They鈥檙e sideways swimmers. Hammerhead sharks spend much of their time tilted to one side in what looks an awkward swimming posture, a tagging study has revealed.
But the weird habit actually makes sense: it seems to be the most energy-efficient way for them to swim.
Most sharks use their large pectoral fins, on the sides of their bodies rather like aircraft wings, to keep them from sinking. The dorsal fin, on a shark鈥檚 back, helps with quick turns, like the rudder on a boat.
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鈥淎s far as we knew, this is how all sharks function,鈥� says at the University of Roehampton in London.
But data from accelerometers and video cameras that Payne and his colleagues attached to five great hammerhead sharks in Australia, Belize and the Bahamas showed otherwise. The tracked sharks spent up to 90 per cent of time swimming at roll angles between 50 and 75 degrees.
Unlike other sharks, the great hammerhead鈥檚 dorsal fin is longer than its pectoral fins. When a great hammerhead tilts to the side, its long dorsal fin increases its 鈥渨ingspan鈥�, allowing it to swim more efficiently. Wind tunnel experiments with an anatomically accurate model of a great hammerhead suggest the sharks use about 10 per cent less energy when they swim this way instead of upright.
鈥淗ere鈥檚 this animal that is reasonably famous; everybody鈥檚 heard of the hammerhead,鈥� Payne says. 鈥淏ut we had really no idea that this behaviour was a normal thing for this animal.鈥�
The energy efficiency hypothesis makes sense to Douglas Adams of the , who has spotted great hammerheads swimming in a rolled position off the east coast of Florida several times. Still, much about how they behave in the wild is unknown, Adams says.
鈥淲e鈥檙e just kind of at the start of learning how a lot of these hammerhead species tick.鈥�
Nature Communications
Read more: Free-diver enlisted to help tag twitchy hammerhead sharks; Great hammerhead shark caught in nature鈥檚 superstar photoshoot
