COMPARATIVE FEEDING ECOLOGY OF SPINNER DOLPHINS (STENELLA LONGIROSTRIS) AND FRASER'S DOLPHINS (LAGENODELPHIS HOSEI) IN THE SULU SEA |
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Authors: | M Louella L Dolar William A Walker Gerald L Kooyman William F Perrin |
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Institution: | Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093–0204, U.S.A. E-mail:;National Marine Mammal Laboratory, National Marine Fisheries Service, NOAA, 7600 Sand Point Bay, N.E., Seattle, Washington 98115, U.S.A.;Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093–0204, U.S.A.;Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 8604 La Jolla Shores Drive, La Jolla, California 92037, U.S.A. |
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Abstract: | Fraser's and spinner dolphins are known to feed on mesopelagic prey, bur their diets and feeding ecologies have not been compared in areas where they are observed together. In this study we examined the stomach contents of both species caught incidentally in a driftnet fishery for tuna in the eastern Sulu Sea. Importance of prey items was determined using the percent occurrence, percent number, and volumetric methods. Mesopelagic fishes, particularly myctophids (mainly Ceratoscopelus warmingi, Diaphus spp. and Myctophum asperum ), were the most important component in the diet of spinner dolphins, whereas in Eraser's dolphins, mesopelagic cephalopods ( Abraliopsis, Onychoteuthis, Histioteuthis , and Chiroteuthis ), and crustaceans ( Notostomos elegans, Acanthephyra quadrispinosa , and Acanthephyra carinata ) appeared to be equally important as the myctophid species. Fraser's dolphins appeared to feed preferentially on larger prey and had more diversified prey (Shannon's diversity index = 1.2) than spinner dolphins (diversity index = 0.9). Vertical distributions of the prey items summarized from published literature indicate that spinner dolphins forage in the upper 200 m and probably occasionally to as deep as 400 m, whereas Fraser's dolphins have a wider vertical foraging range, from near the surface to probably as deep as 600 m. |
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Keywords: | Philippines diet myctophids cetaceans spinner dolphin Stenella longirostris Fraser's dolphin Lagenodelphis hosei squids |
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