Whales and sounds

Marine biologists and oceanographers are working together to investigate the death of two beaked whales off the coast of Baja California last month — the latest in a string of whale strandings and deaths linked to underwater acoustic noise. Previous beaked whale strandings and deaths have been associated with medium-to-high frequency acoustic noise, generated by US Navy and other NATO forces, but the Baja deaths are the first to implicate low-frequency noise as possibly harmful to marine mammals.On September 24, the dead whales were discovered on the shore of an island in the Sea of Cortez by a group of vacationing marine biologists. One of them, Jay Barlow, is head of coastal marine mammal research in California for the National Marine Fisheries Service. After finding the whales, he and his companions spotted a vessel in the bay and radioed for help, only to learn that it was engaged in underwater seismic experiments. The research vessel Maurice Ewing, from Columbia University's Lamont-Doherty Earth Observatory, was using low-frequency acoustic noise to image continental margins (where continents break apart). The extreme rarity of beaked whale strandings suggested to the biologists that the death of two whales and the ship's activities were related, Barlow told The Scientist. Michael Purdy, director of Lamont-Doherty, said that as soon as he heard of the deaths, he shut down the Ewing's research, which is funded by the National Science Foundation (NSF). However, because a direct link between the deaths and the Ewing's activities could not be established — a necropsy could not be conducted due to the whales' decomposition — the Ewing resumed its experiments last week. Purdy has met with officials at the National Oceanic and Atmospheric Administration (NOAA), which oversees the Fisheries Service, about the incident. And NSF Ocean Sciences Division director James Yoder is consulting with Barlow and colleagues to further investigate the potential problem.In the meanwhile, Purdy told The Scientist, he has instituted a number of new measures to minimize the possible danger to marine mammals, although he is still uncertain that the Ewing was responsible for the whales' death. The vessel has mapped 500,000 miles of ocean floor using the same technique for years without incident, he noted. In addition, the ship's position was estimated to be 30-40 miles away from where the whales were found. Though the ship's equipment was capable of producing 220 decibels, Purdy said that at that distance the expected noise level would be well below the 180-decibel guideline recommended by the Fisheries Service as safe for marine life.Nonetheless, Purdy has reduced the intensity of the signal used in the Ewing's mapping experiments, and the researchers are observing more stringent guidelines for where and when they can conduct experiments. In addition, Lamont-Doherty has provided funding for aerial monitoring of the areas where the Ewing researchers wish to work, to detect marine mammal activity and any new strandings.However, the National Resources Defense Council (NRDC) environmental group is "strenuously" objecting to resumption of the Ewing's experiments, according to Joel Reynolds, an attorney with the group. The NRDC is currently involved in litigation to stop the US Navy from testing a new sonar system, and Reynolds believes that the Fisheries Service and the Navy are trying to characterize whale strandings as a problem solely associated with mid-frequency noise. Reynolds dismisses the conclusion that because there have been no known previous incidents, low-frequency noise does not affect marine mammals. "Most of the time, they wouldn't know if there had been a problem. It was sheer coincidence that scientists learned of the stranding. If you're not looking, you're not going to see it," he said. Purdy said that he regrets the "us versus them" attitude that pits environmentalists against researchers. "We are oceanographers here. We spend huge chunks of our life at sea. We want to do everything possible to reduce the potential for impact on marine mammals. We need to work closely together and figure out what the best compromises are."

Whales and sounds

Low-frequency acoustic noise implicated in Baja California whale deaths.

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