|Scientific Name:||Sphyrna lewini|
|Species Authority:||(Griffith & Smith, 1834)|
|Infra-specific Taxa Assessed:|
Sphyrna couardi Cadenat, 1951
Zygaena lewini Griffith & Smith, 1834
|Red List Category & Criteria:||Endangered A2bd+4bd ver 3.1|
|Assessor(s):||Baum, J., Clarke, S., Domingo, A., Ducrocq, M., Lamónaca, A.F., Gaibor, N., Graham, R., Jorgensen, S., Kotas, J.E., Medina, E., Martinez-Ortiz, J., Monzini Taccone di Sitizano, J., Morales, M.R., Navarro, S.S., Pérez-Jiménez, J.C., Ruiz, C., Smith, W., Valenti, S.V. & Vooren, C.M.|
|Reviewer(s):||Musick, J.A. & Fowler, S.L. (Shark Red List Authority)|
The Scalloped Hammerhead (Sphyrna lewini) is a coastal and semioceanic hammerhead shark that is circumglobal in coastal warm temperate and tropical seas, from the surface and intertidal to at least 275 m depth. Although it is wide ranging, there is genetic evidence for multiple subpopulations. All life-stages are vulnerable to capture as both target and bycatch in fisheries: large numbers of juveniles are captured in a variety of fishing gears in near shore coastal waters, and adults are taken in gillnets and longlines along the shelf and offshore in oceanic waters. Population segregation and the species' aggregating habit make large schools highly vulnerable to fisheries and means that high CPUEs can be recorded, even when stocks are severely depleted. Hammerhead shark fins are more highly valued than other species because of their high fin ray count, leading to increased targeting of this species in some areas. Where catch data are available, significant declines have been documented: both species-specific estimates for S. lewini and grouped estimates for Sphyrna spp combined suggest declines in abundance of 50-90% over periods of up to 32 years in several areas of its range, including South Africa, the northwest and western central Atlantic and Brazil. Interviews with fishermen also suggest declining trends. Similar declines are also inferred in areas of the species' range from which specific data are not available, but fishing pressure is known to be high. Although S. lewini is relatively fecund compared to other large sharks (with litters of 12-38 pups) the generation period is greater than 15 years in the Gulf of Mexico and its life-history characteristics mean that it resilience to exploitation is relatively low. Given the major declines reported in many areas of this species' range, increased targeting for its high value fins, low resilience to exploitation and largely unregulated, continuing fishing pressure from both inshore and offshore fisheries, this species is assessed as Endangered globally.
In addition to the Endangered global assessment, a number of regional assessments have also been designated for this species as follows: Endangered A2bd+4bd in the Northwest Atlantic and Western Central Atlantic, Vulnerable A2bd in the Southwest Atlantic, Endangered A4bd in the Western Indian Ocean, Endangered A4bd in the Eastern Central and Southeast Pacific, Vulnerable in the Eastern Central Atlantic and Data Deficient in Australia.
Northwest and Western Central Atlantic (including Caribbean Sea)
Estimates of trends in abundance are available from two long-term research surveys conducted on the U.S. east coast, both of which indicate this species has undergone substantial declines in this region (98% between 1972 and 2003, and an order of magnitude between 1975 and 2005). A third survey comparing catch rates between 1983/84 with those in 1993-95 showed a decline of two-thirds, while a survey beginning more recently showed increases in catch rates of juveniles. Standardized catch rates from the U.S. pelagic longline fishery show declines in Sphyrna spp. Of 89% between 1986 and 2000 (according to the logbook data) and declines of 76% between 1992 and 2005 (according to observer data). The other information for this species from this region comes from Belize, where it has been heavily fished since the 1980s and fishermen have reported dramatic declines, which led to the end of the fishery. Fishing pressure is sustained in Belize by Guatemalan fishermen.
Sphyrna lewini faces two main threats related to fisheries in this region: 1) fishing of juveniles and neonates on the continental shelf by gillnets and trawl nets and 2) fishing of adults by gillnets (only in Brazil) and longlines on the continental shelf and oceanic waters, mostly for fins. Catches are inadequately recorded and landings data do not reflect the numbers finned and discarded at sea. The species is taken by fisheries throughout all parts of its life-cycle and greater demand for shark fins and flesh has resulted in a substantial increase in retention rates and targeting of sharks. In view of the intensive fisheries in the coastal and offshore areas where S. lewini occurs in this region and documented declining trends where the species has been heavily fished in other areas of its range, the species is assessed as Vulnerable in the Southwest Atlantic.
Western Indian Ocean
Catch per unit effort of S. lewini declined significantly from 1978-2003 in shark nets off the beaches of Kwa-Zulu Natal, South Africa, suggesting a 64% decline over this period. Sphyrna lewini is captured throughout much of its range in the Indian Ocean, including illegal targeting of the species in several areas. Landings reported to FAO in Oman, surveys of landings sites in Oman and interviews with fishermen there also suggest that catches of S. lewini have declined. The species faces heavy fishing pressure in this region, and similar declines in abundance are also inferred in other areas of its range in this region. Given continued high fishing pressure, observed and inferred declines, the species is assessed as Endangered in this region.
Eastern Central and Southeast Pacific
This species is heavily exploited through its range in the Eastern Pacific. Of particular concern is increasing fishing pressure at adult aggregating sites such as Cocos Island (Costa Rica) and the Galapagos Islands (Ecuador), and along the slopes of the continental shelf where high catch rates of juveniles can be obtained. The number of adult individuals at a well-known S. lewini aggregation site in the Gulf of California (Espiritu Santo seamount) has declined sharply since 1980. Large hammerheads were also formerly abundant in coastal waters off Central America, but were reportedly depleted in the 1970s. A comparison of standardized catch rates of pelagic sharks (species-specific information was not available) in the EEZ of Costa Rica from 1991-2000 showed a decrease of 60%. In Ecuador, landings (grouped for the family Sphyrnidae) peaked in 1996 and declined until 2001. Illegal fishing for shark fins is occurring around the Galapagos. There are no species specific data for these fisheries, but S. lewini is one of the most common species around the Galapagos and given the high value of its fins, it is very likely being targeted. Divers and dive guides in the Galapagos have noted a severe decrease in shark numbers and schools of hammerhead sharks. Given continued high fishing pressure, observed and inferred declines, the species is assessed as Endangered in this region.
Eastern Central Atlantic
Although there are no data on species-specific trends in abundance for S. lewini in this region, fishing pressure from pelagic longline fleets in this area is high and potentially comparable to that in the Northwest and Western Central Atlantic, where significant declines in abundance of S. lewini have been documented. The larger hammerhead shark, Sphyrna mokarran, is assessed as Critically Endangered in this region, from which it has apparently virtually disappeared. There is also concern for S. lewini in this area and although it is still present in the catches, catches are comprised entirely of juveniles in some areas. Given continued high fishing pressure throughout this species' shelf habitat off Western Africa and the declining trends observed in other areas of this species' range where it is fished, it is considered to meet the criteria for at least Vulnerable in this region.
There has been a large increase in the illegal, unregulated and unreported (IUU) fishing in northern Australia recently. Hammerheads are known to feature in the catches, and are suspected targets for their large valuable fins, although no specific data are available. Further study is urgently required to determine the status of S. lewini in this region.
|Range Description:||The Scalloped Hammerhead has a circumglobal distribution in coastal warm temperate and tropical seas (Compagno in prep).
In the Western Atlantic the species ranges from New Jersey to Uruguay, including Gulf of Mexico and Caribbean Sea (A. Domingo pers. obs. 2007, Compagno in prep).
This shark possibly occurs in the Mediterranean Sea and around the Azores. Probably present all along the western Africa coast, confirmed from Mauritania, Senegal, Gambia, Ivory Coast, Guinea, Guinea Bissau, Sierra Leone, Gabon, and Congo (Compagno in prep, M. Ducrocq pers. obs. 2006).
Recorded from South Africa (Western Cape to kwaZulu-Natal), Maldives, and Red Sea to Pakistan, India, Myanmar (Compagno in prep).
In the Western pacific, this shark occurs from Thailand, Vietnam, Indonesia, China (including Taiwan, Province of China), Japan, Philippines, Australia (Queensland, Western Australia), New Caledonia (Compagno in prep).
In the Eastern Pacific, the Scalloped Hammerhead ranges from southern California and Gulf of California to Panama, Ecuador and possibly northern Peru (Compagno in prep). Also Hawaii and Tahiti (Compagno in prep.).
Native:Angola (Angola); Anguilla; Antigua and Barbuda; Aruba; Australia (Queensland, Western Australia); Bahamas; Bahrain; Barbados; Belize; Benin; Brazil; Cameroon; Cape Verde; Cayman Islands; China; Colombia; Congo; Costa Rica; Côte d'Ivoire; Cuba; Djibouti; Dominica; Dominican Republic; Ecuador; Egypt; El Salvador; Equatorial Guinea; Eritrea; French Guiana; Gabon; Gambia; Ghana; Grenada; Guadeloupe; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras; India; Indonesia; Iran, Islamic Republic of; Iraq; Jamaica; Japan; Kuwait; Liberia; Maldives; Mauritania; Mexico; Myanmar; Namibia; New Caledonia; Nicaragua; Nigeria; Oman; Pakistan; Panama; Philippines; Puerto Rico; Qatar; Saint Kitts and Nevis; Saint Lucia; Saint Vincent and the Grenadines; Sao Tomé and Principe; Saudi Arabia; Senegal; Sierra Leone; South Africa; Suriname; Taiwan, Province of China; Thailand; Togo; Trinidad and Tobago; United Arab Emirates; United States (Alabama, California, Delaware, Florida, Georgia, Hawaiian Is., Louisiana, Maryland, Mississippi, New Jersey, North Carolina, South Carolina, Texas, Virginia); Uruguay; Venezuela, Bolivarian Republic of; Viet Nam; Yemen
|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 – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Recent studies indicate that the Northwest Atlantic, Caribbean Sea and Southwest Atlantic populations of this species are each genetically distinct from each other, and from Eastern Central Atlantic and Indo-Pacific populations (D. Chapman and M. Shivji, Nova Southeastern University unpublished data). The boundaries between each population are not yet completely defined due to sampling constraints, but the "Caribbean Sea" population includes Belize and Panama and the "U.S. Gulf Of Mexico" sample covers from Texas to south-western Florida, the boundary or transition zone will be in between Texas and Northern Belize (D. Chapman and M. Shivji, Nova Southeastern University pers. comm. 2007). Further studies are planned to obtain more samples from the Caribbean Sea. Adult site fidelity and annual homing to seamounts are known to occur in the Gulf of California (Klimley 1988, Klimley unpublished data).|
|Habitat and Ecology:||
This is a coastal and semi-oceanic pelagic shark, found over continental and insular shelves and in deep water near to them, ranging from the intertidal and surface to at least 275 m depth (Compagno in prep.). The pups of this species tend to stay in coastal zones, near the bottom, occurring at high concentrations during summer in estuaries and bays (Clarke 1971, Bass et al. 1975, Castro 1983). They have been observed to be highly faithful to particular diurnal core areas (Holland et al. 1993) and sometimes form large schools which migrate to higher latitudes in summer (Stevens and Lyle 1989).
Horizontal migration is observed from inshore bays to a pelagic habitat as the sharks grow. This species segregates by sex, with females migrating offshore earlier and at smaller sizes than males. In the Gulf of Mexico and northern Australia, it was observed that males less than 1 m long were more abundant over the continental shelf, but females bigger than 1.5 m dominated areas near the edge of the shelf. Adults spend most of the time offshore in midwater and females migrate to the coastal areas to have their pups (Clarke 1971, Bass et al. 1975, Klimley and Nelson 1984, Branstetter 1987, Klimley 1987, Chen et al. 1988, Stevens and Lyle 1989). Nursery areas are found in shallow inshore waters, while the adults are found offshore (Compagno 1984, Holland et al. 1993, Kotas et al. 1995, Lessa et al. 1998). Neonates and juveniles are known to shoal in confined coastal pupping areas for up to two years before moving out to adult habitat (Holland et al. 1993). In the Northwest and Western Central Atlantic, the coastal area between South Carolina and central Florida is believed to be an important nursery area (Castro 1993). In southern Brazil, near-term gravid females migrate inshore to nursery grounds (at 2-10 m depth; bottom water temperature of 20-24°C) and give birth in spring (November-February) (Dono et al. in prep., Vooren and Lamónaca 2003). Juveniles then remain between the shore and 100 m depth (Vooren 1997, Kotas et al. 1998). In northern Brazil (latitude 3°S), this species appears to breed at a smaller size and have lower fecundity than reported elsewhere (Lessa et al. 1998).
Throughout the species' range in the Eastern Pacific, parturition is thought to occur between May and July in shallow nursery areas (Ruiz et al. 2000, Torres-Huerta 1999). The northern Gulf of California and Bahía Almejas on the Pacific coast of Baja California Sur appear to be important pupping and possible nursery grounds.
The species is viviparous with a yolk-sac placenta. Only the right ovary is functional. In Taiwanese (POC) waters, ovum development takes approximately 10 months and ova reach a maximum diameter of 40-45 mm. The number of oocytes in the ovarium can be as many as 40-50 per female (Chen et al. 1988). The gestation period is around 9-12 months, with birth in spring and summer. The average number of embryos in the uterus ranges from 12-41 and females pup every year. Newborn size ranges from 31-57 cm (Castro 1983; Compagno 1984; Branstetter 1987; Chen et al. 1988; Stevens and Lyle 1989; Chen et al. 1990; Oliveira et al. 1991, 1997; Amorim et al. 1994; White et al. 2008). Predation on pups and juveniles is high, mainly by other carcharhinids and even by adults of the same species. This is probably the most significant source of natural mortality on the population (Clarke 1971, Branstetter 1987, Branstetter 1990, Holland et al. 1993), and may explain, in evolutionary terms, the higher fecundity of this species compared to some other sharks.
Maximum size reported by different studies, ranged from 219-340 cm TL for males and 296-346 cm for females (Clarke 1971, Bass et al. 1975b, Schwartz 1983, Klimley and Nelson 1984, Stevens 1984, Branstetter 1987, Chen et al. 1988, Stevens and Lyle 1989, Chen et al. 1990). Males mature between 140-198 cm TL and females at around 210-250 cm TL (Compagno 1984b, Branstetter 1987, Chen et al. 1990, Carrera and Martinez in prep., White et al. 2008). Branstetter's (1987) growth study in the Gulf of Mexico found asymptotic length for both sexes of 329 cm TL and 253 cm fork length (FL), with an index of growth rate of k = 0.073 y-1. Piercy et al.'s (2007) more recent study used Fork Length (FL) rather than total length (TL) and suggested faster growth, with asymptotic length of 214.8 cm FL for males and 233.1 cm FL for females, with an index growth rate of k=0.13 year-1 for males and k=0.09 year-1 for females. It is unclear whether these differences are related to sample size, methodology or changes resulting from a density-dependent compensatory response to population depletion. In Ecuadorian waters, Carrera-Fernández and Martínez-Ortíz (2007) found that females matured at 225 cm TL, reaching a maximum size of 302 cm TL, and males matured at 190 cm TL, reaching a maximum size of 282 cm TL.
The age and size of first maturity has been studied in several different areas; the Gulf of Mexico, Western Central Atlantic, Taiwanese (Province of China) waters, Northwest Pacific and Mexican waters, Eastern Central Pacific. Branstetter (1987) estimated that males mature at 10 years, 180 cm TL and females at 15 years, 250 cm TL in the Gulf of Mexico. During a recent study by Piercy et al. (2007) on the age and growth of S. lewini in the Gulf of Mexico the oldest age estimate obtained was 30.5 years for both males and females. Whereas, Chen et al. (1990) estimated that males mature at 3.8 years, 198 cm TL and females at 4.1 years, 210 cm in Taiwanese Pacific waters and Anislado-Tolentino and Robinson-Mendoza (2001) estimated that males mature at 4.3 years and females at 5.8 years in the Mexican Pacific waters. Both studies in the Gulf of Mexico show that this species appears to grow more slowly and have smaller asymptotic sizes than reported in the Pacific Ocean. The vast differences in age and growth reported between Taiwanese Pacific waters/Mexican Pacific waters and other oceanic regions may arise from different interpretation of vertebral band formation rather than true geographic variation (W. Smith pers. comm.). Current published age estimates of S. lewini from the Mexican Pacific and Taiwanese Pacific are based on growth estimates that assume the deposition of two centrum annuli per year (Chen et al. 1990, Ansilado-Tolentino and Robinson-Mendoza 2001), whereas studies in the Gulf of Mexico assume the deposition of one growth band per year (Branstetter 1987, Piercy et al. 2007). The Pacific estimates have not been validated and the deposition of two centrum annuli has not been confirmed in any other shark species to date (W. Smith pers. comm.), therefore these estimates should be viewed with caution. Previous evidence of the deposition of two annual bands in the Shortfin Mako Shark (Isurus oxyrinchus), has not proven to be valid and this may be the case for S. lewini (Campana et al. 2002). If growth data presented by Chen et al. (1990) were converted to reflect a one growth band per year hypothesis, then the results of these studies would agree more closely. Validation of the periodicity of growth-band deposition is required for both the Pacific and Atlantic populations to resolve this issue (Piercy et al. 2007).
Comparing different estimates for the values of k on S. lewini (0.054-0.160 yr-1), by different authors, suggests that this is a "medium growth species" (Branstetter 1987). Smith et al. (1998) estimated the intrinsic rate of increase at MSY of 0.028.
Adult S. lewini feed on mesopelagic fish and squids. In certain areas stingrays of the (Dasyatis spp.) are the preferred food. Pups and juveniles feed mainly on benthic reef fishes (e.g., scarids and gobiids), demersal fish and crustaceans. (Bigelow and Schroeder 1948, Clarke 1971, Bass et al. 1975, Compagno 1984, Branstetter 1987, Stevens and Lyle 1989).
|Use and Trade:||This shark's fins are highly valued and they are being increasingly targeted in some areas in response to increasing demand for shark fins. Hammerhead shark species S. zygaena and S. lewini were found to represent at least 4-5% of the fins auctioned in Hong Kong, the world's largest shark fin trading center (Clarke et al. 2006a). Hammerhead shark fins are generally high value compared to other species because of their high fin ray count (S. Clarke unpubl. data). It is estimated that between 1.3 and 2.7 million S. zygaena or S. lewini are represented in the shark fin trade each year or, in biomass, 49,000 to 90,000 mt (Clarke et al. 2006b).|
The Scalloped Hammerhead is taken as both a target and bycatch by trawls, purse-seines, gillnets, fixed bottom longlines, pelagic longlines and inshore artisanal fisheries. The latter catch large numbers of pups and juveniles in some regions. The species' aggregating habit makes them vulnerable to capture in large schools. This also means that they may appear more abundant in landings, where they are caught in high, localised concentrations. Intense fishing pressure can deplete regional stocks rapidly, and re-colonization of depleted areas from neighboring regions is expected to be a slow and complex process. This species is expected to have a low resilience to exploitation because of its life-history characteristics (Maguire et al. 2006).
This species' fins are highly valued and they are being increasingly targeted in some areas in response to increasing demand for shark fins. Hammerhead shark species S. zygaena and S. lewini were found to represent at least 4-5% of the fins auctioned in Hong Kong, the world's largest shark fin trading center (Clarke et al. 2006a). Hammerhead shark fins are generally high value compared to other species because of their high fin ray count (S. Clarke unpubl. data). It is estimated that between 1.3 and 2.7 million S. zygaena or S. lewini are represented in the shark fin trade each year or, in biomass, 49,000 to 90,000 mt (Clarke et al. 2006b).
Northwest and Western Central Atlantic (including Caribbean Sea)
In the USA this species is caught in both commercial coastal shark bottom longline and gillnet fisheries and the pelagic longline fishery, where it suffers high mortality (Piercy et al. 2007). It is also taken in recreational shark fisheries. The USA pelagic longline fishery has operated since the 1960s and encompasses the entire range of this species in the Northwest and Western Central Atlantic, from the equator to about 50°N. Although this is quite a fecund shark, its late age at maturity in this region (15 years) will render it quite vulnerable to overexploitation, and limit its recovery potential.
Estimates of trends in abundance of Sphyrna spp. are available from standardized catch rate indices of the U.S.A. pelagic longline fishery, from logbook data between 1986 and 2000 and from observer data between 1992 and 2005. The area covered by this fishery, ranging from the equator to about 50°N, encompasses the range of this species in these two regions. Although this fishery will not sample individuals closest to the coast, the sample size of hammerheads recorded in the logbook data (the majority of which are thought to be S. lewini) is substantial, with over 60,000 recorded during this period. This subpopulation of Scalloped Hammerhead sharks is estimated from the logbook data to have declined by 89% over the 15 year time period, from 1986-2000 (Baum et al. 2003), which is less than one generation. A more recent analysis of the pelagic longline observer data indicates that Sphyrna spp. declined by 76% between 1992 and 2005 (Baum et al. in prep.). The pelagic longline fishery has operated in these regions since the 1960s, thus declines from 1986 were certainly not from virgin population abundance.
Using logistic regression of S. lewini, Ha (2006) showed that the probability of capture in a fisheries independent sampling program off Virginia, USA, declined by an order of magnitude between 1975 and 2005. Species-specific trends in abundance are available for S. lewini from a shark-targeted longline survey conducted annually between 1972 and 2003 near Cape Lookout, North Carolina, by Dr. F.J. Schwarz at the University of North Carolina. Standardized CPUE from this research survey based on a sample size of 495 S. lewini indicates that it has declined by 98% over this 32 year time period (Myers et al. 2007). Off southern Carolina, Ulrich (1996) reported a 66% decrease between 1983/84 and 1991/95. In contrast to all other data, a more recent research survey (1989-2005) along the southeast U.S. coast shows a significant increase in juvenile scalloped hammerheads (Myers et al. 2007).
Off the Atlantic coast of Belize hammerheads were fished heavily by longline in the 1980s and early 1990s (R.T. Graham pers. obs. 2006). Hammerheads are a favoured target species for their large fins. 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. 2006). However, the pressure is still sustained by fishers driving into Belizean waters from Guatemala (R.T. Graham pers. obs. 2006). 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) is 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 high. Sphyrna lewini is also taken in various fisheries along the Caribbean coast of South America. It is taken in artisanal gillnet fisheries targeting mackerel off Guyana, Trinidad and Tobago and in pelagic tuna fisheries of the eastern Caribbean (Chan A Shing 1999).
The Scalloped Hammerhead faces two main threats related to fisheries in this region: 1) fishing of juveniles and neonates on the continental shelf by gillnets and trawl nets (Vooren and Lamónaca 2003, Kotas and Petrere 2002, Doño 2008); and 2) fishing of adults by gillnets (only in Brazil) and longlines on the continental shelf and oceanic waters, mostly for fins (Kotas et al. 2001, Kotas and Petrere 2002, Kotas and Petrere 2003, Zerbini and Kotas 1998). The species therefore faces intensive fishing pressure throughout its range in this area and at all points in its life cycle. Because all Brazilian fisheries statistics for hammerhead sharks are grouped under the headings "shark" or "hammerhead shark", it is not possible to determine species-specific trends. Annual landings of hammerhead sharks (six species of hammerhead sharks occur off Brazil) in the ports of Rio Grande and Itajaí (Brazil) combined increased rapidly from ~30 t in 1992 to 700 t in 1994, after which catches decreased, fluctuating between 100-300 t from 1995-2002. The majority of this catch was taken by surface gillnet fisheries that targeted hammerhead sharks on the outer shelf and slope between 27° and 35°S (Kotas 2004, Vooren et al. 2005). Neonates and small juveniles are caught in coastal waters by directed gillnet fishing and as bycatch by bottom trawls (Vooren and Klippel 2005). In the inshore nursery area (depths down to 10 m), neonates are fished intensively by coastal gillnets and are also caught as bycatch by shrimp trawl, pair trawl and intensive recreational fisheries. Their abundance in coastal waters has decreased markedly as a result (Haimovici and Mendonça 1996, Kotas et al. 1995, 1998, Kotas and Petrere 2002, Vooren and Lamónaca unpublished data). Finning of hammerhead sharks, with discarding of the carcasses at sea, is often practised (Kotas 2004, Vooren and Klippel 2005). Fisheries statistics only refer to the landed carcasses and therefore the true extent of catches is unknown.
In southern Brazil and northern Uruguay, adult hammerhead catches (S. lewini and S. zygaena) by monofilament longliners are highest in winter and spring at the shelf edge and the continental slope between 30° and 35°S (Kotas and Petrere 2002). The Brazilian pelagic fishery based in Santos catches significant numbers of sharks, including S. lewini (Amorim et al. 1998). Until 1997, most of this shark catch was discarded but greater demand for fins and flesh has resulted in a substantial increase in retention rates and targeting of sharks (Bonfil et al. 2005). Because hammerhead shark fins are highly valued for their high fin-ray count, this species is unlikely to be released alive. The artisanal fishing fleet in São Paulo has operated since 1996 and also takes sharks. The majority of the hammerheads caught by this fishery were newborns or juveniles (Bonfil et al. 2005). In Uruguay (oceanic coast) some neonates are also captured (together with S. zygaena) in artisanal gill nets, in summer (between December and February) (A. Domingo pers. obs. 2007). In view of the intensive fisheries in the coastal and offshore areas where S. lewini occurs in this region and documented declining trends where the species has been heavily fished in other areas of its range, the species is assessed as Vulnerable in the Southwest Atlantic.
Eastern Central Atlantic
Data to indicate trends in abundance are generally not available for the Eastern Central Atlantic. Zeeberg et al. (2006) suggest that similar population trends for hammerheads (grouped) to those documented in the Northwest Atlantic can be expected in the Northeast and Eastern Central Atlantic because longline fleets in this area exert comparable fishing effort, and effort is seen to shift from western to eastern Atlantic waters (Buencuerpo et al. 1998, Serafy et al. 2004, Zeeberg et al. 2006). European industrial freeze trawlers targeting small pelagic fish (Sardinella, sardine, and horsemackerel) operate on the northwestern African shelf nearly year-round with five to ten large vessels (9,000-18,000 horse power). A study of bycatch rates in more than 1,400 trawl sets off Mauritania from 2001-2005, showed that Sphyrna species combined represented 42% of total bycatch during this period (Zeeberg et al. 2006).
Hammerheads are caught by both inshore artisanal fisheries and offshore European fisheries operating along the coast of western Africa. The Subregional workshop for sustainable management of sharks and rays in West Africa, 26-28 April 2000 in St Louis, Senegal (Anonymous 2000) noted the high threat to sharks in the West African region and a noticeable decline in the CPUE of total sharks and rays. Walker et al. (2005) also noted that there is concern for Sphyrna lewini off Mauritania, with catches comprised exclusively of juveniles, often newborn. 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).
This species is frequently caught along the western African coast and is heavily targeted by driftnets and fixed gillnets from Mauritania to Sierra Leone (M. Ducrocq pers. comm. 2006). There is anecdotal evidence for some declines in catches off Senegal and Gambia (M. Ducrocq pers. comm. 2006). Juveniles are very susceptible to coastal fisheries using drift or fixed gill nets such as sole, sciaenid and Sepia spp fisheries (M. Ducrocq pers. comm. 2006). They were taken as bycatch in the milk shark fishery and in the Banc d'Aguin national park, Mauritania, until the fishery was stopped in 2003 and they are still caught in large quantities in the Sciaenid fishery. A specialized artisanal fishery for carcharhinid and sphyrnid species was introduced in Sierra Leone in 1975, and since then fishing pressure has been continuous (M. Seisay pers. obs. 2006).
Western Indian Ocean
Reliable species-specific catch information is available for shark nets set off the beaches of Kwa-Zulu Natal, South Africa, in the southewestern Indian Ocean, from 1978-2003 (Dudley and Simpfendorfer 2006). Catch per unit effort of S. lewini declined significantly during this period from approximately 5.5/km net/year to approximately 2/km net/year (Dudley and Simpfendorfer 2006). This fishery independent data indicates a decline of approximately 64% over a 25 year period. About 120 longline vessels were reportedly operating illegally in coastal waters of the western Indian Ocean prior to 2005, and this number was expected to increase (IOTC 2005). These vessels are primarily targeting hammerhead sharks and Giant Guitarfish (Rhynchobatus djiddensis) for their fins (Dudley and Simpfendorfer 2006). Illegal fishing by industrial vessels and shark finning are reported in other areas of the Indian Ocean also (Young et al. 2006). Dudley and Simpfendorfer (2006) also report large catches of newborn Sphyrna lewini by prawn trawlers on the Tudela Bank, South Africa, ranging from an estimated 3,288 in 1989 to 1,742 in 1992, with almost 98% mortality. An inshore, artisanal fishery that uses multiple gear types (including seine nets and gillnets) along the coast of Mozambique and takes sharks as bycatch also potentially affects S. lewini (Dudley and Simpfendorfer 2006).
Sphyrna lewini is captured in various other fisheries throughout the rest of its range in the Indian Ocean. Few species-specific data are available from other areas, however, declines are also likely to have occurred in other areas where this species is heavily fished. Other countries with major fisheries for sharks include the Maldives, Kenya, Mauritius, Seychelles and United Republic of Tanzania (Young et al. 2006). Sharks are considered fully to over-exploited in these waters (Young et al. 2006). Landings data are available from FAO for Oman since 1985. Sphyrna lewini is one of five dominant species in the catches of Oman. Landings of sharks for Oman varied between 2,800-8,300 t, since 1985, with peaks noted from 1986-1988 and 1995-1997. After 1997 landings continued to decline to under 4,000 t in 2000 (FAO 2008). Oman has a long-established traditional shark fishery (Henderson et al. 2007). Henderson et al. (2007) surveyed landings sites in Oman between 2002 and 2003 and report a notable decline in catches of S. lewini in 2003, although the trend varied between areas. Henderson et al. (2007) note that large pelagic sharks such as S. lewini were displaced during 2003 by smaller shark species. Although it is possible that this is due to sampling bias, informal interviews with fishermen revealed a general trend of declining shark catches over the last number of years, particularly large pelagic species (Henderson et al. 2007). Artisanal gillnet and longline fisheries also target sharks off Madagascar for their fins, which are exported in the international shark fin trade. A study of directed shark fisheries at two sites in southwest Madagascar from 2001-2002 showed that hammerhead sharks represented 29% of sharks caught and 24% of the total wet weight, but species-specific data are not available because fishermen do not differentiate between S. lewini and S. zygaena (McVean et al. 2006).
Fishing pressure is also high in other areas of the Indian Ocean and Western Pacific, with many countries in this region among the largest shark fishing nations in terms of global catch in the world (Clarke and Rose 2005, SEAFDEC 2006). Indonesia has the largest chondrichthyan fishery in the world, with a reported 105,000 and 118,000 tonnes landed in 2002 and 2003 respectively (White et al. 2006). This species is a target and bycatch of shark longline, tuna gillnet fisheries and trawls in several areas of this region (White et al. 2006, SEAFDEC 2006). The species is utilised for its fins (high value in adults), meat, skin and cartilage (White et al. 2006, SEAFDEC 2006). White et al. (2008) suggest that this species is prone to overfishing in Indonesian waters, where substantial catches of S. lewini are taken in gillnet and longline fisheries. They found that almost all of the S. lewini caught by gillnetting, and the majority caught by longlining, were immature, and were therefore removed from the population before they had the opportunity to breed. Inshore fishing pressure is intense throughout Southeast Asia and juveniles and neonates are very heavily exploited, with large numbers of immature sharks in catches in other areas also (SEAFDEC 2006). Foreign vessels are also reported to target sharks in eastern Indonesian waters (Clarke and Rose 2005). Given the marked declines in this species' abundance in areas for which data are available, there is every reason to suspect that declines have also occurred in other areas of the Indian Ocean and Western Pacific, where fishing pressure is high.
Japanese data on hammerhead species are limited, but reported landings in Japan's coastal ports totaled 11-34 mt annually between 2000 and 2004 with an average of 24 mt per annum. No CPUE trends are available (Japan Fisheries Agency 2006).
Eastern Central and Southeast Pacific
Throughout this species' range in the Eastern Pacific, juveniles and neonates are heavily exploited in directed fisheries, and are also taken as bycatch of shrimp trawlers and coastal fisheries targeting teleost fish. Fishing pressure directed at juveniles also appears to have increased in parts of the Gulf of California and in Costa Rica, and is likely to be increasing elsewhere as other, more valuable fishery stocks are depleted. Patchy distribution resulting from aggregating behavior of adults and the use of historic nurseries, where neonates shoal with spatially confined movements, make this species particularly easy to target. As in other areas, the large fins of this species are highly prized for their value in the international shark fin trade. Increased fishing pressure from international longline fleets in the Eastern Central Pacific and Southeast Pacific, driven by increasing demand for fins, is of concern. Furthermore, as traditional and coastal fisheries in Central America are depleted, domestic fleets have increased pressure at adult aggregating sites such as Cocos Island (Costa Rica) and the Galapagos Islands (Ecuador), or along the slopes of the continental shelf where high catch rates of juveniles can be obtained (Vargas and Arauz 2001).
In the Gulf of California, Sphyrna lewini is a common catch in the directed artisanal elasmobranch fisheries of Sonora, Sinaloa, Baja California, and Baja California Sur, Mexico. Juveniles, including neonates, dominate the overall landings of this species; most are less than 100 cm total length (Bizzarro et al. in press). Bottom set gillnets and longlines produce the majority of the catch. Adults are landed in artisanal pelagic longline and gillnet fisheries, but represented less than 20% of the total S. lewini observed in artisanal catches during 1998 and 1999 fisheries surveys (Bizzarro et al. In Press). The indirect take by trawlers and artisanal teleost and shrimp fishermen is unknown. Landings data for 1996-1998 from the Gulf of Tehauntepec, Mexico, indicates that Scalloped Hammerheads were the second most important shark caught in the artisanal shark fishery, representing 36% of the total catch from a sample of 8,659 individuals (Soriano-Velassquez et al. 2002). The size of the individuals in this sample is unknown. Marquez (2000) reports that this species represented only 4.61% of the total catch of the artisanal fishery in the Gulf of California, contrasting with reports for Sinaloa, Mexico in 1994, 1995 and 1996, in which scalloped hammerheads represented 80.3%, 52.54% and 85.68% of the shark catch respectively (Marquez 2000). Off Pacific Guatemala, the importance of this species in the fishery landings appears to vary across areas, from 6% (n=339) to 74% (n=800) of the total catch from 1996-1999 (Ruiz and Ixquiac 2000). Data from El Salvador collected from July of 1991 to June of 1992, indicate this species represented 11.9% of the landed catch in a sample of 412 (Villatoro and Rivera 1994).
The number of adult individuals at a well-known S. lewini aggregation site in the Gulf of California (Espiritu Santo seamount) has declined sharply since 1980. In 1981 Klimley and Nelson estimated the size of a school at 525 individuals using Lincon Index mark recapture methods. Between 1998 and 2004 at least 20 attempts have been made to recreate this study, however in most cases fewer than 8 individuals have been observed at one time (Klimley 1999, Klimley and Jorgensen unpublished data).
Large hammerheads were formerly abundant in coastal waters off Central America, but were reportedly depleted in the 1970s (Cooke 1990). Industrial longlining initiated in the early 1980s, and again large hammerheads provided valuable fins for this market. A comparison of standardized catch rates of pelagic sharks (species-specific information was not available) in the EEZ of Costa Rica from 1991-2000 showed a decrease of 60% (Arauz et al. 2004). In 1991, sharks formed 27% of the total catch. In 2000, only 7.64% of the total catch was sharks, and in 2003 this decreased further to 4.9% of the total catch, 58.2% (Arauz et al. 2004). In 2001 and 2003, scalloped hammerheads only constituted 0.14% and .09% of the total catch by individuals, respectively.
In Ecuador, catch records (grouped for the entire family Sphyrnidae) indicate a peak of approximately 1,000 tons in 1996, followed by a steady reduction until 2001 (Herrera et al. 2003). Landings in the port of Manta (accounting for 80% of shark landing in Ecuador) of S. lewini, caught by artisanal longline and drift net fleet were about 160 t in 2004, 96 t in 2005 and 82 t (2006). Artisanal fishery landings into the port of Manta for Sphyrna spp declined by 51% between 2004 and 2006 (Martínez-Ortíz et al. 2007). According to Carrera-Fernández and Martínez-Ortíz (2007) the percentage of juveniles in landings is 83% for females and 71% for males. Most of the landings for this species (74%) take place between January and June.
Divers and dive guides in the Galapagos have noted a severe decrease in shark numbers and schools of hammerhead sharks (P. Zarate pers. comm.). Illegal fishing around the Galapagos is not only practiced by fishermen from the Galapagos, but also by the industrial and artisanal fleet from continental Ecuador and international fleets (Coello 2005). These illegal fisheries target sharks for their fins. There are no species specific data for these fisheries, but S. lewini is one of the most common species around the Galapagos (J. Martinez pers.obs.), and given the high value of fins of this species, it is very likely that it is targeted in illegal finning activities. In an effort to help stopping the illegal finning occurring in the Galapagos, the Ecuadorian Government issued Decree 2130 in 2004 prohibiting fin export from Ecuador. Unfortunately, the Decree had the reverse effect of establishing illegal trade routes, with fins being exported mainly via Peru and Colombia where there is no finning ban in place. Interviews with fishermen and traders in both Ecuador and Peru suggested that illegal trade routes operated for fins transported both from Ecuador and directly from Galapagos to Peru (Saenz 2005, WildAid 2005). Ecuador then abolished Decree 2130 and issued two new Decrees (482 and 902) in 2007 which establish better controls; traceability of the exported products; re-confirm the prohibition of finning established in 1993; a database on trade and establish as State policy the National Action Plan for the Conservation and Management of Ecuadorian Sharks (PAT - Ec).
There has been a large increase in 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. There is an urgent need to obtain data to form an accurate assessment of the population in this region.
Scalloped hammerhead is a member of the family Sphyrnidae, which is listed on Annex I, Highly Migratory Species, of the UN Convention on the Law of the Sea. States are urged 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 highly migratory species. It is also essential to improve and sustain data collection and develop stock assessments for this species. Listing on international resource management agreements, such as the Convention on Migratory Species (CMS) could help to drive improvements in national and regional management and facilitate collaboration between states, for this species and other migratory sharks.
The adoption of shark finning bans by fishing states (e.g., USA, Australia), regional entities (EU) and regional fisheries organisations (e.g., ICCAT, IOTC, IATTC, WCPFC) is accelerating and should increasingly prevent the capture of oceanic sharks for their fins alone.
Management plans, fishing regulation, and monitoring programs are needed throughout this species' range.
Northwest Atlantic and Western Central Atlantic (including Caribbean Sea)
In the U.S. this species is included in the Large Coastal Shark complex management unit, on U.S. Highly Migratory Species Fishery Management Plan (National Marine Fisheries Service: Federal Fisheries Management Plan for Atlantic Tuna, Swordfish and Sharks). There are, however, no management measures specific to this species, and no stock assessments. Efforts to limit catches of this species, and increased monitoring of incidental catches in commercial fisheries are both recommended.
In Brazil, there are laws restricting the length of pelagic gillnets and banning trawl fishing at a distance of less than three nautical miles from shore (equivalent depths of less than about 10 m), however enforcement of these laws has been difficult. Therefore trawling in inshore nursery grounds has continued and gillnetting within nursery areas is not regulated. Some fisheries along the coast are poorly documented and the multi-species nature of many of the fisheries makes species-specific regulation very difficult. Therefore, it is recommended that coastal protected sea areas are established, in which fishing is banned, to protect nursery grounds.
In 1998, the Brazilian Government's Environmental Agency (IBAMA - Brazilian Institute for the Environment and Natural Renewable Resources) made a first effort to control "finning" by issuing a federal regulation (Portaria IBAMA nnordm; 121 of August 24th, 1998), prohibiting shark finning by all vessels licensed to fish in Brazilian waters (Kotas et al. 2002). The enforcement of this law has been proven difficult and probably will require international financial aid, trained personnel for sampling work along the main fishing harbours and the establishment of a national observer program (Kotas et al. 2002).
Eastern Central and Southeast Pacific
There are no species-specific measures in place for S. lewini in the Eastern Pacific, although steps are being taken towards the management of elasmobranch fisheries. In Ecuador the current regulations prohibit shark fishing in the core zone of the Galápagos marine reserve, however extensive poaching has been reported. Ecuador issued two new Decrees (482 and 902) in 2007 which establish better controls; traceability of the exported products; re-confirm the prohibition of finning established in 1993; a database on trade and establish as State policy the National Action Plan for the Conservation and Management of Ecuadorian Sharks (PAT - Ec). In Mexico, some known adult aggregating sites are protected within the Revillagigedo Island archipelago, however enforcement is lacking and there are many reports of poaching. Protection of known nursery adult aggregating sites is recommended. Estimates of acceptable catch rates should be viewed with precaution until there is more certainty in age and growth parameters.
Although Australian fisheries are generally well-managed, the recent increase in illegal, unreported and unregulated (IUU) fishing vessels in the waters of northern Australia is of concern for this species.
|Citation:||Baum, J., Clarke, S., Domingo, A., Ducrocq, M., Lamónaca, A.F., Gaibor, N., Graham, R., Jorgensen, S., Kotas, J.E., Medina, E., Martinez-Ortiz, J., Monzini Taccone di Sitizano, J., Morales, M.R., Navarro, S.S., Pérez-Jiménez, J.C., Ruiz, C., Smith, W., Valenti, S.V. & Vooren, C.M. 2007. Sphyrna lewini. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 19 April 2015.|