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Tiny computers help track Lake Huron fish: Devices to determine harvest levels
Tuesday, July 01, 2003

The Detroit News, By Eric Pope / Special to The Detroit News

Hundreds of salmon, trout and other fish are swimming in Lake Huron with minicomputers implanted inside them, helping the state collect information that will improve Michigan's sports and commercial fishing.

Computerized devices about an inch long record the water temperature and depth the fish prefer, adding information to a computer model the state Department of Natural Resources uses to determine stocking levels and harvest limits for commercial and sport fishermen as well as the Indian fish catch under an 1836 treaty, according to Jim Johnson, DNR station manager at the Alpena Fishery Station.

Biologists know water temperature affects the digestion of fish, and that data will help build a better database for the food consumption and growth rates of fish. Professors and students at Michigan State University are working on the database.

The data will help scientists, for example, make more precise adjustments to salmon stocking levels.

The study began in 1998 when biologists surgically inserted the devices in the abdominal cavities of more than 300 lake trout in Lake Huron. The computer processors and memory chips were programmed to record the temperature of the water the fish were in every 75 minutes for up to 14 months.

Biologists are now using the next generation of devices, which cost about $300 and record water temperature and depth for trout, salmon, white fish, lake sturgeon and sea lamprey. This year, the Great Lakes Fishery Commission and the U.S. Fish and Wildlife Service will spend $155,000 on the project.

That's a bargain, according to biologist Roger Bergstedt of the U.S. Geological Survey, who runs the study from the Hammond Bay Biological Station.

"It would cost millions to get the data with research vessels, if you could get it at all," he said. "The fish are getting the information for you."

There's a $100 reward for the data-laden fish, which have a tag near the dorsal or pelvic fin. So far, 85 of 700 lake trout with the recording devices have been returned.

The program so far has given scientists more information on the sea lamprey, a nonindigenous species that sucks blood from much larger lake trout, killing many. Recovered thermometer tags show that the lake trout strain from New York's Finger Lakes live at an average temperature of 44.6 degrees during the late summer, compared to 47.3 degrees for native Great Lakes strains.

"We know that sea lampreys attack and kill fewer Finger Lakes trout," said Bergstedt, noting that sea lamprey also consume less blood at lower temperatures.


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