Scientists have proved that whales flee from military sonar used to hunt submarines, providing a possible explanation for studies that have connected naval exercises around the world to unusual mass strandings of whales and dolphins.
Beaked whales, the most common casualty of the strandings, were shown to be highly sensitive to sonar. However, a second study also revealed unexpectedly that blue whales, the largest animals on Earth, which have suffered a 95 percent decline in population in the past century, also abandoned feeding and swam rapidly away from sonar noise.
The strong response observed in the beaked whales occurred at noise levels that were well below those allowed for US Navy exercises.
“This result has to be taken into consideration by regulators and those planning naval exercises,” said Stacy DeRuiter, of Scotland’s University of St Andrews, who led one of the teams in the study.
Sarah Dolman, at the Whale and Dolphin Conservation charity, said: “For whales and dolphins listening is as important as seeing is for humans — they communicate, locate food and navigate using sound.
“Noise pollution threatens vulnerable populations, driving them away from areas important to their survival, and at worst injuring or even causing the deaths of some whales and dolphins,” she added.
Dolman, who explained that there were no accepted international standards for noise pollution, said there was an urgent need to re-evaluate the environmental impacts of military activities.
The US navy part-funded the studies, but said the findings showed behavioral responses, not actual harm. Nonetheless, Kenneth Hess, a US navy spokesman, said permit conditions for naval exercises were reviewed annually.
“We will evaluate the effectiveness of our marine mammal protective measures in light of [the] new research findings,” Hess said.
Unusual mass strandings, where multiple species of whale and dolphin beach at several locations simultaneously, have soared since military sonar was introduced in the 1950s. Beachings can be fatal.
The strandings occur every year. In May this year a scientific analysis concluded that the deaths in June 2008 of 26 stranded common dolphins at Falmouth Bay, Cornwall, was most likely due to naval activity.
Beaked whales are the most common species caught up in unusual mass strandings, perhaps because they are more scared by noises sounding like killer whales.
Researchers used suction cups to attach digital devices to Cuvier’s beaked whales off the southern California coast, to measure the noise they were exposed to and gauge their response. When a simulated military sonar signal was sounded at 200 decibels and between 100km and just over 1.6km away, the whales at first stopped feeding and swimming. They then swam rapidly away from the noise, and some made unusually deep and long dives. DeRuiter said the mammals stopped feeding for up to seven hours, which was unusual.
The second study, also off southern California, estimated that a blue whale spooked by sonar missed out on more than a tonne of krill, a day’s worth of food.
Jeremy Goldbogen of Cascadia Research in Olympia, Washington, said: “We suggest that sonar-induced disruption of feeding could have significant ... impacts on individual baleen whale fitness and the health of their populations.”