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In the landscape under the ocean's surface, where light is scarce and sound travels four times faster than in air, many marine mammals use sound to communicate, navigate, and find food. Toothed whales make noises and listen to how the noises bounce back to them to determine the position and size of underwater objects. This process is called echolocation. Navies around the world use sound in similar ways, relying on active sonar to locate targets.
Marine biologists are sounding the alarm that the increased use of underwater sonar over the past 50 years may be harming some toothed whale populations. Military sonar can be four times as loud as a whale call. Scientists have found convincing evidence that military sonar can interfere with the hearing, communication, and behavioral patterns of dolphins and whales. This can result in stress, injury, or even death. When and where the U.S. Navy can use sonar is an ongoing controversy. The California Coastal Commission is tasked with protecting California's ocean and the animals that live in it. The U.S. Navy has rejected the Commission's recommendations for reducing or avoiding sonar use in sensitive conditions during testing and training exercises off the California coast.
Navy spokesperson Alex Stone has said that at least one of the Commission's recommendations-increasing the size of shutdown areas when toothed whales are present-would negatively impact "training realism." The Coastal Commission says its recommendations would bring the Navy into compliance with the Coastal Act, which requires special protection be given to "areas and species of biological and economic significance."
The Navy estimates that its planned activities could change the natural behavior patterns of as many as 1.78 million marine mammals each year, affecting migration, surfacing, nursing, breeding, feeding, or sheltering. Another 336 could sustain injuries each year such as temporary or permanent hearing loss or "bubble lesions" that cause symptoms similar to decompression sickness. As many as 26 animals may die.
Mass strandings are events in which groups of marine mammals beach themselves. Most beached dolphins and whales die. Navy sonar most likely is responsible for a number of mass strandings around the world. According to a 2004 International Whaling Commission report, tactical mid-frequency sonar was the probable cause of 10 mass strandings near Japan in an area used for U.S. Navy training. The exact cause for mass strandings remains unclear. Scientists have found that sonar may cause widespread hearing loss, which can affect marine mammals' ability to navigate.
The U.S. Navy already has reduced mid-frequency sonar levels since 2004, but those adjustments may not be enough. A study published in 2013 found that Cuvier's beaked whales off the California coast displayed a strong avoidance response to recordings that sounded like mid-frequency active sonar signals, even when the signals were at lower levels than those the U.S. Navy is allowed to use now.
The Coastal Commission recommendations rejected by the Navy include:
The U.S. Navy doesn't have to follow the Commission's recommendations, but under the Marine Mammal Protection Act it does need a permit from the National Marine Fisheries Service for the "incidental" harassment or injury of dolphins and whales. The Navy's proposal for a 5-year marine permit renewal is currently under review. A decision is expected in November 2013.
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Norene Griffin is a freelance writer with a weakness for science news, art, and Pinterest. She lives in the San Francisco Bay Area with her husband and son.
Copyright © 1996-2013, Eric H. Chudler, University of Washington