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Deep mystery: why sea turtles plumb the depths
(Agencies)
Updated: 2008-08-09 20:57 A turtle trying to avoid becoming some fish's lunch would surely swim a bit more vigorously that usual, but the data collected indicates they were in no hurry as they plunged. Moreover turtles spent several hours at the surface just before deep diving, probably to boost oxygen efficiency. "Hanging out at the surface would be a daft strategy for avoiding predators, because that is where they can spot your silhouette," said Houghton. As for keeping cool, temperatures don't drop much after the 350-meter mark, so there's little incentive to go any deeper. But the food hypothesis, the study found, may be at least half right: even if the turtles don't eat the food they find at extreme depth, they probably find the food they will eat -- later on. Leatherbacks like to dine on surface-dwelling jellyfish, but during the months spent traveling from their tropical breeding grounds in the Caribbean to cooler waters, they rely on jellyfish-like animals that form long colonies during the day at depths of about 600 meters. The turtles, Houghton speculates, dive when the sun is out to find the colonies, and then wait for them to surface at night to begin feasting. This would explain why the leatherbacks often loiter in the same area for days or weeks after such a deep dive, he said. |
