About Sphyrna tiburo (Linnaeus, 1758)
This shark, the bonnethead shark, is defined by a broad, smooth, spade-shaped head. It has the smallest hammer-shaped cephalofoil of any species in the genus Sphyrna. Its upper body is grey-brown, while its underside is a lighter color. Adult bonnethead sharks typically measure 80–90 cm (2.6–3.0 ft) long, and the maximum recorded size is around 150 cm (4.9 ft). The generic name Sphyrna likely comes from a misspelling of sphyra, the Greek word for "hammer"; the specific epithet tiburo comes from the Spanish word tiburón, which means "shark". This species is found along both coasts of the Americas, in areas where water temperature is usually warmer than 70 °F (21 °C). In the Atlantic Ocean, its range extends from New England, where it is rare, south to the Gulf of Mexico and Brazil. In the Pacific Ocean, it ranges from southern California south to northern Peru. During the summer, it is common in inshore waters off the Carolinas and Georgia; it can be found off Florida and in the Gulf of Mexico during spring, summer, and fall. In winter, bonnethead sharks move closer to the equator, where waters are warmer. While the species remains abundant in the North Atlantic Ocean and Gulf of Mexico, it has become much less common in the Caribbean Sea, and has been nearly extirpated from most of its range in the South Atlantic and Pacific. It typically inhabits shallow estuaries and bays that sit over seagrass, mud, or sandy substrates. The bonnethead shark is viviparous. Females reach sexual maturity at around 81 cm (32 inches) in length, while males reach sexual maturity at around 61 cm (24 inches). Between four and twelve pups are born in late summer and early fall, each measuring 300 to 330 mm (12 to 13 in) long. Bonnethead sharks have one of the shortest gestation periods of any shark, at only 4.5–5.0 months. One female bonnethead shark has produced a pup via parthenogenesis. The birth occurred at the Henry Doorly Zoo in Nebraska, and DNA analysis confirmed a perfect genetic match between the mother and the pup.
