When waters are murky, how do seals find fish? They don’t have a sonar apparatus like whales, and yet they somehow hunt successfully in the dark.
It turns out that the seals follow fish trails by sensing very subtle water pressure changes with their whiskers. In a study published in the Journal of Experimental Biology, investigators trained harbor seals to give a visual signal indicating the direction of a “swimming” rubber fin that mimicked a fish. They then blindfolded and placed headphones on the seals to test their ability to hunt without sight or sound cues.
Not only were the seals able to detect the “fish’s” movements, their whiskers may be able to distinguish even more precise information than just their prey’s whereabouts. Senior author Wolf Hanke of the Marine Science Centre at the University of Rostock, Germany, told BBC News, “They seem to be able to discriminate between different shapes, which might even mean they discriminate between different species of fish.”1
The authors found evidence that the seals track the direction that a fish swims by sensing its underwater wakes, or trails of slightly disturbed water, that linger for up to 35 seconds. To do this, seals detect and interpret “the structure and spatial arrangement of the vortices” that spin off from a fish’s underwater trail.2….
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