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Walleye stockimage

SWAN LAKE – Let’s call it “CSI: Swan Lake.”

When two walleye were captured in the lake last October during a Montana Fish, Wildlife and Parks gill-net sampling operation, actual biologists were able to determine that so-called "bucket biologists" are trying again to vandalize a Montana fishery.

Microchemistry analysis of the inner ear bones of the walleye determined the two fish had not been born in Swan Lake.

That in all likelihood means somebody illegally transported and released them here, according to FWP Region 1 fisheries manager Mark Deleray.

They are the first walleye ever found here, Deleray said. It is a predatory fish that could adversely impact Swan Lake’s native bull trout population, as well as its kokanee salmon fishery, he said.

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The inner ear bones are called otoliths. FWP spokesman John Fraley explains that fish incorporate the chemical makeup of the water in which they live into the otoliths, which then serve as a type of “chemical fingerprint” that can reconstruct the movements and origins of fish.

FWP fisheries biologist Sam Bourret said lake trout otoliths from Swan Lake were used to verify the lake’s signature.

“We see a significant change over time in the chemical profile of the otoliths, indicating that the two walleye were recently introduced into Swan Lake,” Bourret says. “It appears that the walleye were introduced in 2015.”

That’s not the only thing the microchemistry analysis of the inner bones can reveal.

It can also tell FWP where the walleye came from.

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That, however, becomes a process of elimination. FWP biologists must find otoliths from another body of water that match the otoliths from the walleye found in Swan Lake.

Fraley said they’ve already ruled out Lake Francis, near Valier, and Noxon Reservoir, as sources of the Swan Lake walleye, and biologists are analyzing walleye from other lakes in the region.

It is illegal to move any live fish from the water where it is caught. Penalties range from fines and the loss of fishing, hunting and trapping privileges, to liability for the costs of attempting to eliminate or mitigate the effects of bucket biology.

A host of organizations, led by Trout Unlimited, make it possible for a reward of up to $30,000 to be offered for information leading to a conviction of the person or persons who illegally introduced the walleye into Swan Lake.

Anyone with information can call 1-800-TIP-MONT. Callers can remain anonymous, and may still be eligible for the cash reward.

Attempts to mitigate the effects of illegal fish introductions cost Montana taxpayers hundreds of thousands of dollars, Deleray said, and in most cases, can never be undone.

Meantime, any more walleye caught in Swan Lake, the Swan River and its tributaries are under a mandatory kill order approved by the Fish and Wildlife Commission. Said walleye must be killed, frozen and reported to the agency within 24 hours, which will make arrangements for it to be turned over within 10 days.

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