New study proposed for Swan Lake fish

Montana Fish, Wildlife and Parks is seeking public comments on a plan to size up the lake trout population in Swan Lake.

The proposal for a "depletion population estimate" is actually a continuing effort - aggressive gill netting was carried out last fall for a population study using a different method.

"The work we did last fall was an attempt at a mark-recapture estimate," said Jim Vashro, regional fisheries manager. "However, they did not get enough recaptures to get a valid estimate."

More than 26 miles of gill nets were set in the lake by a Wisconsin-based fishing contractor, catching more than 2,000 lake trout over a three-week period in September. That was considered an impressive catch, and an indication that the lake trout population is growing rapidly.

But for some reason the recatch of marked fish was lower than expected. Vashro said excessive mortality of fish that were caught and released, or marked fish moving out of netting areas, or simply a population that is too large to get an adequate number of recaptures are all possibilities.

Vashro said the latest proposal calls for similar netting tactics using a different method for estimating the lake trout population: "It's based on declining catch rates … As you start, you should have a high catch rate, and as you remove fish, your catch rate should decline. And looking at that rate of decline, you should be able to estimate the number of fish in the population."

And there will be another major difference.

"In this one, we'll actually be removing lake trout we capture," Vashro said.

Edible lake trout will be distributed to food banks or to the Fish, Wildlife and Parks wildlife rehabilitation center in Helena.

"Hopefully, it will give us a good population estimate," Vashro said, noting that the work also will provide valuable information on lake age classes, growth rates and other population characteristics.

The work that has been done has honed netting success. "We've identified some areas where they do concentrate," Vashro said.

The proposal calls for three weeks of netting in August or September, a time when at least half the lake's adult bull trout population will be in spawning streams.

The lake-trout invasion is considered a serious threat to what was one of Montana's healthiest populations of bull trout, a threatened species under the Endangered Species Act.

Lake trout were first detected in the lake in 1998, when anglers started catching and reporting 20- to 30-inch fish. In 2003, a nine-inch juvenile was caught in a gill net, indicating the population was reproducing.

Once a population estimate is developed, strategies for suppressing the population will be considered. The netting planned for this summer will provide some indication of whether that method can be effective in suppressing lake trout.

Vashro said any suppression effort will involve an additional proposal and environmental assessment.

The public can comment on this summer's netting proposal through June 10. A draft environmental assessment outlining the proposal is available for review at Montana Fish, Wildlife and Parks headquarters on Meridian Road in Kalispell or on the department's Web site, http://www.fwp.mt.gov, under "recent public notices."

Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com