Gulf Research Reports Volume 2, Number 2 Ocean Springs, Mississippi OCTOBER 1966 Gulf Research Reports Volume 2 Issue 2 January 1966 Oyster Abundance in Apalachicola Bay Florida in Relation to Biotic Associations Influenced by Salinity and Other Factors R.W Menzel Florida State University N.C. Hulings Florida State University R.R. Hathaway Florida State University DOI: 10.18785/grr.0202.01 Follow this and additional works at: http:/ / aquila.usm.edu/ gcr O Part of the Marine Biology Commons Recommended Citation Menzel, R., N. Hulings and R. Hathaway. 1966. Oyster Abundance in Apalachicola Bay, Florida in Relation to Biotic Associations Influenced by Salinity and Other Factors. Gulf Research Reports 2 (2): 73-96. Retrieved from http:// aquila.usm.edu/gcr/vol2/iss2/! This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized administrator of The Aquila Digital Community. For more information, please contact Joshua.Cromwell(o)usm.edu. OYSTER ABUNDANCE IN APALACHICOLA BAY, FLORIDA IN RELATION TO BIOTIC ASSOCIATIONS INFLUENCED BY SALINITY AND OTHER FACTORS 1 by R. W. Menzel, N. C. Hulings and R. R. Hathaway Oceanographic Institute, Florida State University Tallahassee, Florida Abstract From June 1955 through May 1957, stations on three oyster reefs were sampled quantitatively at intervals and all oysters and associated macroscopic organisms were recorded per unit area. Station I was a privately leased "natural” reef, consisting of higher places exposed at low water, with a salinity range of 22.7*36.6 o/oo and was fairly productive. Station 11, depth ca. two meters, was the least saline, range 1.2-29,3 °Joo, and was considered very productive for natural reef. Station III, depth one meter, salinity range 7.5-35.7 °/oo, was depleted although there was an abundant spatfall. Depth and bottom types as well as salinity were found to delimit certain species of animals. Analysis of past records showed that the bay had formerly been less saline; there was an extended drought in the water- shed before and during the investigation. As a result several species of animals less euryhaline than oysters became established on some of the reefs. At Station 111, two serious oyster enemies, Thais haemastoma Say and Menippe mercenaria Conrad were abundant . A field experiment at this station during the second year pointed to these two enemies as the main cause of the depletion of the reef. Near the end of the investigation rainfall became more nearly normal and the lowest salinities were recorded at this time. The reduction in salinity, especially at Station 111, eliminated many of the less euryhaline species, including drills and stone crabs, and the reef later regained its former productivity. i Contribution No. 213, Oceanographic Institute, Florida State University. This study was supported by a contract with the U. S. Fish and Wildlife Service through Saltonstall-Kennedy Funds. 73 Introduction Apalachicola Bay, Franklin County, is the center of oyster produc- tion in Florida, producing about 85% of the state’s crop. Quantitative samples were made of the oysters and associated biota to determine if such sampling would delineate a non-productive oyster reef from a productive one. The presence or absence of certain organisms, especially known oyster enemies, as well as their abundance, was correlated with salinity and other physical factors. Stations were established on non-productive and produc- tive oyster reefs of high and low salinities and shallow and deep water. The study extended from June 1955 through May 1957. There have been several studies of the oyster reefs in the region of East Bay, Indian Lagoon, St. Vincent Sound, Apalachicola Bay, St. George Sound, which are known collectively as Apalachicola Bay. IngersolJ (1881) mentioned the oyster fishery of the area and later Swift ( 1897 ) made an extensive survey of the region. Moore (1897) discussed the organisms collected by Swift. Danglade (1917) studied ail the oyster reefs of the region and attempted to determine the density of oysters on several of the producing reefs. Pearse and Wharton (1938), in their study of the oyster "leech”, gave considerable information on the biota and hydrography of the region. Ingle and Dawson (1953) made a recent survey of the oyster reefs and have published on the spawning, setting, growth and con- ditions of the oysters (Ingle, 1951a; Ingle and Dawson, 1950, 1952). DESCRIPTIONS OF STATIONS AND METHODS Three stations (described below) were selected for study because they represented different ecological conditions (Figure 1), STATIONS IN APALACHICOLA BAY Figure 1. Map of Apalachicola Bay showing locations and bottom salinity ranges of stations. 7 4 Station I Station I was a reef located in the middle of Indian Lagoon on privately leased ground that is harvested sporadically. At mean low water the top of the reef is exposed. The top of the reef is approximately one* half meter higher than the lower edges. The surrounding area has a mud bottom and an average depth of less than one meter at mean low water. The reef is relatively small, about 175 meters long and 20 meters wide in the middle, and tapers gradually at both ends. Bottom salinities during this study ranged from 22,7 o/oo to 36.6 o/oo (Table 1). Although many single oysters were present, the majority occurred in clusters up to about ten. The oysters were more numerous on the lower edges of the reef than on the higher middle part, which had more shells and smaller oysters and a firmer substrate than the lower edges. Though not large, oysters were thick-shelled, deep-cupped, and rounded. Station II Station II was located in polluted water north of Gorrie Bridge where the depth was from 2 to 3 meters. The main reef of oysters is rather narrow and extends about 500 meters northward from the bridge. The bottom is firm on the reef (it was estimated that the shells and oysters were a foot or more thick), but is fairly soft in other areas. The maximum size of the oysters was greater than at Station I. This reef was opened for commercial exploitation each winter during the investigation, when the pollution cleared. The bottom salinity ranged from 1.2 o/oo to 29.3 o/oo (Table 1). Station III Station III was established on St. Vincent Bar. The reef is exten- sive, and although several small sectors are exposed at low water, most of it is under a meter or more of water, Masses of shell fragments (mainly oyster) cover the reef. The bar is in an exposed position in the bay and is subject to the vagaries of estuarine conditions. The currents are swifter here than at any of the other stations. The general location of the sampling was in a depth of one meter at low tide. The bar is reported to have been productive in former years, and the dense masses of shells support this. During the investigation, however, it produced no market oysters, although spatfall was heavy. The bottom salinity ranged from 7.5 o/oo to 35-7 o/oo (Table 1). Field Procedures During the first year of observation (June 1955-May 1956) sampling trips were made to all stations at approximately monthly intervals. During the second year, Station 111 was sampled at monthly intervals, but Stations I and II only seasonally. Each station was sampled quantitatively by collecting all the oysters and the associated macroscopic organisms in a measured area. Frames were made with areas of one square meter and one-fourth square meter. In sampling Station I, two transects, ten meters apart, each one meter wide and 20 meters long, were established parallel to the short axis of the reef. Samples were taken from one transect and near (but outside) the 75 TABLE I Monthly bottom salinity reading (o/oo) and surface temperature (°C) at the three stations in Apalachicola Bay Date 1 o/oo °C II o/oo °C Ill o/oo °C 1955 June 36.3 28.5 — 27.5 — — July 31.0 33.0 — 29.5 — — Aug 29.1 32.0 — 32.1 — — Sept 22.9 27.5 — 27.3 28.5 29.5 Oct 29.5 23.0 — 22.9 29.0 23.0 Nov 31.2 23.0 28.6 19.0 18.8 21.0 Dec 29.1 8.1 27.2 10.2 17.3 12.1 1956 Jan 30.4 13.6 6.6 11.0 22.7 13.7 Feb 23.5 15.0 1.2 14.0 13.7 16.0 Mar 32.9 13.0 7.1 14.1 32.1 14.4 Apr 35.3 19.2 — — 10.3 19.5 May 36.6 27.1 26.8 23.3 16.2 26.0 June — — 29.3 28.0 35.7 29.0 July — — 26.5 29.0 34.4 29.0 Aug 32.3 32.9 — — 27.5 30.0 Sept — — — — 22.6 28.0 Oct — — — — 19.7 24.4 Nov 30.7 20.5 — — 24.3 19.0 1957 Jan 27.8 16.4 — — 35.7 14.9 Feb. — — — — — — Mar — — 19.7 17.0 30.6 16.5 Apr — — — — 10.6 20.0 May 27.0 24.0 — — 7.5 24.0 76 other. The second transect was left and treated -as a control area. Two one-fourth square meter samples were taken from each edge and two from the middle of the reef. The reef was usually sampled at the low tide when it was either exposed or in very shallow water. At Station II an attempt was first made to anchor a one-meter square frame to the bottom and to tong all oysters and other organisms within the frame. This was abandoned and SCUBA was used thereafter. After the reef was located, the frame was cast at random from a motor launch. The diver then collected all material by hand from the enclosed area of the frame. Three one-square-meter samples were taken the first year and four one-fourth-square-meter samples were taken the second year at each sampling. At Station III, because of the shallow water SCUBA was not used, but hand collections were made with the aid of a face mask. Surface water temperatures and bottom salinity samples, were taken and a U.S.C.G. and G.S. hydrometer (Emil Griener and Co.) was used to determine salinity (Table I). On September 7, 1956, surface and bottom samples were taken at 30 minute intervals at Station III, over a 12 hour period. A field experiment was conducted at Station III during the second period of observation in which an attempt was made to protect oysters from predators. Baskets were constructed of one-half inch mesh hardware cloth and filled with twelve liters of the shelly bottom material, from which all large predators were removed. Twenty-four such baskets were utilized. Two of the baskets were removed for examination concurrently with four one-fourth-square meter bottom samples, during each trip to the station. One hundred large oysters from Station I and 100 from Station II were transplanted to Station III for mortality studies. These oysters (25 per basket) w'ere placed in baskets similar to those containing the shelly bottom material. These experiments yielded some information but were not completed because the baskets were lost after several months. Laboratory Procedures All the samples were analyzed in the laboratory at Florida State University. The oysters were measured to the nearest half-millimeter in length and numbers tabulated in size intervals; Interval M 1 M - oysters below 10 mm long (not recorded except for Station III); Interval ''2” - oysters between 10.0 and 19.5 mm long; . . . ; Interval 'T4” - oysters between 130.0 and 139.5 mm long. Recent mortality in the various size intervals was estimated by the fouling on the shells. The determination of the species composition of oysters from Station III was made by opening and examining the shells of approximately 100 oysters. The species Ostrea equestris Say was abundant at this station along with the commercial oyster Crassostrea virginica (Gmelin). A twelve liter sample of culled oysters from Stations I (edges of reef) and II was counted, weighet! to the nearest gram in the shell and shucked; the volume of the drained meat was measured to the nearest milliliter. All of the conspicuous faunal elements were identified and particular attention was given to enemies and possible enemies of oysters. Abund- ance of each species was estimated during the first year as follows: abund- ant (”A”) - more than 10 per square meter; common ("C”) - 4 to 10 per 77 square meter; rare ("R”) - 1 to 3 per square meter; present ("P”) - no estimate of numbers could be made (e.g., blue crabs, encrusting bryzoans). The number per unit area was determined for some species, mostly during the second year of study. The data have been tabulated as numbers per square meter. Oysters from the several stations were examined for Dermosystidium marinum Mackin, Owen and Collier by use of the thio- glycolate method. Although samples were usually taken at monthly intervals, numbers of oysters are given on a seasonal or quarterly basis. The quarters are January-March, April-June, Juiy-September and October-December. Thus the seasonal data will include an average of as many as nine one-square- meter samples for Station II during the first year of observations and as few as four one-fourth-square-meter samples for this station during the second year. RESULTS AND DISCUSSION Salinity The ranges of salinities for the stations are shown in Figure 1 and Table 1. Since these were monthly samples, they can give only a general idea of the hydrographic conditions. The salinity samples taken during the present investigation show wide fluctuations but salinity was generally highest at Station I, slightly less at Station III, and lowest at Station II. This sequence would be expected from the location of the several stations. Previous investigations in the bay have shown rapid and wide fluctuations in salinities, influenced by freshets, tides, currents, and wind direction and velocity (Dawson, 1955a; Ingle and Dawson, 1950, 1953). The twelve-hour survey at Station III showed that the salinity varied nearly 4 o/oo at the surface and nearly 5 o/oo at the bottom during the period. Concurrent samples taken at the surface and bottom never differed more than 3.4 o/oo; the majority showed top-to-bottom difference of less than 0.5 o/oo. There was little tidal exchange at this date because of a strong easterly wind. Possibly under other conditions, when there would be more in-and-out water movement, the hourly fluctuations as well as the stratification in salinity would be greater. Station III is a shallow water station and stratification was found to be greater in deeper water. Station II, which had the deepest water of all stations (and was also closest to the influence of river runoff), sometimes had top-to-bottom differences of as much as 20 o/oo. Salinities recorded by previous investigations (Pearse and Wharton, 1938; Ingle and Dawson, 1950; Dawson, 1955a) and those of the present investigation are summarized in Table 2. These data indicate that overall salinity was higher than during the earlier investigations. There had been an extended drought in the watershed of Apalachicola Bay, but beginning 78 in the spring of 1957, precipitation had become more normal, and the lowest salinities during the present study were recorded at this time. The salinity of the area should become more stable due to the construction of the Woodruff Dam on Apalachicola River and the opening of passes to the Gulf through the barrier islands, both of which were completed since the termination of this investigation. TABLE 2 Comparison of salinities (o/oo) taken in Apalachicola Bay region in 1935-36, 1949-50, 1953-54, and 1955-57. Investigator Station I Station III Station II and Date Depth Low High Low High Low High Pearse and Surface 5.97 32.45 0.00 20.19 0.40 32.46 Wharton 1935-36 Bottom 5.97 34.41 0.10 28.66 0.60 34.58 Ingle and Surface 16.1 43.8 — — 2.6 39.4 Dawson 1949-50 Dawson 1953-54 Surface 18.4 37.2 1.2 18.4 4.1 35.1 Present Surface — — 0.0 25.8 7.5 35.1 authors 1955-57 Bottom 22.7 36.6 1.2 29.3 7.5 35.7 Spatfall In the following discussion the presence of a large number of oysters in the smaller size intervals is assumed to indicate recent spatfall. Ostrea equestris, a s well as Crassostrea virginica, occurred at Stations I and III (sometimes in equal numbers at Station III) but the discussion and the figures are only of Crassostrea . The heaviest spatfalls at Station I on the edges of the reef occurred during the fall of 1955 and the summer of 1956 (Figure 2). On the middle of the reef the greatest numbers of small oysters were found during the fall in both years (Figure 3)* 79 TOTAL NUMBER DCAC Figure 2 Figure »l«f KII INtKAVALf litC IH1MVMJ Mil Seasonal average total number of Crassostrea and number dead per square meter in each size group during sampling period, STATION I, edge. TOTAL NUMBER DEAD ■ JULY- SEPT, 1956 OCT. -DEC. 1956 1 hay 057 AVERAGE JMsl— l rdlL m 1 2 I4i« T flic |IZ( IMTCRVAM IIXC INTMVAC* iJH IMtiHVAU • tXC iMftHVAUf Seasonal average total number of Crassostrea and number dead per square meter in each size group during sampling period, STATION I, middle. 80 Station II never had a heavy spatfail (Figure 4). It is surprising that the oysters in this area maintained such a level of abundance since there was a constant loss from mortality and harvesting. The area has fewer natural enemies than other stations examined and the lack of enemies probably accounts for the sustained production despite the low spatfail. Ingle and Dawson (1953) also found that, generally, the spatfail was lighter on the less saline reefs. Station III had a heavy spatfail during both years of the investiga- tion. Figure 5 indicates that spatfail on the bottom was greatest in the summer and fall. Spatfail in the baskets (Figure 6) was heavy at all times, but especially in the spring. Monthly data (not shown) indicate heaviest spatfail in late May and June. TOTAL NUMgtft DCAD JULY 1 9 54 OCT. - NC V 1956 MARCH I9ST AVERAGE M m t n ■ 3 * » 10 1 U tl 12 t) X J» 4* V 3 w * 20- 10 A 4# S» i Z 20 10 she intervals s;ec intervals slit ihTi/tVAia she intervals Figure 4. Seasonal average total number of Crassostrea and number dead per square meter in each size group during sampling period. STATION II. 81 TOTAL NUMBER DEAD Figure 6. Seasonal average total number of Crassostrea and number dead per basket in each size group during sampling period, STA- TION 111. 83 Mortality The mortality data, based on a judgment of recent deaths, are very conservative estimates. The difference in growth rates of fouling organ- isms at various times of the year, the time of separation of the valves of various size oysters and other factors, all make it difficult to determine recent mortality. Gunter, Dawson and Demoran (1956) have discussed problems which apply here in determining oyster mortality. At Station I the mortality was greater on the middle of the reef than on the edges and was less the first year than the second (Figures 2, 3). Station II had much less mortality than Station I (Figure 4). Mortality was very high at Station III during all periods of the year. The oysters in the baskets had less mortality that those on the bottom (Figures 5, 6). Mortality was heaviest in summer and fall, especially on the edges of the reef at Station I. The high summer and fall mortality is correlated with the greater activity of predators and incidence of disease during these seasons. A more detailed discussion of the mortality at Station III is given by Menzel, Hulings and Hathaway (1957). On the average the greater proportion of dead oysters at all the stations was found in the larger size groups, but these data are due partly to the method used in determining mortality. Growth and Size Oyster growth is very rapid in the Apalachicola Bay area (Ingle and Dawson, 1952). Shell size increases throughout the year. Our data show some evidence of growth in the change in modal length between sampling periods. At some stations, however, the mode remained the same throughout the period because of the mortality and recruitment. At Station I, few oysters reached 100 mm in length (Figures 2 and 3). The average modal length at the edge of the reef was 40.0-49.5 mm. In the middle of the reef, the modal length was 20.0-29.5 mm. Samples of oysters collected at Station II showed a progressive increase in length (Figure 4). In September 1955 the mode was at 40,0- 49-5 mm, and throughout the year this value increased until July 1956, when a maximum modal length of 80.0-89.5 mm was reached. In the following sampling period ( October-November, 1956) a clear bi modal distribution in length was found. It appears, from the length distribution found at the two periods, that a spatfall occurred during the summer. At Station II, number of oyster per square meter, especially larger oysters, decreased during the spring, perhaps because of commercial harvesting as well as mortality. At Station III, measurements were made of samples from the bottom and from basket culture. No oysters reached a length greater than 50 mm on the bottom and the majority were between 10 and 30 mm long (Fig- 84 ure 5). In samples from the baskets (Figure 6), growth was reflected in increasing numbers of larger oysters during the year, although the modal length remained constant. Market Oysters Oyster farming in Apalachicola Bay has not developed commen- surately with the potential that exists, despite the abundance of seed oysters and the fast growth. Most of the market oysters are produced from more or less wild stock, despite extensive shell plantings for cultch in certain areas and experimental plantings by the State Board of Conservation to demonstrate the feasibility of oyster culture. TABLE 3 Weights (gm) in shell and volume (ml) of shucked meat of oysters from a 12-liter sample at Stations I and II Date Total No. Oysters I II Total Weight I II Meat Volume I II 1955 Aug. 120 — 8,530 — 490 — Sept. 167 100 9,451 8,750 550 420 Oct. 192 142 10,115 7,600 600 675 Nov. 150 77 10,185 7,450 725 510 Dec. 114 — 10,450 — 750 — 1956 Jan. 111 87 10,200 8,400 750 725 Feb. 113 95 9,560 7,600 750 850 Mar. 108 99 8,800 8,180 650 650 Apr. 131 — 8,590 — 890 — May 110 126 8,100 8,300 725 550 June — 116 — 9,550 — 620 July — 93 — 9,250 — 525 Aug. 108 — 8,175 — 525 — Nov. 110 88 6,750 8,250 520 675 1957 Jan. 101 9,435 950 Mar. — 93 — 9,050 — 690 May 116 — 9,793 — 985 — 85 TABLE 4 Organisms found at the three stations in Apalachicola Bay, Florida Stations Organisms I II III Fungus Dermocystidium marinum Mackin, X X X Owen and Collier Porifera Cliona vastifica Hancock X o X Coelenterata Astrangia sp. O o X Bryozoa Membranipora sp. X X X Platyhelminthes Bucephalus cuculus McCrady X X o Stylo chus frontalis Verrill X X X Annelida Neanthus succinea (Frey and Leukart) X X X Sabella sp. X X o Polydora websteri Hartman X X X Arthropoda Balanus eburneus Gould X X X Callinectes sapidus Rathbun X X X Clibevnarius vittatus (Bose) o o X Menippe mercenaria Say X X X Neopanope packardi (Kingsley) o o X N. texana Stimpson X X X Panopeus sp. o o X Petrolisthes armatus (Gibbes) X X X Synalpheus minus (Say) X o X Mollusca - Gastropoda Anachis obesa (Adams) o X X Cerithiopsis greeni (Adams) o o X 86 Crepidula plana Say X X X Epitonium sp. o o X Kurtziella sp. o o X Melongena corona Gmelin X o o Mitrella lunata (Say) o X X Odostomia impressa Say X X X Pol inices, duplicatus (Say) o o X Sella adamsl H. C. Lea o o X Thais haemastoma Conrad X o X Triphora nigrocincta (Adams) o o X Mollusca * Pelecypoda Abra ae quails Say o X o Anadara transversa Say X X X Anomia simplex Orbigny X X X Brachidontes exustus (L.) X o X B . recurvus (Rafinesque) X X X Chione cancellata L. o o X Crassostrea virginica (Gmelin) X X X Corbula sp. o o X Mar testa smithi (Try on) X X X Mulinia lateralis (Say) o X o Noetia ponder osa Say o o X Ostrea equeslris Say X o X Semele bellastriata Conrad o o X Tr achy car dium muricatum L. o o X Fishes Hypleurochilus germinatus (Wood) o o X Hypsoblennius hentz (LeSueur) o o X H. ianthus (J. and G.) o o X Opsanus beta (G. and B.) o o X X — Present O — Not found 87 Although the oysters from Station I were of a smaller shell size than those at Station II (Figures 2, 3, 4) they often yielded more meat per unit measure (Table 3). This was especially true during the summer months. Visual inspection at time of shucking showed that the meats from Station I were generally in better condition than those from Station II. The drop in meat yield during the summer and the rise in the period from December through March, is typical of other oysters in the Gulf (Gunter, 1942; Hopkins, Mackin and Menzel, 1953). A rough estimate can be made of the production of live market oysters for Stations I and II. Figures are calculated from the data of average numbers of live oysters over 70 mm long per square meter and the numbers of oysters of this size needed to fill a 12 liter container. These data may be converted to bushels per acre. For Station I, only the west and east edges of the reef are used, and at this station the estimate was about 225 bushels of live market oysters per acre during the period of the investigation. At Station II, the yield was estimated to be an aver- age of 715 bushels per acre during the period. At times, especially in November 1955 and 1956, before the reef was opened for commercial exploitation, the yield would have been twice as high. The yield from Station I, though not exceptional, was fairly good, especially when the ease of harvesting from a very shallow reef is taken into consideration. The yield from Station II is considered exceptional for a natural oyster bed, since this reef was subject to intensive harvesting each year. When the reef was open, the oystermen concentrated their efforts in this area. Despite the restricted season (because of pollution) the harvesting of oysters from this area was probably as complete as from other areas that were open for tonging throughout the season. After several weeks many tongers left the area of Station II and returned to areas that had formerly been less productive, but were now comparatively more so. Association of Organisms on Oyster Reefs Apalachicola Bay is usually very turbid and probably for this reason macroscopic algae are not conspicuous. Species ol green algae were seen on several occasions during the winter months at Station III when the water was less turbid, but no records were kept. Only animals are dis- cussed here, except for the pathogenic fungus Dermocystidium. marinum. The organisms found and the stations where they occurred are in Table 4. Table 5 gives quantitative data on selected animals. The dis- cussion that follows is mainly of the oyster enemies. The pathogenic fungus Dermocystidium marinum occurs in Apa- lachicola Bay (Dawson 1955b) and was found at all the stations during the present investigation. The mortality of the larger oysters at the stations during the summer months suggested Dermocystidium marinum disease (Mackin 1951a, 1952; Ray, 1954). In the survivors of one of the growth baskets at Station HI, infection ranged from none to heavy (Menzel, Hulings and Hathaway, 1957). The boring sponge Cliona vastifera was present at all stations in the shells of older oysters and in dead shells. This was the only species of Cliona found in the bay. 88 TABLE 5 Occurrence of several animals at the three stations in Apalachicola Bay estimated during period, August 1955-May 1956; numbers given per square meter during period, June 1956-May 1957. Neopanope Petrolisthes Anachis Brachidontes Brachidontes Crepidula Odostomia t ex ana ar?natus obesa exustus recnrvus plana impressa Date 1 11 III I II III I II III I II III I II III I II III I II III Aug. 1955 A C __ R R _ O c _ A O R A . A A _ C C A Sept. 1955 A C A C R A O c C A O A R A R A A A C C A Oct 1955 A c A R R A O c C A O A R A R A A A c C A Nov. 1955 A c A R R A O c c A O A R A R A A A c C A Dec. 1955 A c A R R A O c c A O A R A R A A A c A A Jan. 1956 A c A R R A O c c A O A R A R A A A c A A Feb. 1956 A c A C R A O c c A O A R A R A A A c A A Mar. 1956 A c A C R A O c c A O A R A R A A A c A A c\ Apr. 1956 A c A R R A O c c A O A R A R A A A c A A 00 May 1956 A c A R R A O c c A O A R A R A A A c A A Average A c A R+R A O c c A O A R A R A A A c A- A June 1956 7 62 — 1 12 - — 6 5 — 0 — — 42 1 — 35 A — 73 84 July 1956 . — 3 80 — 0 43 — 0 1 — 0 A — 136 3 — 41 A — 44 33 Aug. 1956 35 — 20 12 — 40 0 - — 11 23 — A 3 — 0 A — . A 8 ■ — 75 Sept. 1956 — — 100 — — 52 — — 16 — . — 168 — — 4 — — 40 — — 83 Oct 1956 — — 59 — — 5 — — 16 — — 26 — — 0 — — 11 — — 96 Nov. 1956 13 1 106 5 1 4 0 2 60 — 0 16 — 16 6 20 16 6 6 Ill 21 Jan. 1957 18 , — . 80 11 — 4 0 — 56 32 — 130 3 — 0 48 — 40 68 — 98 Feb. 1957 — — . 64 — — 2 — — 48 16 — 48 — — 0 — — 52 — — 86 Mar. 1957 — 9 15 — 0 4 — 3 28 — 0 A — 12 7 — 12 78 — 36 62 Apr. 1957 — — 90 — — 1 — — 13 — — 208 — — 0 — — 34 — — 52 May 1957 29 — 42 0 — 0 0 — 8 35 — 42 1 — 0 55 — 10 10 — 25 Average 23.8 5.0 65.3 7.0 0.5 15.2 0.0 2.8 23.8 26.5 0.0 91.1 1.8 51.5 1.9 41.0 26.0 33.9 23.0 66.0 65.0 The flatworm Stylochus frontalis, sometimes called the oyster wafer or leech ( =S . inimicus , vide Hyman, 1940), was the subject of an extensive study by Pearse and Wharton (1938). They found that damage to oysters may be considerable when the worms occur in large concentrations, but concluded that they never cause extermination of the population in a particular locality. The worm was found in concentrations up to 50 per square meter at Station III on several occasions. The worms were also found at other stations and hence salinity was not a limiting factor in their distribution in the areas under study. The oyster mortality rate did not reflect their presence or absence. The cercariae of Bucephalus cuculus were found at all stations (Table 4). The highest percentage of infection was at Station I. In one sample 20% (20 oysters examined) were infected. Although Hopkins (1956a) has stated that heavy infections effectively castrate oysters and probably cause death, the w r orm was never found in epidemic numbers in Apalachicola Bay and the overall effect was probably of minor im- portance. Several investigators have found that mudworms, Polydora ivebsteri, damage oysters (Lunz, 1940, 1941; Mackin and Cauthron, 1952; see also Owen, 1957). Mudworms were fairly abundant at all stations, with the largest numbers at Station II, with as many as 20 Polydora blisters per oyster, covering an estimated 50% of the inside surfaces. The infestations found during the present study were not so severe as commonly found by investigators in South Carolina and Louisiana. It is concluded that mud- worms did not cause oyster mortality directly. Stone crabs, Menippe mercenaria, are serious predators of oysters (Menzel and Hopkins, 1955). No detailed analysis was made of all the dead oysters, but broken shells, indicative of stone crab predation, were seen at all localities. No satisfactory quantitative sampling method was devised for this burrowing crab, but it is estimated that up to one large crab (carapace over 75 mm wide) was present per square meter at Sta- tions 1 and III. Sometimes up to a dozen small crabs (carapace under 50 mm wide) were found per square meter at these stations. Up to five small stone crabs (carapace les sthan 20 mm wide) were found in the two baskets examined monthly at Station III. Stone crabs were recorded from Station II up to the January 1956 examination, but w r ere never found after this date. They disappeared after the first recorded salinity drop, even though higher salinities w r ere recorded subsequently in May, June, and July, 1956. This is an indication that stone crabs are not tolerant of low salinities. Past observations by the senior author in Louisiana indi- cated that the stone crab is limited by salinities below 12-15 °/oo. Stone crabs were probably one of the main enemies of oysters, especially at Sta- tion III. Blue crabs, Callinectes sapulus , were usually abundant, except in the coldest months, even though actual numbers were not recorded because of the sampling method. Lunz (1947) found blue crabs to be important oyster predators in pond culture in South Carolina. Menzel and Hopkins (1955) and Menzel and Nichy (1958) showed that they destroy small oysters and sometimes larger ones. Menzel and Nichy found that blue crabs destroyed oyster on intertidal reefs when the oysters were weakened by high temperatures. Blue crabs were probably a factor in the mortality observed in this investigation, especially on the middle of the reef at Station I. 90 The snail Odostomia impressa was present at all stations and was especially common at Stations 11 and 111 (high and low salinity stations). Salinity evidently was not a limiting factor in the area under study. Hopkins (1956b) found that O. impressa feeds on large oysters and Allen (1958) mentions oysters, other mollusks, worms, and ascidians as food. No detailed examinations were made of the damage caused by the gastro- pod and it was not possible to relate the oyster mortality to the abundance of the snail. The crown conch Melongena corona at times was a conspicuous element on the oyster reef at Station I and has been observed with the proboscis inserted into oysters. Gunter and Menzel (1957) first recorded the crown conch as an oyster predator. Hathaway (1957) and Menzel and Nichy (1958) concluded, however, that it is an oyster enemy of minor importance in this area. This gastropod has been discussed more recently by Hathaway and Woodburn (1961). The boring clam Martesia smiths does not feed on the oyster, but uses the shell as a habitat as do boring sponges and mudworms. Boring clams were most abundant at Station II in larger oysters. No correlation could be made with mortality or the condition of the oysters, although a more thorough investigation might reveal such association. The southern oyster drill Thais hacmastoma has been called the most serious oyster enemy in the Gulf of Mexico region (Butler, 1954). Mackin (1951b) states that where the drill occurs in abundance, along with the fungus parasite, Dermo cystidiutn marinum, the drill probably causes a higher proportion of the oyster mortality. The drill was abundant at Station III (Figure 7), but was found at no other station except for one drill at Station I. The importance of the drill as an ovster enemy at Station III has been discussed by Menzel, Hulings and Hatnaway (1957). The basket experiments at this station pointed strongly to predation as the cause of depletion of this reef. At Station III there were numerous Thais egg cases during the season of 1956, but none was found in the spring of 1957. Even more noteworthy is the fact that no small snails were collected in any of the samples. It appears from the sizes and the fouled and eroded appearance of the shells that all the snails were more than one year old. Growth rate of drills in this particular area is unknown. Ingle (1951b) found that drills increased 12.2 mm in height in 82 days at Coral Gables, Florida. Butler (1953) found that they can reach a height of 55 mm in five months after hatching; however, he found that some six-month-old drills were larger than those that were thirty-six months old. This would imply that some three-year-old drills are under 60 mm. The maximum age attained by the drill is not known. In the present study the average size as well as the ranges in size were about the same for the first year’s observations as for the second (Figure 7). The most likely explanation is that the drills on the reef were adult and were growing only slowly. It is evident from the lack of small drills that there was no recruit- ment from the surrounding population during the two years of the study. The reef was re-sampled on October 8, 1957, when the bottom salinity measured 8.5 °/oo, and a search of several square meters revealed one live drill buried under several centimeters of shells. This was an adult snail (ca. 60 mm in height) and the operculum was tightly closed. It is probable that a population of snails became established on 91 NUMBER | AVERAGE HEIGHT ■ Figure 7. Numbers and average heights (mm) of Thais haemastoma per square meter during sampling period. Range in size from 52 to 84 mm. 92 AVERAGE HEIGHT (mmJ this station when the salinity was favorable for them. Adult snails prob- ably survived the occasional lowering of salinity by closing the opercula. Butler (1953) found the snail to be limited by an average salinity below 15 o/oo. In addition many of the sessile animals that occur on an oyster reef probably have an adverse effect on oysters, especially in competition for food and space. For example, Engle and Chapman (1951) found that heavy attachment of mussels adversely affected the conditions of oysters. At the two high salinity stations, the oyster Ostrea equestris occurred. This species was often very abundant at Station III, sometimes making up half of the numbers of oysters. It was found in small numbers on the extreme lower edges of the reef at Station I. Menzel (1955) has shown that O. equestris is stenohaline and also that it is subtidal. It is noteworthy that O. equestris had disappeared entirely from Station III on the May 11, 1957 examination, nor were any found when the reef was re-sampled in October 1957. The two species of hooked mussels ( Brachidontes exustus and B. recurvus) are fairly good salinity indicators. B . exustus is confined to fairly high salinity, B. recurvus is more euryhaline (although it was less abundant at Station III than at Station 11, Table 5). The mud crab, Neopanope texana, was more abundant at the higher salinity stations and the same was true for the flat crab, Pctrolistbes armatus (Table 5). Some of the animals seemed to be limited more by other factors, such as bottom types and depth of water, than by salinity. Anachis obesa was more abundant at Station III than II, but it did not occur at Station I, perhaps because of the mud bottom, or the water depth, or both (Table 5). Mulinta lateralis was the only animal recorded exclusively from Station II, but its absence from other stations was probably due to factors other than salinity, since Simmons (1957) found this species in the Laguna Madre, Texas where the salinity is greater than normal oceanic waters. Gunter (1955) has shown that in Texas waters the mortality of oysters increases over a rising salinity gradient from the inner bays towards the sea. Our own studies show that oyster mortality at a given station increases as the salinity rises following dry weather conditions. Both studies lead to the conclusion that the euryhaline Virginia oyster is strongly affected by salinity changes, indirectly through salinity influences on its predators and parasites. Grave (1905) has previously noted that oysters are subject to greater predation and parasitism at higher salinities. Special Study of Station III The reef at Station III formerly produced market oysters, but it had become depleted in the five years or so before the present investiga- tion. A detailed report has been given by Menzel, Hulings and Hathaway (1957) of this station. Previous data on hydrographic conditions in the bay indicate generally lower salinities in the past than were found in this study (Table 2). The probable cause of the depletion of oysters at Sta- tion III was predation by animals with higher salinity requirements than oysters, notably stone crabs and drills. There was abundant spatfall. Some oysters, which were protected from large predators, reached a length of over 70 mm by the early spring of 1957 in contrast to unprotected oysters that were never larger than 50 mm in length (Figures 5, 6). 93 Station III was re-sampled on October 8, 1957. At this time one basket was recovered which had been left from the experiment begun in May 1956. In addition a random bottom sample of 24 liters was taken. The maximum size of the oysters found on the bottom and in the basket was no greater than it had been the previous spring. Rainfall had been continuous and rather heavy during the summer of 1957 and the salinity had undoubtedly remained low. The absence of Ostrea equestris and the presence of only one live Thais haem as tom a with tightly closed operculum (12 dead shells found) corroborate the above statement. The salinity at the time of sampling in October 1957 was 8.5 °/oo. From the evidence, predation during the summer period of 1957 may be largely discounted. The oysters should have reached larger sizes during this period than they had attained the previous spring. Because of growth, this reef should have supported a commercial fishery by the winter of 1957-58. It was predicted by Menzel, Hulings and Hathaway (1957), that with a return to normal rainfall, that the reef would become productive. St. Vincent Reef did become productive again, but no oysters of commercial size were obtained until the fall of 1958, one year later than expected. SUMMARY 1. A study was made of three oyster reefs of differing ecological conditions in Apalachicola Bay area during the period from June 1955 through May 1957. Periodic quantitative samples of oysters and associated macroscopic organisms were taken, with particular emphasis on known oyster enemies. 2. Samples were taken at approximately monthly intervals during the first year at all stations and during the second year, one station (sub- tidal with high salinity) was sampled monthly and the other two season- ally. 3. During the second year some oysters were protected from two of the known enemies, drills and stone crabs, by wire baskets at the station (III) with high salinity that was sampled monthly. The protected oysters showed less mortality and reached a greater size than the unprotected oysters at this station. 4. The numbers sizes and mortality of oysters and of the associated animals differed from station to station and could be correlated with salinity, the past salinity regime, type of bottom and depth of water. 5. Salinity seemed to be the most important limiting factor on the oyster populations, but the strongest influence is indirect in that low salinity precludes the presence of important predators. The overall salinity increased shortly before the present study, correlated with an extended drought, and allowed certain oyster enemies less resistant than oysters to euryhaline conditions to become established on reefs. The depletion of a formerly productive reef occurred when the enemies became established. With increased rainfall and lowered salinities, the reef regained its former productivity. ACKNOWLEDGEMENT The writers thank Dr. Philip A. Butler, Bureau of Commercial Fish- eries and the Florida State Board of Conservation for aid and suggestions. 94 LITERATURE CITED Allen, J. Frances. 1958. Feeding habits of two species of Odostomia Nautilus, July: 11-15. Butler, P. A. 1953- The Southern oyster drill. Proc. Natl. Shellfish, Assoc., 44: 67-75. — . . 1954. Summary of our knowledge of the oyster in the Gulf of Mexico. U. S. Fish. Bull., 89: 479-489. Danglade, E. 1917. Conditions and extent of the natural beds and barren bottoms in the vicinity of Apalachicola, Florida. Rept. U. S. Comm. Fish, for 1916. App. V: 1-68. Dawson, C. E. 1955a. A contribution to rhe hydrography of Apalachicola Bay, Florida. Publ. Inst. Mar. Sci., 1V(1): 12-95. 1955b. Observations on the incidence of Dermo- cystidium marinum in oysters of Apalachicola, Florida. Texas Journ. Sci. VII(l): 47-56. Engle, J. B. and C. R. Chapman. 1951. Oyster condition affected by at- tached mussels. Proc. Natl, Shellfish. Assoc., 42: 9 pp. Grave, Caswell. 1905. Investigations for the promotion of the oyster industry of North Carolina. Rept. U. S. Comm. Fisheries 29: 247-341. Gunter, G- 1942. Seasonal condition of Texas oysters. Proceedings and Transactions of the Texas Academy of Science, 26: 53-5 4. 1955. Mortality of oysters and abundance of certain associates as related to salinity. Ecology, 36(4): 601-605. Gunter, G., C. E. Dawson and W. J. Demoran. 1956. Determination of how long oysters have been dead by studies of their shells. Proc. Natl. Shellfish, Assoc., 47: 31-32. Gunter, G. and R. W. Menzel, 1957. The crown conch, Melongena corona , as a predator upon the Virginia oyster. The Nautilus, 70(3) : 84-87. Hathaway, R. R. 1957. The crown conch, Melongena corona Gmelin, its habits, sex ratios, and possible relationship to the oyster. Proc. Natl. Shellfish. Assoc., 48: 189-194. Hathaway, R. R. and K. D. Woodburn. 1961. Studies on the crown conch, Melongena corona Gmelin. Bull. Mar. Sci. Gulf and Caribb., 11(1) : 45-65. Hopkins, S. H. 1956a. Our present knowledge of the oyster parasite, ’‘Bucephalus”. Proc. Natl. Shellfish. Assoc., 47: 58-61. . , ... 1956b. Odostomia impressa prasitizing Southern oysters. Science, 124(3223): 628-629. Hopkins, S. H., J. G. Mackin and R. W. Menzel. 1953. The annual cycle of reproduction, growth and fattening in Louisiana oysters. Proc. Natl, Shellfish. Assoc., 44: 39-50. Hyman, Libbie H. 1940. The polyclad flatworms of the Atlanic Coast of the United States and Canada. Proc. U. S. Natl. Mus., 89: 449-495. Ingersoll, E. 1881. The oyster industry. U. S. Fish. Comm., 4: 1-252. Ingle, R. M. 1951a. Spawning and setting of oysters in relation to sea- sonal environmental changes. Bull. Mar. Sci. Gulf and Caribb., 1 (2); 111-135. 1951b. Notes on the growth of Thais haesmastoma jloridana and Thais rustica. Proc. Natl. Shellfish. Assoc., 42: 12-14. Ingle, R. M. and C. E. Dawson. 1950. Variations in salinity and its rela- 95 tion to the Florida oyster. Salinity variation in Apalachicola Bay Proc. Gulf and Caribb. Fish Inst.* 3; 35-42. * 1952. Growth of the American oyster, Crassos- trea virginica (Gmelin), in Florida waters. Bull. Mar. Sci. Gulf and Caribb,, 2(2): 393-404. 1953- A survey of Apalachicola Bay, Florida, State Board of Conservation. Tech. Ser. 10. Lunz, G. R. Jr. 1940. The annelid worm, Polydora, as an oyster pest. Sci. 92: 310. 1941. Polydora as an oyster pest in South Caro- lina water: J. Elisha Mitchell Sci. Sco., 57: 273-283. 1947. Callinectes versus Ostrea. J. Elisha Mitchell Sci. Soc., 63: 81. Mackin, J. G. 1951a. Incidence of infection of oysters by Dermocystidium marinum in the Barataria Bay area of Louisiana. Proc. Natl. Shell- fish. Asso., 42: 22-35. — , — 1951b. Diseases of oysters and their relation to the Gulf Coast oyster industry. Proc. Gulf and Caribb. Fish Inst., 3: 24 (abstract). — 1952. Histopathology of infection of Crassostrea virginica (Gmelin) by Dermocystidium marinum Mackin, Owen and Collier, Bull. Mar. Sci. Gulf and Caribb., 1(1): 72*87. Mackin, J. G. and F. F. Cauthron. 1952. Effects of heavy ionfestations of Polydora ivebsteri Hartman on Crassostrea virginica (Gmelin) in Louisiana waters. Proc. Natl. Shellfish. Assoc., 43: 14-24. Menzel, R. W. 1955. Some phases of the biology of Ostrea equestris Say and a comparison with Crassostrea virginica (Gmelin). PubL Inst, Mar. Sci., IV(1): 69*153. Menzel, R. W. and S. H. Hopkins. 1955. Crabs as predators of oysters in Louisiana. Proc. Natl. Shellfish. Assoc., 46- 177-184. Menzel, R. W., N. C. Hulings and R. R. Hathaway. 1957. Causes of oyster depletion in St. Vincent Bar, Apalachicola Bay, Florida. Proc. Natl. Shellfish. Assoc., 48: 66-71. Menzel, R. W. and F. E. Nichy. 1958. Studies of the distribution and feeding habits of some oyster predators in Alligator Harbor, Florida. Bull. Mar. Sci. Gulf and Caribb., 8: 125-145- Moore, H. F. 1897. Report of the specimens collected from the oyster beds of St. Vincent Sound, Apalachicola Bay and St. George Sound, Florida, during the winter of 1895-96. Rept. U. S. Comm. Fish, for 1896: 218-221. Owen, H. M. 1957- Ethiological studies on oyster mortality. II Polydora vuebsteri Hartman - (Polychaeta: Spionidae). Bull. Mar. Sci. Gulf and Caribb., 7(1): 35-46. Pearse, A, S. and G. W. Wharton. 1937. The oyster "leech”, Stylochus inimicus Palombi, associated with oysters on the coasts of Florida. Ecol. Monogr., 8: 605-655. Ray, S. M. 1954. Biological studies of Dermocystidium marinum, a fun- gus parasite of oysters. Rice Institute Pamp., Special Issue. 1-114. Simmons, E. G. 1957. An ecological survey of the upper Laguna Madre of Texas. Publ. Inst. Mar. Sci. (Univ. Texas), IV<2): 156-200. Swift, F. 1897. Report of a survey of the oyster regions of St. Vincent Sound, Apalachicola Bay and St. George Sound, Florida. Dept. U. S. Fish. Comm, for 1896: 187-217. 96 Gulf Research Reports Volume 2 Issue 2 January 1966 Habits ofjuvenile Fishes in Two Rhode Island Estuaries Mohammed Saeed Mulkana DOI: 10.18785/grr.0202.02 Follow this and additional works at: http:/ / aquila.usm.edu/ gcr O Part of the Marine Biology Commons Recommended Citation Mulkana, M. S. 1966. Habits ofjuvenile Fishes in Two Rhode Island Estuaries. Gulf Research Reports 2 (2): 97-167. Retrieved from http://aquila.usm.edu/gcr/vol2/iss2/2 This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized administrator of The Aquila Digital Community. For more information, please contact Joshua.Cromwell(S)usm.edu. The Growth And Feeding Habits of Juvenile Fishes In Two Rhode Island Estuaries by MOHAMMED SAEED MULKANA 97 TABLE OF CONTENTS Page ABSTRACT 100 LIST OF FIGURES . . 101 LIST OF TABLES - 102 I. INTRODUCTION — 103 II. REVIEW OF THE LITERATURE 106 III. METHODS AND MATERIALS . - 107 IV. THE ENVIRONMENT .. - 109 A. Topographic and Edaphic Features 109 1. Topography 109 2. Hydrographic zones 110 3. Edaphic and biological aspects Ill B. Hydrography ..... 113 1. Salinity „ 113 2. Temperature 113 V. RESULTS 116 A. Occurrence and Abundance of Fishes 116 1. Total Abundance 116 2. Population Components .... . 116 3. Relative Abundance ... 121 4. Horizontal Distribution . 127 B. Growth .... 129 1. Pseudopleuronectes americanus .... 129 2. Brevoortia tyr annus - .. , r * 131 3. Menidia menidia . 132 C. Food and Feeding Habits 136 1. Pseudopleuronectes americanus .... 136 2. Menidia menidia 146 3. Brevoortia tyrannus 153 D. Predators and Parasites 156 VI. DISCUSSION .... 157 VII. SUMMARY . .... 162 VIII. ACKNOWLEDGEMENTS 163 IX. BIBLIOGRAPHY 164 99 ABSTRACT The basic purpose oj this work was to gain information on the possible role of some Rhode Island estuaries as nursery grounds for young migrant and resident species of fishes. The areas selected were , the lower Pettaquamscutt River and the lower Point Judith Pond, both in the town of Narragansett , Rhode Island. The seining operations were carried through summer and early fall of 1962 when these estuaries are heavily used as nursery grounds. Major features of the occurrence , abundance and distribution of young fishes were deduced by examining samples from seine hauls. Thirty- six species were recorded from the lower river while only twenty-four species occurred in the lower pond. The abundance of fishes rose with a rise in tempera- ture and declined with decreasing temperature, but no correlation was observed between maximum temperature and maximum number of individ- uals occurring at any time. The number of species and the abundance of individual fish were highest at the seaward station (St a. II) in the lower river. Among the selected species , the abundance of Menidia menidia was two to three times higher at Middle Bridge (Sta. II) than at any other station. The behavior of Pseudopleuronectes americanus, found primarily at seaward stations, and the migrant species Brevoortia tyrannus observed at landward stations, is discussed. The species P. americanus grew at the rate of 10 mm per month, but exhibited no variation in gro wth in the two estuarine systems. The popu- lations of B. tyrannus from the lower Pettaquamscutt River had a growth rate that was almost twice that of populations in the lower Point Judith Pond. The growth rate of these species in Rhode Island waters compare favorably with similar data from other studies. The juvenile M. menidia demonstrated a higher rate of growth at seaward stations in both the areas, especially in the lower river. forty-three types of prey organisms belonging to diverse taxonomic groups were identified from stomach contents of P. americanus and thirty- nine types were noted in the gut contents of M. menidia. Analysis of the degree of fullness indicated markedly high percentage of full stomachs in the two study areas. However the degree of fullness was comparatively less in fish occurring in the lower pond. The scarcity of food in the lower pond, apparently forced M. menidia (51-80 mm) to feed upon phytoplank- ton as a substitute food or " forced diet”. In P. americanus and M. menidia a change in diet was noted with change in size. The taxon, B. tyrannus, which depended upon phytoplankton and suspended organic matter, did not show any change in food with change in body size. While no effective predation was observed, an infection by the sporo- zoan parasites, Glugea hertwigi, was marked in both Osmerus mordax and P. americanus. Low catches of P. americanus were perhaps due to higher infection. A comparison of the parameters of abundance, growth and food habits reveal that the two estuarine systems are suitable nursery grounds, and that the lower river is a more favorable nursery than the lower pond. 100 LIST OF FIGURES Figure Page 1. Map of Pettaquamscutt River estuary showing location of seining stations — 104 2. Map of Point Judith Pond estuary with locations of seining stations - * — 105 3. The distribution of hydrographical zones in the Pettaquaras cutt River and the lower Point Judith Pond — 112 4. Surface and bottom salinities recorded from July 11 to Octo- ber 20, 1962 in the lower Pettaquamscutt River and in the lower Point Judith Pond 114 5. Surface and bottom salinities recorded from the lower Point Judith Pond — 115 6. Surface temperature measurements recorded from July 11 to October 20, 1962 in the lower Pettaquamscutt River and in the low T er Point Judith Pond .... 117 7. Variations in the total abundance of fishes and temperature at weekly intervals in the lower Pettaquamscutt River and the lower Point Judith Pond , 120 8. Variations in abundance of migrant and resident species of fishes at weekly intervals in the lower Pettaquamscutt River and in the lower Point Judith Pond - — r — - — 122 9. Variations in the weekly catches of Menidia menidia during the summer and early fall of 1962 at four seining stations 124 10. Variations in weekly catches of Pseudopleuronectes ameri - canus and Brevoortia tyrannus in the lower Pettaquamscutt River j -r- - ... 125 11. Variations in weekly catches of Pseudopleuronectes ameri - canus and Brevoortia tyrannus in the lower Point Judith Pond 126 12. The class size (in cms) distribution of the selected species at four seining stations . _ 128 13. Test of the significance of the differences of average weekly growth of Pseudopleuronectes americanus collected from the lower river and the lower pond stations 130 14. Comparison of the average growth data of Brevoortia tyrannus Collected from the lower pond the lower river stations 133 15. Comparison of the average growth data of Menidia menidia caught at the lower river stations 135 16. Comparison of the average growth of Menidia menidia caught at the lower pond stations «. 137 17. Growth rates of the three selected species caught at the lower river stations .. . 138 18. Growth rates of the three selected species caught at the lower pond stations - 139 19. Variations between different size groups of juvenile Pseudo- pleuronectes americanus and the size of the prey organisms 145 20. Variations between different size groups of Menidia menidia and the size of the prey organisms found in the lower river 152 21. Variations between different size groups of Menidia menidia size of the prey organisms and the dietary shift noted in population at the lower pond stations 154 101 LIST OF TABLES Table Page I A summary of occurrence and distribution of juvenile and adult fishes collected from four seining stations in lower Pettaquamscutt River and lower Point Judith Pond, Rhode Island, during July 11 to October 20, 1962 118 II. Relative abundance of the Major species in order of their ranks with respect to all species collected from July 11 to October 20, 1962 from the lower Pettaquamscutt River and the lower Point Judith Pond, R. I. 123 III. List of food organisms of juvenile Pseudopleuronectes ameri- canus from the lower Pettaquamscutt River (Stas. I and II combined), and the lower Point Judith Pond (Sta. IV only), including average number per stomach (A/S), percentage frequency of occurrence (PF), size groups of juvenile fish (in mm) and prey size _ 140 IV. Variations in relative degree of stomach fullness of three sizes (in mm) of Pseudopleuronectes americanus collected from the lower Pettaquamscutt River and the lower Point Judith Pond. Table includes number and percentage of stomachs with or without food 144 V. List of food organisms of juvenile and adult Menidia menidia from the lower Pettaquamscutt River (Stas. I and II com- bined) and the lower Point Judirh Pond (Stas. Ill and IV combined) including average number per gut (A/G), per- centage frequency of occurrence (PF), size groups of the fish (in mm) and size of the prey species 147 VI. Variations in relative degree of gut fullness in three size classes Menidia menidia in lower Pettaquamscutt River and lower Point Judith Pond . ... ... 151 VII. The average volume and number of cells per gut in various class sizes of Menidia menidia that ate only phytoplankton in the lower Point Judith Pond 153 VIII. Variations in the relative degree of stomach fullness in three sizes (in mm) of juvenile Brevoortia tyrannus from lower Pettaquamscutt River and lower Point Judith Pond 155 IX. Number and percentage of juvenile Pseudopleuronectes americanus infected with Glugea hertwigi collected from the lower Pettaquamscutt River and the lower Point Judith Pond 156 102 I. INTRODUCTION The purpose of this work was to evaluate selected Rhode Island estuaries as nursery grounds for juvenile fishes. The juvenile stage in the life history of fishes follows the emergence from larval life to an inde- pendent young phase. At this stage survival becomes dependent on physio- logical and morphological fitness, availability of suitable types of food, and protective adaptations to minimize predator and parasite invasion and over-population pressure. The immature young of coastal and offshore fishes of many species spend their critical juvenile period in protected, food-rich estuaries. Often the success of stocks in a fishery is dependent on the presence of areas suitable as nursery grounds. Greely (1939), Warfel and Merriman (1944) and Pearcy and Rich- ards (1962), who studied the seasonal variations and ecology of juvenile and adult fishes along the New England Coast, and Shuster (1959) who conducted similar investigations in Delaware Bay estuaries, all reported a great abundance of fish-of-the-year of various species in the shallow waters of coastal ponds, estuaries, and bays. Fish's (1938-42 unpubl.) observations in Rhode Island waters point to the same conclusions. Infor- mation from all of these sources provides strong evidence that estuarine environments play a vital role in the survival and maintenance of stocks of the coastal and offshore fisheries of commercial significance. The present work is an attempt to gain information on the role of two estuaries in Rhode Island as nursery grounds for young fishes of coastal and offshore species. Emphasis was laid on the seasonal changes of young fish populations with respect to their total and relative abund- ance and distributional patterns. An idea of the success of these estuaries as nurseries was gained through growth studies and analyses of the feeding habits of three species, the winter flounder, Pseudopleuronectes americanm, the Menhaden, Brevoortia tyr annus, and the Silversides, Menidia menidia. These species in general are benthic, pelagic and omnivorous respectively in behavior and food habits. The diverse feeding habits should provide information on the overall available food present in an environment. The average growth rate of these species should be a function of the success of the feeding niches occupied by these species. The coast of Rhode Island has a series of salt ponds and estuaries lying both parallel and perpendicular to Rhode Island and Block Island sounds. By definition (Emery et. al., 1957) coastal ponds or lagoons are former embayments which have been partially isolated from coastal waters by barrier sand bars. Some estuaries, especially along the shores of south- ern New England, represent drowned glacial outwash stream valleys. Roch- ford (1951) described estuaries as bodies of water in which chlorinity and salts and other properties are subjected to an alteration by inflow of fresh water and sea water in certain ratios during the tidal cycle. Further there exists a persistent circulation and exchange between the estuarine system and adjoining neritic waters. The present studies were conducted in certain areas of the Petta- quamscutt River and Point Judith Pond estuaries in the town of Narra- gansett, Rhode Island (Fig. 1 and 2). The area under study in the lower Pettaquamscutt River lies within a "gradient zone", a zone having a dis- tinct salinity gradient. The seining stations in Point Judith Pond were 103 Fig. 1. Map of Pettaquamscutt River Estuary showing location of seining stations. 104 Fig. 2. Map of Point Judith Pond Estuary with locations of seining stations. 105 located in the lower pond, characterized as the 'marine zone” according to Rochford (1951) where near-neritic conditions exist. The river estuaries are generally considered more productive than coastal ponds and lagoons (Riley, 1937; Rochford, 1951 and Emery et al, 1957). Consequently the diverse environmental conditions existing in the two estuarine systems should provide an opportunity to study the varia- tions in abundance, average growth of young fishes and the available food in the particular feeding niches of selected species of fishes. In de- scribing the overall occurrence and abundance of juvenile fishes some parameters for the adults of some of the smaller resident species also were included. These fishes though of no direct commercial importance, play a significant role as a food supply, as special competitors and as predators for other juvenile species of economic significance in the estuaries. II. REVIEW OF LITERATURE Fluctuations in fish populations have been an important concern to man since neolithic times. The pursuit of knowledge through biological investigations long remained directed towards the study of adult fishes. Early studies by Jordan (1896-1900) in North and Middle America, Smith’s (1898) investigations in the Woods Hole region, and Tracy’s (1906, 1910) work in Rhode Island water all pertain to the occurrence and systematics of regional fish fauna. Quantitative studies of young fish started recently in these areas. Hjort (1926) theorized that the numerical prominence of a year class is determined at a very early stage. Hjort’s early methods and attempts to determine spawning and nursery areas brought him to the conclusion that fishes early in their life histories tend to localize in particular ecologi- cal habitats. Greely’s (1939) investigation in the estuaries, creeks and oceanic inlets in Long Island Sound during the summer led him to assume that these environments may not constitute spawning areas for various species but are important rearing grounds for young fishes from remote spawning centers. The results of the analysis of seasonal abundance and distributional patterns of young and adult fishes by Warfel and Merriman (19 44) in southern New England waters point to the direct influence of temperature on immigration and emmigration of migrant species. The results manifest that factors like population density, age, depth and meterological condi- tions probably determine the distribution of young fishes. Adolf (1925) found that marine organisms can tolerate drastic changes in the osmotic environment more effectively than fresh water forms. Horton (1958) observed strictly marine forms in fairly brackish water environments in the upper reaches of the Pettaquamscutt River, Rhode Island, indicating that young marine immigrant species may successfully thrive in all of the salinity regimes in an estuary. Based upon the ecological studies of larvae, juvenile and adult fishes of the Mystic River estuary, Pearcy and Richards (1962) contended that estuaries may be important as spawning grounds, nurseries for juvenile fishes and feeding grounds for adult forms of resident and migrant species. Hiatt and Strasbury (I960) analysed the relationship for 233 species of fishes in many diverse types of ecological niches in the coral reefs of the Marshall Islands. Their description of feeding types illustrates the 106 feeding habits and food requirements of fishes that utilize energy from different trophic levels. While this detailed study attempted to explain self-adjusted steady state equilibria existing in great varieties of reef habitats, the principles deduced may also be applicable to ecosystem studies in estuarine environments. Richards (1963) studying the feeding ecology of juvenile fishes in Long Island Sound, indicated that sporadic immigra- tion of migrant species may not cause interspecific competition if super- abundant and well distributed food is present. Richards suggested that the mobility of prey and predator species common in a temperate marine environment, such as Long Island Sound, is an important factor indicative of the success of the various feeding niches. Ivlev’s (1954a) investigation on the ecology of the feeding habits of fishes showed that with an increase in available food, the daily ration approaches a maximum ration. The application of this principle suggests that in an environment with ample food, young fishes are attracted whose fast early growth may require large quantities of food. Ricker (1946) reports that small fish eat more per unit body weight than large fish, hence the rate of feeding could affect the size of the fish. Pearcy (1962) conducted studies on the quantitative aspects of abundance, growth, survival and mortality of larvae and juvenile stages of Pseudapleuronectes americanus in the Mystic River Estuary. Com- paring the biomass and productivity measurements of the Mystic River Estuary with that of Long Island Sound, he concluded that some estuaries are more productive than some neritic environments and serve as nursery areas for young fishes. Shuster (1959) working on the biological evalua- tion of the Delaware River Estuary points out that estuaries are important spawning and nursery areas and contribute effectively to the economy of the coastal fisheries. III. METHODS AND MATERIALS Stations: The selection of the stations was based upon Fish’s results (1938-42 Unpubl. ) of seining operations in the lower Pettaquamscutt River and certain other ponds and estuaries in Rhode Island, easy access from the shore and maximum seining area available with practicable depth. Two stations were established in the lower Pettaquamscutt River and in the lower Point Judith Pond about three kilometers apart (Figs. 1, 2). The seining operations were carried out in the lower Pettaquamscutt River at the Bridgetown Bridge (Station I), and at the Middle Bridge (Station II); and in lower Point Judith Pond at Harbor Island (Station III) and at Galilee (Station IV). For brevity in the following account the study areas in each of the estuaries will be referred to as '’lower pond” (lower Point Judith Pond) and "lower river” (lower Pettaquamscutt River). Seining Operations: Seining was carried out at selected stations only during the ebb tide. A fifteen- meter-long, shore seine with quarter-inch (6.4 mm) mesh was employed. Within the center of the seine a square of 1 mm mesh netting (2m x 2m) was fastened to ensure capture of small fishes. The seine was fished parallel to the shore from low water mark to a point 15m perpen- dicular to the shore, and was swept for 15m in either direction. At the end of each seine haul a capture arc was formed and the lower weighted end was drawn first thus pursing the seine to retain the catch. A strictly identical seining procedure was followed throughout the survey period. From the seine hauls numerical abundance of all species was noted. 107 Preservation: A subsample of at least thirty randomly selected specimens of the more abundant species of fishes were retained for further analysis. The fishes were placed in 2% formalin. The formalin concentration was slowly increased to 10%. The procedure allowed the formalin to diffuse into the alimentary tract to stop further digestion and subsequent decomposi- tion of the gut contents. Abdominal cavities of some fishes of selected species were incised before final preservation. The formalin was saturated with sodium tetraborate (Na 2 B 4 0 7 ) or calcium carbonate (Ca Co 3 ) to neutralize the acid and to keep the gut contents softened for identification. Temperature: Surface water temperature was measured at each station weekly 5 meters from the shore during ebb tide using a mercury thermometer to the nearest 0,2 °C. Salinity: Surface and bottom salinity was determined by a conductivity method each week, using an electronic salinometer designed and built by J. T. Conover. Bottom water samples were taken with a sampler consisting of a polyethylene tube stoppered at both ends and equipped with a glass tube at the lower end. The salinity of a series of surface and bottom water samples was determined along the north-south axis of both estuaries at ebb and flood tides, during one 24-hour tidal cycle on July 21, 1963. From these data salinity ratios during a complete tidal cycle were computed to aid in the zoning of the estuaries after Rochford (1951). Precipitation: Rainfall data were obtained from the Monthly Climatological Sum- mary of the New England Region compiled by the U. S. Weather Bureau. The rainfall recorded by the Weather Bureau at the Hillsgrove Municipal Air Port in Providence, was used for both estuaries. Identification and Counta: Fishes from each sample were identified and counts were recorded and used to determine total and relative abundance. Two species, Pseu - dopleuronecies americanus and Brevoortia tyrannus, which occurred in significant numbers and have economic importance, and a most abundant small species, Menidia me nidi a, were selected for a detailed study. These fishes have diverse food habits and provide a good trophic picture of the environment. Age Groups: The separation of the young of the zero plus class of P. americanus and B. tyrannus presented no problem since the criterion of standard length, distance from snout to hypeural plate alone, is a reliable tool to distinguish zero group from older groups in these species (Pearcy, 1962, and McHugh et at., 1959)* To confirm this assumption for P. americanus in the separation of age groups, scales and otoliths were examined following the annulus interpretation given by Welsh (1924), Berry (1959) and others. For an interpretation of scales of B. tyrannus the writer followed criteria laid down by Hile (1948), Westman and Nigrelli (1955) and McHugh et al. (1959). No reliable information is available for the exact size range of the zero age group for Menidia menidia. Williams (I960) 108 considered fish of second year class as above the minimum size of 50 mm. The juvenile fish could be distinguished during early summer, but in late summer and fall an admixture of young and adult fish of overlapping size groups made it impossible to distinguish the young from the adults. The data were analysed by a graphical method (see below) which gives the size range and demonstrates the possible growth in such groups. Growth Computations: In view of marked fluctuations in the sample sizes of the selected species, the data were processed and computations made using an improved graphical method by Hubbs and Hubbs (1953) based upon an analysis of variance. Graphical analysis demonstrates the significance of differences between the series of samples as well as the degree of reliance on the results. The average values of standard lengths for the selected species were used to draw growth curves. For complete detail see legend for figure 13. Food Analysis: The food study was based on an analysis of stomach contents. It is, however, important to couple such studies with a determination of the types and abundance of food present in the environment. Due to the preliminary nature of the present work and to the time factor only stomach contents were considered in this study. The food present in a stomach is in a less advanced state of digestion than in the intestine and permits better identification. In the absence of a well defined stomach as in the case of Menidia menidia, gut contents were used for food analysis. The following methods were employed for food study: 1) The occurrence method determines the palatibiliry of food (Allen, 1935 and Hartley, 1947). 2) The average stomach content method demonstrates the relative importance of individual prey species (Covill, 1959 and others). 3) The fullness method is a special extension of total volume method and estimates variation in quantity of food in various size groups, areas and seasons. The size of each food organism was also measured using an ocular micrometer. All collections of each selected species from each estuary were combined, and a sample of 150 fish was taken randomly for food analysis. Fishes were categorized in three arbitrary size groups to find variations in food with respect to sizes of fishes. A fair number of stomachs or alimentary tracts from each size group, depending upon the number available, were individually dissected, the contents identified and counts made in a Sedgewick-Rafter cell or a larger improvised counting chamber under 60 X magnification. Later on stomachs or alimentary tracts were grossly studied in groups Gf ten. In the case of Menidia menidia collected from the lower Point Judith Pond, the volumes of gut contents of various size groups were determined. The gut contents which were comprised entirely of phytoplankton, were diluted, and from aliquots the number of organisms per cubic millimeter was determined. IV. THE ENVIRONMENT A. Topographic and Edaphic Features 1. Topography. The Pettaquamscutt River Estuary represents a drowned river valley 109 in the post-glacial topography of a coastal plain. From its source at Pausacaco Pond in North Kingstown, the estuary extends southerly for 9 kilometers to its mouth which discharges into West Passage of Narra- gansett Bay. Near Sprague Bridge an arm of this estuary extends for 2.1 kilometers in a southwesterly direction ending blindly as the very shallow Pettaquamscutt Cove. The north-south axis of this estuary lies between latitude 4l°26'N and 4l°3rN and at longitude 71°27'30”W (Fig. 1). The river is 6 meters to 0.8 kilometers broad and has a narrow constricted mouth facing southeast. The interesting and unusual features of this estuarine system are the presence of two deep stagnant basins north of the Bridgetown Bridge which are separated from the rest of the estuarine system by shallow sills. These are kettle holes, filled with stagnant high- salinity water. Only the surface water, a few meters deep, undergoes a change in salinity during the tidal cycle. Mixing into the stagnant zone may occur when strong hurricane winds roil the river water (Jeffries and Smayda, 1954; Horton, 1958). The Point Judith Pond is one of the Largest salt ponds along the coast of Rhode Island, measuring 6.3 kilometers from the breachway at Block Island Sound to Silver Spring Cove and from 90 meters to 2.1 kilo- meters in width (U. S. Geological Survey, 1957). The boundaries are located between 4V22' and 41*27’N latitudes and 71 3 29’ and 71°32‘W longitudes (Fig. 2). The Saugatucket River drains into the upper Pond which opens through a narrow constricted passage, "The Narrows,” into the considerably larger lower Pond. The flow of river in the lower pond is considerably less in camparison to the river inflow in the river estuary, since there is no significant salinity gradient in the greater part of the pond (Fig. 3). The lower pond is linked to Potter Pond through a narrow stream facing west and discharges southerly in Block Island Sound through the Point Judith Harbor of Refuge. The tidal flats, small coves, bars, shoals and islands are the chief topographical features in the pond estuary. Tidal amplitudes and currents in this estuary are strongly influ- enced by the presence of breakwaters, jetties and the irregularity of shore line and bottom contours. 2. Hydrographical Zones. Based on the salinity conflict (modified from chlorinity conflict) after Rochford (1951), the estuaries were classified into various zones, following Rochford’s assumption that ecological variations in these zones were characteristics of these environments in any estuary. Four zones were identified in the Pettaquamscutt River estuary. a) ''Marine Zone.” The salinity ratio at ebb and flood observed during a tidal cycle was 1:1. According to Rochford (1951) the absence of a salinity conflict, a ratio of change, during a tidal cycle in an area helps categorize it as a "marine zone.” This zone lies between the entrance from the West Passage to Sprague Bridge (Figs, 1 and 3). b) "Tidal Zone.” This zone marks the development of slight changes in salinity from ebb to flood tide and has maximum development of intertidal mud flats, and very shallow areas. The area between the northern boundary of Pettaquamscutt Cove to a kilometer towards Middle Bridge (Sta. II) has a salinity ratio of 1:1.1. In addition, Pettaquamscutt Cove having extensive intertidal mud flats, a characteristic feature of a tidal zone, may also be considered within the same domain. 110 c) "Gradient Zone.” This zone demonstrates a maximum salinity conflict in this estuary, with a ratio of 2:3. The limits of this zone extend from the vicinity of Middle Bridge to the entrance of Gilbert Stuart Brook (Figs. 1 and 3). The lower portion of the river in this zone has a com- paratively narrow channel, a characteristic feature of such a zone (Rich- ford, 1951). The deep saline pockets, represented by kettle holes do not ordinarily disturb the gradient, since the water below the sills, a few meters deep, remains uninfluenced by the tidal cycle, d) "Fresh Water Zone”. No saline water is present in this zone. The entire Gilbert Stuart Brook system was considered as the fresh water zone (Fig. 3). Only two zones could be defined in the lower Point Judith Pond. The area is dominated by the "marine zone.” The salinity ratio found between ebb and flood tide was about 1:1, characteristic of this zone. In the Upper Pond the gradient and fresh water zones are present, but so constricted or small in area as to be of little importance to the estuary as a system. The lower pond however has a series of coves with well-developed extensive intertidal mud flats. 3. Edaphic and Biological Aspects. Pettaquamscutt River , The area involved in this study lies within the "gradient zone” (Fig. 3) extending from Bridgetown Bridge (Sta. I) to Middle Bridge (Sta. II). The depth in the mid-channel at low tide is about 2 meters at Station I and 2.5 meters at Station II. The depth at the seining area of Station 1 varied between 0.6 m and 1.5 m. The depth at Station II was between 0.6 m and 1.2 m. McMaster (1953), in describ- ing the bottom topography of the estuary from Bridgetown Bridge to Middle Bridge, indicated that the bottom near the Bridgetown Bridge is sandy with isolated patches of silty sand w'hich changes to a mixture of soft silty sand and mud near the lower bridge (Sta. II). Sparse beds of Zostera marina occur near Bridgetown Bridge and increase in abundance down the river towards the lower station. South of Middle Bridge the bottom is composed of soft silty sand and thick stands of Zostera marina. The Eel grass becomes heavily epiphytized during the warm season. The Lower Point Judith Pond. The seining stations located within the lower pond characterized as "marine zone” extend from the Bluff Hill Cove to Harbor Island (Figs. 2 and 3). The depth in this area varies be- tween 0.6 m and 3 m. The depth at seining Station III, Harbor Island, varied between 0.6 m and 1.5 m, while at Galilee (Sta. IV) it was between 0.6 m and 1.2 m. Although the breakwater riprap minimizes the effect of waves, the north-south axis of the lower pond is markedly influenced by fast water circulation because of nearness to the open ocean. The bottom along the channel is rocky or sandy, except for inlets and coves. Along the east side of the lower pond, from Harbor Island southward, the bottom is lined with coarse sand, pebbles and cobbles especially near the shore lines of the islands centrally located in the pond basin. The Harbor Island Station has massive plant beds including Entermorpha linza, Scyto- siphon lomentaria, Viva lactuca, Eucus vesiculosis as well as minor plant species. The plants serve as a protection for young fish against predators and the epibiota are probably an important food source. At the lower extremity of Bluff Hill Cove (Sta. IV) the bottom consists of soft clayey silt with a high organic content which gives away to a silty sand towards the breachway. The plant life is sparse and the area is comparatively much shallower than that of the Harbor Island station (Sta. III). Ill z 5 24 w 20 ' o.5 mile ’ SAMPLING STATIONS AVERAGE SALINITY AT FLOOO TIDE AVERAGE SALINITY AT EBB TIDE Fig. 3- Distribution of hydrographical zones in Pettaquamscutt River and the lower Point Judith Pond estuaries (after Rochford, 1951). LEGEND FOR FIGURE 3. The area between the arrows in each graph indicates the study areas in the two estuaries. The stations marked with asterisks represent deep basins separated from one another and from the rest of the estuary by shallow sills. The vertical salinity gradient below a few meters in depth demains stable, and stagnant conditions exist in these salt pockets (Jeffries and Smayda, 1954; Hicks, 1958). Data for the bottom water were taken from samples at three meters depth in these basins; consequently, the differences in the salinity ratios at ebb and flood tide were much smaller than they would have been if the high salinity water in the kettle holes had been considered. The water samples were taken on July 21, 1963. which had followed a long draught period (Climatological Data from New England Region, U. S. Weather Bureau). The salinity values shown are abnormally high as compared with average salinity data in these areas (Jeffries and Smayda, 1954; Hicks, 1958; Horton, 1958). 112 B. HYDROGRAPHY 1. Salinity. A strong salinity gradient was observed in the lower Pettaquamscutt River, while conditions in the lower Point Judith Pond were almost neritic (Figs. 3 and 5). Considerable variations in salinity occurred especially in the lower river, the difference between 9.8 and 15.1 o/oo. The brack- ish water conditions exist at this station because of its nearness to a fresh water source. The range in salinity noted at the more seaward station (Sta. II) was highest, varying between 20.3 to 32.3 °/oo. The abrupt fluctuations in salinity were apparently caused by heavy precipitation during early September and October (Fig. 4). The rate of inflow of fresh water which depends upon seasonal precipitation is assumed to be the major factor influencing changes in salinity. Strong or hurricane winds very infrequently produce a significant increase in salinity by stirring up stagnant water from the upper basins (Jeffries and Smayda, 1954; Horton, 1958). The Point Judith Pond estuary while it is narrow at the transition, the breechway, broadens considerably in the mid-region. The surface and bottom salinities in the lower pond, though not markedly diverse, indicate an apparent vertical stratification because of probable net non- tidal drift upstream at the bottom and net non-tidal drift downstream at the surface. The Point Judith Pond is a shallow estuary. Stommel and Farmer (1953) indicated possible overmixing in such estuaries, and sug- gested that salinity in the upstream is determined by the throttling action of the narrow transition. In the lower pond which covers three-fourths of the entire pond, the seasonal salinity variation never exceeded more than 2 o/oo at the two extremities (Sta. Ill and Sta. IV). The seasonal surface salinity at Harbor Island ranged between 28.5 to 31.5 o/oo. The narrow range and low variations compared with those observed in the lower Pettaquamscutt River suggest that the salinity regime of the lower pond is greatly influenced by neritic waters. Furthermore the fluctuations in salinity in the lower pond were also correlated with the precipitation (Fig. 5). 2. Temperature. The surface temperature measured during summer and early fall at both stations in the lower river ranged between 23.8°C and 14.2°C. The temperature remained comparatively high in October at the Middle Bridge station perhaps because of the shoalness of the area (Fig. 6). The maxi- mum temperature values were observed in August and the minimum in October. The temperature in the lower pond maintained a fairly constant level until September 14. The seasonal range in temperature varied be- tween 24.2°C to 14.2°C. The decrease in temperature was rapid from mid September to the last sampling date in October. Although the seaward station in the lower pond is shallower, no marked variation in temperature was apparent between the two stations (Fig. 6). The fast renewal of water, and near shore conditions may be factors in support of this con- stancy. The seasonal fall in temperature compared well with data from other New England estuaries such as Great Pond, Falmouth (Conover, 1958). 113 Fig. 4. Surface and bottom salinity (in o/oo) at stations I and II in the lower Pettaquamscutt River from July 11 to October 20, 1962. The vertical bars indicate rainfall in centimeters. 114 Fig. 5. Surface and bottom salinity (in o/oo) in the lower Point Judith Pond from July 11 to October 20, 1962. The vertical bars indicate rainfall in centimeters. 115 V. RESULTS A. Occurrence and Abundance of Fishes The juveniles and adults of forty-one species of fishes were collected from July 11 to October 20, 1962 in the lower Pettaquamscutt River and in the lower Point Judith Pond (Table I). Migrants of diadromous species contributed largely to the total number of species observed during the survey period. Thirty-six species occurred in the lower Pettaquamscutt River and twenty-four were recorded from the lower Point Judith Pond. Horton (1958) has reported juveniles and adults of 15 additional species of fishes from upper Pettaquamscutt River. His report includes the addi- tional marine forms, Hyporhamphus unifasciatns, Pallachim virens, Gadns callarias, Trinectes maculatus , Selene vomer , Seriola zonata, Alectis ciliaris, Tracbinotus falcatus, T. carol 'mus and Roccus saxatilia , and the fresh water taxa Ameiurus nebulosus, Esox niger, Vundalm diaphnus , and Perea jlavescens. The species, hucania parva, recorded from ail four stations and Tracbmocepbalus myops collected at Bridgetown Bridge (Sta. I) have not been previously reported from Rhode Island estuaries or coastal ponds. The abundance and distribution of young fishes have been described under the appropriate headings below. 1. Total Abundance. Total abundance represents the total number of juvenile and adult fishes captured at weekly intervals in each estuary (Fig. 7). The most significant observation in the lower Pettaquamscutt River was the appear- ance of the largest number of individuals in late July with pronounced pulses in August and a gradual decrease in numbers until the end of the seining operation in October (Fig. 7). Variations in the total catches for each sampling period were influ- enced by the five dominant species Menidia menidia, Pundulus beteroclitus, F. majalis, Apcltes quadracus and Cyprinodon varie gains. Populations of Brevoortia tyrannus appeared at irregular intervals and when present, this species comprised the major taxon in the catches. Merriman (1947) and Shaw (I960) reported that B. tyrannus appears either in large numbers or not at all in a given habitat at any one time because of its precise schooling behavior. In the lower Pond a single major pulse in total abundance of young fish occurred during late August followed by a fast decline in late October. Although the fluctuation in total abundance in both estuaries differed, one feature common to both areas was a rise in total abundance during the greater part of August, followed by a marked decline during the rest of the survey period. 2. Population Components. During the warm season there was a complex influx into the estuaries of young fishes from two sources, the heads of the estuaries and the coastal and offshore waters. As a consequence it was necessary to group the fish populations into various components. The term ''component” here is used to designate various types of migratory and resident groups. On the basis of information from reports of Bigelow and Schroeder (1953) and Pearcy and Richards (1962), Wheatland (1956) and Merriman and Sclar (1956) 116 Fig. 6. Surface temperature at four seining stations in the lower Petta- quamscutt River and the lower Point Judith Pond from July 11 to October 20, 1962. 117 Table I. A summary of occurrence and distribution of juvenile and adult fishes collected from four seining stations in lower Pettaquams- cutt River and lower Point Judith Pond, Rhode Island, during July 11 to October 20, 1962. Number of Stations fishes collected Number of recorded species Salinity Range o/oo I. Bridgetown Bridge 1705 27 9.8 - 15.1 11 . Middle Bridge 6987 30 20.3 - 32.1 III. Harbor Island 5049 23 28.05- 32.6 IV. Galilee 5219 17 28.05- 31.5 MARINE AND BRACKISH WATER SPECIES TOTAL ABUNDANCE OF EACH SPECIES STATIONS RESIDENT SPECIES I II III IV 1 . Cyprinodon variegatus (Lacepede) Sheepshead minnow 197 700 41 426 2. Fundulus heteroclitus (Linnaeus) Common mummichog 235 676 996 1468 3. Fundulus majalis (Walbaum) Striped mummichog 71 378 491 1315 4. Lucania parva (Baird and Girard) Rain-water fish 1 2 1 2 5. Micro gadus tom-cod (Walbaum) Tomcod — 2 - — “ 6. Apeltes quadracus (Mitchill) Four-spined stickleback 23 2045 101 507 7. Gasterosteus aculeatus (Linnaeus) Three-spined stickleback 6 129 519 49 8. Fungi tins pungitius (Linnaeus) Nine-spined stickleback — 7 ■ 9. Syngnatbus fuscus (Storer) Pipefish 31 26 13 5 10. Roccus americanus (Gmelin) White perch 75 ' * ‘ “ 11. Tautoga onitis (Linnaeus) Tautog — 24 59 6 12. Tautogolabrus culspersus (Walbaum) Cunner — 16 36 29 13. Gobiosoma bosci (Lacepede) Naked Goby 1 — — — 14. Frionotus evolans (Linnaeus) Striped sea robin 1 3 15. Myxo ccpbalus aeneus (Mitchill) Grubby sculpin — 2 1 3 16. Menidia menidia (Linnaeus) Silversides 718 2377 1586 1155 17. Pseudopleuronectes americanus (Walbaum) Winter flounder 17 379 3 103 18. Opsanus tau (Linnaeus) Toadfish 1 7 1 118 STATIONS MIGRANT SPECIES I II III IV 1. Brevoortia tyr annus ( Latrobe ) Menhaden 162 66 922 131 2. Clupea barengus (Linnaeus) Sea herring 4 — — — 3. Anchoa mil chilli (Cuvier et Valenciennes) Anchovy 1 2 177 5 4. Osmerus mordax (Mitchill) Smelt — — 84 5 5. Tracbmocephalus my ops (Forster) 1 — — — 6. OUclAC 11M1 Strongylura marina (Walbaum) Atlantic needlefish — 2 — — 7. Vropbycis cbuss (Walbaum) Squirrel hake? — 1 — — 8. Lutjanus griseus (Linnaeus) Grey Snapper 3 1 - 9. Pristigenys alia (Gill) Short big eye 1 3 * — ' _ 10. Pomatomus saltatrix (Linnaeus) Bluefish — ‘ — ' 1 — 11. Caranx crysos (Mitchill) Hardtail 58 — ■ — — 12. Stenotomus versicolor (Mitchill) Scup Chaetodon ocellatus (Bloch) Butterfly fish — — 6 — 13. — — 4 — 14. Sphyraena borealis (DeKay) Northern barracuda ' ‘ 1 15. Mugil cephalus (Linnaeus) Mullet 2 12 — 1 16. Paralicbtbys dentatus (Linnaeus) Summer flounder 1 1 — — 17. Alutera schoepfii (Walbaum) Unicornfish — 1 1 — 18. Monocantbus hispidus (Linnaeus) Filefish 2 36 4 9 19. Sphaeroides maculatus (Bloch and Schneider) Puffer ANADROMOUS SPECIES: 2 5 1. Alosa aestivalis (Mitchill) Blueback 11 16 — — 2. Alosa pseudokarengus (Wilson) Alewife CATADROMOUS SPECIES: 78 68 1. Anguilla rostrata (LeSueur) American eel FRESH WATER SPECIES: 2 3 1. Micropterus salmoides (Lacepede) Largemouth bass — 1 — — 119 TEMPERATURE °C various species were grouped into the following components ( Table I ) : 1) Resident species, species that spend a great part of their life in local estuarine environments; 2) seasonal migrants, including offshore and inshore coastal waters, immature forms as well as southern species from the lower latitudes; 3) immature fishes of anadromous species; 4) im- mature catadromous forms, and 5) fresh water fish. Although there were more migrant species of fishes recorded during the survey than resident forms, the number of resident species occurring in both estuaries during the survey period was always significantly larger. In the lower Pettaquamscutt River there was a rapid increase in the num- ber of resident species during the first month (Fig. 8). By contrast, migrant species maintained a steady population level after the first rise in the number of species. A peak in the abundance of both endemic and migrant species populations occurred in the early part of September. The highest number of resident species populations observed at any one time during the survey period was 13 (Fig- 8). However only seven migrant species were recorded during the highest pulse in September. Only 10 migrant species were recorded from the lower pond in com- parison with 17 collected from the lower river. A rapid increase in number of species in the catches was noted from July 18 to August 14. Two pulses occurred on September 14 and October 4, followed by a sharp decrease in October (Fig. 8). 3. Relative Abundance. The analysis of relative abundance of all species of fishes, indicates the relative ranks for each major species contributing to the bulk of popu- lations of fishes from all the seining stations (Table II). The relative abundance and rank data of three selected species indicate the ranks with respect to major species at weekly intervals (Figs. 9-11 and Table II). A common feature of these data from all collections was the presence of a few dominant species represented by a large number of individuals and a large number of subordinate species represented by few individuals. The major species in order of abundance were Menidia menidia, Fundulus beteroclitus, F. majalis, Apelles, quadracus, Cyprinodon varie gains, Brevoorlia tyr annus and Gasterosteus aculeatus, (Table II). Other com- monly occurring species were Pseudopleuronectes americanus, Tautoga onitis, Tautogolabrus adspersus, Syngnathus fuscus , and Alosa pseudo- barengus. The species Osmerus mordax and Ancboa miUhilli comprised the major species on certain dates (date on file). The taxa, Roccus ameri- canus and Caranx crysos, were common only at the landward station in the lower Pettaquamscutt River and appeared consistently. Among the selected species, Af. menidia was usually first in order of abundance and a major species in most of the catches in both estuaries at all stations. The fluctuations in relative abundance were more pro- nounced at both seaward stations. (Figs. 2 and 9)- Though the number of individuals in the catches was fewer at Station I (Figs. 1 and 9)* these fish maintained comparatively steady population level in both estuaries at both landward stations. An apparent existing fluctuation in catches may be due to the schooling behavior of this species as reported by Shaw (I960). 121 SUMMARY 1. An extensive sampling project in Mississippi Sound and adjacent waters was carried out during the two years between November 1962 and the end of October 1964. 2. Postlarval pink shrimp were reported from this area for the first time. 3. The salinity regime in the years was very different. 4. From a total of 31 stations established, four were selected as being suitable for use in long term studies of postlarval abundance. 5. Indices of abundance developed from the catch of postlarvae at the selected stations predicted the 1964 catch of both white and brown shrimp within ten per cent, 6. Determination of the relative abundance of postlarval penaeid shrimp by season and area in Mississippi Sound and adjacent waters seems to be feasible, but reliability of the indices has not been fully established. Refinement of the indices and several more years experience will be re- quired to refine the predictions. REFERENCES Baxter, Kenneth N. 1962. Abundance of postlarval shrimp — One index of future shrimp- ing success. Proceedings of the Gulf and Carribean Fisheries Institute, Fifteenth Annual Session, November, 1962, pp 79-87. Collier, Albert and Joel W. Hedgpeth 1950. An introduction to the hydrography of tidal water of Texas. Publications of the Institute of Marine Science, University of Texas, vol. 1, no. 2, pp. 125-179. Lindner, Milton J. and William W. Anderson 1956, Growth, migrations, spawning and size distribution of shrimp Penaeus seiiferus , United States Fish and Wildlife Service, Fishery Bulletin 106, vol. 56, pp. 553-645. Phleger, F. B. 1954. Ecology of Foraminifera and Associated Micro-organisms from Mississippi Sound and Environs, Amer. Assoc. Pet. Geol. Bull., Vol. 38, no. 4, pp. 584-647. Priddy, R. Crisler, M., Sebren, P., Powell, D., and Burford, H. 1955. Sediments of Mississippi Sound and Inshore Water. Mississippi State Geological Survey, University of Mississippi, Bulletin 82, 53 pp. Renfro, William C. 1962. Small beam net for sampling postlarval shrimp. In: Galveston Biological Laboratory — Fishery research for the year ending June 30, 1962. United States Fish and Wildlife Service, Circular 161, pp. 86-87. 212 Table II. Relative abundance of the major species in order of their ranks with respect to all species collected from July 11 to October 20, 1962 from the lower Pettaquamscutt River and the lower Point Judith Pond, R. I. Lower Pettaquamscutt River Lower Point Judith Pond Species Station I Relative Rank % Station II Relative Rank % Station III Relative Rank % Station IV Relative Rank % 1. Menidia menidia 42.1 1 30.4 1 31.5 1 22 3 2. Fundulm heteroclitus 13.8 2 9.7 4 18.9 2 28.2 1 3. Fundulm majalis 4.16 7 5.4 6 9.7 5 25.2 2 4 Apeltes quadracus 1.35 10 28.8 2 2 7 9.4 4 5. Cyprinodon variegatus 11.55 3 10 3 .81 10 8.1 5 6. Brevoortia tyrannus 9.45 4 .94 9 18 3 2.5 6 7. Gasterosteus aculeatus .35 13 1.85 7 10.4 4 .95 8 8. Pseudopleuronectes americanus .99 11 5.44 5 .05 15 1.95 7 9. Alosa pseudoharengus 4.6 5 .97 8 — — — — 10. Sygnathus fuscus 1.72 9 .37 11 .2 12 .09 12 11. Tautoga onitis — — .34 12 1.17 9 .12 11 12. F autogolabrus adspersus — — .23 13 .7 11 .55 9 13. Roccus americanus 4.4 6 — — — — — — 14. Caranx crysos 3.4 8 — — — — — — 15. Monocanthus hispidus .12 16 .51 10 .07 14 .17 10 CATCH/ WEEK CATCH /WEEK JULY AUG. SEPT. OCT. JULY AUG. SEPT. OCT. Fig. 10. Variations in weekly catches of juvenile Pseudopleuronectes americanus and Brevoortia tyr annus from July 11 to October 20, 1962 in lower Pettaquamscutt River. 125 CATCH / WEEK Fig. 11. Variations in weekly catches of juvenile Pseudopleuronectes americanus and Brevoortia tyr annus from July 11 to October 20, 1962, in lower Point Judith Pond. 126 The taxon, Brevoortia tyrannus ranked sixth in order of abundance (Table II), but the appearance of this species was extremely variable from week to w r eek. Its greatest abundance was at the more landward station at Harbor Island in the lower Pond for most of September (Figs. 2, 10 and 11), and at the seaward station during the later half of August and early October. These fish were collected in significant numbers during mid-September at the landward station in the lower Pettaquamscutt River (Fig. 1) and at the seaward station in mid-August and early September. Pseudopleuronectes americanus ranked eighth in abundance among the total species recorded. This taxon was relatively common at the sea- ward stations in both estuaries (Figs. 1, 2, 10 and 11). These fish were not numerous at the upper stations of either estuary. Only three second- year class individuals appeared at Harbor Island. The low efficiency of the "shore seine” on a rocky irregular bottom may have affected the catch record from this station. 4. Horizontal Distribution. Disparity in distributional patterns of young fish was demonstrated by various migrant and resident species along the north-south axis of the study areas in the two estuaries. Juvenile Brevoortia tyr annus tended to move seaward as they grew as the season progressed. This taxon was par- ticularly abundant at Harbor Island (Sta. Ill, Fig. 2) from August 28 to September 14. The size of the young fish in the first catch from this station varied between 29 and 44 mm. The mean length of the individuals in the last sample taken on September 14 was 52 mm. By early October these fish had grosvn to a mean size of 58 mm, but by this time they occu- pied the seaward station in the Lower pond. McHugh et ah (1959) reported that populations of B. tyrannus move towards the sea as they grow and that consequently the mean size is greater at the seaward end of estuaries. A similar pattern of ditsribution was apparent in the lower Pettaquamscutt River. A greater number of individuals appeared at the landward station in August (Figs. 1 and 10). But the larger sized fish collected at two consecutive occasions during October were mainly from the seaward sta- tion (Figs. 1, 10 and 14). Two anadromous species, Alosa pseudo harengus and A. aestivalis, occurred only in the river estuary (Table I). These fishes appear to populate the river from July to late September as immature emigrants. It would be expected that these species behave as other anadromous species wherein the breeding populations enter brackish or fresh water environ- ments from the sea during spawning season, the young emigrants moving out from the estuaries as they grow. The lower Point Judith Pond, which covers more than three-fourths of the entire area, is subjected to near- seawater salinity (Figs. 4 and 5). This N/neritic condition (Fig. 3) should be adverse for spawning activities by anadromous species. Since no young fish of the two species appeared in catches throughout the survey period these observations indicate that the pond is probably not serving as a spawning area for these fishes. The taxon, Pseudopleuronectes americanus, usually spawns in winter at the heads of estuaries (Bigelow and Schroeder, 1953; Perlmutter, 1939). Pearcy (1952) found that young fish move down stream as they grow. Only three individuals of the first year class appeared at Bridgetown Bridge (Sta. I, Fig. 1). A great number of the same year class fish were captured from Middle Bridge (Sta. II, Fig. 1). Fourteen second year class fish 127 Fig. 12. Variations in class size (cms.) distribution of selected species at four seining stations. were caught only at the landward station throughout the survey period (Figs. 1 and 12). These observations reveal that probably juvenile fish of. the first year class occupy seaward stations by late summer. Second-year or older classes of fish either populate the more inland portions of estu- aries (Figs. U 2 and 12), or wander randomly, since larger fish rarely were seen at the seaward stations in either estuary. In lower Point Judith Pond only three specimens of P. americanus of the second-year class were caught at Harbor Island during the entire study period. The larger samples of this species were collected at the seaward station (Sta. IV, Fig. 2). The species Memdia menidia which appeared consistently at all four stations in both the estuaries in considerable abundance, had a greater abundance of size group 40-50 mm at the more seaw r ard stations in the two estuaries. The size group 30-40 mm was more common at the landward stations (Figs. 1, 2 and 12). Only two fish, possibly belonging to third- year class (120 mm) were collected from the landward station in the lower Point Judith Pond. The taxa Caranx crysos, Clupea harengus, Roccus americanus and Gobiosoma bosci ocurred only at Station I (Table II, Fig. I). A few species represented by Sfrongylura marina, Microgadus tomcod , Urophycis chuss and Micropier us salmoides were taken only from Middle Bridge area (Sta- ll, Fig. 1 ) , and in very small numbers. The catches of Sphyraena borealis, Pomatomus salialrix and Chastodon ocellatus were exclusively recorded from Harbor Island. The species Tautoga onitis and Tautogolabrus adspersus never appeared at Bridgetown Bridge Station. These fishes were common and frequently were found at Middle Bridge Station and Harbor Island, exhibiting mimicking behavior in massive beds of Zostera marina and various types of algae (Table II, Figs, 1 and 2). B. GROWTH Growth is a measure of production and an important means of study- ing ecological variations in various types of environments. The growth study of selected species of fishes of zero-year class includes the rate of growth-in-lengrh in the two estuarine systems under study. The average length of each sample used in graphic analysis was also employed to determine growth rates. The growth of each species has been dealt with separately. 1. Pseudopleuronectes americanus , While controversy exists on the exact spawning period of this species, Pearcy (1952), Perlmutter (1939) and Bigelow and Schroeder (1953) concluded that P. americanus is essentially a winter spawner. The juvenile winter flounder, consisting of 11 samples and totaling 382 individuals taken from the lower Pettaquamscutt River, provided average lengths used in comparing series of samples in computing rates of growth. The first sample collected on July 11 included juvenile fish with a mean length of 26 mm, and a size range between 15 and 44 mm. These fish were probably four to six months old at that time (Bigelow and Schroeder, 1953). The first two samples, taken at an interval of one week in July (Fig- 13) showed 50% overlap of black bars. Such a degree of overlap indicates little significance in the differences between samples and a low reliance on growth increments. This situation appears when 129 Fig. 13. Average growth of juvenile Pseudopleauronectes americanus collected July 11 to October 20, 1962. 130 LEGEND FOR FIGURE 13 The vertical lines in the histograms (Figs. 13-16) indicate size range of standard lengths in each sample. The horizontal lines are means. The black bar on either side of the mean represents two standard errors of mean (2 6 M), and the black bar and white bar combined on either side of the mean is the standard deviation ( 6 ). The standard errors express a measure of reliability, while standard deviation is a measure of disper- sion. For a detailed description see Hubbs and Perlmutter (1942) and Hubbs and Hubbs (1933). The sample sizes, given at the top of the vertical lines representing 30 or more individuals, are sub-samples from larger collections. The rest of the samples are actual sample sizes. samples are compared at week intervals. But given an interval of two weeks or a month, the samples in almost all cases show less than one-third overlap. Significant differences do appear between samples and a reliance on growth increments can then be demonstrated. The samples collected during the latter half of August showed significant differences between samples. The size of the fish when first caught in early August in the Pond estuary (Sta. IV, Fig. 2) ranged between 26 mm to 50 mm, with a mean length of 35 mm. The increase in the average length of the juvenile fish from early August to early October (Fig. 13) was between 35 and 56 mm with a growth rate of 10.5 mm per month. Though these results compare favorably with other studies (Pearcy, 1962) pertaining to this species, the single method of sampling and the small sample sizes do not lend thorough examination of differences in variations in growth between the study areas in the two estuaries. Seining operations coupled with intensive otter- trawling would probably manifest a more exact picture of growth and variations in the two environments. 2. Brevoortia tyr annus. Since B. tyrannus has a split spawning season, it is important to know the approximate age at which the fish first appeared in catches. Kuntz and Radcliffe (1917) reported that B. tyrannus spawns in summer in Woods Hole and in late fall in Chesapeake Bay. Wheatland (1956) observed two peaks in egg production in this species in Long Island Sound, one in June and the other in September. Herman (1958) found that this fish spawns in Narragansett Bay from May to August and again in October. Age estimates for this species, according to scale studies by Hile (1948) and others, show all fish captured were fish-of-the-year and were approxi- mately three to four months old when they first appeared in catches (Fig. 14). In the present study the sporadic appearance of B, tyrannus , a school- ing species, dictated the necessity of pooling the data from both lower and upper stations in each estuary. The limitations of this decision are fully recognized by the writer. The study of the growth rate of B. tyrannus in the lower Point Judith Pond was based on data from 1053 individuals from seven samples. The first sample collected on August 14 consisted of 79 fish, with a size range between 27 and 36 mm and a mean length of 33 mm. The two samples taken on August 14 and August 21, displayed significant differ- ence, hence mean values of these samples are reliable (Fig. 14). The late 131 August and early September data had a marked overlap (Fig. 14). The resulting low reliance on mean length measurements is probably due to the small sample sizes. The samples collected from September 14 to Octo- ber 4 showed much wider variations in the sizes of the individual fish and displayed marked overlap of black bars, with respect to weekly inter- vals. But in two of these samples the standard deviation is more than twice the two standard errors on either side of the means, signifying that valid differences exist between the two samples (Hubbs and Perlmutter, 1942). The graphical analysis demonstrated two distinct groups among all the samples. As this species schools precisely according to size (McHugh, 1959), it seemed that fish appearing after September 4 represented various populations, The mean standard length of the first group collected from August 14 to September 4 increased from 31 to 38 mm, with a growth increment of 7 mm per month (Fig. 18). The first sample of the second group taken on September 14 was caught only at the landward station while the rest of the samples were taken from seaward stations (Figs. 1, 2 and 11). The increase in average length observed was from 52 to 58 mm or an increase of 6 mm in three weeks (Fig.18). McHugh et ah (1959) contended that schools of B. tyr annus of precise size groups form a distinct size gradient from one end of the estuary to the other. McHugh insisted that a single rate of growth for a given age group of such a widely ranging species occupying an estuary is not tenable. The presence of two distinct groups and catches of larger fish mainly at seaward stations during late September and October (Figs. 10*12) point to analogy with McHugh’s findings. However the growth data for this species compares favorably with studies of Warfel and Merriman (1944) and McHugh et ah (1959) The average lengths of seven samples consisting of 228 individuals collected from the low T er Pettaquamscutt River, were used for growth study. Two distinct groups of zero-year class fish were present in this estuarine system as well (Fig. 14). The significant differences existed between samples collected from mid-August to early September. The black bars of the samples taken during the rest of September demonstrated marked overlapping thus negating the possibility of significance in differences (Fig. 14). The mean length for all samples collected from mid-August to early . September showed an increase from 25 to 43 mm (Fig. 17). This increase of 18 mm per month for the population in the lower Pettaquamscutt River estuary was more than twice the growth rate estimated for young fish collected during the same period from the lower Point Judith Pond (Figs. 17 and 18). However the growth was insignificant in the rest of the three samples which were composed of individuals of diverse size ranges. The sporadic appearance of this schooling species was another factor which created irregularity in catches and hence made it difficult to trace the exact picture of growth (McHugh et ah, ibid). 3. Menidia menidia. There is no definite growth study of juvenile or adult Menidia menidia . The wide range of sizes present in all samples during the present survey created a problem in the attempt to distinguish the zero-plus group. Merriman (1947) and Bigelow and Schroeder (1953) found that sizes ranging from fry of 2.5 cm (1 inch) long to adult sizes are present during the summer months. Williams (I960) and Shaw (I960) consider the 132 STANDARD LENGTH IN mm STANDARD LENGTH IN mm 80 20H ' JULY 1 AUG. t SEPT. 1 OCT. ^ Fig. 14. Average growth of juvenile Brevoortia tyrannus collected from July 11 to October 20, 1962. Method of presentation is the same as given in Fig. 13. 133 minimum size of an adult fish to be 50 mm. Spawning is reported to occur from May through July (Herman, 1958) in New England waters. From July to early September juvenile fish could be separated from other age groups, because of a marked distinction in sizes. For the remaining period fast growing juvenile and slow growing adult fish occurred in a complex admixture of sizes from which the zero-plus group could not be sorted out with certainty. It is possible that the small sized fish may rapidly disappear from the estuaries, perhaps retreating to deep water in the cooler part of the season (Hildebrand and Schroeder, 1928). Thirteen samples from Bridgetown Bridge (Sta. I, Fig. 1) consisting of over 500 fish provided data for comparison. The samples collected from July 11 to September 3 demonstrated significant differences when collected at semi-monthly or monthly intervals. The marked overlapping in samples taken from late August to early September seemed due to influx of larger numbers of small size individuals which also tended to diminish the mean growth in these samples (Fig. 15). The samples collected from September 9 to October 20 contained both juvenile and adult fish. Although significant differences were observed in these collections, the relative composition of the samples including juvenile and adult fish of uncertain age groups invalidated the mean values given. The average length of juvenile fish rapidly increased from July 11 to September 3 attaining a size range from 19 to 35 mm. The growth increments were insignificant for three weeks from August 16 to September 3, due to an inclusion of a larger number of smaller sized individuals (data on file). The growth rate of the juvenile fish was 8 mm per month (Fig. 17). There is uncertainty in establishing a growth rate for fish taken from September 9 to October 20, because of the admixture of juve- nile and adult fish of various sizes. From 13 samples consisting of over 1500 fish from Middle Bridge (Sta. II), juvenile fish could confidently be separated out from the first eight samples. These samples taken from July 11 to August 2 demon- strated significant differences. The increase in average growth of young fish in these samples (13 to 27 mm) suggests that the growth rate is more rapid during the early juvenile phase (Figs. 15 and 17). Samples taken during early August show an overlap in black bars, probably due to the small sample sizes. The insignificant differences in collections from Aug- ust 16 to September 3 is apparently due to the appearance of schools of similar sized individuals in the catches. The overall increase observed in growth from July 11 to September 3 was from 12 mm to 40 mm, or 14 mm per month (Fig. 17). Although significant differences between the samples are apparent, the problem of uncertain age group composition negated the possibility of estimating exact rates of growth for this species after September 3. Although there were variations in average growth, the samples from the lower pond demonstrated a similar pattern of growth when compared to the catches from the lower river. The collections made from the Harbor Island (Sta. Ill) indicated significant differences at semi-monthly intervals (Fig. 16). The samples taken from September 4 to September 22 and October 4 to October 20, included a higher number of smaller size young fish in September samples and a higher number of larger size fish in Octo- ber collections. The significance of differences between these samples 134 STANDARD LENGTH IN mm STANDARD LENGTH IN mm ' JULY 1 AUG. 1 SEPT. 1 OCT. 1 Fig. 15. Average growth of M^enidm menidia (Juvenile and adult) col- lected from the lower Pettaquamscutt River from July 11 to October 20, 1962. Method of presentation is the same as given in Fig. 13. 135 may be misleading because of the admixture of juvenile and adult fish in the catches. The growth rate for juvenile fish collected from July 11 to August 28 was 7 mm per month. This rate is similar to that for juvenile fish caught at the landward station (Sta. I) in the lower Pettaquamscutt River (Fig. 18). The larger size range of these young fish (Fig. 16) indicated spawning had occurred earlier at the landward station (Sta. Ill) in the lower Pond. The same phenomenon was noted in the lower River (Sta. I). The juvenile fish taken from Station IV, lower Point Judith Pond, between July 11 to August 28 demonstrated significant differences between the weekly samples (Fig. 16). Hence the average growth increments are reliable. The sample taken in early August indicates an influx of com- paratively small size individuals in the schools (Fig. 16). The samples collected from September 4 to October 20 differed significantly with the exception of the late September samples. These differences between average sizes probably are due to a gradual retreat of the small size fish into deeper water. The increase in average growth noted between July 11 and August 28 in juvenile fish was 19 mm, a growth rate of 11 mm per month (Fig. 18). These figures compare favorably with data from Station II, in the lower Pettaquamscutt River. The results support the assumption that the growth rate was higher for this species at the seaward stations in both the estuaries. C. FOOD AND FEEDING HABITS The analysis of food based upon the stomach contents of the selected species evinced variation in abundance and varieties of prey organisms in the study areas in the two estuaries. The results provided evidence for the assumed possible differences in food resources between a "gradient zone" habitat, Lower Pettaquamscutt River, and "marine zone" habitat. Lower Point Judith Pond (Fig. 3, Tables III and V). Polychaetes were the most important dietary constituent of Pseudo pleuronectes americanus, while crustaceans comprised the chief food of Menidia menidia, In the lower pond, however, 46% of group II ( 3 1*50 mm) and 100% of group III (51-80 mm) of M. menidia fed on phytoplankton. Heavy sporozoan infection in P. americanus was associated with depletion of food in the stomachs. Phytoplankton and suspended organic matter was the principle food of Brevoortia tyr annus and no correlation was observed between the size of fish and change in food. The juvenile fish of the species selected for food studies were separated into three size groups ranging between 10-30 mm (Group I), 31-60 mm (Group II), and 61-80 mm (Group III) to study change in food with respect to size of fishes. The minimum size of mature M. menidia is considered to be 50 mm (Williams, I960): this figure was used as limit for Group II (Table V). 1. Pseudopleuronectes americanus . Polychaetes were the basic food organisms, while isopods, amph ipods and ostracods were the essential dietary elements of the juvenile fish. Sand, mud and fecal pellets accompanied the food. A preference for larger food organisms was noted with increasing size of the young (Fig. 19). 136 STANDARD LENGTH IN mm STANDARD LENGTH IN STANDARD LENGTH STANDARD LENGTH IN mm Fig. 18. Rate of growth of Pseudopleuronectes americanus , Brevoortia tyrannus and Menidia menidia seined from the lower Point Judith Pond from July 11 to October 20, 1962. 139 Table III. List of food organisms of juvenile Pseudopleuronectes americanus from the lower Pettaquamscutt River (Stas. I and II combined), and the lower Point Judith Pond (Sta. IV only) including average number per stomach (A/S), per- centage frequency of occurrence (PF), size groups of juvenile fish (in mm) and prey size. LOWER PETTAQUAMSCUTT RIVER LOWER POINT JUDITH POND Prey 10-30 mm 31-60 mm 61-80 mm 10-30 mm 31-60 mm 61-80 mm size Prey Species A/S PF A/S PF A/S PF A/S PF A/S PF A/S PF (mm) Phytoplankton 2.2 6.9 2.7 6 — — — — — — — — .05-.2 Coelenterata Hydroids (Broken) — — — — — — — — — — 3.25 25 3-5 mm Nemertean — — — — — — .25 25 .22 6.8 — — 4.5-8 © Polychaeta:- Prionospio malmgreni 2.1 38 .92 12 8.3 47.6 .75 25 .32 22 1 25 5-8 Neantbes sucdnea — — .08 4 — — — — 14 6.8 .75 25 5-9 Neantbes caudata — — — — 1.4 13.4 — — — — — — 5-7 Neantbes virens .1 1.7 .3 16 6 73.5 — — .24 13.6 — — 6-15 Drilonereis longa — — — — — — — — .05 1.7 — — 1.3 Nephthys incisa — — .12 4 .06 6.7 — — .05 5.1 .25 25 4.5-8 Lumbrinereis sp. — — .08 2 .27 6.7 — — .017 1.7 — — 6.9 Arabella sp. — — .02 2 — — — — — — — — 6 Spio sp. .03 1.7 .18 4 .53 13.4 — — .25 11.8 — — 5-15 Unidentified Polychaetes .42 24.1 .86 28 10 73.5 1.25 25 .32 13 1 25 5-8 Oligochaeta — — — — — — .25 25 — — — — 3 Table III. (Continued) LOWER PETTAQUAMSCUTT RIVER Prey Species 10-30 A/S mm PF 31-60 A/S mm PF 61-80 mm A/S PF Crustacea Cladocera:- Evadne nordmanni — — — — — — Copepoda:- Copepodids .06 1.7 — — — — Harpacticoida 2.55 29.3 .16 4 — — Ostracoda:- Cylindroleberis mariae .72 10.4 .66 12 4.1 6.7 Sarsiella atnericana .74 12 .22 6 .27 6.7 Pontocypris edwardsi 48.3 27.6 .4 8 — — Cumacea : - Cyclaspis varians .09 5.2 .08 4 — — Oxyurostylis smithi — — .1 4 .06 6.7 Amphipoda;- Ampelisca sp. 1.43 29.3 .36 12 .8 26.6 Carinogammatits mucronatus — — .12 2 — — Microdeutopus gryllotalpa — — .08 4 — — Gammarus anmdatus — — .04 2 — — Corophium cylindricum — — — — — — Lembos smithi ■ — — .36 8 .2 13.4 LOWER POINT JUDITH POND 10-30 mm 31-60 mm 61-80 mm Prey size A/S PF A/S PF A/S PF (mm) — — .1 5.1 — — .11 1.5 25 — — — — .4-. 5 8.5 100 1.58 32 1.75 25 .35-.S5 — — — — — — 1.2-1.5 — — • — * — .25 25 3-4.5 .75 50 .54 17 1.25 50 1.5-4.5 — — — — — — 4-6 — — .15 5.1 — — 3-4.5 — — — — 4.25 25 2-3 .5 25 .64 27.2 — — 2-4.5 Table III. (Continued) LOWER PETTAQUAMSCUTT RIVER LOWER POINT JUDITH POND Prey 10-30 mm 31-60 mm 61-80 mm 10-30 mm 31-60 mm 61-80 mm size Prey Species A/S PF A/S PF A/S PF A/S PF A/S PF A/S PF (mm) Unifiola sp. — — .02 2 — — — . — . — — — — 6.5 Amphitboe sp. — — — — .2 6.7 .75 50 .2 6.6 — — 4-7.5 Amphipod - unidentified — — .2 6 .06 6.7 — — — — — — 3-4.5 Isopoda:- Cyatbura carinata — — — — .27 20 — — — — — — 4.5-8 Edo tea inontosa .83 22.4 1.54 34 .27 6.7 .25 25 .57 22 — — 2-6 Edotea triloba .1 3.4 — — — — — — .05 3.39 — — 2-6 heptochelia savignyi .03 1.7 — — 3.2 6 .5 25 1.14 55.6 — — 1-1.3 Leptochelia sp. — — .42 2 .06 6.7 — — .12 5.1 — — 1.5-2 Idothea viridis — — .02 2 — — — — .12 5.1 — — 6 Decapoda:- Crago septemspinosus — — — — — — — — — — 2.5 25 1.5 Chironomid larvae — — .08 4 — — — — — — — — 2-3.5 Gastropod larvae .03 1.7 .04 2 — — — — .05 1.7 — — .05 -.075 Bivalve larvae .17 5.2 — — .2 13.4 1 50 — — — — .9-1.5 Invertebrate eggs 1.26 12 .44 4 — — 2.75 50 — — 5.25 25 .025-15 Fish scales .03 1.7 — — .3 13.4 — — .48 10.2 — — 3.5-6 Total number of fish analysed 58 50 15 5 59 12 Empty stomachs 16 8 3 1 22 2 THE LOWER PETTAQUAMSCUTT RIVER; From a total of 150 fish studied, 27 had empty stomachs (Table V). The species P. ameri- canus feeds normally during the daytime (Pearcy, 1962); all seine hauls were taken only during the day and the small amount of food in the stomachs of the fish probably was due to heavy sporozoan infection. Table III shows the relative importance of various food organisms. PREY SPECIES: Among the polychaetes, Prionospio mahngreni (3-8 mm) was the most important food for all the three size groups of juvenile fish. Phelps (personal communication) found an abundance of this species in Charlestown Pond. Neanthes virens (5-15 mm), found in 73.5% of the stomachs in group III, was common as a food in other groups (Table III). A considerable number of polychaetes, fragmented and altered by digestion, were labelled "Unidentified." Other species, Nephthys incisa, Neanthes caudata , Neanthes succinea, Arabella sp. and Lumbrinerels sp. were less abundant. Often a single individual comprised the bulk of the stomach contents. Among isopods, the second most important group of food organisms, Edotea montosa ( 2-6 mm ) , were frequently noted in the stomach. Isopods were relatively easy to identify because of minimum deterioration. Leptochelia savigni and Leptochelia sp., exhibiting a striking sexual dimorphism and represented mostly by females, were included among other comparatively less important isopod species (Table III). All young fish ranging between 10-80 mm consumed Ampelisca sp., the most common amphipod. Pearcy (1962) reported that P. americanus feeds upon Ampelisca sp. more than any other amphipod. Seven other amphipod species, listed in Table III, were absent in stomachs of group 1 juvenile fish. The amphipods Car inogam mar us, Microdeutopus, Gammarus, Lembos, Unciola and several unidentified forms were present in the diet of group II, while group III consumed Lembos, Unciola as well as some unidentified forms. The ostracods, Pontocypris edwardsi (0.6-0.8 mm), were most significant numerically in group I (Table III). Two larger species, Cylindroleberis mariae (1.2-1.5 mm) and Sariella americana (0.9T.2 mm), were present in all size groups. The most important components of "miscellaneous" food were harpacticoids, invertebrate eggs, chironomid larvae and fecal pellets. VARIATION WITH SIZE: Since all collections were made during daylight no day and night variation in feeding was involved. The degree of fullness of stomachs varied with the size of the fish. The percentage of empty stomachs in group I was 21.6% while in group II, it was 13-8% (Table IV). The percentage of stomachs with traces to 25% fullness was higher in group I. In group III only 18 fish were analysed, but the per- centage of stomachs with 25-100% fullness w T as higher than that of group I. The overall picture of stomach fullness does indicate relative increases in stomach contents as a function of body size (Table IV). With progressive increases in size, young P. americanus tended to prefer larger prey organisms. In the group 1 juvenile fish, Pontocypris edwardsi, the smallest astracod species observed, averaged 48.3 per stomach. Eggs and harpacticoids were very abundant in the diet of this group. The smaller polycbaete species, Prionospio malmgreni (5-8 mm) occurred in 38% of the stomachs with an average of 2.1 per stomach. Larger poly- chaetes were scarce in the diet (Fig, 19). Ampelisca (1. 5-4.5 mm), a 143 comparatively small amphipod, was the only type observed in the diet of this group. Table IV. Variations in relative degree of stomach fullness of three sizes (in mm) of P. americanus collected from the lower Petta- quamscutt River and the lower Point Judith Pond. Table includes number and percentage of stomachs with or without food. Degree of Fullness 10-30 (N) ) mm % 31-60 mm (N) % 61-80 (N) mm % LOWER PETTAQUAMSCUTT RIVER Empty stomachs 16 21.6 8 13.8 3 16.6 Trace to 25% fullness 9 12.2 3 5.2 1 5.5 25 to 50% fullness 11 14.8 12 20.7 4 22.2 More than 50% to total fullness 38 51.4 35 60.3 10 55.5 Total 74 58 18 LOWER POINT JUDITH POND Empty stomachs 1 20 22 27.1 2 14.3 Trace to 25% fullness 2 40 16 19.8 5 35.6 25 to 50% fullness — — 12 14.8 4 28.6 More than 50% to total fullness 2 40 31 38.3 3 21.4 Total 5 81 14 In group II young fish the data show diminishing selection for smaller prey organisms and an increasing preference for larger organisms (Fig. 19). The stomachs in group III (61-80 mm) young fish were devoid of eggs, harpaticoids and Pontocypris edwardsi indicating least preference for smaller species. Though P, americanus is euryphagous, results of stomach aualysis indicate that smaller fish tend to select smaller prey species. Seasonal variations: During the summer months, no apparent varia- tions in prey species with time were noted. Richards (19o3) reported that all groups of prey are eaten by P. americanus during the summer, while in other seasons particular species such as nemerteans and hydroids are absent in their stomachs. Both of these food groups were present in the stomachs of young fish only from the salt pond estuary. THE LOWER POINT JUDITH POND: From the lower pond 100 individuals that appeared in catches only at the seaward station were available for study. Twenty-five stomachs were found empty (Table IV), while the remaining 75 were 25% to 100% full. The depletion of food in the stomachs was associated with parasitic infection in the young fish in this estuary (see pp 78). While polychaetes were the principle food, isopods and amphipods were among the major food items (Table III). Ostracod species were not noted in the diet of fish in the study area in this estuary. The important species and groups that comprised the bulk of the diet of young fish in 144 Fig. 19. Variations between different size groups of juvenile Pseudo- pleuronectes americanus and size of the prey organisms collected from the lower Pettaquamscutt River. 145 the lower Pettaquamscutt River were also present in the food of young fish from the lower pond. Miscellaneous food organisms in the diet including the cladoceran, Evadne nordmanni, nemerteans, oligochaete, actinozoa and the polychaete, Drilonereis longa, were noted particularly (Table 111). A remarkable feature in the pond estuary was a high percentage of empty stomachs or those with only traces of food (Table IV) . According to the general size classification 81% of rhe young fish were categorized as group II (3T60 mm). The exact picture of size variation between young fish and their prey species could not be traced because of the high percentage of stomachs with little or no food present together with the marked inequality in number of fish in each group. An apparent scarcity in available food in the feeding niches of the lower salt pond may be one reason for a greater number of stomachs containing little or no food. VARIATIONS BETWEEN THE ESTUARIES: The percentage of empty stomachs of young fish in the lower river was 18% as compared with 25% in the lower pond. The percentage of stomachs with traces to 25% fullness was higher in the lower pond by 1 4.4% (Table IV). One of the principal groups of organisms, ostracods, was entirely absent in stomachs of young fish in the lower pond. On the average there were fewer important food organisms such as polychaetes, amphipods and isopods per stomach in the lower pond (Table III). Various types of taxonomic groups represented in the diet were also few in the feeding niches of the lower pond environment. 2. Menidia menidia. The species, Menidia menidia , demonstrated omnivorous feeding habits. In the lower Pettaquamscutt River the nature of the food varied with size of fish from a mixture of plant and animal food to a strictly carnivorous diet. In the lower Point Judith Pond the young fish were largely dependent upon plant food (Table V and VI). Forty-six per cent of group II (31-60 mm) and all of the group III (61-80 mm) fish ate plant food, THE LOWER PETTAQUAMSCUTT RIVER: The organisms con- stituting the important food components of the diet of young fish (10-30 mm) were diatoms, harpacticoids, rotifers, nauplii of Balanus sp., and invertebrate eggs (Table V, Fig. 20). Harpacticoids, calanoid copepods, and Balanus nauplii comprised the principal diet of groups 11 and 111. Amphipods, isopods and Hymenoptera were also significant as important food components of these two groups. THE PREY ORGANISMS: While inclusion of diatoms may be considered incidental in the food of group 111, these were the essential dietary components for groups I and II. The more commonly occurring species were Gryosigma spencerii, Gyrosigma sp., Grammatophora marina, Nitzschia sp., Coscinodiscus sp., and Navicula sp. Invertebrate eggs in 30% of the fish were evidently important food items in the diet of young fish (10-30 mm). Rotifers were present in 35.3% of the fish analysed, mostly of group 1. The copepods recorded from the gut content were predomi- nantly adults, including Paracalanus parvus, Acartia tonsa, Temora longi- cornis, and Pseudocalanus minutus. The harpacticoids occurring in the diet of 72.7% of the fish examined constituted important food components 146 Table V. List of food organisms of juvenile and adult Menidta menidta from the lower Pettaquamscutt River (Stas. 1 and II combined) and the lower Point Judith Pond (Stas. Ill and IV combined) including average number per gut (A/G), percentage frequency of occurrence (PR), size groups of the fish (in mm) and size of the prey species. Prey Species LOWER 10-30 A/G PETTAQUAMSCUTT RIVER mm 31-50 mm 5T80 mm PF A/G PF A/G PF LOWER POIN1 10-30 mm A/G PF ' JUDITH 31-50 mm A/G PF POND Prey size (mm) Phytoplankton 34.1 89 24.6 66 5.4 51.5 537 100 146 100 .05-.15 Hydroid medusae .14 4.7 .03 2.4 — — — — — — 1.3-1. 8 mm Rotifers 27.5 34.9 2.5 58.5 .85 21.2 — -— — — .07-. 1 Polychaete larvae unident. — — .5 2.4 — — — — — — 3 Crustacea Calanoid Copepods:- Acavtia tonsa 2.14 14.2 3.42 31.6 31 51.1 1. 1-1.3 Paracalanus parvus 1.05 11.1 11.8 20.3 31.2 30.5 — — — — .8-1.0 Temora longicornis — — — — .06 3 — — — — 1.3 Pseudo calanus minutus — — — — 11.2 27 — — — — .7-.88 Harpactlcoida 18.9 71 34.5 100 13.4 70 4.4 76 13 100 .45-63 Cyclopoida:- O it bona similis .76 9.5 25.6 17.1 .61 12.1 .45-,6 Copilia sp. — — — — .06 3 — — — — 3 mm Copepod nauplii 1.4 22.2 .17 2.44 — — 332 100 152 100 .125-.2 Copepodids .317 11.1 .36 4.8 — — 33.7 66.8 — — .3-.45 Table V. (Continued) LOWER PETTAQUAMSCUTT RIVER LOWER POINT JUDITH POND Prey 10-30 mm 31-50 mm 5180 mm 10-30 mm 31-50 mm size Prey Species A/G PF A/G PF A/G PF A/G PF A/G PF (mm) Ostracoda : - Pontocypris edtvardsi 1.05 14 — — — — — — — — •5-.7 Sarsiella americana — — .22 14.6 .12 6 — — — — .8-1.2 Cumacea:- Oxyurostylis smithi — — 1 4.75 — — — — — — 2.5-4 Cyclaspis varians — — — — .27 7.3 — — — — 2.5-3.5 Amphipoda:- Lembos smithi — — .365 9.8 .42 15 — — — — 1. 7-2.5 Microdeutopus gryllotalpa — — .17 7.3 .06 6 — — — — 2.0-3.0 Carinogammarus mucronatus — — .122 7.3 .03 .01 — — — — 2.7-3.3 Amphithoe sp. — — .049 4.8 — — — — — — 1.8-3.1 Ampelisca sp. .19 6.3 .122 7.3 .97 21.2 .33 19.1 1.12 62.6 1.0-1.75 Isopoda:- Leptochelia savignyi .19 7.9 .56 12.2 .21 3 — — .625 41 .55-1.0 Cyathura carinata — — .073 4.8 .166 6 — — — 2.0-3.0 Tanais cavolinii — — — — .18 6 — — — — 1.5-2. 5 Idothea viridis — . — .073 7.3 . — , — — — — — 3.2 Table V. ( Continued ) LOWER PETTAQUAMSCUTT RIVER LOWER POINT JUDITH POND Prey 10-30 mm 31-50 mm 51-80 mm 10-30 mm 31-50 mm size Prey Species A/G PF A/G PF A/G PF A/G PF A/G PF (mm) Cirripedia:- Balanus sp. (nauplii) 17.4 60 85 56.1 29.7 45.5 — — — — .6-1.2 Decapoda:- Pagurus sp. zoae — — — — — — — — .47 9.3 .2-3.5 Decapod larvae unident. .142 4.7 .27 7.3 .06 3 — — — — 1.2-2. 5 £ Insecta:- Chironomid larvae .1 7.9 .122 9.8 .09 6 .071 4.9 — — 2.0-3.5 Hymenoptera — — .76 31.6 1.27 24.2 — — .03 3.1 2.5-5. 5 Arachnida .05 4.7 .025 2.44 .12 6 — — — — 2.5-3.5 Bivalve larvae .05 6.4 — — — — — — — — .6-1.2 Gastropod larvae .49 11.1 .29 12.2 — — — — — — .075-.125 Invertebrate eggs 17 46 5.98 26.9 4.25 15.2 13.8 40.5 .97 31.3 .025-.05 Fecal pellets .05 1.59 — — — — .166 7.15 .5 15.4 .15-.25 Fish scales .86 42.9 .98 41.5 1.21 33.4 — — — — 1.5-2. 5 Fish eggs .05 3.18 .315 7.3 .18 9 — — — — .8-1.1 Total number of fish analysed 69 45 36 45 34 Empty guts 6 4 3 3 2 in all size groups. The cyclopoid, Oithona similis, was significant in group II fish. The isopod, Leptochelia savignyi, was eaten by all size groups of fish. Other isopod species consumed by young and adult fish (31-80 mm) were, Cyathura carinata, Tanais cavolini, and ldotbea viridis. Ampelisca sp. was the only amphipod in the gut contents of group I fish (Table V), while the five species listed above were consumed by groups II and III. Hymenopterous insects significantly occurred in groups II and III and often comprised the bulk of the gut contents. Although the hymenoptera was well represented it is doubtful if this group, mostly represented by ants, serves as a regular source of food. These insects are probably inci- dentally introduced in water. The chironomid larvae, which usually occur in fresh water environments, are swept down into brackish water from the fresh water area. These were fed on by all three size groups. Decapod larvae, cumacids, gastropod larvae and fish eggs were the prominent "mis- cellaneous groups”. The prey including larger organisms, such as amphi- pods, isopods and gastropod larvae were predominantly fed upon from the substratum or Zostera and Ruppia leaf blades. VARIATION WITH SIZE: No day and night variations in feeding are known in M. menidia. The degree of fullness of the gut in various size groups indicates that fish were caught during the active feeding period which was always during the daylight hours (Table VI). Though the usual food for the larger group (51-80 mm) was scarce, there was an appar- ent indication of increase in gut fullness with increase in size of the fish (Fig. 20). Phytoplankton as an important dietary component became less and less important with progressive growth of the young fish (Table V). In group I (10-30 mm) young fish largely depended upon small size prey organisms. Rotifers (-07-.1 mm) average 27.5 per gut while harpacticoids (.45-.63 mm), occurring in 71% of the gut, averaged 18.9 per gut. Inverte- brate eggs and Balanus nauplii were present in 46% and 60% of the fish examined and averaged 17 and 17.4 per gut respectively. Other prey organisms including the larger crustaceans were insignificantly represented in the gut contents. In group II (31"50 mm) fish phytoplankton were less important as diet, harpacticoids occurred in 100% of the fish examined, copepods and Balanus nauplii occurred in larger numbers as compared with the amount consumed by group I fish (Fig. 20). Invertebrate eggs and rotifers, im- portant dietary components of group I fish, were insignificant in group II fish. In addition some species of amphipods and isopods became increas- ingly important in the diet (Table V). In group II larger size prey organisms were characteristic of the diet indicating an apparent preference for larger prey with the increase in size. The group III (51-80 mm) fish followed a similar trend in the dietary shift demonstrating greater dependence on larger food organisms. An average of 5-4 phytoplankton per gut seem to be incidently ingested along with other prey. Copepods were the most important food component. The species Acartia tonsa and Paracalanus parvus were highest in abund- ance in the gut contents and averaged 31 and 31.2 per gut respectively. The insects, Hymenoptera, ocurred in 24.3% of the guts analysed. Isopods and amphipods were also common in this group (Table V). There was 150 Table VI. Variation in relative degree of gut fullness in three size classes of Menidia menidia in the lower Pettaquamscutt River and the lower Point Judith Pond. Table shows the number (N) and percentage (%) of gut with or without food. Figures with asterisk indicate fish that ate phytoplankton. Degree of Fullness 10-30 (N) mm (%) 31-50 (N) mm (%) 51-80 (N) mm (%) LOWER PETTAQUAMSCUTT RIVER Empty gut 6 8.7 4 8.9 3 8.3 Traces to 25% fullness 15 21.7 11 24.4 15 41.6 25 to 50% fullness 21 30.4 7 15.6 11 30.6 More than 50% to total fullness 27 39.2 23 51.1 7 19.5 Total 69 45 36 LOWER POINT JUDITH POND Empty gut 3 6.7 2 3.2 • — — Traces to 25% fullness 5 11.1 4 6.4 ■ — ■ — 25 to 50% fullness 16 35.1 15 23-8 — — More than 50% to total fullness 21 46.1 13 20.6 42* 100 29* 46 Total 45 63 42 however no apparent change in the supply of food during the study period, covering summer and early fall. LOWER POINT JUDITH POND: The fish in the lower pond largely depended upon phytoplankton as diet. The group I and over 50% of group II fish ate mixed plant and animal food, while 46% of group II and all the fish of size group III consumed phytoplankton. PREY ORGANISMS: The major food items observed in the gut contents were: phytoplankton, copepod nauplii, copepodids, invertebrate eggs and to some extent harpacticoids. Inclusion or phytoplankton, as either an important component or the entire diet, was apparent in all the three size groups (Tables V and VII). The results of the analyses of plant food (Table VII and Fig. 2 IB) indicate that there was an increase in volume per gut with increase in size of fish and an average of 768 cells/mm 3 . The plant food consisting chiefly of littoral benthic diatoms included mostly Gyrosigma spencerii and Gyrosigma sp. in addition to less abundant species as mentioned in the description of the vegetable diet of the fish in the study area of the river estuary. Copepod nauplii averaged 332 per gut in group I and 152 in group II. Copepodids and invertebrate eggs found in over 66% and 40% respectively in size group I (10-30 mm), were insignificant in group II. There was an apparent scarcity of larger Crustacea, and other taxonomic groups. The prey, Ampelisca sp., chironomid larvae and fecal pellets in group I were listed as '’miscellaneous food” items, while in the group II, 151 LOWER PETTAQUAMSCUTT RIVER Size group 10-30mm. Number of fish 63. Size Group 31-50mm. Number of fish 41. Size group 51-80mm. Number of fish 33. C I G IS c, o u >. XI & IB CO 60 Ck 4J 4> Ck 3 cS •a uT a r c •— 1 JS "rt Zm Zm 0 PS el X 5 Fig. 20. Variation between size groups of Menidia menidia and size of the prey species (given against each bar). 152 Table VII. The average volume and number of cells per gut in various class sizes of Menidia menidia that ate only phytoplankton in the Lower Point Judith Pond. Class size in mm Average Vol. in cc/gut Average Number of cells/cc Average Number of cells/gut 30-40 0.04 768,000 29,720 40-50 0.05 768,000 39,936 50-60 0.125 768,000 96,000 60-70 0.218 768,000 167,424 70-80 0.214 768,000 164,352 Leptochelia savignyi, Pagurus sp. zoeae, Hymenoptera and fecal pellets represented a similar category. VARIATION WITH SIZE: The analysis of the gut contents showed the presence of two major food components; the minute developmental stages of Crustacea and phytoplankton (Table V, Fig. 21). The micro- scopic mixed plant and animal food perhaps suited the feeding habits of the small s«ze (10*30 mm) fish. The larger size fish (3T80 mm) were possibly unable to feed on minute organisms effectively in the pelagic environment, hence picked up food from the substratum as mouthfuls which contained diatoms, organic debris and fecal pellets (Tables V and VII). Brodski and Jankovskaya (1935) indicated a similar behavior in the eastern sardine, Sardinops melanosticta, which feeds effectively on phytoplankton in the absence of zooplankton, the normal diet of this species. A similar situation was non-existent in the lower river. Here the larger fish ace larger crustaceans and other food organisms. The inclusion of phyto- plankton in their diet seemed to be incidental. 3. Brevoortia ty r annus. A controversy exists regarding the nature of the primary food of Brevoortia tyrannus. Peck (1894) examining the food of juvenile and adult fish from Buzzards Bay, Massachusetts, during the summer period, described it as consisting of suspended organic matter and phytoplankton, with small crustaceans as supplementary food. Peck gave no quantitative data for plant matter in his food habit studies. Richards (1963) described the food of young B. tyrannus during winter as consisting primarily of crustaceans without any inclusion of plant food. Other workers reported that the diet was composed of oozy mud (Verrill, 1871), and others as plant debris, miscroscopic plants and small crustaceans (Goode, 1880; Bigelow and Schroeder, 1953). Richards (1963) did not account for any seasonal variation in the basic diet. By combining data and observations from this and Peck's summer studies, together with Richards’ winter studies it seems evident that seasonal changes in feeding habits are indicated. In the 150 fish of this species examined from each estuary most of the stomachs had only traces of food while the gizzards were always full (Table VIII). The high percentage of empty stomachs may have been due to a 153 LOWER POINT JUDITH POND Size group 10-30mm. Number of fish 42. Size group 31-50mm. Number of fish 32. Number of fish 50. Fig. 21. A. Variations between size groups of Menidia menidia and size of the prey species. Rig. 2 l.B. Variations in number of phytoplankton per gut relative to class sizes of Menidia menidia. 154 rapid transfer of food to the gizzards since these latter organs were always found full. The stomach contents were comprised chiefly of unidentifiable organic matter including soft organic or so-called ' oozy mud” and unicellular algae, predominantly Peridinium sp. Diatoms were uncommon and harpacticoids, copepod nauplii, and copepodids occurred rarely in samples from both the estuaries. Peck (1894) stated, while the only food noted was unicellular algae, polychactes and crustaceans were altogether absent in day samplings. These observations are analogous to the findings of the present study. Fifteen different types of organisms were identified to species or genera and groups represented by dinoflagella tes, Peridinium, Dinopbysis, Gleno - dinium, diatoms, Gyrosigma spencerii, Gyrosigma sp., Acnathes, Grama- tophora, Navtcula, Coscinodiscus, Rbizosoiinia, and other groups included copepod nauplii, copepodids, harpacticoids and infusorians. These organ- isms constituted just a small fraction of the diet in comparison to the free organic matter. There was no change in type of food with progressively increasing size of the young fish (Richards, 1963). The analogous earlier observations may have discouraged serious quantitative studies, because the material observed in summer period does not lend itself to a reliable quantitative determination. Table VIII. Variations in the relative degree of stomach fulless of three class sizes (in mm) of juvenile Brevoortia tyr annus from the lower Pettaquamscutt River and the lower Point Judith Pond. Table represents number (N) and percentage (%) of stomachs with or without food. Degree of stomach 10-30 mm (N) (%) (N) (%) fullness (N) <%) 31-60 mm 61-80 mm LOWER PETTAQUAMSCUTT RIVER Empty stomach 1 3.7 18 16.1 — — Traces to 23% fullness 23 85.2 74 66 9 81.7 25 to 50% fullness 3 11.1 13 11.6 2 18.2 More than 50% to total fullness — — 7 6.3 — — Total 27 112 11 LOWER POINT JUDITH POND Empty stomachs 2 5.3 9 9.9 — — Traces to 25% fullness 29 76.3 53 58.2 15 71.1 25 to 50% fullness 7 18.4 24 26.4 6 28.9 More than 50% to total fullness — — 5 5.5 — Total 38 91 21 155 D. PREDATORS AND PARASITES Large size fish were uncommon in the seine hauls. The stomachs of adult Roccus americanus, Opsanus tau, Tautoga onitis, Menidia menidia and juvenile Carom c crysos (40-60 mm) captured during seining were examined. Only Opsanus tau, Caranx crysos and Menidia menidia were found feeding on juvenile Anchova mitcbilli and Menidia menidia. No valid picture of the overall predation can be traced because adult fishes are least vul- nerable to shore seining. Piscivorous birds, Larus sp., the herring gull, Sterna sp., the common tern and Ph ala croc or ax sp., the cormorants, were observed feeding on fry throughout the survey period in the lower parts of both estuaries. Pearcy (1962) reported an abundance of cormorants in the Mystic River estuary during late summer and fall, and Steven (1933) in England showed 40% of the diet of cormorants to be flatfishes. Infections of sporozoan parasites was surprisingly common in Pseudopleuronectes americanus and Osmerns mordax. Ectoparasites were uncommon and were only found infesting Alosa pseudoharengus, Fundulus heteroclitus and F. majalis. These were represented by Argultis junduli, Argulus sp. and Caligus sp. Endoparasites were observed in B. tyrannus, P. americanus, and Al. menidia during food analysis, including nematodes, cestodes and sporozoans. The sporozoan parasite, Glugea hertwigi, was visible through the translucent body wall of Osmerus mordax, while equally heavy infection was also observed in P. americanus. Glugea hertwigi occur- red as white globules attached to gut epithelium or infesting the outside walls of the alimentary tracts. In heavy infection the lumen of the ali- mentary tracts were either fully loaded with Glugea colonies or these were thickly embedded on the outside body walls. In instances of light infec- tion a few r scattered globular structures were loosely attached inside or dorsal to the alimentary tracts. In all cases of heavy infection alimentary tracts were devoid of food, and indicated greater susceptibility to other parasites. Table IX shows the degree of infection in P. americanus. Table IX. Number (N) and percentage (%) of juvenile Pseudopleuro- nectes americanus infected with Glugea hertwigi collected from the lower Pettaquamscutt River and the lower Point Judith Pond. Class in mm Number of fish Light Infection (N) (%) Heavy Infection (N) (%) LOWER PETTAQUAMSCUTT RIVER 10-30 244 29 11.9 11 4.9 31-60 116 7 6 3 2.6 61-80 36 3 8.3 — — LOWER POINT JUDITH POND 10-30 5 1 20 — — 31-60 81 13 18 6 7.4 61-80 14 3 21.4 1 7.1 156 The data indicate that a considerable number of fish were infected. Through accurate estimation of mortality may require extensive sampling, these data suggest a high mortality may have occurred especially in group I (10-30 mm). Kudo (1947) and Duijn (1956) found that a host dies when heavily infected with Glugea hertwigi because of a degeneration of the large number of cells attacked. VI. DISCUSSION Spring and summer seasons mark the spawning activities in most of the species of fishes in New England waters (Merriman and Sclar, 1952; Wheatland, 1956; and Herman, 1958). Following the larval phases of growth, the young fish are faced with the problem of protection from predators and a search for abundant food. At this stage estuaries become important as nursery grounds for young fishes. A significant influx of juvenile immigrant species from offshore and from lower latitudes and the emigration of anadromous forms was noted as temperature increased during early summer (Fig. 7). Although the abundance of fishes followed the general pattern of rise and decline in temperature, no correlation was observed between maximum temperature and maximum abundance (Fig. 7). The differential temperature tolerance in various species may be a contributing factor for a lack of correlation. Warfel and Merriman (1944) have reported that maximum temperatures are nor accurate indicators of a great number of species. Salinity is a determining factor limiting the distribution of fishes within the various segments of an estuary. The stenohaline species, espec- ially the fresh water forms, may be limited within a narrow range of salinity. Marine forms are usually more euryhaline and are able to withstand wide ranges in salinity (Herre, 1956). A few brackish and fresh water fishes occurred in both the study areas (Table I) where salinity ranged between 10-32 o/oo and 28-32 o/oo in the lower river and the lower pond respec- tively. Even at Bridgetown Bridge, where salinity varied between 9.8 - 15 o/oo mostly marine forms were captured. The only fresh water species recorded was Micropterus salmoides , collected from the Middle Bridge area (Sta. II, Fig. 1). Adolf (1925), in discussing the tolerance of marine and fresh water organisms, suggested that marine organisms are better adapted to changes in the osmotic environment than are fresh water forms. The lack of relationship between the fluctuation in salinity and fluctuation in marine fish population is indicative of the fact that these forms can adjust to wide salinity changes in the environment. Further, the number of marine species recorded from the lower river was one and a half times higher than those captured in the lower pond (Table I) indicating an apparent preference for an area with pronounced variation in salinity (Figs. 4 and 5). The species, Pseudopleuronectes americanus, Brevoortia tyrannus and Menidia menidia, which were used for detailed study, also gave evidence of changes in distributional behavior with respect to spawning seasons, age and thermal tolerance. The juvenile P. americanus of zero year class were caught mostly at lower stations in shoaler water (Table I, and pp. 15). As the larvae of this species grow they move down stream (Bigelow and Schroeder, 1953; Pearcy, 1962) and occupy stations closer to the mouth of estuaries during summer. The preference for shoaler areas with higher temperature (Figs. 6 and 12 and pp. 15) explains why a few individuals 157 caught at upper comparatively deeper stations in both localities were either mostly or all second year class fish. Huntsman and Sparks (1924) reported a higher incipient lethal temperature for smaller flounder than for larger ones. The difference in temperature tolerance may explain why larger fish may prefer deep water in summer. The influx of Brevoortia tyrannus in the two estuaries was apparent because of the great abundance of small fish at landward stations during September. Although the schools of "precise size" individuals of this species move up and down the estuaries during the nursery period, the presence of a few fish of diverse sizes only at the seaward stations in October suggests an outward migration at this time of the year (bigs. 10 and 11). The species, Alenidia menidia, forms schools of similar sized individ- uals (Shaw, I960) and because fish of all sizes, above 2.5 cm (1 in.), occur all the year round (Bigelow and Schroeder, 1953) patches of various size groups were found at all the stations. Because of extreme adaptability of this species to changes in temperature and salinity its abundance was markedly high at ail the four stations. The measure of total abundance and distribution depends upon the reliability of catches. The catch relia- bility in turn may depend upon a number of factors, such as distance from the fresh water source, the tide and especially the temperature, which is the dominant factor. Day (1951) reported that any one factor cannot be the sole determinant of the distribution of organisms in estuaries. Although the total abundance and distribution are markedly influenced by tempera- ture fluctuations, it is suspected that slight changes in temperature caused marked fluctuations in the catches (Fig. 7). The phenomenon seems to be a recurring process of overcrowding and dispersal. Such a pattern is well illustrated in the total catches in the lower Pettaquamscutt River. As Warfel and Merriman (1944) suggested, that under optimum living con- ditions population density may reach a super-saturation point at which time the ensuing population pressure forces a dispersal followed by another build up process. No relationship was observed between the total number of species and the total number of individuals occurring at any one time. These data demonstrate (Fig. 7) that there were peaks in numbers of individuals occurring in late August, while the largest numbers of species in general were recorded during September in both the areas under study. The migrant species Such as Luljanus griseus, Trachinocepbalus myops and Chaetodon oceliatus, enter Rhode Island waters as stray individuals from remote spawn- ing centers quite late in summer. The late entry of these fishes contributed markedly to increases in number of species. However, because there were too few individuals, total abundance in these areas remained unaffected. Other species such as B. tyrannus that spawn in coastal and offshore waters, and Alosa pseudobarengus, that spawn in some Rhode Island estuaries ap- pear in schools sporadically following the temperature rhythm and tend to influence the total catches. In addition to physical and chemical variables and general migration trends of many species, the environments, characterized by various types of substrates and variable profusion of benthic plant life, serve to attract or discourage large populations of fishes. The greater number of species and individuals of most species preferred habitats at Harbor Island, in the lower pond and at Middle Bridge, in the lower river, where luxurious 158 growth of Zostera-algal communities occur. These habitats especially in the Middle Bridge area, in the lower river, apparently provide plant cover and abundant food supply, the primary needs of the juvenile fishes, and are therefore, major attractions to large populations of considerable number of species of young fishes (Table I). A fewer species of young fishes frequented the Bridgetown Bridge area, in the low r er river, and the seaward station, in the lower pond, where a paucity of plant life prevails. The data for growth and food studies of young fishes were combined for both the stations in each estuary. Hence, these data represent the consequences of all the environmental influences in each estuarine system. A higher profusion of benthic plant life in the Middle Bridge area, is reflected in beter conditions for growth of young fishes and greater abundance of food in the lower river as compared to those in the lower pond. Another useful aspect of the habitats with profusion of benthic plant life, is a case of mimicry exhibited by species including Tautoga onitis and Tautogolabrus adspersus, a useful adaptation for protection in these habitats. The growth studies were conducted during summer season, the period of thermal maximum. The higher temperature results in increased metabo- lic activity (Prossor and Brown et al ., 1962), and particularly influences the rate of growth in poikilothermic animals including fishes (Rounsefell and Everhart, 1953). Although the lower river was preferred by most species and held a greater abundance of prey organisms, no variation in average growth was observed for P. americanus in both the study areas. Probably due to small sample sizes the variation in growth did not become apparent. How- ever, the growth increments were significant (Pigs. 13, 17 and 18). The average growth of the young fish from the lower river and the lower pond compares favorably with growth of juvenile P, americanus in the Mystic River estuary, an area considered to be highly productive (Pearcy, 1962). The statistical analysis of growth data of juvenile B. lyr annus showed that two distinct groups in each estuarine system studied (Pig. 14) The first group, appearing from mid-August to mid-September comprising four samples of "precise size" individuals, showed significant and statisti- cally adequate growth in each of the study areas. The rate of growth per month for this species in the lower river was double that of the fish from the lower pond (Pig. 14). Although there is marked irregularity in sample sizes because of the schooling habit of this species, comparative food studies of the feeding niches also reflect the better environmental conditions in the lower river. The rest of the samples were composed of individuals with diverse size range which perhaps had strayed off from the various schools during emigration. The growth rates in such samples markedly differed from the previous samples (Figs. 17 and 18). McHugh et al. (1959) have found that a single rate of growth for this widely ranging species in an estuary is untenable. Although no comparable growth study of Menidia menidia is avail- able, the growth data of this small sized species (Figs. 15-18) indicate that significant growth increments occur from early July to early Septem- ber. Indications of variation in growth were observed in the two estuarine environments, and between the two stations within each individual estuary (Pigs. 15-18). The higher rate of growth in the lower river is indicative of a higher productivity in comparison to that of the lower pond. This 159 correlation is also corroborated by environmental and food habit studies (Table V and pp. 15). The differences in variation occurring between the stations in each estuary were probably due to late spawning at seaward stations. The higher rate of growth at seaward stations (Figs. 17 and 18) indicated smaller fish of the same year class grow faster. The success of feeding niches in the two estuarine systems studied depends upon the presence of abundant, palatable food and habitat condi- tions. The food resources in the lower Pettaquamscutt River, an area with conditions varying from neritic to brackish water and profusion growth of plant life with attendant epibiota, were comparatively abundant and suited to the food habits of all size groups of progressively growing fishes. In the lower Point Judith Pond where neritic conditions prevail, the less abundant animal food was reflected in the low diversity of prey organisms (Tables III and V). The higher percentage of empty stomachs in Pseudopleuronectes americanus and presence of phytoplankton as substi- tute diet or "forced diet' 1 in the gut contents of Menidia menidia may account for the low efficiency of the trophic environment in the lower pond. The food study of the individual species further illustrated this variation in the trophic picture. The prey of P. americanus represented a w'ide variety of organisms from both the pelagic and benthic environments (Table III). Although P. americanus is a euryphagous species (Pearcy, 1962), the three arbitrarily selected groups from the lower river demonstrated a preference for larger and more varied types of food organisms, with increase in size (Fig. 19 and Table III). The small juvenile fish (10-30 mm) largely ate harpacti- coids, Pontocypris edwardsi, invertebrate eggs, and few species of larger organisms. The inclusion of large sizes and the diverse nature of the prey including polychaetes, amphipods and isopods in the diet of young fish of size groups 31-60 mm and 61-80 mm is doubtless due to a greater adaptability of the larger young fish to capture larger and more varied types of food organisms. The stomach fullness method indicated a greater percentage of full stomachs, noted in the lower river, as function of size. While the essential dietary components were present in the food com- ponents of P. americanus from the low'er pond, the quantity and diversity in the prey organisms was low in comparison to those occurring in the lower river (Table III). Shelbourne (1953) in the plaice, Pleuronectes platessa , and Pearcy (1962) in P. americanus have observed diurnal feeding behavior. Since the catches represent day samplings, a high percentage of stomachs with little or no food, observed in the lower pond, indicate that there was a low abundance of prey organisms. Any interpretation on the basis of higher digestive rates in one estuary than the other may be erroneous as the fish of the same species were caught at the same time of the day, with lesser food in the stomachs in one environment as compared to that in the other environment. From these observations it would seem that in some river estuarine systems with a distinct salinity gradient, environmental conditions are apt to be more successful in terms of feeding niches for young fish than the estuarine environments with near neritic conditions such as the lower pond. Pearcy (1962) compared his results of production of young P. americanus from the Mystic River estuary with those of Richards (1963) from Long island Sound and contended that seventy times higher values for the estuary point to higher productivity in the small estuaries as compared to the near Sound area. 160 The data obtained for Menidia menidia, an omnivorous fish, allowed further insight into the trophic environment of the feeding niches, in both the study areas. While the diet of this species in the lower river contained a mixture of plants and animalsj the fish demonstrated largely or wholly a dependence upon phytoplankton in the lower pond. The food of Al. menidia which was rich in phytoplankton for small size (10-30 mm) fish in the lower river, essentially was composed of phytoplankton, rotifers, harpacticoids and calanoid copepods, Balanus nauplii and invertebrate eggs. With a successive increase in the size of the fish, the phytoplankton in the diet became negligible. Calanoids, harpacticoids and Balanus nauplii were the important food components for larger fish (31-80 mm). It seems that the smaller fish preyed upon minute and less mobile food organisms including phytoplankton. Later with increased size and speed these fish could feed on a great variety of larger and more mobile food organisms. Bhattacharyya ( 1957 ) reported a similar gradual dietary change from vege- table food to a carnivorous diet in postlarval herring (35 mm). The small size fish consumed more phytoplankton in the lower pond due to an apparent lack of minute prey organisms (Table V) . Forty-six per cent of the size group 31-50 mm and all of size group 51-80 mm fish ate plant food. One possible interpretation may be that due to a scarcity of carnivorous food, the fish would be forced to seek a substitute diet or so-called '‘forced diet." In this case the substitute diet was phytoplankton, primarily benthic littoral diatoms, fecal pellets and detrital material (Brodski and Jankovskaya, 1935). There is no information to the author’s knowledge concerning the nutritive value of such food. However there was indication of comparatively slow rate of growth in the pood estuary where fish largely depended upon phytoplankton. The excessive grazing by these fish on plant food, the only available substitute, may be prepara- tory for the winter season, when active feeding is probably minimal. There is no well defined study on the food habits of Brevoortia tyrannus. Controversy exists on the nature of its primary food and feeding habits. The results of the present study and comparison with other avail- able data on the food habits of this species indicate that the primary food during summer and fall is phytoplankton and suspended organic matter while in winter crustaceans constitute the basic diet (Peck, 1894; Richards et al., 1963 ), The diet of this species according to the present study includes dinoflagellates, diatoms, and a very large fraction of unidentifiable organic matter (see pp. 76). The average and percentage occurrence methods employed for analysis of food for other species were obviously not useful for this type of material. The stomach fullness method showed most of the stomachs were empty or traces to 25% full (Table VIII). Gizzards and intestines were always full which indicated that food transfer from stomach to the gizzards probably took place in a very short time. Since the diet of B . tyrannus in summer and fall included phyto- plankton and suspended organic matter, its abundance in the pond estuary can immediately be realized from the food habits of Al. menidia. Further- more the rates of growth in both estuarine systems favorably compare with data from other studies (Welsh et al., 1924; McHugh et al., 1959) and indicate that the nutrition for this species must have been adequate in both environments. The predators and most parasites did not seem to harm the popu- lations of young fishes. However the sporozoan parasites, Glugea hertwigi, 161 common in Osmerus mordax and P. americanus , Indicated harmful effects in the latter species. The comparative higher infection and markedly low catches of P. americanus in the lower pond to an extent of almost one- fourth the collections from the lower river point to possible mortality that may have incurred (Tables 1 and IX). Almost total depletion of food in heavily infected stomachs indicated feeding may have been adversely affected by presence of these parasites, but average growth in both the study areas did not show any variation, possibly due to an inequality in sample sizes. But in all cases of heavy infection, the digestive tissues were found badly attacked and showed signs of obliteration. Kudo (1947) and Duijn (1956) found dead and dying cells in infected tissues in fishes caused by Glugea hertwigi and allied species, and have reported that the host dies in advanced stages of the disease. While there are indications of some mortality caused by the infection, at the present preliminary state of study exact estimates are not possible. This problem needs a thorough investigation to determine the extent of mortality caused by these parasites. The results show that in this instance a river estuarine system with greater river influences is a more important nursery area than a pond estuarine system with neritic conditions. The conclusions derived from the present study provide some basis for launching detailed and compre- hensive future ecological studies of young fishes in other estuaries along the coast of Rhode Island, Narragansett Bay and its tributaries. These estuaries probably play an important role in maintaining the bay and coastal fisheries. VII. SUMMARY 1. Shore seining of juvenile fishes was carried out in the lower Petta- quamscutt River and the lower Point Judith Pond from July 11 to October 20, 1962. 2. Based on the salinity "conflict” during a tidal cycle the lower Petta- quamscutt River is characterized as a "gradient zone” having a distinct salinity gradient while the lower Point Judith Pond (Figs. 1 and 2) is characterized as a "marine zone" which has near neritic conditions. 3. In a total of 41 species of young fishes 36 were recorded from the low'er river and 24 from the lower pond. Fifteen species in the lower river and 11 in the lower pond appeared consistently; the rest appeared sporadically or were rare. Sixteen species recorded from the lower river and four from the lower pond were found only in those localities and not the other. 4. The abundance and diversity of various species of young fishes pro- vided evidence that these two estuarine environments are heavily used as nursery grounds. 5. The abundance of young fishes fluctuated with the rise and decline in temperature. The greatest abundance of fishes was observed in mid- August while a few individuals of resident species remained in catches in late October. 6. No correlation between changes in salinity and in abundance of fishes was noticed. But anadromous, catadromous and certain other species (Table I) occurred only in the river estuary, where the salinity gradient extends from near neritic conditions to a fresh water environ- ment. 162 7. There was no relationship observed between maximum abundance of fishes and maximum number of species appearing at any one time. Peaks in abundance of fishes were recorded in late July and August while peaks in species occurred in September. 8. The growth computations of certain selected species demonstrated that weekly intervals are too short to deduce satisfactory growth rates. Semimonthly or monthly intervals exhibited significant rates of growth. The estimation of an accurate rate of growth of Menidia menidia appearing in September and October was not possible be- cause of an admixture of fish of uncertain age groups. 9. The abundance and diversity of taxonomic groups of food organisms was greater in the Pettaquamscutt River estuary. 10. Young P. americanus and Af. menidia demonstrated change in pref- erence for larger prey organisms with the change in size of the young fishes in both estuarine systems. Juvenile B. tyrannm consumed the same type of diet irrespective of increases in size. 11. Both juvenile and adult Af, menidia depended largely on phytoplank- ton as food in the pond estuary. An apparent scarcity of carnivorous food motivated the larger fish to substitute phytoplankton as "forced diet.” 12. The lower Pettaquamscutt River has greater river influences, and a higher profusion of benthic plant life than the lower Point Judith Pond. The environmental conditions observed in the lower river indicate that the former estuarine system is more favorable as a nursery ground for the young fishes. 13. While predators and most parasites did not demonstrate any noticeable harm to fish populations, infection by the sporozoan parasite Glugea hertwigi, was a possible cause of low catches of P. americanus par- ticularly in the lower pond. 1 4. Based on the analyses of results, the parameters of abundance growth and food habits of selected species indicated the lower river estuary as the more favorable nursery ground. VIII. ACKNOWLEDGEMENTS The writer wishes to express his thanks to Dr. John T. Conover for his sincere interest, guidance and assistance in preparing the manuscript. I am indebted to Dr. Charles J. Fish for the suggestion of this problem, for his continuous guidance and for providing gear for seining operations. Appreciation is also extended to Dr. Harry P. Jeffries and Dr. Donald J. Zinn for their helpful criticism. Thanks are also extended to Dr. Saul B. Saila and Thomas A, Gaucher for their help with the growth data and programming the statistical treatments. 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Information Series, Publ. No. 3, University of Delaware Marine Lab. 1-77 pp. Smith, H. M. 1898. The fishes found in the vicinity of Woods Hole. Bull. U. S. Fish. Comm., 1897. 17: 85-111. Steven, G. A. 1933. The food consumed by Shags and Cormorants around the shores of Cornwall (England). J. Mar. Biol. Ass. U.K., 19: 277- 292 . Stommel, H., and H. G. Farmer. 1953. Control of salinity in an estuary by transition. Jour. Mar. Res., 12(1): 13-20. Tracy, H. C. 1906. A list of the fishes of Rhode Island. 36th Ann. Rept. Comm, of Inland Fisheries, Rhode Island: 38-99. . 1910. Annotated list of fishes known to inhabit the waters of Rhode Island. 40th Ann. Rept. Comm, of Inland Fisheries, Rhode Island: 35-176. Verril, A. E. 1871. On the food and habits of some marine fishes. Amer. Nat., 5: 399. Warfel, H. E. and D. Merriman. 1944. Studies on the marine resources of south New England. 1. An analysis of the fish population of the shore 2 one, Bull. Bingham Oceanogr. Coll., 9(2): 1-91. Welsh, W. W., and C. M. Breder, Jr. 1924. Contribution to life histories of Sciaenidae of the eastern United States Coast. Bull. U. S. Bur. Fish., 39: 141-201. Westman, J. R., and R. F. Nigrelli. 1955. Preliminary studies of menhaden and their mass mortalities in Long Island Sound and New Jersey waters. N. Y. Fish, and Game, jour., 2: 142-153- Wheatland, S. B. 1956. Oceanography of Long Island Sound, 1952-1953. VII. Pelagic fish eggs and larvae. Bingham Oceanogr. Coll., 15: 234- 314. Wilson, C. B. 1932. The copepods of the Woods Hole region. Bull. Nat. Mus., No. 158. 635 pp. 167 Gulf Research Reports Volume 2 Issue 2 January 1966 A Bibliography of Anomalies of Fishes, Supplement 1 C.E. Dawson DOI: 10.18785/grr.0202.03 Follow this and additional works at: http:/ / aquila.usm.edu/ gcr O Part of the Marine Biology Commons Recommended Citation Dawson, C. 1966. A Bibliography of Anomalies of Fishes, Supplement 1. Gulf Research Reports 2 (2): 169-176. Retrieved from http://aquila.usm.edu/gcr/vol2/iss2/3 This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized administrator of The Aquila Digital Community For more information, please contact Joshua.Cromwell(S)usm.edu. A Bibliography Of Anomalies Of Fishes Supplement 1 C. E. DAWSON The original bibliography (Gulf Res. Repts. 1(6), 1964) has, re- portedly, been of considerable value to workers interested in the teratology of fishes and other vertebrates. The present supplement is the first of a proposed series which will attempt to include all new and pertinent publi- cations as well as those which have previously been overlooked. The overall usefullness of the bibliography should be enhanced by its mainte- nance on a relatively current basis. Supplements will be issued irregularly and will normally include 75 to 100 new citations. In the interest of continuity, the original format and subject index headings have been retained. Supplemental citations will be serially num- bered and prefixed by the letter "S”. Acknowledgement is made to colleagues who have provided reprints of their publications and to those who have called my attention to omissions in the original bibliography. 169 BIBLIOGRAPHY S-l Alperin, I. M, 1965. Recent records of pugheaded striped bass from New York. N. Y. Fish Game J. 12(1) ; 1 14-115, 3 figs. S-2 Amaoka, K. 1964. First record of sinistrality in Poecilopsetta plinfbus (Jordan and Starks) a pleuronectid fish of Japan. Bull. Misaki Mar. biol. Inst., Kyoto Univ. 7:9-17, 3 figs. S-3 Andreu, B. 1955. Un nuevo caso de hermafroditismo en Sardina pilchardus Walb. de la ria Vigo. Invest, pesq. 2:3-7. S-4 Anon. 1953. Passage of fish over Bonneville Dam, Columbia River, Oregon and Washington, 1952. Ann. Rept, U. S. Army Eng., Portland, Oregon. S-5 Anwand, K. 1961. Fin weiterer Fund eines Heringszwitters ( Clupea barengus L.). LA further discovery of a herring hermaphro- dite! Z. Fisch. 10(4/5) : 383-386. S-6 Barcellos, B. N. 1962. Anoraalias do esqueleto da corvina. Cienc. e Cult. 14(2) :111-113, 2 figs. S-7 Barlow, G. W. 1963. Species structure of the gobiid fish Gillicb - tbys mirabilis from coastal sloughs of the eastern Pacific. Pacif. Sci. 17(1): 47-72, 13 figs. S-8 Beardsley, A. J. and Florton, H. F. 1965. An ambicolored starry flounder from Yaquina Bay, Oregon. Calif. Fish Game 51(2): 126-128, fig. S-9 Bell, G. R. 1961. Penetration of spines from a marine diatom into the gill tissue of lingcod ( Ophiodon elongatus). Nature, Lond. 192(4799): 279-280, 4 figs. S-10 Berinkey, L. 1959- A Lucioperca volgensis with a deformed head from the River Danube. Opusc. zool. Inst, zoosyst. Univ. buda- pest 31:23-27, 2 figs. S-ll Blackett, R. F. and Armstrong, R. H. 1965. Collection of two abnormal Dolly Varden: one with two dorsal fins, the other with incomplete pigmentation. Trans, Amer. Fish. Soc. 94(4): 408-409, fig. S-12 Cadenat, J. i960. Notes d'lchtyologie ouest-africaine 32. -Sur un cas d’intersexualite chez un Requin de l’espece Centrophorus lusitanicus Bocage et Capelle 1864. Bull. Inst, franc. Afr. noire (A) 22(4): 1428-1430, 3 figs. S-13 1962. Notes d’lchtyologie ouest-africaine 38. - Documents pour servir a la recherche des mecanismes de d4- placement et de remplacement des dents chez les Requins. Bull. Inst, franc. Afr. noire(A) 24(2) : 551-579, 62 figs. S-14 Cheek, R. P. 1965. Pugheadedness in an American shad. Trans. Amer. Fish. Soc. 94(1) -.97-98, fig. S-l 5 Chhapgar, B. F. 1964. A monster of the spotted duck-billed ray, Aeioba/us narinari, Copeia 1964(3) : 587-588, 2 figs. S-16 Clark, E. 1964. Spinal deformity noted in a bull shark. Underw. Nat. 2(3):25-28. S-17 Datta Gupta, A. K. and Tilak, R. 1962. A note on the deformity of Heteropneustes fossilis Bloch (Heteropneustidae: Siluroidea). Zool. Polon. 12(3):305-398, 2 figs. 170 S-18 Davidson, F. A, 1934. The homing instinct and age at maturity of pink salmon ( Oncorhynchus gorbuscha) . Bull. U. S. Bur. Fish. 48(15): 27-39. S-19 DeLacy, A. C. and Batts, B. S. 1963. A search for racial character- istics in the Columbia River smelt. Contr. Sch. Fish. Univ. Wash. 147:30-32. S-20 and Dryfoos, R. L. 1965. The longfin smelt in Lake Washington. Contr. Sch. Fish. Univ. Wash. 184:37. S-21 Desbrosses, P. 1931. Poissons de Chaiut. Traumatismes de la bouche chez la dorade commune. Les problemes qu'ils posent, concernant la biolog ie de cette espece. Rev. Trav. Off. Pech. marit. 4(1 ): 183-196. S-22 Du Buit, M. H. 1964. Une raie anormale trouvee a Concarneau. Bull. Mus. Hist, nat., Paris 36(2) : 180-184, 3 figs. S-23 Dutt, S. 1959. Biometric studies on Sardinella spp. off Waltair Coast. Proc. 1st AlMndia Congr. Zool. 1939(2) :286-298, fig. S-24 ... 1961. Biometric studies on Sardinella spp. off Waltair Coast. 2. Sardinella gibbosa Blkr, J, zool. Soc. India 13(1) : 78-89. S-25 Eigenmann, C. H. 1894. On the viviparous fishes of the Pacific coast of North America. Bull. U. S. Fish. Comm. 12:371-478. S-26 Feider, Z., et al, 1959- Une rare anomalie de la branchie chez le saurel de la Mer Noire ( Tracburus trachurus mediterraneus) . Lucrar. Stat. zool. mar. Agigeo (Vol. festiv) 1959:147-149, 2 pis. S-27 Fitch, J. E. 1963. A review of the fishes of the genus Pleuromchthys. Contr. Sci. Los Angeles Cty. Mus. 76.1-33. S-28 Follett, W. I., McCormick, R. B., and Best, E. A. I960. First records of sinistrality in Microstomus pacificus (Lockingcon) and Glyptocephalus zacbirus Lockington, pleuronectid fishes of western North America, with meristic data. Copeia 1960(2) : 112-119, 2 figs. S-29 Fry, D. H., Jr. 1961. Some problems in the marking of salmonids. Bull. Pacif. Mar. Fish. Comm. 5:78-83. S-30 Fuller, A. S. 1961. An intra-pericardial hepatic intrusion in the common dogfish. Nature, Lond. 192(4799) : 280, fig. S-31 Gabriel, M. L. 1944, Factors affecting the number and form of vertebrae in Fundulus heteroclitus. J. exp. Zool, 95(1) : 105-147. S-32 Geus, A. 1961. Uber eine siamesische Zwillingsbildung bei einem Manchen Lebtsles reliculatus Peters. Aquar.-u. Terra. Z. 14: 217-219, 5 figs. S-33 Godet, R. 1961. Un cas d’hermaphrodisme chez le Protoptere (Poisson Dipneuste). Ann. Fac. Sci. Univ. Dakar 6:145-149, 2 pis., fig. S-34 Goriunova, A. I. 1961. Deformatsiia chesun u serebrianogo karasia. (The deformation of scales in silver crucian). Vop. lkhtiol. 1(18) :52-58. S-35 Honma, Y. 1964. Notes on the specimens of halfbeaks, Hemir- hamphus sajori (T. & S.), bound their heads or trunks with rubber bands. Collect. & Breed. 26(2) : 1-3, fig. 171 S-36 1964. Notes on the encephalocele ( hernia cerebri ) found in a young salmonid fish, the koayu, Plecoglossus altivelis Temminck et Schlegel. Bull, Jap. Soc. sci. Fish. 30(11) :912- 917, pi., fig. S-37 and Duyven£ de Wit, J. J. 1961. Teratologic observations in rhodine species and hybrids (Cyprinidae). 1. Three specimens with abnormal heads. Annot. zooi. jap. 34: 133-158. S-38 . and Tamura, E. 1964. Notes on the deformity of dorsal fin in a specimen of Japanese char, the Nikko-iwana, Salvelinus leucomaenis pluvius. Collect. & Breed. 26(12): 368- 369, 2 figs. S-39 Ingalls, T. H. and Murakami, U. 1962. Cyclopia, ectromelia, and other monstrosities in zebra fish. Arch. Environ. Health 5: 114-121. S-40 Isaacson, P. A. 1965. Pugheadedness in the black perch, Embiotoca jacksoni. Trans. Amer. Fish. Soc. 94(1) :98. S-41 Kandlcr, R. 1932. Unsicherheiten bein Bestitnmung der Wirbel- zahl infolge Verwachsungserscheinungen. J. Cons. 7(3):373- 385, 7 figs. S-42 Klausewitz, W. 1961. Ein bemerkenswerter Fall von Albinismus bei Acantkobthalmus sernicinctus. Aquar,-u. Terrar. Z. 14: 9-10, fig. S-43 Kozikowska, Z. 1961. Interesting deviations from usual form in the lateral line of the carp ( Cyprinus carpio L.) from the breeding ponds near Radziadz in Silesia. Zool. Polon. 10(4): 333-336, illus. S-44 Krupauer, V. 1961. Take u kapra se muzeme setkat s hermafro- ditismem. (We also find hermaphroditism in carp). Csl. Rybarst, 9:134-135. S-45 Lamont, J. M. 1961. Fish with rubber bands. Scot. Fish. Bull. 15:17-18. S-46 Lawler, G. H. I960. A mutant pike, Esox lucius. J. Fish. Res. Bd. Can. 17(5) :647-654. S-47 1964. A northern pike, Esox lucius, with an accessory fin. J. Fish. Res. Bd. Can. 21 (6); 1547, fig. S-48 1965. Fin anomalies in the white sucker, Cato- stomus commersoni, population in Heming Lake, Manitoba. J. Fish. Res. Bd. Can. 22(1) :219-220, fig. S-49 Lea, R. N. 1965. A lahontan redsidc, Ricbardsonius egregius (Girard), lacking pelvic fins. Calif. Fish Game 51(4):300. S-50 Leonards, L. 1963. Possible albino adult chinook salmon observed. Res. Briefs Ore. Fish Comm. 9(1) :67- S-51 Lewis, D. E. 1961. Sockeye salmon, Oncorhynchus nerka, without a dorsal fin. Copeia 1961 ( 1 ) : 116-1 17, 2 figs. S-52 McCrimmon, H. R. and Bidgood, B. 1965. Abnormal vertebrae in the rainbow trout with particular reference to electrofishing. Trans. Amer. Fish. Soc. 94 ( 1 ) : 84-88, 3 figs. 172 S-53 Meinken, H. 1961. Nochmals "Em albinotischea Clarias ”. Aquar.-u. Terrar. Z. 14:329-330, fig. S-54 Miller, G. C. 1964. An aberrant green sturgeon from the lower Columbia River. Res. Briefs Ore. Fish Comm. 10(l):70-72, 2 figs. S-55 Morgan, A. R, and Gerlach, A. R. 1950. Striped bass studies on Coos Bay in 1949 and 1950. Contr. Fish Comm. Ore. 14:1-31. S-56 Neill, W. T. 1950. A channel catfish with a forked barbel. Copeia 1950<4):317. S-57 Ochiai, A. 1964. An aberrant frogfish from Japan. Bull. Misaki Mar. biol. Inst. Kyoto Univ, 5:39-41, fig. S-58 Olshanskaya, O. L. I960. Urodstva u eniseiskoi sterliadi. (Abnor- malities in Yenisey sterlet). Yop. Ikhtiol. 16:191-195, 2 figs. S-59 O’Riordan, C. E. 1961. A variation of the flounder Platicbthys jlessus (L.) from Co. Wexford. Irish Nat. J. 13(9) : 213-214. S-60 Orska, J. 1962. Anomalies in the vertebral columns of the pike ( Esox lucins L.). Acta biol. cracov. Zool. 5(2) -.327-345, illus. S-61 Paiva, M. P. 1961. Um case de ausencia da nadadeira adiposa em Pygocentrus nattereri Kner, I860. Bol. Soc. Cear. Agron. 2:45- 46, fig. S-62 — 1965. On a pelvicless specimen of Pygocentrus piraya (Cuvier, 1820) from Jaguaribe River basin, Brazil. Copeia 1965(1); 110. S-63 Raja, B. T. A. 1963. An instance of hermaphroditism in the Indian oil sardine, Sardinella longiceps (Cuv. & Val.). J. Mar. biol. Ass. India 5(1): 148-150, fig. S-64 Raju, G. I960. A case of hermaphroditism and some other gonadal abnormalities in the skipjack Katsutvonus pelamis (Linnaeus). J. Mar. biol. Ass. India 2(1) -.95-102, 5 figs. S-65 Reed, R. J. 1954. Hermaphroditism in the rosyface shiner, Notropis rubellus. Copeia 1954(4) :293-294. S-66 Regan, J. D. 1961. Melanism in the poeciliid fish, Gambusia affinis (Baird and Girard). Amer. Midi. Nat. 65 ( 1 ) : 139-143, 2 figs. S-67 Reichenback * Klinke, H. H. 1961. Ein Nase - Nerfling - Bastard [ Chondro stoma nasus (L.) x Idus idus (L.) J mit abnorm verlangerten Flossen. Allg. FischZtg. 86(5) :151-152. S-68 Rich, W. H. and Holmes, H. B. 1929. Experiments in marking young chinook salmon in the Columbia River, 1916 to 1927. Bull. U. S. Bur. Fish. 44:215-264. S-69 Rietze, H. L. 1954. Naturally missing fins from chum salmon. Res. Briefs Ore. Fish Comm. 5(1) :26. S-70 Sachs, W. B. 1961. Ein albinotischer Clarias. Aquar.-u. Terrar. Z. 14:268-269, fig. S-71 Saemundsson, B. 1909- Oversigt over Islands fiske. Skr. Komm. Havunders 5 : 1-140. S-72 SalekhoYa, L. P. 1961. Hermaphroditism of Diplodus annularis (L.). (in Russian). Trav. Sebast. biol. Sta. 14:257-268, 10 figs. S-73 Sathyanesan, A. G. 1962. On the abnormal dorsal fin of the teleost Labeo calbasu (Ham.). Sci. & Cult. 28 ( 12) : 588-589, illus. 173 S-74 Schwartz, F. J. 1965. A pugheaded menhaden from Chesapeake Bay. Underw. Nat. 3(l):22-44, 3 figs. S-75 Shchupakov, L. G. and Kharchenko, L. N. I960. Anomalies among interspecific hybrids of whitefishes produced in Ural commercial fish farms, (in Russian), in Distant Hybridization of Plants and Animals, pp. 520-531. S-76 Shulyak, G. S. 1961. Cases of atypical structure of the intestine in carp. (Russian with English summary). Dopov. Akad. Nauk. ukr. RSR 3:384-386, 3 figs. S-77 Singh, T. P. and Sathyanesan, A. G. 1961. An instance of herma- phroditism in the catfish Mystus vittatus (Bloch). Curr. Sri. 30:302-303, 2 figs. S-78 Sommani, E. 1962. Interessante caso di mostruosita in esemplare di tinea ( Tinea tinea L.). Boll. Pesca Piscic. Idrobiol. 15(2): 109*193. S-79 Steffens, W. 1961. Flossenschadingungen beim Hecht {Esox Indus). Biol. Zbl. 80(1) : 79*84. S-80 Templeman, W. 1965. Some abnormalities in skates {Raja) of the Newfoundland area. J. Fish. Res. Bd. Can. 22(1) :237-238, 4 figs. S-81 Tester, A. L. 1949. Populations of herring along the west coast of Vancouver Island on the basis of mean vertebral number, with a critique of the method. ]. Fish. Res. Bd. Can. 7(7): 403*420. S-82 Tschvertner, U, 1956. Untersuchungen ueber den einfluss einiger Milienfaktoren auf die Entwicklung des Hechtes (Esox Indus L.). Arch. Hydrobiol. 24(3) : 123-152. S-83 Uchida, R. N. 1961. Hermaphrodite skipjack. Pacif. Sci. 15:294- 296, 3 figs. S-84 Vastesaeger, M., et al. 1961. L’atherosclerose spontanee du thon rouge ( Thynnus tbynnus L.). Bull. Cent. Etud. Rech. sci., Biarritz 3:449-435, 4 figs. S-85 Walker, J. M. and Taylor, H. L. 1965. A brook trout with no anal fin. Progr. Fish Cult. 27(4): 233, fig. S-86 Ward, J. W. and Dodds. R. P., Jr. 1965. Observations upon a natural population of normal, hemicaudate, and decaudate gold- fish, Carassius aura/ns. J. Miss. Acad. Sci. 11:191-195, fig. S-87 White, J. C, Jr. and floss, D. E, 1964. Another record of incom- plete ambicoloration in the summer flounder, Paralichtbys dentatus . Chesapeake Sci. 5(3): 151-152, fig. S-88 Williamson, II. C. 1909- Abnormal skate {Raia drcularis and Raia clavata ). Rep. Fish. Bd. Scot. 28(3) :64, 3 figs. S-89 Wunder, W. 1956. Leistungs prufungsversuche beim Karpfen 1955. Ergebnisse aus bayerischen Teichwirtscbaften. Arch. FischWiss. 7(1): 17-30. S-90 I960. Erbliche Flossenfelder beim Karpfen und ihr Einfluss auf die Wachstrumsleistung. Arch. FischWiss. 11: 106-119, 14 figs. S-91 1961. Formveranderung der Schwimmblase des Karpfens bei Wirbelsaulenverkrummung. Allg. FischZgt. 86(8) : 236-238. 174 TAXONOMIC INDEX Acanthopthalmus semicinctus — S42. Aetobatus narinari — SI 5. Acipenser — S58. medirostris — S54. Alosa sapidissima — S4, Sl4. Brevoortia tyrannus — S74. Carassius auraius — S86. Car char hinus leucas * — S16. Carp — S34, S44, S76, S90, S91. Catostomus commersoni — S48. Centropborus lu sit attic us — S12. Chondrostoma nasus — S67. Clarias — S53, S70. Clupea — S4l. harettgus — S5. Coregonus albula ladogensis — S75. lav ar tens — S75. Cymatogaster aggregata — S25. Cyprinus carpio — S43, S89. Diplodus annularis — S72. Embiotoca jacksoni — S40. Esox lucius — S46, S47, S60, S79, S82. Fundulus heteroclitus — S31. Gam bust a af finis — S66. Gillichthys mirabilis — S7. Glyptocephalus zachirus — S28. Hemirhamphus sajori — S3 5. Heteropneustes fossilis — S17. Ictalurus lacustris punctatus — S56. Idus idus — S67. Katsuwonus pelamis — S64. Labco calbasu — S73. Lebistes reticulatus — S3 2. Lucioperca volgensis — S10. Micropogon furnieri — S6. Microstomus pacificus — S28. My st us v hiatus — S77. Notropis rubellus — S6 5. Oncorhynchus gorbuscha — S18. keta S69. nerka — S51. tshawytscba — S50, S68. Ophiodon elongatus — S9. Pagellus — S21. Paralicbtbys dentatus — S87. Platichthys flessus — S59. stellatus — S8. Plecoglossus altivelis — S3 6, Pleuronectes — S4l. Pleuronichthys — S27. Poecilopsetta plinthus — S2. Pygocentrus natter eri — S6l. piraya — S62. Raia circular is — S88. clavata — S88. Raja clavata — S22. jenseni — S80. laevis — S80. radial a — S71, S80. Rhombus — S41. Richardsonius egregius — S49. Roccus saxatilis — SI, S74. Salnto gairdneri — S52. Salvelinus fontinalis — S85. leucomaenis pluvius — S38. malma — SI 1. Sardina pilch at' dus — S3. Sardinella fimbriata — S23. gibbosa — S24. Ion gi ceps — S63. Scyliorhinus canicula — S30. Thyttnus thynnus — S84. Tinea tinea — S78. Trachurus trachurus mediterraneus — S26. 175 SUBJECT INDEX Abnormal coloration — S 46. Albinism — Sll, S42, S50, S53, S70. Ambicoloration — S8, S27, S59, S87. Anal fin. etc. — S85. Barbels — S56. Body (misc.) — S6, S46. Caudal fin, etc. — S54, S86. Cyclopia — S39. Dorsal fin, etc. — S7, Sll, S38, S48, S51, S73. Fins (misc.) — S7, S18, S19, S20, S22, S29, S48, S54, S57, S6l, S67, S68, S69, S90. Gills, etc. — S26. Head (misc.) — S10, S36, S37, S39. Internal organs, fasciae, etc. — S30, S76, S91. Lateral line, etc. — S43. Melanism — S66. Mouth, jaws, etc. — S7, S21. Pectoral fin, etc. — S15, S22, S48, S71, S80. Pelvic fin, etc. — S47, S48, S49, S54, S62. Pug-head, etc. — SI, S14, S25, S40, S74, S80. Reversal — - S2, S28. Scales, etc. — S34, S54. Sex organs, hermaphroditism, etc. — S3, S4, S5, S12, S33, S44, S55, S63, S64, S65, S72, S75, S77, S83. Teeth, etc. — S13. Twins, double monsters, etc. — S32. Vertebral — S7, S16, S23, S24, S31, S41, S52, S60, S80, S81, S84, S86, S91. Wounds — S9, S33, S35, S79. 176 Gulf Research Reports Volume 2 Issue 2 January 1966 Studies of Annual Abundance ofPostlarval Penaeid Shrimp in the Estuarine Waters of Mississippi, As Related to Subsequent Commercial Catches J.Y Christmas Gulf Coast Research Laboratory Gordon Gunter Gulf Coast Research Laboratory Patricia Musgrave Gulf Coast Research Laboratory DOI: 10.18785/grr.0202.04 Follow this and additional works at: http:/ / aquila.usm.edu/ gcr O Part of the Marine Biology Commons Recommended Citation Christmas, ]., G. Gunter andP. Musgrave. 1966. Studies of Annual Abundance ofPostlarval Penaeid Shrimp in the Estuarine Waters of Mississippi, As Related to Subsequent Commercial Catches. Gulf Research Reports 2 (2): 177-212. Retrieved from http:// aquila.usm.edu/gcr /vol2/iss2/4 This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized administrator of The Aquila Digital Community. For more information, please contact Joshua.Cromwell(o)usm.edu. STUDIES OF ANNUAL ABUNDANCE OF POSTLARVAL PENAEID SHRIMP IN THE ESTUARINE WATERS OF MISSISSIPPI, AS RELATED TO SUBSEQUENT COMMERCIAL CATCHES 1 by J. Y. Christmas, Gordon Gunter and Patricia Musgrave Gulf Coast Research Laboratory, Ocean Springs, Mississippi THE PROBLEM During the past fifteen years the landings of commercial shrimp at Mississippi ports have varied by a factor of three and even from one year to the next the catch has varied by a factor of 2.5. These facts are shown in table 1. The dollar values of the landings have varied somewhat less, about 2.1 at the most, as shown in the same table, because as fewer shrimp are caught the price goes up and vice versa. Thus the law of supply and demand causes shrimp prices to vary less than total landings. The above figures refer to Mississippi landings from all waters of the Gulf Coast, chiefly Louisiana, with lesser amounts from Mississippi, Alabama and a very little from Florida and Texas. The commercial shrimp catch figures for Mississippi Sound have only been available since 1956. The annual catches are shown in table 2. This includes all three species of commercial shrimp. The area includes a small part of Mississippi Sound that lies in Alabama, and the figures do not include the outside waters of Mississippi. Therefore, the figures do not represent the total annual catches from Stare waters. Table 2 shows that Mississippi production has varied by a factor greater than three since 1956. Not all shrimp taken in Mississippi Sound are landed in the State. Insofar as some shrimp caught within the State are carried out of it and some caught outside of the State are brought into it, it is most probable that the Mississippi Sound production plus the shrimp taken in the Gulf off Mississippi make up about half of the State landings. Between 1956 and 1964 the annual catch in the Sound varied from an amount equivalent to 27 to 46 per cent of the State landings, the average being 3 6 per cent per year. The initial catches when the shrimp season opens are made mostly in the Sound and it is a matter of considerable economic importance to the local industry to know what the abundance of the commercial population will be from year to year. Additionally, many shrimp taken in the open Gulf off the Mississippi coast come from the Sound originally. Several workers and several lines of evidence have shown that the i Supported by United States Bureau of Commercial Fisheries contracts 14-17-0002-43, 14-17-0002-81-A and 14-17-0002-101 with the Gulf Coast Research Laboratory, which extended from 1 November 1962 to 31 October 1964, 177 Table 1. Mississippi Landings of Commercial Shrimp. Heads on Weight Thousand pounds Thousand dollars 1950 9,460 2,071 1951 7,475 1,470 1952 6,800 1,611 1953 8,517 2,301 1954 8,261 1,534 1955 13,617 2,504 1956 10,912 2,753 1957 9,569 2,617 1958 6,476 2,377 1959 11,319 2,345 I960 11,031 2,899 1961 4,408 1,281 1962 6,104 2,220 1963 9,375 2,484 1964 4,034 1,805 Table 2. Mississippi Sound (areas 01 LI on weight in thousand pounds Shrimp Data, U. S. Bureau of and 012.1) total catch, heads (Conversion from Gulf Coast Commercial Fisheries). 1956 2991 1957 3194 1958 2504 1959 5167 1960 4234 1961 1584 1962 2147 1963 2225 1964 2295 178 shrimp life cycle is very short, probably about 15 to 16 months, for the very small fraction reaching the largest adult size. Additionally, a great deal of commercial fishing is carried out upon sub-adult populations within the bays and shallow Gulf. In fact most shrimp that are caught have never spawned. These shrimp grow up within one warm season and they are derived from larvae which make their way to inside waters from the off- shore spawning areas. Thus, it has been surmised for a long time that prediction of at least the relative abundance of the future shrimp could be deduced from studies of the numbers of young or juvenile shrimp in the bays right after they have completed their larval immigration. The first work on this problem was carried out by Baxter (1962) at the Galveston Laboratory of the Bureau of Commercial Fisheries. He sam- pled one area at the entrance of Bolivar Pass, leading into Galveston Bay, with a beam trawl. Work at the Gulf Coast Research Laboratory in Mississippi Sound was carried out under contract with the Bureau of Commercial Fisheries, and was initiated on 1 November 1962. The contract was terminated on 31 October 1964, although the work has been carried out on a reduced scale since that time. The present report covers the period of the contract. Th© Goar Used A small beam trawl of such size that it could be dragged by one man was used in this program. In part this gear was used because it would give data comparable to what had been collected before by Baxter and in part because it was quite suitable for sampling small organisms in shallow waters. This gear was figured and described by Renfro (1963). It was also described by Baxter (1963) in the following words: "Samples are collected semiweekly using a hand-drawn beam trawl fitted with a plankton net at the cod end (Renfro, In press). The net is 5 feet wide (along both cork and lead lines) by 2 1/3 feet long. The wings are made of nylon material having 50 holes per square centimeter. The body tapers to a canvas cylinder about 5 inches in diameter and 8 inches long. A l2-in T #l-mesh plankton net with a removable bucket is fitted over the collar. The plankton net is secured by a snap and ring arrange- ment. "Around both collar and plankton net is fitted a 2 1/4-foot section of light canvas which acts as chafing gear. A 7-foot piece of 3/16-inch stainless steel cable, onto which are threaded additional lead weights, serves as the net’s lead line. The ends of the cable are attached by means of swivels to the ends of a 6-foot length of 11/16-inch stainless steel pipe which constitutes the beam. To the cork line are threaded five 2 3/4-inch sponge floats. The cork line ends are tied directly to the beam, 8 inches from either end. A 15-foot length of nylon parachute cord serves as the bridle line. The effective opening of the net unit is approximately 5.8 square feet.” The net used in Mississippi differed from the one described by Baxter by two minor modifications. (1) The canvas section around the plankton net and collar was made longer than the Galveston net to prevent wear on the bag of the plankton net, (2) A short line was attached to a bight of the bridle to allow walking outside of the path of the net instead of in 179 front of it. A strap loop was attached to the end of the line for easier handling. Sampling Procedure The following description of the method of sampling is given by Baxter: "The sample is taken in the following manner. A 6-foot stake ( V 2 - inch galvanized tubing) with 150 feet of nylon parachute cord attached, is driven into the ground at the shoreline. The cord is payed out and stretched taut parallel to the water line. Using the cord as a constant radius, the operator pulls the net assembly along the bottom in a half circle. This method is duplicated each time so that standard tows are obtained. The depth of tow varies from 0 to 4 feet depending on tidal conditions and roughness of the water. The effective length of each tow is about 470 feet, the volume of water sampled is 2,477 cubic feet, and the bottom area traversed is 1,958 square feet." In collecting the Mississippi samples the operators did not walk in in front of the net because it was thought this would unduly disturb the bottom. Thus, the man pulling the net walked outside of the smaller semi- circle the net traversed around the stake. At one station, number 31, the water was too deep for wading and the net was pulled for a fixed distance along the shore. For various reasons this station was not visited regularly. After the tow was made the net was washed to remove as much mud and sand as possible. The net contents often included large amounts of vegetable debris. The washing usually reduced the total sample to an amount which could be placed in a gallon jar. A solution of 40% for- maldehyde was added to this jar. The water temperature, to the nearest tenth of a degree C, was taken by the simple process of holding the thermometer in the water. A water sample at the bottom was taken in a citrate bottle and returned to the laboratory where hydrometers were used to determine salinities. Tidal conditions, wind direction and estimated velocity, state of the sea and sky and general observations of turbidity of the water were recorded. Stations The location of all stations is given in table 3. These locations are shown on plate 1, which is a map of the Mississippi Sound area. A short description of each station area may be given as follows: STATION 1 — Davis Bay Located along East Beach of Ocean Springs, this station has a fairly firm sand bottom along its marsh-lined beach changing to a soft mud bot- tom in deeper water. A drainage ditch empties into the bay at the eastern edge of the station area. STATION 4 — East End of Deer Island Located along the western end and southern side of Little Deer Island (Fawn Island), the bottom of this station varies from firm sand to soft mud with a sand -mud combination being rhe usual case. Along the western edge of the station area is a small marsh bed. Extensive grass beds ( Ruppia maritima) and an abundance of hermit crabs in the station area are seasonal occurrences. 180 STATION 8 — West End of Horn Island, North Shore This station has a sand beach as the southern border and a clean, firm sand bottom. Shifting sand, causing increased depth, required shifting of this station location back and forth over an area within about a mile of the end of the island. STATION 11 — Belle Fontaine Beach, East at Jetty The sand bottom of this station is usually covered with a V 2 -6 inch layer of soft mud. The water in the area is generally quite muddy with a large amount of debris which makes a dark swash mark on the clean white sand beach. Dredging operations at this station changed the bottom so that the station location was moved east approximately one mile in August 1963. STATION 13 — Horn Island, Horseshoe The firm sand bottom of this station is spattered with occasional small grass patches. The sand beach border and the depth of water vary frequently. STATION 14 — Round Island This station has a sand beach with a clean, hard sand bottom, STATION 15 — Pascagoula River, Island off Spanish Point This station has a sand beach with its bottom varying from soft mud to firm sand. Spoil in the station area from the dredging of the Pascagoula Channel caused the abandonment of this station in October 1963. STATION 18 — Henderson Point, East at Jetty Sand beach with firm, clean sand bottom. STATION 19 — Bayou Caddy, East of Entrance Bordered by a sand beach and sea wall, this station has a fairly firm mud-sand bottom with shells along the sea wall. Usually there is much trash washed into the station area. STATION 20 — Cedar Point, Bay of St. Louis The haul here is made around a large marsh bed. The bottom varies from firm mud-sand to soft mud with occasional grass patches. STATION 21 — Shell Beach, Bay St. Louis (Oblate Fathers Property) The beach at this station is composed primarily of shells. The bottom is relatively soft mixture of red clay, sand, pebbles, and shells. STATION 22 — East End of Horn Island Sand beach with firm, clean sand bottom. STATION 23 — Gaston Point, Gulfport Beach Sand beach with firm sand bottom. Occasionally mud-sand bottom. STATION 24 — North Point, Cat Island Sand beach and firm sand bottom with approximately half of sam- pling area covered with grass beds. STATION 25 — West End of Ship Island Sand beach with firm, clean sand bottom. 181 Table 3. Location of Stations Shrimp Postlarval Studies Sta. No. Latitude Longitude 1 30° 23' 36” N 88° 48’ 31” W 4 30° 21’ 25” N 88° 48’ 34” W 8 30° 14' 42” N 88° 46’ 11” w 11 30° 20' 31” N 88° 45’ 47” w 13 30° 14' 03” N 88° 39’ 13” w 14 30° 17' 58” N 88° 35’ 28” w 15 30° 20' 12” N 88° 34’ 07” w 18 30° 18’ 10” N 89° 17’ 25” w 19 30° 15' 35” N 89° 25’ 27” w 20 30° 20' 35” N 89° 20’ 48” w 21 30° 22' 30” N 89° 19’ 28” w 22 30° 13’ 21” N 88° 33’ 32” w 23 30° 21’ 22” N 89° 06’ 48” w 24 30° 15’ 06” N 89° 03’ 36” w 25 30° 12’ 40” N 88° 58’ 54” w 26 30° 14' 42” N 88° 52’ 25” w 27 30°