Oil booms: whales don't avoid noise of seismic exploration.

Field tests in the Gulf of Mexico suggest that sperm whales there don't swim away from boats conducting seismic surveys of the seafloor. However, the surveys' noise--typically generated during the hunt for oil and natural gas deposits--may be having subtle effects on the whales' feeding behavior.

Scientists use a device called an air gun to probe the seafloor. A burst of compressed air at the ocean's surface creates intense pressure pulses that travel through the water. The intensity and timing of the echoes from the ocean bottom provide information about buried geological structures. Biologists have been concerned that such pulses may damage a whale's hearing or mask the clicks that whales make to home in on food, says Patrick J. Miller, a marine biologist at the University of St. Andrews in Scotland.

To investigate the effects of seismic surveys, Miller and his colleagues tagged eight whales with devices that recorded each animal's depth, orientation in the water, movements, and the sounds that it heard or made. The devices, held on by suction cups, recorded information about each whale for an hour or so before and during nearby seismic surveys.

For most of the tagged whales, diving patterns didn't change after seismic surveys began, Miller reported last week in Baltimore at the spring meeting of the American Geophysical Union. Even when air gun-firing boats passed as close as I kilometer, the animals didn't substantially change the direction in which they were swimming. This observation hints that the animals aren't directly harmed by the seismic activity, says Miller.

However, tagged whales expended a little less energy searching for food and emitted fewer clicks associated with homing in on prey during the seismic surveys than they had before those surveys commenced, says Miller. Although those differences aren't statistically significant, perhaps because of the small number of whales studied, Miller says that such changes in behavior could reduce the animals' food gathering during seismic surveys. He explains that funding isn't available to continue the work using more whales.

Aquatic creatures may not be as disturbed by noise from seismic tests as people have presumed, says Penny Barton, a marine geophysicist at the University of Cambridge in England. During a seismic survey last year off the coast of Mexico's Yucatan peninsula, she and her colleagues placed a video camera on the seafloor in 20-meter-deep water to observe the fish there. Even though a vessel with its air guns blasting passed within 180 m of the camera, fish didn't change their behavior, she says.

The effort expended to mitigate the effects of seismic surveys on marine life can drastically reduce the effectiveness of scientific expeditions, says Barton. During last year's expedition, her team interrupted data collection 14 times to avoid exposing dolphins and sea turtles to potentially damaging levels of submarine sound. Furthermore, because the researchers had to visually confirm that animals remained at a safe distance, they couldn't fire air guns at night or when waves were high. In all, they collected only about 40 percent of the data that they could have otherwise, she reported at the meeting in Baltimore.