Hammerhead sharks are well known and easy to identify, but their cousins, the bonnethead sharks, are less recognized. They are smaller, much more timid, and have less pronounced heads. They can be commonly seen in many aquariums and they have the exotic look of a hammerhead without the size and potential aggression.
Scientific & Common Names
Kingdom - Animalia
Phylum - Chordata
Class - Chondrichthyes
Subclass - Elasmobranchii
Superorder - Selachimorpha
Order - Carcharhiniformes
Family - Sphyrnidae
Genus – Sphyrna
Species – Sphyrna tiburo
Common Names – Bonnethead shark, shovelhead shark
Bonnetheads can reach up to five feet but the average is more like three. They can be found along both coasts of North and South America from New England to Brazil and, on the west coast, from California to Ecuador. Unusual in sharks, bonnetheads display sexual dimorphism, which means that males and females look different from one another. The males have a noticeable bulge near the rostral (nose) section.
Females will produce between 6-8 pups, which are birthed live in the summer or fall. Each pup will be about a foot long. The gestation is only five months, which is among the shortest for all sharks. Grassy areas are then used as nurseries to protect the young as they mature, but they must fend for themselves from birth.
Bonnetheads prefer shallow waters of bays and estuaries in the western Atlantic and eastern Pacific. Research suggests that individuals do not range far and that there is little mixing between populations. They feed primarily on crustaceans, although they will feed on other invertebrates as well as fish. Their teeth are designed to both grab soft prey (with their front, small and sharp teeth) and to crush hard shelled prey (using their large rear molars). They are not any threat to humans and no attacks have ever been documented.
Bonnethead sharks (along with hammerheads) have probably evolved their unique characteristics to help with electroreception. Sharks have a long fossil history dating from 450 million years ago, predating dinosaurs. Today, there are nearly five hundred recognized species of shark with more still to be discovered.
Despite pressure from fisheries - both direct and incidental - bonnethead sharks are not considered to be in any danger and they are listed as Least Concern. The biggest threat comes from the shrimping industry where, in the past, hundreds of thousands of bonnetheads were caught as by-catch each year. There are fishing limits in many areas to keep the placid little shark from becoming overfished.
International Union for Conservation of Nature and Natural Resources (IUCN)
The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)
The Book of Sharks by Richard Ellis
The Shark Handbook: The Essential Guide for Understanding the Sharks of the World by Dr. Greg Skomal, Nick Caloyianis(Photographer)
The Encyclopedia of Sharks by Steve Parker
Sharks: History and Biology of the Lords of the Sea by Angelo Mojetta