Stenella longirostris, Spinner Dolphin [+]

Kingdom Animalia Phylum Chordata Class Mammalia Order Cetacea Family Delphinidae Genus Stenella species: Stenella longirostris [+ITIS +WoRMS]

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Description & Behavior

The spinner dolphin, Stenella longirostris (Gray, 1828), aka long-snouted spinner dolphin, measure about 2 m in length and weigh about 90 kg. They have small, pointed flippers and a curved dorsal fin at the center of the body. Spinner dolphins are dark gray on the dorsal side with a lighter gray area that runs from the eyes to the tail. The ventral side is white.

Spinner dolphin, Stenella longirostris

Common names for the geographic varieties of Stenella longirostris found in the Pacific include: the Costa Rican, Eastern, whitebelly, and Hawai'ian or Gray's. A dwarfed form of this species is found in the Gulf of Thailand. The regional populations vary in size. The Eastern spinner dolphin is slightly smaller than the Costa Rican measuring between 1.65-1.8 m in length and weighing about 61 kg, compared to the Costa Rican spinner's length of about 2 m and 91 kg weight.

There are four subspecies of spinner dolphins:

1. Gray's spinner, S. longirostris longirostris
2. Eastern (whitebelly) spinner, S. longirostris orientalis
3. Costa Rican spinner, S. longirostris centroamericana
4. dwarf spinner dolphin, S. longirostris roseiventris

Body shape and color also vary regionally, but in general spinner dolphins are small cetaceans with slender bodies. Most have long thin beaks with the exception of the Atlantic short-snouted spinner. This species has more teeth than others; between 45-65 sharp, pointed teeth are found in each side of both the upper and lower jaws. They have small pointed flippers, and are variations of gray in color with white ventral sides.

Spinner dolphins are a very gregarious species frequently traveling together in schools and with other species, such as the spotted dolphin and humpback whales. In the eastern tropical Pacific, spinner dolphins swim with yellowfin tuna, which has resulted in great numbers of spinner dolphins caught as bycatch in purse-seines.

The characteristic spinning of this species is thought to be used for communication as it is often observed when a school are scattered. Another theory is that the spinning may be related to the removal of parasites or of remoras, a fish species that a type of fish with a modified dorsal fin used to attach itself by suction to marine life for the removal of parasites.

World Range & Habitat

The spinner dolphin, Stenella longirostris, is found all over the world. Costa Rican spinner dolphins are found in large schools of >1,000 in coastal waters off the west coast of Central America. The Eastern spinner also inhabits the waters off the west coast of Central America, but farther offshore in deeper waters than the Costa Rican spinner. The Eastern spinner is also found in deep waters off the coast of Mexico. This subspecies also travels in very large schools of >1,000. The whitebelly spinner is also found off the coast of Mexico, but farther out in the open sea than the Eastern spinner. The whitebelly also inhabits the northern Pacific coast of South America in large schools of >1,000. The Hawai'ian spinner is found throughout the Hawai'ian Islands traveling in somewhat smaller groups of >200, and in the Gulf of Mexico, Caribbean, and mid-Atlantic to the northwest coast of Africa.

» GBIF occurrence data in Google Earth [Tips] | Ocean Biogeographic Information System (OBIS) (World Distribution) [about]

Feeding Behavior (Ecology)

Spinner dolphins, Stenella longirostris, feed at night on small fish and squid. Known predators are sharks, orca (killer whales), and possibly false killer whales, pygmy killer whales, and pilot whales.

Life History

Female spinner dolphins, Stenella longirostris, reach sexual maturity at about 4-7 years, males at about 7-10 years. The gestation period lasts about 10.5 months, and calves are nursed for 1-2 years. The calving interval is between 2-3 years.

Conservation Status/Additional Comments

Spinner dolphins, Stenella longirostris, particularly whitebelly and eastern spinner dolphins in the eastern tropical Pacific, have significantly decreased in population size due to entanglement in the purse-seine nets used by the tuna fishing industry. They are commonly found swimming in large schools above schools of yellowfin tuna, and are therefore used by fishermen to target yellowfin schools. Purse seines capture marine life indiscriminately causing declines in spinner dolphin populations as large as 80% since the 1960s when the use of purse seines began. Spinner dolphins are often found in aquariums because they survive in captivity.