Blue whales disturbed by seismic surveys: scientists

Seismic surveys used for oil and gas prospecting on the sea floor are a disturbance for blue whales, the world's biggest animal and one of its rarest species, biologists reported on Wednesday.

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

The 11-day experiment was conducted during a period when 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.

"On the days when the vessel was operating, the whales called more than two and a half times more frequently than on days when the vessel was not operating," Di Iorio told AFP.

For humans, "it would be the same as if you were next to a roadworks hammer and have to shout or repeat what you say," she said.

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

"Blue whales are rather solitary whales which swim all the time, are highly dispersed and always travelling, and 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."

One concern is that oil and gas prospecting is venturing out into ever-deeper water, and little is known about the impact this might have on whales' feeding and migratory patterns.

The paper appears in Biology Letters, a journal of Britain's Royal Society.

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

Numerous beachings of whales, dolphins and porpoises have occurred over the past decade, prompting a finger of blame to be pointed at warship exercises.

Measuring up to nearly 33 metres (100 feet) and weighing as much as 180 tonnes, the blue whale (Balaenoptera musculus) was hunted almost to extinction until it was given international protection in 1966.

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

Before large-scale whale hunting, there may have been more than a quarter of a million of the giant mammals.