Montana's Invasive Trout in for a Real Shock

Invasive Brook Trout in Montana may be in for a real shock, as wildlife officials are considering using electrofishing to selectively remove the species from state streams, according to new research.

The shocking approach would be an alternative to using fish toxicants known as piscicides that negatively affect all gill-breathing organisms.

Westslope Cutthroat Trout (WCT), which are native to Montana, are experiencing severe declines throughout much of their historical range as Brook Trout push them out of their rightful habitat. And unless something is done to stop these bullying invasive fish, it is likely that WCT will not be around by the next century. The use of piscicides, such as rotenone or antimycin, to eradicate these fish is a common practice, but a concerning one to some wildlife officials because of the loss of native fish during treatments.

"Piscicides are a valuable tool to remove non-native fish," Wildlife Conservation Society Ecologist Brad Shepard said in a statement. "But where non-native and native fish co-exist in smaller streams, a potential alternative method, electrofishing, can be used to remove specific unwanted species, while reducing impacts on WCT or other native fish and macro-invertebrates."

To see whether electrofishing would be a suitable substitute, researchers from the Wildlife Conservation Society, Montana State University, Montana Department of Fish, Wildlife and Parks, and the US Geological Survey tried out the unconventional method on six study streams located throughout the upper Missouri River basin in Montana. Researchers wearing a backpack "shocker" - using a wand anode while dragging a cable cathode - shocked the unsuspecting fish and then collected the stunned Brook Trout. While the non-native species were removed, the native fish were returned.

Brook trout were successfully eradicated over a period of 4-8 years from four of six treatment sites, showing that electrofishing is both relatively quick and effective at removing invasive trout species. Small streams could be rid of Brook Trout in as little as three years if multiple removals were conducted each year, researchers say.

The findings were published in the North American Journal of Fisheries Management.