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Spinner dolphins

Classification: Gray classified Stenella longirostris in 1828 - the specific name referring to this species' long snout. There are no subspecies, but there are four distinct Eastern Pacific forms: the Eastern, the Whitebelly, the Costa Rican and the Hawaiian.

Spinner dolphins are the smallest of Hawaii's common dolphins. They are generally between five and six feet in length and weigh 130 to 200 pounds. Hawaii has its own subspecies that is easy to recognize by its distinctive "three-tone" color pattern which consists of a sharply defined dark gray "cape" on their backs, a stripe of lighter gray on their sides and a white or pink belly.

The Latin name derives from ‘longus’ for long and ‘rostrum’ for snout or beak. The common name for this dolphin derives from its behaviour - these dolphins typically spin around on their longitudinal axis as they breach, although they are often seen breaching in the normal way. The name Long-snouted spinner dolphin is now obsolete (Prof. W. Perrin, Scripps Institution of Oceanography, pers. com.) it derives from the time when scientists thought that the Clymene dolphin ( then called the ‘short-snouted spinner dolphin) was of the same species. It is now known that they are two different species and so both names have been simplified. The long-snouted spinner dolphin is now known only as the Spinner dolphin and the short-snouted dolphin is known as the Clymene dolphin.

Description: The Spinner Dolphin is a slender creature with a long, thin beak to which the distinct forehead slopes gently. The dorsal varies with both age and geographical form; it can lean forward, be curved, or be completely triangular in shape. The flippers are long and pointed, and a a stripe links it to the eyes. Eastern Pacific and Costa Rican animals are mainly grey, with other forms usually two- or three-tone. Both the Hawaiian and Whitebelly forms have a dark grey or black dorsal cape, paler flanks and sides, and a creamy-white belly. All forms measure between 1.3 and 2.1m in length, and weigh between 45-75kg.

Range: The spinner dolphin's presence in the Arabian Gulf was first evidenced by skulls found on UAE offshore islands in 1995. Sightings have since been made 20 kilometres off the city of Dubai, but its range here continues to at least 100 kilometres west of Abu Dhabi and stretches eastwards around the Musandam peninsula into the Indian Ocean. Fishermen of Fujairah claim to encounter it and its close relatives, the spotted dolphin (S. attenuata ) and striped dolphin (S. coeruleoalba), well offshore.

The Influence of Man: Spinner Dolphins are often targeted in the purse-seine and yellowfin tuna fisheries of the eastern Pacific Ocean. Elsewhere, many of these dolphins are accidentally killed in gillnets, and also taken in harpoon fisheries. Some individuals have been kept successfully in captivity for at least 10 years.

Physical Description:The spinner dolphin is a slender species, with an extremely long, thin beak. Also, the head is very slender at the apex of the melon. The dorsal fin ranges from slightly falcate to erect and triangular. In adult males of some populations, the dorsal fin may become so canted forward that it looks as if it were stuck on backwards and the tail stock may become very deepened, with an enlarged post-anal keel of connective tissue. Spinners generally have dark eye-to-flipper stripes and dark lips and beak tips. In spinners, there are 45-62 pairs of very fine, pointed teeth in each jaw. This is more than in any other cetacean species except the franciscana.Individuals of most spinner dolphin populations have a three-part color pattern (dark gray cape, light gray sides, and white belly) and only minor differences in appearance of males and females. These animals are called Gray's spinner dolphins (S. l. longirostris).In the eastern tropical Pacific (ETP), there are three other forms. Eastern spinners (S. l. orientalis) have a monotone steel gray color pattern, with white only as patches around the genitals and axillae. They have the most exaggerated sexual dimorphism. Central American spinners (S. l. centroamericana), previously called Costa Rican spinners, are poorly known, but appear to have a similar color pattern, although it apparently lacks the white ventral patches. Central American spinners are also longer, with longer beaks than eastern spinners. A third type of spinner dolphin in the ETP, often called the whitebelly spinner, appears to represent a hybrid between eastern spinner and Gray's spinner dolphins. Whitebelly spinners are more robust, with a two-part color pattern and less exaggerated sexual dimorphism than the other stocks in the ETP. Finally, there is a dwarf form of the spinner dolphin (S. l. roseiventris), which is found in waters of Southeast Asia and northern Australia. It has an erect to falcate dorsal fin, a tripartitie color patter, and proportionately large flippers and dorsal fin.Geographical forms of spinner dolphins have not been well described for most areas, with the exception of the eastern Pacific. Animals of the above described forms, or other undescribed stocks, may exist elsewhere as well.Newborn spinner dolphins are about 75-80 cm long; adults reach 2 m (females) and 2.4 m (males). They reach weights of at least 77 kg. Eastern spinners are the smaller and Central American spinners the larger of the subspecies in the ETP. Dwarf spinners reach maximum lengths of only about 1.58 m.

Feeding:This species takes midwater fish and squid, and is different from other dolphins in that it feeds by night.