KALISPELL – Wildlife investigators have used a kind of biological fingerprinting to unravel the origin of a pair of walleye illegally introduced in a northwestern Montana lake.

The Flathead Beacon reported that Montana Fish, Wildlife and Parks biologists analyzed tiny bones from the two fishes’ inner ears. Those bones contain details of the water chemistry from where fish have lived.

By comparing the findings to studies on walleye from other known populations in the state, the biologists determined the fish came from Lake Helena. That’s roughly 130 miles to the southeast of Swan Lake, where they were discovered in October 2015.

Walleye breed prolifically so if a population takes hold in Swan Lake it would pose a significant threat to bull trout, a native fish that’s prized among fishers.