Bonnethead Shark (Sphyrna tiburo)

The bonnethead shark (Sphyrna tiburo), also known as the bonnet shark, bonnet nose shark, and shovelhead shark is one of nine species of hammerhead sharks. These sharks all have a unique hammer or shovel-shaped heads. The bonnethead has a shovel-shaped head with a smooth edge.

The head shape of the bonnethead may help it more easily find prey. A 2009 study found that bonnethead sharks have a nearly 360-degree vision and excellent depth perception.

These are social sharks that are most often found in groups numbering from 3 up to 15 sharks.

More About the Bonnethead Shark

Bonnethead sharks are about 2 feet long on average and grow to a maximum length of about 5 feet. Females typically are larger than males. Bonnetheads have a grayish-brown or gray back that often has dark spots and a white underside. These sharks need to swim continuously to supply fresh oxygen to their gills.

Classifying the Bonnethead Shark

The following is the scientific classification of the bonnethead shark:

• Kingdom: Animalia
• Phylum: Chordata
• Subphylum: Gnathostomata
• Superclass: Pisces
• Class: Elasmobranchii
• Subclass: Neoselachii
• Infraclass: Selachii
• Superorder: Galeomorphi
• Order: Carcharhiniformes
• Family: Sphyrnidae
• Genus: Sphyrna
• Species: tiburo

Habitat and Distribution

Bonnethead sharks are found in subtropical waters in the Western Atlantic Ocean from South Carolina to Brazil, in the Caribbean and Gulf of Mexico and in the Eastern Pacific Ocean from southern California to Ecuador. They live in shallow bays and estuaries.

Bonnethead sharks prefer water temperatures over 70 F and make seasonal migrations to warmer waters during the winter months. During these trips, they may travel in large groups of thousands of sharks. As an example of their travels, in the U.S. they are found off the Carolinas and Georgia in the summer, and further south off Florida and in the Gulf of Mexico during the spring, fall and winter.

How the Sharks Feed

Bonnethead sharks eat primarily crustaceans (especially blue crabs), but will also eat small fish, bivalves, and cephalopods.

Bonnetheads feed mostly in the daytime. They swim slowly toward their prey, and then quickly attack the prey, and crush it with their teeth. These sharks have a unique two-phase jaw closing. Instead of biting their prey and stopping once their jaw is closed, bonnetheads continue to bite their prey during their second phase of jaw closing. This increases their ability to specialize in hard prey, like crabs. After their prey is crushed, it is suctioned into the shark's esophagus.

Shark Reproduction

Bonnethead sharks are found in groups organized by gender as spawning season approaches. These sharks are viviparous... meaning that they give birth to live young in shallow waters after a 4- to 5-month gestation period, which is the shortest known for all sharks. The embryos are nourished by a yolk sac placenta (a yolk sac attached to the mother's uterine wall). During development inside the mother, the uterus becomes separated into compartments that house each embryo and its yolk sac. There are 4 to 16 pups born in each litter. The pups are about 1 foot long and weigh about half a pound when born.

Shark Attacks

Bonnethead sharks are considered harmless to humans.

Conserving Sharks

Bonnethead sharks are listed as "least concern" by the IUCN Red List, which says that they have one of "highest population growth rates calculated for sharks" and that despite fishing, the species is abundant. These sharks may be caught for display in aquariums and used for human consumption and for making fishmeal.

References and Further Information

• Bester, Cathleen. Bonnethead. Florida Museum of Natural History. Accessed July 4, 2012.
• Cortés, E. 2005. Sphyrna tiburo. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1. Accessed July 3, 2012.
• Carpenter, K.E. Sphyrna tiburo: Bonnethead. Accessed July 4, 2012.
• Compagno, L., Dando, M. and S. Fowler. 2005. Sharks of the World. Princeton University Press.
• Krupa, D. 2002. Why the Hammerhead Shark's Head is In the Shape It's In. American Physiological Society. Accessed June 30, 2012.
• Viegas, J. 2009. Scalloped Hammerhead and Bonnethead Sharks have 360 Degree Vision. Accessed June 30, 2012.
• Wilga, C. D. and Motta, P. J. 2000. Durophagy in Sharks: Feeding Mechanics of the Hammerhead Sphyrna tiburo. The Journal of Experimental Biology 203, 2781–2796.