Wide heads give hammerhead sharks exceptional vision

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Washington, Nov 27 (ANI): The distinctive head shape of the hammerhead shark gives these them an excellent binocular vision, reveals a new study.

According to lead researcher Michelle McComb from Florida Atlantic University, the wider the head the better the shark's binocular vision, and hence its perception of distance.

It also gives these sharks an ability to see through 360 degrees.

The research team focussed their study on juvenile scalloped hammerheads sharks and bonnethead sharks and tested their eyesight.

They tested the field of view in each shark's eyes by sweeping a weak light in horizontal and vertical arcs around each eye and recorded the eye's electrical activity.

After the analysis, team found that the scalloped hammerheads had the largest monocular visual field, at an amazing 182 deg., and the bonnethead had a 176 deg. visual field, which was bigger than that of the pointy nosed blacknose and lemon sharks, at 172 deg. and 159 deg., respectively.

Having collected the animals' monocular visual fields, the team plotted the visual fields of both eyes on a chart of each fish's head to see whether they overlapped and surpringly they did.

The scalloped hammerhead had a massive binocular overlap of 32 deg. in front of their heads (three times the overlap in the pointy nosed species) while the bonnet head had a respectable 13 deg. overlap.

And when the team measured the binocular overlap of the shark with the widest hammerhead, the winghead shark, it was a colossal 48 deg.

The hammerheads' wide heads certainly improved their binocular vision and depth perception.

The researchers also found that the bonnethead and scalloped hammerheads have an excellent stereo rear-view: they have a full 360 deg. view of the world.

"When we first started the project we didn't think that the hammerhead would have binocular vision at all. We thought no way; we were out there to dispel the myth," said McComb.

"But despite their preconceptions, the team have shown that the sharks not only have outstanding forward stereovision and depth perception, but a respectable stereo rear view too, which is even better than the TV shows would have us believe," added.

The study appears in The Journal Of Experimental Biology. (ANI)

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