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Safe from Sound?

Nova Scotia fishermen say that snow crabs are threatened by the search for new undersea oilfields. CBU physicist Dr. Geoffrey Lee-Dadswell is using computer models to help solve the debate

It deals with unimaginably large things. It deals with incredibly small things. It deals with things that might not even exist at all. Modern physics is all about the highly intangible, the hypothetical, the what if.

But a real-world question like protecting Nova Scotia’s snow crabs from undersea oilfield testing? That’s Dr. Geoffrey Lee-Dadswell’s what if.

The theoretical physicist from Cape Breton University hopes his research will help resolve tensions between local snow crab fishermen and the petroleum industry, which identifies potential drilling areas by measuring how sound waves reflect off undersea rock strata.

The crab fishermen say that the extreme sound levels generated by these tests are harming crab populations, and could eventually destroy their industry.

The mechanics of creating an acoustic wave, Lee-Dadswell explains, are simple: “You have a ship towing air guns, like big pistons. You pump them up to high pressure and then open them up, and all that high-pressure air comes rushing out: you get a big boom.”

And these booms are extremely loud. So loud, in fact, that the sound wave tears the sea apart, creating vacuums in the water and generating vast amounts of heat. The booms are also known to damage the lungs and ears of whales, and the swim bladders of fish.

Organs with air cavities are the most vulnerable body parts because resonance magnifies the vibrations and can burst them. Environmental groups vigorously protest these often-fatal effects, so the oil industry now uses “soft starts,” which increase in intensity and encourage marine vertebrates to move away from the test area.

But as Lee-Dadswell points out: “That won’t work with crabs—because crabs can’t swim away. That’s part of the reason why there is still concern: no-one has really studied what happens to invertebrates ... because they don’t have any air cavities in them. But I do find it very difficult to believe that you can go setting off 255-decibel sounds and not have some impact.”

In 2003–4 a working group comprising representatives from the oil and fishing industries, and the Department of Fisheries and Oceans, showed that crabs do not suffer severe tissue damage after seismic testing—but it failed to determine whether or not they suffer lesser or longer-term effects.

Which is where Geoffrey Lee-Dadswell’s expertise in nano-physics comes in: sound waves behave in a similar way to the molecular systems he usually studies. Using sophisticated mathematical software, he has been able to devise a complex set of equations to show how the entire range of frequencies from an air-gun explosion would pass through a crab’s shell and from one tissue to another—and whether they would cause any damage. The calculations are so processor-intensive, he says, that it would have been impractical even 10 years ago. And as for doing these calculations by hand—“It would take you your whole life or longer!”

Although he was at first sceptical of the earlier report, Lee-Dadswell’s initial results do seem to suggest that seismic testing causes no serious damage to the crabs. He speculates that when fisherman report a dip in their catch after seismic testing, this may be due to the crabs lying low whilst they clean themselves of sediment thrown up by the shock wave.

Lee-Dadswell stresses that before he can give the crabs a clean bill of health, many other factors need to be worked into the calculations, including further laboratory work on the acoustic properties of crab tissues. But even if his research ultimately does prove that seismic testing has a measurable effect on crustaceans, he says that knowing their acoustic signature could help oil engineers make preventative changes, such as restricting the blasts to less damaging frequencies.

Whilst it takes him outside his usual work at the atomic level, Dr Lee-Dadswell is delighted to be involved in the project: “It makes me feel very good to be doing work that may go towards protecting sea life from possible damage. That’s really my main interest in this. I’ve always been interested in what sort of social and environmental impact my research could have.”

Geoffrey Lee-Dadswell is an assistant professor in the Department of Math, Physics and Geology, Cape Breton University. His research is funded by the Offshore Energy Environmental Research (OEER), a consortium of Nova Scotia universities and the Nova Scotia Department of Energy, which seeks to establish scientific guidelines for the oil industry.