Spinner dolphin
Stenella longirostris
Threat Index

Max Length:
Male: 2.35 m
Female: 2.10 m
Calf: 0.75 - 0.85 m

Max Weight:
Male: 82 kg

Est. Population: 1,400,000

Diet: fish, squid, shrimp

IUCN Listing: DD (S. l. Orientalis listed as VU)
CMS Appendix: II (eastern tropical Pacific and Southeast Asian populations)
CITES Appendix: II
Synonym:
Spinner dolphin, Long-beaked dolphin, Long-snouted dolphin, Spinner

Related Projects:
WDCS Supported project in Fiji

Classification:
There are several different forms of spinner dolphins, and confusion abounds on whether they are distinct species or merely genetic variations of the same species. Currently, four subspecies are recognised; (1) S. l. longirostris – Gray's spinner dolphin is the 'typical' spinner dolphin, found in temperate and tropical zones of all the world's oceans (except the eastern tropical Pacific and some areas in southeast Asia); (2) S. l. orientalis – Eastern spinner dolphins are found only in offshore areas of the eastern tropical Pacific Ocean; (3) S. l. centroamericana – Central American spinner dolphins are found only in coastal areas of the eastern tropical Pacific; (4) S. l. roseiventris; this dwarf form of spinner dolphin is found in Southeast Asia and northern Australia. An additional form of spinner dolphin found in offshore waters of the eastern tropical Pacific, the 'whitebelly', is thought to be a possible fifth subspecies. Spinner dolphins are one of only two recognised species that performs spins when leaping out of the water.

Appearance:
The spinner dolphin has rather distinctive colouration, with a dark grey back, a lateral band of lighter grey along the side, and a paler, sometimes white or pinkish belly. The various subspecies found in the eastern tropical Pacific lack this tri-colouration and are mostly varying shades of grey with white patches on their undersides. The spinner dolphin has a long slender beak with black 'lips', a long slender body, small flippers, and the dorsal fin is generally tall, upright, triangular or slightly falcate. Large males in the eastern tropical Pacific often have a forward leaning dorsal fin and a keel above and below the tail stock which becomes more pronounced with age. It may be confused with many other types of dolphins, but observation of colouration and its unique spinning behaviour will lead to positive identification.

Behaviour:
The spinner dolphin is highly energetic, and capable of amazing leaps and, as indicated by its name, spins. Leaping up to 3m out of the water, it may complete as many as seven revolutions before re-entering the water. It is thought that the spinning leaps may be a form of communication for the highly social spinner dolphin. They are known to approach boats and bow ride for periods of up to 30 minutes, which is longer than most other dolphin species. The spinner dolphin generally travels in groups of 5 to 200 individuals, though they have been seen in groups of over 1,000 with other species of dolphins. They often feed at night on small pelagic fish, squid, and shrimp, while resting inshore in coastal waters during the day.

Distribution:
Yellow-fin tuna tend to associate with spinner dolphins and spotted dolphins and, which in turn leads to considerable bycatch from the tuna fishery. It is thought that the numbers of spinner dolphins in the eastern tropical Pacific have been reduced to less than one third of their original size with no sign of recovery. Their highly acrobatic behaviour also caused spinner dolphins to be targeted for aquariums in earlier years but they have a poor survival record in captivity and targeted hunts nowadays are for food and/or bait. The species was classified as Data Deficient by the IUCN in 2008. However, as the species is composed of several subspecies and regional populations, they recommend that the conservation status of each be assessed as the available estimates of abundance and removals suggest that some of them may fall into a Threatened category. Threats to this species include bycatch, intentional catch, prey depletion, and human disturbance from harassment by dolphin watching boats who target the spinner dolphins when they are resting in shallow waters during daylight hours.