|Scientific Name:||Sphyrna mokarran (Rüppell, 1837)|
Zygaena mokarran Rüppell, 1837
|Taxonomic Source(s):||Rüppell, W.P.E.S. 1838. Neue Wirbelthiere zu der Fauna von Abyssinien gehörig. Fische des Rothen Meeres.|
|Red List Category & Criteria:||Endangered A2bd+4bd ver 3.1|
|Assessor(s):||Denham, J., Stevens, J.D., Simpfendorfer, C., Heupel, M.R., Cliff, G., Morgan, A., Graham, R., Ducrocq, M., Dulvy, N.K., Seisay, M., Asber, M., Valenti, S.V., Litvinov, F., Martins, P., Lemine Ould Sidi, M., Tous, P. & Bucal, D.|
|Reviewer(s):||Dudley, S.F.J., Musick, J.A., Fowler, S.L., Kyne, P.M., Cavanagh, R.D. & Valenti, S.V.|
A large, widely distributed, tropical hammerhead shark largely restricted to continental shelves. Sphyrna mokarran is highly valued for its fins (in target and incidental fisheries), suffers very high bycatch mortality and only reproduces once every two years, making it vulnerable to over-exploitation and population depletion. Generally regarded as solitary, and is therefore unlikely to be abundant wherever it occurs. Previously observed from Mauritania to Angola, reportedly abundant from November to January in Senegal, and in October in Mauritania, stocks have since collapsed and it is recognized as one of the four most threatened species by member states of the Sub Regional Fishing Commission. Although there is very little species specific data available, the absence of recent records give cause to suspect a decline of at least 80% in the past 25 years. Fishing proceeds unmanaged and unmonitored, resulting in an assessment of Critically Endangered in the Eastern Atlantic. Although not targeted in the Northwest Atlantic and Gulf of Mexico it is taken as by-catch in several fisheries and suffers greater than 90% vessel mortality. Two time series data sets (pelagic logbook, large pelagic survey) have shown a decline in the catch of Sphyrna spp. since 1986. Difficulties in species identification and accurate recording make an assessment of this species very difficult, however low survival at capture makes it highly vulnerable to fishing pressure, whether directed or incidental. It is therefore assessed as Endangered in the Northwest Atlantic and Gulf of Mexico, based on a suspected decline of at least >50% over the past 10 years. The decline is poorly documented and has not been curtailed. In the Southwest Indian Ocean this species is assessed as Endangered based on a continued decline in catch rate of 79% reported for the period 1978 to 2003. It is uncertain whether these declines reflect highly localized stock depletion or whether they reflect a general decline in the Southwest Indian Ocean, but large numbers of longline vessels have been reported to be operating illegally in coastal waters of the western Indian Ocean where they are targeting primarily hammerhead sharks and giant guitarfish Rhynchobatus djiddensis. Sphyrna mokarran is found along the northern coast of Australia. A large increase in the illegal, unregulated and unreported (IUU) fishing in northern Australia in the last few years points to great concern that this species is being increasingly targeted for its valuable large fins. Recent Risk Assessments of northern Australian elasmobranchs indicate that it may be 'high-risk' however, due to a lack of data to form the basis of an accurate assessment, the species is considered Data Deficient in Australia at the present time. Further investigation of its status there is required. Given its vulnerability to depletion, low survival at capture and high value for the fin trade this species is considered to meet the criteria for Endangered globally based on the available evidence for declines of >50%. There is an urgent need for data collection in other parts of its range, but considering the high value of its fins and high fishing pressure in other parts of its range, similar declines are likely to have occurred elsewhere.
|Previously published Red List assessments:|
|Range Description:||The great hammerhead ranges widely throughout the tropical waters of the world, from latitudes 40°N to 35°S (Last and Stevens 1994). It is apparently nomadic and migratory, with some populations moving polewards in the summer, as off Florida and in the South China Sea (Compagno in prep. b). |
Widespread in the south-west Indian Ocean but in South Africa is confined to the KwaZulu-Natal coast, where it co-exists with the scalloped hammerhead S. lewini, also an inhabitant of the tropic, and the smooth hammerhead S. zygaena, which favours cooler waters (Cliff 1995, Bass et al. 1975). There is a pupping and nursery ground in a coastal mangrove estuarine area of southern Belize (R.T. Graham pers. obs).
Native:Algeria; Anguilla; Antigua and Barbuda; Aruba; Australia (Ashmore-Cartier Is., Australian Capital Territory, Coral Sea Is. Territory, New South Wales, Northern Territory, Queensland); Bahamas; Bangladesh; Belize; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Brazil (Alagoas, Amapá, Bahia, Ceará, Espírito Santo, Fernando de Noronha, Maranhão, Pará, Paraíba, Paraná, Pernambuco, Piauí, Rio de Janeiro, Rio Grande do Norte, Rio Grande do Sul, Santa Catarina, São Paulo, Sergipe); British Indian Ocean Territory (Chagos Archipelago); Cambodia; Cape Verde; Cayman Islands; China (Fujian, Guangdong, Guangxi, Hainan, Shanghai, Zhejiang); Colombia; Costa Rica (Cocos I.); Cuba; Curaçao; Djibouti; Dominica; Dominican Republic; Ecuador; Egypt (Sinai); El Salvador; Eritrea; France (Clipperton I.); French Guiana; French Polynesia (Marquesas, Society Is., Tuamotu, Tubuai Is.); French Southern Territories (Mozambique Channel Is.); Grenada; Guadeloupe; Guatemala; Guyana; Haiti; Honduras (Honduran Caribbean Is.); Hong Kong; India (Andhra Pradesh, Goa, Gujarat, Karnataka, Kerala, Maharashtra, Orissa, Pondicherry, Tamil Nadu, West Bengal); Indonesia; Iran, Islamic Republic of; Iraq; Israel; Jamaica; Japan; Jordan; Kenya; Kuwait; Libya; Macao; Madagascar; Malaysia (Peninsular Malaysia, Sabah, Sarawak); Martinique; Mauritius (Rodrigues); Micronesia, Federated States of ; Montserrat; Morocco; Mozambique; Myanmar; New Caledonia; Nicaragua (Nicaraguan Caribbean Is.); Oman; Pakistan; Palau; Panama; Philippines; Pitcairn; Puerto Rico (Navassa I.); Qatar; Saint Barthélemy; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Saudi Arabia; Senegal; Seychelles (Aldabra); Sint Maarten (Dutch part); Somalia; South Africa (KwaZulu-Natal); Spain; Sri Lanka; Sudan; Suriname; Taiwan, Province of China (Kin-Men, Ma-tsu-Pai-chuan); Tanzania, United Republic of; Trinidad and Tobago; Tunisia; Turks and Caicos Islands; United Arab Emirates; United States (Alabama, California, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Texas); Venezuela, Bolivarian Republic of (Aves I., Venezuelan Antilles); Viet Nam; Yemen (North Yemen, Socotra, South Yemen)
|FAO Marine Fishing Areas:|
Atlantic – northeast; Atlantic – eastern central; Atlantic – southwest; Atlantic – southeast; Atlantic – northwest; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Mediterranean and Black Sea; Pacific – western central; Pacific – eastern central; Pacific – northwest; Pacific – southwest; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Sphyrna mokarran is a coastal-pelagic and semi-oceanic tropical hammerhead occurring close inshore and well offshore, over the continental shelves, island terraces, and in passes and lagoons of coral atolls, as well as over deep water near land, at depths ranging from near-surface to over 80 m (Compagno in prep. b). The maximum total size is reported as 550 to 610 cm by Compagno (in prep. b), though 400 cm is more common for a mature adult (Compagno in prep. b, Last and Stevens 1994). Males mature at about 234 to 269 cm, and reach at least 341 cm, and females mature at about 250 to 300 cm and reach 482 to 549 cm (Compagno in prep. b). S. mokarran is viviparous, with a yolk-sac placenta. Litter size ranges from 6 to 42 pups after 11 months' gestation (Compagno in prep. b). Size at birth is 50 to 70 cm. Females breed once every two years (Stevens and Lyle 1989). Pups are born in late spring to summer in the Northern Hemisphere and between December and January off Australia (Compagno in prep. b, Last and Stevens 1994). |
The diet includes fish (mainly demersal species), other elasmobranchs, crustacea and cephalopods (Compagno in prep. b). Strong et al. (1990) observed a large (ca 4 m) great hammerhead feeding on a southern stingray Dasyatis americana (disc width 1.5 m).
|Movement patterns:||Full Migrant|
Due to the distinctive head shape of this genus, it is typical for catches to be reported at the genus level, Sphyrna spp. Therefore, it is rare to find fisheries statistics that are specific to one species of hammerhead shark. Due to the great hammerhead?s preference for warmer waters, it can be expected to make up a greater proportion of tropical catches of hammerheads than more temperate fisheries. Sphyrna mokarran is taken by target and bycatch, fisheries (Dudley and Simpfendorfer 2006, Zeeberg et al. 2006) and is regularly caught in the tropics, with longlines, fixed bottom nets, hook-and-line, and possibly with pelagic and bottom trawls (Compagno in prep). Hammerhead sharks, S. mokarran in particular, have been noted as a favoured target species due to the size of their fins (R.T. Graham pers. comm). Fin prices are rising, driven by the Asian Fin market (R.T. Graham pers. obs).
There was a directed shark fishery operated by Taiwan around the northern coast of Australia that regularly caught great hammerheads up until 1986 (Stevens and Lyle 1989). Other possible threats include sport fishing (Pepperell 1992) and capture in anti-shark measures around the beaches of Australia and South Africa (Paterson 1990, Cliff 1995). Bonfil (1994) gives an overview of global shark fisheries. This species is mentioned specifically with reference to fisheries in Brazil, East USA and Mexico, however Sphyrna spp. are mentioned in the majority of tropical fisheries cited.
Mainly taken by drift gillnets, bottom gillnets and on longlines, hook and line, pelagic and bottom trawls (Schneider 1990). This species is a bycatch in both the industrial and artisanal fisheries but a specialised artisanal fishery for charcharhinid and sphyrnid species was introduced in Sierra Leone in 1975, and since then fishing pressure has not decreased (M. Seisay pers. obs). The Subregional workshop for sustainable management of sharks and rays in West Africa, 26-28 April 2000 in St Louis, Senegal (Ducrocq 2002) noted the high threat to sharks in the west African region and a noticeable decline in the CPUE of total sharks and rays. This workshop identified S. mokkarran as particularly threatened. The subsequent sub-regional plan of action for sharks of West Africa (member states of the Sub Regional Fishing Commission) states that landings of S. mokarran have collapsed and lists this as one of the four most threatened species, deserving the greatest attention in the whole region (Ducrocq 2002).
Previously observed from Mauritania to Angola, reportedly abundant from November to January in Senegal, and in October in Mauritania (Cadenat and Blache 1981). However, recent scientific trawl surveys off Guinea-Bissau, Mauritania, Senegal, Gambia and Guinea-Conakry between 20 to 1,000 m have failed to record it, except in very low numbers off Guinea-Conakry and one record from Senegal in 1995 (FISA unpublished data). Anecdotal evidence from interviews with fishermen in Senegal, Guinea-Bissau and Guinea suggest there was a large decline in all shark species during the 1990s and that S. mokarran is almost extirpated from these areas (M. Ducrocq pers. obs.).
Data are lacking as there is little species specific data collection in the region, however this is a very distinctive species with a large dorsal fin which is highly valued for the shark fin trade. Increased targeting of sharks began in the 1970s, when a Ghanaian fishing community settled in the Gambia and established a commercial network throughout the region, encouraging local fishermen to target sharks for exportation to Ghana. By the 1980s many fishermen were specialising in catching sharks, resulting in a decline in overall shark populations (Walker et al. 2005). There has been rapid growth in the shark fin market in this region, for export to the Far East, and yearly production of dried fins exported from Guinea-Bissau alone is estimated at 250 t (dry weight) (Walker et al. 2005). Sphyrna species combined represented 42% of bycatch in the European industrial pelagic trawl fishery off Northwest Africa (Zeeberg 2006).
Although there are very little species specific data available, the absence of recent records and region-wide recognition of the extent of the decline, give cause to suspect that the population has decreased by least 80% in the past 25 years. Fisheries in this region remain largely unmonitored and unmanaged, leading to an assessment of Critically Endangered in the Eastern Atlantic.
Southwest Indian Ocean
This species is widely distributed in the SW Indian Ocean and is a summer migrant to KwaZulu-Natal (KZN) (east coast of South Africa), where the annual catch in the KZN shark nets is 11 sharks (1978 to 1999), consisting mainly of adolescents and adults. Over this period there has been a significant decline in annual catch (18 to 4 sharks) and catch rate (0.5 to 0.2 sharks.km-net-1.yr-1 (p = 0.000) (Dudley 2002). A continued decline in catch rate was reported for the period 1978 to 2003 (Dudley and Simpfendorfer 2006). Over this period, regression of catch and catch rate against year revealed a significant decline in annual catch from 18 to two sharks (89%) and in catch rate from 0.44 to 0.09 sharks.km-net-1.yr-1 (79%) (S. Dudley pers. obs. 2006). It is uncertain whether these declines reflect highly localized stock depletion or whether they reflect a general decline in the Southwest Indian Ocean, but large numbers of longline vessels have been reported to be operating illegally in coastal waters of the western Indian Ocean where they are targeting primarily hammerhead sharks and giant guitarfish Rhynchobatus djiddensis (IOTC 2005 in Dudley and Simpfendorfer 2006). This species is generally regarded as solitary, and is therefore unlikely to be abundant wherever it occurs. This is in contrast to other large hammerheads, such as Sphyrna lewini which forms large schools. Sphyrna mokarran, like other hammerheads, readily takes baited hooks and is sought after for its fins. Based on these characteristics, together with the decline of 79% in catch rates in the KZN shark nets, this species is assessed as Endangered in the southwest Indian Ocean.
This species is caught primarily as a bycatch in the pelagic longline, bottom longline and net fisheries along the northwest Atlantic and Gulf of Mexico. It is also caught in the recreational fishery. The species represents 0.7% of the species catch and suffers from greater than 90% at-vessel fishing mortality in the U.S. bottom longline fishery (Commercial Shark Fishery Observer Program unpubl. data). The U.S. pelagic fishery logbook data has shown a decline close to 90%, however this data-set is known for inaccurate data reporting (Beerkircher et al. 2002). There is probably a lack of reporting of the catch of great hammerheads because this species is routinely finned and discarded, which is illegal in the US Atlantic Federal Waters (Commercial Shark Fishery Observer Program unpub. data). Both the pelagic and bottom longline observer programs have recorded a 2 to 3:1 ratio for S. Lewini to S. mokarran. The meat is not valuable but the fins are high grade and bring in a good price, thus finning still occurs in the U.S. fishery. Interview with shark fishermen in Belize indicate that hammerheads (S. mokarran in particular) are a favoured target species for their large fins (R.T. Graham pers. obs.). Fin prices are rising above US$50/lb in the neighbouring countries of Guatemala, driven by Asian buyers, according to these interviews (R.T. Graham pers. obs). This species is probably caught in other fisheries but is usually placed in a combined "hammerhead" category. Species identification (S. mokarran vs. S. lewini) a large obstacle in the proper assessment of this species. The high at-vessel fishing mortality for both species of hammerhead makes the threat of fishing even greater for this species. In the Pacific Ocean off of Guatemala this species is caught as by-catch in the commercial longline fishery.
There appear to be little data for landings and catch effort for this species in Central America and the Caribbean. Off the coast of Belize hammerheads were fished heavily by longline in the 1980s and early 1990s. Interviews with fishermen indicate that the abundance and size of Sphyrnids has declined dramatically in the past 10 years as a result of over exploitation, leading to a halt in the Belize based shark fishery (R.T. Graham pers. obs). However, the pressure is still sustained by fishers driving into Belizean waters from Guatemala (R.T. Graham pers. obs). The Cuban directed shark fishery (longline) between 1983 and 1991 recorded S. mokarran (subadults and juveniles) as one of 23 species caught. Since 1992 small increases in mean sizes were noted, indicating partial recovery of the species. In Mexico between November 1993 and December 1994 (Tamaulipas, Veracruz, Tabasco, Campeche and Yucatan) 901 vessels were monitored every day. Sphyrna mokarran represented 86% of the total catch.
The difficulty in species identification and accurate recording make an assessment of this species very difficult. However, low survival at capture makes this species very vulnerable to fishing pressure, whether directed or incidental. This species is listed as Endangered in the Northwest Atlantic under criterion A2 based on a suspected decline of at least >50% over the past 10 years. The decline is poorly documented and has not been curtailed.
There has been a large increase in the illegal, unregulated and unreported (IUU) fishing in northern Australia in the last few years (J. Stevens pers. obs.). Several initiatives are underway to identify which species are being taken and in what quantities. Hammerheads are known to feature in the catches, and are suspected targets for their large valuable fins, although no specific data are available. Some domestic boats are also suspected to be targeting species for their fins in the Northern Territory, and this likely includes hammerheads (J. Stevens pers. obs). It is not a productive species and is coming out at the "high-risk" end in recent Risk Assessments of northern Australian elasmobranchs (J. Stevens pers. obs). There is concern that this species is being increasingly targeted, and therefore an urgent need to obtain data to form an accurate assessment of the population in this region.
There are no known species specific conservation measures in place for S. mokarran.
This species is listed on Annex I, Highly Migratory Species, of the UN Convention on the Law of the Sea, which urges States to cooperate over the management of these species. No such management yet exists. Precautionary adaptive collaborative management of target and bycatch fisheries is urgently needed for this unproductive shark. It is also essential to improve data collection and develop stock assessments for this species.
The adoption of shark finning bans by fishing states (e.g., USA, Australia), regional entities (EU) and regional fisheries organisations (ICCAT) is accelerating and should increasingly prevent the harvesting of hammerhead sharks for their fins alone.
In the U.S. this species is managed as a Large Coastal Shark on U.S. Highly Migratory Species Fishery Management Plan (National Marine Fisheries Service: Federal Fisheries Management Plan for Atlantic Tuna, Swordfish and Sharks).
In South Africa there is a shark bycatch limit in the tuna longline fishery of 10% of the weight of tuna landed, and a recreational line fishery Bag Limit of one shark per angler per day.
|Citation:||Denham, J., Stevens, J.D., Simpfendorfer, C., Heupel, M.R., Cliff, G., Morgan, A., Graham, R., Ducrocq, M., Dulvy, N.K., Seisay, M., Asber, M., Valenti, S.V., Litvinov, F., Martins, P., Lemine Ould Sidi, M., Tous, P. & Bucal, D. 2007. Sphyrna mokarran. The IUCN Red List of Threatened Species 2007: e.T39386A10191938.Downloaded on 24 September 2018.|
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