Wednesday, October 27, 2010

Ball 15. Fish Whispers

Rolf Korneliussen listens to fish. The Norse acoustician has been studying ways of using sound waves to identify fish species deep below the ocean surface. His research has shown that it’s possible to catalog telltale echo signatures, basically acoustic fingerprints, of species such as mackerel, capelin, squid and Norway pout.

Although even a weekend angler’s 14-footer can be rigged with a fish finder, the relatively crude sonar technology does little more than reflect the presence of a moving thing below the boat—possibly a fish, but not necessarily. More sophisticated sonar devices have had somewhat better luck identifying individual species, although they are far from reliable.

As a result, sonar has been of limited use to marine biologists concerned with monitoring vast—or, as the case may be, dwindling—stocks of critical ocean species like mackerel, herring and cod.

Korneliussen’s software relies on a technology called frequency-dependent backscatter—the reflection of sound waves in their direction of origin—as the main method for identifying fish species underwater. To improve the accuracy, it also incorporates measures of backscattering strength, geographical position, school-shape and other details that can be unique to particular species.

Korneliussen, of the Institute of Marine Research in Bergen, said the system

can be trained to identify several species. Currently our identification library contains Atlantic mackerel, herring, capelin, southern krill, northern krill, sand-eel and squid

However, he added, for some species the technique remains less definitive than it is for mackerel.

For the moment, the acoustic technology is best suited to scientific research, as it requires calibrated echosounders, but it has significant implications for the commercial fishing industry, Korneliussen said.

In Norwegian waters, any fish that is caught has to be delivered on land, so catching the wrong species—or catching a species at the wrong time of year—could cost quite a bit in lost income.

However, he added,

the scientific software has been modified to fit the commercial fishing fleet since we feel obligated to make new scientific methods available to them, but the software is currently not ready for general use by fishermen.

Korneliussen reported his latest findings in the ICES Journal of Marine Science.

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