ANIMALS
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Large marine predators including great white sharks regularly spend time in the ocean’s twilight and midnight zones, far beneath the depths at which they feed, in a discovery that has mystified scientists. In a new study, data from 12 species of large predatory fish, including sharks, billfish and tunas, showed they regularly spent time in the mesopelagic zone, also known as the twilight zone, which stretches between the depths of 200 to 1,000 metres. They were also seen in the midnight zone, 1,000 to 3,000 metres beneath the ocean’s surface. “How, when and where they access the deep ocean certainly varies, but the clear anecdotal answer is that the deep ocean seems like an important habitat, regardless of the predator species,” said Camrin Braun, an assistant scientist at the Woods Hole Oceanographic Institution (WHOI).
As part of the new study, researchers matched the diving patterns of 344 electronically tagged predatory fish, including great white sharks, tiger sharks, whale sharks, yellowfin tuna and swordfish, with shipboard sonar over a cumulative period of 46,659 days to identify which species regularly deep dive into the twilight and midnight zones.
Their findings showed a correlation between dives and the location of the deep scattering layer. This ocean layer is so densely packed with small fish and other marine organisms it is sometimes mistaken for the seafloor. Creatures of the deep scattering layer rise up to the surface at night to feed, then sink back down to the twilight zone in the day. This suggests that marine predators feed on animals in the deep scattering layer. However, the team also discovered many dive far deeper than the deep scattering layer extends, for reasons unknown. Great white sharks dive
