|Scientific Name:||Stenella longirostris|
|Species Authority:||(Gray, 1828)|
|Infra-specific Taxa Assessed:|
|Taxonomic Notes:||Recent genetic work suggests that the genus Stenella is paraphyletic, and it is likely that the Delphininae will be restructured in coming years (LeDuc et al. 1999). Some species, including the Spinner Dolphin, may move to different genera. Four subspecies of Spinner Dolphins are currently recognized: S. l. longirostris (Gray’s spinner), S. l. orientalis (eastern spinner), S. l. centroamericana (Central American Spinner) and S. l. roseiventris (Dwarf Spinner) (Perrin 2002). Smaller individuals in Arabian waters (in both the Red Sea and Persian Gulf) may represent an undescribed subspecies (Van Waerebeek et al. 1999).|
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor/s:||Bearzi, G., Bjørge, A., Forney, K.A., Hammond, P.S., Karkzmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y. , Wells, R.S. & Wilson, B.|
|Reviewer/s:||Rojas-Bracho, L. & Smith, B.D.|
The eastern Spinner Dolphin population has ceased to decline but shows no clears signs of recovery. While there are few estimates of abundance and takes available in regions other than the eastern tropical Pacific, they are taken throughout their range by a diverse number of direct and indirect fisheries; some of these indirect takes may evolve into directed takes. Annual takes on the order of hundreds or thousands have been reported from countries in the Indian Ocean. These kills may comprise a large proportion of the global population. More information is needed before the possibility of a global decline of 30% or more can be eliminated.
|Range Description:||The Spinner Dolphin ranges through tropical and subtropical zones in both hemispheres. Limits are near 40°N and 40°S.
Stenella longirostris longirostris occurs mainly around oceanic islands in the tropical Atlantic, Indian, and western and central Pacific east to about 145°W (Rice 1998). However, the distribution in the Atlantic is not well known, especially in South American and African waters; the known range can be expected to expand considerably in those areas with increased attention to the cetacean faunas there. The southernmost record is from New Zealand, more than 2,000 km south of what is thought to be the normal range but still well north of sub-Antarctic waters (Perrin and Gilpatrick 1994).
Stenella longirostris orientalis inhabits pelagic waters of the eastern tropical Pacific (ETP) east of about 145°W, from 24°N off Baja California south to 10°S off Peru, but exclusive of the range of the following subspecies (Perrin 1990).
Stenella longirostris centroamericana is found in coastal waters over the continental shelf of the ETP, from the Gulf of Tehuantepec in southern Mexico southeast to Costa Rica (Perrin 1990).
Stenella longirostris roseiventris is distributed in shallow waters of inner Southeast Asia, including the Gulf of Thailand, the Timor and Arafura Seas off northern Australia, and other similar shallow waters off Indonesia and Malaysia. It is replaced in deeper and outer waters by the larger pelagic subspecies S. l. longirostris (Perrin et al. 1999, Kahn pers. comm. to W. Perrin 2007).
The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
Native:American Samoa (American Samoa); Anguilla; Argentina; Aruba; Australia; Bahamas; Bahrain; Bangladesh; Belize; Bermuda; Brazil; British Indian Ocean Territory; Brunei Darussalam; Cambodia; Cape Verde; Cayman Islands; China; Cocos (Keeling) Islands; Colombia; Comoros; Cook Islands; Costa Rica; Côte d'Ivoire; Cuba; Djibouti; Dominica; Dominican Republic; Ecuador (Galápagos); Egypt; El Salvador; Fiji; French Polynesia; Ghana; Guam; Guatemala; Guinea; Honduras; Hong Kong; India (Andaman Is., Nicobar Is.); Indonesia; Iran, Islamic Republic of; Jamaica; Japan (Honshu); Kenya; Kiribati; Liberia; Madagascar; Malaysia; Maldives; Marshall Islands; Martinique; Mauritius; Mexico; Micronesia, Federated States of; Mozambique; Myanmar; Netherlands Antilles; New Caledonia; Nicaragua; Niue; Northern Mariana Islands; Oman; Pakistan; Panama; Papua New Guinea; Peru; Philippines; Puerto Rico; Réunion; Saint Helena, Ascension and Tristan da Cunha; Saint Kitts and Nevis; Saint Lucia; Saint Vincent and the Grenadines; Samoa; Saudi Arabia; Senegal; Seychelles; Singapore; Solomon Islands; Somalia; South Africa (KwaZulu-Natal); Sri Lanka; Suriname; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Tonga; Trinidad and Tobago; Tuvalu; United States (Hawaiian Is., New Jersey); United States Minor Outlying Islands; Uruguay; Vanuatu; Venezuela; Viet Nam; Virgin Islands, British; Virgin Islands, U.S.
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northwest; Atlantic – southeast; Atlantic – southwest; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Pacific – eastern central; Pacific – northwest; Pacific – southeast; Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||There were about 801,000 (CV=37%) whitebelly spinners (S. l. orientalis X S. l. longirostris intergrades) in the ETP in 2000 (Gerrodette et al. 2005). The eastern spinner dolphin (the population most heavily impacted by the ETP tuna fishery) numbered about 613,000 (CV=22%) in 2003, and despite large reductions in the kill is recovering at an estimated rate of only 1.1% per year, an estimate that is not statistically different from zero (Gerrodette and Forcada 2005). There are estimated to be 11,971 (CV=71%) spinner dolphins in the northern Gulf of Mexico (Waring et al. 2006), and 3,351 (CV=74%) in Hawaiian waters (Barlow 2006). There are no abundance estimates for the dwarf subspecies. Dolar et al. (1997) estimated abundance in the southern part of the Sulu Sea and north-eastern Malaysian waters at 4,000 individuals. For the southeastern Sulu Sea, Dolar et al. (2006) estimated abundance at about 31,000 (CV=27%) Spinner Dolphins. The numbers listed above add up to more than a million spinner dolphins: numerous other regional populations in the Atlantic, Indian and Pacific Oceans have not been surveyed.|
|Habitat and Ecology:||
In most tropical waters, nearly all records of spinner dolphins are associated with inshore waters, islands or banks. Around Hawaii Sspinner Dolphins depend on the availability of sheltered shallow bays for use as resting areas during the day. In the ETP, however, Spinner Dolphins occur in very large numbers on the high seas many hundreds of kilometers from the nearest land. Spinner Dolphins favour a specific habitat in the ETP, called by oceanographers "tropical surface water;" it is typified by unusual conditions of shallow mixed layer, shoal and sharp thermocline, and relatively small annual variation in surface temperature (Reyes 1991, Perrin and Gilpatrick 1994). There they are often found in close association with Pantropical Spotted Dolphins, Yellowfin Tuna (Thunnus albacares) and birds of several species. The dwarf form of the Spinner Dolphin in Southeast Asian waters apparently inhabits a shallow coral reef habitat (Perrin and Gilpatrick 1994). In the north-central and western Gulf of Mexico, Stenella longirostris is found over intermediate bottom depths, its distribution overlapping with that of purely pelagic and purely coastal species (Davis et al. (1998).
Most Spinner Dolphins feed predominantly at night, on small (<20 cm) midwater fish of many different families (including myctophids), squids, and sergestid shrimps (Perrin et al. 1973; Dolar et al. 2003). Dwarf Spinner Dolphins are exceptional, however; they feed (presumably during daylight hours) on small, reef-associated organisms (benthic reef fishes and invertebrates) (Perrin et al. 1999).
The association of Spinner Dolphins with Spotted Dolphins and Yellowfin Tuna results in their entanglement in tuna purse seines in the ETP. This is the second-most important species of dolphin involved in the tuna fishery (after the pantropical spotted dolphin) (Gerrodette 2002). The population of the eastern Spinner Dolphin subspecies S. l. orientalis is estimated to have been reduced by 65% by the tuna fishery kills (Reilly et al. 2005). Since the Inter-American Tropical Tuna Commission (IATTC) implemented per-vessel mortality limits on the international fleet, the mortality for the eastern and whitebelly forms combined decreased, to 389 in 2005 (IATTC 2006). Although current mortality is greatly reduced, the eastern form appears to be recovering slowly. Potential factors such as fishery-related stress, unobserved mortality due to calf separation and orphaning during fishing operations (Archer et al. 2001), possible mortality by small vessels that do not carry observers, and under-reporting of mortality have been suggested as possible reasons the eastern Spinner’s slow recovery (Gerrodette and Forcada 2005).
Throughout their range, Spinner Dolphins are taken as bycatch in purse-seine, gillnet, and trawl fisheries (Perrin et al. 1994, Donahue and Edwards 1996), often in high numbers. Spinner Dolphins are the most abundant dolphin in the Indian Ocean (Balance and Pitman 1998) and are taken throughout the region. In the Indian Ocean, annual takes of hundreds of Spinner Dolphins have been reported bycaught in the few fisheries that have been examined in India (Lal Mohan 1994), and annual takes in the thousands have been reported in Sri Lanka (Leatherwood and Reeves 1991, Lal Mohan 1994). Takes in other areas are unknown, but may be substantial. Unknown numbers have been taken in the tuna purse-seine fishery in the eastern Atlantic (Donahue and Edwards 1996) and in small-scale gillnet fisheries in the western Atlantic (Siciliano 1994). Dolphins taken incidentally in the Philippines and Venezuela are utilized for shark bait and human consumption (Dolar et al. 1994, Perrin and Gilpatrick 1994). Dwarf Spinners are caught incidentally in shrimp trawls in the Gulf of Thailand (Perrin et al. 1999). There are likely to be undocumented fisheries interactions off West Africa (Jefferson et al. 1993; Perrin and Gilpatrick 1994). Zerbini and Kotas (1998) report on by-catches in Brazilian drift-net fisheries and Cockcroft (1990) on animals entangled in shark nets off KwaZulu-Natal, South Africa.
In some cases, human use of by-caught Spinner Dolphins has led to direct fisheries. Direct kills occur in several areas, including the Caribbean, Sri Lanka, the Philippines (Dolar 1994), Taiwan, and Indonesia (Perrin and Gilpatrick 1994; J. Wang pers. comm., Kahn 2004). Spinners may also be so taken in West Africa (Van Waerebeek et al. 1999).
Tourist development may affect the habitat and viability of spinner dolphins in some regions, for example at Fernando de Noronha Island, Brazil (Reyes 1991), in Hawaii (Lammers 2004) and in Bali, Indonesia (T. Jefferson pers. comm.). The habit of resting in shallow coastal waters during the day leads to problems of harassment by dolphin-watching boats.
The species is listed in Appendix II of CITES.
Spinner Dolphins, as with other species impacted by the ETP tuna purse-seine fishery are managed both 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 (Bayliff 2001).
The species is composed of several subspecies and regional populations. The conservation status of each of these should be assessed. The available estimates of abundance and removals suggest that some of them may fall into a Threatened category.
|Citation:||Bearzi, G., Bjørge, A., Forney, K.A., Hammond, P.S., Karkzmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y. , Wells, R.S. & Wilson, B. 2012. Stenella longirostris. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 20 May 2013.|
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