Biologists near Thompson Falls have been netting and electrofishing walleye in Noxon Reservoir in the lower Clark Fork Drainage the last two weeks as a way to monitor fishery populations, according to the Montana Fish, Wildlife and Parks.
Walleye were first detected in the reservoir in 1991 as the result of several illegal introductions. In 2000, standardized annual monitoring was implemented to monitor trends in fish abundance and showed that walleye were naturally reproducing. Walleye abundance gradually increased between 2000 and 2009, but catch rates increased dramatically after that.
In this spring’s sampling, the FWP said a total of 61 walleye were collected through netting and nighttime electrofishing. Biologists said these walleye mostly ranged from 17 to 22 inches in length, with some smaller and larger fish. Two fish larger than 26 inches will be distributed for wildlife rehabilitation because of public health advisories.
Since the detection of walleye in Noxon Reservoir, fisheries managers have been concerned about how the new nonnative species may affect the fishery. Walleye are voracious predators capable of efficiently exploiting their prey base, FWP says. Based on case histories across the West, when introduced into new waters the highly fertile walleye have the ability to quickly over-populate and reduce prey species, causing populations of forage species such as perch to crash. Following the loss of forage, the overpopulated walleye often stunt. The addition of a new predator will also have to come at the expense of popular largemouth and smallmouth bass and pike fisheries, the FWP said.
The FWP also said predation by walleye could also affect the success of an ongoing multi-million dollar fisheries mitigation program funded by Avista, PPL Montana and government agencies to protect and enhance the threatened bull trout and other native fish such as westslope cutthroat in the lower Clark Fork and Lake Pend O’Reille.
According to a life history study completed in 2009, walleye were spawning in a small portion of the reservoir between Flatiron Ridge fishing access and Prospect Creek.
FWP said additional information is needed before managers can determine management objectives. If it’s determined that suppression is feasible and warranted an environmental assessment will be prepared prior to implementation.
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