Wednesday, August 3, 2011

Hammerheads - Sharks Apart from the Rest

Next to the infamous great white, the hammerhead is probably the most recognizable shark in the world. The distinctive shape of its head is undeniable, but there are a few other things you may not know about hammerheads that make them uniquely different from other sharks.
Photo: Barry Peters
First off, the hammerhead is not just one species of shark. Though the large Great Hammerhead may be the best known, there are actually nine different species of hammerheads in two separate genera. The two largest species are the great hammerhead and the smooth hammerhead at 20 and 16 feet in length, respectively. Most other varieties are significantly smaller, with the 3 foot long bonnethead shark being the smallest.
Bonnethead shark - Photo: Valerie Everett
Unlike most sharks which are lone hunters, hammerheads usually congregate in schools. Depending upon species and conditions these schools can range from just a few individuals to thousands of sharks in a single location. They primarily hunt for crustaceans and small fish near the ocean floor with the largest varieties preferring to hunt stingrays. All except the largest species’ are considered harmless to humans.

Another interesting characteristic is the way hammerheads reproduce. Unlike most sharks, hammerheads do not lay eggs. Rather, their young are nourished in a yolk sack inside the female. After the yolk as been depleted, these yolk sack structures, which are more akin to leather than to an egg, are laid by the female and the pups are born. Hammerhead shark litters can range from 12-40 pups each depending on species.

So what is up with the shape of that head anyway? Like all sharks, hammerheads have electroreceptor sensory pores called ampullae of Lorenzine that allow them to detect the electrical fields given off by other animals. It is believed that the hammerhead’s wide head allows these pores to be more spread out, thus allowing the hammerhead to detect prey more easily than other sharks. It is also thought that the wide spacing of the eyes gives hammerheads binocular vision, and it is known that great hammerheads will use their heads to pin prey against the ocean floor.
Photo: Su Neko

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