Spinner dolphin (Stenella longirostris)

Also known as: long-beaked dolphin, long-snouted dolphin
  
French: Dauphin Longirostre
Spanish: Delfín Tornillón, Estenela Giradora
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderCetartiodactyla
FamilyDelphinidae
GenusStenella (1)
SizeLength: 129 – 235 cm (2)
Weight23 – 78 kg (2)

Classified as Data Deficient (DD) on the IUCN Red List (1), and is listed on Appendix II of CITES (3). Subspecies: Eastern spinner dolphin, Stenella longirostris orientalis, is classified as Vulnerable (VU) on the IUCN Red List (1).The eastern tropical Pacific and Southeast Asian populations are listed on Appendix II of CMS (4).

The acrobatic spinner dolphin is the most common small cetacean in many tropical open seas, where it can be seen spinning high in the air (hence its common name) or riding the bow waves of boats (5). The small and slender spinner dolphin varies geographically in colouration and size, but can be identified by its relatively long, slender beak and triangular dorsal fin (5). The most common colour pattern is three-part: dark grey on the back, lighter grey along the sides, and white or very light grey underneath. A darker grey stripe runs from the eye to the flipper, bordered above by a narrow, light line (2).

The spinner dolphin inhabits most tropical waters of the world, and can also occur in sub-tropical and warm temperate waters (2), approximately between 30 to 40 degrees north and 20 to 30 degrees south (5). At present, four subspecies are recognised (6) (7): S. l. longirostris (Gray’s spinner dolphin), which occurs in all tropical seas; S. l. orientalis (Eastern spinner dolphin), found in open waters of the eastern tropical Pacific; S. l. centroamericana (Costa Rican or Central American spinner dolphin), which inhabits continental shelf waters off western Central America and southern Mexico (6); and S.l. roseiventris, (dwarf spinner dolphin) which inhabits shallow waters of Southeast Asia (7).

The spinner dolphin is typically thought of as a tropical high seas species, but it also inhabits shallow reef areas, coastal areas, and subtropical and warm temperate waters (5) (7).

Spinner dolphins move about the oceans in schools; groups that vary in size from just a few dolphins to over a thousand. They commonly school with other species such as pantropical spotted dolphins, or small toothed whales (5). In such schools, spinner dolphins are known to undertake migrations, following prey or warm water currents (8). In Hawaii, spinner dolphins usually spend their days resting in shallow bays near deep water, and then move offshore at dusk and feed as they move substantial distances along the shore (8). Pelagic spinner dolphins feed primarily on small mesopelagic fish, squids and shrimps, and dive down to depths of 300 meters to catch their prey (8). The dwarf spinner dolphin feeds on reef fishes and other benthic organisms (7)

Mating in spinner dolphins appears to be promiscuous, and like many small dolphins, true courtship behaviour can be observed, such as mutual caressing between the male and female (9). The breeding system may vary geographically, with some populations showing a greater degree of polygyny than others (10). Calves are born every three years, after a gestation period of about ten months (2). The mother nurses the calf for up to two years (2), and they form a bond that lasts a lifetime (8). Females reach sexual maturity between four and seven years, whereas males do not reach maturity until between seven and ten years (2).

The purpose of the energetic spinning behaviour of the spinner dolphin is not known. It has been suggested that the large cloud of bubbles created by the powerful spin and splash landing may act as an echolocation target, to allow a widely dispersed school of dolphins to communicate (5). Another theory is that the spinning may dislodge hitch-hiking remoras, or the spinning may, at times, simply be play (5).

Spinner dolphins in the eastern tropical Pacific have been killed incidentally since the early 1960s by tuna purse seine fisheries. They were caught in such large numbers that the population of S. l. orientalis was reduced to less than one third of its original size (5). Following raised awareness of the number of dolphins killed in tuna purse seine fisheries, measures were implemented to reduce dolphin by-catch. Today spinner dolphins continue to be killed in this way, although in greatly reduced numbers (6). However, continued chase, capture and release of large numbers in the fishery may be preventing the population from recovering (11).

In Sri Lanka and the Philippines, large numbers of spinner dolphins have also been captured in gillnets and killed by harpoons for the past 20 years (6), and local harpoon fisheries exist in several more locations throughout the world. Incidentally captured dolphins are consumed by local people, or used as shark bait, and this has led to the development of markets and fisheries directed at dolphins (5) (8). The takes in these fisheries may be unsustainable (5).

The eastern tropical Pacific and Southeast Asian populations of the spinner dolphin are listed on Appendix II of the Convention on Migratory Species (CMS). This means that the spinner dolphin is a migratory species that needs, or would significantly benefit from international co-operation, and the convention encourages the range states to conclude global or regional agreements (4). The spinner dolphin is also listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this species should be carefully regulated (3). The value of dolphins as a tourist attraction offers countries and communities an incentive to protect these beautiful animals. Fernando de Noronha National Marine Park; (an archipelago off equatorial Brazil) was established in 1988, to provide nominal protection to spinner dolphins and support dolphin watching tourism (12), and it has been reported that in Zanzibar, the value of spinner dolphins for tourism far exceeded that of using them as bait for sharks (8). It is hoped that with meaningful laws, the will and resources to enforce them, continued attention by non-governmental organizations and efforts to make the public aware of the intrinsic value of their endemic dolphins (13), this charismatic species will continue spinning in our oceans forever.

For further information on spinner dolphins and their conservation see

Authenticated (14/09/07) by William F. Perrin, Senior Scientist for Marine Mammals, National Marine Fisheries Service, Southwest Fisheries Science Centre.
http://swfsc.noaa.gov/

  1. IUCN Red List (June, 2009)
    http://www.iucnredlist.org
  2. Perrin, W.F. (1998) Stenella longirostris. Mammalian Species, 599: 1 - 7.
  3. CITES (August, 2007)
    http://www.cites.org
  4. Convention on Migratory Species (August, 2007)
    http://www.cms.int/
  5. Perrin, W.F. (2002) Spinner dolphin. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.
  6. Reeves, R.R., Smith, B.D., Crespo, E.A. and di Sciara, G.N. (2003) Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World's Cetaceans. IUCN, Gland, Switzerland and Cambridge, UK.
  7. Perrin, W.F., Dolar, M.L.L. and Robineau, D. (1999) Spinner dolphins (Stenella longirostris) of the western Pacific and Southeast Asia: pelagic and shallow-water forms. Marine Mammal Science, 15: 1029 - 1053.
  8. Culik, B.M., Würtz, M. and Gerkman, B. (2002) Review on Small Cetaceans: Distribution, Behaviour, Migration and Threats. Convention on Migratory Species, Bonn, Germany. Available at:
    http://www.cms.int/reports/small_cetaceans/data/S_longirostris/s_longirostris.htm
  9. Würsig, B. (2002) Courtship behaviour. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.
  10. Perrin, W.F. and Mesnick, S.L. (2003) Sexual ecology of the spinner dolphin, Stenella longirostris: geographic variation in mating system. Marine Mammal Science, 19: 462 - 483.
  11. Gerrodette, T. and Forcada, J. (2005) Non-recovery of two spotted and spinner dolphin populations in the eastern tropical Pacific Ocean. Marine Ecology Progress Series, 291: 1 - 21.
  12. Reeves, R.R. (2002) Conservation efforts. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.
  13. Perrin, W.F. (1999) Selected examples of small cetaceans at risk. In: Twiss, J.R. and Reeves, R.R. (Eds) Conservation and management of marine mammals. Smithsonian Institution Press, Washington, D.C.