All walleye caught on the Thompson chain of lakes in Lincoln County must be killed immediately and the entire fish turned over to Montana Fish, Wildlife and Parks under an emergency regulation adopted Thursday by the Fish and Wildlife Commission.
The “catch and kill” regulation is in response to two female walleye captured in Upper Thompson Lake on Oct. 9 during a regular fish survey. It marked the first documented detection of the non-native predator in Lincoln County.
The walleye, each of which were found in separate nets, were 18 and 21 inches long. The catch and kill regulation covers Upper, Middle and Lower Thompson lakes, since they're all connected.
“Additional monitoring is occurring to determine the presence of walleye in the other parts of the Thompson chain of lakes,” Eileen Ryce, administrator of the Fisheries Division of FWP, told the Fish and Wildlife Commission on Thursday. “Adopting this regulation will allow it to be in place for the remainder of the open water season and published in the 2020 regulation booklet.”
Adult walleye are considered top predators, meaning humans are the only threat to their existence. Young walleye and their eggs are susceptible to being eaten by other fish.
Female walleye can lay up to 400,000 eggs a year. They spawn in the spring, and FWP isn't sure when the two were dumped into the Thompson Lake chain.
Earlier, state officials called the illegal introduction of walleye into Upper Thompson Lake costly and time consuming to try to remove.
Walleye permanently upset the balance of Canyon Ferry Reservoir after they were planted in the Missouri River waterways, and a good portion of Thursday’s Fish and Wildlife morning meeting centered on how to balance walleye and trout in Canyon Ferry, Holter and Hauser reservoirs.
The catch and kill regulation is meant to ensure that any walleye captured by anglers will be used by FWP to collect additional data on individual fish. FWP biologists will collect otoliths — an inner ear bone — and fin clips and scales from the Upper Thompson Lake walleye to determine where the fish were born and their ages.
Otolith tests on walleye discovered in Swan Lake in 2015 showed they were brought over from Lake Helena. Catch and kill regulations were instituted on that lake, and no new walleye were detected.
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