Interesting news today on the whale/ocean-noise beat, as boffins have calculated that back when the oceans were full of whales they were hugely noisier than they are today. Rising levels of human-caused noise in the oceans, which have long been theorised to be a source of distress for cetaceans, are very quiet by comparison to the massed whale music of yesteryear.

"Three hundred and fifty thousand fin whales in the North Atlantic may have contributed 126 decibels – about as loud as a rock concert – to the ocean ambient sound level in the early 19th century," says Michael Stocker of Ocean Conservation Research. Stocker was presenting OCR's new study yesterday at the annual conference of the Acoustical Society of America.

Use of whaling records to determine just how many whales were harvested from the ocean over the course of industrialized whaling is difficult because the captains were taxed on their catch and therefore had an incentive to “fudge” the numbers. Some captains kept two sets of books. After the collapse of the Soviet Union, some of the real reports began surfacing. In one example the Soviets initially reported taking approximately 2,710 humpback whales from the late 1950s to the mid-1960s. The newer data reveal the actual number was closer to 48,000.

This more accurate data was supported by population estimates using mitochondrial DNA, which does not change through female lines of a species. Thus the current diversity in DNA can serve as a proxy for historic population numbers.

Stocker and his colleague John Reuterdahl used these methods to come up with improved population numbers for whales back through the era before modern whaling, and then used these numbers to estimate how noisy the oceans were back then.

It turns out that while humans are indeed creating more of a racket underwater than we used to do, we haven't yet approached the levels of noise that the old-time massed whales used to make:

In the modern ocean, the background noise can be ten times louder than it was just 50 years ago. But new modeling based on recently published data suggests that 200 years ago – prior to the industrial whaling era - the ocean was even louder than today due to the various sounds whales make.

That said, Stocker cautions that human noises from shipping, naval sonar etc are different from those made by whales, just as a loud rock concert is different from a pneumatic drill even though both are similarly noisy.

"Anthropogenic noise is often broader band and differently textured than natural noise, so the impacts are likely different as well," he says. "Investigating these differences and their impact on marine life is the topic of intense research.”

Previous research has indicated that whales may not be able to hear some human-caused noise at all (for instance mid-frequency active sonar). However other noise sources such as ship propellers can generate sounds squarely in the same frequency bands as whalesong. ®

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