September 23, 2009

Seismic Surveys Stress Blue Whales

Seismic surveys used for oil and gas prospecting on the sea floor are a disturbance for the rare blue whales, AFP reported.

The calls of blue whales were recorded at a feeding ground in Canada's St. Lawrence estuary in August 2004, according to team members Lucia Di Iorio of Zurich University, Switzerland, and Christopher Clark, an acoustics specialist at the Cornell Laboratory of Ornithology in New York.

The study, appearing in Biology Letters, a journal of Britain's Royal Society, documented the 11-day experiment while a survey vessel was using a "sparker," a low-to-medium power device that sends an acoustic pulse to the sea floor and picks up the reflected signal to get a picture of the topography.

Di Iorio told AFP that the whales called two and a half times more frequently on days when the vessel was operating than on days when it wasn't.

She likened the noise created by the vessels to standing next to a jackhammer and having to shout or repeat what you say.

Further work would show whether blue whales suffered stress or other problems from the acoustic kerfuffle, Di Iorio said.

She added that while blue whales are rather solitary whales that swim all the time, they are highly dispersed and always traveling.

"Feeding areas are places where they have the chance to get together in a small range and with a lot of social activity as well. Being disturbed during social interactions that don't occur very often could have an influence, perhaps in mating, but we can't really say for sure, or what kind or if it is short term or long term," Di Iorio said.

Experts say oil and gas prospecting is venturing out into ever-deeper water and creating more concern for the whale's audio safety. The researchers suggest the whales are having to "repeat information", as some of their calls are blocked or degraded by the seismic bangs.

Meanwhile, little is known about the impact this might have on whales' feeding and migratory patterns.

A separate experiment in April reported in the same journal found that very loud, repeated blasts of sonar caused an Atlantic bottlenose dolphin to temporarily lose its hearing.

Warship exercises have been suspected of causing numerous beachings of whales, dolphins and porpoises over the past decade.

Until being granted international protection in 1966, the blue whale (Balaenoptera musculus), which measures up to nearly 100 feet and weighs as much as 180 tons, was hunted almost to extinction.

A Canadian study from 2002 put the global numbers of the whale at between 5,000 and 12,000, although estimates of this species' population today vary widely.

Experts suggest there may have been more than a quarter of a million of the giant mammals before large-scale whale hunting.

Several companies involved in the Sakhalin Energy consortium agreed to suspend seismic work after seeing evidence that it was driving the critically endangered western gray whale away from its summer feeding ground.

Experts believe there are only around 130 of the species surviving today.


On the Net: