Underwater listening devices yield discoveries about endangered large whales

Autonomous data-recording devices equipped with hydrophones, deployed in remote waters off Alaska, have been used to track seasonal occurrences of blue, fin, humpback, North Pacific right, bowhead, and sperm whales

Why whales emit their characteristic calls remains largely a biological mystery, but listening for the distinctive underwater sounds provides a valuable way to track the movements of endangered large whales. Autonomous data-recording devices equipped with hydrophones (underwater microphones), deployed in remote waters off Alaska, have been used in recent years to track seasonal occurrences of blue, fin, humpback, North Pacific right, bowhead, and sperm whales, an article in the January 2006 issue of BioScience reports.

Because whale calls can be detected and recognized over tens of miles, such devices (which emit no sound) have added to scientific knowledge of the movements and calling behavior of these marine mammals. The findings have been particularly important in parts of the world, such as the seas near Alaska, where standard visual surveys are often hampered by darkness and bad weather.

The article, by Sue E. Moore of the National Oceanic and Atmospheric Administration’s (NOAA’s) Alaska Fisheries Science Center and three coauthors, describes the use of two types of recorders, one developed by NOAA’s Pacific Marine Environmental Laboratory and the other by the Scripps Institution of Oceanography. The devices are attached to hydrophones that are held at different distances from the ocean floor and are equipped with disk drives able to store tens of gigabytes of data. This allows them to operate for months at a time before they are recovered and the data accessed. Acoustic surveys using the devices have been conducted in the Gulf of Alaska, the southeastern Bering Sea, and the western Beaufort Sea, and have already yielded surprising discoveries about whales. Sperm whales, for example, have been detected in the Gulf of Alaska year-round, although this species has been generally thought to migrate to midlatitudes in winter. And critically endangered North Pacific right whales have been detected acoustically in locations where they were formerly abundant but have not been seen in decades. The results from acoustic whale surveys conducted to date could pave the way for more sophisticated acoustic surveys that would provide data in close to real time.