Are whales dying of terror?

When naval ships and other sea vessels use sonar, many whale species flee for their lives; some even strand themselves on beaches in a desperate attempt to escape. Now, scientists have discovered the most likely reason: The loud sounds trigger the same fear response as when the animals hear calls emitted by one of their most terrifying predators: killer whales.

“It’s a great study,” says Robin Baird, who investigates the effects of sonar on dolphins and whales (collectively known as cetaceans) at Cascadia Research Collective, a marine science nonprofit. The work should help scientists predict which species are most susceptible to humanmade sounds, says Baird, who was not involved with the project.

Scientists know some cetaceans, such as harbor porpoises and beaked whales, flee from sonar, whereas others, such as pilot whales, seem indifferent. To figure out why, Patrick Miller, a marine biologist at the University of St. Andrews, and colleagues attached sound and dive recording tags (with suction cups) to randomly chosen members of four whale species—sperm, humpback, long-finned pilot, and northern bottlenoses—in the Norwegian Sea, above the Arctic Circle. The team tracked the animals from a research vessel, then followed them in a smaller boat that was either silent or transmitted three types of sounds: sonar in the 1- to 4-kilohertz band (similar to naval sonar), and clicks emitted by two types of killer whales—those that eat fish exclusively and those that prey exclusively on marine mammals, including other cetaceans. (Although the two types of killer whale are not known to interbreed, they have not yet been identified as separate species.)

All four cetacean species slowed their foraging on fish, sea cucumbers, squid, and other prey when they heard either naval sonar or mammal-eating killer whale sounds, the team reports today in the Proceedings of the National Academy of Sciences. Northern bottlenose whales stopped foraging completely when they heard either sound, whereas humpback, long-finned pilot, and sperm whales reduced their foraging anywhere from 50% to nearly 100%.