Hammerhead sharks have binocular vision

London : The wing-like heads of hammerhead sharks with their widely spaced eyes give the creatures excellent binocular vision, scientists have found The bizarre appearance of hammerhead sharks has led generations of marine biologists to ponder the same question: why the wide face?

Part of the answer may now be at hand. Eye tests on species caught off the coasts of Florida and Hawaii show that the wider the head the better the shark's binocular vision, and hence its perception of distance.

The fish are thought to have evolved their wide, wing-like skulls to enhance their sense of smell and ability to pick up electrical activity from other marine life, but the latest study is the first to investigate the role eyesight may have played.

"One of the things they say on TV shows is that hammerheads have better vision than other sharks, but no one had ever tested this," said Michelle McComb, a marine biologist at Florida Atlantic University.

Of the nine species of hammerhead shark, the aptly named "winghead" has the most pronounced cranial features, with a skull as wide as half its body length. The more inconspicuous bonnethead shark has the most narrow skull of all hammerheads.

The scientists caught hammerheads and other shark species, such as lemon sharks and blacknose sharks, and transported them back to the laboratory for eye tests.

The researchers then worked out the size of the visual field for each eye in the different shark species.

The eye tests showed that the bonnethead shark had a modest 13 degree overlap in the visual fields of its eyes, while the winghead had an enormous 48 degree overlap, giving it a much broader field of 3D vision. The study appears in the Journal of Experimental Biology.

— Guardian News & Media Ltd