Szedlmayer and Lee: Diet shifts of Lut/anus campechanus 



373 



20 



15 



10 



16 48 45 41 37 41 32 30 20 15 8 6 



20 



40 60 80 

 Size class (mm) 



100 120 140 



Figure 10 



Fish prey from open habitat. Stomach contents by specific 

 volume over 10-mm size classes of red snapper (Lut/anus 

 campechanus) from the northern Gulf of Mexico. Num- 

 bers on the upper axis are the number of red snapper that 

 contained prey for each respective size class. 



5 17 44 59 31 37 34 40 28 28 35 29 13 15 15 5 3 



3 - 



Fish 

 Reef 



Habitat 



Blennndae 



Centropristis 



Halichoeres 



Ophichthidae 



Serranidae 



Serranus 



Triglidae 



unid 



HI 





o 



80 100 120 140 160 180 200 220 240 

 Size class (mm) 



Figure 11 



Fish prey from reef habitat. Stomach contents by spe- 

 cific volume over 10-mm size classes of red snapper 

 (Lutjanus campechanus) from the northern Gulf of 

 Mexico. Numbers on the upper axis are the number of red 

 snapper that contained prey for each respective size class. 



high percentage of stomachs with food (48%) compared to 

 past studies. Rooker ( 1995 ) also showed a high percentage 

 (69%; 312 out of 449 stomachs) of schoolmaster snapper 

 (Lutjanus apodus) contained prey, when fish were col- 

 lected from depths similar to those of the our study ( 1 to 27 

 ml. The higher percentage of stomachs with prey found in 

 our study compared to past studies of red snapper ( Stea- 

 rns, 1884; Camber.1955; Moseley, 1966) may be due to the 

 shallower depths sampled (18 m; DeMartini et al., 1996). 

 Juvenile red snapper showed feeding patterns similar 

 to many other marine fishes. After settlement, from ap- 

 proximately 20 to 60 mm SL, they showed a wide-ranging 

 diet that included shrimp, copepods, chaetognaths, and 

 squid. Prey fish were also found in the stomachs of the 

 smallest red snapper collected (15-20 mm SL) but were 

 not a dominant component. Sweatman (1993) reported 

 similar results for the snapper Lutjanus quinquelineatus, 

 ranging from 24 to 29 mm SL, i.e., piscivorous in the first 

 few days after settlement. Above 60 mm SL, fish prey 

 tended to dominate specific volume, but not by feeding less 

 on shrimp because shrimp continued to be an important 

 prey. Squid became another dominant component of red 

 snapper diet at about 100 mm SL and also continued as an 

 important prey up to 240 mm SL. Unfortunately, sample 

 size was reduced above 230 mm SL, and it was difficult 

 to estimate if squid and fish continued as dominant prey 

 components above these size classes. Sedberry and Cuellar 

 ( 1993 ) reported a similar shift in diets of reef-associated 

 vermilion snapper (Rhomboplites aurorubens). This spe- 



cies shifted from small crustaceans to fishes and cepha- 

 lopods over a size range similar to that of red snapper in 

 the present study. Moseley ( 1966 ) reported a "slow transi- 

 tion from zooplankton to macro animals for red snapper 

 sizes between 40 and 90 mm" — a transition that probably 

 included fish prey that he did not specifically identify. 

 Bradley and Bryan (1975), showed a shift in juvenile red 

 snapper diets with size (25-325 mm FL). Their smallest 

 red snapper keyed on invertebrates, then showed a sharp 

 increase in dependency upon prey fish above 175 mm 

 FL, when Batrachoididae (toadfish) became a dominant 

 component. These shifts in diet are important in helping 

 to identify fish habitat and are potentially key aspects of 

 early survival. 



Red snapper showed two major habitat shifts in their 

 first year. Juvenile red snapper first settled from the 

 plankton to benthic substrate near 20 mm SL ( Szedlmayer 

 and Conti, 1999 ). The present study showed a second shift 

 from open habitat to reef habitat starting at about 70 mm 

 SL (Fig. 3). No fish smaller than 70 mm were collected 

 from the reefs, and smaller red snapper were rarely ob- 

 served on these reefs from SCUBA visual surveys. No fish 

 larger than 160 mm SL were caught from the open habitat 

 but were present on the reefs. This finding suggested that 

 red snapper had shifted to reef habitat by 160 mm SL but 

 also may have avoided trawl gear as described earlier for 

 age-0 red snapper (Bradley and Bryan, 1975) and age-0 

 summer flounder (Paralichthys dentatus) (Szedlmayer 

 and Able, 1993). However, no large (150-300 mm) red 



