COMPARATIVE-STUDY OF THE DIETS OF THE BLUE CRABS CALLINECTES-SIMILIS AND C-SAPIDUS FROM A MUD-BOTTOM HABITAT IN MOBILE-BAY, ALABAMA

Diets of Callinectes similis and C. sapidus collected from the same open bay locality in Mobile Bay, Alabama, were investigated. Fish, bivalve, brachyuran, and gastropod remains constituted the 4 most common prey items for both species. The cumulative Index of Relative Importance (IRI) of these 4 food groups was 85% in C. similis and 91% in C sapidus, suggesting that both Callinectes spp. forage primarily on these 4 prey groups. To examine ontogenetic shift in diets, individuals of C similis were sorted into 3 size classes (29-50, 51-80, and 81-111-mm carapace widths) representing juvenile, premature, and sexually mature stages. We found statistically significant differences in the hierarchy and proportions of the main prey types among size classes examined. There was no significant difference in the diet of male and female C. similis. Relatively high percentage of dietary overlap between C. similis and C. sapidus suggests that these crabs probably utilize common resources in areas of habitat overlap in Mobile Bay, Alabama.