The first detailed study of the effects of naval sonar on whales shows that whales flee from prime feeding sites when navy tests begin – leaving them famished when they finally return.
Blainville's beaked whales, Mesoplodon densirostris, use echolocation clicks to track down prey in the lightless depths they hunt in, a kilometre or more below the surface.
To find out whether the whales are disturbed by naval sonar operations, Peter Tyack of Woods Hole Oceanographic Institution, Massachusetts, and colleagues tracked the activity of Blainville's beaked whales during exercises at a US navy centre near Andros Island, Bahamas. The area encompasses an underwater canyon that is a prime hunting ground for these deep-diving whales.
By satellite tagging one whale and listening out for the echolocation clicks of others using underwater microphones, the team found that whales stopped echolocating and moved away from the area during the tests. Once the exercises stopped, a day and a half went by before the whales returned (PLoS One, DOI: 10.1371/journal.pone.0017009).
A related study found that three days after the tests ended, the whales began to echolocate like crazy – possibly indicating they were ravenous on their return to a prime feeding ground (Marine Mammal Science, DOI: 10.1111/j.1748-7692.2010.00457.x).
Robin Baird of the Cascadia Research Collective, based in Olympia, Washington, believes the use of underwater microphones is "a great approach", but points out that the whales' behaviour may not be typical of those that live away from sonar test ranges.
Brandon Southall of Southall Environmental Associates in Santa Cruz, California, an author on the PLoS One study, says that is a fair criticism. "[Whales] get used to what's happening around them," he says, adding that research currently under way is aimed at incorporating the reactions of whales that aren't accustomed to sonar.
Image: Michael Nolan/Specialist Stock. This post originally appeared on New Scientist.