Biologists got alarmed when the killer whales (orcas) of Washington State's Puget Sound started disappearing.

Using high technology supersensitive microphones, Ken Balcomb has been eavesdropping on the region's resident killer whales. Unlike migratory orcas, these ones spend their whole lives among sounds.

Years of research revealed a disturbing trend: healthy adult orcas were disappearing without a precise reason. When Balcomb's equipment was blasted by a cacophony from a passing Navy vessel, scientists knew they started to unveil the puzzle.

Cetaceans (whales and dolphins) rely on ultrasounds to investigate their environment and the navy sonar could have disturbed their sense of orientation.

The active sonar, using underwater sound waves to detect other vessels, has been charged for provoking mass strandings of whales and dolphins. There had been a number of mass strandings coinciding with naval exercises in the northern hemisphere.

The Australian Sea Power Centre is worried that the beaked whale is potentially threatened by underwater sound. But some ask for more researches and say that navy anti-submarine training may not be necessarily affected by massive limitations on the use of sonar due to the concerns for adverse effects on whales.

A recent analysis revealed a lack of scientific data to prove the effects of sonar on whales. However, the circumstantial proofs linked to whale strandings ask for the necessity to manage the potentially harmful impact of some types of sonar.

"However, uncertainties about marine mammals remain and there is a risk that overly precautionary measures and prescriptive management could impact unnecessarily on the RAN's training role at sea," warned the researchers.

The passive sonar uses sensitive microphones to listen for the faint sounds emitted by enemy vessels. The US Federal Government has not approved the prohibition of active sonar, but the navy follows strategies aiming to decrease harmful effects.