What makes sharks so fast in the water

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Scientists have discovered what makes sharks so difficult to out-race.

In a study published in a recent issue of the Proceedings of the Royal Society B.  Brooke Flammang and coauthors visualised water flow generated by the shark tail using a volumetric imaging technique previously used only in engineering.

Applying their technique to Spiny dogfish (Squalus acanthias) and Chain dogfish (Scyliorhinus retifer) swimming in flow tanks, the authors found that a shark's tail creates twice as many jets of water as other fishes’ tails when it swings from side to side during swimming.

This smooths out the thrust generated by the tail and possibly helps the shark to swim more efficiently.

The sharks were found to stiffen their tail in midswing, and were thought to do so using a muscle in the tail that senior author Flammang had earlier studied. "That provides a big advantage," Flammang says. Instead of just getting a push as the tail reaches the extent of its bend, the shark has added thrust midswing. It may be allowing the animal to produce almost continuous thrust".

The authors hope that the results of their study could be applied to designing more efficient underwater vehicles.

For more information, see the paper: Flammang, BE, GV Lauder, DR Troolin and T Strand (2011) Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure. Proceedings of the Royal Society B: Biological Sciences 278, pp. 3670–3678.

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