Biologists with Montana Fish Wildlife & Parks have traced the origin of two illegally introduced walleye discovered in Swan Lake.
FWP announced Tuesday that researchers traced the fish back to Lake Helena by looking at their otoliths, or inner ear bones.
Dillon Tabish is with Fish Wildlife & Parks.
“Otoliths are calcium carbonate structures found in the inner ear bones of fish," he said. "Think of them like fingerprints. And they can help researchers trace where fish are born and what waters they’ve been swimming in.”
FWP caught the walleye in Swan Lake during a gill-net operation in October 2015.
That marked the first time the species was discovered in the lake and raised concerns about the illegal introduction of yet another non-native fish in Montana’s waters.
“It’s a serious issue. Illegal introductions can really harm fisheries, they can hurt recreational opportunities for fishermen and women, they can collapse ecosystems, alter food webs," he said. "You know in this instance, walleye are really highly predacious and that can hurt the native bull trout population as well as the kokanee salmon fishery.”
Approximately 600 confirmed illegal introductions have occurred in more than 250 water bodies across Montana, and half of these have occurred in Montana’s portion of the Columbia River Basin.
Tabish says this is one of the first instances where FWP biologists have used otolith research as an investigative tool to look at these illegal fish introductions.
Though FWP is a step closer, the perpetrators who released the walleye into Swan Lake have yet to be caught.
The state of Montana offers rewards of more than $15,000 for information about illegal fish introductions. Montana Trout Unlimited has pledged a reward of $20,000 for a tip that results in the conviction of the individual or individuals responsible for illegally introducing the walleye into Swan Lake.
Anyone with possible information on who introduced walleye into Swan Lake is encouraged to call 1-800-TIP MONT.