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Scalloped Hammerhead
Sphyrna lewini
Open ocean, seamounts, and coastal waters in tropical and warm-temperate seas.
Characteristic hammer-shaped head with a notched (scalloped) leading edge. Schools in large numbers at seamounts.
Identification
The scalloped hammerhead is identified by the distinctive scallop (three notches) on the leading edge of its cephalofoil. The head is slightly more curved than in the great hammerhead or smooth hammerhead. Adults reach 4.3 meters.
Distribution & Habitat
Scalloped hammerheads range across tropical and warm-temperate seas globally. They are pelagic as adults but pupping grounds are often in coastal estuaries. Major aggregation sites include Cocos Island (Costa Rica), the Galapagos (especially Darwin and Wolf), and Malpelo (Colombia).
Behavior
During the day, scalloped hammerheads form enormous schools — sometimes hundreds of animals — around seamounts and islands where strong currents bring prey and cleaner fish. Researchers still debate why this species schools: hypotheses include social hierarchy, navigation, and predator avoidance. At night, the schools disperse and individual animals hunt alone.
Where to See Them
Cocos (Costa Rica), Galapagos, and Malpelo are the classic sites. These are advanced liveaboard destinations with strong currents — technical experience and a negative-entry descent are usually required. Keep close to the reef or wall, stay calm, exhale slowly to minimize bubble noise, and let the sharks come to you.
Circumglobal in tropical and subtropical waters. Famous sites: Cocos (Costa Rica), Galapagos, Malpelo (Colombia).
Forms large daytime schools at cleaning stations around seamounts and oceanic islands. Solitary and dispersed at night while hunting.
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