Whales and the Knife's Edge

One of the big questions in marine mammal research these days is how Navy mid-frequency sonar kills marine mammals.  Some scientists have looked to decompression sickness, or "the bends," for an answer, since investigators have repeatedly found bends-like symptoms in animals that sonar has left dying on shore.  An important new paper out in Respiratory Physiology and Neurobiology adds fuel to that already stoked fire.

The new study modeled how several species of beaked whales manage their nitrogen levels as they go on their long foraging dives.  It turns out that these deep-diving creatures are living daily on a kind of knife's edge, with enough nitrogen in their tissues to produce a severe case of the bends in land animals.  The paper suggests that the whales adjust their dives to keep their nitrogen levels from maxing out - a life-saving move that a whale's frantic response to sonar would make difficult.

The Navy likes to remind us that the "bends" theory is just that - a theory.  And that's a fair point.  But some theories are better than others, and this one is supported now by at least four peer-reviewed papers on tissue pathology, two on dive physiology, and two on diving behavior, not to mention a succession of review papers, conference proceedings, and expert panels.  There are no leading competitors. 

All of this research has significant implications for marine wildlife.  Beaked whales make up about one-fourth of all whale, dolphin, and porpoise species on earth, and the evidence increasingly shows that many of these remarkable animals live in small, discrete populations that are highly vulnerable to human change.  And whatever theory proves correct, there is no question that naval sonar is gravely injuring whales at sea.

Consensus in the scientific community stands behind habitat avoidance as the best available measure for reducing harm to beaked whales and other species.  Until now, though, the Navy has generally refused to adopt such measures, "saying [as today's AP story puts it] that there isn't enough scientific evidence to require them." 

If the Navy doesn't care for the new paper, maybe it might have a look at another that came out last year.  That one was entitled, "Navy sonar and cetaceans: Just how much does the gun need to smoke before we act?"