Bonnethead Shark

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Bonnethead Shark

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.


Content List

1. Scientific & Common Names

2. Characteristics

a. Breeding

b. Behavior

3. History

4. Present Status

5. References


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


Characteristics

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.


Breeding

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.


Behavior

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.


History

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.


Present status

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.


References

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