High-intensity naval sonar poses a serious threat to whales, dolphins and porpoises that depend on sound to survive, says a report by the United Nations Environment Programme.
The study lends the first official support to claims by environmental groups that military manoeuvres are responsible for the increasing incidence of mass whale beachings. "We know about other threats such as over-fishing, hunting and pollution [but] a new and emerging threat to cetaceans is that of increased underwater sonars," said Mark Simmonds, of the Whale and Dolphin Society. "These low-frequency sounds travel vast distances, hundreds if not thousands of kilometres from the source."
A coalition of environmental groups launched by, among others, Jean-Michel Cousteau, son of the ocean explorer Jacques Cousteau, sued the US Navy in October, over its use of sonar, saying the ear-splitting sounds violated environmental protection laws. The lawsuit is aimed at vessels that use mid-frequency sonar to locate submarines and underwater objects. The navy has 60 days to respond.
Tests on the bodies of seven whales that died near Gran Canaria in 2002 found haemorrhages and inner-ear damage, which experts said was caused by high-intensity, low-frequency sonar used in the area, it added. There are no laws governing noise pollution in the oceans, but western governments, considered largely responsible with their increased military presence in the seas, say they need more research before taking action.
The Australian Department of Defence has admitted two minehunters used short-range, high-frequency sonar to search for a 360-year-old Dutch wreck off Marion Bay, where 110 pilot whales died in two beachings last month.
But the defence officials denied any responsibility for the strandings, saying the first one happened while the ships were still anchored off the Tasmanian capital, Hobart, a significant distance to the west. "The later presence of the two ships in the area is purely coincidental," a spokesman said.
Environmentalists say the ear-splitting sounds can disrupt the navigation systems of whales and dolphins. Underwater seismic testing by the oil and gas industries has also been implicated. But the closest exploration work to Marion Bay last week was in the waters between Tasmania and Victoria, 275 miles north.
Tasmania has one of the world's highest rates of whale beachings, and Marion Bay is a notorious blackspot. In 1998, 110 pilot whales died after beaching themselves there.
And in 2004, 115 pilot whales and bottle-nosed dolphins died in two strandings off nearby Maria Island, prompting the Australian government to set up a national database of such incidents.
Wildlife officials said that the latest deaths may have been caused by the animals becoming disoriented by the topography of the area, on the island's south-eastern coast. Mark Pharaoh, of the Tasmanian Parks and Wildlife Service, said: "The most common belief here is that since these strandings are so regular, it's basically difficult country for a whale to navigate in."
Another wildlife officer, Ingrid Albion, said: "Only one of them has to get into trouble and make a wrong turn, and they'll actually call the rest of the pod to them."
Researchers at the University of Tasmania have suggested beachings may be linked to a 10-year cycle of increased wind strengths over the Southern Ocean. Changes in the earth's magnetic field and pursuit by killer whales are among other theories.
Animal protection groups have for years lobbied to restrict the use of sonar, saying the sound blasts disorient the sound-dependent creatures and cause bleeding from the eyes and ears.
Mr Simmonds added: "This is a hugely serious concern because these animals need sound to navigate, to find their food, to communicate and to mate."
A report by the International Whaling Commission's scientific committee said the link between sonar and whale deaths was "very convincing and appears overwhelming".