Ice-breakers drive whales away

September 26, 2000

Is the din in the Arctic a headache for endangered beluga whales?

NOISY ice-breakers may be scaring threatened beluga whales away from their preferred habitats in the Arctic and even damaging their hearing, say researchers in Canada. They have developed software that might help ice-breaker crews-and other noisy industries-to work more quietly.

Beluga numbers in parts of the Canadian Arctic are declining, according to Christine Erbe of the Institute of Ocean Sciences in Sidney, British Columbia. The reasons for this are unclear, she says. While overfishing and chemical pollution are thought to be major culprits, noise may also be a factor. "Since the industrialisation of the Arctic, the beluga's habitat has become very noisy," says Erbe. "Shipping is still increasing, with more passenger vessels and more support vessels-some of which are ice-breakers." So Erbe and her colleague David Farmer tried to predict the effect of ship noise on the animals. The researchers analysed the subsea noise from a powerful coastguard ice-breaker in the Beaufort Sea, off Canada's north-western coast.

An ice-breaker has two main sources of noise: its "bubbler" and its propellers. The bubbler is a high-pressure air-venting system along the keel that protects the hull by pushing away fragments of broken ice. The continuous bubbling noise has a sound pressure level of around 192 decibels. Meanwhile, the ice-breaker's screw produces cavitation noise levels of 197 dB, rising to 205 dB when the ship is running at full power to ram the ice.

Erbe and her colleagues fed the data into a computer simulation they developed that mimics the beluga's hearing. They found that the vessels are noisy enough to mask beluga communications, inducing behavioural changes almost 14 kilometres from the ice-breaker. If the disturbance affects behaviour such as mating, nursing or feeding, the animals might be "permanently scared away from critical habitat", the pair report. Hearing damage can occur after 20 minutes' exposure to the sound up to 4 kilometres away, the simulation suggests. But Mike Glew, ice operations officer for the Canadian Coast Guard's Arctic region, doubts that ice-breakers will ever get close enough to damage beluga hearing. "Areas of ice that provide breathing holes for sea mammals are unlikely to need ice-breakers," he says.

Erbe hopes the simulation software might now be used by scientists studying broader noise effects on sea mammals. By analysing long-range effects of noise patterns, they could advise icebreaker operators, oil rigs and ocean dredgers on ways to alleviate noise at crucial times.
Author: Paul Marks

Source: Journal of the Acoustical Society of America (vol 108, p 1332)

New Scientist issue: 30 September 2000


New Scientist

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