Spinner dolphins (Stenella longirostris) of the western Pacific and Southeast Asia: Pelagic and shallow-water forms

A dwarf form of the spinner dolphin has been reported from the Gulf of Thai land, while more typical large spinner dolphins have been described from Ja panese waters and other localities in the western Pacific. These reports ha ve been based on very few specimens. Our purpose in this study was to deter mine the affinities of spinner dolphins throughout the region based on larg er samples and to review their taxonomic status, with an hypothesis of two widespread ecotypic forms, or subspecies. We examined 213 osteological spec imens, from a tuna gillnet fishery in the Philippines, from the former Taiw anese shark gillnet fishery in the Timer and Arafura Seas off northern Aust ralia, from the Gulf of Thailand, from other areas in the western Pacific a nd Southeast Asia, from the eastern Indian Ocean, and from the Central and South Pacific. Results show that spinner dolphins from the deep inner water s of the Philippines conform to the large pelagic type of spinner dolphin t hat inhabits the Central and South Pacific, the western Pacific and the eas tern Indian Ocean. The skull is similar in size and shape to the holotype s pecimen of S. langirostris (from unknown locality). This form feeds primari ly on small mesopelagic fishes and squids. Spinner dolphins from the shallo w waters of inner Southeast Asia represented in the sample, including the G ulf of Thailand, Timer Sea and Arafura Sea, are smaller in body and skull s ize, have fewer teeth and vertebrae, and feed mainly on benthic and coral r eef fishes and invertebrates. We hypothesize that this form also inhabits t he Java Sea and other shallow waters throughout inner Indonesia and Malaysi a. We redescribe a subspecies corresponding to the small form and based pn Delphinus roseiventris Wagner 1846 from the Arafura Sea, designating a neot ype and paraneotype specimens.