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Spinner Dolphin[1]
Size comparison against an average human
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Eutheria
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genus: Stenella
Species: S. longirostris
Binomial name
Stenella longirostris
(Gray, 1828)
Spinner Dolphin range

The Spinner Dolphin (Stenella longirostris) is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which they spin longitudinally along their axis as they leap through the air.

Contents

Taxonomy

The Spinner Dolphin is sometimes referred to as the Long-snouted Dolphin, particularly in older texts, to distinguish it from the similar Clymene Dolphin which is often called the Short-snouted Spinner Dolphin. The species was described by John Gray in 1828. There are four named subspecies:

  • Eastern Spinner Dolphin (S. l. orientalis), from the tropical eastern Pacific.
  • Central American or Costa Rican Spinner Dolphin (S. l. centroamericana), also found in the tropical eastern Pacific.
  • Gray's or Hawaiian Spinner Dolphin (S. l. longirostris), from the central Pacific Ocean around Hawaii but represents a mixture of broadly similar subtypes found worldwide.
  • Dwarf Spinner Dolphin (S. l. roseiventris), first found in the Gulf of Thailand.

However the species display greater variety than these subspecies might indicate. A hybrid form characterized by its white belly inhabits the eastern Pacific. Other less distinct groupings inhabit other oceans.

The name comes from the Latin term for long-beaked.

Physical description

The Spinner Dolphin is usually dark gray, with darker patches in the tail stock, back and throat. Usually it has a creamy-white patch on the belly, though this varies considerably. Their beaks are distinctively long and thin, with a dark tip. The fins, also, are lengthy for dolphins of this size. The dorsal fin is erect and leans forward in older males found in the Eastern Pacific Ocean. Spinner Dolphins are the most variable in form of all cetaceans.

Adults vary in length from 129–235 centimetres (51–93 in) and weight from 23–78 kilograms (51–170 lb). Gestation requires about 10 months. Females reach maturity at four to seven years. Males require seven to ten years. Their longevity is unknown.

Group sizes vary from just a few animals up to thousands.

They often ride boats' bow-waves.

Spinning

A possible reason for the animal's spinning is that males spin to attract females. Another suggestion is that the bubbles may act as a target for echolocation by other individuals in the school. Spinning may also be play.

Individuals have been spotted completing at least 14 spinning jumps in quick succession.

In the Atlantic Ocean Spinner Dolphins may be mistaken for the Clymene Dolphin which also spins, but not to such a regular and dramatic extent. Spinner Dolphins may successfully mate with other species such as Bottlenose Dolphin and both varieties of Spotted Dolphin.

Population and distribution

Video showing dolphins spinning above the surface
Spinner dolphins video taken at Midway Atoll
Photo of single dolphin leaping above the ocean surface
Spinner Dolphin at Midway Atoll

Spinner Dolphins occur in deep tropical waters in all of the world's tropical oceans. Although mainly inhabiting the open ocean, they are sometimes found near the shores of island chains such as Hawaii. Their greatest density occurs between the Tropic of Cancer and Tropic of Capricorn. The species roughly divides up into geographical areas corresponding to the different subspecies. Total population is unknown, and it was dramatically reduced by fishing activity in the eastern Pacific Ocean. This species is still regarded as endangered.

Communication

Photo from above of 8 dolphins at and below the surface
A pod of Spinner Dolphins in Kauai, Hawaii

Dolphin echolocate and communicate using click-whistles and pulsed sounds. Echolocation enables dolphins to track objects in dim or dark water and to, in effect, see much further than their eyes will allow. Their complex array of whistle sounds allow dolphins to talk to one another. Spinners can identify themselves with sounds they make by trailing bubbles from their blowholes -- sounds called signature whistles.

Spinner dolphins also communicate by slapping the water with various body parts. For instance, “nose-outs” occur when the beak is thrust above the surface. This action is common when the pod is emerging from a rest period. Tail slaps often indicate impending danger or indicate a dive. Head slaps, side slaps, and back slaps are most frequently seen as the pod accelerates. Last, and most spectacular, are the spins themselves. Many animals spin repeatedly, with each spin tending to get smaller and smaller, finishing with an emphatic side slap.

The power of the spin can pick up through their echolocation—may be the real purpose of the spin.

Spinner dolphins maximize their splash by twisting around to land in a belly-flop, or back-flop. Spins are most frequently performed while the school is spread out across the water. A spinning dolphin may be signaling to the others: "here I am. . . . here is where I am going. . . " The effect of many dolphins spinning and leaping at once, defines the envelope of the pod—that is, its size, direction, and speed of travel.

Feeding

Photo of dolphin leaping above the surface

Dolphins hunt mostly at night as the “scattering layer” of marine life, which has spent the day at depths of 3,000 feet (910 m) rises toward the surface to feed on plankton. They eat fish, jellyfish, krill, squid, shell-less snails, as well as copepods. Before diving into the layer, the pod assembles, possibly to protect themselves from other predators who feed there, such as sharks, which are natural dolphin predators. The spinners form small subgroups and spread out across the sea. Time after time, the dolphins dive into the utter darkness at 800 feet (240 m) or more. They use their teeth to grasp and immobilize their prey rather than to chew.

Spread across miles of water, the school coordinates its activities through sound—and through spinning—which can reach an explosive crescendo in the darkness. Echolocating pod-mates, spinners can use their whistles to unite with others for defense. By dawn, the spinners regroup and eating stops. They likely will shelter during the day near shore.

Human interaction

Photo of beach shoreline
Sancho Beach - beyond is a reserve for some 600 spinner dolphins

Spinner Dolphins have been studied both in the wild and in captivity in Hawaii. Up to two million Spinner Dolphins, mostly eastern and white-bellied varieties, were killed in the thirty years after purse seine fishing for tuna was introduced in the 1950s. The process killed probably half of all Eastern Spinner Dolphins. See Pantropical Spotted Dolphin for a discussion. Spinner dolphins in Hawaii can expect multiple daily visits to their nearshore resting grounds.

References

  1. ^ Mead, James G. and Robert L. Brownell, Jr (November 16, 2005). Wilson, D. E., and Reeder, D. M. (eds). ed. Mammal Species of the World (3rd edition ed.). Johns Hopkins University Press. pp. 723–743. ISBN 0-801-88221-4. http://www.bucknell.edu/msw3/browse.asp?id=14300091.  
  2. ^ Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B. (2008). Stenella longirostris. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 7 October 2008.

External links

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Simple English

File:Spinner dolphin
A Spinner Dolphin.

The Spinner Dolphin (Stenella longirostris) is a small oceanic dolphin. It is found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which they will spin longitudinally along their axis as they leap through the air.

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Look up Stenella longirostris in Wikispecies, a directory of species

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