Michael Jasny, director of the NRDC Marine Mammal Project, contributed this article to LiveScience's Expert Voices: Op-Ed & Insights.

On June 9, 2008, at least 60 dolphins stranded along the coast of Cornwall, England, in what was by far the largest common dolphin mortality ever seen in British waters. For hours, rescuers tried to lead them back to sea — often unsuccessfully, as some of the animals were panicked and others just milled about in tight circles, resistant to saving. The forensic investigation that followed involved 24 experts from five countries and multiple government agencies.

Now their verdict is in, and the most probable cause was naval exercises.

For several days before the strandings, the British Royal Navy ran a large, multinational event (which included the U.S. Navy and involved active sonar and other disruptive activities) off the Cornish coast. That event, the investigators concluded, was closely correlated in space and time with the dolphins entering Falmouth Bay and eventually coming ashore. All other possible causes — disease, algal blooms, malnourishment — were eliminated. [Worst-Ever Right Whale Die-Off Continues to Puzzle]

The implication of naval exercises in a mass stranding will come as no surprise to those who have followed this issue in the United States. Nor will the Royal Navy's perfunctory denials in media accounts, which seem awfully similar to what we have heard over the years from the U.S. Navy.

In the case of mass strandings, what Navy officials always seem to demand after the fact is some definitive, minute-by-minute record of the victims' movements before beaching, as though it were possible to stick a tag on every whale and dolphin in the sea. Until biologists can provide that infeasible level of proof, the U.S. Navy refuses responsibility. But really, the Cornwall case is simple: a gun was fired, there were bodies, and no one else was in the room.

It's long past time for navies on both sides of the Atlantic to stop denying the obvious and do something meaningful to reduce harm, like putting especially vulnerable habitat off-limits to dangerous training. Unfortunately, in the United States, that may be something we have to fight for.

The reason is that proposed federal regulations would permit the U.S. Navy to harm marine mammals more than 30 million times over the next five years. This gargantuan number encompasses more than 5 million instances of temporary hearing loss — a significant impact for species like whales and dolphins that depend on hearing for their survival. And, it includes more than 10,000 cases of permanent injury and nearly 350 deaths from underwater explosions, vessel collisions and sonar exercises. Of course these are the U.S. Navy's estimates; the reality could be even worse.

In Southern California, which sees the lion's share of U.S. Navy training on the West Coast, biologists are concerned that the U.S. Navy's range has become a population sink for deep-diving beaked whales, a family of marine mammal species that is acutely vulnerable to high-powered naval sonar. And, new research on the same range shows that U.S. Navy sonar silences the foraging calls of blue whales over vast distances. That's a big problem since Southern California represents a globally important foraging area for that endangered species.

The U.S. Navy, still in denial mode, likes to claim that it has safely operated off California and other places for decades, but just like in Cornwall, that argument is wearing very thin.

Denial has its consequences, however. Neither the latest science nor its own dramatic estimates of harm has moved the U.S. Navy to identify better means of protecting whales and other marine life. Instead, it is proposing the same meager protective measures — visually monitoring a narrow strip around its vessels — that the scientific community and the courts have repeatedly found inadequate. By contrast, avoiding important habitat is universally acknowledged to be the most effective available measure.

More than 550,000 people have signed a petition at Signon.org calling for an end to the killing and harassment of marine mammals by U.S. Navy sonar. With the new investigative findings in Britain adding to the pile of evidence of harm, perhaps now the U.S. authorities will do the right thing. Denial is no longer an option.

The views expressed are those of the author and do not necessarily reflect the views of the publisher. This article was originally published on .