| Summary |
The trophic interactions of the red drum Sciaenops ocellatus have been previously researched. However diet data on the largest adults (>750mm TL) are very limited. As fisheries management moves towards a goal of multi-species and ecosystem-based strategies, information on trophic inter-relationships of the system must be characterized for effective understanding and application to future modelling efforts and management decisions. Predatory effects on forage species are an important component of this, and examining the diet of the predator is the most efficient way to identify prey species interactions and potential removal rates through predation mortality. Red drum abundance has increased since the implementation of more conservative management strategies and major decreases in commercial fishing effort on the species. Because of these changes in abundance and the lack of diet data for larger adult red drum, this study was conducted to identify the trophic relationships and potential forage species effects of these predators. This study will 1) Identify, classify, and compare diets of large adult red drum in North Carolina and South Carolina and 2) synthesize a pooled standardized diet composition from all previously published red drum diet studies across its range (excluding larvae). First, the trophic relationships of large adult red drum (>750mm TL), Sciaenops ocellatus, in the coastal waters of South Carolina (N=146) and North Carolina (N=51), from 2007-2011 were examined. Stomach samples were collected by North Carolina Division of Marine Fisheries and South Carolina Department of Natural Resources during their annual fall longline surveys. Red drum in North Carolina fed predominantly on blue crab (Callinectes sapidus) which made up 51% of the diet by number and occurred in 48% of the stomachs. The diet of red drum in South Carolina was more diverse that in North Carolina, where red drum consumed mostly Atlantic menhaden (Brevoortia tyrannus) and a diverse group of marine decapods and brachyurans. Prey species contribution varied between years, with increases in blue crab in North Carolina red drum and Atlantic menhaden for South Carolina red drum. The differences in diet between the states are likely because of prey assemblage differences between the predominantly estuarine habitat in North Carolina and the coastal marine habitat in South Carolina. Although the diet composition of red drum was different between SC and SC they fed at similar trophic levels. Secondly, ten previously published diet studies on red drum (excluding larval diets) were collected via a thorough literature search and diet data were pooled by prey group and size-class of the predator. Standardized diet compositions were examined and analyzed by cluster analysis to determine groupings of similarity. Juvenile and sub-adult red drum had very similar diets on each coast, feeding on mysids, shrimp, and crabs, which was attributed to their inhabiting similar nursery areas. Adult red drum diets were similar, feeding mostly on fish and crabs. This was attributed to adults residing in coastal waters instead of the inshore nursery areas. This study has made the adult diet of red drum and a large-scale diet characterization of the species available for application to future management. |
