whales shout

 

The Sunday Times
14 November 2010

Author: Jonathan Leake

 

Noise from shipping, wind farms and oil exploration is forcing whales to raise their mating calls to make themselves heard.

Whales are having to shout to make themselves heard. Scientists have found their calls have become 10 times louder over the past 50 years as they battle against the roar of ships’ engines, propellers and sonar.

Wind farm construction is adding to the din, creating constant low-frequency pulses, as do seismic surveys for oil.

The findings come as the seas around Britain have become some of the world’s noisiest because of shipping traffic and wind farm construction. Some experts fear the noise will drive many whales away from the seas around Britain altogether.

“The rumbling noises emitted by ships and marine installations have similar frequencies to those used by whales,” said Peter Tyack, a marine biologist at the Woods Hole Oceanographic Institution in Massachusetts.

“We found that whales are trying to adapt either by emitting much louder noises or by calling at higher frequencies. It’s like they’ve turned from a bass into a tenor.”

Whales are renowned for their ability to communicate using low-frequency noises. The soundwaves are hardly deadened at all by water, so larger species such as blue whales, which emit the lowest frequencies, might communicate over hundreds of miles.

Because the number of most large whale species is now estimated at less than 5% of their natural level, the ability to communicate over such distances could be vital to finding mates, but Tyack and other scientists fear human-induced noise risks drowning out or ruining the mating songs.

“The whales are not just getting louder. Their messages are getting simpler and repeated more often, just like a human forced to shout,” said Tyack. “It also means they spend more energy on communicating.”

Susan Parks, an assistant professor of acoustics and ecology at Pennsylvania State University, worked with Tyack and other colleagues to attach temporary recording devices to the backs of 14 right whales.

The tags recorded the whales’ calls and background noise, as well as the animals’ depth, orientation and direction of travel. The researchers compared the sounds emitted by the whales against different levels of background noise.

All 14 whales had to emit calls about 10-12 times more powerful than this ambient noise in order to be heard.

The need to call out more loudly means modern whale communication is likely to be limited to shorter distances, because of the background noise and because louder calls have a shorter wavelength that is more quickly deadened by water. The louder “shouts” also consume much more energy.

In the research, two whales that were recorded only in high-noise surroundings were shouting all the time, sometimes reaching 150 decibels.

Sounds in the oceans are not directly comparable to those in the air, but a jet taking off would emit about 140 decibels.

One question was whether noise increases in the past 50 years have caused long-term changes in whale communication. In a separate study, Parks and her colleagues compared the sounds emitted by modern whales with recordings from the 1950s to the 1970s.

The results showed that human noise, mainly shipping, has increased by 10-100 times above the earlier levels.

The implication is that whales have been forced to start shouting to be heard – particularly in noisier waters.

One key question is whether the whales are no longer calling as often as in the past. Parks suspects this is because the whales she observed emitted few calls: “Like being in a loud room, you talk louder to be heard – but if it’s noisy enough you just stop trying.”

Other experts are also concerned. Ian Boyd, director of the sea mammal research unit at St Andrews University, said there was strong evidence that whales were vulnerable to human-induced noise: “Human noise is doubling every decade so we could be seeing some very severe impacts.”

Further research is likely to be complicated. One problem is that the sea is a noisy place, with wind, currents, rain and thunderstorms contributing.

Humans have already had a serious impact by destroying more than 95% of whale stocks, a change that will have made the oceans rather less noisy. “There is a lot of natural noise, but it varies with loud and quiet periods, whereas shipping noise is more constant,” Tyack said.

“For whales there are so few left that finding each other over the din could be crucial to keeping species going.” There is one slightly embarrassing finding for scientists: some of the largest noises in the ocean come from them. “Ironically, the sonars used on research ships are among the loudest sounds whales might hear,” said Boyd.

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