It seemed simple: To prevent marine mammals from becoming ensnared in fishing nets, scare them away with high-pitched noisemakers. But a paper published in the spring issue of the Marine Technology Journal suggests that for some species, acoustic "pingers" do more harm than good.
Each year some 80,000 dolphins and thousands of other marine mammals snag in nets worldwide; most die. Two years ago, a report in Nature suggested that pingers, which emit periodic high-frequency underwater bursts, had markedly reduced the accidental catch of harbor porpoises in the Gulf of Maine's groundfish fishery. Why they work is still a mystery: They may cause discomfort, interfere with marine mammals' echolocation, or become associated with nets. Nonetheless, at least 14 more fisheries around the world have recently adopted the devices.
Now one of the authors of the Nature paper warns that pingers may produce "a whole array of unintended consequences." For example, writes Scott Kraus, research director of the New England Aquarium's Edgerton Research Laboratory, at one mid-Atlantic shad fishery pingers drove away shad as well as porpoises even though the shad weren't supposed to be affected by the sounds. In the Pacific Northwest, salmon aquaculturists found that devices intended to fend off marauding seals instead became seals' "dinner bells." And Kraus cites preliminary evidence that New Zealand's endangered Hector's porpoises may actually be attracted to the pings. "Every fishery is different," writes Kraus, "and every ... species has different hearing and sound production abilities."
How ocean sounds affect different marine species "is something we are only just beginning to understand," says Greg Early, associate scientist with the Edgerton Research Lab. He agrees with Kraus and his Duke University colleague Andrew Read that it's best to play it safe and run a trial at every fishery where pingers are under consideration.