Food Habits and Sex Ratios of Dolphin Coryphaena hippurus Captured in the Western Atlantic Ocean off Hatteras, North Carolina

Dolphin caught by charter boats fishing over the Continental Shelf in 1961–63 were examined to determine food habits and sex ratios. Most important prey (listed according to percent of total prey weight) were: Exocoetidae (26%), Scombridae (22%), Carangidae(12%), Balistidae (9%), and Coryphaenidae (5%). Males constituted a significant majority (61%) of large dophin (801–1,275 mm fork length). Most (71%) small dolphin (450–600 mm) were females. Large dolphin of both sexes were generally captured in open water, while small female dolphin were usually associated with tide‐lines (areas where current patterns cause accumulations of floating Sargassum and other flotsam). In 1963, tide‐lines were infrequently encountered by charter boats. Decreased charter boat catches, increased abundance of young males in the fishery, and impaired foraging by small female dolphin resulted. We hypothesize that male dolphin (which are heavier than females of similar length) leave the sanctuary of the tide‐line at an earlier age than females to forage for large prey in the open ocean. Thus, most small dolphin captured near tide‐lines and associated flotsam are females. Most large dolphin captured by trolling are males, because their significantly greater weight per unit of length results in more voracious feeding and increased selection by the charter boat fishery.