SCALLOPED HAMMERHEAD

View all available Scalloped hammerhead shark images in the Shark Pictures Database

Common Names: Scalloped Hammerhead

Latin Name: Sphyrna lewini

Family: Sphyrnidae  

Identification: Leading edge of hammer arched with well defined indentations. Pectoral fins have dark tips. Pelvic fins not falcate. Body grey  to greyish brown. Ventral surface pale.   

Size: Maximum length 420 cm. 42 - 55 cm at birth.  

Habitat: In shore to off shore sea mounts. Adults are pelagic.  Intertidal to 275 meters.

Abundance and distribution: Circumtropical/temperate.

Behavior:  One of very few large sharks observed schooling in great numbers. Diet consists of bony fishes, sharks, rays, crustaceans, and octopus.

Reproduction: Viviparous. The hammerhead are considered the most highly evolved of the shark families.

Conservation Status: ENDANGERED. 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.

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. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>
 

Observations: Scalloped hammerheads have been well documented swimming in huge schools around various sea mounts off of central and South America. They apparently  use cleaning stations in these areas to rid themselves of parasites.

Photographs: Yonaguni Island, Ryukyu Archipelago, Japan.  

Similar species: Great hammerhead distinguished by straighter leading edge of hammer, proportionately taller dorsal fin, and often larger size. 

Reaction to divers: Shy. Very difficult to approach when viewed in schooling behaviour. Most divers have better success when using rebreathers. Can be aggressive making close passes in baited situations.

Diving logistics: Various operators  go from La Paz to the sea mounts in the Sea of Cortez to view schooling Scalloped hammerheads but in recent years the schools have dwindled due to heavy over fishing. The Galapagos, Malpelo, and Cocos Island remain the best places for close encounters but all stocks are stressed by longlining and numbers vary from year to year. El Nino years may see less hammerheads as the water becomes too warm at recreational scuba depths and the sharks stay deeper. Following El Nino years may see the best schooling activity as the sharks are then in dire need of the cleaning stations that they were unable to reach the previous year. The undersea hunter out of Costa Rica travels to Cocos for 1-2 week long trips that also expose divers to silkies, whitetips, silvertips, occasional whale sharks, marbled rays, and other species of elasmos.

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