(x+D) of each metamorphic stage of Pacific sanddabs, Citharichthys sordidus, from 1990 and 1991 at depth-strati- fied stations. If both numbers within a pair were = 0, that pair was deleted from the analysis. Mean Depth pair n diff. SE t P Stage 2 10 m - 30 m 16 0.08 0.3686 0.2217 0.8276 30 m - 110 m 15 0.53 0.2073 2.5674 0.0224 10 m - 110 m 14 0.65 0.3890 1.6758 0.1176 Stage 3 10 m - 30 m 14 0.09 0.4787 0.1846 0.8564 30 m- 110 m 17 0.25 0.2058 1.2234 0.2389 10 m- 110 m 16 0.34 0.3987 0.8649 0.4007 Stage 4 10 m - 30 m 10 -0.55 0.4237 -1.3017 0.2254 30 m- 110 m 12 -0.05 0.3156 -0.1684 0.8693 10 m- 110 m 13 -0.51 0.3946 -1.2940 0.2247 Stage 5 10 m - 30 m 15 -0.77 0.3505 -2.1952 0.0455 30 m- 110 m 16 -0.35 0.2927 -1.1901 0.2525 10 m- 110 m 13 -0.70 0.3931 -1.7859 0.0994 vided the widest horizontal spatial coverage (salin- ity at 30 m was not available for nearshore stations because of the shallow bottom depth). 522 Fishery Bulletin 93(3). 1995 Slage 2 Stage 3 Stage 4 Stage 5 Pacific Sanddabs □ A O * Speckled Sanddabs 1,800 * * 1,600 * 1,400 ** * * * * * * « - 1 1,200 * * * * * o _ 3 eter _ lith Diam 00 8 0 aV\ a @ Oto n D DcPB D 400 mDgrff^ CD D° 200 20 25 30 35 40 45 50 20 25 30 35 40 45 50 Standard Length (mm) Figure 5 Otolith diameter versus standard length of metamorphic stages of Pacific and speck- led sanddabs, Citharichthys sordidus and C. stigmaeus, collected in 1990 and 1991. Pacific Speckle Shallow (10 m) Mid-depth (30 m) Deep (110 m) Depth distn led sanddab in 1990 and different de significant ( depth. Stage 2 Stage 3 Stage 4 Stage 5 Figure 6 butions of metamorphic stages of Pacific and speck- s, Citharichthys sordidus and C. stigmaeus, collected 1991, based on paired comparisons of abundance at jths (Tables 3 and 4). Small dotted lines indicate non- P>0.05) trends of decreased abundance at the given Contours for sweep 1 of the May-June survey of 1990 showed a pattern of recent or ongoing upwelling occurring off Point Reyes and the Davenport area (see Fig. 1 for place names) as evidenced by the filaments of higher salinity water projecting seaward and shoreward impinge- ment of lower salinity, more oce- anic water (Simpson, 1987) at the surface north of Point Reyes (Fig. 8). The contours for sweep 2 in- dicated a reduction in offshore transport due to upwelling, with lower salinities closer to shore (Fig. 8). The contours for sweep 3 showed upwelling activity oc- curring off Point Reyes but not off Davenport (Fig. 8). The contours for the May-June survey of 1991 showed pronounced seaward filaments off Point Reyes and Davenport during sweep 1, which indicated recent or ongoing upwelling (Fig. 9). During sweep 2, upwelling was still evident off Davenport, but owing to problems with the CTD, patterns off Point Reyes were not easily discernible (Fig. 9). During sweep 3, there was a relaxation of upwelling as evidenced by the lack of seaward-projecting filaments of higher salin- ity water (Fig. 9). The overlaid abundances of stages 2 and 5 showed that large abundances of stage-5 indi- viduals of both species generally occurred nearshore and could be found within centers of upwelling (Figs. 8 and 9 off Davenport and Monterey Bay; Fig. 9 off Point Reyes). In con- trast, large numbers of stage-2 individuals of both species were relatively more abundant in the offshore transitional zone between coastal water (nearshore, high salinity due to up- welling) and oceanic water (offshore, low salin- ity) (Figs. 8 and 9). In addition, large numbers of stage-2 individuals were observed nearshore in the area north of Point Reyes during sweep 1 of 1990 associated with the shoreward im- pingement of oceanic water (Fig. 8). Although the effects of upwelling would be expected to be most intense near the surface, no significant differences in the abundances of the metamorphic stages of either sanddab spe- cies were observed between upwelling and non- upwelling areas at the shallow trawl depth of Sakuma and Larson: Distribution of Citharichthys sordidus and C stigmaeus 523 Table 4 Paired comparison f-tests of log-transformed abundance (lnU+li) of each metamorphic stage of speckled sanddabs, Citharichthys stigmaeus, from 1990 an d 1991 at depth- stratified stations. If both numbers within a pair were = 0, that pair was deleted from the analysis. Mean Depth pair n diff. SE t P Stage 2 10m - 30 m 21 -0.08 0.2339 -0.3240 0.7493 30m - 110 m 18 0.49 0.2408 2.0436 0.0568 10m - 110 m 14 0.52 0.3199 1.6392 0.1251 Stage 3 10m - 30 m 23 -0.46 0.2438 -1.8982 0.0709 30m - 110 m 17 0.51 0.2350 2.1629 0.0460 10m - 110 m 16 0.44 0.2647 1.6492 0.1199 Stage 4 10m - 30 m 17 -0.79 0.2212 -3.5700 0.0026 30m - 110 m 14 0.67 0.2532 2.6485 0.0201 10m - 110 m 10 0.05 0.2604 0.1739 0.8658 Stage 5 10m - 30 m 10 -0.72 0.4615 -1.5548 0.1544 30m - 110 m 4 -0.27 0.3705 -0.7186 0.5243 10m -110 m 5 0.11 0.4416 0.2584 0.8088 Table 5 Spearman rank correlations of log- transformed abundance lln(x+ll of each metamorphic stage of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, col- lected at standard stations during 1990 and 1991 (signifi- cance probabilities of each correlation are listed in bold type under the coefficients). Pacific sanddabs (n = 257) Stage 2 Stage 3 Stage 4 Stage 5 Stage 2 Stage 3 Stage 4 Stage 5 0.58 0.31 0.06 0.0001 0.0001 0.3559 0.62 0.47 0.13 0.0001 0.0001 0.0316 0.15 0.37 0.38 0.0181 0.0001 0.0001 0.04 0.13 0.53 0.4827 0.0346 0.0001 Stage 2 Stage 3 Stage 4 Stage 5 Speckled sanddabs (n = 257) 38 I 37 Surface 123 30 m 122 123 Longitude (°W) 122 Figure 7 Salinity contours at the surface compared with salinity contours at 30 m depth during 1990 sweep 1. 524 Fishery Bulletin 93(3). 1995 10 m (Table 6; Fig. 10). However, at the mid-depth of 30 m, stages 2 and 3 of Pacific sanddabs were sig- nificantly less abundant in upwelling areas than in non-upwelling areas, and stages 2 and 3 of speckled sanddabs showed a strong tendency for decreased abundance in upwelling areas (Table 6; Fig. 10). In contrast, stage 5 in each species tended to be more abundant in upwelling areas than in non-upwelling areas (Table 6; Fig. 10). Discussion Pacific Sanddabs 1990 Sweep 1 Speckled Sanddabs Sweep 2 Sweep 3 122 123 Longitude (°W) Figure 8 Salinity contours at the surface during the May-June survey of 1990 with overlaid abundances of stages 2 (represented by squares) and 5 (represented by asterisks) of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus. Size of each symbol is proportional to the abundance. During the springtime series covered by this study, metamor- phosis in both sanddab species occurred at a wide range of sizes, indicating little growth in body size during metamorpho- sis (Figs. 3 and 5). Later meta- morphic stages tended to occur in deeper water than did earlier stages; Pacific sanddabs shifted to deeper water at earlier stages than speckled sanddabs (Tables 3 and 4; Fig. 6). Later metamor- phic stages of both sanddabs oc- curred nearer to shore than ear- lier stages, despite the upwel- ling-associated offshore advec- tion of surface waters (Table 6; Figs. 8-10). Given the reported variabil- ity of size at metamorphosis in both sanddab species (Ahlstrom et al., 1984; Matarese et al., 1989), it was not surprising to observe a large amount of over- lap in the SL's of the different metamorphic stages (Fig. 3). Kendall (1992) reported that speckled sanddabs settled at ages ranging from 113 to 324 days. In general, she found that larger, recently settled individu- als had spent more time in the plankton than smaller recently settled ones (Kendall, 1992). Kendall (1992) also reported that settlement marks on the otoliths of speckled sanddabs were generally observed at an otolith radius of 400-450 urn. This corresponds to the otolith diameters observed in stage-5 individuals, indicating that these individuals were prepared to settle (Figs. 4 and 5). An important aspect of meta- morphosis in flatfishes is the Sakuma and Larson: Distribution of Citharichthys sordidus and C stigmaeus 525 ossification of bony structures (Ahlstrom et al., 1984). The large increase in otolith size observed in later metamorphic stages of both sanddab species may be attributable to the transition from a planktonic form to a benthic form. Jenkins (1987) observed acceler- ated otolith growth in relation to growth in length at the be- ginning of metamorphosis for the flatfish Rhombosolea tap- irina, which resulted in signifi- cant alterations in otolith incre- ment morphology. One alter- ation in otolith morphology ob- served in pelagic stage Pacific sanddabs was the formation of accessory growth primordia. Accessory growth primordia first occurred in stage-3 indi- viduals and completely enclosed the otolith by stage 5 (Broth- ers1). Toole et al. (1993) found that the initiation of accessory primordia formation was coin- cident with the onset of eye mi- gration in Dover sole, Micro- stomas paciftcus, and that the completion of accessory primor- dia formation occurred either during the final stages of eye migration in pelagic individuals or shortly after settlement. Metamorphosis in some flat- fish can take place in as little as five hours, as in Cynoglossus macrostomus (Ahlstrom et al., 1984), or up to nine months, as in Microstomas pacificus (Markle et al., 1992). The small increase in length seen in metamorphos- ing sanddabs (Figs. 3 and 5) suggests a relatively rapid meta- morphosis relative to growth. However, if metamorphosis oc- curred very rapidly, then the probability of collecting meta- morphosing specimens would be small (Laroche et al., 1982; Ahlstrom et al., 1984). The large numbers of later stages col- lected in 1991 and the large otolith sizes in later stages sug- gest that metamorphosis in both sanddab species occurs over a more prolonged period of time (Figs. 5, 8, and 9). Prelimi- nary results from Pacific sanddab otoliths indicate that the transition from stage 3 to stage 5 takes ap- proximately three weeks (Brothers1). Kendall's (1992) data on otolith radius at age indicate that the tran- sition from individuals with otolith radii correspond- Pacific Sanddabs 1991 Sweep 1 Speckled Sanddabs Sweep 2 Sweep 3 123 122 123 Longitude (°W) Figure 9 Salinity contours at the surface during the May-June survey of 1991 with overlaid abundances of stages 2 (represented by squares) and 5 (represented by asterisks) of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus. Size of each symbol is proportional to the abundance. 526 Fishery Bulletin 93(3), 1995 Table 6 Comparison of standard scores of log- transformed abundance (ln(x+ll) of each metamorphic stage of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, in upwelling and non-upwelling areas during 1990 and 1991 (upwelling areas were defined as having surface salinities >33.6 ppt and surface temperatures <11.0°C). Means and standard errors are shown in Figure 10. Degrees of freedom less than (n1-l)+(n2-l) indicate cases with unequal variances. Pacific sanddabs Speckled sanddabs Stage t df P Stage t df P Shallow trawls (upwelling n=36, non-upwelling n=44) 2 0.6797 78.0 0.4987 2 -0.4730 76.2 0.6375 3 0.6911 76.4 0.4916 3 0.6346 78.0 0.5275 4 0.1171 78.0 0.9071 4 0.4846 78.0 0.6293 5 -0.4135 77.0 0.6804 5 -0.3190 78.0 0.7506 Mid-depth trawls (upwelling n=63, non-upwelling n=99) 2 -2.3877 159.9 0.0181 2 -1.7268 160.0 0.0861 3 -3.0253 160.0 0.0029 3 -1.7147 160.0 0.0883 4 -0.5325 160.0 0.5951 4 0.7201 160.0 0.4275 5 0.9655 160.0 0.3259 5 1.5650 100.4 0.1207 0.3 0.2 0.1 0 -0.1 -0.2 i -0.3 ing to stage 3 to those corre- sponding to stage 5 takes ap- proximately five weeks. Morphological changes associ- ated with metamorphosis prob- ably decrease the buoyancy of pelagic sanddabs. Laroche et al. (1982) found an increase in otolith growth relative to growth in length at metamorphosis for Parophrys vetulus, which was similar to that observed for the two sanddab species in this study and for Rhombosolea tapirina (Jenkins, 1987). Reared Paro- phrys vetulus that were close to settlement frequently rested on their sides on the bottom and swam with their bodies at an angle (Laroche et al., 1982). This behav- ior may be related to decreased buoyancy as a result of the ossifi- cation of bony structures and to the large increase in otolith size (Laroche et al., 1982). In addition, the gas bladder is lost during meta- morphosis in some species of flat- fish, including the related Atlan- tic species Citharichthys arctifrons (Richardson and Joseph, 1973; Ahlstrom et al., 1984). Laidig2 observed that the gas bladder was reduced in stage-4 Pacific sanddabs and absent in 90% of stage-5 specimens. Upwelled Non-upwelled Mid-depth 0.3 0.2 - 1 T 1 0.1 " i 1 * 1 0 4 1 -0.1 ^ i -0.2 | i -0.3 i Pacific Sanddabs Shal ow Speckled Sanddabs 1 1 T 1 T ■ i 7 - i * T 1 1 ♦ I " • 1 1 H 1 1 i 1 * 1 * 1 | i 1 1 " 1 - - 1 1 T i ♦ i I 1 1 1 1 1 1 1 1 \ 1 Stage 2 Stage 3 Stage 4 Stage 3 Stage 4 Stage 5 Stage 5 Stage 2 Figure 10 Mean standard scores and standard errors of metamorphic stages of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, collected in shallow and mid-depth trawls during 1990 and 1991 in upwelling and non-upwelling areas (upwelling=surface salinity >33.6 ppt and surface temperature <11°C). 2 Laidig, T. E. Tiburon Laboratory, Southwest Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 3150 Paradise Drive, Tiburon, CA 94920. Personal commun., 1994. Sakuma and Larson: Distribution of Cithanchthys sordidus and C stigmaeus 527 The decrease in buoyancy due to increased otolith size, the ossification of other bony structures, and the loss of the gas bladder may account for the deeper bathymetric distribution of later metamorphic stages in both sanddab species (Tables 3 and 4; Fig. 6). The greater water density at deeper depths may reduce the energy expenditure required for less buoyant fish to remain pelagic; however, beyond a given range of SL and otolith size, individuals may sink more rap- idly. Therefore, the decrease in buoyancy may account directly for the deeper bathymetric distribution of later-stage pelagic sanddabs, although fish may be- haviorally seek deeper water as well. Lenarz et al. (1991) reported that younger, smaller juveniles of the shortbelly rockfish, Sebastes jordani, were found deeper in the water column than larger individuals during May-June. It was suggested that the smaller individuals were adapted to seeking deeper water as a method of avoiding offshore ad- vection due to upwelling ( Lenarz et al., 1991). In con- trast, the early stages of both sanddab species showed a shallower distribution than the later stages (Tables 3 and 4; Fig. 6). The shallow distribution of early stages may explain the comparisons of abundance in upwelling and non-upwelling areas for the 30-m depth trawls, which suggest that early stages are subject to offshore advection due to coastal upwelling (Table 6; Figs. 6, 8, 9, and 10). The offshore advec- tion of early stages may also explain their predomi- nantly offshore distribution (Figs. 8 and 9). The lack of significant differences in abundance between upwelling and non-upwelling areas for the shallow depth trawls observed in both sanddab spe- cies might be explained by the fact that the majority of these trawls were conducted nearshore where early stages were generally less abundant and that later stages were generally less abundant at the shal- low trawl depth (Tables 3, 4, and 6; Figs. 6, 8, 9, and 10). In contrast, the 30-m mid-depth trawls, in which most metamorphic stages occurred, were more widely distributed and probably indicated better the rela- tion between upwelling and the distribution of meta- morphic stages (Tables 3, 4, and 6; Fig. 6). Figure 10 shows a change in distribution of metamorphic stages in the 30-m mid-depth trawls; earlier stages tended to be more abundant in water that had not been up- welled recently, whereas later stages were more abundant in recently upwelled water. The reduction in abundance of early stages in trawls within upwelling areas may have been due to the fact that these stages were present predomi- nantly offshore while upwelling events occurred nearshore (Figs. 8 and 9). However, the large abun- dances of stage-2 individuals of both species observed nearshore north of Point Reyes during sweep 1 of 1990 associated with an extension of oceanic waters toward shore (Fig. 8) and the large abundances of stage-2 individuals occurring within the transitional areas between offshore oceanic waters and nearshore coastal waters (Figs. 8 and 9) suggest that these early stages were subject to transport by ocean currents. Analysis of California Cooperative Oceanic Fisher- ies Investigations (CalCOFI) data by Ahlstrom and Moser (1975) and Loeb et al. (1983) indicated that the larvae of both sanddab species were collected both nearshore and well offshore. Therefore, sanddabs of both species are probably passive drifters during their early life history stages as evidenced by the pre- dominantly offshore distribution of their early meta- morphic stages (Figs. 8 and 9) and the somewhat dis- persed distribution of their larvae (Ahlstrom and Moser, 1975; Loeb et al., 1983). In contrast to the distributional patterns of early stage metamorphic sanddabs, the tendency for later stages of both species to be more abundant in up- welling areas was probably due to the fact that later stage individuals occurred predominantly nearshore (Figs. 8 and 9). Although large numbers of stage-5 individuals of both species occurred within upwelling plumes (Figs. 8 and 9), large abundances of stage-5 individuals could also be found nearshore in areas outside of the upwelling plumes (Figs. 8 and 9). Be- cause later-stage individuals were more abundant at deeper depths, they were probably less suscep- tible to offshore advection by upwelling. The deeper and more shoreward distribution of later-stage sanddabs parallels the observations of Barnett et al. ( 1984) on later stages of northern anchovy, Engraulis mordax, white croaker, Genyonemus lineatus, and queenfish, Seriphus politus, off southern California. Larson et al. (1994) also found that late-stage pe- lagic juvenile rockfish (Sebastes spp.) off central Cali- fornia had a more shoreward distribution, although there was no evidence that later-stage fish were dis- tributed at greater depths (Lenarz et al., 1991). In summary, it appears that physical changes in metamorphosing sanddabs are correlated with changes in their depth distributions; more developed, less buoyant individuals occur deeper in the water column (Fig. 6). This may influence the horizontal distributions of pelagic sanddabs in the upwelling regions off central California. Early-stage sanddabs present within the upper mixed layer would be sub- ject to offshore advection associated with coastal upwelling or to onshore advection associated with downwelling (Table 6; Figs. 8-10). In contrast, the deeper distribution of later-stage sanddabs decreases their susceptibility to upwelling-associated offshore advection and could potentially lead to onshore ad- vection facilitated by the shoreward movement of 528 Fishery Bulletin 93(3], 1995 deeper water (Tables 3 and 4; Fig. 6). In addition, the vertical and horizontal distributions of both early and late-stage sanddabs may have a substantial be- havioral component; however, the means to resolve such behavioral patterns is beyond the scope of this study. Acknowledgments We thank the crew of the RV David Starr Jordan and the staff of the Tiburon Laboratory. James Bence assisted us in early data analysis. William Lenarz, Thomas Niesen, Stephen Ralston, Jean Rogers, and an anonymous reviewer made helpful comments on this manuscript. Literature cited Ahlstrom, E. U ., and H. G. Moser. 1975. Distributional atlas of fish larvae in the California Current region: flatfishes, 1955-1960. Calif. Coop. Oce- anic Fish. Invest. Rep. Atlas No. 23, 207 p. Ahlstrom, E. H ., K. Amaoka, D. A. Hensley, H. G. Moser, and B. Y. Sumida. 1984. Pleuronectiformes: development. In H. G. Moser, W. J. Richards, D. M. Cohen, M. P. Fahay, A. W. Kendall Jr., and S. L. Richardson (eds.), Ontogeny and systematics of fishes, p. 640-670. Am. Assoc. Ichthyologists and Herpe- tologists Spec. Publ. 1, 760 p. Arora, H. L. 1951. An investigation of the California sanddab Citha- richthys sordidus (Girard). Calif. Fish Game 37:3-42. Bailey, K. M., and R. C. Francis. 1985. Recruitment of Pacific Whiting, Merluccius productus, and the ocean environment. Mar. Fish. Rev. 47(2):8-15. Barnett, A. M., A. E. Jahn, P. D. Sertic, and W. Watson. 1984. Distribution of ichthyoplankton off San Onofre California, and methods for sampling very shallow coastal waters. Fish. Bull. 82:97-111. Ford, R. R. 1965. Distribution, population dynamics and behavior of a bothid flatfish, Citharichthys stigmaeus. Ph.D. diss., Univ. California, San Diego, 243 p. Goldberg, S. R., and S. Pham. 1987. Seasonal spawning cycle of the speckled sanddab, Citharichthys stigmaeus (Bothidae). Bull. Southern Ca- lif. Acad. Sci. 86(3):164-166. Golden Software, Inc. 1990. SURFER, version 4, reference manual. Golden Soft- ware, Inc., Golden, CO, 496 p. Jenkins, G. P. 1987. Age and growth of co-occurring larvae of two floun- der species, Rhombosolea tapirina and Ammotretis rostratus. Mar. Biol. 95:157-166. Kendall, M. L. 1992. Determination of age and settlement date in juve- nile speckled sanddabs, Citharichthys stigmaeus, using daily increments on otoliths. M.S thesis, San Francisco State Univ., 59 p. Kramer, S. H. 1990. Habitat specificity and ontogenetic movements of juvenile California halibut, Paralichthys californicus , and other flatfishes in shallow waters of southern California. Ph.D. diss. Univ. Calif., San Diego, 266 p. Laroche, J. L., S. L. Richardson, and A. A. Rosenberg. 1982. Age and growth of a pleuronectid, Parophrys vetulus, during the pelagic larval period in Oregon coastal waters. Fish. Bull. 80:93-104. Larson, R. J., W. H. Lenarz, and S. Ralston. 1994. The distribution of pelagic juvenile rockfish of the genus Sebastes in the upwelling region off central California. Calif. Coop. Oceanic Fish. Invest. Rep. 35: 175-221. Lenarz, W. H., R. J. Larson, and S. Ralston. 1991. Depth distributions of late larvae and pelagic juve- niles of some fishes of the California Current. Calif. Coop. Oceanic Fish. Invest. Rep. 32:41-46. Loeb, V. J., P. E. Smith, and H. G. Moser. 1983. Geographical and seasonal patterns of larval fish species structure in the California Current area, 1975. Calif. Coop. Oceanic Fish. Invest. Rep. 24:132-151. Markle, D. F., P. M. Harris, and C. L. Toole. 1992. Metamorphosis and an overview of early-life-history stages in Dover sole Microstomas pacificus. Fish. Bull. 90:285-301. Matarese, A. C, A. W. Kendall Jr., D. M. Blood, and B. M. Vinter. 1989. Laboratory guide to early life history stages of north- east Pacific fishes. U.S. Dep. Commer., NOAATech. Rep. NMFS 80, 652 p. 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. Parrish, R. H., C. S. Nelson, and A. Bakun. 1981. Transport mechanisms and reproductive success of fishes in the California Current. Biol. Oceanogr. 1(2): 175-203. Pearcy, W. G., M. J. Hosie, and S. L. Richardson. 1977. Distribution and duration of pelagic life of larvae of Dover sole, Microstomus pacificus; rex sole, Glyptocephalus zachirus; and petrale sole, Eopsetta jordani, in waters off Oregon. Fish. Bull 75:173-183. Rackowski, J. P., and E. K. Pikitch. 1989. Species profiles: life histories and environmental re- quirements of coastal fishes and invertebrates (Pacific Southwest) — Pacific and speckled sanddabs. U.S. Fish Wildl. Serv. Biol. Rep. 82(11.1107). U.S. Army Corps of Engineers, TR EL-82-4, 18 p. Richardson, S. 1 ... and E. B. Joseph. 1973. Larvae and young of western Atlantic bothid flat- fishes Etropus microstomus and Citharichthys arctifrons in the Chesapeake Bight. Fish. Bull. 71:735-767. Roughgarden, J., S. Gaines, and H. Possingham. 1988. Recruitment dynamics in complex life cycles. Science 241:1460-1466. Sakuma, K. M. 1992. Pelagic distributions of juvenile sanddabs (Citha- richthys sordidus and C. stigmaeus) off central California. M.S. thesis, San Francisco State Univ., 78 p. SAS Institute Inc. 1988. SAS/STAT user's guide, release 6.03 ed. SAS Insti- tute Inc., Cary, NC, 1028 p. Schwing, F. B., S. V. Ralston, D. M. Husby, and W. H. Lenarz. 1990. The nearshore physical oceanography off the central California coast during May-June 1989: a summary of CTD data from juvenile rockfish surveys. U.S. Dep. Commer., NOAATech. Memo. NMFS-SWFSC-153, 142 p. Sakuma and Larson: Distribution of Citharichthys sordidusand C. stigmaeus 529 Schwing, F. B., D. M. Husby, N. Garfield, and D. E. Tracy. 1991. Mesoscale oceanic response to wind events off cen- tral California in spring 1989: CTD surveys and AVHRR imagery. Calif. Coop. Oceanic Fish. Invest. Rep. 32:47-62. Simpson, J. J. 1987. Transport processes affecting the survival of pelagic fish stocks in the California current. Am. Fish. Soc. Symp. 2:39-60. Toole, C. L., D. F. Markle, and P. M. Harris. 1993. Relationships between otolith microstructure, microchemistry, and early life history events in Dover sole, Microstomus pacificus. Fish. Bull. 91:732-753. Wyllie Echeverria, T., W. H. Lenarz, and C. A. Reilly. 1 990. Survey of the abundance and distribution of pelagic young- of-the-year rockfish, Sebastes, off central California. U.S. Dep Commer., NOAATech. Memo. NMFS-SWFC-147, 125 p. Abstract. Nine new species of hagfishes (Myxinidae, Myxine ) from the Pacific and Atlantic coasts of North and South America are described and a key is offered to the new world hagfishes. New data are presented for Myxine circifrons from the eastern Pacific Ocean, M. limosa from the northwest- ern Atlantic Ocean, and M. affinis and M. australis from in and near the Straits of Magellan. Myxine limosa is removed from the synonymy of M. glutinosa. The nine new species occur as follows: M. hubbsi along the Pacific coast from San Francisco, California, to Valparaiso, Chile; M. hubbsoides and M. pequenoi near Valdivia, Chile; M. mccoskeri and M. robinsi in the southern portion of the Caribbean Sea; M. fernholmi, M. knappi, and M. dorsum near the Falkland Islands, and M. debueni in the Straits of Magellan. Myxine mccoskeri and M. pequenoi are regarded as dwarfed, containing nearly mature eggs or testes at total lengths of 230 and 175 mm, respectively. Hermaphroditism is often found in individuals of M. hubbsi, M. limosa, and M. affinis. Review of new world hagfishes of the genus Myxine (Agnatha, Myxinidae) with descriptions of nine new species Robert L. Wisner Charmion B. McMillan Marine Biology Research Division. 0202 University of California, San Diego La Jolla, California 92093-0202 Manuscript accepted 7 December 1994. Fishery Bulletin 93:530-550 (1995). Hagfishes (slime eels) are cartilagi- nous, eel-like, abundant bottom- dwelling scavengers occurring at depths ranging from a few to at least 2,400 meters. Myxine is one of the six recognized genera in the "agnathan" family Myxinidae (Nel- son, 1994). In the new world it com- prises eight species in the Atlantic Ocean and six in the Pacific (refer- ences in this study); species occur- ring in the Straits of Magellan also may occur in either ocean. The ge- nus Myxine, which presently con- tains 19 species including those in this study, is characterized princi- pally by all the efferent gill pouch ducts discharging into a single ap- erture on each side, the left being confluent with the pharyngocutan- eous duct. This character is shared by the genera Neomyxine Richard- son, 1953, and Nemamyxine Richard- son, 1958. Neomyxine is further char- acterized by having paired lateral finfolds in the prebranchial region, as well as the usual ventral finfold posterior to the gill apertures. In Nemamyxine, the body is extremely slender and the ventral finfold ex- tends far forward nearly to the anteriormost prebranchial slime pores. In all other myxinids the ven- tral finfold does not extend anterior to the pharyngocutaneous duct. Head grooves ("lateral lines" of ear- lier authors) are lacking in genus Myxine as are the external eyespots common in genus Eptatretus (McMil- lan and Wisner, 1984). Hermaphro- ditism does not occur in our mate- rial of M. circifrons but is not un- common in M. limosa, M. affinis, M. australis, and M. hubbsi and occurs in two of the three specimens of M. hubbsoides. The remaining new species have too few specimens to state with certainty whether or not hermaphroditism occurs among them. Great variation in develop- mental stages of eggs occurs among specimens of the same length and possibly age, which supports a widely held belief that hagfishes spawn throughout the year. As eggs mature, the polar caps enlarge into dome-like structures containing anchor filaments that are connected to the eggs when they are extruded. With one exception (a female M. limosa discussed below), eggs of all specimens examined here were not fully mature; polar caps were not vis- ible, nor were they still encapsulated. This study of new world hag- fishes, the latest by us in a series on the family Myxinidae begun by Carl L. Hubbs (deceased), includes all 14 known species of Myxine from the Pacific and Atlantic coasts of North and South America. We have added old world M. glutinosa to all tables for comparison with the closely related M. limosa. Of the other four 530 Wisner and McMillan: Review of new world hagfishes of the genus Myxine 531 known species, M. ios from the eastern Atlantic and M. capensis from South Africa are compared briefly with the new world species M. pequenoi. Both M. garmani, and M. paucidens Regan, 1913 are known only from Japan and are not closely related to any new world species. The number of new species (nine) from near the coasts only, suggests a need for further and more intensive collecting throughout the world. Methods Methods of counting and measuring generally fol- low those of Fernholm and Hubbs (1981) and McMillan and Wisner ( 1984). All measurements are in mm, and body proportions (Table 1) are in percent of total length. Features used in measuring and counting are shown in Figures 1 and 2, and geo- graphic distribution in Figure 3. Counts of slime pores (Tables 2-5) and unicusps (Table 6) represent the left side only because we have found no signifi- cant differences between the left and right sides. Occasionally one extra gill pouch occurs, usually on one side only and much smaller than normal; one less pouch rarely occurs on either side. The one to three slime pores which may occur over the pharyngocutaneous duct are included in the prebranchial pore count. In all species of Myxine only two fused cusps (a multicusp) occur on the posterior set of cusps (inner row of Fernholm and Hubbs, 1981 ) in contrast to either two or three on the anterior set. This latter character is used to group species (Tables 1-7). Some terms have appeared previously in myxinid accounts without clear definition. We offer precise definition of these and some new terms used in this study: rostrum, rounded to pointed, fleshy extension lying over the nasal orifice between the anteriormost pairs of barbels; head, from tip of ros- trum to a vertical from wrinkled tissue below the mouth; face, ventral aspect of head; mouth, the elon- gate slit in face which opens to permit extrusion of cusps for feeding (Fig. 2A); multicusp, a unit of two or three cusps (teeth of other authors), fused together at bases (Fig. 2B); unicusp, a single unfused cusp (Fig. 2C); pores (slime pores), the small openings along the ventral aspect of body which emit mucus; gill aperture (GA), the opening through which wa- ter discharges to the exterior after passing through the gill pouches; PCD, the external opening of the pharyngocutaneous duct, always on the left side and usually confluent with the left gill aperture in Myxine (or posteriormost GA in Eptatretus); ventral finfold (VFF), a band of thin, fleshy tissue extending along ventral midline of body between PCD and origin of cloaca (Fig. 1); cloaca, the slit-like ventral opening anterior to tail through which body wastes and sexual products discharge; and caudal finfold (CFF), the band of thin fleshy tissue extending around tail, end- ing dorsally about over origin of cloaca (Fig. 1). Colors are determined after scraping away the coating of coagulated slime (mucus). Although given in the descriptions, color is subjective and may change greatly with preservation; therefore, the use of counts is preferred as a more distinguishing char- acter. Because eggs are similar in all species, we have not used them as a species character. They vary widely in length and diameter and in developmental stages, ranging from tiny to nearly mature in females of the same length. Accurate measurement of diam- eter is hindered in eggs deformed because of crowd- ing in life or during preservation; many are some- what flattened and diameters may vary as much as 1.5 mm in the same specimen. We have not provided photographs or drawings of individual species since F G Figure 1 Sketch of a Myxine showing features used in measuring and counting: A-G = total length (TL); A-B = prebranchial length; C = opening of the pharyngocutaneous duct (PCD); D = ventral finfold (VFF), D'= enlarged portion of VFF with dashed line indicating the ap- proximate difference between a well and a weakly developed VFF; E = origin of cloaca; E-G = tail length; F = caudal finfold (CFF). The many slime pores along the sides are indicated by a few small circles near PCD and cloaca. 532 Fishery Bulletin 93(3). 1995 there are no distinguishing external features other these materials were obtained follows the Acknowl- than those characters given in the key. A list of the edgment section. Institutional abbreviations are materials examined and of the collections where listed as in Leviton, et al. (1985). Key to new world hagfishes (Genus Myxine) la A 3-cusp multicusp on anterior set, a 2-cusp multicusp on posterior set of cusps 2 lb A 2-cusp multicusp on both the anterior and posterior sets of cusps 6 2a Gill pouches 6, rarely 7 3 2b Gill pouches 5 4 3a VFF well developed, 3-7 mm high, mounted on thick triangular base extending from the ventral surface; last few prebranchial pores in an uneven line, resembling the letter W; total pores 112-121 M. fernholmi 3b VFF vestigial, not mounted on triangular fleshy base; last few prebranchial pores in a straight line; total pores 103- 104 M. debueni 4a Anterior unicusps 6-9; total cusps 36-48; total pores 77-92; color light brown, often lighter dorsally than ventrally M. mccoskeri 4b Anterior unicusps more than 9 each side 5 5a Anterior unicusps 11-13; total cusps 56-58; total pores 92-100; VFF usually low (3-6 mm); head and barbels pale M. robinsi 5b Anterior unicusps 7-13; total cusps 43-56; total pores 80-102; VFF usually prominent, averaging 5 mm (1-12 mm); head and barbels usually pale M. circifrons 6a Gill pouches 7; anterior unicusps 4; posterior unicusps 5-6; total cusps 26-28 M. pequenoi 6b Gill pouches 6, rarely 7 7 7a CFF extending forward dorsally 2-3 times tail length; total pores 108-109; VFF low, (3-5 mm) M. dorsum 7b CFF not extending forward dorsally much beyond a vertical above cloacal origin 8 8a Prominent whitish band on ventral surface; VFF usually well developed 9 8b No prominent ventral whitish band 10 9a Ventral whitish band not extending above line of trunk pores, but often extending to face; color dark reddish-brown; total cusps 38—46 M. affinis 9b Ventral whitish band extending above line of trunk pores, often increasing as wide blotches between GA and face; body brown to purplish; total cusps 29-38 M. australis 10a VFF moderately to well developed 11 10b VFF vestigial, or nearly so 12 11a Color bluish gray to brownish, head pale; whitish mid-dorsal narrow stripe extending forward a variable distance; total cusps 42—48; total pores 101-119 M. mcmillanae lib Color pinkish-brown to various shades of purple, often dark; head usually pale; narrow whitish streak of variable length extending along dorsal midline from CFF; total cusps 30-49; total pores 89-118 M. limosa 12a VFF nearly vestigial, 1-3 mm high; color pinkish to bluish; head pale; prebranchial pores 31-32; trunk pores 61-65; total pores 108-110 M. knappi 12b VFF vestigial; color brown to purplish-black; prebranchial pores 18-31; trunk pores 58-72; total pores 91-116 13 13a Color light to dark purplish-brown; occasional pale blotches ventrally; total pores 101-109; VFF variably vestigial to 8 mm high M. hubbsi 13b Color dark brown to blackish; no pale blotches ventrally; head only slightly pale; total pores 111-116; VFF vestigial, intermittently absent M. hubbsoides Wisner and McMillan: Review of new world hagfishes of the genus Myxine 533 Systematics Myxine circifrons Garman, 1 899 Myxine circifrons Garman, 1899: 344 "Albatross Sta- tion 3395; 7°30'36"N, 78°W; 730 fm (1,336 m) tem- perature 38.5°F; bottom rocky." Diagnosis A 3-cusp multicusp on anterior sets of cusps; five gill pouches each side; color blackish to dark reddish-brown, anteriormost portion of head pale. Description Counts and proportions are given in Tables 1-7. Body robust, slightly deeper than wide; snout bluntly pointed, rostrum short, variably tri- angular to bluntly rounded; cusps short, stout; ante- rior multicusps bulbous at bases, the free tips about equal in length to bulbous portion; tail length about 13% of TL, its depth about 40% of its length; VFF usually well developed, but may be vestigial, rang- ing in height from 1 to 12 mm, averaging about 5 mm; CFF high, extending around tail to about over cloaca, thickened dorsally; body color dark, grayish- black to reddish-brown; anterior portion of head paler, often whitish to near vertical from margin of face, occasionally extending into the prebranchial region; barbels color of head; VFF and CFF same color as body, without pale margins; GA and slime pores often with narrow pale margins; total cusps 43-56; total slime pores 80-102; numbers of large eggs (20 mm and longer) range from 15 to 18 in females of 435 mm TL, largest egg 28 x 7 mm. Distribution From near San Francisco, California, to north-central Chile at depths of about 700 to 1,860 Rostrum Head \\\ length I I MoUth Figure 2 (A) sketch of ventral aspect of a myxinid head, identifying the terms used in the text: (B) and (C), sketches of a 3- cusp and a 2-cusp multicusp, with two adjacent unicusps. m (Fig. 3). We find no significant differences in counts or proportions throughout this extensive range of about 11,000 kilometers. Comments Sex ratios in our material are equal off southern California (n=220) but unequal near the mouth of the Gulf of California fn= 136), 66% female to 34% male, and Costa Rica to northern Chile (n-54), 59% female to 41% male. We find no hermaphrodit- Figure 3 Areas of occurrence of new world species of Myxine: 1 = M. circifrons, from near San Francisco, California, to north-central Chile; 2 = M. hubbsi, from near San Fran- cisco, California, to near Valparaiso, Chile; 3 = M. hubbsoides and 4 = M. pequenoi, off south-central Chile; 5 = M. fernholmi, from near Valdivia, Chile to Falkland Islands, S.E. Atlantic Ocean; 6 = M. dorsum and 7 = M. debueni, Straits of Magellan; 8 = M. australis, principally in Straits of Magellan; two collections off Chile, and one near Pta. Nuevo, Argentina; 9 = M. afftnis, Straits of Magellan; 10 = M. knappi, near the Falkland Islands; 11 = M. mccoskeri, 12 = M. robinsi, and 13 = M. mcmillanae, southern Caribbean Sea; 14 = M. limosa, Davis Strait, Greenland, southerly to eastern portion of the Gulf of Mexico. 534 Fishery Bulletin 93(3). 1995 ism in 320 specimens exceeding 350 mm TL, a mini- mum length arbitrarily chosen as offering reliable sex determination. Myxine mccoskeri new species Holotype SIO70-363, female, 201 mm, taken at 09°39'N, 78°60'W, 530-560 m, 1 October 1970. Paratypes SIO70-363, 2 ( 117, 170 mm), taken with the holotype; SIO90-117, 1 (235 mm), 11°46'N, 67°05'W, 1, 100-1,174 m (formerly UMML 29269); USNM 325212, 2 (170, 235 mm), 11°30'N, 72°26'W, 530-567 m (formerly UMML 28722); CAS 79537, 2 (170, 235 mm), 12°13'N, 75°50'W, depth unknown (formerly UMML 29884); MCZ 48809, 2 (218, 264 mm), 11°35'N, 62°52'W, 512-547 m; MCZ 41634, 1 (254 mm), 11°35'N, 62°59'N, 439-476 m. Diagnosis A 3-cusp multicusp on anterior sets of cusps; five gill pouches each side; VFF weakly devel- oped, often nearly vestigial, 0-5 mm high; color dark brown, often lighter dorsally than ventrally; a dwarf species, mature at about 300 mm TL. Description Counts and proportions are given in Tables 1-7. Body slender, slightly deeper than wide, its width about 75% of its depth; tail narrow, its length about 15% of TL, its depth about 33% of its length. VFF usually low, ranging in height from 0-5 mm, average 2 mm; CFF prominent, its margins thin, the internal supporting rays visible; snout rather sharply pointed, rostrum elongate, bluntly pointed; cusps long, slender, sharp, the bases of multicusps slightly bulbous; body variably pale to medium or dark brown, the head and ventral aspects anterior to GA lighter than body; posterior to GA the ventral aspect is notably darker toward end of tail, a pale band extends dorsally to over the cloaca, the general aspect being reverse countershading; VFF and CFF color of body, usually without, or with faintly expressed, pale margins; barbels very slightly or not at all pig- mented; GA with narrow pale margins, slime pores without; total slime pores 77-92; total cusps 36-48. A 264-mm-TL paratype (MCZ 48809) contains only four large eggs, each about 18x7 mm; in addition, two other females (218, 222 mm) contain four and five eggs, about 15x5 mm. We consider this species dwarfed because of the short length of females with such large eggs. Etymology We name this species for John E. McCosker, Director, Steinhart Aquarium, San Fran- cisco, for his work on Caribbean and Panamanian fishes, and for making the first specimens of this species available to us. Distribution Known only from the southern Carib- bean Sea (Fig. 3). Comments Shimizu (1983) reported as Myxine sp. three specimens (273-320 mm TL) from off Suriname at 310 m, with 3-cusp multicusps on anterior sets of cusps, 38 total cusps, and 87-90 total slime pores; number of gill pouches and sexual maturity not stated. Color was described as "Body color white on snout, gradually becoming blackish, and uniformly black behind posterior half of head." The cusp and slime pore counts agree well with M. mccoskeri; how- ever, the white snout as described and shown in the color photo from Shimizu, is whiter than those on our specimens of M. mccoskeri. This feature and the blackish body are more like those of M. robinsi (de- scribed below); however, the latter has more total cusps (56-58) and total pores (94-104). Myxine robinsi new species Holotype SIO90-149, ripe female, 475 mm TL, taken at 11°37'N, 60°50'W, in a 40-ft otter trawl be- tween 783 and 1281 m (formerly UMML 29270, date of capture not recorded). Paratypes SIO90-149, 1 (510 mm) taken with the holotype; USNM 325213, 1 (540 mm); 11°37'N, 60°59'W (formerly UMML 29877); MCZ 101239, 1 (460 mm), 10°03'N, 7620'W, (formerly UMML 22807), 675-966 fm [1,235-1,768 m]. Diagnosis A 3-cusp multicusp on anterior set of cusps; five gill pouches each side; whitish on head and continuing to first few prebranchial pores, and light dorsally to about over GA; body light to me- dium brown. Description Counts and proportions are given in Tables 1-7. Body rather robust, slightly deeper than wide; tail length about 13% of TL, its depth about 38% of its length; VFF moderately well developed, 3-6 mm high; CFF prominent, extending around tail to about over cloacal origin, thickening dorsally; ros- trum variably rounded to bluntly conical; anterior unicusps long, slender, sharp, curved near tips; bases of anterior multicusps slightly bulbous; color light to medium brown; head whitish continuing to first few prebranchial pores; a decreasingly paler area, often blotchy, extends posteriorly along dorsal sur- face and often laterally to near GA; slime pores and GA with no or very pale margins; VFF and CFF color of body, without pale margins. One female 475 mm TL contains six large eggs, 29-31 mm long by 11-12 mm wide, arranged in a single row. Wisner and McMillan: Review of new world hagfishes of the genus Myxine 535 Etymology We name this new species for both C. Richard and Catherine Robins, University of Miami Rosenstiel School of Marine and Atmospheric Sci- ences, for their works on the marine fauna of the tropical western Atlantic, particularly the Caribbean area. Distribution Known only from the type material from the southern Caribbean Sea (Fig. 3). Discussion Myxine circifrons, M. mccoskeri, andM. robinsi may be closely related. Each has a 3-cusp multicusp on the anterior sets of cusps and are the only species of Myxine known to have only five gill pouches each side. Counts and most body proportions overlap, which invites speculation that prior to the permanent establishment of the Panamanian land barrier, M. circifrons may have occupied the Carib- bean area. If true, M. robinsi evolved primarily to a lighter color and M. mccoskeri to a dwarfed state, with fewer anterior unicusps, trunk and total slime pores, as well as a strikingly different color pattern. All counts for M. robinsi are similar to those for M. circifrons. However, despite these similarities, we hold M. mccoskeri and M. robinsi to be specifically distinct from M. circifrons. Although Myxine mcmillanae is also from the same area (see below), we do not consider it related because it has a 2-cusp multicusp on both anterior and posterior sets of cusps and six gill pouches rather than five. One other spe- cies with 3-cusp multicusps on anterior row is M. garmani, known only from Japan and distinct from the three species described above that have six gill pouches rather than five and a wide geographical separation. Myxine fernholmi new species Holotype ISH 257-1978, female, 555 mm TL, taken at 49°29'S, 58°56*W, 200-ft bottom trawl, 400 m, 6 June 1968. Paratypes SIO90-138, 1 (790 mm), 53°00'S, 64°00'W (formerly ISH 108-1971); SIO90-139, 1 (575 mm), 33°39'S, 72°09'W, 1,170-1,480 m; ZIL 791-966, 1 (665 mm), 54°35'S, 57°30'W, 135-145 m. Diagnosis A 3-cusp multicusp on anterior sets of cusps, total cusps 34-37; six gill pouches each side; tail length 10% or less of TL; last four prebranchial pores forming an irregular line which resembles the letter W. Description Counts and proportions are given in Tables 1-7. Body moderately robust, slightly deeper than wide; tail short, 8-10% of TL, its depth about half its length; VFF extending 3-7 mm, and mount- ed on a prominent fleshy triangular extension along the ventral surface; CFF thin, high, extending around tail to about over cloacal origin; reddish supporting rays visible on most specimens; rostrum triangular, the tip slightly rounded; unicusps long, slender, sharp, slightly curved at tips; bases on anterior multicusps bulbous, posterior multicusps not bul- bous; last four prebranchial slime pores anterior to GA in an irregular line forming a pattern resembling the letter W; all slime pores tiny; tail pores 7-9, total slime pores 112-121; color variably pale, yellowish, or light bluish-pink; GA with prominent pale mar- gins, slime pores with less prominent; females with only immature eggs, 2-8 mm long. Etymology We name this species for Bo Fernholm, Museum of Natural History, Stockholm, for his work on the physiology, anatomy, and systematics of Myxinidae. Distribution Known only from the type material taken off south- central Chile and near the Falkland Islands, southwestern Atlantic Ocean (Fig. 3). Myxine debueni new species Holotype SIO90-140, male, 570 mm TL, taken at 53°39'S, 70°14'W, 300 m, 27 April 1970, Straits of Magellan. Paratype SIO90-140, male 545 mm TL, taken with the holotype. Diagnosis A 3-cusp multicusp on anterior sets of cusps; six gill pouches each side; VFF absent; tail short, 8-9% of TL; rostrum triangular, the tip pointed; prebranchial slime pores in a straight line anterior to GA. Description Counts and proportions are given in Tables 1-7. Body slender, nearly cylindrical; tail short, 8-9% of TL; depth about 40% of length; VFF absent; CFF prominent, thickened at margin, extend- ing around tail to over cloacal origin; head narrow, pointed, rostrum triangular, the tip pointed; unicusps long, slender, sharp, slightly curved; bases of multicusps not bulbous; prebranchial slime pores in a straight line anterior to GA. The two specimens appear to have been "dry-burned" from insufficient preservative, causing the skin to harden and become a dark reddish-brown color on damaged portion, mostly dorsally Undamaged part of body is pale blu- ish-gray anterior to GA; posteriorly a pale pinkish color continues to tail; CFF with narrow pale mar- gins, slime pores with very narrow ones. 536 Fishery Bulletin 93(3). 1995 Etymology We name this species for Fernando DeBuen in recognition of his extensive work on fishes of South America. Distribution Known only from the two specimens from the Straits of Magellan (Fig. 3). Comments This species and M. fernholmi (de- scribed above) are similar in that each has a tail length of 10% or less of TL and a somewhat longer trunk length than other species treated here. Each has a 3-cusp multicusp on the anterior sets of cusps; they differ primarily in M. debueni lacking a VFF (prominent in M. fernholmi); also, the last four prebranchial pores lie in a straight line not forming the letter W. Myxine hubbsi new species. Synonymy Myxine circifrons Chirichigno, 1968:383 (description; a 2-cusp multicusp on anterior set of cusps; northern Peru to Gulf of Panama). Holotype SI065-452, female, 515 mm TL, taken at 32°38'N, 118°08°4'W, 25 September 1965, bottom trap, 2,009 m. Paratypes SI065-452, 82 (209-522 mm), taken with the holotype; SIO68-60, 36 (120-484 mm), 23°07'N, 109°16'W, 1,830 m; SI068-61, 2 (350, 400 mm), 23°06'N, 109°13'W, 2,196 m; SI073-293, 16 (230-480 mm), 09°24'N, 85°06'W, 1,107 m; SI092-114, 7 (260- 450 mm), 03°41'S, 81°36'W, 2,440 m; SI092-115, 7 (290-420 mm), 08°26'S, 80°36'W, 1,830-1,930 m; SI072-176, 8 (326-473 mm), 21°37'S, 70°55'W, 2,114 m; CAS 79536, 10 (280-445 mm), taken with the ho- lotype, CAS 77360, 3 (322-410 mm), 31°00'N, 118°06'W, 1,739 m (formerly SI065-451); LACM 45786-1, 18 (222-456 mm), 32°40'N, 118°12'W, 1,742 m (formerly SI065-451); USNM 325214, 16 (258-486 mm), 32°39'N, 118°11'W, 1,830 m, (formerly SI068- 676); MCZ 101240, 6 (275-460 mm), 32°41'N, 118°12'W, 1,823 m. Diagnosis A 2-cusp multicusp on both anterior and posterior sets of cusps; six gill pouches each side (very rarely 5 or 7); body nearly cylindrical; VFF low to vestigial; rostrum rounded; color light to dark brown- ish-purple to nearly black; head and barbels pale. Description Counts and proportions are given in Tables 1-7. Body nearly cylindrical, its width nar- rowing posteriorly; tail length about 10% of TL, its depth about 38% of its length; VFF weakly devel- oped, often vestigial or absent. Of 205 specimens, 155 (75%), VFF ranges in height between 3 and 4 mm, and between 6 and 8 mm in only 4 specimens; CFF well developed, often thick at margin, ending over cloacal origin; head bluntly pointed, rostrum short, rounded; multicusps small, short, bulbous at bases; unicusps slender, sharp; body color variably light to dark purplish-black, rarely with pale blotches; head usually pale anteriorly; all barbels pale; VFF and CFF color of body; GA with narrow pale margins; slime pores only occasionally with pale margins. From 7 to 15 large eggs, ranging between 17x6 and 24x8 mm, occur in eight females (415-450 mm TL); all other females have small eggs. The largest number of eggs (15) occur in a female of 440 mm TL. Etymology We name this species for our deceased friend and mentor Carl L. Hubbs, primarily for his foresight in instigating the worldwide study on hagfishes. Distribution Known from 33°N to 34°S, at depths from about 1,100 to 2,440 m (Fig. 3). As in M. circifrons (discussed above), we find no significant differences in counts or proportions over this range of about 9,000 km. Comments The sex ratio in our material is ex- tremely unbalanced; of 150 specimens, 114 (76%) are female, 35 (23%) hermaphroditic, and 6 (0.4%) male. Although there were few large eggs (7-15), no eggs were lost since no specimens were opened prior to our examination. Bichromatism is rare; only five of 36 specimens from near Cape San Lucas, Baja Cali- fornia, Mexico (SIO68-60), are notably bichromatic with colors generally bluish-purple ventrally and laterally, the dorsal areas pinkish. Most bodies are pale anterior to GA, with occasional small to large bluish blotches; similar bichromatism occurs in five of nine specimens off San Diego, California. Myxine hubbsoides new species Holotype SIO90-143, hermaphroditic female, 826 mm TL, taken at 34°00'S, 72°14'W, 880 m, formerly MNHMC 80047). Paratypes SIO90-141, hermaphroditic female, 702 mm TL, 34°21'S, 78°18'W, 820 m (formerly MNHMC 80043); SIO90-142, female, 651 mm TL, 34°14'S, 72°21'W, 735 m (formerly MNHMC 80044). Diagnosis A 2-cusp multicusp on both the anterior and posterior sets of cusps; six gill pouches each side; VFF vestigial or nearly so, often absent; total pores 111-116. Wisner and McMillan: Review of new world hagfishes of the genus Myxine 537 Description Counts and proportions are given in Tables 1-7. Body slender, cylindrical; tail length about 12% of TL, its depth about 35% of its length; VFF very low, portions intermittently absent; CFF variably well developed, ranging between thick at cloaca and around tail to thin dorsally, ending about over cloaca; rostrum broadly rounded at tip; all cusps in anterior sets bul- bous at bases, those of posterior sets not bulbous; all unicusps straight or only slightly curved; body color blackish-brown with no pale areas or spots; head only slightly paler; face pale to slightly past mouth; barbels almost entirely pale; GA and slime pores with very narrow pale margins. The 702-mm paratype (SIO90- 141) has 49 dark brown eggs as large as 17x5 mm, with many tiny round eggs scattered among them; the holo- type has many eggs to about 11 mm, but was not opened fully for count; well-developed testicular tissue present posterior to eggs; the 651-mm paratype is spent or im- mature and has very few tiny eggs present. Etymology The name hubbsoides refers to the simi- larity to Myxine hubbsi described above. Distribution Known only from off central Chile be- tween Coquimbo and Punta Topocalma (Fig. 3). Myxine pequenoi new species. Holotype SIO90-145, 183 mm TL, maturing female, taken at 41°29'S, 74°09'W, 185 m. Paratype SIO90-146, 175 mm TL, mature male, taken at 40°44'S, 74°14'W, 215 m. Diagnosis A 2-cusp multicusp on both anterior and posterior sets of cusps; total cusps 26-28; seven gill pouches each side; VFF nearly vestigial; total slime pores 81-85; a dwarfed species. Etymology We name this species for German Pequeno R., Instituto de Zoologia, Universidad Aus- tral de Chile, Valdivia, for his work on the fishes of Chile and for making specimens available to us. Distribution Known only from the type specimens taken south of Valdivia, Chile, about 41°S, 74°W (Fig. 3). Discussion Within the genus Myxine, only three species have seven gill pouches (except rarely in M. hubbsi and M. mcmillanae). These three are M. capensis Regan, 1913, from off South Africa (22° to 25°S, 16°17°W), M. ios Fernholm, 1981, from south- west of Ireland (40° to 41°N, 12° to 13°W) and M. pequenoi (described above) from off Chile. Propor- tions of the three species are quite similar despite the dwarfed condition of M. pequenoi, but significant differences occur in certain counts. Those for M. pequenoi are given first followed in parentheses by those for M. capensis and M. ios. Total cusps 26-28 (36-43, 44-49); prebranchial slime pores 22-23 (26- 28-28-36); total slime pores 81-88 (92-110, 103- 117). Body colors are similar in all three species ex- cept that M. ios from near Ireland has a white head; the others do not. Myxine paucidens (known only from Japan) has the same number of unicusps as M. pequenoi (4 on anterior and 5 on posterior sets of cusps) but is distinctly different with six gill pouches, as well as having wide geographical separation. Myxine dorsum new species Holotype ISH 99-1971, 440 mm female, taken at 54°25'S, 59°42'W, 140-ft bottom trawl, 112 m. Paratype SI092-21 (formerly ZIN 722-966), 490 mm female, taken at 49°16'S, 57°02'W, bottom trawl, 630-650 m. Description Counts and proportions are given in Tables 1-7. Body slender, slightly deeper than wide; tail about 12% of TL, its depth about 30% of its length; VFF very low; CFF thick at margin, thinner around tail, ending well behind a vertical from origin of cloaca; rostrum short, sharply pointed; barbels small, pale; all cusps have bulbous bases, with sharp, slen- der points; seven gill pouches; head and body me- dium brown, lighter ventrally; GA and slime pores with narrow pale margins; VFF and CFF with pale margins; holotype with 10 maturing eggs to 10x4 mm; most eggs in a single row; paratype with well-devel- oped testes. We regard this species as dwarfed be- cause of the advanced sexual development of these two small specimens, 175 and 183 mm TL (even smaller than M. mccoskeri described above). Diagnosis A 2-cusp multicusp on both the anterior and posterior sets of cusps; six gill pouches; VFF low, 2.0 mm high; CFF extending forward dorsally as a ridge beyond a vertical from cloacal origin three to four times the length of tail; total slime pores 108- 113; color light pinkish-brown. Description Counts and proportions are given in Tables 1-7. Body moderately slender, slightly deeper than wide; tail about 13% of TL, its depth 40% of its length; VFF low, 2.0 mm, mounted on a prominent fleshy narrow triangular base extending 4-7 mm from body and defined by an intermittent suture-like line below the rows of pores; a structure similar to that of M. fernholmi (described above) but much less strongly developed; CFF wide, thick ventrally, thin- 538 Fishery Bulletin 93(3). 1995 ning around tail and dorsally; prominent dorsal ridge extending anteriorly as a finfold to 4.3 times tail length in holotype and 3.2 times in paratype; body light pinkish-brown, the original label states "life- long color pink"; VFF and CFF pale; GA and slime pores with narrow pale margins; holotype with 9 well- developed eggs to 19x5 mm; paratype with 8 similar eggs to 18x6 mm; eggs widely and irregularly spaced; only a few paired. Etymology The name dorsum, from Latin mean- ing "ridge," refers to the far forward extension of the CFF dorsally as a ridge to three or four times length of tail. Distribution Southwestern Atlantic Ocean between 112 and 650 m (Fig. 3). Discussion Although the two specimens are slightly wrinkled and hardened, the integuments cannot be stretched laterally and down far enough to eliminate the dorsal ridges. In addition, a suture-like line par- allels the base of these ridges, ending at the point where downward stretching fails to eliminate them. This feature is not previously reported in species of Myxine; in all others, CFF extends dorsally little more than half a tail length forward of a vertical from cloa- cal origin. Myxine knappi new species Holotype SIO90-144, 565-mm female, taken at 49°16'S, 57°02'W, 24 March 1965, 630-650 m. Paratypes SIO90-144, 2 (510,560 mm TL) taken with the holotype. Diagnosis A 2-cusp multicusp on both the anterior and posterior sets of cusps; six gill pouches each side; tail slime pores 11-14; rostrum broadly rounded; VFF nearly vestigial; color pinkish-blue, head and barbels slightly paler than body; total slime pores 116-123. Description Counts and proportions are given in Tables 1-7. Body slender, slightly deeper than wide; tail length about 13% of TL, its depth about 33% of its length; VFF low and variably developed; in the holotype it is 2.5 to 3.5 mm high; in a paratype (510 mm TL) it is less than 1.0 mm high to about 60 mm anterior to cloaca where it increases to 3.0 mm high, continuing to cloaca; CFF prominent around tail, thickened ventrally; in the 510 mm paratype CFF extends forward of a vertical from cloacal origin about half the tail length; rostrum broadly rounded at tip; cusps robust, bluntly pointed, bases of multicusps slightly bulbous; 1-2 slime pores over GA; body color pinkish to bluish, one paratype more pink than blue; head pale to about over mouth; barbels pale; VFF entirely pale; CFF color of body, without pale mar- gin; GA and slime pores with narrow pale margins; a label in the package containing the bluish speci- men states "life-long color blue." The pinkish speci- men was packaged separately with label stating "life- long color pink"; holotype with 15 large eggs to 26x7 mm; pink paratype with 12 eggs as large as 18x6 mm. Etymology We name this species for Leslie W. Knapp, Director, Department of Fishes, Smithsonian Sorting Center, primarily for supplying us with study material. Discussion This species and M. dorsum appear to be closely related, differing primarily in far forward extension of CFF in M. dorsum; this feature is weakly expressed in a paratype of M. knappi by an exten- sion of about half the tail length. Distribution Known only from near the Falkland Islands (Fig. 3). Comments A discrepancy exists in recorded dates of capture. The "life-long pink" specimen has a label stating the date of capture as "March 24, 1935"; the label with the two "life-long blue" specimens (pack- aged separately) states "March 24, 1965." All other data, handwriting, and label paper are identical; therefore we assume the date of 1935 to be in error because we know of no Russian research vessel col- lecting near the Falkland Islands in 1935. Because of the poor condition of one of the paratypes, it was not possible to obtain accurate body measurements or slime pore counts; however, we were able to count the cusps. Myxine australis .Jenyns, 1 842 Myxine australis Jenyns, 1842:159 (description: "col- ored like an earthworm but more leaden, beneath yellowish, head purplish; Tierra del Fuego"). Synonymy Myxine acutifrons Garman, 1899:347 (from original description: rostrum acute, resembling a barbel; color dark brown, lighter ventrally; ante- rior two teeth of each series confluent to bases). Diagnosis 2-cusp multicusp on both anterior and posterior sets of cusps; six gill pouches each side; head pointed, rostrum variably acute to rounded at tip; VFF low, averaging less than 2 mm; CFF narrow; a Wisner and McMillan. Review of new world hagfishes of the genus Myxine 539 wide yellow ventral band extends slightly above rows of slime pores, continuing in a variably wide band to the yellow face. Description Counts and proportions are given in Tables 1-7. Body slightly deeper than wide; tail slen- der, width about 33% of its length, its length 15% of TL; head narrow, pointed; tip of rostrum variably acute to rounded; a 2-cusp multicusp on both the anterior and posterior sets of cusps; VFF usually low, 0-6 mm, averaging 1.6 mm; CFF thin and wide around slender tail; body color reddish to dark brown, top of head dark; prominent yellow band ventrally extending slightly above rows of slime pores, con- tinuing forward and widening into large blotches anterior to GA and to yellow face; large eggs range in numbers and sizes between 9 (24x8 mm) in a 330 mm female, and 16 (21x7 mm) in one of 345 mm TL. Distribution Principally in and near the Straits of Magellan; however, three collections are from farther north (two off Argentina: 48°18'S, 65°06'W, and 50°00'S, 68°30'W, and one off Chile at 48°29'S, 78°46'W). Frequently taken with M. affinis (Fig. 3). Comments The sex ratio of our material is unbal- anced: of 86 specimens, 71 are female, 12 male, and 3 hermaphroditic. Although the multicusp pattern and number of gill pouches is the same as M. affinis, M. australis may be distinguished by fewer unicusps, fewer trunk and total pores, and shorter TL of ma- ture specimens. Myxine affinis Giinther, 1 870 Synonymy Muraenoblenny olivacea Lacepede, 1803: 6524 ("olive without spots, ventral surface whitish; no pectoral fins, no appearance of other fins; copious slime production"); presumably from the Straits of Magellan [nomen dubium]. Myxine affinis Giinther, 1870, Catalog 8:511 ("Eleven rather stout teeth in each of two series, the foremost strongest and more confluent at the base than the others. Hab. ? Twelve inches long") Norman, 1937:2-8 (examination of type; 11 teeth in each series; body too dried and hardened for slime pore counts). Diagnosis A 2-cusp multicusp on both the anterior and posterior sets of cusps; six gill pouches each side; VFF variably developed; color reddish-brown to purple. Description Counts and body proportions are given in Tables 1-7. Body slightly deeper than wide; ros- trum triangular, tip rounded; barbels dark at base, pale distally; VFF yellowish , usually low, averaging 3 mm, but ranging from 0.5 to 13 mm, only 3 speci- mens with VFF between 8 and 13 mm; CFF wide, rarely with pale margin; tail about 15% of TL, its depth about 38% of its length; body reddish-brown to purple, head region somewhat lighter; narrow yel- low band ventrally limited to below the lines of pores, often extending as intermittent patches to the yel- lowish face; GA and slime pores with narrow pale margins; numbers and sizes of large eggs range from 36 (20x6 mm) in a female of 550 mm TL to 17 (26x9 mm) in one of 475 mm TL. Distribution Within or closely adjacent to the Straits of Magellan (Fig. 3). Comments Frequently taken with M. australis but distinguished by higher unicusp and trunk slime pore count, as well as by generally larger eggs and a longer body. Sex ratio of our material is unbalanced; of 256 specimens sexed, 171 (67%) are female, 48 (19%) male and 37 (14%) hermaphroditic. Myxine mcmillanae Hensley, 1 99 1 Myxine mcmillanae Hensley, 1991:1040-1043. Diagnosis A 2-cusp multicusp on both the anterior and posterior sets of cusps; six gill pouches (rarely seven) each side; color dark bluish-gray to brown; head whitish to first slime pores. Description Counts and proportions are given in Tables 1-7. Body slightly deeper than wide; tail length 13% of TL, its depth 40% of its length; of 43 specimens two have seven pouches on the left side, one has seven on right side; VFF 3-6 mm high; body dark bluish-gray to brown; head pale to first slime pores; rostrum trian- gular, rounded at tip; VFF, CFF and margins of PCD, GA and slime pores pale; 7 to 11 large eggs (27-36 by 8—9 mm); the polar caps weakly developed. Distribution Known only from the Caribbean Sea, west and southwest of Puerto Rico and from St Croix, U.S. Virgin Islands (Fig. 3). Comment Hensley ( 199 1 ) did not report on the sex of his material. The 10 specimens available to us (SI090-21) were all females. No hermaphroditism was noted. Myxine limosa Girard, 1858 Myxine limosa Girard, 1858:223-224. (abundance: Grand Manan Isle; Bay of Fundy; 50 fm). 540 Fishery Bulletin 93(3). 1995 Synonymy Myxine atlanticus Regan, 1913:398 (Western North Atlantic, 44°27'N, 58°10'W; 120 fm; counts, proportions). Diagnosis A 2-cusp multicusp on both the anterior and posterior sets of cusps; six gill pouches each side; head rather pointed, rostrum triangular, bluntly pointed; color reddish-brown to dark purple; head often pale; occasional ventral blotches; VFF variably low to high; a narrow pale streak on dorsal midline usually present. Description Counts and body proportions are given in Tables 1-7. Body slender, nearly cylindrical; tail slender, 12-17% of TL, its depth about 30% of its length; VFF low, 0-4 mm (average 1.6 mm); CFF prominent, thin, thickening dorsally; head pointed, rostrum bluntly triangular; body color varying shades of reddish-brown to blackish-purple; head only slightly pale; occasional pale blotches ventrally; VFF and CFF usually with pale margins; GA and slime pores with prominent pale margins; a narrow pale streak of variable length usually present on dorsal midline; females (368-385 mm TL) contain 12 to 20 large eggs, 17x5 to 27x8 mm; a 385 mm female con- tains 14 fully developed eggs, 16x6 to 17x8 mm, all linked by anchor filaments. Distribution Between Davis Strait (66°N) and south to Florida, between 75 and 1,006 m; one specimen (383 mm TL) from Campeche Bank, Gulf of Mexico, at 24°25'N, 87°38'W. Discussion Since its description, M. limosa has of- ten been identified as M. glutinosa L. (1758) from the eastern North Atlantic (ENA), but we find two characters involving coloration that distinguish the two. All descriptions and our findings on ENA mate- rial indicate a grayish-pink color; in contrast, all our western North Atlantic (WNA) material is reddish- brown to blackish-purple. Girard (1858) indicated reddish to dark brown or black. In addition to the much darker coloration, most WNA specimens have a narrow pale streak along the dorsal midline ex- tending forward from CFF an average of 46% (18- 80% of TL). This pale streak is not mentioned by any author offering color descriptions of WNA material, and it is not present in ENA material available to us (180 from Skagerrak, Denmark; SIO59-50). This streak appears to result from white connective tis- sue binding skin to the dorsal midline in conjunc- tion with an overlying unpigmented streak in the skin. Removal of the overlying skin and examina- tion with the aid of strong backlighting shows this band to be present only in WNA material. Also, a difference in maximum lengths exists between ma- ture specimens of M . limosa and. M. glutinosa. Of 250 specimens of the former, the longest is 510 mm TL, and 133 exceed 400 mm, averaging 445 mm TL. Tambs-Lyche (1969:283) reported "maximum 450 mm" for ENA material. Conel (1917:78) recorded a maximum length of 79 cm from off South Harpswell, Maine, and stated that of 20 specimens, only three were between 31 and 36 cm; all others were from 50 to 79 cm. We have not seen any that large, and no further description of the 20 specimens was given. Comments Apparently all previous authors have assumed that M. glutinosa occurs across the North Atlantic Ocean, but Saemundsson (1949) did not in- clude it in his list of fishes from Iceland. However, Konstantinov and Shchegelov ( 1958: 1745) stated "On June 16, 1956, near the eastern coast of Iceland, at the depth of 940 m, a M. glutinosa L., 28.5 cm long, was caught in a Sigsbee trawl." We consider these two species closely related, and have included M.glutinosa in all the tables for comparison with M. limosa. Discussion Owing to the absence of a fossil record, we are un- able to state with certainty whether or not the new world species treated herein are monophyletic or polyphyletic. However, monophyly is assumed, based on the synapomorphic character of having all bran- chial ducts on either side combined into one single external opening posterior to the gill pouches. Also, monophyly of Myxine is supported by allozyme stud- ies of hagfish from three continents.1 Relationships among these 14 species are in gen- eral somewhat obscure on the basis of body propor- tions and most counts. Although some means differ (Tables 1-7), considerable overlap in ranges of counts tends to mask significance. Only two species (both new) differ notably in body proportions (Table 1); all 12 others are very similar. M. fernholmi has a shorter prebranchial length and a correspondingly longer trunk length and shorter tail. Myxine debueni also has somewhat shorter prebranchial and tail lengths, but the trunk length is similar to that of other spe- cies, except for M. fernholmi. The few specimens available (2 to 4) in 7 of the 14 species inhibits specu- lation as to relationships, geographical separation notwithstanding. Most counts are similar for most 1 Fernhom, B. Swedish Museum of Natural History, Section for Vertebrate Zoology, P.O. Box 50007, 5-110405, Stockholm, Swe- den. Personal commun., May 1994. Wisner and McMillan: Review of new world hagfishes of the genus Myxine 54! a t- a 00 o CM t- CO CO r~ CO ao «? 2 3 CO CO C32 00 CO CO «-t t- «4 O 1 CO t~ 1 in I m 1 10 4 a (M CM lO "** CM 0 o O CM c— CO CO ao "? ao «? « c4 O0 «f '~> CM uO ^ 1 CM ^4 i> 1 CO m •* 1 CO CO ■* 1 CO a as l—i CM CT3 1—1 3 CO u CO Cm c- ■^J" O CO *1 a <7 N CO CK «? "5 CO ™ 1 CO ^4 CO ^4 ,°4 CO "4 CO "4 a> c- CM »o i-H CO Cj CM M s O C .2 _ CM uO d) — CO ao «? =^> co /^ CO "5 J, s 2 lO t> c— in CO CO O a t- 1 CM rH ■* 1 CO 1/3 _L tO 1 CO ^4 10 4 e -& CM lO t— i ■a c co CO ■3 — 1 <^ 3 3 CM o en o •c CO ^ <0 c^ CO ao «> 10 CO 2 7 to ■* 1 CM ao CO 1 m 1 CO m I m I ■5 3 a OS CM uo ^-i X c § CO *1 -ce in to m 00 =M fj. CM CO CM ^J* uo ^r <* in Cm o CO 1 o 3 i C3^ •* A -4 ^4 ^4 '4 CO 0) o m CM lO "3 J2 | o QJ c o a CO 3 cj OS Ol O CO P. 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CD 3 ao a c ^ « ^ «T3 Si a. co e M c § * 1 s c d c CO •a 's >> > cd u cd M o 2 2 Z £ co CO 1 T3 O "o c ,5 o i— '- a CD > o '3 542 Fishery Bulletin 93(3), 1995 OS lO o 00 *J i-hi— i(Mcx)tnc~-tx>iocomcoooGO<-< »-i i-h CO 00 iH ^ ^H (N iH r-4 tH Tf CM _3 i — 1 "5b ao a oq en *! h N i— iaO©COO©t^OiCOl>iO(Nooaj It) CO CN CO CO 0 HNWWCOWNHHH 00 CO CM 73 « c as • "? lO CM Ih ^^ co Nw^a^ot^iNiotor-HtocoNt' rH CO — 1 50 H O i-H i— 1 i—l O CO ■c 3 rH q C3 +n> s? C g a) o. CD rS ^ 1 l-H rH CM -— o CO 4-3 C o -it S * co co cm h O CM -e CM c ed u £1 c 0) . fcj — o en a. GO t5 CM CM fH 3 o <*- S e 3 o o *1 CM iH rH ■>t £ DQ Lh o c '■& si § rH co m lO -* CM o -^ "3 CM (M S 5 ft en 3 cj to t CO o CM *f rHCOCCOOCOOmCilUO-CfOrHCM CM rH in co N»)hO)>«5«HH ■* CM iV. 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(h * h- co <0 3 u o a. "3 eo "* 3 Tt [- en O O -r 05 1— 1 o o CM 00 d 4-> (4-1 o co t. V .O E 3 CO a -a CM CM Z 00 3 u o S CO CO u o V >-l CN ^ ■* CD ■w C V) 10 ^ -c rH 05 rl .-I ■* o o a DO -.*. 3 ^ 4-» 3 * 1 _, in CO in _ O CM m q S ^H a s co 3 cc o c CO » 3 00 o t— tjq CO iH co CO CM ■* ■* o o d CO s *«-• TS O m oo • ~" S" Z e-i a. C- 00 35 3 ,_, 01 CO ■* in CO II ,n IH Wisner and McMillan: Review of new world hagfishes of the genus Myxine 545 B CO ■^" o lO iS 'cj cn HcNcNOiQOOJOiHOHcc^air'OiOLnio^ --< cn coco i— 1 ~H »— 1 .— 1 .— I ^. 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CO Oj 3 CO CO CD co cn -^ ai in oo in co cn Tf ai x oo in ^ in o co ^h co »-< cnoj CO bJ S- ^H ^ CN CN Tt in in *^ CO CO i-H ^H CN ^H tJ«CO s* Tl- ■S 5 CD s <- m O -— Co CIS CD c~ooc^o^cNco^incot^coai0^cNcOTt'incoi^ooaiO^CNco^incoi>ccc^ortCNcoTi'incoi^ooc3jO'--'CNcO'* 546 Fishery Bulletin 93(3). 1995 0 CO o o o lO m si t-H 00 ■* rH ■* iri CN CO rH in ■* CO CN 00 H CN co in CN 3 i — 1 CN i-i CN "si O o a CO in in cn in o oo in co ,— I O 00 CO in co CN Tj< i> rH CO CN t> CO --i CO cu 3 u a o o Cm 0 o in o % s MO t- a> a> •* 0> CO rH t~ 05 CO 4-> s lO CN 00 Tj< CO 00 V u CO lH o 'E CD s o o Vi m m ^ '3 H>*Ot- CN cc "* I> CO 00 CN 00 CO Oi 00 7-i a> o r—t CO O a, CN rH m CN CN m T3 V) d CO o o . *0 in m !h S£ rH rH CN rH in iri r^ CO O 00 m co O CN 05 iH CN CM CJ5 CN 1> •c 3 rH ^ c % e -w 'h c ■p-s £ <*-. CO ft, a J3 *t CN ^H co rH rH rH CO o -»-» e co J3 -« CD 43 0) a DQ o JO C o S rH rH CN CN CN 2 a o o CO 3 u "0 '■£3 S 3 c "* 1 c> CN CN T-* ^-t CN u a Cu o CO 0, cs 3 co u CO to rH r-t t-* rH CN rH in CN rH in k u 0 0 CJ 'E U CU 0) •w •£ OB a 0 CO a CO a 60 O B O «o *J NOOlO^^Oifl'CJim^'^H c- cb rH (N H N r^ H CO CO DO a CO cu 3 a u c o «*» e o o *| CO ^t Ol O Ol CO CO co in CO ^H -# ■* CO O CO s o o •c CD CO o co o IS i£. '-iooocoinm'*io CD Q. CD rC * 1 rH riri CO -r- c cu J= -a H-» 0 £ t C o S= E rH CO •<* **- Q. o O CO -a CO 3 CO u 'o a CO '-5 E o c 5 3 o r- 1 f-H CM 2 a CO cu o 3 rs CD u CN CO CU • o 3 C «=; jj iH CO ■C* ," «2 * t- 3 CO -C a CO o 3 CO o CJ ^ ■ -o "" 3 cocoascO'cfcDiotTfcO'-i O CD "3 H H HI ^ M H rt O CO o •C CM -t-s t*-i o c rH rH CM -Q e CO a CO . cu 3 £ cu 13 3 CJ Ct-t s iH CM fH ■<* O -r* CO *1 CO C u o 'C CO ■-J CM rH rH T* -fc- bq e ^ -S a ^ -O c 9 o k. in a -ct CO 3 CJ C rH rH rH CM rH CM CM « CO ^ rH O rl -a. CM -* ~3 IS § B s a. O CO 3 eg tc m c ^OiTj'OOr^r^inaiOCOO'rj'rH CO OS Q HCDCOOD-CC^CO rH rH ■* CO rt m t) k. o CO a VI 3 Cj O 1 COC-COOlOHNCOflOcOt-COOlOHMCOflOtOt-CCOlOHNCO^fflOt-CO II II CMCNNMCOcocococococococOCO^^TjtTj'^^^^itTflOlClOlOiflWlOlOlO £ IH 548 Fishery Bulletin 93(3), 1995 species; numbers of trunk and total slime pores dif- fer more widely, but there is frequent overlap. The total numbers of cusps (Table 7) show the greatest differences between species. The height of VFF shows considerable intraspecific variation; for example, in Myxine circifrons it varies between 1 and 12 mm. Both the numbers of fused cusps and the number of gill pouches are constant with only rare or aberrant variation and are extremely useful in separating the 14 species into groups. Five species have a 3-cusp multicusp on the anterior set of cusps. Of these five, M. circifrons, M. mccoskeri, and M. robinsi have 5 gill pouches and M. fernholmi and M. debueni have 6; the only new world species with 7 gill pouches is M. pequenoi. The remaining eight species have 6 gill pouches and a 2-cusp multicusp in both anterior and posterior sets of cusps. An additional, possibly diag- nostic character is that Myxine mccoskeri and M. pequenoi mature at much smaller sizes than do the other species, and are here regarded as dwarfed. Prior to the permanent Panamanian land bridge, M. circifrons of the tropical Pacific, and M. mccoskeri and M. robinsi of the southern Caribbean Sea, may have represented the same species. Only these three species have five gill pouches; they also have in com- mon the 3-cusp multicusp on the anterior row, and the anterior portions of the heads of M. circifrons and M. robinsi are notably and consistently whiter than in any of the other species. M. mccoskeri may have independently developed a dwarfed condition as well as a unique color pattern of reverse counter- shading, fewer trunk pores, and anterior unicusps. Hermaphroditism occurs frequently in all the large collections except in Myxine circifrons. The fact that in such a large number of hagfishes examined, only one specimen was found with fully developed fila- ments suggests that eggs are extruded very soon af- ter becoming fully mature, regardless of time of year. We have found no indications of sexual dimorphism in color, body proportions, TL, or slime pore counts. Acknowledgments We greatly appreciate the efforts of all persons un- known to us but responsible for making material available. In particular we thank R. M. McCon- naughey for his expertise and efforts in the trapping of hagfishes. We also thank R. Melendez and G. Pequeno for contributing specimens from southern Chile. M. Stehmann, Institute fur Seefischerei, Ham- burg, kindly provided valuable material from near the Falkland Islands and high latitudes of the North- western Atlantic Ocean. We are grateful to the Zoo- logical Institute, Academy of Sciences, Leningrad, for specimens from the southwestern Atlantic Ocean. We thank R. H. Rosenblatt, H. J. Walker, Bo Fernholm, and J. S. Nelson for critically reading the manuscript and offering valuable suggestions, and R. M. McMillan for technical assistance in word processing. Material examined Myxine circifrons SI067-118 (51), 38°00'N, 123°31'W, 732 m; SI064-449 (38), 32°54'N, 117°38'W, 961 m; SI059-257 (13), 32°35'N, 117°28'W, 1,208 m; SI074-611 (65), San Diego Trough, 1,201 m; SI066-7 (34), 32°32'N, 117°27'W, 1,190 m; SI068- 119 (34), 32°27'N, 117°27'W, 1,244 m; SI069-227 (15), 31°35'N, 116°05'W, 1,202 m; SI068-118 (110), 25°37'N, 109°43'W, 1,244 m; SI068-59 (14), 23°07'N, 109°19"W, 1,281 m; SIO68-60 (6), 23°07'N, 109°11'W, 1,830 m; SI068-119 (25), 25°36'N, 109°45'W, 1,491 m; SIO73-290 (4), 09°48'N, 85°42"W, 994 m; SI073-293 (3), 09°23'N, 85°00'W, 1,107 m; SI073-294 (17), 09°24'N, 85°06'W, 900 m; SI069-148 (7), 02°02'S, 81°10'W, 1,000 m; SIO90-26 (1), 03°15'S, 80°53'W, 960 m; SIO90-27, (1), 03°15'S, 80°55'W, 960 m; SIO90-25, (2), 04°10'S, 81°27'W, 1,860 m; MCZ 49585 (1), 33°17'S, 77°05'W, 1,510 m. Twelve specimens from IMARPE, with incomplete data, taken between 08°S and 17°S, 71° and 81°W, between 800 and 1,500 m. Myxine hubbsi SI092-127 (223), 32°40'N, 118°12'W, 1,830 m; SI065-451 (19), 32°40'N, 118°12'W, 1,742 m; SI065-452 (82), 32°38'N, 118°08'W, 2,009 m; SI068-676 (16), 32°39'N, 118°11'W, 1,830 m; SI071-116 ( 1 ), 28°52'N 115°50'W, 2,004 m; SI068- 60 (37), 23°08'N, 109°16W, 1,830 m; SI068-61 (2), 23°06'N, 109°13'W, 2,196 m; SI073-293 ( 16), 09°24'N, 85°06W, 1,107 m; SI083-288 (1), 09°44'N, 85°00'W, 2,181 m; SI073-293 (1), 09°24'N, 85°00'W, 1,102 m; SI092-114 (11), 03°41'S, 81°36'W, 2,440 m; SI092-115 (7), 08°26'S, 80°37'W, 1,930 m; SI072-176 (8), 21°37'S, 70°55'W, 2,114 m; MCZ-44897 (2), 34°12'S, 72°76'W, 1,475 m. Examined, but not listed, are numerous collections of few specimens each from off southern California. Myxine australis SI078-39 (8), 45036'S, 74°11'W, 120 m; SIO78-40 (80), 50°30'S, 75°20'W, 80 m; SI078-41 (2), 54°15'S, 70°58'W, 4 m; SI078-43 (1), 55°03'S, 68°10'W, 30 m; SI078-44 (3), 55°49'S, 67°30'W; SI078-45 (2), 55°10'S, 65°30'W, 146 m; SI078-49 (3), 54°46'S, 64°03'W, 23 m; SI078-51 (18), 54°45'S, 64°10'W, 14 m; USNM 3939 (20), 42°29'S, 78°46'W; AMNH 4098 (2), 51°10'S, 69°30W; FURG-? (4), 48°18'S, 65°06"W; the following collections lack stated depths but were taken in the area of the Straits of Magellan: MCZ 32518 (1); MCZ 8351 (6); MCZ 3836 (16); MCZ 3836 (16); Wisner and McMillan: Review of new world hagfishes of the genus Myxine 549 MCZ 8837 (22); MCZ 8839 (30); MCZ 8842 (10); MCZ 24972 (19); MCZ 35198 (1); USNM 103769 (1); USNM 117329 (1); USNM 153595 (1); USNM 267750 ( 1 ); AMNH 4098 (2); SU 22678 ( 1 ); IU 2124 ( 1 ); IU 4293 ( 1 ). Myxine affinis SI078-39 (8), 45°36'S, 74°11'W, 120 m; SIO78-40 (39), Isla Madre de Dios, Chile, 80 m; SI078-41 (62), 54°14'S, 70°06W, 4 m; SI078-42 (7), 54°52'S, 70°58'W, 60 m; SI078- 43 (21), 55°03'S, 68°10'W, 30 m; SIO 78-44 (15), 54°45'S, 64°09'W; SI078-45 (4) Bahia Windhond, Chile, 146 m; SIO78-50 (3), 54°54'S, 64°10'W, 14 m; SI078-51 (31), 54°45'S, 64°10'W, 14 m; SI083-121 (2), 54°22'S, 71°22'W. The following collections lack stated depths and coordi- nates but were taken in the area of the Straits of Magellan: MCZ 35198 (12); MCZ 8836 (3); MCZ 8837 (7); MCZ 8839 (1); MCZ 8840 (6); MCZ 8841 (11); MCZ 24972 (1); USNM 77377 ( 1);USNM 26715 (1); USNM 39039 (2); USNM 39140 (1); USNM 17418 (1); FMNH 9820 (3); SU 22678 (1). Myxine limosa SI074-181 (28), 36°43.2'N, 74°38,W, 300 m; SI074-185 (3), 37°05'N, 74°39'W, 280-360 m; SI074-187 (4), 36°36'N, 79°42'W, 316 m; SI074-188 ( 1 1, 38°18'N, 73°35'W, 215-250 m; SI074-189 (4). 37°27'N, 74°30'W, 120-320 m; SI074- 190 (5), 36°19'N, 74°47'W, 310-400 m; SI075-677 (5), 41°54'N, 69°50'W, 75 m; SI075-678 (1), 41°53'N, 68°07'W, 183 m; SI075-679 (2), 49°09'N, 66°56'W; SIO75-680 (5), 42°30'N, 66°04'W; SI075-681 (3), 43°02'N, 64°32'W; SI075- 682 (1), 42°33'N,66°58'W, 293 m; SI075-683 (6), 42°26'N, 68°44'W; SI075-684 (1), 42°30'N, 69°20'W; SI075-685 (2), 42°31'N, 69°42'W, 275 m; SI075-686 (4), 42°33'N, 69°48'W, 275 m; SI075-689 (3), 37°05'N, 74°40'W, 280-360 m; SI077- 101 (1), 39°35'N, 72°04'W, 201 m; SIO77-102 (1), 39°32'N, 72°22'W, 375-512 m; SIO77-103 (1), 41°32'N, 68°29"W, 86 m; SIO77-104 (1), 41°51,N, 68°05'W, 88 m; SIO77-105 (3), 39°12'N, 72°29'W, 302 m; SIO77-106 (1), 39°05'N, 72°43'W, 234 m; SIO77-107 (4), 38°30'N, 73°19'W, 220 m; SI077- 108 (1), 37°28'N, 74°24'W, 191 m; SI077-119 (2), 37°54'N, 74°00'W, 261 m; ISH6-1965 (1), 45°06'N, 54°46'W; ISH42- 1970 (1), 40°25'N, 68°10'W, 220-230 m; ISH-1987 (3), 66°38.6'N, 56°38.2'W, 540 m; ISH-7238-1982 (2), 66°04'N, 56°13.9'W, 323 m; ISH63-1987 (1), 63°05'N, 52°13'W, 127- 155 m; ISH431-1986 (1), 57°38'N, 18°13'W, 1,006 m; ISH5- 1965 (1), 45°06'N, 54°48'W, 180-260 m; ISH2-1970 (1), 45°00'N, 54°47'W, 175 m; ISH23-1961 (33), 44°19'N, 54°27'W, 175 m; ISH42-1970 (1), 40°25'N, 68o10'W, 230 m; ISH3653-1979 (1), 33°45.8'N, 76°05.6'W, 608 m. Literature cited Chirichigno, F. N. 1968. Nuevos registros para la ictiofauna marina del Peru. Institute del Mar del Peru l(8):37-503. Conel, J. L. 1917. The urogenital system of myxinoids. J. Morph. 29 (1):75-164. Fernholm, B. 1981. A new species of hagfish of the genus Myxine, with notes on other eastern Atlantic myxinids. J. Fish. Biol. 19:73-82. Fernholm, G., and C. L. Hubbs. 1981. Western Atlantic hagfishes of the genus Eptatretus (Myxinidae) with descriptions of two new species. Fish. Bull. 79:69-83. Garman, S. 1899. Reports of an exploration of the west coasts of Mexico, Central and South America and off the Galapagos Islands, in charge of Alexander Agassiz, by the U.S. Fish Commis- sion Steamer "Albatross," during 1891, Lieut. Cmdr. Z. L. Tanner, U.S.N, commanding. XXVI: The fishes. Mem. Mus. Comp. Zool. Harvard College 24:1-431. Girard, C. 1858. Ichthyological notices. Proc. Acad. Nat. Sci. of Phila- delphia (printed 1859):223-224. Gunther, A. 1870. Catalogue of the Physostomi, containing the fami- lies Gymnotidae, Symbranchidae, Muraenidae, Pegasidae, and of the Lophobranchii, Plectognathi, Dipnoi, Ganoidei, Chondroopterygii, Cyclostomata. Leptocarcdii in the Brit- ish Museum. Catalogue of the Fishes in the British Mu- seum, London, 549 p. Hensley, D. A. 1991. Myxine mcmillanae, a new species of hagfish (Myxinidae) from Puerto Rico and the U.S. Virgin Islands. Copeia 1991 (41:1040-1043. Jenyns, L. 1842. Fish. In C. Darwin (ed.), The zoology of the voyage of HMS Beagle, under the command of Captain Fitzroy, R.N. during the years 1832 to 1836, part 4. Smith, Elder, and Co., London. Konstantinov, K. G., and V. D. Shchegelov. 1958. Myxine glutinosa of the Iceland Shores. Zoologi- cheskii Zhurnal. Vol. 37, Part 2, No. 1745. [In Russian, English summary.] Lacepede, B. G. 1803. Histoire naturelle de poisssons. Vol. XI, 138- 652. Chez Plasson, Paris. Leviton, A. E., R. H. Gibbs Jr., E. Heal, and C. E. Dawson. 1985. Standards in herpetology and ichthyology. Part 1: Standard symbolic codes for institutional resource collections in herpetology and ichthyology. Copeia 1985 ( 3 ):802-832. Linnaeus, C. 1758. Systema naturae. Regnum animali, 824 p. McMillan, C. B., and R. L. Wisner. 1984. Three new species of seven gilled hagfishes (Myxinidae, Eptatretus) from the Pacific Ocean. Proc. Calif. Acad. Sci. 43 (161:249-267. Nelson, J. S. 1994. Fishes of the world, 3rd ed. John Wiley and Sons, Inc., New York. Norman, J. R. 1937. Coast fishes. Part II: The Patagonian region (includ- ing the Straits of Magellan). Discovery Reports 16:1-150. Regan, C. T. 1913. A revision of the myxinoids of the genus Myxine. Ann. and Mag. Nat. Hist. (Ser. 8) 11:395-398. Richardson, L. R. 1953. Neomyxine n. s. (Cyclostomata) based on Myxine biniplicata Richardson and Jowett 1951, and further data on the species. Trans. R. Soc. N.Z. 81, (part 3):379-383. 1958. A new genus and species of Myxinidae (Cyclo- stomata). Trans. R. Soc. N.Z., 81 (Part 3): 283-287. 550 Fishery Bulletin 93(3). 1995 Saemundsson, B. 1949. The zoology of Iceland; marine pisces. Vol. 4, Part 72:72-150. E. Munksgaard, Reykjvik. Shimizu, T. 1983. Myxinidae. Myxine. In T. Uyeno, K. Matsuura, and E. Fujii (eds.), Fishes trawled off Suriname and French Guiana, 519 p. Japan Fishery Resource Center, National Sci- ence Museum, Tokyo. [In Japanese with English summaries.] Tambs-Lyche, H. 1969. Notes on the distribution and ecology of Myxine glutinosa. Fisk. Dir. Skr. Havunders 15:279-284. Abstract. Growth of the blacklip abalone, Haliotis rubra, was estimated from 1,464 individuals that were tagged and left at large for up to five years at seven sites in New South Wales, Aus- tralia. Both the shape of the fitted growth curves and the average growth rates differed significantly among sites, separated by only 1-20 km. There was also significant variation in the growth of individual abalone within sites and this variation differed among sites. Abalone at sites where they grew quickly reached larger lengths and were morphologically different from those at sites where they grew slowly. For example, the shells of abalone from sites where they grew slowly were wider and heavier at a given length than those from sites where they grew quickly. The implication that rates of growth in width are less variable than growth in length suggests that a mini- mum legal width limit may be more appropriate than the present size limit that is based on length. A minimum legal width limit would redistribute fishing effort away from sites where abalone grow in length quickly towards sites where they grow slowly, including sites which are presently unfished be- cause few individuals reach the mini- mum legal length. If this were possible, it would reduce the differences in exploi- tation among sites which, at present, have the potential to seriously deplete populations at sites where individuals grow quickly. Covariation between growth and morphology suggests alternative size limits for the blacklip abalone, Haliotis rubra, in New South Wales, Australia Duncan G. Worthington Neil L. Andrew Gary Hamer NSW Fisheries Research Institute RO. Box 21. Cronulla NSW 2230 Australia Manuscript accepted 24 January 1995. Fishery Bulletin 93:551-561 (1995). Legal restrictions on the minimum size of individuals allowed to be harvested are used to manage many fisheries. The theory behind their use asserts that by delaying the harvest of individuals until they have grown to a certain size, both yield and egg production can be in- creased (Beverton and Holt, 1957). Appropriate minimum size limits have traditionally been estimated by considering average rates of growth, mortality, and reproduction (Goodyear, 1993). Spatial variation in demography can complicate the use of a single size limit for a stock by making different size limits ap- propriate in different areas. En- forcement of different size limits over large spatial scales is possible (e.g. Guzman del Proo, 1992), but if demography varies over small dis- tances, appropriate size limits are difficult to enforce. A common finding of studies on the growth of abalone has been that individuals at different sites can grow at markedly different rates (Sainsbury, 1982; Breen, 1986; Tegner et al., 1989). Despite this, there have been few systematic at- tempts to determine the spatial scale over which differences in growth occur (see Day and Fleming, 1992, for a review). Nonetheless, it is apparent that growth can vary among regions separated by hun- dreds of kilometers (Nash, 1992) and among sites separated by tens of kilometers (Breen, 1986). As well as differing in their rate of growth, abalone that grow quickly will, in general, reach larger sizes than aba- lone that grow slowly (e.g. McShane, 1992; Nash, 1992). Consequently, many abalone fisheries contain populations with individuals that grow very slowly to only small sizes (Sloan and Breen, 1988; Tegner et al., 1989; Nash, 1992). Because minimum legal sizes are, in general, enforced over areas larger than those over which such variation in growth can occur, these sites often remain unfished. Commercial fishing of abalone Haliotis rubra in New South Wales (NSW), Australia began in the early 1960's. Initially, divers harvested abalone of any size, but in 1973 a minimum legal length limit of 100 mm was introduced. This length limit was chosen to ensure that aba- lone recruiting to the fishery had reproduced at least once after reaching sexual maturity at ap- proximately 80-90 mm. As fishing pressure increased through the 1970's and 1980's, it became appar- ent that the length limit of 100 mm 551 552 Fishery Bulletin 93(3), 1995 was not conserving enough egg production (Hamer, 1983). In response, the minimum legal length limit was increased in a series of increments from 100 mm in 1979 to 115 mm in 1987. An unfortunate conse- quence of these increases was the concentration of fishing effort at sites where abalone grew quickly and to large sizes (see also McShane, 1992). Because of this high level of effort and the limited dispersal of larval abalone (Prince et al., 1987), such sites were often overexploited, whereas in other areas where abalone grew more slowly to smaller sizes the popu- lations were underexploited. In this study, we describe a tagging study of varia- tion in the growth of Haliotis rubra at seven sites along the NSW coast. These sites were grouped into four locations encompassing most of the geographi- cal range of the fishery. This provides an indication of the variability in growth of the species at three spatial scales: among locations separated by hundreds of km, among sites separated by 1-20 km, and among indi- vidual abalone within the sites. In addition we describe morphological differences among the abalone that ap- pear to be related to their rate of growth. This link be- tween growth and morphology suggests that a mini- mum legal width limit may be more appropriate than the present size limit based on length. curve for all recaptured individuals and in the rela- tionship among morphological variables (see below). Small (=2 x 10 mm), numbered plastic tags were attached to abalone with a cyano-acrylate glue be- tween 20 May 1975 and 3 October 1981. This proce- dure required that abalone be removed from the water and their shells dried with compressed air before tagging. Individuals were chosen to make the size range at tagging representative of the popula- tion at each site. The maximum diameter (i.e. length) of each shell was measured to the nearest 0.5 mm, and the abalone were then replaced in the area near where they were collected. Samples of these tagged abalone were recaptured at opportunistic times be- tween 11 December 1975 and 18 May 1982. Patterns in growth Estimates of growth were obtained by using proce- dures based on a mark-recapture analogue of Schnute's ( 1981) general growth model (see Francis, in press). Schnute's model relates size to age by sev- eral parameters, including two (o and b) which com- bine to describe a range of traditional growth curves including the von Bertalanffy (a > 0, b = 1), Richards Materials and methods Sites and tags used Abalone were tagged at seven sites, spanning almost 1,000 km of coastline, that were chosen because they were commonly used by commercial divers in the NSW abalone fishery (Fig. 1). Six of the sites were grouped into three loca- tions (Broughton Island, Sydney, and Eden) each with two sites (referred to as I and II) separated by between 1 and 20 km. The single site at Merrys Beach was approximately midway between those at Sydney and Eden (Fig. 1). Supplementary tagging was also done at Bittangabee Bay near Eden (Fig. 1). This site was not commonly used by commercial fishermen because few in- dividuals reached lengths above the 115-mm minimum legal limit. Esti- mates of growth parameters for Bittan- gabee Bay were not calculated sepa- rately because only 20 individuals were recaptured. These abalone were, how- ever, used in the estimation of a growth 150 E 35 S Broughton Island Eden Merrys Beach Vu \a S Ficm ^-*MB ^BB X 2km ^^Aii \t j£> 5km Figure 1 Map of Australia (inset) and New South Wales (NSW), showing the posi- tion of eight sites within four locations where blacklip abalone, Haliotis rubra, were tagged. Sites I and II within each location are as indicated on the maps; BB = Bittangabee Bay, MB = Merrys Beach. Worthington et al.: Alternative size limits for Haliotis rubra in New South Wales, Australia 553 (a > 0, b < 0), logistic (a > 0, b = -1), and Gompertz (a > 0, b = 0) models (Schnute, 1981). Francis (in press) reparameterized this model to express ob- served increments in length during tagging (AY") as a function of the observed length at tagging (Yt) and time at liberty (At). The model can be repara- meterized further, so that growth can be described in terms of average annual growth for individuals of a given size (see Francis, 1988a). The general model where both a * 0 and 6*0, was AY -Yl+{Ytb + c(l-e t where At In y$-yb •> yb2%-yUb2 A-yb + yb2-4 yi + ga and A2 = and y2+g2- The model was fitted to the observed increments by using maximum likelihood (Francis, 1988b). Param- eters estimated during this process include the mean annual growth rates (g1 andg2) at two sizes (yx and y2) and the parameter b. These parameters together combine to define the parameter a, and hence the shape of the fitted growth curve. Several other parameters were also considered, and were included in the model if they significantly improved the fit (see Francis, 1988b). Two param- eters describing seasonal variation in growth were examined by replacing At above with At + i(j)t - (f>t ) where for any time itt) _ u(sm(2n[t, -w])) and t, and tr are the times at tagging and recapture. The parameters u and w then describe the ampli- tude and phase of seasonality in growth, respectively. A parameter describing variation in growth among individuals was also examined, where the mean (u ) and standard deviation (o ) of the expected incre- ment in length were related by v<"£ where v is the coefficient of variation in growth. A parameter describing contamination by outliers was also examined, but it never added significantly to the model (see Francis 1988b). The error model used considered errors due to variation in growth and measurement by AY obs AYeD where the observed increment in length (AYo6s) was a function of that predicted by the growth model (AY) and errors due to variation in growth (eg) and mea- surement iem ), assuming eg ~ Nil, og) and £^ ~ Nium, &, >-, u C 01 3 cr 30 20 10 0 r-nji 1 1 1 n Tru Broughton Island I n=124 30 -i 20 10 0 30 20 10 0 i n 4^-f — i — 1 1 1 — \ — * — t— r Broughton Island II n = m ^m 11 30- 20- 10- 0 30 20 LD tru Sydney I n= 113 Sydney II n = 341 JX. EL 30 20 10- 0 r-rfi tu Merrys Beach n =205 Eden I n = 377 30-] 20 10 0 FFTriT Vu- Eden II n = \26 20 40 60 80 100 120 140 160 Length (mm) B 40 1 20- 40 -i 20- nJii 40-| 20 40 20- rn-t-i,~i 40-i 20- mrrnn 40 20- 0 HL 40-i 20 0 rfHm .., 0 12 3 4 Time (years) Figure 2 Distribution of (A) length at marking [Yt) and (B) time at liberty (At) for re- captured blacklip abalone, Haliotis rubra, at seven sites. Worthington et al.: Alternative size limits for Hahotis rubra in New South Wales, Australia 555 Patterns in growth The shape of the fitted growth curve differed signifi- cantly among sites U-tests, P<0.05; Table 1). At Broughton Island I and Sydney I, the fitted growth curve was similar to a traditional von Bertalanffy shape (a > 0, b = 1 in Table 1), whereas at Eden II it was more similar to a Gompertz shape (a > 0, b ~ 0 in Table 1 ), and at Merrys Beach more similar to a logistic shape (a > 0, b = -1 in Table 1). All curves were asymptotic and expected growth approached zero (Fig. 3B). The size at which expected growth equalled zero differed among sites and ranged from 118 mm at Merrys Beach to 151 mm at Broughton Island II (Fig. 3B; Table 1). Estimates of average annual growth rates differed significantly among the seven sites (Table 1). Aba- lone at the two sites on Broughton Island had faster rates of growth than all other sites. At Broughton Island II a 65-mm abalone was expected to grow to the 115-mm length limit in approximately 18 months (Fig. 3A). Above 115 mm, growth declined rapidly so that in the next year expected growth was less than 10 mm. The rate of de- cline in growth rate then slowed, and growth was expected to con- tinue until 151 mm (Fig. 3; Table 1). In contrast, growth at Sydney I was much slower; a 65-mm indi- vidual was expected to take almost 9 years to grow to 115 mm (Fig. 3A). Growth rate declined at an approxi- mately constant rate throughout life (i.e. approximating a von Bert- alanffy growth curve) until indi- viduals were expected to have no growth at 126 mm (Fig. 3; Table 1 ). At Merrys Beach, abalone were expected to grow from 65 mm to 90 mm within a year, but then growth declined rapidly and indi- viduals were expected to grow only just above the minimum length limit of 115 mm (Fig. 3A). Growth rates at Sydney II and Eden II were not significantly different at any of the standard sizes (Table 1). There was significant variation in growth among individual aba- lone within all sites (Table 1). Variation in growth among aba- lone at Merrys Beach was signifi- cantly less than that at all other sites and significantly greater at Broughton Island II, Sydney I, and Eden I U-tests, P<0.05). The stan- dard deviation of the observed growth increment ranged from 0.29 times the expected increment at Merrys Beach to 0.87 times the expected increment at Eden I (Table 1). This range implies that two-thirds of the abalone at Merrys Beach will grow between 0.71 and 1.29 times the expected increment, whereas at Eden I, two-thirds of the abalone will grow be- tween 0.13 and 1.87 times the expected increment (Fig. 4). Parameters representing seasonal variation in rates of growth significantly improved the fit of the model at three of the seven sites (Table 1). At Broughton Island II, peak growth rates occurred during late October at 1.9 times the minimum growth rate in late April. In contrast, peak growth rates at both Sydney II and Eden I occurred in December at a rate 2.0 and 2.9 times the minimum, respectively 2 4 6 Time (years) 2 4 6 Time (years) 10 B i>) 20 40 60 80 100 120 140 Length (mm) 50 30 10 0 -10 20 40 60 80 100 120 140 Length (mm) Figure 3 Predicted mean growth of blacklip abalone, Haliotis rubra; (A) over 10 years for individuals of a given size and (B) over 1 year for individuals of a range of sizes. Growth is shown from (i) 40 mm at sites where many small abalone were tagged and (ii) 65 mm at sites where few small abalone were tagged up to the size of the largest abalone. Sites are abbreviated as follows: BI and BII = Broughton Island I and II; SI and SII = Sydney I and II; MB = Merrys Beach; EI and EII = Eden I and II. 556 Fishery Bulletin 93(3). 1995 Table 1 Estimates of growth parameters and their standard errors (in brackets) for blacklip abalone, Haliotis rubra, from tag returns at seven sites. Parameters estimated during fitting are shown in light type; those defined by the fitted parameters are shown in bold. Expected annual growth rate at 65, 90, and 115 mm is shown asg65, g30 &n&gu5, respectively. See Materials and Methods section for a description of other parameters. Blanks occur where parameters did not add significantly to the fitted model. Parameter Site Broughton Island Sydney Merrys Beach Eden I II I II I II Curve shape parameters b 1.33 (0.30) 7.58(1.13) 1.33(0.41) 0.25 (0.09) -0.74(0.12) 0.50 (0.37) 0.04(0.10) a 0.59 (0.13) 0.11 (0.05) 0.20 (0.06) 0.66 (0.08) 0.89 (0.08) 0.22 (0.04) 0.71 (0.14) Growth rate parameters ggjlmm-year-1) 33.68 (1.52) 46.93 (2.78) 12.25(0.77) 28.66(0.78) 24.63 (0.60) 12.71 (0.92) 28.80(0.96) gggimm-year-1) 22.24(0.95) 24.11(1.39) 6.91 (0.52) 19.58 (0.67) 15.22(0.34) 9.14(0.49) 19.87(0.69) gu5 (mmyear-1) 11.52(0.62) 8.36(0.62) 2.06(0.91) 8.87 (0.77) 2.21 (0.42) 4.86(0.28) 8.85 (1.40) Seasonal parameters u (year) 0.31 (0.08) 0.48 (0.05) 0.33 (0.07) w (year) -0.19(0.01) 0.00(0.01) -0.01 (0.03) Growth variability parameter v 0.54(0.04) 0.73 (0.05) 0.76(0.06) 0.48 (0.02) 0.29 (0.01) 0.87 (0.05) 0.39(0.02) Asymptote (mm) 143 151 126 133 118 140 133 Largest abalone (mm) 151 152 124 132 130 143 129 n 124 178 113 341 205 377 126 May Jul Sep Time (months) Figure 4 Predicted mean growth (solid line) and 50% confidence in- tervals (dashed line) of 65-mm blacklip abalone, Haliotis rubra, over one calender year at two sites. (Fig. 4). At Broughton Island I, Sydney I, Merrys Beach, and Eden II there was no evidence of any sig- nificant seasonal variation in growth rates (Table 1 ). Relation of growth to morphology There were differences in the morphology of abalone among sites. For example, the shells of abalone re- captured from Merrys Beach were, on average, wider, heavier, and had a larger ridge than individuals of the same length from Sydney II (Fig. 5). There was a significant difference among sites in the slope of each of the relationships (<-tests, P<0.05), suggesting that the difference in morphology of individuals among sites changed with length. The shell of a 100-mm abalone from Merrys Beach was, on average, approxi- mately 5 mm wider, 8.3 g heavier, and had a 1.7 mm larger ridge than the shell of a 100-mm abalone from Sydney II (Fig. 5). Differences in the width and ridge of shells among the sites increased with length, whereas differences in the weight of shells decreased with length (Fig. 5). The width, weight, and ridge of all shells were each significantly correlated with the other variables (width vs. weight r=0.76; width vs. ridge r=0.58; weight vs. ridge r=0.68; n=390 for all correlations). Abalone from sites where their average growth was faster were morphologically different from those Worthington et al.: Alternative size limits for Haliotis rubra in New South Wales, Australia 557 where their average growth was slower (Fig. 6). The residuals of the general growth model were significantly higher at sites such as those at Broughton Island, Sydney II, and Eden II than at Eden I, which was, in turn, significantly higher than Merrys Beach and Sydney I, or Bittangabee Bay Otests, P<0.05; Fig. 6). This ranking corresponds closely with the estimates of average growth rates in Table 1. The residu- als of the relation between length and the inde- pendent variables width, weight, and ridge were generally higher at sites where growth was also high (Fig. 6). That is, given their width, weight, and ridge, abalone at sites where they grew quickly were longer than those where they grew slowly. Alternatively, shells of abalone of a given length at sites where they grew quickly were thinner, lighter, and had a smaller ridge than those at sites where they grew slowly. Discussion Patterns in growth The intense spatial variation in growth that we observed for Haliotis rubra in NSW appears to be characteristic of abalone populations world- wide (Day and Fleming, 1992). At the smallest spatial scale, there was significant variation in the growth rate of abalone within sites. At a larger scale, both average rates of growth and the magnitude of within-site variation differed among sites separated by only 1—20 km. Per- haps the most likely explanation for variation in growth over these smaller spatial scales in- volves variation in the supply of food, related to local habitat and hydrographic conditions (Day and Fleming, 1992). At the largest spatial scale, average growth rates at the two sites on Broughton Island were significantly higher than all others. Broughton Island is approxi- mately 300 km farther north than any of the other sites, and abalone around the island are likely to be exposed to higher water tempera- tures than abalone farther south. Water tem- perature is known to affect the growth rate of abalone (Day and Fleming, 1992), but the trend in NSW stands in contrast to that found for H. rubra in Tasmania, where abalone grow more slowly in the warmer, northern areas (Nash, 1992). Several previous studies have found a relation be- tween the rate of growth and maximum size of aba- lone at a site (Shepherd and Hearn, 1983; McShane et al., 1988; Sloan and Breen, 1988; Nash, 1992). In 120 B 4.50 £ 4.251 Merrys Beach C » Sydney II r = 0.44 90 100 110 Length (mm) 120 Figure 5 Relationship between shell length and (A) shell width, (B) shell weight, and (C) shell ridge for blacklip abalone, Haliotis rubra, recaptured from two sites. Filled circles and arabic numerals denote abalone from Sydney II, and open squares and roman numerals denote abalone from Merrys Beach. Numerals denote the number of coincident points, and the lines were fitted by least- squares. general, abalone at sites where they grow quickly reach larger sizes than those at sites where they grow slowly. A similar situation appears to exist in NSW where abalone from the two sites on Broughton Is- land had the fastest average growth rates and reached the largest shell lengths (i.e. >150 mm, Table 1). In comparison, the slowest average growth rates 558 Fishery Bulletin 93(3). 1995 2.5" ^^ >> i.s- o o .s & 0.5" o 6 -a -0.5- 3 T) U -1.5" OS -2.5 "> 1 SI MB HI + [SII [SII Bn1 -113 5 Residual (growth) Figure 6 Average residual from growth and morphological relation- ships for blacklip abalone, Haliotis rubra, recaptured from eight sites. Vertical and horizontal bars are standard er- rors. Sites are abbrieviated as follows: BI and BII = Broughton Island I and II; SI and SII = Sydney I and II; MB = Merrys Beach; EI and EII = Eden I and II; BB = Bittangabee Bay. were recorded at Sydney I where the largest abalone was smaller than those at all other sites (i.e. 124 mm, Table 1). Despite this general relationship, slow rates of growth were recorded at Eden I, but growth was expected to continue until 140 mm, and many aba- lone were found over 130 mm in length. Direct comparison of growth rates estimated by different studies are complicated by the variety of methods used for tagging and analysis. For example, tags attached by wire through an abalone's respira- tory pore can affect growth (McShane et al., 1988), and growth parameters estimated from tagging and age-length data need to be interpreted differently (Francis, 1988a). Any comparison of growth rates among studies can also be confounded by the growth model used to fit the observed increments (e.g. com- pare estimates of growth from the different models used in Tables 1 and 2). When fitted with a similar growth model to past studies, our estimates of the growth of abalone in NSW span almost the entire range of those from similar studies in other states of Australia (Table 2). In addition, estimates of growth at the two sites on Broughton Island are consistently higher than any previously reported natural growth rates for the species. Relation of growth to morphology Differences in the morphology of individuals among populations have been reported for a range of gas- tropod species including abalone (see review by Vermeij, 1980). Despite the significance of variation in the morphology of Haliotis rubra in NSW, differ- ences among sites were not large (e.g. compare with those of Breen and Adkins, 1982). There was also substantial variation in the morphology of individu- als within sites. Despite little evidence, explanations for the variation in morphology of abalone usually concentrate on environmental rather than on genetic factors (McShane et al., 1988). As for other gastro- pods, it is likely that all aspects of shell growth that result in morphological differences are influenced by a variety of factors including exposure to wave ac- tion, diet, and water temperature (Tissot, 1992; Belda et al., 1993). Although we only present evidence to suggest that differences in morphology of the shell exist among populations of Haliotis rubra, there is also evidence for related morphological variation in the soft tissues (McShane et al., 1988). Differences in the morphology of Haliotis rubra among sites were related to differences in growth. At sites where they grew slowly, the shells of aba- lone were wider, heavier, and had a broader ridge than those at sites where they grew quickly. These observations are similar to those made on other spe- cies of abalone (e.g. Breen and Adkins, 1982; Shep- herd and Hearn, 1983; Tissot, 1988) and perhaps are not surprising considering that the processes pro- posed to influence both growth and morphology are similar. Inclusion of the slow-growing population at Bittangabee Bay strengthened the relation between growth and morphology that was evident among the seven sites where extensive tagging was done. Ex- tensive tagging was not done at Bittangabee Bay because few animals grow above the present 115-mm legal length limit and hence the site is rarely fished by commercial divers. Because of the relationship be- tween the maximum size reached by abalone at a site and their growth rate, very slow growing sites are rarely visited by commercial divers and, consequently, were not chosen for tagging in this study. As a result, our estimates of growth represent the higher end of the range of growth rates for abalone in NSW. The increased width and weight of shells from aba- lone that grew slowly in length imply that rates of shell growth in width and weight are more consis- tent among sites than growth in length. This might be explained by increased synthesis of the organic matrix of the shell when energy is plentiful (Palmer, 1992) and can be devoted to expansion of the mantle at the growing edge and hence to rapid growth in length (Belda et al., 1993). Alternatively, when less energy is available, reduced synthesis of the organic matrix may result in a slower expansion of the grow- ing edge of the mantle, causing slower growth in length and proportionally more growth in width and weight (Vermeij, 1980). Such an explanation would Worthmgton et al.: Alternative size limits for Haliotis rubra In New South Wales. Australia 559 not require any variation in the rate of incorporation of calcium-carbon- ate, which may continue regardless of the rate of synthesis of the organic matrix (see similar arguments for fish otoliths in Gauldie and Radtke, 1990). Because calcium-carbonate dominates a shell by weight (Palmer, 1992), if the rate of incorporation of calcium-carbonate was similar among different populations, the total weight of the shell might be a reli- able indicator of the age of the aba- lone (see the literature on use of the weight of otoliths to age fish, e.g. Worthington et al., in press). The ability to age abalone is obviously desirable, but much doubt exists about present techniques of ageing, particularly for Haliotis rubra (Mc- Shane and Smith, 1992). This uncer- tainty emphasizes the need to inves- tigate alternative methods to age abalone, one of which may be shell weight (Worthington et al., unpubl. data). Potential for alternative size limits The present 115-mm minimum legal length limit is enforced along the entire coast of NSW for both the com- mercial and recreational fisheries. This size limit was chosen by consid- ering average rates of growth, mor- tality, and reproduction in an attempt to maximize yield from the entire stock. The intense spatial variation in growth that we have described creates several problems which combine to restrict the effectiveness of the length limit. For example, because the 115-mm length limit was chosen by con- sidering average rates of growth, it is less appropri- ate for sites where abalone grow faster or slower than average. At sites where they grow quickly, abalone rapidly reach the minimum legal length and may be harvested before contributing significantly to levels of egg production. Because of the limited dispersal of larval abalone (Prince et al., 1987), such sites have a limited capability to recover after fishing and hence may easily become overexploited. In contrast, at sites where they grow slowly, abalone take a longer time to reach the minimum legal length limit, and few are removed by divers. Consequently, rates of egg production may be high but they do not contribute Table 2 Comparison of estimates of growth for blacklip abalone, Haliotis rubra. Note the estimated growth of abalone below 80 mm from Prince et al. ( 1988) was determined by analysis of size-frequency distributions; all other estimates were derived from tags glued to the external surface of the shell. Expected annual growth rate at 65, 90, and 115 mm is shown asgg5, ggo, andgn5, respectively. Study and location 865 f>90 &U5 £„ k (mmyeai -1) (mm) (year"1) Shepherd and Hearn South Australia 1983 21.3 14.1 6.9 139 0.34 21.3 14.4 7.6 143 0.32 26.4 18.0 9.7 144 0.41 McShane et al., 1988 Victoria 13.1 6.8 0.5 117 0.29 16.5 9.2 1.8 121 0.35 16.1 10.2 4.3 133 0.27 Prince et al., 1988 Tasmania 21.0 12.6 6.3 140 0.29 McShane and Smith, 1992 Victoria 26.9 19.2 11.5 152 0.37 16.5 9.2 1.8 121 0.35 7.8 4.3 0.8 121 0.15 This study, NSW Broughton Island I 38.0 25.7 13.3 142 0.68 II 28.0 19.8 11.5 150 0.40 Sydney I 16.3 9.3 2.3 123 0.33 II 32.1 21.1 10.1 138 0.58 Merrys Beach 22.6 11.7 0.9 117 0.57 Eden I 18.0 12.1 6.2 141 0.27 II 30.4 17.9 5.5 126 0.69 significantly to other populations because of the re- stricted dispersal of larvae (see also Tegner, 1993). In addition, because of the link between growth rate and the maximum length of abalone at a site, as the maximum length of abalone at the site is below the minimum length limit, many populations can never be fished. Different length limits related to the growth of abalone at a site would be desirable, but considering the small spatial scales over which sig- nificant differences in growth can occur, their enforce- ment would be impractical. An alternative approach to applying different length limits would be to enforce a size limit based on shell width. Because of the differences in mor- phology of abalone among sites with different growth rates, a width limit would allow individuals from sites where they grow slowly to be removed at shorter lengths than those where they grow quickly. This 560 Fishery Bulletin 93(3), 1995 would have two potentially desirable consequences. First, it would distribute effort more evenly across sites with the entire range of growth rates. This would occur because more abalone could be collected from sites where they grow slowly, and less would be available at sites where they grow quickly. Follow- ing the progressive increase in length limit during the 1980's, most fishing became concentrated at sites where abalone grew quickly (see also McShane, 1992). As described above, the length limit at these sites was also lower than appropriate, which in combination with the intense fishing effort, so that populations at sites where growth was fast were exploited at considerably higher rates than those for other populations. The second desirable consequence of enforcing a width limit would be to allow the collection of aba- lone from sites that are presently unfished because abalone grow very slowly and few reach the mini- mum legal length (i.e. as stunted abalone). If an ap- propriate width could be chosen, more abalone would be available for collection at sites where they grow slowly, making it viable for divers to visit such sites. There is some evidence to suggest that growth rates of individuals at sites where they appear stunted are limited by a lack of available food (Shepherd and Hearn, 1983). By removing individuals, more food may be available to those that remain and their growth rates may, in turn, increase. Considering the frequency of studies reporting covariation in growth and morphology of abalone, we suggest that alternative size limits appear to have the potential to improve the management of many abalone fisheries. The intense spatial variation in growth and related differences in morphology of Haliotis rubra in NSW, and the ease with which shell width can be measured, make a size limit based on width a potential alternative to the present length limit. The application of a width limit would allow abalone that have grown at different rates to be har- vested at different lengths, essentially enforcing dif- ferent length limits over very small spatial scales. As a consequence, the potentially damaging imbal- ance in exploitation rates among sites with different rates of growth in length would be avoided. Acknowledgments DGW and NLA would like to acknowledge the fore- sight of GH in the initiation of the tagging program and in the subsequent retention of recaptured shells. Others who helped tag and recapture abalone include T Butcher and J. Matthews. R. I. C. C. Francis pro- vided us with Grotag, and G. Gordon and M. Krogh helped with programming. N. Bentley, P. Brett, P. Fairweather, D. Ferrell, R. I. C. C. Francis, and W. Nash helped improve various drafts of the manuscript. Literature cited Belda, C. A., C. Cuff, and D. Vellowlees. 1993. Modification of shell formation in the giant clam, Tridacna gigas, at elevated nutrient levels in sea water. Mar. Biol. 117:251-257. Beverton, R. J. H., and S. H. Holt. 1957. On the dynamics of exploited fish populations. U.K. Minist. Agric. Fish. Fish. Invest. (Ser. 2) 19, 533 p. Breen, P. A. 1986. Management of the British Columbia fishery for northern abalone {Haliotis kamtschatkana) . Can. Spec. Publ. Fish. Aquat. Sci. 92:300-312. Breen, P. A., and B. E. Adkins. 1982. Observations of abalone populations on the north coast of British Columbia, July 1980. Can. MS Rep. Fish. Aquat. Sci. 1633, 55 p. Day, R. W., and A. E. Fleming. 1992. The determinants and measurement of abalone growth. InS.A. Shepherd, M.J. Tegner, and S. A. Guzman del Proo (eds.), Abalone of the world: biology, fisheries and culture, p. 141-168. Fishing News Books, Oxford. Francis, R. I. C. C. 1988a. Are growth parameters from tagging and age-length data comparable? Can. J. Fish. Aquat. Sci. 45:936-942. 1988b. Maximum likelihood estimation of growth and growth variability from tagging data. N.Z. J. Mar. Fresh- water Res. 22:42-51. In press. An alternative mark-recapture analogue of Schnute's growth model. Fish. Res. Gauldie, R. W., and R. L. Radtke. 1990. Microincrementation: facultative and obligatory pre- cipitation of otolith crystal. Comp. Biochem. Physiol. 97A: 137-144. Goodyear, P. C. 1993. Spawning stock biomass per recruit in fisheries man- agement: foundation and current use. Can. Spec. Publ. Fish. Aquat. Sci. 120:67-81. Guzman del Proo, S. A. 1992. A review of the biology of abalone and its fishery in Mexico. In S. A. Shepherd, M. J. Tegner, and S. A. Guzman del Proo (eds.), Abalone of the world: biology, fisheries and culture, p. 341-360. Fishing News Books, Oxford. Hamer, G. 1983. NSW abalone stock assessment shows effort should be reduced. Aust. Fish. 42:7-11. McShane, P. E. 1992. Exploitation models and catch statistics of the Victo- rian fishery for abalone Haliotis rubra. Fish. Bull. 90:139-146. McShane, P. E., and M. G. Smith. 1992. Shell growth checks are unreliable indicators of age of the abalone Haliotis rubra (Mollusca: Gastropoda). Aust. J. Mar. Freshwater Res. 43:1215-1219. McShane, P. E., M. G. Smith, and K. H. H. Beinssen. 1988. Growth and morphometry in abalone {Haliotis rubra Leach) from Victoria. Aust. J. Mar. Freshwater Res. 39:161-166. Nash, W. J. 1992. An evaluation of egg-per-recruit analysis as a means Worthington et al.: Alternative size limits for Haliotis rubra in New South Wales, Australia 561 of assessing size limits for blacklip abalone {Haliotis rubra ) in Tasmania. In S. A. Shepherd, M. J. Tegner, and S. A. Guzman del Proo(eds.), Abalone of the world: biology, fish- eries and culture, p. 318-338. Fishing News Books, Oxford. Palmer, A. R. 1992. Calcification in marine molluscs: How costly is it? Proc. Natl. Acad. Sci. USA 89: 1379-1382. Prince, J. D., T. L. Sellers, W. B. Ford, and S. R. Talbot. 1987. Experimental evidence for limited dispersal of haliotid larvae (genus Haliotis;Mo\\usca: Gastropoda). J. Exp. Mar. Biol. Ecol. 106:243-263. Prince, J. D., T. L. Sellers, W. B. Ford, and S. R. Talbot. 1988. Recruitment, growth, mortality and population struc- ture in a southern Australian population of Haliotis rubra (Mollusca: Gastsropoda). Mar. Biol. 100:75-82. Sainsbury, K. J. 1982. Population dynamics and fishery management of the New Zealand abalone Haliotis iris. I: Population structure, growth, reproduction and mortality. N.Z. J. Mar. Fresh- water Res. 16:147-161. Schnute, J. 1981. A versatile growth model with statistically stable parameters. Can. J. Fish. Aquat. Sci. 38:1128-1140. Shepherd, S. A., and W. S. Hearn. 1983. Studies on southern Australian abalone (Genus Haliotis). IV: Growth of H. laevigata and H. ruber. Aust. J. Mar. Freshwater Res. 34:461-745. Sloan, N. A., and P. A. Breen. 1988. Northern abalone, Haliotis kamtschatkana, in Brit- ish Columbia: fisheries and synopsis of life history information. Can. Spec. Publ. Fish. Aquat. Sci. 103, 46 p. Tegner, M. J. 1993. Southern California abalones: Can stocks be rebuilt using marine harvest refugia? Can. J. Fish. Aquat. Sci. 50:2010-2018. Tegner, M. J., P. A. Breen, and C. E. Lennert. 1989. Population biology of red abalones, Haliotis rufescens, in southern California and management of the red and pink, H. corrugata, abalone fisheries. Fish. Bull. 87:313-339. Tissot, B. N. 1988. Morphological variation along intertidal gradients in a population of black abalone, Haliotis cracherodii Leach, 1814. J. Exp. Mar. Biol. Ecol. 117:71-90. 1992. Water movement and the ecology and evolution of the Haliotidae. In S. A. Shepherd, M. J. Tegner, and S. A. Guzman del Proo (eds.), Abalone of the world: biology, fish- eries and culture, p. 34—45. Fishing News Books, Oxford. Vermeij, G. J. 1980. Gastropod shell growth rate, allometry, and adult size: environmental implications. In D. C. Rhoads and R. A. Lutz (eds.), Skeletal growth in aquatic organisms, p. 379-394. Plenum Press, New York. Worthington, D. G., P. Doherty, and A.J. Fowler. In press. Variation in the relationship between otolith weight and age: implications for the estimation of age of two tropical damselfish {Pomacentrus moluccensis and P. wardi). Can. J. Fish. Aquat. Sci. An analysis of weekly fluctuations in catena bili ty coefficients* Steven M. AtrarT* Joseph G. Loesch School of Marine Science, Virginia Institute of Marine Science College of William and Mary, Gloucester Point, Virginia 23062 Analyses of time series of commer- cial catch statistics are usually made with an implied assumption that catchability remains constant. Although the annual catchability from year to year may remain fairly constant, this assumption is rarely, if ever, valid for catchability within a season. Changes in catchability, abundance, and fishing all contrib- ute to fluctuations in the catch from a fish stock (Clark and Marr, 1956; Pope and Garrod, 1975). Behavioral changes due to size or age may cause variations in catchability (Morrissy and Caputi, 1981). By ex- amining the within-season changes in catchability, it may be possible to discern properties of a stock that are not apparent when only annual time intervals are examined. The objective of this study was to develop a means to estimate weekly within-season catchability coefficients of a stock and to dem- onstrate how examination of these short-term fluctuations might be useful in a stock analysis. Atlantic menhaden, Brevoortia tyrannus, was selected as a model because of the availability of a time series of weekly catch-at-age data for this species. Methods Data Weekly menhaden catch-at-age (in numbers) and vessel-landings data from 1968 to 1982 were made avail- able by the Beaufort Laboratory, National Marine Fisheries Service (NMFS), Beaufort, North Carolina. Migrating menhaden stratify by age and size (Nicholson, 1971b); therefore, the stock was divided into age groups to eliminate differ- ences in catchability due to age-spe- cific (and size-specific) migration patterns. Calculation of weekly abundances Abundance estimates with con- stant time intervals of one week were needed to allow between-year comparisons of weekly catchability and to conform to the Beaufort Laboratory's system of reporting catches. Such short time intervals usually resulted in consecutive in- tervals of zero catches commonly occurring near the beginning and end of a sequence of weekly land- ings data for a given year and age group. Murphy (1965) developed a method for estimating abundance and fishing mortality rates on a co- hort offish when catches are known within time intervals and when an estimate of instantaneous fishing mortality for one time interval and natural mortality for all time inter- vals are available. A restriction on this method is that the time inter- vals must be of equal duration and that each time interval must con- tain catches. Tomlinson ( 1970) pre- sented a generalization of Murphy's method, which allowed for variable time intervals and zero catches, provided that the first and last time intervals each contain catches and that two or more consecutive zeros do not occur. The normal method for ensuring that consecutive zero's do not occur in the catch data is to pool time in- tervals containing zero catches with adjacent nonzero intervals. In this study it was desirable to keep the time intervals fixed, even if it results in consecutive zeros in the catch data. A modification of Tomlinson's method was used, which allows for any number of con- secutive zeros, provided that the first and last time intervals contain catches. Extension to Tomlinson's model A catch ratio, i?-, can be constructed between catch in the current and subsequent time interval. The ra- tio for interval i is given by (Eq. 4 in Tomlinson, 1970) R, C, E, ■ (1) where Ci,Ci j = number of fish caught in time in- tervals i, f+1; F- - instantaneous fish- ing mortality in time interval i; M(. = instantaneous nat- ural mortality in time interval i; E{, Ei+l = exploitation rate in time intervals i, ' Contribution 1932 of the College of Will- iam and Mary, Virginia Institute of Ma- rine Science, School of Marine Science, Gloucester Point, Virginia 23062. ** Present address: Gulf of Mexico Fishery Management Council 5401 West Kennedy Boulevard, Suite 331 Tampa, Florida 33609-2486 Manuscript accepted 13 February 1995. Fishery Bulletin 93:562-567 (1995). 562 NOTE Atran and Loesch: An analysis of fluctuations in catchability coefficients 563 If catch in time interval i+1 is zero, then the ratio Rt is zero and the subsequent ratio Ri+l is undefined. In this case, the ratio can be constructed between the current time interval and the second subsequent interval. This ratio (Rl+1) is given by Equation 5 in Tomlinson, 1970, as !+1 * C " E, (2) The above equation is Tomlinson's extension to Murphy's catch equation. This can be further extended to include any number of intermediate time intervals with zero catch. A generalized form of the catch ratio between any two time intervals i and i+k, where the catches for all intermediate time intervals is zero, is (3) Given an estimate of natural mortality rate and fish- ing mortality rate for the final time interval, F's for the previous time intervals can be solved by estimat- ing E{ x expU-(.F+M-)]. This can be estimated from Ei+k by rearranging Equation 3 as E,e t,(F+M,) C E e~(w*f,'+l)""'~H"*-lAf''+*-l) - l i - h (4) Ji+k where C is nonzero, and all catches between t- and ti+k are zero. Ft may be found by iteration after in- serting the result of Equation 4 in the following equa- tion (Equation 9 in Tomlinson, 1970) E,e t,(Fl+M,) _ Et{e t,(F,+M, ) 1) F+M, (5) Once the F.'s have been estimated, the F('s can be estimated by inserting the value of the above equa- tion into the following: (the value of Equation 5) hi~ jJfTm-) After calculating the F-'s and F 's, the population size at the start of each time interval (AT) can be esti- mated from Nt =-L, where E, <>0. E, To demonstrate the use of this extension to Tomlinson's method for solving the catch equation, the computer program MURPHY (Abramson, 1971), which implements Tomlinson's model, was modified to incorporate the extension for consecutive zeros to estimate weekly abundance and fishing mortalities for the Atlantic menhaden purse-seine fishery. The catch data were broken up into weeks and into age groups within a week. Constant parameters used In addition to catch-at-age data, virtual population analysis (VPA) requires estimates of instantaneous natural mortality for all time intervals and an esti- mate of instantaneous fishing mortality for one time interval. Natural mortality was assumed constant and a weekly value of 0.0087 (annual M=0.45) was adopted on the recommendation of the Beaufort Labo- ratory Estimates of fishing mortality for the final week of landings data in each year were obtained from Table 13 of Broadhead et al.1 for the years 1968— 76 and for age groups 0-5. For age groups 6-8 the values for age 5 were used. For the years 1977-82, the average values for the years 1968-76 for each age group were used (1968-75 for age group 0). In each case, the annual value of F from the table was divided by the number of weeks in the year that had landings data to obtain a weekly F. Instantaneous fishing mortality values were probably overestimated because catch generally declined at the end of the season. However, in the backward solution to the catch equation, the value for F tends to converge to- ward its true value for a given M. Therefore, the er- ror in abundance estimates due to this overestima- tion of F should be minor at the beginning of each year's landing data, although it may result in the underestimation of abundance toward the end. Defining effort An index of fishing effort was needed to calculate a catchability coefficient. The number of vessels with landings in a given week (vessel-week) is commonly used as the unit of fishing effort in studies of the menhaden purse-seine fishery and was the unit used in this study. Menhaden vessels generally operate continuously throughout all or part of the fishing season, fishing every day, as weather permits, un- (7) 1 Broadhead, G., C. Grimes, J. Loesch, W. Nelson, G. Sakagawa, and K. West. 1980. Report of the Atlantic menhaden popula- tion dynamics subcommittee to the Atlantic menhaden scien- tific and statistical committee on the status of the Atlantic men- haden stock and fishery. Unpubl. manuscr.. 68 p. 564 Fishery Bulletin 93(3). 1995 less they are in port for repairs. Any time period that assumes continuous fishing and accounts for unpro- ductive fishing days should be a satisfactory unit of fishing effort (Nicholson, 1971a). Number of land- ings as a unit of effort assumes continuous fishing. Although the number of days that a given vessel was fishing in a week was unknown it was assumed that variations were randomly and normally distributed. Calculation of weekly catchability coefficients The catchability coefficient is defined as the fraction of a fish stock that is caught by a defined unit of fishing effort (Ricker, 1975). The relation between catch, effort, abundance, and catchability is (Sokal and Rohlf, 1981) was used to test for signifi- cant differences in annual patterns of weekly catchability coefficients for each age group between years. This is the nonparametric analog to the para- metric analysis of variance (ANOVA) randomized complete block design, but the rankings of the vari- ates within each block are used rather than the ac- tual measurements. A nonparametric test was used because the relative degree of weekly fluctuations from year to year may vary owing to biotic or abiotic factors. Thus, heterogeneity of variance between years may be expected, making a parametric model inappropriate. Results [fit = g,Nt , (8) where ( Clf)t = average catch per unit of effort over period t; Nt = average abundance during period t; and qt = catchability during period t. The VPA estimates of abundance are for the be- ginning of a time period. For the short, one-week time periods used in this study, average abundance in a period is assumed to approximate (Nf + Nf+1)/2. Av- erage catch per unit of effort in a time period can be calculated as total catch divided by total effort for that period. The above equation can thus be rear- ranged to define the catchability coefficient as Catc i 0 003- 0004- 00025- 0003 ■ 0 002- 00015 ■i" 0002 0 001- 0 001- ;J k i\\\w\ 0 0005- ■-It ¥ hi 0 5 10 15 20 25 30 35 40 45 S< ) 0 5 10 15 20 25 30 35 40 4S 5C Week Age 6 0 005 0004- - 0003 0 002 0001 ■■A- 0 S 10 15 20 25 30 35 40 45 9 Week ) Figure 1 Mean and range of weekly catchability coefficients for Atlantic menhaden, Brevoortia tyrannus, from 1968 to 1982. 566 Fishery Bulletin 93(3), 1995 Discussion Virtual population analysis assumes that there is complete recruitment for a set of age classes and that availability remains constant for all recruited age classes. The existence of sharp initial and ending seasonal catchability peaks is probably due to un- derestimation of abundance at the beginning and end of the season from the VPA method. This indicates that VPA can be biased when availability fluctuates. Virtual population analysis measures the "virtual" abundance, that which appears to the fishery to be there, rather than absolute abundance. Early in the season, when the menhaden are migrating into the fishing area from their wintering grounds, only part of the stock is available for exploitation. Changes in availability, or accessibility, can affect the catchability coefficient (Cushing, 1968). Marr (1951) showed that catchability is directly related to availability. How- ever, because VPA assumes that there is full avail- ability, abundance is underestimated. If the abun- dance is underestimated, then the catchability coef- ficient will be overestimated (Shardlow and Hilborn, 1985). Theoretically, this first peak should extend to in- finity prior to the start of the season when VPA is used to estimate abundance, because availability at this point in time is zero. If abundance had been measured with a method independent of the fishery catch statistics, such as mark-recapture, catchability estimates would have been based on absolute rather than on virtual abundance and there would not have been an early season peak. The rise from zero or near- zero catchability which occurs in many of the plots, particularly with older age groups, may be due to an earlier or faster migration of these age groups into the fishing area or to more complete recruitment of the age group at the start of the season. Younger age groups are not completely recruited into the fishery, but by age 2, the menhaden are fully recruited into the Atlantic coast purse-seine fishery (Atlantic Men- haden Management Board, 1981). If availability is at or near maximum by the time of the first catch, VPA will not underestimate abundance, and conse- quently catchability will not be overestimated. One advantage of examining within-season fluctuations of catchability, therefore, may be to assess when the stock becomes available to the fishery. After the initial peak, a gradual rise in catchability can be seen as the season progresses, most likely due to a decrease in abundance during a period of full availability. This observation is consistent with Schaaf (1975), who reported a logarithmic inverse relation between annual values of catchability and abundance of menhaden. An increase in this rate might result if stock abundance during the season were decreasing faster than normal, and it would then be an indicator of overfishing. The pattern of catchability for age-0 menhaden differs from that of the other age groups in that there is no initial peak and landings begin much later in the season (Fig. 1). Age-0 menhaden are fished ex- tensively in the North Carolina fall fishery which is largely directed toward these fish. Paloheimo and Dickie ( 1964) stated that when fishermen selectively apply their effort toward some schools, the result is variance in the catchability coefficient depending on age, species, and relative abundance. This effect is apparent in the plot of average weekly catchability coefficient for age-0 menhaden. When the age-0 men- haden, commonly referred to as "peanuts," migrate out of Virginia and North Carolina estuaries, they become readily available close to shore where they dominate the landings, usually in December and January. Acknowledgments This manuscript is based on a thesis submitted by Steven Atran to the School of Marine Science of the College of William and Mary in partial fulfillment of the requirements for an MA. degree. Herbert Aus- tin, David Evans, George Grant, and Robert Huggett of the School of Marine Science, and Douglas Vaughan of the NMFS Beaufort Laboratory reviewed an earlier draft of the manuscript and made many helpful comments and suggestions. John Merriner and Douglas Vaughan provided access to the NMFS Atlantic menhaden catch and effort database. Literature cited Abramson, N. J. 1971. Computer programs for fish stock assessment. FAO Fisheries Technical Paper 101, var. pages. Atlantic Menhaden Management Board. 1981. Fishery management plan for Atlantic men- haden. Atlantic States Marine Fisheries Commission, Fish. Manage. Rep. 2, 134 p. Clark, F. N., and J. C. Marr. 1956. Population dynamics of the Pacific sardine. Calif. Coop. Oceanic Fish. Invest. Progress Rep., p. 11-48. Cushing, D. H. 1968. Fisheries biology. Univ. Wisconsin Press, Madison, WI, 200 p. Hollander, R. L., and D. A. Wolfe. 1973. Nonparametric statistical analysis. John Wiley and Sons, New York, NY, 503 p. Marr, J. C. 1951. On the use of the terms abundance, availability and ap- parent abundance in fishery biology. Copeia 1951(21:163-169. NOTE Atran and Loesch: An analysis of fluctuations In catchability coefficients 567 Morrissy, N. M., and N. Caputi. 1981. Use of catchability equations for population estima- tion of marron, Cherax tenuimanus (Smith) (Decapoda: Parastacidae). Aust. J. Mar. Freshwater Res. 32:213-225. Murphy, G. I. 1965. A solution of the catch equation. J. Fish. Res. Board Can. 22(11:191-202. Nicholson, W. R. 1971a. Changes in catch and effort in the Atlantic menha- den purse-seine fishery 1940-68. Fish. Bull. 69:765-781. 1971b. Coastal movements of Atlantic menhaden as in- ferred from changes in age and length distributions. Trans. Am. Fish. Soc. 100:708-716. Paloheimo, J. E., and L. M. Dickie. 1964. Abundance and fishing success. Rapp. Cons. Explor. Mer 155:153-163. Pope, J. G., and D. J. Garrod. 1975. Sources of error in catch and effort quota regulations with particular reference to variations in the catchability coefficient. Int. Comm. Northwest Atl. Fish. Res. Bull. 11:17-30. Ricker, W. W. 1975. Computation and interpretation of biological statistics offish populations. Fish. Res. Board Can. Bull. 191, 382 p. Schaaf, W. E. 1975. Fish population models: potential and actual links to ecological models. In C. S. Russell (ed.), Ecological modelling in a resource management framework: resources for the future, working paper QE-1, p. 211-239. John Hopkins Univ. Press, Baltimore, MD. Shardlow, T., and R. Hilborn. 1985. Density-dependent catchability coefficients. Trans. Am. Fish. Soc. 114:436-438. Sokal, R. R., and F. J. Rohlf. 1981. Biometry, 2nd ed. W. H. Freeman and Company, San Francisco, CA, 859 p. Tomlinson, P. K. 1970. A generalization of the Murphy catch equation. J. Fish. Res. Board Can. 27:821-825. Temperature influence on postovulatory follicle degeneration in Atlantic menhaden, Brevoortia tyrannus Gary R. Fitzhugh Department of Zoology, Box 7617 North Carolina State University Raleigh, North Carolina 27695-761 7 Present address: The institute for Fishery Resource Biology Florida State University and Southeast Fisheries Science Center National Marine Fisheries Service, NOAA 3500 Delwood Beach Road, Panama City, Florida 32408-7403 William F. Hettler Beaufort Laboratory, Southeast Fisheries Science Center National Marine Fisheries Service, NOAA 101 Pivers Island Road, Beaufort, North Carolina 28516-9722 The occurrence of postovulatory fol- licles within the ovaries offish is a positive indication of spawning, be- cause they are the evacuated fol- licles following ovulation. There- fore, their frequency of occurrence may be used to test factors influ- encing reproduction. For example, postovulatory follicles can be used to estimate spawning frequency, which in turn is used to estimate spawning biomass (Hunter and Macewicz, 1985). Their state of de- generation can be assessed from histological sections of the ovary to estimate the time elapsed since spawning for females sampled in the wild. In addition, the occur- rence of postovulatory follicles might be useful to test hypotheses about events that may trigger spawning and benefit larval trans- port (see Taylor, 1984; Checkley et al., 1988). A requisite for applying this his- tological method of determining spawning frequency is validation of the duration that postovulatory fol- licles can be detected in field samples. This has been done through closely timed observations of spawning in the field and by laboratory-induced spawning and subsequent sam- pling of female gonads (Hunter and Macewicz, 1985). Laboratory spawn- ing offers more certainty in deter- mining the time of spawning and facilitates more precise measure- ment of the degeneration time of postovulatory follicles. Uncertainty regarding the duration of post- ovulatory follicles has led to ques- tions about estimates of spawning frequency (Brown-Peterson et al., 1988; Fitzhugh et al., 1993; and Goldberg et al., 1984). Variation in the duration of postovulatory follicles may be largely due to the particular species involved and its preferred spawning temperature (Hunter and Macewicz, 1985). Atlantic menhaden spawn across a wide geographic range of U.S. coastal Atlantic waters (Cape Canaveral, Florida, to Martha's Vineyard, Massachusetts) and probably over a wide range of tem- perature as well (Judy and Lewis, 1983). Eggs have been collected between the 15° and 20°C surface isotherms in the mid-Atlantic Bight (Kendall and Reintjes, 1974). We wished to examine differences in postovulatory follicle duration and age at stage due to temperature in Atlantic menhaden. As a prelimi- nary step to future estimation of spawning frequencies, our objective was to characterize postovulatory follicle degeneration and validate postovulatory follicle duration for Atlantic menhaden induced to spawn at different temperatures in the laboratory. Materials and methods Adult menhaden were collected near Harker's Island, North Caro- lina, between mid-August and mid- September 1988, 1990, 1991, and 1992. During each period, menha- den were maintained in outside tanks under ambient flow-through conditions until mid-October to mid-November when they were moved to inside tanks to begin conditioning for spawning. We in- duced spawning in either December (1990) or March (1988, 1991, 1992) with methods reported by Hettler (1981). Menhaden of both sexes were conditioned to spawn by means of intraperitoneal injections of human chorionic gonadotropin (HCG) and carp pituitary extract (CP). We gave injections between 0800 and 1000 hours on successive days, and spawning usually oc- curred the night following the sec- ond (CP) injection. Spawning was induced under three temperature regimes; 14.8- 15.7°C for one group in December 1990; 17.9-18.2°C for one group in March 1992; and 19-20°C for groups in March 1988, December 1990, and March 1991. Groups of menhaden ranged from 22 to 31 Manuscript accepted 13 March 1995. Fishery Bulletin 93:568-572 ( 1995). 568 NOTE Fitzhugh and Hettler: Postovulatory follicle degeneration in Brevoortia tyrannus 569 individuals and the male to female ratio was about equal. In December 1990, only 12 individuals were induced to spawn at the coldest temperature regime (7 were subsequently identified as females). For each group, acclimation and holding temperatures were held constant prior to spawning and for the week following spawning. The time of spawning was estimated the following morning when eggs were collected and identified to stage (Ferraro, 1980). Males were identified by the presence of free-flowing milt just prior to the CP in- jection and were marked by clipping the left pecto- ral fin. Females (identified as not having a fin clip) were sampled up to 4 days following spawning and killed in a solution of MS-222. We excised a tissue section from the middle right ovarian lobe from each female and fixed it in 10% neutral buffered forma- lin. Tissue samples were dehydrated, embedded in paraffin, sectioned, stained with Gill's hematoxylin and eosin for histological observation. Our interpretation of the histological states of the postovulatory follicles follows Hunter and Macewicz (1985), and the promi- nent features we observed are summarized in Table 1. Results and discussion The postovulatory follicle, which is the evacuated follicle remaining in the ovary following ovulation of the hydrated oocyte, is characterized by an outer Table 1 Distinguishing features for the stages of postovulatory fol- licle degeneration' in Atlantic menhaden, Brevoortia tyrannus. Stage Characteristics of postovulatory follicles 1 Granulosa cells are aligned and granulosa-layer nuclei appear linear in orientation. Some lymphocytes and vacuoles may appear in the postovulatory follicle, signaling initial degeneration. 2 Loss of linear arrangement of granulosa layer nuclei; cell membranes and columnar/cuboidal shape of granulosa layer is no longer distinct. Lumen is still clearly visible. 3 Although irregular postovulatory follicle shape is still detectable, fewer folds are apparent as the lumen becomes reduced and is no longer distinct. 4 Linear appearance of the granulosa layer is no longer distinct; postovulatory follicle not readily distinguished from atretic oocytes. ' Adapted from Hunter and Macewicz, 1985. thecal layer and an inner epithelial granulosa layer (Fig. 1). Many species show similar features in postovulatory follicle degeneration (Hunter and Macewicz, 1985) to those that we noted for Atlantic menhaden. Onset of degeneration was evident when vacuoles and eosinophils were detected within the postovulatory follicle (Fig. 1A). The granulosa layer appeared contorted or folded but the granulosa cells and their nuclei imparted a linear or cordlike ap- pearance (Fig. 1A). Initially, the lumen was appar- ent but narrowed and became less distinct with time (Fig. 1, B and C). We also noted that the linear ar- rangement of the granulosa cell nuclei became less distinct with time (Fig. IB). Vacuolization of the fol- licle increased (Fig. 1C), and a point was reached when the lumen was no longer evident. The postovulatory follicle became reduced in size but the folded appearance of the granulosa layer remained evident and aided in identifying the postovulatory follicle (Fig. 1C). We used this point in degeneration to define the postovulatory follicle duration because as the postovulatory follicle aged further (e.g. Fig. ID), there were no exact features that could distin- guish it from old atretic follicles (preovulatory fol- licles) that remain after an intact oocyte undergoes atresia (Goldberg et al., 1984; Hunter and Macewicz, 1985). While atresia of oocytes occurs predominately at the end of a spawning season, it is common to ob- serve some oocytes undergoing atresia throughout the spawning season (Hunter and Macewicz, 1985). We also observed some atresia of vitellogenic oocytes in our samples. Since preovulatory follicles can be present and at some point are not distinguishable from postovulatory follicles, we can only estimate the dura- tion that the postovulatory follicles may be identified. The 54 females sampled after spawning from the three temperature regimes ranged in size from 200 to 250 mm fork length which is typical of 2 to 3 year- olds (Nicholson and Higham, 1964). All females (rc=35) from the warm regime (19-20°C) that were sampled within about 40 hours of spawning (deter- mined from the collection and identification of stages of fertilized eggs) displayed detectable postovulatory follicles (100% spawned). Eleven of the twelve fe- males sampled from the 17.9-18.2°C series displayed postovulatory follicles (92% spawned). Six females from the cold series (14.8-17.7°C) contained vitellogenic oocytes, indicating an advanced repro- ductive state; one female possessed cortical alveolar stage oocytes — an immediate precursor to the vitellogenic stage (deVlamming, 1983). However, only 4 of 7 females from the cold series possessed detect- able postovulatory follicles (57% spawned). The re- duced temperatures appeared to diminish our abil- ity to induce spawning. 570 Fishery Bulletin 93(3), 1995 ft^S POF .w 2 "•"ft*! r*f3i •:».♦:• I D 30 cm per second) from reef 2 to reef 1 in five minutes or less. Us- ing the natural water flow and bot- tom topography as references, I fol- lowed the same path between the two reefs during each census. All fish observed within 20 m (the ap- proximate limit of my visibility) to either side or end of this quasi- transect (total search area includ- ing reefs =5,600 m2) were counted and measured. Fork lengths (FL) were estimated visually within 5 m of fish by comparing subjects to a known scale, the 30-cm length of a hand-held underwater slate. Fish were placed into one of three size classes relative to my slate: 20, 30, and >40 cm FL (shorter than, equal to, and longer than the slate, re- spectively). Lutjanus analis swam into the current (positive rheo- taxis); therefore once I had passed Manuscript accepted 1 February 1995. Fishery Bulletin 93:573-576 ( 1995). 573 574 Fishery Bulletin 93(3), 1995 a fish, I did not encounter that fish again during the drift. To confirm the accuracy of my underwater FL estimates, I compared markings on my slate (1-cm increments) with structural relief that L. analis rested on or passed by at reef 1. 1 repeated this prac- tice until I could discern between the three size classes ±5 cm from distances up to 5 m away. On each sampling date, I performed three repli- cate drifts from reef 2 to reef 1. Size frequencies were derived from the largest number of fish counted in each of three size classes, irrespective of replicate, because the number offish in each size class was at least equal to the greatest number of that size class seen during a single drift (Sale and Douglas, 1981). Results and discussion Four individual L. analis were recognized from cen- sus to census for periods up to one year. Fish were identified by body size, scars, fin anomalies, or shape of the black upper-body spot. However, owing to the wary nature of L. analis, it was difficult to remain within close proximity of subjects to identify ad- equately all fish by this method. Although individu- als were considered resident, it is possible that oth- ers were transient or wandering fish. Still, my ob- servations are consistent with a previous study (Beaumariage, 1969) that indicated little movement in adult L. analis. On each sampling date, up to 56 L. analis were counted and measured at the study site. Fish ranged in size from 15 cm FL (half the length of my under- water slate) to 65 cm FL (>twice the length of my slate). Small (20-cm-FL), medium (30-cm-FL), and large (>40-cm-FL) L. analis were aged 1+ yr, 2+ yr, and 3+ yr, respectively (sensu Claro, 1981; Mason and Manooch, 1985). The number of small and me- dium-size fish observed varied from 6 to 24 and 12 to 25, respectively. The number of large fish never exceeded 13 (Table 1). From April to July, fish sizes were normally distributed; however, during August, fish sizes became negatively skewed. On 23 Febru- ary 1992, water clarity was extremely poor (<5 m), which may account for the low number of small fish recorded on this date (Table 1). The causes for seasonal variation in the size struc- ture of L. analis are difficult to isolate from my ob- servations; however, some inferences can be drawn from previous studies. For example, the increase of small fish in late August (Table 1) corresponds well with the peak recruitment to seagrass beds reported for juvenile L. analis (<7 cm FL) during August (Springer and McErlean, 1962) and September (Garcia-Arteaga et al., 1990). Jones (1990) described a similar pattern in ambon damselfish, Pomacentrus amboinensis, Bleeker, 1868, and showed that adult densities increased in proportion to juvenile recruit- ment success after a two-year period (=maturation time). The simultaneous decrease in medium-size fish during August (Table 1) is not easily explained. The population structure of unexploited reef fish is de- termined by a complex sequence of events that in- cludes recruitment, demographic changes (i.e. mor- tality, migration, and growth), and ecological pro- cesses such as habitat structure, resource availabil- ity, and intraspecific competition (Jones, 1991). For instance, variable patterns in growth can have a major and direct influence on the size structure of a population (Jones, 1991). Individuals that grow faster may subordinate conspecifics and establish a domi- nance hierarchy (Forrester, 1990). Once established, hierarchies are often extremely stable (Morse, 1980). For example, where individually recognized recruits were followed over time, juvenile humbug, Dascyllus aruanus (Linnaeus, 1758), never outgrew other group members in size during an eight-month period (Forrester, 1990). Lutjanus analis exhibits much variation in length for a specific age (Mason and Manooch, 1985) but matures sexually at fork lengths above 38 cm (Claro, 1981). In the central Bahamas, L. analis form groups of variable-size fish that occupy seagrass meadows Table 1 Size frequencies of mutton snapper Lutjanus analis, sampled from a population associated with two artificial patch reefs located off Lee Stocking Is land, Exuma Cays, Bahamas. Fork lengths were estimated visually by corn- paring fish to a cnown scale (30-cm length of a hand-held underwater slate) and are ±5 cm. Fork length (cm) Total no. sampled Sample date 20 30 >40 22 May 91 6 21 8 35 1 July 91 16 25 5 46 29 July 91 11 24 11 46 24 August 91 23 12 6 41 5 October 91 16 12 10 38 7 December 91 22 13 6 41 23 February 92 6 20 10 36 20 March 92 23 18 7 48 19 April 92 8 23 13 44 18 May 92 10 22 6 38 17 June 92 12 22 5 39 16 August 92 24 18 9 51 26 October 92 19 17 9 45 14 December 92 18 25 13 56 NOTE Mueller: Size structure of Lutjanus analis 575 near inlets and patch reefs (Dennis1). Size-specific asymmetries in both social and foraging behaviors suggest that these groups form dominance hierar- chies (Mueller, 1994; Mueller et al., 1994). Assum- ing that large L. analis did not migrate from the study site (Beaumariage, 1969; author's personal observ. ) and given that higher proportions of aggressive en- counters occur among medium-size and large fish compared with small fish (Mueller et al., 1994), it is possible that the few large, dominant L. analis lim- ited the number of medium-size fish on site through social interactions (sensu Doherty 1983; Jones, 1987; Forrester, 1990). However, because empirical evi- dence is not available to support this conclusion, ex- periments should be designed to test whether large L. analis are a limiting factor. Changes in the size structure of L. analis between 1991 and 1992 (i.e. the shift from small towards medium-size fish; Table 1) may also be related to growth. For example, small L. analis (1+ yr) feed proportionally more often than medium-size or large fish during daylight hours (0600-1730) and are in- volved in very few intraspecific encounters (Mueller et al., 1994). By limiting their interactions with con- specifics, small fish ostensibly have more time and energy available for growth (>0.8 cm/mo during years 1 and 2; Claro, 1981; Mason and Manooch, 1985). Fur- ther studies may be designed to test this hypothesis. In conclusion, managers of reef fisheries are chal- lenged with determining whether shifts in the size structure of populations are due to normal recruit- ment and postrecruitment events or to fishing pres- sure. For example, low abundance of a certain size class may be due to intraspecific competition (Doherty, 1983; Jones, 1987; Forrester, 1990) or growth rather than to the effects of fishing. How- ever, previous studies also indicate lower average size and abundance offish captured on exploited reefs as opposed to unexploited reefs (see review by Russ, 1991). I have provided evidence of seasonal varia- tion in the size structure of L. analis associated with unfished reefs. Although potential biases exist, this information should be useful for making relative com- parisons with analogous populations subjected to fishing pressure. Acknowledgments I would like to thank G. D. Dennis and R. I. Wicklund for helpful advice and encouragement. This research was supported by a grant from the National Under- 1 Dennis, G. Caribbean Marine Research Center, 805 E. 46th Place, Vero Beach, FL 32963. Unpubl. data, 1992. sea Research Program, National Oceanic and Atmo- spheric Administration, U.S. Department of Com- merce and by the Caribbean Marine Research Center. Literature cited Beaumariage, D. S. 1969. Returns from the 1965 Schlitz tagging program in- cluding a cumulative analysis of previous results. Fla. Dep. Nat. Resour., Mar. Res. Lab., Tech. Ser. 59, 38 p. Bortone, S. A., and J. L. Williams. 1986. Species profiles: life histories and environmental re- quirements of coastal fishes and invertebrates (South Florida) — gray, lane, mutton and yellowtail snappers. U.S. Fish Wildl. Serv., Biol. Rep. 82, 18 p. Brownell, W. N., and W. E. Rainey. 1971. Research and development of deepwater commercial and sport fisheries around the Virgin Islands Plateau. Caribb. Res. Inst. Contrib. 3, 88 p. Claro, R. 1981. Ecologia y ciclo de vida del pargo criollo, Lutjanus analis (Cuvierl, en la plataforma Cubana. Inf. Cient.-Tec. Inst. Oceanol. Acad. Cienc. (Cuba) 186, 83 p. 1983. Dinamica estacional de algunas indicadores morfofisiolbgicas del pargo criollo, Lutjanus analis (Cuvier), en la plataforma Cubana. Rep. Invest. Inst. Oceanol. Acad. Cienc. Cuba 22:1-14. Craik, W. J. S. 1981. Underwater survey of coral trout Plectropomus leopardus (Serranidae) populations in the Caprieornia sec- tion of the Great Barrier Reef Marine Park. Proc. 4th Int. Coral Reef Symp. 1:53-58. Doherty, P. J. 1983. Tropical territorial damselfishes: Is density limited by aggression or recruitment? Ecology 64:176-190. Erhardt, H. 1978. Elektronenmikroskopische untersuchungen an den eihullen vonLutjanus analis (Cuvier and Valenciennes, 1828) (Lutjanidae, Perciformis, Pisces). Biol. Zbl. 97:181-187. Erhardt, H., and W. Meinel. 1977. Beitrage zur Biologie von Lutjanus analis (Cuvier and Valenciennes 1828 )( Lutjanidae, Perciformis, Pisces) an der kolumbianischen Atlantikkuste. Int. Revue Gesamt. Hydrobiol. 62:161-171. Forrester, G. E. 1990. Factors influencing the juvenile demography of a coral reef fish. Ecology 71:1666-1681. Garcia-Arteaga, J. P., R. Claro, L. M. Sierra, and E. Valdes-Munoz. 1990. Caracteristicas del reclutamiento a la plataforma de los juveniles de peces neriticos en la region oriental del Golfo de Batabano. In R. Claro ( ed. ), Asociaciones de peces en el Golfo de Batabano, p. 96-121. Editorial Academia, Habana, Cuba. Gulf of Mexico Fishery Management Council. 1992. Help proposed for mutton snapper. Gulf Fish. News 12(4):2. Jones, G. P. 1987. Competitive interactions among adults and juveniles in a coral reef fish. Ecology 68:1534-1547. 1990. The importance of recruitment to the dynamics of a coral reef fish population. Ecology 71:1691-1698. 1991. Postrecruitment processes in the ecology of coral reef fish populations: a multifactorial perspective. In P. F. Sale 576 Fishery Bulletin 93(3). 1995 (ed.), The ecology of fishes on coral reefs, p. 294—327. Aca- demic Press, CA. Mason, D. L., and C. S. Manooch. 1985. Age and growth of mutton snapper along the East Coast of Florida. Fish. Res. 3:93-104. Morse, D. H. 1980. Behavioral mechanisms in ecology. Harvard Univ. Press, Cambridge, 383 p. Mueller, K. W. 1994. Gregarious behaviour in mutton snapper in the Exuma Cays. Bahamas J. Sci. l(3):17-22. Mueller, K. W., G. D. Dennis, D. B. Eggleston, and R. I. Wicklund. 1994. Size-specific social interactions and foraging styles in a shallow water population of mutton snapper, Lutjanus analis (Pisces: Lutjanidae), in the central Bahamas. Environ. Biol. Fishes 40:175-188. Palazon, J. L., and L. W. Gonzalez. 1986. Edad y crecimiento del pargo cebal, Lutjanus analis (Cuvier 1828) (Teleostei: Lutjanidae) en la isla de Margarita y alrededores, Venezuela. Invest. Pesq. 50:151-166. Pozo, E. 1979. Edad y crecimiento del pargo criollo (Lutjanus analis, Cuvier 1828) en la plataforma nororiental de Cuba. Rev. Cub. Invest. Pesq. 4:1-24. Rojas, L. E. 1960. Estudios estadisticos y biologicos sobre el pargo cri- ollo, Lutjanus analis. Cent. Invest. Pesq. Notas sobre Invest. 2, 16 p. Russ, G. R. 1985. Effects of protective management on coral reef fishes in the central Philippines. Proc. 5th Int. Coral Reef Congr. 4:219-224. 1991. Coral reef fisheries: effects and yields. In P. F. Sale (ed.). The ecology of fishes on coral reefs, p. 601-635. Aca- demic Press, CA. Sale, P. F., and W. A. Douglas. 1981. Precision and accuracy of visual census technique for fish assemblages on coral patch reefs. Environ. Biol. Fishes 6:333-339. Springer, V. G., and A. J. McErlean. 1962. Seasonality of fishes on a South Florida shore. Bull. Mar. Sci. Gulf Caribb. 12:39-60. Stoner, A. W., and V. J. Sandt. 1991. Experimental analysis of habitat quality for juvenile conch in seagrass meadows. Fish. Bull. 89:693-700. Occurrence and group characteristics of minke whales, Balaenoptera acutorostrata, m Massachusetts Bay and Cape Cod Bay Margaret A. Murphy Cetacean Research Program, Center for Coastal Studies Provincetown, Massachusetts 02657 The minke whale, Balaenoptera acutorostrata, is one of the small- est of the baleen whales. Despite exploitation by the whaling indus- try in recent years, comparatively little is known about the biology and behavior of this species. The minke has a cosmopolitan distribu- tion, although recent biochemical studies suggesting large genetic differences between oceanic popu- lations (Amos and Dover, 1991; Hoelzel and Dover, 1991; van Pijlen et al., 1991; Wada and Numachi, 1991; Wada et al., 1991) have cast some doubt on the long-held belief that all populations constitute a single species. As is the case for most baleen whales, minke whales appear to migrate to high latitudes in the summer for feeding and to travel to tropical waters in the win- ter for birthing (Horwood, 1989; Mitchell, 1991). However, specific breeding grounds have yet to be unequivocally identified, and it is unknown whether both sexes and all age classes in a population un- dertake the migration to low lati- tudes. In some temperate, subtropi- cal, and tropical areas, minke whales are observed throughout the year (Ivashin and Votrogov, 1981; Best, 1982; Gong, 1987; Stern, 1990), although it is unclear whether these sightings represent year-round residency on the part of particular individuals or a more general movement through the area by members of one or more populations. In recent years, much has been learned about other mysticetes through long-term studies based on the identification of individual whales (see Hammond etal., 1990). Unfortunately, minke whales lack the great variability in natural markings that have facilitated de- tailed investigations of larger confamilials (such as humpback whales, Megaptera novaeangliae). This, together with the difficulty of photographing them owing to their small size and great speed, has hin- dered studies based on photo- graphic identification, although studies of small localized popula- tions have been possible (Dorsey, 1983; Dorsey et al., 1990; Stern et al., 1990). In general, however, studies of free-ranging minke whales have been few, and their population structure, social organi- zation, and migratory movements remain poorly understood. Minke whales are commonly ob- served in the waters of Massachu- setts Bay and Cape Cod Bay in New England, and since 1979, sightings of this species have been routinely recorded from both commercial whalewatching vessels and dedi- cated surveys. In this paper, sight- ing records are examined in an ef- fort to describe the temporal distri- bution, seasonal abundance, and feeding behavior of minke whales in this region. These data are then compared with information re- ported for this species from other areas, notably within the North Atlantic. Methods Study area The study area includes the coastal region dominated by Cape Cod Bay and Massachusetts Bay along the northeastern coast of the United States (Fig. 1). Cape Cod Bay is a semi-enclosed sandy basin with a maximum depth of 60 m. Massa- chusetts Bay lies north of Cape Cod; depths range from 40 m to 100 m except on Stellwagen Bank, an elongated glacial feature of sand and gravel approximately 25 km in length, which has a minimum depth of 18 m. Effort Data were collected between 1979 and 1992. The total number of cruises conducted during this pe- riod was 10,249 (this figure excludes those made in certain weather con- ditions, as noted below); of these, 9,728 (94.9%) were made from 30- m commercial whalewatching ves- sels operating between April and October of each year from Province- town, Massachusetts. Additional cruises («=374) were made from a 12-m diesel-powered research ves- sel beginning in the autumn of 1983, and 77 cruises were made from a 14-m auxiliary ketch begin- ning in the autumn of 1985. The remaining non-whalewatch cruises were made primarily from a 5-m inflatable boat. Because virtually all of the whalewatching trips were approximately four hours in length, Manuscript accepted 15 December 1994. Fishery Bulletin 93:577-585 (1995). 577 578 Fishery Bulletin 93(3). 1995 rr 56' Copt Ann Sr S^ ' ' ' *' ihHh 0 5 10 u- — _i F 0 10 20 kltomtttri .3d ■■■.y-C" - > •jl * MASSACHUSETTS '«• -1 ; x *\ x \ 1 Aj €^ \'' %1 \ \ \ CAPE COD ^ \\ \ \ ) BAY 7' \ '• '' { " *■ */""' 1 % \ j A ' ^^3 Cape Cod "S *a&sry\ '■' ■""-.. 65" 27' Figure 1 Map of minke whale, Balaenoptera acutorostrata, study area: are located off the northeastern coast of the United States. Massachusetts Bay and Cape Cod Bay all cruises of eight hours or more were broken into separate four-hour blocks in an attempt to standard- ize temporal effort. Cruises aboard the 12-m research vessel ran four fixed tracks in Cape Cod Bay between January and May each year. The tracks ranged from six to nine nautical miles in length and were approximately four nautical miles apart. These cruises searched specifi- cally for North Atlantic right whales, Eubalaena glacialis; however, all marine mammal sightings were recorded. Owing to frequent unfavorable weather, the tracks were not surveyed equally; ef- fort was concentrated mainly in the more sheltered eastern portion of the Bay. Cruises aboard the 14-m ketch occurred throughout the year and ran either four fixed tracks on Stellwagen Bank or directed searches in areas where large concentrations of whales had been recently reported or were known to have occurred in the past. The fixed tracks covered the southern portion of Stellwagen Bank, although two of the tracks extended northward to include the northwest corner of the Bank. The tracks on the southern portion of the Bank ranged from six to nine nautical miles in length, all tracks being approxi- mately three nautical miles apart from one another. Again, all cetacean sightings were noted, although the majority of these cruises were directed prima- rily toward humpback whales. The remaining non- whalewatch cruises were nonrandom, searching ar- eas where large numbers of whales had been recently NOTE Murphy: Occurrence and group characteristics of Balaenoptera acutorostrata 579 reported. All whalewatching cruises were nonrandom and search tracks for these cruises were generally decided by the captain of the vessel. Search effort was based on four-hour trips. It was not possible to quantify precisely observer effort; time spent searching inevitably varied somewhat between trips. However, because at least one observer was searching for whales constantly for the duration of each cruise (both on the whalewatching cruises and dedicated surveys), it is unlikely that significant dif- ferences existed in effort between months or years. Furthermore, because all trips were primarily fo- cused on larger mysticetes, virtually all sightings of minke whales were opportunistic; consequently, search effort towards this species was effectively even throughout the study period. To minimize the possi- bility that minke whales were present but not sighted owing to bad weather conditions, all cruises con- ducted in fog or in sea states above Beaufort 4 were excluded from analysis. The total number of cruises for each month of all years is summarized in Table 1. The following information was routinely collected: date, time, location (by using LORAN-C) and, where determinable, group size and behavior. Although photographs were occasionally taken during this study, the resulting data are not discussed here. The following terms are used in this paper: single- ton refers to a lone animal, group refers to two or more animals that were considered associated if they were swimming side by side and were generally co- ordinating their speed and direction of movement during their surfacing and diving behavior. Animals that were farther apart and did not show such coor- dination of movement were not considered associated. It is possible that two or more minke whales that were not side by side were in acoustic contact and therefore associating; however, such associations are impossible to identify in the field and were not con- sidered in this study. Feeding refers to a whale ob- served with its mouth open or lunging at the surface where prey was visible in the water. It is highly likely that there were other instances in this study when feeding occurred below the surface but could not be observed; consequently, the feeding rates reported here should be considered minimum values. Calf refers to an animal considered to be a first-year calf if it was observed in close association with a large whale and was not more than half the apparent length of the latter (presumed to be the mother). Results Temporal distribution There was a significant difference in the sighting rate of minke whales (number of whales observed per trip) from year to year (x213 = 2188.7, P<0.001); the maxi- mum sighting rate was recorded in 1989 and the minimum in 1982 and 1986 (Fig. 2). Minke whales were observed in all months except January and February and showed significant differences in abun- dance by month (pooled overyears) (Fig. 3). Pairwise comparisons of mean monthly values for the period of greatest effort (March through October) were con- ducted by using a one-way analysis of variance and are revealed in Table 2. There were no significant differences in the number of sightings between the months of March, April, May, and June (hereafter col- lectively termed "spring"), nor between July, August, September, and October (hereafter referred to as "sum- mer-autumn") (Table 2). However, three of the four months of spring differed significantly from those of summer-autumn in all pairwise comparisons. The ex- ception was March, for which sighting rates were not significantly different from those of any other month. Calves Only three calves were observed during the entire study period. Each sighting occurred at a different time of year: 8 May 1981, 3 October 1989, and 28 August 1991. Two of the calves were part of a pair, and the third was part of a group of three. Table 1 The number of cruises conducted each year and each month for all years combined (1979-92) for minke whales, Balaenoptera acutorostrata, in Massachusetts Bay and Cape Cod Bay. Cruises in fog or where the sea state exceeded Beaufort 4 were excluded. Year Month (all years combined) 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec No. of cruises 127 207 414 517 630 723 789 878 875 972 989 979 1110 1039 No. of cruises 26 57 114 532 1409 1625 2091 2118 1415 793 44 25 580 Fishery Bulletin 93(3). 1995 Group-size frequency A total of 5,806 minke whale sightings were recorded for which the group size could be reliably determined. Observed group-size frequency ( x=1.06, SD=0.315) for singletons (rc=5,536) was 95.3%, for pairs (n=223) 3.8%, and for trios (n=46) 0.8%. With the exception of a single group of five whales, no groups larger than three were observed during this study. Feeding behavior A total of only 27 (0.4%) of 6,266 sightings involved confirmed feeding at the surface. These sightings occurred in all months between May and October inclusively. In 24 of the 27 sightings of feeding, group size was recorded: single animals accounted for 21 (87.5%) of these, two sightings involved pairs, and one sighting a group of three whales. 9 -, 8 - 75 7 - 59 f 6 J I 5- 1/1 ro 4 - _c 5 3- 2 16 0 4 2 12 2 - 7 1 7 5 7 -r L -17 10 ) 1 5 1 - 1979 1980 1981 1982 1963 1984 1986 1966 1987 1968 1969 1990 1991 1992 Year Figure 2 Observed variations in occurrence (mean and standard devia- tion) of minke whales, Balaenoptera acutorostrata, by year { 1979- 92) in Massachusetts Bay and Cape Cod Bay. Numbers above the bars represent maximum value for any one trip in that year. 7 - 6 Q- a a. i/i 4 3 2 H 1 * -f- ] I I f \ i i i Jan Feb Mar Apr May Jin Jul Aug Sep Oct Nov Dec Month Figure 3 Observed variations in occurrence (mean and standard error) of minke whales, Balaenoptera acutorostrata, in Massachusetts Bay and Cape Cod Bay by month for all years (1979-92) of the study. Discussion Temporal occurrence Minke whales appear to arrive in the waters of Cape Cod Bay and Massachusetts Bay in the early spring and in some years occurred as late as December. The considerable interannual variability in the abundance of minke whales probably reflects variation in effort (see Table 1) or fluctuations, or both, in the abundance and distribution of prey That it may be linked to the latter is suggested by the very low sighting rates recorded in 1986 and 1987, two years in which the local abundance of sand lance (Am- modytes spp. ) is known to have been at a mini- mum and when other piscivorous mysticetes were largely absent from the study area (Payne et al., 1990). However, the concentration of ef- fort on other mysticetes (and consequently on areas preferred by them) may have introduced a bias against minke whale sightings if these whales exhibit significant differences in habi- tat preference (this is currently unknown). Interannual variability in abundance has also been reported in other areas and has been simi- larly linked to prey availability, as well as to effort and, in Arctic areas, distribution of sea ice (Sigurjonsson, 1982; Larsen and 0ien, 1988). There was also considerable variation in abundance from month to month. The data re- ported here indicate a distinct peak in abun- dance beginning in July and continuing through September. No minke whales were observed in January or February: although this may have been due to the markedly decreased sampling effort during these two months, this appears unlikely given the dedicated (i.e. non-whale- watching) nature of the surveys conducted at this time and the frequently calm conditions which were a prerequisite for such cruises. This general pattern of occurrence (abundant in summer, scarce or absent in winter) is simi- lar to that reported for other high-latitude NOTE Murphy: Occurrence and group characteristics of Balaenoptera acutorostrata 581 Table 2 Results ( from a one-way analysis of variance) of pairwise comparison of monthly mean sighting rates for minke whales, Balaenoptera acutorostrata in Massachusetts Bay and Cape Cod Bay ( 1979-92). Figures shown are P values significant differences are shown in bold type. Month Apr May Jun Jul Aug Sep Oct Mar 0.69 0.88 0.98 0.06 0.05 0.06 0.08 Apr 0.64 0.44 0.01 0.01 0.01 0.02 May 0.76 0.01 0.01 0.01 0.02 Jun 0.01 0.01 0.01 0.02 Jul 0.19 0.10 0.13 Aug 0.47 0.58 Sep 0.87 minke whale populations, including those elsewhere in the North Atlantic. Data from Newfoundland, Ice- land, and West Greenland show a similar seasonal distribution in which minke whales arrive in spring, are most abundant during mid- to late summer and begin to leave in the autumn (Sergeant, 1963; Mitchell and Kozicki, 1975; Kapel, 1980; Sigur- jonsson, 1982). However, a few minke whales have been reported off western Newfoundland and Iceland in both November and December (Sergeant, 1963; Sigurjonsson, 1982), and minke whales have occa- sionally been caught off West Greenland between November and February (Kapel, 1980). The same seasonal occurrence is seen in the waters off Nor- way and in the Arctic where a few whales have been observed through the winter ( Jonsgard, 1951 ). High- latitude areas of the North Pacific and the Antarctic are also characterized by a seasonal distribution simi- lar to that observed in the North Atlantic (Shimadzu, 1980; Dorsey, 1983; Gong, 1987; Stern, 1990). Since most of these studies were not based on identified individuals, it is not clear whether minke whales in these areas are resident for long periods or whether the reported sightings represent short-term occu- pancy or transient passage by numerous animals. If the apparent decrease in abundance of minke whales in Massachusetts Bay in autumn and winter is, as suggested above, unrelated to effort, it may reflect a migration of most minke whales to lower latitudes at that time of year. Data on the winter distribution of minke whales are scarce. In the south- western North Atlantic, minke whales have been reported in the waters between Bermuda and the Antilles between the months of January and March (Mitchell, 1991; Mattila and Clapham, 1989; Mattila et al., in press). Stranding data show evidence of the presence of minke whales in the waters off Florida from December to February.1 Winter sightings, while infrequent, have also been reported in the western Gulf of Maine and in waters southeast of Cape Cod (CeTAP2). In the Southern Hemisphere, minke whales are also reported in lower latitudes during the winter. Off Brazil, as well as in the waters of the southwest- ern Indian Ocean, minke whales are mainly present in winter and spring (Williamson, 1975; Best, 1982). However, some have been reported trapped in sea ice in the Antarctic between May and October (Tay- lor, 1957); this finding, together with year-round sightings of minke whales in areas such as Califor- nia (Stern, 1990), Greenland, Norway, and the Arc- tic suggests that a few animals may overwinter at higher latitudes. Calves During the fourteen years of this study only three minke whale calves were observed. Sightings of minke whale calves in high-latitude areas of the North Atlantic are rare; this is not the case for cer- tain other mysticetes (e.g. humpback whales [Clapham and Mayo, 1987]; fin whales, Balaenoptera physalus [Clapham and Seipt, 1991]; North Atlantic right whales [Hamilton and Mayo, 1990]). Only two minke whale calf sightings were reported in the 1982 Cetacean and Turtle Assessment Program (CeTAP) study, both occurring just south of Cape Cod (one in 1 Mead, J. Curator of marine mammals at the Smithsonian In- stitution. Natl. Mus. Nat. History, Smithsonian Institution, Washington, D.C. 20560. Unpubl. data, 1992. 2 CeTAP (Cetacean and Turtle Assessment Program). 1982. Char- acterization of marine mammals and turtles in the mid- and North Atlantic areas of the U.S. Outer Continental Shelf. Final Rep. of the Cetacean and Turtle Assessment Program, Univ. Rhode Island, to the Bureau of Land Management, Washing- ton, D.C. 582 Fishery Bulletin 93(3), 1995 April and the other in June). In the waters off Que- bec, one pair (adult and calf) was observed in late July (Perkins and Whitehead, 1977). Similarly, calves have not been reported in the waters off the west coast of the United States (Dorsey, 1983) and are also not commonly observed on the high-latitude feeding grounds in the Southern Hemisphere (Kasamatsu et al., 1988). In the North Atlantic, the majority of minke whale calf sightings have occurred in lower latitudes. In the southwestern North Atlantic, calves have been sighted in the waters between Bermuda and the Antilles (Mitchell, 1991) as well as in the northern Leeward Islands (Mattila and Clapham, 1989). One possible explanation for the absence of calves in higher latitudes is that minke whales wean their calves before entering these waters. According to Jonsgard (1951), North Atlantic minkes are thought to calve between November and March, and nursing is believed to last for only four to five months. This information would concur with reports of no or few lactating females found during the summer off both Norway (Jonsgard, 1951) and Newfoundland (Ser- geant, 1963; Mitchell and Kozicki, 1975). In the Southern Hemisphere, it also appears that females wean their calves before reaching higher lati- tudes (Best, 1982; Kato and Miyashita, 1991). How- ever, there is evidence (at least in the Southern Hemi- sphere) that pairs (mother and calf) may remain in low or middle latitudes until weaning occurs (Kato and Miyashita, 1991), which suggests that some minke whale populations segregate by reproductive class. Segregation by both sex and age class has been described in many minke whale populations. Whal- ing data from the North Atlantic, the North Pacific, and the Southern Hemisphere suggest that minke whales segregate by sex during their summer mi- gration (Jonsgard, 1980; Kasamatsu and Ohsumi, 1981; Sigurjonsson, 1982; Larsen and 0ien, 1988; Wada, 1989) as well as on their feeding grounds (Jonsgard, 1980; Ohsumi, 1983; Larsen and 0ien, 1988; Wada, 1989; Kato et al., 1990a). Segregation by maturational class has also been recorded in minke whales (Best, 1982; Ohsumi, 1983; Wada, 1989; Kato et al., 1990a). Jonsgard (1951) suggested that newly weaned calves and juveniles off Norway probably do not migrate north together with larger animals, which is in agreement with data reported by Wada (1989) for areas off the Pacific coast of Japan. Neither the sex nor age class of the minke whales in the waters of Cape Cod and Massachusetts Bay areas is known because it is not currently possible to determine either in the field. Stranding data from this area give a mean length for minke whales of 505 cm (n=35, SD= 140.3 cm); comparison of this fig- ure with data on lengths of individuals caught in North Atlantic whaling operations (Jonsgard, 1951; Sergeant, 1963; Mitchell and Kozicki, 1975; Christensen, 1981) would suggest that the majority of animals that have stranded here were immature. The sex ratio of stranded animals was approximately even. Whether this sample is representative of the general population or only of those more likely to strand is unknown. Group size In this study approximately 95% of all minke whale sightings were singletons. Single animals appear to predominate in other studied areas, although there is evidence of group size changing by season, lati- tude, sex and age class, and when prey is present. In some cases, however, it is unclear whether animals reported in large groups (particularly when feeding) are actually associated with or are simply attracted to a common location by the presence of prey. Data from the Mingan Islands in the Gulf of Saint Lawrence show that minke whales are usually soli- tary, although they are seen in large coordinated groups of five to fifteen animals when actively feed- ing.3 Aerial surveys conducted off Iceland in June and July reported a mean school size of 1.1 (Gunn- laugsson et al., 1988). Jonsgard (1951) found that minke whales tend to travel alone off the western coast of Norway, noting only a few sightings consist- ing of pairs; in the Arctic, single animals were pre- dominant in catches, although groups of three to ten animals were more common than pairs. In the west- ern North Pacific off the Chukotka coast, sightings were usually of single animals. However, when po- lar cod arrive in late June and in July, minke whales are often observed in groups of five or six animals (Ivashin and Votrogov, 1981); again, it is not clear whether such groups are truly associated according to the definition of 'group' used here. Information on minke whales in the Southern Hemisphere also in- dicates variabilty in group size with changes in lati- tude and season as well as with differences in matu- rational class (Williamson, 1975; Best, 1982; Kato et al., 1989; Kato et al., 1990b). The group size frequency of minke whales observed in the Massachusetts Bay and Cape Cod Bay areas did not appear to change with time of year or with the presence of prey (on the basis of sightings where confirmed feeding occurred). Because the majority 3 Sears, R., F. W. Wenzel, and J. M. Williamson. 1981. Behavior and distribution observations of Cetaeea along the Quebec north shore (Mingan Islands), summer-fall 1981. Mingan Islands Cetacean Study, Montreal, Unpubl. Rep., 72 p. NOTE Murphy: Occurrence and group characteristics of Balaenoptera acutorostrata 583 of sightings were singletons it is possible that sex or age class has little or no effect on group size in this area, unless one sex or class is disproportionately represented here. The apparent predominance of immature whales among stranded specimens may reflect a similar overrepresentation of juveniles in the general population; if this is the case, the abun- dance of singletons would agree with the finding of Kato et al. (1990b) that immature animals along with ma- ture males tend to be solitary, whereas mature females usually form schools, especially near the pack ice. lar to that reported from other areas such as the western coast of North America where minke whales appear to act independently of each other even though several individuals may be present in the same area while feeding (Hoelzel et al., 1989; Dorsey et al., 1990). According to many studies (Ivashin and Votrogov, 1981; Bushuev, 1991, Sears et al.3), minke whales tend to group together when food is abundant, but it was unclear whether these animals were feed- ing cooperatively or were drawn to the same area by the availability of food and were feeding independently. Feeding behavior In this study less than one percent of all minke whale sightings involved confirmed feeding behavior. The CeTAP study (1982) also reported relatively few sightings of surface feeding. The lack of surface feed- ing in the study area is odd given that sympatric confamilials are commonly observed feeding (e.g. humpback whales [Payne et al., 1986]; fin whales [Overholtz and Nicolas, 1979]). In other areas of the North Atlantic, minke whales are observed feeding, displaying surface lunges and rolling (Sears et al.3; Haycock and Mercer4). Near the San Juan Islands, off the west coast of North America, minke whales also exhibit lunging and rolling behavior during feed- ing (Hoelzel et al., 1989; Dorsey et al., 1990). Off the San Juan Islands minke whales appear to prey mainly on small schooling fish (juvenile herring, Clupea harengus; sand lance, Ammodytes spp.) (Dorsey, 1983; Dorsey et al., 1990), which are also the principal food source for minke whales off the Mingan Islands (Sears et al.3). Both humpback and fin whales feed primarily on herring or sand lance in the southern Gulf of Maine (Overholtz and Nicolas, 1979; Payne et al., 1990); many observers assume that these fish also represent a principal prey of minke whales, a belief which is strengthened by the scarcity of minke whales in Massachusetts Bay dur- ing 1986 and 1987 when the local sand lance popula- tion crashed (Payne et al., 1990). However, it is not understood why these minke whales rarely exhibit feeding behavior at the surface, unless whales in this area either exploit fish schools at greater depths than do whales recorded for other feeding grounds or em- ploy a foraging technique that does not utilize the surface for catching prey. Nearly all minke whales observed feeding during this study were singletons, a finding which is simi- 4 Haycock, C. R., and S. N. Mercer. 1984. Observations and notes on the abundance and distribution of cetaceans in the Eastern Bay of Fundy near Brier Island, Nova Scotia, in August and September 1984. Unpubl. Rep. Conclusion In general, both the yearly and seasonal distribu- tion of minke whales in Massachusetts Bay and Cape Cod Bay is similar to that found for other popula- tions of this species. The data in this study also gen- erally agree with other published information per- taining to group size, feeding behavior, and the oc- currence of mother-and-calf pairs. Unfortunately, because the social structure and group composition of the minke whales observed in this study are un- known, it is impossible to determine whether or not the minke whales of Massachusetts and Cape Cod bays exhibit the same segregational patterns that have been suggested for other populations of this species in both the northern and southern hemi- spheres. It would also be valuable to explore whether individual minke whales return to the same area from year to year as documented off the west coast of North America, or whether the minke whales seen here represent transient individuals from one or more populations. Continued study with an emphasis on photographic identification of individuals is greatly needed as well as continued work in the biopsy of individuals throughout the year in order to gain some insight on the sex ratio, genetic structure, and group composition of this and other populations. Acknowledgments This manuscript would not have been possible with- out the help and support of many. I thank Phil Clapham for his insight and time, without whom sta- tistical analyses would not have been so much fun. In addition, I thank the researchers at the Center for Coastal Studies for their suggestions and all around interest in minke whales, the naturalists aboard the Dolphin Fleet whalewatch vessel for their great (and much appreciated) effort in collecting in- formation on this species, and lastly, the Dolphin Fleet captains and crew for acknowledging that 584 Fishery Bulletin 93(3), 1995 minkes really are whales and for allowing me extra time to see whether they really do anything besides breathe. This study was made possible in part by funding for data management provided by the U.S. National Marine Fisheries Service (Northeast Fish- eries Center) under contract 50-EANF-9-00033. Literature cited Amos, W., and G. A. Dover. 1991. The use of satellite DNA sequences in determining population differentiation in the minke whale. Rep. Int. Whaling Comm. (special issue 13):235-244. Best, P. B. 1982. Seasonal abundance, feeding, reproduction, age and growth in minke whales off Durban (with incidental ob- servations from the Antarctic). Rep. Int. Whaling Comm. 32:759-786. Bushuev, S. G. 1991. Distribution and feeding of minke whales in Antarc- tic Area I. Rep. Int. Whaling Comm. 41:303-312. Christensen, I. 1981. Age determination of minke whales, (Balaenoptera acutorostrata ) from laminated structures in the tympanic bullae. Rep. Int. Whaling Comm. 31:245-253. Clapham, P. J., and C. A. Mayo. 1987. Reproduction and recruitment of individually iden- tified humpback whales, Megaptera novaeangliae, observed in Massachusetts Bay, 1979-1985. Can. J. Zool. 65:2853- 2863. Clapham, P. J., and I. E. Seipt. 1991. Resighting of independent fin whales, Balaenoptera physalus, on maternal summer ranges. J. Mamm. 72(41:788-790. Dorsey, E. M. 1983. Exclusive adjoining ranges in individually identified minke whales (Balaenoptera acutorostrata ) in Washington State. Can. J. Zool. 61:174-181. Dorsey, E. M., J. S. Stern, A. R. Hoelzel, and J. Jacobsen. 1990. Minke whales [Balaenoptera acutorostrata ) from the west coast of North America: individual recognition and small-scale site fidelity. Rep. Int. Whaling Comm. (spe- cial issue 12):357-368. Gong, Y. 1987. A note on the distribution and abundance of minke whales in Korean waters. Rep. Int. Whaling Comm. 37:281-284. Gunlaugsson, T., S. Sigurjonsson, and G. P. Donovan. 1988. Aerial survey of cetaceans in the coastal waters of Iceland, June-July 1986. Rep. Int. Whaling Comm. 38:489-500. Hamilton, P. K., and C. A. Mayo. 1990. Population characteristics of right whales (Eubaleana glacialis) observed in Cape Cod and Massachusetts Bays, 1978-1986. Rep. Int. Whaling Comm. (special issue 12):203-208. Hammond, P. S., S. A. Mizroch, and G. P. Donovan (eds.). 1990. Individual recognition of cetaceans: use of photo-iden- tification and other techniques to estimate population parameters. Rep. Int. Whaling Comm. (special issue 12), Cambridge, 440 p. Hoelzel, A. R., and G. A. Dover. 1991. Mitochondrial D-loop DNA variation within and be- tween populations of minke whales (Balaenoptera acutorostrata). Rep. Int. Whaling Comm. (special issue 131:171-182. Hoelzel, A. R., E. M. Dorsey, and S. J. Stern. 1989. The foraging specializations of individual minke whales. Anim. Behav. 38:786-794. Horwood, J. W. 1989. The biology and exploitation of the minke whale. CRC Press, Boca Raton, FL, 238 p. Ivashin, M. V., and L. M. Votrogov. 1981. Minke whales (Balaenoptera acutorostrata david- soni), inhabiting inshore waters of the Chukotka coast. Rep. Int. Whaling Comm. 31:231. Jonsgard, A. 1951. Studies on the little piked whale or minke whale. Norsk Hvalfangsttid. 40:209-232. 1980. On the sex proportion in Norwegian minke whaling. Rep. Int. Whaling Comm. 30:389. Kapel, F. O. 1980. Sex ratio and seasonal distribution of catches of minke whales in West Greenland. Rep. Int. Whaling Comm. 30:195-199. Kasamatsu, K, and S. Ohsumi. 1981. Distribution pattern of minke whales in the Antarc- tic with special reference to sex ratio in the catch. Rep. Int. Whaling Comm. 31:345-348. Kasamatsu, F., D. Hembree, G. Joyce, L. Tsunoda, R. Rowlett, and T. Nakano. 1988. Distribution of cetacean sightings in the Antarctic: results obtained from the IWC/IDCR minke whale assess- ment cruises, 1978/79 to 1983/84. Rep. Int. Whaling Comm. 38:449-188. Kato, H., and T. Miyashita. 1991. Migration strategy of southern minke whales in re- lation to reproductive cycles estimated from foetal lengths. Rep. Int. Whaling Comm. 41:363-369. Kato, H., H. Hiroyama, Y. Fujise, and K. Ono. 1989. Preliminary report of the 1987/88 Japanese feasibil- ity study of the special permit proposal for southern hemi- sphere minke whales. Rep. Int. Whaling Comm. 39:235- 248. Kato, H., H. Kishino, and Y. Fujise. 1990a. Some analyses on age composition and segregation of southern minke whales using samples obtained from the Japanese feasibility study in 1987/88. Rep. Int. Whaling Comm. 40:249-256. Kato, H., Y. Fujise, H. Yoshino, S. Nakagawa, M. Ishida, and S. Tanifuji. 1990b. Cruise report and preliminary analysis of the 1988/ 89 Japanese feasibility study of the special permit proposal for southern hemisphere minke whales. Rep. Int. Whal- ing Comm. 40:289-300. Larsen, F., and N. Oien. 1988. On the discreteness of stocks of minke whales at east and west Greenland. Rep. Int. Whaling Comm. 38:251-255. Mattila, D. K., and P. J. Clapham. 1989. Humpback whales, Megaptera novaeangliae, and other cetaceans on Virgin Bank and in the northern Lee- ward Islands, 1985 and 1986. Can. J. Zool. 67:2201-2211. Mattila, D. K., P. J. Clapham, O. Vasquez, and R. Bowman. In press. Occurrence, population composition and habitat use of humpback whales in Samana Bay, Dominican Republic. Can. J. Zool. Mitchell, E. D. 1991. Winter records of the minke whale (Balaenoptera NOTE Murphy: Occurrence and group characteristics of Balaenoptera acutorostrata 585 acutorostrata acutorostrata Lacepede 1804) in the south- ern North Atlantic. Rep. Int. Whaling Comm. 41:455—457. Mitchell, E. D., and V. M. Kozicki. 1975. Supplementary information on minke whales (Balaenoptera acutorostrata) from Newfoundland fishery. Can. J. Zool. 32:985-994. Ohsumi, S. 1983. Minke whales in the coastal waters of Japan in 1981 with special reference to their stock boundary. Rep. Int. Whaling Comm. 33:365-371. Overholtz, W. J., and J. R. Nicolas. 1979. Apparent feeding by the fin whale, Balaenoptera physalus, and humpback whale, Megaptera novaeangliae, on the American sand lance, Ammodytes amerieanus, in the Northwest Atlantic. Fish. Bull. 77:285-287. Payne, P. M., J. R. Nicolas, L. O'Brien, and K. D. Powers. 1986. The distribution of the humpback whale, Megaptera novaeangliae, on Georges Bank and in the Gulf of Maine in relation to densities of the sand eel, Ammodytes amerieanus. Fish. Bull. 84:271-277. Payne, P. M., D. N. Wiley, S. B. Young, S. Pittman, P. J. Clapham, and J. W. Jossi. 1990. Recent fluctuations in the abundance of baleen whales in the southern Gulf of Maine in relation to changes in selected prey. Fish. Bull. 88:687-696. Perkins, J., and H. Whitehead. 1977. Observations on three species of baleen whales off northern Newfoundland and adjacent waters. J. Fish. Res. Board Can. 34(9):1436-1440. Sergeant, D. E. 1963. Minke whales, Balaenoptera acutorostrata Lacepede, of the western North Atlantic. J. Fish. Res. Board Can. 20(6):1489-1504. Shimadzu, Y. 1980. Basis of fishing effort for minke whaling in the Antarctic. Rep. Int. Whaling Comm. 30:425-433. Sigurjdnsson, J. 1982. Icelandic minke whaling 1914-1980. Rep. Int. Whaling Comm. 32:287-295. Stern, S. J. 1990. Minke whales (Balaenoptera acutorostrata) of the Monterey Bay area. M.S. thesis, San Francisco State Univ., San Francisco, CA, 289 p. Stern, S. J., E. M. Dorsey, and V. L. Case. 1990. Photographic catchability of individually identified minke whales (Balaenoptera acutorostrata) oi the San Juan Islands, Washington and Monterey Bay area, Cali- fornia. Rep. Int. Whaling Comm. (special issue 12): 127-133. Taylor, R. J. F. 1957 An unusual record of three species of whale being re- stricted to pools in Antarctic sea-ice. Proc. Zool. Soc. Lond. 129:325-331. van Pijlen, I., W. Amos, and G. A. Dover. 1991. Multilocus DNA fingerprinting applied to the minke whale (Balaenoptera acutorostrata). Rep. Int. Whaling Comm. (special issue 13):245-254. Wada, S. 1989. Latitudinal segregation of the Okhotsk Sea-West Pacific stock of minke whales. Rep. Int. Whaling Comm. 39:229-233. Wada, S., T. Kobayashi, and K. I. Numachi. 1991. Genetic variability and differentiation of mitochon- drial DNA in minke whales. Rep. Int. Whaling Comm. (special issue 13):203-216. Wada, S., and K. I. Numachi. 1991. Allozyme analyses of genetic differentiation among the populations and species of the Balaenoptera. Rep. Int. Whaling Comm. (special issue 131:125-154. Williamson, G. R. 1975. Minke whales off Brazil. Sci. Rep. Whales Res. Inst., Tokyo 27:37-59. Activities of juvenile green turtles, Chelonia mydas, at a jettied pass in South Texas Maurice L. Renaud James A. Carpenter Jo A. Williams Galveston Laboratory, Southeast Fisheries Science Center National Marine Fisheries Service, NOAA 4700 Ave. U, Galveston, Texas 77551 Sharon A. Manzella-Tirpak U.S. Army Corps of Engineers 2000 Fort Point Blvd., Galveston, Texas 77553 Green turtles, Chelonia mydas, have a worldwide distribution in tropical and subtropical regions. Primary nesting areas in the Atlan- tic region are located at Ascension Island, Aves Island, Costa Rica, and Surinam. The east coast of Florida has the largest breeding assem- blage in the United States. The spe- cies is listed as endangered by the International Union for the Conser- vation of Nature (IUCN) (Groom- bridge, 1982) and is listed as threat- ened in all areas, except for breed- ing populations in Florida and the Pacific coast of Mexico, which are listed as endangered (National Marine Fisheries Service, 1991). During most of the nineteenth century, green turtles were abun- dant throughout Texas, including the lower Laguna Madre (Hilde- brand, 1982; Doughty, 1984). Com- mercial harvest of these turtles peaked in 1890; Texas landings in- creased to about 2,160 turtles (265,000 kg) from an estimated 89 turtles (10,909 kg) in 1880. By the early twentieth century the fishery had collapsed (Doughty, 1984). Understanding habitat needs has been recognized as an essential el- ement for successful recovery of sea turtle stocks in the Gulf of Mexico (Thompson et al., 1990). Distribu- tion, movements, and feeding hab- its of pelagic hatchlings are un- known. Little research has been conducted on sea turtle populations in Texas. Published stranding data suggest that Texas nearshore and inshore waters are important habi- tats for juvenile and subadult sea turtles (Rabalais and Rabalais, 1980; Manzella and Williams, 1992). Recent tracking and mark- recapture studies on green turtles indicate that jetties and channel entrances along the south Texas coast serve as summer developmen- tal habitats for this species1,2 (Manzella et al., 1990; Shaver, 1990, 1994). This is supported by higher numbers of sightings in south Texas versus the upper Texas and west Louisiana coasts (Will- iams and Manzella, 1991). Turtles using jetties and channel entrances could interact with hu- man activities, such as channel dredging, shrimping, and recre- ational fishing and boating. The level of such interaction is depen- dent on the nature and degree of jetty and channel utilization. Stud- ies conducted during 19911,2 indi- cated that green turtles may utilize jetty habitat to a greater degree than other habitats within Brazos- Santiago Pass, on the basis of sightings and the behavior of a single radio-tracked turtle. The objectives of our study were to de- scribe juvenile green turtle move- ments within Brazos-Santiago Pass, Texas. We hypothesized that juvenile green turtles select jetty habitat over other habitats within Brazos-Santiago Pass. Materials and methods Study area The study was conducted in the Brazos Santiago Pass area, South Padre Island, Texas (Fig. 1). The pass, extending from the tip of the jetties to the western edge of Bar- racuda and Dolphin Coves, links the Laguna Madre to the Gulf of Mexico. Landry et al.1 character- ized habitat types within the pass. Using their data, we designated four habitats in the pass area. The jetty habitat extended 10 m from the visible jetty, with water depths up to 3 m. It contained par- tially exposed and submerged gran- ite boulders and rubble, which de- creased in density as distance from the jetty increased. The highest density and concentration of sessile organisms were found in this habi- tat. Barnacles (Balanus sp.), sea urchins (Arbacia punctulata), and 1 Landry, A, Jr., D. Costa, B. Williams, and M. Coyne. 1992. Turtle capture and habi- tat characterization study. Final Rep. sub- mitted to the U.S. Army Corps of Engi- neers, Galveston District, 2000 Fort Point Blvd., Galveston, TX 77553, 112 p. 2 Renaud, M., G. Gitschlag, E. Klima, S. Manzella, and J. Williams. 1992. Track- ing of green (Chelonia mydas) and logger- head (Caretta caretta) sea turtles using radio and sonic telemetry at South Padre Island, Texas. June-September 1991. Fi- nal Rep. to the U.S. Army Corps of Engi- neers, Galveston District, 2000 Fort Point Blvd., Galveston, TX 77553, 52 p. Manuscript accepted 5 December 1994. Fishery Bulletin 93:586-593 (1995). 586 NOTE Renaud et al.: Activities of juvenile Chelonia mydas 587 three algal species (Ulva fasciata, Podina vickersiae, and Bryocladia thysigera), were the most abundant organisms associated with jetty structure.1 The near-jetty habitat encompassed areas of barren bottom and scattered boulders on both the Gulf and pass side of the jetty. Chan- nel habitat, the dredged portion of the Brownsville Ship Channel between the jetties, extended seaward from Barracuda and Dolphin Coves to the tip of the jetties. It was character- ized by a scoured bottom, nearly void of vegeta- tion. Water depths ranged from 10 to 15.2 m and averaged 12.5 m. Channel width was about 90 m for most of its length. East of the coves, the distance from the jetty to the channel edge ranged from 115 to 152 m. Barren rippled sand, water depths up to 7.5 m, and few organisms were noted within the cove habitat. Capture of sea turtles Turtles were obtained from Texas A&M Univer- sity (TAMU) Institute of Marine Life Science personnel, who were conducting a netting and habitat characterization study at Brazos- Santiago Pass.3 Turtles were captured either through use of entanglement nets (45.7-91.5 m long, 3.7—7.3 m deep, 12.7 cm bar mesh) set at the Gulf side of the South Jetty, or by encir- cling a targeted turtle in the shallow coves with the entanglement net. For turtles exhibiting strong site fidelity, 1-m diameter cast nets were used for some captures along the jetties. Tagging activities Following capture, turtles were transported 1- 2 km to a holding facility where they were kept for 24-48 hours. We recorded turtle weights, straight. and curved carapace lengths and widths, and applied radio and sonic transmit- ters. Telonics radio transmitters ( 180 g) with 40- cm antennas were fitted with fiberglass to the second neural scute of nine turtles, and Sonotronics sonic transmitters (36 g) were bolted to the posterior marginal scutes. Turtles were designated Tl through T9. The weight of the backpack-type transmitters never exceeded 3 Landry, A., Jr., D. Costa, M. Coyne, K. St. John, and B. Williams. 1993. Sea turtle capture and habitat charac- terization: South Padre Island and Sabine Pass, TX en- virons. Final Rep. submitted to the U.S. Army Corps of Engineers, Galveston District, 2000 Fort Point Blvd., Galveston, TX 77553, 109 p. South Padre Island Gull ol Mexico N Dolphin / ^^fcsL- • Point / ^^3> •p.w.v.w rs.tim T3 ; >v Barracuda Cove 12 7 T8 \ -~\^ri 7 Range 2369 \ ^^iJr "I. 7 T1 4900 84 6 9i m >--*-]} TEXAS \ .7 T2 / T3 31168 7654 7374 416 179 575 \ Brazos Island Vi^ / T° 3519 312 29.0 3I3SCZE3:l<:':l '•'' T9 1 ''' I^^T-^ Range Core Hours T7 2274 198 134 T4 6926 130 718 T9 6578 1748 10 8 South Padre Island Gull ol Mexico Dolphin Point .L,„ ......w^crrfg-t.ii-J-x^ T6 NSMJ 3752 195 NSSJ 3303 46 SSSJ 195 T5 2323 1748 17.6 108 2.7 570 Figure 1 Range (m2), core area (m2), and total hours tracked for individual green turtles, Chelonia mydas, T1-T9, duringAugust-September 1992. Core area is displayed in solid black and range is enclosed by a solid line for all turtles except T2. T2 has a shaded area representing its core area and a dashed line surrounding its range. For T6, NSNJ = north side of north jetty, NSSJ = north side of south jetty, and SSSJ = south side of south jetty. An inset of the state of Texas with an arrow showing our area of study is located in the upper third of the figure. 588 Fishery Bulletin 93(3), 1995 10% of the weight of the turtle, in accordance with the safety recommendations of Brander and Cochran (1969), Bradbury et al. (1979), Aldridge and Bringham (1988), and Byles and Keinath ( 1990). Tracking Turtles were released at their capture sites between 0900 and 1600 hours. We used a Telonics TR2/TS1 receiver-scanner connected to a directional 5-element Yagi antenna to monitor radio transmitters until they became detached from turtles. Maximum radius of signal reception with this equipment is approxi- mately 16 km. When weather prohibited tracking by vessel, turtles were monitored from land. Sonic trans- mitters were monitored by using a Dukane direc- tional hydrophone with a receiving range between 0.6 and 1.1 km. Sonic tracking alone was used when a turtle had lost its radio transmitter but retained its sonic transmitter or when a second turtle was present in the area of a turtle being monitored by radio. Data were collected for 12 hours each day. All hours of the day and night were included by offsetting each day's start time by two hours from that of the previ- ous day. We attempted daily to locate every turtle with a functioning transmitter. Up to five turtles were tracked during each day. Geographic location was recorded when a turtle was sighted or its position obtained with sonic telemetry. Reference marks were painted at 50-m intervals on jetty boulders, west- ward from the seaward tip of each jetty. Locations of turtles were determined with respect to reference marks and to visual estimates of perpendicular dis- tance from the jetties. When possible, turtle locations >40 m from the jetty were recorded by means of a portable global positioning system. The total time spent between jetty reference marks was calculated for each turtle. Each turtle position was given a weight equal to time spent at that position. These weighted positions were then used to calculate a mean position for each turtle. Minimum observation time used for this analysis was 5 minutes. Range (area containing 95% of locations) and core area (area containing 50% of locations) were developed by us- ing the minimum convex polygon method (Mohr, 1947), modified to exclude nonwater areas. To dis- cern differences in movement patterns, the ranges and core areas for each turtle were determined for dawn (0500-0900 h), day (0900-1700 h), dusk (1700- 2100 h), and night (2100-0500 h) if at least three days were sampled and >5 h of tracking information were available for a turtle within a time period. To obtain an index of turtle movements, the distance and time between surfacing events were calculated for each turtle and used to estimate mean speed of movements for dawn, day, dusk, night, and all times combined. Surface and submergence behavior Surface and submergence times were calculated for each turtle affixed with a radio transmitter. Data collected on the day of release were omitted from analyses of ranges and of surface or submergence behaviors. Surface time was considered to be the in- terval between the beginning and ending of radio signals (i.e. when the turtle was within 40 cm of the ocean surface). Submergence time was denned as the interval between the end of a radio signal and the beginning of the next signal (i.e. when the turtle was deeper than 40 cm). Overall mean surface and sub- mergence times, and day, night, dawn, and dusk means were calculated for each turtle. A surface or submergence interval overlapping two time periods was included in the period containing the majority of the interval. Statistical methods Distribution of variables (surface and submergence times, movement speed) were tested with the Shapiro-Wilk test for normality (oc=0.05). The Kruskall-Wallis analysis was used to test for differ- ences in means between dawn, day, dusk, and night (a=0.05) (Sokal and Rohlf, 1981) when the null hy- pothesis (normal distribution) was rejected. If a sig- nificant difference was indicated, a means test de- scribed by Conover (1980) was used to determine which means differed, again by using a=0.05. Results Sea turtle movement patterns Nine green turtles (29.1-47.9 cm straight carapace length [SCL], 2.6-14.8 kg) were tracked from 14 to 58 days from 31 July to 26 September 1992 (Table 1). Differences in tracking periods were due to dif- ferent capture dates and variable tag retention. In addition, on some days certain turtles could not be located owing to inclement weather. All turtles moved away from the jetties immediately following release. Those released between the jetties entered the deeper waters of the channel, but T8, released on the Gulf side of the south jetty, moved south, roughly parallel to the beach. Seven turtles returned to the jetties within an hour. T6 and T7 went offshore after enter- ing the channel and returned to the jetties the next NOTE Renaud et al.: Activities of juvenile Chelonia mydas 589 Table 1 Percent total submergence time (PTST), maximum sub- mergence time (MST, minutes), weight (kg), straight cara- pace length (SCL, cm), and dates tracked for nine green turtles, Chelonia mydas, at South Padre Island, Texas. Turtle PTST MST Weight SCL Date Tl 88.8 24.3 14.8 47.9 31 Jul -26 Sep T2 92.4 21.4 11.5 44.7 01 Aug-25 Sep T3 96.3 32.9 3.1 30.1 01 Aug-26 Sep T4 80.8 31.2 2.7 29.1 01 Aug-26 Sep T5 90.1 25.4 2.6 29.2 01 Aug-26 Sep T6 96.3 39.8 3.6 31.5 02 Aug-26 Sep T7 93.1 25.8 3.9 33.3 06 Aug-26 Sep T8 96.5 37.8 3.4 31.5 09 Aug-26 Sep T9 97.8 38.1 4.1 33.0 10 Aug-23 Sep day. Seven turtles remained in the general area of their capture throughout the study period. Of the others, T6 used three areas along both jetties and T7 moved extensively along both jetties before mov- ing up the channel and into South Bay. Only data from the pass were used in analyses for T7. Daily movements of turtles along the jetties ranged from less than 50 m to more than 1,000 m. Mean rate of movement ranged from 8 m/h to 568 m/h (Table 2). The least movement occurred at night, ranging from 8-127 m/h. Seventy percent of all loca- tions were within 5 m of the jetties. Only 0.3% were within channel boundaries, including five channel crossings. Overall areal ranges of turtles remaining in the jetty area were from 2,274 to 31,168 m2. Over- all core areas ranged from 130 to 7,374 m2. Five of the nine turtles tracked had ranges re- stricted to the north side of the south jetty (Fig. 1). Northerly winds, in excess of 20 knots, coincided with the movement of T6 from the windward side of the north jetty into protected waters near the south jetty by day 14. Mean locations for three turtles (Tl, T4, and T5) were within 400 m of the Barracuda Cove beach. The mean location of T2 was about 650 m from the beach, about halfway up the jetty. The only turtle that had significantly different mean locations for different time periods was Tl (P<0.05). The mean dusk location of Tl was about 250 m closer to the jetty tip than its mean dawn and day locations and over 400 m closer than its mean night location. T3, on the south side of the north jetty, also showed greater westward movement at night than at any other time (P<0.05). Table 2 Mean distance (m) moved by hour by time period for nine green turtles, Chelor ia mydas, tracked near South Padre Island, Texas. A line above mean movements indicates no significant difference (ot=0.05). Turtle Time of day Tl Period Day Dusk Night Dawn T2 Mean distance Period 127 161 401 251 Night Dawn Day Dusk Mean distance 8 148 440 568 T3 Period Dusk Day Dawn Mean distance 20 102 323 T4 Period Night Dusk Dawn Day Mean distance 25 223 243 330 T5 Period Night Day Dawn Dusk Mean distance 45 144 108 191 T6 Period Dusk Day T7 Mean distance Period 59 225 Night Dawn Day T8 Mean distance Period 9 496 517 Dawn Dusk Day Mean distance 171 195 201 T9 Period Day Dawn Mean distance 114 149 Submergence and surface behavior Tracking was conducted for a total of 108 hours at dawn, 247 h during the day, 60 h at dusk, and 151 h at night. Time spent submerged ranged from 80.8 to 97.8% and averaged 91% for all turtles (Table 1 ). Sub- mergence time ranged from 0.02 to 39.8 minutes. Overall mean submergence time varied from 1.9 to 6.1 min between turtles. Surface time ranged from 1 to 1,146 seconds. Overall mean surface time varied from 8.5 to 26.5 seconds. A breakdown of submergence time by turtle re- vealed that 99% of all turtle submergences were <20 min, 74-96% were <10 min, and 38-64% were <1 min (Fig. 2). Submergence patterns were significantly different when data were analyzed by dawn, day, dusk, and night (Table 3). The number of sub- mergences >10 min was higher at night than at other time periods for every turtle tracked at night. A breakdown of surface time by turtle revealed that 99% of all turtle surfacings were <120 sec, 67-92% were <15 sec, and 41-77% were <5 sec (Fig. 2). Sur- face patterns also were significantly different when 590 Fishery Bulletin 93(3), 1995 Id ^^ gDoz gQaz gaQ gaQ gaoz gD T4 T5 T6 T7 T8 T9 Figure 2 Green turtle, Chelonia mydas, submergence and surface durations by specified time intervals in hours, dawn (0500-0900), day (0900- 1700), dusk (1700-2100), and night (2100-0500). data were analyzed by dawn, day, dusk, and night (Table 3). The number of surfacings >15 sec was higher at night than at other periods for every turtle tracked at night. The mean surface time was signifi- cantly higher at night than at all other time periods for four of six turtles tracked at night. Discussion Movements and habitat use Habitat use by juvenile green turtles in the Brazos- Santiago Pass was not proportional to available habi- tat.1,2 The jetty habitat, which contained extensive algal mats, received a disproportionately high amount of use, suggesting that turtles possibly con- gregated there for food. Analysis of stomach contents of juvenile green turtles by Landry et al.3 sup- port the utilization of algal food sources. Turtles in this study were seen feeding on algal growth along the jetties, especially at dusk. The abundance of food may account for the high site fidelity and small core areas. Other studies of similar-size green turtles de- scribed their food source as algae ( Wershoven and Wershoven, 1989; Wershoven and Wer- shoven, 1991), both algae and sea grasses (Burke et al., 1991), and primarily sea grasses (Ogden et al., 1983). Mendonca ( 1983), working with larger turtles (7.8-54.5 kg) postulated that green turtles prefer sea grass. Sea grasses were present within 1 km of the jetty habitat of our study area.4 One turtle from our study entered and remained in a sea grass habitat for over a month; how- ever, no fecal or stomach samples were taken while it was in this habitat. Bjorndal et al. (1991) suggested that green turtles possess gut microflora for digestion of both algae and seagrass and that the relative abundance of microbial species would vary in response to longterm changes in diet. Therefore, turtles could take advantage of a local abundance in either food source. All of the turtles in this study had small ranges of movement. A juvenile green turtle tracked at the jetties in 1991 also showed lim- ited movements.2 The most limited move- ments were at night, suggesting that resting was most common at night. This hypothesis is supported in studies by Bjorndal (1980), Mendonca (1983), and Ogden et al. (1983) who documented resting areas for turtles at night coupled with a shorter range of move- ments compared with activity during the day. Mendonca ( 1983) noted that during summer months the resting sites of green turtles on consecutive nights were within meters of the previous night's rest site. The reason for the westward movements of Tl at night is unknown. The more sheltered jetty habitat adjacent to the cove may have been preferred for rest- ing at night, whereas a broader stretch of the jetty was utilized for daytime foraging activities. Turtles at the jetties apparently have an abundant food source in proximity to resting sites. In contrast, Mendonca (1983) recorded areal ranges of 0.48 to 4 Quammen, M., and C. Onuf. 1991. Laguna Madre: seagrass changes continue decades after salinity reduction. Rep. to the National Wetlands Center, U.S. Fish Wildl. Serv., Cam- pus Box 39, 6300 Ocean Dr., Corpus Christi, TX 78412, 27 p. NOTE Renaud et al: Activities of juvenile Chelonia mydas 591 5.06 km2 for juvenile green turtles. Ogden et al. (1983) found turtles moved up to 0.5 km between feeding and resting sites, but they did not report ranges of movement. Turtles appeared to select for the south jetty. Landry et al.3 also recorded many more turtle sightings at the south jetty than at the north jetty. Of two turtles caught at the north jetty, only one remained there longer than two weeks. The other moved to the south jetty during northerly winds in excess of 20 knots. Because of its accessibility, the north jetty received much more use by the public than the south jetty. The effect of this disproportionate use on turtle presence or behavior, or both, during the study is unknown. Submergence behavior Green turtle behavior was characterized by numer- ous short submergences and surfacings. Sub- mergences <5 min occurred mostly during dusk and dawn when active periods of foraging were observed. We felt this was a direct effect of the shallow habitat occupied by the turtles. The transmitter antenna could be exposed at times when the turtle was still submerged. Submergence >10 min was observed at night and minimally during the afternoon. Submergence durations by green turtles in our study was similar to that for green turtles studied by Renaud et al.2 Eighty-nine to ninety-nine percent of the submergences were <10 min in duration and 17-56% were <1 minute. Mean submergence times for turtles in our study were considerably shorter than the mean submergence times of Kemp's ridleys found by Byles ( 1989) ( 18.1 min), and Mendonca and Pritchard (1986) (16.7 min). This may be a result of the different habitats and feeding behaviors of Kemp's ridleys and the green turtles in our study. Our turtles also were smaller than turtles in the other two studies. The percentage of submerged time for each 24-h day ranged from 80.8-97.8%. The turtles with the three lowest percent submerged times were observed for long periods with their antenna only partially exposed. This behavior undoubtedly lowered their submerged to surface ratio. Balazs (1994), through satellite telemetry, found that two migrating adult green turtles in the Pacific Ocean spent 95-96% of their time submerged. Renaud and Carpenter ( 1994) found percent submerged time to be 90.0-95.7% for three satellite-tracked juvenile loggerhead turtles, Caretta caretta, in the Gulf of Mexico. Two satellite- tracked juvenile Kemp's ridley sea turtles, in the Atlantic and Gulf of Mexico, had percent submerged times of 94.0-98.6% (Renaud, in press). Byles ( 1989), Table 3 Mean surface and submergence times ( nearest sec ) by time period, for nine green turtles, Chelonia mydas, tracked near South Padre Island, Texas. Aline above mean values indi- cates no significant difference (a=0.05). D = day; K = dusk; N = night; W = dawn. Turtle Time of day Tl Surface Submerge T2 Surface Submerge T3 Surface Submerge T4 Surface Submerge T5 Surface Submerge T6 Surface Submerge T7 Surface Submerge T8 Surface Submerge T9 Surface Submerge D5 K60 N47 Kll N172 W13 W214 D236 D15 K21 Will N26 DHL! K143 W153 N320 N56 N1371 N35 D12 W13 K16 D327 D19 K58 D5 K70 W366 K446 K24 W29 D102 W13 W108 N169 K19 N20 N187 D102 W109 W7 Dll K15 N80 N13 N258 W125 D9 D321 K501 K12 W14 W123 D145 K184 D5 W6 K9 K171 D174 W175 W6 W212 D6 D313 studying adult Kemp's ridleys in the Gulf of Mexico with satellite telemetry, found that they spent an average 96% of the time submerged. A study of radio- tracked loggerheads with 64.0-91.9 cm carapace length (straight or curved not specified) in the Canaveral Channel, Florida, revealed that they averaged 96.2% of the time submerged (Kemmerer et al., 1983). 592 Fishery Bulletin 93(3), 1995 Channel use During our study, turtles remained primarily near the jetties, probably because food was abundant there and virtually absent in the channel and barren bot- tom areas. Turtles were found in the channel <0.3% of the time. They appeared to use the channel for transit to other areas or as presumed escape cover. Conclusions Our data, combined with numerous sightings of turtles at the jetty3 and with the fact that there was no appreciable movement away from the jetties by tracked turtles, support the hypothesis that juvenile green turtles in Brazos-Santiago Pass, south Texas, selected for jetty habitat over other habitats avail- able. If this pattern is consistent for all times that green turtles inhabit the pass, then it would indi- cate that potential harm from hopper dredging or channel boat traffic would be minimal. Our study included only nine turtles and was limited to August- September 1992. Therefore, caution should be used in extrapolating our results to other years or times of the year. The study was timed to coincide with the period of highest turtle abundance in the pass. Data gathered by TAMU indicate that use of the pass by green turtles increases during June-September.13 Turtles appear to be rare from December to March and gradually begin to increase in numbers starting in April. We were unable to monitor turtle behavior during dredging, because no dredging was done dur- ing the study; therefore, we do not know how dredg- ing of the channel may affect behavior of turtles oc- cupying the jetty habitat. Because green turtles are herbivorous, there is very little danger of hook and line captures from jetty fish- ing. The greatest impact on turtle behavior may be sim- ply that of human activity on the jetties. The level of that impact is currently unknown. We encourage fur- ther study, particularly during other times of the year. Acknowledgments We would like to acknowledge several organizations and their personnel for assistance in making this work possible: the U.S. Army Corps of Engineers (Galveston and New Orleans Districts) for funding the research, Texas A&M University for capturing sea turtles and characterizing habitats in the lower Laguna Madre, the University of Texas Pan Ameri- can Coastal Studies Laboratory for making their fa- cility available to hold turtles, and the U.S. Coast Guard Station at South Padre Island for use of their base to store our tracking vessel. Special thanks go to Gregg Gitschlag for development of the turtle monitoring system along the jetties. 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[Available from NTIS, 5285 Port Royal Road, Springfield, VA 22161.1 Sokal, R. R., and F. J. Rohlf. 1981. Biometry, 2nd edition. W. H. Freeman, New York, NY, 859 p. Thompson, N., T. Henwood, S. Epperly, R. Lohoefener, G. Gitschlag, L. Ogren, J. Mysing, and M. Renaud. 1990. Marine turtle habitat plan. U.S Dep. Commer., NOAATech. Memo. NMFS-SEFC-255, 20 p. [Available from NTIS, 5285 Port Royal Road, Springfield, VA 22161.] Wershoven, J. L., and R. W. Wershoven. 1991. Juvenile green turtles in their nearshore habitat of Broward County, Florida: a five year review. In M. Salmon and J. Wyneken (compilers), Proceedings of the eleventh annual workshop on sea turtle biology and conservation, p. 121-123. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SEFC-302. [Available from NTIS, 5285 Port Royal Road, Springfield, VA 22161.] Wershoven, R. W., and J. L. Wershoven. 1989. Assessment of juvenile green turtles and their habi- tat in Broward County, Florida waters. In S. A. Eckert., K. L. Eckert, and T H. Richardson (compilers), Proceed- ings of the ninth annual workshop on sea turtle biology and conservation, p. 185-187. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SEFC-232. [Available from NTIS, 5285 Port Royal Road, Springfield, VA 22161.] Williams, J. A., and S. A. Manzella. 1991. Sea turtle sightings at passes on the Texas Gulf coast. In M. Salmon and J. Wyneken (compilers), Proceed- ings of the eleventh annual workshop on sea turtle biology and conservation, p. 188-190. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SEFC-302. [Available from NTIS, 5285 Port Royal Road, Springfield, VA 22161.] Determination of age and growth of swordfish, Xiphias gladius L., 1 758, in the eastern Mediterranean using ana\-f\n spines George Tserpes Institute of Marine Biology of Crete RO. Box 22 1 4. 7 1 0 03 Iraklion. Greece Nikolaos Tsimenides University of Crete, Department of Biology RO. Box 1470, 711 10 Iraklion, Greece in anal-fin spines used for age de- termination of swordfish are depos- ited annually. Because Ehrhardt (1992) reported that the von Bert- alanffy growth function did not ad- equately represent swordfish growth, we propose a second objec- tive, namely to compare the growth function proposed by Ehrhardt (1992) with the standard von Bertalanffy model for representing growth of Mediterranean sword- fish. Materials and methods Estimates of growth rates of bill- fish are important because they are necessary elements of population dynamics models used in the as- sessment of stocks for this family offish. Otoliths have been used for ageing most billfish species (Radtke, 1983; Radtke and Hurley, 1983; Wilson and Dean, 1983; Prince et al., 1984; Hill et al., 1989) but sev- eral authors have pointed out that the use of dorsal- and anal-fin spines are more practical in terms of ease of collection and processing (Berkeley and Houde, 1983; Hedge- peth and Jolley, 1983; Hill et al., 1989; Tsimenides and Tserpes, 1989). Other skeletal structures such as vertebrae have rarely been used and results have been poor (Prince et al., 1984; Hill et al., 1989). The swordfish, Xiphias gladius, is a cosmopolitan billfish species that is highly exploited in the At- lantic Ocean and the Mediterra- nean Sea. In the Mediterranean the average size of harvested swordfish has declined over the last decade such that juveniles compose as much as 50-80% of the catch (Di Natale, 1990; Tserpes et al., 1993). However, the existence of contra- dictory estimates of growth param- eters makes assessment of sword- fish stocks difficult (Anonymous, 1990; 1993). Age of swordfish has been esti- mated from otoliths (Radtke and Hurley, 1983; Wilson and Dean, 1983), and sections of anal-fin spines (Berkeley and Houde, 1983 ). Of these ageing methods only Ehrhardt (1992) achieved partial validation of the anal-fin method through marginal increment analy- sis. This analysis assumes that time of annulus formation corre- sponds to the time when marginal increments are minimal, and it has been widely used to determine the timing of annual increment forma- tion in otoliths and scales of vari- ous fish species (Wenner et al., 1986; Maceina et al., 1987). Al- though the assumption of the analysis is valid for any ageing structure, the method has rarely been applied to structures other than otoliths and scales. Tsimenides and Tserpes (1989) conducted growth studies on sword- fish from the Aegean sea using anal-fin spines but did not attempt validation. They concluded that there was "a degree of uncertainty" in age estimates due to the loss of the first annulus in older animals. The primary goal of this paper is to determine whether growth bands Fish sampling and spine preparation A total of 1,325 swordfish samples were obtained from commercial longline catches landed at the ports of Kalimnos (n = 782), Kithnos (rc = 185), and Chania (n-358) in the Aegean sea. These ports, located on the islands of Kalimnos, Kithnos, and Crete are part of a national project addressing the fishery and biology of swordfish in the Greek seas (De Metrio et al., 1989). Samples were collected from 1987 to 1992 during alternate months from February to October. How- ever, most were collected from May to September when the majority of catches occur. Measurements of lower-jaw fork length (LJFL to nearest cm) were taken for all fish, sex was deter- mined, and the anal fin removed and frozen for storage. In the labo- ratory, fins were thawed and sec- tions of the second spine of the anal fin were prepared for reading ac- cording to the method described by Tsimenides and Tserpes (1989). Specifically, each anal fin was im- mersed in boiling water for a few minutes before the second spine was removed, freed from skin and tissue, cleaned with water, and left- Manuscript accepted 13 March 1995. Fishery Bulletin 93:594-602 (1995). 594 NOTE Tserpes and Tsimenides. Determination of age and growth of Xiphias gladius 595 to dry completely. A section about 2 cm thick was cut with an electric saw from each dried spine at the point where the spine flares (condyle). Each section was placed in a plastic cylinder (3 cm diameter and 2 cm height) which was then filled with liquid resin. These were left to dry for at least 12 hours, the plastic case was removed, and two or three sections about 1 mm thick were cut distally with a "Stuers" accutom. Age determination Spine sections were read under a binocular micro- scope at 12x magnification by using reflected light and a dark background. The distances from the fo- cus to the edge of the section on the dorsal rim (spine radius) and from the focus to each annulus were measured with an optical micrometer. Sections were read by two readers and identical counts were ob- tained in >80% of the cases; samples were consid- ered unreadable and were excluded from the analy- sis if discrepancies in counts could not be resolved. Typically, broad opaque bands and narrow trans- lucent ones could be seen alternating outwards from the central core. Translucent bands that form around the entire circumference of the spine were consid- ered to be annuli and the total number of these bands was recorded (Fig. 1). Age classes were assigned on the basis of the num- ber of annuli and the following characteristics of the bands: 1) the disappearance of the first annulus from older fish and 2) the existence of multiple bands mainly in larger fish. Preliminary analysis of LJFL measurements taken in nursery areas of the Aegean sea have shown that swordfish reach a length of about 80-90 cm at one year of age. The first annulus could be seen in fish of this size at an average dis- tance of 1.5 mm (SD=0.08) from the focus, but it was usually not visible at lengths greater than 100 cm (Fig. 1). In such cases, and if the total spine radius was greater than 1.5 mm, one year was added to the assigned age. As described by Berkeley and Houde ( 1983), multiple bands are those which form around the entire circumference of the spine such that the distance between them is substantially less than that of the preceding and following annual bands. In these cases, the clearest band was considered an annulus and the others were ignored. However, if it was not possible to identify such a band, the specimen was considered unreadable. When the opaque-translucent zonation was such that annuli could not be defined, such specimens were also considered unreadable. Data analysis The marginal increment ratio (MIR) was estimated for each specimen according to the formula: MIR = (S-r)/S, Figure 1 Sections of second anal-fin spine with five growth zones (A) and one growth zone (B) used for age determination of swordfish, Xiphias gladius, from the eastern Mediterranean. First annulus is miss- ing in section (A) whereas it can be clearly seen in section (B). Estimated location of first annulus in section (A), based on its location in section (B), is indicated by an arrow. Lower-jaw fork lengths (LJFL) of animals (A) and (B) were 162 and 95 cm, respectively. 596 Fishery Bulletin 93(3), 1995 where S = spine radius; and r = radius of the most recent annulus. n The mean MIR and the standard deviation were computed for each month and age separately. Mar- ginal increment analysis was not performed for age 1 because the first annulus was usually missing, nor for ages greater than 5 because of a lack of sufficient number of samples. Estimates of theoretical growth in length were obtained by fitting mean monthly length-at-age data to two forms of the von Bertalanffy growth equation: 1 ) the standard form and 2 ) the generalized form as proposed by Chapman (1961). Lt=L^l-e-k^) L{^S)-(L^S)-l{0l-s,)e-kn-Su V (r2=0.99) (r2=0.99) Female Sexes combined (r2=0.99) (r2=0.99) k~ 5 203.076 0.241 -1.205 226.525 238.582 292.967 0.210 0.185 0.020 -1.165 -1.404 0.000 -1.434 274.914 385.503 0.037 0.011 0.000 0.002 -1.140 -1.393 due to the small variance of the recorded values rather than to a morphometric discrimination be- tween sexes. This can be seen by solving the equa- tions for different spine-radius values. For example, the computed LJFL values for a spine radius of 2 mm are: 1) 95.73 for males and 96.47 cm for females from the linear method; and 2) 99.29 for males and 99.98 for females from the nonlinear method. The LJFL at the end of each year of life was backcalculated for each individual and these lengths were averaged for males and females separately to obtain mean back-calculated lengths at age. These generally agreed with lengths at age predicted by the growth models and show that females grow faster than males after an estimated age of 3 years (Table 3). Discussion Swordfish anal-fin spines have been used previously for ageing Atlantic swordfish (Berkeley and Houde, 1983). Ehrhardt (1992) attempted to validate the method by means of marginal increment analysis and reported that growth bands 1 to 4 were deposited annually during the winter months. Results of mar- ginal increment analysis of the present study dem- onstrated that growth bands for fish 2 to 5 years of age are deposited annually. In both the previous cases, marginal increment analysis was successful in showing the seasonality of band deposition; how- ever, although these results partially validate the method, it cannot be considered successful until all reported ages of each population are validated (Beamish and McFarlane, 1983). Marginal increment analysis has also been successful in elucidating the time of annulus formation in dorsal spines of Tandanus tandanus (Davis, 1977). It is unlikely, how- ever, that application of marginal increment analy- sis to older ages, in which spine growth is consider- ably reduced, would show any seasonality in band deposition. In general, validation of ages of older fish requires either a mark-recapture study or the iden- Table 3 Back-calculated and predicted lower jaw fork length 5 (LJFL-cm) at age for swordfish, Xiphias gladius, from the eastern Mediterranean. Back-calculated Back-calculated Predicted Predicted Age (proportional formula) (nonlinear method) (standard von Bertalanffy) (generalised von Bertalanffy) Male Female Male Female Male Female Male Female 1 _ _ 83.71 82.76 83.79 82.52 2 106.85 108.84 110.82 112.98 109.28 109.99 110.30 112.03 3 126.14 128.44 131.03 136.06 129.36 132.06 129.03 133.00 4 141.34 145.48 146.28 153.79 145.15 149.96 143.81 149.48 5 153.80 159.88 158.22 167.15 157.55 164.46 156.10 163.04 6 165.06 172.64 168.19 178.00 167.30 176.21 166.65 174.52 7 173.32 182.24 177.11 186.76 174.96 185.74 175.87 184.41 8 190.17 193.10 180.98 193.47 184.05 193.04 9 195.16 196.67 185.72 199.73 191.38 200.63 NOTE Tserpes and Tsimenides: Determination of age and growth of Xiphias gladius 599 tification of known-age fish in the population (Beamish and McFarlane, 1983). The present work showed that annuli are formed from late spring to early summer which is the spawn- ing period for swordfish in the Mediterranean (Palco et al., 1981). Since it has been suggested that sword- fish use particular spawning grounds in the Medi- terranean (Rey, 1988; Cavallaro et. al., 1991), annu- lus formation may be related to migration of fish to these grounds. A relation between annulus forma- tion and migration has been suggested for the At- lantic swordfish as well (Berkeley and Houde, 1983). Our findings indicate that anal-fin spines are use- ful for ageing swordfish. These are important because Age 2 0.30 j 6 025 - 15 f e io 29 21 L f ,73 I" 146 H 0.20 ■ 0.15 - 0.10 • 0.05 o ■ .3 9* .3 33.3 «rt +J to Aee 3 0.30 j b i- 025 - 0.20 - [' ■ { 29 r 23 26 42 24 t- c 0.15 - 0.10 E 0.05 - m 0> O Feb Mai Apr May Jun Jul Aug Sep Oct c 030 - Age 4 025 , 0.20 c en 0.15 0.10 0.05 13 (■ 3 29 i- h a* .2 9- « 3 Ji. 3 v M 0.30 Age 5 025 020 0.15 5 3 6 0.10 " 4 « ^ 2 6 (■ 0.05 f - - ' Month Figure 3 Mean monthly marginal increment ratio for swordfish. Xiphias gladius, ages 2-5 from the eastern Mediterranean. Vertical bars represent ±1 SE. Numbers are sample sizes. 250 r 21)0 ^^- 150 x^ 100 /' / Males so f n=32 i 0 4 8 12 16 Age (yr) "ork length (cm) o o o 1 >oo / Females t-> > 50 0 i II 4 8 12 16 Age (yr) 250 r 200 150 ■ /^ 100 / Both sexes f n=74 i 50 0 4 8 12 16 Age (yr) generalized VB Figure 4 Standard and generalized von Bertalanffy ( VB ) growth curves for swordfish, Xiphias gladius, from the eastern Mediterranean; n = sample size. 600 Fishery Bulletin 93(3), 1995 Table 4 Estimated lower-jaw fork length the Mediterranean (M). s (LJFL to nearest cm) at age for swordfish, Xiphias gladius, from studies in the Atlantic (A) and Age Berkeley and Houde ( 1983) (A) Radtke and Hurley (1983) (A) Wilson and Dean (1983) (A) Ehrhardt(1992) (A) Tsimenides and (M) Tserpes (1989) Male Female Male Female Male Female Male Female Male Female 1 97.2 98.0 84 73 116.9 122.9 89.7 89.8 103.2 103.1 2 118.5 119.9 98 85 123.3 130.6 117.0 118.9 129.5 129.1 3 136.0 139.7 110 114 130.2 138.8 137.3 142.9 148.1 149.3 4 150.4 157.8 122 131 137.4 147.5 153.4 161.3 161.4 165.0 5 162.3 174.3 133 147 145.0 156.8 168.9 177.2 170.8 177.3 6 172.0 189.3 143 160 153.0 166.6 181.8 189.6 177.5 186.8 7 180.0 202.9 153 172 161.5 177.1 195.3 204.4 185.2 194.2 8 186.6 215.3 161 183 170.4 188.2 206.1 214.7 swordfish have no scales and otoliths are not ame- nable to traditional ageing techniques owing to their small size (Ovchinnikov, 1970; Becket, 1974). Suc- cessful otolith readings have been performed only through the application of scanning electron micros- copy (Radtke and Hurley, 1983; Wilson and Dean, 1983). Moreover, the use of spines has the advan- tage that the material can be obtained relatively eas- ily without reducing the economic value of the fish. The main problems associated with the spine method are the existence of multiple bands and the missing first annulus. An experienced reader can overcome the problem of multiple bands by determining whether they continue around the entire circumfer- ence of the spine and by recording their distance from the preceding and following annuli. The problem of the missing first annulus in larger fish can be re- solved by identifying its position on sections from younger specimens where the annulus is visible. Dif- ficulties in defining the location of the first annulus in older animals have also been reported for Atlantic swordfish (Berkeley and Houde, 1983) and Pacific blue marlin, Makaira nigricans (Hill et al., 1989). Ehrhardt (1992) suggested that the standard von Bertalanffy growth function does not adequately rep- resent the growth of swordfish and proposed the use of the generalized growth function of Chapman ( 1961). The present estimates of r2 indicate that both models describe swordfish growth equally well over the age ranges considered and give almost identical results for the first eight years of growth (Fig. 4). Although the extrapolation of regression curves be- yond the data is not advisable, it is interesting to note that the generalized model gives much more realistic results for ages less than one because it forces the growth curve to pass close to the origin of both axes. On the other hand, estimates of asymp- totic length from this model are questionable because it is unlikely that females have lower asymptotic lengths than males, given that all the large animals in the sample were female. Therefore, the general- ized model appears to overestimate asymptotic length (especially that of males). Although results of both back-calculation methods generally agreed with the values predicted by the growth equations, the estimates of the nonlinear method are in slightly closer agreement (Table 3). The use of a nonlinear function for the LJFL spine- radius relation is preferable because it is more real- istic for small animals, which have near zero spine- radius values and very small LJFL values. Ehrhardt ( 1992) also suggested the use of a nonlinear function to describe the LJFL spine-radius relation. Growth studies carried out in the Atlantic together with previous work (Tsimenides and Tserpes, 1989) have shown that females grow faster than males (Table 4). Therefore, the calculation of a common growth equation is not valid and may be useful for management purposes only under certain circum- stances. However, it should be noted that in previ- ous work (Tsimenides and Tserpes, 1989), lengths at age were overestimated because the position of the first annulus was misidentified. In the case of swordfish it seems that the use of a relatively wide range of size data and mean values for fitting the growth curves has resulted in rela- tively unbiased estimates of swordfish growth pa- rameters in the eastern Mediterranean. Since all Mediterranean swordfish are proposed to belong to the same stock (Magoulas et al., 1993), our findings NOTE Tserpes and Tsimenides: Determination of age and growth of Xiphias gladtus 601 are appropriate for assessment studies of this stock. The use of the standard von Bertalanffy growth model is recommended for such studies because the general- ized model overestimates the asymptotic length, an essential parameter for population dynamics models. Acknowledgments We wish to thank two anonymous reviewers for their useful comments at an earlier version of this manuscript. Literature cited Anonymous. 1990. International Commission for the Conservation of Atlantic Tunas (ICCAT). Collective volume of scientific papers, Vol. XXXIII, Madrid, Spain, 200 p. 1993. International Commission for the Conservation of Atlantic Tunas (ICCAT). Collective volume of scientific papers, Vol. XL(1), Madrid, Spain, 473 p. Bagenal, T. B., and F. W. Tesch. 1978. Age and growth. In T. B. Bagenal (ed.), Methods for assessment offish production in fresh waters, 3rd ed., p. 101-136. Blackwell Scientific Pubis., Oxford, U.K. Beamish, R. J., and G. A. McFarlane. 1983. The forgotten requirement for age validation in fish- eries biology. Trans. Am. Fish. 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L. 1983. Istiophorid otoliths: extraction, morphology, and pos- sible use as ageing structures. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 8:123-129. Radtke, R. L., and P. C. F. Hurley. 1983. Age estimation and growth of broadbill swordfish, Xiphias gladius , from the NW Atlantic based on external features of otoliths. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 8:145-150. Rey, J. C. 1988. Comentarios sobre las areasde reproduccion del pez espada (Xiphias gladius) en el Atlantico y Mediter- raneo. In Int. Comm. Conserv. Atlantic Tunas (ICCAT) collective volume of scientific papers, Vol. XXVII, p. 180- 192. [In Spanish, English summary.] 602 Fishery Bulletin 93(3), 1995 Tserpes, G., P. Peristeraki, and N. Tsimenides. 1993. Greek swordfish fishery; some trends in the size com- position of the catches. In Int. Comm. Conserv. Atlantic Tunas (ICCAT) collective volume of scientific papers, Vol. XL (1), Madrid, Spain, p. 137-140. Tsimenides, N., and G. Tserpes. 1989. Age determination and growth of swordfish Xiphias gladius L., 1758 in the Aegean Sea. Fish. Res. 8:159-168. Wenner, C. A., W. A. Roumillat, and C. W. Waltz. 1986. Contributions to the life history of black sea bass, Centropristis striata, off the southeastern United States. Fish. Bull. 84:723-741. Wilkinson, L. 1988. Systat: the system for statistics. Systat Inc., Evanston, IL, 822 p. Wilson, C. A., and J. M. Dean. 1983. The potential use of sagittae for estimating age of Atlantic swordfish, Xiphias gladius. U.S. Dep. Commer. NOAATech. Rep. NMFS 8:151-156. Zar, J. H. 1984. Biostatistical analysis, 2nd ed. Prentice-Hall, Englewood Cliffs, NJ, 718 p. Fishery Bulletin Guide for Contributo Atmosph "Mi National Marine teries Service Scientific Editor Editorial Committee Dr. Andrew E. Dizo Dr. Linda L. Jones Natio Dr. Ri D. Methot I Dr. Theodore \X Dr. Joseph E. Powr im D. Smith Managing Editor U.S. Department of Commerce Seattle, Washington Volume 93 Number 4 October 1995 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 furnished by NMFS, in any advertising or sales promotion which would indicate or imply that NMFS approves, recommends, or endorses any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the adver- tised product to be used or purchased because of this NMFS publication. Fishery Bulletin . Contents Articles OCT 1 6 1995 Woods Ho!:, 603 Brodeur, Richard D., Morgan S. Busby, and Matthew T. Wilson Summer distribution of early life stages of walleye pollock, Theragra chalcogramma, and associated species in the western Gulf of Alaska 6 1 9 Crabtree, Roy E., Edward C. Cyr, and John M. Dean Age and growth of tarpon, Megalops atlanticus, from South Florida waters 629 Ferreira, Beatrice P., and Garry R. Russ Population structure of the leopard coralgrouper, Plectropomus leopardus, on fished and unfished reefs off Townsville, Central Great Barrier Reef, Australia 643 Lowerre-Barbieri, Susan K., Mark E. Chittenden Jr., and Luiz R. Barbieri Age and growth of weakfish, Cynoscion regalis, in the Chesapeake Bay region with a discussion of historical changes in maximum size 657 Mertz, Gordon, and Ransom A. Myers Estimating the predictability of recruitment 666 Mojica, Raymond, Jr., Jonathan M. Shenker, Christopher W. Harnden, and Daniel E. Wagner Recruitment of bonefish, Albula vulpes, around Lee Stocking Island, Bahamas 675 Morse, Wallace W, and Kenneth W Able Distribution and life history of windowpane, Scophthalmus aguosus, off the northeastern United States Fishery Bulletin 93(4). 1995 694 Porch, Clay E. Trajectory-based approaches to estimating velocity and diffusion from tagging data 7 1 0 Ralston, Stephen, and Daniel F. Howard On the development of year-class strength and cohort variability in two northern California rockfishes 721 Sakuma, Keith M., and Thomas E. Laidig Description of larval and pelagic juvenile chilipepper, Sebastes goodei (family Scorpaenidae). with an examination of larval growth 732 Williams, John G., and Gene M. Matthews A review of flow and survival relationships for spring and summer Chinook salmon, Oncorhynchus tshawytscha, from the Snake River Basin Notes 741 Forney, Karin A. A decline in the abundance of harbor porpoise, Phocoena phocoena, in nearshore waters off California, 1986-93 749 Jackson, George D. Seasonal influences on statolith growth in the tropical nearshore loliginid squid Loligo chinensis (Cephalopoda: Loliginidae) off Townsville, North Queensland, Australia 753 Merrick, Richard L, Robin Brown, Donald G. Calkins, and Thomas R. Loughlin A comparison of Steller sea lion, Eumetopias jubatus, pup masses between rookeries with increasing and decreasing populations 759 Sainte-Marie, Bernard, and Chantal Carriere Fertilization of the second clutch of eggs of snow crab, Chionoecetes opilio, from females mated once or twice after their molt to maturity 765 Awards 766 Index AbStfclCt. — A midwater trawl sur- vey was conducted during July 1991, to examine the large-scale distribution patterns of late larval and early juve- nile walleye pollock, Theragra chalco- gramma, and associated fish taxa in the western Gulf of Alaska. Gear compari- sons between the anchovy and Methot trawls were conducted to evaluate which was the more efficient sampler for the size range of T. chalcogramma present during this time of the year. Both gears showed similar densities through the dominant size class offish caught, but the Methot trawl caught significantly more T. chalcogramma in the smallest (mostly larval ) size ranges available. Accordingly, a grid of stations was occupied in which only the Methot trawl was used. Although 53 fish taxa were collected overall in the 61 Methot trawls, the majority (84%) of the larval catch con- sisted of only five taxa: flathead sole, Hippoglossoides elassodon ; walleye pol- lock, T. chalcogramma: arrowtooth flounder, Atheresthes stomias; Pacific cod, Gadus macrocephalus; and uniden- tified sculpins, Icelinus spp. Theragra chalcogramma and G. macrocephalus were the dominant (>99'7r) juveniles collected in the survey. The highest catches of larval (13-25 mm SL) and juvenile (26-52 mm SL) T. chalco- gramma were found inshore along the Alaska Peninsula and near offshore is- land groups. Recurrent Group Analy- sis and Two-way Indicator Species Analysis both showed that T. chalco- gramma tended to be frequently asso- ciated with a large heterogeneous grouping of taxa, including G. macro- cephalus, several pleuronectids, and other winter-spring spawning species. The rankings of the dominant taxa in the Methot trawl survey exhibited a greater coherence to the rankings of adult fishes from bottom trawl surveys in the previous year than did those of an ichthyoplankton survey that used bongo nets a few months earlier than the Methot trawl survey. Summer distribution of early life stages of walleye pollock, Theragra chalcogramma, and associated species in the western Gulf of Alaska* Richard D. Brodeur Morgan S. Busby Matthew T. Wilson Alaska Fisheries Science Center, National Marine Fisheries Service 7600 Sand Point Way NE, Seattle, Washington 981 15-0070 Manuscript accepted 15 June 1995. Fishery Bulletin 93:603-618 (1995). The spatiotemporal distribution of the pelagic early life stages of ma- rine fishes is influenced by a num- ber of biotic and oceanographic pro- cesses. Thus, with sufficient elapsed time since spawning, the distribu- tion of late larvae and early juve- niles of many species shows only a limited relationship to the distribu- tion of spawning adults. The taxa that make up an assemblage of lar- val fishes show a high diversity of sizes, stage durations, morpholo- gies, and behaviors (Moser, 1981; Matarese et al., 1989; Moser and Smith, 1993) that can affect their distribution patterns in a dynamic and fluid environment, as is the situation in most coastal areas. The early larval stages have received the most attention from fisheries oceanographers because of their presumed importance in regulating recruitment variability but also be- cause of the ease of sampling such weakly swimming organisms (Heath, 1992). Recent observations, how- ever, have given rise to the sugges- tion that later larval and early ju- venile stages may be as important as early larval stages in regulating year-class strength (Peterman et al., 1988; Campana et al., 1989; Bailey and Spring, 1992), which has stimulated development of new sampling gear to quantitatively as- sess the abundance of larger ichthyo- plankton and micronekton (Methot, 1986; Munk, 1988; Potter et al., 1990; Dunn et al., 1993). The Fisheries Oceanography Co- ordinated Investigations (FOCI) program is a joint effort by scien- tists at the Alaska Fisheries Science Center (AFSC) and the Pacific Ma- rine Environmental Laboratory (PMEL) to understand the biologi- cal and physical processes which cause variability of recruitment in commercially valuable fish and shellfish stocks in Alaskan waters. The primary goal of the FOCI pro- gram is to understand the effects of the biotic and abiotic environment on the early life stages of walleye pollock, Theragra chalcogramma, in the western Gulf of Alaska (Schu- macher and Kendall, 1991). A sec- ondary objective is to provide quan- titative estimates of population size to predict recruitment strength for fisheries management (Schumacher and Kendall, 1991; Bailey and Spring, 1992). Other than the study of Hinckley et al. (1991) in late Contribution 0216 from the Fisheries Oceanography Coordinated Investigations Program of the National Oceanic and At- mospheric Administration. 603 604 Fishery Bulletin 93(4), 1995 June, no data are available on the distribution and abundance patterns of late larval or early juvenile T. chalcogramma during mid-summer, when they are at a size that makes them vulnerable to plankton gear. Moreover, little is known about the relation- ship of T. chalcogramma distribution to that of the other common ichthyoplankton taxa that are caught with the same type of gear. Our aim in this study was to examine the large-scale distribution patterns of age-0 T. chalcogramma and their associations with other larval and juvenile fishes. We also estimate for the first time the relative abundance of age-0 T. chalcogramma compared with other co-occurring early life history stages of marine fish taxa present during mid-summer on the continental shelf in the western Gulf of Alaska. Miller Freeman from 23 to 31 July 1991 (Dewitt and Clark1). The Methot trawl was selected as the most appropriate sampling gear for this stage of T. chalcogramma life history on the basis of previ- ous gear comparisons (Shima and Bailey, 1994). The 5-m2 rigid frame trawl (2x3 mm oval mesh) is de- signed to sample micronekton that evade smaller plankton nets and that pass through the mesh of larger trawls (Methot, 1986). A grid of stations per- pendicular to the coast along the Alaska Peninsula was occupied (Fig. 1) and 61 successful Methot trawls were completed (39 day and 22 night), with repeat tows at several stations. All tows were made at an average ship speed of 6 km-h"1 and in a double ob- lique pattern to within 10-20 m of the bottom. Tem- perature profiles were taken at each station by us- ing expendable bathythermographs. Methods A FOCI survey of late larval and early juvenile T. chalcogramma was conducted aboard the NOAA ship 1 Dewitt, C, and J. Clark. 1993. Fisheries Oceanography Coor- dinated Investigations: 1991 field operations report. NOAA Data Rep. ERL PMEL-41, 112 p. -57°N yM, + + + + Shumagin Islands ^r; + + + + Sanak Island Gulf of Alaska 166°W 164° ~~ I — 162° - 1 — 160° 56° -55° 54° -53° 158° 156° Figure 1 Grid stations sampled during July 1991 with the Methot trawl and location of study area within the North Pacific Ocean (inset). Brodeur et al.: Summer distribution of early life stages of Theragra chalcogramma 605 Because we were uncertain whether any larger T. chalcogramma were present at the time of sam- pling, we conducted a set of gear comparisons at four different stations to examine whether the Methot trawl was adequately sampling the largest age-0 in- dividuals available. Paired tows (2 pairs during the day and 2 at night) were made with the Methot trawl and an anchovy trawl. The anchovy trawl has a vari- able mouth opening depending on depth and was estimated to range from 110 to 135 m2 for the four tows on the basis of the relationships given by Wil- son et al. (in press). The trawl body contained vari- able-size mesh grading from 15.2 cm (stretched) in the forward section to 3.8 cm in the codend, which contained a 3-mm liner. At each gear comparison sta- tion, oblique tows with each gear type were done in random order down to the same depth. Standard- ized catches of T. chalcogramma in each gear were compared by length categories by using a nested ANOVA, with haul as the nesting factor. The trawl samples were preserved in 5% formalin buffered with marble chips. The samples were later sorted in the laboratory and all the fish were re- moved. Fish were identified by using Hart (1973), Eschmeyer et al. (1983), and Matarese et al. (1989). Standard length (SL) of all fish was measured to the nearest millimeter with a stage micrometer or mea- suring board. Larval and juvenile stages were sepa- rated by using a combination of information on length of transformation and osteology provided by Matarese et al. (1989) and Busby (unpubl. data). Larval and juvenile T. chalcogramma and Pacific cod, Gadus macrocephalus, were separated at 25.0 mm SL by using the criteria of Dunn and Matarese (1987). Raw numbers of larvae and juveniles from each taxon collected were converted to number per unit area or density per volume filtered. Consistent with the results of previous studies on larval and juvenile T. chalcogramma (Hinckley et al., 1991; Shima and Bailey, 1994), we did not find significant density dif- ferences overall between day and night sampling (Mann- Whitney Test, P=0.09); thus, we did not make corrections in our abundance estimates for time of day of sampling. Total abundance of each taxon in the study area was calculated by multiplying the weighted mean catch per 10 m2 for each station by the polygonal area represented by that station (see Richardson [1981] and Kendall and Picquelle [1990] for details). Abundances were calculated separately for both larval and juvenile G. macrocephalus and T. chalcogramma and then summed for the total abundance for each taxon. Classification of the catches was done with analy- ses by using both occurrence and abundance data. Species associations were identified on the basis of co-occurrence of taxa in catches by using Recurrent Group Analysis (Fager, 1957). This analysis places taxa that co-occur into groups based on an affinity level set at 0.4, as previously used for other assem- blage analyses in this region (Kendall and Dunn, 1985; Doyle et al., 1995). Only taxa that occurred in more than 15% of the collections were included in this analysis. A second type of hierarchical classifi- cation was performed on the abundance data to see whether a different technique produced different results in identifying assemblages. Two-way Indica- tor Species Analysis, a polythetic, divisive technique (Gauch, 1982), was used in conjunction with the pro- gram TWINSPAN (Hill, 1979). This analysis starts with all the entities (taxa or stations) belonging to one group and then ordinates them by reciprocal averaging. Each group is progressively divided until it contains no more than the predetermined min- imum number of members, as opposed to an agglo- merative technique, such as cluster analysis, which starts with individual entities and progressively com- bines them. Station groupings were also formed by using TWINSPAN, and these were described in re- lation to the species matrix on the basis of whether a particular taxon had a high or low affinity with that station grouping. To interpret the ecological significance of these sta- tion groupings, we examined environmental and sta- tion variables such as water depth and temperatures from different depth intervals available from expend- able bathythermograph data taken at each station. We also calculated station position variables, such as distance from nearest land (including islands) and alongshore distance from a line perpendicular to the coast just northeast of our first transect of stations (Fig. 1). Differences among the median values for all variables by the different TWINSPAN groupings were tested by using a Kruskal-Wallis test. We compared the abundance estimates from the 1990 AFSC Gulf of Alaska groundfish trawl survey with those determined from the Methot trawl sur- vey and another ichthyoplankton survey conducted a few months earlier than our study. The trawl sur- vey took place from 1 June to 9 September 1990, cov- ered a broader area of the Gulf of Alaska (132- 170°W), and sampled depths ranging from 20 to 530 m (see Stark and Clausen [1995] for additional sam- pling details). For the purposes of this analysis, only abundances from the western Gulf of Alaska strata (506 stations) were summarized. Abundances for each stratum were estimated by dividing the bio- mass of each species caught by its mean weight (given in Stark and Clausen [1995]), and then these were summed across all depths and strata. 606 Fishery Bulletin 93(4). 1995 Ichthyoplankton collections were made at 92 stations off Kodiak Island and the Alaska Peninsula (151- 159°W) from 17 to 25 May 1991 by using a 60-cm bongo with either 333- or 505-um mesh. Processing of these samples and abundance estimates were done as de- scribed for the Methot trawl collections. More complete sampling details are provided by Dewitt and Clark.1 Results Gear comparisons The two gear types did not show significant differ- ences in overall mean standardized catches of age-0 T. chalcogramma for the four paired gear-compari- son hauls, but when the densities were partitioned by size offish, the Methot trawl caught significantly more fish in the smallest size groups, although there were no density differences between the two gears for the size groups >35 mm (Fig. 2). Although it was not possible to examine diel differences in overall age-0 densities for both gear types from only four stations taken in different locations, it appears that the catchability of small T. chalcogramma by the anchovy trawl is relatively poor during the daytime. In all four comparisons, the Methot trawl caught smaller individuals and a broader overall range of age-0 sizes than did the anchovy trawl, but the distributions of lengths were significantly different in only two of the four tows (Fig. 3). The overall average (+SD) length of individuals caught by the Methot net was 34.5 (±7.0) mm, whereas the average length offish caught by the anchovy trawl was 36.3 (±4.5) mm. Taxonomic composition and abundance Altogether, 53 larval and 4 juvenile taxa were iden- tified in the Methot trawl survey (Tables 1 and 2). Several taxa, notably Sebastes spp. and Cyclop- teridae, were probably represented by several as yet unidentifiable species; therefore, the overall taxo- nomic diversity was probably underestimated. The family Cottidae exhibited the greatest diversity, with at least 15 taxa represented (Table 1). Hippoglossoides elassodon, T. chalcogramma, and, to a lesser extent, Atheresthes stomias, G. macro- cephalus, and Icelinus spp., were the dominant taxa collected on the basis of mean density (Table 1). Hippoglossoides elassodon larvae were the most abundant overall and occurred at all but one station. Most of the fish caught were late-stage larvae, but T. chalcogramma and G. macrocephalus were also rep- resented by a large number of juveniles (Table 2). On the basis of total abundance in the study area, H. elassodon, T. chalcogramma, and A. stomias are clearly the most abundant taxa; there is less distinc- tion among the rest of the dominant taxa (Fig. 4). The abundance of H. elassodon (3.24 x 1010 fish) was almost three times that of the next most abundant species T. chalcogramma (larvae and juveniles com- bined: 1.12 x 1010 fish) and represented 53.6% of the estimated total abundance of ichthyoplankton in the survey area (6.04 x 1010 fish). Spatial and length-distribution patterns The geographic and length distributions of the six most abundant larvae and T. chalcogramma and G. macrocephalus juveniles are shown in Figures 5-8. The distribution of T. chalcogramma larvae and that of juveniles were very similar, with centers of abundance near the Semidi and Shumagin Islands (Fig. 5). Gadus macrocephalus juveniles tended to be distributed slightly more offshore and farther west (downcurrent) than were larvae (Fig. 6). Hippogloss- oides elassodon larvae were found in greatest num- bers near the Alaska Peninsula and Shumagin Is- lands, whereas A. stomias larvae were collected over a broad size range and displayed no distinct patterns of distribution (Fig. 7). In contrast, Icelinus spp. lar- vae showed a narrow size distribution and were found in high concentrations northeast of Sanak Island 16 12 E o ° a o 8 ^|= Anchovy I 1= Methot XL Standard Length (mm) Figure 2 Comparison of the standardized catches for the Methot and anchovy trawl by length category in the gear com- parison tows. Brodeur et al.: Summer distribution of early life stages of Theragra chalcogramma 607 Day hauls Night hauls P<0.01 ■ Anchovy D M.lhol P<0.01 o o c 15 20 40 45 I I I I I I I 15 20 35 40 P = 0.12 P = 0.99 JU tlL 15 20 26 30 36 40 45 15 20 25 30 35 40 45 Standard length (mm) Figure 3 Comparison of the length distributions by haul for the Methot and anchovy trawls for the four paired comparisons done at different stations. Also shown are the results of a Kolmogorov-Smirnov test in which the distributions of each gear type were compared. (Fig. 8). Sebastes spp. catches also comprised rela- tively small larvae and were found almost exclusively at offshore stations but were evenly distributed among these stations (Fig. 8). Species associations The Recurrent Group Analysis identified one main grouping of taxa that showed a common affinity level of at least 0.40 (Fig. 9). Curiously, the nine taxa with the highest densities were members of this group- ing, even though the groupings are formed on the basis of common occurrences. Zaprora silenus lar- vae were associated with eight of the nine taxa but showed a low association with Sebastes spp. larvae. The larval and juvenile stages of T. chalcogramma and G. macrocephalus occurred within the same species group- ing and thus were not differentiated in this analysis. The TWINSPAN results were similar to the Re- current Group Analysis in that a large grouping was formed. However, in this instance, Sebastes spp. lar- vae were not closely related to this grouping, but Ammodytes hexapterus larvae were related (Fig. 10). H. elassodon T. chalcogramma A. stomias Icelinus spp. Liparis spp. G. macrocephalus Sebastes spp. P. bi I meal us B. alascanus Lumpenus spp. A. hexapterus P. isolepis Z. silenus Pleuronectes sp. II E. zachlrus 6 7 8 9 10 Log10 number Figure 4 The estimated total abundance in the survey area for the 15 most abundant taxa collected in the Methot trawl sur- vey. Abundances for Theragra chalcogramma, Gadus macrocephalus, and Zaprora silenus include combined to- tals for larval and juvenile stages. 608 Fishery Bulletin 93(4), 1995 Table 1 Summary offish larvae collected in Methot trawls during 1991. Scientific names follow Robins et al. ( 1991 ) with the exception of the family Agonidae which follows Kanayama (1991). Mean Length Percent abundance range Scientific name Common name occurrence (no./lOOOm3) SL(mm) Clupea pallasi Pacific herring 1.64 <0.01 21.8 Mallotus villosus capelin 3.28 0.01 52.0-60.0 Thaleichthys pacificus eulachon 3.28 <0.01 63.0-75.0 Bathylagus pacificus Pacific blacksmelt 1.64 <0.01 19.0 Leuroglossus schmidti northern smoothtongue 8.19 0.01 22.0-34.0 Stenobrachius leucopsarus northern lampfish 1.64 <0.01 10.8 Gadus macrocephalus Pacific cod 34.43 0.15 15.1-22.0 Microgadus proximus Pacific tomcod 1.64 <0.01 17.5-18.5 Theragra chalcogramma walleye pollock 78.69 1.03 13.0-25.0 Gadidae unidentified gadids 18.03 0.04 15.1-22.0 Macrouridae unidentified grenadiers 1.64 <0.01 28.0 Sebastes spp. unidentified rockfishes 49.18 0.30 6.0-18.0 Artedius fenestralis padded sculpin 1.64 <0.01 12.0 Artedius harringtoni scalyhead sculpin 3.28 <0.01 11.1-11.7 Artedius lateralis smoothhead sculpin 1.64 <0.01 10.9 Ruscarius meanyi Puget Sound sculpin 3.28 0.01 12.0-15.1 Clinocottus acuticeps sharpnose sculpin 3.28 0.01 13.0-15.0 Clinocottus embryum calico sculpin 1.64 <0.01 13.0 Dasycottus setiger spinyhead sculpin 6.56 0.01 15.0-21.8 Icelinus borealis northern sculpin 1.64 <0.01 13.5 Icelinus spp. unidentified sculpins 72.13 0.57 10.0-18.0 Malacocottus zonurus darkfin sculpin 1.64 <0.01 10.0 Nautichthys oculofasciatus sailfin sculpin 1.64 <0.01 23.2 Psychrolutes paradoxus tadpole sculpin 3.28 <0.01 15.9-16.3 Psychrolutes sigalutes soft sculpin 4.92 0.01 12.0-17.0 Radulinus asprellus slim sculpin 6.56 0.01 13.0-16.0 Rhamphocottus richardsoni grunt sculpin 6.56 0.02 11.7-14.4 Cottidae unidentified sculpins 3.28 0.01 15.0-18.0 Anoplagonus inermis smooth alligatorfish 1.64 <0.01 19.0 Bathyagonus alascanus gray starsnout 68.85 0.21 10.5-19.0 Bathyagonus infraspinatus spinycheek starsnout 27.87 0.04 12.0-18.0 Bathyagonus spp. unidentified poachers 1.64 <0.01 12.0 Leptagonus frenatus sawback poacher 1.64 <0.01 26.2 Aptocyclus ventricosus smooth lumpsucker 13.11 0.02 8.5-14.0 Liparis spp. unidentified snailfishes 63.93 0.29 9.5-27.0 Careproctus spp. unidentified snailfishes 1.64 0.01 10.7-17.8 Cyclopteridae unidentified snailfishes 1.64 0.01 15.0 Ronquilus jordani northern ronquil 1.64 <0.01 12.5 Lumpenus maculatus daubed shanny 4.92 0.01 44.0-53.0 Lumpenus spp. unidentified pricklebacks 16.39 0.14 37.0-59.0 Cryptocanthodes aleutensis dwarf wrymouth 6.56 0.01 26.2-32.2 Ptilichthys goodei quillfish 4.92 <0.01 91.0-105.0 Zaprora silenus prowfish 26.23 0.05 9.6-30.0 Ammodytes hexapterus Pacific sand lance 22.95 0.10 38.5-57.0 Atheresthes stomias arrowtooth flounder 72.13 0.60 15.0-40.0 Embassichthys bathybius deepsea sole 4.92 0.01 10.2-15.3 Errex zachirus rex sole 26.23 0.06 19.0-39.5 Hippoglossoides elassodon flathead sole 98.36 7.52 12.0-36.0 Hippoglossus stenolepis Pacific halibut 6.56 0.01 20.4-24.0 Platichthys stellatus starry flounder 6.56 0.01 8.1-9.5 Pleuronectes bilineatus rock sole 65.58 0.26 10.0-27.0 Pleuronectes sp. II' unidentified sole 19.67 0.05 7.0-18.0 Pleuronectes isolepis butter sole 13.11 0.06 13.5-19.5 1 See Matarese et al. (1989). Brodeur et al.: Summer distribution of early life stages of Theragra chalcogramma 609 Summary of juvenile Table 2 fish collected in Methot trawls during 1991. Scientific name Common name Percent occurence Mean abundance (no./1000m3) Length range SL (mm) Gadus macrocephalus Theragra chalcogramma Leptagonus frenatus Zaprora silenus Pacific cod walleye pollock sawback poacher prowfish 65.57 88.52 3.28 11.48 0.44 1.42 <0.01 0.02 26.0-43.5 26.0-52.0 30.0-31.0 31.0-71.0 56°.30'N ■ 56°.00' 55°. 30' - 55°.00' 54°.30' 54°00' ■ • r 1 lil iii_, i i i C^z* 0.20 c / ^ • §0.15 o I sp^" • «• 8" o.io a. 0 • 0.05- J • . 5 10 15 20 25 30 35 40 45 50 5 S / /— V . "> -tf • Standard Length (mm) /<■ N0./1000M3 ^ o ' . ■ y ** • • 0-1.0 • *& • 1.0- 2.0 • 2.0 - 3.0 • 3.0 - 4.0 ^a • 4.0 - 5.0 • 5.0 - 6.0 >%,«' • ' ' Theragra chalcogramma larvae # 6.0 - 7.0 % > 7.0 i ■ i ' i i ' I ' l ' l ' I ' I I 1 ■ 1 56°.30'N ■ 56°.00' 55°.30' 55°00' 54°30' 54°.001 Theragra chalcogramma Juveniles NO ./1000M 3 . 0 - 1 0 • 1 .0 - 2 0 • 2.0 - 3 0 • 3.0 - 4 0 • 4.0 - 5 0 • 5.0 - 6 0 • 6.0 - 7 0 • > 7 0 166°W 164° 162° 160° 158° 156° Figure 5 Distribution of larval and juvenile stages of Theragra chalcogramma in the study area. Also shown are the stan- dardized length distributions for each life stage (inset). 610 Fishery Bulletin 93(4). 1995 56°.30'N ■ 56-.00' 55°.30' - 55°.00' • 54°.30' - 54". 00' - 0.25 0.20 | 0,5 o O0.10 £ 0.05 0.00 10 15 20 25 30 35 40 45 50 55 Standard Length (mm) ^* ■V-7 a~* o Gadus macrocephalus larvae NO ./1000M 3 • 0 - 1 0 • 1 .0 - 2 0 • 2.0 - 3 0 • 3.0 - 4 0 • 4.0 - 5 0 • 5.0 - 6 0 • 6.0 - 7 0 • > 7 0 i.i. =*= i -4= — i- = i i i i 56°.30'N ■ 0.12 c=> c / x£w O • S 0.09 o / 3?& '' «• 56°.00' ■ f 0.06 a. . ° 0.03 lllllrnn / ^j^jv^ • • 5 10 15 20 25 30 35 40 45 50 55 / //\i-. Jl / T3 55°.30' - Standard Length (mm) / \ ( /~^ *r~i N0./1O00M3 55°.00' - r^W^O • . 'V \ • 0-1.0 / %~ • ^b • 1.0-2.0 / ^^^ • 2.0 - 3.0 • 3.0 - 4.0 54°30' - V— ^ . ^a • • 4.0 - 5.0 • 5.0 - 6.0 54° 00' - -v-7 o^'p-' m ' ' Gadus macrocephalus juveniles 0 6.0 - 7.0 £ > 7.0 I ' i ' i 1 i ' i ' i ' i ' i ' 1 ' 1 >> 166°W 164° 162° 160° 158° 156° Figure 6 Distribution of larval and juvenile stages of Gadus macrocephalus in the study area. Also shown are the standard- ized length distributions for each life stage (inset). Gadus macrocephalus larvae were differentiated from juveniles on the basis of this analysis. Four station groupings were recognized by TWINSPAN (Fig. 11). An inshore group (group 4) showed a high positive association for G. macro- cephalus, T. chalcogramma, and//, elassodon larvae and a negative association for Sebastes spp. larvae (Table 3). An offshore group (group 3) showed a high affinity for Sebastes spp. and Bathyagonus alascanus larvae and a low affinity for A. hexapterus, H. elassodon, and Icelinus spp. larvae. Many taxa, in- cluding larval and juvenile T. chalcogramma, H. elassodon, A. hexapterus, Lumpenus spp., and A. stomias showed high affinities, whereas Bathyagonus infraspinatus and Sebastes spp. larvae showed low affinities with a widely scattered midshelf grouping (group 2). Finally, a poorly defined grouping (group 1) was positively associated with Sebastes spp. lar- vae and negatively with G. macrocephalus and Z. silenus larvae. Ichthyoplankton densities were rela- Brodeur et al.: Summer distribution of early life stages of Theragra chalcogramma 61 I i.i' ==>= , *r= ■ 1 i / ( /^» n^\J» • • • • ^* • Hlppoglossoides elassodon larvae i 1 ' 1 ' 1 ' l ' 1 ■ 1 i 1 • • «• • • • • 56°.30'N ■ 56°.00' ■ 0.12 |o.09 o £0.06 Q. 0.03 u l 55°.30' ■ 5 10 15 20 25 30 35 40 45 50 5 Standard Length (mm) 55°.00' - 54°30' ■ 54°.0CV ■ NO./1000M3 0 - 5.0 • 5.0 - 10.0 • 10.0 - 15.0 • 15.0 - 20.0 • 20.0 - 25.0 • 25.0 - 30.0 • > 30.0 1 1 ' =T= 1 ' 1 i \ , = =t= i i i i i i i i = i i i i .I 6°.30'N ■ 0.08 c >/ x^w O |o.06 o • «• setoff • O0.04 ^~& K ^^• 0 y. 0.02 mf IIIL • • • 55°.30' - 5 10 15 20 25 30 35 40 45 Standard Length (mm) 50 5 / ( f o3 " • • • • ft JJr^p^o * ■ • x Iks^^ ° ^ fA 4* • • ■ NO./1000M3 55°.0CV - 0-1.0 • 1.0- 2.0 • 2.0 - 3.0 • • 3.0 - 4.0 54°.30' ■ V — y ^a • • 4.0 - 5.0 • 5.0 - 6.0 >^>«: • Atheresthes stomias larvae • 6.0 - 7.0 # > 7.0 54°.00' - 1 ' i j — =t= ■ i ' i ' i ' i ' i i 1 ' 1 '' 166°W 164° 162° 160° 158° 156° Figure 7 Distribution of larvae of Hippoglossoides elassodon and Ath eresthes stomias in the study area. Also shown are the standardized length distributions for each species (inset). tively high in group-2 and group-4 stations and low in group- 1 and group-3 stations (Table 3). Station groups showed little correspondence with the environmental variables examined. Distance from shore was the only variable that showed a clear relationship to the station groups (Table 4). Group 3 (offshore) and group 4 (inshore) were clearly differ- entiated from the remaining two midshelf groups. Although group 4 was the closest to shore, it also showed the greatest average bottom depth. Group 2 exhibited the shallowest mean depth and warmest mean surface temperature of the four station group- ings (Table 4). Among the six variables examined, only distance from shore (P<0.001) and water tem- perature at 50 m depth (P=0.048) showed significant differences among the four groupings. In addition, the group closest to shore (group 4) had the warmest temperatures at 50 m ( 3c=7.1°C) and the one farthest from shore (Group 3) was colder ( x=6.4°C) at 50 m than the intermediate groupings (Fig. 11). 612 Fishery Bulletin 93(4), 1995 56°.30'N se^oo' • 55°.30' ■ 55°.00' ■ 54°.30' 54°.00' 5 10 15 20 25 30 35 40 45 50 55 Standard Langth (mm) -J? tf-=: ^* .<=3 Icelinus spp. larvae NO./IOOOM3 0-1.0 0 - 2.0 0 - 3.0 0 0 0 0 4.0 5.0 6.0 7.0 7.0 SF 166°W 164° 162° 160° 158° iii i • 1 1 ■ 1 I ' I 56°.30'N ■ 56°.00' ■ 0.30 c0.25 O £0.20 o §■0.15 £0.10 0.05- J IL • J' 0 a t 55°.30' 5 10 15 20 25 30 35 40 45 50 5 Standard Langth (mm) • 55°.00' ■ 54°.30' • 54°.00' • ~xj3s?' c-j "" . Sebasfes spp. larvae N0./1000M3 0-1.0 a 1.0- 2.0 • 2.0 - 3.0 • 3.0 - 4.0 • 4.0 - 5.0 • 5.0 - 6.0 a 6.0 - 7.0 a> > 7.0 ■ — 1 i ■ i 1 i ' i ' i ■ i ' i 156° Figure 8 Distribution of larvae of Icelinus spp. and Sebastes spp. in the study area. Also shown are the standardized length distributions for each species (inset). Comparison of abundance rankings with other surveys The abundance rankings of the dominant taxa esti- mated showed some similarities among the three sur- veys (Table 5). The six most abundant taxa in the bottom trawl surveys were represented in the 10 most abundant taxa in both ichthyoplankton surveys, but the coherence was stronger (top three species the same) for the July Methot trawl survey than for the May bongo-net survey. The seventh most abundant species in the trawl survey, Errex zachirus, was ranked 14th in the Methot trawl collections but did not appear in the bongo-net sampling. A comparison of the ranks of only the taxa that were mutually present in samples from each gear type showed that the trawl survey was more similar in ranking to the Methot trawl survey data (Spearman Rank Correla- tion, r - 0.50) than to the bongo-net survey data (r = 0.23). Brodeur et al.: Summer distribution of early life stages of Theragra chalcogramma 613 Ammodytes hexaptervs (14) — Bathyagonus infraspinatus (17) = W- ee Errex zachirus (16) Gadus macrocephalus (42) ■ Theragra chalcogramma (57) • Hippoglossoides elassodon (60) Liparis spp. (39) Atheresthes stomias (44) - Pleuronectes bilineatus (40) • Icetinus spp. (45) Bathyagonus alascanus (42) - Sebastes spp. (30) Lumpanus spp. (10) Zaprora silenus (22) Figure 9 Results of the Recurrent Group Analysis showing the main grouping (within box) and associated taxa (outside box) at an affinity level of 0.40. The numbers in parentheses are the occurrences of each taxon. Discussion Despite the relatively large biomass of adult fishes that inhabit this re- gion, the mid-summer abundance and distribution patterns of ichthyo- plankton have received little atten- tion. The one previous study (Hinck- ley et al., 1991), which used a Methot trawl to sample the western Gulf of Alaska in June and July 1987, exam- ined only the distribution of late lar- val and early juvenile T. chalco- gramma. The highest densities of this species were found east of the Shumagin Islands, a finding that was similar to what we found. The only other surveys conducted during the summer employed net gear with small mouth openings (see Kendall and Dunn [1985] and references therein) and caught mainly eggs and early larvae. Some of the differences in species composition between the most commonly used ichthyoplankton gear (e.g. bongo nets) and that used in this study are likely due to extrusion of smaller larvae through the meshes of the Methot net. For example, one of the numeri- cally dominant taxa collected during June and July in small-mesh bongo-net gear is Bathymaster spp. (Kendall and Dunn, 1985; Rugen2) which did not, however, occur in our Methot trawl collections. Since Bathymaster spp. larvae average only around 10 mm Lumpenus spp. G. macrocephalus (I) Z. silenus Sebastes spp. Liparis spp. B. alascanus E. zachirus T. chalcogramma (l+l) *■ hexapterus G. macrocephalus (j) H. elassodon A. stomias I eel in us spp. P. bilineatus B. infraspinatus Figure 10 Taxa groupings resulting from the Two-way Indicator Species Analysis. The larval (Z) and juvenile (j) stages of Theragra chalcogramma and Gadus macrocephalus are indicated separately. in length in early June (Rugen2), they are probably too small to be caught by the Methot trawl in July. Conversely, some taxa (e.g. T. chalcogramma) that 2 Rugen, W. C. 1990. Spatial and temporal distribution of lar- val fish in the Western Gulf of Alaska, with emphasis on the period of peak abundance of walleye pollock (Theragra chalcogramma) larvae. NWAFC Proc. Rep. 90-01, 162 p. Alaska Fish. Sci. Cent, Natl. Mar. Fish. Serv., NOAA, 7600 Sand Point Way NE, Seattle, WA 98115-0070. 614 Fishery Bulletin 93(4), 1995 Table 3 Two-way table of dominant taxa showing the station and species groups as determined by TWINSPAN. Numbers in parentheses represent the number of stations in each sta- tion group. The numbers within the matrix correspond to the mean density (no./lOOO m3) of that taxon for each sta- tion grouping ( — = taxon not present). Life stages of T. chalcogramma and G. macrocephalus are designated af- ter species name (l=larvae, j=juvenile). The total ichthyoplankton for each station group represents all spe- cies including the rare taxa not included in the TWINSPAN analysis. Station group Taxon 1 (13) 2 (6) 3 (22) 4 (19) Lumpenus spp. G. macrocephalus (1) A. hexapterus 0.02 1.05 0.02 0.02 0.08 0.66 0.09 0.38 0.05 H. elassodon 5.02 13.10 2.11 14.15 T. chalcogramma (1) 0.36 1.96 0.28 2.53 G. macrocephalus (j) 0.44 0.53 0.36 0.71 Icelinus spp. 0.70 1.88 0.28 0.44 P. bilineatus 0.34 0.24 0.10 0.40 A. stomias 0.44 2.18 0.44 0.45 T. chalcogramma (j) 0.63 6.33 0.70 1.35 B. infraspinatus 0.06 — 0.03 0.05 Z. silenus — 0.10 0.30 0.08 B. alascanus 0.19 0.15 0.31 0.15 Liparis spp. 0.30 0.42 0.36 0.16 E. zachirus 0.10 0.12 0.02 0.04 Sebastes spp. 0.47 0.21 1.04 0.08 Total ichthyoplankton Mean 9.16 29.74 5.52 21.11 Standard deviation 3.63 5.19 2.84 8.12 spawn during spring are poorly sampled as late lar- vae and early juveniles by bongo-net gear in sum- mer (Shima and Bailey, 1994). Another study that examined the distribution of late larvae and early juveniles in our study area used neuston sampling gear, which tends to capture signifi- cantly larger specimens than do bongo nets (Doyle et al., 1995). These collections, however, were made mostly before June, and the taxonomic composition of the catch was markedly different from that of the present study in that only 3 of the 15 most abundant larvae (A. hexapterus, T. chalcogramma, and Mallotus villosus) caught in the neuston nets occurred in our samples. One motivation for conducting ichthyoplankton surveys is to provide an alternative estimate to trawl surveys for the abundance of commercially exploit- able fishes (Heath, 1992). Although there are biases involved with both ichthyoplankton and trawl sur- veys that may result in an incomplete picture of true fish population sizes, it is of interest to compare the results of these two assessment methodologies for the stocks in the western Gulf of Alaska (Kendall and Dunn, 1985). Trawl surveys tend to exclude small and cryptic taxa, particularly those that inhabit untrawlable bottom types. Diel differences in verti- cal distribution and aggregation patterns may also influence trawl survey abundance estimates. Ichthyo- plankton surveys are restricted to sampling only the life stages that are pelagic at the time of the survey, therefore they are strongly dependent on the timing of spawning and the mode of development. Moreover, extrapolation of catches to population abundance requires additional information on basic life history strategies (e.g. hatch size, pelagic/demersal eggs, num- ber of spawning events, oviparity/viviparity), spawn- ing locations, population egg production, and mortal- ity rates. Differences in life history patterns may explain some of the disparities observed between the trawl and ichthyoplankton rankings. Two abundant trawl species, Pleuronectes asper and Microstomous pacificus, spawn in late spring and early summer off Alaska (Hirschberger and Smith, 1983; Matarese et Table 4 Mean values of station and environmental variables for the four TWINSPAN station groups. Numbers in paren- theses below each station group represent the number of stations in each group. Standard deviations are given in parentheses below each mean. Mean variables Station group l (13) 2 3 (6) (22) 4 (19) Surface temperature (°C) 12.80 (0.68) 13.06 12.83 (1.10) (1.41) 12.73 (0.83) 50-m temperature (°C) 6.89 (1.01) 6.99 6.44 (0.95) (1.19) 7.06 (0.54) 100-m or bottom temperature (°C) 6.22 (0.83) 6.42 6.05 (0.75) (1.07) 6.38 (0.55) Bottom depth (m) 103.5 (24.8) 87.0 116.4 (39.9) (54.9) 137.9 (48.3) Distance from shore (km) 28.8 (17.8) 25.9 54.4 (19.7) (33.6) 13.9 (9.7) Distance alongshore (km) 233.4 (205.2) 263.6 282.8 (127.2) (223.4) 224.3 (103.1) Brodeur et al.: Summer distribution of early life stages of Theragra chalcogramma 615 Gulf of Alaska 1 1 r 166°W 164° 162° "1 1 160° TWINSPAN Groups A -1 ♦ -2 • -3 ■ -4 I 158° I 156° 57°N 56° 55° 54° 53° Figure 1 1 Station groupings from Two-way Indicator Species Analysis displayed on a map of the study area. See Table 3 for the dominant species comprising each station group- ing. Also shown are the isotherms at 50 m measured at the time of sampling. al., 1989) and are not usually repre- sented as larvae in Gulf of Alaska ichthyoplankton sampling (Kendall and Dunn, 1985; Rugen2). Rex sole, Errex zachirus, spawn in the south- ern part of their range and are also rarely found in ichthyoplankton col- lections in the area. The other domi- nant trawl species, Clupea pallasi, spawns demersally in shallow water, and the early life stages are gener- ally restricted to nearshore environ- ments. Conversely, several taxa that are abundant in the ichthyoplankton samples are not well represented in the trawl sampling. These include fish of small maximum size (e.g. A. hexapterus, Icelinus spp., Liparis spp.), nearshore distribution (e.g. B. alascanus, Z. silenus, Lumpenus spp.) (Hart, 1973), or mesopelagic species that are found primarily off- shore, but whose larvae are advected onshore (e.g. Stenobrachius leucopsarus Despite the limitations involved with ichthyoplankton abundance surveys wi Table 5 The top 10 most abundant taxa in the western Gulf of Alaska based on re- search trawl surveys during the summer of 1990 and on ichthyoplankton sur- veys during May and July of 1991. Rank Trawl survey Bongo-net survey Methot survey 1 A. stomias T. chalcogramma H. elassodon 2 T. chalcogramma A. hexapterus T. chalcogramma 3 H. elassodon Bathymaster spp. A. stomias 4 Sebastes spp.' A. stomias G. macrocephalus 5 P. bilineatus H. elassodon Icelinus spp. 6 G. macrocephalus Sebastes spp. Sebastes spp. 7 E. zachirus S. leucopsarus P. bilineatus2 8 P. asper G. macrocephalus Liparis spp. 9 C. pallasi P. bilineatus2 B. alascanus 10 M. pacificus Icelinus spp. Lumpenus spp. ' Because larvae of Sebastes are presently not identifiable to species, all adult rockfishes from the trawl survey were combined into this category. 2 Includes larvae of Pleuronectes sp. II which are morphologically similar to P. bilineatus. Adults were not distinguished in the trawl survey. ). gear type (Suthers and Frank, 1989), our sampling conducting with a relatively small number of Methot trawls dur- th only one ing mid-summer of 1991 provided abundance 616 Fishery Bulletin 93(4), 1995 rankings that were quite similar to the groundfish abundance rankings estimated during 1990 and were much more similar than those estimated from larval collections only two months earlier in 1991. Addi- tional collections taken earlier in 1991 (late April and early May) showed even less coherence with the adult groundfish community (Brodeur, unpubl. data). Ap- parently, many of the smaller species not vulnerable to the survey trawls leave the plankton and settle to rocky habitats or in nearshore areas during the sum- mer, leaving many of the numerically dominant gadids and pleuronectids to be sampled. We chose to correlate the rankings rather than the actual abun- dance of species among the surveys because small differences in timing of spawning relative to the tim- ing of the survey can have drastic effects on abun- dance owing to mortality and changes in catchability. For example, on the basis of the Methot trawl catches, H. elassodon appear to be much more abundant than T. chalcogramma in our survey area. This may be due to the fact that they hatch out about one month later than pollock (Rugen2) and thus have undergone substantially less larval mortality. Subsequent stud- ies have also indicated that the 1991 year class of T. chalcogramma had very high larval mortality owing to either poor feeding conditions or to advection off the shelf (Bailey et al., 1995), resulting in very low recruitment that year (Bailey et al.3). The similarity in the species groupings found with the two methods (Recurrent Group Analysis and TWINSPAN), each of which uses different resolutions of the same data (presence/absence vs. abundance), substantiates the conclusion that certain taxa tend to be associated in our study area. Whether these groupings result from behavioral aggregation by cer- tain species that have been adapted to a particular habitat (Frank and Leggett, 1983) or whether hy- drographic conditions passively transport larvae spawned in the same area to the same nursery area (Richardson et al., 1980; Olivar, 1987; Sabates and Maso, 1990), or some combination of both (Cowen et al., 1993), cannot be determined from our data. How- ever, many of the specimens collected in the Methot net may no longer be considered passive organisms because they can actively swim against currents while seeking out or remaining within favorable habi- tats. Because juvenile fishes respond not only to en- vironmental conditions but also readily respond to the presence of conspecifics and potential predators (Olla et al., in press), several factors can influence their distribution patterns in natural conditions. The lack of clearly defined boundaries between the station groups that we observed may be characteris- tic of this dynamic environment. In our study area, vigorous mixing and strong currents (Reed and Schumacher, 1986) do not allow formation of well- defined mesoscale physical boundaries (see also Doyle et al., 1995). However, the mid-summer ichthyo- plankton community appears to reflect a large-scale onshore to offshore gradient of environmental charac- teristics that include midwater temperatures. The ultimate usefulness of age-0 surveys for pre- dicting year-class strength depends upon the rela- tive mortality pressure occurring after the survey period. Although managers seek information on the relative strength of a year class as early as possible, the accuracy and precision of the index may be low for this life history stage for species that suffer vari- able late juvenile predation losses. For T. chalco- gramma, substantial predation upon juveniles may occur in late summer (Livingston4), which may af- fect the magnitude of subsequent recruitment dur- ing some, if not all, years. A distinct advantage for early or mid-summer surveys of juveniles is that fish at this stage have not developed complicated diel vertical and inshore migrations or complex aggrega- tion and schooling patterns that generally make later stage assessment so difficult (Koeller et al., 1986; God0 et al., 1991; Lough and Potter, 1993; Wilson et al., in press). Determining whether year-class strength for this population is set by mid-summer will require more years of abundance estimates, as well as sampling for several other life history stages in months both before and after the period surveyed in this study (Bailey and Spring, 1992; Bailey et al.3). Acknowledgments We extend our appreciation to Sarah Hinckley for designing the study and for serving as Chief Scien- tist on the cruise. We thank Jay Clark and Bill Rugen for technical assistance in data analysis, Kathy Mier for statistical assistance, Leslie Lawrence for pro- cessing the temperature data, and Art Kendall, Kevin Bailey, Ann Matarese, Geoff Moser, Bill Rugen, and two anonymous reviewers for comments on earlier drafts of the manuscript. 3 Bailey, K. M., R. D. Brodeur, and A. B. Hollowed. Cohort sur- vival patterns of walleye pollock, Theragra chalcogramma, in Shelikof Strait, Alaska: a critical factor analysis. Submitted to Fisheries Oceanography. 4 Livingston, P. A. 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Abstract. — We examined 1,469 tarpon, Megalops atlanticus, ranging from 102 to 2,045 mm fork length (FL) collected in South Florida waters from 1988 to 1993. Females had a mean length of 1,677 mm FL (n=322) and were significantly larger than males, which had a mean length of 1,447 mm FL (n=125). Ages of 977 tarpon were estimated from thin-sectioned otoliths (sagittae). Eighteen tarpon were marked with oxytetracycline (OTC) to form a reference point on the otolith and were held in captivity for periods ranging from 13 to 50 months. Exami- nation of OTC-marked otoliths sug- gested that a single annulus was formed each year. Marginal increments of young of the year and 1-year-old tar- pon showed a single annual minimum during April-June. Tarpon are long- lived and reach a maximum age of at least 55 years. Growth of the tarpon in our study was rapid until an age of about 12 years and then slowed consid- erably. Male tarpon (rc = 141) ranged from 0 to 43 years in age, and female tarpon (rc=298) ranged from 0 to 55 years in age. The von Bertalanffy growth equation for females was FL = 1,818( l _e<-o-io3iA*M-i.4io») and for males was FL = 1,567(1 -e'-01231^"157511). Es- timates of the von Bertalanffy growth parameters L_ and K for males and fe- males were significantly different. Pre- dicted lengths of females were greater than those of males for all ages greater than 4 years. Age and growth of tarpon, Megalops atlanticus, from South Florida waters* Roy E. Crabtree Florida Marine Research Institute, Department of Environmental Protection 100 Eighth Avenue SE, St. Petersburg, Florida 33701-5095 Edward C. Cyr Office of Protected Resources, National Marine Fisheries Service 1335 East-West Highway, Silver Spring, Maryland 20910 John M. Dean Institute of Public Affairs, University of South Carolina Columbia, South Carolina 29208 Manuscript accepted 24 April 1995. Fishery Bulletin 93:619-628 (1995). Tarpon, Megalops atlanticus, are large, migratory, elopomorphic fish that frequent coastal and inshore waters of the tropical and subtropi- cal Atlantic Ocean. In the western Atlantic, tarpon regularly occur from Virginia's eastern shore to Central Brazil and throughout the Caribbean Sea and the Gulf of Mexico (Wade, 1962; Hildebrand, 1963; de Menezes and Paiva, 1966; Zale and Merrifield, 1989). In South Florida and parts of Central America, tarpon are the basis of economically important recreational fisheries. In Florida, the fishery is intensely regulated, and anglers are required to purchase a permit before harvest- ing a fish. Since the establishment of the permit system in 1989, the harvest of tarpon in Florida has declined to less than 100 fish per year, and the fishery is now mostly catch-and-release. Tarpon occur in a variety of habitats ranging from freshwater lakes and rivers to off- shore marine waters, but large tar- pon targeted by Florida's fishery are most abundant in estuarine and coastal waters. In Florida, the fish- ery is seasonal; most tarpon are caught during May^July, although some fish are caught in all months. Tarpon life history has not been adequately described. Breder ( 1944) examined gonads of tarpon from Florida waters but did not fully de- scribe either temporal spawning patterns or age and size at sexual maturity. De Menezes and Paiva (1966) macroscopically examined gonads of tarpon from Brazilian waters and reported on temporal spawning patterns and size at sexual maturity. Most information on tarpon reproduction in Florida waters has been inferred from early life history studies (Smith, 1980; Crabtree et al., 1992; Crabtree, 1995). Larval distribution patterns suggest that tarpon in Florida wa- ters spawn offshore from May through August (Smith, 1980; Crab- * Contribution 1054 of the Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, SC. 619 620 Fishery Bulletin 93(4). 1995 tree et al., 1992; Crabtree, 1995). Smith (1980) esti- mated the length of the larval phase to be 2-3 months, but little is known about the processes that transport larvae from offshore spawning grounds to inshore juvenile habitat. Metamorphic larvae are typically found inshore in mangrove-lined estuaries but also occur in temperate Spartina marshes (Har- rington, 1958 and 1966; Erdman, 1960; Wade, 1962; Mercado and Ciardelli, 1972; Tucker and Hodson, 1976; Chacon et al., 1992). Young-of-the-year (YOY) tarpon occur in small stagnant pools and sloughs of various salinities and have been reported from North Carolina (Hildebrand, 1934), Georgia (Rickards, 1968), Florida (Wade, 1962 and 1969), Texas (Simpson, 1954; Marwitz, 1986), Caribbean islands (Beebe, 1927; Breder, 1933), and Central America (Chacon et al., 1992). Age and growth of tarpon are poorly documented. Previous age estimates based on the examination of scales suggest a maximum life span of about 15 years (Breder, 1944; de Menezes and Paiva, 1966). Studies on a variety of species show that scales are not reli- able for ageing long-lived fishes and that scale-de- rived age estimates are typically lower than esti- mates derived from sectioned otoliths (Beamish and McFarlane, 1983; Casselman, 1983). Ageing of tar- pon based on sectioned otoliths is needed to evalu- ate the accuracy of the ages estimated by Breder (1944) and de Menezes and Paiva (1966). In this ar- ticle, we describe age and growth of tarpon from South Florida waters on the basis of an examination of sectioned otoliths. Methods We obtained tarpon from a variety of sources through- out South Florida from April 1988 to November 1993. Most large fish (>1,100 mm FL) were obtained from taxidermists in Fort Myers and Fort Lauderdale; the fish had been caught in either the Florida Keys or Boca Grande Pass on Florida's Gulf coast (26°43'N, 82°16'W). A second source of large fish was tourna- ments held in the Keys, Boca Grande Pass, and the Tampa Bay area (27°40'N, 82°35'W). All large tar- pon were caught with hook-and-line gear. Small tar- pon (<1,100 mm FL) were taken with cast nets, hook- and-line gear, electroshockers, trammel nets, and gill nets at various locations in South Florida. Young-of- the-year tarpon were caught most effectively with cast nets of various mesh sizes and ranging in ra- dius from 2.1 to 3.1 m. We sampled YOY tarpon monthly from November 1988 to April 1991 at two sites in South Florida. On the Atlantic coast, we sampled Jack Island State Park (27°30'N, 80°18'W), a 159.5-ha, impounded saltmarsh immediately ad- jacent to the Indian River Lagoon. The site consisted of a series of ditches that surrounded brackish wet- lands and that were connected by flood gates to the Indian River Lagoon. The second site was located on the Gulf coast approximately 1.6 km south of U.S. Highway 41 and 3.2 km east of Collier-Seminole State Park near Naples (25°58'N, 81°33'W). This site con- sisted of a series of mangrove-lined ponds and bor- row ditches resulting from road construction in the salt marsh. Standard length (SL), fork length (FL), and total length (TL) were measured to the nearest millime- ter (mm). All lengths reported are fork lengths. Large tarpon (>1,100 mm) were weighed to the nearest 0.5 kg, and smaller tarpon were weighed to the nearest gram. Otoliths (sagittae) were removed, cleaned with bleach (5.25% sodium hypochlorite), and rinsed first in water and then in 95% ethanol. Otoliths were stored dry or in 95% ethanol until sectioned. Sex was recorded and confirmed histologically. Undamaged otoliths were weighed to the nearest 0.01 mg. Weights of left and right otoliths were not significantly different (paired <-test, n-270, £=0.039, P=0.97); therefore, otolith weights were pooled for analysis. If both left and right otolith weights were available for an individual fish, the mean of the two weights was calculated. Linear regressions were fit to log10-transformed otolith weight and age data and were compared with a £-test (Zar, 1984). Generally, the left sagitta was used for age esti- mation; however, if the left otolith was broken, lost, or destroyed during processing, the right otolith was substituted. We prepared otoliths for age estimation by embedding them in Spurr (Secor et al., 1992), a high-density plastic medium. A 1-2 mm thick trans- verse section containing the otolith core was cut with a Beuhler Isomet low-speed saw with a diamond blade. The section was mounted on a microscope slide with thermoplastic glue (CrystalBond 509 adhesive) and polished with wet and dry sandpaper (grit sizes ranging from 220 to 2,000) until the annuli were vis- ible. Sections were then polished on a Beuhler pol- ishing cloth with 0.05-(i gamma alumina powder to remove scratches. Annuli were counted three times by each of two independent readers using compound microscopes. Mean counts of each reader were not significantly different (paired /-test, n=l,099, £=1.30, P=0.193); therefore, all six counts were used to cal- culate a mean age. All counts and measurements were made along the ventral sulcal ridge (Fig. 1A); the dor- sal ridge was used only as an aid to interpretation. Measurements were made with an ocular micrometer. Tarpon otoliths were often difficult to interpret; therefore, we established the following criteria to Crabtree et al.: Age and growth of Megalops atlanticus 621 Figure 1 Transverse sections of tarpon, Megalops atlanticus, otoliths. (A) Section from a 25- year-old tarpon ( 1,727 mm FL) showing the annuli counted for age estimation. Scale bar = 500 u. (B) Section from a 2-year-old tarpon (506 mm FL) showing the notch formed on the edge of the sulcal ridge. Scale bar = 500 u. (C) Section from a 33-year- old tarpon ( 1.615 mm FL) showing confluent annuli that were interpreted as a single annual mark. Marks 2a and 2b were counted as a single annulus. Scale bar = 50 u. 622 Fishery Bulletin 93(4), 1995 provide a consistent basis for determining whether an annulus should be counted as an annual mark. For the 4-5 annual marks closest to the core, a notch was usually present on the ventral edge of the sulcal ridge (Fig. IB). The notch was typically accompanied by an annulus extending outward to the otolith's ventral margin. If a distinct notch was present, the annulus was counted even if the mark extending outward was indistinct. Confluent annuli were counted as a single annual mark unless the two an- nuli were confluent for only a short distance (Fig. 1C). If many confluent marks were present, the otolith was rejected as unreadable. Annulus counts for individual otoliths often showed some level of variation among readings. We estab- lished criteria for accepting or rejecting individual otoliths by calculating a coefficient of variation (CV) = (S/yx 100%), where S = the standard error of counts for a given otolith, and y~ = the mean annu- lus count for a given otolith. CV precision criteria were calculated as CV = ^J(nxd2)/t2 , where n=the number of readings for a given otolith (6), c?=the de- viation allowed between the estimated mean incre- ment count and the true count for a given otolith, and t-a one-tailed Student's ^-statistic with a =0.05 and re-1 degrees of freedom. We allowed a maximum deviation (d) of 10%, which corresponds to a CV of 12.16%. After six readings were completed, otoliths for which there were significant disagreements among readings (CV>12.16%) were again examined by both readers in an attempt to reconcile differences. After discussing possible explanations for the vari- ability among readings, a decision was made regard- ing the readability of the otolith. If both readers judged the otolith to be readable, it was again read independently by each reader without knowledge of the previous readings. The reading showing the larg- est difference from the mean of all readings was then discarded and replaced by a new reading. This pro- tocol was repeated twice, and if the CV remained >12.16%, the otolith was rejected. Tarpon typically spawn during May-August (Crabtree et al., 1992; Crabtree, 1995), and annulus formation took place during January-May. Conse- quently, annulus counts were not always equivalent to age in years. To resolve this discrepancy, fish col- lected before 1 July (the approximate middle of the spawning season) that had recently formed an an- nulus during the winter or spring (determined on the basis of the proximity of the annulus to the otolith's margin) were assigned an age one less than the annulus count. Fish collected after 1 July were assigned an age equal to the annulus count. The von Bertalanffy (1957) growth equation FLt =LJl-e{~Kl'-to>)) was fit to observed age-length data with the nonlinear regression procedure of Statgraphics. Likelihood-ratio tests were used to compare parameter estimates (Kimura, 1980; Cerrato, 1990). Length-weight regressions were cal- culated by linear regression of log10-transformed data and were compared with a £-test (Zar, 1984). Tarpon were captured from the Sebastian River, located on Florida's Atlantic coast, by electroshocking or with trammel nets for age-validation experiments (Table 1). After capture, fish were sedated with MS- 222, measured for fork length, and tagged with dart- type tags. After tagging, tarpon were injected with Liquamycin LA-200 (200-mg oxytetracycline [OTC]/ mL) in the dorsal musculature at a dosage of 100- mg OTC per kg fish weight. Fish weight was esti- mated with a length-weight equation. Tarpon were then transported to one of three holding facilities located in Florida, where they were held for 13 to 50 months (Table 1). Two fish were held in a 25-m by 13-m by 2.7-m deep public aquarium at Mote Ma- rine Laboratory in Sarasota, six were held in a 33.5- m by 5.5-m by 0.75-m deep pond at the Keys Marine Laboratory in Long Key, and 10 were held in a 9.1-m diameter by 2.0-m deep tank at the Florida Marine Research Institute's Stock Enhancement Research Facility (SERF) at Port Manatee. Fish were held at ambient temperatures in all facilities except in SERF, where heaters were used during the winter to pre- vent temperatures from dropping below 14°C. Tar- pon were fed as much frozen fish as they would con- sume at least three times a week. Otolith sections were examined with a compound microscope (40- lOOx) equipped with ultraviolet light so that the fluo- rescent OTC marks could be detected. Results The 1,469 tarpon we examined ranged from 102 to 2,045 mm in length; 740 (50.4%) of these were YOY or 1-year-old fish (<400 mm). Of these 740 small fish, we examined 179 histologically but could sex only 11 (6.1%); consequently, the sex of most YOY and 1-year- old tarpon was unknown and they were excluded from sex-specific regressions. Neither slopes U-test, df=602, £=0.039, P=0.484) nor elevations (t-test, df=603, £=0.205, P=0.419) of the length-weight equa- tions for male and female tarpon were significantly different. The pooled length-weight equation for sexed and unsexed fish and the relationships between SL, FL, and TL are presented in Table 2. Female tarpon attained larger sizes than did males. Among the fish that we sexed, females ranged from 331 to 2,045 mm in length (median=l,635 mm, upper quartile= 1,752 mm, n=412) and were signifi- Crabtree et al. : Age and growth of Megalops atlanttcus 623 Table 1 Data for oxytetracycline (OTC (-injected tarpon, Megalops atlanticus. Otolith measurements were made along the ventral sulcal ridge from the otolith core to the OTC mark, annuli, and the otolith's edge. Measurements were made to the annulus at or just before the OTC mark and all subsequent annuli. Holding facilities are MOTE = Mote Marine Laboratory, KML = Keys Marine Laboratory, and SERF = Florida Marine Research Institute's Stock Enhancement and Research Facility. Specimen number Holding facility Injected Sacrificed Months held Age (years) Distance from core (mm) Date Fork length (mm Date Fork ength (mm) OTC mark Annulus Annulus Annulus Annulus Annulus Otolith edge 1137 MOTE March 89 580 Oct 90 675 20 ? 1.61 1.60 1.84 1138 MOTE March 89 518 Oct 90 686 20 4 1.59 1.60 1.69 1.78 1486 KML March 90 640 Sep 92 791 32 5 1.51 1.50 1.57 1.65 1.71 1487 KML March 90 663 Sep 92 762 32 7 2.06 2.06 2.16 2.29 2.35 1488 KML March 90 Sep 92 749 32 6 2.06 2.07 2.16 2.39 2.45 1489 KML March 90 617 Sep 92 785 32 6 1.53 1.53 1.67 1.75 1.82 1490 KML March 90 548 Sep 92 727 32 4 1.33 1.32 1.41 1.49 1.61 1568 KML March 90 May 94 802 50 9 1.84 1.84 1.88 1.94 2.00 2.04 2.04 1548 SERF Sep 92 570 Oct 93 762 13 ? 1.67 1.80 1549 SERF Sep 92 Oct 93 859 13 ? 1.94 1.96 1559 SERF Sep 92 890 May 94 1,005 21 •> 2.25 2.25 2.35 2.37 1560 SERF Sep 92 670 May 94 805 21 7 1.84 1.81 1.86 1.98 1.98 1561 SERF Sep 92 May 94 790 21 5 1.65 1.63 1.67 1.80 1.86 1562 SERF Sep 92 750 May 94 900 21 8 2.04 2.04 2.16 2.24 2.25 1563 SERF Sep 92 670 May 94 900 21 6 1.84 1.81 1.88 1.99 2.00 1564 SERF Sep 92 May 94 805 21 4 1.53 1.44 1.55 1.76 1.78 1565 SERF Sep 92 615 May 94 850 21 9 1.51 1.76 1566 SERF Sep 92 760 May 94 950 21 1 1.80 1.82 1.86 cantly larger than males, which ranged from 203 to 1,884 mm in length (median=l,346 mm, upper quartile = 1,467 mm, rc=203; Mann-Whitney [/-test, P<0.001). The recreational harvest of tarpon in Florida consisted principally of large fish. Among the fish sampled from the recreational fishery, females ranged from 1,193 to 2,040 mm in length (mean = 1,677 mm, SD=141.5, n=322) and were significantly larger than males, which ranged from 901 to 1,884 mm in length (mean=l,447 mm, SD=130.2, rc = 125; f-test, £=15.77, P<0.001). We examined OTC-marked otoliths from 18 tar- pon (Table 1). Individuals showed increases in length ranging from 95 mm in 20 months to 235 mm in 21 months. Otoliths from 12 fish ranging in age from 4 to 9 years showed the expected pattern of otolith growth; one annulus had been formed per year. One tarpon (specimen number 1549) showed little otolith growth and formed no visible annuli while in captiv- ity. Two tarpon (specimen numbers 1559 and 1566) that were sacrificed in May, 21 months after OTC injection, had lower annulus counts than expected. Otoliths from these two fish showed little growth distally to the annulus during their first winter or spring in captivity. Otoliths from three other tarpon (specimen numbers 1137, 1548, and 1565) were prob- lematic, and we were unable to estimate their ages. Annuli on these otoliths were indistinct, and we would have judged these otoliths to be unreadable had they come from wild fish. Five of the six fish whose otoliths were problematic were held in the heated facility at SERF and the other one was held at Mote Marine Laboratory. Otoliths from all six tarpon held in the flow-through facility at Keys Marine Labo- ratory had the expected pattern of one annulus per year. Marginal-increment analysis of otoliths from YOY and 1-year-old tarpon suggested that one annulus formed each year. Young-of-the-year tarpon formed an annual mark sometime between December and May, and all YOY and 1-year-old tarpon otoliths had formed a first annulus by June (Fig. 2A). Mean mar- ginal increments showed a seasonal minimum dur- ing April-June and a maximum in November (Fig. 2B). Marginal-increment analysis of older tarpon was not possible because of the incomplete seasonal cov- erage and limited sample sizes. 624 Fishery Bulletin 93(4), 1995 Table 2 Length-length, length-weight, and otolith weight-age re- gressions for tarpon, Megalops atlanticus, from South Florida waters. TL = total length (mm), FL = fork length (mm), SL = standard length (mm), WT = weight (kg), OWT = otolith weight (g), and AGE= age in years. Sample fork- length range for all length-length regressions was 106- 2,045 mm and for length-weight regressions was 102-2,045 mm; age range for the otolith weight-age regressions was 1-55 years for females and 1-43 years for males. Values in parentheses are standard errors. y=a+hX FL SL 1,342 10.8404 (0.6339) 1.0423 (0.0007) FL TL 1,061 -10.8096 (0.8084) 0.8967 (0.0007) SL FL 1,342 -9.9770 (0.6131) 0.9588 (0.0007) SL TL 1,051 -21.1779 (1.0181) 0.8606 (0.0009) TL FL 1,061 12.6345 (0.8937) 1.114 (0.0009) TL SL 1,051 25.5839 (1.1622) 1.1607 (0.0012) log10WT log10FL 1,262 -7.9156 (0.0124) 2.9838 (0.0045) log10OWT (females) log10AGE 193 -1.2083 (0.0199) 0.5476 (0.0152) log10OWT (males) log10AGE 106 -1.1734 (0.0183) 0.4614 (0.0162) 0.999 0.999 0.999 0.999 0.999 0.999 0.997 0.872 0.886 Of 1,231 otoliths processed for age estimation, 138 (11.2%) were judged unreadable by one or both read- ers and were not assigned ages, and an additional 116 (9.4%) otoliths were rejected for having high variation among readings (CV>12.16%); thus 977 (79.4%) otoliths were accepted for age estimates. Of these 977 otoliths, 470 (48.1%) were from YOY tar- pon. The length-frequency distribution offish whose otoliths were rejected because they were unsuitable for age estimation was not significantly different from that of all fish whose otoliths were examined (X2=12.4, df=19,P=0.86). Tarpon are long-lived; the oldest fish examined was a 2,045-mm female estimated to be 55 years old. The oldest male was 43 years old and had a length of 1,710 mm. Tarpon growth was rapid until an age of about 12 years, after which growth slowed consider- ably (Fig. 3). Likelihood-ratio tests showed a signifi- Month Figure 2 (A) Percentage (by month) of otoliths from young-of-the- year and 1-year-old tarpon, Megalops atlanticus, that had formed a first annulus. (B) Monthly mean marginal incre- ment width and standard deviation for otoliths from young- of-the-year and 1-year-old tarpon. Table 3 Parameter estimates for the von Bertalanffy growth model for tarpon, Megalops atlanticus, collected in Florida. Val- ues in parentheses are standard errors. Sex n LJ mm) K to r2 Males 141 1,566.6 (23.65) 0.123 (0.0090) -1.575 (0.2519) 0.933 Females 298 1,817.7 (16.14) 0.103 (0.0049) -1.410 (0.2158) 0.930 cant difference in the overall von Bertalanffy growth models for males and females (%2=122.70, df=3, P<0.001, Table 3). Estimates of L^ (x2=51.31, df=l, P<0.001) and#(5c2=4.48, df=l,P=o7o36) also differed between the sexes, while to was not significantly dif- ferent (x2=0.28, df=l, P=0.58). Lengths at age pre- dicted by the von Bertalanffy equation agreed with the average observed lengths of both female and male tarpon (Fig. 3). Predicted lengths at age of females were greater than those of males for all ages greater than 4 years (Table 4). Crabtree et al.: Age and growth of Megalops atlanticus 625 Estimated age (years) Figure 3 Average observed lengths (± two standard deviations) and predicted lengths from the von Bertalanffy growth model for male and female tarpon, Megalops atlanticus. 0.5 Males ^___ '. 0.4 n-104 . ^ ■ 0.3 ■ e&^^ '■ 0.2 .■V^- 3 0.1 ■ x :- weight a, s i i - ' -C Females "o O o-6 n-192 0.4 ; ^J^^^f \ 0.2 ■;yy "' : 0 ■ ^ : 0 10 20 30 40 50 60 Estimated age (years) Figure 4 Growth of otoliths (g) of male and female tarpon, Megalops atlanticus. The equation for the regression of log10-trans- formed data is presented in Table 2. Otolith weight was significantly related to age (Fig. 4). The slopes of the otolith weight-age equations (Table 2) were significantly different for males and females (f-test, £=3.69, df=295, P<0.001). Discussion We obtained tarpon from a variety of fishery-inde- pendent and fishery-dependent sources; conse- quently, our sample was biased towards certain size classes, and the size-frequency distribution of our sample may not reflect that of the population. Most small fish (<1,100 mm) came from fishery-indepen- dent sources, and larger fish were sampled from the recreational fishery. Our size distributions were bi- modal and contained many small and large fish, but only a few fish 900-1,200 mm in length because these intermediate-size fish were too large to be sampled effectively by our gear and were rarely harvested in the recreational fishery. The size frequency of tar- pon sampled from the recreational fishery was prob- ably biased towards larger individuals. Most fish were caught during tournaments or were kept as tro- phies to be mounted by a taxidermist; presumably in both situations anglers selectively kept larger fish. Sometimes tournaments imposed minimum size re- quirements of as much as 50 kg on the fish harvested. Because males were typically smaller than females and rarely exceeded 45 kg, our samples from the rec- reational fishery contained roughly twice as many females as males, but this probably does not reflect the population's sex ratio. Among the smaller tar- pon (<1,100 mm) obtained from fishery-independent sources, there were 79 males and 85 females and the sex ratio was not significantly different from 1:1 ()C2=0.230, df=l,P=0.064). Age-validation experiments with OTC-marked otoliths supported the hypothesis that tarpon otoliths formed annual marks. Otoliths from 3 of the 18 OTC- injected tarpon showed fewer than the expected num- ber of increments. These fish showed relatively little otolith growth following capture, and we were un- able to resolve annuli that might have been present on the otolith's margin. We could not read the otoliths from three other tarpon and were unable to validate the periodicity of annulus formation for these fish. It is not surprising that several otoliths from OTC experiments were rejected as unreadable because almost 21% of otoliths from wild fish were unreadable; 626 Fishery Bulletin 93(4), 1995 Table 4 Average observed and predicted fork lengths (mm) for male, female, and unsexed tarpon, Megalops atlanticus Values in paren- theses are standard error and sample iize. Age Males Females Unsexed Average Average Average (yr) observed Predicted observed Predicted observed 0 321(26.5;6) 276 362(24.9;3) 246 239(2.3;461) 1 440(10.0;11) 425 434(13.5;10) 400 396(21.0;21) 2 552 (26.7;9) 557 607(26.0;12) 538 547(11.9;20) 3 626(31.0;12) 674 621(23.6;12) 664 626(32.1;9) 4 806(140.9;3) 777 645 (23.9;9) 777 5 940(20.8;3) 869 830 (36.6;6) 878 786(154.0;2) 6 918(45.4;4) 950 831 (58.7;4) 970 7 774(16.5;2) 1,021 1,130 (94.8;4) 1,053 8 909(1) 1,084 903 (22.5;2) 1,128 1,143(1) 9 1,140 1,044 (95.3;4) 1,196 1,100(1) 10 1,480(1) 1,189 1,337 (41.5;2) 1,256 11 1,359(13.0,2) 1,233 1,391 (36.9;3) 1,311 921 (1) 12 1,205 (52.3;3) 1,272 1,435(1) 1,361 1,310 (68.0;2) 13 1,295 (69.6;6) 1,306 1,601 (152.5;2) 1,406 14 1,392 (29.7;5) 1,336 1,495 (39.6;4) 1,446 15 1,435 (60.7;5) 1,363 1,568 (30.4;7) 1,482 1,385 (114.5;2) 16 1,400 (26.9;7) 1,386 1,602 (38.2;8) 1,515 1,538(1) 17 1,451 (2.3;3) 1,407 1,684 (31.4;5) 1,545 1,317 (39.7;5) 18 1,450 (23.0;8) 1,426 1,527 (39.2;9) 1,572 19 1,443 (47.9;5) 1,442 1,633 (20.9;10) 1,596 20 1,428 (42.8;3) 1,456 1,571 (49.1;7) 1,617 21 1,465 (143.0;3) 1,469 1,691 (19.9;16) 1,637 22 1,417 (61.3;3) 1,480 1,589 (41.8;6) 1,655 1,397(1) 23 1,473 (76.0;2) 1,490 1,695 (37. 7;12) 1,671 1,397(1) 24 1,470 (5.0;2) 1,499 1,656 (23. 1;17) 1,685 1,750(1) 25 1,550 (190.0;2) 1,507 1,625 (47.0;7) 1,698 1,498 (152.0;2) 26 1,639 (114.5;2) 1,514 1,691 (24.1;6) 1,710 27 1,513 (30.2;6) 1,520 1,710 (50.8;8) 1,720 28 1,438 (55.7;4) 1,525 1,715 (34.6;9) 1,730 1,675(1) 29 1,648 (119.2;3) 1,530 1,706 (38.5;9) 1,738 1,848 (120.5;2) 30 1,534 1,818 (18. 2;5) 1,746 31 1,460(1) 1,538 1,760 (29.7;15) 1,753 32 1,604 (16.0;2) 1,541 1,824(61.8;6) 1,759 33 1,525(1) 1,544 1,741 (38.6;8) 1,765 1,473(1) 34 1,489 (32.8;3) 1,547 1,782 (37.6;3) 1,770 35 1,549 1,658 (25.3;6) 1,775 36 1,570 (60.0;2) 1,551 1,802 (19.2;5) 1,779 37 1,422(1) 1,553 1,830 (38. 1;5) 1,783 38 1,450(1) 1,555 1,741 (85.0;3) 1.786 39 1,473(1) 1,556 1,846 (77.0;4) 1,789 40 1,557 1,827 (52.4;3) 1,792 41 1,448 (38.0;2) 1,558 1,800(1) 1,795 42 1,559 1,835 (115.0;2) 1,797 1,580(1) 43 1,710(1) 1,560 1,718 (49.5;3) 1,799 44 1,965 (75.0;2) 1,801 45 1,802 46 1,755 (50.3;3) 1,804 47 1,805 48 1,727 (127.0;2) 1,806 1,679 (73.0;2) 49 1,656 (44.1;3) 1,808 50 1,762 (63.2;3) 1,809 51 1,809 52 1,810 53 1,811 54 1,800(1) 1,812 55 2,045(1) 1,812 Crabtree et al.: Age and growth of Megalops atlanticus 627 thus, we expected at least this percentage of otoliths from captive fish to be unreadable. Indeed, it is likely that captive conditions and nonseasonal food avail- ability diminished the seasonal nature of otolith growth in captive fish and thereby increased the dif- ficulties in otolith interpretation. Our use of heaters at SERF during the winter reduced the seasonal change in water temperature; five of the six fish with problematic otoliths were held at this facility. We used the heaters at SERF during winter cold fronts when water temperatures might have reached low lev- els lethal to tarpon. Otoliths from all six of the tarpon held in the flow-through facility at Keys Marine Labo- ratory, where water at ambient temperature was con- tinuously pumped from Florida Bay, showed the ex- pected pattern of one annulus formed per year. Marginal-increment analyses also supported our hypothesis that the marks we counted formed once per year. The consistent marginal-increment minima observed for YOY and 1-year-old tarpon suggest that the marks present on otoliths of these fish were an- nual marks formed during winter or spring. Additional support for the validity of our age esti- mates comes from the life span of a captive tarpon placed in the John G. Shedd Aquarium in Chicago, Illinois, in November 1935. This tarpon was still alive in April 1994 and was at least 59 years old1 confirm- ing that tarpon can reach ages of more than 50 years as our data suggest. Tarpon otoliths had annuli on both the dorsal and ventral sulcal ridges that were similar in appearance to validated annuli in other species. Typically, an- nuli on the ventral ridge were more easily distin- guished, and annulus counts from this ridge were usually higher than annulus counts from the dorsal ridge. Some otoliths had regions where bands were distorted, unclear, or confluent, making counts diffi- cult or impossible. In other otoliths, portions of the sulcal ridge were dark in color and annuli were ob- scured. Our rejection of many otoliths as unreadable could have biased our growth-parameter estimates, but the size distribution of tarpon with otoliths judged to be unreadable was not significantly differ- ent from that of all tarpon examined for age and growth. Thus, we did not systematically reject a higher proportion of larger and presumably older fish than smaller and presumably younger tarpon. We do not know if rejected otoliths tended to come from faster- or slower-growing tarpon; this is a potential source of bias in our growth-parameter estimates. We could not sex most of the 0-, 1-, and 2-year-old tarpon examined and this is another potential source 1 Anderson. James A. 1994. Assistant Curator of Fishes, John G. Shedd Aquarium, Chicago, IL. Personal commun. of bias in our growth models. Observed lengths at age for the males and females we could sex at ages 0-2 were larger than the observed lengths of unsexed fish (Table 4). It is likely that the 0-, 1-, and 2-year- old fish we could sex were precocious and thus larger than comparably aged fish that we could not sex. Consequently, our sex-specific growth models were biased towards larger fish at these young ages; how- ever, the predicted lengths at age from both sex-spe- cific growth models at ages 0, 1, and 2 were between the observed lengths of sexed and unsexed fish, thus this bias was probably small. In addition, because both growth models included over 40 year classes, this bias probably had little effect on our growth- parameter estimates. Tarpon scales do not appear to be suitable for age estimation. Scale-derived estimates of tarpon longev- ity by Breder ( 1944 ) and de Menezes and Paiva ( 1966 ) suggested a maximum age of only 15 years, much lower than our otolith-derived estimate of 55 years and the known age of captive tarpon. De Menezes and Paiva ( 1966) presented scale-derived estimates of von Bertalanffy growth parameters for tarpon and estimated that for males, Lm= 2,062 mm, #=0.084, andt =0.20 and for females,! =2,633, #=0.065, and t =0.17. These estimates are probably biased by a consistent underestimation of ages and are consid- erably different from our otolith-derived estimates. Scale-derived estimates of Lx are unrealistically high and are much larger than the maximum size documented for any tarpon. Acknowledgments We thank the Don Hawley Foundation and the Pate Foundation, and in particular Capt. Mike Collins and Billy Pate for their support of this project. We also thank Ike Shaw Taxidermy, Pflueger Taxidermy, the Boca Grande Fishing Guides Association, the Florida Keys Fishing Guides Association, the Gold Cup Tar- pon Tournament, the Suncoast Tarpon Roundup, and Millers Marina for providing the specimens we ex- amined. Many people participated in portions of this study including Renee Bishop, Laura Crabtree, Chris Harnden, Victor Neugebauer, Derke Snodgrass, Connie Stevens, and Fred Cross and other employ- ees of the Florida Game and Freshwater Fish Com- mission. Jim Colvocoresses, Stu Kennedy, Judy Leiby, Mike Murphy, Kevin Peters, Jim Quinn, and Ken Sulak made helpful comments that improved the manuscript. Llyn French assisted in the preparation of figures. Grant Gilmore provided support for field collections. Buck Dennis, Bill Gibbs, Bill Halstead, Victor Neugebauer, and John Swanson participated 628 Fishery Bulletin 93(4). 1995 in the design and maintenance of tarpon holding fa- cilities. We also thank personnel at Mote Marine Laboratory and at the Keys Marine Laboratory for their cooperation. This project was supported in part under funding from the Department of the Interior, U.S. Fish and Wildlife Service, Federal Aid for Sportfish Restoration Project Number F-59; the Florida Marine Fisheries Commission; the Don Hawley Foundation; and the Pate Foundation. Por- tions of these data were included in a dissertation submitted by E. C. Cyr as partial fulfillment of the requirements of the Ph.D. degree, University of South Carolina. Literature cited Beamish, R. J., and G. A. McFarlane. 1983. The forgotten requirement for age validation in fish- eries biology. Trans. Am. Fish. Soc. 112:735-743. Beebe, W. 1927. A tarpon nursery in Haiti. Bull. N.Y. Zool. Soc. 30:141-145. Breder, C. M. 1933. Young tarpon on Andros Island. Bull. N.Y. Zool. Soc. 36:65-67. 1944. Materials for the study of the life history of Tarpon atlanticus. Zoologica 29:217-252. Casselman, J. M. 1983. Age and growth assessment offish from their calci- fied structures — techniques and tools. In E. D. Prince and L. M. Pulos (eds.), Proceedings of the international work- shop on age determination of oceanic pelagic fishes: tunas, billfishes, and sharks, p. 1-17. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 8. Cerrato, R. M. 1990. Interpretable statistical tests for growth comparisons using parameters in the von Bertalanffy equation. Can. J. Fish. Aquat. Sci. 47:1416-1426. Chacon Chaverri, D., and W. O. McLarney. 1992. Desarrollo temprano del sabalo, Megalops atlanticus (Pisces: Megalopidae). Rev. Biol. Trop. 40:171-177. Crabtree, R. E. 1995. Relationship between lunar phase and spawning ac- tivity of tarpon, Megalops atlanticus, with notes on the distribution of larvae. Bull. Mar. Sci. 56:895-899. Crabtree, R. E., E. C. Cyr, R. E. Bishop, L. M. Falkenstein, and J. M. Dean. 1992. Age and growth of tarpon, Megalops atlanticus, lar- vae in the eastern Gulf of Mexico, with notes on relative abundance and probable spawning areas. Environ. Biol. Fish. 35:361-370. de Menezes, M. F., and M. P. Paiva. 1966. Notes on the biology of tarpon, Tarpon atlanticus (Cuvier and Valenciennes), from coastal waters of Ceara State, Brazil. Arq. Estac. Biol. Mar. Univ. Fed. Ceara 6:83-98. Erdman, D. S. 1960. Larvae of tarpon, Megalops atlantica, from the Anasco River, Puerto Rico. Copeia 1960:146. Harrington, R. W. 1958. Morphometry and ecology of small tarpon, Megalops atlantica Valenciennes, from transitional stage through onset of scale formation. Copeia 1958:1-10. 1966. Changes through one year in the growth rates of tar- pon, Megalops atlanticus, Valenciennes, reared from mid-metamorphosis. Bull. Mar. Sci. 16:863-883. Hildebrand, S. F. 1934. The capture of a young tarpon, Tarpon atlanticus, at Beaufort, North Carolina. Copeia 1934:45-46. 1963. Family Elopidae. In H. B. Bigelow (ed.), Fishes of the western North Atlantic. Mem. Sears Found. Mar. Res. Yale Univ. 1(3):111-131. Kimura, D. K. 1980. Likelihood methods for the von Bertalanffy growth curve. Fish. Bull. 77:765-776. Marwitz, S. R. 1986. Young tarpon in a roadside ditch near Matagorda Bay in Calhoun County, TX. Texas Parks Wildl. Dep., Coastal Fish. Branch, Manage. Data Ser. No. 100, 8 p. Mercado, J. E., and A. Ciardelli. 1972. Contribucion a la morfologia y organogenesis de los leptocefalos del sabalo Megalops atlanticus (Pisces: Mega- lopidae). Bull. Mar. Sci. 22:153-184. Rickards, W. L. 1968. Ecology and growth of juvenile tarpon, Megalops atlanticus, in a Georgia salt marsh. Bull. Mar. Sci. 18:220-239. Secor, D. H., J. M. Dean, and E. H. Laban. 1992. Otolith removal and preparation for microstructural examination. In D. K. Stevenson and S. E. Campana (eds.), Otolith microstructure examination and analysis, p. 19-57. Can. Spec. Publ. Fish. Aquat. Sci. 117. Simpson, D. G. 1954. Two small tarpon from Texas. Copeia 1954:71-72. Smith, D. G. 1980. Early larvae of the tarpon, Megalops atlantica Valenciennes (Pisces: Elopidae), with notes on spawning in the Gulf of Mexico and the Yucatan Channel. Bull. Mar. Sci. 30:136-141. Tucker, J. W„ and R. G. Hodson. 1976. Early and mid-metamorphic larvae of the tarpon, Megalops atlanticus, from the Cape Fear River estuary, North Carolina, 1973-1974. Chesapeake Sci. 17:123-125. von Bertalanffy, L. 1957. Quantitative laws in metabolism and growth. Q. Rev. Biol. 32:217-231. Wade, R. A. 1962. The biology of the tarpon, Megalops atlanticus, and the ox-eye, Megalops cyprinoides, with emphasis on larval development. Bull. Mar. Sci. 12:545-603. 1969. Ecology of juvenile tarpon and effects of dieldrin on two associated species. Tech. Pap. Bur. Sport Fish. Wildl. 41:1-85. Zale, A. V., and S. G. Merrifield. 1989. Species profiles: life histories and environmental re- quirements of coastal fishes and invertebrates (South Florida )— ladyfish and tarpon. U.S. Fish Wildl. Serv. Biol. Rep. 82(11.104). U.S. Army Corps Eng. TR EL-82-4, 17 p. Zar, J. H. 1984. Biostatistical analysis. Prentice Hall, Englewood Cliffs, NJ, 718 p. Abstract. Samples of Plectro- pomus leopardus collected at two reefs (Glow and Yankee) that have been closed to fishing since 1987 were com- pared with samples collected at two reefs (Grub and Hopkinson) that were open to fishing to investigate the effects of a 3-4 year closure on the size, age, and sex structure of leopard coral- grouper (also known as "coral trout") populations. There were no significant differences in mean size and age be- tween protected reefs and unprotected reefs. However, mean size and age var- ied significantly between the two pro- tected and the two unprotected reefs. In the two reefs closed to fishing, the population structure was dominated by the presence of a strong year class which settled in early 1984, indicating the occurrence of strong interannual fluctuations in recruitment. A similar pattern was not observed on the reefs open to fishing, suggesting that fishing mortality may have caused the de- crease in abundance of this strong year class on the open reefs. Sex change oc- curred over a wide range of sizes and ages on the four reefs. A comparison of the frequency of developmental stages between reefs indicated significant variation. The two unprotected reefs had a smaller proportion of males, but that seemed to be compensated for by a larger proportion of transitional-stage fish and young males. Although the dis- tribution of developmental stages in the populations was different, the same fi- nal female: male balance was achieved. This suggests that for the leopard coralgrouper, sex change results from a combination of developmental and behavioral processes. Differences in age structure were more obvious than dif- ferences in the size structure between closed and open reefs, suggesting that age structure may be far more useful than size structure for comparisons of fishing effects on long-lived fishes such as Epinephelinae serranids. Compari- sons of open and closed reefs based solely on mean sizes may fail to detect important differences. Population structure of the leopard coralgrouper, Plectropomus leopardus, on fished and unfished reefs off Townsville, Central Great Barrier Reef, Australia Beatrice R Ferreira Departamento de Oceanografia Universidade Federal de Pernambuco Recife-Pernambuco CEP 50.739-540, Brasil Garry R. Russ Department of Marine Biology James Cook University of North Queensland Townsville Q48 1 1 , Australia Manuscript accepted 24 April 1995. Fishery Bulletin 93:629-642 ( 1995). Fishing is one of the most important human exploitative activities on coral reefs (Munro, 1983; Munro and Williams, 1985; Russ, 1991). It has been suggested that fishing may have a greater impact upon fish populations and communities of coral reefs than upon those of temperate seas because of the more territorial nature of most coral reef fish (Russ, 1991). Therefore, the impact of fishing on populations and communities of coral reef fishes has been of considerable interest. Large predatory species are especially af- fected by overfishing owing to life history characteristics such as slow growth, high longevity, low rates of natural mortality, and limited adult mobility (Plan Development Team [PTD], 1990; Russ, 1991). Fishing is known to cause selec- tive removal of larger (and presum- ably older) individuals, thus reduc- ing their proportion in the popula- tion (Ricker 1969; Miranda et al., 1987 ). Although evidence for effects of fishing on the size structure of populations of coral reef fishes is strong (Munro, 1983; PDT, 1990), there is little evidence for effects of fishing on age structure, probably because of the perceived difficulties in age determination of tropical fishes (Manooch, 1987). On the Great Barrier Reef, for example, information on age structure from a number of reefs exists for only one species, the damselfish Poma- centrus moluccensis (Doherty and Fowler, 1994). In the presence of high variability in size at age, in- formation on age structure can provide information on harvesting effects not obtainable by size-struc- tured data alone. Different growth processes can also be associated with selective fishing mortality (Parma and Deriso, 1990), enhanc- ing the importance of analyzing age in assessments of the the effects of fishing on such populations. Sequential hermaphroditism is common among coral reef fishes (Thresher, 1984). Bannerot et al. (1987) modelled the resilience of protogynous populations to exploi- tation and concluded that a definite risk existed in managing these stocks by traditional yield-per-re- cruit models under high fishing pressure. The effects of selective removal of larger individuals (pre- sumably mostly males) on the sex 629 630 Fishery Bulletin 93(4). 1995 ratio of a population, however, will depend on the mechanisms controlling sex reversal. For example, for protogynous populations, if female to male sex change is determined by size or age, a decline in the proportion of males will be expected. Such effects have been reported by Thompson and Munro (1983) in comparing populations of serranids subjected to different levels of fishing pressure in the Caribbean. In contrast, no fishing-related effects were detected by Reeson (1983) on populations of scarids. Social induction of sex change is known or claimed for many species offish (Shapiro, 1987). If this is the case, se- lective removal of larger individuals would induce female to male sex change, compensating for the ef- fects of fishing on the sex ratio. Consequently, a re- duction in the average size and age of sex change would be expected. A widely recognized management strategy in the conservation of reefs is the implementation of ma- rine fisheries reserves, areas designed to protect stocks of reef fish and habitats from all forms of ex- ploitation (PDT, 1990; Williams and Russ, 1994). The first marine protected area was established in Florida in 1930. Since then, protected marine areas have been implemented all over the world (PDT, 1990). In Australia, the first protected marine areas were es- tablished in the Capricornia Section of the Great Barrier Reef Marine Park in 1981, under the first zoning plan to come into operation (Craik, 1989). Evidence suggests that long-term spatial closure to fishing increases the density, biomass, average size, and fecundity of reef fishes (see PDT, 1990; Russ, 1991; Russ et al., in press, for reviews, but see DeMartini, 1993). Furthermore, by enabling popu- lations of reef fishes to attain or maintain natural levels, marine reserves have been suggested as a means to help maintain or even enhance yields of fishes from areas adjacent to the reserves (Russ, 1985; Alcala and Russ, 1990). The spatial structure of coral reefs provides an excellent opportunity to test for the effects of differ- ent management alternatives (Hilborn and Walters, 1992). The importance of experimental investigations on the effects of fishing on coral reefs that are used as replicate experimental units has been pointed out by various authors (Russ, 1991; Hilborn and Walters, 1992; Walters and Sainsbury1). Yet, in spite of the high expectations placed on marine reserves, few direct tests exist on the effects of such protection on yields of marine resources (Alcala and Russ, 1990). The leopard coralgrouper (also known as "coral trout"), Plectropomus leopardus, is a long-lived, protogynous hermaphroditic fish that represents a very important fishery resource over the Great Bar- rier Reef, Australia. With approximately 1,200 tonnes caught annually, the leopard coralgrouper is the larg- est single component in the annual commercial catch of Queensland line-fishing (Trainor, 1991). Because of its importance, the leopard coralgrouper has been the subject of many studies on the effects of fishing. These studies have compared the abundance and size structure of populations from open and closed reefs on the Great Barrier Reef (see Williams and Russ, 1994, for review). Most of these studies were con- ducted by using underwater visual census (UVC) techniques. Increased average size of the leopard coralgrouper on reefs closed to fishing was detected in most cases (Craik, 1981; Ayling and Ayling2'3; Ayling and Mapstone4). Beinssen5 used UVC, line fishing, and mark-release-recapture techniques to investigate the effects of a 3.5 year closure on Boult Reef and detected a significant increase in average size of leopard coralgrouper. The same reef was sub- sequently opened to fishing and after 18 months a significant decrease in the average size of leopard coralgrouper was detected (Beinssen5). No study, however, has investigated the effects of fishing on the age and sex structure of leopard coralgrouper populations. The age and growth of Plectropomus leopardus has been recently validated (Ferreira and Russ, 1994), making it possible to use age as an indi- cator of changes in population structure under dif- ferent levels of fishing pressure and through time. In 1987 a zoning plan was established in the cen- tral section of the Great Barrier Reef Marine Park, Australia, dividing the area into zones that allowed different activities. Under this plan, fishing was ex- cluded from some areas. In this study, samples taken from reefs in the central section of the Great Barrier Reef located in areas closed to fishing (National Park Zones) since 1987, are compared with samples taken from reefs located in areas open to fishing (General Use Zones). The effects of this 3-4 year closure on 1 Walters, C, and K. Sainsbury. 1990. Design of a large scale experiment for measuring effects of fishing on the Great Bar- rier Reef. Unpubl. Rep. to the Great Barrier Reef Marine Park Authority (GBRMPA), Australia, 47 p. 2 Ayling, A. M., and A. L. Ayling. 1984. A biological survey of selected reefs in the Capricorn section of the Great Barrier Reef Marine Park. Unpubl. Rep. to GBRMPA, Australia, 25 p. 3 Alying, A. M., and A. L. Ayling. 1986. A biological survey of selected reefs in the Capricorn section of the Great Barrier Reef Marine Park. Unpubl. Rep. to GBRMPA, Australia, 25 p. 4 Ayling, A. M„ and B. P. Mapstone. 1991. Unpubl. data col- lected for GBRMPA from a biological survey of reefs in the Cairns section of the Great Barrier Reef Marine Park. Unpubl. Rep. to GBRMPA, Australia, 30 p. 5 Beinssen, K. 1989. Results of the Boult Reef replenishment area study. Rep. to GBRMPA, Australia, 28 p. Ferreira and Russ. Population structure of Plectropomus leopardus 631 the size, age, and sex structure of leopard coral- grouper populations are investigated. Materials and methods Four mid-shelf reefs off Townsville, Central Great Barrier Reef (Fig. 1), were chosen as the sample reefs for this experiment. Two reefs, Grub and Hopkinson, were located in the General Use Zones and were open to spear-fishing, whereas the other two, Glow and Yankee, were located in National Park Zones, and had been closed to line fishing since September 1987. The four reefs were sampled twice a year, during June— July and September-October, in 1990 and 1991 $ i Palm 4, Islands Gi0%y Yankee #*"«! Hopkinson <£* GnibCi' 3> 9 ^ & Magnetic Island 25 Nautical miles Figure 1 Map showing the location of the sampled reefs: Glow and Yankee (closed to fishing) and Grub and Hopkinson (open to fishing). (Table 1). During each sampling trip, a crew of four line fishermen fished one reef per day (during the daylight hours) for a period of approximately four hours. The same vessel was used for each trip. The fishing crew was relatively consistent in composition, and overall fishing ability was presumably consis- tent between trips. Laboratory analysis All fish were measured and weighed, and their otoliths and gonads were removed. The gonads were preserved in FAAC (formaldehyde 4%, acetic acid 5%, calcium chloride 1.3%) on board, sectioned, and stained by using the standard techniques described in Ferreira (1993). Each gonad was classified into one of the following gonadal developmen- tal stages, following Ferreira (1993, 1995): Immature female: no evidence of prior spawning. Mature female: evidence of prior spawning or active vitellogenesis. Transitional-stage: gonads with proliferat- ing testicular tissue in the presence of degener- ating ovarian tissue. Dorsal sperm sinuses absent. Young male: post-transitional, newly trans- formed testis. Dorsal sperm sinuses formed. Ovarian tissue dominating the lamellae. Mature male: developed testes, presenting typical lobular form and presence of intra- lobular or "central" sperm sinuses. To determine the age of each fish, the otoliths were read whole and sectioned by following the method described by Ferreira and Russ (1992). The number of opaque zones or rings were counted from the center to the margin of each otolith. Because leopard coralgrouper recruit- ment occurs in the first months of the year (Doherty et al., 1994), the birth date was as- signed as 1 January. Opaque zones are formed once a year, from July to November (Ferreira and Russ, 1994); therefore, they were counted only when there was further deposition of a translucent zone, i.e. from December onwards. In this way, the number of rings corresponded to the real age of the fishes. Statistical analysis Nested analyses of variance (reefs nested within fishing status) were used to compare mean age and size of leopard coralgrouper between closed and open reefs (=fishing status). Factorial analyses of variance and Kruskal- Wallis tests 632 Fishery Bulletin 93(4). 1995 Table 1 Dates and number of leopard coralgrouper, Plectropomus leopardus, collected with standardized fishing effort in each one-day sampling trip. Closed Open Glow Yankee Grub Hopkinson Jun-Jul 1990 51 18 9 14 Sep-Oct 1990 49 42 11 17 Jun-Jul 1991 74 54 14 30 Sep-Oct 1991 23 11 15 15 Total 197 125 49 76 were used to compare mean size and age of leopard coralgrouper on the four reefs, independent of the reef fishing status. Multiple comparisons were per- formed by using post hoc tests (Tukey-Kramer, level of significance P=<0.05), and pair- wise comparisons by using Kolmogorov-Smirnov tests. Schnute's growth function ( 1981) was used to fit length-at-age data of leopard coralgrouper for each reef by using standard nonlinear optimization methods (Wilkinson, 1989). Schnute's model includes the von Bertalanffy, Richards, Gompertz, logistic, and linear growth mod- els, which correspond simply to limiting parameter values. To test for differences in size at age between reefs, the linear regressions were compared by us- ing analysis of covariance. Chi-square contingency tables were used to compare the frequency of sexes between reefs. The assumptions of normality and homoscedasticity were examined and data were transformed if needed (transformed data are indi- cated in tables). Level of significance used was P<0.05. Results There were no significant differences in mean size and age between protected reefs and unprotected reefs (fishing status). However, the mean sizes and ages varied significantly between reefs within fish- ing status level (Table 2). Post hoc tests showed that mean size and mean age were larger for Glow (closed) than for all other reefs, whereas mean ages for Grub (open) were smaller than for all other reefs. The mean sizes were not significantly different for Yankee, Hopkinson, and Grub, and the mean ages were not significantly dif- ferent for Yankee and Hopkinson (Fig. 2). Growth Schnute's growth function was fitted to size-at-age data for each reef. The submodel corresponding to the von Bertalanffy formula (b=l) provided a good fit to the data from all reefs (Fig. 3). The estimated "a" ( corresponding to the von Bertalanffy K) for Grub, however, approached zero, indicating that the data could be described also by a linear regression model. Ferreira and Russ (1994) found that for the leop- ard coralgrouper, estimates of growth parameters are affected greatly by different age ranges of size-at- age data. Therefore, for comparison of growth be- tween reefs, the age range was limited to age classes occurring at all four reefs (2 to 10 years), and Schnute's growth function was fitted to these trun- cated data. For Hopkinson, Grub, and Glow, esti- mates of "a" approached zero (Table 3), indicating close to linear growth over the age range 2 to 10 years. As the estimate of "a" for Yankee was also low, simple linear models were fitted to the data from all four reefs for comparative purposes (Table 3). Analysis of the sum of squares indicated that linear models were Table 2 Nested analysis of variance comparing mean size and age of leopard coralgrouper, Plectropomus leopardus, from reefs open and closed to fishing. The difference between residual degrees of freedom in the two tables is due to the fact that for some individuals age was not determined, df = degrees of freedom; SS = sum of squares; MS = mean square. Source df SS MS F-value Dependent variable: FL (cm) Fishing status 1 Reef (fishing status) 2 Residual 443 Dependent variable: Log age (years) Fishing status 1 Reef (fishing status) 2 Residual 413 393.6 531.1 18870.6 0.931 0.422 9.61 393.6 265.5 42.6 0.931 0.211 0.023 1.48 6.23 4.41 9.07 P-value 0.35 0.002 0.17 0.0001 Ferreira and Russ: Population structure of Plectropomus leopardus 633 A 45- I ■ 44- n U. 43- I ■ u 42- 1 ■ o ■ 41 - GLOW YANKEE CLOSED GRUB HOPKJNSON OPEN B 6.5- I ■ 6- I 1 1 5-5- -1- 5 - t 1 4.5- GLOW YANKEE CLOSED GRUB HOPKINSON OPEN Figure 2 (A) Mean fork length of leopard coralgrouper, Plectropomus leopardus, for each reef, and stan- dard error bars (years pooled). (B) Mean age of leopard coralgrouper for each reef, and standard error bars (years pooled). Sample sizes are pre- sented in Table 1. more appropriate to describe the growth data over the age range 2 to 10 years for all reefs with the excep- tion of Yankee, for which an asymptotic model was more appropriate. No significant differences were observed between the linear regressions obtained for each reef (P=0. 276), indicating that the mean size at age (and therefore growth) did not vary significantly between the four reefs. Analysis of the age and size distributions at each reef Glow and Yankee, the two closed reefs, had very strong modes in the year classes 6 and 7 (Fig. 4). In separating age distribution by year (Fig. 5), it is clear that these modes represented a strong year class that comprised 6-year-olds in 1990 and 7-year-olds in 1991. This result rules out the possibility of selec- tion towards one year class by fishing gear or bias in age determination. This strong year class was not as obvious on the unprotected reefs (Fig. 5). At Table 3 Schnute's (1981) parameter "a" and r2 values for nonlin- ear and linear growth models for leopard coralgrouper, Plectropomus leopardus, ages 2 to 10 years. Closed Open Glow Yankee Grub Hopkinson Nonlinear r2 Linear r2 0.080 0.450 0.445 0.102 0.546 0.448 0.004 -0.040 0.754 0.669 0.754 0.666 Hopkinson, year class 6 formed a small mode in 1990, but the pattern was not consistent, because year class 7 was not strong in 1991. At Grub, younger ages were proportionally more abundant; the mode was in the 3-year-old class for two consecutive years. The 6+ year-old age class of 1990 and the 7+ year- old age class of 1991 settled onto the reefs at the beginning of 1984. Because Glow and Yankee have been closed to fishing since 1987 and age of recruit- ment to the fishery is approximately 3 years of age (Ferreira and Russ, 1994), the individuals settling onto Glow and Yankee in 1984 were protected from fish- ing for most of their lives. Modal progression was not particularly evident in the size distributions (Fig. 6). Sex structure The distribution of developmental stages by size and age (Fig. 7) indicated that sex change occurs over a wide range of sizes and ages on the four reefs. The frequencies of developmental stages observed for each reef (Table 4) were compared by using chi- square analysis. The frequencies were significantly different between all reefs (P<0.05), with the excep- tion of the frequencies observed for Yankee and Hopkinson (P=0.246). For the calculation of sex ra- tio, frequencies of young males were pooled with fre- quencies of mature males, because individuals in both categories were sexually potential males. The result- ing sex ratios (Table 4) were not significantly differ- ent among reefs (P=0.09). There were no significant differences between pro- tected and unprotected reefs, but some differences between reefs were detected. The mean size of ma- ture females was not significantly different between reefs (one-way ANOVA, P=0.10). The mean age of mature females, however, was significantly different between reefs (log (age), P=0.008); mature females from Glow were significantly older than mature fe- males from Grub (post hoc, P<0.05). Age and size of 634 Fishery Bulletin 93(4), 1995 GLOW VB (b = 1 ) r2 = 0.466 YANKEE VB (b = 1 ) r2 = 0.546 L. = 68.69, K=0.101. f, = - 4.215 C = 68.872, K= 0.102, f„ =- 3.884 79 79 6t 5* 4» LrT: < ■ Jn' • : ■ 1 lur 1 • \Jt\ ■ • ' 3» X i9 A 19 l* 1* 1* « 3 6 9 12 15 8 * 1* 15 c 24 £ GRUB linear (b=1, a = 0) ^ = 0.754 HOPKINSON VB (b = 1) ^ = 0.718 FL = 26.57 + 3.016 x AGE U = 76.007, K= 0.091, (, = -3.614 7t y " - . a--*"""" 4* 3t • >lf-!- za z« ■ i» 1« ■ • 3 6 9 1Z IS "« 3 6 9 12 IS Age (years) Figure 3 Size-at-age data and estimated growth curve for leopard coralgrouper, Plectropomus leopardus, from each sampled reef. Table 4 Frequency (%) of each developmental stage and sex Plectropomus leopardus, at the four reefs. ratio (mature females young and mature males) of leopard coralgrouper, Immature Mature female female Transitional Young Mature Sex male male ratio Closed Glow 1 0 8 8 38 1.7:1 (1%) 59%) (6%) (6%) (28%) Yankee 4 40 16 11 3 0.91:1 (4%) (38%) (15%) (11%) (32%) Open Grub 7 15 10 7 5 1.25:1 (16%) (34%) (23%) (16%) (11%) Hopkinson 5 36 9 4 15 1.9:1 (7%) (52%) (13%) (6%) (22%) Ferreira and Russ: Population structure of Plectropomus leopardus 635 CLOSED 35 t -' ■■ j 30 f J. ■H SO 5S 60 6S I ork I cngth (cm) GLOW ■ SO h,m 40 1 1 30 20 Li'. 10 0 mm r h 12 14 Age (years) Age (years) OPEN Age (years) HOPKINSON Fork length (cm) HOPKINSON 10 12 Figure 4 Size- and age-frequency distribution of leopard coralgrouper, Plectropomus leopardus, for each reef, 1990 and 1991 data combined. transitional-stage fish were not significantly differ- ent between reefs (FL:P=0.24, log(age),P=0.11). Size of young males was not significantly different be- tween reefs (P=0.2) but ages of young males were significantly different (P=0.03); young males from Glow were significantly older than young males from Grub (post hoc, P<0.05). Age of mature males was not significantly different between reefs (P=0.22). However size of mature males varied significantly between reefs (P=0.001); mature males at Yankee were significantly smaller than mature males at Hopkinson (post hoc P<0.05). 636 Fishery Bulletin 93(4). 1995 CLOSED OPEN 1990 6 8 10 12 14 16 1991 \Z 14 16 1990 lloi'KINSON 1? 14 16 14 16 1991 HOPKINSON 0 2 4 6 8 10 1? 14 16 0 2 4 6 Age (years) Figure 5 Age distribution of leopard coralgrouper, Plectropomus teopardus, for each reef in each sampling year. Ferreira and Russ: Population structure of Plectropomus leopardus 637 1990 1991 25 30 1990 CLOSED 1991 OPEN 60 65 25 30 50 55 60 65 60 65 25 HOPKINSON 25 30 35 40 45 50 55 60 65 HOPKINSON 50 55 60 65 25 30 35 40 45 SO 55 60 65 Fork length (cm) Figure 6 Size distribution of leopard coralgrouper, Plectropomus leopardus, for each reef in each sampling year. 638 Fishery Bulletin 93(4), 1995 Discussion There are several important assump- tions in a comparison of the effects of fishing on populations from areas that are open with those that are closed to fishing. The first assumption is that protection is enforced so as to guaran- tee effective fishing closure. In the Great Barrier Reef Marine Park, aerial surveillance is conducted on a regular basis and fines are levied on those who fish illegally. Although violations still occur, the fishing pressure is likely to be considerably lower on the closed reefs. The second assumption is that the effects offish movements across closed and open boundaries do not mask the effects of protection from fishing on the population structure. The minimum dis- tance between two study reefs was of 1.6 km, and depth between reefs of the order of 40-60 m. Tagging studies have shown that reef fishes are highly site- attached, and most studies on move- ments of serranids have not shown sig- nificant movements across distances and depths such as those existing on the present study (PDT, 1990). Davies6 con- ducted extensive tagging studies on leopard coralgrouper and showed that fish exhibited extremely limited inter- reef movement in a study of six reefs in the Central Great Barrier Reef. Expected effects of fishing are a re- duction in the size and age range and average size and age of the population (Russ, 1991). In addition, line fishing might select for the larger and older individuals in a population (Ricker, 1969; Miranda et al., 1987), which would exacerbate this effect. Significant differences between size and age struc- tures on closed and open reefs, however, will depend largely on the duration of closure in relation to species longevity and fishing mortality. Therefore, a third assumption is that the duration of ef- fective closure is great enough (in rela- tion to the longevity of the target species c 3 o- 3.6 kg, or =8 lb) in Chesapeake and Delaware Bays. Methods A total of 4,137 weakfish were collected in 1989-92 from pound-net, haul-seine, and gillnet fisheries in the Chesapeake Bay region. On each sampling date either a 22.7 kg (50 lb) box of each available market grade (fish large enough to be sold for human con- sumption, graded as small, medium, or large) or the total catch was purchased and processed for biologi- cal data. Because boxes could not be randomly se- lected, our size and age compositions were not ex- pandable to the overall fishery. However, Chittenden ( 1989a) found little or no variation in fish size (total length) among boxes, within grades. To obtain year- round samples, 344 fish were collected in winter (when weakfish do not occur in Chesapeake Bay: Pearson, 1941; Massmann et al., 1958) from the trawl fishery operating in Virginia and North Carolina shelf waters north of Cape Hatteras. Since age-1 fish are not fully recruited to market grades (see Size and Age Composition heading in Results section), an ad- ditional 200 age-1 and young-of-the-year fish were collected by the Virginia Institute of Marine Science (VIMS) juvenile trawl survey from May to August 1990-92 in Chesapeake Bay. Details on sampling design and gear of the VIMS survey can be found in Chittenden (1989b) and Geer et al. (1990). To increase the number of large fish in this study for comparison of maximum size and age in Chesa- peake and Delaware Bays: 1) 35 fish were collected from the 1992 World Championship Weakfish Tour- nament in Dover, Delaware; 2) 10 fish (>3.6 kg total weight) from Delaware Bay and 5 fish (>3.6 kg total weight) from Chesapeake Bay were collected from commercial catches in 1992 and 1993; and 3) 41 fish (>500 mm total length) taken in Delaware Bay in 1985 and 1986 by Villoso ( 1989) were included in the analysis. Fish >3.6 kg (=8 lb) or >500 mm total length (TL) were targeted because these fish were beyond the range common in our regular Chesapeake Bay samples (see Size and Age Composition heading in Results section). To evaluate historic trends in maxi- mum size and abundance of large fish, the annual number of citation-size fish and the total weight (TW) of the largest fish reported were obtained from the Virginia Saltwater Fishing Tournament (1958-92) and from the Delaware State Fishing Tournament (1968-92). Citation-size fish are large and rare enough to be considered trophy fish. Citation size may change if larger fish become more numerable (e.g. weakfish citation size has fluctuated from 1.8 to 5.5 kg in the Chesapeake Bay over the past 25 years). In general, collections were processed for biologi- cal data as follows: fish were sexed, measured for TL (nearest mm), total gutted weight (TGW, nearest gram), and gonad weight (GW, nearest gram). Gut- ted weights included GW and were used (rather than total weights) because weakfish are piscivorous and can swallow fish a third of their own weight, a char- acteristic that could greatly bias somatic weights (Lowerre-Barbieri, 1994). Somatic weight (SW) was calculated as TGW minus GW. Otoliths from 3,290 fish were sectioned and aged by using the validated method described in Lowerre- Barbieri et al. ( 1994). Of 1,191 otoliths read by two separate readers, 99.8% of the assigned ages agreed. In addition, otolith annuli did not show severe crowd- ing at older ages and were easily distinguished (even in a 17-year-old, the oldest fish aged [Fig. 1]). More than 95% of the fish sampled were aged each year except 1990. In 1990, when many small fish were sampled, those to be aged (794 out of 2,098) were selected by systematic subsampling. Ages were as- signed assuming 1 January as an arbitrary birthdate (Jearld, 1983; Shepherd, 1988). This birthdate was selected so that fish of the same year class collected in April and May — before annuli form (Lowerre- Barbieri et al., 1994) — would be assigned the same age as those collected after annuli had formed. Lowerre-Barbieri et al.: Age and growth of Cynoscion regalis 645 To determine whether the population growth rate was representative of the true growth rate (i.e. whether there was not size-selective mortality within year classes), size at first annulus formation was evaluated for sectioned otoliths from fish ages 1-12 (Ricker, 1975). Otolith radius to the first annulus (distance from the nucleus to the proximal edge of the first annulus) was measured by using a Via- 100 camera and monitor system with a dissecting micro- scope at 24x (Lowerre-Barbieri et al., 1994). Mea- surements were taken on 403 Chesapeake Bay fish collected in 1989 and 1992-93 and on 47 Delaware Bay fish from 1992 to 1993. Given the strong rela- tionship between otolith radius and fish total length (Lowerre-Barbieri et al., 1994), size of the otolith at the first annulus was considered an indicator offish size at age 1. A one-way analysis of variance (ANOVA) was used to determine whether otolith size at first annulus was significantly different by age. Growth was evaluated by using nonlinear regression (Marquardt method) to fit the von Bertalanffy model (Ricker, 1975) to observed, individual lengths of Chesa- peake Bay fish ages 1-12. To remove seasonal effects, only fish collected in April and May were used for cal- culations. These months are the period when 1 ) somatic growth rate increases; 2) otolith annuli form; and 3) the largest range of sizes and ages occur in Chesapeake Bay. Finally, to examine differences in growth by sex, observed mean size at age in Chesapeake Bay was cal- culated for each sex and compared by using a Mest. Figure 1 Transverse otolith section of an age-17 weakfish, Cynoscion regalis, caught in May 1985 in Delaware Bay. Arrows indicate annuli. Linear regression was used to determine a SW-TL relationship on log-transformed data from fish col- lected in Chesapeake Bay. To include the greatest possible range of sizes ( 188-875 mm TL and 71-6,137 g SW), data were pooled over gears ( pound nets, haul seines, and gill nets). A i-test was used to determine if the slope of the SW-TL regression was signifi- cantly different from 3 — a slope of 3 indicating iso- metric growth. When only TL was given in the his- toric literature, conversions were made by using a TGW-TL relationship based on fish collected in April and May in Chesapeake Bay 1989-93, ranging from 20 to 6,276 g TGW and from 140 to 875 mm TL. This same relationship was used to estimate TL for cita- tion-size fish. All data were analyzed by using statistical meth- ods available in SAS ( 1988). Model assumptions were evaluated by examination of residuals (Draper and Smith, 1981). Rejection of the null hypothesis was based on an a level of 0.05, unless otherwise noted, and F-tests in ANCOVA were based on type III sums of squares (Freund and Littell, 1986). Results Size and age composition Most weakfish collected from Chesapeake Bay com- mercial fisheries during 1989-92, excluding those targeted for their large size, were 200-600 mm TL (98%) and ages 1—4 years (97%). However, ob- served sizes ranged from approxi- mately 200 mm TL to 850 mm TL, and observed ages ranged from 1 to 8 years (Fig. 2). The smallest fish (=200 mm TL) collected from market grades were similar each year. However, the largest ob- served fish varied from approxi- mately 650 mm TL in 1990 to 850 mm TL in 1989 and 1992. In 1990, a larger percentage (78%) of small (<300 mm TL), young weakfish were collected and no fish were older than age 5 (Fig. 2). Most of these small fish (<300 mm TL) were collected by haul seine and pound net (Fig. 3), whereas gill nets caught fish primarily in the 300-400 mm TL range. Weakfish were not fully re- cruited to market grades until age 2. Young-of-the-year and yearling 646 Fishery Bulletin 93(4), 1995 1989 fish occurred in Chesapeake Bay, making up 99% (rc=200) of the fish analyzed from the VIMS juvenile trawl survey. However, young-of-the-year fish were not present in mar- ket grades, and yearlings were not fully recruited, as evident by their low fre- quency in annual age compo- sitions (Fig. 2). Older, larger weakfish oc- curred in Chesapeake Bay primarily in the spring, when they appeared to arrive be- fore younger fish. Fish age 4 and older occurred in the spring in relatively large numbers, making up 51% and 27% of April and May samples (1989-92), respec- tively (Fig. 4). However, few fish older than age 4 were sampled after May, and they never made up more than 8% of the fish observed in later months. In contrast, few age- 1 fish were observed in either market grade samples or in the VIMS trawl survey until June, after which they made up roughly 30% of the mar- ket grade fish sampled. Mean monthly size at age also differed seasonally. Mean size at ages 3-6 of Chesapeake Bay fish collected in April and May, 1989-92, were larger than those collected in Au- gust and September (Table 1). In 1992, mean monthly TL of age-2 and age-3 fish (the most abundant ages in the samples) decreased steadily from April through July (Fig. 5). Although the pattern was less clearly defined in other years, a decrease in mean TL for the observed age-3 fish from April to June was evident. The mean TL of age-2 fish also declined from April to May in 1991 and 1992. There was no evidence that weakfish from Dela- ware Bay reached a larger maximum size or age than those in Chesapeake Bay. Maximum observed age of Chesapeake Bay fish was 12. However, annual ob- 200 300 400 500 700 800 n=2,079 200 300 400 500 600 900 n=1 ,146 n=403 200 300 600 700 800 900 Age (years) Total length (mm) Figure 2 Age and length frequencies of Chesapeake Bay weakfish, Cynoscion regalis, by year (1989-92) pooled over gears. Sample sizes are indicated above each age. Total annual sample size is noted for lengths. served maximum age of fish not selected for their large size varied: 8 in 1989 (n=378), 5 in 1990 (ra=775), 6 in 1991 (n=l,110), and 7 in 1992 (n=391). Maxi- mum observed age in Delaware Bay was 11. Fish older than age 6 were rare in both regions. Only four fish >3.6 kg were collected in 1992 in Chesapeake Lowerre-Barbieri et al.: Age and growth of Cynoscion regalis 647 n=191 Pound net >4,n ■j? i 40-| /si, 634 Haul seine O 100 200 300 400 500 600 700 4°1 n=254 Gill nel IVmiiI^hiiiiiiimiimmmimi 0 100 200 300 400 SOO 600 700 Total length (mm) Figure 3 Length frequencies of Chesapeake Bay weak- fish, Cynoscion regalis, by gear in 1990. Bay — three age 6 and one age 10. In Delaware Bay in 1992, seven fish were collected — one age 4, one age 5, four age 6, and one age 8. An additional six fish >3.6 kg were collected at the 1992 World Cham- pionship Weakfish Tournament in Delaware, all age 6. In 1993, only four fish >3.6 kg were collected — one age-12 fish from Chesapeake Bay, and three fish from Delaware Bay, ages 6, 8, and 11. Maximum TL ob- served in both regions was 875 mm. Maximum TGW was 6.3 kg in Chesapeake Bay and 6.6 kg in Dela- ware Bay. Ten fish collected from Delaware Bay >age 8 were similar in size to the two fish collected in Chesapeake Bay (See Fig. 7 below). Growth Weakfish size (TL) was a poor predictor offish age. Ages 1 and 2 were the only groups which did not Table 1 Mean total length (TL) at age for Chesapeake Bay weak- fish, Cynoscion regalis , collected in April-May and August- September, 1989-92. n Mean n Mean Age April-May April — May Aug-Sep Aug-Sep 1 89 176 311 251 2 246 311 516 312 3 246 411 119 402 4 213 511 50 507 5 46 558 8 549 6 13 631 2 626 have overlapping size distributions (Fig. 6). In con- trast, TL's of fish (ages 2-5) collected in April and May, showed broad ranges, much overlap, and mul- tiple modes (Fig. 6). A fish 350 mm TL or 350 g TGW (Table 2) could potentially be any of these ages (2-5). Observed size at age was used to estimate weak- fish growth, because there was no evidence of size- selective mortality. Mean size at first annulus showed no consistent pattern with increasing age (Table 3), and no significant differences were found between sizes at first annulus by age («=540, F=1.75, P=0.06). Weakfish growth was well described by the von Bertalanffy model (Fig. 7). The von Bertalanffy curve was calculated for pooled sexes because weakfish show no readily observed sexual dimorphism. Al- though lengths at age were similar for both sexes, mean TL's at age were usually larger for females than for males, and significantly so for ages 2 and 3 (Table 4). Mean observed TL's of pooled male and female Chesapeake Bay weakfish in April and May were 176, 311, 412, 510, 558, and 631 mm for ages 1-6, respec- tively. Despite the high variability in size at age, observed lengths at ages 1-12 showed a good fit (r2=0.98) to the von Bertalanffy model (Fig. 7). The model's estimated parameters, asymptotic standard errors, and 95% confidence intervals fell within a reasonable range, given the observed data (Table 5). Although the SW-TL relationship of weakfish col- lected in Chesapeake Bay differed significantly by sex (ANCOVA, P<0.05), the equations (male SW=9.1xlO"6 TL31 and female SW=6.9xlO"6 TL305) and coefficients of determination (r2=0.99) were simi- lar for both sexes. Therefore, an equation for pooled sexes was calculated (Fig. 8): SW = 6.0 x 10~6TL3 °4 (r2=0.99, n =3,742). The slope (b=3.04, SE=0.005) was not significantly different from 3 U-test, £=0.002, P>0.05) indicating 648 Fishery Bulletin 93(4), 1995 April 12 3 4 5 6 7 100-| May 12 3 4 5 6 7 -1 — I 1 r- 12 3 4 5 6 7 ou- J uly 50- 223 i i7 72 34 ~1 • 2 9 10 1234567 ,0°T August 9 10 1234567 Age (years) Figure 4 Age-frequency distributions of Chesapeake Bay weakfish, Cynoscion regalis, by month, pooled over the years 1989-92. Sample size is indicated above each bar. isometric growth. The TGW to TL relationship for April and May was TGW = 4.7 x lfr6TL3 13 (r2=0.99, n=950). Historic trends in maximum size and age Older weakfish were collected in Delaware Bay in 1985-86 than in 1992-93. The mean age offish >3.6 kg in 1985-86 was 9.6 years, significantly higher than that in 1992-93 (6.4 yr; /=3.14, n=26, P<0.05). Of the 10 fish >3.6 kg in 1985-86, one was age 4, one age 6, two age 8, two age 9, one age 11, two age 12, and one age 17. In contrast, the maximum age ob- served in 1992-93 was only 11, and of the 16 fish >3.6 kg only three of them were older than age 6. Maximum sizes of weakfish began to increase in Chesapeake and Delaware Bays in the early 1970s, concurrent with the recovery of the weakfish fish- ery. From 1958 to 1968, the largest weakfish reported to the Virginia Saltwater Fishing Tournament was 3.1 kg (662 mm TL, Fig. 9). Similarly, the largest fish caught in Delaware Bay in 1968 and 1969 (when citation records began) was 2.6 kg (626 mm TL). However, in 1970 maximum size in Chesapeake Bay was >3.1 kg(662 mm TL) for the first time since 1958, and maximum size in Delaware Bay increased from Lowerre-Barbieri et al.: Age and growth of Cynoscion regalis 649 6OO-1 1990 0 600 r age 2 - age 3 Apr May Jun Jul Aug Sep Oct Month Figure 5 Mean monthly total lengths at age 2 and 3 of Chesapeake Bay weakfish, Cynoscion regalis, 1990-92. Sample size is indicated next to each point. 2.6 kg (626 mm TL) in 1969 to 3.9 kg (712 mm TL) in 1970. By 1973 maximum weight had more than doubled, compared with that in the late 1960's, with 6.4 kg (834 mm TL) in Virginia and 5.9 kg (813 mm TL) in Delaware. Maximum sizes continued to in- crease until 1985 and remained high until 1989 in Virginia and 1990 in Delaware. The abundance of large fish in Chesapeake and Delaware Bays also increased in the early 1970's, concurrent with the increase in maximum size. From 1958 to 1968, only 64 fish >1.8 kg (556 mm TL) were reported in Virginia (Fig. 10). Similarly in 1968 and 1969, only 13 fish >1.4 kg (513 mm TL) were reported Age 6 (n=29) p Age 5 (n=62) Age 4 {n =223) Age 3 (n=264) 0 Age 2 (n=291) ~Age 1 (n=93) 200 400 600 800 Total length (mm) Figure 6 Length frequencies at age for weakfish, Cynoscion regalis, collected in April and May 1989-92, pooled over gears and locations. Table 2 Mean total gutted weights (TGW), range and standard er- rors at age for Chesapeake Bay and Delaware Bay weak- fish, Cynoscion regalis, collected in April and May, pooled over gears, 1989-93. Age n Mean (g) Range (g) Standard error 1 91 49 20-161 2.4 2 285 310 113-1,038 10.3 3 263 778 160-2,099 28.3 4 223 1,494 342-3,866 37.4 5 62 2,126 284-4,031 105.0 6 29 3,268 1,507-5,360 197.3 7 1 3,257 — — 8 4 5,230 3,370-6,475 591.5 9 1 5,311 — — 10 1 6,260 — — 11 1 6,190 — — 12 1 6,276 — — in Delaware Bay. However the number offish >1.8 kg (556 mm TL) reported in Virginia increased from 2 in 1969 to 83 in 1970. Similarly, in Delaware Bay, the number of fish >1.4 kg (513 mm TL) increased from 12 in 1969 to 121 in 1970. By 1980, 1,399 fish >5 kg (771 mm TL) received citations in Virginia, and 1,229 fish >4.6 kg (751 mm TL) received cita- tions in Delaware. Both Chesapeake and Delaware Bay have recently shown a marked decrease in maximum size and abundance of large weakfish. The number of large 650 Fishery Bulletin 93(4), 1995 1000 n=854 r2=0.98 c S S o 500 ■ cf Chesapeake Bay, 1989-93 ±9 Chesapeake Bay, 1989-93 09 Delaware Bay. 1985/1986 °cf Delaware Bay, 1992/1993 a9 Delaware Bay. 1992/1993 0 2 4 6 8 10 12 14 16 18 Age (years) Figure 7 Observed lengths at age and fitted von Bertalanffy regres- sion line for Chesapeake Bay weakfish, Cynoscion regalis, in April and May and for three fish from Delaware Bay. Weakfish in the asymptotic size range collected in Dela- ware Bay are included as reference points but were not used in calculations. Table 3 Mean, range, and standarc error of otolith sizes at first annulus (mm) for weakfish Cynoscion regali i, ages 1-12 (no age-9 fish were collected) from Chesapeake Bay and Delaware Bay Age n Mean (g) Range (g) Standard error 1 111 0.84 0.61-1.09 0.010 2 167 0.86 0.61-1.09 0.007 3 137 0.83 0.61-1.15 0.009 4 76 0.84 0.64-1.06 0.010 5 24 0.85 0.59-1.08 0.022 6 18 0.88 0.73-1.20 0.025 7 1 0.80 — — 8 3 0.80 0.76-0.88 0.038 10 1 0.67 — — 11 1 0.84 — — 12 1 0.90 — — fish reported in Virginia dropped sharply in 1981 and has remained low. Only 12 fish >5.45 kg (792 mm TL) were reported in 1989 and 1990, no fish in 1991, and 3 fish >5.0 kg (771 mm TL) in 1992. During 1990- 92, maximum size in Virginia was below 6 kg (817 mm TL) for the first time since 1972. Delaware Bay reported large numbers offish >4.6 kg (751 mm TL) until 1989. However, the number offish >5.0 kg (771 mm TL) decreased from 981 in 1989 to 11 in 1990. Only 18 fish have been reported since 1990. In 1991, 7000 -i 3500 - E o 450 Total length (mm) 900 Figure 8 Somatic weight-length relationship of weakfish, Cynoscion regalis, in the Chesapeake Bay region, 1989-93. 10-1 0) 5 A 11 -year-old A 10-year-old ■ Delaware Bay o Chesapeake Bay 1965 1 ' I ' i i 1975 Year 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1985 1995 Figure 9 Maximum total weights of weakfish, Cynoscion regalis, reported in the Delaware Sport Fishing Tournament and the Virginia Saltwater Fishing Tournament, 1958-1992. The oldest and two heaviest fish from the present study are included as reference points. maximum size of Delaware Bay fish dropped below 7.5 kg (878 mm TL) for the first time since 1981, and remained low in 1992. Discussion Size and age composition Most weakfish in Chesapeake Bay in 1989-93 were 200-600 mm TL and ages 1-4, but fish as old as age Lowerre-Barbien et al.: Age and growth of Cynosaon regalis 651 Table 4 Mean total length Cynoscion regalis, and r-test results ( (mm) at age by sex of male and female weakfish, from Chesapeake Bay in April and May 1989-92, a = 0.05,* = P<0.05). Age Mean TL males n Mean TL females n r-value Significance 1 176.3 42 175.9 47 0.14 NS 2 295.8 76 318.3 170 3.33 * 3 376.5 70 425.7 174 5.10 * 4 501.8 100 518.0 112 1.67 NS 5 553.9 24 562.5 22 0.37 NS 6 735.0 7 752.0 6 0.40 NS Table 5 Von Bertalanffy model parameter estimates, standard er- rors and 95^ confidence intervals estimated for weakfish, Cynoscion regalis, in the Chesapeake Bay region collected in April and May 1989-93. Parameter K tn Standard 95% confidence Estimate error intervals 918.89 58.09 804.87-1032.91 0.19 0.02 0.15-0.24 -0.13 0.09 -0.29-0.04 12 and as large as 875 mm TL were observed. Popu- lation size and age compositions could not be esti- mated from our samples, because they were not ran- domly selected and came from several gear types. How- ever, our samples should represent the population range. Hildebrand and Schroeder (1928) reported a similar size range ( 76-838 mm TL, n =280 ) in the 1920's. However, Massmann ( 1963 ) reported most weakfish in the 1950s were <300 mm TL, with a maximum size of 445 mm TL (rc=14,516) and a maximum age of 5. Chesapeake Bay weakfish are fully recruited to market grades by age 2. Joseph ( 1972 ) also reported age 2 as the first age fully recruited to the Chesa- peake Bay pound net catch. However, yearlings some- times make up a large portion of the commercial catch, as we observed in 1990, and clearly are vul- nerable to the gear — especially pound nets and haul seines. Such small, young fish are often sold as scrap and do not show up in market grades. McHugh ( 1960 ) found weakfish to be the second most important food fish in scrap from the Chesapeake Bay pound-net fishery, and Massmann ( 1963 ) reported the number of weakfish in pound-net scrap often exceeded that in market grades. Thus, although Chesapeake Bay weakfish are fully recruited to market grades at age 2, age at recruitment to pound nets and haul seines is younger. Large, older weakfish occur seasonally in Chesapeake Bay. From 1989 to 1992, older fish ( ages 4 and older) were relatively abundant only in April and May. Hilde- brand and Schroeder (1928) and Mass- mann ( 1963) also reported seasonal avail- ability of large weakfish in Chesapeake Bay. Although Massmann ( 1963 ) collected few weakfish >2 lb (0.91 kg) or age 4, the largest fish in his study (2- and 3-year- olds) were relatively more abundant in April and May, similar to the present study. However, Hildebrand and Schroeder ( 1928) reported weakfish >3 lb ( 1.36 kg) to be more common in both spring and late fall. Thus, although large fish occur regularly in the spring, their appearance in the fall may be variable. 2000 1000 Delaware Bay B nig S 32 kg D 4 6 kg ■ SO kg wgH Chesapeake Bay 1960 1970 1980 1990 Year Figure 10 Number of weakfish, Cynoscion regalis, citations reported in the Delaware Sport Fishing Tournament and the Vir- ginia Saltwater Fishing Tournament, 1958-92. Minimum citation weights are indicated by year. In 1972, the Dela- ware citation weight changed mid-year from 1.4 to 2.3 kg. 652 Fishery Bulletin 93(4), 1995 Age compositions of weakfish in Chesapeake Bay commercial catches are affected by migration. The pattern found in this study — of older fish arriving in Chesapeake Bay in April and May and then appar- ently leaving approximately when yearlings arrive — was also reported by Nesbit ( 1954) and Massmann (1963). This pattern indicates that Chesapeake Bay catches at any one time do not accurately represent relative weakfish abundance at age in the Bay. It is not known whether the old fish that occur in Chesa- peake Bay originated there, nor is it known where they go after leaving the Bay. It has been reported that some weakfish that spend their younger years in Chesapeake Bay migrate farther north as they grow older, and that large fish are more abundant farther north (Pearson, 1932; Nesbit, 1954; Perlmutter et al., 1956). The location of large fish may also vary from year to year. For example, fish >age 4 made up only 4.5% of our 1990 Chesapeake Bay samples but 17.1% and 17.6% of the 1991 and 1992 samples, respectively. The occurrence of a 17-year-old fish suggests past estimates of weakfish longevity and natural mortal- ity may need to be reevaluated. The maximum age previously reported was age 12 (Shepherd, 1988 ). How- ever, all former maximum ages were based on scales, which underage weakfish older than age 6 (Lowerre- Barbieri et al., 1994). The 17-year-old was aged as 7 by using scales (Villoso, 1989) — suggesting older fish may have occurred in the late 1970's and early 1980's but were underaged. The occurrence of a 17-year-old seems to indicate weakfish are longer-lived and experience lower natural mortality than previously believed, given the relationship between longevity and natural mor- tality (Hoenig, 1983; Gulland, 1983; Vetter, 1988). Growth Adult weakfish size at age showed a large range and much overlap. Broad size-at-age distributions have been reported for weakfish and attributed to the long spawning season from May through August (Welsh and Breder, 1923; Massmann et al., 1958; Thomas, 1971; Chao and Musick, 1977). An extended spawn- ing season affects size at age in two ways: 1) true age at first annulus deposition varies from 7 to 12 months, depending on birthdate; and 2) fish born in different months encounter different environments, e.g. temperature, salinity, and prey availability, which affect larval growth (Goshorn and Epifanio, 1991) and mortality rates (Thomas, 1971). In addi- tion, spawning pulses may result in several distinct size groups or modes within juvenile size distribu- tions (Massmann et al., 1958; Thomas, 1971). Delaware Bay fish did not demonstrate a greater longevity or maximum size than Chesapeake Bay fish in 1992-93. Maximum age was 11 in Delaware Bay and 12 in Chesapeake Bay. Maximum size in both regions was 875 mm TL. This is in contrast to Shep- herd and Grimes' (1983) hypothesis that weakfish show different regional patterns, longevity and growth being lowest in the South Atlantic region, in- termediate in the Chesapeake Bay region, and high- est in Delaware Bay and northward. Shepherd and Grimes (1983) observed a maximum age of 11 (810 mm TL) in the northern region and 6 (710 mm TL) in the Chesapeake Bay region. However, they sampled the two regions differently. Samples repre- senting the Chesapeake Bay region came only from a NMFS groundfish trawl survey along the Atlantic coast, whereas sampling in more northern regions included commercial fisheries within Gardiners Bay, New York; Sandy Hook Bay, New Jersey; and Dela- ware Bay. Because large fish are able to avoid trawls (Gunderson, 1993), estimates of maximum age may have been inaccurate owing to their sampling method (Hawkins, 1988). The Virginia Saltwater Fishing Tournament data show that more than 1,000 fish >5 kg (771 mm TL) were captured in 1980, indicating that large fish did occur in the area. Recent studies have reported similar asymptotic lengths for weakfish throughout their range. Our estimate of Lm (919 mm TL) is comparable to recent estimates from different regions: 893 mm TL from Delaware Bay (Villoso, 1989) and 917 mm fork length from North Carolina (Hawkins, 1988). In contrast, Shepherd and Grimes (1983) reported much lower L^ estimates for the Chesapeake Bay region (686 mm TL) and North Carolina (400 mm TL). Differential migration by size is an alternative explanation for the reported higher abundance of large, presumably older weakfish in the northern end of the range (Pearson, 1932; Nesbit, 1954; Perlmutter et al., 1956). Because swimming speed is a function of body size (Moyle and Cech, 1988), larger weakfish would be expected to travel faster and farther than smaller fish in a given amount of time. If weakfish constitute a single coastwide stock, as genetic re- search suggests (Crawford et al., 1988; Graves et al., 1992), and most fish overwinter off North Carolina (Pearson, 1932; Hawkins, 1988), then larger fish would arrive in northern estuaries before smaller ones in the spring. This is the pattern observed in Chesapeake Bay (Hildebrand and Schroeder, 1928; Massmann, 1963; the present study) and Delaware Bay (Feldheim, 1975; Villoso, 1989). In addition, be- cause larger fish would travel farther north, they would be more abundant at the northern end of the weakfish range, thus causing a size-dependent distributional pattern similar to that reported for Atlantic menha- den, Brevoortia tyrannus (Ahrenholz et al., 1987). Lowerre-Barbieri et al.: Age and growth of Cynoscion regalis 653 The complex spatial and temporal distribution of weakfish may also affect estimates of seasonal growth. Growth of temperate-water fish usually fol- lows the seasonal cycle; it is faster in summer and slower in winter (Moreau, 1987). Juvenile weakfish have been shown to grow rapidly during June-Sep- tember (Mercer, 1985). However, mean size at age for Chesapeake Bay weakfish ages 3-6, was smaller in fall-caught than in spring-caught fish (Nesbit, 1954, the present study). Thus, it may be difficult to follow seasonal growth patterns in Chesapeake Bay commercial catches. Historic trends in maximum size and age The population structure of Chesapeake Bay weak- fish has dramatically fluctuated since the 1920's. Hildebrand and Schroeder ( 1928) reported that most fish in Chesapeake Bay commercial catches weighed from 0.5 lb to 3 lb (0.23 kg to 1.36 kg) and that 6-10 lb fish (2.72-4.54 kg) were not uncommon. By the 1950's, however, Massmann (1963) reported that most fish were about 0.25 lb (0.11 kg) and few weighed more than 2 lb (0.91 kg). Massmann ( 1963) concluded that the uniformity in size structure from Before 1950 New York: Max TL=865 mm Max age =8° Delaware: Chesapeake Bay: Max. TL=720 mm North Carolina: Max. 396=8*"" 1950-69 1970-93 Max. TL=760 mm" Max TL=950 mm Max age=6° Max age=l2s Max. TL=392 mm" Max TL=960 mm Max age=4tf Max age=9° Max. TL=445 mm* Max TL=875 mm Max age=5* Max. age=!2' Max age=6' Max age=1l' Figure 1 1 Commercial landings of weakfish, Cynoscion regalis, coastwide (hatched bars) and in Chesapeake Bay (black bars), 1925-89, with maximum reported sizes and ages (in years) for periods of high and low landings. Taken from: "Nesbit ( 1954), Terlmutter et al. (1956), Taylor (1916), ^reported in Seagraves (1981), 'Massmann ( 1963), IVlerriner ( 1973 ), ^Shepherd ( 1988), ''Villoso ( 1989), 'present study, ^Hawkins (1988). 1954 to 1958 indicated that there were no large fluc- tuations in year-class abundance; rather, he sug- gested that the weakfish population had stabilized at a low level of abundance. In 1970, however, the maximum size and number of large fish began to increase, peaking in 1980. Although the maximum size and number of large fish have declined recently, the current maximum size of 875 mm TL and maxi- mum age of 12 remain well above those for the 1950's and 1960's (445 mm TL and age 5) (Massmann, 1963; Joseph, 1972). Similar historic changes in maximum size and age have been reported over much of the weakfish range, with higher maximum ages and sizes during periods of higher landings and presumed abundance (Fig. 11). During the high landings of 1925-45, the maxi- mum size was 865 mm TL (Nesbit, 1954), and maxi- mum age was 8 (Perlmutter et al., 1956). However, during the 1950's and 1960's when landings were low, maximum size decreased to 760 mm TL and the maximum reported age was 6 years (Perlmutter et al., 1956). In the 1970's and 1980's, maximum size and age increased to 960 mm TL (Villoso, 1989) and 12 years (Shepherd, 1988), concurrent with increased weakfish landings. Because all previous ages were based on scales, the historic pattern of higher maxi- mum ages during periods of higher landings are probably valid, even though actual ages may have been underestimated. Citation data indicate an abrupt increase in maximum size and abundance of large weakfish in Delaware Bay in 1970 and in Chesapeake Bay in 1971. Maxi- mum size rose steadily from 1970 to 1979 and then remained rela- tively constant until 1989 in both areas. Abundance of increasingly large fish (Fig. 10) also rose until 1980 in Chesapeake Bay and 1989 in Delaware Bay. Although these data have no estimates of effort associated with them, the general pattern appears accurate. Greater effort might increase the number of rare, large individuals being caught even if their abundance remained constant, but it would not be expected to cause such a dramatic change in the numbers and size of large fish being caught (i.e. in Chesapeake Bay no fish >3.5 kg TW from 1958 to 1969 to more than 1,000 fish >5 kg TW in 654 Fishery Bulletin 93(4), 1995 1980). In addition, citation-size fish have recently declined even though recreational effort has re- mained high. The increased abundance of large, presumably older fish apparently reflects increased recruitment or year-class strength in the late 1960's. There is no evidence that fishing mortality decreased. In con- trast, effort increased during this same period ( Wilk, 1981), and peak regional landings shifted to North Carolina, where exploitation of smaller weakfish is higher than in more northern regions (Hawkins, 1988). The importance offish born in the late 1960's is indicated by the increase offish > 1.8 kg (556 mm TL) in Chesapeake Bay and >1.4 kg (513 mm TL) in Delaware Bay in 1970 and 1971, respectively. Based on current TGW-at-age data (Table 2), the age of these fish would be 4-5 years, and they would have born between 1965 and 1967. By 1976, these fish would be 9-11 years old and >5 kg TGW. The step- wise increase in abundance of fish >5 kg in Chesa- peake Bay and offish >4.6 kg in Delaware Bay from 1976 to 1980 indicates that more fish were growing into this size range than were being removed, which would be expected if large numbers of several strong year classes were reaching age 8 or older during this time period. Several lines of evidence suggest more than one year class contributed to the increase in abundance of large weakfish in the 1970's and 1980's. First, in Chesapeake Bay the number of citation-size fish >5 kg in 1980 was larger than the number of citation- size fish >1.8 kg in 1970. Similarly, in Delaware Bay the number of citation size fish >4.6 kg in 1986 was larger than the number of citation-size fish >1.4 kg in 1971 and 1972. If only one year class was involved, the number offish surviving to older and larger sizes would decrease rather than increase. Second, the pattern in Delaware Bay — of increasing numbers of fish >4.6 kg from 1975 to 1980, with a decrease in 1981 and 1982 and then a second increase until 1986 — suggests the contribution of more than one year, class. Third, it is unlikely that the more than 1,300 fish >5.0 kg recorded in Delaware Bay in 1987 were solely from the late 1960's year classes, because they would then be 19-21 years old. The factors which produced the large year classes and allowed large numbers of weakfish to survive to older ages are not clear. Joseph (1972) suggested re- productive failure as the cause of the low landings in the 1950's and 1960's, and thus increased repro- ductive output and recruitment in the late 1960's could have caused increased year-class strength. That there was a shift in recruitment appears to be corroborated by the fact that weakfish larvae were rare in Chesapeake Bay in the 1960's (Joseph, 1972); yet in 1971-73 Olney (1983) found them to be sec- ond in abundance only to the bay anchovy, Anchoa mitchilli. Such a large shift in recruitment should be reflected in juvenile indices. However, the index of juvenile weakfish abundance, based on trawl surveys of the York River, Virginia, from 1955 to 1982, showed only a small increase in abundance in 1968 — one that did not exceed levels in the 1950's — a larger peak in 1970, and an extreme peak in 1980 (Mercer, 1985). In addition to variable recruitment, there also may have been changes in adult natural mortality rates. Such fluctuations are not uncommon, although they are difficult to document (Vetter, 1988; Hilborn and Walters, 1992). Factors such as increased food avail- ability, which would increase reproductive output (Houde, 1989), would also be expected to decrease adult natural mortality rates. Future research is necessary to understand better fluctuations in year-class strength and interactions between weakfish and other species. Stock-wide mortality rates need to be estimated and weakfish migration needs to be understood better. It is espe- cially important that ages be based on sectioned otoliths — a validated ageing technique — so that fu- ture estimates of growth parameters, mortality, and longevity can be better compared over time and space. Acknowledgments We would like to thank the Chesapeake Bay com- mercial fishermen, James Owens, and the people working at the Delaware Weakfish Sport Fishing Tournament for helping us obtain the samples. Ri- chard Seagraves provided us with information on the Delaware fishery as well as otolith samples. Rogerio Teixeira and Cindy Cooksey helped with sectioning otoliths. We would like to thank three anonymous reviewers for their helpful suggestions to improve the manuscript. Financial support was provided by the College of William and Mary, Virginia Institute of Marine Science, and by a Wallop/Breaux Program Grant from the U.S. Fish and Wildlife Service through the Virginia Marine Resources Commission For Sport Fish Restoration, Project No. F-88-R3. L. R. Barbieri was partially supported by a scholarship from CNPq, Ministry of Science and Technology, Bra- zil (Process no. 203581/86-OC). Literature cited Ahrenholz, D. W., W. R. Nelson, and S. P. Epperly. 1987. 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The structure and growth of the scales of the sque- teague and the pigfish as indicative of life history. U.S. Bur. Fish., Bull. 34:285-330. Thomas, D. L. 1971. The early life history and ecology of six species of drum (Sciaenidae) in the lower Delaware River, a brack- ish tidal estuary. Ichthyol. Assoc. Bull. 3, 247 p. Vaughan, D. S., R. J. Seagraves, and K. West. 1991. An assessment of the status of the Atlantic weakfish stock, 1982-1988. Atl. States Mar. Fish. Comm. Spec. Rep. 21, Wash. DC, 29 p. Vetter, E. F. 1988. Estimation of natural mortality in fish stocks: a review. Fish. Bull. 86:25-43. Villoso, E. P. 1989. Reproductive biology and environmental control of spawning cycle of weakfish, Cynoscion regalis (Bloch and Schneider), in Delaware Bay. Ph.D. diss., Univ. Delaware, Newark, NJ, 295 p. Welsh, W. W., and C. M. Breder Jr. 1923. Contributions to life histories of Sciaenidae of the east- ern United States coast. Bull. U.S. Bur. Fish. 39:141-201. Wilk, S. J. 1979. Biological and fisheries data on weakfish, Cynoscion regalis ( Bloch and Schneider). U.S. Dep. Commer., NOAA Tech. Ser. Rep. 21, NMFS Sandy Hook Lab., Highlands, NJ, 49 p. 1981. The fisheries for Atlantic croaker, spot, and weakfish. In H. Clepper (ed.), Marine recreational fish- eries symposium VI, p. 59-68. Sportfishing Institute, Washington, D.C. AbStTclCt. A simple analytical technique is developed for estimating the predictability of recruitment, that is, correlations between recruitment and stage-specific mortalities or abun- dances. The method requires the input of estimates of the variability of stage- specific mortalities, which may be cal- culated from mean stage-specific mor- talities by applying a published regres- sion. It is shown that modification of this regression to compensate for sam- pling error in field measurements of abundance significantly reduces the estimated standard deviation of log-re- cruitment, which is an important fac- tor in the predictability calculations. It is concluded that the prospects for pre- dicting recruitment from egg or larval surveys or from environmental vari- ables are quite poor for fish stocks showing the typical distribution of mor- tality across stages. Estimating the predictability of recruitment Gordon Mertz Ransom A. Myers Science Branch, Department of Fisheries and Oceans Northwest Atlantic Fisheries Centre PO. Box 5667, St. John's, Newfoundland A1C 5X1 Manuscript accepted 7 May 1995. Fishery Bulletin 93:657-665 ( 1995). The problem of predicting recruit- ment remains central to fisheries science (e.g. Bradford, 1992). Ap- proaches to this task may involve finding environmental correlates of recruitment or the field sampling of prerecruit life history stages. In this study we present simple analytical formulae that permit one to esti- mate the potential explainable vari- ance of recruitment without the use of detailed, specific data. Certain environmental factors may be correlated with recruitment. Wind speed has been proposed as a determinant of recruitment because storm-driven mixing can disperse larvae and their prey reducing food availability (Lasker, 1975, 1981; Buckley and Lough, 1987; Peter- man and Bradford, 1987). Larval food supply may also be influenced by the lag between appearance of larvae and the peak abundance of their prey (Cushing, 1990). The in- tensity of turbulence may control the frequency of contact between larvae and their prey (Rothschild and Osborn, 1988). Larvae may be exported to inhospitable waters by the action of wind driven currents (Nelson et al., 1977) or by the in- cursion of Gulf Stream rings (Flierl and Wroblewski, 1985; Myers and Drinkwater, 1989). (For thorough discussions of environmental influ- ences on recruitment see Fogarty [1993] or Wooster and Bailey [1989].) In each example noted above, some measurable physical quantity may be plausibly postu- lated to be a proxy for (say) larval mortality, in a qualitative sense; it is our aim to quantify the expected predictive power of an environmen- tal variable. Alternatively but much more expensively, larval mortality could be estimated from field stud- ies (Butler, 1991). We calculate the likely strengths of the correlations between mortality for an early life history stage and recruitment. A related problem that is addressed is the correlation between recruit- ment and abundance in an early life history stage, which can be deter- mined from field studies (Pete rman et al., 1988; Bradford, 1992). This treatment is an analytical comple- ment to the simulation studies pre- sented in Bradford (1992). In the analysis to follow we first show how variability of mortality may be estimated from mean mor- tality while accounting for the ef- fect of sampling error in the field measurements. We then proceed to formulate simple relationships per- mitting the calculation of the cor- relation coefficients between log- transformed or raw recruitment and stage-specific mortality or abundance, using only estimates of variability in stage-specific mortal- ity. These two sets of analyses are then combined to provide estimates of the predictability of recruitment for a number of fish species. 657 658 Fishery Bulletin 93(4). 1995 Methods and analysis Variability of mortality To calculate correlations between stage-specific mor- talities (or abundances) and recruitment, we required estimates of variability of mortality for each stage. Bradford ( 1992) compiled from the literature a large set of data on mortality rates and their interannual variabilities for the prerecruit stages of marine fishes. From this consolidation of data, Bradford regressed the interannual variance of daily mortality on its mean (averaged over years). We adopt the following notation: M represents an estimate of M from a single year's survey (often only two abundance estimates are used to calculate M); M represents the average over a number of years of M values; Var(M) is the estimate of the variance of the mortality calculated from a number of years of M data. Note that Var(M) is not equal to the true variance, Var(M), an issue dealt with below. Bradford found the following fit, holding across both stages and species: ln[Var(M)] = 2.231 In M - 1.893 (r2 = 0.90; P<0.0001 ). We can re- write this relation as Var(M) = 0.15M 2.2 (1) This very appealing relationship specifies an almost constant CV for mortality; however, it is unclear if it is affected by measurement error. When mortality is calculated from the difference of two field estimates of log abundance each with error e, the following relationships hold: M = (VT)[\nN(t1 ) - In N(t2 ) + e(t2 ) - e(*a )], (2) where tt is the time of the ith observation. This re- duces to the right-hand side of Equation 3 when n=2, and decreases asymptotically as 1/rc for large n. For 10 evenly spaced observations, the estimation error vari- ance will be approximately reduced by one-half, com- pared with the case of two observations. To a good ap- proximation, Equation 3 will provide a good estimate of the estimation error variance because only a few per- cent of the data used by Bradford had n larger than 10. Predictability of recruitment: no density dependence We can write recruitment as R(t) = E(t)exp[-(C1(t) + C2U) + ...)], (5) where t refers to a specific year, E is the total num- ber of eggs produced, and C, is the cumulative mor- tality in stage /'. To be specific, we designate i - 1 for the egg stage, i = 2 for early larvae, i = 3 for late larvae, and i - 4 for juveniles. In accord with Equation 5, the abundance of prerecruits, iV,, at the end of stage i, is NiU) = E(t)exp[-(Cl(t) + C2(t) + ... + Cl(t))]. (6) These equations form the basis of the forthcoming analysis. Let Cl(t) = Cl + AC, (t), and \nEit) = \nE + MnE(t), then \nR(t) = \nR + AlnE-(AC1(t) + ... + AC4(t)).a) It follows from Equation 6 that Var(M) = Var(M) + (21 T2 )ai (3) where N represents the true abundance, o£ is the standard deviation of the estimation error e, and T = t2-iv Approximately 70% of the mortality estimates in Bradford (1992) were obtained as the difference of two abundance estimates. When mortality is estimated from a regression equation, by using a slope of log numbers versus time with n observations equally spread over time inter- val T, then we can use the standard formula in re- gression for the variance of the estimate of a slope to obtain (4) I>-^)2 T'n{n + \) (n-1)2 (2n±l_n±l\ I 6 ' 4 J lnN,(t) = \nN,+A\nE-(AC1(t) + ... + AC4(t)). (8) Equations 7 and 8 are general, they hold whether or not correlations are present between stages. We make immediate use of these equations to examine the predictability of recruitment in the absence of inter- stage correlations, a simple case which serves well to illustrate the technique. In the following calculations we concentrate on environmentally induced recruitment variations and neglect the contribution of interannual variations in egg production. Accordingly, we remove the stock ef- fect from data-based estimates of recruitment vari- ability before comparison with model-based values. Only trivial modifications are necessary to include the egg production factor should this be desired. In the absence of interstage correlations of mortality, it is easily shown that Mertz and Myers: Estimating the predictability of recruitment 659 (tfln(m)) =(<7cl)2+... + (CFc,-)2 (9) where oln(„;l is the standard deviation of In Nit and oci is the standard deviation of C,. Correspondingly, (C7Infi)2=(CTcl)2+... + (CTc4)2. (10) We designate the correlation coefficient relating log recruitment and log abundance in stage i to be rni, and the corresponding coefficient relating log recruit- ment and stage-specific mortality to be rcr With Equa- tions 7, 8, 9, and 10, it is easily demonstrated that u\nim) (11) this relation holds for i = 1,2,3; for i = 4, one has a correlation coefficient of 1.0, because we have stipu- lated that abundances are evaluated at the end of a given stage. Corresponding to Equation 11 we have (12) °infl Predictability of recruitment: density dependence We prescribe density dependence of the form dis- cussed by Myers and Cadigan ( 1993, a and b), which is the same form as that used in key factor analysis (Varley and Gradwell, 1960; Manly, 1990; Bradford, 1992). In this formulation, mortality during the ju- venile stage is increased (decreased) for years in which larval abundance is high (low). Specifically, AC4 = aAlnN3 +e, (13) where a gauges the strength of the density-depen- dence and £ (which should not be identified with the e introduced in section 2) represents the portion of juvenile mortality uncorrected with late-larval abundance. It follows that 2 2/ \2 2 tfc4=« (' J" J°° p(R,Cl)dRdCl-C,R . (18) The joint probability p(i?,C,) is obtained through d(\nR) dR ' (19) p(R,Ci) = p(lnR,Ci) 660 Fishery Bulletin 93(4), 1995 and, by assuming that In R and C are normal, p(ln R,Ct) may be obtained from standard texts: p(ln#,C() 2KOXnRocl{l-r'*)1 ■ (20) sources cited in Bradford (1992), the sampling pe- riod for the surveys providing mortality estimates and then plotted In M versus In T in order to test for the existence of a power law relationship between these two variables (Fig. 1). The regression (Fig. 1) yields In M = -0.991 In T + 0.776, or, equivalently exp -1 2(1- r.7) '(AC,)2 2rclAC,AR (Alnfi)2 ' aci°\nR „2 Equations 20 and 19 may be substituted into Equa- tion 18 to obtain an expression for r'ci . The integrations in Equation 18 can be straight- forwardly executed to show that CTln/? r 2 i1/2 [exp(ffi„R)-lJ (21) It is evident from this expression that if o]nB is small, then r'ci = rci. An identical result holds for the coefficient of cor- relation between R and In Nn designated r,'u; it is given by Mnfl r 2 11/2 [exp(crlnfl)-lj (22) M=2.17T' (24) This apparent tendency of M and T~l to covary may stem from the existence of excluded regions of the M , T~l plane. If M is small, mortality will be de- tectable only if sampling times are well separated, implying that small M corresponds to large T. Simi- larly, if M is large, the interval between samples cannot be great, because the abundance will possi- bly decline rapidly below the threshold of detectabil- ity; thus, large M corresponds to small T. We can now use Equation 24 to obtain a relation for the true variance of M, Var(M), by substituting Equations 1 and 3 and then substituting Equation 24 into the result, with the outcome Var(M) = (0.15M 0.2 0A2af)M2. (25) Even for a given life history stage, there can be great differences in the estimation error for abundance. For the Peterman (1981) salmon smolt study, a£ = 0.08, whereas for the juvenile groundfish surveys examined in Myers and Cadigan (1993, a and b), o£ The coefficient of correlation between R and Nn des- ignated r„" , can be found through a procedure analo- gous to that employed in the calculation of rc' . The result is exp(rm(TlnRa]nim))-l [exp (crfn R ) - l] ' [exp (cr,2n( ni)) - 1] 1/2 (23) In the limit that aln(m)«l, Equation 23 reduces to Results Variability of mortality To obtain a relationship between the true variance of mortality, Var(M), and mean mortality we can sub- stitute Equation 3 into Equation 1. However, it must be borne in mind that there is likely to be a relation- ship between M and T (Taggart and Frank, 1990). To address this problem, we extracted, from the , ^ "•-.".. -2 - , • # .. • s * * • • CT -4 - o • • • r. . •• * ■ -6 - > • • : •• • * ' - 1 I I I i i 2 3 4 5 6 7 logr Figure 1 The natural logarithm of the daily mortality rate versus the natural logarithm of the sampling dura- tion for prerecruit stages of marine fish, based on sources listed in Bradford ( 1992). Mertz and Myers: Estimating the predictability of recruitment 661 15 10 5 0 0 15 £ 10 CD l 5 LL 0 0 8 6 4 2 0 All data jhI«. 0 0.5 1.0 15 2.0 All but North Sea ■■■■■I 0 0.5 1.0 1.5 2.0 North Sea JL 0 Histogra mation ( groundfi Cadigan 0 0.5 1.0 1.5 20 SD of estimation error ( aE ) Figure 2 ms of the standard deviation of the esti- rror of log abundance for the juvenile sh survey data treated in Myers and 1993. aandb). has a median value of about 0.75 (Fig. 2). Of neces- sity, the discussion of the importance of measurement error cannot be precise. We examine the effect of oE in the interval 0.3 to 0.5, a range about midway be- tween 0.08 and 0.75, on the variance of M estimates. If the error in the log-transformed survey abun- dances is characterized by oE = 0.3 (corresponding to a CV of approximately 30% in the untransformed abundances), then for the range of mortalities in Bradford's regression, M ~ 10-* to 0.4d_1, Equation 25 shows that estimation error accounts for 309;- ( up- per end of range) to 100% (lower end of range) of the variance in M. In other words, the true variance in M amounts to between 0% (lower end of range) and 70% (upper end of range) of the variance of M. If of = 0.5, then the true variance represents 09c (lower end of range) to 20% of the estimated variance of M. Of more interest is the range of mortalities for major fish species, entered in Table 1 of Bradford (1992), M =10"2 to 10-1 d-1. For this range, with oE = 0.3, we find that the true variance constitutes about one-half of the estimated variance of M. If oE = 0.5, then the true variance is estimated to make no contribution to the estimated variance. On the basis of these num- bers, but somewhat arbitrarily, we assume, for the range M = 10~2 to 10_1 d_1, that the true variance represents 25% of the estimated variance of M, so that Var(M) = 0.04 M 2 or am - 0.2M , (26) where om is the standard deviation of M. Finally, we wish to utilize Equation 26 to obtain a relationship between the interannual variability in cumulative mortality in a given stage and the mean cumulative mortality. Since the M values in Bradford's data base are largely stage averages, the cumulative mortality is just C = M ts, where ts is the stage duration. It also follows that the standard de- viation of cumulative mortality ac, is given by ac = Omts. Applying these relations to Equation 26, we arrive at oc = 0.2 C , where we have placed a bar over the C to indicate that we are relating the interannual variability of C (represented by ac) to its mean value ( C ). We can be more specific, since Bradford's re- gression applies across stages, and make the stan- dard deviation and mean specific to each stage i: 0.2C, (27) The coefficient in Equation 27 is only half as large as that in Bradford's regression (i.e. the square root of the factor 0.15 which appears in Equation 1). This adjustment of slope, arising from correction for esti- mation error, could be too severe (Bradford and Ca- bana, in press; Bradford1); nevertheless, we take Equation 27 at face value, use it to predict oinJi, and compare the derived values to data. In the discus- sion we comment on the influence of the slope param- eter in Equation 27 on the predictability calculations. Predictability of recruitment: no density dependence In Table 1 we present the estimates of the correlation coefficients derived from Equations 11 and 12; in the final column the calculated olnfl, from Equation 10, appears. If we had used relation ( Equation 1 ) in the calculation of clnR, without adjusting for measurement error, then the calculated values of alnR would be one and a half times as large. It is evident that (Fig. 3) o]nR is overestimated for cod, anchovies, and plaice. Myers and Cadigan ( 1993, a and b) have shown that density- dependent juvenile mortality can be expected to ap- preciably attenuate larval variability in cod and plaice. 1 Bradford, M. Dept. 1994. Fisheries and Oceans, West Van- couver Laboratory, 4160 Marine Dr., West Vancouver. B.C. V7V 1NG, Canada. Personal commun. 662 Fishery Bulletin 93(4). 1995 cod 20 2.5 Herring Anchovies I 00 0.5 Plaice _ 0.0 0 5 10 15 2.0 SD of log Ricker residuals B Cod 00 05 2 0 2.5 Herring ■III. 00 05 10 15 20 Anchovies 0 0 0 5 10 15 2 0 Plaice 1 00 05 10 15 20 SD of log recruitment Figure 3 (A) Histograms of the standard deviation of the log-recruitment residuals from a Ricker fit to the stock-recruit relation for four species of marine fish. (B) Histograms of the standard deviation of log recruitment (without adjustment for stock size) for four species of marine fish. Predictability of recruitment: density dependence It is evident from Equation 15 that the effect of posi- tive a is to reduce alnfl, which is desirable here, be- cause the formulation with a = 0 overestimated o]nB for cod and plaice (Table 1). We now select cod for closer examination, since there are reliable estimates for the strength of den- sity dependence in this species (Myers and Cadigan [1993a]). Our parameter a corresponds to 1-A, in Myers and Cadigan (1993a). They found that X, was typically about 0.5 for a cod stock, suggesting a = 0.5. With this specification we find from Equation 15 that olnfl = 0.58, which is in good agreement with Figure 3A. For this case, a = 0.5, the correlation be- tween AC4 and Aln/V3 is 0.6, so that about 36% of the variance in juvenile mortality is related to larval abundance (see Eq. 13). With a fixed we have recalculated, rcl and rni, for cod using the equations above, and have displayed them in Table 2 along with their counterparts calcu- lated for Table 1 (for which a = 0 was assumed). It is apparent that the prescribed density dependence has appreciably lowered the correlation coefficients. There is a particularly large reduction in rc4, stem- ming from the fact that the juvenile mortality has two components which tend to offset one another (in the limit £ - 0, in Equation 13, juvenile mortality will actually be positively correlated with recruit- ment). Thus, realistic levels of density dependence (Myers and Cadigan, 1993a) have the effect of sub- stantially reducing the predictability of log-recruit- ment from prerecruit mortalities or abundances. Predictability of raw recruitment For olaR = 0.5 we find from Equation 21, r'nlra = 0.94 and for olnR = 1.0 we have r^/rei = 0.76. It is evident that the predictability of raw recruitment ( r'ci ) declines relative to the predictability of log re- cruitment (r„) as olnfi increases. In Table 3 we have completed the presentation for the cod case, showing the r'ci,r'ni,r^ in comparison to Mertz and Myers. Estimating the predictability of recruitment 663 Table 1 Calculated parameters relevant to the predictability of recruitment analysis, for four fish species: ac, is the standard deviation of total mortality for stage i; 0|ni„,i is the standard deviation of log abundance in stage i; C\nR is the stan- dard deviation of the log recruitment; rc, is the coefficient of correlation be- tween log recruitment and mortality for stage t; r„, is the coefficient of correla- tion between log recruitment and log abundance in stage i. The quantities Oinfl, rcl, and r„, were calculated by assuming no inter-stage correlations. Egg Early larvae Late larvae Juveniles Cod Or, 0.22 0.32 0.58 0.58 alnn = 0.91 Oln(ni) 0.22 0.39 0.70 0.91 \rci\ 0.24 0.35 0.64 0.64 r„, 0.24 0.43 0.77 1.0 Herring oc, 0.21 0.16 0.48 0.79 OlnJJ = 0.96 Olnlni) 0.21 0.26 0.55 0.96 IrJ 0.22 0.17 0.49 0.82 r„, 0.22 0.28 0.57 1.0 Anchovy a* 0.35 0.32 0.79 0.65 OlnR = 113 0ln(n,] 0.35 0.47 0.92 1.13 1 rci 1 0.31 0.28 0.70 0.57 I'm 0.31 0.42 0.82 1.0 Plaice o(., 0.52 0.21 0.70 0.39 CJl„K = 0.97 Clnlm) 0.52 0.56 0.90 0.97 1 rci 1 0.53 0.22 0.72 0.40 r™ 0.53 0.57 0.92 1.0 the rci , rm. It is clear in these examples that predict- ability is lost when one works with the untrans- formed recruitment or abundance. Peterman et al. (1988) have investigated the pre- dictability of recruitment from surveys of prerecruit abundances. Equations 22 and 23 shed some light on how predictability is influenced by log transform- ing the prerecruit abundances. Recall that when cxln(m)«l, then rn" = r'ni, i.e. the raw recruitment is predicted equally well by abundance or log abun- dance. However, if oln(ni-, is considerably larger than alnfi, then r'm > r£ (e.g. for olnfl = 1.0, o^ = 2.0, rni = 0.5, then /•„',■ = 0.38, whereas rn" = 0.18). Conversely, ifolnfi is considerably larger than aln(ni> then, r,"t > r'm (e.g. for a]nR = 2.0, aln(n,, = 1.0, rm = 0.5, then r,'u = 0.14 and r£ = 0.18). This implies that whether or not one will achieve a better correlation between re- cruitment and log abundance (of pre recruits) than between recruitment and abundance depends on the relative magnitudes of olnR and oln(m). Discussion CV for mortality The incorporation of estimates of measurement error into the relation- ship between variability of mortality and mean mortality indicates that the slope coefficient (see Eq. 27), which is the mortality CV, may be substantially altered by measure- ment error. However, removal of the error component does not destroy the intuitively appealing approximate proportionality between variability of mortality and its mean. In the presence or absence of den- sity dependence the slope parameter in Equation 27 does not affect the predictability of log recruitment; see Equations 11, 12, 16, and 17. Increas- ing this parameter inflates o]n(nh and oc, but it also increases olnfl by the same proportion, leaving the corre- lation coefficients rni and rci un- changed. This invariance of the cor- relation coefficients with respect to the mortality CV is a useful result stemming from our treatment of the predictability problem. The predict- ability of raw recruitment is influenced by the mortality CV, because a]nR de- pends on this CV and because alnB af- fects the correlation coefficients for raw recruitment (Eqs. 21 and 22). The true size of the mortality CV cannot be deter- mined with certainty, because the degree of inflation of the true CV by measurement error cannot be ac- curately ascertained. However, Equation 27, which specifies a mortality CV of only 0.2, gives reasonable estimates for the magnitude of the recruitment vari- ability (alnff ). Comparison of Table 1 and Figure 3A shows that Equation 27 (with Equation 10) over- predicts the median olnE in three cases (cod, ancho- vies, and plaice). Underestimation of recruitment variability due to ageing errors by 20-30% (Bradford, 1991; Bradford1) could rectify this discrepancy. For cod and plaice it is likely that density dependence is in part responsible for the discrepancy between cal- culated (from Equation 27) and empirical values of olaR (see Myers and Cadigan, 1993, a and b). In any case, the approximate agreement between cal- culated and observed values of olaff is powerful veri- fication for the general validity of Bradford's (1992) regressions. 664 Fishery Bulletin 93(4), 1995 Table 2 The coefficients of correlation for log recruitment of cod (see Table 1) versus stage-specific mortality, rcl, and for log recruitment versus stage-specific log abundance, rnl. The label "no d.d." implies absence of density dependence; the label "d.d." signifies that the parameters were calcu- lated for the density-dependent case. Early Egg larvae Late larvae Juveniles 1 rCI I (no d.d.) 0.24 0.35 0.64 0.64 \rcl ■ 1 (d.d.) 0.19 0.28 0.50 0.28 1 r„, |(no d.d.) 0.24 0.43 0.77 1.0 \rni l(d.d) 0.19 0.33 0.60 1.0 Research needs For research purposes one may seek correlations between recruitment and an environmental variable assumed to be a proxy for mortality during some prerecruit stage. It is apparent that there is no mean- ingful distinction between log recruitment and raw recruitment for the purposes of correlation analysis provided olnfi < 0.4. For the optimal case of minimal density dependence, correlations between log recruit- ment and mortality seldom exceed 0.6 to 0.7 (Table 1). This implies that any environmental variable that is to serve as a proxy for mortality must be very tightly correlated with mortality if there is to be a significant correlation between the proxy variable and recruitment. Similar results were found by Bradford ( 1992). Management needs The criterion for successful recruitment prediction for stock management suggested by Walters (1989) requires that the proxy should explain 80% of the variance in log recruitment, or, equivalently, rci , rni = 0.9. Equations 11 and 12 allow a ready appraisal of the likelihood of meeting this criterion; the applica- tion of these equations yields the results in Table 1, indicating that this criterion is never fulfilled un- less one samples late in the juvenile phase. The in- clusion of density dependence (Eqs. 16 and 17) gen- erally reduces the correlation coefficients rcl and rm. These findings agree with those of Bradford (1992). A management strategy requiring predictions of recruitment (rather than log recruitment) is not likely to be viable if the stock under consideration has high recruitment variability. For a stock with alrLff = 1.0, if 80% of the log recruitment variance can be explained by a proxy, only 46% (Eq. 21 or 22) of Table 3 The coefficients of correlation for log recruitment of cod versus stage-specific mortality, rcl\ for recruitment versus stage-specific mortality, r^; for log recruitment versus stage-specific log abundance, r„,; for recruitment versus stage-specific log abundance, r'm ; and for recruitment ver- sus stage-specific abundance, rn" . All examples shown are calculated for the density-dependent mortality case. Egg Early larvae Late larvae Juveniles |rci| 0.19 0.28 0.50 0.28 1 r'd 1 0.17 0.26 0.46 0.26 \rm\ 0.19 0.33 0.60 1.0 1 r'm I 0.17 0.30 0.55 0.92 \rm\ 0.19 0.33 0.60 1.0 1 C 1 0.17 0.30 0.55 1.0 the variance of recruitment itself will be explained by this proxy. For a oinR of 1.5, appropriate to some herring stocks, only 21% of recruitment variance could be explained by a proxy accounting for 80% of log recruitment variance. These calculations bear on the question of whether or not large year classes can be predicted (Bradford and Cabana, in press; Ander- son, 1988). Capturing the size of a large year class requires an estimate of raw (rather than log-trans- formed) recruitment; however, those stocks which produce the most notable year classes (those with large olnR) are the least predictable. Summary The analysis presented here complements that of Bradford (1992). We have shown that correction for measurement error can appreciably reduce the CV for mortality, while not destroying the appealing pro- portionality between variability of mortality and mean mortality. We have demonstrated that in many cases the predictability of recruitment can be deter- mined analytically. It is evident from our treatment that raw recruitment is considerably less predictable than log recruitment for stocks with high recruitment variability. Our results concur with those of Bradford, suggesting that the prospects of predicting recruit- ment from egg or larval surveys or from environmen- tal variables are quite poor. However, it must be borne in mind that some fish stocks will deviate from the general pattern, and thus it is quite conceivable that there will be fish stocks for which a critical stage exists, allowing recruitment predictions from (say) larval abundances. Mertz and Myers: Estimating the predictability of recruitment 665 Acknowledgments We are grateful to M. Bradford and J. Hutchings for their comments on an earlier draft of this manuscript. We have profited from discussions with M. Fogarty. This research was supported in part by the North- ern Cod Science Program of Canada's Department of Fisheries and Oceans. Literature Cited Anderson, J. T. 1988. A review of size dependent survival during pre- recruit stages offish in relation to recruitment. J. North- west Atl. Fish. Sci. 8:55-66. Bradford, M. J. 1991. Effects of aging errors on recruitment time series es- timated from sequential population analysis. Can. J. Fish. Aquat. Sci. 48:555-558. 1992. Precision of recruitment estimates from early life stages of marine fishes. Fish. Bull. 90:439-453. Bradford, M. J., and G. Cabana. In press. Interannual variability in survival rates and the causes of recruitment variation. In Early life history and recruitment in fish populations. Chapman and Hall, NY. Buckley, L. J., and R. G. Lough. 1987. Recent growth, biochemical composition, and prey field of larval haddock [Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) on Georges Bank. Can. J. Fish. Aquat. Sci. 44:14-25. Butler, J. L. 1991. Mortality and recruitment of Pacific sardine, Sardi- nops sagax, larvae in the California Current. Can. J. Fish. Aquat. Sci. 48:1713-1723. Cushing, D. H. 1990. Plankton production and year-clear strength in fish populations: an update of the match/mismatch hypothe- sis. Adv. Mar. Biol. 26:249-293. Fleirl, G. R., and J. S. Wroblewski. 1985. The possible influence of warm core Gulf Stream rings upon shelf water larval fish distribution. Fish. Bull. 83:313-330. Fogarty, M. J. 1993. Recruitment in randomly varying environments. ICES J. Mar. Sci. 50:247-260. Lasker, R. 1981. Factors contributing to variable recruitment of the northern anchovy (Engraulis mordax) in the California Current: contrasting years 1975 through 1978. ICES Rapp. Proc.-Verb. 178:375-388. 1975. Field criteria for survival of anchovy larvae: the re- lation between inshore chlorophyll layers and successful first feeding. Fish. Bull. 73:453-462. Manly, B. F. 1990. Stage-structured populations. Chapman and Hall, London, 187 p. Myers, R. A., and K. Drinkwater. 1989. The influence of Gulf Stream warm core rings on re- cruitment offish in the Northwest Atlantic. J. Mar. Res. 47:635-656. Myers, R. A., and N. G. Cadigan. 1993a. Density-dependent juvenile mortality in marine demersal fish. Can. J. Fish. Aquat. Sci. 50:1576-1590. 1993b. Is juvenile natural mortality in marine demersal fish variable? Can. J. Fish. Aquat. Sci. 50:1591-1598. Nelson, W. M., M. Ingham, and W. Schaaf. 1977. Larval transport and year-class strength of Atlantic menhaden, Brevoortia tyrannus. Fish. Bull. 75:23-41. Peterman, R. M. 1981. Form of random variation in salmon smolt-adult re- lations and its influence on production estimates. Can. J. Fish. Aquat. Sci. 38:1113-1119. Peterman, R. M., and M. J. Bradford. 1987. Wind speed and mortality rate of a marine fish, the northern anchovy {Engraulis mordax). Science 235:354-356. Peterman, R. M., M. J. Bradford, N. C. H. Lo, and R. D. Methot. 1988. Contribution of early life history stages to interannual variability in recruitment of northern anchovy {Engraulis mordax). Can. J. Fish. Aquat. Sci. 45:8-16. Rothschild, B. J., and T. Osborn. 1988. The effects of turbulence on plankton contact rates. J. Plank. Res. 10:465-474. Taggart, C. T., and K. T. Frank. 1990. Perspectives on larval fish ecology and recruitment processes: probing the scales of relationships. In K. Sherman, C. M. Alexander, and B. D. Gold (eds.). Large marine ecosystems: patterns, processes and yields, p. 151- 164. Am. Assoc. Adv. Sci., Wash. DC. Varley, G. C, and G. R. Gradwell. 1960. Key factors in population studies. J. Anim. Ecol. 29:299-401. Walters, C. J. 1989. Value of short-term forecasts of recruitment varia- tion for harvest management. Can. J. Fish. Aquat. Sci. 46:1969-1976. Wooster, W. W., and K. M. Bailey. 1989. Recruitment of marine fishes resisted. In R. J. Beamish, and G. A. McFarlane (eds.), Effects of ocean vari- ability on recruitment and an evaluation of parameters used in stock assessment models, p. 153-159. Can Spec. Publ. Fish. Aquat. Sci. 108. Abstract. The onshore move- ment of settlement-stage bonefish, Albula vulpes, leptocephali was moni- tored over four consecutive winters ( 1990-91 to 1993-94) and summer 1992 near Lee Stocking Island, Exuma Cays, Bahamas. Total catch over the four win- ters ranged from 316 to 1,421 fish per 70-day sampling period, whereas 1,112 were taken during the single 72-day summer sampling period. An analysis of otoliths from 87 fish collected dur- ing the last winter indicated continu- ous spawning activity during the fall and early winter and an estimated lar- val duration of 41 to 71 days. The col- lection of larvae in summer 1992 sug- gested that spawning continues until late spring. Virtually all recruiting lep- tocephali were collected at night and in the upper 1 m of the water column. Time-series analysis of the four winters linked together by lunar date revealed a strong cyclical pattern of recruitment, with a period of 30 days, and a strong association with the number of hours of flood tide occurring under dark, moonless conditions. The one major peak in the summer samples occurred during the first 12 days of sampling when the hours of dark flood tide was at its maximum level for the month; subsequent dark periods had low lev- els of recruitment. There were no strong associations between recruit- ment levels and wind and current pat- terns. These data suggest that the cy- clical pattern in hours of dark flood tide creates "windows of opportunity" for the leptocephali to move onshore at times that minimize their vulnerabil- ity to visual predators in reefs and seagrass beds. Recruitment of bonefish, Albula vulpes, around Lee Stocking Island, Bahamas Raymond Mojica Jr. East Volusia County Mosquito Control District 1 600 Aviation Center Parkway Daytona Beach, Florida 32114 Jonathan M. Shenker Christopher W. Harnden* Daniel E. Wagner Department of Biological Sciences, Florida Institute of Technology 1 50 West University Boulevard Melbourne, Florida 32901 Manuscript accepted 15 December 1994. Fishery Bulletin 93:666-674 ( 1995). The bonefish, Albula vulpes, is found in the tropical western Atlan- tic and supports substantial recre- ational fisheries in south Florida, the Bahamas, and many Caribbean islands. Despite their importance as a sport fish, there is little quantita- tive information available about the abundance of adults in different lo- cations, the temporal trends in popu- lation sizes, and the recruitment pro- cesses that may have a considerable influence on the size and spatial dis- tribution of adult populations. Adult bonefish typically inhabit shallow sand and seagrass flats, of- ten in water less than half a meter deep, and feed on crabs, bivalves, shrimp, and small benthic fishes (Bruger, 1974; Colton and Alevizon, 1983). Some information on the sea- sonality of reproduction is available, but the temporal and spatial scales of spawning activity or spawning behavior itself have not been de- scribed. In the Florida Keys, spawn- ing occurs from October to May.1 Examination of gonads of fishes col- lected in the Bahamas indicated that fish in spawning condition also predominated between October and May, although some ripe fish were found throughout the year.2 In the pelagic environment, Albula leptocephalous larvae grow to lengths of up to 70 mm prior to settlement. On the basis of the tem- poral occurrence of ripe females and the subsequent appearance of meta- morphosing leptocephali, Pfeiler et al. (1988) proposed a larval dura- tion of six to seven months for Al- bula sp. from the Gulf of California. As the leptocephali move from off- shore to the shallow nursery and adult habitats, their length de- creases approximately 509r during their metamorphosis into juveniles. Pfeiler (1984) investigated the movement of Albula sp. leptocephali as they entered a hypersaline la- goon (estero) in the Gulf of Califor- nia. Although sampling was limited to 15-20 minute periods of flood tide on 33 nights from February through May, Pfeiler suggested that larvae Coaffiliated with the Florida Department of Environmental Protection, 328 West Hibiscus Boulevard, FIT/ARL Building, Room 120. Melbourne, FL 32901 1 Crabtree, R. E. 1994. Florida Depart- ment of Environmental Protection, Marine Research Institute, St. Petersburg, FL. Personal commun. 2 Colton, D. E. 1994. 27395 Vista Del Toro Road, Salinas, CA. Personal commun. 666 Mojica et al.: Recruitment of A/bula vulpes 667 moved into the lagoon during the first several hours of the flood tide and that there was no movement into or out of the lagoon during the ebb tide. Although the leptocephali of Albula vulpes have been found throughout the Caribbean from Brazil to Bermuda and the southwestern Gulf of Mexico (Smith, 1989), few previous studies have investigated the larval biology of the species or their movement from the pelagic realm to the shallow juvenile habi- tat (e.g. Eldred, 1967; Thompson and Deegan, 1982). This study presents data on the recruitment of meta- morphic A. vulpes in the Bahamas as they move from the deep pelagic Exuma Sound onto the shal- low Great Bahama Bank near Lee Stocking Island (LSI). Data collected over four consecutive 70-day winter sampling seasons and one summer season were used to evaluate the effects of various environ- mental parameters that have been shown to influ- ence recruitment of a variety of taxa (Shenker et al., 1993; Thorrold et al., 1994, a and b). The otoliths of 87 individuals that recruited during the 1993-94 winter season were examined to determine the presumed spawning (hatching) dates and to estimate the larval duration of A. vulpes in the Bahamas. Materials and methods Data collection Larval bonefish were collected with moored channel nets suspended in two tidal passes on the western edge of Exuma Sound, Bahamas, immediately north of Lee Stocking Island (Fig. 1). Winter sampling was conducted from 17 December 1990 to 28 February 1991, 13 Decem- ber 1991 to 26 February 1992, 12 December 1992 to 25 February 1993, and 10 December 1993 to 23 February 1994. Summer data were collected from 25 June to 4 September 1992. Station locations, net designs, and sampling protocols are detailed in Shenker et al. (1993) and Thorrold et al. ( 1994a). To summarize, each of three stations (corresponding to stations 1, 2, and 3 in Shenker et al., 1993) were equipped with both a surface net (mouth area=2 m wide xl m deep) and a midwater net (2 mx2 m) which fished the 2-4 m deep layer. Samples were re- moved from the 3-mm mesh nets after dawn and before dusk each day. In this study, we pooled catches among all six nets. Because less than 10% of the A. vulpes larvae were taken in the day samples, our analysis focuses on only the samples collected at night. Wind speed and direction data during the first, third, and fourth winters, and the one summer were collected hourly at a Campbell Scientific weather station on LSI. During the second winter, the weather station was inoperative and measurements were re- corded twice daily with a hand-held anemometer. After statistical analysis of a summer period when hand-held anemometer and weather-station data were recorded, it was determined that the hand-held anemometer data were consistent with those of the weather station (Thorrold et al., 1994b). No weather data were available for the month of December dur- ing the third winter or for the period from 1 through 10 January 1994. Current patterns were monitored with a General Oceanics Mark II current meter moored on the shelf edge at a depth of 10 meters (Fig. 1). Hourly current data were recorded for one month during the first Figure 1 Location of Lee Stocking Island, Bahamas, and channel-net stations. 668 Fishery Bulletin 93(4), 1995 winter (23 January to 22 February), throughout the entire second and fourth winters, and for the one summer sampling period. Current meter data were not available for the entire third winter. For analy- sis, hourly wind and current data were averaged over 24 hours to generate estimates of mean flow, which were then decomposed into along-shore and cross- shelf components of motion. Data analysis The A. vulpes leptocephali from all six nets for each night during the winter sampling periods were summed for time-series analysis. To analyze the re- lationship between recruitment patterns and lunar phase, time series of fish abundances for the four winters were joined according to lunar month. Nine days were deleted from the beginning and six days from the end of 1991-92 (winter 2), and three days were deleted from the beginning of 1993-94 to en- sure continuity with respect to the lunar month. Analyses were carried out on the resultant 277-day period. The time series was log 10 (x+1) transformed to minimize the influence of several large peaks in the data. All time-series analyses were completed by using the statistical package Mesosaur (Kuznetsov and Khalileev, 1991). A periodogram of the recruitment data was con- structed to identify dominant periodicities within the 277-day time series. An autocorrelation function was then plotted to describe more accurately the cyclical patterns of the data. Finally a cross-correlation was run between the abundance time series and the cor- responding "hours of dark flood tide" of each night, which previous studies had identified as an impor- tant variable affecting recruitment patterns of a number of taxa (Shenker et al., 1993; Thorrold et al., 1994b). The hours of dark flood tide is a measure of the total number of flood tide(s) that occur between sunset and sunrise under moonless conditions. This variable differs from lunar phase in a subtle but sig- nificant manner: as the time of moonrise becomes progressively later over consecutive nights, greater portions of the evening flood tide occur during dark- ness prior to moonrise. Because significant auto- correlations exist in both the larval abundance and the tidal time series, the resultant correlation coeffi- cients could not be assigned statistical significance, and therefore confidence limits are shown only for reference. These plots can be used to center periodi- cities in recruitment with respect to the hours of dark flood tide. Cross-correlations were used to examine responses of recruiting larvae to wind and current patterns. Because wind and current data were collected incon- sistently over the four winters, each year was ana- lyzed separately. Significant autocorrelations present in both recruitment and environmental data meant that standard correlation coefficients would be arti- ficially high (Chatfield, 1979). To remove the effects of these autocorrelations, ARIMA (Auto Regressive Integrated Moving Average) models were fitted to all data. Residuals generated from the ARIMA models were then used in the cross-correlations. Only those correlations that identified a response of larvae to particular wind and current patterns on a lag of up to three days (i.e. fish moving onshore up to three days after a specific wind or current pattern) are presented. Occasional correlations at lags of greater than three days were observed but are difficult to interpret in a biological sense and may be statistical artifacts. Although the one set of summer data was not long enough to permit rigorous analysis for cyclical pat- terns, and the level of recruitment was generally too low for correlation with environmental conditions, the data were examined for resemblance to patterns identified by the time series and correlation analy- ses of the winter data sets. Otolith analysis Otoliths were removed from 150 of the 875 larvae collected throughout the 1993-94 winter season. All fishes collected during this winter were preserved in 70% ethanol. Specimens selected for analysis were chosen from each day when recruits were captured. However, preservation problems in some larger samples prevented a more detailed examination of the hatching patterns of large pulses of recruits. Sagittae were dissected and mounted in cyanurate glue on a labelled glass slide. After curing for 24 hours, otoliths were polished down to the midplane with a graded series of lapping papers with grits ranging from 9 to 0.3 microns. A circle etched into the slide with an electronic engraver prevented the cyanurate glue from dislodging from the slide dur- ing polishing. Prepared slides were projected onto a computer screen at lOOOx by using a Sony TR81 cam- era integrated through a Macintosh 2CI computer equipped with Media-Grabber. This greatly facili- tated counting and allowed two readers indepen- dently to view the otolith(s) back- to-back under simi- lar lighting conditions. Otoliths were randomized and each otolith was read twice by each reader; if the different readers obtained mean counts within five increments of each other, the mean values were av- eraged and used for analysis. The otolith was dis- carded if differences in mean counts were greater than five increments. A total of 87 of the 150 mounted otoliths met this readability criterion. Mojica et al.: Recruitment of Albula vulpes 669 Results Winter environmental conditions Winds in Exuma Sound during the four winters gen- erally blew from the east or southeast; there is a con- siderable cross-shelf component of motion across the shelf edge that runs northwest-southeast (Fig. 2). The predominant along-shore component of the wind was towards the northwest. Passage of occasional storm fronts or cold fronts with winds from the northeast was characterized by cross-shelf winds at velocities exceed- ing 5 m-sec-1 and by along-shore flow to the southeast. Currents on the outer edge of the shelf flowed pre- dominantly along the shelf toward the northwest with only a weak cross-shelf component of motion (Fig. 2). Flow onto the shelf, and occasional current reversals along the shelf to the southeast were typi- cally associated with the passage of storm fronts (Shenkeretal., 1993). The hours of dark flood tide cycled throughout the study, ranging from 0 to 7 hours per night (Fig. 3). The nights with 0 hours of dark flood tide occurred when the full moon was visible during the entire night flood tide. During the week after each full moon, moonrise became progressively later each night, and the amount of flood tide occurring between sunset and moonrise increased rapidly. Temporal patterns of recruitment during winter A total of 3,079 A. vulpes leptocephali were collected during the 277 nights of sampling over four winters (Fig. 3). Recruitment levels varied greatly among years; a low of 316 leptocephali were taken the first winter and 1,421 during the third winter. Several large peaks in recruitment, reaching a maximum of 190 fish/night, were detected during the third and fourth winters. Over all four years, 90.2% of the lep- tocephali were captured by the nets fishing the up- per 1 meter of the water column. Periodogram analysis of A. vulpes recruitment in- dicated a very strong cycle with a period of 30.7 days, which suggests a lunar or tidally influenced cycle (Fig. 4). Autocorrelation of recruitment data (Fig. 4) also identified cycling centered around 30 days. Cross-correlations between recruitment and hours of dark flood tide (Fig. 4) showed a strong positive association on nights with a high degree of flood tide occurring during moonless portions of the night and a negative relationship centered around the full moon. Cross-shelf wind Along-shore wind 199091 1991-92 1992-93 Cross-shelf current 1990-91 1991-92 1992-93 1993-94 Along-shore current 'Y W 30 20 10 0 -10 -20 -30 Figure 2 Cross-shelf (above line=movement offshore, below line=movement onshore land along-shore (above line=to northwest, below line=to southeast) components of motion for wind and currents at Lee Stocking Island. Dotted vertical lines indicate where years are joined by lunar date. Solid bars on abscissae indicate when no data were available. 670 Fishery Bulletin 93(4), 1995 200 150 100 • •••• •••• 1990-91 1991-92 1992-93 1993-94 n = 316 n=467 n= 1,421 n = 87S • • • • 1990-91 1991-92 • • • • • 1992-93 1993-94 Figure 3 The total hours per night when the moon was below the horizon and the tide was flooding (hours of dark flood) throughout the four winter study periods (top graph). Dotted vertical lines indicate where years are joined by lunar date. Circles on abscissae indicate new moons. Total abundance of bonefish, Albula vulpes, larvae col- lected by channel nets during the four consecu- tive winters (bottom graph). Values above each year indicate total catch. Few significant correlations between recruitment of bonefish and oceanographic or meteorological con- ditions were detected (Table 1). Recruitment was positively correlated with along-shore winds to the northwest with a lag of zero days for the 1991-92 season, whereas recruitment peaks the following winter lagged winds to the southeast by three days. No significant relationships between along-shore winds and recruitment were found during the other two winters, nor were relationships detected between recruitment and cross-shelf winds or either cross- shelf or along-shore currents. Temporal patterns of recruitment during summer A total of 1.112A. vulpes leptocephali were collected during summer 1992. Over 76% of these fishes were O O o 30 9.5 5.6 4 3.1 2.5 2.1 Cycling period (days) -0.2 5 10 15 20 25 30 35 40 45 Lag (days) o o "°'6-20 -15 -10 -5 0 5 10 15 20 Lag (days) Figure 4 Periodogram plot of logged larval concentrations of bonefish, Albula vulpes (top graph), auto- correlation function of log (rc + 1) larval abundance l middle graph) and cross-correlation function of log (n + 1) larval abundance with hours of dark flood tide (bottom graph). All analyses were con- ducted on the 277-day period which resulted from joining the four years of recruitment (and hours of dark flood) by lunar date. Dashed lines in autocorrelation and cross-correlation plots indi- cate approximate 95% confidence intervals. The cross-correlation plot coincides with lunar days starting with the new moon (lag of zero). taken during the first 12 days of the 72-day sam- pling season, and a peak of 160 leptocephali were taken during a single night (Fig. 5). Although this sampling period is too short for time-series analysis, recruitment appears to be limited to periods with relatively high amounts of flood tide occurring un- Mojica et al.: Recruitment of Albula vulpes 671 der moonless conditions (Fig. 5). The single peak in recruitment was not associated with specific wind or cur- rent patterns (data not shown); the very low numbers of fishes collected during following months precluded use of correlation analysis to exam- ine the relationship between recruit- ment and environmental conditions. Larval ages and spawning patterns Though the formation of daily otolith increments for A. vulpes has yet to be confirmed, the daily formation of increments in Anguilla japonica lep- tocephali has been verified (Ume- zawa et al., 1989). We thus assumed that increments are produced daily in bonefish and that deposition of increments begins at hatching. Given these assumptions, the average lar- val duration was 56 days, a range of Table 1 Results of cross-correlation analyses between recruitment of A. vulpes and along-shore and cross-shelf wind and current vectors for four winters. The table shows all significant correlation coefficients between larval recruitment and wind and current data, with a lag corresponding to the number of days indicated. Positive correlations indicate signficiant relationships with trans- port to the northwest (along-shore component) or offshore (cross-shelf compo- nent!. Numbers below years in parenthesis indicate the number of days used in each analysis. NS = not significant (a=0. 05 ). ID = insufficient current meter data for analysis. Year 1990-1991 (72) 1991-1992 (62) 1992-1993 (55) 1993-1994 (58) Wind Current Along-shore Cross-shelf Along-shore Cross-shelf NS 0.28/0 days -0.22/3 days NS NS NS NS NS ID NS ID NS ID NS ID NS D E '' ■ '"'■ '"■■ ■■■'■■■ ■ litfll J July August Summer 1992 Figure 5 Abundance of bonefish, Albula vulpes, larvae collected each night from 24 June to 4 Septem- ber 1992 (top graph) and hours of dark flood tide during the sampling period (bottom graph). 41-71 days (Fig. 6). Regression analysis of back-cal- culated hatching date and recruitment date revealed a strong relationship. Backcalculation of hatching dates from otolith data indicated continuous spawn- ing from mid-October through early January (Fig. 6). The maximum number of otoliths examined per day was 7 for fish recruiting on 30 January. The back- calculated spawning dates of these fish ranged from 16 November to 27 December. Discussion Variation in the recruitment of tropical marine fishes is considered to be a dominant influence on the size and distribution of adult populations. Doherty and Fowler (1994) have shown that variations in the re- cruitment of a reef-dwelling territorial pomacentrid over a ten-year period could explain 909c of the varia- tion in adult populations. Dramatic variability in larval recruitment has been detected by light trap surveys (e.g. Doherty, 1987; Milicich et al., 1992), visual surveys (e.g. Sale, 1980; Robertson et al., 1988; Robertson, 1992), and calculation of settlement pat- terns from otoliths (e.g. Thresher et al., 1989; Wellington and Victor, 1989). Recent work in the Bahamas (Shenker et al., 1993;Thorroldet al., 1994, a and b) and French Polynesia (Dufour and Gazlin, 1993) have shown that moored channel nets can be used to monitor onshore larval movement directly 672 Fishery Bulletin 93(4), 1995 E 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 Larval duration Dec Nov Recruit = 52 187*1 11 (hatch) . R1 = 0 89 • n = 87 y/ • • • • * .^^ • '-Bee Jan Feb Recruitment date Figure 6 Frequency distribution of estimated larval duration (top graph) and relationship between estimated hatching date and recruitment date (bottom graph) of bonefish, Albula vulpes, collected during winter 1993-94. through tidal passes and can help elucidate the pat- terns of recruitment and mechanisms driving trans- port. Although adult population sizes of highly mo- bile fishes such as Albula vulpes have yet to be mea- sured, it is likely that whatever variation does occur in the abundance of adults is at least partially af- fected by recruitment variability. A virtually universal pattern observed by studies on daily recruitment of tropical marine fishes is the association of peaks of recruitment with dark phases of the lunar cycle (Pfeiler, 1984; Robertson et al., 1988; Robertson, 1992; Dufour and Gazlin, 1993; Shenker et al., 1993; Thorrold et al., 1994, a and b). This pattern may be a function of a lunar spawning cycle, followed by a fixed larval duration. Alterna- tively, it may be an active response of fishes, enabling them to remain in the plankton until dark conditions permit them to move onshore, thus enabling them to avoid the "wall of mouths" of visual predators along reef edges (Hamner et al., 1988) and at settlement sites. Our data suggest that A. vulpes follows the latter strategy. Analysis of larval otoliths of winter recruits (assuming that otolith increments are deposited daily, beginning at hatching) indicates that these fish spawn continuously from late October through De- cember (Fig. 6). However, owing to preservation prob- lems with some of the large recruitment pulses (>100 animals/night) in winter 1993-94, when otolith analyses were performed, we cannot exclude the pos- sibility that the level of spawning activity varies over time. Significant spawning activity in the Bahamas probably extends until spring, with the large pulse of recruitment in late June 1992 presumably result- ing from spawning in April and May. After hatching, leptocephali remained in the pe- lagic environment of Exuma Sound for 41-71 days (with a mean of 56 d) in winter 1993-94. Despite this relatively broad range of larval duration, the metamorphosing larvae exhibited a very strong cy- clical recruitment pattern (Fig. 4) that was not con- sistently related to meteorological conditions or cur- rents measured along the shelf-edge seaward of the sampling stations (Table 1). This response supports the contention of Thorrold et al. (1994, a and b) that various species can actively control their onshore movements in certain environments, perhaps by de- laying their metamorphosis until suitable environ- mental conditions or opportunities develop (Welling- ton and Victor, 1989). However, variable shrinkage of leptocephali, due to different times between cap- ture, death in the nets, and preservation, prevented backcalculation of growth rates and a test of the abil- ity of A. vulpes to delay metamorphosis. In series of ichthyoplankton surveys from Janu- ary through February 1991, A. vulpes leptocephali were found to be widely dispersed at night over a transect extending from the shelf edge near LSI to 24 km offshore (Drass, 1992), indicating that some larvae were always close enough to the shore so that they might become entrained in the flood tides crossing the narrow shelf. Despite the continuous presence of leptocephali close to the coast, however, their onshore movement was temporally restricted. The occurrence of favorable low nocturnal illumina- tion levels may be the parameter that limits cross- shelf movement of larvae to specific "windows of op- portunity." These windows of opportunity were de- fined by the relationship between lunar and tidal conditions. During bright, moonlit nights, recruit- ment levels were very low (Figs. 3 and 5); recruit- ment increased as larger amounts of night-time flood tide occurred prior to the progressively later moon- rise. Extremely little recruitment occurred on nights when there were less than two hours of nocturnal flood tide under moonless conditions, whereas the Mojica et a/.: Recruitment of Albula vulpes 673 Hours of dark flood tide per night Figure 7 Number of bonefish, Albula vulpes, collected versus hours of flood tide occurring under moonless conditions. Most recruitment occurred on nights with >4 hours of flood tide under moonless conditions. great majority of recruitment was observed on nights with more than four hours of dark flood tide (Fig. 7). The restriction of recruitment to these windows of opportunity may be responsible for the apparent bi- modality in the age distribution of leptocephali (Fig. 6), although larger numbers of organisms need to be examined to test this possibility. Additional work is needed to determine whether onshore movement is concentrated in specific portion(s) of a flood tide and how cloud cover can affect lunar illumination and recruitment. Active vertical migration may be the mechanism by which larvae influence the timing of onshore mi- gration (Shenkeret al., 1993). Early larvae were dis- tributed through the pelagic environment of Exuma Sound to depths of 25-50 m (Drass, 1992). Migra- tion of settlement-stage individuals toward the sur- face only under dark night conditions could enhance the entrainment of larvae into onshore tidal and wind-driven flow. The fact that over 90% of the A. vulpes larvae were taken by the channel nets in the upper 1 m of the water column during dark-night recruitment pulses, when only a relatively few lar- vae were found 2-4 m below the surface, indicates that these leptocephali do indeed selectively utilize the surface layer during their onshore movement. The recruitment of A. vulpes leptocephali varied greatly among days, months, and years. This vari- ability was generally not correlated with specific wind or shelf-edge current patterns (Table 1), unlike the very close association between a major settlement episode of Nassau grouper, Epinephelus striatus, and a storm event at LSI in February 1991 (Shenker et al., 1993). Recruitment of A. vulpes was thus more similar to that of other taxa recruiting near LSI (e.g. Bothidae and Labridae) that showed a lunar period- icity in recruitment but not a strong association with environmental parameters (Thorrold et al., 1994, a and b). The lack of strong correlation between envi- ronmental conditions and recruitment and the high degree of recruitment variability among months and years suggest that the processes controlling the sup- ply of larvae are acting prior to their onshore move- ment in Exuma Sound. These processes span the range from spawning success to larval survival in the pelagic environment and will require additional sampling for evaluation of their potential roles as bottle- necks in the population of A. vulpes in the Bahamas. Acknowledgments This research was conducted at the Caribbean Ma- rine Research Center's station on Lee Stocking Is- land and was funded by grants from the National Undersea Research Program of the National Oceano- graphic and Atmospheric Administration. The au- thors would like to thank Doug Markle and an anony- mous reviewer for their constructive and insightful comments. Special thanks are due to E. Maddox, H. Patterson, S. Thorrold, and E. Wishinski for their contributions. Otolith analysis was greatly facilitated by using K. Clark's Macintosh work station (NSF Grant BIR 8951326). We thank all of the staff on Lee Stocking Island who assisted with this project and the army of volunteers who made it possible. Literature cited Bruger, G. E. 1974. Age, growth, food habits, and reproduction of bone- fish, Albula vulpes, in south Florida waters. Fl. Mar. Res. Publ. 3, 20 p. Chatfield, C. 1979. The analysis of time series: an introduction. Chap- man and Hall, London. Colton, D. E., and W. S. Alevizon. 1983. Feeding ecology of bonefish in Bahamian waters. Trans. Am. Fish. Soc. 112:178-184. Doherty, P. J. 1987. Light traps: selective but useful devices for quanti- fying the distributions and abundances of larval fishes. Bull. Mar. Sci. 41:423^131. Doherty, P. J., and A. J. Fowler. 1994. An empirical test of recruitment limitation in a coral reef fish on the Great Barrier Reef. Science (Wash. D.C.) 263:935-939. Drass, D. M. 1992. Onshore movements and distribution of leptocephali (Osteichthyes: Elopomorpha) in the Bahamas. M.S. the- sis, Florida Institute of Technology, Melbourne. FL, 85 p. 674 Fishery Bulletin 93(4), 1995 Dufour, V., and R. Gazlin. 1993. Colonization patterns of reef fish larvae to the la- goon at Moorea Island, French-Polynesia. Mar. Ecol. Prog. Ser. 102:143-152. Eldred, B. 1967. Larval bonefish, Albula vulpes (Linnaeus, 1758) (Albulidae), in Florida and adjacent waters. Fl. Board Conserv. Mar. Res. Lab. Leafl. Ser. 4, l(3):l-4. Hamner, W. M., M. S. Jones, J. H. Carleton, L. R. Hauri, and D. M. Williams. 1988. Zooplankton, planktivorous fish, and water currents on a windward reef face: Great Barrier Reef, Australia. Bull. Mar. Sci. 42:459-479. Kuznetsov, S., and A. Khalileev. 1991. Mesosaur: a companion to SYSTAT. JV Dialogue and SYSTAT, Inc., Evanston, Illinois. Milicich, M. J., M. G. Meekan, and P. J. Doherty. 1992. Larval supply: a good predictor of recruitment of three species of reef fish (Pomacentridae). Mar. Ecol. Prog. Ser. 86:153-166. Pfeiler, E. 1984. Inshore migration, seasonal distribution and sizes of larval bonefish, Albu la, in the Gulf of California. Environ. Biol. Fishes 10:117-122. Pfeiler, E., M. A. Mendoza, and F. E. Manrique. 1988. Premetamorphic bonefish {Albula sp.) leptocephali from the Gulf of California with comments on life history. Environ. Biol. Fishes 21:241-249. Robertson, D. R. 1992. Patterns of lunar settlement and early recruitment in Caribbean reef fishes in Panama. Mar. Biol. 114:527-537. Robertson, D. R., D. G. Green, and B. C. Victor. 1988. Temporal coupling of reproduction and recruitment of larvae of a Caribbean reef fish. Ecology 69:370-381. Sale, P. F. 1980. The ecology of fishes on coral reefs. Oceanogr. Mar. Biol. Annu. Rev. 18:367-421. Shenker, J. M., E. D. Maddox, E. Wishinski, S. Pearl, S. R. Thorrold, and N. Smith. 1993. Onshore transport of settlement-stage Nassau Grou- per (Epinephelus striatus) and other fishes in Exuma Sound, Bahamas. Mar. Ecol. Prog. Ser. 98:31-43. Smith, D. G. 1989. Order Elopiformes: families Elopidae, Megalopidae, Albulidae: Leptocephali. In E. B. Bohlke (ed.), Fishes of the Western North Atlantic. Part 9, Vol. 2: Leptocephali, p. 961-972. Thompson, B. A., and L. A. Deegan. 1982. Distribution of ladyfish (Elops saurus) and bonefish (Albula vulpes) leptocephali in Louisiana. Bull Mar. Sci. 32(4):936-939. Thorrold, S. R., J. M. Shenker, E. Wishinski, R. Mojica, and E. D. Maddox. 1994a. Larval supply of shorefishes to nursery habitats around Lee Stocking Island, Bahamas. I: Small-scale dis- tribution patterns. Mar. Biol. 118:555-566. Thorrold, S. R., J. M. Shenker, E. D. Maddox, R. Mojica, and E. Wishinski. 1994b. Larval supply of shorefishes to nursery habitats around Lee Stocking Island, Bahamas. II: Lunar and oceanographic influences. Mar. Biol. 118:567-578. Thresher, R. E., P. L. Colin, and L. J. Bell. 1989. Planktonic duration, distribution and population structure of western and central Pacific damselfishes (Pomacentridae). Copeia 1989: 420-434. Umezawa, A., K. Tsukamoto, and K. Mori. 1989. Daily growth increments in the larval otolith of the Japanese eel, Anguilla japonica. Jpn. J. Ichthyol. 35: 434-439. Wellington, G. M., and B. C. Victor. 1989. Planktonic larval duration of one hundred species of Pacific and Atlantic damselfishes (Pomacentridae). Mar. Biol. 101:557-567. ADStraCt. — The windowpane, Scophthalmus aquosus, is a shallow water (<110 m), resident species of the Middle Atlantic Bight (and adjacent estuaries) and Georges Bank, although it may undergo short (both inshore-off- shore and alongshore) migrations in response to seasonal temperature changes. Spawning occurred through- out the Middle Atlantic Bight during the period from 1977 to 1987 but was most pronounced on Georges Bank. The timing of spawning, determined from the collection of 2-4 mm larvae, varied with location; and a split spawning sea- son (April-May and October-Novem- ber) was evident in the Middle Atlan- tic Bight. Spawning on Georges Bank peaked in August. Although spawning occurred over a broad temperature range (5-23°C), the optimal tempera- ture was 16-19°C in the Middle Atlan- tic Bight and 13-16°C on Georges Bank. Larval development occurred in areas of spawning and was most prolonged on Georges Bank, where the largest larvae (13-20 mm) were consistently found. Few larvae >8 mm were cap- tured in the Middle Atlantic Bight. On the basis of samples from southern New Jersey, settlement probably occurs on the continental shelf and in adjacent estuaries of the Middle Atlantic Bight. The growth patterns of young of the year varied with the timing of spawn- ing and subsequent settlement. In the first six months, fish of the spring- spawned cohort grew to 11-19 cm TL whereas those of the fall-spawned co- hort grew to just 4-8 cm TL within that time. These data contribute to our un- derstanding of the distribution and early life history of windowpane on the continental shelf, though the role of es- tuaries in the Middle Atlantic Bight is incompletely known. Distribution and life history of windowpane, Scophthalmus aquosus, off the northeastern United States Wallace W. Morse James J. Howard Laboratory National Marine Fisheries Service, NOAA Highlands, New Jersey 07732 Kenneth W. Able Marine Field Station, Institute of Marine and Coastal Sciences Rutgers University, 800 Great Bay Blvd. Tuckerton, New Jersey 08087 Manuscript accepted 24 April 1995. Fishery Bulletin 93:675-693 ( 1995). 675 The windowpane, Scophthalmus aquosus, is an endemic bothid of the northwest Atlantic Ocean and is distributed from the Gulf of Saint Lawrence (47°N) to Florida (27°N) (Scott and Scott, 1988) but is most abundant from Georges Bank (42°N) to Chesapeake Bay (38°N) (Bigelow and Schroeder, 1953; Dery and Livingstone, 1982). Windowpane are distributed in shallow waters (<110 m, mostly <56 m) (Wenner and Sedberry, 1989; Thorpe, 1991). Their distribution extends shore- ward to depths of 1-2 m ( Warfel and Merriman, 1944) and they are of- ten abundant in large estuaries such as Chesapeake Bay (Hilde- brand and Schroeder, 1928), Dela- ware Bay (de Sylva et al., 1962), Sandy Hook Bay (Wilk and Silver- man, 1976), Long Island Sound (Moore, 1947), and Narragansett Bay (Oviatt and Nixon, 1973; Jeffries and Johnson, 1973). Distribution patterns of juveniles and adults on the continental shelf between Nova Scotia and Cape Hatteras, North Carolina, are similar and indicate limited seasonal movement (Dery and Livingstone, 1982; Azarovitz and Grosslein, 1987; Thorpe, 1991). However, tagging experiments showed that some adults traveled about 150 km along the coast in three months (Moore, 1947). Juve- niles (<24 cm total length [TL]) in the Georges Bank area were concen- trated along the southern boundary of the bank and inshore along Long Island during spring (mean depth 26.6 m) and on the central portion of the bank in fall (mean depth 38.3 m) (Wigley and Gabriel, 1991). Re- cent estimates of length at sexual maturity show that 50% were ma- ture between 21 and 23 cm TL (O'Brien etal., 1993). Windowpane are currently ex- ploited for human consumption, pri- marily in the Georges Bank area. Annual commercial landings from 1975 through 1988 averaged 2.03 million kg and peaked in 1985 at 4.21 million kg (ICNAF, 1977-85; NAFO, 1982-91). Relative abun- dance indices estimated from Na- tional Marine Fisheries Service (NMFS) research trawl surveys (Azarovitz, 1981) for 1964-89 show considerable year-to-year fluctua- tions in both numbers and biomass (Thorpe, 1991). Peaks in biomass appear to have occurred on Georges Bank during the mid-to-late-1970's and again in the mid-1980's. Gonadal development (Wilk et al., 1990) and egg and larval distribu- 676 Fishery Bulletin 93(4), 1995 tions (Colton and St. Onge, 1974; Smith et al., 1975; Colton et al., 1979; Morse et al., 1987), show that spawning occurs from April through December. There is contradictory evidence for a split spawning sea- son. Gonadal development (Wilk et al., 1990) indi- cated that spawning off New Jersey and New York peaks in May and again in September. Split spawn- ing was reported to occur off Virginia and North Caro- lina (Smith et al., 1975) for Long Island Sound (Wheatland, 1956) and for Great South Bay, New York (Dugay et al., 1989; Monteleone, 1992). How- ever, other studies found no evidence for a split spawning season in either Long Island Sound (Perlmutter, 1939) or in ocean waters north of Vir- ginia (Smith et al., 1975). In addition, Colton and St. Onge (1974) collected larvae on Georges Bank from July to November and found no indication of a split spawning season. Spawning apparently occurs at bottom water temperatures of 6-20°C (Bigelow and Schroeder, 1953; Wheatland, 1956; Smith et al., 1975). Most spawning (70%) off Virginia and North Carolina was found over bottom temperatures be- tween 8.5 and 13.5°C; spawning stopped when tem- peratures exceeded 15°C (Smith et al., 1975). This study presents analyses of the reproductive seasonality of windowpane based on seasonal shifts in larval abundance and on their relationships to bottom water temperatures. Bottom trawl catches and published accounts of distribution and abun- dances are used to follow the fate of the young flat- fish after they settle to the bottom. Together these data describe the seasonal distribution, abundance, and life history of windowpane in the Middle Atlan- tic Bight and on Georges Bank. Materials and methods Larvae Data from a variety of sources have been analyzed (Table 1). Larval windowpane were collected from continental shelf waters from Cape Hatteras, North Carolina, to Nova Scotia during NMFS Marine Re- sources Monitoring, Assessment, and Prediction (MARMAP) surveys from 1977 to 1987 (Sherman, 1980). Surveys were conducted six to eight times each year and occupied 150-180 stations (Fig. 1). At each station, a 61-cm bongo net array was lowered to within 5 m of the bottom or to a maximum depth of 200 m. Fish larvae from a 0.505-mm mesh net were identified to the lowest taxon possible, enumerated, measured (±0.1 mm) and rounded to the nearest whole millimeter as either notochord or standard length. Catches were standardized to the number of larvae under 100 m2 of sea surface on the basis of the depth of the tow and the volume of water filtered (Sibunka and Silverman, 1984, 1989). An additional Table 1 Sources of data on sampling areas. windowpane, Scophthalmus aquosus, that were analyzed for this study. See Figures 1 and 2 for location of Source Life stage Location Collecting gear Sampling years Sampling depths (m) Number of samples Number offish collected NMFS, MARMAP (Sherman, 1980) Larvae Nova Scotia- Cape Hatteras Bongo nets 1977-1987 8-1,500 8,787 14,177 NMFS, Groundfish (Azarovitz, 1981) Juveniles and adults Nova Scotia- Cape Hatteras Bottom trawl 1982-1990 5-366 7,099 26,433 Massachusetts Trawl Survey (Howeetal., 1979) Juveniles and adults Coastal Massachusetts Bottom trawl 1982-1990 4-82 1,688 21,272 Milstein and Thomas, 1977 Eggs, larvae, juveniles, and adults Great Bay, Mullica River, Beach Haven Ridge, NJ Beach seines, Plankton nets, Bottom trawls 1972-1975 Seines: < 2 Plankton: 1.5-19.5 Trawls: 1-45 Seines: 1,524 Plankton: 166 Trawls: 717 127 801 5,309 New Jersey Trawl Survey' Juveniles and adults Coastal New Jersey Bottom trawl 1988-1992 5-27 603 25,580 See Footnotes 3 and 4 in the text. Morse and Able: Distribution and life history of Scophthalmus aquosus 677 44 42" 40° 38 - 36" N W 76 Figure 1 Sampling area for planktonic larvae in the northeastern United States, based on NMFS/MARMAP sampling stations, and important localities that are mentioned in the text. Typical sampling array of stations shown by dots. See Table 1 for further details. Middle Atlantic Bight = subareas 1- 6, Georges Bank = subarea 7. length-dependent correction was made to the catches to account for differences in day, night, and twilight catchability (Morse, 1989). Preliminary analysis of larval occurrence and bottom depth revealed that larvae are restricted to waters <100 m deep; there- fore, only stations <100 m deep were used for calcu- lating larval catch statistics. In addition, larvae were extremely rare north of 42°N (caught at only 24 of 2,470 stations); therefore, this area was not consid- ered in the analysis. Mean catches of windowpane larvae were calculated by using the Delta method of Pennington (1983). Graphical plots of the distribu- tion and abundance of larvae are presented as the average catch per 100 m2 within 625 km2 blocks of the survey area. Eggs and larvae were sampled at estuarine and inner continental shelf sites during 1972-75 (Table 1; Fig. 2). These sites included the Mullica River (water depth 1.8-10.6 m), Great Bay (1.5-10.7 m), Little Egg Inlet (4.6-8.8 m), in the vi- cinity of sand ridges outside Little Egg Inlet (3.0- 16.5 m), and farther offshore of the sand ridge sites ( 16.2-23.5 m). At continental shelf sites, 15-minute tows were made at the sur- face ( 1.0-m plankton net, 0.5-mm mesh), at midwater and bottom depths (0.5-m plankton net, 0.5-mm mesh), and as ob- lique tows (bongo samplers, 0.2-m or 0.36-m diameter, 0.5-mm mesh). In the estuary tow times were reduced to 5- 10 minutes but the same three nets were used at the same depths. Esti- mates of water volume filtered were de- termined with a flowmeter. Juveniles and adults Juvenile and adult windowpane (2-48 cm TL ) were collected during the semi- annual bottom trawl surveys of NMFS, Northeast Fisheries Science Center, from 1982 to 1991 (Azarovitz, 1981), during inshore surveys of the Common- wealth of Massachusetts Division of Marine Fisheries from 1988 to 1992 (Howe et al.1), and during the New Jer- sey Bureau of Marine Fisheries surveys from 1988 to 1992 (Byrne2-3). All three surveys used a stratified random-sam- pling design, and strata were based on depth and latitude. NMFS spring and fall surveys sampled about 350 stations during a 6—8 week period from Cape Fear, North Carolina, to Nova Scotia in depths from 3 to 366 m. Commonwealth of Massachusetts Division of Marine Fisheries sampled approximately 80-90 stations within 55-m depths in state coastal waters during May and September. New Jersey Bureau of Marine Fisheries sampled 25-39 stations in state coastal wa- ters within 27 m of water every 6-10 weeks. For the analysis of NMFS bottom trawl and plank- ton surveys, the sampling area was divided into seven subareas (Fig.l). Data from monthly collections of larval, juvenile, and adult windowpane near Little Egg Inlet, New Jersey, during 1973-74 (Fig. 2) were Howe, A. B., D. Maclsaac, B. T. Estrella, and F. J. Germano Jr. 1979. Fishery resource assessment, coastal Massa- chusetts. Completion Rep., Massachusetts Div. Mar. Fish., Commercial Fish. Res. Div. Project No. 3-287-R-l, 34 p. Byrne, D. M. 1988. Inventory of New Jersey's coastal waters. New Jersey Dep. Environmental Protection, Div. Fish, Game, Wildl. Mar. Fish. Admin., Bur. Mar. Fish. Annual Rep. to U.S. Fish. Wildl. Serv. Byrne, D. M. 1990. Inventory of New Jersey's coastal waters. NJDEP, Div. Fish., Game, Wildl, Mar. Fish. Admin., Bur. Mar. Fish. Annual Rep. to U.S. Fish. Wildl. Serv. 678 Fishery Bulletin 93(4). 1995 summarized from Thomas et al.,4 Thomas et al.,5 and Milstein and Thomas (1977). Results Spawning season and location We assumed that the temporal and spatial patterns of the distribution and abundance of the smallest lar- vae (2-4 mm) indicated the timing and the areas of spawning on the continental shelf (Fig. 3). Larvae were distributed from nearshore to mid-shelf in subareas 1-6 and over the shallower portion of subarea 7. The highest average concentrations of small larvae occurred in subarea 7, especially in the central portion. Larvae 2-4 mm long were first cap- tured in April in subareas 1-3 and by May they were in all subareas (Table 2). Catches in subareas 1—4 clearly showed a split spawning sea- son (Fig. 4), and similar, though less pronounced, patterns were evident in subareas 5 and 6. A peak in abun- dance of small larvae occurred in May and a larger peak occurred in November in subareas 1-4. Subar- eas 4—5 showed light spawning dur- ing spring and a significant peak in October. In subarea 6, split spawn- ing was less discernible; only a slight peak in abundance of small larvae occurred in June, but major spawning was indicated in October. There was unimodal spawning, with the peak abundance in August, in subarea 7. Fall catches of small larvae in subareas 1—6 are often 5—20 times higher than peak catches earlier in the year. ♦ Seine Stations ■ Ichthyoplankton Stations • Trawl Stations W •sw**5 0 Kilometers 5 Figure 2 Sampling locations for seine, trawl, and ichthyoplankton samples in southern New Jersey habitats in the vicinity of Great Bay during 1970-74 based on Milstein and Thomas (1977). Site 2 includes all stations offshore of site 1. See Figure 1 for general location of sampling area. 4 Thomas, D. L., C. B. Milstein, T. R. Tatham, R. C. Bieder, F. J. Margraf, D. J. Danila, H. K. Hoff, E. A. Illjes, M. M. McCullough, and F. A. Swiecicki. 1974. Ecological studies in the bays and other waterways near Little Egg Inlet and in the ocean in the vicinity of the site for the Atlantic generating station, New Jersey. Progress Rep. for the period January-December 1973. Vol. 1: Fishes. Ichthyological Associates, Inc., 709 p. 5 Thomas, D. L., C. B. Milstein, T. R. Tatham, R. C. Bieder, D. J. Danila, H. K. Hoff, D. P. Swiecicki, R. P. Smith. G. J. Miller, J. J. Gift, andM.C. Wyllie. 1975. Ecological studies in the bays and other waterways near Little Egg Inlet and in the ocean in the vicinity of the site for the Atlantic generating station, New Jersey. Progress Rep. for the period January-December 1974. Vol. I: Fishes. Ichthyological Associates, Inc., 490 p. The monthly progression of the peak catches of 2—4 mm larvae from the southern extreme of the study area in May to subarea 7 in July-September and the return of peak catches to subareas 1-3 in November indicate that water temperature may be controlling spawning times and areas (Fig. 4). Win- dowpane probably spawn on or near the bottom; therefore bottom water temperatures were used to indicate spawning temperatures. Only stations with bottom depths <100 m are presented. The maximum abundance of 2-4 mm larvae occurred at tempera- tures 15-19°C in subareas 1-6 and at 14-15°C in subarea 7 (Fig. 5). The range of bottom temperatures where larvae were caught was 5— 23°C. The broadest range of temperatures for 2-4 mm larvae was in sub- area 5. Maximum temperature of occurrence was highest in subarea 1 at 23°C and gradually decreased Morse and Able: Distribution and life history of Scophthalmus aquosus 679 northward to 16°C in subarea 7. Minimum tempera- tures ranged from 5 to 9°C, but no clear latitudinal trend was evident. Over 80% of all larvae 2-4 mm long throughout the study area were collected over Figure 3 Distribution and abundance of windowpane, Scophthalmus aquosus, larvae for three size classes, based on NMFS/MARMAP sample col- lections. See Table 1 for additional details. bottom temperatures 16-19°C, which indicate pre- ferred spawning temperatures. Only in subareas 5 and 7 were larvae captured in significant numbers at temperatures below 15°C. Over 859c of larvae in subarea 7 occurred at temperatures 13-16°C, and 16°C was also the maximum bottom temperature recorded in subarea 7. Although the preferred spawning temperature range (16-19°C) spans just 4°C, the total range of temperatures (5-23°C) indicates that spawning may not be tied exclusively to water temperatures. In subareas 1-3, bottom waters in the preferred range of temperature ( 16-19°C) are available most months (Fig. 6). However, even though spawning in these subareas is bimodal (see Fig. 4), the peak in spawn- ing clearly occurs at 17°C (see Fig. 5). In subarea 7, spawning occurs at the highest bottom temperatures recorded (13-16°C) in this subarea (Fig. 6). These temperatures are available from July through No- vember (Fig. 6), a range that nearly corresponds to the months of maximum spawning ( Table 2; Fig. 4). Thus, in subarea 7 the occurrence of the highest tempera- 200 100 0 150 75 Subarea 7 ill! Subarea 6 ,1. 160 80 Subarea 5 -■■_■ Il rvae/100 r o o 3 O O C Subarea 4 . m — _ -1 300 200 100 Subarea 3 .1 400 200 0 60 40 20 Subarea 2 1 Subarea 1 . 1 1 Monthl; Scophtht onNMF J FMAMJ JASOND Month Figure 4 / abundance 2-4 mm windowpane, limits aquosus, larvae by subarea, based S/MARMAP sampling. 680 Fishery Bulletin 93(4). 1995 Table 2 Abundance (mean number/100 m2) of windowpane, Scophthalmus aquosus, larvae by subarea and length (mm) from MARMAP surveys off northeastern United States during 1977-87. N: = total number of stations sampled; N0 = number of stations with windowpane; Mn = mean number/100 m2 for 2-20 mm larvae; and SE = standard error of Mn. January February Subareas Subareas Length (mm) 10 11 12 13 14 15 16 17 18 19 20 W« Mn SE 1.22 1.65 1.53 0.90 4.82 2.42 0.84 30 18 24 25 60 52 65 2 1 2 0 1 0 0 1.20 2.68 1.99 1.61 0.85 2.68 1.38 1.61 March Subareas 60 0 41 0 52 0 45 0 39 1 1.03 1.03 41 0 87 0 April Subareas Length (mm) 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 W« Mn SE 0.66 0.51 1.05 1.56 0.30 0.56 121 99 111 102 145 115 89 1 0 0 0 1 0 0 0.28 0.72 0.28 0.72 77 50 80 107 169 112 187 2 1 2 0 0 0 0 0.53 0.59 2.81 0.37 0.59 2.21 Morse and Able Distribution and life history of Scophthalmus aquosus 681 Table 2 (continued) May June Subareas Subareas Length (mm) 1 2 3 4 5 6 7 1 2 3 4 5 6 7 2 1.92 9.08 3.14 7.86 10.98 0.22 4.17 6.11 12.55 5.72 3 11.86 28.37 21.29 14.67 5.28 3.21 0.71 0.46 5.16 19.89 6.81 6.42 4 11.24 11.75 7.14 2.75 1.70 0.74 3.12 1.19 5.75 9.61 4.23 5 4.97 6.03 2.60 1.00 0.63 3.49 3.12 3.14 1.68 6 2.03 1.73 0.78 1.12 1.07 2.36 0.75 7 0.77 1.06 1.07 0.37 1.14 0.86 0.29 0.36 8 0.92 0.47 0.25 9 1.63 10 0.45 11 12 0.21 13 14 15 0.21 16 17 18 0.35 19 20 Wi 130 86 112 111 167 121 171 65 48 66 73 93 75 81 ^0 38 28 38 18 22 1 2 1 3 6 16 34 3 8 Mn 48.44 120.31 61.70 22.68 14.44 1.43 0.9 2.54 11.77 7.56 26.32 73.41 25.35 23.87 SE 11.75 35.83 13.19 7.84 4.17 1.43 0.6 2.54 7.65 3.33 9.30 15.62 18.47 12.26 July August Subareas Subareas Length (mm) 1 2 3 4 5 6 7 1 2 3 4 5 6 7 2 1.25 0.24 0.57 6.01 0.98 1.99 6.57 0.51 2.29 4.95 10.73 3 1.34 1.77 4.78 12.08 4.23 15.78 5.06 1.57 2.29 3.54 43.10 4 0.47 2.82 8.82 1.95 17.74 1.15 0.66 0.27 0.78 3.44 27.05 5 0.51 2.78 6.44 1.03 21.00 0.18 0.85 0.65 15.49 6 1.83 2.29 3.15 13.79 0.52 3.36 10.08 7 0.95 1.70 0.41 13.58 0.30 0.44 0.45 9.28 8 0.92 1.25 9.62 0.34 1.74 8.05 9 0.64 0.41 4.03 1.50 5.66 10 0.07 9.25 3.49 11 3.89 1.27 2.71 12 2.22 0.31 2.23 13 0.20 0.88 0.43 14 0.21 0.88 0.12 0.48 15 0.67 0.46 16 0.47 0.12 17 0.41 0.33 18 0.21 19 20 0.24 f, 70 53 93 112 172 106 130 113 90 104 100 148 114 184 No 2 2 5 25 58 14 49 4 4 0 2 19 15 88 Mn 2.67 2.15 4.73 31.08 105.97 25.38 370.70 15.37 4.46 1.96 12.62 33.67 402.90 SE 2.07 1.52 2.23 7.49 18.68 7.61 85.96 12.42 2.47 1.56 3.25 12.61 69.39 682 Fishery Bulletin 93(4). 1995 Table 2 (continued) September October Subareas Subareas Length (mm) 1 2 3 4 5 6 7 1 2 3 4 5 6 7 2 0.92 2.62 0.37 5.02 4.79 14.36 2.78 7.42 23.15 16.83 7.26 3.05 3 0.39 3.16 0.86 12.67 34.27 22.09 3.22 27.73 40.14 36.13 21.79 15.46 4 1.89 0.53 12.97 5.50 13.86 1.55 3.50 13.93 17.11 10.47 11.05 13.79 5 4.83 2.69 15.01 8.92 2.60 2.89 5.15 12.85 6 0.48 0.70 11.81 2.74 2.49 2.02 3.57 8.02 7 2.53 9.32 1.17 1.04 0.48 1.48 7.02 8 6.89 1.30 0.26 0.36 3.79 9 5.17 0.86 0.80 2.24 10 1.14 7.94 0.20 1.73 11 3.69 2.78 12 11.18 1.20 13 0.50 0.79 0.41 14 0.56 0.20 0.28 15 0.98 16 0.23 17 0.41 18 0.44 0.08 19 0.84 0.18 20 N, 89 70 85 55 78 58 66 38 23 39 86 144 144 207 N0 3 3 10 3 15 12 39 1 5 9 27 70 43 93 Mn 0.89 2.11 13.14 2.58 64.64 46.80 396.08 1.14 19.13 147.66 211.80 198.13 129.16 258.85 SE 0.56 1.26 4.83 1.79 28.72 18.85 93.03 1.14 10.28 94.39 85.34 39.61 29.41 39.61 November December Subareas Subareas Length (mm) 1 2 3 4 5 6 7 1 2 3 4 5 6 7 2 14.79 27.50 35.64 4.83 4.25 3 43.69 68.11 70.02 36.63 24.93 1.20 3.74 2.68 4 26.22 29.84 41.32 11.90 13.18 1.32 6.11 7.83 9.47 1.95 5 10.01 9.87 17.29 5.07 6.77 1.57 2.50 4.89 1.83 6 7.11 2.48 12.07 4.65 2.03 4.89 4.37 7 1.74 0.20 7.87 0.68 0.62 2.36 6.89 2.20 3.79 8 0.63 0.88 0.88 0.77 3.45 2.52 2.96 1.95 9 0.48 1.58 3.48 10 0.21 0.45 4.75 1.60 11 1.59 1.24 12 13 14 15 0.49 16 17 1.61 18 0.52 19 0.64 20 Wl 87 55 76 68 89 86 118 0 6 12 17 67 66 86 N0 31 14 24 29 39 5 22 0 2 1 18 3 0 Mn 210.47 364.35 247.31 116.86 80.4 3.63 28.05 27.7 27.35 58.6 3.92 SE 90.79 196.19 109.43 37.2 18.16 1.64 7.13 20.54 27.35 17.36 2.23 Morse and Able: Distribution and life history of Scophthalmus aquosus 683 1 3 5 7 9 11 13 15 17 19 21 23 25 Temperature °C Figure 5 Abundance of 2-4 mm windowpane, Scophthalmus aquosus, larvae by subarea relative to bottom water tem- perature during 1977-87. tures, which approaches the preferred temperatures, suggests that spawning here may be triggered by the highest temperatures available. Subareas 4 and 5 are intermediate, with preferred temperatures available from July to November (Fig. 6); yet spawning occurs from May to December (Table 2; Fig. 4). Peak spawn- ing occurs in October, a full three months later than the first record of preferred spawning temperatures. Larval distribution and abundance Larvae were captured every month on the continen- tal shelf (Table 2). January-April catches were very low in subareas 1-3 and 5 and were totally absent elsewhere. Larvae were caught in all subareas in May and were most abundant in subarea 2. By June, lar- val abundances were highest in subarea 4, and from July to October subarea 7 had the highest larval catches. Throughout August and September, abun- dances in subareas 5 and 6 were intermediate, and o Month Figure 6 Monthly temperature means and ranges by subarea of the continental shelf of the northeastern U.S. during 1977-87. Shaded bar is the preferred spawning tem- peratures (16-19°C) for windowpane, Scophthalmus aquosus. catches in subareas 1—4 remained very low. By Octo- ber, catches of larvae decreased somewhat in sub- area 7 and increased in all other subareas. Novem- ber catches showed a continued decline in subarea 7 and began to decrease in subareas 4-6. Catches in- creased to their highest levels in subareas 1 and 2, whereas subarea 3 catches remained at October lev- els. In December, no larvae were captured in sub- area 7, a few large larvae occurred in subarea 3, and only moderate catches were made in subareas 4-6. The nearly total absence of larvae in subareas 1—4 during December is attributed to the low number of stations sampled and not necessarily to the disap- pearance of larvae within this area. The size of larvae captured on the continental shelf varies between subareas (Table 2). Few larvae >8 mm were captured in subareas 1-4; only 18 of 3,282 sta- 684 Fishery Bulletin 93(4), 1995 tions contained these larvae. In subareas 5 and 6, 27 of 2,461 stations had larvae >8 mm long. Larvae >13 mm were captured in only 10 of 5,743 stations in subareas 1-6. In contrast, in subarea 7, 89 of 1,473 stations had >8 mm larvae and 31 stations had >13 mm larvae. In an attempt to interpret the trend of increasing maximum lengths from south to north, the abundances at length and mortality estimates for larvae <20 mm, grouped by subarea, were calcu- lated (Table 3). The maximum larval length of catches >0.1/100m2 and mortality for each subarea is shown in Figure 7. If avoidance of the sampling gear occurs because of settlement within a narrow size interval (e.g. 1-3 mm), then the catches should show a pre- cipitous decrease in abundance at settlement. No such abrupt decrease can be seen in the data (see Tables 2 and 3); thus the declines in abundance with size are due to other causes. Alternatively, if we as- sume that decreases in larval abundance are due to mortality, then the percentage of mortality per mm of growth is highest in subarea 1 (63%), intermedi- ate in subareas 2-5 (range 48-56%), declines to 38% in subarea 6, and is lowest in subarea 7 (30%). Esti- mated mortalities are inversely related to the maxi- mum lengths of captured fish and decrease from south to north along the coast (Fig. 7). The relatively high mortality indicated for larvae in subareas 1—5 could explain the truncated larval length frequen- cies seen there, particularly during the months of July-October (Table 2). Larger larvae in the Middle Atlantic Bight sub- areas may move into or are more abundant in shal- low nearshore areas of the continental shelf and es- tuaries and thus may not be available to the collect- Subareas Figure 7 Length-dependent mortality rates and the maxi- mum larval lengths of catches >0. 1/100 m2 by sub- area from NMFS MARMAP sampling of window- pane, Scophthahnus aquosus, off the northeast United States. ing gear. Typically, NMFS/MARMAP sampling is not undertaken in estuaries and is limited to depths >10 m on the continental shelf. During the MARMAP study, approximately 13% of all tows were taken in depths <20 m, whereas only 0.3% were taken in wa- ter depths <10 m. In the vicinity of Little Egg Inlet, New Jersey, larvae were abundant on the inner con- tinental shelf and in the estuary (Fig. 8). Eggs and larvae were least abundant in the Mullica River, more abundant farther down the estuary in Great Bay and at Little Egg Inlet, and most abundant on the adja- cent portion of the inner continental shelf (Fig. 8). Eggs and larvae were abundant in the estuary dur- ing spring, but both were most abundant on the con- tinental shelf during the fall. Juvenile and adult distribution and abundance Windowpane are distributed over much of the conti- nental shelf, as well as in estuaries in the Middle Atlantic Bight. Large juvenile and adult windowpane (>10 cm TL) were collected from the western portion of the Gulf of Maine to Cape Hatteras, North Caro- lina (Figs. 9, 10), in depths from 5 to 207 m. In the Gulf of Maine, there were few fish of this size col- lected from coastal Maine, but they were more abun- dant off the coast of Massachusetts, subarea 6 (Fig. Eggs □ Site 1 ■ Site 2 SS Little Egg Inlet I I Great Bay ■ Mullica River 0^ 250 Larvae 1 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Month Figure 8 Monthly patterns of distribution and abundance of win- dowpane, Scophthahnus aquosus, eggs and larvae from the vicinity of Little Egg Inlet, New Jersey, during 1972-75, as modified from Milstein and Thomas ( 1977). See Figure 2 for sampling locations. Morse and Able Distribution and life history of Scophthalmus aquosus 685 Table 3 Mean number (Mn) of windowpane, Scophthalmus aquosus, larvae (number/100 m2) by length (in mm) for seven subareas off northeastern United States, 1977-87 N = Total number of stations sampled in each subarea. An exponential equation, Mn = a x exp( -bL 1, was fit to the data. NQ - = number of stations with windowpane arvae; SE = standard error of the mean; Mi %) = estimated mortality as %~mm (i.e. lOOQ-exp(-b)) SEE = standard error of the estimate; and lL = length interval fit to the equation. Subarea 1 Subarea 2 Subarea 3 Subarea 4 Length (mm) N0 Mn SE ^0 Mn SE N0 Mn SE N0 Mn SE 2 23 2.71 0.87 28 4.81 1.44 34 4.49 1.31 40 4.83 1.17 3 48 7.39 1.84 34 12.18 3.67 69 11.94 2.55 77 11.30 2.10 4 37 4.82 1.15 35 5.70 1.33 44 6.15 1.49 46 4.43 0.96 5 26 1.92 0.51 20 2.44 0.73 22 3.03 0.91 36 1.83 0.34 6 14 1.17 0.38 13 0.65 0.20 20 1.75 0.55 17 1.22 0.35 7 7 0.37 0.15 5 0.29 0.16 14 1.24 0.43 8 0.39 0.16 8 1 0.08 0.08 3 0.27 0.16 5 0.23 0.11 7 0.36 0.15 9 1 0.02 0.02 1 0.09 0.09 2 0.17 0.13 10 — — — — — — 4 0.19 0.10 2 0.04 0.03 11 — — — — — — — — — — — 12 1 0.05 0.05 1 0.04 0.04 — — — 13 — — — 1 0.06 0.06 — — — 14 1 0.07 0.07 — — — — — — 1 0.03 0.03 15 — — — — — — 1 0.06 0.06 — — — 16 — — — — — — — — — — — 17 — — — — — — 1 0.03 0.03 — 18 19 1 0.06 0.06 — — — — — — — — — 20 — — — — — — — — — — N 716 543 744 768 a 233.28 133.26 82.22 79.70 b 0.981 0.822 0.653 0.713 M (%) 62.5 56.0 48.0 51.0 r2 0.96 0.98 0.95 0.97 SEE 0.457 0.301 0.376 0.263 h 3-9 3-9 3-10 3-8 Subarea 5 Subarea 6 Subarea 7 Length (mm) ^0 Mn SE ^0 Mn SE ^0 Mn SE 2 104 5.77 0.78 37 3.28 0.65 78 4.84 0.74 3 169 12.59 1.33 55 8.18 1.45 174 16.68 1.88 4 110 6.41 0.76 38 3.54 0.65 165 12.98 1.37 5 67 2.93 0.41 19 1.60 0.40 136 10.75 1.28 6 38 1.42 0.25 16 1.59 0.48 122 7.29 0.86 7 22 0.86 0.21 8 0.53 0.20 95 6.55 0.93 8 11 0.35 0.12 4 0.33 0.19 70 4.65 0.77 9 8 0.44 0.22 5 0.56 0.30 33 2.74 0.67 10 1 0.01 0.01 4 0.20 0.10 34 3.18 0.79 11 1 0.06 0.06 2 0.25 0.20 29 2.15 0.55 t2 — — — 1 0.04 0.041 19 1.86 0.64 13 2 0.05 0.04 1 — — 14 0.39 0.12 14 1 0.01 0.01 — — — 10 0.31 0.11 15 1 0.04 0.04 — — — 13 0.31 0.09 16 — — — — — — 3 0.12 0.07 17 — — — 1 0.05 0.05 4 0.11 0.06 18 1 0.02 0.02 — — — 4 0.11 0.06 19 1 0.03 0.03 — — — 4 0.12 0.07 20 — — — — — — 2 0.05 0.04 N 1286 841 1852 a 134.70 24.43 67.64 b 0.754 0.481 0.358 M(%) 53.0 38.2 30.1 9 0.89 0.92 0.96 SEE 0.788 0.467 0.387 h 3-11 3-12 3-20 686 Fishery Bulletin 93(4). 1995 9). Small juveniles (<10 cm TL) show a similar dis- tributional pattern, although they tend to be more abundant in shallower depths. Few have been col- lected in the Gulf of Maine, but they were distrib- uted over most of Georges Bank, especially in the central portion. They were found closer to shore in the Middle Atlantic Bight than on Georges Bank. Small juveniles (<10 cm TL) were found in 4-82 m in Massachusetts nearshore waters, but their average capture depth was 23 m. In New Jersey nearshore waters (5-27 m), larger juveniles and adults were Juvenile Wmdowpane SPRING and FALL 2-10cmTolal Length NMFS Bottom Trawl Surveys 1 982-1 991 h|36° W«s Figure 9 Occurrence of two size classes of windowpane, Scoph- thalmus aquosus, from spring and fall NMFS groundfish surveys during 1982-91. abundant during all months, but small juveniles (<10 cm TL) were rare (Fig. 11). The seasonal patterns of abundance of window- pane, based on NMFS bottom trawl survey catches, varied markedly on the continental shelf (Table 4). Fall catches offish <10 cm TL in subareas 1-5 aver- aged <0.01 individuals per tow, 0.22 per tow in sub- area 6, and 6.24 per tow in subarea 7. Spring catches of these fish ranged from 0.07 to 0.46 fish per tow across all subareas, with the highest catches in sub- areas 2 and 3, which were 30 to 50 times higher than those in the fall. In contrast to catches offish <10 cm TL, catches offish 11-20 cm TL showed little variation across subareas in the fall (0.72-1.82 fish/tow), whereas spring catches were low in subareas 1 and 2 (0.09 fish/ tow) and high in subareas 5 and 6 ( 1. 15-1.25 fish/tow). In general, adult fish (>20 cm TL) catches were consis- tently low in subarea 1, increased along the coast in subareas 2-6, and peaked in subarea 7. This pattern of adult catches differed for fish 21-30 cm TL in the spring, when the peak catches occurred in subarea 3. The NMFS and Massachusetts fall and spring bot- tom trawl surveys were analyzed to determine whether the abundance of small juvenile window- pane reflects the areal patterns in larval distribu- tion and abundance mentioned above. NMFS sta- tions, for spring and fall combined, at which win- dowpane ( 11-48 cm TL) were captured are shown in Figure 9A, and stations that contained juveniles (<10 cm TL) are shown in Figure 9B. Although adults occur in the northern Gulf of Maine, no juveniles were collected there. The spatial patterns of abundance for juveniles on the continental shelf coincide with the patterns of abundance for larvae (see Figs. 3 and 9B). The inverse relationship of catches of juveniles in the fall with larval mortality (r=-0.99, P<0.05 ) seems to support the conclusion that mortality is controlling recruitment; however, spring catches show no such re- lationship (r=0.12, P<0.93). To test the possibility that juveniles migrate to an area nearshore (<10 m depths) or to estuarine habitats in the southern part of the sur- vey area in the fall and were not sampled by the trawl gear, we calculated the weighted mean capture depths in each subarea for five size classes (Table 4). Small juveniles (<10 cm TL) were captured at only 4 of 779 stations in subareas 1-4 in the fall at depths of 10-24 m. Larger juveniles (11-20 cm TL) were more abun- dant and were captured at weighted mean depths 17— 19 m. Adults (21-30 cm TL) were found in slightly deeper water (means= 22-27 m) and adults >30 cm TL were captured at only 12 stations in mean depths from 14 to 38 m. Weighted mean depths of capture within each subarea differed little between fall ( 10—38 m) and spring (15-47 m) surveys or between size classes, al- though a weak trend of increasing depth with size was Morse and Able: Distribution and life history of Scophthalmus aquosus 687 FALL SPRING Length (cm) Figure 10 Length-frequency distribution of windowpane, Scophthalmus aquosus, from subareas indicated in Figure 1 during NMFS fall and spring groundfish sur- veys. See Table 1 for additional details. evident. However, these results do not clearly indicate an inshore movement of juvenile fish during fall on the continental shelf, although eggs, larvae, and juveniles can be found in some estuaries. Juvenile length frequencies and growth Understanding patterns of age composition and growth in our study area is confounded by location and timing of spawning. For our purposes we will follow the patterns for Georges Bank (subarea 7) and the Middle Atlantic Bight off New Jersey (subarea 4), because they appear quite different. In subarea 7, where there is a specific peak in spawning, larvae first appear in relatively large numbers in June at sizes ranging from 2 to 6 mm (Table 2). They reach peak abundance in August when they range from 2 to 20 mm (Table 2; Fig. 4). By the fall they are well represented in bottom trawl collections at sizes of 2—14 cm TL (Fig. 10). By spring they are probably represented by the two smaller modes over the range from 3 to 16 cm TL (Fig. 10). The similar size ranges from fall to spring suggest that little or no growth occurs over the winter. By the following fall, this group has probably attained sizes of >17 cm TL and cannot be separated from older fish by length alone 688 Fishery Bulletin 93(4). 1995 15 10 5 0 15 10 5 0 15 10 5 15 10 5 J ^-rtft M January ..,,!. February ^rfiiNTnTiv March ^-Tffff April 18 12 6 0 15 j 10! 51 0 t 121 -ffi May June ^nWlflHfrru-. August rfumiTrTTfrm-^ September ^^ftftfltoh October ■w-rTffF Sb^. November ^ttfflit.,.^0^":. 3 5 7 9 1113 15 17 19 2123 25 27 29 3133 35 37 39 4143 45 Length (cm) Figure 1 1 Monthly length-frequency distribution for windowpane, Scophthalmus aquosus, collected during an inshore trawl survey off the coast of New Jersey, 1988-92. See Table 1 for additional details. (Fig. 10). In subarea 4 off New Jersey, where spawn- ing was shown to be bimodal, the earliest peak was in May and the second was in October-November (Fig. 4; Table 2). However, there is no evidence of large numbers of small juveniles in the spring or fall in the NMFS survey (Fig. 10) or in the monthly catches of the New Jersey trawl surveys (Fig. 11). Conversely, in the vicinity of Little Egg Inlet, New Jersey, the appearance of eggs and larvae in both the estuary and in nearshore ocean waters corre- sponds well with two spawning periods (Fig. 7). Evi- dence of spring-spawned fish is first indicated by small numbers at 4 cm TL in June (Fig. 12). By July, these fish are 3-8 cm TL and in August they are 4- 11 cm TL. In September, catches of small fish de- creased, and fish lengths ranged from 8 to 17 cm TL. Catches of these spring-spawned fish further de- creased by October, when very few juveniles were captured. This same cohort first appeared in nearshore surveys off New Jersey in August and by September the fish were 11-19 cm TL (Fig. 11). By October they cannot be easily differentiated from older fish on the basis of length, but some of these fish were probably captured in the fall collections by NMFS surveys on the continental shelf (Fig. 10). They do not appear to be abundant in estuary or ocean collections until the following April-May when most are >16 cm TL (Fig. 12). Fall-spawned larvae were first collected in Septem- ber in subarea 4 at lengths of 2-4 mm (Fig. 4; Table 2). The peak abundance was in October and Novem- ber when they were 2-10 mm. These fish first ap- peared as settled juveniles in the vicinity of Little Egg Inlet in November at 3-4 cm TL, and by Decem- ber they were 4-7 cm TL (Fig. 12). Fall-spawned ju- veniles were not evident in the nearshore (Fig. 10) or in deep-water surveys (Fig. 12). During January- March, fish 4-8 cm TL were abundant in the ocean catches and may not have grown much during these cold-water months (Fig. 12). From March to May, small juveniles moved gradually into the bay and began to grow again. A clear separation between the fall-spawned fish (5-12 cm TL) and the spring- spawned fish (>16 cm TL) can be seen in May (Fig. 12 ). The fall-spawned fish continued to grow and were 18-26 cm TL by October when they were about 1 year old. They may not have grown during the late fall and winter, given the similarities in length fre- quencies from October to December. These fish left the bay beginning in June, and by October few fall- spawned fish were present in the bay. The evidence for the existence of spring- and fall-spawned cohorts is most evident in July and August in New Jersey where both are represented by the two dominant length-frequency modes in both the bay and the adjacent ocean (Fig. 12). Discussion Distribution and abundance Windowpane is a resident of the Middle Atlantic Bight and Georges Bank, although it does show some small-scale seasonal inshore-offshore movement. Evidence from ocean trawl surveys throughout the study area showed little difference in the preference of juveniles for relatively shallow waters from spring and fall depth distributions (Table 4). Evidence from tagging experiments in Long Island Sound (Moore, 1947 ) indicates that windowpane do not undertake ex- tensive migrations in response to either seasonal temperature changes or for purposes of spawning. How- ever, research trawl surveys show some evidence of an offshore movement during winter in response to low Morse and Able: Distribution and life history of Scophthalmus aquosus 689 Table 4 Summary of fall and spring catches (depths <100 m) of win dowpane, Scophtha Imus aquosus . from NMFS groundfish trawl sur- veys off the northeast United States, 1982-91. Nt = total stations s ampled; D = mean depth of N ;tf„ = lumber of stations with windowpane; M( = mean catch per tow for Nt; and D0 = weighted mean depth of Nn. See Figu re 1 for location of subareas. Subarea Season *i Dm Length (cm) <10 11-20 21-30 31-40 >40 N0 M, D0 ^0 M, D0 ^0 M, Do ^0 M, Do ^0 M, So 1 Fall 178 31 1 0.01 17 34 0.72 18 9 0.15 27 1 0.01 30 0 _ _ 2 Fall 185 31 1 <0.01 24 53 1.42 19 40 0.57 27 0 — — 0 — — 3 Fall 209 35 1 <0.01 22 66 1.82 19 77 2.27 27 6 0.03 38 0 — — 4 Fall 211 38 1 <0.01 10 52 1.18 17 91 2.61 22 5 0.04 14 0 — — 5 Fall 384 36 4 0.01 15 89 1.28 41 176 4.33 43 59 0.22 47 0 — — 6 Fall 306 49 18 0.22 31 57 1.05 33 105 6.67 35 64 1.35 39 5 0.02 42 7 Fall 435 65 70 6.24 47 76 0.78 48 166 5.61 51 155 2.60 49 2 <0.01 47 1 Spring 199 33 15 0.21 17 10 0.09 22 47 1.04 23 3 0.02 23 0 _ 2 Spring 179 33 21 0.46 15 11 0.09 19 94 3.34 22 8 0.04 26 0 — — 3 Spring 209 33 25 0.34 18 28 0.68 17 118 6.95 19 22 0.14 20 0 — — 4 Spring 226 40 12 0.16 16 31 0.39 17 99 4.36 20 23 0.16 26 2 0.01 47 5 Spring 436 39 18 0.09 24 142 1.15 57 258 5.23 63 146 1.07 47 2 0.01 41 6 Spring 305 49 16 0.07 33 79 1.25 53 147 4.17 53 105 1.94 40 5 0.02 43 7 Spring 368 65 23 0.23 52 43 0.27 73 143 3.40 73 167 2.14 52 4 0.01 57 water temperatures (Wigley and Gabriel, 1991; Lange and Lux6). There appears to be evidence of latitudinal varia- tion in depth preference from south to north (Table 4). The actual depth preference in subareas 1-4 may be shallower than indicated because NMFS seldom samples in depths <10 m. For example, in subarea 4, juveniles migrated or settled into an estuary dur- ing spring and tended to move into the ocean during summer (Fig. 12). Few juvenile windowpane were caught inside the estuary by the fall when they had reached lengths between 18 and 26 cm TL. These seasonal movements in and out of estuaries and bays may account for the larger numbers of juveniles taken on the continental shelf in the Middle Atlantic Bight in the spring (Table 4; Fig. 10), although the lack of small juveniles in nearshore waters off New Jersey (Fig. 10) is difficult to explain. In contrast, the Mas- sachusetts trawl survey, which sampled similar depths to those in the New Jersey trawl survey, cap- tured large numbers of juvenile windowpane in the fall. Clearly juvenile windowpane are also a compo- nent of fish assemblages in other estuaries on the 6 Lange, A. M. T., and F E. Lux. 1978. Review of the other flounder stocks (winter flounder, American plaice, witch floun- der and windowpane flounder) off the Northeast United States. U.S. Dep. Commer., NMFS, Northeast Fish. Sci. Cen- ter, Woods Hole Lab. Ref. No. 78-44, Woods Hole, MA 02543. basis of reports from Narragansett Bay (Herman, 1963), Long Island Sound (Moore, 1947), Sandy Hook Bay (Wilk and Silverman, 1976), Delaware Bay (de Sylva et al., 1962), Chesapeake Bay (Hildebrand and Schroeder, 1928), North Carolina (Weinstein, 1979), South Carolina (Wenner et al., 1982), and Georgia ( Dahlberg, 1972 ). Thus, further sampling in the shal- low nearshore ocean waters and in adjacent estuar- ies will be necessary to understand completely the nature of seasonal movements and the patterns of habitat use of juveniles, at least in subareas 1-5. Timing and location of spawning The extensive latitudinal sampling program has helped to discern the seeming inconsistency in the literature regarding the presence of a bimodal spawn- ing season. Split spawning (i.e. peaks in spring and fall) has been previously reported in Long Island Sound, New York (Wheatland, 1956), Great South Bay, New York (Monteleone, 1992), and on the conti- nental shelf off Virginia and North Carolina (Smith et al., 1975). However, Colton et al. (1979), Perlmutter (1939), and Smith et al. ( 1975) reported no evidence for split spawning north of Virginia. We found evi- dence for a split spawning season in all areas except Georges Bank (Fig. 4). Taken together, the available information shows that windowpane begin spawn- 690 Fishery Bulletin 93(4), 1995 ED ESTUARY ■ OCEAN FEBRUARY E 3 DECEMBER 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 Length (cm) Figure 12 Length-frequency distribution of windowpane, Scoph- thalmus aquosus, by month, based on collections in the estuarine and ocean in the vicinity of Little Egg Inlet, New Jersey, as modified from Milstein and Thomas ( 1977). Es- tuarine samples represent all samples not taken in the ocean. Station locations are indicated in Figure 2. ing at the southern portion of the Middle Atlantic Bight (south of Chesapeake Bay) in April or May. Peak spawning progresses northward as waters warm, and spawning reaches Georges Bank by July and August. As waters cool during fall, spawning moves south to off New York and New Jersey, and by Novem- ber spawning is again centered in the southern part of the Middle Atlantic Bight. The split spawning season pattern has also been verified for New Jersey in the vicinity of Little Egg Inlet (Fig. 8) and farther south at Hereford's Inlet, New Jersey (Keirans, 1977). Seasonally varying temperatures clearly influ- enced the timing of spawning. We found maximum numbers of small larvae at temperatures between 16 and 19°C in subareas 1-5 (Fig. 5), except on Georges Bank where the maximum larval abundance occurred at temperatures (13-16°C), approximately those reported by Smith et al. (1975). They found 70% of small larvae over bottom water temperatures between 8.5 and 13.5°C between Cape Hatteras and Block Island (subareas 1-5). It appears that spawn- ing during the single year (1965-66) of their study occurred at temperatures around 6°C, colder than our findings from a data set that was more exten- sive both temporally and latitudinally. Reports of eggs from Great Bay (Fig. 8) and Hereford's Inlet (Keirans, 1977), New Jersey, Chesa- peake Bay, Virginia (Olney, 1983; Olney and Boehlert, 1988), Long Island Sound (Wheatland, 1956; Richards, 1959; Perlmutter, 1939), Great South Bay on Long Island (Monteleone, 1992), and Narragansett Bay, Rhode Island (Herman, 1963; Bourne and Govoni, 1988), strongly suggest that spawning oc- curs in the lower portions of estuaries in the Middle Atlantic Bight. These sources imply that the influ- ence of estuaries on the early life history of window- pane may be important in the Middle Atlantic Bight. Age and growth Growth after settlement was markedly different be- tween the spring- and fall-spawned cohorts in New Jersey waters. The spring-spawned cohort grew quickly during the summer and reached sizes of 11— 19 cm TL in September, approximately 4 months later (Fig. 12). The fall-spawned cohort, exposed to winter temperatures soon after settlement, appar- ently did not grow during the winter and grew to only 4-8 cm TL six months later in March (Fig. 12). Thus, the timing of spawning (spring vs. fall) influ- ences growth rates and the age and size composition of young of the year. Reported estimates of growth from scale annuli, regardless of spawning season, were quite different. In studies for Long Island Sound and North Caro- lina age-2+ fish averaged only 11.7 cm TL (Moore, 1947) and 10-13 cm TL (Shelton, 1979), respectively. Sizes at age 1 reported for our study area were 18 cm TL (Grosslein and Azarovitz, 1982) and 14.5 cm TL (Thorpe, 1991) and were more consistent with our results, although the season of spawning could easily affect size at age. Clearly, more detailed stud- ies of spawning times and their effects on age com- position and growth of juveniles are needed before we can completely understand the population dynam- ics of this species. Nursery areas In general, the distribution of larvae and juveniles on the continental shelf coincided and showed that Morse and Able: Distribution and life history of Scophthalmus aquosus 691 at least some juveniles settled in areas of larval con- centration, although this pattern was not as strong for the Middle Atlantic Bight as it was for Georges Bank. Larval abundance on Georges Bank was high and recently settled juveniles were clearly abundant there in the fall but less so in the spring (Fig. 10). Slightly larger individuals were also evident off Massachusetts in the fall (Fig. 10), but they were not caught in the deeper waters of the continental shelf further south (subareas 1-5, Fig. 10). Size at settlement appears to differ between Georges Bank and the Middle Atlantic Bight. Larvae >10 mm were collected only rarely in the Middle Atlantic Bight but were relatively abundant on Georges Bank. This pattern of catches could arise from 1 ) the large lar- vae avoiding capture by transforming and settling earlier in the south, 2) the differences in mortality between regions, or 3) the unavailability of larger larvae to the sampling gear because they entered the unsampled surf-zone or the numerous estuaries in the southern part of the study area. This last possi- bility is clearly not an option for Georges Bank lar- vae that do not make extensive migrations (50-75 km) to the nearshore areas of Massachusetts. We have shown that mortality estimates are higher in the Middle Atlantic Bight than on Georges Bank. Settlement in estuaries in the Middle Atlantic Bight is also possible because larger planktonic larvae (K. W. Able, D. A. Witting, and M. P. Fahay, unpubl. data) and small juveniles were collected from these areas in New Jersey (this study, Figs. 8 and 12; Allen et al., 1978), Delaware (Pacheco and Grant, 1973), and Long Island (Warfel and Merriman, 1944). Yet to be resolved are the reasons for the differences in the size of larvae and the apparent mortalities in the dif- ferent geographic regions, as well as for the subsequent effect of size on settlement and the location of nursery areas throughout the range of windowpane. Acknowledgments We wish to thank the following people for access to datasets: T Azarovitz for the NMFS bottom trawl survey data, A. Howe for the Massachusetts trawl survey data, D. Byrne for the New Jersey trawl data, and D. Witting for the Great Bay ichthyoplankton data. Literature cited Allen, D. M., J. P. Clymer III, and S. S. Herman. 1978. Fishes of the Hereford Inlet Estuary, southern New Jersey. Lehigh Univ. and the Wetlands Inst., 138 p. Azarovitz, T. R. 1981. A brief historical review of the Woods Hole Labora- tory trawl survey time series. In W. G. Doubleday and D. Rivard (eds. ), Bottom trawl surveys, p. 62-67. Can. Spec. Publ. Fish. Aquat. Sci. 58. Azarovitz, T. R., and M. D. Grosslein. 1987. 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An immunochemically assisted ichthyoplankton sur- vey with elaboration on species specific antigens of fish egg vitellins; southern New Jersey barrier island-lagoon complex. Ph.D. diss., Lehigh Univ., Bethlehem, PA, 159 p. Milstein, C. B., and D. L. Thomas. 1977. Summary of ecological studies for 1972-1975 in the bays and other waterways near Little Egg Inlet and in the ocean in the vicinity of the proposed site for the Atlantic Generating Station, New Jersey. Ichthyolog. Assoc, Bull. 18, 757 p. Monteleone, D. M. 1992. Seasonality and abundance of ichthyoplankton in Great South Bay, New York. Estuaries 15:230-238. Moore, E. 1947. Studies on the marine resources of southern New England. VI: The sand flounder, Lophopsetta aquosa (Mitchell ); a general study of the species with special empha- sis on age determination by mean of scales and otoliths. Bull. Bingham Oceanogr. Collect. Yale Univ. ll(3):l-79. Morse, W. W. 1989. Catchability, growth, and mortality of larval fishes. Fish. 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Statistical Bull. 38, 307 p O'Brien, L., J. Burnett, and R. K. Ralph. 1993. Maturation of nineteen species of finfish off the North- east coast of the United States, 1985-1990. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 113, 66 p. Olney, J. E. 1983. Eggs and early larvae of the bay anchovy, Anchoa mitchilli, and the weakfish, Cynoscion regalis, in lower Chesapeake Bay with notes on associated ichthyo- plankton. Estuaries 6( 1 ):20-35. Olney, J. E., and G. W. Boehlert. 1988. Nearshore ichthyoplankton associated with seagrass beds in the lower Chesapeake Bay. Mar. Ecol. Prog. Ser. 45:33-43. Oviatt, C. A., and S. W. Nixon. 1973. The demersal fish of Narragansett Bay: an analysis of community structure, distribution and abundance. Estuarine Coastal Mar. Sci. 1:361-378. Pacheco, A. L., and G. C. Grant. 1973. Immature fishes associated with larval Atlantic men- haden at Indian River Inlet, Delaware, 1958-61. In A. L. Pacheco (ed.), Proceedings of a workshop on egg, larval and juvenile stages of fish in Atlantic Coast estuaries. NOAA Tech. Report No. 1, Middle Atlantic Coastal Fisheries Center, 78-117 p. Pennington, M. 1983. Efficient estimators of abundance, for fish and plank- ton surveys. Biometrics 39:281-286. Perlmutter, A. 1939. Section I : An ecological survey of young fish and eggs identified from tow-net collections. In A biological sur- vey of the salt waters of Long Island, 1938, Part II, p. 11- 71. N.Y Conserv. Dep. Suppl. 28th Annu. Rep., 1938, Salt- water Surv. 15. Richards, S. W. 1959. Pelagic fish eggs and larvae of Long Island Sound. Bull. Bingham Oceanogr. Collect. Yale Univ. 17:95-124 Scott, W. P., and M. G. Scott. 1988. Atlantic fishes of Canada. Can. Bull. Fish. Aquat. Sci. 219, 731 p. Shelton, S. T. 1979. The age, growth and food habits of the windowpane flounder, Scophthalmus aquosus (Mitchill), in the lower Cape Fear River estuary and adjacent ocean. M.S. the- sis, East Carolina Univ., Greenville, NC, 42 p. Sherman, K. 1980. MARMAP, a fisheries ecosystem study in the North- west Atlantic: fluctuations in ichthyoplankton-zooplank- ton components and their potential for impact on the system. In F P. Diemer, F J. Vernberg, and D. R. Mirkes (eds.), Advanced concepts in ocean measurement for ma- rine biology, p. 9-37. Belle W. Baruch Inst. Mar. Biol. Coastal Res., Univ. South Carolina Press. Sibunka, J. I >., and M. J. Silverman. 1984. MARMAP surveys of the continental shelf from Cape Hatteras, North Carolina, to Cape Sable, Nova Scotia (1977-1983). Atlas No. 1. Summary of Operations. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-F/NEC-33, 306 p. 1989. MARMAP surveys of the continental shelf from Cape Hatteras, North Carolina, to Cape Sable, Nova Scotia (1984-1987). Atlas No. 3. Summary of Operations. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-F/NEC-68, 197 p. Smith, W. G., J. D. Sibunka, and A. Wells. 1975. 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L., M. H. Shealy Jr., and P. A. Sandifer. 1982. A profile of the fish and decapod crustacean commu- nity in a South Carolina estuarine system prior to flow Morse and Able: Distribution and life history of Scophthalmus aquosus 693 alteration. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-757, 17 p. Wheatland, S. B. 1956. Oceanography of Long Island Sound, 1952-1954. VII: Pelagic fish eggs and larvae. Bull. Bingham Oceanogr. Collect. Yale Univ. 15:234-314. Wigley, S. E., and W. L. Gabriel. 1991. Distribution of sexually immature components of 10 Northwest Atlantic groundfish species based on Northeast Fisheries Center bottom trawl surveys 1968-86. U.S. Dep. 17 p. Commer., NOAA Tech. Memo. NMFS-F/NEC-80, Wilk, S. J., and M. J. Silverman. 1976. Summer benthic fish fauna of Sandy Hook Bay, New Jersey. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-698, 16 p. Wilk, S. J., W. W Morse, and L. L. Stehlik. 1990. Annual cycles of gonad-somatic indices as indicators of spawning activity for selected species of finfish collected from the New York Bight. Fish. Bull. 88:775-786. Abstract. Several new models are developed to estimate the velocity and diffusion of a population from tag- ging data. The new estimators apply the inverse principle to the individual trajectories of recovered tags rather than to their local abundance. These models require fewer assumptions and less information than do published abundance-based methods. Techniques are presented for a variety of circum- stances, and both discrete and continu- ous parameterizations of the velocity field are included. The sensitivity of the estimators to violations of the assump- tions was examined numerically by us- ing stochastic simulations. The results suggest that the estimators are fairly robust but may fail under certain con- ditions. Extensions to accommodate these situations are discussed. Trajectory-based approaches to estimating velocity and diffusion from tagging data Clay E. Porch Southeast Fisheries Science Center National Marine Fisheries Service, NOAA 75 Virginia Beach Drive, Miami, Florida 33149 Manuscript accepted 17 April 1995. Fishery Bulletin 93:694-709 ( 1995). Tagging experiments have often been used to delineate animal move- ments. Historically, many of the analyses were limited to graphical portrayals of apparent migration routes and simple measures of the net swimming speed. Beverton and Holt (1957) introduced more rigor- ous treatments of tagging data based on the pioneering work of Skellam (1951). They postulated that the Fickian diffusion equation would be an adequate model for the dispersion of fish due to random motions and developed a technique for estimating the diffusion coeffi- cient from tagging data. Subse- quently, Jones (1959, 1976) devel- oped a simple estimation procedure that distinguished the diffusion and net drift of returned tags. Saila and Flowers (1969) proposed using a special case of the advection-diffu- sion equation (Fickian diffusion with constant velocity) to model fish migration and developed a numeri- cal technique to estimate the diffu- sion coefficient and net drift. More recently, Sibert and Founder ( 1994) advocated the use of a more general form of the advection-diffusion equation that allows for mortality and discrete changes in velocity among areas. They also developed a new estimation procedure based on fitting numerical predictions to the observed distribution of recov- ered tags. Similar methods have been applied to the movements of passive tracers in the ocean by Fiadero and Veronis (1984) and Wunsch(1989). Beverton and Holt (1957) recog- nized that the solutions to advec- tion-diffusion equations are greatly complicated by heterogeneous dif- fusion rates and irregular boundary conditions (e.g. coastlines). They suggested replacing the diffusion equation with a system of area-spe- cific equations linked together by transfer coefficients that measure the movement across the boundary of adjacent areas (box models). This simple abstraction, as well as oth- ers like it, has received considerable attention in recent years, and a number of papers have dealt with estimating the transfer coefficients from tagging data (Beverton and Holt, 1957; Sibert, 1984; Hilborn, 1990; Deriso et al., 1991; Hampton, 1991; Schweigert and Schwarz, 1993; Kleiber and Fonteneau, 1994; Salvado, 1994). In principle box models are not very realistic be- cause they assume that movement within and among boxes occurs in- stantaneously, but in practice they may approximate the dynamics well enough to be useful. All of the aforementioned proce- dures (except Jones's) estimate the movement of a population from the local abundance of recovered tags. In contrast, the methods developed in this paper estimate movement from the trajectories of recovered tags. Strictly speaking, the new models address the advection (ex- 694 Porch: Estimating velocity and diffusion from tagging data 695 pected velocity) and diffusion of a population. As such, they should provide useful alternatives for estimat- ing the movement parameters of the advection-dif- fusion equation or individual-based simulations. They are applicable to box models only to the extent that such box models are analogous to finite differ- ence approximations to the advection-diffusion equa- tion. (In that case the transfer coefficients can be written as functions of the local velocity and diffu- sion rates.) This article is divided into five sections. The first section highlights the conceptual differences between trajectory-based and abundance-based estimators of velocity. The mathematical details of the proposed trajectory models are developed next. Section two focuses on the process of advection and section three on the process of diffusion. The performance of the models and their sensitivity to violations of the as- sumptions are evaluated by using stochastic simu- lations in the fourth section. Finally, some practical considerations and extensions to the methodology are discussed. General concepts Velocity, advection, and diffusion defined The term 'velocity' refers to the speed and direction in which an object (tag) moves. Mathematically, the velocity U at position x and time t is defined by the differential equation at (1) The map of U that assigns a velocity to each point in space and time is called the velocity field. In theory, the position of any given tag at any given time can be predicted from its velocity history by in- tegrating Equation 1. In application, however, it is usually more practical to describe the collective ve- locity histories of a group of tags in terms of a com- mon expected component u(x,t) and unique random components u'(x,t). The expected component is known as the advection field, and the random component gives rise to the diffusion field. By using this descrip- tion, the position xiT of the i'th tag after T units of time can be expressed in the general form <,o+r tio+T xlT = xl0 + \u(xt,t)dt+ \u'(xt,t)dt, (2) ',0 tto where xw and ti0 are the initial position and time, respectively. The first integral in Equation 2 determines the expected position of the tag, and the second integral determines the displacement of the tag relative to its expectation. In terms of a group of tags with com- mon starting points, the first integral describes the advection of the group as a whole, and the second integral determines how the group spreads about its expected center of mass. Approaches to estimating velocity The purpose of estimating movement rates and other parameters from tagging data is usually to elucidate the behavior of a larger population — often within the context of managing that population. Any such ap- plication implicitly assumes that the tagged and untagged members of the population move the same way. This basic tenet is accepted throughout the re- mainder of this article. The discussion in this sec- tion focuses on the ancillary assumptions that dif- ferent estimation approaches must make. The classical formula for estimating the advection of a tag is " = 772/ iT WO (3) i=i where n is the number of observations. Jones ( 1959, 1976) developed an alternative formula, which, in the present notation, is liT ~ -SO i=l (4) The practicality of the estimators (Eqs. 3 and 4) is limited because for these the advection field is as- sumed to be relatively constant, which is unlikely over the temporal and spatial scales relevant to popu- lation management. Therefore, it will often be prof- itable to enlist a more dynamic model of advection. The parameters of the dynamic model can be esti- mated by minimizing an appropriate objective func- tion of some measure of the effect of advection on the population. To date, the measure of choice for tagging data has been the local abundance of recov- ered tags. The measure used in this article is the trajectory of each individual tag. The accuracy of any estimator depends on the as- sumptions behind the construction of the objective function. These involve assumptions regarding the probability density of the measure and the structure 696 Fishery Bulletin 93(4). 1995 of the measure's predictor. To illustrate, consider a least- squares objective function whose measure is the num- ber N of tags recovered in each area a and season s: t,o + T, ^^(Nas-Nasf (5) The predictor, N, is a function of the parameters of the underlying population dynamics and advection models. In theory, the parameter estimates that minimize Equation 5 are unbiased if the measure (N) is nor- mally distributed with constant variance and the models behind the predictor are correct. It is gener- ally recognized, however, that the probability den- sity of recoveries is nonnormal and the variance in N may differ widely among areas and seasons, both of which imply that the least-squares solution is in- appropriate. For this reason, most of the recent lit- erature has favored maximum-likelihood solutions based on the multinomial distribution instead. The condition of the predictor ( N ) is more diffi- cult to assess because it embodies a suite of assump- tions regarding all relevant aspects of the popula- tion dynamics. The local abundance of tags may be affected by processes common to both the tagged and untagged populations (e.g. natural and fishing mor- tality) as well as by processes that are unique to the tagged population (e.g. tag-induced mortality, tag shedding, and failures to report recovered tags). It would be advantageous to develop a predictor that does not need to account for all the complex pro- cesses affecting tag recoveries, but it is clear that a measure other than abundance must be used. The trajectories of individual tags, which can be predicted from their velocity history alone, is one such mea- sure. Tag recovery rates are relevant to trajectories only in the sense that they determine those most likely to be represented in the sample. That is, re- covery rates dictate the probability density of ob- served (recovered) trajectories, but not the predic- tor. This point, though subtle, has important implica- tions with respect to relaxing the assumptions required to produce unbiased estimates of the advection field. Consider that the expected position of a tag after liberty time T follows from Equation 2: l,n+T, E[xlT] = xl0 + \u(x,,t)dt. (6) The expected position of a recovered tag under the same conditions is ER[xlT] = xl0+ \u(xt,t)dt + Er u'(xt,t)dt where the subscript R indicates that the expectation includes recovered tags only. The second integral dropped out of the unconditional expectation in Equa- tion 6 because u' is, by definition, a random variable with mean equal to zero. The same would not gener- ally be true of the expectation of recovered tags be- cause some vectors of u ' may be more likely to be recovered than others — changing the probability den- sity in some unknown way. Suppose there exists an objective function 0[x,x] (maximum likelihood or otherwise) that can produce unbiased estimates of E[xlT] from a random sample of all potential trajectories xjT. (The construction of this function will be discussed later.) The same ob- jective function will also produce unbiased estimates from a random sample of recovered tags provided Ef tio+Ti \u'{xt,t)dt (7) This constraint is satisfied if either u ' is everywhere identically zero or the probability of recovering a tag is independent of its velocity. The latter condition is effectively equivalent to assuming that the processes that influence tag recovery are homogeneous in space and time. It satisfies Equation 7 because it implies that the relative likelihood of observing any given displacement depends solely on the probability den- sity of u' . By definition, the expectation of u' at ev- ery point is zero and therefore the expectation of the integral sum of u' is also zero. It has been shown that, subject to Equation 7, tra- jectory-based estimators can provide unbiased esti- mates of the population advection field without re- covery rates having to be considered. One can imag- ine many practical situations where Equation 7 would be approximately satisfied. The spatial and temporal distribution of recovery rates would not normally be a significant factor in experiments in- volving radio-tracked drifter buoys or ultrasonic tags. Similarly, variations in the velocity of individuals might be expected to be small compared with the average velocity of a population undergoing a sea- sonal spawning migration. Where Equation 7 is not met, however, tags moving at different velocities may not be equally represented in the recovered sample. Porch: Estimating velocity and diffusion from tagging data 697 If, for example, faster tags were more likely than slower tags to move into a region where recovery rates are high, then the speed of the advection field would be overestimated. At this point it seems convenient to examine the proposed trajectory models in closer detail, noting that recovery factors other than advection do not need to be considered when Equation 7 is satisfied. The more complicated matter of accounting for variations in re- covery rates when Equation 7 is not met is deferred to the Discussion section at the end of this article. Trajectory-based predictors for estimating advection This section focuses on developing the predictor for the directed (advective) component of motion from the trajectories of recovered tags. The remaining portion of the objective function, which quantifies the differences between the observed and predicted val- ues of the measure, depends on the nature of the probability density and is discussed in detail in the subsequent section entitled "Diffusion and the ob- jective function." The general form of the trajectory predictor may be written t,n + T, \dx = \u(xt,t)dt , (8) where xiT = predicted position of tag i after time at liberty T\ u = estimated advection field; xiQ = initial position of tag i; and ti0 = initial date of tag i. In order to use this prediction equation, one must be able to evaluate the integral on the right. There are two ways to address this problem. One way is to break the temporal and spatial domain into small strata where the advection rates are approximately con- stant and then to assemble a picture of the large-scale advection field in piece-wise fashion. The other way is to define explicitly a dynamic model of the advection field and to evaluate the integral directly. Each ap- proach is developed in a separate subsection below. Piece-wise models This approach seeks to assemble a picture of the over- all advection field from estimates of the advection fields in smaller strata. An independent estimate of the average advection in each space and time strata can be obtained from any tag that has remained in that strata the entire time between its release and recovery (or between any two position updates) by using the formula HT Wo If observations are available for most of the strata of interest, the entire advection field can be para- meterized quite nicely by using a two-way analysis of variance (AN OVA) model: : U + A„ + SQ + /„„ + £, (9) where u u \ I.. e, = the observed velocity of tag i; the overall mean velocity; the main effect of area a on u\ the main effect of season s on u; the area/season interaction effect; and the error associated with tag i. In two spatial dimensions a separate AN OVA would apply to each velocity component: ut = u + Aau + Ssu + Iasu + elu , vi =v+Aav+Ssv+Iasv+eiv, where w( = the observed velocity in the direction of the first dimension; v- = the observed velocity in the direction of the second dimension; Aa = the main effect of area a on u or v; Ss = the main effect of season s on u or v; I = area/season interaction effect on u or v; and £. = the errors associated with tag i. Interpolation routines other than ANOVA may also be used to describe the overall advection field, but ANOVA provides a convenient framework for test- ing whether the advection rates vary among strata. Such tests are valid if the velocity variances are the same in all strata; otherwise one must employ an equivalent nonparametric approach. ANOVA or other interpolation algorithms are well suited to situations where the positions of tags can be updated frequently. They are especially promis- ing for programs that employ remote tracking de- vices such as radio or ultrasonic tags (e.g. Quinn, 1988; Hines and Wolcott, 1990; Schulz and Berg, 1992). In some cases the biology of the organism may even permit effective visual tracking (e.g. Stacho- witsch, 1979). The ANOVA approach is less suited to 698 Fishery Bulletin 93(4). 1995 conventional tagging programs because the ability to record the position of the tag is largely beyond the control of the investigator. In this situation a suffi- cient number of tags would need to be released in each season and area strata to ensure that at least a few would be recovered before straying into other strata. The recovery times must also be short enough to avoid biasing the results toward slower moving tags. A more flexible estimation procedure, which is ca- pable of incorporating trajectories that reflect the combined effects of several different movement pat- terns, can be derived by reformulating Equation 8 as t,n+T, J u{x,t) J dt. (10) If u(x,t) is held constant within specific space and time strata but allowed to vary among strata, then Equation 10 may be piece-wise integrated. The solu- tion simplifies to ^s+i ~ts~ xs+l - when u > 0, and Bn ^s+l ~h~ when u < 0. la+l,s xs+l ~ Ba-\-Ba ua-\,s Un,s+Bii' (11) un,s + ^n+i> (12) Here uas = velocity in area a during season s; Ba = boundaries of the areas (see Fig. 1); a = first area occupied by the tag during season s; £2 = last area occupied by the tag during season s; ts = date at the onset of the s'th season; and xs = position of tag at onset of s'th season. With these recursions, the position of the tag at the end of each season can be computed from the tag's position at the end of the previous season by using an estimate of the advection field. This proce- dure can then be applied sequentially to compute the expected position of the tag at the date when it was recovered from its initial position. The "best" esti- mates of the strata-specific advection rates would minimize some objective function of the differences Area a Area a+1 Area a+2 ► ► ► Sa+2 Ba*3 Figure 1 Schematic of a region divided into three areas illustrating the definition of the area boundaries, B. between the observed recovery positions and those pre- dicted with the recursions. (The appropriate objective function will be discussed in the section on diffusion. ) The sequential procedure itself is accomplished by first determining the starting season s0 and starting area a for each tag from the date and position where it was released. The position of the tag at the end of the first season (start of season s0+l) can then be obtained from the recursions, by replacing x and t with the position and date of release. The recursions are then applied as given until the last season, which is determined by the recovery date. Finally, the formula for estimating the recovery position is obtained by re- placing ts+l in the recursions with the recovery date. Continuous models The approach proposed in this section involves de- veloping an adequate continuous model of the ad- vection field, u(x,t), and solving Equation 8 for* as a function of t. To illustrate, consider a fish population migrating out of a basin. Suppose each fish swims initially at speed uQ in the positive x direction and increases its speed as it proceeds. Further, suppose that periodically the fish are either helped or hin- dered by sinusoidal oscillations in the water currents. A reasonable model for the velocity of the fish might be u(x,t) - U(.+ ax + bsin[ct]. The solution is ._ "o , asin[c£] + ccos[c^] at o— — s 7. (-/e a2+c2 (13) where | uQ | 6asin[c<0] + ccos[c,-0„ 7=1! 0* The coefficient of error is analogous to the familiar coefficient of variation except that the true values of the parameters are used in place of the average of their estimates. Alow CE, therefore, implies that the estimates are both unbiased and precise. Factor levels Two advection models were consid- ered: the sinusoidal model dx/dt = u0 + ax + bsin[ct], discussed earlier in connection with Equation 13, and a discrete model with two areas and semi-annual seasons. The parameters of the first model — w0, a, b, andc — were valued at 8.6 kmday-1, 0.004 day-1, 17.3 kmday-1, and 2;t/365 day-1, respectively. The para- meters of the second model are the area and season- specific constant advection rates. The rates in areas 1 and 2 were set equal to 5 and 10 kmday"1 during the first season and -7 and -4 km- day * during the second season. Area 1 extended from negative infin- ity to 1,000 km and area 2 extended from 1,000 km to positive infinity. Two diffusivity (fil2) levels, 0.95 and 822 km2-day"1, were examined. These levels were derived by assum- ing that tagged fish move according to the bilateral random walk model (see Porch, 1993) with an aver- age speed of 0.5 or 6 meters per second and change direction an average of once per minute or once ev- ery five minutes, respectively. The effects of variations in tag recovery rates were evaluated by dividing the relevant spatial domain into two zones and by varying the likelihood of re- covering a tag between them. Three such scenarios were considered. In the first, the probability of re- covery was the same in both zones. In the second, the probability of recovery was ten times higher in zone A than in zone B (1.0 versus 0.1). In the third scenario, no tags were recovered in zone B. The boundary separating recovery zones A and B differed with the advection models. The demarcation point was x - 400 km in the sinusoidal model and x = 0 km in the discrete model. Test data Each test data set was generated by simu- lating the individual paths of a prescribed number of tags (n). The release positions were randomly as- signed values between 0 and 200 km when the sinu- soidal advection model was used and were between -1,000 and 1,000 km when the discrete model was 702 Fishery Bulletin 93(4). 1995 employed. The release dates were randomly assigned values between day 0 and day 365. These choices mimic an opportunistic tagging program where the number of tags released is relatively constant dur- ing the year. The recovery dates were obtained by randomly selecting the liberty times from an expo- nential distribution with parameter Z (instantaneous mortality rate) equal to 0.4 yr-1. The displacement of each tag due to advection was computed from its release position and from release and recovery dates by using the solutions to the de- terminate advection models described above. The solution to the sinusoidal model is given by Equa- tion 13, and the solution to the discrete model is given by Equations 11 and 12. The diffusive effect of ran- dom motions was then simulated by adding a ran- dom normal deviate with mean 0 and variance pT km2. Next, an acceptance-rejection criterion was invoked to determine whether or not the tag would be recovered. Candidate tags located in recovery zone A were unconditionally accepted, but candidate tags located in zone B were accepted only with probabil- ity P ( = 1.0, 0.1, or 0). This was done by generating a uniform random number between 0 and 1 and by excluding the tag if that number was greater than the prescribed recovery probability. The process described above was repeated until a total of n recovery positions were accepted. Normally distributed errors (with variance 25 km2) were then added to each of the accepted release and recovery positions to simulate imprecise position reporting. In this way an artificial sample of n tag recoveries was created. Estimation The predictors were fitted to the test data by minimizing the weighted least-squares sur- face described by Equation 19. The predicted posi- tions were calculated by substituting estimates of the parameters into the same advection equations used to generate the data. This allowed the analyses to focus on the interactions of recovery rates and veloc- ity variance without the confounding effects of model misspecification. The minimization was accomplished by using the Nelder-Mead simplex algorithm AMOEBA (Press et al., 1986), which, although slower than derivative-based methods such as Marquardt's algorithm, is less sensi- tive to the discontinuities in the solution surface asso- ciated with discrete advection models. Heavy penal- ties were imposed to prevent the search from extend- ing beyond the bounds of a reasonable domain. For example, the maximum possible sustained speed of a migrating tuna might be the sum of the cruising speed of the fish and the maximum speed of the water cur- rents. The AMOEBA search was restarted at the point PQ, where a minimum had been found, to avoid local anomalies in the solution surface. Subsequent "re- starts" continued until five consecutive sets of pa- rameter estimates differed by less than one percent. New vertices were selected for each restart by using the formula Pu = P 0jc ,0.5A5, (i,j = X ,co) where P. is the value of the/th coordinate (param- eter) in the z'th vertex of the initial simplex, K is a standard normal variate, and 8- is equal to one if i equals j and zero otherwise. Results This section is divided into two parts, each focusing on the results pertaining to one of the two types of advection models. Sinusoidal model The estimation procedure generally behaved very well when the frequency (c) of the sinusoidal oscilla- tions was known and the diffusivity was low (0.95 km2-day_1). The CE's, which reflect both accuracy and precision, were very low regardless of the distribu- tion of recovery rates (Fig. 2). For the most part, the estimator continued to perform well at high diffusivities ( 822 knrday1 ). When the recovery prob- abilities were the same in both zones, the estimates were unbiased and the CE's rapidly decreased with increasing sample size to less than 10 percent. The estimates were only slightly biased and similarly precise even with a tenfold difference between the recovery probabilities. It was only when no tags were recovered in zone B (i.e. beyond the 400-km demar- cation) that the estimates were significantly biased. The trends were very similar to those described above when the frequency parameter c was estimated along with the other three parameters. A few of the runs, however, failed to converge to acceptable solu- tions— the weighted least-squares function being an order of magnitude greater than that expected, given the known diffusivity. This problem is not surpris- ing considering the oscillatory nature of any peri- odic surface. Even if the true values of the other pa- rameters were known, the surface map of the objec- tive function would be characterized by local peaks and valleys that vary with the estimate of c. This behavior is demonstrated by a simplified model of the residual sum of squares (Fig. 3). Although the ampli- tudes of the peaks and valleys in the more complicated Porch: Estimating velocity and diffusion from tagging data 703 o O Sample size Figure 2 Coefficients of error of the estimates for the parameters of the sinusoidal model. The graphs on the left give the coefficients of error (CE's) under weak diffusivity and the graphs on the right give the CE's under strong diffusivity. The three curves in each graph correspond to zone B recovery probabilities of 0.0 (squares), 0.1 (triangles), and 1.0 (crosses). model vary (the lowest valley presumably occurring in the vicinity of the true values of the parameters), sev- eral of the valleys may be deep enough such that the estimation routine finds a false global minimum. The convergence problem was eliminated when the search was confined to a relatively restricted range of periodicities and was supplied with good initial guesses. In practice, adequate initial guesses and relatively narrow ranges can usually be deduced even from anecdotal data, therefore this should not prove too serious a limitation to the method. In cases where the periodicity is totally unknown, one should search the entire feasible domain with as fine a resolution as possible. Piece-wise discrete model The coefficients of error associated with each para- meter were, for the most part, very low when the diffusivity was low (Fig. 4). However, the estimates pertaining to area 2 were highly biased and impre- cise when the probability of recovering a tag was 0.0 in zone B. This is not unexpected given that exclud- ing recoveries in zone B (x>0 km) all but eliminates the possibility that any of the recovered tags would ever have encountered area 2 (x> 1,000 km). Thus, there is essentially no information on the advection in area 2 and the estimation routine fails. A similar result was not observed when the recovery probabil- 704 Fishery Bulletin 93(4), 1995 25 mm; Woodbury3), additional adjustments were performed in a two-step process. Individual fish ages were predicted from standard length [SL] measurements by using linear inverse growth curves (age-f[Sh]) that were estimated for each species during the 10-year period from 1983 to 1992. Specifically, the predicted age of species s in yeary at standard length / is r . = ccsy + fisyl, where the a and /? were estimated by least-squares re- gressions of age-length data gathered from micro- scopic examination of otolith daily increments (see Laidig et al., 1991; and Woodbury and Ralston, 1991 ). If otolith data were unavailable in a particular year, growth parameters were estimated from an analy- sis of covariance of all the yearly data, by assuming a common slope (daysmm-1) and the mean of interannual intercepts. For each haul conducted and each species sampled (subscripts not included), abundances offish of dif- ferent ages were then adjusted to a common age by using an exponential model with a constant mortal- ity rate (Z), i.e. N; = A//exp[-Z(r*-rsW)], where Nf is the adjusted number of individuals of length /, N{ is the unadjusted number, and r is the common age to which abundances were adjusted. In all calculations x was set equal to 100 d, which is generally representative of pelagic juvenile rockfish ages during May-June (Woodbury and Ralston, 1991), and Z was fixed at 0.04 d"1. This latter figure was based on combined estimates of mortality rate for 1) larval shortbelly rockfish, S. jordani (Ralston et al.1); 2) settled juvenile blue rockfish (Adams and Howard4); 3) pelagic juvenile Pacific cod, Gadus macrocephalus, and northern anchovy (Bradford, :( Woodbury, D. 1993. Natl. Mar. Fish. Serv., NOAA, 3150 Para- dise Dr., Tiburon, CA 94920. Unpubl. data. 4 Adams, P. B., and D. F. Howard. Natural mortality of blue rockfish (Sebastes mystinus ) during their first year in nearshore benthic habitats. Manuscript submitted to Fishery Bulletin. 1992); and 4) pelagic juvenile Pacific whiting, Merluccius productus (Hollowed, 1992). The A^* were then summed over all lengths occurring within a haul, yielding a haul-specific catch of each rockfish species sampled that was adjusted for variability in length composition. Final calculation of abundance statistics from our midwater trawl surveys was based upon simple loga- rithmic transformation of the data, i.e.y ■- = \oge[Xjk + 0.1], where x k is the length-adjusted catch taken in haul j located in stratum k = 1 to 7. We estimated the individual stratum means, variances, and stan- dard errors for each sweep using conventional pro- cedures appropriate to a stratified sampling design (Cochran, 1977). The equally weighted stratified mean was then used as a sweep-specific index of pe- lagic juvenile abundance. Lastly, because the avail- ability of pelagic juveniles to midwater trawling shows marked seasonal change, the maximum value of the stratified mean (among sweeps completed in a year) was used to estimate relative annual abun- dance, i.e. year-class strength. Direct underwater observation surveys Nearshore assessments were made by underwater observers by using SCUBA at four locations on the northern California coast (Fig. 1). Two of the study sites, Dark Gulch (lat. 39°14'N; long. 123°46'W) and Salmon Point (lat. 39°12'N; long. 123°46'W) in Mendocino County, were monitored since 1983. In 1984, nearshore assessments were initiated at Horse- shoe Point (lat. 38°36'N; long. 123°22'W) and at Fisk Mill Cove (lat. 38°35'N; long. 123°21'W) in Sonoma County, 100 km to the south. Each study site covers approximately 0.5 ha and consists of high-relief rocky reefs surrounded by lower reefs and boulders, interspersed by occasional sand patches. Vertical water clarity was measured from the boat with a white, plastic Secchi disk 20 cm in diameter. Horizontal water clarity at a bottom depth of 10 m was determined by estimating the distance at which rock surfaces could be clearly observed. Counts were not made when conditions were turbu- lent, nor when visibility was less than 4 m. Observations for estimating year-class strength began in late July, when settlement of pelagic juve- niles was essentially complete, and continued through the end of September. Young-of-the-year fish were distinguished from older cohorts by their size (40-50 mm SL in July), and from other species by characteristic pigment patterns. Strip-transect counts were made between the hours of 1000 and 1400 by observers using SCUBA over bottom depths of 5-22 m. At each study site, Ralston and Howard: Year-class strength and cohort variability in Sebastes mystmus and 5. flavidus 713 40 39 3 38 37 M I I Granite Canyo i i i i i i i f i 125 124 123 122 Longitude (°W) Figure 1 Map of the study area showing the location of trawl stations and diving sites where direct underwater observations of settled juvenile rockfish were made in Mendocino and Sonoma counties (1983-921. Temperature data were collected daily at Bodega Bay, the Farallon Islands, and Granite Canyon. ward direction during the transect. Af- ter 1-3 counts the observer made right- angle changes in direction, which re- sulted in thorough coverage of the study area. The number of daily counts at a site ranged from 10 to 35 ( x =18.8). Counts were excluded from data analyses when it was obvious that the distribution of juveniles was influenced by unusual conditions. For example, sampling sometimes coincided with a period of convergence when food-rich oceanic waters moved into nearshore surface layers. The distribution of ju- veniles was very different at these times, as they ascended into the upper 2 m of the water column to feed. Annual indices of settled juvenile abundance were calculated separately for blue and yellowtail rockfish in Mendocino and Sonoma counties. Be- cause variances increased with the means, individual strip-transect counts were first log-transformed to stabilize the variance. The annual index was then simply calculated as the mean of all counts, e.g. 1 Isct=-Yll°Sel-Cisct + 1l where Isct is the index for species s in county c in year t , and n is the number of counts (Clsct) conducted; the sampling precision of the index is given by the standard error of the mean. the abundance of young-of-the-year juveniles was as- sessed along haphazard transects by a series of timed 1-minute counts that covered approximately 20 m. Observers maintained a constant swimming speed, gazing ahead at all times during the counts. Transects started on the outside edge of the kelp bed and followed a series of arbitrary compass headings covering the offshore portion of the study site. After completing counts in deeper habitats, observers pro- gressed into shallower water. Species and number of juveniles observed each minute were recorded on a plastic slate with the aid of a watch fastened in the upper corner to monitor time. Observers swam 2 m off the bottom and counted young-of-the-year rockfishes within 3 m in any for- Interannual variability in year- class strength As in many other species, recruitment in rockfish is highly variable and is described well by the log-nor- mal distribution (Bence et al., 1993; Fogarty, 1993). An accepted way to portray relative levels of varia- tion among different sets of data is through use of the coefficient of variation (CV). The CV of the log- normal distribution is unusual, being independent of the mean and equal to [exp(cr2 ) - 1]1/2 , where 0s is the variance of logarithms of the log-normally dis- tributed variable (Johnson and Kotz, 1970). To compare and contrast levels of variation in rock- fish year-class strength at specific life history stages, CVs of annual time series were calculated. Because individual annual abundance statistics were usually 714 Fishery Bulletin 93(4). 1995 estimated with some error, given by the standard error of the mean, and because variance terms are additive, this measurement error was subtracted from the total interannual variance in year-class strength prior to calculation of the CV, i.e. 2 2 2 ocv = oT0T - ae CV = V(eCT" - 1) . An estimate of measurement error ( o£ ) was obtained as the mean of the squared standard error estimates (sIt2) of the annual index /, averaged over the k years that data were available, 02£ 14- t=\ Likewise, the total variance in the index (aTOT2) was estimated simply as the sample variance of the in- dex (It), ^■2 °TOT 1 * 1 * iy t=i For small sample sizes (&<50) and large CV's (>2.0), there is a positive bias in this estimator (Finney, 1941). We determined the magnitude of the bias by Monte Carlo simulation (Naylor et al., 1966), and we applied a bias correction term to each CV estimated. Shore station sea-surface temperature Sea-surface temperature (SST) and salinity are re- corded daily at the University of California Bodega Bay Marine Laboratoiy (BB), the Point Reyes Bird Observatory facility on Southeast Farallon Island (FI), and at the California Department of Fish and Game Laboratory at Granite Canyon (GC) (Walker et al., 1993). SST data from all three sites are gener- ally indicative of hydrographic conditions offshore over the continental shelf (Fig. 1). Interannual fluctuations in SST within the cen- tral California study region were estimated by using an analysis of variance (AN OVA) model applied to the shore station data, i.e. SSTy^ii + aj+Pj+Yt+e, ijk i where SSTt k is the sea-surface temperature recorded at shore station i U'=BB, FI, or GC) on calendar date j {/=1,..., 90} in year k {k=1980,..., 1992}, n is the popu- lation mean SST, and sijk is a normally distributed error term. Only the first 90 days of the calendar year were included in the analysis because blue and yellowtail rockfish are winter-spawning species (Wyllie Echeverria, 1987) and a measure of the aver- age SST prevailing from birth to completion of the late larval stage was desired. Year effects (yk) in the model were obtained by calculating population mar- ginal means (i.e. least-square means), providing year- specific estimates of SST at average levels of the a; and P (see Searle et al. [1980] for further discussion). Results Annual abundance indices of pelagic juvenile blue and yellowtail rockfishes captured by midwater trawl were quite variable (Table 1; Fig. 2). The CVs of these abundance indices were 1.98 and 1.19, respectively, over the 10-year period from 1983 to 1992. Years of high abundance for both species were 1985, 1987, 1988, and 1991, whereas years of low abundance were 1983, 1986, and 1992. A similar pattern was evident in the data collected by direct underwater observations of recently settled rockfish juveniles in Mendocino and Sonoma Coun- ties (Table 1; Fig. 2), although levels of interannual variation in abundance for these species was some- what greater. Specifically, estimated CV's ranged 92 93 Figure 2 Interannual trends in the abundance of blue [Sebastes mystinus) and yellowtail iSebastes flavidus) rockfishes based on trawl surveys of pelagic juveniles and direct un- derwater observations of settled young-of-the-year fish ( 1983-92). The dashed vertical line shows when the trawl survey was changed from one to three sweeps, (see Meth- ods section). Ralston and Howard: Year-class strength and cohort variability in Sebastes mystinus and S flavidus 715 Table 1 Coefficients of variation in rockfish year-class strength at selected life history stages. All pelagic and settled juvenile results are based on this study. Within-year measurement error ( o"f ) removed for egg, pelagic juvenile, and settled juvenile life history stages (see Methods section). Young-of-the-year Species Egg Pelagic juvenile Settled juvenile Entry to fishery Sebastes mystinus Sebastes flavidus Sebastes entomelas Sebastes goodei Sebastes paucispinis 0.10' 1.98 1.19 2.25 1.49 0.96 3.06-3.68 2.59-2.69 0.60-0.87 0.823 1.39* 0.725 ' Eldridge and Jarvis (1995). 2 Tagart (Footnote 2 in the text). 3 Rogers and Lenarz. 1993. Status of the widow rockfish stock in 1993, Appendix B. In Appendices to the status of the Pacific Coast groundfish fishery through 1993 and recommended acceptable bio- logical catches for 1994. Pacific Fishery Management Council, 2000 SW First Ave., Suite 420, Portland, OR. 4 Rogers and Bence. 1993. Status of the chilipepper rockfish stock in 1993, Appendix D. In Appendices to the status of the Pacific Coast groundfish fishery through 1993 and recommended acceptable bio- logical catches for 1994. Pacific Fishery Management Council, 2000 SW First Ave., Suite 420, Portland, OR. 5 Bence and Rogers. 1992. Status of bocaccio in the Conception/ Monterey/Eureka INPFC areas in 1992 and recommendations for management in 1993, Appendix B. In Appendices to the status of the Pacific Coast groundfish fishery through 1992 and recommended acceptable biological catches for 1993. Pacific Fishery Management Council, 2000 SW First Ave., Suite 420, Portland, OR. from 3.06 to 3.68 for blue rockfish and from 2.59 to 2.69 for yellowtail rockfish. The observational data also indicated that 1985, 1987, 1988, and perhaps 1991, were relatively strong years, whereas 1983, 1992, and to some extent 1986, were weak years. There were highly significant correlations between direct observation counts of settled juvenile rockfish at Mendocino and Sonoma Counties. For blue rock- fish the correlation was 0.925 (P<0.005) and for yel- lowtail rockfish it was 0.887 (P<0.005). The greatest disparity in abundance between these localities oc- curred in 1991, when counts of the two species at Mendocino County were low, both in comparison with observations at Sonoma County and with catches in the trawl survey. The time series of midwater trawl and direct ob- servational data were also well correlated (Fig. 3). For example, results for blue rockfish, Sebastes mystinus, showed highly significant (P<0.005) posi- tive correlations in excess of 0.80 at both the Mendocino and Sonoma sites. Similarly, the correla- tion between trawl survey estimates of yellowtail rockfish, Sebastes flavidus, abundance and direct counts of this species at Sonoma County (r=0.799) was significant (P<0.01). The comparison between the trawl data and Mendocino County counts (r=0.577) was marginally insignificant (0.1024 mm SL) that the shrinkage rate was negligible relative to total size. All samples were collected off central California between Cypress Point (36°35'N latitude) and Salt Point (38°35'N latitude). A total of 283 fish were examined, including 138 large specimens (>20 mm SL), 130 small specimens (<20.1 mm SL), and 15 pre-extrusion larvae. Large specimens were identified from meristic characters and pigment patterns (i.e. melanophore patterns, because other pigments such as xanthophores are not retained well in ethanol [Matarese et al., 1989]) as described previously in Chen ( 1986), Matarese et al. ( 1989), Moreland and Redly ( 1991 ), and Laroche.2 Small specimens were initially identified by using pigment patterns developed from a size series (Kendall and Lenarz, 1987) based on the pigment patterns of pre-extrusion larvae and on the smallest individuals with complete meristic characters. Pig- ment patterns were recorded on each specimen ex- amined. Dorsal-, anal-, and pectoral-fin ray counts were recorded on specimens >8.1 mm SL, and the number of gill rakers on the first gill arch were recorded on a subset of 50 large specimens. Morphometric data, including head length, snout length, snout to anus distance, eye diameter, body depth at the pectoral fin base, body depth at the anus, and pectoral fin length, were taken on 20 specimens ( all preserved in 95% ethanol ) ranging in size from 5.3 mm NL to 22.0 mm SL. Measurements were recorded in mm by using a dissecting microscope connected to a video camera and computer. Terminology for morpho- metries followed Richardson and Laroche ( 1979). In order to examine the development of head spines, 20 specimens ranging in size from 6.1 mm NL to 22.0 mm SL were stained with Alizarin Red-S. In addition, because it is often used as a diagnostic character, the presence or absence of supraocular spines was noted in all large specimens. Terminol- ogy for head spination followed Richardson and Laroche (1979). Otolith characters have recently been shown to be helpful in identifying late larval and pelagic juve- nile Sebastes spp. (Laidig and Ralston, 1995). In par- ticular, the otoliths of S. goodei develop a distinctive optical pattern (i.e. a dark inner ring surrounding a dark primordium) during the pre-extrusion larval stage (Laidig and Ralston, 1995). Consequently, otoliths were removed from 50 specimens (4.6 mm NL to 10.7 mm SL) to help confirm the initial pig- ment-based identifications of larval S. goodei. For comparison, otoliths were also removed from 52 lar- val Sebastes of unknown species (3.7 mm NL to 8.2 mm SL) that had pigment patterns similar to, but slightly different from, those of larval S. goodei. Otoliths of S. goodei and other Sebastes spp. were removed from specimens collected at the same sites to determine whether the pigment patterns described in this study were accurately distinguishing S. goodei from other Sebastes spp. Other Sebastes spp. were distinguished from S. goodei by one or all of the fol- lowing characteristics: absence of pigment on the cranium and nape, presence of pigment on the tip of the lower jaw, presence of pigment on the cleithral region, and presence of pigment on the caudal area. Sebastes jordani and S.paucispinis were not included in the other Sebastes spp. category because they were easily identified on the basis of distinctive pigment patterns and morphometries (Moser et al., 1977). Otoliths were examined under a compound micro- scope connected to a video camera and computer with a working magnification of l,250x. The radius of the Sakuma and Laidig: A description of larval and pelagic Sebastes goodei 723 extrusion check, the total radius, and the pre-extru- sion optical pattern were recorded on all otoliths ex- amined. Pre-extrusion optical patterns (as previously described in Laidig and Ralston, 1995) were recorded as being either "strong," "weak," or "absent." "Strong" patterns were readily visible and required very little focusing for resolution. In "weak" patterns, the dark inner ring surrounding the primordium was not readily visible without fine focusing. "Absent" pat- terns were devoid of the pre-extrusion optical pat- tern described for S. goodei (Laidig and Ralston, 1995). Ages were recorded only from otoliths with clear, distinct daily rings. Ages were obtained follow- ing the methods described in Laidig et al. ( 1991 ) and Woodbury and Ralston (1991). Results General development Larval S. goodei were extruded at a size of 4.5 to 5.8 mm NL. Notochord flexion began at 5.7 to 6.5 mm NL and was complete at 8.1 to 8.8 mm SL. Meristic counts were similar to those reported by Chen ( 1986), Moreland and Reilly (1991), and Laroche2 (Table 1). In late-stage flexion and recently flexed individuals a full complement of pectoral-fin rays was present, while the pelvic, dorsal, and anal fins had begun forming. By 9.0 mm SL, the full complement of pec- toral-, pelvic-, dorsal-, and anal-fin rays had devel- Table 1 Frequency of occurrence of dorsal- anal- and pectoral-fin ray, and gill-raker counts in chilipepper, Sebastes goodei . Frequency of Percent Character Count occurrence occurrence Dorsal-fin rays 13 10 6.6 14 106 70.2 15 34 22.5 16 1 0.7 Anal-fin rays 8 157 90.2 9 17 9.8 Pectoral-fin rays 16 12 7.8 17 138 90.2 18 3 2.0 Gill rakers 33 1 2.0 34 21 42.0 35 14 28.0 36 10 20.0 37 4 8.0 oped. Accurate gill-raker counts were obtained only on large specimens (>20 mm SL). Changes in body shape in S. goodei were related to notochord flexion (Table 2). During flexion, body depth at the pectoral-fin base and at the anus in- creased substantially (Table 2). Also during flexion, pectoral-fin length increased with the development of the full complement of fin rays (Table 2). In addi- tion, head length, snout length, snout to anus dis- tance, and eye diameter all showed a marked increase during flexion (Table 2). Head spines first appeared in S. goodei at approxi- mately 6.1 mm NL; the pterotic and the second an- terior and third posterior preoperculars were the first to form (Table 3). During late flexion (approximately 7.5 mm NL), the anterior and the second through fifth posterior preopercular series, the postoculars, and the parietals were evident (Table 3). The pari- etals were serrate and longer than the nuchals, which developed in postflexion individuals (approximately 8.5 mm SL). The first superior infraorbital also was evi- dent in postflexion individuals (Table 3). The third spine of the posterior preopercular series was always the long- est. By 14.0 mm SL, the opercular, inferior infraorbitals, supracleithral, and posttemporal spines had developed and by 20.0 mm SL the nasal and tympanic spines were evident (Table 3). Coronal spines were not observed on any of the specimens (Table 3). Supraocular spines, previously unrecorded in S. goodei (Moreland and Reilly, 1991; Laroche2), were observed on 11% of the large individuals ( >20 mm SL )( Table 4 ). Specimens with supraocular spines ranged in size from 32.0 to 50.2 mm SL, indicating some variability in the occurrence of this characteristic in the pelagic juvenile stage (Table 4). Pigment patterns Pre-extrusion larvae ranging in size from 5.0 to 5.8 mm NL had a group of 6 to 12 melanophores on the cranial region, 2 to 5 melanophores on the nape, pig- ment on the dorsal region of the gut, and a series of 15 to 25 melanophores lining the ventral body that did not extend anteriorly beyond the third postanal myomere (Fig. 1A). Recently extruded larvae (1 to 2 days old) ranging in size from 4.5 to 5.7 mm NL had more developed pigment on the cranium and nape than did pre-ex- trusion larvae and had pigment on the dorsal region of the gut and a series of 13 to 17 melanophores lin- ing the ventral body that did not extend anterior to the fourth postanal myomere (Table 5). Pigment on the cranium persisted throughout development. By 5.7 to 6.1 mm NL (3 to 5 days old), pigment on the outer blade of the pectoral fin became evident (Table 5; Fig. IB). During flexion, melanophores became 724 Fishery Bulletin 93(4), 1995 Table 2 Morphometric measurements of chilipepper, Sebastes goodei larvae of various size. All measurements are in mm Specimens between the dashed lines were undergoing notochord flexion. Head Snout Snout to anus Eye Body depth at Body depth Pectoral- SL length length distance diameter pectoral base at anus fin length 5.3 1.06 0.27 1.73 0.39 0.85 0.45 0.35 5.4 1.07 0.28 1.80 0.45 0.90 0.47 0.33 5.6 1.03 0.33 1.83 0.44 0.97 0.43 0.38 5.8 1.05 0.30 1.98 0.47 0.98 0.45 0.41 6.0 1.16 0.32 1.95 0.47 0.98 0.48 0.42 6.1 1.12 0.30 2.03 0.48 1.00 0.44 0.43 6.6 1.40 0.32 2.45 0.49 1.15 0.57 0.74 6.7 1.43 0.36 2.50 0.56 1.16 0.57 0.78 6.8 1.45 0.39 2.50 0.58 1.17 0.59 0.75 7.3 1.80 0.52 2.77 0.67 1.46 0.84 1.01 8.0 2.56 1.00 3.99 0.80 1.99 1.18 1.60 8.1 2.70 1.07 4.20 0.95 2.10 1.60 1.75 8.3 3.00 1.05 4.25 1.01 2.15 1.57 1.88 8.7 3.18 1.13 4.65 1.10 2.51 1.72 1.92 9.1 3.45 1.33 4.75 1.24 2.40 1.90 2.07 9.6 3.61 1.21 5.12 1.38 2.79 2.08 2.28 12.2 4.50 1.35 7.34 1.65 3.16 2.37 3.34 13.9 4.92 1.76 7.97 1.75 3.55 2.72 3.54 20.1 6.50 2.04 10.40 2.40 4.85 3.88 5.28 22.0 8.46 2.73 12.34 2.54 5.71 4.92 6.02 evident on the dorsal surface anterior to the eyes (Table 5). None of the preflexion and flexion larvae were pig- mented on the cleithral region or caudal area. After flexion (>15 days old), pigment lining the ventral body was greatly reduced; approximately 8 melanophores were present either on or near the articulations of the anal-fin rays, and/or on the ven- tral midline of the caudal peduncle (Fig. 1C). In ad- dition, nape pigment had become imbedded in postflexion individuals. Upon completion of flexion, melanophores had also begun to develop on the pelvic fin and along the posterior portion of the dorsal body surface underlying the soft dorsal fin ( Table 5; Fig. 1C ). At 11.0 mm SL (>40 days old), additional melano- phores had developed on the dorsal body surface un- derlying the spinous dorsal fin, and melanophores ex- tended into the fin membranes (Table 5; Fig. ID). In addition, pigment was evident along the blade of the pelvic fin, had covered the outer half of the pectoral fin, and had begun to develop on the surface of the oper- culum (Table 5; Fig. ID). Pigment on the anterior tip of the lower jaw and on the hypural region had begun to occur at 11.8 mm SL, and pigment along the dorsal body surface continued to increase (Table 5). By 12.0 mm SL, the melanophores lining the dor- sal body surface had begun to form the first body bar above the opercular region (Table 5). The first body bar and all subsequent body bars formed initially from the dorsal surface and extended ventrally with development. Pigment along the lateral midline of the body had begun to develop on the caudal region by 14.0 mm SL, and the second body bar had begun to develop underneath the spinous dorsal fin at 14.5 mm SL (Table 5; Fig. IE). Pigment began to develop along the ventral and posterior regions of the eye orbit at 18.7 mm SL (Table 5). By 28.0 mm SL, pigment on the ventral and poste- rior regions of the eye orbit, the dorsal surface ante- rior to the eyes, the surface of the operculum, the dorsal body surface, the lateral midline of the body, the hypural region, and on the membranes of the spinous dorsal fin were all well developed (Table 5; Fig. IF). The ventral terminus of the first body bar was projected forward and the second body bar be- gan to develop a similar pattern (Fig. IF). In addi- tion, the remaining three body bars had begun form- ing with the first appearance of the third body bar just anterior to the soft dorsal fin, with the fourth body bar directly under the soft dorsal fin, and with the fifth body bar on the caudal region (Table 5). Pec- toral- and pelvic-fin pigment had become less promi- nent by 29.0 mm SL, with melanophores on only the Sakuma and Laidig: A description of larval and pelagic Sebastes goodei 725 Figure 1 Developmental series of chilipepper, Sebastes goodei. (A) 5.5-mm pre-extrusion larvae; (B) 6.9-mm larvae; (C) 9.1-mm larvae; (D) 11.1-mm larvae; (El 16.5-mm larvae; (F) 26.5-mm pelagic juvenile; (G) 35.6-mm pelagic juvenile; and (H) 54.3-mm pelagic juvenile. outer quarter of the pectoral fin. Pigment along the ventral body surface was either absent or occurred sparsely (1 to 7 melanophores) on or near the anal- fin ray articulations and/or on the ventral surface posterior to the anal fin. At 34.2 mm SL, individuals had begun to lose al- most all their pectoral- and pelvic-fin pigment, while the third body bar had become almost fully devel- oped (Fig. 1G). The second and third body bars had developed a forward projecting pattern similar to the 726 Fishery Bulletin 93(4). 1995 Figure 1 (continued) Sakuma and Laidig: A description of larval and pelagic Sebastes goodei 727 Table 3 Development of head spines in chilipepper, Sebastes goodei. '1" indicates that spine if present and "0" indicates that spine is absent. Spine Standard length (mm) 6.1 6.3 7.5 7.7 8.2 8.5 9.2 9.6 10.0 10.7 11.7 12.2 13.4 13.8 14.1 16.8 18.8 19.4 21.5 22.0 Pterotic 1 1 1 1 1 1 1 1 1 1 1 1 11111 1 1 1 Preoperculars 1st Anterior 0 0 1 1 1 1 1 1 1 1 1 1 1 1 2nd Anterior 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3rd Anterior 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1st Posterior 0 0 0 0 0 0 1 1 1 1 1 1 1 1 2nd Posterior 0 0 1 1 1 1 1 1 1 1 1 1 1 1 3rd Posterior 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4th Posterior 0 0 1 1 1 1 1 1 1 1 1 1 1 1 5th Posterior 0 0 1 1 1 1 1 1 1 1 1 1 1 1 Preocular 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Supraocular 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Postocular 0 0 1 1 1 1 1 1 1 1 Parietal 0 0 1 1 1 1 1 1 1 1 Infraorbitals 1st Inferior 0 0 0 0 0 0 0 1 1 1 2nd Inferior 0 0 0 0 0 0 0 0 0 1 3rd Inferior 0 0 0 0 0 0 0 0 0 0 0 0 10 11 1st Superior 0 0 0 0 0 1 1 1 1 1 2nd Superior 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 3rd Superior 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4th Superior 0 0 0 0 0 0 0 0 0 0 Nuchal 0 0 0 0 0 1 1 1 1 1 Postemporals Inferior 0 0 0 0 1 1 1 1 1 1 Superior 0 0 0 0 0 0 0 0 0 1 Supracleithral 0 0 0 0 0 1 1 1 1 1 Operculars Inferior 0 0 0 0 0 0 0 0 1 1 Superior 0 0 0 0 1 1 1 1 1 1 Nasal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 11 Tympanic 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Coronal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 first body bar (Fig. 1G). By 38.3 mm SL, the fourth and fifth body bars were fully developed but did not develop the forward projecting pattern of the first three body bars (Table 5). In addition, pectoral- and pelvic-fin pigment had disappeared (Table 5). The largest individual examined was 58.3 mm SL, which had all 5 body bars fully developed and well- developed pigment on the anterior tip of the lower jaw, the ventral and posterior region of the eye orbit, the dorsal surface anterior to the eyes, the hypural region, the entire dorsal body surface, and the spinous dorsal fin (Table 5; Fig. 1H). Pigment on the lateral midline surface had become indiscernible owing to the increased pigmentation of the lateral surface. The barred pattern had become slightly ob- scured by mottling over the dorsal lateral surface. Pectoral- and pelvic-fin pigments were recorded for a few of the larger individuals, but these were a re- sult of 1 to 4 solitary melanophores located usually on one fin only (Table 5). Cheek bars and pigment on the anal fin were not observed on any of the speci- mens examined (Table 5). 728 Fishery Bulletin 93(4). 1995 Otolith analysis The extrusion check radius in S. goodei otoliths was significantly larger than that of other Sebastes spp. (S. goodei mean=14.84 u, SD=0.577; other Sebastes spp. mean=12.03 u, SD=0.869; £=19.29, df=89, P=0.0001) (Fig. 2). In addition, "strong" patterns were observed in the majority of S. goodei specimens, Which provided confirmation of the initial pigment- based identifications but which occurred in only a small minority of other Sebastes spp. (Table 6). The extru- sion check radius of the other Sebastes spp. otoliths with "strong" patterns ranged from 11.6 to 12.4 u, which was much smaller than the extrusion check radius range of 13.7 to 16.5 p observed for S. goodei. An exponential model provided a good fit for SL versus total otolith radius with no discernible pat- tern in the residuals (r2=0.933)(Fig. 3), whereas a linear model was used to regress SL on age (r2=0.909)(Fig. 4). The slope of the linear regression indicated a growth rate of 0.135 mm-day-1 (Fig. 4). The model's estimate of size at age 0 was 5.1 mm, which closely approximates the observed sizes of pre- extrusion (5.0 to 5.8 mm NL) and recently extruded Table 4 Frequency of occurrence of supraocular pepper, Sebastes goodei. spi nes in chili- Supraocular spine Frequency of occurrence Percent occurrence Neither side One side Both sides 119 14 1 88.0 10.4 0.7 Table 5 Proportions of chilipepper, Sebastes goodei, with me lanophores present at various pigment loci averaged over 2.0- mm size bins (range of +/- 1.0 mm). SL : = standard length in mm. FLEX = flexion stage where ' 0" indicates preflexion, "1 " indicates un dergoing flexion, and "2 ' indicates that flexion is complete, n = number of specimens examined. Definitions ol pigment loci are as follows: LJ = anterior tip of the lower jaw EYE = posterioventral edge of the sye orbit; HEAD = cranial surface (including nape pigment); FACE = dorsal surface anterior to the eyes; OPER = operculum; CHK = radiating cheek bars; DORS = = dorsal body surface; VENT = ventral body surface; MID = along the lateral midline; HYP = hypural region; DFIN = = spinous dorsal fin AFIN = anal fin; PEC = blade of the pectoral fin PEL = pelvic fin; Bl = first (most anterior) body bar; B2 = second body bar; B3 = third body bar; B4 = fourth body bar; and B5 = fifth body bar (on peduncle). SL FLEX n LJ EYE HEAD FACE OPER CHK DORS ve;nt MID HYP DFIN AFIN PEC PEL Bl B2 B3 B4 B5 4 0 11 0.0 0.0 1.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6 1 54 0.0 0.0 1.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.4 0.0 0.0 0.0 0.0 0.0 0.0 8 2 21 0.0 0.0 1.0 0.4 0.0 0.0 0.4 1.0 0.0 0.0 0.0 0.0 1.0 0.2 0.0 0.0 0.0 0.0 0.0 10 2 16 0.0 0.0 1.0 0.9 0.0 0.0 0.6 1.0 0.0 0.0 0.0 0.0 1.0 0.5 0.0 0.0 0.0 0.0 0.0 12 2 15 0.3 0.0 1.0 0.9 1.0 0.0 1.0 1.0 0.2 0.3 0.9 0.0 1.0 1.0 0.3 0.0 0.0 0.0 0.0 14 2 8 0.6 0.0 1.0 1.0 1.0 0.0 1.0 1.0 0.4 0.3 1.0 0.0 1.0 1.0 0.6 0.3 0.0 0.0 0.0 16 2 2 0.5 0.0 1.0 1.0 1.0 0.0 1.0 1.0 0.5 1.0 1.0 0.0 1.0 1.0 1.0 0.0 0.0 0.0 0.0 18 2 2 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 0.5 1.0 1.0 0.0 1.0 1.0 1.0 0.0 0.0 0.0 0.0 20 2 5 0.6 0.6 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 22 2 13 0.6 0.9 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 24 2 5 0.8 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 26 2 6 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 0.0 0.0 0.2 28 2 8 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 0.5 0.3 0.5 30 2 6 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.8 0.8 1.0 1.0 1.0 0.7 0.7 32 2 6 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.8 1.0 1.0 1.0 1.0 0.8 1.0 34 2 6 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.8 0.8 1.0 1.0 1.0 0.7 1.0 36 2 6 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.7 0.8 1.0 1.0 1.0 1.0 1.0 38 2 7 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.4 0.6 1.0 1.0 1.0 1.0 1.0 40 2 3 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 42 2 3 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 44 2 7 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 46 2 13 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 48 2 9 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 50 2 11 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 52 2 16 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.3 0.0 1.0 1.0 1.0 1.0 1.0 54 2 5 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.4 0.0 1.0 1.0 1.0 1.0 1.0 56 2 2 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.5 0.0 1.0 1.0 1.0 1.0 1.0 58 2 2 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 0.5 0.5 1.0 1.0 1.0 1.0 1.0 Sakuma and Laidig: A description of larval and pelagic Sebastes goodei 729 E 3 '5 C 12 ■ Sebastes goodei + Sebastes spp * * 9 » * * * * * * * S°oVo° °o 8; o 0 oc^eofc 0° °@ ° o o o0qo 0 O Standard Length (mm) Figure 2 Comparison of standard length versus extrusion check ra- dius between chilipepper, Sebastes goodei, and other Sebastes spp. Otolith Radius = 1.528e°"5,SL / — 150 E 3 * / * (a nj 100 CE -C O S 50 * / / * 4 5 6 7 8 9 10 11 12 Standard Length (mml Figure 3 Model of otolith radius (otolith growth) versus standard length for chilipepper, Sebastes goodei. Predicted values of the growth curve (exponential function) are represented by a solid line. (4.5 to 5.7 mm NL) larvae. In comparison to the other Sebastes spp., S. goodei was significantly larger at any given age f ANCOVA, df=l, 99, P=0.0001)(Fig. 4). Discussion The ability to identify larval and juvenile S. goodei can potentially lead to future studies on the spatial and temporal extent of spawning and the estimation of larval production biomass for this species based on larvae and juveniles collected in standard plank- ton studies (Moser and Butler, 1987; Ralston et al.3). Preflexion S. goodei larvae can be distinguished from other Sebastes spp. off central California by the pres- ence of pigment on the cranium and nape (evident even in pre-extrusion larvae), and by the absence of pigment on the dorsal midline surface, the tip of the lower jaw, the caudal area, and the cleithral region (Fig. 1, A and B). In general, extrusion and pre-ex- trusion larvae of other Sebastes spp. that have been described in the literature either lack pigment on the cranium and the nape and/or possess pigment on at least one of the other areas described above (Morris, 1956; Moser et al., 1977; Moser and Ahl- strom, 1978; Moser and Butler, 1981, 1987; Stahl- Johnson, 1985; Kendall and Lenarz, 1987; Matarese et al., 1989; Wold, 1991; Moreno, 1993; Laroche2), Based on a cluster analysis by Wold (1991) and ex- isting descriptions of early larvae (Westrheim, 1975; Moser et al., 1977; Stahl-Johnson, 1985; Moser and Butler, 1987; Matarese et al., 1989; Wold, 1991; Moreno, 1993; Laroche2), other Sebastes spp. com- monly found in the study region with larval pigment patterns similar to S. goodei include S. entomelas, S. flavidus, S. melanops, S. mystinus, S. pinniger, S. ruberrimus, and members of the subgenus Sebastomus, which includes S. chlorostictus, S. constellatus, S. helvomaculatus, and S. rosaceus. Otolith analysis showed that other Sebastes spp. with similar pigmen- tation had otolith characters significantly different from those of S. goodei (Fig. 2; Table 6) indicating that S. goodei could be accurately identified solely on the ba- sis of pigment patterns described in this study (Fig. 1, A and B). It should be noted that pigment on the cleithral region has not always been documented, be- cause it may be partially obscured by the operculum in some specimens and, therefore, overlooked. To avoid identification problems, the operculum should be lifted to reveal the pigment on the cleithral region. Juvenile S. goodei can be distinguished from other Sebastes spp. off central California by their distinc- tive barred pigment pattern (Fig. 1, G and HXMatarese et al., 1989; Moreland and Reilly, 1991; Laroche2). The forward projecting pattern of the first three body bars readily distinguishes S. goodei from other barred Sebastes spp., such as S. saxicola and S. caurinus, in which the body bars do not project forward (Matarese et al., 1989; Laroche2). Meristic characters can also be used to distinguish S. goodei from these other barred Sebastes spp. because the modal anal-fin-ray count in S. goodei is 8, whereas the modal counts for S. saxicola and S. caurinus are 7 and 6 respectively (Chen, 1986; Matarese et al., 1989; Moreland and Reilly, 1991). Although the ma- jority of S. goodei did not possess supraocular spines, 730 Fishery Bulletin 93(4), 1995 * * * - Sebastes goodet * Sebastes spp. O "°B8 °° 3 6e*° * o 3 >8 o o SL = 5.089 + 0.135Age -ogo ° Age (days) Figure 4 Comparison of age at length for chilipepper, Sebastes goodei, and other Sebastes spp. The solid line represents the predicted values of the growth curve (linear regres- sion) for larval Sebastes goodei alone. this characteristic is variable (Table 4). Such vari- ability has been reported in other species, including S. entomelas, S. flavidus, S. melanops, and S. mystinus (Laroche and Richardson, 1981 ), and should be taken into account when using this characteristic in the identification process. The identification of S. goodei larvae, initially based on pigment patterns, can be confirmed by us- ing otolith characters, given the distinctive optical pattern and the relatively large extrusion check ra- dius (Fig. 2; Table 6). The mean extrusion check ra- dius of 14.84 [i (SD=0.577) in larvae from this study is similar to the mean extrusion check radius of 15.15 \i (SD=0.89) in pelagic juveniles reported by Laidig and Ralston (1995). Although the use of otoliths is more labor intensive than the use of pig- ment patterns or meristic characters, otoliths can provide relatively accurate identifications when pig- ment patterns and meristic characters yield dubi- ous results or when pigment patterns and meristic characters are compromised (e.g. in identification of specimens from stomach contents). Studies have shown that otolith characters can be used to sepa- rate both species (Hecht and Appelbaum, 1982; Vic- tor, 1987; Gago, 1993;) and stocks (Messieh, 1972; McKern et al., 1974; Rybock et al., 1975). Laidig and Ralston (1995) have found distinctive otolith char- acters in S. auriculatus, S. flavidus, S. goodei, S. jordani, S. mystinus, and S. paucispinis. Therefore, the use of otolith characters may be very useful in the identification of other species. It appears that S. goodei grows slower during the larval stage (Fig. 4) than during the juvenile stage (Woodbury and Ralston, 1991). The growth rate of Table 6 Frequency of occurrence of the pre-extrusion optical pat- tern in chilipepper, Sebastes goodei, otoliths and its occur- rence in the otoliths of other Sebastes spp. with similar larval pigment patterns. Optical Frequency of Percent Species pattern occurrence occurrence S. goodei Strong 38 76.0 Weak 10 20.0 Absent 2 4.0 Other Strong 4 7.7 Sebastes spp. Weak 14 26.9 Absent 34 65.4 0.135 mm-day-1 for larvae during the first 40 days in this study (Fig. 4) is relatively slow in comparison with the 0.399 to 0.555 mm-day"1 growth rates re- ported by Woodbury and Ralston ( 1991 ) for S. goodei juveniles 35 to 170 days old. Laidig et al. (1991) ob- served a similar trend of slow growth during the lar- val stage and accelerated growth during the juve- nile stage in S. jordani. During the first 20 days of life, S. jordani had a growth rate of approximately 0.165 mm-day-1, whereas at 35 to 165 days, the growth rate was 0.53 mm-day-1. Laidig et al. (1991) also indicated that owing to notochord flexion, early larval growth in S. jordani was slightly sigmoidal rather than linear. Growth for S. goodei probably follows a similar pattern, but because of the small sample size in this study, such a pattern could not accurately be discerned. Acknowledgments We would like to thank the officers and the crew of the RV David Starr Jordan and all the scientists who participated in the collection of samples. Special thanks to Ralph DeFelice for his illustrations and to Stephen Ralston for his assistance in the otolith analysis. Geoffrey Moser, Arthur Kendall, and Will- iam Lenarz made helpful suggestions on early versions of the manuscript. Literature cited Chen, L. 1986. Meristic variation in Sebastes (Scorpaenidae), with an analysis of character association and bilateral pattern and their significance in species separation. U.S. Dep. Commer., NOAATech. Rep. NMFS 45, 17 p. Sakuma and Laidig: A description of larval and pelagic Sebastes goodei 731 Eschmeyer, W. N., E. S. Herald, and H. Hammann. 1983. A field guide to Pacific coast fishes. Houghton Mifflin Co., Boston, MA, 336 p. Gago, F. J. 1993. Morphology of the saccular otoliths of six species of lanternfishes of the genus Symbolophorus (Pisces: Myctophidae). Bull. Mar. Sci. 52(3):949-960. Hecht, T., and S. Appelbaum. 1982. Morphology and taxonomic significance of the otoliths of some bathypelagic Anguilloidei and Saccopharyngoidei from the Sargasso Sea. Helgol. Meeresunters. 35:301-308. Hunter, J. R., and N. C. -H. Lo. 1993. Ichthyoplankton methods for estimating fish biomass introduction and terminology. Bull. Mar. Sci. 53:723-727. Kendall, A. W., Jr. 1991. Systematics and identification of larvae and juveniles of the genus Sebastes. Environ. Biol. Fishes 30: 173-190. Kendall, A. W., Jr., and W. H. Lenarz. 1987. Status of early life history studies of northeast Pacific rockfishes. In Proceedings of the international rockfish sym- posium; October 1986, Anchorage, Alaska, p. 99-128. Alaska Sea Grant Rep. 87-2, Univ. Alaska, Fairbanks. Laidig, T. E., and S. R. Ralston. 1995. The potential use of otolith characters in identifying larval rockfish {Sebastes spp.). Fish. Bull. 93:166-171. Laidig, T. E., S. R. Ralston, and J. R. Bence. 1991. Dynamics of growth in the early life history of shortbelly rockfish Sebastes jordani. Fish. Bull. 89:611-621. Laroche, W. A., and S. L. Richardson. 1981. Development of larvae and juveniles of the rockfishes Sebastes entomelas and S. zacentrus (family Scorpaenidae) and occurrences off Oregon, with notes on head spines of S. mystinus, S. flavidus, and S. melanops. Fish. Bull. 79:231-257. Laroche, J. L., S. L. Richardson, and A. A. Rosenberg. 1982. Age and growth of a pleuronectid, Parophrys vetulus, during the pelagic larval period in Oregon coastal waters. Fish. Bull. 80:93-104. Matarese, A. C, A. W. Kendall Jr., D. M. Blood, and B. M. Vinter. 1989. Laboratory guide to early life history stages of north- east Pacific fishes. U.S. Dep. Commer., NOAATech. Rep. NMFS 80, 652 p. McKern, J. L., H. F. Horton, and K. V. Koski. 1974. Development of steelhead trout iSalmo gairdneri) otoliths and their use for age analysis and for separating summer from winter races and wild from hatchery stocks. J. Fish. Res. Board Can. 31:1420-1426. 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. Moreland, S. L., and C. A. Reilly. 1991. Key to the juvenile rockfishes of central California. In T. E. Laidig and P. B. Adams ( eds. ), Methods used to identify pelagic juvenile rockfish ( genus Sebastes ) occurring along the coast of central California, p. 59-180. U.S. Dep. Commer., NOAATech. Memo., NMFS SWFSC-166, 180 p. Moreno, G. 1993. Description of the larval stages of five northern Cali- fornia species of rockfishes (family Scorpaenidae ) from rear- ing studies. U.S. Dep. Commer., NOAATech. Rep. NMFS 116, 18 p. Morris, R. W. 1956. Early larvae of four species of rockfish, Sebas- todes. Calif. Fish Game 42:149-153. 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. Moser, H. G., and J. L. Butler. 1981. Description of reared larvae and early juveniles of the calico rockfish, Sebastes dallii. Calif. Coop. Oceanic Fish. Invest. Rep. 22:88-95. 1987. Descriptions of reared larvae of six species of Sebastes. In W. H. Lenarz and D. R. Gunderson (eds.), Widow rockfish: proceedings of a workshop, Tiburon, Cali- fornia, December 11-12, 1980, p. 19-29. U.S. Dep. Commer., NOAATech. Rep. NMFS 48. Moser, H. G., E. H. Ahlstrom, and E. M. Sandknop. 1977. Guide to identification of scorpionfish larvae (family Scorpaenidae) in the eastern Pacific with comparative notes on species of Sebastes and Helicolenus from other oceans. U.S. Dep. Commer., NOAATech. Rep. NMFS Circ. 402, 71 p. Radtke, R. L. 1989. Larval fish age, growth, and body shrinkage: infor- mation available from otoliths. Can. J. Fish. Aquat. Sci. 46:1884-1894. Richardson, S. L., and W. A. Laroche. 1979. Development and occurrence of larvae and juveniles of the rockfishes Sebastes crameri, Sebastes pinniger, and Sebastes helvomaculatus (family Scorpaenidae) off Oregon. Fish. Bull. 77:1-46. Rybock, J. T., H. F. Horton, and J. L. Fessler. 1975. Use of otoliths to separate juvenile steelhead trout from juvenile rainbow trout. Fish. Bull. 73:654-659. Seeb, L. W., and A. W. Kendall Jr. 1991. Allozyme polymorphisms permit the identification of larval and juvenile rockfishes of the genus Sebastes. Environ. Biol. Fishes 30:191-201. Stahl-Johnson, K. L. 1985. Descriptive characteristics of reared Sebastes caurinus and S. auriculatus larvae. In A. W. Kendall Jr. and J. B. Marliave (eds.), Descriptions of early life history stages of selected fishes, p. 65-76. Can. Tech. Rep. Fish. Aquat. Sci. 1359. Victor, B. C. 1987. Growth, dispersal, and identification of planktonic labrid and pomacentrid reef-fish larvae in the eastern Pa- cific Ocean. Mar. Biol. ( Berl. ) 95: 145-152. Westrheim, S. J. 1975. Reproduction, maturation, and identification of lar- vae of some Sebastes (Scorpaenidae) species in the north- east Pacific Ocean. J. Fish. Res. Board Can. 32:2399- 2411. Wilkins, M. E. 1980. Size composition, age composition, and growth of chilipepper, Sebastes goodei , and bocaccio, S. paucispinis, from the 1977 rockfish survey. Mar. Fish. Rev. 42(3^1):48-53. Wold, L. 1991. A practical approach to the description and identifi- cation of Sebastes larvae. M.S. thesis. California State Univ. Hayward, 88 p. Woodbury, D., and S. Ralston. 1991. Interannual variation in growth rates and back-cal- culated birthdate distributions of pelagic juvenile rock- fishes (Sebastes spp. ) off the central California coast. Fish. Bull. 89:523-533. Wyllie Echeverria, T. 1987. Thirty-four species of California rockfishes: maturity and seasonality of reproduction. Fish. Bull. 85:229-250. Abstract. A flow and survival re- lationship, based on 1970's research, for juvenile chinook salmon, Oncorhynchus tshawytscha, that migrate through the Snake and Columbia Rivers is the foun- dation of many fishery managers' rec- ommendations for modifications to the hydropower system to stem the decline of populations recently listed under the Endangered Species Act. However, a review of the 1970's data found that estimated fish survivals through the hydropower system reflected conditions that no longer exist and that between 1977 and 1979 these estimated surviv- als were negatively biased. Debris en- trained in front of, and throughout, the fish collection system of the uppermost dam on the Snake River resulted in fish descaling and most likely poor fish sur- vival. Under the lowest flow conditions, decreased survival due to increased travel time was exacerbated by spo- radic or less than optimal turbine op- erations, or both, which further delayed fish passage through the dams and, at the uppermost dam, subjected fish to debris for longer periods of time. Use of flow and survival relationships based on yearly estimates of juvenile migrant survival in the 1970's will probably not accurately predict survival of spring- migrating juvenile chinook salmon un- der present conditions. This is particu- larly true for survival predictions dur- ing low-flow conditions. A review of flow and survival relationships for spring and summer chinook salmon, Oncorhynchus tshawytscha, from the Snake River Basin John G. Williams Gene M. Matthews Coastal Zone and Estuarine Studies Division, Northwest Fisheries Science Center National Marine Fisheries Service, NOAA 2725 Montlake Boulevard East, Seattle, Washington 981 12-2097 Manuscript accepted 17 April 1995. Fishery Bulletin 93:732-740 ( 1995). The Columbia River watershed his- torically has produced more chinook salmon, Oncorhynchus tshawytscha, than any other river system in the world (Netboy, 1980). The majority of the spring chinook salmon origi- nated in the Snake River Basin (Fulton, 1968). In the early 1880's, spring and summer chinook salmon provided commercial fisheries in the lower Columbia River with average annual catches of 17.7 million kilo- grams (Craig and Hacker, 1940). Heavy exploitation by these fisher- ies, however, caused a substantial depletion of the dominant summer stock; the fisheries, therefore, con- centrated on the spring and fall stocks (Craig and Hacker, 1940; Gangmark, 1957). Summer chinook salmon populations from the mid- and upper Columbia River contin- ued to decline such that by 1964 the commercial fishery for all summer fish was closed. By this time, Snake River Basin spring and summer chinook salmon accounted for ap- proximately 78 percent of the re- maining upper river populations (Fulton, 1968). The primary causes of stock de- clines in the early years were over- fishing, habitat destruction, and damming of tributaries for water withdrawal and small-scale hydro- power (Craig and Hacker, 1940). Concern about the potential im- pacts on upstream salmonid migra- tion and the loss of downstream migrant juveniles passing through turbines at mainstem hydropower projects was expressed even before construction of Bonneville Dam (Fig. 1)( Griffin, 1935). Because the river flow during the time of the juvenile migration generally far exceeded the capacity of the power- house turbines, most fisheries re- search related to migrant salmonid passage was directed toward adults and the development of adequate upstream passage facilities for them at dams. However, some research on juvenile salmonid survival through turbines was conducted in the early 1940's1 after construction of Bonne- ville Dam and in 1954 after con- struction of McNary Dam (Schoene- man et al., 1961). The first comprehensive program to study of juvenile salmonid mi- grants in the mainstem Columbia and Snake Rivers was initiated in 1961 by the Secretary of the U.S. Department of Interior. The pro- gram was instigated by construc- tion of the high-head Brownlee Dam 1 Holmes, H. B. 1952. Loss of salmon fin- gerlings in passing Bonneville Dam as de- termined by marking experiments. U.S. Fish Wildl. Serv. Unpubl. manuscr., 62 p. 732 Williams and Matthews: Flow and survival relationships for Oncorhynchus tshawytscha 733 MONTANA Figure 1 Map of the Columbia River Basin. on the middle Snake River (Hells Canyon area) in 1958 and in anticipation of low-head dams autho- rized, but not yet constructed, for the lower Snake River (the stretch from its confluence with the Co- lumbia River upstream to the confluence of the Clearwater River). As part of these efforts, one group of researchers from the Bureau of Commercial Fish- eries (now the National Marine Fisheries Service [NMFS]) began studies with juvenile chinook salmon from the Snake River Basin to determine migration rates in relation to flow through areas of impounded and unimpounded stretches of the Snake and Colum- bia Rivers (Raymond, 1968). As the Lower Snake River dams and John Day Dam on the Lower Co- lumbia River were completed, NMFS expanded these studies to estimate, in addition, the survival of fish passing through these impoundments. Raymond ( 1979) summarized the results of research from 1964 through 1975; results from 1976 through 1983 were detailed in a number of unpublished contract reports to the U.S. Army Corps of Engineers (COE).2 2 Sims, C. W., W. W. Berkley, and R. C. Johnsen. 1977. Effects of power peaking operations on juvenile salmon and steelhead trout migrations — progress 1976. Report to U.S. Army Corps 2 (Continued) of Engineering, Portland, OR, 44 p. Northwest Fish. Sci. Cent., NMFS. Sims, C. W., W. W. Bentley, and R. C. Johnsen. 1978. Effects of power peaking operations on juvenile salmon and steelhead trout migrations — progress 1977. Report to U.S. Army Corps of En- gineering, Portland, OR, 52 p. Northwest Fish. Sci. Cent., NMFS. Raymond, H. L., and C. W. Sims. 1980. Assessment of smolt migration and passage enhancement studies for 1979. Re- port to U.S. Army Corps of Engineering, Portland, OR, 48 p. Northwest Fish. Sci. Cent., NMFS. Sims, C. W., J. G. Williams, D. A. Faurot, R. C. Johnsen, and D. A. Brege. 1981. Migrational characteristics of juvenile salmon and steelhead in the Columbia River Basin and re- lated passage research at John Day Dam. Report to U.S. Army Corps of Engineering, Portland, OR, 61 p. Northwest Fish. Sci. Cent., NMFS. Sims, C. W., R. C. Johnsen, and D. A. Brege. 1982. Migra- tional characteristics of juvenile salmon and steelhead in the Columbia River System — 1981. Report to U.S. Army Corps of Engineering, Portland, OR, 16 p. Northwest Fish. Sci. Cent., NMFS. Sims, C. W., A. E. Giorgi, R. C. Johnsen, and D. A. Brege. 1983. Migrational characteristics of juvenile salmon and steel- head in the Columbia River Basin — 1982. Report to U.S. Army Corps of Engineering, Portland, OR, 35 p. Northwest Fish. Sci. Cent., NMFS. Sims, C. W., A. E. Giorgi, R. C. Johnsen, and D. A. Brege. 1984. Migrational characteristics of juvenile salmon and steelhead in the Columbia River Basin — 1983. Report to U.S. Army Corps of Engineering, Portland, OR, 31 p. Northwest Fish. Sci. Cent., NMFS. 734 Fishery Bulletin 93(4), 1995 The methods used by NMFS researchers to esti- mate migration rates, timing, and survival were de- tailed by Raymond (1979). In brief, unique batch marks were applied by some combination of freeze brands and fin clips to yearling (stream-type mi- grants which were offspring of spring and summer stocks) wild or hatchery chinook salmon collected at hatcheries, from scoop traps and purse-seines, and/ or at hydroelectric dams. The marked chinook salmon were then released from the collection sites and re- captured at downstream scoop-trap or purse-seine sites, or from gatewells or collection facilities at dams. The estimated population of chinook salmon pass- ing a capture site was derived from the formula N = n/CE, where N - the estimate of the total num- ber of chinook salmon passing (either for the un- marked population as a whole or for specific mark groups); n = the number of chinook salmon collected (unmarked or marked); and CE = the collection effi- ciency. Collection efficiency was determined from separate groups of chinook salmon that were collected semiweekly at each capture site from the unmarked population offish that was passing each capture site and subsequently marked uniquely for semiweekly upstream releases at each capture site. Estimates of collection efficiency for each site were derived from the formula CE = (r/(R-10%R) x 100%), where CE = the collection efficiency; R = the number of chinook salmon marked and released upstream specifically for collection efficiency estimates; and r = the num- ber of chinook salmon recaptured from collection ef- ficiency (R) releases. The number of chinook salmon released was decreased by 10% to account for sus- pected mortalities due to handling, marking, release procedures, and migration between the upstream release site back to the capture site. These methods also assumed that any adverse effects of handling, marking, and/or release procedures were equal for all release groups (Raymond, 1979). Collection efficiency generally decreased as river flow increased. At Ice Harbor Dam, collection effi- ciency curves were fitted by regression techniques to paired data sets of individual collection efficiency estimates with the corresponding mean river flow during the period the estimates were made (Ray- mond, 1979). These curves were then used in future years to predict collection efficiency under various flows. At other capture sites, the data were consid- ered too variable to develop reliable collection effi- ciency curves. In these cases, real-time estimates of collection efficiency were continually obtained dur- ing the period when fish were captured at the site. The population estimate (AD was made in the fol- lowing manner: if 15 marked chinook salmon of a particular group or 2,000 unmarked chinook salmon were captured at a collection site during a 24-hour period when the CE = 2%, then the estimated num- ber of marked chinook salmon or the total number of unmarked chinook salmon which passed the collec- tion site during the period would have been 750 (15/ 0.02) or 100,000 (2,000/0.02). Total population esti- mates were the sum of daily population estimates over the period of time when a specific, marked group of fish passed the site or over the period when the unmarked population passed. Travel time of marked fish between two sites was determined by subtracting the date of release from a collection site (or the median passage date offish at one capture site) from the median date of passage at a downstream capture site. Migration rates of fish were determined by dividing the distance between two sites by the travel-time estimate between the two sites. Survival estimates were made by dividing the population estimate at a downstream capture site by either the number offish released at an upstream collection site or the population estimate at a cap- ture site. Nearly all fish used for marking in the first study years were products of natural spawning. The per- centage of hatchery chinook salmon varied with hatchery output each year, but 100% of the Snake River stock was wild before 1966. Raymond (1988) estimated that from 1966 to 1969 hatchery fish rep- resented about 15% of the chinook salmon migration that reached the upper dam (Ice Harbor Dam, 1966- 68; Lower Monumental Dam, 1969) on the lower Snake River. According to his estimates, this percent- age increased to 45-55% from 1970 to 1976 (the up- per dam was Little Goose Dam, 1970-74; Lower Granite Dam, 1975-present) and averaged greater than 80% from 1981 to 1984. The 1973-79 NMFS yearly point estimates of sur- vival (Fig. 2) (1973-75 in Raymond [1979]; 1976-79 [see Footnote 2]) were used by NMFS researchers3 to indicate the effects of the recently completed Snake River hydropower dams on juvenile fish survival. Particularly low juvenile fish survivals were observed under the low-flow conditions in 1973 and 1977, whereas survival estimates did not vary much un- der a broad range of higher flows. In the early 1990's, computer models were developed by the Northwest Power Planning Council, state fishery agencies, and tribes in the Pacific Northwest to predict survivals of juvenile fish migrating from Lower Granite Dam 3 Sims, C. W., and F. J. Ossiander. 1981. Migrations of juve- nile chinook salmon and steelhead trout in the Snake River from 1973 to 1979, a research summary. Final Report to U.S. Army Corps of Engineering, Portland, OR, 31 p. Northwest Fish. Sci. Cent., NMFS. Williams and Matthews: Flow and survival relationships for Oncorhynchus tshawytscha 735 40 50 60 70 80 90 100 110 120 130 140 150 160 170 Flow (kefs) Figure 2 Survival estimates for juvenile spring and summer chinook salmon, Oncorhynchus tshawytscha, migrating through the upper dam (Little Goose Dam, 1973-74; Lower Granite Dam, 1975-79) on the lower Snake River to either John Day Dam (1976-79) or The Dalles Dam (1973-75) compared with the average river flow at Ice Harbor Dam during the period (±7 days ) of peak migration for the years 1973 through 1979 (data from Sims and Ossiander [1981][see Footnote 3]). system (1973 and 1977) were mainly a result of low survival in the Snake River. Although the low flows increased travel time, more significantly, the en- tire migrant fish population was sub- jected to debris problems at the upper- most Snake River dam. Additionally, as a result of low flows, turbine operations were cut dramatically during nighttime hours (when fish normally pass dams) so that fish were delayed further and thus subjected to the effects of the de- bris for longer periods. We then com- pared the low 1970s survival estimates with some Snake River survival esti- mates of recent years. Data review Effects of dam operations and debris on fish condition to Bonneville Dam under present river conditions. To calibrate the models, they were fitted to the 1970s NMFS flow and survival data (after altering them to represent the turbine, bypass, and spill conditions that existed in the 1970's). However, present river conditions and dam opera- tions differ substantially compared with those in the 1970's. Further, detections in recent years of marked fish that migrated through the Snake River to McNary Dam under relatively low flows indicate that juvenile fish survive at a rate substantially higher than that which would be predicted from flow and survival relationships derived from the 1970's data. Because recent information is not in agreement with past data, but because the 1970's data are the foun- dation of some of the present computer models, we initiated a critical review of the NMFS data from the 1970's to determine whether these data were still relevant. We initially reviewed all the NMFS data files from which estimates of survival were reported. These included original NMFS field notes, analyses of mark and recapture data, and yearly research summaries. We also reviewed field notes and data summaries from other concurrent NMFS research that docu- mented the condition of fish collected at dams. On reviewing the original data, we determined that the lowest estimates of survival within the hydropower Juvenile salmon mortality for Snake River migrants was initially somewhat minimized because when the dams were first built, they were equipped with only three operating turbine units. This limited the amount of flow through the powerhouses to approxi- mately 1,840-1,980 nv^s"1 (65-70 thousand cubic feet per second [kefs]). From 35 to 75% of the total river flow (and a presumed equal percentage of the fish population) passed over the spillways during the spring seaward migration. Except under conditions where high atmospheric gas supersaturation de- creased survival ( Ebel and Raymond, 1976), survival of juvenile migrant fish through spillways was gen- erally estimated at greater than 97% (Raymond, 1988). Three additional turbines were added to Ice Harbor Dam in 1975, to Little Goose and Lower Gran- ite Dams in 1978, and to Lower Monumental Dam in 1979. This led to progressively less uncontrolled spill in the Snake River and a concomitant increase in fish passing through turbine intakes. To decrease fish mortality in the turbines, many of the fish that passed into turbine intakes at Little Goose and Lower Granite Dams were diverted to bypass and collec- tion facilities (Smith and Farr, 1975; Matthews et al., 1977). However, the potential benefit of these bypass systems in decreasing the mortality of fish entering turbine intakes was compromised prima- rily because of debris that had collected at the dams. With the exception of Ice Harbor Dam (which had a debris boom installed), huge amounts of woody de- bris began to accumulate at the upstream face, in 736 Fishery Bulletin 93(4). 1995 the forebay, and on the trashracks of the dams as the Lower Snake River dams were constructed. Most of the debris accumulated at the uppermost dam in any given period. With periods of high spill, some debris passed downstream through spillways, but as the volume of spill decreased, the trash load at the upper dam increased. By 1979 at Lower Granite Dam, debris extended upstream from the dam approximately 1 km (Fig. 3). The debris that collected at Little Goose and Lower Granite Dams after their construction pro- vided a continual supply of woody material that clogged trashracks, accumulated in the gatewells, and collected throughout the fish facilities. Gatewell orifices and all other components of the bypass systems were continu- ally obstructed by debris. Although debris was con- stantly in the forebay s, attempts were made to remove it from the trashracks. However, the rakes that were used to clear the trashracks were ineffective and in- stead, large, heavy-steel beams were occasionally low- ered down the trashracks in an attempt to push im- pinged debris to the bottom. As judged by water levels and turbulence in the gatewells, this procedure met with limited success. To compound problems, when first constructed the fish facilities at Lower Granite and Little Goose Dams had undersized plumbing systems and other poorly designed components through which fish moved. Lower Granite Dam had only 20.3-cm dia- meter orifices to the bypass system which were of- ten plugged and required continual efforts (usually futile) by fish workers to remove debris to maintain unobstructed flows. During peak collection periods at the collection facilities, workers often required 1 hour, and at times up to 3 hours, to transfer fish from one of the five raceways into a fish transport barge. Occasionally, the 6-inch transfer lines would com- pletely plug with debris and fish. The effect of debris throughout the bypass and collection systems was to increase fish injury, descaling, and ultimately mortality from dam passage (Table 1). Total mor- talities at Lower Granite Dam were often so high (personal observations by the authors) that indi- vidual dead fish could not be counted. Most often, we kept volumetric estimates (buckets full) of dead fish dipnetted from tail-screens in raceways. The fish not collected at the uppermost dam passed through either the spillway or through the trashracks and then the turbines. Although not measured, the mor- tality of fish that were not collected at the upper- most dam, but which passed through the debris on the trashracks and then the turbines, probably was higher than that at downstream dams where debris on the trashracks was much less of a problem. For example, in 1979, fish sampled from the gatewells at Little Goose Dam showed far less descaling (a re- duction of 50%) after the trashracks at Lower Gran- Figure 3 Debris in the forebay of Lower Granite Dam, 1979. Williams and Matthews: Flow and survival relationships for Oncorhynchus tshawytscha 737 Table 1 Average facility-caused descaling and delayed mortality for groups of un- marked and marked Snake River spring and summer chinook salmon. Oncorhynchus tshawytsch i, smolts collected at Little Goose or Lower Gran- ite Dams from 1972 through 1990. Smolts were held approximately 48 hours before oi • after truck transport to an aree below Bonnevi le Dam. Facility-caused Unmarked-fish Marked-fish descaling delayed mort. delayed mort. Year Dam (%) (%) (%) Not Transported 1972 Little Goose 19.6 <1.0; 17.6 21.8 1978 Lower Granite 7.5 20.6 13.8 1979 Lower Granite 5.3 5.0 1980 Lower Granite 4.0 2.2 1986 Lower Granite 3.7 0.3 1987 Lower Granite 3.3 1.1 1989 Lower Granite 2.3 1.1 1990 Lower Granite 3.6 1.3 Transported 1972 Little Goose 16.0 12.2 10.0 1973 Little Goose 19.6 15.3 17.2 1975 Lower Granite 13.0 11.5 1976 Little Goose 11.5 3.2 6.1 Lower Granite 7.0 4.1 4.7 1977 Little Goose 23.9 21.3 42.5 Lower Granite 26.0 31.4 30.0 1978 Little Goose 20.0 12.7 13.1 Lower Granite 7.5 11.2 17.1 1979 Little Goose 8.1 19.8 Lower Granite 5.3 10.0 1980 Lower Granite 4.0 1.9 ite Dam were partially cleared of debris with the steel beam.4 Fish passage conditions were particularly bad at Little Goose Dam in 1973 and Lower Granite Dam in 1977 because river flows were so low that little (1973) to no (1977) spill occurred at Snake River dams. Thus, nearly all fish had to pass through trashracks at dams into either the turbines or the debris-laden bypass systems. Additionally, it was not unusual for one or more turbines to operate at full or nearly full capacity for relatively short periods dur- ing the evening peak load and then shut down for relatively long periods (authors' personal observa- tions). At other times, one or two turbines were op- erated at partial capacity for relatively long periods. The slowing or stopping of turbines probably delayed dam passage by reducing or stopping the flow into each turbine and, thus, fish were not attracted to the bypass. Under these conditions in 1977, 10— 14% of spring and summer chinook salmon smolts within 140 m of the fore- bay at Lower Granite Dam were descaled (a fish was considered descaled if it was missing 10-100% of its scales), whereas fish sampled 400 m to 2 km upstream showed no descaling.5 These observa- tions suggest that fish were delayed at the dam and that they swam in and out of the debris-covered trashracks, possi- bly while loads were adjusted or when velocities were insufficient to draw fin- gerlings completely into the bypasses or through the turbines. For fish that passed into the collection facility, an average of 26.0% were descaled. Under similar conditions at Little Goose Dam, the percentage offish descaled averaged 19.6 and 23.0% in 1973 and 1977, re- spectively, probably because they hit something during passage through the trashracks or bypass system. (The high level of descaling observed in 1977 most likely resulted from the fact that fish had previously passed Lower Granite Dam.) When debris partially occluded openings through which fish passed, it not only provided objects that the fish hit but caused increased water velocity through the remaining open area. Thus, fish hit the debris with more force as the amount of debris in- creased. A fish with external injury, such as descaling, would likely have had internal injury as well. To de- termine the relationship between descaling percent- age (as a measure of total injury) and mortality within a short time period, random samples of by- pass fish were collected during some years and held in tanks with flow-through river water. The rate of mortality during approximately 48 hours of holding was measured, and the extent to which this was de- pendent upon descaling percentage was evaluated. Facility-caused descaling was highly positively cor- related with delayed mortality for marked untrans- ported fish (#=0.94, P<0.002) and unmarked trans- ported fish (#=0.90, P<0.007), whereas it was fairly 4 Smith, J. R., G. M. Matthews, L. R. Basham, S. Achord, and G. T. McCabe. 1980. Transportation operations on the Snake and Columbia Rivers, 1979. Report to U. S. Army Corps of Engineering, Walla Walla, WA, 28 p. Northwest Fish. Sci. Cent., NMFS. 5 Park, D. L., J. R. Smith, E. Slatick, G. M. Matthews, L. R. Basham, and G. A. Swan. 1978. Evaluation offish pro- tective facilities at Little Goose and Lower Granite Dams and a review of mass transportation activities, 1977. Report to U.S. Army Corps of Engineering, Portland, OR, 60 p. Northwest Fish. Sci. Cent., NMFS. 738 Fishery Bulletin 93(4), 1995 positively correlated for marked transported fish CR=0.77, P<0.075) (Table 1). Too few unmarked untransported groups were observed to examine the correlation. Further, we did not use the limited data because the <1.0% delayed mortality measured in one of the 1973 tests is inexplicable (the NMFS an- nual report6 for the year stated that the results were "somewhat surprising," considering that migrants passing the dam suffered, in actuality, a 50% mor- tality). Although not evident from the summary table (Table 1), in the 1970s most of the descaled fish were missing considerably more than 10% of their scales as compared with present conditions where highly descaled fish are the exception rather than the rule. Annual survival estimates were lowest for 1973 and 1977 (Fig. 2), the two years with the lowest river flows and the highest levels of descaling at the up- per dam. The relatively low survivals may well have been greatly influenced by debris-related problems at the upper dams and were compounded by the low river flows in these two years. In 1980, the COE began removing debris from the Lower Granite Dam forebay, and in 1981 a perma- nent debris rake was installed and used for the first time to remove debris from the trashracks (effective rakes to remove debris from trashracks were also built during the 1980's for other dams). In 1983, a temporary boom was placed upstream from Lower Granite Dam to divert new debris away from the powerhouse. The temporary boom was replaced by a permanent structure in 1984. Debris is now diverted away from the powerhouse and removed from the river, and trashracks are systematically cleaned. Additionally, the bypass systems at Lower Granite and Little Goose Dams have been substantially modi- fied and improved. For example, pipe and orifice sizes have been increased so that what little debris enters the systems does not cause problems. Fish and de- bris separators have been modified so that fish are separated under water and they exit after separa- tion via large flumes rather than small pipes. Descaling and 48-hour delayed mortality in recent years have been much less than those observed in the 1970's (Table 1), even under "relatively" low-flow conditions such as occurred in 1987. To verify improved migratory conditions for chinook salmon smolts after debris problems had been eliminated or greatly controlled in the Snake River, we compared historic with recent Snake River survival estimates. Survival estimates in the 1970's over a 2- or 3-dam stretch under moderate to high river flows ranged from 33 to 50% (Raymond, 1979). Over a comparable 2-and 3-dam stretch in 1993 and 1994, survival estimates were 77%7 and 66%8, re- spectively. For low-flow conditions, we estimated survival of PIT-tagged (passive-integrated-transpon- der-tagged) (Prentice et al., 1990) chinook salmon smolts from Little Goose Dam to McNary Dam in 1992 by using Raymond's ( 1979) techniques for com- paring populations of fish that passed both dams. We used 50 and 75% collection efficiency estimates for the two dams, respectively. Flows were similar in 1973 and 1992 (Fig. 4); however, our 1992 survival estimate (which covered three dams and reservoirs, but not the most upstream dam) was 81% compared with 12% for two dams and reservoirs in 1973 (Raymond, 1979). Discussion and conclusions The argument for a flow-survival relationship for juvenile salmonid migrants, based on the 1973-79 NMFS yearly point estimates of inriver survival (Fig. 2), is heavily influenced by the low survivals esti- mated for 1973 and 1977 under low-flow conditions. Low survival of river migrants (both above and through the hydropower system) certainly occurred during the 1973 and 1977 low-flow years. However, the estimated low fish survivals within the hydro- power system resulted more likely from fish encoun- ters with debris at dams (encounters which were in- creased because of low flows and exacerbated by spo- radic turbine operations) than from river discharge. Data collected in the past few years on PIT-tagged fish that migrated under low to moderately-low flow conditions, comparable to those in the 1970's, indi- cated a substantially higher survival of juvenile smolts. Under present conditions, low flows during the spring migration may not lead to direct losses of mi- grant fish as high as those in the 1970's within the 6 Ebel, W. J., R. W. Krcma, and H. L. Raymond. 1973. Evaluation of fish protection facilities at Little Goose Dam and review of other studies relating to protection of juvenile salmonids in the Columbia and Snake Rivers, 1973. Report to U.S. Army Corps of Engineering, Portland, 52 p. Northwest Fish. Sci. Cent., NMFS. 7 Iwamoto, R. N„ W. D. Muir, B. P. Sandford, K. W. Mclntyre, D. A. Frost, J. G. Williams, S. G. Smith, and J. R. Skalski. 1994. Survival estimates for the passage of juvenile chinook salmon through Snake River dams and reservoirs. Report to the Bonneville Power Admin., Portland, OR, 140 p. Northwest Fish. Sci. Cent., NMFS, and Univ. Washington. B Muir, W D., S. G. Smith, R. N. Iwamoto, D. J. Kamikawa, K. W. Mclntyre, E. P. Hockersmith, B. P. Sandford, P. A. Ocker, T. E. Ruehle.J. G.Williams, and J. R. Skalski. 1994. Survival es- timates for the passage of juvenile chinook salmon through Snake River dams and reservoirs, 1994. Report to the Bonneville Power Admin., Portland, OR, 174 p. Northwest Fish. Sci. Cent., NMFS, and Univ. Washington. Williams and Matthews: Flow and survival relationships for Oncorhynchus tshawytscha 739 Figure 4 Comparison of 1973 and 1992 Snake River flows during the spring juve nile salmonid seaward migration. Table 2 Changes in average runoff (in thousands of cubic feet per second) in the Columbia River at The Dalles Dam. May June July 1926-58 1959-75 1976-91 283 250 206 353 344 199 224 211 132 hydropower corridor, but past research definitely showed that low flows increased travel time (Ray- mond, 1979). Certainly adult returns of spring and summer chinook salmon have been greatly reduced in most years since the mid-1970's (Matthews and Waples, 1991). This poor return has coincided with a substantial decrease in lower Columbia River flows during the late spring and early summer smolt mi- grations as a result of completion of storage reser- voirs in the upper Columbia River Basin (Table 2). The decreased volume of freshwater entering the estuary and ocean may have delayed entry offish to the ocean or may have changed the ecology of the system sufficiently to affect predator-prey interac- tions above and below the trophic level of the juve- nile migrant fish and, thus, their survival. The 1970's juvenile survival estimates made by NMFS in average-to-high flow years also reflected the effects of debris for the proportion of the popula- tion that passed through the juvenile collection and bypass systems. These survival estimates are prob- ably lower than those for present passage conditions, even when one accounts for the installation of new bypass systems at dams where they did not exist in the 1970's. Thus, they do not apply to present-day migrants in the Snake and Columbia River hydropower system, and we recommend they not be used by modelers, unless substantial modifica- tions are made to adjust for the errors that we have discussed. We also recom- mend continued emphasis on research to provide up-to-date survival estimates under present system conditions, be- cause the data gathered to date do not cover a wide range of flows. Acknowledgments We thank the staff of the Northwest Fisheries Science Center for many help- ful editorial suggestions. We particu- larly thank Steve Mathews from the University of Washington whose helpful suggestions led to sub- stantial revisions to the manuscript. Literature cited Craig, J. A., and R. L. Hacker. 1940. The history and development of the fisheries of the Columbia River. Fish. Bull. 49:133-216. Ebel, W. J., and H. L. Raymond. 1976. Effect of atmospheric gas supersaturation on salmon and steelhead trout of the Snake and Columbia Rivers. Mar. Fish. Rev. 38:1-14. Fulton, L. A. 1968. Spawning areas and abundances of chinook salmon {Oncorhynchus tshawytscha) in the Columbia River Ba- sin— past and present. U.S. Fish. Wildl. Ser. Special Sci. Rep. 571. Gangmark, H. A. 1957. Fluctuations in abundance of Columbia River chinook salmon 1928-54. U.S. Fish. Wildl. Ser. Special Sci. Rep. 189, 21 p. Griffin, L. E. 1935. Certainties and risks affecting fisheries connected with damming the Columbia River. Northwest Sci. 9:25-30. Matthews, G. M., and R. S. Waples 1991. Status review for Snake River spring and summer chinook salmon. U.S. Dep. Commer., NOAATech. Memo. NMFS F/NWC-200, 75 p. Matthews, G. M., G. A. Swan, and J. R. Smith. 1977. Improved bypass and collection system for protection of juvenile salmon and steelhead trout at Lower Granite Dam. Mar. Fish. Rev. 39(7): 10-14. Netboy, A. 1980. The Columbia River salmon and steelhead trout. Univ. Washington Press, Seattle, WA, 180 p. Prentice, E. F., T. A. Flagg, and C. S. McCutcheon. 1990. PIT-tag monitoring systems for hydroelectric dams and fish hatcheries. Am. Fish. Soc. Symp. 7:323-334. 740 Fishery Bulletin 93(4), 1995 Raymond, H. L. 1968. Migration rates of yearling chinook salmon in rela- tion to flows and impoundments in the Columbia and Snake Rivers. Trans. Am. Fish. Soc. 97:356-359. 1979. Effects of dams and impoundments on migrations of juvenile chinook salmon and steelhead from the Snake River, 1966 to 1975. Trans. Am. Fish. Soc. 108:505-529. 1988. Effects of hydroelectric development and fisheries enhancement on spring and summer chinook salmon and steelhead in the Columbia River basin. N. Am. J. Fish. Manage. 8:1-24. Schoeneman, D. E., R. T. Pressey, and C. O. Junge. 1961. Mortalities of downstream migrant salmon at McNary Dam. Trans. Am. Fish. Soc. 90:58-72. Smith, J. R., and W. E. Fair. 1975. Bypass and collection system for protection of juve- nile salmon and trout at Little Goose Dam. Mar. Fish. Rev. 37(21:31-35. A decline in the abundance of harbor porpoise, Phocoena phocoena, in nearshore waters off California, 1986-93 Karin A. Forney Southwest Fisheries Science Center National Marine Fisheries Service, NOAA RO. Box 271, La Jolla. California 92038 Harbor porpoise, Phocoena pho- coena, have been caught incidentally in set gill nets off the central Cali- fornia coast since at least 1958 (Norris and Prescott, 1961). The annual mortality of harbor porpoise caught in gill nets in this region peaked in the mid-1980's and then gradually declined (Barlow and Forney, 1994) as fishing effort de- creased following the implementa- tion of restrictions and area clo- sures in order to protect marine mammals, sea birds, and sport fish- eries (Barlow et al., 1994). In 1986, a series of aerial line-transect sur- veys was initiated jointly by the California Department of Fish and Game and the National Marine Fisheries Service to monitor trends in abundance of the central Cali- fornia harbor porpoise population. Harbor porpoise in this region are managed separately from animals found off northern California and Oregon, because movement of ani- mals along the U.S. West Coast appears limited, and fishery-in- duced mortality is restricted to cen- tral California (Barlow and Hanan, in press). An analysis of covariance model applied to the first five an- nual surveys (1986-90) failed to detect a significant trend in abun- dance (Forney et al., 1991); how- ever, simulations revealed that sta- tistical power to detect trends, given the level of variability observed in the 741 time series, was low with only five survey years. A minimum often sur- vey years was estimated as necessary to provide sufficient power. Additional surveys utilizing the same methodology were conducted in 1991 and 1993, completing an eight-year time series. In updating the analysis of trends in central California harbor porpoise abun- dance for the period 1986-93, 1 an- ticipated either that 1) no signifi- cant trend would be identified be- cause of low power, or 2) an increase in abundance might be detected because the population was ex- pected to be recovering after the reduction in fishery-induced mor- tality. However, a declining trend in central California harbor por- poise abundance was identified for the period 1986-93. Because of the surprising nature of this result and because of the management impli- cations, this report presents the updated 1986-93 analysis and in- cludes additional data from the 1989-1993 aerial surveys in north- ern California for the first time. Methods A complete description of both field and analytical methodology can be found in Forney et al. (1991), and only a brief summary of the meth- ods used is provided here. Field methods Aerial line-transect surveys were conducted from late summer to early fall (15 August through 15 November) of the years 1986-91, and 1993. In each survey year, a set of 26 transects between Point Con- ception and the Russian River (Fig. 1A) was replicated as often as weather permitted (generally 4-8 times) to monitor the central Cali- fornia harbor porpoise population. Beginning in 1989, a set of 17 ad- ditional transects between the Rus- sian River and the California-Or- egon border (Fig. IB) was surveyed 1-3 times per field season to moni- tor the northern California popu- lation. The transects followed a zig- zag pattern designed to survey sys- tematically between the coast and the 92-m (50-fathom) isobath, which is the depth range in which the majority of harbor porpoise are expected to be found in this region (Barlow, 1988). The only deviation from this design occurred outside San Francisco Bay, where the 92- m (50-fathom) contour is located too far offshore for safe operation of the survey aircraft; in this region, the transect lines extended only to the 55-m (30-fathom) contour. Total transect length was 916 km, and under good weather conditions all transects could be surveyed in two days. The survey platform was a high-wing, twin-engine Partenavia P-68 aircraft outfitted with two bubble windows for lateral viewing and with a belly port for downward viewing. The survey team consisted of three observers (situated left, right, and belly) and one data re- corder. Line-transect methods were followed with sighting distances calculated from the angle of decli- nation to the sighting (obtained with a hand-held clinometer) and from the aircraft's altitude. Surveys were flown at about 167-185 km/hr (90-100 knots) airspeed and 213 m Manuscript accepted 8 June 1995. Fishery Bulletin: 741-748 (1995). 742 Fishery Bulletin 93(4), 1995 34°N- 124°W 57V Point St. George 15 56^ 55/ 54 53i 521 w CALIFORNIA 50 v\ Cape Mendocino 4^i ■fcVv Area 3 4sVl ■ 41jP 46\ I acij-ic VJcean 45|\ 44V Russian \N River \ «\ ^ «VJ 4l\ Figure 1 Flight transects and defined areas for aerial surveys for harbor porpoise, Phocoena phocoena, in (A) central California (transects 1-26; areas 1 and 2) and IB) northern California (transects 41-57; area 3). Transect 7 was combined with transect 8 after 1986 and is not shown. (700 ft) altitude. Flights were conducted only when weather conditions were good (Beaufort sea states 0-3, mostly with clear or partly cloudy skies). Sight- ing information and environmental conditions were recorded and updated throughout the survey by us- ing a laptop computer connected to the aircraft's LO- RAN navigation system. Analytical methods The number of porpoise observed per kilometer of search effort was used as a measure of relative abun- dance. These data were stratified by Beaufort sea state (0-1, 2, and 3), area (transects 1-14 and 15-26 in central California, and 41-57 in northern Califor- nia; see Fig. 1), and percent cloud cover (<25%; >25%). After log-transformation, a stepwise selection pro- cedure was used to construct an analysis of covari- ance model of the form: P = n + a1 + a2+... + 8(y-y) + £, (1) where P is the log-transformed value of the number of porpoise seen per kilometer + 0.001; /u is the mean value of P; the a's are factors influencing apparent porpoise abundance (such as sea state); S is the coef- ficient for the covariate year (y); y is the mean year; and e is a random error term. This additive model for the log-transformed data is equivalent to a mul- tiplicative model for the actual data (stratification variables such as sea state are expected to change the fraction of animals observed, and thus have a multiplicative effect). Variability caused by unequal survey coverage in each combination of sea state, percent cloud cover, and geographic area was in- cluded in the model by weighting by the number of kilometers flown. The analysis was done separately for central California alone (transects 1-26) and for both central and northern California (transects 1— 26 and 41-57). Previous simulations (Forney et al., 1991) indicated that power would still be low with this eight-year time series; therefore, the critical value for type-I error was set at a - 0.10. This was expected to provide a power of approximately 60% to detect a large change in abundance of ±10% per year but would still have low power (approximately 25%) to detect trends on the order of ±5% per year. Results A summary of survey coverage (total kilometers sur- veyed, percent surveyed under good conditions) and NOTE Forney: Decline in the abundance of Phocoena phocoena 743 Table 1 Summary of harbor porpoise Phocoena ph ocoena, aerial survey data collected 1986-1993 in central and northern California. Areas 1, 2, and 3 correspond to transects 1- 14, 15-26, and 41-57, respectively (see Fig . 1). "% good conditions" is defined as 100 times the total kilometers surveyed with Beaufort sea states 0-2 and <25% cloud cover, divided by the total number of kilometers flown in all conditions. " — " = no surveys were flown; SD = standard deviation. Area Year 1986 1987 1988 1989 1990 1991 1993 1 no. of sightings 36 28 15 22 18 12 9 no. of porpoise 62 47 20 44 29 20 17 mean group size ± SD 1.72 ± 0.91 1.68 ± 1.79 1.33 ± 0.49 2.00+ 1.41 1.61 ± 1.04 1.67 ± 0.65 1.89 ± 0.93 km surveyed 1,767 1,618 1,834 1,653 1,887 1,066 1,941 % good conditions 56.4% 66.7% 31.3% 32.4% 60.3% 56.5% 68.7% 2 no. of sightings 63 44 88 60 57 43 69 no. of porpoise 104 76 154 134 126 76 149 mean group size ± SD 1.65 ± 1.17 1.73 ± 1.11 1.75 ± 1.18 2.23 ± 1.51 2.21 ± 1.47 1.77 ± 1.11 2.24 ± 1.61 km surveyed 1,282 1,463 2,086 1,607 1,751 669 1,919 % good conditions 55.9% 34.3% 36.0% 42.1% 32.0% 58.9% 59.9% 3 no. of sightings 44 173 87 143 no. of porpoise — — — 76 296 166 246 mean group size ± SD — — — 1.73 ± 1.21 1.71 ± 1.27 1.91 ± 1.02 1.72 ± 1.40 km surveyed — — — 804 1,084 612 966 % good conditions — — — 34.1% 67.3% 77.9% 88.0% sighting information (number of sightings, number of porpoise, and mean group size) is provided in Table 1 for each year and region. Survey coverage was com- parable in most years, but owing to poor weather throughout the 1991 field season, only about half of the usual replication was obtained during this year. Differences also occurred in the proportion of survey effort obtained under good sighting conditions, defined as Beaufort sea states 0-2 and as less than 25% cloud cover. Consistent dif- ferences in encounter rates, measured as the number of porpoise observed per kilo- meter surveyed, are apparent between the three defined areas (Fig. 2). Substantially higher encounter rates occurred in north- ern California than in central California, and the lowest encounter rates occurred south of Monterey Bay, in the southern end of this population's range. The best model obtained by the stepwise selection procedure for central California data included area, Beaufort sea state, and cloud cover as categorical variables, and year as the covariate (Table 2). All four factors were significant at a = 0.10, with probabilities ranging from 0.0001 to 0.0798 (Table 3). With the exception of the inclu- sion of the covariate year in the model, these results are qualitatively the same as those for the analysis of the first five years of data (Forney et al., 1991). 0.7 1 0.5- 0.3- 0.2- 0.1- AREA1 -III III. lie AREA 2 ll i.lll AREA 3 L 1 3 5 8 10 12 14 16 18 20 22 24 26 42 44 46 48 50 52 54 56 2 4 6 9 1113 15 17 19 21 23 25 41 43 45 47 49 51 53 55 Transect number Figure 2 Mean number of harbor porpoise, Phocoena phocoena, observed per kilometer on each of the surveyed transects. Only data obtained under good survey conditions (Beaufort sea state 0-2, <25% cloud cover) are included. Transect and area numbers correspond to those shown in Figure 1. 744 Fishery Bulletin 93(4), 1995 Table 2 Stepwise model building procedure for the 1986-93 central California aerial survey data. Parameters marked in bold indicate variables that were included in the model at each step. P=ln( porpoise/km + 0.001); jj = mean value of P; BF = Beaufort sea state; AR = area; CL = cloud cover, and YR = year. Interaction effects are represented with an asterisk between the variables. Step number and base model 1 2 P = H P = m+AR 3 P = n + AR + BF 4 5 P = H+AR + BF+ CL P = fi +AR + BF+CL + YR Probability value for tested additional variables BF: 0.0183 BF: 0.0009 AR: 0.0001 CL: 0.0013 CL: 0.0379 YR: 0.3514 YR: 0.4606 CL: 0.0003 YR: 0.5508 BF*AR: 0.7567 YR: 0.0798 BF*AR: 0.7823 BF*AR: 0.8043 BF*CL: 0.9131 BF*CL: 0.8981 CL*AR: 0.1640 CL*AR: 0.1344 YR*AR: 0.2783 YR*BF: 0.7010 YR*CL: 0.7943 Table 3 Results of analysis of covariance for central California and combined central and northern California aerial survey data. The complete model simultaneously includes all variables marked in bold in Table 2. SE = = standard error Central and Source Central California northern California df F P df F P Model 5 15.70 0.0001 6 22.64 0.0001 Area 1 52.75 0.0001 2 48.30 0.0001 Beaufort sea state 2 8.71 0.0004 2 11.26 0.0001 Cloud cover 1 17.18 0.0001 1 18.91 0.0001 Year 1 3.16 0.0798 1 3.04 0.0850 Error 73 85 r2 0.5182 0.6151 Year coefficient (SE) -0.098 (0.055) -0.087 (0.050) Annual rate of change 9.3% 8.3% The important difference is that the five-year time series did not reveal a trend in abundance, whereas the analysis including the new (1991 and 1993) data indicated a decline in harbor porpoise abundance in central California during the eight-year period 1986- 93. To investigate the possibility that animals may have moved northward into northern California, the analysis was repeated with northern California as a third area stiatum. The results were essentially the same: the year effect was slightly less pronounced but still significant at a = 0.10 (Table 3). Figure 3 shows a plot of relative abundance (porpoise observed per kilometer) in each of the three defined areas for the period 1986-93, adjusted for the effects of sea state and cloud cover (based on the parameters of the best-fitting model). The combined relative abun- dance for all of central California, calculated as an average of the val- ues of porpoise per kilometer for ar- eas 1 and 2, weighted by the propor- tion of the total study area encom- passed by each (33.6% for area 1; 66.4% for area 2), is indicated by a dashed line in Figure 3. Discussion The indication of a declining trend in abundance is somewhat surprising, given that the central California population of harbor porpoise was expected to be recovering from im- pacts of heavy fishery-related mortal- ity prior to about 1987 (Barlow and Forney, 1994). The point estimate for the decline corresponds to a 9.3% per year decrease (coefficient of variation, CV=0.56) in harbor porpoise abundance for central California (or 8.3%, CV=0.56, if northern California surveys are in- cluded in the analysis); however, the confidence in this value is low because of the low power of the test. There are a number of possible explanations for the observed decline, including 1) statistical error, 2) movement of animals out of the study area, 3) ef- fects of fishery-related mortality, and 4) change in natural mortality and net reproduction. Each of these possibilities will be discussed separately below. Statistical error It is possible that the results of the test are incor- rect, that is, an a-error ( detecting a trend although NOTE Forney Decline in the abundance of Phocoena phocoena 745 0.40- I R 0.30- ■& 0.10- o.oo Area 1 85 86 87 89 90 Year 92 93 94 Figure 3 Relative abundance of harbor porpoise, Phocoena phocoena, for the period 1986-93. Relative abundance is defined as the num- ber of porpoise observed per kilometer surveyed, adjusted for the effects of sea state and cloud cover on sighting rates. Areas corre- spond to those shown in Figure 1. The combined relative abun- dance for all central California was calculated as an average of the adjusted values of porpoise per kilometer for areas 1 and 2, weighted by the proportion of the total study area encompassed by each (33.6% of the total study area was in Area 1; 66.4% was in area 2). in fact the population is stable) or /-error (detecting a decline when the population is in fact increasing; Forney et al., 1991) has occurred. The latter is ex- pected to be virtually zero for this eight-year time series (Forney et al., 1991). The former was set at 0.10 a priori in order to increase power. Assuming symmetry, this should have resulted in a 5% prob- ability of detecting a decline if the population were in fact stable. Movement of animals out of the study area In recent years, an increasing body of evidence indi- cates that long-term changes have occurred in the California Current during the last few decades, in- cluding an increase in surface water temperature and sea level height (Roemmich, 1992), a decrease in zoop- lankton abundance ( Roemmich and McGowan, 1995), and changes in the size of seabird populations (Ainley et al., 1994). There has also been a dramatic increase in the abundance of short-beaked common dolphins, Delphinus delphis, off California (Barlow, 1995; Forney et al., 1995), possibly due to a northward shift in the distribution of this tropical and warm-tem- perate species (Anganuzzi and Buckland, 1994). A northward range extension into central California has also been documented for another tropical and warm-temperate species, the bottlenose dol- phin, Tursiops truncatus, following the El Nino event of 1982-83 (Wells et al., 1990). This spe- cies now is seen regularly in nearshore waters off central California, within the range of the harbor porpoise. Similarly, harbor porpoise in central Califor- nia may have shifted their distribution out of the study area (either to the north or farther offshore) in response to environmental changes, causing an apparent decline in abundance in the nearshore region. Unfortunately, no detailed data on harbor porpoise distributions and oceanographic conditions are available to test this hypothesis. However, it is noteworthy that the relative abundance of harbor porpoise in central California (dashed line in Fig. 3) exhib- its a significant negative correlation (or=0.05, Pearson correlation coefficient r=— 0.79, P=0.035) with 1986-93 September sea-surface temperature anomalies off Monterey Bay,1 de- spite the coarse nature of these two measure- ments. Thus, in years when sea-surface tem- peratures were warmer, the relative abundance of harbor porpoise (a temperate species) was lower, and vice versa. This may be indicative of movement of harbor porpoise in relation to changes in sea-surface temperature (or to other environmental factors that are correlated with sea- surface temperature), but it is not known whether harbor porpoise move northward or offshore in re- sponse to such environmental changes. Studies of pollutant ratios in animals along the U.S. West Coast suggest that harbor porpoise do not move frequently between central and northern Cali- fornia (Calambokidis and Barlow, 1991). Consistent with these observations, a shift of animals from cen- tral to northern California is not indicated in the analysis of this aerial survey series because the de- clining trend is still significant when northern Cali- fornia data are included. However, power to detect trends reliably in the northern portion of the study area is probably low, given only four surveys in this region. Additional surveys will improve the ability to detect a northward shift within California, if one is present. It is important to note, however, that har- bor porpoise off northern California show a continu- The sea-surface temperature anomaly is defined as the devia- tion of the mean monthly sea-surface temperature in a given year from the long-term mean for that month. Thus positive anomalies indicate warmer than average months and vice versa. Oceanographic Monthly Summary, U.S. Dep. Commer., NOAA, National Ocean Service, available from NOAA/NOS, Ocean Products Branch, 5200 Auth Road, Room 100, Camp Springs, MD 20746. 746 Fishery Bulletin 93(4). 1995 ous distribution into waters off Oregon (Barlow, 1988; Barlow et al., 1988), where they are managed sepa- rately because of jurisdictional boundaries. Without simultaneous surveys in Oregon, a more widespread shift in distribution cannot be ruled out. Alternatively, harbor porpoise may have changed their distribution in relation to distance from shore or water depth. The surveys extended only to approxi- mately the 92-m (50-fa thorn) depth contour. Although the majority of harbor porpoise are expected to be found inshore of this depth (Barlow, 1988), an in- crease in the proportion of animals found in deeper waters could cause an apparent decline within the 0-92 m (0-50 fathom) study area. This hypothesis cannot presently be tested because detailed surveys for harbor porpoise in waters deeper than 92 m have not been conducted off California, and inferences for offshore areas cannot readily be drawn on the basis of distribution patterns inshore of 92 m depth. Effects of fishery-related mortality If the detected decline in harbor porpoise abundance along the California coast is a real phenomenon, then one possible cause for the decline may be incidental mortality of this species in California set gillnet fish- eries. Although annual mortality is thought to have gradually declined from about 200-300 animals per year in 1980-87 to about 30-50 animals annually in the last few years (Barlow and Forney, 1994), there was no observer program to monitor mortality in set gillnet fisheries from April 1987 to June 1990. Total mortality estimates for these unmonitored years are based on kill rates for the 1990-91 fishing season and on estimated 1987-90 fishing effort (Perkins et al.2). These estimates are accurate only if the mor- tality observed in the 1990—91 fishing season is rep- resentative of 1987-90 rates. If fishery-related mor- tality of harbor porpoise was in fact higher during 1987-90, this may have contributed to a decline in abundance greater than is apparent from the mor- tality estimates (see Perkins et al.2). Absolute abundance estimates for central Califor- nia harbor porpoise have recently been updated on the basis of pooled data from the 1988-93 aerial sur- veys, yielding an estimate of 4,120 (CV=0.22) har- bor porpoise (Barlow and Forney, 1994). Assuming an otherwise stable population, 9.3% of the popula- tion, or roughly 350-450 animals, would have had to be removed during each year of the study period in order to cause the decline indicated by the analysis for central California. The fishery-related mortality estimates range from 12 animals in 1993 to 197 ani- mals in 1986 and have large standard errors, but the upper 95% lognormal confidence limits of the mortality estimates are lower than 9.3% of the popu- lation estimate in all years since 1984 (derived from data in Perkins et al.2; Hanan et al.3,4; Konno5; Julian6,7). Although these mortality estimates as- sumed fishing effort was known without bias, when in fact it may have been underestimated (Julian7), fishery-related mortality alone does not appear to be responsible for the decline in harbor porpoise abundance within the central California study area. However, potential effects of age or sex bias in har- bor porpose mortality and potential time lags in the impact of such takes are unknown. Change in natural mortality and net reproduction An increase in natural mortality (e.g. due to increased predation, disease, or a reduced food supply) could contribute to a decline in abundance. Natural mor- tality rates for harbor porpoise are not known. The small size of harbor porpoise may make them vul- nerable to shark and killer whale predation, but there is no evidence (i.e. from strandings) to suggest that predation rates may have been higher during the past eight years than in prior time periods. Harbor por- poise appear to be opportunistic feeders: market squid, Loligo opalescens, spotted cusk eel, Chilara taylori, and northern anchovy, Engraulis mordax, are known to be prominent components of their diet in the Monterey Bay region (Sekiguchi, 1987; Dorfman, 1990); however, both studies indicate that the north- ern anchovy is the most important of these prey 2 Perkins, P., J. Barlow, and M. Beeson. 1994. Report on pin- niped and cetacean mortality in California gillnet fisheries: 1988-90. Admin. Rep. LJ-94- 11 . Southwest Fisheries Science Center, Natl. Mar. Fish. Serv., P.O. Box 271, La Jolla, CA92038. 3 Hanan, D. A., S. L. Diamond, and J. P. Scholl. 1986. An esti- mate of harbor porpoise mortality in California set net fisher- ies April 1, 1984 through March 31, 1985. Admin Rep. SWR- 86-16, 38 p. Available from Southwest Region, 300 S. Ferry St., Terminal Island, CA 90731. 4 Hanan, D.A., S. L. Diamond, and J. P. Scholl. 1987. An esti- mate of harbor porpoise mortality in California set net fisher- ies April 1, 1985 through March 31, 1986. Final rep. to Na- tional Marine Fisheries Service, Southwest Region, 300 S. Ferry St., Terminal Island, CA 90731. 5 Konno, E. S. 1990. Estimates of sea lion, harbor seal and harbor porpoise mortalities in California set net fisheries for the 1987-88 fishing year. Draft rep. available from California Department of Fish and Game, P.O. Box 271, La Jolla, CA 92038. 6 Julian, F 1993. Pinniped and cetacean mortality in Califor- nia gillnet fisheries: preliminary estimates for 1992. Int. Whaling Comm. Working Paper SC/45/022, 29 p. 7 Julian, F 1994. Pinniped and cetacean mortality in Califor- nia gillnet fisheries: preliminary estimates for 1993. Int. Whaling Comm. Working Paper SC/46/OH, 28 p. NOTE Forney. Decline in the abundance of Phocoena phocoena 747 items. In recent years, California Cooperative Oce- anic Fisheries Investigations (CalCOFI) surveys have revealed a decline in California anchovy populations (Jacobsen et al., 1994), and the occurrence of this species in the diet of California sea lions, Zalophus californianus, off southern California has decreased markedly since 1991. 8 Based on these considerations, an alternate hypothesis for the observed decline in harbor porpoise abundance is that the population has been affected by a decline in a major food source, the northern anchovy. However, too few stranded or in- cidentally caught harbor porpoise have been avail- able recently for examination of food habits ( Peltier et al., 1993, 1994; Lennert et al., 1994;), and data are presently insufficient to test the possibility of such a relationship. Conclusions Despite a reduction in fishery-related mortality, the harbor porpoise population in nearshore waters off central California appears to have declined between 1986 and 1993. Potential causes of this decline are poorly understood, and further studies are impera- tive. Recent restrictions on coastal gillnet fisheries have substantially reduced harbor porposie mortal- ity in central California. If the decline was caused primarily by fishery-related mortality, then the popu- lation should exhibit a stable or increasing trend over the next several years. Continuation of the aerial- survey time series will provide a means of detecting such a trend. Additional research should also address possible relationships between the density and distri- bution of harbor porpoise and environmental conditions (such as water temperature and prey availability). Acknowledgments Financial support and personnel were provided by the National Marine Fisheries Service (Southwest Regional Office and Southwest Fisheries Science Center) and the California Department of Fish and Game (CDFG). The observers and data recorders were J. Barlow, M. Beeson, J. Carretta, D. DeMaster, S. Diamond, T. Farley, D. Fink, T. Gallegos, D. Hanan, A. Hudoff, L. Jones, E. Konno, S. Kruse, M. Larson, J. Lecky, T. Lee, M. Lowry, R. Pitman, J. Scholl, J. Sisson, and B. Taylor (and K.A.F). Aircraft were char- tered from Aspen Helicopters, Inc. and contracted Lowry, M. 1994. Southwest Fisheries Science Center, Natl. Mar. Fish. Serv., P.O. Box 271, La Jolla, CA 92038. Personal commun. from CDFG. Pilots were B. Cheney, B. Cole, J. Drust, B. Hansen, D. Hansen, L. Heitz, K. Lankard, E. Schutze, J. Turner, R. Riediger, R. Throckmorton, and R. Van Benthuysen. The computer data acquisition software was written by J. Cubbage and modified by J. Barlow. Aerial surveys were conducted under Ma- rine Mammal Protection Act Permit 748 and NOAA Sanctuary permits GFNMS/MBNMS-03-93 and MBNMS-11-93. Drafts of this manuscript were re- viewed by J. Barlow, S. Benson, R. Brownell, J. Carretta, P. Dayton, D. DeMaster, J. Enright, T. Gerrodette, F. Julian, R. Neal, and two anonymous reviewers. I thank all for their useful comments and constructive criticism. Literature cited Ainley, D. G., W. J. Sydeman, S. A. Hatch, and U. W. Wilson. 1994. Seabird population trends along the west coast of North America: causes and the extent of regional concor- dance. Stud. Avian Biology 15:119-133. Anganuzzi, A., and S. Buckland. 1994. Relative abundance of dolphins associated with tuna in the eastern Pacific Ocean: analysis of 1992 data. Rep. Int. Whaling Comm. 44:361-366. Barlow, J. 1988. Harbor porpoise, Phocoena phocoena, abundance es- timation for California, Oregon and Washington: I. Ship surveys. Fish. Bull. 86:417-432. 1995. The abundance of cetaceans in California waters. Part I: Ship surveys in summer and fall of 1991. Fish. Bull. 93:1-14. Barlow J., and K. A. Forney. 1994. An assessment of the 1994 status of harbor porpoise in California. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SWFSC-205, 17 p. Barlow J., and D. Hanan. (In press). An assessment of the status of harbor porpoise in central California. Rep. Int. Whaling Comm. Spec. Issue. Barlow, J., C. W. Oliver, T. D. Jackson, and B. L. Taylor. 1988. Harbor porpoise, Phocoena phocoena, abundance es- timation for California, Oregon, and Washington: II. Aerial surveys. Fish. Bull. 86:433-444. Barlow, J., R. W. Baird, J. E. Heyning, K. Wynne, A. M. Manville II, L. F. Lowry, D. Hanan, J. Sease, and V. N. Burkanov. 1994. A review of cetacean and pinniped mortality in coastal fisheries along the west coast of the U.S. and Canada and the east coast of the USSR. Rep. Int. Whaling Comm. Spec. Issue 15:405-426. Calambokidis, J., and J. Barlow. 1991. Chlorinated hydrocarbon concentrations and their use for describing population discreteness in harbor por- poises from Washington, Oregon and California. In J. E. Reynolds III and D. K. Odell (eds.). Marine mammal strandings in the United States, p. 101-110. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 98. Dorfman, E. J. 1990. Distribution, behavior, and food habits of harbor por- 748 Fishery Bulletin 93(4), 1995 poises (Phocoena phocoena) in Monterey Bay. M.S. the- sis, San Jose State Univ., San Jose, CA, 57 p. Forney, K. A., J. Barlow, and J. V. Carretta. 1995. The abundance of cetaceans in California waters. Part II: Aerial surveys in winter and spring of 1991 and 1992. Fish. Bull. 93:15-26. Forney, K. A., D. Hanan, and J. Barlow. 1991. Detecting trends in harbor porpoise abundance from aerial surveys using analysis of covariance. Fish. Bull. 89:367-377. Jacobsen, L., N. C. II. Lo, and J. T. Barnes. 1994. A biomass-based assessment model for northern an- chovy, Engraulis mordax. Fish. Bull. 92:711-724. Lennert, C, S. Kru.se, M. Beeson, and J. Barlow. 1994. Estimates of incidental marine mammal bycatch in California gillnet fisheries for July through December, 1990. Rep. Int. Whaling Comm. Spec. Issue 15:449-463. Norris K. S., and J. H. Prescott. 1961. Observations on Pacific cetaceans of California and Mexican waters. Univ. California Publ. Zool., Los Ange- les, CA, 401 p. Peltier, K. M., S. J. Chivers, and S. Kruse. 1993. Composition of the 1991 incidental kill of small ceta- ceans in the eastern tropical Pacific US tuna fishery and two California gillnet fisheries. Rep. Int. Whaling Comm. 43:401-406. Peltier, K. M., S. J. Chivers, and W. T. Norman. 1994. Composition of the incidental kill of odontocetes in the eastern tropical Pacific US tuna fishery and two California gill- net fisheries for 1992. Rep. Int. Whaling Comm. 44:353-359. Roemmich, D. 1992. Ocean warming and sea level rise along the south- west U.S. coast. Science (Wash. D.C.) 257:373-375. Roemmich, D. and McGowan, J. 1995. Climatic warming and the decline of zooplankton in the California Current. Science (Wash. D.C.) 267:1324- 1326. Sekiguchi K. 1987. Occurrence and behavior of harbor porpoises (Phocoena phocoena) at Pajaro Dunes, Monterey Bay, California. M.S. thesis, San Jose State Univ., San Jose, CA, 49 p. Wells, R. S., L. J. Hansen, A. Baldridge, T. P. Dohl, D. L. Kelly, and R. H. Defran. 1990. Northward extension of the range of bottlenose dol- phins along the California coast. In S. Leatherwood and R. R. Reeves (eds.). The bottlenose dolphin, p. 421- 431. Academic Press, Inc., San Diego, CA. Seasonal influences on statolith growth in the tropical nearshore loliginid squid Loligo chinensis (Cephalopoda: Loliginidae) off Townsville, North Queensland, Australia George D. Jackson Department of Marine Biology, James Cook University of North Queensland Townsville, Queensland 48 1 1 . Australia Present Address: Department of Zoology University of Western Australia. Nedlands. Perth, Western Australia 6009, Australia son and Campana, 1992), much of the work with statolith ageing and validation is still preliminary in nature. However, evidence does support daily periodicity in sta- tolith increment production in many species (Jackson, 1994) al- though there is an ongoing need for further validation and ageing stud- ies. Because age and population information is already available for Loligo chinensis1 (Jackson, 1990b, 1993; Jackson and Choat, 1992), this study was undertaken to see if seasonal differences in growth rate are reflected in statolith-size:body- size relationships in this tropical nearshore squid. Information is currently accumu- lating on age, growth, and matu- rity rates of squids, with a number of studies focusing on tropical and warm water species (eg. Jackson, 1990, a and b; Arkhipkin and Mik- heev, 1992; Bigelow, 1992; Jackson and Choat, 1992; Arkhipkin and Nekludova, 1993; Jackson, 1993; Laptikhovsky et al., 1993; Young and Mangold, 1994; see also Jack- son, 1994, for review). The interpre- tation of growth phenomena in squids is complicated owing to the high degree of temperature depen- dency in growth (O'Dor and Wells, 1987; Forsythe and Hanlon, 1989). Moreover, growth is highly variable even within particular temperature regimes (Lipinski, 1986; Natsukari et al., 1988). The use of validated daily increments in statoliths is a convincing tool for determining both the rate of growth and its vari- ance. However, there is also the po- tential that temperature-induced variation in growth rates might be reflected in statolith growth rates. Recent work on the uncoupling between otolith size and fish size ( see Campana and Jones, 1992 ) has indicated that individual variation in growth rates can have profound effects on soma-otolith relation- ships. While such features make analysis such as back calculation of individual size less than straight- forward (Campana, 1990), they do provide a mechanism for detecting past growth histories (or perhaps even past environmental histories) to which a fish has been exposed. For example, if two similar-sized fish of the same species show con- siderable disparity in otolith size, it suggests that the individual with the larger otolith has grown slower (e.g. Reznick et al., 1989; Wright et al., 1990). Lipinski et al. (1993) have also documented substantial uncoupling in squid statolith growth and in growth of the mantle in Todaropsis eblanae and Todarodes angolensis off southern Africa. Statolith increments are pro- duced daily in Loligo chinensis (Jackson, 1990b) as well as in other loliginid squids such as Alloteuthis subulata (Lipinski, 1986), Loligo opalescens (Yang et al., 1986), Loliolus noctiluca (Jackson, 1990b), and Sepioteuthis lessoniana (Jack- son, 1990a; Jackson et al., 1993). However, compared with fish otolith analysis in which there is a substantial number of ageing and increment validation studies (e.g. Campana and Neilson, 1985; Steven- Materials and methods Individuals of Loligo chinensis were captured by using paired otter trawls (each net consisted of an 11- m gape and 3.8-cm mesh). Trawls were towed for approximately 20 minutes at a speed of 2-2.5 knots. Samples were taken in Cleveland Bay (19°15'S,146°50,E) in water <20 m deep off Townsville, North Queensland. Statoliths were ob- tained from squid caught during two seasonal periods, 12 January 1989 (austral summer, n-35) and 13 July 1989 (austral winter, rc=33). Squid were preserved in 10% buff- 1 It is now known that the species Loligo chinensis which is found in shallow tropi- cal waters off North Queensland is a dis- tinct species from L. chinensis which is found elsewhere in the tropical Indo-Pa- cific. J. Yeatman. 1993. James Cook Univ. of North Queensland. Personal commun. Furthermore, all Loligo species in Australian waters will probably be re- ferred to as Photololigo in the future. Un- til this is resolved, I have referred to the species of this study as Loligo chinensis which is the same species referred to as Photololigo cf. chinensis (east coast form) in Dunning et al. (1994) and Photololigo sp. 3 in Yeatman and Benzie ( 1994). Manuscript accepted 19 June 1995. Fishery Bulletin 93:749-752 ( 1995). 749 750 Fishery Bulletin 93(4), 1995 ered seawater formalin and subsequently transferred to 70% ethanol. Mantle length (ML) measurements (nearest mm) were taken on the preserved individu- als. Statoliths were removed shortly after preserva- tion and mounted in Crystal Bond thermoplastic ce- ment. Total increment number was determined (with a camera lucida attached to an Olympus BH compound microscope) as the mean of three consecutive counts that differed less than 10% from the mean (see also Jackson and Choat, 1992; Jackson, 1993). Statolith length (to the nearest 10 urn) was measured with an eyepiece micrometer (with an Olympus BH com- pound microscope) along the longest axis from the dorsal dome to the tip of the rostrum. Results For the summer population, the relationship between statolith length and mantle length as well as sta- tolith length and age was curvilinear. However, both 1800 ■g 1600 3 5 1400 z UJ —I t 1200 o < U 1000 800 Winter Summer C 20 40 60 80 100 120 140 160 180 200 MANTLE LENGTH (mm) 1800 1600 5 1400 1200 1000 800 B Summer Winter 0 20 40 60 80 100 120 140 160 180 200 AGE (days) Figure 1 The relationship between (A) statolith length and mantle length and (B) statolith length and age for summer (Janu- ary) and winter (July) samples of Loligo chinensis. relationships were linear for the winter population (Fig. 1; Table 1). Because all relationships were not linear, an analysis of covariance could not be applied to these data sets. However, a paired £-test was used to compare statolith lengths of similar-sized males and females (mantle lengths between 90 and 110 mm, rc=24) from both January (summer) and July (win- ter). Squid statoliths from the July sample were sig- nificantly longer than statoliths from the January sample (P<0.05). The relationship between statolith length and mantle length (Fig. 1A) suggested that somatic growth was greater than statolith growth as size in- creases (i.e. in larger squids the mantle was increas- ing in length faster than was the statolith). More- over, in general, for any given length, a winter squid had larger statoliths than its summer counterpart. There were also considerable seasonal differences in the growth of the statolith with age (Fig. IB). There was a rapid increase in statolith length in summer over a relatively short period from 60 to 100 days. In contrast, statolith growth was much slower in the winter; the statolith gradually increased in length from 80 to 170 days. However, statoliths eventually reached a greater length in the older, winter-popu- lation squids. This feature was a factor of age be- cause winter squids were not longer than summer squids. In comparing similar-aged squids between seasons, for any given age, a summer squid generally had a larger statolith than its winter counterpart. Discussion Current research on fish somatic-otolith growth re- lationships provides a background for the possible mechanisms underlying somatic-statolith growth relationships for L. chinensis. The relationship be- tween both statolith length and mantle length and statolith length and age shows striking similarities to otolith length versus fish length and age studies. Mosegaard et al. (1988), Secor and Dean (1989), Reznick et al. ( 1989), Wright et al.( 1990), and Mugiya and Tanaka ( 1992) have shown that slower-growing fish have larger otoliths than similar-sized, faster- growing fish. Furthermore, for striped bass, Morone saxatilis, and Atlantic salmon, Salmo salar, slower- growing fish have larger otoliths at any given size, al- though faster-growing fish have larger otoliths at any given age (Secor and Dean, 1989; Wright et al., 1990). A similar relationship is evident between statolith length and both mantle length and age for L. chinensis. These teleost studies provide insights into the growth dynamics of squid. The slower growing indi- viduals of L. chinensis (winter population) had larger NOTE Jackson: Seasonal influences on statolith growth in Loligo chinensis 751 Table 1 Regression equations for the relationship between mantle length and statolith length and for age and statolith length for individuals of Loligo chinensis collected in both summer and winter. ML = mantle length. All regressions were highly significant 'P<0.001). Season Relationship Equation Summer ML vs. statolith length 38 Summer Age vs. statolith length 38 Winter ML vs. statolith length 33 Winter Age vs. statolith length 33 y = -238.4+ 731.2 logx y = -1585.8 + 1470.6 logx y = 849.4 + 5.03x y = 672.7 + 5.3x 0.84 0.63 0.91 0.67 statoliths because they were in reality much older than similar-sized, faster-growing squids (summer population). Alternatively, when statolith length and individual age were compared, faster-growing squids had larger statoliths than slower-growing squids for a given age because the individual itself was consid- erably larger (e.g. in the summer, squids were reach- ing adult sizes at around 80 days whereas in the winter, 80-day squid were still juveniles). Morris andAldrich (1985) have suggested that sta- tolith length may be a better indicator of squid age than increment number because they observed less variation in the mantle length:statolith length rela- tionship than in the mantle length:age relationship in Illex illecebrosus. However, the seasonal difference in the relationship between the statolith and the soma of L. chinensis suggests that this technique should be used cautiously until further research into temperature effects is conducted (see also Campana, 1990; Lipinski et al., 1993). On the basis of labora- tory observations, Forsythe and Hanlon (1989) and Forsythe ( 1993) have suggested that even fairly small variations in ambient temperature can have a marked effect on somatic growth rates. Temperature has also been shown to be an important influence on growth rates of Sepia australis in the field (Roeleveld et al., 1993). This preliminary study withL. chinensis suggests that temperature variation will not only greatly influence somatic growth but statolith growth as well. The uncoupling of statolith growth and so- matic growth in squid is certainly an area that de- serves further research (see Lipinski et al., 1993). Statoliths are structures which have accentuated both the differences and similarities between cepha- lopods and fish. The increment structure and the growth of the statolith in relation to the squid soma are remarkably similar to that of the otolith in fish. In contrast, the enumeration of growth increments in both otoliths and statoliths have accentuated very different growth strategies and life histories (e.g. Jackson and Choat, 1992; Alford and Jackson, 1993) of two organisms that are biologically very different but nevertheless show many similarities. Acknowledgments I would like to thank J. H. Choat for comments throughout this project, C. H. Jackson for reading the manu- script, R. Black for assistance with figure preparation, and the crew of the research vessel James Kirby for specimen collection. This research was supported by grants from the James Cook University of North Queensland Research Funding Panels. Literature cited Alford, R. A., and G. D. Jackson. 1993. Do cephalopods and larvae of other taxa grow asymptotically? Am. Nat. 141:717-728. Arkhipkin, A., and A. Mikheev. 1992. Age and growth of the squid Sthenoteuthis pteropus (Oegopsida: Ommastrephidae) from the Central-East Atlantic. J. Exp. Mar. Biol. Ecol. 163:261-276. Arkhipkin, A., and N. Nekludova. 1993. Age, growth and maturation of the loliginid squids Alloteuthis africana and A. subulata on the West African Shelf. J. Mar. Biol. Assoc. U.K. 1993. 73:949-961. Bigelow, K. A. 1992. Age and growth in paralarvae of the mesopelagic squid Abralia trigonura based on daily growth increment in statoliths. Mar. Ecol. Prog. Ser. 82:31-40 Campana, S. E. 1990. How reliable are growth back-calculations based on otoliths? Can. J. Fish. Aquat. Sci. 47:2219-2227. Campana, S. E., and J. D. Neilson. 1985. Microstructure of fish otoliths. Can. J. Fish. Aquat. Sci. 42:1014-1032. Campana, S. E., and C. M. Jones. 1992. Analysis of otolith microstructure data. In D. K. Stevenson and S. E. Campana (eds.), Otolith microstruc- ture examination and analysis, p. 73-100. Can. Spec. Publ. Fish. Aquat. Sci. 117. Dunning, M., S. McKinnon, C. C. Lu, J. Yeatman, and D. Cameron. 1994. Demersal cephalopods of the Gulf of Carpentaria, Australia. Aust. J. Mar. Freshwater Res. 45:351-374. Forsythe, J. W. 1993. A working hypothesis on how seasonal temperature change may impact the field growth of young cepha- lopods . In T. Okutani, R. K. O'Dor, and T. Kubodera ( eds. ), Recent advances in cephalopod fisheries biology, p. 133- 143. Tokai Univ. Press, Tokyo. Forsythe, J. W., and R. T. Hanlon. 1989. Growth of the Eastern Atlantic Squid, Loligo forbesi Steenstrup (Mollusca: Cephalopoda). Aquacult. Fish. Manage. 20:1-14. Jackson, G. D. 1990a. Age and growth of the tropical nearshore loliginid 752 Fishery Bulletin 93(4), 1995 squid Sepioteuthis lessoniana determined from statolith growth-ring analysis. Fish. Bull. 88:113-118. 1990b. The use of tetracycline staining techniques to de- termine statolith growth ring periodicity in the tropical loliginid squids Loliolus noctiluca and Loligo chinensis. Veliger 33:395-399. 1993. Seasonal variation in reproductive investment in the tropical loliginid squid Loligo chinensis and the small tropi- cal sepioid Idiosepius pygmaeus . Fish. Bull. 91:260-270. 1994. Application and future potential of statolith incre- ment analysis in squids and sepioids. Can. J. Fish. Aquat. Sci. 51: 2612-2625. Jackson, G. I)., and J. H. Choat. 1992. Growth in tropical cephalopods: an analysis based on statolith microstructure. Can. J. Fish. Aquat. Sci. 49:218-228. Jackson, G. I ).. A. I. Arkhipkin, V. A. Bizikov, and R. T. Hanlon. 1993. Laboratory and field corroboration of age and growth from statoliths and gladii of the loliginid squid Sepioteuthis lessoniana (Mollusca: Cephalopoda). In T. Okutani, R. K. O'Dor, and T. Kubodera (eds.). Recent advances in cephalo- pod fisheries biology, p. 189-199. Tbkai Univ. Press, Tokyo. Laptikhovsky, V. V., A. I. Arkhipkin, and A. A. Golub. 1993. 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Genetic structure and distribution of Photololigo spp. in Australia. Mar. Biol. (Berl.) 118:79-87. Young, R. E., and K. M. Mangold. 1994. Growth and reproduction in the mesopelagic-bound- ary squid Abralia trigonura. Mar. Biol. (Berl.) 119: 413-421. A comparison of Steller sea lion, Eumetopias jubatus, pup masses between rookeries with increasing and decreasing populations Richard L. Merrick National Marine Mammal Laboratory, Alaska Fisheries Science Center National Marine Fisheries Service. NOAA 7600 Sand Point Way NE, Seattle. Washington 98 II 5 Robin Brown Oregon Department of Fish and Wildlife 2040 SE Marine Science Drive, Bldg. 3 Newport. Oregon 97365 Donald G. Calkins Alaska Department of Fish and Game 333 Raspberry Road Anchorage, Alaska 99502 Thomas R. Loughlin National Marine Mammal Laboratory, Alaska Fisheries Science Center National Marine Fisheries Service, NOAA 7600 Sand Point Way NE, Seattle. Washington 98 1 I 5 The Steller sea lion, Eumetopias jubatus, population in Alaska has decreased by 629c since the late 1970's (Merrick et al., 1987; Lough- lin et al., 1992; Sease et al., 1993). Declines occurred at all 33 rooker- ies in the Gulf of Alaska and Aleu- tian Islands, although numbers at five rookeries in Southeast Alaska and Oregon increased. The sever- ity of the declines at affected rook- eries led the National Marine Fish- eries Service (NMFS) to list the species as threatened throughout its range under the Endangered Species Act ( 1990). The proximate cause for the decline appears to be chronically reduced juvenile (ages 0-3 yr) survival. After the early 1980's, juveniles were in far lower abundance on rookeries than in the 1970's (Merrick etal., 1988; NMFS1). During the summers of 1987-88, 424 female pups were marked at the Alaska rookery on Marmot Is- land. According to the life table con- structed for the area from data col- lected in the 1970's (York, 1994; Calkins and Pitcher2), close to 90 females should have survived to 1994. Biologists returning to the site from 1991 through 1994 have relocated less than 25 animals (NMFS1). York (1994) found that changes in the population size and the age structure of adult females were consistent with a decrease in juvenile survival. Also, the mass of juvenile animals in the 1980's was significantly less than that found in the 1970's (Calkins and Goodwin3). The age when juvenile survival decreases remains unknown. One hypothesis is that early pup sur- vival has decreased. Although num- bers of pups observed dead on the rookeries have been consistently low during and immediately after the pupping season (NMFS1), it is difficult to measure early survival of Steller sea lion pups because car- casses rapidly disappear from rook- eries (due to storms, tides, and scavengers). An alternative ap- proach to counting dead pups is to study the potential survival of live pups found on the rookeries. Pup mass provides useful infor- mation on juvenile survival because of the presumed relationship be- tween mass and survival. Heavier juvenile mammals have a higher probability of survival than do lighter individuals for a variety of species including grey seals, Hali- choerus grypus, wolves, Canis lupus, humans, Homo sapiens, Columbian ground squirrels, Sperm- ophilus columbianus, and northern fur seals, Callorhinus ursinus (Coulson and Hickling, 1964; van Ballenberghe and Mech, 1975; Terrenato et al., 1981; Murie and Boag, 1984; Baker and Fowler, 1992). Weighing pups also has ad- vantages over measurements of general condition (e.g. blood-based indices) — it is noninvasive, has minimal impacts on rookeries, and can provide a large, widespread 1 National Marine Mammal Laboratory, National Marine Fisheries Service, 7600 Sand Point Way NE, Seattle, WA 98115. Unpubl. data, 1994. 2 Calkins, D. G., and K. W. Pitcher. 1982. Population assessment, ecology, and trophic relationships of Steller sea lions in the Gulf of Alaska. In Environmental assessment of the Alaskan continental shelf, p. 455-546. Final Rep. 19 to OCSEAP (Outer Continental Shelf Envi- ronment Assessment Program). 3 Calkins, D. G., and E. Goodwin. 1988, Investigations of the decline of Steller sea lions in the Gulf of Alaska. Unpubl. rep., 76 p. Available from National Marine Mammal Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115. Manuscript accepted 27 May 1995. Fishery Bulletin 93:753-758 (1995). 753 754 Fishery Bulletin 93(4). 1995 sample size at minimal cost (when incorporated into other research). Our hypothesis was that if the cause of the decline affected the health of pups, then pups should be smaller at rookeries with declining populations than at rookeries with increasing populations. We exam- ined this hypothesis by comparing the masses of pups weighed during 1987-94 at rookeries documented as having either increasing (Oregon and Southeast Alaska) or decreasing (Gulf of Alaska and Aleutian Island) populations (NMFS4). In this note, we present our analyses of sex-based and temporal variability in pup masses, compare masses obtained from the two groups of rookeries, discuss potential sources of bias in the mass measurements, and conclude with a comment on the possible source(s) of the observed differences in pup masses. Methods Data collection Steller sea lion pupping is synchronous from central California to the Aleutian Islands (Bigg, 1985; Merrick, 1987). The median pupping date is 12-13 June; viable births begin in late May and continue through the end of June. We weighed pups from 26 June to 8 July, before pups were sufficiently mobile to es- cape into the water, as part of pup censuses conducted at the rookeries. Pups aggregated into small pods (10-20 pups each) after adult animals had been cleared from the rookery during the census. Individuals in a pod were captured by hand, sexed, tagged on both foreflippers, bagged into a hoop net, and weighed to the nearest kilogram. Lengths were not measured because of the difficulty in obtaining precise measurements from pups that have not been anesthetized. The first pod selected was typically at the fringe of the rookery and subsequent pods were se- lected from areas progressively closer to the center of the rookery. Pods were sampled until the desired sample size (usually 50 pups per site) was reached. A total of 1,245 Steller sea lion pups (616 females and 629 males) were weighed at twelve rookeries (Table 1; Fig. 1) in four ar- 4 NMFS. 1995. Status review of the Steller sea lion {Eumetopias jubatus). Unpubl. rep, 120 p. Avail- able from National Marine Mammal Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115. eas during 1987-94 in Oregon, Southeast Alaska, the Gulf of Alaska, and the Aleutian Islands. During 1987-94, populations at the Oregon and South- east Alaska sites increased 5-15%, whereas popula- tions at the Gulf of Alaska and Aleutian Island sites decreased 20-50% (Table 1) (Loughlin et al., 1992; Sease et al., 1993; NMFS4). Data analysis Differences in mean mass by sex of pup were ana- lyzed for each site separately and then for the whole data set. All subsequent analyses were performed separately for each sex. Short-term interannual variation (during 1987-94) in mean pup mass was tested separately for one rook- ery in each of three geographic areas — Rogue Reef (Oregon), Marmot Island (Gulf of Alaska), and Ugamak Island (Aleutian Islands). For each of these sites the weight of pups was measured on roughly the same day for two or three years (Table 1). Long- term interannual variation was tested separately for the Sugarloaf and Marmot Island rookeries by com- paring their 1992-93 masses with data collected by ■"""/an Islands. ..-''T\|| ) - . : «* \ Ugamak \ \ \ Sequam I North Pacific Ocean 75°N ■30° 180° 135°W Figure 1 Steller sea lion, Eumetopias jubatus, rookeries at which pups were weighed during 1965-94. NOTE Merrick et al.: Eumetopias jubatus pup masses 755 Table 1 Steller sea lion, Eumetopias jubatus, mean pup masses (kg) by date, sex, and rookery, collected during 1987-94. n indicates number of pups weighed, and SD indicates standard deviation of the mean value. T-value represents the Student's t calculated for the comparison of male and female masses for the site and year combination. All <-tests were significant at P<0.01. Site Weighing date Oregon Rogue Reef 30Jun 1987 29Jun 1888 7 Jul 1990 SE Alaska (Forrester Island Complex) North Rock 28 Jun 1990 Cape Horn Rock and Lowrie 29 Jun 1990 Gulf of Alaska Sugarloaf 1 Jul 1992 Marmot 30 Jun 1987 30 Jun 1988 8 Jul 1993 Chirikof 26 Jun 1990 Atkins 30 Jun 1991 Aleutian Islands Ugamak 2 Jul 1990 3 Jul 1991 3 Jul 1993 Akutan 7 Jul 1992 Bogoslof 5 Jul 1990 Seguam 27 Jun 1994 Ulak 3 Jul 1994 56 46 20 56 64 23 89 29 19 27 24 28 25 15 20 23 27 25 Female mass Male mass Mean (kg) SD Mean (kg) SD f-value 20.70 3.39 44 24.90 3.33 6.20 20.00 3.38 54 23.40 3.66 4.79 21.38 2.90 25 23.88 3.85 2.41 24.10 3.03 49 26.40 4.69 3.02 25.70 3.31 70 29.60 4.89 5.36 23.30 3.57 27 27.30 3.88 5.84 25.40 3.68 60 29.20 4.20 2.81 26.40 4.05 21 29.70 4.16 3.54 29.70 5.51 32 35.60 5.89 3.77 22.20 3.18 34 28.00 4.60 5.50 28.40 3.70 26 31.60 4.60 2.70 27.40 3.70 22 32.50 6.70 3.42 30.30 3.60 25 36.40 4.30 5.44 28.10 4.05 35 33.90 5.57 3.63 31.80 4.72 30 37.80 5.75 3.87 28.70 3.90 27 36.00 5.60 5.26 26.98 5.00 23 35.51 4.96 6.01 30.44 4.28 25 38.50 5.53 5.79 Alaska Department of Fish and Game (ADF&G5) in 1965 and 1975 (Table 2; ADF&G). To our knowledge, these are the only data on pup size that have been collected prior to our study. Variation in mean pup mass within the 26 June- 8 July weighing period was analyzed for Oregon, the Gulf of Alaska, and the Aleutian Islands by using a linear regression of the natural log of mean mass from a weighing against weighing day. Significance and equality of slopes of the regressions were tested with a Student's ^-statistic. Mean pup masses collected for the 26-30 June period were compared for the Oregon, Southeast Alaska, and Gulf of Alaska regions by using Student's ^-statistic. Means and standard errors were calcu- lated for each area's weighings by treating each weighing as a separate strata; calculations were per- formed by methods of stratified random sampling 5 Alaska Department of Fish and Game, 333 Raspberry Road, Anchorage, AK 99518. Unpubl. data, 1976. (Cochran, 1977). Mean pup masses obtained from the Gulf of Alaska and Aleutian Islands were compared by using an analysis of covariance (with weighing day as the covariate) because of the 14-day spread in weighing days at these locations. Note that to use an analysis of covariance, the slopes of the regres- sion of mass against weighing date were first com- pared for the Gulf of Alaska and Aleutian Islands to ensure homogeneity of slopes. Results Male pups ( x =30.5 kg, standard error [SE]=0.3) were significantly heavier (£=318.8, P<0.01) than female pups ( £=26.2 kg, SE=0.212) for all sites combined. Males were also significantly heavier at all individual rookeries in all years sampled (Table 1; P<0.01). The only significant interannual variation in mean pup masses for 1987-94 was for female pups at Ugamak Island (F-4. 15, P=0.04). No significant inter- 756 Fishery Bulletin 93(4), 1995 annual differences were found in mean female mass at the other three sites or in male masses at any site. Both female {F=8.6, P<0.01) and male (F=12.9, P<0.01) pups weighed at Marmot Island in 1993 were significantly heavier than pups weighed at the rookery in 1975, though the weighings oc- curred a week later in 1975. Mean mass of pups weighed at Sugarloaf Island in 1965, 1975, and 1992 were not significantly different for either female {F=3. 1, P=0. 1) or male (F=1.3, P=0.5) pups. However, two of the 1965 and 1975 weighings were conducted two weeks later than the 1992 weighing. Mean male mass increased significantly in the Gulf of Alaska during the 26 June-8 July weighing pe- riod (£=2.9, P=0.05, r2=0.68). However, there was not a significant relationship between weighing day and mean mass for males in Oregon or the Aleutian Is- lands, nor for females in any of the three geographic areas. The slopes of the regression of mean pup mass against weighing day were not significantly differ- ent for the Gulf of Alaska and Aleutian Islands for female (£=0.26, P>0.5) and male (£=0.57, P>0.5) pups. Mean mass increased significantly for both sexes from Oregon to Southeast Alaska to the Gulf of Alaska and Aleutian Islands. Oregon female (£=105.1, P<0.01) and male (£=79.3, P<0.01) pups were signifi- cantly lighter than their counterparts in Southeast Alaska (Fig. 2). Mean mass of Southeast Alaska fe- male (£=29.4, P<0.01) and male (£=36.9, P<0.01) pups was significantly less than that of Gulf of Alaska pups. Gulf of Alaska female and male pups were both significantly lighter than Aleutian Island female (P=6.0, P=0.03) and male (P=16.3, P<0.01) pups. Discussion Our expectations in this study were either that there would be no significant differences in mean pup mass between rookeries or that pups at rookeries with declining populations would be smaller than pups at rookeries with increasing populations. Considerable research by scientists at NMFS, ADF&G, and other research facilities has focused on comparing the con- dition of pups between Southeast Alaska and the Gulf of Alaska, because it has been assumed that the op- posing population trends in the two areas were a result of some limiting factor (e.g. lack of food or dis- ease) affecting only the Gulf of Alaska population, Table 2 Steller sea lion, Eumetopias jubatus, pup masses (kg) by date, sex, and rookery, collected during 1965 and 1975 at Sugarloaf and Marmot Islands in the Gulf of Alaska, n indicates number of pups weighed, and SD indicates standard devia- tion of the mean value. Site Weighing date Female mass Male mass n Mean (kg) SD n Mean (kg) SD Sugarloaf 1 Jul 1965 7 19.70 2.27 13 24.90 2.73 14 Jul 1965 9 23.80 3.13 11 29.30 5.83 13 Jul 1975 16 23.90 3.04 35 27.40 6.99 Marmot 17 Jul 1975 21 25.30 3.92 29 30.80 4.35 Male 35 - X 30 25 X X II w> Oregon SE Alaska Gulf of Alaska Aleutians . — - W5 35 Female 30 X 25 .-*- X J_ T Oregon SE Alaska Gulf of Alaska Aleutians Location Figure 2 Steller sea lion, Eumetopias jubatus, mean pup masses (kg) by sex and area during 1987-94. Error bars represent 95% confidence intervals around the mean. NOTE Merrick et al.: Eumetopias jubatus pup masses 757 and that this factor could be expressed in the condi- tion of the pups. We were surprised to find that pups were heavier at rookeries with decreasing populations (i.e. in the Gulf of Alaska and Aleutian Islands) than at rooker- ies with increasing populations (i.e. in Southeast Alaska and Oregon). We were also surprised to find that mean pup mass at Marmot and Sugarloaf Is- land in 1992-93 was equal to or greater than that of pups weighed at the sites in 1965 and 1975 (prior to the onset of the decline). The implications of these findings to the search for the ultimate cause of the Alaskan Steller sea lion population decline are twofold. First, the large size of pups in the areas of declining population suggests that pup condition is not compromised in the first month postpartum and that the factor reducing ju- venile survival acts after the neonatal period. Second, the larger pup size in declining populations implies that pregnant and early postpartum females in those popu- lations are not having difficulty finding prey. We have considered possible biases that could have influenced these results (Trites, 1991). Some bias may be associated with the unknown birth date of the pups weighed. To obtain masses of known-age ani- mals, it is necessary to capture pups soon after birth. The cost of obtaining a large, geographically repre- sentative sample by such an approach is prohibitive. Such an approach would increase the mortalities of weighed pups (due to abandonment), would greatly disrupt the rookeries (days of repeated captures would be necessary), and would be very expensive. Because pupping is synchronized throughout the range, a random selection of pups from each site during the same time period should provide samples that are representative of the same age structure. A biased sample could also result if pups were not selected at random. Lighter pups have been selected from pup pods by handlers in some studies of north- ern fur seal pups (Roppel et al.6). However, all pups from a pod were weighed in our study. A bias could still remain if pup mass varied systematically through the rookery (e.g. smaller pups aggregated at the periphery, larger pups in the center), or if pups aggregated by size within the rookery. We selected pups from pods at both the periphery and the center of rookeries. In addition, pups at the time of the weighings had not yet begun to group together. The lack of significant interannual variation during this study indicates that the bias was (if present) consis- 6 Roppel, A. Y, P. Kozloff, and A. E. York. 1981. Population assessment, Pribilof Islands: pup weighing. In P. Kozloff* ed. ), Fur seal investigations, p. 16-21 U.S. Dep. Commer., NOAA, Nat. Mar. Fish. Serv., Northwest Alaska Fish. Sci. Cent. Pro- cessed Rep. 81-2. tent over time. The variation in mean pup mass at rookeries and between the 1970's and the present appears to be real and could be explained in several ways. First, the increase of two years in the average age of Gulf of Alaska adult females since 1976-78 (York, 1994) has probably increased the average size of reproduc- ing female sea lions (Calkins and Pitcher2). North- ern fur seal data suggest that larger females pro- duce larger pups (NMFS4). If Steller sea lions are similarly affected, then the increase in mean size of pups in the Gulf of Alaska since 1976-78 would be partly due to the increased average size of reproduc- ing females. There are no data on female age or size from Southeast Alaska or Oregon with which to evaluate the contribution of this factor to differences between geographic areas. In addition, the larger size of pups in the Gulf of Alaska to Aleutian Island area could be a phenotypic expression of the genetic dif- ferences found between this area and the Southeast Alaska to Oregon area (Bickham et al., in press). Finally, the greater mass of pups at rookeries with reduced populations could be a density-dependent response to reduced competition among adult females for food. Studies of the foraging effort of postpartum females currently being conducted in Southeast Alaska and the Gulf of Alaska will be useful in test- ing this hypothesis. Acknowledgments We would like to thank the many biologists from the Alaska Department of Fish and Game, Oregon De- partment of Fish and Wildlife, National Marine Fish- eries Service, U.S. Fish and Wildlife Service (Oregon Coastal Refuge Office), and the University of Alaska, as well as others who helped weigh pups. In particu- lar, we thank R. Ream (NMFS), L. Rea (University of Alaska), and D. McAllister (ADF&G). We would also like to thank personnel from the All-Union Sci- entific Research Institute of Sea Fisheries and Ocean- ography ( VNIRO) — V. Shevlyagin, and V. Vladimirov. This work was authorized under Marine Mammal Protection Act permits 584, 809, and 854. Lastly, we thank J. Baker, L. Fritz, H. Huber, R. Small, M. Schwartz, A. Trites, A. York, and two anonymous re- viewers for their review of this manuscript. Literature cited Baker, J. D., and C. W. Fowler. 1992. Pup weight and survival of northern fur seals Callorhinus ursinus. J. Zool. (Lond.) 227:231-238. 758 Fishery Bulletin 93(4), 1995 Bigg, M. A. 1985. Status of the Steller sea lion (Eumetopias jubatus) and California sea lion (Zalophus californianus) in British Columbia. Can. Spec. Publ. Fish. Aquat. Sci. 77, 20 p. Bickham, J. W., J. C. Patton, and T. R. Loughlin. In press. High variability for control-region sequences in a marine mammal: implications for conservation and ma- ternal phylogeny of Steller sea lions {Eumetopias jubatus). J. Mammal. Cochran, W. G. 1977. Sampling techniques. J. Wiley and Sons, New York, NY, 428 p. Coulson, J. C, and G. Hickling. 1964. The breeding biology of the grey seal, Halichoerus grypus (Fab 2.), on the Fame Islands, Northumberland. J. Anim. Ecol. 33:485-512. Loughlin, T. R., A. L. Perlov, and V. A. Vladimirov. 1992. Range-wide survey and estimation of total abundance of Steller sea lions in 1989. Mar. Mamm. Sci. 8:220-229. Merrick, R. L. 1987. Behavioral and demographic characteristics of north- ern sea lion rookeries. M.S. thesis, Oregon State Univ., Corvallis, OR, 124 p. Merrick, R. L., T. R. Loughlin, and D. G. Calkins. 1987. Decline in abundance of the northern sea lion, Eumetopias jubatus, in Alaska, 1956-86. Fish. Bull. 85:351-365. Merrick, R., P. Gearin, S. Osmek, and D. Withrow. 1988. Field studies of northern sea lions at Ugamak Island, Alaska during the 1985 and 1986 breeding seasons. U.S. Dep. Commer., NOAATech. Memo. NMFS F/NWC-43, 60 p. Murie, J. < >., and D. A. Boag. 1984. The relationship of body weight to overwinter survival in Columbian ground squirrels. J. Mamm. 65:688-690. Sease, J. L., J. P. Lewis, D. C. McAllister, R. L. Merrick, and S. M. Mello. 1993. Aerial and ship-based surveys of Steller sea lions (Eumetopias jubatus) in Southeast Alaska, the Gulf of Alaska, and Aleutian Islands during June and July 1992. U.S. Dep. Commer., NOAA Tech. Memo. NMFS AFSC-17, 57 p. Terrenato, L., M. F. Gravina, and L. Ulizzi. 1981. Natural selection associated with birth weights. 1: Selection intensity and selective deaths from birth to one month of life. Ann. Hum. Genet. 45:55-63. Trites, A. 1991. Biased estimates of fur seal pup mass: origins and implications. Can. J. Fish. Aquat. Sci. 48:2436-2442. Van Ballenberghe, V., and L. D. Mech. 1975. Weights, growth, and survival of timber wolf pups in Minnesota. J. Mamm. 56:44-63. York, A. 1994. Population dynamics of northern sea lions, 1976- 85. Mar. Mamm. Sci. 10:38-51. Fertilization of the second clutch of eggs of snow crab, Chionoecetes opilio, from females mated once or twice after their molt to maturity Bernard Sainte-Marie Direction des Sciences des Peches, Institut Maurice-Lamontagne Mmistere des Peches et des Oceans, 850 Route de la Men C.P. 1 000 Mont-Joli. Quebec, Canada G5H 3Z4 Chantal Carriere Departement d'Oceanographie. Universite du Quebec a Rimouski, Rimouski, Quebec, CANADA G5L 3A1 Females of the commercially impor- tant genus Chionoecetes (Brachyura: Majidae) copulate and extrude eggs for the first time soon after a ter- minal molt to maturity (Watson, 1972; Adams, 1982). Females pre- paring for the molt to maturity are termed "pubescent," those bearing a first clutch are "primiparous," and those bearing a second or subse- quent clutch are "multiparous." Spermathecae allow females to store sperm that is not expended at spawning (Watson, 1970; Adams and Paul, 1983; Beninger et al., 1988). The importance of sperm stored from the first mating to reproduc- tive output is partially documented for the Tanner crab, Chionoecetes bairdi (Adams and Paul, 1983; Paul and Paul, 1992), but remains largely unknown for the snow crab, Chionoecetes opilio (Elner and Beninger, 1992). Watson (1970) ob- served that some female C. opilio hatched a clutch and then extruded a new clutch of fertilized eggs with- out remating. Assuming that copu- lation occurs only at the molt to maturity, he concluded that female C. opilio can produce more than one batch of fertile eggs from a single mating (also see Watson, 1972). Subsequently, field and laboratory studies have shown that multipa- rous females of C. opilio and of C. bairdi can, and often do, mate be- fore extruding a new clutch (Adams, 1982; Paul, 1984; Taylor et al., 1985; Conan and Comeau, 1986; Hooper, 1986; Claxton et al., 1994; Moriyasu and Conan1). Be- cause the female C. opilio that Wat- son observed spawning were of un- known reproductive history (i.e. number of matings and clutches), the conclusion that one mating is sufficient to produce more than one viable clutch is suspect and war- rants further investigation. In C. bairdi, the viability of stored sperm apparently decreases over time, and some multiparous females may fail to spawn or may extrude unfertilized eggs when iso- lated from males for more than one breeding season (Paul, 1984). Fur- thermore, in laboratory experi- ments with C. bairdi, Paul and Paul ( 1992) found that 10 out of 11 females did not receive enough sperm at the first mating to fertil- ize more than one clutch. These in- vestigators suggested that this may also be the case for C. opilio. How- ever, Sainte-Marie and Lovrich ( 1994) estimated that primiparous C. opilio usually have enough stored sperm to fertilize at least one additional clutch. Therefore, we compared the size of the second clutch and the proportion of divided (i.e. fertilized) eggs for female C. opilio mated only at the molt to maturity with those values ob- tained for females with access to males at a second spawning. Materials and methods Males and pubescent females were collected in Baie Sainte-Marguer- ite (ca. 50°06'N, 66°35'W), north- west Gulf of Saint Lawrence, from September through October 1991, and in March 1992. Carapace width (CW) of females and males, and right chela height (CH) of males, were measured to the nearest 0.1 mm as described in Sainte-Marie and Hazel (1992). Males >40 mm CW were classified on the basis of chela allometry into either of two sperm-producing forms (Comeau and Conan, 1992), designated ado- lescent or adult following terminol- ogy in Sainte-Marie et al. (in press). (Other investigators have used the terms "small-clawed," "morpho- metrically immature," or "juvenile" to designate adolescent males, and "large-clawed" or "morphometri- cally mature" to designate adult males.) Classification was initially done by visual comparison of indi- vidual male measurements with scatterplots of CH on CW for a large sample of males from the source site, and verified a posteriori by using a site-appropriate discrimi- nant function from Sainte-Marie and Hazel (1992). Crabs were segregated by sex in tanks of either 1,400 or 2,000 L with flowing seawater. The mean temperature of seawater over the year following the first mating of females was 1.5°C, and monthly 1 Moriyasu, M., and G. Y. Conan. 1988. Aquarium observation on mating behav- ior of snow crab, Chionoecetes opilio. Int. Counc. Explor. Sea CM. (Council meet- ing) 1988/k:9, 14 p. Manuscript accepted 27 March 1995. Fishery Bulletin 93:759-764 (1995). 759 760 Fishery Bulletin 93(4). 1995 means ranged from a low of 0.1°C in March 1992 to a high of 3.0°C in August 1992 (daily records: low of- 0.3°C and high of 6.5°C). Photoperiod was controlled to correspond to natural light rhythms. Individual crabs were identified by a plastic tag tied around the basipodite of one of the fourth or fifth pereiopods. Crabs were fed frozen shrimp (Pandalus borealis) semi weekly. Beginning in January 1992, tanks were checked twice daily for molting individuals. Less than 12 hours after molting to maturity, each female was placed in a 120-L tank that was either empty or contained one male. Male mates were hard- shelled adult crabs in either of three size categories, 40-60, 80-100, and 120-140 mm CW, or hard-shelled adolescent crabs of 80-100 mm CW. Actual size ranges were 48.6-59.8, 82-99.4, and 120.3-138.3 mm CW for adult males, and 80.1-99.8 mm CW for ado- lescent males. The female was left in the tank until either eggs were extruded or 24 hours had elapsed. The female was then allowed to harden her shell for 5-6 days in isolation and was monitored daily to de- tect delayed egg extrusion. Finally, the female was retagged and transferred to a communal holding tank for females. Males were used once only and then held in communal tanks for up to 14 months after mat- ing, to determine whether they would moult. Egg color of each primiparous female was moni- tored at least every 2-3 months in order to evaluate development of the clutch. About one month before the anticipated period of hatching, i.e. May to June 1993, females bearing ripe eggs were isolated in ei- ther 90- or 120-L tanks with flowing seawater. One hard-shelled adult male of 78.8-119.5 mm CW was introduced into the tanks of randomly selected fe- males in each of two groups, representing those fe- males that had initially mated either with adoles- cent (3 females remated) or with adult (17 females remated) males. The tanks were monitored once a day to detect the onset of hatching and, where ap- propriate, mating behavior. Ten to 12 weeks after the second clutch was ex- truded, a sample of at least 25 eggs was taken at the base of each of the eight pleopods of 58 females. Pleo- pods on the right-hand side were assigned numbers 1 to 4, and those on the left-hand side were assigned numbers 5 to 8, from front to rear. During sampling, females did not shed or lose more than =50 eggs in excess of those removed by the observer. Samples of eggs from each pleopod were fixed and stained to reveal nuclear DNA by means of a technique adapted from Dube et al. (1985) and Dufresne et al. (1988). Eggs were fixed for one hour in a solution of 97% glucamine-acetate (GA) buffer, 2% formaldehyde, and 1% Triton, and then rinsed in GA buffer. The GA buffer was composed of 250 mM N-methyl glucamine, 250 mM potassium gluconate, 50 mM Hepes, and 10 mM EGTA, adjusted to pH 7.4 with glacial acetic acid. Eggs were then stained for one hour in a solution of 0.5 ug Hoescht dye per mL of GA buffer and were then rinsed twice and preserved in GA buffer at 4°C. The numbers of divided and undivided eggs in each pleopod sample were determined by epifluorescent microscopy. Females were examined to evaluate clutch size one week after eggs were sampled from second clutches. Female abdomens were indexed for repleteness with eggs on a scale of 0 (empty) to 4 (very full). The index of clutch size is similar to the more refined percent clutch statistic, where actual clutch size is rated as a percentage of the largest clutch a female decapod of a given size can hold (Blau, 1986). The egg replete- ness index and the percent clutch statistic both cor- relate significantly with the actual number of eggs held by a female decapod (Shields et al., 1990; Sainte- Marie, unpubl. data). Results and discussion Females molted to maturity from 8 January to 12 April 1992 and ranged in size from 49.7 to 74.4 mm postmolt CW. Only females that survived until Au- gust 1993 were analyzed in this study. Overall mor- tality of females from time of maturity molt until August 1993 was 50.3% (of 155) but was unrelated to mating status (mated or unmated) or to the mate's identity (maturity, CW). Of the 11 adolescent males that were mated, eight molted 3-57 days ( x =30 d) after mating, one molted 384 days after mating, and two died within 14 months of mating. No adult male molted over the 14-month period, consistent with the hypothesis that adult males are in anecdysis (O'Halloran, 1985; Conan and Comeau, 1986). Of the nine females that were initially unmated, only four extruded a first clutch (Table 1 ) four or more days after their molt to maturity. All of the 68 fe- males that initially mated extruded a first clutch: 56 did so while in the presence of their mate and 12 extruded later, i.e. 1-5 days after separation from their mate. First clutches did not develop and hatch on the four females that were unmated and on the 12 females that were mated but slow to spawn. Sainte-Marie and Lovrich (1994) reported that de- layed spawning occurred in C. opilio when few or no sperm were delivered to females at mating. These authors hypothesized that females can gauge the contents of their spermathecae and, when insuffi- ciently inseminated, postpone extrusion in expecta- tion of a more fecund mate. By comparison, only two females that extruded eggs while in the presence of their mate failed to hatch their first clutch. Clutches NOTE Sainte-Marie and Carriere: Fertilization of Chionoecetes opilio 76! Table 1 Mating and spawning history of female snow crab, Chionoecetes opilio, that were not paired with a male after their molt to maturity or that were paired with a male but lost their first clutch. Male mates were adolescent or adult. Median and range (in parentheses) for clutch size and percentage of divided eggs are given for the second clutch. Clutch size is based on a 0 (empty) to 4 (very full) scale for abdomen repleteness with eggs. Calculation of median clutch size includes females with no eggs (scored as 0). The percentage of divided eggs is followed by the number of clutches examined, in superscript. Second clutch Male after molt Total number of females Females with first clutch Male at second spawning Females with second clutch Size % Divided eggs No Adolescent Adult 9 3 11 4 3 11 No No Adult No 0.0 (0-3) 2.5(1-4) 2.0 1.0(0-4) 0.0"=1 97.5"=1 4.2 (0-56.7)"'4 carried by the 18 unsuccessful primiparous females started to show signs of degradation about 2-A months after spawning as many or all eggs changed from bright to pale orange and eventually became almost white, and clutches were sloughed or lost within 8-10 months of spawning. The relatively high, 20.6%, incidence of first clutch loss recorded for mated females may be a laboratory artifact resulting from the 24-hour time limit for mating and noncompetitive mating context. We examined 516-1,769 eggs from each second clutch of six females that lost their first clutch and of 52 females that hatched their first clutch, for a combined total of 54,808 eggs. Divided eggs were at the 128- or 256-cell stage. In 24 out of 55 females that carried at least some divided eggs, the ratio of divided eggs to total number of eggs in the pleopod sample was not independent of pleopod position (x test, P<0.05). One female had 89.5-100% divided eggs on pleopods 1-7, but no egg was divided on pleopod 8. Eggs from this female were sampled a second time to confirm the observation. The heterogeneous dis- tribution of divided eggs in some clutches was not expected and to our knowledge has not yet been docu- mented. Most previous studies contain little or no information on methods for sampling and determin- ing viability of eggs. The reason for the contagious distribution of divided eggs is unknown. Perhaps attachment of eggs to individual pleopods is orderly and follows an extrusion hierarchy, and sperm in the fertilization chamber is temporarily or permanently depleted during extrusion. Nevertheless, our find- ing underscores the importance of sampling eggs from throughout the clutch when assessing fertili- zation success. We estimated the overall proportion of divided eggs in a clutch as the mean of propor- tions of divided eggs on each of the eight pleopods. Among females that lost their first clutch, 38.9% did not spawn a second time (Table 1), and the re- mainder extruded second clutches from February to March 1993. In the latter group, second clutches con- tained 0-56.7% divided eggs when females had no access to males or 97.5% divided eggs in the case of one female that was paired with a male at the sec- ond spawning (Table 1). Most females that were initially mated with adult males and then hatched a first clutch of eggs pro- duced a large second clutch with a high percentage of divided eggs without remating (Fig. 1; Table 2). Of the 34 successful primiparous females that mated only at the molt to maturity, only two (5.9%) did not spawn a second time, whereas two others produced second clutches with <60% divided eggs (Fig. 1). There was no significant difference in the size of the second clutch (Kruskal-Wallis test, H=4.60, P=0.10) or in the percentage of divided eggs in the second clutch (#=2.50, P=0.29) among groups of females mated only at the molt to maturity by adult males with CW's of 40-60 mm (median clutch size: 3.0, median percentage divided eggs: 88.9%, rc=13), 80- 100 mm (4.0, 96.0%, n=8), or 120-140 mm (3.0, 94.6%, n=8). These data are consistent with the number of sperm cells stored by female Chionoecetes after the first spawning being unrelated to male CW (Adams and Paul, 1983; Sainte-Marie and Lovrich, 1994). Similarly, our data, although limited, indicate that stored sperm from adolescent males also resulted in the production of a large second clutch containing a high proportion of divided eggs, and was as effective as stored sperm from adult males (Fig. 1; Table 2). Although virgin females mated with adolescent males store as many sperm as those mated with adult males, Sainte-Marie and Lovrich (1994) speculated that the longevity of adolescent sperm might be less than that of adult sperm because of a higher sperm- cell to seminal-plasma ratio in ejaculate. However, this was not apparent after one year of storage. 762 Fishery Bulletin 93(4). 1995 5% o 4 - A 3 2 1 0 et □ m w a HA M A 1 11 A 10% A |k 20% 40% 100% 10 100 Log (percent undivided eggs + 1) Figure 1 Scattergram of clutch size and percentage undivided eggs for second clutches of female snow crab, Chionoecetes opilio, that hatched their first clutch. Females were mated either with adolescent (squares) or adult (triangles) males after their molt to maturity and were subse- quently prevented (open symbols) or allowed (solid symbols) to mate with an adult male at second spawning. The open triangle in the lower right corner of the scattergram represents two females with no clutch. Among successful primiparous females, there was no significant difference in the size of the second clutch ( Kruskal-Wallis test, #=2.45, P=0. 12 ) or in the percentage of divided eggs (H=0A4, P=0.51) between those with (median clutch size: 3.0, median percent- age divided eggs: 96.9%, n=20) and those without (3.0, 96.3%, n=34) access to males at second spawning (also see Table 2). It is likely that remating occurred in a majority of females with access to males at second spawning because we ob- served precopulatory embraces in 18 of 20 pairs and copulation in five pairs. Al- though the proportion of divided eggs in second clutches was high for females iso- lated from males, one might have expected an even higher proportion in females paired with males owing to the potential for acquiring additional, fresh sperm. However, it was hypothesized for C. opilio that stored sperm can be evacuated from the spermathecae by the second mate us- ing his gonopods (Beninger et al., 1991; Elner and Beninger, 1992). If this or any other mechanism to prevent a rival's sperm from fertilizing eggs (see for ex- ample Diesel, 1990) exists in C. opilio, then successive matings would not contribute additively to the pool of sperm available to fertilize a new clutch. Nevertheless, our results indicate that the viability and num- ber of sperm remaining in spermathecae after one year of storage were not limiting for the fertilization of a second clutch in fe- males mated only at the molt to maturity. The success of female C. opilio in fertil- izing a second clutch of eggs with stored sperm and the contrasting failure of female C. bairdi (Paul and Paul, 1992) can probably be explained by the = 10-fold greater number of sperm cells stored after the first spawning by C. opilio (Sainte-Marie and Lovrich, 1994). Moreover, mean size and fecun- dity of females are less in C. opilio than in C. bairdi (Haynes et al., 1976); therefore, fewer sperm cells are mobilized to fertilize a clutch in the former species. Table 2 Median and range (in parentheses) of clutch size and percentage of divided eggs for second clutches of female snow crab, Chionoecetes opilio, that were paired with a male after their molt to maturity and that hatched their first clutch. First male mates were adolescent or adult; all second male mates were adult. Clutch size is based on a 0 (empty) to 4 (very full) scale for abdomen repleteness with eggs. Calculation of median clutch size includes females with no eggs (scored as 0). The Kruskal-Wallis test was used to compare clutch size and percentage of divided eggs for females in different experimental treatments: //-statistic and probability level (P) are shown. Adult male Second clutch Male after molt at second spawning n Size % Divided eggs Adolescent No 5 3.0(2-4) 98.3(93.6-99.7) Yes 3 3.0(1-4) 91.8(11.2-99.3) Adult No 29 3.0(0-4) 95.5(0.0-100.0) Yes 17 3.0(1-4) 97.0(72.1-99.7) H = 2.50 // = 5.15 P = 0.48 P = 0.16 NOTE Sainte-Mane and Carnere: Fertilization of Chionoecetes opilio 763 Although our laboratory findings suggest that sperm stored at the first mating is effective for fer- tilizing the second clutch in C. opilio, these findings cannot be indiscriminately extrapolated to the field, for at least two reasons. First, the importance of sperm stores in wild Chionoecetes females might fluc- tuate interannually (Beninger et al., 1988; Paul and Paul, 1992). In the northwest Gulf of Saint Lawrence, the intensity of recruitment to the first benthic in- star of C. opilio varies among years in an apparently recurrent pattern: five consecutive, moderate-to- strong year classes alternate with three consecutive, weak year classes (Sainte-Marie et al., in press, and unpubl. data). Given that adult snow crab are anecdysic and that there exist marked differences between the sexes in size and age at adulthood, re- cruitment pulses cause adult sex ratios and charac- teristics of breeding males to change considerably over time (Ennis et al., 1990; Comeau et al., 1991; Sainte-Marie et al., in press). Thus, in some years, the number or quality, or both, of males available for mating with pubescent females might be limiting and this could conceivably result in a decrease in the pro- portion of primiparous females having received enough sperm to fertilize a second clutch. Second, our laboratory experiments pertain only to a one-year reproductive cycle. However, under some natural conditions female C. opilio incubate their eggs for 24-27 months (Kanno, 1987; Mallet et al.2, 1993; Sainte-Marie, 1993), instead of the =12-month dura- tion observed in our laboratory and inferred for many wild populations (e.g. Ito, 1967; Watson, 1969; Kon, 1980). Mallet et al.2 suggested that this difference is due to temperature: in the Gulf of Saint Lawrence, egg development would take two years for females in their usual deep-water habitat (-1° to 1°C year- round), but only one year for females that stayed for some time in warmer shallow waters. In the former case, effective fertilization of the second clutch in which stored sperm was used would thus depend on sperm surviving in sufficiently high numbers over a 2-year period. Clearly, a better understanding of the interrelations between population and reproductive dynamics, sperm delivery, sperm longevity (viabil- ity), and the duration of sperm storage is necessary before any general statement can be made about the importance of stored sperm to reproductive output in C. opilio. 2 Mallet, P., G. Y. Conan, and M. Moriyasu. 1993. Periodicity of spawning and duration of incubation time for Chionoecetes opilio in the Gulf of St. Lawrence. Int. Counc. Sea CM. [coun- cil meeting] 1993/K:26, 19. Acknowledgments We thank Y. Gauthier and M. Belanger for help in the laboratory, and G. A. Lovrich, J.-M. Sevigny, B. D. Smith, and anonymous reviewers for comments on the manuscript. This work was funded by the Quebec Federal Fisheries Development Program. Literature cited Adams, A. E. 1982. The mating behavior of Chionoecetes bairdi. In B. Melteff (ed.), Internation symposium on the genus Chionoecetes, p. 233-272. Lowell Wakefield Fish. Symp. Ser., Univ. Alaska, Fairbanks, Sea Grant Rep. 82-10. Adams, A. E., and A. J. Paul. 1983. Male parent size, sperm storage and egg production in the crab Chionoecetes bairdi (Decapoda, Majidae). Int. J. Invertebr. Reprod. 6:181-187. Beninger, P. G., R. W. Elner, T. P. Foyle, and P. H. Odense. 1988. Functional anatomy of the male reproductive system and the female spermatheca in the snow crab Chionoecetes opilio (O. Fabricius) (Decapoda: Majidae) and a hypoth- esis for fertilisation. J. Crustacean Biol. 8:322-332. Beninger, P. G., R. W. Elner, and Y. Poussart. 1991. The gonopods of the majid crab Chionoecetes opilio <0. Fabricius). J. Crustacean Biol. 11:217-228. Blau, S. F. 1986. Recent declines of red king crab (Paralithodes camtschatica) populations and reproductive conditions around the Kodiak Archipelago, Alaska. Can. Spec. Publ. Fish. Aquat. Sci. 92:360-369. Claxton, W. T., C. K. Govind, and R. W. Elner. 1994. Chela function, morphometric maturity, and the mating embrace in male snow crab, Chionoecetes opilio. Can. J. Fish. Aquat. Sci. 51:1110-1118. Comeau, M., and G. Y. Conan. 1992. Morphometry and gonad maturity of male snow crab, Chionoecetes opilio. Can. J. Fish. Aquat. Sci. 49:2460- 2468. Comeau, M., G. Y. Conan, G. Robichaud, and A. Jones. 1991. Life history patterns and population fluctuations of snow crab {Chionoecetes opilio) in the fjord of Bonne Bay on the west coast of Newfoundland, Canada — from 1983 to 1990. Can. Tech. Rep. Fish. Aquat. Sci. 1817, 73 p. Conan, G. Y., and M. Comeau. 1 986. Functional maturity and terminal molt of male snow crab, Chionoecetes opilio. Can. J. Fish. Aquat. Sci. 43:1710-1719. Diesel, R. 1990. Sperm competition and reproductive success in the decapod Inachus phalnagium (Majidae): a male ghost crab that seals off rivals' sperm. J. Zool. (Lond.) 220:213-223. Dube, F., T. Schmidt, C. H. Johnson, and D. Epel. 1985. The hierarchy of requirements for an elevated intra- cellular pH during early development of sea urchin embryos. Cell 40:657-666. Dufresne, L., M. Desroches, C. Bourgault, C. Gicqaud, and F. Dube. 1988. Relationships between intracellular pH, protein syn- thesis, and actin assembly during parthenogenetic activa- tion of sea urchin eggs. Biochem. Cell Biol. 66:780-791. 764 Fishery Bulletin 93(4). 1995 Elner, R. W., and P. G. Beninger. 1992. The reproductive biology of snow crab, Chionoecetes opilio: a synthesis of recent contributions. Am. Zool. 32:524-533. Funis, G. P., R. G. Hooper, and D. M. Taylor. 1990. Changes in the composition of snow crab (Chiono- ecetes opilio) participating in the annual breeding migra- tion in Bonne Bay, Newfoundland. Can. J. Fish. Aquat. Sci. 47:2242-2249. Haynes, E., J. R. Karinen, J. Watson, and D. J. Hopson. 1976. Relation of number of eggs and egg length to cara- pace width in the brachyuran crabs Chionoecetes bairdi and C. opilio from the southeastern Bering Sea and C. opilio from the Gulf of St. Lawrence. J. Fish. Res. Board Can. 33:2592-2595. Hooper, R. G. 1986. A spring breeding migration of the snow crab, Chionoecetes opilio (O. Fabr. ), into shallow water in Newfoundland. Crustaceana (Leiden) 50:257-264. Ito, K. 1967. Ecological studies on the edible crab, Chionoecetes opilio O. Fabricius in the Japan Sea. 1: When do female crabs first spawn and how do they advance into the follow- ing reproductive stage? Bull. Jpn. Sea Reg. Fish. Res. Lab. 17:67-84. (Fish. Res. Board Can. Transl. Ser. No. 1103). Kanno, Y. 1987. Reproductive ecology of Tanner crab in the South Western Okhotsk Sea. Nippon Suisan Gakkashi 53:733- 738. (Can. Transl. Fish. Aquat. Sci. 5628) Kon, T. 1980. Studies on the life history of the Zuwai crab, Chionoecetes opilio (O. Fabricius). Spec. Publ. Sado Mar. Biol. Stn., Niigata Univ., Ser. 2, 64 p. (Can. Transl. Fish. Aquat. Sci. 5634) O'Halloran, M. J. 1985. Moult cycle changes and the control of moult in the male snow crab, Chionoecetes opilio. M.S. thesis, Dal- housie Univ., Halifax, Nova Scotia, 183 p. Paul, A. J. 1984. Mating frequency and viability of stored sperm in the Tanner crab Chionoecetes bairdi (Decapoda, Majidae). J. Crustacean Biol. 4:375-381. Paul, A. J., and J. M. Paul. 1992. Second clutch viability of Chionoecetes bairdi Rath- bun (Decapoda: Majidae) inseminated only at the matu- rity molt. J. Crustacean Biol. 12:438-441. Sainte-Marie, B. 1993. Reproductive cycle and fecundity of primiparous and multiparous female snow crab, Chionoecetes opilio, in the northwest Gulf of Saint Lawrence. Can. J. Fish. Aquat. Sci. 50:2147-2156. Sainte-Marie, B., and F. Hazel. 1992. Moulting and mating of snow crabs, Chionoecetes opilio (O. Fabricius), in shallow waters of the northwest- ern Gulf of Saint Lawrence. Can. J. Fish. Aquat. Sci. 49:1282-1293. Sainte-Marie, B., and G. A. Lovrich. 1994. Delivery and storage of sperm at first mating of fe- male Chionoecetes opilio (Brachyura, Majidae) in relation to size and morphometric maturity of male parent. J. Crustacean Biol. 14:508-521. Sainte-Marie, B., S. Raymond, and J.-C. Brethes. In press. Growth and maturation of the benthic stages of male snow crab, Chionoecetes opilio (Brachyura, Majidae). Can. J. Fish. Aquat. Sci. Shields, J. D., D. E. Wickham, S. F. Blau, and A. Kuris. 1990. Some implications of egg mortality caused by symbi- otic nemerteans for data acquisition and management strategies of red king crabs, Paralithodes camtschatica. In Proceedings of the international symposium on king and Tanner crabs, p. 383-395. Univ. Alaska, Alaska Sea Grant Rep. 90-04. Taylor, D. M., R. G. Hooper, and G. P. Ennis. 1985. Biological aspects of the spring breeding migration of snow crabs, Chionoecetes opilio, in Bonne Bay, Newfound- land (Canada). Fish. Bull. 83:707-711. Watson, J. 1969. Biological investigations on the spider crab, Chionoe- cetes opilio. Can. Fish. Rep. 13:24-47. 1970. Maturity, mating, and egg-laying in the spider crab, Chionoecetes opilio. J. Fish. Res. Board Can. 27:1607- 1616. 1972. Mating behavior in the spider crab, Chionoecetes opilio. J. Fish. Res. Board Can. 29:447-449. Publication Awards, 1 994 National Marine Fisheries Service, NOAA The Publications Advisory Committee of the National Marine Fisheries Service is pleased to announce the awards for best publications authored by NMFS scientists and published in the Fishery Bulletin for Volume 92 and in the Marine Fisheries Review for Volume 55. Eligible papers are nominated by the Fisheries Science Centers and Regional Offices and are judged by the NMFS Editorial Board. Only articles that significantly contribute to the understanding and knowledge of NMFS-related studies are eligible. We offer congratulations to the following authors for their outstanding efforts. Fishery Bulletin, Volume 92 Marine Fisheries Review, Volume 55 Outstanding Publication Outstanding Publication Prager, Michael H. Nitta, Eugene T., and John R. Henderson. A suite of extensions to a nonequilibrium surplus-production A review of interactions between Hawaii's fisheries and model. Fish. Bull. 92:374-389. protected species. Mar. Fish. Rev. 55(2):83-92. Outstanding Publication Honorable Mention Jacobson, Larry D., Nancy C. H. Lo, Pooley, Samuel G. and J. Thomas Barnes. A biomass-based assessment model for northern anchovy, Hawaii's marine fisheries: some history, long-term trends, Engraulis mordax. Fish. Bull. 92:711-724. and recent developments. Mar. Fish. Rev. 55(2)7-19. 765 Fishery Bulletin Index Volume 93 (1-4), 1995 List of Titles 93(1) 1 The abundance of cetaceans in California waters. Part I: Ship surveys in summer and fall of 1991, by Jay Barlow 15 The abundance of cetaceans in California waters. Part II: Aerial surveys in winter and spring of 1991 and 1992, by Karin A. Forney, Jay Barlow, and James V. Carretta 27 Larval development of King George whiting, Sillaginodes punctata, school whiting, Sillago bassensis, and yellow fin whiting, Sillago schomburgkii (Percoidei: Sillaginidae), from South Australian waters, by Barry D. Bruce 44 Responses of Tanner crabs, Chionoecetes bairdi, exposed to cold air, by Mark G. Carls and Charles E. O'Clair 57 Demographic analysis of the Atlantic sharpnose shark, Rhizoprionodon terraenovae, in the Gulf of Mexico, by Enric Cortes 67 Evaluation of a video camera technique for indexing abundances of juvenile pink snapper, Pristipomoides filamentosus, and other Hawaiian insular shelf fishes, by Denise M. Ellis and Edward E. DeMartini 78 Evolution of cytochrome b in the Scombroidei (Teleostei): molecular insights into billfish (Istiophoridae and Xiphiidae) relationships, by John R. Finnerty and Barbara A. Block 97 Assignment of Homarus capensis (Herbst, 1792), the Cape lobster of South Africa, to the new genus Homarinus (Decapoda: Nephropidae), by Irv Kornfield, Austin B. Williams, and Robert S. Steneck 103 Ageing of three species of tropical snapper (Lutjanidae) from the Gulf of Carpentaria, Australia, using radiometry and otolith ring counts, by David A. Milton, Stephen A. Short, Michael F. O'Neill, and Stephen J. M. Blaber 116 Age and growth estimates of the dusky shark, Carcharhinus obscurus, in the western North Atlantic Ocean, by Lisa J. Natanson, John G. Casey, and Nancy E. Kohler 127 Maturity, spawning, and seasonal movement of arrow- tooth flounder, Atheresthes stomias, off Washington, by Martha H. Rickey 139 Marine turtle populations on the east-central coast of Florida: results of tagging studies at Cape Canaveral, Florida, 1986-1991, by Jeffrey R. Schmid 152 Growth rates of captive dolphin, Coryphaena hippurus, in Hawaii, by Daniel D. Benetti, Edwin S. Iversen, and Anthony C. Ostrowski 158 Modification and comparison of two fluorometric techniques for determining nucleic acid contents of fish larvae, by Michael F. Canino and Elaine M. Caldarone 166 The potential use of otolith characters in identifying larval rockfish (Sebastes spp.), by Thomas E. Laidig and Stephen Ralston 172 Changes in spatial patchiness of Pacific mackerel, Scomber japonicus, larvae with increasing age and size, by Yasunobu Matsuura and Roger Hewitt 179 Growth and morphology of larval and juvenile captive bred yellowtail snapper, Ocyurus chrysurus, by Cecilia M. Riley, G. Joan Holt, and Connie R. Arnold 186 Validation of otolith-based ageing and a comparison of otolith and scale-based ageing in mark-recaptured Chesapeake Bay striped bass, Morone saxatilis, by David H. Secor, T. Mark Trice, and Harry T. Hornick 191 An evaluation of six marking methods for age-0 red drum, Sciaenops ocellatus, by Stephen T. Szedlmayer and Jeffrey C. Howe 196 Stranding and mortality of humpback whales, Megaptera novaeangliae, in the mid- Atlantic and southeast United States, 1985-1992, by David N. Wiley, Regina A. Asmutis, Thomas D. Pitchford, and Damon P. Gannon 93(2) 209 217 Confidence of otolith ageing through the juvenile stage for Atlantic menhaden, Brevoortia tyrannus, by Dean W. Ahrenholz, Gary R. Fitzhugh, James A. Rice, Stephen W. Nixon, and Wilson C. Pritchard Description of the starving condition in summer flounder, Paralichthys dentatus, early life history stages, by Gustavo A. Bisbal and David A. Bengtson 231 Neustonic ichthyoplankton in the western Gulf of Alaska during spring, by Miriam J. Doyle, William C. Rugen, and Richard D. Brodeur 254 Aerial surveys for sea turtles in North Carolina inshore waters, by Sheryan P. Epperly, Joanne Braun, and Alexander J. Chester 262 Assessing habitat use by nekton on the continental slope using archived videotapes from submersibles, by James D. Felley and Michael Vecchione 274 Distribution, migration, and growth of juvenile chinook salmon, Oncorhynchus tshawytscha, off Oregon and Washington, by Joseph P. Fisher and William G. Pearcy 766 INDEX: TITLES Fishery Bulletin 93( 1-4), 1995 767 290 Providing quantitative management advice from stock abundance indices based on research surveys, by Thomas E. Helser and Daniel B. Hayes 299 Nutritional dynamics of reproduction in viviparous yellowtail rockfish, Sebastes flavidus, by Elizabeth C. Norton and R Bruce MacFarlane 93(3) 429 Early life history of black sea bass, Centropristis striata, in the mid-Atlantic Bight and a New Jersey estuary, by Kenneth W. Able, Michael P. Fahay, and Gary R. Shepherd 308 Approximations for solving the catch equation when it involves a "plus group," by Victor R. Restrepo and Christopher M. Legault 315 The influence of temperature on cohort- specific growth, survival, and recruitment of striped bass, Morone saxatilis, larvae in Chesapeake Bay, by Edward S. Rutherford and Edward D. Houde 333 Condition of larval walleye pollock, Theragra chalcogramma, in the western Gulf of Alaska assessed with histological and shrinkage indices, by Gail H. Theilacker and Steven M. Porter 346 Revised estimates of incidental kill of dolphins (Delphinidae) by the purse-seine tuna fishery in the eastern tropical Pacific, 1959-1972, by Paul R. Wade 355 Killer whale, Orcinus orca, depredation on longline catches of bottomfish in the southeastern Bering Sea and adjacent waters, by Kazunari Yano and Marilyn E. Dahlheim 373 Ascent rates, vertical distribution, and a thermal model of development of orange roughy, Hoplostethus atlanticus, eggs in the water column, by John R. Zeldis, Paul J. Grimes, and Jonathan K. V. Ingerson 386 Consistent yearly appearance of age-0 walleye pollock, Theragra chalcogramma, at a coastal site in southeastern Alaska, 1973-1994, by H. Richard Carlson 391 Radiometric analysis of blue grenadier, Macruronus novaezelandiae, otolith cores, by Gwen E. Fenton and Stephen A. Short 397 Seasonal depth distribution of the crystal shrimp, Penaeus brevirostris (Crustacea: Decapoda, Penaeidae), and its possible relation to temperature and oxygen concentration off southern Sinaloa, Mexico, by Hector Garduno-Argueta and Jose A. Calderon- Perez 403 The diet of the swordfish Xiphias gladius Linnaeus, 1758, in the central east Atlantic, with emphasis on the role of cephalopods, by Vincente Hernandez-Garcfa 412 Length-weight relationships for 13 species of sharks from the western North Atlantic, by Nancy E. Kohler, John G. Casey, and Patricia A. Turner 419 An analysis of the length-weight relationship of larval fish: limitations of the general allometric model, by Pierre Pepin 446 Population estimates of Pacific coast groundfishes from video transects and swept-area trawls, by Peter B. Adams, John L. Butler, Charles H. Baxter, Thomas E. Laidig, Katherine A. Dahlin, and W. Waldo Wakefield 456 Food habits of estuarine staghorn sculpin, Leptocottus armatus, with focus on consumption of juvenile Dungeness crab, Cancer magister, by Janet L. Armstrong, David A. Armstrong, and Stephen B. Mathews 471 Larval distribution and transport of penaeoid shrimps during the presence of the Tortugas Gyre in May-June 1991, by Maria M. Criales and Thomas N. Lee 483 Growth and reproduction of the common dolphin, Delphinus delphis Linnaeus, in the offshore waters of the North Pacific Ocean, by Richard C. Ferrero and William A. Walker 495 The feasibility of direct photographic assessment of giant bluefin tuna, Thunnus thynnus, in New England waters, by Molly Lutcavage and Scott Kraus 504 Egg and larval development of laboratory-reared gulf flounder, Paralichthys albigutta, and southern flounder, P. lethostigma (Pisces, Paralichthyidae), by Allyn B. Powell and Theresa Henley 516 Distribution of pelagic metamorphic-stage sanddabs Citharichthys sordidus, and C. stigmaeus within areas of upwelling off central California, by Keith M. Sakuma and Ralph J. Larson 530 Review of new world hagfishes of the genus Myxine (Agnatha, Myxinidae) with descriptions of nine new species, by Robert L. Wisner and Charmion B. McMillan 551 Covariation between growth and morphology suggests alternative size limits for the blacklip abalone, Haliotis rubra, in New South Wales, Australia, by Duncan G. Worthington, Neil L. Andrew, and Gary Hamer 562 An analysis of weekly fluctuations in catchability coefficients, by Steven M. Atran and Joseph G. Loesch 568 Temperature influence on postovulatory follicle degeneration in Atlantic menhaden, Brevoortia tyrannus, by Gary R. Fitzhugh and William F. Hettler 573 Size structure of mutton snapper, Lutjanus analis, associated with unexploited artificial patch reefs in the central Bahamas, by Karl W. Mueller 768 INDEX: TITLES Fishery Bulletin 93| 1-4), 1995 577 Occurrence and group characteristics of minke whales, Balaenoptera acutorostrata, in Massachusetts Bay and Cape Cod Bay, by Margaret A. Murphy 686 Activities of juvenile green turtles, Chelonia mydas, at a jettied pass in South Texas, by Maurice L. Renaud, James A. Carpenter, Jo A. Williams, and Sharon A. Manzella-Tirpak 594 Determination of age and growth of swordfish, Xiphias gladius L., 1758, in the eastern Mediterranean using anal-fin spines, by George Tserpes and Nikolaos Tsimenides Jonathan M. Shenker, Christopher W. Harnden, and Daniel W. Wagner 675 Distribution and life history of windowpane, Scophthalmus aquosus, off the northeastern United States, by Wallace W. Morse and Kenneth W. Able 694 Trajectory-based approaches to estimating velocity and diffusion from tagging data, by Clay E. Porch 710 On the development of year-class strength and cohort variability in two northern California rockfishes, by Stephen Ralston and Daniel F. Howard 93(4) 603 Summer distribution of early life stages of walleye pollock, Theragra chalcogramma, and associated species in the western Gulf of Alaska, by Richard D. Brodeur, Morgan S. Busby, and Matthew T. Wilson 619 Age and growth of tarpon, Megalops atlanticus, from South Forida waters, by Roy E. Crabtree, Edward C. Cyr, and John M. Dean 629 Population structure of the leopard coralgrouper, Plectropomus leopardus, on fished and unfished reefs off Townsville, Central Great Barrier Reef, Australia, by Beatrice P. Ferreira and Garry R. Russ 643 Age and growth of weakfish, Cynoscion regalis, in the Chesapeake Bay region with a discussion of historical changes in maximum size, by Susan K. Lowerre- Barbieri, Mark E. Chittenden Jr., and Luiz R. Barbieri 657 Estimating the predictability of recruitment, by Gordon Mertz and Ransom A. Myers 666 Recruitment of bonefish, Albula vulpes, around Lee Stocking Island, Bahamas, by Raymond Mojica Jr., 721 Description of larval and pelagic juvenile chilipepper, Sebastes goodei (family Scorpaenidae), with an examination of larval growth, by Keith M. Sakuma and Thomas E. Laidig 732 A review of flow and survival relationships for spring and summer chinook salmon, Oncorhynchus tshawytscha, from the Snake River Basin, by John G. Williams and Gene M. Matthews 741 A decline in the abundance of harbor porpoise, Phocoena phocoena, in nearshore waters off California, 1986-93, by Karin A. Forney 749 Seasonal influences of statolith growth in the tropical nearshore loliginid squid Loligo chinensis (Cephalopoda: Loliginidae) off Townsville, North Queensland, Australia, by George D. Jackson 753 A comparison of Stellar sea lion, Eumetopias jubatus, pup masses between rookeries with increasing and decreasing populations, by Richard L. Merrick, Robin Brown, Donald G. Calkins, and Thomas R. Loughlin 759 Fertilization of the second clutch of eggs of snow crab, Chionoecetes opilio, from females mated once or twice after their molt to maturity, by Bernard Sainte-Marie and Chantal Carriere Fishery Bulletin Index Volume 93 (1-4), 1995 List of Authors Able, Kenneth W. 429,675 Adams, Peter B. 446 Ahrenholz, Dean W. 209 Andrew, Neil L. 551 Armstrong, David A. 456 Armstrong, Janet L. 456 Arnold, Connie R. 179 Asmutis, Regina A. 196 Atran, Steven M. 562 Barbieri, Luiz R. 643 Barlow, Jay 1,15 Baxter, Charles H. 446 Benetti, Daniel D. 152 Bengtson, David A. 217 Bisbal, Gustavo A. 217 Blaber, Stephen J. M. 103 Block, Barbara A. 78 Braun, Joanne254 Brodeur, Richard D. 231,603 Brown, Robin 753 Bruce, Barry D. 27 Busby, Morgan S. 603 Butler, John L. 446 Caldarone, Elaine M. 158 Calderon-Perez, Jose A. 397 Calkins, Donald G. 753 Canino, Michael F. 158 Carls, Mark G. 44 Carlson, H. Richard 386 Carpenter, James A. 586 Carretta, James V. 15 Carriere, Chantal 759 Casey, John G. 116,412 Chester, Alexander J. 254 Chittenden Jr., Mark E. 643 Cortes, Enric 57 Crabtree, Roy E. 619 Criales, Maria M. 471 Cyr, Edward C. 619 Dahlheim, Marilyn E. 355 Dahlin, Katherine A. 446 Dean, John M. 619 DeMartini, Edward E. 67 Doyle, Miriam J. 231 Ellis, Denise M. 67 Epperly, Sheryan P. 254 Fahay, Michael P. 429 Felley, James D. 262 Fenton, Gwen E. 391 Ferreira, Beatrice P. 629 Ferrero, Richard C. 483 Finnerty, John R. 78 Fisher, Joseph P. 274 Fitzhugh, Gary R. 209,568 Forney, Karin A. 15, 741 Gannon, Damon P. 196 Garduno-Argueta, Hector 397 Grimes, Paul J. 373 Hamer, Gary 551 Harnden, Christopher W. 666 Hayes, Daniel B. 290 Helser, Thomas E. 290 Henley, Theresa 504 Hernandez-Garcia, Vincente 403 Hettler, William F. 568 Hewitt, Roger 172 Holt, G.Joan 179 Hornick, Harry T. 186 Houde, Edward D. 315 Howard, Daniel F. 710 Howe, Jeffrey C. 191 Ingerson, Jonathan K.V. 373 Iversen, Edwin S. 152 Jackson, George D. 749 Kohler, Nancy E. 116,412 Kornfield, Irv 97 Kraus, Scott 495 Laidig, Thomas E. 166, 446, 721 Larson, Ralph J. 516 Lee, Thomas N. 471 Legault, Christopher M. 308 Loesch, Joseph G. 562 Loughlin, Thomas R. 753 Lowerre-Barbiere, Susan K. 643 Lutcavage, Molly 495 MacFarlane, R. Bruce 299 Manzella-Tirpak, Sharon A. 586 Mathews, Stephen B. 456 Matsuura, Yasunobu 172 Matthews, Gene M. 732 McMillan, Charmion B. 530 Merrick, Richard L. 753 Mertz, Gordon 657 Milton, David A. 103 Mojica, Raymond, Jr. 666 Morse, Wallace W. 675 Mueller, Karl W. 573 Murphy, Margaret A. 577 Myers, Ransom A. 657 Natanson, Lisa J. 116 Nixon, Stephen W. 209 Norton, Elizabeth C. 299 O'Clair, Charles E. 44 O'Neill, Michael F. 103 Ostrowski, Anthony C. 152 Pearcy, William G. 274 Pepin, Pierre 419 Pitchford, Thomas D. 196 Porch, Clay E. 694 Porter, Steven M. 333 Powell, Allyn B. 504 Pritehard, Wilson C. 209 Ralston, Stephen 166, 710 Renaud, Maurice L. 586 Restrepo, Victor R. 308 Rice, James A. 209 Rickey, Martha H. 127 Riley, Cecilia M. 179 Rugen, William C. 231 Russ, Garry R. 629 Rutherford, Edward S. 315 Sainte-Marie, Bernard 759 Sakuma, Keith M. 516,721 Schmid, Jeffrey R. 139 Secor, David H. 186 Shenker, Jonathan M. 666 Shepherd, Gary R. 429 Short, Stephen A. 103,391 Steneck, Robert S.97 Szedlmayer, Stephen T. 191 Theilacker, Gail H. 333 Trice, T. Markl86 Tserpes, George594 Tsimenides, Nikolaos594 Turner, Patricia A. 412 Vecchione, Michael 262 Wade, Paul R. 345 Wagner, Daniel E. 666 Wakefield, W. Waldo 446 Walker, William A. 483 Wiley, David N 196 Williams, Austin B. 97 Williams, Jo A. 586 Williams, John G. 732 Wilson, Matthew T. 603 Wisner, Robert L. 530 Worthington, Duncan G. 551 Yano, Kazunari 355 Zeldis, John R. 373 769 Fishery Bulletin Index Volume 93 (1-4), 1995 List of Subjects Abalone, blacklip 551 Abundance — see also Population studies cetaceans 1, 15 dolphin common 1, 15 Dall's porpoise 1 northern right whale 1, 15 Pacific white-sided 1,15 Risso's 15 striped 1 flounder, windowpane 675 groundfish 446, 675 ichthyoplankton, Gulf of Alaska 231 indices of 290 larvae flounder, windowpane 675 methods of estimation 290, 495 porpoise, harbor 741 salmon, Pacific 274 snapper, pink 67 trawl vs. video 446 trends in 741 trout, coral — see Coralgrouper, leopard turtle, sea 254 weakfish 643 wolffish, Atlantic 290 whale 1 beaked 15 blue 1 fm 1 humpback 1, 15 minke 15, 577 sperm 1, 15 Aerial survey cetaceans 15, 741 tuna, giant bluefin 495 turtles, sea 254 Age at sexual maturity dolphin, common 483 flounder, arrowtooth 127 shark, dusky 1 16 shark, sharpnose 57 Age determination Atlantic menhaden 209 bass, striped 186 chilipepper 721 coralgrouper 629 eggs, orange roughy 373 flounder, windowpane 675 grenadier, blue 391 otoliths Atlantic menhaden 209 bass, striped 186 coralgrouper 629 grenadier, blue 391 radiometric 103, 391 rockfish 166 snapper 103 tarpon 619 weakfish 643 radiometric 103, 391 rockfish 166 scales 186 shark, dusky 116 snapper 103 statoliths, loliginid squid 749 swordfish, spines 594 tarpon 619 vertebrae 116 weakfish 643 Age validation bass, striped 186 menhaden, Atlantic 209 radiometric 103 snapper 103 tarpon 619 Age structure 629 Alaska gulf of 333,603 ichthyoplankton 231,603 pollock, walleye, larvae 333, 386, 603 sea lion, Steller 753 walleye pollock, juveniles 386 Albula vulpes 666 Allometry 419 Anarhichas lupus 290 Anoplopoma fimbria 355 Approximations, catch equation 308 Aquaculture 152, 179 Ascent rate, eggs 373 Assemblage analysis 603 Atheresthes stomias 127, 355 Atlantic Bight South menhaden, Atlantic 209 mid- bass, black sea 429 flounder, windowpane 675 Atlantic Ocean bass, black sea 429 nekton, demersal 262 flounder gulf 504 summer 217, 504 windowpane 675 hagfish 530 lobster, Cape 97 menhaden, Atlantic 209, 562, 568 shark, dusky 116 sharks, length-weight relationships 412 snapper, yellowtail 179 swordfish 403 tarpon 619 tuna, giant bluefin 495 turtles, sea 254 whale humpback 196 minke 577 wolffish, Atlantic 290 Atresia, ovarian 568 Australia abalone, blacklip 551 coralgrouper, leopard 629 grenadier, blue 391 Sillaginidae 27 snapper 103 squid 749 whiting 27 King George 27 school 27 yellow fin 27 Bahama Islands bonefish 666 snapper, mutton 573 Balaenoptera 1 acutorostrata 15, 577 musculus 1 physalus 1 Bass black sea 429 striped 186, 315 Bathymaster signatus 355 Behavior crab, Tanner 44 minke whale, feeding 577 shrimp, crystal 397 turtle, green 586 walleye pollock, juveniles 386 Bering Sea crab, Tanner 44 whale, killer 355 von Bertalanffy growth shark, dusky 1 16 swordfish 594 tarpon 603 turtle, sea 139 Bias, perception 1 Billfish 78, 403, 594 Biochemical analysis flounder, summer 217 larvae, RNA/DNA ratio 158, 217 Biological indicators 158, 217, 608 Bonefish 666 Brevoortia tyrannus 209, 562, 568 Bycatch 132,345,483,741 California cetaceans 1, 15, 741 Gulf of 397 rockfish 710 sanddab 516 Cancer magister 456 Carcharhinus obscurus 116 Caribbean snapper, mutton 573 Carolina coast nekton, demersal 262 turtles, sea 254 Carretta carretta 139, 254 770 INDEX: SUBJECTS Fishery Bulletin 93(1-4), 1995 771 Catchability coefficient 562 Catch equation 308 Catch-per-unit-of-effort flounder, arrowtooth 127 Catch rates, long line depredation, killer whale 355 Centnopristis striata 429 Cephalopoda — see Squid Cetacean 1, 15, 196, 345, 355, 741; See also Dolphin; Whale Chelonia mydas 139, 254, 586 Chemical marking drum, red 191 menhaden, Atlantic 209 Chesapeake Bay bass, striped 186, 315 weakfish 643 Chilipepper 198,721 Chinook salmon, juvenile 274, 732 Chionoecetes bairdi 44 Chionoecetes opilio 412, 759 Citharichthys sordidus 516 Citharichthys stigmaeus 516 Classification — see Taxonomy Cohort analysis 308 Cohort variability 710 Columbia River chinook salmon, juvenile 732 Compensation 710 Condition 333 sea lion, Steller 753 Consumption, by staghorn sculpin 456 Continental shelf 429, 675 Continental slope 262 Coralgrouper, leopard 629 Coral reef fishes 573, 629 Coryphaena hippurus 152 Coryphaenidae — see Dolphin [fish] Covariation growth-morphology 551 Crab Dungeness 456 snow 412, 759 Tanner 44 Cynoscion regalis — see Weakfish Cytochrome b 78 Dam passage 732 Deep sea 262 Degeneration, postovulatory follicle 568 Delphinidae — see Dolphin Delphinus capensis — see Dolphin, common Delphinus delphis — see Dolphin, common Demography shark, Atlantic sharpnose 57 Depredation rates 355 Depth distribution eggs, orange roughy 373 flounder, arrowtooth 127 ichthyoplankton 231 sanddab 516 shrimp, crystal 397 shrimp, larvae 471 Development flounder, summer and gulf 504 eggs, orange roughy 373 Sillaginidae, larvae 27 snapper, yellowtail 179 whiting 27 King George 27 school 27 yellow fin 27 year-class strength 710 Diet sculpin, staghorn 456 swordfish 403 Dispersal, larval shrimp 471 Distribution bass, black sea 429 bonefish, larvae 666 chinook salmon, juvenile 274 cetaceans 1, 15 dolphin common 1, 15 northern right whale 1,15 Pacific white-sided 1, 15 Risso's 15 spinner eastern 345 whitebelly 345 spotted 345 striped 1 flounder, windowpane 675 ichthyoplankton, Gulf of Alaska 231, 603 mackerel, Pacific 172 pollock, walleye 603 sanddab 516 shrimp, larvae 471 whale 1 beaked 15 blue 1 fin 1 humpback 1, 196 minke 15, 577 sperm 1 DNA mitochondrial 78, 97 RNA/DNA ratio 158,217 Dolphin 1, 15 common 1, 15, 483 long-beaked 1 short-beaked 1 Dall's porpoise 1 northern right whale 1, 15 Pacific spp. 1, 15, 345 Pacific white-sided 1,15 Risso's 15 spinner eastern 345 whitebelly 345 spotted 345 striped 1 Dolphin [fish] 152 Drift nets 483 Drum 191 Dungeness crab 456 Early life history studies Atlantic menhaden, daily ageing 209 bass, black sea 429 bonefish 666 chjlipepper 721 flounder, windowpane 675 larvae, length-weight relationships 419 mackerel, Pacific 172, 217 menhaden, Atlantic 209 pollock, walleye 386, 603 juveniles 386 larvae 333 sanddab 516 shrimp 471 snapper, yellowtail 179 rockfish 166,710 Sillaginidae 27 whiting 27 King George 27 school 27 yellow fin 27 Egg studies bass, striped 315 crab, Tanner 44 flounder, arrowtooth 127 flounder, summer and gulf 504 roughy, orange 373 Elasmobranchs 57, 412 Embryology 373 Endangered species 586, 753 Energetics rockfish, yellowtail 299 Environmental effects bass, striped 315 bonefish recruitment 666 crab, Tanner 44 egg ascent rates 373 sanddab, distribution 516 shrimp, crystal 397 shrimp, distribution 471 Estuarine studies bass, black sea 429 crab, Dungeness 456 sculpin, staghorn 456 turtles, sea 254 weakfish 643 Eumetopias jubatus 753 Evolution — Scombroidei 78 Fecundity shark, Atlantic sharpnose 57 Feeding — see Food habits Fertility, snow crab 759 Fin spines, ageing 594 Fisheries oceanography 516 Fishery coralgrouper, leopard 629 coral reef fishes 573, 629 groundfish, Bering Sea, killer whale depredation 355 recreational 619 reef 629 shark, Atlantic sharpnose 57 tuna, eastern tropical spp. 345 dolphin bycatch 345 Fishery interactions dolphin, common 483 killer whale-groundfish 355 tuna-dolphin 345 Fishery management abalone, blacklip 551 772 INDEX: SUBJECTS Fishery Bulletin 93| 1-4 ), 1995 mathematical methods 290, 308 abundance estimation, methods 290, 308, 495 models 290 catch equation 308 shark, Atlantic sharpnose 57 shark, Atlantic spp. 412 size limits, abalone 551 Fishery reserves, marine coralgrouper, leopard 629 Fishes, coral reef 573, 629 Flatfishes 127, 504, 516, 675 Florida shrimp, larvae 471 snapper, yellowtail 179 tarpon 619 turtles, sea 139 Flounder arrowtooth 127, 355 gulf 504 summer 217, 504 windowpane 675 Fluorometry 158 Follicle, postovulatory 568 Food habits killer whale longline depredation 355 sculpin, staghorn 456 swordfish 403 Gear comparison 67, 446 Genetic studies lobster, Cape 97 Scombroidei 78 species identification lobster, Cape 97 Geographic variation sea turtle abundance 254 Georges Bank flounder, windowpane 675 Gompertz model 419 Gonadosomatic index 127 Grampus griseus — see Dolphin, Risso's Green turtles 586 Grenadier, blue 391 Grey trout 643 Groundfish 446 Growth — see also Age determination abalone, blacklip 551 bass, black sea 429 chilipepper 721 chinook salmon, juvenile 274 covariation with morphology 551 dolphin, common 483 dolphin [fish] 152 drum, red 191 flounder, windowpane 675 menhaden, Atlantic 209 shark, Atlantic sharpnose 57 shark, dusky 116 snapper 103 yellowtail 179 squid 749 striped bass, larvae 315 swordfish 594 tarpon 619 turtles, sea 139 weakfish 643 Gulf of Alaska ichthyoplankton 231, 603 pollock, walleye 603 larvae 333 Gulf of Mexico shark, Atlantic sharpnose 57 shrimp, crystal 397 turtle, green 586 Habitat bass, black sea 429 nekton, demersal 262 turtle, green 586 walleye pollock, juveniles 386 Haliotis rubra 551 Harbor porpoise 741 Hawaiian Islands dolphin [fish] 152 snapper, pink 67 Hawaiian Islands fishery snapper, pink 67 Herd characteristics, cetacean 577 Hippoglossus stenolepis 355 Histological condition 333 Histology 217,333 Homarinus capensis 97 Homarus americanus 97 capensis 97 gammarus 97 Hoplostethus atlanticus — see Roughy, orange Hydrography sanddab 516 shrimp, crystal 397 shrimp, larvae 471 Hypoxia 397 Ichthyoplankton 231,603 Identification chilipepper 721 flounder, larvae 504 hagfish 530 rockfish 166 whiting 27 King George 27 school 27 yellow fin 27 Impact assessment chinook salmon survival 732 fishing on populations dynamics 629 temperature on Tanner crab 44 Interannual variation bonefish, recruitment 666 harbor porpoise, abundance 741 walleye pollock, recruitment 386 Juvenile studies bass, black sea 429 chilipepper 721 crab, Tanner 44 green turtle 586 menhaden, Atlantic 209 pollock, walleye 386 rockfish 710 salmon, chinook 274, 732 sea lion, Steller 753 snapper pink 67 yellowtail 179 Lagenorhynchus obliquidens 1, 15 Larval studies bass, striped 315 chilipepper 721 drum, red 191 flounder gulf 504 summer 217, 504 windowpane 675 Gulf of Alaska 231,333 length-weight relationships 419 mackerel, Pacific 172 menhaden, Atlantic 209 pollock, walleye 333, 603 RNA/DNA ratio 158 rockfish 710 identification 166 shrimp 471 Sillaginidae 27 snapper, yellowtail 179 whiting 27 King George 27 school 27 yellow fin 27 Latitudinal variation bass, black sea 429 Steller sea lion, pup mass 753 weakfish, size 643 Length at maturity 127 Length-frequency analysis shark, dusky 116 Length studies — see also Age determination snapper, mutton 573 Length-weight relationships 412,419 Lepidochelys kempii — see Sea turtle, Kemp's ridley Leptocottus armatus 456 Life history dolphin, common 483 flounder summer 217 windowpane 675 pollock, walleye 207 shark, Atlantic sharpnose 57 Line transect 1, 15, 254, 741 Lipid 299 Liver 299 Lissodelphis borealis 1,15 Lobster American 97 Cape 97 European 97 Loliginidae — see Squid Loligo chinensis 749 Longline, bottom 355 Lutjanus — see Snapper analis 573 erythropterus — see Snapper, scarlet INDEX: SUBJECTS Fishery Bulletin 93(1-4), 1995 773 malabaricus — see Snapper, Malabar sebae — see Snapper, red emperor Mackerel, Pacific 172 Macruronus novaezelandiae — see Grenadier, blue Mahimahi 152 Management — see Fishery management Marine mammal 1, 15, 196 Marking methods 191,209 Mark-recapture 186, 694 Massachusetts Bay 577 Mass stranding, humpback whales 196 Mathematical methods abundance estimation 274 catehability coefficient, estimation 562 catch equation, solving 308 estimation from tags 694 estimation, weight-length relationships 412,419 recruitment prediction 657 Mating 759 Maturity dolphin, common 483 flounder, arrowtooth 127 Mediterranean 594 Megalops atlanticus 619 Megaptera novaeangliae 1, 15, 196 Menhaden, Atlantic 209, 562 Meristics flounder, larvae 504 whiting 27 King George 27 school 27 yellow fin 27 Mesoplodon spp. 15 Metamorphosis sanddab 516 Methods ageing comparison of scales and otoliths 186 radiometry 103, 391 spines 594 biochemical indicator 158 marking 191 radiometric ageing 391 Mexico shrimp, crystal 397 Microchemistry, otolith 166, 391 Mid-Atlantic Bight bass, black sea 429 nekton, demersal 262 flounder, windowpane 675 menhaden, Atlantic 209 Migration — see Movements Minke whale 577 Mitochondrial DNA analysis billfish 78 lobster 97 Models abundance 290 allometric 419 catch equation 308 demographic shark, Atlantic sharpnose 57 diffusion 694 egg thermal history 373 recruitment 657 velocity 694 virtual population analysis 308 Molecular phylogeny 78 Monitoring snapper, pink 67 tuna, giant bluefin 495 Morone saxatilis 186,315 Morphology abalone, blacklip 551 lobster 97 otolith 391 Sillaginidae, larvae 27 snapper, yellowtail 179 whiting, larvae 27 King George 27 school 27 yellow fin 27 Morphometries flounder, summer 217 turtles, sea 139 Mortality chinook salmon, juvenile 732 crab, Tanner 44 dolphin Pacific spp. 345 spinner eastern 345 whitebelly 345 spotted 345 due to killer whale depredation 355 due to tagging 191 estimation of 657 flounder, windowpane 675 shark, Atlantic sharpnose 57 striped bass, larvae 315 whale, humpback 196 Movements bass, black sea 429 bonefish, larvae 666 chinook salmon, juvenile 274, 732 estimation from tag data 694 flounder arrowtooth 127 windowpane 675 models of 694 shrimp, larvae 471 turtles, green 586 turtles, sea 139, 254 Multivariate analysis 262 Muscle, proximate composition 299 Mutton snapper 573 Myxine spp. 530 Neuston 231 New genus 97 New species 530 New Jersey 429 New Zealand, orange roughy 373 Northern sea lion 753 Nucleic acid analysis 158 Nursery 429 Nutritional condition 158,217,333 sea lion, Steller 753 dynamics 299 Ocyurus chrysurus 179 Oncorhynchus tshawytscha — see Salmon, chinook Ontogenetic changes 172, 217, 516 Oreinus orca 355 Oregon chinook salmon, juvenile 333 sea lion, Steller 753 Otoliths ageing bass, striped 186 larvae 315 chilipepper 721 grenadier, blue 391 menhaden, Atlantic 209 radiometric 103, 391 snapper 103 tarpon 619 weakfish 643 annuli validation 209 bonefish 666 microchemistry 166, 391 rockfish 166 sanddab 516 snapper 103 species identification 166 Ovarian atresia 568 Ovary, proximate composition 299 Ovulation 568 Oxygen 397 Pacific Ocean cetaceans 1, 15, 345 chilipepper 721 chinook salmon, juvenile 274 crab, Dungeness 456 dolphin 1, 15 common 1,15,483 eastern tropical Pacific spp. 345 mortality 345 northern right whale 1, 15 Pacific white-sided 1, 15 Risso's 15 spinner eastern 345 whitebelly 345 spotted 345 flounder, arrowtooth 127 hagfish 530 harbor porpoise 74 1 mackerel, Pacific 172 pollock, walleye, larvae 333 rockfish 166,710 yellowtail 299 sanddab 516 sculpin, staghorn 456 shrimp, crystal 397 snapper, pink 67 whale 1, 15 beaked 15 humpback 1, 15 minke 15 sperm 1,15 774 INDEX: SUBJECTS Fishery Bulletin 93(1-4), 1995 Pacific Ocean, eastern tropical dophin mortality 345 spinner eastern 345 whitebelly 345 spotted 345 Pacific Ocean, North chinook salmon, juvenile 274 crab, Tanner 44 dolphin, common 483 flounder, arrowtooth 127 groundfish, abundance 446 harbor porpoise 741 pollock, walleye, larvae 333 Paralichthys albigutta 504 dentatus 217,504 lethostigma 504 Patchiness, larval 172 Penaeidae — see Shrimp Penaeus breuirostris — see Shrimp, crystal Perception bias 1 Photography tuna schools 495 Phocoena phocoena 741 Phocoenoides dalli 1 Photololigo chinensis 749 Physeter macrocephalus — see Whale, sperm crab, Tanner 44 Pinnipedia — see Seals Plectropomus leopardus — see Coralgrouper, leopard Plus group 308 Pollock, walleye 333, 386, 603 Population dynamics coralgrouper, leopard 629 sea lion, Steller 753 shark, Atlantic sharpnose 57 snapper, pink 67 Population studies harbor porpoise 741 shark, Atlantic sharpnose 57 shark, dusky 116 snapper mutton 573 pink 67 Porpoise — See Dolphin Postovulatory follicle 568 Power analysis 446, 741 Prawn — See also Shrimp Predation — see also Mortality rates Pristipomoides filamentosus — see Snapper, pink Protein 299 Proximate analysis rockfish, yellowtail 299 Purse seine tuna, eastern Pacific spp. 345 Radiometric ageing 103, 391 Radio tracking 586 Recruitment bass, black sea 429 bass, striped 315 bonefish 666 coralgrouper 629 pollock, walleye 386 predicting 657 rockfish 710 sanddab 516 shrimp, penaeid 471 Reef, artificial 573 Reef fishes snapper, mutton 573 Reinhardtius hippoglossoides 355 Reproduction dolphin, common 483 flounder, arrowtooth 127 rockfish, yellowtail 299 Reproductive biology crab, snow 759 dolphin, common 483 flounder, arrowtooth 127 menhaden, Atlantic 568 rockfish, yellowtail 299 RNA/DNA ratio 158,217 Rockfish 166, 710 blue 710 chilipepper 166, 721 identification 166 widow 166 yellowtail 166, 299, 710 Roughy, orange 373 ROV 446 Sablefish — see Anoplopoma fimbria Salmon, chinook, juvenile 274, 732 Sanddab 516 Scales, ageing bass, striped 186 School structure tuna, giant bluefin 495 Sciaenops ocellatus 191 Scombroidei 78 Scomber japonicus 172 Scophthalmus aquosus 675 Seals Sea lion, Steller 753 Searcher 355 Seasonal studies bass, black sea 429 bonefish, recruitment 666 crystal shrimp, distribution 397 flounder, arrowtooth 127 ichthyoplankton 231,603 pollock, walleye 603 rockfish, yellowtail 299 squid, growth 749 turtles, green 586 turtles, sea 139 whale, minke 577 Sebastes — see Rockfish auriculatus 166 entomelas — see Rockfish, widow flavidus — see Rockfish, yellowtail goodei — see Rockfish, chilipepper jordani — see Rockfish, shortbelly mystinus 166, 710 paucispinis 166 saxicola 166 Selectivity killer whale depredation 355 Sensitivity analysis 694 Serranidae — see Coralgrouper, leopard Sex structure 629 Sexual maturity — see also Reproductive biology dolphin, common 483 flounder, arrowtooth 127 Shark Atlantic sharpnose 57 Atlantic spp., length-weight relationships 412 dusky 116 Ship survey 1 Shrimp crystal 397 penaeid 471 Shrinkage 333 Sillaginidae 27 Sillaginodes punctata 27 Sillago bassensis 27 Sillago schomburgkii 27 Size estimation — see Age determination Size limits, blacklip abalone 551 Size-selectivity flounder, arrowtooth 127 killer whale, longline depredation 355 Size structure coralgrouper, leopard 629 snapper, mutton 573 Slime eel 530 Snapper Malabar 103 mutton 573 pink 67 red emperor 103 scarlet 103 yellowtail 179 Snow crab 759 Sonic tracking 586 South Africa 97 South America 530 Spawning — see also Reproductive biology flounder arrowtooth 127 windowpane 675 menhaden, Atlantic 568 Species association nekton, demersal 262 ichthyoplankton, Gulf of Alaska 231, 603 tuna-dolphin 345 turtles, sea 139 Species identification hagfish 530 lobster 97 rockfish 166 whiting, larval 27 Sperm storage 759 Spines, ageing 594 Squid in diet of swordf ish 403 loliginid 749 INDEX: SUBJECTS Fishery Bulletin 93(1-4), 1995 775 statolith growth 749 Staghorn sculpin 456 Statolith 749 Steller sea lion 753 Stenella attenuate — see Dolphin, spotted coeruleoalba — see Dolphin, striped longirostris — see Dolphin, spinner Stock assessment abundance indices 290 catchability coefficient, estimation 562 catch equation, approximations 308 Stranding, humpback whale 196 Stress crab, Tanner 44 Survey, aerial cetaceans 15 tuna, giant bluefin 495 Survey abundance estimates from 290, 446 aerial harbor porpoise 74 1 tuna, giant bluefin 495 turtles, sea 254 comparison of video and trawl 446 fishery independent 710 ship, cetaceans 1 video nekton, demersal 262 groundfish 446 snapper, pink 262 visual 573 Survival — see Mortality Swordfish 403, 594 Tagging abalone, blacklip 551 comparison of methods 191 estimation from movements 694 velocity and diffusion 694 shark, dusky 116 turtles, sea 139 Taxonomy billfish 78 flounder spp. 504 hagfish 530 lobster 97 Scombroidei 78 Temperature and abundance of striped bass, larvae 315 and development of crab, Tanner 44 eggs, orange roughy 373 and distribution of shrimp, crystal 397 and postovulatory follicle degeneration 568 Temporal variation catchability coefficient 562 crystal shrimp, distribution 397 minke whale, distribution 577 proximate composition 299 walleye pollock, juvenile abundance 386 weakfish, size 643 Theragra chalcogramma 333,386,603 Thunnus albacares 345 Thunnus thynnus 495 Tortugas gyre 471 Transect, line 1, 15, 573 Transport, larval shrimp, penaeid 471 Tuna, giant bluefin 495 Turbot, Greenland 355 Turtles, marine — see Turtles, sea Turtles, sea green 139,254 Kemp's ridley 139, 254 loggerhead 139,254 Uncertainty 290 Unexploited population 573, 629 Upwelling 516 Validation, age 103, 186, 209, 619 Vertebrae, ageing 116 Vertical distribution eggs, orange roughy 373 ichthyoplankton 231 sanddab 516 shrimp crystal 397 larvae 471 Video, survey 67, 262, 446 Virginia bass, striped 186 Virtual population analysis 308 Visual survey 573, 577 Walleye pollock — see Pollock, walleye Washington chinook salmon, juvenile 333 flounder, arrowtooth 127 Weakfish 643 Weight-length relationships 412,419 Whale beaked 15 blue 1 fin 1 humpback 1, 15, 196 killer 355 minke 15, 577 sperm 1, 15 Xiphias gladius 594 Year-class strength 710 Yellowtail rockfish 299, 710 Ziphius spp. 15 Superintendent of Documents Subscription Order Form *5178 I IYES, enter my subscnption(s) as follows: subscriptions to Fishery Bulletin (FB) for $30.00 per year ($37.50 foreign). 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