Study: Some sharks have stereo rear vision

BOCA RATON, Fla., Dec. 1 (UPI) -- Florida Atlantic University researchers say they have determined the wide heads of hammerhead sharks give the animal exceptional stereo vision.

University researchers Michelle McComb, Stephen Kajiura and Timothy Tricas said they wanted to discover how wide a hammerhead's field of view is and whether they could have binocular vision.

Fishing for juvenile scalloped hammerheads off Hawaii and bonnethead sharks around Florida, the team landed the fish and transported them to local labs to test the fish's eyesight.

Having determined 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. They did. The scientists said the scalloped hammerhead had a massive binocular overlap of 32 degrees in front of their heads, while the bonnetheads had a 13 degree overlap.

When the team measured the binocular overlap of the shark with the widest hammerhead, the winghead shark, they found it was a colossal 48 degrees.

Finally, the team factored in the sharks' eye and head movements and found the forward binocular overlaps were 69 degrees for the scalloped hammerheads and 52 degrees for the bonnetheads. Even more surprisingly, the team realized the bonnethead and scalloped hammerheads have an excellent stereo rear-view -- a full 360-degree view of the world.

The study appears in the Nov. 27 issue of The Journal of Experimental Biology.