杏吧原创

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鈥攁nd other noisy industries鈥攖o 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. 鈥淪ince
the industrialisation of the Arctic, the beluga鈥檚 habitat has become very
noisy,鈥� says Erbe. 鈥淪hipping is still increasing, with more passenger vessels
and more support vessels鈥攕ome of which are ice-breakers.鈥� 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鈥檚 north-western coast.

An ice-breaker has two main sources of noise: its 鈥渂ubbler鈥� 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鈥檚 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鈥檚 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 鈥減ermanently scared away from
critical habitat鈥�, the pair report.

Hearing damage can occur after 20 minutes鈥� exposure to the sound up to 4
kilometres away, the simulation suggests. But Mike Glew, ice operations officer
for the Canadian Coast Guard鈥檚 Arctic region, doubts that ice-breakers will ever
get close enough to damage beluga hearing. 鈥淎reas of ice that provide breathing
holes for sea mammals are unlikely to need ice-breakers,鈥� 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.