bottlenose whale
© unknownA northern bottlenose whale stranded in Scotland
Scientists say man-made noise equipment, including anti-seal sonar devices used in fish farms, is driving deep-water animals such as whales to shore, where they die.

A northern bottlenose whale was washed up dead on a beach in Prestatyn, North Wales, on Saturday morning, the tenth of the species to become trapped or stranded on British shores this year.

Scientists are blaming not just military sonar, but a large range of man-made noises that they fear are driving the normally deep-water animals to shore.

The week before, another of the 10m (33ft) whales became trapped in a small Scottish loch. Rescuers managed to push the distressed animal out of Loch Eil and halfway to safety but on Friday morning the whale was found dead.

"The whales are migrating at this time of year, so we normally do see more of them, but to have so many washing up is a little strange. There's an enormous amount of man-made noise out at sea off the northwest of Scotland, and we can't rule out that this is what causing them to come ashore," said Mark Simmonds, Director of Science for the Whale and Dolphin Conservation Society.

Northern bottlenose whales are acutely sensitive to sound, for like other beaked whales they use sonic pulses for hunting. The noise of oil exploration (which uses loud underwater explosions to help geologists search for undiscovered reserves), wind farm construction and shipping are all possible culprits.

"It seems military sonar caused the mass beaching of dolphins we saw in Cornwall last year, but this is different," said Dr Simmonds. Once close to shore, northern bottlenose whales are easily disoriented, Mr Simmonds believes. Lochs can act as "whale traps", which confuse the animals into swimming into ever more enclosed waters. This time last year another whale of the same species got trapped in Loch Eil.

"There's some kind of phenomenon in this loch that is funnelling them in. Once in, it seems that other noises may have prevented the whale from leaving," said Mr Simmonds.

Fish farms use 'Acoustic Harassment Devices' in an effort to dissuade seals from looting from their nets. While designed to be used intermittently, it appears that at least some fish farms leave theirs running continually.

"It's an awful siren sound - very, very loud," said Dr Patrick Miller of the Sea Mammal Research Unit in St Andrews. "There's quite a bit of research that says they have more effect on cetaceans than seals. It may very well be that the seal-scarer had a big effect on keeping the animal inside the loch."

"Standing on the shore of a Scottish loch it might seem silent, but stick a microphone in the water and it's now an incredibly noisy environment," said Mr Simmonds. "Sound travels 1,000 times faster underwater than it does through air."

The Loch Eil whale was only persuaded to leave when a nearby fish farm had turned off its seal-scaring device. Volunteers from the Marine Life Rescue Unit then used underwater loudspeakers to play sounds of their own - including a recording of a hunting killer whale - to push the 10-metre whale back out to sea.

"Although we think of these as open ocean animals, for so many to come in there may be something we're missing," said Dr. Millar. "Maybe they're looking for food. We just know so little about the animals it's difficult to make strong conclusions."

A study found that 109 northern bottlenose whales had stranded on the coasts of the UK and Ireland between 1800 and 2002. September was the month that saw most incidents, and coincides with their annual migration southwards. Although the number of reported strandings is increasing, Mr Simmonds cautioned that heightened public awareness and concern may mean dead whales are more likely to be reported.