Featured Elasmobranch- Scalloped Bonnethead

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Featured Elasmobranch- Scalloped Bonnethead

Featured Elasmobranch

March 2011

Photo Credit: Russ Robertson

Scalloped Bonnethead



Identification: Like other members of the highly-derived family Sphyrnidae, the scalloped bonnethead possesses a distinctive dorso-ventrally flattened head. Color is uniformly gray above, fading to white ventrally with no prominent fin markings. Among the smallest of hammerhead species, the scalloped bonnethead can be distinguished from the similar scoophead (S. media) and bonnethead (S. tiburo) sharks by its broadly-arched, mallet-shaped snout, narrow mouth, and nearly straight anal fin rear margin [see the featured elasmobranch archives for the scalloped hammerhead (September 2008), great hammerhead (July 2008), bonnethead (June 2008), and smooth hammerhead (November 2005) for comparison with other hammerheads that occur within its range].

Size: Probably the smallest of the hammerhead species, the scalloped bonnethead reaches a maximum total length (TL) of under 1 m (92 cm). Males reach reproductive maturity at approximately 67 cm TL. Pups are born at approximately 23 cm TL.

Distribution: This shark is distributed from the eastern Pacific from the Gulf of California to Peru.

Habitat: The species inhabits nearshore environments on the continental shelf.

Biology: Little is known about this species. Like other hammerheads, the scalloped bonnethead’s reproductive mode is viviparous with yolk sac placenta. Fecundity is low, with a reported litter size of 2.

General interest: Fisheries details for this uncommon species are lacking, but it is likely taken in artisanal inshore fisheries where it occurs. Given the current lack of biological information, low fecundity, and limited geographic range of this species, the scalloped bonnethead has been listed as Near Threatened on the IUCN Red List of Threatened Species.

By Megan V. Winton
Pacific Shark Research Center
Moss Landing Marine Laboratories
8272 Moss Landing Road, Moss Landing, CA 95039