Monday, March 28, 2011

Whales and Sonar: Woods Hole research proves changes in behavior

The long-standing controversy over the effect of sonar signals on whales has festered over the years primarily due to that fact that the whale's supposed adverse reaction to the electronics sounds was theorized, implied, but never definitively proven. All evidence was anecdotal.

The Woods Hole Oceanographic Institution has changed all that with a recently published study in PLoS One. Here is an overview from SeaWeb on this important research:

Whales Change Behavior to Avoid Navy Sonar
U.S. Navy photo by Ari S. <span class=Friedlaender" height="167" width="250">
By studying whales fitted with electronic tags, researchers have been able to ascertain that beaked whales alter their behavior in response to naval sonar. Friedlaender, U.S. Navy

Researchers from the Woods Hole Oceanographic Institution (WHOI) have become the first to conclude definitively that naval sonar affects whale behavior and movement. This follows years of anecdotal evidence linking naval exercises with mass strandings of several species of cetaceans. The research team developed experiments to slowly increase the level of sonar directed at a tagged whale, to stop exposure as soon as the whale started responding, to measure that exposure and to define the response.

"These experiments were very difficult to develop, and it was a major breakthrough simply to be able to develop a study that could safely study these responses," said Peter Tyack of WHOI, the lead author of the study, which was published in the online open-access journal PLoS One. "All three times that tagged beaked whales were exposed experimentally to playback of sounds when they were foraging at depth, they stopped foraging prematurely and made unusually long and slow ascents to the surface, moving away from the sound."

The team then monitored reactions of beaked whales during actual sonar exercises on a naval testing range where an array of underwater microphones, or hydrophones, covered the seafloor, allowing whale sounds to be monitored over 600 square miles (1,554 square kilometers). "During actual sonar exercises, beaked whales were primarily detected near the periphery of the range, on average 10 miles (16 kilometers) away from the sonar transmissions. Once the exercise stopped, beaked whales gradually filled in the center of the range over 2 to 3 days," they write. In a press release, Tyack said that the research shows beaked whales are particularly sensitive to sound, and that they altered their behavior when exposed to sound levels below those previously believed. But, he added, "The observations on the naval range suggest that while sonar can disrupt the behavior of the whales, appropriate monitoring and management can reduce the risk of stranding."

Source: Tyack, P., et al. 2011. Beaked whales respond to simulated and actual navy sonar. PLoS One 6(2011): e17009; doi:10.1371/journal.pone.0017009.

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