Sphyrna tiburo
bonnethead shark
(Also: bonnethead)

The bonnethead is confined to the warm waters of the western hemisphere. It ranges from New England, where it is rare, to the Gulf of Mexico and Brazil and from southern California to Ecuador. It is common in the inshore waters of the Carolinas and Georgia in summer, and off Florida and in the Gulf of Mexico in spring, summer, and fall (Castro, 1987).

S. tiburo is believed to migrate southward in winter or to deeper offshore waters in Florida and the Gulf of Mexico, but little is known about its movements. It often travels in schools of five to fifteen individuals. Migrating schools of hundreds and even thousands of these sharks have been reported (Parsons1993).

The characteristic shovel- or bonnet-shaped head makes this hammerhead the easiest to identify. Body moderately compact; head flattened, spade-shaped front margin of head not lobed without nasal grooves, the anterior margin of the head is evenly rounded between the eyes; mouth arched; mouth corners posterior to oculonarial expansion. The frontal teeth have erect, smooth-edged cusps, while subsequent teeth have oblique cusps; the outermost teeth of the lower jaw are modified into flat crushers. First dorsal fin high, originating slightly posterior to base of pectoral fin; second dorsal with rear lobe not well developed, higher and shorter than anal one; eyes separated from nasal grooves by a distance of 1.5 times diameter of eye. Some are dark brown in the lateral dorsal region, lighter in ventral region while others are gray or greensih gray above and paler below. Average size is 70-100 cm (28-39 in.) Maximum size is about 110 cm (43 in.) These are the smallest of family Sphyrnidae (Cortes and Parsons,1996).

A special body fluid, cerebrospinal fluid, is used for personal communication in S. tiburo. It is also known as the Cl- excess. This chemical allows S. tiburo to let others know it is in the area. Not much is known about the cerebrospinal fluid of these sharks because not enough studies have been done on this species (Rall,1967).

There are few data on how the bonnethead shark moves as well as few data about the mating behavior.

This species must remain in motion at all times in order to survive. Sharks breathe through their gills and in order to receive oxygen they must force their gills open by swimming. Also, they sink if they do not keep moving (Rall 1967).

The diet of S. tiburo is dominated by crustaceans, consisting mostly of blue crabs, but also it feeds upon shrimp, mollusks, and small fishes. Seagrasses were also found in stomach contents.

It was found that stomach content weight of females was higher than that of males, probably because females, due to reproduction, have a higher energy budget. They need to feed more in order to store energy for when they reproduce (Cortes , Manire, and Hueter,1996).

Only one attack on humans by this species has been recorded, and it is generally considered to be harmless.

This species is used commercially as dried meat similar in quality to second-class cod; the meat is dark and frequently is consumed fresh. However, even though marketed, it is of little or no economic importance to man.