IUCN Red List Assessment
Red List Category
Red List Criteria
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.