Just a snorkel will suffice to spy these distinctive predators congregating beneath the waves
Mike Dilger’s WILDLIFE SPECTACLES The broadcaster, naturalist and tour guide shares the most breathtaking seasonal events in the world
SHOALING SCALLOPED HAMMERHEADS
With just over 500 different species of shark classified, and a further two dozen waiting to be formally scientifically named, shark taxonomy is not for the faint-hearted. But there is one group that surely everyone would immediately recognise: the hammerheads.
Sporting a wide, flattened head that is uniquely shaped like a double-headed hammer, it’s not hard to see how these sharks got their name. The eyes and nostrils are located at either end of the ‘hammer’ – or cephalofoil, as it’s technically called.
The explanation behind the shape of the hammerhead’s head has long been debated. While undoubtedly giving the sharks extra lift, the cephalofoil may also help them make sharper turns in the water. The widely spaced eyes allow for effective stereoscopic vision, while the head’s broad shape also houses a sense organ known as the ampullae of Lorenzini. Packed with electroreceptors and operating like an underwater metal detector, it helps the sharks to detect prey hidden on or just under the sea-floor sediment.
Of the nine species of hammerhead, the ‘scalloped’ can be distinguished by the notches along the leading edge of its cephalofoil, which produce a distinct scalloping effect. The females tend to be larger than the males – reaching up and and the species’ bronze-grey back and white underside
help camouflage the shark from prey and potential predators, both above and below in the water column.
Though widespread, the scalloped hammerhead is most commonly encountered in the Hammerhead Triangle, situated between the islands of Cocos, Malpelo and the Galápagos in the eastern Pacific. While it can be relatively easily observed at a number of sites, particularly around seamounts (submarine mountains), there are only a few places where it gathers in large numbers. As most apex predators operate either as ‘lone wolves’ or in small cohorts, this is considered highly unusual behaviour. These groups, or ‘shivers’, of sharks tend to consist mostly of females, with the males remaining out in deeper waters.
At locations such as the
