About Stenella longirostris (Gray, 1828)
Spinner dolphins (Stenella longirostris) are small, slim-built cetaceans. Adult individuals typically measure 129–235 cm in length and have a body mass of 23–79 kg. This species has an elongated rostrum, and a triangular or subtriangular dorsal fin. Most spinner dolphins have tripartite color patterns: the dorsal area is dark gray, the sides are light gray, and the underside is pale gray or white. A dark band runs from the eye to the flipper, which is bordered above by a thin, light line. This species shows more geographic variation in body form and coloration than other cetaceans. In the open waters of the eastern Pacific, these dolphins have relatively small skulls with short rostra. A dwarf form of spinner dolphin lives around Southeast Asia. In this subspecies, a dark dorsal cape softens the distinctness of their tripartite color patterns. Offshore subspecies tend to have a paler cape that does not extend as far. In certain subspecies, some males may have upright fins that slant forward. Some eastern Pacific spinner dolphin populations have backwards-facing dorsal fins, and males can develop dorsal humps and upturned caudal flukes. The spinner dolphin inhabits nearly all tropical and subtropical waters located between 40°N and 40°S. This species primarily lives in coastal waters, around islands, or on banks. However, in the eastern tropical Pacific, spinner dolphins live far from shore. Spinner dolphins may use different habitats depending on the season. They feed mainly on small mesopelagic fish, squids, and sergestid shrimps, and will dive 200–300 m to reach these prey items. Hawaiian spinner dolphins are nocturnal feeders that forage in deep scattering layers, which host many prey species. The dwarf spinner dolphin may feed mostly on benthic fish in reefs and shallow water. Off Oahu, Hawaii, spinner dolphins forage at night and cooperatively herd prey into very dense patches. They swim around the prey in a circle, and a pair may swim through the circle to catch prey. Spinner dolphins are preyed on by sharks. Other possible predators include killer whales, false killer whales, pygmy killer whales, and short-finned pilot whales. They are susceptible to both external parasites such as barnacles, and internal parasites including nematodes, trematodes, cestodes, and acanthocephalans; remoras are also found externally on the species.
