Diel feeding patterns of red snapper on artificial reefs in the north-central Gulf of Mexico

Diets of red snapper Lutjanus campechanus were compared among four diel feeding periods (dawn, day, dusk, and night) and among three standard length size-classes: small (200-299 mm), medium (300-399 mm), and large (400-499 mm). Fish were collected from August through October 2000 in the north-central Gulf of Mexico. A total of 432 stomachs were examined, of which 164 (37%) contained prey. Size-class influenced diets; diets of small red snapper were dominated by fish, those of medium red snapper by fish and tunicates, and those of large red snapper by crabs and fish. Red snapper fed on prey from several different habitats. Small red snapper fed mostly on reef and sand prey types; medium red snapper fed on similar portions of reef, sand, and mixed prey types; and large red snapper fed on mixed prey types. Adjusting for fish size, mean gut fullness was significantly lower for the dusk than for the day period. Fish were the most important prey for all periods. The second most important prey group changed with period: stomatopods for dawn, tunicates for day, and crabs for dusk and night periods. Prey habitat type also varied over periods. Sand prey type dominated dawn and dusk periods, whereas reef prey type dominated day and night periods. We used multidimensional scaling analysis to compare the relative influence of diel period to size-class on red snapper diets. This analysis suggested that fish size-class had a greater influence on red snapper diet than did period. However, with size effects removed, red snapper still showed significant diet shifts with periods.