Depths of Basking Shark Puzzle Plumbed

Until recently, the winter whereabouts of the basking shark has stymied marine biologists. But according to a report published online in Current Biology, the mystery has finally been solved. Behind the whale shark, the basking shark is the world’s second largest fish, commonly observed following plankton blooms on the water’s surface during summer and autumn months. However, this massive and highly migratory species would virtually disappear come winter.

Through satellite tagging and geolocation conducted over the past few years, researchers concluded this spring that the animals migrate through the western Atlantic Ocean in the winter, traveling as far as South America and sometimes remaining at depths of up to 1,000 meters for months at a time, enabling them to evade humans. The surprising results of the study challenge the notion that basking sharks are a cool-water species.

The findings also highlight the need for greater basking shark protections throughout their range, which now includes tropical waters. They also indicate that the sharks’ global population may be smaller than previously thought. The new information is particularly significant, since the species has experienced drastic declines and is listed as "vulnerable" on the International Union for Conservation of Nature’s Red List of Threatened Species.

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