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'Whales can't even hear naval sonar' says Navy boffin

Enormous CT scanner used to probe spermwhale's noggin

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A boffin funded by the US Navy has used a gigantic CT scanner, normally employed for inspecting space rockets, to X-ray the head of a whale. The results apparently indicate that naval sonars can't be the cause of whale beachings, as the mighty cetaceans are unable to hear the relevant frequencies.

The boffin in question is Dr Ted Cranford, whale expert at San Diego State University. He describes what he does in this way:

My work focuses primarily upon the functional morphology of biosonar, particularly sound generation and transmission, but also sound reception in toothed whales. I like to combine technological tools and traditional anatomic techniques to develop new or innovative methods to interrogate the structure/function complex.

One technological tool the doc has put to use is "a giant CT scanner, originally designed to inspect solid-fuel rocket motors".

"After scanning the head of a sperm whale, I subsequently reconstructed it using 3-D computer graphics tools to gain virtual access to the internal in situ anatomic geometry," reports Cranford, whose work is sponsored in part by the Office of Naval Research and the Chief of Naval Operations' Environmental Readiness Division.

Both these organisations have a deep interest in the details of whales' bio-sonar abilities, as it is frequently suggested by environmentalist groups that naval sonar confuses or distresses the mighty creatures - perhaps causing tragic beaching incidents. Similar claims are made with respect to dolphins.

But the ONR announced yesterday that Cranford's latest findings "suggest that mid-frequency active sonar sounds are largely filtered, or 'muffled', before reaching the animal’s ears. The findings also suggest that higher frequencies used by whales to hunt prey are heard at amplified levels without any dampening."

Mid-frequency active sonar has been in widespread naval use since World War II, though it has only been fingered by pro-whale activists as a cause of beaching in recent times - and beachings are rare, whereas sonar is used constantly in exercises. There have been protracted legal struggles between the US navy and environmental groups in the US courts over the issue, and similar allegations have been made regarding beachings in the UK.

Cranford's whale X-rays would seem to cast doubt on the protesters' assertions, at least in the case of whales - though he aims to check out dolphins too.

"These findings are promising," says the doc. "Our next step is to reproduce the study with a similar species for which hearing tests are available, such as the bottlenose dolphin. If we obtain like results, it will help to validate this new discovery."

Other recent research has backed up the idea that mid-frequency sonar could only harm dolphins' hearing in highly unusual circumstances.

This could be good news for whales and dolphins both, as it might mean that media and environmentalist attention will shift away from naval operations and away from beachings - a very minor problem for cetaceans - onto rather more serious problems. Commercial fishing, for instance, is thought to kill 1,000 marine mammals every day.

On the other hand, given the traditionally strong linkage between whale/dolphin activism and dislike of the military, possibly not. ®

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