SUMMER FOODS OF TEXAS COASTAL 

 FISHES RELATIVE TO AGE AND HABITAT 



Age and habitat are often ignored as factors which 

 simultaneously influence the diets of demersal 

 fishes. Studies of fish foods by age (size) or habitat 

 (depth of capture, substrate) either summarize foods 

 over all sizes and depths (Henwood et al. 1978), con- 

 struct several size or depth groupings to equalize 

 sampling effort (Overstreet and Heard 1978; 

 Mericas 1981), or establish arbitrary size or capture 

 depth ranges for ontogenetic or depth-related 

 analyses (Rogers 1977; Divita et al. 1983). In this 

 paper, we analyze the stomach contents of seven 

 species of Texas coastal fishes with respect to both 

 age and habitat. 



Materials and Methods 



Fishes examined in our study were taken from trawl 

 catches by the NOAA RV Oregon II and the Texas 

 Parks and Wildlife Department RV Western Gulf be- 

 tween sunset and sunrise in waters 7-73 m deep along 

 the entire Texas coast. Each vessel towed a 12.2 m 

 semiballoon trawl with tickler chain at 5-6 km/h. The 

 species collected from the family Sciaenidae are 

 sand seatrout, Cynoscion arenarius; silver seatrout, 

 C. nothus; spot, Leiostomus xanthurus; and Atlantic 

 croaker, Micropogonias undulatus; from the family 

 Sparidae, longspine porgy, Stenotomus caprinus; 

 and from the family Trichiuridae, Atlantic cut- 

 lassfish, Trichiurus lepturus. Fishes were collect- 

 ed by depth ranges (7-17, 18-44, or 45-73 m) and 

 preserved in 3.7% formaldehyde-seawater. These 

 depth ranges correspond to distinctive habitats 

 (substrates) as reported by Grady (1971), Flint 

 and Rabalais (1980), and Gallaway and Reitsema 

 (1981): sand or muddy-sand (7-17 m), sand-silt- 

 clay (18-44 m), and silty-sand or silty-clay (45- 

 73 m). 



In the laboratory, fishes from each depth range were 

 measured (standard length, SL, or total length, TL, 

 where applicable) and further separated into either 

 age-0 or age-I classes, based upon data summarized 

 by the Gulf of Mexico Fishery Management Council 

 (1980) or upon unpublished personal data on 

 gonadal maturation. Fishes were presumed to have 

 reached age I at the following lengths: longspine 

 porgy, 75 mm SL; spot, 100 mm SL; Atlantic croaker, 

 125 mm SL; sand and silver seatrouts, 150 mm SL; 

 hardhead catfish, 200 mm SL; and Atlantic 

 cutlassfish, 400 mm TL. No age II individuals were 

 collected. For each species, the stomach contents of 

 all individuals in a given age/depth category were 



combined and washed through sieves to separate 

 similar-sized food items (Carr and Adams 1972), 

 which were identified and enumerated micro- 

 scopically and then dried at 80°-90°C for 24 h. The 

 dry weights of the various food items were calculated 

 from their numerical proportions and converted to 

 percentages of total food dry weight. Stomach con- 

 tents were identified to broad but exclusive 

 categories such as sand, diatoms, shrimps, or fishes. 

 Fish bones and scales without associated flesh were 

 often found in hardhead catfish stomachs and were 

 thus given a category. Animal fragments not distinct- 

 ly referable to any taxon were also categorized. Fine 

 organic matter not referable to any other category 

 was termed detritus. Prey fishes, shrimps, and crabs 

 were identified to family or genus when possible. 

 Within each species, diet similarities among age/ 

 depth categories were compared by the Spearman 

 rank correlation coefficient, r s (Fritz 1974). 



Results 



The stomach contents of the four sciaenid fishes are 

 summarized in Table 1 , and those of the other three 

 species in Table 2. Intraspecific diet similarities are 

 given in Table 3. The effect of depth of capture on 

 diets of spot and Atlantic cutlassfish could not be 

 evaluated, since the majority of individuals were 

 collected from a single depth range (7-17 m and 18- 

 44 m, respectively). Correlations between diets of 

 age-0 and age-I spot (r s = 0.069) and between diets of 

 age-0 and age-I Atlantic cutlassfish (r s = 0.399) were 

 not significant. Age-0 spot consumed more infaunal 

 organisms, such as polychaetes and nematodes, and 

 nearly twice as much detritus as age-I spot, which 

 captured proportionately more epifaunal prey such 

 as fishes, amphipods, and shrimps. While both age 

 classes of Atlantic cutlassfish preyed primarily upon 

 fish, age-I individuals also exploited squids. Small 

 sample size (three stomachs) for the age-0 Atlantic 

 cutlassfish is probably responsible for the lack of diet 

 correlation. 



Sand and silver seatrouts fed both in the water 

 column and near the bottom. Diets of three of the four 

 age/depth categories of sand seatrout were 

 significantly correlated, primarily because fishes and 

 shrimps were the favored prey. The exception was 

 the diet of age-0 sand seatrout in 18-44 m waters in 

 which squids were the primary prey. The most fre- 

 quently identified sand seatrout prey taxa were 

 anchovies, Anchoa, and roughback shrimp, Trachy- 

 penaeus sp. Silver seatrout also preyed upon fishes 

 and shrimps, but only the age-0 diets in the two in- 

 habited depth ranges were correlated. The data on 



FISHERY BULLETIN: VOL. 81. NO. 3, 1983. 



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