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Stenella longirostris:   (click for more)

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FAO Names
En - Spinner dolphin, Fr - Dauphin longirostre, Sp - Estenela giradora.
3Alpha Code: DSI     Taxonomic Code: 4220403202
Diagnostic Features
The spinner dolphin is a slender dolphin, 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 stocks, 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.

  Spinner dolphins generally have dark eye-to-flipper stripes and dark lips and beak tips. There are 3 subspecies known. The individuals of most spinner dolphin stocks in the world have a threepart colour pattern (dark grey cape, light grey sides, and white belly) and only minor differences in appearance of males and females. These animals (illustrated above) are called Gray's spinner dolphins (Stenella longirostris longirostris).

In the eastern tropical Pacific, there are 3 other forms. Eastern spinner dolphins (Stenella longirostris orientalis) have a monotone steel grey colour pattern, with white only as patches around the genitals and axillae. They have the most exaggerated sexual dimorphism. Central American spinner dolphins (Stenella longirostris centroamericana), previously called Costa Rican spinners, are poorly known, but appear to have a similar colour pattern, although it may lack the white ventral patches. A third type of spinner dolphin in the eastern tropical Pacific, often called the whitebelly spinner dolphin, appears to represent a hybrid between eastern spinner and Gray's spinner dolphins. Whitebelly spinners are more robust, with a two-part colour pattern and less exaggerated sexual dimorphism than the other stocks in the eastern tropical Pacific. Geographical forms of spinner dolphins have not been well described for most areas, with the exception of the eastern Pacific; although a dwarf form has been described from the Gulf of Thailand. Animals of the above described forms, or other undescribed stocks, may exist elsewhere as well.

  In spinner dolphins, there are 45 to 62 pairs of very fine, pointed teeth in each jaw. This is more than in almost any other cetacean species.

 
Can be confused with: From a distance, other long-snouted oceanic dolphins can look like spinner dolphins. Spinner dolphins are most likely to be confused with clymene dolphins in the Atlantic, but careful attention to colour pattern differences and head and body shape differences will allow them to be distinguished.

Geographical Distribution
The range of the spinner dolphin is nearly identical to that of the pantropical spotted dolphin, encompassing oceanic tropical and subtropical zones in both hemispheres. Limits are near 40°N and 40°S.
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Habitat and Biology
The spinner dolphin is named for its habit of leaping from the water and spinning up to 7 times on its long axis, before falling back to the water. This is one of the most aerial of all dolphins. Herd sizes range from less than 50 up to several thousand. Associations with pantropical spotted dolphins are common in the eastern tropical Pacific.
Calving peaks in different populations range from late spring to autumn.  Spinner dolphins of most populations feed predominantly at night, on mid-water fish and squid, and rest during much of the day. Their association with pantropical spotted dolphins and yellowfin tuna results in their entanglement in tuna purse seines in the eastern tropical Pacific.
Size
Newborn spinner dolphins are about 75 to 80 cm long; adults reach 2 m (females) and 2.4 m (males). They reach weights of at least 77 kg. Eastern spinner dolphins are the smaller and Central American spinner dolphins the larger of the subspecies in the eastern tropical Pacific.
Interest to Fisheries

Conservation Status : Both the whitebelly and eastern spinner forms have been heavily involved in the tropical Pacific tuna purse seinesfishery. The numbers of eastern spinners have been reduced significantly in the last few decades by this fishing practice. Catches of spinner dolphins also occur in the Caribbean, Australia, Japan, Thailand, the Philippines, and Sri Lanka; in this last area up to 15 000 are killed each year in gillnets and by hand-harpooning. There are likely to be fisheries interactions off West Africa.
IUCN:  Insufficiently known.
Source of Information
Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
 
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