KALISPELL — An old and tested technology was applied in a new way to track down the origin of the two illegally planted walleyes in Swan Lake in 2015.
The tool, perfected over the past year, could be used to catch people responsible for illegal introductions that can lead to lost recreational fishing opportunities, a collapse of ecosystems and altered food webs.
Montana Fish, Wildlife and Parks fisheries biologist Sam Bourret was well versed in the application of using microchemistry analysis on the calcium carbonate structures of the inner ear bones of salmon — used to trace down their home streams — when he came to work in northwest Montana two years ago.
That summer other fisheries biologists were using gill nets to capture lake trout, another illegally introduced species, from Swan Lake when the two walleyes were found.
“It was a very alarming discovery,” Bourret said. “Walleye are a voracious predator that can easily alter a fishery.”
Bourret put the skills he gained tracking down the origins of individual salmon to work to see if he could determine the home waters of the walleye.
Every water body has a unique chemistry created by the area’s underlying geology. That chemical information is stored in the inner ear, called the otolith in fish.
The information that he gathered from the otoliths of the two walleyes caught in Swan Lakes indicated they had been hatched elsewhere. It also found they were introduced to the lake sometime in the spring of 2015.
Bourret had biologists send him samples from walleye captured in 12 of the state’s most popular walleye fisheries. When he compared the geochemical information gleaned from the Swan Lake walleye, Bourret found a match. The walleyes had originated in Lake Helena, a lake about 10 miles from Helena.
“Illegal fish introductions are a huge problem both ecologically and socially,’ Bourret said. “Fish managers have few tools to combat the pervasive issue. This research gives managers a tool in their arsenal to help convict perpetrators.”
Biologists have confirmed about 600 illegal introductions in more than 250 water bodies across Montana. Half of those have occurred in the state’s portion of the Columbia River Basin.
So far, no more walleye have been captured in Swan Lake. Right after the walleye were captured, FWP officials added regulations that required all walleye caught in the lake to be immediately killed and reported.
“It was a good sign to learn that the fish were moved there and wasn’t a breeding population,” Bourett said.
FWP and Montana Trout Unlimited have established a reward of up to $35,250 for information leading to the conviction of whomever was responsible for the illegal introduction.
“We need help from local citizens to catch those responsible for the illegal introduction,” said FWP Region One Fisheries Manager Mark Deleray. “We expect the large reward will result in information.”
Anyone with possible information on the Swan Lake illegal introduction can call 1-800-TIP MONT. Callers do not have to identify themselves.