Blue sharks use large, swirling ocean currents, known as eddies, to fast-track their way down to feed in the ocean twilight zone—a layer of the ocean between 200 and 1000 meters deep containing the largest fish biomass on Earth, according to new research by the Woods Hole Oceanographic Institution (WHOI) and the Applied Physics Lab at the University of Washington (UW).
Blue sharks use large, swirling ocean currents, known as eddies, to fast-track their way down to feed in the ocean twilight zone—a layer of the ocean between 200 and 1000 meters deep containing the largest fish biomass on Earth, according to new research by the Woods Hole Oceanographic Institution (WHOI) and the Applied Physics Lab at the University of Washington (UW). Their findings were published August 6, 2019, in the journal Proceedings of the National Academy of Sciences.
Researchers tagged more than a dozen blue sharks off the U.S. Northeast Coast and monitored them for nine months. The tags relayed data back to the researchers via satellite, revealing that the sharks had spent a good portion of their days diving these whirling pockets of warm water down to the ocean twilight zone hundreds of meters below the surface. There, they’d spend an hour or so foraging for food like small fish and squid before returning to the surface to warm up before diving again.
Dives were less frequent at night, when many twilight zone animals make their daily migration from the ocean’s mid-water to feed at the surface. Camrin Braun, an ocean ecologist at UW and lead author of the study, said that an evening trip likely isn’t worth the effort for hungry blue sharks since the zone isn’t particularly well stocked after dark.
Read more at Woods Hole Oceanographic Institution
Photo: Blue sharks are considered a “near threatened” species due to heavy fishing pressure on populations across the globe. CREDIT: Nuna Sá
