Biologists report that the project to sample the lake trout population in Swan Lake came off successfully. The fish sampling took place over a three-week period from September 17-October 4. Short-set gill nets were used to capture fish alive for marking and release. The goal of the sampling was to capture, mark, and release alive as many lake trout as possible, so that a population estimate could be achieved.
Biologists set 26.5 miles of gill net, at various locations around Swan Lake. The nets were checked about every two hours during morning and evening. The catch included 2,174 lake trout; of these 1,391 received small tags to aid in population estimates. Biologists reported that 783 lake trout died during the operation or were kept for sampling purposes. Thirty large lake trout weighing up to 22 pounds received sonic tags so their movements could be followed. Biologists are already tracking these larger fish and are tentatively identifying some spawning locations around the lake.
A total of 378 bull trout were caught; 237 of these bull trout were released alive. The 141 bull trout killed during sampling was well within the mortality guidelines determined prior to this large project. Some bull trout are killed during the standard annual fall netting that was deferred this year because of this project. The catch of non-trout species was lower than expected and included mostly northern pikeminnow (203 fish), suckers (212), mountain whitefish (32), and kokanee (39). In addition to the gill nets, biologists used two large trap nets deployed on the bottom in deep water. These trap nets caught fewer fish totaling 39 lake trout and 20 bull trout.
The pool of tagged lake trout will yield a large amount of information as the project continues. The project will provide valuable information that can be used to help manage the Swan Lake fishery in light of the growing lake trout population.
Lake trout were first noted in the Swan drainage in 1998 and evidence has indicated the population is growing rapidly. This recent sampling confirms this. These predacious fish threaten the popular bull trout and kokanee fishery in the lake. Swan Lake is presently one of the few places in the nation where the daily limit is one bull trout per day. Anglers
should carefully identify any trout caught and take care in releasing bull trout; they are encouraged to keep lake trout if they can positively identify them. The daily limit on lake trout in Swan Lake is 10 fish. Anglers are asked to report to FWP any large lake trout caught which contain a sonic tag in the body cavity.
The lake trout project on Swan Lake is being conducted through a collaborative interagency effort under a collection permit issued by Montana Fish, Wildlife & Parks. This net sampling was carried out by a contractor under the supervision of the U.S. Fish and Wildlife Service (contact: Wade Fredenberg, Creston Fish and Wildlife Center, 758-6872; Scott Hawxhurst, FWP, 751-4544) and data analysis will be conducted by the Montana Cooperative Fishery Research Unit from Montana State University. Cooperators include Montana Fish, Wildlife & Parks, the U. S. Fish and Wildlife Service, U.S. Forest Service, Montana Trout Unlimited, and Bonneville Power Administration.