Spinner dolphin

Spinner dolphin[1]
A spinner dolphin in the Red Sea
Size compared to an average human
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)
Subspecies
  • S. l. orientalis
  • S. l. centroamericana
  • S. l. longirostris
  • S. l. roseiventris
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 it spins along its longitudinal axis as it leaps through the air. It is a member of the family Delphinidae of toothed whales.

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. The four named subspecies are:

The species, though, displays 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 species name comes from the Latin term for long-beaked.

Description

Spinner dolphins are small cetaceans with a slim build. Adults are typically 129–235 cm long and reach a body mass of 23–79 kg.[3] This species has an elongated rostrum[4] and a triangular or subtriangular dorsal fin.[4] Spinner dolphins generally have tripartite color patterns. The dorsal area is dark gray, the sides light gray, and the underside pale gray or white.[5] Also, a dark band runs from the eye to the flipper, bordered above by a thin, light line. However, the spinner dolphin has more geographic variation in form and coloration than other cetaceans. In the open waters of eastern Pacific, dolphins have relatively small skulls with short rostra.[4] A dwarf form of spinner dolphin occurs around southeast Asia.[6] In these same subspecies, a dark dorsal cape dims their tripartite color patterns.[7] Further offshore, subspecies tend to have a paler and less far-reaching cape.[8] In certain subspecies, some males may have upright fins that slant forward.[7] Some populations of spinner dolphin found in the eastern Pacific have bizarre backwards-facing dorsal fins, and males can have strange humps and upturned caudal flukes.[9]

Ecology

The spinner dolphin lives in nearly all tropical and subtropical waters between 40°N and 40°S.[10] The species primarily inhabits coastal waters, islands, or banks. However, in the eastern tropical Pacific, dolphins live far from shore.[11] Spinner dolphins may use different habitats depending on the season.[12]

The spinner dolphin feeds mainly on small mesopelagic fish, squids, and sergestid shrimps, and will dive 200–300 m to feed on them.[13] Spinner dolphins of Hawaii are nocturnal feeders and forage in deep scattering layers, which contain many species. The dwarf spinner dolphin may feed mostly on benthic fish in reefs and shallow water.[6] Off Oahu, Hawaii, spinner dolphins forage at night and cooperatively herd their prey into highly dense patches.[14] They swim around the prey in a circle and a pair may swim through the circle to make a catch.[14] Spinner dolphins are in turn preyed on by sharks. Other possible predators include the killer whale, the false killer whale, the pygmy killer whale and the short-finned pilot whale.[15] They are susceptible to parasites, both external ones like barnacles and remoras, and internal ones, like nematodes, trematodes, cestodes and acanthocephalans.[4]

Behavior and life history

In certain regions, such as Hawaii and northern Brazil, dolphins spend the daytime resting in shallow bays near deep water.[16] At dusk, they travel offshore to feed. They travel along the shore during foraging trips, and the individuals that occupy the same bay may change daily.[16] Some individual dolphins do not always go to a bay to rest; however, in Hawaii, dolphins do seem to return to the same site each trip.[17] Spinner dolphins live in an open and loose social organization.[18] The spinner dolphins of Hawaii live in family groups, but also have associations with others beyond their groups.[4] Mothers and calves form strong social bonds. Spinner dolphins seem to have a promiscuous mating system, with individuals changing partners for up to some weeks. A dozen adult males may gather into coalitions.[18] Vocalizations of spinner dolphins include whistles, which may be used to organize the school, burst-pulse signals, and echolocation clicks.[19] The spinner dolphin has a 10-month gestation period, and mothers nurse their young for one to two years. Females are sexually mature at four to seven years, with three-year calving intervals, while males are sexually mature at seven to 10 years.[4] Breeding is seasonal, more so in certain regions than others.[4]

Spinning behavior

Spinner dolphins are known for their acrobatics and aerial behaviors. A spinner dolphin comes out of the water front first and twists its body as it rises into the air.[20] When it reaches its maximum height, the dolphin descends back into the water, landing on its side. A dolphin can make two to 5.5 spins in one leap; the swimming and rotational speed of the dolphin as it spins underwater affects the number of spins it can do while airborne. These spins may serve several functions.[20] Dolphins may also make nose-outs, tail slaps, flips, head slaps, "salmon leaps", and side and back slaps.

Conservation status

Tens of thousands of spinner dolphins, mostly eastern and white-bellied varieties, were killed in the 30 years after purse seine fishing for tuna began in the 1950s.[4] The process killed probably half of all eastern spinner dolphins. They have also been contaminated by pollutants such as DDT and PCBs.[4] Spinner dolphins, as with other species affected by ETP tuna purse-seine fishing, are managed nationally by the coastal countries and internationally by the IATTC. The IATTC has imposed annual stock mortality limits on each purse seine and promulgated regulations regarding the safe release of dolphins.[2]

The eastern tropical Pacific and Southeast Asian populations of the spinner dolphin are listed on Appendix II[21] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), since they have an unfavourable conservation status or would benefit significantly from international co-operation organized by tailored agreements.[22]

In addition, the spinner dolphin is covered by Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU)[23] and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU).

Spinner dolphins in Hawaii receive multiple daily visits to their near-shore resting grounds, with boats taking people out daily to snorkel and interact with the local dolphin population. Such activities are increasingly coming under criticism on the grounds of possible harm to the dolphins,[24] and efforts are being made both to educate the public in order to minimise human impact on the dolphins, and to bring in regulations to govern these activities.[25]

Images

See also

References

  1. ↑ Mead, J.G.; Brownell, R.L., Jr. (2005). "Order Cetacea". In Wilson, D.E.; Reeder, D.M. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 723–743. ISBN 978-0-8018-8221-0. OCLC 62265494.
  2. 1 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. Retrieved 7 October 2008.
  3. ↑ Perrin, W. F, Dolar, MLL, Chan, CM, and Chivers, SJ (2005). Length-weight relationships in the spinner dolphin, Marine Mammal Science 21:765-778.
  4. 1 2 3 4 5 6 7 8 9 Perrin WF (1998) "Stenella longirostris". Mamm Spec 599: 1-7.
  5. ↑ WF Perrin, (1972) "Color patterns of spinner porpoises (Stenella cf. S. longirostris) of the eastern Pacific and Hawaii, with comments on delphinid pigmentation". Fish. Bull. (US) 70: 983-1003.
  6. 1 2 William F Perrin, Nobuyuki Miyazaki, Toshio Kasuya (1989) "A of the spinner dolphin (Stenella longirostris) from Thailand". Marine Mammal Science 5(3): 213-227.
  7. 1 2 Perrin WF (1990) "Subspecies of Stenella longirostris (Mammalia: Cetacea: Delphinidae)". Proc Biol Soc Washington 103 (2): 453- 463.
  8. ↑ WF Perrin, PA Akin, (1991) "Geographic variation in external morphology of the spinner dolphin Stenella longirostris in the eastern Pacific and implications for conservation". Fishery Bulletin 89:411-428.
  9. ↑ Nelson, Bryan (November 2011). "Why does this dolphin have its fin on backwards?". Retrieved January 2013.
  10. ↑ Jefferson TA, Leatherwood S, Webber MA (1993) FAO Species identification guide. Marine mammals of the world. UNEP/FAO, Rome, 320 pp.
  11. ↑ David WK Au and Wayne L. Perryman (1985) Dolphin habitats in the eastern tropical Pacific. Fishery Bulletin 83:623-643.
  12. ↑ Fiedler, P. C., and S. B. Reilly. (1994) "Interannual variability of dolphin habitats in the eastern tropical Pacific. II: effects on abundances estimated from tuna vessel sightings, 1975 - 1990". Fishery Bulletin 92:451-463.
  13. ↑ Dolar MLL, Walker WA, Kooyman GL, Perrin WF (2003) "Comparative feeding ecology of spinner dolphins (Stenella longirostris) and Fraser's dolphins (Lagenodelphis hosei) in the Sulu Sea". Mar Mamm Sci 19: 1-19.
  14. 1 2 Benoit-Bird K, Au W (2003) "Hawaiian spinner dolphins aggregate midwater food resources through cooperative foraging". Acoust Soc Am 114: 2300.
  15. ↑ Norris KS, Würsig B, Wells RS, Würsig M (1994) The Hawaiian spinner dolphin. U Cal Press, Berkeley, Cal., USA.
  16. 1 2 Wursig B, Wells RS, Norris KS Würsig M, "A spinner dolphins day" pp. 65-102. in: Norris KS, Würsig B, Wells RS, Würsig M (1994) The Hawaiian spinner dolphin. U Cal Press, Berkeley, Cal., USA.
  17. ↑ Marten K, Psarakos S (1999) "Long-term site fidelity and possible long-term associations of wild spinner dolphins (Stenella longirostris) seen off Oahu, Hawaii". Mar Mamm Sci 15: 1329-1336.
  18. 1 2 Norris KS, Johnson CM, Schools and schooling, pp 234-242 in Norris KS, Würsig B, Wells RS, Würsig M (1994) The Hawaiian spinner dolphin. U Cal Press, Berkeley, Cal., USA.
  19. ↑ Brownlee SM, Norris KS. "The acoustic domain" in Norris KS, Würsig B, Wells RS, Würsig M (1994) The Hawaiian spinner dolphin. U Cal Press, Berkeley, Cal., USA.
  20. 1 2 Frank E Fish, Anthony J Nicastro, Daniel Weihs (2006) "Dynamics of the aerial maneuvers of spinner dolphins", Journal of Experimental Biology.
  21. ↑ "Appendix II" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009.
  22. ↑ Convention on Migratory Species page on the Spinner dolphin, Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia
  23. ↑ Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region
  24. ↑ http://www.fpir.noaa.gov/PRD/prd_swim_with_wild_dolphins.html
  25. ↑ http://www.halekeokeo.com/pgs/dolphins.php

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