photo by Wade Fredenberg/USFWS

Saying goodbye to non-native lake trout in Swan Lake

For thousands of years, native bull trout populations have thrived in the Swan Valley. While trout populations in many parts of Montana are increasingly threatened by the invasion of non-native trout species, Bigfork Dam has helped to isolate the Swan’s bull trout from this threat.

In the late 1990s, however, anglers began catching adult lake trout from Swan Lake and the Swan River. Then, in 2003, a juvenile lake trout was caught -- the first evidence that lake trout were reproducing in the Swan River system. As the number of documented young lake trout grew during the next couple of years, so did biologists’ worries that this non-native invader was becoming a growing threat to bull trout populations in Swan Lake, as well as nearby Lindbergh and Holland Lakes. And with increasing water temperatures, even in Montana’s coldest lakes and streams, this threat is likely to grow in the coming years, because Lake trout outcompete and hybridize with native bull trout at warmer temperatures.

To try to deal with this new threat to our native trout fisheries, the Swan Valley Bull Trout Working Group was formed in 2004. They describe the situation like this: “If left unchecked, it is only a matter of time until lake trout become the dominant piscivore in the Swan River ecosystem.” A partnership of state, federal and tribal agencies and Montana Trout Unlimited, the working group has made substantial progress in addressing the lake trout threat in a very short time.

Three years ago, the working group began an experimental lake trout eradication project in Swan Lake. While native bull trout are upstream to spawn and lake trout are isolated in the lake’s deeper water, this project has netted and removed more than 10,000 non-native lake trout (2009 season figures). This is believed to be more than half of the lake trout population of Swan Lake. The largest of these fish are sent away to provide food at local food banks.

Programs like these can make a huge difference in conserving native trout fisheries, through the combined efforts of federal and tribal agencies, local citizens, and fisheries biologists working together to come up with creative and effective solutions.

For more information on how the Swan Valley Bull Trout Working Group is working to restore native bull trout, visit the link to the right.