by Suzanne Vernon
For the Pathfinder
July 2, 1998
An angler reportedly caught a single lake trout two weeks ago in the Swan River near the mouth of Woodward Creek, about 17 miles upstream from Swan Lake. This is the first lake trout known to have been caught by any means in the Swan system. Biologists worry that lake trout could impact the existing fishery if they become established in the Swan system.
The lake trout weighed 8.74 pounds and was 28.6 inches long. The fish was a mature, egg-bearing female in good condition; its stomach was empty. Based on growth rings on its scales, the fish appears to be 8 or 9 years old with a one-year growth spurt at age 5.
It is not known whether this is an isolated individual fish or something more significant. To date, FWP spring gill netting and fall trap netting in Swan Lake, and electrofishing surveys sin the Swan River have never found a lake trout in the Swan system above Bigfork Dam. The fish ladder at the dam was completely blocked in 1993 to fish passage. Prior to that fish passage was very limited. It is possible that the lake trout found last week originally scaled the fish ladder, or it may have been transplanted into the Swan system illegally.
Swan Lake supports one of the best bull trout populations in Montana; bull trout were listed recently as threatened by the U.S. Fish and Wildlife Service. Bull trout are coexisting in the system with Mysis shrimp and kokanee. In other waters, including Flathead Lake, the combination of Mysis shrimp and lake trout caused bull trout and kokanee populations to plummet. Fisheries Manager Jim Vashro notes that the establishment of lake trout in Swan Lake could cause a reduction in the bull trout population and a loss of opportunity to fish for bull trout in Swan Lake.
FWP will continue to monitor fish populations in the Swan system. Anglers are asked to report any lake trout catches in the Swan River or in Swan Lake.