Why do sonar-sensitive beaked whales continue to hunt near naval test ranges?
Beaked whales dive up to depths of 3,000 meters several times a day in order to catch deep-sea squids, but little is understood about where they decide to dive. Although they appear to be sensitive to mid-frequency sound waves, operational Navy sonars, beaked whales continue to hunt within naval sonar ranges. The Acoustical Ocean Ecology Group sought to understand why these areas, rather than areas with less mid-frequency Navy sonar activity, were uniquely valuable to the beaked whales. We also wanted to determine whether or not their responses to the presence of sonar in these areas could be detrimental to their population.
What we discovered is that while areas in and adjacent to the range were geographically similar, the presence of deep-sea squid was drastically different. Not only did the sonar-heavy areas that beaked whales consistently inhabit contain higher concentrations of squid, but the squid were also much larger. Most importantly, the squid in these preferred areas were much more clustered, resulting in squid being close to each other—and thus making it easy for a whale holding its breath to capture more than one on each of its 10 daily dives. Because each dive made by a beaked whale is energetically costly and time limited, these squid-rich areas remain important habitat for beaked whales, despite naval activities. This surprising “patchiness,” in which certain parts of seemingly indistinguishable ocean are actually quite different biologically, indicates that the deep sea is much less homogeneous than scientists first believed.
