Feeding Ecology of Spottail Pinfish (<I>Diplodus Holbrooki</I>)

BULLETIN OF MARINE SCIENCE. 55(2-3): 363-374. 1994

FEEDING ECOLOGY OF SPOTTAIL PINFISH (DIPLODUS HOLBROOK!) FROM AN ARTIFICIAL AND NATURAL REEF IN ONSLOW BAY, NORTH CAROLINA

Lisa A. Pike and David G. Lindquist

ABSTRACT The purpose of this study is to compare diet composition and sources for spottail pinfish (Diplodus holbrooki) from adjacent innershelf artificial and natural reefs located 8 km offshore in Onslow Bay, North Carolina. Different size classes of spottail pinfish, season of capture (spring or summer), and prey habitat (hardbottom, softbottom or planktonic) were compared for each reef. Spottail pinfish had an overall omnivorous diet of 50% benthic algae, 30% benthic animals, 15% planktonic animals and 5% miscellaneous animal prey, by volume. Seasonal variation in diet was apparent. More planktonic food items and crustaceans were eaten in the spring and diet shifted to include more algae and benthic foods in the summer. There was no difference in the amount of algae eaten by fish of different size classes though larger fish consumed less planktonic foods and smaller fish consumed more benthic foods. The diets of 96 spottail pinfish (60-160 mm SL) at the artificial and natural reef show 88% similarity. While some food items (bryozoans, amphipods) differed significantly between reefs, the proportion of prey types (benthic animal, algae, planktonic animal) in the diet were not different overall between reefs. Prey associated with softbottom habitats were a minor « I% total diet) part of the diet.

Artificial and natural reefs provide a hard substrate for benthic prey, which then attract commercially and recreationally important reef fishes (Chester et aI., 1984; Bohnsack and Sutherland, 1985; Hueckel and Buckley, 1987). Some gut content studies indicate that fish are not feeding on reef-associated foods (Randall, 1963; Russell, 1975; Murdy, 1979; Grimes, 1979; Hobson and Chess, 1978; Mottett, 1981; Kakimoto, 1982; Steimle and Ogren, 1982; Bolden, 1990). However, others have found diets with mixtures of hard- and softbottom prey from fishes inhabiting temperate artificial reefs (Prince and Gotshall, 1976; Hueckel, 1980; Hueckel and Slayton, 1982; Jessee et aI., 1985; Mottett, 1985; Hobson and Chess, 1976, 1986; Hueckel and Buckley, 1987; Burk, 1990; Lindquist et aI., 1994). A comparison of diets between a subtropical artificial and a natural reef off the Florida east coast revealed dissimilar diets of reef associated prey for the gray triggerfish (Balistes capriscus), while the pigfish (Orthopristis chrysoptera) had a similar diet composed of softbottom prey (Vose, 1990). In general, trophic pathways involving artificial reefs are not well studied (Bohnsack and Sutherland, 1985). Spottail pinfish (Diplodus holbrooki) have been identified as one of the more abundant reef-associated fish off North Carolina (Clavijo et aI., 1989; Lindquist et aI., 1989). Previous studies on the diet of spottail pinfish from subtropical Florida indicate an ontogenetic shift related to changes in dentition, from a car- nivorous juvenile to a herbivorous adult (Reid, 1954; Carr and Adams, 1972, 1973; Livingston, 1982; Hastings et aI., 1976; Stoner and Livingston, 1984). A few studies have examined populations from North Carolina jetties (Lindquist et aI., 1985; Hay and Sutherland, 1988). Hay and Sutherland (1988) found that spottail pinfish collected from a rubble-mound jetty in North Carolina had a diet consisting almost entirely of algae. They refer to the spottail pinfish as an important temperate herbivore. However, Lindquist et aI. (1985) found that spottail

363 364 BULLETIN OF MARINE SCIENCE. VOL. 55. NO. 2-3. 1994 pinfish collected from another North Carolina jetty had a diet consisting of only 30% epiphytic algae along with a variety of benthic crustaceans. The purpose of our study is to answer the following questions: What are the sources of prey supporting spottail pinfish at adjacent artificial and natural reefs? Does the diet of spottail pinfish at a warm temperate innershelf reef vary with fish size or season (spring vs. summer)?

MATERIALS AND METHODS

Study Sile.-The study site selected consists of two reefs: an artificial train car reef (AR) and a natural limestone ledge reef (NR), both lying approximately 7.5 kIn southeast of Masonboro Inlet in Onslow Bay, North Carolina. The reefs arc in 17-19 m of water. The AR is a state-maintained and buoyed reef (AR372). The train cars have collapsed since deployment in 1986 and provide irregular relief, generally only 0.5 m but occasionally reaching 3.7 m. The NR is approximately 0.8 km southwest of the train cars and consists of a limestone ledge overhang with patches of sand in many areas. It provides a consistent vertical relief approaching 2.5 m. The NR is approximately 0.8 km in length (Bolden, 1990). Benthic maeroalgae are present at both reefs, as are barnacles, bryozoans, hydroids and sponges. The NR also has some gorgonians and coral (Oculina sp.). Fish Collection and Diet Analysis.-Specimens used in stomach analyses were collected with SCUBA from April to September, 1990, between 0900 and 1100 and between 1300 and 1430, at both reefs. The collection was divided into three separate periods based on water temperature so that data could be analyzed to determine if there was a seasonal shift in diet. During period I (April-May) water temperatures were low, ranging from 15° to 25°C (x = 19°C, N = 20). In period 2 (June) mean water temperatures increased, and ranged from 23° to 26°C (x = 25°C, N = 13). Period 3 (July-September) had the highest water temperatures, ranging from 27° to 30°C (x = 29°C, N = 22). The fish were placed into four arbitrarily defined size classes to determine if an ontogenetic shift in diet occurrs: 60-85, 86-110, 111-135, and 136-160 mm standard length (SL). Prey categories were grouped ac- cording to habitat as benthic hardbottom, benthic softbottom, planktonic or benthic (substrate unknown or demersal). Habitat designations were based on literature references (Ruppert and Fox, 1988), com- munications (J. L. Barnard, Smithsonian Institute) and our own observations. Fish were fixed in the field with 20% buffered formalin injected directly into the gut cavity (Windell, 1968). Guts were removed from esophagus to anus and measured. Relative gut lengths were indexed by dividing total gut length by SL (AI-Hussaini, 1947). Visual estimates of stomach fullness were made on a scale of 0-4: 0 (empty) and 4 (completely full). The relative volume of each prey type was determined by placing them, in unifornl thickness, on a gridded plate (Hellawell and Abel, 1971; Hyslop, 1980). The number of grids covered was used to estimate the relative volume (I square of 0.5 mm thickness = 1.125 mm3) of the stomach contents that organism type composed. No count of algae, hydroids nor bryozoans was determined, therefor the numerical value for these prey items was not considered. Relative frequency of occurrence was determined as the percentage of fish containing a specific food item. Percent number and percent volume were also determined for specific prey types. Animal prey items that constituted less than I% of the total volume, and unidentifiable animal prey, were placed in a miscellaneous category. Sl2Irensen'scoefficient of community similarity, as recommended in Brower and Zar (1984), was used to compare the diets of fish (using diet items >1% of the diet only) at the artificial reef with those from the natural reef. Factorial ANOVAs and Duncan's multiple range tests, provided by SAS PROC GLM and PROC MEANS, were used to analyze the data (trans- formed to logarithms).

RESULTS Fish Length.-The mean SL of fish caught did not significantly differ between reefs (Fig. 1). The mean SL of fish caught at both reefs combined, or at either reef, within each of the three collection periods, also did not differ significantly. Gut Length and FulLness.-Mean relative gut length for all fish was 1.3. Relative gut lengths did not differ significantly between size classes, reef or collection period. Mean stomach fullness was 2.4 (between 1h and * full) for all fish. Mean stomach fullness did not differ significantly between time of day (morning or afternoon) or collection periods. Stomach fullness was different (P < 0,05) for PIKE AND LINDQUIST; SPOTTAIL PINFISH REEF DIET 365

20 • AR11AClAL ( 4 8 ) ~ NATURAL ( 48 ) 18

>- 12 ~ w 10 ::> o w 8 ...II:

o 60-85 86 -110 111-135 136-160 " III IV SIZE CLASS (mm STANDARD LENGTH)

Figure I. Size frequency and sample sizes of the selected size classes of 96 spottail pinfish from the artificial and natural reef. fish of different sizes. Size class I had the fullest stomachs and mean stomach fullness decreased as fish size increased (Fig. 2). Diet Analysis.-Nine species of red algae plus one brown alga and six phyla of invertebrates, as well as fish remains, occurred in the stomachs of the 96 spottail pinfish examined (Table I). Most of the algae found in the stomachs were intact and consisted of large pieces that were not macerated. Also, many pieces of algae had bryozoans or hydroids still attached. Sand was also observed in most stomachs but did not vary in amount by reef or, reefs combined or separated, by collection period or size class.

4.0

3.5

rJl rJl 3.0 w Z ...J ~...J 2.5 LI.. :I: (.) 2.0 <{ :E o f- 1.5 rJl Z <{ 1.0 w :E 0.5

0.0 60-85 (n:17) 86-110 (n:29) 111-135 (n:31) 136-160 (n:19)

SIZE CLASS (mm SL)

Figure 2. Mean and standard error of the mean for spottail pinfish stomach fullness from the artificial and natural reefs. 366 BULLETIN OF MARINE SCIENCE. VOL. 55. NO. 2-3, 1994

Table 1. A list of the prey items and their habitat designations found in the stomachs of spottail pinfish captured at innershelf artificial and natural reefs in Onslow Bay, North Carolina (BH = benthic hardbottom, BS = benthic softbottom, P = planktonic, U = unknown habitat, B = benthic, substrate unknown or demersal)

Cnidaria Diplostraca P Hydrozoa BH Cladocera Sertularia Evadne sp. Dynamena cornicina Tanaidacea B Leptomedusae Isopoda U Campanularia sp. Ostracoda BS Annelida Bryozoa BH Polychaeta Gymnolaemata Spionidae Chordata Polydora sp. (larvae) P Urochordata Mollusca Larvacea Gastropoda Oikopleura sp. P Eggs BH Vertebrata Bivalvia Osteichthyes Arcoida sp. (juvenile) BS Eggs P Arthropoda Scales U Crustacea Larvae P Copepoda Algae Calanoidea Rhodophyta Eucalanus spp. P Nemaliales Centropages sp. P Acrochaetiaceae Undinula vulgaris P Acrochaetium spp. BH Temora sp. P Chaetangiaceae Cyclopoidea Scinaia complanata BH Corycaeus sp. P Gigartinales Cirripedia Gracilariaceae Thoracica Gracilaria folifera BH Balanomorpha Rhodymeniales Balanus sp. BH Champiaceae Mysidacea Champia parvula BH Neomysis sp. B Lomentaria baileyana BH Amphipoda Ceramiales Gammaridea Ceramiaceae Stenothoidae sp. BH Griffithsia globulifera BH Microjassa sp. BH Delesseriaceae Ampelisca sp. BH Hypoglossum tennuifolium BH Ph otis reinhardi BH Rhodemelaceae Photis macrocoxa BH Polysiphonia spp, BH Ericthonius rubricornis BH Chondria littoralis BH Ericthonius brasiliensis BH Phaeophyta Stenothoe minuta BH Sphacelariales lschyrocerus anguipes BH Sphacelariaceae Podoceropsis nitida BH Sphacelaria tribuloides BH Caprellidea Metacaprella sp. B Decapoda Caridae B Brachyuran zqea P

In order of decreasing frequency of occurrence, algae, crustaceans, miscellaneous items, and larvaceans, were the dominant foods of fish caught at both NR and AR (Fig. 3). By number, algae, hydroids and bryozoans excluded, gastropod eggs were dominant at AR, although these were clustered in three stomachs. Though gastropod eggs were found in several fish (N = 6) from both reefs, the greatest number and volume were found in fish (N = 3) caught at AR. These fish PIKE AND LINDQUIST: SPOTTAIL PINFISH REEF DIET 367 A 100 90 80 70 i 60 w 50 0 II: w 40 Q. 30

20 10 8 0 70

50 ~ z 40 w U II: w 30 Q.

0 C ICJ % MEAN VOLUME 70 111I % MEAN NUMBER 60 e:::l % FREC. OCCUR.

~ 50 Z w 40 U II: W 30 Q. 20

0 w Ul Ul Ul Ul Ul Ul Ul z z z 0 w ~ ;:, < < < (5 Iii ~ 0 9 w w 0 a: w w < u U N :x:< 0 z < < 0 0 0 < > > > u Do ...J a: a: :x: > ...J In;:, ...J 0 a: III 0 a: W :3 Do u u In Ul ~< :i DIET ITEM

Figure 3. Percent mean volume, percent mean number, and percent frequency of occurrence of major (> I % of total diet) dietary items found in the stomachs of spottail pinfish. Standard error of the mean is shown. A. Both reefs combined. B. Artificial reef. C. Natural reef. were caught on three separate dates. Percent by volume was selected as the most reliable index, since algae, hydroids and bryozoans were uncountable. By volume, algae were the dominant food items at both sites. There were significantly more bryozoans eaten at NR while significantly more gammarid and caprellid amphi- 368 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994

• ALGAE r:a BEN'TMlCAHlMAl.. .. • PLANKTONIC ••••••••••L CiI MISCEl ••.••NEOUS

SIZE CLASS (mm SLI • 60-85 (17) Gl 8s.110 (29) g 111-135 (31) [J 136-180 (19) Ii " .o !; ~ 20 . "

ARTIFICIAL <"81 NATURAL (48) &ENTHIC ANIMAL PLANKTONIC ANIMAl MISCELl.ANEOUS

COLLECTION PERIOD • APRIL-MAY (32) GJ JUNE (45) § JUl V-SEPT (19)

BENTHIC ANIMAL PLANKTONIC ANIMAL MISCELLANEOUS

Figure 4 (upper left). Percent mean volume, standard error of the mean, and sample size in parenthesis, of the prey categories found in the stomachs of spottail pinfish collected from the artificial and natural reef.

Figure 5 (upper right). Percent mean volume, standard error of the mean, and sample size in parenthesis, of the prey categories found in the stomachs of spotlail pinfish of different sizes.

Figure 6 (lower center). Percent mean volume, standard error of the mean, and sample size in parenthesis, of the prey categories found in the stomachs of spottail pinfish caught at different times during the collection period, pods were eaten at AR. AJI other diet items did not differ significantly by volume, nor did the proportion of benthic animal, planktonic animal, or algal prey types in the diet (Fig. 4). Sfijrensen's coefficient of community similarity results indicates that the diet of spottail pinfish caught at the two reefs are 88% similar. Because the diet was similar at both reefs, diet data were pooled for comparisons between size classes and collection periods. Percent volume, Duncan's multiple range test results and significance values for diet items eaten by spottail pinfish at both reefs, by size class and coJlection period, are given in Tables 2 and 3. There was no significant difference in the volume of algae eaten by spottail pinfish in the four size classes. OveraJl, less planktonic food items were eaten by spottail pinfish in size class IV than smaller fish, and fish in size classes I and II ate more benthic foods (Fig. 5). The fish caught in period one ate a significantly larger volume of planktonic items (specifically cladocerans, larval polychaetes, larvaceans and copepods) than were eaten in period two or three (Fig. 6). Crustaceans were also more abundant in the diet of spottail pinfish caught in periods one and two, especiaIJy the copepods, cladocerans and mysids and juvenile caridean shrimp. Fish caught in periods two and three ate a significantly greater volume of algae. Fish caught in period three had a greater proportion of bryozoans and hydroids in their diet than did fish caught in period one.

DISCUSSION Our study suggests that spottail pinfish are generalist-omnivores, rather than primarily herbivorous. Our data show a lower proportion of algae in the diet of PIKE AND LINDQUIST: SPOTTAIL PINFISH REEF DIET 369

Table 2. Percent volume of the major (> I % of total diet) dietary items found in spottail pinllsh stomachs: analysis by size class (I = 60-85, II = 86-110, III = 111-135, IV = 136-160 mm SL) and collection period (I = April/May, 2 = June, 3 = July-September)

Size class Period

[ II III IV I II III Diet item (N) (17) (29) (31) (19) (32) (45) (17) Algae 25.3 52.5 62.5 26.9 17.4 56.0 56.9 Arthropoda Crustacea Copepoda 4.7 1.9 1.5 0.7 9.7 0.7 0.2 Amphipoda Gammaridea 8.2 1.6 0.5 0.8 1.5 2.7 0.8 Caprellidae 11.8 0.6 0.1 0.5 0.9 2.9 0.1 MysidacealCaridean 0.7 0.3 0.8 0.0 2.8 0.1 0.1 Diplostraca Cladocera 1.5 0.7 0.9 0.0 5.3 0.0 0.0 Cirripedia Balanomorpha 1.0 3.9 0.4 5.3 2.7 1.3 4.1 Mollusca Gastropoda 1.6 1.0 0.0 30.3 1.5 4.9 0.1 Annelida Polychaeta Spionidae 1.6 1.2 1.4 0.0 7.6 0.0 0.0 Bryozoa 7.7 19.5 14.8 1.0 2.9 16.3 18.6 Cnidaria Hydrozoa 4.3 7.3 4.7 2.1 0.5 4.9 10.9 Chordata Urochordata Larvacea 22.8 5.5 8.8 10.7 36.1 5.6 0.5 Miscellaneous 8.8 4.3 3.6 21.7 11.1 4.6 7.7 spottail pinfish at the warm temperate innershelf reefs, than reported for fish of equal size caught in seagrass beds off Florida (Carr and Adams, 1972, 1973; Stoner and Livingston, 1984), or for fish caught on a warm temperate jetty near Beaufort, North Carolina (Hay and Sutherland, 1988). However, samples of spottail pinfish from the jetty consisted of a sample taken on one day in September, 1986. Florida populations of spottail pinfish were sampled in all months of the year, although samples were taken from seagrass habitats, not from a hard substrate habitat, and samples were not analyzed by season (Carr and Adams, 1972, 1973; Stoner and Livingston, 1984; Livingston, 1982). Our study also indicates that the spottail pinfish have a seasonal shift in diet from planktonic invertebrates in the spring to algae and attached invertebrates in the summer and early fall. Epiphytic algae were the dominant food items in the diet (55-90%) of subtropical populations of spottail pinfish, but spottail pinfish from our warm temperate innershelf habitats consumed a smalIer proportion of algae (45-57%) and ate relatively little algae (I 5-20%) in the spring. The algae we found in the stomach contents of spottail pinfish are epiphytes common offshore of North Carolina in the spring. Some of the algae are also common in summer, fall, or winter (Ka- praun, 1980). The amount of algae eaten by the different size classes did not vary, and we did not see a switch to a predominantly algal diet at any particular size. Large juvenile and subadult spottail pinfish (60-135 mm SL) ate a greater proportion of planktonic food items, and spottail pinfish 60-110 mm SL ate more benthic animal prey than larger spottail pinfish. However, Carr and Adams (1972, 1973) found plankton to be a significant part of the diet only in fish smaller than 25 mm SL. Stoner and Livingston (1984) did not consider plankton as an im- 370 BULLETIN OF MARINE SCIENCE, VOL 55, NO, 2-3, 1994

Table 3, A comparison of the dietary items (by volume) for spoltail pin fish collected from an artificial and a natural reef, by collection period (I = April/May, 2 = June, 3 = Ju]y-September) and size class (I = 60-85,2 = 86-110,3 = 111-135,4 = 136-]60 mm SL), F values and significance levels (* P < 0,05, ** P < 0,01, *** P < 0,001) are given, Duncan's multiple range test results arranged in order of decreasing volume, Underlines show lack of statistical difference,

Overall diet

Diet item Site Season Size class

Planktonic food 0,04 15,88*** 2,93* NR AR 123 I 324 --- -- Benthic animal food 0,0] \,00 3,96** ---NR AR 3 2 I ---2 143 Benthic a]gal food 0,08 4,54* 0,78 AR NR 3 2 ] ---324 I Crustaceans 3,88 5,06** \,60 NR AR I 2 3 I 234 ------Copepods 0,02 ] 8,29*** 1,90 NR AR 123 I 234 Gammarid amphipods 8,37** 0,16 3,5] * AR NR --2 I 3 2 143 Caprellid amphipods 4,15* 0,01 3,42* AR NR --2 I 3 ---124 3 Barnacles 0,06 0,18 1,43 ---AR NR 2 3 I ---241 3 Cladocerans OA8 ] 5,74*** U8 ---NR AR 123 ---I 324 Mysids/Caridcans 2,76 9AO** 3,10* NR---AR I 2 3 ---I 324 Hydroids 0,13 4,08* U6 ---AR NR 3 2 I ---2 I 3 4 Larval polychactes 0,63 12,64*** 2,05 NR AR I 2 3 ---1 324 Bryozoans 7,10** 3,49* 3,75** NR AR 3 2 1 2 1 3 4 - - Larvaceans 0,01 5,99* 3,55* NR AR I 2 3 ] 342 --- - Gastropod eggs 0,10 0,60 0,19 AR NR 2 I 3 4 2 I 3

portant part of the diet of spottail pinfish, The benthic animal foods eaten by spottail pinfish in this study were hardbottom associated, consistent with results reported by Carr and Adams (1972, 1973) and Stoner and Livingston (1984), Softbottom associated foods were not important in the diet of spottail pinfish in our study. Hay and Sutherland (1988) suggest that the Sparidae have a competitive advantage because they can switch to algae when crustaceans are depleted. Other families, Kyphosidae and Mugilidae (Hay and Sutherland, 1988) also have omnivores that include variable amounts of algae in their diets. It is noteworthy that our relative gut length data suggest that spottail pinfish fall into AI-Hussaini's (1947) crustacean-feeding carnivore group. Spottail pinfish appear to have a relatively short gut length even for an omnivore. Schoener (1982) noted that similar prey organisms are found on natural and artificial reefs from the same general area. Overall comparisons of the diet of PIKE AND LINDQUIST: SPOTTAIL PINFISH REEF DIET 371 spottail pin fish between the AR and NR show similar (88%) diets, suggesting that the two reefs function similarly in regard to food resources. Spottail pinfish appear to rely largely on reef associated foods (bryozoans, barnacles, hydroids and algae) and much less on planktonic food, and almost no softbottom foods are eaten. This is in agreement with Lindquist et al. (1985) and Hay and Sutherland (1988) show- ing that spottai] pinfish eat foods associated with the surface of rubble-mound jetties. Buckley and Hueckel (1985) showed that while fish may initially come to an artificial reef for shelter or orientation, they soon become foragers on reef- produced items. Phytoplankton, which are consumed by zooplankton and hardbottom associated organisms, and macroa]gae are the primary producers of the food chain supporting spottail pinfish. Our study agrees with the conventional view of a phytoplankton and benthic macroa]gae based food chain for reef-associated fishes and gives little support to the hypothesis that softbottom prey supported by microalgae are important diet items for this species (Cahoon and Tronzo, 1988; Cahoon, 1989; Cahoon et aI., ]990a; Cahoon et aI., ]990b). The shift to a more algal-dominated diet in June corresponds with warming water temperatures. North Carolina is an important boundary region where tropical species reach their northernmost distribution, and many temperate species reach their southernmost limit (MacIntyre and Pilkey, ]969; Day et aI., 197]; Kapraun and Zechman, ]982; Peckol and Searles, ]984; Searles and Schneider, ]980). A]gae may also become acceptable prey when either digestibility or rate of digestion increases at higher, summertime water temperatures. Competition brought on by increased recruitment of larval invertebrates and fishes (Co]ton et aI., ]979; Powles and Stender, ]976) to the reefs in the spring, or the risk of predation may be another reason for this seasonal shift in diet. Hueckel and Buck- ley (]987) note that as an artificial reef increases in age, the food resources and predator populations associated with the reef also increase. Predators of spottail pinfish include barracuda, mackerel, bluefish, crevalle jack, groupers and snappers (Darcy, 1985). Little attention has been given to the possibility that predators also may alter a forager's choice of diet items within a habitat (Dill, ]983). Mitte]bach and Chesson (1987) show that predators exert a strong influence on the habitat use and thus diet of their prey. Piscivorous fishes can cause their prey fish to switch habitats, reduce foraging distances, or limit feeding time, and thus intake (Schmitt and Holbrook, 1985). Piscivorous fishes may have forced the spottail pinfish to leave the more optimal food (in terms of energy per time) found in a more risky (in terms of predation) planktonic environment, for the less optimal algal foods in a relatively safer (in terms of cover) environment. While some or all of these factors may have contributed to the diet shift seen in spottail pinfish at a warm temperate innershelf reef, more work needs to be done to substantiate the causa] factors. Future work should more accurately de- scribe the plankton community and benthic community throughout the collection period, and also should determine the timing and abundances of possible com- petitors and predators that enter the study area.

ACKNOWLEDGMENTS

NOAA's Undersea Research Center at the University of North Carolina at Wilmington provided support for this research under grant Nos. NA80AA-8-00081 and NA88AA-D-UR004. The UNC Sea Grant College Program also supported this research under grant No. R/MRR-I. We thank the Doherty Foundation, the North Carolina Wildlife Federation, and the Topsail Saltwater Fishing Club for assis- tance with this project. Many thanks go to L. B. Cahoon, M. H. Posey, 1. E. C1avijo, D. E Kapraun, 372 BULLETIN OF MARINE SCIENCE. VOL. 55. NO. 2-3. 1994

J. L. Barnard, A. B. McCrary, and the graduate students who helped in various ways. This is contri- bution number 087 from the UNCW Center for Marine Science Research.

LITERATURE CiTED

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DATEACCEPTED: May 5, 1993.

ADDRESS: Department of Biological Sciences and Center for Marine Science Research. University of North Carolina at Wilmington, Wilmington, North Carolina 28403-3297.