Microchemistry analysis of the inner ear bones (otoliths) of two walleye that were caught in Swan Lake showed that the walleye were not born in the lake. The walleye were caught during FWP gill net sampling operations in October. FWP Region One Fisheries Manager Mark Deleray says that the fish apparently were transported and released in the lake as part of an illegal fish introduction.
“We see a significant change over time in the chemical profile of the otoliths, indicating that the two walleye were recently introduced into Swan Lake,” says FWP Fisheries Biologist Sam Bourret. “It appears that the walleye were introduced in 2015.” Bourret noted that lake trout otoliths from Swan Lake were used to verify the lake’s chemical signature.
FWP Biologists are now analyzing patterns of walleye from lakes around the region that potentially served as a source for the walleye. Already, the analyses have shown that the walleye did not originate in Lake Francis (near Conrad) or Noxon Reservoir. Walleye from other lakes could be tested to search for a match. Fish incorporate the chemical makeup of the water into their otoliths, which then serves as a chemical fingerprint that can reconstruct the movements and origin of the fish.
Deleray noted that these were the first walleye reported from Swan Lake, and it is assumed that these fish originated from an illegal fish introduction. Illegal fish introductions have caused problems in hundreds of waters across the state, costing hundreds of thousands of dollars to rectify. In most cases, the illegal introduction cannot be undone often leading to lost fishing opportunity. In this case, walleye are highly predacious and could impact the native bull trout as well as the kokanee salmon fishery in Swan Lake.
Deleray notes that the FWP Commission approved a mandatory kill regulation for walleye in Swan Lake, Swan River, and Tributaries. All walleye caught by anglers must be kept and immediately killed. Walleye must be reported to FWP within 24 hours, and arrangements made for the entire fish to be turned into FWP within 10 days (assume frozen)
State law makes it illegal to introduce or transplant fish in Montana unless authorized by the Fish and Wildlife Commission. The release of any live fish into any Montana pond, lake, stream, or river without FWP authorization is strictly forbidden. Penalties can range from fines, loss of fishing, hunting, and trapping privileges, plus liability for the costs to eliminate or mitigate the effects of the violation. Anglers cannot move any live fish from the water in which the fish are caught. The reward for information leading to a conviction of the person (s) who introduced walleye into Swan Lake is up to $30,000, mainly contributed by Trout Unlimited, with contributions from other groups including: Walleyes Unlimited, Fishing Outfitters Association of Montana, Invasive Species Action Network, Montana Bass Federation Nation, Montana Pikemasters, Montana Wildlife Federation, and Walleyes Forever.
Deleray asks anyone with information on who introduced walleye into Swan Lake to call 1-800-TIP MONT. Callers do not need to identify themselves and may be eligible for the cash reward.