Great Hammerhead

Great Hammerhead

The hammerhead shark is probably one the most bewildering animals in the sea because of the distinctive but well-recognized shape of their head. In total, there are seven species of hammerhead sharks, but you won’t find them all in the Dutch Caribbean. The largest member of the family, the great hammerhead (Sphyrna mokkaran) is occasionally sighted on the reefs and is considered one of the most remarkable encounters to have as a diver. But because of increasing fishing pressure and a very low reproductive output, it is estimated that globally, great hammerheads have declined by 80% in the last 25 years. Therefore, it is now listed as an endangered species on the IUCN Red List.

A question on the mind of most people that see a hammerhead shark is why they developed such a particular wide head shape. This question has been on the minds of researchers for a long time but now seems to have been answered. In addition to the advantage of having an increased amount of electric sensors on their snout, with which they can detect their prey, the shape appears to make it less strenuous to swim because it lessens the drag of the water. On top of that, scientists also found out that hammerheads usually swim slightly tilted to optimally reduce the water drag.

In the Dutch Caribbean, it is unknown how hammerheads use the area but it may just be a vagrant species, as tracking studies from the United States demonstrated that great hammerheads are highly migratory species that undertake journeys of hundreds of miles. The biology of great hammerheads is mostly an enigma, but it is known that they can grow as much as six meters long, although a length of four meters is more common. You can find the species both close inshore over the reef, as well as migrating further offshore over deeper waters, depending on their life stage and the time of year. It takes a young hammerhead shark many years to mature for reproduction, which doesn’t happen until they’re about 2,5 meters long. After that, females start giving birth one every two years to 6-42 pups growing in at 50-70 cm. The diet of hammerhead consists of shellfish, squid, and other fish, including southern stingrays.

Hammerhead shark fins are relatively large and therefore highly valued on the Asian market as an ingredient for shark fin soup. To keep feeding this demand, hammerheads are increasingly targeted in some areas. Fortunately, this is not the case in the Dutch Caribbean, although research does show that about 5% of all shark fins on the Hong Kong market are hammerheads, including specimens from the Western Atlantic Ocean. Also, despite what their impressive size would suggest, hammerhead sharks are very prone to stress, which makes them highly vulnerable to even catch-and-release fishing practices. Thus illustrating the importance to protect hammerhead shark throughout the wider Caribbean region to ensure they will remain to patrol our islands as great guardians of the reef.

Skills

Posted on

December 7, 2016