Whale sharks that make lengthy dives into the cold ocean depths to forage tend to spend a lot of time at the surface warming up afterward, a new study suggests. Researchers tagged four whale sharks with devices that recorded water depth and temperature, among other factors, at least once every minute. Typically these immense creatures, the world's largest fish, traveled directly to and from the surface and spent very little time at the deepest portion of their dives. But in about one dive of every six, the animals dove deep—on average, to depths of about 340 meters—and spent about 145 minutes there, presumably foraging. Analyses of data for these lengthy dives reveal that the colder the waters were at maximum depth, the more time the whale sharks spent basking at the surface immediately afterward, the researchers report online today in the Journal of the Royal Society Interface. This hints that the cold-blooded fish are using their postdive respites to regain body heat lost while swimming in the frigid deep. Regaining body heat may help the creatures better digest their recent meals, the researchers note, because the warmer the whale sharks are, the more quickly and efficiently their metabolic activity proceeds.
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