NOAA to test fish-finding technology

Autonomous underwater device tracks tagged fish

Posted: Thursday, January 07, 2010

It looks like a little torpedo and acts like a submarine, except instead of searching out an enemy, the device finds fish.

John Eiler/ Noaa Fisheries
John Eiler/ Noaa Fisheries

Researchers at the Alaska Fisheries Science Center's Auke Bay Laboratories will test the fish tracker this spring. The device was developed by Tom Grothues, a Rutgers University Marine Field Station scientist.

"It's a robot," Grothues said. "It's programmed and told what to do but then it makes some decisions on its own and acts accordingly."

Autonomous underwater vehicles are not new. They are used to map the ocean floor, hunt for mines and study shipwrecks, among other uses. The idea to use them to track fish came to Grothues during his migration research on the East Coast.

"I study fish offshore and it's hard to get to them," he said. "I was thinking we could do better."

Looking for a tagged fish in the ocean is surely the proverbial needle in the haystack. Scientists first implant fish with an acoustic tag and release them, then have to go about finding them again. It is time consuming and costly.

Traditional methods of finding tagged fish are from ocean vessels or "acoustic arrays," which are long lines left in the ocean to create an invisible curtain scientists hope the fish swim through.

"The fish may or may not pass that way," said scientist John Eiler, with the Auke Bay science center, whose experience with this type of retrieval system has been challenged by strong local currents.

"They have their limitations," he said.

The device Grothues developed takes a factory-built autonomous underwater vehicle and adds a sensor that listens for the acoustic fish tags. When it finds one, it makes a record of its location.

The new device can be launched from a dock, or two or three could be launched from a vessel, potentially tripling the amount of data collected and chances of finding fish, Grothues said. He is set to bring the device to Juneau in May.

In addition to tracking tagged fish, the device measures all kinds of things of interest to scientists, such as ocean oxygen levels, currents, river plume dispersals, salinity, temperature and depth.

The device can't get around by satellite unless it's on the surface, so it finds its way like an old pilot - by using dead reckoning and a compass. A couple of buoys are thrown into the water and the device uses triangulation to get better oriented.

Grothues said with these techniques, it can navigate complicated shorelines or underwater canyons to look for fish.

The point of the Juneau study is to find strengths and weaknesses in the prototype so that it can be improved. The project is a partnership between NOAA, the Alaska Department of Fish and Game, University of Alaska Fairbanks and Rutgers University.

If the test goes well, the fish tracker could be used in the future to study Southeast's important commercial and forage fish, such as halibut, rockfish, pollock and herring, said Alaska Fisheries Science Center Director Doug DeMaster.

• Contact reporter Kim Marquis at 523-2279 or

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