Montana Fish, Wildlife and Parks is taking public comment on a proposal to assess the effectiveness of using modified “electrofishing” equipment to destroy nonnative lake trout eggs and embryos in Swan Lake.
The agency recently released a draft environmental assessment outlining details of the proposed three-year study, which would occur annually beginning either in late September or early October of this year.
The project is anticipated to cost between $77,000 and $96,000 each year, with money obtained through FWP using Bonneville Power Administration funding. The first year’s funding has been secured.
Electrofishing is a standard method of nonlethal fish sampling, in which electricity is used to stun fish so they can be studied. The fish return to normal after a brief period.
The proposed study, however, would help fisheries biologists determine whether electrofishing can be used to kill eggs and embryos as an additional tool in suppressing lake trout populations.
In 2009, FWP launched an experimental gill netting program to remove lake trout from Swan Lake.
“The use of gill nets has proven effective in capturing large numbers of lake trout in Swan Lake,” the EA states. “However, due to the relatively high fecundity of lake trout, early life history survival may have a significant effect on population growth rates.
“Therefore, researchers have suggested that lake trout suppression activities may benefit from targeted destruction of lake trout embryos in order to cause year class failure and further reduce population growth rates.”
During the study’s first two years, according to the environmental assessment, eggs and sperm would be collected from adult lake trout. Fertilized eggs would be placed in experimental enclosures in Swan Lake at depths of roughly 15-30 feet. The enclosures would be exposed to a voltage gradient of about 15 volts per inch.
Information gained from these first two years, the proposal states, “would be used to perform an experimental destruction of lake trout embryos at a larger spatial scale,” such as entire spawning sites, during the third year of the study.
The Swan drainage, according to FWP, has one of Montana’s “most stable and healthy” bull trout populations, along with kokanee salmon and northern pike fisheries. Biologists say the voracious lake trout pose a significant threat to these populations, with bull trout the highest concern because they are native.
Lake trout either entered Swan Lake by ascending the Bigfork Dam fish ladder prior to its closure in 1993, fisheries biologists believe, or they were illegally introduced. FWP biologists say an expanding lake trout population will lead to the collapse of the kokanee population in Swan Lake and declines in the bull trout population.
“If effective, (electrofishing) will help halt expansion of the lake trout population in Swan Lake and, with the ongoing experimental gill net removal program, begin to cause a downward trajectory in the future growth of the lake trout population,” the environmental assessment states.
A copy of the draft environmental assessment can be found online at http://fwp.mt.gov/news/publicNotices/environmentalAssessments/speciesRemovalAndRelocation/pn_0053.html.
The public comment period runs through Thursday Sept. 29. Comments should be emailed to [email protected] or mailed to Montana Fish, Wildlife and Parks, Region 1 Fisheries Biologist Leo Rosenthal, 490 N. Meridian Rd., Kalispell MT 59901.