Feeding Habits of Indo-Pacific Humpback Dolphins (<I>Sousa chinensis</I>) Stranded in Hong Kong

Dietary information derived from the examination of stomach contents of 29 Indo-Pacific humpback dolphins (Sousa chinensis) stranded in Hong Kong waters is presented in this study. Humpback dolphins in this area have a diet comprised nearly exclusively of fish. Prey spectrum from the 15 dolphins with contents includes a minimum of 24 species of fish, and one species of cephalopod. The croaker (Johnius sp.) was the most frequent and numerically most important prey, followed by the lionhead (Collichthys lucida) and anchovies (Thryssa spp.). The fish families Sciaenidae, Engraulidae, Trichiuridae, and Clupeidae accounted for over 93% of all prey consumed. Most of these prey are common in murky, brackish waters of estuaries and often occur in large shoals. There is some dietary overlap with finless porpoises (Neophocaena phocaenoides); the two species share some 13 fish species, but only anchovies figure among the top five prey for both species. In addition, finless porpoises rely more heavily on cephalopods (squids, cuttlefishes, and octopus) and may venture into deeper, clearer waters during foraging, whereas humpback dolphins seem to exploit demersal and shoaling fish of productive estuaries. The stocks of some fish species important in the diet of humpback dolphins may have been subjected to heavy exploitation by the fisheries in Hong Kong waters. Behavioral observations of dolphins feeding in association with pair trawlers suggest a somewhat different prey preference for some dolphins from the results of this study.