Fear Could Help Explain the Behavior of Animals in the Ocean | TS Digest


While sifting through data from an echosounder deployed off the coast of central California in 2010, master’s student Sam Urmy noticed what looked like acoustic interference. Although most of the data showed the movements of marine animals swimming above the device, occasionally there’d be a spike that “looked very similar to what you’d get if there was another ship nearby operating the same kind of echogram,” he says. He realized the spikes were due to dolphins, which were using echolocation and sending smaller animals scattering.

The observation got him thinking about predator avoidance as a driver of animal movements, and he recently returned to the idea as a postdoc working with Kelly Benoit-Bird at the Monterey Bay Aquarium Research Institute. Using a fresh, year-long echosounder data set, plus statistical modeling, the pair concluded that dolphins and other predators cause fish to flee—typically, to deeper waters—and that fish schools trigger similar reactions in zooplankton, creating a continuous ballet of vertical movements as everyone tries to avoid being eaten. Along with better-studied factors such as day-night cycles, this fear behavior likely motivates animal movement all over the oceans, suggests Urmy, now at the National Oceanic and Atmospheric Administration (NOAA).

Deepwater Echo Integrating Marine Observatory System (DEIMOS), an upward looking echo sounder package, at the Monterey Accelerated Research System (MARS) ocean observatory, located at approximately 900 meters deep in Monterey Bay.

© 2009 MBARI

“It’s very interesting to get such a long, detailed view of these movements of smaller animals in the pelagic zone,” says Michael Heithaus, a marine ecologist at Florida International University who was not involved in the work. While the findings aren’t surprising—there are many examples of fear driving animal behavior—it’s impressive to demonstrate it across the food web like this, he notes, adding that it will be important to determine how short-term movements translate to longer-term trends in survival and population sizes. Plus, he adds, “I’d love to see how this plays out in different locations.”

S.S. Urmy, K.J. Benoit-Bird, “Fear dynamically structures the ocean’s pelagic zone,” Curr Biol, doi:10.1016/j.cub.2021.09.003, 2021.

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