SCALLOPED HAMMERHEAD

Photograph copyright by Tom Burns all rights reserved

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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.  

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: .  

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.

Other diving locations submitted by readers: 

References and further reading:  

     Reef Sharks and Rays of the World. Scott W. Michael. Sea Challengers.

     Sharks and Rays - Elasmobranch Guide of the World. Ralf M. Hennemann. IKAN.