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PUTTING THE `G' INTO AGILITY
kathryn{at}biologists.com
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Evolution is strange! Does it make sense to be able to pull a 5 g force turn if you get motion sick?
Sea lions are hardly the most gainly animals on land, but when they slide into the sea, their clumsy gait is transformed, and there's no doubt which environment suits them best as they twist and turn through the waves. Although sea lions haven't gone to the same lengths as other mammals that returned to the ocean, what makes these mammals one of the ocean's most agile swimmers? Frank Fish decided to find out how sea lions manoeuvre around tight turns to catch their next meal (p. 667). Working with Jenifer Hurley and Daniel Costa in California, Fish videoed two sea lions as they swam back and forth in a large tank, ready to analyse the animals' contortions as they turned back on themselves.
As the animals swam to and fro, they kept their bodies streamlined by keeping their fins tucked in. But as soon as they needed to turn, they moved their flippers away from their side, inclined their heads and suddenly flipped round, turning their bodies into a tight U shape before resuming their efficient streamlined position once they were heading back the way they had just come. When Fish calculated the force exerted on the animal's body as they turned tail in less than half a second, he discovered that turning sea lions can pull as much as 5 g force during a turn! But how do sea lions outmanoeuvre other sea dwelling mammals? As Fish explains, sea lions are more agile, simply because they are less stable in the water.
References
Fish, F. E., Hurley, J. and Costa, D. P.
(2003). Maneuverability by the sea lion Zalophus
californianus: turning performance of an unstable body design.
J. Exp. Biol. 206,667
-674.
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