Sonar will be tested on Alaska salmon count

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ANCHORAGE — Ultrasound technology will be tested as a way to estimate the number of salmon that make it upriver to spawn.

Engineers at the University of Washington's Applied Physics Laboratory developed a long-range ultrasound-video system about a year ago and will test it on the Kenai River in July.

State biologists long have used sonar to count fish swimming up the Kenai, but at times it has been impossible to differentiate between red salmon and king salmon or to calculate whether enough kings make it upriver to spawn.

The new ultrasound device delivers images crisp enough to resemble video of salmon moving upstream. It shoots 96 sonar beams at high frequency and can discern objects up to 100 feet away, designers say.

Software accompanying the sonar automatically counts and measures the length of passing fish.

"It represents a quantum leap in what you can do with acoustics," said Brett Huber, director of the Kenai River Sportfishing Association, which is paying $10,000 for the testing.

"You've probably seen sonograms of babies. That's what this does. I mean, you can see the fins on the fish."

If the camera can successfully peer through the Kenai's cold, silt-choked water and dense fish this summer — conditions known to trip up less sophisticated sonar systems — the state will begin buying the $80,000 units, said Debby Burwen, a state fisheries biologist who specializes in sonar counting.

The state has used sonar to count fish in the Kenai River since 1985. The existing split-beam sonar, installed in 1995, had been considered state of the art. That system produces wormlike images of the sonar readings printed out on paper.

Biologists rely on that to open, close and restrict fishing, affecting the Kenai's multimillion-dollar sport and commercial fisheries.