Netting on Swan Lake wraps up

The final report isn’t in, but some new discoveries were made during this year’s experimental gill netting on Swan Lake.

Montana Fish, Wildlife and Parks has been gill netting on Swan Lake since 2009 in an attempt to reduce the non-native lake trout population. 

While data is still being analyzed and compiled from this year’s netting, state fisheries biologist Leo Rosenthal said catch numbers appeared to be similar to last year. Biologists this year discovered a new spawning area on Swan Lake. Biologists previously knew of only one spawning area in the lake.

Crews conduct the netting twice a year, for about three weeks. In August, juvenile lake trout are targeted and in October the netting operation targets spawning adults.  The goal is to learn if this level of gillnetting is effective at controlling lake trout populations and establish a plan to protect the native bull trout and kokanee salmon.

Lake trout were first discovered in Swan Lake in 1998, the same year that bull trout were classified as a threatened species under the Endangered Species Act. Swan Lake has been home to one of the strongest bull trout populations in Montana and the Columbia River Basin. 

The discovery of lake trout in the Swan caused alarm because of the species’ reputation of rapidly expanding and dominating fish communities. Concern increased in 2003 when biologists gillnetted juvenile lake trout in Swan Lake during low-intensity sampling. The discovery of young fish indicated wild reproduction was occurring. In sampling the next year seven more juvenile lake trout were caught, and in 2005, 28 were caught.

Biologists continued to monitor fish populations in the lake, and in a 2006 Montana State University survey, which captured trout for tag implants, 194 lake trout were caught, and 110 bull trout were caught.

Over the next two years further research was conducted to more closely determine the number of lake trout in Swan Lake. They came up with about 8,800.

In 2009 Montana Fish, Wildlife and Parks initiated a three-year gillnetting experiment to see if the method was effective at controlling lake trout populations, in a way that benefited the bull trout and kokanee. Between 2009 and 2011, 20,000 lake trout were removed from Swan Lake.

However, it was still unknown how the netting affected the lake trout population. In May 2012 Fish, Wildlife and Parks proposed to extend the removal project for another five years to further evaluate the effectiveness.

While similar netting experiments have been conducted on other lakes with no definitive success, Swan Lake is different because of the early stage of lake trout establishment. There is also significant data recorded from before lake trout were discovered, which will help determine the effectiveness of the netting efforts, Rosenthal said.

“This is early enough in the establishment of lake trout that it provides some of the better opportunities to do something like this,” Rosenthal said. “It’s a test. Every one of those lakes is different from each other. It’s really a case by case basis.”

The project costs approximately $90,000 a year and is funded by Fish, Wildlife and Parks and the Swan Valley Bull Trout Working Group, which comprises five government agencies and Trout Unlimited.

Fish, Wildlife and Parks also tracks the population of bull trout and kokanee every year.

The kokanee salmon, while not native, are an important fish from a recreational perspective.

While bull trout had seen a bit of a decline those fish populations seem to have stabilized, Rosenthal said. 

The goal of the netting project isn’t to get rid of lake trout, but to control the population before they change the dynamic of Swan Lake.

The project will be completed in 2016, at which time biologist hope to be able to create a management plan based on what they’ve learned during the project. “I’m hoping the data will speak for itself,” Rosenthal said.